Electrode processes at the glass carbon/LiCl-CuCl-CuCl2 melt interface

The kinetics of the electrode processes occurring at the glass carbon/LiCl-CuCl-CuCl₂ $\left( {N_{CuCl - CuCl_2 } = 0 - 7.5 mol \% } \right)$ melt interface is studied by the coulostatic method, single current pulse chronopotentiometry, and stationary voltammetry at a temperature of 950 K and the atmospheric pressure of chlorine over a melt. The exchange current densities in the molten mixtures are determined by the coulostatic method. These data are used to calculate the transfer coefficient (?? = 0.54 ± 0.06) and the rate constant of the electrode reaction Cu²⁺ + e ^? ai Cu⁺ (k _S = 0.26 ± 0.02 cm/s). The results of stationary voltammetry in the cathode potential region reveal pronounced limiting currents up to the precipitation of metallic copper on an electrode. The experimental data obtained by chronopotentiometry are used to find the transition times for various current densities over the entire concentration range under study. The dependences plotted in the i??^1/2 = f(i) coordinates suggest the presence of a chemical homogeneous reaction preceding the electrode process. The total value of the rate constants of the forward and back reactions is estimated to be ??2. The copper mono- and dichloride concentrations are determined in the concentration range under study.     

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.     

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.     

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.     

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.     

Differential nm23 gene expression at the fetal-maternal interface

The product of the nm23 gene has been proposed as a candidate tumour metastasis suppressor protein. A strong association has been observed between reduced expression of the nm23 gene and acquisition of metastatic behaviour in some tumour cells, including breast cancer and melanoma, but not in others, such as neuroblastoma and colon, cervical and thyroid cancers. During the early gestation period both human and murine trophoblast cells exhibit in vitro invasive properties similar to those of neoplastic cells. Such invasive properties, however, disappear in the late stage of gestation. In the present study, we examined the abundance of nm23 mRNA from various fetal-maternal interface tissues (uterus, decidua, placenta and embryo) during early (day 8), mid (day 14) and late (day 18) stages of gestation in CD1 mice, in order to determine whether nm23 plays any anti-invasive and/or biological roles during gestation. nm23 was found to be expressed in all the tissues during the early and mid stages of gestation. The expression levels were, however, variable among different tissues and development stages. In the early stage, nm23 mRNA levels were the highest and similar among tissues from the uterus, decidua, placenta and embryo. In the mid stage, the mRNA levels were reduced significantly in the uterus, decidua and placenta, but not in the embryo. In the late stage, nm23 mRNA was further reduced to the extent that it could not be seen in the decidua, was barely seen in the uterus and was weakly present in the placenta. However, the mRNA level of the embryo in the late stage was still high and similar to the early stage. We also examined nm23 expression in trophoblast cells from normal human term placenta and a highly metastatic human choriocarcinoma cell line, JAR. nm23 expression was significantly higher in JAR than in normal placenta, indicating that nm23 does not appear to have an anti-metastatic function in this cell line. Several cytokines--interleukin 2 (IL-2), tumour necrosis factor alpha (TNF-alpha) and interferon gamma (IFN-gamma)--and prostaglandin E2 (PGE2) known to modulate tumour growth and metastasis were examined to determine whether they regulate nm23 expression in JAR in vitro. The B16F10 melanoma cell line was used as control. No effect was found in the JAR cell line, whereas TNF-alpha, IFN-gamma and PGE2 down-regulated nm23 expression in the B16F10 cell line.(ABSTRACT TRUNCATED AT 400 WORDS)     

The migration of grain-boundary grooves at the solid-liquid interface

When a solid-liquid interface is intersected by a grain boundary, a grain-boundary groove forms at the interface. Experiments have been carried out using camphene (a transparent analogue of a metal in terms of solidification behaviour) which show that, if the grain boundary is not perpendicular to the interface, the groove will be dragged laterally across the interface. This effect has been modelled in a thin sandwich of silicone oil by mechanically dragging a cusp of oil across an otherwise undisturbed oil surface. The present work is relevant to the development of growth textures during the slow solidification of relatively pure metallic melts.