A macrokinetic approach to crystallization applied to a new thermoplastic polyimide (New TPI) as a model polymer

The application of a new macrokinetic approach to polymer crystallization is applied in this work to a new thermoplastic polyimide (New TPI) recently developed as a matrix of advanced polymer matrix composites. The slow crystallization kinetics presented by New TPI in the entire range between the glass-transition temperature and the melting point makes TPI an excellent model polymer for testing crystallization models. In the approach presented here the variation of the induction time with the temperature is included in the Nakamura model for nonisothermal crystallization, and a simplified expression of the kinetic constant as a function of the temperature is adopted. The proposed model is verified through a comparison with a complete set of experimental data, ranging from the melting point to the glass-transition temperature of the polymer, obtained in isothermal and nonisothermal conditions. Moreover phase transformation diagrams (TTT and CCT plots) are presented, providing a fundamental tool for understanding the crystallization behavior of semicrystalline matrices and to determine the more appropriate processing conditions. © 1995 John Wiley & Sons, Inc.     

Synchronous Digital Hierarchy statistical simulation of pointer activity

Pointer activity in Synchronous Transport Module 1 (STM1) networks is presented based on simulated models of various STM1 network payload configurations. A statistical clock model is used to simulate the effects of clocking instabilities. The clock model used is based upon an RMS Time Interval Error (RMSTIE) metric and conforms to the RMSTIE mask as defined by CCITT and other standards committees. Traditional pointer activity studies have been done on a behavioural basis, minimizing byte by byte calculations to reduce simulation time and resolution of results. Additionally, previous studies have examined the effects of constant clock frequency offsets on pointer activity. This study approaches the problem by using byte by byte calculations coupled with a statistical clock model and constant frequency offsets to determine pointer generation and interactions at a level of detail not presented previously. The results of this study are the expected nature of pointer activity in Synchronous Digital Hierarchy (SDH) networks for clock instabilities within the CCITT clock stability specifications.     

Primary gamma delta cell clones can be defined phenotypically and functionally as Th1/Th2 cells and illustrate the association of CD4 with Th2 differentiation

The division of CD4+ alpha beta T cells into Th1 and Th2 subsets has become an established and important paradigm. The respective activities of these subsets appear to have profound effects on the course of infectious and autoimmune diseases. It is believed that specific programs of differentiation induce the commitment of an uncommitted Th0 precursor cell to Th1 or Th2. A component of these programs is hypothesized to be the nature of MHC-peptide antigen presentation to the alpha beta T cell. It has heretofore remained uncertain whether a Th1/Th2 classification likewise defines, at the clonal level, gamma delta T cells. Such cells do not, as a general rule, express either CD4 or CD8 alpha beta, and they do not commonly recognize peptide-MHC. In this report, gamma delta cell clones are described that conform strikingly to the Th1/Th2 classification, both by cytokine expression and by functional activities of the clones in vitro and in vivo. Provocatively, both the gamma delta cell clones and primary gamma delta cells in vivo showed a strong association of the Th2 phenotype with CD4 expression. These results are discussed with regard to the immunoregulatory role that is increasingly emerging for gamma delta cells.     

Transient clouds in Titan's lower atmosphere

The 1980 encounter by the Voyager 1 spacecraft with Titan, Saturn's largest moon, revealed the presence of a thick atmosphere containing nitrogen and methane (1.4 and approximately 0.05 bar, respectively). Methane was found to be nearly saturated at Titan's tropopause, which, with other considerations, led to the hypothesis that Titan might experience a methane analogue of Earth's vigorous hydrological cycle, with clouds, rain and seas. Yet recent analyses of Voyager data indicate large areas of super-saturated methane, more indicative of dry and stagnant conditions. A resolution to this apparent contradiction requires observations of Titan's lower atmosphere, which was hidden from the Voyager cameras by the photochemical haze (or smog) in Titan's stratosphere. Here we report near-infrared spectroscopic observations of Titan within four narrow spectral windows where the moon's atmosphere is ostensibly transparent. We detect pronounced flux enhancements that indicate the presence of reflective methane condensation clouds in the troposphere. These clouds occur at a relatively low altitude (15+/-10 km), at low latitudes, and appear to cover approximately 9 per cent of Titan's disk.     

The role of perceived barriers and relational support in the educational and vocational lives of urban high school students.

Drawing on developmental contextual theory, the authors examined the relationship of perceived barriers and support with school engagement and vocational attitudes among 9th-grade urban high school students in 2 studies. Study 1 (N=174) showed that both perceived barriers and perceived support from family kin were associated with youths' commitment to school and aspirations for success in their future careers. Study 2 (N=181) replicated and extended Study 1, demonstrating that perceived barriers, general perceptions of support, and kinship support were associated with behavioral and attitudinal indexes of school engagement, as well as with aspirations for career success, expectations for attaining career goals, and the importance of work in one's future. The findings contribute to efforts to identify individual and contextual factors relevant to the educational and vocational lives of urban minority youth. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

GENERATION, CONTROL, ANO RECOVERY OF ORGANIC PYROLYSIS PRODUCTS IN UNDERGROUND COAL GASIFICATION

The organic chemical substances present in UCG- affected subsurface waters are formed by the thermal degradation of coal. After a UCG reactor is shut down, the sensible heat contained in the rubble pile is sufficient to continue coa1 pyrolysis. If the pyrolysis products are not removed. they become a potential source of sub surface water contamination. Heat transfer into the coal seam and migration c if chemical substances after reactor shutdown can be sub stantially reduced by a controlled influx of water through the cavity side wal1s and removal of produced fluids from the reactor.     

Distinct roles of the interleukin-7 receptor alpha chain in fetal and adult thymocyte development revealed by analysis of interleukin-7 receptor alpha-deficient mice

Mouse mutants lacking expression of the IL-7 receptor (IL-7R) alpha chain are defective in thymopoiesis. The adult thymus has multiple defects, including reduced cell numbers and proportions of the more mature thymocyte subsets, a complete absence of CD25+ cells and a reduced level of RAG1 and RAG2 expression. We show here that, in contrast to the profound developmental arrest observed in the adult thymus, fetal thymocytes from IL-7Ralpha-/- mice have normal proportions of all of the major thymocyte subpopulations, including CD25+ thymocytes and the most mature single-positive subsets. Moreover, normal levels of RAG1 and RAG2 were observed. Total thymocyte numbers, however, remained reduced. These data suggest that the IL-7Ralpha chain is a key regulator of both survival and proliferation during thymocyte development but that it is not essential for the production of T cells during fetal thymopoiesis.     

The examination of myofascial face pain and its relationship to psychological distress among women.

In this study, 110 female myofascial face pain patients were assessed monthly for 10 months on measures of pain, distress, and stressful life events. D. A. Kenny and A. J. Zautra's (1995) structural equation model for examining the separate trait, state, and error components of the variables was used to analyze the data. Both pain and distress had sizable trait variance, and the trait components were correlated. The 2 variables also showed sizable state variance, and the states of pain covaried with states of distress. A significant time-lagged relationship between the 2 variables was found: Increases in distress led to elevations in pain 1 mo later. Stressful life events arising from major social roles were also associated with greater distress, but not pain. Illness events unrelated to the pain syndrome were associated with both pain and distress. (PsycINFO Database Record (c) 2010 APA, all rights reserved)