Preparation of high resistivity antimony selenide by zone refining

A two-step zone refining process to obtain high resistivity Sb₂Se₃ ($\text{? > 10}{}^7\text{Ω}\text{cm}$) with a good yield is described. It is shown how the deviations from the stoichiometry may be conveniently controlled by measurements of the electrical resistivity and by differential thermoanalysis.     

Evolutionary Design of Fuzzy Logic Based Position Controller for Mobile Robot

This paper develops a fuzzy logic based position controller whose membership functions are tuned by genetic algorithm. The main goal is to ensure successful velocity and position trajectories tracking between the mobile robot and the virtual reference cart. The proposed fuzzy controller has two inputs and two outputs. The first input represents the distance between the mobile robot and the reference cart. The second input is the angle formed by the straight line defined with the orientation of the robot, and the straight line that connects the robot with the reference cart. The outputs represent linear and angular velocity commands, respectively. The performance of the fuzzy controller is validated through comparison with previously developed mobile robot position controller based on control Lyapunov functions (CLF). Simulation results indicate good performance of position tracking while at the same time a substantial reduction of the control torques is achieved.     

Unlocking diamond's potential as an electronic material

In this paper, we review the suitability of diamond as a semiconductor material for high-performance electronic applications. The current status of the manufacture of synthetic diamond is reviewed and assessed. In particular, we consider the quality of intrinsic material now available and the challenges in making doped structures suitable for practical devices. Two practical applications are considered in detail. First, the development of high-voltage switches capable of switching voltages in excess of 10 kV. Second, the development of diamond MESFETs for high-frequency and high-power applications. Here device data are reported showing a current density of more than 30 mA mm(-1) along with small-signal RF measurements demonstrating gigahertz operation. We conclude by considering the remaining challenges which will need to be overcome if commercially attractive diamond electronic devices are to be manufactured.     

Microstructure and Composition of Primary and Recycled Single Grains of YBCO,GdBCO‐Ag,and SmBCO‐Ag Bulk Superconductors

The widespread use of single grain RE‐Ba‐Cu‐O [(RE)BCO] bulk superconductors, where RE is typically Sm, Gd, or Y, is, in part, limited by the relatively high costs of precursor powders and the low success rate of the manufacturing process. Both these problems can be addressed by recycling primary‐processed grains in which the initial growth process has failed in some way. Key to the use of recycled grains in practical applications is an assurance that their properties and performance are not inferior to those of primary grown grains. In this work, we describe the differences between the growth process, microstructure, and properties of primary and recycled (RE)BCO single grains. We observe that the mechanism of growth is the same for both primary and recycled single grain samples in all three RE‐based systems investigated. In the recycling process additional liquid‐rich phase powder is provided beneath a failed sample, whereby this liquid phase infiltrates upwards and contributes a sufficient concentration of additional RE species at the growth front to enable samples to grow relatively easily in the form of single grains by producing a more uniform composition at the growth front, which leads directly to an increased tolerance to the presence of Ag and Ce‐rich agglomerates. Importantly, we observe that the recycled samples have a much more uniform composition, and therefore exhibit more uniform superconducting properties, than single grain samples fabricated by a primary grown process.     

Deficits in complex motor functions, despite no evidence of procedural learning deficits, among HIV+ individuals with history of substance dependence.

Human immunodeficiency virus (HIV) and drugs of abuse affect common neural systems underlying procedural memory, including the striatum. The authors compared performance of 48 HIV seropositive (HIV+) and 48 HIV seronegative (HIV-) participants with history of cocaine and/or heroin dependence across multiple Trial Blocks of three procedural learning (PL) tasks: Rotary Pursuit (RP), Mirror Star Tracing (MST), and Weather Prediction (WP). Groups were well matched on demographic, psychiatric, and substance use parameters, and all participants were verified abstinent from drugs. Mixed model analyses of variance revealed that the individuals in the HIV+ group performed more poorly across all tasks, with a significant main effect of HIV serostatus observed on the Mirror Star Tracing and a trend toward significance obtained for the Rotary Pursuit task. No significant differences were observed on the Weather Prediction task. Both groups demonstrated significant improvements in performance across all three procedural learning tasks. It is important to note that no significant Serostatus × Trial Block interactions were observed on any task. Thus, the individuals in the HIV+ group tended to perform worse than those in the HIV- group across all trial blocks of procedural learning tasks with motor demands, but showed no differences in their rate of improvement across all tasks. These findings are consistent with HIV--associated deficits in complex motor skills, but not in procedural learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Steam reforming of liquid hydrocarbons over a nickel-alumina spinel catalyst

Interest in steam reforming of liquid hydrocarbons is growing due to the necessity of developing reliable alternatives for their use in fuel cells. In particular, solid oxide fuel cells, which can operate with mixtures of H₂ and CO, are excellent candidates for being fed with liquid fuels coming from both fossil and renewable sources. Fossil-derived, synthetic diesel is an interesting option.In this work, an Al₂O₃-ZrO₂-supported nickel-alumina spinel was tested in a lab-scale isothermal packed-bed reactor as a catalyst of steam reforming of propane, hexadecane and tetralin as surrogates of constitutive families of all commercially available diesel fuels.The results show that the reaction reaches equilibrium at reaction severities lower than those reported in the literature. When operated at steam excess of 250%, carbon formation is not higher than expected by theoretical thermodynamic equilibrium calculations, and no significant catalyst deactivation is observed over the test durations. Scanning electron microscopy of the fresh and used catalyst surfaces shows no significant quantities of carbon.