Library

Notes: Three types of oxygen precipitate morphologies at 1050 °C have been identified to be plate-type, pyramidal, and polyhedral. This study was carried out using a set of slices with the same initial oxygen concentration but varying carbon concentrations. The morphology is shown to depend on carbon concentration and heat treatment. It is demonstrated that increasing carbon concentration tends to change the morphology from the plate to polyhedra and enhance the nucleation rate at low temperatures.

Notes: A systematic comparison of precisely characterized resonant tunneling structures is presented. A self-consistent band bending calculation is used to model the experimentally observed resonant peak positions. lt is found that the peak positions can be accurately modeled if the nominal characterization parameters are allowed to vary within the measurement accuracy of the characterization. As a result, it is found that the asymmetries in the current-voltage characteristics are solely explainable by tunnel barrier thickness fluctuations.

Notes: We have investigated the effect of post-growth thermal annealing on the defect surface of patterned GaAs on silicon. Significant improvements in defect structure of the patterned GaAs were observed by transmission electron microscopy (TEM) after short anneal times (15 min) at temperatures as low as 750 °C. At anneal temperatures of 950 °C, long-range single-crystal lateral regrowth of the original polycrystalline GaAs deposited over the amorphous patterning mask was observed. Micro-Raman spectroscopic characterization of the GaAs grown on the oxide/nitride mask corroborated the TEM results by showing a significant improvement in the crystalline quality of patterned GaAs on silicon following post-growth annealing.

Notes: The misfit dislocation configurations in initial GaAs islands grown on silicon were studied by high-resolution electron microscopy. Misfit dislocations, especially 60° type and stacking faults, were observed to generate from near the edges of the islands. Large steps on the substrate surface were observed to help the nucleation of these dislocations. The presence of threading dislocations in thicker films is attributed to the misfit dislocation segments in initial GaAs islands. A mechanism is proposed to explain the propagation and multiplication of misfit dislocations during the coalescence of islands and their subsequent growth.

Notes: High-resolution electron microscopy was applied to investigate the effect of post-annealing on the defect structure at the GaAs/Si interface. This study indicates that annealing results in dislocation rearrangement at the interface to form the majority of Lomer's dislocations with their Burgers vectors parallel to the interface. Dislocations with inclined Burgers vectors (type 2) at the interface after annealing are often observed at steps introduced by the substrate surface roughness. This observation is discussed in terms of the shrinking of stacking faults and microtwins and the preferential nucleation of both stacking faults (or microtwins) and type 2 dislocations at surface steps.

Notes: Twenty-four-hour intragastric acidity was measured in 10 patients with past history of duodenal ulcer on the fourth day of dosing with placebo, and either 150 mg ranitidine given twice or four times daily. The order the treatments was randomized and a double-blind design was employed. Ranitidine (150 mg) b.d. decreased median integrated 24-h intragastric acidity by 65.1%, nocturnal acidity by 89.1%, and daytime acidity by 54.6% (all P 〈 0.01 compared to placebo). The corresponding decreases with 150 mg ranitidine q.d.s. were 62.3, 89.9 and 48.8%, respectively (all P 〈 0.01 compared to placebo). There were no significant differences between the two dosage regimens of ranitidine (P 〉 0.05).This study shows that giving extra doses of 150 mg ranitidine during the day does not increase the degree of suppression of intragastric acidity.

Notes: Abstract The variable-interval time-averaging (“VITA”) algorithm has been tested in a variety of turbulent boundary layers for its ability to detect shear-stress-producing motions from hot-wire signals. A “VITA + LEVEL” scheme (which uses criteria for both short-time variance and short-time average, i.e.“level”) has been devised, and used in several different boundary layers. This scheme yields length-scale statistics that are acceptably independent of the conditioning criteria, which the VITA scheme does not.

Notes: Summary Previous experiments have shown that during prey-catching behavior (orienting, snapping) in response to a worm-like moving stripe common toads.Bufo bufo (L.) exhibit a contrast-and direction-dependent edge preference. To a black (b) stripe moving against a white (w) background (b/w), they respond (R*) preferably toward the leading (l) rather the trailing (t) edge (R l * 〉 R t * ), thus displaying ‘head preference’. If the contrastdirection is reversed (w/b), the stripe's trailing edge is preferred (R l * 〈 R t * ), hence showing ‘tail preference’. In the present study, neuronal activities of retinal classes R2 and R3 and tectal classes T5(2) and T7 have been extracellularly recorded in response to leading and trailing edges of a 3 ° × 30 ° stripe simulating a worm and traversing the centers of their excitatory receptive fields (ERF) horizontally at a constant angular velocity in variable movement direction (temporo-nasal or naso-temporal). The behavioral contrast-direction dependent edge preferences are best resembled by the responses (R) of prey-selective class T5(2) neurons (Rl∶ Rt=10∶1 for b/w, 0.3∶1 for w/b) and T7 neurons (Rl∶Rt=6∶1 for b/w, 0.4∶1 for w/b); the T7 responses may be dendritic spikes. This property can be traced back to off-responses dominated retinal class R3 neurons (Rl∶Rt=6∶1 for b/w, 0.5∶1 for w/b), but not to class R2 (Rl∶Rt =1.2∶1 for b/w and 0.9∶1 for w/b). The respective edge preference phenomena are independent of the direction of movement. When stimuli were moved against a stationary black-white structured background, the ‘head preference’ to the black stripe and the ‘tail preference’ to the white stripe were maintained in class R3, T5(2), and T7 neurons. If the stripe traversed the ERF together with the structured background in the same direction at the same velocity, the responses of tectal class T5(2) and T7 neurons were strongly inhibited, particularly in the former. Responses of retinal R2 neurons in comparable situations could be reduced by about 50%, while class R3 neurons responded to both the stimulus and the moving background structure. The results support the concept that the prey feature analyzing system in toads applies principles of (i) ‘parallel’ and (ii) ‘hierarchial’ information processing. These are (i) divergence of retinal R3 neuronal output contributes to stimulus edge positioning and (in combination with R2 output) area evaluation intectal neurons and to stimulus area evaluation and (in combination with R4 output) sensitivity for moving background structures inpre tectal neurons; (ii) convergence of tectal excitatory and pretectal inhibitory inputs specify the property of prey-selective tectal T5(2) neurons which are known to project to bulbar/spinal motor systems.