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PubMed2005

[Malfunction simulation by spaceflight training simulator].

OBJECTIVE: To implement malfunction simulation in spaceflight training simulator. METHOD: The principle of malfunction simulation was defined according to spacecraft malfunction predict and its countermeasures. The malfunction patterns were classified, and malfunction type was confirmed. A malfunction simulation model was established, and the malfunction simulation was realized by math simulation. RESULT: According to the requirement of astronaut training, a spacecraft subsystem malfunction simulation model was established and realized, such as environment control and life support, GNC, push, power supply, heat control, data management, measure control and communication, structure and so on. CONCLUSION: The malfunction simulation function implemented in the spaceflight training simulator satisfied the requirements for astronaut training.

Accidents, Aviation↗
PubMed2006

Worm algorithm and diagrammatic Monte Carlo: a new approach to continuous-space path integral Monte Carlo simulations.

A detailed description is provided of a new worm algorithm, enabling the accurate computation of thermodynamic properties of quantum many-body systems in continuous space, at finite temperature. The algorithm is formulated within the general path integral Monte Carlo (PIMC) scheme, but also allows one to perform quantum simulations in the grand canonical ensemble, as well as to compute off-diagonal imaginary-time correlation functions, such as the Matsubara Green function, simultaneously with diagonal observables. Another important innovation consists of the expansion of the attractive part of the pairwise potential energy into elementary (diagrammatic) contributions, which are then statistically sampled. This affords a complete microscopic account of the long-range part of the potential energy, while keeping the computational complexity of all updates independent of the size of the simulated system. The computational scheme allows for efficient calculations of the superfluid fraction and off-diagonal correlations in space-time, for system sizes which are orders of magnitude larger than those accessible to conventional PIMC. We present illustrative results for the superfluid transition in bulk liquid 4He in two and three dimensions, as well as the calculation of the chemical potential of hcp 4He.

Journal Article↗
PubMed2004

Theoretical simulation of K(+)-based mechanisms for regulation of capillary perfusion in skeletal muscle.

Muscle fibers release K(+) into the interstitial space upon recruitment. Increased local interstitial K(+) concentration ([K(+)]) can cause dilation of terminal arterioles, leading to perfusion of downstream capillaries. The possibility that capillary perfusion can be regulated by vascular responses to [K(+)] was examined using a theoretical model. The model takes into account the spatial relationship between functional units of muscle fiber recruitment and capillary perfusion. Diffusion of K(+) in the interstitial space was simulated. Two hypothetical mechanisms for vascular sensing of interstitial [K(+)] were considered: direct sensing by arterioles and sensing by capillaries with stimulation of feeding arterioles via conducted responses. Control by arteriolar sensing led to poor tissue oxygenation at high levels of muscle activation. With control by capillary sensing, increases in perfusion matched increases in oxygen demand. The time course of perfusion after sudden muscle activation was considered. Predicted capillary perfusion increased rapidly within the first 5 s of muscle fiber activation. The reuptake of K(+) by muscle fibers had a minor effect on the increase of interstitial [K(+)]. Uptake by perfused capillaries was primarily responsible for limiting the increase in [K(+)] in the interstitial space at the onset of fiber activation. Vascular responses to increasing interstitial [K(+)] may contribute to the rapid increase in blood flow that is observed to occur after the onset of muscle contraction.

Animals↗
PubMed2004

Performance of directional microphones for hearing aids: real-world versus simulation.

The purpose of this study was to assess the accuracy of clinical and laboratory measures of directional microphone benefit. Three methods of simulating a noisy restaurant listening situation ([1] a multimicrophone/multiloudspeaker simulation, the R-SPACE, [2] a single noise source behind the listener, and [3] a single noise source above the listener) were evaluated and compared to the "live" condition. Performance with three directional microphone systems differing in polar pattern (omnidirectional, supercardioid, and hypercardioid array) and directivity indices (0.34, 4.20, and 7.71) was assessed using a modified version of the Hearing in Noise Test (HINT). The evaluation revealed that the three microphones could be ordered with regard to the benefit obtained using any of the simulation techniques. However, the absolute performance obtained with each microphone type differed among simulations. Only the R-SPACE simulation yielded accurate estimates of the absolute performance of all three microphones in the live condition. Performance in the R-SPACE condition was not significantly different from performance in the "live restaurant" condition. Neither of the single noise source simulations provided accurate predictions of real-world (live) performance for all three microphones.

Adult↗
PubMed2004

[A simulation facility for low temperature water surface environment].

OBJECTIVE: To simulate the water environment during floating status after astronauts returned and splashed down on the sea because of space capsule emergency in the launching stage. METHOD: Environmental temperature in the laboratory and water-temperature in the tank were auto-controlled individually according to heat charge calculation. To meet the need of maintaining the uniformity of water-temperature, the structure of the water circulation pipeline was specially designed to increase thread-conflux and laminar flow effect. RESULT: It was proved that the experimental system satisfied the requirements for medical research and evaluation by its high precision and uniformity which even exceeded the design requirements. After acceptance, its performance was further proved in the field experiment of "the medical evaluation of the soak and cold resisting garment." CONCLUSION: The equipment provides satisfactory experimental condition for medical evaluation of the space suit used in the "Shenzhou" space capsule and simulated the low-temperature water environment for studies of human reaction in the floating status and medical evaluation of relative products in the area of aerospace.

Aerospace Medicine↗
PubMed2006

Nonlinear dynamics and self-organization of rotary molecular motor ensembles.

The coupled nonlinear dynamics of rotary motor ensembles and an embedding fluid medium are simulated on the basis of Navier-Stokes equations. The model description considers space-dependent rotation of motors and a spatially inhomogeneous motor distribution as well as spatial fluctuations in molecular properties. The mutual influence of motor rotations and fluid dynamics as well as spatial inhomogeneities of their molecular properties are self-consistently included. Space-time simulations visualize the complex interplay between the fluid dynamics and motor rotation and show that the dynamic coupling to the environment via the velocity field as well as the spatial inhomogeneity and distribution of rotors determines the overall behavior of the motor complex. Depending on the initial molecular distribution, rotation frequency, and fluid dynamics a spatial self-organization or a chaotic behavior may arise.

Computer Simulation↗
PubMed1999

Contributory factors to orthostatic intolerance after simulated weightlessness.

Various factors may contribute to orthostatic intolerance (OI) observed after space flights or simulated weightlessness such as bed rest experiments: individual physical and physiological factors (arterial blood pressure (BP), height), physiological changes induced by real or simulated weightlessness (hypovolaemia, increase in venous distensibility), and space flight or simulation conditions (duration and counter-measure application). Our purpose was to test which of these factors were dominant in contributing to the OI. This was assessed in 47 healthy men participating in bed rest experiments of 4, 14, 28, 30 and 42 days, with or without counter-measures (medical stockings, lower-body negative pressure (LBNP), LBNP + muscular exercise). Nineteen subjects did not finish the orthostatic test (60 degrees head-up tilt or stand test) after bed rest. The occurrence of OI was associated with greater height, low resting BP, greater changes in resting lower-limb venous distensibility throughout the bed rest, and absence of counter-measures.

Adult↗
PubMed2005

Single crystal and powder diffraction characterization of three polymorphic forms of Acitretin.

Acitretin [all-trans-9-(4-methoxy-2,3,6-trimethylphenyl)-3,7-dimethyl-2,4,6,8-nonatetraenoic acid or 3-methoxy-2-methyl-17-nor-1,2,3,4-tetradehydroretinoic acid], a widely marketed oral synthetic retinoid, introduced for clinical use as effective therapy against psoriasis, was found to crystallize in three polymorphic modifications (hereafter, I, II, and III), the crystal structures of which have been determined by single-crystal diffractometry (form I) or X-ray powder diffraction methods (form II and III) from conventional laboratory data only. In these latter cases, real space techniques (simulated annealing and whole-profile pattern matching) have been employed. Polymorph I crystallizes in space group P2(1), Z = 8, with unit cell parameters a = 7.894(1), b = 58.454(6), c = 8.161(1) angstroms, beta = 102.04(1) degrees, and V = 3682.9(8) angstroms3. Polymorph II crystallizes in space group P2(1)/n, Z = 4, with unit cell parameters a = 13.999(2), b = 10.714(1), c = 12.465(2) angstroms, beta = 98.76(5) degrees, and V = 1847.9(3) angstroms3. Polymorph III crystallizes in space group P2(1)/c, Z = 4, with unit cell parameters a = 3.0751(4), b = 4.0487(4), c = 14.956(2) angstroms, beta = 100.41(7) degrees, and V = 1831.3(4) angstroms3. Polymorph I, found to be identical with that deposited in the European Pharmacopeia, shows four crystallographically independent Acitretin molecules, arranged in pairs through conventional hydrogen-bonded carboxylic dimers; also in form II, carboxylic dimers are observed, located on crystallographic inversion centres, while in form III, a catameric arrangement of the carboxylic residues, winding up about the rather short monoclinic axis, generates one-dimensional chains of hydrogen-bonded Acitretin molecules. Thermal analysis showed that form I can be quantitatively transformed into form II by moderate heating near 200 degrees C, under vacuum. These results show that ab initio structural studies from conventional laboratory X-ray powder diffraction (XRPD) data are fully providing the opportunity to investigate the structural aspects of moderately complex substances also in the absence of single crystals, disclosing the crystal chemistry of a few polymorphs of pharmaceutically relevant species.

Acitretin↗
PubMed2004

Hormonal changes during long-term isolation.

Confinement and inactivity induce considerable psychological and physiological modifications through social and sensory deprivation. The aim of the SFINCSS-99 experiment was to determine the cardiovascular and hormonal pattern of blood volume regulation during long-term isolation and confinement. Simulation experiments were performed in pressurized chambers similar in size to the volumes of modern space vehicles. Group I consisted of four Russian male volunteers, who spent 240 days in a 100-m(3 )chamber. Group II included four males (one German and three Russians) who spent 110 days in isolation (200-m(3) module). The blood samples, taken before, during and after the isolation period, were used to determine haematocrit (Ht), growth hormone (GH), active renin, aldosterone, and osmolality levels. From the urine samples, electrolytes, osmolality, nitrites, nitrates, cortisol, antidiuretic hormone (ADH), aldosterone, normetanephrine and metanephrine levels were determined. The increase in plasma volume (PV) that is associated with a tendency for a decrease in plasma active renin is likely to be due to decreased sympathetic activity, and concords with the changes in urinary catecholamine levels during confinement. Urinary catecholamine levels were significantly higher during the recovery period than during confinement. This suggests that the sympathoadrenal system was activated, and concords with the increase in heart rate. Vascular resistance is determined by not only the vasoconstrictor but also vasodilator systems. The ratio of nitrite/nitrate in urine, as an indicator of nitric oxide release, did not reveal any significant changes. Analysis of data suggests that the duration of the isolation was a main factor involved in the regulation of hormones.

Adaptation, Physiological↗
PubMed2006

Worm algorithm for continuous-space path integral monte carlo simulations.

We present a new approach to path integral Monte Carlo (PIMC) simulations based on the worm algorithm, originally developed for lattice models and extended here to continuous-space many-body systems. The scheme allows for efficient computation of thermodynamic properties, including winding numbers and off-diagonal correlations, for systems of much greater size than that accessible to conventional PIMC simulations. As an illustrative application of the method, we simulate the superfluid transition of 4He in two dimensions.

Journal Article↗
PubMed2004

Modeling natural attenuation of chlorinated ethenes under spatially varying redox conditions.

A three-dimensional model for the transport and reductive dechlorination of chlorinated ethenes in ground-water systems with variable redox conditions is demonstrated and applied to a pilot test for accelerated natural attenuation of trichloroethene (TCE). The rate and extent of biotransformation of TCE and chlorinated progeny is controlled by the dominant terminal electron accepting process (TEAP) that is simulated over space and time. The solute transport code, Sequential Electron Acceptor Model, 3D-transport, (SEAM3D) which simulates aerobic and sequential anaerobic biodegradation of organic carbon, is modified to implement the equations. Results of a generic model for TCE transport in ground-water systems with different redox conditions demonstrate that the degree of chlorinated ethene attenuation is influenced by background concentrations of aqueous- and solid-phase electron acceptors, but that model results are sensitive to other input parameters (inhibition coefficients, maximum rate of reductive dechlorination, biomass concentrations, and ground-water velocity). Simulation results of enhanced in situ bioremediation using dissolved organic carbon as a reducing agent show that spatial and temporal changes in the dominant TEAP and the subsequent rate of reductive dechlorination are adequately represented with the model. Initial concentrations of Fe(III) and the dechlorinating microbial population influence the simulated time lag observed during the pilot test.

Biodegradation, Environmental↗
PubMed1998

Molecular modeling of HIV-1 coreceptor CCR5 and exploring of conformational space of its extracellular domain in molecular dynamics simulation.

The chemokine receptor CCR5 functions as a major fusion coreceptor for macrophage-tropic human immunodeficiency virus entry into cell. Here we report a three-dimensional model of CCR5 built using molecular modeling approach. Because the virus binds to extracellular domain of the receptor, special attention was given to conformational flexibility, hydrogen bonding, and environmental polarity properties of this protein part. Such data were obtained in the result of molecular dynamics study of the extracellular domain. It was shown that during the simulation the extracellular segments form a compact globular domain with numerous long-range hydrogen bonds between them. First loop of the receptor stays quite rigid while N-terminal region and loops 2, 3 are rather flexible. A number of amino acid residues disposed in unfavourable environment and, therefore, potentially involved in binding of CCR5 to viral glycoproteins and chemokines, was delineated. Comparison of the results with available experimental data permits a proposal that such residues in loop-1 and N-terminal part of the receptor are important for HIV-1 entry, while those in loops 2 and 3 participate in ligand binding. Perspectives of rational alteration of virus-binding activity of CCR5 are discussed.

Amino Acid Sequence↗
PubMed2001

Risk analysis: divergent models and convergent interpretations.

Material presented at a NASA-sponsored workshop on risk models for exposure conditions relevant to prolonged space flight are described in this paper. Analyses used mortality data from experiments conducted at Argonne National Laboratory on the long-term effects of external whole-body irradiation on B6CF1 mice by 60Co gamma rays and fission neutrons delivered as a single exposure or protracted over either 24 or 60 once-weekly exposures. The maximum dose considered was restricted to 1 Gy for neutrons and 10 Gy for gamma rays. Proportional hazard models were used to investigate the shape of the dose response at these lower doses for deaths caused by solid-tissue tumors and tumors of either connective or epithelial tissue origin. For protracted exposures, a significant mortality effect was detected at a neutron dose of 14 cGy and a gamma-ray dose of 3 Gy. For single exposures, radiation-induced mortality for neutrons also occurred within the range of 10-20 cGy, but dropped to 86 cGy for gamma rays. Plots of risk relative to control estimated for each observed dose gave a visual impression of nonlinearity for both neutrons and gamma rays. At least for solid-tissue tumors, male and female mortality was nearly identical for gamma-ray exposures, but mortality risks for females were higher than for males for neutron exposures. As expected, protracting the gamma-ray dose reduced mortality risks. Although curvature consistent with that observed visually could be detected by a model parameterized to detect curvature, a relative risk term containing only a simple term for total dose was usually sufficient to describe the dose response. Although detectable mortality for the three pathology end points considered typically occurred at the same level of dose, the highest risks were almost always associated with deaths caused by tumors of epithelial tissue origin.

Aerospace Medicine↗
PubMed1996

The NASA OCEAN project--an ocean-space analog

An advanced life support system (ALS) with bioregenerative components may one day be required for long-term, deep space exploration, in extended missions to Mars or in establishing long-term bases on the moon. Intensive research programs on such ALS systems have been ongoing throughout the National Aeronautics and Space Administration (NASA) since 1988. Notably, projects have been initiated at the John F. Kennedy Space Center (KSC), Ames Research Center (ARC), and the Lyndon B. Johnson Space Center (JSC). The KSC ALS work has been named the "Breadboard Project" because of its approach developing the components and combining them into a breadboard to understanding the bioregenerative ALS picture [also called a Controlled Ecological Life Support System (CELSS)] in smaller pieces, similar to an electronic "breadboard." The Breadboard Project has been involved for 7 years in the study of higher crops grown in a 113 m3 chamber--the longest operating and largest such closed, controlled growth chamber in the world. This chamber has proven itself to be very successful in growing a wide variety of crops from seedlings to harvest and in helping researchers understand the complex biological cycle of such edible plants in closed, environmentally controlled environments. Because the system's ultimate use will be a more challenging environment, moving a specially designed piece of the system into extreme conditions was an important test. Engineers at KSC developed a compact, portable, functional plant module for testing in the world's only fixed seafloor laboratory at Key Largo, FL. The laboratory, called MarineLab, is operated out of the facilities of the Marine Resources Development Foundation in a lagoon of some 10 m depth. The project was called the OCEAN project (Ocean CELSS Experimental Analog NASA).

Ecological Systems, Closed↗
PubMed2000

Analysis of edible oil processing options for the BIO-Plex advanced life support system.

Edible oil is a critical component of the proposed plant-based Advanced Life Support (ALS) diet. Soybean, peanut, and single-cell oil are the oil source options to date. In terrestrial manufacture, oil is ordinarily extracted with hexane, an organic solvent. However, exposed solvents are not permitted in the spacecraft environment or in enclosed human tests by National Aeronautics and Space Administration due to their potential danger and handling difficulty. As a result, alternative oil-processing methods will need to be utilized. Preparation and recovery options include traditional dehulling, crushing, conditioning, and flaking, extrusion, pressing, water extraction, and supercritical extraction. These processing options were evaluated on criteria appropriate to the Advanced Life Support System and BIO-Plex application including: product quality, product stability, waste production, risk, energy needs, labor requirements, utilization of nonrenewable resources, usefulness of by-products, and versatility and mass of equipment to determine the most appropriate ALS edible oil-processing operation.

Arachis↗
PubMed1999

Measures of spatial structure in samples of genotypes for multiallelic loci.

Various spatial autocorrelation statistics have been widely used both in theoretical population genetics and to study the spatial distribution of diploid genotypes in many plant and animal populations. However, previous simulation studies have considered only diallelic loci. In this paper, we use a large number of space-time simulations to characterize for the first time the parametric and statistical values of Moran's I-statistics for converted individual genotypes as well as for join-count statistics. A wide range of levels of dispersal and numbers of alleles and allele frequencies are modelled and the results reveal the different general effects of each of these factors on these statistics. We also examine the range of appropriate sampling designs and sizes for which predicted values can be interpolated for specific sampling schemes for any given population genetic field survey. Numbers of alleles and allele frequencies each affect some statistics but not others. The results indicate generally low standard deviations. The results also develop precise and efficient methods of estimating gene dispersal, based on the various autocorrelation measures of standing spatial patterns of genetic variation within populations. The results also extend these methods to loci with multiple alleles, typical of those studied through modern molecular methods.

Alleles↗
PubMed2005

Interpersonal issues in space: Shuttle/Mir and beyond.

Anecdotal reports from space and results from space analogue experiments on Earth have suggested a number of interpersonal issues that may negatively affect crewmember performance and well-being. We examined some of these issues in a questionnaire survey of 54 astronauts and cosmonauts who had flown in space and in a 135-d Mir Space Station simulation study in Moscow. We also conducted a NASA-funded study involving missions to the Mir Space Station, where 5 U.S. astronauts, 8 Russian cosmonauts, and 42 U.S. and 16 Russian mission control subjects completed weekly mood and group climate questionnaires. There were few findings that supported hypothesized changes in tension and group behavior in terms of time on-orbit. Crewmembers reported decreasing leader support in the second half of their mission, and U.S. astronauts gave evidence for a novelty effect in the first few weeks. There was strong support for our hypothesized displacement of tension and negative emotions from crewmembers to mission control personnel and from mission control personnel to management. There were several significant differences in response between Americans vs. Russians and crewmembers vs. mission control personnel. These findings have training countermeasure implications for future on-orbit space missions. During expeditionary type space missions, such as a trip to Mars, additional interpersonal stressors will need to be dealt with. These include increased crew autonomy, more dependence on onboard technical resources, communication delays with the Earth, increased isolation and monotony, and the Earth-out-of-view phenomenon.

Aerospace Medicine↗