Spring 2010 Colloquium Series
Colloquia are at 4pm, Thursdays, in 100 Willamette Hall and are preceded by coffee, tea, and cookies at 3:40 in the Willamette Atrium.
The organizer of the Spring Term Colloquia is: Jens Nöckel
Apr 1, 2010
University of California, Irvine
Prospects and Techniques for the Direct Detection of Dark Matter
There are now dozens of groups around the world engaged in the search for dark matter with laboratory experiments. The sensitivity of these experiments has increased rapidly over the last several years. I’ll discuss the experimental challenges and the widely varying techniques that are being employed to overcome them.
Apr 8, 2010
University of Oregon
The Discovery of the Two Fluid Theory and Second Sound in Helium II
Colleagues and friends recently celebrated the one hundredth birthday of Laszlo Tisza at MIT. Tisza’s discovery of the two fluid model of Helium II and prediction of second sound were recalled on that occasion. We review the controversial discovery of second sound and its modern applications. The two fluid theory of Helium II and the prediction of the existence of two forms of sound propagation make Laszlo “Laci” Tisza one of the important figures of twentieth century physics. Tisza died on April 15, 2009, his obituary is in the July issue of Physics Today. In this talk we explore the remarkable story of the discovery of second sound and mention some of the ways in which second sound is enabling landmark studies in quantum turbulence and prospects for observing second sound in a uniform superfluid gas of ultracold Fermi atoms.
Apr 15, 2010
Center for Biological Physics, Arizona State University
Geometric order and movement patterns in embryonic epithelia: informing controversy using theory and computation
Embryonic development remains one of the most fascinating and yet poorly understood areas of biology. I will describe two recent examples of quantitative experimental measurements, both pertaining to embryonic epithelial tissues, which have been the subject of some controversy. The first is the apparent universality of cell neighbor statistics. The second concerns the mechanisms underlying the fundamental process of primitive streak formation in the avian embryo (which is also directly relevant to early human development). My group has been applying theoretical and computational tools, inspired by physics methodologies, to both examples. Whether our results have inflamed or resolved the controversies remains to be seen. Encouraging is the fruit borne from a tight-knit connection between theoretical biological physics and experimental biology.
Apr 22, 2010
Applied Physics In The Pharmaceutical Industry
Development of new therapies for human health is an extremely difficult endeavor. While there has been tremendous advancement in scientific understanding of human biology, translation of this new knowledge into pharmacological therapies has been poor. Indeed the success rate for introduction of a novel chemical compound into the human population is only 1/10,000, and perhaps significantly less. One approach to improve success is to incorporate a more mechanistic understanding of how molecules interact with human physiology and biological targets. Key to this approach is the adaption and development of computational and physics/physical-chemical approaches in drug discovery and development. In this presentation, an overview of select approaches using physics-based concepts to assist in drug development will be discussed. Case studies will be presented to demonstrate the utility of these approaches. The presentation will conclude with a discussion of possible future directions for physics-based approaches within the pharmaceutical industry.
Apr 29, 2010
Department of Physics, Berkeley
Grabbing the cat by the tail: Discrete steps by a DNA packaging motor and the inter-subunit coordination in a ring-ATPase
As part of their infection cycle, many viruses must package their newly replicated genomes inside a protein capsid. Bacteriophage phi29 packages its 6.6 mm long double-stranded DNA into a 42 nm dia. x 54 nm high capsid using a multimeric ring motor that belongs to the ASCE (Additional Strand, Conserved E) superfamily of ATPases. A number of fundamental questions remain as to the coordination of the various subunits in these multimeric rings. The portal motor in bacteriophage phi29 is ideal to investigate these questions and is a remarkable machine that must overcome entropic, electrostatic, and DNA bending energies to package its genome to near-crystalline density inside the capsid. Using optical tweezers, we find that this motor can work against loads of up to ~55 picoNewtons on average, making it one of the strongest molecular motors ever reported. We establish the force-velocity relationship of the motor. Interestingly, the packaging rate decreases as the prohead fills, indicating that an internal pressure builds up due to DNA compression attaining the value of ~6 MegaPascals at the end of the packaging. We show that the chemical energy of ATP is converted into mechanical work during phosphate release. Using ultra-high resolution optical tweezers, we determined the step size of the motor and established the coordination of the ATPases around the ring. We propose a comprehensive model of the operation of this motor.
May 6, 2010
Department of Physics and Astronomy, Michigan State University
Fluctuation-induced switching: scaling, control, and fragility
The rate of metastable decay displays scaling behavior near bifurcation points. We will discuss this scaling for different mechanisms of classical and quantum fluctuations in systems far from thermal equilibrium, including Josephson bifurcation amplifiers, which are used for quantum measurements. The phenomenon of quantum activation will be described. The effect of non-Gaussian noise will be considered. We will also describe the distribution of paths followed in switching, the exponential sensitivity of the switching rates to dynamical perturbations, and the related symmetry breaking transition in modulated cold atom systems. The nonanalytic behavior of the effective switching activation energy with varying parameters will be outlined.
May 13, 2010
Norman Bridge Laboratory of Physics, Caltech
Quantum Networks with Single Atoms, Photons, and Phonons
Fundamental interactions between light and matter can be
harnessed for the implementation of Quantum Networks [Nature 453, 1023
(2008)]. Functionality for diverse tasks in Quantum Information Science is
achieved by coherent quantum-optical interconnects involving single atoms,
photons, and phonons.
Host: van Enk
May 20, 2010
Department of Physics and Astronomy, University of Nebraska, Lincoln
The Aharonov-Bohm effect: Force versus Phase
The Aharonov-Bohm effect will be discussed. What is it, what does it mean, what work has been and should still be done, and can we use it for anything? These questions and the relation between the “Feynman paradox” and the Aharonov-Bohm effect will be addressed.
Image: Magnetic field lines (blue) and vector field lines (green) for a solenoid that are relevant for the AB-effect are shown. For a description see Physics Today september 2009.
Host: van Enk
May 27, 2010
Department of Physics and Applied Physics, Yale University
New measurements of persistent currents in normal metal rings
One of the most remarkable predictions of the quantum theory of electronic circuits is that a small loop of resistive metal can have a perpetual current flowing through it in the absence of any applied voltage. This “persistent” current is directly analogous to the motion of electrons around the nucleus of an atom, and the prediction that it could be observed in realistic devices generated considerable excitement —- twenty five years ago.
Since then, experiments in this area have produced confusing results at odds with theory and even with other experiments. To address this long-standing controversy we developed a new type of detector for persistent currents which offers much greater sensitivity and a less-invasive measurement than was previously possible. Our results have made possible a painfully detailed
comparison between experiment and theory. I will describe these results, which seem to give the clearest picture yet of persistent currents in resistive metals.
Jun 3, 2010
University of Oregon
Non-linear Psychometric Thresholds for Physics and Mathematics
Intro Astronomy as an Educational Tool
We analyze 5 years of student records at the University of Oregon to estimate the probability of success (as deﬁned by superior undergraduate record; sufficient for admission to graduate school) in Physics and Mathematics as a function of SAT-M score. We ﬁnd evidence of a non-linear threshold: below SAT-M score of roughly 600, the probability of success is very low. Interestingly, no similar threshold exists in other majors, such as Sociology, History, English or Biology, whether on SAT combined, SAT-R or SAT-M. Our ﬁndings have signiﬁcant implications for the demographic makeup of graduate populations in mathematically intensive subjects, given the current distribution of SAT-M scores.
We also examine the scores of 5 years of intro astronomy classes
to compare SAT and GPA predictions and the impact on grade inflation.