PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Space Simulation”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 127 records · Page 7Linked to original sources
PubMed2001

Derivation of electron and photon energy spectra from electron beam central axis depth dose curves.

A method for deriving the electron and photon energy spectra from electron beam central axis percentage depth dose (PDD) curves has been investigated. The PDD curves of 6, 12 and 20 MeV electron beams obtained from the Monte Carlo full phase space simulations of the Varian linear accelerator treatment head have been used to test the method. We have employed a 'random creep' algorithm to determine the energy spectra of electrons and photons in a clinical electron beam. The fitted electron and photon energy spectra have been compared with the corresponding spectra obtained from the Monte Carlo full phase space simulations. Our fitted energy spectra are in good agreement with the Monte Carlo simulated spectra in terms of peak location, peak width, amplitude and smoothness of the spectrum. In addition, the derived depth dose curves of head-generated photons agree well in both shape and amplitude with those calculated using the full phase space data. The central axis depth dose curves and dose profiles at various depths have been compared using an automated electron beam commissioning procedure. The comparison has demonstrated that our method is capable of deriving the energy spectra for the Varian accelerator electron beams investigated. We have implemented this method in the electron beam commissioning procedure for Monte Carlo electron beam dose calculations.

Algorithms↗
PubMed1989

Immunocompetent cells producing humoral mediators of bone tissue mineral metabolism during space flight simulation.

During 120-day and 370 day hypokinesia the possibility has been shown of manifestation of mechanism of immunological regulation of osteoclast functions. Supernatants of mononuclear peripheral blood cells which were in vitro nitrogen-stimulated, had an increased potential for resorption in 45Ca-labelled mice fetus long bone organ cultures. Resorbing activity was increased in mononuclear supernatants from some of the subjects exposed to 120-day hypokinesia and from all subjects exposed to 370-day hypokinesia. This variable returned to base-line values after completion of the bed-rest period. Lymphocyte in vitro proliferative activity decreased at the end of hypokinesia and during the initial days of recovery, and the number of active T-rosetting cells was, on the contrary increased. This suggested a possible activation of part of immunocompetent cell population potentially producing humoral regulators of bone cell functions in vivo. A study of a group of healthy males performing their routine daily activity and of patients with local osteoporosis (paradontitis) showed significant differences between normal subjects and patients, confirming the informative value of the method used and allowed to establish approximate limits of physiological variations of the values.

Adult↗
PubMed1990

Simulation of space adaptation syndrome on earth.

The three Spacelab D-1 Scientist Astronauts were exposed to a 1 1/2 h 3 g centrifuge run in the supine position, resulting in a linear 3 g acceleration in the x-direction. They used their space experience to evaluate their readapting to normal gravity and compared their observations with 'Space Adaptation Syndrome'. After the centrifuge runs, the vestibular visual system appeared to be modified in a very specific and reproducible manner. Readapting to the normal 1 g environment took at least 6 h. During this period there was a striking similarity to the astronaut's experience during adaptation to weightlessness in space. A series of vestibular tests were then performed, confirming these subjective findings.

Adaptation, Physiological↗
PubMed2004

Brownian dynamics in Fourier space: membrane simulations over long length and time scales.

A simulation algorithm for elastic membrane sheets is presented. Overdamped stochastic dynamics including hydrodynamic coupling to surrounding solvent and arbitrary external forces are generated by employing Fourier modes of the sheet as the primary dynamic variables. Simulations over the micron length scale and second time scale are easily achieved. The dynamics of a lipid bilayer attached to an underlying network of cytoskeletal filaments is used to estimate the diffusion constant of membrane-bound proteins on the surface of the red blood cell.

Animals↗
PubMed1964

Exposure of microorganisms to simulated extraterrestrial space ecology.

Spores of five test organisms, Bacillus subtilis var. niger, Bacillus megaterium, Bacillus stearothermophilus, Clostridium sporogenes and Aspergillus niger and soils were exposed, while under ultra high vacuum to temperatures of from -190 degrees C to +170 degrees C for 45 days. Up to a temperature of 25 degrees C no loss in viability of the test spores were noted when compared to original populations maintained at room temperature at atmospheric pressure over a desiccant. At elevated temperatures differences in resistivity occurred so that at 88 degrees C only B. subtilis var. niger and A. niger survived in appreciable numbers. At 107 degrees C only A. niger spores survived, but none were recoverable after exposure to 120 degrees C. In comparison B. subtilis var. niger survived at atmospheric pressure and 90 degrees C for 5 days while none of the other spores were viable after 48 hours. Four groups of organisms in soil, mesophilic aerobes and anaerobes, molds and actinomycetes were similarly tested in the vacuum chamber. From one soil sample only actinomycetes survived 120 degrees C, whereas one other soil sample yielded viable bacteria after exposure to 170 degrees C. The resistance of the isolates to high temperatures in the absence of soil is being evaluated. Several organisms have been found to resists 120 degrees C in ultra-high vacuum for 4-5 days, and experiments at higher temperatures are in progress. When irradiated with gamma rays from a cobalt-60 source, there was a difference between vacuum dried test spores irradiated while still under vacuum to those exposed to air immediately before irradiation. A reduction of from one-third to one-ninth of the viability of spores irradiated in vacuum occurred with vacuum-treated spores irradiated in air.

Aspergillus niger↗
PubMed1990

A case of tumour simulating pulp space infection.

General practitioners and accident and emergency departments are often involved in the management of hand or finger sepsis. Such cases are usually easily diagnosed and treated. We report a more serious disorder which may mimic the condition and cause diagnostic confusion.

Aged↗