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 847 records · Page 47Linked to original sources
PubMed2006

Characterizing warfare in red teaming.

Red teaming is the process of studying a problem by anticipating adversary behaviors. When done in simulations, the behavior space is divided into two groups; one controlled by the red team which represents the set of adversary behaviors or bad guys, while the other is controlled by the blue team which represents the set of defenders or good guys. Through red teaming, analysts can learn about the future by forward prediction of scenarios. More recently, defense has been looking at evolutionary computation methods in red teaming. The fitness function in these systems is highly stochastic, where a single configuration can result in multiple different outcomes. Operational, tactical and strategic decisions can be made based on the findings of the evolutionary method in use. Therefore, there is an urgent need for understanding the nature of these problems and the role of the stochastic fitness to gain insight into the possible performance of different methods. This paper presents a first attempt at characterizing the search space difficulties in red teaming to shed light on the expected performance of the evolutionary method in stochastic environments.

Algorithms↗
PubMed2005

F-statistics of clonal diploids structured in numerous demes.

Abstract The expected apportionment of genetic diversity in diploid clonal organisms structured in numerous subpopulations is explored. Under the specific assumptions considered, corresponding, for instance, to clonal pathogens infecting a large number of hosts, the co-ancestry between individuals within subpopulations is the only nontrivial quantity. Thus the population structure can be fully described either by F(ST) or F(IS), as F(ST) = -F(IS)/(1 - F(IS)). We show that, for most of the parameter space considered, including simulations where equilibrium is not reached and/or where homoplasy is high, the number of effective migrants is most accurately estimated as Nm = -(1 + F(IS))/4F(IS). We further propose a criterion to test for the absence of cryptic sexual reproduction based on the F-statistics F(IS) and F(ST), which is applied to three previously published empirical data sets.

Computer Simulation↗
PubMed1979

Estimates of cable parameters in lamprey spinal cord neurones.

1. Two micro-electrodes were used to penetrate giant interneurones in the isolated lamprey spinal cord. A brief (50--100 microsec) current pulse was applied to one electrode while the other recorded the voltage transient response. 2. A formal analysis of the voltage transient was achieved by the simplifying reduction of each neurone. Somas were treated as a parallel combination of resistance and capacitance. Dendrite trees were reduced to an equivalent cylinder (Rall, 1959). 3. The voltage transients were analysed according to the procedure suggested by Jack & Redman (1971b) to estimate the cable parameters governing the passive propagation of transmembrane potentials. Membrane time constant (tau m), dendritic to soma conductance ratio (rho 00), and electrotonic length (L) of the equivalent cylinder were estimated from these data. 4. In thirty-two interneurones it was possible to determine the membrane time constant, but rho 00 and L were determined in only twenty-two. 5. For the twenty-two neurones in which all cable parameters were estimated, the electrotonic length of the equivalent cylinder was similar to that found for cat spinal motoneurones (1--2 space constants). 6. Simulations of the voltage transient using the Rall model of the motoneurone as developed by Jack & Redman (1971b) resulted in a voltage response which closely ditted the experimental data. 7. These results suggest that the Rall model of the motoneurone accurately describes the propagation of passive transmembrane potentials in lamprey spinal cord neurones. It is further concluded that the time constant for soma and dendritic membrane is similar in these neurones.

Animals↗
PubMedDate not supplied

Phase-encode order and its effect on contrast and artifact in single-shot RARE sequences.

Substantial manipulation of tissue contrast can be achieved by varying the order in which phase-encode values are applied to individual echoes within a 128-echo single-shot rapid acquisition relaxation enhanced (RARE) sequence. Appropriate ordering can then permit imaging of short T2 species like muscle and white matter with single-shot RARE. For sequential phase encoding with an arbitrary initial phase-encode value, the timing of the zero phase (ZP) encoded echo is found to be analogous to the echo time (TE) of standard spin-echo sequences. This is demonstrated qualitatively with human brain images and is verified quantitatively with NiCl2 phantoms by correlating the time constant for signal decay with ZP echo time, with transverse relaxation times T2, as obtained with a 128-echo Carr-Purcell-Meiboom-Gill (CPMG) imaging sequence. Banding artifacts accompanying the discontinuous traverse through K space are experimentally demonstrated in a rectangular phantom and expressions are developed for determining the dependence of this artifact on the phase-encode gradient increments and durations, the ZP echo number, echo spacing, and T2. Simulations based on the expressions are shown to be useful for characterizing the observed "banding" artifacts perpendicular to the phase-encode direction and for predicting the extent of tissue-tissue overlap to be expected with the use of this ultrafast rf echo planar imaging method.

Brain↗
PubMed1975

Lymphographic Demonstration of a Retroperitoneal Lymphangioma.

Lymphangiomas are rare, benign tumors which may become opacified during lymphography and may be confused with malignant lymph node disease. A case is reported in which lymphography showed focal collections of contrast material retained for several days in dilated lymphatic spaces which initially simulated metastatic disease.

Female↗
PubMed1984

Microbiological assessment of dental plaque on bovine enamel implants worn intra-orally in children.

Nine caries-active children, each from six to nine years old, wore small removable enamel implants intra-orally for four weeks as part of an effort to develop removable model systems for studying dental plaque in fissures. The implants, consisting of two enamel cubes arranged to simulate a fissural space, were cemented in box preparations in stainless steel crowns on pulpotomized primary molars. Upon removal, the fissural spaces were opened to facilitate plaque harvesting. The plaque samples were cultured, and enamel decalcification of the plaque-exposed surfaces was measured. Quantitative microbial values were compared with those of natural fissure plaque samples from both caries-active (CA) and caries-and restoration-free (CF) children, also from six to nine years old. Streptococcus mutans and S. sanguis levels of fissural insert plaque (FI) and natural fissural plaque from (CA) were similar. Both contained higher S. mutans levels than did plaque from (CF). FI harbored higher concentrations of Lactobacillus and Actinomyces species and lower concentrations of Neisseria species. Otherwise, FI plaque resembled natural fissure plaque. Microhardness of FI plaque-exposed enamel decreased significantly compared with pre-experimental values and showed a significant negative correlation with values for total lactobacilli on selective media, and for S. mutans on non-selective media.

Actinomyces↗
PubMed2003

Indirect measurement of a laser communications bit-error-rate reduction with low-order adaptive optics.

In experimental measurements of the bit-error rate for a laser communication system, we show improved performance with the implementation of low-order (tip/tilt) adaptive optics in a free-space link. With simulated atmospheric tilt injected by a conventional piezoelectric tilt mirror, an adaptive optics system with a Xinetics tilt mirror was used in a closed loop. The laboratory experiment replicated a monostatic propagation with a cooperative wave front beacon at the receiver. Owing to constraints in the speed of the processing hardware, the data is scaled to represent an actual propagation of a few kilometers under moderate scintillation conditions. We compare the experimental data and indirect measurement of the bit-error rate before correction and after correction, with a theoretical prediction.

Journal Article↗
PubMed2006

Laparoscopic gastric banding in the rat model as a means of videolaparoscopic training.

BACKGROUND: The development of laparoscopy in bariatric surgery has attracted a large number of surgeons. Learning this method for future clinical practice requires intensive training with inert tissues, simulators and experimental surgery in animals. Performing these procedures in small animals, with the same equipment used in humans, is feasible, allowing familiarization with and comprehension of the basic techniques. Wistar rats weighing 300-600 g were used. The animals were kept in standard laboratory conditions. A laparoscopic video-system, Veress needle, three ports, a 0 degree optic, a laparoscopic needle-holder, two 5-mm graspers, a 5-mm dissection clamp and a 5-mm scissors were used. An orogastric catheter with three 4-0 nylon sutures and one 6-0 nylon suture were also utilized. For the gastric band, we used a plastic device similar to the human gastric band. The present study describes a simple, inexpensive and reproducible technique for laparoscopic gastric banding in a rat model utilizing the same instruments developed for humans. The experimental rat model is more motivating than simulators, requires less space, and has easier maintenance compared with bigger animals, and consequently allows the use of more animals for teaching, training and application in many scientific studies.

Animals↗
PubMed2005

Cell population dynamics modulate the rates of tissue growth processes.

The development and testing of a discrete model describing the dynamic process of tissue growth in three-dimensional scaffolds is presented. The model considers populations of cells that execute persistent random walks on the computational grid, collide, and proliferate until they reach confluence. To isolate the effect of population dynamics on tissue growth, the model assumes that nutrient and growth factor concentrations remain constant in space and time. Simulations start either by distributing the seed cells uniformly and randomly throughout the scaffold, or from an initial condition designed to simulate the migration and cell proliferation phase of wound healing. Simulations with uniform seeding show that cell migration enhances tissue growth by counterbalancing the adverse effects of contact inhibition. This beneficial effect, however, diminishes and disappears completely for large migration speeds. By contrast, simulations with the "wound" seeding mode show a continual enhancement of tissue regeneration rates with increasing cell migration speeds. We conclude that cell locomotory parameters and the spatial distribution of seed cells can have profound effects on the dynamics of the process and, consequently, on the pattern and rates of tissue growth. These results can guide the design of experiments for testing the effectiveness of biomimetic modifications for stimulating tissue growth.

Algorithms↗
PubMed1975

[Attenuation and smoothness of injected signals in a Rijlant network].

The V.C.G. methods must handle the E.K.G. information through weighing systems, because of the volume and the eccentric location of the heart in the chest, of the inhomogeneity of the surrounding tissues and of the irregular shape of the body surface. Most of these weighing systems use compensating networks. On the other hand, Rijlant simulates an homogeneous medium where the cardiac currents spread and where remote observation would eliminate much of the distorsions. In order to understand how such a simulated medium operates, we drive it by means of sinusoidal waves and we observe how the amplitude and the phase of the signals change when we switch on the different leads. Each value recorded at a same level in the network may be considered as the sum of a true proximity effect added to an other component depending upon the lead orientation. The latter is referred to a mixed result of the driving waves that we call "the modulus effect". From the injection level to the other levels, the proximity effect rapidly vanishes while the modulus effect does not disappear until grounded level is reached. The decrease of the modulus effect either to zero (grounded level) or to a finite value (free end of the network) is not expressed as a formula because Rijlant's network does not simulate an euclidian space. We conclude that, at least as the proximity effect is concerned, the instrument performs what it is expected to do.

Heart↗
PubMed1998

Zinc distribution in various tissues, (brain, eye, skin, muscle and blood) of rat during hindlimb suspension.

Postural changes in 1-G environment induce well documented haemodynamic changes. On going from Earth's 1-G environment to the microgravity of space a marked cephalic blood volume shift occurs in humans with a subsequent loss of 2-3 L of fluid determined by diuresis and decreased fluid intake. Moreover, a number of transient changes in serum concentrations of sodium, potassium and calium have been observed in astronauts during spaceflight. It is conceivable that changes in the fluid status, and reduced muscle activities, which are changed by the microgravity environment, would also result in redistribution of some trace elements, such as zinc, copper and manganese. In particular, zinc metabolism, directly involved in many physiological processes, can be altered by a wide variety of factors including stress, rest, exercise, hormones and diet. Some of the microgravity-induced responses in space can be simulated in humans by using the posture of head-down tilt, and in rat by using the posture of hindlimb suspension. The aim of the present study was to investigate the effects of hindlimb suspension for 3-14 days on sodium, potassium and zinc content in various rat tissues including blood, muscle, brain, eye and nose's skin.

Animals↗
PubMed1991

Effects of hypergravity on adherent human cells.

In recent years, accumulating evidence has shown that microgravity or hypergravity may affect cell growth and differentiation. Since it is not easy to carry out researches in space or to simulate weightlessness on earth, we conducted experiments on simulated hypergravity (2 to 15 g) by using a centrifuge (radius: 80 cm; speed motor: 180 rpm). We looked for the effects of chronic hypergravity (7 to 10 days) on cultures of three human cell lines: lung or dermic fibroblasts and lung adenocarcinoma A 549 cells. The results showed a significant decrease (10-20%, P<0.05) in cell proliferation connected to a significant decrease (20-50%, P<0.01) in culture DNA content under hypergravity, but only for lung fibroblasts. The protein content was never disturbed. Dermic fibroblast elastase activity was enhanced (8-13%, P<0.02) under 15 g. Total phospholipid content as well as relative amounts of phospholipid components, analysed by thin layer chromatography, were unchanged in A 549 cells.

Adenosarcoma↗
PubMed2002

Effects of treatments potentially influencing the supply of assimilate on its partitioning in sugarcane.

Two pot experiments and one field experiment were conducted on sugarcane to assess the effects of treatments expected to change total carbon assimilation on the partitioning of assimilate. In the first experiment pots of cultivars CP and N14 were arranged to simulate normal field spacing. At 5 months, plants were partially defoliated or left intact. In the subsequent four months, defoliation resulted in a small (not significant) decrease in total dry mass increment; it increased the proportional partitioning of assimilates to leaves in N14, whilst in CP it increased the proportional partitioning to stems. In both cultivars defoliation increased proportional allocation to non-structural dry matter, and thus sucrose, in the stem. In the second experiment pots of cv. CP were grown at normal spacing for 4 months, then left untreated, shaded, or placed further apart. During the subsequent four months shading decreased total dry matter increment, but increased proportional partitioning to the stems, and within stems to non-structural dry matter, and so sucrose. Widened spacing increased total assimilation, but decreased proportional allocation to stems; partitioning within the stems was not affected. In the field experiment plants of both cultivars were partially defoliated at 6 months, or left intact. Defoliation resulted in only a very small decrease in stem dry mass increment during the subsequent four months (leaves were not measured). Within the stem partial defoliation caused proportionally increased partitioning to non-structural dry matter, hence to sucrose. The results suggest that sucrose storage receives priority in the allocation of assimilate, rather than representing the accumulation of assimilate not required for vegetative growth.

Adaptation, Physiological↗
PubMed2005

Mechanical counter-pressure vs. gas-pressurized spacesuit gloves: grip and sensitivity.

INTRODUCTION: An elastic mechanical counter pressure (MCP) glove for spacesuits is under development. In this study we compared handgrip and pinch grip strength levels for the MCP glove and the current extravehicular mobility unit (EMU) gas-pressurized glove. METHODS: We employed handgrip and pinch grip dynamometers to assess strength levels and von Frey monofilaments to evaluate hand sensitivity. Tests were conducted with the gloved hand inserted in an evacuation chamber at 200 mmHg below atmospheric pressure to simulate conditions in space. RESULTS: Average bare hand strength was 463 N and decreased to 240 N for EMU and 250 N for MCP. Pinch grip and key grip testing showed no difference among conditions. However, there was a significant decrease in palmar grip strength from 111 N barehanded to 67 N in both gloves. Barehanded endurance time was 160 s and dropped to 63 and 69 s for EMU and MCP, respectively. Sensitivity was significantly better for MCP compared with the EMU. DISCUSSION: The MCP glove improved hand sensitivity when compared with the EMU glove and performed as well as the EMU glove in terms of overall handgrip strength, endurance at 25% of maximum handgrip strength, pinch grip, palmar grip, and key grip tests. Improvements in fabric composition and glove design may further improve ergonomic and other functional parameters of the MCP glove.

Adult↗
PubMedDate not supplied

[Effect of exogenous cardiosynchronized contrapulsation on human regional and central hemodynamics].

Variations in regional and central hemodynamics of man under the influence of exogenous contrapulsation (ECP) were examined rheographically. In recumbent subjects, ECP increased cerebral pulse blood filling, particularly of the vertebrobasilar system. It appears that the significant increase of the tone of arterioles and veins may be important when it becomes necessary to correct cerebral circulation in the situations that may lead to brain ischemia. It has been found that in the orthostatic tilt test ECP can be an effective tool for enhancing brain and lung blood supply and increasing stroke volume, cardiac output and blood pressure. This may help maintain homeostasis and improve orthostatic tolerance. The observation that ECP may facilitate blood supply of the vitally important organs, specifically brain, enables us to recommend this procedure to be used at an early stage of readaptation after simulation or real space flights.

Adaptation, Physiological↗
PubMed1996

Experimental extrinsic allergic alveolitis and pulmonary angiitis induced by intratracheal or intravenous challenge with Corynebacterium parvum in sensitized rats.

Extrinsic allergic alveolitis and pulmonary sarcoidosis are granulomatous diseases of the lung for which clinical presentation and anatomic site of granuloma formation differ. Extrinsic allergic alveolitis is caused by inhaled antigens, whereas the nature and source of the inciting antigen in sarcoidosis is unknown. To test the hypothesis that the route via which antigen is introduced to the lung contributes to the clinicopathological presentation of pulmonary granulomatous disease, rats immunized with intravenous (i.v.) Corynebacterium parvum were challenged after 2 weeks with either intratracheal (i.t.) or i.v. C. parvum. The granulomatous inflammation elicited by i.t. challenge predominantly involved alveolar spaces and histologically simulated extrinsic allergic alveolitis. In contrast, the inflammation induced by i.v. challenge was characterized by granulomatous angiitis and interstitial inflammation simulating sarcoidosis. Elevations of leukocyte counts and TNF levels in bronchoalveolar fluid, which reflect inflammation in the intra-alveolar compartment, were much more pronounced after i.t. than after i.v. challenge. Tumor necrosis factor, interleukin-6, CC chemokine, CXC chemokine, and adhesion molecule mRNA and protein expression occurred in each model. In conclusion, i.t. or i.v. challenge with C. parvum in sensitized rats caused pulmonary granulomatous inflammation that was histologically similar to human extrinsic allergic alveolitis and sarcoidosis, respectively. Although the soluble and cellular mediators of granulomatous inflammation were qualitatively similar in both disease models, the differing anatomic source of the same antigenic challenge was responsible for differing clinicopathological presentations.

Alveolitis, Extrinsic Allergic↗
PubMed1997

Two-dimensional models of tumour angiogenesis and anti-angiogenesis strategies.

There is a very strong link between the vascularization of a tumour and the spread of the disease, both locally and to distant sites (Gimbrone et al., 1974, J. Natl. Cancer Inst. 52, 413-27; Muthukkaruppan et al., 1982, J. Natl. Cancer Inst. 69, 699-704; Ellis & Fiddler, 1995, Lancet 346, 388-9). A tumour becomes vascularized by a process known as angiogenesis. Tumour angiogenesis is initiated by the release of diffusible substances by the tumour, whereby neighbouring capillary vessels are stimulated to grow and eventually penetrate the tumour. Anti-angiogenesis has been proposed as a potential strategy for the treatment of cancer (Folkman, 1995, Nature Med. 1, 21-31; Harris et al., 1996, Breast Cancer Res. Treat. 38, 97-108). In this paper, a mathematical model of the development of the tumour vasculature is presented. By suitable manipulation of the model parameters, we simulate various anti-angiogenesis strategies and we examine the roles that haptotaxis and chemotaxis may play during the growth of the neovasculature. The model is simulated in two space dimensions (on a square domain) so that it is, in theory, experimentally reproducible and any predictions of the model can therefore be tested.

Angiogenesis Inducing Agents↗
PubMedDate not supplied

Mucous gel transport in a simulated cough machine: effects of longitudinal grooves representing spacings between arrays of cilia.

Under some conditions, such as inhalation injury, an array of longitudinal channels without cilia may be formed on the epithelial surface, affecting mucus transport in the lung during coughing. Moreover, in certain cases of the diseased state of the lung, immotile cilia remain embedded in the serous fluid and may form channels in the direction of air motion during coughing, providing a resistance-free pathway for serous layer fluid and assist in mucus clearance. To understand this phenomenon, we have conducted experiments with mucous gel simulants (MGS) in a simulated cough machine (SCM) using soap solution as a serous layer simulant (SLS). The channel structure of the airway surface was modeled by introducing bottom plates with longitudinal grooves about 10 cm long having different depths, widths and number of grooves. It was shown that mucous gel transport increases as the cross-sectional area occupied by channel grooves increases. The effects of sinusoidal constriction and mucous gel filance were also investigated in this model system. It was found that mucous gel transport increases in the constricted case (minimum gap, 3 mm, and maximum gap, 9 mm) in comparison with that in the parallel case (constriction gap of 9 mm). The effect of increasing the mucous gel filance was to decrease the transport,, as reported in previous studies.

Cilia↗