Search for Dislocation Free Helium 4 Crystals.

The giant plasticity of [Formula: see text]He crystals has been explained as a consequence of the large mobility of their dislocations. Thus, the mechanical properties of dislocation free crystals should be quite different from those of usual ones. In 1996-1998, Ruutu et al. published crystal growth studies showing that, in their helium 4 crystals, the density of screw dislocations along the c-axis was less than 100 per cm[Formula: see text], sometimes zero. We have grown helium 4 crystals using similar growth speeds and temperatures, and extracted their dislocation density from their mechanical properties. We found dislocation densities that are in the range of 10[Formula: see text]-10[Formula: see text] per cm[Formula: see text], that is several orders of magnitude larger than Ruutu et al. Our tentative interpretation of this apparent contradiction is that the two types of measurements are somewhat indirect and concern different types of dislocations. As for the dislocation nucleation mechanism, it remains to be understood.

Elastic properties of solid helium.

Following recent torsional oscillator measurements which appear to show the 'non-classical rotational inertia' which characterizes a supersolid, a number of experiments have searched for evidence of unusual behavior in other properties. We have developed a new technique for measuring the shear modulus of solid helium at low frequencies and small strains. In hexagonal close packed (4)He, the shear modulus increases dramatically below 200 mK, the temperature range where decoupling is seen in torsional oscillators. The modulus anomaly is frequency independent, depends strongly on strain amplitude, and is very sensitive to (3)He impurities. In these and other ways, the shear modulus closely mirrors the torsional oscillator behavior and it is clear that the two phenomena are closely related. We attribute the shear modulus effects to the elastic response of mobile dislocations and their pinning by (3)He impurities at low temperatures. A question then arises: are the modulus increases responsible for the frequency changes seen in torsional oscillator experiments? The expected frequency shifts appear to be much too small to explain the apparent decoupling, nor can elastic effects explain the 'blocked annulus' results or the behavior in small pores. In order to clarify the relationship between the shear modulus and torsional oscillator behaviors, we have recently made modulus measurements on (3)He, where no supersolid response is expected. Since dislocation motion depends on crystal structure it was important that these measurements be extended to the hexagonal close packed phase of (3)He, not just the body centered cubic phase.

Calcified occlusion of the right coronary artery in Kawasaki disease: evidence of myocardial ischaemia using cardiac technetium-99m-tetrofosmin perfusion single-photon emission computed tomography.

We report the case of a 14-year-old boy who developed Kawasaki disease at 5 months of age. The patient developed severe aneurysmal disease of both the left and right coronary arteries. He eventually developed total calcified occlusion of the right coronary artery despite long-term treatment with aspirin. Catheterisation showed no antegrade flow into the right coronary artery, with retrograde flow from the left coronary system into the right coronary. At the most recent follow-up he was asymptomatic, with normal exercise tolerance and a negative exercise stress test. Single-photon emission computed tomography (SPECT) myocardial perfusion imaging was carried out during stress and at rest using intravenous persantine (dipyridamole) and technetium-99m tetrofosmin. During stress, there were prominent left ventricular apical and anteroseptal defects, which normalised at rest. SPECT during stress and at rest may detect subclinical ischaemia and influence further management options in such patients.

Mexican agencies reach teenagers.

PIP: The Gente Joven project of the Mexican Foundation for Family Planning (MEXFAM) trains young volunteers in 19 cities to spread messages about sexually transmitted diseases and population growth to their peers. They also distribute condoms and spermicides. It also uses films and materials to spread its messages. The project would like to influence young men's behavior, but the Latin image of machismo poses a big challenge. It would like to become more responsible toward pregnancy prevention. About 50% of adolescents have sexual intercourse, but few use contraceptives resulting in a high adolescent pregnancy rate. Many of these pregnant teenagers choose not to marry. Adolescent pregnancy leads to girls leaving school, few marketable skills, and rearing children alone. Besides women who began childbearing as a teenager have 1.5 times more children than other women. Male involvement in pregnancy prevention should improve these statistics. As late as 1973, the Health Code banned promotion and sales of contraceptives, but by 1992 about 50% of women of reproductive age use contraceptives. The Center for the Orientation of Adolescents has organized 8 Young Men's Clubs in Mexico City to involve male teenagers more in family planning and to develop self-confidence. It uses a holistic approach to their development through discussions with their peers. A MEXFAM study shows that young men are not close with their fathers who tend to exude a machismo attitude, thus the young men do not have a role model for responsible sexual behavior. MEXFAM's work is cut out for them, however, since the same study indicates that 50% of the young men believe it is fine to have 1 girlfriend and 33% think women should earn more than men. A teenager volunteer reports, however, that more boys have been coming to him for contraception and information than girls in 1992 while in other years girls outnumbered the boys.^ieng