Flare build up: 21 May 1980

The decaying solar active region that crossed the central meridian on May 20, 1980 at latitude S13° produced a major flare (2B/X1) at 2054 on May 21. This region was a target of the international Flare Buildup Study and was well observed. The buildup was characterized by little flare activity during two days prior to the major flare but a great deal of activity in the filament that separated the opposite magnetic polarities of the active region. Large proper motions of sunspots and magnetic fields suggest that the magnetic field was stressed prior to the flare. The immediate trigger of the flare appears to have been an eruption of new magnetic flux in the center of the active region. The new flux erupted in a configuration that decreased the net flux of the active region and contributed to the decay of the region.     

Forces acting on a foreign particle near a solidification front

The interaction of inert foreign particles and a solid-liquid interface during solidification is considered. The viscous drag on the particle which produces a force on the interface is calculated under general assumptions as well as the disjoining force for small particles and the buoyancy force for large ones.     

Identification of specific gravity sensitive signal transduction pathways in human A431 carcinoma cells.

Epidermal growth factor (EGF) activates a well characterized signal transduction cascade in human A431 epidermoid carcinoma cells. The influence of gravity on EGF-induced EGF-receptor clustering and early gene expression as well as on actin polymerization and actin organization have been investigated. Different signalling pathways induced by the agents TPA, forskolin and A23187 that activate gene expression were tested for sensitivity to gravity. EGF-induced c-fos and c-jun expression were decreased in microgravity. However, constitutive beta-2 microglobulin expression remained unaltered. Under simulated weightlessness conditions EGF- and TPA-induced c-fos expression was decreased, while forskolin- and A23187-induced c-fos expression was independent of the gravity conditions. These results suggest that gravity affects specific signalling pathways. Preliminary results indicate the EGF-induced EGF-receptor clustering remained unaltered irrespective of the gravity conditions. Furthermore, the relative filamentous actin content of steady state A431 cells was enhanced under microgravity conditions and actin filament organization was altered. Under simulated weightlessness actin filament organization in steady state cells as well as in EGF-treated cells was altered as compared to the 1 G reference experiment. Interestingly the microtubule and keratin organization in untreated cells showed no difference with the normal gravity samples. This indicates that gravity may affect specific components of the signal transduction circuitry.     

Aircraft vertical profile implementation using directed-graphmethods

Aircraft vertical profile simulation is realized using a demand-driven minimal-calculation directed graph structure to reduce calculation time and to force synchronization of the performance measurement functions with the system state variables. Performance-directed model adaptation makes dynamic vertical profile path corrections, in the presence of fixed drag variations, possible. Drag variations ranging from +10% to -10% yielded fuel consumption improvements of less than 1% in the majority of the cases. Calculation time improvement for path simulation ranges from a factor of 1.19 in the worst case to 1.5 in the best case     

Three Mile Island? Lessons for America

The great fear of a nuclear castastrophe is the prime lesson learned from the Three Mile Island accident. This fear is real and creates a major risk to our society. Although the probability of a major release of radioactivity occurring at a given plant in a given year is low, the rapidly increasin number of plants around the world increases the probability that such a catastrophe will occur someplace in the next few years. When a major release does occur, people will demand an end to the use of energy from nuclear power. We are at grave risk in not having an alternative, in not providing a choice in time. The alternatives are clearly defined. But we need to see that the resources are made available to develop them.     

High Power Needs for Commercial Satellites

This overview paper presents estimates of the photovoltaic power systems needed on commercial communications spacecraft in the year 2000. These are developed in the form of power requirements based on extrapolation of the historical growth in communications traffic and are about 5 to 15 kW. The paper also addresses the key technology drivers in these photovoltaic systems. The importance of reducing mass in the power system is described in terms of the tradeoff with communications systems mass to maximize communications revenue. It surveys solar array components and subsystems to meet these future requirements and attempts to identify the development candidates with a large payoff potential and a high probability of successful development.     

A review of long drop tubes as a supplement/alternative to space experiments

The 100 meter high drop tube at the Marshall Space Flight Center has proven to be a viable facility for studies of containerless solidification. Advantages are that experiments are inexpensive and large numbers of specimens can be processed rapidly. It would not be unusual to run ten specimens in a day. Another significant advantage is that the undercooling behavior can be followed with sufficient sensitivity to easily detect the onset of recalescence and subsequent events.Disadvantages are the restrictions on specimen sizes and types of alloys that can be run in a microgravity environment. Practical specimen sizes range between 50 mg and 500 mg depending on the type of furnace being used. Refractory alloys can be processed in a vacuum (about 10^?5 torr) and therefore at microgravity. Non-refractory alloys demand an atmosphere (about 200 torr) to obtain appreciable undercooling before impact at the bottom of the tube. Under these conditions significant g forces result.Because of the present limitations of the 100 meter drop tube, the most definitive work has been done on niobium based alloys. Large amounts of undercooling have been observed routinely and the effects of undercooling on microstructure have been characterized in detail. X-ray diffraction, scanning electron microscopy, and transmission electron microscopy have been used to determine types of phases, amounts of phases, and compositions of phases. It is clear, as would be expected, that the results bear some resemblance to rapid solidification processing by quenching. However, there are dissimilarities due to the uniqueness of solidification by deep undercooling without quenching in long drop tubes and accompanying recalescence effects.     

Growth and development of cultured carrot cells and embryos under spaceflight conditions

Morphogenetically competent proembryonic cells and well-developed somatic embryos of carrot at two levels of organization were exposed for 18.5 days to a hypogravity environment aboard the Soviet Biosatellite Cosmos 1129. It was confirmed that cultured totipotent cells of carrot can give rise to embryos with well-developed roots and minimally developed shoots. It was also shown that the space hypogravity environment could support the further growth of already-organized, later somatic embryonic stages and give rise to fully developed embryo-plantlets with roots and shoots.