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.     

High performance capillary electrophoresis in microgravity environment.

In the last two decades, capillary electrophoresis has developed to a very quick and accurate analysis technique. With micellar techniques even uncharged particles can be analysed. The field of capillary electrophoresis is broad and shows an overlap with HPLC. The equipment for capillary electrophoresis is very compact, low in weight, energy consumption and waste production.     

A multioutput LLC-type parallel resonant converter

When an LLC-type parallel resonant converter (LLC-PRC) operates above resonant frequency, the switching transistors can be turned off at zero voltage. Further study reveals that the LLC-PRC possesses the advantage of lower converter voltage gain as compared with the conventional PRC. Based on the analytic results derived, a complete set of design curves from which a systematic design procedure is developed is obtained. Experimental results from a 150-W, 150-kHz, multioutput LLC-type PRC power supply are presented     

Three-dimensional target motion analysis using angle and frequency measurements

It is well known that passive target tracking by a single observer, commonly referred to as target motion analysis (TMA), can be done using angle and/or frequency measurements. Depending on the measurement set, different passive tracking procedures result: angle-only tracking (AOT), frequency-only tracking (FOT), and angle/frequency tracking (AFT). Whereas the two-dimensional passive tracking problem has been solved for a multitude of scenarios, thus giving a good insight into the parametric dependences, the three-dimensional problem has been discussed only in a few specific cases. To get a deeper insight into the parametric dependences of three-dimensional TMA, this work analyzes AOT and AFT in typical three-dimensional Airborne Warning and Control System (AWACS) scenarios. A Cramer Rao (CR) analysis of the problem reveals the parametric dependences of both methods and gives a clear idea of the increase in estimation accuracy by using AFT instead of AOT. The results obtained in this way are well confirmed by Monte Carlo simulations taking maximum likelihood (ML) as estimation procedure.     

The interannual variability of the earth's radiation budget components as observed from space

Based on the 1974–78 NOAA data, characteristic features of the variability of the Earth's radiation budget and its components over the area of the Northern Atlantic have been analyzed. Calculations of the mean square deviation for the ERB and its components have let to the conclusions that anomalous regions of maximum variability may be considered as energy-active zones.     

Precision orbit determination for TOPEX/Poseidon using TDRSS doppler tracking data

Precision orbit determination on the TOPEX/Poseidon (T/P) altimeter satellite is now being routinely achieved with sub-5cm radial and sub-15 cm total positioning accuracy using state-of-the-art modeling with precision tracking provided by a combination of: (a) global Satellite Laser Ranging (SLR) and Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS), or (b) the Global Positioning System (GPS) Constellation which provides pseudo-range and carrier phase observations. The geostationary Tracking and Data Relay Satellite System (TDRSS) satellites are providing the operational tracking and communication support for this mission. The TDRSS Doppler data are of high precision (0.3 mm/s nominal noise levels). Unlike other satellite missions supported operationally by TDRSS, T/P has high quality independent tracking which enables absolute orbit accuracy assessments. In addition, the T/P satellite provides extensive geometry for positioning a satellite at geostationary altitude, and thus the TDRSS-T/P data provides an excellent means for determining the TDRS orbits. Arc lengths of 7 and 10 days with varying degrees of T/P spacecraft attitude complexity are studied. Sub-meter T/P total positioning error is achieved when using the TDRSS range-rate data, with radial orbit errors of 10.6 cm and 15.5 cm RMS for the two arcs studied. Current limitations in the TDRSS precision orbit determination capability include mismodeling of numerous TDRSS satellite-specific dynamic and electronic effects, and in the inadequate treatment of the propagation delay and bending arising from the wet troposphere and ionosphere.     

Modelling mesoscale processes in the global geospace system

Intermediate or mesoscale processes mediate the transfer of mass, momentum, and energy across the dynamic solar wind-magnetosphere interface, and the propagation of this input through the system to the ionosphere and atmosphere. The Dartmouth-Berkeley-Minnesota theory team has identified a number of mesoscale phenomena to be investigated as part of the GGS program, including: (1) effects of upstream density fluctuations on magnetopause dynamics, (2) three-dimensional reconnection, (3) magnetopause depletion layer studies, (4) ring current interaction with Pc 1 and Pc 5 waves, (5) generation of ion Larmor-scale current layers in the near Earth plasmasheet, (6) test particle studies in the magnetotail, (7) simulation of magnetosphere- ionosphere coupling including effects of kinetic Alfvén waves and (8) auroral acceleration region studies of the effects of kinetic Alfvén waves on particle distribution functions. A broad range of techniques will be implemented including ideal and reduced MHD, two fluid, hybrid, particle-in-cell and test particle simulations. Detailed comparison of simulation results with GGS satellite and ground based data will be undertaken.     

Solar cycle effects upon the relationship of Ne and Te in the F-region

Employing Atmsophere Explorer-C measurements made in 1974, just prior to solar minimum, Brace and Theis /1/ demonstrated that a remarkably consistent inverse relationship existed between the electron density N_e and temperature T_e in the F-region. In this paper we use later data from AE-C, taken when solar activity was rising (1975–1978), and Dynamics Explorer-2 data taken at solar maximum (1981), to examine how the temperature and density relationship changes with solar activity. We find that the solar maximum T_e is a factor of two larger than the solar minimum T_e for the same values of N_e. T_e does not necessarily increase with solar activity, however, because N_e increases enough to approximately cancel the effect of higher solar extreme ultraviolet heating. We find that the effect of solar activity can be accounted for by a simple function of the F_10.7 cm index that multiplies the solar minimum equation of Brace and Theis /1/.     

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.     

Thermal and nonthermal flare emission observed with the Nobeyama Radio Heliograph

The early phases of three flares, observed by the Nobeyama Radio Heliograph, are studied. Nonthermal and thermal radio sources are identified by comparison with soft X-ray images taken by the Soft X-ray Telescope onboard the Yohkoh satellite. Two of the flares are mainly of nonthermal origin and their location coincides with one of the footpoints of soft X-ray loops. Another flare has both thermal and nonthermal components which start to brighten simultaneously. This suggests that particle acceleration and plasma compression develop simultaneously.