Theory of correlations in partly labelled homopolymer melts

Small-angle neutron scattering by a polymer melt with partly tagged chains is considered. When several types of chain (differently labelled) are present in the system a new long-range correlation effect which modifies the scattering spectrum is predicted. This effect will arise because of the chemical polydispersity of the sample. A general formalism is developed to calculate the scattering intensity and is applied to special cases: diblock and triblock chains. It is shown that even a small chemical polydispersity leads to important long-range fluctuations and modifies the scattering spectrum substantially.     

A Nonvolatile Organic Memory Device Using ITO Surfaces Modified by Ag‐Nanodots

We report on a single‐layer organic memory device made of poly(N‐vinylcarbazole) embedded between an Al electrode and ITO modified with Ag nanodots (Ag‐NDs). Devices exhibit high ON/OFF switching ratios of 10⁴. This level of performance could be achieved by modifying the ITO electrodes with some Ag‐NDs that act as trapping sites, reducing the current in the OFF state. Temperature dependence of the electrical characteristics suggest that the current of the low‐resistance state can be attributed to Schottky charge tunnelling through low‐resistance pathways of Al particles in the polymer layer and that the high‐resistance state can be controlled by charge trapping by the Al particles and Ag‐NDs.     

Les qualités psychométriques de l'échelle de comportements d'adaptation Loranger-Pépin.

Presents results of 3 studies on the psychometric properties of the LP-ABC (M. Loranger and M. Pépin, 1993), a French-language instrument for assessing general functioning in adults with mental retardation. The studies involved a total of 299 male and female Canadian adults with mental retardation. Results confirm the internal consistency, construct validity, criterion validity, discriminant validity, interrater reliability, and test–retest reliability of the LP-ABC. (English abstract) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Preparation of Poly(D,L-Lactide/Glycolide) Nanoparticles of Controlled Particle Size Distribution: Application of Experimental Designs

This study investigates the use of the solvent evaporation method for preparing acid and glycolic acid-based copolymer nanoparticles. Initially, appropriate technological and formulation factors for elaboration of polymeric particles were selected by screening. Most favourable results were obtained using polyvinyl alcohol as a dispersing agent and a high pressure homogenizer to reduce the droplet size of the emulsion initially formed. On the basis of the conclusion thus drawn, a composite rotational experimental design was employed to evaluate the joint influence of three formulation variables (phase volume ratio of the emulsion formed, polymer concentration and homogenization pressure) on the micromeritic properties of the suspension finally obtained (mean particle size, coefficient of variation and polydispersity of the particle size distribution). Analysis of variance corresponding to the experimental design, showed a significant influence of the volume phase ratio and the polymer concentration on the mean particle size and the coefficient of variation, whereas the polydispersity is also affected by the homogenization pressure. Considering this information, a 3² experimental factorial design was then selected to investigate the possible interaction between the phase volume ratio and the concentration of polyvinyl alcohol in the aqueous phase. Analysis of variance and subsequent sequencial regression analysis evidenced last hypothesis providing the way to determine the experimental conditions required to achieve a specific particle size distribution.     

Autothermal two-stage gasification of low-density waste-derived fuels

In order to increase the efficiency of waste utilization in thermal conversion processes, pre-treatment is advantageous. With the Herhof Stabilat^® process, residual domestic waste is upgraded to waste-derived fuel by means of biological drying and mechanical separation of inerts and metals. The dried and homogenized waste-derived Stabilat^® fuel has a relatively high calorific value and contains high volatile matter which makes it suitable for gasification. As a result of extensive mechanical treatment, the Stabilat^® produced is of a fluffy appearance with a low density. A two-stage gasifier, based on a parallel-arranged bubbling fluidized bed and a fixed bed reactor, has been developed to convert Stabilat^® into hydrogen-rich product gas. This paper focuses on the design and construction of the configured laboratory-scale gasifier and experience with its operation. The processing of low-density fluffy waste-derived fuel using small-scale equipment demands special technical solutions for the core components as well as for the peripheral equipment. These are discussed here. The operating results of Stabilat^® gasification are also presented.     

Retrospective Versus Prospective Statements and Outcome of Presidential Elections

This study investigates retrospective and prospective voting from a communication perspective, looking to see whether there is relationship between election outcome and the relative emphasis U.S. presidential candidates place on retrospective (past) versus prospective (future) utterances in campaign messages. The sample includes a variety of presidential campaign messages (acceptance addresses, primary and general television spots, debates, direct mail advertising) from several campaigns (1948–2004) by numerous candidates. In the primary phase of the campaign, there is no difference between winners and losers in relative emphasis on retrospective and prospective statements. However, in the general phase of the presidential campaign, winners use a significantly larger proportion of retrospective (and a smaller proportion of prospective) utterances than losers. Furthermore, the relationship between emphasis on retrospective utterances and election outcome was larger for incumbents than challengers (but significant for both types of candidates). These findings support retrospective voting in the general, but not the primary, campaign.     

Measuring interdiffusion at an interface between two elastomers with tapping-mode and contact-resonance atomic force microscopy imaging

Despite the common use of tapping-mode atomic force microscopy to image composites or polymer blends, very few studies have focused on the measurement of the interdiffusion at an interface between two polymers in contact. In this study, we show how to assess the interphase between two polymers with two methods. First, stable and robust tapping conditions are established, and the problem of the phase contrast is discussed. Second, a contact-resonance method is presented: the tip in contact with the sample is electrostatically excited at its resonance frequency by a self-controlled oscillator. The gain and frequency images allow us to measure the interdiffusion width. Both methods (using high and weak mechanical solicitation) give the same assessment of the interdiffusion width. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Multifunctional hydrogels that promote osteogenic hMSC differentiation through stimulation and sequestering of BMP2

The extracellular environment controls many cellular activities thereby linking external material cues to internal cell function. By better understanding these processes, synthetic extracellular material niches can be tailored to present cells with highly regulated physical and/or chemical cues that promote or suppress selected cell functions. Here, poly(ethylene glycol) (PEG) hydrogels were functionalized with fluvastatin-releasing grafts and growth factor binding heparin domains to enable the dynamic exchange of information between the material and cells from the outside-in and inside-out (i.e., bidirectional signaling). By incorporating a fluvastatin-releasing graft and carefully controlling the dose and temporal release, materials were designed to promote bone morphogenic protein (BMP2) and alkaline phosphatase (ALP) production by human mesenchymal stem cells (hMSCs). When the release of fluvastatin was controlled to occur over 2 weeks, BMP2 and ALP production was increased 2.2-fold and 1.7-fold, respectively, at day 28 compared to hMSCs cultured in the absence of fluvastatin. By introducing a heparin functionality into the gel to sequester and localize the hMSC-produced BMP2, the osteogenic differentiation of hMSCs was further augmented over fluvastatin delivery alone. Osteopontin and core binding factor α1 gene expression was 6-fold and 4-fold greater for hMSCs exposed to fluvastatin in the presence of the heparin functionalities, respectively. These results demonstrate how multifunctional gels that interact with cells in a bidirectional manner can efficiently promote selected cell functions, such as the osteogenic differentiation of hMSCs.