Microscopic Model for Sequential Tunneling in Semiconductor Multiple Quantum Wells

We propose a selfconsistent microscopic model of vertical sequential tunneling through a multi-quantum well.The model includes a detailed description of the contacts,uses the Transfer Hamiltonian for expressions of the current and it treats the Coulomb interaction within a mean field approximation. We analyze the current density through a double well and a superlattice and study the formation of electric field domains and multistability coming from the Coulomb interaction. Phase diagrams of parameter regions (bias, doping in the heterostructure and in the contacts,etc) where the different solutions exist are given.Comment: 4 pages, 8 Postscript Figure

Neutrino telescopes under the ocean: The case for ANTARES

Neutrino telescopes offer an alternative way to explore the Universe. Several projects are in operation or under construction. A detector under the ocean is very promising because of the very accurate angular resolution that it provides. The ANTARES project is intended to demonstrate the feasibilty of such a detector.Comment: Talk given at the Neutrino98 conference, Takayama, Japan, June 4-9, 199

Current self-oscillations, spikes and crossover between charge monopole and dipole waves in semiconductor superlattices

Self-sustained current oscillations in weakly-coupled superlattices are studied by means of a self-consistent microscopic model of sequential tunneling including boundary conditions naturally. Well-to-well hopping and recycling of charge monopole domain walls produce current spikes (high frequency modulation) superimposed on the oscillation. For highly doped injecting contacts, the self-oscillations are due to dynamics of monopoles. As the contact doping decreases, a lower-frequency oscillatory mode due to recycling and motion of charge dipoles is predicted. For low contact doping, this mode dominates and monopole oscillations disappear. At intermediate doping, both oscillation modes coexist as stable solutions and hysteresis between them is possible.Comment: 4 pages, 4 figure

Possibilité d'observation, par le télescope Antares, de neutrinos de haute énergie associés aux sursauts gamma et validation des techniques de détection à l'aide d'un prototype

PARIS7-Bibliothèque centrale (751132105) / SudocSudocFranceF

Bifurcation behavior of a superlattice model

We present a complete description of the stationary and dynamical behavior of semiconductor superlattices in the framework of a discrete drift model by means of numerical continuation, singular perturbation analysis, and bifurcation techniques. The control parameters are the applied DC voltage (φ) and the doping (ν) in nondimensional units. We show that the organizing centers for the long time dynamics are Takens–Bogdanov bifurcation points in a broad range of parameters and we cast our results in a φ-ν phase diagram. For small values of the doping, the system has only one uniform solution where all the variables are almost equal. For high doping we find multistability corresponding to domain solutions and the stationary solutions may exhibit chaotic spatial behavior. In the intermediate regime of ν the solution can be time-periodic depending on the bias. The oscillatory regions are related to the appearance and disappearance of Hopf bifurcation tongues which can be sub- or supercritical. These results are in good agreement with most of the experimental observations and also predict new interesting dynamical behavior.Junta de Andalucía PB97-008

Sociedad civil y política exterior: ¿hacia un nuevo apradigma? : Algunas consideraciones en torno a la cuestión "Papeleras"

En el transcurso de los últimas años—gracias a fenómenos tales como la globalización, la erosión del vínculo representativo y la democracia centrada en los medios— la sociedad civil se ha visto revitalizada como un actor clave en la construcción del espacio público y en la orientación de las políticas públicas en general. El presente trabajo pretende analizar hasta que punto esta tendencia puede ser observada en el ámbito de las relaciones internacionales, más específicamente dentro de la formulación de la política exterior; y, a su vez, considerar si esto puede significar la consolidación de un nuevo paradigma dentro de la disciplina. Para tal fin se tomará como estudio de caso, desde la perspectiva de la participación de los actores no estatales —léase: grupos de interés, ONGs, asambleas vecinales, medios de comunicación—, el conflicto argentino-uruguayo por la instalación en este último país de dos plantas de procesamiento de celulosa; para, finalmente, ver su incidencia dentro de la política exterior argentina. Principalmente, se analizará el rol y la relevancia de la Asamblea Ciudadana Ambientalista de Gualeguaychú en la formación de dicha política.Mesa Políticas exteriores latinoamericanas: temas, actores y procesosInstituto de Relaciones Internacionale

The influence of anthropogenic activities on the concentration of pesticides, physicochemical and microbiological properties in the Chumbao river, Andahuaylas, Perú

The province of Andahuaylas is located in the region of Apurimac, a Peruvian city located in the Andes. Andahuaylas has three important districts: San Jerónimo, Andahuaylas and Talavera. These areas are highly populated, and their buildings are close to the Chumbao River. This research aimed to determine the influence of anthropogenic activities on the concentration of pesticides, physicochemical and microbiological characteristics in the Chumbao River. Five agricultural activities, 19 organochlorine pesticides, and 25 organophosphorus pesticides were studied. Eighteen physicochemical properties and two microbiological properties were also studied at seven sampling points along the Chumbao River during the rainy and dry seasons. Several veterinary and agricultural products were identified in the agricultural activities studied. However, no significant concentration values of organochlorine and organophosphate pesticides were found; no weed control products were found. In the case of livestock farming, albendazole and ivermectin are frequently used as anthelmintics. Organophosphate and pyrethroid insecticides are used to control flies and other ectoparasites. Several pesticides have been identified in the surveys in the case of quinoa, potato, and corn crops. Some of the physicochemical and microbiological properties are above environmental quality standards according to current Peruvian regulations; these properties increase at points where wastewater is discharged directly into the river. The study evidenced a progressive deterioration of water quality in the Chumbao River caused by anthropic activities in the basin. These may cause infectious and parasitic diseases in the urban population of the Chumbao river valley