Crystallization kinetics for SiO2 formed during SiC fiber oxidation in steam

The crystallization kinetics for SiO₂ formed by oxidation of Hi-Nicalon^™-S SiC fiber between 800 and 1600°C in Si(OH)₄(g) saturated steam were determined. Glass SiO₂ scale always formed first. Glass scale eventually crystallized to cristobalite, and during further oxidation the scale formed directly as cristobalite. Growth stress relaxed by viscous flow in SiO₂ that formed as glass. Cristobalite formed by crystallization of this glass was relatively undeformed. In SiO₂ that formed directly as cristobalite, growth stress relaxed by intense plastic deformation accompanied by dynamic recrystallization. There were therefore two layers in cristobalite scale: a heavily deformed inner layer and an undeformed outer layer. These layers were distinguished by TEM. SiO₂ crystallization times were determined from the thicknesses of undeformed cristobalite and the SiC oxidation kinetics for glass scale formation. SiO₂ crystallization kinetics were determined from the crystallization time distributions at different SiC oxidation temperatures in steam. For all temperatures the crystallization time growth exponent (n) was 1. There was a large decrease in crystallization rate between 1000 and 1100°C. Between 800 and 1000°C the activation energy (Q) for crystallization was 65 kJ/mol, between 1100 and 1500°C it was 110 kJ/mol, and at 1600°C it was ~500 kJ/mol. Analysis methods and results are discussed.     

The development of a code of ethics for Canadian psychologists.

Over the past 5 yrs, the Canadian Psychological Association has been in the process of developing a new code of ethics for Canadian psychologists. Reasons for this effort are outlined, and the previously used American Psychological Association code is examined in terms of 4 main purposes of ethics codes: to help establish a group as a profession; to act as a support and guide to individual professionals; to help meet the responsibilities of being a profession; and to provide a statement of moral principle that helps the individual professional resolve ethical dilemmas. (French abstract) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Resonant tunneling quantum-dot diodes: physics, limitations, andtechnological prospects

The authors discuss the electronic structure and properties of the present generation of resonant-tunneling quantum-dot structures. Quantum dots are zero-dimensional semiconductor nanostructures, i.e., structures in which an electron is quantum-mechanically confined in all three spatial dimensions. Quantum dots appear to represent a viable structure to allow the continued downscaling of critical circuit geometries beyond the currently perceived limits for conventional VLSI devices. As they are currently fabricated, however, quantum-dot diodes have impediments which prevent the full realization of their potential. The authors assess these limitations and discuss measures for their solution     

Goniometric motion controller for the superconducting coil in amagnetic stereotaxis system

For the purpose of positioning the 80 kg, 2 T superconducting coil/cryostat used in the developmental version of a magnetic stereotaxis system, a four degree-of-freedom goniometer has been designed, built, and tested. Computer-controlled, stepping motor actuators enable movement of the coil via either joystick, keyboard, or translator-module keypad commands. An integral arrangement of counterweights and counterbalances minimizes the overall weight and size of the goniometer, while maintaining static and dynamic stability during operation. As much of the structure as possible has been made of nonmagnetic materials (mostly aluminum) to minimize distortion of the superconducting coil's field. In this paper, we present the design principles for the goniometer, describe the essential features of its construction, and discuss its performance characteristics and limitations. We also discuss a strategy for performing precision magnetic stereotaxis procedures with an arrangement of static superconducting coils.     

On the division of short-term and working memory: An examination of simple and complex span and their relation to higher order abilities.

Research has suggested that short-term memory and working memory (as measured by simple and complex span tasks, respectively) are separate constructs that are differentially related to higher order cognitive abilities. This claim is critically evaluated by reviewing research that has compared simple and complex span tasks in both experimental and correlational studies. In addition, a meta-analysis and re-analyses of key data sets were conducted. The review and analyses suggest that simple and complex span tasks largely measure the same basic subcomponent processes (e.g., rehearsal, maintenance, updating, controlled search) but differ in the extent to which these processes operate in a particular task. These differences largely depend on the extent to which phonological processes are maximized and variability from long list lengths is present. Potential methodological, psychometric, and assessment implications are discussed and a theoretical account of the data is proposed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Long-lived and transferable tumor immunity in mice after targeted interleukin-2 therapy

A major goal of tumor immunotherapy is the induction of tumor-specific T cell responses that are effective in eradicating disseminated tumor, as well as mounting a persistent tumor-protective immunity. We demonstrate here that a genetically engineered fusion protein consisting of human/mouse chimeric anti-ganglioside GD2 antibody and human interleukin-2 is able to induce eradication of established B78-D14 melanoma metastases in immunocompetent syngeneic C57BL/6J mice. This therapeutic effect is mediated by host immune cells, particularly CD8+ T cells and is associated with the induction of a long-lived immunity preventing tumor growth in the majority of animals when challenged up to four months later with B78-D14 cells. This effect was tumor-specific, since no cross-protection against syngeneic, ganglioside GD2+ EL-4 thymoma cells was observed. Furthermore, this tumor-specific protection can be transmitted horizontally to naive, syngeneic SCID mice by passive transfer of CD8+ T lymphocytes derived from immune animals. These results suggest that antibody-targeted delivery of cytokines provides a means to elicit effective immune responses against established tumors in the immunotherapy of neoplastic disease.     

Theoretical modeling of densification during activated solid-state sintering

Activated solid-state sintering relies on the addition of low concentrations of grain boundary segre-gating species to increase diffusion rates. In this article, enhanced diffusion through an activated layer at the grain boundaries has been modeled for the case of tungsten sintered with transition element additions. Both constant heating rates and isothermal sintering are considered. As in classical treatments, sintering is divided into three stages, but modifications are proposed based on recent observations and theories regarding packing coordination, pore morphology, pore location, grain growth, and pore-grain boundary separation. The intermediate and final stages of sintering are al-lowed to overlap based on the amount of closed porosity to account for both pore closure early in the process and the gradual increase in packing coordination with densification. Mean curvature theory is used to estimate pore curvature during the intermediate stage of sintering. In the final stage, pores are modeled on both the corners of a tetrakaidecahedron and on its square facets. The pore location has only a small effect on densification, while the grain boundary mobility is more of a factor. The model allows pore-grain boundary separation to match experimentally measured grain sizes. The model predictions are compared to dilatometer curves of pure tungsten and tungsten sintered with additions of Co, Fe, Ni, and Pd. For the Co- and Fe-activated samples, the model is modified to account for an increase in diffusional activation energy due to dissolution of the activator in tungsten. Formerly Director of Materials Development, P/M Lab, Department of Engineering Science and Mechanics, The Pennsylvania State University.     

Rehearsal-plus: Coping with fire emergencies and reducing fire-related fears

The relative impact of two experimental conditions—rehearsal-plus and behavioral rehearsal—was assessed to determine their influence on acquiring and maintaining fire evacuation skills, as well as reducing fire-related fears. These experimental conditions were compared with two control groups, attention control and wait-list control. The subjects were 40 second- and third-grade children who were randomly assigned to the four groups. Behavioral rehearsal subjects received fire evacuation skills training and verbally rehearsed these skills. Rehearsal-plus subjects were taught fire evacuation skills and a strategy targeting reduction of fire-related fears. Attention control and wait-list control subjects were not taught evacuations skills or fear reduction. All subjects' evacuation skills and fear of fire-related stimuli were assessed at pre-, post-, and follow-up tests. No pretest differences were observed. At post-test, the rehearsal-plus group reported significantly more fear reduction than the other three groups. Behavioral rehearsal and rehearsal-plus groups displayed significantly more evacuation skills than the control groups. At follow-up, the rehearsal-plus group had retained more of their evacuation skills than the control groups; no differences were found among groups concerning fear reduction at this time. We concluded that rehearsal-plus appears to be useful in acquiring and maintaining fire evacuation skills, as well as reducing fire-related fears.Please send reprint requests to Dr. Russell T. Jones, Psychology Department, Virginia Tech University, Blacksburg, VA 24061-0436.