Phase-field approach to simulate BCC-B2 phase separation in the AlnCrFe2Ni2 medium-entropy alloy

Journal of Materials Science - Phase separation is a relevant mode of transformation for microstructure development in multicomponent alloys. Its occurrence can drastically alter the composition...     

Distinguishable patterns of connectivity in serum immunoglobulins from SLE patients and healthy individuals

Given that normal individuals maintain significant levels of serum autoantibodies that share many characteristics with those found in association with autoimmune diseases (AID), it has been proposed that disease could result from defects in supraclonal regulation, namely deviations of normal patterns of immunoglobulin (Ig) connectivity. Using conventional methods, together with a recently developed technique to quantitatively score a variety of V-region-dependent serum IgG interactions, the authors have now compared serum Ig connectivity in a group of patients with systemic lupus erythematosus (SLE) to healthy controls. The results demonstrate the existence of V-region interactions of serum IgG and IgM in SLE patients and healthy donors, with comparable connectivity titres, diversity and average affinities (microM range), but a wider individual variation and a tendency for higher F(ab')2 directed reactivities in the group of SLE patients. Multivariate statistics analysis of the data derived from reactivity patterns on F(ab')2 subsets, however, distinguished the two groups of donors, and demonstrated a larger dispersion and wider time-dependent variations in the patient population, as compared to healthy controls. The authors conclude that SLE is associated with circulating antibody repertoires that deviate from the patterns and levels of V-region connectivity characteristic of healthy individuals. These findings may shed light on the mechanisms of disease maintenance, and on the basis for the therapeutic effects of normal polyclonal Igs at high doses.     

AIDS; new developments. I. HIV tests: time for a more active policy

Until recently, an HIV test was of limited importance for persons who had been at risk for HIV as effective drugs were not available. With the advent of a new generation of antiretroviral drugs with beneficial effect after early treatment, knowledge of the HIV serostatus has become of more importance to asymptomatic persons. There is no need for a mass screening campaign however, as there is no cure as yet.     

Functional diversity and clonal frequencies of reactivity in the available antibody repertoire

Our objective was to determine the effect of level and chemical form of dietary selenium on productivity of beef cows, concentrations of triiodothyronine (T3), and thyroxine (T4) in plasma, and immunoglobulins (IgG and IgM) in plasma and colostrum of cows. Pregnant cows (n = 60) were randomly allocated among four dietary treatments of 20, 60, or 120 ppm Se as selenite and 60 ppm as selenomethionine from selenized yeast (SeY) in salts offered free-choice. Treatments began 90 d prepartum and continued through the second parturition. Treatments did not affect the final body weights of cows or birth weights or weaning weights of calves. At parturition, cows given salt with 20 ppm Se as selenite had lower (P < . 05) concentrations of Se in blood than cows with access to higher-Se salts. Treatments affected (P < .01) the concentration of T3 and the ratio of T3:T4 in plasma of cows. The concentration of T3 in plasma of cows with access to salt with 20 ppm Se was 14% lower than that in cows supplemented with 60 ppm Se as selenite or SeY. Plasma IgG in cows and calves, colostrum, and Se concentrations in colostrum, casein, and whey were lowest (P < .01) for cows given salt with only 20 ppm Se. Thus, salts with concentrations of 60 and 120 ppm Se improved measures of Se status in cows and calves. Consideration should be given to the concentrations of T3 and IgG when determining the nutritional requirements for Se in cattle.     

Ethylene-propylene copolymers by a supported Ziegler-Natta catalyst based on TiCl4/MgCl2

Ethylene-propylene copolymers have been prepared by using Ziegler-Natta catalysts based on TiCl₄, MgCl₂, PCl₃ and (n-Bu)₃PO₄. The catalysts TiCl₄/MgCl₂/PCl₃ and TiCl₄/MgCl₂/(n-Bu)₃PO₄ were prepared by reacting TiCl₄ with pretreated MgCl₂. The support was prepared by ball milling of MgCl₂ with varied amounts of PCl₃ or (n-Bu)₃PO₄. The addition of PCl₃ has remarkably increased the MgCl₂ surface area in comparison with (n-Bu)₃PO₄. The effects of PCl₃ and (n-Bu)₃PO₄ on ethylene homopolymerization, ethylene-propylene copolymerization and on copolymer properties were evaluated. The catalyst system containing PCl₃ permitted to synthesize propylene-ethylene copolymers with up to 75% (w/w) of propylene and provided control of copolymer crystallinity. The reduction of the copolymer molecular weight distribution suggested that PCl₃ acted as an internal donor, poisoning some active catalytic sites. Received: 2 April 1997/Revised: 6 June 1997/Accepted: 18 June 1997     

Rheological and morphological properties of high‐density polyethylene and poly(ethylene–octene) blends

The rheological and morphological properties of blends based on high‐density polyethylene (HDPE) and a commercial ethylene–octene copolymer (EOC) produced by metallocene technology were investigated. The rheological properties were evaluated in steady and dynamic shear experiments at 190°C in shear rates ranging from 90 s^?1 to 1500 s^?1 and frequency range between 10^?1 rad/s and 10² rad/s, respectively. These blends presented a high level of homogeneity in the molten state and rheological behavior was generally intermediate to those of the pure components. Scanning electron microscopy (SEM) showed that the blends exhibit dispersed morphologies with EOC domains distributed homogeneously and with particle size inferior to 2 μm. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2240–2246, 2002     

The role of Lewis bases on the improvement of the stereospecificity and activity of TiCl3/AlClEt2 catalyst system

Summary The effect of di-n-butyl ether (DBE) in the synthesis of a highly active propylene polymerization catalyst was studied. Electron-donors having ester and phosphate groups (ethyl benzoate-EB, diisobutyl phthalate-DIBP and tri-n-butyl phosphate-TBP) were added as second internal bases (IB₂) to the catalysts prepared by the reduction of TiCl₄ with AlClEt₂ (DEAC) in the presence of DBE as a first internal base (IB₁). The crystalline forms were examined for all catalyst samples by X-ray method. Special attention has been paid to the -TiCl₃ samples showing the best catalytic properties. These catalysts were evaluated in propylene polymerization in the absence and presence of external bases (EB, DIBP and DBE). The effects of internal and external bases on the catalyst activity and stereo-specificity are discussed.     

Brazilian scientific production in science education

In the present study we analyzed the Brazilian scientific production in the area of science education. The study was structured on: data by research groups registered in Conselho Nacional de Desenvolvimento Científico e Tecnológico; analysis of the post-graduate strictu sensu programs; analysis of theses and dissertations linked to post-graduate programs; and papers in international databases. Our research was conducted strictly via world wide web, from December 2009 to September 2010. It was found that both number of research groups, researchers, post-graduate programs, thesis, dissertations and papers presented a marked increase, especially in the last decade (from 2000 onwards). The major research centers were found to be located in public universities from Brazilian southeast and south regions. However, it was observed a tendency of decentralization, due to a recent investment in new public universities in the other Brazilian regions. So, this study sought to present an overview of the scientific production about science education and we expect that this information can help to expand the vision about the development of this research area in Brazil.     

Periodic orbits of oval billiards on surfaces of constant curvature

In this paper, we define and study the billiard problem on bounded regions on surfaces of constant curvature. We show that this problem defines a two-dimensional conservative and reversible dynamical system, defined by a Twist diffeomorphism, if the boundary of the region is an oval. Using these properties and defining good perturbations for billiards, we show that having only a finite number of nondegenerate periodic orbits for each fixed period is an open property for billiards on surfaces of constant curvature and a dense one on the hyperbolic plane. We finish this paper studying the stability of these nondegenerate orbits.