Articles de revues : « Electron Clouds »

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Lehmann, Andrew, et Mark Wardle. « Diffusion of cosmic-ray electrons in the Galactic centre molecular cloud G0.13–0.13 ». Proceedings of the International Astronomical Union 9, S303 (octobre 2013) : 434–38. http://dx.doi.org/10.1017/s1743921314001082.

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AbstractThe Galactic center (GC) molecular cloud G0.13–0.13 exhibits a shell morphology in CS J = (1 − 0), with ∼ 105 solar masses and expansion speed ∼ 20 km s−1, yielding a total kinetic energy ∼ 1051 erg. Its morphology is also suggestive of an interaction with the nonthermal filaments of the GC arc. 74 MHz emission indicates the presence of a substantial population of low energy electrons permeating the cloud, which could either be produced by the interaction with the arc or accelerated in the shock waves responsible for the cloud's expansion. These scenarios are explored using time dependent diffusion models.With these diffusion models, we determine the penetration of low-energy cosmic-ray electrons accelerated into G0.13–0.13 and calculate the spatial distribution of the cosmic-ray ionization and heating rates. We show that the 6.4 keV Fe Kα line emission associated with the electron population provides an observational diagnostic to distinguish these two acceleration scenarios.We discuss the implications of our results for understanding the distinct character of clouds in the central molecular zone compared to clouds in the Galactic disk, and how GC nonthermal filaments interact with molecular clouds.

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Bakhareva, O. A., V. Yu Sergeev et I. A. Sharov. « On the Formation of a Plasma Cloud at the Ablation of a Pellet in a High-Temperature Magnetized Toroidal Plasma ». JETP Letters 117, n^o 3 (février 2023) : 207–13. http://dx.doi.org/10.1134/s0021364022603190.

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The investigation of cold secondary plasma clouds near pellets ablating in the hot plasma of magnetic confinement devices (tokamaks and stellarators) provides valuable information on the physical characteristics of a pellet cloud. In this work, the characteristic sizes of emitting clouds around fusible polystyrene pellets and refractory carbon pellets have been analyzed. The calculation of the ionization length of C+ ions in both carbon and hydrocarbon clouds has shown that the contribution of only hot electrons is insufficient to ensure the experimentally observed decay lengths of the CII line intensity. Taking into account the strong shielding of the electron flux of the background plasma in the hydrocarbon pellet cloud, the ionization of C+ ions in this cloud is determined predominantly by electrons of the cold plasma of the cloud. Shielding near a refractory carbon pellet is weak because its ablation rate is lower. The contributions from hot electrons of the surrounding plasma and cold electrons of the pellet cloud to the ionization of C+ ions are comparable in the case of carbon pellets.

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Le Bars, G., J. Loizu, J. Ph Hogge, S. Alberti, F. Romano, J. Genoud et I. G. Pagonakis. « First self-consistent simulations of trapped electron clouds in a gyrotron gun and comparison with experiments ». Physics of Plasmas 30, n^o 3 (mars 2023) : 030702. http://dx.doi.org/10.1063/5.0136340.

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We report on the initial validation of the novel code FENNECS, which simulates the spontaneous formation of trapped electron clouds in coaxial geometries with strong externally applied azimuthal flows and in the presence of a residual neutral gas. For this purpose, a realistic gyrotron electron gun geometry is used in the code, and a self-consistent electron cloud build-up is simulated. The predicted electronic current resulting from these clouds that is collected on the gun electrodes is simulated and successfully compared with the previous experimental results for configurations with different externally applied electric and magnetic fields. These different configurations effectively modify the size and depth of the trapping potential wells responsible for the confinement of the electron clouds. This investigation also provides further insight into the link between potential well depth and resulting electronic current.

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John, P. I. « Physics of toroidal electron clouds ». Plasma Physics and Controlled Fusion 34, n^o 13 (1 décembre 1992) : 2053–59. http://dx.doi.org/10.1088/0741-3335/34/13/039.

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Tkachev, A. N., et S. I. Yakovlenko. « Electron clouds around charged particulates ». Technical Physics 44, n^o 1 (janvier 1999) : 48–52. http://dx.doi.org/10.1134/1.1259250.

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Dimant, Y. S., et M. M. Oppenheim. « Interaction of plasma cloud with external electric field in lower ionosphere ». Annales Geophysicae 28, n^o 3 (11 mars 2010) : 719–36. http://dx.doi.org/10.5194/angeo-28-719-2010.

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Abstract. In the auroral lower-E and upper-D region of the ionosphere, plasma clouds, such as sporadic-E layers and meteor plasma trails, occur daily. Large-scale electric fields, created by the magnetospheric dynamo, will polarize these highly conducting clouds, redistributing the electrostatic potential and generating anisotropic currents both within and around the cloud. Using a simplified model of the cloud and the background ionosphere, we develop the first self-consistent three-dimensional analytical theory of these phenomena. For dense clouds, this theory predicts highly amplified electric fields around the cloud, along with strong currents collected from the ionosphere and circulated through the cloud. This has implications for the generation of plasma instabilities, electron heating, and global MHD modeling of magnetosphere-ionosphere coupling via modifications of conductances induced by sporadic-E clouds.

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Zhang, Tao. « Average value of the shape and direction factor in the equation of refractive index ». Modern Physics Letters B 31, n^o 29 (17 octobre 2017) : 1750263. http://dx.doi.org/10.1142/s0217984917502633.

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The theoretical calculation of the refractive indices is of great significance for the developments of new optical materials. The calculation method of refractive index, which was deduced from the electron-cloud-conductor model, contains the shape and direction factor [Formula: see text]. [Formula: see text] affects the electromagnetic-induction energy absorbed by the electron clouds, thereby influencing the refractive indices. It is not yet known how to calculate [Formula: see text] value of non-spherical electron clouds. In this paper, [Formula: see text] value is derived by imaginatively dividing the electron cloud into numerous little volume elements and then regrouping them. This paper proves that [Formula: see text] when molecules’ spatial orientations distribute randomly. The calculations of the refractive indices of several substances validate this equation. This result will help to promote the application of the calculation method of refractive index.

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del Valle, Maria V. « Gamma-rays from reaccelerated cosmic rays in high-velocity clouds colliding with the Galactic disc ». Monthly Notices of the Royal Astronomical Society 509, n^o 3 (11 novembre 2021) : 4448–56. http://dx.doi.org/10.1093/mnras/stab3206.

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ABSTRACT High-velocity clouds moving towards the disc will reach the Galactic plane and will inevitably collide with the disc. In these collisions, a system of two shocks is produced, one propagating through the disc and the other develops within the cloud. The shocks produced within the clouds in these interactions have velocities of hundreds of kilometres per second. When these shocks are radiative they may be inefficient in accelerating fresh particles; however, they can reaccelerate and compress Galactic cosmic rays from the background. In this work, we investigate the interactions of Galactic cosmic rays within a shocked high-velocity cloud, when the shock is induced by the collision with the disc. This study is focused in the case of radiative shocks. We aim to establish under which conditions these interactions lead to significant non-thermal emission, especially gamma-rays. We model the interaction of cosmic ray protons and electrons reaccelerated and further energized by compression in shocks within the clouds, under very general assumptions. We also consider secondary electron–positron pairs produced by the cosmic ray protons when colliding with the material of the cloud. We conclude that nearby clouds reaccelerating Galactic cosmic rays in local shocks can produce high-energy radiation that might be detectable with existing and future gamma-ray detectors. The emission produced by electrons and secondary pairs is important at radio wavelengths, and in some cases it may be relevant at hard X-rays. Concerning higher energies, the leptonic contribution to the spectral energy distribution is significant at soft gamma-rays.

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Stein, Benjamin P. « An “orbital glass” of electron clouds ». Physics Today 58, n^o 3 (mars 2005) : 9. http://dx.doi.org/10.1063/1.4796921.

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Zharkova, Valentina V., et Taras Siversky. « Formation of electron clouds during particle acceleration in a 3D current sheet ». Proceedings of the International Astronomical Union 6, S274 (septembre 2010) : 453–57. http://dx.doi.org/10.1017/s1743921311007472.

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AbstractAcceleration of protons and electrons in a reconnecting current sheet (RCS) is investigated with the test particle and particle-in-cell (PIC) approaches in the 3D magnetic configuration including the guiding field. PIC simulations confirm a spatial separation of electrons and protons towards the midplane and reveal that this separation occur as long as protons are getting accelerated. During this time electrons are ejected into their semispace of the current sheet moving away from the midplane to distances up to a factor of 103 – 104 of the RCS thickness and returning back to the RCS. This process of electron circulation around the current sheet midplane creates a cloud of high energy electrons around the current sheet which exists as long as protons are accelerated. Only after protons gain sufficient energy to break from the magnetic field of the RCS, they are ejected to the opposite semispace dragging accelerated electrons with them. These clouds can be the reason of hard X-ray emission in coronal sources observed by RHESSI.

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Dremin, Igor M. « Positronia’ Clouds in Universe ». Universe 7, n^o 2 (12 février 2021) : 42. http://dx.doi.org/10.3390/universe7020042.

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The intense emission of 511 keV photons from the Galactic center and within terrestrial thunderstorms is attributed to the formation of parapositronia clouds. Unbound electron–positron pairs and positronia can be created by strong electromagnetic fields produced in interactions of electrically charged objects, in particular, in collisions of heavy nuclei. Kinematics of this process favors abundant creation of the unbound electron–positron pairs with very small masses and the confined parapositronia states which decay directly to two 511 keV quanta. Therefore, we propose to consider interactions of electromagnetic fields of colliding heavy ions as a source of low-mass pairs which can transform to 511 keV quanta. Intensity of their creation is enlarged by the factor Z4 (Z is the electric charge of a heavy ion) compared to protons with Z = 1. These processes are especially important at very high energies of nuclear collisions because their cross sections increase proportionally to cube of the logarithm of energy and can even exceed the cross sections of strong interactions which may not increase faster than the squared logarithm of energy. Moreover, production of extremely low-mass e+e−-pairs in ultraperipheral nuclear collisions is strongly enhanced due to the Sommerfeld-Gamow-Sakharov (SGS) factor which accounts for mutual Coulomb attraction of non-relativistic electrons to positrons in case of low pair-masses. This attraction may lead to their annihilation and, therefore, to the increased intensity of 511 keV photons. It is proposed to confront the obtained results to forthcoming experimental data at NICA collider.

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Dieckmann, M. E. « The formation of relativistic plasma structures and their potential role in the generation of cosmic ray electrons ». Nonlinear Processes in Geophysics 15, n^o 6 (3 novembre 2008) : 831–46. http://dx.doi.org/10.5194/npg-15-831-2008.

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Abstract. Recent particle-in-cell (PIC) simulation studies have addressed particle acceleration and magnetic field generation in relativistic astrophysical flows by plasma phase space structures. We discuss the astrophysical environments such as the jets of compact objects, and we give an overview of the global PIC simulations of shocks. These reveal several types of phase space structures, which are relevant for the energy dissipation. These structures are typically coupled in shocks, but we choose to consider them here in an isolated form. Three structures are reviewed. (1) Simulations of interpenetrating or colliding plasma clouds can trigger filamentation instabilities, while simulations of thermally anisotropic plasmas observe the Weibel instability. Both transform a spatially uniform plasma into current filaments. These filament structures cause the growth of the magnetic fields. (2) The development of a modified two-stream instability is discussed. It saturates first by the formation of electron phase space holes. The relativistic electron clouds modulate the ion beam and a secondary, spatially localized electrostatic instability grows, which saturates by forming a relativistic ion phase space hole. It accelerates electrons to ultra-relativistic speeds. (3) A simulation is also revised, in which two clouds of an electron-ion plasma collide at the speed 0.9c. The inequal densities of both clouds and a magnetic field that is oblique to the collision velocity vector result in waves with a mixed electrostatic and electromagnetic polarity. The waves give rise to growing corkscrew distributions in the electrons and ions that establish an equipartition between the electron, the ion and the magnetic energy. The filament-, phase space hole- and corkscrew structures are discussed with respect to electron acceleration and magnetic field generation.

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Le Bars, G., J. Ph Hogge, J. Loizu, S. Alberti, F. Romano et A. Cerfon. « Self-consistent formation and steady-state characterization of trapped high-energy electron clouds in the presence of a neutral gas background ». Physics of Plasmas 29, n^o 8 (août 2022) : 082105. http://dx.doi.org/10.1063/5.0098567.

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This study considers the self-consistent formation and dynamics of electron clouds interacting with a background neutral gas through elastic and inelastic (ionization) collisions in coaxial geometries similar to gyrotron electron guns. These clouds remain axially trapped as the result of crossed magnetic field lines and electric equipotential lines creating potential wells similar to those used in Penning traps. Contrary to standard Penning traps, in this study, we consider a strong externally applied radial electric field which is of the same order as that of the space-charge field. In particular, the combination of coaxial geometry, strong radial electric fields, and electron collisions with the residual neutral gas (RNG) present in the chamber induce non-negligible radial particle transport and ionization. In this paper, the dynamics of the cloud density and currents resulting from electron–neutral collisions are studied using a 2D3V particle-in-cell code. Simulation results and parametric scans are hereby presented. Finally, a fluid model is derived to explain and predict the cloud peak density and peak radial current depending on the externally applied electric and magnetic fields, and on the RNG pressure.

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Despringre, V., et D. Fraix-Burnet. « Relativistic Electron-Positron Clouds in VLBI Jets ». Symposium - International Astronomical Union 175 (1996) : 443–44. http://dx.doi.org/10.1017/s0074180900081390.

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Extragalactic jets have always had two characteristics : the presence of knots and the requirement for particle acceleration. Shock fronts provide an explanation for both. However, the knotty appearance is less obvious at kp-scale on very high resolution observations from the VLA and the HST. The evidence for shock fronts is therefore weakened. At the pc-scale (or VLBI scale), a lot of these blobs are moving superluminally and they have been interpreted and modelled as shock fronts in a relativistic jet.

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Cohen, R. H., A. Friedman, M. Kireeff Covo, S. M. Lund, A. W. Molvik, F. M. Bieniosek, P. A. Seidl, J. L. Vay, P. Stoltz et S. Veitzer. « Simulating electron clouds in heavy-ion accelerators ». Physics of Plasmas 12, n^o 5 (mai 2005) : 056708. http://dx.doi.org/10.1063/1.1882292.

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Padovani, Marco, Shmuel Bialy, Daniele Galli, Alexei V. Ivlev, Tommaso Grassi, Liam H. Scarlett, Una S. Rehill, Mark C. Zammit, Dmitry V. Fursa et Igor Bray. « Cosmic rays in molecular clouds probed by H₂ rovibrational lines ». Astronomy & ; Astrophysics 658 (février 2022) : A189. http://dx.doi.org/10.1051/0004-6361/202142560.

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Context. Low-energy cosmic rays (<1 TeV) play a fundamental role in the chemical and dynamical evolution of molecular clouds, as they control the ionisation, dissociation, and excitation of H2. Their characterisation is therefore important both for the interpretation of observations and for the development of theoretical models. However, the methods used so far for estimating the cosmic-ray ionisation rate in molecular clouds have several limitations due to uncertainties in the adopted chemical networks. Aims. We refine and extend a previously proposed method to estimate the cosmic-ray ionisation rate in molecular clouds by observing rovibrational transitions of H2 at near-infrared wavelengths, which are mainly excited by secondary cosmic-ray electrons. Methods. Combining models of interstellar cosmic-ray propagation and attenuation in molecular clouds with the rigorous calculation of the expected secondary electron spectrum and updated electron-H2 excitation cross sections, we derive the intensity of the four H2 rovibrational transitions observable in cold dense gas: (1−0)O(2), (1−0)Q(2), (1−0)S(0), and (1−0)O(4). Results. The proposed method allows the estimation of the cosmic-ray ionisation rate for a given observed line intensity and H2 column density. We are also able to deduce the shape of the low-energy cosmic-ray proton spectrum impinging upon the molecular cloud. In addition, we present a look-up plot and a web-based application that can be used to constrain the low-energy spectral slope of the interstellar cosmic-ray proton spectrum. We finally comment on the capability of the James Webb Space Telescope to detect these near-infrared H2 lines, which will make it possible to derive, for the first time, spatial variation in the cosmic-ray ionisation rate in dense gas. Besides the implications for the interpretation of the chemical-dynamic evolution of a molecular cloud, it will finally be possible to test competing models of cosmic-ray propagation and attenuation in the interstellar medium, as well as compare cosmic-ray spectra in different Galactic regions.

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Owens, M. J., N. U. Crooker et T. S. Horbury. « The expected imprint of flux rope geometry on suprathermal electrons in magnetic clouds ». Annales Geophysicae 27, n^o 10 (26 octobre 2009) : 4057–67. http://dx.doi.org/10.5194/angeo-27-4057-2009.

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Abstract. Magnetic clouds are a subset of interplanetary coronal mass ejections characterized by a smooth rotation in the magnetic field direction, which is interpreted as a signature of a magnetic flux rope. Suprathermal electron observations indicate that one or both ends of a magnetic cloud typically remain connected to the Sun as it moves out through the heliosphere. With distance from the axis of the flux rope, out toward its edge, the magnetic field winds more tightly about the axis and electrons must traverse longer magnetic field lines to reach the same heliocentric distance. This increased time of flight allows greater pitch-angle scattering to occur, meaning suprathermal electron pitch-angle distributions should be systematically broader at the edges of the flux rope than at the axis. We model this effect with an analytical magnetic flux rope model and a numerical scheme for suprathermal electron pitch-angle scattering and find that the signature of a magnetic flux rope should be observable with the typical pitch-angle resolution of suprathermal electron data provided ACE's SWEPAM instrument. Evidence of this signature in the observations, however, is weak, possibly because reconnection of magnetic fields within the flux rope acts to intermix flux tubes.

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Abelha, Thais S., Geovane G. A. de Souza et Marco Bregant. « Comparing different methods of position reconstruction considering 1D readout of GEM detectors ». Journal of Physics : Conference Series 2340, n^o 1 (1 septembre 2022) : 012049. http://dx.doi.org/10.1088/1742-6596/2340/1/012049.

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Abstract Gas Electron Multiplier (GEM) based detectors contain microstructures that provide amplification, via avalanche multiplication, for the charges generated due to ionizing radiation. The readout of the detector is responsible for collecting electrons multiplied by the GEM structure and it may be position sensitive. In this preliminary study, we created algorithms to compare the error of three different methods for position reconstruction. All these methods are based on weighted averages. In the algorithm we modeled an electron cloud as a normalized Gaussian function that is collected by a 1D readout of strips affected by white noise, then we made a clustering algorithm to identify the strips that collected the electron cloud. The method that uses the weight equal to squared charges shows the highest errors for narrow clouds, when the σ value (standard deviation of a Gaussian function) is closer to the strip width. Nonetheless, the errors of the three methods get similar results for a σ approximately equal to the width of one and a half strips.

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Alcocer, Giovanni. « Mass & ; Quark Symmetry : Mass and Mass Cloud (The Yin Yang) : Atom Binding Energy ; Molecules Binding Energy ; Binding energy between the nucleons in the nucleus ; Particle Interaction Energy between particle and antiparticle ; Quark Symmetry & ; Quark Confinement ». Mediterranean Journal of Basic and Applied Sciences 06, n^o 03 (2022) : 01–34. http://dx.doi.org/10.46382/mjbas.2022.6301.

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The symmetry occurs in most of the phenomena explained by physics, for example, a particle has positive or negative charges, and the electric dipoles that have the charge (+q) and (-q) which are at a certain distance (d), north or south magnetic poles and for a magnetic bar or magnetic compass with two poles: North (N) and South (S) poles, spins up or down of the electron at the atom and for the nucleons in the nucleus In this form, the particle should also have mass symmetry. For convenience and due to later explanations, I call this mass symmetry or mass duality as follows: mass and mass cloud. The mass cloud is located in the respective orbitals given by the Schrödinger equation. The orbitals represent the possible locations or places of the particle which are determined probabilistically by the respective Schröndiger equation. For example and for the proton, the positive charge is concentrated in its mass nucleus with an uncharged mass cloud around its nucleus distributed in the orbitals or mass clouds. For the electron, the negative charge is concentrated in its mass nucleus with an uncharged mass cloud around its nucleus distributed in the orbitals or mass clouds. Besides, in the formation of the hydrogen atom, a part of the mass cloud of the proton interacts with the mass cloud of the electron, and the total mass-energy lost in this interaction is transformed into electromagnetic energy according to Einstein's equation: E=mc2 and the variant mass formula discovered and developed by myself: Giovanni Alcocer Variant Formulas. Therefore, the electron and proton are bound together in the hydrogen atom due to the electrostatic force between the two particles and the mass cloud of the electron and proton with some mass cloud lost in the interaction and converted to electromagnetic energy or photons. Then, it is right to assume this mass symmetry, since the electron and the proton in the interaction of the mass cloud lose mass but do not lose electric charge. In this form, it is justified the existence of a mass cloud. Therefore, the main function of the mass cloud is the binding energy. The mass cloud interaction generates binding energy between the electrons and the nucleus in the atom through the protons and between the nucleons in the nucleus: protons with protons, neutrons with neutrons, and protons with neutrons. The nuclear force between two nucleons is characterized by being strong and short-range. Also, it can be justified by the existence of the mass cloud: the mass clouds of nucleons within the nucleus interact with each other without any effect on the proton charge. In the same form and due to the quarks having mass and charge (and inclusive colors), the quarks have also the same mass symmetry: mass and mass cloud. Thus, the electrical charge is stored in the mass of the quarks and the mass cloud allows the confinement or the respective binding between quarks. Then, the following questions are explained and answered simply in this research article: why a particle does not exist with only one quark? why the quarks are confined to the nucleus? and which is the origin of the nuclear forces? On other hand, there are particles with two quarks (mesons), particles with three quarks (baryons) and then, it is very probable to find particles with more than three quarks (quaternions). This scientific research presents evidence of the existence of mass symmetry: mass and mass cloud and the interaction between the mass cloud of the particles (The Yin Yang Interaction) based on Einstein's equation and in the Variant Mass formula for the Electron in the atom discovered and demonstrated by myself where experimental results are detailed.

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Yuan, Shaohua, Nizar Naitlho, Roman Samulyak, Bernard Pégourié, Eric Nardon, Eric Hollmann, Paul Parks et Michael Lehnen. « Lagrangian particle simulation of hydrogen pellets and SPI into runaway electron beam in ITER ». Physics of Plasmas 29, n^o 10 (octobre 2022) : 103903. http://dx.doi.org/10.1063/5.0110388.

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Numerical studies of the ablation of pellets and shattered pellet injection (SPI) fragments into a runaway electron beam in ITER have been performed using a time-dependent pellet ablation code [Samulyak et al., Nucl. Fusion, 61(4), 046007 (2021)]. The code resolves detailed ablation physics near pellet fragments and large-scale expansion of ablated clouds. The study of a single-fragment ablation quantifies the influence of various factors, in particular, the impact ionization by runaway electrons and cross-field transport models, on the dynamics of ablated plasma and its penetration into the runaway beam. Simulations of SPI performed using different numbers of pellet fragments study the formation and evolution of the ablation clouds and their large-scale dynamics in ITER. The penetration depth of the ablation clouds is found to be of the order of 50 cm.

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Tahani, M., R. Plume, J. C. Brown et J. Kainulainen. « Helical magnetic fields in molecular clouds ? » Astronomy & ; Astrophysics 614 (juin 2018) : A100. http://dx.doi.org/10.1051/0004-6361/201732219.

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Context. Magnetic fields pervade in the interstellar medium (ISM) and are believed to be important in the process of star formation, yet probing magnetic fields in star formation regions is challenging. Aims. We propose a new method to use Faraday rotation measurements in small-scale star forming regions to find the direction and magnitude of the component of magnetic field along the line of sight. We test the proposed method in four relatively nearby regions of Orion A, Orion B, Perseus, and California. Methods. We use rotation measure data from the literature. We adopt a simple approach based on relative measurements to estimate the rotation measure due to the molecular clouds over the Galactic contribution. We then use a chemical evolution code along with extinction maps of each cloud to find the electron column density of the molecular cloud at the position of each rotation measure data point. Combining the rotation measures produced by the molecular clouds and the electron column density, we calculate the line-of-sight magnetic field strength and direction. Results. In California and Orion A, we find clear evidence that the magnetic fields at one side of these filamentary structures are pointing towards us and are pointing away from us at the other side. Even though the magnetic fields in Perseus might seem to suggest the same behavior, not enough data points are available to draw such conclusions. In Orion B, as well, there are not enough data points available to detect such behavior. This magnetic field reversal is consistent with a helical magnetic field morphology. In the vicinity of available Zeeman measurements in OMC-1, OMC-B, and the dark cloud Barnard 1, we find magnetic field values of − 23 ± 38 μG, − 129 ± 28 μG, and 32 ± 101 μG, respectively, which are in agreement with the Zeeman measurements.

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Zaveri, Puravi, P. I. John, K. Avinash et P. K. Kaw. « Low-aspect-ratio toroidal equilibria of electron clouds ». Physical Review Letters 68, n^o 22 (1 juin 1992) : 3295–98. http://dx.doi.org/10.1103/physrevlett.68.3295.

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Nieves-Chinchilla, Teresa, et Adolfo F. Viñas. « Solar wind electron distribution functions inside magnetic clouds ». Journal of Geophysical Research : Space Physics 113, A2 (février 2008) : n/a. http://dx.doi.org/10.1029/2007ja012703.

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Bastrukov, S. I., J. Yang et D. V. Podgainy. « Helicoidal magneto-electron waves in interstellar molecular clouds ». Monthly Notices of the Royal Astronomical Society 330, n^o 4 (mars 2002) : 901–6. http://dx.doi.org/10.1046/j.1365-8711.2002.05168.x.

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Douglas, John E. « Visualization of electron clouds in atoms and molecules ». Journal of Chemical Education 67, n^o 1 (janvier 1990) : 42. http://dx.doi.org/10.1021/ed067p42.

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Wright, C. Alan, et Santiago D. Solares. « On Mapping Subangstrom Electron Clouds with Force Microscopy ». Nano Letters 11, n^o 11 (9 novembre 2011) : 5026–33. http://dx.doi.org/10.1021/nl2030773.

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Das, Amita, et Predhiman Kaw. « Instability of elliptical vortex cores in electron clouds ». Physics Letters A 164, n^o 5-6 (avril 1992) : 419–23. http://dx.doi.org/10.1016/0375-9601(92)90106-v.

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Jones, T., A. Morgan et R. Richards. « Primary blasting in a limestone quarry : physicochemical characterization of the dust clouds ». Mineralogical Magazine 67, n^o 2 (avril 2003) : 153–62. http://dx.doi.org/10.1180/0026461036720092.

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Airborne dust generated by primary blasting was collected in Taffs Well Quarry, just north of Cardiff, Wales. Collections of airborne particulate matter were also made in the nearby village of Morganstown at the same time as the blasting collections. The explosions were recorded on a motor-driven camera and a digital video camera. These images show that the dust clouds generated by the explosions consist of three distinct components; a reddish-grey dust cloud, followed by a light grey dust cloud, and finally a pale grey cloud that stayed near the blast face. It is believed that the reddish-grey cloud was composed mostly of mineral grains, as evidenced by the chiefly red colour of the dolomitic limestone rock in the quarry. The whiter clouds contained more explosive combustion particles (diesel soot). The samples were studied by analytical scanning electron microscopy, very high-resolution field emission scanning electron microscopy, and image analysis. The two different components (minerals and diesel soot) can be readily seen under high-resolution electron microscopy. Any consideration of the possible adverse health effects or nuisance value of this dust needs to consider both of these components. A size distribution of the quarry particles shows that soot particles dominate the assemblage under 2 mm, whereas the mineral grains are more abundant over 2 mm. This contrasts with the Morganstown particle sizes, where the two components show similar size distributions. The determination of the mineralogy of the quarry dust and Morganstown particles has shown highly complex and heterogeneous mixtures, though some distribution patterns are emerging. It is concluded that much of the dust in Morganstown probably originated from sources other than the quarry, such as other local industries, roads and construction sites.

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Kucherov, Olexandr. « Direct Visualization of Si and Ge Atoms by Shifting Electron Picoscopy ». Applied Functional Materials 2, n^o 4 (30 décembre 2022) : 10–16. http://dx.doi.org/10.35745/afm2022v02.04.0002.

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The picoscopy images of the Si/Ge(100) system were analyzed, and electron cloud densitometry of silicon is presented in this study. The picoscopy is used to distinguish Ge, Si, and other chemical elements because different atoms have different densities of electron clouds. This result is in full accordance with Kucherov's law which states that the current passed through an electron cloud is proportional to the density of the cloud. The picoscopy image has shown Si crystals, Si/Ge solid solution, and their interface as the single crystal without defects. Local deformations in crystals were investigated using methods of direct visualization of individual atoms and measuring the distance of the center of atoms from the node of the crystal lattice. Visual сrystallography becomes a new way to study applied functional materials. This is the first publication on the real structure of a silicon atom.

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Kandagalla, Shivananda, Hrvoje Rimac, Vladimir A. Potemkin et Maria A. Grishina. « Complementarity principle in terms of electron density for the study of EGFR complexes ». Future Medicinal Chemistry 13, n^o 10 (mai 2021) : 863–75. http://dx.doi.org/10.4155/fmc-2020-0265.

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The complementarity principle is a well-established concept in the field of chemistry and biology. This concept is widely studied as the lock-and-key relationship between two structures, such as enzyme and ligand interactions. These interactions are based on the overlap of electron clouds between two structures. In this study, a mathematical relation determining complementarity of intermolecular contacts in terms of overlaps of electron clouds was examined using a quantum orbital-free AlteQ method developed in-house for 64 EGFR–ligand complexes with experimentally measured binding affinity data. A very high correlation was found between the overlap of ligand and enzyme electron clouds and the calculated terms, providing a good basis for prognosis of bioactivity and for molecular docking studies.

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Paul, Daniel, Manfred Grieser, Florian Grussie, Robert von Hahn, Leonard W. Isberner, Ábel Kálosi, Claude Krantz et al. « Experimental Determination of the Dissociative Recombination Rate Coefficient for Rotationally Cold CH⁺ and Its Implications for Diffuse Cloud Chemistry ». Astrophysical Journal 939, n^o 2 (1 novembre 2022) : 122. http://dx.doi.org/10.3847/1538-4357/ac8e02.

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Abstract Observations of CH+ are used to trace the physical properties of diffuse clouds, but this requires an accurate understanding of the underlying CH+ chemistry. Until this work, the most uncertain reaction in that chemistry was dissociative recombination (DR) of CH+. Using an electron–ion merged-beams experiment at the Cryogenic Storage Ring, we have determined the DR rate coefficient of the CH+ electronic, vibrational, and rotational ground state applicable for different diffuse cloud conditions. Our results reduce the previously unrecognized order-of-magnitude uncertainty in the CH+ DR rate coefficient to ∼20% and are applicable at all temperatures relevant to diffuse clouds, ranging from quiescent gas to gas locally heated by processes such as shocks and turbulence. Based on a simple chemical network, we find that DR can be an important destruction mechanism at temperatures relevant to quiescent gas. As the temperature increases locally, DR can continue to be important up to temperatures of ∼600 K, if there is also a corresponding increase in the electron fraction of the gas. Our new CH+ DR rate-coefficient data will increase the reliability of future studies of diffuse cloud physical properties via CH+ abundance observations.

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Adachi, Kouji, Yutaka Tobo, Makoto Koike, Gabriel Freitas, Paul Zieger et Radovan Krejci. « Composition and mixing state of Arctic aerosol and cloud residual particles from long-term single-particle observations at Zeppelin Observatory, Svalbard ». Atmospheric Chemistry and Physics 22, n^o 21 (10 novembre 2022) : 14421–39. http://dx.doi.org/10.5194/acp-22-14421-2022.

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Abstract. The Arctic region is sensitive to climate change and is warming faster than the global average. Aerosol particles change cloud properties by acting as cloud condensation nuclei and ice-nucleating particles, thus influencing the Arctic climate system. Therefore, understanding the aerosol particle properties in the Arctic is needed to interpret and simulate their influences on climate. In this study, we collected ambient aerosol particles using whole-air and PM10 inlets and residual particles of cloud droplets and ice crystals from Arctic low-level clouds (typically, all-liquid or mixed-phase clouds) using a counterflow virtual impactor inlet at the Zeppelin Observatory near Ny-Ålesund, Svalbard, within a time frame of 4 years. We measured the composition and mixing state of individual fine-mode particles in 239 samples using transmission electron microscopy. On the basis of their composition, the aerosol and cloud residual particles were classified as mineral dust, sea salt, K-bearing, sulfate, and carbonaceous particles. The number fraction of aerosol particles showed seasonal changes, with sulfate dominating in summer and sea salt increasing in winter. There was no measurable difference in the fractions between ambient aerosol and cloud residual particles collected at ambient temperatures above 0 ∘C. On the other hand, cloud residual samples collected at ambient temperatures below 0 ∘C had several times more sea salt and mineral dust particles and fewer sulfates than ambient aerosol samples, suggesting that sea spray and mineral dust particles may influence the formation of cloud particles in Arctic mixed-phase clouds. We also found that 43 % of mineral dust particles from cloud residual samples were mixed with sea salt, whereas only 18 % of mineral dust particles in ambient aerosol samples were mixed with sea salt. This study highlights the variety in aerosol compositions and mixing states that influence or are influenced by aerosol–cloud interactions in Arctic low-level clouds.

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Pratt, Kerri A., Andrew J. Heymsfield, Cynthia H. Twohy, Shane M. Murphy, Paul J. DeMott, James G. Hudson, R. Subramanian, Zhien Wang, John H. Seinfeld et Kimberly A. Prather. « In Situ Chemical Characterization of Aged Biomass-Burning Aerosols Impacting Cold Wave Clouds ». Journal of the Atmospheric Sciences 67, n^o 8 (1 août 2010) : 2451–68. http://dx.doi.org/10.1175/2010jas3330.1.

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Abstract During the Ice in Clouds Experiment–Layer Clouds (ICE-L), aged biomass-burning particles were identified within two orographic wave cloud regions over Wyoming using single-particle mass spectrometry and electron microscopy. Using a suite of instrumentation, particle chemistry was characterized in tandem with cloud microphysics. The aged biomass-burning particles comprised ∼30%–40% by number of the 0.1–1.0-μm clear-air particles and were composed of potassium, organic carbon, elemental carbon, and sulfate. Aerosol mass spectrometry measurements suggested these cloud-processed particles were predominantly sulfate by mass. The first cloud region sampled was characterized by primarily homogeneously nucleated ice particles formed at temperatures near −40°C. The second cloud period was characterized by high cloud droplet concentrations (∼150–300 cm−3) and lower heterogeneously nucleated ice concentrations (7–18 L−1) at cloud temperatures of −24° to −25°C. As expected for the observed particle chemistry and dynamics of the observed wave clouds, few significant differences were observed between the clear-air particles and cloud residues. However, suggestive of a possible heterogeneous nucleation mechanism within the first cloud region, ice residues showed enrichments in the number fractions of soot and mass fractions of black carbon, measured by a single-particle mass spectrometer and a single-particle soot photometer, respectively. In addition, enrichment of biomass-burning particles internally mixed with oxalic acid in both the homogeneously nucleated ice and cloud droplets compared to clear air suggests either preferential activation as cloud condensation nuclei or aqueous phase cloud processing.

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Goicoechea, Javier R., François Lique et Miriam G. Santa-Maria. « Anomalous HCN emission from warm giant molecular clouds ». Astronomy & ; Astrophysics 658 (27 janvier 2022) : A28. http://dx.doi.org/10.1051/0004-6361/202142210.

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Hydrogen cyanide (HCN) is considered a good tracer of the dense molecular gas that serves as fuel for star formation. However, recent large-scale surveys of giant molecular clouds (GMCs) have detected extended HCN rotational line emission far from star-forming cores. Such observations often spectroscopically resolve the HCN J = 1–0 (partially also the J = 2–1 and 3–2) hyperfine structure (HFS). A precise determination of the physical conditions of the gas requires treating the HFS line overlap effects. Here, we study the HCN HFS excitation and line emission using nonlocal radiative transfer models that include line overlaps and new HFS-resolved collisional rate coefficients for inelastic collisions of HCN with both para-H2 and ortho-H2 (computed via the scaled-infinite order sudden approximation up to Tk = 500 K). In addition, we account for the role of electron collisions in the HFS level excitation. We find that line overlap and opacity effects frequently produce anomalous HCN J = 1–0 HFS line intensity ratios (i.e., inconsistent with the common assumption of the same Tex for all HFS lines) as well as anomalous HFS line width ratios. Line overlap and electron collisions also enhance the excitation of the higher J rotational lines. Our models explain the anomalous HCN J = 1–0 HFS spectra observed in the Orion Bar and Horsehead photodissociation regions. As shown in previous studies, electron excitation becomes important for molecular gas with H2 densities below a few 105 cm−3 and electron abundances above ~10−5. We find that when electron collisions are dominant, the relative intensities of the HCN J = 1–0 HFS lines can be anomalous too. In particular, electron excitation can produce low-surface-brightness HCN emission from very extended but low-density gas in GMCs. The existence of such a widespread HCN emission component may affect the interpretation of the extragalactic relationship HCN luminosity versus star-formation rate. Alternatively, extended HCN emission may arise from dense star-forming cores and become resonantly scattered by large envelopes of lower density gas. There are two scenarios – namely, electron-assisted (weakly) collisionally excited versus scattering – that lead to different HCN J = 1–0 HFS intensity ratios, which can be tested on the basis of observations.

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Boamah, Mavis D., Kristal K. Sullivan, Katie E. Shulenberger, ChanMyae M. Soe, Lisa M. Jacob, Farrah C. Yhee, Karen E. Atkinson, Michael C. Boyer, David R. Haines et Christopher R. Arumainayagam. « Low-energy electron-induced chemistry of condensed methanol : implications for the interstellar synthesis of prebiotic molecules ». Faraday Discuss. 168 (2014) : 249–66. http://dx.doi.org/10.1039/c3fd00158j.

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In the interstellar medium, UV photolysis of condensed methanol (CH₃OH), contained in ice mantles surrounding dust grains, is thought to be the mechanism that drives the formation of “complex” molecules, such as methyl formate (HCOOCH₃), dimethyl ether (CH₃OCH₃), acetic acid (CH₃COOH), and glycolaldehyde (HOCH₂CHO). The source of this reaction-initiating UV light is assumed to be local because externally sourced UV radiation cannot penetrate the ice-containing dark, dense molecular clouds. Specifically, exceedingly penetrative high-energy cosmic rays generate secondary electrons within the clouds through molecular ionizations. Hydrogen molecules, present within these dense molecular clouds, are excited in collisions with these secondary electrons. It is the UV light, emitted by these electronically excited hydrogen molecules, that is generally thought to photoprocess interstellar icy grain mantles to generate “complex” molecules. In addition to producing UV light, the large numbers of low-energy (<20 eV) secondary electrons, produced by cosmic rays, can also directly initiate radiolysis reactions in the condensed phase. The goal of our studies is to understand the low-energy, electron-induced processes that occur when high-energy cosmic rays interact with interstellar ices, in which methanol, a precursor of several prebiotic species, is the most abundant organic species. Using post-irradiation temperature-programmed desorption, we have investigated the radiolysis initiated by low-energy (7 eV and 20 eV) electrons in condensed methanol at ∼ 85 K under ultrahigh vacuum (5 × 10⁻¹⁰ Torr) conditions. We have identified eleven electron-induced methanol radiolysis products, which include many that have been previously identified as being formed by methanol UV photolysis in the interstellar medium. These experimental results suggest that low-energy, electron-induced condensed phase reactions may contribute to the interstellar synthesis of “complex” molecules previously thought to form exclusively via UV photons.

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Brüggen, Marcus, Evan Scannapieco et Philipp Grete. « The Launching of Cold Clouds by Galaxy Outflows. V. The Role of Anisotropic Thermal Conduction ». Astrophysical Journal 951, n^o 2 (1 juillet 2023) : 113. http://dx.doi.org/10.3847/1538-4357/acd63e.

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Abstract Motivated by observations of multiphase galaxy outflows, we explore the impact of isotropic and anisotropic electron thermal conduction on the evolution of radiatively cooled, cold clouds embedded in hot, magnetized winds. Using the adaptive-mesh refinement code AthenaPK, we conduct simulations of clouds impacted by supersonic and transonic flows with magnetic fields initially aligned parallel and perpendicular to the flow direction. In cases with isotropic thermal conduction, an evaporative wind forms, stabilizing against instabilities and leading to a mass-loss rate that matches the hydrodynamic case. In anisotropic cases, the impact of conduction is more limited and strongly dependent on the field orientation. In runs with initially perpendicular fields, the field lines are folded back into the tail, strongly limiting conduction, but magnetic fields act to dampen instabilities and slow the stretching of the cloud in the flow direction. In the parallel case, anisotropic conduction aids cloud survival by forming a radiative wind near the front of the cloud, which suppresses instabilities and reduces mass loss. In all cases, anisotropic conduction has a minimal impact on the acceleration of the cloud.

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Caselli, Paola. « The Fractional Ionization in Molecular Cloud Cores ». Symposium - International Astronomical Union 197 (2000) : 41–50. http://dx.doi.org/10.1017/s0074180900164666.

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Ions and electrons play a key role in the chemical and dynamical evolution of interstellar clouds. Gas phase ion–molecule reactions are major chemical routes to the formation of interstellar molecules. The ionization degree determines the coupling between the magnetic field and the molecular gas through ion–neutral collisions, and thus regulates the rate of star formation. In the theoretical determination of the degree of ionization we run into several sources of uncertainty, including the poorly known cosmic ray flux and metal depletion within the cores, the penetration of UV radiation deep into regions of high visual extinction due to cloud inhomogeneities, and the ionization rate increase in the proximity of young stellar objects which may be strong X–ray emitters. Observational estimates of electron (or ion) fractions x(e) (≡ n(e)/n(H2), where n(e) and n(H2) are the electron and molecular hydrogen number densities, respectively) in dense cloud cores are thus of considerable interest. In this paper, I will review recent improvements in the estimates of the ion fraction in dense cores and point out the difficulties in determining x(e).

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Harrison, Stephen, Alexandre Faure et Jonathan Tennyson. « CN excitation and electron densities in diffuse molecular clouds ». Monthly Notices of the Royal Astronomical Society 435, n^o 4 (10 septembre 2013) : 3541–46. http://dx.doi.org/10.1093/mnras/stt1544.

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Pynzar’, A. V. « The electron density in clouds of turbulent interstellar plasma ». Astronomy Reports 60, n^o 3 (mars 2016) : 332–43. http://dx.doi.org/10.1134/s1063772916030124.

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Tanabe, Y., et K. Ohtaka. « Overlap integral between two electron clouds at different sites ». Physical Review B 34, n^o 6 (15 septembre 1986) : 3763–72. http://dx.doi.org/10.1103/physrevb.34.3763.

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Poznanski, Roman R., Lleuvelyn A. Cacha, Ahmad Z. A. Latif, Sheik H. Salleh, Jalil Ali, Preecha Yupapin, Jack A. Tuszynski et Tengku M. Ariff. « Molecular orbitals of delocalized electron clouds in neuronal domains ». Biosystems 183 (septembre 2019) : 103982. http://dx.doi.org/10.1016/j.biosystems.2019.103982.

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Khirwadkar, S. S., P. S. Pathak, S. Chaturvedi et P. I. John. « 2-D Guiding Centre Simulation of Toroidal Electron Clouds ». Journal of Computational Physics 132, n^o 2 (avril 1997) : 291–98. http://dx.doi.org/10.1006/jcph.1996.5636.

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Sauvaud, J. A., P. Koperski, T. Beutier, H. Barthe, C. Aoustin, J. J. Thocaven, J. Rouzaud, E. Penou, O. Vaisberg et N. Borodkova. « The INTERBALL-Tail ELECTRON experiment : initial results on the low-latitude boundary layer of the dawn magnetosphere ». Annales Geophysicae 15, n^o 5 (31 mai 1997) : 587–95. http://dx.doi.org/10.1007/s00585-997-0587-z.

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Abstract. The Toulouse electron spectrometer flown on the Russian project INTERBALL-Tail performs electron measurements from 10 to 26 000 eV over a 4<pi> solid angle in a satellite rotation period. The INTERBALL-Tail probe was launched on 3 August 1995 together with a subsatellite into a 65° inclination orbit with an apogee of about 30 RE. The INTERBALL mission also includes a polar spacecraft launched in August 1996 for correlated studies of the outer magnetosphere and of the auroral regions. We present new observations concerning the low-latitude boundary layers (LLBL) of the magnetosphere obtained near the dawn magnetic meridian. LLBL are encountered at the interface between two plasma regimes, the magnetosheath and the dayside extension of the plasma sheet. Unexpectedly, the radial extent of the region where LLBL electrons can be sporadically detected as plasma clouds can reach up to 5 RE inside the magnetopause. The LLBL core electrons have an average energy of the order of 100 eV and are systematically field-aligned and counterstreaming. As a trend, the temperature of the LLBL electrons increases with decreasing distance to Earth. Along the satellite orbit, the apparent time of occurrence of LLBL electrons can vary from about 5 to 20 min from one pass to another. An initial first comparison between electron- and magnetic-field measurements indicates that the LLBL clouds coincide with a strong increase in the magnetic field (by up to a factor of 2). The resulting strong magnetic field gradient can explain why the plasma-sheet electron flux in the keV range is strongly depressed in LLBL occurrence regions (up to a factor of \\sim10). We also show that LLBL electron encounters are related to field-aligned current structures and that wide LLBL correspond to northward interplanetary magnetic field. Evidence for LLBL/plasma-sheet electron leakage into the magnetosheath during southward IMF is also presented.

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FAZEKAS, Patrik, et Hiroyuki SHIBA. « VARIATIONAL THEORY OF CORRELATED FERMI-LIQUID STATE IN THE KONDO LATTICE MODEL ». International Journal of Modern Physics B 05, n^o 01n02 (janvier 1991) : 289–308. http://dx.doi.org/10.1142/s0217979291000183.

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A variational wave function is constructed and studied for the spin-compensated Fermi-liquid-type ground state in the Kondo lattice model. The spins of the localized f-electrons are compensated by overlapping conduction-electron clouds. In accordance with Luttinger’s theorem, the volume enclosed by the Fermi surface corresponds to the total number of electrons, i.e., it includes the f-electrons as well as the conduction electrons. An approximate analytic treatment of the correlated heavy Fermi liquid is given by using the Gutzwiller approximation.

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McCall, Benjamin J. « Dissociative recombination of cold and its interstellar implications ». Philosophical Transactions of the Royal Society A : Mathematical, Physical and Engineering Sciences 364, n^o 1848 (22 septembre 2006) : 2953–63. http://dx.doi.org/10.1098/rsta.2006.1876.

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plays a key role in interstellar chemistry as the initiator of ion–molecule chemistry. The amount of observed in dense interstellar clouds is consistent with expectations, but the large abundance of seen in diffuse clouds is not easily explained by simple chemical models. A crucial parameter in predicting the abundance of in diffuse clouds is the rate constant for dissociative recombination (DR) with electrons. The value of this constant has been very controversial, because different experimental techniques have yielded very different results, perhaps owing to varying degrees of rotational and vibrational excitation of the ions. If the value of this rate constant under interstellar conditions were much lower than usually assumed, the large abundance could be easily explained. In an attempt to pin down this crucial rate constant, we have performed DR measurements at the CRYRING ion storage ring in Stockholm, using a supersonic expansion ion source to produce rotationally cold ions. These measurements suggest that the DR rate constant in diffuse clouds is not much lower than usually assumed and that the abundant must be due to either a low electron fraction or a high ionization rate.

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Johansson, L. E. B. « Chemistry in the LMC and SMC ». Symposium - International Astronomical Union 178 (1997) : 515–24. http://dx.doi.org/10.1017/s0074180900009670.

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Molecular abundances derived in a sample of CO complexes in the Magellanic Clouds are discussed. With a possible exception of HCO+, the chemical compositions observed in this sample show a striking uniformity. The data indicate that the molecular concentrations are down by a factor of 5 in the SMC, relative those observed in a cloud associated with the H II region N159 in the LMC. A similar difference seems to exist within the LMC, between the 30 Doradus region and the N159 area. An estimate of the electron abundance in the N159 cloud is presented, based on a recent detection of DCO+.

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Barlow, M. J. « Chemical Abundances from Planetary Nebulae in the Magellanic Clouds ». Highlights of Astronomy 10 (1995) : 476–79. http://dx.doi.org/10.1017/s1539299600011813.

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AbstractHeavy element abundances, in particular those of oxygen, obtained from recent spectroscopic surveys of Magellanic Cloud planetary nebulae (PN), are reviewed and compared with those derived for H regions and objects in our own galaxy. These abundances have been based on collisionally excited lines and are very sensitive to the adopted electron temperature. There is increasing evidence that temperature or density fluctuations within nebulae lead to the electron temperatures being overestimated, with the corollary that the heavy element abundances have been underestimated.

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Padovani, Marco, Alexei V. Ivlev, Daniele Galli et Paola Caselli. « Cosmic-ray ionisation in circumstellar discs ». Astronomy & ; Astrophysics 614 (juin 2018) : A111. http://dx.doi.org/10.1051/0004-6361/201732202.

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Context. Galactic cosmic rays (CRs) are a ubiquitous source of ionisation of the interstellar gas, competing with UV and X-ray photons as well as natural radioactivity in determining the fractional abundance of electrons, ions, and charged dust grains in molecular clouds and circumstellar discs. Aims. We model the propagation of various components of Galactic CRs versus the column density of the gas. Our study is focussed on the propagation at high densities, above a few g cm−2, especially relevant for the inner regions of collapsing clouds and circumstellar discs. Methods. The propagation of primary and secondary CR particles (protons and heavier nuclei, electrons, positrons, and photons) is computed in the continuous slowing down approximation, diffusion approximation, or catastrophic approximation by adopting a matching procedure for the various transport regimes. A choice of the proper regime depends on the nature of the dominant loss process modelled as continuous or catastrophic. Results. The CR ionisation rate is determined by CR protons and their secondary electrons below ≈130 g cm−2 and by electron-positron pairs created by photon decay above ≈600 g cm−2. We show that a proper description of the particle transport is essential to compute the ionisation rate in the latter case, since the electron and positron differential fluxes depend sensitively on the fluxes of both protons and photons. Conclusions. Our results show that the CR ionisation rate in high-density environments, such as the inner parts of collapsing molecular clouds or the mid-plane of circumstellar discs, is higher than previously assumed. It does not decline exponentially with increasing column density, but follows a more complex behaviour because of the interplay of the different processes governing the generation and propagation of secondary particles.

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Sattonnay, G., S. Bilgen, B. Mercier, D. Longuevergne, S. Della-Negra et I. Ribaud. « Role of surface chemistry in conditioning of materials in particle accelerators ». Journal of Physics : Conference Series 2420, n^o 1 (1 janvier 2023) : 012083. http://dx.doi.org/10.1088/1742-6596/2420/1/012083.

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Abstract For the vacuum scientists and the accelerator community, finding solutions to mitigate pressure rises induced by electron, photon and ion desorption, and also beam instabilities induced by ion and electron clouds is a major issue. Along the time, changes in the surface chemistry of vacuum chambers are observed during beam operations, leading to modifications of: outgassing rates, stimulated desorption processes and secondary emission yields (SEY). To understand the role of the surface chemistry of air exposed materials in the electron conditioning process, typical air exposed materials used in particle accelerators : thin film coatings (NEG, i.e a Ti-Zr-V alloy, and carbon), copper (and its oxides Cu2O and CuO) and niobium were conditioned by low energy electron irradiation for a better understanding of electron-cloud effect. First, SEY was measured to understand the changes of surface conditioning upon particle irradiation; then, surface chemistry evolution after electron irradiation was investigated by both XPS and TOF-SIMS analyses using the ANDROMEDE facility at IJCLab. Finally, the relationship between the surface chemistry and the conditioning phenomenon will be discussed.

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Pasmanik, D. L., V. Y. Trakhtengerts, A. G. Demekhov, A. A. Lyubchich, E. E. Titova, T. Yahnina, M. J. Rycroft, J. Manninen et T. Turunen. « A quantitative model for cyclotron wave-particle interactions at the plasmapause ». Annales Geophysicae 16, n^o 3 (31 mars 1998) : 322–30. http://dx.doi.org/10.1007/s00585-998-0322-4.

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Abstract. The formation of a zone of energetic electron precipitation by the plasmapause, a region of enhanced plasma density, following energetic particle injection during a magnetic storm, is analyzed. Such a region can also be formed by detached cold plasma clouds appearing in the outer magnetosphere by restructuring of the plasmasphere during a magnetic storm. As a mechanism of precipitation, wave-particle interactions by the cyclotron instability between whistler-mode waves and electrons are considered. In the framework of the self-consistent equations of quasi-linear plasma theory, the distribution function of trapped electrons and the electron precipitation pattern are found. The theoretical results are compared with experimental data obtained from NOAA satellites.Key words. Magnetospheric physics · Energetic particles · Precipitating and trapped · Plasma waves and instabilities

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