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Results for “Space Simulation”

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At least 163 records · Page 9Linked to original sources

PubMed1986

Animal studies of life shortening and cancer risk from space radiation.

The U.S. Air Force study of the delayed effects of single, total body exposures to simulated space radiation in rhesus monkeys is now in its 21st year. Observations on 301 irradiated and 57 age-matched control animals indicate that life expectancy loss from exposure to protons in the energy range encountered in the Van Allen belts and solar proton events can be expressed as a logarithmic function of the dose. The primary causes of life shortening are cancer and endometriosis (an abnormal proliferation of the lining of the uterus in females). Life shortening estimates permit comparison of the risk associated with space radiation exposures to be compared with that of other occupational and environmental hazards, thereby facilitating risk/benefit decisions in the planning and operational phases of manned space missions. Calculations of the relative risk of fatal cancers in the irradiated subjects reveal that the total body surface dose required to double the risk of death from cancer over a 20-year post exposure period varies with the linear energy transfer (LET) of the radiation. The ability to determine the integrated dose and LET spectrum in space radiation exposures of humans is, therefore, critical to the assessment of lifetime cancer risk.

Animals↗

PubMed2004

Group interactions during space missions.

INTRODUCTION: Previous anecdotal reports from space and results from space simulation studies on Earth have suggested that the group interactions of crewmembers during space missions can be problematic in ways that can negatively affect crew safety and the accomplishment of mission goals. METHODS: To assess the interpersonal environment of space crewmembers, we used a set of standard questionnaires that were completed by 5 astronauts, 8 cosmonauts, and 58 American and Russian mission control personnel who participated in the Shuttle/Mir Program. RESULTS: Although we did not find strong evidence supporting predicted decrements in tension and cohesion during the second half of the missions, we did find that both crewmembers and mission control personnel displaced unpleasant emotions to monitoring personnel outside of their group. We also found significant differences between Americans and Russians in terms of measures of satisfaction with their interpersonal and work environments. CONCLUSIONS: These findings suggest a number of countermeasures to help future space crews deal with potential maladaptive group interactions. These countermeasures address issues at the time of selection, during prelaunch training, during the mission itself, and after the crew returns to Earth.

Astronauts↗

PubMed2001

Permanent depression of plasma cGMP during long-term space flight.

The purpose of this study was to investigate plasma concentrations of cyclic guanosine monophosphate (cGMP) and atrial natriuretic peptide (ANP) during and after real and simulated space flight. Venous blood was obtained 3 min after the beginning and 2 min after the lower body negative pressure maneuver in two cosmonauts preflight (supine), inflight, and postflight (supine) and in five other subjects before, at the end, and 4 days after a 5-day head-down tilt (-6 degrees) bed rest. In cosmonaut 1 (10 days in space), plasma cGMP fell from preflight 4.3 to 1.4 nM on flight day 6, and was 3.0 nM on the fourth day after landing. In cosmonaut 2 (438 days in space), it fell from preflight 4.9 to 0.5 nM on on flight day 3, and stayed <0.1 nM with 5, 9, and 14 months in space, as well as on the fourth day after landing. Three months after the flight his plasma cGMP was back to normal (6.3 nM). Cosmonaut 2 also displayed relatively low inflight ANP values but returned to preflight level immediately after landing. In a ground-based simulation on five other persons, supine plasma cGMP was reduced by an average of 30% within 5 days of 6 degrees head-down tilt bed rest. The data consistently demonstrate lowered plasma cGMP with real and simulated weightlessness, and a complete disappearance of cGMP from plasma during, and shortly after long-duration space flight.

Adult↗

PubMed1979

An exploration of perception of body boundary, personal space, and body size in elderly persons.

A study of 108 elderly persons using the Body Distortion Questionnaire and the personal space simulation technique test did not support hypotheses that elderly persons with a large personal space will have a larger distortion of body boundary, a larger perception of large body size, a smaller perception of small body size, a larger distortion of body size, and a larger body distortion than elderly persons with a small personal space. The analyses with one-tail t tests showed elderly persons with a small personal space have a larger perception of large body size and a larger distortion of body size than elderly persons with a large personal space. When the extremes of personal space were used the results were the same. Males have a larger personal space and greater distortion of skin perceptions than females.

Aged↗

PubMedDate not supplied

Bone and body mass changes during space flight.

Body mass, calcium and skeletal changes occur in humans who have worked in microgravity. Physiologic changes are seen as early as one week and are still occurring 312 days into space flight. The physiologic changes in bone and mineral metabolism may be among those which limits long duration space flight if an adequate countermeasure is not developed. The purpose of this paper is to summarize what is known about calcium dynamics and bone mineral changes as well as associated changes of body mass induced by space flight. The data reported is from a variety of studies conducted in both actual and simulated space flight.

Aerospace Medicine↗

PubMedDate not supplied

[Effect of actoprotectors on the work capacity of operators during modeling of various factors of space flight].

This paper presents experimental findings indicating that bemithyl, an actoprotective agent, has a beneficial effect on the health status and work capacity of operators during simulated space flight and 56-hour continuous work. The drug enhanced psychophysiological tolerance of the operators and improved the quality of their work: the quality of their compensatory tracking was on the average 10% higher, the number of errors of their porsuit tracking was 1.8 times lower, and the time of visual signal detection was 2.4 times shorter as compared to the placebo controls.

Adaptation, Physiological↗

PubMedDate not supplied

Development and use of an animal model for investigations on rotator cuff disease.

Although both intrinsic and extrinsic factors have been implicated in the cause of rotator cuff disease, previous studies have not been designed to test hypotheses of this disease, partly because of the lack of an appropriate animal model. Thirty-three animals were evaluated according to a 34 item checklist of criteria to determine their appropriateness as an animal model for investigations on the rotator cuff. Only the rat shoulder satisfactorily fulfilled all criteria, with a prominent supraspinatus tendon passing under an enclosed arch. Once the rat was identified, 36 rats were randomized to three experimental groups. One group (n = 12) was treated with an intratendinous injection of bacterial collagenase simulating an acute intrinsic injury, another group (n = 12) was treated with an acromial alteration to reduce the subacromial space simulating an external compression, and the third group (n = 12) was treated with a combination of both modifications. Significant increases in cellularity, number of fibroblasts, and collagen disorganization were seen in all experimental tendons compared with a contralateral control group. Semiquantitative grading of histologic sections revealed marked changes in all groups at 4 and 8 weeks. Injuries appeared to be healing at 12 weeks except in the combination group, which seemed to demonstrate persistent alterations. This study supports the rat as an appropriate model for investigating rotator cuff disease. In addition, this study demonstrates that both intrinsic and extrinsic alterations can induce changes in the supraspinatus tendon, which may have similarities to human tendon disease.

Animals↗

PubMed2004

Modelling 6 MV photon beams of a stereotactic radiosurgery system for Monte Carlo treatment planning.

The goal of this work is to build a multiple source model to represent the 6 MV photon beams from a Cyberknife stereotactic radiosurgery system for Monte Carlo treatment planning dose calculations. To achieve this goal, the 6 MV photon beams have been characterized and modelled using the EGS4/BEAM Monte Carlo system. A dual source model has been used to reconstruct the particle phase space at a plane immediately above the secondary collimator. The proposed model consists of two circular planar sources for the primary photons and the scattered photons, respectively. The dose contribution of the contaminant electrons was found to be in the order of 10(-3) of the total maximum dose and therefore has been omitted in the source model. Various comparisons have been made to verify the dual source model against the full phase space simulated using the EGS4/BEAM system. The agreement in percent depth dose (PDD) curves and dose profiles between the phase space and the source model was generally within 2%/1 mm for various collimators (5 to 60 mm in diameter) at 80 to 100 cm source-to-surface distances (SSD). Excellent agreement (within 1%/1 mm) was also found between the dose distributions in heterogeneous lung and bone geometry calculated using the original phase space and those calculated using the source model. These results demonstrated the accuracy of the dual source model for Monte Carlo treatment planning dose calculations for the Cyberknife system.

Models, Theoretical↗

PubMed1990

Reproduction in the space environment: Part I. Animal reproductive studies.

Mankind's exploration and colonization of the frontier of space will ultimately depend on men's and women's ability to live, work, and reproduce in the space environment. This paper reviews animal studies, from microorganisms to mammals, done in space or under space-simulated conditions, which identify some of the key areas which might interfere with human reproductive physiology and/or embryonic development. Those space environmental factors which impacted almost all species included: microgravity, artificial gravity, radiation, and closed life support systems. These factors may act independently and in combination to produce their effects. To date, there have been no studies which have looked at the entire process of reproduction in any animal species. This type of investigation will be critical in understanding and preventing the problems which will affect human reproduction. Part II will discuss these problems directly as they relate to human physiology.

Animals↗

PubMed2001

Quantification of solute entry into cochlear perilymph through the round window membrane.

The administration of drugs to the inner ear via the round window membrane is becoming more widely used for both clinical and experimental purposes. The actual drug levels achieved in different regions of the inner ear by this method have not been established. The present study has made use of simulations of solute movements in the cochlear fluids to describe the distribution of a marker solute in the guinea pig cochlear fluid spaces. Simulation parameters were derived from experimental measurements using a marker ion, trimethylphenylammonium (TMPA). The distribution of this ion in the cochlea was monitored without volume disturbance using TMPA-selective microelectrodes sealed into the first and second turns of scala tympani (ST). TMPA was applied to perilymph by irrigation of the intact round window membrane with 2 mM solution. At the end of a 90 min application period, TMPA in the first turn, 1.4 mm from the base of ST, reached an average concentration of 330 microM (standard deviation (S.D.) 147 microM, n = 8). TMPA in the second turn, 7.5 mm from the base of ST reached a concentration of 15 microM (S.D. 33 microM, n = 5). The measured time courses of TMPA concentration change were interpreted using the Washington University Cochlear Fluids Simulator (V 1.4), a public-domain program available on the internet at http ://oto.wustl.edu/cochlea/. Simulations with parameters producing concentration time courses comparable to those measured were: (1) round window permeability: 1.9 x 10(-80 cm/s; (2) ST clearance half-time: 60 min; (3) longitudinal perilymph flow rate: 4.4 nl/min, directed from base to apex. Solute concentrations in apical regions of the cochlea were found to be determined primarily by the rate at which the solute diffuses, balanced by the rate of clearance of the solute from perilymph. Longitudinal perilymph flow was not an important factor in solute distribution unless the bony otic capsule was perforated, which rapidly caused substantial changes to solute distribution. This study demonstrates the basic processes by which substances are distributed in the cochlea and provides a foundation to understand how other applied substances will be distributed in the ear.

Animals↗

PubMedDate not supplied

[Biological research in space].

The paper presents the results of investigations carried out during the last two decades on various biological objects--microorganisms, plant seeds, insects, higher and lower plants, fish and amphibians--in real and simulation space flights. The paper discusses the current knowledge of the biological role of gravity and possible mechanisms of adaptation to weightlessness as well as the suitability of different biological objects for further space studies. Most experiments conducted in real space flights have lent support to the theoretical studies of the level and limits of weightlessness effects upon biological systems. Analysis of the data obtained in space and ground-bound experiments suggests that molecular processes are indifferent to an altered gravity and that energy metabolism plays an important role in adaptation of biological systems to zero-g.

Adaptation, Physiological↗

PubMed2004

Accurate Monte Carlo simulations for nozzle design, commissioning and quality assurance for a proton radiation therapy facility.

Monte Carlo dosimetry calculations are essential methods in radiation therapy. To take full advantage of this tool, the beam delivery system has to be simulated in detail and the initial beam parameters have to be known accurately. The modeling of the beam delivery system itself opens various areas where Monte Carlo calculations prove extremely helpful, such as for design and commissioning of a therapy facility as well as for quality assurance verification. The gantry treatment nozzles at the Northeast Proton Therapy Center (NPTC) at Massachusetts General Hospital (MGH) were modeled in detail using the GEANT4.5.2 Monte Carlo code. For this purpose, various novel solutions for simulating irregular shaped objects in the beam path, like contoured scatterers, patient apertures or patient compensators, were found. The four-dimensional, in time and space, simulation of moving parts, such as the modulator wheel, was implemented. Further, the appropriate physics models and cross sections for proton therapy applications were defined. We present comparisons between measured data and simulations. These show that by modeling the treatment nozzle with millimeter accuracy, it is possible to reproduce measured dose distributions with an accuracy in range and modulation width, in the case of a spread-out Bragg peak (SOBP), of better than 1 mm. The excellent agreement demonstrates that the simulations can even be used to generate beam data for commissioning treatment planning systems. The Monte Carlo nozzle model was used to study mechanical optimization in terms of scattered radiation and secondary radiation in the design of the nozzles. We present simulations on the neutron background. Further, the Monte Carlo calculations supported commissioning efforts in understanding the sensitivity of beam characteristics and how these influence the dose delivered. We present the sensitivity of dose distributions in water with respect to various beam parameters and geometrical misalignments. This allows the definition of tolerances for quality assurance and the design of quality assurance procedures.

Algorithms↗

PubMed1981

Survival of microorganisms in space: a review.

Spores of Bacillus subtilis were exposed to selected factors of space (vacuum, solar UV radiation, heavy ions of cosmic radiation), and their response was studied after recovery. These investigations were supplemented by ground-based studies under simulated space conditions. The vacuum of space did not inactivate the spores. However, vacuum-induced structural changes in the DNA, and probably in the proteins, caused a supersensitivity to solar UV radiation. This phenomenon is caused by the production of specific photoproducts in DNA and protein, which cannot be removed by normal cellular repair processes. In vegetative bacterial cells, exposed to vacuum, cell dehydration led to damage of the cell membrane, which could be partly repaired during subsequent incubation. The high local effectiveness of the cosmic heavy ions further decreases the chance that spores can survive for any length of time in space. Nonetheless, a spore travelling through space and protected from ultraviolet radiation could possibly survive an interplanetary journey. Such a situation favors panspermia as a possible explanation for the origin of life.

Bacillus subtilis↗

PubMed2000

A virtual source model for Monte Carlo modeling of arbitrary intensity distributions.

A photon virtual source model was developed for simulating arbitrary, external beam, intensity distributions using the Monte Carlo method. The source model consists of a photon fluence grid composed of a matrix of square elements, located 25-cm downstream from the linear accelerator target. Each particle originating from the fluence map is characterized by the seven phase space parameters, position (x, y, z), direction (u, v, w), and energy. The map was reconstructed from fluence and energy spectra acquired by modeling components of the linear accelerator treatment head using the Monte Carlo code MCNP4B. The effect of contaminant electrons is accounted for by the use of a sub-source derived from a phase-space simulation of a 25-MV linac treatment head using the code BEAM. The BEAM sub-source was incorporated into the MCNP4B phase-space model and is sampled using a field-size dependent sampling ratio. A Gaussian blurring kernel is convolved with the photon fluence map to account for the finite focal spot size and scattering effects from structures such as the flattening filter and MLC leaves. Depth dose and profile source calculations for 6-MV and 25-MV photon beams, for 5 x 5 cm2, 10 x 10 cm2, and 15 x 15 cm2 field sizes, are in good agreement with measurement and are well within acceptability criteria suggested by the AAPM Task Group Report No. 53. Irregular field calculations compared with film measurement and with a 3-D pencil beam algorithm show that the source model is capable of accurately simulating arbitrary MLC fields.

Biophysical Phenomena↗

PubMed2001

Control systems with stochastic feedback.

In this paper we use the analogy of Parrondo's games to design a second order switched mode circuit which is unstable in either mode but is stable when switched. We do not require any sophisticated control law. The circuit is stable, even if it is switched at random. We use a stochastic form of Lyapunov's second method to prove that the randomly switched system is stable with probability of one. Simulations show that the solution to the randomly switched system is very similar to the analytic solution for the time-averaged system. This is consistent with the standard techniques for switched state-space systems with periodic switching. We perform state-space simulations of our system, with a randomized discrete-time switching policy. We also examine the case where the control variable, the loop gain, is a continuous Gaussian random variable. This gives rise to a matrix stochastic differential equation (SDE). We know that, for a one-dimensional SDE, the difference between solution for the time averaged system and any given sample path for the SDE will be an appropriately scaled and conditioned version of Brownian motion. The simulations show that this is approximately true for the matrix SDE. We examine some numerical solutions to the matrix SDE in the time and frequency domains, for the case where the noise power is very small. We also perform some simulations, without analysis, for the same system with large amounts of noise. In this case, the solution is significantly shifted away from the solution for the time-averaged system. The Brownian motion terms dominate all other aspects of the solution. This gives rise to very erratic and "bursty" behavior. The stored energy in the system takes the form a logarithmic random walk. The simulations of our curious circuit suggest that it is possible to implement a control algorithm that actively uses noise, although too much noise eventually makes the system unusable. (c) 2001 American Institute of Physics.

Journal Article↗

PubMed2004

Feature activated molecular dynamics: an efficient approach for atomistic simulation of solid-state aggregation phenomena.

An efficient approach is presented for performing efficient molecular dynamics simulations of solute aggregation in crystalline solids. The method dynamically divides the total simulation space into "active" regions centered about each minority species, in which regular molecular dynamics is performed. The number, size, and shape of these regions is updated periodically based on the distribution of solute atoms within the overall simulation cell. The remainder of the system is essentially static except for periodic rescaling of the entire simulation cell in order to balance the pressure between the isolated molecular dynamics regions. The method is shown to be accurate and robust for the Environment-Dependant Interatomic Potential (EDIP) for silicon and an Embedded Atom Method potential (EAM) for copper. Several tests are performed beginning with the diffusion of a single vacancy all the way to large-scale simulations of vacancy clustering. In both material systems, the predicted evolutions agree closely with the results of standard molecular dynamics simulations. Computationally, the method is demonstrated to scale almost linearly with the concentration of solute atoms, but is essentially independent of the total system size. This scaling behavior allows for the full dynamical simulation of aggregation under conditions that are more experimentally realizable than would be possible with standard molecular dynamics.

Chemistry, Physical↗

PubMed2000

Can daily centrifugation prevent the haematocrit increase elicited by 6-degree, head-down tilt?

A measure to counteract the effects of low or zero gravity is required for long-term space flight, such as the manned Mars mission scheduled by the National Aeronautics and Space administration (NASA) for 2014. We conducted a series of centrifugation experiments with humans, using a short-arm centrifuge (radius 1.8 m, made by First Medical Co., Tokyo, Japan). We employed 6-degree, head-down tilt (HDT) for 4 days to simulate space flight. Ten healthy male volunteers underwent 4-day HDT and a 2-G daily centrifuge load for 60 min in the +Gz direction and measurements, such as haematocrit, 24-h urine volume, body weight and electrocardiogram (ECG) were made. There was no significant increase in the haematocrit during the HDT period, although our previous studies had shown a significant increase during HDT. A 60-min daily load of +2 Gz appears to be effective in reversing the haematocrit increase due to 4-day HDT.

Adult↗

PubMed2002

UV photochemistry of DNA in vitro and in Bacillus subtilis spores at earth-ambient and low atmospheric pressure: implications for spore survival on other planets or moons in the solar system.

Two major parameters influencing the survival of Bacillus subtilis spores in space and on bodies within the Solar System are UV radiation and vacuum, both of which induce inactivating damage to DNA. To date, however, spore survival and DNA photochemistry have been explored only at the extremes of Earth-normal atmospheric pressure (101.3 kPa) and at simulated space vacuum (10(-3)-10(-6) Pa). In this study, wild-type spores, mutant spores lacking alpha/beta-type small, acid-soluble spore proteins (SASP), naked DNA, and complexes between SASP SspC and DNA were exposed simultaneously to UV (254 nm) at intermediate pressure (1-2 Pa), and the UV photoproducts cis,syn-thymine-thymine cyclobutane dimer (c,sTT), trans,syn-thymine-thymine cyclobutane dimer (t,sTT), and "spore photoproduct" (SP) were quantified. At 101.3 kPa, UV-treated wild-type spores accumulated only SP, but spores treated with UV radiation at 1-2 Pa exhibited a spectrum of DNA damage similar to that of spores treated at 10(-6) Pa, with accumulation of SP, c,sTT, and t,sTT. The presence or absence of alpha/beta-type SASP in spores was partly responsible for the shift observed between levels of SP and c,sTT, but not t,sTT. The changes observed in spore DNA photochemistry at 1-2 Pa in vivo were not reproduced by irradiation of naked DNA or SspC:DNA complexes in vitro, suggesting that factors other than SASP are involved in spore DNA photochemistry at low pressure.

Atmospheric Pressure↗