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.

SourceResearch connectionFrom yearThrough year

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

At least 379 records · Page 21Linked to original sources

PubMed1994

Methods for measurement and control of leakage in CELSS and their application and performance in the Biosphere 2 facility.

Atmospheric leakage between a CELSS and its surround is driven by the differential pressure between the two. In an earth-based CELSS, both negative and positive differential pressures of atmosphere are created as the resultant of three influences: thermal expansion/contraction, transition of water between liquid and vapor phases, and external barometric pressure variations. The resultant may typically be on the order of 5000 pascals. By providing a flexible expansion chamber, the differential pressure range can be reduced two, or even three, orders of magnitude, which correspondingly reduces the leakage. The expansion chamber itself can also be used to measure the leak rate. Independent confirmation is possible by measurement of the progressive dilution of a trace gas. These methods as employed at the Biosphere 2 facility have resulted in an estimated atmospheric leak rate of less than 10 percent per year.

Air Conditioning↗

PubMed1995

Principles of protein folding--a perspective from simple exact models.

General principles of protein structure, stability, and folding kinetics have recently been explored in computer simulations of simple exact lattice models. These models represent protein chains at a rudimentary level, but they involve few parameters, approximations, or implicit biases, and they allow complete explorations of conformational and sequence spaces. Such simulations have resulted in testable predictions that are sometimes unanticipated: The folding code is mainly binary and delocalized throughout the amino acid sequence. The secondary and tertiary structures of a protein are specified mainly by the sequence of polar and nonpolar monomers. More specific interactions may refine the structure, rather than dominate the folding code. Simple exact models can account for the properties that characterize protein folding: two-state cooperativity, secondary and tertiary structures, and multistage folding kinetics--fast hydrophobic collapse followed by slower annealing. These studies suggest the possibility of creating "foldable" chain molecules other than proteins. The encoding of a unique compact chain conformation may not require amino acids; it may require only the ability to synthesize specific monomer sequences in which at least one monomer type is solvent-averse.

Amino Acid Sequence↗

PubMed2003

[Physical simulation of human body metabolism in sealed module on the ground].

OBJECTIVE: To provide a test platform for experimental verification of environmental control and life support system (ECLSS) of manned spacecraft on the ground. METHOD: According to characters of ECLSS ground simulation test, simulation of human body metabolism was divided into different units, and a ground metabolic simulator was designed. RESULT: The ground metabolic simulator accurately simulated human body metabolic oxygen consumption, carbon dioxide production, water and heat productions in the sealed module. CONCLUSION: The physical method for simulating human body metabolism is feasible and has the advantages of high precision and easiness of control. It can be used for verifying and appraising the function of ECLSS.

Carbon Dioxide↗

PubMed1991

Changes in body fluid compartments during a 28-day bed rest.

The extravascular fluid responses to real or simulated space-flight are not well-documented. In this study serial isotope measurements were used to obtain measurements of the body fluid responses of 10 22-29-year-old men during 28 d of simulated microgravity (bed rest). The subjects were maintained on a controlled metabolic diet for 7 d before the study, during 14 d of ambulatory control, 28 d of horizontal bed rest, and 14 d of ambulant recovery. Fluid compartments were measured on control days 1 and 9, bed rest days 2, 14, and 28, and recovery days 7 and 14. By day 2 of bed rest, plasma volume (PV) and extra-cellular volume (ECV) decreased significantly by an average 209 and 533 ml, respectively. Red cell volume (RCV) and total body water (TBW) decreased more slowly, with average losses of 128 and 1,316 ml, respectively, after 28 d of bed rest. Early in the bed rest, TBW loss was mostly from the ECV. Thereafter, the TBW deficit was derived from the intracellular compartment, which decreased an average of 838 ml after 28 d. These results suggest losses from all fluid compartments during bed rest, with no evidence of restoration of ECV after 1-2 weeks.

Adult↗

PubMed2005

Circadian rhythms, sleep, and performance in space.

Maintaining optimal alertness and neurobehavioral functioning during space operations is critical to enable the National Aeronautics and Space Administration's (NASA's) vision "to extend humanity's reach to the Moon, Mars and beyond" to become a reality. Field data have demonstrated that sleep times and performance of crewmembers can be compromised by extended duty days, irregular work schedules, high workload, and varying environmental factors. This paper documents evidence of significant sleep loss and disruption of circadian rhythms in astronauts and associated performance decrements during several space missions, which demonstrates the need to develop effective countermeasures. Both sleep and circadian disruptions have been identified in the Behavioral Health and Performance (BH&P) area and the Advanced Human Support Technology (AHST) area of NASA's Bioastronautics Critical Path Roadmap. Such disruptions could have serious consequences on the effectiveness, health, and safety of astronaut crews, thus reducing the safety margin and increasing the chances of an accident or incident. These decrements oftentimes can be difficult to detect and counter effectively in restrictive operational environments. NASA is focusing research on the development of optimal sleep/wake schedules and countermeasure timing and application to help mitigate the cumulative effects of sleep and circadian disruption and enhance operational performance. Investing research in humans is one of NASA's building blocks that will allow for both short- and long-duration space missions and help NASA in developing approaches to manage and overcome the human limitations of space travel. In addition to reviewing the current state of knowledge concerning sleep and circadian disruptions during space operations, this paper provides an overview of NASA's broad research goals. Also, NASA-funded research, designed to evaluate the relationships between sleep quality, circadian rhythm stability, and performance proficiency in both ground-based simulations and space mission studies, as described in the 2003 NASA Task Book, will be reviewed.

Adaptation, Physiological↗

PubMed1975

Traumatic pericardial hematoma simulating tricuspid valve obstruction.

A large pericardial hematoma caused profound hypoxia, cyanosis, and hypotension in a patient who had sustained trauma in an automobile accident. Angiographic and cardiac catheterization findings suggested intracardiac obstruction at the level of the tricuspid valve. This case emphasizes that localized accumulations of blood or fluid within the pericardial space can simulate intracardiac masses or valve obstruction. Partial pericardiectomy was curative in this patient.

Accidents, Traffic↗

PubMedDate not supplied

The effects of background noise on cognitive performance during a 70 hour simulation of conditions aboard the International Space Station.

A total of twenty-five subjects were cloistered for a period of 70 hours, five at a time, in a hyperbaric chamber modified to simulate the conditions aboard the International Space Station (ISS). A recording of 72 dBA background noise from the ISS service module was used to simulate noise conditions on the ISS. Two groups experienced the background noise throughout the experiment, two other groups experienced the noise only during the day, and one control group was cloistered in a quiet environment. All subjects completed a battery of cognitive tests nine times throughout the experiment. The data showed little or no effect of noise on reasoning, perceptual decision-making, memory, vigilance, mood, or subjective indices of fatigue. Our results suggest that the level of noise on the space station should not affect cognitive performance, at least over a period of several days.

Adult↗

PubMed1997

Gramicidin S production by Bacillus brevis in simulated microgravity.

In a continuing study of microbial secondary metabolism in simulated microgravity, we have examined gramicidin S (GS) production by Bacillus brevis strain Nagano in NASA High Aspect Rotating Vessels (HARVs), which are designed to simulate some aspects of microgravity. Growth and GS production were found to occur under simulated microgravity. When performance under simulated microgravity was compared with that under normal gravity conditions in the bioreactors, GS production was found to be unaffected by simulated microgravity. The repressive effect of glycerol in flask fermentations was not observed in the HARV. Thus the negative effect of glycerol on specific GS formation is dependent on shear and/or vessel geometry, not gravity.

Anti-Bacterial Agents↗

PubMed2002

Hierarchy of simulation models in predicting structure and energetics of the Src SH2 domain binding to tyrosyl phosphopeptides.

Structure and energetics of the Src Src Homology 2 (SH2) domain binding with the recognition phosphopeptide pYEEI and its mutants are studied by a hierarchical computational approach. The proposed structure prediction strategy includes equilibrium sampling of the peptide conformational space by simulated tempering dynamics with the simplified, knowledge-based energy function, followed by structural clustering of the resulting conformations and binding free energy evaluation of a single representative from each cluster, a cluster center. This protocol is robust in rapid screening of low-energy conformations and recovers the crystal structure of the pYEEI peptide. Thermodynamics of the peptide-SH2 domain binding is analyzed by computing the average energy contributions over conformations from the clusters, structurally similar to the predicted peptide bound structure. Using this approach, the binding thermodynamics for a panel of studied peptides is predicted in a better agreement with the experiment than previously suggested models. However, the overall correlation between computed and experimental binding affinity remains rather modest. The results of this study show that small differences in binding free energies between the Ala and Gly mutants of the pYEEI peptide are considerably more difficult to predict than the structure of the bound peptides, indicating that accurate computational prediction of binding affinities still remains a major methodological and technical challenge.

Crystallography, X-Ray↗

PubMed2003

Ensemble averaging and multiple statistical testing of EMG activities of cyclically repeated body motions. A tool for muscle function analysis in experimental and clinical orthopaedics.

Coupled with suitable computerized signal recording and processing methods surface electromyography can be a powerful tool for the analysis of muscle activity in specific body movements. It can be used for this purpose in experimental and in clinical diagnostic orthopaedics as well as in physiotherapy. We describe in this paper a motion analysis system comprising this feature. It has been employed for the diagnosis of the basic angular kinematics and muscle function in human gait and other cyclically repeatable movements of the human locomotive system. Changes in the temporal characteristics of the movements and the muscle activity due to changed physical or experimental conditions can be systematically investigated this way. Such changes can be the result of surgical and/or conservative orthopaedic therapy, a long term physiotherapeutic program, or modified walking conditions as in experimental orthopaedics. They are displayed and validated by signal ensemble averaging and subsequent multiple statistical testing (e.g. by a suitably adapted Bonferroni criterion). The efficiency of the system is demonstrated by an exemplary gait analysis of selected kinematic and muscular effects caused by an experimental simulation of a leg length inequality.

Algorithms↗

PubMed1993

Alterations of body temperature, feeding, drinking, and sleep-wake circadian rhythms in Rhesus monkey during a 19 day Spacelab flight simulation.

Previous experiments performed with mammals during spaceflight suggest that microgravity may affect the circadian timekeeping system. However, this system could also be influenced by other factors related to the spaceflight environment, such as the animal compartment. The Rhesus project is a joint program of C.N.E.S. and N.A.S.A in which investigators in various disciplines of physiology will take advantage of flights of the Spacelab to study problems that interest them, using the Rhesus monkey as animal model. The technical characteristics of the Rhesus Research Facility in the Spacelab have been described elsewhere. In order to clarify the influence of the spaceflight environment, other than microgravity itself, on the circadian timekeeping system, we evaluated the characteristics of the circadian rhythms of body temperature, food and water intake, and sleep-wake cycles in Rhesus monkeys during the first 19-day flight simulation of this project.

Animals↗

PubMed2001

Large-size space laboratory for biological orbit experiments.

The study of space factors on living systems has great interest and long-term experiments during orbital flight will be important tool for increasing our knowledge. Realization of such experiments is limited by constraints of modern space stations. A new technology of large-size space laboratory for biological experiments has been developed on the basis of polymerization techniques. Using this technique there are no limits of form and size of laboratory for a space station that will permit long term experiments on Earth orbit with plants and animals in sufficient volume for creation of closed self-regulating ecological systems. The technology is based on experiments of the behavior of polymer materials in simulated free space conditions during the reaction of polymerization. The influences of space vacuum, sharp temperature changes and space plasma generated by galactic rays and Sun irradiation on chemical reaction were evaluated in their impact on liquid organic materials in laboratory conditions. The results of our study shows, that the chemical reaction is sensitive to such space factors. But we believe that the technology of polymerization could be used for the creation of space biological laboratories in Earth orbit in the near future.

Cosmic Radiation↗

PubMed2005

Structure determination of the 1/1 alpha/beta mixed lactose by X-ray powder diffraction.

The mixed form of alpha/beta lactose was obtained by heating amorphous alpha-lactose at 443 K. NMR spectroscopy determined the stoichiometry of this mixed compound to be 1/1. The X-ray powder diffraction pattern was recorded at room temperature with a sensitive curved detector (CPS 120). The structure was solved by real-space methods (simulated annealing) followed by Rietveld refinements with soft constraints on bond lengths and bond angles. The H atoms of the hydroxyl groups were localized by minimization of the crystalline energy. The cell of 1/1 alpha/beta lactose is triclinic with the space group P1 and contains two molecules (one molecule of each anomer). The crystalline cohesion is achieved by networks of O-H...O hydrogen bonds. The width of the Bragg peaks is interpreted through a microstructural approach in terms of isotropic strain effects and anisotropic size effects.

Carbohydrate Conformation↗

PubMed1984

A model for the distribution and clearance of inert substances in subcutaneous tissue.

The subcutaneous space has received attention in recent years as a route for the continuous administration of drugs and implantation of drug delivery systems. Yet little work has been devoted to an examination of the mass transport (distribution) of drugs in the subcutaneous space and the factors that influence their rate of clearance. A mathematical model is developed to describe the spreading and resorption of substances infused into the subcutaneous space. It simulates radial diffusion and flow in the direction of spreading as well as lateral convection into the systemic circulation. An analytic solution is obtained for the distribution of the substance as a function of time and position in the subcutaneous space. Two independent parameters, v (Péclét no.) and H (generalized Biot no.), are found to control the transport. Examples are presented to illustrate the effects of these parameters on the distribution of substances in the subcutaneous space.

Absorption↗

PubMed1998

Swimming kinematics and respiratory behaviour of xenopus laevis larvae raised in altered gravity

We examined the respiratory behaviours and swimming kinematics of Xenopus laevis tadpoles hatched in microgravity (Space Shuttle), simulated microgravity (clinostat) and hypergravity (3 g centrifuge). All observations were made in the normal 1 g environment. Previous research has shown that X. laevis raised in microgravity exhibit abnormalities in their lungs and vestibular system upon return to 1 g. The tadpoles raised in true microgravity exhibited a significantly lower tailbeat frequency than onboard 1 g centrifuge controls on the day of landing (day0), but this behaviour normalized within 9 days. The two groups did not differ significantly in buccal pumping rates. Altered buoyancy in the space-flight microgravity tadpoles was indicated by an increased swimming angle on the day after landing (day1). Tadpoles raised in simulated microgravity differed to a greater extent in swimming behaviours from their 1 g controls. The tadpoles raised in hypergravity showed no substantive effects on the development of swimming or respiratory behaviours, except swimming angle. Together, these results show that microgravity has a transient effect on the development of locomotion in X. laevis tadpoles, most notably on swimming angle, indicative of stunted lung development. On the basis of the behaviours we studied, there is no indication of neuromuscular retardation in amphibians associated with embryogenesis in microgravity.

Journal Article↗

PubMed2001

Myelin as longitudinal conductor: a multi-layered model of the myelinated human motor nerve fibre.

The myelin sheath is normally regarded as an electrical insulator. Low values of radial conductance and capacitance have been measured, and in electrical models of myelinated axons the contribution of longitudinal conduction within the sheath has been ignored. According to X-ray diffraction studies, however, myelin sheaths comprise alternate lipid and aqueous layers, and the latter may be expected to have a low resistivity. We propose a new model of myelinated axons in which the aqueous layers within the myelin provide appreciable longitudinal and radial conductance, the latter via a spiral pathway. We have investigated the likely contribution of these conductive paths within the myelin to the electrical properties of a human motor nerve fibre by computer simulation, representing the myelin sheath as a series of interconnecting parallel lamellae. With this new model, action potential conduction has been simulated along a 20-node cable, and the electrotonic responses to 100-ms depolarizing and hyperpolarizing current pulses have been simulated for a uniformly polarized fibre. We have found that the hypothesis of a longitudinally conducting myelin sheath improves our previous model in two ways: it is no longer necessary to make implausible assumptions about the resistivity or width of the periaxonal space to simulate realistic electrotonus, and the conduction velocity is appreciably faster (by 8.6%).

Electric Conductivity↗

PubMed2005

Space as the final frontier in stochastic simulations of biological systems.

Recent technological and theoretical advances are only now allowing the simulation of detailed kinetic models of biological systems that reflect the stochastic movement and reactivity of individual molecules within cellular compartments. The behavior of many systems could not be properly understood without this level of resolution, opening up new perspectives of using computer simulations to accelerate biological research. We review the modeling methodology applied to stochastic spatial models, also to the attention of non-expert potential users. Modeling choices, current limitations and perspectives of improvement of current general-purpose modeling/simulation platforms for biological systems are discussed.

Animals↗

PubMedDate not supplied

Effect of intracellular unstirred layer on apparent reflection coefficient for urea in inner medullary collecting duct: a computer simulation.

In the vasopressin-stimulated inner medullary collecting duct (IMCD), urea is transported through a pathway which is distinct from a water channel. Therefore, no frictional interaction between urea and water should occur at the membrane level, and the reflection coefficient for urea must be close to unity. However, the presence of unstirred layers in the vicinity of membranes causes solute concentration polarization, leading to an underestimation of the reflection coefficient (apparent reflection coefficient). When the value is determined across the perfused renal tubular wall, the intracellular space also constitutes an unstirred layer. The profile of solute and water transport across the system consisting of two membranes and the interposed intracellular space was simulated by a computer to examine the effect of unstirred layer on the value of apparent reflection coefficient. The model demonstrated that the imposed osmotic gradient across the tubular epithelial is decreased at each membrane interface. Under conditions of minimal unstirred layers in the bathing fluid, the existence of the intracellular constraints to diffusion cause considerable underestimation of the reflection coefficient. The higher the membrane permeability of urea and the smaller the diffusion coefficient of urea in the intracellular space, the greater becomes the magnitude of the underestimation. Thus, the measured apparent reflection coefficient for urea may become significantly less than the estimated value, leading to a reduction of the effective transmural osmotic driving force.

Animals↗