149 research outputs found
Self-consistent resonance absorption with two layer profile steepening
Resonance absorption of p-polarized light, incident at angle 6 on a flowing, stratified plasma, is analyzed; profile steepening within (i) a layer around the turning point, and (ii) a thinner,embedded sublayer at the critical surface is taken into account self-consistently. The entire
steepened region is taken as collisionless and isothermal. The structure of the main layer shows a variety of regimes, depending on how the flow crosses a sonic point. The structure of the sublayer is also determined; it is entirely subsonic (with no wave breaking) for a well-defined,broad parameter range. Density changes across both layer and sublayer, and fractional absorption, are given in terms of [(wavelength)2 Xintensity/temperature], and
(temperature/mec2). The flow outside the double structure is also analyzed for particular conditions
Direct Vlasov simulations of electron-attracting cylindrical Langmuir probes in flowing plasmas
Current collection by positively polarized cylindrical Langmuir probes immersed in flowing plasmas is analyzed using a non-stationary direct Vlasov-Poisson code. A detailed description of plasma density spatial structure as a function of the probe-to-plasma relative velocity U is presented. Within the considered parametric domain, the well-known electron density maximum close to the probe is weakly affected by U. However, in the probe wake side, the electron density minimum becomes deeper as U increases and a rarified plasma region appears. Sheath radius is larger at the wake than at the front side. Electron and ion distribution functions show specific features that are the signature of probe motion. In particular, the ion distribution function at the probe front side exhibits a filament with positive radial velocity. It corresponds to a population of rammed ions that were reflected by the electric field close to the positively biased probe. Numerical simulations reveal that two populations of trapped electrons exist: one orbiting around the probe and the other with trajectories confined at the probe front side. The latter helps to neutralize the reflected ions, thus explaining a paradox in past probe theory
Pseudo-K\"ahler Lie algebras with abelian complex structures
We study Lie algebras endowed with an abelian complex structure which admit a
symplectic form compatible with the complex structure. We prove that each of
those Lie algebras is completely determined by a pair (U,H) where U is a
complex commutative associative algebra and H is a sesquilinear hermitian form
on U which verifies certain compatibility conditions with respect to the
associative product on U. The Riemannian and Ricci curvatures of the associated
pseudo-K\"ahler metric are studied and a characterization of those Lie algebras
which are Einstein but not Ricci flat is given. It is seen that all
pseudo-K\"ahler Lie algebras can be inductively described by a certain method
of double extensions applied to the associated complex asssociative commutative
algebras
Under-reporting bicycle accidents to police in the COST TU1101 international survey: Cross-country comparisons and associated factors
Police crash reports are often the main source for official data in many countries. However, with the exception of fatal crashes, crashes are often underreported in a biased manner. Consequently, the countermeasures adopted according to them may be inefficient. In the case of bicycle crashes, this bias is most acute and it probably varies across countries, with some of them being more prone to reporting accidents to police than others. Assessing if this bias occurs and the size of it can be of great importance for evaluating the risks associated with bicycling. This study utilized data collected in the COST TU1101 action âTowards safer bicycling through optimization of bicycle helmets and usageâ. The data came from an online survey that included questions related to bicyclists' attitudes, behaviour, cycling habits, accidents, and patterns of use of helmets. The survey was filled by 8655 bicyclists from 30 different countries. After applying various exclusion factors, 7015 questionnaires filled by adult cyclists from 17 countries, each with at least 100 valid responses, remained in our sample. The results showed that across all countries, an average of only 10% of all crashes were reported to the police, with a wide range among countries: from a minimum of 0.0% (Israel) and 2.6% (Croatia) to a maximum of a 35.0% (Germany). Some factors associated with the reporting levels were type of crash, type of vehicle involved, and injury severity. No relation was found between the likelihood of reporting and the cyclist's gender, age, educational level, marital status, being a parent, use of helmet, and type of bicycle. The significant under-reporting â including injury crashes that do not lead to hospitalization â justifies the use of self-report survey data for assessment of bicycling crash patterns as they relate to (1) crash risk issues such as location, infrastructure, cyclists' characteristics, and use of helmet and (2) strategic approaches to bicycle crash prevention and injury reduction.Fil: Shinar, D.. Ben Gurion University of the Negev; IsraelFil: Valero Mora, Pedro. Universidad de Valencia; EspañaFil: van Strijp Houtenbos, M.. Institute For Road Safety Research; PaĂses BajosFil: Haworth, N.. Queensland University of Technology; AustraliaFil: Schramm, A.. Queensland University of Technology; AustraliaFil: de Bruyne, G.. Universiteit Antwerp; BĂ©lgicaFil: Cavallo, V.. No especifĂca;Fil: Chliaoutakis, J.. No especifĂca;Fil: Pereira Dias, Joao. Instituto Superior Tecnico; PortugalFil: Ferraro, Ottavia Eleonora. Universita Degli Studi Di Pavia; ItaliaFil: Fyhri, Aslak. No especifĂca;Fil: Sajatovic, Anika Hursa. No especifĂca;Fil: Kuklane, Kalev. Lund University; SueciaFil: Ledesma, Ruben Daniel. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - Mar del Plata. Instituto de PsicologĂa BĂĄsica, Aplicada y TecnologĂa. Universidad Nacional de Mar del Plata. Facultad de PsicologĂa. Instituto de PsicologĂa BĂĄsica, Aplicada y TecnologĂa.; ArgentinaFil: CalvĂ© Mascarell, Oscar. Ben Gurion University of the Negev; IsraelFil: Morandi, A.. Universita Degli Studi Di Pavia; ItaliaFil: Muser, Markus. No especifĂca;Fil: Otte, Diettmar. No especifĂca;Fil: Papadakaki, M.. No especifĂca;Fil: SanmartĂn, J.. Universidad de Valencia; EspañaFil: Dulf, D.. No especifĂca;Fil: Saplioglu, M.. No especifĂca;Fil: Tzamalouka, Georgia. No especifĂca
Three-Body Dynamics and Self-Powering of an Electrodynamic Tether in a Plasmasphere
The dynamics of an electrodynamic tether in a three-body gravitational environment are investigated. In the classical two-body scenario the extraction of power is at the expense of orbital kinetic energy. As a result of power extraction, an electrodynamic tether satellite system loses altitude and deorbits. This concept has been proposed and well investigated in the past, for example for orbital debris mitigation and spent stages reentry. On the other hand, in the three-body scenario an electrodynamic tether can be placed in an equilibrium position fixed with respect to the two primary bodies without deorbiting, and at the same time generate power for onboard use. The appearance of new equilibrium positions in the perturbed three-body problem allow this to happen as the electrical power is extracted at the expenses of the plasma corotating with the primary body. Fundamental differences between the classical twobody dynamics and the new phenomena appearing in the circular restricted three-body problem perturbed by the electrodynamic force of the electrodynamic tether are shown in the paper. An interesting application of an electrodynamic tether placed in the Jupiter plasma torus is then considered, in which the electrodynamic tether generates useful electrical power of about 1 kW with a 20-km-long electrodynamic tether from the environmental plasma without losing orbital energy
Extended parametric resonances in nonlinear Schrodinger systems
We study an example of exact parametric resonance in a extended system ruled
by nonlinear partial differential equations of nonlinear Schr\"odinger type. It
is also conjectured how related models not exactly solvable should behave in
the same way. The results have applicability in recent experiments in
Bose-Einstein condensation and to classical problems in Nonlinear Optics.Comment: 1 figur
The ESA "Plasma Laboratory in Space" study
The European Space Agency has initiated, in the context of its General Studies Programme, a study of the
possible use of space for studies in pure and applied plasma physics, in areas not traditionally covered by âspace plasma physicsâ. A team of experts has been set-up to review a broad range of area including industrial
plasma physics and pure plasma physics, astrophysical and solar-terrestrial areas. A set of experiments have been identified that can potentially provide access to new phenomena and to allow advances in several fields
of plasma science. These experiments concern phenomena on spatial scale (102 to104 m) intermediate between what is achievable on ground experiment and usual solar system plasma observations
Plasma kinetics issues in an ESA study for a plasma laboratory in space
A study supported by the European Space Agency (ESA), in the context of its General Studies Programme, performed an investigation of the possible use of space for studies in pure and applied plasma physics, in areas not traditionally
covered by âspace plasma physicsâ. A set of experiments have been identified that can potentially provide access to new phenomena and to allow advances in several fields of plasma science. These experiments concern phenomena on a
spatial scale (101â104 m) intermediate between what is achievable on the ground and the usual solar system plasma observations. Detailed feasibility studies have been performed for three experiments: active magnetic experiments, largescale discharges and long tetherâplasma interactions. The perspectives opened by these experiments are discussed for magnetic reconnection, instabilities,
MHD turbulence, atomic excited states kinetics, weakly ionized plasmas,plasma diagnostics, artificial auroras and atmospheric studies. The discussion is also supported by results of numerical simulations and estimates
Space demostration of bare electrodynamic tape-tether technology on the sounding rocket S520-25
A spaceflight validation of bare electro dynamic tape tether technology was conducted. A S520-25 sounding rocket was launched successfully at 05:00am on 31 August 2010 and
successfully deployed 132.6m of tape tether over 120 seconds in a ballistic flight. The electrodynamic performance of the bare tape tether employed as an atmospheric probe was measured. Flight results are introduced through the present progressive report of the
demonstration and the results of flight experiment are examined as the premier report of the international cooperation between Japan, Europe, USA and Australia. Future plans for maturing space tether technology, which will play an important role for future space activities, are also discussed
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