SEARCH · Search PubMed

Results for “GRAVITATION”

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 271 records · Page 15Linked to original sources

PubMed2000

Improvements to the sensitivity of gravitational clustering for multiple neuron recordings.

We outline two improvements to the technique of gravitational clustering for detection of neuronal synchrony, which are capable of improving the method's detection of weak synchrony with limited data. The advantages of the enhancements are illustrated using data with known levels of synchrony and different interspike interval distributions. The novel simulation method described can easily generate such test data. An important dependence of the sensitivity of gravitational clustering to the interspike interval distribution of the analysed spike trains is described.

Action Potentials↗

PubMed2006

Numerical computation on magnetothermal air jet in gravitational and nongravitational fields.

Two-dimensional numerical computations were carried out in order to elucidate the effect of a Kelvin force on the air in two coaxial circular pipes with open ends under both gravitational and nongravitational fields. The outer pipe with open ends corresponds to the bore space of the superconducting magnet. The inner pipe with open ends is assumed to be placed inside this bore space. The sidewall of the outer pipe is cooled isothermally. The central region of the inner pipe is heated isothermally and the other region is thermally insulated. The magnetic gradient that was produced by the electric current circulating within the circular electric coil was applied to air in two coaxial circular pipes with a thermal gradient. Moreover, the present numerical computations were carried out by changing the relative positions of the circular electric coil and the inner pipe. In both gravitational and nongravitational fields, when the circular electric coil was placed at the end of the heated region of the inner pipe, the Kelvin force was produced in the inner pipe and the magnetothermal air jet was created. As a result, the hotter air rapidly flowed out from the end of the inner pipe. These phenomena could be successfully explained by considering the temperature dependence of the mass magnetic susceptibility of air according to Curie's law.

Journal Article↗

PubMed2003

Sensing and control in dual-recycling laser interferometer gravitational-wave detectors.

We introduce length-sensing and control schemes for the dual-recycled cavity-enhanced Michelson interferometer configuration proposed for the Advanced Laser Interferometer Gravitational Wave Observatory (LIGO). We discuss the principles of this scheme and show methods that allow sensing and control signals to be derived. Experimental verification was carried out in three benchtop experiments that are introduced. We present the implications of the results from these experiments for Advanced LIGO and other future interferometric gravitational-wave detectors.

Journal Article↗

PubMed2005

Development of a frequency-detuned interferometer as a prototype experiment for next-generation gravitational-wave detectors.

We report on our prototype experiment that uses a 4-m detuned resonant sideband extraction interferometer with suspended mirrors, which has almost the same configuration as the next-generation, gravitational-wave detectors. We have developed a new control scheme and have succeeded in the operation of such an interferometer with suspended mirrors for the first time ever as far as we know. We believe that this is the first such instrument that can see the radiation pressure signal enhancement, which can improve the sensitivity of next-generation gravitational-wave detectors.

Journal Article↗

PubMed1991

Oriented movement of statoliths studied in a reduced gravitational field during parabolic flights of rockets.

During five rocket flights (TEXUS 18, 19, 21, 23 and 25), experiments were performed to investigate the behaviour of statoliths in rhizoids of the green alga Charo globularia Thuill. and in statocytes of cress (Lepidium sativum L.) roots, when the gravitational field changed to approx. l0(-4) g (i.e. microgravity) during the parabolic flight (lasting for 301-390 s) of the rockets. The position of statoliths was only slightly influenced by the conditions during launch, e.g. vibration, acceleration and rotation of the rocket. Within approx. 6 min of microgravity conditions the shape of the statolith complex in the rhizoids changed from a transversely oriented lens into a longitudinally oriented spindle. The center of the statolith complex moved approx. 14 micrometers and 3.6 micrometers in rhizoids and root statocytes, respectively, in the opposite direction to the originally acting gravity vector. The kinetics of statolith displacement in rhizoids demonstrate that the velocity was nearly constant under microgravity whereas it decreased remarkably after inversion of rhizoids on Earth. It can be concluded that on Earth the position of statoliths in both rhizoids and root statocytes depends on the balance of two forces, i.e. the gravitational force and the counteracting force mediated by microfilaments.

Actin Cytoskeleton↗

PubMed1988

Gravitational effects on mammalian cells.

In this paper we present first the results of our most recent investigations on gravitational effects on the activation of human lymphocytes: by immunoenzymatic staining and by using concanavalin A (Con A) coated to red blood cells (RBC) we demonstrate that the increase of activation measured at 10xg is due to a simultaneous activation of T- and B-lymphocytes whereas at 1xg only T-cells are stimulated. Conversely, activation of T-cells by chemical modification of the membrane with sodium periodate is depressed at 10xg. Secondly, experiments performed in the centrifuge as well as in the clinostat with Friend, K-562, and hybridoma cells show that each cell line develops its own adaptation reaction to gravitational stress.

B-Lymphocytes↗

PubMed1996

Gravitational physiology of human immune cells: a review of in vivo, ex vivo and in vitro studies.

The study of the function of immune cells in microgravity has been studied for more than 20 years in several laboratories. It is clear today that the immune system is depressed in more than 50% of the astronauts during and after space flight and that the activation of T lymphocytes by mitogens in vitro changes dramatically. This article gives an overview of the gravitational studies conducted by our laboratory in Spacelab, in MIR station, in sounding rockets and on the ground in the clinostat and the centrifuge. Three experimental approaches are followed in our work: (i) Ex vivo studies are performed with blood samples drawn from astronauts; (ii) in vivo studies are based on the application of seven antigens to the skin of the astronauts; (iii) in vitro studies are carried out with immune cells purified from the blood of healthy donors (not astronauts). The data from our in vivo and ex vivo studies are in agreement with those of other laboratories and show that the immunological function is depressed in the majority of astronauts as a consequence of the stress of space flight rather than by a direct influence of gravity on the cell. Immune depression may become a critical hazard on long duration flights on space stations or to other planets. In vitro experiments show that cultures of free-floating lymphocytes and monocytes undergo a dramatic depression of activation by the mitogen concanavalin A, while activation is more than doubled when the cells are attached to microcarrier beads. Such effects may be attributed to both direct and indirect effects of gravitational unloading on basic biological mechanisms of the cell. While the in vitro data are very important to clarify certain aspects of the biological mechanism of T cells activation, they are not descriptive of the changes of the immunological function of the astronauts.

Animals↗

PubMed1996

Relative role of low- and high pressure reflexes on sympathetic activity in humans during simulated gravitational stress.

In order to determine the relative role of low- and high-pressure reflexes, respectively, on forearm sympathetic nerve activity (fSNA), 10 normal male subjects underwent a 4-step (5 min each) graded lower body negative pressure (LBNP) from -10 to -50 mmHg. Central venous pressure (CVP) and stroke volume gradually decreased (p<0.05), and arterial pulse pressure (PP) abruptly decreased at LBNP of -50 mmHg. Mean arterial pressure (MAP) remained unchanged. Forearm venous plasma norepinephrine concentration (fvNE) increased significantly at LBNP of -35 mmHg (p<0.05) and with a further sharp increase during LBNP of -50 mmHg (p<0.05). High degrees of intra-individual correlations were observed between changes in Log [fvNE] and CVP (r-values from -0.78 to -0.96, p<0.01). We conclude that low-pressure reflexes are the major determinants of fSNA during non-hypotensive gravitational stress (MAP and PP unchanged). When the gravitational stress is more pronounced, a decrease in PP further augments fSNA through inhibition of high-pressure arterial baroreflexes.

Adult↗

PubMed1997

Mechanisms of vascular adaptation to long-term orthostatic gravitational loading.

Frequent symptoms and serious complaints related to orthostatic intolerance are among the important reasons for investigating the long-term control mechanisms of blood vessels especially those of veins. Previously we studied perfused and superfused saphenous vein segments from rats maintained in head-up tilt position for two weeks. It was found that passive lumen capacity and acute pressure induced myogenic response of these vessels increased substantially without measurable change in wall thickness. Sympathetic component of the smooth muscle cell membrane potential determined in vivo was also significantly enhanced in this vein, but no such change was seen in the saphenous artery and in the brachial vessels. In a separate study, rarefaction of microvessels was found in the hind limb oxydative muscles after two-week tilting, while muscular water content was unaltered. These results suggest that long-term gravitational loading may induce adaptive rearrangement of the blood vessel functions. The aim of the present study was to quantitate and compare the density of nerve fiber terminals as well as their synaptic vesicle population in the wall of saphenous vein and artery from tilted rats to those obtained from rats which were maintained in horizontal, control position. It was hypothetized that adaptation of blood vessels to long-term gravitational loading might include also a morphological restructuring of the vascular adrenergic innervation.

Adaptation, Physiological↗

PubMed1999

Detection of apoptosis in chloroplasts and nuclei in different gravitational environments.

Plant cells either die by "accident" (traumatic cell death) or by "design" (programmed cell death; PCD). There is clear evidence that cell death during plant development and interactions with the environment involves PCD (in Gray and Johal, 1998). K. daigremontiana reproduces asexually by forming plantlets from leaf indentations which fall to soil and convert into adult plants. In nature, its entire plant body except leaf-plantlets senesces as consequence of floral differentiation or stressful environmental conditions. At unit gravity, PCD precedes plantlet detachment from the mother-leaf, leading to an abscission scar after plantlet fall. Earlier experiments have shown that leaf-plantlet formation and asexual reproduction increased with short duration hypergravity treatments and decreased in simulated hypergravity (Pedroso and Durzan, 1998). The present experiments were designed to determine if and what type of cell death occurs following gravitational changes, and the sequence of events leading to it. Our study shows that changes in gravitational environment cause a burst in nitric oxide, followed by a sequence of events that may ultimately led to programmed cell death by apoptosis.

Apoptosis↗

PubMed1977

The effect of increased gravitational stress on bone.

To assess the effects of an altered gravitational state on the physical properties of bone, fifteen sexually mature chickens were centrifuged for 18 weeks. The gravitational forces were gradually increased to allow the chickens to adapt to the increased load. For the last 4 weeks of the experiment, the animals were subjected to a force of 3 x gravity. After sacrifice the tibias were removed and fractured in torsion. Bone diameters, cortical thickness and ash content of the tibias were determined. Histological preparations of the bone specimens were also examined. When the centrifuged animals were compared with control chickens of comparable size and weight, there was no significant change in bone strength or fracture pattern, although the centrifuged birds had smaller mid-tibial shaft diameters and thicker cortices. The mean percentage bone ash for the centrifuged birds was 68.2% which is an accepted value for dry bone ash of adult chickens. Bone density was the same for both centrifuged and control birds. The birds lost an average of 465 grams of body mass during their 18 weeks on a centrifuge.

Adaptation, Physiological↗

PubMed2002

[Effects of gravitational unloading on blood supply of working muscles].

Exposure to the conditions of simulated gravitational unloading (head down tilting, dry immersion) produces a material effect on blood supply of working muscles in humans that may depend on type of work (local or global) and posture (vertical or horizontal). Peak blood flow in the calf after exposure to HDT and dry immersion reduces by 7 to 20% and the post-contraction hyperemia (PCH) following a standard work of the calf extensors noticeably increases. In contrast to PCH, blood flow during natural locomotion diminishes as a result of simulated gravitational unloading. Standard bicycling by sitting and supine human subjects moderates and exaggerates the post-work hyperemia, respectively. Consideration is given to possible causes of these effects.

Bicycling↗

PubMed2002

Remote controlled equipment for multiple blood withdrawal in gravitational physiology experiments.

Electro-mechanical equipment for multiple blood withdrawal from small experimental animals applied to a centrifuge with maximal 6g gravitational overloading has been developed and tested. The equipment consists of a transmitter and receiver equipped by microcomputers. Active rotor stepping motors are driving four pairs of syringes. It is also possible to measure the instantaneous gravitational force using an accelerometric transducer. This telemetrically regulated blood sampling allows studying selective effects of hypergravity during centrifugation. It can be also used for study of microgravity effects in the animal organism during space flights for the understanding of the mechanism of the changes of the activity of neuroendocrine system and metabolic processes.

Journal Article↗

PubMed2006

[Changes in the pancreas structure after exposure of the body to gravitational overloads].

The aim of this study was to determine the changes in the pancreas structure after acute and chronic exposure of organism to gravitational overloads (GO). The experiments were conducted in 36 outbred albino male rats, 12 rats formed the control group. GO effect was modeled using the centrifuge; the value of the overload thus created amounted to 4,0-6,0 gravitational units. Pancreas structure was studied using histological, electron microscopic and morphometric methods. It was found that after acute exposure to GO, mainly the reactive changes were demonstrated all the pancreatic structures studied: acinocytes, endocrinocytes, blood vessels and nervous apparatus. Chronic exposure to GO resulted in both reactive modifications, similar to those described after an acute exposure, and various compensatory-adaptive and destructive changes.

Animals↗

PubMed1994

[Manifestation of lung tuberculosis as soft tissue tumor (gravitation abscess in mediastinal lymphadenitis) of the thoracic wall in a 32-year-old woman].

In a 32-year-old female appeared after a period of weeks with pain in the back and left flank a tumor (8 x 6 cm in size) in the anterior axillary line (9.-11. rib). The patient was afebril and in good condition. X-rays and Contrast-CT findings showed round shaped infiltrations in both upper lobes of the lung, widening of the mediastinum (right paratracheal) and left pleural effusion. The mediastinal mass showed "rim enhancement" and "central low density areas", which is typical for liquefaction of caseous material in tuberculous lymphadenitis and gravitation abscess. The tumor was resected incompletely, because there was connection to the 8. intercostal space. In the cross-section the tumor appeared grey-white, histologically there was caseous material surrounded by epitheloid cells and Langhans giant cells, as to see in tuberculous gravitation abscess. Ziehl-Neelsen-staining of resected material and bronchial secret was negative, but of both specimen Mycobacterium tuberculosis was cultured. The patient got a therapy with INH, Ethambutol, Pyrazinamid and Rifampicin. Regression of the parenchymal fokus and the mediastinal lymphadenitis was observed.

Adult↗

PubMedDate not supplied

Safe and effective fluid management by automated gravitation during hysteroscopy.

OBJECTIVE: The automated gravitational Vario Flow system with weighing-based electronic fluid deficit indicator was used in order to reduce the risk of fluid intravasation during continuous flow hysteroscopic procedures. Early experiences are reported. METHODS: Between August 1996 and July 1997, the Vario Flow with fluid deficit indicator and alarm system was used in 203 hysteroscopic operations. Between January 1994 and August 1996 the Vario Flow without fluid deficit indicator was used in 240 hysteroscopic operations. In all, there were 443 hysteroscopic operations: 301 metroplasties, 20 endometrial ablations, 10 cases of lysis of synechiae, 58 myomectomies and 54 polypectomies. The data on fluid deficit before and after the introduction of the electronic fluid deficit indicator were similar. RESULTS: Fluid deficit indicator was proved highly efficient in 203 operations. It provided the information on fluid deficit at any moment during hysteroscopic operations. Besides intrauterine pressure, the actual fluid deficit has become one of the leading parameters during our continuous flow hysteroscopic procedures. CONCLUSIONS: We therefore conclude that by using an automated gravitational system with fluid deficit indicator and alarm system, the safety for patients during hysteroscopic procedures has been increased.

Automation↗

PubMed1993

Early amphibian (anuran) morphogenesis is sensitive to novel gravitational fields.

Anuran amphibian embryos (Xenopus laevis and Rana dybowskii) are sensitive to novel gravitational fields. Under simulated weightlessness, (i) the location of the first horizontal cleavage furrow was shifted toward the vegetal pole at the eight-cell stage; (ii) the position of the blastocoel was more centered, and the number of cell layers in the blastocoel roof was increased at the blastula stage; (iii) the dorsal lip appeared closer to the vegetal pole at the gastrula stage; and (iv) head and eye dimensions were enlarged at the hatching tadpole stage. Effects of simulated hypergravity were opposite to those of simulated weightlessness, except that hypergravity, unlike simulated weightlessness, reduced the number of primordial germ cells in feeding tadpoles. Despite those dramatic differences in the early embryogenesis, tadpoles at the feeding stage are largely indistinguishable from controls.

Animals↗

PubMed1993

Effect of injury on mast cells of rat gastrocnemius muscle with respect to gravitational exposure.

The proteolytic enzyme, chymase, was used to identify mast cells in rat gastrocnemius muscles which were crush-injured or incised in order to determine if mast cells exhibited proliferation and degranulation. Some of the crush-injured rats were subjected to 0 g for 14 days after injury on the Cosmos 2044 satellite to study the effects of weightlessness on the mast cell response. A variety of ground-based injured models were used, including a group of hindlimb-unloaded animals acting as controls and testing the suitability of the hindlimb-unloaded animal as a model for muscle healing during weightlessness. In most cases, the numbers of mast cells and their apparent size increased after injury. When mast cell degranulation was evident, the granules containing chymase often were free in the loose connective tissue and along the edge of myofibers. The mast cell response was most exaggerated in animals subjected to 0 g and least visible in the hindlimb-unloaded ones. Thus, gravitational stress may influence mast cell physiology and the hindlimb-unloaded animal may not be a good model for investigating muscle healing.

Animals↗