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

Analytical study of non Gaussian fluctuations in a stochastic scheme of autocatalytic reactions

A stochastic model of autocatalytic chemical reactions is studied both numerically and analytically. The van Kampen perturbative scheme is implemented, beyond the second order approximation, so to capture the non Gaussianity traits as displayed by the simulations. The method is targeted to the characterization of the third moments of the distribution of fluctuations, originating from a system of four populations in mutual interaction. The theory predictions agree well with the simulations, pointing to the validity of the van Kampen expansion beyond the conventional Gaussian solution.Comment: 15 pages, 8 figures, submitted to Phys. Rev.

An inverse problem in quantum statistical physics

International audienceWe address the following inverse problem in quantum statistical physics: does the quantum free energy (von Neumann entropy + kinetic energy) admit a unique minimizer among the density operators having a given local density $n(x)$? We give a positive answer to that question, in dimension one. This enables to define rigourously the notion of local quantum equilibrium, or quantum Maxwellian, which is at the basis of recently derived quantum hydrodynamic models and quantum drift-diffusion models. We also characterize this unique minimizer, which takes the form of a global thermodynamic equilibrium (canonical ensemble) with a quantum chemical potential

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

Guía metodológica para el uso de escenarios de visión para identificar percepciones de manejo forestal comunitario

El Manejo Forestal Comunitario (MFC) es una práctica de gestión ambiental comunitaria que se propone como una opción de desarrollo sostenible para las comunidades rurales en diferentes países con bosques. Los actores y actoras que participan de estas iniciativas orientan sus decisiones según su forma de entender los objetivos, metas, estrategias y retos del MFC. No obstante, estos criterios a menudo no son establecidos explícitamente, lo que puede ocasionar malentendidos, obstáculos y conflictos. Para construir un MFC más efectivo e inclusivo es necesario entender estas diversas perspectivas y tomarlas en cuenta. Esta guía presenta un método para orientar a los actores del MFC en ese esfuerzo, facilitar los consensos, evitar conflictos y promover iniciativas más sostenibles y económicamente viables: los escenarios de visión. Para ello, se basa en un estudio implementado por el Centro para la Investigación Forestal Internacional (CIFOR) en 2020, el cual tenía como objetivo identificar cuáles son esas perspectivas en el caso peruano, invitar a reflexionar sobre las prácticas, estrategias y normas actuales; y evaluar si existen las condiciones para avanzar hacia el MFC que las actoras y los actores anhelan

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