Events Archive

Feb
23
2012
Angular momentum, stability and fragmentation in 3D attractive Bose-Einstein condensates
Trapped attractive atomic Bose-Einstein condensates (BECs) in three spatial dimensions are known to exist for some finite time only. This is because the gas is prone to self-collapse, due to the attractive nature of the interaction. The 'mainstream' way to describe the state of the condensate is a mean-field (MF) theory, that assumes total condensation of the system.  In this talk I will introduce the notion of fragmentation, in contrast to coherence, and show that the states of definite angular momentum of the 3D many-body system cannot be condensed MF states. With this at hand, I examine the impact of the angular momentum to the stability of the attractive gas and show that there...
Feb
22
2012
Stochasticity in gene expression and its regulation by non-coding RNAs
One of the fundamental problems in biology is understanding how phenotypic variations arise in individuals. Phenotypic variation is generally attributed to genetic or environmental factors. However, in several important cases, phenotypic variations are observed even among genetically identical cells in homogeneous environments. Recent research indicates that such `non-genetic individuality' can arise due to intrinsic stochasticity in the process of gene expression. Correspondingly there is a need to develop a framework for quantitative modeling of stochastic gene expression and its regulation. Of particular interest is modeling of regulation by non-coding...
Feb
21
2012
Fish robotics: understanding the diversity of fish locomotion using mechanical devices
There are over 28,000 species of fishes, and a key feature of this remarkable evolutionary diversity is a great variety of propulsive systems used by fishes for maneuvering in the aquatic environment.  Fishes have numerous control surfaces (fins) which act to transfer momentum to the surrounding fluid.  In this presentation I will discuss the results of recent experimental kinematic and hydrodynamic studies of fish fin function, and their implications for the construction of robotic models of fishes.  Recent high-resolution video...
Feb
20
2012
Strong-field atomic physics in the x-ray regime
The advent of x-rays sources with unprecedented intensity will enable the study of nonlinear physics in the high frequency regime. In 2009, a physicist dream became reality with the commissioning of the world’s first x-ray free-electron laser, the LCLS, at SLAC. In contrast to low frequency strong-field physics where valence electrons react to the optical field, at high frequency the atom will be ionized from the inside out. The question remains as to whether the atomic response to x-rays will be adequately described by low-order perturbation theory or necessitate a non-perturbative description which is more commonly used at low-frequency. In this talk, these issues will...
Feb
16
2012
Low metallicity star formation: a nursery for compact binary mergers?
Most predictions for binary compact object formation are normalized to the present-day Milky Way population. In this talk, I suggest the merger rate of black hole binaries could be exceptionally sensitive to the ill-constrained fraction of low-metallicity star formation that ever occurred on our past light cone. I discuss whether and how observations might distinguish binary evolution uncertainties from this strong trend, both in the near future with well-identified electromagnetic counterparts and in the more distant future via third-generation gravitational wave detectors.
Feb
15
2012
Gene Regulation by Riboswitches: From Folding Landscape to System Level Description
Feb
13
2012
Frontiers in Science Public Lecture Featuring Doug Osheroff, Nobel Prize WInner
Doug Osheroff, professor of physics at Stanford University and a Nobel Laureate in Physics, will present a lecture on "How Advances in Science Are Made."
Feb
13
2012
How Advances in Science Are Made
   
Feb
09
2012
Making Realistic Galaxies in Your Computer
 Cosmological hydrodynamical simulations are a useful tool for following the formation and evolution of galaxies over long timescales, but we must prescribe accurate models for the physics on small scales, below the resolution limits of our simulations. I investigate several different "subgrid models" at these scales to see what their effects are on a single Milky Way sized galaxy evolved from just after the Big Bang until the present. I grade the success of each model on how well it matches the dynamics of typical disk galaxies, creates a realistic star formation history, and produces a reasonable circumgalactic halo.
Feb
09
2012
Spin-Nematic Squeezing in a Spin-1 BEC
Squeezed states allow interferometers to surpass the standard quantum limit of the Heisenberg uncertainty principle.  Here we study spin-nematic squeezing of a spin-1 condensate following a quench through a nematic-ferromagnetic quantum phase transition.  We observe up to -8.3 dB squeezing in the variance of the spin-nematic quadratures.  This squeezing is observed for negligible occupation of the squeezed modes and is analogous to optical two-mode vacuum squeezing [1]. 1. C.D. Hamley, C.D. Gerving, T.M. Hoang, E.M. Bookjans, and M.S. Chapman, “Spin-Nematic Squeezed Vacuum in a Quantum Gas,” To appear in Nature...

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