Quartz microbalance study of4He and H2 on sodium

A quartz microbalance technique has been used to study the growth of⁴He and H₂ adsorbed on sodium. In contrast to cesium, adsorption of⁴He and H₂ do occur on a sodium surface.     

Convection in a concentric annulus with heat generating porous media and a permeable inner boundary

The effects of a permeable inner boundary on the maximum temperature and the convective flows were investigated numerically for a two-dimensional horizontal annulus containing a uniformly heat generating porous media. The time-dependent governing equations were nondimensionalized and put into an explicit finite difference numerical form. The finite difference equations were obtained from truncated Taylor series expansions using a central differencing scheme. Nondimensional temperatures and streamlines were obtained for heat generation rates ranging from 20 to 1,500 W/m³ corresponding to a range of modified Rayleigh numbers of 324 to 24,340 and for several combinations of isothermally heated wall conditions for annuli of radius ratio of 2. It was found that multi-cellular flows occur at the highest Rayleigh numbers investigated.     

Simple approximations of the DC flux influence on the core losspower electronic ferrites and their use in design of magnetic components

The effect of DC flux on the core loss is examined for the practical range of power and frequency. Relevant core loss equations are derived and applied to an optimization algorithm to determine the minimum core loss at a given ratio of s (DC flux density to AC peak flux density). It has been found that the curves of hysteresis loss density versus the ratio of s exhibit a peak at a critical ratio. Below or above this critical ratio, the loss density decreases drastically. On the other hand, the curves of eddy-current loss density versus the ratio of s exhibits a minimum point at a critical ratio. Below or above this critical ratio, the loss density increases gradually     

High-power 980-nm AlGaAs/InGaAs strained quantum-well laser grown by OMVPE

High-power lattice-strained AlGaAs/InGaAs graded index separate-confinement heterostructure (GRINSCH) quantum-well lasers emitting at a 980-nm wavelength have been grown by organometallic vapor phase epitaxy (OMVPE) and fabricated with a self-aligned ridge-waveguide structure. Using a 3- mu m-wide and 750- mu m-long AR-HR coated laser, 30 mV of optical power was coupled into optical fibers with 28.6% efficiency. A dominating single-lobe far-field radiation pattern was obtained from a wedge-shaped ridge-waveguide laser for output power as high as 240 mW with a maximum output power of 310 mW.<>     

Regulating contents and furnishings.

The criteria in the 1991 edition of the Life Safety Code are a first attempt to address the fire hazards associated with upholstered furniture and mattresses. Recognizing that the criteria do not represent a complete hazard analysis, it is anticipated that the subcommittee will continue its efforts and will evaluate the appropriateness of additional criteria. The NFPA Standards Council also has appointed a Technical Committee on Contents and Furnishings, which will meet in August 1991. This committee will have primary responsibility for developing fire hazard calculation procedures and documents that other committees can use to control the fire hazards of contents and furnishings.     

The on-line texture analysis of steel strips

A new on-line texture-analyzing system and its application to nondestructive r value determination is discussed. In addition to providing a brief theoretical background and describing the instrumental set-up, the article presents off-line measurements with this equipment and demonstrates the high accuracy of the determined r-values. A special feature of the unit is the possibility to simultaneously measure the most important r values—r₀, r₄₅, r₉₀, and r_m.     

Rapid isothermal processing for fabrication of GaAs-basedelectronic devices [HBTs]

The use of rapid isothermal processing (RIP) is detailed for each of the three annealing steps in the fabrication of heterostructure-based devices such as heterojunction bipolar transistors (HBTs). RIP can be used for the alloying of ohmic metal contacts, annealing of ion-bombarded regions for device isolation or parasitic capacitance reduction, and for conventional implant activation annealing. High-speed (f_T=65 GHz) HBTs were achieved using RIP for all of the required heating steps. The authors compare the use of several types of silicon carbide-coated graphite susceptors for eliminating slip formation on 2- and 3-in-diameter GaAs wafers during high-temperature implant activation annealing     

Ordered dynamic channel assignment scheme with reassignment inhighway microcells

An ordered dynamic channel assignment with reassignment (ODCAR) scheme is proposed, and its performance is studied in a highway microcellular radio environment. Channels are assigned in an ordered basis in conjunction with a minimax algorithm under cochannel interference constraints, to provide high capacity and to alleviate worst case channel congestion in each microcell. Simulation results show significant performance improvements in terms of channel utilization and probability of call failure, at the expense of an increase in complexity and call switching requirements     

Recovery of monomers and fillers from high-temperature-vulcanized silicone rubbers—combined effects of solvent, base and fillers

The depolymerization of high-temperature-vulcanized (HTV) silicone rubbers containing filler silica and alumina into cyclosiloxane monomers and spontaneous recovery of fillers were studied. First, HTV silicone rubber was treated with different types of solvents in the presence of KOH to find that a triad mixture of diethylamine, methanol and hexane was appropriate not only to dissolve the silicone rubber to a suspension but also to separate fillers completely by filtration. The filtrate was distilled to remove solvent first and then give pure cyclosiloxane monomers in 76–84% yields. Second, the rubbers were treated with other types of triad mixture of solvents and bases, e.g. tetramethylammonium hydroxide, hexane and diethylamine. After filtration, residue was again treated with the amine and hexane to recover clean fillers in 83–93% yields. Cyclosiloxane monomers were also obtained from the combined filtrates in 67–78% yields.