25 research outputs found
A multiband envelope function model for quantum transport in a tunneling diode
We present a simple model for electron transport in semiconductor devices
that exhibit tunneling between the conduction and valence bands. The model is
derived within the usual Bloch-Wannier formalism by a k-expansion, and is
formulated in terms of a set of coupled equations for the electron envelope
functions. Its connection with other models present in literature is discussed.
As an application we consider the case of a Resonant Interband Tunneling Diode,
demonstrating the ability of the model to reproduce the expected behaviour of
the current as a function of the applied voltageComment: 8 pages, 4 figure
A New Strategy for Deep Wide-Field High Resolution Optical Imaging
We propose a new strategy for obtaining enhanced resolution (FWHM = 0.12
arcsec) deep optical images over a wide field of view. As is well known, this
type of image quality can be obtained in principle simply by fast guiding on a
small (D = 1.5m) telescope at a good site, but only for target objects which
lie within a limited angular distance of a suitably bright guide star. For high
altitude turbulence this 'isokinetic angle' is approximately 1 arcminute. With
a 1 degree field say one would need to track and correct the motions of
thousands of isokinetic patches, yet there are typically too few sufficiently
bright guide stars to provide the necessary guiding information. Our proposed
solution to these problems has two novel features. The first is to use
orthogonal transfer charge-coupled device (OTCCD) technology to effectively
implement a wide field 'rubber focal plane' detector composed of an array of
cells which can be guided independently. The second is to combine measured
motions of a set of guide stars made with an array of telescopes to provide the
extra information needed to fully determine the deflection field. We discuss
the performance, feasibility and design constraints on a system which would
provide the collecting area equivalent to a single 9m telescope, a 1 degree
square field and 0.12 arcsec FWHM image quality.Comment: 46 pages, 22 figures, submitted to PASP, a version with higher
resolution images and other supplementary material can be found at
http://www.ifa.hawaii.edu/~kaiser/wfhr
Glow discharge in low pressure plasma PVD: mathematical model and numerical simulations
In this paper we analyze the problem of glow discharge in low pressure plasma
in industrial plant, for chambers of different shapes and various working
parameters, like pressure and electric potential. The model described is based
upon a static approximation of the AC configuration with two electrodes and a
drift diffusion approximation for the current density of positive ions and
electrons. A detailed discussion of the boundary conditions imposed is given,
as well as the full description of the mathematical model. Numerical
simulations were performed for a simple 1D model and two different 2D models,
corresponding to two different settings of the industrial plant. The simpler
case consists of a radially symmetric chamber, with one central electrode
(cathode), based upon a DC generator. In this case, the steel chamber acts as
the anode. The second model concerns a two dimensional horizontal cut of the
most common plant configuration, with two electrodes connected to an AC
generator. The case is treated in a "quasi-static" approximation. The three
models show some common behaviours, particularly including the main expected
features, such as dark spaces, glow regions and a wide "plasma region".
Furthermore, the three shown models show some similarities with previously
published results concerning 1D and simplified 2D models, as well as with some
preliminary results of the full 3D case.Comment: 16 pages, 11 figures, in pres
Uso de escenarios de visión para identificar percepciones de manejo forestal comunitario en el Perú
Investigadores del Centro para la Investigación Forestal Internacional (CIFOR) implementaron métodos de escenarios futuros con grupos focales para identificar y analizar las perspectivas de quienes promueven el MFC en el Perú
Going into COP26 and getting it right: Forests, agriculture, ecosystems and nature for climate change mitigation and adaptation
Forests, trees and the transformation of agriculture remain a proven mitigation and adaptation pathway, which must receive substantially more support in terms of funding and capacity development. Protecting and restoring habitats is a powerful way to boost resilience to the impacts of climate change
Où en sommes nous ? Outil pour réfléchir au processus, aux progrès et aux priorités de votre forum multipartite
Ce manuel explique comment se servir de Où en sommes nous ? outil qui permet de réfléchir et d’assurer un suivi participatif dans les forums multipartites (multi-stakeholder forums ou MSF en anglais). Ces MSF sont des espaces où un vaste éventail de parties prenantes, concernées par une région ou un sujet particulier, entament un dialogue, prennent des décisions et/ou mettent en oeuvre des activités en vue de réaliser des objectifs communs liés au paysage. Où en sommes nous ? est utile pour instaurer des conditions permettant à un forum multipartite d’atteindre son ou ses objectif(s) équitablement et efficacement. Nous indiquons ici étape par étape le processus à suivre