Internally coated air-cooled gas turbine blading

Ten candidate modified nickel-aluminide coatings were developed using the slip pack process. These coatings contain additives such as silicon, chromium and columbium in a nickel-aluminum coating matrix with directionally solidified MAR-M200 + Hf as the substrate alloy. Following a series of screening tests which included strain tolerance, dynamic oxidation and hot corrosion testing, the Ni-19A1-1Cb (nominal composition) coating was selected for application to the internal passages of four first-stage turbine blades. Process development results indicate that a dry pack process is suitable for internal coating application resulting in 18 percent or less reduction in air flow. Coating uniformity, based on coated air-cooled blades, was within + or - 20 percent. Test results show that the presence of additives (silicon, chromium or columbium) appeared to improve significantly the ductility of the NiA1 matrix. However, the environmental resistance of these modified nickel-aluminides were generally inferior to the simple aluminides

Accretion Disk Temperatures of QSOs: Constraints from the Emission Lines

QSO emission-line spectra are compared to predictions based on theoretical ionizing continua of accretion disks. Observed line intensities do not show the expected trend of higher ionization with higher accretion disk temperature as derived from the black hole mass and accretion rate. This suggests that, at least for accretion rates close to the Eddington limit, the inner disk does not reach temperatures as high as expected from standard disk theory. Modified radial temperature profiles, taking account of winds or advection in the inner disk, achieve better agreement with observation. This conclusion agrees with an earlier study of QSO continuum colors as a function of disk temperature. The emission lines of radio-detected and radio-undetected sources show different trends as a function of disk temperature.Comment: 9 pages, 8 figures, submitted to Ap

Ray-optical negative refraction and pseudoscopic imaging with Dove-prism arrays

A sheet consisting of an array of small, aligned Dove prisms can locally (on the scale of the width of the prisms) invert one component of the ray direction. A sandwich of two such Dove-prism sheets that inverts both transverse components of the ray direction is a ray-optical approximation to the interface between two media with refractive indices +n and –n. We demonstrate the simulated imaging properties of such a Dove-prism-sheet sandwich, including a demonstration of pseudoscopic imaging

The treatment of zero eigenvalues of the matrix governing the equations of motion in many-body Green's function theory

The spectral theorem of many-body Green's function theory relates thermodynamic correlations to Green's functions. More often than not, the matrix governing the equations of motion has zero eigenvalues. In this case, the standard text-book approach requires both commutator and anti-commutator Green's functions to obtain equations for that part of the correlation which does not lie in the null space of the matrix. In this paper, we show that this procedure fails if the projector onto the null space is dependent on the momentum vector. We propose an alternative formulation of the theory in terms of the non-null space alone and we show that a solution is possible if one can find a momentum-independent projector onto some subspace of the non-null space. To do this, we enlist the aid of the singular value decomposition (SVD) of the equation of motion matrix in order to project out the null space, thus reducing the size of the matrix and eliminating the need for the anti-commutator Green's function. We extend our previous work, dealing with a ferromagnetic Heisenberg monolayer and a momentum-independent projector onto the null space, where both multilayer films and a momentum-dependent projector are considered. We develop the numerical methods capable of handling these cases and offer a computational algorithmus that should be applicable to any similar problem arising in Green's function theory.Comment: 16 pages, 7 figure

HIV / AIDS prevalence testing - merits, methodology and outcomes of a survey conducted at a large mining organisation in South Africa

Objectives: To determine the HIV prevalence rate at Anglo Platinum, a large, multinational organisation operating in South Africa (Gauteng, Limpopo and North-West), and to assess the merits, methodology and outcomes of the survey. Methods: A sample of 11 339 individuals, representing 18.4% of the organisation's employees, were tested for HIV. HIV prevalence was determined using the Wellcozyme HIV 1+2 GACELISA test (oral fluid assay), and variables such as age, site, grade and gender were analysed. Results: The overall prevalence rate was 24.6% (95% confidence interval (CI): 20.4 - 28.8), translating into approximately 15 167 HIV-infected individuals. Interestingly, there was considerable variation in prevalence between sites within the same geographical regions, highlighting the limitations of using data obtained from antenatal HIV surveillance surveys. As an example, the prevalence at sites in Limpopo province ranged from 9.8% to 19%, with the same basic demographic data in terms of race, age and gender. Conclusions: The survey data enabled the organisation to plan resource allocation appropriately for each business unit following their commitment to the treatment of infected employees with antiretroviral therapy. These baseline prevalence data also provide an opportunity for monitoring of proposed interventions using cross-sectional surveys at designated intervals in the future. South African Medical Journal Vol. 96(2) 2006: 134-13

Do Beliefs about Knowledge Predict Occupational Therapy Students’ Critical Thinking? A Longitudinal Correlational Study

Beliefs about knowledge and knowing, or epistemic and ontological cognition (EOC), are potential influences on critical thinking, yet little research exploring these relationships has been published in educational literature or in occupational therapy (OT). This study examined the association between domain-general and OT-specific EOC and critical thinking in OT students. The Epistemological Beliefs Inventory, modified Four-Quadrant Scale, and Watson-Glaser Critical Thinking Appraisal were administered to a convenience sample of 102 OT students, before and after the didactic portion of an OT program. Results of logistic regression indicated that only the general belief in an omniscient authority as a source of knowledge was a statistically significant predictor of critical thinking, both before and after the didactic portion of the program. These findings partially support the hypothesis that EOC and critical thinking are related. Domain-general EOC and OT-specific ontological cognition also became more sophisticated over time, but OT-specific epistemic cognition and critical thinking did not change significantly