Swimming in Granular Media

We study a simple model of periodic contraction and extension of large intruders in a granular bed to understand the mechanism for swimming in an otherwise solid media. Using an event-driven simulation, we find optimal conditions that idealized swimmers must use to critically fluidize a sand bed so that it is rigid enough to support a load when needed, but fluid enough to permit motion with minimal resistance. Swimmers - or other intruders - that agitate the bed too rapidly produce large voids that prevent traction from being achieved, while swimmers that move too slowly cannot travel before the bed re-solidifies around them i.e., the swimmers locally probe the fundamental time-scale in a granular packing

Death kinetics of Escherichia coli in goat milk and Bacillus licheniformis in cloudberry jam treated by ohmic heating

In recent years, the world’s food industry has focused increasing attention on electrical techniques of food processing. Ohmic heating is one of these techniques that can be considered as a high temperature short time and a purely bulk heating method, having potential applications in processes such as blanching, evaporation and pasteurization in the food industry. However such technology would have to assure the microbiological safety obtained by the conventional cooking methods. Concerning this, the influence of heat treatment by ohmic and conventional technology on death kinetic parameters (D and z values) of Escherichia coli ATCC® 25922 was studied in goat milk. In ohmic treatment lower D values were obtained (D60ºC = 4.2 min, D63ºC = 1.9 min, D65ºC = 0.86 min) as compared to conventional treatment (D63ºC = 3.9 min, D65ºC = 3.5, D67ºC = 2.8 min, D75ºC = 1.5 min). The increase of temperature required for a ten fold decrease in D value was also lower in the ohmic inactivation (z = 8.4 ºC) comparing with the conventional inactivation (z = 23.1 ºC). The death kinetics for Bacillus licheniformis ATCC® 14580 spores in cloudberry jam were also studied under both types of heat inactivation (ohmic and conventional) and similar conclusions were drawn for the D values; lower D values were also obtained for ohmic treatment (D70ºC = 57.1 min, D75ºC = 25.2 min, D80ºC = 7.2 min) as compared to conventional treatment (D70ºC = 85.3 min, D75ºC = 51.0, D80ºC = 18.1 min, D85ºC = 6.0 min, D90ºC = 1.6 min). However, between the z values obtained for those treatments (z ohmic = 11.1 ºC and z conventional = 11.4 ºC) the differences were not significant. In general the results of present work indicate that the ohmic heating provides quicker death kinetics. This opens the perspective for shorter, less aggressive treatments

Effects of demographic stochasticity on biological community assembly on evolutionary time scales

We study the effects of demographic stochasticity on the long-term dynamics of biological coevolution models of community assembly. The noise is induced in order to check the validity of deterministic population dynamics. While mutualistic communities show little dependence on the stochastic population fluctuations, predator-prey models show strong dependence on the stochasticity, indicating the relevance of the finiteness of the populations. For a predator-prey model, the noise causes drastic decreases in diversity and total population size. The communities that emerge under influence of the noise consist of species strongly coupled with each other and have stronger linear stability around the fixed-point populations than the corresponding noiseless model. The dynamics on evolutionary time scales for the predator-prey model are also altered by the noise. Approximate $1/f$ fluctuations are observed with noise, while $1/f^{2}$ fluctuations are found for the model without demographic noise

Transport Properties of Carbon Nanotube C60_{60} Peapods

We measure the conductance of carbon nanotube peapods from room temperature down to 250mK. Our devices show both metallic and semiconducting behavior at room temperature. At the lowest temperatures, we observe single electron effects. Our results suggest that the encapsulated C$_{60}$ molecules do not introduce substantial backscattering for electrons near the Fermi level. This is remarkable given that previous tunneling spectroscopy measurements show that encapsulated C$_{60}$ strongly modifies the electronic structure of a nanotube away from the Fermi level.Comment: 9 pages, 4 figures. This is one of two manuscripts replacing the one orginally submitted as arXiv:cond-mat/0606258. The other one is arXiv:0704.3641 [cond-mat

The Escherichia coli RutR transcription factor binds at targets within genes as well as intergenic regions.

The Escherichia coli RutR protein is the master regulator of genes involved in pyrimidine catabolism. Here we have used chromatin immunoprecipitation in combination with DNA microarrays to measure the binding of RutR across the chromosome of exponentially growing E. coli cells. Twenty RutR-binding targets were identified and analysis of these targets generated a DNA consensus logo for RutR binding. Complementary in vitro binding assays showed high-affinity RutR binding to 16 of the 20 targets, with the four low-affinity RutR targets lacking predicted key binding determinants. Surprisingly, most of the DNA targets for RutR are located within coding segments of the genome and appear to have little or no effect on transcript levels in the conditions tested. This contrasts sharply with other E. coli transcription factors whose binding sites are primarily located in intergenic regions. We suggest that either RutR has yet undiscovered function or that evolution has been slow to eliminate non-functional DNA sites for RutR because they do not have an adverse effect on cell fitness

Nonequilibrium Microscopic Distribution of Thermal Current in Particle Systems

A nonequilibrium distribution function of microscopic thermal current is studied by a direct numerical simulation in a thermal conducting steady state of particle systems. Two characteristic temperatures of the thermal current are investigated on the basis of the distribution. It is confirmed that the temperature depends on the current direction; Parallel temperature to the heat-flux is higher than antiparallel one. The difference between the parallel temperature and the antiparallel one is proportional to a macroscopic temperature gradient.Comment: 4 page

Primary role of the barely occupied states in the charge density wave formation of NbSe2

NbSe2 is a prototypical charge-density-wave (CDW) material, whose mechanism remains mysterious so far. With angle resolved photoemission spectroscopy, we mapped out the CDW gap and recovered the long-lost nesting condition over a large broken-honeycomb region in the Brillouin zone, which consists of six saddle band point regions with high density of states (DOS), and large regions away from Fermi surface with negligible DOS at the Fermi energy. We show that the major contributions to the CDW come from these barely occupied states rather than the saddle band points. Our findings not only resolve a long standing puzzle, but also overthrow the conventional wisdom that CDW is dominated by regions with high DOS.Comment: 5 pages, 4 figure

First principles investigations of the electronic, magnetic and chemical bonding properties of CeTSn (T=Rh,Ru)

The electronic structures of CeRhSn and CeRuSn are self-consistently calculated within density functional theory using the local spin density approximation for exchange and correlation. In agreement with experimental findings, the analyses of the electronic structures and of the chemical bonding properties point to the absence of magnetization within the mixed valent Rh based system while a finite magnetic moment is observed for trivalent cerium within the Ru-based stannide, which contains both trivalent and intermediate valent Ce.Comment: 6 pages, 7 figures, for more information see http://www.physik.uni-augsburg.de/~eyert