Physics and Astronomy Calendar

Week of Monday, October 14th 2019


Monday, October 14th 2019
12:15 pm:
Speaker: Zach Pace, U-Wisconsin, Madison
Subject:  Kiloparsec-resolved and galaxy-integrated stellar masses in the SDSS-IV/MaNGA survey

A galaxy's stellar mass is one of its most fundamental properties, but it remains challenging to measure reliably, as there are important degeneracies between stellar age, metallicity, and interstellar dust. Furthermore, with the advent of very large optical spectroscopic surveys, efficient methods that operate reliably on low signal-to-noise spectra are needed. I present a method for inferring properties of stellar populations, which relies on a library of composite stellar populations, and obtains a low-dimensional spectral basis set through principal component analysis (PCA) of the associated model spectra. This method is used to estimate resolved stellar mass-to-light ratios for ~6500 galaxies in the MaNGA survey. I will then discuss the tension between these estimates and those of dynamical mass surface density from the DiskMass survey, outline the hazards of relying on galaxy-integrated stellar mass-to-light estimates, and finally show some preliminary results that compare atomic gas content, stellar mass, and radial gas-phase metallicity variations.

Faculty Host: Lucy Fortson

Tuesday, October 15th 2019
11:15 am:
Nuclear Physics Seminar in Tate 301-20
Speaker: Alessandro Roggero, University of Washington
Subject: Quantum Computing for Nuclear Physics

Quantum Computers have the potential to dramatically extend the reach of our theoretical modelling of complex quantum many body systems. In this talk I will explore the impact that this technology can have on the study of structure and reactions of atomic nuclei. As an example, an ab-initio description of nuclear dynamics is currently out of reach for most systems of interest, however with only a mid-sized quantum computer efficient calculations of both inclusive and exclusive nuclear cross sections would be possible. In particular I will present an application of this strategy to describe reactions of relevance for long base-line neutrino experiments.
Current generations quantum devices are however too small and too noisy to already tackle realistic problems in nuclear physics, in the last part of the talk I will discuss some of the challenges one has to face when implementing practical quantum algorithms on today's quantum processors using a simple toy model for the triton as example.

1:25 pm:
Space Physics Seminar in Tate 201-20
Speaker: Sheng Tian
Subject: Observations on MHD-scale properties of dipolarization in the earth's magnetosphere during geomagnetic storms"
1:25 pm:
Special Public Lecture in B-75 Amundson Hall
Speaker: Sabine Hossenfelder Frankfurt Institute for Advanced Studies
Subject: How Beauty Leads Physics Astray

To develop fundamentally new laws of nature, theoretical physicists often rely on arguments from beauty. Simplicity and naturalness in particular have been strongly influential guides in the foundations of physics ever since the development of the standard model of particle physics. In this lecture I argue that arguments from beauty have led the field into a dead end and discuss what can be done about it.

3:30 pm:
CESTA Seminar in 110 PAN
Speaker: Joey Talghader, Electrical and Computer Engineering, UMN
Subject: Distributed Sensing: When are our sensors too small to be smart?

Distributed sensor networks are proliferating in products and systems through the economy, and their technological capabilities are rising at a rapid rate. At present, most sensors are either directly connected to the networks of which they are a part, for example in automobiles, or they are large and complex enough that they have on-board power and can connect periodically to the global telecommunication system, for example in remote weather stations. These types of sensors are often called "smart" sensors because they can take advantage of power supplies, communications devices, microelectronic data processing, software, and other resources that are part of their individual unit or the system to which they are directly or indirectly connected.

However, future systems may have sensors that travel passively, say by fluid flow, wind, or water and, further, have dimensions of a few microns or less. Such sensors cannot be “smart” in the traditional way we define the term. The difficulty is not merely miniaturization; instead, there are fundamental issues of diffraction for remote communication and volume power density for batteries or photovoltaic cells that prevent independent operation.

This talk will discuss these issues and present two examples of distributed sensors that must operate in environments where smart sensing is difficult. The first sensors are semi-autonomous particles for sensing metal-ion concentration in fluids. The devices were designed to be released in numbers to collect statistical data as they flow through microchannels. They incorporate a monolithically integrated photovoltaic (PV) power supply and use a resonant cantilever mass sensor to detect electrodeposited metal at the tip of a cantilever. Individual devices correctly predict, within about a factor of two, the metal ion concentration even when operating off of scavenged light from a room lamp. The current sensors operate at powers of about 50nW, and are integrated into a total volume below 0.046mm3. The second sensors are also particles but designed to measure temperature inside explosions, perhaps the harshest environment on earth. The sensor particles are embedded in or around an explosive device and disperse with the explosion. The thermoluminescence (TL) of the oxide microparticles gives direct information on temperature and time because the trapped charges that ultimately give rise to TL have a probability of detrapping that follows an Arrhenius-type relationship. The effects of maximum temperature on the intensity ratios of various luminescent peaks have been compared with first-order kinetics theory and predict temperatures to within 5% or better.

These types of passive, “dumb” sensors are absolutely necessary in certain critical environment but present challenges of incorporation into traditional distributed networks. We hope to contribute to CESTA by addressing some of these challenges.


Wednesday, October 16th 2019
Speaker: Mingda Li, MIT, Nuclear Science and Engineering
Subject: Quantized Dislocations

A dislocation, just like a phonon, is a type of atomic lattice displacement but subject to an extra topological constraint. However, unlike the phonon which has been quantized for decades, the dislocation has long remained classical. In this talk we introduce our recent theoretical effort to quantize a dislocation, the “dislon” theory [1], by emphasizing a few predictions on tailoring electronic and thermal properties in a dislocated crystal, along with some initial agreement with recent simulations and experiments. By establishing a concept that complex defects can naturally be described by a quantum field, quantum many-body theory may be applied to explain complex disordered materials at a new level of clarity.
[1] M. Li, “Quantized Dislocations”, J. Phys.: Condens. Matter 31, 083001 (2019).

Faculty Host: Martin Greven
Speaker: Mingda Li, MIT, Nuclear Science and Engineering
Subject: Quantized Dislocations

A dislocation, just like a phonon, is a type of atomic lattice displacement but subject to an extra topological constraint. However, unlike the phonon which has been quantized for decades, the dislocation has long remained classical. In this talk we introduce our recent theoretical effort to quantize a dislocation, the “dislon” theory [1], by emphasizing a few predictions on tailoring electronic and thermal properties in a dislocated crystal, along with some initial agreement with recent simulations and experiments. By establishing a concept that complex defects can naturally be described by a quantum field, quantum many-body theory may be applied to explain complex disordered materials at a new level of clarity.
[1] M. Li, “Quantized Dislocations”, J. Phys.: Condens. Matter 31, 083001 (2019).

Faculty Host: Martin Greven
7:00 pm:
14th Annual Misel Family Lecture in McNamara Alumni Center 
Speaker: Professor Charles M. Marcus, Niels Bohr Institute
Subject: “Quantum Computing: Why, How, and When”

This lecture is about a future technology, quantum computing, which uses known laws of quantum physics to compute in new ways. Within this technology challenge are at least two profound questions in basic science: which problems can be sped up with a quantum computer, and how can inadvertent measurement be avoided. After a few introductory comments about the first question, this lecture will concern mostly the second question, and will explore some options and the challenges of each.


Thursday, October 17th 2019
10:10 am:
Biophysics Seminar in 120 PAN
Speaker: Jared Hennen, UMN, Mueller Lab
Subject: Protein mobility and local volume fluctuations identify membrane binding of proteins within the sub-resolution structure of the nuclear envelope

The nuclear envelope (NE) consists of two concentric nuclear membranes that surrounds the nucleus from the cytoplasm in eukaryotic cells. The two nuclear membranes are separated by a thin fluid layer, referred to as the lumen, which is densely packed with proteins. These proteins are implicated in important cellular processes, such as mechano-regulated gene expression. The molecular details of these regulation processes, which typically require the formation of protein complexes, are not well understood due to a lack of techniques for the physical characterization of protein assembly in the NE of living cells. While recent progress has been made using fluorescence fluctuation spectroscopy (FFS) to quantify the assembly states of NE proteins in their native environment, monitoring the interaction of proteins with the membrane during assembly remains an unsolved problem. This is a significant shortcoming because membrane binding is often associated with conformational changes in proteins that are critical to cellular signaling pathways. Particularly vexing for studying membrane association is the close proximity of the nuclear membranes, which are only separated by the approximately 40 nm thick lumen. Thus, optical resolution is insufficient to directly distinguish luminal and membrane-bound NE proteins by fluorescence imaging methods.

To overcome this obstacle, we examined protein mobility within the NE by FFS methods. While membrane association has been detected using mobility in other regions of the cell, the confined spatial structure of the NE requires us to check the validity of the Stokes-Einstein relation for luminal proteins. In addition, we explore the temperature-dependent mobility of soluble and membrane-bound proteins in the NE as a potential marker for differentiating these populations. Finally, we look at the undulations of the nuclear membranes, which introduce local volume changes. This process is detected by FFS as an additional fluctuation signal for luminal proteins, but is absent for membrane-bound proteins. We harness this difference to provide a second, independent tool for identifying membrane-bound NE proteins. These new techniques are then applied to investigate the membrane association of two proteins native to the NE: SUN2, a constituent protein of the Linker of Nucleoskeleton and Cytoskeleton (LINC) complex, and the AAA+ ATPase torsinA.

12:10 pm:
Speaker: Trevor Knuth and Claudia Scarlata
3:35 pm:
14th Annual Misel Colloquium in Tate Hall B50
Speaker: Professor Charles M. Marcus, Niels Bohr Institute
Subject: “Majorana zero modes: a new kind of ‘particle’, and where it can be found”

This colloquium will present the idea of particles with non-abelian statistics and give an example that seems to occur in nature, the Majorana zero mode. “[In] nature” as used here means in man-made one-dimensional hybrid material structures near absolute zero. The relevance of Majorana modes to quantum computing will be addressed as well.


Friday, October 18th 2019
12:20 pm:
Speaker: Dmitry Chichinadze
Subject: "Possible origin of nematic superconductivity in twisted bilayer graphene".
Faculty Host: Boris Shklovskii
12:30 pm:
Speaker: Edgar Shaghoulian (Cornell U.)
Subject: TBA
2:30 pm:
No Colloquium. Physics Colloquium speaker Thurs: Charles M. Marcus, Niels Bohr Institute
4:40 pm:
Speaker: Cynthia Cattell
Subject: Understanding particle acceleration is space plasmas using radio waves and lab plasma experiments

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