Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Space Simulation”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the 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
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↗
PubMed1995

The feasibility of Doppler monitoring during EVA.

During extravehicular activities (EVA) outside the spacecraft, astronauts have to work under reduced pressure in a space suit. This pressure reduction induces the risk of decompression sickness (DCS) by the formation of gas bubbles from excess nitrogen dissolved in the organism by breathing air at normal pressure. Under laboratory conditions the gas bubbles moving in the blood stream can be detected by the non-invasive ultrasonic Doppler method. By early detection of excessive bubble formation the development of DCS symptoms may be prevented by early application of preventative measures. The method could also be useful when applied in the space suit in order to compare the results of laboratory tests with operational results, because there is a discrepancy according to the DCS risk of laboratory experiments and actual EVA missions, where no symptoms have been reported yet. A prototype Doppler sensor has been developed and implemented in the Russian Orlan suit. To investigate the feasibility of this method under simulated space conditions, the equipment has been used in a series of 12 thermovacuum chamber tests with suited subjects, where intravenous bubble formation was compared to unsuited control experiments. In more than 50% of the suited tests good Doppler recordings could be achieved. In some cases with unsatisfying results the signal could be improved by breathholding. Although the results do not yet allow any conclusion about a possible difference between suited and unsuited subjects due to the small number of tests performed, the method proved its feasibility for use in EVA suits and should be further developed to enhance the safety of EVA procedures.

Aerospace Medicine↗
PubMed1998

Evaluation of risk from space radiation with high-energy heavy ion beams.

The most challenging radiation in space consists of fully ionized atomic elements with high energy for which only the few lowest energy ions can be stopped in shielding materials. The health risk from exposure to these ions and their secondary radiations generated in shield materials is poorly understood since there are few human data and a systematic study in relevant animal model systems has not been made. The accuracy of risk prediction is described as the major limiting factor in the management of space radiation risk. The expected impact of systematic studies is examined using the limited available biological data and models. Given the limitations of current predictions, models must be developed that are able to incorporate the required fundamental scientific data into accurate risk estimates. The important radiation components that can be provided for laboratory testing are identified. The use of ground-based accelerator beams to simulate space radiation is explained and quantitative scientific constraints on such facilities are derived. Three facilities, one each in the United States, in Germany and in Japan, currently have the partial capability to satisfy these constraints. A facility has been proposed using the Brookhaven National Laboratory Booster Synchrotron in the United States; in conjuction with other on-site accelerators, it will be able to provide the full range of heavy ion beams and energies required.

Aerospace Medicine↗
PubMed2002

Outbreak of head pediculosis during SFINCSS-99 isolation experiment.

This short case report presents the development and treatment of a head lice outbreak during a space simulation experiment. The confinement experiment was conducted from July 1999 to March 2000 at the State Research Center of the Russian Federation Institute for Biomedical Problems in Moscow. Following a symptom period of up to 9 wk before diagnosis and treatment, 3 wk of treatment were required to remove all nits from those infected. Recommendations are made with regard to prevention of such infections during space missions. Treatment altered performance and comfort of crews, took time out of other duties, and even affected relations between crewmembers. The case is made for the development of a public health agenda in space research and medical space programs.

Adult↗
PubMed1993

[Dielectric behavior of isolated rat submandibular glands: simulation with a vesicle-inclusion cell model].

In an attempt to correlate the passive electrical properties of the secretory tissue with its structure, I measured AC admittances for isolated rat submandibular glands, over the frequency range between 100 Hz and 500 MHz. Animals were divided into three groups: control and treatment with two different secretagogues, isoproterenol and pilocarpine. Dielectric dispersions observed from control glands had two characteristic frequencies at 2.6 kHz and 59 kHz; the former was of the alpha-type and the latter of the beta-type. Secretagogue-stimulated glands exhibited broader beta-dispersion curves. These dispersion data were analysed on the basis of a "two-shell model" with vesicle inclusions, in which two concentric shells represent the cell membrane and the nuclear envelope, and membrane-bounded vesicles are meant for secretory granules dispersed in the inter-shell space. Simulation by this model generated a good fit to data from the three groups. The analyses revealed that: (i) electric capacities for the cell and granular membranes were 2.1 and 0.9 microF/cm2, respectively; (ii) the conductivity of extracellular matrix was close to that of blood plasma; (iii) the conductivity ratio between cytoplasm and extracellular matrix was approx. 0.4; and (iv) the conductivity ratio between intragranular space and cytoplasm was approx. 0.7.

Animals↗
PubMedDate not supplied

High speed electrophoresis simulation for optimization of continuous flow electrophoresis and high performance capillary techniques: Part I. Computer model.

A computer program for high-speed simulation and optimization of electrophoretic processes has been developed for carrier-free systems of all kinds. The calculations are based on the one-dimensional dynamic (transient-state) model. The three-dimensional geometry of the simulation space can be chosen deliberately. With a highly efficient transport algorithm instead of complicated integration schemes for the transport equations, the calculation time can be effectively spent on various important parameters such as ionic strength, temperature, Joule heat, activity coefficients and concentration changes due to membranes. The parameter set of any carrier free electrophoretic method (i.e., continuous-flow electrophoresis, capillary isotachophoresis and high performance capillary zone electrophoresis) can be imported directly into the computer program by means of a graphic user interface. The program performs overnight-simulation of any electrophoretic system containing up to 15 components.

Computer Simulation↗
PubMed1999

Hormonal changes in humans during spaceflight.

Readers of this review may feel that there is much more that we do not know about space endocrinology than what we know. Several reasons for this state of affairs have been given: 1. the complexity of the field of endocrinology with its still increasing number of known hormones, releasing factors and precursors, and of the interactions between them through various feedback mechanisms 2. the difficulty in separating the microgravity effects from the effects of stress from launch, isolation and confinement during flight, reentry, and postflight re-adaptation 3. the experimental limitations during flight, such as limited number of subjects, limited number of samples, impossibility of collecting triple samples for pulsatile hormones like growth hormone 4. the disturbing effects of countermeasures used by astronauts 5. the inadequacy of postflight samples for conclusions about inflight values 6. limitations of conclusions from animal experiments and space simulation studies The endocrinology field is divided in to nine systems or axes, which are successively reviewed: 1. Rapid bone demineralization in the early phase of spaceflight that, when unopposed, leads to catastrophic effects after three months but that slows down later. The endocrine mechanism, apart from the effect of exercise as a countermeasure, is not yet understood. 2. The hypothalamic-pituitary-adrenal axis is involved in stress reactions, which complicate our understanding and makes postflight analysis dubious. 3. In the hypothalamic-pituitary-gonadal axis, pulsatility poses a problem for obtaining representative values (e.g., for luteinizing hormone). Reproduction of rats in space is possible, but much more needs to be known about this aspect, particularly in women, before the advent of space colonies, but also in males because some evidence for reversible testicular dysfunction in space has been found. 4. The hypothalamic-pituitary-somato-mammotrophic axis involves prolactin and growth hormone. The latter also acts as a stress hormone and its secretion is greatly decreased in spaceflown rats, but not in astronauts, which may be due to differences in the regulation of growth hormone secretion between rats and humans. 5. The hypothalamic-pituitary-thyroid axis involves the thyroid hormones thyroxine and triiodothyronine, which are lowered in space, suggesting mild hypothyroidism. 6. The renin-angiotensin-aldosterone axis, which regulates water and electrolytes, involves antidiuretic hormone and two natriuretic peptides and shows paradoxical behavior in space. 7. Erythrocyte mass regulation involves erythropoietin, and space anemia is still not explained. 8. The endocrine pancreas involves insulin and glucagon, with loss of insulin sensitivity in space due to lack of exercise, which phenomenon requires more study before the advent of space colonies. 9. The sympathetic system acts through epinephrine, norepinephrine and dopamine and seems to have an increased activity in space in contrast to what had been widely believed. From the foregoing conclusions, it is clear that much further study is needed in all fields of space endocrinology. On the other hand, future studies will allow us to understand what happens in a given endocrine subsystem in the absence of the "gravity factor", the perturbing factor to which the human race has become adapted through thousands of years of evolution. This should provide us with a fuller understanding of the internal homeostatic mechanisms. An important point is that some endocrine systems seem to undergo changes in space that resemble those observed during senescence, but after spaceflight, recovery always occurs within weeks or months after return. This is particularly true for the systems regulating bone and muscle metabolism and reproduction, exactly as happens with the immune, neurosensory, and cardiovascular systems. Further space research may help us find new insights in the pathophysiology of aging and hopefully define novel prev

Animals↗
PubMed1993

[Human gas and energy exchange in space flight and simulation research].

Human gas-energy exchange under extreme conditions is considered in the above work. Major attention is given to energy exchange and external respiration of humans in space flight, as well as in the models of space vehicles and during simulation of physiological effects of weightlessness.

Energy Metabolism↗
PubMed1994

Simulation of exchanges of multiple gases in bubbles in the body.

This communication introduces a system of equations, for numerical solution, which simulates the generation, growth, and decay of bubbles. The system is an advance over previous works because it allows for simultaneous diffusion of any number of gases. Our purpose for developing the system is to gain insight into the bubbles that occur in the body in decompression sickness (DCS). We validate the calculation system by matching observed data of DCS bubbles and of large subcutaneous gas pockets in rats. We demonstrate how a temporary supersaturation and bubble formation can occur without change of ambient pressure when there is a change in the inert gas being breathed. With exposures to hypobaric environments, such as when astronauts work in space, simulations show that O2, CO2, and water vapor add appreciably to volume of bubbles and affect the diffusion of inert gas.

Atmospheric Pressure↗
PubMed1985

Space flight visual simulation.

In this paper, based on the scenes of stars seen by astronauts in their orbital flights, we have studied the mathematical model which must be constructed for CGI system to realize the space flight visual simulation. Considering such factors as the revolution and rotation of the Earth, exact date, time and site of orbital injection of the spacecraft, as well as its orbital flight and attitude motion, etc., we first defined all the instantaneous lines of sight and visual fields of astronauts in space. Then, through a series of coordinate transforms, the pictures of the scenes of stars changing with time-space were photographed one by one mathematically. In the procedure, we have designed a method of three-times "mathematical cutting." Finally, we obtained each instantaneous picture of the scenes of stars observed by astronauts through the window of the cockpit. Also, the dynamic conditions shaded by the Earth in the varying pictures of scenes of stars could be displayed.

Astronauts↗
PubMed2000

Cancer incidence for Swedish twins studied by means of bivariate frailty models.

Cancer incidence rates for Swedish twins born between 1928 and 1965 and who both were alive at age 30 are studied by means of bivariate frailty models. Altogether, 7,280 fraternal (DZ) and 4,699 identical (MZ) twin pairs were followed up through December 31, 1995, for cancer status. The association between cancer incidence rates was statistically greater among the MZ than among the DZ pairs and stronger between women than between men; however, the magnitude of this association is relatively small and decreases over time. The relative decrease in dependency (association) is most easily detected using shared frailty models but may also be demonstrated, at least for women, using correlated frailty models. We also demonstrate that estimates of the correlation coefficient are similar when using any correlated frailty models derived from the power variance family but that these estimates disagree regarding the age at which the dependence is most important. The relative importance of dependence across age may sometimes be more interesting than the correlation coefficient itself. The latter may usually be estimated using alternative methods. Furthermore, when estimating correlation coefficients close to the boundary of the parameter space, simulation studies indicate that the correlated inverse Gaussian frailty model is more robust than the gamma frailty model.

Adult↗
PubMed1999

Anomalous rotational resonance spectra in magic-angle spinning NMR.

Magic-angle spinning NMR spectra of samples containing dilute spin-1/2 pairs display broadenings or splittings when a rotational resonance condition is satisfied, meaning that a small integer multiple of the spinning frequency matches the difference in the two isotropic shift frequencies. We show experimental rotational resonance NMR spectra of a 13C2-labeled retinal which are in qualitative disagreement with existing theory. We propose an explanation of these anomalous rotational spectra involving residual heteronuclear couplings between the 13C nuclei and the neighboring 1H nuclei. These couplings strongly influence the rotational resonance 13C spectrum, despite the presence of a strong radiofrequency decoupling field at the 1H Larmor frequency. We model the residual heteronuclear couplings by differential transverse relaxation of the 13C single-quantum coherences. We present a superoperator theory of the phenomenon and describe a numerical algorithm for rapid Liouville space simulations in periodic systems. Good agreement with experimental results is obtained by using a biexponential transverse relaxation model for each spin site.

Magnetic Resonance Spectroscopy↗
PubMed1998

Model Analysis of Spatial Patterns in Mountain Pine Beetle Outbreaks.

The mountain pine beetle [MPB, Dendroctonus ponderosae Hopkins (Coleoptera: Scolytidae)] is an aggressive bark beetle, one that typically needs to kill host trees in order to successfully reproduce. This ecological adaptation has resulted in an organism that is both economically important and ecologically significant. Even though significant resources have been expended on MPB research, and a great deal of knowledge exists regarding individual aspects of MPB ecology, some of the most basic questions regarding outbreaks remain unanswered. In our opinion, one reason for the lack of synthesis and predictive power is the inadequate treatment of spatial dynamics in outbreak theories. This paper explicitly addresses the role of spatial dynamics in the precipitation and propagation of MPB outbreaks. We first describe a spatially dynamic model of the MPB/forest interaction that includes chemical ecology, spatial redistribution of beetles, attack, and resulting host mortality. The model is a system of 6 coupled, partial differential equations with 7 state variables and 20 parameters. It represents an attempt to capture the relatively complex predator/prey interaction between MPB and host trees by including the minimum phenomenological descriptions necessary for ecological credibility. This system of equations describes the temporal dynamics of: beetle attraction as a function of pheromone concentration; the change in numbers of flying and nesting beetles; tree resistance/susceptibility; and tree recovery from attack. Spatial dynamics are modeled by fluxes due to gradients in pheromones and kairomones, and the random redistribution of beetles in absence of semiochemicals. We then use the parameterized model to explore three issues central to the ecology of MPB/forest interaction. The first of these is in response to the need for objective ways to compare patterns of successful beetle attacks as they evolve in space. Simulation results indicate that at endemic levels, the pattern of successful attacks are determined almost exclusively by the underlying distribution of susceptible host trees (environmental determinism). As an outbreak develops, the pattern of successfully attacked trees switches to one that is dynamically driven by the self-generated semiochemical landscape (dynamic determinism). This switch from an environmentally determined spatial pattern to a dynamically driven pattern is the hallmark of an outbreak. We discuss the application of a spatial correlation coefficient that can be used to differentiate between the spatial distribution of killed trees in endemic and outbreak phases. The second issue we address through simulation is synchrony in adult emergence. Synchronous adult emergence is critical for the mass attack strategy necessary for overcoming tree defenses. Results from these simulations indicate that the degree of synchrony in adult emergence can have important consequences for assessing the risk of an outbreak. The final issue we investigate through simulation is the effect of spatial pattern of nurse trees (those successfully attacked the previous year) on outbreak potential. Simulations indicated that the spatial proximity of nurse trees was an important determinant of subsequent successful attacks. We conclude with a discussion of the general implications of our simulation experiments. Copyright 1998 Academic Press.

Journal Article↗
PubMed1996

Response of Bacillus subtilis spores to dehydration and UV irradiation at extremely low temperatures.

Spores of Bacillus subtilis have been exposed to the conditions of extreme dehydration (argon/silica gel; simulated space vacuum) for up to 12 weeks at 298 K and 80 K in the dark. The inactivation has been correlated with the production of DNA-double strand-breaks. The temperature-dependence of the rate constants for inactivation or production of DNA-double strand-breaks is surprisingly low. Controls kept in the frozen state at 250 K for the same period of time showed no sign of deterioration. In another series of experiments the spores have been UV irradiated (253.7 nm) at 298 K, 200 K and 80 K after exposure to dehydrating conditions for 3 days. Fluence-effect relationships for inactivation, production of DNA-double strand-breaks and DNA-protein cross-links are presented. The corresponding F37-values for inactivation and production of DNA lesions are significantly increased only at 80 K (factor of 4 to 5). The data indicate that the low temperatures that prevail in the outer parts of the Solar System or at the nightside of Mars or the Moon are not sufficiently low to crucially inhibit inactivation by dehydration. Our data place further constraints on the panspermia hypothesis.

Bacillus subtilis↗
PubMed1994

EVA design: lessons learned.

Extravehicular Activities (EVAs) are very demanding and specialized space flight activities. There are many aspects to consider in the design of hardware, tools, and procedures to be used on an EVA mission. To help minimize costs and optimize the EVA productivity, experience shows that astronauts should become involved early in the design process.

Astronauts↗
PubMed1994

EVA: European plans.

The current status of European EVA (extravehicular activity) plans is reviewed. The major difference to already existing EVA scenarios in U.S.A. and Soviet Union consists in the adoption of a higher suit pressure, namely 500 hPa. The results of a study concerned with the physiological consequences of this adoption are presented, including recommendations for protective procedures and their necessary experimental validation. A certain discrepancy between laboratory experimental decompression data and EVA operational results is discussed, leading to the identification of several items which may influence space decompression. Microgravity and the influence of the space suit itself are most likely factors in the explanation of this discrepancy, and both experimental procedures and technological developments are proposed to clarify their role for the future design of EVA procedures.

Aerospace Medicine↗
PubMed1995

EVA-related activities in Japan.

Recognizing the importance and fertility of the extra vehicular activity technologies in future space development and utilization, some related research activities have been conducted in Japan, though it has not committed itself to developing its own manned space flight capability. The purpose of this paper is to introduce and evaluate these EVA-related activities and to indicate the next step for Japan to get into the era of manned space activities including EVA in reality.

Carbon Dioxide↗