Fall 2008 Physics Colloquium Schedule

University of Colorado Department of Physics

Colloquia are Wednesdays at 4 PM, Duane G1B20 unless otherwise noted

Coffee, tea, and cookies before regular colloquia at 3:45 PM in Duane G1B31

Upcoming Colloquia:

August 27

Ian McNulty, Argonne National Laboratory
Host: Margaret Murnane
Title: A perfect storm: lensless x-ray imaging at the nanometer scale
Abstract: The confluence of three recent technical breakthroughs has resulted in a "perfect storm" in nanometer-resolution x-ray imaging. Brilliant sources of coherent x-rays, megapixel array detectors, and powerful numerical phase retrieval methods have engendered a rapidly advancing new capability for imaging the internal structure of three-dimensional objects, unhampered by the limitations of x-ray lenses. Third-generation synchrotron sources have mainly fueled this progress until now. The next generation of coherent pulsed x-ray sources - both large-facility and laboratory scale - is promising for x-ray nanoscopy in the femtosecond regime, where ordering during magnetic phase transitions could be frozen in time and organelles within intact biological cells could be studied without radiation damage artifact. This talk reviews advances in lensless x-ray coherent diffraction imaging and considers exciting new directions in the materials, condensed matter, energy, and life sciences this technique may take in the near future.

September 3

Jed Buchwald, Caltech
Host: Allan Franklin
Title: The Newtonian Origins of Experimental Error
Abstract: In the mid-1750s the English mathematician Thomas Simpson tried to convince astronomers that it was a good idea to average multiple measurements. He had much work to do, because neither astronomers nor physicists were in the habit of combining multiple measurements to produce a best final value. How then did experimenters and observers work with discrepant data before statistical methods became common at the beginning of the 19th century? We will first tour the worlds of Tycho Brahe, Robert Hooke, Ren? Descartes and Johannes Hevelius to see how they worked with data. And then we turn to the young Isaac Newton, who developed an altogether novel way with measurements, the very way that became ever after the foundation of experimental method, for it was Newton who first decided that bad numbers could be put together to generate good ones.

September 10

Steve Olsen, University of Hawaii
Host: David Bartlett
Title: The XYZ exotic(?) Mesons
Abstract: There has been considerable interest in recent years in the possible existence of hadrons that do not fit into the quark-antiquark meson or three-quark baryon arrangements prescribed by the Constituent Quark Model of Gell-Mann and Zweig. This revival of interest was initially stimulated by numerous claims for observation of pentaquark baryon states. In addition, the BES e+e- collider experiment in China as well as the BaBar and Belle e+e- B-factory experiments have reported observation of a umber of mesons --most notably the X(1835), X(3872), Y(4260) & the Z(4430)-- that do not match neatly to expectations for conventional quark-antiquark mesons. While the evidence for the existence of pentaquark baryons now seems pretty dubious, the existence of at least the the X & Y of the XYz mesons is experimentaly well established. For these states, the main question, and the subject of this talk, is whether or not they are elements of some new type of spectroscopy or, instead, evidence of deficiencies in our basic understanding of how quarks combine together to form hadrons.

September 17

David Wineland, NIST
Host: Dan Dessau
Title: Quantum information processing and quantum metrology with trapped ions
Abstract: Over the last decade or so, there has been an explosion of activity in quantum information processing (QIP). Arguably, Shor's algorithm for efficiently factoring large numbers stimulated much of the interest; however experimentally, this application remains a distant goal. Nearer-term possibilities include practical quantum communication and quantum simulation. Also, we can apply some simple QIP procedures to metrology; examples where entanglement can lead to improved detection sensitivity in interferometry and spectroscopy are discussed in the context of trapped ions. If we can eventually apply some of these techniques to large numbers of ions, we might realize a direct analog of Schroedinger's cat, a bizarre situation in which Prof. Schroedinger's cat is simultaneously dead and alive.

September 24

Barry Zink, University of Denver
Host: Kyle McElroy
Title: Electron and Phonon Transport in Thermoelectric Thin Films and Nanostructures
Abstract: Energy solutions for the coming decades require broad-based investigation into a range of technologies. Clean, high-efficiency energy technologies are likely to involve devices that employ more than one route to energy conversion. For example, adding a thermoelectric generator to a solar cell could improve the efficiency of overall energy production by converting unused thermal energy to electric energy. Though recent years have seen significant advances, the new developments in materials that will allow thermoelectric devices to fully realize their potential for energy conversion remain elusive. Nanoscale engineering of materials, made possible by modern tools for patterning and manipulation of matter at small length scales, has shown early promise and may lead to rapid improvement in thermoelectrics. A fairly wide range of fundamental studies reveal that the electronic, vibrational, and magnetic excitations in such systems can behave much differently than in bulk, equilibrium phases, but some measurements that are particularly important for thermoelectrics remain very challenging for systems such as thin films and nanowires. This talk will briefly introduce the challenges of thermal measurements of small samples, consider the fascinating physics of such systems, and describe our current work toward identifying potential breakthroughs in thermoelectric materials through direct experimental studies of electronic, vibrational, and magnetic excitations in small structures and novel materials.

October 1

Paul Chaikin, New York University
Host: Ivan Smalyukh
Title: Toward Self-Replication with Colloids
Abstract: We want to make a non-'biokleptic' system which can self-replicate. The idea is to design colloids with specific and reversible and irreversible interactions, introduce seed motifs, and cycle the system in such a way that a copy is made. Repeating the cycle would double the number of offspring in each generation leading to exponential growth. We're not there yet! We use colloidal particles with bound DNA sequences for reversible recognition. DNA allows us to independently fine tune the strength and the temperature dependence of the interparticle interactions. They now "work" - recognize, cycle and can be permanently attached as well. So the talk will be on where we are, how we got there and where we're going.

October 8

B. Lee Roberts, Boston University
Host: John Cumalat
Title: Muon (g-2) - A Probe of the Standard Model and Beyond
Abstract: Since the experiments of Stern and Gerlach, magnetic moments of "elementary" particles have been important in our quest to understand subatomic physics. The first "QED loop calculation" was done by Schwinger to explain the larger than expected hydrogen hyperfine structure. The definitive measurement of the electron's anomaly by Kusch and Foley followed and agreed well with Schwinger's calculation of a_e = (a/2 p). The muon's anomaly, which is sensitive to a broad range of physics beyond the standard model, will be discussed in a historical context, following the intellectual development of modern physics through the 20th century. Experiment E821 at Brookhaven will be described, as well as possible improvements, which are highly desirable since the present value of the muon anomaly, appears to differ from the standard-model value.

October 15

Joseph Fowler, Princeton University
Host: Eric Zimmerman
Title: The Atacama Cosmology Telescope: Mapping the Microwave Background to Understand Cosmic Inflation and Structure Formation
Abstract: Mapping the primordial cosmic microwave background (CMB) has proven to be an unrivaled tool for learning about cosmic history over a wide range of timescales. Measurements made to date have contributed greatly to our current age of "precision cosmology", but future observations at finer angular scales still promise new features. The epoch when massive galaxy clusters formed can be probed through the Sunyaev-Zel'dovich effect, while the immensely earlier era of inflation influences the same maps through the slope of their spatial power spectrum. Gravitational lensing of the CMB itself might even be within reach of current instruments.
The Atacama Cosmology Telescope (ACT) has just begun observing the microwave sky at 140 through 280 GHz with over 3000 detectors. ACT exemplifies many of the technical challenges involved in measuring sky brightness with parts-per-million accuracy, along with the technical advances from sites like NASA-Goddard and NIST that propel the latest CMB experiments.

October 22

Young S. Lee, Massachusets Institute of Technology
Host: Michael Hermele
Title: The physics of frustration in low dimensions: the quest for the quantum spin liquid
Abstract: I will describe our recent experimental progress on the quest for the "holy grail" of spin frustration. One of the central issues in condensed matter physics involves understanding the exotic phases which emerge from collections of interacting electrons. New states of matter may be produced if quantum effects and frustration conspire to prevent the ground state from achieving classical order. In particular, I will explain some new physics we have learned from neutron and x-ray scattering measurements on quantum magnets based on one- and two- dimensional lattices. Materials based on the kagome lattice appear to be ideal hosts for studying spin-frustration as well as the possiblity of a quantum spin liquid ground state.

October 29

Jorge Piekarewicz, Florida State University
Host: Jim Shepard
Title: The Many Faces - and Phases - of Neutron Stars
Abstract: Understanding the nuclear matter equation of state (EOS) is a central goal of nuclear physics that cuts across a variety of disciplines. Indeed, the limits of nuclear existence, the structure of neutron stars, and the dynamics of core-collapse supernova, all depend critically on the nuclear matter EOS. In this talk I will concentrate on the EOS of cold baryonic matter with special emphasis on its impact on the structure and dynamics of neutron stars. In particular, I will discuss the many fascinating phases that are encountered as one travels from the low-density crust to the high-density core.

November 5

Kevin Lesko, Lawrence Berkeley Laboratory
Host: Eric Zimmerman
Title: The Deep Underground Science and Engineering Laboratory at Homestake
Abstract: The US National Science Foundation and the US underground science community are well into the campaign to establish a world-class, multi-disciplinary deep underground science and engineering laboratory - DUSEL. The NSF's review committee, following the first two NSF solicitations, selected Homestake as the prime site to be developed into an international, multidisciplinary, world-class research facility. Homestake DUSEL will provide much needed underground research space to help relieve the worldwide shortage, particularly at great depth, and will develop research campuses at different depths to suite the research requirements for the coming decades. The State of South Dakota has demonstrated remarkable support for the project and has secured the site with the transfer of the former Homestake Gold Mine and has initiated re-entry and rehabilitation of the facility to host a modest interim science program with state funds and those from a substantial philanthropic donor. I review the scientific case for DUSEL including the 2008 P5 report establishing a national initiative to create a long baseline neutrino program linking DUSEL to Fermilab, the recent (S-4) solicitation funding development of the experimental program to be included with the facility in the NSF proposal, and the near-term physics experiments underdevelopment in Homestake in advance of DUSEL construction funding.

November 12

Steven Pollock, University of Colorado
Host:
Title: Understanding Educational Reforms: Impacts of Physics Education Research at CU
Abstract: Physics education research (PER) has resulted in new materials, approaches to teaching, and theoretical understanding of student learning in physics. PER has influenced practices in our own courses at CU, impacting thousands of students, as well as a growing number of current and future teachers. While the field has demonstrated positive impact in many different instances, remarkably little work has gone into understanding how research-based, educational reforms are replicated and sustained. This talk will discuss some of the data we have collected at CU over the past half dozen years, investigating transfer of innovations from one institution to another, differences among our own courses, and resulting impacts on students over time. Such data provide a base from which educators can make informed decisions about difficult choices in curriculum, methods, resource allocation, and teaching focus. I will present a variety of measures of learning for different populations of students in our courses, longitudinal data on our majors, and outcomes for future high school science teachers resulting from our innovative Learning Assistant program.

November 19

Jamie Nagle, University of Colorado
Host:
Title: What have we learned about the Quark Gluon Plasma? And what does it mean?
Abstract:The high-energy heavy-ion collider at Brookhaven National Laboratory has been studying interactions of ultra-relativisitc nuclei starting in 2000. Over the last eight years, the hottest nuclear matter on earth has been studied extensively and now we can describe some of the material properties of the matter, often termed the quark gluon plasma. Amongst these properties are near perfect fluidity and extreme opacity. We will describe the experimental techniques, how the properties are determined, and connections to other areas of physics.

November 26: No colloquium: Thanksgiving Break

December 3

Paul Goldbart, University of Illinois
Host: Michael Hermele
Title: Strands of Superconductivity at the Nanoscale
Abstract: Abstract: Superconducting circuitry can now be fabricated at the nanoscale by depositing suitable materials on to individual molecules, such as DNA or carbon nanotubes. In this talk I shall examine various themes that arise when superconductivity is explored in this new regime, including thermal barrier crossing and quantum tunneling by the superconducting condensate, as well as the impact of magnetism on nanosuperconductivity. I shall focus on a fascinating class of circuits: nanoscale superconducting quantum interference devices (or n-SQUIDs). After describing how they are made, I shall pay particular attention to the electrical resistance of these devices and, especially, its sensitivity to magnetic fields and patterns of supercurrent. These features hint at possible uses of n-SQUIDs, such as for mapping the quantum phase of superconducting order and testing for superconducting correlations in novel materials and settings.

December 10

Michelle Wang, Cornell University
Host: Meredith Betterton
Title: Unpacking DNA at the Single Molecule Level
Abstract: The cell nucleus is a highly dynamic reaction center for many DNA-based cellular processes, as well as an effective compaction center for DNA storage. The basic packing unit of chromatin is the nucleosome. Even this lowest level of genomic compaction presents a strong barrier to many DNA-binding cellular factors. In a coordinated and regulated fashion, DNA associated with nucleosomes must be made transiently accessible to permit many essential processes, such as transcription, DNA replication, recombination, and repair. Nucleosome stability and structure thus are intimately involved in the regulation of genetic information storage and retrieval.
Nucleosome packing and unpacking are kinetic and mechanical in nature, involving translocation, rotation, force, and torque. Single molecule mechanical studies are ideally suited to probe these processes and have become powerful complementary tools to traditional biochemical and molecular biological approaches. They permit direct mechanical measurements of strengths and locations of histone-DNA interactions and how these interactions are governed by DNA sequences, histone covalent modifications and variants, and nucleosome remodeling. I will discuss our progress in mechanical studies of nucleosome stability and structure with specific focus on results obtained from optical trapping studies.

Colloquium schedules from previous semesters can be found here

Contact:

Eric D. Zimmerman