Sugarcane bagasse cellulose/HDPE composites obtained by extrusion

Natural fibers used in this study were both pre-treated and modified residues from sugarcane bagasse. Polymer of high density polyethylene (HDPE) was employed as matrix in to composites, which were produced by mixing high density polyethylene with cellulose (10%) and Cell/ZrO₂·nH₂O (10%), using an extruder and hydraulic press. Tensile tests showed that the Cell/ZrO₂·nH₂O (10%)/HDPE composites present better tensile strength than cellulose (10%)/HDPE composites. Cellulose agglomerations were responsible for poor adhesion between fiber and matrix in cellulose (10%)/HDPE composites. HDPE/natural fibers composites showed also lower tensile strength in comparison to the polymer. The increase in Young’s modulus is associated to fibers reinforcement. SEM analysis showed that the cellulose fibers insertion in the matrix caused an increase of defects, which were reduced when modified cellulose fibers were used.     

Modification of vermiculite by polymerization and carbonization of glycerol to produce highly efficient materials for oil removal

Impregnation and reaction of glycerol (Gly) on the surface of expanded vermiculite (EV) was used to produce a highly efficient absorbent to remove water spilled oils. The vermiculite was impregnated by glycerol containing 1, 2 and 4 mol% of H₂SO₄ at EV/Gly ratios, i.e. 1/1, 1/2 and 1/3, and heated to 380, 580 and 750 °C. SEM, TG, BET specific surface area, and Raman analyses indicated that glycerol at 380 °C forms a polymer layer. At higher temperatures, the polymer decomposed to form porous carbon covering the EV surface. These materials were investigated for the removal of three different oils, i.e. diesel, soybean and engine oil spilled on water. The obtained results showed a remarkable increase on oil removal of 600% compared to the non-modified EV.     

A note on the properties of power-transformed returns in long-memory stochastic volatility models with leverage effect

The autocorrelation function (acf) of powered absolute returns and their cross-correlations with original returns are derived, for any value of the power parameter, in the context of long-memory stochastic volatility models with leverage effect and Gaussian noises. These autocorrelations and cross-correlations generalize and correct recent results on the acf of squared and absolute returns.     

A contribution to the interpretation of polymer viscoelasticity in DMTA testing

Some ideas relevant to the prevailing viscoelasticity interpretations of dynamic mechanical thermal analysis (DMTA) experiments are presented. The main aspect is the inclusion of kinetic energy and inertia as variables, seeing the relaxing mass constantly increasing during strain, assigning inertial variation and not viscosity to energy dissipation. The equations developed make it possible to obtain the values of important viscoelastic properties, under in any experimental condition, with the data taken from previous experiments.     

Dweb model: Representing Web 2.0 dynamism

Due to the increase in the number and popularity of applications such as e-commerce or on-line booking systems, typical of the Web 2.0, dynamic contents are becoming more and more frequent. This trend suggests the review of widely accepted paradigms and models for the World Wide Web. As a system that is continuously changing, both in the offered applications and in its infrastructure, performance evaluation studies are a main concern to provide sound proposals when designing new web-related systems. Although the dynamism in the workload characterization has also been tackled in previous research, it has not been modeled in a precise way yet because of its complex nature.In this paper we propose the Dweb model which represents the dynamism of current web applications in the workload characterization. Dweb is based on three main concepts that allow to model dynamic workload: navigation, workload test and workload distribution. In addition, a dynamic workload generator has been implemented to show the practical application of the proposed model, which has been illustrated through a case study.     

Phosphorus‐containing poly(ester‐imide)–polydimethylsiloxane copolymers

New phosphorus‐containing poly(ester‐imide)‐polydimethylsiloxane copolymers were prepared by solution polycondensation of 1,4‐[2‐(6‐oxido‐6H‐dibenz < c,e > < 1, 2 > oxaphosphorin‐6‐yl)]naphthalene‐bis(trimellitate) dianhydride with a mixture of an aromatic diamine (1,3‐bis(4‐aminophenoxy)benzene) and α,ω‐bis(3‐aminopropyl)oligodimethylsiloxane of controlled molecular weight, in various ratios. Poly(amic acid) intermediates were converted quantitatively to the corresponding polyimide structures using a solution imidization procedure. The polymers are easily soluble in polar organic solvents, such as N‐methyl‐2‐pyrrolidone and N,N‐dimethylformamide, as well as in less polar solvents such as tetrahydrofuran. They show good thermal stability, the decomposition temperature being above 370 °C. The glass transition temperatures are in the range 165–216 °C. Solutions of the polymers in N‐methyl‐2‐pyrrolidone exhibit photoluminescence in the blue region. Copyright © 2010 Society of Chemical Industry     

Influence of caring youth sport contexts on efficacy-related beliefs and social behaviors.

Understanding what factors influence positive youth development has been advocated by youth development researchers (P. L. Benson, 2006; J. S. Eccles & J. A. Gootman, 2002). Consequently, the purpose of this study was to examine whether perceptions of a caring youth sport context influenced prosocial and antisocial behavior through efficacy-related beliefs, that is, positive and negative affective self-regulatory efficacy (ASRE) and empathic self-efficacy (ESE). Multiethnic youths taking part in summer sport programs (N = 395) completed a questionnaire that measured perceptions of the caring climate, ESE, ASRE, and social behavior. Structural equation modeling was used to test whether ASRE and ESE mediated the relationship between caring and social behaviors. Findings revealed that perceptions of caring positively predicted ASRE and ESE. In turn, positive ASRE positively predicted ESE. Prosocial behaviors were positively linked to ESE, whereas antisocial behaviors were negatively predicted by positive ASRE. The results suggest that caring influences prosocial and antisocial behavior because such contexts develop youths' ability to monitor, manage, and control positive affect, which in turn enhances their belief in their ability to empathize. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Raspberry seed extract effect on the ferroxidase activity of ceruloplasmin isolated from plasma

In this study, the effect of the raspberry seed extract (RSE) on the ferroxidase activity of ceruloplasmin (Cp) isolated from healthy male subject serum was analyzed. The ferroxidase activity of Cp was determined by spectrophotometry using Fe(II) – histidine complex and ferrozine as a chromogenic reagent. The ferroxidase activity of ceruloplasmin was demonstrated in dose-dependent way within the range 22–66 μg/ml. The effect of RSE on Fe(II) concentration, measured as the decrease of Fe(II) concentration in samples and expressed as ΔFe(II), was found to be a dose-dependent within the range 1.20–51.56 μg dm/ml. The ferroxidase activity of Cp was influenced by the RSE within its studied range. However, the addition of the highest concentration of RSE (51.56 μg dm/ml) to the sample containing the highest level of Cp (66 μg/ml) did not affect its ferroxidase activity. It may be suggested that the competition for Fe(II) as the substrate limits the effect of RSE on Cp activity and causes no further changes in Fe(II) elimination.     

Development of pH-responsive poly(methylmethacrylate-co-methacrylic acid) membranes using scCO2 technology. Application to protein permeation

Porous membranes were developed in a two step process using supercritical CO₂ technology. Copolymers of methyl methacrylate (MMA) and methacrylic acid (MAA) were synthesized for the first time in supercritical carbon dioxide (scCO₂), being identified by ¹H NMR and FT-IR. The influence of the feed monomer ratio on their morphology, average molecular weight and T_g was studied. These PMMA-co-PMAA copolymers were then used in the preparation of thin pH-responsive membranes by scCO₂-assisted phase inversion method. The prepared films were characterized by scanning electron microscopy, mercury porosimetry, dynamical mechanical analysis, swelling and contact angle measurements, in order to study their morphology, pH-responsive character, hydrophilicity and viscoelastic properties by changing the monomer ratio composition of the copolymer from 5 to 50 wt% of MAA with respect to the total mass of monomers. PMMA-co-PMAA membranes were then tested for a potential application as protein filtration devices. Bovine serum albumin (BSA) was used as a model protein and permeation measurements were performed at three different pHs (4.5, 5.0 and 7.4). The PMMA–PMAA (90:10) membrane showed a good performance in terms of BSA amount filtrated, with distinct profiles at different pH, and consequently capable to assume an efficient role in protein filtration processes.