13,954 research outputs found
Non-Commutative Tools for Topological Insulators
This paper reviews several analytic tools for the field of topological
insulators, developed with the aid of non-commutative calculus and geometry.
The set of tools includes bulk topological invariants defined directly in the
thermodynamic limit and in the presence of disorder, whose robustness is shown
to have non-trivial physical consequences for the bulk states. The set of tools
also includes a general relation between the current of an observable and its
edge index, relation that can be used to investigate the robustness of the edge
states against disorder. The paper focuses on the motivations behind creating
such tools and on how to use them.Comment: Final version (some arguments were corrected
Statistical Analysis of Spectral Line Candidates in Gamma-Ray Burst GRB870303
The Ginga data for the gamma-ray burst GRB870303 exhibit low-energy dips in
two temporally distinct spectra, denoted S1 and S2. S1, spanning 4 s, exhibits
a single line candidate at ~ 20 keV, while S2, spanning 9 s, exhibits
apparently harmonically spaced line candidates at ~ 20 and 40 keV. We evaluate
the statistical evidence for these lines, using phenomenological continuum and
line models which in their details are independent of the distance scale to
gamma-ray bursts. We employ the methodologies based on both frequentist and
Bayesian statistical inference that we develop in Freeman et al. (1999b). These
methodologies utilize the information present in the data to select the
simplest model that adequately describes the data from among a wide range of
continuum and continuum-plus-line(s) models. This ensures that the chosen model
does not include free parameters that the data deem unnecessary and that would
act to reduce the frequentist significance and Bayesian odds of the
continuum-plus-line(s) model. We calculate the significance of the
continuum-plus-line(s) models using the Chi-Square Maximum Likelihood Ratio
test. We describe a parametrization of the exponentiated Gaussian absorption
line shape that makes the probability surface in parameter space
better-behaved, allowing us to estimate analytically the Bayesian odds. The
significance of the continuum-plus-line models requested by the S1 and S2 data
are 3.6 x 10^-5 and 1.7 x 10^-4 respectively, with the odds favoring them being
114:1 and 7:1. We also apply our methodology to the combined (S1+S2) data. The
significance of the continuum-plus-lines model requested by the combined data
is 4.2 x 10^-8, with the odds favoring it being 40,300:1.Comment: LaTeX2e (aastex.cls included); 41 pages text, 10 figures (on 11
pages); accepted by ApJ (to be published 1 Nov 1999, v. 525
SL(2,C) Chern-Simons theory and the asymptotic behavior of the colored Jones polynomial
We clarify and refine the relation between the asymptotic behavior of the
colored Jones polynomial and Chern-Simons gauge theory with complex gauge group
SL(2,C). The precise comparison requires a careful understanding of some
delicate issues, such as normalization of the colored Jones polynomial and the
choice of polarization in Chern-Simons theory. Addressing these issues allows
us to go beyond the volume conjecture and to verify some predictions for the
behavior of the subleading terms in the asymptotic expansion of the colored
Jones polynomial.Comment: 15 pages, 7 figure
Effect of Electrolyte Balance in Low-Protein Diets on Broiler Performance and Tibial Dyschondroplasia Incidence
A proper dietary electrolyte balance (DEB) is essential to ensure an optimum acid-base equilibrium and broiler performance. In low-CP diets, this balance can be affected by reduction of soybean meal and inclusion of high levels of synthetic amino acids. Although, some studies have related low-protein diets supplemented with amino acids and DEB, these relations are not well explained, because some research demonstrates confusion about the deficiency and balance of nutrients. The objective of these experiments was to evaluate the DEB effects of diets with low levels of protein supplemented with amino acids on broiler performance and bone development. Results indicated that DEB and CP content influenced broiler chick performance in the starter and growing periods. There was no significant effect due to the interaction between DEB and CP content for tibial dyschondroplasia incidence (TD) or in bone breaking resistance during the growing period of either experiment. The incidence of TD was reduced with 253 mEq/kg DEB in the starter period
SU(2) Non-Abelian Holonomy and Dissipationless Spin Current in Semiconductors
Following our previous work [S. Murakami, N. Nagaosa, S. C. Zhang, Science
301, 1348 (2003)] on the dissipationless quantum spin current, we present an
exact quantum mechanical calculation of this novel effect based on the linear
response theory and the Kubo formula. We show that it is possibxle to define an
exactly conserved spin current, even in the presence of the spin-orbit coupling
in the Luttinger Hamiltonian of p-type semiconductors. The light- and the
heavy-hole bands form two Kramers doublets, and an SU(2) non-abelian gauge
field acts naturally on each of the doublets. This quantum holonomy gives rise
to a monopole structure in momentum space, whose curvature tensor directly
leads to the novel dissipationless spin Hall effect, i.e., a transverse spin
current is generated by an electric field. The result obtained in the current
work gives a quantum correction to the spin current obtained in the previous
semiclassical approximation.Comment: 14 pages, 2 figures, added some discussions, to appear in Phys. Rev.
The nucleoside analog GS-441524 strongly inhibits feline infectious peritonitis (FIP) virus in tissue culture and experimental cat infection studies.
Feline infectious peritonitis (FIP) is a common and highly lethal coronavirus disease of domestic cats. Recent studies of diseases caused by several RNA viruses in people and other species indicate that antiviral therapy may be effective against FIP in cats. The small molecule nucleoside analog GS-441524 is a molecular precursor to a pharmacologically active nucleoside triphosphate molecule. These analogs act as an alternative substrate and RNA-chain terminator of viral RNA dependent RNA polymerase. We determined that GS-441524 was non-toxic in feline cells at concentrations as high as 100 uM and effectively inhibited FIPV replication in cultured CRFK cells and in naturally infected feline peritoneal macrophages at concentrations as low as 1 uM. We determined the pharmacokinetics of GS-441524 in cats in vivo and established a dosage that would sustain effective blood levels for 24 h. In an experimental FIPV infection of cats, GS-441524 treatment caused a rapid reversal of disease signs and return to normality with as little as two weeks of treatment in 10/10 cats and with no apparent toxicity
Spin-torque efficiency enhanced by Rashba spin splitting in three dimensions
We examine a spin torque induced by the Rashba spin-orbit coupling in three
dimensions within the Boltzmann transport theory. We analytically calculate the
spin torque and show how its behavior is related with the spin topology in the
Fermi surfaces by studying the Fermi-energy dependence of the spin torque.
Moreover we discuss the spin-torque efficiency which is the spin torque divided
by the applied electric current in association with the current-induced
magnetization reversal. It is found that high spin-torque efficiency is
achieved when the Fermi energy lies on only the lower band and there exists an
optimal value for the Rashba parameter, where the spin-torque efficiency
becomes maximum.Comment: 7 pages, 5 figure
Spin-orbit lateral superlattices: energy bands and spin polarization in 2DEG
The Bloch spinors, energy spectrum and spin density in energy bands are
studied for the two-dimensional electron gas (2DEG) with Rashba spin-orbit (SO)
interaction subject to one-dimensional (1D) periodic electrostatic potential of
a lateral superlattice. The space symmetry of the Bloch spinors with spin
parity is studied. It is shown that the Bloch spinors at fixed quasimomentum
describe the standing spin waves with the wavelength equal to the superlattice
period. The spin projections in these states have the components both parallel
and transverse to the 2DEG plane. The anticrossing of the energy dispersion
curves due to the interplay between the SO and periodic terms is observed,
leading to the spin flip. The relation between the spin parity and the
interband optical selection rules is discussed, and the effect of magnetization
of the SO superlattice in the presence of external electric field is predicted.Comment: 6 pages, 5 figures, reported at the International Conferences
"Nanophysics and Nanoelectronics" (Nizhny Novgorod, Russia, March 2006) and
"Nanostructures: Physics and Technology" (St Petersburg, Russia, June 2006
1D Modeling for Temperature-Dependent Upflow in the Dimming Region Observed by Hinode/EIS
We have previously found a temperature-dependent upflow in the dimming region
following a coronal mass ejection (CME) observed by the {\it Hinode} EUV
Imaging Spectrometer (EIS). In this paper, we reanalyzed the observations along
with previous work on this event, and provided boundary conditions for
modeling. We found that the intensity in the dimming region dramatically drops
within 30 minutes from the flare onset, and the dimming region reaches the
equilibrium stage after 1 hour later. The temperature-dependent upflows
were observed during the equilibrium stage by EIS. The cross sectional area of
the fluxtube in the dimming region does not appear to expand significantly.
From the observational constraints, we reconstructed the temperature-dependent
upflow by using a new method which considers the mass and momentum conservation
law, and demonstrated the height variation of plasma conditions in the dimming
region. We found that a super radial expansion of the cross sectional area is
required to satisfy the mass conservation and momentum equations. There is a
steep temperature and velocity gradient of around 7 Mm from the solar surface.
This result may suggest that the strong heating occurred above 7 Mm from the
solar surface in the dimming region. We also showed that the ionization
equilibrium assumption in the dimming region is violated especially in the
higher temperature range.Comment: accepted for publication in The Astrophysical Journa
Berry phase in Magnetic Superconductors
In magnetic systems, electronic bands often acquire nontrivial topological
structure characterized by gauge flux distribution in momentum (k)-space. It
sometimes follows that the phase of the wavefunctions cannot be defined
uniquely over the whole Brillouin zone. In this Letter we develop a theory of
superconductivity in the presence of this gauge flux both in two- and
three-dimensional systems. It is found that the superconducting gap has "nodes"
as a function of k where the Fermi surface is penetrated by a gauge string.Comment: 4 pages, 3 figures, substantial changes in the presentation, to be
published in Phys. Rev. Let
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