Analysis of the impedance of a coaxial, large-bore copper-vaporlaser

The impedance of the laser head of a 100-W copper-vapor laser is investigated. The laser head is of a coaxial geometry, which is commonly used for longitudinally electrically excited, pulsed-gas lasers. The plasma conductivity is estimated using the available data on plasma parameters. The effect of radial gradient of the gas temperature and electron density is considered. The tube inductance and capacitance are estimated and the combined effect is demonstrated. The skin effect is considered. A method to calculate the exact influence of the skin effect on the tube impedance is presented. The full calculation procedure is demonstrated for the case of a 100-W, 8-cm-diameter, copper-vapor laser. The consequent impedance is used to calculate the laser current under given excitation conditions. Very good agreement exists between the calculated and measured laser current. The metal-sleeve diameter is found that is optimal for power matching     

The effect of window fraction on the deadtime of Anger cameras: concise communication

The deadtime characteristics of an Anger camera are analyzed using a model consisting of a paralyzable front end and nonparalyzable display circuits. This model differs from previous deadtime analyses in that it considers the change in the fraction of counts passed by the pulse height analyzer as a function of the true count rate. Deadtime curves are analyzed for a Pho/Gamma IV Anger camera using 10%, 20%, and 35% windows.     

Diagnosis of disturbed children.

Asserts that although there has been agreement that diagnosis of disturbed children is an important part of professional concern and service, activities labeled "diagnostic" or "evaluative" have not always been clearly in the disturbed child's interest. Psychology and psychologists have much to offer in developing more effective diagnostic procedures for disturbed children, especially in terms of identifying those children vulnerable or at risk for severe disturbance of adult adjustment. It is suggested that concerns with cost-effectiveness may have been responsible for such practices as inadequate testing. Guidelines are suggested for proper diagnostic evaluation of disturbed children. (27 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The effect of solvent choice on the mechanical properties of carbon nanotube–polymer composites

The effect of solvent choice on the mechanical properties of polymer nanotube composites has been investigated. Composites of double-walled nanotubes in polyvinyl alcohol were fabricated using water, DMSO and NMP as solvents. Various amounts of solvent remained trapped in both polymer and composite films even after drying as measured thermogravimetrically. In general, the glass transition temperature decreased as solvent content increased. However, deviations from this behavior suggested the presence of trapped NMP at the polymer–nanotube interface. Both static and dynamic mechanical measurements showed increases in mechanical properties on the addition of nanotubes for water and DMSO-based composites. However, for NMP-based composites, the mechanical properties were reduced compared to the polymer at room temperature. However, the NMP-based composites became significantly stiffer than their polymer counterparts at elevated temperatures suggested thermally assisted NMP desorption from the interface. Unlike the calorimetric measurements, dynamic mechanical measurements of the glass transition temperature showed no significant anomalies, again suggesting desorption of NMP from the interface at higher temperature. This work shows that solvent choice can have a dramatic effect on the mechanical properties of polymer–nanotube composites.     

Effect of Incidence Angle on the Impact-Wear Behavior of Silicon Nitride

Experiments were conducted by repeatedly hammering a silicon nitride (Si₃N₄) ball on a polished different Si₃N₄ material at different incidence angles: 45°, 60°, 75°, and 90°. Material removal during impact was dominated by the delamination process, which involved abrasion and fracturing of the parent material, compaction of pulverized debris into a film, nucleation of cracks along the film/substrate interface, and lateral propagation of the interfacial cracks. The dependency of repeated impact wear on the incidence angle involved a combination of the effects of normal and tangential stresses on surface deformation. The contrasting influences of these stresses resulted in a minimization of impact wear of the polished Si₃N₄ material at incidence angles in the range of 60°-75°.     

Friction and wear of titanium alloys sliding against metal, polymer, and ceramic counterfaces

Recent advances in lower-cost processing of titanium, coupled with its potential use as a light weight material in engines and brakes has renewed interest in the tribological behavior of titanium alloys. To help establish a baseline for further studies on the tribology of titanium against various classes of counterface materials, pin-on-disk sliding friction and wear experiments were conducted on two different titanium alloys (Ti-6Al-4V and Ti-6Al-2Sn-4Zr-2Mo). Disks of these alloys were slid against fixed bearing balls composed of 440C stainless steel, silicon nitride, alumina, and polytetrafluoroethylene (PTFE) at two speeds: 0.3 and 1.0 m/s. The friction coefficient and wear rate were lower at the higher sliding speed. Ceramic sliders suffered unexpectedly higher wear than the steel slider. The wear rates, ranked from the highest to the lowest, were alumina, silicon nitride, and steel, respectively. This trend is inversely related to their hardness, but corresponds to their relative fracture toughness. Comparative tests on a Type 304 stainless steel disk supported the fracture toughness dependency. Energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) analyses confirmed the tendency of Ti alloys to transfer material to their counterfaces and suggested possible tribochemical reactions between the ceramic sliders and Ti alloy disks. These reaction products, which adhere to the ceramic sliders, may degrade the mechanical properties of the contact areas and result in high wear. The tribochemical reactions along with the fracture toughness dependency helped explain the high wear on the ceramic sliders.     

Microstructural alterations associated with friction drilling of steel,aluminum, and titanium

Friction drilling, also called thermal drilling, is a novel sheet metal hole-making process. The process involves forcing a rotating, pointed tool through a sheet metal workpiece. The frictional heating at the interface between the tool and workpiece enables the softening, deformation, and displacement of work-material and creates a bushing surrounding the hole without generating chip or waste material. The bushing can be threaded and provides the structural support for joining devices to the sheet metal. The research characterizes the microstructures and indentation hardness changes in the friction drilling of carbon steel, alloy steel, aluminum, and titanium. It is shown that materials with different compositions and thermal properties affect the selection of friction drilling process parameters, the surface morphology of the bore, and the development of a highly deformed layer adjacent to the bore surface.     

Über die Autoxidation einiger monocyclischer Olefine

Studies on the Autoxidation of Some Monocyclic Olefins The autoxidations of cyclopentene, cyclohexene, cycloheptene, cyclooctene, cycloocta-1,5-diene, 1-methylcyclopentene, 1-methylcyclohexene, 1-methylcycloheptene, 1-methylcyclooctene, methylene cyclopentene, and methylene cyclohexene with pure oxygen under normal pressure were studied. The epoxides formed were determined gaschromatographically. In most cases also the products of allylic oxidation were analyzed and their structures elucidated after reduction to the corresponding allyl alcohols. The portions of high boiling or polymeric products which could not be detected gaschromatographically and also the real yields of epoxides were determined by balance experiments in the presence of inert internal standards.     

Untersuchungen zur Oxidation von α-substituierten Styrolen. I. Reaktivität und Produktbildung bei der Oxidation von Styrol-Derivaten

Studies on the Oxidation of α-Substituted Styrenes. I. Reactivity and Formation of Reaction Products During the Oxidation of Styrene Derivatives The liquid phase oxidation of α-tert. -butyl-, α-bromo-, α-chloro-, and α-methyl styrene with pure oxygen was investigated in a closed apparatus in chlorobenzene solution and in presence of cumene and of cumene hydroperoxide in the temperature range 35–125°C. The product yields were determined gaschromatographically. The differences of the activation energies of the epoxide formation and the parallel reactions were calculated. They amount to 27–38 kJ/mol. The epoxide selectivity increases with increasing temperature and decreases with increasing concentration of cumene. Relative chain propagation constants related to the tertiary CH-bond of cumene were determined from cooxidation experiments.