Effect of Impurities on Sic Whisker Morphology

Thermal decomposition of polymeric organosilicon, as precursor to Sic whiskers, in the presence of impurities such as alkali and alkaline-earth metals and aluminum resulted in glass beads or droplets on the β-Sic whiskers. Semiquantitative analysis of typical whiskers and whiskers with glass beads were performed using a transmission electron microscope equipped with an energy-dispersive X-ray spectrometer and a scanning transmission electron microscope equipped with an electron energy loss spectrometer. The major impurities identified were correlated with the processing method employed     

A school community in disaster: Primary and secondary prevention in situational crisis.

Provides a preliminary model for preventive local school psychological service (SPS) intervention in an extreme emergency. Following a terrorist attack on an Israeli town's neighborhood, the local SPS reorganized its staff to make its service available to the neighborhood schools, using the primary prevention and the secondary prevention models. The implementation of these models' principles is demonstrated, basic emergency issues facing the mental-health agent are delineated, and selection of specific techniques under explicit stress conditions is described. (32 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Analytical studies on some microconstituents in 2024 aluminum alloy

X-ray analysis of α(FeMnCuSi), (Fe,Mn,Cu) Al₆ and Al₇Cu₂Fe particles in a Rheocast 2024 alloy were performed both with bulk samples in the microprobe (on relatively large particles) and with thin sections in the electron microscope. Some procedures were suggested for dealing with the spatial resolution problems of the microprobe; the qualitative application of the thin section technique was found (with certain precautions) to be informative with moderate effort, and the need was emphasized for establishment of the thin section technique as fully quantitative. The Al₇Cu₂Fe in these samples, formed from (Fe,Mn,Cu)Al₆ during annealing, contained excess Mn and was thought from electronmicroscopic observations to be in a segregated nonequilibrium condition. Formerly with the University of Illinois at Urbana-Champaign     

Enhancing students' test coping skills: Report of a psychological health education program.

We tested the effectiveness of a teacher-implemented psychological health education program designed to improve students' test coping skills in the classroom. Four hundred ninety-seven Israeli students, drawn from 24 fifth- and sixth-grade elementary school classes, were randomly assigned to experimental and control conditions by homeroom class. Students were trained to practice rational self-analysis and exploration, relaxation and deep-breathing exercises, positive self-statements, positive self-reinforcement, and coping imagery. The training program consisted of five workshop sessions held in the classroom and implemented by homeroom teachers specifically trained for the task. Overall, the cognitive training program was shown to significantly improve students' levels of performance on three cognitive measures, although it negligibly affected test anxiety score. On the whole, these results support the feasibility and effectiveness of a teacher-based program for the improvement of students' test coping skills and subsequent test performance. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Microstructure Comparison of Transparent and Opaque CVD SiC

Transparent, translucent, and opaque regions of high- purity bulk SiC, produced by CVD, have been characterized for physical properties as well as microstructure and chemical purity to correlate degree of transparency with other material characteristics. A good correlation was obtained between SiC vis-a-vis IR transmission and its microstructure. The transparent material is highly oriented toward the (111) direction and is characterized by pure, essentially defect-free, cubic β-SiC columnar grains of size 5–10 μm. The translucent material of various colors is mostly cubic in structure but contains large amounts of twins, usually as complex mixtures of several twinning variants and secondary twinning within a single "grain." Opaque CVD SiC is randomly oriented, does not exhibit columnar grains, and contains one directional disorder with hexagonal (α-SiC) symmetry in a majority of grains and high density of dislocations elsewhere.     

A study of the effect of variable surface conditions on the outdoor heat stress using a mathematical model of the atmospheric boundary layer

A one-dimensional model of the atmospheric and soil boundary layers is used to study the climate near the ground (micro-climate) under variable surface conditions. The model is based on the assumption that at any given moment a balance of energy exists at the interface separating the atmosphere from the ground. The solar and sky radiation are specified, and the temperature, wind, and humidity at 300 meters, and the temperature 32 cm under the soil surface are given as upper and lower boundary conditions. The surface conditions (e.g., vegetation cover) are simulated by specifying the surface albedo, α, the roughness parameter, Z₀ and a parameter related to the nature of evaporation from the surface. The model produces results of temperature and humidity as a function of time and height. These results are used to derive a simple comfort index which is compared under different surface conditions.     

High-Temperature Mechanical Properties and Microstructures for Hot-Pressed Silicon Nitrides with Amorphous and Crystalline Intergranular Phases

Four-point flexure tests were performed at 1100° to 1350°C on two hot-pressed silicon nitrides, one in which the grain-boundary phase was amorphous and one in which it was largely crystalline. Fracture stress and relative K_1c were plotted vs temperature. Fracture regions were analyzed by scanning and transmission electron microscopy. Grain-boundary phases affected high-temperature fracture significantly.     

Simple planar modeling of asymmetric shear buildings for lateral forces

A simple plane frame model is described for the lateral load analysis—static and dynamic—of frames in multistory buildings including biaxial load effects. By taking advantage of the shear force-axial force and the torque-bending moment analogies it is possible to model the spatial behavior of the structure, and to consider the combined effects of bidirectional shear due to lateral and torsional displacements on columns pertaining to two orthogonal frames. A numerical example is given.     

Microscopic Mechanisms of Oxidation in SiC-Whisker-Reinforced Mullite/ZrO2 Matrix Composites

The oxidation of SiC whiskers, contained in alkoxide-derived mullite-based matrices and exposed in air at 1000–1350°C for up to 1000 h, has been studied by analytical TEM, high-resolution SEM, and XRD. Silicon carbide whiskers were effectively protected from oxidation when embedded in a pure mullite matrix, but oxidized considerably when embedded in mullite/ZrO₂ matrices. The oxidation mechanisms varied with matrix composition and exposure temperature. At 1350°C the amorphous layer first crystallized as cristobalite, then gradually incorporated alumina. At later times, the mullite portion of the mullite/ZrO₂ matrix dissolved extensively into the layer. Also, the zirconia particles reacted with silica to form zircon. At 1200°C less extensive interdiffusion and chemical reaction occurred, and the silica layer devitrified into cristobalite and quartz. At 1000°C no interdiffusion or chemical reaction was seen, and the silica layer tended to devitrify into quartz. The thickness of the oxide layer around a SiC whisker in a particular matrix depended on the morphology and composition of grains abutting it or adjacent to it.