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At least 253 records · Page 14Linked to original sources
PubMed1994

An extended cellular space method for simulating autocatalytic oligonucleotides.

Self-replicating nucleotides and other self-replicating molecules are an active area of study today by organic chemists. Such studies are important for improving our understanding of the origins of life. Computational studies of self-replicating molecules could increase our insight into their properties, but existing computational techniques have been limited in their usefulness for such reactions (numerical simulation of differential equations requires reaction rate constants that are difficult to obtain, cellular automata models are too restrictive for modeling molecular movements and bindings, etc.). We have thus developed an efficient modified cellular automata method that supports the study of self-replicating oligonucleotides. We explain this method and illustrate its use with a specific self-replicating (autocatalytic) deoxyribohexanucleotide.

Algorithms↗
PubMed2005

Partial averaging and the centroid virial estimator for stereographic projection path-integral simulations in curved spaces.

We develop and test three different partial averaging theories for the stereographic projection path integral in curved spaces. Additionally, we adapt and test the centroid virial estimator for the kinetic energy in curved spaces. We tested both a confining as well as a nonconfining potential for the particle in a ring. All three partial averaging theories are demonstrated to converge linearly in the asymptotic region with k(-2)max, the number of Fourier coefficients. We use an error estimator to determine the optimal parameters for an extrapolation to infinite kmax. We verify that the centroid virial estimator (derived from the primitive DeWitt path-integral formula) converges to the kinetic energy for both confining and nonconfining potentials.

Journal Article↗
PubMed2000

[Lipid peroxidation and activity of diagnostically important blood enzymes in rats during 35 days head-down suspension].

In the experiment with 35-d head-down suspension of rats concentrations of lipid peroxidation (LPO) products and values of antioxidant defense (AOD) parameters were determined in the lever, skeletal muscles, myocardium, and blood plasma. In addition, activity of 11 plasma enzymes characteristics of these tissues was evaluated. LPO was found to be activated in the lever, myocardium and skeletal muscles in the first and 4-5 weeks of suspension. The period between weeks 2 and 4 marked phase variation of LPO intensity which could have baseline or increased values. Plasma LPO was inhibited due to AOD activation pointing to compensatory processes on the level of organism and absence of pathologies in the organs and tissues under study. As a rule, activity of the plasma enzymes directly or indirectly participating in energy metabolism was reduced. Enzymes-catalysts of other types of metabolism predominantly elevated activity during LPO intensification. Canonic analysis established a significant correlation of LPO, AOD and activity of plasma enzymes, and LPO and AOD in the rat's lever and plasma enzymes. These correlations between LPO, AOD and activity of diagnostically important enzymes can be used to diagnose and predict changes in the state of organism caused by simulated factors of space flight.

Animals↗
PubMed1989

Simulation of Space-Adaptation Syndrome on Earth.

The three Spacelab D-1 Scientist Astronauts were exposed to a 1.5 h centrifuge run in the supine position, resulting in a linear 3 g acceleration. They used their space experience to evaluate their readaptation to normal gravity and compared their observations with 'Space Adaptation Syndrome'. After the centrifuge runs, the vestibular visual system appeared to be modified in a very specific and reproducible manner. Readaptation to the normal 1 g environment took at least 6 h. During this period there was a striking similarity to the astronauts' experience during adaptation to weightlessness in space. Vestibular tests were subsequently performed, which confirmed these subjective findings.

Adaptation, Physiological↗
PubMed2000

[Transmission and exchange of genetic information during bacterial conjugation in ground-based simulations of the factors of orbital flight].

Control laboratory experiments on bacterial conjugation under simulated spaceflight conditions were performed with the use of new equipment (bioreactor RECOMB-2 and container BIOMAGNISTAT) within the RSA-NASA science program. External parameters were selected and the plan of simulation of a space experiment was verified to ensure high efficiency of the conjugative transfer of chromosomal and plasmid DNA and storage of hybrids on the ground. Genetic analysis of conjugative hybrids E. coli supported the hypothesized possibility of transfer of a whole bacterial chromosome during conjugation that will lead to relative stabilization of the diploid state. Earlier this hypothesis was used to interpret results of experiments performed on MIR in 1992-1993. Hence, the ground laboratory investigations proved the conclusion about high probability of transfer of large fragments or even a whole chromosome during space flight. Screening of the geomagnetic field by BIOMAGNISTAT increases the probability of conjugative contacts between cells and is likely to slightly inhibit the processes of recombination.

Conjugation, Genetic↗
PubMed2001

Development of a space radiation Monte Carlo computer simulation based on the FLUKA and ROOT codes.

This NASA funded project is proceeding to develop a Monte Carlo-based computer simulation of the radiation environment in space. With actual funding only initially in place at the end of May 2000, the study is still in the early stage of development. The general tasks have been identified and personnel have been selected. The code to be assembled will be based upon two major existing software packages. The radiation transport simulation will be accomplished by updating the FLUKA Monte Carlo program, and the user interface will employ the ROOT software being developed at CERN. The end-product will be a Monte Carlo-based code which will complement the existing analytic codes such as BRYNTRN/HZETRN presently used by NASA to evaluate the effects of radiation shielding in space. The planned code will possess the ability to evaluate the radiation environment for spacecraft and habitats in Earth orbit, in interplanetary space, on the lunar surface, or on a planetary surface such as Mars. Furthermore, it will be useful in the design and analysis of experiments such as ACCESS (Advanced Cosmic-ray Composition Experiment for Space Station), which is an Office of Space Science payload currently under evaluation for deployment on the International Space Station (ISS). FLUKA will be significantly improved and tailored for use in simulating space radiation in four ways. First, the additional physics not presently within the code that is necessary to simulate the problems of interest, namely the heavy ion inelastic processes, will be incorporated. Second, the internal geometry package will be replaced with one that will substantially increase the calculation speed as well as simplify the data input task. Third, default incident flux packages that include all of the different space radiation sources of interest will be included. Finally, the user interface and internal data structure will be melded together with ROOT, the object-oriented data analysis infrastructure system. Beyond the benefits of 'objectivity', ROOT's incorporation will also provide a graphical user interface with powerful tools for input prior to the calculation, as well as for data analysis and visualization of the results.

Computer Simulation↗
PubMedDate not supplied

[Ion-regulating function of the human kidneys during prolonged space flight and in simulation studies].

Ten cosmonauts who performed 30- to 175-day space flights on board Salyut-4 and Salyut-6, and 50 test subjects exposed to head-down tilt (-4 degrees) for 182 days were examined. In actual and stimulated weightlessness renal excretion of calcium and potassium increased, reaching maximum during the 4-6th weeks. Before and after flight the test subjects were exposed to loading salt tests. Renal excretion of calcium and potassium in response to the loading tests with their salts postflight was much higher than preflight. During the potassium chloride load the aldosterone content in blood correlated with potassium excretion, and during the calcium lactate load an increase in calcium excretion was paralleled by a decrease in the parathormone content in blood. It is most likely that the negative balance of ions in weightlessness is associated with the reduced capacity of tissues to retain electrolytes due to the decreased ion pool. It was shown that electrolyte balance can be beneficially influenced by exercises.

Aldosterone↗