Chemical-mechanical polishing of SiO2 thin films studied by X-ray reflectivity

Specular X-ray reflectivity from SiO₂ thin films prepared on silicon substrates by plasma-enhanced chemical vapor deposition showed the films to have a characteristic width of the decay in density at the free surface of 17 Å, to be about three-quarters the density of -quartz, and to have an interfacial layer at the silicon interface that was of the order of 100 Å wide and less dense than the bulk of the film. After chemical-mechanical polishing the characteristic width of the decay in density at the free surface was reduced to 10 Å; furthermore, the near-surface region to a depth of 30 Å had a greater density than the as-deposited film. Off-specular reflectivity confirmed that the decrease in characteristic width at the free surface was due to reduced roughness upon polishing and also revealed that the lateral correlation length in the limit of long wavelengths was the same for both polished and unpolished samples. The compression of the near-surface region during polishing is believed to enhance the dissolution of SiO₂ into the slurry which is necessary to achieve smooth surfaces.     

Synthesis of (R,S)-10-methyloctadecanoic acid (tuberculostearic acid) and key chiral 2-methyl branched intermediates

Tuberculostearic acid, (R)-10-methyloctadecanoic acid, is a characteristic component of pathogenic mycobacteria and related organisms. Sensitive detection of this acid in infected material allows rapid detection of mycobacterial disease. A novel, convergent synthesis of tuberculostearic acid and key chiral intermediates is described in this communication, to provide a reference compound. Racemic and (R)- and (S)-1-iodo-2-methyldecanes were synthesised from 1-octanal and 1-carboethoxyethylidenetriphenylphosphorane as initial starting materials. 1-Hydroxyoct-7-yne was made from 1,6-hexanediol by two alternative methods and coupled with the above racemic iodide. Hydrogenation and oxidation of the resulting (R,S)-10-methyloctadec-7-yn-1-ol gave racemic tuberculostearic acid.     

The effect of substitution of Mn or Al on the hydrogen sorption characteristics of CeNi5

The hydrides of the ternary alloys of CeNi_5?xM_x (M = Mn or Al and x = 0.5 and 0.75) have been prepared and investigated. The absorption plateau pressure of the system CeNi₅—H is reduced 8- to 75-fold, by the replacement of Ni by Mn (or Al), without significantly impairing its hydrogen capacity. This substitution has great influence in reducing the hysteresis effect associated with the hydrogen absorption and desorption. The hysteresis and plateau-sloping factors are very low compared with that in Mischmetal-Ni₅ hydride. The enthalpies and entropies of hydrogenation and dehydrogenation for CeNi_5?xM_x are computed and found to be in the range 20–25 kJ(mole H₂)^?1) and ～90–100 J(K mole H₂)^?1, respectively. The high effective entropies of the hydride (high configurational entropy of H in the lattice) are attributed to extensive hydrogen disorder in the interstitial sites of the CeNi_5?xM_x lattice. Desorption of the hydrogen in the two-phase region (α + β) for CeNi_4.25Mn_0.75-H follows first-order kinetics with an activation energy of ～33 ± 1 kJ(mole)^?1. The favorable physiochemical properties of CeNi_5?xMn_x-H system make it very attractive for applications.     

A geriatric and gerontologic perspective on the effects of medical conditions on older drivers: discussion of Waller.

In discussing Waller's paper, we build on his review of medical conditions and the risk of motor vehicle accidents (MVAs) using principles derived from geriatrics, gerontology, and health services research. Three approaches are suggested. The medical model uses discrete diseases as risk factors, but despite its utility and appeal, this model does not sufficiently characterize health and functional status to be the sole approach, and future investigative efforts should at least consider severity of illness concepts. The functional status model emphasizes a functional and physiological approach to health status, but despite its successful application in geriatric assessment and its investigative promise, functional status can be difficult to measure and has not been validated in relation to MVA risk. Finally we consider a behavioral model and within that framework discuss the relation of depressive and other emotional illnesses as well as social vitality to driving patterns and MVA occurrence.     

Scales of geography, time, and population: the study of violence as a public health problem

OBJECTIVES: In this study, data on violent deaths in the Bronx, New York City, from the 1970, 1980, and 1990 censuses were analyzed. METHODS: The incidence and areal density of intentional deaths were mapped by health area. Simple and stepwise regressions between violent death measures and other factors were performed. RESULTS: The incidence of deaths at levels of those in the highest 1970 quintile spread so that by 1990 only 2 areas saw incidences at levels of the lowest 1970 quintile. Overcrowding, socioeconomic status, population, population change, and drug deaths in simple regressions and overcrowding, socioeconomic status, and low-weight births in stepwise regressions correlated significantly with violent death incidence or density. CONCLUSIONS: Understanding the spatiotemporal development of violence can contribute to public policy on violence.     

A brief review of the ionic conductivity enhancement for selected oxide electrolytes

The advantages of lowering the operation temperature of SOFCs have attracted great interest worldwide. One of the major barriers to decreasing the operation temperature is the ohmic loss of the electrolyte. Maximizing the electrolyte ionic conductivity is of significant importance, especially in the absence of new electrolyte materials. The ionic conductivity of electrolytes can be influenced by many parameters. There has been an enormous effort in the literature for the improvement of the electrolyte ionic conductivity. From a practical point of view, this paper reviews various approaches to enhancing the ionic conductivity of polycrystalline zirconia- and ceria-based oxide electrolytes in the light of composition, microstructure, and processing. Suggestions are given for future work.     

Successful weight loss in a self-taught, self-administered program

There is little evidence concerning the effectiveness of self-help materials for weight control. The purpose of this research was to evaluate a self-help weight-loss program. Obese (body fat > or = 25.0%, range = 25.0-48.6%, mean +/- SEM = 36.5 +/- 1.3%) men (n = 14) and women (n = 21) were given a workbook detailing a behavior modification approach to weight loss that emphasizes self-monitoring of diet and exercise behaviors, and then sent home for 6 months to learn how to lose weight on their own. A group of 9 controls (CONT) who did not get a workbook were used for comparison. ANOVA showed that the experimental group (EXP) lost 8.1 +/- 0.9 (mean +/- SEM) kg body weight, 6.4 +/- 0.8 kg fat, and 3.9 +/- 0.6% body fat; all significant over time (p < 0.001) and different from the CONT (p < 0.0001) who showed no change in these variables. The EXP also reduced their fat intake (% of joules) from 36.1 +/- 1.0% to 27.9 +/- 1.3% (p < 0.0001), increased their carbohydrate intake from 45.7 +/- 1.2% to 50.0 +/- 1.7% (p < 0.007) and their protein intake from 16.3 +/- 0.05% to 20.7 +/- 0.7% (0 < 0.03), all of which were significantly different (p < 0.03) than the CONT who did not change. Dietary fiber increased in the EXP from 19.8 +/- 1.4 to 27.3 +/- 2.2 g/d (p < 0.001) even with a significant reduction in energy intake (11.3 +/- 0.6 vs. 8.9 +/- 0.5 Mj/d; p < 0.0001).(ABSTRACT TRUNCATED AT 250 WORDS)     

Focus groups as a knowledge elicitation technique: an exploratorystudy

The authors examine whether one technique for group knowledge elicitation, focus groups, can provide different thoughts and judgments about a problem than individual interviews. The experimental situation was based on the resolution of an ill-structured problem by experienced subjects in a field setting. Videotaped scenarios were used to describe the situation for knowledge acquisition. Ten subjects were used, five for individual interviews and five for the focus groups. It was found that focus groups performed better in generating original responses than individual interviews and that focus groups were at least as good as individual interviews in terms of the quality and acceptability of ideas