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 1,243 records · Page 69Linked to original sources
PubMed1979

Elastomeric impression materials: effect of bulk on accuracy.

Impression trays were fabricated providing 2, 4, and 6 mm spaces to determine the stability and accuracy of nine elastomeric impression materials on a simulated full crown preparation steel die. The interface space of 2 mm produced the most accurate impressions for all of the materials tested. All impression materials except one fell within the revised American Dental Association Specifications. The clinical-type tests, using castings on dies poured from these materials, corroborated the acceptance of those materials and techniques exhibiting the least dimensional change.

Dental Impression Materials↗
PubMed1999

Simulation of the primate motor cortex and free arm movements in three-dimensional space: a robot arm system controlled by an artificial neural network.

It has been recently discovered that neuronal activity in the primate motor cortex varies in an orderly fashion with the direction of movement of behaving monkeys in three-dimensional (3-D) space. Furthermore, cell activity is highest in a certain direction, the cell's preferred direction, and decreases progressively in other directions. For a particular movement direction, each cell makes a contribution in the direction of its preferred direction to yield a neuronal population vector that points in the direction of movement well before the movement begins. Simulation of motor cortical activity is useful with a randomly selected Poisson distribution. Poisson spike trains are used as input to an artificial neural network (ANN) that produces motor actions in the form of a Cartesian coordinate to a PUMA robotic arm system. The ANN consists of a three-layered feed-forward system that uses a specific cosine algorithm as synaptic weights between the interconnected units described in the angle between the preferred direction vector of the neuron and the movement vector. The robot responds to commands, generating actual trajectories in close agreement with desired trajectories. It is shown that the time-varying motor output is controlled by the impulse activity with a good estimate of the direction of movement with 100-150 cells.

Animals↗
PubMed1998

Ecological cultivation ark (ECA) project--mutation and evolution of micro-organisms in space.

Ecological cultivation capsules (ECC), that is a materially sealed microcosm. composed of primary producers, consumers and bacteria as a decomposer were developed in order to cultivate bacteria without any artificial operation for long duration more than 10 years in space. It is planned to be left on the space station to study the process that bacteria in MIR space station had acquired their resistance to cosmic ray radiation as well as ultra-violet light. As contrasted with the space experiment, bacteria are cultivating in the ECC on the ground to trace the changes of bacteria under the simulated radiation dose in Earth orbit.

Bacillus subtilis↗
PubMed2005

Systemic betamethasone accelerates functional recovery after a crush injury to rat sciatic nerve.

PURPOSE: The aim of the study was to evaluate the effect of perioperatively systemically administered betamethasone on nerve recovery (within or outside a confined space) after induced nerve crush injury. MATERIALS AND METHODS: The sciatic nerve of 40 adult Wistar rats was crushed. In half of the animals, the injured nerve was entrapped in a silicone tube to simulate the environment of a closed space, and in the other half the nerve was left to heal. Half of the rats in each group were treated with subcutaneous betamethasone (2 mg/kg body weight/day) during the first 24 hours, starting preoperatively, whereas the other half, the control animals, were given the same amount of physiological saline. All animals underwent preoperative and postoperative walking track analysis (toe spread [TS] and intermediate toe spread [ITS]) twice weekly for 6 weeks. RESULTS: For nonconfined space groups, there was no significant difference between the 2 groups (P = .052 for ITS and P = .315 for TS) during the first 2 weeks. Starting from the end of the second week, animals treated with betamethasone recovered more rapidly than did the controls (P < .001) and continued to do so until the end of the observation period. In the confined space groups, there was a significant difference between the 2 groups for ITS (P < .001) and for TS (P < .05) during the first 2 weeks. The difference continued at almost the same level of significance (P = .001) for ITS, whereas for TS, the difference disappeared after the second week. CONCLUSIONS: We conclude that short-term perioperative administration of betamethasone has a beneficial effect on the recovery of the injured rat sciatic nerve.

Animals↗
PubMedDate not supplied

Three-dimensional spectral signal-to-noise ratio for a class of reconstruction algorithms.

A three-dimensional (3D) version of the spectral signal-to-noise ratio (SSNR)-based resolution measure is introduced. The measure is defined for a class of 3D reconstruction algorithms that use interpolation in Fourier space. The statistical properties of the SSNR are discussed and related to the properties of another resolution measure, the Fourier shell correlation (FSC). The new measure was tested on 3D structures calculated from a simulated set of quasi-evenly spaced 2D projections using a nearest-neighbor interpolation and a gridding algorithm. In the latter case, the results agree very well with the FSC-based estimate, with the exception of very high SSNR values. The main applicability of the 3D SSNR is tomography, where due to the small number of projections collected, FSC cannot be used. The new measure was applied to three sets of tomographic data. It was demonstrated that the measure is sufficiently sensitive to yield theoretically expected results. Therefore, the 3D SSNR opens up the possibility of evaluating the quality of tomographic reconstructions in an objective manner. The 3D distribution of SSNR is of major interest in single-particle analysis. It is shown that the new measure can be used to evaluate the anisotropy of 3D reconstructions. The distribution of SSNR is characterized by three anisotropy indices derived from principal axes of the 3D inertia covariance matrix of the SSNR. These indices are used to construct a 3D Fourier filter which, when applied to a 3D reconstruction of a macromolecule, maximizes the SNR in real space and minimizes real-space artifacts caused by uneven distribution of 2D projections.

Algorithms↗
PubMed2001

Probing molecular conformations with electron momentum spectroscopy: the case of n-butane.

High-resolution (e,2e) measurements of the valence electronic structure and momentum-space electron density distributions of n-butane have been exhaustively reanalyzed in order to cope with the presence of two stable structures in the gas phase, namely the all-staggered and gauche conformers. The measurements are compared to a series of Boltzmann-weighted simulations based on the momentum-space form of Kohn-Sham (B3LYP) orbital densities, and to ionization spectra obtained from high-level [ADC(3)] one-particle Green's Function calculations. Indubitable improvements in the quality of the simulated (e,2e) ionization spectra and electron momentum profiles are seen when the contributions of the gauche form of n-butane are included. Both the one-electron binding energies and momentum distributions consistently image the distortions and topological changes that molecular orbitals undergo due to torsion of the carbon backbone, and thereby exhibit variations which can be traced experimentally. With regard to the intimate relation of (e,2e) cross sections with orbital densities, electron momentum spectroscopy can therefore be viewed as a very powerful, but up to now largely unexploited, conformational probe. The study also emphasizes the influence of thermal agitation in photoionization experiments of all kind.

Journal Article↗
PubMed2006

On the use of orientational restraints and symmetry corrections in alchemical free energy calculations.

Alchemical free energy calculations are becoming a useful tool for calculating absolute binding free energies of small molecule ligands to proteins. Here, we find that the presence of multiple metastable ligand orientations can cause convergence problems when distance restraints alone are used. We demonstrate that the use of orientational restraints can greatly accelerate the convergence of these calculations. However, even with this acceleration, we find that sufficient sampling requires substantially longer simulations than are used in many published protocols. To further accelerate convergence, we introduce a new method of configuration space decomposition by orientation which reduces required simulation lengths by at least a factor of 5 in the cases examined. Our method is easily parallelizable, well suited for cases where a ligand cocrystal structure is not available, and can utilize initial orientations generated by docking packages.

Biophysics↗
PubMed2005

Can morphogenesis be understood in terms of physical rules?

Because the morphogenesis of biological systems is not fully understood, researches from various points of view are necessary. The present author has recently made computer simulations with his colleagues to construct branching systems of human organs, such as the lung airway and the liver blood vessels. In the simulations certain rules are assumed to govern bifurcating processes of the systems. These rules are expressed in terms of physical and geometrical concepts, such as minimum energy consumption and uniform filling of branches in the space of organs. Results of computer simulation are quite similar to real structures. However, actual mechanisms of morphogenesis, i.e. effects of genes or proteins, are not considered in these studies. In this article, the present work is discussed in relation to the concept of biological pattern formation by Meinhardt and a recent study by Miura and Shiota on lung growth.

Computer Simulation↗
PubMed2003

Emergent properties in small-scale societies.

A multi-agent simulation is used to explore the relationship between the micro and the macro levels in small-scale societies. The simulation demonstrates, using an African hunter-gatherer group (the !Kung san) as a case study, the way in which population stability may arise from culturally framed, micro-level decision making by women about spacing of births. According to the simulation, population stability as an emergent property has different implications, depending on resource density. Data on Australian hunter-gatherer groups are presented that support the implications of the simulation. !Kung san micro-level cultural rules on incestuous marriages are shown to have macro-level consequences in the form of marriages between residential camps. Between-camp marriages have significant implications for access to resources and thereby for population dynamics of the group as a whole.

Birth Intervals↗
PubMedDate not supplied

Efficacy of Doppler ultrasound [correction of utrasound] for screening symptoms of decompression sickness during simulated extravehicular activities.

Doppler ultrasound is frequently used for monitoring circulating microbubbles during decompression to assess the symptoms of Decompression Sickness (DCS). This analysis was carried out to evaluate its effectiveness for screening symptoms of DCS during simulated extravehicular activities (EVA). The information from various hypobaric chamber studies carried out at the NASA Johnson Space Center, Houston, TX was used in this analysis (n=516). The circulating microbubbles were detected in the precordial area in 42% (218/516), and symptoms were reported in 16% (81/516) of these exposures. The accuracy of Doppler-detectable bubbles (Spencer grades) on all symptoms of DCS was examined by calculating measures of sensitivity and specificity. The efficacy of Doppler as a screening device was examined by calculating their positive predictive value (PPV) and negative predictive value (NPV). The results of these analyses indicated that the sensitivity of Doppler decreased, and the PPV increased with higher Spencer grades. However, the likelihood of detecting true negative cases (NPV) was consistently higher with all bubble grades. Due to the high false-positive rate and low prior probabilities of the risk of DCS, Doppler was found to be more useful to identify those who did not develop DCS, than to detect positive cases of DCS in the simulated EVA exposures.

Decompression Sickness↗
PubMed2000

Body fluid regulation in micro-gravity differs from that on Earth: an overview.

Similar to the response to central hypervolemic conditions on Earth, the shift of blood volume from the legs to the upper part of the body in astronauts entering micro-gravity should, in accordance with the Henry-Gauer mechanism, mediate diuresis and natriuresis. However, fluid balance and kidney function experiments during various space missions resulted in the surprising observation that the responses qualitatively differ from those observed during simulations of hypervolemia on Earth. There is some evidence that the attenuated responses of the kidney while entering weightlessness, and also later during space flight, may be caused by augmented fluid distribution to extravascular compartments compared to conditions on Earth. A functional decoupling of the kidney may also contribute to the observation that renal responses during exposure to micro-gravity are consistently weaker than those during simulation experiments before space flight. Deficits in body mass after landing have always been interpreted as an indication of absolute fluid loss early during space missions. However, recent data suggest that body mass changes during space flight are rather the consequences of hypocaloric nutrition and can be overcome by improved nutrition schemes. Finally, sodium-retaining humoral systems are activated during space flight and may contribute to a new steady-state of metabolic balances with a pronounced increase in body sodium compared to respective conditions on Earth. A revision of the classical "micro-gravity fluid shift" scheme is required.

Body Fluids↗
PubMed1996

Influence of altered gravity on the cytochemical localization of cytochrome oxidase activity in central and peripheral gravisensory systems in developing cichlid fish.

Cichlid fish larvae were reared from hatching to active free swimming under different gravity conditions: natural environment, increased acceleration in a centrifuge, simulated weightlessness in a clinostat and near weightlessness during space flight. Cytochrome oxidase activity was analyzed semiquantitatively on the ultrastructural level as a marker of regional neuronal activity in a primary, vestibular brainstem nucleus and in gravity receptive epithelia in the inner ear. Our results show, that gravity seems to be positively correlated with cytochrome oxidase activity in the magnocellular nucleus of developing fish brain. In the inner ear the energy metabolism is decreased under microgravity concerning utricle but not saccule. Hypergravity has no effect on cytochrome oxidase activity in sensory inner ear epithelia.

Animals↗
PubMed2001

Validity of microgravity simulation models on earth.

Many studies have used water immersion and head-down bed rest as experimental models to simulate responses to microgravity. However, some data collected during space missions are at variance or in contrast with observations collected from experimental models. These discrepancies could reflect incomplete knowledge of the characteristics inherent to each model. During water immersion, the hydrostatic pressure lowers the peripheral vascular capacity and causes increased thoracic blood volume and high vascular perfusion. In turn, these changes lead to high urinary flow, low vasomotor tone, and a high rate of water exchange between interstitium and plasma. In contrast, the increase in thoracic blood volume during a space mission is combined with stimulated orthosympathetic tone and lowered urine flow. During bed rest, body tissues are compressed by pressure from gravity, whereas microgravity causes a negative pressure around the body. The differences in renal function between space and experimental models appear to be explained by the physical forces affecting tissues and hemodynamics as well as by the changes secondary to these forces. These differences may help in selecting experimental models to study possible effects of microgravity.

Baroreflex↗
PubMed1989

In vitro determination of midfoot motion.

Midfoot motion was determined using an in vitro model. Ten fresh-frozen below-the-knee amputation specimens were instrumented by inserting reference pins into each of the bones of the hindfoot, midfoot and metatarsals. Dorsiflexion-planatar flexion and supination-pronation were simulated and the reference pin location in three dimensional space was determined. Comparing the location of the reference pins at each simulated position, motion was determined. Motion occurring through each articulation (dorsiflexion-plantar flexion/supination-pronation) in degrees was: talonavicular (7.0/17.7), calcaneocuboid (2.3/7.3), naviculo-medial cuneiform (5.0/7.3), naviculo-middle cuneiform (5.2/3.5), naviculo-lateral cuneiform (2.6/2.1), medial cuneiform-first metatarsal (3.5/1.5), middle cuneiform-second metatarsal (0.6/1.2), lateral cuneiform-third metatarsal (1.6/2.6), cuboid-fourth metatarsal (9.6/11.1), and cuboid-fifth metatarsal (10.2/9.0).

Foot↗
PubMed1991

[Response analysis for an approximate 3-D image reconstruction in cone-beam SPECT].

Cone-beam Single Photon Emission Computed Tomography (SPECT) offers the potential for a large increase in sensitivity as compared with parallel hole or fan-beam collimation. Three-dimensional image reconstruction was approximately accomplished by backprojecting filtered projections using a two-dimensional fan-beam algorithm. The cone-beam projection data were formed from mathematical phantoms as analytically derived line integrals of the density. In order to reduce the processing time, the filtered projections were backprojected into each planes parallel to the circle on which the focal point moved. Discrepancy of source position and degradation of resolution were investigated by computer simulation in three-dimensional image space. The obtained results suggest that, the nearer to the central plane or the axis of rotation, the less image degradation is performed. By introducing a parameter of angular difference between the focal point and fixed point in the image space during rotation, degradation of the reconstructed image can be estimated for any cone-beam SPECT system.

Algorithms↗
PubMedDate not supplied

[Human histamine and serotonin levels during neuro-emotional stress].

Levels of histamine and serotonin in blood of test subjects kept on a Salyut space diet were measured during their simulated rise to an altitude of 8,000 m, anticipation of an exposure to acceleration, and mental work. During simulated rise the level of histamine increased and histaminopectic activity of serum decreased. During anticipation of centrifugation the serotonin concentration grew. Levels of histamine and serotonin did not vary significantly in the test subjects kept on the space diet with certain food supplements.

Adult↗
PubMed1991

Telescience testbed in human space physiology.

The present telescience testbed study was conducted to evaluate the feasibility of physiological experimentation under restricted conditions such as during simulated weightlessness induced by using a water immersion facility, a reduced capacity of laboratory facilities, a delay and desynchronization of communication between investigator and operator, restrictions of different kinds of experiments practiced by only one operator following a limited time line and so on. The three day's experiments were carried out following the same protocols. The operators were changed every day, but was the same the first and the third day. The operators were both medical doctors but not all round experts in the physiological experimentation. The experimental objectives were: 1) ECG changes by changing water immersion levels, 2) blood pressure changes, 3) ultrasonic Echo-cardiographic changes, 4) laser Doppler skin blood flowmetry in a finger, 5) blood sampling to examine blood electrolytic and humoral changes. The effectiveness of the testbed experiment was assessed by evaluating the quality of the obtained data and estimating the friendliness of the operation of the telescience to investigators and operators.

Aerospace Medicine↗