Double-propagation mode in short-gap spark discharges driven by HV pulses with sub-ns rise time

The object of this study is the investigation of spark discharges ignited by unipolar positive rectangular high voltage (HV) pulses with 200 ps rise time and (15 ± 2) kV amplitude with 3 ns duration full width at half maximum in synthetic air in a 1.2 mm pin-to-pin gap (tungsten electrodes) at atmospheric pressure. The discharge development was recorded by synchronised iCCD and streak camera measurements in single-shot operation, revealing a two-stage propagation mode. The discharge started with a fast initial breakdown across the entire gap (∼10 mm ns−1) during the HV slope, followed by a much slower (∼0.1 mm ns−1) propagation originating from both electrodes towards the gap centre. The combination of high-resolution diagnostics with numerical modelling indicated that the initial breakdown phase is caused by the rapid increase of electric field strength during the steep HV slope, which leads to the simultaneous fast propagation of a positive and a negative streamer

Upscaling from single- to multi-filament dielectric barrier discharges in pulsed operation

A study on the scalability of discharge characteristics of a single-filament dielectric barrier discharge (DBD) to a spatially one-dimensional multi-filament arrangement driven by the same high-voltage (HV) pulses was performed for a gas mixture of 0.1 vol% O2 in N2 at 1 bar. Both arrangements feature a 1 mm gap with dielectric-covered electrodes featuring two hemispherical alumina caps for the single-filament and two parallel alumina-tubes for the multi-filament arrangement. The DBDs were characterised by electrical measurements (for peak current, energy, and power) accompanied by iCCD and streak imaging to determine the filament number and the discharge development in the gas gap and on the surfaces. It was found that the electrical quantities scale with a constant factor between the single- and multi-filament arrangement, which is expected to be related to the filament number. In the multi-filament arrangement, the pulsed operation leads to filament formation in the entire gap in lateral direction within less than 2 ns. Furthermore, particular breakdown or discharge inception regimes were identified for the multi-filament DBDs. These regimes could be generated at the falling slope of asymmetrical HV pulses featuring e.g. a double-streamer propagation, which was previously reported for single-filament DBDs. Consequently, it was proven that the discharge manipulation by varying the HV pulse widths obtained for single-filament DBDs can also be applied in a one-dimensional multi-filament arrangement, i.e. an upscaling based on the knowledge for single-filament DBDs seems to be generally possible

Extended reaction kinetics model for non-thermal argon plasmas and its test against experimental data

An extended reaction kinetics model (RKM) suitable for the analysis of weakly ionised, non-thermal argon plasmas with gas temperatures around 300 K at sub-atmospheric and atmospheric pressures is presented. It considers 23 different species including electrons as well as the ground state atom, an atomic and molecular ion, four excited molecular states, and 15 excited atomic states of argon, where all individual 1s and 2p states (in Paschen notation) are included as a separate species. This 23-species RKM involves 409 collision processes and radiative transitions and recent electron collision cross section data. It is evaluated by means of results of time- and space-dependent fluid modelling of argon discharges and their comparison with measured data for two different dielectric barrier discharge configurations as well as a micro-scaled atmospheric-pressure plasma jet setup. The results are also compared with those obtained by use of a previously established 15-species RKM involving only the two lumped 2p states 2p10…5 and 2´p4 … 1. It is found that the 23-species RKM shows generally better agreement with experimental data and provides more options for direct comparison with measurements than the frequently used 15-species RKM

Advanced fluid modeling and PIC/MCC simulations of low-pressure ccrf discharges

Comparative studies of capacitively coupled radio-frequency discharges in helium and argon at pressures between 10 and 80 Pa are presented applying two different fluid modeling approaches as well as two independently developed particle-in-cell/Monte Carlo collision (PIC/MCC) codes. The focus is on the analysis of the range of applicability of a recently proposed fluid model including an improved drift-diffusion approximation for the electron component as well as its comparison with fluid modeling results using the classical drift-diffusion approximation and benchmark results obtained by PIC/MCC simulations. Main features of this time- and space-dependent fluid model are given. It is found that the novel approach shows generally quite good agreement with the macroscopic properties derived by the kinetic simulations and is largely able to characterize qualitatively and quantitatively the discharge behavior even at conditions when the classical fluid modeling approach fails. Furthermore, the excellent agreement between the two PIC/MCC simulation codes using the velocity Verlet method for the integration of the equations of motion verifies their accuracy and applicability

Impact of the electrode proximity on the streamer breakdown and development of pulsed dielectric barrier discharges

The impact of the electrode proximity on the streamer breakdown and development of pulsed-driven dielectric barrier discharges (DBDs) in a single-filament arrangement has been investigated in a gas mixture of 0.1 vol% O2 in N2 at 0.6 bar and 1.0 bar. The gap distance was varied from 0.5 mm to 1.5 mm, and the applied voltage was adapted correspondingly to create comparable breakdown conditions in the gap. The development of the DBDs was recorded by an iCCD and a streak camera system, while fast electrical measurements provided insight into discharge characteristics such as the transferred charge and consumed energy. The results demonstrate that breakdown in a smaller gap is characterised by a slower streamer propagation but a significantly higher acceleration. It can therefore be concluded that the proximity of the cathode has a strong impact on the characteristics of the streamer breakdown. However, after the streamer has crossed the gap, the discharge structure in front of the anode was found to be the same independent of the actual gap distance

Impact of Credit on the Relative Well?Being of Women: Evidence from the Grameen Bank

summary This study examines the impact of credit on women's relative well?being in Grameen Bank's credit programmes. Using a bargaining model of the household, as extended by Amartya Sen, well?being has been defined in terms of three sets of capabilities: (i) autonomy, (ii) control over decision?making within the family, and (iii) relative access to household resources. It is hypothesised that the relative well?being of women and men depends on their respective bargaining power, which in turn depends on three factors: breakdown position, perceived contribution to the family and perceived self?interest. The hypothesis has been tested using a two?stage estimation method to avoid the potential problem of simultaneity bias that may be caused by the self?selection problem. Results indicate that involvement in credit has improved the relative well?being of women in some dimensions, but not in others. Some reasons are advanced for this partial success in improving women's well?being

The effect of positive end-expiratory pressure on pulse pressure variation

OBJECTIVES: To determine the effect of different levels of positive end-expiratory pressure (PEEP) on pulse pressure variation (PPV). DESIGN: An observational study. SETTING: Operating theatres of a tertiary training hospital. SUBJECTS: Ventilated patients who required intra-arterial blood pressure monitoring. OOUTCOME MEASURES: PPV during different levels of PEEP. METHOD: Patients were anaesthetised by means of a standard technique and ventilated with a tidal volume of 9 ml/kg ideal body mass. The PPV was calculated at PEEP levels of 2, 5, 8 and 10 cmH2O. PPV was compared at the various PEEP levels. RESULTS: PPV at a PEEP of 8 cmH2O and 10 cmH2O was significantly larger than that at 2 cmH2O (p-value < 0.001). PPV at a PEEP of 10 cmH2O was significantly larger than that at 8 cmH2O (p-value < 0.001). PPV at a PEEP of 8 cmH2O was larger than that at 5 cmH2O (p-value = 0.002). PPV at a PEEP of 2 and 5 cmH2O did not differ significantly (p-value = 0.194). CONCLUSION: We have demonstrated that, in patients with normal lungs, PEEP has a significant influence on PPV. PPV may be overestimated if PEEP ≥ 8 cmH2O is applied in patients who are ventilated with a tidal volume of 9 ml/kg. It is recommended that in patients with healthy lungs PPV should be measured at a standardised PEEP of ≤ 5 cmH2O.http://www.sajaa.co.za/index.php/sajaaam2013ay201

Biochemical parameters of silver catfish (Rhamdia quelen) after transport with eugenol or essential oil of Lippia alba added to the water

The transport of live fish is a routine practice in aquaculture and constitutes a considerable source of stress to the animals. The addition of anesthetic to the water used for fish transport can prevent or mitigate the deleterious effects of transport stress. This study investigated the effects of the addition of eugenol (EUG) (1.5 or 3.0 mu L L-1) and essential oil of Lippia alba (EOL) (10 or 20 mu L L-1) on metabolic parameters (glycogen, lactate and total protein levels) in liver and muscle, acetylcholinesterase activity (AChE) in muscle and brain, and the levels of protein carbonyl (PC), thiobarbituric acid reactive substances (TBARS) and nonprotein thiol groups (NPSH) and activity of glutathione-S-transferase in the liver of silver catfish (Rhamdia quelen; Quoy and Gaimard, 1824) transported for four hours in plastic bags (loading density of 169.2 g L-1). The addition of various concentrations of EUG (1.5 or 3.0 mu L L-1) and EOL (10 or 20 mu L L-1) to the transport water is advisable for the transportation of silver catfish, since both concentrations of these substances increased the levels of NPSH antioxidant and decreased the TBARS levels in the liver. In addition, the lower liver levels of glycogen and lactate in these groups and lower AChE activity in the brain (EOL 10 or 20 mu L L-1) compared to the control group indicate that the energetic metabolism and neurotransmission were lower after administration of anesthetics, contributing to the maintenance of homeostasis and sedation status.Fundacao de Amparo a Pesquisa do Estado do Rio Grande do Sul (FAPERGS/PRONEX) [10/0016-8]; Conselho Nacional de Pesquisa e Desenvolvimento Cientifico (CNPq) [470964/2009-0]; Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior (CAPES); CNPqinfo:eu-repo/semantics/publishedVersio

The Geometry of D=11 Null Killing Spinors

We determine the necessary and sufficient conditions on the metric and the four-form for the most general bosonic supersymmetric configurations of D=11 supergravity which admit a null Killing spinor i.e. a Killing spinor which can be used to construct a null Killing vector. This class covers all supersymmetric time-dependent configurations and completes the classification of the most general supersymmetric configurations initiated in hep-th/0212008.Comment: 30 pages, typos corrected, reference added, new solution included in section 5.1; uses JHEP3.cl