David L. Rabinowitz

A reduced estimate of the number of kilometre-sized near-Earth asteroids

Near-Earth asteroids are small (diameters < 10 km), rocky bodies with orbits that approach that of the Earth (they come within 1.3 AU of the Sun). Most have a chance of approximately 0.5% of colliding with the Earth in the next million years. The total number of such bodies with diameters > 1 km has been estimated to be in the range 1,000–2,000, which translates to an approximately 1% chance of a catastrophic collision with the Earth in the next millennium. These numbers are, however, poorly constrained because of the limitations of previous searches using photographic plates. (One kilometre is below the size of a body whose impact on the Earth would produce global effects.) Here we report an analysis of our survey for near-Earth asteroids that uses improved detection technologies. We find that the total number of asteroids with diameters > 1 km is about half the earlier estimates. At the current rate of discovery of near-Earth asteroids, 90% will probably have been detected within the next 20 years.

Effect of Human Growth Hormone on Muscle and Adipose Tissue Metabolism in the Forearm of Man

Previous reports concerning the effects of human, bovine, and porcine growth hormone on carbohydrate and fat metabolism are disparate. Growth hormone has been variously stated to be without effect, to increase, to depress, and to have a biphasic action on glucose uptake of excised rat hemidiaphragm (1-5), on isolated perfused rat heart (6, 7), and on the blood glucose concentration of man and rat (8, 9). With respect to effects on fat metabolism, injection of growth hormone consistently provokes, within a matter of hours, a rise in plasma free fatty acids (FFA) (10, 11), but in those experiments where earlier effects have been looked for, an initial hypolipacidemia has been reported (12, 13). These observations have been difficult to reconcile with reports of poor or erratic lipolytic activity displayed by growth hormone preparations on excised rat adipose tissue (14). Much of the conflicting literature may arise from use of impure pituitary extracts, inadequate recognition of species specificity for growth hormones, and use of pharmacologic doses of the

The Action of Insulin in Man in the Postabsorptive and Postprandial States With a Note on Some Applications of its Action in Determining Muscle Fuel in Man

IT is the purpose of this communication to review aspects of insulins action on skeletal muscle and adipose tissue in vivo, from which arise some ideas concerning the day to day role of insulin in intact man. The experimental tool employed was the forearm of man. Subjects were studied during the morning hours after a 12 to 14 hour fast. Catheters were placed in the brachial artery (A) and in draining ipsilateral forearm deep (DV) and superficial (SV) veins. Forearm blood flow was measured by indicator dilution techniques based on the continuous infusion of Evans blue dye. Samples were taken at regular intervals from each of the catheters, and the concentration of selected metabolites was measured. A-DV concentration differences reflect, in the main, the metabolism of forearm muscle, but also undoubtedly of the adipose tissue that mingles with muscle; A-SV differences reflect chiefly the metabolism of subcutaneous adipose tissue. The technique lends itself nicely to the examination of local effects of hormones. The hormone, insulin in the present experiments, is added to the solution containing the blue dye, and infused at constant rate into the brachial artery to produce the desired local concentration of hormone in the arm. The total amount of hormone is so small, however, that its arrival in the general circulation stimulates no measurable contra-response. Thus one observes as far as possible only the effects of the hormone on forearm tissues.

New home for NEAT on the 1.2m/B37 at AMOS

The NASA/JPL Near Earth Asteroid Tracking (NEAT) Program was in operation using the Maui GEODSS as its observing platform for about three years starting in late 1995 and continuing into 1998. In October of 1998 the NASA/AFSPC Near Earth Object Working Group (NEOWG) recommended that the NASA/JPL NEAT program be moved to the AMOS 1.2 m/B37 telescope. This paper describes the technical efforts that were required to facilitate the move. The task requirements specified that the modified 1.2 m/B37 system be capable of producing a field of view (FOV) greater than or equal to 1.4 degrees X 1.4 degrees at the NEAT camera focal plane. Further, it was specified that no modifications be made to the 1.2 m/B37 mirror or the NASA/JPL camera. Thus, activity focused on the development of suitable focal reduction optics (FRO). A new headring and spider, based on the original design, were also built to receive the NEAT FRO and the NASA/JPL camera. Operation of the NEAT system, for asteroid search and discovery, will be autonomous and remotely directed from NASA/JPL. Finally, the potential for use of the NEAT system as regards the satellite metric mission will also be presented.