Binary and ternary particulate composites. II. Tensile behavior over a wide range of strain rates

Tensile properties of both a binary material, i.e., polystyrene (PS) reinforced by 15 vol % of glass beads, and ternary composites, i.e., showing either a maleated styrene/ethylene-co-butylene/styrene copolymer or a styrene-co-methacrylic acid copolymer (SAMA) adduct at the PS/glass-beads interface, are analyzed at room temperature and over a wide range of strain rates. Because the poor quality of the adhesion at the PS/glass-beads interface, the fracture toughness of these binary composites is strongly reduced, whatever the strain rate. The presence of the rubbery interlayer does not change the deformation mechanisms of the composite and the work to break is not significantly enhanced. This results from the poor compatibility between PS and the rubbery interphase leading to the debonding of coated glass beads. The good adhesion quality at the interfaces between phases in the ternary composite showing the SAMA adduct, i.e., SAMA/glass-beads and PS/SAMA interfaces, hinders the decohesion phenomenon. This results in an improvement in both the transfer load and the maximum strength. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 1041–1046, 1997     

Gene and protein expression in the myometrium in pregnancy and labor

Microarray technologies widen our comprehension of the major structural and metabolic transformations which affect the myometrium from the very beginning of pregnancy until parturition. The results are coherent with the mass of information which was accumulated previously, primarily on the basis of studies of selected critical factors. They highlight the activation of precise signaling pathways, some of which may have been previously under evaluated. The remodelling and maturation processes that the myometrium undergoes in pregnancy appear clearly as phenomena which last during the full course of gestation. Comparatively, the onset of labor is perhaps the phenomenon which remains the least well described by these methods of analysis. Nevertheless, genomic studies constitute a necessary first step of orientation and help establishing new links between the generic signaling pathways that are activated during the normal or pathological gestation. These studies also represent an indicative step that will have to be paralleled, in the future, with the results of the systematic proteomic analysis of the myometrium.     

Field mapping with nanometer-scale resolution for the next generation of electronic devices

In order to improve the performance of today's nanoscaled semiconductor devices, characterization techniques that can provide information about the position and activity of dopant atoms and the strain fields are essential. Here we demonstrate that by using a modern transmission electron microscope it is possible to apply multiple techniques to advanced materials systems in order to provide information about the structure, fields, and composition with nanometer-scale resolution. Off-axis electron holography has been used to map the active dopant potentials in state-of-the-art semiconductor devices with 1 nm resolution. These dopant maps have been compared to electron energy loss spectroscopy maps that show the positions of the dopant atoms. The strain fields in the devices have been measured by both dark field electron holography and nanobeam electron diffraction.     

Edge location in SAR images: performance of the likelihood ratiofilter and accuracy improvement with an active contour approach

The likelihood ratio edge detector is an efficient filter for the segmentation of synthetic aperture radar (SAR) images. We show that this filter provides biased location of the edge, when the window does not have the same orientation as the edge. A phenomenological model is proposed to characterize this bias. We then introduce an efficient technique to refine edge location: the statistical active contour. The combination of these two methods permits to achieve accurate and regularized edge location.     

Creep Failure Analysis of Bars Sustaining Constant Tensile Loads

Life time and failure modes are predicted for metallic barssustaining tensile creep. Experimental results show that a ductile or a`brittle' mode of fracture occurs depending respectively on whether thenominal applied stress is large or small. The analysis is based on amodeling of void nucleation and growth in which damage evolution iscontrolled by two mechanisms of plastic flow in the matrix material.Fracture is supposed to occur when the porosity attains a critical valuewhich depends on the mode of fracture considered. Experimental resultsare explained and described in terms of the proposed model.     

Tie-Over Bolster Pressure Dressing Improves Outcomes of Skin Substitutes Xenografts on Athymic Mice

The efficacy of skin substitutes is established for the treatment of burn injuries, but its use is not limited to this condition. This technology has the potential to improve the treatment of various conditions by offering highly advanced and personalized treatments. In vivo studies are challenging but essential to move to clinical use in humans. Mice are the most widely used species in preclinical studies, but the main drawback of this model is the limited surface area of the graft in long-term transplantation studies caused by the displacement and the contraction of the graft. We improved the conventional surgical procedures by stabilizing the chamber covering the graft with intramuscular sutures and by adding a tie-over bolster dressing. The current study was therefore performed to compare outcomes of skin grafts between the conventional and optimized skin graft model. Human self-assembled skin substitutes (SASSs) were prepared and grafted to athymic mice either by the conventional method or by the new grafting method. Graft healing and complications were assessed using digital photographs on postoperative days 7, 14, and 21. Similar structure and organization were observed by histological staining. The new grafting method reduced medium and large displacement events by 1.26-fold and medium and large contraction events by 1.8-fold, leading to a 1.6-fold increase in graft surface area compared to skin substitutes grafted with the usual method. This innovation ensures better reproducibility and consistency of skin substitute transplants on mice.     

Molecular dynamics study of UO2 symmetric tilt grain boundaries around [001] axis

Molecular dynamics and CRG empirical potential are used in this work to study the symmetrical tilt grain boundaries around the [001] axis in UO₂. The analysis of atomic structures obtained by simulation shows excellent agreement with the Read and Schokley model (Read WT, Shockley W. Dislocation Models of Crystal Grain Boundaries. Physical Review. 1950;78:275) predicting the existence of regular dislocations in these grain boundaries. We calculated their energy of formation and cleavage as well as the energy of formation of Schottky defects and incorporation of xenon and krypton atoms in their proximity. This allowed us to determine how these properties evolve for this series of grain boundaries presenting similar geometric characteristics, as a function of the misorientation angle. In addition, the boundary between small and large misorientation grain boundaries has been determined around 20°, close to the value of 15° reported in literature.     

Characterization of a chemically modified β-amylase immobilized on porous silica

β-Amylase was coupled to a periodate oxidized dextran by reductive alkylation in the presence of sodium cyanoborohydride. The loss of activity (57%) during the cross-linking of the enzyme was the result of steric hindrance near the catalytic site. In order to verify this hypothesis, the residual activity was determined with substrates of variable molecular size. The residual activity was inversely proportional to the particulate size of the substrate. Increases in residual activity, of up to 53% were obtained using an orientated chemical modification in the presence of a substrate which protects the catalytic site. Native and dextran-conjugated β-amylase were immobilized on an amino activated silica by a classical method using glutaraldehyde for the native enzyme and by reductive alkylation for the modified enzyme. The relative activity of the enzymes obtained after this insolubilization was very high for the modified amylase, 45% for a medium enzyme concentration, compared with 4% at the same concentration for the native enzyme. This difference can be attributed to the variation of the length of the space arm between the silica and the enzyme. The soluble β-amylase dextran conjugate had a superior thermoresistance to that of the native enzyme; its optimal temperature of activity was 5°C higher than that of the native enzyme. This stabilization may be attributable to a rigidification of the protein structure. Immobilization of both native and modified enzymes on a amino silica resulted in thermostabilization of the enzymes. The optimal temperature of activity was 70°C for the native immobilized β-amylase (some 10°C higher than that of the native enzyme) and 75°C for the chemically modified, and subsequently immobilized, β-amylase. The immobilized forms of the enzymes were used for 14 days at 55°C in continuous substrate processing. The greater eflciency of the chemically modified β-amylase was demonstrated by a four-fold increase in maltose production compared to the classical method of immobilization. A kinetic study confirmed the stabilization of the β-amylase by a reduction of the rate constant of inactivation of the different modified enzymes.