Results from the Energetic Gamma-Ray Experiment Telescope (EGRET) on the Compton Observatory

The Energetic Gamma-Ray Experiment Telescope (EGRET) on the Compton Gamma Ray Observatory covers the high energy gamma ray energy range, approximately 30 MeV to 30 GeV, with a sensitivity considerably greater than earlier high energy gamma-ray satellites. Thus far, 4 pulsars have been detected and their properties measured, including in 3 cases the energy spectrum as a function of phase. The details of the galactic plane are being mapped and a spectra of the center region has been obtained in good agreement with that expected from cosmic ray interactions. The Magellanic clouds have been examined with the Large Magellanic Cloud having been detected at a level consistent with it having a cosmic ray density compatible with quasi-stable equilibrium. Sixteen Active Galactic Nuclei (AGN's) have been seen thus far with a high degree of certainty including 12 quasars and 4 BL Lac objects, but no Seyferts. Time variation has been detected in some of these AGN's.     

Radiation protection against early and late effects of ionizing irradiation by the prostaglandin inhibitor indomethacin.

Protective effects of indomethacin, a prototype prostaglandin-inhibiting agent, against early and late sequelae of radiation injury (after X-rays or gamma rays) in mice were investigated. The following tissues or organs were examined: hematopoietic tissue, esophagus, jejunum, colon, lung, hair follicles, and tissues involved in the development of radiation-induced leg contractures. In addition, the effect of indomethacin was tested against radiation-induced carcinogenesis. In all experiments, the radiation was delivered as a single dose. Indomethacin led to significant protection of hematopoietic tissue, by a factor of 1.3. There was also some protection against radiation-induced pneumonitis and against radiation-induced carcinogenesis (protection factor of 1.2). The other tissues tested showed no change in their radioresponse after being treated with indomethacin. Thus, indomethacin can act as a radioprotective agent against both early and late sequelae of radiation, but its effect is dependent on the tissue tested. This protection is smaller than that observed with WR-2721. However, indomethacin combined with WR-2721 produced a radioprotective effect greater than the radioprotection achieved by individual treatments.     

Dissipative Solitary Kinetic Alfvén Waves and Electron Acceleration in the Solar Corona

Nonthermal electrons play a major role during solar flares since not only they contain a large amount of the released energy but also they provide important information of the flaring physics through their nonthermal radiation in radio and hard X-ray bands. In a recent work Wu (Phys. Plasmas 10 (2003) 1364) proposed that dissipative solitary kinetic Alfvén wave (DSKAW) with a local shock-like structure could provide an efficient acceleration mechanism for energetic electrons in a low-β plasma. In the present paper dynamical characteristics of the DSKAW acceleration mechanism in solar coronal plasmas are studied and its application to the acceleration of flaring electrons is discussed.     

Improved motion-mode estimation

Hybrid trackers incorporating a non-Markov modal model have been proposed. However, these algorithms use a restricted measurement set to identify the modal state. It is shown here that a renewal process model, along with broader measurement fusion, enhances modal classification in such estimators.     

Protein crystal growth aboard the U.S. space shuttle flights STS-31 and STS-32.

The first microgravity protein crystal growth experiments were performed on Spacelab I by Littke and John. These experiments indicated that the space grown crystals, which were obtained using a liquid-liquid diffusion system, were larger than crystals obtained by the same experimental system on earth. Subsequent experiments were performed by other investigators on a series of space shuttle missions from 1985 through 1990. The results from two of these shuttle flights (STS-26 and STS-29) have been described previously. The results from these missions indicated that the microgravity grown crystals for a number of different proteins were larger, displayed more uniform morphologies, and yielded diffraction data to significantly higher resolutions than the best crystals of these proteins grown on earth. This paper presents the results obtained from shuttle flight STS-32 (flown in January, 1990) and preliminary results from the most recent shuttle flight, STS-31 (flown in April, 1990).     

Five millinewton field emission thruster testing

A compact cluster of two 80-mm-wide emitters has been designed, built and tested. The field emission thruster using this cluster is able to produce thrust in excess of 5 mN at high mass efficiency.     

Heavy ion measurement on LDEF.

A stack of CR-39 track detectors was exposed on the NASA satellite LDEF and recovered after almost 6 years in space. The quick look analysis yielded heavy ion tracks on a background of low energy secondaries from proton interactions. The detected heavy ions show a steep energy spectrum which indicates a radiation belt origin.     

Search for life on Mars: evaluation of techniques.

An important question for exobiology is, did life evolve on Mars? To answer this question, experiments must be conducted on the martian surface. Given current mission constraints on mass, power, and volume, these experiments can only be performed using proposed analytical techniques such as: electron microscopy, X-ray fluorescence, X-ray diffraction, alpha-proton backscatter, gamma-ray spectrometry, differential thermal analysis, differential scanning calorimetry, pyrolysis gas chromatography, mass spectrometry, and specific element detectors. Using prepared test samples consisting of 1% organic matter (bovine serum albumin) in palagonite and a mixture of palagonite, clays, iron oxides, and evaporites, it was determined that a combination of X-ray diffraction and differential thermal analysis coupled with gas chromatography provides the best insight into the chemistry, mineralogy, and geological history of the samples.     

Operation of an experimental algal gas exchanger for use in a CELSS.

Concepts of a CELSS anticipate the use of photosynthetic organisms (higher plants and algae) for air revitalization. The rates of production and uptake of carbon dioxide and oxygen between the crew and the photosynthetic organisms are mismatched. An algal [correction of aglal] system used for gas exchange only will have the difficulty of an accumulation or depletion of these gases beyond physiologically tolerable limits (in a materially closed system the mismatch between assimilatory quotient (AQ) and respiratory quotient (RQ) will be balanced by the operation of the waste processor). We report the results of a study designed to test the feasibility of using environmental manipulations to maintain physiologically appropriate atmospheres for algae (Chlorella pyrenoidosa) and mice (Mus musculus strain DW/J) in a gas-closed system. Specifically, we consider the atmosphere behavior of this system with Chlorella grown on nitrate or urea and at different light intensities and optical densities. Manipulation of both the photosynthetic rate and AQ of the alga has been found to reduce the mismatch of gas requirements and allow operation of the system in a gas-stable manner. Operation of such a system in a CELSS may be useful for reduction of buffer sizes, as a backup system for higher plant air revitalization and to supply extra oxygen to the waste processor or during crew changes. In addition, mass balance for components of the system (mouse, algae and a waste processor) are presented.     

Cosmic ray exposure factors for Shuttle altitudes derived from calculated cut-off rigidities.

The allowed cosmic radiation flux accessible to an earth-orbiting spacecraft is a complex function of the satellite position and the geomagnetic cutoff characteristics at each zenith and azimuth angle at each position. We have determined cosmic ray exposure factors for the galactic cosmic ray spectrum for typical shuttle altitudes and inclinations up to 50 degrees. We have utilized d world grid of trajectory-derived cutoff rigidity calculations at 400 km altitude to determine geomagnetic transmission functions that permit a simple and direct calculation of the allowed cosmic ray spectrum to a 400 km satellite orbit. If the interplanetary cosmic ray spectrum is multiplied by the orbit-averaged geomagnetic transmission function the result is the allowed cosmic ray spectrum at the spacecraft.