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MAGNETOHYDRODYNAMIC SIMULATIONS OF RECONNECTION AND PARTICLE ACCELERATION: THREE-DIMENSIONAL EFFECTS

KOWAL, Grzegorz; PINO, E. M. de Gouveia Dal; LAZARIAN, A.
Fonte: IOP PUBLISHING LTD Publicador: IOP PUBLISHING LTD
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
36.63%
Magnetic fields can change their topology through a process known as magnetic reconnection. This process in not only important for understanding the origin and evolution of the large-scale magnetic field, but is seen as a possibly efficient particle accelerator producing cosmic rays mainly through the first-order Fermi process. In this work we study the properties of particle acceleration inserted in reconnection zones and show that the velocity component parallel to the magnetic field of test particles inserted in magnetohydrodynamic (MHD) domains of reconnection without including kinetic effects, such as pressure anisotropy, the Hall term, or anomalous effects, increases exponentially. Also, the acceleration of the perpendicular component is always possible in such models. We find that within contracting magnetic islands or current sheets the particles accelerate predominantly through the first-order Fermi process, as previously described, while outside the current sheets and islands the particles experience mostly drift acceleration due to magnetic field gradients. Considering two-dimensional MHD models without a guide field, we find that the parallel acceleration stops at some level. This saturation effect is, however, removed in the presence of an out-of-plane guide field or in three-dimensional models. Therefore...

Fast magnetic reconnection and energetic particle acceleration

LAZARIAN, A.; KOWAL, G.; VISHNIAC, E.; PINO, E. de Gouveia Dal
Fonte: PERGAMON-ELSEVIER SCIENCE LTD Publicador: PERGAMON-ELSEVIER SCIENCE LTD
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
36.47%
Our numerical simulations show that the reconnection of magnetic field becomes fast in the presence of weak turbulence in the way consistent with the Lazarian and Vishniac (1999) model of fast reconnection. We trace particles within our numerical simulations and show that the particles can be efficiently accelerated via the first order Fermi acceleration. We discuss the acceleration arising from reconnection as a possible origin of the anomalous cosmic rays measured by Voyagers. (C) 2010 Elsevier Ltd. All rights reserved.; NSF[AST 0808118]; NASA[NNX09AH78G]; NSF Center for Magnetic Self-Organization

Influences of the load centre of gravity on heavy vehicle acceleration

Navarro, H. A.; Canale, A. C.
Fonte: Inderscience Enterprises Ltd Publicador: Inderscience Enterprises Ltd
Tipo: Artigo de Revista Científica Formato: 17-47
ENG
Relevância na Pesquisa
36.66%
The aim of this paper is to analyse the influence of the load centre of gravity on heavy vehicle acceleration. This analysis is done through a method in which a vehicle centre of gravity map is used. A model for the driving force is presented for bus, truck and tractor-semi trailer combinations. The proposed model takes into consideration the resistance forces (drag, rolling resistance, translation and rotation acceleration, climbing resistance) and the 4 X 2 traction system. The positions of the vehicle centre of gravity as a function of the position of the load centre of gravity are determined. The vehicle acceleration is calculated based on the position of the load centre of gravity. This study analyses the acceleration of one of the Mercedes-Benz do Brasil tractor-semitrailer vehicle. A comparison of the acceleration for different maximum adhesion coefficients and ramps are presented, showing new results. An example showing the variations of the load centre of gravity position with the acceleration time and distance is provided. The load centre of gravity position is important for vehicle safety and the efficiency and economy in the transportation of the load.

Suppressing Fermi acceleration in a two-dimensional non-integrable time-dependent oval-shaped billiard with inelastic collisions

Oliveira, Diego F. M.; Leonel, Edson Denis
Fonte: Elsevier B.V. Publicador: Elsevier B.V.
Tipo: Artigo de Revista Científica Formato: 1009-1020
ENG
Relevância na Pesquisa
36.47%
Some dynamical properties of a classical particle confined inside a closed region with an oval-shaped boundary are studied. We have considered both the static and time-dependent boundaries. For the static case, the condition that destroys the invariant spanning curves in the phase space was obtained. For the time-dependent perturbation, two situations were considered: (i) non-dissipative and (ii) dissipative. For the non-dissipative case, our results show that Fermi acceleration is observed. When dissipation, via inelastic collisions, is introduced Fermi acceleration is suppressed. The behaviour of the average velocity for both the dissipative as well as the non-dissipative dynamics is described using the scaling approach. (C) 2009 Elsevier B.V. All rights reserved.

Fermi acceleration with memory-dependent excitation

Leonel, Edson Denis; Marinho, Eraldo P.
Fonte: Elsevier B.V. Publicador: Elsevier B.V.
Tipo: Artigo de Revista Científica Formato: 4927-4935
ENG
Relevância na Pesquisa
36.47%
Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); Some scaling properties for a classical particle confined to bounce between two walls, where one wall is fixed and the other one moves in time according to a random signal with a memory length are studied. We have considered two different kinds of collisions of the particle with the moving wall namely: (i) elastic and (ii) inelastic. The dynamics of the model is described in terms of a two-dimensional nonlinear mapping. For the case of elastic collisions, we show that the memory of the stochastic signal affects directly the behaviour of the average velocity of the particle. It then exhibits different slopes for the average velocity at different stages of the series with beta congruent to 3/4 for a short time, beta congruent to 1 for the average stage and beta congruent to 1/2 for a long time, as predicted by the Central Limit Theorem, therefore leading to the Fermi acceleration. The situation where inelastic collisions are taken into account yields a more drastic change, particularly suppressing the Fermi acceleration. (c) 2009 Elsevier B.V. All rights reserved.

Zero, minimum and maximum relative radial acceleration for planar formation flight dynamics near triangular libration points in the Earth-Moon system

Salazar, F. J. T.; Masdemont, J. J.; Gomez, G.; Macau, E. E.; Winter, O. C.
Fonte: Elsevier B.V. Publicador: Elsevier B.V.
Tipo: Artigo de Revista Científica Formato: 1838-1857
ENG
Relevância na Pesquisa
36.63%
Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); Processo FAPESP: 08/06066-5; Processo FAPESP: 11/08171-3; Processo FAPESP: 11/50151-0; Processo FAPESP: 13/03233-6; Assume a constellation of satellites is flying near a given nominal trajectory around L-4 or L-5 in the Earth-Moon system in such a way that there is some freedom in the selection of the geometry of the constellation. We are interested in avoiding large variations of the mutual distances between spacecraft. In this case, the existence of regions of zero and minimum relative radial acceleration with respect to the nominal trajectory will prevent from the expansion or contraction of the constellation. In the other case, the existence of regions of maximum relative radial acceleration with respect to the nominal trajectory will produce a larger expansion and contraction of the constellation. The goal of this paper is to study these regions in the scenario of the Circular Restricted Three Body Problem by means of a linearization of the equations of motion relative to the periodic orbits around L-4 or L-5. This study corresponds to a preliminar planar formation flight dynamics about triangular libration points in the Earth-Moon system. Additionally...

Proton-driven plasma wakefield acceleration: a path to the future of high-energy particle physics

Assmann, R.; Bingham, R.; Bohl, T.; Bracco, C.; Buttenschön, B.; Butterworth, A.; Caldwell, A.; Chattopadhyay, S.; Cipiccia, S.; Feldbaumer, E.; Fonseca, R. A.; Goddard, B.; Gross, M.; Grulke, O.; Gschwendtner, E.; Holloway, J.; Huang, C. K.; Jaroszynski
Fonte: IOP Publishing Ltd Publicador: IOP Publishing Ltd
Tipo: Artigo de Revista Científica
Publicado em //2014 ENG
Relevância na Pesquisa
36.47%
WOS:000340055300014 (Nº de Acesso Web of Science); New acceleration technology is mandatory for the future elucidation of fundamental particles and their interactions. A promising approach is to exploit the properties of plasmas. Past research has focused on creating large-amplitude plasma waves by injecting an intense laser pulse or an electron bunch into the plasma. However, the maximum energy gain of electrons accelerated in a single plasma stage is limited by the energy of the driver. Proton bunches are the most promising drivers of wakefields to accelerate electrons to the TeV energy scale in a single stage. An experimental program at CERN—the AWAKE experiment—has been launched to study in detail the important physical processes and to demonstrate the power of proton-driven plasma wakefield acceleration. Here we review the physical principles and some experimental considerations for a future proton-driven plasma wakefield accelerator.

Acceleration measurements using smartphone sensors: Dealing with the equivalence principle

Monteiro,Martín; Cabeza,Cecilia; Marti,Arturo C.
Fonte: Sociedade Brasileira de Física Publicador: Sociedade Brasileira de Física
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/03/2015 EN
Relevância na Pesquisa
36.54%
Acceleration sensors built into smartphones, i-pads or tablets can conveniently be used in the physics laboratory. By virtue of the equivalence principle, a sensor fixed in a non-inertial reference frame cannot discern between a gravitational field and an accelerated system. Accordingly, acceleration values read by these sensors must be corrected for the gravitational component. A physical pendulum was studied by way of example, and absolute acceleration and rotation angle values were derived from the measurements made by the accelerometer and gyroscope. Results were corroborated by comparison with those obtained by video analysis. The limitations of different smartphone sensors are discussed.

System-on-a-Chip (SoC) based Hardware Acceleration in Register Transfer Level (RTL) Design

Niu, Xinwei
Fonte: FIU Digital Commons Publicador: FIU Digital Commons
Tipo: Artigo de Revista Científica Formato: application/pdf
Relevância na Pesquisa
36.69%
Today, modern System-on-a-Chip (SoC) systems have grown rapidly due to the increased processing power, while maintaining the size of the hardware circuit. The number of transistors on a chip continues to increase, but current SoC designs may not be able to exploit the potential performance, especially with energy consumption and chip area becoming two major concerns. Traditional SoC designs usually separate software and hardware. Thus, the process of improving the system performance is a complicated task for both software and hardware designers. The aim of this research is to develop hardware acceleration workflow for software applications. Thus, system performance can be improved with constraints of energy consumption and on-chip resource costs. The characteristics of software applications can be identified by using profiling tools. Hardware acceleration can have significant performance improvement for highly mathematical calculations or repeated functions. The performance of SoC systems can then be improved, if the hardware acceleration method is used to accelerate the element that incurs performance overheads. The concepts mentioned in this study can be easily applied to a variety of sophisticated software applications. The contributions of SoC-based hardware acceleration in the hardware-software co-design platform include the following: (1) Software profiling methods are applied to H.264 Coder-Decoder (CODEC) core. The hotspot function of aimed application is identified by using critical attributes such as cycles per loop...

Effect of energy losses and interactions during diffusive shock acceleration: applications to SNR, AGN and UHE cosmic rays

Protheroe, R.
Fonte: Elsevier Science BV Publicador: Elsevier Science BV
Tipo: Artigo de Revista Científica
Publicado em //2004 EN
Relevância na Pesquisa
36.66%
I discuss the shape of the high energy end of the spectrum of particles arising from diffusive shock acceleration in the presence of (i) additional diffusive escape from the accelerator, (ii) continuous energy losses, (iii) energy changes arising from interactions. The form of the spectrum near cut-off is sensitive to these processes as well as to the momentum-dependence of the diffusion coefficients and the compression ratio, and so the spectrum of any radiation emitted by the accelerated particles may reflect the physical conditions of the acceleration region. Results presented in this paper have applications in interpreting the spectral energy distributions of many types of astrophysical object including supernova remnants (SNR), active galactic nuclei (AGN) and acceleration sources of ultra high energy cosmic rays (UHE CR). Except for extremely nearby sources, spectral features imprinted on the spectrum of UHE CR during the acceleration process will be largely eroded during propagation, but the spectrum of UHE neutrinos produced in interactions of UHE CR with radiation, both during cosmic ray acceleration and subsequent propagation through the cosmic microwave background radiation, contains sufficient information to determine the cut-off momentum of the UHE CR just after acceleration for reasonable assumptions. Observation of these UHE neutrinos by the Pierre Auger Observatory may help in identifying the sources of the highest energy cosmic rays.; Submitted to Cornell University’s online archive www.arXiv.org in 2007 by Protheroe...

Interactions of UHE cosmic ray nuclei with radiation during acceleration: consequences for the spectrum and composition

Allard, D.; Protheroe, R.
Fonte: E D P Sciences Publicador: E D P Sciences
Tipo: Artigo de Revista Científica
Publicado em //2009 EN
Relevância na Pesquisa
36.63%
In this paper, we study the diffusive shock acceleration of cosmic-ray protons and nuclei, taking all the relevant interaction processes with photon backgrounds into account. We investigate how the competition between protons and nuclei is modified by such acceleration parameters as the acceleration rate, its rigidity dependence, the photon density, and the confinement capability of the sources. We find that protons are likely to be accelerated to higher energies than nuclei in the case of interaction-limited acceleration processes, whereas nuclei are accelerated to higher energies than protons for confinement-limited acceleration. Finally, we discuss our results in the context of possible astrophysical accelerators and in the light of recent cosmic-ray data; D. Allard and R. J. Protheroe; © ESO 2009

Mass entrainment and turbulence-driven acceleration of ultra-high energy cosmic rays in Centaurus A

Wykes, S.; Croston, J.; Hardcastle, M.; Eilek, J.; Biermann, P.; Achterberg, A.; Bray, J.; Lazarian, A.; Haverkorn, M.; Protheroe, R.; Bromberg, O.
Fonte: E D P Sciences Publicador: E D P Sciences
Tipo: Artigo de Revista Científica
Publicado em //2013 EN
Relevância na Pesquisa
36.59%
Observations of the FR I radio galaxy Centaurus A in radio, X-ray, and gamma-ray bands provide evidence for lepton acceleration up to several TeV and clues about hadron acceleration to tens of EeV. Synthesising the available observational constraints on the physical conditions and particle content in the jets, inner lobes and giant lobes of Centaurus A, we aim to evaluate its feasibility as an ultra-high-energy cosmic-ray source. We apply several methods of determining jet power and affirm the consistency of various power estimates of ~1 × 10⁴³ erg s⁻¹. Employing scaling relations based on previous results for 3C 31, we estimate particle number densities in the jets, encompassing available radio through X-ray observations. Our model is compatible with the jets ingesting ~3 × 10²¹ g s⁻¹ of matter via external entrainment from hot gas and ~7 × 10²² g s⁻¹ via internal entrainment from jet-contained stars. This leads to an imbalance between the internal lobe pressure available from radiating particles and magnetic field, and our derived external pressure. Based on knowledge of the external environments of other FR I sources, we estimate the thermal pressure in the giant lobes as 1.5 × 10⁻¹² dyn cm⁻²...

Dependence of the head injury criterion and maximum acceleration on headform mass and initial velocity in tests simulating pedestrian impacts with vehicles

Hutchinson, T.
Fonte: ASME-Amer Soc Mechanical Eng Publicador: ASME-Amer Soc Mechanical Eng
Tipo: Artigo de Revista Científica
Publicado em //2013 EN
Relevância na Pesquisa
36.54%
Impact testing of pedestrian headforms is usually conducted at one velocity and with one mass of headform, but real impacts occur at a range of velocities and masses. A method is proposed to predict the Head Injury Criterion (HIC) and similar quantities at other velocities from their values observed under test conditions. A specific assumption is made about acceleration during the impact as related to displacement, its differential (instantaneous velocity), mass of headform, and initial velocity: namely, that it is the product of a power function of displacement (representing a possibly nonlinear spring) and a term that includes a type of damping. This equation is not solved, but some properties of the solution are obtained: HIC, maximum acceleration, and maximum displacement are found to be power functions of mass of headform and initial velocity. Expressions for the exponents are obtained in terms of the nonlinearity parameter of the spring. Simple formulae are obtained for the dependence of HIC, maximum acceleration, and maximum displacement on velocity and mass. These are relevant to many types of impact.; T. P. Hutchinson

The Acceleration Vector of a Rigid Body

Featherstone, Roy
Fonte: Sage Publications Inc Publicador: Sage Publications Inc
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
36.69%
This paper explains the relationship between two existing representations of rigid-body acceleration in a 6-D vector: conventional acceleration, which is the concatenation of two 3-D acceleration vectors, and spatial acceleration, which is the time deriva

Assessment of turbulence model performance: Severe acceleration with large integral length scales

Yang, Xiaoyu; Tucker, Paul G.
Fonte: Elsevier Publicador: Elsevier
Tipo: Article; accepted version
EN
Relevância na Pesquisa
36.66%
This is the author accepted manuscript. The final version is available from Elsevier via http://dx.doi.org/10.1016/j.compfluid.2015.12.007; Turbulence is substantially laminarised, when the mean flow experiences streamwise acceleration above a certain critical acceleration parameter. Recently, to essentially reveal aero engine intake acceleration scenarios, Direct Numerical Simulations (DNS) have been performed for turbulent flow through a rapidly contracting channel. On average, the streamwise acceleration parameter K_s is of the magnitude of 1?10^?5. Converged statistics show that it is the streamwise acceleration that causes the first term of the production rate for u?u? to be negative. This initiates the degeneration towards laminar flow and also closes the usual wall turbulence self-sustaining mechanism. Further downstream, the progressive turbulence recovery is largely streamwise dominant. Importantly, the laminarisation effects are lagging to the rate of contraction. To assess the corresponding turbulence model performance and for better modelling, for the same flow configurations, Reynolds-averaged Navier-Stokes (RANS) predictions are compared, using some available Reynolds-stress (RSM) and eddy-viscosity models. These are the second-order closure with the strain-? formulation...

On Certain Non-linear and Relativistic Effects in Plasma-based Particle Acceleration

Sahai, Aakash Ajit
Fonte: Universidade Duke Publicador: Universidade Duke
Tipo: Dissertação
Publicado em //2015
Relevância na Pesquisa
36.78%

Plasma-based particle acceleration holds the promise to make the applications that revolve around accelerators more affordable. The central unifying theme of this dissertation is the modeling of certain non-linear and relativistic phenomena in plasma dynamics to devise mechanisms that benefit plasma-accelerators. Plasma acceleration presented here has two distinct flavors depending upon the accelerated particle mass which dictates the acceleration structure velocity and potential. The first deals with ion acceleration, where acceleration structure velocities are a significant fraction of the speed of light, with major applications in medicine. The second focusses on the acceleration of electrons and positrons for light-sources and colliders where the acceleration structures are wakefields with phase-velocities near the speed of light.

The increasing Lorentz factor of the laser-driven electron quiver momentum forms the basis of Relativistically Induced Transparency Acceleration (RITA) scheme of ion acceleration. Ions are accelerated by reflecting off a propagating acceleration structure, referred to as a snowplow, formed by compression of ponderomotively driven electrons excited in front of a high intensity laser pulse at the critical layer. Its velocity is controlled by tailoring the laser pulse rise-time and rising density gradient scale-length. We analytically model its induced transparency driven propagation with a 1-D model based on the linearized dispersion relation. The model is shown to be in good agreement with the weakly non-linear simulations. As the density compression rises into the strongly non-linear regime...

Experimental study of the collective acceleration of deuterons

Floyd, L.E.; Destler, William
Fonte: American Institute of Physics Publicador: American Institute of Physics
Tipo: Artigo de Revista Científica
EN_US
Relevância na Pesquisa
36.54%
The collective acceleration of deuterons by an intense relativistic electron beam has been studied experimentally. The accelerated ion energy spectra for various different experimental configurations has been measured using stacked foil activation analysis. The spectra extend to energies below the injected electron beam energy, and thus allow estimates of the net efficiency of the acceleration process. The effect of variations in electron beam power and applied magnetic field on the acceleration process are also discussed. Journal of Applied Physics is copyrighted by The American Institute of Physics.

Sensitivity to the acceleration of looming stimuli

Trewhella, James; Edwards, Mark; Ibbotson, Michael
Fonte: Blackwell Science Asia Publicador: Blackwell Science Asia
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
36.59%
The aim of this study was to determine if observers could discriminate between looming stimuli simulating targets approaching the observers at either constant or non-constant speeds. Discrimination between accelerating and constant-speed approaches improved after 70-90 trials for accelerations >2 m/s2. For lower accelerations the ability to discriminate was poor regardless of the trial number. Following the learning phase, observers were able to identify accelerating targets from constant-speed approaches fairly consistently at performance levels of 70-75% for accelerations as low as 4 m/s2 and at 80-96% for accelerations of 6-14 m/s2. Observers' accuracy in identifying decelerating from constant-speed targets did not increase as a function of increasing deceleration. In fact, observers had a slight bias to select the constant-speed stimulus as being the decelerating stimulus. In summary, the sensitivity to acceleration for simulated motion in depth is poor, but increases as acceleration increases and sensitivity to acceleration is far greater than for deceleration.

Classes de Aceleração : “Pedagogia” da inclusão ou da exclusão?; Acceleration Classes: “Pedagogy” of inclusion or exclusion?

Hanff, Beatriz Bittencourt Collere; UFSC - Florianópolis - SC; Barbosa, Raquel; UDESC - Florianópolis - SC; Koch, Zenir Maria; UDESC - Florianópolis - SC
Fonte: Núcleo de Publicações do CED - UFSC Publicador: Núcleo de Publicações do CED - UFSC
Tipo: info:eu-repo/semantics/article; info:eu-repo/semantics/publishedVersion; Formato: application/pdf
Publicado em 01/01/2002 POR
Relevância na Pesquisa
36.54%
O objetivo do presente artigo é debater a implantação da política nacional das Classes de Aceleração em Santa Catarina, mais especificamente no município de Florianópolis, a partir de 1998, tendo por base a pesquisa “A pedagogia da repetência em questão: um estudo de caso junto às classes de aceleração”. Realizada em duas etapas, essa pesquisa procurou analisar, os condicionamentos históricos dos processos de implantação, formação de professores e outros relacionados com o trabalho docente e seus resultados, possibilitando caracterizar as diferenças existentes entre as propostas de aceleração, num diagnóstico preliminar em seis escolas da rede pública estadual e municipal. Nas entrevistas realizadas com professores, articuladores e coordenadores foram colhidos relatos sobre o processo de implantação, as dúvidas, a formação docente e a assessoria, as experiências pedagógicas, a integração das classes no interior das escolas e os processos de isolamento. As classes de aceleração serviram para alterar as relações pedagógicas internas na escola...

Student use of vectors in the context of acceleration

Flores-García,S; Terrazas,S.M; González-Quezada,M.D; Chávez Pierce,J.L; Escobedo Soto,S
Fonte: Sociedad Mexicana de Física Publicador: Sociedad Mexicana de Física
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/12/2008 EN
Relevância na Pesquisa
36.59%
A functional understanding of Newton's second law as a vector equation requires that students be able to reason about forces and acceleration as vectors. In this paper, we present data describing students' conceptual difficulties with vector quantities such as acceleration. These data suggest that after traditional instruction in introductory physics, some students do not recognize the vector nature of this quantity. Other students do not have the requisite procedural knowledge to determine acceleration, and are therefore unable to reason qualitatively about Newton's second law. We describe some specific procedural and reasoning difficulties we have observed in students' use of vectors quantities. In addition, we describe instructional difficulties in mechanics that we observed on the basis of our research into student understanding. Some modifications in the instruction were intended to improve students' understanding of the vector nature of acceleration, and to promote student use of vectors when solving mechanics problems. Finally, we describe initial measurements of the effectiveness of these modifications