Experimental study of the reduction of field emission by gas injection in vacuum for accelerator applications

LGEP 2014 ID = 1590International audienceField emission current from surfaces under vacuum and at high field strengths can be reduced by the injection of gas into the evacuated volume. In this paper, the effects of H 2 , He, N 2 , and Ar on this "dark" current emitted from a tungsten carbide point cathode for 2 cm gap distance is studied. Exposure to any of these gases at pressures on the order of 10 −3 –10 −2 Pa was found to reduce the emission current by up to 90% with a time constant on the order of ∼1 minute as compared to the current at 10 −6 Pa. The effect was strongly dependent on the gas nature, with Ar and N 2 having larger effects at lower pressures than He and H 2 . The reduction was reversible, with the current increasing to near its original value with a time constant on the order of ∼1–10 minutes after pumping down. The effect of the gas remained in the absence of electric field, whatever the gas pressure. Mechanisms for these and related phenomena are discussed

Children struggle beyond preschool-age in a continuous version of the ambiguous figures task

Children until the age of five are only able to reverse an ambiguous figure when they are informed about the second interpretation. In two experiments, we examined whether children’s difficulties would extend to a continuous version of the ambiguous figures task. Children (Experiment 1: 66 3- to 5-year olds; Experiment 2: 54 4- to 9-year olds) and adult controls saw line drawings of animals gradually morph—through well-known ambiguous figures—into other animals. Results show a relatively late developing ability to recognize the target animal, with difficulties extending beyond preschool-age. This delay can neither be explained with improvements in theory of mind, inhibitory control, nor individual differences in eye movements. Even the best achieving children only started to approach adult level performance at the age of 9, suggesting a fundamentally different processing style in children and adults

Applications biomédicales des plasmas froids

International audienceLes plasmas froids, en raison de leurs propriétés électrostatiques, émissives, thermiques et chimiques trouvent de nombreuses applications industrielles. Ces dernières décennies, des avancées significatives ont été obtenues en recherche pour le développement d’applications médicales. Des dispositifs médicaux ont aujourd’hui reçu un marquage CE et sont utilisés en milieu hospitalier. Mais un effort de recherche significatif et interdisciplinaire est encore nécessaire pour progresser dans ce domaine

Atmospheric Pressure Humid Argon DBD Plasma for the Application of Sterilization - Measurement and Simulation

Abstract⎯Hydrogen, oxygen, and hydrogen peroxide have been measured downstream of an atmospheric pressure humid argon dielectric barrier discharge. The yield of the three species was studied as a function of the discharge power and gas flow rate. Hydrogen peroxide was measured after dissolution into water downstream of the discharge, while hydrogen and oxygen were measured in the gas phase. The production rates of both hydrogen and oxygen were found to be at least one order of magnitude greater than that of hydrogen peroxide. In all cases, the molar rate of molecular hydrogen production was more than twice that of molecular oxygen. At various total gas flow rate, and over a range of energy density of 0 to 1500 J/L, the concentration of hydrogen found at the reactor outlet varied from 0 to 1000 ppm, while oxygen reached a maximum concentration of about 400 ppm. The corresponding concentration of hydrogen peroxide that was calculated to have been in the reactor outlet gas did not exceed 11 ppm. Mechanisms for this system based on experiments and a numerical model are presented. The results of experiments on the use of post-discharge effluent gas of humid argon plasma for sterilization purposes (inactivation of E. Coli) bacteria are also presented and discussed in relation to the results of the chemical measurements and simulations

Decontamination of Escherichia coli biofilm by positive and negative DC corona discharge in air

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