54 research outputs found
Genome characterization and population genetic structure of the zoonotic pathogen, streptococcus canis
Background - Streptococcus canis is an important opportunistic pathogen of dogs and cats that can also infect a wide range of additional mammals including cows where it can cause mastitis. It is also an emerging human pathogen.
Results - Here we provide characterization of the first genome sequence for this species, strain FSL S3-227 (milk isolate from a cow with an intra-mammary infection). A diverse array of putative virulence factors was encoded by the S. canis FSL S3-227 genome. Approximately 75% of these gene sequences were homologous to known Streptococcal virulence factors involved in invasion, evasion, and colonization. Present in the genome are multiple potentially mobile genetic elements (MGEs) [plasmid, phage, integrative conjugative element (ICE)] and comparison to other species provided convincing evidence for lateral gene transfer (LGT) between S. canis and two additional bovine mastitis causing pathogens (Streptococcus agalactiae, and Streptococcus dysgalactiae subsp. dysgalactiae), with this transfer possibly contributing to host adaptation. Population structure among isolates obtained from Europe and USA [bovine = 56, canine = 26, and feline = 1] was explored. Ribotyping of all isolates and multi locus sequence typing (MLST) of a subset of the isolates (n = 45) detected significant differentiation between bovine and canine isolates (Fisher exact test: P = 0.0000 [ribotypes], P = 0.0030 [sequence types]), suggesting possible host adaptation of some genotypes. Concurrently, the ancestral clonal complex (54% of isolates) occurred in many tissue types, all hosts, and all geographic locations suggesting the possibility of a wide and diverse niche.
Conclusion - This study provides evidence highlighting the importance of LGT in the evolution of the bacteria S. canis, specifically, its possible role in host adaptation and acquisition of virulence factors. Furthermore, recent LGT detected between S. canis and human bacteria (Streptococcus urinalis) is cause for concern, as it highlights the possibility for continued acquisition of human virulence factors for this emerging zoonotic pathogen
Three-dimensional flux states as a model for the pseudogap phase of transition metal oxides
We propose that the pseudogap state observed in the transition metal oxides
can be explained by a three-dimensional flux state, which exhibits
spontaneously generated currents in its ground state due to electron-electron
correlations. We compare the energy of the flux state to other classes of mean
field states, and find that it is stabilized over a wide range of and
. The signature of the state will be peaks in the neutron diffraction
spectra, the location and intensity of which are presented. The dependence of
the pseudogap in the optical conductivity is calculated based on the parameters
in the model.Comment: submitted to Phys. Rev. B on January 8, 200
Spin Susceptibility and Gap Structure of the Fractional-Statistics Gas
This paper establishes and tests procedures which can determine the electron
energy gap of the high-temperature superconductors using the model
with spinon and holon quasiparticles obeying fractional statistics. A simpler
problem with similar physics, the spin susceptibility spectrum of the spin 1/2
fractional-statistics gas, is studied. Interactions with the density
oscillations of the system substantially decrease the spin gap to a value of
, much less than the mean-field value of
. The lower few Landau levels remain visible, though broadened
and shifted, in the spin susceptibility. As a check of the methods, the
single-particle Green's function of the non-interacting Bose gas viewed in the
fermionic representation, as computed by the same approximation scheme, agrees
well with the exact results. The same mechanism would reduce the gap of the
model without eliminating it.Comment: 35 pages, written in REVTeX, 16 figures available upon request from
[email protected]
Paired States in the Even Integer Quantum Hall Effect
We argue that a new type of quantum Hall state requiring non-perturbative
Landau level mixing arises at low electron density. In these states, up and
down spin electrons pair to form spinless bosons that condense into a bosonic
quantum Hall state. We describe a wavefunction for a paired quantum Hall state
at and argue that it is stabilized by a BCS instability arising in flux
attachment calculations. Based on this state, we derive a new global phase
diagram for the integral quantum Hall effect with spin. Additional experimental
implications are discussed.Comment: uufile, includes 4 page revtex file and 1 figure fil
Confinement of Slave-Particles in U(1) Gauge Theories of Strongly-Interacting Electrons
We show that slave particles are always confined in U(1) gauge theories of
interacting electron systems. Consequently, the low-lying degrees of freedom
are different from the slave particles. This is done by constructing a dual
formulation of the slave-particle representation in which the no-double
occupany constraint becomes linear and, hence, soluble. Spin-charge separation,
if it occurs, is due to the existence of solitons with fractional quantum
numbers
Effective Field Theory and Integrability in Two-Dimensional Mott Transition
We study the Mott transition in a two-dimensional lattice spinless fermion
model with nearest neighbors density-density interactions. By means of a
two-dimensional Jordan-Wigner transformation, the model is mapped onto the
lattice XXZ spin model, which is shown to possess a Quantum Group symmetry as a
consequence of a recently found solution of the Zamolodchikov Tetrahedron
Equation. A projection (from three to two space-time dimensions) property of
the solution is used to identify the symmetry of the model at the Mott critical
point as U_q(sl(2))xU_q(sl(2)), with deformation parameter q=-1. Based on this
result, the low-energy Effective Field theory for the model is obtained and
shown to be a lattice double Chern-Simons theory with coupling constant k=1
(with the standard normalization). By further employing the Effective Filed
Theory methods, we show that the Mott transition that arises is of topological
nature, with vortices in an antiferromagnetic array and matter currents
characterized by a d-density wave order parameter. We also analyze the behavior
of the system upon weak coupling, and conclude that it undergoes a quantum
gas-liquid transition which belongs to the Ising universality class.Comment: 36 page
On the Current Carried by `Neutral' Quasiparticles
The current should be proportional to the momentum in a Galilean-invariant
system of particles of fixed charge-to-mass ratio, such as an electron liquid
in jellium. However, strongly-interacting electron systems can have phases
characterized by broken symmetry or fractionalization. Such phases can have
neutral excitations which can presumably carry momentum but not current. In
this paper, we show that there is no contradiction: `neutral' excitations {\em
do} carry current in a Galilean-invariant system of particles of fixed
charge-to-mass ratio. This is explicitly demonstrated in the context of spin
waves, the Bogoliubov-de Gennes quasiparticles of a superconductor, the
one-dimensional electron gas, and spin-charge separated systems in 2+1
dimensions. We discuss the implications for more realistic systems, which are
not Galilean-invariant
Berezinskii-Kosterlitz-Thouless Transition in Spin-Charge Separated Superconductor
A model for spin-charge separated superconductivity in two dimensions is
introduced where the phases of the spinon and holon order parameters couple
gauge-invariantly to a statistical gauge-field representing chiral
spin-fluctuations. The model is analyzed in the continuum limit and in the
low-temperature limit. In both cases we find that physical electronic phase
correlations show a superconducting-normal phase transition of the
Berezinskii-Kosterlitz-Thouless type, while statistical gauge-field excitations
are found to be strictly gapless. The normal-to-superconductor phase boundary
for this model is also obtained as a function of carrier density, where we find
that its shape compares favorably with that of the experimentally observed
phase diagram for the oxide superconductors.Comment: 35 pages, TeX, CSLA-P-93-
Topological Phase Diagram of a Two-Subband Electron System
We present a phase diagram for a two-dimensional electron system with two
populated subbands. Using a gated GaAs/AlGaAs single quantum well, we have
mapped out the phases of various quantum Hall states in the density-magnetic
filed plane. The experimental phase diagram shows a very different topology
from the conventional Landau fan diagram. We find regions of negative
differential Hall resistance which are interpreted as preliminary evidence of
the long sought reentrant quantum Hall transitions. We discuss the origins of
the anomalous topology and the negative differential Hall resistance in terms
of the Landau level and subband mixing.Comment: 4 pages, 4 figure
Quasiholes and fermionic zero modes of paired fractional quantum Hall states: the mechanism for nonabelian statistics
The quasihole states of several paired states, the Pfaffian, Haldane-Rezayi,
and 331 states, which under certain conditions may describe electrons at
filling factor or 5/2, are studied, analytically and numerically, in
the spherical geometry, for the Hamiltonians for which the ground states are
known exactly. We also find all the ground states (without quasiparticles) of
these systems in the toroidal geometry. In each case, a complete set of
linearly-independent functions that are energy eigenstates of zero energy is
found explicitly. For fixed positions of the quasiholes, the number of
linearly-independent states is for the Pfaffian, for the
Haldane-Rezayi state; these degeneracies are needed if these systems are to
possess nonabelian statistics, and they agree with predictions based on
conformal field theory. The dimensions of the spaces of states for each number
of quasiholes agree with numerical results for moderate system sizes. The
effects of tunneling and of the Zeeman term are discussed for the 331 and
Haldane-Rezayi states, as well as the relation to Laughlin states of electron
pairs. A model introduced by Ho, which was supposed to connect the 331 and
Pfaffian states, is found to have the same degeneracies of zero-energy states
as the 331 state, except at its Pfaffian point where it is much more highly
degenerate than either the 331 or the Pfaffian. We introduce a modification of
the model which has the degeneracies of the 331 state everywhere including the
Pfaffian point; at the latter point, tunneling reduces the degeneracies to
those of the Pfaffian state. An experimental difference is pointed out between
the Laughlin states of electron pairs and the other paired states, in the
current-voltage response when electrons tunnel into the edge. And there's more.Comment: 43 pages, requires RevTeX. The 14 figures and 2 tables are available
on request at [email protected] (include mailing address
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