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Sample records for streamers sprites leaders

  1. Diameter-speed relation of sprite streamers

    International Nuclear Information System (INIS)

    Kanmae, T; Stenbaek-Nielsen, H C; McHarg, M G; Haaland, R K

    2012-01-01

    Propagation and splitting of sprite streamers has been observed at high temporal and spatial resolution using two intensified high-speed CMOS cameras recording at 10 000 and 16 000 frames per second. Concurrent video recordings from a remote site provided data for triangulation allowing us to determine accurate altitude scales for the sprites. Diameters and speeds of the sprite streamers were measured from the high-speed images, and the diameters were scaled to the reduced diameters based on the triangulated locations. The sprite streamers with larger reduced diameter move faster than those with smaller diameter; the relation between the reduced diameter and speed is roughly linear. The reduced diameters at ≈65-70 km altitude are larger than streamer diameters measured at ground pressure in laboratory discharges indicating a deviation from the similarity law possibly due to the effects of the photoionization and an expansion of the streamer head along its propagation over a long distance. The reduced diameter and speed of the sprite streamers agree well with the diameter-velocity relation proposed by Naidis (2009 Phys. Rev. E 79 057401), and the peak electric field of the sprite streamers is estimated to be approximately 3-5 times the breakdown threshold field. (paper)

  2. Optical Emissions of Sprite Streamers in Weak Electric Fields

    Science.gov (United States)

    Liu, N.; Pasko, V. P.

    2004-12-01

    Sprites commonly consist of large numbers of needle-shaped filaments of ionization [e.g., Gerken and Inan, JASTP, 65, 567, 2003] and typically initiate at altitudes 70-75 km in a form of upward and downward propagating streamers [Stanley et al., GRL, 26, 3201, 1999; Stenbaek-Nielsen et al., GRL, 27, 3829, 2000; McHarg et al., JGR, 107, 1364, 2002; Moudry et al., JASTP, 65, 509, 2003]. The strong electric fields E exceeding the conventional breakdown threshold field Ek are needed for initiation of sprite streamers from single electron avalanches and recent modeling studies indicate that streamers propagating in fields E>Ek experience strong acceleration and expansion in good agreement with the above cited observations [Liu and Pasko, JGR, 109, A04301, 2004]. The initiated streamers are capable of propagating in fields substantially lower than Ek [Allen and Ghaffar, J. Phys. D: Appl. Phys., 28, 331, 1995] and it is expected that a significant part of sprite optical output comes from regions with EEk). Additionally, the values of electric fields inside of the streamer channel are always well below Ek and since the excitation coefficients for optical emissions are very sensitive to the driving electric field magnitude most of the optical luminosity of streamers in this case arises from streamer tips, indicating that observed streamer filaments in many cases may be produced by time averaging of optical luminosity coming from localized regions around streamer tips as streamers move through an instrument's field of view. We will discuss pressure dependent differences of optical emissions at different sprite altitudes, and important similarities between observed sprite streamers and recent time resolved (van Veldhuizen et al., IEEE Trans. Plasma Sci., 30, 162, 2002; Yi and Williams, J. Phys. D. Appl. Phys., 35, 205, 2002].

  3. Study of Streamers in Gradient Density Air: Table Top Modeling of Red Sprites

    Science.gov (United States)

    Opaits, D. F.; Shneider, M. N.; Howard, P. J.; Miles, R. B.; Milikh, G. M.

    2009-12-01

    Sprites and blue jets develop in the upper atmosphere where ambient density changes drastically over their lengths. Theoretical analysis of Red Sprites [1] and Blue Jets [2,3] are based on the streamer tip parameters’ functional dependence on a local gas density N(h). At the moment there is a lack of experimental data for streamer propagation in a non-uniform ambient gas density. Small scale experiments in controllable conditions are important for validation of analytical models as well as numerical simulations, which can be used for the investigation of real scale plasma phenomena that develop above thunderclouds. Controllable, non-uniform gas density can be achieved in laboratory conditions in super sonic nozzles, fast centrifuges or gas filled tubes with a non-uniform temperature distribution along the axis. The latter approach was used in the present work. A quartz tube, approximately one foot in length, was filled with air at different pressures. A density gradient was created by heating up the top of the tube while keeping the bottom at room temperature. The discharge was initiated by applying a high voltage pulse to a pin electrode at the top of the tube while a flat electrode was grounded at the bottom. Similar to Red Sprites, the streamer propagates downwards into a region of higher density and stops before reaching the lower electrode while the top electrode remains under high potential. This work will present results of streamer propagation at different pressures and voltages. Measurements of current-voltage characteristics as well as integral images will be presented. 1. Y. P.Raizer, G. M. Milikh, M. N. Shneider, and S. V. Novakovski (1998), J. Phys. D: Appl. Phys. 31, 3255-3264. 2. Y. P.Raizer, G. M. Milikh, and M. N. Shneider (2006), Geophys. Res. Lett., 33, L23801 3. Y .P.Raizer, G. M. Milikh, and M. N. Shneider (2007), J. Atmos. & Solat-Terr. Phys, 69, 925-938

  4. Towards a fluid model for the streamer-to-leader transition in lightning channels.

    Science.gov (United States)

    Malagón, Alejandro; Luque, Alejandro

    2017-04-01

    , such as impact ionization, attachment and detachment. Using this model we plan to test the hypothesis that leader stepping results from an attachment instability that creates low-conductivity, high-field regions in a streamer corona, as recently discussed for sprites in [2]. With our detailed model for gas heating and expansion we will investigate whether the attachment instability leads to heating of air to a temperature high enough to develop space stems. A positive answer to this question would elucidate the physical mechanism of leader stepping. References [1] R.J. LeVeque. Finite Volume Methods for Hyperbolic Problems. Cambridge Texts in Applied Mathematics. Cambridge University Press, 2002. [2] A. Luque, H. C. Stenbaek-Nielsen, M. G. McHarg, and R.K. Haaland. Srpite beads and glows arising from the attachment instability in streamer channels. J. Geophys. Res. (Space Phys), 121, 2016.

  5. Simulation of the vibrational chemistry and the infrared signature induced by a Sprite streamer in the mesosphere

    Science.gov (United States)

    Romand, F.; Payan, S.; Croize, L.

    2017-12-01

    Since their first observation in 1989, effect of TLEs on the atmospheric composition has become an open and important question. The lack of suitable experimental data is a shortcoming that hampers our understanding of the physics and chemistry induced by these effects. HALESIS (High-Altitude Luminous Events Studied by Infrared Spectro-imagery) is a future experiment dedicated to the measurement of the atmospheric perturbation induced by a TLE in the minutes following its occurrence, from a stratospheric balloon flying at an altitude of 25 km to 40 km. This work aims to quantify the local chemical impact of sprites in the stratosphere and mesosphere. In this paper, we will present the development of a tool which simulates (i) the impact of a sprite on the vibrational chemistry, (ii) the resulting infrared signature and (iii) the propagation of this signature through the atmosphere to an observer. First the Non Local Thermodynamic Equilibrium populations of a background atmosphere were computed using SAMM2 code. The initial thermodynamic and chemical description of atmosphere comes from the Whole Atmosphere community Climate Model (WACCM). Then a perturbation was applied to simulate a sprite. Chemistry due to TLEs was computed using Gordillo-Vazquez kinetic model. Rate coefficients that depend on the electron energy distribution function were calculated from collision cross-section data by solving the electron Boltzmann equation (BE). Time evolutions of the species densities and of vibrational populations in the non-thermal plasma consecutive to sprite discharge were simulated using the computer code ZDPlasKin (S. Pancheshn et al.). Finally, the resulting infrared signatures were propagated from the disturbed area through the atmosphere to an instrument placed in a limb line of sight using a line by line radiative transfer model. We will conclude that sprite could produce a significant infrared signature that last a few tens of seconds after the visible flash.

  6. Experimental Study on Branch and Diffuse Type of Streamers in Leader Restrike of Long Air Gap Discharge

    International Nuclear Information System (INIS)

    Chen She; Zeng Rong; Zhuang Chijie; Zhou Xuan; Ding Yujian

    2016-01-01

    One of the main problems in the Ultra High Voltage (UHV) transmission project is to choose the external insulation distance, which requires a deep understanding of the long air gap discharge mechanism. The leader-streamer propagation is one of most important stages in long air gap discharge. In the conductor-tower lattice configuration, we have measured the voltage, the current on the high voltage side and the electric field in the gap. While the streamer in the leader-streamer system presented a conical or hyperboloid diffuse shape, the clear branch structure streamer in front of the leader was firstly observed by a high speed camera in the experiment. Besides, it is found that the leader velocity, width and injected charge for the branch type streamer are greater than those of a diffuse type. We propose that the phenomenon results from the high humidity, which was 15.5-16.5 g/m 3 in our experiment. (paper)

  7. The effect of reduced air density on streamer-to-leader transition and on properties of long positive leader

    International Nuclear Information System (INIS)

    Bazelyan, E M; Raizer, Yu P; Aleksandrov, N L

    2007-01-01

    New results of observations of the leader process in a pressure chamber are presented for reduced air pressures. The analysis of these data and observations of the leader discharge in peak regions shows that the length of the leader tip and some other characteristics vary by several times as pressure decreases from 1 to 0.3 atm, whereas, under the conditions considered, the leader velocity remains almost independent of air density, the leader current being the same. These data are used to extract relationships between discharge parameters. It is shown that, at reduced air densities, electric field in a 'young' section of the leader channel exceeds electric field in the streamer zone. Therefore, transition of the leader process to the final-jump phase is not inevitably followed by a breakdown of the gap for reduced pressures, as opposed to the discharge in atmospheric pressure air. The model suggested previously by the authors for the streamer-to- leader transition at atmospheric pressure is amended to take into account hydrodynamic expansion of the channel and used to simulate the process at a relative air density of 0.3. The calculated results are used to interpret the observations of the leader process at reduced air pressures

  8. Stepwise expansion of a surface dielectric barrier discharge as a result of alternation in formation of streamers and leaders

    International Nuclear Information System (INIS)

    Akishev, Yu; Aponin, G; Balakirev, A; Grushin, M; Petryakov, A; Karal'nik, V; Trushkin, N

    2013-01-01

    Spatial–temporal development of the plasma sheet structure in a surface dielectric barrier discharge (SDBD) powered with a single long pulse of negative polarity is traced. Ambient air and Ar at atmospheric pressure are used as plasma-forming gases. It is found that current regimes and spatial structures occurring at the development of a long-pulsed discharge differ cardinally as compared with those of a short-pulsed SDBD. In the case of long-pulsed SDBDs, the expansion of the barrier area covered by the plasma sheet and seeded with a surface negative charge occurs in a stepwise manner due to cyclic alternation (one after another) in generation of surface streamers and formation of hot surface leaders from the streamers due to streamer–leader transitions. Leaders, in their turn, initiate new streamers, which serve again as precursors for next-step leader formation, and so on. However, the crucial role in surface charge deposition is played not by streamers and leaders but by a diffusive plasma sheet (DPS), which slowly extends from the sides of streamers and leaders. The expansion of the DPS occurs due to the ionization wave propagating from the sides of the streamers and leaders. The difference in spatial structures of a single long-pulsed and a steady-state sin SDBD is studied. In high-frequency sin SDBDs at negative half-cycle there are only leaders and DPS, but there are no streamers. The reason is that there is no necessity for the formation of leaders due to streamer–leader transitions—leaders are formed at the previous cycle and do not decay strongly till the beginning of the next cycle, and they recover themselves without streamers. (paper)

  9. The multiscale nature of streamers

    International Nuclear Information System (INIS)

    Ebert, U; Montijn, C; Briels, T M P; Hundsdorfer, W; Meulenbroek, B; Rocco, A; Veldhuizen, E M van

    2006-01-01

    Streamers are a generic mode of electric breakdown of large gas volumes. They play a role in the initial stages of sparks and lightning, in technical corona reactors and in high altitude sprite discharges above thunderclouds. Streamers are characterized by a self-generated field enhancement at the head of the growing discharge channel. We briefly review recent streamer experiments and sprite observations. Then we sketch our recent work on computations of growing and branching streamers, we discuss concepts and solutions of analytical model reductions and we review different branching concepts and outline a hierarchy of model reductions

  10. The multiscale nature of streamers

    Energy Technology Data Exchange (ETDEWEB)

    Ebert, U [Centrum voor Wiskunde en Informatica (CWI), PO Box 94079, 1090GB Amsterdam (Netherlands); Faculty of Physics, Eindhoven University of Technology, PO Box 513, 5600MB Eindhoven (Netherlands); Montijn, C [Centrum voor Wiskunde en Informatica (CWI), PO Box 94079, 1090GB Amsterdam (Netherlands); Briels, T M P [Faculty of Physics, Eindhoven University of Technology, PO Box 513, 5600MB Eindhoven (Netherlands); Hundsdorfer, W [Centrum voor Wiskunde en Informatica (CWI), PO Box 94079, 1090GB Amsterdam (Netherlands); Meulenbroek, B [Centrum voor Wiskunde en Informatica (CWI), PO Box 94079, 1090GB Amsterdam (Netherlands); Rocco, A [Centrum voor Wiskunde en Informatica (CWI), PO Box 94079, 1090GB Amsterdam (Netherlands); University of Oxford, Department of Statistics, 1 South Parks Road, Oxford OX1 3TG (United Kingdom); Veldhuizen, E M van [Faculty of Physics, Eindhoven University of Technology, PO Box 513, 5600MB Eindhoven (Netherlands)

    2006-05-15

    Streamers are a generic mode of electric breakdown of large gas volumes. They play a role in the initial stages of sparks and lightning, in technical corona reactors and in high altitude sprite discharges above thunderclouds. Streamers are characterized by a self-generated field enhancement at the head of the growing discharge channel. We briefly review recent streamer experiments and sprite observations. Then we sketch our recent work on computations of growing and branching streamers, we discuss concepts and solutions of analytical model reductions and we review different branching concepts and outline a hierarchy of model reductions.

  11. Successes and Problems of Conventional Breakdown Theory of Sprites

    Science.gov (United States)

    Pasko, V. P.

    2004-12-01

    Sprite phenomenon is one of the most frequently observed forms of transient luminous events occurring at mesospheric/lower ionospheric altitudes, which is directly related to the lightning activity in underlying thunderstorms [Sentman et al., GRL, 22, 1205, 1995]. In this talk we will provide overview of conventional breakdown theory of sprites, which is build on original ideas advanced by C.T.R. Wilson [Wilson, Proc. Phys. Soc. Lond., 37, 32D, 1925]. We will discuss similarity properties of electrical discharges as a function of gas pressure and a selected set of results of recent laboratory studies of filamentary channels of ionization (termed streamers) [e.g., van Veldhuizen et al., IEEE Trans. Plasma Sci., 30, 162, 2002; Yi and Williams, J. Phys. D. Appl. Phys., 35, 205, 2002], which are directly applicable for understanding of high spatial resolution imagery of sprites revealing many internal filamentary features with transverse spatial scales ranging from tens to a few hundreds of meters [Gerken and Inan, JASTP, 65, 567, 2003]. The specific set of features, which can be successfully explained by existing conventional theory of sprites and which we will discuss in this talk, include: (1) sprite halos [Barrington-Leigh et al., 106, 1741, 2001]; (2) the observed diffuse and streamer regions of sprites [Pasko and Stenbaek-Nielsen, GRL, 29, 1440, doi:10.1029/2001GL014241, 2002]; (3) the observed ELF radiation from sprites [Cummer et al., GRL, 25, 1281, 1998; Pasko et al., GRL, 25, 3493, 1998]; (4) the observed spatial transverse scales of streamers in sprites; (5) the observed high-speed vertical development of sprites; and (6) the detections of short bursts of blue emissions from sprites (see [Liu and Pasko, JGR, 109, A04301, doi:10.1029/2003JA010064, 2004] for experimental references and recent modeling results pertaining to items (4), (5) and (6)). The talk will be concluded with a discussion of a set of unsolved problems in exiting sprite theory, which include

  12. Extremely far from equilibrium: the multiscale dynamics of streamers

    Science.gov (United States)

    Ebert, Ute

    2012-10-01

    Streamers can emerge when high voltages are applied to gases. At their tips, the electric field is strongly enhanced, and electron energies locally reach distributions very far from equilibrium, with long tails at high energies. These exotic electron energies create radiation and chemical excitations at very low energy input, as the gas stays cold while the ionization front passes. Applications are multiple: highly efficient O* radical production in air for disinfection, combustion gas cleaning, plasma assisted combustion, plasma bullets in medicine etc. In that sense, streamers can be considered as very efficient converters of pulsed electric into chemical energy, in particular, if the electric circuits are optimized for the application. Streamers are also ubiquitous in nature, e.g., in the streamer corona of lightning leaders, in sprite discharges high above the clouds; and streamers also seem to contribute to generating gamma-ray flashes and even to electron-positron beams in active thunderstorms. Unravelling the intrinsic mechanisms of streamers is challenging: they can move with up to one tenth of the speed of light, and they have an intricate nonlinear structure with a hierarchy of scales. I will review how theory and experiment deal with these structures, and I will discuss the basic differences between positive and negative streamers, electron acceleration at streamer tips and the consecutive radiation and chemical reactions, the propagation mechanism of positive streamers in different gases, streamer velocities and diameters varying over at least two orders of magnitude, streamer branching and interaction, and their three-dimensional tree structure. Both theory and experiment work with a patchwork of methods, and geophysics can provide movies that cannot be taken in the lab. I will sketch the state and outline open questions.

  13. Bent paths of a positive streamer and a cathode-directed spark leader in diffuse discharges preionized by runaway electrons

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Cheng; Shao, Tao, E-mail: st@mail.iee.ac.cn; Wang, Ruixue; Yan, Ping [Institute of Electrical Engineering, Chinese Academy of Sciences, Beijing 100190 (China); Key Laboratory of Power Electronics and Electric Drive, Chinese Academy of Sciences, Beijing 100190 (China); Tarasenko, Viktor F.; Beloplotov, Dmitry V.; Lomaev, Mikhail I.; Sorokin, Dmitry A. [Institute of High Current Electronics, Russian Academy of Science, Tomsk 634055 (Russian Federation); National Research Tomsk State University, 36 Lenin Ave., Tomsk 634050 (Russian Federation)

    2015-03-15

    Diffuse discharges preionized by runaway electrons can produce large-area homogeneous discharges at elevated pressures, which is an intriguing phenomenon in the physics of pulsed discharges. In this paper, runaway-electron-preionized diffuse discharge (REP DD) was obtained in a wide pressure range (0.05–0.25 MPa), and under certain conditions a positive streamer and a cathode-directed spark leader could be observed to propagate at some angles to the applied (background) electric field lines. For a 16-mm gap at an air pressure of 0.08–0.1 MPa, the percentage of pulses in which such propagation is observed is about 5%–50% of their total number, and in the other pulses such bent paths could not be observed because there is even no streamer or cathode-directed spark leader in diffuse discharges. In our opinion, such propagation of the positive streamer and the cathode-directed spark leader at some angle to the background electric field lines owes to different increase rates of the electron density in different regions of the discharge volume under REP DD conditions. Therefore, during the formation of a REP DD, the increase of the electron density is inhomogeneous and nonsimultaneous, resulting in an electron density gradient at the ionization wave front.

  14. Bent paths of a positive streamer and a cathode-directed spark leader in diffuse discharges preionized by runaway electrons

    International Nuclear Information System (INIS)

    Zhang, Cheng; Shao, Tao; Wang, Ruixue; Yan, Ping; Tarasenko, Viktor F.; Beloplotov, Dmitry V.; Lomaev, Mikhail I.; Sorokin, Dmitry A.

    2015-01-01

    Diffuse discharges preionized by runaway electrons can produce large-area homogeneous discharges at elevated pressures, which is an intriguing phenomenon in the physics of pulsed discharges. In this paper, runaway-electron-preionized diffuse discharge (REP DD) was obtained in a wide pressure range (0.05–0.25 MPa), and under certain conditions a positive streamer and a cathode-directed spark leader could be observed to propagate at some angles to the applied (background) electric field lines. For a 16-mm gap at an air pressure of 0.08–0.1 MPa, the percentage of pulses in which such propagation is observed is about 5%–50% of their total number, and in the other pulses such bent paths could not be observed because there is even no streamer or cathode-directed spark leader in diffuse discharges. In our opinion, such propagation of the positive streamer and the cathode-directed spark leader at some angle to the background electric field lines owes to different increase rates of the electron density in different regions of the discharge volume under REP DD conditions. Therefore, during the formation of a REP DD, the increase of the electron density is inhomogeneous and nonsimultaneous, resulting in an electron density gradient at the ionization wave front

  15. Modeling the plasma chemistry of stratospheric Blue Jet streamers

    Science.gov (United States)

    Winkler, Holger; Notholt, Justus

    2014-05-01

    Stratospheric Blue Jets (SBJs) are upward propagating discharges in the altitude range 15-40 km above thunderstorms. The currently most accepted theory associates SBJs to the development of the streamer zone of a leader. The streamers emitted from the leader can travel for a few tens of kilometers predominantly in the vertical direction (Raizer et al., 2007). The strong electric fields at the streamer tips cause ionisation, dissociation, and excitation, and give rise to chemical perturbations. While in recent years the effects of electric discharges occurring in the mesosphere (sprites) have been investigated in a number of model studies, there are only a few studies on the impact of SBJs. However, chemical perturbations due to SBJs are of interest as they might influence the stratospheric ozone layer. We present results of detailed plasma chemistry simulations of SBJ streamers for both day-time and night-time conditions. Any effects of the subsequent leader are not considered. The model accounts for more than 500 reactions and calculates the evolution of the 88 species under the influence of the breakdown electric fields at the streamer tip. As the SBJ dynamics is outside the scope of this study, the streamer parameters are prescribed. For this purpose, electric field parameters based on Raizer et al. (2007) are used. The model is applied to the typical SBJ altitude range 15-40 km. The simulations indicate that SBJ streamers cause significant chemical perturbations. In particular, the liberation of atomic oxygen during the discharge leads to a formation of ozone. At the same time, reactive nitrogen and hydrogen radicals are produced which will cause catalytic ozone destruction. Reference: Raizer et al. (2007), J. Atmos. Solar-Terr. Phys., 69 (8), 925-938.

  16. An improved model to determine the inception of positive upward leader–streamer system considering the leader propagation during dark period

    International Nuclear Information System (INIS)

    Xie Shijun; He Junjia; Chen Weijiang

    2013-01-01

    Stem–leader transition and front-streamer inception are two essential conditions for the inception of positive upward leader–streamer system (LSS). Previous models have not considered the initial-leader propagation during dark period and have not been verified systematically. In this paper, a series of positive upward discharge simulation experiments was designed and carried out. Characteristic parameters of the discharge process related to the inception of positive upward LSS, namely, the first-corona inception voltage, the first-corona charge, the dark period, and the LSS inception voltage, were obtained. By comparing these experiment results with simulation results calculated using previous models, it was found that it is improper to assume that the length of the initial leader is a fixed value. Finally, an improved inception model of positive upward LSS considering the leader propagation during dark period was developed and verified with experiment results.

  17. Electron density in surface barrier discharge emerging at argon/water interface: quantification for streamers and leaders

    Science.gov (United States)

    Cvetanović, Nikola; Galmiz, Oleksandr; Synek, Petr; Zemánek, Miroslav; Brablec, Antonín; Hoder, Tomáš

    2018-02-01

    Optical emission spectroscopy, fast intensified CCD imaging and electrical measurements were applied to investigate the basic plasma parameters of surface barrier discharge emerging from a conductive water electrode. The discharge was generated at the triple-line interface of atmospheric pressure argon gas and conductive water solution at the fused silica dielectrics using a sinusoidal high-voltage waveform. The spectroscopic methods of atomic line broadening and molecular spectroscopy were used to determine the electron densities and the gas temperature in the active plasma. These parameters were obtained for both applied voltage polarities and resolved spatially. Two different spectral signatures were identified in the spatially resolved spectra resulting in electron densities differing by two orders of magnitude. It is shown that two discharge mechanisms take a place: the streamer and the leader one, with electron densities of 1014 and 1016 cm-3, respectively. This spectroscopic evidence is supported by the combined diagnostics of electrical current measurements and phase-resolved intensified CCD camera imaging.

  18. Dependence of positive and negative sprite morphology on lightning characteristics and upper atmospheric ambient conditions

    Science.gov (United States)

    Qin, Jianqi; Celestin, Sebastien; Pasko, Victor P.

    2013-05-01

    Carrot sprites, exhibiting both upward and downward propagating streamers, and columniform sprites, characterized by predominantly vertical downward streamers, represent two distinct morphological classes of lightning-driven transient luminous events in the upper atmosphere. It is found that positive cloud-to-ground lightning discharges (+CGs) associated with large charge moment changes (QhQ) tend to produce carrot sprites with the presence of a mesospheric region where the electric field exceeds the value 0.8Ek and persists for >˜2 ms, whereas those associated with small QhQ are only able to produce columniform sprites. Columniform sprites may also appear in the periphery of a sprite halo produced by +CGs associated with large QhQ. For a sufficiently large QhQ, the time dynamics of the QhQ determines the specific shape of the carrot sprites. In the case when the sufficiently large QhQ is produced mainly by an impulsive return stroke, strong electric field is produced at high altitudes and manifests as a bright halo, and the corresponding conductivity enhancement lowers/enhances the probability of streamer initiation inside/below the sprite halo. A more impulsive return stroke leads to a more significant conductivity enhancement (i.e., a brighter halo). This conductivity enhancement also leads to fast decay and termination of the upper diffuse region of carrot sprites because it effectively screens out the electric field at high altitudes. On the contrary, if the sufficiently large QhQ is produced by a weak return stroke (i.e., a dim halo) accompanied by intense continuing current, the lightning-induced electric field at high altitudes persists at a level that is comparable to Ek, and therefore an extensive upper diffuse region can develop. Furthermore, we demonstrate that `negative sprites' (produced by -CGs) should be necessarily carrot sprites and most likely accompanied by a detectable halo, since the initiation of upward positive streamers is always easier

  19. Streamer Evaporation

    Science.gov (United States)

    Suess, Steven T.; Wang, A. H.; Wu, Shi T.; Nerney, S.

    1998-01-01

    Evaporation is the consequence of slow plasma heating near the tops of streamers where the plasma is only weakly contained by the magnetic field. The form it takes is the slow opening of field lines at the top of the streamer and transient formation of new solar wind. It was discovered in polytropic model calculations, where due to the absence of other energy loss mechanisms in magnetostatic streamers, its ultimate endpoint is the complete evaporation of the streamer. This takes, for plausible heating rates, weeks to months in these models. Of course streamers do not behave this way, for more than one reason. One is that there are losses due to thermal conduction to the base of the streamer and radiation from the transition region. Another is that streamer heating must have a characteristic time constant and depend on the ambient physical conditions. We use our global Magnetohydrodynamics (MHD) model with thermal conduction to examine a few examples of the effect of changing the heating scale height and of making ad hoc choices for how the heating depends on ambient conditions. At the same time, we apply and extend the analytic model of streamers, which showed that streamers will be unable to contain plasma for temperatures near the cusp greater than about 2xl0(exp 6) K. Slow solar wind is observed to come from streamers through transient releases. A scenario for this that is consistent with the above physical process is that heating increases the near-cusp temperature until field lines there are forced open. The subsequent evacuation of the flux tubes by the newly forming slow wind decreases the temperature and heating until the flux tubes are able to reclose. Then, over a longer time scale, heating begins to again refill the flux tubes with plasma and increase the temperature until the cycle repeats itself. The calculations we report here are first steps towards quantitative evaluation of this scenario.

  20. Electric fields and electron energies in sprites and temporal evolutions of lightning charge moment

    International Nuclear Information System (INIS)

    Adachi, T; Hiraki, Y; Yamamoto, K; Takahashi, Y; Fukunishi, H; Hsu, R-R; Su, H-T; Chen, A B; Mende, S B; Frey, H U; Lee, L C

    2008-01-01

    The fundamental electrodynamical coupling processes between lightning and sprites are investigated. By combining the observed spectral data with the Monte Carlo swarm experiments, reduced electric fields and electron energies in sprite streamers and halos are estimated. The obtained fields inside sprite halos (70-97 Td with an analysis error of ±5 Td) are lower than the conventional breakdown field, E k ∼ 128 Td, indicating a significant reduction of electrons associated with halos while those in sprite streamers (98-380 Td with an error of ±50 Td) are higher than E k , suggesting that a significant ionization process drives their formation and development. A combined analysis of photometric and electromagnetic data makes it possible to estimate temporal evolutions of lightning charge moment. It is found that lightning discharges with a short time scale (∼1 ms) and a moderate amount of charge moment (∼400 C km) produce discernible halos. On the other hand, lightning discharges with a large amount of charge moment (∼1300 C km) produce streamers regardless of their time scale. The results obtained are comprehensively interpreted with both the conventional breakdown field necessary for the formation of streamers and the electric field necessary for the production of optical emissions of halo which is sensitive to the time scale of the thundercloud field due to the significant reduction of electrons.

  1. Spectrum of Sprite Halos

    Czech Academy of Sciences Publication Activity Database

    Gordillo-Vázquez, F.J.; Luque, A.; Šimek, Milan

    2011-01-01

    Roč. 116, č. 9 (2011), A09319-A09319 ISSN 0148-0227 Institutional research plan: CEZ:AV0Z20430508 Keywords : sprites * halos * spectroscopy Subject RIV: BL - Plasma and Gas Discharge Physics Impact factor: 3.021, year: 2011 http://www.trappa.iaa.es/sites/all/files/papers/isi_journal_papers/2011/2011_08.pdf

  2. The Sprite 2003 Campaign

    DEFF Research Database (Denmark)

    Neubert, T.; Laursen, S.; Rasmussen, I. L.

    2003-01-01

    During the northern hemisphere summer of 2003, from July 18 to September 18, a sprite observation campaign was conducted with measurements from Southern Europe, coordinated with measurements from the magnetically conjugate region in South Africa. The goal of the campaign was to investigate...... emissions. The presentation will give an overview of the campaign, the meteorological conditions, and present some first results....

  3. Chemistry of sprite discharges through ion-neutral reactions

    Directory of Open Access Journals (Sweden)

    Y. Hiraki

    2008-07-01

    Full Text Available We estimate the concentration changes, caused by streamer discharge in sprites, of ozone and related minor species as odd nitrogen (NOx and hydrogen (HOx families in the upper stratosphere and mesosphere. The streamer has an intense electric field and high electron density at its head, where a large number of chemically-radical ions and atoms are produced through electron impact on neutral molecules. After its propagation, densities of minor species can be perturbed through ion-neutral chemical reactions initiated by the relaxation of these radical products. We evaluate the production rates of ions and atoms using an electron kinetics model and by assuming that the electric field and electron density are in the head region. We calculate the density variations mainly for NOx, Ox, and HOx species using a one-dimensional model of the neutral and ion composition of the middle atmosphere, including the effect of the sprite streamer. Results at the nighttime condition show that the densities of NO, O3, H, and OH increase suddenly through reactions triggered by the first atomic nitrogen and oxygen product, and electrons just after streamer initiation. It is shown that NO and NO2 still remain for 1 h by a certain order of increase with their source-sink balance, predominantly around 60 km; for other species, increases in O3, OH, HO2, and H2O2 still remain in the range of 40–70 km. From this affirmative result of long-time behavior previously not presented, we emphasize that sprites would have the power to impact local chemistry at night. We also discuss the consistency with previous theoretical and observational studies, along with future suggestions.

  4. Chemistry of sprite discharges through ion-neutral reactions

    Science.gov (United States)

    Hiraki, Y.; Kasai, Y.; Fukunishi, H.

    2008-07-01

    We estimate the concentration changes, caused by streamer discharge in sprites, of ozone and related minor species as odd nitrogen (NOx) and hydrogen (HOx) families in the upper stratosphere and mesosphere. The streamer has an intense electric field and high electron density at its head, where a large number of chemically-radical ions and atoms are produced through electron impact on neutral molecules. After its propagation, densities of minor species can be perturbed through ion-neutral chemical reactions initiated by the relaxation of these radical products. We evaluate the production rates of ions and atoms using an electron kinetics model and by assuming that the electric field and electron density are in the head region. We calculate the density variations mainly for NOx, Ox, and HOx species using a one-dimensional model of the neutral and ion composition of the middle atmosphere, including the effect of the sprite streamer. Results at the nighttime condition show that the densities of NO, O3, H, and OH increase suddenly through reactions triggered by the first atomic nitrogen and oxygen product, and electrons just after streamer initiation. It is shown that NO and NO2 still remain for 1 h by a certain order of increase with their source-sink balance, predominantly around 60 km; for other species, increases in O3, OH, HO2, and H2O2 still remain in the range of 40 70 km. From this affirmative result of long-time behavior previously not presented, we emphasize that sprites would have the power to impact local chemistry at night. We also discuss the consistency with previous theoretical and observational studies, along with future suggestions.

  5. Positive streamers in air and nitrogen of varying density: experiments on similarity laws

    International Nuclear Information System (INIS)

    Briels, T M P; Van Veldhuizen, E M; Ebert, U

    2008-01-01

    Positive streamers in ambient air at pressures from 0.013 to 1 bar are investigated experimentally. The voltage applied to the anode needle ranges from 5 to 45 kV, the discharge gap from 1 to 16 cm. Using a 'slow' voltage rise time of 100-180 ns, the streamers are intentionally kept thin. For each pressure p, we find a minimal diameter d min . To test whether streamers at different pressures are similar, the minimal streamer diameter d min is multiplied by its pressure p; we find this product to be well approximated by p · d min = 0.20 ± 0.02 mm bar over two decades of air pressure at room temperature. The value also fits diameters of sprite discharges above thunderclouds at an altitude of 80 km when extrapolated to room temperature (as air density rather than pressure determines the physical behaviour). The minimal velocity of streamers in our measurements is approximately 0.1 mm ns -1 = 10 5 m s -1 . The same minimal velocity has been reported for tendrils in sprites. We also investigate the size of the initial ionization cloud at the electrode tip from which the streamers emerge, and the streamer length between branching events. The same quantities are also measured in nitrogen with a purity of approximately 99.9%. We characterize the essential differences with streamers in air and find a minimal diameter of p · d min = 0.12 ± 0.02 mm bar in our nitrogen.

  6. Reconnection and merging of positive streamers in air

    Energy Technology Data Exchange (ETDEWEB)

    Nijdam, S; Geurts, C G C; Van Veldhuizen, E M; Ebert, U, E-mail: s.nijdam@tue.n [Department of Applied Physics, Eindhoven University of Technology, PO Box 513, 5600 MB Eindhoven (Netherlands)

    2009-02-21

    Pictures show that streamer or sprite discharge channels emerging from the same electrode sometimes seem to reconnect or merge though their heads carry electric charge of the same polarity; one might therefore suspect that reconnections are an artefact of the two-dimensional projection in the pictures. Here we use stereo photography to investigate the full three-dimensional structure of such events. We analyse reconnection, possibly an electrostatic effect in which a late thin streamer reconnects to an earlier thick streamer channel, and merging, a suggested photoionization effect in which two simultaneously propagating streamer heads merge into one new streamer. We use four different anode geometries (one tip, two tips, two asymmetric protrusions in a plate and a wire), placed 40 mm above a flat cathode plate in ambient air. A positive high voltage pulse is applied to the anode, creating a positive corona discharge. This discharge is studied with a fast ICCD camera, in many cases combined with optics to enable stereoscopic imaging. We find that reconnections as defined above occur frequently. Merging on the other hand was only observed at a pressure of 25 mbar and a tip separation of 2 mm, i.e. for a reduced tip distance of p{center_dot}d = 50 {mu}m bar. In this case the full width at half maximum of the streamer channel is more than 10 times as large as the tip separation. At higher pressures or with a wire anode, merging was not observed.

  7. Reconnection and merging of positive streamers in air

    International Nuclear Information System (INIS)

    Nijdam, S; Geurts, C G C; Van Veldhuizen, E M; Ebert, U

    2009-01-01

    Pictures show that streamer or sprite discharge channels emerging from the same electrode sometimes seem to reconnect or merge though their heads carry electric charge of the same polarity; one might therefore suspect that reconnections are an artefact of the two-dimensional projection in the pictures. Here we use stereo photography to investigate the full three-dimensional structure of such events. We analyse reconnection, possibly an electrostatic effect in which a late thin streamer reconnects to an earlier thick streamer channel, and merging, a suggested photoionization effect in which two simultaneously propagating streamer heads merge into one new streamer. We use four different anode geometries (one tip, two tips, two asymmetric protrusions in a plate and a wire), placed 40 mm above a flat cathode plate in ambient air. A positive high voltage pulse is applied to the anode, creating a positive corona discharge. This discharge is studied with a fast ICCD camera, in many cases combined with optics to enable stereoscopic imaging. We find that reconnections as defined above occur frequently. Merging on the other hand was only observed at a pressure of 25 mbar and a tip separation of 2 mm, i.e. for a reduced tip distance of p·d = 50 μm bar. In this case the full width at half maximum of the streamer channel is more than 10 times as large as the tip separation. At higher pressures or with a wire anode, merging was not observed.

  8. Sprites and Early ionospheric VLF perturbations

    Science.gov (United States)

    Haldoupis, Christos; Amvrosiadi, Nino; Cotts, Ben; van der Velde, Oscar; Chanrion, Olivier; Neubert, Torsten

    2010-05-01

    Past studies have shown a correlation between sprites and early VLF perturbations, but the reported correlation varies widely from ~ 50% to 100%. The present study resolves these large discrepancies by analyzing several case studies of sprite and narrowband VLF observations, in which multiple transmitter-receiver VLF links with great circle paths (GCPs) passing near a sprite-producing thunderstorm were available. In this setup, the multiple links act in a complementary way that makes the detection of early VLF perturbations much more probable compared to a single VLF link that can miss several of them, a fact that was overlooked in past studies. The evidence shows that sprites are accompanied by early VLF perturbations in a one-to-one correspondence. This implies that the sprite generation mechanism may cause also sub-ionospheric conductivity disturbances that produce early VLF events. However, the one-to-one "sprite to early" event relationship, if viewed conversely as "early to sprite", appears not to be always reciprocal. This is because the number of early events detected in some cases was considerably larger than the number of sprites. Since the great majority of the early events not accompanied by sprites was caused by positive cloud to ground (+CG) lightning discharges, it is possible that sprites or sprite halos were concurrently present in these events as well but were missed by the sprite-watch detection system. In order for this option to be resolved we need more studies using highly sensitive optical systems capable of detecting weaker sprites, sprite halos and elves.

  9. Stability of Streamer Chamber

    Science.gov (United States)

    Wada, Toshiaki; Ogawa, Masato; Takahashi, Kaoru; Sugiyama, Tsunetoshi; Kobayashi, Shigeharu; Kohno, Hirobumi

    1982-08-01

    The quality of tracks obtained from a streamer chamber is studied through the measurement of the streamer brightness. The stability of streamer tracks depends on the value of the high voltage applied and its shape. By using a single conical-type spark gap as the pulse shaper, stable brightness of the streamer tracks is attained. The data on the streamer brightness are compared with the result by Bulos et al. and it is found that the brightness is more strongly affected by field parameters than in their result.

  10. Stability of streamer chamber

    International Nuclear Information System (INIS)

    Wada, Toshiaki; Ogawa, Masato; Takahashi, Kaoru; Sugiyama, Tsunetoshi; Kobayashi, Shigeharu; Kohno, Hirobumi.

    1982-01-01

    The quality of tracks obtained from a streamer chamber is studied through the measurement of the streamer brightness. The stability of streamer tracks depends on the value of the high voltage applied and its shape. By using a single conical-type spark gap as the pulse shaper, stable brightness of the streamer tracks is attained. The data on the streamer brightness are compared with the result by Bulos et al. and it is found that the brightness is more strongly affected by field parameters than in their result. (author)

  11. Subionospheric VLF signatures and their association with sprites observed during EuroSprite 2003

    DEFF Research Database (Denmark)

    Mika, A.; Haldoupis, C.; Marshall, R.A.

    2005-01-01

    In this study, VLF observations during EuroSprite-2003 are analyzed in connection with many sprites observed above thunderstorms in central France. The sprites were detected with a sensitive camera from the Observatoire du Pic du Midi in the Pyrenees overlooking storms monitored by the French nat...

  12. Parameterisation of the chemical effects of sprites in the middle atmosphere

    DEFF Research Database (Denmark)

    Enell, C.F.; Arnone, E.; Adachi, T.

    2008-01-01

    ion-neutral chemical model has been extended for this purpose and applied together with estimated rates of ionisation, excitation and dissociation based on spectroscopic ratios from ISUAL on FORMOSAT-2. This approach is used to estimate the NOx and ozone changes for two type cases. The NOx......Transient luminous events, such as red sprites, occur in the middle atmosphere in the electric field above thunderstorms. We here address the question whether these processes may be a significant source of odd nitrogen and affect ozone or other important trace species. A well-established coupled...... enhancements are at most one order of magnitude in the streamers, which means a production of at most 10 mol per event, or ( given a global rate of occurrence of three events per minute) some 150-1500 kg per day. The present study therefore indicates that sprites are insignificant as a global source of NOx...

  13. Modeling of a new electron-streamer acceleration mechanism

    Science.gov (United States)

    Ihaddadene, K. M. A.; Dwyer, J. R.; Liu, N.; Celestin, S. J.

    2017-12-01

    Lightning stepped leaders and laboratory spark discharges in air are known to produce X-rays [e.g., Dwyer et al., Geophys. Res. lett., 32, L20809, 2005; Kochkin et al., J. Phys. D: Appl. Phys., 45, 425202, 2012]. However, the processes behind the production of these X-rays are still not very well understood. During discharges, encounters between streamers of different polarities are very common. For example, during the formation of a new leader step, the negative streamer zone around the tip of a negative leader and the positive streamers initiated from the posiive part of a bidirectional space leader strongly interact. In laboratory experiments, when streamers are approaching a sharp electrode, streamers with the opposite polarity are initiated from the electrode and collide with the former streamers. Recently, the encounter between negative and positive streamers has been proposed as a plausible mechanism for the production of X-rays by spark discharges [Cooray et la., JASTP, 71, 1890, 2009; Kochkin et al., J. Phys. D: Appl. Phys., 45, 425202, 2012], but modeling results have shown later that the increase of the electric field involved in this process, which is above the conventional breakdown threshold field, is accompanied by a strong increase of the electron density. The resulting increase in the conductivity, in turn, causes this electric field to collapse over a few tens of picoseconds, preventing the electrons reaching high energies and producing significant X-ray emissions [e.g., Ihaddadene and Celestin, Geophys. Res. Lett., 45, 5644, 2015]. In this work, we will present simulation results of a new electron acceleration mechanism for producing runaway electron energies above hundred keV. The mechanism couples multiple single streamers and streamer head-on collisions, similar to a laboratory discharge, and is suitable for explaining the high-energy X-rays produced by discharges in air and by lightning stepped leaders.

  14. Optical diagnostics of streamer discharges in atmospheric gases

    Czech Academy of Sciences Publication Activity Database

    Šimek, Milan

    2014-01-01

    Roč. 47, č. 46 (2014), s. 463001-463001 ISSN 0022-3727 R&D Projects: GA ČR(CZ) GAP205/12/1709 Grant - others:Rada Programu interní podpory projektů mezinárodní spolupráce AV ČR(CZ) M100431201 Program:M Institutional support: RVO:61389021 Keywords : streamer * optical diagnostics * laser-induced fluorescence * LIF * TALIF * red-sprite Subject RIV: BL - Plasma and Gas Discharge Physics Impact factor: 2.721, year: 2014 http://iopscience.iop.org/0022-3727/47/46/463001/pdf/0022-3727_47_46_463001.pdf

  15. Positive streamers in air and nitrogen of varying density: experiments on similarity laws

    Energy Technology Data Exchange (ETDEWEB)

    Briels, T M P; Van Veldhuizen, E M; Ebert, U [Department of Applied Physics, Technische Universiteit Eindhoven, P O Box 513, 5600 MB Eindhoven (Netherlands)], E-mail: ebert@cwi.nl, E-mail: e.m.v.veldhuizen@tue.nl

    2008-12-07

    Positive streamers in ambient air at pressures from 0.013 to 1 bar are investigated experimentally. The voltage applied to the anode needle ranges from 5 to 45 kV, the discharge gap from 1 to 16 cm. Using a 'slow' voltage rise time of 100-180 ns, the streamers are intentionally kept thin. For each pressure p, we find a minimal diameter d{sub min}. To test whether streamers at different pressures are similar, the minimal streamer diameter d{sub min} is multiplied by its pressure p; we find this product to be well approximated by p {center_dot} d{sub min} = 0.20 {+-} 0.02 mm bar over two decades of air pressure at room temperature. The value also fits diameters of sprite discharges above thunderclouds at an altitude of 80 km when extrapolated to room temperature (as air density rather than pressure determines the physical behaviour). The minimal velocity of streamers in our measurements is approximately 0.1 mm ns{sup -1} = 10{sup 5} m s{sup -1}. The same minimal velocity has been reported for tendrils in sprites. We also investigate the size of the initial ionization cloud at the electrode tip from which the streamers emerge, and the streamer length between branching events. The same quantities are also measured in nitrogen with a purity of approximately 99.9%. We characterize the essential differences with streamers in air and find a minimal diameter of p {center_dot} d{sub min} = 0.12 {+-} 0.02 mm bar in our nitrogen.

  16. Hunting Elusive SPRITEs with Spitzer

    Science.gov (United States)

    Kohler, Susanna

    2017-05-01

    In recent years, astronomers have developed many wide-field imaging surveys in which the same targets are observed again and again. This new form of observing has allowed us to discover optical and radio transients explosive or irregular events with durations ranging from seconds to years. The dynamic infrared sky, however, has remained largely unexplored until now.Infrared ExplorationExample of a transient: SPIRITS 14ajc was visible when imaged by SPIRITS in 2014 (left) but it wasnt there during previous imaging between 2004 and 2008 (right). The bottom frame shows the difference between the two images. [Adapted from Kasliwal et al. 2017]Why hunt for infrared transients? Optical wavelengths dont allow us to observe events that are obscured, such that their own structure or their surroundings hide them from our view. Both supernovae and luminous red novae (associated with stellar mergers) are discoverable as infrared transients, and there may well be new types of transients in infrared that we havent seen before!To explore this uncharted territory, a team of scientists developed SPIRITS, the Spitzer Infrared Intensive Transients Survey. Begun in 2014, SPIRITS is a five-year long survey that uses the Spitzer Space Telescope to conduct a systematic search for mid-infrared transients in nearby galaxies.In a recent publication led by Mansi Kasliwal (Caltech and the Carnegie Institution for Science), the SPIRITS team has now detailed how their survey works and what theyve discovered in its first year.The light curves of SPRITEs (red stars) lie in the mid-infared luminosity gap between novae (orange) and supernovae (blue). [Kasliwal et al. 2017]Mystery TransientsKasliwal and collaborators used Spitzer to monitor 190 nearby galaxies. In SPIRITS first year, they found over 1958 variable stars and 43 infrared transient sources. Of these 43 transients, 21 were known supernovae, 4 were in the luminosity range of novae, and 4 had optical counterparts. The remaining 14 events

  17. The Sprite 2005 Observation Campaign

    DEFF Research Database (Denmark)

    Chanrion, Olivier Arnaud; Crosby, Norma; Armone, Enrico

    2007-01-01

    The four year "Coupling of Atmospheric Layers (CAL)" EU FP5 Research Training Network project studied unanswered questions related to transient luminous events (sprites, jets and elves) in the upper atmosphere. Consisting of ten scientific work-packages CAL also included intensive training and ou......, to develop their organisational skills, and to enhance their ability to communicate their activities. The campaign was a unique opportunity to train and strengthen skills that will be an asset to their future careers and, overall, was most successful....

  18. An analysis of five negative sprite-parent discharges and their associated thunderstorm charge structures

    Science.gov (United States)

    Boggs, Levi D.; Liu, Ningyu; Splitt, Michael; Lazarus, Steven; Glenn, Chad; Rassoul, Hamid; Cummer, Steven A.

    2016-01-01

    In this study we analyze the discharge morphologies of five confirmed negative sprite-parent discharges and the associated charge structures of the thunderstorms that produced them. The negative sprite-parent lightning took place in two thunderstorms that were associated with a tropical disturbance in east central and south Florida. The first thunderstorm, which moved onshore in east central Florida, produced four of the five negative sprite-parent discharges within a period of 17 min, as it made landfall from the Atlantic Ocean. These negative sprite-parents were composed of bolt-from-the-blue (BFB), hybrid intracloud-negative cloud-to-ground (IC-NCG), and multicell IC-NCGs discharges. The second thunderstorm, which occurred inland over south Florida, produced a negative sprite-parent that was a probable hybrid IC-NCG discharge and two negative gigantic jets (GJs). Weakened upper positive charge with very large midlevel negative charge was inferred for both convective cells that initiated the negative-sprite-parent discharges. Our study suggests tall, intense convective systems with high wind shear at the middle to upper regions of the cloud accompanied by low cloud-to-ground (CG) flash rates promote these charge structures. The excess amount of midlevel negative charge results in these CG discharges transferring much more charge to ground than typical negative CG discharges. We find that BFB discharges prefer an asymmetrical charge structure that brings the negative leader exiting the upper positive charge region closer to the lateral positive screening charge layer. This may be the main factor in determining whether a negative leader exiting the upper positive region of the thundercloud forms a BFB or GJ.

  19. Analysis of thunderstorm and lightning activity associated with sprites observed during the EuroSprite campaigns

    DEFF Research Database (Denmark)

    Soula, S.; van der Velde, O.; Montanyà, J.

    2009-01-01

    During the summers of 2003 to 2006 sprites were observed over thunderstorms in France by cameras on mountain tops in Southern France. The observations were part of a larger coordinated effort, the EuroSprite campaigns, with data collected simultaneously from other sources including the French rad...... a subsequent CG flash (median value case of a lightning process associated with a sprite consisted of 7 CG flashes....

  20. Self-quenching streamers

    International Nuclear Information System (INIS)

    Atac, M.; Tollestrup, A.V.; Potter, D.

    1982-01-01

    Self quenching streamers in drift tubes have been observed both optically and electronically. The streamers of 150-200 μm width extend out from the anode wire to 1.5 to 3 mm at atmospheric pressures. Electronic measurements at a two atomsphere pressure show pulses into a 50 Ω load with a rise time of 5 ns, a decay time of 40 ns, and an amplitude of 30 mV. Details of the experiments are discussed. There was no detectable residue on an anode wire after exposing it to 2x10 9 streamers for a 1 mm section. (orig.)

  1. Sprite-producing Convective Storms within the Colorado Lightning Mapping Array

    Science.gov (United States)

    Lyons, W. A.; Cummer, S. A.; Rison, W.; Krehbiel, P. R.; Lang, T. J.; Rutledge, S. A.; Lu, G.; Stanley, M. A.; Ashcraft, T.; Nelson, T. E.

    2012-12-01

    The multi-year, multi-institution effort entitled Physical Origins of Coupling to the Upper Atmosphere from Lightning (PhOCAL), has among its goals to qualitatively understand the meteorology and lightning flash characteristics that produce the unusual and/or very energetic lightning responsible for phenomena such as sprites, halos, elves, blue jets and gigantic jets, collectively known as Transient Luminous Events (TLEs). A key task is to obtain simultaneous video, ideally with a high-speed imager (HSI), of both a TLE and its parent lightning discharge, within the domain of a 3-D Lightning Mapping Array (LMA). While conceptually simple, this task is logistically quite complicated. In 2012, a new 15-station Colorado LMA (COLMA) became operational, covering northeastern Colorado, with the Yucca Ridge Field Station (YRFS) near its western edge. The National Charge Moment Change Network (CMCN), which since 2007 has been documenting sprite-class +CGs (those with impulse change moment changes >100 C km), indicates that a strong gradient of energetic +CGs exists west-to-east through the COLMA, with the most likely region for sprite-producing storms being in the COLMA eastern fringes (western Kansas and Nebraska). Yet, on 8 and 25 June, 2012, intense convective systems formed in the COLMA along and just east of the Front Range, producing severe weather and intense lightning. On the 8th, four sprite parent +CGs were captured at 3000 fps from YRFS with the sprites confirmed by dual (conventional speed) cameras in New Mexico. In a second storm on the 25th, viewing conditions prevented +CG video acquisition, but sprites were logged over the COLMA and detailed reconstructions of the discharges are being made. The parent discharges often began as upward negative leaders propagating into a mid-level positive charge layer at 8-10 km. They often originated within or near the convective core before expanding outward into a stratiform region and involving several hundred square

  2. Streamer chamber: pion decay

    CERN Multimedia

    1992-01-01

    The real particles produced in the decay of a positive pion can be seen in this image from a streamer chamber. Streamer chambers consist of a gas chamber through which a strong pulsed electric field is passed, creating sparks as a charged particle passes through it. A magnetic field is added to cause the decay products to follow curved paths so that their charge and momentum can be measured.

  3. Electric jets following the occurrence of sprites

    Science.gov (United States)

    Lee, L.; Chou, J.; Huang, S.; Chang, S.; Wu, Y.; Lee, Y.; Kuo, C.; Chen, A. B.; Su, H.; Hsu, R.; Frey, H. U.; Mende, S. B.; Takahashi, Y.; Lee, L.

    2010-12-01

    Sprites are discharges occurring at the altitudes ~40 to 90 km, which are usually associated with positive cloud-to-ground lightning (+CGs). Electric jets, which include blue jets (BJs) with the terminal altitude of ~40km and gigantic jets (GJs) emanating to the lower ionosphere, are upward discharges from the cloud tops toward the upper atmosphere. From previous ground observations, it has been reported that the secondary discharges (“palm-tree” [Heavner, 2000] or “sprite-initiated secondary TLEs” [Marshall and Inan, 2007]) following sprites occurred in altitudes between the cloud top and the bottom of the sprite. From July 2004 to June 2010, ISUAL has recorded dozens of events which resemble the secondary TLEs. From image and photometric data recorded by ISUAL, all these secondary TLEs have the characteristics of jets, so we call these events “secondary jets”. These secondary jets are categorized into two groups according to their emanating horizontal positions in relative to the sprites. Group-I secondary jets occurred in the cloud top region which is directly below the sprites. The terminal altitude is ~ 40-50km for most of group-I secondary jets. Several group-I secondary jets appear to originate from the cloud top region below the symmetric center of the clustering sprites and then propagate toward the lower ionosphere. While the group-II secondary jets originate from region outside the shielding area of the clustering sprites. In this paper, the image and the photometric characteristics of the secondary jets will be presented and the possible generating mechanisms will be discussed.

  4. Fluid and hybrid models for streamers

    Science.gov (United States)

    Bonaventura, Zdeněk

    2016-09-01

    Streamers are contracted ionizing waves with self-generated field enhancement that propagate into a low-ionized medium exposed to high electric field leaving filamentary trails of plasma behind. The widely used model to study streamer dynamics is based on drift-diffusion equations for electrons and ions, assuming local field approximation, coupled with Poisson's equation. For problems where presence of energetic electrons become important a fluid approach needs to be extended by a particle model, accompanied also with Monte Carlo Collision technique, that takes care of motion of these electrons. A combined fluid-particle approach is used to study an influence of surface emission processes on a fast-pulsed dielectric barrier discharge in air at atmospheric pressure. It is found that fluid-only model predicts substantially faster reignition dynamics compared to coupled fluid-particle model. Furthermore, a hybrid model can be created in which the population of electrons is divided in the energy space into two distinct groups: (1) low energy `bulk' electrons that are treated with fluid model, and (2) high energy `beam' electrons, followed as particles. The hybrid model is then capable not only to deal with streamer discharges in laboratory conditions, but also allows us to study electron acceleration in streamer zone of lighting leaders. There, the production of fast electrons from streamers is investigated, since these (runaway) electrons act as seeds for the relativistic runaway electron avalanche (RREA) mechanism, important for high-energy atmospheric physics phenomena. Results suggest that high energy electrons effect the streamer propagation, namely the velocity, the peak electric field, and thus also the production rate of runaway electrons. This work has been supported by the Czech Science Foundation research project 15-04023S.

  5. Fine structure of sprites and proposed global observations

    DEFF Research Database (Denmark)

    Mende, S.B; Frey, H.U.; Rairden, R.l.

    2002-01-01

    structures of columniform sprites (C sprites) consisted of slant directed, nearly vertically aligned columns of intense pinpoint like beads. The distance of the sprites from the observer was measured and the altitude and vertical spacing of the beads were estimated. The distribution of beads showed...... bore-sighted photometers. The imager will locate the sprites near the earth limb and make global synoptic measurements while the photometers will measure the spectral and temporal properties of sprites and other upper atmospheric luminous phenomena in a number of different wavelength regions...

  6. Multiple ion species fluid modeling of sprite halos and the role of electron detachment from O- in their dynamics

    Science.gov (United States)

    Liu, N.

    2011-12-01

    ambient value, so that there is no attachment "hole" forming in that region that is commonly observed in previous modeling work. According to recent work by Qin et al. [JGR, 116, A06305, 2011], electron density must be around 10^3 1/m^3 or less at sprite initiation altitude in order for individual streamers to form. This requires the ambient electron density at the sprite initiation altitude to be close to 10^3 1/m^3 from our results, because electron density is not greatly decreased below the halo front. In addition, the large downward extent of the halo shown by our results may offer an explanation for the initiation of sprite streamers at 65-70 km altitude observed previously.

  7. 2d axisymmetric "beam-bulk" modelling of the generation of runaway electrons by streamers.

    Science.gov (United States)

    Chanrion, Olivier; Bonaventura, Zdenek; Bourdon, Anne; Neubert, Torsten

    2017-04-01

    We present results from a 2d axisymmetric numerical model of streamers based on a "beam-bulk" approach which describes cold electrons with a fluid model and high energy electrons with a particle model. The interest is motivated by the generation of runaway electrons by streamers which may participate in the recently observed TGFs and which challenge the modelling. Runaway electrons are known to be generated from streamers when the electric field in its negative tip is of sufficient magnitude. After overtaking the streamer tip, runaways can affect the streamer propagation ahead and may produce high energy photons through the bremsstrahlung process. In conventional model of streamers, the evolution of the streamer discharge is mostly governed by cold electrons. By including runaway electrons, we model their production, their impact on the discharge propagation and can address their role in TGFs. Results of streamer propagation in leader electric field show that the runaway electrons accelerate the streamers, reduce the electric field in its tip and enlarge its radius by pre-ionizing the gas ahead. We observed that if we increase the electric field, the discharge is getting more diffuse, with a pattern driven by the increase in runaway induced ionisation.

  8. A mechanism for leader stepping

    Science.gov (United States)

    Ebert, U.; Carlson, B. E.; Koehn, C.

    2013-12-01

    The stepping of negative leaders is well observed, but not well understood. A major problem consists of the fact that the streamer corona is typically invisible within a thunderstorm, but determines the evolution of a leader. Motivated by recent observations of streamer and leader formation in the laboratory by T.M.P. Briels, S. Nijdam, P. Kochkin, A.P.J. van Deursen et al., by recent simulations of these processes by J. Teunissen, A. Sun et al., and by our theoretical understanding of the process, we suggest how laboratory phenomena can be extrapolated to lightning leaders to explain the stepping mechanism.

  9. What Are Red Sprites? An Art and Science Collaboration

    Science.gov (United States)

    McLeish, P.

    2013-04-01

    Sprites are fleeting luminous shapes that shoot into the upper atmosphere during large thunderstorms as lightning simultaneously reaches down to Earth. For at least a century scientists have attempted to confirm and explain the existence of sprites with visual images and data. Peter McLeish's images, Lightning's Angels, supplement the documentation of sprites by exploring the properties of this natural phenomenon through digitally enhanced oil encaustic paintings set to music in a six-minute film.

  10. Small Winter Thunderstorm with Sprites and Strong Positive Discharge

    Science.gov (United States)

    Suzuki, Tomoyuki; Hayakawa, Masashi; Michimoto, Koichiro

    A sprite campaign was conducted in the Hokuriku area of Japan during a winter of 2004/2005. On the basis of a combined analysis of the data from various instruments (CCD cameras, radar, VHF/LF∼MF lightning mapping system, field mill network, and ELF detector), we studied meteorological and electrical structures for winter thunderstorms and sprite-producing positive discharge. Typical winter sprite parent thunderstorms had a meso-scale cloud area with embedded small convective cells. Some small winter thunderstorms accompanied by the most frequent sprite events were found to cause 2∼3 sprite events during a short interval of about 3∼5 min. When the sprites were observed, the extent of the convective cells at 20 dBZ counter was atmost ∼20 × 20 km. The VHF sources associated with sprites were located near south of the convective cell and were mapped within very small areas of at most ∼10 × 10 km. This fact shows that some small winter thunderstorms can generate large positive charge associated with sprites. We will present the analysis of such a small thunderstorms with sprites and positive lightning discharges.

  11. Generation of elves by sprites and jets

    International Nuclear Information System (INIS)

    Taranenko, Y.; Roussel-Dupre, R.; Yukhimuk, V.; Symbalisty, E.

    1997-01-01

    Recent years of observations of the upper atmosphere and the lower ionosphere brought a fascinating collection of new phenomena including optical, radio, and gamma-ray emissions originating in the 20 to 90 km altitude range. Up to now, the most diverse phenomenology has emerged from the optical observations which have led to the identification of red sprites, blue jets, blue starts, and elves. Most of the studies have concentrated on relating such phenomena in the upper atmosphere to regular lightning discharges in the troposphere. The sprite/jet discharge itself can be caused by the runaway air breakdown, or regular air breakdown. The standard theory for optical airglow transients in the lower ionosphere above the thunderstorms also known as elves suggests that they are produced during interaction of electromagnetic pulses (EMP) from lightning with the lower ionosphere. Heating of the ambient electrons by the EMP in the D region can result in excitation of optical emissions once the optical excitation thresholds are reached. In this paper the authors suggest that in addition to this mechanism elves can be caused by an EMP generated by sprites and jets

  12. Prediction of TARANIS Observations of TGF's and Optical Emissions from Red Sprites

    Science.gov (United States)

    Nelson, M. A.

    2006-12-01

    TARANIS (Tool for the Analysis of Radiation from Lightning and Sprites) is a French (CNES, Centre National D'Etudes Spatiales) micro-satellite that is scheduled for launch in 2009. This will be the first satellite that will measure coincident gamma-rays and optical emissions from atmospheric discharges. These measurements will provide important clues concerning the physics of discharges that produce gamma-rays and will provide more definitive evidence of the role of conventional breakdown versus runaway breakdown than is currently available. While a variety of discharges may be associated with Transient Gamma Ray Flashes (TGF's), this study will focus on emissions expected from red sprites. Future studies will focus on other types of discharges (for example, gigantic jets or blue jets) to see whether they should produce detectable signal levels at both gamma-ray and optical frequencies. The source of terrestrial TGF's is a matter of debate at this time. Many experts in the field have interpreted the data associated with the RHESSI (Reuven Ramaty High Energy Solar Spectroscopic Imager) satellite to be indicative that the discharges associated with terrestrial gamma-rays are not associated with sprites. However, RHESSI was not designed for the purpose of collecting gamma-ray measurements from terrestrial discharges; does not possess a coincident optical measurement capability; and must average data over many events to predict a spectrum. We will present a statistical analysis of the relative efficiencies of the RHESSI and TARANIS satellite designs for the detection of TGF's associated with sprites. We will show results from a fully 2-D electromagnetic model (UNIMAX, the Unified Maxwell code) and an optical model (POEM, the Physics Based Optical Emission Model) to demonstrate the level of agreement between the simulations and the gamma-ray spectrum measurements and optical measurements (camera, photometer, and spectral measurements) for several different classes of

  13. Streamers and their applications

    Science.gov (United States)

    Pemen, A. J. M.

    2011-10-01

    In this invited lecture we give an overview of our 15 years of experience on streamer plasma research. Efforts are directed to integrating the competence areas of plasma physics, pulsed power technology and chemical processing. The current status is the development of a large scale pulsed corona system for gas treatment. Applications on biogas conditioning, VOC removal, odor abatement and control of traffic emissions have been demonstrated. Detailed research on electrical and chemical processes resulted in a boost of efficiencies. Energy transfer efficiency to the plasma was raised to above 90%. Simultaneous improvement of the plasma chemistry resulted in a highly efficient radical generation: O-radical production up to 50% of the theoretical maximum has been achieved. A major challenge in pulsed power driven streamers is to unravel, understand and ultimately control the complex interactions between the transient plasma, electrical circuits, and process. Even more a challenge is to yield electron energies that fit activation energies of the process. We will discuss our ideas on adjusting pulsed power waveforms and plasma reactor settings to obtain more controlled catalytic processing: the ``Chemical Transistor'' concept.

  14. Bacterial streamers in curved microchannels

    Science.gov (United States)

    Rusconi, Roberto; Lecuyer, Sigolene; Guglielmini, Laura; Stone, Howard

    2009-11-01

    Biofilms, generally identified as microbial communities embedded in a self-produced matrix of extracellular polymeric substances, are involved in a wide variety of health-related problems ranging from implant-associated infections to disease transmissions and dental plaque. The usual picture of these bacterial films is that they grow and develop on surfaces. However, suspended biofilm structures, or streamers, have been found in natural environments (e.g., rivers, acid mines, hydrothermal hot springs) and are always suggested to stem from a turbulent flow. We report the formation of bacterial streamers in curved microfluidic channels. By using confocal laser microscopy we are able to directly image and characterize the spatial and temporal evolution of these filamentous structures. Such streamers, which always connect the inner corners of opposite sides of the channel, are always located in the middle plane. Numerical simulations of the flow provide evidences for an underlying hydrodynamic mechanism behind the formation of the streamers.

  15. Ionizing potential waves and high-voltage breakdown streamers.

    Science.gov (United States)

    Albright, N. W.; Tidman, D. A.

    1972-01-01

    The structure of ionizing potential waves driven by a strong electric field in a dense gas is discussed. Negative breakdown waves are found to propagate with a velocity proportional to the electric field normal to the wavefront. This causes a curved ionizing potential wavefront to focus down into a filamentary structure, and may provide the reason why breakdown in dense gases propagates in the form of a narrow leader streamer instead of a broad wavefront.

  16. Laboratory experiments cannot be utilized to justify the action of early streamer emission terminals

    International Nuclear Information System (INIS)

    Becerra, Marley; Cooray, Vernon

    2008-01-01

    The early emission of streamers in laboratory long air gaps under switching impulses has been observed to reduce the time of initiation of leader positive discharges. This fact has been arbitrarily extrapolated by the manufacturers of early streamer emission devices to the case of upward connecting leaders initiated under natural lightning conditions, in support of those non-conventional terminals that claim to perform better than Franklin lightning rods. In order to discuss the physical basis and validity of these claims, a self-consistent model based on the physics of leader discharges is used to simulate the performance of lightning rods in the laboratory and under natural lightning conditions. It is theoretically shown that the initiation of early streamers can indeed lead to the early initiation of self-propagating positive leaders in laboratory long air gaps under switching voltages. However, this is not the case for positive connecting leaders initiated from the same lightning rod under the influence of the electric field produced by a downward moving stepped leader. The time evolution of the development of positive leaders under natural conditions is different from the case in the laboratory, where the leader inception condition is closely dependent upon the initiation of the first streamer burst. Our study shows that the claimed similarity between the performance of lightning rods under switching electric fields applied in the laboratory and under the electric field produced by a descending stepped leader is not justified. Thus, the use of existing laboratory results to validate the performance of the early streamer lightning rods under natural conditions is not justified

  17. ELF/VLF signatures of sprite-producing lightning discharges observed during the 2005 EuroSprite campaign

    DEFF Research Database (Denmark)

    Greenberg, E.; Price, C.; Yair, Y.

    2009-01-01

    ) discharges had peak current intensities between +8 and +130 kA whereas their charge moment changes (CMC) ranged from 500 to 3500 C km. Furthermore, the peak current reported by the Météorage lightning network are well correlated with the amplitudes of the VLF bursts, while showing poor correlation......%) an ELF transient was not associated with sprite occurrence, suggesting that long continuing current of tens of ms may not always be a necessary condition for sprite production, a finding which influences the estimation of the global sprite rate based on Schumann resonance (SR) measurements....

  18. Analyses of electron runaway in front of the negative streamer channel

    Science.gov (United States)

    Babich, L. P.; Bochkov, E. I.; Kutsyk, I. M.; Neubert, T.; Chanrion, O.

    2017-08-01

    X-ray and γ-ray emissions, observed in correlation with negative leaders of lightning and long sparks of high-voltage laboratory experiments, are conventionally connected with the bremsstrahlung of high-energy runaway electrons (REs). Here we extend a focusing mechanism, analyzed in our previous paper, which allows the electric field to reach magnitudes, required for a generation of significant RE fluxes and associated bremsstrahlung, when the ionization wave propagates in a narrow, ionized channel created by a previous streamer. Under such conditions we compute the production rate of REs per unit streamer length as a function of the streamer velocity and predict that, once a streamer is formed with the electric field capable of producing REs ahead of the streamer front, the ionization induced by the REs is capable of creating an ionized channel that allows for self-sustained propagation of the RE-emitting ionization wave independent of the initial electron concentration. Thus, the streamer coronas of the leaders are probable sources of REs producing the observed high-energy radiation. To prove these predictions, new simulations are planned, which would show explicitly that the preionization in front of the channel via REs will lead to the ionization wave propagation self-consistent with RE generation.

  19. Land Streamer Surveying Using Multiple Sources

    KAUST Repository

    Mahmoud, Sherif

    2014-12-11

    Various examples are provided for land streamer seismic surveying using multiple sources. In one example, among others, a method includes disposing a land streamer in-line with first and second shot sources. The first shot source is at a first source location adjacent to a proximal end of the land streamer and the second shot source is at a second source location separated by a fixed length corresponding to a length of the land streamer. Shot gathers can be obtained when the shot sources are fired. In another example, a system includes a land streamer including a plurality of receivers, a first shot source located adjacent to the proximal end of the land streamer, and a second shot source located in-line with the land streamer and the first shot source. The second shot source is separated from the first shot source by a fixed overall length corresponding to the land streamer.

  20. SPRITE: the Spitzer proposal review website

    Science.gov (United States)

    Crane, Megan K.; Storrie-Lombardi, Lisa J.; Silbermann, Nancy A.; Rebull, Luisa M.

    2008-07-01

    The Spitzer Science Center (SSC), located on the campus of the California Institute of Technology, supports the science operations of NASA's infrared Spitzer Space Telescope. The SSC issues an annual Call for Proposals inviting investigators worldwide to submit Spitzer Space Telescope proposals. The Spitzer Proposal Review Website (SPRITE) is a MySQL/PHP web database application designed to support the SSC proposal review process. Review panel members use the software to view, grade, and write comments about the proposals, and SSC support team members monitor the grading and ranking process and ultimately generate a ranked list of all the proposals. The software is also used to generate, edit, and email award letters to the proposers. This work was performed at the California Institute of Technology under contract to the National Aeronautics and Space Administration.

  1. Land Streamer Surveying Using Multiple Sources

    KAUST Repository

    Mahmoud, Sherif; Schuster, Gerard T.

    2014-01-01

    are fired. In another example, a system includes a land streamer including a plurality of receivers, a first shot source located adjacent to the proximal end of the land streamer, and a second shot source located in-line with the land streamer and the first

  2. Effect of inhomogeneities on streamer propagation: II. Streamer dynamics in high pressure humid air with bubbles

    International Nuclear Information System (INIS)

    Babaeva, Natalia Yu; Kushner, Mark J

    2009-01-01

    The branching of electric discharge streamers in atmospheric pressure air, dense gases and liquids is a common occurrence whose origins are likely found with many causes, both deterministic and stochastic. One mechanism for streamer branching may be inhomogeneities in the path of a streamer which either divert the streamer (typically a region of lower ionization) or produce a new branch (a region of higher ionization). The propagation and branching of streamers in liquids is likely aided by low density inhomogeneities, bubbles; however, modeling of streamers in liquids is made difficult by the lack of transport coefficients. As a first step towards understanding the propagation and branching of streamers in liquids, we investigated the consequences of random inhomogeneities in the form of low pressure bubbles on the propagation of streamers in high pressure humid air. By virtue of their lower density, bubbles have larger E/N (electric field/gas number density) than the ambient gas with larger rates of ionization. The intersection of a streamer with a bubble will focus the plasma into the bubble by virtue of that higher rate of ionization but the details of the interaction depend on the relative sizes of the bubble and streamer. When a streamer intersects a field of bubbles, the large E/N in the bubble avalanches seed electrons produced by photoionization from the streamer. Each bubble then launches both a negative and positive going streamer that may link with those from adjacent bubbles or the original streamer. The total process then appears as streamer branching.

  3. The SPRITE and POS-SPRITE user report: An extensible calculation of particle, positron and electron implantation in solids

    International Nuclear Information System (INIS)

    Ritley, K.A.; Ghosh, V.J.; Lynn, K.G.; McKewown, M.; Welch, D.O.

    1997-01-01

    SPRITE (Simulation of Particle Reemission, Implantation and Transmission--Extensible) is a Fortran computer program designed to model the transport of a stream of energetic particles as they scatter through a solid or multilayer. SPRITE is intended to be a user-friendly and easily-extensible engine for performing basic transport calculations, and SPRITE incorporates such physics as is required to simulate the transport process, but specifically omits the details of the scattering mechanisms. PSPRITE is a Fortran computer program, built around the SPRITE transport engine and incorporating physical information necessary for modeling the implantation and thermalization of a stream of positrons or electrons with a solid. This document is intended to be the primary source of information and the only operations manual for SPRITE and the POS-SPRITE family of programs. This information includes the mode of operation of SPRITE, the format of the required and optional file types, as well as information about the output and results of the calculation. Information about installing and running these programs on a variety of computer systems will not be addressed in this report. Such information is rapidly expanding as these programs are adapted to run on different platforms, and thus the user can expect such information to be contained with the source code distribution set. Detailed information about the calculations of the structure of the POS-SPRITE programs are provided in this report, but detailed benchmark comparisons between the output of these calculations and experimental data are an active topic of research, and they refer the reader to the published literature for this information

  4. An Analysis of Two Thunderstorms Producing Five Negative Sprites on 12 September 2014

    Science.gov (United States)

    Boggs, L.; Liu, N.; Splitt, M. E.; Lazarus, S. M.; Cummer, S. A.; Rassoul, H.

    2015-12-01

    We present a detailed analysis of the thunderstorms and the parent lightning discharge morphologies of five confirmed negative sprites taking place in two different thunderstorms. These two thunderstorms took place in east-central and south Florida on 12 September 2014. We utilized several lightning location networks, remote magnetic field measurements, dual polarization radar, and balloon borne soundings in our analysis. Each parent discharge was immediately preceded by intra-cloud (IC) discharges between the mid-level negative and upper positive charge regions. This either allowed a second upward negative leader to escape the upper positive charge region, or encouraged a downward negative leader to be initiated and connect with ground. The discharges found in this study support the findings of Lu et al., 2012 [JGR,117, D04212, 2012] that negative sprite-parent lightning consists primarily of hybrid intra-cloud negative cloud-to-ground (IC-NCG) and bolt-from-the-blue (BFB) lightning. Our work finds these unique discharges form in thunderstorms that have an excess of mid-level negative charge and weakened upper positive charge. Due to this charge structure, these unusual discharges transfer more charge to the ground than typical negative cloud-to-ground discharges. Our study suggests that the key difference separating bolt-from-the-blue and gigantic jet discharges is an asymmetric charge structure. This acts to bring the negative leader exiting the thundercloud closer to the lateral positive screening layer, encouraging the negative leader to turn towards ground. This investigation reveals IC discharges that involve multiple convective cells and come to ground as a negative CG discharge, a breed of hybrid IC-NCG discharges, also transfer more negative charge to ground than typical negative CG discharges and are able to initiate negative sprites. From this work, the charge structures mentioned above resulted from tall, intense convective cells with low CG flash

  5. Testing an hydrogen streamer chamber

    CERN Multimedia

    1975-01-01

    A 2x10 cm gap streamer chamber, 35x55 cm2 in surface, was built and tested at CERN. Good tracks of cosmic rays were obtained up to atmospheric pressure, see F. Rohrbach et al, CERN-LAL (Orsay) Collaboration, Nucl. Instr. Methods 141 (1977) 229. Michel Cathenoz stand on the center.

  6. Compression and Processing of Space Image Sequences of Northern Lights and Sprites

    DEFF Research Database (Denmark)

    Forchhammer, Søren Otto; Martins, Bo; Jensen, Ole Riis

    1999-01-01

    Compression of image sequences of auroral activity as northern lights and thunderstorms with sprites is investigated.......Compression of image sequences of auroral activity as northern lights and thunderstorms with sprites is investigated....

  7. Optical observations geomagnetically conjugate to sprite-producing lightning discharges

    Directory of Open Access Journals (Sweden)

    R. A. Marshall

    2005-09-01

    Full Text Available Theoretical studies have predicted that large positive cloud-to-ground discharges can trigger a runaway avalanche process of relativistic electrons, forming a geomagnetically trapped electron beam. The beam may undergo pitch angle and energy scattering during its traverse of the Earth's magnetosphere, with a small percentage of electrons remaining in the loss cone and precipitating in the magnetically conjugate atmosphere. In particular, N2 1P and N2+1N optical emissions are expected to be observable. In July and August 2003, an attempt was made to detect these optical emissions, called "conjugate sprites", in correlation with sprite observations in Europe near . Sprite observations were made from the Observatoire du Pic du Midi (OMP in the French Pyrenées, and VLF receivers were installed in Europe to detect causative sferics and ionospheric disturbances associated with sprites. In the Southern Hemisphere conjugate region, the Wide-angle Array for Sprite Photometry (WASP was deployed at the South African Astronomical Observatory (SAAO, near Sutherland, South Africa, to observe optical emissions with a field-of-view magnetically conjugate to the Northern Hemisphere observing region. Observations at OMP revealed over 130 documented sprites, with WASP observations covering the conjugate region successfully for 30 of these events. However, no incidences of optical emissions in the conjugate hemisphere were found. Analysis of the conjugate optical data from SAAO, along with ELF energy measurements from Palmer Station, Antarctica, and charge-moment analysis, show that the lightning events during the course of this experiment likely had insufficient intensity to create a relativistic beam.

    Keywords. Ionosphere (Ionsophere-magnetosphere interactions; Ionospheric disturbances; Instruments and techniques

  8. Optical observations geomagnetically conjugate to sprite-producing lightning discharges

    Directory of Open Access Journals (Sweden)

    R. A. Marshall

    2005-09-01

    Full Text Available Theoretical studies have predicted that large positive cloud-to-ground discharges can trigger a runaway avalanche process of relativistic electrons, forming a geomagnetically trapped electron beam. The beam may undergo pitch angle and energy scattering during its traverse of the Earth's magnetosphere, with a small percentage of electrons remaining in the loss cone and precipitating in the magnetically conjugate atmosphere. In particular, N2 1P and N2+1N optical emissions are expected to be observable. In July and August 2003, an attempt was made to detect these optical emissions, called "conjugate sprites", in correlation with sprite observations in Europe near . Sprite observations were made from the Observatoire du Pic du Midi (OMP in the French Pyrenées, and VLF receivers were installed in Europe to detect causative sferics and ionospheric disturbances associated with sprites. In the Southern Hemisphere conjugate region, the Wide-angle Array for Sprite Photometry (WASP was deployed at the South African Astronomical Observatory (SAAO, near Sutherland, South Africa, to observe optical emissions with a field-of-view magnetically conjugate to the Northern Hemisphere observing region. Observations at OMP revealed over 130 documented sprites, with WASP observations covering the conjugate region successfully for 30 of these events. However, no incidences of optical emissions in the conjugate hemisphere were found. Analysis of the conjugate optical data from SAAO, along with ELF energy measurements from Palmer Station, Antarctica, and charge-moment analysis, show that the lightning events during the course of this experiment likely had insufficient intensity to create a relativistic beam. Keywords. Ionosphere (Ionsophere-magnetosphere interactions; Ionospheric disturbances; Instruments and techniques

  9. Evolution of streamer groups in nonthermal plasma

    Energy Technology Data Exchange (ETDEWEB)

    Okubo, M., E-mail: mokubo@me.osakafu-u.ac.jp [Department of Mechanical Engineering, Osaka Prefecture University, 1-1 Gakuen-cho, Naka-ku, Sakai 599-8531 (Japan)

    2015-12-15

    Nonthermal plasmas (NTPs) induced by atmospheric nanosecond pulsed corona discharge have been studied for controlling pollution from combustors, such as boilers, incinerators, and diesel engines. In high-speed short-width high-voltage pulsed corona discharge-induced plasmas, primary streamer evolution is followed by secondary streamer evolution. Though this phenomenon is known experimentally, the details of the structures of the streamers and their evolution mechanisms have not been fully clarified. In this letter, we perform quasi two-dimensional numerical analysis of nonequilibrium NTP induced by a nanosecond positive pulsed corona discharge. The continuum fluid equations for two-temperature nonequilibrium NTP are used as governing equations. In this study, 197 gas phase reactions for 25 chemical species and 21 surface reactions on the inner glass wall surface are considered in an air plasma under atmospheric pressure. The simulated behavior of the streamer groups agrees with experimental observations. Soon after the voltage increases on the reactor, primary streamers are formed, which may transit the complete gap, disappearing near the peak voltage. Next, second streamers appear, disappearing at the end of the applied voltage pulse. The streamer wavelength and the distance between the streamers in the axial direction are determined. Moreover, ozone generation is shown to be more significant in the secondary streamer. This simulation will allow better predictions for nanosecond positive pulsed plasma systems.

  10. Evolution of streamer groups in nonthermal plasma

    Science.gov (United States)

    Okubo, M.

    2015-12-01

    Nonthermal plasmas (NTPs) induced by atmospheric nanosecond pulsed corona discharge have been studied for controlling pollution from combustors, such as boilers, incinerators, and diesel engines. In high-speed short-width high-voltage pulsed corona discharge-induced plasmas, primary streamer evolution is followed by secondary streamer evolution. Though this phenomenon is known experimentally, the details of the structures of the streamers and their evolution mechanisms have not been fully clarified. In this letter, we perform quasi two-dimensional numerical analysis of nonequilibrium NTP induced by a nanosecond positive pulsed corona discharge. The continuum fluid equations for two-temperature nonequilibrium NTP are used as governing equations. In this study, 197 gas phase reactions for 25 chemical species and 21 surface reactions on the inner glass wall surface are considered in an air plasma under atmospheric pressure. The simulated behavior of the streamer groups agrees with experimental observations. Soon after the voltage increases on the reactor, primary streamers are formed, which may transit the complete gap, disappearing near the peak voltage. Next, second streamers appear, disappearing at the end of the applied voltage pulse. The streamer wavelength and the distance between the streamers in the axial direction are determined. Moreover, ozone generation is shown to be more significant in the secondary streamer. This simulation will allow better predictions for nanosecond positive pulsed plasma systems.

  11. NATO Advanced Study Institute on Sprites, Elves and Intense Lightning Discharges

    CERN Document Server

    Füllekrug, Martin; Rycroft, Michael J

    2006-01-01

    Particularly intense lightning discharges can produce transient luminous events above thunderclouds, termed sprites, elves and jets. These short lived optical emissions in the mesosphere can reach from the tops of thunderclouds up to the ionosphere; they provide direct evidence of coupling from the lower atmosphere to the upper atmosphere. Sprites are arguably the most dramatic recent discovery in solar-terrestrial physics. Shortly after the first ground based video recordings of sprites, observations on board the Space Shuttle detected sprites and elves occurring all around the world. These reports led to detailed sprite observations in North America, South America, Australia, Japan, and Europe. Subsequently, sprites were detected from other space platforms such as the International Space Station and the ROCSAT satellite. During the past 15 years, more than 200 contributions on sprites have been published in the scientific literature to document this rapidly evolving new research area.

  12. Experimental investigations on the physics of streamers

    NARCIS (Netherlands)

    Nijdam, S.

    2011-01-01

    Streamers are rapidly extending ionized fingers that can appear in gasses, liquids and solids. They are generated by high electric fields but can penetrate into areas where the background electric field is below the ionization threshold. Streamers occur in nature as a precursor to sparks and

  13. Pulsed positive corona streamer propagation and branching

    International Nuclear Information System (INIS)

    Veldhuizen, E.M. van; Rutgers, W.R.

    2002-01-01

    The propagation and branching of pulsed positive corona streamers in a short gap is observed with high resolution in space and time. The appearance of the pre-breakdown phenomena can be controlled by the electrode configuration, the gas composition and the impedance of the pulsed power circuit. In a point-wire gap the positive corona shows much more branching than in the parallel plane gap with a protrusion. In air, the branching is more pronounced than in argon. The pulsed power circuit appears to operate in two modes, either as an inductive circuit creating a lower number of thick streamers or as a resistive circuit giving a higher number of thin streamers. A possible cause for branching is electrostatic repulsion of two parts of the streamer head. The electric field at the streamer head is limited, the maximum values found are ∼170 kV cm -1 in air and ∼100 kV cm -1 in argon. At these maximum field strengths, the electrons have 5-10 eV energy, so the ionization is dominated by two-step processes. Differences between argon and ambient air in the field strength at which streamers propagate are ascribed to the difference in de-excitation processes in noble and molecular gases. The fact that the pulsed power circuit can control the streamer structure is important for applications, but this effect must also be taken into account in fundamental studies of streamer propagation and branching. (author)

  14. Pulsed positive corona streamer propagation and branching

    Energy Technology Data Exchange (ETDEWEB)

    Veldhuizen, E.M. van [Department of Physics, Technische Universiteit Eindhoven, Eindhoven (Netherlands)]. E-mail: e.m.v.veldhuizen@tue.nl; Rutgers, W.R. [Department of Physics, Technische Universiteit Eindhoven, Eindhoven (Netherlands)

    2002-09-07

    The propagation and branching of pulsed positive corona streamers in a short gap is observed with high resolution in space and time. The appearance of the pre-breakdown phenomena can be controlled by the electrode configuration, the gas composition and the impedance of the pulsed power circuit. In a point-wire gap the positive corona shows much more branching than in the parallel plane gap with a protrusion. In air, the branching is more pronounced than in argon. The pulsed power circuit appears to operate in two modes, either as an inductive circuit creating a lower number of thick streamers or as a resistive circuit giving a higher number of thin streamers. A possible cause for branching is electrostatic repulsion of two parts of the streamer head. The electric field at the streamer head is limited, the maximum values found are {approx}170 kV cm{sup -1} in air and {approx}100 kV cm{sup -1} in argon. At these maximum field strengths, the electrons have 5-10 eV energy, so the ionization is dominated by two-step processes. Differences between argon and ambient air in the field strength at which streamers propagate are ascribed to the difference in de-excitation processes in noble and molecular gases. The fact that the pulsed power circuit can control the streamer structure is important for applications, but this effect must also be taken into account in fundamental studies of streamer propagation and branching. (author)

  15. Fast imaging of streamer propagation

    International Nuclear Information System (INIS)

    Veldhuizen, E.M. van; Baede, A.H.F.M.; Hayashi, D.; Rutgers, W.R.

    2001-01-01

    Recently measurement methods are becoming available to study the corona discharge in more detail. One of the most promising methods is laser-induced fluorescence to determine radical density. Recent improvements in CCD cameras makes it now possible to improve measurements of the discharge structure to a resolution of 1 ns in time and 10 μm in space. This paper shows the first results of the spontaneous emission of a point-to-plane corona discharge in air using such a camera. It clearly indicates that the 2-D approach for streamer propagation under these conditions is insufficient

  16. Fast imaging of streamer propagation

    Energy Technology Data Exchange (ETDEWEB)

    Veldhuizen, E.M. van; Baede, A.H.F.M.; Hayashi, D.; Rutgers, W.R. [Eindhoven Univ. of Technology (Netherlands). Dept. of Applied Physics

    2001-07-01

    Recently measurement methods are becoming available to study the corona discharge in more detail. One of the most promising methods is laser-induced fluorescence to determine radical density. Recent improvements in CCD cameras makes it now possible to improve measurements of the discharge structure to a resolution of 1 ns in time and 10 {mu}m in space. This paper shows the first results of the spontaneous emission of a point-to-plane corona discharge in air using such a camera. It clearly indicates that the 2-D approach for streamer propagation under these conditions is insufficient.

  17. More evidence for a one-to-one correlation between Sprites and Early VLF perturbations

    Science.gov (United States)

    Haldoupis, C.; Amvrosiadi, N.; Cotts, B. R. T.; van der Velde, O. A.; Chanrion, O.; Neubert, T.

    2010-07-01

    Past studies have shown a correlation between sprites and early VLF perturbations, but the reported correlation varies widely from ˜50% to 100%. The present study resolves these large discrepancies by analyzing several case studies of sprite and narrowband VLF observations, in which multiple transmitter-receiver VLF pairs with great circle paths (GCPs) passing near a sprite-producing thunderstorm were available. In this setup, the multiple paths act in a complementary way that makes the detection of early VLF perturbations much more probable compared to a single VLF path that can miss several of them, a fact that was overlooked in past studies. The evidence shows that visible sprite occurrences are accompanied by early VLF perturbations in a one-to-one correspondence. This implies that the sprite generation mechanism may cause also sub-ionospheric conductivity disturbances that produce early VLF events. However, the one-to-one visible sprite to early VLF event correspondence, if viewed conversely, appears not to be always reciprocal. This is because the number of early events detected in some case studies was considerably larger than the number of visible sprites. Since the great majority of the early events not accompanied by visible sprites appeared to be caused by positive cloud to ground (+CG) lightning discharges, it is possible that sprites or sprite halos were concurrently present in these events as well but were missed by the sprite-watch camera detection system. In order for this option to be resolved we need more studies using highly sensitive optical systems capable of detecting weaker sprites, sprite halos and elves.

  18. Photometric Characteristics of Sprites and Elves Derived from JEM-GLIMS Nadir Observations (Invited)

    Science.gov (United States)

    Sato, M.; Takahashi, Y.; Adachi, T.; Kobayashi, N.; Mihara, M.; Ushio, T.; Morimoto, T.; Suzuki, M.; Yamazaki, A.; Inan, U.; Linscott, I.

    2013-12-01

    implies that the light sources exist not only in the troposphere but also in the mesosphere. At the image data obtained by the narrow-band filter camera (LSI-2), a pancake structure with bright spots was confirmed. Thus, we attributed the pancake structure and bright spots to a sprite halo and sprite streamers, respectively. We further analyzed a transient optical event obtained at 01:41:00.466 UT on March 30, 2013. In this event very strong pulse signals are detected only by PH1 (150-280 nm) and PH4 (600-900 nm). Since the field-of-view (FOV) of PH4 is 86.8 deg., which is larger than that of other PH channels (FOV=42.7 deg.), a lightning discharge seems to be occurred within PH4 FOV but without FOV of the other PH channels. Nevertheless, the existence of the strong FUV emission detected by PH1 means the occurrence of elves. At the presentation, we will show the results derived from LSI and PH data analysis and will discuss the photometric characteristics more in detail.

  19. Magnetic field influence on the selfquenching streamer discharge

    International Nuclear Information System (INIS)

    Alekseev, G.D.; Korytov, A.V.

    1987-01-01

    The influence of the magnetic field on the selfquenching streamer discharge characteristics is investigated. In the field about 10 kGs streamer charge is decreased several per cent (change of charge is due to amplitude decreasing of signal). In the transition region from limited-proportional to streamer mode magnetic field results in increasing of probability of avalanche developing into a streamer

  20. More evidence for a one-to-one correlation between Sprites and Early VLF perturbations

    DEFF Research Database (Denmark)

    Haldoupis, C.; Amvrosiadi, N.; Cotts, B. R. T.

    2010-01-01

    Past studies have shown a correlation between sprites and early VLF perturbations, but the reported correlation varies widely from ∼50% to 100%. The present study resolves these large discrepancies by analyzing several case studies of sprite and narrowband VLF observations, in which multiple...... VLF events. However, the one‐to‐one visible sprite to early VLF event correspondence, if viewed conversely, appears not to be always reciprocal. This is because the number of early events detected in some case studies was considerably larger than the number of visible sprites. Since the great majority...

  1. Streamers in water and other dielectric liquids

    International Nuclear Information System (INIS)

    Kolb, J F; Joshi, R P; Xiao, S; Schoenbach, K H

    2008-01-01

    Experimental results on the inception and propagation of streamers in water generated under the application of high electric fields are reviewed. Characteristic parameters, such as breakdown voltage, polarity of the applied voltage, propagation velocities and other phenomenological features, are compared with similar phenomena in other dielectric liquids and in gases. Consequently, parameters that are expected to influence the development of streamers in water are discussed with respect to the analogous well-established models and theories for the related mechanisms in gases. Most of the data support the notion that an initial low-density nucleation site or gas-filled bubble assists the initiation of a streamer. Details of this theory are laid out explaining the observed differences in the breakdown originating from the anode versus the cathode locations. The mechanisms can also be applied to streamer propagation, although some observations cannot be satisfactorily explained.

  2. Track photographing in 8-m streamer chamber

    International Nuclear Information System (INIS)

    Anisimova, N.Z.; Davidenko, V.A.; Kantserov, V.A.; Rybakov, V.G.; Somov, S.V.

    1981-01-01

    A system for obtaining data from a streamer chamber intended for measuring muon polarization is described. An optical scheme for photographing of tracks in the chamber is given. The photographing process is complicated at the expense of large dimensions and module structure of the chamber as well as due to insufficient for direct photographing brightness of streamers. The system described was tested during a long time in a physical experiment. More than 100 thousand photos have been taken by its means [ru

  3. Fully kinetic particle simulations of high pressure streamer propagation

    Science.gov (United States)

    Rose, David; Welch, Dale; Thoma, Carsten; Clark, Robert

    2012-10-01

    Streamer and leader formation in high pressure devices is a dynamic process involving a hierarchy of physical phenomena. These include elastic and inelastic particle collisions in the gas, radiation generation, transport and absorption, and electrode interactions. We have performed 2D and 3D fully EM implicit particle-in-cell simulation model of gas breakdown leading to streamer formation under DC and RF fields. The model uses a Monte Carlo treatment for all particle interactions and includes discrete photon generation, transport, and absorption for ultra-violet and soft x-ray radiation. Central to the realization of this fully kinetic particle treatment is an algorithm [D. R. Welch, et al., J. Comp. Phys. 227, 143 (2007)] that manages the total particle count by species while preserving the local momentum distribution functions and conserving charge. These models are being applied to the analysis of high-pressure gas switches [D. V. Rose, et al., Phys. Plasmas 18, 093501 (2011)] and gas-filled RF accelerator cavities [D. V. Rose, et al. Proc. IPAC12, to appear].

  4. Dancing red sprites and the lightning activity in their parent thunderstorm

    Science.gov (United States)

    Bór, József; Zelkó, Zoltán; Hegedüs, Tibor; Jäger, Zoltán; Mlynarczyk, Janusz; Popek, Martin; Betz, Hans-Dieter

    2016-04-01

    Red sprites are brief optical emissions initiated in the mesosphere by intense tropospheric lightning discharges. A group of red sprites, in which the elements appear in rapid succession with some lateral offset from one another is referred to as a dancing sprite event. The occurrence of such events implies that significant and sequential charge removal extending to large regions of the thunderstorm can take place in the underlying cloud system. In this work, we examine the relation of the locations and observation times of appearing sprite elements to the temporal and spatial distribution of the lightning activity in a specific sprite-active thunderstorm. The selected mesoscale convective system (MCS) composed of several extremely active thundercloud cells crossed Central Europe from South-West to North-East through Germany, Austria, the Czech Republic, and Poland on the night of 6 August, 2013. This MCS has triggered over one hundred sprites including several dancing sprite events. Video recordings of sprites captured from Sopron, Hungary (16.6°E, 47.7°N) and Nydek, Czech Republic (18.8°E, 49.7°N) were used to identify dancing sprite events and to determine the exact locations of the appearing sprite elements by a triangulation technique used originally to analyze meteor observations. Lightning activity in the MCS can be reviewed using the database of LINET lightning detection network which fully covers the region of interest (ROI). The poster demonstrates how cases of sequential charge removal in the thunderstorm can be followed by combining the available information on the occurrence time, location, polarity, and type (CG/IC) of detected lightning strokes in the ROI on one hand and the occurrence time and location of elements in dancing sprite events on the other hand.

  5. Streamer knotwilg branching: sudden transition in morphology of positive streamers in high-purity nitrogen

    International Nuclear Information System (INIS)

    Heijmans, L C J; Clevis, T T J; Nijdam, S; Van Veldhuizen, E M; Ebert, U

    2015-01-01

    We describe a peculiar branching phenomenon in positive repetitive streamer discharges in high purity nitrogen. We name it knotwilg branching after the Dutch word for a pollard willow tree. In a knotwilg branching a thick streamer suddenly splits into many thin streamers. Under some conditions this happens for all streamers in a discharge at about the same distance from the high-voltage electrode tip. At this distance, the thick streamers suddenly bend sharply and appear to propagate over a virtual surface surrounding the high-voltage electrode, rather than following the background electric field lines. From these bent thick streamers many, much thinner, streamers emerge that roughly follow the background electric field lines, creating the characteristic knotwilg branching. We have only found this particular morphology in high purity nitrogen at pressures in the range 50 to 200 mbar and for pulse repetition rates above 1 Hz; the experiments were performed for an electrode distance of 16 cm and for fast voltage pulses of 20 or 30 kV. These observations clearly disagree with common knowledge on streamer propagation. We have analyzed the data of several tens of thousands of discharges to clarify the phenomena. We also present some thoughts on how the ionization of the previous discharges could concentrate into some pre-ionization region near the needle electrode and create the knotwilg morphology, but we present no final explanation. (paper)

  6. Radio Frequency Electromagnetic Radiation From Streamer Collisions.

    Science.gov (United States)

    Luque, Alejandro

    2017-10-16

    We present a full electromagnetic model of streamer propagation where the Maxwell equations are solved self-consistently together with electron transport and reactions including photoionization. We apply this model to the collision of counter-propagating streamers in gaps tens of centimeters wide and with large potential differences of hundreds of kilovolts. Our results show that streamer collisions emit electromagnetic pulses that, at atmospheric pressure, dominate the radio frequency spectrum of an extended corona in the range from about 100 MHz to a few gigahertz. We also investigate the fast penetration, after a collision, of electromagnetic fields into the streamer heads and show that these fields are capable of accelerating electrons up to about 100 keV. By substantiating the link between X-rays and high-frequency radio emissions and by describing a mechanism for the early acceleration of runaway electrons, our results support the hypothesis that streamer collisions are essential precursors of high-energy processes in electric discharges.

  7. ADS and CDS streamer generation as function of pulsed parameters

    NARCIS (Netherlands)

    Winands, G.J.J.; Liu, Z.; Heesch, van E.J.M.; Pemen, A.J.M.; Yan, K.

    2008-01-01

    Streamer plasmas can be used to remove pollutants from gases. As a result of the complex mechanisms involved during streamer initiation and propagation, the related knowledge is incomplete. During the last few years, extensive research was performed to determine typical streamer properties (such as

  8. Saffman-Taylor streamers: Mutual finger interaction in spark formation

    NARCIS (Netherlands)

    Luque, A.; Brau, F.; Ebert, U.

    2008-01-01

    Bunches of streamers form the early stages of sparks and lightning but theory presently concentrates on single streamers or on coarse approximations of whole breakdown trees. Here a periodic array of interacting streamer discharges in a strong homogeneous electric field is studied in density or

  9. Proceedings of workshop on streamer chamber

    International Nuclear Information System (INIS)

    Itoh, Hidihiko; Takahashi, Kaoru; Hirose, Tachishige; Masaike, Akira

    1978-08-01

    For high accuracy observation of multiple-body reactions, a vertex detector of high efficiency is essential. A bubble chamber, though excellent for tracks detection, is problematic in statistics accuracy. The vertex detector with a wire chamber, while better in this respect, difficult in multiple-particle detection etc. The workshop has had several meetings on a streamer chamber as a detector combining features of both bubble chamber and counter, with emphasis on tracks observation in avalanche mode and recordings not using films. Contents are on streamer chamber gas, analytical photography, data processing, simulation program, etc. (Mori, K.)

  10. Stereo-photography of streamers in air

    International Nuclear Information System (INIS)

    Nijdam, S.; Moerman, J. S.; Briels, T. M. P.; Veldhuizen, E. M. van; Ebert, U.

    2008-01-01

    Standard photographs of streamer discharges show a two-dimensional projection. Here, we present stereophotographic images that resolve their three-dimensional structure. We describe the stereoscopic setup and evaluation, and we present results for positive streamer discharges in air at 0.2-1 bar in a point-plane geometry with a gap distance of 14 cm and a voltage pulse of 47 kV. In this case, an approximately Gaussian distribution of branching angles of 43 deg. ±12 deg. is found; these angles do not significantly depend on the distance from the needle or on the gas pressure

  11. iOS Game Development using SpriteKit Framework with Swift Programming Language

    OpenAIRE

    Gurung, Lal

    2016-01-01

    iOS is a mobile operating system for Apple manufactured phones and tablets. Mobile Gaming Industries are growing very fast, and compatibility with iOS is becoming very popular among game developers. The aim of this Bachelor’s thesis was to find the best available game development tools for iOS platform. The 2D game named Lapland was developed using Apple’s own native framework, SpriteKit. The game was written with the SpriteKit programming language. The combination of SpriteKit and Swift...

  12. Stochastic and deterministic causes of streamer branching in liquid dielectrics

    International Nuclear Information System (INIS)

    Jadidian, Jouya; Zahn, Markus; Lavesson, Nils; Widlund, Ola; Borg, Karl

    2013-01-01

    Streamer branching in liquid dielectrics is driven by stochastic and deterministic factors. The presence of stochastic causes of streamer branching such as inhomogeneities inherited from noisy initial states, impurities, or charge carrier density fluctuations is inevitable in any dielectric. A fully three-dimensional streamer model presented in this paper indicates that deterministic origins of branching are intrinsic attributes of streamers, which in some cases make the branching inevitable depending on shape and velocity of the volume charge at the streamer frontier. Specifically, any given inhomogeneous perturbation can result in streamer branching if the volume charge layer at the original streamer head is relatively thin and slow enough. Furthermore, discrete nature of electrons at the leading edge of an ionization front always guarantees the existence of a non-zero inhomogeneous perturbation ahead of the streamer head propagating even in perfectly homogeneous dielectric. Based on the modeling results for streamers propagating in a liquid dielectric, a gauge on the streamer head geometry is introduced that determines whether the branching occurs under particular inhomogeneous circumstances. Estimated number, diameter, and velocity of the born branches agree qualitatively with experimental images of the streamer branching

  13. KickSat: A Crowd-Funded Technology Demonstration Mission for the Sprite ChipSat

    Data.gov (United States)

    National Aeronautics and Space Administration — KickSat is a cubesat technology demonstration mission designed to demonstrate the deployment and operation of prototype sprite "ChipSats" (femtosatellites) developed...

  14. First satellite measurements of chemical changes in coincidence with sprite activity

    Science.gov (United States)

    Arnone, Enrico; São Sabbas, Fernanda; Kero, Antti; Soula, Serge; Carlotti, Massimo; Chanrion, Olivier; Dinelli, Bianca Maria; Papandrea, Enzo; Castelli, Elisa; Neubert, Torsten

    2010-05-01

    The last twenty years have seen the discovery of electric discharges in the Earth's atmosphere above thunderstorms, the so-called sprites and jets. It has been suggested that they impact the atmospheric chemistry and possibly affect the ozone layer through their repeated occurrence. Whereas theoretical studies and laboratory experiments suggest enhancement of such gasses as nitrogen oxides by up to hundreds of percent within sprites, a definitive detection of their chemical effects have to date been unsuccessful. In this paper, we report on the first measurements of atmospheric chemical perturbations recorded in coincidence with sprite activity. A striking event occurred on 25 August 2003 when the MIPAS spectrometer onboard the Envisat satellite recorded spectroscopic measurements soon after a sequence of 11 sprites observed above Corsica (France) by Eurosprite ground facilities (details of the convective system are discussed in a companion paper by São Sabbas et al.). The measurements show an enhancement of ambient nitrous oxide by 80% at 52 km altitude in the region above the parent thunderstorm. The recorded chemical changes imply sprites can exert significant modification of the atmospheric chemistry at a regional scale, confirming model and laboratory predictions of sprite-chemistry, and requiring a new estimate of their global impact. The results of the analysis and their implications are discussed.

  15. Electron acceleration during streamer collisions in air

    DEFF Research Database (Denmark)

    Köhn, Christoph; Chanrion, Olivier; Neubert, Torsten

    2017-01-01

    charge fields, with a Monte Carlo scheme accounting for collisions and ionization. We present the electron density, the electric field, and the velocity distribution as functions of space and time. Assuming a background electric field 1.5 times the breakdown field, we find that the electron density......High-voltage laboratory experiments show that discharges in air, generated over a gap of one meter with maximal voltage of 1 MV, may produce X-rays with photon energies up to 1 MeV. It has been suggested that the photons are bremsstrahlung from electrons accelerated by the impulsive, enhanced field...... during collisions of negative and a positive streamers. To explore this process, we have conducted the first self-consistent particle simulations of streamer encounters. Our simulation model is a 2-D, cylindrically symmetric, particle-in-cell code tracing the electron dynamics and solving the space...

  16. Do lightning positive leaders really "step"?

    Science.gov (United States)

    Petersen, D.

    2015-12-01

    It has been known for some time that positive leaders exhibit impulsive charge motion and optical emissions as they extend. However, laboratory and field observations have not produced any evidence of a process analogous to the space leader mechanism of negative leader extension. Instead, observations have suggested that the positive leader tip undergoes a continuous to intermittent series of corona streamer bursts, each burst resulting in a small forward extension of the positive leader channel. Traditionally, it has been held that lightning positive leaders extend in a continuous or quasi-continuous fashion. Lately, however, many have become concerned that this position is incongruous with observations of impulsive activity during lightning positive leader extension. It is increasingly suggested that this impulsive activity is evidence that positive leaders also undergo "stepping". There are two issues that must be addressed. The first issue concerns whether or not the physical processes underlying impulsive extension in negative and positive leaders are distinct. We argue that these processes are in fact physically distinct, and offer new high-speed video evidence to support this position. The second issue regards the proper use of the term "step" as an identifier for the impulsive forward extension of a leader. Traditional use of this term has been applied only to negative leaders, due primarily to their stronger impulsive charge motions and photographic evidence of clearly discontinuous forward progression of the luminous channel. Recently, due to the increasing understanding of the distinct "space leader" process of negative leader extension, the term "step" has increasingly come to be associated with the space leader process itself. Should this emerging association, "step" = space leader attachment, be canonized? If not, then it seems reasonable to use the term "step" to describe impulsive positive leader extension. If, however, we do wish to associate the

  17. The First Sprite Observation from Moscow in the Direction of Tver Region Associated with Repetitive Lightning Discharge

    International Nuclear Information System (INIS)

    Sorokin, L.V.

    2017-01-01

    The summer thunderstorms 2016 in the central part of Russia produced heavy precipitations and were accompanied by huge amount of lightning. During these events we provide the Sprite observation from Moscow. On the 18 August we caught two Sprites on the distance from 260 km to 290 km in the Tver region. It is important to underline that both Sprites occurred after the rare repetitive lightning discharge and the multiple lightning discharge. These types of lightning are rare in the Moscow region and more habitual for the tropical thunderstorms in Equator area. Due to the Climate Change and Global Warming the Sprites are common for the Russian Federation now. (author)

  18. Streamer model for high voltage water switches

    International Nuclear Information System (INIS)

    Sazama, F.J.; Kenyon, V.L. III

    1979-01-01

    An electrical switch model for high voltage water switches has been developed which predicts streamer-switching effects that correlate well with water-switch data from Casino over the past four years and with switch data from recent Aurora/AMP experiments. Preclosure rounding and postclosure resistive damping of pulseforming line voltage waveforms are explained in terms of spatially-extensive, capacitive-coupling of the conducting streamers as they propagate across the gap and in terms of time-dependent streamer resistance and inductance. The arc resistance of the Casino water switch and of a gas switch under test on Casino was determined by computer fit to be 0.5 +- 0.1 ohms and 0.3 +- 0.06 ohms respectively, during the time of peak current in the power pulse. Energy lost in the water switch during the first pulse is 18% of that stored in the pulseforming line while similar energy lost in the gas switch is 11%. The model is described, computer transient analyses are compared with observed water and gas switch data and the results - switch resistance, inductance and energy loss during the primary power pulse - are presented

  19. The ILAN sprite campaigns in Israel: results from 7 years of observations

    Science.gov (United States)

    Yair, Yoav; Rubanenko, Lior; Katzenelson, Dor; Rosenthal, Neta; Mezuman, Keren; Price, Colin

    2014-05-01

    The ILAN (Imaging of Lightning And Nocturnal flashes, http://ilanteam.com/) campaigns have been conducted since 2004 from Israel, observing winter thunderstorms in the eastern Mediterranean. We searched for transient luminous events using the standard commercial CCD cameras (Watec N100, 902H2 Ultimate) and the UFO-capture software for event detection, commonly used by other TLE- research groups in Europe and Japan. Winter thunderstorms mostly occur in conjunction with the passage of cold fronts in Cyprus lows, and thus TLEs are best observed when the storms are 200-300 km west of the Israeli coastline, above the Mediterranean Sea. We present statistical analysis of 505 sprites observed in 7 winter campaigns from 2006/7-2012/13. Results show a clear peak in the frequency of sprite detections, with maximum values (above 40% of events) between 00:30-02:50 LST (Local Standard Time, UT+2). This distribution is very different from that of lightning in the region, which peaks ~ 05:00 LST over the sea (Altaratz et al., 2001), hinting at the different temporal behavior of +CG flashes, known to be the major producers of sprites. The morphological distribution of 339 sprites is dominated by column sprites (49.3%) with angels (33.0%) and carrots (25.7%) being less frequent. This is similar to reports of winter sprites over the Sea of Japan (Matsudo et al., 2007). Other shapes (trees, wishbones, etc.; Bór, 2013) appear quite rarely. Single element events constitute 16.8% of observations, with 83.2% containing 2 elements or more. Clusters of homogenous types are slightly more frequent than mixed ones (55%). In some rare cases we observed 12-23 elements in a single sprite. The number of elements and the temporal distribution of different sprite types will be presented and compared with the properties of the parent thunderstorms. Altaratz, O., Levin Z. and Y. Yair, 2001: Winter thunderstorms in Israel - a study with lightning location systems and weather radar. Month. Weath. Rev

  20. Streamer properties and associated x-rays in perturbed air

    Science.gov (United States)

    Köhn, C.; Chanrion, O.; Babich, L. P.; Neubert, T.

    2018-01-01

    Streamers are ionization waves in electric discharges. One of the key ingredients of streamer propagation is an ambient gas that serves as a source of free electrons. Here, we explore the dependence of streamer dynamics on different spatial distributions of ambient air molecules. We vary the spatial profile of air parallel and perpendicular to the ambient electric field. We consider local sinusoidal perturbations of 5%-100%, as induced from discharge shock waves. We use a cylindrically symmetric particle-in-cell code to simulate the evolution of bidirectional streamers and compare the electron density, electric field, streamer velocity and electron energy of streamers in uniform air and in perturbed air. In all considered cases, the motion is driven along in decreasing air density and damped along increasing air density. Perturbations of at most 5%-10% change the velocity differences by up to approximately 40%. Perturbations perpendicular to the electric field additionally squeeze or branch streamers. Air variations can thus partly explain the difference of velocities and morphologies of streamer discharges. In cases with large perturbations, electrons gain energies of up to 30 keV compared to 100 eV in uniformly distributed air. For such perturbations parallel to the ambient electric field, we see the spontaneous initiation of a negative streamer; for perpendicular perturbations, x-rays with energies of up to 20 keV are emitted within 0.17 ns.

  1. Modeling the stepping mechanism in negative lightning leaders

    Science.gov (United States)

    Iudin, Dmitry; Syssoev, Artem; Davydenko, Stanislav; Rakov, Vladimir

    2017-04-01

    It is well-known that the negative leaders develop in a step manner using a mechanism of the so-called space leaders in contrary to positive ones, which propagate continuously. Despite this fact has been known for about a hundred years till now no one had developed any plausible model explaining this asymmetry. In this study we suggest a model of the stepped development of the negative lightning leader which for the first time allows carrying out the numerical simulation of its evolution. The model is based on the probability approach and description of temporal evolution of the discharge channels. One of the key features of our model is accounting for the presence of so called space streamers/leaders which play a fundamental role in the formation of negative leader's steps. Their appearance becomes possible due to the accounting of potential influence of the space charge injected into the discharge gap by the streamer corona. The model takes into account an asymmetry of properties of negative and positive streamers which is based on well-known from numerous laboratory measurements fact that positive streamers need about twice weaker electric field to appear and propagate as compared to negative ones. An extinction of the conducting channel as a possible way of its evolution is also taken into account. This allows us to describe the leader channel's sheath formation. To verify the morphology and characteristics of the model discharge, we use the results of the high-speed video observations of natural negative stepped leaders. We can conclude that the key properties of the model and natural negative leaders are very similar.

  2. Seeking sprite-induced signatures in remotely sensed middle atmosphere NO2: latitude and time variations

    International Nuclear Information System (INIS)

    Arnone, E; Carlotti, M; Papandrea, E; Ridolfi, M; Kero, A; Enell, C-F; Turunen, E; Rodger, Craig J; Arnold, N F; Dinelli, B M

    2009-01-01

    Recent research on sprites shows these and other transient luminous events can exert a local impact on atmospheric chemistry, although with minor effects at global scales. In particular, both modelling and remote sensing work suggest perturbations to the background NO x up to a few tens of per cent can occur above active sprite-producing thunderstorms. In this study we present a detailed investigation of MIPAS/ENVISAT satellite measurements of middle atmospheric NO 2 in regions of high likelihood of sprite occurrence during the period August to December 2003. As a proxy of sprite activity we used ground based WWLLN detections of large tropospheric thunderstorms. By investigating the sensitivity of the analysis to the characteristics of the adopted strategy, we confirm the indication of sprite-induced NO 2 enhancements of about 10% at 52 km height and tens of per cent at 60 km height immediately after thunderstorm activity, as previously reported by Arnone et al (2008b Geophys. Res. Lett. 35 5807). A further analysis showed the enhancement to be dominated by the contribution from regions north of the Equator (5 deg. N to 20 deg. N) during the first 30 to 40 days of the sample (i.e. the tail of Northern Hemisphere summer) and in coincidence with low background winds.

  3. Parallel sparse direct solvers for Poisson's equation in streamer discharges

    NARCIS (Netherlands)

    M. Nool (Margreet); M. Genseberger (Menno); U. M. Ebert (Ute)

    2017-01-01

    textabstractThe aim of this paper is to examine whether a hybrid approach of parallel computing, a combination of the message passing model (MPI) with the threads model (OpenMP) can deliver good performance in streamer discharge simulations. Since one of the bottlenecks of almost all streamer

  4. Photoionization in negative streamers : fast computations and two propagation modes

    NARCIS (Netherlands)

    Luque, A.; Ebert, U.M.; Montijn, C.; Hundsdorfer, W.

    2007-01-01

    Streamer discharges play a central role in electric breakdown of matter in pulsed electric fields, both in nature and in technology. Reliable and fast computations of the minimal model for negative streamers in simple gases such as nitrogen have recently been developed. However, photoionization was

  5. Streamer head structure: role of ionization and photoionization

    International Nuclear Information System (INIS)

    Nudnova, M M; Starikovskii, A Yu

    2008-01-01

    Results from experiments and numerical modelling of streamer propagation are presented. The 2D hydrodynamic numerical description of the pulsed discharge based on the local ionization and photoionization models adequately describes the streamer shape and dynamics over a wide range of pressures and voltages. This work presents a method for imaging the instantaneous emission distribution in the streamer head. A method for restoring the electrodynamic radius of the streamer head was developed on the basis of the streamer head images that were obtained with subnanosecond exposure time. The electrodynamic radius has been determined as the distance between the maxima of the electric field at the position where the streamer head transforms into the streamer channel. The dependence of the electrodynamic radius on voltage and pressure has been determined. We show that a 2D numerical model using hydrodynamic approximation predicts the streamer characteristics with an accuracy of about 15% in the 0.5-1 atmosphere pressure range and up to 40% in the 0.2-0.3 atmosphere pressure range for a voltage of U from 20 kV up to 40 kV in the 30 and 40 mm discharge gap.

  6. Influences of the pulsed power supply on corona streamer appearance

    NARCIS (Netherlands)

    Veldhuizen, van E.M.; Briels, T.M.P.; Grabowski, L.R.; Pemen, A.J.M.; Ebert, U.M.

    2005-01-01

    Pulsed positive corona streamers in air are studied by images obtained with an intensified CCD camera. Using a switched capacitor power supply, thin streamers are observed that branch. A power supply consisting of a 4-stage transmission line transformer gives pulses of much higher current to the

  7. Streamer discharges can move perpendicularly to the electric field

    NARCIS (Netherlands)

    Nijdam, S.; Takahashi, E.; Teunissen, J.; Ebert, U.

    2014-01-01

    Streamer discharges are a primary mode of electric breakdown in thunderstorms and high voltage technology; they are generally believed to grow along electric field lines. However, we here give experimental and numerical evidence that streamers can propagate nearly perpendicularly to the background

  8. Structure of positive streamers inside gaseous bubbles immersed in liquids

    International Nuclear Information System (INIS)

    Babaeva, Natalia Yu; Kushner, Mark J

    2009-01-01

    Electric discharges and streamers in liquids typically proceed through vapour phase channels produced by the streamer or in gaseous bubbles. The bubbles can originate by enthalpy changes produced by the discharge or can be artificially injected into the liquid. Experiments on streamers in bubbles immersed in liquids have shown that the discharge propagates either along the surface of the bubble or through the volume of the bubble as in conventional streamer propagation in air. In this paper we report on results of a computational investigation of streamer propagation through bubbles immersed in liquids. We found that the dielectric constant of the liquid in large part determines the path the streamer takes. Streamers in bubbles immersed in a liquid with a high permittivity preferentially propagate along the surface of the bubble. Liquids with low permittivity can result in the streamer propagating along the axis of the bubble. The permittivity at which this transition occurs is a function of the applied voltage, size of the bubble and the conductivity of the liquid. (fast track communication)

  9. Quenching gases for limited-streamer operation

    Energy Technology Data Exchange (ETDEWEB)

    Rapp, P

    1986-04-01

    Charge spectra and efficiencies of the limited-streamer mode are presented as a function of quencher fraction and high voltage for several gas mixes. The goal was to find a working gas of low hydrocarbon content in order to relieve safety concerns about the flammability of the large gas volume contained in the hadron calorimeter of the OPAL detector at LEP. No suitable low-hydrocarbon quenching mix is found. The charge spectra from these quenchers develop secondary peaks and long tails as full efficiency is approached, leading to catastrophic breakdown near the onset of full efficiency.

  10. Quenching gases for limited-streamer operation

    Energy Technology Data Exchange (ETDEWEB)

    Rapp, P

    1986-04-01

    Charge spectra and efficiencies of the limited-streamer mode are presented as a function of quencher fraction and high voltage for several gas mixes. The goal was to find a working gas of low hydrocarbon content in order to relieve safety concerns about the flammability of the large gas volume contained in the hadron calorimeter of the OPAL detector at LEP. No suitable low-hydrocarbon quenching mix is found. The charge spectra from these quenchers develop secondary peaks and long tails as full efficiency is approached, leading to catastrophic breakdown near the onset of full efficiency. (orig.).

  11. Kinetics of a plasma streamer ionization front

    Science.gov (United States)

    Taccogna, Francesco; Pellegrini, Fabrizio

    2018-02-01

    A streamer is a non-linear and non-local gas breakdown mode. Its large-scale coherent structures, such as the ionization front, are the final results of a hierarchical cascade starting from the single particle dynamics. Therefore, this phenomenon covers, by definition, different space and time scales. In this study, we have reproduced the ionization front formation and development by means of a particle-based numerical methodology. The physical system investigated concerns of a high-voltage ns-pulsed surface dielectric barrier discharge. Different reduced electric field regimes ranging from 50 to 500 Td have been considered for two gases: pure atomic Ar and molecular N2. Results have shown the detailed structure of the negative streamer: the leading edge, the head, the interior and the tail. Its dynamical evolution and the front propagation velocity have been calculated for the different cases. Finally, the deviation of the electron energy distribution function from equilibrium behavior has been pointed out as a result of a fast and very localized phenomenon.

  12. Runaway electrons from a ‘beam-bulk’ model of streamer: application to TGFs

    DEFF Research Database (Denmark)

    Chanrion, Olivier Arnaud; Bonaventura, Z.; Cinar, Deniz

    2014-01-01

    -energy electrons and ions. For a negative streamer discharge, we show how electrons are accelerated in the large electric field in the tip of the streamer and travel ahead of the streamer where they ionize the gas. In comparison to the results obtained with a classical fluid model for a negative streamer, the beam...

  13. Streamer properties and associated x-rays in perturbed air

    DEFF Research Database (Denmark)

    Köhn, C; Chanrion, O; Babich, L P

    2018-01-01

    Streamers are ionization waves in electric discharges. One of the key ingredients of streamerpropagation is an ambient gas that serves as a source of free electrons. Here, we explore thedependence of streamer dynamics on different spatial distributions of ambient air molecules. We varythe spatial...... profile of air parallel and perpendicular to the ambient electric field. We consider localsinusoidal perturbations of 5%–100%, as induced from discharge shock waves. We use acylindrically symmetric particle-in-cell code to simulate the evolution of bidirectional streamers andcompare the electron density...

  14. Adaptive decoding of MPEG-4 sprites for memory-constrained embedded systems

    NARCIS (Netherlands)

    Pastrnak, M.; Farin, D.S.; With, de P.H.N.; Cardinal, J.; Cerf, N.; Delgrnage, O.

    2005-01-01

    Background sprite decoding is an essential part of object-based video coding.The composition and rendering of a final scene involves the placing of individual video objects in a predefined way superimposed on the decoded background image. The MPEG-4 standard includes the decoding algorithm for

  15. Limited streamer chamber testing and quality evaluation in ASTRA

    International Nuclear Information System (INIS)

    Anzivino, G.; Bianco, S.; Casaccia, R.

    1991-01-01

    Limited streamer chambers are extensively used for high-energy and nuclear physics experiments in accelerator and underground laboratories. The tracking system of LVD, an underground experiment to study muons and nutrino astronomy, will use roughly 15000 limited streamer chambers and 100000 external pickup strips with digital readout electronics. In the article the different aspects of chamber operation that serve to establish a testing procedure and to define acceptance criteria for selecting reliable and long-life devices, are discussed. The procedures and the results obtained from a long-term test to evaluate streamer chamber quality, based upon a sample of 2900 items, are described. The selection tests and the long-term observations have been performed in the ASTRA laboratory, established at the Laboratori Nazionali di Frascati to carry out quality control procedures for streamer chambers on a large scale and in a controlled environment

  16. Avalanche and streamer mode operation of resistive plate chambers

    International Nuclear Information System (INIS)

    Cardarelli, R.; Makeev, V.; Santonico, R.

    1996-01-01

    A resistive plate chamber was operated at voltages increasing in steps of 200 V over a 3 kV interval and the transition between the avalanche and streamer modes was studied. The avalanche amplitude was observed to be exponentially dependent on the operating voltage up to a value, characteristic of the gas, where the avalanche saturation occurs and delayed streamer signals start to appear. Signal waveforms, charge and timing distributions are reported. (orig.)

  17. The dynamics of streamer formation and its growth mechanism

    International Nuclear Information System (INIS)

    Zalikhanov, B.Zh.

    2004-01-01

    We report the results of experimental studies of physical processes responsible for the transformation of the electron avalanche to the streamer and its growth towards the cathode. The new experimental data on the mechanism of formation and the structure of the streamer allow a more concrete understanding of the pattern of evolution of long spark discharges, including the lightning, and the interrelation of basic processes in such discharges. (author)

  18. Mechanisms important to later stages of streamer system development

    Science.gov (United States)

    Lehtinen, N. G.; Carlson, B.; Kochkin, P.; Østgaard, N.

    2017-12-01

    Typical streamer modeling focuses on the propagation of the streamer head and thus neglects processes such as electron detachment, electron energy relaxation, and thermalization of the electron energy distribution. These mechanisms, however, may become important at later stages of streamer system development, in particular following streamer collisions. We present a model of a later-stage streamer system development which includes these processes. A linear analysis suggests that these processes under some conditions can lead to new effects, such as excitation of waves similar to striations in the positive column of a glow discharge. Such instabilities do not occur if these mechanisms are neglected under the same conditions, although previous modeling suggested existence of wave-like phenomena during the streamer propagation [Luque et al, 2016, doi:10.1002/2015JA022234]. In the sea-level pressure air, the obtained striation-like waves may manifest as very high frequency range (>10 MHz) oscillations in plasma parameters and may have been detected in the electrode current and electromagnetic radiation measurements during laboratory spark experiments. We discuss whether the longitudinal electric field in such waves can efficiently transfer energy to charged particles, because such a process may play a role in production of x-rays.

  19. Propagation of ELF Radiation from RS-LC System and Red Sprites in Earth-Ionosphere Waveguide

    Directory of Open Access Journals (Sweden)

    M. K. Paras

    2012-10-01

    Full Text Available In this paper, two different mechanisms return stroke-lateral corona (RS-LC system and red sprites which excite Earth-ionosphere waveguide have been discussed. The electric and magnetic fields from RS-LC system and red spites in the Earth-ionosphere waveguide have been calculated. It has been found that red sprites contribute to the Schumann resonances (SR greatly as compared to the RS-LC system.

  20. Propagation of a plasma streamer in catalyst pores

    Science.gov (United States)

    Zhang, Quan-Zhi; Bogaerts, Annemie

    2018-03-01

    Although plasma catalysis is gaining increasing interest for various environmental applications, the underlying mechanisms are still far from understood. For instance, it is not yet clear whether and how plasma streamers can propagate in catalyst pores, and what is the minimum pore size to make this happen. As this is crucial information to ensure good plasma-catalyst interaction, we study here the mechanism of plasma streamer propagation in a catalyst pore, by means of a two-dimensional particle-in-cell/Monte Carlo collision model, for various pore diameters in the nm-range to μm-range. The so-called Debye length is an important criterion for plasma penetration into catalyst pores, i.e. a plasma streamer can penetrate into pores when their diameter is larger than the Debye length. The Debye length is typically in the order of a few 100 nm up to 1 μm at the conditions under study, depending on electron density and temperature in the plasma streamer. For pores in the range of ∼50 nm, plasma can thus only penetrate to some extent and at very short times, i.e. at the beginning of a micro-discharge, before the actual plasma streamer reaches the catalyst surface and a sheath is formed in front of the surface. We can make plasma streamers penetrate into smaller pores (down to ca. 500 nm at the conditions under study) by increasing the applied voltage, which yields a higher plasma density, and thus reduces the Debye length. Our simulations also reveal that the plasma streamers induce surface charging of the catalyst pore sidewalls, causing discharge enhancement inside the pore, depending on pore diameter and depth.

  1. Towards a fully kinetic 3D electromagnetic particle-in-cell model of streamer formation and dynamics in high-pressure electronegative gases

    International Nuclear Information System (INIS)

    Rose, D. V.; Welch, D. R.; Clark, R. E.; Thoma, C.; Zimmerman, W. R.; Bruner, N.; Rambo, P. K.; Atherton, B. W.

    2011-01-01

    Streamer and leader formation in high pressure devices is dynamic process involving a broad range of physical phenomena. These include elastic and inelastic particle collisions in the gas, radiation generation, transport and absorption, and electrode interactions. Accurate modeling of these physical processes is essential for a number of applications, including high-current, laser-triggered gas switches. Towards this end, we present a new 3D implicit particle-in-cell simulation model of gas breakdown leading to streamer formation in electronegative gases. The model uses a Monte Carlo treatment for all particle interactions and includes discrete photon generation, transport, and absorption for ultra-violet and soft x-ray radiation. Central to the realization of this fully kinetic particle treatment is an algorithm that manages the total particle count by species while preserving the local momentum distribution functions and conserving charge [D. R. Welch, T. C. Genoni, R. E. Clark, and D. V. Rose, J. Comput. Phys. 227, 143 (2007)]. The simulation model is fully electromagnetic, making it capable of following, for example, the evolution of a gas switch from the point of laser-induced localized breakdown of the gas between electrodes through the successive stages of streamer propagation, initial electrode current connection, and high-current conduction channel evolution, where self-magnetic field effects are likely to be important. We describe the model details and underlying assumptions used and present sample results from 3D simulations of streamer formation and propagation in SF 6 .

  2. Towards a fully kinetic 3D electromagnetic particle-in-cell model of streamer formation and dynamics in high-pressure electronegative gases

    Science.gov (United States)

    Rose, D. V.; Welch, D. R.; Clark, R. E.; Thoma, C.; Zimmerman, W. R.; Bruner, N.; Rambo, P. K.; Atherton, B. W.

    2011-09-01

    Streamer and leader formation in high pressure devices is dynamic process involving a broad range of physical phenomena. These include elastic and inelastic particle collisions in the gas, radiation generation, transport and absorption, and electrode interactions. Accurate modeling of these physical processes is essential for a number of applications, including high-current, laser-triggered gas switches. Towards this end, we present a new 3D implicit particle-in-cell simulation model of gas breakdown leading to streamer formation in electronegative gases. The model uses a Monte Carlo treatment for all particle interactions and includes discrete photon generation, transport, and absorption for ultra-violet and soft x-ray radiation. Central to the realization of this fully kinetic particle treatment is an algorithm that manages the total particle count by species while preserving the local momentum distribution functions and conserving charge [D. R. Welch, T. C. Genoni, R. E. Clark, and D. V. Rose, J. Comput. Phys. 227, 143 (2007)]. The simulation model is fully electromagnetic, making it capable of following, for example, the evolution of a gas switch from the point of laser-induced localized breakdown of the gas between electrodes through the successive stages of streamer propagation, initial electrode current connection, and high-current conduction channel evolution, where self-magnetic field effects are likely to be important. We describe the model details and underlying assumptions used and present sample results from 3D simulations of streamer formation and propagation in SF6.

  3. Towards a fully kinetic 3D electromagnetic particle-in-cell model of streamer formation and dynamics in high-pressure electronegative gases

    Energy Technology Data Exchange (ETDEWEB)

    Rose, D. V.; Welch, D. R.; Clark, R. E.; Thoma, C.; Zimmerman, W. R.; Bruner, N. [Voss Scientific, LLC, Albuquerque, New Mexico 87108 (United States); Rambo, P. K.; Atherton, B. W. [Sandia National Laboratories, Albuquerque, New Mexico 87185 (United States)

    2011-09-15

    Streamer and leader formation in high pressure devices is dynamic process involving a broad range of physical phenomena. These include elastic and inelastic particle collisions in the gas, radiation generation, transport and absorption, and electrode interactions. Accurate modeling of these physical processes is essential for a number of applications, including high-current, laser-triggered gas switches. Towards this end, we present a new 3D implicit particle-in-cell simulation model of gas breakdown leading to streamer formation in electronegative gases. The model uses a Monte Carlo treatment for all particle interactions and includes discrete photon generation, transport, and absorption for ultra-violet and soft x-ray radiation. Central to the realization of this fully kinetic particle treatment is an algorithm that manages the total particle count by species while preserving the local momentum distribution functions and conserving charge [D. R. Welch, T. C. Genoni, R. E. Clark, and D. V. Rose, J. Comput. Phys. 227, 143 (2007)]. The simulation model is fully electromagnetic, making it capable of following, for example, the evolution of a gas switch from the point of laser-induced localized breakdown of the gas between electrodes through the successive stages of streamer propagation, initial electrode current connection, and high-current conduction channel evolution, where self-magnetic field effects are likely to be important. We describe the model details and underlying assumptions used and present sample results from 3D simulations of streamer formation and propagation in SF{sub 6}.

  4. Gas heating dynamics during leader inception in long air gaps at atmospheric pressure

    International Nuclear Information System (INIS)

    Liu, Lipeng; Becerra, Marley

    2017-01-01

    The inception of leader discharges in long air gaps at atmospheric pressure is simulated with a thermo-hydrodynamic model and a detailed kinetic scheme for N 2 /O 2 /H 2 O mixtures. In order to investigate the effect of humidity, the kinetic scheme includes the most important reactions with the H 2 O molecule and its derivatives, resulting in a scheme with 45 species and 192 chemical reactions. The heating of a thin plasma channel in front of an anode electrode during the streamer to leader transition is evaluated with a detailed 1D radial model. The analysis includes the simulation of the corresponding streamer bursts, dark periods and aborted leaders that may occur prior to the inception of a propagating leader discharge. The simulations are performed using the time-varying discharge current in two laboratory discharge events of positive polarity reported in the literature as input. Excellent agreement between the simulated and the experimental time variation of the thermal radius for a 1 m rod-plate air gap discharge event reported in the literature has been found. The role of different energy transfer and loss mechanisms prior to the inception of a stable leader is also discussed. It is found that although a small percentage of water molecules can accelerate the vibrational-translational relaxation to some extent, this effect leads to a negligible temperature increase during the streamer-to-leader transition. It is also found that the gas temperature should significantly exceed 2000 K for the transition to lead to the inception of a propagating leader. Otherwise, the strong convection loss produced by the gas expansion during the transition causes a drop in the translational temperature below 2000 K, aborting the incepted leader. Furthermore, it is shown that the assumptions used by the widely-used model of Gallimberti do not hold when evaluating the streamer-to-leader transition. (paper)

  5. Red sprites and blue jets: Thunderstorm-excited optical emissions in the stratosphere, mesosphere, and ionosphere

    International Nuclear Information System (INIS)

    Sentman, D.D.; Wescott, E.M.

    1995-01-01

    Recent low light level monochrome television observations obtained from the ground and from the space shuttle, and low light level color and monochrome television images obtained from aboard jet aircraft, have shown that intense lightning in mesoscale thunderstorm systems may excite at least two distinct types of optical emissions that together span the space between the tops of some thunderstorms and the ionosphere. The first of these emissions, dubbed ''sprites,'' are luminous red structures that typically span the altitude range 60--90 km, often with faint bluish tendrils dangling below. A second, rarer, type of luminous emission are ''blue jets'' that appear to spurt upward out of the anvil top in narrow cones to altitudes of 40--50 km at speeds of ∼100 km/s. In this paper the principal observational characteristics of sprites and jets are presented, and several proposed production mechanisms are reviewed. copyright 1995 American Institute of Physics

  6. Modeling of plasma chemistry in a corona streamer pulse series in air

    International Nuclear Information System (INIS)

    Nowakowska, H.; Stanco, J.; Dors, M.; Mizeraczyk, J.

    2002-01-01

    The aim of this study is to analyse the chemistry in air treated by a series of corona discharge streamers. Attention is focused on the conversion of ozone and nitrogen oxides. In the model it is assumed that the streamer head of relatively small geometrical dimensions propagates from the anode to the cathode, leaving the streamer channel behind. Any elemental gas volume in the streamer path is subjected first to the conditions of the streamer head, and next to those of the streamer channel. The kinetics of plasma-chemical processes occurring in the gas is modeled numerically for a single streamer and a series of streamers. The temporal evolution of 25 chemical compounds initially present or produced in air is calculated. (author)

  7. Particle-in-cell modeling of streamer branching in CO2 gas

    KAUST Repository

    Levko, Dmitry

    2017-07-07

    The mechanism of streamer branching remains one of the unsolved problems of low-temperature plasma physics. The understanding of this phenomenon requires very high-fidelity models that include, for instance, the kinetic description of electrons. In this paper, we use a two-dimensional particle-in-cell Monte Carlo collisional model to study the branching of anode-directed streamers propagating through short cathode-anode gap filled with atmospheric-pressure CO2 gas. We observe three key phenomena leading to the streamer branching at the considered conditions: flattening of the streamer head, the decrease of the streamer head thickness, and the generation at the streamer head of electrons having the energy larger than 50 eV. For the conditions of our studies, the non-homogeneous distribution of such energetic electrons at the streamer head is probably the primary mechanism responsible for the streamer branching.

  8. ELF and VLF signatures of sprites registered onboard the low altitude satellite DEMETER

    Directory of Open Access Journals (Sweden)

    J. Błęcki

    2009-06-01

    Full Text Available We report the observation of ELF and VLF signature of sprites recorded on the low altitude satellite DEMETER during thunderstorm activity. At an altitude of ~700 km, waves observed on the E-field spectrograms at mid-to-low latitudes during night time are mainly dominated by up-going 0+ whistlers. During the night of 20 July 2007 two sprites have been observed around 20:10:08 UT from the observatory located on the top of the mountain Śnieżka in Poland (50°44'09" N, 15°44'21" E, 1603 m and, ELF and VLF data have been recorded by the satellite at about 1200 km from the region of thunderstorm activity. During this event, the DEMETER instruments were switched in the burst mode and it was possible to register the wave forms. It is shown that the two sprites have been triggered by two intense +CG lightning strokes (100 kA occurring during the same millisecond but not at the same location. Despite the distance DEMETER has recorded at the same time intense and unusual ELF and VLF emissions. It is shown that the whistler wave propagates from the thunderstorm regions in the Earth-ionosphere guide and enters in the ionosphere below the satellite. They last several tens of milliseconds and the intensity of the ELF waveform is close to 1 mV/m. A particularly intense proton whistler is also associated with these emissions.

  9. On increasing the efficiency of a streamer semiconductor laser

    International Nuclear Information System (INIS)

    Rusakov, K I; Parashchuk, V V

    2007-01-01

    The influence of intense electric and optical fields produced by a streamer discharge in wide-gap semiconductors on their spectroscopic properties is studied. The effect is manifested in the reversible change of the luminescence parameters of the active medium. Methods are proposed for increasing the service life and efficiency of a streamer laser in limiting regimes, which are based on the use of semiconductor protective layers of a certain crystallographic orientation and a crystal microrelief with the size of elements of the order of the wavelength of light. Streamer emission was observed and studied in new promising Eu:CaGa 2 S 4 and Eu:Ca 4 Ga 2 S 7 materials. (lasers)

  10. Reversal film development for streamer chamber track photographs

    International Nuclear Information System (INIS)

    Bahr, J.

    1982-01-01

    It is the aim of this work to create a method of photographic development specially adapted to streamer image recording, i.e., with high sensitivity, only two signal levels, low dependence of the track signal on image intensity having a great jitter and noise suppression. The method has to be suitable for machine development of high speed films. A reversal photographic development was used to realize these demands, whereby strong fogging in the first step negative development and a solving process for silver bromide after blackening are specially introduced process stages. This results in a step-function shaped characteristic curve with small transition region having only two signal levels, i. e., independence of streamer image density, good resolution, fine grain, suppression of flares and low noise in the signal of the clear streamer images

  11. A theory of the stepped leader in lightning

    International Nuclear Information System (INIS)

    Lowke, J.J.

    1999-01-01

    There is no generally accepted explanation of the stepped leader behaviour in terms of basic physical processes. Existing theories generally involve significant gas heating within the stepped leader. In the present paper, the stepped nature of the leader is proposed to arise due to a combination of two physical phenomena. Electron transport is dominant over ion transport, during the luminous step stage, because electron mobilities are about 100 times larger than ion mobilities, and the streamer front velocity is determined by electron ionization effects. During the dark time between steps, there are only ions and charge transport is very much slower. The second effect leading to stepped behaviour arises because the electric field required for electric breakdown in air prior to a discharge is ∼30kV/cm, and is very much higher than the electric field of 5kV/cm that is required to sustain a glow discharge in air. During the luminous step stage, electrons tend to produce space charges to make a uniform field in the streamer of ∼5kV/cm. During the dark time between steps, there are no electrons but only ions. Time is required for ion drift to produce a space charge sheath of negative ions at the head of the streamer to produce a field of ∼30kV/cm sufficient for electron ionization to produce a new luminous step

  12. Use of a streamer chamber for low energy nuclear physics

    Energy Technology Data Exchange (ETDEWEB)

    Van Bibber, K.; Pang, W.; Avery, M.; Bloemhof, E.

    1979-10-01

    A small streamer chamber has been implemented for low energy heavy ion reaction studies at the LBL 88-inch cyclotron. The response of the chamber to light and heavy ions below 35 MeV/nucleon has been examined. The limited sensitivity of light output as a function of ionization works to advantage in recording a wide variety of tracks in the same photograph whose energy loss may vary considerably. Furthermore, as gas targets are attractive for several reasons, we have investigated the suitability of Ar and Xe for use in streamer chambers.

  13. Use of a streamer chamber for low energy nuclear physics

    International Nuclear Information System (INIS)

    Van Bibber, K.; Pang, W.; Avery, M.; Bloemhof, E.

    1979-10-01

    A small streamer chamber has been implemented for low energy heavy ion reaction studies at the LBL 88-inch cyclotron. The response of the chamber to light and heavy ions below 35 MeV/nucleon has been examined. The limited sensitivity of light output as a function of ionization works to advantage in recording a wide variety of tracks in the same photograph whose energy loss may vary considerably. Furthermore, as gas targets are attractive for several reasons, we have investigated the suitability of Ar and Xe for use in streamer chambers

  14. Self-quenching streamer discharge in a wire chamber

    International Nuclear Information System (INIS)

    Alekseev, G.D.; Kruglov, V.V.; Khazins, D.M.

    1982-01-01

    A summary is given of the investigation of a new mode of operation of a wire chamber involving a self-quenching streamer discharge. The history of the question is briefly discussed. The main characteristics of the self-quenching mode and the influence of the composition and pressure of the gas mixture and the geometrical parameters of the chamber on the characteristics are described. The mechanism of a self-quenching streamer discharge is analyzed. Detectors working in this mode are described, and the prospects for its future use are discussed

  15. Pulsed and streamer discharges in air above breakdown electric field

    NARCIS (Netherlands)

    A.B. Sun (Anbang); H.J. Teunissen (Jannis); U. M. Ebert (Ute)

    2013-01-01

    htmlabstractA 3D particle model is developed to investigate the streamer formation in electric fields above the breakdown threshold, in atmospheric air (1bar, 300 Kelvin). Adaptive particle management, adaptive mesh refinement and parallel computing techniques are used in the code. Photoionization

  16. Hexagon and stripe patterns in dielectric barrier streamer discharge

    International Nuclear Information System (INIS)

    Dong Lifang; He Yafeng; Yin Zengqian; Chai Zhifang

    2004-01-01

    We present a specially designed dielectric barrier discharge (DBD) system for the study of pattern formation. Hexagon and stripe patterns have been observed in a streamer discharge in a DBD for the first time. The phase diagram of pattern types as a function of applied voltage is given

  17. Multisource waveform inversion of marine streamer data using normalized wavefield

    KAUST Repository

    Choi, Yun Seok

    2013-09-01

    Multisource full-waveform inversion based on the L1- and L2-norm objective functions cannot be applied to marine streamer data because it does not take into account the unmatched acquisition geometries between the observed and modeled data. To apply multisource full-waveform inversion to marine streamer data, we construct the L1- and L2-norm objective functions using the normalized wavefield. The new residual seismograms obtained from the L1- and L2-norms using the normalized wavefield mitigate the problem of unmatched acquisition geometries, which enables multisource full-waveform inversion to work with marine streamer data. In the new approaches using the normalized wavefield, we used the back-propagation algorithm based on the adjoint-state technique to efficiently calculate the gradients of the objective functions. Numerical examples showed that multisource full-waveform inversion using the normalized wavefield yields much better convergence for marine streamer data than conventional approaches. © 2013 Society of Exploration Geophysicists.

  18. Branching of positive discharge streamers in air at varying pressures

    NARCIS (Netherlands)

    Briels, T.M.P.; Veldhuizen, van E.M.; Ebert, U.M.

    2005-01-01

    The formation of positive streamers in a 17-mm gap in air is studied at pressures varying in the range from 1010 to 100 mbar. An intensified charge coupled device camera is used to image the discharge. At high pressures, the discharge shows many branches, while at low pressure, fewer branches arise.

  19. Pseudo-spectral 3D simulations of streamers

    NARCIS (Netherlands)

    A. Luque (Alejandro); U. M. Ebert (Ute); C. Montijn (Carolynne-Sireeh); W. Hundsdorfer (Willem); J. Schmidt; M. Simek; S. Pekarek; V. Prukner

    2007-01-01

    textabstractA three-dimensional code for the simulation of streamers is introduced. The code is based on a fluid model for oxygen-nitrogen mixtures that includes drift, diffusion and attachement of electrons and creation of new charge carriers through impact ionization and photo-ionization. The

  20. KELVIN-HELMHOLTZ INSTABILITY OF A CORONAL STREAMER

    Energy Technology Data Exchange (ETDEWEB)

    Feng, L.; Gan, W. Q. [Key Laboratory of Dark Matter and Space Astronomy, Purple Mountain Observatory, Chinese Academy of Sciences, 210008 Nanjing (China); Inhester, B., E-mail: lfeng@pmo.ac.cn [Max-Planck-Institut fuer Sonnensystemforschung, Max-Planck-Str.2, D-37191 Katlenburg-Lindau (Germany)

    2013-09-10

    Shear-flow-driven instability can play an important role in energy transfer processes in coronal plasma. We present for the first time the observation of a kink-like oscillation of a streamer that is probably caused by the streaming kink-mode Kelvin-Helmholtz instability (KHI). The wave-like behavior of the streamer was observed by the Large Angle and Spectrometric Coronagraph Experiment C2 and C3 on board the SOlar and Heliospheric Observatory. The observed wave had a period of about 70-80 minutes, and its wavelength increased from 2 R{sub Sun} to 3 R{sub Sun} in about 1.5 hr. The phase speeds of its crests and troughs decreased from 406 {+-} 20 to 356 {+-} 31 km s{sup -1} during the event. Within the same heliocentric range, the wave amplitude also appeared to increase with time. We attribute the phenomena to the MHD KHI, which occurs at a neutral sheet in a fluid wake. The free energy driving the instability is supplied by the sheared flow and sheared magnetic field across the streamer plane. The plasma properties of the local environment of the streamer were estimated from the phase speed and instability threshold criteria.

  1. Positive streamer initiation from raindrops in thundercloud fields

    DEFF Research Database (Denmark)

    Babich, L. P.; Bochkov, E. I.; Kutsyk, I. M.

    2016-01-01

    required for the streamer formation is larger than the measured thunderstorm fields. Therefore, the results of simulations suggest that second mechanisms must operate to amplify the local field. Such mechanisms could be electric field space variations via collective effects of many hydrometeors or runaway...

  2. Nongeometrically converted shear waves in marine streamer data

    NARCIS (Netherlands)

    Drijkoningen, G.G.; El Allouche, N.; Thorbecke, J.W.; Bada, G.

    2012-01-01

    Under certain circumstances, marine streamer data contain nongeometrical shear body wave arrivals that can be used for imaging. These shear waves are generated via an evanescent compressional wave in the water and convert to propagating shear waves at the water bottom. They are called

  3. Multisource waveform inversion of marine streamer data using normalized wavefield

    KAUST Repository

    Choi, Yun Seok; Alkhalifah, Tariq Ali

    2013-01-01

    Multisource full-waveform inversion based on the L1- and L2-norm objective functions cannot be applied to marine streamer data because it does not take into account the unmatched acquisition geometries between the observed and modeled data. To apply

  4. Particle based 3D modeling of positive streamer inception

    NARCIS (Netherlands)

    H.J. Teunissen (Jannis)

    2012-01-01

    htmlabstractIn this report we present a particle based 3D model for the study of streamer inception near positive electrodes in air. The particle code is of the PIC-MCC type and an electrode is included using the charge simulation method. An algorithm for the adaptive creation of super-particles is

  5. The Saturn Probe Interior and aTmosphere Explorer (SPRITE) Mission

    Science.gov (United States)

    Simon, Amy; Banfield, Donald; Atkinson, David; SPRITE Science Team

    2018-01-01

    A key question in planetary science is how the planets formed in our Solar System, and, by extension, in exoplanet systems. The abundances of the noble gases (He, Ne, Ar, Kr, Xe), heavy elements (C, N, O, S), and their isotopes provide important forensic clues as to location and time of formation in the early Solar System. Jupiter and Saturn contain most of the planetary mass in our solar system, and their chemical fingerprints will distinguish between competing models of the formation of all the planets. After the end of the Cassini mission, some of these elements have only ambiguous values above the cloud tops, while others (particularly the noble gases) have not been measured at all. Resolving this requires direct in situ measurements. The proposed NASA New Frontiers Saturn PRobe Interior and aTmosphere Explorer (SPRITE) mission delivers an instrumented entry probe from a carrier relay spacecraft that also provides context imaging. The powerful probe instrument suite is comprised of a Quadrupole Mass Spectrometer, a Tunable Laser Spectrometer, and an Atmospheric Structure Instrument including a Doppler Wind Experiment and a simple backscatter nephelometer. These instruments measure the elemental and isotopic abundances of helium, the heavier noble gases, and the major elements, as well as constraining cloud properties, 3-D atmospheric dynamics, and disequilibrium chemistry to at least 10 bars in Saturn's troposphere. In situ measurements of Saturn's atmosphere by SPRITE will provide a significantly improved context for interpreting the results from the Galileo probe, Juno, and Cassini missions. SPRITE will revolutionize our understanding of the formation and evolution of the gas giant planets, and ultimately the present-day structure of the Solar System.

  6. Motion-sensitized SPRITE measurements of hydrodynamic cavitation in fast pipe flow.

    Science.gov (United States)

    Adair, Alexander; Mastikhin, Igor V; Newling, Benedict

    2018-06-01

    The pressure variations experienced by a liquid flowing through a pipe constriction can, in some cases, result in the formation of a bubble cloud (i.e., hydrodynamic cavitation). Due to the nature of the bubble cloud, it is ideally measured through the use of non-optical and non-invasive techniques; therefore, it is well-suited for study by magnetic resonance imaging. This paper demonstrates the use of Conical SPRITE (a 3D, centric-scan, pure phase-encoding pulse sequence) to acquire time-averaged void fraction and velocity information about hydrodynamic cavitation for water flowing through a pipe constriction. Copyright © 2018 Elsevier Inc. All rights reserved.

  7. The effect of coronae on leader initiation and development under thunderstorm conditions and in long air gaps

    International Nuclear Information System (INIS)

    Aleksandrov, N.L.; Bazelyan, E.M.; Carpenter Jr, R.B.; Drabkin, M.M.; Raizer, Yu P.

    2001-01-01

    The initiation and development of a leader is theoretically studied by considering an electrode which is embedded in a cloud of space charge injected by a corona discharge. The focus is on the initiation of upward lightning from a stationary grounded object in a thundercloud electric field. The main results are also applicable to the leader process in long laboratory air gaps at direct voltage. Simple physical models of non-stationary coronae developing in free space near a solitary stressed sphere and of a leader propagating in the space charge cloud of coronae are suggested. It is shown that the electric field redistribution due to the space charge released by the long corona discharge near the top of a high object hinders the initiation and development of an upward leader from the object in a thundercloud electric field. The conditions for the formation of corona streamers that are required to initiate a leader are derived. The criteria are obtained for a leader to be initiated and propagate in the space charge cloud. A hypothesis is proposed that the streamers are never initiated near the top of a high object under thunderstorm conditions if at ground level there is only a slowly-varying electric field of the thundercloud. The streamers may be induced by the fast-rising electric field of distant downward leaders or intracloud discharges. (author)

  8. Positive and negative streamers in ambient air: measuring diameter, velocity and dissipated energy

    Energy Technology Data Exchange (ETDEWEB)

    Briels, T M P; Kos, J; Van Veldhuizen, E M; Ebert, U [Department of Applied Physics, Technische Universiteit Eindhoven, PO Box 513, 5600 MB Eindhoven (Netherlands); Winands, G J J [Department of Electrical Engineering, Technische Universiteit Eindhoven, PO Box 513, 5600 MB Eindhoven (Netherlands)], E-mail: e.m.v.veldhuizen@tue.nl, E-mail: ebert@cwi.nl

    2008-12-07

    Positive and negative streamers are studied in ambient air at 1 bar; they emerge from a needle electrode placed 40 mm above a planar electrode. The amplitudes of the applied voltage pulses range from 5 to 96 kV; most pulses have rise times of 30 ns or shorter. Diameters, velocities and energies of the streamers are measured. Two regimes are identified; a low voltage regime where only positive streamers appear and a high voltage regime where both positive and negative streamers exist. Below 5 kV, no streamers emerge. In the range from 5 to 40 kV, positive streamers form, while the negative discharges only form a glowing cloud at the electrode tip, but no streamers. For 5-20 kV, diameters and velocities of the positive streamers have the minimal values of d = 0.2 mm and v {approx} 10{sup 5} m s{sup -1}. For 20-40 kV, their diameters increase by a factor of 6 while the voltage increases only by a factor of 2. Above the transition value of 40 kV, streamers of both polarities form; they strongly resemble each other, though the positive ones propagate further; their diameters continue to increase with applied voltage. For 96 kV, positive streamers attain diameters of 3 mm and velocities of 4 x 10{sup 6} m s{sup -1}; negative streamers are about 20% slower and thinner. An empirical fit formula for the relation between velocity v and diameter d is v = 0.5d{sup 2} mm{sup -1} ns{sup -1} for both polarities. Streamers of both polarities dissipate energies of the order of several millijoules per streamer while crossing the gap.

  9. Positive and negative streamers in ambient air: measuring diameter, velocity and dissipated energy

    International Nuclear Information System (INIS)

    Briels, T M P; Kos, J; Van Veldhuizen, E M; Ebert, U; Winands, G J J

    2008-01-01

    Positive and negative streamers are studied in ambient air at 1 bar; they emerge from a needle electrode placed 40 mm above a planar electrode. The amplitudes of the applied voltage pulses range from 5 to 96 kV; most pulses have rise times of 30 ns or shorter. Diameters, velocities and energies of the streamers are measured. Two regimes are identified; a low voltage regime where only positive streamers appear and a high voltage regime where both positive and negative streamers exist. Below 5 kV, no streamers emerge. In the range from 5 to 40 kV, positive streamers form, while the negative discharges only form a glowing cloud at the electrode tip, but no streamers. For 5-20 kV, diameters and velocities of the positive streamers have the minimal values of d = 0.2 mm and v ∼ 10 5 m s -1 . For 20-40 kV, their diameters increase by a factor of 6 while the voltage increases only by a factor of 2. Above the transition value of 40 kV, streamers of both polarities form; they strongly resemble each other, though the positive ones propagate further; their diameters continue to increase with applied voltage. For 96 kV, positive streamers attain diameters of 3 mm and velocities of 4 x 10 6 m s -1 ; negative streamers are about 20% slower and thinner. An empirical fit formula for the relation between velocity v and diameter d is v = 0.5d 2 mm -1 ns -1 for both polarities. Streamers of both polarities dissipate energies of the order of several millijoules per streamer while crossing the gap.

  10. Controlling branching in streamer discharge by laser background ionization

    International Nuclear Information System (INIS)

    Takahashi, E; Kato, S; Furutani, H; Sasaki, A; Kishimoto, Y

    2011-01-01

    Irradiation with a KrF laser controlled the positive streamer branching in atmospheric argon gas. This laser irradiation changed the amount of background ionization before the streamer discharge. Measuring the ionization current allowed us to evaluate the initial electron density formed by the KrF laser. We observed characteristic feather-like branching structure and found that it was only suppressed in the irradiated region. The threshold of ionization density which can influence the branching was evaluated to be 5 x 10 5 cm -3 . The relationship between the size of avalanche head and mean distance between initial electrons explained this suppression behaviour. These experimental results support that the feather-like structure originates from the branching model of Loeb-Meek, a probabilistic merging of individual avalanches.

  11. Double streamer phenomena in atmospheric pressure low frequency corona plasma

    International Nuclear Information System (INIS)

    Kim, Dan Bee; Jung, H.; Gweon, B.; Choe, Wonho

    2010-01-01

    Time-resolved images of an atmospheric pressure corona discharge, generated at 50 kHz in a single pin electrode source, show unique positive and negative corona discharge features: a streamer for the positive period and a glow for the negative period. However, unlike in previous reports of dc pulse and low frequency corona discharges, multistreamers were observed at the initial time stage of the positive corona. A possible physical mechanism for the multistreamers is suggested.

  12. Two-dimensional simulation of positive and negative streamers in air

    International Nuclear Information System (INIS)

    Babaeva, N.Yu.; Naidis, G.V.

    1998-01-01

    The paper deals with 2D numerical simulation of positive and negative streamers in air at atmospheric pressure. The dynamics of an axially symmetric streamer based on a charged sphere is described by a coupled system of equations for the electric field and the density of charged particles. The results of simulation show that the production rate of radicals in short sphere-plane gaps depends only weakly on the discharge conditions, that the streamer velocity in uniform field depends linearly on the streamer length, and the field corresponding to the negative streamer propagation with a constant velocity is 2-3 times greater than that obtained with a positive streamer. (J.U.)

  13. A Slow Streamer Blowout at the Sun and Ulysses

    Science.gov (United States)

    Seuss, S. T.; Bemporad, A.; Poletto, G.

    2004-01-01

    On 10 June 2000 a streamer on the southeast limb slowly disappeared from LASCO/C2 over approximately 10 hours. A small CME was reported in C2. A substantial interplanetary CME (ICME) was later detected at Ulysses, which was at quadrature with the Sun and SOHO at the time. This detection illustrates the properties of an ICME for a known solar source and demonstrates that the identification can be done even beyond 3 AU. Slow streamer blowouts such as this have long been known but are little studied. We report on the SOHO observation of a coronal mass ejection (CME) on the solar limb and the subsequent in situ detection at Ulysses, which was near quadrature at the time, above the location of the CME. SOHO-Ulysses quadrature was 13 June, when Ulysses was 3.36 AU from the Sun and 58.2 degrees south of the equator off the east limb. The slow streamer blowout was on 10 June, when the SOHO-Sun-Ulysses angle was 87 degrees.

  14. A nautical study of towed marine seismic streamer cable configurations

    Energy Technology Data Exchange (ETDEWEB)

    Pedersen, Egil

    1996-12-31

    This study concerns marine seismic surveying and especially the towed in-sea hardware which is dominated by recording cables (streamers) that are extremely long compared to their diameter, neutrally buoyant and depth controlled. The present work aims to examine the operations from a nautical viewpoint, and the final objective is to propose improvements to the overall efficiency of marine seismic operations. Full-scale data were gathered from seismic vessels in order to identify which physical parameters affect the dynamic motion of the towing vessel and its in-sea hardware. Experimental test programmes have been carried out, and data bases with the hydrodynamic characteristics of the test equipment have been established at speeds comparable to those used in seismic operations. A basic analysis tool to provide dynamic simulations of a seismic streamer cable has been developed by tailoring the computer program system Riflex, and the validation and accuracy of this modified Riflex system are evaluated by performing uncertainty analyses of measurements and computations. Unexpected, low-frequency depth motions in towed seismic streamer cables occasionally take place when seismic data are being acquired. The phenomenon is analysed and discussed. 99 refs., 116 figs., 5 tabs.

  15. A nautical study of towed marine seismic streamer cable configurations

    Energy Technology Data Exchange (ETDEWEB)

    Pedersen, Egil

    1997-12-31

    This study concerns marine seismic surveying and especially the towed in-sea hardware which is dominated by recording cables (streamers) that are extremely long compared to their diameter, neutrally buoyant and depth controlled. The present work aims to examine the operations from a nautical viewpoint, and the final objective is to propose improvements to the overall efficiency of marine seismic operations. Full-scale data were gathered from seismic vessels in order to identify which physical parameters affect the dynamic motion of the towing vessel and its in-sea hardware. Experimental test programmes have been carried out, and data bases with the hydrodynamic characteristics of the test equipment have been established at speeds comparable to those used in seismic operations. A basic analysis tool to provide dynamic simulations of a seismic streamer cable has been developed by tailoring the computer program system Riflex, and the validation and accuracy of this modified Riflex system are evaluated by performing uncertainty analyses of measurements and computations. Unexpected, low-frequency depth motions in towed seismic streamer cables occasionally take place when seismic data are being acquired. The phenomenon is analysed and discussed. 99 refs., 116 figs., 5 tabs.

  16. Probing photo-ionization: simulations of positive streamers in varying N2:O2 mixtures

    OpenAIRE

    Wormeester, G; Pancheshnyi, S; Luque, A A; Nijdam, S Sander; Ebert, UM Ute

    2010-01-01

    htmlabstractPhoto-ionization is the accepted mechanism for the propagation of positive streamers in air though the parameters are not very well known; the efficiency of this mechanism largely depends on the presence of both nitrogen and oxygen. But experiments show that streamer propagation is amazingly robust against changes of the gas composition; even for pure nitrogen with impurity levels below 1 ppm streamers propagate essentially with the same velocity as in air, but their minimal diame...

  17. Numerical modeling of positive streamer in air in nonuniform fields: Efficiency of radicals production

    International Nuclear Information System (INIS)

    Kulikovsky, A.A.

    2001-01-01

    The efficiency of streamer corona depends on a number of factors such as geometry of electrodes, voltage pulse parameters, gas pressure etc. In a past 5 years a two-dimensional models of streamer in nonuniform fields in air have been developed. These models allow to simulate streamer dynamics and generation of species and to investigate the influence of external parameters on species production. In this work the influence of Laplacian field on efficiency of radicals generation is investigated

  18. The influence of bremsstrahlung on electric discharge streamers in N2, O2 gas mixtures

    DEFF Research Database (Denmark)

    Köhn, Christoph; Chanrion, Olivier; Neubert, Torsten

    2017-01-01

    Streamers are ionization filaments of electric gas discharges. Negative polarity streamers propagate primarily through electron impact ionization, whereas positive streamers in air develop through ionization of oxygen by UV photons emitted by excited nitrogen; however, experiments show that posit...

  19. Leader propagation in uniform background fields in SF6

    International Nuclear Information System (INIS)

    Seeger, M; Niemeyer, L; Bujotzek, M

    2009-01-01

    The breakdown mechanism of compressed SF 6 in gas insulation is known to be controlled by stepped leader propagation. This process is still not well understood in uniform and weakly non-uniform background fields with small electrode protrusions, such as particles or surface roughness. In a previous publication an investigation of partial discharges and breakdown in uniform background fields that focused on streamer and leader inception mechanisms was presented (Seeger et al 2008 J. Phys. D: Appl. Phys. 41 185204). In this paper we present for the first time a physical leader propagation model that consistently describes the observed phenomena in uniform background fields in SF 6 . The model explains two different types of leader breakdown; these can be associated with the precursor and the stem mechanisms. It also yields the parameters of stepped leader propagation, which include step lengths, associated step charges, step times and fields and temperatures in the leader channel. Further, it explains the features of arrested leaders in uniform background fields. The model predicts the range of parameters under which arrested and breakdown leaders occur in good agreement with the experimental data.

  20. A novel pulsed corona discharge reactor based on surface streamers for diesel exhaust remediation

    Energy Technology Data Exchange (ETDEWEB)

    Malik, M.A.; Schoenbach, K.H. [Old Dominion Univ., Norfolk, VA (United States). Frank Reidy Research Center for Bioelectrics

    2010-07-01

    Modelling of surface streamers along insulating surfaces to determine the dielectric strength of insulators in high voltage systems has shown that surface streamers consist of a positive streamer head followed by quasi-neutral plasma in the channel behind and surrounded by a layer of positive charges. This paper described a novel pulsed corona discharge reactor which utilized such surface streamers along insulating surfaces. The electrodes were comprised of a stainless steel wire anode of 150 mm in diameter stretched along the surface of a glass sheet and two parallel aluminum strips as cathodes. An eight-stage Marx bank, was used to produce the surface streamers in nitrogen-oxygen mixtures at atmospheric pressure. The paper described the experimental study with particular reference to the schematics of a surface streamer plasma reactor and the dimensions of discharge spaces of three reactors. The purpose of the study was to find the optimum conditions for energy yield and effective destruction of nitrogen oxides from diesel engine exhaust. It was concluded that surface streamers generate a more diffuse plasma. Energy costs for production of ozone or nitrogen dioxide that require reactions with bulk gas molecules were nearly the same in surface streamer discharges as in volume streamer discharges. 12 refs., 1 tab., 7 figs.

  1. Evaluation of pulsed streamer corona experiments to determine the O* radical yield

    International Nuclear Information System (INIS)

    Van Heesch, E J M; Winands, G J J; Pemen, A J M

    2008-01-01

    The production of O* radicals in air by a pulsed streamer plasma is studied by integration of a large set of precise experimental data and the chemical kinetics of ozone production. The measured data comprise ozone production, plasma energy, streamer volume, streamer length, streamer velocity, humidity and gas-flow rate. Instead of entering input parameters into a kinetic model to calculate the end products the opposite strategy is followed. Since the amount of end-products (ozone) is known from the measurements the model had to be applied in the reverse direction to determine the input parameters, i.e. the O* radical concentration.

  2. Evaluation of pulsed streamer corona experiments to determine the O* radical yield

    Science.gov (United States)

    van Heesch, E. J. M.; Winands, G. J. J.; Pemen, A. J. M.

    2008-12-01

    The production of O* radicals in air by a pulsed streamer plasma is studied by integration of a large set of precise experimental data and the chemical kinetics of ozone production. The measured data comprise ozone production, plasma energy, streamer volume, streamer length, streamer velocity, humidity and gas-flow rate. Instead of entering input parameters into a kinetic model to calculate the end products the opposite strategy is followed. Since the amount of end-products (ozone) is known from the measurements the model had to be applied in the reverse direction to determine the input parameters, i.e. the O* radical concentration.

  3. Probing photo-ionization: experiments on positive streamers in pure gases and mixtures

    International Nuclear Information System (INIS)

    Nijdam, S; Van de Wetering, F M J H; Blanc, R; Van Veldhuizen, E M; Ebert, U

    2010-01-01

    Positive streamers are thought to propagate by photo-ionization; the parameters of photo-ionization depend on the nitrogen : oxygen ratio. Therefore we study streamers in nitrogen with 20%, 0.2% and 0.01% oxygen and in pure nitrogen as well as in pure oxygen and argon. Our new experimental set-up guarantees contamination of the pure gases to be well below 1 ppm. Streamers in oxygen are difficult to measure as they emit considerably less light in the sensitivity range of our fast ICCD camera than the other gases. Streamers in pure nitrogen and in all nitrogen-oxygen mixtures look generally similar, but become somewhat thinner and branch more with decreasing oxygen content. In pure nitrogen the streamers can branch so much that they resemble feathers. This feature is even more pronounced in pure argon, with approximately 10 2 hair tips cm -3 in the feathers at 200 mbar; this density can be interpreted as the free electron density creating avalanches towards the streamer stem. It is remarkable that the streamer velocity is essentially the same for similar voltage and pressure in all nitrogen-oxygen mixtures as well as in pure nitrogen, while the oxygen concentration and therefore the photo-ionization lengths vary by more than five orders of magnitude. Streamers in argon have essentially the same velocity as well. The physical similarity of streamers at different pressures is confirmed in all gases; the minimal diameters are smaller than in earlier measurements.

  4. Probing photo-ionization: experiments on positive streamers in pure gases and mixtures

    Energy Technology Data Exchange (ETDEWEB)

    Nijdam, S; Van de Wetering, F M J H; Blanc, R; Van Veldhuizen, E M; Ebert, U, E-mail: s.nijdam@tue.n [Eindhoven University of Technology, Department Applied Physics, PO Box 513, 5600 MB Eindhoven (Netherlands)

    2010-04-14

    Positive streamers are thought to propagate by photo-ionization; the parameters of photo-ionization depend on the nitrogen : oxygen ratio. Therefore we study streamers in nitrogen with 20%, 0.2% and 0.01% oxygen and in pure nitrogen as well as in pure oxygen and argon. Our new experimental set-up guarantees contamination of the pure gases to be well below 1 ppm. Streamers in oxygen are difficult to measure as they emit considerably less light in the sensitivity range of our fast ICCD camera than the other gases. Streamers in pure nitrogen and in all nitrogen-oxygen mixtures look generally similar, but become somewhat thinner and branch more with decreasing oxygen content. In pure nitrogen the streamers can branch so much that they resemble feathers. This feature is even more pronounced in pure argon, with approximately 10{sup 2} hair tips cm{sup -3} in the feathers at 200 mbar; this density can be interpreted as the free electron density creating avalanches towards the streamer stem. It is remarkable that the streamer velocity is essentially the same for similar voltage and pressure in all nitrogen-oxygen mixtures as well as in pure nitrogen, while the oxygen concentration and therefore the photo-ionization lengths vary by more than five orders of magnitude. Streamers in argon have essentially the same velocity as well. The physical similarity of streamers at different pressures is confirmed in all gases; the minimal diameters are smaller than in earlier measurements.

  5. High-resolution seismic reflection surveying with a land streamer

    Science.gov (United States)

    Cengiz Tapırdamaz, Mustafa; Cankurtaranlar, Ali; Ergintav, Semih; Kurt, Levent

    2013-04-01

    In this study, newly designed seismic reflection data acquisition array (land streamer) is utilized to image the shallow subsurface. Our acquisition system consist of 24 geophones screwed on iron plates with 2 m spacing, moving on the surface of the earth which are connected with fire hose. Completely original, 4.5 Kg weight iron plates provides satisfactory coupling. This land-streamer system enables rapid and cost effective acquisition of seismic reflection data due to its operational facilities. First test studies were performed using various seismic sources such as a mini-vibro truck, buffalo-gun and hammer. The final fieldwork was performed on a landslide area which was studied before. Data acquisition was carried out on the line that was previously measured by the seismic survey using 5 m geophone and shot spacing. This line was chosen in order to re-image known reflection patterns obtained from the previous field study. Taking penetration depth into consideration, a six-cartridge buffalo-gun was selected as a seismic source to achieve high vertical resolution. Each shot-point drilled 50 cm for gunshots to obtain high resolution source signature. In order to avoid surface waves, the offset distance between the source and the first channel was chosen to be 50 m and the shot spacing was 2 m. These acquisition parameters provided 12 folds at each CDP points. Spatial sampling interval was 1 m at the surface. The processing steps included standard stages such as gain recovery, editing, frequency filtering, CDP sorting, NMO correction, static correction and stacking. Furthermore, surface consistent residual static corrections were applied recursively to improve image quality. 2D F-K filter application was performed to suppress air and surface waves at relatively deep part of the seismic section. Results show that, this newly designed, high-resolution land seismic data acquisition equipment (land-streamer) can be successfully used to image subsurface. Likewise

  6. Characteristics of lightning leader propagation and ground attachment

    Science.gov (United States)

    Jiang, Rubin; Qie, Xiushu; Wang, Zhichao; Zhang, Hongbo; Lu, Gaopeng; Sun, Zhuling; Liu, Mingyuan; Li, Xun

    2015-12-01

    The grounding process and the associated leader behavior were analyzed by using high-speed video record and time-correlated electric field change for 37 natural negative cloud-to-ground flashes. Weak luminous grounded channel was recognized below the downward leader tip in the frame preceding the return stroke, which is inferred as upward connecting leader considering the physical process of lightning attachment, though not directly confirmed by sequential frames. For stepped leader-first return strokes, the upward connecting leaders tend to be induced by those downward leader branches with brighter luminosity and lower channel tip above ground, and they may accomplish the attachment with great possibility. The upward connecting leaders for 2 out of 61 leader-subsequent stroke sequences were captured in the frame prior to the return stroke, exhibiting relatively long channel lengths of 340 m and 105 m, respectively. The inducing downward subsequent leaders were of the chaotic type characterized by irregular electric field pulse train with duration of 0.2-0.3 ms. The transient drop of the high potential difference between stepped leader system and ground when the attachment occurred would macroscopically terminate the propagation of those ungrounded branches while would not effectively prevent the development of the existing space stem systems in the low-conductivity streamer zone apart from the leader tip. When the ungrounded branches are of poor connection with the main stroke channel, their further propagation toward ground would be feasible. These two factors may contribute to the occurrence of multiple grounding within the same leader-return stroke sequence.

  7. Temperature and pressure effects on the properties of positive streamers in air

    NARCIS (Netherlands)

    Huiskamp, T.; Heesch, van E.J.M.; Beckers, F.J.C.M.; Hoeben, W.F.L.M.; Pemen, A.J.M.

    2012-01-01

    In this paper we present experimental results on how the properties of positive, pulsed streamers in air depend on E/n (E is the applied electric field and n is the gas density). Streamers are generated in a wire-cylinder reactor at constant voltage (so constant E). The density is changed either by

  8. Study on the streamer inception characteristics under positive lightning impulse voltage

    Directory of Open Access Journals (Sweden)

    Zezhong Wang

    2017-11-01

    Full Text Available The streamer is the main process in an air gap discharge, and the inception characteristics of streamers have been widely applied in engineering. Streamer inception characteristics under DC voltage have been studied by many researchers, but the inception characteristics under impulse voltage, and particularly under lightning impulse voltage with a high voltage rise rate have rarely been studied. A measurement system based on integrated optoelectronic technology has been proposed in this paper, and the streamer inception characteristics in a 1-m-long rod-plane air gap that was energized by a positive lightning impulse voltage have been researched. We have also measured the streamer inception electric field using electrodes with different radii of curvature and different voltage rise rates. As a result, a modified empirical criterion for the streamer inception electric field that considers the voltage rise rate has been proposed, and the wide applicability of this criterion has been proved. Based on the streamer inception time-lag obtained, we determined that the field distribution obeys a Rayleigh distribution, which explains the change law of the streamer inception time-lag. The characteristic parameter of the Rayleigh distribution lies in the range from 0.6 to 2.5 when the radius of curvature of the electrode head is in the range from 0.5 cm to 2.5 cm and the voltage rise rate ranges from 80 kV/μs to 240kV/μs under positive lightning impulse voltage.

  9. Experiments on how photo- and background ionization affect positive streamers: oxygen concentration, repetition and radioactivity

    NARCIS (Netherlands)

    Nijdam, S.; Veldhuizen, van E.M.; Ebert, U.

    2011-01-01

    Positive streamers in air and other oxygen-nitrogen mixtures are generally believed to propagate against the electron drift direction due to photo-ionization. Photo-ionization is the non-local ionization of O2-molecules by UV radiation from excited N2-molecules. This facilitates the streamer

  10. Evaluation of a charged coupled device camera for streamer chamber applications

    International Nuclear Information System (INIS)

    Holmgren, D.; Wallick, W.; Kenyon, R.; Lubatti, H.J.

    1978-01-01

    The response of a charged coupled device to a Ne light source is studied and compared to the Kodak SO-143 film commonly used for streamer chamber applications. It is found that the CCD-202 cooled to -10 0 C is considerably more sensitive than the film. A test of a CCD-based measurement system observing a streamer chamber is described. 3 refs

  11. SYMPATHETIC FILAMENT ERUPTIONS FROM A BIPOLAR HELMET STREAMER IN THE SUN

    International Nuclear Information System (INIS)

    Yang Jiayan; Jiang Yunchun; Zheng Ruisheng; Bi Yi; Hong Junchao; Yang Bo

    2012-01-01

    On 2005 August 5, two solar filaments erupted successively from different confined arcades underlying a common overarching multiple-arcade bipolar helmet streamer. We present detailed observations of these two events and identify them as sympathetic filament eruptions. The first (F1) is a small active-region filament located near the outskirts of the streamer arcade. It underwent a nonradial eruption, initially moving in the interior of the streamer arcade and resulting in an over-and-out coronal mass ejection. The second filament (F2), a larger quiescent one far away from F1, was clearly disturbed during the F1 eruption. It then underwent a very slow eruption and finally disappeared completely and permanently. Because two belt-shaped diffuse dimmings formed along the footprints of the streamer arcade in the first eruption and persisted throughout the complete disappearance of F2, the eruption series are interpreted as sympathetic: the simple expansion of the common streamer arcade forced by the F1 eruption weakened magnetic flux overlying F2 and thus led to its slow eruption, with the dimming formation indicating their physical connection. Our observations suggest that multiple-arcade bipolar helmet-streamer configurations are appropriate to producing sympathetic eruptions. Combined with the recent observations of unipolar-streamer sympathetic events, it appears that a multiple-arcade unipolar or bipolar helmet streamer can serve as a common magnetic configuration for sympathetic eruptions.

  12. Circuit dependence of the diameter of pulsed positive streamers in air

    Energy Technology Data Exchange (ETDEWEB)

    Briels, T M P [Department of Applied Physics, Technische Universiteit Eindhoven, PO Box 513, 5600MB Eindhoven (Netherlands); Kos, J [Department of Applied Physics, Technische Universiteit Eindhoven, PO Box 513, 5600MB Eindhoven (Netherlands); Veldhuizen, E M van [Department of Applied Physics, Technische Universiteit Eindhoven, PO Box 513, 5600MB Eindhoven (Netherlands); Ebert, U [Department of Applied Physics, Technische Universiteit Eindhoven, PO Box 513, 5600MB Eindhoven (Netherlands)

    2006-12-21

    The diameter and branching structure of positive streamers in ambient air are investigated with a fast iCCD camera. We use different pulsed power circuits and find that they generate different spatial streamer structures. The electrodes have a point-plane geometry and a distance of 40 or 80 mm, and the peak voltages over the discharge gap are up to 60 kV. Depending on circuit and peak voltage, we observe streamers with diameters varying gradually between 0.2 and 2.5 mm. The streamer velocity increases with the diameter, ranging from 0.07 to 1.5 mm ns{sup -1}, while the current density within the streamers stays almost constant. The thicker streamers extend much further before they branch than the thinner ones. The pulsed power supplies are a switched capacitor supply with an internal resistance of 1 k{omega} and a transmission line transformer supply with an impedance of 200 {omega}; additional resistors change the impedance as well as the voltage rise time in the case of the capacitor supply. We observe that short rise times and low impedance create thick streamers close to the pointed electrode, while a longer rise time as well as a higher impedance create thinner streamers at the same peak voltage over the discharge.

  13. Circuit dependence of the diameter of pulsed positive streamers in air

    International Nuclear Information System (INIS)

    Briels, T M P; Kos, J; Veldhuizen, E M van; Ebert, U

    2006-01-01

    The diameter and branching structure of positive streamers in ambient air are investigated with a fast iCCD camera. We use different pulsed power circuits and find that they generate different spatial streamer structures. The electrodes have a point-plane geometry and a distance of 40 or 80 mm, and the peak voltages over the discharge gap are up to 60 kV. Depending on circuit and peak voltage, we observe streamers with diameters varying gradually between 0.2 and 2.5 mm. The streamer velocity increases with the diameter, ranging from 0.07 to 1.5 mm ns -1 , while the current density within the streamers stays almost constant. The thicker streamers extend much further before they branch than the thinner ones. The pulsed power supplies are a switched capacitor supply with an internal resistance of 1 kΩ and a transmission line transformer supply with an impedance of 200 Ω; additional resistors change the impedance as well as the voltage rise time in the case of the capacitor supply. We observe that short rise times and low impedance create thick streamers close to the pointed electrode, while a longer rise time as well as a higher impedance create thinner streamers at the same peak voltage over the discharge

  14. Study on the streamer inception characteristics under positive lightning impulse voltage

    Science.gov (United States)

    Wang, Zezhong; Geng, Yinan

    2017-11-01

    The streamer is the main process in an air gap discharge, and the inception characteristics of streamers have been widely applied in engineering. Streamer inception characteristics under DC voltage have been studied by many researchers, but the inception characteristics under impulse voltage, and particularly under lightning impulse voltage with a high voltage rise rate have rarely been studied. A measurement system based on integrated optoelectronic technology has been proposed in this paper, and the streamer inception characteristics in a 1-m-long rod-plane air gap that was energized by a positive lightning impulse voltage have been researched. We have also measured the streamer inception electric field using electrodes with different radii of curvature and different voltage rise rates. As a result, a modified empirical criterion for the streamer inception electric field that considers the voltage rise rate has been proposed, and the wide applicability of this criterion has been proved. Based on the streamer inception time-lag obtained, we determined that the field distribution obeys a Rayleigh distribution, which explains the change law of the streamer inception time-lag. The characteristic parameter of the Rayleigh distribution lies in the range from 0.6 to 2.5 when the radius of curvature of the electrode head is in the range from 0.5 cm to 2.5 cm and the voltage rise rate ranges from 80 kV/μs to 240kV/μs under positive lightning impulse voltage.

  15. CCD camera system for use with a streamer chamber

    International Nuclear Information System (INIS)

    Angius, S.A.; Au, R.; Crawley, G.C.; Djalali, C.; Fox, R.; Maier, M.; Ogilvie, C.A.; Molen, A. van der; Westfall, G.D.; Tickle, R.S.

    1988-01-01

    A system based on three charge-coupled-device (CCD) cameras is described here. It has been used to acquire images from a streamer chamber and consists of three identical subsystems, one for each camera. Each subsystem contains an optical lens, CCD camera head, camera controller, an interface between the CCD and a microprocessor, and a link to a minicomputer for data recording and on-line analysis. Image analysis techniques have been developed to enhance the quality of the particle tracks. Some steps have been made to automatically identify tracks and reconstruct the event. (orig.)

  16. Pulsed Streamer Discharge Characteristics of Ozone Production in Dry Air

    OpenAIRE

    Samaranayake, W.J.M.; Miyahara, Y.; Namihira, T.; Katsuki, S.; Sakugawa, T.; Hackam, R.; Akiyama, H.; ナミヒラ, タカオ; カツキ, スナオ; アキヤマ, ヒデノリ; 波平, 隆男; 勝木, 淳; 秋山, 秀典

    2000-01-01

    Experimental investigation of HV short pulsed streamer discharges in dry air-fed ozonizers under various operating conditions are reported. Ozone concentration, energy input and ozone production yield (efficiency) were measured at various voltages (14 to 37 kV), pulse repetition rates (25 to 400 pulses per second, pps), flow rates (1.5 to 3.0 1/min) and different gap spacings (10 to 20 mm) at a pressure of 1.01×105 Pa in dry air. A spiral copper wire (1 mm in diameter) made to a cylindrical c...

  17. LEADER 2

    DEFF Research Database (Denmark)

    Daniels, G H; Hegedüs, L; Marso, S P

    2015-01-01

    AIMS: To report preliminary data on baseline serum calcitonin concentrations and associated clinical characteristics in a global population with type 2 diabetes before liraglutide or placebo randomization. METHODS: The ongoing LEADER trial has enrolled 9340 people with type 2 diabetes and at high......) baseline serum calcitonin values were 3.9 (1.0 to >7.6) ng/l in men and 1.0 (1.0 to >1) ng/l in women. Serum calcitonin was >10 ng/l in 14.6% of men and in 0.96% of women. In sex-specific multivariable linear analysis of covariance models, a reduced glomerular filtration rate (GFR) was associated...... with higher serum calcitonin concentrations that were statistically significant. A 20 ml/min/1.73 m(2) decrease in estimated GFR (eGFR) was associated with a 14% increase in serum calcitonin in women and an 11% increase in men. CONCLUSIONS: In the LEADER population, the prevalence of elevated serum calcitonin...

  18. The EuroSprite2005 Observational Campaign: an example of training and outreach opportunities for CAL young scientists

    Directory of Open Access Journals (Sweden)

    O. Chanrion

    2007-07-01

    Full Text Available The four year "Coupling of Atmospheric Layers (CAL" EU FP5 Research Training Network project studied unanswered questions related to transient luminous events (sprites, jets and elves in the upper atmosphere. Consisting of ten scientific work-packages CAL also included intensive training and outreach programmes for the young scientists hired. Educational activities were based on the following elements: national PhD programmes, activities at CAL and other meetings, a dedicated summer school, and two European sprite observational campaigns. The young scientists were strongly involved in the latter and, as an example, the "EuroSprite2005" observational campaign is presented in detail. Some of the young scientists participated in the instrument set-up, others in the campaign logistics, some coordinated the observations, and others gathered the results to build a catalogue. During the four-month duration of this campaign, all of them took turns in operating the system and making their own night observations. The ongoing campaign activities were constantly advertised and communicated via an Internet blog. In summary the campaign required all the CAL young scientists to embark on experimental work, to develop their organisational skills, and to enhance their ability to communicate their activities. The campaign was a unique opportunity to train and strengthen skills that will be an asset to their future careers and, overall, was most successful.

  19. Effect of electric field configuration on streamer and partial discharge phenomena in a hydrocarbon insulating liquid under AC stress

    International Nuclear Information System (INIS)

    Liu, Z; Liu, Q; Wang, Z D

    2016-01-01

    This paper concerns pre-breakdown phenomena, including streamer characteristics from a fundamental perspective and partial discharge (PD) measurements from an industrial perspective, in a hydrocarbon insulating liquid. The aim was to investigate the possible changes of the liquid’s streamer and PD characteristics and their correlations when the uniformity of the AC electric field varies. In the experiments, a plane-to-plane electrode system incorporating a needle protrusion was used in addition to a needle-to-plane electrode system. When the applied electric field became more uniform, fewer radial branches occurred and streamer propagation towards the ground electrode was enhanced. The transition from streamer propagation dominated breakdown in divergent fields to streamer initiation dominated breakdown in uniform fields was evidenced. Relationships between streamer and PD characteristics were established, which were found to be electric field dependent. PD of the same apparent charge would indicate longer streamers if the electric field is more uniform. (paper)

  20. An adaptive grid refinement strategy for the simulation of negative streamers

    International Nuclear Information System (INIS)

    Montijn, C.; Hundsdorfer, W.; Ebert, U.

    2006-01-01

    The evolution of negative streamers during electric breakdown of a non-attaching gas can be described by a two-fluid model for electrons and positive ions. It consists of continuity equations for the charged particles including drift, diffusion and reaction in the local electric field, coupled to the Poisson equation for the electric potential. The model generates field enhancement and steep propagating ionization fronts at the tip of growing ionized filaments. An adaptive grid refinement method for the simulation of these structures is presented. It uses finite volume spatial discretizations and explicit time stepping, which allows the decoupling of the grids for the continuity equations from those for the Poisson equation. Standard refinement methods in which the refinement criterion is based on local error monitors fail due to the pulled character of the streamer front that propagates into a linearly unstable state. We present a refinement method which deals with all these features. Tests on one-dimensional streamer fronts as well as on three-dimensional streamers with cylindrical symmetry (hence effectively 2D for numerical purposes) are carried out successfully. Results on fine grids are presented, they show that such an adaptive grid method is needed to capture the streamer characteristics well. This refinement strategy enables us to adequately compute negative streamers in pure gases in the parameter regime where a physical instability appears: branching streamers

  1. Surface streamer propagations on an alumina bead: experimental observation and numerical modeling

    Science.gov (United States)

    Kang, Woo Seok; Kim, Hyun-Ha; Teramoto, Yoshiyuki; Ogata, Atsushi; Lee, Jin Young; Kim, Dae-Woong; Hur, Min; Song, Young-Hoon

    2018-01-01

    A surface streamer in a simplified packed-bed reactor has been studied both experimentally (through time-resolved ICCD imaging) and theoretically (through two-dimensional numerical modeling). The propagation of streamers on an alumina spherical bead without catalytic coating shows three distinct phases—the generation and propagation of a primary streamer (PS) with a moderate velocity and electric field, fast PS acceleration with an enhanced electric field, and slow secondary streamer (SS) propagation. The velocity of the streamer is less than that of propagation in a gaseous media. The electric field and velocity at the streamer front are maximized when a PS propagates during the interval from the midpoint of the bead to the bottom electrode. The SS exhibits a much lower velocity and electric field compared with the PS. The PS velocity is affected by an external applied voltage, especially when it approaches the ground electrode. However, that of the SS remains constant regardless of the voltage change. The simulation shows that the PS exhibits a high electric field mainly created by the space charge induced by electrons, whereas the SS relies on ion movement with electron decay in a charge-filled thin streamer body.

  2. Two-Dimensional Electron Density Measurement of Positive Streamer Discharge in Atmospheric-Pressure Air

    Science.gov (United States)

    Inada, Yuki; Ono, Ryo; Kumada, Akiko; Hidaka, Kunihiko; Maeyama, Mitsuaki

    2016-09-01

    The electron density of streamer discharges propagating in atmospheric-pressure air is crucially important for systematic understanding of the production mechanisms of reactive species utilized in wide ranging applications such as medical treatment, plasma-assisted ignition and combustion, ozone production and environmental pollutant processing. However, electron density measurement during the propagation of the atmospheric-pressure streamers is extremely difficult by using the conventional localized type measurement systems due to the streamer initiation jitters and the irreproducibility in the discharge paths. In order to overcome the difficulties, single-shot two-dimensional electron density measurement was conducted by using a Shack-Hartmann type laser wavefront sensor. The Shack-Hartmann sensor with a temporal resolution of 2 ns was applied to pulsed positive streamer discharges generated in an air gap between pin-to-plate electrodes. The electron density a few ns after the streamer initiation was 7*1021m-3 and uniformly distributed along the streamer channel. The electron density and its distribution profile were compared with a previous study simulating similar streamers, demonstrating good agreement. This work was supported in part by JKA and its promotion funds from KEIRIN RACE. The authors like to thank Mr. Kazuaki Ogura and Mr. Kaiho Aono of The University of Tokyo for their support during this work.

  3. Dependence of streamer density on electric field strength on positive electrode

    Science.gov (United States)

    Koki, Nakamura; Takahumi, Okuyama; Wang, Douyan; Takao, N.; Hidenori, Akiyama; Kumamoto University Collaboration

    2015-09-01

    Pulsed streamer discharge plasma, a type of non-thermal plasma, is known as generation method of reactive radicals and ozone and treatment of exhausted gas. From our previous research, the distance between electrodes has been considered a very important parameter for applications using pulsed streamer discharge. However, how the distance between electrodes affects the pulsed discharge hasn't been clarified. In this research, the propagation process of pulsed streamer discharge in a wire-plate electrode was observed using an ICCD camera for 4 electrodes having different distance between electrodes. The distance between electrodes was changeable at 45 mm, 40 mm, 35 mm, and 30 mm. The results show that, when the distance between electrodes was shortened, applied voltage with a pulse duration of 100 ns decreased from 80 to 60.3 kV. Conversely, discharge current increased from 149 to 190 A. Streamer head velocity became faster. On the other hand, Streamer head density at onset time of streamer head propagation didn't change. This is considered due to the electric field strength of streamer head at that time, in result, it was about 14 kV/mm under each distance between electrodes.

  4. Probing background ionization: positive streamers with varying pulse repetition rate and with a radioactive admixture

    International Nuclear Information System (INIS)

    Nijdam, S; Van Veldhuizen, E M; Ebert, U; Wormeester, G

    2011-01-01

    Positive streamers need a source of free electrons ahead of them to propagate. A streamer can supply these electrons by itself through photo-ionization, or the electrons can be present due to external background ionization. Here we investigate the effects of background ionization on streamer propagation and morphology by changing the gas composition and the repetition rate of the voltage pulses, and by adding a small amount of radioactive 85 Kr. We find that the general morphology of a positive streamer discharge in high-purity nitrogen depends on background ionization: at lower background ionization levels the streamers branch more and have a more feather-like appearance. This is observed both when varying the repetition rate and when adding 85 Kr, though side branches are longer with the radioactive admixture. But velocities and minimal diameters of streamers are virtually independent of the background ionization level. In air, the inception cloud breaks up into streamers at a smaller radius when the repetition rate and therefore the background ionization level is higher. When measuring the effects of the pulse repetition rate and of the radioactive admixture on the discharge morphology, we found that our estimates of background ionization levels are consistent with these observations; this gives confidence in the estimates. Streamer channels generally do not follow the paths of previous discharge channels for repetition rates of up to 10 Hz. We estimate the effect of recombination and diffusion of ions and free electrons from the previous discharge and conclude that the old trail has largely disappeared at the moment of the next voltage pulse; therefore the next streamers indeed cannot follow the old trail.

  5. A study of the self-quenched streamer mode using a nitrogen laser

    International Nuclear Information System (INIS)

    An Jigang; Anderson, K.J.; Merritt, F.S.; Oreglia, M.; Pilcher, J.E.; Possoz, A.; Schappert, W.; Chicago Univ., IL

    1988-01-01

    The characteristics and mechanism of the self-quenched streamer mode have been explored using laser induced ionization. Both the size of the streamer signal and the transformation from proportional to streamer mode depend on high voltage and the primary ionization density. Two nearby tracks influence each other mainly by space charge effects. The zone of influence depends on relative drift time of the tracks but is less than 3 mm along the anode. The influence is less with argon-free strong quenching gas mixtures. (orig.)

  6. A large streamer chamber muon tracking detector in a high-flux fixed-target application

    CERN Document Server

    Adams, D; Adeva, B; Arik, E; Arvidson, A; Badelek, B; Ballintijn, M K; Bardin, G; Baum, G; Berglund, P; Betev, L; Bird, I G; Birsa, R; Björkholm, P; Bonner, B E; De Botton, N R; Boutemeur, M; Bradamante, Franco; Bravar, A; Bressan, A; Bültmann, S; Burtin, E; Cavata, C; Crabb, D; Cranshaw, J; Çuhadar-Dönszelmann, T; Dalla Torre, S; Van Dantzig, R; Derro, B R; Deshpande, A A; Dhawan, S K; Dulya, C M; Dyring, A; Eichblatt, S; Faivre, Jean-Claude; Fasching, D; Feinstein, F; Fernández, C; Forthmann, S; Frois, Bernard; Gallas, A; Garabatos, C; Garzón, J A; Gaussiran, T; Gilly, H; Giorgi, M A; von Goeler, E; Görtz, S; Golutvin, I A; Gómez-Tato, A; Gracia, G; De Groot, N; Grosse-Perdekamp, M; Gülmez, E; Haft, K; Von Harrach, D; Hasegawa, T; Hautle, P; Hayashi, N; Heusch, C A; Horikawa, N; Hughes, V W; Igo, G; Ishimoto, S; Iwata, T; Kabuss, E M; Kageya, T; Karev, A G; Kessler, H J; Ketel, T; Kiryluk, J; Kiryushin, Yu T; Kishi, A; Kiselev, Yu F; Klostermann, L; Krämer, Dietrich; Kröger, W; Kurek, K; Kyynäräinen, J; Lamanna, M; Landgraf, U; Lau, K; Layda, T; Le Goff, J M; Lehár, F; de Lesquen, A; Lichtenstadt, J; Lindqvist, T; Litmaath, M; Loewe, M; Magnon, A; Mallot, G K; Marie, F; Martin, A; Martino, J; Matsuda, T; Mayes, B W; McCarthy, J S; Medved, K S; Meyer, W T; Van Middelkoop, G; Miller, D; Miyachi, Y; Mori, K; Moromisato, J H; Nassalski, J P; Naumann, Lutz; Niinikoski, T O; Oberski, J; Ogawa, A; Ozben, C; Parks, D P; Pereira, H; Penzo, Aldo L; Perrot-Kunne, F; Peshekhonov, V D; Piegaia, R; Pinsky, L; Platchkov, S K; Pló, M; Pose, D; Postma, H; Pretz, J; Pussieux, T; Pyrlik, J; Rädel, G; Reyhancan, I; Reicherz, G; Rijllart, A; Roberts, J B; Rock, S E; Rodríguez, M; Rondio, Ewa; Rosado, A; Roscherr, B; Sabo, I; Saborido, J; Sandacz, A; Sanders, D; Savin, I A; Schiavon, R P; Schiller, A; Schüler, K P; Segel, R E; Seitz, R; Semertzidis, Y K; Sergeev, S; Sever, F; Shanahan, P; Sichtermann, E P; Simeoni, F; Smirnov, G I; Staude, A; Steinmetz, A; Stiegler, U; Stuhrmann, H B; Szleper, M; Teichert, K M; Tessarotto, F; Thers, D; Tlaczala, W; Trentalange, S; Tripet, A; Tzamouranis, Yu; Ünel, G; Velasco, M; Vogt, J; Voss, Rüdiger; Weinstein, R; Whitten, C; Windmolders, R; Willumeit, R; Wislicki, W; Witzmann, A; Zamiatin, N I; Zanetti, A M; Zaremba, K; Zhao, J

    1999-01-01

    Arrays of limited streamer tubes of the Iarocci type were deployed in our experiment at CERN as part of a forward muon detector system with provisions for the beam to pass through the center of each panel in the array. A total of sixteen 4 m x 4 m panels were assembled with inductive readout strips on both sides of each panel. An active feedback system was deployed to regulate the high voltage to the streamer tubes to insure a constant efficiency for minimum ionizing particles. The arrays were operated in this environment for over five years of data taking. Streamer tube track-reconstruction efficiencies and tube replacement rates are reported.

  7. Persuasion: A Leader's Edge

    National Research Council Canada - National Science Library

    McGuire, Mark

    2002-01-01

    .... Nevertheless, today's leaders should realize the need for persuasion. In one manner or another, leaders depend on persuasive rhetoric to convince, encourage, and energize superiors, peers, and subordinates...

  8. Vacuum surface flashover and high pressure gas streamers

    International Nuclear Information System (INIS)

    Elizondo, J.M.; Krogh, M.L.; Smith, D.; Stolz, D.; Wright, S.N.

    1997-07-01

    Pre-breakdown current traces obtained during high pressure gas breakdown and vacuum surface flashover show similar signatures. The initial pre-breakdown current spike, a flat constant current phase, and the breakdown phase with voltage collapse and current surge differ mostly in magnitude. Given these similarities, a model, consisting of the initial current spike corresponding to a fast precursor streamer (ionization wave led by a photoionizing front), the flat current stage as the heating or glow phase, and the terminal avalanche and gap closure, is applied to vacuum surface flashover. A simple analytical approximation based on the resistivity changes induced in the vacuum and dielectric surface is presented. The approximation yields an excellent fit to pre-breakdown time delay vs applied field for previously published experimental data. A detailed kinetics model that includes surface and gas contributions is being developed based in the initial approximation

  9. Diagnostics and modeling of high pressure streamer induced discharges

    International Nuclear Information System (INIS)

    Marode, E.; Dessante, P.; Deschamps, N.; Deniset, C.

    2001-01-01

    A great variety of diagnostic has been applied to gain information on basic parameter governing high pressure nonthermal filamentary plasmas (and namely streamer induced filamentary discharges). Apart from electrical diagnostics, gas discharge, in contrast with solid state physics, can greatly benefit from all optical techniques owing to its ''transparent'' state. Emission and absorption spectroscopy, as well as LIF or CARS (talk are given during this meeting on these two techniques) are among such specific possibilities. The figures gained from these diagnostic measurements has generally no meaning by itself. They must be worked out, by means of calibrated former results, and/or by using them as input in high pressure plasma modeling. Mixing experimental and modeling approach is necessary for reaching relevant physical knowledge of the high pressure filamentary discharges processes. It is shown that diffusion, and thermal space and time distribution, must fully be taken into account

  10. Preliminary Analysis of IR Cloudtop Temperatures of Sprite Producing Storms over Argentina Observed from Brazil, and Comparison with US Case Study

    Science.gov (United States)

    Sao Sabbas, F. T.; Pautet, P.; Taylor, M. J.; Pinto, O.; Thomas, J.; Solorzano, N.; Holzworth, R.; Bailey, M.; Schuch, N.; Michels, M.

    2006-12-01

    We will present the preliminary results of the cloudtop temperature characteristics of two very active sprite- producing Mesoscale Convective System (MCS) which occurred over Argentina in the evening of February 22, and March 04, 2006. These were prolific storms, e.g. the first one produced more than 400 TLEs, including sprites, halos and possibly elves. The events were observed from the INPE Observatorio Espacial Sul-OES (Southern Space Observatory), located at the center of Rio Grande do Sul State, the most Southern State of Brazil. Except for the lack of triangulated locations for the sprites and halos recorded, the methodology used for this study is the same as for the paper Sao Sabbas and Sentman [2003], where a sprite producing storm over the central U.S. was observed during the night of July 22, 1996. We analyzed the IR satellite data provided by GOES-12 and the lightning information from the Brazilian Lightning Detection Network in combination with data from the World Wide Lightning Location Network WWLLN. We will also show a comparison between the obtained results and the results presented at the Sao Sabbas and Sentman [2003] paper. Sao Sabbas, F.T. and D. D. Sentman, Dynamical Relationship of IR Cloudtop Temperatures With Occurrence Rates of Cloud-to-Ground Lightning and Sprites, Geophys. Res. Lett., 30 (5), 40-1-40-4, 2003.

  11. Local electron mean energy profile of positive primary streamer discharge with pin-plate electrodes in oxygen—nitrogen mixtures

    International Nuclear Information System (INIS)

    Sima Wen-Xia; Peng Qing-Jun; Yang Qing; Yuan Tao; Shi Jian

    2013-01-01

    Local electron mean energy (LEME) has a direct effect on the rates of collisional ionization of molecules and atoms by electrons. Electron-impact ionization plays an important role and is the main process for the production of charged particles in a primary streamer discharge. Detailed research on the LEME profile in a primary streamer discharge is extremely important for a comprehensive understanding of the local physical mechanism of a streamer. In this study, the LEME profile of the primary streamer discharge in oxygen-nitrogen mixtures with a pin-plate gap of 0.5 cm under an impulse voltage is investigated using a fluid model. The fluid model includes the electron mean energy density equation, as well as continuity equations for electrons and ions and Poisson's electric field equation. The study finds that, except in the initial stage of the primary streamer, the LEME in the primary streamer tip tends to increase as the oxygen-nitrogen mole ratio increases and the pressure decreases. When the primary streamer bridges the gap, the LEME in the primary streamer channel is smaller than the first ionization energies of oxygen and nitrogen. The LEME in the primary streamer channel then decreases as the oxygen-nitrogen mole ratio increases and the pressure increases. The LEME in the primary streamer tip is primarily dependent on the reduced electric field with mole ratios of oxygen-nitrogen given in the oxygen-nitrogen mixtures. (physics of gases, plasmas, and electric discharges)

  12. Fractal multiplication of electron avalanches and streamers: new mechanism of electrical breakdown?

    International Nuclear Information System (INIS)

    Ficker, T

    2007-01-01

    Long-lasting problems concerning peculiar statistical behaviour of high populated electron avalanches have been analysed. These avalanches are precursors of streamer breakdown in gases. The present streamer theory fails in explaining severe systematic deviations from the Furry statistics that is believed to be a governing statistical law. Such a deviated behaviour of high populated avalanches seems to be a consequence of a special pre-breakdown mechanism that is rather different from that known so far in discharge physics. This analysis tends towards formulating a modified theoretical concept supplementing the streamer theory by a new statistical view of pre-streamer states. The correctness of the concept is corroborated by a series of experiments

  13. Computational Studies of Positive and Negative Streamers in Bubbles Suspended in Distilled Water

    KAUST Repository

    Sharma, Ashish; Levko, Dmitry; Raja, Laxminarayan L.

    2017-01-01

    We perform computational studies of nanosecond streamers generated in helium bubbles immersed in distilled water under high pressure conditions. The model takes into account the presence of water vapor in the gas bubble for an accurate description

  14. Application of multi-source waveform inversion to marine streamer data using the global correlation norm

    KAUST Repository

    Choi, Yun Seok; Alkhalifah, Tariq Ali

    2012-01-01

    Conventional multi-source waveform inversion using an objective function based on the least-square misfit cannot be applied to marine streamer acquisition data because of inconsistent acquisition geometries between observed and modelled data

  15. Multi-source waveform inversion of marine streamer data using the normalized wavefield

    KAUST Repository

    Choi, Yun Seok; Alkhalifah, Tariq Ali

    2012-01-01

    Even though the encoded multi-source approach dramatically reduces the computational cost of waveform inversion, it is generally not applicable to marine streamer data. This is because the simultaneous-sources modeled data cannot be muted to comply

  16. Particle-in-cell modeling of streamer branching in CO2 gas

    KAUST Repository

    Levko, Dmitry; Pachuilo, Michael; Raja, Laxminarayan L

    2017-01-01

    The mechanism of streamer branching remains one of the unsolved problems of low-temperature plasma physics. The understanding of this phenomenon requires very high-fidelity models that include, for instance, the kinetic description of electrons

  17. Auroral streamers: characteristics of associated precipitation,convection and field-aligned currents

    Directory of Open Access Journals (Sweden)

    V. A. Sergeev

    2004-01-01

    Full Text Available During the long-duration steady convection activity on 11 December 1998, the development of a few dozen auroral streamers was monitored by Polar UVI instrument in the dark northern nightside ionosphere. On many occasions the DMSP spacecraft crossed the streamer-conjugate regions over the sunlit southern auroral oval, permitting the investigation of the characteristics of ion and electron precipitation, ionospheric convection and field-aligned currents associated with the streamers. We confirm the conjugacy of streamer-associated precipitation, as well as their association with ionospheric plasma streams having a substantial equatorward convection component. The observations display two basic types of streamer-associated precipitation. In its polewardmost half, the streamer-associated (field-aligned accelerated electron precipitation coincides with the strong (≥2–7μA/m2 upward field-aligned currents on the westward flank of the convection stream, sometimes accompanied by enhanced proton precipitation in the adjacent region. In the equatorward portion of the streamer, the enhanced precipitation includes both electrons and protons, often without indication of field-aligned acceleration. Most of these characteristics are consistent with the model describing the generation of the streamer by the narrow plasma bubbles (bursty bulk flows which are contained on dipolarized field lines in the plasma sheet, although the mapping is strongly distorted which makes it difficult to quantitatively interprete the ionospheric image. The convective streams in the ionosphere, when well-resolved, had the maximal convection speeds ∼0.5–1km/s, total field-aligned currents of a few tenths of MA, thicknesses of a few hundreds km and a potential drop of a few kV across the stream. However, this might represent only a small part of the associated flux transport in the equatorial plasma sheet.

    Key words. Ionosphere (electric fiels and

  18. Application of CA and NN for event recognition in experiments DISTO and STREAMER

    International Nuclear Information System (INIS)

    Bussa, M.P.; Ivanov, V.V.; Kisel, I.V.; Pontecorvo, G.B.

    1997-01-01

    An algorithm for charged particle recognition and event identification applying a cellular automaton (CA) model and a multi-layer neural network (NN) has been developed for the DISTO experiment under way at Saturne (Saclay, France). A further development of the model will be applied for particle recognition in the Dubna Streamer Chamber Spectrometer (DSCS) for studying pion-nucleus absorption (experiments DISTO and STREAMER). (orig.)

  19. Method of detection of transition radiation by wire chambers operating in self-quenching streamer mode

    International Nuclear Information System (INIS)

    Akopdzhanov, G.A.; Bityukov, S.I.; Dzhelyadin, R.I.; Zaitsev, A.M.; Lapin, V.V.; Saraikin, A.I.

    1984-01-01

    A method for detecting X-ray transition radiation against the background of the signal from relativistic charged particles is suggested that is based on the use of peculiarities of the development of self-queenching streamer mode. The self-qunching streamer discharge in the Xe + isobutane mixture is experimentally registered. The effect of separation of signals from the relativistic particle and from soft X-ray, is obtained

  20. Influence of Auroral Streamers on Rapid Evolution of Ionospheric SAPS Flows

    Science.gov (United States)

    Gallardo-Lacourt, Bea; Nishimura, Y.; Lyons, L. R.; Mishin, E. V.; Ruohoniemi, J. M.; Donovan, E. F.; Angelopoulos, V.; Nishitani, N.

    2017-12-01

    Subauroral polarization streams (SAPS) often show large, rapid enhancements above their slowly varying component. We present simultaneous observations from ground-based all-sky imagers and flows from the Super Dual Auroral Radar Network radars to investigate the relationship between auroral phenomena and flow enhancement. We first identified auroral streamers approaching the equatorward boundary of the auroral oval to examine how often the subauroral flow increased. We also performed the reverse query starting with subauroral flow enhancements and then evaluated the auroral conditions. In the forward study, 98% of the streamers approaching the equatorward boundary were associated with SAPS flow enhancements reaching 700 m/s and typically hundreds of m/s above background speeds. The reverse study reveals that flow enhancements associated with streamers (60%) and enhanced larger-scale convection (37%) contribute to SAPS flow enhancements. The strong correlation of auroral streamers with rapid evolution (approximately minutes) of SAPS flows suggests that transient fast earthward plasma sheet flows can often lead to westward SAPS flow enhancements in the subauroral region and that such enhancements are far more common than only during substorms because of the much more frequent occurrences of streamers under various geomagnetic conditions. We also found a strong correlation between flow duration and streamer duration and a weak correlation between SAPS flow velocity and streamer intensity. This result suggests that intense flow bursts in the plasma sheet (which correlate with intense streamers) are associated with intense SAPS ionospheric flows perhaps by enhancing the ring current pressure and localized pressure gradients when they are able to penetrate close enough to Earth.

  1. A streamer tube detector for operation at high rates in the CPLEAR experiment at CERN

    International Nuclear Information System (INIS)

    Bennet, J.M.; Carroll, M.; Cawley, E.L.; Dodgson, M.; Fry, J.R.; Gabathuler, E.; Gamet, R.; Harrison, P.; Harrison, P.F.; Haselden, A.R.; Hayman, P.J.; King, D.; Maley, P.D.; Sacks, L.E.; Sanders, P.M.

    1996-01-01

    The design and instrumentation of a streamer tube detector for operation in the high rate environment of the CPLEAR experiment at CERN is described. A study of gas mixtures for use in the streamer tube is discussed. The final mixture of 46% argon, 50% isobutane, 4% methylal and 0.01% freon produces an axial resolution of 1.5 cm with an efficiency of 98% per layer. (orig.)

  2. Streamer Motives and User-Generated Content on Social Live-Streaming Services

    OpenAIRE

    Friedlander, Mathilde B.

    2017-01-01

    Three most popular information services, Periscope, Ustream, and YouNow, vicarious for all Social Live-Streaming Services (SLSSs), are investigated to analyze their streamers' motivations and the user-generated content. Additionally, we collected demographic data (gender and age). More than 7,500 streams by users from the U.S., Germany, and Japan were observed. Main streamer motivations on SLSSs are boredom, socializing, the need to reach a specific group, the need to communicate, and fun. Im...

  3. Preparation of water-soluble carbon nanotubes using a pulsed streamer discharge in water

    International Nuclear Information System (INIS)

    Imasaka, Kiminobu; Suehiro, Junya; Kanatake, Yusuke; Kato, Yuki; Hara, Masanori

    2006-01-01

    A novel technique for the preparation of water-soluble carbon nanotubes was demonstrated using a pulsed streamer discharge generated in water. The technique involved chemical reactions between radicals generated by the pulsed streamer discharge and carbon nanotubes. The pulsed streamer-treated carbon nanotubes were homogeneously dispersed and well solubilized in water for a month or longer. The mechanism of solubilization of carbon nanotubes by the pulsed streamer discharge is discussed based on FTIR spectroscopy and optical emission spectra measurements. FTIR spectroscopy revealed that -OH groups, which are known to impart a hydrophilic nature to carbon material, were introduced on the carbon nanotube surface. Optical emission spectra from the pulsed streamer plasma showed that highly oxidative O * and H * radicals were generated in water. These results suggest that the functionalization of the carbon nanotube surface by -OH group can be attributed to the O * and H * radicals. An advantage of the proposed method is that there is no need for any chemical agents or additives for solubilization. Chemical agents for solubilization are generated from the water itself by the electrochemical reactions induced by the pulsed streamer discharge

  4. Spectral analysis of the light emitted from streamers in chlorinated alkane and alkene liquids

    International Nuclear Information System (INIS)

    Ingebrigtsen, S; Bonifaci, N; Denat, A; Lesaint, O

    2008-01-01

    We have studied the time-averaged optical emission from fast positive and negative non-breakdown streamers under pulsed divergent field conditions in five chlorocarbon liquids, namely, dichloromethane, 1,2-dichloroethane, tetrachloromethane, trichloroethene and tetrachloroethene. We have accumulated light emitted from the first 10-15 μm trail of a few thousand streamers. We have also briefly studied single breakdown arcs in tetrachloromethane. Atomic lines of hydrogen, chlorine and carbon as well as excited states of C 2 radicals (Swan bands) have been observed, with sufficient resolution for evaluating line and band-shapes. The characteristic broadening, shift and asymmetry of atomic lines varied significantly between the liquids. Differences between the two streamer polarities were comparatively small. Densities of electrons and neutrals in the illuminated phase have been deduced from broadening of atomic lines, atomic excitation temperatures from absolute line intensities and rotational and vibrational temperatures from the Swan bands. The gas densities of the propagating streamers were generally very high (∼10% of critical) and with a high degree of ionization (∼1 per mille ). Dichloromethane and 1,2-dichloroethane produced re-illuminating streamers with densities close to atmospheric conditions, in agreement with a rapid pressure relaxation. Rotational temperatures were high and in the range 2 x 10 3 -6 x 10 3 K for the different liquids. Results can be interpreted to suggest a partial local thermodynamic equilibrium in the streamer plasmas.

  5. Computational Studies of Positive and Negative Streamers in Bubbles Suspended in Distilled Water

    KAUST Repository

    Sharma, Ashish

    2017-01-05

    We perform computational studies of nanosecond streamers generated in helium bubbles immersed in distilled water under high pressure conditions. The model takes into account the presence of water vapor in the gas bubble for an accurate description of the chemical kinetics of the discharge. We apply positive and negative trigger voltages much higher than the breakdown voltage and study the dynamic characteristics of the resulting discharge. We observe that, for high positive trigger voltages, the streamer moves along the surface of the gas bubble during the initial stages of the discharge. We also find a considerable difference in the evolution of the streamer discharge for positive and negative trigger voltages with more uniform volumetric distribution of species in the streamer channel for negative trigger voltages due to formation of multiple streamers. We also observe that the presence of water vapor does not influence the breakdown voltage of the discharge but greatly affects the composition of dominant species in the trail of the streamer channel.

  6. Flow Analysis of a Rising Crude Oil Micro-Droplet Affected by Attached Microbial Streamers

    Science.gov (United States)

    Amaro, Matthew; White, Andrew; Jalali, Maryam; Sheng, Jian

    2017-11-01

    Microfluidic experiments show bacteria flowing past a pinned crude oil droplet produce microbial aggregates and streamers on the oil-water interface. High speed DIC microscopy at 1000 fps for 1 sec with a sampling interval of 10 min captures the evolving flow and bacterial motility as well as adhesion, aggregation and streamer events. With bacteria as tracers, velocity measurements are acquired with in-house PIV-assisted PTV software. Flow fields with spatial resolution 2.5 μm are measured around an O(100) μm drop in a 700 ×700 μm window. Full budgets of the 2D Navier-Stokes equation are faithfully resolved to determine pressure gradients by performing the balance over a control volume enclosing the droplet. Pressure gradients are integrated over the border of the control region to obtain pressure profiles at the leading and trailing edges. A momentum balance can be used to determine the drag induced by the drop and any attached streamers. Cases with and without streamers and their differing flow features are presented. Additionally streamers produce nonzero curl in the pressure gradient field providing a tool for identifying the position of otherwise invisible streamers. Ongoing experiments and future applications of the tools presented here will be discussed. Funded by GoMRI, NSF, ARO.

  7. An Atlantic streamer in stratospheric ozone observations and SD-WACCM simulation data

    Science.gov (United States)

    Hocke, Klemens; Schranz, Franziska; Maillard Barras, Eliane; Moreira, Lorena; Kämpfer, Niklaus

    2017-03-01

    Observation and simulation of individual ozone streamers are important for the description and understanding of non-linear transport processes in the middle atmosphere. A sudden increase in mid-stratospheric ozone occurred above central Europe on 4 December 2015. The GROund-based Millimeter-wave Ozone Spectrometer (GROMOS) and the Stratospheric Ozone MOnitoring RAdiometer (SOMORA) in Switzerland measured an ozone enhancement of about 30 % at 34 km altitude (8.3 hPa) from 1 to 4 December. A similar ozone increase is simulated by the Specified Dynamics Whole Atmosphere Community Climate (SD-WACCM) model. Further, the global ozone fields at 34 km altitude (8.3 hPa) from SD-WACCM and the satellite experiment Aura/MLS show a remarkable agreement for the location and timing of an ozone streamer (large-scale tongue-like structure) extending from the subtropics in northern America over the Atlantic to central Europe. This agreement indicates that SD-WACCM can inform us about the wind inside the Atlantic ozone streamer. SD-WACCM shows an eastward wind of about 100 m s-1 inside the Atlantic streamer in the mid-stratosphere. SD-WACCM shows that the Atlantic streamer flows along the edge of the polar vortex. The Atlantic streamer turns southward at an erosion region of the polar vortex located above the Caspian Sea. The spatial distribution of stratospheric water vapour indicates a filament outgoing from this erosion region. The Atlantic streamer, the polar vortex erosion region and the water vapour filament belong to the process of planetary wave breaking in the so-called surf zone of the northern midlatitude winter stratosphere.

  8. Properties of self-quenching streamer (SQS) tubes

    International Nuclear Information System (INIS)

    Koori, N.; Nohtomi, A.; Hashimoto, M.; Yoshioka, K.; Kumabe, I.

    1989-01-01

    The self-quenching streamer (SQS) mode of gas counters have been widely used for measuring high energy particles. The authors have very recently found that all the rare gas (He, Ne, Ar and Xe) mixtures with quenching gas of CH 4 , C 2 H 6 , C 3 H 8 , iso-C 4 H 10 or CO 2 can be used as gas mixtures for the SQS mode except Ne- and He-mixtures with CH 4 or CO 2 . Further studies on the properties of this mode are needed for its application to monitoring devices. Properties of a self-quenching tube are discussed here from this point of view. Gas multiplication properties, pulse shape of current signals, and dead zone are measured under several gas pressures equal to or less than one atomospheric pressure. Either the SQS or GM mode can be obtained by changing the gas pressure with a cylindrical gas counter. The operation mode of the counter may be correctly determined from the dead zone measurement. The measurements show that the SQS and GM modes are exclusive, even though SQS's can be simultaneously formed with a GM discharge. The counting rate capability of the SQS mode is higher than that of the GM mode by about one order of magnitude. Thus, SQS tubes are suitable for use in high flux radiation fields. (N.K.)

  9. Rare-gas dependence of the self-quenching streamer

    International Nuclear Information System (INIS)

    Yoshioka, K.; Hashimoto, M.; Koori, N.; Kumabe, I.; Ohgaki, H.; Matoba, M.

    1989-01-01

    The self-quenching streamer (SQS) mode is understood these days as one of the basic modes of gas counter operation. In the present work, the SQS transition is clearly observed for Ar-, Kr- and Xe-mixtures with CH 4 , C 2 H 6 , C 3 H 8 , isoC 4 H 10 and CO 2 , and for He- and Ne-mixtures with C 2 H 6 , C 3 H 8 and isoC 4 H 10 . For He- and Ne-mixtures with CH 4 or CO 2 , the GM discharge is developed instead of the SQS transition. The avalanche size at the transition voltage decreases, in the order of He-, Ne-, Ar-, Kr- and Xe-mixtures, except for He-mixtures with CH 4 or CO 2 . The mechanisms of the SQS transition proposed by Atac et al. and Zhang have disadvantages in explaining all these results. If the photo-ionization is assumed as in Atac's mechanism, energetic photons whose yield is sufficiently large are needed for the SQS transition. The interaction between metastable states of rare gases proposed by Zhang may be energetically capable of producing electrons for the transition; effects of quenching gas in mixtures cannot be explained by this mechanism. Further investigation is necessary for microscopic processes occurring in the avalanche development. More detailed information is required on the atomic reaction cross sections of photo-ionization, radiative recombination, etc. (N.K.)

  10. Leaders of the profession and 'professional' leaders

    DEFF Research Database (Denmark)

    Bøje, Jakob Ditlev; Frederiksen, Lars Frode

    of the professional complex according to a Parsonian perspective) and a more distinct leader identity associated with business, management, and accountancy. We will attempt to go beyond some of the manifest expectations of school leaders, including expectations of their training programmes, and show how being...

  11. Jesus the Strategic Leader

    National Research Council Canada - National Science Library

    Martin, Gregg

    2000-01-01

    Jesus was a great strategic leader who changed the world in many ways. Close study of what he did and how he did it reveals a pattern of behavior that is extremely useful and relevant to the modern strategic leader...

  12. Developing Global Transformational Leaders

    DEFF Research Database (Denmark)

    Ramsey, Jase R.; Rutti, Raina M.; Lorenz, Melanie P.

    2016-01-01

    Despite significant increases in training and development of global managers, little is known about the precursors of transformational leadership in Multilatinas. While prior cross-cultural literature suggests that being an autocratic leader is ideal in Multilatinas, using transformational...... leadership theory, we argue that global leaders of Multilatinas embrace a more humanistic approach to leadership because of the importance of relationships between leaders and their followers. Additionally, we argue that global leaders with high levels of cultural intelligence will have high levels...

  13. Multi-source waveform inversion of marine streamer data using the normalized wavefield

    KAUST Repository

    Choi, Yun Seok

    2012-01-01

    Even though the encoded multi-source approach dramatically reduces the computational cost of waveform inversion, it is generally not applicable to marine streamer data. This is because the simultaneous-sources modeled data cannot be muted to comply with the configuration of the marine streamer data, which causes differences in the number of stacked-traces, or energy levels, between the modeled and observed data. Since the conventional L2 norm does not account for the difference in energy levels, multi-source inversion based on the conventional L2 norm does not work for marine streamer data. In this study, we propose the L2, approximated L2, and L1 norm using the normalized wavefields for the multi-source waveform inversion of marine streamer data. Since the normalized wavefields mitigate the different energy levels between the observed and modeled wavefields, the multi-source waveform inversion using the normalized wavefields can be applied to marine streamer data. We obtain the gradient of the objective functions using the back-propagation algorithm. To conclude, the gradient of the L2 norm using the normalized wavefields is exactly the same as that of the global correlation norm. In the numerical examples, the new objective functions using the normalized wavefields generate successful results whereas conventional L2 norm does not.

  14. Electron densities and energies of a guided argon streamer in argon and air environments

    International Nuclear Information System (INIS)

    Hübner, S; Hofmann, S; Van Veldhuizen, E M; Bruggeman, P J

    2013-01-01

    In this study we report the temporally and spatially resolved electron densities and mean energies of a guided argon streamer in ambient argon and air obtained by Thomson laser scattering. The plasma is driven by a positive monopolar 3.5 kV pulse, with a pulse width of 500 ns and a frequency of 5 kHz which is synchronized with the high repetition rate laser system. This configuration enables us to use the spatial and temporal stability of the guided streamer to accumulate a multitude of laser/plasma shots by a triple grating spectrometer equipped with an ICCD camera and to determine the electron parameters. We found a strong initial n e -overshoot with a maximum of 7 × 10 19  m −3 and a mean electron energy of 4.5 eV. This maximum is followed by a fast decay toward the streamer channel. Moreover, a 2D distribution of the electron density is obtained which exhibits a peculiar mushroom-like shape of the streamer head with a diameter significantly larger than that of the emission profile. A correlation of the width of the streamer head with the expected pre-ionization channel is found. (paper)

  15. Numerical simulation for production of O and N radicals in an atmospheric-pressure streamer discharge

    International Nuclear Information System (INIS)

    Komuro, Atsushi; Ono, Ryo; Oda, Tetsuji

    2012-01-01

    A streamer discharge model is developed to analyse the characteristics of a pulsed positive streamer discharge in point-to-plane electrodes filled with oxygen-nitrogen mixed gas at room temperature and atmospheric pressure. In this paper we study the mechanisms of O and N radical production in an atmospheric-pressure streamer discharge. To confirm the validity of the simulation model, the discharge emission of light and the discharge current are compared with experimental data at several voltages in gas mixtures with 2-20% oxygen concentrations. The calculated streak picture and the axial distribution of streamer luminous intensity are in good agreement with our previous experimental results. After demonstrating the reliability of the model, we performed a numerical study on radical production by the streamer discharge. The experimentally obtained axial distributions of oxygen radical production in O 2 (20%)/N 2 and nitrogen radical production in O 2 (2%)/N 2 are successfully reproduced in our simulation. For the production of nitrogen radicals, two-step dissociation through the vibrationally excited states is predominant. (paper)

  16. Elementary Mathematics Leaders

    Science.gov (United States)

    Fennell, Francis; Kobett, Beth McCord; Wray, Jonathan A.

    2013-01-01

    Elementary school mathematics leaders often come to the realization that their position, however titled and determined, although dedicated to addressing needs in math teaching and learning, also entails and directly involves leadership. Elementary school math specialists/instructional leaders (referenced here as elementary mathematics leaders, or…

  17. Aliasing of the Schumann resonance background signal by sprite-associated Q-bursts

    Science.gov (United States)

    Guha, Anirban; Williams, Earle; Boldi, Robert; Sátori, Gabriella; Nagy, Tamás; Bór, József; Montanyà, Joan; Ortega, Pascal

    2017-12-01

    The Earth's naturally occurring Schumann resonances (SR) are composed of a quasi-continuous background component and a larger-amplitude, short-duration transient component, otherwise called 'Q-burst' (Ogawa et al., 1967). Sprites in the mesosphere are also known to accompany the energetic positive ground flashes that launch the Q-bursts (Boccippio et al., 1995). Spectra of the background Schumann Resonances (SR) require a natural stabilization period of ∼10-12 min for the three conspicuous modal parameters to be derived from Lorentzian fitting. Before the spectra are computed and the fitting process is initiated, the raw time series data need to be properly filtered for local cultural noise, narrow band interference as well as for large transients in the form of global Q-bursts. Mushtak and Williams (2009) describe an effective technique called Isolated Lorentzian (I-LOR), in which, the contributions from local cultural and various other noises are minimized to a great extent. An automated technique based on median filtering of time series data has been developed. These special lightning flashes are known to have greater contribution in the ELF range (below 1 kHz) compared to general negative CG strikes (Huang et al., 1999; Cummer et al., 2006). The global distributions of these Q-bursts have been studied by Huang et al. (1999) Rhode Island, USA by wave impedance methods from single station ELF measurements at Rhode Island, USA and from Japan Hobara et al. (2006). The present work aims to demonstrate the effect of Q-bursts on SR background spectra using GPS time-stamped observation of TLEs. It is observed that the Q-bursts selected for the present work do alias the background spectra over a 5-s period, though the amplitudes of these Q-bursts are far below the background threshold of 16 Core Standard Deviation (CSD) so that they do not strongly alias the background spectra of 10-12 min duration. The examination of one exceptional Q-burst shows that appreciable

  18. The good leader.

    Science.gov (United States)

    Bottles, K

    2001-01-01

    What are the traits of successful leaders and can they be applied to those of us in health care? Leaders must deal with conflict to get a group of people to move in the same direction. Successful leaders learn to have difficult conversations that increase understanding and morale and creatively deal with the inevitable interpersonal conflicts present in every organization made up of people. Another useful trait for a leader during uncertain and chaotic times is the ability to see things as they really are, rather than as we wish or believe them to be. Successful leaders are also usually optimists who level with their co-workers.

  19. Initiation of Positive Streamers near Uncharged Ice Hydrometeors in the Thundercloud Field

    Science.gov (United States)

    Babich, L. P.; Bochkov, E. I.

    2018-05-01

    Since the threshold electric field required for breakdown of air is much higher than the maximum field strength measured in thunderstorm clouds, the problem of lightning initiation still remains unsolved. According to the popular hypothesis, lightning can be initiated by a streamer discharge in the field enhanced near a hydrometeor. To verify the adequacy of this hypothesis, the development of a positive streamer propagating along the thunderstorm electric field in the vicinity of an ice needle at an air pressure corresponding to an altitude of 5 km (which is typical of the lightning initiation conditions) was simulated numerically. The hydrometeor dimensions are determined at which streamers can be initiated at different strengths of the thunderstorm electric field.

  20. Influence of gas mixture and primary ionization on the performance of limit streamer mode tubes

    International Nuclear Information System (INIS)

    An Jigang; Anderson, K.J.; Merritt, F.S.; Oreglia, M.; Pilcher, J.E.; Possoz, A.; Schappert, W.; Chicago Univ., IL

    1988-01-01

    We report a study of the dependence of limited streamer mode operation on gas composition. Results are given for the plateau onset voltage, plateau length, charge versus voltage, charge spectra and pulse width for various fractions of (Ar, CO 2 , pentane) and (Ar, isobutane). In addition, a series of argon-free strong quenching gas mixtures has been studied which have very attractive characteristics. Chamber lifetime tests for these are also reported. As part of a study of the nature of the limited streamer mode mechanism, the response to X-rays and minimum ionizing particles are compared and differences noted. The character of the primary ionization is found to have a clear effect on the chamber response even in the streamer region. (orig.)

  1. Possibilities to improve sensitivity and rendering of detail of streamer chamber track photographs

    Energy Technology Data Exchange (ETDEWEB)

    Baehr, J

    1975-01-01

    Streamer chambers are increasingly used as effective particle detectors in the field of experimental elementary particle physics. The photographic recording of high energy events in streamer chambers is limited by performance of current photographic silver-halide layers. Similar limiting problems occur in other fields as well, e.g., in astronomy, x-ray medicine and photogrammetry; therefore methods have been developed to increase sensitivity and improve the information transfer of the emulsion. In this paper these methods have been classified and summarized under the aspect of their application to streamer image recording. Proposals for further investigations are given. Especially the applicability of these methods, their possibility of combination to large film lengths should be investigated The detective quantum efficiency (DQE) is proposed as criterion to estimate and compare the different methods.

  2. A PIC-MCC code for simulation of streamer propagation in air

    DEFF Research Database (Denmark)

    Chanrion, Olivier Arnaud; Neubert, Torsten

    2008-01-01

    A particle code has been developed to study the distribution and acceleration of electrons in electric discharges in air. The code can follow the evolution of a discharge from the initial stage of a single free electron in a background electric field to the formation of an electron avalanche...... and its transition into a streamer. The code is in 2D axi-symmetric coordinates, allowing quasi 3D simulations during the initial stages of streamer formation. This is important for realistic simulations of problems where space charge fields are essential such as in streamer formation. The charged...... particles are followed in a Cartesian mesh and the electric field is updated with Poisson's equation from the charged particle densities. Collisional processes between electrons and air molecules are simulated with a Monte Carlo technique, according to cross section probabilities. The code also includes...

  3. Simulation of subnanosecond streamers in atmospheric-pressure air: Effects of polarity of applied voltage pulse

    Energy Technology Data Exchange (ETDEWEB)

    Babaeva, N. Yu.; Naidis, G. V. [Joint Institute for High Temperatures, Russian Academy of Sciences, Moscow 125412 (Russian Federation)

    2016-08-15

    Results of simulation of subnanosecond streamer propagation in corona gap configuration, obtained in the framework of 2D fluid model, are presented. Effects related with the polarity of a voltage pulse applied to the stressed electrode are discussed. It is argued that these effects (dependence of the discharge current and propagation velocity on the polarity of applied voltage) observed in experiments can be attributed to the difference in initial (preceding the streamer formation) distributions of charged species inside the gap. This difference can be caused by preionization (at negative polarity) of the gas inside the discharge gap by runaway electrons. Calculated streamers have large widths (up to 1 cm) and move with velocities in the range of 10{sup 9}–10{sup 10 }cm s{sup −1}, similar to experimental data.

  4. Studies of the stability and sistematics of operation of the DELPHI plastic streamer tubes

    International Nuclear Information System (INIS)

    Alekseev, G.D.; Bilenky, M.S.; Bonyushkin, Yu.Ye.; Korrytov, A.V.

    1989-01-01

    The influeNce of gas pressure and temperature, slight changes in a gas mixture, self-sustaining discharge, aging, different deviations in the detector geometry on the operation of the DELPHI plastic streamer tubes is studied. The contribution of these factors to the DELPHI hadron calorimeter energy resolution is estimated. The major influence is found to be due to atmospheric pressure fluctuations (∼ ±1% streamer charge change per ±1 Torr). The question of the choice of a gas mixture is studied as well. Maximal streamer charge is shown to be independent of component concentrations in the Ar:CO 2 :i-C 4 H 10 ) or C 5 H 12 ) gas mixtures. 23 refs.; 21 figs.; 1 tab

  5. MHD Simulations of the Eruption of Coronal Flux Ropes under Coronal Streamers

    Energy Technology Data Exchange (ETDEWEB)

    Fan, Yuhong, E-mail: yfan@ucar.edu [High Altitude Observatory, National Center for Atmospheric Research, 3080 Center Green Drive, Boulder, CO 80301 (United States)

    2017-07-20

    Using three-dimensional magnetohydrodynamic (MHD) simulations, we investigate the eruption of coronal flux ropes underlying coronal streamers and the development of a prominence eruption. We initialize a quasi-steady solution of a coronal helmet streamer, into which we impose at the lower boundary the slow emergence of a part of a twisted magnetic torus. As a result, a quasi-equilibrium flux rope is built up under the streamer. With varying streamer sizes and different lengths and total twists of the flux rope that emerges, we found different scenarios for the evolution from quasi-equilibrium to eruption. In the cases with a broad streamer, the flux rope remains well confined until there is sufficient twist such that it first develops the kink instability and evolves through a sequence of kinked, confined states with increasing height until it eventually develops a “hernia-like” ejective eruption. For significantly twisted flux ropes, prominence condensations form in the dips of the twisted field lines due to runaway radiative cooling. Once formed, the prominence-carrying field becomes significantly non-force-free due to the weight of the prominence, despite having low plasma β . As the flux rope erupts, the prominence erupts, showing substantial draining along the legs of the erupting flux rope. The prominence may not show a kinked morphology even though the flux rope becomes kinked. On the other hand, in the case with a narrow streamer, the flux rope with less than one wind of twist can erupt via the onset of the torus instability.

  6. Time characteristics of a self quenching streamer in the coexistence region

    International Nuclear Information System (INIS)

    Han Jiaxiang; Li Cheng; Xu Zizong; Chen Honfang

    1994-01-01

    Experimental studies on the time correlation between electrical signals in the primary avalanche and optical signals which are emitted in the avalanches of the limited proportional mode and the self quenching streamer (SQS) mode have demonstrated that there exists a weak optical emission which is almost simultaneous with the limited proportional avalanche, that a streamer pulse in the SQS mode has a few nanoseconds delay relative to the primary avalanche, and that the spread of the delay (FWHM) is also a few nanoseconds. ((orig.))

  7. The differences between storms driven by helmet streamer CIRs and storms driven by pseudostreamer CIRs

    OpenAIRE

    Borovsky, Joseph E.; Denton, Michael

    2013-01-01

    A corotating interaction region (CIR) is formed when fast coronal hole origin solar wind overtakes slow solar wind and forms a region of compressed plasma and magnetic field. The slow wind upstream of the coronal hole fast wind can be either of helmet streamer origin or pseudostreamer origin. For a collection of 125 CIR-driven geomagnetic storms, the slow wind ahead of each CIR is examined; for those storm not containing ejecta, each CIR is categorized as a helmet streamer CIR (74 of the 125 ...

  8. Some properties of the streamer tube system of the charm neutrino detector

    International Nuclear Information System (INIS)

    Bergsma, F.; Dorenbosch, J.; Jonker, M.

    1982-01-01

    The fine-grain and low-density neutrino calorimeter of the CHARM Collaboration has been designed to measure the energy and the direction of particle showers. To further improve the spatial resolution the calorimeter has been upgraded by adding 20,000 aluminium tubes, working in the limited streamer mode. Each subunit is now equipped with crossed wire planes. Results of a new energy calibration of the upgraded detector using electron and pion beams from 5 to 140 GeV/c, and on the angular and spatial resolution are presented. The use of the streamer tube system to discriminate between electromagnetic and hadronic showers is discussed

  9. High-voltage test and training of plastic streamer tubes for the DELPHI hadron calorimeter

    International Nuclear Information System (INIS)

    Alekseev, G.D.; Cellar, S.; Khomenko, B.A.; Korytov, A.V.; Kulinich, P.A.; Micelmacher, G.V.; Sedykh, Yu.V.; Toledo, R.

    1987-01-01

    The results of high-voltage test and training of plastic streamer tubes of the DELPHI hadron calorimeter are presented. The testing technique is considered in detail. The equipment for high-voltage training consists of a mini-computer, CAMAC-electronics, a controllable high-voltage supply and a digital ampermeter. The experimental results shows that high-voltage training of streamer tubes improves their characteristics. The value of dark current decreased up to 1 μA. The operational voltage range increased by a value more than 300 V

  10. Authenticating the Leader

    DEFF Research Database (Denmark)

    Garmann Johnsen, Christian

    2018-01-01

    In the wake of a series of corporate scandals, there has been a growing call for authentic leadership in order to ensure ethical conduct in contemporary organizations. Authentic leadership, however, depends upon the ability to draw a distinction between the authentic and inauthentic leader......’s inverted Platonism, the paper challenges the practice by which authentic leaders are distinguished from inauthentic leaders. In conclusion, the paper suggests that an adequate concept of authentic leadership should consider how ethics can occur when the authentic leader is able to critically reflect his...

  11. Electrons in the solar corona. Pt. 3. Coronal streamers analysis from balloon-borne coronagraph

    Energy Technology Data Exchange (ETDEWEB)

    Dollfus, A; Mouradian, Z [Observatoire de Paris, Section de Meudon, 92 (France)

    1981-03-01

    During a balloon flight in France on September 13, 1971, at altitude 32 000 m, the solar corona was cinematographed from 2 to 5 Rsub(sun) during 5 hr, with an externally occulted coronagraph. Motions in coronal features, when they occur, exhibit deformations of structures with velocities not exceeding a few 10 km s/sup -1/; several streamers were often involved simultaneously; these variations are compatible with magnetic changes or sudden reorganizations of lines of forces. Intensity and polarization measurements give the electron density with height in the quiet corona above the equator. Electron density gradient for one of the streamers gives a temperature of 1.6 x 10/sup 6/ K and comparisons with the on-board Apollo 16 coronal observation of 31 July, 1971 are compatible with the extension of this temperature up to 25 Rsub(sun). Three-dimensional structures and localizations of the streamers are deduced from combined photometry, polarimetry and ground-based K coronametry. Three of the four coronal streamers analysed have their axis bent with height towards the direction of the solar rotation, as if the upper corona has a rotation slightly faster than the chromosphere.

  12. Numerical simulations and conformal analysis of growing and branching negative discharge streamers

    NARCIS (Netherlands)

    Montijn, C.; Meulenbroek, B.; Ebert, U.; Hundsdorfer, W.

    2005-01-01

    The dynamics of an anode-directed streamer can be described by advection-diffusion equations for the charged particles, including a local field-dependent impact ionization term, and coupled to the Poisson equation for the electric field. We present the results of new simulations that use a local

  13. Spatially hybrid computations for streamer discharges with generic features of pulled fronts: I. Planar fronts

    NARCIS (Netherlands)

    C. Li (Chao); U. M. Ebert (Ute); W. Hundsdorfer (Willem)

    2010-01-01

    textabstractStreamers are the first stage of sparks and lightning; they grow due to a strongly enhanced electric field at their tips: this field is created by a thin curved space charge layer. These multiple scales are already challenging when the electrons are approximated by densities. However,

  14. Experimental Investigation of Pulsed Nanosecond Streamer Discharges for CO2 Reforming

    Science.gov (United States)

    Pachuilo, Michael; Levko, Dima; Raja, Laxminarayan; Varghese, Philip

    2016-09-01

    Rapid global industrialization has led to an increase in atmospheric greenhouse gases, specifically carbon dioxide levels. Plasmas present a great potential for efficient reforming of greenhouse gases. There are several plasma discharges which have been reported for reforming process: dielectric barrier discharges (DBD), microwave discharges, and glide-arcs. Microwave discharges have CO2 conversion energy efficiency of up to 40% at atmospheric conditions, while glide-arcs have 43% and DBD 2-10%. In our study, we analyze a single nanosecond pulsed cathode directed streamer discharge in CO2 at atmospheric pressure and temperature. We have conducted time resolved imaging with spectral bandpass filters of a streamer discharge with an applied negative polarity pulse. The image sequences have been correlated to the applied voltage and current pulses. From the spectral filters we can determine where spatially and temporally excited species are formed. In this talk we report on spectroscopic studies of the discharge and estimate plasma properties such as temperature and density of excited species and electrons. Furthermore, we report on the effects of pulse polarity as well as anodic streamer discharges on the CO2 conversion efficiency. Finally, we will focus on the effects of vibrational excitation on carbon dioxide reforming efficiency for streamer discharges. Our experimental results will be compared with an accompanying plasma computational model studies.

  15. Numerical simulation of positive streamer development in thundercloud field enhanced near raindrops

    DEFF Research Database (Denmark)

    Babich, L. P.; Bochkov, E. I.; Kutsyk, I. M.

    2016-01-01

    As the threshold field strength for the breakdown in air significantly exceeds the maximum measured thundercloud strength 3 kV/cm/atm, the problem of lightning initiation remains unclear. According to the popular idea, lightning can be initiated from streamer discharges developed in the enhanced...

  16. Pseudo-spectral 3D simulations of streamers with adaptively refined grids

    NARCIS (Netherlands)

    Luque, A.; Ebert, U.; Montijn, C.; Hundsdorfer, W.; Schmidt, J.; Simek, M.; Pekarek, S.; Prukner, V.

    2007-01-01

    A three-dimensional code for the simulation of streamers is introduced. The code is based on a fluid model for oxygen-nitrogen mixtures that includes drift, diffusion and attachement of electrons and creation of new charge carriers through impact ionization and photo-ionization. The electric field

  17. Simulating streamer discharges in 3D with the parallel adaptive Afivo framework

    NARCIS (Netherlands)

    H.J. Teunissen (Jannis); U. M. Ebert (Ute)

    2017-01-01

    htmlabstractWe present an open-source plasma fluid code for 2D, cylindrical and 3D simulations of streamer discharges, based on the Afivo framework that features adaptive mesh refinement, geometric multigrid methods for Poisson's equation, and OpenMP parallelism. We describe the numerical

  18. TEMPERATURE AND EXTREME-ULTRAVIOLET INTENSITY IN A CORONAL PROMINENCE CAVITY AND STREAMER

    Energy Technology Data Exchange (ETDEWEB)

    Kucera, T. A. [NASA/GSFC, Code 671, Greenbelt, MD 20771 (United States); Gibson, S. E.; Schmit, D. J. [HAO/NCAR, P.O. Box 3000, Boulder, CO 80307-3000 (United States); Landi, E. [Department of Atmospheric, Oceanic and Space Science, Space Research Building, University of Michigan, 2455 Hayward St., Ann Arbor, MI 48109-2143 (United States); Tripathi, D. [Inter-University Centre for Astronomy and Astrophysics, Post Bag-4, Ganeshkhind, Pune University Campus, Pune 411 007 (India)

    2012-09-20

    We analyze the temperature and EUV line emission of a coronal cavity and surrounding streamer in terms of a morphological forward model. We use a series of iron line ratios observed with the Hinode Extreme-ultraviolet Imaging Spectrograph (EIS) on 2007 August 9 to constrain temperature as a function of altitude in a morphological forward model of the streamer and cavity. We also compare model predictions to the EIS EUV line intensities and polarized brightness (pB) data from the Mauna Loa Solar Observatory (MLSO) Mark 4 K-coronameter. This work builds on earlier analysis using the same model to determine geometry of and density in the same cavity and streamer. The fit to the data with altitude-dependent temperature profiles indicates that both the streamer and cavity have temperatures in the range 1.4-1.7 MK. However, the cavity exhibits substantial substructure such that the altitude-dependent temperature profile is not sufficient to completely model conditions in the cavity. Coronal prominence cavities are structured by magnetism so clues to this structure are to be found in their plasma properties. These temperature substructures are likely related to structures in the cavity magnetic field. Furthermore, we find that the model overestimates the EUV line intensities by a factor of 4-10, without overestimating pB. We discuss this difference in terms of filling factors and uncertainties in density diagnostics and elemental abundances.

  19. Application of dimensional analysis to ozone production by pulsed streamer discharge in oxygen

    Energy Technology Data Exchange (ETDEWEB)

    Buntat, Z; Harry, J E; Smith, I R [Department of Electronic and Electrical Engineering, Loughborough University, Loughborough, Leicestershire LE11 3TU (United Kingdom)

    2003-07-07

    This paper describes the use of dimensional analysis in investigating the effects of the electrical and the discharge configuration parameters on ozone production in oxygen, by means of a pulsed streamer discharge. Ozone destruction factors are taken into account in the model, and predicted results are shown to be in good agreement with experimental findings.

  20. Loeb's and streamer-based mechanism for negative corona current pulses

    International Nuclear Information System (INIS)

    Vagnerova, L.; Skalny, J.D.; Cermak, M.

    1998-01-01

    The negative point-to-plane corona discharge in electronegative gaseous mixtures is studied experimentally and the basic mechanisms controlling the corona phenomena are discussed. The typical shapes of the current pulse waveforms observed in experiments with the nitrogen-freon mixtures are explained in terms of the theory by Loeb and of the positive-streamer-based model. (J.U.)

  1. Two-dimensional potential and charge distributions of positive surface streamer

    International Nuclear Information System (INIS)

    Tanaka, Daiki; Matsuoka, Shigeyasu; Kumada, Akiko; Hidaka, Kunihiko

    2009-01-01

    Information on the potential and the field profile along a surface discharge is required for quantitatively discussing and clarifying the propagation mechanism. The sensing technique with a Pockels crystal has been developed for directly measuring the potential and electric field distribution on a dielectric material. In this paper, the Pockels sensing system consists of a pulse laser and a CCD camera for measuring the instantaneous two-dimensional potential distribution on a 25.4 mm square area with a 50 μm sampling pitch. The temporal resolution is 3.2 ns which is determined by the pulse width of the laser emission. The transient change in the potential distribution of a positive surface streamer propagating in atmospheric air is measured with this system. The electric field and the charge distributions are also calculated from the measured potential profile. The propagating direction component of the electric field near the tip of the propagating streamer reaches 3 kV mm -1 . When the streamer stops, the potential distribution along a streamer forms an almost linear profile with the distance from the electrode, and its gradient is about 0.5 kV mm -1 .

  2. Application of multi-source waveform inversion to marine streamer data using the global correlation norm

    KAUST Repository

    Choi, Yun Seok

    2012-05-02

    Conventional multi-source waveform inversion using an objective function based on the least-square misfit cannot be applied to marine streamer acquisition data because of inconsistent acquisition geometries between observed and modelled data. To apply the multi-source waveform inversion to marine streamer data, we use the global correlation between observed and modelled data as an alternative objective function. The new residual seismogram derived from the global correlation norm attenuates modelled data not supported by the configuration of observed data and thus, can be applied to multi-source waveform inversion of marine streamer data. We also show that the global correlation norm is theoretically the same as the least-square norm of the normalized wavefield. To efficiently calculate the gradient, our method employs a back-propagation algorithm similar to reverse-time migration based on the adjoint-state of the wave equation. In numerical examples, the multi-source waveform inversion using the global correlation norm results in better inversion results for marine streamer acquisition data than the conventional approach. © 2012 European Association of Geoscientists & Engineers.

  3. Application of dimensional analysis to ozone production by pulsed streamer discharge in oxygen

    CERN Document Server

    Buntat, Z; Smith, I R

    2003-01-01

    This paper describes the use of dimensional analysis in investigating the effects of the electrical and the discharge configuration parameters on ozone production in oxygen, by means of a pulsed streamer discharge. Ozone destruction factors are taken into account in the model, and predicted results are shown to be in good agreement with experimental findings.

  4. Application of dimensional analysis to ozone production by pulsed streamer discharge in oxygen

    International Nuclear Information System (INIS)

    Buntat, Z; Harry, J E; Smith, I R

    2003-01-01

    This paper describes the use of dimensional analysis in investigating the effects of the electrical and the discharge configuration parameters on ozone production in oxygen, by means of a pulsed streamer discharge. Ozone destruction factors are taken into account in the model, and predicted results are shown to be in good agreement with experimental findings

  5. Application of dimensional analysis to ozone production by pulsed streamer discharge in oxygen

    Science.gov (United States)

    Buntat, Z.; Harry, J. E.; Smith, I. R.

    2003-07-01

    This paper describes the use of dimensional analysis in investigating the effects of the electrical and the discharge configuration parameters on ozone production in oxygen, by means of a pulsed streamer discharge. Ozone destruction factors are taken into account in the model, and predicted results are shown to be in good agreement with experimental findings.

  6. Positive streamers in air of varying density : experiments on the scaling of the excitation density

    NARCIS (Netherlands)

    Dubrovin, D.; Nijdam, S.; Clevis, T.T.J.; Heijmans, L.C.J.; Ebert, U.; Yair, Y.; Price, C.

    2015-01-01

    Streamers are rapidly extending ionized finger-like structures that dominate the initial breakdown of large gas volumes in the presence of a sufficiently strong electric field. Their macroscopic parameters are described by simple scaling relations, where the densities of electrons and of excited

  7. Observations of electric discharge streamer propagation and capillary oscillations on the surface of air bubbles in water

    Energy Technology Data Exchange (ETDEWEB)

    Sommers, B S; Foster, J E [Department of Nuclear Engineering and Radiological Science, University of Michigan, Ann Arbor, MI, 48109 (United States); Babaeva, N Yu; Kushner, Mark J [Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, MI, 48109 (United States)

    2011-03-02

    The propagation of electric discharge streamers inside bubbles in liquids is of interest for the remediation of toxins in water and plasma-based surgical instruments. The manner of streamer propagation has an important influence on the production of reactive species that are critical to these applications. Streamer propagation along the surface of electrode-attached bubbles of air in water, previously predicted by numerical simulations, has been experimentally imaged using a fast frame-rate camera. The successive pulsing of the streamer discharge inside the bubbles produced oscillations along the air-water interface. Subsequent streamers were observed to closely follow surface distortions induced by such oscillations. The oscillations likely arise from the non-uniform perturbation of the bubble driven by the electric field of the streamer and were found to be consistent with Kelvin's equation for capillary oscillations. For a narrow range of applied voltage pulse frequencies, the oscillation amplitude increased over several pulse periods indicating, potentially, resonant behaviour. We also observed coupling between bubbles wherein oscillations in a second bubble without an internal discharge were induced by the presence of a streamer in a fixed bubble. (fast track communication)

  8. Radially and temporally resolved electric field of positive streamers in air and modelling of the induced plasma chemistry

    Science.gov (United States)

    Hoder, T.; Šimek, M.; Bonaventura, Z.; Prukner, V.; Gordillo-Vázquez, F. J.

    2016-08-01

    The initial stages of transient luminous events (TLEs) occurring in the upper atmosphere of the Earth are, in a certain pressure range, controlled by the streamer mechanism. This paper presents the results of the first laboratory experiments to study the TLE streamer phenomena under conditions close to those of the upper atmosphere. Spectrally and highly spatiotemporally resolved emissions originating from radiative states {{\\text{N}}2}≤ft({{\\text{C}}3}{{\\Pi}u}\\right) (second positive system) and \\text{N}2+≤ft({{\\text{B}}2}Σu+\\right) (first negative system) have been recorded from the positive streamer discharge. Periodic ionizing events were generated in a barrier discharge arrangement at a pressure of 4 torr of synthetic air, i.e. simulating the pressure conditions at altitudes of ≃37 km. Employing Abel inversion on the radially scanned streamer emission and a 2D fitting procedure, access was obtained to the local spectral signatures within the over 106  m s-1 fast propagating streamers. The reduced electric field strength distribution within the streamer head was determined from the ratio of the \\text{N}2+/{{\\text{N}}2} band intensities with peak values up to 500 Td and overall duration of about 10 ns. The 2D profiles of the streamer head electric fields were used as an experimentally obtained input for kinetic simulations of the streamer-induced air plasma chemistry. The radial and temporal computed distribution of the ground vibrational levels of the radiative states involved in the radiative transitions analyzed (337.1 nm and 391.5 nm), atomic oxygen, nitrogen, nitric oxide and ozone concentrations are vizualized and discussed in comparison with available models of the streamer phase of Blue Jet discharges in the stratosphere.

  9. Preliminary study on the modelling of negative leader discharges

    International Nuclear Information System (INIS)

    Arevalo, L; Cooray, V

    2011-01-01

    Nowadays, there is considerable interest in understanding the physics underlying positive and negative discharges because of the importance of improving lightning protection systems and of coordinating the insulation for high voltages. Numerical simulations of positive switching impulses made in long spark gaps in a laboratory are achievable because the physics of the process is reasonably well understood and because of the availability of powerful computational methods. However, the existing work on the simulation of negative switching discharges has been held up by a lack of experimental data and the absence of a full understanding of the physics involved. In the scientific community, it is well known that most of the lightning discharges that occur in nature are of negative polarity, and because of their complexity, the only way to understand them is to generate the discharges in laboratories under controlled conditions. The voltage impulse waveshape used in laboratories is a negative switching impulse. With the aim of applying the available information to a self-consistent physical method, an electrostatic approximation of the negative leader discharge process is presented here. The simulation procedure takes into consideration the physics of positive and negative discharges, considering that the negative leader propagates towards a grounded electrode and the positive leader towards a rod electrode. The simulation considers the leader channel to be thermodynamic, and assumes that the conditions required to generate a thermal channel are the same for positive and negative leaders. However, the magnitude of the electrical charge necessary to reproduce their propagation and thermalization is different, and both values are based on experimental data. The positive and negative streamer development is based on the constant electric field characteristics of these discharges, as found during experimental measurements made by different authors. As a computational tool

  10. Radio-Frequency Emissions from Streamer Collisions: Implications for High-Energy Processes.

    Science.gov (United States)

    Luque, A.

    2017-12-01

    The production of energetic particles in a discharge corona is possibly linked to the collision of streamers of opposite polarities [Cooray et al. (2009), Kochkin et al. (2012), Østgaard et al. (2016)]. There is also experimental evidence linking it to radio-frequency emissions in the UHF frequency range (300 MHz-3 GHz) [Montanyà et al. (2015), Petersen and Beasley (2014)]. Here we investigate these two links by modeling the radio-frequency emissions emanating from an encounter between two counter-propagating streamers. Our numerical model combines self-consistently a conservative, high-order Finite-Volume scheme for electron transport with a Finite-Difference Time-Domain (FDTD) method for electromagnetic propagation. We also include the most relevant reactions for streamer propagation: impact ionization, dissociative attachment and photo-ionization. Our implementation benefits from massive parallelization by running on a General-Purpose Graphical Processing Unit (GPGPU). With this code we found that streamer encounters emit electromagnetic waves predominantly in the UHF range, supporting the hypothesis that streamer collisions are essential precursors of high-energy processes in electric discharges. References Cooray, V., et al., J. Atm. Sol.-Terr. Phys., 71, 1890, doi:10.1016/j.jastp.2009.07.010 (2009). Kochkin, P. O., et al., J. Phys. D, 45, 425202, doi: 10.1088/0022-3727/45/42/425202 (2012). Montanyà, J., et al., J. Atm. Sol.-Terr. Phys., 136, 94, doi:10.1016/j.jastp.2015.06.009, (2015). Østgaard, N., et al., J. Geophys. Res. (Atmos.), 121, 2939, doi:10.1002/2015JD024394 (2016). Petersen, D., and W. Beasley, Atmospheric Research, 135, 314, doi:10.1016/j.atmosres.2013.02.006 (2014).

  11. Temperature and EUV Intensity in a Coronal Prominence Cavity and Streamer

    Science.gov (United States)

    Kucera, T. A.; Gibson, S.E.; Schmit, D. J.; Landi, E.; Tripathi, D.

    2012-01-01

    We analyze the temperature and EUV line emission of a coronal cavity and surrounding streamer in terms of a morphological forward model. We use a series of iron line ratios observed with the Hinode Extreme-ultraviolet Imaging Spectrograph (EIS) on 2007 Aug. 9 to constrain temperature as a function of altitude in a morphological forward model of the streamer and cavity. We also compare model prediction of the EIS EUV line intensities and polarized brightness (pB) data from the Mauna Loa Solar Observatory (MLSO) MK4. This work builds on earlier analysis using the same model to determine geometry of and density in the same cavity and streamer. The fit to the data with altitude dependent temperature profiles indicates that both the streamer and cavity have temperatures in the range 1.4-1.7 MK. However, the cavity exhibits substantial substructure such that the altitude dependent temperature profile is not sufficient to completely model conditions in the cavity. Coronal prominence cavities are structured by magnetism so clues to this structure are to be found in their plasma properties. These temperature substructures are likely related to structures in the cavity magnetic field. Furthermore, we find that the model overestimates the line intensities by a factor of 4-10, while overestimating pB data by no more than a factor of 1.4. One possible explanation for this is that there may be a significant amount of material at temperatures outside of the range log T(K) approximately equals 5.8 - 6.7 in both the cavity and the streamer.

  12. 3D streamers simulation in a pin to plane configuration using massively parallel computing

    Science.gov (United States)

    Plewa, J.-M.; Eichwald, O.; Ducasse, O.; Dessante, P.; Jacobs, C.; Renon, N.; Yousfi, M.

    2018-03-01

    This paper concerns the 3D simulation of corona discharge using high performance computing (HPC) managed with the message passing interface (MPI) library. In the field of finite volume methods applied on non-adaptive mesh grids and in the case of a specific 3D dynamic benchmark test devoted to streamer studies, the great efficiency of the iterative R&B SOR and BiCGSTAB methods versus the direct MUMPS method was clearly demonstrated in solving the Poisson equation using HPC resources. The optimization of the parallelization and the resulting scalability was undertaken as a function of the HPC architecture for a number of mesh cells ranging from 8 to 512 million and a number of cores ranging from 20 to 1600. The R&B SOR method remains at least about four times faster than the BiCGSTAB method and requires significantly less memory for all tested situations. The R&B SOR method was then implemented in a 3D MPI parallelized code that solves the classical first order model of an atmospheric pressure corona discharge in air. The 3D code capabilities were tested by following the development of one, two and four coplanar streamers generated by initial plasma spots for 6 ns. The preliminary results obtained allowed us to follow in detail the formation of the tree structure of a corona discharge and the effects of the mutual interactions between the streamers in terms of streamer velocity, trajectory and diameter. The computing time for 64 million of mesh cells distributed over 1000 cores using the MPI procedures is about 30 min ns-1, regardless of the number of streamers.

  13. The physics of pulsed streamer discharge in high pressure air and applications to engine techonologies

    Science.gov (United States)

    Lin, Yung-Hsu

    The goal of this dissertation is to study high pressure streamers in air and apply it to diesel engine technologies. Nanosecond scale pulsed high voltage discharges in air/fuel mixtures can generate radicals which in turn have been shown to improve combustion efficiency in gasoline fueled internal combustion engines. We are exploring the possibility to extend such transient plasma generation and expected radical species generation to the range of pressures encountered in compression-ignition (diesel) engines having compression ratios of ˜20:1, thereby improving lean burning efficiency and extending the range of lean combustion. At the beginning of this dissertation, research into streamer discharges is reviewed. Then, we conducted experiments of streamer propagation at high pressures, calculated the streamer velocity based on both optical and electrical measurements, and the similarity law was checked by analyzing the streamer velocity as a function of the reduced electric field, E/P. Our results showed that the similarity law is invalid, and an empirical scaling factor, E/√P, is obtained and verified by dimensional analysis. The equation derived from the dimensional analysis will be beneficial to proper electrode and pulse generator design for transient plasma assisted internal engine experiments. Along with the high pressure study, we applied such technique on diesel engine to improve the fuel efficiency and exhaust treatment. We observed a small effect of transient plasma on peak pressure, which implied that transient plasma has the capability to improve the fuel consumption. In addition, the NO can be reduced effectively by the same technique and the energy cost is 30 eV per NO molecule.

  14. Developing Successful Global Leaders

    Science.gov (United States)

    Training, 2011

    2011-01-01

    Everyone seems to agree the world desperately needs strong leaders who can manage a global workforce and all the inherent challenges that go with it. That's a big part of the raison d'etre for global leadership development programs. But are today's organizations fully utilizing these programs to develop global leaders, and, if so, are they…

  15. Leader Training Conference Report.

    Science.gov (United States)

    Michigan-Ohio Regional Educational Lab., Inc., Detroit.

    The purpose of this conference was to prepare key people in the field of education to function as inservice education leaders in their respective settings. It called for participants to learn what the MOREL inservice education program is and what it hopes to accomplish, to identify the role and functions of the inservice education leader, and to…

  16. Lessons from Leaders.

    Science.gov (United States)

    Schuh, John H.

    2002-01-01

    A semistructured interview protocol was used to present perspectives on leadership from five national leaders in student affairs. Several major themes emerged. Issues were discussed about leaderships; how they manage difficulties; what work were they most proud of; and what was their advice for aspiring leaders. Reviews limitations and…

  17. Leaders from Nursing's History.

    Science.gov (United States)

    Fondiller, Shirley H.; And Others

    1995-01-01

    Looks at the lives and accomplishments of four leaders in professional nursing: (1) Loretta Ford, who championed the cause of nurse practitioners; (2) Mable Staupers, a pioneer in community health and nursing; (3) Janet Geister, a leader in private nursing; and (4) Isabel Stewart, who led the movement to standardize nursing education. (JOW)

  18. Nursing science leaders.

    Science.gov (United States)

    Ortiz, Mario R

    2015-04-01

    This introduces the guest author's column on perspectives on the development of leaders in science. The need for leadership in science is discussed and a model for the development of science leaders in nursing is outlined. © The Author(s) 2015.

  19. Air Force Senior Leaders

    Science.gov (United States)

    Force TV Radio Week in Photos About Us Air Force Senior Leaders SECAF CSAF CMSAF Biographies Adjunct Professors Senior Mentor Biographies Fact Sheets Commander's Call Topics CCT Archive CSAF Reading List 2017 Media Sites Site Registration Contact Us Search AF.mil: Home > About Us > Air Force Senior Leaders

  20. A case study of lightning attachment to flat ground showing multiple unconnected upward leaders

    Science.gov (United States)

    Cummins, Kenneth L.; Krider, E. Philip; Olbinski, Mike; Holle, Ronald L.

    2018-04-01

    On 10 July 2015, a cloud-to-ground (CG) lightning flash that produced two ground terminations was photographed from inside the safety of a truck in southern New Mexico. An analysis of archived NLDN data verified that this was a two-stroke flash, and a close-up view of the first stroke shows that it also initiated at least 12 unconnected, upward leaders (or "streamers") near the ground termination. No unconnected upward leaders were seen near the second ground attachment. After combining an analysis of the photograph with information provided by the NLDN, we infer that the first stroke was of negative (normal) polarity, had modest peak current, and struck about 460 m (± 24%) from the camera. Attachment occurred when an upward-propagating positive leader reached an inferred height of about 21 m above local ground. The second stroke struck ground about 740 m from the camera, and the height of its attachment leader is estimated to be 15 m. The estimated lengths of the unconnected upward leaders in the two-dimensional (2-D) plane of the first stroke range from 2 to 8 m, and all appear to be located within 15 m (2-D) of the main ground termination, with 24% uncertainty. Many of the unconnected upward leaders (inferred to be positive) exhibit multiple upward branches, and most of those branches have upward-directed forks or splits at their ends. This is the first report showing such extensive branching for positive upward leaders in natural lightning strikes to ground. None of the upward leaders can be seen to emanate from the tops of tall, isolated, or pointed objects on the ground, but they likely begin on small plants and rocks, or flat ground. In terms of lightning safety, this photo demonstrates that numerous upward leaders can be produced near a lightning strike point and have the potential to damage or cause injury at more than one specific point on the ground.

  1. A model for electric field enhancement in lightning leader tips to levels allowing X-ray and γ ray emissions

    DEFF Research Database (Denmark)

    Babich, L. P.; Bochkov, E. I.; Kutsyk, I. M.

    2015-01-01

    A model is proposed capable of accounting for the local electric field increase in front of the lightning stepped leader up to magnitudes allowing front electrons to overcome the runaway energy threshold and thus to initiate relativistic runaway electron avalanches capable of generating X......-ray and ray bursts observed in negative lightning leader. The model is based on an idea that an ionization wave, propagating in a preionized channel, is being focused, such that its front remains narrow and the front electric field is being enhanced. It is proposed that when a space leader segment, formed...... that the ionization channels of streamers limit the lateral expansion of the ionization wave, thereby enhancing the peak electric field to values allowing an acceleration of low-energy electrons into the runaway regime where electrons efficiently generate bremsstrahlung. The results suggest that the inhomogeneous...

  2. Proportionality for Military Leaders

    National Research Council Canada - National Science Library

    Brown, Gary D

    2000-01-01

    .... Especially lacking is a realization that there are four distinct types of proportionality. In determining whether a particular resort to war is just, national leaders must consider the proportionality of the conflict (i.e...

  3. Authenticating the Leader

    DEFF Research Database (Denmark)

    Johnsen, Christian Garmann

    As authentic leadership, with its dictum of being true to the self, has become increasingly influential among practitioners and mainstream leadership scholars, critical writers have drawn attention to the negative consequences of this development. Yet, few scholars have investigated the problem...... of authentication within discourse of authentic leadership. If authentic leadership is to make any sense, it is necessary to be able to distinguish the authentic from the inauthentic leader – in other words, it is necessary to authenticate the leader. This paper uses Gilles Deleuze’s reading of Plato as the point...... of departure for discussing the problem of authentication – separating the authentic leader form the inauthentic one – in the leadership guru Bill George’s model of authentic leadership. By doing so, the paper offers a way of conceptualizing the problem of authenticating leaders, as well as challenging...

  4. Persuasion: A Leader's Edge

    National Research Council Canada - National Science Library

    McGuire, Mark

    2002-01-01

    .... Persuasive argument is a vital aspect of strategic leadership. Any leader faced with the inherent complexities of leading his or her organization through transformational change must be capable of persuading...

  5. Senior Leader Credibility

    National Research Council Canada - National Science Library

    Moosmann, Christopher

    2000-01-01

    .... Leadership at senior levels involves a different type of work than at lower organizational levels and this requires leaders to possess a different set of skills, knowledge, and attributes in order to be successful...

  6. Leading Strategic Leader Teams

    National Research Council Canada - National Science Library

    Burleson, Willard M

    2008-01-01

    .... Although only 1 to 2 percent of the Army's senior leaders will attain a command position of strategic leadership, they are assisted by others, not only by teams specifically designed and structured...

  7. Leader self-definition and leader self-serving behavior

    NARCIS (Netherlands)

    Rus, Diana; van Knippenberg, Daan; Wisse, Barbara

    The present research investigated the relationship between leader self-definition processes and leader self-serving behaviors. We hypothesized that self-definition as a leader interacts with social reference information (descriptive and injunctive) in predicting leader self-serving actions Six

  8. A study on the equivalent electric circuit simulation model of DBD streamer and glow alternate discharge

    International Nuclear Information System (INIS)

    Yao, J; Zhang, Z T; Xu, S J; Yu, Q X; Yu, Z; Zhao, J S

    2013-01-01

    This paper presents a dynamic simulating model of the dielectric barrier discharge (DBD), structured as an equivalent electric circuit of the streamer and glow discharge generated alternately in DBD. The main parameters of DBD have been established by means of analysing the structural characteristics of a single discharge cell. An electrical comprehensive Simulink /MATLAB model was developed in order to reveal the interaction of the adjacent two discharge cell. A series of simulations was carried out in order to estimate the key structural parameters that affect the alternate streamer and glow discharge mode. The comparison results of experimental and simulate indicate that there exists a close similarity of the current waveforms graphic. Therefore, we can grasp a deep understanding mechanism of the dielectric barrier discharge and optimize the plasma reactor.

  9. High voltage pulse system for the streamer chamber supply of the GIBS spectrometer

    International Nuclear Information System (INIS)

    Aksinenko, V.D.; Glagoleva, N.S.; Dement'ev, E.A.; Kaminskij, N.I.; Matyushin, A.T.; Matyushin, V.T.; Rozhnyatovskaya, S.A.; Ryakhovskij, V.N.; Nurgozhin, N.N.; Khusainov, E.K.

    1987-01-01

    Results of development and testing of high voltage pulse system HVPS for the streamer chamber supply of the GIBS spectrometer are presented. HVPS consists of the following basic blocks: nanosecond pulse high voltage generator, high voltage charging supply, trigger generator, chamber parameter control devices, gas-oil vacuuming supply systems, auxiliary and fire-prevention devices. The system blocks are described. Experimental results of HVPC testing are presented. HVPC provides a reliable (10 5 operations) of streamer chamber supply with high voltage pulse parameters: amplitude - 500 kV, amplitude instability (0.5-1.5)%, pulse duration - 12 ns, delay time - 500 ns, delay instability (2.5-5)%, mean frequency of output a signals - 0.1 Hz

  10. Multisource full waveform inversion of marine streamer data with frequency selection

    KAUST Repository

    Huang, Yunsong; Schuster, Gerard T.

    2013-01-01

    Multisource migration with frequency selection is now extended to multisource full waveform inversion (FWI) of supergathers for marine streamer data. There are three advantages of this approach compared to conventional FWI for marine streamer data. 1. The multisource FWI method with frequency selection is computationally more efficient than conventional FWI. 2. A supergather requires more than an order of magnitude less storage than the the original data. 3. Frequency selection overcomes the acquisition mismatch between the observed data and the simulated multisource supergathers for marine data. This mismatch problem has prevented the efficient application of FWI to marine geometries in the space-time domain. Preliminary result of applying multisource FWI with frequency selection to a synthetic marine data set suggests it is at least four times more efficient than standard FWI.

  11. OBSERVATIONS OF A HYBRID DOUBLE-STREAMER/PSEUDOSTREAMER IN THE SOLAR CORONA

    Energy Technology Data Exchange (ETDEWEB)

    Rachmeler, L. A.; Seaton, D. B. [Royal Observatory of Belgium, Avenue Circulaire 3, 1180 Brussels (Belgium); Platten, S. J. [School of Mathematics and Statistics, University of St. Andrews, North Haugh, St. Andrews, Fife KY16 9SS (United Kingdom); Bethge, C. [Kiepenheuer-Institut für Sonnenphysik, Schöneckstrasse 6, D-79104 Freiburg (Germany); Yeates, A. R., E-mail: rachmeler@oma.be [Department of Mathematical Sciences, Durham University, Science Laboratories, South Road, Durham DH1 3LE (United Kingdom)

    2014-05-20

    We report on the first observation of a single hybrid magnetic structure that contains both a pseudostreamer and a double streamer. This structure was originally observed by the SWAP instrument on board the PROBA2 satellite between 2013 May 5 and 10. It consists of a pair of filament channels near the south pole of the Sun. On the western edge of the structure, the magnetic morphology above the filaments is that of a side-by-side double streamer, with open field between the two channels. On the eastern edge, the magnetic morphology is that of a coronal pseudostreamer without the central open field. We investigated this structure with multiple observations and modeling techniques. We describe the topology and dynamic consequences of such a unified structure.

  12. Streamer propagation velocity to anode and to cathode in He, Xe, N2 and SF6

    International Nuclear Information System (INIS)

    Yakovlenko, S.I.

    2004-01-01

    One studied mechanism of ionization propagation in a solid gas associated with propagation of background electrons in heterogenous electric field. The mentioned mechanism does not depend on the sign of field projection on ionization propagation direction. One derived analytical expression for ionization front rate. The mentioned expression conforms well with numerical calculations. Dependence of wave ionization front rate as a function of a field intensity on boundary of streamer for He, Xe, N 2 and SF 6 is tabulated [ru

  13. Streamer-induced emission and spectrometric determination of basic plasma parameters

    Czech Academy of Sciences Publication Activity Database

    Šimek, Milan

    2004-01-01

    Roč. 54, suppl.C (2004), C778-C783 ISSN 0011-4626. [Symposium on Plasma Physics and Technology /21./. Praha, 14.06.2004-17.06.2004] R&D Projects: GA AV ČR IAA1043403 Institutional research plan: CEZ:AV0Z2043910 Keywords : optical diagnostics * discharge * streamer Subject RIV: BL - Plasma and Gas Discharge Physics Impact factor: 0.292, year: 2004

  14. Pulse shape of the self quenching streamer counter in the coexistence region

    International Nuclear Information System (INIS)

    Chen Hongfang; Han Jiaxiang; Li Cheng; Xu Zizong

    1996-01-01

    The pulse shape of the electrical signal out of the counter operating in the self-quenching streamer (SQS) mode is obtained and the time correlation between the primary avalanche and the SQS avalanche is measured and studied. The results yield more information in the coexistence region about the time jitters in the process of the SQS avalanche than that shown in our last paper. (orig.)

  15. An Extreme-ultraviolet Wave Generating Upward Secondary Waves in a Streamer-like Solar Structure

    Science.gov (United States)

    Zheng, Ruisheng; Chen, Yao; Feng, Shiwei; Wang, Bing; Song, Hongqiang

    2018-05-01

    Extreme-ultraviolet (EUV) waves, spectacular horizontally propagating disturbances in the low solar corona, always trigger horizontal secondary waves (SWs) when they encounter the ambient coronal structure. We present the first example of upward SWs in a streamer-like structure after the passing of an EUV wave. This event occurred on 2017 June 1. The EUV wave happened during a typical solar eruption including a filament eruption, a coronal mass ejection (CME), and a C6.6 flare. The EUV wave was associated with quasi-periodic fast propagating (QFP) wave trains and a type II radio burst that represented the existence of a coronal shock. The EUV wave had a fast initial velocity of ∼1000 km s‑1, comparable to high speeds of the shock and the QFP wave trains. Intriguingly, upward SWs rose slowly (∼80 km s‑1) in the streamer-like structure after the sweeping of the EUV wave. The upward SWs seemed to originate from limb brightenings that were caused by the EUV wave. All of the results show that the EUV wave is a fast-mode magnetohydrodynamic (MHD) shock wave, likely triggered by the flare impulses. We suggest that part of the EUV wave was probably trapped in the closed magnetic fields of the streamer-like structure, and upward SWs possibly resulted from the release of slow-mode trapped waves. It is believed that the interplay of the strong compression of the coronal shock and the configuration of the streamer-like structure is crucial for the formation of upward SWs.

  16. A Series of Jets that Drove Streamer-Puff CMEs from Giant Active Region of 2014

    Science.gov (United States)

    Panesar, Navdeep K.; Sterling, Alphonse C.; Moore, Ronald L.

    2016-01-01

    We investigate characteristics of solar coronal jets that originated from active region NOAA 12192 and produced coronal mass ejections (CMEs). This active region produced many non­-jet major flare eruptions (X and M class) that made no CME. A multitude of jets occurred from the southeast edge of the active region, and in contrast to the major-­flare eruptions in the core, six of these jets resulted in CMEs. Our jet observations are from SDO/AIA EUV channels and from Hinode/XRT, and CME observations are from the SOHO/LASCO C2 coronograph. Each jet-­driven CME was relatively slow-­moving (approx. 200 - 300 km/s) compared to most CMEs; had angular width (20deg - 50deg) comparable to that of the streamer base; and was of the "streamer­-puff" variety, whereby a pre-existing streamer was transiently inflated but not removed (blown out) by the passage of the CME. Much of the chromospheric-­temperature plasma of the jets producing the CMEs escaped from the Sun, whereas relatively more of the chromospheric plasma in the non-CME-producing jets fell back to the solar surface. We also found that the CME-producing jets tended to be faster in speed and longer in duration than the non-CME-­producing jets. We expect that the jets result from eruptions of mini-filaments. We further propose that the CMEs are driven by magnetic twist injected into streamer-­base coronal loops when erupting twisted mini-filament field reconnects with the ambient field at the foot of those loops.

  17. Two-coordinate mini drift chamber operating in a self-quenching streamer mode

    International Nuclear Information System (INIS)

    Chernenko, S.P.; Smykov, L.P.; Zanevskij, Yu.V.

    1993-01-01

    Two-coordinate mini drift chambers operating in a self-quenching streamer mode have been developed. The tests have demonstrated these chambers to possess an extended counting plateau, a high operating stability and a high uniformity of efficiency over detecting area. The space resolution along anode wires is not worse than 250μm; the expected space resolution for the second coordinate is about 100 μm

  18. Filaments in curved streamlines: rapid formation of Staphylococcus aureus biofilm streamers

    International Nuclear Information System (INIS)

    Kevin Kim, Minyoung; Drescher, Knut; Shun Pak, On; Stone, Howard A; Bassler, Bonnie L

    2014-01-01

    Biofilms are surface-associated conglomerates of bacteria that are highly resistant to antibiotics. These bacterial communities can cause chronic infections in humans by colonizing, for example, medical implants, heart valves, or lungs. Staphylococcus aureus, a notorious human pathogen, causes some of the most common biofilm-related infections. Despite the clinical importance of S. aureus biofilms, it remains mostly unknown how physical effects, in particular flow, and surface structure influence biofilm dynamics. Here we use model microfluidic systems to investigate how environmental factors, such as surface geometry, surface chemistry, and fluid flow affect biofilm development of S. aureus. We discovered that S. aureus rapidly forms flow-induced, filamentous biofilm streamers, and furthermore if surfaces are coated with human blood plasma, streamers appear within minutes and clog the channels more rapidly than if the channels are uncoated. To understand how biofilm streamer filaments reorient in flows with curved streamlines to bridge the distances between corners, we developed a mathematical model based on resistive force theory of slender filaments. Understanding physical aspects of biofilm formation of S. aureus may lead to new approaches for interrupting biofilm formation of this pathogen. (paper)

  19. Laboratory coupling tests for optimum land streamer design over sand dunes surface

    KAUST Repository

    Almalki, Hashim

    2012-02-26

    The cost of data acquisition in land is becoming a major issue as we strive to cover larger areas with seismic surveys at high resolution. Over sand dunes the problem is compounded by the week coupling obtain using geophones, which often forces us to bury the phone. A major challenge is designing such a land streamer system that combines durability, mobility and the required coupling. We share a couple of such designs and discuss the merits behind such designs and test their capability. The testing includes, the level of coupling, mobility and drag over sand surfaces. For specific designs loose sand can accumulate inside the steamer reducing its mobility. On the other hand, poor coupling will attenuate the high frequencies and cause an effective delay in the signal. The weight of the streamer is also an important factor in both mobility and coupling as it adds to the coupling it reduces the mobility of the streamer. We study the impact of weight and base plate surface area on the seismic signal quality, as well as the friction factor of different designs.

  20. Analysis and interpretation of the performance degradation of glass Resistive Plate Chambers operated in streamer mode

    CERN Document Server

    Calcaterra, A; Patteri, P; Piccolo, M; Della Mea, G; Restello, S; Ferri, F; Musella, P; Redaelli, N; Tabarelli de Fatis, T; Tinti, G; Mannocchi, G; Trinchero, G

    2007-01-01

    The long-term stability of Resistive Plate Chambers (RPCs) with glass electrodes was studied for one year with a dedicated test station hosting about 10 m2 of detectors. RPCs were operated in streamer mode with a ternary gas mixture containing argon (27%), isobutane (9%) and tetrafluoroethane (64%). Environmental conditions were kept under control and, in particular, the water pollution in the gas, deemed responsible for the degradation of glass RPC performance, was monitored never to exceed 30 ppm in the exhaust line. Evidence for a substantial aging of the detectors was observed, resulting in a loss of efficiency correlated to an increased rate of spurious streamers. This can be ascribed to the chemical attack of the glass surface by hydrofluoric acid formed in the streamer process, as confirmed by detailed morphological and chemical analyses of the electrode surface. Our results strengthen the indication that the instability of glass RPCs in the long term is related to the use of fluorocarbons as quenching...

  1. Exploring Leader Identity and Development.

    Science.gov (United States)

    Priest, Kerry L; Middleton, Eric

    2016-01-01

    Taking on a leader identity can be a motivating force for pursuing leader development. This chapter explores the reciprocal and recursive nature of identity development and leader development, emphasizing how shifting views of self influence one's motivation to develop as a leader. © 2016 Wiley Periodicals, Inc., A Wiley Company.

  2. Underlying mechanisms of transient luminous events: a review

    Directory of Open Access Journals (Sweden)

    V. V. Surkov

    2012-08-01

    Full Text Available Transient luminous events (TLEs occasionally observed above a strong thunderstorm system have been the subject of a great deal of research during recent years. The main goal of this review is to introduce readers to recent theories of electrodynamics processes associated with TLEs. We examine the simplest versions of these theories in order to make their physics as transparent as possible. The study is begun with the conventional mechanism for air breakdown at stratospheric and mesospheric altitudes. An electron impact ionization and dissociative attachment to neutrals are discussed. A streamer size and mobility of electrons as a function of altitude in the atmosphere are estimated on the basis of similarity law. An alternative mechanism of air breakdown, runaway electron mechanism, is discussed. In this section we focus on a runaway breakdown field, characteristic length to increase avalanche of runaway electrons and on the role played by fast seed electrons in generation of the runaway breakdown. An effect of thunderclouds charge distribution on initiation of blue jets and gigantic jets is examined. A model in which the blue jet is treated as upward-propagating positive leader with a streamer zone/corona on the top is discussed. Sprite models based on streamer-like mechanism of air breakdown in the presence of atmospheric conductivity are reviewed. To analyze conditions for sprite generation, thunderstorm electric field arising just after positive cloud-to-ground stroke is compared with the thresholds for propagation of positively/negatively charged streamers and with runway breakdown. Our own estimate of tendril's length at the bottom of sprite is obtained to demonstrate that the runaway breakdown can trigger the streamer formation. In conclusion we discuss physical mechanisms of VLF (very low frequency and ELF (extremely low frequency phenomena associated with sprites.

  3. Leaders produce leaders and managers produce followers

    Science.gov (United States)

    Khoshhal, Khalid I.; Guraya, Salman Y.

    2016-01-01

    Objectives: To elaborate the desired qualities, traits, and styles of physician’s leadership with a deep insight into the recommended measures to inculcate leadership skills in physicians. Methods: The databases of MEDLINE, EMBASE, CINAHL, and the Cochrane Library were searched for the full-text English-language articles published during the period 2000-2015. Further search, including manual search of grey literature, was conducted from the bibliographic list of all included articles. Medical Subject Headings (MeSH) keywords “Leadership” AND “Leadership traits” AND “Leadership styles” AND “Physicians’ leadership” AND “Tomorrow’s doctors” were used for the literature search. This search followed a step-wise approach defined by the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA). The retrieved bibliographic list was analyzed and non-relevant material such as abstracts, conference proceedings, letters to editor, and short communications were excluded. Finally, 21 articles were selected for this review. Results: The literature search showed a number of leadership courses and formal training programs that can transform doctors to physician leaders. Leaders can inculcate confidence by integrating diverse views and listening; supporting skillful conversations through dialogue and helping others assess their influence and expertise. In addition to their clinical competence, physician leaders need to acquire the industry knowledge (clinical processes, health-care trends, budget), problem-solving skills, and emotional intelligence. Conclusion: This review emphasizes the need for embedding formal leadership courses in the medical curricula for fostering tomorrow doctors’ leadership and organizational skills. The in-house and off-campus training programs and workshops should be arranged for grooming the potential candidates for effective leadership. PMID:27652355

  4. Electric field determination in streamer discharges in air at atmospheric pressure

    International Nuclear Information System (INIS)

    Bonaventura, Z; Bourdon, A; Celestin, S; Pasko, V P

    2011-01-01

    The electric field in streamer discharges in air can be easily determined by the ratio of luminous intensities emitted by N 2 (C 3 Π u ) and N 2 + (B 2 Σ u + ) if the steady-state assumption of the emitting states is fully justified. At ground pressure, the steady-state condition is not fulfilled and it is demonstrated that its direct use to determine the local and instantaneous peak electric field in the streamer head may overestimate this field by a factor of 2. However, when spatial and time-integrated optical emissions (OEs) are considered, the reported results show that it is possible to formulate a correction factor in the framework of the steady-state approximation and to accurately determine the peak electric field in an air discharge at atmospheric pressure. A correction factor is defined as Γ = E s /E e , where E e is the estimated electric field and E s is the true peak electric field in the streamer head. It is shown that this correction stems from (i) the shift between the location of the peak electric field and the maximum excitation rate for N 2 (C 3 Π u ) and N 2 + (B 2 Σ u + ) as proposed by Naidis (2009 Phys. Rev. E 79 057401) and (ii) from the cylindrical geometry of the streamers as stated by Celestin and Pasko (2010 Geophys. Res. Lett. 37 L07804). For instantaneous OEs integrated over the whole radiating plasma volume, a correction factor of Γ ∼ 1.4 has to be used. For time-integrated OEs, the reported results show that the ratio of intensities can be used to derive the electric field in discharges if the time of integration is sufficiently long (i.e. at least longer than the longest characteristic lifetime of excited species) to have the time to collect all the light from the emitting zones of the streamer. For OEs recorded using slits (i.e. a window with a small width but a sufficiently large radial extension to contain the total radial extension of the discharge) the calculated correction factor is Γ ∼ 1.4. As for OEs observed

  5. [Identification of community leaders].

    Science.gov (United States)

    Chevalier, S; Dedobbeleer, N; Tremblay, M

    1995-01-01

    Although many methods of measuring leadership have been developed in sociological studies, there are few articles on the feasibility of these methods. The goal of this study was to verify the feasibility of the "modified positional-reputational approach" developed by Nix. The study was conducted in a small community located north of Montreal. Nix's questionnaire was translated, adapted and administered to 49 key informants. Two hundred and fourteen leaders were selected. Three types of leaders were identified: the legitimizers, the effectors and the activists. Through a sociometric analysis, we established links between the different leaders and we described the power structure of the community. Despite a few shortcomings, Nix's approach was found extremely useful.

  6. Radial dependence of surface streamer-channel luminosity: experimental evidence of Gaussian radiative profiles in Ar and N2

    International Nuclear Information System (INIS)

    Šimek, M; Ambrico, P F

    2012-01-01

    Radial distributions of electronically excited species produced during surface streamer propagation were obtained by applying the Abel inverse transform to projected luminosities of single streamers. The streamers were generated in an argon and nitrogen surface coplanar dielectric barrier discharge at atmospheric pressure and their magnified microscopic images were registered with high time resolution. Selected regions of the projected luminosities were processed by the Abel inverse transform procedure based on the Hankel–Fourier method assuming cylindrical symmetry of the streamer channel. Projected as well as Abel-inverted profiles were fitted by Gaussian functions. It is shown that the projected profiles, in addition to the Abel-inverted ones, can be well approximated by the sum of two coaxial Gaussians with two different half-widths and weights. The sharper Gaussian component with higher weight characterizes the radial dependence of the primary cathode-directed streamer-channel luminosity. The second (broader) Gaussian component probably originates either from the pre-breakdown Townsend phase or from the second wave propagating towards the anode. (paper)

  7. Effect of Fe{sub 3}O{sub 4} nanoparticles on positive streamer propagation in transformer oil

    Energy Technology Data Exchange (ETDEWEB)

    Lv, Yuzhen, E-mail: yzlv@ncepu.edu.cn [Beijing Key Laboratory of High Voltage and EMC, School of Electric and Electronic Engineering, North China Electric Power University, Beijing, 102206 (China); School of Energy, Power and Mechanical Engineering, North China Electric Power University, Beijing, 102206 (China); Wang, Qi; Ge, Yang [Beijing Key Laboratory of High Voltage and EMC, School of Electric and Electronic Engineering, North China Electric Power University, Beijing, 102206 (China); Zhou, You [Hunan Province Key Laboratory of Smart Grids Operation and Control, Changsha University of Science and Technology, Changsha, 410076 (China); Li, Chengrong, E-mail: lcr@ncepu.edu.cn; Qi, Bo [Beijing Key Laboratory of High Voltage and EMC, School of Electric and Electronic Engineering, North China Electric Power University, Beijing, 102206 (China); State Key Laboratory of Alternate Electrical Power System with Renewable Energy Sources, North China Electric Power University, Beijing, 102206 (China)

    2016-03-15

    Fe{sub 3}O{sub 4} nanoparticles with an average diameter of 10 nm were prepared and used to modify streamer characteristic of transformer oil. It was found that positive streamer propagation velocity in transformer oil-based Fe{sub 3}O{sub 4} nanofluid is greatly reduced by 51% in comparison with that in pure oil. The evolution of streamer shape is also dramatically affected by the presence of nanoparticles, changing from a tree-like shape with sharp branches in pure oil to a bush-like structure with thicker and denser branches in nanofluid. The TSC results reveal that the modification of Fe{sub 3}O{sub 4} nanoparticle can greatly increase the density of shallow trap and change space charge distribution in nanofluid by converting fast electrons into slow electrons via trapping and de-trapping process in shallow traps. These negative space charges induced by nanoparticles greatly alleviate the electric field distortion in front of the positive streamer tip and significantly hinder the propagation of positive streamer.

  8. Numerical simulation of evolution of electron-hole avalanches and streamers in silicon in a uniform electric field

    International Nuclear Information System (INIS)

    Kyuregyan, A. S.

    2010-01-01

    Numerical simulation of origination and evolution of streamers in Si is performed for the first time. It is assumed that an external electric field E 0 is constant and uniform, the avalanche and streamer are axially symmetric, and background electrons and holes are absent. The calculations have been performed in the context of the diffusion-drift approximation with impact and tunneling ionization, Auger recombination, and electron-hole scattering taken into account. The most realistic values of the ionization and recombination rates, diffusion coefficients, and drift mobilities of electrons and holes have been used. It is shown that the features of evolution of avalanches and streamers are generally consistent with the result obtained previously for a hypothetic semiconductor with equal kinetic coefficients for electrons and holes. Asymmetry of these coefficients (mostly, the impact-ionization coefficients) manifests itself only at the initial stage of evolution. However, with time, two exponentially self-similar streamers are formed, differing only in the sign of charge of fronts and directions of their propagation. Empirical dependences of the main parameters of streamers on E 0 in the range of 0.34-0.75 MV/cm have been derived for this most important stage of evolution.

  9. Fundamentals for New Leaders

    Science.gov (United States)

    2015-06-12

    awareness .......................................................................................................38 Self- education ...natural take-charge person; I am an introvert , so I don’t really influence others; If everyone is a leader, then who is following?; and, leadership roles...from Texas A&M University. He is also the owner of Sigma Breakthrough Technologies and served as its chief executive officer. Dr. Zinkgraf has over

  10. Empowering Leaders & Learners

    Science.gov (United States)

    Umphrey, Jan

    2013-01-01

    Trevor Greene, the 2013 MetLife/NASSP National High School Principal of the Year, empowers staff members and students to be the best teachers and learners they can be and provides the community resources to support them. In this article, Greene, principal of Toppenish High School in Washington, shares his biggest motivator as a school leader and…

  11. World-Class Leaders

    Science.gov (United States)

    Weinstein, Margery

    2012-01-01

    Future leaders' creativity and problem-solving skills have been honed in leadership courses, but that doesn't mean they are ready to use those skills to further a company's place in the world. With emerging markets in Asia, South America, and other areas of the world, a workforce needs to have an understanding of and interest in cultures beyond…

  12. Strategic Military Leaders - Leading Tomorrow

    National Research Council Canada - National Science Library

    Kit, Ng W

    2008-01-01

    .... Four key leadership competencies stand out. We need strategic leaders who are good at doing the right things and doing things right leaders who have the mental agility to choose the correct goals to achieve, the social intelligence to inspire...

  13. Combining lightning leader and relativistic feedback discharge models of terrestrial gamma-ray flashes

    Science.gov (United States)

    Dwyer, J. R.

    2016-12-01

    Lightning leader models of terrestrial gamma-ray flashes (TGFs) are based on the observations that leaders emit bursts of hard x-rays. These x-rays are thought to be generated by runaway electrons created in the high-field regions associated with the leader tips and/or streamers heads. Inside a thunderstorm, it has been proposed that these runaway electrons may experience additional relativistic runaway electron avalanche (RREA) multiplication, increasing the number and the average energy of the electrons, and possibly resulting in a TGF. When modeling TGFs it is important to include the discharge currents resulting from the ionization produced by the runaway electrons, since these currents may alter the electric fields and affect the TGF. In addition, relativistic feedback effects, caused by backward propagating positrons and backscattered x-rays, need to be included, since relativistic feedback limits the size of the electric field and the amount of a RREA multiplication that may occur. In this presentation, a lightning leader model of terrestrial gamma-ray flashes that includes the effects of the discharge currents and relativistic feedback will be described and compared with observations.

  14. Formation of ball streamers at a subnanosecond breakdown of gases at a high pressure in a nonuniform electric field

    Science.gov (United States)

    Beloplotov, D. V.; Tarasenko, V. F.; Sorokin, D. A.; Lomaev, M. I.

    2017-11-01

    The formation of a diffuse discharge plasma at a subnanosecond breakdown of a "cone-plane" gap filled with air, nitrogen, methane, hydrogen, argon, neon, and helium at various pressures has been studied. Nanosecond negative and positive voltage pulses have been applied to the conical electrode. The experimental data on the dynamics of plasma glow at the stage of formation and propagation of a streamer have been obtained with intensified charge-coupled device and streak cameras. It has been found that the formation of ball streamers is observed in all gases and at both polarities. A supershort avalanche electron beam has been detected behind the flat foil electrode in a wide range of pressures in the case of a negatively charged conical electrode. A mechanism of the formation of streamers at breakdown of various gases at high overvoltages has been discussed.

  15. Gas sampling calorimeter studies in proportional, saturated avalanche, and streamer modes

    International Nuclear Information System (INIS)

    Atac, M.; Bedeschi, F.; Yoh, J.; Morse, R.; Procario, M.

    1982-01-01

    Recently, satisfactory new results were obtained at SLAC from gas sampling calorimeters running in the saturated avalanche mode within the energy range of 1.5 to 17.5 GeV. To study the higher energy behavior of this mode, more tests were carried out in the M4 beamline at Fermilab. This paper contains results obtained from the MAC prototype electromagnetic and hadronic calorimeters running in the proportional, saturated avalanche, and the streamer regions for energies between 12 and 150 GeV

  16. SIMUL - a program for the simulation of interactions in the streamer chamber RISK

    International Nuclear Information System (INIS)

    Friebel, W.; Gajewski, J.; Halm, I.

    1976-08-01

    A program for the simulation of interactions in the streamer chamber RISK is described. This program allows first investigations and tests for planning and preparing experiments. In the program the trajectories of all particles taking part in the interaction are computed. Selected points are projected onto film planes serving as measurement points for the use in the geometrical reconstruction. The program is used for testing a geometry program. But it also seems to be very helpful in investigating counter and trigger constellations and in the calculation of counting rates and trigger effectivities. (author)

  17. A Handbook for Teacher Leaders.

    Science.gov (United States)

    Pellicer, Leonard O.; Anderson, Lorin W.

    This handbook is written for teachers in leadership roles, including team leaders, lead teachers, department chairpersons, and master teachers. Part 1, "The Nature of School Leadership," is devoted to a description of teacher leaders and how they lead. Results are provided from research on teacher leaders, and persistent obstacles to…

  18. Barium fluoride crystals and self-quenching streamer chambers as a position sensitive gamma-ray detector

    International Nuclear Information System (INIS)

    Salomon, M.; DeMooy, S.; Ruggier, L.

    1985-01-01

    We have studied the possibility of using selfquenching streamer chambers to detect photoelectrons produced by a photoconverter in conjunction with Barium Fluoride scintillators. With the purpose to obtain a high efficiency detector, we attempted to combine a BaF 2 scintillator with a gas chamber operating at large electric fields and a high fraction of quenching gas like self-quenching streamer (SQS) chamber, as the electric fields at the cathode could be made larger than in the proportional mode. Furthermore, previous results indicated that in this mode, part of the large amplification was obtained through strong absorption of uv photons near the anode

  19. Are radiography lecturers, leaders?

    International Nuclear Information System (INIS)

    Hendry, Julie Anne

    2013-01-01

    This review article aims to explore the concept of radiography lecturers acting as leaders to their student followers. Through a brief review of the literature, a definition of leadership is suggested and some leadership theories explored. The path-goal theory, leader–member exchange theory and the contemporary theory of transformational leadership are examined more closely. Links between lecturer-leader behaviour and student motivation and learning are tentatively suggested with transformational leadership appearing to offer the optimal leadership style for lecturers to adopt. The paucity of literature relating directly to radiography is acknowledged and areas for further research are suggested. The article concludes with some of the author's practical ideas for incorporating transformational leadership styles and behaviours into radiography education today

  20. Evaluation of the effectiveness of light streamer tori-lines and characteristics of bait attacks by seabirds in the western North Pacific.

    Directory of Open Access Journals (Sweden)

    Noriyosi Sato

    Full Text Available To improve the effectiveness of tori-lines it is necessary to evaluate the ability of tori-lines to mitigate seabird bycatch and determine what kind of seabird species gather during line settings, attack the bait and are incidentally caught. We conducted two experiments in the western North Pacific and examined the effectiveness for seabird mitigation of light streamer tori-lines which have no long streamers but many light (short streamers and are mainly used in the North Pacific area. Firstly, the effectiveness of two different types of tori-line (light streamer (1 m and long streamer (up to 7 m tori-line and of two different colors (yellow and red of light streamers for seabird bycatch avoidance was evaluated using 567 sets based on data from 20 offshore surface commercial longliners. No significant difference in the bycatch number between the different tori-line types and streamer colors was found. Secondly, we investigated the characteristics of the seabird bycatch in the North Pacific and the effectiveness of three different types of streamers (light, hybrid and modified light types by detailed observations of seabird attacks using a chartered longline vessel. Although the appearance rate of albatrosses and shearwaters were 40.9% and 27.7%, Laysan albatross was the main seabird species that followed the vessel but shearwaters seldom followed the vessel and did not aggregate during line setting. In all attacks on bait observed during line settings, 81% and 7% were by albatrosses and shearwaters, respectively. In the number of primary attacks by Laysan albatrosses which attacked most aggressively of all seabirds, there were no significant differences among the tori-line types. No individuals of shearwater were caught. The results of both experiments indicated that light streamer tori-lines were as effective as tori-lines with long streamers for mitigating seabird bycatch in the North Pacific.

  1. What makes a leader?

    Science.gov (United States)

    Goleman, D

    1999-01-01

    Superb leaders have very different ways of directing a team, a division, or a company. Some are subdued and analytical; others are charismatic and go with their gut. And different of situations call for different types of leadership. Most mergers need a sensitive negotiator at the helm whereas many turnarounds require a more forceful kind of authority. Psychologist and noted author Daniel Goleman has found, however, that effective leaders are alike in one crucial way: they all have a high degree of what has come to be known as emotional intelligence. In fact, Goleman's research at nearly 200 large, global companies revealed that emotional intelligence--especially at the highest levels of a company--is the sine qua non for leadership. Without it, a person can have first-class training, an incisive mind, and an endless supply of good ideas, but he still won't make a great leader. The components of emotional intelligence--self-awareness, self-regulation, motivation, empathy, and social skill--can sound unbusinesslike. But exhibiting emotional intelligence at the workplace does not mean simply controlling your anger or getting along with people. Rather it means understanding your own and other people's emotional makeup well enough to move people in the direction of accomplishing your company's goals. In this article, the author discusses each component of emotional intelligence and shows through examples how to recognize it in potential leaders, how and why it leads to measurable business results, and how it can be learned. It takes time and, most of all, commitment. But the benefits that come from having a well-developed emotional intelligence, both for the individual and the organization, make it worth the effort.

  2. The NFP Strategic Leader

    Science.gov (United States)

    2010-01-01

    Daniel Goleman , Emotional Intelligence (New York: Bantam, 1995). 2. David V. Day and Robert G. Lord, “Executive Leadership and Organizational Performance...preference are emotional decision mak- ers and are, therefore, not firmly wedded to a decision once made. The truth Winter2009-10 39 is that both Thinking... emotional tagging) can cause experienced leaders to make wrong decisions because they fail to recognize errors associated with these responses.33

  3. What makes a leader?

    Science.gov (United States)

    Goleman, D

    1998-01-01

    Superb leaders have very different ways of directing a team, a division, or a company. Some are subdued and analytical; others are charismatic and go with their gut. And different situations call for different types of leadership. Most mergers need a sensitive negotiator at the helm, whereas many turnarounds require a more forceful kind of authority. Psychologist and noted author Daniel Goleman has found, however, that effective leaders are alike in one crucial way: they all have a high degree of what has come to be known as emotional intelligence. In fact, Goleman's research at nearly 200 large, global companies revealed that emotional intelligence--especially at the highest levels of a company--is the sine qua non for leadership. Without it, a person can have first-class training, an incisive mind, and an endless supply of good ideas, but he still won't make a great leader. The components of emotional intelligence--self-awareness, self-regulation, motivation, empathy, and social skill--can sound unbusinesslike. But exhibiting emotional intelligence at the workplace does not mean simply controlling your anger or getting along with people. Rather, it means understanding your own and other people's emotional makeup well enough to move people in the direction of accomplishing your company's goals. In this article, the author discusses each component of emotional intelligence and shows through examples how to recognize it in potential leaders, how and why it leads to measurable business results, and how it can be learned. It takes time and, most of all, commitment. But the benefits that come from having a well-developed emotional intelligence, both for the individual and the organization, make it worth the effort.

  4. Learning with leaders.

    Science.gov (United States)

    Bunkers, Sandra S

    2009-01-01

    This column focuses on ideas concerning leaders and leadership. The author proposes that leadership is about showing up and participating with others in doing something. "Mandela: His 8 Lessons of Leadership" by Richard Stengel is explored in light of selected philosophical writings, literature on nursing leadership, and nurse theorist Rosemarie Rizzo Parse's humanbecoming leading-following model. Teaching-learning questions are then posed to stimulate further reflection on the lessons of leadership.

  5. Leader Development for a Transforming Army

    National Research Council Canada - National Science Library

    Yackley, Stephen G

    2005-01-01

    .... The development of future strategic leaders requires an increased emphasis from senior leaders on subordinate leader development, combined with a method to enhance developmental feedback to these subordinate leaders...

  6. The wise leader.

    Science.gov (United States)

    Nonaka, Ikujiro; Takeuchi, Hirotaka

    2011-05-01

    In an era of increasing discontinuity, wise leadership has nearly vanished. Many leaders find it difficult to reinvent their corporations rapidly enough to cope with new technologies, demographic shifts, and consumption trends. They can't develop truly global organizations that operate effortlessly across borders. And they find it tough to ensure that their people adhere to values and ethics. The authors assert that leaders must acquire practical wisdom, or what Aristotle called phronesis: experiential knowledge that enables people to make ethically sound judgments. Wise leaders demonstrate six abilities: (i) They make decisions on the basis of what is good for the organization and for society. (2) They quickly grasp the essence of a situation and fathom the nature and meaning of people, things, and events. (3) They provide contexts in which executives and employees can interact to create new meaning. (4) They employ metaphors and stories to convert their experience into tacit knowledge that others can use. (5) They exert political power to bring people together and spur them to act. (6) They use apprenticeship and mentoring to cultivate practical wisdom in orders.

  7. Storm-time Convection Dynamics Viewed from Optical Auroras: from Streamer to Patchy Pulsating Aurora

    Science.gov (United States)

    Yang, B.; Donovan, E.; Liang, J.; Grono, E.

    2016-12-01

    In a series of statistical and event studies we have demonstrated that the motion of patches in regions of Patchy Pulsating Aurora (PPA) is very close to if not exactly convection. Thus, 2D maps of PPA motion provides us the opportunity to remote sense magnetospheric convection with relatively high space and time resolution, subject to uncertainties associated with mapping between the ionosphere and magnetosphere. In this study, we use THEMIS ASI aurora observations (streamers and patchy pulsating aurora) combined with SuperDARN convection measurements, Swarm ion drift velocity measurements, and RBSP electric field measurements to explore the convection dynamics in storm time. From 0500 UT to 0600 UT on March 19 2015, convection observations across 5 magnetic local time (MLT) inferred from the motion of PPA patches and SuperDARN measurements show that a westward SAPS (Subauroral Polarized Streams) enhancement occurs after an auroral streamer. This suggests that plasma sheet fast flows can affect the inner magnetospheric convection, and possibly trigger very fast flows in the inner magnetosphere.

  8. Streamer Motives and User-Generated Content on Social Live-Streaming Services

    Directory of Open Access Journals (Sweden)

    Friedlander, Mathilde B.

    2017-03-01

    Full Text Available Three most popular information services, Periscope, Ustream, and YouNow, vicarious for all Social Live-Streaming Services (SLSSs, are investigated to analyze their streamers' motivations and the user-generated content. Additionally, we collected demographic data (gender and age. More than 7,500 streams by users from the U.S., Germany, and Japan were observed. Main streamer motivations on SLSSs are boredom, socializing, the need to reach a specific group, the need to communicate, and fun. Important content categories on all three SLSSs are chatting, sharing information, 24/7, and 'slice of life.' We were able to identify differences between users from the U.S., Germany, and Japan as well as between the users of Periscope, Ustream, and YouNow. The main motive to stream in the U.S. is to reach a specific group, while in Japan it is socializing, and in Germany boredom. The top content category for both, YouNow as well as Periscope, is to chat; on Ustream it is 24/7 (i.e., webcams.

  9. Spatially hybrid computations for streamer discharges with generic features of pulled fronts: I. Planar fronts

    International Nuclear Information System (INIS)

    Li Chao; Ebert, Ute; Hundsdorfer, Willem

    2010-01-01

    Streamers are the first stage of sparks and lightning; they grow due to a strongly enhanced electric field at their tips; this field is created by a thin curved space charge layer. These multiple scales are already challenging when the electrons are approximated by densities. However, electron density fluctuations in the leading edge of the front and non-thermal stretched tails of the electron energy distribution (as a cause of X-ray emissions) require a particle model to follow the electron motion. But present computers cannot deal with all electrons in a fully developed streamer. Therefore, super-particle have to be introduced, which leads to wrong statistics and numerical artifacts. The method of choice is a hybrid computation in space where individual electrons are followed in the region of high electric field and low density while the bulk of the electrons is approximated by densities (or fluids). We here develop the hybrid coupling for planar fronts. First, to obtain a consistent flux at the interface between particle and fluid model in the hybrid computation, the widely used classical fluid model is replaced by an extended fluid model. Then the coupling algorithm and the numerical implementation of the spatially hybrid model are presented in detail, in particular, the position of the model interface and the construction of the buffer region. The method carries generic features of pulled fronts that can be applied to similar problems like large deviations in the leading edge of population fronts, etc.

  10. Stress response of Escherichia coli induced by surface streamer discharge in humid air

    International Nuclear Information System (INIS)

    Doležalová, Eva; Prukner, Václav; Lukeš, Petr; Šimek, Milan

    2016-01-01

    Inactivation of Escherichia coli by means of surface streamer discharge has been investigated to obtain new insights into the key mechanisms involved, with a particular emphasis placed on the microbial response to plasma-induced stress. The surface streamer discharge was produced in coplanar dielectric barrier discharge electrode geometry, and was driven by an amplitude-modulated ac high voltage in humid synthetic air at atmospheric pressure. The response to plasma-induced stress was evaluated by using conventional cultivation, sublethal injury and resazurin assay and the LIVE/DEAD ® BacLight ™ Bacterial Viability kit. Compared to conventional cultivation, the LIVE/DEAD ® test labels bacteria with damaged membranes, while resazurin assay tracks their metabolic activity. Our results clearly demonstrate that the treated bacteria partly lost their ability to grow properly, i.e. they became injured and culturable, or even viable but nonculturable (VBNC). The ability to develop colonies could have been lost due to damage of the bacterial membrane. Damage of the membranes was mainly caused by the lipid peroxidation, evidencing the key role of oxygen reactive species, in particular ozone. We conclude that the conventional cultivation method overestimates the decontamination efficiency of various plasma sources, and must therefore be complemented by alternative techniques capable of resolving viable but nonculturable bacteria. (paper)

  11. STUDENT AWARD FINALIST: Oxygen Pathways in Streamer Discharge for Transient Plasma Ignition

    Science.gov (United States)

    Pendleton, S. J.; Bowman, S.; Singleton, D.; Watrous, J.; Carter, C.; Lempert, W.; Gundersen, M. A.

    2011-10-01

    The use of streamers for the ignition of fuels, also known as transient plasma ignition (TPI), has been shown in a variety of engines to improve combustion through decreased ignition delay, increased lean burn capability and increased energy release relative to conventional spark ignition. The mechanisms behind these improvements, however, remain poorly understood. Temperature measurements by optical emission spectroscopy demonstrate that ignition by TPI is a nonthermal process, and thus is almost entirely dependent on the production and presence of electron impact-created active species in the discharge afterglow. Of particular interest are active oxygen species due to their relatively long lifetimes at high pressures and the pivotal role they play in combustion reactions. In order to elucidate the oxygen pathways, here we report the investigation of the temporal evolution of the populations of atomic oxygen and ozone by use of two-photon absorption laser induced fluorescence (TALIF) and UV absorption, respectively. Experimental results are presented and compared to kinetic modeling of the streamers. Future experiments are proposed to better understand the physics behind TPI. Supported by NSF, AFOSR, NumerEx-ONR, AFRL-WPAFB.

  12. Experimental study of the positive leader velocity as a function of the current in the initial and final-jump phases of a spark discharge

    International Nuclear Information System (INIS)

    Andreev, A. G.; Bazelyan, E. M.; Bulatov, M. U.; Kuzhekin, I. P.; Makalsky, L. M.; Sukharevskij, D. I.; Syssoev, V. S.

    2008-01-01

    A positive leader in air at gap lengths of up to 8 m was studied experimentally on an open experimental stand. The voltage source was a 6-MV pulsed voltage generator or an artificial charged aerosol cloud. The dependence of the leader velocity on the current in the range 0.2-8 A was determined by simultaneously recording the optical picture and electric parameters of the discharge. Particular attention was paid to the final-jump phase of the discharge, when the gap was completely bridged by the streamer zone of the leader. It is shown that the character of the dependence of the leader velocity on the current in this phase remains unchanged; hence, the final-jump phase can be used in experiments in which the current has to be varied within a wide range. For this purpose, one can use a damping resistance, which is inefficient in the initial phase. The parameters of the power-law dependence of the leader velocity on the current at currents of a few amperes are established reliably. It is found that the power-law dependence with constant parameters is inapplicable to calculate the leader velocity at currents of about 0.1 A, which correspond to the lower limit of the leader viability.

  13. The effect of temperature on pulsed positive streamer discharges in air over the range 292 K–1438 K

    Science.gov (United States)

    Ono, Ryo; Ishikawa, Yuta

    2018-05-01

    The effect of temperature on pulsed positive streamer discharges in air is measured by comparing atmospheric-pressure, high-temperature discharges with low-pressure, room-temperature discharges at the same air densities n and discharge voltages. Both discharges have the same reduced electric field E/n, so the differences between the two discharges only depend on the temperature, which is varied from 292 K to 1438 K. Temperature affects the discharge pulse energy most significantly; at 1438 K, the energy of an atmospheric-pressure discharge pulse is approximately 30 times larger than that of the corresponding 20.5 kPa, room-temperature discharge. Temperature also affects the shapes of the streamers when K, but no significant effect is observed for K. There is also no significant temperature effect on the spatially integrated intensity of N2(C–B) emission. However, temperature strongly affects the ratio of the integrated emission intensity to the discharge energy. No effect of the temperature is observed on the propagation velocity of the primary streamer or on the length of the secondary streamer.

  14. Streamer discharge inception in a sub-breakdown electric field from a dielectric body with a frequency dependent dielectric permittivity

    NARCIS (Netherlands)

    A. A. Dubinova (Anna); C. Rutjes (Casper); U. M. Ebert (Ute)

    2015-01-01

    htmlabstractWe study positive streamer inception from the tip of an elongated ice particle. The dielectric permittivity of ice drops from 93 to 3 for electric fields changing on the millisecond timescale [1]. We demonstrate that this effect can be important on the nanosecond time scale of

  15. Tritons for the study of the charge-exchange reactions with the LHE streamer chamber: status and some possibilities

    International Nuclear Information System (INIS)

    Avramenko, S.A.; Belikov, Yu.A.; Golokhvastov, A.I.; Kirillov, A.D.; Khorozov, S.A.; Komolov, L.N.; Lukstin'sh, Yu.; Rukoyatkin, P.A.

    1997-01-01

    The 6 and 9 GeV/c secondary tritons, produced in the 4 He+A→ 3 H+X reaction, were used to study the charge-exchange reactions using a streamer chamber in magnetic field. The triton formation schemes, the beam parameters achieved as well as a way to reduce the beam momentum spread are given in the paper

  16. Comparison of Positive Streamers in Liquid Dielectrics with and without Nanoparticles Simulated with Finite-Element Software

    Directory of Open Access Journals (Sweden)

    Juan Velasco

    2018-02-01

    Full Text Available In this paper, a comparison of positive streamer diffusion propagation is carried out in three configurations of oil transformers: mineral transformer oil, mineral oil with solid dielectric barriers, and a nanofluid. The results have been solved using a finite-element method with a two-dimensional (2D axi-symmetric space dimension selected. Additionally, previous results from other research has been reviewed to compare the results obtained. As expected, it is confirmed that the nanoparticles improve the dielectric properties of the mineral oil. In addition, it is observed that the dielectric solid blocks the propagation of the streamer when it is submerged with a horizontal orientation, thus perpendicular to the applied electric field. The computer used, with four cores (each 3.4 GHz and 16 GB of RAM, was not sufficient for performing the simulations of the models with great precision. However, with these first models, the tendency of the dielectric behavior of the oil was obtained for the three cases in which the streamer was acting through the transformer oil. The simulation of these models, in the future, in a supercomputer with a high performance in terms of RAM memory may allow us to predict, as an example, the best concentration of nanoparticles to retard the streamer inception. Finally, other dielectric issues will be predicted using these models, such as to analyze the advantages and drawbacks of the presence of dielectrics inside the oil transformer.

  17. Building leaders paving the path for emerging leaders

    CERN Document Server

    Stoner, Charles R

    2013-01-01

    Although the selection and development of emerging leaders is fundamental to organizational growth and success, many organizations are facing a troubling scenario - a striking gap between the leaders they need and the talent available to assume the mantle of leadership. This book, grounded in empirical investigations and philosophical insights into the study of leadership, is designed to help emerging leaders bridge the gap between 'new leader' and confident, respected difference maker. From the development of leadership skills to the practice and application of successful strategies, award-wi

  18. Perceptions of political leaders.

    Science.gov (United States)

    David Schmitz, J; Murray, Gregg R

    2017-01-01

    Partisan identification is a fundamental force in individual and mass political behavior around the world. Informed by scholarship on human sociality, coalitional psychology, and group behavior, this research argues that partisan identification, like many other group-based behaviors, is influenced by forces of evolution. If correct, then party identifiers should exhibit adaptive behaviors when making group-related political decisions. The authors test this assertion with citizen assessments of the relative physical formidability of competing leaders, an important adaptive factor in leader evaluations. Using original and novel data collected during the contextually different 2008 and 2012 U.S. presidential elections, as well as two distinct measures obtained during both elections, this article presents evidence that partisans overestimate the physical stature of the presidential candidate of their own party compared with the stature of the candidate of the opposition party. These findings suggest that the power of party identification on political behavior may be attributable to the fact that modern political parties address problems similar to the problems groups faced in human ancestral times.

  19. Teaching Leaders to Lead Themselves: An Emerging Leader Exercise

    Science.gov (United States)

    Chavez, Carolyn I.; Gomez, Claudia; Valenzuela, Marcus; Perera, Yasanthi B.

    2017-01-01

    This article describes an exercise that allows students to experience and understand the importance of perception in leader emergence. Based on implicit leadership theories, this exercise asks students to provide one another with anonymous feedback about what extent they exhibit various trait-based leader behaviors. This exercise, which can be…

  20. Online Leader Training Course: Nebraska Equine Extension Leader Certification

    Science.gov (United States)

    Cottle, Lena; D'Angelo, Nicole

    2015-01-01

    The Nebraska Equine Advancement Level Leader Certification Program is an online learning tool that clarifies principles of the Nebraska 4-H Equine Advancement Programs. Through an online Moodle course through eXtension.org, 4-H leaders and Extension educators are able to fulfill the certification requirement from any location before allowing youth…

  1. Performance of the MACRO limited streamer tubes for estimates of muon energy

    CERN Document Server

    Giorgini, M

    2002-01-01

    The MACRO limited streamer tubes can be operated in drift mode by using the TDCs included in the QTP system. In this way a considerable improvement in the space resolution is obtained, allowing the analysis of muon tracks in terms of multiple scattering effects and the energy estimates of muons crossing the detector. We present the results of two dedicated tests, performed with the CERN PS-T9 and SPS-X7 beams, to provide a full check of the electronics and to exploit the feasibility of the analysis. Using a neural network, we are able to estimate the muon energies up to E/sub mu / approximately = 40 GeV. The test beam data provide then an absolute energy calibration, which allows to apply the method to the MACRO data. (5 refs).

  2. Modelling of lightning streamer formation and propagation in wind turbine blades

    DEFF Research Database (Denmark)

    Candela Garolera, Anna; Holbøll, Joachim; Madsen, Søren Find

    2013-01-01

    of the air termination in enhancing the electric field and attracting the lightning discharge, thus shielding the blade surface and preventing electrical breakdown of the blade material. However, the number and location of the discrete receptors may be difficult to establish, since their performance....... The present paper presents a method to investigate the origin and propagation of streamers from different conductive elements of the blade when exposed to a high electric field. The calculations are performed using dynamic simulations with the finite element method, and the results have been correlated...... with high voltage tests in the laboratory. The algorithms developed are intended to be a new and improved tool for the design of the blade lightning protection system, in particular to assess the effectiveness of the air termination system and the effects of internal conductive materials. The simulation...

  3. Multipoint Ignition of a Gas Mixture by a Microwave Subcritical Discharge with an Extended Streamer Structure

    Science.gov (United States)

    Aleksandrov, K. V.; Busleev, N. I.; Grachev, L. P.; Esakov, I. I.; Ravaev, A. A.

    2018-02-01

    The results of experimental studies on using an electrical discharge with an extended streamer structure in a quasioptical microwave beam in the multipoint ignition of a propane-air mixture have been reported. The pulsed microwave discharge was initiated at the interior surface of a quartz tube that was filled with the mentioned flammable mixture and introduced into a microwave beam with a subbreakdown initial field. Gas breakdown was initiated by an electromagnetic vibrator. The dependence of the type of discharge on the microwave field strength was examined, the lower concentration threshold of ignition of the propane-air mixture by the studied discharge was determined, and the dynamics of combustion of the flammable mixture with local and multipoint ignition were compared.

  4. A Barrel IFR Instrumented With Limited Streamer Tubes for BABAR Experiment

    International Nuclear Information System (INIS)

    Andreotti, M.; Ferrara U.; INFN, Ferrara

    2006-01-01

    The new barrel Instrumented Flux Return (IFR) of BABAR detector will be reported here. Limited Streamer Tubes (LSTs) have been chosen to replace the existing RPCs as active elements of the barrel IFR. The layout of the new detector will be discussed: in particular, a cell bigger than the standard one has been used to improve efficiency and reliability. The extruded profile is coated with a resistive layer of graphite having a typical surface resistivity between 0.2 and 0.4 MOhm/square. The tubes are assembled in modules and installed in 12 active layers of each sextant of the IFR detector. R and D studies to choose the final design and Quality Control procedure adopted during the tube production will be briefly discussed. Finally the performances of installed LSTs into 2/3 of IFR after 8 months of operations will be reported

  5. Speed of streamers in argon over a flat surface of a dielectric

    Energy Technology Data Exchange (ETDEWEB)

    Sobota, A; Kramer, N J; Van Veldhuizen, E M; Stoffels, W W; Haverlag, M [Eindhoven University of Technology, Department of Applied Physics, PO Box 513, 5600MB Eindhoven (Netherlands); Lebouvier, A [Ecole Polytechnique de l' Universite d' Orleans, 12 rue de Blois, BP 6744, 45067 Orleans Cedex 2 (France); Manders, F [Advanced Development Lighting, Philips Lighting, Mathildelaan 1, 5611 BD, Eindhoven (Netherlands)], E-mail: a.sobota@tue.nl

    2009-01-07

    A pin-pin electrode geometry was used to study the velocities of streamers propagating over a flat dielectric surface and in gas close to the dielectric. The experiments were done in an argon atmosphere, at pressures from 0.1 to 1 bar, with repetitive voltage pulses. The dielectric surface played a noticeable role in discharge ignition and propagation. The average speed of the discharge decreased with higher pressure and lower voltage pulse rise rate. It was higher when the conductive channel between the electrodes was formed over the dielectric, rather than through the gas. Space resolved measurements revealed an increase in velocity of the discharge as it travelled towards the grounded electrode.

  6. The acceleration of electrons at a spherical coronal shock in a streamer-like coronal field

    Energy Technology Data Exchange (ETDEWEB)

    Kong, Xiangliang, E-mail: kongx@sdu.edu.cn; Chen, Yao, E-mail: yaochen@sdu.edu.cn [Shandong Provincial Key Laboratory of Optical Astronomy and Solar-Terrestrial Environment, and Institute of Space Sciences, Shandong University, Weihai, Shandong 264209 (China); Guo, Fan, E-mail: guofan.ustc@gmail.com [Theoretical Division, Los Alamos National Laboratory, Los Alamos, NM 87545 (United States)

    2016-03-25

    We study the effect of large-scale coronal magnetic field on the electron acceleration at a spherical coronal shock using a test-particle method. The coronal field is approximated by an analytical solution with a streamer-like magnetic field featured by partially open magnetic field and a current sheet at the equator atop the closed region. It shows that the closed field plays the role of a trapping agency of shock-accelerated electrons, allowing for repetitive reflection and acceleration, therefore can greatly enhance the shock-electron acceleration efficiency. It is found that, with an ad hoc pitch-angle scattering, electron injected in the open field at the shock flank can be accelerated to high energies as well. In addition, if the shock is faster or stronger, a relatively harder electron energy spectrum and a larger maximum energy can be achieved.

  7. Display of a proton-proton interaction as seen in the streamer chamber of NA5

    CERN Multimedia

    CERN PhotoLab

    1979-01-01

    This experiment was performed by the Bari-Cracow-Liverpool-Munich (MPI)-Nijmegen Collaboration using the unseparated H2 beam in the EHN1 hall. The setup consisted of a three-gap streamer chamber (2x1.4x0.72 m3) inside a superconducting vertex magnet, large magnetostrictive spark chambers, proportional chambers and beam defining counters. A large acceptance electron and hadron calorimeter completed the setup. Particles from beam interactions on a target, 36.5 cm long, 2 cm in diameter (for liquid hydrogen) located inside the chamber at its entrance were photographed. Multiplicities, rapidity distributions, and correlations were studied for interactions with a large value for the sum of the transverse momenta.

  8. Speed of streamers in argon over a flat surface of a dielectric

    International Nuclear Information System (INIS)

    Sobota, A; Kramer, N J; Van Veldhuizen, E M; Stoffels, W W; Haverlag, M; Lebouvier, A; Manders, F

    2009-01-01

    A pin-pin electrode geometry was used to study the velocities of streamers propagating over a flat dielectric surface and in gas close to the dielectric. The experiments were done in an argon atmosphere, at pressures from 0.1 to 1 bar, with repetitive voltage pulses. The dielectric surface played a noticeable role in discharge ignition and propagation. The average speed of the discharge decreased with higher pressure and lower voltage pulse rise rate. It was higher when the conductive channel between the electrodes was formed over the dielectric, rather than through the gas. Space resolved measurements revealed an increase in velocity of the discharge as it travelled towards the grounded electrode.

  9. The limited streamer tubes system for the SLD warm iron calorimeter

    International Nuclear Information System (INIS)

    Benvenuti, A.C.; Camanzi, B.; Piemontese, L.; Zucchelli, P.; Calcaterra, A.; De Sangro, R.; De Simone, P.; De Simone, S.; Gallinaro, M.; Peruzzi, I.; Piccolo, M.; Bacchetta, N.; Bisello, D.; Castro, A.; Galvagni, S.; Loreti, M.; Pescara, L.; Wyss, J.; Battiston, R.; Biasini, M.; Bilei, G.M.; Checcucci, B; Mancinelli, G.; Mantovani, G.; Pauluzzi, M.; Santocchia, A.; Servoli, L.; Carpinelli, M.; Castaldi, R.; Cazzola, U.; Dell'Orso, R.; Pieroni, E.; Vannini, C.; Verdini, P.G.; Byers, B.L.; Escalera, J.; Kharakh, D.; Messner, R.L.; Zdarko, R.W.; Johnson, J.R.

    1992-01-01

    The SLD detector at the Stanford Linear Accelerator Center is a general purpose device for studying e + ε - interaction at the Z 0 . The SLD calorimeter system consists of two parts: a lead Liquid Argon Calorimeter (LAC) with both electromagnetic (22 radiation lengths) and hadronic sections (2.8 absorption lengths) housed inside the coil, and the Warm Ion limited streamer tubes Calorimeter (WIC) outside the coil which uses as radiator the iron of the flux return for the magnetic field. The WIC completes the measurement of the hadronic shower energy (∼85% on average is contained in the LAC) and it provides identification and tracking for muons over 99% of the solid angle. In this note we report on the construction, test and commissioning of such a large system

  10. Limited Streamer Tubes for the BaBar Instrumented Flux Return Upgrade

    International Nuclear Information System (INIS)

    Lu, C.

    2005-01-01

    Starting from the very beginning of their operation the efficiency of the RPC chambers in the BaBar Instrumented Flux Return (IFR) has suffered serious degradation. After intensive investigation, various remediation efforts had been carried out, but without success. As a result the BaBar collaboration decided to replace the dying barrel RPC chambers about two years ago. To study the feasibility of using the Limited Streamer Tube (LST) as the replacement of RPC we carried out an R and D program that has resulted in BaBar's deciding to replace the barrel RPC's with LST's. In this report we summarize the major detector R and D results, and leave other issues of the IFR system upgrade to the future publications

  11. Effect of streamer plasma air purifier on sbs symptoms and performance of office work

    DEFF Research Database (Denmark)

    Zhang, X.J.; Fang, Lei; Wargocki, Pawel

    2011-01-01

    Subjective experiments were conducted to evaluate the effect of a streamer plasma air purifier on perceived air quality, SBS symptoms and performance of office work during 5-hour exposure of 32 recruited subjects in field laboratory in which real materials were used to establishing a realistic...... level of air pollution. Intensity of SBS symptoms were indicated using visual-analogue scales. Subjects’ performance was evaluated with several computer tasks. The results show that operation of the air purifiers improved perceived air quality and reduced the odor intensity of indoor air. Eye dryness...... symptom was found significantly improved when the air purifiers were used but no other SBS symptoms or performance of office work were improved when the air purifiers were in operation compared to the condition when they were off....

  12. In situ ecophysiology of Aigarchaeota from an oxic, hot-spring filamentous 'streamer' community

    Science.gov (United States)

    Beam, J.; Jay, Z.; Tringe, S. G.; Glavina del Rio, T.; Rusch, D.; Schmid, M.; Wagner, M.; Inskeep, W.

    2014-12-01

    The candidate phylum Aigarchaeota contains thermophilic archaea from terrestrial, subsurface, and marine geothermal ecosystems. The phylogeny and metabolic potential of Aigarchaeota has been deduced from several recent single-cell amplified genomes; however, an accurate description of their metabolism, potential ecological interactions, and role in biogeochemical cycling is lacking. Here we report possible ecological interactions and the in situ metabolism of an uncultivated lineage of Aigarchaeota from an oxic, terrestrial hot-spring filamentous 'streamer' community (Octopus Spring, pH = 8; T = 78 - 84 °C, Yellowstone National Park, Wyoming, USA). Fluorescence in situ hybridization (FISH) was combined with detailed genomic and transcriptomic reconstruction to elucidate the ecophysiological role of Aigarchaeota in these streamer communities. This novel population of Aigarchaeota are filamentous (~500 nm diameter by ~10-30 μm length), which is consistent with the morphology predicted by the presence and transcription of a single actin-encoding gene. Aigarchaeota filaments are intricately associated with other community members, which include both thermophilic bacteria and archaea. Metabolic reconstruction suggests that this aigarchaeon is an aerobic, chemoorganotroph. A single heme copper oxidase complex was identified in de novo genome assemblies, and was highly transcribed in environmental samples. Potential electron donors include acetate, fatty acids, sugars, peptides, and aromatic compounds. Transcripts related to genes specific to each of these potential electron donors were identified, indicating that this population of Aigarchaeota likely utilizes a broad range of reduced carbon substrates. Potential electron donors for this population may include extracellular polymeric substances produced by other microorganisms in close proximity. Flagellum genes were also highly transcribed, which suggests a potential mechanism for motility and/or cell-cell attachment

  13. Globally Deghosting for Marine Streamer with Alternating Minimization Approach in Frequency-slowness Domain

    Science.gov (United States)

    Wang, C.; Zhu, Z.; Gu, H.; Liu, C.; Liu, Z.; Jiao, Z.

    2017-12-01

    The ghost effects of the sea surface can generate notch in marine towed-streamer data, which results in narrow bandwidth of seismic data. Currently, deghosting is widely utilized to increase the bandwidth of the seismic data or the images. However, most of the conventional deghosting algorithms havenot considered the error of streamer depth causing a biased ghost-delay time (τ) with respect to primary reflection and amplitude difference coefficient (r) between ghost and primary reflection varies with offset due to rugged seabed and target depth variation. We proposed a ghost filtering operator considering the protentional biases within the ghost-delay time (τ) and the amplitude difference coefficient (r). The up-going wavefield (u), ghost-delay time (τ) and amplitude difference coefficient (r) can be obtained by utilizing alternating minimization approach for minimizing the difference between actual wavefield and theoretical wavefield in frequency-slowness domain. The main idea is to alternatively updating u, τ and r in each iteration: we update u by least-squares when we keep τ and r constant; and we then keep u constant and optimize over τ and r with a closed-form solution which is closely related to matched filtering. The convergence of the proposed algorithm is guaranteed since we have closed-form solutions for each stage. The experiments on synthetic record confirmed the reliability of the proposed algorithm. We also demonstrate our proposed method in marine VDS shot acquisition. After migration stack processing, our ghosting method significantly increases the bandwidth of the average amplitude, amplitude energy of the medium and high frequency spectrum, improving resolution of medium and deep reflection and providing higher signal-to-noise ratio with clear break point. This research is funded by China Important National Science & Technology Specific Projects (2016ZX05026001-001).

  14. Group leaders optimization algorithm

    Science.gov (United States)

    Daskin, Anmer; Kais, Sabre

    2011-03-01

    We present a new global optimization algorithm in which the influence of the leaders in social groups is used as an inspiration for the evolutionary technique which is designed into a group architecture. To demonstrate the efficiency of the method, a standard suite of single and multi-dimensional optimization functions along with the energies and the geometric structures of Lennard-Jones clusters are given as well as the application of the algorithm on quantum circuit design problems. We show that as an improvement over previous methods, the algorithm scales as N 2.5 for the Lennard-Jones clusters of N-particles. In addition, an efficient circuit design is shown for a two-qubit Grover search algorithm which is a quantum algorithm providing quadratic speedup over the classical counterpart.

  15. Leading Your Leaders

    Science.gov (United States)

    Hale, Wayne N.

    2008-01-01

    Even though working on a problem has been your primary effort for the past year, your leadership may have heard about this once in a briefing a decade ago. Now they are basically clueless. Pretend that you are talking to your daughter's fifth-grade class. Explain how your complicated gizmo works. If possible, do not use acronyms. Define your terms. Put your work in context. Assume your leader has no idea what you do, who you work for, or what your gizmo does. That is a good place to start. Remember, taking the next century to study the problem or spending the Gross National Product to invent a new solution are probably not going to be acceptable solutions. Real engineers and technicians build real hardware that works in the real world in a reasonable manner within a reasonable time at a reasonable cost. True, skimping on time or money can cause mistakes, but folks whose gizmos are delayed unreasonably or cost more than is practical get their programs canceled, force the business into bankruptcy, or give the market over to the competition. Real engineers and technicians always consider cost and schedule in their work. Raising questions is important. However, we are in the business of doing things. Engineers and technicians are paid to get things done. Yes, you have to identify the problem, frame the design, identify the tests, perform the analysis, and assemble the hardware. But the goal is to solve the problem. Nobody ever said flying in space was easy. We make it look easy the same way that an Olympic champion makes her sport look easy: by working hard at improving performance every day. Better are the results of a well-defined test. Remember that a test on a laboratory bench is always an approximation of reality, and rules similar to those for good analysis also apply. One should always be mindful of Mechelay's rule: "It is better to be stupid than to run a stupid test." Often we try to overtest. If a piece of hardware passes an unbelievably difficult test, then

  16. The uncompromising leader.

    Science.gov (United States)

    Eisenstat, Russell A; Beer, Michael; Foote, Nathaniel; Fredberg, Tobias; Norrgren, Flemming

    2008-01-01

    Managing the tension between performance and people is at the heart of the CEO's job. But CEOs under fierce pressure from capital markets often focus solely on the shareholder, which can lead to employee disenchantment. Others put so much stock in their firms' heritage that they don't notice as their organizations slide into complacency. Some leaders, though, manage to avoid those traps and create high-commitment, high-performance (HCHP) companies. The authors' in-depth research of HCHP CEOs reveals several shared traits: These CEOs earn the trust of their organizations through their openness to the unvarnished truth. They are deeply engaged with their people, and their exchanges are direct and personal. They mobilize employees around a focused agenda, concentrating on only one or two initiatives. And they work to build collective leadership capabilities. These leaders also forge an emotionally resonant shared purpose across their companies. That consists of a three-part promise: The company will help employees build a better world and deliver performance they can be proud of, and will provide an environment in which they can grow. HCHP CEOs approach finding a firm's moral and strategic center in a competitive market as a calling, not an engineering problem. They drive their firms to be strongly market focused while at the same time reinforcing their firms' core values. They are committed to short-term performance while also investing in long-term leadership and organizational capabilities. By refusing to compromise on any of these terms, they build great companies.

  17. Tartus alustas tegevust LEADER infokeskus

    Index Scriptorium Estoniae

    2005-01-01

    Tartus alustas tegevust LEADER infokeskus, mille eesmärk on informeerida ja nõustada maakondade omavalitsustöötajate, ettevõtjate ning MTÜde esindajaid, kes on huvitatud Eesti riikliku arengukava meetme "Kohaliku initsiatiivi arendamine - LEADER-tüüpi meetme raames toetuse saamisest ning selleks vajalike partnerlusel põhinevate kohalike tegevusgruppide loomisest"

  18. Future Leaders: The Way Forward?

    Science.gov (United States)

    Earley, Peter; Weindling, Dick; Bubb, Sara; Glenn, Meli

    2009-01-01

    The recruitment and retention of senior school leaders is high on the UK Government's agenda with much attention currently being given to succession planning. Future Leaders and other fast track leadership development programmes are, in part, a response to this "crisis" brought about by demographic change--many headteachers are due to…

  19. From the Field: Learning Leaders

    Science.gov (United States)

    Weigel, Kathleen; Jones, Richard

    2015-01-01

    Leadership is essential to successful schools. One of the ways to support effective school leadership is to share ideas and best practices to address the common challenges faced by school leaders. This question and response format addresses common challenges and questions from practicing school leaders in the manner that a mentor might respond to…

  20. Ethical leader behavior and leader effectiveness: the role of prototypicality and trust

    NARCIS (Netherlands)

    Kalshoven, K.; den Hartog, D.N.

    2009-01-01

    The study examines factors that mediate the impact of ethical leader behavior on leader effectiveness. Little is known about how ethical leadership impacts leader effectiveness. We hypothesized that prototypicality and trust sequentially mediate the relationship between ethical leader behavior and

  1. Kinetics and dynamics of nanosecond streamer discharge in atmospheric-pressure gas bubble suspended in distilled water under saturated vapor pressure conditions

    KAUST Repository

    Sharma, Ashish; Levko, Dmitry; Raja, Laxminarayan L; Cha, Min

    2016-01-01

    We perform computational studies of nanosecond streamer discharges generated in helium bubbles immersed in distilled water under atmospheric pressure conditions. The model takes into account the presence of water vapor in the gas bubble

  2. Sub-nanosecond delays of light emitted by streamer in atmospheric pressure air: Analysis of N2( C3Πu) and N2+(B2Σ u +) emissions and fundamental streamer structure

    Czech Academy of Sciences Publication Activity Database

    Hoder, T.; Bonaventura, Z.; Bourdon, A.; Šimek, Milan

    2015-01-01

    Roč. 117, č. 7 (2015), 073302-073302 ISSN 0021-8979 R&D Projects: GA ČR(CZ) GAP205/12/1709 Institutional support: RVO:61389021 Keywords : streamer * optical diagnostics * nitrogen * emission Subject RIV: BL - Plasma and Gas Discharge Physics Impact factor: 2.101, year: 2015 http://scitation.aip.org/content/aip/journal/jap/117/7/10.1063/1.4913215

  3. Kinetics and dynamics of nanosecond streamer discharge in atmospheric-pressure gas bubble suspended in distilled water under saturated vapor pressure conditions

    KAUST Repository

    Sharma, Ashish

    2016-09-08

    We perform computational studies of nanosecond streamer discharges generated in helium bubbles immersed in distilled water under atmospheric pressure conditions. The model takes into account the presence of water vapor in the gas bubble for an accurate description of the discharge kinetics. We find that the dynamic characteristics of the streamer discharge are different at low and high positive trigger voltages with the axial streamer evolution dominant for low voltages and a surface hugging mode favored for high voltages. We also find a substantial difference in initiation, transition and evolution stages of discharge for positive and negative trigger voltages with the volumetric distribution of species in the streamer channel much more uniform for negative trigger voltages on account of the presence of multiple streamers. We observe that the presence of water vapor does not affect the breakdown voltage even for oversaturated conditions but significantly influences the composition of dominant species in the trail of the streamer as well as the flux of the dominant species on the bubble surface. © 2016 IOP Publishing Ltd.

  4. Remembering the Leaders of China.

    Science.gov (United States)

    Fu, Mingchen; Xue, Yan; DeSoto, K Andrew; Yuan, Ti-Fei

    2016-01-01

    In two studies, we examined Chinese students' memory for the names of the leaders of China. In Study 1, subjects were cued with the names of periods from China's history. Subjects listed as many leaders as possible from each period and put them in the correct ordinal position when they could (see Roediger and DeSoto, 2014). Results showed that within each period, a primacy effect and sometimes a recency effect emerged. Moreover, the average recall probability for leaders within a specific period was a function of the ordinal position of the period. In Study 2, we asked another group of subjects to identify the sources through which they were able to recall each leader. We found that most subjects remembered leaders due to class and coursework. We also found a relation between a leader's recall probability and the amount of information available on that leader on the Internet. Our findings further imply that the serial position function captures the form of collective memory.

  5. A southeastern Mediterranean PV streamer and its role in December 2001 case with torrential rains in Israel

    Directory of Open Access Journals (Sweden)

    S. O. Krichak

    2007-01-01

    Full Text Available A precipitation event of unprecedented intensity took place over northern part of Israel during 4 December 2001–5 December 2001. The case was associated with formation of a Cyprus Low cyclone over the Asia Minor. In the current study the synoptic developments over the eastern part of the Mediterranean region are simulated with the MM5 nonhydrostatic model and analyzed based on dynamic tropopause patterns calculated from the simulation results. According to the results, a powerful potential vorticity (PV streamer system played a major role in the process over the southeastern Mediterranean region. The PV streamer created conditions for seclusion of moist air masses from the equatorial East Africa and Atlantics during the cyclone development. Condensation of the moisture, associated with the latent heat release processes have contributed to the intense thunderstorm activity and heavy precipitation of the event.

  6. Towards User-Friendly Spelling with an Auditory Brain-Computer Interface: The CharStreamer Paradigm

    Science.gov (United States)

    Höhne, Johannes; Tangermann, Michael

    2014-01-01

    Realizing the decoding of brain signals into control commands, brain-computer interfaces (BCI) aim to establish an alternative communication pathway for locked-in patients. In contrast to most visual BCI approaches which use event-related potentials (ERP) of the electroencephalogram, auditory BCI systems are challenged with ERP responses, which are less class-discriminant between attended and unattended stimuli. Furthermore, these auditory approaches have more complex interfaces which imposes a substantial workload on their users. Aiming for a maximally user-friendly spelling interface, this study introduces a novel auditory paradigm: “CharStreamer”. The speller can be used with an instruction as simple as “please attend to what you want to spell”. The stimuli of CharStreamer comprise 30 spoken sounds of letters and actions. As each of them is represented by the sound of itself and not by an artificial substitute, it can be selected in a one-step procedure. The mental mapping effort (sound stimuli to actions) is thus minimized. Usability is further accounted for by an alphabetical stimulus presentation: contrary to random presentation orders, the user can foresee the presentation time of the target letter sound. Healthy, normal hearing users (n = 10) of the CharStreamer paradigm displayed ERP responses that systematically differed between target and non-target sounds. Class-discriminant features, however, varied individually from the typical N1-P2 complex and P3 ERP components found in control conditions with random sequences. To fully exploit the sequential presentation structure of CharStreamer, novel data analysis approaches and classification methods were introduced. The results of online spelling tests showed that a competitive spelling speed can be achieved with CharStreamer. With respect to user rating, it clearly outperforms a control setup with random presentation sequences. PMID:24886978

  7. LIF study of N2(A3+u, v=0-10) vibrational kinetics under nitrogen streamer conditions

    Czech Academy of Sciences Publication Activity Database

    Šimek, Milan; Ambrico, P. F.; Prukner, Václav

    2015-01-01

    Roč. 48, č. 26 (2015), s. 265202-265202 ISSN 0022-3727 R&D Projects: GA ČR(CZ) GAP205/12/1709 Institutional support: RVO:61389021 Keywords : nitrogen metastable * streamer * optical diagnostics * laser-induced fluorescence * LIF Subject RIV: BL - Plasma and Gas Discharge Physics Impact factor: 2.772, year: 2015 http://dx.doi.org/10.1088/0022-3727/48/26/265202

  8. Mapping the base of sand dunes using a new design of land-streamer for static correction applications

    KAUST Repository

    Almalki, H.

    2012-05-16

    The complex near-surface structure is a major problem in land seismic data. This is more critical when data acquisition takes place over sand dune surfaces, where the base of the sand acts as a trap for energy and, depending on its shape, can considerably distort conventionally acquired seismic data. Estimating the base of the sand dune surface can help model the sand dune and reduce its harmful influence on conventional seismic data. Among the current methods to do so are drilling upholes and using conventional seismic data to apply static correction. Both methods have costs and limitations. For upholes, the cost factor and their inability to provide a continuous model is well realized. Meanwhile, conventional seismic data lack the resolution necessary to obtain accurate modeling of the sand basement. We developed a method to estimate the sand base from land-streamer seismic acquisition that is developed and geared to sand surfaces. Seismic data acquisition took place over a sand surface in the Al-Thumamah area, where an uphole is located, using the developed land-streamer and conventional spiked geophone systems. Land-streamer acquisition not only provides a more efficient data acquisition system than the conventional spiked geophone approach, but also in our case, the land-streamer provided better quality data with a broader frequency bandwidth. Such data enabled us to do accurate near-surface velocity estimation that resulted in velocities that are very close to those measured using uphole methods. This fact is demonstrated on multiple lines acquired near upholes, and agreement between the seismic velocities and the upholes is high. The stacked depth seismic section shows three layers. The interface between the first and second layers is located at 7 m depth, while the interface between second and third layers is located at 68 m depth, which agrees with the uphole result. 2012 The Author(s).

  9. Behaviour of OH radicals in an atmospheric-pressure streamer discharge studied by two-dimensional numerical simulation

    International Nuclear Information System (INIS)

    Komuro, Atsushi; Ono, Ryo; Oda, Tetsuji

    2013-01-01

    The production process of OH radicals in an atmospheric-pressure streamer discharge is studied. A streamer discharge model is developed to analyse the characteristics of a pulsed positive streamer discharge in point-to-plane electrodes filled with humid air at atmospheric pressure. The results indicate that the behaviour of OH radicals in and after the discharge pulse is characterized by three reaction processes: ‘OH-production’, ‘OH-cycle’ and ‘OH-recombination’. The first process of OH-production includes dissociation reactions of H 2 O with O( 1 D) and N 2 (a' 1 Σ u - ), which are the main production processes of OH in the discharge. Immediately after the OH-production process, the OH radicals are destroyed by a reaction with O( 3 P) to form O 2 and H. Then the subsequent reactions produce OH again through the reaction of H + HO 2 , which is the OH-cycle process. Finally, the OH radicals are consumed by the OH-recombination process. (paper)

  10. Observed tail current systems associated with bursty bulk flows and auroral streamers during a period of multiple substorms

    Directory of Open Access Journals (Sweden)

    C. Forsyth

    2008-02-01

    Full Text Available We present a multi-instrument study of a substorm bursty bulk flow (BBF and auroral streamer. During a substorm on 25 August 2003, which was one of a series of substorms that occurred between 00:00 and 05:00 UT, the Cluster spacecraft encountered a BBF event travelling Earthwards and duskwards with a velocity of ~500 km s−1 some nine minutes after the onset of the substorm. Coincident with this event the IMAGE spacecraft detected an auroral streamer in the substorm auroral bulge in the Southern Hemisphere near the footpoints of the Cluster spacecraft. Using FluxGate Magnetometer (FGM data from the four Cluster spacecraft, we determine the field-aligned currents in the BBF, using the curlometer technique, to have been ~5 mA km−2. When projected into the ionosphere, these currents give ionospheric field-aligned currents of ~18 A km−2, which is comparable with previously observed ionospheric field-aligned currents associated with BBFs and auroral streamers. The observations of the BBF are consistent with the plasma "bubble" model of Chen and Wolf (1993. Furthermore, we show that the observations of the BBF are consistent with the creation of the BBF by the reconnection of open field lines Earthward of a substorm associated near-Earth neutral line.

  11. Observed tail current systems associated with bursty bulk flows and auroral streamers during a period of multiple substorms

    Directory of Open Access Journals (Sweden)

    C. Forsyth

    2008-02-01

    Full Text Available We present a multi-instrument study of a substorm bursty bulk flow (BBF and auroral streamer. During a substorm on 25 August 2003, which was one of a series of substorms that occurred between 00:00 and 05:00 UT, the Cluster spacecraft encountered a BBF event travelling Earthwards and duskwards with a velocity of ~500 km s−1 some nine minutes after the onset of the substorm. Coincident with this event the IMAGE spacecraft detected an auroral streamer in the substorm auroral bulge in the Southern Hemisphere near the footpoints of the Cluster spacecraft. Using FluxGate Magnetometer (FGM data from the four Cluster spacecraft, we determine the field-aligned currents in the BBF, using the curlometer technique, to have been ~5 mA km−2. When projected into the ionosphere, these currents give ionospheric field-aligned currents of ~18 A km−2, which is comparable with previously observed ionospheric field-aligned currents associated with BBFs and auroral streamers. The observations of the BBF are consistent with the plasma "bubble" model of Chen and Wolf (1993. Furthermore, we show that the observations of the BBF are consistent with the creation of the BBF by the reconnection of open field lines Earthward of a substorm associated near-Earth neutral line.

  12. Teambuilding: A Strategic Leader Imperative

    National Research Council Canada - National Science Library

    Putko, Christopher J

    2006-01-01

    .... An Army Training and Leader Development Panel (ATLDP) - 2001 cited team building components in need of improvement to include command climate empowerment of subordinates, mentorship, counseling, accountability, and feedback...

  13. Potential Leaders and Democratic Values

    Science.gov (United States)

    Monsma, Stephen V.

    1971-01-01

    Indicates that potential contenders for public office are likely to be more knowledgeable, interested, and libertarian than the average citizen. Concludes that these differences exist before leaders are elected and that this discrimination is functional in a democracy. (MB)

  14. Employees' Perceptions of Their Leaders

    Directory of Open Access Journals (Sweden)

    Golubović-Stojanović Aleksandra

    2016-06-01

    Full Text Available This paper presents the research about employees and the leaders who are included in leading the organization, as an important segment of the modern business. The aim of this research is to show the real picture about presence new strategies of leaders in the organizations, as well as the analysis of the perception of employees about their leaders. The research in business organizations conducted on the sample of leaders and employees. The construction of high-quality questionnaire represents the important segment of modern statistical and business researches. The issues in questionnaire construction are very complex and they are in the focus of all statistical and research methodologies. It was conducted on the sample of at least 250 examinees (employees in bigger companies in Serbia. Research results showed that understanding communication satisfaction, with its link to job satisfaction, should provide an ability to better target resources to improve communication satisfaction issues.

  15. Information Operations: Training the Leaders

    National Research Council Canada - National Science Library

    Ferriter, Michael

    1999-01-01

    The purpose of this project is to determine if the Army's officer education and training systems adequately prepare our leaders to operate within, and to deploy, fight, and win in the Information Age...

  16. Types of Leader in Organisation

    OpenAIRE

    Marian Aurelian Bârgău

    2015-01-01

    Besides leading theories of people in one way or another from different angles reveal the types of leaders who can meet in business management literature contains classifications of management styles, which take into account different criteria or viewpoints. The word “leadership‟ has been used in various aspects of human endeavor such as politics, businesses, academics, social works, etc. Previous views about leadership show it as personal ability. The individual leader traits dep...

  17. Leader competencies in virtual organization

    OpenAIRE

    Bulinska-Stangrecka, Helena

    2018-01-01

    This paper discusses the competence required in the leadership of virtual organization. The specics of virtual organization presents a challenge to traditional managerial styles. In order to achieve success in virtual environment, a leader must develop specic abilities. This analysis examines the uniqueness of the virtual organization, including team work and management. The last part presents ndings and summaries regarding e€ective e-leadership requirement. A virtual leader ma...

  18. Remembering the Leaders of China

    Directory of Open Access Journals (Sweden)

    Mingchen eFu

    2016-03-01

    Full Text Available In two studies, we examined Chinese students’ memory for the names of the leaders of China. In Study 1, subjects were cued with the names of periods from China’s history. Subjects listed as many leaders as possible from each period and put them in the correct ordinal position when they could (see Roediger & DeSoto, 2014. Results showed that within each period, a primacy effect and sometimes a recency effect emerged. Moreover, the average recall probability for leaders within a specific period was a function of the ordinal position of the period. In Study 2, we asked another group of subjects to identify the sources through which they were able to recall each leader. We found that most subjects remembered leaders thanks to class and coursework. We also found a relation between a leader’s recall probability and the amount of information available on that leader on the Internet. Our findings further imply that the serial position function captures the form of collective memory.

  19. Low-mass X-ray binaries and globular clusters streamers and arcs in NGC 4278

    Energy Technology Data Exchange (ETDEWEB)

    D' Abrusco, R.; Fabbiano, G. [Harvard-Smithsonian Astrophysical Observatory, 60 Garden Street, Cambridge, MA 02138 (United States); Brassington, N. J. [Center for Astrophysics Research, University of Hertfordshire, College Lane Campus, Hatfield, Hertordshire, AL10 9AB (United Kingdom)

    2014-03-01

    We report significant inhomogeneities in the projected two-dimensional spatial distributions of low-mass X-ray binaries (LMXBs) and globular clusters (GCs) of the intermediate mass elliptical galaxy NGC 4278. In the inner region of NGC 4278, a significant arc-like excess of LMXBs extending south of the center at ∼50'' in the western side of the galaxy can be associated with a similar overdensity of the spatial distribution of red GCs from Brassington et al. Using a recent catalog of GCs produced by Usher et al. and covering the whole field of the NGC 4278 galaxy, we have discovered two other significant density structures outside the D {sub 25} isophote to the W and E of the center of NGC 4278, associated with an overdensity and an underdensity, respectively. We discuss the nature of these structures in the context of the similar spatial inhomogeneities discovered in the LMXBs and GCs populations of NGC 4649 and NGC 4261, respectively. These features suggest streamers from disrupted and accreted dwarf companions.

  20. Composite film fabricated on biomedical material with corona streamer plasma processing to mitigate bacterial adhesion

    Science.gov (United States)

    Alhamarneh, Ibrahim; Pedrow, Patrick; Eskhan, Asma; Abu-Lail, Nehal

    2011-10-01

    Composite films might control bacterial adhesion and concomitant biofouling that afflicts biomedical materials. Different size molecules of polyethylene glycol (PEG) with nominal molecular weights 600, 2000, and 20000 g/mol were used to synthesize composite films with plasma processing and dip-coating procedures on surgical-grade 316L stainless steel. Before dip-coating, the substrate was pre-coated with plasma-polymerized di(ethylene glycol) vinyl ether (pp-EO2V) in an atmospheric pressure corona streamer plasma reactor. The PEG dip-coating step followed immediately in the same chamber due to the finite lifetime of radicals associated with freshly deposited pp-EO2V. Morphology of the composite film was investigated with an ESEM. FTIR confirmed incorporation of pp-EO2V and PEG species into the composite film. More investigations on the composite film were conducted by XPS measurements. Adhesion of the composite film was evaluated with a standard peel-off test. Stability of the composite film in buffer solution was evaluated by AFM. AFM was also used to measure the film roughness and thickness. Polar and non-polar contact angle measurements were included.

  1. NO-γ emissions from streamer discharges: direct electron impact excitation versus resonant energy transfer

    International Nuclear Information System (INIS)

    Liu Ningyu; Pasko, Victor P

    2010-01-01

    It has been established that production of NO-γ emission in pulsed corona discharges is dominated by the energy transfer from N 2 (A 3 Σ u + ) to the NO ground state NO(X 2 Π r ) while direct excitation by electron impact is negligible. However, recent studies suggest that the electron impact excitation plays a more important role. In this work, we report modelling results of NO-γ emission associated with streamer discharges using two cross section data sets available in the literature. The first set was originally reported by Mojarrabi et al (1996 Phys. Rev. A 54 2977-82) and later updated by Brunger et al (2000 J. Phys. B: At. Mol. Opt. Phys. 33 809-19); the second set was published by Hayashi (1990 Nonequilibrium Processes in Partially Ionized Gases (NATO Advanced Science Institutes Series, Series B, Physics vol 220) ed M Capitelli and J N Bardsley (New York: Plenum) pp 333-40). According to the results, the role played by the electron impact excitation in the production of NO-γ is drastically different when different cross sections are used. The results indicate that the first data set leads to better agreement with experimental measurements. (fast track communication)

  2. On the data compression at filmless readout of the streamer chamber information

    International Nuclear Information System (INIS)

    Bajla, I.; Ososkov, G.A.; Prikhod'ko, V.I.

    1980-01-01

    It is supposed that the system of filmless detecting and processing the visual information from ''RISK'' streamer chamber will comprise the effective on-line data compression algorithm. The role of the basic methodological principles of chamber image film processing in Righ Energy Physics for building up such system is analysed. On the basis of this analysis the main requirements are formulated that have to be fulfilled by the compression algorithm. The most important requirement consists in securing the possibility of the input data reprocessing, if problems in the off-line recognition occur. Using a vector system representation of primary data, the on-line data compression philosophy is proposed that embodies the following three principles: universality, parallelism and input data reconstructibility. Excluding of the recognition procedure from the on-line compression algorithm causes the compression factor reduction. The hierarchic structure of the compression algorithm consisting of (1) sorting, (2) filtering, (3) compression for an additional increasing of the compression ratio is proposed

  3. Three-dimensional magnetohydrodynamic simulations of in situ shock formation in the coronal streamer belt

    International Nuclear Information System (INIS)

    Zaliznyak, Yu.; Keppens, R.; Goedbloed, J.P.

    2003-01-01

    A numerical study of an idealized magnetohydrodynamic (MHD) configuration consisting of a planar wake flow embedded into a three-dimensional (3D) sheared magnetic field is presented. The simulations investigate the possibility for in situ development of large-scale compressive disturbances at cospatial current sheet-velocity shear regions in the heliosphere. Using a linear MHD solver, the systematical investigation of the destabilized wavenumbers, corresponding growth rates, and physical parameter ranges for dominant 3D sinuous-type instabilities in an equilibrium wake-current sheet system was done. Wakes bounded by sufficiently supersonic (Mach number M s >2.6) flow streams are found to support dominant fully 3D sinuous instabilities when the plasma beta is of order unity. Fully nonlinear, compressible 2.5D and 3D MHD simulations show the self-consistent formation of shock fronts of fast magnetosonic type. They carry density perturbations far away from the wake's center. Shock formation conditions are identified in sonic and Alfvenic Mach number parameter space. Depending on the wake velocity contrast and magnetic field magnitude, as well as on the initial perturbation, the emerging shock patterns can be plane-parallel as well as fully three-dimensionally structured. Similar large-scale transients could therefore originate at distances far above coronal helmet streamers or at the location of the ecliptic current sheet

  4. Radiation thickness gauge using beta particle sensitivity controlled open air corona streamer counter

    International Nuclear Information System (INIS)

    Fouad, L.; El-Hazek, S.; El-Araby, S.

    1999-01-01

    Beta particles have been used extensively in radio gauging applications when measurements of foil thicknesses are desired. Using beta particle open air corona streamer counter (point-grid-plane) as a thickness gauge is presented. This gauge consists of two similar counters with two similar Sr-90 beta sources. One counter-source combination is called standard unit, and the other counter-source combination is called measuring unit in which the required foil thickness can be measured by inserting it between the source and the counter. The signals from the counters are amplified with the same gain factor and the net difference between their responses is measured using specially designed electronic circuit. By this way any change that takes place in the operating medium (variation of parameters of open air i.e. temperature, humidity...etc) can similarly affect the two units, the errors in the measurements caused by them are cancelled, and the only response is due to the measured foil thickness. A theoretical model is suggested to explain and analyze the overall response of the gauge system and calculate the calibration thickness gauge constant. All theoretical findings are confirmed by experiments

  5. Simultaneous emissions of X-rays and microwaves from long laboratory sparks and downward lightning leaders

    Science.gov (United States)

    Montanya, J.; Oscar, V. D. V.; Tapia, F. F.

    2017-12-01

    Since the discovery of the Terrestrial Gamma-ray Flashes more than 20 years ago, investigations on high energy emissions from natural lightning and high voltage laboratory sparks gained significant interest. X-ray emissions from lightning as well from high voltage laboratory sparks have in common the role played by negative leaders/streamers. On the other hand, negative leaders are well known to produce much more VHF and microwave radiation than positive leaders. Moreover, in previous works, microwave emissions from lightning leaders have been attributed to Bremsstrahlung process. The object of this work is to investigate if X-rays and RF microwave emissions share the same origin. We present simultaneous measurements of X-rays and microwaves in high voltage sparks and natural lightning. The instrumentation consists on a NaI(Tl) and LaBr3 scintillation detectors and two different receivers. One is fix tuned at 2.4 GHz with a bandwidth of 5.5 MHz. The second can be tuned at any frequency up to 18 GHz with different selectable bandwidths of 10 MHz, 40 MHz and 100 MHz. In the laboratory, results have shown that all the sparks presented microwave radiation before the breakdown of the gap, either X-rays were detected or not. In the cases where X-rays were identified, microwave emissions peaked at the same time (in the microsecond scale). We found that the power amplitudes of the microwave emissions are related to the applied voltage to the gap. In the same configuration, those cases where X-rays were detected microwave emissions presented higher power levels. The results suggest that in some part of the discharge electrons are very fast accelerated allowing, in some cases, to reach enought energy to produce X-rays. In the field, we have found similar results. On 13th of June of 2015 a bipolar cloud-to-ground flash struck 200 m close to the Eagle Nest instrumented tower (Spanish Pyrenees, 2536 m ASL). The flash presented four strokes and, in all of them, microwave

  6. What Is an Innovative Educational Leader?

    Science.gov (United States)

    Marron, Joseph M.; Cunniff, Dan

    2014-01-01

    This paper outlined the traits of an innovative educational leader in our changing society. It discussed the difference in a manager and leader, as well as the specific dispositions that differentiate the innovative educational leader from what many consider the average leader. The authors used the acronym "HELPSS" to highlight the…

  7. Kansas nurse leader residency programme: advancing leader knowledge and skills.

    Science.gov (United States)

    Shen, Qiuhua; Peltzer, Jill; Teel, Cynthia; Pierce, Janet

    2018-03-01

    To evaluate the effectiveness of the Kansas Nurse Leader Residency (KNLR) programme in improving nurses' leadership knowledge and skills and its acceptability, feasibility and fidelity. The Future of Nursing Report (Institute of Medicine, 2011) calls for nurses to lead change and advance health. The 6-month KNLR programme was developed by the Kansas Action Coalition to support nurses' leadership development. Nurses (n = 36) from four nursing specialties (acute care, long-term care, public health and school health) participated in the programme. The adapted Leader Knowledge and Skill Inventory was used to assess leadership knowledge and skills. Programme acceptability, feasibility and implementation fidelity also were evaluated. The programme completion rate was 67.7% (n = 24). Programme completers had significantly improved self-assessed and mentor-assessed leadership knowledge and skills (p leaders are critical for successful transition into management positions. © 2017 John Wiley & Sons Ltd.

  8. The Emotional Intelligence of Leaders as Antecedent to Leader-Member Exchanges: A Field Study

    Science.gov (United States)

    Barbuto, John E., Jr.; Bugenhagen, Marilyn J.

    2009-01-01

    Eighty elected leaders and 388 followers were sampled to test the relationships between leaders' emotional intelligence and the quality of leader-member exchange. Results of the field study found a significant relationship between leaders' emotional intelligence (total) and leader-member exchange quality. Specific subscales of emotional…

  9. Narcissistic leaders: An asset or a liability? Leader visibility, follower responses, and group-level absenteeism.

    Science.gov (United States)

    Nevicka, Barbara; Van Vianen, Annelies E M; De Hoogh, Annebel H B; Voorn, Bart C M

    2018-03-19

    Although narcissists often emerge as leaders, research has thus far shown inconsistent results on the relationship between leader narcissism and effectiveness in the eyes of followers. Here we draw on leader distance theory (Shamir, 1995) and implicit leader theory (Lord & Maher, 1991) to propose that followers' assessment of a narcissistic leader and followers' overall job attitudes depend on the leader's visibility to the followers. The more opportunities followers have to observe narcissistic leaders the more they will experience these leaders' toxic behavior (e.g., exploitativeness) and the less they will perceive the leader as effective. To test our hypotheses we collected multisource, longitudinal data from 175 retail stores and obtained subjective (followers' perceptions of leader effectiveness and their overall job attitudes) as well as objective (leaders' organizational experience at time of hire, employee absenteeism trends) indices of leader functionality. Results showed that narcissistic leaders had less organizational experience at the time they were hired. Moreover, when followers had fewer opportunities to observe their leader, leader narcissism was positively related to perceived leadership effectiveness and job attitudes. However, when followers had more opportunity to observe their leader, the positive relationship disappeared. Finally, leader narcissism was neither positively nor negatively associated with absenteeism, whereas absenteeism declined over time under non-narcissistic leaders. These findings advance our knowledge of how followers respond to narcissistic leaders and how these leaders function in organizational settings where they have legitimate positions of power. (PsycINFO Database Record (c) 2018 APA, all rights reserved).

  10. Analyses of electron runaway in front of the negative streamer channel

    DEFF Research Database (Denmark)

    Babich, L. P.; Bochkov, E. I.; Kutsyk, I. M.

    2017-01-01

    X-and γ-ray emissions, observed in correlation with negative leaders of lightning and long sparks of high-voltage laboratory experiments, are conventionally connected with the bremsstrahlung of high-energy runaway electrons (REs). Here we extend a focusing mechanism, analyzed in our previous paper...

  11. Preliminary investigation into laser high voltage interaction in the case of streamer-to-leader process using a high power CO2 laser

    CSIR Research Space (South Africa)

    West, NJ

    2006-01-01

    Full Text Available This paper describes the preliminary small-scale experiments conducted in order to investigate the influence of intensely focused laser light produced by a CO2 laser on high voltage fields. The laser used operated at a maximum energy of 430 mJ per...

  12. Travel opinion leaders and seekers

    DEFF Research Database (Denmark)

    Yoo, Kyung-Hyan; Gretzel, Ulrike; Zach, Florian

    2011-01-01

    While opinion leadership has been recognized as important in tourism, there has been very little empirical research investigating the phenomenon. Given new developments in social media technologies, it is especially important to understand whether travel opinion leadership and seeking are drivers...... of specific social media perceptions and behaviours. Based on an online survey of US online travellers, this paper seeks to identify travel opinion leaders and seekers and their characteristics. Further, the research conducted investigated linkages between travel opinion leadership/seeking and travel social...... media use. The findings suggest that travel opinion leadership and seeking are distinct but connected. Both opinion leaders and seekers are technology savvy, young, educated, involved in travel planning and engaged in social media use for travel. What distinguishes opinion leaders is their greater...

  13. Preparing nurse leaders for 2020.

    Science.gov (United States)

    Huston, Carol

    2008-11-01

    This article highlights eight leadership competencies likely to be an essential part of the nurse leader's repertoire in 2020. Planning for the future is difficult, even when environments are relatively static. When environments are dynamic, the challenges multiply exponentially. Unfortunately, few environments have been more unpredictable in the 21st century than health care. The healthcare system is in chaos, as is much of the business world. It is critical then that contemporary nursing and healthcare leaders identify skill sets that will be needed by nurse leaders in 2020 and begin now to create the educational models and management development programs necessary to assure these skills are present. Essential nurse leader competencies for 2020 include: (i) A global perspective or mindset regarding healthcare and professional nursing issues. (ii) Technology skills which facilitate mobility and portability of relationships, interactions, and operational processes. (iii) Expert decision-making skills rooted in empirical science. (iv) The ability to create organization cultures that permeate quality healthcare and patient/worker safety. (v) Understanding and appropriately intervening in political processes. (vi) Highly developed collaborative and team building skills. (vii) The ability to balance authenticity and performance expectations. (viii) Being able to envision and proactively adapt to a healthcare system characterized by rapid change and chaos. Nursing education programmes and healthcare organizations must be begin now to prepare nurses to be effective leaders in 2020. This will require the formal education and training that are a part of most management development programmes as well as a development of appropriate attitudes through social learning. Proactive succession planning will also be key to having nurse leaders who can respond effectively to the new challenges and opportunities that will be presented to them in 2020.

  14. Combined Logistics Officers Advanced Course (CLOAC): Leader Development for Future Ordnance Strategic Leaders

    National Research Council Canada - National Science Library

    Shipley, Claude

    1998-01-01

    Formal training is one of the methods for development of strategic leaders. The development of strategic Ordnance leaders is rooted initially with an officer first becoming competent as a leader and knowledgeable in their technical skills...

  15. Future Leaders Institute: Rising Leaders and the AACC Competencies

    Science.gov (United States)

    Wallin, Desna L.

    2012-01-01

    The overall mission of the American Association of Community Colleges (AACC) is "Building a Nation of Learners by Advancing America's Community Colleges." A significant component of this mission statement involves the development of leadership. The AACC believes that leadership can be learned and is committed to supporting and growing leaders. In…

  16. Multisource least-squares migration of marine streamer and land data with frequency-division encoding

    KAUST Repository

    Huang, Yunsong; Schuster, Gerard T.

    2012-01-01

    Multisource migration of phase-encoded supergathers has shown great promise in reducing the computational cost of conventional migration. The accompanying crosstalk noise, in addition to the migration footprint, can be reduced by least-squares inversion. But the application of this approach to marine streamer data is hampered by the mismatch between the limited number of live traces/shot recorded in the field and the pervasive number of traces generated by the finite-difference modelling method. This leads to a strong mismatch in the misfit function and results in strong artefacts (crosstalk) in the multisource least-squares migration image. To eliminate this noise, we present a frequency-division multiplexing (FDM) strategy with iterative least-squares migration (ILSM) of supergathers. The key idea is, at each ILSM iteration, to assign a unique frequency band to each shot gather. In this case there is no overlap in the crosstalk spectrum of each migrated shot gather m(x, ω i), so the spectral crosstalk product m(x, ω i)m(x, ω j) =δ i, j is zero, unless i=j. Our results in applying this method to 2D marine data for a SEG/EAGE salt model show better resolved images than standard migration computed at about 1/10 th of the cost. Similar results are achieved after applying this method to synthetic data for a 3D SEG/EAGE salt model, except the acquisition geometry is similar to that of a marine OBS survey. Here, the speedup of this method over conventional migration is more than 10. We conclude that multisource migration for a marine geometry can be successfully achieved by a frequency-division encoding strategy, as long as crosstalk-prone sources are segregated in their spectral content. This is both the strength and the potential limitation of this method. © 2012 European Association of Geoscientists & Engineers.

  17. Stable isotope labeling confirms mixotrophic nature of streamer biofilm communities at alkaline hot springs

    Directory of Open Access Journals (Sweden)

    Florence eSchubotz

    2015-02-01

    Full Text Available Streamer biofilm communities (SBC are often observed within chemosynthetic zones of Yellowstone hot spring outflow channels, where temperatures exceed those conducive to photosynthesis. Nearest the hydrothermal source (75-88°C SBC comprise thermophilic Archaea and Bacteria, often mixed communities including Desulfurococcales and uncultured Crenarchaeota, as well as Aquificae, Thermus, each carrying diagnostic membrane lipid biomarkers. We tested the hypothesis that SBC can alternate their metabolism between autotrophy and heterotrophy depending on substrate availability. Feeding experiments were performed at two alkaline hot springs in Yellowstone National Park: Octopus Spring and ‘Bison Pool’, using various 13C-labeled substrates (bicarbonate, formate, acetate and glucose to determine the relative uptake of these different carbon sources. Highest 13C uptake, at both sites, was from acetate into almost all bacterial fatty acids, particularly into methyl-branched C15, C17 and C19 fatty acids that are diagnostic for Thermus/Meiothermus and some Firmicutes as well as into universally common C16:0 and C18:0 fatty acids. 13C-glucose showed a similar, but a 10 to 30 times lower uptake across most fatty acids. 13C bicarbonate uptake, signifying the presence of autotrophic communities was only significant at ‘Bison Pool’ and was observed predominantly in non-specific saturated C16, C18, C20 and C22 fatty acids. Incorporation of 13C-formate occurred only at very low rates at ‘Bison Pool’ and was almost undetectable at Octopus Spring, suggesting that formate is not an important carbon source for SBC. 13C uptake into archaeal lipids occurred predominantly with 13C acetate, suggesting also that archaeal communities at both springs have primarily heterotrophic carbon assimilation pathways. We hypothesize that these communities are energy-limited and predominantly nurtured by input of exogenous organic material, with only a small fraction being

  18. Multisource least-squares migration of marine streamer and land data with frequency-division encoding

    KAUST Repository

    Huang, Yunsong

    2012-05-22

    Multisource migration of phase-encoded supergathers has shown great promise in reducing the computational cost of conventional migration. The accompanying crosstalk noise, in addition to the migration footprint, can be reduced by least-squares inversion. But the application of this approach to marine streamer data is hampered by the mismatch between the limited number of live traces/shot recorded in the field and the pervasive number of traces generated by the finite-difference modelling method. This leads to a strong mismatch in the misfit function and results in strong artefacts (crosstalk) in the multisource least-squares migration image. To eliminate this noise, we present a frequency-division multiplexing (FDM) strategy with iterative least-squares migration (ILSM) of supergathers. The key idea is, at each ILSM iteration, to assign a unique frequency band to each shot gather. In this case there is no overlap in the crosstalk spectrum of each migrated shot gather m(x, ω i), so the spectral crosstalk product m(x, ω i)m(x, ω j) =δ i, j is zero, unless i=j. Our results in applying this method to 2D marine data for a SEG/EAGE salt model show better resolved images than standard migration computed at about 1/10 th of the cost. Similar results are achieved after applying this method to synthetic data for a 3D SEG/EAGE salt model, except the acquisition geometry is similar to that of a marine OBS survey. Here, the speedup of this method over conventional migration is more than 10. We conclude that multisource migration for a marine geometry can be successfully achieved by a frequency-division encoding strategy, as long as crosstalk-prone sources are segregated in their spectral content. This is both the strength and the potential limitation of this method. © 2012 European Association of Geoscientists & Engineers.

  19. Ethical leader behavior and leader effectiveness: the role of prototypicality and trust

    OpenAIRE

    Kalshoven, K.; den Hartog, D.N.

    2009-01-01

    The study examines factors that mediate the impact of ethical leader behavior on leader effectiveness. Little is known about how ethical leadership impacts leader effectiveness. We hypothesized that prototypicality and trust sequentially mediate the relationship between ethical leader behavior and perceived leader effectiveness. The group prototype forms an ideal representation of the group’s identity, prescribing appropriate attitudes and behaviors. Ethical leaders are role models and thus a...

  20. DC-driven plasma gun: self-oscillatory operation mode of atmospheric-pressure helium plasma jet comprised of repetitive streamer breakdowns

    Science.gov (United States)

    Wang, Xingxing; Shashurin, Alexey

    2017-02-01

    This paper presents and studies helium atmospheric pressure plasma jet comprised of a series of repetitive streamer breakdowns, which is driven by pure DC high voltage (self-oscillatory behavior). The repetition frequency of the breakdowns is governed by the geometry of discharge electrodes/surroundings and gas flow rate. Each next streamer is initiated when the electric field on the anode tip recovers after the previous breakdown and reaches the breakdown threshold value of about 2.5 kV cm-1. One type of the helium plasma gun designed using this operational principle is demonstrated. The gun operates on about 3 kV DC high voltage and is comprised of the series of the repetitive streamer breakdowns at a frequency of about 13 kHz.

  1. Track reconstruction method in a small volume self-shunted streamer chamber - analysis of the errors for low energy electrons

    International Nuclear Information System (INIS)

    Parizet, M.J.; Augerat, J.; Avan, M.; Ballet, M.; Vialle, M.

    1977-01-01

    A programme has been worked out to reconstruct electron tracks of low energy (from 100 keV to 2 MeV) curved by a magnetic field in a small streamer chamber (size 10x11x51 cm 3 ). Before a study of the problems involved in the experimental set-up, the geometrical programme is described and the different errors are evaluated. Finally the accuracies on kinetic energies and angles which can be obtained for low energy elctron tracks are given. (Auth.)

  2. Radially and temporally resolved electric field of positive streamers in air and modelling of the induced plasma chemistry

    Czech Academy of Sciences Publication Activity Database

    Hoder, T.; Šimek, Milan; Bonaventura, Z.; Prukner, Václav; Gordillo-Vázquez, F.J.

    2016-01-01

    Roč. 25, č. 4 (2016), č. článku 045021. ISSN 0963-0252 R&D Projects: GA ČR(CZ) GA15-04023S Grant - others:Rada Programu interní podpory projektů mezinárodní spolupráce AV ČR(CZ) M100431201 Program:M Institutional support: RVO:61389021 Keywords : streamer * electric field * Blue Jet * air plasma chemistry * transient luminous event Subject RIV: BL - Plasma and Gas Discharge Physics Impact factor: 3.302, year: 2016 http://iopscience.iop.org/article/10.1088/0963-0252/25/4/045021/meta

  3. Understanding the Supplemental Instruction Leader

    Science.gov (United States)

    James, Adrian; Moore, Lori

    2018-01-01

    This article explored the learning styles and leadership styles of Supplemental Instruction (SI) leaders at Texas A&M University, and the impact of those preferences on recurring attendance to their sessions. The Learning Style Inventory, the Multifactor Leadership Questionnaire, and a demographic instrument were administered to SI leaders…

  4. Do leaders affect ethical conduct?

    NARCIS (Netherlands)

    d'Adda, Giovanna; Darai, Donja; Pavanini, Nicola; Weber, Roberto A.

    2017-01-01

    We study whether leaders influence the unethical conduct of followers. To avoid selection issues present in natural environments, we use an experiment in which we create simple laboratory firms and assign leadership roles at random. In our first experiment, firms engage in competition and unethical

  5. LEADER-tegevusest / Ene Sarapuu

    Index Scriptorium Estoniae

    Sarapuu, Ene

    2009-01-01

    Läänemaa LEADER-tegevusgrupi eesmärk on maakonna kui terviku ühtne areng, et kogu Läänemaa oleks vajalike teenustega kaetud ning ettevõtjad julgeks ning suudaks uute teenuste ja toodetega turule tulla

  6. Competition policy and market leaders

    Czech Academy of Sciences Publication Activity Database

    Maci, I.; Žigić, Krešimir

    -, č. 375 (2008), s. 1-29 ISSN 1211-3298 R&D Projects: GA MŠk LC542 Institutional research plan: CEZ:MSM0021620846 Keywords : competition policy * market leaders * innovation Subject RIV: AH - Economics http://www.cerge-ei.cz/pdf/wp/Wp375.pdf

  7. Competition policy and market leaders

    Czech Academy of Sciences Publication Activity Database

    Maci, Ilir; Žigić, K.

    -, č. 375 (2008), s. 1-29 ISSN 1211-3298 R&D Projects: GA MŠk LC542 Institutional research plan: CEZ:AV0Z70850503 Keywords : competition policy * market leaders * innovation Subject RIV: AH - Economics http://www.cerge-ei.cz/pdf/wp/Wp375.pdf

  8. Ethical Tensions and Academic Leaders

    Science.gov (United States)

    Ehrich, Lisa Catherine; Kimber, Megan; Cranston, Neil; Starr, Karen

    2011-01-01

    Internationally universities have been characterised by shrinking government funding, fierce competition for student enrolments, and greater pressures to become commercially viable. It is against this complex background that academic leaders have been required to confront and resolve a multitude of conflicting interests as they seek to balance a…

  9. Women Religious Leaders and Stress.

    Science.gov (United States)

    Rayburn, Carole A.; And Others

    This study examined stress, strain, and coping mechanisms in women religious leaders. Subjects were nuns (N=51), Reform women rabbis (N=45), Episcopal women priests (N=32), United Methodist clergywomen (N=45) and Presbyterian clergywomen (N=45), matched for age and years on the job and pulpit assignments. All subjects were given the Osipow and…

  10. New Teachers as Literacy Leaders

    Science.gov (United States)

    Turner, Jennifer D.; Applegate, Anthony J.; Applegate, Mary DeKonty

    2011-01-01

    In this article, the authors speak directly to new teachers in order to encourage them to be literacy leaders in their classrooms and schools. They offer the following suggestions in the hope of inspiring these new teachers: (1) Develop your vision of teaching and be true to it; (2) Be creative in using instruction that works; (3) Team with…

  11. The psychology of ethical leaders

    NARCIS (Netherlands)

    N. Hoogervorst (Niek)

    2012-01-01

    textabstractThe collateral damage to companies caused by unethical behaviour can be enormous, especially when it is perceived to be systemic within an organisation. We look to leaders to set an example. So how can they be encouraged to set aside selfinterest and provide an ethical role model for

  12. Strategic Communications for School Leaders

    Science.gov (United States)

    Gunther, Vicki; McGowan, James; Donegan, Kate

    2011-01-01

    Gunther, McGowan and Donegan draw on their own experiences and those of others in the field, to explain the importance of communication in school leadership. In focusing on the communication process--why it's critical for schools, and how it can be executed well--they make the case that communication must be a primary emphasis for leaders, not an…

  13. Types of Leader in Organisation

    Directory of Open Access Journals (Sweden)

    Marian Aurelian Bârgău

    2015-05-01

    Full Text Available Besides leading theories of people in one way or another from different angles reveal the types of leaders who can meet in business management literature contains classifications of management styles, which take into account different criteria or viewpoints. The word “leadership‟ has been used in various aspects of human endeavor such as politics, businesses, academics, social works, etc. Previous views about leadership show it as personal ability. The individual leader traits depend not only on personal abilities and his characteristics, but in special on the characteristics of the situation and environment in which he finds himself. People could become members of an organization in other to achieve certain personal objectives, the extent to which they are active members depends on how they are convinced that their membership will enable them to achieve their predetermined objectives. The leader will support an organization if he believes that through it his personal objectives and goals could be met otherwise the person’s interest will decline. The type leader or style of leading in an organization is one of the factors that play significant role in enhancing or retarding the interest and commitment of the individuals in the organization.

  14. Three Nightmare Traits in Leaders

    Directory of Open Access Journals (Sweden)

    Reinout E. de Vries

    2018-06-01

    Full Text Available This review offers an integration of dark leadership styles with dark personality traits. The core of dark leadership consists of Three Nightmare Traits (TNT—leader dishonesty, leader disagreeableness, and leader carelessness—that are conceptualized as contextualized personality traits aligned with respectively (low honesty-humility, (low agreeableness, and (low conscientiousness. It is argued that the TNT, when combined with high extraversion and low emotionality, can have serious (“explosive” negative consequences for employees and their organizations. A Situation-Trait-Outcome Activation (STOA model is presented in which a description is offered of situations that are attractive to TNT leaders (situation activation, situations that activate TNT traits (trait activation, and the kinds of outcomes that may result from TNT behaviors (outcome activation. Subsequently, the TNT and STOA models are combined to offer a description of the organizational actions that may strengthen or weaken the TNT during six career stages: attraction, selection, socialization, production, promotion, and attrition. Except for mainly negative consequences of the TNT, possible positive consequences of TNT leadership are also explored, and an outline of a research program is offered that may provide answers to the most pressing questions in dark leadership research.

  15. Women Administrators as Instructional Leaders

    Science.gov (United States)

    Horner, Beth A.

    2013-01-01

    Women are under-represented in educational research and are much less likely to hold administrative positions than are men. This study, using the Liberal Feminist Theory and Structural Barrier Theory, proffers possible explanations for this phenomenon. Four women leaders were interviewed to gain insight into their instructional leadership…

  16. Numerical modelling of radiation in 2+ and- systems of nitrogen accounting non-stationary excited states population in a streamer discharge

    International Nuclear Information System (INIS)

    Djakov, A.F.; Bobrov, J.K.; Jourguelenas, J.V.

    2000-01-01

    Measurement of spectral bands intensity allows to obtain a valuable information on plasma temperature and electron density - the parameters having critical influence on chemical reactions and efficiency of plasma chemistry applications. At present the interest in streamer discharges is becoming more important because of their applications to flue gas treatment and ozone generation. For a streamer discharge in air the molecular spectral bands of the second positive and first negative systems of nitrogen are the most intensive ones. However, both the registration of radiation and interpretation of the received data are very complicated problems. (Authors)

  17. The failure-tolerant leader.

    Science.gov (United States)

    Farson, Richard; Keyes, Ralph

    2002-08-01

    "The fastest way to succeed," IBM's Thomas Watson, Sr., once said, "is to double your failure rate." In recent years, more and more executives have embraced Watson's point of view, coming to understand what innovators have always known: Failure is a prerequisite to invention. But while companies may grasp the value of making mistakes at the level of corporate practices, they have a harder time accepting the idea at the personal level. People are afraid to fail, and corporate culture reinforces that fear. In this article, psychologist and former Harvard Business School professor Richard Farson and coauthor Ralph Keyes discuss how companies can reduce the fear of miscues. What's crucial is the presence of failure-tolerant leaders--executives who, through their words and actions, help employees overcome their anxieties about making mistakes and, in the process, create a culture of intelligent risk-taking that leads to sustained innovation. Such leaders don't just accept productive failure, they promote it. Drawing from their research in business, politics, sports, and science, the authors identify common practices among failure-tolerant leaders. These leaders break down the social and bureaucratic barriers that separate them from their followers. They engage at a personal level with the people they lead. They avoid giving either praise or criticism, preferring to take a nonjudgmental, analytical posture as they interact with staff. They openly admit their own mistakes rather than trying to cover them up or shifting the blame. And they try to root out the destructive competitiveness built into most organizations. Above all else, failure-tolerant leaders push people to see beyond traditional definitions of success and failure. They know that as long as a person views failure as the opposite of success, rather than its complement, he or she will never be able to take the risks necessary for innovation.

  18. Leadership, Leaders, and Leading (Part One).

    Science.gov (United States)

    Dean, Peter J.

    2002-01-01

    Presents an historical overview of the leadership literature. Highlights include "great man" theories; studies of leaders' traits; studies of leaders' behavioral style; studies of leadership functions; and studies of the situational aspects of leadership. (LRW)

  19. The Nurse Leader Role in Crisis Management.

    Science.gov (United States)

    Edmonson, Cole; Sumagaysay, Dio; Cueman, Marie; Chappell, Stacey

    2016-09-01

    Leaders from the American Organization of Nurse Executives describe the dynamic state of today's healthcare system related to crisis management. Adaptive leadership, driven by strong values and morality, can guide leaders and organizations through the most difficult times.

  20. Rapid temperature increase near the anode and cathode in the afterglow of a pulsed positive streamer discharge

    Science.gov (United States)

    Ono, Ryo

    2018-06-01

    The spatiotemporal evolution of the temperature in the afterglow of point-to-plane, pulsed positive streamer discharge was measured near the anode tip and cathode surface using laser-induced predissociation fluorescence of OH radicals. The temperature exhibited a rapid increase and displayed a steep spatial gradient after a discharge pulse. The rate of temperature rise reached 84 K μs‑1 at mm, where z represents the distance from the anode tip. The temperature rise was much faster than in the middle of the gap; it was only 2.8 K μs‑1 at mm. The temperature reached 1700 K near the anode tip at s and 1500 K near the cathode surface at s, where t represents the postdischarge time. The spatial gradient reached 1280 K mm‑1 near the anode tip at s. The mechanism responsible for the rapid temperature increase was discussed, including rapid heating of the gas in the early postdischarge phase (s), and vibration-to-translation energy transfer in the later postdischarge phase (s). The high temperatures near the anode tip and cathode surface are particularly important for the ignition of combustible mixtures and for surface treatments, including solid-surface treatments, water treatments, and plasma medicine using pulsed streamer discharges.

  1. Effects of pulse frequency of input power on the physical and chemical properties of pulsed streamer discharge plasmas in water

    Science.gov (United States)

    Ruma; Lukes, P.; Aoki, N.; Spetlikova, E.; Hosseini, S. H. R.; Sakugawa, T.; Akiyama, H.

    2013-03-01

    A repetitive pulsed-power modulator, which employs a magnetic pulse compression circuit with a high-speed thyristor switch, was used to study the effects of the pulse repetition rate of input power on the physical and chemical properties of pulsed discharges in water. Positive high-voltage pulses of 20 kV with repetition rates of up to 1 kHz were used to generate a discharge in water using the point-to-plane electrode geometry. By varying the pulse repetition rate, two distinct modes of the discharge plasma were formed in water. The first mode was characterized by the formation of a corona-like discharge propagating through water in the form of streamer channels. The second mode was formed typically above 500 Hz, when the formation of streamer channels in water was suppressed and all plasmas occurred inside a spheroidal aggregate of very fine gas bubbles surrounding the tip of the high-voltage electrode. The production of hydrogen peroxide, degradation of organic dye Acid Orange 7 (AO7) and inactivation of bacteria Escherichia coli by the discharge in water were studied under different discharge plasma modes in dependence on the pulse repetition rate of input power. The efficiency of both chemical and biocidal processes induced by the plasma in water decreased significantly with pulse repetition rates above 500 Hz.

  2. Effects of pulse frequency of input power on the physical and chemical properties of pulsed streamer discharge plasmas in water

    International Nuclear Information System (INIS)

    Ruma; Aoki, N; Hosseini, S H R; Sakugawa, T; Akiyama, H; Lukes, P; Spetlikova, E

    2013-01-01

    A repetitive pulsed-power modulator, which employs a magnetic pulse compression circuit with a high-speed thyristor switch, was used to study the effects of the pulse repetition rate of input power on the physical and chemical properties of pulsed discharges in water. Positive high-voltage pulses of 20 kV with repetition rates of up to 1 kHz were used to generate a discharge in water using the point-to-plane electrode geometry. By varying the pulse repetition rate, two distinct modes of the discharge plasma were formed in water. The first mode was characterized by the formation of a corona-like discharge propagating through water in the form of streamer channels. The second mode was formed typically above 500 Hz, when the formation of streamer channels in water was suppressed and all plasmas occurred inside a spheroidal aggregate of very fine gas bubbles surrounding the tip of the high-voltage electrode. The production of hydrogen peroxide, degradation of organic dye Acid Orange 7 (AO7) and inactivation of bacteria Escherichia coli by the discharge in water were studied under different discharge plasma modes in dependence on the pulse repetition rate of input power. The efficiency of both chemical and biocidal processes induced by the plasma in water decreased significantly with pulse repetition rates above 500 Hz. (paper)

  3. Recruiting leaders: an analysis of leadership advertisements

    NARCIS (Netherlands)

    den Hartog, D.N.; Caley, A.; Dewe, P.

    2007-01-01

    Recruiting the right leaders is an important challenge for organisations. How do organisations find these leaders? This article looks at the recruitment of leaders through advertisements. We address to what extent the 'vocabulary of leadership' originating in influential leadership theories is

  4. A Phenomenology of Outdoor Education Leader Experiences

    Science.gov (United States)

    Field, Stephanie C.; Lauzon, Lara L.; Meldrum, John T.

    2016-01-01

    Limited qualitative research exists on the experiences of outdoor education leaders. The purpose of this phenomenological study was to explore the job-related experiences of outdoor education leaders within and outside the workplace. Five participants who had experience as outdoor education leaders completed in-depth, one-on-one interviews about…

  5. Identifying Opinion Leaders to Promote Behavior Change

    Science.gov (United States)

    Valente, Thomas W.; Pumpuang, Patchareeya

    2007-01-01

    This article reviews 10 techniques used to identify opinion leaders to promote behavior change. Opinion leaders can act as gatekeepers for interventions, help change social norms, and accelerate behavior change. Few studies document the manner in which opinion leaders are identified, recruited, and trained to promote health. The authors categorize…

  6. Women Leaders in Oxford House.

    Science.gov (United States)

    Timpo, Phyllis; Price, Temple; Salina, Doreen; Witek, Caroline; Pommer, Nicole; Jason, Leonard A

    2014-01-01

    This qualitative study examined women assuming leadership roles in Oxford Houses, which are communal, democratically run recovery settings for substance use disorder. Semi-structured interviews were conducted with 10 women Oxford House leaders who shared their thoughts and experiences on leadership. Several themes emerged from qualitative data analysis, most notably that stepping up and accepting a leadership role in Oxford House had a positive effect on self-esteem, which is vital to women with a history of substance abuse. Barriers to leadership were also identified such as negative interpersonal relationships with other women. A number of methods mentioned to increase the number of women leaders included: developing workshops, providing positive encouragement, and accessing existing female role models. The implications of this study are discussed.

  7. How to grow great leaders.

    Science.gov (United States)

    Ready, Douglas A

    2004-12-01

    Few leaders excel at both the unit and enterprise levels. More than ever, though, corporations need people capable of running business units, functions, or regions and focusing on broader company goals. It's up to organizations to develop leaders who can manage the inherent tensions between unit and enterprise priorities. Take the example of RBC Financial Group, one of the largest, most profitable companies in Canada. In the mid-1990's, RBC revamped its competitive strategy in a couple of ways. After the government announced that the Big Six banks in Canada could neither merge with nor acquire one another, RBC decided to grow through cross-border acquisitions. Additionally, because customers were starting to seek bundled products and services, RBC reached across its traditional stand-alone businesses to offer integrated solutions. These changes in strategy didn't elicit immediate companywide support. Instinctively, employees reacted against what would amount to a delicate balancing act: They would have to lift their focus out of their silos while continuing to meet unit goals. However, by communicating extensively with staff members, cross-fertilizing talent across unit boundaries, and targeting rewards to shape performance, RBC was able to cultivate rising leaders with the unit expertise and the enterprise vision to help the company fulfill its new aims. Growing such well-rounded leaders takes sustained effort because unit-enterprise tensions are quite real. Three common conditions reinforce these tensions. First, most organizational structures foster silo thinking and unimaginative career paths. Second, most companies lack venues for airing and resolving conflicts that arise when there are competing priorities. Third, many have misguided reward systems that pit unit performance against enterprise considerations. Such long-established patterns of organizational behavior are tough to break. Fortunately, as RBC discovered, people can be trained to think and work

  8. Women Leaders in Oxford House

    OpenAIRE

    Timpo, Phyllis; Price, Temple; Salina, Doreen; Witek, Caroline; Pommer, Nicole; Jason, Leonard A.

    2014-01-01

    This qualitative study examined women assuming leadership roles in Oxford Houses, which are communal, democratically run recovery settings for substance use disorder. Semi-structured interviews were conducted with 10 women Oxford House leaders who shared their thoughts and experiences on leadership. Several themes emerged from qualitative data analysis, most notably that stepping up and accepting a leadership role in Oxford House had a positive effect on self-esteem, which is vital to women w...

  9. Leader Affect and Leadership Effectiveness: How leader affective displays influence follower outcomes

    OpenAIRE

    Visser, Victoria

    2013-01-01

    textabstractThe aim of this dissertation is to uncover the relationship between leader affective displays and leadership effectiveness. Five empirical studies were conducted to test the influence of several leader affective displays on different follower outcomes that indicate leadership effectiveness. The results showed that leader happy displays enhance followers’ creative performance, whereas leader sad displays enhance followers’ analytical performance. In addition, a leader displaying ha...

  10. Negative surface streamers propagating on TiO2 and γ-Al2O3-supported Ag catalysts: ICCD imaging and modeling study

    Science.gov (United States)

    Kim, Hyun-Ha; Teramoto, Yoshiyuki; Ogata, Atsushi; Kang, Woo Seok; Hur, Min; Song, Young-Hoon

    2018-06-01

    Surface streamers propagating on the surface of titanium dioxide (TiO2) and alumina (γ-Al2O3) were studied in negative polarity using intensified charge coupled device (ICCD) imaging and numerical simulation. Detailed time-resolved ICCD images of cathode-directed streamers (CDSs) emanating from a ground electrode are first presented in this report. Instead of primary streamers in positive polarity, only a glow-like discharge appeared in the early stage at the cathode under negative polarity. After this discharge disappeared, a counter-propagating CDS initiated from the ground electrode (anode). Numerical simulation indicated that strong electric fields at the pellet-anode and the formation of positive ion rich local spots were the main reason for the CDS formation near the ground electrode. The maximum velocity was 750 km s‑1 for Ag-supported γ-Al2O3 and 550 km s‑1 for Ag-supported TiO2, respectively. In contrast to the CDS in the gas-phase with a positive polarity, the CDS in a catalyst packed-bed under negative polarity showed more branching and a larger number of streamers in the presence of oxygen than in pure N2.

  11. Diffusion of πsup(+-) mesons on D, 3He, 4He with a streamer self-shunted camera in a magnetic field

    International Nuclear Information System (INIS)

    Atanasov, A.; Angelescu, T.; Balea, O.; Balestra, F.; Busso, L.; Garfagnini, R.

    1975-01-01

    A streamer self-shunted camera has been developed with the study of interactions of πsup(+-) mesons on D, 3 He, 4 He. The camera can operate at high beam currents (10 sup(5)/10sup(6)ssup(-1)), so processes with small cross sections can be studied

  12. An Estimate of Solar Wind Velocity Profiles in a Coronal Hole and a Coronal Streamer Area (6-40 R(radius symbol)

    Science.gov (United States)

    Patzold, M.; Tsurutani, B. T.; Bird, M. K.

    1995-01-01

    Total electron content data obtained from the Ulysses Solar Corona Experiment (SCE) in 1991 were used to select two data sets, one associated with a coronal hole and the other with coronal streamer crossings. (This is largely equatorial data shortly after solar maximum.) The solar wind velocity profile is estimated for these areas.

  13. The impact of previous leaders on the evaluation of new leaders: an alternative to prototype matching.

    Science.gov (United States)

    Ritter, Barbara A; Lord, Robert G

    2007-11-01

    In 2 studies, this research demonstrated the existence of leader transference, a cognitive process whereby mental representations of previous leaders are activated and used for evaluation when new, similar leaders are encountered. The 1st study demonstrated that exposure to a new leader who was similar to a past leader led to erroneous generalization of leader characteristics and associated underlying attributions. The 2nd study showed that expectations of just treatment and abuse were also subject to transfer from old to new, similar leaders, although positive and negative affective responses were not. Results suggested that individuals exposed to a leader who was not reminiscent of an old leader were more likely to use a general leader prototype to form leader expectations, whereas individuals exposed to a leader who was similar to an old leader activated a significant other mental representation for use in making judgments. These results have implications for individual- and relational-level processes as characterized by implicit leadership theory and leader-member exchange theory as well as macro theories of leader succession and organizational culture change. (c) 2007 APA

  14. THE POSSIBLE ROLE OF CORONAL STREAMERS AS MAGNETICALLY CLOSED STRUCTURES IN SHOCK-INDUCED ENERGETIC ELECTRONS AND METRIC TYPE II RADIO BURSTS

    Energy Technology Data Exchange (ETDEWEB)

    Kong, Xiangliang; Chen, Yao; Feng, Shiwei; Wang, Bing; Du, Guohui [Shandong Provincial Key Laboratory of Optical Astronomy and Solar-Terrestrial Environment, and Institute of Space Sciences, Shandong University, Weihai, Shandong 264209 (China); Guo, Fan [Theoretical Division, Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Li, Gang, E-mail: yaochen@sdu.edu.cn [Department of Space Science and CSPAR, University of Alabama in Huntsville, Huntsville, AL 35899 (United States)

    2015-01-10

    Two solar type II radio bursts, separated by ∼24 hr in time, are examined together. Both events are associated with coronal mass ejections (CMEs) erupting from the same active region (NOAA 11176) beneath a well-observed helmet streamer. We find that the type II emissions in both events ended once the CME/shock fronts passed the white-light streamer tip, which is presumably the magnetic cusp of the streamer. This leads us to conjecture that the closed magnetic arcades of the streamer may play a role in electron acceleration and type II excitation at coronal shocks. To examine such a conjecture, we conduct a test-particle simulation for electron dynamics within a large-scale partially closed streamer magnetic configuration swept by a coronal shock. We find that the closed field lines play the role of an electron trap via which the electrons are sent back to the shock front multiple times and therefore accelerated to high energies by the shock. Electrons with an initial energy of 300 eV can be accelerated to tens of keV concentrating at the loop apex close to the shock front with a counter-streaming distribution at most locations. These electrons are energetic enough to excite Langmuir waves and radio bursts. Considering the fact that most solar eruptions originate from closed field regions, we suggest that the scenario may be important for the generation of more metric type IIs. This study also provides an explanation of the general ending frequencies of metric type IIs at or above 20-30 MHz and the disconnection issue between metric and interplanetary type IIs.

  15. Temporal development and chemical efficiency of positive streamers in a large scale wire-plate reactor as a function of voltage waveform parameters

    Science.gov (United States)

    Winands, G. J. J.; Liu, Z.; Pemen, A. J. M.; van Heesch, E. J. M.; Yan, K.; van Veldhuizen, E. M.

    2006-07-01

    In this paper a large-scale pulsed corona system is described in which pulse parameters such as pulse rise-time, peak voltage, pulse width and energy per pulse can be varied. The chemical efficiency of the system is determined by measuring ozone production. The temporal and spatial development of the discharge streamers is recorded using an ICCD camera with a shortest exposure time of 5 ns. The camera can be triggered at any moment starting from the time the voltage pulse arrives on the reactor, with an accuracy of less than 1 ns. Measurements were performed on an industrial size wire-plate reactor. The influence of pulse parameters like pulse voltage, DC bias voltage, rise-time and pulse repetition rate on plasma generation was monitored. It was observed that for higher peak voltages, an increase could be seen in the primary streamer velocity, the growth of the primary streamer diameter, the light intensity and the number of streamers per unit length of corona wire. No significant separate influence of DC bias voltage level was observed as long as the total reactor voltage (pulse + DC bias) remained constant and the DC bias voltage remained below the DC corona onset. For those situations in which the plasma appearance changed (e.g. different streamer velocity, diameter, intensity), a change in ozone production was also observed. The best chemical yields were obtained for low voltage (55 kV), low energetic pulses (0.4 J/pulse): 60 g (kWh)-1. For high voltage (86 kV), high energetic pulses (2.3 J/pulse) the yield decreased to approximately 45 g (kWh)-1, still a high value for ozone production in ambient air (RH 42%). The pulse repetition rate has no influence on plasma generation and on chemical efficiency up to 400 pulses per second.

  16. Temporal development and chemical efficiency of positive streamers in a large scale wire-plate reactor as a function of voltage waveform parameters

    Energy Technology Data Exchange (ETDEWEB)

    Winands, G J J [EPS Group, Department of Electrical Engineering, Eindhoven University of Technology, 5600 MB, Eindhoven (Netherlands); Liu, Z [EPS Group, Department of Electrical Engineering, Eindhoven University of Technology, 5600 MB, Eindhoven (Netherlands); Pemen, A J M [EPS Group, Department of Electrical Engineering, Eindhoven University of Technology, 5600 MB, Eindhoven (Netherlands); Heesch, E J M van [EPS Group, Department of Electrical Engineering, Eindhoven University of Technology, 5600 MB, Eindhoven (Netherlands); Yan, K [EPS Group, Department of Electrical Engineering, Eindhoven University of Technology, 5600 MB, Eindhoven (Netherlands); Veldhuizen, E M van [EPG Group, Department of Applied Physics, Eindhoven University of Technology, 5600 MB, Eindhoven (Netherlands)

    2006-07-21

    In this paper a large-scale pulsed corona system is described in which pulse parameters such as pulse rise-time, peak voltage, pulse width and energy per pulse can be varied. The chemical efficiency of the system is determined by measuring ozone production. The temporal and spatial development of the discharge streamers is recorded using an ICCD camera with a shortest exposure time of 5 ns. The camera can be triggered at any moment starting from the time the voltage pulse arrives on the reactor, with an accuracy of less than 1 ns. Measurements were performed on an industrial size wire-plate reactor. The influence of pulse parameters like pulse voltage, DC bias voltage, rise-time and pulse repetition rate on plasma generation was monitored. It was observed that for higher peak voltages, an increase could be seen in the primary streamer velocity, the growth of the primary streamer diameter, the light intensity and the number of streamers per unit length of corona wire. No significant separate influence of DC bias voltage level was observed as long as the total reactor voltage (pulse + DC bias) remained constant and the DC bias voltage remained below the DC corona onset. For those situations in which the plasma appearance changed (e.g. different streamer velocity, diameter, intensity), a change in ozone production was also observed. The best chemical yields were obtained for low voltage (55 kV), low energetic pulses (0.4 J/pulse): 60 g (kWh){sup -1}. For high voltage (86 kV), high energetic pulses (2.3 J/pulse) the yield decreased to approximately 45 g (kWh){sup -1}, still a high value for ozone production in ambient air (RH 42%). The pulse repetition rate has no influence on plasma generation and on chemical efficiency up to 400 pulses per second.

  17. Temporal development and chemical efficiency of positive streamers in a large scale wire-plate reactor as a function of voltage waveform parameters

    International Nuclear Information System (INIS)

    Winands, G J J; Liu, Z; Pemen, A J M; Heesch, E J M van; Yan, K; Veldhuizen, E M van

    2006-01-01

    In this paper a large-scale pulsed corona system is described in which pulse parameters such as pulse rise-time, peak voltage, pulse width and energy per pulse can be varied. The chemical efficiency of the system is determined by measuring ozone production. The temporal and spatial development of the discharge streamers is recorded using an ICCD camera with a shortest exposure time of 5 ns. The camera can be triggered at any moment starting from the time the voltage pulse arrives on the reactor, with an accuracy of less than 1 ns. Measurements were performed on an industrial size wire-plate reactor. The influence of pulse parameters like pulse voltage, DC bias voltage, rise-time and pulse repetition rate on plasma generation was monitored. It was observed that for higher peak voltages, an increase could be seen in the primary streamer velocity, the growth of the primary streamer diameter, the light intensity and the number of streamers per unit length of corona wire. No significant separate influence of DC bias voltage level was observed as long as the total reactor voltage (pulse + DC bias) remained constant and the DC bias voltage remained below the DC corona onset. For those situations in which the plasma appearance changed (e.g. different streamer velocity, diameter, intensity), a change in ozone production was also observed. The best chemical yields were obtained for low voltage (55 kV), low energetic pulses (0.4 J/pulse): 60 g (kWh) -1 . For high voltage (86 kV), high energetic pulses (2.3 J/pulse) the yield decreased to approximately 45 g (kWh) -1 , still a high value for ozone production in ambient air (RH 42%). The pulse repetition rate has no influence on plasma generation and on chemical efficiency up to 400 pulses per second

  18. Mathematical Formulation of the Remote Electric and Magnetic Emissions of the Lightning Dart Leader and Return Stroke

    Science.gov (United States)

    Thiemann, Edward M. B.

    Lightning detection and geolocation networks have found widespread use by the utility, air traffic control and forestry industries as a means of locating strikes and predicting imminent recurrence. Accurate lightning geolocation requires detecting VLF radio emissions at multiple sites using a distributed sensor network with typical baselines exceeding 150 km, along with precision time of arrival estimation to triangulate the origin of a strike. The trend has been towards increasing network accuracy without increasing sensor density by incorporating precision GPS synchronized clocks and faster front-end signal processing. Because lightning radio waveforms evolve as they propagate over a finitely conducting earth, and that measurements for a given strike may have disparate propagation path lengths, accurate models are required to determine waveform fiducials for precise strike location. The transition between the leader phase and return stroke phase may offer such a fiducial and warrants quantitative modeling to improve strike location accuracy. The VLF spectrum of the ubiquitous downward negative lightning strike is able to be modeled by the transfer of several Coulombs of negative charge from cloud to ground in a two-step process. The lightning stepped leader ionizes a plasma channel downward from the cloud at a velocity of approximately 0.05c, leaving a column of charge in its path. Upon connection with a streamer, the subsequent return stroke initiates at or near ground level and travels upward at an average but variable velocity of 0.3c. The return stroke neutralizes any negative charge along its path. Subsequent dart leader and return strokes often travel smoothly down the heated channel left by a preceding stroke, lacking the halting motion of the preceding initial stepped leader and initial return stroke. Existing lightning models often neglect the leader current and rely on approximations when solving for the return stroke. In this thesis, I present an

  19. Responsible leader behavior in health sectors.

    Science.gov (United States)

    Longest, Beaufort

    2017-02-06

    Purpose The purpose of this paper is to expand attention to responsible leader behavior in the world's health sectors by explaining how this concept applies to health sectors, considering why health sector leaders should behave responsibly, reviewing how they can do so, and asserting potential impact through an applied example. Design/methodology/approach This paper is a viewpoint, reflecting conceptualizations rooted in leadership literature which are then specifically applied to health sectors. A definition of responsible leader behavior is affirmed and applied specifically in health sectors. Conceptualizations and viewpoints about practice of responsible leader behavior in health sectors and potential consequences are then discussed and asserted. Findings Leadership failures and debacles found in health, but more so in other sectors, have led leadership researchers to offer insights, many of them empirical, into the challenges of leadership especially by more clearly delineating responsible leader behavior. Practical implications Much of what has been learned in the research about responsible leader behavior offers pathways for health sector leaders to more fully practice responsible leadership. Social implications This paper asserts and provides a supporting example that greater levels of responsible leader behavior in health sectors hold potentially important societal benefits. Originality/value This paper is the first to apply emerging conceptualizations and early empirical findings about responsible leader behavior specifically to leaders in health sectors.

  20. Establishing the Next Generation at Work : Leader Generativity as a Moderator of the Relationships Between Leader Age, Leader-Member Exchange, and Leadership Success

    NARCIS (Netherlands)

    Zacher, Hannes; Rosing, Kathrin; Henning, Thomas; Frese, Michael

    In this study, the authors investigated leader generativity as a moderator of the relationships between leader age, leader-member exchange, and three criteria of leadership success (follower perceptions of leader effectiveness, follower satisfaction with leader, and follower extra effort). Data came

  1. IS and Business Leaders' Strategizing

    DEFF Research Database (Denmark)

    Hansen, Anne Mette

    adopted an alternative view in which IS strategy represents a shared understanding of the role of IS within the organization. The assumption in these studies is that IS and business leaders constantly negotiate their understandings of the role of IS and strategic objectives as a basis for investment...... to the IS strategy literature by providing a detailed and rich description of IS and business leaders’ learning during IS strategizing. Second, it informs organizational learning theory by providing fundamental new insights to the 4I framework, extending our knowledge of its core constructs and revealing a potential...

  2. Leaders break ground for INFINITY

    Science.gov (United States)

    2008-01-01

    Community leaders from Mississippi and Louisiana break ground for the new INFINITY at NASA Stennis Space Center facility during a Nov. 20 ceremony. Groundbreaking participants included (l to r): Gottfried Construction representative John Smith, Mississippi Highway Commissioner Wayne Brown, INFINITY board member and Apollo 13 astronaut Fred Haise, Stennis Director Gene Goldman, Studio South representative David Hardy, Leo Seal Jr. family representative Virginia Wagner, Hancock Bank President George Schloegel, Mississippi Rep. J.P. Compretta, Mississippi Band of Choctaw Indians representative Charlie Benn and Louisiana Sen. A.G. Crowe.

  3. ACADEMIC ADVISORS: VALUES EDUCATED LEADERS

    Directory of Open Access Journals (Sweden)

    Brizeida Mijares

    2008-07-01

    Full Text Available The purpose of this article is to study the academic advisors’ profile from the attitudes in the learning process view point, being the center of which the need that as an educator, the advisor has to be a leader educated in values. The research was documental, according to the theoretical contributions of Arana and Batista (2006,  Ortega and Minguez (2001 and Denis (2000, among others. It is concluded that an academic advisor in values allows individual and collective trasnformation and an education without values as its center, it is a hollow and useless education.

  4. Leader charisma and affective team climate: the moderating role of the leader's influence and interaction.

    Science.gov (United States)

    Hernández Baeza, Ana; Araya Lao, Cristina; García Meneses, Juliana; González Romá, Vicente

    2009-11-01

    In this study, we evaluate the role of leader charisma in fostering positive affective team climate and preventing negative affective climate. The analysis of a longitudinal database of 137 bank branches by means of hierarchical moderated regression shows that leader charisma has a stronger effect on team optimism than on team tension. In addition, the leader's influence and the frequency of leader-team interaction moderate the relationship between charisma and affective climate. However, whereas the leader's influence enhances the relationship between leader charisma and positive affective climate, the frequency of interaction has counterproductive effects.

  5. Enhanced shock wave generation via pre-breakdown acceleration using water electrolysis in negative streamer pulsed spark discharges

    Science.gov (United States)

    Lee, Kern; Chung, Kyoung-Jae; Hwang, Y. S.

    2018-03-01

    This paper presents a method for enhancement of shock waves generated from underwater pulsed spark discharges with negative (anode-directed) subsonic streamers, for which the pre-breakdown process is accelerated by preconditioning a gap with water electrolysis. Hydrogen microbubbles are produced at the cathode by the electrolysis and move towards the anode during the preconditioning phase. The numbers and spatial distributions of the microbubbles vary with the amplitude and duration of each preconditioning pulse. Under our experimental conditions, the optimum pulse duration is determined to be ˜250 ms at a pulse voltage of 400 V, where the buoyancy force overwhelms the electric force and causes the microbubbles to be swept out from the water gap. When a high-voltage pulse is applied to the gap just after the preconditioning pulse, the pre-breakdown process is significantly accelerated in the presence of the microbubbles. At the optimum preconditioning pulse duration, the average breakdown delay is reduced by 87% and, more importantly, the energy consumed during the pre-breakdown period decreases by 83%. This reduced energy consumption during the pre-breakdown period, when combined with the morphological advantages of negative streamers, such as thicker and longer stalks, leads to a significant improvement in the measured peak pressure (˜40%) generated by the underwater pulsed spark discharge. This acceleration of pre-breakdown using electrolysis overcomes the biggest drawback of negative subsonic discharges, which is slow vapor bubble formation due to screening effects, and thus enhances the efficiency of the shock wave generation process using pulsed spark discharges in water.

  6. Hydrophilic property of 316L stainless steel after treatment by atmospheric pressure corona streamer plasma using surface-sensitive analyses

    Energy Technology Data Exchange (ETDEWEB)

    Al-Hamarneh, Ibrahim, E-mail: hamarnehibrahim@yahoo.com [Department of Physics, Faculty of Science, Al-Balqa Applied University, Salt 19117 (Jordan); Pedrow, Patrick [School of Electrical Engineering and Computer Science, Washington State University, Pullman, WA 99164 (United States); Eskhan, Asma; Abu-Lail, Nehal [Gene and Linda Voiland School of Chemical Engineering and Bioengineering, Washington State University, Pullman, WA 99164 (United States)

    2012-10-15

    Highlights: Black-Right-Pointing-Pointer Surface hydrophilic property of surgical-grade 316L stainless steel was enhanced by Ar-O{sub 2} corona streamer plasma treatment. Black-Right-Pointing-Pointer Hydrophilicity, surface morphology, roughness, and chemical composition before and after plasma treatment were evaluated. Black-Right-Pointing-Pointer Contact angle measurements and surface-sensitive analyses techniques, including XPS and AFM, were carried out. Black-Right-Pointing-Pointer Optimum plasma treatment conditions of the SS 316L surface were determined. - Abstract: Surgical-grade 316L stainless steel (SS 316L) had its surface hydrophilic property enhanced by processing in a corona streamer plasma reactor using O{sub 2} gas mixed with Ar at atmospheric pressure. Reactor excitation was 60 Hz ac high-voltage (0-10 kV{sub RMS}) applied to a multi-needle-to-grounded screen electrode configuration. The treated surface was characterized with a contact angle tester. Surface free energy (SFE) for the treated stainless steel increased measurably compared to the untreated surface. The Ar-O{sub 2} plasma was more effective in enhancing the SFE than Ar-only plasma. Optimum conditions for the plasma treatment system used in this study were obtained. X-ray photoelectron spectroscopy (XPS) characterization of the chemical composition of the treated surfaces confirms the existence of new oxygen-containing functional groups contributing to the change in the hydrophilic nature of the surface. These new functional groups were generated by surface reactions caused by reactive oxidation of substrate species. Atomic force microscopy (AFM) images were generated to investigate morphological and roughness changes on the plasma treated surfaces. The aging effect in air after treatment was also studied.

  7. Gender differences in Assessments of Party Leaders

    DEFF Research Database (Denmark)

    Kosiara-Pedersen, Karina; Hansen, Kasper Møller

    2015-01-01

    Is there a relationship between party leader gender and voters' assessments? Yes, according to theses on gender identity and stereotyping. A voter survey during the 2011 Danish general election allows for a comprehensive analysis of a less likely case with four male and four female party leaders...... of gender does not increase with age, actually, the opposite is the case among men since younger male voters have smaller sympathy for female party leaders. Furthermore, there is no support for the expectation that voters with more education or with higher levels of political interest and knowledge are more....... Female party leaders are assessed more positively by female voters than male voters both in regard to general party leader sympathy and assessment of specific characteristics, whereas it is not the case that male party leaders are assessed more positively by male voters than female voters. The impact...

  8. The Decision Calculus of Terrorist Leaders

    OpenAIRE

    J. Tyson Chatagnier; Alex Mintz; Yair Samban

    2012-01-01

    This article contributes to the literature on terrorist group decision-making by introducing a new procedure, Applied Decision Analysis, in an attempt to understand how leaders of terrorist organizations make decisions. We examine twenty-three decisions taken by leaders of three terrorist organizations: Al-Qaeda, Hamas, and Hizballah. We also demonstrate the use of the Applied Decision Analysis procedure to uncover the "Decision DNA" or “decision code” of leaders of such organizat...

  9. Competitive Pricing by a Price Leader

    OpenAIRE

    Abhik Roy; Dominique M. Hanssens; Jagmohan S. Raju

    1994-01-01

    We examine the problem of pricing in a market where one brand acts as a price leader. We develop a procedure to estimate a leader's price rule, which is optimal given a sales target objective, and allows for the inclusion of demand forecasts. We illustrate our estimation procedure by calibrating this optimal price rule for both the leader and the follower using data on past sales and prices from the mid-size sedan segment of the U.S. automobile market. Our results suggest that a leader-follow...

  10. Why the world needs moral leaders

    DEFF Research Database (Denmark)

    Mehlsen, Camilla

    2009-01-01

    The educational system plays a huge role in developing the moral leaders of tomorrow. The Quarterly takes a closer look at diversity in South Africa's schools, at the young generation in China, and at the making of moral leaders with both a global and local mindset.......The educational system plays a huge role in developing the moral leaders of tomorrow. The Quarterly takes a closer look at diversity in South Africa's schools, at the young generation in China, and at the making of moral leaders with both a global and local mindset....

  11. Leader Affect and Leadership Effectiveness: How leader affective displays influence follower outcomes

    NARCIS (Netherlands)

    V.A. Visser (Victoria)

    2013-01-01

    textabstractThe aim of this dissertation is to uncover the relationship between leader affective displays and leadership effectiveness. Five empirical studies were conducted to test the influence of several leader affective displays on different follower outcomes that indicate leadership

  12. Leader trust and employee voice : The moderating role of empowering leader behaviors

    NARCIS (Netherlands)

    Gao, L.; Janssen, O.; Shi, K.

    This paper explored how employees' trust in their leader interacted with empowering leader behaviors in promoting employee voice. Using data collected from 314 employees in the telecommunication industry in China, we found that the relationship between leader trust and employee voice became more

  13. Leader self-sacrifice and leadership effectiveness: The moderating role of leader prototypicality

    NARCIS (Netherlands)

    van Knippenberg, B.M.; van Knippenberg, D.

    2005-01-01

    Self-sacrificing behavior of the leader and the extent to which the leader is representative of the group (i.e., group prototypical) are proposed to interact to influence leadership effectiveness. The authors expected self-sacrificing leaders to be considered more effective and to be able to push

  14. Leader emergence through interpersonal neural synchronization.

    Science.gov (United States)

    Jiang, Jing; Chen, Chuansheng; Dai, Bohan; Shi, Guang; Ding, Guosheng; Liu, Li; Lu, Chunming

    2015-04-07

    The neural mechanism of leader emergence is not well understood. This study investigated (i) whether interpersonal neural synchronization (INS) plays an important role in leader emergence, and (ii) whether INS and leader emergence are associated with the frequency or the quality of communications. Eleven three-member groups were asked to perform a leaderless group discussion (LGD) task, and their brain activities were recorded via functional near infrared spectroscopy (fNIRS)-based hyperscanning. Video recordings of the discussions were coded for leadership and communication. Results showed that the INS for the leader-follower (LF) pairs was higher than that for the follower-follower (FF) pairs in the left temporo-parietal junction (TPJ), an area important for social mentalizing. Although communication frequency was higher for the LF pairs than for the FF pairs, the frequency of leader-initiated and follower-initiated communication did not differ significantly. Moreover, INS for the LF pairs was significantly higher during leader-initiated communication than during follower-initiated communications. In addition, INS for the LF pairs during leader-initiated communication was significantly correlated with the leaders' communication skills and competence, but not their communication frequency. Finally, leadership could be successfully predicted based on INS as well as communication frequency early during the LGD (before half a minute into the task). In sum, this study found that leader emergence was characterized by high-level neural synchronization between the leader and followers and that the quality, rather than the frequency, of communications was associated with synchronization. These results suggest that leaders emerge because they are able to say the right things at the right time.

  15. The physician leader as logotherapist.

    Science.gov (United States)

    Washburn, E R

    1998-01-01

    Today's physicians feel helpless and angry about changing conditions in the medical landscape. This is due, in large part, to our postmodernist world view and the influence of corporations on medical practice. The life and work of existentialist psychiatrist Viktor Frankl is proposed as a role model for physicians to take back control of their profession. Physician leaders are in the best position to bring the teachings and insight of Frankl's logotherapy to rank-and-file physicians in all practice settings, as well as into the board rooms of large medical corporations. This article considers the spiritual and moral troubles of American medicine, Frankl's answer to that affliction, and the implications of logotherapy for physician organizations and leadership. Physician executives are challenged to take up this task.

  16. Educators as Serving Leaders in the Classroom and on Campus

    Science.gov (United States)

    Bowman, Richard

    2014-01-01

    Counterintuitively, the more one develops as a leader, the less of a leader one becomes. What do great leaders do? Great leaders are ambitious first and foremost for the cause, the mission, the work--not themselves. Educators as "serving leaders" sense that every action they take, together with every decision that they make, either…

  17. Mastering the leader role : how individuals in leader roles increase leader role efficacy and trust in subordinates, (re)construct leader identities, and attempt to craft leader roles that fit

    OpenAIRE

    Gjerde, Susann

    2018-01-01

    People have a psychological need to master their environment and the roles they enact (Ashforth, 2001). Individuals who take on leader roles are no exception. However, as the leader role is filled with complex, demanding, conflicting and ambiguous role expectations (Conger & Fishel, 2007; Denis, Langley, & Pineault, 2000; Levin, 2010) mastering the leader role may be particularly challenging. This thesis addresses three complementary approaches to mastering the leader role and deals with each...

  18. Water Cluster Leaders Meeting Summary Report 2016

    Science.gov (United States)

    As part of its efforts to support environmental technology innovation clusters, U.S. EPA hosted a Water Technology Innovation Cluster Leaders Meeting on September 25, 2016, in New Orleans, Louisiana. The meeting was an opportunity for cluster leaders from across the globe to meet...

  19. Political leader survival : does competence matter?

    NARCIS (Netherlands)

    Yu, Shu; Jong-A-Pin, Richard

    We examine whether economic and military competence of political leaders affect their duration in office. We introduce leader heterogeneity in the selectorate theory of Bueno de Mesquita et al. (2003) and derive the hypothesis that in the presence of a revolutionary threat, economic competence is

  20. World Biotechnology Leaders to Gather for Conference

    Science.gov (United States)

    Biotechnology Leaders to Gather for Conference For more information contact: e:mail: Public Affairs biotechnology leaders gather in Fort Collins, CO May 2-6 for the 21st Symposium on Biotechnology for Fuels and special session on funding opportunities for U.S. biotechnology projects. More than 175 presentations are

  1. Educating Native Students: Inspiring Future Leaders.

    Science.gov (United States)

    Lee, Tiffany

    2003-01-01

    A 7-week summer program for college-bound American Indian students prepares them for college and trains them to become leaders. Through role playing a fictitious Native tribe, students encounter realistic dilemmas similar to those facing tribal governments and realize that tribal leaders' decisions involve many social and political issues…

  2. Model checking the HAVi leader election protocol

    NARCIS (Netherlands)

    J.M.T. Romijn (Judi)

    1999-01-01

    textabstractThe HAVi specification proposes an architecture for audio/video interoperability in home networks. Part of the HAVi specification is a distributed leader election protocol. We have modelled this leader election protocol in Promela and Lotos and have checked several properties with the

  3. Modern American Agricultural Leaders: Four from Iowa.

    Science.gov (United States)

    Colbert, Thomas B.

    1991-01-01

    Profiles four Iowans who became agricultural leaders and committed themselves to addressing farmers' needs: Henry Wallace, James R. Howard, Milo Reno, and Ruth Buxton Sayre. Identifies farm organizations with which each was affiliated, such as the Farm Bureau and the Farmers' Union. Summarizes each leader's major accomplishments and political…

  4. Learning Leadership: Becoming an Outdoor Leader

    Science.gov (United States)

    Enoksen, Elisabeth; Lynch, Pip

    2018-01-01

    Recent leadership research has demonstrated a need for better understanding the process of becominga leader because it might be qualitatively different to being a leader. If so, there is likely to be a need for pedagogies designed deliberately to support first-time outdoor leadership experiences and any such pedagogies must be informed by the…

  5. District Leaders' Framing of Educator Evaluation Policy

    Science.gov (United States)

    Woulfin, Sarah L.; Donaldson, Morgaen L.; Gonzales, Richard

    2016-01-01

    Purpose: Educator evaluation systems have recently undergone scrutiny and reform, and district and school leaders play a key role in interpreting and enacting these systems. This article uses framing theory to understand district leaders' interpretation and advancement of a state's new educator evaluation policy. Research Methods: The article…

  6. The Called, Chosen, and Faithful Leader

    Science.gov (United States)

    Davis, Hartwell T. Paul

    2009-01-01

    Leaders are made, not born. Like so many other of life's complex issues, the question of nature vs. nurture in leadership is one that is analyzed, researched, and debated by educators, philosophers, social scientist, and even leaders themselves. Leadership has been dissected as to personality, character, and behavior. Researchers have developed…

  7. Mood and the evaluation of leaders

    NARCIS (Netherlands)

    Schyns, Birgit; Sanders, Karin

    2003-01-01

    Research on the evaluation of leaders has shown that evaluation ratings are prone to several biases. The present study deals with one possible bias, namely, the relationship between mood and the perception or evaluation of a leader. The affect-as-information framework, which indicates that mood

  8. Wire- and cathode pulses in a counter of square cross section with a thin wire as central conductor operating in limited streamer mode

    Science.gov (United States)

    Carli, Ch.; Erd, Ch.; Leder, G.; Pernicka, M.; Regler, M.; Schnizer, B.

    1989-11-01

    Streamer tubes are becoming increasingly important in high-energy physics experiments. They are used as drift tubes for the localisation of charged-particle tracks, and also as sampling devices in sandwich calorimeters with cathode readout only. The streamer pulses carry charges which are several orders of magnitude larger than pulses from proportional chambers; this provides a good signal-to-noise ratio and makes them appropriate for a wide field of applications in highly compact detectors. The signals induced on the cathodes are also important for measuring — in addition to the anode wire - a second coordinate, and for resolving ambiguities in track recognition. When connecting the signals from two opposite cathodes to the two inputs of a differential amplifier, a left/right bit could be added after suitable buffering via the same signal line as used for time digitalisation. Another essential feature is the association of time information from the anode wire and the cathode. For the streamer tube used in this experiment the pulses induced on the cathode on either side of the particle, and on the anode, are measured by a fast analog-to-digital converter. A simple two-dimensional model ρ( r, θ) at t = 0, without any time-dependent effects other than a constant electron drift velocity of 50 μm/ns, is used to compare the charge distribution in a streamer with the measurements of the pulse lengths at the two opposite cathode strips. First the field generated by a static voltage is calculated. Then the effect of a "space charge" is evaluated. The Green's function of the square domain is a prerequisite for determining the field and the surface charge distribution on the electrodes. It is obtained from that of a concentric circular counter by a conformal mapping. Representations of Green's functions are calculated by series expansions.

  9. The Effect of Pulsed Streamer-like Discharge in Liquid on Transcriptional Activation of Retrotransposon Genes of a Red Alga, Porphyra Yezoensis

    OpenAIRE

    Ohno, T.; Li, Z.; Lin, X.F.; Zhang, W.B.; Takano, H.; Takio, S.; Namihira, T.; Akiyama, H.; オオノ, ツヨシ; ナミヒラ, タカオ; アキヤマ, ヒデノリ; 大野, 剛史; 浪平, 隆男; 秋山, 秀典

    2007-01-01

    Retrotransposons are mobile genetic elements thataccomplished transposition via an RNA intermediate.These elements can be transcriptionally activated by stressfactors, such as UV light, ozone, pathogens, woundingand drought. A red alga, porphyra yezoensis has recentlybeen recognized as a model plant for fundamental andapplied study in marine biological science. In this paper,pulsed streamer-like discharge in liquid was used as a newstress condition, and the transcription level of a copia-like...

  10. Leader power and leader self-serving behavior : The role of effective leadership beliefs and performance information

    NARCIS (Netherlands)

    Rus, Diana; van Knippenberg, Daan; Wisse, Barbara

    2010-01-01

    In this research we investigated the role played by leader power in determining leader self-serving behavior. Based on an integration of insights from research on the determinants of leader behavior and the power-approach theory, we hypothesized that with higher leader power leader self-serving

  11. What about the leader? Crossover of emotional exhaustion and work engagement from followers to leaders.

    Science.gov (United States)

    Wirtz, Nina; Rigotti, Thomas; Otto, Kathleen; Loeb, Carina

    2017-01-01

    Although a growing body of research links leadership behavior to follower health, comparatively little is known about the health effects of being in the lead. This longitudinal study of 315 team members and 67 leaders examined the crossover of emotional exhaustion and work engagement from followers to leaders. Leader emotional self-efficacy was tested as a moderator in the crossover process. Multiple regression analyses revealed that followers' work engagement was positively related to leaders' work engagement eight months later, controlling for followers' tenure with the leader, leader gender, autonomy, workload, and work engagement at Time 1. Leaders' emotional self-efficacy did not moderate the crossover of work engagement. Followers' emotional exhaustion was not directly related to leaders' emotional exhaustion over time. We did find a significant interaction effect for follower emotional exhaustion and leader emotional self-efficacy. This study is the first to show that crossover of emotional exhaustion and work engagement can unfold over time from team members to leaders. Main theoretical implications lie in the finding that-in line with job demands-resources theory-followers' psychological states can pose a demand or resource for leaders, and influence their well-being. For practitioners, our results offer valuable insights regarding the design of organizational health interventions as well as leadership development measures. (PsycINFO Database Record (c) 2016 APA, all rights reserved).

  12. Affective match: Leader emotions, follower positive affect, and follower performance

    NARCIS (Netherlands)

    Damen, F.; van Knippenberg, B.M.; van Knippenberg, D.

    2008-01-01

    Leader emotions may play an important role in leadership effectiveness. Extending earlier research on leader emotional displays and leadership effectiveness, we propose that the affective match between follower positive affect (PA) and leaders' emotional displays moderates the effectiveness of

  13. Factors supporting dentist leaders' retention in leadership.

    Science.gov (United States)

    Tuononen, T; Lammintakanen, J; Suominen, A L

    2017-12-01

    The aim was to study factors associated with staying in a dentist leadership position. We used an electronic questionnaire to gather data from 156 current or former Finnish dentist leaders in 2014. Principal component analysis categorized statements regarding time usage and opportunities in managerial work into five main components. Associations between these main component scores and the tendency to stay as a leader were analyzed with logistic regression. Out of the five main components, two were significantly associated with staying as a leader: 'career intentions', which represented intent to continue or to leave the leadership position; and 'work time control opportunities', which represented how leaders could control their own work time. Other factors that supported staying were leadership education, more work time available for leadership work, and lower age. The main component 'work pressure' decreased, although not significantly, the odds of continuing; it included lack of leadership work time, and pressure from superiors or subordinates. Leaders have important roles in health care, ensuring everyday operations as well as developing their organizations to meet future challenges. Knowledge of these supporting factors will enable dentist leaders and their organizations to improve working conditions in order to recruit and retain motivated and competent persons. In addition, well-designed education is important to inspire and encourage future leaders. Copyright© 2017 Dennis Barber Ltd.

  14. Understanding health policy leaders' training needs.

    Directory of Open Access Journals (Sweden)

    Carey Roth Bayer

    Full Text Available We assessed the training needs of health policy leaders and practitioners across career stages; identified areas of core content for health policy training programs; and, identified training modalities for health policy leaders.We convened a focus group of health policy leaders at varying career stages to inform the development of the Health Policy Leaders' Training Needs Assessment tool. We piloted and distributed the tool electronically. We used descriptive statistics and thematic coding for analysis.Seventy participants varying in age and stage of career completed the tool. "Cost implications of health policies" ranked highest for personal knowledge development and "intersection of policy and politics" ranked highest for health policy leaders in general. "Effective communication skills" ranked as the highest skill element and "integrity" as the highest attribute element. Format for training varied based on age and career stage.This study highlighted the training needs of health policy leaders personally as well as their perceptions of the needs for training health policy leaders in general. The findings are applicable for current health policy leadership training programs as well as those in development.

  15. Are you a collaborative leader?

    Science.gov (United States)

    Ibarra, Herminia; Hansen, Morten T

    2011-01-01

    Social media and technologies have put connectivity on steroids and made collaboration more integral to business than ever. But without the right leadership, collaboration can go astray. Employees who try to collaborate on everything may wind up stuck in endless meetings, struggling to reach agreement. On the other side of the coin, executives who came of age during the heyday of "command and control" management can have trouble adjusting their style to fit the new realities. In their research on top-performing CEOs, Insead professors Ibarra and Hansen have examined what it takes to be a collaborative leader. They've found that it requires connecting people and ideas outside an organization to those inside it, leveraging diverse talent, modeling collaborative behavior at the top, and showing a strong hand to keep teams from getting mired in debate. In this article, they describe tactics that executives from Akamai, GE, Reckitt Benckiser, and other firms use in those four areas and how they foster high-performance collaborative cultures in their organizations.

  16. How To Build a Leader?

    Directory of Open Access Journals (Sweden)

    Adrian Majuru

    2015-05-01

    Full Text Available Romania lacks a ”map of the future”. This chart of the future depends just on the human factor. More specifically, on the continuous investment in the human factor. During the last 2 decades of freedom of attitude, very few positive and sustained steps have been taken through solid arguments, with clear reference points and stages that have to be followed .It is absolutely compulsory to rebuild with new tools, as a surprise for the opponents and as an optimalsolution for the supporters. This would be a new, superior creation, with an invincible astonishing result. This new tool means an effort of retraining, with a view to getting better, professional skills.This study proposes a comparative analysis, 80 years later, following the physiognomy, the attitudes and examples of good practice regarding the social mechanism through which a youngster could be calibrated into a leader of his generation, as well as finding the obstacles of the present social system. Besides the historical, social and cultural perspective of this analysis, we would take into account elements of socialethology and anthropology, and the whole thing would be built and based on an analysis with a prognosis effect for the next generation, starting from the history of the last 30 years and discussing the effects this\\r\

  17. Trust in direct leaders and top leaders: A trickle-up model.

    Science.gov (United States)

    Fulmer, C Ashley; Ostroff, Cheri

    2017-04-01

    Low levels of employee trust in top leaders pose challenges to organizations with respect to retention, performance, and profits. This research examines how trust in top leaders can be fostered through the relationships individuals have with their direct leaders. We propose a trickle-up model whereby trust in direct leaders exerts an upward influence on trust in top leaders. Drawing on the group value model, we predict that direct leaders' procedural justice serves as the key mechanism in facilitating the trickle-up process. Further, this process should be particularly strong for employees high on vertical collectivism, and the trickled-up trust in top leaders should exert a stronger impact on employees' overall performance in the organization than trust in direct leaders. Multiphase and multisource data from 336 individuals support these hypotheses. The findings advance our understanding of trust and leadership by highlighting that trust in leaders at different levels does not form independently and that trust in leaders trickles up across hierarchical levels. (PsycINFO Database Record (c) 2017 APA, all rights reserved).

  18. Internationalization in schools - perspectives of school leaders

    DEFF Research Database (Denmark)

    Egekvist, Ulla Egidiussen; Lyngdorf, Niels Erik; Du, Xiangyun

    2017-01-01

    This paper explores how internationalization ideas in primary and lower secondary schools can be developed through the acquisition of international experience abroad by leaders. The study was inspired by existing literature on internationalization and leadership, and theories of experiential...... learning and reflection. Empirically, qualitative material was derived from a study of nineteen Danish school leaders participating in an eight-day delegation visit to China. This study shows that international experience for leaders can be used to develop ideas for internationalization at the school level...

  19. Circumbinary, not transitional: on the spiral arms, cavity, shadows, fast radial flows, streamers, and horseshoe in the HD 142527 disc

    Science.gov (United States)

    Price, Daniel J.; Cuello, Nicolás; Pinte, Christophe; Mentiplay, Daniel; Casassus, Simon; Christiaens, Valentin; Kennedy, Grant M.; Cuadra, Jorge; Sebastian Perez, M.; Marino, Sebastian; Armitage, Philip J.; Zurlo, Alice; Juhasz, Attila; Ragusa, Enrico; Laibe, Guillaume; Lodato, Giuseppe

    2018-06-01

    We present 3D hydrodynamical models of the HD 142527 protoplanetary disc, a bright and well-studied disc that shows spirals and shadows in scattered light around a 100 au gas cavity, a large horseshoe dust structure in mm continuum emission, together with mysterious fast radial flows and streamers seen in gas kinematics. By considering several possible orbits consistent with the observed arc, we show that all of the main observational features can be explained by one mechanism - the interaction between the disc and the observed binary companion. We find that the spirals, shadows, and horseshoe are only produced in the correct position angles by a companion on an inclined and eccentric orbit approaching periastron - the `red' family from Lacour et al. Dust-gas simulations show radial and azimuthal concentration of dust around the cavity, consistent with the observed horseshoe. The success of this model in the HD 142527 disc suggests other mm-bright transition discs showing cavities, spirals, and dust asymmetries may also be explained by the interaction with central companions.

  20. The dean as spiritual leader.

    Science.gov (United States)

    Evans, C

    1998-06-01

    These are hard times for medical school deans--high turnover among deans, the fiscal distress of many medical schools, the gap between what deans expect the job will be and what is required of them, the stark differences between what the job of dean is today and what it was in the past, and the threats to the academic missions of education and research. Using stories, anecdotes, and parables, the authors illustrates how these very difficulties might be an opportunity to rethink the role of deans and to re-examine the attributes and skills required of successful deans today. The ultimate goals of medical education have not changed, but the drastic nature of the changes taking place all around, and within, medical education make it more critical than ever to keep in mind what is really important. Deans must be exquisitely attuned to what is really important and they must make sure that the academic medical community never loses sight of what that is. To do that, deans must be deeply rooted personally in the enduring values and commitments that inform medicine as a profession and a vocation and in the fundamental values of medical education and scholarship; they must personify and embody these values; and they must remind us of these values and inspire us to embrace them and be guided by them. This is the sense in which deans must be "spiritual" leaders--that is, through their personal example, they must rekindle and engage the spirit of those working on behalf of the academic mission. While the need for fiscal expertise, management skills, and diplomatic and interpersonal skills in deans is widely acknowledged, the need for sensitivity to the spiritual dimensions of the work of deans has not received the attention it deserves.

  1. Creative leaders create 'unsung heroes':leader creativity and subordinate organizational citizenship behavior

    Institute of Scientific and Technical Information of China (English)

    Xiao Deng; Zhishuang Guan

    2017-01-01

    As leader creativity is found to be effective at promoting outcomes for organizations,more and more organizations select creative individuals as leaders.However,the influence of leader creativity has not received enough attention.Thus,this research seeks to focus on the potential influences of leader creativity in organizations.Based on social cognitive theory,we explore the relationship between leader creativity and subordinate organizational citizenship behavior (OCB).We find that leader creativity is positively related to subordinate OCB,and perceived team creative efficacy mediates the relationship.Moreover,creative self-efficacy moderates the relationships between perceived team creative efficacy and subordinate OCB.We then discuss implications and limitations,and suggest directions for future research.

  2. Leaders as Corporate Responsibility Spokesperson: How Leaders Explain Liabilites Via Corporate Web Sites?

    Directory of Open Access Journals (Sweden)

    Burcu Öksüz

    2014-12-01

    Full Text Available The aim of this paper is to reveal the corporate social responsibility (CSR understandings of corporations from the leaders’ perspective and discuss how leaders define and explain CSR practices their organizations executed as spokesperson via social media channels of their organizations.  In this context, a content analysis aiming to display the ideas of Turkey’s top 250 corporations’ leaders (CEO, chairman of the board, general manager designated by Istanbul Chamber of Industry in 2013. The leader messages about different dimensions of CSR and CSR practices that are partaking in corporate web sites were examined. According to the results of the analysis, it is found that the leaders act as responsible leaders, and also the spokesperson of their corporations. In addition it is found out that responsible leaders included multiplexed information on different dimensions and various practices of CSR in their social media messages.

  3. Interprofessional Care and Role of Team Leaders.

    Science.gov (United States)

    Kaini, B K

    2015-01-01

    Interprofessional care is an essential part of the health service delivery system. It helps to achieve improved care and to deliver the optimal and desired health outcomes by working together, sharing and learning skills. Health care organisation is a collective sum of many leaders and followers. Successful delivery of interprofessional care relies on the contribution of interprofessional care team leaders and health care professionals from all groups. The role of the interprofessional care team leader is vital to ensuring continuity and consistency of care and to mobilise and motivate health care professionals for the effective delivery of health services. Medical professionals usually lead interprofessional care teams. Interprofessional care leaders require various skills and competencies for the successful delivery of interprofessional care.

  4. ROLES OF LOCAL LEADERS ON WILDLIFE CONSERVATION ...

    African Journals Online (AJOL)

    OYELEYE DABV

    2018-03-01

    Mar 1, 2018 ... It also assessed the level of interaction and perception of people within the host community on the park. ... management is in good touch with the leaders of the host communities. However ..... An International Multi-Disciplinary.

  5. LEADER jõudis Eestisse / Harda Roosna

    Index Scriptorium Estoniae

    Roosna, Harda, 1956-

    2006-01-01

    EL-i maaelu toetusprogrammi LEADER+ rakendamist on katsetatud Põlva-, Valga-, Pärnu- ja Võrumaal. Hiiumaal arutletakse programmi rakendamiseks vajaliku tegevusgrupi moodustamise üle märtsis. Lisad: Ajalugu; Näited

  6. Choosing a public-spirited leader

    DEFF Research Database (Denmark)

    Markussen, Thomas; Tyran, Jean-robert

    2017-01-01

    In this experiment, voters select a leader who can either act in the public interest, i.e. make efficient and equitable policy choices, or act in a corrupt way, i.e. use public funds for private gain. Voters can observe candidates⿿ pro-social behavior and their score in a cognitive ability test...... prior to the election, and this fact is known to candidates. Therefore, self-interested candidates have incentives to act in a pro-social manner, i.e. to pretend to be public-spirited leaders. We find that both truly pro-social and egoistic leaders co-exist, but that political selection is ineffective...... in choosing public-spirited leaders. The main reason is that egoistic candidates strategically pretend to be pro-social to increase their chances of winning the election....

  7. Yelavarthy Nayudamma: Scientist, Leader, and Mentor Extraordinary

    Indian Academy of Sciences (India)

    Home; Journals; Resonance – Journal of Science Education; Volume 19; Issue 10. Yelavarthy Nayudamma: Scientist, Leader, and Mentor Extraordinary. J Raghava Rao T Ramasami. General Article Volume 19 Issue 10 October 2014 pp 887-899 ...

  8. Understanding the relationship between followers and leaders.

    Science.gov (United States)

    Kean, Susanne; Haycock-Stuart, Elaine

    2011-12-01

    Contemporary healthcare policies tend to imply that successful leadership can be attributed to a single leader. Such an understanding of leadership ignores the significant contribution followers make to successful leadership and their influence on leaders. In reality, followers rarely simply follow leaders. Following is a complex process that depends on the context and involves followers making judgements about prospective leaders while deciding whether or not to follow them. This interdependence is ignored all too often or misunderstood by those who see leadership as something that can resolve the problems of the NHS. Using data from a study of leadership in community nursing in which the authors were involved, they argue that senior staff who ignore followers and their contribution to leadership do so at the peril of their organisations.

  9. What Type of Project Leader Are You?

    DEFF Research Database (Denmark)

    Lund Pedersen, Carsten; Ritter, Thomas

    2018-01-01

    Everyone has their own way of organising a project. Read about the four types of leadership, and why a diversity of types is good for any organisation. And take the quiz: What type of project leader are you?......Everyone has their own way of organising a project. Read about the four types of leadership, and why a diversity of types is good for any organisation. And take the quiz: What type of project leader are you?...

  10. Understanding leader representations: Beyond implicit leadership theory

    OpenAIRE

    Knee, Robert Everett

    2006-01-01

    The purpose of the present study was to establish evidence for the suggested integration of the theories of connectionism and leadership. Recent theoretical writings in the field of leadership have suggested that the dynamic representations generated by the connectionist perspective is an appropriate approach to understanding how we perceive leaders. Similarly, implicit leadership theory (ILT) explains that our cognitive understandings of leaders are based on a cognitive structure that we u...

  11. Frequency and timing of leaders' mediation attempts

    OpenAIRE

    Demirağ, Elif Gizem; Demirag, Elif Gizem

    2015-01-01

    How do a state's political regime type and power status influence leader's mediation attempts? This study develops an explanation as a response to this question derived from the democratic peace theory which underlines the role of democratic norms in motivating state leaders to play a third party role in peace processes. Based on this approach, the expectation is that democratic country representatives are more likely to mediate especially in the early stage of their careers. In addition, I a...

  12. Medical Leaders in Taiwan During Japanese Colonization

    Directory of Open Access Journals (Sweden)

    Ming-Tung Wang

    2011-03-01

    Full Text Available Japan established the medical system in Taiwan during its 50 years of occupation, which evolved into the present National Taiwan University Hospital system. This paper summarizes the biographies of 97 Japanese leaders in various medical disciplines during the Japanese occupation of Taiwan. These leaders were among the elite of Japan, with superior intellectual, social and economic status, who helped to establish the important attributes of medical professionals in Taiwan, such as a good academic background, heritage, and research skills.

  13. Developing Senior Leaders for the Reserve Components

    Science.gov (United States)

    2017-01-01

    expectation other than rudimentary dialogues on career paths. Some senior leaders are superb mentors , but this appears to be a result of the personality... mentoring discussions, as well as resources and senior -level attention to these expectations, could complement individual development plans and structured...including senior leaders. This extends to the reserve components (RC) and their “critical bridge to the civilian population, infusing the Joint

  14. Leader as visionary. Leadership education model.

    Science.gov (United States)

    Aroian, Jane

    2002-01-01

    Developing nurse leaders for today and tomorrow is a priority considering the powerful relationship between leadership strength and the influence of the nursing profession in the future of health care. This article addresses leadership theories and research as they relate to visionary leadership. Education for visionary leadership is also addressed including the competencies and skill sets for effective visionary leaders. Visioning is a powerful force for change in shaping organizations and building teams for the future.

  15. Bossing or serving?: How leaders execute effectively.

    Science.gov (United States)

    Kerfoot, Karlene

    2008-04-01

    Many new leaders believe that the way to get things done is to be autocratic and directive. Successful leadership is a negotiated process with the employees that must be mutually satisfying for the evolution into a high-performing unit or organization. Well-intentioned leaders often overlook the very simple truth of learning to help people move forward in their work and to treat people as decent human beings.

  16. Bossing or serving? How leaders execute effectively.

    Science.gov (United States)

    Kerfoot, Karlene

    2007-01-01

    Many new leaders believe that the way to get things done is to be autocratic and directive. Successful leadership is a negotiated process with the employees that must be mutually satisfying for the evolution into a high-performing unit or organization. Well-intentioned leaders often overlook the very simple truth of learning to help people move forward in their work and to treat people as decent human beings.

  17. Perspectives on healthcare leader and leadership development

    OpenAIRE

    Scott, Elaine S.

    2010-01-01

    Elaine S ScottCollege of Nursing, Graduate Nursing Science Department, East Carolina University, Greenville, NC USAAbstract: Healthcare delivery systems are complex entities that must merge the best of administrative and clinical practices into a new model of leadership. But, despite growing recognition that healthcare organizational leaders must partner with clinical leaders to address patient safety, evidence based practice, financial sustainability, and capacity, tensions between the group...

  18. On the Transition from Initial Leader to Stepped Leader in Negative Cloud-to-ground Lightning

    Science.gov (United States)

    Stolzenburg, M.; Marshall, T. C.; Karunarathne, S.; Orville, R. E.

    2017-12-01

    High-speed video and electric field change (E-change) data are used to describe the first 5 ms of a natural negative cloud-to-ground (CG) flash. These observations reveal differences in appearance of both the video luminosity and the E-change pulses before the leader transitions to propagating as a negative stepped leader (SL). During the initial breakdown (IB) stage, the initial leader advances intermittently forward in jumps of 78-175 m, at intervals of 100-280 μs, and in separate bursts that are bright for a few 20-μs video frames. The IB pulses accompanying these luminosity bursts have long duration, large amplitude, and a characteristic bipolar shape in nearby E-change observations. In the time between IB pulses, the initial leader is very dim or not visible during the earliest 1-2 ms of the IB stage. Over the next few milliseconds, the leader propagation transitions to an early SL phase, in which the leader tips advance 20-59 m forward at more regular intervals of 40-80 μs during relatively dim and brief steps. In the E-change data, the accompanying SL pulses have very short duration, small amplitude, and are typically unipolar. These data indicate that when the entire initial leader length behind the lower end begins to remain illuminated between bursts, the propagation mode changes from IB bursts to SL steps, and the IB stage ends. Additional differences in initial leader character are evident during the return stroke, as its luminosity speed decreases sharply upon reaching the topmost initial leader section of the channel, and that section of channel does not saturate the video intensity. Results of these analyses support a prior hypothesis that the early initial leader development occurs in the absence of a continuously hot channel, and consequently, the initial leader propagation is unlike the self-propagating advance of the later stepped leader.

  19. Creating tomorrow's leaders today: the Emerging Nurse Leaders Program of the Texas Nurses Association.

    Science.gov (United States)

    Sportsman, Susan; Wieck, Lynn; Yoder-Wise, Patricia S; Light, Kathleen M; Jordan, Clair

    2010-06-01

    The Texas Nurses Association initiated an Emerging Nurse Leaders Program as an approach to engaging new nurses in the leadership of the professional association. This article explains the program's origin, the commitment of the Texas Nurses Association to this process, the implementation of the plan, and the discussions that launched a new way of connecting leaders across generations. Further, it is an approach that any professional organization can use to encourage the involvement of new leaders.

  20. VISION- REQUIREMENT FOR A SUCCESSFUL LEADER

    Directory of Open Access Journals (Sweden)

    Angela - Olimpia Lobonea (Oltean

    2014-12-01

    Full Text Available These people were called in the past chiefs, rulers. Now they are known as leaders. After management by objectives, strategic planning, project organization, this concept appears as a tool called "fourth generation". It is called VISION. Leadership and vision exist in the actual sense, which has become modern a few decades ago, managing to gather during this time a variety of scientific instruments. The connection between these two domains creates a certain type of leader, the visionary leader. The hypothesis from which we start is that all active leaders have a vision of what needs to be accomplished, and the inability to predict something that could be provided involves loss the capacity of the leader. Without vision, the energy reaches the lowest quotas, production decreases, terms limits are exceeded and human resources begin to dissipate.. The conclusion is that visionary leaders are endowed with multiple attributes (multiple intelligence, even if sometimes the role of intuition and unconscious in building vision at the expense of reason that is based on experience and facts is exaggerated.

  1. Leader narcissism and follower outcomes: The counterbalancing effect of leader humility.

    Science.gov (United States)

    Owens, Bradley P; Wallace, Angela S; Walker, Angela S; Waldman, David A

    2015-07-01

    [Correction Notice: An Erratum for this article was reported in Vol 100(4) of Journal of Applied Psychology (see record 2015-29666-001). The last name of the second author was misspelled in the Online First version of the article. All versions of this article have been corrected.] In response to recent calls to theorize and examine how multiple leader characteristics may work together in their effects, the current research examines how leader narcissism and humility interact to predict perceived leader effectiveness and follower (i.e., direct-report) job engagement and performance. Although an examination of leaders who are narcissistic yet humble may seem oxymoronic and even paradoxical, researchers have suggested that seemingly contradictory personal attributes may exist simultaneously and may actually work together to produce positive outcomes. Results from survey data from followers and leaders working for a large health insurance organization showed that the interaction of leader narcissism and leader humility is associated with perceptions of leader effectiveness, follower job engagement, and subjective and objective follower job performance. Together, these results suggest that narcissistic leaders can have positive effects on followers when their narcissism is tempered by humility. (c) 2015 APA, all rights reserved).

  2. Leader-Member Exchange Theory in Higher and Distance Education

    Science.gov (United States)

    Power, Robert Leo

    2013-01-01

    Unlike many other prominent leadership theories, leader-member exchange (LMX) theory does not focus on the specific characteristics of an effective organizational leader. Rather, LMX focuses on the nature and quality of the relationships between a leader and his or her individual subordinates. The ideal is for a leader to develop as many…

  3. It takes chutzpah: oncology nurse leaders.

    Science.gov (United States)

    Green, E

    1999-01-01

    Chutzpah, according to the Oxford Dictionary of Current English (1996) is a slang term from the Yiddish language which means shameless audacity. Chutzpah has been used to identify people with courage who take on situations that others avoid and somehow achieve the impossible. Tim Porter-O'Grady (1997) recently wrote that management is dead, and has been replaced by process leadership. Health care organizations have made shifts from hierarchical structures to process or program models where people have dual/multiple reporting/communication relationship. In this new orientation, management functions of controlling, directing, organizing and disciplining are replaced by process leadership functions of coordinating, facilitating, linking and sustaining (Porter O'Grady, 1997). Herein lies the challenge for oncology nurse leaders: "what lies behind us and what lies before us are tiny matters compared to what lies within us" (Ralph Waldo Emerson). Leadership is not a function of job title. The evidence for this is clear in current practice.... There are no/few positions of nurse leaders. Titles have changed to eliminate the professional discipline, and reflect a non-descript orientation. The new titles are process leaders, program leaders, professional practice leaders. Nurse leaders need new points of reference to take in the challenges of influencing, facilitating and linking. Those points of reference are: principle-centered leadership, integrity and chutzpah. This presentation will focus on examining current thinking, defining key characteristics and attributes, and using scenarios to illustrate the impact of leadership. We, as leaders in oncology nursing, must use chutzpah to make positive change and long-term gains for patient care and the profession of nursing.

  4. Lessons Learnt of Thai Women Environmental Leaders

    Directory of Open Access Journals (Sweden)

    Sittipong Dilokwanich

    2015-07-01

    Full Text Available During the past few decades, Thai women have learned how to extent their roles from a care taker of children and a household to natural resources and environmental protection and management in local and inter-regional communities. Due to the application of National Economic and Social Development Plans, rapid resource exploitation has brought in natural resource and environmental degradation all over the country threatening communal security. For this reason, there have been a number of emerging environmental leaders who want to correct directions of national development, especially Thai woman environmental leaders who are taking a successful role of environmental guardian in their communities. This research attempts to explore why they took leadership role in environment, how they work so successful as an environmental guardian, and what their next move is. During early 2013 till mid-2014, there are 28 Thai woman leaders who received the award of Thai Environmental Conservation Mother from the Faculty of Environment and Resource Studies, Mahidol University between 2004 and 2012. They were in-depth interviewed and collected data were preceded by content analysis. Their lessons learnt show that most leaders saved their communities' environment and natural resources from the intervention of new development activities. Most of them had their parents as a good role model in environmental management who provide knowledge of morals and environmental ethics as a good basic of leadership while some shared their husband's responsibility in the same matter. Significantly, teamwork is their working style with the assistance of public participation to hold teamwork and collaboration of the community. Almost all leaders had systematic working with talents of patience, gentleness and sensitivity. The working network also broadens their new information and knowledge between practitioners. In the same time, more than half of the leaders can prepare their

  5. In praise of the incomplete leader.

    Science.gov (United States)

    Ancona, Deborah; Malone, Thomas W; Orlikowski, Wanda J; Senge, Peter M

    2007-02-01

    Today's top executives are expected to do everything right, from coming up with solutions to unfathomably complex problems to having the charisma and prescience to rally stakeholders around a perfect vision of the future. But no one leader can be all things to all people. It's time to end the myth of the complete leader, say the authors. Those at the top must come to understand their weaknesses as well as their strengths. Only by embracing the ways in which they are incomplete can leaders fill in the gaps in their knowledge with others' skills. The incomplete leader has the confidence and humility to recognize unique talents and perspectives throughout the organization--and to let those qualities shine. The authors' work studying leadership over the past six years has led them to develop a framework of distributed leadership. Within that model, leadership consists of four capabilities: sensemaking, relating, "visioning," and inventing. Sensemaking involves understanding and mapping the context in which a company and its people operate. A leader skilled in this area can quickly identify the complexities of a given situation and explain them to others. The second capability, relating, means being able to build trusting relationships with others through inquiring (listening with intention), advocating (explaining one's own point of view), and connecting (establishing a network of allies who can help a leader accomplish his or her goals). Visioning, the third capability, means coming up with a compelling image of the future. It is a collaborative process that articulates what the members of an organization want to create. Finally, inventing involves developing new ways to bring that vision to life. Rarely will a single person be skilled in all four areas. That's why it's critical that leaders find others who can offset their limitations and complement their strengths. Those who don't will not only bear the burden of leadership alone but will find themselves at the helm

  6. On the Simulation of the Interception of Lightning Dart Leaders

    OpenAIRE

    Long, Mengni; Becerra, Marley; Thottappillil, Rajeev

    2015-01-01

    This paper presents the numerical evaluation of the propagation of positive upward connecting leaders under the influence of lightning dart leaders. The simulation is performed with the self-consistent leader inception and propagation model - SLIM-. An analytical expression is derived for calculating the charge per unit length required to thermalize a new upward leader segment. The simulation is validated with two dart leader attachment events in a lightning triggering experiment reported in ...

  7. Leaders' Personal Wisdom and Leader-Member Exchange Quality : The Role of Individualized Consideration

    NARCIS (Netherlands)

    Zacher, Hannes; Pearce, Liane K.; Rooney, David; McKenna, Bernard

    Business scholars have recently proposed that the virtue of personal wisdom may predict leadership behaviors and the quality of leader-follower relationships. This study investigated relationships among leaders' personal wisdom-defined as the integration of advanced cognitive, reflective, and

  8. Leader to Leader: Enduring Insights on Leadership from the Drucker Foundation's Award-Winning Journal.

    Science.gov (United States)

    Hesselbein, Frances, Ed.; Cohen, Paul M., Ed.

    Amid unprecedented social, demographic, and economic changes, leaders must enhance performance and deliver desired results. The growing importance of managing the explosion in information requires attention to defining organizational missions and visions. The 37 chapters in this work are divided into 7 parts. Part 1, "On Leaders and…

  9. A Comparison of Student Leader and Non Leader Attitudes Toward Legalizing Marihuana

    Science.gov (United States)

    Bittner, John R.; Cash, William B.

    1971-01-01

    The data tends to imply that campus leaders have attitudes on the issue of marihuana legalization which conform to the norms of a major midwestern university sampling. Drug education programs might include student leaders with local credibility and who may possess attitudes very similar to their peers. (Author/BY)

  10. Sustaining leaders of cancer support groups: the role, needs, and difficulties of leaders.

    Science.gov (United States)

    Butow, Phyllis; Ussher, Jane; Kirsten, Laura; Hobbs, Kim; Smith, Katharine; Wain, Gerald; Sandoval, Mirjana; Stenlake, Annie

    2005-01-01

    Cancer support groups are an important source of support for cancer patients, yet little is known about the characteristics of, and barriers to, effective leadership, and the training needs of both professionally trained and untrained leaders. This study explored the views of 179 leaders of 184 cancer support groups in NSW, Australia, regarding these issues. Four hundred and sixteen members of 50 groups selected from the larger cohort completed questionnaires eliciting the importance of group processes, including leader qualities, and satisfaction with group leadership. Finally, members of nine groups participated in focus groups regarding effective group processes. The importance of the leader(s) was emphasized in all stages of the research. Fifty-nine percent of group leaders were currently experiencing a difficulty, primarily related to infrastructure or group process. Three characteristics of effective leaders were identified: educational qualities, facilitation skills, and personal qualities. There is clearly a need to develop and evaluate effective interventions to maintain leaders in these roles, if the proven benefits for cancer patients are to be protected.

  11. Leadership and Leader Developmental Self-Efficacy: Their Role in Enhancing Leader Development Efforts.

    Science.gov (United States)

    Murphy, Susan Elaine; Johnson, Stefanie K

    2016-01-01

    This chapter describes the role of two types of self-efficacy-leader self-efficacy and leader developmental efficacy-for enhancing leadership development. Practical implications for designing and developing leadership programs that take into account these two types of self-efficacy are discussed. © 2016 Wiley Periodicals, Inc., A Wiley Company.

  12. Leaders in social networks, the Delicious case.

    Science.gov (United States)

    Lü, Linyuan; Zhang, Yi-Cheng; Yeung, Chi Ho; Zhou, Tao

    2011-01-01

    Finding pertinent information is not limited to search engines. Online communities can amplify the influence of a small number of power users for the benefit of all other users. Users' information foraging in depth and breadth can be greatly enhanced by choosing suitable leaders. For instance in delicious.com, users subscribe to leaders' collection which lead to a deeper and wider reach not achievable with search engines. To consolidate such collective search, it is essential to utilize the leadership topology and identify influential users. Google's PageRank, as a successful search algorithm in the World Wide Web, turns out to be less effective in networks of people. We thus devise an adaptive and parameter-free algorithm, the LeaderRank, to quantify user influence. We show that LeaderRank outperforms PageRank in terms of ranking effectiveness, as well as robustness against manipulations and noisy data. These results suggest that leaders who are aware of their clout may reinforce the development of social networks, and thus the power of collective search.

  13. Leaders in social networks, the Delicious case.

    Directory of Open Access Journals (Sweden)

    Linyuan Lü

    Full Text Available Finding pertinent information is not limited to search engines. Online communities can amplify the influence of a small number of power users for the benefit of all other users. Users' information foraging in depth and breadth can be greatly enhanced by choosing suitable leaders. For instance in delicious.com, users subscribe to leaders' collection which lead to a deeper and wider reach not achievable with search engines. To consolidate such collective search, it is essential to utilize the leadership topology and identify influential users. Google's PageRank, as a successful search algorithm in the World Wide Web, turns out to be less effective in networks of people. We thus devise an adaptive and parameter-free algorithm, the LeaderRank, to quantify user influence. We show that LeaderRank outperforms PageRank in terms of ranking effectiveness, as well as robustness against manipulations and noisy data. These results suggest that leaders who are aware of their clout may reinforce the development of social networks, and thus the power of collective search.

  14. ICCD microscopic imaging of a single micro-discharge in surface coplanar DBD geometry: determination of the luminous diameter of N-2 and Ar streamers

    Czech Academy of Sciences Publication Activity Database

    Šimek, Milan; Ambrico, P. F.; Prukner, Václav

    2011-01-01

    Roč. 20, č. 2 (2011), 025010-025010 ISSN 0963-0252. [European Sectional Conference on Atomic and Molecular Physics of Ionized Gases (ESCAMPIGXX)/20th./. Novi Sad , SERBIA, 13.07.2010-17.07.2010] R&D Projects: GA ČR GA202/08/1106 Institutional research plan: CEZ:AV0Z20430508 Keywords : surface barier discharge * streamer * imaging Subject RIV: BL - Plasma and Gas Discharge Physics Impact factor: 2.521, year: 2011 http://iopscience.iop.org/0963-0252/20/2/025010/pdf/0963-0252_20_2_025010.pdf

  15. Evolution of N2(A3Σ+u) in streamer discharges: influence of oxygen admixtures on formation of low vibrational levels.

    Czech Academy of Sciences Publication Activity Database

    Šimek, Milan; Ambrico, P. F.; Prukner, Václav

    2017-01-01

    Roč. 50, č. 50 (2017), č. článku 504002. ISSN 0022-3727 R&D Projects: GA ČR(CZ) GA15-04023S Institutional support: RVO:61389021 Keywords : nitrogen * air * streamer * laser-induced fluorescence * LIF Subject RIV: BL - Plasma and Gas Discharge Physics OBOR OECD: Fluids and plasma physics (including surface physics ) Impact factor: 2.588, year: 2016 http://iopscience.iop.org/article/10.1088/1361-6463/aa96f3

  16. When is a leader considered as a good leader? Perceived impact on teammates’ confidence and social acceptance as key ingredients

    OpenAIRE

    Fransen, Katrien; Vanbeselaere, Norbert; De Cuyper, Bert; Vande Broek, Gert; Boen, Filip

    2018-01-01

    Effective leadership is perceived as a key factor for optimal team functioning. The present study aimed to identify the characteristics of athlete leaders with respect to four different leadership roles (i.e., task leader, motivational leader, social leader, and external leader), while recognizing the surrounding team context. Furthermore, we aimed to identify the most decisive characteristics for a player’s perceived leadership quality on each of these leadership roles. An on-line survey was...

  17. How to be a good academic leader.

    Science.gov (United States)

    Detsky, Allan S

    2011-01-01

    Individuals who take on leadership positions in academic health science centers help facilitate the mission of those institutions. However, they are often chosen on the basis of success in the core activities in research, education and patient care rather than on the basis of demonstrated leadership and management skills. Indeed, most academic leaders in the past have "learned on the job." This commentary provides practical advice on how to be an effective leader on the basis of the author's experiences as a Division Head and Chief of Medicine. It covers six themes (vision, managerial style, knowledge, people skills, organizational orientation and personal development) and offers 21 specific suggestions, one for each year of the author's leadership. It is hoped that this experience-derived advice will help future leaders in academic medicine.

  18. Characterizing leader sequences of CRISPR loci

    DEFF Research Database (Denmark)

    Alkhnbashi, Omer; Shah, Shiraz Ali; Garrett, Roger Antony

    2016-01-01

    The CRISPR-Cas system is an adaptive immune system in many archaea and bacteria, which provides resistance against invading genetic elements. The first phase of CRISPR-Cas immunity is called adaptation, in which small DNA fragments are excised from genetic elements and are inserted into a CRISPR...... array generally adjacent to its so called leader sequence at one end of the array. It has been shown that transcription initiation and adaptation signals of the CRISPR array are located within the leader. However, apart from promoters, there is very little knowledge of sequence or structural motifs...... sequences by focusing on the consensus repeat of the adjacent CRISPR array and weak upstream conservation signals. We applied our tool to the analysis of a comprehensive genomic database and identified several characteristic properties of leader sequences specific to archaea and bacteria, ranging from...

  19. Internationalization in schools - perspectives of school leaders

    DEFF Research Database (Denmark)

    Egekvist, Ulla Egidiussen; Lyngdorf, Niels Erik; Du, Xiangyun

    2017-01-01

    This paper explores how internationalization ideas in primary and lower secondary schools can be developed through the acquisition of international experience abroad by leaders. The study was inspired by existing literature on internationalization and leadership, and theories of experiential...... through reflections of lived experiences, participation in meaningful activities, and active engagement in interaction with international and local colleagues. However, the realization of ideas depends on various elements, including leadership, teacher engagement, policy support, and financial support....... learning and reflection. Empirically, qualitative material was derived from a study of nineteen Danish school leaders participating in an eight-day delegation visit to China. This study shows that international experience for leaders can be used to develop ideas for internationalization at the school level...

  20. The Quality Of Leader/Employee Relationship

    Directory of Open Access Journals (Sweden)

    F. J. Carstens

    2006-11-01

    Full Text Available This study set out to investigate what role the quality of the relationship between business leaders and their employees played in the performance of their business. The study compared the business performance of forty-five area managers in one of the major listed banks in South Africa with their specific leader/employee relationship profiles. The research approach was quantitative and of a correlational nature. The results indicate that although certain elements within the relationship between business leaders and employees indeed have an influence on business performance this alone was not a sufficient condition. The study suggested that the dimensions relating to vision, trust, accountability and decision- making have the strongest influence on business performance. Further research in this area is suggested.