EXOSAT observations of the BL Lac object Mkn 421

The BL Lac object Mkn 421 was observed by EXOSAT four times over a period of six days in February 1984. Significant X-ray variability was apparent on a timescale of less than a day, but with no accompanying spectral change. The source exhibited a very soft power law X-ray spectrum with an extremely low intrinsic column density (N_H10²⁰ cm^–2). There was no evidence for an additional hard component attributable to synchrotron self-Compton emission. The observations when combined with other published data imply that significant changes occur in the form of the broad-band UV/X-ray continuum of this source.     

Bars — A dual bistatic auroral radar system for the study of electric fields in the Canadian sector of the auroral zone

One instrument of the Canadian Auroral Network for the Open Program Unified Study (CANOPUS) is a pulsed dual bistatic auroral radar system (BARS) for the mapping of ionospheric electric fields, using the STARE technique originated by R.A. Greenwald [14]. The Canadian system is presently in the specification and design phases, with the objective of being operational by mid-1984. This paper describes the geometry of the BARS system, the design considerations, and the planned data and control network.     

Scientific results from the pioneer Saturn infrared radiometer

The Pioneer 11 Infrared Radiometer instrument made observations of Saturn and its rings in broadband channels centered at 20 and 45 μm and obtained whole-disk information on Titan. A planetary average effective temperature of 96.5±2.5 K implies a total emission 2.8 times the absorbed sunlight. Correlation with radio science results implies that the molar fraction of H₂ is 90±3% (assuming the rest is He). Temperatures at the 1 bar level are 137 to 140 K; regions appearing cooler may be overlain by a cloud acting as a 124 K blackbody surface. A minimum temperature averaging 87 K is reached near 0.06 bars. Ring boundaries and optical depths are consistent with those at optical wavelengths. Ring temperatures are 64–86 K on the south (illuminated) side, ～54 K on the north (unilluminated) side, and at least 67 K in Saturn's shadow. There is evidence for a south to north drop in ring temperatures. Titan's 45 μm brightness temperature is 75±5 K.     

Dynamic imaging and RCS measurements of aircraft

Results on radar cross section (RCS) measurements and inverse synthetic aperture radar images of a Mooney 231 aircraft using a ground-to-air measurement system (GTAMS) and a KC-135 airplane using an airborne radar are presented. The Mooney 231 flew in a controlled path in both clockwise and counterclockwise orbits, and successively with the gear down, flaps in the take-off position and with the speed brakes up. The data indicates that RCS pattern measurements from both ground-based and airborne radar of flying aircraft are useful and that the inverse synthetic aperture radar (ISAR) images obtained are valuable for signature diagnostics     

M-ary sequential hypothesis tests for automatic targetrecognition

Several forms of sequential hypothesis testing algorithms are described and their performance as classification algorithms for automatic target recognition is evaluated and compared. Several forms of parameteric algorithms, as well as a sequential form of a useful nonparametric algorithm are considered. The primary focus is the design of algorithms for automatic target recognition that produce maximally reliable decisions while requiring, on the average, a minimum number of backscatter measurements. The tradeoffs between the average number of required measurements and the error performance of the resulting algorithms are compared by means of Monte-Carlo simulation studies     

Some aspects of the early evolution of photosynthesis.

The early evolution of a photocatalytic system of the porphyrin type, able to efficiently collect and utilize solar energy for primary electron transfer is discussed. Experimental results concerning some spectral and photochemical properties of the porphyrins, biosynthetic precursors of chlorophyll and their complexes with polymeric templates are reviewed. Protoporphyrin IX associated with pigmented proteinoid is demonstrated to be a favourable candidate for a role of a photosensitizer of the first photosynthetic reaction centers. The origin and early evolution of the photosynthetic electron transfer chain and of the phosphorylating mechanism are discussed with emphasis on the energetic mechanisms of archaebacteria.     

Effects of increased shielding on gamma-radiation levels within spacecraft.

The Shuttle Activation Monitor (SAM) experiment was flown on the Space Shuttle Columbia (STS-28) from 8-13 August, 1989 in a 57 degrees, 300 km orbit. One objective of the SAM experiment was to determine the relative effect of different amounts of shielding on the gamma-ray backgrounds measured with similarly configured sodium iodide (NaI) and bismuth germante (BGO) detectors. To achieve this objective twenty-four hours of data were taken with each detector in the middeck of the Shuttle on the ceiling of the airlock (a high-shielding location) as well as on the sleep station wall (a low-shielding location). For the cosmic-ray induced background the results indicate an increased overall count rate in the 0.2 to 10 MeV energy range at the more highly shielded location, while in regions of trapped radiation the low shielding configuration gives higher rates at the low energy end of the spectrum.     

Analysis of GPS and Loran-C performance for land vehicle navigationin the Canadian Rockies

Loran-C and GPS were assessed for vehicular navigation along selected roads of British Columbia during the winter of 1991. The general topography of this mountainous area is described, together with the specific topographic features and tree coverage characteristics of the 2000 km of roads tested on the mainland and on Vancouver Island. The configuration and characteristics of the Loran C Canadian West Coast chain along the roads used are described. The portable vehicle-mounted system used to collect and analyze the Loran-C and GPS signals along road profiles is described. The performance of Loran-C is analyzed in terms of signal to noise ratios (SNR), field strength, and time-difference distortions, as measured by differential GPS. These distortions, which can reach several hundred meters over distances of less than 20 km, are analyzed in terms of topographic features. The possibility of using these time-independent distortions to calibrate Loran-C for use along the above roads is discussed. Masking of GPS signals due to topographic features and tree coverage along the roads is analyzed. A comparative analysis of both Loran-C and GPS is presented in terms of signal availability and accuracy     

Reduced lymphocyte activation in space: role of cell-substratum interactions.

We investigated the effect of substratum adhesiveness on stimulated lymphocyte blastogenesis by reducing and blocking cell adhesion with poly (2-hydroxyethyl methacrylate) (poly-HEMA) in a simple on-ground system. Cells grown on medium-thick and thick poly-HEMA films were rounded in shape and displayed no signs of spreading. By contrast, on tissue culture plastic and very thin poly-HEMA films, they showed clear signs of spreading. The mitogenic response of lymphocytes grown on thick poly-HEMA films was reduced by up to 68% of the control (tissue culture plastic). Interferon-gamma production was near zero when the cells were grown on the least adhesive substratum. On uncoated plastic, activated lymphocytes subjected to high gravity (20g) exhibited an increased proliferation rate (40%) compared with 1g. By contrast, on poly-HEMA, high gravity did not improve lymphocyte responsiveness. These results show that activated lymphocytes need to anchor and spread prior to achieving an optimal proliferation response. We conclude that decreased lymphocyte adhesion could contribute to the depressed in vitro lymphocyte responsiveness found in the microgravity conditions of space flight.