Charged Particles (charged + particle)

Distribution by Scientific Domains
Distribution within Physics and Astronomy


Selected Abstracts


Quantum dynamics of a discontinuously kicked charged particle in harmonic, symmetric double, or triple wells

INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 6 2009
S. Ghosh
Abstract The quantum dynamics of a charged particle in a harmonic trap in the presence of discontinuous reversals of a homogeneous or an inhomogeneous electric field is studied. The dynamics reveals classically expected patterns in harmonic wells. In a symmetric double-well potential, the discontinuously switched low intensity homogeneous electric field does not appear to assist tunneling, whereas an inhomogeneous electric field is found to assist the process. Resonance like enhancement is noticed at a critical reversal frequency. Dynamics in a triple well is also analyzed under similar conditions. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009 [source]


GeV-acceleration of electron by a superintense ultrashort laser pulse

LASER PHYSICS LETTERS, Issue 8 2004
A. Bahari
Abstract New mechanism of laser acceleration of a charged particle is discovered and explained. Particle acceleration with focused beam of superintense ultrashort laser pulse is determined by a combination of ponderomotive forces at rising and falling edges of laser pulse and a longitudinal component of laser electric field. We found that acceleration of electron, which moves along the laser wavevector, is crucially depends on whether or not the electron reaches the region z , zR behind the laser focus (here zR is the Rayleigh length). Interpretation of this effect consists in that the laser longitudinal electric field at the electron trajectory in this region is a unidirectional one (oscillatory in the case of laser linear polarization and slowly varying in the case of laser circular polarization). Due to this effect it is possible to overcome the negative influence of a phase slippage in the particle- wave interaction, which substantially suppresses electron acceleration. We revealed also that the physical reason of a unidirectional influence of laser longitudinal electric field on accelerating electron in the region z , zR consists in the difference in phase velocities of transverse and longitudinal components of a focused laser field. Owing to this mechanism, lasers of ultimate present-day parameters enable electron acceleration up to the energy , , 1 GeV. Moreover, electron acceleration along the laser wavevector (in contrast to techniques currently considered) is not sensitive to field initial phase (there is no bunch effect), it is possible to accelerate slow electrons (electrons need not to be preaccelerated to relativistic velocities), and there are no problems with a removal of accelerated electron from the laser field. (© 2004 by ASTRO, Ltd. Published exclusively by WILEY-VCH Verlag GmbH & Co. KGaA) [source]


Semi-classical calculation of resonant states of a charged particle interacting with a metallic surface

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 10 2005
John Jairo Zuluaga
Abstract We assess the applicability of the semi-classical approach of Herman,Kluk with filter diagonalization to determine resonant states of either the electron-surface system or the ion-surface system. An effective potential model of the interaction of an electron with a ruthenium metallic surface is used. The evolution of the wave-function and the resonant states of this system are calculated. Analogous results for the interaction of the system formed by the H, and the ruthenium surface are presented. For the calculation of the resonances, the semi-classical wave-function is found, and the autocorrelation function between the initial and final wave-functions is calculated, from which the position and width of the resonances are extracted by using the harmonic inversion by filter diagonalization. The results are compared with results available in the literature for similar models obtained by quantum calculations using fast Fourier Transform. The positions of the lower-lying resonances found with the semi-classical and quantum approaches match closely, while the values of the widths of the resonances show larger discrepancies. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


Influence of the Wall Characteristics on the Development of MARFE in Tokamaks

CONTRIBUTIONS TO PLASMA PHYSICS, Issue 7-9 2006
O. Marchuk
Abstract Multifaceted asymmetric radiation from the edge (MARFE) normally develops in fusion devices close to the density limit. MARFE is considered a result of thermal instabilities excited under critical conditions through different mechanisms: impurity radiation, recycling of neutral particles, anomalous transport of charged particles and energy. Recent experiments on tokamaks TEXTOR and JET show that plasma-wall interaction, leading to release of recycling neutrals and impurities, plays a very important role for the formation of MARFE. In the present contribution we develop further the MARFE models based on the instability of particle recycling on the tokamak wall by including a simple description for the release of recycling neutrals from the wall surface into the plasma. This development takes into account the time delay between the out flow of charged particles from the plasma and in flux of neutrals. The linear stability analysis shows that this does not change the critical plasma density for the MARFE formation but modifies significantly the growth rate of unstable perturbations developing when the density exceeds the threshold. These findings are confirmed in a non-linear consideration by solving the equations for the particle, momentum and energy transfer in the plasma coupled with the wall particle balance equations. This is done in a one-dimensional approximation by taking into account the variation of the main plasma parameters in the poloidal direction and making averaging in the radial direction over the plasma edge width of the penetration depth of neutrals. The intrinsic poloidal asymmetry of the system, defining the MARFE localization, is introduced by the Shafranov shift of magnetic flux surfaces. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


Computer-assisted 2-D agarose electrophoresis of Haemophilus influenzae type B meningitis vaccines and analysis of polydisperse particle populations in the size range of viruses: A review

ELECTROPHORESIS, Issue 4 2007
Dietmar Tietz Dr.
Abstract When protein,polysaccharide conjugated vaccines were first developed for the immunization of small children against meningitis caused by infection with Haemophilus influenzae type b (Hib), the vaccine preparations varied in immunogenicity. Testing for immunogenicity was time-consuming and alternative analytical procedures for determining vaccine quality were unsatisfactory. For example, due to the very high molecular weight of the vaccine particles, immunogens could only be physically characterized as a fraction in the void volume of Sepharose gel filtration. In search of better analytical methods, a computer-assisted electrophoretic technique for analyzing such vaccines was developed in the period from 1983 to 1995. This new approach made it possible to analyze highly negatively charged particles as large as or larger than intact viruses. 2-D gel patterns were generated that varied depending on the conditions of the particular vaccine preparation and were therefore characteristic of each vaccine sample. Thus, vaccine particle populations with a continuous size variation over a wide range (polydisperse) could be characterized according to size and free mobility (related to particle surface net charge density). These advances are reviewed in this article, since the developed methods are still a promising tool for vaccine quality control and for predicting immunogen effectiveness in the production of vaccines. The technique is potentially beneficial for Hib immunogens and other high-molecular-mass vaccines. Additional biomedical applications for this nondenaturing electrophoretic technique are briefly discussed and detailed information about computational and mathematical procedures and theoretical aspects is provided in the Appendices. [source]


Charge-induced clustering in multifield particulate flows

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 7 2005
T. I. Zohdi
Abstract The present work extends recent results in Zohdi (Int. J. Solids Struct., in press; Proc. Roy. Soc., in press) to develop models and robust solution strategies for the direct simulation of the dynamical flow of charged particles undergoing simultaneous contact, surface reactions and heat transfer. Emphasis is placed on the possibility of particle clustering which can lead to the formation of cluster-structures within the particulate flow. A recursive ,staggering' solution scheme is developed, whereby the time-steps are adaptively adjusted to control the rates of convergence within each time-step, and hence, the error associated with the incomplete resolution of the coupled interaction between the various fields and associated constraints. Representative numerical simulations are provided in order to illustrate the character of the model and the solution strategy. Copyright © 2004 John Wiley & Sons, Ltd. [source]


Quantum statistics of charged particles and fingerprints of wigner crystallization in D dimensions

INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 15 2006
N. H. March
Abstract After a brief summary of the physical arguments underlying Wigner's original concept in 1934 of a quantal electron crystal, theoretical interpretation of a number of experimental findings are presented. These include (i) low-density carriers in semiconductors in applied magnetic fields in both three, and recently two, dimensions; and (ii) low-temperature phase diagram of underdoped high Tc cuprates; fullerides with relatively low Tc are also referred to in a related context. Interpretation of areas (i) and (ii) focuses on the relevance of both Fermi,Dirac and anyonic (fractional) statistics, the latter in relation to the proposed melting curve of the two-dimensional (2D) magnetically induced Wigner solid into the Laughlin liquid phase, which is the seat of the fractional quantum Hall effect. A brief discussion follows of crystalline phases additional to the Wigner solid, namely Skyrmion and Hall crystals. Bose,Einstein statistics is then referred to, but now in relation to finite-size confined quantal assemblies, with fingerprints of Wigner molecules the focus. Finally, quasi-1D lattices are considered, both in Bechgaard salts and in the very recent single-electron counting experiment of Bylander et al. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006 [source]


Decay in time for a one-dimensional two-component plasma

MATHEMATICAL METHODS IN THE APPLIED SCIENCES, Issue 18 2008
Robert Glassey
Abstract The motion of a collisionless plasma is described by the Vlasov,Poisson (VP) system, or in the presence of large velocities, the relativistic VP system. Both systems are considered in one space and one momentum dimension, with two species of oppositely charged particles. A new identity is derived for both systems and is used to study the behavior of solutions for large times. Copyright © 2008 John Wiley & Sons, Ltd. [source]


Diffusive radiation in Langmuir turbulence produced by jet shocks

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2007
G. D. Fleishman
ABSTRACT Anisotropic distributions of charged particles including two-stream distributions give rise to generation of either stochastic electric fields (in the form of Langmuir waves, Buneman instability) or random quasi-static magnetic fields (Weibel and filamentation instabilities) or both. These two-stream instabilities are known to play a key role in collisionless shock formation, shock,shock interactions, and shock-induced electromagnetic emission. This paper applies the general non-perturbative stochastic theory of radiation to study electromagnetic emission produced by relativistic particles, which random walk in the stochastic electric fields of the Langmuir waves. This analysis takes into account the cumulative effect of uncorrelated Langmuir waves on the radiating particle trajectory giving rise to angular diffusion of the particle, which eventually modifies the corresponding radiation spectra. We demonstrate that the radiative process considered is probably relevant for emission produced in various kinds of astrophysical jets, in particular, prompt gamma-ray burst spectra, including X-ray excesses and prompt optical flashes. [source]


Instabilities in two-fluid magnetized media with inter-component drift

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2002
P. V. Tytarenko
Abstract We analyse the stability of a magnetized medium consisting of a neutral fluid and a fluid of charged particles, coupled to each other through a drag force and exposed to differential body forces (for example, as the result of radiation forces on one phase). We consider a uniform equilibrium and simple model input physics, but do not arbitrarily restrict the relative orientations of the magnetic field, slip velocity and wavevector of the disturbance. We find several instabilities and classify these in terms of wave resonances. We briefly apply our results to the structure of SiO maser regions appearing in the winds from late-type stars. [source]


Lattice modes in a system of charge rotators in a plasma environment

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 11 2004
S. V. Vladimirov
Abstract Three dimensional rotatory modes of oscillations in a one-dimensional chain of rod-like charged particles or dust grains in a plasma are investigated. An oscillatory dependence on wavenumber and a critical dependence on the relative strengths of the confining potential is found. The characteristic frequency range for the oscillatory modes is of the order of the dust plasma frequency. The azimuthal and colatitudinal modes show opposite characteristics in the near and far interparticle distance regimes, respectively. The rods are shown to move, or switch to the relevant equilibrium, dependind on the confining parameters. This is an example of a phase change phenomenon which is analogous to that observed in liquid crystals. The ability to line up rods in different directions, by alternating the relative sizes of the confining potentials, is a powerful tool for applications. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


Cathode Current Density Distributions in High Power Impulse and Direct Current Magnetron Sputtering Modes

PLASMA PROCESSES AND POLYMERS, Issue S1 2009
Gregory Clarke
Abstract During the operation of high power impulse magnetron sputtering discharges, peak currents in excess of 1,000 A may be observed, leading to large instantaneous power levels. To investigate this method of operation, a series of planar probes have been constructed that allow for the spatial and temporal variations of current across the surface of a cathode to be assessed. These measurements provide information on the flux of charged particles to and from the cathode whilst it is being sputtered. Under operating conditions that led to a peak current of 140 A, measured current densities varied spatially from ,0.1 to 1.5 A,·,cm,2. By the use of a simple model, the measured current densities were used to predict the sputtering rate of the cathode, which allowed for the erosion profile and target lifetime to be estimated. The results suggest that, with regard to sputtering, operating in HiPIMS mode may be less energy efficient than operating in DC mode, but may achieve a higher target utilisation fraction. [source]


A new look at the quantum mechanics of the harmonic oscillator

ANNALEN DER PHYSIK, Issue 7-8 2007
H.A. Kastrup
Abstract In classical mechanics the harmonic oscillator (HO) provides the generic example for the use of angle and action variables and I > 0 which played a prominent role in the "old" Bohr-Sommerfeld quantum theory. However, already classically there is a problem which has essential implications for the quantum mechanics of the (,,I)-model for the HO: the transformation is only locally symplectic and singular for (q,p) = (0,0). Globally the phase space {(q,p)} has the topological structure of the plane ,2, whereas the phase space {(,,I)} corresponds globally to the punctured plane ,2 -(0,0) or to a simple cone with the tip deleted. From the properties of the symplectic transformations on that phase space one can derive the functions h0 = I, h1 = Icos , and h2 = - Isin , as the basic coordinates on {(,,I)}, where their Poisson brackets obey the Lie algebra of the symplectic group of the plane. This implies a qualitative difference as to the quantum theory of the phase space {(,,I)} compared to the usual one for {(q,p)}: In the quantum mechanics for the (,,I)-model of the HO the three hj correspond to the self-adjoint generators Kj, j = 0,1,2, of certain irreducible unitary representations of the symplectic group or one of its infinitely many covering groups, the representations being parametrized by a (Bargmann) index k > 0. This index k determines the ground state energy of the (,,I)-Hamiltonian . For an m -fold covering the lowest possible value for k is k = 1/m, which can be made arbitrarily small by choosing m accordingly! This is not in contradiction to the usual approach in terms of the operators Q and P which are now expressed as functions of the Kj, but keep their usual properties. The richer structure of the Kj quantum model of the HO is "erased" when passing to the simpler (Q,P)-model! This more refined approach to the quantum theory of the HO implies many experimental tests: Mulliken-type experiments for isotopic diatomic molecules, experiments with harmonic traps for atoms, ions and BE-condensates, with charged HOs in external electric fields and the (Landau) levels of charged particles in external magnetic fields, with the propagation of light in vacuum, passing through strong external electric or magnetic fields. Finally it may lead to a new theoretical estimate for the quantum vacuum energy of fields and its relation to the cosmological constant. [source]