We describe a new calorimeter for measuring heat capacity in the range 1–35 K, using a silicon chip bolometer as sample holder, temperature sensor, and sample heater. The apparatus is capable of measuring very small samples (1–500 mg), and may be used with a number of different experimental methods.
This article will review the electrical and optical properties of thin film electroluminescent (EL) displays. A simple electrical model for thin film electroluminescent (TFEL) device operation will be presented and used to describe the luminance and power consumption of TFEL devices. The basic material characteristics that are desirable for EL phosphors will be described. Progress in the development of multicolor and full color EL displays will be presented including device structures and phosphor advancements. Recent work on devices that combine EL technology with high resolution active matrix circuitry to achieve high resolution displays for head-mounted applications will be described.
A calorimetric technique was used to accurately determine the dielectric loss tangent of both additive−free and commerical grades of polyethylene at liquid−helium temperature. We found that the loss tangent of polyethylene often exhibits a broadened dielectric relaxation peak. Although this peak is centered in the kilohertz region, its existence increases the loss tangent at 60 Hz. Thus, the possibility of the elimination or reduction of this peak is important in evaluating the suitability of polyethylene as an insulator for a superconducting ac power transmission line. We have measured the intrinsic dielectric loss tangent of polyethylne and have found it to be ∼5×10−6. In addition, by systematically studying the influence of chemical additives on the dielectric loss, we have found the conditions necessary to obtain polyethylene exhibiting this low loss using present industrial production methods.
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