Top-Seeded Melt-Growth of YBa2Cus3Ox Crystals for Neutron Diffraction Studies

We have grown cubic centimeter-size crystals of YBa₂Cu₃O _x suitable for neutron studies, by a top-seeded melt-growth technique. Growth conditions were optimized with an eye toward maximizing phase purity. It was found that the addition of 2% Y₂BaCuO₅ and 0.5% Pt (by mass) were required to prevent melt loss and to obtain the highest crystallinity. A neutron diffraction study on a mosaic of six such crystals found that the final Y₂BaCuO₅ concentration was 5%, while other impurity phases comprised less than 1% by volume. The oxygen content was set to x = 6.5, the crystals were detwinned, and then carefully annealed to give the well-ordered ortho-II phase. The neutron study determined that 70% of the mosaic's volume was in the majority orthorhomic domain. The neutron (006) and (110) rocking curve widths were ～1° per crystal and ～2.2° for the mosaic, and the oxygen chain correlation lengths were >100 Å in the a- and b-directions and ～50 Å in the c-direction.     

Reproducibility of brachial ultrasonography and flow-mediated dilatation (FMD) for assessing endothelial function

Minimally invasive plastic surgery has expanded beyond the original confines of aesthetic applications to encompass all our endeavors in an attempt to restrict the size of surgical scars, limit postoperative discomfort, and hasten recovery of function. This evolution has already delineated methods to raise our workhorse muscle flaps and has negated the risks of laparotomy for various visceral flaps. It is then only a logical progression to use these endoscopic techniques to harvest fascial flaps so as to avoid the notorious donor site morbidity of the fasciocutaneous flap, which has certainly hindered the rapid acceptance of these otherwise valuable flaps. Endoscopic-facilitated elevation of a local adipofascial flap is described for which little or no additional skin incisions need ever be made.     

Brazing as a means of sealing ceramic membranes for use in advanced coal gasification processes

Coal is potentially a very inexpensive source of clean hydrogen fuel for use in fuel cells, turbines, and various process applications. To realize its potential however, efficient low-cost gas separation systems are needed to provide high purity oxygen that will enhance the coal gasification reaction and to extract hydrogen from the resulting gas product stream. Several types of inorganic membranes are being developed for hydrogen or oxygen separation, including porous alumina, transition metal oxide perovskites, and zirconia. Because they form the heart of the working device, numerous advances have been made in the fabrication and performance of these membrane materials. However, less emphasis has been placed on the materials that will be used in the balance of the device; in particular, the seals that bond the functional ceramic to the metallic structural component. In an effort to begin addressing this issue, we have examined ceramic-to-metal brazing as a method of sealing a model set of gas separation component materials: yttria-stabilized zirconia and stainless steel. In comparative high-temperature exposure testing of joints prepared using commercial brazes and a newly conceived braze alloy, the commercial material proved to be unsuitable due to excessive oxidation. On the other hand, the new material not only displayed superior oxidation resistance, but also excellent hermeticity in prototypic membrane testing.     

The temperature dependence of elastic nonlinearity in metal-matrix composites

Thermal stresses are very important in determining the strength of composites. In metal-matrix composites, these stresses are generated at the matrix-reinforcement interface as a result of the difference in thermal expansion coefficients of matrix and reinforcement during solidification. In order to evaluate these stresses, we studied the effect of temperature on the second- and third-order elastic constants in two metalmatrix composites consisting of the aluminum alloys 8091 and 7064 and silicon carbide particles up to 20% volume fraction. The elastic constants were determined at the temperatures 0, 25 and 55°C using measurements of absolute as well as changes of ultrasonic velocities as a function of applied stress. The values of these constants are used to calculate the acoustic nonlinearity parameters. In both composites, the acoustic nonlinearity parameters increase with the amount of reinforcement, which is opposite to that previously observed in aluminum alloys containing second-phase precipitates. Also, the temperature behavior of the nonlinearity parameters in the composites are opposite to those in the aluminum matrices. These differences in behavior are interpreted as due to the presence of thermal stresses at the matrix-reinforcement interface, and give promise to the possibility of using these parameters in the nondestructive evaluation of these stresses in metal-matrix composites.     

Cell cycle regulation of the Saccharomyces cerevisiae polo-like kinase cdc5p

Progression through and completion of mitosis require the actions of the evolutionarily conserved Polo kinase. We have determined that the levels of Cdc5p, a Saccharomyces cerevisiae member of the Polo family of mitotic kinases, are cell cycle regulated. Cdc5p accumulates in the nuclei of G2/M-phase cells, and its levels decline dramatically as cells progress through anaphase and begin telophase. We report that Cdc5p levels are sensitive to mutations in key components of the anaphase-promoting complex (APC). We have determined that Cdc5p-associated kinase activity is restricted to G2/M and that this activity is posttranslationally regulated. These results further link the actions of the APC to the completion of mitosis and suggest possible roles for Cdc5p during progression through and completion of mitosis.