Modeling Emission from the First Explosions: Pitfalls and Problems

Observations of the explosions of Population III (Pop III) stars have the potential to teach us much about the formation and evolution of these zero-metallicity objects. To realize this potential, we must tie observed emission to an explosion model, which requires accurate light curve and spectra calculations. Here, we discuss many of the pitfalls and problems involved in such models, presenting some preliminary results from radiation-hydrodynamics simulations.Comment: 6 pages, 3 figures, proceedings of 'The First Stars and Galaxies: Challenges for the Next Decade", Austin, TX, March 8-11, 201

Dynamics of semiflexible polymers in a flow field

We present a method to investigate the dynamics of a single semiflexible polymer, subject to anisotropic friction in a viscous fluid. In contrast to previous approaches, we do not rely on a discrete bead-rod model, but introduce a suitable normal mode decomposition of a continuous space curve. By means of a perturbation expansion for stiff filaments, we derive a closed set of coupled Langevin equations in mode space for the nonlinear dynamics in two dimensions, taking into account exactly the local constraint of inextensibility. The stochastic differential equations obtained this way are solved numerically, with parameters adjusted to describe the motion of actin filaments. As an example, we show results for the tumbling motion in shear flow

Evaluation of renal allograft function early after transplantation with diffusion-weighted MR imaging

Aims: To determine the inter-patient variability of apparent diffusion coefficients (ADC) and concurrent micro-circulation contributions from diffusion-weighted MR imaging (DW-MRI) in renal allografts early after transplantation, and to obtain initial information on whether these measures are altered in histologically proven acute allograft rejection (AR). Methods: DW-MRI was performed in 15 renal allograft recipients 5-19days after transplantation. Four patients presented with AR and one with acute tubular necrosis (ATN). Total ADC (ADCT) was determined, which includes diffusion and micro-circulation contributions. Furthermore, diffusion and micro-circulation contributions were separated, yielding the "perfusion fraction” (FP), and "perfusion-free” diffusion (ADCD). Results: Diffusion parameters in the ten allografts with stable function early after transplantation demonstrated low variabilities. Values for ADCT and ADCD were (×10−5mm2/s) 228 ± 14 and 203 ± 9, respectively, in cortex and 226 ± 16 and 199 ± 9, respectively, in medulla. FP values were 18 ± 5% in cortex and 19 ± 5% in medulla. FP values were strongly reduced to less than 12% in cortex and medulla of renal transplants with AR and ATN. FP values correlated with creatinine clearance. Conclusion: DW-MRI allows reliable determination of diffusion and micro-circulation contributions in renal allografts shortly after transplantation; deviations in AR indicate potential clinical utility of this method to non-invasively monitor derangements in renal allograft

Spread of Plague Among Black-Tailed Prairie Dogs Is Associated With Colony Spatial Characteristics

Sylvatic plague (Yersinia pestis) is an exotic pathogen that is highly virulent in black-tailed prairie dogs (Cynomys ludovicianus) and causes widespread colony losses and individual mortality rates \u3e95%. We investigated colony spatial characteristics that may influence inter-colony transmission of plague at 3 prairie dog colony complexes in the Great Plains. The 4 spatial characteristics we considered include: colony size, Euclidean distance to nearest neighboring colony, colony proximity index, and distance to nearest drainage (dispersal) corridor. We used multi-state mark–recapture models to determine the relationship between these colony characteristics and probability of plague transmission among prairie dog colonies. Annual mapping of colonies and mark–recapture analyses of disease dynamics in natural colonies led to 4 main results: 1) plague outbreaks exhibited high spatial and temporal variation, 2) the site of initiation of epizootic plague may have substantially influenced the subsequent inter-colony spread of plague, 3) the longterm effect of plague on individual colonies differed among sites because of how individuals and colonies were distributed, and 4) colony spatial characteristics were related to the probability of infection at all sites although the relative importance and direction of relationships varied among sites. Our findings suggest that conventional prairie dog conservation management strategies, including promoting large, highly connected colonies, may need to be altered in the presence of plague