Zoran Lj. Petrovic

Modelling of anomalous Doppler broadened lines, thermalization of electrons and the role of radicals in discharges at high E/N

In this paper we show how Monte Carlo technique developed for swarm studies may be applied to model some real discharges or to provide data for realistic plasma models. In all cases discussed here the Monte Carlo technique without self consistent field is driven to a much greater level of complexity than usually found in swarm studies. We discuss three conceptually quite different situations that require exact modelling by Monte Carlo Simulations (MCS). The first is the case of transport in gases where degree of dissociation is large and thereby radicals formed by the discharge may affect the transport coefficients. Based on recent calculations for electron CFX radical cross sections we calculated how transport coefficients would be affected by the presence of radicals in pure CF4 and CF4/Ar mixtures covering range of abundances often found in plasma etching devices. The second case studied here is modelling of thermalization of high energy electrons in the atmospheric gases as an attempt to provide the basis for detection of very high energy cosmic particles. In that case pressure dependent emission efficiency is studied as a function of electron energy and the system is developed to an arbitrary degree of secondary electron production. Finally we give some recent advances and current status of modelling of high E/N discharges operating in Townsends regime in hydrogen where anomalous broadening was observed and explained by fast neutral excitation in both directions along and against the acceleration due to electric field.

Electron, Ion and Atom Collisions Leading to Anomalous Doppler Broadening in Hydrogen

DC high E/N swarm experiment (self sustained discharge operating in the Townsend regime) may be modeled directly and exactly as it does not require self consistent calculation of the electric field and is thus open to a simple Monte Carlo simulation that may include complexity at the level of representation of collisional events. Thus such an experiment operating under swarm conditions is the best way to test the mechanism of generation of anomalously large Doppler broadening that was often observed in low pressure discharges.In this paper we show revised results of modeling of Doppler profiles by using a well tested Monte Carlo procedure and revised models of heavy particle collisions. In particular we study the importance of fast H2 and fast H particles, the effect of different models of angular distribution of particles scattered of the surface and of the molecules and we study the role of the energy losses due to vibrational excitation.

Comparison of results of sensory and chemical and physico-chemical investigations of fresh chilled beef packaged in vacuum during storage in retail conditions

Vacuum packaging of fresh meat can contribute to prolonged shelf-life, slower chemical changes in meat, and maintaining of desirable sensoric properties. The main goal of this work was the comparative examination of sensory and chemical properties relevant for oxidative and hidrolytic changes of cooled fresh beef cuts (m.quadriceps femoris) in vacuum packaging, and the determination of interdependence of hydrolytical and oxidative changes regarding to sensory characteristics. The beef flank cuts taken from primal cuts (quarters) of 3 Simmental steers (average weight of 400 kg; one steer per testing cycle) after slaughtering, dressing and cooling were taken for the experiment. Cutting and packaging in vacuum thermo-shrinkable multilayered bags was performed in the industrial meat establishment, within 40 hours after slaughtering. The vacuum packaged beef cut samples were stored under controlled temperature conditions (0-2°C) in refrigerated retail show case. During the night, samples were removed from show case and stored in cold storage room in the same establishment (0-4°C). This method was repeated as daily routine during examination period. Sensory and chemical examination dynamics was set as: day 1 (immediately after packaging), days 15, 21 and 28 in each particular testing cycle (3). Sensory properties were evaluated by using quantitative-descriptive test, on a scale of 1 to 5. The following properties were evaluated: appearance of meat, the colour of meat surface, the colour of meat intersection, structure, texture, smell of the fresh meat, smell of the meat after cooking, taste of the meat after cooking and roasting. The examined chemical properties indicating oxidative and hydrolytic changes were: acid value, peroxide number, TBA test (test with thiobarbituric acid to determinate malonaldehide content), TVB-N (total volatile basic nitrogen), aw (water activity value) and pH. Sensory and chemical qualities of vacuum packaged beef flank under established storage conditions were acceptable in all three testing cycles, ending with the 21st day. In the first and second cycle, in most cases, there were confirmed medium to strong correlations of all examined chemical parameters with the sensoric characteristics of beef. In the third cycle, the registered above mentioned correlations between chemical parameters and sensory properties were classified as negative weak correlations.

Effect Of Anode Surface on Doppler Profile in Townsend Discharge in Pure Hydrogen

In this work we show results of Monte Carlo modeling of electrons and heavy particles induced spatially resolved emission intensity or the Doppler profile in pure H2 discharge focusing on anode boundary. In particular we present study of fast H2 and fast H particles, scattered both at the surface and of the molecules. Since the anode boundary is characterized by a large electron flux, role of electron reflection and production of secondary electrons at the anode surface is part of the complete picture of spatial emission profile. In this work we verify our models of electron backscattering from the anode including both the reflection and the secondary electron production by making comparisons with the drift tube experiments. In order to achieve consistency with our previous results we select conditions of simulation appropriate for very high E/N (E‐electric field, N‐gas density) that are selected from experimental Townsend discharges in pure H2.