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

Fundamental limits for non-contact transfers between two bodies

We investigate energy and momentum non-contact exchanges between two arbitrary flat media separated by a gap. This problem is revisited as a transmission problem of individual system eigenmodes weighted by a transmission probability obtained either from fluctuational electrodynamics or quantum field theory. An upper limit for energy and momentum flux is derived using a general variational approach. The corresponding optimal reflectivity coefficients are given both for identical and different media in interaction.Comment: accepted in Phys. Rev. B rapid communicatio

Évolution temporelle de l’envasement des retenues de barrages de Tunisie

La mobilisation et l’exploitation des eaux de surface sont des pratiques anciennes en Tunisie. Les aménagements réalisés au cours du siècle dernier sont exposés à un alluvionnement plus ou moins accéléré. La capacité de stockage des retenues des barrages est sujette à une réduction progressive au cours du temps. Cette perte de capacité, parfois élevée, dépasse les prévisions de l’alluvionnement de la retenue. La quantification des sédiments piégés se base soit sur les bilans de matière solide à l’échelle d’une retenue, soit sur des levés bathymétriques ou topographiques. Les Modèles Numériques de Terrain (MNT) des retenues sont de plus en plus utilisés. Les différentes évaluations sont entachées d’une incertitude. Les retenues des barrages tunisiens perdent annuellement 0,5 % à 1 % de leur capacité par alluvionnement. L’analyse des résultats de mesures montre que l’alluvionnement est lié à l’hydrologie du cours d’eau, à la gestion de la réserve d’eau et aux manoeuvres de dévasement. La comparaison entre les résultats de mesures de l’alluvionnement et les prévisions des projets met en évidence des différences parfois relativement importantes qui sont dues au régime hydrologique des cours d’eau. En effet, une crue exceptionnelle peut provoquer un alluvionnement nettement supérieur à la moyenne annuelle en régime hydrologique normal. Les retenues méandriformes sont comblées rapidement alors que les retenues linéaires offrent la possibilité de soutirage de quantités importantes de sédiments. Les moyennes annuelles des pertes de capacité des barrages en exploitation et des barrages projetés jusqu’à 2010 permettent de quantifier les volumes des sédiments piégés à 500 Mm3. En 2030, la perte de capacité de stockage des barrages en exploitation pourrait atteindre 43 % de leur capacité initiale. Les aménagements amont et les travaux de conservation des eaux et des sols permettent de réduire le taux d’alluvionnement et de prolonger la durée de vie des grands réservoirs.The mobilization and exploitation of surface water are ancient practices in Tunisia. Installations carried out during last century are exposed to a greater or lesser degree of accelerated silting. The storage capacity of reservoirs is progressively reduced over the course of time. This sometimes accelerated loss of capacity of reserves by silting exceeds the forecasts of hydraulic installation projects. The quantification of trapped sediments is based on the assessment of a reservoir’s retained solid matter, either by bathymetric or topographic rising or by Digital Models of Grounds (DMG) corresponding to different dates. These various evaluations of the sediments trapped in reservoirs are, however, sullied with uncertainty. Tunisian reservoirs lose 0.5% to 1% of their storage capacity to silting annually. The analysis of the results presented in this study shows that silting is related to three factors: river hydrology, water reserve management and dredging operations. The comparison between the silting results and the project forecasts highlights relatively significant differences which may be due to river hydrology. Indeed a significant rising in water level can cause an increase in silting above the annual average found during normal hydrological modes. While meandering reservoirs are quickly filled with sediment, linear reservoirs can undergo dredging to remove a significant quantity of sediment. The annual averages in storage capacity losses of the dam under exploitation and its projections up to the year 2010 enable us to quantify the volumes of the sediment trapped as 500 Mm3. In 2030, the loss of storage capacity of the studied reservoirs may reach 43% of their initial storage capacities. Installations upstream and soil and water conservation efforts may reduce the rate of silting and prolong the lifespan of large dams

Anisotropic thermal magnetoresistance for an active control of radiative heat transfer

We predict a huge anisotropic thermal magnetoresistance (ATMR) in the near-field radiative heat transfer between magneto-optical particles when the direction of an external magnetic field is changed with respect to the heat current direction. We illustrate this effect with the case of two InSb spherical particles where we find that the ATMR amplitude can reach values of up to 800% for a magnetic field of 5 T, which is many orders of magnitude larger than its spintronic analogue in electronic devices. This thermomagnetic effect could find broad applications in the fields of ultrafast thermal management as well as magnetic and thermal remote sensing.Comment: 6 pages, 4 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 $(x,y)$ 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

Could Alfa fibers substitute glass fibers in composite materials?

In the present work polyester resin composites with Alfa fibers in the form of pulp were prepared and their properties were compared with those of polyester resin reinforced with glass fibers, the latter composites being widely used for structural applications. The composites were prepared using two manufacturing processes, namely hand lay-up and vacuum molding, to assess the influence of the process on the composites properties. Firstly, the tensile properties for the two composites were evaluated. The composites thermal properties were studied by differential scanning calorimetry and thermogravimetric analysis. Finally, the morphology of a glass fiber composite (GFC) and Alfa pulp composite (APC) was analyzed by scanning electron microscopy, to characterize the composites surface and cross-sections.The authors would like to thank CTC (Centre technique de la Chimie) for their valuable help during mechanical testing. The company Solutions Composites, especially Mr.Adel Hammami is gratefully acknowledged for financial and material support. The authors also wish to thank the members of the Department of Polymer Engineering University of Minho, Guimarães, Portugal for their valuable cooperation. This research work is carried out as part of a mobidocPhD, a program financed by the European Union within Pasri Projet. M.C Paiva acknowledges the Portuguese Foundation for Science and Technology (FCT) and the European program FEDER/COMPETE for the financial support through project PEst-C/CTM/ LA0025/2013 (LA 25-2015-2017)

On the minimization problem of sub-linear convex functionals

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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

Many-body radiative heat transfer theory

In this Letter a N-body theory for the radiative heat exchange in thermally non equilibrated discrete systems of finite size objects is presented. We report strong exaltation effects of heat flux which can be explained only by taking into account the presence of many body interactions. Our theory extends the standard Polder and van Hove stochastic formalism used to evaluate heat exchanges between two objects isolated from their environment to a collection of objects in mutual interaction. It gives a natural theoretical framework to investigate the photon heat transport properties of complex systems at mesoscopic scale

Antimicrobial, antioxidant and phytochemical investigation of Balanites aegyptiaca (L.) Del. edible fruit from Sudan

The methanol extract of the fruit (edible mesocarp) of Balanites aegyptiaca (L.) Del., a popular plant from Sudan, widely employed in Sudanese folk medicine was screened for antimicrobial, antioxidant and some active phytochemical compounds. The extract showed the presence of saponin, terpenoids, phenolic compounds and alkaloids. The methanolic extract of the fruits extracted from B. aegyptiaca exhibited a strong antioxidant activity in the DPPH assay and a potent capacity in preventing linoleic acid oxidation. Methanol extracts (50 and 100 mg/ml) were tested on several microbial strains using agar-well diffusion, minimum inhibitory concentration (MIC), minimum bacterial concentration (MBC) and minimum fungal concentration (MFC) methods. These experiments were performed on ten bacterial strains (five Gram-positives and five Gram-negatives) and four fungal strains. Methanol extracts, particularly at concentration of 100 mg/ml was found to be active against all bacterial and fungal strains and it was comparable to standard antibiotics Gentamicin and Amphotericin B. These findings support some of the traditional applications of the fruit of B. aegyptiaca against microbial aliments. It is therefore recommended that further studies regarding fractionation, separation and purification of these active antimicrobial compounds are required, in addition to toxicological evaluation in vivo.Key words: Balaneties aegyptiaca, antibacterial, antifungal, phytochemical, antioxidant, methanol extract