6,316 research outputs found
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 worldâs 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 ATCCÂź 25922 was studied in goat milk. In ohmic treatment lower D
values were obtained (D60ÂșC = 4.2 min, D63ÂșC = 1.9 min, D65ÂșC = 0.86 min) as compared to conventional
treatment (D63ÂșC = 3.9 min, D65ÂșC = 3.5, D67ÂșC = 2.8 min, D75ÂșC = 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 ÂșC)
comparing with the conventional inactivation (z = 23.1 ÂșC). The death kinetics for Bacillus
licheniformis ATCCÂź 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 (D70ÂșC = 57.1 min, D75ÂșC = 25.2 min, D80ÂșC = 7.2 min) as
compared to conventional treatment (D70ÂșC = 85.3 min, D75ÂșC = 51.0, D80ÂșC = 18.1 min, D85ÂșC = 6.0 min,
D90ÂșC = 1.6 min). However, between the z values obtained for those treatments (z ohmic = 11.1 ÂșC and z
conventional = 11.4 ÂșC) 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 fluctuations are observed with
noise, while fluctuations are found for the model without demographic
noise
Transport Properties of Carbon Nanotube C 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 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 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
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