95 research outputs found
Polarization-sensitive absorption of THz radiation by interacting electrons in chirally stacked multilayer graphene
We show that opacity of a clean multilayer graphene flake depends on the
helicity of the circular polarized electromagnetic radiation. The effect can be
understood in terms of the pseudospin selection rules for the interband optical
transitions in the presence of exchange electron-electron interactions which
alter the pseudospin texture in momentum space. The interactions described
within a semi-analytical Hartree--Fock approach lead to the formation of the
topologically different broken--symmetry states characterized by Chern numbers
and zero-field anomalous Hall conductivities.Comment: 6 pages, final versio
The research of qualitative indicators of gas pipelines during the operation
The operation of gas pipelines is a complex of technical measures, aimed at preservation of the main stock of gas pipeline transportation facilities. The purpose of these measures is to maintain and to restore the initial operational capabilities of gas pipelines, in general and in particular areas. The line section of gas pipelines has the largest size and cost. Naturally determined process of changing the quality of gas pipelines during the operation is accompanied by the accumulation and development of damages, failures; this determines the objective need to restore the quality of operation. The practical running of the line section of gas pipelines is characterized by a certain flow of failures; therefore it is necessary to ensure the required level of reliability of the gas pipeline during the entire period of operation. The quality control study of the inter-settlement gas pipeline section was conducted, and graphs of dependence of gas pipeline quality parameters on time were presented in the work.Keywords: line section of the gas pipeline, technological state, failures in operation, gas pipeline operation, control and quality parameters of the gas pipeline
Curved One-Dimensional Wire as a Spin Rotator
We propose a semiconductor structure that can rotate the electron spin
without using ferromagnetic contacts, tunneling barriers, external radiation
etc. The structure consists of a strongly curved one-dimensional ballistic wire
with intrinsic spin-orbit interactions of Rashba type. Our calculations and
analytical formulae show that the proposed device can redistribute the current
densities between the two spin-split modes without backscattering and, thus,
serve as a reflectionless and high-speed spin switcher. Using parameters
relevant for InAs we investigate the projection of current density spin
polarization on the spin-quantization axis as a function of the Rashba
constant, external magnetic field, and radius of the wire's curvature.Comment: 10 pages, 6 figures; replaced with considerably extended versio
The electronic properties of bilayer graphene
We review the electronic properties of bilayer graphene, beginning with a
description of the tight-binding model of bilayer graphene and the derivation
of the effective Hamiltonian describing massive chiral quasiparticles in two
parabolic bands at low energy. We take into account five tight-binding
parameters of the Slonczewski-Weiss-McClure model of bulk graphite plus intra-
and interlayer asymmetry between atomic sites which induce band gaps in the
low-energy spectrum. The Hartree model of screening and band-gap opening due to
interlayer asymmetry in the presence of external gates is presented. The
tight-binding model is used to describe optical and transport properties
including the integer quantum Hall effect, and we also discuss orbital
magnetism, phonons and the influence of strain on electronic properties. We
conclude with an overview of electronic interaction effects.Comment: review, 31 pages, 15 figure
Observation of coherent transients in ultrashort chirped excitation of an undamped two-level system
The effects of Coherent excitation of a two level system with a linearly
chirped pulse are studied theoretically and experimentally (in Rb (5s - 5p)) in
the low field regime. The Coherent Transients are measured directly on the
excited state population on an ultrashort time scale. A sharp step corresponds
to the passage through resonance. It is followed by oscillations resulting from
interferences between off-resonant and resonant contributions. We finally show
the equivalence between this experiment and Fresnel diffraction by a sharp
edge.Comment: 4 pages, 4 figures, to appear in PR
Exact eigenstate analysis of finite-frequency conductivity in graphene
We employ the exact eigenstate basis formalism to study electrical
conductivity in graphene, in the presence of short-range diagonal disorder and
inter-valley scattering. We find that for disorder strength, 5, the
density of states is flat. We, then, make connection, using the MRG approach,
with the work of Abrahams \textit{et al.} and find a very good agreement for
disorder strength, = 5. For low disorder strength, = 2, we plot the
energy-resolved current matrix elements squared for different locations of the
Fermi energy from the band centre. We find that the states close to the band
centre are more extended and falls of nearly as as we move away
from the band centre. Further studies of current matrix elements versus
disorder strength suggests a cross-over from weakly localized to a very weakly
localized system. We calculate conductivity using Kubo Greenwood formula and
show that, for low disorder strength, conductivity is in a good qualitative
agreement with the experiments, even for the on-site disorder. The intensity
plots of the eigenstates also reveal clear signatures of puddle formation for
very small carrier concentration. We also make comparison with square lattice
and find that graphene is more easily localized when subject to disorder.Comment: 11 pages,15 figure
Detecção de emissão espontânea de luz em ensaios de colimetria aplicados ao monitoramento de efluentes sanitários
Mechanisms of HIV-associated lymphocyte apoptosis: 2010
The inevitable decline of CD4T cells in untreated infection with the Human immunodeficiency virus (HIV) is due in large part to apoptosis, one type of programmed cell death. There is accumulating evidence that the accelerated apoptosis of CD4T cells in HIV infection is multifactorial, with direct viral cytotoxicity, signaling events triggered by viral proteins and aberrant immune activation adding to normal immune defense mechanisms to contribute to this phenomenon. Current antiviral treatment strategies generally lead to reduced apoptosis, but this approach may come at the cost of preserving latent viral reservoirs. It is the purpose of this review to provide an update on the current understanding of the role and mechanisms of accelerated apoptosis of T cells in the immunopathogenesis of HIV infection, and to highlight potential ways in which this seemingly deleterious process could be harnessed to not just control, but treat HIV infection
CCR5 interaction with HIV-1 Env contributes to Env-induced depletion of CD4 T cells in vitro and in vivo
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