4,837 research outputs found
Analysis of a diffusive effective mass model for nanowires
We propose in this paper to derive and analyze a self-consistent model
describing the diffusive transport in a nanowire. From a physical point of
view, it describes the electron transport in an ultra-scaled confined
structure, taking in account the interactions of charged particles with
phonons. The transport direction is assumed to be large compared to the wire
section and is described by a drift-diffusion equation including effective
quantities computed from a Bloch problem in the crystal lattice. The
electrostatic potential solves a Poisson equation where the particle density
couples on each energy band a two dimensional confinement density with the
monodimensional transport density given by the Boltzmann statistics. On the one
hand, we study the derivation of this Nanowire Drift-Diffusion Poisson model
from a kinetic level description. On the other hand, we present an existence
result for this model in a bounded domain
Giant spin-dependent photo-conductivity in GaAsN dilute nitride semiconductor
A theoretical and experimental study of the spin-dependent photoconductivity
in dilute Nitride GaAsN is presented. The non linear transport model we develop
here is based on the rate equations for electrons, holes, deep paramagnetic and
non paramagnetic centers both under CW and pulsed optical excitation. Emphasis
is given to the effect of the competition between paramagnetic centers and non
paramagnetic centers which allows us to reproduce the measured characteristics
of the spin-dependent recombination power dependence. Particular attention is
paid to the role of an external magnetic field in Voigt geometry. The
photoconductivity exhibits a Hanle-type curve whereas the spin polarization of
electrons shows two superimposed Lorentzian curves with different widths,
respectively related to the recombination of free and trapped electrons. The
model is capable of reproducing qualitatively and quantitatively the most
important features of photoluminescence and photocurrent experiments and is
helpful in providing insight on the various mechanisms involved in the electron
spin polarization and filtering in GaAsN semiconductors.Comment: 10 pages, 5 figure
Application of Finite-Time Stability Concepts to the Control of ATM Networks
When dealing with the stability of a system, a distinction should be made between classical Lyapunov Stability and Finite-Time Stability (FTS) (or Short-Time Stability). The concept of Lyapunov Asymptotic Stability is largely known to the control community; on the other hand a system is said to be finite-time stable if, once we fix a time-interval, its state does not exceeds some bounds during this time-interval. Often asymptotic stability is enough for practical applications, but there are some cases where large values of the state are not acceptable, for instance in the presence of saturations. In these cases, we need to check that these unacceptable values are not attained by the state; for these purposes FTS could be used. Some early results on FTS can be found in [9], [12] and [8]; more recently the concept of FTS has been revisited in the light of recent results coming from Linear Matrix Inequalities (LMIs) theory, which has allowed to find less conservative conditions guaranteeing FTS and finite time stabilization of uncertain, linear continuous-time systems (see [3]). In this note we consider the problem of applying some sufficient conditions for finite time stabilization to design the control algorithm of an ATM network described via a discrete-time system. The extended abstract is organized as follows: in Section 2 we provide a sufficient condition for finite time stabilization of a discrete time system; in Section 3 we detail the model of an ATM network; finally in Section 4 some concluding remarks and plans for the final version of the paper are given
Room temperature Giant Spin-dependent Photoconductivity in dilute nitride semiconductors
By combining optical spin injection techniques with transport spectroscopy
tools, we demonstrate a spin-photodetector allowing for the electrical
measurement and active filtering of conduction band electron spin at room
temperature in a non-magnetic GaAsN semiconductor structure. By switching the
polarization of the incident light from linear to circular, we observe a Giant
Spin-dependent Photoconductivity (GSP) reaching up to 40 % without the need of
an external magnetic field. We show that the GSP is due to a very efficient
spin filtering effect of conduction band electrons on Nitrogen-induced Ga
self-interstitial deep paramagnetic centers.Comment: 4 pages, 3 figure
An effective mass theorem for the bidimensional electron gas in a strong magnetic field
We study the limiting behavior of a singularly perturbed
Schr\"odinger-Poisson system describing a 3-dimensional electron gas strongly
confined in the vicinity of a plane and subject to a strong uniform
magnetic field in the plane of the gas. The coupled effects of the confinement
and of the magnetic field induce fast oscillations in time that need to be
averaged out. We obtain at the limit a system of 2-dimensional Schr\"odinger
equations in the plane , coupled through an effective selfconsistent
electrical potential. In the direction perpendicular to the magnetic field, the
electron mass is modified by the field, as the result of an averaging of the
cyclotron motion. The main tools of the analysis are the adaptation of the
second order long-time averaging theory of ODEs to our PDEs context, and the
use of a Sobolev scale adapted to the confinement operator
H? Gain Scheduling for Discrete-Time Systems with Control Delays and Time-Varying Parameters: a BMI Approach
In this paper, the problem of gain scheduling for time-varying systems with time delays is investigated. By using a memory at the feedback loop, a discrete gain scheduled controller which minimizes an upper bound to the ,Hscrinfin performance of the closed loop system is determined. The design conditions, expressed in terms of bilinear matrix inequalities, are obtained from the Finsler\u27s Lemma combined with the Lyapunov theory. The extra variables introduced by the Finsler\u27s Lemma represent an alternative way in the search of better system behavior. The time-varying uncertainties are modeled using polytopic domains. The controller is obtained by the solution of an optimization problem formulated only in terms of the vertices of the polytope. No grids in the parametric space are used. Numerical examples illustrate the efficiency of the proposed approach
H? filtering of time-varying systems with bounded rates of variation
In this paper, the problem of robust filter design for time-varying discrete-time polytopic systems with bounded rates of variation is investigated. The design conditions are obtained by using a parameter-dependent Lyapunov function and the Finsler\u27s Lemma. A robust filter, that minimizes an upper bound to the H? performance of the estimation error, is obtained as the solution of an optimization problem. A more precise geometric representation of the parameter time variation was used in order to obtain less conservative design conditions. Robust filters for time-invariant, as well as arbitrarily time-varying, polytopic systems can be obtained as a particular case of the proposed method. Numerical examples illustrate the results
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