Cathode fall characteristics in a dc atmospheric pressure glow discharge

Copyright 2003 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the authors and the American Institute of Physics. This article appeared in the Journal of Applied Physics and may be found at: http://link.aip.org/link/?JAPIAU/94/5504/1Atmospheric pressure glow discharges are attractive for a wide range of material-processing applications largely due to their operation flexibility afforded by removal of the vacuum system. These relatively new atmospheric plasmas are nonequilibrium plasmas with gas temperature around 100 °C and electron temperature in the 1–10 eV range. Their appearance is characteristically diffuse and uniform, and their temporal features are repetitive and stable. Of the reported numerical studies of atmospheric glow discharges, most are based on the hydrodynamic approximation in which electrons are assumed to be in equilibrium with the local electric field. Spectroscopic and electrical measurements suggest however that the cathode fall region is fundamentally nonequilibrium. To this end we consider a hybrid model that treats the cathode fall region kinetically but retains a hydrodynamic description for the region between the thin cathode fall layer and the anode. Using this hybrid model, a helium discharge system excited at dc is studied numerically for a very wide current density range that spans from Townsend dark discharge, through normal glow discharge, to abnormal glow discharge. Numerical results confirm many distinct characteristics of glow discharges and compare well with that of low-pressure glow discharges. Generic relationships, such as that between the electric field and the current density, are also established and are in good agreement with experimental data. This hybrid model is simple and insightful as a theoretical tool for atmospheric pressure glow discharges

Physiological and autonomic stress responses after prolonged sleep restriction and subsequent recovery sleep in healthy young men

Purpose Sleep restriction is increasingly common and associated with the development of health problems. We investigated how the neuroendocrine stress systems respond to prolonged sleep restriction and subsequent recovery sleep in healthy young men. Methods After two baseline (BL) nights of 8 h time in bed (TIB), TIB was restricted to 4 h per night for five nights (sleep restriction, SR, n = 15), followed by three recovery nights (REC) of 8 h TIB, representing a busy workweek and a recovery weekend. The control group (n = 8) had 8 h TIB throughout the experiment. A variety of autonomic cardiovascular parameters, together with salivary neuropeptide Y (NPY) and cortisol levels, were assessed. Results In the control group, none of the parameters changed. In the experimental group, heart rate increased from 60 +/- 1.8 beats per minute (bpm) at BL, to 63 +/- 1.1 bpm after SR and further to 65 +/- 1.8 bpm after REC. In addition, whole day low-frequency to-high frequency (LF/HF) power ratio of heart rate variability increased from 4.6 +/- 0.4 at BL to 6.0 +/- 0.6 after SR. Other parameters, including salivary NPY and cortisol levels, remained unaffected. Conclusions Increased heart rate and LF/HF power ratio are early signs of an increased sympathetic activity after prolonged sleep restriction. To reliably interpret the clinical significance of these early signs of physiological stress, a follow-up study would be needed to evaluate if the stress responses escalate and lead to more unfavourable reactions, such as elevated blood pressure and a subsequent elevated risk for cardiovascular health problems.Peer reviewe

Optical Spectra of Small-Scale Sprite Features Observed at 10,000 fps

Spectra of small-scale sprite structures, downward and upward propagating streamers, glow, and beads, were recorded with a slitless spectrograph at 10,000 frames per second (fps) from aircraft missions in 2009 and 2013. The spectra are dominated by emissions from molecular nitrogen, the first positive band in the red, and in the blue the second positive band plus the first negative band of molecular nitrogen ions. The excitation threshold for the blue emissions is higher than for the red emissions, so the blue/red ratio can, in principle, be used as a proxy for the electron energy leading to the emissions. We extracted for analysis time series of spectra from 11 sprites: 18 time series from downward propagating streamers, 6 from upward propagating streamers, 14 from glow, and 12 from beads. The total number of spectra in the 50 time series is 953. Blue emissions are almost exclusively associated with streamers indicating the more energetic nature of streamers compared with glow and beads. Both downward and upward propagating streamers start and end with low blue emissions indicating time variations in the associated processes. Because the red and blue nitrogen emissions are significantly affected by quenching, which is altitude dependent, and we do not have sufficiently accurate altitudes, the observed spectral blue/red ratios cannot be directly applied to sprite models. ©2020. American Geophysical Union. All Rights Reserved.We gratefully acknowledge the support of the NSF/NCAR High Performance Instrumented Airborne Platform for Environmental Research (HIAPER) project, as well as the pilots and technical staff that made the HIAPER Gulfstream V missions possible. We also acknowledge the contribution by T. Kanmae who did the early analysis of the spectra, and discussions with N. Liu, F. J. Pérez‐Invernón, and A. Malagón‐Romero. The research has been supported in part by National Science Foundation grants 1104441 to the University of Alaska Fairbanks and 1201683 to the US Air Force Academy. A. Luque was supported by the European Research Council (ERC) under the European Union H2020 programme/ERC grant agreement 681257.Peer reviewe

Effective species for ignition of premixed burner flame in effluent of dielectric barrier discharge

The ignition probability of a premixed burner flame was improved in the effluent of a dielectric barrier discharge. In addition, the propagation speed of the flame kernel was increased by the dielectric barrier discharge. The increase in the propagation speed of the flame kernel was more significant in the region close to the nozzle of the effluent gas. We measured the spatial distributions of the densities of OH and atomic oxygen in the effluent. We found that the axial decay of the density of atomic oxygen was steeper than that of the OH density under the experimental conditions. By comparing the spatial distributions of the radical densities with that of the propagation speed of the flame kernel, we concluded that atomic oxygen works more effectively than OH in improving the ignition probability of the premixed burner flame

How to Compartment Secrets: Trust Everybody, but Cut the Cards

Part 1: Invited PaperInternational audienceSecret sharing splits a secret s into $$\ell$$ shares in such a way that $$k\le \ell$$ shares suffice to reconstruct s. Let $$\rho _{i,j}$$ be the probability that shareholder i disclose their share to shareholder j, with $$0 \le i,j < n$$.Given $$k \le \ell \le n$$, to whom $$\ell$$ individuals should we hand shares, if we wish to minimize the probability that one of them reconstitutes s