Ionization Phenomena in a Gas-Particle Plasma

Particles in a plasma can appreciably change the electron density from the value it would assume if the particles were not present. The case of pure particle ionization, in which there is only thermionic emission from the particles and no gas ionization, is first considered. It is established that the potential and the charge distributions can be divided into a strong shielding regime, in which most of the free electrons are packed close to the particle surfaces in regions of high potential, and its direct opposite, a weak shielding regime. In both regimes, the free-electron content of the plasma is most readily altered by variations in the particle size, rather than in the work function or particle temperature. The suppression of one form of ionization by the other when both particle and gas contribution to the electron density are comparable is next investigated. In the case of gaseous ionization enhancement it is shown that, if the thermionically emitting particles are hotter than the gas, the electron temperature will also be higher than that of the gas and the gaseous ionization thereby enhanced. Lastly, it is shown that in some transient situations, the particles are able to control the time rate of change of the electron density

Build Time Estimations for Large Scale Modelling

Achieving speedy results in model making is very much desired if not a necessity in ahnost any manufacturing industry. There is no doubt that rapid prototyping contributes to this process. It is generally considered that when compared to conventional machining techniques like nlilling, the current rapid prototyping systems appear to be much faster. This is certainly true for complex,slnall objects. I-Iowever, this is not alwaysa,pplicable to simple, large and bulky parts. There are a number of projects and systems concentrating on the fabrication of large models. Work is being carried out at the University ofHong Kong, using milling. along with slicing technology. This.report compares some ofthe rapid prototyping systems witl1milling. Milling is an established technology and recent developments in materials and nlachines used in Inilling nlake it a good alternative to rapid prototyping when itcomes to largesyale nl0delling.Mechanical Engineerin

Computer program ETC improves computation of elastic transfer matrices of Legendre polynomials P/0/ and P/1/

Computer program ETC improves computation of elastic transfer matrices of Legendre polynomials P/0/ and P/1/. Rather than carrying out a double integration numerically, one of the integrations is accomplished analytically and the numerical integration need only be carried out over one variable

Design Guide for Bearings Used in Cryogenic Turbopumps and Test Rigs

Cryogenic bearings are a unique and specialized area of the overall group of bearings that are used every day in industrial and aerospace applications. Cryogenic bearings operate in a unique environment that is not experienced by most bearing applications. The high speeds of turbomachinery, flow of cryogenic coolants, use of nonstandard materials, and lack of lubrication place unique demands on cryogenic bearings that must be met for the safety and success of the mission. To meet the goals of safety and success, requirements are put on the designer, manufacturer, and user that are not normally applied to off-the-shelf bearings. The designer has to have knowledge of the operating conditions, rotational speeds, loads, stresses, installation methods, inspection criteria, dimensional requirements, and design and analytical tools. The manufacturer needs to be aware of the materials used for cryogenic bearings, special heat treatments required, cleanliness of the processes, and inspection techniques to ensure a good product. The user needs to be aware of the safe handling practices to eliminate corrosion and debris, correct installation and removal procedures, pre- and post-test inspections, and the documentation that follow the bearings. This guide is based on the experiences of engineers at NASA Marshall Space Flight Center (MSFC) that have been involved in bearing research and testing along with specific bearing references that have been written. It is not meant to be a bearing design textbook for cryogenic bearing applications. These are available from many authors. Its purpose is to help the designer, manufacturer, or user in the application of cryogenic bearings to better understand the requirements placed on these bearings

ETC - A Fortran 4 program for computing the multigroup P/0/ and P/1/ elastic transfer coefficients

Fortran 4 program for calculating multigroup elastic transfer coefficient

Approximation in LQG control of a thermoelastic rod

Control and estimator gains are computed for linear-quadratic-Gaussian (LQG) optimal control of the axial vibrations of a thermoelastic rod. The computations are based on a modal approximation of the partial differential equations representing the rod, and convergence of the approximations to control and estimator gains is the main issue

Astrometric observations of comets and minor planets

Comets and planet crossing asteroids are observed so that accurate positions can be determined. The observations are made with the Palomar 1.5 m telescope equipped with a CCD array. The combination of telescope and detector is quite effective at recording faint comets and minor planets. This proves useful for early acquisition of comets and asteroids returning for a new opposition. The resulting positions permit accurate orbits to be determined and allow the properties of the comets and asteroids to be measured by other observers using a variety of techniques. Recoveries and other notable observations of comets and planet crossing asteroids observed during the past years are discussed

Asteroid families, dynamics and astrometry

The proper elements and family assignments for the 1227 Palomar-Leiden Survey asteroids of high quality were tabulated. In addition to the large table, there are also auxiliary tables of Mars crossers and commensurate objects, histograms of the proper element distributions, and a discussion. Probably the most important part of the discussion describes the Mars crossing boundary, how the closest distances of approach to Mars and Jupiter are calculated, and why the observed population of Mars crossers should bombard that planet episodically rather than uniformly. Analytical work was done to derive velocity distributions of family forming events from proper element distributions subject to assumptions which may be appropriate for cratering events. Software was developed for a microcomputer to permit plotting of the proper elements. Three orthogonal views are generated and stereo pairs can be printed when desired. This program was created for the study of asteroid families. The astrometry task is directed toward measuring and reducing positions on faint comets and the minor planets with less common orbits. The observational material is CCD frames taken with the Palomar 1.5 m telescope. Positions of 10 comets and 16 different asteroids were published on the Minor Planet Circulars