Structure and water—oil emulsifying properties of asphaltenes

Alphaltenes were selected on the basis of their capacity to form water—oil emulsions. They were characterized by electron microscopy, surface group analysis, g.p.c. and low-angle X-ray scattering. It appears that the high stability of water-oil emulsions is related to the ‘structuring’ capacity of asphaltenes at the water-oil interface. Some asphaltenes are able to form regularly stacked layers, resembling the behaviour of surfactant liquid crystals.     

A prospective, controlled study of Helicobacter pylori seroprevalence in coronary artery disease

OBJECTIVE: Recent studies have suggested that chronic infections may be a risk factor for coronary artery disease. The aim of this study was to determine whether Helicobacter pylori (H. pylori) infection was an independent risk factor for coronary artery disease. METHODS: A total of 179 patients undergoing coronary angiography for suspected coronary artery disease were prospectively studied. Angiograms were read by experienced invasive cardiologists blinded to the results of H. pylori serology, which was determined by a validated multiwell ELISA assay. RESULTS: A total of 121 patients (68%) had evidence of coronary artery disease, whereas 58 patients (32%) had normal coronary angiograms. Of the 121 patients with coronary artery disease, 29 had single vessel disease, 39 had double vessel disease, and 53 had triple vessel disease, respectively. There was no significant difference in seroprevalence of H. pylori infection in patients with and without coronary artery disease (p = 0.63). The odds ratio (after adjustment for other known risk factors) for coronary artery disease in H. pylori-infected subjects was 0.45 (95% CI = 0.15, 1.37; p = 0.107). In patients with coronary artery disease, H. pylori infection did not increase the likelihood of severe disease (odds ratio for triple vessel disease = 0.53; 95% CI 0.18, 1.60; p = 0.201). CONCLUSION: H. pylori infection rates are similar in patients with normal and abnormal coronary arteries, and infection with H. pylori is not an independent risk factor for coronary artery disease. In patients who have coronary artery disease, H. pylori infection is not a risk factor for more severe disease. These data argue against a causal role for H. pylori in the pathogenesis of coronary artery disease.     

Thermorheological analysis of glass beads-filled polymer melts

The complex viscosity of two thermoplastic polymer melts (high density polyethylene and polystyrene) filled with polydisperse glass beads (10–53 μm) has been studied in the domain of linear viscoelasticity as a function of frequency, temperature, and filler concentration. In the experimental windows examined, the complex viscosity can be well described by a new empirical model, which contains a Cross-type viscosity model for the frequency dependence, a Quemada-type model for the filler concentration dependence, and a compensation effect for the temperature dependence. This model allows the prediction of the complex viscosity of a glass bead-filled thermoplastic melt provided only four parameters are known, namely: the average maximum packing volume fraction characteristic of the filler geometry and size distribution, the flow activation energy of the thermoplastic, the shear-thinning parameter, and an adjustable parameter, also characteristic of the thermoplastic.     

Editorial

Higher-Order and Symbolic Computation -     

Multiscale morphology and thermo‐mechanical history of poly(vinyl chloride) (PVC)

The multiscale morphology of rigid poly(vinyl chloride) (PVC) formulations (in the nanometre to the micrometre range) was investigated by high resolution scanning electron microscopy, ultra‐small‐, small‐ and wide‐angle X‐ray scattering, as a function of thermo‐mechanical history. It has been shown that the hierarchical structure of PVC grains, when in the dry blend, disappeared during gelation that combines mechanical stress (ie shear stress and hydrostatic pressure) and heating. Nevertheless, the memory of the presence of the smallest particles (domains with diameters of about 80 nm) containing dense amorphous PVC and nanoscaled crystallites, has been highlighted by the study of the change of the microstructure when PVC was reprocessed with high mechanical deformation at a lower temperature than the previous gelation temperature. As a result, the main phenomena occurring during gelation were, in a first step, the disappearance of the hierarchical structure of the grains and, in a second step, the inter‐diffusion of the chains across the frontiers of the primary particles (mechanically reversible), but maintaining the domain structure. The crystalline microstructure was affected by thermo‐mechanical history, but the gelation level should not be estimated strictly in relation to the crystalline morphology. Copyright © 2004 Society of Chemical Industry     

Potential interest of anti-ischemic agents for limiting cyclosporin A nephrotoxicity

Chronic administration of cyclosporin A induces nephrotoxicity in humans. This is related to a cyclosporin A-induced constriction of afferent glomerular arterioles and mesangial cells, which leads to a decrease in filtration pressure and creatinine clearance. Afterwards, cellular lesions are observed involving mainly tubular atrophy and interstitial fibrosis, both of which are nonspecific. The initial mechanism of its toxicity is not clearly explained. The current pharmacological approach is symptomatic in order to counteract or minimize the consequences of a prime cause, which still remains to be defined. However, cyclosporin A has a deletereous effect on mitochondrial functions and mainly on ATP synthesis, which occurs when Ca2+ accumulates in matrix mitochondria. The effects of trimetazidine, an antischemic drug used in the treatment of angina pectoris, have been assessed. This drug is effective in experimental models of hypoxia induced by cyclosporin A: it restores ATP synthesis previously decreased by Ca2+ and cyclosporin A, and releases a part of Ca2+ excess accumulated by mitochondria at concentrations reached in humans at usual dosage regimens. At higher concentrations, it reverses the mitochondrial permeability transition previously generated (opened) by Ca2+ and a pro-oxidant such as terbutylperoxide (t-BH). It was also observed that trimetazidine does not modify the immunosuppressive effects of cyclosporin A in various models. These data suggest that nephrotoxicity of cyclosporin A is not irrevocably linked to its immunosuppressive effect but that it may be possible to counteract at least partly its nephrotoxic effects without altering its effectiveness in preventing graft rejection.     

High-Reynolds number solutions of Navier-Stokes equations using incremental unknowns

The unsteady 2D Navier-Stokes equations on an unregularized driven cavity are solved in vorticity-streamfunction variables using Incremental Unknowns. Periodic asymptotic solutions have been found for Re = 10000 and Re = 12500.     

Excimer Laser Processing of Nodular Iron

Excimer laser processing is expected to improve the wear properties and the oxidation resistance of cast iron surfaces. In the present study, an XeCl laser prototype was used to change the surface morphology of nodular iron samples under high energy ultraviolet exposure. Roughness evolution results from ablation and, above all, from moving of the molten superficial layer, due to both high temperature and pressure involved during the laser shot. Conventional metallography was carried out to determine the mechanisms governing the modification of surface profiles. These were shown to be both a wide and a local phenomena, i.e. involved at two different scales: that of the laser spot and that of the nodule. The plasma high pressure applied to the surface moves the molten material towards the periphery of the spot, where it freezes by self quenching with a high cooling rate. The surface profile is also modified by the formation of a rim surrounding each solid heterogeneity such as graphite spheroids. The width of the rims did not depend on the sizes of nodules or inclusions. The study suggests a wave emission mechanism to interpret formation of the rims.