Thermal properties and thermal shock resistance of γ-Y 2Si2O7

Thermal properties, namely, Debye temperature, thermal expansion coefficient, heat capacity, and thermal conductivity of γ-Y 2Si2O7, a high-temperature polymorph of yttrium disilicate, were investigated. The anisotropic thermal expansions of γ-Y2Si2O7 powders were examined using high-temperature X-ray diffractometer from 300 to 1373 K and the volumetric thermal expansion coefficient is (6.68±0.35) × 10-6 K-1. The linear thermal expansion coefficient of polycrystalline γ-Y2Si2O7 determined by push-rod dilatometer is (3.90±0.4) × 10-6 K-1, being very close to that of silicon nitride and silicon carbide. Besides, γ-Y2Si2O7 displays a low-thermal conductivity, with a κ value measured below 3.0 W·(m·K) -1 at the temperatures above 600 K. The calculated minimum thermal conductivity, κmin, was 1.35 W·(m·K) -1. The unique combination of low thermal expansion coefficient and low-thermal conductivity of γ-Y2Si2O7 renders it a very competitive candidate material for high temperature structural components and environmental/thermal-barrier coatings. The thermal shock resistance of γ-Y2Si2O7 was estimated by quenching dense materials in water from various temperatures and the critical temperature difference, ΔTc, was determined to be 300 K.

Hot corrosion of γ-Y2Si2O7 in strongly basic Na2CO3 molten salt environment

γ-Y2Si2O7 is a promising candidate both for high temperature structural applications and as thermal barrier coatings due to its unique combination of properties, such as high melting point, good machinability, high thermal stability, low linear thermal expansion coefficient (3.9 × 10-6 K-1, 25-1400 °C) and low thermal conductivity (<3 W/m K above 300 °C). In this work, the hot corrosion behavior of γ-Y2Si2O7 in strongly basic Na2CO3 molten salt at 850-1000 °C for 20 h in flowing air was investigated. In the employed conditions, multi-layer corrosion scales with total thickness less than 90 μm were formed. At 850-900 °C, the outmost layer of the scale was composed of the reprecipitation of Y2O3, the bottom of a Si-rich Na2O·xSiO2 (x > 3.65) melt layer, and the middle of a NaYSiO4 layer. At 1000 °C, the corrosion products turned out to be a mixture of NaY9Si6O26 and Si-rich Na2O·xSiO2 (x > 3.65). In all cases, a thin layer of protective SiO2 formed under the Na2O·xSiO2 melt and protected the bulk material from further corrosion.

Water balance modelling in a tropical watershed under deciduous forest (Mule Hole, India): Regolith matric storage buffers the groundwater recharge process

Accurate estimations of water balance are needed in semi-arid and sub-humid tropical regions, where water resources are scarce compared to water demand. Evapotranspiration plays a major role in this context, and the difficulty to quantify it precisely leads to major uncertainties in the groundwater recharge assessment, especially in forested catchments. In this paper, we propose to assess the importance of deep unsaturated regolith and water uptake by deep tree roots on the groundwater recharge process by using a lumped conceptual model (COMFORT). The model is calibrated using a 5 year hydrological monitoring of an experimental watershed under dry deciduous forest in South India (Mule Hole watershed). The model was able to simulate the stream discharge as well as the contrasted behaviour of groundwater table along the hillslope. Water balance simulated for a 32 year climatic time series displayed a large year-to-year variability, with alternance of dry and wet phases with a time period of approximately 14 years. On an average, input by the rainfall was 1090 mm year(-1) and the evapotranspiration was about 900 mm year(-1) out of which 100 mm year(-1) was uptake from the deep saprolite horizons. The stream flow was 100 mm year(-1) while the groundwater underflow was 80 mm year(-1). The simulation results suggest that (i) deciduous trees can uptake a significant amount of water from the deep regolith, (ii) this uptake, combined with the spatial variability of regolith depth, can account for the variable lag time between drainage events and groundwater rise observed for the different piezometers and (iii) water table response to recharge is buffered due to the long vertical travel time through the deep vadose zone, which constitutes a major water reservoir. This study stresses the importance of long term observations for the understanding of hydrological processes in tropical forested ecosystems. (C) 2009 Elsevier B.V. All rights reserved.

Charge-order-driven multiferroic properties of Y1-xCaxMnO3

Dielectric measurements on the charge-ordered insulators, Y1-xCaxMnO3 (x = 0.4. 0.45 and 0.5), show maxima in the dielectric constant around the charge ordering transition temperature while magnetic measurements show the presence of weak ferromagnetic interactions at low temperatures. Besides the magnetic field dependence of the dielectric constant, these manganites also exhibit second harmonic generation. Thus, the charge-ordered Y1-xCaxMnO3 compositions are multiferroic and magnetoelectric, in accordance with theoretical predictions. Magnetoelectric properties are retained in small particles of Y0.5Ca0.5MnO3. (C) 2008 Elsevier Ltd. All rights reserved.

Cup products for groups and commutators

We give it description, modulo torsion, of the cup product on the first cohomology group in terms of the descriptions of the second homology group due to Hopf and Miller.

Women's health and a framework convention on global health

This paper considers the role for a Framework Convention on Global Health in addressing key challenges in women’s health at a global level. Part I analyses the conceptualization of health in terms of human rights and the linking of women’s rights and human rights. Part II seeks to identify pressing issues for women’s health, articulating 10 key challenges for women’s health. Part III considers the proposal for a Framework Convention on Global Health to meet global health needs. Finally, Part IV asks whether international law can provide a valuable platform to support recognition and achievement of women’s health rights and identifies key elements for supporting and promoting women’s health.

Prognostic tumour markers in pancreatic cancer

Background. Pancreatic cancer is one of the major causes of cancer death in the industrialised world. The overall survival of patients with ductal pancreatic adenocarcinoma is poor: 5-year survival is only 0.2 to 4%. Tumour stage and histological grade are used as prognostic markers in pancreatic cancer. However, there are differences in survival within stages and histological grades. New, additional and more accurate prognostic tools are needed. Aims. The purpose of this study was to investigate whether the tissue expression of potential and promising tumour markers p27, tenascin C, syndecan-1, COX-2 and MMP-2 are associated with clinicopathological parameters in pancreatic cancer. The expression of p27, tenascin C and syndecan-1 was also evaluated in acute and chronic pancreatitis. The main purpose in the study was to find new prognostic markers for pancreatic adenocarcinoma. Patients. The study included 147 patients with histologically verified pancreatic adenocarcinoma treated at Helsinki University Central Hospital from 1974 to1998. Methods. The expression of tumour marker antigens was demonstrated by immunohistochemistry using monoclonal antibodies against p27, syndecan-1, tenascin C, COX-2 and MMP-2. The results were compared with clinicopathological variables, i.e. age, sex, TNM stage and histological grade. Survival analyses were performed with univariate Kaplan-Meier life-tables and the log-rank test, while multivariate analyses were performed using Cox regression. Results. Pancreatic adenocarcinomas expressed p27, syndecan-1, tenascin C, COX-2 and MMP-2 in 30, 94, 92, 36 and 50% of the samples, respectively. Loss of p27 expression was associated with poor prognosis in stage I and II pancreatic cancer. Stromal syndecan-1 expression was an independent prognostic marker in pancreatic cancer, whereas epithelial syndecan-1 expression predicted better prognosis only in stage I and II disease. Tenascin C expression did not correlate with survival but was associated with differentiation. COX-2 expression was associated with poor outcome and was an independent prognostic factor. Epithelial MMP-2 correlated with poor prognosis in pancreatic cancer. Conclusion: p27 and epithelial syndecan-1 are prognostic markers in early (stage I and II) pancreatic cancer. Stromal syndecan-1, COX-2 and epithelial MMP-2 are prognostic factors in ductal pancreatic adenocarcinoma.

Thermal properties of MOSi2 with minor aluminum substitutions

Mo(Si1-xAlx)(2) compositions (x = 0-0.1) have been prepared by a modified SHS route under uniaxial hydrostatic pressure. Oxidation studies carried out by thermal analysis and sheet resistivity indicate an improvement in the low temperature (700-900 K) oxidation resistance with increasing aluminum addition. Dilatometric results show a decrease in the a value up to x = 0.05 substitution. With the aluminum substitution, both thermal expansion coefficient and thermal conductivity show decrease in their values except in the biphasic region. The x = 0.05 composition containing both C11(b) and C40 phases is a promising material for high temperature thermal barrier coating as it shows higher oxidation resistance and a similar K/alpha value as compared to pure MoSi, (c) 2006 Elsevier Ltd. All rights reserved.