160 research outputs found
Holographic RG flow of the shear viscosity to entropy density ratio in strongly coupled anisotropic plasma
We study holographic RG flow of the shear viscosity tensor of anisotropic,
strongly coupled N=4 super-Yang-Mills plasma by using its type IIB supergravity
dual in anisotropic bulk spacetime. We find that the shear viscosity tensor has
three independent components in the anisotropic bulk spacetime away from the
boundary, and one of the components has a non-trivial RG flow while the other
two have a trivial one. For the component of the shear viscosity tensor with
non-trivial RG flow, we derive its RG flow equation, and solve the equation
analytically to second order in the anisotropy parameter 'a'. We derive the RG
equation using the equation of motion, holographic Wilsonian RG method, and
Kubo's formula. All methods give the same result. Solving the equation, we find
that the ratio of the component of the shear viscosity tensor to entropy
density 'eta/s' flows from above '1/4pi' at the horizon (IR) to below '1/4pi'
at the boundary (UV) where it violates the holographic shear viscosity
(Kovtun-Son-Starinets) bound and where it agrees with the other longitudinal
component.Comment: 17 pages, 2 figures, slight change on the title, more background
material added, references added, accepted for publication in JHE
Ionization of hydrogen and hydrogenic ions by antiprotons
Presented here is a description of the ionization of hydrogen and hydrogenic
ions by antiproton-impact, based on very large scale numerical solutions of the
time-dependent Schr\"odinger equation in three spatial dimensions and on
analysis of the topology of the electronic eigenenergy surfaces in the plane of
complex internuclear distance. Comparison is made with other theories and very
recent measurements.Comment: RevTex document, 11 pages, 4 Postscript figures are available from
the authors, in press Phys. Rev. Let
Ionization via Chaos Assisted Tunneling
A simple example of quantum transport in a classically chaotic system is
studied. It consists in a single state lying on a regular island (a stable
primary resonance island) which may tunnel into a chaotic sea and further
escape to infinity via chaotic diffusion. The specific system is realistic : it
is the hydrogen atom exposed to either linearly or circularly polarized
microwaves. We show that the combination of tunneling followed by chaotic
diffusion leads to peculiar statistical fluctuation properties of the energy
and the ionization rate, especially to enhanced fluctuations compared to the
purely chaotic case. An appropriate random matrix model, whose predictions are
analytically derived, describes accurately these statistical properties.Comment: 30 pages, 11 figures, RevTeX and postscript, Physical Review E in
pres
Doping the holographic Mott insulator
Mott insulators form because of strong electron repulsions, being at the
heart of strongly correlated electron physics. Conventionally these are
understood as classical "traffic jams" of electrons described by a short-ranged
entangled product ground state. Exploiting the holographic duality, which maps
the physics of densely entangled matter onto gravitational black hole physics,
we show how Mott-insulators can be constructed departing from entangled
non-Fermi liquid metallic states, such as the strange metals found in cuprate
superconductors. These "entangled Mott insulators" have traits in common with
the "classical" Mott insulators, such as the formation of Mott gap in the
optical conductivity, super-exchange-like interactions, and form "stripes" when
doped. They also exhibit new properties: the ordering wave vectors are detached
from the number of electrons in the unit cell, and the DC resistivity diverges
algebraically instead of exponentially as function of temperature. These
results may shed light on the mysterious ordering phenomena observed in
underdoped cuprates.Comment: 27 pages, 9 figures. Accepted in Nature Physic
Universality of anomalous conductivities in theories with higher-derivative holographic duals
E. coli Nissle 1917 Affects Salmonella Adhesion to Porcine Intestinal Epithelial Cells
BACKGROUND: The probiotic Escherichia coli strain Nissle 1917 (EcN) has been shown to interfere in a human in vitro model with the invasion of several bacterial pathogens into epithelial cells, but the underlying molecular mechanisms are not known. METHODOLOGY/PRINCIPAL FINDINGS: In this study, we investigated the inhibitory effects of EcN on Salmonella Typhimurium invasion of porcine intestinal epithelial cells, focusing on EcN effects on the various stages of Salmonella infection including intracellular and extracellular Salmonella growth rates, virulence gene regulation, and adhesion. We show that EcN affects the initial Salmonella invasion steps by modulating Salmonella virulence gene regulation and Salmonella SiiE-mediated adhesion, but not extra- and intracellular Salmonella growth. However, the inhibitory activity of EcN against Salmonella invasion always correlated with EcN adhesion capacities. EcN mutants defective in the expression of F1C fimbriae and flagellae were less adherent and less inhibitory toward Salmonella invasion. Another E. coli strain expressing F1C fimbriae was also adherent to IPEC-J2 cells, and was similarly inhibitory against Salmonella invasion like EcN. CONCLUSIONS: We propose that EcN affects Salmonella adhesion through secretory components. This mechanism appears to be common to many E. coli strains, with strong adherence being a prerequisite for an effective reduction of SiiE-mediated Salmonella adhesion
Holographic Flow of Anomalous Transport Coefficients
We study the holographic flow of anomalous conductivities induced by gauge
and gravitational Chern-Simons terms. We find that the contribution from the
gauge Chern-Simons term gives rise to a flow that can be interpreted in terms
of an effective, cutoff dependent chemical potential. In contrast the
contribution of the gauge-gravitational Chern-Simons term is just the
temperature squared and does not flow.Comment: 26 pages, no figure
The genome sequence of E. coli W (ATCC 9637): comparative genome analysis and an improved genome-scale reconstruction of E. coli
Background: Escherichia coli is a model prokaryote, an important pathogen, and a key organism for industrial biotechnology. E. coli W (ATCC 9637), one of four strains designated as safe for laboratory purposes, has not been sequenced. E. coli W is a fast-growing strain and is the only safe strain that can utilize sucrose as a carbon source. Lifecycle analysis has demonstrated that sucrose from sugarcane is a preferred carbon source for industrial bioprocesses
The usability of recycled carbon fibres in short fibre thermoplastics: interfacial properties
The objective of this study was to investigate the feasibility of combining discontinuous recycled carbon fibres with polypropylene, to produce a low-cost, high specific stiffness material for high-volume applications. The inherent low affinity of carbon fibre and polypropylene motivated a detailed study of the surface characteristics of carbon fibre and interfacial behaviour between the two materials, using the microbond test. The effects of removing the sizing from the fibres, as well as introducing a maleic anhydride-grafted polypropylene coupling agent, were extensively investigated. Polypropylene was found to degrade when prepared under atmospheric conditions; therefore, it was necessary to form droplets under nitrogen. Removal of the sizing from the fibre using pyrolysis and solvolysis techniques altered the surface morphology of the fibre and increased the interfacial shear strength (IFSS) by 4 and 33 %, respectively. A more significant improvement in the fibre–matrix adhesion was achieved by adding a maleic anhydride coupling agent at 2 wt%, which increased the IFSS by 320 %
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