Passively cooled glass CO2 laser tubes for severe environments

The objective of this effort was to design a glass CO2 laser tube that could survive the Titan 3 C launch environment and at the same time provide adequate thermal conductivity to maintain the wall of the laser tube below approximately equal to 50 C for efficient lasing. The approach that was taken to satisfy these requirements was to pot the tube in an aluminum heat sink using a space qualified polyurethane potting material. Two configurations of the laser tube successfully passed the complete Titan 3 C qualification level sine and random vibration specification and satisfied the thermal requirements. Fabrication details and test results are presented that indicate this could be a practical solution for laser tubes used in a severe environment and where flowing coolants are impractical or undesirable

The CO2 laser frequency stability measurements

Carbon dioxide laser frequency stability data are considered for a receiver design that relates to maximum Doppler frequency and its rate of change. Results show that an adequate margin exists in terms of data acquisition, Doppler tracking, and bit error rate as they relate to laser stability and transmitter power

Evaluation of lubricants for ball bearings at high temperatures

Calcium fluoride-barium fluoride coating on ball bearing cages or as fillers in porous bearing cages lubricate bearings successfully for operations in air at temperatures of 1200 to 1500 degrees F

Lead oxide ceramic makes excellent high-temperature lubricant

A dry lubricant coating in ceramic form consisting of 95 percent lead monoxide and 5 percent silicon dioxide withstood a temperature of 1200 deg F, with a bearing operating at various atmospheric pressures. From this testing, there was no galling or metal transfer of the bearing

Severe Loss Probabilities in Portfolio Credit Risk Models

We derive explicit sharp bounds on the distribution of the number of defaults from a pool of obligors with common probability of default and default correlation. These bounds are extremely wide, implying that default probabilities and default correlations only very loosely determine probabilities of severe portfolio losses. Our results quantify and thereby reinforce Gordy’s (2002) statement that “Capital decisions ... depend on higher moments”.Portfolio Credit Risk Models

Narrow 87Rb and 133Cs hyperfine transitions in evacuated wall-coated cells

An extension of work on wall-coated cells was made to include observation by a triple resonance technique of the 0-0 hyperfine transitions in 87Rb and 133Cs. Conventional RF excited lamps were used. Interest in such cells is for possible application in atomic clocks. The Rb cell would appear to remain especially promising in this respect

Fundamental considerations for future solid lubricants

Properties important to the performance of solid lubricants are discussed. Those properties include shear characteristics, coherence between particles, resistance to cold flow, adherence to the substrate, applicable chemical thermodynamics and kinetics of materials and environments, polymorphism, and rheology. The following generalizations are made: (1) chemical thermodynamics and kinetics are powerful tools for use in determining the useful environments and methods of application for solid film lubricants; (2) the primary requirement for a solid lubricant is low shear strength; (3) the rheology of solid film constituents and formulations is likely to be of vital importance to performance and life; and (4) adherence and mobility of surface films is another primary requirement for long lived solid lubricants

Saline Conversion and Ice Structures from Artificially Grown Sea Ice

The environment of cold regions is generally viewed as inhospitable, primarily due to application of ideal processes and techniques suitable to temperate zones. The work herein is a step toward solving two environmental problems. The first involves the supply of inexpensive, potable water in Arctic regions, the lack of which is a severe detriment to development. Although water does exist in the Arctic, it is neither available in potable form during many months of the year nor does it occur in sufficient quantity near the point of use. Principally, this lack is caused by the aridness of the Arctic and the shallowness of fresh water sources which, for all practical purposes, do not exist but freeze completely each winter season. The remaining liquid water source is the sea. Arctic problems are then similar to other arid regions where the conversion of sea water to potable water or the transmission of potable water to desired locations is necessary. Cold temperatures generally preclude transmission except over very short distances. Desalination by freezing sea water is a much reported process and has been included among the desalination processes under study worldwide. The advantage of this method in the Arctic is the cold winter-time temperature for freezing and the existence of adequate solar energy in the summer for melting self purified ice. Power requirements are greatly reduced using these natural phenomena. The second aspect of this study concerns the use of artificially grown sea ice as a structural material, thinking primarily in terms of coastal facilities such as docks, jetties, islands, platforms, etc. At sufficiently high latitudes, the summer ablation can be controlled to the point where major structures can be maintained intact during the summer. The unit cost of material is quite low because of low energy requirements. The results of this study show that each of these sea water uses have considerable promise. Desalination to potable level was accomplished. Ice growth rates were obtained which indicate that ice structures of substantial size can be built.This project was accomplished under a matching grant between the Office of Water Resources Research, Department of the Interior, and the University of Alaska, Arctic Environmental Engineering Laboratory. Funds available under this grant purposefully did not anticipate the heavy logistic expense in moving the project and equipment from Fairbanks to Kotzebue, Alaska. Therefore, a major third contributor was the Alaska Air National Guard, Kulis Air Force Base, Alaska. The support offered by the officers and men of the Alaska Air National Guard was excellent and greatly appreciated