Lasing behavior in DCM-doped PVK microcavity

A surface emitting microcavity was formed by sandwiching a polymer film containing PVK, Alq(3) and DCM between a distributed Bragg reflector (DBR) with a reflectivity of 99% and a silver film (300 nm). The lasing phenomenon was observed in DCM-doped PVK microcavity. The full width at half maximum (FWHM) was 0.6 nm with the peak wavelength at 603 nm. The threshold energy for lasing was estimated to be about 2.5 mu J per pulse. (C) 2000 Published by Elsevier Science S.A. All rights reserved.

La DCM : un síndrome de gran incidencia actual.

Estudio del proceso atencional en niños con disfunción cerebral mínima. Comprobar la influencia del color en la atención de niños disfuncionados. La hipótesis planteada es: si se varía una de las propiedades del estímulo, asociándole color, la función de atención selectiva aumenta en su ejecución. Compuesta por 100 niños de un colegio público de EGB de zona rural, de los cursos tercero a quinto. Los sujetos integrantes del grupo experimental presentaban síntomas de DCM; los del grupo control no presentaban síntomas especiales. Los sujetos se asignaron a cuatro grupos, uno de los grupos experimental y otro de los de control se sometieron a la condición de color, para la ejecución de la prueba de atención. Los otros dos grupos la realizaron en condición de blanco. La variable independiente coincide con el estímulo y consiste en la variación del blanco a color en siete tarjetas (mostradas al niño). La variable dependiente fue la atención selectiva del individuo, revelada por medio de la diferencia de ejecución en una tarea doble de apareamiento. TALE, Raven, Godenough, Bender para la selección de la muestra. Para la prueba de atención: dos juegos de siete cartas iguales de color blanco con el dibujo de un animal en la parte inferior y un objeto casero en la superior, catorce cartas con los dibujos anteriores, pero asociando un color, siete cartas con solo un dibujo en la parte superior, cartulina con la silueta de las siete cartas con solo el animal, cartulina con las siete cartas pegadas con el animal dibujado en la parte inferior. El diseño experimental del tipo factorial de bloques al azar, contrasta la significación estadística de la prueba. La ejecución fue mayor para el grupo bajo la condición de color: el color se asocia selectivamente y favorece la atención eficaz. Los niños disfuncionados que contaron con la variable color, puntuaron prácticamente como los 'normales' en condiciones standard. Importancia de la utilización del color en textos y técnicas educativas: favorece la atención y ayuda a mejorar la conducta escolar como consecuencia inmediata.

Bond graph models of DC-DC converters operating in both CCM and DCM

In this paper, Bond Graphs are employed to develop a novel mathematical model of conventional switched-mode DC-DC converters valid for both continuous and discontinuous conduction modes. A unique causality bond graph model of hybrid models is suggested with the operation of the switch and the diode to be represented by a Modulated Transformer with a binary input and a resistor with fixed conductance causality. The operation of the diode is controlled using an if-then function within the model. The extracted hybrid model is implemented on a Boost and Buck converter with their operations to change from CCM to DCM and to return to CCM. The vector fields of the models show validity in a wide operation area and comparison with the simulation of the converters using PSPICE reveals high accuracy of the proposed model, with the Normalised Root Means Square Error and the Maximum Absolute Error remaining adequately low. The model is also experimentally tested on a Buck topology.

DCM Boost interleaved converter for operation in AC and DC to trolleybus application

This paper is based on the development and experimental analysis of a DCM Boost interleaved converter suitable for application in traction systems of electrical vehicles pulled by electrical motors (Trolleybus), which are powered by urban DC or AC distribution networks. This front-end structure is capable of providing significant improvements in trolleybuses systems and in the urban distribution network costs, and efficiency. The architecture of proposed converter is composed by five boost power cells in interleaving connection, operating in discontinuous conduction mode. Furthermore, the converter can operate as AC-DC converter, or as DC-DC converter providing the proper DC output voltage range required by DC or AC adjustable speed drivers. Therefore, when supplied by single-phase AC distribution networks, and operating as AC-DC converter, it is capable to provide high power factor, reduced harmonic distortion in the input current, complying with the restrictions imposed by the IEC 61000-3-4 standards. The digital controller has been implemented using a low cost FPGA and developed totally using a hardware description language VHDL and fixed point arithmetic. Thus, two control strategies are evaluated considering the compliance with input current restrictions imposed by IEC 61000-3-4 standards, the regular PWM modulation and a current correction PWM modulation. In order to verify the feasibility and performance of the proposed system, experimental results from a 15 kW low power scale prototype are presented, operating in DC and AC conditions.

Oceanography during TYDEMAN cruise DCM (DeepChlorMax) to the Equatorial Atlantic

The cruise with RV Tydeman was devoted to study permanently stratified plankton systems in the (sub)tropical ocean, which are characterised by a deep chlorophyll peak between 80 and 150 m. To minimise lateral effects by horizontal transport of nutrients and organic matter from river outflow and upwelling regions, stations were selected in the middle of the North Atlantic Ocean between the continents of America and Africa. (5 - 35° N and 50 - 15° W). Here the vertical distributions of light and nutrients control the abundance and growth of autotrophic algae in the thermically stratified water column. This phytoplankton is numerically dominated by the prokaryotic picoplankters Synechococcus spp. and Prochlorococcus spp., which are smaller than 2 ?m. The productivity of the 100 to 150 m deep euphotic zone can be high, because a high heterotrophic/autotrophic biomass ratio induces a rapid regeneration of nutrients and inorganic carbon. Primary grazers are mainly micro-organisms such as heterotrophic nannoflagellates and ciliates, which feed on the small algae and on bacteria. Heterotrophic bacteria can outnumber the autotrophic algae, because their number is related to the substrate pools of dissolved and particulate dead organic matter. These DOC and detritus pools reach equilibrium at a concentration, where the rate of their production (proportional to algal biomass) equals their mineralisation and sinking rate (proportional to the concentration and weight of POC and detritus). At a relatively low value of the weight-specific loss rates, the equilibrium concentration of these carbon pools and their load of bacteria can be high. The bacterial productivity is proportional to the mineralisation rate, which in a steady state can never be higher than the rate of primary production. Hence the ratio in turnover rate of bacteria and autotrophs tends to be reciprocally proportional to their biomass ratio.