Physical Sciences

White-Light Whispering-Gallery-Mode Optical Resonators

Overlapping resonator modes are exploited to obtain wide, high-Q spectra. Whispering-gallery-mode (WGM) optical resonators can be designed to exhibit continuous spectra over wide wavelength bands (in effect, white-light spectra), with ultrahigh values of the resonance quality factor (Q) that are nearly independent offrequency. White-light WGM resonators have potential as superior alternatives to(1) larger, conventional optical resonators in ring-down spectroscopy, and (2) optical-resonator/electro-opticalmodulator structures used in coupling of microwave and optical signals in atomic clocks. In these and other potential applications, the use of white-light WGM resonators makes it possible to relax the requirement of high-frequency stability of lasers, thereby enabling the use of cheaper lasers.

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Ice-Borehole Probe

The art of borehole imaging has been extended to deep, cold, wet, high-pressure environments. An instrumentation system has been developed for studying interactions between a glacier or ice sheet and the underlying rock and/or soil. Prior borehole imaging systems have been used in well-drilling and mineral-exploration applications and for studying relatively thin valley glaciers, but have not been used for studying thick ice sheets like those of Antarctica.

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Alpha-Voltaic Sources Using Liquid Ga as Conversion Medium

These units would offer long life and high energy-conversion efficiency. A family of proposed miniature sources of power would exploit the direct conversion of the kinetic energy of a particles into electricity. In addition to having long operational lives, these sources are expected to operate with energy-conversion efficiencies from 70 to 90 percent.

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Using Satellite Data in Weather Forecasting: I

The GOES Product Generation System (GPGS) is a set of computer codes and scripts that enable the assimilation of real-time Geostationary Operational Environmental Satellite (GOES) data into regional weather forecasting mathematical models. The GPGS can be used to derive such geophysical parameters as land surface temperature, the amount of precipitable water, the degree of cloud cover, the surface albedo, and the amount of insolation from satellite measurements of radiant energy emitted by the Earth and its atmosphere. GPGS incorporates a priori information (initial guesses of thermodynamic parameters of the atmosphere) and radiometric measurements from the geostationary operational environmental satellites along with mathematical models of physical principles that govern the transfer of energy in the atmosphere. GPGS solves the radiative-transfer equation and provides the resulting data products in formats suitable for use by weather-forecasting computer programs. The data-assimilation capability afforded by GPGS offers the potential to improve local weather forecasts ranging from 3 hours to 2 days — especially with respect to temperature, humidity, cloud cover, and the probability of precipitation. The improvements afforded by GPGS could be of interest to news media, utility companies, and other organizations that utilize regional weather forecasts.

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Sensors for Using Times of Flight To Measure Flow Velocities

No calibrations are needed to use these thinfilm sensors. Thin-film sensors for measuring flow velocities in terms of times of flight are undergoing development. These sensors are very small and can be mounted flush with surfaces of airfoils, ducts, and other objects along which one might need to measure flows. Alternatively or in addition, these sensors can be mounted on small struts protruding from such surfaces for acquiring velocity measurements at various distances from the surfaces for the purpose of obtaining boundary-layer flow-velocity profiles.

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Design and Selection Considerations for High-Temperature Aerospace Accelerometers

Considerations include material selection, construction, and radiation tolerance. Accelerometers used for shock and vibration measurement in extreme environments require special consideration in the design and manufacturing process. Certain unique applications can require the same accelerometer to function from -54 to 649 °C (-65 to 1,200 ° F). This might include such applications as vibration measurement on gas turbine engines, in flight, or in test cells; rocket motor vibration measurements; and thruster vibration. These accelerometers also may need to function in nuclear radiation environments, and possibly in a combination of temperature extremes and radiation. This might include nuclear power generation or space vehicle applications. Materials and construction must then be selected not only to enhance high temperature performance, but also to allow operation in the presence of gamma and neutron radiation

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Microscale Regenerative Heat Exchanger

Materials and dimensions are chosen to optimize performance at microscale. The device illustrated in Figure 1 is designed primarily for use as a regenerative heat exchanger in a miniature Stirling engine or Stirling-cycle heat pump. A regenerative heat exchanger (sometimes called, simply, a “regenerator” in the Stirling-engine art) is basically a thermal capacitor: Its role in the Stirling cycle is to alternately accept heat from, then deliver heat to, an oscillating flow of a working fluid between compression and expansion volumes, without introducing an excessive pressure drop. These volumes are at different temperatures, and conduction of heat between these volumes is undesirable because it reduces the energy-conversion efficiency of the Stirling cycle. Hence, among the desired characteristics of a regenerative heat exchanger are low pressure drop and low thermal conductivity along the flow axis.

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