Design of the HEAO Main Bus Shunt Regulator

The High Energy Astronomy Observatory (HEAO) main bus regulator contains a redundant error amplifier (REA) and a 12-section sequenced shunt transconductance amplifier (STA) in which not more than three and not less than one shunt section are in an active control mode regardless of a failure in any one of the twelve sections. The part of the work concerned with the shaping of the frequency response of the REA and STA minor feedback loops and of the teolator major feedback loop is described. Emphasis is on the application of a general design technique embodying a "design-analyze-measure iteration loop," in which a first-cut design and analysis is corrected ard improved after experimental observation of discrepancies and deficiencies. In particular, an incipient high-frequency oscillation was thereby reliably eliminated. It is demonstrated that analysis techniques involving a minimum of algebra can provide full quantitative information on an efficient and reliable system design.     

Residual stresses and endurance strength under tension-compression in the conditions of stress concentration

Residual stresses and endurance strength of specimens with stress concentrators are considered. The results obtained make it possible to predict the fatigue limit of strengthened parts with concentrators in the case of tension-compression.     

BBXRT and Ginga observations of AGN

The X-ray properties of Active Galactic Nuclei (AGN) support recent theories which unify the Seyfert 1 nuclei with the Seyfert 2's and radio-quiet quasars. In these objects the underlying spectrum is strongly distorted by the effects of reflection from the accretion flow and by absorption in partially ionised material. These obscure any intrinsic changes in the spectrum, making it difficult (though not impossible) to constrain the nature of the emission process. Conversely, there is no evidence for either of these spectral distortions in the radio-loud AGN, supporting the hypothesis that the X-rays are dominated by beamed emission from the relativistic jet.     

EUVITA — An extreme UV imaging telescope array with spectral capability

EUVITA is a set of 8 extreme UV normal incidence imaging telescopes, each of them sensitive in a narrow band (λ/Δλ = 15 to 80), centered at wavelengths between 50 and 175 Å. Each telescope has an effective area of a few cm²; a field of view of 1.2° and a spatial resolution of 10 arcsec.

EUVITA will be flown on the Russian mission SPECTRUM X-G. This satellite will be launched in a highly eccentric orbit with a period of 4 days, allowing long, uninterrupted observations (e.g. 10⁵ seconds). EUVITA's narrow spectral bands allow the measurement of source parameters such as temperature or power law index as well as interstellar absorption, and will resolve groups of strong lines emitted by optically thin hot plasmas.     

Force sensitivity of plant gravisensing.

Rotation at 4, 10, 50 and 100 rpm on a horizontal clinostat and in microgravity exerts limited effects on the morphogenesis of lettuce and cress root statocytes and statoliths if compared with the vertical control or 1 g spaceflight reference centrifuge. However, the average distance of statoliths from the distal wall increases. The pattern of plastid location of microgravity-grown and that of clino-rotated samples has been determined at 10, 50, and 100 rpm. Experiments on the centrifuge-clinostat and spaceflight centrifuge (acceleration forces of 0.005 to 1 g) revealed that the average statolith location depends on the amplitude of acropetally or basipetally directed mass acceleration. Decreasing the acropetally directed force from 1 g to 0.4 g dislocates statoliths towards the cell center possibly mediated by the elastic forces of the cytoskeleton. In statocytes formed on the clinostat or in microgravity, the majority of statoliths are located at the center of the cell. To force the statoliths from the center of the statocyte towards one of its poles, a threshold mass acceleration of 0.01 g is required. Statocytes with centrally-located statoliths are considerably more effective in transducing a gravistimulus than those with distally-located plastids. The latent time of the graviresponse is shorter and the response itself is enhanced in roots grown on the clinostat compared to vertically grown samples. The early phases of graviperception are independent of root growth conditions since presentation time and g-threshold are similar for roots grown stationary and those on a clinostat. We propose a sequence of events in gravitropic stimulation that considers not only the lateral displacement of statoliths, as predicted by the starch-statolith hypothesis, but also its longitudinal motion, together with differential gravisensitivity of mechanotransducing structures along the lower-most longitudinal cell wall.