Feb
20
Teaser:

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
Teaser:

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
13
Teaser:

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
Teaser:

 

 

Feb
09
Teaser:

 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
Teaser:

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...

Feb
08
Teaser:

Cadherins constitute a large family of Ca2+-dependent adhesion molecules in the Inter-cellular junctions that play a pivotal role in the assembly of cells into specific three-dimensional tissues.  Although the molecular mechanisms underlying cadherin-mediated cell adhesion are still not fully understood, it seems likely that both cis dimers that are formed by binding of extracellular domains of two cadherins on the same cell surface, and trans-dimers formed between cadherins on opposing cell surfaces, are critical to trigger the junction formation.

Here we present a new multiscale computational strategy to model the process of junction formation...

Feb
06
Teaser:

The development of the technology for trapping atoms in the vacuum and cooling them to ultralow temperatures has opened up the exciting new field of cold atom physics.  This field provides a new domain of applications for local quantum field theory, an approach whose previous applications have been primarily in high energy particle physics and have involved energy scales that are more than 20 orders of magnitude higher.  I will describe a systematic approximation method for quantum field theory called Effective Field Theory that has proved to be a powerful framework for addressing many important problems in ultracold atoms.

Jan
23
Teaser:

The heart is an electro-mechanical system in which, under normal conditions, electrical waves propagate in a coordinated manner to initiate an efficient contraction. In pathologic states, propagation can destabilize and exhibit period-doubling bifurcations that can result in both quasiperiodic and spatiotemporally chaotic oscillations. In turn, these oscillations can lead to single or multiple rapidly rotating spiral or scroll waves that generate complex spatiotemporal patterns of activation that inhibit contraction and can be lethal if untreated. Despite much study, little is known about the actual mechanisms that initiate, perpetuate, and terminate...

Jan
18
Teaser:

Embryogenesis and regeneration are among the most striking and beautiful phenomena in nature. For a physicist, this brings together many major themes—pattern formation, information processing, the mechanics of complex fluid-like materials—that are essential for our understanding of life more broadly. In my talk I will give two examples on the important role of tissue mechanics for these phenomena.

First, I will discuss how a macroscopic tissue property, specifically tissue surface tension, is connected to the properties of the constituent cells, such as cortical tension and adhesion. I will directly compare theoretical...

Jan
12
Teaser:

Departing from the context of CoGeNT and COUPP, two direct searches for WIMP dark matter, we will inspect the recent landscape of anomalies observed by these and several other detectors. The aim of this talk is to communicate an appreciation for the subtleties inherent to experimental efforts in this field, and for the considerable difficulties that await for those trying to make sense of WIMP search observations (or lack thereof).

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