A comparison of reflector antenna designs for wide-angle scanning

Conventional reflector antennas are typically designed for up to + or - 20 beamwidths scan. An attempt was made to stretch this scan range to some + or - 300 beamwidths. Six single and dual reflector antennas were compared. It is found that a symmetrical parabolic reflector with f/D = 2 and a single circular waveguide feed has the minimum scan loss (only 0.6 dB at Theta sub 0 = 8 deg, or a 114 beamwidths scan). The scan is achieved by tilting the parabolic reflector by an angle equal to the half-scan angle. The f/D may be shortened if a cluster 7 to 19 elements instead of one element is used for the feed. The cluster excitation is adjusted for each new beam scan direction to compensate for the imperfect field distribution over the reflector aperture. The antenna can be folded into a Cassegrain configuration except that, due to spillover and blockage considerations, the amount of folding achievable is small

Self-Regulation in a Web-Based Course: A Case Study

Little is known about how successful students in Web-based courses self-regulate their learning. This descriptive case study used a social cognitive model of self-regulated learning (SRL) to investigate how six graduate students used and adapted traditional SRL strategies to complete tasks and cope with challenges in a Web-based technology course; it also explored motivational and environmental influences on strategy use. Primary data sources were three transcribed interviews with each of the students over the course of the semester, a transcribed interview with the course instructor, and the students’ reflective journals. Archived course documents, including transcripts of threaded discussions and student Web pages, were secondary data sources. Content analysis of the data indicated that these students used many traditional SRL strategies, but they also adapted planning, organization, environmental structuring, help seeking, monitoring, record keeping, and self-reflection strategies in ways that were unique to the Web-based learning environment. The data also suggested that important motivational influences on SRL strategy use—self-efficacy, goal orientation, interest, and attributions—were shaped largely by student successes in managing the technical and social environment of the course. Important environmental influences on SRL strategy use included instructor support, peer support, and course design. Implications for online course instructors and designers, and suggestions for future research are offered

A comparison of reflector antenna designs for wide-angle scanning

Conventional reflector antennas are typically designed for up to + or - 20 beamwidths scan. An attempt was made to stretch this scan range to some + or - 300 beamwidths. Six single and dual reflector antennas were compared. It is found that a symmetrical parabolic reflector with f/D = 2 and a single circular waveguide feed has the minimum scan loss (only 0.6 dB at Theta sub 0 = 8 deg, or a 114 beamwidths scan). The scan is achieved by tilting the parabolic reflector by an angle equal to the half-scan angle. The f/D may be shortened if a cluster 7 to 19 elements instead of one element is used for the feed. The cluster excitation is adjusted for each new beam scan direction to compensate for the imperfect field distribution over the reflector aperture. The antenna can be folded into a Cassegrain configuration except that, due to spillover and blockage considerations, the amount of folding achievable is small

Atmospheric Moisture Content Effects on Ionic Liquid Wettability of Alumina

The contact angles or wettability of 7 Ionic Liquids, on an alumina substrate, have been measured under two different storage conditions. The first using a small amount of moisture content, the second with no moisture content. The contact angle of Ionic Liquid droplets on an alumina substrate were measured using an Attension Theta instrument with automated software. The results show that a small amount of moisture improves the wettability of the Ionic Liquid – alumina system and therefore subsequent uses of these liquids with alumina should take this into consideration

Helical Tubes in Crowded Environments

When placed in a crowded environment, a semi-flexible tube is forced to fold so as to make a more compact shape. One compact shape that often arises in nature is the tight helix, especially when the tube thickness is of comparable size to the tube length. In this paper we use an excluded volume effect to model the effects of crowding. This gives us a measure of compactness for configurations of the tube, which we use to look at structures of the semi-flexible tube that minimize the excluded volume. We focus most of our attention on the helix and which helical geometries are most compact. We found that helices of specific pitch to radius ratio 2.512 to be optimally compact. This is the same geometry that minimizes the global curvature of the curve defining the tube. We further investigate the effects of adding a bending energy or multiple tubes to begin to explore the more complete space of possible geometries a tube could form.Comment: 10 page

Inversiones públicas en el Perú (1900-1968): una aproximación cuantitativa

El presente documento se propone reconstruir el patrón de comportamiento de la inversión pública peruana entre 1900 y 1968, a partir de nuevas evidencias empíricas extraídas de los Balances y Cuentas Generales de la República que han permitido elaborar series estadísticas completas del gasto fiscal a lo largo de todo el período examinado. Al proceder de esta manera hemos buscado responder, entre otras, a las siguientes interrogantes: ¿Cuál fue el monto del gasto fiscal total destinado a realizar obras públicas durante los distintos gobiernos que tuvieron bajo su administración el aparato estatal? ¿Qué tipo de obras se ejecutaron y qué orden de prioridades revelaban nuestros gobernantes en sus decisiones de inversión? Y, finalmente, ¿qué grado de autonomía relativa mostró el Estado en su política de inversiones públicas en relación a las presiones ejercidas por los grupos de poder locales

Computational Model for Microbubble Enhanced Performance of Airlift Bioreactor (ALB)

This paper presents a computational model for microbubble enhanced performance of an airlift bioreactor (ALB). Five different bubble diameters were defined in the model under the same conditions (440 µm to 1 mm bubble diameter). The computational model parameters and the size of the ALB were defined by referring to experimental work done previously. The main objective of the model is to study the effect of bubble size on the rising velocity and the liquid flow velocity in the airlift reactor (ALB). The results obtained from the computational model shows that microbubbles have a better performance over larger bubbles because microbubbles have better gas hold up due to slow rise velocity and are able to increase the flow velocity due to their high surface area to volume ratio

W-band 0.3W PHEMT MMIC power amplifier module

A compact (1.8 by 3.0 by 3.8 cm) WR-10 waveguide amplifier module providing 310-mW power output, 20-dB gain, and 5 GHz of 1-dB bandwidth at a center frequency of 96 GHz is described. The module is comprised of 22 identical PHEMT chips, 4-way microstrip power combiners and dividers, and a 4-way waveguide power combiner

Obtenção, caracterização e avaliação do potencial antioxidante de farinha de endosperma e de casca de pinhão para fins alimentícios.

Resumo. Disponível online. MIPE

Persistent postoperative granulation tissue following vaginal prolapse repair

To report rates and risk factors for persistent postoperative granulation tissue (GT) in women undergoing reconstructive vaginal prolapse surgery