Eric Sembrat's Test Bonanza

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.

Diffusion of single molecules and organelles in living cells has attracted considerable interest. The motion so essential for intra- and intercellular transport, regulation, and signaling, and hence for the life within cells exhibits surprising deviations from normal Brownian motion. Using optical tweezers combined with single particle tracking inside living cellular organisms we study intracellular diffusion of nano-sized organelles inside living cells. The temperature increase caused by absorption by the laser light as well as the potential physiological damage are important also to consider and will be addressed [1,2]. Lipid granules inside living S. pombe yeast cells perform anomalous diffusion, with subdiffusion being most predominant at short time-lags, and the biological functions giving motility footprints at longer time-lags [3]. At very short timescales, the subdiffusion of lipid granules is well described by the laws of continuous time random walk theory and at longer timescales the granule motion is consistent with fractional Brownian motion. Ordinary Brownian diffusion exhibits ergodicity: long time averages of a measured process for a single particle are equal to the corresponding average over a statistical ensemble. Ergodicity is also fulfilled for anomalous processes governed by fractional Brownian motion. In our analysis of the passive diffusion of liquid granules in living fission yeast cells and in endothelial cells we demonstrate that the diffusion is not only anomalous, but that ergodicity is indeed violated on biochemically relevant time scales [4,5]. Ergodicity breaking implies that time averages based on individual trajectories are random variables, such that our common wisdom associated with the picture of Brownian motion fails. While ergodicity breaking is expected in large live organisms it is surprising to find it already for a small particle essentially coupled to a thermal heat bath thus indicating that basic concepts of statistical Physics must be replaced when we analyze certain aspects of biomolecular dynamics in the cell.

1. A. Kyrsting, P.M. Bendix, D.G. Stamou, and L.B. Oddershede, Nano Letters, vol 11 p.888-892 (2011).
2. M.B. Rasmussen, L.B. Oddershede, H. Siegumfeldt, Applied and Environmental Microbiology, vol.74, no.8 (2008).
3. I.M. Tolic-Nørrelykke, E.-L. Munteanu, G. Thon, L. Oddershede, and K. Berg-Sørensen, PRL, vol.93, p.078102 (2004).
4. J.H. Jeon, V. Tejedor, S. Burov, E. Barkai, C. Selhuber, K. Berg-Sørensen, L. Oddershede, R. Metzler, PRL, vol. 106 p.048103 (2011).
5. N. Leijnse, J.-H. Jeon, S. Loft, R. Metzler, L.B. Oddershede, EPJ accepted (2012).

mso-ansi-language:EN-US;mso-fareast-language:EN-US;mso-bidi-language:AR-SA">Although we now know that microorganisms rule the oceans - controlling productivity and biogeochemical cycles - we largely ignore how they are affected by typical flow conditions. Here I present microfluidic and millifluidic experiments, combined with mathematical models, to show that fluid flow can have profound effects on the biomechanics of swimming microorganisms. I illustrate this for two cases of directed motility, or 'taxis'. In the first case - 'gyrotaxis' - the coupling of hydrodynamic shear and bottom-heaviness, typical of many phytoplankton species, causes intense clustering of cells in layers and patches, which can have profound effects on population dynamics. In the second case - 'rheotaxis' - the coupling of shear and the chiral shape of bacterial flagella leads to a previously unrecognized torque on cells, which can hamper motility and thus foraging in the sea.  

Anderson localization (AL) is a ubiquitous interference phenomenon in which waves fail to propagate in a disordered medium.  We observe three-dimensional AL of non-interacting ultracold matter by allowing a spin-polarized atomic Fermi gas to expand into a disordered potential that is creating using optical speckle.  A two-component density distribution emerges consisting of an expanding mobile component and a non-diffusing localized component. We extract a mobility edge that increases with the disorder strength, whereas the thermally averaged localization length is shown to decrease with disorder strength and increase with particle energy. Progress toward combining disordered fermions with an optical lattice in order to realize the disordered (Fermi-) Hubbard model will be discussed.

Gamma-Ray Bursts (GRBs) are the brightest light sources in the Universe, as well as the most distant sources known. These characteristics, combined with their powerlaw spectra, make them ideal cosmological probes. In this talk I will discuss how GRBs are impacting several areas of extragalactic astrophysics and cosmology. In particular, I will show how they can be used to trace the evolution of the mean density and clumpiness of the interstellar medium with redshift, and the properties of dust in high-z galaxies. Detection of GRBs at very high redshifts can help set constraints on the small-scale power spectrum of density fluctuations. High-resolution observations of long GRBs allow to shed light on the properties of their massive star progenitors.  Statistical studies of short GRBs can improve our understanding of evolutionary binary scenarios.

Most of the baryons in the present universe are missing. This talk gives a historical review of the issue, followed by some highlights of current theoretical and observational effort to understand it.

In this exciting event, three lectures will be presented from world renown Chef Jose Andres and Harvard Physics Professors Michael P. Brenner and David A. Weitz.  Awards will also be presented to the top Dekalb County high school student submissions for the Squishy Physics photography contest in conjunction with the Fernbank Science Center, with all the submissions on display at the event.

Most of what we eat is squishy - behaving as a solid on a plate, or as a liquid when processed in your mouth.  Squishy Physics investigates materials that are soft and easy to deform and, in most cases, are made from mixtures of phases.  The lectures will cover interesting and entertaining physical questions that are critical to cooking and understanding the properties of food.

I describe a unified approach to locating key material transport barriers in unsteady flows induced by two-dimensional, non-autonomous dynamical systems. Seeking transport barriers as minimally stretching material lines, one obtains that such barriers must be shadowed by minimal geodesics under the metric induced by the Cauchy-Green strain tensor field associated with the flow map. As a result, snapshots of transport barriers can be explicitly computed as trajectories of ordinary differential equations. Using this approach, hyperbolic barriers (generalized stable and unstable manifolds), elliptic barriers (generalized KAM curves) and parabolic barriers (generalized shear jets) can be found with high precision in temporally aperiodic flows defined over a finite time interval. I illustrate these results on unsteady flows arising in mechanics and fluid dynamics.

We study the effect of electron-electron interaction on the resistivity of a metal where umklapp scattering is either not effective or suppressed. This can happen in cases such as in a metal near a Pomeranchuk quantum phase transition or in a system with low density of carriers, e.g., the surface states of three-dimensional (3D) topological insulators. In such cases, one must consider both interactions and disorder to obtain a finite and T dependent resistivity. The existence of the Fermi-liquid (T^2) term in resistivity of a two-dimensional (2D) metal, as we show, then depends on 1) dimension (2D vs 3D), 2) geometry (concave vs convex), and 3) topology (simply vs multiply connected) of the Fermi surface. In the case of 3D topological insulators of the Bi_2Te_3 family, upon doping the Fermi surface of 2D metallic surface states changes its shape from convex to concave due to hexagonal warping, while still being too small to allow for umklapp scattering. We show that the T^2 term in the resistivity is present only in the concave regime and demonstrate that the resistivity obeys a universal scaling form valid for an arbitrary 2D Fermi surface near a convex/concave transition.

The workshop will provide a general introduction into numerical relativity and in code development within large collaborations.  The number of addendees are limited, and while registration is free, it is required. In order to register, write an email to workshop@einsteintoolkit.org.