15,586 research outputs found

    Are we winning?! A team challenge to engage students in the large lecture introductory communication course

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    The development and implementation of a semester‐long team challenge in an introductory level communication course is described. The team challenge was developed to encourage active engagement of students with large lecture material and to build community within lab sections of the course. Teaching assistants were trained to observe and record participation, distraction, and attendance levels in the large lecture portion of a hybrid course, ‘Fundamentals of Communication.’ Assessment of the team challenge as a case study reveals higher levels of verbal participation and attendance, and lower levels of distractions (i.e. use of cell phones, side conversations, late arrivals to class). In addition, there were other unexpected outcomes related to the way in which students were dispersed in the lecture hall. Results are discussed along with implications pertaining to the role of teaching assistants, the utility of competition versus collaboration in academia, and the definition of participation across all student populations

    A robust spectral method for finding lumpings and meta stable states of non-reversible Markov chains

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    A spectral method for identifying lumping in large Markov chains is presented. Identification of meta stable states is treated as a special case. The method is based on spectral analysis of a self-adjoint matrix that is a function of the original transition matrix. It is demonstrated that the technique is more robust than existing methods when applied to noisy non-reversible Markov chains.Comment: 10 pages, 7 figure

    Development of a 425 Foot Diameter Passive Communication Satellite with Self Erecting Properties Monthly Progress Report No. 21m, Feb. 1966

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    Processing equipment modifications and product development of glass fibers for passive communication satellit

    Using Anisotropic Micro-Scale Topography to Manipulate the Wettability of Aluminum and Reduce the Retention of Water

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    A method is described for fabricating controlled micro-scale, topographical features on aluminum surfaces for the purpose of exploiting those features to affect the surface wettability. Using a photolithographic approach, a photoresist-masked surface is subjected to a plasma etch in a mixture of gaseous BCl3 and Cl2. Parallel grooves, microns to tens of microns in width, depth and spacing are studied, because this geometry is scaleable for mass production by roll-to-roll micro-embossing, and because the anisotropic nature of these features provides a directional change in wettability that can reduce the retention of water on the surface. Aluminum was studied because it is naturally hydrophilic and widely used in wet-surface heat exchanger applications, because of its low cost and excellent mechanical and thermal properties. Water droplets placed on a micro-grooved aluminum surface using a micro-syringe exhibit significantly increased apparent contact angles, and for water condensed onto an inclined, micro-grooved surface, the droplet volume at incipient sliding is reduced by more than 50% compared to droplets on a surface without micro-grooves. No chemical surface treatment is necessary to achieve this water repellency; it is accomplished solely through the anisotropic surface topography. The droplet geometry shows an elongated base contour relative to a surface without micro-grooves, and discontinuities in the three-phase contact line are also introduced by the grooves. A mechanistic model is presented for predicting the critical droplet size on micro-grooved surfaces. This model extends earlier work by accounting for the droplet geometry and contact-line changes caused by the micro-grooves. The model is validated through comparisons of predicted to measured critical droplet sizes, and it is then used to provide guidance for the development of surfaces with enhanced water drainage behavior. In a broad range of air-cooling applications, water retention on the air-side surface of metallic heat exchangers is problematic, because it can reduce the air-side heat transfer coefficient, increase core pressure drop, and provide a site for biological activity. In refrigeration systems, the accumulation of frost on metallic fins requires periodic defrosting and reduces energy efficiency. When water is retained on these surfaces following the defrost cycle, ice is more readily formed in the subsequent cooling period, and such ice can lead to shorter operation times before the next defrost is required. Thus the management and control of water droplets on heat-transfer and airhandling surfaces is vital to energy efficiency, functionality, and maintenance in air-cooling systems. The microstructured surfaces introduced in this work are proposed for use in air-cooling and dehumidifying applications, but they may have other applications where the management of liquids on a surface is important.Air Conditioning and Refrigeration Project 166Air Conditioning and Refrigeration Project 20

    Heat Transfer and Pressure Drop in a Developing Channel Flow with Streamwise Vortices

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    Experiments to assess the heat transfer and pressure-drop effects of delta-wing vortex generators placed at the entrance of developing channel flows are reported in this study. The experimental geometry simulates common heat exchanger configurations and tests are conducted over a velocity range important to heating, air conditioning and refrigeration. An innovative liquid-crystal thermography technique is used to determine the local and average Nusselt numbers for an isoflux channel wall, and conventional methods are used to determine the Fanning friction factor. Vortex generators with aspect ratios of A = 2 and A = 4 are studied at attack angles of a. = 20?? to 45????. The results indicate that the streamwise vortices generated by a delta wing can enhance local Nusselt numbers by more than 200% in a developing channel flow. Under some conditions, the spatially average Nusselt number nearly doubled for a heat transfer area that was 37 to 63 times the wing area. The Fanning friction factor increased by a few percent to nearly 60%, depending on the Reynolds number.Air Conditioning and Refrigeration Project 4

    Vapor-Liquid Equilibria for R-32 and R-410A Mixed With a Polyol Ester: Non-Ideality and Local Composition Modeling

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    Vapor-liquid equilibria (VLE) data were obtained over a wide range of mixture composition and saturation conditions for difluoromethane (R-32) mixed with a polyol ester oil (POE). These data were correlated using the following local composition models from the literature: Wilson, Heil, Wang and Chao, Tsuboka and Katayama, NRTL, and UNIQUAC. The results were used to evaluate the suitability of these models in predicting the saturation behavior of the R-32/POE mixture. The Heil model had the best performance, with a 2-a error of 4.81 % in predicted saturation pressure; UNIQUAC was the worst, with a 2-a pressure error of more than 12%. Using VLE results from the literature for pentafluoroethane (R-125) mixed with the same oil and model parameters for that mixture, and attempt was undertaken to make a priori predictions of the P-T-x behavior of a blend containing R-32, R-125 and the oil (R-410A/POE). Data were obtained for this blend, and the results indicate that the Heil model can make such predictions with a 2:' a pressure error of about 11 %.Air Conditioning and Refrigeration Project 5

    Study made of anodized aluminum circuit boards

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    Hard coated aluminum circuit boards demonstrate the feasibility of obtaining an electrical power circuit of high packaging density with very high thermal conductivity and mechanical strengths

    A Fundamental Study of Refrigerant Line Transients

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