Physics and Astronomy Calendar

semester, 2018


Friday, January 5th 2018
Speaker: No colloquium this week.

Wednesday, January 10th 2018
12:00 pm:
Community Recognition Luncheon in Tate B50 lobby

QUESTIONS? Contact Julie at jjmurphy@umn.edu or 612-625-6928

Speaker:  Jaebak Kim, Korea University
Subject:  Search for CP violation using T-odd correlations in D0 → K+K−π+π− decay / The 3-dimensional level one track trigger for the Belle II experiment

We search for CP violation using T-odd correlation in the singly Cabbibo suppressed D0 -> K+K-pi+pi- decay at the KEKB asymmetric e+e- collider. The D+- particles are reconstructed to tag the D0 particles and a triple product using the momentum of the D0's daughter particles is calculated. Cuts and vetos are applied to the reconstructed sample. A two dimensional simultaneous fit using four sub-samples depending on the triple product and D0 flavor while using the invariant mass of D0 and the invariant mass difference between D+ and D0 particles as the two dimensions is performed. The T-odd correlation and systematics are calculated.

The next generation e+ e- collision experiment called Belle II will start colliding particles this year. It will search for new physics using high precision measurements which were not possible before. The precision will be achieved by using a high luminosity beam. Due to the luminosity of the beam, there must be an fast and efficient trigger system in order to record the physics relevant data. The Belle II level 1 trigger system is a combination of sub-trigger FPGA based systems, where the main triggers are the central drift chamber (CDC) trigger and electromagnetic calorimeter detector trigger (ECL) trigger. Between them the CDC trigger finds the momentum and vertex position of charged tracks. These precise information will then be used to determine whether the event has
interesting physics or not. If the event is determined to be physics relevant, the DAQ system will record the detector data to disk. The level 1 CDC trigger consists of 7 types of boards. They are the Frontend boards, Merger boards, TSF boards, 2D finder board, Event time finder board, 3D tracker boards, and Neural Network boards. Each board has a specific function that makes tracking charged track possible with high precision.


Friday, January 12th 2018
Speaker: No colloquium this week.

Monday, January 15th 2018

Tuesday, January 16th 2018
12:20 pm:
Space Physics Seminar in Tate 301-20
There will be no seminar this week.

Wednesday, January 17th 2018
1:25 pm:
Speaker: Jeff Derby (Dept. of Chemical Engineering and Materials Science, U of M)
Subject: The synergy of modeling and novel experiments for melt crystal growth research

Our understanding of crystal growth fundamentals and processes are advanced when the synergy between mathematical models and novel experiments is exploited. We present recent examples of how modeling and experiments together have enabled the identification of fundamental mechanisms important during the growth of bulk crystals from the melt.

We first discuss how microgravity experiments, carried out via sounding rockets, motivated a reexamination of classical theories for foreign particle engulfment during crystal growth. Via the development and application of rigorous numerical models, we were able, for the first time in over a decade of research on this system, to quantitatively describe data on the engulfment of SiC (silicon carbide) particles during the growth of crystalline silicon. Moreover, model results identified previously unascertained mechanisms responsible for the behavior of this system and, via this insight, provided insight for analytical derivation of a new scaling law for the dependence of critical engulfment velocity on particle size.

We finish with an overview of exciting, new research that employs neutron imaging to directly “see,” in operando, the bulk growth of scintillator crystals during a gradient-freeze process. We argue that the synergies of “seeing” via both models and neutron imaging will improve our fundamental understanding and provide for a closed-loop approach for optimizing the growth of large, single crystals from the melt.

This research was supported in part by NASA NNX10AR70G, DOE/NNSA DE-NA0002514, DOE/NNSA/DNN R&D (LBNL subcontract AC0205CH11231); no official endorsement should be inferred.

Faculty Host: Paul Crowell
3:35 pm:
To be announced.

Thursday, January 18th 2018
10:10 am:
Biophysics Seminar in PAN 120
Speaker: John Yin, University of Wisconsin
Subject: Paths to biological polymers: an insight from virus infections and origins of life

(1) Given the genome of a virus and PubMed, how well could one predict the one-step growth of the virus? Decades of biochemical and biophysical studies on bacteriophage T7, incorporated into a chemical kinetic model for template-dependent processes of transcription, translation, and genome replication, as well as particle assembly and release, enabled simulation of one-step growth behavior that recapitulated the experimentally observed kinetics of phage growth. Extension of the model and experiments to study the effects of host-cell physiology on phage growth highlighted the host cellular protein synthesis machinery as a key limiting resource for phage growth.
(2) Given amino acid monomers, but no cells, no templates and no protein synthesis machinery, how might the monomers nevertheless form polymers? The synthesis of peptide bonds between amino acids is a condensation reaction that is generally disfavored in aqueous solutions. However, we have found that for appropriate initial conditions of pH and temperature, drying of amino acids can promote their condensation to form peptides.
So what is the common insight from (1) and (2)? The often neglected “nurture” part of “nature versus nurture” can be important. The kinetics of phage growth depends on the physiological state of its host cell, and the de novo synthesis of a polypeptide species critically depends on the acidity and temperature of its initial solution. In short, we are all products of our environments.

Faculty Host: J. Woods Halley
3:35 pm:
Speaker: Harvey Brown, Philosophy of Physics, University of Oxford
Subject: Quantum Bayesianism (QBism): the way to understand the quantum world

The recent philosophy of Quantum Bayesianism, or QBism, represents an attempt to solve the traditional puzzles in the foundations of quantum theory by denying the objective reality of the quantum state. Einstein had hoped to remove the spectre of nonlocality in the theory by also assigning an epistemic status to the quantum state, but his version of this doctrine was recently proved to be inconsistent with the predictions of quantum mechanics. In this talk, I present plausibility arguments, old and new, for the reality of the quantum state, and expose what I think are weaknesses in QBism as a philosophy of science. (The talk is based on this paper: http://philsci-archive.pitt.edu/12978/


Friday, January 19th 2018
10:10 am:
Nuclear Physics Seminar in Tate 201-20
To be announced.
12:20 pm:
Speaker: Evan Moen
Subject: Spin Transport in Superconducting Spin Valves
Speaker: No colloquium this week.
Speaker: Harvey Brown, Philosophy of Physics, University of Oxford
Subject: "How Einstein Came to Use the Action-Reaction Principle in Promoting his Theory of Gravity"
Refreshments served at 3:15 p.m.

Einstein regarded as one of the triumphs of his 1915 theory of gravity — the general theory of relativity — that it vindicated the action–reaction principle, while Newtonian mechanics as well as his 1905 special theory of relativity supposedly violated it. In this talk I examine why Einstein came to emphasise this position several years after the development of general relativity. Several key considerations are relevant to the story: the connection Einstein originally saw between Mach’s analysis of inertia and both the equivalence principle and the principle of general covariance, the waning of Mach’s influence owing to de Sitter’s 1917 results, and Einstein’s detailed correspondence with Moritz Schlick in 1920. (The talk is based on ‘Einstein, the reality of space, and the action-reaction principle’, H.R.B. and Dennis Lehmkuhl, in Einstein, Tagore and the Nature of Reality, Partha Ghose (ed.), Routledge, London and New York, 2016; pp. 9-36. arXiv:1306.4902v1.)

4:40 pm:
Speaker: Priscilla Cushman, University of Minnesota
Subject: SuperCDMS - searching for dark matter
4:40 pm:
Organizational Meeting. Time and place of seminar will resume to match class schedule next week.

Monday, January 22nd 2018
1:25 pm:
To be announced.

Tuesday, January 23rd 2018
12:20 pm:
Space Physics Seminar in Tate 301-20
To be announced.
2:30 pm:
Speaker: Chun Shen, Brookhaven National Laboratory
Subject: Going with the flow— the nuclear phase diagram at the highest temperatures and densities

Nuclear matter has a complex phase structure, with a deconfined Quark-Gluon Plasma (QGP) expected to be present under conditions of extreme pressure and temperature. The hot QGP filled the universe about few microseconds after the Big Bang. This hot nuclear matter can be generated in the laboratory via the collision of heavy atomic nuclei at high energy. I will review recent theoretical progress in studying the transport properties the QGP at almost zero baryon density. The recent beam energy scan experiments at the Relativistic Heavy-Ion Collider (RHIC) offer a unique opportunity to study the nuclear phase diagram in a hot and baryon-rich environment. I will focus on the development of a comprehensive framework that is able to connect the fundamental theory of strong interactions with the RHIC experimental observations. This dynamical framework paves the way for quantitative characterization of the QGP and for locating the critical point in the nuclear phase diagram. These studies will advance our understanding of strongly interacting many-body systems and build interconnections with other areas of physics, including string theory, cosmology, and cold atomic gases.


Wednesday, January 24th 2018
1:30 pm:
Speaker: Fiona Burnell (University of Minnesota)
Subject: Signatures of gapless boundary modes in Kitaev spin liquids

Recent progress in synthesizing insulators with a new type of dominant spin-exchange interaction, known as the Kitaev interaction, has opened new possibilities for experimentally realizing spin liquid compounds. Among the distinctive features of these spin liquids is the possibility that they can harbour protected gapless boundary modes which carry spin but not charge. This possibility raises a challenge of how best to detect these chargeless boundary modes. I will discuss two possibilities — Raman scattering and the heat capacity — as well as what such measurements can reveal about the bulk phase.

Faculty Host: Paul Crowell
Speaker: Dr. Shilpi Jain. National Central University Taiwan.
Subject: Search for H-->Zgamma—>llgamma with the CMS detector
Note change of time and room from previous announcement.

Jain will talk about the search for a Higgs boson decaying into a Z boson and a photon. The analysis is performed using a dataset recorded by the CMS experiment at the LHC from proton-proton collisions at a centre-of-mass energy of 13 TeV corresponding to an integrated luminosity of 35.9 fb-1. Limits are set on the cross section of a standard model Higgs boson decaying to electron or muon pairs and a photon. The expected exclusion limits at 95% confidence level are between 9 and 4 times the standard model cross section in the mass range of 120 and 130 GeV.


Thursday, January 25th 2018
10:10 am:
Biophysics Seminar in 120 PAN
Speaker: Ryan Marshall, UMN
Subject: Rapid and scalable characterization of CRISPR technologies using a cell-free transcription-translation system (TXTL)

CRISPR-Cas systems offer versatile technologies for genome engineering, yet their implementation has been outpaced by ongoing discoveries of new Cas nucleases and anti-CRISPR proteins. We present the use of E. coli cell-free transcription-translation (TXTL) systems to vastly improve the speed and scalability of CRISPR characterization and validation. TXTL can express active CRISPR machinery from added plasmids and linear DNA, and TXTL can output quantitative dynamics of DNA cleavage and gene repression—all without protein purification or live cells. We use TXTL to measure the dynamics of DNA cleavage and gene repression for single and multi-effector CRISPR nucleases, predict gene repression strength in E. coli, determine the specificities of diverse anti-CRISPR proteins, develop a fast and scalable screen for protospacer-adjacent motifs, and show that dCas9 bound to a protospacer can be displaced. These examples underscore how TXTL can facilitate the characterization and application of CRISPR technologies across their many uses.

3:35 pm:
There will be no colloquium this week

Friday, January 26th 2018
08:00 am:
Untitled in Physics
10:10 am:
Nuclear Physics Seminar in Tate 201-20
There will be a special nuclear physics seminar on Tuesday this week.
12:20 pm:
Speaker: Nicholas Lewellyn
Subject: Magnetic Field tuned superconductor-metal transition in InOx

Quantum phase transitions are an interesting topic in condensed matter physics that has been studied extensively. One example of a quantum phase transition is the superconductor-insulator transition in InOx. These transitions are typically studied using scaling analysis. In the case of a field tuned transition this starts with measuring various resistance versus field isotherms. The field at which the isotherms cross is taken as the critical field and used in the scaling analysis and to find the critical exponents. However, in some systems, such as one of our InOx thin films, there is not a single crossing, instead the crossing is smeared out resulting in a temperature dependent critical field and critical exponents. Detailed transport measurements of the superconductor-metal transition in this sample suggest that this temperature dependent behavior may be the result of a quantum Griffiths singularity. Similar behavior how been observed by other groups in different materials that also undergo superconductor-metal transitions.

Speaker: Jorn Kersten (Bergen U., Norway)
Subject: Late Kinetic Decoupling and Self-Interacting Dark Matter

The cosmological LambdaCDM standard model faces some problems related to the formation of structures at relatively small scales, most notably the missing-satellites problem, the cusp-core problem, the too-big-to-fail problem, and the diversity problem. I will advertise late kinetic decoupling of dark matter as a mechanism to address the missing satellites problem. Afterwards, I will describe a model involving self-interacting dark matter and sterile neutrinos that can tackle all four small-scale problems.

Speaker: No colloquium this week.
Speaker: Nancy Tomes, Department of History, Stony Brook University
Subject: "’Recovery’ as Concept, Model, and Movement in the Mental Health Field: the Challenge of Writing a ‘History of the Present’"
Refreshments served at 3:15 p.m.

Since the 1980s, the recovery concept has become central to efforts to empower people with severe and persistent mental illness. Advocates of the recovery model stress the importance of non-medical measures, such as supported employment, supported housing, strong community networks and perhaps most importantly, the support and leadership of other people with lived experience of mental illness. My talk will explore both the history and the historiography of the recovery model in the mental health field. I will discuss how the approaches that emerged in the 1970s and 1980s differed from previous attempts at “after care” for ex-mental patients, and look at their overlap with contemporary developments in addiction treatment and the disability rights movement. Finally, I will discuss criticisms of the recovery movement and its place in late 20th c. “reforms” of the welfare state as an example of how historical scholarship intersects with contemporary advocacy concerns and policy issues.

3:35 pm:
Speaker: Miranda Straub
Subject:  Instructor beliefs about homework

This talk will present the initial analysis of 25 physics instructor interviews from post-secondary institutions around the state of Minnesota. The interviews focused on problem solving, and this talk will highlight beliefs about homework. Specifically, what do instructors think students should do and learn while they are doing homework.

4:40 pm:
Speaker: Ke Wang, University of Minnesota
Subject: Quantum Control in 2D Van der Waals Nanostructures

Monday, January 29th 2018
12:15 pm:
There will be no seminar this week.
3:30 pm:
FTPI Special Seminar in Tate 301-20
Speaker: Maxim Pospelov
Subject: "Widening the net in search for New Physics"
Candidate for FTPI Faculty Position

Following spectacular confirmation of the Standard Model at the LHC, the emphasis of particle physics shifts towards searches for physics beyond Standard Model. The clues for new physics may be hidden in cosmological data that suggest the dominance of dark matter and dark energy throughout the Universe. I will describe some recent aspects of widening the search for new physics focussing on light dark matter and in general on light weakly coupled states. I will introduce constraints on dark matter - electron scattering that result from a new phenomenon, the reflection of dark matter from the solar interior. I will also argue that besides conventional probes of light weakly coupled states, further insight can be gained by involving precision AMO tools, and describe some recent experimental activity in this direction.

Faculty Host: Keith Olive

Tuesday, January 30th 2018
12:20 pm:
Space Physics Seminar in Tate 301-20
Speaker: Oleksiy Agapitov, Space Sciences Laboratory, University of California, Berkeley
Subject: Nonlinear wave-particle and wave-wave interactions in the outer radiation belt: physical mechanisms and observational effects
1:00 pm:
FTPI Special Seminar in Tate 201-20
Speaker: Maxim Pospelov
Subject: "Light Z' coupled to poorly conserved currents"
Candidate for FTPI Faculty Position
Faculty Host: Keith Olive
3:30 pm:
Speaker: Damjan Pelc, University of Minnesota
Subject: New ways to learn about quantum materials
Refreshments will be served at the meeting so don't forget to bring your favorite mug.

I will discuss two unusual experimental techniques currently being developed for the study of quantum materials: nonlinear magnetic response and uniaxial pressure. They can be used to detect and modify the fundamental symmetries of materials, with great potential for new insights. In particular, I will examine the symmetry properties of nonlinear magnetic susceptibility, with applications in the study of chiral superconductors. Furthermore, I will present a novel approach to uniaxial pressure experiments, which can easily be combined with various other techniques to investigate the effects of broken structural symmetries.


Wednesday, January 31st 2018
1:30 pm:
Speaker: Sergey Frolov, University of Pittsburgh
Subject: Quantum dot chains as emulators of topological superconductors

Tunneling spectroscopy measurements on one-dimensional superconducting hybrid materials have revealed signatures of Majorana fermions which are the edge states of a bulk topological superconducting phase. We couple strong spin-orbit semiconductor InSb nanowires to conventional superconductors (NbTiN, Al) to obtain additional signatures of Majorana fermions and to explore the magnetic-field driven topological phase transition. Specifically, we map out the phase diagram of the topological phase in the space of Zeeman energy and chemical potential, and investigate the apparent closing and re-opening of the superconducting gap. We investigate how the topological superconducting phase would manifest in finite size systems, by electrostatically splitting the wire into segments of varied length. By chaining up several segments of a nanowire, we are realizing a quantum simulator of the Kitaev chain with tunable on-site energies and couplings between the sites, a step towards quantum simulation with semiconductor nanostructures.

Faculty Host: Vlad Pribiag
3:35 pm:
To be announced.

Thursday, February 1st 2018
10:10 am:
Biophysics Seminar in 120 PAN
Speaker: Joseph Muretta, University of Minnesota, Biochemistry, Molecular Biology and Biophysics
Subject: Adventures in Biophysics: Lysine Acetylation Tunes Mechanochemical Coupling and Force Output in a Mitotic Kinesin
Speaker: Claudia Scarlata
3:35 pm:
Speaker: Mark Bell, University of Minnesota
Subject: Nuclear Weapons and International Politics Today

Nuclear weapons are back in the news. This talk provides an overview of the most important and pressing current issues relating to nuclear weapons and international politics, including ongoing US-North Korea tensions, US nuclear modernization and the US Nuclear Posture Review, the extent of presidential authority over nuclear weapons, the risk of nuclear proliferation by U.S. allies and adversaries, and the recent nuclear ban treaty. The talk places these current issues within a broader historical context and discusses the extent to which today's nuclear concerns represent continuity or change from previous eras.

Faculty Host: Robert Lysak

Friday, February 2nd 2018
10:10 am:
Nuclear Physics Seminar in Tate 201-20
There will be no seminar this week.
12:20 pm:
Speaker:  Zedong Yang, University of Minnesota
Subject: Towards spin injection into semiconductor nanowires

InSb nanowires have been established as a versatile materials platform for realizing Majorana bound states and for investigating spin-orbital interaction (SOI) and large effective g-factor. By coupling InSb nanowires to ferromagnetic (FM) contacts, a spin-polarized current can be injected into the nanowires and subsequently controlled by electric fields. We will report on our progress fabricating nanowire devices with FM electrodes in local spin-valve geometry, as well as discussing our low-temperature transport experiments on these devices.

Speaker: Liliana Velasco-Sevilla (Bergen U., Norway)
Subject: How multi-Higgs Physics Could Uncover the Nature of Flavour
1:35 pm:
There is no seminar this week.
Speaker: No colloquium this week.
Speaker: Marc Swackhamer, School of Architecture, University of Minnesota
Subject: "Hypernatural: Architecture's New Relationship with Nature" - MCPS Annual Science Studies Symposium
Refreshments served at 3:15 p.m.

Recent decades have witnessed the increasing popularity of nature-focused movements in architecture, such as sustainability, biophilia, biomimicry, biodesign, and emergent design. These movements are dramatically altering the relationship between the designed environment and the natural world, and although overlaps exist, there is no common discourse that unites these areas of study. A holistic framework is therefore needed to address these disparate areas of inquiry, the full spectrum of their operations, and their common goals and methodologies. This talk will address the ways in which architectural designers increasingly work directly with natural processes—rather than against them—in order to amplify, extend, or exceed natural capacities.

4:40 pm:
Speaker: Jochen Mueller, University of Minnesota
Subject: Physics of the cell: From viral assembly to fluctuating membranes

Monday, February 5th 2018
Speaker: Jeff Pedelty, NASA
Subject: Jeff will share his diverse experiences while working for NASA and its industrial partners.

Jeff earned a B.S. in physics from the Iowa State University in 1981 and a Ph.D. in astrophysics from the University of Minnesota in 1988. His thesis combined observational radio astronomy with Professor Rudnick and computational fluid dynamics with Professor Woodward. Since leaving Minnesota he has worked for NASA’s Goddard Space Flight Center in Greenbelt, MD. He supported the Nobel-winning Cosmic Background Explorer (COBE), the Earth science missions Landsat 7, 8, and 9, and the Joint Polar Satellite System (JPSS-1) weather satellite. He also worked in the areas of high performance computing, signal and image processing, astrobiology, and remote sensing science. For the past 10 years he has worked for the Landsat Project onsite at Ball Aerospace in Boulder, CO and at Orbital ATK in Gilbert, AZ.

12:15 pm:
There will be no seminar this week.

Tuesday, February 6th 2018
12:20 pm:
Space Physics Seminar in Tate 301-20
Speaker: Dr. Ricky Egeland, High Altitude Observatory, National Center for Atmospheric Research.
Subject: A Critical Rossby Number for Sun-Like Variability

Despite centuries of observation and decades of theoretical work, the ~11 year solar magnetic sunspot cycle remains one of the longest-standing unsolved problems in astrophysics. Additional insights can be made using synoptic observations of proxies for magnetism in other stars, where the varied stellar properties set the conditions for separate "dynamo experiments." We examine the decadal-scale variability in Ca II H & K emission of the Sun and a set of 26 solar analog stars within ~5% of the solar effective temperature but with varied mean rotation. Using a quantitative metric for determining cycle quality, we find that cycles of the highest quality—like the Sun's—occur in the stars with slower rotation and lower mean activity. Reexamining the results of a larger set of ~100 stars from the Baliunas et al. 1995 study of Mount Wilson H & K emission, we find again that the highest quality cycles occur for low activity and high Rossby number, the ratio of the rotation period to the convective turnover time. Guided by these observations, we propose the hypothesis that Sun-like variability—either a clean, monoperiodic cycle or flat activity analogous to the Maunder Minimum—occurs in G- and K- type main-sequence stars if and only if the Noyes et al. 1984 semi-empirical Rossby number is larger than 1.5, or equivalently if the star is on the low-activity side of the Vaughan-Preston gap. These results demonstrate the critical role of the Rossby number in determining the behavior of stellar dynamos.

2:30 pm:
Speaker: David Radice, Princeton University
Subject:  Multimessenger astrophysics with numerical relativity
Candidate for the Nucear Theory Assistant Professor position

How are neutron stars formed and what is inside them? What is the
engine powering short gamma-ray bursts? What is the astrophysical site
of production of heavy elements? Multimessenger observations of
compact binary coalescence and core-collapse supernovae might provide
us with the key to answer these and other important open questions in
theoretical astrophysics. However, multimessenger astronomy also poses
new challenges to the theorists who need to develop models for the
joint interpretation of all data channels. In this talk, I will
present recent theoretical results. I will review the landmark
multimessenger observation of merging neutron stars, and I will
discuss its interpretation and implication in the light of results
from first-principles simulations. Finally, I will discuss future
challenges and prospective for this nascent field.


Wednesday, February 7th 2018
1:30 pm:
Speaker: Cristian Batista, University of Tennessee
Subject: Pairing from strong repulsion in the triangular lattice Hubbard model

The generation of an effective attraction between electrons out of the bare Coulomb repulsion is a long sought-after goal of the condensed matter community. In this talk I will introduce a pairing mechanism between holes in the dilute limit of doped frustrated Mott insulators. We will see that magnons provide a strong glue in the infinitely repulsive limit of the triangular lattice Hubbard model. The strongly attractive hole-magnon interaction is a manifestation of a “counter-Nagaoka” theorem: the single-hole kinetic energy is minimized for an antiferromagnetically ordered state. We will demonstrate that the resulting hole-magnon attraction is strong enough to bind a second hole and to form a hole-hole-magnon three-body bound state. Remarkably, the binding energy of this “composite Cooper pair” is rather strong, while its effective mass still has a moderate value, giving rise to relatively high transition temperature for superconductivity in the dilute limit. I will discuss a few interesting consequences of this new mechanism for unconventional superconductivity.

Work done in collaboration with Shangshun Zhang (University of Tennessee) and Wei Zhu (Los Alamos National Laboratory).

Faculty Host: Natalia Perkins
Speaker: Yassin Haddad, Imperial College London
Subject: Latest Results on Higgs to Diphotons from CMS

The most-recent results on Higgs to diphotons measurements from CMS will be reviewed. (Speaker is a candidate for a postdoctoral research position and will be presenting by video)


Thursday, February 8th 2018
10:10 am:
Biophysics Seminar in 120 PAN
No Seminar This Week
Speaker: Liliya Williams and Stou Sandalski
3:35 pm:
Speaker: Cristian Batista, University of Tennessee
Subject: Skyrmions and Vortices in Magnetic Systems

The history of magnetism dates back to earlier than 600 b.c., but it is only in the twentieth
century that scientists have begun to understand it, and develop technologies based on this
understanding. The new experimental techniques that were developed over twentieth century
allowed physicists to discover new forms of magnetism that they called “antiferromagnets”.
Unlike ferromagnets, the magnetic moments of antiferromagnets point along different directions
in such a way that the magnetic unit cell has no net magnetic moment. Typical configurations of
antiferromagnets are spiral orderings arising from competing exchange interactions or from the
Ruderman–Kittel–Kasuya–Yosida (RKKY) interaction between magnetic moments embedded
in metallic environments.
The new century started with the observation of a new generation of antiferromagnets
comprising more exotic magnetic textures, such as skyrmion and vortex crystals [1-3]. These
textures were unveiled thanks to the enormous progress made in real and reciprocal space
visualization techniques. We will discuss a few attractive properties of these novel phases and
the simple principles that should guide the experimental search. For instance, we will see that an
external magnetic field can induce a skyrmion crystal phase in hexagonal lattices (lattices with
six equivalent orientations for the spiral ordering) with easy-axis anisotropy [4-10]. Moreover,
we will see that magnetic skyrmions behave as mesoscale particles, which can order in different
three-dimensional structures, such as face centered tetragonal and hexagonal closed packed
crystals [10].
References
[1] U. Rößler, A. Bogdanov, and C. Pfleiderer, Nature 442, 797 (2006).
[2] A. N. Bogdanov and D. A. Yablonskii, Sov. Phys. JETP 68, 101 (1989).
[3] A. Bogdanov and A. Hubert, Journal of Magnetism and Magnetic Materials 138, 255 (1994).
[4] S. Hayami, S.-Z. Lin, and C. D. Batista, Phys. Rev. B 93, 184413 (2016).
[5] A. O. Leonov and M. Mostovoy, Nature Communications 6, 8275 (2015).
[6] Shi- Zeng Lin, Satoru Hayami and C. D. Batista, Phys. Rev. Lett. 116, 187202 (2016).
[7] C. D. Batista, S-Z. Lin, S. Hayami and Y. Kamiya, Reports on Progress in Physics, Volume 79, 8
(2016).
[9] Satoru Hayami, Shi-Zeng Lin, Yoshitomo Kamiya, and Cristian D. Batista, Phys. Rev. B 94, 174420.
[10] Shi-Zeng Lin and C. D. Batista, arXiv:1707.05818v1.

Faculty Host: Natalia Perkins

Friday, February 9th 2018
10:10 am:
Nuclear Physics Seminar in Tate 201-20
There will be a special nuclear physics seminar on Tuesday this week.
12:20 pm:
Speaker: Xuzhe Ying, University of Minnesota
Subject: Topological Metals

I will discuss how to obtain a gapless phase from a topological gapped phase by breaking both time reversal and inversion symmetry. The specific model would be 2D p+ip chiral superconductor. 2D chiral superconductor belongs to symmetry class D with particle-hole symmetry and could support chiral Majorana. A supercurrent could break inversion symmetry and make system gapless. I'm going to discuss that particle-hole symmetry guarantees that there is a metallic phase which is distinct from trivial metal.

Speaker: Robert Lasenby (Perimeter)
Subject: Searching for Weakly Coupled New Particles with Stellar Cooling

Many theories of beyond Standard Model physics include new light, weakly-coupled particles, which can be challenging to search for experimentally. The high densities and temperatures in stellar cores allow them to produce such particles in large numbers, while the large volume to surface area ratio of stars enhances the relative effects of such production on stellar energy transfer and cooling. This makes stellar observations into a sensitive probe of new particles. I’ll describe how the plasma environment in stellar cores can parametrically alter the rates for these processes, and how this can significantly change the constraints and discovery potential for some new particle candidates. I’ll also discuss some other situations where in-medium effects are important in the search for weakly-coupled new physics.

Speaker: Terry Jones, University of Minnesota
Subject: Interstellar Polarization

This talk will start with a bit of retrospective on my career in astronomy, after which I will focus on the topic of interstellar polarization. I will concentrate on work done here at the University of Minnesota, up to current work using MMTPol on the MMT and HAWC+ on SOFIA. The primary science goal of this work is to study the magnetic field geometry in all phases of the interstellar medium, and determine what limitations there are to that effort. Lastly, I will describe some future trends.

Speaker: Jacqueline Feke, Department of Philosophy, University of Waterloo
Subject: "Ptolemy's Ethics"
Refreshments served at 3:15 p.m.

Why did Ptolemy devote his time to the mathematical sciences, especially astronomy? The answer lies in his brief ethical statement in the first chapter of the Almagest. Coopting virtue ethics for the mathematician, Ptolemy argues that the best life is the one devoted to mathematics, where the mathematician configures his soul in accordance with the good order in the heavens. In this paper, I analyze this ethical statement and argue that to understand why and how astronomical objects serve as ethical exemplars in Ptolemy’s philosophy we must look to his Harmonics. It is because musical pitches, heavenly bodies, and human souls are all characterized by harmonic ratios that the study of either harmonics or astronomy can lead to the good life.

3:35 pm:
Speaker: Kaylee Ganser
Subject: The Effect of Active Learning Classes on Introductory Physics Student Performance at UMN-Duluth

In order to determine the effect the new active learning classroom had on academic gains for introductory physics students at UMN-Duluth, we analyzed three data sets: the scores from a diagnostic test given at both the beginning and end of the semester (the Force Concept Inventory) and the scores from a common problem on the final exam (scored using a common checklist) for Spring 2016, and the FCI scores for Fall 2016. For the Spring 2016 semester, we
compared 3 Active Learning classes with a lecture group as a control, and for Fall 2016, all sections were Active Learning. For Spring 2016, we found that, for sufficiently ‘Active Learning’ style based teaching methods, the active learning classroom improved student scores compared to previous data, but the lecture section failed as a control due to various factors. For the Fall 2016 classes, the academic gains were less than both of Spring 2016’s data sets and past data, which indicates that additional criteria beyond simply moving into an Active Learning style classroom may be necessary to improve student scores or that students are learning skills not testable by the FCI. Academic gains made by women and racial minority students are suggestive of an improvement in active learning classes, but more data is needed to determine the true extent of this effect.

4:40 pm:
Speaker: Vincent Noireaux, University of Minnesota
Subject: DNA programmed dynamical systems outside cells: from gene circuits to self-assembly

Monday, February 12th 2018
12:15 pm:
Speaker: Lawrence Rudnick, UMN
Subject: The Stormy Life of Galaxy Clusters

This is a modified version of my plenary talk from the recent AAS Meeting. Regular cosmo seminar attendees will have seen some of this before, but this talk puts things into a larger, and hopefully useful, context.

Galaxy clusters, the largest gravitationally bound structures, hold the full history of their baryonic evolution, serve as important cosmological tools and allow us to probe unique physical regimes in their diffuse plasmas. With characteristic dynamical timescales of 107-109 years, these diffuse thermal and relativistic media continue to evolve, as dark matter drives major mergers and more gentle continuing accretion. The history of this assembly is encoded in the plasmas, and a wide range of observational and theoretical investigations are aimed at decoding their signatures. X-ray temperature and density variations, low Mach number shocks, and "cold front" discontinuities all illuminate clusters' continued evolution. Radio structures and spectra are passive indicators of merger shocks, while radio galaxy distortions reveal the complex motions in the intracluster medium. Deep in cluster cores, AGNs associated with brightest cluster galaxies provide ongoing energy, and perhaps even stabilize the intracluster medium. In this talk, we will recount this evolving picture of the stormy ICM, and suggest areas of likely advance in the coming years.

3:30 pm:
Speaker: Katherine Freese
Subject: The Dark Matter in the Universe
Candidate for FTPI Faculty Position

“What is the Universe made of?” This question is the longest outstanding problem in all of modern physics, and it is one of the most important research topics in cosmology and particle physics today. The bulk of the mass in the Universe is thought to consist of a new kind of dark matter particle, and the hunt for its discovery in on. I'll start by discussing the evidence for the existence of dark matter in galaxies, and then show how it fits into a big picture of the Universe containing 5% atoms, 25% dark matter, and 70% dark energy. Neutrinos only constitute ½% of the content of the Universe, but much can be learned about neutrino properties from cosmological data. Leading candidates for the dark matter are Weakly Interacting Massive Particles (WIMPs), axions, and sterile neutrinos. WIMPs are a generic class of particles that are electrically neutral and do not participate in strong interactions, yet have weak-scale interactions with ordinary matter. There are multiple approaches to experimental searches for WIMPS: at the Large Hadron Collider at CERN in Geneva; in underground laboratory experiments; with astrophysical searches for dark matter annihilation products, and upcoming searches with the James Webb Space Telescope for Dark Stars, early stars powered by WIMP annihilation. Current results are puzzling and the hints of detection will be tested soon. At the end of the talk I'll briefly turn to dark energy and its effect on the fate of the Universe.

Faculty Host: Keith Olive

Tuesday, February 13th 2018
12:20 pm:
Space Physics Seminar in Tate 301-20
There will be no seminar this week.
1:00 pm:
FTPI Special Seminar in Tate 201-20
Speaker: Katherine Freese
Subject:  Inflationary Cosmology: Theoretical Developments and Status in light of Cosmic Microwave Background Data
Candidate for FTPI Faculty Position
Faculty Host: Keith Olive
3:30 pm:
Speaker: Maria Navarro Gastiasoro, University of Minnesota
Subject: "Superconductivity in Strontium Titanate"

Wednesday, February 14th 2018
1:25 pm:
Speaker: Damjan Pelc (University of Minnesota)
Subject: Inhomogeneous charge localization in the cuprates

I will discuss new experimental results and insights into the physics of cuprate high-temperature superconductors, providing an overarching framework for understanding these materials.
Motivated by transport measurements, I will consider an inhomogeneous Mott-like (de)localization model wherein exactly one hole per copper-oxygen unit is gradually delocalized with increasing doping and temperature. The model comprehensively captures pivotal unconventional experimental results, including the temperature and doping dependence of the pseudogap phenomenon, the strange-metal linear temperature dependence of the planar resistivity, and the doping dependence of the superfluid density. The simple model greatly demystifies the cuprate phase diagram, and points to a local superconducting pairing mechanism involving the (de)localized hole. The spatial inhomogeneity of the localization gap is thus expected to cause a distribution of superconducting gaps as well, leading to superconducting percolation. Accordingly, for several representative cuprates the superconducting diamagnetism, nonlinear conductivity, and paraconductivity exhibit an unusual temperature dependence above Tc that is captured by a simple percolation model. The results show that that intrinsic, universal gap inhomogeneity is highly relevant to understanding the properties of the cuprates.

Faculty Host: Paul Crowell
To be announced.

Thursday, February 15th 2018
10:10 am:
Biophysics Seminar in 120 PAN
Speaker: Jasmine Foo, School of Mathematics, University of Minnesota
Subject: Impact of the tumor microenvironment on drug resistance in cancer

Despite the effectiveness of many therapies in reducing tumor burden during the initial phase of treatment, the emergence of drug resistance remains a primary obstacle in cancer treatment. Tumors are comprised of highly heterogeneous, rapidly evolving cell populations whose dynamics can be modeled using evolutionary theory. In this talk I will describe some mathematical models of the evolutionary processes driving drug resistance in cancer, and demonstrate how these models can be used to provide clinical insights. These models will be applied to study the impact of dosing schedules and the tumor microenvironment on the emergence of drug resistance in lung cancer.

3:35 pm:
Speaker: Mark Saffman (University of Wisconsin)
Subject: Quantum computing with simple and complex atoms
Refreshments in atrium after the Colloquium.

Quantum computing is a few decades old and is currently an area where there is great excitement, and rapid developments. A handful of distinct approaches have shown the capability of on demand generation of entanglement and execution of basic quantum algorithms.

One of the daunting challenges in developing a fault tolerant quantum computer is the need for a very large number of qubits. Neutral atoms are one of the most promising approaches for meeting this challenge. I will give a snapshot of the current status of quantum computing in general and atomic quantum computing in particular. The atomic physics underlying our ability to control neutral atom qubits will be described, and I will show how one of the most complicated atoms in the periodic table may lead to some simple solutions to hard problems.

Faculty Host: Paul Crowell

Friday, February 16th 2018
10:10 am:
Nuclear Physics Seminar in Tate 201-20
There will be no seminar this week.
12:20 pm:
Speaker: Jianlong Fu
Subject: Majorana representations of spin and the Kitaev honeycomb model

Quantum spin liquid has been studied intensively in recent years. Among various types of spin liquid, the Kitaev model is unique because it is exactly solvable. Kitaev’s original solution is based on Majorana representation of spin. In this talk, I will discuss three types of Majorana representation of spin and argue that they can be linked together by Dirac spinor representation of SO(4) group. Then, I will discuss an alternative solution of the Kitaev model using another Majorana representation and talk about aspects of the solution.

Speaker: No seminar this week
Speaker: Evan Skillman, MIfA
Subject: The Resolved Stellar Populations JWST Early Release Science Program

Our JWST ERS program will obtain deep multi-band NIRCam and NIRISS imaging of three resolved stellar systems within 1 Mpc. We will use this broad science program to optimize observational setups and to develop data reduction techniques that will be common to JWST studies of resolved stellar populations. We will combine our expertise in HST resolved star studies with these observations to design, test, and release point spread function (PSF) fitting software specific to JWST. PSF photometry is at the heart of resolved stellar populations studies, but is not part of the standard JWST reduction pipeline. Our program will establish JWST-optimized methodologies in six scientific areas: star formation histories, measurement of the sub-Solar mass stellar IMF, extinction maps, evolved stars, proper motions, and globular clusters, all of which will be common pursuits for JWST in the local Universe. Our observations will be of high archival value (e.g., for calibrating stellar evolution models, measuring properties of variable stars, and searching for metal-poor stars) and will provide blueprints for the community to efficiently reduce and analyze JWST observations of resolved stellar populations.

Speaker: Cynthia Connolly, School of Nursing, University of Pennsylvania
Subject: "A 'Big Business Built for Little Customers:' Children and the Flavored Aspirin Market in the United States, 1948–1973"
Refreshments served at 3:15 p.m.

By the early postwar era, new children’s consumer goods such as sweetened cereals, toys, games, and books flooded the market. In September, 1947, the bright orange-colored St. Joseph Aspirin for Children joined them amid a wave of creative marketing for what became known as candy aspirin. An immediate success, flavored low dose aspirin reshaped medical, nursing, and parental responses to pediatric fever and pain. Unfortunately, however, its popularity with children resulted in an unintended consequence—a 500% increase in aspirin poison rates within a few years. While pediatricians and public health activists argued for warning labels and reconfigured bottles that made it harder for children to access the pills, the aspirin industry went on the offense, using tactics similar to those of the cigarette industry— challenge the problem’s existence; the data underpinning the science; deflect blame onto parents; and mount a public relations campaign aimed at confusing the public. This paper analyzes a complicated set of negotiations at the junction of science, commerce, and childhood. In an era rife with child protection rhetoric, debates surrounding children’s aspirin in the years between 1948 and 1973 reveal the competition among stakeholders to “speak” for children, the many negotiations regarding how to determine children’s “best interests,” and what can happen when recommendations for children’s well-being challenge the economic well-being of major corporations.

3:35 pm:
To be announced.
4:40 pm:
Speaker: Paul Crowell, University of Minnesota
Subject: Spin Transport and Dynamics in Metals and Semiconductors

Monday, February 19th 2018
09:30 am:
Thesis Defense in Tate-301
Speaker: Kate Raach, University of Minnesota
Subject: Characterization, Optimization, and Operation of TES Bolometers for EBEX
Please note time of defense was incorrect in previous message.
12:15 pm:
Speaker: Marcelo Alvarez, UC Berkeley, Berkeley Center for Cosmological Physics
Subject:  The Bright Future of Reionization with 21 cm and CMB Observations

In the coming decade we will witness the completion of CMB and 21 cm experiments that promise to lift the veil on reionization. Up until now, the details of reionization have remained shrouded in mystery across the chasm of space and time that separates us from the billion years after the big bang in which it occured, more than 12 billion years ago and 30 billion light years away due to cosmic expansion. CMB observations probe the distribution of what we think was a complicated network of growing and overlapping ionized bubbles created by UV and X-ray ancient dwarf galaxies and newborn supermassive black holes, while 21 cm observations probe the neutral patches left behind. As such, these two types of observations provide complementary information about the first billion years. I will discuss the exciting new prospects for understanding reionization by analyzing upcoming 21 cm and CMB observations jointly, emphasizing how simulations can help us avoid the pitfalls associated with teasing out the faint signals from nearby foregrounds, instrumental noise, and systematics.

Faculty Host: Shaul Hanany
3:30 pm:
Speaker: Mithat Unsal
Subject: Decoding path integrals: Resurgence and mass gap
Candidate for FTPI Faculty Position

I will provide an introductory level overview of recent
applications of resurgent trans-series and Picard-Lefschetz theory to
quantum mechanics and quantum field theory.
Resurgence connects local perturbative data with global topological
structures. In quantum mechanical systems, this program provides a
constructive relation between different saddles. For example, in
certain cases it has been shown that all information around the
instanton saddle is encoded in perturbation theory around the
perturbative saddle. In quantum field theory, such as sigma-models
compactified on a circle, neutral bions provide a semi-classical
interpretation of the elusive IR-renormalon, and fractional kink
instantons lead to the non-perturbatively induced mass gap exactly of
order of the strong scale. I also describe the concept of hidden
topological angle, a phase associated with Lefschetz thimbles.
Hidden topological angle may provide destructive/constructive
interference effects between equally dominant saddles in the Lefschetz
thimble decomposition, providing resolution to some time standing
puzzles in non-perturbative analysis.

Faculty Host: Keith Olive

Tuesday, February 20th 2018
12:20 pm:
Space Physics Seminar in Tate 301-20
Speaker: Pat Meyers, University of Minnesota
Subject: Extremely low frequency electromagnetic waves and gravitational-wave detectors

The current generation of gravitational-wave (GW) detectors has already made phenomenal discoveries. One of the next frontiers of GW astrophysics is a measurement of the stochastic gravitational-wave background (SGWB). The SGWB is a superposition of many unresolvable stellar sources of GWs and potentially GWs from the earliest epochs of the Universe. Current searches for an SGWB rely on long cross-correlation measurements made with data from detectors separated by thousands of kilometers. The most likely source of correlated noise between detectors this far apart is extremely low frequency, persistent, electromagnetic waves like Schumann resonances. I'll discuss how these waves are produced, some recent measurements made using a global network of magnetometers, and how the waves can couple into GW detectors. Finally, I'll discuss development of methods to budget for and potentially subtract them from the GW data.

1:00 pm:
FTPI Special Seminar in Tate 201-20
Speaker: Mithat Unsal
Subject: Phase transitions, semi-classics and anomalies
Candidate for FTPI Faculty Position
Faculty Host: Keith Olive
2:30 pm:
Speaker:  Jorge Noronha, Universidade de Sao Paulo
Subject: Unveiling the secrets of nature's primordial liquid
Candidate for the Nucear Theory Assistant Professor position

Microseconds after the Big Bang, the Universe cooled into an exotic phase of matter. There the fundamental building blocks of Quantum Chromodynamics (QCD), known as quarks and gluons, were not confined inside the core of atomic nuclei. Tiny specks of this early Universe matter, called the Quark-Gluon Plasma (QGP), are now being copiously produced in heavy ion collisions at both RHIC and the LHC. These experiments provide overwhelming evidence that the QGP flows like a nearly frictionless strongly coupled liquid over distance scales not much larger than the size of a proton. Thus, the QGP formed in particle colliders is the hottest, smallest, densest, most perfect liquid known to humanity. Yet, the theoretical underpinnings behind the liquid-like behavior of QCD matter remain elusive.

In this talk I will present first principles calculations performed within string theory and relativistic kinetic theory that have shed new light on the emergence of hydrodynamic behavior in QCD and challenged the very foundations of fluid dynamics. New techniques to determine the real time, far-from-equilibrium dynamics of QCD in the large baryon density regime will also be discussed to lead current experimental efforts to discover critical phenomena in the fundamental theory of strong interactions.


Wednesday, February 21st 2018
1:25 pm:
Speaker: Erez Berg (U of Chicago)
Subject: Transport beyond the quasiparticle picture: a view from the large-N limit

In normal metals, the electron's mean free path is much larger than its wavelength, allowing a semiclassical treatment of transport. Conversely, whenever scattering is so strong that the mean free path becomes comparable to the electron's wavelength, the concept of a quasiparticle becomes ill defined, and a new theoretical framework is needed. I will introduce a family of lattice models for interacting electrons that can be solved exactly in the limit of a large number of interacting electron flavors and/or phonon modes. Depending on details, these models exhibit either "resistivity saturation" at high temperatures to a value of the order of the quantum of resistance, or "bad metallic behavior" where the resistivity grows without bound with increasing temperature. Translationally invariant higher-dimensional generalizations of the Sachdev-Ye-Kitaev model can capture a variety of phenomena arising purely from electron-electron interactions, including local criticality, non-Fermi liquid, and marginal Fermi liquid behavior. I will describe the implications of these results for the problem of non-quasiparticle transport at large, local quantum criticality, and fundamental bounds on dissipation rates in quantum systems.

Faculty Host: Rafael Fernandes
To be announced.

Thursday, February 22nd 2018
10:10 am:
Biophysics Seminar in 120 PAN
No Seminar This Week - Biophysical Society Meeting
Speaker: Avery Garon and Scott Thaller
3:35 pm:
Speaker: Erez Berg (University of Chicago)
Subject: Critical Metals: Lessons from quantum Monte Carlo studies

Critical phenomena are one of the cornerstones of classical statistical mechanics. Quantum critical points (i.e., continuous phase transitions at zero temperature) in insulating materials are relatively well understood, by analogy with classical critical points in one spatial dimension higher. In contrast, the theory of quantum critical behavior in metals is still, to a large degree, open. Such metallic critical points are believed to play an important role in the physics of several "strongly correlated" materials, such as high temperature superconductors. Fortunately, many classes of metallic quantum critical points can be simulated efficiently using quantum Monte Carlo without the notorious "sign problem", which often hinders numerical simulations of fermionic systems. I will describe some recent progress along these lines, and how it sheds new light on some of the outstanding puzzles in the field.

Faculty Host: Rafael Fernandes

Friday, February 23rd 2018
10:10 am:
Nuclear Physics Seminar in Tate 201-20
There will be no seminar this week.
12:20 pm:
Speaker: James Delles, University of Minnesota
Subject: Thermally Activated Hopping over a Barrier in a Mesoscale Permalloy System

Thermally activated hopping between energy minima in a double well system is expected to follow an Arrhenius Law. Experiments have shown that the rate of switching between two wells is proportional to the Boltzmann factor but little work has been done to probe the nature of the characteristic dwell time. A square, permalloy, mesoscale dot with an applied magnetic field can be used to create a double well system to explore the characteristic dwell time. I will show that the characteristic dwell time has an exponential dependence on the height of the barrier. There is a significant quantitative disagreement between accepted models of the dwell time and our results.

Speaker: Daniel Chung (U. Wisconsin, Madison)
Subject: Searching for Axionic Blue Isocurvature Perturbations

If the Peccei-Quinn symmetry breaking field is displaced from its minimum
during inflation, the axion isocurvature spectrum is generically strongly
blue tilted with a break transition to a flat spectrum. A test of this
scenario with the Planck and BOSS DR11 data will be presented. Encouraging
results and its implications for future probes of axions and inflationary
cosmology will be discussed.

Speaker: Attila Kovacs (SAO)
Subject: Far-infrared frontiers

The far-infrared (FIR) and (sub)millimeter bands provide us with unique views of structure formation in the Universe and the Galaxy alike. At these wavelengths we have the most adept probes of active star-formation that sample almost all of the reionized Universe (z~1--10) with essentially no bias. The Sunyayev Zel'dovich effect traces the assembly of galaxy clusters regardless of cosmological distance. Locally, in the Galaxy, FIR polarimetry probes the magnetic environments and dust properties around optically obscured young stars and cores, while FIR spectroscopy can spy on the ices in planetary disks. I will also highlight some of the ground-braking recent and upcoming instrumentation and technologies I work on to can deliver this scientific treasure trove.

Speaker: Nahyan Fancy, Department of History, DePauw University
Subject: "Did Humoral Theory Undergo any Changes in Post-Avicennan Medicine? Examples from the Commentaries of Ibn al-Nafīs (d. 1288) and his Successors in Western Eurasia"
Refreshments served at 3:15 p.m.

It has long been maintained that Galenic/Hippocratic humoral theory reigned supreme in Islamic societies from when Greek medical texts were translated into Arabic in the ninth century till the arrival of European colonial powers in the nineteenth. Historians have provided various explanations for the persistence of humoral theory in Islamic societies ranging from the (alleged) religious prohibition against dissection to a predisposition amongst medical writers towards systematizing and summarizing rather than critical inquiry. Yet, medical writers engaged critically with medical theory in their commentaries on the Canon of Medicine and the Epitome. The leading figure in this critical engagement was Ibn al-Nafīs (d. 1288). Underlying his modification of humoral theory was a sustained critique of the Galenic physiological and anatomical understanding of digestion. Consequently, the paper provides evidence for Ibn al-Nafīs conducting anatomical observations on dead animals. Moreover, the fact that his new proposals were debated and accepted by later Islamic physicians counters the prevalent assumption that his works were ignored in the later period, and thus raises the distinct possibility that these new ideas on the humors and digestion were appropriated by Renaissance physicians such as Jean Fernel.

3:35 pm:
To be announced.
4:40 pm:
To be announced.

Monday, February 26th 2018
12:15 pm:
There will be no seminar this week.

Tuesday, February 27th 2018
12:20 pm:
Space Physics Seminar in Tate 301-20
Practice Talks for the upcoming Chapman Conference on Particle Dynamics in the Earth's Radiation Belts.
3:30 pm:
Speaker: Samuel Lederer, MIT
Subject: High temperature superconductivity and strange metal behavior near a metallic quantum critical point

It has long been conjectured that quantum critical points (QCPs) are at the root of some of the most fascinating phenomena in the solid state, including the high temperature superconductivity and “strange metal” behavior of cuprate superconductors. Though much progress has been made in the theory of QCPs, those which occur in metals (and are likely relevant to the high temperature superconductors) are still poorly understood despite more than four decades of effort. Using Quantum Monte Carlo techniques, my collaborators and I have performed the first numerically exact simulations of a model which realizes a metallic QCP towards an Ising nematic ordered phase. I will discuss our results, which include numerous phenomena already observed in experiment, and comment on future avenues towards a solution of this difficult and rich problem in quantum statistical mechanics.

Faculty Host: Rafael Fernandes

Wednesday, February 28th 2018
1:25 pm:
Speaker: Various speakers
Subject: APS March Meeting Practice Talks
Speaker:  Hajime Muramatsu, University of Minnesota
Subject: Leptonic Decays of Charmed Mesons at BESIII

BESIII now holds the world's largest e+e- annihilation samples taken at Ecm = 3.773 and 4.178 GeV which produce copious charmed mesons, D0, D+, and Ds+. In this talk, I report our on-going studies on D+ -> l nu and Ds -> l nu (l = mu and tau). These allow us to determine the elements of the CKM matrix within the standard model, to test the unitarity of the second rows of the CKM matrix, probe lepton universality, as well as to calibrate the LQCD calculations of the decay constants, fD(s)+.


Thursday, March 1st 2018
10:00 am:
Thesis Defense in 110 PAN
Speaker: Eric Bullock, University of Minnesota
Subject: Polarization Angle Calibration and B-Mode Characterization with the BICEP and Keck Array CMB Telescopes
This is the public portion of Mr. Bullock's Thesis Defense. His advisor is Clem Pryke
10:10 am:
Biophysics Seminar in 120 PAN
Speaker: Tanner Akkin, Associate Professor of Biomedical Engineering, University of Minnesota
Subject: Development of a Serial Optical Coherence Scanner for Visualizing and Mapping the Brain with Microscopic Resolution

The feasibility of mapping and imaging the brain with microscopic resolution is presented. A serial optical coherence scanner, which combines a polarization-sensitive optical coherence tomography and a tissue slicer, distinguishes white matter and gray matter and visualizes nerve fiber tracts that are as small as a few tens of micrometers. The technique utilizes the retardance contrast that arise due to the myelination of nerve fibers and the axis orientation contrast that determine the 2D orientation of the nerve fibers, and the technique can be adapted to measure the inclination angle of the fiber, completing the 3D orientation. This scanner could reveal biomarkers for disease onset and progression, and support development of therapeutics.

Journal Club is canceled to make time for people to attend the Sara Seager colloquium at at 4:00 p.m.
4:00 pm:
Speaker: Sara Seager, MIT
Subject: Mapping the Nearest Stars for Habitable Worlds
Joint Colloquium with Earth Sciences (Nier Lecture). Note later start time.

Bio:

"Sara Seager is a planetary scientist and astrophysicist at the Massachusetts Institute of Technology where she is a Professor of Planetary Science, Professor of Physics, Professor of Aerospace Engineering, and holds the Class of 1941 Professor Chair. She has pioneered many research areas of characterizing exoplanets with concepts and methods that now form the foundation of the field of exoplanet atmospheres. Her present research focus is on the search for life by way of exoplanet atmospheric “biosignature” gases. Professor Seager works on space missions for exoplanets including as: the PI of the CubeSat ASTERIA; the Deputy Science Director of the MIT-led NASA Explorer-class mission TESS; and as a lead of the Starshade Rendezvous Mission (a space-based direct imaging exoplanet discovery concept under technology development) to find a true Earth analog orbiting a Sun-like star. Among other accolades, Professor Seager was elected to the US National Academy of Sciences in 2015, is a 2013 MacArthur Fellow, is a recipient of the 2012 Sackler Prize in the Physical Sciences, and has Asteroid 9729 named in her honor."

Abstract:

Thousands of exoplanets are known to orbit nearby stars and small rocky planets are established to be common. The ambitious goal of identifying a habitable or inhabited world is within reach. But how likely are we to succeed? We need to first discover a pool of planets in their host star’s “extended” habitable zone and second observe their atmospheres in detail to identify the presence of water vapor, a requirement for all life as we know it. Life must not only exist on one of those planets, but the life must produce “biosignature gases” that are spectroscopically active, and we need to be able to sort through a growing list of false-positive scenarios with what is likely to be limited data. The race to find habitable exoplanets has accelerated with the realization that “big Earths” transiting small stars can be both discovered and characterized with current technology, such that the James Webb Space Telescope has a chance to be the first to provide evidence of biosignature gases. Transiting exoplanets require a fortuitous alignment and the fast-track approach is therefore only the first step in a long journey. The next step is sophisticated starlight suppression techniques for large ground-and space-based based telescopes to observe small exoplanets directly. These ideas will lead us down a path to where future generations will implement very large space-based telescopes to search thousands of all types of stars for hundreds of Earths to find signs of life amidst a yet unknown range of planetary environments. What will it take to identify such habitable worlds with the observations and theoretical tools available to us?

Nier Info:

Professor A.O. Nier

A.O. Nier served as a highly distinguished faculty member of the Physics Department for 42 years starting in 1938. He was actively involved in research up to the time of his death in 1994. A firm believer in “pursuits of knowledge - in areas which cross traditional lines” he had an enormous impact on the geological sciences by his pioneering work on isotope abundances and measurements of many elements which are used in radiometric age determinations of geologic materials. He received many national and international awards in recognition of his discoveries and contributions to Physics, Geological Sciences and many other fields.


Friday, March 2nd 2018
10:10 am:
Nuclear Physics Seminar in Tate 201-20
There will be no seminar this week.
12:20 pm:
Speaker: Various speakers
Subject: APS March Meeting Practice Talks
Speaker: Andrew Spray, (IBS, Daejon, Korea)
Subject: Constraints and Phenomenology of Semi-Annihilating Dark Matter

Semi-annihilation describes processes with an initial state of two dark matter particles, and a final state of one plus standard model states. It is a generic feature of dark matter whenever the symmetry group enforcing stability is not a discrete Z2. Semi-annihilation changes the expected signals in current dark matter searches. With the bounds on standard thermal dark matter becoming very strong, now is the ideal time to ask to what extent those bounds apply to semi-annihilation, and what interesting parameter space remains. In this talk, explore the parameter space in a generic, bottom-up approach. We discuss the subtleties involved with semi-annihilation of fermionic dark matter, the role of additional unstable dark sector particles, and the interplay of semi-annihilation and the non-perturbative Sommerfeld effect. We discuss how semi-annihilation may relate to various anomalies seen in cosmic ray searches. Finally, we use an effective field theory approach to place limits in as model-independent a fashion as possible. We find that current searches are effective for processes with coloured final states, but significant model space for semi-annihilation still remains.

Speaker: Dr. Mateusz Ruszkowski, U. Michigan
Subject: The role of cosmic rays in stellar and supermassive black hole feedback

I will discuss the role of cosmic rays in stellar and supermassive black hole feedback. I will argue that cosmic rays are likely to play a very important role across a large range of distance scales -- from the scales of individual galaxies to the scales comparable to those of cool cores of galaxy clusters.

Regarding the galactic scale feedback, I will focus on supernova and cosmic ray driven winds. Galactic outflows play an important role in galaxy evolution and, despite their importance, detailed understanding of the physical mechanisms responsible for the driving of these winds is lacking. Although cosmic rays comprise only a tiny fraction of interstellar particles by number, they carry energy comparable to that in the thermal gas. I will describe a suite of global 3D MHD numerical simulations that focus on the dynamical role of cosmic rays injected by supernovae, and specifically on the impact of cosmic ray transport along the magnetic fields. Our results show that this microphysical effect can have a significant impact on the wind launching depending on the details of the plasma physics.

Regarding the feedback on galaxy cluster scales, I will discuss results from our simulations of black hole jets in cool cores of galaxy clusters including the effects of cosmic rays. I will argue that cosmic ray heating of the intracluster medium (ICM) may be a very important heating mechanism both in the tenuous and cold phases of the ICM while not violating observational constraints.

While largely an unexplored territory in the context of galactic winds and AGN feedback, cosmic ray feedback is an important process facilitating launching and efficient driving of galactic-scale winds in starburst galaxies and heating of the ICM and remains the subject of intense research.

Faculty Host: Thomas W. Jones
Speaker: Alisa Bokulich, Department of Philosophy, Boston University
Subject: "Using Models to Correct Data: Paleodiversity and the Fossil Record"
Refreshments served at 3:15 p.m.

It has long been recognized that models play a crucial role in science, and in data more specifically. However, as our philosophical understanding of theoretical models has grown, our view of data models has arguably languished. In this talk I use the case of how paleontologists are constructing data-model representations of the history of paleodiversity from the fossil record to show how our views about data models should be updated. In studying the history and evolution of life, the fossil record is a vital source of data. However, as both Lyell and Darwin recognized early on, it is a highly incomplete and biased representation. A central research program to emerge in paleontology is what D. Sepkoski has called the “generalized” (or what I prefer to call “corrected”) reading of the fossil record. Building on this historical work, I examine in detail the ways in which various models and computer simulations are being used to correct the data in paleontology today. On the basis of this research I argue for the following: First, the notion of a data model should be disentangled from the set-theoretic, ‘instantial’ view of models. Data models, like other models in science, should be understood as representations. Second, representation does not mean perfectly accurate depiction. Data models should instead be assessed as adequate-for-a-purpose. Third, the ‘purity’ of a data model is not a measure of its epistemic reliability. I conclude by drawing some parallels between data models in paleontology and data models in climate science.

3:35 pm:
Speaker: Miranda Straub, University of Minnesota
Subject: Discussions of papers regarding uncertainty in physics education

We will be discussing papers regarding uncertainty in physics education. The first paper is a model of quantitative uncertainty that can be used in science education, and the second is a study of uncertainty in a physics course. Both papers will be presented with questions to be discussed. Muffins provided.
Learning About Measurement Uncertainties in Secondary Education: A Model of the Subject Matter
Priemer, B. & Hellwig, J. Int J of Sci and Math Educ (2018) 16: 45. https://doi.org/10.1007/s10763-016-9768-0

When and Why Are the Values of Physical Quantities Expressed with Uncertainties? A Case Study of a Physics Undergraduate Laboratory Course
Caussarieu, A. & Tiberghien, A. Int J of Sci and Math Educ (2017) 15: 997. https://doi.org/10.1007/s10763-016-9734-x

4:40 pm:
There will be no seminar this week.

Monday, March 5th 2018
12:15 pm:
Speaker: Zewei Xiong, UMN
Subject:  Active-sterile neutrino oscillations in the neutrino-driven wind

Neutrino-driven winds from a proto-neutron star made in a core-collapse supernova have been studied extensively as a site for production of elements heavier than the Fe group. The absorption of electron neutrinos and antineutrinos on free nucleons not only provide the heating to drive the wind, but also determine the neutron-to-proton ratio, or equivalently the electron fraction of the wind, which is a critical parameter for nucleosynthesis. Flavor mixing between electron neutrino (antineutrino) and a sterile species that lacks normal weak interaction can potentially impact the dynamics and nucleosynthesis of the wind. We have implemented this active-sterile mixing in a steady-state model of the wind. We find that mixing with a sterile neutrino of ~1eV in mass can significantly affect the electron fraction and hence, nucleosynthesis in the wind.

Faculty Host: Yong-Zhong Qian

Tuesday, March 6th 2018
12:20 pm:
Space Physics Seminar in Tate 301-20
There will be no seminar this week.
2:30 pm:
Speaker: Jennifer Barnes, Columbia University
Subject: Nuclear Physics with Multi-Messenger Astronomy
Candidate for the Nucear Theory Assistant Professor position

The first detection in August 2017 of a binary neutron star merger in gravitational and electromagnetic waves marked the beginning of the era of multi-messenger astronomy. Future detections of neutron star-neutron star (NSNS) and neutron star-black hole (NSBH) mergers will allow astrophysicists to understand these systems in unprecedented detail, and test key theories about these exotic events. Two questions are especially interesting from a nuclear physics standpoint. First, what is the structure of ultra-dense neutron stars? Second, what is mergers' role in seeding the Universe with heavy elements synthesized via rapid neutron capture (the r-process)?
I will discuss how observations of mergers can help us answer these questions.
I will focus particularly on the radioactive transients that accompany mergers (the so-called "kilonovae"), and explain how recent theoretical advances allow us to use kilonova observations to constrain open questions in nuclear astrophysics.


Wednesday, March 7th 2018
1:30 pm:
No Seminar this week. APS March Meeting.
To be announced.

Thursday, March 8th 2018
10:10 am:
Biophysics Seminar in 120 PAN
Speaker: Elizabeth Smith (Elias Puchner lab), School of Physics and Astronomy, University of Minnesota
Subject: Characterization of Ire1 interactions and dynamics with quantitative super-resolution microscopy

Quantitative Super-Resolution Microscopy is a powerful technique to study biological processes below the diffraction limit. In this work, we employ our intracellular calibrated Photoactivated Localization Microscopy (PALM) technique to perform quantitative molecular counting of proteins involved in the unfolded protein response (UPR). The UPR is a signaling pathway which dynamically regulates endoplasmic reticulum (ER) protein folding capacity in response to cellular stress. As is true with many signaling pathways, the spatiotemporal organization of the UPR-specific biomolecules is an inherent feature of the pathway activation and downstream response. Specifically, in response to stress, Ire1 (a bifunctional transmembrane kinase/endoribonuclease) oligomerizes and forms discrete signaling clusters which recruit and splice an mRNA encoding a transcription activator. Using PALM in conjunction with traditional fluorescence microscopy we characterize the interactions and dynamics of Ire1 at wild type expression levels in yeast cells. Specifically, we quantify the oligomeric state, of Ire1 under stressed and unstressed conditions, track the motion of Ire1 during signaling activity, and determine the sensitivity and resolution of spatial cross-correlation in a model system combining traditional and super-resolution fluorescencemicroscoy in the same protein construct (Ire1_yeGFP_mEos2). Finally we perform colocalization experiments with downstream UPR biomolecules to further characterize the role of Ire1 signaling centers in control of gene expression. This study provides insight into the spatiotemporal organization of Ire1 and its downstream partners in the signaling response of the UPR.

Speaker: Trevor Knuth and Terry Jones
3:35 pm:
Tate Grand Opening

Friday, March 9th 2018
10:10 am:
Nuclear Physics Seminar in Tate 201-20
There will be a special nuclear physics seminar on Tuesday this week.
12:20 pm:
There will be no seminar this week.
Speaker: Stephen Martin (Northern Illinois U.)
Subject: Quasi-fixed points from scalar sequestering in supersymmetry

The little hierarchy problem of supersymmetry has to do with the question of why the electroweak breaking scale is small compared to the increasingly stringent lower limits on superpartner masses from the LHC. I discuss the possibility of addressing this problem by using hidden sector superconformal renormalization effects. This drives the soft supersymmetry breaking scalar squared mass terms in the Minimal Supersymmetric Standard Model towards quasi-fixed points in the infrared. I discuss the features of such models, and the extent to which the quasi-fixed point effects may ameliorate the little hierarchy problem.

Speaker: David Sand, U. Arizona
Subject: Unveiling the Physics and Progenitors of Cosmic Explosions with a One Day Cadence Supernova Search

Supernovae (SNe) are a linchpin for understanding the chemical evolution and star formation history of the Universe. Despite progress, some of the most basic questions about SNe persist, and we seek to answer the question: What are the explosion mechanisms and progenitor star systems of SNe? In the early hours to days after explosion, SNe provide clues to how they explode, and what their
progenitor star systems were. Observing these ephemeral signatures requires a fast search cadence and immediate spectroscopic response, a dual feat which has been difficult to achieve. Motivated by the need to discover, and study, SNe within the first day of explosion, we have begun a one-day cadence SN search of nearby galaxies (D<40 Mpc; also known as the DLT40 Survey) with a PROMPT 0.4-m telescope directly tied to the robotic FLOYDS spectrographs, a pair of instruments that I helped to develop. Here I will highlight our team's initial discoveries, with an eye towards what will be achievable with future time domain
surveys -- perhaps including nearly automated follow-up of LSST transients and Advanced LIGO gravitational wave events with the suite of Steward Observatory's small telescopes.

Faculty Host: M. Claudia Scarlata
There will be no colloquium this week
3:35 pm:
Speaker: Karl A. Smith, Morse-Alumni Distinguished University Teaching Professor, Professor of Civil, Environmental and Geo- Engineering, Emeritus, University of Minnesota
Subject: Engineering Education Research: Emergence, Current Status, and Future Directions

Engineering education research has been part of the landscape of engineering education for many years and began to be formalized with the creation of the American Society for Engineering Education Educational Research and Methods Division over 40 years ago. The field achieved significant advancement with the creation of PhD granting engineering education departments in the mid-2000s.
The seminar focuses on the historical roots of engineering education research, summarizes the current status, and offers some thoughts on the future.
The speaker has been active in engineering education research since the early 1970s and played a major role in the development of the first engineering education PhD granting department.

4:40 pm:
Speaker: Lee Penn
Subject: Diversity Committee workshop

Tuesday, March 13th 2018
12:20 pm:
Space Physics Seminar in Tate 301-20
No Seminar this week, spring break

Thursday, March 15th 2018
08:00 am:
Untitled in Physics
08:00 am:
Untitled in Physics
10:10 am:
Biophysics Seminar in 120 PAN
No Seminar This Week (Spring Break)
Speaker: No Journal Club - Spring Break
3:35 pm:
Subject: There will be no colloquium this week due to Spring Break

Friday, March 16th 2018
SPRING BREAK - No seminar this week
Speaker: No colloquium this week - Spring Break

Monday, March 19th 2018
12:15 pm:
No Seminar This Week

Tuesday, March 20th 2018
12:20 pm:
Space Physics Seminar in Tate 301-20
Speaker: David Malaspina, LASP, University of Colorado
Subject: Plasma Boundaries: Bridging Macro-Scale and Micro-Scale Plasma Physics

Plasma physics research is frequently focused on either macro-scale or micro-scale processes, often treating them as independent. Yet recent advances in spacecraft instrumentation, simulation, and laboratory studies are breaking down that paradigm, demonstrating that interactions between large and small scales are critical to understand and predict the behavior of systems as diverse as laboratory plasmas, the solar wind, and the terrestrial magnetosphere. In each of these systems, plasma boundaries act as a bridge between scales. Macro-scale plasma motions drive boundary formation, micro-scale instabilities develop or are spatially sorted as a consequence of these boundaries, and finally, the aggregate effect of many micro-scale interactions modifies the macro-scale system. Examples of interaction between macro- and micro-scale physical processes mediated by plasma boundaries in laboratory plasmas, the solar wind and the terrestrial inner magnetosphere will be discussed, with a focus on observational data.

3:30 pm:
Speaker: Laxman Raju Thoutam and Sajna Hameed.
Subject: Novel Electronic and Magnetic Properties in Rare-Earth Titanates: YTiO3 & NdTiO3.

Wednesday, March 21st 2018
1:25 pm:
Speaker: Li He, University of Minnesota
Subject: Optomechanical measurement of photon spin angular momentum and optical torque in integrated photonic devices
This week's sack lunch talk will be on Wed. at the usual CM seminar time and place

Photons carry spin angular momentum when circularly or elliptically polarized. During light-matter interaction, transfer of angular momentum induces optical torque. Here, we demonstrate the measurement of the spin angular momentum of photons propagating in a silicon waveguide and the use of optical torque to actuate rotational motion of an optomechanical device. We show that the sign and magnitude of the optical torque are determined by the photon polarization states that are synthesized on the chip. Our study reveals the mechanical effect of photon’s polarization degree of freedom and demonstrates its control in integrated photonic devices.

Faculty Host: Paul Crowell
2:30 pm:
Speaker: Aleksey Cherman, University of Washington
Subject: Symmetries, order parameters, and the phase diagram of nuclear matter
Candidate for the Nucear Theory Assistant Professor position

The phases of matter at extreme temperatures and densities are essentially determined by strong nuclear interactions. But for most temperatures and densities, we lack the theoretical tools to efficiently study QCD, the quantum field theory describing the strong nuclear force. For instance, in much of the phase diagram of QCD, there are very few well-defined order parameters to label its phases. I will describe recent advances in understanding the symmetries and order parameters of QCD, with a focus on the implications for understanding the phase diagram of nuclear matter as a function of temperature and density.

To be announced.

Thursday, March 22nd 2018
10:10 am:
Biophysics Seminar in 120 PAN
Speaker: Yahor Savich (David Thomas lab), School of Physics and Astronomy, University of Minnesota
Subject: Myosin Orientation in a Functioning Muscle Fiber With High Angular Resolution

We have measured the orientation of myosin in a muscle fiber bundle using electron paramagnetic resonance (EPR) and a bifunctional spin label (BSL), with angular resolution of a few degrees. Despite advances in cryo-EM, fluorescence, and small-angle X-ray diffraction, these techniques do not provide high-resolution structural information about myosin heads in vitro under functional conditions. A pair of (i,i+4) Cys residues were engineered on an alpha-helix in the regulatory light chain (RLC). By exchanging endogenous RLC with BSL-labeled RLC on oriented muscle fibers, we were able to resolve angular distributions in several biochemical states due to the stereospecific attachment of BSL’s two disulfide bonds. In this setup, the accurate determination of BSL’s angular coordinates allowed us to determine the orientation of individual structural elements with respect to the muscle fiber axis. Addition of ATP in the absence of Ca, relaxing the muscle, shifted the orientational distribution to a much more disordered distribution. This work is inspired by growing therapeutic interest in super-relaxed myosin state, which predicts presence of order in relaxation.

Speaker: Sharan Banagiri and Larry Rudnick
3:35 pm:
Speaker: Pablo Jarillo-Herrero (MIT)
Subject: Magic Angle Graphene: a New Platform for Strongly Correlated Physics

The understanding of strongly-correlated quantum matter has challenged physicists for decades. Such difficulties have stimulated new research paradigms, such as ultra-cold atom lattices for simulating quantum materials. In this talk I will present a new platform to investigate strongly correlated physics, based on graphene moiré superlattices. In particular, I will show that when two graphene sheets are twisted by an angle close to the theoretically predicted ‘magic angle’, the resulting flat band structure near the Dirac point gives rise to a strongly-correlated electronic system. These flat bands exhibit half-filling insulating phases at zero magnetic field, which we show to be a Mott-like insulator arising from electrons localized in the moiré superlattice. Moreover, upon doping, we find electrically tunable superconductivity in this system, with many characteristics similar to high-temperature cuprates superconductivity. These unique properties of magic-angle twisted bilayer graphene open up a new playground for exotic many-body quantum phases in a 2D platform made of pure carbon and without magnetic field. The easy accessibility of the flat bands, the electrical tunability, and the bandwidth tunability though twist angle may pave the way towards more exotic correlated systems, such as quantum spin liquids.

Faculty Host: Vlad Pribiag

Friday, March 23rd 2018
10:10 am:
Nuclear Physics Seminar in Tate 201-20
There will be a special nuclear physics seminar on Wednesday this week.
12:20 pm:
Speaker: Daniel Sheehy, LSU
Subject: Interface symmetry and non-helical states in topological insulator-semiconductor heterostructures
Note: this seminar is in addition to the one on Wednesday. Please note change of day, time and room, This week only.

Topological insulators (TIs) possess topologically-protected helical
surface states that are immune to non-magnetic disorder and described
by a relativistic "Dirac" Hamiltonian. Similar states are expected
at the interface between a TI and any topologically trivial material.
I will discuss recent work showing that the interface states at the
boundary between a topologically-trivial semiconductor (SE) and a TI
possess a much richer phenomenology compared to the helical surface
states, including complex spin textures and broken helicity.

Faculty Host: Rafael Fernandes
Speaker: Gokce Basar (U. Illinois, Chicago)
Subject: Going with the flow: a solution to the sign problem

I will explore the generalization of the Feynman path integral in quantum field theory to complexified fields, and explain how it can be utilized to tackle the famous "sign problem". The sign problem prevents first principle studies of real-time dynamics and finite density systems via lattice field theory and appears in many different areas in physics. I will discuss both conceptual and computational aspects of this idea and give examples of several interacting quantum field theories where it successfully solves the sign problem.

Speaker: Dr. Jordan Stone, U. Arizona
Subject: Thermal Infrared Probes of Exoplanetary Systems with LBTI

Understanding the gas-giant planet formation process is confused by the fact that it appears multiple formation routes produce objects a few times the mass of Jupiter, where the low-mass tail of the stellar mass function and the high-mass tail of the planet mass function overlap. Distinguishing the formation route for particular objects is challenging but important to create the clean samples necessary to constrain both the planet formation process and the tail-end of the star/brown dwarf-formation process. In particular, constraining the disk-based planet formation mechanism for gas-giants is important because their dynamical dominance affects the formation of terrestrial and ice-giant planets. System architecture and atmospheric composition both provide formation indicators for gas-giants because disk-based formation results in non-hierarchical orbits and atmospheric metal enrichment, as seen in Jupiter and Saturn. I will discuss two programs which I lead with LBTI to probe the outer architecture of planetary systems and to characterize the atmospheres of gas-giant exoplanets. I will also provide an update on the LBTI HOSTS survey for exozodiacal dust around nearby stars. HOSTS is nearing completion and will provide essential information for the design of future space missions that aim to image habitable zone terrestrial planets in reflected light.

Faculty Host: Charles E. Woodward
Speaker: Rebecca Kluchin, Department of History, California State University - Sacramento
Subject: "Court-Ordered Cesarean Sections in 1980s America"
Refreshments served at 3:15 p.m.

In June 1987, Angela Carder was twenty-seven years old, married, pregnant, and in remission from cancer. Twenty-five weeks into her pregnancy, she learned that the disease had returned and metastasized in her right lung. Her prognosis was terminal and her condition deteriorated rapidly. When George Washington University Hospital administrators learned that Carder was dying and lacked a plan to save her fetus, they initiated an emergency legal hearing to determine their responsibility to her pregnancy. A judge ordered Carder to undergo an immediate cesarean section. The baby lived two hours. Carder died two days later.

Carder’s parents appealed the decision and in 1990, the District of Columbia Court of Appeals ruled in their favor. The Carder case became national news and entered popular culture when the popular television show LA Law ran an episode based on it. But the Carder case did not occur in a vacuum; in fact, one month before Carder died, the New England Journal of Medicine published an article that revealed twenty-one prior attempts of court-ordered cesarean sections, eighteen of which were successful. Eighty-one percent of patients forced to undergo surgery were women of color and twenty-four percent were non-English speakers. The media attention granted to the Carder case obscured the other forced cesareans and erased women of color from the story. This paper reveals this hidden reproductive history, places it in the context of other reproductive abuses, and locates women of color at the center of the story instead of on the periphery. It argues that court-ordered cesarean sections simultaneously continued the long history of reproductive abuses directed at women of color and represented a new form of abuse specific to the post-Roe era and the politics of legal abortion.

3:35 pm:
Speaker: Brita L. Nellermoe, University of St. Thomas, St. Paul, MN
Subject: Piaget and Vygotsky as a Foundation for Physics Education

The educational psychology of Swiss psychologist Jean Piaget and Soviet psychologist Lev Vygotsky shaped the 20th Century's understanding of how children and adults learn. These learning theories are the basis for much of the late 20th and early 21st century reform of science education in the United States. This talk will discuss the similarities and differences of Piaget and Vygotsky's theories of learning and how they apply to current Physics Education curriculum.

4:40 pm:
Subject: Special topics - auxiliary skills

Monday, March 26th 2018
12:15 pm:
Speaker: Liliya L.R. Williams, UMN
Subject: Relaxation of dark matter halos: distribution in energy and angular momentum

The problem of figuring out the properties of steady-state configuration of dark matter halos has a long history. I will recap some of that, including our contribution to it. I will summarize our results concerning relaxation in terms of energy, and discuss our ongoing work on incorporating angular momentum. I will also present a comparison of theoretical predictions with observations and simulations.


Tuesday, March 27th 2018
Speaker: Michael Fogler, University of California, San Diego
Subject: Hyperbolic waves in Nature: from nano to Ter(r)a

Waves with a hyperbolic dispersion relation are exotic yet surprisingly widespread phenomena that occur in anisotropic media with internal resonances. Such media have been investigated in numerous fields, ranging from condensed matter physics to plasma physics to optics to fluid dynamics and geophysics. Hyperbolic waves can be found in magnetic materials, in both usual and topological insulators, in superconductors, as well as in our oceans, beaches, atmosphere, and space. The characteristic lengths and frequencies of such waves vary vastly, from atomic to cosmic. However, they all exhibit certain common attributes, such as strict directionality, diverging density of states, and anomalous reflection. This talk will contain a primer on hyperbolic materials, a recipe for the death ray, and a report on our nano-optics studies of hyperbolic phonon-polaritons in new quasi-2D materials such as graphene and hexagonal boron nitride.

References:

1. L. V. Brown et al, “Nanoscale Mapping and Spectroscopy of Nonradiative Hyperbolic Modes in Hexagonal Boron Nitride Nanostructures,” Nano Lett. 18, 1628 (2018).
2. A. J. Giles et al., "Imaging of Anomalous Internal Reflections of Hyperbolic Phonon-Polaritons in Hexagonal Boron Nitride," Nano Lett. 16, 3858 (2016).
3. S. Dai et al., “Subdiffractional focusing and guiding of polaritonic rays in a natural hyperbolic material,” Nature Comms 6, 6963 (2015).
4. S. Dai et al., “Tunable Phonon Polaritons in Atomically Thin van der Waals Crystals of Boron Nitride”, Science 343, 1125 (2014).

Faculty Host: Boris Shklovskii

Wednesday, March 28th 2018
2:30 pm:
Speaker: Paul Canfield (Iowa State)
Subject: Synthesis as the Heart of New Materials Physics
Note special time: seminar starts at 2:30 (not 1:25)

Design, discovery, growth and characterization of novel materials is at the heart of New Materials Physics. One of the key steps is deciding what materials to study or try to grow. In this talk I will try to enunciate and elaborate the motivations for making/studying specific compounds. Many examples from current research will be touched upon and discussed. Humor of all types will be used to lighten the load and make the time fly by.

Faculty Host: Martin Greven
3:30 pm:
Space Physics Seminar in Physics 201-20
Speaker: Barry Mauk, APL
Subject: Comparing the energetic particle populations of planetary magnetospheres

We compare planetary magnetospheres in different ways. Do we observe the same phenomenology? Are the same physical processes in play? It is, in fact, a challenge to compare planetary space environments quantitatively in a fashion that leads to a more predictive understanding. I examine here the differences and similarities of the strongly magnetized planetary magnetospheres of the solar system by examining their most energetic particle populations. For both trapped electron radiation and energetic ions comprising ring current populations, updated and extended versions of the classic Kennel-Petschek theory provide reasonable metrics for quantitatively comparing the populations of all of the strongly magnetized planetary magnetospheres. These comparisons are substantially revealing with regard to the character and states of the space environments of the respective planets. Comparisons between Earth and Jupiter are of particular interest in that these two environments are representative of the extremes of magnetospheric conditions; one the canonical solar-wind-driven magnetosphere and the other the canonical rotationally-driven magnetosphere. And yet, both are extremely active and energetic in their own ways.

Faculty Host: Robert Lysak
To be announced.

Thursday, March 29th 2018
10:10 am:
Biophysics Seminar in 120 PAN
Speaker: Wesley Errington, Molecular Cell Engineering Laboratory, University of Minnesota
Subject: Integrating experimental and computational approaches to elucidate mechanisms of binding in multivalent proteins

Multivalent proteins are ubiquitous in nature and can provide unique, exploitable properties in therapeutic applications such as increased affinity or multi-target specificity. Despite the importance of these proteins in fundamental and applied biomedical research, mechanistic quantitative descriptions of their binding kinetics are limited. We have considered such multivalent protein-protein interactions to be driven by three key variables: the binding affinity of individual monomer units, the linker length/structure between the monomers, and the overall valency of each multivalent protein. Using model synthetic proteins in which all three of these variables can be independently tuned, we have performed surface plasmon resonance experiments to quantify the kinetics of association and dissociation as a function of affinity, linker, and valency. In parallel, we developed a mechanistic model based on mass-action kinetics that explictly enumerates all possible microstates that participate in the binding reaction. Integration of these quantitative experimental and computational approaches has elucidated a number of interesting findings, including the role of valency in generating non-canonical reaction kinetics, that will be discussed. Our approach should enable better understanding of dynamic behaviors in natural multivalent proteins and lead to more rational optimization of multivalent therapeutics.

Speaker: Brian O'Neill
3:35 pm:
Speaker: Barry Mauk, APL
Subject: New perspectives on Jupiter’s novel space environment and aurora from NASA’s Juno mission

B. H. Mauk, The Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland, USA (Barry.Mauk@jhuapl.edu)

Jupiter’s uniquely powerful auroras are thought to be symptoms of Jupiter’s attempt to spin up its space environment and shed angular moment (albeit minuscule amounts). The processes involved connect together such disparate phenomena as the volcanoes of Jupiter’s moon Io and the Jupiter-unique synchrotron emissions imaged from ground radio telescopes at Earth. While the power sources for auroral processes at Earth and Jupiter are known to be very different, it has been expected that the processes that convert that power to auroral emissions would be very similar. NASA’s Juno mission, now in a polar orbit at Jupiter, is dramatically altering this view about how Jupiter’s space environment operates. Auroral processes are much more energetic than expected, generating beams of electrons with multiple MeV energies and with directional intensities that can be more intense than the electrons within Jupiter’s radiation belts. The most intense auroral emissions appear to be generated by processes that have no precedent within Earth auroral processes. And, the auroral generation processes are poorly correlated, unexpectedly, with any large-scale electric currents thought necessary to regulate the interactions between Jupiter’s spinning atmosphere and space environment. These and other findings are discussed, along with presentation of Juno’s broader mission and discoveries.

Faculty Host: Robert Lysak

Friday, March 30th 2018
10:10 am:
Nuclear Physics Seminar in Tate 201-20
There will be no seminar this week.
12:20 pm:
Speaker: Bo Xiong, University of Minnesota
Subject: Haldane Exclusion Statistics: beyond Fermion and Boson

Haldane exclusion statistics is one of the many attempts to interpolate between Fermi and Bose cases. However, the distribution function of Haldane statistics is still an open question, parallel to the well-known Fermi and Bose distribution function. I’ll discuss the negative weight problem of Yongshi Wu’s distribution function of Haldane statistics, Murthy and Shankar’s solution and our improvement.

Speaker: Hooman Davoudiasl (Brookhaven)
Subject: Long Range Dark Matter Forces and New Views on Old Problems

We entertain the possibility that a long range force may act on dark matter. The potential coupling of this force to baryons and leptons could lead to new ways of thinking about some of the open questions in particle physics. Here, we mainly focus on scalar forces with various coupling strengths and ranges and examine some of the ways in which they can affect interpretations of dark matter direct detection, neutrino oscillations, or cosmological data.

Speaker: Lou Stolger, Space Telescope
Subject: The Rates of Supernovae, Far and Near

For nearly two decades, the Hubble Space Telescope has been heavily used to locate supernovae in high redshift environments, with the primary goal of improving constraints on the nature of dark energy. Along the way we have made surprising observations on the nature of supernovae themselves, and clues to their elusive progenitor mechanisms, some of which are difficult to reconcile with observations at much lower redshift. From complete volumetric supernova rate histories that now extend to z > 2 we find type Ia supernova delay-time distributions are consistent with a power law index of -1, but with the fraction of prompt (t_d < 500 Myr) is less than expected from various ground-based surveys. Core collapse supernova rates trace the cosmic star formation rate history, but require stellar progenitors more massive than has been seen in deep studies of nearby events (M > 20 M_sol). I’ll detail some interesting discoveries from our recent campaigns on clusters of galaxies, and also discuss what we expect to find with the James Webb Space Telescope, launching in 2018, and with WFIRST in the 2020s.

Speaker: Susan Rensing, Department of Women's & Gender Studies, University of Wisconsin - Oshkosh
Subject: HSTM Alumni Lecture - "‘A Coldly Scientific Venture’: Unwed Mothers and the Eugenic Baby Panic"
Refreshments served at 3:15 p.m.

In January of 1928, the New York World set off a firestorm of controversy with a front page story about a wealthy widow, Grace Burnham, who had “mated lovelessly” as a eugenic experiment. Newspapers rushed to seek out stories of other women who were conceiving eugenic babies by selecting a man purely for reproduction, not for marriage. Unlike the wholesome eugenic babies that won ribbons in Better Baby Contests at state fairs, these eugenic babies were portrayed as potential Frankensteins--creations of science run amok. Moral condemnation raged in editorials across the nation as experts weighed in with their opinions about this alarming trend. This talk will use the eugenic baby panic as a cultural lens to examine fears about science bereft of morality in the late 1920s and early 1930s.

3:35 pm:
Speaker: Jie Yang (PER Group from University of Minnesota)
Subject: Quantify the difficulty of physics problems

Assessment methods are broadly recognised as integral to effective instruction. Student performance on tests are a common way for instructors to gauge their instructional effectiveness. However, Lack of alignments of problem difficulty between instructors, institutions, and courses is the major obstacle to make use of authentic student performance data gathered by most classes and used by instructors. In this presentation, I will describe the development and validation of a simple difficulty assessment for assessing open response physics problems’ difficulty. It quantify the difficulty of physics problems. It can be used to compare test or homework problems , or to craft instruction material.


Monday, April 2nd 2018
12:15 pm:
Speaker: Matt Gomer, UMN
Subject:  Lensing degeneracies and their effect on H_0 measurements

At present, there is a 3σ discrepancy between the local measurements of H0 and those derived from CMB observations. To explore whether or not this is significant, the current goal is to constrain H0 to within 1%, optimally using methods independent from these two. One potential method is to use the time delays between multiple images of gravitationally lensed system as an absolute measure of distance independent of either the distance ladder or CMB modelling. In order to accomplish this at the 1% level, it is critical that the lens system is modelled to similar precision. Unfortunately, there exist lensing degeneracies such as the mass sheet degeneracy which can result in the same set of observables using different mass distributions. Unless these degeneracies can be broken, measurements of H0 will be biased by an unknown amount. In this talk, I detail current efforts to quantify these biases and explore what the future holds for this method.

Faculty Host: Liliya L.R. Williams

Tuesday, April 3rd 2018
12:20 pm:
Space Physics Seminar in Tate 301-20
Speaker: Xianzhe Jia, University of Michigan, Dept. of Climate and Space Physics and Engineering
Subject: Global MHD Simulations of Saturn’s Magnetosphere

At Saturn’s orbital distance of ~ 9.5 AU, the low solar wind dynamic pressure and weak interplanetary magnetic field interact with the planet to create a magnetosphere that dwarfs Earth’s magnetosphere. While the form of Saturn’s magnetospheric cavity is still the result of solar wind stresses, many properties of the Kronian magnetosphere are determined largely by internal processes associated with the planet’s rapid rotation and the stresses arising from internal plasma sources dominated by the icy moon, Enceladus. Coupling between the planetary ionosphere and the magnetosphere through electric currents plays a vital role in determining the global configuration and dynamics of Saturn’s magnetosphere. To understand the large-scale behavior of the solar wind-magnetosphere-ionosphere interaction, we have applied the global MHD model, BATSRUS, to Saturn that couples the solar wind, the magnetosphere, and the ionosphere and incorporates key mass-loading processes associated with Enceladus and its extended neutral cloud. Here we present results from our global simulations carried out to understand how the various internally and externally driven processes influence Saturn’s magnetosphere, and discuss their implications for interpreting Cassin in-situ observations. We will also show results from an atmospheric vortex model we have developed that offers valuable insight into the physical processes that drive the ubiquitous periodic modulations of particles and fields properties observed by Cassini throughout the Saturnian magnetosphere.

3:30 pm:
Speaker: John Dewey and Joseph Batley, Chemical Engineering and Material Science
Subject: Integration of perovskites into non-local spin valves for the study of spin transport in oxides“

Wednesday, April 4th 2018
1:25 pm:
Speaker: Sung-Sik Lee, Perimeter Institute
Subject: Low-energy effective field theories for non-Fermi liquids

Non-Fermi liquids are exotic metallic states which do not support well defined quasiparticles. Due to strong quantum fluctuations and the presence of extensive gapless modes near the Fermi surface, it has been difficult to understand universal low-energy properties of non-Fermi liquids. In this talk I will discuss recent progress made on field theories for non-Fermi liquids. Based on a dimensional regularization scheme which tunes the co-dimension of Fermi surface, critical exponents that control scaling behaviors of physical observables can be computed in controlled ways. The systematic expansion provides important insight into strongly interacting non-Fermi liquids. This allows us to find the non-perturbative solution for the strange metal realized at the antiferromagnetic quantum critical point in 2+1 dimensions, and predict the exact critical exponents that can be experimentally tested in layered systems.

Faculty Host: Andrey Chubukov
To be announced.

Thursday, April 5th 2018
10:10 am:
Biophysics Seminar in 120 PAN
Speaker: James M. Carothers, Department of Bioengineering, University of Washington
Subject:  Multi-state design of kinetically-controlled RNA aptamer ribosensors

Metabolite-responsive RNA regulators that react to changing conditions through molecular interactions are widespread in biology. In many of these systems, kinetic control mechanisms coordinate co-transcriptional RNA folding with metabolite binding and enable outputs that are highly-sensitive and highly-selective to target ligands. Although synthetic riboswitches exhibiting kinetic control have been identified by chance, it has not been possible to intentionally engineer kinetically-controlled RNA aptamer devices. Consequently, kinetic control mechanisms that could otherwise be exploited to overcome functional limits imposed by the thermodynamics of molecular recognition have remained beyond reach. We recently developed a novel approach for multi-state, co-transcriptional RNA folding design that has allowed us to engineer kinetically-controlled RNA aptamer ribosensors. In this architecture, in vitro selected RNA aptamers are coupled through a timer domain to a toehold-mediated strand displacement (TMSD) actuator such that co-transcriptional ligand-binding generates fluorescence from DNA gates through TMSD. We have shown that ribosensors can be transcribed in situ and used to analyze metabolic production directly from engineered microbial cultures, establishing a new class of cell-free biosensors. We found that kinetically-controlled ribosensors exhibited 5-10 fold greater ligand sensitivity than a thermodynamically-controlled device. And, we further demonstrated that a second aptamer, promiscuous for aromatic amino acid binding, could be assembled into kinetic ribosensors with 45-fold improvements in ligand selectivity. I will present these results and discuss the broader implications of this work for engineering RNA aptamer devices and overcoming thermodynamic constraints on molecular recognition through the design of kinetically-controlled responses.

Faculty Host: Vincent Noireaux
Speaker: Nathan Eggen and Roberta Humphreys
3:35 pm:
Speaker: Alessandra Corsi, Texas Tech
Subject: Multi-messenger time-domain astronomy: GW170817 and the future

On 2017 August 17, the field of gravitational-wave (GW) astronomy made the big leagues with a dazzling discovery. After several GW detections of black hole (BH)-BH mergers with no convincing electromagnetic counterparts, advanced LIGO and Virgo scored their first direct detection of GWs from a binary neutron star (NS) merger, an event dubbed GW170817. Soon after the GW discovery, GW170817 started gifting the astronomical community with an electromagnetic counterpart spanning all bands of the spectrum. In this talk, I will review what we have learned from GW170817, what questions remain open, and what are the prospects for future EM-GW studies of the transient sky.

Faculty Host: Vuk Mandic

Friday, April 6th 2018
10:10 am:
Nuclear Physics Seminar in Tate 201-20
There will be no seminar this week.
12:20 pm:
Speaker: Tianbai Cui, University of Minnesota
Subject: Impact of damping on superconducting gap oscillations induced by Terahertz pulses

We investigate the interplay between gap oscillations and damping in the dynamics of superconductors taken out of equilibrium by strong optical pulses with sub-gap Terahertz frequencies. A semi-phenomenological formalism is developed in which damping is incorporated by relaxation and dephasing processes within the electronic subsystem, which correspond to T1 and T2 times in the standard pseudospin language for BCS superconductors. Comparing with data on NbN that we report here, we argue that the superconducting dynamics in the picosecond time scale, after the pump is turned off, is governed by the T2 process.

Speaker: Elena Caceres (U. Texas, Austin)
Subject: Rotating Traversable Wormholes
There will be no colloquium this week.
Speaker: Stuart Glennan, Department of Philosophy, Butler University
Subject: “Compositional Minimalism”
Refreshments served at 3:15 p.m.

In her paper, “Causality and Determination,” Elizabeth Anscombe advanced an approach to causation that Peter Godfrey-Smith has dubbed “causal minimalism.” In this approach, causation is not one thing, but many. Causal relations depend upon a heterogeneous set of specific activities – like bonding, pushing, tearing or fighting. My aim in this talk is to pursue a related strategy for compositional relations between parts and wholes – whether these be between atoms and molecules, tissues and organs, or children and families. Composition, like causation, is not one thing, but many – largely because parts are bound into wholes by causal relations.

3:35 pm:
Speaker: Lori Patrick, University of Minnesota
Subject: Active learning: what are faculty and student perceptions across disciplines and how should we train teaching assistants to use it?

Active learning teaching techniques – such as clicker questions, group work, think-pair-share, and other activities – benefit all students and can close the achievement gap for under-represented minority, first-generation, and female students in STEM disciplines. Consequently, many courses have been integrating these techniques into their labs and lectures. Several initiatives have focused on training faculty, however there has been relatively little emphasis, at least in biology, to understand faculty and student perceptions of active learning and how these perceptions differ by discipline. Even less is known about graduate student perceptions of active learning and the best strategies to train teaching assistants to use active learning. This talk will focus on some of the work being conducted in the Department of Biology Teaching and Learning to address these questions.

3:35 pm:
Speaker: Kenji Ishii, Synchrotron Radiation Research Center (SPring-8), Japan
Subject: Momentum-resolved charge and spin excitations in cuprate superconductors
PLEASE NOTE TIME AND DATE CHANGE FOR THIS SEMINAR.

In the last two decades, energy resolution of resonant inelastic x-ray scattering (RIXS) has been significantly improved, and RIXS is now established as a momentum-resolved spectroscopy using synchrotron radiation x-rays. Since the beginning of RIXS, cuprate superconductors have been intensively studied. In addition to the interest of superconductivity at the high transition temperature and related phenomena, such as pseudogap and a competing phase with charge order, doped cuprates are important and suitable for the study of the electronic structure of the doped Mott insulator. This is because relatively simple theoretical models with a few orbitals are applicable to describe the electronic structure near the Fermi energy. I will present charge and spin excitations in cuprates observed with RIXS at Cu K-, Cu L3- and O K-edges focusing on the energy range from eV to sub-eV. In this range, charge and spin excitations show characteristic momentum dependence with respective energy scale of hopping energy of electron (t) and exchange interaction of spin (J).

Faculty Host: Martin Greven

Monday, April 9th 2018
12:15 pm:
Speaker: Jose Diego, Consejo Superior de Investigaciones Cientificas, CSIC
Subject: The Universe at Extreme Magnification

Galaxies and galaxy clusters can magnify objects at cosmic distances by large factors. To first order the maximum possible magnification depends on i) the mass of the lens and ii) the size of the background object. Small objects, like stars, can be magnified by factors of several thousand when the lens is a galaxy cluster. Kelly et al. 2018 discovered the first star at cosmological distance magnified by such extreme factors. I will show how the properties of the magnification can be altered by intervening microlenses (from the macrolens) and how this can be used to constrain the amount of dark matter that is in compact form. Gravitational Waves (GW) are another example, where the signal originates from an incredibly small source. I will show how the most massive events detected by LIGO can be re-interpreted as strongly lensed events at z~1-2 by groups of galaxies or small clusters at z~0.3.

Faculty Host: Patrick Kelly

Tuesday, April 10th 2018
12:20 pm:
Space Physics Seminar in Tate 301-20
There will be no seminar this week.

Wednesday, April 11th 2018
1:25 pm:
Speaker: Xiaojia Wang (University of Minnesota)
Subject:  Ultrafast Optical Characterization of Thermal Transport in Micro/nanostructured Materials and across Interfaces
Faculty Host: Paul Crowell
Speaker: Ruchi Gupta, Southern Methodist University
Subject: Measurement of gluon fusion and vector boson fusion Higgs boson production cross-sections in the H→ WW*→ eνμν decay channel in pp collisions at sqrt(s) = 13 TeV

The Higgs boson production cross-sections in proton-proton collisions are measured using the events in the H→WW*→eνμν decay channel. The measured cross sections probe the Higgs boson couplings to heavy bosons and to gluons. The proton-proton collision data were produced at the Large Hadron Collider at a centre-of-mass energy of 13 TeV and recorded by the ATLAS detector in 2015 and 2016, corresponding to an integrated luminosity of 36.1 fb−1.


Thursday, April 12th 2018
10:10 am:
Biophysics Seminar in 120 PAN
Speaker: Aaron Engelhart, Department of Genetics, Cell Biology, and Development, University of Minnesota
Subject:  Hold the water! Probing nucleic acid hydration with alternative solvents

Nucleic acids adopt a myriad of roles in life ranging from their well-known role in simple information transfer (in DNA and mRNA) to functional behaviors including catalysis (in ribozymes including the ribosome) and ligand binding (in riboswitches). The folding of these polymers is intimately connected with the environment afforded by the solvent in which they fold: water. Water dictates the folding behavior of nucleic acids in a variety of ways, including hydrophilic interactions (with the phosphate backbone as well as dissolved cations); nonclassical hydrophobic interactions (which promote base stacking); and minor groove binding of water (as well as cations), which has been known since the first atomic-resolution crystal structures of DNA shown by Drew and Dickerson. We recently showed that, remarkably, nucleic acids can form stable secondary structures in an essentially anhydrous solvent - a so-called "deep eutectic solvent" (DES) formed from a 2:1 molar mixture of urea and choline chloride. Despite the absence of water, a range of secondary structures fold in DES. I will discuss our results using alternative solvents to examine the role of hydration in nucleic acid folding.

Speaker: Karl Young
3:35 pm:
Speaker: Doug Glenzinski, Fermilab
Subject: A Rare Opportunity - the Mu2e Experiment at Fermilab

The muon, a heavy cousin of the electron, was discovered in 1936. Since
that time they have only ever been observed to do one of two things: 1)
scatter or 2) decay into final states that include a combination of
charged leptons and neutrinos. A new experiment at Fermilab - the Mu2e
experiment - is going to look for a third thing: a muon trapped in atomic
orbit that interacts with the nucleus to produce an electron and nothing
else. This is a process that's predicted to occur very very rarely, maybe
once every 10^15 decays,(or less!). But this very rare decay will probe
new physics mass scales up to 10,000 TeV/c^2 and may hold the key to
understanding physics at its most fundamental level. The Mu2e experiment
is an ambitious endeavor whose goal is to observe this very rare
interaction for the first time - a discovery that could help reveal a new
paradigm of particle physics.

Faculty Host: Kenneth Heller

Friday, April 13th 2018
10:10 am:
Nuclear Physics Seminar in Tate 201-20
There will be no seminar this week.
12:20 pm:
Speaker: Zhen Jiang, University of Minnesota
Subject: The temperature and doping dependence of the inverse spin Hall effect in GaAs

The study of spintronics includes 3 tasks: the generation, manipulation and detection of spin polarization. The inverse spin Hall effect(ISHE), which converts pure spin currents to electric currents, is an important way to detect spin accumulation. Although it has been used widely, its origins are not necessarily understood. For example, the ISHE in GaAs has been found to be surprisingly large in n-GaAs(doped with Si), and at low temperatures it is very sensitive to hyperfine fields. In this talk, I will present my measurements on devices with channels of varying doping at different temperatures. The goal of this experiment is to study the ISHE in a regime where the complications of hyperfine interactions are absent.

Speaker: Kristian Jensen (San Francisco State U.)
Subject: A Zoo of Bosonization Dualities

There has been substantial progress toward establishing a landscape of non-supersymmetric dualities in three dimensions. These dualities equate Chern-Simons gauge theories coupled to matter, and relate theories of fundamental fermions to those of fundamental bosons. I will discuss a proposal for a new “master” duality between Chern-Simons theory coupled to fundamental bosons and fermions, which if correct summarizes most of these “3d bosonization” dualities.

Speaker: No speaker this week.
Faculty Host: M. Claudia Scarlata
Speaker: Lawrence Principe, Department of History of Science & Technology, Johns Hopkins University
Subject: "Wilhelm Homberg’s Laboratories and Instruments: Doing Chymistry in Early Modern France"
Refreshments served at 3:15 p.m.

One of chemistry’s chief characteristics is its union of head and hand, theory and practice, and the subsequent need for workspaces and instruments doing chemistry practically. Wilhelm Homberg (1653-1715), the chief chymist of the Parisian Académie Royale des Sciences, worked in many different spaces over the course of his remarkable career. Starting in 1702, he worked in what was called at the time “the most magnificent laboratory that chymistry had ever known”--a workspace specially-built for him in the Royal Palace by his patron (and collaborator) Philippe II, duc d’Orléans, the future Regent of France. Philippe also outfitted this laboratory with the most extraordinary--and costly--scientific instrument of time, and Homberg enjoyed exclusive access to it. This talk examines the various workspaces Homberg used, highlighting the results that he achieved and their relation to spaces and instruments, the role of patronage, and the changing nature of chymistry in the period.

3:35 pm:
Speaker: Laura McCullough, UW-Stout
Subject: Women in Physics Leadership.

Women in Physics Leadership: Women’s representation in physics has increased to 20% and now is holding steady. Women’s representation in physics leadership positions is much smaller. Whether as department chair, journal editor, or professional society president, women are much less visible as leaders in the physics community. Data on women’s leadership in physics will be shared, and discussion will be encouraged.


Monday, April 16th 2018
12:15 pm:
No Seminar this Week
Speaker:  Professor Sudhakar Prasad, University of New Mexico and University of Minnesota
Subject: The Modern Imaging Paradigm: There is Plenty of Room in the Middle

Every modern imaging system is comprised of optical, sensing, and computational modules that work in an integrated fashion to perform a dedicated imaging task as efficiently as possible. This new paradigm of imaging, called integrated or computational imaging, has enabled spectacular advances in probing remote objects and environments. I will illustrate this paradigm with an important application, namely Lord Rayleigh's classic resolution limit on the separability of two closely-spaced point sources from their images. I will show why such a limit has become a mere relic, one that has been usurped spectacularly by modern advances in image processing, new imaging methodologies, and ingenious work-arounds. Yet the best pair resolution that one can hope to achieve seems to be fundamentally limited by the number of signal photons available when making direct image measurements on the source pair. I will discuss a new approach of pair super-resolution that can qualitatively improve upon this seemingly insuperable photon limit, with quantum estimation theory revealing the ultimate bound on this phenomenon. Rather surprisingly, as I will also show, one can attain this quantum bound in certain limits in all three spatial dimensions with purely classical measurements that are not image based, but rather utilize coherent projections of the optical wave front. Phase does matter, even when imaging incoherent objects.


Tuesday, April 17th 2018
12:20 pm:
Space Physics Seminar in Tate 301-20
Speaker: Kendra Bergstedt, University of Minnesota
Subject: An Investigation of the Dayside Response of the Magnetosphere to Interplanetary Shocks: Dependence on Shock Parameters and Interplanetary Magnetic Field
This is the honors thesis presentation for Ms. Bergstedt
Faculty Host: Cynthia Cattell
1:30 pm:
Thesis Defense in PAN 110
Speaker: Timothy Peterson, University of Minnesota
Subject: Characterization of spin transport, torques, and dynamics in Heusler compound-based epitaxial structures
This is the public portion of Mr. Peterson's Thesis Defense. His advisor is Paul Crowell.
3:30 pm:
Speaker: Zach Anderson and Yang Tang, University of Minnesota
Subject: Doping dependence of the antiferromagnetic response of HgBa2CuO4+δ

Antiferromagnetic correlations have been argued to be the cause of the d-wave superconductivity and of the pseudogap phenomena exhibited by the cuprates. Neutron scattering measurements of the antiferromagnetic response have been reported for a number of cuprates, but our study of structurally simple HgBa2CuO4+δ (Hg1201) shows several features distinct from what has been found in other materials. In particular, at most dopings and temperatures we see a gapped Y-shaped magnetic dispersion in contrast to the X-shaped response seen in other cuprates. We will discuss our ongoing efforts to understand the doping dependence of the magnetic spectrum in Hg1201.


Wednesday, April 18th 2018
1:25 pm:
Speaker: Morten Christensen (University of Minnesota)
Subject:  Magnetic order in the iron pnictides and the impact of spin-orbit coupling

The iron pnictides represent a new family of unconventional superconductors in which superconductivity appears in close proximity to a magnetically ordered phase. In this talk I will review the magnetic order of the iron pnictides and discuss recent discoveries in the magnetic phase diagram, focusing on the reorientation of magnetic moments observed to occur in hole-doped compounds. Considering the impact of magnetic fluctuations on the phase diagram I will argue that even the modest spin-orbit coupling observed in iron pnictides has important consequences and cannot be neglected.

Faculty Host: Paul Crowell
To be announced.
7:00 pm:
Kaufmanis Public Lecture in McNamara Alumni Center
Speaker: Victoria Kaspi, McGill University
Subject: Astronomy's Newest Extragalactic Mystery: Fast Radio Bursts!

In 2007, astronomers discovered a new mysterious cosmic phenomenon: Fast Radio Bursts. These events consist of short, intense blasts of radio waves arriving from far outside our Milky Way galaxy. Their origin is unknown, however Fast Radio Bursts appear ubiquitous in our Universe, with roughly 1000 arriving every day over the full sky. I will discuss the Fast Radio Burst mystery and what is presently known about it, and describe a revolutionary new radio telescope being built in Canada that will soon enable astronomers worldwide to make major progress in our understanding of the FRB puzzle.


Thursday, April 19th 2018
10:10 am:
Biophysics Seminar in 120 PAN
Speaker: Ashim Rai, (postdoc in Shiv’s lab) Department of Genetics, Cell Biology and Development, University of Minnesota
Subject: Biophysical regulation of myosin VI motility by cargo adaptor proteins

: Cargo transport by motor proteins organizes the cell interior. On cellular cargoes, the binding of motor proteins is mediated by cargo adaptor proteins. Initially thought of as passive scaffolds for motor proteins, cargo adaptor proteins have recently been shown to directly affect motor function through structural studies. However, a biophysical mechanism of cargo adaptor-mediated regulation of motor activity is still lacking. In this study, we have tried to address this problem in the context of the minus-end directed actin motor, Myosin VI. Through direct measurements of adapter-mediated changes in myosin VI motility, conformation and dimerization, we have tried to establish a structure-function relationship between myosin VI and its cargo adaptor proteins. We find that binding to cargo adaptor has a potentiating effect on myosin VI velocity and processivity which is mediated through a combination of auto inhibition release, lever arm extension and dimerization of the myosin VI motor.

Speaker: Evan Tyler and John Phillips
3:35 pm:
Speaker: Victoria Kaspi, McGill University.
Subject: Astronomy's Newest Extragalactic Mystery: Fast Radio Bursts!

Fast Radio Bursts (FRBs) are a newly discovered astrophysical phenomenon consisting of short (few ms) bursts of radio waves.FRBs occur roughly 1000 times per sky per day. From their dispersion measures,these events are clearly extragalactic and possibly generally at cosmological distances. One FRB is known to repeat and indeed has been localized to a dwarf galaxy at redshift 0.2. Nevertheless, the origin of FRBs, whether repeating or not, is presently unknown. In this talk I will review FRB properties as well as highlight efforts to find FRBs, including a new Canadian radio telescope,CHIME, that is predicted to make major progress on the FRB problem.


Friday, April 20th 2018
10:10 am:
Nuclear Physics Seminar in Tate 201-20
There will be no seminar this week.
12:20 pm:
Speaker: Hanteng Wang, University of Minnesota
Subject: Interplay between interaction and disorder: Existence of many-body mobility edge in a modified Sachdev-Ye-Kitaev model.

Sachdev-Ye-Kitaev (SYK) model is a strongly correlated disordered model which exhibits many interesting properties, such as non-Fermi liquid behavior, AdS/CFT correspondence, and maximally chaoticity. In this talk, I will introduce a modified SYK model to investigate the interplay between interaction and disorder numerically. By adding constrain in coupling constant of SYK, a many-body "mobility edge" in the spectrum can be found by checking the nearest neighbor spacing distribution. When choosing a specific basis of many-body Hilbert space, one can find localized and delocalized wavefunction in Fock space. A discussion of connection and difference between chaoticity and locality of the states in this model will also be present.

Speaker: Nobuchika Okada (U. Alabama)
Subject: SU(5) x U(1)_X grand unification with Minimal Seesaw and Z′-portal dark matter

We propose a grand unified SU(5) x U(1)_X model, where the standard SU(5) grand unified theory is supplemented by minimal seesaw and a right-handed neutrino dark matter with an introduction of a global Z_2-symmetry. In the presence of three right-handed neutrinos (RHNs), the model is free from all gauge and mixed-gravitational anomalies. The SU(5) symmetry is broken into the Standard Model (SM) gauge group at M_GUT = 4 x 10^16 GeV in the standard manner, while the U(1)_X symmetry breaking occurs at the TeV scale, which generates the TeV-scale mass of the U(1)_X gauge boson (Z′ boson) and the three Majorana RHNs. A unique Z_2-odd RHN is stable and serves as the dark matter (DM) in the present Universe, while the remaining two RHNs work to generate the SM neutrino masses through the minimal seesaw. We investigate the Z′-portal RHN DM scenario in this model context, and find that the constraints from the DM relic abundance and the search results for a Z′ boson resonance at the Large Hadron Collider (LHC) are complementary to narrow down the allowed parameter region, which will be fully covered by the future LHC experiments (for the Z′ boson mass < 5 TeV). We also briefly discuss the successful implementation of baryogenesis and cosmological inflation scenarios in the present model.

Speaker: No colloquium - See info for the Kaufmanis Public Lecture on the 18th
Speaker: Roberta Humphreys, Minnesota Institute for Astrophysics, University of Minnesota
Refreshments served at 3:15 p.m.

In December 2016, the prominent woman astronomer Vera Rubin passed away. Numerous articles lauding her accomplishments credited Vera with the discovery of dark matter or at least the confirmation of it. Vera was a member of the National Academy of Sciences, a recipient of the National Medal of Science, plus numerous awards and recognition. She was also a strong and often outspoken advocate for women in science. My story begins in 1971 when Margaret Burbidge, the best known woman in astronomy, turned down the Annie Jump Cannon Award of the American Astronomical Society (AAS) on the grounds that it was discriminatory. This was the Society's oldest award and the only one exclusively for women. This created an image crisis for the AAS. One of the consequences was the first Working Group on the Status of Women in Astronomy. Vera and I were on that committee. We established a strong supportive and professional relationship. At one point our research briefly overlapped regarding the motions of stars and gas in galaxies. I'll briefly describe some of the highlights of Vera's discoveries -- including the rotation curves of galaxies and dark matter.

3:35 pm:
Speaker: Jennifer Docktor, University of Wisconsin – La Crosse Dept. of Physics
Subject: Using the Claim, Evidence, and Reasoning Framework to Develop Prospective Teachers’ Scientific Explanations in Physics

The Framework for K-12 Science Education provides a common vision for what students should know and be able to do upon finishing high school. It proposes that students should learn science by engaging in the practices used by scientists, such as planning and carrying out investigations, modeling, and developing explanations based on evidence. However, most prospective K-12 teachers have limited preparation for how to teach science using these practices. In this study, one section of a physical science course for elementary education majors received explicit instruction and scaffolding on using the Claim, Evidence, and Reasoning (CER) framework for constructing scientific explanations and one section served as a comparison group. I will describe the study design, course curriculum, assessment data collected, and scoring rubrics. A preliminary analysis indicates a relationship between prospective teachers’ abilities to construct scientific explanations using the CER framework and their long term retention of physical science content.

4:40 pm:
Career Panel in Tate 120
Subject: Careers in Industry and Academia for Physics PhDs
Everyone welcome, see abstract for full information.

This career panel will give students a taste of some of the career paths taken by UMN graduates and other physics PhDs. Panel members span a variety of jobs in local industry and in academic positions at universities or research labs. Many of the panel participants are alumni of the UMN Physics and Astrophysics PhD programs.

Everyone is welcome. This event is a great opportunity for students to learn about PhD career paths in academia and in industry and to ask our panelists any questions about their experiences. While the panel may be of special interest to graduate students pursuing a PhD, it would also be beneficial to undergraduate students curious about career paths. To aid in planning, please RSVP at this link by Monday, April 16: https://goo.gl/forms/r9QB0eNquCfQUPdz1.

Panel participants:

Mohac Tekmen, Medtronics
Xifeng Han, Seagate
Luis Hernandez, BAE Systems
Dan Endean, Honeywell
Fiona Burnell, University of Minnesota
Gerry Ruch, University of St. Thomas
Jeff Stehr, NASA / Booz Allen & Hamilton

The event will begin at 4:40 with a short presentation on physics PhD career statistics by Shaul Hanany, followed by brief remarks by the panelists. The bulk of the time will be devoted to Q&A. Some time will be reserved toward the end of the event for informal discussion.

Contact Lindsay Glesener (glesener@umn.edu) with any questions about the event.


Monday, April 23rd 2018
12:15 pm:
Speaker: Qi Wen, UMN
Subject: Broadband anti-reflection coatings using “moth-eye” structures in millimeter and submillimeter astronomy

Wasting is evil, let alone wasting the light signal from billions years ago that can potentially reveal the secrets of the Universe. Unfortunately, optical elements in a telescope, such as lenses and filters, reflect part of the light back to sky. In millimeter and submillimeter astronomy, broadband anti-reflection coatings (ARC) are more desired than ever for foreground modeling. In this talk, I will introduce the subwavelength structures (SWS) or so called “moth-eye” structures as an emerging type of broadband ARC in millimeter and submillimeter astronomy.

Faculty Host: Shaul Hanany
4:40 pm:
Speaker: Irene Moskowitz (University of Minnesota)
Subject: Bolometer Response to Elevation Angle in EBEX: How can we detect evidence of inflation in the early universe?
Faculty Host: Paul Crowell

Tuesday, April 24th 2018
12:20 pm:
Space Physics Seminar in Tate 301-20
Speaker: Zac Cohen, University of Minnesota
Subject:  STEREO Observations of Waves in the Ramp Regions of Interplanetary Shocks
This is seminar is also the public portion of Mr. Cohen's Masters' Thesis Defense.

Wednesday, April 25th 2018
1:15 pm:
Speaker: Vlad Pribiag (University of Minnesota)
Subject: Spin-Dependent Transport and Superconductivity in SrTiO3-Based Heterostructures
NOTE SPECIAL TIME: Seminar starts at 1:15
Faculty Host: Paul Crowell

Thursday, April 26th 2018
10:10 am:
Biophysics Seminar in 120 PAN
Speaker: Gianluigi Veglia, Department of Biochemistry, Molecular Biology & Biophysics, University of Minnesota
Subject: Role of conformational dynamics on protein kinases function and dysfunction

Eukaryotic protein kinases (EPKs) are phosphoryl transferase that mediate several signaling events and constitute major pharmaceutical targets. cAMP-dependent protein kinase A is a prototypical kinase of paramount biological importance as it is involved in a myriad of cellular processes. Using nuclear magnetic resonance (NMR) spectroscopy, we probed the enzyme’s intramolecular allosteric network along the catalytic cycle. We discovered that kinase A conformational motions are highly organized and correlated during turnover. Fast dynamics in the ps-ns time scale are directly linked to the conformational entropy of binding, revealing the mechanisms for positive and negative allosteric cooperativity that drive both substrate binding and product release. Slow dynamics in the in the micro second to milli second time scale are responsible for the conformational transitions from catalytically incompetent to competent states. Disruption of these dynamics leads to dysfunctional signaling and disease. Since the C-subunit of protein kinase A is highly conserved within the kinase family, the present study offers unprecedented mechanistic insights into intramolecular signaling for designing novel kinase activators or inhibitors.

Speaker: Sourabh Chauhan
3:35 pm:
Speaker: John Bush, MIT
Subject: Hydrodynamic quantum analogs

Droplets walking on a vibrating fluid bath exhibit several features previously thought to be exclusive to the microscopic, quantum realm. These walking droplets propel themselves by virtue of a resonant interaction with their own monochromatic wavefield, and represent the first macroscopic realization of a pilot-wave system of the form proposed for microscopic quantum dynamics by Louis de Broglie in the 1920s. New experimental and theoretical results allow us to rationalize the emergence of quantum-like behavior in this hydrodynamic pilot-wave system in a number of settings, and explore its potential and limitations as a quantum analog.

Faculty Host: J. Woods Halley

Friday, April 27th 2018
10:10 am:
Nuclear Physics Seminar in Tate 201-20
To be announced.
12:20 pm:
Speaker: Kexin Feng, University of Minnesota
Subject: Signatures of unusual edge physics in the specific heat of Kitaev spin liquids

Some new candidate Kitaev spin liquid material has recently been found in the experiment. Qualitative signatures of spin liquids are important to identify them. We try to explore the features of unusual edge physics in the specific heat. We find that, the fluxe excitation has some edge effects in specific heat. We also show that there is zero-temperature degenerate entropy which indicates the existence of gapless edge mode.

Speaker: Mustafa Amin (Rice U)
Subject: Inflation Ends, What’s next ?

How did inflation end? For a broad class of "simple", observationally consistent inflationary models, I will present results regarding: (1) Nonlinear fragmentation and soliton formation in the inflaton field, (2) the equation of state of the universe after inflation. For sufficiently complex models, I will highlight some universal results from stochastic particle production during inflation and reheating, and discuss their implications for initial curvature perturbations from the early universe.

2:00 pm:
Speaker: Masaaki Matsuda, ORNL
Subject: Magnetic correlations in the vicinity of the superconducting state in CrAs and MnP
Please note time and date change for this seminar. This week only.

CrAs and MnP exhibit superconductivity under pressure with a maximum transition temperature of ~2 K at 2 GPa and ~1 K at 8 GPa, respectively. Since Cr and Mn have the spin degree of freedom, elucidating the magnetic contribution to the superconductivity is crucial to understand the pairing mechanism. A helical structure is the magnetic ground state at ambient pressure in both materials. We performed neutron scattering studies in both materials under pressure. With applying pressure, the helicity and magnetic moment of the helical structure gradually change in CrAs [1], whereas MnP shows a more complicated phase diagram [2]. Most importantly, we found that both materials show helical structure in the vicinity of the superconducting phase, although the directions of the propagation vectors are different. We also studied the chemical pressure effect on static and dynamic magnetic properties in CrAs [1]. The results suggest a coupling between the magnetism and the superconductivity.

[1] M. Matsuda et al., submitted to PRX.
[2] M. Matsuda et al., Phys. Rev. B 93, 100405(R) (2016).

Speaker: Dr. Christian Veillet, Large Binocula Telescope Observatory (LBTO)
Subject: The Large Binocular Telescope Observatory

With its two 8.4m mirrors on a common mount that can be combined to form an interferometer with a baseline of 23m, complemented with adaptive secondary mirrors, the Large Binocular Telescope provides unprecedented ground-based resolution at near- and mid-infrared wavelengths. With a suite of state of the art instruments nearing completion, the observatory is moving to full operation while adding new capabilities such as ground-layer AO and new AO-fed instrumentation. We will explore the various fields in which LBT has already contributed and stress the importance of the years to come for bringing to fruition the investment made by the LBT partners (UMN is one of theme!) and place LBT as the forerunner of the next generation telescopes scheduled to see first light in the mid-2020s.

Faculty Host: Charles E. Woodward
Speaker: Richard Samuels, Department of Philosophy, The Ohio State University
Subject: "How to Acquire Number Concepts: A New Puzzle (With Stewart Shapiro and Eric Snyder)"
Refreshments served at 3:15 p.m.

Philosophers and psychologists have long been interested in how human beings learn mathematical concepts in general, and natural number concepts, in particular. Efforts to explain how such concepts are learned, however, have resulted in a number of puzzles and problems, which have led some to conclude that these concepts cannot be learned. In this talk, we first sketch some of the more important of these puzzles, and then articulate a new one that rests upon an apparent tension between two of the best empirical probes into our natural number concepts – linguistic semantics and developmental psychology. On the face of it, the dominant views in these respective fields are in tension with each other, so that if the semanticists are right, then our best accounts of how natural number concepts are learned must be wrong. Having set out this puzzle in some detail, we argue that a structuralist conception of the naturals offers a partial resolution of this apparent tension.

3:35 pm:
Speaker: Dr. Sashank Varma, Department of Educational Psychology, University of Minnesota
Subject: How We Understand Mathematics

Mathematicians, logicians, and philosophers have contemplated for millennia the question of how people understand mathematics – of how its concepts can be both abstract and unreasonably effective for describing the physical world and engineering it to our purposes. Over a much shorter time scale – the last 50 years or so – psychologists and neuroscientists have begun taking a naturalized approach to this question, regarding mathematics as a phenomenon to be explained using the scientific method. This research has revealed how people understand fundamental numerical and arithmetical concepts, the neural correlates of this understanding, and its remarkable conservation across evolution and development. And increasingly, this research is revealing the mental mechanisms that support understanding of advanced, abstract concepts from number theory, geometry, and topology. In this talk, I review some of this research, including my own work. I also connect these scientific efforts to earlier, more introspective efforts to understand the nature of mathematics.

4:40 pm:
Please note: Carolyn Bishoff's workshop rescheduled to next week

Monday, April 30th 2018
12:15 pm:
Speaker:  Andre Luiz De Gouvea, Northwestern
Subject: Chiral Dark Sectors, Neutrino Masses, and Dark Matter

The Physics behind nonzero neutrino masses and the nature of the so-called dark matter remain elusive. Both, however, point to new degrees of freedom that couple very weakly to the known Standard Model degrees of freedom. I explore the possibility that these new degrees of freedom are the matter particles of a new chiral gauge symmetry under which the Standard Model degrees of freedom are gauge singlets. In more detail, I discuss on mechanism for constructing chiral gauge theories and present two concrete models: one based on a U(1) chiral gauge theory, the other on an SU(3)xSU(2) chiral gauge theory.

Faculty Host: M. Claudia Scarlata
4:40 pm:
Speaker: David-Michael Poehlmann
Subject: Gadolinium-loaded Plastic Scintillator for Neutron Detection
Faculty Host: Paul Crowell

Tuesday, May 1st 2018
12:20 pm:
Space Physics Seminar in Tate 301-20
There will be no seminar this week.

Wednesday, May 2nd 2018
Speaker: Michael Krohn, University of Colorado
Subject: Utilizing Boosted Higgs Bosons at CMS

Thursday, May 3rd 2018
10:10 am:
Biophysics Seminar in 120 PAN
Speaker: Ibrahim Cisse, Department of Physics, Massachusetts Institute of Technology
Subject: Super-resolution imaging of transcription in living mammalian cells

Protein clustering is a hallmark of genome regulation in mammalian cells. However, these clusters often emerge from weak or transient interactions between component biomolecules at length scales and with temporal dynamics not readily attained in live cell imaging. My lab focuses on pushing single molecule and super-resolution techniques to enable the detection and characterization of weak or transient biomolecular assemblies with very high spatial and temporal resolutions directly in living mammalian cells. We discovered that very transient clusters of RNA Polymerase II (Pol II) correlate with mRNA synthesis at gene loci. For endogenous β-actin genes in live mouse embryonic fibroblasts, we observe that short-lived (~8 s) Pol II clusters correlate with basal mRNA output. During serum stimulation, a stereotyped increase in Pol II cluster lifetime correlates with a proportionate increase in the number of mRNAs synthesized. Our findings suggest that transient clustering of Pol II may constitute a pre-transcriptional regulatory event that predictably modulates nascent mRNA output.

10:10 am:
Speaker: Ryan Schmitz
Subject: A Computational Evaluation of Neutron and Photon Detection in Plastic Scintillators
Faculty Host: Paul Crowell
Speaker: Jamie Cheshire and Pat Kelly
3:35 pm:
Speaker: Jeffrey Bub, Maryland
Subject: Discussions Over a Beer: Bohr, Einstein, Bell, and all that
Student awards will be distributed at the beginning of the Colloquium.

The Bohr-Einstein debate about the foundations of quantum mechanics is something physicists tend to think of as the sort of thing you might discuss over a beer after you’ve spent the day doing real physics. Following John Bell’s seminal 1964 paper on nonlocality, there’s a new game in town influenced by developments in quantum information. I’ll discuss the significance of this new wave in quantum foundations for the dispute that separated Bohr and Einstein. (Bring your own beer.)

Faculty Host: Michel Janssen

Friday, May 4th 2018
09:00 am:
Friday, May 4 - Sunday, May 6 2018

9:00 AM - Yingfei Gu (Harvard University): Pedagogical Presentation: Introduction to Out-of-Time-Order Correlation Functions
10:30 AM - Jacobus (Jack) Verbaarschot (Stony Brook University): Spectral Properties of the SYK Model
11:10 AM - Vladimir Rosenhaus (University of California, Santa Barbara): All-Point Correlation Functions in SYK
11:50 AM - Dmitry Bagrets (University of Cologne): Quantum Ergodicity in the SYK Model
2:00 PM - Leon Balents (University of California, Santa Barbara): A Strongly Correlated Metal Built from SYK Models
2:40 PM - John McGreeby (University of California, San Diego): Strange Metals from Local Quantum Chaos
4:00 PM - Cenke Xu (University of California, Santa Barbara): A Candidate Theory for the "Strange Metal" Phase at Finite Energy Window
4:40 PM - Subir Sachdev (Harvard University): Z2 Fractionalized Phases of a Solvable, Disordered, t-J Model

Faculty Host: Alex Kamenev
10:10 am:
Nuclear Physics Seminar in Tate 201-20
There will be no seminar this week.
12:20 pm:
Speaker: Gino Graziano, University of Minnesota
Subject: Towards Microwave Studies of Josephson Junctions Based on InAs Quantum Wells with an Epitaxial Superconductor

Two-dimensional electron gases (2DEGs) with strong spin-orbit coupling are expected to host topological states in the presence of superconductivity and broken time-reversal symmetry. Josephson junctions based on such 2DEGs are predicted to exhibit an unconventional current-phase relation, characterized by a component at twice the Josephson frequency due to the presence of gapless topological Andreev bound states. In order to study the current-phase relation of these bound states, progress towards characterization of the microwave response of Josephson junctions based on InAs quantum wells proximitized with epitaxial Al.

Speaker: Yanou Cui (U. California, Riverside)
Subject: Cosmic Archaeology with Gravitational Waves from Cosmic Strings

Cosmic strings are generic cosmological predictions of many extensions
of the Standard Model of particle physics, such as a U(1) symmetry breaking phase transition in the early universe or remnants of superstring theory. Unlike other topological defects, cosmic strings can reach a scaling regime that maintains a small fixed fraction of the total energy density of the universe from a very early epoch until today. If present, they will oscillate and generate gravitational waves with a frequency spectrum that imprints the dominant sources of total cosmic energy density throughout the history of the universe. In this talk I will demonstrate that current and future gravitational wave detectors, such as LIGO and LISA, could be capable of measuring the frequency spectrum of gravitational waves from cosmic strings and discerning the energy composition of the universe at times well before primordial nucleosynthesis and the cosmic microwave background where standard cosmology has yet to be tested. This work establishes a benchmark case that gravitational waves may provide an unprecedented, powerful tool for probing the evolutionary history of the very early universe.

Speaker: Dr. Silvia Protopapa, U. Maryland
Subject: Probing the Formation and Evolution of the Solar System Through Compositional Analysis

Over the past decade, the synergy of ground- and space-based observations, modeling efforts, and laboratory studies has highlighted vital information on the composition of solar system bodies. I will discuss some of the latest results from New Horizons at Pluto and contrast them with emerging trends seen in other trans-Neptunian objects and comets – the primitive remnants of the planetesimal disk from which the outer planets formed. I will demonstrate how characterizing the composition of these objects, which requires performing laboratory measurements and applying advanced modeling techniques to interpret state-of-the-art ground- and space-based observational data, improves our understanding of the primordial solar nebula and the accretion processes that led to the formation of the planets. I will also outline future work and perspectives in light of recent results.

Faculty Host: Charles E. Woodward
There will be no colloquium this week.
3:35 pm:
No seminar; Practice presentation
4:40 pm:
Speaker: Carolyn Bishoff, Physics, Astronomy and Earth Sciences Librarian
Subject: Workshop on data management

Saturday, May 5th 2018
09:00 am:
Friday, May 4 - Sunday, May 6 2018

9:00 AM - Johanna Erdmenger (University of Wuerzburg): Pedagogical Presentation: Introduction to Gauge/Gravity Duality
10:30 AM - Herman Verlinde (Princeton University): On the Geometry of the Firewall: Partially Entangled States in SYK
11:10 AM - Antal Jevicki (Brown University): Space-Time in the Sachdev-Ye-Kitaev Model
11:50 AM - Juan Maldacena (Institute for Advanced Study, Princeton University): Eternal Traversable Wormholes
2:00 PM - Erez Berg (University of Chicago): Solvable Models for Non-Quasiparticle Transport
2:40 PM - Ehud Altman (University of California, Berkeley): Computing Quantum Thermalization Dynamics: From Quantum Chaos to Emergent
3:50 PM - Gabor Sarosi (University of Pennsylvania): The Boundary Dual of the Bulk Symplectic Structure
4:30 PM - Shinsei Ryu (University of Chicago): Sine-Square Deformation of Conformal Field Theory
5:10 PM - POSTER SESSION

Faculty Host: Alex Kamenev

Sunday, May 6th 2018
08:00 am:
Friday, May 4 - Sunday, May 6 2018

9:00 AM - Erez Berg (University of Chicago): Pedagogical Presentation: Scrambling, SYK, and Condensed Matter
10:00 AM - Yingfei Gu (Harvard University): Entanglement in the SYK Models
11:00 AM - Andreas Ludwig (University of California, Santa Barbara): Entanglement Spectra of Symmetry Protected Topological (SPT) Phases and Boundary Conformal Field Theory
11:40 AM - Johanna Erdmenger (University of Wuerzburg): Holographic Kondo Models
12:20 PM - Julian Sonner (Universite de Geneve): Thermalisation and Black Holes in Low-Dimensional AdS/CFT
1:00 pm - Workshop ends. Thank you for your participation!

Faculty Host: Alex Kamenev

Monday, May 7th 2018
12:15 pm:
There will be no seminar this week.

Tuesday, May 8th 2018
12:20 pm:
Space Physics Seminar in Tate 301-20
There will be no seminar this week.

Wednesday, May 9th 2018
1:30 pm:
There will be no seminar this week.
There will be no seminar this week.

Thursday, May 10th 2018
10:10 am:
Biophysics Seminar in 120 PAN
Speaker:  Hyun Youk, Kavli Institute of Nanoscience, TU Delft, Netherlands
Subject: Restarting life on demand: Distinguishing dormancy from death by resuming life in yeast

Stopping life indefinitely and then resuming it at the press of a button is an idea that has captivated movie makers, science fiction writers, and the general public. An open question is whether one can indeed completely stop and then resume, after many years, the life of any animals, including humans. Yeast spores are ideal for investigating the halting and resuming of cellular life. Yeast spores do not outwardly appear to be living – they neither move nor divide, exist without any external energy sources, and are believed to maintain faint, if any, intracellular dynamics. While we know how yeasts form spores when they are starved of nutrients and how a newly introduced energy source (glucose) “wakes-up” the spores and cause them to re-enter replicative life, little is known about the processes that occur, if any, inside the spores during dormancy before glucose is added, how long the dormancy can last (and what determines this timeline), and why some spores cannot wake up (thus considered dead) after a long enough time without any nutrients. We explored these questions by investigating how glucose, the necessary energy source, germinates yeast spores (i.e., restart cell replication). In doing so, we discovered that spores that are conventionally thought to be dead are, in fact, merely dormant. We found that not all spores germinate despite encountering abundant glucose. These un-germinated spores are primed so that they germinate faster upon encountering more glucose. Surprisingly, inducing expression of a useless gene that neither aids nor interferes cell growth, in dormant spores promotes germination. Crucially, we quantify an intrinsic ability by dormant spores to express genes – an intrinsic gene-expression rate. By tuning this, we could tune the probability that a spore germinates and even allow spores that glucose could not germinate, to germinate. Finally, we show that causing spores to use their stored resources to make useless proteins, while dormant, dramatically lengthens by months the time that spores escape death by months. We explain these observations with a simple mathematical model. These results provide quantitative insights into differences between death and dormancy.
______________________________________

Faculty Host: Elias Puchner
3:35 pm:
There will be no colloquium this week.

Friday, May 11th 2018
10:10 am:
Nuclear Physics Seminar in Tate 201-20
There will be no seminar this week.
12:20 pm:
There will be no seminar this week.
1:00 pm:
Thesis Defense in 301-20 Tate
Speaker: Anthony Young
Subject: Post-merger configurations of gravitationally bound dark matter systems
This is the public portion of Mr. Young's thesis defense. His advisor is Liliya Williams.
There will be no colloquium this week
There will be no colloquium this week.
3:35 pm:
There will be no seminar this week.
4:40 pm:
There will be no seminar this week.

Tuesday, May 15th 2018
11:00 am:
Speaker: Yuan Li, Peking University
Subject:  Topological Spin Excitations in a Highly Interconnected 3D Spin Lattice

The recent discovery of topological semimetals, which possess distinct electron-band crossing with non-trivial topological characteristics, has stimulated intense research interest. By extending the notion of symmetry-protected band crossing into one of the simplest magnetic groups, namely by including the symmetry of time-reversal followed by space-inversion, we predict the existence of topological magnon-band crossing in three-dimensional (3D) antiferromagnets. The crossing takes on the forms of Dirac points and nodal lines, in the presence and absence, respectively, of the conservation of the total spin along the ordered moments. In a concrete example of a Heisenberg spin model for a “spin-web” compound, we theoretically demonstrate the presence of Dirac magnons over a wide parameter range using the linear spin-wave approximation, and obtain the corresponding topological surface states [1].

Inelastic neutron scattering experiments have then been carried out to detect the bulk magnon-band crossing in a single-crystal sample. The highly interconnected nature of the spin lattice suppresses quantum fluctuations and facilitates our experimental observation, leading to remarkably clean experimental data and very good agreement with spin-wave calculations. The predicted topological band crossing is confirmed [2].

[1] K. Li et al., PRL 119, 247202 (2017).
[2] W. Yao et al., arXiv:1711.00632.

Faculty Host: Martin Greven
1:00 pm:
Thesis Defense in Tate-301-20
Speaker: Michael Janas, University of Minnesota
Subject: Applications of Semiclassical Theory in Statistical and Quantum Mechanics
This is the public portion of Mr. Janas' thesis defense. His advisor is Alex Kamenev.

Since the initiation of quantum theory in the early 20th century, semiclassical methods have been a perenniel source of insight into a diverse range of phenomena. In spite of this history, however, there remain interesting and insightful applications of semiclassical theory to physics. This thesis advances this programme in several directions. First, we consider the statistical mechanics of multivalent 1D Coulomb gases and demonstrate how the semiclassical WKB method may be used to expose its thermodynamic properties. In doing so, we develop ideas from algebraic topology and complex Riemann surfaces. Moving to quantum theory proper, these tools are applied fruitfully to the phenomenon of spin tunneling oscillations in magnetic molecules with large instrinsic spin. Moving away from the WKB approximation, these ideas from complex analysis also proved crucial in exposing universal finite-size scaling effects in 1D lattice systems such as the Su-Schrieffer-Heeger model of polyacetylene and the Kitaev chain. The thesis closes by considering the the weak noise theory of the KPZ equation and thereby discover a novel phase transition in its large deviation statistics. This last chapter will be the topic of the public portion of the thesis defense.


Wednesday, May 16th 2018
09:00 am:
US CMS 2018 Collaboration Meeting in John T. Tate Hall
May 16-19, 2018
Faculty Host: Roger Rusack
09:00 am:
Wednesday, May 16 - Saturday, May 19 2018

8:45 AM Registration
8:55 AM Opening Remarks
PNICTIDES I
9:00 AM Takasada Shibauchi (Tokyo University): Unusual BCS-BEC crossover in Fe(Se,S) superconductors
9:30 AM Sergey Borisenko (Leibniz Institute for Solid State and Materials Research (IFW) Dresden): Electronic structure and 3D gap functions of iron-based superconductors
10:00 AM Matthew Watson(University of St. Andrews): Nematic order and the superconducting gap in FeSe
10:30 AM COFFEE BREAK
10:50 AM Brian Andersen(Kobenhavns Universitet):Orbital selective quasi-particle interference and Cooper pairing in FeSe
11:20 AM Jian Kang (Florida State University): Interplay between superconductivity and nematicity in iron-based superconductors
11:50 AM Luca DeMidici (ESPCI, Paris): Hund’s correlated metals
TOPOLOGY
12:20 PM Dung-Hai Lee(University of California, Berkeley): Does vortex Majorana zero mode imply topological non-trivial superconductivity?
12:50 PM LUNCH BREAK

2:10 PM Neven Barisic (Vienna University of Technology):A fresh view of the unusual properties of the cuprates
CUPRATES 1
2:40 PM Ivan Bozovic (Brookhaven National Laboratory): What is really extraordinary in cuprate superconductors?
3:10 PM Subir Sachdev (Harvard University):SYK gauge theories
3:40 PM COFFEE BREAK
4:00 PM Louis Taillefer (Universite de Sherbrooke): The Quantum Critical Point of Cuprate Superconductors
4:30 PM Yuji Matsuda (Kyoto Univeristy): Thermodynamic evidence for a nematic phase transition at the onset of pseudogap in YBCO and Hg1201
5:00 PM Nigel Hussey (Radboud University): A Tale of Two Metals: contrasting criticalities in the cuprates and pnictides
5:30 PM RECEPTION AND POSTER SESSION

Faculty Host: Andrey Chubukov

Thursday, May 17th 2018
09:00 am:
US CMS 2018 Collaboration Meeting in John T. Tate Hall
May 16-19, 2018
Faculty Host: Roger Rusack
09:00 am:
Wednesday, May 16 - Saturday, May 19 2018

9:00 AM - Girsh Blumberg (Rutgers University): Nematicity and superconductivity in multi-band Fe-based superconductors
9:30 AM - Avraham Klein (FTPI, University of Minnesota): Identifying Mechanisms of Quantum Nematic Transitions from the Dynamic Susceptibility
10:00 AM - Pengcheng Dai (Rice University): Local orthorhombic lattice distortions in the paramagentic tetragonal phase of superconducting NaFe_{1-x} Ni_x As
10:30 AM - Coffee Break
11:00 AM - Chris Homes (Brookhaven National Laboratory): Optical Effects in Multiband Conductors and Superconductors
11:30 AM - Joseph Orenstein (University of California, Berkeley): Optical Probes of Symmetry Breaking in Magnetic and Superconducting BaFe2(As1-xPx)2
12:00 PM - Gabriel Kotliar (Rutgers University) TBA
12:30 PM - Lunch Break
2:00 PM - Jean-Marc Triscone (University of Geneva): Confinement and Superconductivity at the LaAIO3/SrTiO3 Interface and Related Systems
2:30 PM - Susanne Stemmer (University of California, Santa Barbara): Carrier Density Control of Magnetism and Hall Effects in Doped EuTiO3 Films
3:00 PM - Han Fu (University of Chicago): Anomalous Transport Properties of SrTiO3 Accumulation Layers
3:30 PM - Coffee Break
4:00 PM - Willem Rischau (University of Geneva): Superconductivity and Ferroelectricity in Strontium Titanate
4:30 PM - James Rondinelli (Northwestern University): Interplay of Correlation, Local Structure, and Inversion Symmetry in Noncentrosymmetric Metals
5:00 PM - Vlad Pribiag (University of Minnesota): Magnetism and Superconductivity in SrTiO3-based Heterostructures
5:30 PM - Maria Navarro Gastiasoro (FTPI, University of Minnesota): Normal and superconducting states of SrTiO3

Faculty Host: Andrey Chubukov

Friday, May 18th 2018
09:00 am:
US CMS 2018 Collaboration Meeting in John T. Tate Hall
May 16-19, 2018
Faculty Host: Roger Rusack
09:00 am:
Wednesday, May 16 - Saturday, May 19 2018

9:00 AM - Christian Batista (University of Tennessee, Knoxville): Dynamical Structure Factor of the Triangular Heisenberg Model
9:30 AM - Collin L. Broholm (Johns Hopkins): The Quest for a Quantum Spin Liquid
10:00 AM - Yuan Li (Peking University): Spin-orbit coupling and gapped magnetic excitations in iron-based superconductors
10:30 AM - Coffee Break
11:00 AM - Senthil Todadri (Massachusetts Institute of Technology): Origin of Mott Insulator and Superconductivity in Twisted Graphene Bilayers
11:30 AM - Oscar Vafek (National High Magnetic Field Laboratory): Superconductivity on the Brink of Spin-Charge Order in Doped Honeycomb Bilayer
12:00 PM - Liang Fu (Massachusetts Institute of Technology): Metal-Insulator Transition and Superconductivity in Graphene Superlattices
12:30 PM - Lunch Break
2:00 PM - Chandra Varma (University of California - Riverside) Topological Fluctuations in 2D-dissipative quantum XY Model: Linear in T and linear in H resistivity and other strange metal properties
2:30 PM - Riccardo Comin (Massachusetts Institute of Technology): Resonant X-Ray Studies of Electronic Orders in Quantum Solids
3:00 PM - John Tranquada (Brookhaven National Laboratory): Evidence Against an Antiferromagnetic Quantum Critical Point in La(2-x)Sr(x)CuO(4)
3:30 PM - Coffee Break
4:00 PM - Claudio Giannetti(Universita Cattolica del Sacro Cuore): Ultrafast orbital manipulation and Mott physics in multi-band correlated materials
4:30 PM - Peter Littlewood (University of Chicago): TBA
5:00 PM - Damjan Pelc (University of Minnesota): Nonlinear Response in Unconventional Superconductors

Faculty Host: Andrey Chubukov
1:00 pm:
Thesis Defense in 110 PAN
Speaker: Li He, University of Minnesota
Subject: Exploiting the spin of photons and electrons in light-matter interaction
This is the public portion of Mr. He's Thesis Defense. His advisor is Mo Li.

In light-matter interaction, the conservation of angular momentum requires the angular momentum transfer either between light and matter or within various thermodynamic reservoirs of materials, which consequently gives rise to a plethora of intriguing phenomena such as mechanical motion, charge current and magnetization. This dissertation focuses on the roles of photon spin and electron spin in light-matter interaction. The angular momentum transfer in three different scenarios are studied.First, we present the measurement of spin angular momentum of light propagating in a silicon waveguide. The continuous evolution of light polarization along propagation results in the exchange of angular momentum between light and medium and thus an optical torque to twist the waveguide. We demonstrate the use of optical torque to excite the torsional motion of an on-chip optomechanical device, which enables the coupling between optical and mechanical degrees of freedom. Second, we show the optical manipulation of surface electrons in 3D topological insulator Bi2Se3 using circularly polarized light. The transfer of angular momentum manifests itself in the spin-dependent optical selection rules and the generation of helicity-dependent photocurrent at zero bias voltage. Finally, we present the all-optical manipulation of magnetic order in ferrimagnetic alloy GdFeCo using sub-picosecond laser pulses as the ultrafast stimuli. The instantaneous heating of the electron temperature due to light absorption triggers the energy and angular momentum exchange among electron, spin and lattice reservoirs and leads to the switching of magnetization. As a step towards device application, we demonstrate an magnetic tunnel junction that can be switched all-optically without any external magnetic fields.

3:35 pm:
Thesis Defense in 129 Amundson
Speaker: Taher Ghasimakbari, University of Minnesota
Subject: Simulation Studies of Correlations, Dynamics and Phase Transitions in Diblock Copolymer Melts
This is the public portion of Mr. Ghasimakbari's thesis defense. His advisor is Prof. David Morse.

Saturday, May 19th 2018
09:00 am:
US CMS 2018 Collaboration Meeting in John T. Tate Hall
May 16-19, 2018
Faculty Host: Roger Rusack
09:00 am:
Wednesday, May 16 - Saturday, May 19 2018

9:00 AM - Erez Berg (University of Chicago): Quantum Critical Metals
9:30 AM - Emanuel Gull (University of Michigan): Charge Order in the Extended Hubbard Model
10:00 AM - Steven Kivelson (Stanford University): Superconductivity at Intermediate Coupling
11:00 AM - Sung-Sik Lee (Perimeter Institute): Kondo Effect in the Antiferromagnetic Quantum Critical Metal
11:30 AM - Artem Abanov (Texas A&M Univeristy): Non-BCS Superconductivity Near a Quantum-Critical Point
12:00 PM - Yuxuan Wang (University of Illinois): Second-Order Topological Superconductors

Faculty Host: Andrey Chubukov

Monday, May 21st 2018
11:00 am:
Thesis Defense in PAN 110
Speaker: Hannah Rogers, University of Minnesota
Subject: Effective Field Theory Analysis and Active Neutron Veto Design for the Cryogenic Dark Matter Search.
This is the public portion of Ms. Roger's Thesis Defense. Her advisor is Vuk Mandic.

Wednesday, May 23rd 2018

Thursday, May 24th 2018
3:30 pm:
Speaker: Professor Ian Mann, University of Alberta
Subject: “On the role of fast inwards and outwards ULF wave radial diffusion in shaping radiation belt morphology “

Monday, May 28th 2018

Friday, June 8th 2018

Monday, June 11th 2018

Friday, June 22nd 2018
8:30 pm:
Universe in the Park in Cedar Creek Ecosystem Science Reserve

Events are scheduled Fridays and Saturdays (rain or shine), usually beginning in June and ending mid-August. Presentations typically run from 8:30 to 10:00 or 11:00pm, including telescope observing.

Cedar Creek Ecosystem website


Friday, June 29th 2018
3:00 pm:
Thesis Defense in PAN 110
Speaker: Ilana Percher, University of Minnesota
Subject: 2D Mott Hopping of Vortices in an Amorphous Indium Oxide Film
This is the public portion of Ms. Percher's Thesis Defense. Her adviser is Allen Goldman

Saturday, June 30th 2018
8:30 pm:
Universe in the Park in Lowry Nature Center

Events are scheduled Fridays and Saturdays (rain or shine), usually beginning in June and ending mid-August. Presentations typically run from 8:30 to 10:00 or 11:00pm, including telescope observing.

Lowry Nature Center


Sunday, July 1st 2018
11:00 am:
Thesis Defense in Tate 201-20
Speaker: Vihang Mehta
Subject: Studying the building blocks of the Universe: Star-formation in low mass galaxies
This is the public portion of Vihang's PhD defense

Wednesday, July 4th 2018

Thursday, July 5th 2018
10:00 am:
Thesis Defense in PAN 110
Speaker: Jie Yang, University of Minnesota
Subject: Development and Validation of a Physics Problem Difficulty Measure
This is the public portion of Ms. Yang's thesis defense. Her Adviser is Ken Heller.
2:00 pm:
Thesis Defense in 110 PAN
Speaker: Yang Tang, University of Minnesota
Subject: Neutron Scattering Study of the Cuprate Superconductor HgBa_2CuO_{4+\delta}'
This is the public portion of Mr. Tang's thesis defense. His advisor is Martin Greven.

Saturday, July 7th 2018
8:30 pm:
Universe in the Park in William O'Brien State Park

Events are scheduled Fridays and Saturdays (rain or shine), usually beginning in June and ending mid-August. Presentations typically run from 8:30 to 10:00 or 11:00pm, including telescope observing.

William O'Brien State Park


Thursday, July 12th 2018
1:00 pm:
Thesis Defense in Tate 201-20
Speaker: Michael Gordon, University of Minnesota
Subject: Massive Stars: An Infrared Exploration Across the HR Diagram
This is the public portion of Michael's PhD defense

Saturday, July 14th 2018
8:30 pm:
Universe in the Park in Afton State Park

Events are scheduled Fridays and Saturdays (rain or shine), usually beginning in June and ending mid-August. Presentations typically run from 8:30 to 10:00 or 11:00pm, including telescope observing.

Afton State Park


Friday, July 20th 2018
8:00 pm:
Minnesota Sky-lights in Southwest sky
Jupiter just below the Moon

Friday, July 27th 2018
8:30 pm:
Universe in the Park in Dodge Nature Center

Events are scheduled Fridays and Saturdays (rain or shine), usually beginning in June and ending mid-August. Presentations typically run from 8:30 to 10:00 or 11:00pm, including telescope observing.

Dodge Nature Center


Saturday, July 28th 2018
8:30 pm:
Universe in the Park in Lowry Nature Center

Events are scheduled Fridays and Saturdays (rain or shine), usually beginning in June and ending mid-August. Presentations typically run from 8:30 to 10:00 or 11:00pm, including telescope observing.

Lowry Nature Center


Wednesday, August 1st 2018
Speaker: Vihang Mehta
Subject: This is the public portion of Vihang's PhD defense.

Friday, August 3rd 2018
Speaker: Ming Li
This is the public portion of Ming's PhD defense

Saturday, August 4th 2018
8:30 pm:
Universe in the Park in Afton State Park

Events are scheduled Fridays and Saturdays (rain or shine), usually beginning in June and ending mid-August. Presentations typically run from 8:30 to 10:00 or 11:00pm, including telescope observing.

Afton State Park


Monday, August 6th 2018
11:00 am:
Thesis Defense in PAN 110
Speaker: Vladimir Bychkov, University of Minnesota
Subject: Escaping Events at the NOvA Far Detector
This is the public portion of Mr. Bychkov's thesis defense. His advisor is Gregory Pawloski.

Tuesday, August 7th 2018
11:00 am:
Thesis Defense in 201-20 Tate
Speaker: Micaela Bagley, University of Minnesota
Subject: Reionization from Z to A: Lessons from z~6-7 Lyman-alpha emitters and local analogs of high-redshift galaxies
This is the public portion of Ms. Bagley's PhD defense. Her Advisor is Claudia Scarlata.

Wednesday, August 8th 2018
09:00 am:
Presentations from 9-3

Thursday, August 9th 2018
12:00 pm:
REU Poster Session in PAN 110
Poster session with pizza.

Friday, August 10th 2018
8:30 pm:
Universe in the Park in Lake Maria State Park

Events are scheduled Fridays and Saturdays (rain or shine), usually beginning in June and ending mid-August. Presentations typically run from 8:30 to 10:00 or 11:00pm, including telescope observing.

Lake Maria State Park


Saturday, August 11th 2018
8:30 pm:
Universe in the Park in William O'Brien State Park

Events are scheduled Fridays and Saturdays (rain or shine), usually beginning in June and ending mid-August. Presentations typically run from 8:30 to 10:00 or 11:00pm, including telescope observing.

William O'Brien State Park


Monday, August 20th 2018
10:00 am:
Thesis Defense in PAN 110
Speaker: D'Ann Barker
Subject: SuperCDMS Background Models for Low-Mass Dark Matter Searches
This is the public portion of Ms. Barker's Thesis Defense. Her adviser is Prisca Cushman.
5:00 pm:
Speaker: Caner Unal
This is the public portion of Mr. Unal's Thesis Defense. His adviser is Marco Peloso.

Monday, September 3rd 2018

Wednesday, September 5th 2018
1:25 pm:
Speaker: Nikolaos Biniskos, Jülich Centre for Neutron Science JCNS
Subject: Inelastic neutron scattering investigations in the series Mn5-xFexSi3
Postdoctoral candidate

N. Biniskos 1,2, K. Schmalzl 1, S. Raymond 2, S. Petit 3, P. Steffens 4, J. Persson 5 and T. Brückel 6
1JCNS, Forschungszentrum Jülich GmbH, Outstation at ILL, 38000 Grenoble, France
2CEA-Grenoble, INAC MEM, 38000 Grenoble, France
3CEA-CNRS UMR 12, IRAMIS LLB, 91190 Gif-sur-Yvette, France
4Institute Laue-Langevin, BP 156, 38042 Grenoble, France
5JCNS, Forschungszentrum Jülich GmbH, 52425 Jülich, Germany
6JCNS and PGI, JARA-FIT, Forschungszentrum Jülich GmbH, 52425 Jülich, Germany
The magnetocaloric cooling process is based on the magnetocaloric effect (MCE) where entropy changes of a magnetic material in an applied magnetic field are tied to adiabatic changes in temperature. An entropy transfer between crystal lattice and the magnetic spin system has to take place. A large MCE at room temperature and low magnetic field for a material with abundant and environmentally friendly elements opens the way for magnetic cooling devices. The MCE potentially occurs in any magnetic ordering process and inelastic neutron scattering (INS) that microscopically probes the magnetization dynamics is a key tool to tackle the question of the ingredients that favor large MCE.

Mn5-xFexSi3 compounds are showing a moderate MCE (2 to 4 J/kg K depending on x) at low magnetic field change from 0T to 2T, which is promising for magnetic refrigeration applications [2]. The ferromagnetic compound MnFe4Si3 has a magnetic phase transition at about 300K. The magnetic excitation spectrum of the magnetocaloric compound MnFe4Si3 has been investigated by means of polarized and unpolarized INS on single crystals. Spectra were collected in the FM phase (TC ≈ 305 K), as well as in the paramagnetic state, in order to understand the nature of the magnetism in MnFe4Si3. Spin-wave measurements at 1.5 K reveal a strong anisotropy of the magnetic exchange interactions along the (h00) and (00l) reciprocal directions of the hexagonal system, which also manifests itself in the q-dependent linewidths in the paramagnetic state. The correlation lengths indicate a short-range order, while the average linewidth is of the order of kBTC pointing to a behavior typical of many ferromagnets. In addition, the in- and out-of-plane spin fluctuations are found to be isotropic around TC and can be suppressed by a magnetic field of 2 T [3].

The parent compound Mn5Si3 undergoes two antiferromagnetic transitions at TN1=66K (AF1) and TN2=99K (AF2). Experiments with unpolarized INS in the paramagnetic (PM) state and in the AF2 and AF1 phases revealed that AF1 is characterized by sharp spin-waves, but AF2 is characterized by a diffuse signal that resembles the one of the PM state, indicating strong spin fluctuations [4]. These fluctuations may play an essential role in the MCE.

[1] O. Tegus et al., Nature 415 (2002), 150.
[2] Songlin et al., J. Alloys Compounds, 334 (2002), 249–252.
[3] N. Biniskos et al.,. Phys. Rev. B 96, 104407 (2017).
[4] N. Biniskos et al.,. Phys. Rev. Lett. 120, 257205 (2018).

Faculty Host: Martin Greven

Thursday, September 6th 2018
3:35 pm:
Speaker: Andrew Zangwill, Georgia Institute of Technology
Subject: Walter Kohn and the Creation of Density Functional Theory
Refreshments in atrium after the Colloquium.

Today's most popular method for calculating the electronic structure of atoms, molecules, liquids, solids, and plasmas makes no use of the Schrödinger equation or the many-electron wave function. Instead, it exploits a bold hypothesis: the electron density distribution completely characterizes the ground state of a many-electron system. This hypothesis was advanced in 1964-1965 by the theoretical physicist Walter Kohn and two young postdocs. This talk traces Kohn's educational trajectory (from Nazified Vienna to an internment camp in the Canadian forest to the University of Toronto to Harvard University), his professional trajectory (from applied mathematician to nuclear physicist to solid state physicist to the inventor of density functional theory), and the circumstances which led him to win a share of the 1998 Nobel Prize for Chemistry.

Faculty Host: Michel Janssen

Friday, September 7th 2018
12:20 pm:
Speaker: Brenda Knauber
Subject: TBA
Speaker: Andrew Zangwill, Georgia Institute of Technology
Subject: Four Facts Everyone Ought to Know About Science

In 1994, the Nobel Prize-winning theoretical physicist Philip Anderson published an article in The Daily Telegraph of London titled ``Four facts everyone ought to know about science." His `` facts'' are not likely the ones you would choose and my talk draws on extensive biographical research to analyze his choices in detail. What scientific and personal experiences led him to his list? What do his choices say about the scientific philosophy of someone with a legitimate claim to have been the most influential physicist of the second half of the twentieth century? I discuss whether his choices were warranted in 1994 and whether the events of the subsequent twenty-five years might cause him to revise his list.


Wednesday, September 12th 2018
1:25 pm:
Speaker: Elbio Dagotto, University of Tennessee, Knoxville
Faculty Host: Rafael Fernandes

Thursday, September 13th 2018
3:35 pm:
Speaker: Raman Sundrum, University of Maryland College Park
Refreshments in atrium after the Colloquium.
Faculty Host: Tony Gherghetta

Friday, September 14th 2018
12:20 pm:
Speaker: Dmitry Chichinadze
Subject: TBA

Wednesday, September 19th 2018
1:25 pm:
Speaker: Ali Yazdani, Princeton University
Faculty Host: Andrey Chubukov

Thursday, September 20th 2018
3:35 pm:
Speaker: Ali Yazdani, Princeton University
Refreshments in atrium after the Colloquium.

Friday, September 21st 2018
12:20 pm:
Speaker: Scott Dossa
Speaker: Edward Shuryak, State University of New York, Stony Brook; Mithat Ünsal, North Carolina State University; Zohar Komargodski, Weizmann Institute of Science; Cédric Deffayet, Institut d'astrophysique

Edward Shuryak
State University of New York, Stony Brook

Mithat Ünsal
North Carolina State University

Zohar Komargodski
Weizmann Institute of Science

Cédric Deffayet
Institut d'astrophysique de Paris


Monday, September 24th 2018
12:15 pm:
Speaker: Joshua A. Frieman, Fermilab
Faculty Host: Vuk Mandic

Wednesday, September 26th 2018
1:25 pm:
Speaker: Inna Vishik, UC Davis
Faculty Host: Martin Greven

Thursday, September 27th 2018
3:35 pm:
Physics and Astronomy Colloquium in Physics Tate B50
Speaker: Raymond Jeanloz, UC Berkeley
Refreshments in atrium after the Colloquium
Faculty Host: Cynthia Cattell

Friday, September 28th 2018
12:20 pm:
Speaker: Shuhui Luo
Subject: TBA
Speaker: Vladimir Rosenhaus (KITP)

Wednesday, October 3rd 2018
1:25 pm:
Speaker: Reserved for CQM Speaker
Faculty Host: Ke Wang
7:00 pm:
Misel Public Lecture in McNamara Alumni Center, Memorial Hall
Speaker: Professor Nergis Mavalvala, Massachusetts Institute of Technology
Subject: Gravitational Waves: A New Window to the Universe

Recent announcements of the first ever detections of gravitational waves from colliding black holes and neutron stars have launched a new era of gravitational wave astrophysics. I will describe the science, technology, and human story behind these discoveries that provide a completely new window into some of the most violent and warped events in the Universe.


Thursday, October 4th 2018
3:35 pm:
Speaker: Professor Nergis Mavalvala, Massachusetts Institute of Technology
Subject: Gravitational wave detectors: past, present and future
Refreshments in atrium after the Colloquium.

The Laser Interferometer Gravitational-wave Observatory (LIGO) detected gravitational waves for the first time in 2015, and has continued to make discoveries. I will discuss the instruments that made these discoveries, the science so far, and plans for future improvements and upgrades to LIGO.


Friday, October 5th 2018
12:20 pm:
Speaker: Nathan Bosch
Subject: TBA
Speaker: Daniel Harlow (MIT)
Subject: TBA

Wednesday, October 10th 2018
1:25 pm:
Speaker: Joel Moore, UC Berkeley
Faculty Host: Andrey Chubukov

Thursday, October 11th 2018
3:35 pm:
Speaker: Joel Moore, UC Berkeley
Refreshments in atrium after the Colloquium.

Friday, October 12th 2018

Wednesday, October 17th 2018
1:25 pm:
Speaker: Raymond Osborn, Argonne National Laboratory
Faculty Host: Martin Greven

Thursday, October 18th 2018
3:35 pm:
Speaker: Terry Hwa, UCSD
Refreshments in atrium after the Colloquium.
Faculty Host: Elias Puchner

Friday, October 19th 2018
Speaker: reserved
Subject: TBA

Wednesday, October 24th 2018
1:25 pm:
Speaker: Johnpierre Paglione, University of Maryland
Faculty Host: Vlad Pribiag

Thursday, October 25th 2018
10:10 am:
Biophysics Seminar in 120 PAN
Speaker: Oleg Krichevsky, Molecular Biophysics Lab, Ben-Gurion University
Subject:  T cell communication through cytokines follows a simple sink-diffusion model

Immune cells communicate by exchanging cytokines to achieve a context-appropriate response, but the distances over which such communication happens are not known. We used theoretical considerations and experimental models of immune responses in vitro and in vivo to quantify the spatial extent of cytokine communications in dense tissues. Using T cell exchange of IL-2 as a model system, we established that competition between cytokine diffusion and consumption generated spatial niches of high cytokine concentrations with sharp boundaries. The size of these self-assembled niches scaled with the density of cytokine-consuming cells, a parameter that gets tuned during immune responses. In vivo, we measured interactions on length scales of 80–120 um, which resulted in a high degree of cell-to-cell variance in cytokine exposure. Despite the complexity of the immune organs, the profiles of cytokine fields both in vitro and in vivo quantitatively follow the predictions of a simple model, essentially without any free parameters.

Ref. Oyler-Yaniv A, Oyler-Yaniv J, Whitlock B.M, Liu Z, Germain R.N, Huse M, Altan-Bonnet G. and O. Krichevsky (2017) , Immunity, 46, 609-620.

Faculty Host: Elias Puchner
3:35 pm:
Speaker: Steven Gubser, Princeton
Refreshments in atrium after the Colloquium.
Faculty Host: Priscilla Cushman

Friday, October 26th 2018
Speaker: reserved
Subject: TBA

Wednesday, October 31st 2018
1:25 pm:
Speaker: Adam Wei Tsen, University of Waterloo, Institute for Quantum Computing
Faculty Host: Ke Wang

Thursday, November 1st 2018
3:35 pm:
Speaker: Robert Kleinberg, Columbia University & Boston University
Subject: mK to km: How Millikelvin Physics is Reused to Explore the Earth Kilometers Below the Surface
Refreshments in atrium after the Colloquium.

Investigations of the superfluid phases of liquid helium-3 would seem to have little application to the study of rock formations thousands of meters below the surface of the earth. However, the physicist’s tool box is versatile, and techniques used in one field of study can be reused, with appropriate adaptation, in very different circumstances.

The temperature of liquid helium-3 in the millikelvin range can be measured using an unbalanced-secondary mutual inductance coil set designed to monitor the magnetic susceptibility of a paramagnetic salt. The loss signal is discarded by phase sensitive detection. Now consider the task of measuring the electrical conductivity, at centimeter scale, of the earth surrounding a borehole. Turn the mutual inductance coil set inside out, with secondary coils arranged to be unbalanced with respect to the rock wall. Instead of discarding the loss signal, use it to measure conductivity. A sensor based on this principle has been implemented in a widely deployed borehole geophysical instrument, used to estimate the prevailing direction of the wind millions of years ago, or to decide where to drill the next well in an oilfield.

Nuclear magnetic resonance may seem a very improbable measurement of the rock surrounding a borehole. Conventionally, we place the sample (which might be a human being) inside the NMR apparatus. In borehole deployment, the instrument is placed inside sample, the temperature is as high as 175C, pressure ranges to 140 MPa, and measurements must be made while moving at 10 cm/s. Apparatus with these specifications have been deployed worldwide, and are used to measure a number of rock properties, including the distribution of the sizes of pores in sedimentary rock, and the viscosity of oil found therein. They have also been used for geological and oceanographic studies in northern Alaska, and at the seafloor offshore Monterey, California.

Faculty Host: Shaul Hanany

Friday, November 2nd 2018

Wednesday, November 7th 2018
1:25 pm:
Speaker: Jason Petta, Princeton University
Faculty Host: Ke Wang

Thursday, November 8th 2018
3:35 pm:
Speaker: Jason Petta, Princeton University
Refreshments in atrium after the Colloquium.

Friday, November 9th 2018
Speaker: Keisuke Harigaya (IAS, Princeton)
Subject: TBA

Wednesday, November 14th 2018
1:25 pm:
Speaker: Mathias Scheurer, Harvard University
Faculty Host: Rafael Fernandes

Thursday, November 15th 2018
10:10 am:
Biophysics Seminar in PAN 120
Speaker: John Marko, Northwestern University
Subject: Single-molecule studies of protein-DNA interactions

All processing of DNA - transcription, replication, recombination and
repair - depend on the interactions of proteins with DNA. I will discuss
single-molecule methods for analyzing protein-DNA interactions, starting
with the (statistical)-mechanical response of DNA molecules and how
monitoring that can allow novel quantitative studies of proteins that fold
and change topology of DNA molecules. I will then describe a phenomenon
that appears pervasive for biomolecule interactions - "facilitated
dissociation" - that makes rates of turnover of molecular complexes in vivo
very different from what we observe in vitro.

3:35 pm:
Speaker: John Marko, Northwestern University
Subject: Physics of chromosome folding and disentanglement
Refreshments in atrium after the Colloquium.

All biological phenomena depend on genetic information which is encoded
into the base-pair sequence along the very long DNA molecules found in all
living cells. The DNAs in chromosomes, in addition to being biologically
important, are amazing physical objects, being 2 nanometers wide and (in
humans) several centimeters in length. I will explain how the cell takes
care of these long, fragile chromosomal DNAs and how it uses DNA itself as
a key mechanical component of the cell nucleus. Then, during and
following DNA replication, our cells face the gigantic challenge of
figuring out how to topologically separate those long polymers from one
another. I will discuss our current understanding of the "lengthwise
compaction" mechanisms underlying this process, focusing on the interplay
between "loop-extruding" SMC complexes (mainly condensin) and
DNA-topology-changing topoisomerase II.

Faculty Host: Elias Puchner

Friday, November 16th 2018
Speaker: Alba Grassi (SCGP Stony Brook)

Friday, November 23rd 2018
Subject: NO SEMINAR - THANKSGIVING

Wednesday, November 28th 2018
1:25 pm:
Speaker: Reserved for CQM Speaker
Faculty Host: Ke Wang

Thursday, November 29th 2018
3:35 pm:
Speaker: Marco Velli, UCLA
Refreshments in atrium after the Colloquium.
Faculty Host: Robert Lysak

Friday, November 30th 2018
Speaker: Jaroslav Trnka (UC Davis)

Wednesday, December 5th 2018
1:25 pm:
Speaker: Brian Skinner, MIT
Faculty Host: Boris Shklovskii

Thursday, December 6th 2018
3:35 pm:
Speaker: Stacy McGaugh, Case Western
Refreshments in atrium after the Colloquium.
Faculty Host: J. Woods Halley

Friday, December 7th 2018

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