1,953 research outputs found
Bovine Anaplasmosis: An Overview
Bovine Anaplasmosis is an infectious disease of adult cattle caused by the hemotrophic rickettsial parasite Anaplasma marginale. Cattle of all ages may become infected with Anaplasma marginale, but clinical disease increases in severity with age. Anaplasmosis is rarely observed in calveslessthan sixmonths of age. Cattle over three years of age are most susceptible and have the highest mortality rate (30-50%). Anaplasmosis is a cyclical disease with outbreaks occurring every five to seven years. The American National Cattlemen\u27s Association has considered anaplasmosis as a major disease problem with annual losses and disease control estimated to be $300 millio
Analytical calculation of the Green's function and Drude weight for a correlated fermion-boson system
In classical Drude theory the conductivity is determined by the mass of the
propagating particles and the mean free path between two scattering events. For
a quantum particle this simple picture of diffusive transport loses relevance
if strong correlations dominate the particle motion. We study a situation where
the propagation of a fermionic particle is possible only through creation and
annihilation of local bosonic excitations. This correlated quantum transport
process is outside the Drude picture, since one cannot distinguish between free
propagation and intermittent scattering. The characterization of transport is
possible using the Drude weight obtained from the f-sum rule, although its
interpretation in terms of free mass and mean free path breaks down. For the
situation studied we calculate the Green's function and Drude weight using a
Green's functions expansion technique, and discuss their physical meaning.Comment: final version, minor correction
Gate-tunable band structure of the LaAlO-SrTiO interface
The 2-dimensional electron system at the interface between LaAlO and
SrTiO has several unique properties that can be tuned by an externally
applied gate voltage. In this work, we show that this gate-tunability extends
to the effective band structure of the system. We combine a magnetotransport
study on top-gated Hall bars with self-consistent Schr\"odinger-Poisson
calculations and observe a Lifshitz transition at a density of
cm. Above the transition, the carrier density of one
of the conducting bands decreases with increasing gate voltage. This surprising
decrease is accurately reproduced in the calculations if electronic
correlations are included. These results provide a clear, intuitive picture of
the physics governing the electronic structure at complex oxide interfaces.Comment: 14 pages, 4 figure
Parallel electron-hole bilayer conductivity from electronic interface reconstruction
The perovskite SrTiO-LaAlO structure has advanced to a model system
to investigate the rich electronic phenomena arising at polar interfaces. Using
first principles calculations and transport measurements we demonstrate that an
additional SrTiO capping layer prevents structural and chemical
reconstruction at the LaAlO surface and triggers the electronic
reconstruction at a significantly lower LaAlO film thickness than for the
uncapped systems. Combined theoretical and experimental evidence (from
magnetotransport and ultraviolet photoelectron spectroscopy) suggests two
spatially separated sheets with electron and hole carriers, that are as close
as 1 nm.Comment: Phys. Rev. Lett., in pres
Excitons in T-shaped quantum wires
We calculate energies, oscillator strengths for radiative recombination, and
two-particle wave functions for the ground state exciton and around 100 excited
states in a T-shaped quantum wire. We include the single-particle potential and
the Coulomb interaction between the electron and hole on an equal footing, and
perform exact diagonalisation of the two-particle problem within a finite basis
set. We calculate spectra for all of the experimentally studied cases of
T-shaped wires including symmetric and asymmetric GaAs/AlGaAs and
InGaAs/AlGaAs structures. We study in detail the
shape of the wave functions to gain insight into the nature of the various
states for selected symmetric and asymmetric wires in which laser emission has
been experimentally observed. We also calculate the binding energy of the
ground state exciton and the confinement energy of the 1D quantum-wire-exciton
state with respect to the 2D quantum-well exciton for a wide range of
structures, varying the well width and the Al molar fraction . We find that
the largest binding energy of any wire constructed to date is 16.5 meV. We also
notice that in asymmetric structures, the confinement energy is enhanced with
respect to the symmetric forms with comparable parameters but the binding
energy of the exciton is then lower than in the symmetric structures. For
GaAs/AlGaAs wires we obtain an upper limit for the binding energy
of around 25 meV in a 10 {\AA} wide GaAs/AlAs structure which suggests that
other materials must be explored in order to achieve room temperature
applications. There are some indications that
InGaAs/AlGaAs might be a good candidate.Comment: 20 pages, 10 figures, uses RevTeX and psfig, submitted to Physical
Review
Slave-Boson Functional-Integral Approach to the Hubbard Model with Orbital Degeneracy
A slave-boson functional-integral method has been developed for the Hubbard
model with arbitrary, orbital degeneracy . Its saddle-point mean-field
theory is equivalent to the Gutzwiller approximation, as in the case of
single-band Hubbard model. Our theory is applied to the doubly degenerate () model, and numerical calculations have been performed for this model in the
paramagnetic states. The effect of the exchange interaction on the
metal-insulator (MI) transition is discussed. The critical interaction for the
MI transition is analytically calculated as functions of orbital degeneracy and
electron occupancy.Comment: Latex 20 pages, 9 figures available on request to
[email protected] Note: published in J. Physical Society of Japan with
some minor modification
Phase diagrams of correlated electrons: systematic corrections to the mean field theory
Perturbative corrections to the mean field theory for particle-hole
instabilities of interacting electron systems are computed within a scheme
which is equivalent to the recently developed variational approach to the
Kohn-Luttinger superconductivity. This enables an unbiased comparison of
particle-particle and particle-hole instabilities within the same approximation
scheme. A spin-rotation invariant formulation for the particle-hole
instabilities in the triplet channel is developed. The method is applied to the
phase diagram of the t-t' Hubbard model on the square lattice. At the Van Hove
density, antiferromagnetic and d-wave Pomeranchuk phases are found to be stable
close to half filling. However, the latter phase is confined to an extremely
narrow interval of densities and away from the singular filling, d-wave
superconducting instability dominates
Two-Dimensional Axisymmetric Collapse of Thermally Unstable Primordial Clouds
We have performed two-dimensional hydrodynamic simulations of the collapse of
isolated axisymmetric clouds condensing via radiative cooling in a primordial
background gas. In order to study the development of the so-called
``shape-instability'', we have considered two types of axisymmetric clouds,
oblate and prolate clouds of various sizes and with axial ratios of . We find that the degree of oblateness or
prolateness is enhanced during the initial cooling phase. But it can be
reversed later, if the initial contrast in cooling times between the cloud gas
and the background gas is much greater than one. In such cases an oblate cloud
collapses to a structure composed of an outer thin disk and a central prolate
component. A prolate cloud, on the other hand, becomes a thin cigar-shape
structure with a central dense oblate component. The reversal of shape in the
central part of the cooled clouds is due to supersonic motions either along the
disk plane in the case of oblate clouds or along the symmetry axis in the case
of prolate clouds. For a background gas of K and n_h=0.1
\cm3 in a protogalactic halo environment, the mean density of the cloud gas
that has cooled to K increases to or so, in our simulations
where nonequilibrium cooling is adopted and the background gas cools too. The
spherical Jeans mass of such gas is estimated to be about M_J \sim
5\times10^{7}\Msun. In order for cloud mass to exceed the Jeans mass and at
the same time in order for the thermal instability to operate, the initial
cloud size should be around where is the
cooling length.Comment: 31 pages including 12 figures (reduced resolution), to appear in The
Astrophysical Journal (v584 n2 ApJ February 20, 2003 issue). Pdf with full
resolution figures can be downloaded from
ftp://canopus.chungnam.ac.kr/ryu/ryu.pd
Active Microrheology of Networks Composed of Semiflexible Polymers. II. Theory and comparison with simulations
Building on the results of our computer simulation (ArXiv cond-mat/0503573)we
develop a theoretical description of the motion of a bead, embedded in a
network of semiflexible polymers, and responding to an applied force. The
theory reveals the existence of an osmotic restoring force, generated by the
piling up of filaments in front of the moving bead and first deduced through
computer simulations. The theory predicts that the bead displacement scales
like x ~ t^alfa with time, with alfa=0.5 in an intermediate- and alfa=1 in a
long-time regime. It also predicts that the compliance varies with
concentration like c^(-4/3) in agreement with experiment.Comment: 18 pages and 2 figure
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