Engineering topics

Brown, Allan H.

Publications and source records attributed to Brown, Allan H..

4 records

NASA NTRS1993

A proposal to determine properties of the gravitropic response of plants in the absence of a complicating g-force (GTHRES)

Gravitropic responses of oat seedlings (Avena sativa L.) were measured on Earth and in microgravity (IML-1). The seedlings were grown at 1 g either on Earth or on 1 g centrifuges. They were challenged by centripetal accelerations for which the intensity and duration of the stimulations were varied. All stimulation intensities were in the hypogravity region from 0.1 to 1.0 g. All responses occurred either in Spacelab microgravity or during clinorotation on Earth. The experiments were carried out with the same apparatus in Spacelab and on Earth. The experiments addressed a series of scientific questions and useful data were obtained to provide answers to some but not all of those questions.

Brown, Allan H.↗

NASA NTRS1992

Gravitropic responses of plants in the absence of a complicating G-force (6-IML-1)

On the Earth it is patently impossible to measure any tropistic, physiologic, or morphogenic reactions to environmental stimuli without taking into account our planet's gravitational influence on the time course of the test subject's response. It follows that all published reports of quantitative measurements of such responses must have been contaminated by an additional gravity dependent component which probably was not trivial. Our research effort has as its principal scientific objective, the acquisition of experimental data from tests in a microgravity environment that will address a number of basic questions about plants' gravitropic responses to the perception of transversely applied g forces in the hypogravity range, from essentially zero to unit g. Comparable tests on Earth but in the same flight hardware, referred to as the Gravitational Plant Physiology Facility (GPPF), will provide 1 g data for various useful comparisons. Four specific scientific questions are addressed.

Brown, Allan H.↗

NASA NTRS1991

Variable-Speed Instrumented Centrifuges

Report describes conceptual pair of centrifuges, speed of which varied to produce range of artificial gravities in zero-gravity environment. Image and data recording and controlled temperature and gravity provided for 12 experiments. Microprocessor-controlled centrifuges include video cameras to record stop-motion images of experiments. Potential applications include studies of effect of gravity on growth and on production of hormones in corn seedlings, experiments with magnetic flotation to separate cells, and electrophoresis to separate large fragments of deoxyribonucleic acid.

Chapman, David K.↗

NASA NTRS1989

Gravity receptors and responses

The overall process of gravity sensing and response processes in plants may be divided conveniently into at least four components or stages: Stimulus susception (a physical event, characteristically the input to the G receptor system of environmental information about the G force magnitude, its vector direction, or both); information perception (an influence of susception on some biological structure or process that can be described as the transformation of environmental information into a biologicallly meaningful change); information transport (the export, if required, of an influence (often chemical) to cells and organs other than those at the sensor location); and biological response (almost always (in plants) a growth change of some kind). Some analysts of the process identify, between information perception and information transport, an additional stage, transduction, which would emphasize the importance of a transformation from one form of information to another, for example from mechanical statolith displacement to an electric, chemical, or other alteration that was its indirect result. These four (or five) stages are temporally sequential. Even if all that occurs at each stage can not be confidently identified, it seems evident that during transduction and transport, matters dealt with are found relatively late in the information flow rather than at the perception stage. As more and more is learned about the roles played by plant hormones which condition the G responses, the mechanism(s) of perception which should be are not necessarily better understood. However, if by asking the right questions and being lucky with experiments perhaps the discovery of how some process (such as sedimentation of protoplasmic organelles) dictates what happens down stream in the information flow sequence may be made.

Brown, Allan H.↗