Predictive modelling of the properties and toughness of polymeric materials Part II Effect of microstructural properties on the macroscopic response of rubber-modified polymers

The influence of microstructural properties on the macroscopic mechanical behaviour has been studied by finite element predictions of the response of different microstructures of polystyrene (PS) or polycarbonate (PC) containing voids or rubbery particles, subjected to unidirectional extension. The voids represent a low-modulus non-adhering dispersed phase. The rubbery inclusions, which are assumed to be pre-cavitated and perfectly adhering, idealise core-shell particles with a hard rubber shell and a soft non-adhering or pre-cavitated core. The predictions show that the inclusion properties strongly affect the averaged post-yield response of the heterogeneous systems. Especially the post-yield strain softening can be eliminated by the introduction of voids in PC or rubbery particles in PS. Since macroscopic strain softening is believed to be the main cause of catastrophical stress or strain localisations, the softening elimination is believed to be primarily responsible for toughness enhancement of the polystyrene or polycarbonate systems. The results and experiences are extrapolated in order to explain the influence of the absolute length scale of a sub-micron sized morphology on the macroscopic behaviour, especially toughness. Two potential sources of particle-size effects are presented that may result in a stabilised, and thus tougher, macroscopic mechanical response, i.e. the yield stress reduction near a surface or interface because of a locally enhanced mobility of the polymer segments, and the temporary excessive hardening because of a sufficiently small size of the yield zones which results in a reduced effective entanglement distance. The paper concludes with a discussion on the extension of this knowledge to all other, for the moment amorphous, polymers.     

Bound sulphadimidine residues in raw fermented sausage: release under acidic conditions and bioavailability in rats

 Sulphadimidine (SDM), a drug frequently administered to pigs, is partially converted into other compounds by processing meat to produce raw, fermented sausage. With the aid of ¹⁴C-labelled SDM, evidence was obtained that part of the radioactive matter was covalently bound to the matrix. Part of these bound residues could be released in vitro by 4 M HCl at 21  °C or by 0.024 M HCl at 37  °C. Female rats were also able to release bound SDM residues and to excrete these in their urine, in amounts approaching those obtained by treatment with 4 M HCl. Both the parent compound and its main metabolite, N ⁴-acetyl-SDM, were observed in the urine of rats. Received: 29 December 1997 / Revised version: 20 February 1998     

Characterization of composite materials of electroconductive polymer and cobalt as electrocatalysts for the oxygen reduction reaction

Platinum-free electrocatalysts based on electroconductive polymer, modified with cobalt, were prepared and characterized for the oxygen reduction reaction (ORR). The carbon-supported materials were: carbon/polyaniline/cobalt, carbon/polypyrrole/cobalt and carbon/poly(3-methylthiophene)/cobalt. Also the corresponding cobalt-free precursors were studied. EDAX studies show that in cobalt-modified catalysts, significant percentages of cobalt, between 5 and 7% in weight, are present. FTIR, TGA, and EDAX studies confirmed that the addition of cobalt modifies the chemical structure of C–Pani, C–Ppy, and C–P3MT materials. Cyclic voltammetry shows reduction peaks corresponding to the ORR for all materials and kinetic parameters were calculated based on lineal voltammetry using RDE at different rotating speeds. It was found that C–P3MT–Co has highest exchange current densities, followed by C–Ppy and C–Ppy–Co. All samples have Tafel slopes between −110 and −120 V/dec, indicating that the first electron transfer is the decisive step in the global ORR. Potentiostatic tests showed an adequate stability of cobalt-modified samples in acid medium at ORR potentials. Based on the potential range at which ORR occurs, the exchange current density and stability tests, it is concluded that the best material for potential application as fuel cell cathode catalyst is C–Ppy–Co.     

Strategies to Combine the Functions of Ecology and Navigation in the Scheldt Estuary

During recent years, water management in The Netherlands has been broadening its scope by: (a) including aspects of economics, sociology and physical planning, and (b) introducing interactive policy making; this paper illustrates these developments using the Westerschelde estuary as an example. The Westerschelde strategy aims at optimizing the multi-national use of this estuary. The main functions are navigation and ecology, and the paper shows how these functions can be combined. An interactive management model, the 'COSMO-Westerschelde'is described, which assists decision makers in comparing strategies for estuarine management under different scenarios.     

Diabetic gastroparesis: is tube feeding an alternative?

A woman aged 26 with long-standing insulin-dependent diabetes mellitus displayed recurrent periods of nausea, vomiting, abnormal blood sugar levels, weight loss and poor physical condition in spite of a diet and use of propulsive agents. Scintigraphy revealed decelerated gastric evacuation for solid and liquid nutrients. The patient recovered after insertion of a percutaneous endoscopic gastrostomy (PEG) catheter. Diabetic gastroparesis is associated with a vicious circle in which delayed gastric emptying leads to poor glucose regulation with frequent hyperglycaemia, which in its turn adversely affects gastric emptying. Treatment should be aimed at improvement of the gastric motility (for instance by propulsive agents), more accurate glucose regulation and nutritional counselling. If this fails to produce improvement, tube feeding via a permanent nasoduodenal tube or via a PEG catheter constitutes an acceptable alternative for oral nutrition.     

Cell-surface display of a Pseudomonas aeruginosa strain K pilin peptide within the paracrystalline S-layer of Caulobacter crescentus

The paracrystalline surface (S)-layer of Caulobacter crescentus is composed of a single secreted protein (RsaA) that interlocks in a hexagonal pattern to completely envelop the bacterium. Using a genetic approach, we inserted a 12 amino acid peptide from Pseudomonas aeruginosa strain K pilin at numerous semirandom positions in RsaA. We then used an immunological screen to identify those sites that presented the inserted pilin peptide on the C. crescentus cell surface as a part of the S-layer. Eleven such sites (widely separated in the primary sequence) were identified, demonstrating for the first time that S-layers can be readily exploited as carrier proteins to display 'epitope-size' heterologous peptides on bacterial cell surfaces. Whereas intact RsaA molecules carrying a pilin peptide could always be found on the surface of C. crescentus regardless of the particular insertion site, introduction of the pilin peptide at 9 of the 11 sites resulted in some proteolytic cleavage of RsaA. Two types of proteolytic phenomena were observed. The first was characterized by a single cleavage within the pilin peptide insert with both fragments of the S-layer protein remaining anchored to the outer membrane. The other proteolytic phenomenon was characterized by cleavage of the S-layer protein at a point distant from the site of the pilin peptide insertion. This cleavage always occurred at the same location in RsaA regardless of the particular insertion site, yielding a surface-anchored 26 kDa proteolytic fragment bearing the RsaA N-terminus; the C-terminal cleavage product carrying the pilin peptide was released into the growth medium. When the results of this work were combined with the results of a previous study, the RsaA primary sequence could be divided into three regions with respect to the location of a peptide insertion and its effect on S-layer biogenesis: (i) insertions in the extreme N-terminus of RsaA either produce no apparent effect on S-layer biogenesis or disrupt surface-anchoring of the protein; (ii) insertions in the extreme C-terminus either produce no apparent effect on S-layer biogenesis or disrupt protein secretion; and (iii) insertions more centrally located in the protein either have no apparent effect on S-layer biogenesis or result in proteolytic cleavage of RsaA. These data are discussed in relation to our previous assignment of the RsaA N- and C-terminus as regions that are important for surface anchoring and secretion respectively.     

A compact integrated InP-based single-phasar optical crossconnect

The first integrated InP-based polarization independent optical crossconnect is reported. The device can crossconnect signals at four wavelengths independently from two input fibers to two output fibers. Total on-chip loss is less then 16 dB. Device size is 7×9 mm²      

A normalized approach to the design of low-loss optical waveguidebends

A normalized approach for optimal design of abrupt junctions between straight and curved waveguides operating in the whispering gallery mode regime is presented. The optimization includes the widths of both the straight and the curved waveguides, the lateral offset between them, and the bending radius of the curved waveguide. With this approach, optimum bend design is possible from a simple set of formulas or normalized graphs. Predicted transmission losses for optimally designed junctions are well below 0.1 dB     

A meta-analysis of interrater and internal consistency reliability of selection interviews.

A meta-analysis of 111 interrater reliability coefficients and 49 coefficient alphas from selection interviews was conducted. Moderators of interrater reliability included study design, interviewer training, and 3 dimensions of interview structure (standardization of questions, of response evaluation, and of combining multiple ratings). Interactions showed that standardizing questions had a stronger moderating effect on reliability when coefficients were from separate (rather than panel) interviews, and multiple ratings were useful when combined mechanically (there was no evidence of usefulness when combined subjectively). Average correlations (derived from alphas) between ratings were moderated by standardization of questions and number of ratings made. Upper limits of validity were estimated to be .67 for highly structured interviews and .34 for unstructured interviews. (PsycINFO Database Record (c) 2010 APA, all rights reserved)