Infiltration of fibrous preforms by a pure metal: Part V. Influence of preform compressibility

Infiltration by a pure matrix in the presence of preform deformation and partial matrix solidification is analyzed using a bounding approach for the preform rheology where solid metal is present. It is found, using parameters for the infiltration of short alumina fiber preforms by aluminum, that the two bounds are close in comparison to other factors of uncertainty in the prediction of infiltration rate. Using this approach, preform compression is shown to exert a significant influence on the infiltration rate for the system explored; in particular, the analysis shows the existence of an optimal value of applied pressure. Simplifications in the analysis are also presented, which yield fairly accurate results while easing their computation significantly.     

The effects of environmental conditions on the in vitro activity of selected antimicrobial agents against Escherichia coli

Serotonin (5-hydroxytryptamine, 5-HT) may play an important role in the pathogenesis of schizophrenia. Previous studies suggested that the efficacy of atypical neuroleptic drugs (e.g., risperidone and clozapine) on negative symptoms may be related to the 5-HT2a receptor. Although association studies between MspI polymorphism (T102C) and the 5-HT2a receptor gene and schizophrenia have been reported, their results are still controversial. The aim of this study was to examine the association between T102C polymorphism of the 5-HT2a receptor gene and schizophrenia as well as the association between the polymorphism and negative symptoms in a Japanese population (106 patients with schizophrenia and 109 healthy controls). No significant positive associations were observed. Our results suggest that the 5-HT2a receptor gene is not involved in the pathogenesis of schizophrenia or negative symptoms.     

Reactive infiltration processing of aluminum-nickel intermetallic compounds

Aligned nickel wire bundles 4 to 5 cm in length and up to 2.5 cm in diameter are infiltrated by pure aluminum using gas-assisted infiltration, to produce samples having global compositions in the range of 40 to 76 at. pct nickel. As-reacted sample macrostructures feature a large single-phase region of NiAl independent of applied pressure and nickel preform volume fractions in the ranges of 0.15 to 0.3 MPa and 0.23 to 0.44, respectively. These macrostructures also contain, in some cases, either an aluminum-rich zone on top, or nickel-rich phases at the bottom of the sample, depending on the global stoichiometry of the material. Two high-speed digital cameras are used to record the infiltration and reaction processes. The acquired images show that infiltration and reaction are decoupled in time. Infiltration proceeds initially under partial preform saturation, at a rate on the order of 50 cm·s⁻¹. The sample then self-heats for 2 to 3 seconds due to exothermic reaction between aluminum and nickel. Thereafter, a spontaneous combustion front ignites due to local melting of nickel and propagates at an average rate on the order of 5 cm·s⁻¹. Macrostructures and process kinetics are explained by the combined influences of capillarity during infiltration, heat evolved during the reaction, and gravity.     

Feasibility study of AC- and DC-side active filters for HVDCconverter terminals

The authors evaluate the technical and economic feasibility for active filtering of DC-side voltage harmonics and the AC-side current harmonics produced by a HVDC (high voltage direct current) converter. The following designs for the active filter concepts are compared with the existing AC-side and DC-side passive filters used at the Dickinson terminal of the CU HVDC transmission line project: the DC-side active filter consisting of a capacitor coupled current injection source to neutralize the 12th, 24th, and the 36th harmonics actively and the AC-side active filter designed to provide the same fundamental frequency-reactive VARs as the existing passive filters. Controlled currents are injected to filter the 11th and the 13th harmonic current actively. A cost comparison is made between these active filter designs and the cost of the existing passive filter supplied by the United Power Association     

Is semen quality related to the year of birth among Danish infertility clients?

BACKGROUND: There is circumstantial evidence that human sperm count may have declined during past decades. The purpose of this study was to identify the association between semen quality and year of birth. METHODS: The study comprised 8608 men consulting four Danish medical centres from 1968 to 1992 because of infertility. Data on semen quality and urogenital disorders were obtained from medical records while lifestyle data were collected from a subset of the population by a postal questionnaire (response 80%). Semen characteristics were analysed as a linear function of year of birth, centre, season and calendar year at time of semen examination, sexual abstinence and lifestyle factors. Effects of age were accounted for by restriction and stratified analysis. RESULTS: The sperm count declined with increasing year of birth at two of the four centres, but this association disappeared when confounders were adjusted for. Within the subset of men born 1950-1970 we revealed a decrease in the average sperm count by 1.9 mill/ml (95% confidence interval [CI]: 1.45, 2.27) per one advancing year of birth. This finding was consistent across centres even after adjustment for effects of covariates. The proportion of morphologically normal sperm cells changed in parallel with the sperm count, while semen volume did not decline in any time periods. CONCLUSIONS: We found a birth cohort effect on sperm count and morphology among Danish infertile men born after 1950 but not in men born in the first part of the century. The findings are compatible with an environmental impact during prenatal life but the evidence is far from unequivocal.     

Hot dry rock: a new geothermal energy source

A project being conducted by the Los Alamos Scientific Laboratory is attempting to demonstrate the technical and economic feasibility of extracting energy from the hot, dry rock geothermal resource. The system being tested is composed of two deep boreholes drilled into hot, impermeable rock and connected by a hydraulically produced fracture. In September 1977, the circulation loop was closed for the first time and water was circulated through the downhole reservoir and through a pair of 10-MW (thermal) heat exchangers. A series of long-term experiments is planned for 1978 in order to evaluate the thermal, chemical and mechanical properties of the energy extraction system.     

Prognostic values of echocardiography compared with clinical variables in suspected heart disease. Multivariate analysis of long-term prognosprognosis in 456 patients

The aim of the study was to evaluate the prognostic significance of clinical and echocardiographic data in patients referred for echocardiography in a retrospective analysis. Four hundred and fifty-six patients from a district hospital were studied. Survival after three years was 64%. Multivariate analysis identified five factors with independent prognostic information (relative risks of death are shown in brackets): left ventricular wall motion index (WMI) < or = 1.2 by echocardiography (2.5), status as in-patient (2.1), age > 65 years (1.7), clinical heart failure (1.9) and atrial fibrillation (1.5). When information on age, hospitalisation status, heart failure and heart rhythm had already been entered in the Cox model, echocardiographic results such as decreased WMI and dilated right ventricle still gave further prognostic information. We conclude that among conventional clinical and echocardiographic data WMI was the strongest predictor of long-term survival, and, despite prior knowledge of major clinical features, echocardiography provided further prognostic information.     

Comparison of diarrhea induced by ingestion of fructooligosaccharide Idolax and disaccharide lactulose: role of osmolarity versus fermentation of malabsorbed carbohydrate

Whether carbohydrate malabsorption causes diarrhea probably depends on the balance between the osmotic force of the carbohydrate and the compensatory capacity of the colon to dispose of the carbohydrate by bacterial fermentation. The present study evaluated the specific role of the osmolarity by comparing the severity of diarrhea after ingestion of two nonabsorbable carbohydrates, the fructooligosaccharide Idolax and the disaccharide lactulose. Both carbohydrates are readily fermented by the colonic flora but differ in osmolarity, the osmotic force being twice as high for lactulose as for Idolax. Twelve subjects were given increasing doses (0, 20, 40, 80, 160 g/d) of Idolax and lactulose in a crossover design. Every dose level was administered for three days with intervals of one week. Stools were collected on the third day to determine 24-hr volume, concentrations of short-chain fatty acids, L- and D-lactate, residues of Idolax or lactulose, sodium, potassium, pH, osmolarity, and in vitro productions of organic acids. Measured by short-chain fatty acid and lactate formation in a fecal incubation system, the fermentation of Idolax and lactulose was identical and very rapid compared with a range of reference carbohydrates. A laxative effect of both Idolax and lactulose was demonstrated. The increment in fecal volume as a function of the dose administered was twice as high for lactulose (slope of the regression line = 7.3, r = 0.64, P< 10(-5)) as for Idolax (slope = 3.7, r = 0.51, P<10(-3)), i.e., isosmolar doses of lactulose and Idolax had the same effect on fecal volume. The variation in fecal volume was substantial (lactulose 80 g/day: 110-1360 g/day; Idolax 160 g/day: 130-1440 g/day). High responders had earlier and larger fecal excretions of the saccharide compared with low-responders. Fecal volume in carbohydrate-induced diarrhea is proportional to the osmotic force of the malabsorbed saccharide, even though all or the majority of the saccharide is degraded by colonic bacteria. The capacity to modify the diarrhea varies considerably from person to person and is associated with colonic saccharide disposal, whereas the variation in response to isosmolar amounts of different saccharides is small within the same individual.     

Infiltration of fiber preforms by an

Preforms of 20 vol pct SAFFIL alumina fibers are infiltrated with Al-4.4 wt pct Cu-0.3 wt pct Mg using a horizontal die casting machine. Fiber preform temperature is varied from 973 to 673 K. Solute distribution, fiber volume fraction, and matrix microstructure are characterized using optical metallography and electron microprobe analysis. Increases in fiber volume fraction are observed in the composites downstream of the infiltration path. We propose that these result from locking of the compressed fibers by solid metal present during infiltration. With this as- sumption, we find good agreement between theory presented in Parts I [1] and II [2] for solute concentration, fiber volume fraction distributions, as well as matrix microstructure and exper- iments. With an initial preform temperature of 673 K, freckles are found in the composite, which are interpreted to result from the combined effects of pressure and significant enrichment in solute at the infiltration front.