Advanced ceramic material for high temperature turbine tip seals

Ceramic material systems are being considered for potential use as turbine blade tip gas path seals at temperatures up to 1370 1/4 C. Silicon carbide and silicon nitride structures were selected for study since an initial analysis of the problem gave these materials the greatest potential for development into a successful materials system. Segments of silicon nitride and silicon carbide materials over a range of densities, processed by various methods, a honeycomb structure of silicon nitride and ceramic blade tip inserts fabricated from both materials by hot pressing were tested singly and in combination. The evaluations included wear under simulated engine blade tip rub conditions, thermal stability, impact resistance, machinability, hot gas erosion and feasibility of fabrication into engine components. The silicon nitride honeycomb and low-density silicon carbide using a selected grain size distribution gave the most promising results as rub-tolerant shroud liners. Ceramic blade tip inserts made from hot-pressed silicon nitride gave excellent test results. Their behavior closely simulated metal tips. Wear was similar to that of metals but reduced by a factor of six

Congrid eels of the Eastern Pacific and key to their leptocephali

This study indicates that 13 species of congrid larvae belonging to 8 genera occur in the eastern Pacific. The species are: Ariosoma gilberti; Paraconger californiensis; Paraconger sp.; P. dentatus; Chiloconger labiatus; Taenioconger digueti; T. canabus; Gorgasia punctata; G. obtusa; Gnathophis catalinensis; Hildebrandia nitens; Bathycongrus macrurus; and B. varidens. The morphological and anatomical changes undergone during metamorphosis are useful in the identification of the larvae. Larvae are distributed closer to the coastal waters, and are more common from January to May than from June to December. A key to the larvae was developed based on the myotomal counts, adult vertebral counts, pigmentation patterns, and the nature of the teeth and tail tip to distinguish the genera and species. This study shows that Garman's unidentified larvae, Atopichthys acus and A. cingulus, are two different larval stages of Ariosoma gilberti, and points out that Atopichthys dentatus and A. obtusus belong to Paraconger and Gorgasia, respectively. (PDF file contains 25 pages.

Advanced ceramic material for high temperature turbine tip seals

Forty-one material systems were evaluated for potential use in turbine blade tip seal applications at 1370 C. Both ceramic blade tip inserts and abradable ceramic tip shoes were tested. Hot gas erosion, impact resistance, thermal stability, and dynamic rub performance were the criteria used in rating the various materials. Silicon carbide and silicon nitride were used, both as blade tips and abradables. The blade tip inserts were fabricated by hot pressing while low density and honeycomb abradables were sintered or reaction bonded

Molecular hydrogen in the galaxy and galactic gamma rays

Recent surveys of 2.6 mm CO emission and 100 MeV gamma-radiation in the galactic plane reveal a striking correlation suggesting that both emissions may be primarily proportional to the line-of-sight column density of H2 in the inner galaxy. Both the gamma ray and CO data suggest a prominent ring or arm consisting of cool clouds of H2 at a galactocentric distance of approximately 5 kpc with a mean density of approximately 4 atoms/cu cm. The importance of H2 in understanding galactic gamma ray observations is also reflected in the correlation of galactic latitude distribution of gamma rays and dense dust clouds. A detailed calculation of the gamma ray flux distribution in the 0 deg to 180 deg range using the CO data to obtain the average distribution of molecular clouds in the galaxy shows that most of the enhancement in the inner galaxy is due to pion-decay radiation and the 5 kpc ring plays a major role. Detailed agreement with the gamma ray data is obtained with the additional inclusion of contributions from bremsstrahlung and Compton radiation of secondary electrons and Compton radiation from the intense radiation field near the galactic center

Pathogenic Characterization and Therapeutic Development for Fiblrolamellar Hepatocellular Carcinoma

Fibrolamellar hepatocellular carcinoma (FLC) is a rare liver cancer that primarily affects adolescents and young adults. There are no known successful systemic chemotherapies for this disease, and thus, surgery is the only potential path to a cure in patients with FLC. Once the disease has grown or metastasized to a point where surgery is no longer an option, a patient’s chance for survival approaches zero. There is a recurrent genetic deletion in FLC cells, which has been found in almost all FLC tumor samples sequenced to date, but not in normal liver tissue from the same patients. The deletion encompasses ~400kb on chromosome 19 beginning after the first exon of DNAJB1, which codes for a member of the heat shock protein 40 (HSP40/DNAj) family, and ends before the second exon of PRKACA, which codes for the catalytic subunit of protein kinase A (PKAc). The deletion results in a functioning chimeric kinase with exon 1 of DNAJB1 and exons two through ten of PRKACA. In this thesis, I will present my work in two areas with regards to this disease. First, I will present my research working on understanding the pathogenesis of FLC. While we know the oncogene that is responsible for transformation, we do not have a good understanding of how this mutation leads to cancer. I will present proteomic data that shows a unique proteomic and phosphoproteomic signature in FLC and will show that quantification of the PKA system can provide insight into the pathogenesis. In the following chapter, I will present my research on developing the first systemic therapeutic for FLC, by targeting this mutation. I will show how I began by targeting the protein, which proved difficult given the similarities of the mutated protein to the wild-type protein. Then, I will discuss my work on developing an RNA-targeting therapy with antisense oligonucleotides and small interfering RNAs. I will close with a discussion on my thesis work and how I envision future research to continue from what I present here

Coherent pairing states for the Hubbard model

We consider the Hubbard model and its extensions on bipartite lattices. We define a dynamical group based on the $\eta$-pairing operators introduced by C.N.Yang, and define coherent pairing states, which are combinations of eigenfunctions of $\eta$-operators. These states permit exact calculations of numerous physical properties of the system, including energy, various fluctuations and correlation functions, including pairing ODLRO to all orders. This approach is complementary to BCS, in that these are superconducting coherent states associated with the exact model, although they are not eigenstates of the Hamiltonian.Comment: 5 pages, RevTe

“I don’t think I am a learner”: Acts of naming learners at work

The terms “learning” and “learner” are used in discussions of workplace learning as if they were unproblematic and as if workers, organisations and researchers had a common, shared view about what these terms mean. A study of four different workgroups within an organisation in which the discourse of learning was pervasive suggests that having an identity as a learner may not be compatible with being regarded as a competent worker. The politics of naming oneself as a learner are considered and the power of naming learning and learners are discussed. The broader implications for research on workplace learning of such a discursive approach are noted. © 2003, MCB UP Limite