PHYSICS COLLOQUIUM SCHEDULE
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Refreshments will be served starting at 3:15 PM in NPB 2205 Department of Physics Colloquium Committee: Ramond (chair), Chan, Ingersent, Matcheva, Mitselmakher, Petkova (members) |
AUGUST 27 |
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Graduate Student Meeting with Dr. James Fry 4:00pm in 1002 NPB |
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SEPTEMBER 3 |
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| Speaker | Mike Cruise, Univ. of Birmingham | |
| Title | Low and High Frequency Gravitational Wave Astronomy | |
| Abstract | Ground based gravitational wave detectors such as LIGO working in the frequency range 100Hz to 5kHz have been operational for several years and have a development program planned for the immediate future. These target neutron star interactions and a detection should be possible within a few years. The talk will review progress in building detectors for frequencies much lower, and much higher, than LIGO will reach.Very high signal to noise observations will be possible at lower frequencies in the milliHertz range using space based platforms such as LISA. LISA is a joint NASA-ESA collaboration planned for launch in 2020 and will focus on the study of super massive black holes and their role in galaxy formation. The good signal to noise ratio will allow precise exploration of the physics of black holes. At much higher frequencies than the LIGO band, detectors are being developed that respond to Giga-Hertz gravitational waves and even signals at optical frequencies. The science case for these detectors is much more speculative but includes the study of cosmological backgrounds from the Planck era and physics in higher dimensions. | |
SEPTEMBER 10 |
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| Speaker | Jay Lawrence, Dartmouth | |
| Title | Quantum relaxation: Nonexponential Late-Time Decay of Metastable States. Is it Detectable? | |
| Abstract | Quantum dynamics predicts that metastable quantum states should decay more slowly than exponentially at sufficiently late times (typically the predicted decay is algebraic). This means that if a state lives long enough, its life expectancy will begin to increase. The prediction is paradoxical because the slowdown is preceded by many lifetimes of exponential decay with the Golden-rule lifetime, which would seem to suggest that memory doesn't play a role except at the earliest times. I will discuss the origin and nature of the prediction with the examples of tunneling and radiative decay, the ways in which nature tries to hide the effect and make experimental observation difficult, and my skepticism about the only reported experimental observation to date [PRL 96, 163601 (2006)]. Yet, practical obstacles to observation do not resolve the paradox, and experimental observation, though difficult, would be very interesting. | |
SEPTEMBER 17 |
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| Speaker | Stephen Hagen | |
| Title | What we’ve got here is failure to communicate: Noise and microenvironments in bacterial communication | |
| Abstract | We tend to think of bacteria as solitary, unintelligent organisms. In fact, numerous bacterial species engage in a sophisticated chemical signaling behavior that is based on the exchange of small molecules. Many important collective behaviors of a bacterial population are triggered when individual cells detect certain diffusible chemical signals released by their neighbors. The ubiquity of this phenomenon adds a novel twist to microbiology and suggests new avenues for fighting infectious disease. On the other hand, the physical environment of the bacterium is often very heterogeneous and diffusion may be inefficient. At the same time, the genetic “circuitry” that generates and detects the chemical signal is microscopic and therefore subject to stochastic effects. This raises some interesting physical questions: How much information is actually carried by these chemical signals? What can a cell actually learn about its environment from that signal, and how reliably can it respond to that information? Can we even be sure of the “purpose” of the signaling mechanism? I will present a general introduction to bacterial communication with emphasis on the role of noise and microenvironment in chemical signaling. | |
SEPTEMBER 24 |
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SEPTEMBER 29 - Special Colloquium2205 NPB 4:05pm |
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| Speaker | Graham Farmelo, Northeastern | |
| Title | Paul Dirac and the religion of mathematical beauty | |
| Abstract | Paul Dirac was among the great scientific geniuses of the modern age. One of the discoverers of quantum mechanics, the most revolutionary theory of the past century, his contributions had a unique insight, eloquence, clarity, and mathematical power. His prediction of antimatter was one of the greatest triumphs in the history of physics. One of Einstein’s most admired colleagues, Dirac was in 1933 the youngest theoretician ever to win the Nobel Prize in physics. Dirac’s personality is legendary. He was an extraordinarily reserved loner, relentlessly literal-minded and appeared to have no empathy with most people. Yet he was a family man and was intensely loyal to his friends. His tastes in the arts ranged from Beethoven to Cher, from Rembrandt to Mickey Mouse. Based on previously undiscovered archives, The Strangest Man reveals the many facets of Dirac’s brilliantly original mind. A compelling human story, The Strangest Man also depicts a spectacularly exciting era in scientific history. | |
OCTOBER 1 |
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| Speaker | Zlatko Tesanovic, Johns Hopkins | |
| Title | Superconductivity at Dawn of the Iron Age | |
| Abstract | Recent discovery of iron-based high-temperature superconductors hints at a new pathway to the room temperature superconductivity. The new materials feature FeAs layers instead of the signature CuO2 planes of much studied cuprate superconductors. The antiferromagnetism also appears to be involved, although the d-electrons in FeAs seem considerably more mobile than their cuprate cousins. This high mobility, facilitated by a large overlap amongst atomic orbitals of Fe and As, plays a crucial role in warding off Hund's rule and the large local moment magnetism of Fe ions, the archrival of superconductivity. A pedagogical review of the current status of the high-temperature superconductivity field will be presented, highlighting similarities and differences between Fe-pnictides and cuprates and emphasizing the importance of the multiband nature of magnetism and superconductivity in these new materials. | |
OCTOBER 8 |
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| Speaker | Szabolcs Márka, Columbia University | |
| Title | Gravitational Waves and Multimessenger Astrophysics | |
| Abstract | The ultimate promise of gravitational wave astrophysics is to enable the extraction of scientific insight that was hidden from us before. Multimessenger astronomy including gravitational waves shall be a fruitful path toward this goal. Gamma-ray, X-ray, optical, radio and neutrino observations of cataclysmic cosmic events with plausible gravitational wave emission can be used in combination with searches for gravitational waves. Beyond enhancing our ability to identify weaker gravitational wave signatures closes to the noise floor of the detector, multimessenger observations will enhance the quality of the results and enable us to reach conclusions we would not be able to do with gravitational waves alone, such as the possibility to constrain the Hubble constant. After an overview of related past results I will present an outlook on future multimessenger astrophysics enabled through gravitational wave observations. | |
OCTOBER 15 |
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OCTOBER 22 |
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OCTOBER 29 |
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| Speaker | Dr. Tanmay Lele, University of Florida | |
| Title | Title: Force Generation in the Intracellular Cytoskeleton | |
| Abstract | Cell adhesion to the substratum occurs through active force generation by intracellular motor proteins that walk along cytoskeletal filaments. I will present new measurements of the mechanical behavior of modular force generating units called stress fiber sarcomeres inside the living endothelial cell. I will also present recent work on understanding force generation on the intracellular nucleus, and conclude with an application of nanotechnology for manipulating cytoskeletal forces. | |
NOVEMBER 5 |
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| Speaker | Joseph Dwyer, FIT | |
| Title | X-ray Emission from Thunderstorms and Lightning | |
| Abstract | How lightning is initiated in the relatively low electric fields inside thunderclouds and how it can then propagate for tens of kilometers through virgin air are two of the great unsolved problems in the atmospheric sciences. Until very recently it was believed that lightning was entirely a conventional discharge, involving only low-energy (a few eV) electrons. This picture changed completely a few years ago with the discovery of intense x-ray emission from both natural cloud-to-ground lightning and rocket-triggered lightning. This energetic emission cannot be produced by a conventional discharge, and so the presence of x-rays strongly implies that runaway breakdown plays a role in lightning processes. During runaway breakdown, electrons are accelerated through air to nearly the speed of light by strong electric fields. These runaway electrons then emit bremsstrahlung x-rays and gamma-rays during collisions with air. Indeed, the x-ray and gamma-ray emission produced by runaway breakdown near the tops of thunderstorms is bright enough to be seen from outer space, 600 km away. As a result, the physics used for decades to describe thunderstorm electrification and lightning discharges is incomplete and needs to be revisited. | |
NOVEMBER 12 |
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| Speaker | Adam Showman, University of Arizona | |
| Title | Atmospheric circulation of giant planets inside and outside the solar system | |
| Abstract | In addition to the four giant planets in our Solar System (Jupiter, Saturn, Uranus, and Neptune), approximately 400 giant planets have been discovered around other stars. Here I discuss the general problem of the atmospheric circulation on these objects. Our Solar-System giant planets are cold, rapidly rotating objects whose meteorology is dominated by fast east-west jet streams and banded cloud patterns, whose formation mechanisms are poorly understood. Known extrasolar planets span a wide range of conditions, but many of them are extremely close to their stars, receive stellar fluxes ~104 times that of Jupiter, and are thought to be slowly rotating. Recent infrared observations probe the three-dimensional temperature structure of these objects and hint at a vigorous atmospheric circulation with wind speeds exceeding anything known in our Solar System. The wide range of conditions accessed by known giant planets thus opens an opportunity to understand the diversity of atmospheric circulation regimes possible on such planets. In this talk, I will survey the relevant observations, summarize basic dynamical principles relevant to the whole class of giant planets, and describe three-dimensional numerical simulations of the atmospheric circulation of both our Solar-System giant planets and the close-in extrasolar giant planets (the "hot Jupiters"). Our simulations have had success in explaining several previously puzzling observations and provide a framework for interpreting the meteorology of giant planets generally. | |
NOVEMBER 19 |
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| Speaker | Professor T. Senthil, MIT | |
| Title | How might a Fermi surface die? | |
| Abstract | In the last many years a number of metallic solids have been studied that defy understanding within the principles of conventional textbook solid state physics. The most famous are the cuprate high temperature superconductors though many other examples have been found. In this talk I will argue that the mysterious properties of many such materials arises from an imminent `death' of their Fermi surfaces. I will discuss some theoretical ideas on how to kill a Fermi surface, and their implications for experiments. | |
DECEMBER 3 |
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PHYSICS COLLOQUIUM SCHEDULE |
Spring 2010 |
The Colloquia are in Room 1002
NPB on Thursday at 4:05 PM
Refreshments will be served starting at 3:15 PM in NPB 2205 P. Ramond (2-5704, ramond@phys.ufl.edu) |
JANUARY 7 |
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JANUARY 14 |
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| Speaker | Brad Marston | |
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JANUARY 21 |
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| Speaker | Jason Ho | |
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JANUARY 28 |
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FEBRUARY 4 |
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FEBRUARY 11 |
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| Speaker | Humphrey Maris, Brown University | |
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FEBRUARY 18 |
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FEBRUARY 25 |
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| Speaker | Evalyn Gates, University of Chicago | |
| Title | Einstein's Telescope: The Hunt for Dark Matter and Dark Energy | |
| Abstract | Data from a wealth of cosmological observations insist that normal baryonic matter makes up only about 5% of the Universe - dark matter accounts for 23%, while the remaining 72% is not matter of any kind but some strange new substance, dubbed dark energy, about which we know very little. Gravitational lensing - dismissed by Einstein in 1936 as a "most curious effect" that had little chance of ever being observed - is currently one of the most powerful techniques for exploring this dark universe. Using the warps and dimples in spacetime described by Einstein's theory of General Relativity as "cosmic lenses," gravitational lensing allows us to search for black holes and planets within our own Galaxy; to map out the dark matter in distant galaxies, clusters and the cosmic web; and to detect the subtle influence of dark energy on the evolution and formation of structure in the Universe. | |
March 4 |
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| Speaker | Martin Uman, UF Electrical & Computer Engineering | |
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March 11 |
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March 18 |
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March 25 |
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April 1 |
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| Speaker | Talat Rahman, UCF | |
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APRIL 8 |
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| Speaker | Shoucheng Zhang, Stanford University | |
| Title | Topological insulators and topological superconductors | |
| Abstract | Recently, a new class of topological states has been theoretically predicted and experimentally realized. The topological insulators have an insulating gap in the bulk, but have topologically protected edge or surface states due to the time reversal symmetry. In two dimensions the edge states give rise to the quantum spin Hall (QSH) effect, in the absence of any external magnetic field. I shall review the theoretical prediction[1] of the QSH state in HgTe/CdTe semiconductor quantum wells, and its recent experimental observation[2]. The edge states of the QSH state supports fractionally charged excitations[3]. The QSH effect can be generalized to three dimensions as the topological magneto-electric effect (TME) of the topological insulators[4]. Topological insulators Bi2Te3, Bi2Se3 have been discovered theoretically and experimentally to have surface states consisting of a single Dirac cone[5,6,7]. I shall present a realistic experimental proposals to observe the magnetic monopoles on the surface of topological insulators[8]. Topological superconductors and superfluid have been theoretically proposed recently [9], in both two and three dimensions. They have a full pairing gap in the bulk, and their mean field Hamiltonian look identical to that of the topological insulators. However, the gapless surface states consists of a single Majorana cone, containing only half the degree of freedom compared to the single Dirac cone on the surface of a topological insulators. I shall discuss their physics properties and the search for these novel states in real materials. | |
APRIL 15 |
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