The size, shape, density and ring of the dwarf planet Haumea from a stellar occultation.

Haumea-one of the four known trans-Neptunian dwarf planets-is a very elongated and rapidly rotating body. In contrast to other dwarf planets, its size, shape, albedo and density are not well constrained. The Centaur Chariklo was the first body other than a giant planet known to have a ring system, and the Centaur Chiron was later found to possess something similar to Chariklo's rings. Here we report observations from multiple Earth-based observatories of Haumea passing in front of a distant star (a multi-chord stellar occultation). Secondary events observed around the main body of Haumea are consistent with the presence of a ring with an opacity of 0.5, width of 70 kilometres and radius of about 2,287 kilometres. The ring is coplanar with both Haumea's equator and the orbit of its satellite Hi'iaka. The radius of the ring places it close to the 3:1 mean-motion resonance with Haumea's spin period-that is, Haumea rotates three times on its axis in the time that a ring particle completes one revolution. The occultation by the main body provides an instantaneous elliptical projected shape with axes of about 1,704 kilometres and 1,138 kilometres. Combined with rotational light curves, the occultation constrains the three-dimensional orientation of Haumea and its triaxial shape, which is inconsistent with a homogeneous body in hydrostatic equilibrium. Haumea's largest axis is at least 2,322 kilometres, larger than previously thought, implying an upper limit for its density of 1,885 kilograms per cubic metre and a geometric albedo of 0.51, both smaller than previous estimates. In addition, this estimate of the density of Haumea is closer to that of Pluto than are previous estimates, in line with expectations. No global nitrogen- or methane-dominated atmosphere was detected.

The comparative effect of ovarian hormone administration on bone mineral status in oophorectomized rats.

The effect of oophorectomy and hormone replacement therapy on cortical and trabecular bone mass was assessed in Sprague-Dawley rats. Bone mineral density (BMD) of the femur and the lumbar spine was determined by dual photon absorptiometry 4 months after surgery. Femoral mineral content was also determined. A significant decrease in bone density and in calcium content was observed after surgical castration. Bone mineral loss was prevented by either progesterone or estrogen, while the combination of progesterone and estrogen had no effect on the bone mineral content. The present study suggests the possibility that estrogen-progestin treatment may be less effective than a therapy with estrogen alone, and that further study on the effect of progesterone alone would be worthwhile.

[Intertrochanteric osteotomy of the hip. Retrospective (10-18 years) clinical and radiologic study of 30 interventions]. / Osteotomia intertrocanterica dell'anca. Revisione clinica e radiologica a distanza (10-18 anni) di 30 interventi.

The authors report on 28 patients with degenerative arthritis of the hip who underwent intertrochanteric osteotomy of the femur between 1970 and 1978. Two subjects were operated on bilaterally, bringing the total number of hips to 30. The follow-up period averaged 11.8 years. All patients underwent thorough clinical and radiographic examination as well as basography and computed electrogoniometry. The basographic examination consists of analysis of the temporal phases of gait, revealing angular abnormalities of the various joint components of the lower limbs which occur during walking. Processing the data by computer shows any anomaly present in the lower limbs. The results of treatment were good for the most part, and thorough functional examination by computer often revealed a poor radiographic result corresponding to a better clinical result.