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

An improved transient algorithm for the simulation of a resonant tunneling diode

40 pagesA fast algorithm is proposed for the simulation of the transient evolution of a resonant tunneling diode by a multiscale approach. The problem is modeled by the time-dependent Schrödinger-Poisson system. By decomposing the wave function into a non resonant part and a resonant part, the fast algorithm is designed by combining standard finite difference method for the Schrödinger-Poisson equation with proper time-dependent and/or nonlinear transmission boundary condition. In addition, with a suitable interpolation of the non resonant one, an accurate and fast algorithm is presented for the computation of the resonant part via the projection method. With this two scale decomposition, the new numerical method can save the computational time significantly

Anomalous photon thermal Hall effect

We predict an anomalous thermal Hall effect (ATHE) mediated by photons in networks of Weyl semi-metals. Contrary to the photon thermal Hall effect in magneto-optical systems which requires the application of an external magnetic field the ATHE in a Weyl semi-metals network is an intrinsic property of these systems. Since the Weyl semi-metals can exhibit a strong nonreciprocal response in the infrared over a broad spectral range the magnitude of thermal Hall flux in these systems can be relatively large compared to the primary flux. This ATHE paves the way for a directional control of heat flux by localy tuning the magnitude of temperature field without changing the direction of temperature gradient

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 $(x,y)$ 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 $(x,y)$, 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

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

Potentialités androgénétiques du palmier dattier Phoenix dactylifera L. et culture in vitro d'anthères

Genetic potentialities if five male date palm genotypes, and in vitro culture of anthers. The experimental results derived from the study of five date palm (Phoenix dactylifera L.) genotypes indicate that the ability of microspores to divide varies with genotype and culture medium. The highest frequency of microspore division is obtained with the induction medium [Murashige and Skoog (MS 1962) mineral elements, 2,4-dichlorophenoxyacetique (2,4-D), 2-isopentenylaminopurine (2-IP)] containing activated charcoal. The pollinator T106 was considered as the most efficient genotype in our experimentatio

Evaluation of antimicrobial and antioxidant properties of leaves of Emex spinosa and fruits of Citrillus colocynthis from Saudi Arabia

The crude methanol extract of Citrullus colocynthis fruit and Emex spinosa leaves were examined for antimicrobial and antioxidant potentialities. The phytochemical analysis revealed presence of some bioactive principles, such as alkaloids, flavonoids and anthraquinones for E. spinosa and saponin, flavonoids, terpenoids and alkaloids for C. colocynthis. The antimicrobial activities were determined against seven bacterial strains (Proteus vulgaris NCTC 8196, Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 27853, Klebsiella pneumonia ATCC 53651, Salmonella typhi NCTC 0650, Staphylococcus aureus ATCC 25923 and Bacillus cereus NCTC 8236) and one fungal strain (Candida albicans ATCC 7596). E. spinosa leaf methanol extract was most active against fungus, whileC. colocynthis fruit methanol extract was most active against bacteria, particularly E. coli ATCC 25922 and P. aeruginosa ATCC 27853. The antioxidant properties of extracts were investigated in vitro using1,1-diphenyl, 2-picryl hydrazyl (DPPH) radical scavenging assay and in vivo in rats using serological and enzymatic tests. Both plant extracts showed considerable antioxidant activities. The promising findings of this investigation could be used as a novel natural antimicrobial and antioxidant agents.Keywords: Emex spinosa, Citrillus colocynthis, antimicrobial, antioxidant activity.African Journal of Biotechnology Vol. 12(34), pp. 5308-531

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