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At least 235 records · Page 13Linked to original sources
PubMed1993

European isolation and confinement study. Blood pressure, volume-regulating hormones, and electrolytes.

In the ISEMSI confinement experiment we observed three main reactions concerning blood volume regulation: first, a stress activation produced by the high workload that the subjects had to accomplish, both before the isolation period and during the two first weeks of isolation; second, a typical defense reaction to the environment occurred, at least during the two initial days of isolation and later perhaps between crew members themselves; and third, a change in blood volume regulating hormone levels may have been the result of the increase of sympathetic system activity and of dehydration. Confinement is certainly a good and valid method to simulate space station life (with the absence of weightlessness). So, it is interesting to use these confinement studies to perform biological and physiological experiments to obtain greater knowledge, but also to prepare and validate new scientific protocols or new scientific equipment suitable for spaceflights. Even more so, confinement is a good way to prepare and train crew members for long-term space missions. It would seem desirable to confirm the scientific results obtained during the ISEMSI campaign, and especially those for the regulation of the blood volume. This will be done during the next confinement experiment, called EXEMSI, in which four subjects will be subjected to 60 days of confinement.

Adult↗
PubMed1976

[Animal experimental studies on the effects of noise stress on male fertility].

Psychic stress is able to cause male infertility. Stieve found out aspermatogenesis in executed men. Cockett et al. immobilized 5 Macaca-Monkeys 15 to 40 days in capsule module under simulated space flight conditions and detected severe testicular degeneration. Carosi and Calabro reported about workers exposed to industrial noise over a period of years; the number of offspring was found to be much lower than in non exposed families. We examined the effect of noise on the fertility of 21 male guinea pigs. Sounding of 110 dB lasted 3-5 hours daily over a period of 22-31 days. Histological examination of the testicular tissue did not show any disorder of spermatogenesis. We believe that the negative result is attributed to failings in the test arrangement. Sounding only lasted for a maximum of 31 days. However, the duration of spermatogenesis in guinea pigs is about 40 days. Moreover the sounding maximum was only 5 hours per day, yet the time of recovery took 4-5 times longer every day. Consequently the daily short-term depression of the neuroendrocrinium affected the gonadotropine secretion in similarity to the daily biorhythmic variation. Therefore the expected inhibition of fertility by the neuroendrocrinic way could not be demonstrated. Our experiments also revealed another problem. In noise-exposed guinea pigs there was 8.2 per cent tubuli contorti without complete spermatogenesis. Moreover, in the control group even 9.9 per cent of the tubuli was found to be sperm-free. It is not clear why such a contrary reaction occurred. However, it is possible that hormonal stimulation increased temporarily as a result of noise stress. It should be noted that this effect has also been reported by Arguellis.

Acoustic Stimulation↗
PubMed2003

[Development of fixed-base full task space flight training simulator].

Fixed-base full task flight training simulator is a very critical and important integrated training facility. It is mostly used in training of integrated skills and tasks, such as running the flight program of manned space flight, dealing with faults, operating and controlling spacecraft flight, communicating information between spacecraft and ground. This simulator was made up of several subentries including spacecraft simulation, simulating cabin, sight image, acoustics, main controlling computer, instructor and assistant support. It has implemented many simulation functions, such as spacecraft environment, spacecraft movement, communicating information between spacecraft and ground, typical faults, manual control and operating training, training control, training monitor, training database management, training data recording, system detecting and so on.

Astronauts↗
PubMed1994

Rethinking "shape space": evidence from simulated docking suggests that steric shape complementarity is not limiting for antibody-antigen recognition and idiotypic interactions.

The concept of "shape space" is based on the assumption that the relevant properties of individual molecules can be adequately specified by a finite list of N parameters; and that cij, the affinity between molecules i and j, can be specified by an equation of the form: cij = f(xi, xj), where xi and xj are N-dimensional vectors representing the absolute positions of molecules i and j in an objective, referential "shape space", and f is an appropriate function. We have performed simulated docking of the combining sites of immunoglobulin molecules, based on their crystallographic structures. The results suggest that shape complementarity cannot account for the specificity of idiotypic interactions, since in the simulations each pair of docked proteins had a buried surface area as great as that occurring in known complexes. It therefore seems likely that the atomic interactions accounting for the specificity of immunoglobulin recognition are highly relational. This casts doubt on the basic assumptions underlying the shape-space concept, at least in the simple form hitherto used in theoretical modelling of the immune system. In order to be realistic, the dimensionality N would have to be high (more than 20), and the function f would be irregular and discontinuous. Alternatively, if the equation cij = f(xi, xj) is interpreted as a purely formal construction in an abstract "inversion space", its validity is entirely relative to the empirical affinity matrix on which the construction is based. We conclude that at present there is no sure way of adequately characterizing the internal structure of idiotypic affinity matrices; and that models of the immune system should therefore aim at being generic and robust with respect to the structure of the idiotypic affinity matrices of unselected immunoglobulins.

Algorithms↗
PubMed1997

Novel methods of sampling phase space in the simulation of biological systems.

New advances in molecular dynamics and Monte Carlo simulations have led to impressive increases in the speed of sampling phase space for complex biological systems. These methods have been combined with new fast algorithms for computing long range electrostatic interactions for new polarizable force fields. In addition, new methods for sampling low energy molecular conformations allow the rapid determination of thermodynamically dominant regions on the potential-energy surface. Accurate measures of the rate of phase-space sampling should allow both the optimization and the comparison of methods for a particular problem of interest.

Algorithms↗
PubMed2002

[Simulation models of thermal-humidity parameters of the space suit].

The paper describes a mathematical model of and methods of calculating thermal-humidity fields in a spacewalking suit. The authors made an integral calculation of thermal and mass transfer in the spacesuit. A system of equations is solved analytically and numerically with the use of a combined method. As a result of model calculations, determined were integral spacesuit characteristics including total amount of rejected heat, heat rejected by the WC suit, humidity rejected by ventilation, and humidity accumulated in different spacesuit layers. Comparison of calculation and experimental data for spacesuit Orlan showed that maximal differences in temperature, humidity, thermal and humidity flows, and other system parameters did not exceed 13%.

Humans↗
PubMed2002

Nutritional interventions related to bone turnover in European space missions and simulation models.

Low energy intake, low calcium intake, low plasma 25-hydroxy-vitamin D or low calcitriol levels, and high salt intake might support the development of space osteoporosis. Therefore, my colleagues and I monitored the daily energy and calcium intakes in eight astronauts during their respective space missions (Spacelab D2, Euromir 94, Euromir 95). In most of these astronauts, energy intake was reduced by more than 20% compared with their calculated energy expenditure. In all three missions, the average daily calcium intake of the eight astronauts was 25% lower than the German recommended daily allowances of 900 mg/d for healthy people without osteoporosis risk. In some astronauts, the calcium intake was extremely low at 53 and 74 mg/d. Sodium intake in these astronauts varied from 39 mEq/d to a very high intake of 462 mEq/d. As a consequence of these results, we examined in the 21-d Mir 97 mission a preventative dietary approach of high calcium intake of at least 1000 mg/d with vitamin D supplementation (650 IU/d of Ergocalciferol) and constant sodium intake (180 mEq/d). Total serum calcium concentration and urinary calcium excretion significantly increased during this mission. Synthesis of 25-OH-cholecalciferol synthesis was markedly reduced because of inadequate ultraviolet light, whereas total 25-OH-Vitamin D levels were unchanged. However, parathyroid hormone and calcitriol levels decreased significantly. Sodium excretion decreased significantly, resulting in positive sodium balances. Based on these results, dietary calcium and vitamin D do not stabilize bone turnover because markers of bone formation were reduced and markers of bone resorption were increased. We concluded that, in contrast to terrestrial conditions, adequate or even high calcium and vitamin D intakes during microgravity do not efficiently counteract the development of space osteoporosis. Conversely, vitamin K (Konakion) seemed to counteract microgravity-induced reduction of bone formation markers. In the 179-d Euromir 95 mission, investigators administered 10 mg of vitamin K from inflight day 86 to day 136 in one astronaut. During and after supplementation, bone formation markers increased significantly during this part of the mission. Therefore, vitamin K seems to play a significant role in bone turnover during space flight.

Aerospace Medicine↗
PubMed1993

MRI simulation using the k-space formalism.

An MRI simulation method, together with a corresponding computer program, using the k-space formalism has been developed. It uses a FFT algorithm to generate the ideal NMR signal from a user defined object. The k-space trajectory given by a pulse sequence is calculated. And it is used to select elements from the ideal NMR signal. This selection of elements mimic the sampling of the signal in an actual MRI experiment. During the sampling procedure changes in signal amplitude due to relaxation and excitation are introduced as well as signal phase changes due to movement or flow. Artifacts due to stimulated echoes and transversal magnetization that propagate through several repetition periods are also handled. The usefulness of the method is demonstrated by calculations using standard spin-echo sequence as well as modifications introduced in order to generate angiographical images and flow phase images. Further more a fast pulse sequence, echo planar imaging (EPI), is also simulated. The method is faster than previously presented ones. It is capable of generating images (128 x 128 matrix), including more than eight different T1 and T2 combinations, in less than 3 min on a standard 386/387 type IBM compatible PC.

Algorithms↗
PubMed2004

A three-dimensional vertex dynamics cell model of space-filling polyhedra simulating cell behavior in a cell aggregate.

We developed a three-dimensional (3D) cell model of a multicellular aggregate consisting of several polyhedral cells to investigate the deformation and rearrangement of cells under the influence of external forces. The polyhedral cells fill the space in the aggregate without gaps or overlaps, consist of contracting interfaces and maintain their volumes. The interfaces and volumes were expressed by 3D vertex coordinates. Vertex movements obey equations of motion that rearrange the cells to minimize total free energy, and undergo an elementary process that exchanges vertex pair connections when vertices approach each other. The total free energy includes the interface energy of cells and the compression or expansion energy of cells. Computer simulations provided the following results: An aggregate of cells becomes spherical to minimize individual cell surface areas; Polygonal interfaces of cells remain flat; Cells within the 3D cell aggregate can move and rearrange despite the absence of free space. We examined cell rearrangement to elucidate the viscoelastic properties of the aggregate, e.g. when an external force flattens a cell aggregate (e.g. under centrifugation) its component cells quickly flatten. Under a continuous external force, the cells slowly rearrange to recover their original shape although the cell aggregate remains flat. The deformation and rearrangement of individual cells is a two-step process with a time lag. Our results showed that morphological and viscoelastic properties of the cell aggregate with long relaxation time are based on component cells where minimization of interfacial energy of cells provides a motive force for cell movement.

Animals↗
PubMed1996

[Training with a simulator--experiences in space flight].

High technology and automation have not been able to significantly improve flight safety within the last two decades. The main cause of aviation accidents was and is human error. Therefore, the most powerful tools to reduce risks in aviation deal with the human operator on the flight deck. Pilot selection, training and teamwork are of the utmost importance. The simulator is a valuable training aid. Simulation provides realistic scenarios that can be used to train optimal pilot behavior in emergency situations. Many complex abnormal situations can be only managed in teamwork. That is the reason why training programmes for improved team behavior (crew resource management) are becoming more and more important.

Accidents, Aviation↗
PubMed1985

Psychosocial factors affecting simulated and actual space missions.

As space missions become longer and broader in scope, and as crews become more heterogeneous, psychological and interpersonal factors will take on increasing importance. In order to isolate instructive psychosocial issues and trends, a review was made of over 60 American and Russian simulation and spaceflight studies and reports. Although the missions accomplished most of their goals, psychological and social stresses were evident in the crew members. Psychosocial problems tended to relate to mission length. There was evidence that the use of appropriate psychological testing and interpersonal sensitivity training could improve crew selection and ameliorate problems in the simulation studies. It is time to apply this knowledge to actual spaceflight conditions.

Adaptation, Psychological↗
PubMed2004

Car-Parrinello simulations with a real space method.

An approach for Car-Parrinello type molecular dynamics simulations using real space discretized wave functions is presented. The implementation uses a higher order finite difference approximation for the Laplacian in the kinetic energy operator and in the Poisson equation for the evaluation of the Hartree energy. Norm conserving pseudopotentials are employed to replace the nucleus-core interactions. Both nuclei and wave functions are propagated with a second-order Verlet propagator with a timestep comparable to standard plane wave implementations. The orthonormality constraints are fulfilled via Lagrange multipliers. Both periodic and nonperiodic boundary conditions can directly be imposed within the real space approach. In order to maintain energy conservation both forces on the nuclei and the wave functions must be sufficiently accurate. It is shown that the spurious energy dependence on the nuclear positions with respect to the grid points, which is an inevitable artifact of the discretization, is mirrored in the nuclear forces, and does not affect energy conservation. In contrast to the plane wave methodology, the Hartree energy is calculated via an iterative solution of the Poisson equation. As a result, the quality of the forces on the wave function crucially depends on its convergence, as well as on the accuracy of the approximation for the boundary values in nonperiodic calculations. The influence of these factors on the energy conservation is investigated. It is shown that Car-Parrinello simulations can be performed with real space wave functions, given a proper prescription to calculate the Hartree potential is used.

Journal Article↗
PubMed2000

P-SPACE: a program for simulating spatial behavior in small groups.

P-SPACE is a computer program that simulates spatial behavior in a small group of individuals. The program describes how interpersonal distances change through time as a result of changes in microlevel features, such as the minimization of local dissatisfaction. Agents are located in a two-dimensional lattice and can move some discrete space units at each discrete time unit within their neighborhood. A nonsymmetrical matrix of ideal distances between agents must be specified. Agents move in order to minimize their dissatisfaction, defined as a function of the discrepancy between possible future distances and ideal distances between agents. At each iteration, agents will move to those cells in their neighborhoods for which the function is minimized. Depending on the specific values in the ideal-distance matrix, different kinds of social dynamics can be simulated.

Electronic Data Processing↗
PubMed1994

Experimental simulation of proton space radiation environments: a dosimetric perspective.

Three-dimensional dose calculation techniques developed for radiotherapy treatment planning were used to calculate dose distributions from unidirectional, planar rotational and omnidirectional incident radiation (experimental proton beams and solar flares). The calculations predicted regions of high dose within primate heads exposed to 55-MeV protons, supporting the postulate of radiation-induced brain tumors within this population. Comparisons among predicted doses to the human head from solar flares of three different energies demonstrated differences between unidirectional and omnidirectional irradiation in the space environment. The results can be used to estimate dose distributions based on a) limited phantom measurements, or b) nonuniformly incident radiation in orbit; both situations are difficult to replicate under laboratory exposure conditions.

Animals↗