Thermoacoustic refrigeration

A new refrigerator which uses resonant high amplitude sound in inert gases to pump heat is described and demonstrated. The phasing of the thermoacoustic cycle is provided by thermal conduction. This 'natural' phasing allows the entire refrigerator to operate with only one moving part (the loudspeaker diaphragm). The thermoacoustic refrigerator has no sliding seals, requires no lubrication, uses only low-tolerance machine parts, and contains no expensive components. Because the compressor moving mass is typically small and the oscillation frequency is high, the small amount of vibration is very easily isolated. This low vibration and lack of sliding seals makes thermoacoustic refrigeration an excellent candidate for food refrigeration and commercial/residential air conditioning applications. The design, fabrication, and performance of the first practical, autonomous thermoacoustic refrigerator, which will be flown on the Space Shuttle (STS-42), are described, and designs for terrestrial applications are presented

Neural-inspired sensors enable sparse, efficient classification of spatiotemporal data

Sparse sensor placement is a central challenge in the efficient characterization of complex systems when the cost of acquiring and processing data is high. Leading sparse sensing methods typically exploit either spatial or temporal correlations, but rarely both. This work introduces a new sparse sensor optimization that is designed to leverage the rich spatiotemporal coherence exhibited by many systems. Our approach is inspired by the remarkable performance of flying insects, which use a few embedded strain-sensitive neurons to achieve rapid and robust flight control despite large gust disturbances. Specifically, we draw on nature to identify targeted neural-inspired sensors on a flapping wing to detect body rotation. This task is particularly challenging as the rotational twisting mode is three orders-of-magnitude smaller than the flapping modes. We show that nonlinear filtering in time, built to mimic strain-sensitive neurons, is essential to detect rotation, whereas instantaneous measurements fail. Optimized sparse sensor placement results in efficient classification with approximately ten sensors, achieving the same accuracy and noise robustness as full measurements consisting of hundreds of sensors. Sparse sensing with neural inspired encoding establishes a new paradigm in hyper-efficient, embodied sensing of spatiotemporal data and sheds light on principles of biological sensing for agile flight control.Comment: 21 pages, 19 figure

Perceived Equity, Motivation and Final Offer Arbitration in Major League Baseball

Final offer salary arbitration in major league baseball offers a unique institutional arrangement that creates a naturally occurring non-equivalent groups repeated measure research design. The structural arrangements allow for examination of anticipatory expectancy effects and for assessment of behavioral responses consistent with equity theory predictions. Additionally, equity theory can be tested without the methodological problems inherent in defining the referent other. Performance and mobility were examined for major league baseball position players who won and lost their arbitration hearings. Pre-arbitration performance was found to significantly predict arbitration outcome. Despite similar patterns of post-arbitration performance between winners and losers, a significant relationship was noted between losing arbitration and postarbitration performance declines. Analyses also suggested that losers were also significantly more likely to change teams and leave major league baseball. The causality of the relationship between performance and arbitration outcome is discussed along with expectancy and equity effects as they relate to performance and mobility following the arbitration intervention

Mixed Tournaments, Common Shocks, and Disincentives: An Experimental Study

Two well-known hypotheses from the literature on tournaments are that (1) tournaments can filter out common shocks thereby reducing agents risk exposure; and (2) disincentive effects can arise when a tournament scheme is administered on a group of mixed ability agents. While handicapping and/or the creation of homogeneous groups have been suggested as mechanisms for mitigating disincentive effects, it is often impractical to use handicapping schemes and nearly impossible to create a completely homogeneous labor force. Hence, contract administrators who intend to use tournaments to elicit effort must be able to assess the positive effects of tournaments (eliminate common shocks) against the negative effects (disincentive effects). Using economic experiments, we find evidence of disincentive effects under tournaments, although these effects are not as strong as predicted. Moreover, tournaments can be effective at reducing earnings variability when common shocks are important. These results suggest that the benefits of risk reduction from eliminating common shocks might outweigh the disincentive effects arising from mixed tournaments.mixed tournaments, incentives, relative performance contracts, experimental economics, Research Methods/ Statistical Methods, C91 D01, D81, D82, D86,

Preparation of an ultra-cold sample of ammonia molecules for precision measurements

We present experiments in which an ultra-cold sample of ammonia molecules is released from an electrostatic trap and recaptured after a variable time. It is shown that, by performing adiabatic cooling before releasing the molecules and adiabatic re-compression after they are recaptured, we are able to observe molecules even after more than 10 ms of free expansion. A coherent measurement performed during this time will have a statistical uncertainty that decreases approximately as the inverse of the square root of the expansion time. This offers interesting prospects for high-resolution spectroscopy and precision tests of fundamental physics theories