Mjerenje raspodjele elektronske energije u dvama područjima istosmjernog magnetrona za rasprašivanje

The electron energy distribution function (EEDF) at the edge of the cathode fall and positive column regions of Ar and He glow discharge were measured using a single Langmuir probe. The EEDF in the cathode fall region was found to be non-Maxwellian where two groups of electrons were detected. The two groups have no chance to be thermalized since they leave the cathode fall region fast. Sources of the two groups of electrons are discussed. Moreover, EEDF in the positive column region was found to be Maxwellian for both gases. Electrons have a chance to thermalize themselves due to the long plasma lifetime in this region.Primjenom Langmuirove sonde mjerili smo funkciju raspodjele elektronske energije (EEDF) na rubu katodnog tamnog prostora i u pozitivnom stupcu tinjavog izboja u Ar i He. U katodnom tamnom prostoru našli smo ne-Maxwellov EEDF s dvjema grupama elektrona. Ove dvije grupe ne mogu se termalizirati jer brzo napuštaju prostor tinjavog izboja. Raspravljamo uzroke dviju grupa. Međutim, u pozitivnom stupcu smo našli Maxwellovu EEDF. U tom je području trajanje plazme dugo i elektroni se mogu termalizirati

Izravna i neizravna sterilizacija mikroba plazmom

Atmospheric-pressure parallel-plate dielectric barrier discharge has been designed for sterilization of Saccharomyces Cerevisiae and Candida yeasts. Oxygen has been used as the input working gas. The output gas after discharge operation was a mixture of both ozone and oxygen, with concentration that depends on the applied voltage between the electrodes, gap space and gas flow rate. Sterilization process has been done in two ways, by direct exposure to oxygen plasma inside the discharge cell and by indirect exposure to the plasma. Survivor curves, and scanning and transmission electron microscope were used to study the inactivation kinetics and morphology of the yeast surface before and after sterilization. It has been found that the indirect sterilization causes yeast inactivation in a short time, less than three minutes, while the direct sterilization took place in a longer time, more than ten minutes.Sagradili smo posudu s usporednim pločama i dielektričnom pregradom za postizanje izboja na atmosferskom tlaku, namijenjenu za proučavanje sterilizacije mikroba Saccharomyces Cerevisiae i Candida. Radni plin bio je kisik. Izlazni plin iz posude bio je smjesa ozona i kisika, čija je koncentracija ovisna o vaponu izboja među elektrodama, procijepu i brzini protjecanja plina. Sterilizacija se provodila na dva načina, izravnim izlaganjem u izbojnoj posudi i neizravnim izlaganjem plazmi. Za proučavanje kinetike prekida aktivnosti stanične plazme i oblika mikrobne površine rabili smo krivulje preživjelih stanica prije i poslije sterilizacije. Ustanovili smo da neizravna sterilizacija dovodi do prekida aktivnosti mikroba u kratkom vremenu, manje od tri minute, dok je izravna sterilizacija trajala dulje, više od deset minuta

Mjerenje probojnih napona za više katodnih materijala u Townsendovom izboju

The breakdown potentials have been measured for argon and helium discharges using three different cathode materials: aluminium, silver and magnesium. The measurements show that lower breakdown potentials are associated with lower work function of the cathode material. For the three different cathodes, the secondary ionization coefficients have been estimated using the measured values of the breakdown potentials and the first ionization coefficient, in the range 0.60 to 2.25 V/[Pa cm] (80 to 300 V/[torr cm]) for Ar discharge and in the range of 0.15 to 1.80 V/[Pa cm] (20 to 240 V/[torr cm]) for He discharge. The minimum breakdown potential has been found at (pd)min = 80 Pa cm (0.6 torr cm) in Ar discharge and at 530 Pa cm (4.0 torr cm) in He discharge.Mjerili smo probojne potencijale za izboj u argonu i heliju s trima katodnim materijalima: aluminijem, srebrom i magnezijem. Mjerenja pokazuju da su niži probojni naponi povezani s nižim radnim funkcijama. Odredili smo sekundarne ionizacijske koeficijente za te tri vrste katoda na osnovi izmjerenih probojnih napona i prvih ionizacijskih koeficijenata, u području 0.60 to 2.25 V/[Pa cm] za izboj u Ar i u području 0.15 to 1.80 V/[Pa cm] za izboj u He. Najniži probojni napon za izboj u Ar iznosi (pd)min = 80 Pa cm, a za izboj u He 530 Pa cm (4.0 torr cm)

Chemical Quality and Hydrogeological Settings of the El-Farafra Oasis (Western Desert of Egypt) Groundwater Resources in Relation to Human Uses

In the Egyptian deserts, new land reclamation projects have been recently established to meet the increasing-population growth rate and food demand. These projects mainly depend on the different groundwater aquifers. El-Farafra Oasis is one of the "1.5-million-feddan reclamation project" areas recently established in the Western Desert of Egypt where the only available water source is the world's largest fossil freshwater reservoir "the Nubian Sandstone Aquifer System (NSAS)". Groundwater-dependent springs, and their artificial counterpart "drilled wells", are reliable water systems throughout the world. In the present study, hydrochemical parameters were collected in 2015 from 16 different springs and wells of the El-Farafra Oasis, and analyzed using the different water quality indices. The calculated water quality index (WQI), its correlations with the water quality parameters Gibbs, Piper, US Salinity-Lab Staff and Wilcox diagrams, and Principal Component Analysis (PCA) were used to evaluate the groundwater suitability for human drinking and irrigation purposes. WQI values revealed good-to-excellent groundwater quality for human drinking. In addition, the spring and well water samples investigated showed good indices for irrigation activities. Gibbs and Piper's diagrams were presented, with most samples falling into the rock-dominance category, and belonging to hydrogeochemical facies determining the following water types: Mg(HCO3)(2) type water (37.5% of the samples), no dominant ions (mixed water-type category; Ca/MgCl2) (50% of the samples), and, finally, NaCl water type (the remaining 12.5%). The groundwater chemistry in the study area is mainly controlled by rock-water interactions, particularly the dissolution of carbonate rocks and silicate weathering. The elevated nutrient concentrations, in particular nitrates, are most likely due to agricultural activities, indicating substantial anthropogenic activities in the area studied

Influence of shock wave propagation on dielectric barrier discharge plasma actuator performance

Interest in plasma actuators as active flow control devices is growing rapidly due to their lack of mechanical parts, light weight and high response frequency. Although the flow induced by these actuators has received much attention, the effect that the external flow has on the performance of the actuator itself must also be considered, especially the influence of unsteady high-speed flows which are fast becoming a norm in the operating flight envelopes. The primary objective of this study is to examine the characteristics of a dielectric barrier discharge (DBD) plasma actuator when exposed to an unsteady flow generated by a shock tube. This type of flow, which is often used in different studies, contains a range of flow regimes from sudden pressure and density changes to relatively uniform high-speed flow regions. A small circular shock tube is employed along with the schlieren photography technique to visualize the flow. The voltage and current traces of the plasma actuator are monitored throughout, and using the well-established shock tube theory the change in the actuator characteristics are related to the physical processes which occur inside the shock tube. The results show that not only is the shear layer outside of the shock tube affected by the plasma but the passage of the shock front and high-speed flow behind it also greatly influences the properties of the plasma