Understanding of Void Formation in Cu/Sn-Sn/Cu System During Transient Liquid Phase Bonding Process Through Diffusion Modeling

Metallurgical and Materials Transactions B - Transient Liquid Phase (TPL) bounding of Sn foil sandwiched between two Cu foils involves, in the temperature range above the melting point of Sn...     

Postshaking Shear Strain Localization in a Centrifuge Model of a Saturated Sand Slope

This paper presents analyses of a test conducted on a 9-m-radius centrifuge to study the redistribution of pore water during diffusion of earthquake-induced excess pore pressures in a sand slope with embedded silt layers. The centrifuge model developed large postshaking deformations associated with shear strain localization at the interface between the sand and silt layers. Dense arrays of pore pressure transducers provided detailed measurements of pore pressure variations in time and space within the slope. A new data analysis approach is presented in which measured pore-pressures are used to compute flow rates and volumetric strains as a function of time and position throughout the slope. Hydraulic gradients were calculated by numerical differentiation of measured pore-pressure distributions with respect to position. Flow rates that were based on Darcy’s law were then integrated with respect to time to obtain flow quantities, from which volumetric strains were computed. A second data analysis approach that computes volumetric strains on the basis of soil compressibility and changes in pore pressure provided an independent computation of strains in consolidating zones. Results using these data analysis procedures confirm that a dilating (loosening) zone of significant thickness developed in the sand immediately beneath an embedded silt layer that had impeded the drainage of high pore pressures. These results support the hypothesis that the dilating zone corresponds to regions where the mobilized friction angle exceeds the critical state friction angle and that the dilating zone can be initially relatively thick before its size diminishes to the thickness of a thin shear band after the peak friction angle is mobilized. Quantification of the evolution of the size of the dilating zone is a key to understanding the magnitude of deformations associated with void redistribution.     

Proteolytic degradation of rat growth hormone-releasing factor(1-29) amide in rat pituitary and hypothalamus

The identification of peptide bonds vulnerable to tissue peptidases is a valuable approach to design peptide agonists which exhibit a longer duration of action than the native molecules. Therefore, the kinetic of disappearance of rat growth hormone-releasing factor (rGRF(1-29)NH2) and the identification of its metabolites were studied in rat pituitary and hypothalamus. Synthetic rGRF(1-29)NH2 (10 microM) was incubated (0-120 min, 37 degrees C) in the presence of a pituitary (237 +/- 51 micrograms protein/ml) or hypothalamus homogenate (576 +/- 27 micrograms protein/ml). Using analytical high pressure liquid chromatography (HPLC), apparent half-lives of 22 +/- 3 min and 25 +/- 4 min were found in pituitary and hypothalamus, respectively. In both tissues, three degradation products, all less hydrophobic than the native peptide, were detected and isolated by preparative HPLC. The identification of the purified metabolites was ascertained by amino acid analysis, sequencing and chromatography with synthetic homologs. These results indicate that the main sites of cleavage in the pituitary and hypothalamus are Lys21-Leu22 (trypsin-like cleavage site), Leu14-Gly15 and Tyr10-Arg11 (chymotrypsin-like cleavage sites). TLCK and leupeptin did not affect the formation of fragment (1-21)OH while TPCK blocked the cleavage of Leu14-Gly15. The low affinity of fragment (1-21)NH2 for pituitary GRF binding sites suggests that hydrolysis of the Lys21-Leu22 bond inactivates rGRF(1-29)NH2 in this target tissue.     

Influence of the Active Particles on the Self‐Healing Efficiency in Glassy Matrix

In the present paper, we present the influence of the composition of the active particles on the self‐healing property in glass–particles (B, B₄C, VB, V, or VC) composites. The thermogravimetric curves and oxidation kinetics at 700 °C of the active particles are reported. We show that the oxidation rate is higher with vanadium‐based particles than with boron‐base ones, mainly due to the formation of B₂O₃ that acts as a diffusion barrier to oxygen. In situ healing of cracks in composites was observed using high‐temperature environmental scanning electron microscopy (HT‐ESEM). The composition of the phases formed by reaction between the oxidation products and the glassy matrix is systematically determined. Self‐healing occurs as a consequence of oxidation of active particles, which leads to the formation of an oxide, such as V₂O₅ and/or B₂O₃ that is fluid enough to fill in the crack at high temperature. The crack healing is obtained whatever the nature of the active particle.     

CMOS pixels for subretinal implantable prothesis

This work reports on the design, fabrication, and characterization of CMOS pixels for subretinal implants, which seems to be an effective way to recover visual capabilities in some types of blindness. Two possible approaches are presented for CMOS pixel implementation: 1) an approach based on a light-controlled oscillator (LICOS) using a ring oscillator with an odd number of inverters and 2) an approach based on distributing a square signal at each pixel that filters out a number of pulses depending of the light intensity wave across the chip (WATCH). Both types of pixels fabricated in 0.35-/spl mu/m CMOS demonstrate good mimic of the electrical behavior of human retina, with low-power consumption (typically 1 mW for a 14/spl times/14 matrix of pixels) and having small dimensions (75/spl times/78.5 /spl mu/m/sup 2/ for LICOS and 70/spl times/50 /spl mu/m/sup 2/ for WATCH), which make them suitable for practical implants. Experimental validation is reported on physiological solutions. Because of its characteristic, the proposed matrix of pixels could be considered as one of the first stand-alone highly integrated solutions for subretinal implant chips.     

Liquefaction Susceptibility Criteria for Silts and Clays

New liquefaction susceptibility criteria for saturated silts and clays are presented that are based on the mechanics of their stress-strain behavior and which provide improved guidance for selecting engineering procedures for estimating potential strains and strength loss during seismic loading. Monotonic and cyclic undrained loading test data for silts and clays show that they transition, over a fairly narrow range of plasticity indices (PI), from soils that behave more fundamentally like sands (sand-like behavior) to soils that behave more fundamentally like clays (clay-like behavior), with the distinction having a direct correspondence to the type of engineering procedures that are best suited to evaluating their seismic behavior. It is recommended that the term liquefaction be reserved for describing the development of significant strains or strength loss in fine-grained soils exhibiting sand-like behavior, whereas the term cyclic softening failure be used to describe similar phenomena in fine-grained soils exhibiting clay-like behavior. For practical purposes, clay-like behavior can be expected for fine-grained soils that have PI ≥ 7, although a slightly lower transition point for soils with a CL-ML classification (perhaps PI ≥ 5 or 6) would be equally consistent with the available data. Issues related to the practical application of these criteria are discussed.     

High voltage characterization of tin oxide varistors

High current characterization of SnO₂-based varistors have been carried out and the results obtained have been compared with those ZnO-based commercial surge arresters. It is shown that for a high temperature sintering (1350 °C), the leakage current, breakdown voltage and the saturation at high current density are similar between both types of surge arresters. The paper shows, for the first time, that the high breakdown voltage observed with tin dioxide cannot be easily maintained since the saturation of the ceramics is reached for current densities of several amperes per square centimetre.     

Digital marbling: a multiscale fluid model

This paper presents a multiscale fluid model based on mesoscale dynamics and viscous fluid equations as a generic tool for digital marbling purposes. The model uses an averaging technique on the adaptation of a stochastic mesoscale model to obtain the effect of fluctuations at different levels. It allows various user controls to simulate complex flow behaviors as in traditional marbling techniques, as well as laminar and turbulent flows. Material transport is based on an improved advection solution to be able to match the highly detailed, sharp fluid interfaces in marbling patterns. In the transport model, two reaction models are introduced to create different effects and to simulate density fluctuations.