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Biomedical subjects

M Moisan

Publications and source records attributed to M Moisan.

7 recordsLinked to original sources
PubMed2004

Modeling of microwave-sustained plasmas at atmospheric pressure with application to discharge contraction.

The modeling of microwave-sustained discharges at atmospheric pressure is much less advanced than at reduced pressure (<10 Torr) because of the greater complexity of the mechanisms involved. In particular, discharge contraction, a characteristic feature of high-pressure discharges, is not well understood. To describe adequately this phenomenon, one needs to consider that the charged-particle balance in atmospheric-pressure discharges relies on the kinetics of molecular ions, including their dissociation through electron impact. Nonuniform gas heating plays a key role in the radial distribution of the density of molecular ions. The onset of contraction is shown to depend only on radially nonuniform gas heating. The radial nonuniformity of the electric field intensity also plays an important role allowing one, for instance, to explain the lower degree of contraction observed in microwave discharges compared to dc discharges. We present a numerical fluid-plasma model that aims to bring into relief the main features of discharge contraction in rare gases. It calls for surface-wave discharges because of their wide range of operating conditions, enabling a closer check between theory and experiment.

Journal Article↗
PubMed2004

Electron density and gas temperature from line broadening in an argon surface-wave-sustained discharge at atmospheric pressure.

We have used the collisional broadening of neutral argon lines to determine the electron density and gas temperature of a microwave discharge at atmospheric pressure. The gas temperature can be obtained from the Van der Waals broadening, provided that the Stark broadening is negligible. This can be achieved by using lines from low-lying levels (close to the ground state). On the other hand, lines corresponding to transitions from high-lying levels, which are more sensitive to Stark (quadratic) broadening, can be utilized to determine electron density. The electron density values obtained from the quadratic Stark broadening of argon atoms are in reasonable agreement with those derived from the linear Stark broadening of the H(beta) line. The proposed method ensures perturbation-free access to plasma parameters, which is not the case when adding hydrogen to the discharge, even in a small amount, to observe the Balmer series lines.

Journal Article↗
PubMed2001

Low-temperature sterilization using gas plasmas: a review of the experiments and an analysis of the inactivation mechanisms.

Utilizing an ionized gas (plasma) to achieve sterilization is an alternative to conventional sterilization means as far as sterilization of heat-sensitive materials and innocuity of sterilizing agents are concerned. The literature on plasma sterilization is reviewed. A major issue of plasma sterilization is the respective roles of UV photons and reactive species such as atomic and radicals. Insight into this matter is obtained by analyzing the survival curves of microorganisms. In contrast to classical sterilization where such plots show a unique straight line, plasma sterilization yields survival diagrams with two or three different linear segments. Three basic mechanisms are involved in the plasma inactivation of microorganisms: (A) direct destruction by UV irradiation of the genetic material of microorganisms; (B) erosion of the microorganisms atom by atom, through intrinsic photodesorption by UV irradiation to form volatile compounds combining atoms intrinsic to the microorganisms; (C) erosion of the microorganisms, atom by atom, through etching to form volatile compounds as a result of slow combustion using oxygen atoms or radicals emanating from the plasma. In some cases, etching is further activated by UV photons, increasing the elimination rate of microorganisms. These mechanisms make plasma sterilization totally different from classical sterilization techniques and suggest its use to inactivate nonconventional infectious agents such as the abnormal prions.

Bacillus subtilis↗
PubMed1996

Atomic spectroscopy with surface wave plasmas.

The use of microwave induced plasmas, particularly of surface wave plasmas, as detectors in atomic emission spectrometry for elemental analysis is reviewed. Surface wave plasmas have been produced at low HF power and used as gas chromatographic detectors. The analytical performances for the detection of non-metals with a Fourier transform spectrometer and a two-channel filter unit are reported. The excitation behavior of non-metals in helium-based mixed gas-plasmas has also be studied. In particular, the effect of power and of nitrogen concentration on the bromine emission has been systematically investigated. A nine-fold improvement of the detection limits for bromine can be obtained in a high power (900 W) helium-nitrogen (0.1-0.2%) plasma.

Journal Article↗
PubMed1978

General adaptation syndrome and magnetostatic field: effects on sleep and delayed reinforcement of low rate.

In order to study the effects of a magnetostatic field on the organism, continuous exposure was applied and the resulting effects were observed for a period of 20 days. The Ss were four rats which were continually exposed, one by one, to a vertical field of 2800 oersted for uninterrupted periods of time. In a first series of experiments, the variation of the sleeping period for each of the four SS was observed. An evolution quite characteristic of the different phases of the general adaptation syndrome was noted: reaction, counterreaction, and resistance. The same phenomenon was observed in the response under delayed reinforcement of low rate (DRL) at 5 and 10 seconds. In each case, a slowdown of the weight growth was noted. One can thus consider the magnetostatic field as an agent responsible for a nonspecific general effect similar to other stressing agents. These behavioral observations suggest a verification of these effects on the endocrine system and illustrate the necessity of long exposures for the study of specific and nonspecific effects of the exposure to the magnetostatic field.

Adaptation, Psychological↗