Orbital Dependent Exchange-Only Methods for Periodic Systems

Various orbital-dependent exchange-only potentials are studied which exhibit correct long-range asymptotic behaviour. We present the first application of these potentials for polymers and by one of these potentials for molecules. Kohn-Sham type calculations have been carried out for polyethylene in order to make valuable comparison of these potentials with each other as well as with Hartree-Fock and exchange-only LDA methods. The Kohn-Sham band gap obtained with the optimized effective potetial method is corrected with the exchange contribution to the derivative discontinuity of the exchange-correlation potential. The corrected band gap obtained with the Slater's exchange potential is 9.7 eV close to the experiment.Comment: 11 pages, 2 figures. Phys. Rev. B60, 1999, in pres

Solar-Cell Design Based On A Distributed Diode Analysis

The front surface of a p-n junction solar cell has resistive losses associated with the diffused layer, the metal-semiconductor contact, and the grid structure. These losses are analyzed by considering the spatially distributed nature of the p-n junction and the grid conductors. This distributed diode analysis is especially useful for solar cells operated under concentrated sunlight conditions. The results show the dependence of the V-I characteristics and the maximum power output per unit cell on the ratio of the diffused layer resistance to the junction dynamic resistance. This ratio can assist the designer in establishing proper grid structure geometries and should typically be less than 0.1 if the power output per unit cell is to be within 3 percent of that for the lossless case. Experimental measurements are reported which confirm the theoretical calculations. An analysis of the grid conductor losses associated with multiple-connected unit cells shows the disastrous effect that the grid header resistance can have on the performance of a solar cell. The results indicate that the use of a tapered header conductor to decrease the metal coverage may actually worsen cell performance. Copyright © 1978 by The Institute of Electrical and Electronics Engineers, Inc

Deposition of CdTe by spray pyrolysis

We report the spray pyrolysis of thin films of CdTe which show promise as a base material for solar cell applications. The films predominately show a zinc blende structure and appear to be intrinsic. Microprobe analysis indicates an excess of cadmium but this is not detectable by X-ray diffraction or from electrical conduction measurements. Measurements indicate a nominal direct bandgap of 1.47 eV and an absorption coefficient of the order of 104 cm−1. The room temperature electrical resistivity is of the order of 107 Ω cm

Modeling Power Bus Decoupling on Multilayer Printed Circuit Boards

Power bus decoupling designs on multilayer printed circuit boards must adequately account for the power bus interplane capacitance and its consequences for the design. Lumped element models for a power bus on a multilayer printed circuit board where an appreciable or entire portion of a layer is devoted to power and ground have been developed. The models are applicable below the distributed resonances of the board. Analytical, circuit simulation, and experimental studies have been conducted to test the models, investigate the effects of the distributed interplane capacitance of the power bus, and the effect of interconnect inductance associated with surface-mount decoupling capacitors

Analysis of Simple Two-Capacitor Low-pass Filters

The performance of typical low-pass capacitor filters is limited by the mutual inductance between the input and output sides of the filter. This paper describes how two appropriately spaced capacitors can be used to construct a low-pass filter with significantly better high-frequency performance than a one-capacitor filter. Laboratory measurements and numerical simulations are used to quantify the mutual inductance and compare the performance of one- and two-capacitor low-pass filters

Growth Of Tungsten Selenide Films Through Pyrolytic Conversion And Anodic Electrooxidation Of Ammonium Selenotungstate ((NH4)2WSe4)

WxSey thin films have been prepared by the spray pyrolysis and anodic electrodeposition of solutions of ammonium selenotungstate, (NH4)2WSe4, with y/x usually between two and three for the sprayed films and y x\u3e\u3e1 for the electrodeposited films. The sprayed films indicated regions of crystalline WSe2 and have optical absorbance spectra consistent with a mixture of WSe2, WSe3, and selenium. The electrodeposited films are totally amorphous, highly photoconductive, and have optical absorbance spectra typical of amorphous or vitreous selenium. The sprayed films transform into WO3 at temperatures greater than 350°C in the presence of oxygen wile the electrode-posited films tend to evaporate and/or decompose upon annealing. © 1985

FDTD and FEM/MOM Modeling of EMI Resulting from a Trace Near a PCB Edge

PCB traces routed near board edges and carrying high-speed signals are considered to contribute to EMI problems. Consequently, design maxims state that traces that might have intentional or unintentional high frequency components on them be kept away from board edges. This costs valuable surface area as boards become more densely designed. Further, design maxims concerning traces near board edges are not well quantified. The increase in EMI as a trace is routed increasingly closer to the PCB edge has been studied experimentally and with numerical modeling

Variable trust in public health messaging during the first year of the COVID-19 pandemic in Southeast Alaska

Public health messaging in the United States during the COVID-19 pandemic has been variable in effectiveness. Different levels of governmental institutions have different goals and methods; it is unclear how messaging from these disparate levels is received, trusted, and implemented. We investigate the degrees of trust of Alaska Native and non-Alaska Native people in Southeast Alaska for the U.S. federal, Alaska state, and local Southeast Alaskan governments to parse how Southeast Alaskans feel about relative preparation, actions, and public health messaging. We use data collected in two waves of a regional survey: the first in April-June 2020, and the second in November 2020-February 2021. Results indicate that trust in the federal government was significantly lower than in the Alaska state government for each time period, and trust in both federal and state government significantly decreased between the two periods. Trust in the local governments of Southeast Alaska were significantly higher than both state and federal levels, and increased between the two survey waves, albeit insignificantly. We discuss potential drivers of these observations and outline how this can be leveraged for more comprehensive research into how relatively small communities with a large Native presence perceive public health messaging from different sources

Learning through social spaces: migrant women and lifelong learning in post-colonial London

This article shows how migrant women engage in learning through social spaces. It argues that such spaces are little recognised, and that there are multiple ways in which migrant women construct and negotiate their informal learning through socialising with other women in different informal modes. Additionally, the article shows how learning is shaped by the socio-political, geographical and multicultural context of living in London, outlining ways in which gendered and racialised identities shape, construct and constrain participation in lifelong learning. The article shows that one way in which migrant women resist (post)colonial constructions of difference is by engaging in informal and non-formal lifelong learning, arguing that the benefits are (at least) two-fold. The women develop skills (including language skills) but also use their informal learning to develop what is referred to in this article as 'relational capital'. The article concludes that informal lifelong learning developed through social spaces can enhance a sense of belonging for migrant women