166 research outputs found
Spin Hall Effect of Excitons
Spin Hall effect for excitons in alkali halides and in Cu_2O is investigated
theoretically. In both systems, the spin Hall effect results from the Berry
curvature in k space, which becomes nonzero due to lifting of degeneracies of
the exciton states by exchange coupling. The trajectory of the excitons can be
directly seen as spatial dependence of the circularly polarized light emitted
from the excitons. It enables us to observe the spin Hall effect directly in
the real-space time.Comment: 5 pages, 2 figure
Efficacy of a GPGPU-Acceleration to Inundation Flow Simulation in Tonle Sap Lake in Cambodia
A new 2D numerical model is developed for a rapid computation of the seasonal inundation phenomena in Tonle Sap Lake in Cambodia. In order to overcome a huge computational cost for a prolonged analysis over an extensive area, the General-Purpose computing on Graphics Processing Units (GPGPU) technology is applied to the model. The developed model is applied to a solution of seasonal inundation process for the 154 days in 2002. Calculated result is compared with observational data and satellite remote sensing. It is found that the developed model seems to successfully reproduce reasonable progress/regress of inundation. A breakdown of the total elapsed time for the numerical analysis is considered in a detail. It is found that the GPGPU technology can accelerate the solution more than one hundred times faster by employing a simple rectangular mesh and coding to reduce a memory access overhead
GâCSFâdependent neutrophil differentiation requires downregulation of MAPK activities through the Gab2 signaling pathway
Granulocyte colonyâstimulating factor (GâCSF) stimulation of myeloid cells induced tyrosineâphosphorylation of cellular proteins. One of the tyrosineâphosphorylated proteins was found to be a scaffold protein, Grb2âassociated binding protein 2 (Gab2). Another member of Gab family protein, Gab3, was exogenously overexpressed in neutrophil progenitor cells to make the Gab3 protein to compete with the endogenous Gab2 for the GâCSFâdependent signaling. In Gab3âoverexpressed cells, the level of tyrosine phosphorylation of endogenous Gab2 by GâCSF stimulation was markedly downregulated, while the phosphorylation of Gab3 was significantly enhanced. The Gab3âoverexpressed cells continuously proliferated in the medium containing GâCSF and lost the ability to differentiate to the mature neutrophil, characterized by the lobulated nucleus. The GâCSF stimulationâdependent tyrosine phosphorylation of Gab3, the association of SHP2 to Gab3 and the following mitogenâactivated protein kinase (MAPK) activation were prolonged in the Gab3âoverexpressed cells, compared to the parental cells, where the binding of SHP2 to Gab2 protein and thereby the activation of MAPK were not sustained after GâCSF stimulation. Inhibition of MAPK by pharmaceutical inhibitor restored the Gab3âoverexpressed cells to the ability to differentiate to mature neutrophil. Therefore, GâCSFâdependent Gab2 phosphorylation and following its downregulation led the shortâterm MAPK activation. The downregulation of MAPK after transient Gab2 phosphorylation was necessary for the consequent neutrophil differentiation induced by GâCSF stimulation
Spin-Hall effect: Back to the Beginning on a Higher Level
The phenomena of the spin-Hall effect, initially proposed over three decades
ago in the context of asymmetric Mott skew scattering, was revived recently by
the proposal of a possible intrinsic spin-Hall effect originating from a
strongly spin-orbit coupled band structure. This new proposal has generated an
extensive debate and controversy over the past two years. The purpose of this
workshop, held at the Asian Pacific Center for Theoretical Physics, was to
bring together many of the leading groups in this field to resolve such issues
and identify future challenges. We offer this short summary to clarify the now
settled issues on some of the more controversial aspects of the debate and help
refocus the research efforts in new and important avenues.Comment: 4 pages, Summary of the APCTP Workshop on the Spin-Hall Effect and
Related Issue
Effective continuous model for surface states and thin films of three dimensional topological insulators
Two-dimensional effective continuous models are derived for the surface
states and thin films of the three-dimensional topological insulator (3DTI).
Starting from an effective model for 3DTI based on the first principles
calculation [Zhang \emph{et al}, Nat. Phys. 5, 438 (2009)], we present
solutions for both the surface states in a semi-infinite boundary condition and
in the thin film with finite thickness. An effective continuous model was
derived for surface states and the thin film 3DTI. The coupling between
opposite topological surfaces and structure inversion asymmetry (SIA) give rise
to gapped Dirac hyperbolas with Rashba-like splittings in energy spectrum.
Besides, the SIA leads to asymmetric distributions of wavefunctions along the
film growth direction, making some branches in the energy spectra much harder
than others to be probed by light. These features agree well with the recent
angle-resolved photoemission spectra of BiSe films grown on SiC
substrate [Zhang et al, arXiv: 0911.3706]. More importantly, we use the
effective model to fit the experimental data and determine the model
parameters. The result indicates that the thin film BiSe lies in
quantum spin Hall region based on the calculation of the Chern number and the
invariant. In addition, strong SIA always intends to destroy the
quantum spin Hall state.Comment: 12 pages, 7 figures, references are update
Novel Charge Ordering in the Trimer Iridium Oxide BaIrO3
We have prepared polycrystalline samples of the trimer Ir oxide BaIrO3 with
face-shared Ir3O12 trimers, and have investigated the origin of the phase
transition at 182 K by measuring resistivity, thermopower, magnetization and
synchrotron x-ray diffraction. We propose a possible electronic model and
transition mechanism, starting from a localized electron picture on the basis
of the Rietveld refinement. Within this model, BaIrO3 can be basically regarded
as a Mott insulator, when the Ir3O12 trimer is identified to one pseudo-atom or
one lattice site. The transition can be viewed as a transition from the Mott
insulator phase to a kind of charge ordered insulator phase.Comment: 8 pages 5 figures, Crystals (in press
Metataxonomic Analysis of the Uterine Microbiota Associated with Low Fertility in Dairy Cows Using Endometrial Tissues Prior to First Artificial Insemination
The deterioration in reproductive performance in association with low fertility leads to significant economic losses on dairy farms. The uterine microbiota has begun to attract attention as a possible cause of unexplained low fertility. We analyzed the uterine microbiota associated with fertility by 16S rRNA gene amplicon sequencing in dairy cows. First, the alpha (Chao1 and Shannon) and beta (unweighted and weighted UniFrac) diversities of 69 cows at four dairy farms that had passed the voluntary waiting period before the first artificial insemination (AI) were analyzed with respect to factors including farm, housing style, feeding management, parity, and AI frequency to conception. Significant differences were observed in the farm, housing style, and feeding management, except parity and AI frequency to conception. The other diversity metrics did not show significant differences in the tested factors. Similar results were obtained for the predicted functional profile. Next, the microbial diversity analysis of 31 cows at a single farm using weighted UniFrac distance matrices revealed a correlation with AI frequency to conception but not with parity. In correlation with AI frequency to conception, the predicted function profile appeared to be slightly modified and a single bacterial taxon, Arcobacter, was detected. The bacterial associations related to fertility were estimated. Considering these, the uterine microbiota in dairy cows can be varied depending on the farm management practices and may become one of the measures for low fertility
Role of Heat Shock Protein 70 in Induction of Stress Fiber Formation in Rat Arterial Endothelial Cells in Response to Stretch Stress
We investigated the mechanism by which endothelial cells (ECs) resist various forms of physical stress using an experimental system consisting of rat arterial EC sheets. Formation of actin stress fibers (SFs) and expression of endothelial heat-shock stress proteins (HSPs) in response to mechanical stretch stress were assessed by immunofluorescence microscopy. Stretch stimulation increased expression of HSPs 25 and 70, but not that of HSP 90. Treatment with SB203580, a p38 MAP kinase inhibitor that acts upstream of the HSP 25 activation cascade, or with geldanamycin, an inhibitor of HSP 90, had no effect on the SF formation response to mechanical stretch stress. In contrast, treatment with quercetin, an HSP 70 inhibitor, inhibited both upregulation of endothelial HSP 70 and formation of SFs in response to tensile stress. In addition, treatment of stretched ECs with cytochalasin D, which disrupts SF formation, did not adversely affect stretch-induced upregulation of endothelial HSP 70. Our data suggest that endothelial HSP 70 plays an important role in inducing SF formation in response to tensile stress
Theory of orbital state and spin interactions in ferromagnetic titanates
A spin-orbital superexchange Hamiltonian in a Mott insulator with
orbital degeneracy is investigated. More specifically, we focus on a spin
ferromagnetic state of the model and study a collective behavior of orbital
angular momentum. Orbital order in the model occurs in a nontrivial way -- it
is stabilized exclusively by quantum effects through the order-from-disorder
mechanism. Several energetically equivalent orbital orderings are identified.
Some of them are specified by a quadrupole ordering and have no unquenched
angular momentum at low energy. Other states correspond to a noncollinear
ordering of the orbital angular momentum and show the magnetic Bragg peaks at
specific positions. Order parameters are unusually small because of strong
quantum fluctuations. Orbital contribution to the resonant x-ray scattering is
discussed. The dynamical magnetic structure factor in different ordered states
is calculated. Predictions made should help to observe elementary excitations
of orbitals and also to identify the type of the orbital order in ferromagnetic
titanates. Including further a relativistic spin-orbital coupling, we derive an
effective low-energy spin Hamiltonian and calculate a spin-wave spectrum, which
is in good agreement with recent experimental observations in YTiO.Comment: 25 pages, 17 figure
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