Kinetics of thermal barrier oxide interactions with molten silicates

The degradation of thermal barrier coatings (TBCs) by molten silicates (CMAS) represents a significant barrier to increased operation temperatures of gas turbine engines and thus fuel efficiency. A promising mechanism for CMAS mitigation has been found in certain TBC chemistries (e.g. Gd2Zr2O7) that undergo reactive crystallization – the crystallization of new, thermodynamically favored phases, which contain both melt and TBC constituents (e.g. apatite). Significant work has been undertaken to understand the thermodynamics of TBC-CMAS systems and the possible reaction phases, but little quantitative data on the kinetics of these interactions exists today; this includes: the (i) rate of TBC dissolution into the melt, (ii) diffusion of TBC constituents within the melt, and (iii) reaction product crystallization rates. Please click Additional Files below to see the full abstract

Development and evaluation of an intelligent handheld insulin dose advisor for patients with Type-1 diabetes

Diabetes mellitus is an increasingly common, chronic, incurable disease requiring careful monitoring and treatment so as to minimise the risk of serious long-term complications. It has been suggested that computers used by healthcare professionals and/or patients themselves may playa useful role in the diabetes care process. Seven key systems (AIDA, ADICOL, DIABETES, DIAS, IIumaLink, T-IDDM, POIRO) in the area of diabetes decision support, and their underlying techniques and approaches are summarised and compared. The development of the Patient-Oriented Insulin Regimen Optimiser (POIRO) for insulindependent (Type-I) diabetes, and its hybrid statistical and rule-based expert system is then taken forward. The re-implementation and updating of the system for the Palm OS family of modern Personal Digital Assistants (PDAs) is described. The evaluation of this new version in a seven week, randomised, open, cross-over clinical pilot study involving eight patients on short-acting plus long-acting insulin basalbolus regimens showed it to be easy-to-operate, reliable, not time consuming and well liked by patients. Following this, the characteristics and use of all currently available insulin formulations, and the corresponding insulin regimens are summarised. Algorithms to provide dose advice and decision support for patients taking the new rapid-acting, intermediate-acting and premixed insulin formulations are then developed. The user interface is improved and extended, amongst others through the development and use of a model describing individual user's meal time habits. Implementation-related issues encountered are discussed, and further work and future directions are identified and outlined. Motivated by the complex and safety-critical nature of systems such as POIRO, we also report on the use of the B abstract machine notation for the formal specification of the original POIRO system, and focusing on projects and published case studies. review the use of formal methods in the development of medical computer systems

Implications of coupled crystallization and decomposition reactions for CMC processing using polymer derived ceramics

The wider adoption of SiC-based ceramic matrix composites (CMCs) for thermo-structural applications is limited in part by the challenges encountered in processing dense matrices without low melting temperature or oxidation-sensitive phases (i.e. free Si or C). Manufacturing routes utilizing polymer-derived ceramics (PDC) are being developed as a cost-effective method to manufacture CMCs with improved temperature capability. The notional approach involves repeated infiltration of the CMC preform with a preceramic polymer followed by pyrolysis to form an amorphous Si-(O-N)-C matrix. A heat treatment at a higher temperature is necessary to crystallize the PDC, which improves the thermal conductivity, thermal stability, and oxidation resistance compared to the amorphous polymer derived phase. Crystallization occurs by precipitation of SiC, C, and/or Si3N4 while concomitant decomposition reactions produce gaseous SiO and CO. Please click Additional Files below to see the full abstract

Doctor of Philosophy

dissertationLung cancer is the most fatal and second most prevalent type of cancer in the United States with a current five-year survival rate of only 16%. Thus, novel therapeutic agents to both prevent and treat lung cancer are necessary. One such agent is selenium, a micronutrient present in the diet. Epidemiological studies and supplementation trials with selenium have shown it to decrease lung cancer incidence and mortality. Selenium has also been shown to decrease lung tumor burden in animal studies, with the benefit being compound dependent. The mechanisms of action of selenium in cancer remain under investigation, but may relate to cellular redox status regulation. The hypothesis of this work is that distinct selenocompounds alter the cellular redox state of human lung cells through the Nrf2/antioxidant response element (ARE) pathway and the antioxidant selenoprotein thioredoxin reductase 1 (TR1). This hypothesis was tested using three specific aims: 1. Determine the redox effects of selenocompounds in A549 adenocarcinoma cells and BEAS-2B nonmalignant bronchial epithelial cells. 2. Investigate the ability of selenocompounds to activate the Nrf2/ARE pathway in nonmalignant BEAS-2B cells. 3. Determine if TR1 modulates the cytotoxcity of selenocompounds in malignant A549 cells. iv Several selenocompounds were investigated, including the selenoamino acids selenomethionine and selenocystine, the selenocysteine prodrugs 2-butyl selenazolidine- 4(R)-carboxylic acid (BSCA) and 2-cyclohexylselenazolidine-4(R)-carboxylic acid (ChSCA), and methylseleninic acid (MSA). This work indicates that selenium can modulate cellular redox status, but the effects are compound and cell-line specific. Selenocystine and ChSCA induced oxidative stress in A549 cells and activated the Nrf2 pathway in BEAS-2B cells. Selenocystine, ChSCA and BSCA also demonstrated enhanced cytotoxicity in A549 cells with TR1 knockdown, which was related to their ability to deplete intracellular glutathione. MSA produced a reductive stress in A549 cells and activated the Nrf2 pathway in BEAS-2B cells, but its cytotoxicity was not altered by TR1 status. Selenomethionine failed to modulate cellular redox status, activate the Nrf2 pathway, or demonstrate enhanced cytotoxicity with TR1 knockdown. These findings further demonstrate that selenium has compound-dependent redox effects and certain compounds, namely selenocystine and ChSCA, may have actions as both cancer preventive and anti-tumor agents in the lung

Understanding garnet phase stability in Gd/Y/Yb-CMAS systems and influences on multiphase T/EBC-CMAS interactions

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Fundamental challenges in CMAS mitigation

CMAS degradation of thermal and environmental barrier coatings (T/EBCs) is recognized as a fundamental barrier to progress in gas turbine technology; melting of the precursor silicate deposits, typically at ~1200°C, limits the temperature capability of the coatings and by extension the achievable engine efficiency. Molten CMAS dissolves all coating materials of interest in the protection of superalloys and ceramic composites, sometimes with preferential grain boundary penetration, and often leads to the formation of new or modified crystalline phases. Notwithstanding the thermo-chemical attack, the more deleterious form of damage is arguably thermo-mechanical. In TBCs the CMAS melt flows into the network of pores and cracks/segmentations that enable strain tolerance during thermal cycling, stiffening the coating and elevating the strain energy available for delamination. The mitigation strategy is generally based on the reaction of CMAS with the coating material, consuming locally the melt and yielding the precipitation of crystalline phases in sufficient volume to fill in the flow channels and arrest penetration. The extent of stiffening scales with the penetration depth, which depends in turn on a complex interplay between the infiltration, dissolution and crystallization dynamics. Predictive models are hindered by uncertainty in the geometric features of the pore network as well as the paucity of information on the dissolution and crystallization rates, compounded with the evolving composition and viscosity of the melt under the thermal gradient within the coating. Ideally, the reaction should be sufficiently rapid to overwhelm the flow dynamics, so the stiffened layer thickness is minimized. However, most oxides that exhibit the desirable reactivity also lack significant toughening mechanisms, so the reduction in penetration and the increase in strain energy are counteracted by a lower toughness. In essence, a coating with no effective mitigation mechanism but reasonable toughness, like 7YSZ, could in some instances resist thermal cycling induced delamination better than an oxide more resistant to penetration but with a lower toughness. Balancing these attributes represents a grand challenge in TBC design. Penetration is generally not the critical issue in environmental barrier coatings (EBCs), which must be dense to perform effectively as barriers to the permeation of water vapor and, ideally, of oxygen. Consequently, EBCs are selected to minimize thermal expansion mismatch with the CMC substrate. This constraint limits the choice of materials, with rare earth silicates being favored in current systems. These silicates, however, are rapidly attacked by CMAS, especially by melts with higher Ca:Si ratios. While the recession of the EBC material is problematic in itself, the reaction with CMAS results in a layer of reaction products that is poorly matched thermally with the substrate. A source of substantial strain energy arises from this reaction layer, leading to the evolution of cracks that may delaminate the modified layer and/or the underlying EBC, but also penetrate into the bond coat and the CMC. This may expose the latter to environmental degradation of the fibers and the fiber/matrix interfaces that enable damage tolerance. The robustness of the system thus depends not only on the chemical reactivity of the CMAS/coating system but also on the toughness of the different layers, which are generally low. The grand challenge in EBCs is to approach prime reliance because CMCs are arguably less environmentally robust than current superalloys. At a minimum, this demands low reactivity with a relevant spectrum of CMAS compositions, and sufficient toughness to mitigate impact and/or thermo-mechanical damage. This presentation will discuss the state of understanding of these challenges and the tools available to assess the response of the system and effectiveness of the CMAS mitigation approach against a spectrum of melt compositions. The insight is complemented by the presentation of Prof. Poerschke at this conference. Acknowledgments: Presentation based on research contributions by R.W. Jackson, C.S. Holgate, K.M. Wessels, E.M. Zaleski, N. Abdul-Jabbar, B. Lutz, D. Park, J.S. Van Sluytman, M.R. Begley, and F.W. Zok, as well as collaborations with QuesTek Innovations, Pratt & Whitney, Siemens and Honeywell Aerospace. Work sponsored by the Office of Naval Research under awards N00014-08-1-0625, -12-M-0340 and -16-1-2702, as well as by the Pratt & Whitney Center of Excellence in Composites and the Honeywell-UCSB Alliance for Thermal Barrier Coatings

Adhesion of Individual Attachment Setae of the Spider Cupiennius salei to Substrates With Different Roughness and Surface Energy

Dynamic adhesion is a key ability for animals to climb smooth surfaces. Spiders evolved, convergent to geckos, a dry adhesive system made of setae branching into smaller microtrichia ending as spatulae. Several previous studies concentrated either on the whole adhesive claw tuft on the spider´s foot that consists of attachment setae or on the single adhesive contact elements, the microtrichia with spatula-shaped tips. Here, the adhesion of single setae of the spider Cupiennius salei was examined and the morphology of the pretarsus and the fine structure of the setae were studied in further detail. Using individual setae fixed to force sensing cantilevers, their adhesion at different contact angles with a glass substrate was measured as well as their adhesive performance on substrates with different roughness and on smooth surfaces with different surface energies. The results show an individual variability of the adhesive forces corresponding to the seta morphology and especially to the seta tip shape. The tip shapes of the setae vary largely even in neighboring setae of the pretarsal claw tuft that comprises approximately 2,400 setae. Regarding surface energy of the substrate, the adhesion force on hydrophobic polytetrafluoroethylene was 30% of that on a hydrophilic glass substrate, which points to the importance of both van der Waals interactions and hydrogen bonds in spider adhesion

Auswirkungen des DRG-Systems auf die Behandlung in einer Neurologischen Akutklinik

In der vorliegenden Arbeit werden die Auswirkungen der Etablierung des DRG-Systems am Beispiel der Neurologischen Akutklinik Bad Zwesten, einer homogenen 40-Betten-Abteilung innerhalb eines Neurologischen Zentrums mit allen Phasen der neurologischen Behandlung, untersucht. Dazu werden Patientenkollektive vor und nach Einführung des DRG-Systems herangezogen. Verglichen werden die stationär behandelten Patienten der NAK des jeweils ersten Halbjahres 1996 (n = 463) und 2008 (n = 910). Als wesentliche Ergebnisse sind die Veränderungen bezüglich häufigster Hauptdiagnosen, Verweildauer und, in einem hypothetischen Vergleich, der Behandlungserlöse zu sehen