148 research outputs found
Current-voltage characteristics of semiconductor/ferromagnet junctions in the spin blockade regime
It was recently predicted [Phys. Rev. B 75, 193301 (2007)] that spin blockade
may develop at nonmagnetic semiconductor/perfect ferromagnet junctions when the
electron flow is directed from the semiconductor into the ferromagnet. Here we
consider current-voltage characteristics of such junctions. By taking into
account the contact resistance, we demonstrate a current stabilization effect:
by increasing the applied voltage the current density through the junction
saturates at a specific value. The transient behavior of the current density is
also investigated
Spin memristive systems
Recently, in addition to the well-known resistor, capacitor and inductor, a
fourth passive circuit element, named memristor, has been identified following
theoretical predictions. The model example used in such case consisted in a
nanoscale system with coupled ionic and electronic transport. Here, we discuss
a system whose memristive behaviour is based entirely on the electron spin
degree of freedom which allows for a more convenient control than the ionic
transport in nanostructures. An analysis of time-dependent spin transport at a
semiconductor/ferromagnet junction provides a direct evidence of memristive
behaviour. Our scheme is fundamentally different from previously discussed
schemes of memristive devices and broadens the possible range of applications
of semiconductor spintronics
Hall Voltage with the Spin Hall Effect
The spin Hall effect does not generally result in a charge Hall voltage. We
predict that in systems with inhomogeneous electron density in the direction
perpendicular to main current flow, the spin Hall effect is instead accompanied
by a Hall voltage. Unlike the ordinary Hall effect, we find that this Hall
voltage is quadratic in the longitudinal electric field for a wide range of
parameters accessible experimentally. We also predict spin accumulation in the
bulk and sharp peaks of spin-Hall induced charge accumulation near the edges.
Our results can be readily tested experimentally, and would allow the
electrical measurement of the spin Hall effect in non-magnetic systems and
without injection of spin-polarized electrons
New combined PIC-MCC approach for fast simulation of a radio frequency discharge at low gas pressure
A new combined PIC-MCC approach is developed for accurate and fast simulation
of a radio frequency discharge at low gas pressure and high density of plasma.
Test calculations of transition between different modes of electron heating in
a ccrf discharge in helium and argon show a good agreement with experimental
data.
We demonstrate high efficiency of the combined PIC-MCC algorithm, especially
for the collisionless regime of electron heating.Comment: 6 paged, 8 figure
Uncertainty quantification for kinetic models in socio-economic and life sciences
Kinetic equations play a major rule in modeling large systems of interacting
particles. Recently the legacy of classical kinetic theory found novel
applications in socio-economic and life sciences, where processes characterized
by large groups of agents exhibit spontaneous emergence of social structures.
Well-known examples are the formation of clusters in opinion dynamics, the
appearance of inequalities in wealth distributions, flocking and milling
behaviors in swarming models, synchronization phenomena in biological systems
and lane formation in pedestrian traffic. The construction of kinetic models
describing the above processes, however, has to face the difficulty of the lack
of fundamental principles since physical forces are replaced by empirical
social forces. These empirical forces are typically constructed with the aim to
reproduce qualitatively the observed system behaviors, like the emergence of
social structures, and are at best known in terms of statistical information of
the modeling parameters. For this reason the presence of random inputs
characterizing the parameters uncertainty should be considered as an essential
feature in the modeling process. In this survey we introduce several examples
of such kinetic models, that are mathematically described by nonlinear Vlasov
and Fokker--Planck equations, and present different numerical approaches for
uncertainty quantification which preserve the main features of the kinetic
solution.Comment: To appear in "Uncertainty Quantification for Hyperbolic and Kinetic
Equations
Experimental validation of a method for removing the capacitive leakage artifact from electrical bioimpedance spectroscopy measurements
LHC1: a semiconductor pixel detector readout chip with internal, tunable delay providing a binary pattern of selected events
The Omega3/LHCl pixel detector readout chip comprises a matrix of 128 X 16 readout cells of 50 mu m X 500 mu m and peripheral functions with 4 distinct modes of initialization and operation, together more than 800 000 transistors. Each cell contains a complete chain of amplifier, discriminator with adjustable threshold and fast-OR output, a globally adjustable delay with local fine-tuning, coincidence logic and memory. Every cell can be individually addressed for electrical test and masking, First results have been obtained from electrical tests of a chip without detector as well as from source measurements, The electronic noise without detector is similar to 100 e(-) rms. The lowest threshold setting is close to 2000 e(-) and non-uniformity has been measured to be better than 450 e(-) rms at 5000 e(-) threshold. A timewalk of < 10 ns and a precision of < 6 ns rms on a delay of 2 mu s have been measured. The results may be improved by further optimization
Prospects of IMPATT devices based on wide bandgap semiconductors as potential terahertz sources
The Negative Association of Obesity with Subjective Well-Being: Is it All About Health?
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