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

Heavy Quark Spin Symmetry and Heavy Baryons: Electroweak Decays

Heavy quark spin symmetry is discussed in the context of single and doubly heavy baryons. A special attention is paid to the constraints/simplifications that this symmetry imposes on the non-relativistic constituent quark model wave functions and on the b->c semileptonic decays of these hadrons.Comment: Presented at the 21st European Conference on Few-Body Problems in Physics, Salamanca, Spain, 30 August - 3 September 201

Influence of boundary conditions and anthropogenic emission inventories on simulated O3 and PM2.5 concentrations over Lebanon

AbstractThis study investigates the influence of boundary conditions and anthropogenic emission inventories on the simulated O3 and PM2.5 concentrations over a middle-eastern country – Lebanon. The Polyphemus chemical transport model (CTM) is used over Lebanon to simulate O3 and PM2.5 concentrations. Comparisons to measurements at a sub-urban site of Beirut between 2 and 13 July 2011 show that O3 is largely over-estimated when concentrations from a large-scale model are used as boundary conditions, as used in Waked et al. (2013). A global anthropogenic emission inventory (EDGAR-HTAP) is used with Polyphemus, in order to provide anthropogenic emissions for the Middle-East domain. Over Lebanon, sensitivity to emissions and to boundary conditions have been investigated. The comparison of EDGAR-HTAP to Waked et al. (2012) over Lebanon highlights high discrepancies between the inventories both in terms of emission estimates and spatial distribution. However, when studying the sensitivity to boundary conditions, O3 is well modeled when a Middle-East domain and the Lebanon domain are nested and thus achieves better statistics. The observed concentration is 48.8 μg m−3 and the respective concentrations for the simulation using MOZART4 and the one using the Polyphemus/Middle-East are 154.8 and 65.1 μg m−3. As for PM2.5 which is less sensitive to regional transport than O3, the influence of the boundary conditions on the PM2.5 concentrations at the site of comparison is low. The observed concentration is 20.7 μg m−3, while the modeled concentrations are 20.7 and 20.1 μg m−3 respectively

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

Formal Institutions along the Timber Value Chain in Liwale and Ruangwa Districts, Tanzania

In developing an inclusive and sustainable timber value chain institutions are important for structuring and governing the interactions of the actors to effect value creation and addition to timber products Therefore this study aims at assessing the rules and regulations awareness enforcement compliance and costs associated with the timber value chain in Liwale and Ruangwa districts Tanzania Data collection methods for this study includes key informant interviews observation and focus group discussions Secondary Data were also gathered from various sources from within and outside the districts Findings reveal that most people were aware of the rules and regulations involved in value chain but their level of awareness differed depending on factors like education level that an individual timber dealer had time of exposure in the timber business and the goals that each one had on their business Enforcement of the rules and regulations was found to be strong in Liwale compared to Ruangwa district In addition the compliance of the rules and regulations was high in Liwale than in Ruangwa However most of the actors who are timber dealers complained about high costs which is associated with compliance to the rules and regulations governing the busines

Reproductive biology of the Golden grey mullet Liza aurata, in the Gulf of Gabes (central Mediterranean, Tunisia) in the Gulf of Gabes (central Mediterranean, Tunisia)

In spite of its high commercial value, very few information are available on the biological feature of the Golden grey mullet in Tunisian waters (central Mediterranean). These data would be of great help in identifying the current stock state. In this study, Gonado Somatic Index (GSI), Hepato Somatic Index (HSI), condition factor (K), Length at first sexual maturity TL50 was calculated and the fecundity was estimated using the volumetric method. The Gonado Somatic Index (GSI) indicated that the spawning season of the Golden grey mullet extends from October to December. The monthly variation of Hepato-Somatic Index (HSI) indicates that L. aurata saves lipid reserves in liver. The species is sexually mature at 23.73, 23.84 and 23.79 cm TL respectively for female, male and combined sexes. In the present study the sex-ratio was unbalanced, with females dominating among large size individuals (TL > 24 cm). Absolute fecundity with a mean value of 286564 varied from a minimum of 210400 eggs for age 4 and a maximum of 533600 for age 7+

General decay of the solution for a viscoelastic wave equation with a time-varying delay term in the internal feedback

In this paper we consider a viscoelastic wave equation with a time-varying delay term, the coefficient of which is not necessarily positive. By introducing suitable energy and Lyapunov functionals, under suitable assumptions, we establish a general energy decay result from which the exponential and polynomial types of decay are only special cases.Comment: 11 page

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