Physics and Astronomy Colloquium

semester, 2007


Wednesday, January 17th 2007
4:00 pm:
Subject: No seminar this week.

Wednesday, January 24th 2007
4:00 pm:
Speaker: Steve Pierson, Head of Government Relations, American Physical Society
Subject: China and India: A new Sputnik? Federal funding for physical sciences research
Refreshments served in Room 216 Physics at 3:30 p.m.

Federal funding for the physical sciences has been stagnant for nearly 30 years, hindering scientific progress in many regards. Meanwhile, in the last decade, countries like China and India have made impressive strides in improving their science and technology infrastructure, to the extent that U.S. leadership in many scientific fields is, or will soon be, challenged. The United States is also losing high-tech market share and jobs. Just as Sputnik jolted the U.S. into action almost 50 years ago, many believe that the current challenges require a Sputnik-like response. Indeed, in January 2006, President Bush proposed to double the funding for physical sciences basic research. A year later, the proposed increases are yet to be enacted. In this talk, I will discuss the Washington environment for basic research funding, challenges to U.S. science leadership, and the APS efforts to increase science research budgets.


Wednesday, January 31st 2007
4:00 pm:
Speaker: Bolek Wyslouch - MIT
Subject: Heavy-Ion Physics with the CMS Experiment at the Large Hadron Collider
Refreshments served in Room 216 Physics at 3:30 p.m.

The Large Hadron Collider at CERN will collide protons at \sqrt{s} = 14 TeV and lead ions at \sqrt{s_NN} = 5.5 TeV. The new energy regime will allow us to significantly extend and enhance our knowledge of the behavior of the strongly interacting hot nuclear matter recently observed in the heavy-ion collisions at RHIC. The physics program of the Compact Muon Solenoid (CMS) includes the study of heavy-ion collisions. The high energies
available at the LHC will allow high statistics studies of the dense partonic system with hard probes: heavy quarks and quarkonia with an emphasis on the b and Upsilon, high p_T jets, photons, as well as Z bosons. I will present the physics goals of the heavy-ion program at the LHC including examples of the planned physics measurements using the CMS apparatus.


Saturday, February 3rd 2007
4:00 pm:
Speaker: Michael Marder, University of Texas, Austin
Subject: Rising above the gathering storm with U Teach
Refreshments served in Room 216 Physics at 3:30 p.m.

Wednesday, February 7th 2007
4:00 pm:
Speaker: Open Date
Refreshments served in Room 216 Physics at 3:30 p.m.

Wednesday, February 14th 2007
4:00 pm:
Speaker: Alexander Grosberg
Subject: To knot or not to knot: making neckties of polymers
Refreshments served in Room 216 Physics at 3:30 p.m.

The mathematics and physics of knots has a long and fascinating
history, starting from a model of an atom suggested by W.Thompson
(Lord Kelvin). Knots in DNA are abundant and important. Recently, we surveyed the protein data bank and found that evolution for some as yet unknown reason preferred unknotted proteins, although a few beautiful counterexamples were found, including Gordian knot in human ubiquitin hydrolase. In theoretical aspect, the field was long dominated by either highly abstract mathematics or computer simulations. Recently, some progress was made in the direction of physical understanding of knots. In the talk, all these various aspects will be reviewed in some mixture.


Wednesday, February 21st 2007
4:00 pm:
Speaker: Marco Peloso
Subject: Before and After Inflation
Refreshments served in Room 216 Physics at 3:30 p.m.

I will review some aspects of inflationary physics. Inflation
is responsible for producing the ``clean'' homogeneous and isotropic
universe we live in, starting from rather generic initial conditions.
While inflation is very efficient in erasing any information on the
initial state, some trace may have remained on the largest observable
scales, if inflation had a limited duration. Inflation produced the
cosmological perturbations which are imprinted in the Cosmic Microwave
Background (CMB) radiation, and which are the ``seeds'' of the present
galaxies. The recent CMB data measured by WMAP are overall in excellent
agreement with the simplest inflationary prediction. However, they also
present a few unclear features, as for instance a hint for broken
isotropy at the largest scales. In the first part of the talk I will
present an attempt to explain this feature in terms of a primordial
anisotropy which survived a limited amount of inflation. In the second
part, I will instead discuss the reheating stage after inflation,
focusing on the role that nonperturbative effects may have played in
this period.


Wednesday, February 28th 2007
4:00 pm:
Speaker: Ellen Zweibel, University of Wisconsin
Subject: The Generation and Evolution of Astrophysical Magnetic Fields
Refreshments served in Room 216 Physics at 3:30 p.m.

Despite recent advances in cosmology, we still do not understand how or when magnetic fields originated. After reviewing the evidence, I will discuss one particular scenario in which magnetic fields originate in accretion disks, are amplified by a dynamo, are ejected into the ambient medium in a jet, and eventually become pervasive. Certain aspects of the problem are relevant to the formation of the first stars.


Wednesday, March 7th 2007
4:00 pm:
Speaker: Wick Haxton - University of Washington
Subject: What Nuclear Physicists Don't Know About Neutrinos
Refreshments served in Room 216 Physics at 3:30 p.m.

Some intriguing discoveries in neutrino physics have been made in the past decade, clarifying their behavior in vacuum and in matter, and defining their role as a component of dark matter. But a lot remains to be learned. I will describe some of the questions that impact nuclear physics, including neutrinos in quiescent and explosive massive stars, their properties under particle-antiparticle conjugation, and their importance in
a variety of mechanisms for nucleosynthesis.


Wednesday, March 14th 2007
4:00 pm:
Spring Break: No Colloquium this week.

Wednesday, March 21st 2007
4:00 pm:
Speaker: Professor Barry Barish - California Institute of Technology
Subject: "Probing Einstein’s Universe"
Refreshments served in Room 216 Physics following lecture

As a consequence of his theory of general relativity, Einstein predicted the existence of a new physical phenomenon called gravitational radiation. In this theory, concentrations of mass (or energy) warp space-time, and changes in the shape of such objects cause distortions called gravitational waves that propagate through the Universe at the speed of light. Almost 100 years later, these waves so fundamental to Einstein’s theory are yet to be directly observed. A new generation of interferometric detectors represents an ambitious attempt to detect such waves from some of the most spectacular phenomena in the universe: colliding black holes, supernovae and even relic waves from the big bang. The science of gravitational waves, the status of the searches and the prospects for detection will be discussed.


Thursday, March 22nd 2007
4:00 pm:
Speaker: Barry C. Barish, Caltech
Subject: The Next Great Particle Accelerator: The International Linear Collider
Refreshments served in Room 216 Physics at 3:30 p.m.

There is a consensus among the worldwide high energy physics community that a TeV scale linear electron positron collider should be the highest priority long term goal for the field. This next great particle accelerator, together with the Large Hadron Collider (LHC) at CERN, will enable a comprehensive exploration of the TeV energy scale where many of the new phenomena we seek, like supersymmetry or possibly even extra dimensions could reveal themselves. The international community has chosen the superconducting rf technology to be the basis of the international linear collider final design, in anticipation of a construction project to begin in about 2012. A global design effort has been created to guide the R&D and technical design toward construction of the ILC. In this presentation, I will discuss the science motivation, the technology, and will review recent progress and plans toward this exciting future international facility.


Wednesday, March 28th 2007
4:00 pm:
Speaker: Gary Horowitz
Subject: Quantum Black Holes
Refreshments served in Room 216 Physics at 3:30 p.m.

Black holes are a continuing source of mystery. Although their classical properties have been understood since the 1970's, their quantum properties raise some of the deepest questions in theoretical physics. Some of these questions have recently been answered using string theory. I will review these fundamental questions, and the aspects of string theory needed to answer them. I will then explain the recent developments and new insights into black holes that they provide. Some puzzles remain, and I will discuss the prospects for further progress.


Wednesday, April 4th 2007
4:00 pm:
Speaker: No speaker this week due to illness.
Refreshments served in Room 216 Physics at 3:30 p.m.

Wednesday, April 11th 2007
4:00 pm:
Speaker: Aharon Kapitulnik
Subject: Search for Gravity-like Forces at sub-mm distance
Refreshments served in Room 216 Physics at 3:30 p.m.

Recent theories of physics beyond the standard model have predicted deviations from Newtonian gravity at short distances. In order to test these theories, we have a built an apparatus that can measure attonewton-scale forces between small masses separated by distances on the order of 25 microns. A micromachined silicon cantilever was used as the force sensor, and its displacement was measured with a fiber interferometer. We have used our measurements to set bounds on the magnitude alpha and length scale lambda of Yukawa-type deviations from Newtonian gravity; our results presented here yield the best experimental
limit in the range of lambda between 5 and 50 microns. We also discuss initial results from new experiments in which substantial improvements are expected.

1. S.J. Smullin, A.A. Geraci, D.M. Weld, J. Chiaverini, S. Holms, and A. Kapitulnik, Phys. Rev. D 72, 122001-1-20 (2005).


Wednesday, April 18th 2007
4:00 pm:
Speaker: Fran Bagenal, University of Colorado
Subject: Exploring the Giant Magnetosphere of Jupiter
Refreshments served in Room 216 Physics at 3:30 p.m.

Jupiter is a planet of superlatives: it is the most massive planet in the solar system, rotates the fastest, has the strongest magnetic field, and has the most massive satellite system of any planet. These unique properties lead to active volcanoes on Io, a ton per second of sulfur and oxygen being spewed out of the moon, a vast population of energetic plasma trapped in the planet's strong magnetic field, and intense auroral emissions in Jupiter's polar atmosphere. The giant magnetosphere of Jupiter has been explored by telescopes on Earth, Hubble Space Telescope, several spacecraft flying past the planet plus the Galileo spacecraft that spent seven years in orbit. This talk will discuss our current understanding of this huge, dynamic structure and present what we hope to learn from the New Horizons spacecraft as it flies down Jupiter's magnetotail on its way to Pluto (spring 2007) and from the Juno mission (launch due in 2011) that will skim over Jupiter's poles.


Wednesday, April 25th 2007
4:00 pm:
Speaker: Meigan Aronson, Brookhaven National Laboratory and Stony Brook University
Subject: Increasing Faculty Diversity: The Michigan Experience
Refreshments served in Room 216 Physics at 3:30 p.m.

A generation ago, few universities had faculties which reflected the gender and ethnic diversity of the US population. While these
differences have subsequently become less pronounced among social
science and humanity faculties, the composition of science and engineering faculties have been slower to diversify. In this talk I will discuss our efforts at the University of Michigan to improve recruiting and retention of women and minority faculty members. This undertaking is viewed as an institutional transformation, and involves both administrative initiatives, modifications of hiring and promotion policies, and as well faculty development and training. I will review progress so far, and discuss the future of these efforts in light of the Michigan Civil Rights Initiative.


Wednesday, May 2nd 2007
4:00 pm:
Speaker: Ivan Schuller, University of California-San Diego
Subject: Pathological Science
Refreshments served in Room 216 Physics at 3:30 p.m.

I describe and categorize instances in which scientific research
can be categorized as "pathological". Several of these have become "cause celebre" and have received recent extensive attention in the published media. Out of these I draw the 13 Schuller Rules for Pathological Science and describe useful ways in which to judge scientific research.


Wednesday, May 9th 2007
4:00 pm:
This colloquium will resume in the fall.

Wednesday, September 12th 2007
4:00 pm:
Speaker: Juan Collar, Enrico Fermi Institute
Subject: Something Old, Something New
Refreshments served in Room 216 Physics at 3:30 p.m.

We'll discuss two initiatives in astroparticle and neutrino physics at the University of Chicago, both sharing in common the revival and revision of old technologies to address new experimental challenges. COUPP employs ultra-clean heavy liquid bubble chambers to search for WIMP dark matter. COGENT aims at the detection of faint (sub-keV) signals in detectors large enough to allow searches for rare processes, using recently developed p-type point contact Germanium detectors.


Wednesday, September 19th 2007
4:00 pm:
Speaker: Nigel Cooper, Cambridge University
Subject: Spinning Topological Phases out of Cold Atomic Gases
Refreshments served in Room 216 Physics at 3:30 p.m.

One of the most remarkable properties of a superfluid is its response to rotation. The formation of an array of quantized vortex lines is a dramatic manifestation of the macroscopic quantum nature of the superfluid. But what happens if one spins the superfluid so rapidly that the vortex lines become very closely spaced? I shall describe theoretical predictions of the appearance of novel and exotic phases in cold atomic gases at high vortex densities. These include topological phases exhibiting so-called "non-abelian" exchange statistics, with the potential to support universal topological quantum computation.


Wednesday, September 26th 2007
4:00 pm:
Speaker: Susan Coppersmith
Subject: Quantum computing: Opportunities and challenges
Refreshments served in Room 216 Physics at 3:30 p.m.

Quantum-mechanical phenomena such as quantum coherence, interference, nonlocality, and entanglement can be exploited to build new electronic devices and systems that differ fundamentally from current ones. Achieving these advances requires fundamental advances in a variety of disciplines as well as close interdisciplinary collaboration. This talk will discuss how close cooperation between researchers in different disciplines has enabled substantial new progress in the development of quantum dots in silicon/silicon-germanium heterostructures for quantum computing applications.


Wednesday, October 3rd 2007
4:00 pm:
Speaker: Leo P. Kadanoff
Subject: The Good, the Bad and the Awful - Scientific Simulation and Prediction
Refreshments served in Room 216 Physics at 3:30 p.m.

Worthwhile computer simulations are done to explore uncharted territory, resolve a well-posed scientific or technical question, or to make a design choice. Some excellent work is reviewed. Some less happy stories are recounted. I then concentrate my attention upon astrophysical simulations, showing how they can explore possible scenarios for stellar explosions.


Wednesday, October 10th 2007
4:00 pm:
Speaker: Bonnie Fleming
Subject: Unexpected Results from MiniBooNE
Refreshments served in Room 216 Physics at 3:30 p.m.

The MiniBooNE neutrino oscillation experiment at Fermilab has reported first results ruling out a two neutrino oscillation interpretation of the LSND signal. The LSND experiment observed electron anti-neutrino appearance in a muon anti-neutrino beam. Taken with other evidence for neutrino oscillations, the LSND measurement suggests the existence of physics beyond the standard model in the neutrino sector. MiniBooNE has performed two independent and blind oscillation searches for electron neutrino appearance in a muon neutrino beam. In both, analysis selections and fitting procedures were determined before candidate electron neutrino events were examined. While MiniBooNE did not observe oscillations as expected in the analysis region, an excess of events was observed at low energy. There are a number of models suggesting these events could signal new physics. Ongoing studies to understand these events will be presented. A follow-on experiment to address this low energy excess will be described.


Wednesday, October 17th 2007
4:00 pm:
Speaker: Ed Smith, Jet Propulsion Lab, NASA
Subject: The Heliospheric Magnetic Field: Origin, Structure and Interaction with the Solar Wind and Interstellar Medium
Refreshments moved to Main Hall in front or room 148 at 3:30 p.m.

Parts of the solar corona accelerate into space to form the supersonic solar wind that pushes interstellar material out of the solar system to distances beyond 100 AU creating the "bubble" known as the Heliosphere. The solar wind also transports part of the Sun�s dipole magnetic field into the Heliosphere filling it with magnetized plasma. The Heliospheric Magnetic Field (HMF) prevents the interstellar plasma and magnetic field from penetrating into the Heliosphere leading to a sharp boundary separating the solar and interstellar plasmas. Solar wind outflow leaves �holes� in the corona because of the depletion of the coronal density. When solar activity is low, the Sun�s magnetic poles coincide with two large coronal holes in the north and south polar caps that emit high- speed solar wind while lower speed wind originates at lower latitudes. The magnetic dipole and coronal holes are tilted relative to the Sun�s rotation axis and, as the Sun rotates, the fast and slow wind interact introducing large scale heliospheric structure and dynamics involving the HMF and consisting of alternating compression and rarefaction regions. The distinctive compression regions are bounded by collision-less shocks that accelerate solar particles to high energies. Helisopheric dynamics are further enhanced by the penetration of some interstellar constituents into the Heliosphere, namely, neutral gas, electrically- charged interstellar dust and Galactic Cosmic Rays. Both the structure and dynamics of the heliosphere are profoundly affected by the solar cycle. During maximum solar activity, the Sun�s magnetic dipole effectively rotates equator-ward and eventually reverses polarity while the polar coronal holes vanish and then reappear. An overview of these physical phenomena will be presented based principally on 17 years of 3D observations by Ulysses, the first spacecraft to follow a polar orbit carrying it over and under the Sun.


Wednesday, October 24th 2007
4:00 pm:
No Colloquium This Week

Wednesday, October 31st 2007
4:00 pm:
Speaker: Larry Rudnick, Liliya Williams, Marco Peloso, Shaul Hanany, Shea.Brown
Subject: The CMB, Dark Energy, and the Giant Void in the Universe
Refreshments served in Room 216 Physics at 3:30 p.m.

The recent discovery of a giant, 280 Mpc diameter void in the universe involved a number of puzzle pieces - fluctuations in the cosmic microwave background, radio surveys of the nearby universe, the evolution of dark-matter dominated large scale structures, and the role of dark energy in this evolution. We will show how these puzzle pieces come together to create the "late integrated Sachs-Wolfe" effect, one of the perturbations on the CMB as it propagates through the universe and then leads to the discovery of the giant void. We will briefly discuss the implications of this void for our understanding of the development of large scale structure in the universe.


Wednesday, November 7th 2007
4:00 pm:
Speaker: Walter Gekelman
Subject: Three-dimensional current systems produced by colliding plasmas in a background Magnetoplasma
Refreshments served in Room 216 Physics at 3:30 p.m.

Results are presented from an experiment in which two plasmas, initially far denser than a background magnetoplasma, collide as they move across the magnetic field. The dense plasmas are formed when laser beams, nearly orthogonal to the background magnetic field strike two targets. The merging plasmas are observed to carry large diamagnetic currents. The interaction spawns the generation of intense waves in the plasma. The first burst of waves observed, are whistler waves and their dispersion and spatio-temporal structure will be presented. Less than a microsecond after the collision a "magnetic reconnection" event is triggered by the collision and the electric field induced in this event generates a field aligned current. This is the first step in the development of a fully three-dimensional current system. After several ion gyro-periods the current systems become those of shear Alfven waves. As local currents move, small reconnection "flares" occur at many locations throughout the plasma volume. Magnetic field lines associated with these waves are shown in the figure above. The data clearly show that the induced electric field is carried though the system by shear Alfven waves. The relation of this experiment to phenomena in space and astrophysics will be discussed.


Wednesday, November 14th 2007
4:00 pm:
Speaker: Prof.Earl Peterson and Prof.Keith Ruddick
Subject: History of High Energy Physics at Minnesota
Refreshments served in Room 216 Physics at 3:30 p.m.

Wednesday, November 21st 2007
4:00 pm:
No Colloquium This Week

Wednesday, November 28th 2007
4:00 pm:
Speaker: Timothy Newman, Arizona State University, Center for Biological Physics
Subject: Discrete, mesoscale, stochastic dynamics in biological systems: applications to embryogenesis and biochemical networks
Refreshments served in Room 216 Physics at 3:30 p.m.

I will argue that the theory of stochastic processes provides a solid framework for describing biological systems. I will present two applications. The first concerns the development of algorithms capable of modeling large-scale multi-cellular systems, such as the early embryo. I will discuss the Subcellular Element Model (SEM), which is designed to simulate the interactions between thousands of three-dimensional, visco-elastic, deformable cells. The use of the SEM to understand one of the most fundamental embryonic processes - extension of the primitive streak - will be described. The second application is to cycling phenomena. I will discuss a new theoretical mechanism which predicts that intrinsic noise can induce oscillations in populations of small to intermediate size. I will illustrate this phenomena at two very different length scales, using the famous predator-prey system from ecology and non-linear feedback loops in genetic networks.


Wednesday, December 5th 2007
4:00 pm:
Speaker: Thomas Delworth, Geophysical Fluid Dynamics Laboratory, National Oceanic and Atmospheric Administration (NOAA)
Subject: Decadal-scale changes in the Atlantic Ocean - natural variability and human-induced climate change
Refreshments served in Room 216 Physics at 3:30 p.m.

The Atlantic Ocean is an integral component of the global climate
system, transporting in excess of 1 PW of heat poleward. It is anticipated that fluctuations or changes in that heat transport might have important climatic impacts. Here we review observational estimates of past variability and change in the Atlantic, including recent rapid warming. Part of the decadal scale variability in the Atlantic appears to be associated with natural variability of the ocean circulation, modulating the transport of heat poleward, and having a significant impact on the atmosphere. This impact includes modulation of the African and Indian monsoonal systems, tropical Atlantic atmospheric circulation changes of relevance for hurricanes, and an influence on summer climate over North America and Western Europe. While natural variability may have contributed to the most recent rapid warming, a substantial fraction of the recent warming is likely attributable to human-induced climate change. Future projections of Atlantic change are influenced by both anthropogenic forcing and natural variability.


Wednesday, December 12th 2007
4:00 pm:
Speaker: Bob Pepin, U of M
Subject: Stardust Mission
Refreshments served in Room 216 Physics at 3:30 p.m.

Comets are frozen, largely unaltered reservoirs of dust and gases present in the early solar nebula. They are likely to contain well-preserved records of the chemical, mineralogic, and isotopic character of primordial solar-system matter. On January 15, 2006, the Stardust Mission returned to Earth with a cargo of particles collected from the coma of comet Wild 2, the first samples of indisputably cometary matter available for laboratory study. Among these investigations, the noble gases provide unique data on contributions to comets from various solar-system volatile reservoirs, and of physical processing of gases acquired from these reservoirs. In this talk we discuss the first measurements of helium and neon in Stardust material.

One of the surprises in samples collected from an icy object forming, and, for most of its lifetime, residing in the cold outer reaches of the solar system was the discovery in other laboratories that many of its constituent particles are igneous, refractory “rocklets” formed at very high temperatures, presumably close to the early Sun, which were then somehow transported to the trans-Neptunian Kuiper Belt and incorporated into Wild 2 at about the time of the solar system’s birth 4.5 billion years ago. (In retrospect the “rocklets” shouldn’t have been all that astonishing: Ed Ney, Louis Rose and others at Minnesota argued three decades ago from IR spectroscopic data that igneous grains were present in comets). A second and completely unanticipated feature of Stardust matter is the finding here of enormous concentrations of He and Ne that, of known gas acquisition mechanisms, only intense ion irradiation seems able to explain. These two observations, together with isotopic data pointing to Ne similar to that found in primitive meteorites, suggest that gases in Stardust grains were implanted from an ancient, energetic nebular reservoir near the young evolving Sun.


Wednesday, December 19th 2007
This event will resume spring semester.

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