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 LaAlO3_3-SrTiO3_3 interface

The 2-dimensional electron system at the interface between LaAlO$_{3}$ and SrTiO$_{3}$ 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 $2.9\times10^{13}$ cm$^{-2}$. 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$_3$-LaAlO$_3$ 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$_3$ capping layer prevents structural and chemical reconstruction at the LaAlO$_3$ surface and triggers the electronic reconstruction at a significantly lower LaAlO$_3$ 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/Al$_{x}$Ga$_{1-x}$As and In$_{y}$Ga$_{1-y}$As/Al$_{x}$Ga$_{1-x}$As 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 $x$. 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/Al$_{x}$Ga$_{1-x}$As 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 In$_{y}$Ga$_{1-y}$As/Al$_{x}$Ga$_{1-x}$As 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 $D$. 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 ($D = 2$) 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

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

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 $0.5 \leq {R_{\rm c,R}} /{R_{\rm c,z}} \leq 2$. 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 $T_h=1.7\times 10^6$K and n_h=0.1 \cm3 in a protogalactic halo environment, the mean density of the cloud gas that has cooled to $10^4$K increases to $100 n_h$ 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 $1 - 1.5 l_{\rm cool}$ where $l_{\rm cool}$ 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