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

Resonant Acoustic Determination of Complex Elastic Moduli

A simple, inexpensive, yet accurate method for measuring the dynamic complex modulus of elasticity is described. Using a 'free-free' bar selectively excited in three independent vibrational modes, the shear modulus is obtained by measuring the frequency of the torsional resonant mode and the Young's modulus is determined from measurement of either the longitudinal or flexural mode. The damping properties are obtained by measuring the quality factor (Q) for each mode. The Q is inversely proportional to the loss tangent. The viscoelastic behavior of the sample can be obtained by tracking a particular resonant mode (and thus a particular modulus) using a phase locked loop (PLL) and by changing the temperature of the sample. The change in the damping properties is obtained by measuring the in-phase amplitude of the PLL which is proportional to the Q of the material. The real and imaginary parts or the complex modulus can be obtained continuously as a function of parameters such as temperature, pressure, or humidity. For homogeneous and isotropic samples only two independent moduli are needed in order to characterize the complete set of elastic constants, thus, values can be obtained for the dynamic Poisson's ratio, bulk modulus, Lame constants, etc

Torsionally Resonant Toroidal Thermoacoustic Refrigerator

PatentThis invention for the production of high amplitude acoustic standing waves, which can be used for thermo acoustic heat transport purposes, describes the use of a rigid barrier in place of a piston, thereby allowing the suspension of the resonator to be external to the pressurized resonator and allowing an independent choice of motor mechanism, including the use of rotary motors instead of linear motors, while incidently providing a mechanism for circulating external heat transport fluids without requiring additional pumps or heat pipes

Fiber-optic push-pull sensor systems

Fiber-optic push-pull sensors are those which exploit the intrinsically differential nature of an interferometer with concommitant benefits in common-mode rejection of undesired effects. Several fiber-optic accelerometer and hydrophone designs are described. Additionally, the recent development at the Naval Postgraduate School of a passive low-cost interferometric signal demodulator permits the development of economical fiber-optic sensor systems

Confirmation and Disconfirmation of Expectancies During Modeling

To determine the function or confirmation and disconfirmation of expectancy during modeling behavior, 60 primary school children were exposed to a training film (adult male model), and then to three conditions or expectancy confirmation (group C, 100% group CNC, 50%; group NC, 0%) through a second experimental film. Ss\u27 responses were observed under incentive and no-incentive conditions. Though expectancy was not significant, incentive was (p\u3c .01). S responses which matched M\u27s responses in the film showed that confirmation of expectancy did not affect imitative learning. While the perceptual definition of expectancy in this study had no effect, expectancy as a motivational condition and measured during actual observational learning (training film) was discussed as having an effect on number of matching responses in modeling

Buy it Now: A Hybrid Internet Market Institution

This paper analyzes seller choices and outcomes in approximately 700 recent Internet auctions on eBay. The ‘Buy it Now’ option that is available in these auctions allows the seller to supplement or replace the auction with a posted price offer. We use a structural model to control for the endogenous conduct of the auction (e.g., number of bids and bidders) as well as product and seller characteristics. Among other results, we find that the ‘Buy it Now’ option was used more often by sellers with higher ratings (awarded by previous buyers) and sellers offering fewer units; and that posted prices were more prevalent for used items. Sellers obtained higher prices for unused and undamaged items overall, and especially when selling at the ‘Buy it Now’ price.

Seller strategies on eBay: Does size matter?

We examine seller strategies in 1177 Internet auctions on eBay, to understand the diversity of strategies used, and their impacts. Dimensions of strategic choice include the use of a ‘Buy it Now’ option, the level of the starting price, and the use of a secret reserve price. A major focus of our analysis is on differences across sellers with different volumes of sales. The largest volume sellers (termed “retailers”) in our sample employ uniform selling strategies, but lower volume sellers exhibit a wide variety of strategic choices. While some components of sellers’ strategies appear important in raising seller revenue, including starting the auction with a ‘Buy it Now’ offer, the overall impact of seller strategy choices on the outcome appears to be quite small. We interpret this as evidence for the competitiveness of the online auction market for frequently traded items with conventional retail alternatives. An exception is provided by the use of a secret reserve price, which raises the winning bid conditional on a sale, but reduces the probability of a sale. Depending on sellers’ risk aversion and impatience, this may also be an efficient outcome.Internet auctions; posted prices; market institutions