ZrO<Subscript>2</Subscript> coatings on SiC fibers

Zirconia coatings have been produced on Hi-Nicalon fibers via pyrolysis of zirconium oxalates extracted into amine-benzene solutions. X-ray diffraction and electron probe x-ray microanalysis results demonstrate that the pyrolysis of extracts is a viable approach to producing thin zirconia coatings on coreless silicon carbide fibers and that further research is needed to optimize the microstructure of zirconia coatings.     

Effects of initial powder vibrogrinding on the properties of AlN - BN composites

A study has been made on the effects of initial vibroground powders with various grain sizes on the properties of AlN - BN composites. As the specific surface of these powders increases, so do the density, mechanical strength, and thermal resistance of the composites.     

Neighborhood disadvantage moderates associations of parenting and older sibling problem attitudes and behavior with conduct disorders in African American children.

Data from 296 sibling pairs (mean ages 10 and 13 years), their primary caregivers, and census records were used to test the hypothesis that African American children's likelihood of developing conduct problems associated with harsh parenting, a lack of nurturant-involved parenting, and exposure to an older sibling's deviance-prone attitudes and behavior would be amplified among families residing in disadvantaged neighborhoods. A latent construct representing harsh-inconsistent parenting and low levels of nurturant-involved parenting was positively associated with younger siblings' conduct disorder symptoms, as were older siblings' problematic attitudes and behavior. These associations were strongest among families residing in the most disadvantaged neighborhoods. Future research and prevention programs should focus on the specific neighborhood processes associated with increased vulnerability for behavior problems. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Reactivity of platinum nanoaggregates in catalytic reduction of U(VI) with hydrazine in acid solutions

Catalysts Pt/SiO₂ with different size of Pt nanoaggregates were studied in catalytic reduction of U(VI) with hydrazine in solutions of H₂SO₄, HClO₄, and HNO₃. The catalytic activity of the surface Pt atoms of Pt/SiO₂ in this reaction monotonically increases with an increase in the size of metal crystallites on the support, i.e., the negative size effect is observed. Catalytic reduction of U(VI) with hydrazine in H₂SO₄ solutions is significantly faster than in HClO₄ and HNO₃, and in HClO₄ it is slightly faster than in HNO₃. The results were interpreted within the framework of the concept of the energetic nonuniformity of the surface atoms and of the mechanisms of catalytic reduction of U(VI) with hydrazine in acid solutions.     

The influence of strontium on porosity formation in Al-Si alloys

Strontium modification is known to alter the amount, characteristics, and distribution of porosity in Al-Si castings. Although many theories have been proposed to account for these effects, most can be considered inadequate because of their failure to resolve contradictions and discrepancies in the literature. In an attempt to critically appraise some of these theories, the amount, distribution, and morphology of porosity were examined in sand-cast plates of Sr-free and Sr-containing pure Al, Al-1 wt pct Si, and Al-9 wt pct Si alloys. Statistical significance testing was used to verify apparent trends in the porosity data. No apparent differences in the amount, distribution, and morphology of porosity were observed between Sr-free and Sr-containing alloys with no or very small eutectic volume fractions. However, Sr modification significantly changed the amount, distribution, and morphology of porosity in alloys with a significant volume fraction of eutectic. The addition of Sr reduced porosity in the hot spot region of the casting, and the pores became well dispersed and rounded. This result can be explained by considering the combined effect of the casting design and the differences in the pattern of eutectic solidification between unmodified and Sr-modified alloys.     

Temperature dependence of the effective coefficient of Auger recombination in 1.3 μm InAs/GaAs QD lasers

Semiconductor laser heterostructures containing five and ten sheets of InAs/GaAs QDs on GaAs substrates, with an emission wavelength of ～1.3 μm, have been studied. Dependences of the nonradiative lifetime and effective Auger coefficient in QDs are obtained from an analysis of temperature and current dependences of the efficiency of spontaneous radiative recombination. The zero-threshold Auger recombination channel in QDs is shown to dominate at low (below 200 K) temperature, whereas at higher temperatures the quasithreshold channel becomes dominant. The effective 3D Auger coefficient is estimated in the approximation of a spherical QD, and a good agreement with the experimental data is obtained.     

Nonlinear dynamics of a plasma torch generated by a laser pulse of large width

Experimental data on the nonlinear dynamics of a plasma torch generated by a laser pulse of large width acting upon a graphite target are presented and discussed. The mushroom shape of the luminous region and the duration of emission observed in experiment are explained by the development of the Richtmyer-Meshkov instability at the carbon plasma-air interface and by the formation of nanoparticles in the plasma expanding into the buffer gas.     

Synthesis of CN<Subscript>x</Subscript> nanotubes using catalysts prepared from zinc and nickel bimaleates

Nitrogen-containing carbon nanotubes have been prepared via acetonitrile (CH₃CN) pyrolysis at 850°C catalyzed by nanoparticles produced by the thermal decomposition of zinc and nickel bimaleates and their solid solutions. The synthesized samples have been characterized by transmission electron microscopy, x-ray diffraction, and x-ray photoelectron spectroscopy. The results demonstrate that increasing the zinc content of catalyst nanoparticles reduces the yield of carbon nanotubes and increases the nitrogen content of the material. The high synthesis temperature gives rise to zinc vaporization, which influences the growth process, increasing the nanotube diameter, reducing the wall thickness, and lowering the structural perfection of the graphite layers.