36,143 research outputs found
Anti-tumor necrosis factor-alpha therapy during murine Klebsiella pneumoniae bacteremia: increased mortality in the absence of liver injury.
Klebsiella pneumoniae is a leading cause of gram-negative bacterial pneumonia, often resulting in bacteremia concurrent with the localized pulmonary infection. The beneficial role of tumor necrosis factor (TNF)-alpha during pulmonary infection has been well documented; however, consequences of TNF-alpha production during systemic bacterial infection are controversial. A murine model of K. pneumoniae was developed to address this important issue. Liver-associated TNF-alpha mRNA was induced within 30 min after intravenous bacterial inoculation and remained elevated through 6 h before returning to near-baseline at 24 h postinfection. Intravenous K. pneumoniae infection induced liver cellular injury that was completely ablated when mice were pretreated with a neutralizing anti-TNF-alpha antibody. Interestingly, this reduction in liver injury failed to translate into improved survival. Mice receiving anti-TNF-alpha continued to succumb to the infection even out to day 10 postinfection. Bacterial clearance after TNF-alpha neutralization was significantly impaired at later time points during infection. Correlating with impaired bacterial clearance was diminished production of liver-associated MIP-2, MIP-1alpha, MCP-1, and interferon-gamma. Further evidence of diminished antibacterial immune responses was noted when the activational status of splenic natural killer cells in anti-TNF-alpha-treated mice was examined 24 h postinfection. Natural killer cells displayed decreased CD69 expression. Combined, these data indicate that the beneficial effects of TNF-alpha during systemic K. pneumoniae infection outweigh the detrimental effects of TNF-alpha-mediated hepatocyte cellular injury. Anti-TNF-alpha therapy, although preventing liver injury during blood-borne bacterial infection, results in a dampened anti-bacterial host response, resulting in decreased bacterial clearance and overall survival
Critical Fields and Critical Currents in MgB2
We review recent measurements of upper (Hc2) and lower (Hc1) critical fields
in clean single crystals of MgB2, and their anisotropies between the two
principal crystallographic directions. Such crystals are far into the "clean
limit" of Type II superconductivity, and indeed for fields applied in the
c-direction, the Ginzburg-Landau parameter k is only about 3, just large enough
for Type II behaviour. Because m0Hc2 is so low, about 3 T for fields in the
c-direction, MgB2 has to be modified for it to become useful for high-current
applications. It should be possible to increase Hc2 by the introduction of
strong electron scattering (but because of the electronic structure and the
double gap that results, the scatterers will have to be chosen carefully). In
addition, pinning defects on a scale of a few nm will have to be engineered in
order to enhance the critical current density at high fields.Comment: BOROMAG Conference Invited paper. To appear in Supercond. Sci. Tec
Is there a Phase Transition to the Flux Lattice State?
The sharp drops in the resistance and magnetization which are usually
attributed to a phase transition from the vortex liquid state to a crystal
state are explained instead as a crossover between three and two dimensional
behavior, which occurs when the phase coherence length in the liquid becomes
comparable to the sample thickness. Estimates of the width of the crossover
region and the phase coherence length scales are in agreement with experiment.Comment: 4 pages, RevTe
Continuity properties of measurable group cohomology
A version of group cohomology for locally compact groups and Polish modules
has previously been developed using a bar resolution restricted to measurable
cochains. That theory was shown to enjoy analogs of most of the standard
algebraic properties of group cohomology, but various analytic features of
those cohomology groups were only partially understood.
This paper re-examines some of those issues. At its heart is a simple
dimension-shifting argument which enables one to `regularize' measurable
cocycles, leading to some simplifications in the description of the cohomology
groups. A range of consequences are then derived from this argument.
First, we prove that for target modules that are Fr\'echet spaces, the
cohomology groups agree with those defined using continuous cocycles, and hence
they vanish in positive degrees when the acting group is compact. Using this,
we then show that for Fr\'echet, discrete or toral modules the cohomology
groups are continuous under forming inverse limits of compact base groups, and
also under forming direct limits of discrete target modules.
Lastly, these results together enable us to establish various circumstances
under which the measurable-cochains cohomology groups coincide with others
defined using sheaves on a semi-simplicial space associated to the underlying
group, or sheaves on a classifying space for that group. We also prove in some
cases that the natural quotient topologies on the measurable-cochains
cohomology groups are Hausdorff.Comment: 52 pages. [Nov 22, 2011:] Major re-write with Calvin C. Moore as new
co-author. Results from previous version strengthened and several new results
added. [Nov 25, 2012:] Final version now available at springerlink.co
Topological Quantum Compiling
A method for compiling quantum algorithms into specific braiding patterns for
non-Abelian quasiparticles described by the so-called Fibonacci anyon model is
developed. The method is based on the observation that a universal set of
quantum gates acting on qubits encoded using triplets of these quasiparticles
can be built entirely out of three-stranded braids (three-braids). These
three-braids can then be efficiently compiled and improved to any required
accuracy using the Solovay-Kitaev algorithm.Comment: 20 pages, 20 figures, published versio
Energy cost associated with vortex crossing in superconductors
Starting from the Ginzburg-Landau free energy of a type II superconductor in
a magnetic field we estimate the energy associated with two vortices crossing.
The calculations are performed by assuming that we are in a part of the phase
diagram where the lowest Landau level approximation is valid. We consider only
two vortices but with two markedly different sets of boundary conditions: on a
sphere and on a plane with quasi-periodic boundary conditions. We find that the
answers are very similar suggesting that the energy is localised to the
crossing point. The crossing energy is found to be field and temperature
dependent -- with a value at the experimentally measured melting line of
, where is the Lindemann
melting criterion parameter. The crossing energy is then used with an extension
of the Marchetti, Nelson and Cates hydrodynamic theory to suggest an
explanation of the recent transport experiments of Safar {{\em et al.}\ }.Comment: 15 pages, RevTex v3.0, followed by 5 postscript figure
Theta Vectors and Quantum Theta Functions
In this paper, we clarify the relation between Manin's quantum theta function
and Schwarz's theta vector in comparison with the kq representation, which is
equivalent to the classical theta function, and the corresponding coordinate
space wavefunction. We first explain the equivalence relation between the
classical theta function and the kq representation in which the translation
operators of the phase space are commuting. When the translation operators of
the phase space are not commuting, then the kq representation is no more
meaningful. We explain why Manin's quantum theta function obtained via algebra
(quantum tori) valued inner product of the theta vector is a natural choice for
quantum version of the classical theta function (kq representation). We then
show that this approach holds for a more general theta vector with constant
obtained from a holomorphic connection of constant curvature than the simple
Gaussian one used in the Manin's construction. We further discuss the
properties of the theta vector and of the quantum theta function, both of which
have similar symmetry properties under translation.Comment: LaTeX 21 pages, give more explicit explanations for notions given in
the tex
Structural, orbital, and magnetic order in vanadium spinels
Vanadium spinels (ZnV_2O_4, MgV_2O_4, and CdV_2O_4) exhibit a sequence of
structural and magnetic phase transitions, reflecting the interplay of lattice,
orbital, and spin degrees of freedom. We offer a theoretical model taking into
account the relativistic spin-orbit interaction, collective Jahn-Teller effect,
and spin frustration. Below the structural transition, vanadium ions exhibit
ferroorbital order and the magnet is best viewed as two sets of
antiferromagnetic chains with a single-ion Ising anisotropy. Magnetic order,
parametrized by two Ising variables, appears at a tetracritical point.Comment: v3: streamlined introductio
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