Cracks at the ferrite-austenite interface

Bulk specimenss for three point tests are produced from explosion clad austenite-ferrite material by electron beam welding bulk austenite and bulk ferrite to the respective surfaces. By milling, spark-erosion and fatigue cracks are introduced at and parallel to the interface in these specimens. At −30°C the crack extension force is the same for interfacial and bulk cracks in the ferrite. At room temperature the crack extension force for interfacial cracks is half of that for bulk ones, for suinterfacial cracks it lies between the two extremes.     

Proteoglycans at the bone-implant interface

From unincubated quail blastoderms, we have excised, caudal marginal zones (caudally from Rauber's sickle), upper layer fragments covering Rauber's sickle or Rauber's sickle fragments alone (as controls), and placed them on the ventral side of the cranial quadrant of unincubated chicken blastoderms. Also, quail Rauber's sickle fragments, all or not associated with quail endophyll, were placed on the ventral side of isolated central upper layer discs of prestreak chicken blastoderms from which the deep layer was previously removed. Only the Rauber's sickle-derived cells (sickle endoblast cells), placed on unincubated or shortly incubated blastoderms induce, after culture, a primitive streak (PS) and a normal embryo. This indicates, together with previous experimental evidence, that even in the presence of endophyll, neither the deep part of the caudal marginal zone nor the upper layer above it can induce a primitive streak. This experimental study affords further evidence that the function of the avian Rauber's sickle is homologous to the function (mesoderm induction) of the vegetal dorsalizing cells (Nieuwkoop centre) in amphibian blastulas.     

The role of charged residues mediating low affinity protein-protein recognition at the cell surface by CD2

Insights into the structural basis of protein-protein recognition have come principally from the analysis of proteins such as antibodies, hormone receptors, and proteases that bind their ligands with relatively high affinity (Ka approximately 10(9) M-1). In contrast, few studies have been done on the very low affinity interactions mediating cell adhesion and cell-cell recognition. As a site of protein-protein recognition, the ligand binding face of the T lymphocyte cell-cell recognition molecule, CD2, which binds its ligands 10(4)- to 10(5)-fold more weakly than do antibodies and proteases, is unusual in being both very flat and highly charged. An analysis of the effect of mutations and ionic strength on CD2 binding to its ligand, CD48, indicates that these charged residues contribute little, if any, binding energy to this interaction. However, the loss of these charged residues is shown to markedly reduce ligand-binding specificity. Thus, the charged residues increase the specificity of CD2 binding without increasing the affinity. This phenomenon is likely to result from a requirement for electrostatic complementarity between charged binding surfaces to compensate for the removal, upon binding, of water interacting with the charged residues. It is proposed that this mode of recognition is highly suited to biological interactions requiring a low affinity because it uncouples increases in specificity from increases in affinity.     

Mass-transport processes at the steel-enamel interface

Mass-transport processes at the enamel-steel interface were investigated by studying the rheological properties of the enamel and the microstructure of the enamel-steel interface. The thermophysical properties, e.g., the viscosity and spreading behavior of enamel were measured using the rotating bob and the sessile drop techniques, respectively. The results show that the viscosity of the enamel decreases sharply as the FeO concentration increases from 0 to 25 wt pct, while the contact angle changes with the increasing thickness of the NiO precoat. Microstructural characterization also revealed evidence for the presence of an interfacial gradient force (more specifically referred to as the Marangoni convection) confined within the 0- to 80-μm thickness at the enamel-steel interface. This force is responsible for a convective flow, which determines the formation of flow striae at the interface. The striae act as a sink for evolved gases and provide transport away from the enamel-steel interface. In addition, experimental simulation of Marangoni convection (interfacial-gradient force) was carried out by selectively doping the steel surface with excess Fe₂O₃ powder. The presence of convection flow was confirmed by analyzing the pattern of iron oxide particles dispersed across the surrounding enamel layers. Based on the microstructural characterization and the thermophysical data, we propose a mechanism for mass transport at the glass-steel interface.     

Detection of low affinity interactions between peptides and heat shock proteins by chemiluminescence of enhanced avidity reactions (CLEAR)

Protein-protein and protein-peptide interactions that are low affinity in nature preclude the straightforward measurement of binding. To overcome this limitation, a novel method has been devised for stabilizing these weak interactions by increasing the binding avidity. These studies have focused on the binding of peptides to heat shock proteins (with a typical KD of approximately 25 to 50 microM). Multivalent ligands have been created by coupling peptides plus biotin to a neutral carrier molecule, dextran. These peptide-dextran conjugates allow for more avid binding to proteins that have been immobilized on a membrane surface. Detection of signals via enhanced chemiluminescence further increases the sensitivity of the method that has been termed Chemiluminescence of Enhanced Avidity Reactions (CLEAR). The assay is simple, reliable and consistently detects specific binding between heat shock proteins and peptide ligands. CLEAR should be generally applicable to other ligand receptor pairs where the detection of binding is limited by the low affinity of the interaction.     

Biases in three-dimensional structure-from-motion arise from noise in the early visual system

The projected pattern of retinal-image motion supplies the human visual system with valuable information about properties of the three-dimensional environment. How well three-dimensional properties can be recovered depends both on the accuracy with which the early motion system estimates retinal motion, and on the way later processes interpret this retinal motion. Here we combine both early and late stages of the computational process to account for the hitherto puzzling phenomenon of systematic biases in three-dimensional shape perception. We present data showing how the perceived depth of a hinged plane ('an open book') can be systematically biased by the extent over which it rotates. We then present a Bayesian model that combines early measurement noise with geometric reconstruction of the three-dimensional scene. Although this model has no in-built bias towards particular three-dimensional shapes, it accounts for the data well. Our analysis suggests that the biases stem largely from the geometric constraints imposed on what three-dimensional scenes are compatible with the (noisy) early motion measurements. Given these findings, we suggest that the visual system may act as an optimal estimator of three-dimensional structure-from-motion.     

Study of the interface reactions between cells and a biocompatible ceramic

Preliminary results on the modifications induced by the growth of a Chinese Hamster Ovary (CHO) cell line on the surface of a CORD 1014 ceramic cordierite are reported. Results proved that cells strongly modify the crystallography and the chemical composition of the surface and near surface regions of the cordierite.     

The rate of movement of the topochemical interface during gas-solid reactions

The rate of recession of the topochemical interface between a porous core and the product layer is shown to be given by wherer _c is radial position of the interface,R(r_c) the rate of the chemical reaction at the interface and (dC _s/dr)|_{r s} is the gradient of concentration profile of solid reactant in the porous core at the interface. The integration of the above equation can sometimes be achieved analytically but can always be done numerically for even highly complex reaction mechanisms. The equation correctly reduces to previously known solutions when the inner core is impervious to gas diffusion. The utility of the equation is demonstrated by applying it to the industrially important multistage reduction process Mn₃O₄ → MnO — > Mn. The predictions from the theoretical model are compared successfully with experimental data for this reaction. Formerly Student in Department of Metallurgy, University of Strathclyde, Scotland.     

Brittle crack initiation at the elastic-plastic interface

To study fracture initiation near notches experiments were conducted on polycarbonate at room temperature. It could be demonstrated conclusively that cracks are nucleated under the influence of a critical normal stress at the elastic-plastic boundary. Slip line field theory allows the determination of the critical normal fracture stress from the knowledge of the notch root radius and the location of the crack nucleation. For 0.5 in. thick specimens with root radii between 0.001 and 0.01 in. the calculated critical fracture stress of polycarbonate is nearly constant, 21.2 ±0.6 ksi. An analysis of the data in accordance with the theory developed by R. Beeuwkes, Jr. for parabolic notches resulted in critical fracture stress values of approximately 21.5 ksi. Specimens with central holes between 0.04 and 0.05 in. diam also showed crack nucleation below the surface of the hole but the calculated critical fracture stress values were considerably lower, approximately 11.2 ksi. This may be attributed to the loss of plane strain conditions in these 0.5 in. thick specimens. The experimentally observed slip lines in polycarbonate are not orthogonal to each other but intersect at a lower (~80 deg) angle. This may be due to the relief of stresses on unloading and sectioning, and it may indicate that plane strain conditions were not present. Because of its flow characteristics, which are similar to those of metals, and because of its transparency, polycarbonate appears to be a good model material for the study of plastic flow initiated brittle fracture. It could be used to check the theoretical slip line field solutions proposed for a variety of loading conditions.     

On the reactions 2 C + O2 and C + CO2 at very low pressure

In an ultra high vacuum heterogeneous gas reactions such as 2 C + O₂^G → 2 CO^G and C + CO₂^G → 2 CO^G often show a less complicated reaction path than under normal pressure. In the present study the graphite sample is a commercial light‐bulb filament, which is extremely resistant against oxidation. Under low pressure the combustion reaction is of first order with a continuous transition to zero order at temperatures between 900 and 1300 K depending on the oxygen pressure. The Boudouard reaction behaves similarly but obeys zero order only around 2000 K and for CO₂ pressures around 1 bar. The measured and the statistically calculated reaction rates agree well. An insight of the details of the reaction and chemisorption is determined by the evaluation of experiments carried out in an ultra high vacuum using isotopes such as ¹³CO₂^G. The Boudouard equilibrium for graphite can be reached only catalytically, e.g., with sponge iron in statu nascendi.     

T-cell activation: interplay at the interface

Recent studies have shown that, when a T cell interacts with a cognate antigen-presenting cell, an organized adhesive contact is formed between the two cells by a process which involves the dynamic, three-dimensional redistribution of entire signaling assemblies.     

Early and supported hospital discharge: the hospital and community interface

An agent pathogenic for laboratory albino Swiss mice was isolated from a pool of Haemaphysalis punctata ticks collected from cattle on a farm located in Alcácer do Sal county, southern Portugal. The isolated virus was shown to be distinct from but serologically related to virus members of the Bhanja antigenic group. This new virus in the family Bunyaviridae was named Palma for the farm where ticks have been collected for several studies.     

Autodoping effects at the interface of GaAs-Ge heterojunctions

A close-spaced growth process using HCl as the transport agent has been used to deposit epitaxial GaAs on germanium near 600°C. The dependences of the epitaxial surface morphology, bulk epitaxial layer electrical properties, and the autodoping behavior of arsenic in germanium and germanium in GaAs have been studied as a function of substrate temperature, orientation, and HCl concentration. A heavily germanium-doped layer is found in the GaAs at the substrate interface. GaAs layers greater than 12 μm in thickness exhibit mobilities of ≈3000 sq cm per v-sec and carrier concentrations of 1 to 5×10¹⁶ cm^?3. A rate limitation is found for diffusion of arsenic into germanium from the GaAs layer. Optimized conditions for GaAs layer quality and minimal autodoping permit growth of mirror smooth layers on misoriented (111) germanium substrates.