Impurity intrusion in radio-frequency micro-plasma jets operated in ambient air

Space and time resolved concentrations of helium metastable atoms in an atmospheric pressure radio-frequency micro-plasma jet were measured using tunable diode laser absorption spectroscopy. Spatial profiles as well as lifetime measurements show significant influences of air entering the discharge from the front nozzle and of impurities originating from the gas supply system. Quenching of metastables was used to deduce quantitative concentrations of intruding impurities. The impurity profile along the jet axis was determined from optical emission spectroscopy as well as their dependance on the feed gas flow through the jet.Comment: Journal of Physics D: Applied Physics (accepted), 6 page

Toward seamless environments for dispute prevention and resolution

Given the evolution of the Information Technology society, it is now rather simple to acquire products or services in a foreign country. This practice may conduct to the event of conflicts whenever a consumer detects some fault or malfunction in services or products he/she had bought. A situation that may worsen if at the time of the uncovering of the defect, the shopper is already in a different geographical arena. There is thus the need to develop computational tools that may prevent these disputes from even happening. In this work it is proposed the development of seamless intelligent environments for dispute resolution that will surround the user, independently of his/her location. It is described the implementation of a prototype that may provide contextualized real-time information and legal support to consumers. The objective is to decrease the number of disputes due to a poor understanding in relation to the The Law and make justice more personalized and closer to people.The work described in this paper was developed under the TIARAC - Telematics and Artificial Intelligence in Alternative Conflict Resolution Project (PTDC/JUR/71354/2006), which is a research project supported by FCT (Science & Technology Foundation), Portuga

Argon metastable dynamics in a filamentary jet micro-discharge at atmospheric pressure

Space and time resolved concentrations of Ar ($^{3}P_2$) metastable atoms at the exit of an atmospheric pressure radio-frequency micro-plasma jet were measured using tunable diode laser absorption spectroscopy. The discharge features a coaxial geometry with a hollow capillary as an inner electrode and a ceramic tube with metal ring as outer electrode. Absorption profiles of metastable atoms as well as optical emission measurements reveal the dynamics and the filamentary structure of the discharge. The average spatial distribution of Ar metastables is characterized with and without a target in front of the jet, showing that the target potential and therewith the electric field distribution substantially changes the filaments' expansion. Together with the detailed analysis of the ignition phase and the discharge's behavior under pulsed operation, the results give an insight into the excitation and de-excitation mechanisms

Phonon-Assisted Photoluminescence from Indirect Excitons in Monolayers of Transition-Metal Dichalcogenides

The photoluminescence (PL) spectrum of transition-metal dichalcogenides (TMDs) shows a multitude of emission peaks below the bright exciton line, and not all of them have been explained yet. Here, we study the emission traces of phonon-assisted recombinations of indirect excitons. To this end, we develop a microscopic theory describing simultaneous exciton, phonon, and photon interaction and including consistent many-particle dephasing. We explain the drastically different PL below the bright exciton in tungsten- and molybdenum-based materials as the result of different configurations of bright and momentum-dark states. In good agreement with experiments, our calculations predict that WSe2 exhibits clearly visible low-temperature PL signals stemming from the phonon-assisted recombination of momentum-dark K-K′ excitons

Radio-frequency discharges in Oxygen. Part 1: Modeling

In this series of three papers we present results from a combined experimental and theoretical effort to quantitatively describe capacitively coupled radio-frequency discharges in oxygen. The particle-in-cell Monte-Carlo model on which the theoretical description is based will be described in the present paper. It treats space charge fields and transport processes on an equal footing with the most important plasma-chemical reactions. For given external voltage and pressure, the model determines the electric potential within the discharge and the distribution functions for electrons, negatively charged atomic oxygen, and positively charged molecular oxygen. Previously used scattering and reaction cross section data are critically assessed and in some cases modified. To validate our model, we compare the densities in the bulk of the discharge with experimental data and find good agreement, indicating that essential aspects of an oxygen discharge are captured.Comment: 11 pages, 10 figure

Loss mechanisms of negative oxygen ions in an inductively coupled rf discharge

A high fraction of negative ions (approx. 90 %) is observed in a pulsed oxygen rf discharge (13.56 MHz, 10 Pa). At the end of a discharge pulse of 1 ms duration both the axial and the radial density profiles of the negative ions coincide in the centre of the discharge with the density profile of the positive charge carriers. The dominant loss reactions -in particular of the negative ions -can be found from measurements of the temporal decay of the positive and negative charge carriers in the afterglow. Recombination with positive oxygen ions and collisions with atomic oxygen dominate the decay of the negative ions. These observations are consistent with the determination of the atomic oxygen density and determinations of the ion species (plasma monitor). Probe measurements indicate a production of electrons during this late phase. This can be explained by collisions of negative oxygen ions with atoms, whereby oxygen molecules are formed

Particle-in-cell Monte Carlo and fluid simulations of argon-oxygen plasma: Comparisons with experiments and validations

This article was published in the journal, Physics of plasmas and is also available at: http://pop.aip.org/pop/top.jsp or http://dx.doi.org/10.1063/1.2179430Particle-in-cell Monte Carlo collision (PIC-MCC) and fluid simulations of argon-oxygen plasmas in capacitively and inductively coupled plasma reactors are presented. Potential profiles and electron/ ion kinetic information such as electron/ion energy distributions and temperatures are compared with experimental data as well as with other analytical and numerical results. One-dimensional PIC-MCC simulations compare favorably with experimental data obtained in capacitively coupled reactors over a wide range of pressure and power. Two-dimensional fluid simulations of capacitive discharges differs from the results of PIC-MCC simulations as nonlocal effects play an important role in these discharges. Fluid simulations as nonlocal inductively coupled plasmas, however, agree favorably with experimental observations

Aided Cortical Auditory Evoked Potentails for Hearing Instrument Evaluation in Infants

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