Influence of vibrational kinetics in a low pressure capacitively coupled hydrogen discharge

In this paper we present the self consistent coupling of a 2D model of a parallel plate radio frequency discharge in pure hydrogen with a homogeneous chemical kinetics model including H2(X1Σg+,v=0..14) molecules and hydrogen atoms H(n=1-5). The model can estimate the ground state atomic hydrogen density and it was found that the vibrational kinetics changes the H3+ ion density and coupled power to the discharge about 40% when comparing with previous estimates using a simplified kinetics

Systematic characterization of low-pressure capacitively coupled hydrogen discharges

The paper presents a systematic characterization of pure hydrogen capacitively coupled discharges, produced in a parallel plate cylindrical setup. A two-dimensional, time-dependent fluid model is used to describe the production, transport, and destruction of electrons and positive ions H+,H2+, and H3+, at different frequencies(13.56 - 60 MHz), pressures (0.2 - 8 Torr), rf applied voltages (50 - 450 V) and geometric dimensions (1.6 - 12.8 cm radii and 1.6 - 6.4 cm interelectrode distances). A good agreement is found between calculation results and experimental measurements for the coupled electrical power, the plasma potential, and the self-bias potential, at various frequencies and rf applied voltages. However, the model generally underestimates the electron density with respect to its measured values. The paper discusses different space-time events, such as the development of double-ionization structures or the occurrence of field inversion and field reversal phenomena. The dependencies on pressure and frequency of the time-average electric field distribution are analyzed and related to the electron displacement within space-charge sheaths.This study is later used to understand the variations of the hydrogen dissociation rate, with changes in discharge operating conditions. The influence of reactor dimensions on the spatial profiles of the plasma potential, the rf electric field, the electron density, and the electron mean energy are analyzed in terms of discharge symmetry. An investigation of the space-time averaged rf electric field variations, with changes in the applied voltage, pressure, and geometric dimensions is carried out.These variations are shown to follow a universal similarity curve, if an adequate normalization is used when plotting the rf electric field as a function of pressure.This innovative representation of rf discharges allows a univocal definition of a reactor working point, for given operating conditions.Portugal. Ministério da Ciência Tecnologia e Ensino Superior (MTCES). Instituto Superior Técnico (IST). Centro de Física dos Plasmas – PRAXIS XXI (BD/15716/98), SFRH/BD/5012/2001.French Embassy, Gabinete de Relações Internacionais da Ciência e do Ensino Superior (GRICES) - ScientificTechnical Luso-French Cooperation Program - Project 539-B4 - Université Paris-Sud. Laboratoire de Physique des Gaz et des Plasmes

Comparison of apoptotic gene expression profiles between Peyronie's disease plaque and tunica albuginea

PubMed: 23356197Background. The fibrotic plaques of Peyronie's disease and other localized fibrotic conditions have been considered to be the result of an abnormal wound healing process. The potential role of regulatory disorders of apoptosis in abnormal wound healing may also play a role in the development of Peyronie's disease. Objectives. To examine the phenomenon of apoptosis in Peyronie's disease, authors quantified differential levels of gene expression of apoptotic proteins, Fas, Fas Ligand, Bcl-2, p53, Caspase 3 and 8 in Peyronie's plaque and tunica albuginea. Material and Methods. Eight patients with Peyronie's disease undergoing surgical correction of the curvature had biopsy specimens taken from both the Peyronie's plaque and normal tunica albuginea. Messenger RNA expression of the apoptotic proteins in the plaque and normal tunica was measured by reverse transcriptase PCR. Results. Apoptotic gene expression was lower than the housekeeping gene's in half of the tunica albuginea samples and two thirds of the plaque samples. Overall mRNA expressions in the plaque were not significantly different from the normal tunica albuginea. Conclusions. The fibrotic plaques of Peyronie's disease and other localized fibrotic conditions have been considered to be the result of an abnormal wound healing process. The potential role of regulatory disorders of apoptosis in abnormal wound healing may also play a role in the development of Peyronie's disease. In this study, the lower expression of apoptotic genes may cause the persistence of collagen producing cells which were up-regulated for unknown reasons and consequently result in plaque formation. Similar expression levels of apoptotic genes in both tunica albuginea and Peyronie's plaques may be due to the generalized physiopathologic alterations in tunica albuginea that lead to plaque formation at a vulnerable region subjected to recurrent traumas. © Copyright by Wroclaw Medical University

ON THE MECHANISM OF THE RELAXATION PULSE GLOW DISCHARGE

Abstract. A mechanism of the low pressure relaxation glow discharge pulse is presented. Theoretical predictions and experimentally obtained values of discharges parameters are compared. The ion mobility, the secondary electron emission, the ionisation and the electrical parameters have a strong influence on the characteristics while the diffusion is of lesser importance