Semi-solid rapid compression testing of spray-formed hypereutectic Al-Si alloys

The rheology of Al-30Si-5Cu and Al-30Si-5Cu-2Mg spray-formed alloys has been characterized after holding at various times and temperatures, using semisolid rapid compression to obtain load-displacement curves. Microstructures were examined after partial remelting and compression in an attempt to understand the flow behavior. The initial resistance to flow generally increased with holding time at temperature. This increase was attributed to the increased strength of a three-dimensional (3-D) solid silicon network present in these alloys in the semisolid state, with the initial resistance to flow smaller in the magnesium-containing alloys. With increased temperature, the initial resistance decreased due to increased liquid content and grain spheroidization. The viscosity vs shear rate response was studied using the approach of Laxmanan and Flemings. The materials shear thinned rapidly during the test conditions, in which the shear rate rapidly increased from approximately 2.5 to 92 s⁻¹. The results were fitted to a power-law model, and the viscosities showed a drop of approximately two to four orders of magnitude when extrapolated to a shear rate of 1000 s⁻¹ (a typical value in actual component manufacture). The rapid compression test, which is close to conditions present in component manufacture, was shown to have more in common with a shear rate jump experiment, rather than steady-state viscometry.     

World’s largest dry gas seal marks five-year milestone

This case study covers what is believed to be the world’s largest dry-running, non-contacting gas seal, manufactured by John Crane. Recently returned for routine maintenance, it has reached its five-year anniversary while remaining in excellent condition.     

Retrospective analysis of operative ankle fractures

A seroprevalence survey to recently proposed adenovirus (AV) serotypes AV 48 and AV 49, isolated primarily from AIDS patients, was conducted among the San Francisco Men's Health Study cohort. This cohort of homosexual, heterosexual, or bisexual HIV-seronegative and -seropositive men from selected San Francisco census tracts has been studied since 1984. The presence or absence of type-specific antibody in 628 serum specimens from 1989 was determined by microneutralization. Thirty of these subjects (26 positive and four negative) were studied longitudinally. Serum specimens taken at 6-month intervals from 1984 to 1993 were tested to characterize antibody response and to document the advent of these new serotypes. Eight subjects were tested against five other AV serotypes for comparison. AV 48 and AV 49 seroprevalence rates were significantly higher in HIV-seropositives, but infection was not limited to the immunocompromised. Sexual preference was not a significant determinant for AV seroprevalence in HIV-seronegatives. However, the extent and duration of the neutralizing antibody response was strikingly different between homosexuals and heterosexuals: an endemic pattern of continuous reexposure over the 9-year period was seen in 90% of 19 homosexuals, while five of six heterosexuals (83%) had an episodic pattern of exposure with antibody decline to undetectable levels. These data suggest that these viruses may be endemic in some part of the homosexual population and that sexual transmission may be the primary source of continuous reexposure.     

Prostate enlargement in mice due to fetal exposure to low doses of estradiol or diethylstilbestrol and opposite effects at high doses

On the basis of results of studies using high doses of estrogens, exposure to estrogen during fetal life is known to inhibit prostate development. However, it is recognized in endocrinology that low concentrations of a hormone can stimulate a tissue, while high concentrations can have the opposite effect. We report here that a 50% increase in free-serum estradiol in male mouse fetuses (released by a maternal Silastic estradiol implant) induced a 40% increase in the number of developing prostatic glands during fetal life; subsequently, in adulthood, the number of prostatic androgen receptors per cell was permanently increased by 2-fold, and the prostate was enlarged by 30% (due to hyperplasia) relative to untreated males. However, as the free serum estradiol concentration in male fetuses was increased from 2- to 8-fold, adult prostate weight decreased relative to males exposed to the 50% increase in estradiol. As a model for fetal exposure to man-made estrogens, pregnant mice were fed diethylstilbestrol (DES) from gestation days 11 to 17. Relative to controls, DES doses of 0.02, 0.2, and 2.0 ng per g of body weight per day increased adult prostate weight, whereas a 200-ng-per-g dose decreased adult prostate weight in male offspring. Our findings suggest that a small increase in estrogen may modulate the action of androgen in regulating prostate differentiation, resulting in a permanent increase in prostatic androgen receptors and prostate size. For both estradiol and DES, prostate weight first increased then decreased with dose, resulting in an inverted-U dose-response relationship.