Improvement of the Terminal Characteristics of a Slightly Modified d.c. Machine with an Electronically Assisted Commutaion

In [10], we have presented a new d.c. machine arrangement which is especially designed to operate with an electronically assisted commutation. The experiment has succeeded and the modified d.c. machine operates at a power equal to 1.4 times its initial nominal power without any spark under brushes. We present, in this paper, the obtained results.Dans un précédent article [10], nous avons présenté une machine à courant continu dont le collecteur a subi des modifications qui permettent de mieux l'adapter à l'assistance électronique à la commutation. L'expérimentation a réussi et la machine modifiée a fonctionné à une puissance égale à 1,4 fois la puissance nominale de la machine initiale sans aucune production d'étincelles sous les balais. Dans le présent article, nous présentons les résultats obtenus

Determination of sprite streamers altitude based on N 2 spectroscopic analysis

International audienceFuture space missions (e.g., ASIM and TARANIS) are soon to be launched to observe transient luminous events (TLEs) from a nadir-viewing geometry. The mission GLIMS already performed observations of TLEs from a nadir-viewing geometry on board the International Space Station. Although this observation geometry is of first interest to study TLEs, it makes the determination of some quantities, such as streamer altitudes, very difficult. In this study, we propose a method to estimate the altitude of downward propagating sprite streamers using a spectrophotometric approach. Using a plasma fluid model, we simulate sprite streamers at different altitudes and quantify their optical emissions in the Lyman-Birge-Hopfield (LBH) (∼100–260 nm), the first positive (1PN 2) (∼650–1070 nm), and the second positive (2PN 2) (∼330–450 nm) bands systems of molecular nitrogen and the first negative (1NN + 2) (∼390–430 nm) bands systems of N + 2. The estimation of associated ratios allows to trace back the electric field in the streamer head as well as the altitude at which the streamer is propagating owing to different dependencies of quenching processes on the air density. The method takes into account the nonsteady state of the populations of some excited species and the exponential expansion of the streamer. The reported results could potentially be used for all TLEs but is of special interest in the case of column sprites or at the early stage of carrot sprites

Estimation of Physical Properties of Streamers in Transient Luminous Events from Non-Steady State Optical Emissions

International audienceOptical emissions from sprite streamers are used to estimate peak electric fields and electron energies [e.g., Kuo et al., GRL, 32, L19103, 2005; Adachi et al., GRL, 33, L17803, 2006]. It has been shown that significant correction factors need to be used to account for the spatial shift between distributions of optical emissions in streamers and peak electric fields in their heads [Celestin and Pasko, GRL, 37, L07804, 2010]. The latter study involved the excited species N2(C3Πu) and N2+(B2Σu+), whose populations are considered to be in steady state. The species N2(C3Πu) and N2+(B2Σu+) are responsible for the second positive (2PN2) and first negative (1NN2+) band systems of N2 and N2+, respectively. In this work, we show how this technique can be extended to non-steady state optical emissions, such as those produced by N2(a1Πg) and N2(B3Πg) in the form of Lyman-Birge-Hopfield (LBH) and first positive (1PN2) band systems, respectively. Additionally, we simulate numerically downward propagating sprite streamers and their optical emissions for the following band systems: 1PN2, 2PN2, LBH, and 1NN2+, and show how they relate to specific physical properties. This study particularly focuses on improving analysis of observational results from the future missions ASIM (ESA) and TARANIS (CNES) that will detect various optical emissions produced by transient luminous events in the nadir

Estimation of Physical Properties of Streamers in Transient Luminous Events from Non-Steady State Optical Emissions

International audienceOptical emissions from sprite streamers are used to estimate peak electric fields and electron energies [e.g., Kuo et al., GRL, 32, L19103, 2005; Adachi et al., GRL, 33, L17803, 2006]. It has been shown that significant correction factors need to be used to account for the spatial shift between distributions of optical emissions in streamers and peak electric fields in their heads [Celestin and Pasko, GRL, 37, L07804, 2010]. The latter study involved the excited species N2(C3Πu) and N2+(B2Σu+), whose populations are considered to be in steady state. The species N2(C3Πu) and N2+(B2Σu+) are responsible for the second positive (2PN2) and first negative (1NN2+) band systems of N2 and N2+, respectively. In this work, we show how this technique can be extended to non-steady state optical emissions, such as those produced by N2(a1Πg) and N2(B3Πg) in the form of Lyman-Birge-Hopfield (LBH) and first positive (1PN2) band systems, respectively. Additionally, we simulate numerically downward propagating sprite streamers and their optical emissions for the following band systems: 1PN2, 2PN2, LBH, and 1NN2+, and show how they relate to specific physical properties. This study particularly focuses on improving analysis of observational results from the future missions ASIM (ESA) and TARANIS (CNES) that will detect various optical emissions produced by transient luminous events in the nadir

Effect of Blue Jets on Stratospheric Ozone - a model study

International audienceIn the framework of the TARANIS space mission dedicated to the study of transient luminous events, a detailed ion-neutral chemistry model has been developed to simulate the impact of blue jet streamers on stratospheric chemistry. It is based on the MIPLASMO model (Microphysical and Photochemical Lagrangian Model of Ozone) widely used over the last 20 years to interpret balloon and satellite measurements associated with stratospheric ozone. In this study, instead of using a constant reduced electric field value during a streamer pulse time, we used a time-dependent reduced electric field coming from an explicit streamer model. The simulations are performed on day-time/night-time and their duration is two days. Among 117 species in the model, we put the focus on nitrogen, oxygen, chlorine and bromine species, and ozone perturbations. The model results indicate that the impact on both ions and neutral species volume mixing ratios considering a quasi-real streamer (i.e., using a time-varying electric field) is different from previous model studies considering streamer as a simple pulse. These differences will be analyzed in detail as a function of altitude. Validation exercise and preliminary results will be presented

Eye/gaze tracking in web, image and video documents

International audienc

A new d.c. machine arrangement for an electronically assisted commutation

The d.c. machine is the cheapest way to realize variable speed drives. However its performances are limited by the commutator operation. Indeed, the latter wears out very rapidly because of the sparks, even arcings, which appear between the segments and the brushes, in spite of use of commutating poles. Over the last fifteen years, our laboratory has implemented external circuits to assist commutation and alleviate, or even suppress, the main difficulties. This paper presents a new arrangement which seems very promising.La machine à courant continu est le moyen le plus économique pour réaliser des entraînements à vitesse variable. La machine classique voit néanmoins ses performances limitées par la présence du collecteur. En effet, ce dernier, siège d'étincelles voire d'arcs d'origine, électromagnétique s'use vite et constitue de ce fait le point faible de la machine à courant continu. Depuis quelques années, notre laboratoire a mis l'accent sur la recherche de dispositifs externes d'aide à la commutation de ces machines qui remplaceraient avantageusement les pôles auxiliaires. Mais c'est la première fois qu'il expérimente une machine à courant continu de technologie classique mais sans pôles auxiliaires avec un système d'aide à la commutation électronique externe

Effect of Blue Jets on Stratospheric Ozone - a model study

International audienceIn the framework of the TARANIS space mission dedicated to the study of transient luminous events, a detailed ion-neutral chemistry model has been developed to simulate the impact of blue jet streamers on stratospheric chemistry. It is based on the MIPLASMO model (Microphysical and Photochemical Lagrangian Model of Ozone) widely used over the last 20 years to interpret balloon and satellite measurements associated with stratospheric ozone. In this study, instead of using a constant reduced electric field value during a streamer pulse time, we used a time-dependent reduced electric field coming from an explicit streamer model. The simulations are performed on day-time/night-time and their duration is two days. Among 117 species in the model, we put the focus on nitrogen, oxygen, chlorine and bromine species, and ozone perturbations. The model results indicate that the impact on both ions and neutral species volume mixing ratios considering a quasi-real streamer (i.e., using a time-varying electric field) is different from previous model studies considering streamer as a simple pulse. These differences will be analyzed in detail as a function of altitude. Validation exercise and preliminary results will be presented

Modeling of a new electron-streamer acceleration mechanism

International audienceLightning 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

Modeling of a new electron-streamer acceleration mechanism

International audienceLightning 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