Shuttling Activity Research Articles

Performance of a BGO detector in low Earth orbit

A 7.6-cm*7.6-cm BGO (bismuth germanate) detector was flown in the middeck of the Space Shuttle Columbia August 8-13, 1989, as part of the Shuttle Activation Monitor (SAM) experiment. One of the goals of this experiment was to compare the performance of the BGO to that of NaI in the same environment. Twenty-four hours of data in 5-min time bins were recorded with each detector in each of two locations in a high-inclination orbit (57 degrees , 300 km). Pre- aid post-flight low-background counting was preformed for identification of activities induced by the space radiation environment. A number of isotopes attributed to induced activity from exposure to the space radiation environment have been tentatively identified.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The Shuttle activation monitor: a system for direct comparison of gamma-ray detector materials in a space environment

An experimental system which was used to compare gamma-ray detector materials in a space environment is described. Two 3-in*3-in scintillator detectors, NaI and BGO, were flown on the Space Shuttle Columbia as part of the Shuttle Activation Monitor (SAM) experiment. The goals of this experiment were to compare the performance of the two detector materials in the same environment and to measure the variations in dynamic radiation background as a function of geomagnetic coordinates, amount of shielding, and type of detector material. Twenty-four hours of data in 5-min time bins were recorded with each detector in both high-shielding and low-shielding locations in the Orbiter middeck. The high-inclination orbit (57 degrees , 160 nmi) provided exposure to the trapped charged particles in the South Atlantic Anomaly as well as the electrons in the polar regions. The system used specially adapted off-the-shelf hardware for data acquisition and storage. The multichannel analyzer was a commercially available unit with added circuitry to support an active particle shield. Data during the flight were stored using a cassette tape recorder. A preliminary look at some of the data from the first flight is included. >

The space station and Mars

This article presents a plan for reconfiguring the US-international Space Station, which could be used to undertake exploration of Mars. The author believes that there is an urgent need to give a unified purpose to the US Shuttle, Space Station and space science activities, and that planning for an international Mars sample return mission along the lines outlined here could start the US space programme moving again within budgetary requirements.

Effect of Sucrose or Starch Feeding on the Hepatic Mitochondrial Activity of BHE and Wistar Rats

The hypothesis that the effects of dietary sucrose on hepatic lipogenesis could be explained by an effect on mitochondrial respiration was tested. Two groups of male BHE and Wistar rats were fed, from weaning, either a 65% starch or a 65% sucrose diet. Rats were killed at 50–60 days of age by decapitation, and hepatic mitochondria were isolated. Simulated state 3 and state 4 respiration with succinate, pyruvate, or α-ketoglutarate as substrates was determined as were the activities of the α-glycerophosphate and malate-aspartate shuttles. Mitochondria from Wistar rats had higher ADP:O ratios than BHE rats for all three substrates. Respiratory control ratios with succinate or α-ketoglutarate as the substrates were affected by both diet and strain. Respiratory control ratios with pyruvate as a substrate were affected by diet such that sucrose feeding lowered the respiratory control ratio in both BHE and Wistar rats. Shuttle activities were not as markedly affected by strain or diet. We conclude that mitochondrial respiration may be more sensitive to dietary manipulation than mitochondrial shuttle activity.

The shuttling activity of nuclear RNAs is not an artefact of experimental manipulation

These experiments were designed to determine whether the migration of RNA molecules from an implanted nucleus to the host cytoplasm and from there into the host cell nucleus against a concentration gradient might reflect an artefact induced by the process of nuclear transplantation. That is, are RNA molecules, as previously shown for certain nuclear proteins, caused to artefactually leave a manipulated nucleus and then move into the host cell nucleus (as well as return to the grafted nucleus) during the recovery period? A variety of experiments involving different kinds of manipulative sequences and different numbers of nuclear transplantations suggest—but do not prove—that no artefact is involved in the migration of RNA from one nucleus to another but two experiments strongly support the view that the shuttling activity is a normal physiological process. One of the latter involved a determination of the rate of egress of 3H-RNA from an implanted nucleus and reveals that that rate, in contrast with the equivalent rate of egress for labeled proteins which is clearly abnormal after micromanipulation, is totally consonant with the rate of movement of RNA from nucleus to cytoplasm established from experiments that do not involve micromanipulation. The other experiment involves comparison of (1) the amount of radioactivity acquired by an unlabeled nucleus present in the cell at the time a labeled nucleus is implanted with (2) the amount of radioactivity acquired by an unlabeled nucleus implanted after a labeled nucleus had been implanted and had time to recover from any possible operation-induced trauma. With 3H-protein nuclei the host nuclei of (1) acquired much more label than the host nuclei of (2) because in (1) the host nuclei were able to acquire much of the artefactually-released 3H-protein. For the 3H-RNA experiments, however, little difference was found between (1) and (2) in the amount of label acquired by the host cell nuclei. It can be concluded that little, if any, of the non-random shuttling activity of RNA molecules can be a reflection of an artefact.

The effects of ACTH, adrenalectomy and dexamethasone on the acquisition of an avoidance response in rats

Exogenous elevation of circulating ACTH level facilitated the acquisition of a two-way avoidance response at a high but not at a moderate US intensity. Injections of ACTH had no general effect on spontaneous shuttling activity, escape behavior to light-onset, or intertrial responding during avoidance conditioning. Adrenalectomy, which resulted in minimal plasma levels of adrenocortical hormones and, presumably, elevated levels of ACTH, also facilitated avoidance responding. Injection of dexamethasone, a synthetic glucocorticoid and ACTH inhibitor, produced severe weight loss and hypophagia, but did not influence avoidance performance. However, the failure of dexamethasone to affect acquisition of avoidance responding was not related to its effect on body weight and food intake. The action of ACTH on avoidance conditioning is clearly extra-adrenal, but ACTH is not essential to normal performance, at least when high levels of glucocorticoids are present.