The Use of Nitrogen Dioxide to Improve the Superconducting Properties of YBa2Cu3O7

The elemental homogeneity of YBa₂Cu₃O₇ powders can be improved substantially by heating the powder in a nitrogen dioxide-containing atmosphere (e.g., 950°C), followed by annealing in oxygen above 750°C, and slow cooling to room temperature. The improved homogeneity results in a substantially larger flux exclusion signal for the NO₂-treated powder, as measured by ac susceptibility. Moreover, the NO₂-processed powder exhibits a slablike morphology which should be more suitable for grain alignment. A substantial advantage of the NO₂ process is that this process is easily scaled to larger batches and the results are highly reproducible. This is not the case for solid-state reaction processes requiring repeated heating and grinding. The experimental results suggest a mechanism which involves the formation of a small amount of molten Ba(NO₃)₂ which acts as a flux that dissolves the constituents and reprecipitates them as highpurity YBa₂Cu₃O₇. The effects of the various process variables on the properties of the treated powder, and the reproducibility of the process, are discussed.     

Wet Reflectors in Millimeter-Wave Radiometry-Expenrment and Theory

Microwave radiometers are often required to operate under all weather conditions, including those under which an exposed surface of the antenna system becomes wetted by rain. Here we discuss the special case of a wetted flat reflector, with energy at 20.60 and 31.65 GHz linearly and orthogonally polarized at an incidence angle of 45°. The brightness temperatures produced by the wet reflector are computed from conventional theory, and are measured for various thicknesses of water layer. Both theory and experiment show that the brightness temperatures produced by the wet reflector have the same behavior throughout a range of water-layer thicknesses. The impact of these results on design of radiometers for research and operational application is discussed.     

Chronic and temporarily activated causal uncertainty beliefs and stereotype usage.

In 3 studies, we examined the hypothesis that the effects of stereotype usage on target judgments are moderated by causal uncertainty beliefs and related accuracy goal structures. In Study 1, we focused on the role of chronically accessible causal uncertainty beliefs as predictors of a target's level of guilt for an alleged academic misconduct offense. In Study 2, we examined the role of chronic causal uncertainty reduction goals and a manipulated accuracy goal; in Study 3, we investigated the role of primed causal uncertainty beliefs on guilt judgments. In all 3 studies, we found that activation of causal uncertainty beliefs and accuracy concerns was related to a reduced usage of stereotypes. Moreover, this reduction was not associated with participants' levels of perceived control, depression, state affect, need for cognition, or personal need for structure. Results are discussed in terms of their implications for the model of causal uncertainty and, more generally, in terms of the motivational processes underlying stereotype usage. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Children with recently diagnosed diabetes: Interactions within their families.

Analyzed how families with a diabetic child interact and how these patterns differ from other families, using 57 diabetic and 48 acutely ill early adolescents and preadolescents from 2-parent families. The 2 samples were contrasted in terms of enabling and constraining interactions of each family member. Findings reveal that diabetic Ss and their parents expressed significantly more enabling (e.g., focusing, problem-solving, active understanding) speeches than comparable members of the acute illness group. There were indications of particular constraining interactions (devaluing) occurring between fathers and diabetic Ss. Several alternative interpretations are offered to account for these results. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The high-temperature work function behavior of polycrystalline osmium

The thermionic emission behavior of randomly oriented polycrystalline osmium was investigated. Osmium exhibited a low thermionic work function of 4.68 eV at 1800 K which increased rapidly to 5.21 eV at 2600 K. The high temperatures and low pressures of these tests were designed to minimize any residual gas interactions with the sample surface. Still, the possibility that residual gases had some effect on the measured work function was not altogether ruled out. An allotropic phase transformation was considered as a possible explanation for the varying work function; however, X-ray diffraction experiments could not substantiate a new high-temperature phase.     

High-Temperature Oxidation of Boron Nitride: I, Monolithic Boron Nitride

High-temperature oxidation of monolithic boron nitride (BN) is examined at 900–1200°C. Hot-pressed BN and both low- and high-density chemically vapor-deposited BN are studied. The oxidation product is B₂O₃( l ) and the oxidation kinetics are sensitive to crystallographic orientation, porosity, and impurity levels. The B₂O₃ product also reacts readily with ambient water vapor in the test furnace (ppm levels) to form the volatile species HBO₂( g ), leading to overall paralinear kinetics. The linear rate constant extracted from these experiments agreed with that predicted from diffusion of HBO₂( g ) across a static boundary layer.     

A backstepping‐based low‐and‐high gain design for marine vehicles

A backstepping control design for marine vehicles was described in (Marine Control Systems: Guidance, Navigation and Control of Ships, Rigs, and Underwater Vehicles. Marine Cybernetics AS: Trondheim, Norway, 2002). Under a backstepping feedback law, global asymptotic stability of the closed‐loop system can be shown under the assumption of unlimited actuation. This paper addresses the issues that arise in the implementation of a backstepping feedback law by saturating actuators. First, for a given backstepping feedback law, an estimate of the domain of attraction is given for the resulting closed‐loop system under actuator saturation. A high gain component is then constructed and augmented to the original backstepping feedback law. This additional high gain component is shown not to shrink the estimate of the domain of attraction but to possess the ability to improve the closed‐loop response and to reject disturbance. Copyright © 2008 John Wiley & Sons, Ltd.     

Thermally induced changes in metal solubility of contaminated soils is linked to mineral recrystallization and organic matter transformations

Soils are biogeochemical systems under continual modification by biological and chemical processes. Trace element solid-solution partitioning is thus influenced by long-term changes to these solid phases. We study Pb, Cd, Zn, and Cu solution speciation and solid-phase dynamics in two soils of volcanic origin (Te Akatea and Egmont, high in noncrystalline aluminosilicates), an oxisol from Brazil (Oxisol, high in oxides of Al and Fe), and several sludge-treated soils (labeled NYS soils, high in organic materials). Total soluble (by ICP) and labile (by ASV) concentrations of Pb, Cd, Zn, and Cu were determined after incubation of the soils for about 1.5 yr at room (23 degrees C) and elevated (70 degrees C) temperatures. Changes occurring to the solid phases were monitored by FTIR and extraction with oxalate and pyrophosphate. It is shown that induced hydrolysis or decomposition of organic materials in soils results in increases in both labile and total soluble concentrations of Pb, Cd, Cu, and Zn in solution. Labile and total soluble concentrations of Cu and Zn increase concomitantly with dissolved organic carbon (DOC); the nonlabile soluble fraction also increases with increasing DOC. Similarly, the concentration of Cd and Pb in solution increases with increasing DOC; however, most soluble Cd and Pb is asv-labile. Only in the Egmont soil (mineralogy dominated by proto-imogolite allophane) was reduced Pb solubility observed after prolonged equilibration and heating. Lead solubility increased after partial crystallization of amorphous minerals in the Te Akatea and the Oxisol. Thus, for most of the metal-soil systems studied, prolonged thermal treatment at 70 degrees C increased total soluble and asv-labile metals, suggesting that aging effects on metals in contaminated soils could release metals to labile forms in some cases.