2,005 research outputs found
Nuclear spin pumping and electron spin susceptibilities
In this work we present a new formalism to evaluate the nuclear spin dynamics
driven by hyperfine interaction with non-equilibrium electron spins. To
describe the dynamics up to second order in the hyperfine coupling, it suffices
to evaluate the susceptibility and fluctuations of the electron spin. Our
approach does not rely on a separation of electronic energy scales or the
specific choice of electronic basis states, thereby overcoming practical
problems which may arise in certain limits when using a more traditional
formalism based on rate equations.Comment: 9 pages, 2 figure
Tunneling of Bloch electrons through vacuum barrier
Tunneling of Bloch electrons through a vacuum barrier introduces new physical
effects in comparison with the textbook case of free (plane wave) electrons.
For the latter, the exponential decay rate in the vacuum is minimal for
electrons with the parallel component of momentum , and
the prefactor is defined by the electron momentum component in the normal to
the surface direction. However, the decay rate of Bloch electrons may be
minimal at an arbitrary (``hot spots''), and the prefactor
is determined by the electron's group velocity, rather than by its
quasimomentum.Comment: 4 pages, no fig
Effect of hydrogen on deformation structure and properties of CMSX-2 nickel-base single-crystal superalloy
Material used in this study was a heat of the alloy CMSX-2. This nickel-based superalloy was provided in the form of oriented single crystals, solutionized for 3 hrs at 1315 C. It was then usually heat treated as follows: 1050 C/16h/air cool + 850 C/48h/air cool. The resulting microstructure is dominated by cuboidal, ordered gamma precipitates with a volume fraction of about 75% and an average size of 0.5 microns. In brief, the most compelling hydrogen induced-changes in deformation structure are: (1) enhanced dislocation accumulation in the gamma matrix; and (2) more extensive cross-slip of superdislocations in the gamma precipitates. The enhanced dislocation density in gamma acts to decrease the mean free path of a superdislocation, while easier cross slip hinders superdislocation movement by providing pinning points in the form of sessile jobs. Both processes contribute to the increase of flow stress and the notable work hardening that occurs prior to fracture
Tuning of the Gap in a Laughlin-Bychkov-Rashba Incompressible Liquid
We report on our investigation of the influence of Bychkov-Rashba spin-orbit
interaction (SOI) on the incompressible Laughlin state. We find that
experimentally obtainable values of the spin-orbit coupling strength can induce
as much as a 25% increase in the quasiparticle-quasihole gap Eg at low magnetic
fields in InAs, thereby increasing the stability of the liquid state. The
SOI-modulated enhancement of Eg is also significant for filling factors 1/5 and
1/7, where the FQH state is usually weak. This raises the intriguing
possibility of tuning, via the SO coupling strength, the liquid to solid
transition to much lower densities.Comment: 4 pages, 3 figure
Spin injection and electric field effect in degenerate semiconductors
We analyze spin-transport in semiconductors in the regime characterized by
(intermediate to degenerate), where is the Fermi
temperature. Such a regime is of great importance since it includes the lightly
doped semiconductor structures used in most experiments; we demonstrate that,
at the same time, it corresponds to the regime in which carrier-carrier
interactions assume a relevant role. Starting from a general formulation of the
drift-diffusion equations, which includes many-body correlation effects, we
perform detailed calculations of the spin injection characteristics of various
heterostructures, and analyze the combined effects of carrier density
variation, applied electric field and Coulomb interaction. We show the
existence of a degenerate regime, peculiar to semiconductors, which strongly
differs, as spin-transport is concerned, from the degenerate regime of metals.Comment: Version accepted for publication in Phys. Rev.
Effect of antimony on the eutectic reaction of heavy section spheroidal graphite castings
There is a strong demand for heavy section castings made of spheroidal graphite with a fully ferritic matrix, e.g. for manufacturing hubs for windmills. Such castings with slow solidification process are prone to graphite degeneration that leads to a dramatic decrease of the mechanical properties of the cast parts. Chunky graphite is certainly the most difficult case of graphite degeneracy, though it has long been known that the limited and controlled addition of antimony may help eliminate it. The drawback of this remedy is that too large Sb additions lead to other forms of degenerate graphite, and also that antimony is a pearlite promoter. As part of an investigation aimed at mastering low level additions to cast iron melts before casting, solidification of large blocks with or without Sb added was followed by thermal analysis. Comparison of the cooling curves and of the microstructures of these different castings gives suggestions to understand the controlling nucleation and growth mechanisms for chunky graphite cells
T-cell modulation for the treatment of chronic plaque psoriasis with efalizumab (Raptiva (TM)): Mechanisms of action
Psoriasis is a chronic, incurable, auto-immune disorder with cutaneous manifestations. New evidence on the central role of the immune system in the pathogenesis of psoriasis increasingly provides insight into pathogenic steps that can be modulated to provide disease control. Numerous biological therapies are in various stages of clinical development, with expectation of providing enhanced safety and efficacy over currently available psoriasis therapies. Efalizumab, a recombinant humanized monoclonal IgG1 antibody, is a novel targeted T-cell modulator that inhibits multiple steps in the immune cascade that result in the production and maintenance of psoriatic plaques, including initial T-cell activation and T-cell trafficking into sites of inflammation, including psoriatic skin, with subsequent reactivation in these sites. This article reviews the pharmacodynamic, pharmacokinetic and clinical effects observed during phase I, II and III efalizumab trials in patients with moderate to severe chronic plaque psoriasis. Copyright (C) 2004 S. Karger AG, Basel
Classical properties of low-dimensional conductors: Giant capacitance and non-Ohmic potential drop
Electrical field arising around an inhomogeneous conductor when an electrical
current passes through it is not screened, as distinct from 3D conductors, in
low-dimensional conductors. As a result, the electrical field depends on the
global distribution of the conductivity sigma(x) rather than on the local value
of it, inhomogeneities of sigma(x) produce giant capacitances C(omega) that
show frequency dependence at relatively low omega, and electrical fields
develop in vast regions around the inhomogeneities of sigma(x). A theory of
these phenomena is presented for 2D conductors.Comment: 5 pages, two-column REVTeX, to be published in Physical Review
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