Alumina scale growth at zirconia-MCrAlY interface: a microstructural study

High-temperature oxide scale growth at the ceramic-metal interface is a major contributor to the thermomechanical resistance of thermal barrier coatings for hot stages of gas turbines. In order to better understand this phenomenon, microstructural observations of the alumina scales formed at 1100 and 1200 °C under air, between low-pressure plasma-sprayed NiCrAlY and air plasma-sprayed ZrO₂-8.5 wt % Y₂O₃, have been performed by classical and analytical transmission electron microscopy on transverse thin foil specimens. The evolution of the oxide grain morphology from the metal-oxide to the oxide-oxide interface suggests that the scale growth principally takes place at the metal-oxide interface. Segregation of yttrium at oxide grain boundaries has been detected as well as significant quantities of zirconium inside the alumina grains. The oxide growth seems to be dominated by a classical grain-boundary oxygen diffusion mechanism. The presence of zirconium inside the alumina grains also suggests that Al₂O₃ partially forms by chemical reduction of ZrO₂ by AI. The comparison between the microstructures observed and that of alumina scales grown under similar conditions on bare MCrAlY alloys gives some insight into how the ceramic top-coat modifies NiCrAlY high-temperature oxidation mechanisms.     

Excited-state-absorption cross sections and amplifier modeling inthe 1300-nm region for Nd-doped glasses

The performance of Nd³⁺-doped fibre amplifiers is limited by strong excited-state absorption (ESA) of the signal, and, even for fluorozirconate glasses, ESA prevents the important region below 1320 nm from being used. To quantify this limitation and explore alternative host materials, ESA and stimulated-emission cross sections have been measured for a representative group of glass compositions. These parameters have been used in an accurate fiber-amplifier model to provide the first quantitative comparisons of performance for Nd³⁺ -doped glasses in the 1300-nm band as a function of host     

Three-dimensional fracture simulation with a single-domain,direct boundary element formulation

An efficient hypersingular boundary integral equation method for three-dimensional fracture mechanics was presented in a previous paper. The details of the numerical implementation of this method are further discussed herein. In particular, an algorithm for achieving the required differentiability of the crack surface displacement function is discussed. To illustrate the utility of the method, computational results for several strongly interacting multiple-crack geometries are presented. The calculated stress intensity factors are in excellent agreement with those obtained by an approximate analytical method due to Kachanov and Laures.     

Recursive optimal pruning with applications to tree structuredvector quantizers

A pruning algorithm of P.A. Chou et al. (1989) for designing optimal tree structures identifies only those codebooks which lie on the convex hull of the original codebook's operational distortion rate function. The authors introduce a modified version of the original algorithm, which identifies a large number of codebooks having minimum average distortion, under the constraint that, in each step, only modes having no descendents are removed from the tree. All codebooks generated by the original algorithm are also generated by this algorithm. The new algorithm generates a much larger number of codebooks in the middle- and low-rate regions. The additional codebooks permit operation near the codebook's operational distortion rate function without time sharing by choosing from the increased number of available bit rates. Despite the statistical mismatch which occurs when coding data outside the training sequence, these pruned codebooks retain their performance advantage over full search vector quantizers (VQs) for a large range of rates.     

Organizing the production of heat-insulating inserts for ingot-mold hot tops

The Zlatoust Metallurgical Plant has developed a technology that employs semi-dry pressing to make two-layer (composite) heat-insulating inserts for ingot-mold hot tops. The working layer is made of a mixture of materials based on quartz sand, while the insulating layer is based on foamed vermiculate. The binders are sodium silicate solution and commercial lignosulfonate with a density of 1.12–1.20 g/cm³.     

Laparoscopic distal resection of the pancreas with the preservation of the spleen

Management of the pancreatic diseases is still a challenge to the laparoscopic technique. Some experience has been gained in the laparoscopic exploration of the pancreas and staging in cancer. Anatomically the accessibility of the distal pancreas provides the laparoscopic approach technically feasible. Patient and method: A case of insuloma in the tail of the pancreas is presented, where distal pancreatic resection was performed laparoscopically with the preservation of the spleen. In a 55 years old female patient with typical clinical symptoms of hyperinsulinism CT identified a 3 cm large solid tumor in the tail of the pancreas. Complete mobilization of the distal pancreas was enhanced by the use of an ultrasonic dissector (UltraCision). The pancreas is detached from the splenic hilum after dividing the spleen vessels. The pancreas is transected proximally by laparoscopic linear stapler. Preservation of the short gastric vessels provides the necessary blood supply of the spleen following division of the splenic artery and vein. Thus removal of the spleen is not a necessary step in this procedure. The operation was carried out within 4.5 hours. Postoperative course was uneventful, the patient left the hospital on the 5th postoperative day. Advantages of the procedure were the earlier mobilization and shorter recovery time, less postoperative pain. The procedure can be safely performed with a good experience in both pancreatic and laparoscopic surgery.