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Results for “Elementary Particles”

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At least 415 records · Page 23Linked to original sources
PubMed1980

The induction of chromosome aberrations in human lymphocytes by negative phi-mesons under conditions of anoxia and oxygenation.

After a dose of 3.0 Gy in the peak position of the pion depth-dose curve, the ratios between observed chromosome aberration yields under conditions of oxygenation and of anoxia were obtained for lymphocytes exposed at 3 depths in a plastic phantom. These ratios were 3.7, 1.9 and 1.3 in the plateau, peak and post-peak positions, respectively, suggesting a corresponding decrease in the oxygen enhancement ratio.

Aerobiosis↗
PubMed1985

On the stability of cognitive processes.

An empirical and mathematical model for self-organization is proposed, based on elemental properties, on unique interaction and on the combination of hierarchical elements. In the model, higher elements are stabilized by the 'cognitive' (strong) interaction of subelements, disregarding intermediate elements. This is called 'elementary reductionism' and is illustrated by the sequence quarks-elementary particles-atoms-molecules-cells-organisms- societies. Optimal dynamic interaction of nonidentical elements is called 'cognitive stability'. This is compared with thermodynamic equilibrium. The principal differences are outlined.

Actins↗
PubMed1980

Test of a pion range monitor using the radiative capture of pions on protons pi-p leads to n gamma.

The present paper demonstrates that neutron-photon pairs from radiative capture of stopped pions on chemically bound protons can be used to measure the range of negative pions within phantoms or a patient. Experimental results are given for a polyethylene and a water target of realistic size as well as for a Rando phantom. Monte-Carlo calculations were carried out in order to study the influence of various sizes of treatment volumes, detector geometries and neutron scattering within the targets upon the accuracy of the pion range determination. The results reveal clearly that a pion range monitor for the control of therapy plans and for actual patient irradiations can be designed according to the proposed principle. The absorbed dose required for a measurement is of the order of 0.1 Gy for a single pion beam if one aims at an accuracy of range determination of a few millimeters.

Elementary Particles↗
PubMed1975

The effect of diethylstilbestrol on the rate of osseous repair, bone integrity, and plasma calcium in the adult avian.

The effect of diethylstilbestrol on healing experimental osseous defects in adult roosters was studied by means of I-125 photon absorptiometry. Although the two dose levels utilized in this study both resulted in elevated plasma calcium and lipid levels and significantly increased the mineral and organic fractions of femoral bone, diethylstilbestrol treatment over a six-week period had no effect on the rate or magnitude of mineralization in the repairing osseous defect.

Absorption↗
PubMed1998

Formation of plasmid DNA strand breaks induced by low-energy ion beam: indication of nuclear stopping effects.

Plasmid pGEM 3zf(+) was irradiated by nitrogen ion beam with energies between 20 and 100 keV and the fluence kept as 1x10(12)ions/cm2. The irradiated plasmid was assayed by neutral electrophoresis and quantified by densitometry. The yields of DNA with single-strand and double-strand breaks first increased then decreased with increasing ion energy. There was a maximal yield value in the range of 20-100 keV. The relationship between DNA double-strand breaks (DSB) cross-section and linear energy transfer (LET) also showed a peak-shaped distribution. To understand the physical process during DNA strand breaks, a Monte Carlo calculation code known as TRIM (Transport of Ions in Matter) was used to simulate energy losses due to nuclear stopping and to electronic stopping. It can be assumed that nuclear stopping plays a more important role in DNA strand breaks than electronic stopping in this energy range. The physical mechanisms of DNA strand breaks induced by a low-energy ion beam are also discussed.

DNA Damage↗
PubMed1998

Neutron, proton, and photonuclear cross-sections for radiation therapy and radiation protection.

I review recent work at Los Alamos undertaken to evaluate neutron, proton, and photonuclear cross-sections up to 150 MeV (to 250 MeV for protons), based on experimental data and nuclear model calculations. These data are represented in the ENDF format and can be used in computer codes to simulate radiation transport. They permit calculations of absorbed dose in the body from therapy beams, and through use of kerma coefficients allow absorbed dose to be estimated for a given neutron energy distribution. In radiation protection, these data can be used to determine shielding requirements in accelerator environments and to calculate neutron, proton, gamma-ray, and radionuclide production. Illustrative comparisons of the evaluated cross-section and kerma coefficient data with measurements are given.

Carbon↗
PubMed2006

Effect of cosmological neutrinos on discrimination between the two enantiomers of a chiral molecule.

In the framework of an extraterrestrial origin of biological homochirality, universal mechanisms are of particular interest. In this sense we consider the weak parity-violating neutrino-electron interaction through weak charged currents W (+/-) between the relic flux of cosmological neutrinos and the electrons of a chiral molecule. We use the known theoretical result of the split in energy of the two helicity sates of an electron in the cosmic neutrino bath, due to weak charged currents. In the case that electrons of a chiral molecule are submitted to a helicoidal potential due to the nuclear conformation, these electrons have opposite helicities for the two enantiomers of the molecule and consequently the mentioned neutrino-electron interaction would produce a splitting in energy between the two enantiomers. An estimation of this energy for the case of a single electron yields a small value of the order of 10(-26) eV. This value results amplified by the contribution of all the molecular electrons having helicity and other possible mechanisms.

Electrons↗
PubMed2007

The role of supernova neutrinos on molecular homochirality.

Electroweak parity violating interaction between supernova (SN) neutrinos and electrons of a simple chiral molecule is studied related to the origin of molecular homochirality. Appearance of supernova remnants inside molecular clouds favours the interaction of SN-neutrinos with interstellar molecules, leading to a energetic difference between the two enantiomers of the order of 10(-5) eV. This energetic difference is closer to the thermic energy of the interstellar medium, so molecular homochirality could be enhanced in molecular clouds containing supernova remnants inside it due to neutrino interaction.

Elementary Particles↗
PubMed1983

Iodine-123 phenylpentadecanoic acid: detection of acute myocardial infarction and injury in dogs using an iodinated fatty acid and single-photon emission tomography.

The ability of an iodinated fatty acid, iodine-123 phenylpentadecanoic acid (1-123 PPA), and single-photon emission computed tomography (SPECT) to detect myocardium injured by temporary or permanent coronary arterial occlusion was evaluated. In 5 control dogs, 11 dogs that underwent 90 to 120 minutes of fixed left anterior descending coronary artery (LAD) occlusion, and 8 dogs that underwent 90 minutes of temporary LAD occlusion and up to 90 minutes of reflow, 2 to 6 mCi of I-123 PPA were injected and the dogs were imaged with SPECT. Control dogs showed relatively uniform uptake and clearance of I-123 PPA in similar left ventricular (LV) regions. Dogs with permanent LAD occlusion were identified by computer algorithm as having regions of decreased I-123 PPA uptake in the infarct-related area and a reduced rate of I-123 PPA clearance (-9.4% in infarct sectors [washin], +3.7% in sectors adjacent to the area of infarction, and +15.4% in control LV sectors [p less than 0.01]). Dogs with temporary LAD occlusion and reperfusion had decreased clearance of I-123 PPA from the regions with infarction; I-123 PPA clearance was -5.2 +/- 16.4% in infarct sectors, 12.7 +/- 7.4% in periinfarct zones, and 30.4 +/- 12% in control LV regions. These data demonstrate that tomographic analysis of I-123 PPA uptake and clearance permits the relatively noninvasive detection of LV myocardium injured by permanent or temporary LAD occlusion and reperfusion.

Animals↗
PubMed1981

Detection of a phase transition in red cell membranes using positronium as a probe.

Positron lifetimes in human red cell ghost membranes have been measured as a function of temperature from 3 degrees C to 25 degrees C. A marked sudden change in the ortho-positronium annihilation rate was found at 16-18 degrees C during the heating cycle and at 18-20 degrees C in the cooling cycle. Such sudden change of microenvironment in the membranes sensed by ortho-positronium is attributed to the sudden change of water diffusion rate through the membranes which is a consequence of the sudden change in free volume, or fluidities in the lipid layers.

Elementary Particles↗
PubMed1975

Substrate-induced redox change of selenium in glutathione peroxidase studied by x-ray photoelectron spectroscopy.

Glutathione peroxidase showed an X-ray photoelectron spectroscopy signal of the Se 3d (3/2, 5/2) electrons at 54.4 eV. After the addition of the acceptor substrate H2O2, a marked shift of this signal to a value of 58.0 eV was observed. Upon subsequent treatment with the donor substrate glutathione, this chemical shift was reversed and the original signal was obtained. These data demonstrate that the enzyme-bound selenium moiety participates in the catalytic process. From the chemical shift obtained it is concluded that the enzyme shuttles between a selenol or selenol derivative in its reduced form and a seleninyl or selenonyl compound in its oxidized form.

Deuterium↗