Eric Sembrat's Test Bonanza

Given that many diverse astrophysical systems are susceptible to relativistic hydromagnetic turbulence, it is surprising how little is presently known about how they manifest chaotic flow. Of primary interest is to establish a basic understanding of how the small-scale turbulent dynamo, whereby kinetic energy of the flow is converted into magnetic energy, operates in these systems. This process is thought to be instrumental in both stellar and galactic magnetogenesis, and may also be at work in relativistic astrophysical jets and their central engines.

Of equal importance is to understand how magnetic energy decays in the absence of continued stirring by external forces. For example, if magnetic fluctuations are driven locally (in a pulsar magnetosphere for instance) what fraction of the Poynting flux survives to infinity, and how much is trapped by collisions with ambient Alfven waves? Similarly, can turbulent magnetic fields produced by plasma instabilities upstream of a relativistic blast-wave survive long enough into the downstream to be consistent with synchrotron models for GRB afterglow emission?

I will present results from large-scale numerical simulations which are providing answers to some of these questions, and discuss ongoing efforts to answer others. If there is time, I will also explain how simulations of relativistic turbulence can be used to synthesize images of polarized synchrotron emission from giant radio lobes, thereby assessing the possibility that they are in a state of turbulence.

We present and discuss, in the context of the drug discovery pipeline, recent computational developments that enable the virtual screening of massive databases of chemicals against a large number of protein structures. We present "ensemble docking" applications of virtual screening in multiple protein structures that identify new protein ligands and explore biochemical pathways. We also discuss fundamental and challenging aspects of these very large virtual screening approaches.

Biological flows are vital for the conservation of life and indispensable commodity of living organisms. Morphological structures of living organisms and biological flow phenomena in nature have been evolved through a long history. The basic biophysics of several biofluid flow phenomena and the hidden secrets of nature such as blood flow in chicken embryos, blood sucking of mosquitoes, and sap flows in plants have been investigated experimentally by using advanced flow visualization techniques, such as X-ray PIV (particle image veocimetry), holographic PTV (particle tracking veocimetry), time-resolved micro-PIV, etc. Biological samples include insects (blood-sucking mosquitoes, liquid-feeding butterflies), fishes (zebra fish, planktons), animals (blood flows in chicken embryos or rats) and plants (sap flow in xylem vessels of rice or Arabidopsis). Gold nanoparticles developed as tracer particles transmit membranes of organisms without destroying the surrounding tissues. Detailed understanding on these biofluid flow phenomena are helpful to develop creative nature-inspired technologies for practical applications in biomedical science, microfluidics and renewable energy, etc. For example, a micropump consisting of serial-connected two-pump chambers and three diffuser elements was developed based on the revealed blood-sucking mechanism of a female mosquito. When the two pump chambers are operated in a well coordinated manner with a certain phase shift, the bio-inspired pump exhibits a good pumping performance, as appeared in the blood-sucking mosquitoes. The nature-inspired micropump would be utilized in various bio-chips as a liquid-phase sample supplying system. In addition, another bio-inspired micropump that can produce a large pressure gradient was developed by bio-inspiring a liquid-feeding butterfly through a long proboscis.

One of the frontiers in modern cosmology is understanding the end of cosmic dark ages, when the first stars, supernovae, and galaxies transformed the simple early Universe into a state of ever-increasing complexity. I will talk about the possible physics behind the formation of these first luminous objects by presenting the results from our simulations. I will also discuss the possible observational signatures of the cosmic dawn that will be the prime targets for the future telescopes such as the James Webb Space Telescope (JWST).

We use recent constraints on the star formation rate---halo mass---redshift relation to model the host halo environments where short Gamma-Ray Burst (sGRB) progenitors are created.  These halo environments set minimum energy requirements for sGRB progenitors to leave the vicinity of their original galaxy.  We find that the fraction of sGRBs which are hostless is a robust probe of the underlying velocity kick distribution for sGRB progenitors, regardless of uncertainties in the sGRB time-delay distribution and observational systematics.  We use observed constraints on the hostless fraction of sGRBs to rule out several sGRB progenitor classes which cannot supply the necessary velocity kicks.  Finally, we discuss the ability of sGRB galaxy host properties (e.g., stellar mass and morphology) to further constrain model uncertainties.

Many years ago Crick and Klug suggested that sharp bends or kinks have to facilitate strong bending of the double-helix, and accurate theoretical analysis confirms this suggestion. It remains, however, to be determined what is the critical curvature of DNA that prompts the appearance of the kinks. Different experimental approaches to the problem will be briefly reviewed. Attention will be paid to influence of the torsional stress in the double helix on the kink formation. The most reliable data suggest that the stable kinks appear only in torsionally relaxed DNA circles smaller than 70 bp. It is possible that the kinks represent openings of isolated base pairs. Although the probability of these openings in long unstressed DNA molecules is close to 10^-5, it increases sharply in small DNA circles reaching 1 open bp per circle of 70 bp.

Diffusion is an important physical process in many systems, from gases to biological cells. In the simplest case, a diffusing particle undergoes a random walk and its mean squared displacement increases linearly with time. In many cases, however, the diffusion is not ideal: The motion of the diffusing species can be restricted in a variety of ways, leading to  “sub-diffusion” in which the mean squared displacement increases more slowly. I will discuss experiments on the restricted diffusion of tracer particles in soft-matter systems close to a gel transition. Our experimental measurements provide information about the microstructure of the system and its evolution as the system gels on the bulk scale. Computer simulations help to clarify the interpretation of the data. I will also briefly discuss other systems in which restricted diffusion plays an important role.