[en] The microstructure of reaction sintered silicon nitride (RBSN) was changed in a wide range of varying green density, grain size of the silicon starting powder, nitriding conditions, and by introducing artificial pores. The influence of single microstructural parameters on mechanical properties like room temperature strength, creep behaviour, and resistance to thermal shock has been investigated. The essential factors influencing these properties were found to be total porosity, pore size distribution, and the fractions of α- and β-Si₃N₄. In view of high temperature engineering applications of RBSN possibilities to optimize the material's properties by controlled processing are discussed. (orig.)

[en] The primary objective of this textbook is to introduce the finite element method in a clear, concise manner using ismple examples. the author's intent is to provide a book free of jargon and free of abstract theoretical conepts. The approahc is to teach the method through simple one-dimensional problems which can be solved manually. The procedures are then generalized to two and three dimensions

[en] Environmental medicine examines the effects of pollutants on humans. It employs different scientific tools for this purpose: Toxicology, epidemiology and statistics. (orig./DG)

[en] AlN samples have been produced by reaction bonding process using AlN and aluminum powders as starting materials. Different aluminum nitride and aluminum powders ratios were mixed in ethanol media, dried, isostatically and nitrided in (N₂)atmosphere. Results showed that conversion of to AlN depends strongly on the amount of aluminum starting powder and decreased with increasing after a maximum at 25 Al wt %. Changing the particle size and morphology of the aluminum starting powder leads to change in the conversion ratio and microstructure of RBAN ceramics. Typical scanning electron micrographs of RBAN sample indicating primary and secondary aluminum nitride morphology and pore structure. The oxidation behavior of RABN samples showed the weight gain depends on the average particle size, morphology and amount of Al in starting mixture and pore structure. Samples have been manufactured with equi-axed morphology of Al starting powder have thermal conductivity higher than the samples have been manufactured with flake-like morphology. These differences were directly related to the different microstructure of RBAN samples

[en] By means of a N₂-laser pumped dye-laser (Psub(L) approx. 20 kW, Δνsub(L) < 10 GHz) different two-photon resonant four-wave coupling processes in Ba vapour (nsub(Ba) approx. 10¹⁶ cm^-3) using the Ba states 6s8s¹S₀ and 7s5d¹D₂ were investigated. Coherent line radiation with conversion rates up to 10^-3 was generated within the range of lambda = 190-200 nm by sum-frequency mixing νsub(UV) = 2ν₁ + ν₂₂ of 3 laser photons and within the range of lambda = 250-380 nm by coupling νsub(UV) = 2ν₁ +- νsub(IR) of 2 laser photons with one photon vsub(IR) stimulated emitted in laser-induced Ba transitions. For the second coupling type the various nonlinear processes contributing to the formation of the coupling components are discussed. The power of the UV-component as function of intensity and resonance detuning of the laser as well as on the phase-mismatch was calculated on the basis of the small signal theory and compared to the experimental data. (orig.)

[en] The b bar b cross section at the SSC is predicted to be 1-3 mb, and 1-3% of the p-p interactions will produce a b bar b pair. Based on the experience of the CDF collaboration it has been established that the B → J/ψX modes can be found with acceptable background levels in a hadron collider. This paper reports studies of the efficiency for reconstructing the decay B⁰_d → π⁺π^- and of rejection of background due to b bar b. Identification of this decay mode is expected to be more difficult than the B → J/ψX modes due to severe combinatoric backgrounds. Nonetheless, two aspects of B decays will make it possible to extract the B⁰_d → π⁺π^- signal at a hadron collider. The relatively long lifetime of the B meson allows the vertex for the decay B⁰_d → π⁺π^- to be easily isolated from the primary vertex. In addition, the pions from this decay have the maximum momentum of daughters from any B decay and so are more readily separated from low-P_T hadron backgrounds. The results reported here are based on detailed simulation of pattern recognition in vertex fitting using information from a silicon vertex detector. However, the separate issue of track pattern recognition is not addressed, and it is assumed that detector hits are all properly associated with tracks

[en] Despite effective regulations established by professional organizations and business health programs, aluminiumcaused pneumoconiosis still occurs. Therefore, the etiology, clinical appearance, histological confirmation, and X-ray findings are presented from a case which was followed for ten years. The differential diagnosis indicated by the radiologic findings are discussed. (orig.)

[en] QED tree diagrams are calculated with the spinor technique using symbolic algebra. A first program SPINORP1 calculates all topologically distinct diagrams. The input are the number and kinds of particles. A second program SPINORP2 generates a REDUCE source program to evaluate the spinor amplitude for all possible polarizations of the external particles. (orig.)

[en] Abstract only

[en] The influence of the initial grain size of the silicon powder on the microstructure and the resulting mechanical properties are studied. The smaller the grain size of the silicon powders used, the higher will be the degree of reaction at the beginning of the nitridation reaction and the higher the amount of α-modification in the fully nitridated samples. Moreover, the nitrification time can be considerably shortened when fine-grained silicon powders (< 10 μm) are used. Light and scanning electron microscope structural pictures and determination of the pore size distribution with the aid of mercury pressure porosimetry show that the mean pore radius decreases with decreasing initial grain size. While the room-temperature and high-temperature strength increases strongly with decreasing pore radius, the total creep expansion decreases as well as the creep rate. (orig.)