Disorder in Pyrochlore Oxides

Contour plots of disorder reaction energies across a wide variety of A₂B₂O₇ pyrochlore oxides have been produced, using atomistic simulation calculations based on energy-minimization techniques. The cations studied range from Lu³⁺ to La³⁺ on the A site and from Ti⁴⁺ to Ce⁴⁺ on the B site. The present results relate the experimentally observed stability range of the pyrochlore structure to A and B cation size and disorder. Disorder enthalpies decrease dramatically with increasing B cation size, while the rate of increase with A cation size depends markedly on the particular B cation. The association of anion Frenkel and cation antisite disorders is found to be of importance.     

Dispersion Methods of Yttria in Silicon Nitride by Comminution

Sintering additives were incorporated into Si₃N₄ by attrition and ball milling using both Si₃N₄ and Al₂O₃ media. Dispersion of Y₂O₃ was observed by backscattered electron imaging. Attrition milling for only 15 min using an Si₃N₄ medium, was equivalent to 24 h of ball milling. Minimal contamination by the Si₃N₄ was encountered. [Key words: silicon nitride, yttria, comminution, sintering, dispersion.     

A piecewise parabolic C approximation technique for curved boundaries

The parabola, in parametric form, is discussed as a suitable approximation to curved boundaries. The four degrees of freedom are specified locally by Hermite interpolation. This piecewise curve approximation can then be thought of as a locally defined C′ spline. A geometric norm, i.e. one which is invariant under the axes change is constructed and the approximation technique is analysed in this norm. A selection of graphical studies of piecewise approximations to a variety of curves, using this method, is given.     

Colorectal Cancer and Nonfermented Milk,Solid Cheese,and Fermented Milk Consumption: A Systematic Review and Meta-Analysis of Prospective Studies

Colorectal cancer is the second most prevalent cancer worldwide. A systematic review and meta-analysis of prospective studies was conducted to examine the association between intake of different types of dairy foods during adulthood and the development of colorectal cancer, specifically comparing nonfermented milk, solid cheese, and fermented milk. Seven databases were systematically searched and 15 cohort studies selected for inclusion, involving over 900,000 subjects and over 5200 colorectal cancer cases. Meta-analysis resulted in an overall relative risk of colon cancer of 0.74 (95% confidence interval 0.60–0.91) in men consuming nonfermented milk (highest intake category averaging 525 g/day). No association was found between consumption of nonfermented milk and rectal cancer in men or nonfermented milk and colon or rectal cancer in women. No protective association was found between consumption of solid cheese or fermented milk and colorectal cancer. Reasons for the differences in the impact of nonfermented milk, solid cheese, and fermented milk in the colon are discussed. This meta-analysis supports the inverse association between nonfermented milk consumption and risk of colon cancer in men, and provides an evidence base to assist in the formulation of dietary guidelines involving dairy foods.     

Smokers' attitudes and behaviors related to consumer demand for cessation counseling in the medical care setting.

This study describes a new segmentation strategy exploring smokers' interest levels in counseling in the medical care setting in order to understand how public health communications can be designed to increase consumer demand for cessation services within this population. A subsample of 431 smokers from a large, nationally representative mail survey was analyzed and categorized into three cessation-demand groups: Low demand (LD), medium demand (MD), and high demand (HD). HD smokers were most likely to be heavy smokers, to make quitting a high priority, and to have self-efficacy in quitting. MD and LD smokers were less likely than HD smokers to have been told to quit smoking by a health care provider in the past or to believe that counseling is effective. The first step in the regression analysis revealed that age, cigarettes smoked per month, whether smokers were currently trying to quit, and whether they were ever told to quit smoking by their health care provider accounted for 21% of the variance in smokers' interest in smoking cessation counseling, F(4, 234) = 16.49, p<.001. When additional variables on attitudes toward smoking and quitting and perceived effectiveness of receiving counseling in the medical care setting were added to the model, an additional 11% of the variance in smokers' interest in cessation counseling was explained, F(12, 234) = 10.07, p<.001. Results suggest that by categorizing smokers by interest level in cessation counseling, we emerge with three distinct portraits of smokers who might be activated in different ways to increase consumer demand for cessation counseling.     

Multi-scale coupling between two dynamical models for PEMFC aging prediction

In this paper, an approach allowing connecting two numerical models for the simulation of the PEMFC operation and durability at different physical scales is presented. After explaining the interest of coupling them to study the interactions between the fuel cell system and the fuel cell itself, along with lifetime concerns, the feasibility of the task is assessed. Then the numerical approach to achieve this coupling is presented. Finally the response of the coupled models is examined to check its validity, and first results are presented. Predicted fuel cell lifetime trends when changing the stack operation conditions are shown, which highlight the presence of optima concerning temperature, demanded current, pressure and O₂ stoichiometry. Two operation modes are then compared in terms of their impact on the fuel cell performance decay, showing that power cycles are more damaging the fuel cell than nominal operation.     

Envelope-constrained filters with uncertain input

In an envelope-constrained filtering problem with uncertain input the set of possible input waveforms and the set of permissible output waveforms are each defined by envelope constraints (time domain inequalities). The object is to find the optimal (minimal norm) inpulse response for which every waveform in the input envelope evokes a response in the output envelope. The problem is solved by extending earlier results for a single specified input. The solution is further extended to allow for unknown-but-bounded errors in the filter realization.Research supported by the CSIRO and the Australian Research Grants Committee.Part of this work was carried out while the first author was at the Control and Management Systems Division of Cambridge University, UK.     

A Low-Noise Low Input Impedance Amplifier for Magnetic Measurements of Nerve Action Currents

We have developed a low-noise solid-state current-to-voltage amplifier to measure the magnetic fields produced by nerve action currents. The amplifier senses the EMF induced in a toroidal, ferrite-core pickup coil surrounding the nerve by the circumferential magnetic field associated with the axial nerve action currents which propagate past the toroid. In order to obtain low input voltage noise, the input stage of the amplifier consists of 20 preamplifiers in parallel, each containing a discrete bipolar transistor pair. The complete amplifier has an input impedance of 1.33 ?and a minimum noise figure of 15 dB at 100 Hz for a source resistance of 50 ?. The amplifier has sufficient sensitivity to detect the magnetic field of the action potential propagating along a single giant axon.     

On singular stochastic control problems for diffusion with jumps

We consider some cases of control problems for diffusion processes with jumps when the payoff functional does not depend explicitly on the control. We prove the continuity of the optimal cost with a quasi-variational inequality interpreting the problems as the limit of an impulse control problem when the cost of impulse tends to zero. Moreover, we show the existence of an optimal control for some particular situations.     

Effect of hydrocarbon addition on tip opening of hydrogen-air bunsen flames

The effect of hydrocarbon addition on tip opening of lean and stoichiometric hydrogen-air flames is studied computationally by performing two-dimensional numerical simulations. The numerical study reveals that the flame tip of the H₂-air burner stabilized flame is open at lean and stoichiometric mixture conditions. The flame tip closes upon hydrocarbon addition. The tip closing is mainly affected by preferential diffusion of the multi-component mixture and the stretch effects. In the addition of light hydrocarbon (CH₄), the tip closing starts at a higher percentage of hydrocarbon addition in H₂-air flames. Whereas, upon the addition of heavy hydrocarbons such as propane and butane in H₂-air flames, tip closing starts with a lesser amount of hydrocarbon addition. Temperature, OH mole fraction and heat release rate have been investigated, focusing on the flame structure at the tip. The tip opening regime diagram for H₂–CH₄-air, H₂–C₃H₈-air and H₂–C₄H₁₀-air mixtures are presented.