Exciton effective mass enhancement in coupled quantum wells in electric and magnetic fields

We present a calculation of exciton states in semiconductor coupled quantum wells (CQWs) in the presence of electric and magnetic fields applied perpendicular to the QW plane. The exciton Schr\"odinger equation is solved in real space in three dimensions to obtain the Landau levels of both direct and indirect excitons. Calculation of the exciton energy levels and oscillator strengths enables mapping of the electric and magnetic field dependence of the exciton absorption spectrum. For the ground state of the system, we evaluate the Bohr radius, optical lifetime, binding energy and dipole moment. The exciton mass renormalization due to the magnetic field is calculated using a perturbative approach. We predict a non-monotonous dependence of the exciton ground state effective mass on magnetic field. Such a trend is explained in a classical picture, in terms of the ground state tending from an indirect to a direct exciton with increasing magnetic field.Comment: 20 pages, 7 figure

Apollo experience report: A use of network simulation techniques in the design of the Apollo lunar surface experiments package support system

A case study of data-communications network modeling and simulation is presented. The applicability of simulation techniques in early system design phases is demonstrated, and the ease with which model parameters can be changed and comprehensive statistics gathered is shown. The discussion of the model design and application also yields an insight into the design and implementation of the Apollo lunar surface experiments package ground-support system

Drift-diffusion model of the fragmentation of the external ring structure in the photoluminescence pattern of indirect excitons in coupled quantum wells

Under optical excitation, coupled quantum wells are known to reveal fascinating features in the photoluminescence pattern originating from dipole orientated indirect excitons. The appearance of an external ring has been attributed to macroscopic charge separation in the quantum well plane. We present a classical model of non-linear diffusion to account for the observed fragmentation of the external ring into a periodic array of islands. The model incorporates the Coulomb interactions between electrons, holes and indirect excitons. At low temperatures, these interactions lead to pattern formation similar to the experimentally observed ring fragmentation. The fragmentation is found to persist to temperatures above the quantum degeneracy temperature of indirect excitons.Comment: 5 pages, 3 figure

Evolution of a transdisciplinary "One Medicine-One Health" approach to global health education at the University of California, Davis.

In today's world health events in one nation or geographic area often have repercussions for the health and well-being of populations beyond that region; sometimes even globally. In recent years many factors, most notably concern about emerging infectious diseases, have contributed to an increasing appreciation of the interdependency of human, animal and ecosystem health worldwide. Integrated global approaches to improve the health of humans, animals and their shared environments are proving to be in the best interest of many countries. A special symposium and award were established in memoriam to the internationally renowned epidemiologist, Dr. Calvin W. Schwabe, who (while at the University of California, Davis) was a significant advocate of the "One Medicine" approach to public health, calling upon all health professionals, including veterinarians, to work collaboratively and comparatively to improve human health. This paper discusses the evolution of the "One Medicine" concept into a global "One Health" approach to research, training capacity and service infrastructure, focused not only on disease, but also on health at the individual, population, and ecosystem levels. Projects involving UCD faculty which attempt to integrate a One Health approach include the Health for Animals and Livelihood Improvement (HALI) Project in Tanzania, Envirovet Summer Institute, Avian Flu School and Newcastle Immunization Program in Africa, a web-based virtual global health training program, and the Calvin Schwabe One Health Project

Terahertz emitters based on microcavity dipolaritons

We propose the use of dipolaritons -- quantum well excitons with large dipole moment, coupled to a planar microcavity -- for generating terahertz (THz) radiation. This is achieved by exciting the system with two THz detuned lasers that leads to dipole moment oscillations of the exciton polariton at the detuning frequency, thus generating a THz emission. We have optimized the structural parameters of a system with microcavity embedded AlGaAs double quantum wells and shown that the THz emission intensity is maximized if the laser frequencies both match different dipolariton states. The influence of the electronic tunnel coupling between the wells on the frequency and intensity of the THz radiation is also investigated, demonstrating a trade-off between the polariton dipole moment and the Rabi splitting.Comment: 4 pages, 4 figures. This article has been submitted to Applied Physics Letter

Kinetics of the inner ring in the exciton emission pattern in GaAs coupled quantum wells

We report on the kinetics of the inner ring in the exciton emission pattern. The formation time of the inner ring following the onset of the laser excitation is found to be about 30 ns. The inner ring was also found to disappear within 4 ns after the laser termination. The latter process is accompanied by a jump in the photoluminescence (PL) intensity. The spatial dependence of the PL-jump indicates that the excitons outside of the region of laser excitation, including the inner ring region, are efficiently cooled to the lattice temperature even during the laser excitation. The ring formation and disappearance are explained in terms of exciton transport and cooling.Comment: 19 pages, 6 figure

BeppoSAX observations of the Seyfert 1 Galaxy NGC 3516

We present the results of two observations of the bright Seyfert 1 galaxy NGC 3516, obtained with BeppoSAX in 1996 November and 1997 March. Useful signal is detected between 0.2 and 60 keV, allowing for the first time the simultaneous observation of all main spectral features. The source was brighter by a factor 2 at the second epoch of observation. Both spectra present a strong Fe Kalpha line, and a reflection hump at high energy. An absorption edge at 0.8 keV is visible in the later spectrum, but not in the earlier one, indicating that this feature is strongly variable.Comment: to appear in : The Active X-ray Sky: Results from BeppoSAX and Rossi-XTE, Nuclear Physics B Proceedings Supplements, L. Scarsi, H. Bradt, P. Giommi and F. Fiore (eds.), Elsevier Science B.V. 4 pages LateX and 6 ps figures, using espcrc2 and epsfi