Interface Structure in a Polymer Blend in the Presence of Selective Solvents

Energy transfer experiments were carried out on a material composed of poly(methyl methacrylate) (PMMA, 98.5 monomer mol%) and polyisobutylene (PIB, 1.5 monomer mol%), with PMMA labeled with phenanthrene, the donor, and PIB labeled with pyrene, the acceptor. In this material, prepared by nonaqueous dispersion polymerization, all of the PIB is present as a graft copolymer with PMMA. Here we demonstrate that the extent of energy transfer increases enormously when the particles are dispersed in aliphatic hydrocarbon liquids. These swell the PIB phase leading to formation of a diffuse interface where substantial mixing of the PMMA and PIB components occurs. The amount of energy transfer, and hence the amount of swelling, varies significantly among the various solvents.     

Surface characteristics of solvent-cast polymers

Films of poly(methyl methacrylate) (PMMA), polystyrene, and a styrene/acrylic terpolymer have been cast from solutions of varying thermodynamic quality and the film properties studied by inverse gas chromatography and by critical surface tension measurements. Surface properties of the non-polar polystyrene were independent of solvent medium, but significant variations in these properties were observed in the case of PMMA and the terpolymer. Solvent balance also appeared to affect the bulk properties of the latter films, as judged by the penetration rates of interacting liquids. The observations indicate the feasibility of controlling film properties of the solid by the appropriate selection of solution media; a time-dependent variation in solid properties is to be expected, however, as the film structure attains an equilibrium state.     

Source terms in Eulerian–Lagrangian contaminant transport simulation

Standard Eulerian treatment of source terms in Eulerian–Lagrangian numerical simulations results in poor performance at higher Courant numbers. To regain the customary high accuracy of Eulerian–Lagrangian methods under these conditions, a Lagrangian treatment of source terms is needed. It is also important to include the effects of fluid sources as well as contaminant sources. A new Lagrangian source formulation is presented, which has been implemented in a finite element simulator for contaminant transport in rivers and estuaries. Test problems demonstrate the high accuracy of the technique under a range of conditions, and its applicability to general multi‐dimensional problems and unstructured grids. Copyright © 2004 John Wiley & Sons, Ltd.     

Human myeloma cells shed the interleukin-6 receptor: inhibition by tissue inhibitor of metalloproteinase-3 and a hydroxamate-based metalloproteinase inhibitor

Impedance cardiography (ICG) offers a safe, noninvasive, and inexpensive method to track stroke volume estimates over long periods of time. Several modified ICG measurement configurations have been suggested where for convenience or improved performance the standard band electrodes are replaced with electrocardiogram electrodes. This report assesses the sensitivity of the conventional and three modified ICG methods in detecting regional conductivity changes in the simulated human thorax. The theoretical analyses of the measurement sensitivity employ the reciprocity theorem and the lead field theory with a highly detailed, anatomically accurate, three-dimensional computer thorax model. This model is based on the finite-difference element method and the U.S. National Library of Medicine's Visible Human Man anatomy data. The results obtained indicate that the conventional four-band ICG is not specifically sensitive to detect conductivity changes in the region of the heart, aortas, and lungs. Analyzed modified electrode configurations do not reproduce exactly the measurement sensitivity distribution of the conventional four-band ICG. Thus, although the signals measured with modified spot arrangements may appear similar to the four-band configuration, the distribution of the signal origin may not be the same. Changing from band to spot electrodes does not overcome the methodological problems associated with ICG.     

On Multi-valued Surface Properties of PMMA Films

An apparent link between the surface properties of polar group-containing polymers, such as PMMA and Styrene/Acrylic copolymers, and the thermodynamic quality of solvents used in solutions from which the polymers were cast, was described in earlier papers.^1,2 In these polymers, significant variations have been observed in critical surface tensions(γ_c), and in the thermodynamic interaction parameters for selected vapor-polymer pairs, when the configuration of the polymer in solution was varied through the suitable selection of solvents of differing thermodynamic quality. The “solvent history” effect on surface properties of solid film was not detected however for non-polar polymers such as polystyrene (PS).^1,2 Apparently the distinct chain configurations adopted in solution by PMMA are carried over into the solid and result in different proportions of non-polar (backbone) and polar (side chain) moieties being located in the surface layer of the solid. Since only one surface state can correspond to a thermodynamic equilibrium, it may be expected that the film surface properties will change with time, as the thermodynamically preferred state is attained. As a consequence, use properties of these films should also display (initially) the “solvent history” effect, and should vary similarly with time. The present communication is concerned with these points.     

National collective bargaining and employment flexibility in the European building and civil engineering industries

Change in employment practice in the European construction industry is reviewed with particular attention to the effects of flexible working on established arrangements for national collective bargaining. Data derive from European survey research coordinated by Cranfield School of Management in 1995 and from interviews with trade union and employers association representatives in the same period. Membership and support for trade unions and employers associations has weakened, although there are significant differences between countries. The most significant changes in employment practice in construction are found in the increased use of temporary, short term and fixed term contracts; in subcontracting, and in the use of overtime. These changing working practices tend to fragment the workforce and to undermine established systems of institutional interest representation. The distinctive commitment of UK employers to temporary or casual work and to subcontracting is confirmed. The changes contribute to pressure on arrangements established through multi-employer bargaining, although employers and trade union representatives remained committed, at the time of our research, to multi-employer collective agreements.