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At least 595 records · Page 33Linked to original sources
PubMed1978

Negative pion irradiation of mammalian cells. II. A comparative analysis of cell-cycle progression after exposure to pi-mesons and cobalt gamma-rays.

The effect of negative pi-mesons on cell-cycle progression of exponentially-growing V 79 monolayer cultures was examined by flow-microfluorometric analysis. Comparison with proliferative changes of the same cell-line after cobalt gamma-irradiation yielded r.b.e. values (relative biological effectiveness) of 2.2 for both, G2+M accumulation and division delay after irradiation at the pion peak. A dose-dependent prolongation of S-phase was found after Co gamma-irradiation which, however, was not detectable after pi-exposure. This observation is so far the only qualitative difference demonstrated in the effects of the two types of radiation.

Cell Cycle↗
PubMed1980

Negative pion irradiation of mammalian cells. III. A comparative analysis of DNA strand breakage, repair and cell survival after exposure to pi-mesons and X-rays.

The yields of immediate and residual breaks in DNA of X- and peak pion irradiated Chinese hamster cells were measured by hydroxylapatite chromatography in order to investigate the r.b.e. of immediate break production and the relation between residual breaks and survival in the same low dose range of up to 10 Gy. A linear dose response for immediate break induction was observed with an r.b.e. of 0.37 for peak pions, whereas the formation of residual breaks showed a linear-quadratic dose dependence for both types of radiation. The dose-effect curves of residual break can directly be correlated with the corresponding survival curves for both radiation types used indicating that residual breaks are lethal events (most probably unrepaired double strand breaks) formed in this low dose range by single- and multi-hit interactions. Despite their lower efficiency in formation of immediate breaks peak pions produce more residual breaks per dose than X-rays.

Animals↗
PubMed1981

The biological effect of very high energy hadrons.

The meristems of Vicia faba bean roots were irradiated at different depths in water in a 250 GeV/c positive hadron beam from the CERN Super Proton Synchrotron (SPS). The growth during the 10 days following irradiation was determined and compared with results obtained from 60Co gamma-ray exposures. The data indicate a Relative Biological Efficiency (r.b.e.) near to one, independent of the contribution of secondaries to the dose. However, some anomalies in the radiation response of the irradiated beans were noted.

Cobalt Radioisotopes↗
PubMed1983

Dose-effect relationships for induction of cell inactivation and asymmetrical chromosome exchanges in three cell lines by photons and neutrons of different energy.

The impairment of clonogenic capacity as well as the induction of dicentrics and centric rings by different types of radiation was investigated in three lines of mammalian cells (R-1,M; RUC-2 and V-79). The experiments were performed with cells in plateau phase cultures which contain 70-80 per cent of cells in the G0 or prolonged G1 phase of the cell cycle. They were irradiated with 137Cs gamma rays, 300 kV X-rays or 0.5, 4.2 or 15 MeV neutrons. The different types of cells show an appreciable variation in sensitivity to induction of both types of effect, being greatest for 0.5 MeV neutrons, intermediate for 4.2 and 15 MeV neutrons and least for photons. The dose-response relationships for both types of effect were analysed for neutrons in terms of a linear dose coefficient only, while the results for photons required analysis in terms of linear and quadratic coefficients. The effectiveness per unit of dose for cell inactivation is greater than that for induction of dicentrics and centric rings by factors of about 4 to 7. However, dicentrics and centric rings constitute only a fraction of the chromosome aberrations. Maximum r.b.e. values of about 12 at low doses were obtained for 0.5 MeV neutrons.

Animals↗
PubMed1985

Effect of different pion stopping volumes on the radiation response of mouse small intestine.

This radiobiological investigation was based on measurements of crypt cell survival in mouse small intestine when the animals were exposed to 5 cm3 (spot), 350 cm3 and 3010 cm3 (the latter two were spot scans) pion stopping volumes generated by the multi-channel Piotron of the Swiss Institute for Nuclear Research. The experimental data obtained indicate that there was a decrease in biological effectiveness when the pion treatment volume was enlarged, irrespective of whether the pion dose was delivered in a single exposure or in four fractions. The r.b.e. values for pion beams relative to 200 kVp X-rays for the different experimental conditions used in this study are presented. The phenomenon of decreasing biological effectiveness with increasing pion stopping volume may be attributed to the following two factors: (1) when the pion stopping volume is increased there is a corresponding dilution of the high l.e.t. component of the beam; (2) the biological test system used may be sensitive to radiation dose rate which varied by a ratio of about 20 for the pion volumes used in this study.

Animals↗
PubMed1987

Collisional excitation of interstellar cyclopropenylidene.

Theoretical rotational excitation rates were computed for C3H2 in collisions with He atoms at temperatures from 30 to 120 K. The intermolecular forces were obtained from accurate self-consistent field and perturbation theory calculations, and collision dynamics were treated within the infinite-order sudden approximation. The accuracy of the latter was examined by comparing with the more exact coupled states approximation.

Astronomical Phenomena↗
PubMed1995

Parameterization of spectral distributions for pion and kaon production in proton-proton collisions.

Accurate semi-empirical parameterizations of the energy-differential cross sections for charged pion and kaon production from proton-proton collisions are presented at energies relevant to cosmic rays. The parameterizations depend on the outgoing meson momentum and also the proton energy, and are able to be reduced to very simple analytical formulas suitable for cosmic-ray transport.

Cosmic Radiation↗
PubMed2000

The fourfold Democritus on the stage of early modern science.

The renewed success of ancient atomism in the seventeenth century has baffled historians not only because of the lack of empirical evidence in its favor but also because of the exotic heterogeneity of the models that were proposed under its name. This essay argues that one of the more intriguing reasons for the motley appearance of early modern atomism is that Democritus, with whose name this doctrine was most commonly associated, was a figure of similar incoherence. There existed in fact no fewer than four quite different Democriti of Abdera and as many literary traditions: the atomist, the "laughing philosopher," the moralizing anatomist, and the alchemist. Around the year 1600 the doctrines of these literary figures, three of whom had no tangible connection with atomism, began to merge into further hybrid personae, some of whom possessed notable scientific potential. This essay offers the story of how these Democriti contributed to the rise of incompatible "atomisms."

Alchemy↗