Schekochihin, A. A.; Cowley, S. C.; Dorland, W.; Hammett, G. W.; Howes, G. G.; Quataert, E.; Tatsuno, T.
2009-04-23
This paper presents a theoretical framework for understanding plasma turbulence in astrophysical plasmas. It is motivated by observations of electromagnetic and density fluctuations in the solar wind, interstellar medium and galaxy clusters, as well as by models of particle heating in accretion disks. All of these plasmas and many others have turbulentmotions at weakly collisional and collisionless scales. The paper focuses on turbulence in a strong mean magnetic field. The key assumptions are that the turbulent fluctuations are small compared to the mean field, spatially anisotropic with respect to it and that their frequency is low compared to the ion cyclotron frequency. The turbulence is assumed to be forced at some system-specific outer scale. The energy injected at this scale has to be dissipated into heat, which ultimately cannot be accomplished without collisions. A kinetic cascade develops that brings the energy to collisional scales both in space and velocity. The nature of the kinetic cascade in various scale ranges depends on the physics of plasma fluctuations that exist there. There are four special scales that separate physically distinct regimes: the electron and ion gyroscales, the mean free path and the electron diffusion scale. In each of the scale ranges separated by these scales, the fully kinetic problem is systematically reduced to a more physically transparent and computationally tractable system of equations, which are derived in a rigorous way. In the "inertial range" above the ion gyroscale, the kinetic cascade separates into two parts: a cascade of Alfvenic fluctuations and a passive cascade of density and magnetic-fieldstrength fluctuations. The former are governed by the Reduced Magnetohydrodynamic (RMHD) equations at both the collisional and collisionless scales; the latter obey a linear kinetic equation along the (moving) field lines associated with the Alfvenic component (in the collisional limit, these compressive fluctuations
Generalized parallel heat transport equations in collisional to weakly collisional plasmas
NASA Astrophysics Data System (ADS)
Zawaideh, Emad; Kim, N. S.; Najmabadi, Farrokh
1988-11-01
A new set of two-fluid heat-transport equations for heat conduction in collisional to weakly collisional plasmas was derived on the basis of gyrokinetic equations in flux coordinates. In these equations, no restrictions on the anisotropy of the ion distribution function or the collisionality are imposed. In the highly collisional limit, these equations reduce to the classical heat conduction equation of Spitzer and Haerm (1953), while in the weakly collisional limit, they describe a saturated heat flux. Numerical examples comparing these equations with conventional heat transport equations are presented.
Weak turbulence theory for collisional plasmas
NASA Astrophysics Data System (ADS)
Yoon, P. H.; Ziebell, L. F.; Kontar, E. P.; Schlickeiser, R.
2016-03-01
Plasma is an ionized gas in which the collective behavior dominates over the individual particle interactions. For this reason, plasma is often treated as collisionless or collision-free. However, the discrete nature of the particles can be important, and often, the description of plasmas is incomplete without properly taking the discrete particle effects into account. The weak turbulence theory is a perturbative nonlinear theory, whose essential formalism was developed in the late 1950s and 1960s and continued on through the early 1980s. However, the standard material found in the literature does not treat the discrete particle effects and the associated fluctuations emitted spontaneously by thermal particles completely. Plasma particles emit electromagnetic fluctuations in all frequencies and wave vectors, but in the standard literature, the fluctuations are approximately treated by considering only those frequency-wave number regimes corresponding to the eigenmodes (or normal modes) satisfying the dispersion relations, while ignoring contributions from noneigenmodes. The present paper shows that the noneigenmode fluctuations modify the particle kinetic equation so that the generalized equation includes the Balescu-Lénard-Landau collision integral and also modify the wave kinetic equation to include not only the collisional damping term but also a term that depicts the bremsstrahlung emission of plasma normal modes.
Generalized parallel heat transport equations in collisional to weakly collisional plasmas
Zawaideh, E.; Kim, N.S.; Najmabadi, F.
1988-11-01
A new set of two-fluid heat transport equations that is valid from collisional to weakly collisional limits is derived. Starting from gyrokinetic equations in flux coordinates, a set of moment equations describing plasma energy transport along the field lines of a space- and time-dependent magnetic field is derived. No restrictions on the anisotropy of the ion distribution function or collisionality are imposed. In the highly collisional limit, these equations reduce to the classical heat conduction equation (e.g., Spitzer and Haerm or Braginskii), while in the weakly collisional limit, they describe a saturated heat flux (flux limited). Numerical examples comparing these equations with conventional heat transport equations show that in the limit where the ratio of the mean free path lambda to the scale length of the temperature gradient L/sub T/ approaches zero, there is no significant difference between the solutions of the new and conventional heat transport equations. As lambda/L/sub T/..-->..1, the conventional heat conduction equation contains a significantly larger error than (lambda/L/sub T/)/sup 2/. The error is found to be O(lambda/L)/sup 2/, where L is the smallest of the scale lengths of the gradient in the magnetic field, or the macroscopic plasma parameters (e.g., velocity scale length, temperature scale length, and density scale length). The accuracy of the flux-limited model depends significantly on the value of the flux limit parameter which, in general, is not known. The new set of equations shows that the flux-limited parameter is a function of the magnetic field and plasma parameter profiles.
NASA Astrophysics Data System (ADS)
Camporeale, E.; Pezzi, O.; Valentini, F.
2015-12-01
The longstanding problem of collisions in plasmas is a very fascinating and huge topic in plasma physics. The 'natural' operator that describes the Coulombian interactions between charged particles is the Landau (LAN) integral operator. The LAN operator is a nonlinear, integro-differential and Fokker-Planck type operator which satisfies the H theorem for the entropy growth. Due to its nonlinear nature and multi-dimensionality, any approach to the solution of the Landau integral is almost prohibitive. Therefore collisions are usually modeled by simplified collisional operators. Here collisional effects are modeled by i) the one-dimensional Lenard-Bernstein (LB) operator and ii) the three-dimensional Dougherty (DG) operator. In the first case i), by focusing on a 1D-1V phase space, we study recurrence effects in a weakly collisional plasma, being collisions modeled by the LB operator. By decomposing the linear Vlasov-Poisson system in the Fourier-Hermite space, the recurrence problem is investigated in the linear regime of the damping of a Langmuir wave and of the onset of the bump-on-tail instability. The analysis is then confirmed and extended to the nonlinear regime through a Eulerian collisional Vlasov-Poisson code. Despite being routinely used, an artificial collisionality is not in general a viable way of preventing recurrence in numerical simulations. Moreover, recursive phenomena affect both the linear exponential growth and the nonlinear saturation of a linear instability by producing a fake growth in the electric field, thus showing that, although the filamentation is usually associated with low amplitude fluctuations contexts, it can occur also in nonlinear phenomena. On the other hand ii), the effects of electron-electron collisions on the propagation of nonlinear electrostatic waves are shown by means of Eulerian simulations in a 1D-3V (one dimension in physical space, three dimensions in velocity space) phase space. The nonlinear regime of the symmetric
An Extended Magnetohydrodynamics Model for Relativistic Weakly Collisional Plasmas
NASA Astrophysics Data System (ADS)
Chandra, Mani; Gammie, Charles F.; Foucart, Francois; Quataert, Eliot
2015-09-01
Black holes that accrete far below the Eddington limit are believed to accrete through a geometrically thick, optically thin, rotationally supported plasma that we will refer to as a radiatively inefficient accretion flow (RIAF). RIAFs are typically collisionless in the sense that the Coulomb mean free path is large compared to {GM}/{c}2, and relativistically hot near the event horizon. In this paper we develop a phenomenological model for the plasma in RIAFs, motivated by the application to sources such as Sgr A* and M87. The model is derived using Israel–Stewart theory, which considers deviations up to second order from thermal equilibrium, but modified for a magnetized plasma. This leads to thermal conduction along magnetic field lines and a difference in pressure, parallel and perpendicular to the field lines (which is equivalent to anisotropic viscosity). In the non-relativistic limit, our model reduces to the widely used Braginskii theory of magnetized, weakly collisional plasmas. We compare our model to the existing literature on dissipative relativistic fluids, describe the linear theory of the plasma, and elucidate the physical meaning of the free parameters in the model. We also describe limits of the model when the conduction is saturated and when the viscosity implies a large pressure anisotropy. In future work, the formalism developed in this paper will be used in numerical models of RIAFs to assess the importance of non-ideal processes for the dynamics and radiative properties of slowly accreting black holes.
BUOYANCY INSTABILITIES IN A WEAKLY COLLISIONAL INTRACLUSTER MEDIUM
Kunz, Matthew W.; Stone, James M.; Bogdanovic, Tamara; Reynolds, Christopher S. E-mail: jstone@astro.princeton.edu E-mail: chris@astro.umd.edu
2012-08-01
The intracluster medium (ICM) of galaxy clusters is a weakly collisional plasma in which the transport of heat and momentum occurs primarily along magnetic-field lines. Anisotropic heat conduction allows convective instabilities to be driven by temperature gradients of either sign: the magnetothermal instability (MTI) in the outskirts of clusters and the heat-flux buoyancy-driven instability (HBI) in their cooling cores. We employ the Athena magnetohydrodynamic code to investigate the nonlinear evolution of these instabilities, self-consistently including the effects of anisotropic viscosity (i.e., Braginskii pressure anisotropy), anisotropic conduction, and radiative cooling. We find that, in all but the innermost regions of cool-core clusters, anisotropic viscosity significantly impairs the ability of the HBI to reorient magnetic-field lines orthogonal to the temperature gradient. Thus, while radio-mode feedback appears necessary in the central few Multiplication-Sign 10 kpc, heat conduction may be capable of offsetting radiative losses throughout most of a cool core over a significant fraction of the Hubble time. Magnetically aligned cold filaments are then able to form by local thermal instability. Viscous dissipation during cold filament formation produces accompanying hot filaments, which can be searched for in deep Chandra observations of cool-core clusters. In the case of MTI, anisotropic viscosity leads to a nonlinear state with a folded magnetic field structure in which field-line curvature and field strength are anti-correlated. These results demonstrate that, if the HBI and MTI are relevant for shaping the properties of the ICM, one must self-consistently include anisotropic viscosity in order to obtain even qualitatively correct results.
Buoyancy Instabilities in a Weakly Collisional Intracluster Medium
NASA Astrophysics Data System (ADS)
Kunz, Matthew W.; Bogdanović, Tamara; Reynolds, Christopher S.; Stone, James M.
2012-08-01
The intracluster medium (ICM) of galaxy clusters is a weakly collisional plasma in which the transport of heat and momentum occurs primarily along magnetic-field lines. Anisotropic heat conduction allows convective instabilities to be driven by temperature gradients of either sign: the magnetothermal instability (MTI) in the outskirts of clusters and the heat-flux buoyancy-driven instability (HBI) in their cooling cores. We employ the Athena magnetohydrodynamic code to investigate the nonlinear evolution of these instabilities, self-consistently including the effects of anisotropic viscosity (i.e., Braginskii pressure anisotropy), anisotropic conduction, and radiative cooling. We find that, in all but the innermost regions of cool-core clusters, anisotropic viscosity significantly impairs the ability of the HBI to reorient magnetic-field lines orthogonal to the temperature gradient. Thus, while radio-mode feedback appears necessary in the central few× 10 kpc, heat conduction may be capable of offsetting radiative losses throughout most of a cool core over a significant fraction of the Hubble time. Magnetically aligned cold filaments are then able to form by local thermal instability. Viscous dissipation during cold filament formation produces accompanying hot filaments, which can be searched for in deep Chandra observations of cool-core clusters. In the case of MTI, anisotropic viscosity leads to a nonlinear state with a folded magnetic field structure in which field-line curvature and field strength are anti-correlated. These results demonstrate that, if the HBI and MTI are relevant for shaping the properties of the ICM, one must self-consistently include anisotropic viscosity in order to obtain even qualitatively correct results.
Plasma-wall transition in weakly collisional plasmas
Manfredi, G.; Devaux, S.
2008-10-15
This paper reviews some theoretical and computational aspects of plasma-wall interactions, in particular the formation of sheaths. Some fundamental results are derived analytically using a simple fluid model, and are subsequently tested with kinetic simulations. The various regions composing the plasma-wall transition (Debye sheath, collisional and magnetic presheaths) are discussed in details.
Langmuir probe measurements of weakly collisional electropositive RF discharge plasmas
NASA Astrophysics Data System (ADS)
Bryant, Paul; Dyson, Anthony; Allen, John E.
2001-05-01
We report on Langmuir probe measurements of low-pressure (0.1-20 Pa) electropositive plasmas in an RF discharge at 13.56 MHz. From the probe I-V characteristic it is found that the electron density inferred from the ion current in the ion saturation region using radial motion (Allen, Boyd and Reynolds, ABR) theory can be up to one-half that obtained directly from the electron current at the plasma potential. The reduction in the ion current is attributed to orbital motion (OM) of the ions and also to a small number of ion-neutral collisions in the presheath. We show that if a sufficiently large probe is chosen so as to minimize the OM effects then the collisional theory developed by Shih and Levi (1971) can be used to give an appropriate correction factor over a narrow pressure range. The corrected electron density is found to agree with the knee current value to typically 10% for Ar, N2 and Kr plasmas.
Modeling of tokamak divertor plasma for weakly collisional parallel electron transport
NASA Astrophysics Data System (ADS)
Umansky, M. V.; Dimits, A. M.; Joseph, I.; Omotani, J. T.; Rognlien, T. D.
2015-08-01
The parallel electron heat transport in a weakly collisional regime can be represented in the framework of the Landau-fluid model (Hammett et al., 1990). Practical implementation of Landau-fluid transport has become possible due to the recent invention of an efficient non-spectral method for the non-local closure operators (Dimits et al., 2014). Here the implementation of a Landau-fluid based model for the parallel plasma transport is described, and the model is tested for different collisionality regimes against Fokker-Planck simulations. The new method appears to represent the weakly collisional electron transport more accurately than the conventional flux-limiter based models, on the other hand it is computationally efficient enough to be incorporated in comprehensive edge plasma simulations.
Ion drag force on a dust grain in a weakly ionized collisional plasma
Semenov, I. L.; Krivtsun, I. V.; Zagorodny, A. G.
2013-01-15
The problem of calculating the ion drag force acting on a dust grain immersed in a weakly ionized collisional plasma is studied using an approach based on the direct numerical solution of the Vlasov-Bhatnagar-Gross-Krook kinetic equations. A uniform subthermal flow of argon plasma past a spherical dust grain is considered. The numerical computations are performed for a wide range of plasma pressures. On the basis of the obtained results, the effect of ion-neutral collisions on the ion drag force is analyzed in a wide range of ion collisionality. In the collisionless limit, our results are shown to be in good agreement with the results obtained by the binary collision approach. As the ion collisionality increases, the ion drag force is found to decrease sharply and even become negative, i.e., directed oppositely to the plasma flow. A qualitative explanation of this effect is presented and a comparison of our results with those obtained using the drift diffusion approach is discussed. The velocity dependence of the ion drag force in the highly collisional regime is examined. The relationship between the ion and the neutral drag forces in the highly collisional limit is analyzed and the possibility of a superfluid-like behavior of dust grains is discussed.
Laser-pulse compression in a collisional plasma under weak-relativistic ponderomotive nonlinearity
NASA Astrophysics Data System (ADS)
Singh, Mamta; Gupta, D. N.
2016-05-01
We present theory and numerical analysis which demonstrate laser-pulse compression in a collisional plasma under the weak-relativistic ponderomotive nonlinearity. Plasma equilibrium density is modified due to the ohmic heating of electrons, the collisions, and the weak relativistic-ponderomotive force during the interaction of a laser pulse with plasmas. First, within one-dimensional analysis, the longitudinal self-compression mechanism is discussed. Three-dimensional analysis (spatiotemporal) of laser pulse propagation is also investigated by coupling the self-compression with the self-focusing. In the regime in which the laser becomes self-focused due to the weak relativistic-ponderomotive nonlinearity, we provide results for enhanced pulse compression. The results show that the matched interplay between self-focusing and self-compression can improve significantly the temporal profile of the compressed pulse. Enhanced pulse compression can be achieved by optimizing and selecting the parameters such as collision frequency, ion-temperature, and laser intensity.
A new fluid scheme for weakly collisional plasmas: 1. General theory
NASA Astrophysics Data System (ADS)
Chiuderi, C.; Pietrini, P.; Torricelli-Ciamponi, G.
2011-04-01
We present a new approach to the study of two-fluid hydrodynamics of weakly collisional plasma systems, such as those frequently encountered in the astrophysical context. Our starting point is the novel procedure developed in past years by Chen, Rao, and Spiegel (CRS) for the fluid description of semicollisional neutral monoatomic gases. The new system of fluid equations that include viscous and conductive effects has been successfully tested. However, the extension of such a procedure to plasmas is not a straightforward one. We have to deal with (at least) two components, with vastly different values of the masses, and the nature of collisions between charged particles is substantially different from the neutral particle case. We perform a preliminary careful examination of the basic requirements of the CRS method and identify the conditions under which an extension of such method is indeed possible. We then derive the system of fluid equations appropriate to the description of a weakly collisional two-component plasma in the new scheme and discuss the differences with respect to the more familiar Navier-Stokes approach. This paper is therefore of a general theoretical nature. However, we also point out that solar wind is a good testing ground for the newly derived system of fluid equations. This application will be the subject of a subsequent paper.
Rotation of weakly collisional plasmas in tokamaks, operated with Alfv{acute e}n waves
Tsypin, V.S.; Elfimov, A.G.; de Azevedo, C.A.; de Assis, A.S.
1996-12-01
The effect of the kinetic Alfv{acute e}n waves on weakly collisional plasma rotation in tokamaks has been studied for the plateau and banana regimes. The quasistationary rotation velocities and radial electric field have been found. The estimation of these quantities for the Phaedrus-T tokamak [S. Wukitch {ital et} {ital al}., Phys. Rev. Lett. {bold 77}, 294 (1996)] and for the Joint European Torus (JET) [A. Fasoli {ital et} {ital al}., Nucl. Fusion, {bold 36}, 258 (1996)] has been presented. It is shown that the kinetic Alfv{acute e}n waves, which are needed for current drive, change weakly the quasistationary rotation velocities and radial electric field, as found from the experimental data of these tokamaks. In conditions with increased rf power, the plasma rotation and radial electric field can essentially grow up. {copyright} {ital 1996 American Institute of Physics.}
THE STABILITY OF WEAKLY COLLISIONAL PLASMAS WITH THERMAL AND COMPOSITION GRADIENTS
Pessah, Martin E.; Chakraborty, Sagar E-mail: sagarc@iitk.ac.in
2013-02-10
Over the last decade, substantial efforts have been devoted to understanding the stability properties, transport phenomena, and long-term evolution of weakly collisional, magnetized plasmas which are stratified in temperature. The insights gained via these studies have led to a significant improvement of our understanding of the processes that determine the physical evolution and observational properties of the intracluster medium (ICM) permeating galaxy clusters. These studies have been carried out under the assumption that the ICM is a homogeneous medium. This, however, might not be a good approximation if heavy elements are able to sediment in the inner region of the galaxy cluster. Motivated by the need to obtain a more complete picture of the dynamical properties of the ICM, we analyze the stability of a weakly collisional, magnetized plane-parallel atmosphere which is stratified in both temperature and composition. This allows us to discuss for the first time the dynamics of weakly collisional environments where heat conduction, momentum transport, and ion-diffusion are anisotropic with respect to the direction of the magnetic field. We show that depending on the relative signs and magnitudes of the gradients in the temperature and the mean molecular weight, the plasma can be subject to a wide variety of unstable modes which include modifications to the magnetothermal instability (MTI), the heat-flux-driven buoyancy instability (HBI), and overstable gravity modes previously studied in homogeneous media. We also find that there are new modes which are driven by heat conduction and particle diffusion. We discuss the astrophysical implications of our findings for a representative galaxy cluster where helium has sedimented. Our findings suggest that the core insulation that results from the magnetic field configurations that arise as a natural consequence of the HBI, which would be MTI stable in a homogeneous medium, could be alleviated if the mean molecular
The stability of weakly ionized collisional dusty plasma in the presence of flow
Pandey, B. P.; Vranjes, J.; Vladimirov, S. V.
2012-09-15
The stability of weakly ionized and magnetized plasma in the presence of transverse (to the magnetic field) neutral wind is investigated in the present work. The collisional coupling of ambient background flow to the magnetized plasma gives rise to an electric field. In the presence of charged unmagnetized dust, electrostatic fluctuations in such plasma become unstable, with the growth rate dependent on the plasma thermal speed as well as on the dust charge and collision frequencies. This instability is similar to the Farley-Buneman instability. However, unlike Farley-Buneman, where the growth rate is directly dependent on the background flow, this dependence in the present case is only indirect. It is shown that this instability can grow over few seconds in the Earth's lower ionosphere and thus could play an important role in the structure formation.
Numerical study on the stability of weakly collisional plasma in E×B fields
Horký, M.
2015-02-15
Plasma stability in weakly collisional plasmas in the presence of E×B fields is studied with numerical simulations. Different types of ion-neutral collisions are considered in a fully magnetized regime. We study the influence of ion-neutral collisions and the role of collision types on the stability of plasma. It is found that the stability of plasma depends on the type of ion-neutral collisions, with the plasma being unstable for charge exchange collisions, and stable for the elastic scattering. The analysis focuses on the temporal evolution of the velocity phase space, RMS values of the potential fluctuations, and coherent structures in potential densities. For the unstable case, we observe growth and propagation of electrostatic waves. Simulations are performed with a three-dimensional electrostatic particle in cell code.
Vlasov simulations of plasma-wall interactions in a magnetized and weakly collisional plasma
Devaux, S.; Manfredi, G.
2006-08-15
A Vlasov code is used to model the transition region between an equilibrium plasma and an absorbing wall in the presence of a tilted magnetic field, for the case of a weakly collisional plasma ({lambda}{sub mfp}>>{rho}{sub i}, where {lambda}{sub mfp} is the ion-neutral mean-free path and {rho}{sub i} is the ion Larmor radius). The phase space structure of the plasma-wall transition is analyzed in detail and theoretical estimates of the magnetic presheath width are tested numerically. It is shown that the distribution near the wall is far from Maxwellian, so that temperature measurements should be interpreted with care. Particular attention is devoted to the angular distribution of ions impinging on the wall, which is an important parameter to determine the level of wall erosion and sputtering.
NASA Astrophysics Data System (ADS)
Mogavero, Federico; Schekochihin, Alexander A.
2014-06-01
In weakly collisional plasmas such as the intracluster medium (ICM), the viscous stress and the rate of change of the magnetic energy are proportional to the local pressure anisotropy, so subject to constraints imposed by the pressure-anisotropy-driven microinstabilities (mirror and firehose) and controlled by the local instantaneous plasma β. The dynamics of such plasmas can be dramatically different from a conventional magnetohydrodynamic fluid. The plasma is expected to stay locally marginal with respect to the instabilities, but how it does this remains an open question. Two models of magnetic field evolution are investigated. In the first, marginality is achieved via suppression of the rate of change of the field. In the second, the instabilities give rise to anomalous collisionality, reducing pressure anisotropy to marginal - at the same time decreasing viscosity and so increasing the turbulent rate of strain. Implications of these two models are studied in a simplified zero-dimensional setting. In the first model, the field grows explosively but on a time-scale that scales with the initial β, while in the second, dynamical field strength can be reached in one large-scale turbulence turnover time regardless of the initial seed. Both models produce very intermittent fields. Both also suffer from fairly strong constraints on their applicability: for typical cluster-core conditions, scale separation between the fluid motions (with account of suppressed viscous stress) and the miscoscale fluctuations break down at β ˜ 104-105. At larger β (weaker fields), a fully collisionless plasma dynamo theory is needed to justify field growth from a tiny primordial seed. However, the models discussed here are appropriate for studying the structure of the currently observed field as well as large-scale dynamics and thermodynamics of the magnetized ICM or similarly dilute astrophysical plasmas.
Validity of the Taylor hypothesis for linear kinetic waves in the weakly collisional solar wind
Howes, G. G.; Klein, K. G.; TenBarge, J. M.
2014-07-10
The interpretation of single-point spacecraft measurements of solar wind turbulence is complicated by the fact that the measurements are made in a frame of reference in relative motion with respect to the turbulent plasma. The Taylor hypothesis—that temporal fluctuations measured by a stationary probe in a rapidly flowing fluid are dominated by the advection of spatial structures in the fluid rest frame—is often assumed to simplify the analysis. But measurements of turbulence in upcoming missions, such as Solar Probe Plus, threaten to violate the Taylor hypothesis, either due to slow flow of the plasma with respect to the spacecraft or to the dispersive nature of the plasma fluctuations at small scales. Assuming that the frequency of the turbulent fluctuations is characterized by the frequency of the linear waves supported by the plasma, we evaluate the validity of the Taylor hypothesis for the linear kinetic wave modes in the weakly collisional solar wind. The analysis predicts that a dissipation range of solar wind turbulence supported by whistler waves is likely to violate the Taylor hypothesis, while one supported by kinetic Alfvén waves is not.
How LIF has helped to understand ion loss at the boundaries of weakly collisional plasmas
NASA Astrophysics Data System (ADS)
Hershkowitz, N.; Ko, E.; Wang, X.; Oksuza, L.; Halab, A.; Servern, G.
2003-10-01
Recent experiments in weakly collisional multi-dipole plasmas with one and two positive ion species have provided a much better understanding of ion motion in presheaths near the boundaries of such plasmas. Plasma potential was determined with emissive probes, ion density with Langmuir probes and diode laser LIF, ion drift velocity with Mach probes calibrated with LIF, and directly with LIF, and from the phase velocity of ion acoustic waves. LIF provided measurements of the ion velocity distribution functions and showed that ion-neutral charge exchange results in ion "heating" near boundaries. LIF showed that Ar ions in Ar-He plasma exit the plasma at the plasma/sheath boundary with a velocity greater than the Ar ion Bohm velocity. In single species plasma, the same diagnostic shows Ar average ion exit velocity equals the Bohm velocity. ^A Suleyman Demirel University, Physics Dept., Isparta Turkey ^B KACST, Space Research Institute, Riyadh, Saudi Arabia *Work supported by US DOE grant DE-FG02-97ER 54437
Grach, V. S. Garasev, M. A.
2015-07-15
We consider the interaction of a isolated conducting sphere with a collisional weakly ionized plasma in an external field. We assume that the plasma consists of two species of ions neglecting of electrons. We take into account charging of the sphere due to sedimentation of plasma ions on it, the field of the sphere charge and the space charge, as well as recombination and molecular diffusion. The nonstationary problem of interaction of the sphere with the surrounding plasma is solved numerically. The temporal dynamics of the sphere charge and plasma perturbations is analyzed, as well as the properties of the stationary state. It is shown that the duration of transient period is determined by the recombination time and by the reverse conductivity of ions. The temporal dynamics of the sphere charge and plasma perturbations is determined by the intensity of recombination processes relative to the influence of the space charge field and diffusion. The stationary absolute value of the sphere charge increases linearly with the external electric field, decreases with the relative intensity of recombination processes and increases in the presence of substantial diffusion. The scales of the perturbed region in the plasma are determined by the radius of the sphere, the external field, the effect of diffusion, and the relative intensity of recombination processes. In the limiting case of the absence of molecular diffusion and a strong external field, the properties of the stationary state coincide with those obtained earlier as a result of approximate solution.
Gupta, D. N.; Islam, M. R.; Jaroszynski, D. A.; Jang, D. G.; Suk, H.
2013-12-15
Self-focusing a laser beam in collisional plasma is investigated under the weak relativistic-ponderomotive nonlinearity. In this case, the plasma equilibrium density is modified and it causes generation of the nonlinearity due to the Ohmic heating of electrons, collisions, and the weak relativistic-ponderomotive force during the interaction of the laser beam with the plasma. Our theoretical and simulation results show that a significant nonlinearity in laser self-focusing can occur under the weak relativistic-ponderomotive regime for some appropriate simulation parameters.
NASA Astrophysics Data System (ADS)
Sonnino, Giorgio; Peeters, Philippe; Sonnino, Alberto; Nardone, Pasquale; Steinbrecher, György
2015-01-01
In previous works, we derived stationary density distribution functions (DDF) where the local equilibrium is determined by imposing the maximum entropy (MaxEnt) principle, under the scale invariance restrictions, and the minimum entropy production theorem. In this paper we demonstrate that it is possible to reobtain these DDF solely from the MaxEnt principle subject to suitable scale invariant restrictions in all the variables. For the sake of concreteness, we analyse the example of ohmic, fully ionized, tokamak-plasmas, in the weak-collisional transport regime. In this case we show that it is possible to reinterpret the stationary distribution function in terms of the Prigogine distribution function where the logarithm of the DDF is directly linked to the entropy production of the plasma. This leads to the suggestive idea that also the stationary neoclassical distribution functions, for magnetically confined plasmas in the collisional transport regimes, may be derived solely by the MaxEnt principle.
Growth and stabilization of drift-tearing modes in weakly collisional plasmas
NASA Astrophysics Data System (ADS)
Grasso\\ad{a}, D.; Ottaviani, M.; Porcelli\\ad{a}, F.
2002-09-01
In the limit where the electron drift-wave frequency exceeds the electron-ion collision frequency, drift-tearing modes are found to grow with a linear growth rate independent of resistivity and proportional to the product of the electron inertial skin depth and the ion sound Larmor radius. The stabilization of these modes in collisionless and semi-collisional regimes is investigated. The stabilization mechanism is related to the coupling and propagation of drift-acoustic perturbations away from the reconnecting mode-rational surface. Analytic and numerical solutions of the four-field reduced fluid model in the slab geometry approximation with constant electron temperature and negligible ion temperature are presented. The actual stability threshold can occur at values of the normalized tearing mode stability parameter Δ' as high as 102.\\pacs{52.35.P}} \\fnm{1}{Permanent address: Istituto Nazionale Fisica della Materia, Department of Energetics, Politecnico di Torino, Italy
NASA Technical Reports Server (NTRS)
Black, Carrie; Germaschewski, Kai; Bhattacharjee, Amitava; Ng, C. S.
2013-01-01
It has been demonstrated that in the presence of weak collisions, described by the Lenard-Bernstein collision operator, the Landau-damped solutions become true eigenmodes of the system and constitute a complete set. We present numerical results from an Eulerian Vlasov code that incorporates the Lenard-Bernstein collision operator. The effect of the collisions on the numerical recursion phenomenon seen in Vlasov codes is discussed. The code is benchmarked against exact linear eigenmode solutions in the presence of weak collisions, and a spectrum of Landau-damped solutions is determined within the limits of numerical resolution. Tests of the orthogonality and the completeness relation are presented.
Black, Carrie; Ng, C. S.
2013-01-15
It has been demonstrated that in the presence of weak collisions, described by the Lenard-Bernstein (LB) collision operator, the Landau-damped solutions become true eigenmodes of the system and constitute a complete set [C.-S. Ng et al., Phys. Rev. Lett. 83, 1974 (1999) and C. S. Ng et al., Phys. Rev. Lett. 96, 065002 (2004)]. We present numerical results from an Eulerian Vlasov code that incorporates the Lenard-Bernstein collision operator [A. Lenard and I. B. Bernstein, Phys. Rev. 112, 1456 (1958)]. The effect of collisions on the numerical recursion phenomenon seen in Vlasov codes is discussed. The code is benchmarked against exact linear eigenmode solutions in the presence of weak collisions, and a spectrum of Landau-damped solutions is determined within the limits of numerical resolution. Tests of the orthogonality and the completeness relation are presented.
Hamza, A.M.; Sudan, R.N.
1995-03-01
The equations governing the nonlinear evolution of density fluctuations in a low-pressure weakly ionized plasma driven unstable by the ExB or gradient-drift instability were derived by Sudan and Keskinen for addressing the electrostatic turbulence in the E and F regions of the Earth`s ionosphere. The authors have developed a subgrid model suitable for the numerical simulation of these equations which is closely related to renormalized diffusion caused by small-scale fluctuation spectrum. {open_quotes}Dynamical Renormalization Group{close_quotes} (RNG) methods are employed to obtain the renormalized diffusion. This procedure computes the long-wavelength, long-time behavior of density correlations generated by the evolution equation for the plasma stirred by a Gaussian random force characterized by a correlation function {proportional_to} k{sup m} where k is the wavenumber of the forcing function. The effect of small scales on the large-scale dynamics in the limit k{yields}0 and infinite Reynolds number can be expressed in the form of renormalized coefficients; in this case, renormalized diffusion. If one assumes the power spectra to be given by the Kolmogorov argument of cascading of energy through k space then one can derive a subgrid model based on the results of RNG. 27 refs.
Propagation of electromagnetic waves in a weak collisional and fully ionized dusty plasma
NASA Astrophysics Data System (ADS)
Jia, Jieshu; Yuan, Chengxun; Liu, Sha; Yue, Feng; Gao, Ruilin; Wang, Ying; Zhou, Zhong-Xiang; Wu, Jian; Li, Hui
2016-04-01
The propagation properties of electromagnetic (EM) waves in fully ionized dusty plasmas is the subject of this study. The dielectric relationships for EM waves propagating in a fully ionized dusty plasma was derived from the Boltzmann distribution law, taking into consideration the collision and charging effects of the dust grains. The propagation properties of the EM waves in a dusty plasma were numerically calculated and studied. The study results indicated that the dusty grains with an increased radius and charge were more likely to impede the penetration of EM waves. Dust grains with large radii and high charge cause the attenuation of the EM wave in the dusty plasma. The different density of the dust in the plasma appeared to have no obvious effect on the transmission of the EM waves. The propagation of the EM waves in a weakly ionized dusty plasma varies from that in a fully ionized dusty plasma. The results are helpful to analyze the effects of dust in dusty plasmas and also provide a theoretical basis for future studies.
NASA Astrophysics Data System (ADS)
Rosin, M. S.; Schekochihin, A. A.; Rincon, F.; Cowley, S. C.
2011-05-01
Weakly collisional magnetized cosmic plasmas have a dynamical tendency to develop pressure anisotropies with respect to the local direction of the magnetic field. These anisotropies trigger plasma instabilities at scales just above the ion Larmor radius ρi and much below the mean free path λmfp. They have growth rates of a fraction of the ion cyclotron frequency, which is much faster than either the global dynamics or even local turbulence. Despite their microscopic nature, these instabilities dramatically modify the transport properties and, therefore, the macroscopic dynamics of the plasma. The non-linear evolution of these instabilities is expected to drive pressure anisotropies towards marginal stability values, controlled by the plasma beta βi. Here this non-linear evolution is worked out in an ab initio kinetic calculation for the simplest analytically tractable example - the parallel (k⊥= 0) firehose instability in a high-beta plasma. An asymptotic theory is constructed, based on a particular physical ordering and leading to a closed non-linear equation for the firehose turbulence. In the non-linear regime, both the analytical theory and the numerical solution predict secular (∝t) growth of magnetic fluctuations. The fluctuations develop a k-3∥ spectrum, extending from scales somewhat larger than ρi to the maximum scale that grows secularly with time (∝t1/2); the relative pressure anisotropy (p⊥-p∥)/p∥ tends to the marginal value -2/βi. The marginal state is achieved via changes in the magnetic field, not particle scattering. When a parallel ion heat flux is present, the parallel firehose mutates into the new gyrothermal instability (GTI), which continues to exist up to firehose-stable values of pressure anisotropy, which can be positive and are limited by the magnitude of the ion heat flux. The non-linear evolution of the GTI also features secular growth of magnetic fluctuations, but the fluctuation spectrum is eventually dominated by
NASA Astrophysics Data System (ADS)
Lee, Hyo-Chang; Chung, Chin-Wook
2012-10-01
Spatial profiles of the plasma potential and electron energy distribution function (EEDF) were measured in inductively and capacitively coupled plasmas (ICP and CCP) under weakly collisional and nonlocal electron kinetic regimes [1]. The measured EEDF at the discharge center was a bi-Maxwellain distribution with low (T1) and high (T2) electron temperature groups at both the ICP and the CCP, while the EEDF at the radial boundary was closely Maxwellian distribution in the ICP due to cutting of the low energy electrons by relatively large ambipolar potential in this discharge regime. The ambipolar potential in the entire radial region was in the scale of Teff -1.5 Teff, where Teff is the effective electron temperature. At the boundary region with the ion mean free path scale, the ambipolar potential increased abruptly and was about Teff,edge/2, where the Teff,edge is the effective electron temperature at the boundary, which corresponds to the presheath scale. These results of the ICP, which are contrary to the ambipolar potential of the CCP in a nearly free-fall regime [2], are caused by relatively high T1 and a small portion of low energy electron group density to total electron density in the ICP under the weakly collisional and nonlocal electron kinetic regimes. [4pt] [1] H. C. Lee and C. W. Chung, Phys. Plasmas 19 033514 (2012).[0pt] [2] V. A. Godyak, V. P. Meytlis, and H. R. Strauss, IEEE Trans. Plasma Sci. 23 728 (1995).
Chaudhuri, M.; Khrapak, S. A.; Morfill, G. E.
2008-05-15
The ion drag force acting on a small absorbing grain has been calculated in highly collisional plasma with slowly drifting ions taking into account plasma production and loss processes in the vicinity of the grain. It is shown that the strength of the plasma production and loss mechanisms not only affects the magnitude of the ion drag force, but also determines the direction of the force. The parameter regimes for the ''positive'' and ''negative'' ion drag forces have been identified. In addition, the qualitative features of the electric potential distribution around the grain in isotropic conditions (in the absence of the ion drift) are investigated.
Lack of strength; Muscle weakness ... feel weak but have no real loss of strength. This is called subjective weakness. It may be ... flu. Or, you may have a loss of strength that can be noted on a physical exam. ...
Motie, Iman; Bokaeeyan, Mahyar
2015-02-15
A close analysis of dust charging process in the presence of radio frequency (RF) discharge on low pressure and fully ionized plasma for both weak and strong discharge's electric field is considered. When the electromagnetic waves pass throughout fully ionized plasma, the collision frequency of the plasma is derived. Moreover, the disturbed distribution function of plasma particles in the presence of the RF discharge is obtained. In this article, by using the Krook model, we separate the distribution function in two parts, the Maxwellian part and the perturbed part. The perturbed part of distribution can make an extra current, so-called the accretion rate of electron (or ion) current, towards a dust particle as a function of the average electron-ion collision frequency. It is proven that when the potential of dust grains increases, the accretion rate of electron current experiences an exponential reduction. Furthermore, the accretion rate of electron current for a strong electric field is relatively smaller than that for a weak electric field. The reasons are elaborated.
NASA Astrophysics Data System (ADS)
Quiroga, A.; Bermudez, A.; Kornblit, F.; Garcia, F.; Fang, H.; Caceres, J.; Peña, L. M.; Ramos, O.; Viaggio, A.; Santo, C.
2016-01-01
This report summarizes the results of a SIM comparison of magentic properties by means of the susceptometer method. It was carried out by seven SIM laboraories and BIPM. Five standards have been circulated: two OIML weights class E2, two of them with nominal value 1 kg and two of them with nominal value 2 g, and a steel disk. Most of the results were consistent with each other. This final report shows the degree of equivalence achieved by the participants Main text To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).
Energetically consistent collisional gyrokinetics
Burby, J. W.; Brizard, A. J.; Qin, H.
2015-10-01
We present a formulation of collisional gyrokinetic theory with exact conservation laws for energy and canonical toroidal momentum. Collisions are accounted for by a nonlinear gyrokinetic Landau operator. Gyroaveraging and linearization do not destroy the operator's conservation properties. Just as in ordinary kinetic theory, the conservation laws for collisional gyrokinetic theory are selected by the limiting collisionless gyrokinetic theory. (C) 2015 AIP Publishing LLC.
Energetically consistent collisional gyrokinetics
Burby, J. W.; Brizard, A. J.; Qin, H.
2015-10-15
We present a formulation of collisional gyrokinetic theory with exact conservation laws for energy and canonical toroidal momentum. Collisions are accounted for by a nonlinear gyrokinetic Landau operator. Gyroaveraging and linearization do not destroy the operator's conservation properties. Just as in ordinary kinetic theory, the conservation laws for collisional gyrokinetic theory are selected by the limiting collisionless gyrokinetic theory.
Energetically consistent collisional gyrokinetics
Burby, J. W.; Brizard, A. J.; Qin, H.
2015-10-30
Here, we present a formulation of collisional gyrokinetic theory with exact conservation laws for energy and canonical toroidal momentum. Collisions are accounted for by a nonlinear gyrokinetic Landau operator. Gyroaveraging and linearization do not destroy the operator's conservation properties. Just as in ordinary kinetic theory, the conservation laws for collisional gyrokinetic theory are selected by the limiting collisionless gyrokinetic theory. (C) 2015 AIP Publishing LLC.
Recombination and collisionally excited Balmer lines
NASA Astrophysics Data System (ADS)
Raga, A. C.; Castellanos-Ramírez, A.; Esquivel, A.; Rodríguez-González, A.; Velázquez, P. F.
2015-10-01
We present a model for the statistical equilibrium of the levels of H, considering recombinations to excited levels, collisional excitations up from the ground state and spontaneous radiative transitions. This problem has a simple "cascade matrix" solution, describing a cascade of downwards spontaneous transitions fed by both recombinations and collisional excitations. The resulting predicted Balmer line ratios show a transition between a low temperature and a high temperature regime (dominated by recombinations and by collisional excitations, respectively), both with only a weak line ratio vs. temperature dependence. This clear characteristic allows a direct observational identification of regions in which the Balmer lines are either recombination or collisionally excited transitions. We find that for a gas in coronal ionization equilibrium the Halpha and Hbeta lines are collisionally excited for all temperatures. In order to have recombination Halpha and Hbeta it is necessary to have higher ionization fractions of H than the ones obtained from coronal equilibrium (e.g., such as the ones found in a photoionized gas).
Collisional Relaxation of Fine Velocity Structures in Plasmas.
Pezzi, Oreste; Valentini, Francesco; Veltri, Pierluigi
2016-04-01
The existence of several characteristic times during the collisional relaxation of fine velocity structures is investigated by means of Eulerian numerical simulations of a spatially homogeneous force-free weakly collisional plasma. The effect of smoothing out velocity gradients on the evolution of global quantities, such as temperature and entropy, is discussed, suggesting that plasma collisionality can locally increase due to velocity space deformations of the particle velocity distribution function. These results support the idea that high-resolution measurements of the particle velocity distribution function are crucial for an accurate description of weakly collisional systems, such as the solar wind, in order to answer relevant scientific questions, related, for example, to particle heating and energization. PMID:27104713
Collisional Relaxation of Fine Velocity Structures in Plasmas
NASA Astrophysics Data System (ADS)
Pezzi, Oreste; Valentini, Francesco; Veltri, Pierluigi
2016-04-01
The existence of several characteristic times during the collisional relaxation of fine velocity structures is investigated by means of Eulerian numerical simulations of a spatially homogeneous force-free weakly collisional plasma. The effect of smoothing out velocity gradients on the evolution of global quantities, such as temperature and entropy, is discussed, suggesting that plasma collisionality can locally increase due to velocity space deformations of the particle velocity distribution function. These results support the idea that high-resolution measurements of the particle velocity distribution function are crucial for an accurate description of weakly collisional systems, such as the solar wind, in order to answer relevant scientific questions, related, for example, to particle heating and energization.
Collisional Cascades Revisited
NASA Astrophysics Data System (ADS)
Schlichting, Hilke; Pan, M.
2013-01-01
Collisional cascades are believed to be the primary mechanism operating in circumstellar dusty debris disks, and are thought to be important in the Kuiper and Asteroid belt. Collisional cascades transfer mass via destructive collisions from larger bodies to smaller ones. Their widespread occurrence and potential importance in understanding planet formation and planet-disk interactions have motivated detailed studies of collisional cascades. The standard theoretical treatment of collisional cascades derives a steady-state size distribution assuming a single constant velocity dispersion for all bodies regardless of size. We relax this assumption and solve self-consistently for the bodies' steady-state size and size-dependent velocity distributions. Specifically, we account for viscous stirring, dynamical friction, and collisional damping of the bodies' random velocities in addition to the mass conservation requirement typically applied to find the size distribution in a steady-state cascade. The resulting size distributions are significantly steeper than those derived without velocity evolution. For example, accounting self-consistently for the velocities can change the standard q = 3.5 power-law index of the Dohnanyi differential size spectrum to an index as large as q = 4. Similarly, for bodies held together by their own gravity, the corresponding power-law index range 2.88 < q < 3.14 of Pan & Sari (2005) can steepen to values as large as q = 3.26. These differences in the size distribution power law index are very important when estimating the total disk mass, including larger bodies, by extrapolating from the observed dust masses. Our velocity results allow quantitative predictions of the bodies' scale heights as a function of size. Together with our predictions, observations of the scale heights for different-sized bodies in, for example, extrasolar debris disks may constrain the total mass in large bodies stirring the cascade as well as the colliding bodies
Buoyancy instabilities in degenerate, collisional, magnetized plasmas
NASA Astrophysics Data System (ADS)
Chang, Philip; Quataert, Eliot
2010-03-01
In low-collisionality plasmas, anisotropic heat conduction due to a magnetic field leads to buoyancy instabilities for any non-zero temperature gradient. We study analogous instabilities in degenerate collisional plasmas, i.e. when the electron collision frequency is large compared to the electron cyclotron frequency. Although heat conduction is nearly isotropic in this limit, the small residual anisotropy ensures that collisional degenerate plasmas are also convectively unstable independent of the sign of the temperature gradient. We show that the range of wavelengths that are unstable is independent of the magnetic field strength, while the growth time increases with decreasing magnetic field strength. We discuss the application of these collisional buoyancy instabilities to white dwarfs and neutron stars. Magnetic tension and the low specific heat of a degenerate plasma significantly limit their effectiveness; the most promising venues for growth are in the liquid oceans of young, weakly magnetized neutron stars (B <~ 109 G) and in the cores of young, high magnetic field white dwarfs (B ~ 109 G).
Fine velocity structures collisional dissipation in plasmas
NASA Astrophysics Data System (ADS)
Pezzi, Oreste; Valentini, Francesco; Veltri, Pierluigi
2016-04-01
In a weakly collisional plasma, such as the solar wind, collisions are usually considered far too weak to produce any significant effect on the plasma dynamics [1]. However, the estimation of collisionality is often based on the restrictive assumption that the particle velocity distribution function (VDF) shape is close to Maxwellian [2]. On the other hand, in situ spacecraft measurements in the solar wind [3], as well as kinetic numerical experiments [4], indicate that marked non-Maxwellian features develop in the three-dimensional VDFs, (temperature anisotropies, generation of particle beams, ring-like modulations etc.) as a result of the kinetic turbulent cascade of energy towards short spatial scales. Therefore, since collisional effects are proportional to the velocity gradients of the VDF, the collisionless hypothesis may fail locally in velocity space. Here, the existence of several characteristic times during the collisional relaxation of fine velocity structures is investigated by means of Eulerian numerical simulations of a spatially homogeneous force-free weakly collisional plasma. The effect of smoothing out velocity gradients on the evolution of global quantities, such as temperature and entropy, is discussed, suggesting that plasma collisionality can increase locally due to the velocity space deformation of the particle velocity distribution. In particular, by means of Eulerian simulations of collisional relaxation of a spatially homogeneous force-free plasma, in which collisions among particles of the same species are modeled through the complete Landau operator, we show that the system entropy growth occurs over several time scales, inversely proportional to the steepness of the velocity gradients in the VDF. We report clear evidences that fine velocity structures are dissipated by collisions in a time much shorter than global non-Maxwellian features, like, for example, temperature anisotropies. Moreover we indicate that, if small-scale structures
Collisional damping of the geodesic acoustic mode with toroidal rotation. I. Viscous damping
NASA Astrophysics Data System (ADS)
Gong, Xueyu; Xie, Baoyi; Guo, Wenfeng; Chen, You; Yu, Jiangmei; Yu, Jun
2016-03-01
With the dispersion relation derived for the geodesic acoustic mode in toroidally rotating tokamak plasmas using the fluid model, the effect of the toroidal rotation on the collisional viscous damping of the geodesic acoustic mode is investigated. It is found that the collisional viscous damping of the geodesic acoustic mode has weak increase with respect to the toroidal Mach number.
Collisional lifetimes of meteoroids
NASA Astrophysics Data System (ADS)
Soja, R. H.; Schwarzkopf, G. J.; Sommer, M.; Vaubaillon, J.; Albin, T.; Rodmann, J.; Grün, E.; Srama, R.
2016-01-01
Collisions of meteoroids with interplanetary dust grain fragments particles, dispersing larger particles amongst lower mass intervals. Here we use the method of Grün et al. (1985) and the IMEM interplanetary dust model to calculate the collisional lifetimes for different orbits, and for particles in different meteor showers. The timescales are usually long - of order 10^4 years for 1mm grains on Jupiter-family and Hally-type comet orbits. However, near-sun orbits particles suffer more frequent collisions and therefore have much shorter lifetimes. We discuss factors that affect the accuracy of these calculations.
Collisional versus Collisionless Dark Matter.
Moore; Gelato; Jenkins; Pearce; Quilis
2000-05-20
We compare the structure and substructure of dark matter halos in model universes dominated by collisional, strongly self-interacting dark matter (SIDM) and collisionless, weakly interacting dark matter (CDM). While SIDM virialized halos are more nearly spherical than CDM halos, they can be rotationally flattened by as much as 20% in their inner regions. Substructure halos suffer ram-pressure truncation and drag, which are more rapid and severe than their gravitational counterparts tidal stripping and dynamical friction. Lensing constraints on the size of galactic halos in clusters are a factor of 2 smaller than predicted by gravitational stripping, and the recent detection of tidal streams of stars escaping from the satellite galaxy Carina suggests that its tidal radius is close to its optical radius of a few hundred parsecs-an order of magnitude smaller than predicted by CDM models but consistent with SIDM models. The orbits of SIDM satellites suffer significant velocity bias, sigmaSIDM&solm0;sigmaCDM=0.85, and are more circular than CDM satellites, betaSIDM approximately 0.5, in agreement with the inferred orbits of the Galaxy's satellites. In the limit of a short mean free path, SIDM halos have singular isothermal density profiles; thus, in its simplest incarnation SIDM, is inconsistent with galactic rotation curves. PMID:10828999
Transition from Collisionless to Collisional MRI
Prateek Sharma; Gregory W. Hammett; Eliot Quataert
2003-07-24
Recent calculations by Quataert et al. (2002) found that the growth rates of the magnetorotational instability (MRI) in a collisionless plasma can differ significantly from those calculated using MHD. This can be important in hot accretion flows around compact objects. In this paper, we study the transition from the collisionless kinetic regime to the collisional MHD regime, mapping out the dependence of the MRI growth rate on collisionality. A kinetic closure scheme for a magnetized plasma is used that includes the effect of collisions via a BGK operator. The transition to MHD occurs as the mean free path becomes short compared to the parallel wavelength 2*/k(sub)||. In the weak magnetic field regime where the Alfven and MRI frequencies w are small compared to the sound wave frequency k(sub)||c(sub)0, the dynamics are still effectively collisionless even if omega << v, so long as the collision frequency v << k(sub)||c(sub)0; for an accretion flow this requires n less than or approximately equal to *(square root of b). The low collisionality regime not only modifies the MRI growth rate, but also introduces collisionless Landau or Barnes damping of long wavelength modes, which may be important for the nonlinear saturation of the MRI.
Radiation-induced collisional pumping of molecules containing few atoms
Vasil'ev, G.K.; Chernyshev, Y.A.; Makarov, E.F.; Yakushev, V.G.
1986-01-01
The authors analyze the radiation-induced collisional pumping of few-atom molecules by laser emission taking into account both collisional and noncollisional processes of vibrational energy transfer in a molecule. For typical values of the parameters the vibrational energy of the molecules was found to depend on the laser emission intensity; regions of weak absorption, optimum absorption, and saturation appear as the pumping rate rises. Qualitative general conclusions are reached concerning the optimum conditions for the realization, in a medium absorbing laser emission, of either nonequilibrium dissociation or a chemical reaction involving vibrationally excited molecules.
Magnetismo Molecular (Molecular Magentism)
Reis, Mario S; Moreira Dos Santos, Antonio F
2010-07-01
The new synthesis processes in chemistry open a new world of research, new and surprising materials never before found in nature can now be synthesized and, as a wonderful result, observed a series of physical phenomena never before imagined. Among these are many new materials the molecular magnets, the subject of this book and magnetic properties that are often reflections of the quantum behavior of these materials. Aside from the wonderful experience of exploring something new, the theoretical models that describe the behavior these magnetic materials are, in most cases, soluble analytically, which allows us to know in detail the physical mechanisms governing these materials. Still, the academic interest in parallel this subject, these materials have a number of properties that are promising to be used in technological devices, such as in computers quantum magnetic recording, magnetocaloric effect, spintronics and many other devices. This volume will journey through the world of molecular magnets, from the structural description of these materials to state of the art research.
FLYCHK Collisional-Radiative Code
National Institute of Standards and Technology Data Gateway
SRD 160 FLYCHK Collisional-Radiative Code (Web, free access) FLYCHK provides a capability to generate atomic level populations and charge state distributions for low-Z to mid-Z elements under NLTE conditions.
COLLISIONALLY BORN FAMILY ABOUT 87 SYLVIA
Vokrouhlicky, David; Nesvorny, David; Bottke, William F.; Morbidelli, Alessandro E-mail: davidn@boulder.swri.ed E-mail: morby@obs-nice.f
2010-06-15
There are currently more than 1000 multi-opposition objects known in the Cybele population, adjacent and exterior to the asteroid main belt, allowing a more detailed analysis than was previously possible. Searching for collisionally born clusters in this population, we find only one statistically robust case: a family of objects about (87) Sylvia. We use a numerical model to simulate the Sylvia family long-term evolution due to gravitational attraction from planets and thermal (Yarkovsky) effects and to explain its perturbed structure in the orbital element space. This allows us to conclude that the Sylvia family must be at least several hundreds of million years old, in agreement with evolutionary timescales of Sylvia's satellite system. We find it interesting that other large Cybele-zone asteroids with known satellites-(107) Camilla and (121) Hermione-do not have detectable families of collisional fragments about them (this is because we assume that binaries with large primary and small secondary components are necessarily impact generated). Our numerical simulations of synthetic clusters about these asteroids show they would suffer a substantial dynamical depletion by a combined effect of diffusion in numerous weak mean-motion resonances and Yarkovsky forces provided their age is close to {approx}4 billion years. However, we also believe that a complete effacement of these two families requires an additional component, very likely due to resonance sweeping or other perturbing effects associated with the late Jupiter's inward migration. We thus propose that both Camilla and Hermione originally had their collisional families, as in the Sylvia case, but they lost them in an evolution that lasted a billion years. Their satellites are the only witnesses of these effaced families.
Pusztai, I.; Fueloep, T.; Candy, J.; Hastie, R. J.
2009-07-15
The stability of ion temperature gradient (ITG) modes and the quasilinear fluxes driven by them are analyzed in weakly collisional tokamak plasmas using a semianalytical model based on an approximate solution of the gyrokinetic equation, where collisions are modeled by a Lorentz operator. Although the frequencies and growth rates of ITG modes far from threshold are only very weakly sensitive to the collisionality, the a/L{sub Ti} threshold for stability is affected significantly by electron-ion collisions. The decrease in collisionality destabilizes the ITG mode driving an inward particle flux, which leads to the steepening of the density profile. Closed analytical expressions for the electron and ion density and temperature responses have been derived without expansion in the smallness of the magnetic drift frequencies. The results have been compared with gyrokinetic simulations with GYRO and illustrated by showing the scalings of the eigenvalues and quasilinear fluxes with collisionality, temperature scale length, and magnetic shear.
Collisional decoherence reexamined
Hornberger, Klaus; Sipe, John E.
2003-07-01
We rederive the quantum master equation for the decoherence of a massive Brownian particle due to collisions with lighter particles from a thermal environment. Our careful treatment avoids the occurrence of squares of Dirac {delta} functions. It leads to a decoherence rate that is smaller by a factor of 2{pi} compared to previous findings. This result, which is in agreement with recent experiments, is confirmed both by a physical analysis of the problem and by a perturbative calculation in the weak-coupling limit.
Collisional Evolution of Terrestrial Planets
NASA Astrophysics Data System (ADS)
Agnor, C.; Asphaug, E.
2004-12-01
The terrestrial planets are generally thought to have formed via the collisional accumulation of rocky bodies. The characteristics of the planets produced by this process are, to a large degree, determined by their collisional evolution, and their associated differentiation and thermal evolution. Studies of planet formation and planetary collisional evolution have typically been conducted separately. Most works of late-stage planet formation use perfectly inelastic mergers to model collisions (e.g. Agnor, Canup & Levison 1999, Chambers 2001, Levison & Agnor 2003), with certain recognized inadequacies, notably prohibitively large spin angular momentum acquired as a planet grows. To date, studies of the collisional evolution of terrestrial planets has focused on determining the efficacy of single impacts to account for particular planetary characteristics and the formation of satellites (e.g. Benz et al. 1988, Canup & Asphaug 2001, Canup 2004). It has been recognized for some time (Wetherill 1985) that the final characteristics (e.g. spin state, bulk composition, isotopic age) of an accreting planet are determined not by the last or single largest collision but by all of the major collisional encounters in a planet's history (Agnor, Canup & Levison 1999). As demonstrated by our impact models, each major impact changes the silicate to metal ratio, the thermal state, and the spin state, and sets the stage for the subsequent collision. We are studying collisional dynamics and outcomes common to the late stage of terrestrial planet formation. We use smooth particle hydrodynamics model collisions in an effort to identify the range of impact dynamics that allow for accretion (i.e. mass growth instead of mass loss). In our initial study we found that for dynamical environments typical of most late stage accretion models, about half of all collisions between equal mass planetary embryos do not result in accumulation into a larger embryo (Agnor & Asphaug 2004). We will
Trapped-Particle-Mediated Collisional Damping of Nonaxisymmetric Plasma Waves
Kabantsev, A. A.; Driscoll, C. F.
2006-09-01
Weak axial variations in magnetic or electric confinement fields in pure electron plasmas cause slow electrons to be trapped locally, and collisional diffusion across the trapping separatrix then causes surprisingly large trapped-particle-mediated (TPM) damping and transport effects. Here we characterize TPM damping of m{sub {theta}}{ne}0, m{sub z}={+-}1 Trivelpiece-Gould plasma modes in large-amplitude long-lived Bernstein-Greene-Kruskal states. The TPM damping gives {gamma}{sub BGK}/{omega}{approx}10{sup -4} and seems to dominate in regimes of weak interparticle collisions.
Collisional Evolution of Terrestrial Planets
NASA Astrophysics Data System (ADS)
Agnor, C. B.; Asphaug, E. I.
2003-05-01
The currently accepted model for the formation of terrestrial planets describes their growth as the collisional accumulation of rocky or sometimes molten planetesimals. The characteristics of the planets produced by this process are, to a large degree, determined by their collisional evolution, and their associated differentiation and thermal evolution. Studies of planet formation and planetary collisional evolution have typically been conducted separately. Most works of late-stage planet formation use perfectly inelastic mergers to model collisions (e.g. Agnor, Canup & Levison 1999, Chambers 2001, Levison & Agnor 2003), with certain recognized inadequacies, notably rotationally unstable spin rates acquired as a planet grows. Do planets really accrete in this manner? On the other hand, most of the work studying the collisional evolution of terrestrial planets has focused on determining the efficacy of single impacts to account for particular planetary characteristics and the formation of satellites (e.g. Benz et al. 1988, Canup & Asphaug 2001). It has been recognized for some time (Wetherill 1985) that the final characteristics (e.g. spin state, bulk composition, isotopic age) of an accreting planet are determined not by the last or single largest collision (Agnor, Canup & Levison 1999) but by all of the major collisional encounters in a planet's history. As demonstrated in our impact models, each major impact changes the silicate to metal ratio, the thermal state, and the spin state, and sets the stage for subsequent collisions. We have commenced a detailed study of collision dynamics and outcomes common to the late stage of terrestrial planet accretion. We are modeling collisions using smooth particle hydrodynamics to examine, primarily, the regimes of impact that truly allow for accretion (i.e. mass accumulation instead of mass loss). We are also studying the cumulative affect of giant impacts on major planetary characteristics (such as composition and spin) and
Collisionally processed rocks on mars
Horz; Cintala; Rochelle; Kirk
1999-09-24
The Pathfinder landing site on Mars has boulders that may be cratered (Stimpy), split (Chimp), fragmented (Book End and Flat Top), or otherwise partly destroyed (Yogi and Frog) by collisional processes. Atmospheric-entry calculations show that centimeter-sized projectiles survive passage through the martian atmosphere and encounter the surface of Mars at velocities of a few kilometers per second. Craters less than 1 meter in diameter may contribute to the evolution of the martian surface and its soils. PMID:10497123
Collisional decoherence of polar molecules
NASA Astrophysics Data System (ADS)
Walter, Kai; Stickler, Benjamin A.; Hornberger, Klaus
2016-06-01
The quantum state of motion of a large and rotating polar molecule can lose coherence through the collisions with gas atoms. We show how the associated quantum master equation for the center of mass can be expressed in terms of the orientationally averaged differential and total scattering cross sections, for which we provide approximate analytic expressions. The master equation is then utilized to quantify collisional decoherence in a interference experiment with polar molecules.
Petrologic evidence for collisional heating of chondritic asteroids
NASA Technical Reports Server (NTRS)
Rubin, Alan E.
1995-01-01
The identification of the mechanism(s) responsible for heating asteroids is among the major problems in planetary science. Because of difficulties with models of electromagnetic induction and the decay of short-lived radionuclides, it is worthwhile to evaluate the evidence for collisional heating. New evidence for localized impact heating comes from the high proportion of relict type-6 material among impact-melt-bearing ordinary chondrites (OC). This relict material was probably metamorphosed by residual heat within large craters. Olivine aggregates composed of faceted crystals with 120 deg triple junctions occur within the melted regions of the Chico and Rose City OC melt rocks; the olivine aggregates formed from shocked, mosaicized olivine grains that underwent contact metamorphism. Large-scale collisional heating is supoorted by the correlation in OC between petrologic type and shock stage; no other heating mechanism can readily account for this correlation. The occurrence of impact-melt-rock clasts in OC that have been metamorphosed along with their whole rocks indicates that some impact events preceded or accompanied thermal metamorphism. Such impacts events, occurring during or shortly after accretion, are probably responsible for substantially melting approximately 0.5% of OC. These events must have heated a larger percentage of OC to subsolidus temperatures sufficient to have caused significant metamorphism. If collisional heating is viable, then OC parent asteroids must have been large; large OC asteroids in the main belt may include those of the S(IV) spectral subtype. Collisional heating is inconsistent with layered ('onion-shell') structures in OC asteroids (wherein the degree of metamorphism increases with depth), but the evidence for such structures is weak. It seems likely that collisional heating played an important role in metamorphosing chondritic asteroids.
Collisional current drive in two interpenetrating plasma jets
Ryutov, D. D.; Kugland, N. L.; Park, H.-S.; Pollaine, S. M.; Remington, B. A.; Ross, J. S.
2011-10-15
The magnetic field generation in two interpenetrating, weakly collisional plasma streams produced by intense lasers is considered. The generation mechanism is very similar to the neutral beam injection current drive in toroidal fusion devices, with the differences related to the absence of the initial magnetic field, short interaction time, and different geometry. Spatial and temporal characteristics of the magnetic field produced in two counterstreaming jets are evaluated; it is shown that the magnetic field of order of 1 T can be generated for modest jet parameters. Conditions under which this mechanism dominates that of the ''Biermann battery'' are discussed. Other settings where the mechanism of the collisional current drive can be important for the generation of seed magnetic fields include astrophysics and interiors of hohlraums.
Collisional plateaus. [in earth and Venus lithospheres
NASA Technical Reports Server (NTRS)
Morgan, P.; Burke, K.
1985-01-01
Aspects of the geology of collisional plateaus formed by the thickening of continental crust are briefly reviewed. The history of studies of collisional plateaus is summarized, and igneous activity in collisional plateaus is discussed. Isostatic considerations pertaining to these plateaus are addressed, developing models of isostatic support of topography which illustrate the importance of compressional tectonics in the creation of high altitude plateaus. Possible analogous environments on Venus are considered. Finally, the paradox of extension associated with compression in the plateaus is discussed.
QCD Collisional Energy Loss Reexamined
NASA Astrophysics Data System (ADS)
Peshier, A.
2006-11-01
It is shown that at a large temperature and E→∞ the QCD collisional energy loss reads dE/dx˜α(mD2)T2. Compared to previous approaches, which led to dEB/dx˜α2T2ln(ET/mD2) similar to the Bethe-Bloch formula in QED, we take into account the running of the strong coupling. As one significant consequence, due to asymptotic freedom, dE/dx becomes E independent for large parton energies. Some implications with regard to heavy ion collisions are pointed out.
QCD collisional energy loss reexamined.
Peshier, A
2006-11-24
It is shown that at a large temperature and E --> infinity the QCD collisional energy loss reads dE/dx approximately alpha(m(D)2)T2. Compared to previous approaches, which led to dE(B)/dx approximately alpha2 T2 ln(ET/m(D)2) similar to the Bethe-Bloch formula in QED, we take into account the running of the strong coupling. As one significant consequence, due to asymptotic freedom, dE/dx becomes E independent for large parton energies. Some implications with regard to heavy ion collisions are pointed out. PMID:17155739
Chen, Y.; White, R.B.
1997-12-31
A general method for including various collisional effects, such as the drag and diffusion of test particles due to background plasmas, the effect of particle source and sink, and the like-particle Coulomb collisions, is presented. The marker density g is generally unknown along the particle trajectory, and its evaluation depends on the way particles are initially loaded and new particles are injected into the simulation. The method is demonstrated for the problem of the nonlinear evolution of the Toroidicity Induced Alfven eigenmode, driven by energetic {alpha} particles. The saturation amplitude is found to scale with the collision rate in a way as predicted by theory.
Problems of collisional stellar dynamics
NASA Astrophysics Data System (ADS)
Heggie, D. C.
2011-03-01
The discovery of dynamical friction was Chandrasekhar's best known contribution to the theory of stellar dynamics, but his work ranged from the few-body problem to the limit of large N (in effect, galaxies). Much of this work was summarised in the text "Principles of Stellar Dynamics" tep{C1942,C1960}, which ranges from a precise calculation of the time of relaxation, through a long analysis of galaxy models, to the behaviour of star clusters in tidal fields. The later edition also includes the work on dynamical friction and related issues. In this review we focus on progress in the collisional aspects of these problems, i.e. those where few-body interactions play a dominant role, and so we omit further discussion of galaxy dynamics. But we try to link Chandrasekhar's fundamental discoveries in collisional problems with the progress that has been made in the 50 years since the publication of the enlarged edition. There is one other such problem to which Chandrasekhar contributed, though the paper in question tep{C1944} was not reprinted in the book. See Section ref{sec:binaries}. For more on the collisionless problems studied by Chandrasekhar, see the paper by N. Wyn Evans (2011) in the present volume.
THE COLLISIONAL EVOLUTION OF DEBRIS DISKS
Gaspar, Andras; Rieke, George H.; Balog, Zoltan E-mail: grieke@as.arizona.edu
2013-05-01
We explore the collisional decay of disk mass and infrared emission in debris disks. With models, we show that the rate of the decay varies throughout the evolution of the disks, increasing its rate up to a certain point, which is followed by a leveling off to a slower value. The total disk mass falls off {proportional_to}t {sup -0.35} at its fastest point (where t is time) for our reference model, while the dust mass and its proxy-the infrared excess emission-fades significantly faster ({proportional_to}t {sup -0.8}). These later level off to a decay rate of M{sub tot}(t){proportional_to}t {sup -0.08} and M{sub dust}(t) or L{sub ir}(t){proportional_to}t {sup -0.6}. This is slower than the {proportional_to}t {sup -1} decay given for all three system parameters by traditional analytic models. We also compile an extensive catalog of Spitzer and Herschel 24, 70, and 100 {mu}m observations. Assuming a log-normal distribution of initial disk masses, we generate model population decay curves for the fraction of stars harboring debris disks detected at 24 {mu}m. We also model the distribution of measured excesses at the far-IR wavelengths (70-100 {mu}m) at certain age regimes. We show general agreement at 24 {mu}m between the decay of our numerical collisional population synthesis model and observations up to a Gyr. We associate offsets above a Gyr to stochastic events in a few select systems. We cannot fit the decay in the far-infrared convincingly with grain strength properties appropriate for silicates, but those of water ice give fits more consistent with the observations (other relatively weak grain materials would presumably also be successful). The oldest disks have a higher incidence of large excesses than predicted by the model; again, a plausible explanation is very late phases of high dynamical activity around a small number of stars. Finally, we constrain the variables of our numerical model by comparing the evolutionary trends generated from the exploration
Neoclassical Transport Including Collisional Nonlinearity
Candy, J.; Belli, E. A.
2011-06-10
In the standard {delta}f theory of neoclassical transport, the zeroth-order (Maxwellian) solution is obtained analytically via the solution of a nonlinear equation. The first-order correction {delta}f is subsequently computed as the solution of a linear, inhomogeneous equation that includes the linearized Fokker-Planck collision operator. This equation admits analytic solutions only in extreme asymptotic limits (banana, plateau, Pfirsch-Schlueter), and so must be solved numerically for realistic plasma parameters. Recently, numerical codes have appeared which attempt to compute the total distribution f more accurately than in the standard ordering by retaining some nonlinear terms related to finite-orbit width, while simultaneously reusing some form of the linearized collision operator. In this work we show that higher-order corrections to the distribution function may be unphysical if collisional nonlinearities are ignored.
Collisional Aggregation Due to Turbulence
NASA Astrophysics Data System (ADS)
Pumir, Alain; Wilkinson, Michael
2016-03-01
Collisions between particles suspended in a fluid play an important role in many physical processes. As an example, collisions of microscopic water droplets in clouds are a necessary step in the production of macroscopic raindrops. Collisions of dust grains are also conjectured to be important for planet formation in the gas surrounding young stars and to play a role in the dynamics of sand storms. In these processes, collisions are favored by fast turbulent motions. Here we review recent advances in the understanding of collisional aggregation due to turbulence. We discuss the role of fractal clustering of particles and caustic singularities of their velocities. We also discuss limitations of the Smoluchowski equation for modeling such processes. These advances lead to a semiquantitative understanding on the influence of turbulence on collision rates and point to deficiencies in the current understanding of rainfall and planet formation.
Theory of runaway collisional transport
Tessarotto, M. ); White, R.B. )
1993-11-01
The purpose of this paper is to formulate the transport problem for a multispecies rotating toroidal magnetoplasma in the so-called runaway regime, which is defined by an appropriate ordering of relevant characteristic frequencies, in particular, the Larmor frequency, the characteristic acceleration frequency due to the applied electric field and the effective collision frequency, all evaluated at some characteristic speed [ital v][sub 0]. A suitable form of the gyrokinetic equation is obtained to describe the time-dependent, multispecies plasma response to an applied electric field, in toroidal geometry and for a strongly rotating, quiescent, and collisional plasma. Its moment equations are proven to imply the reduction of the energy equation to Joule's law, as well as consequences on the form of Ohm's law and of the Grad--Shafranov equation. To construct an approximate solution of the gyrokinetic equation and to evaluate all relevant fluxes, appearing in the moment equations, a general variational solution method is developed.
Magnetosonic shock wave in collisional pair-ion plasma
NASA Astrophysics Data System (ADS)
Adak, Ashish; Sikdar, Arnab; Ghosh, Samiran; Khan, Manoranjan
2016-06-01
Nonlinear propagation of magnetosonic shock wave has been studied in collisional magnetized pair-ion plasma. The masses of both ions are same but the temperatures are slightly different. Two fluid model has been taken to describe the model. Two different modes of the magnetosonic wave have been obtained. The dynamics of the nonlinear magnetosonic wave is governed by the Korteweg-de Vries Burgers' equation. It has been shown that the ion-ion collision is the source of dissipation that causes the Burgers' term which is responsible for the shock structures in equal mass pair-ion plasma. The numerical investigations reveal that the magnetosonic wave exhibits both oscillatory and monotonic shock structures depending on the strength of the dissipation. The nonlinear wave exhibited the oscillatory shock wave for strong magnetic field (weak dissipation) and monotonic shock wave for weak magnetic field (strong dissipation). The results have been discussed in the context of the fullerene pair-ion plasma experiments.
Universal collisional activation ion trap mass spectrometry
McLuckey, S.A.; Goeringer, D.E.; Glish, G.L.
1993-04-27
A universal collisional activation ion trap comprises an ion trapping means containing a bath gas and having connected thereto a noise signal generator. A method of operating a universal collisional activation ion trap comprises the steps of: providing an ion trapping means; introducing into the ion trapping means a bath gas; and, generating a noise signal within the ion trapping means; introducing into the ion trapping means a substance that, when acted upon by the noise signal, undergoes collisional activation to form product ions.
Universal collisional activation ion trap mass spectrometry
McLuckey, Scott A.; Goeringer, Douglas E.; Glish, Gary L.
1993-01-01
A universal collisional activation ion trap comprises an ion trapping means containing a bath gas and having connected thereto a noise signal generator. A method of operating a universal collisional activation ion trap comprises the steps of: providing an ion trapping means; introducing into the ion trapping means a bath gas; and, generating a noise signal within the ion trapping means; introducing into the ion trapping means a substance that, when acted upon by the noise signal, undergoes collisional activation to form product ions.
Collisional pumping in polarized sodium vapor
Kaplan, S.N.; pyle, R.V.; Ruby, L.; Schlachter, A.S.; Stearns, J.W.; Anderson, L.W.
1986-01-01
Collisional pumping has been proposed as a mechanism for efficient transfer of spin from an electron-spin-polarized target to the nuclei of a fast atom or ion beam. Collisional pumping takes place in low magnetic fields, can give polarization transfer approaching 100%, and offers the potential for producing polarized beams orders of magnitude more intense than presently achieved. Recently reported calculations of electronic spin-exchange cross sections at useful ion-source energies suggest significantly greater rates of pumping than first estimated, and give cause for increased optimism about sucessful implementation. Collisional pumping is described, and beam characteristics are given for prototype polarized source parameters.
Collisional relaxation in a nonintegrable potential
NASA Astrophysics Data System (ADS)
Kandrup, H. E.; Willmes, D. E.
1994-03-01
In galactic dynamics, a test star is assumed typically to follow a smooth trajectory in some slowly varying mean field potential and, in addition, to be subjected to 'random' close encounters with neighboring field stars which are modeled essentially as a Brownian process. With the noteable exception of Pfenniger (1986), most analyses of the collisonal relaxation induced by these close encounters have assumed that the effects of the mean field may be ignored completely, and that it suffices to consider Brownian particles moving in the absence of any systematic potential. The idealization of zero potential is problematic, as is any integrable potential in which all the mean field orbits are stable. For this reason, the paradigm of Brownian motion is reexamined here, allowing for a time-dependent, non-integrable potential, in which some subset of the mean field trajectories correspond to exponentially unstable orbits with positive Liapounov exponent. A nontrivial deterministic equation of motion is convereted into a stochastic differential equation incorporating dynamical friction and delta-correlated white noise, related via a fluctuation-dissipation theorem, and the effects of the friction and noise are analyzed perturbatively. The principal conclusion is that a coupling to a nonintegrable background potential can decrease by orders of magnitude the time scale on which noise and friction modify positions and velocities along an unperturbed, deterministic trajectory. Specifically, one finds that, even in the weak noise limit, perturbations in position and velocity grow exponentially on a time scale tlambda determined by the Liapounov exponent, although, for a strictly time-dependent potential, perturbations in energy and other collisionless invariants will only grow on a much longer relaxation time tr. Some potential implications of this accelerated collisional relaxation are discussed.
Collisional dynamics of the Milky Way
NASA Astrophysics Data System (ADS)
Griv, Evgeny; Gedalin, Michael; Yuan, Chi
1997-12-01
The effect of gravitational (elastic) encounters between stars and giant molecular clouds on the stability of small-amplitude perturbations of the Milky Way's self-gravitating disk is considered, using the exact Landau (Fokker-Planck type) collision integral, and compared with the results obtained by Griv & Peter (1996), who used the simple phenomenological Bhatnagar-Gross-Krook (Bhatnagar et al. 1954) collisional model. The present analysis is carried out for the case of a spatially inhomogeneous, highly flattened system, i.e., an inhomogeneous system in which the thickness is very small in comparison with the disk's radial extension. According to observations (Grivnev & Fridman 1990), the dynamics of a system with rare, kappa (2) >> nu_c (2) (and weak, omega (2) >> nu_c (2) ), interparticle encounters is considered, where kappa is the epicyclic frequency, omega is the frequency of excited waves, and nu_c ~ 10(-9) yr(-1) is the effective frequency of star-cloud encounters. The evolution of the stellar distribution is determined primarily by interactions with collective modes of oscillations - gravitational Jeans-type and gradient-dissipative modes - rather than by ordinary (``close") star-cloud encounters. On the basis of a local kinetic theory, it is shown that the Landau integral and the Bhatnagar et al. model give practically identical results in the case of perturbations with the wavelength lambda that is comparable to the mean epicyclic radius of stars rho , that is, in the case of the most dangerous, in the sense of the loss of stability, gravitational Jeans-type perturbations. The models, however, have essentially different qualitative and quantitative behaviors in the extreme limits of long-wavelength perturbations, (pi rho /lambda )(2) << 1, and of short-wavelength perturbations, (pi rho /lambda )(2) >> 1. Certain observational implications of the present theory are discussed.
Collisional Records in Iron Meteorites
NASA Astrophysics Data System (ADS)
Marti, K.; Lavielle, B.; Jeannot, J.-P.
1995-09-01
The asteroid belt is considered to be the ultimate source of iron meteorites and it would be of considerable interest to obtain a chronology of break-ups of asteroidal objects. However, as multiple fragmentation of such objects did likely occur, the exposure ages date the break-off of iron masses from shielded locations within the immediate parent object. Meteorites which were fragmented in more than one collisional event may have recorded integral effects of cosmic ray interactions in varying geometrical configuration and individual stages may be difficult to unravel; we term such exposure histories "complex". Exposure age histograms based on potassium ages have been discussed by Voshage [1] and he concluded that irons of groups IIIA and IIIB reveal similar histograms and probably were derived from the same parent body. He also noted a cluster for group IVA members ,but no clear evidence for other clusters. We present the collisional evidence based on published noble gas data, coupled to the new production rates which we calculate for central locations, adjusted for off-center locations whenever concentration profiles can be inferred. Unlike potassium ages which show large uncertainties for ages < 300 Ma, T38 ages can be obtained for all iron meteorites. We note, however,that T38 values of five "old" irons are systematically 15% lower than potassium ages. We confirm the evidence for stochastic events for IIIAB and IVA irons. The statistics are improved because of the larger data base. There are interesting clusters also among ages < 100 Ma, in the range which overlaps the histograms of chondrites. Recent reports [2,3] of H-chondritic inclusions in IIE irons, whose exposure ages are consistent with H-chondrite clusters, point to a genetic link. Group IIAB reveals two clusters with T38 < 100 Ma, and both events appear to involve also IIE irons. Clusterings of two thirds of group IIIE members and of group IID irons appear significant. The youngest IVB ages coincide
Collisionality scaling of turbulence and transport in advanced inductive plasmas in DIII-D
NASA Astrophysics Data System (ADS)
Yan, Z.; McKee, G. R.; Petty, C.; Luce, T.; Chen, X.; Holland, C.; Rhodes, T.; Schmitz, L.; Wang, G.; Zeng, L.; Marinoni, A.; Solomon, W.; DIII-D Team
2015-11-01
The collisionality scaling of multiscale turbulence properties and thermal transport characteristics in high-beta, high confinement Advanced Inductive (AI) plasmas was determined via systematic dimensionless scaling experiments on DIII-D. Preliminary estimate indicates a weak collisionality dependence of energy confinement as v* varied by a factor of ~2. Electron density and scaled (~Bt2) temperature profiles are well matched in the scan. Interestingly, low-k density fluctuation amplitudes are observed to decrease at lower v* near ρ ~ 0 . 75 . Ion and electron thermal transport values, computed with ONETWO using experimentally measured profiles and sources, will be presented, along with multi-scale turbulence measurements obtained with various fluctuation diagnostics. Altering collisionality should change the relative contribution of different modes to transport.
Leap frog integrator modifications in highly collisional particle-in-cell codes
NASA Astrophysics Data System (ADS)
Hanzlikova, N.; Turner, M. M.
2014-07-01
Leap frog integration method is a standard, simple, fast, and accurate way to implement velocity and position integration in particle-in-cell codes. Due to the direct solution of kinetics of particles in phase space central to the particle-in-cell procedure, important information can be obtained on particle velocity distributions, and consequently on transport and heating processes. This approach is commonly associated with physical situations where collisional effects are weak, but can also be profitably applied in some highly collisional cases, such as occur in semiconductor devices and gaseous discharges at atmospheric pressure. In this paper, we show that the implementation of the leap frog integration method in these circumstances can violate some of the assumptions central to the accuracy of this scheme. Indeed, without adaptation, the method gives incorrect results. We show here how the method must be modified to deal correctly with highly collisional cases.
IDENTIFYING COLLISIONAL FAMILIES IN THE KUIPER BELT
Marcus, Robert A.; Ragozzine, Darin; Murray-Clay, Ruth A.; Holman, Matthew J.
2011-05-20
The identification and characterization of numerous collisional families-clusters of bodies with a common collisional origin-in the asteroid belt has added greatly to the understanding of asteroid belt formation and evolution. More recent study has also led to an appreciation of physical processes that had previously been neglected (e.g., the Yarkovsky effect). Collisions have certainly played an important role in the evolution of the Kuiper Belt as well, though only one collisional family has been identified in that region to date, around the dwarf planet Haumea. In this paper, we combine insights into collisional families from numerical simulations with the current observational constraints on the dynamical structure of the Kuiper Belt to investigate the ideal sizes and locations for identifying collisional families. We find that larger progenitors (r {approx} 500 km) result in more easily identifiable families, given the difficulty in identifying fragments of smaller progenitors in magnitude-limited surveys, despite their larger spread and less frequent occurrence. However, even these families do not stand out well from the background. Identifying families as statistical overdensities is much easier than characterizing families by distinguishing individual members from interlopers. Such identification seems promising, provided the background population is well known. In either case, families will also be much easier to study where the background population is small, i.e., at high inclinations. Overall, our results indicate that entirely different techniques for identifying families will be needed for the Kuiper Belt, and we provide some suggestions.
Collisional damping rates for plasma waves
NASA Astrophysics Data System (ADS)
Tigik, S. F.; Ziebell, L. F.; Yoon, P. H.
2016-06-01
The distinction between the plasma dynamics dominated by collisional transport versus collective processes has never been rigorously addressed until recently. A recent paper [P. H. Yoon et al., Phys. Rev. E 93, 033203 (2016)] formulates for the first time, a unified kinetic theory in which collective processes and collisional dynamics are systematically incorporated from first principles. One of the outcomes of such a formalism is the rigorous derivation of collisional damping rates for Langmuir and ion-acoustic waves, which can be contrasted to the heuristic customary approach. However, the results are given only in formal mathematical expressions. The present brief communication numerically evaluates the rigorous collisional damping rates by considering the case of plasma particles with Maxwellian velocity distribution function so as to assess the consequence of the rigorous formalism in a quantitative manner. Comparison with the heuristic ("Spitzer") formula shows that the accurate damping rates are much lower in magnitude than the conventional expression, which implies that the traditional approach over-estimates the importance of attenuation of plasma waves by collisional relaxation process. Such a finding may have a wide applicability ranging from laboratory to space and astrophysical plasmas.
Collisional Orientation Transfer Faciliated Polarozation Spectroscopy
NASA Astrophysics Data System (ADS)
Bai, Jianmei; Ahmed, E. H.; Beser, B.; Guan, Y.; Lyyra, A. M.; Ashman, S.; Wolfe, C. M.; Huennekens, J.
2011-06-01
Collisional orientation transfer facilitated V-type double-resonance polarization spectroscopy technique was applied to study the A-b complex of Rb2 and Cs2. Since spectral congestion makes it difficult to find isolated pump transitions for heavy molecules such as Rb2 and Cs2, this technique significantly enlarges the range of rotational levels that can be observed per vibrational level. Collisional satellite lines with ΔJ up to 58 were observed in the Rb2 polarization experiment. In the Cs2 experiment, due to weaker Franck-Condon factors, collisional satellite lines with ΔJMax equals to 12 were observed. Collisional orientation transfer in polarization spectroscopy was first observed with buffer gas pressure of several hundred Torr. The high pressure led to loss of spectral resolution from collisional broadening. Only 1 to 3 Torr of argon buffer gas pressure was used in our experiments to obtain spectra with much higher resolution. Among the six types of possible probe signals, we assigned and analyzed the signals from the V type excitation scheme. The data was used in the global deperturbation analysis of the A-b complex of both Rb2 and Cs2. H. Salami et al. Phys. Rev. A 80, 022515 (2009) Jianmei Bai et al., Phys. Rev. A, to appear (2011) B. Teets et al. Phys. Rev. Lett. 37, 683 (1976) . Okada et al. J. Chem. Phys. 105, 3458 (1996)
On collisional disruption - Experimental results and scaling laws
NASA Technical Reports Server (NTRS)
Davis, Donald R.; Ryan, Eileen V.
1990-01-01
Both homogeneous and inhomogeneous targets have been addressed by the present experimental consideration of the impact strengths, fragment sizes, and fragment velocities generated by cement mortar targets whose crushing strengths vary by an order of magnitude, upon impact of projectiles in the velocity range of 50-5700 m/sec. When combined with additional published data, dynamic impact strength is found to correlate with quasi-static material strengths for materials ranging in character from basalt to ice; two materials not following this trend, however, are weak mortar and clay targets. Values consistent with experimental results are obtainable with a simple scaling algorithm based on impact energy, material properties, and collisional strain rate.
Spatial structure of a collisionally inhomogeneous Bose-Einstein condensate
Li, Fei; Zhang, Dongxia; Rong, Shiguang; Xu, Ying
2013-11-15
The spatial structure of a collisionally inhomogeneous Bose-Einstein condensate (BEC) in an optical lattice is studied. A spatially dependent current with an explicit analytic expression is found in the case with a spatially dependent BEC phase. The oscillating amplitude of the current can be adjusted by a Feshbach resonance, and the intensity of the current depends heavily on the initial and boundary conditions. Increasing the oscillating amplitude of the current can force the system to pass from a single-periodic spatial structure into a very complex state. But in the case with a constant phase, the spatially dependent current disappears and the Melnikov chaotic criterion is obtained via a perturbative analysis in the presence of a weak optical lattice potential. Numerical simulations show that a strong optical lattice potential can lead BEC atoms to a state with a chaotic spatial distribution via a quasiperiodic route.
Jeans stability in collisional quantum dusty magnetoplasmas
Jamil, M.; Asif, M.; Mir, Zahid; Salimullah, M.
2014-09-15
Jeans instability is examined in detail in uniform dusty magnetoplasmas taking care of collisional and non-zero finite thermal effects in addition to the quantum characteristics arising through the Bohm potential and the Fermi degenerate pressure using the quantum hydrodynamic model of plasmas. It is found that the presence of the dust-lower-hybrid wave, collisional effects of plasma species, thermal effects of electrons, and the quantum mechanical effects of electrons have significance over the Jeans instability. Here, we have pointed out a new class of dissipative instability in quantum plasma regime.
DOE R&D Accomplishments Database
Lee, T. D.
1957-06-01
Experimental results on the non-conservation of parity and charge conservation in weak interactions are reviewed. The two-component theory of the neutrino is discussed. Lepton reactions are examined under the assumption of the law of conservation of leptons and that the neutrino is described by a two- component theory. From the results of this examination, the universal Fermi interactions are analyzed. Although reactions involving the neutrino can be described, the same is not true of reactions which do not involve the lepton, as the discussion of the decay of K mesons and hyperons shows. The question of the invariance of time reversal is next examined. (J.S.R.)
Trapped-Particle-Mediated Collisional Damping of Non-Axisymmetric Plasma Waves
Kabantsev, Andrey A.; Driscoll, C. Fred
2006-10-18
Weak axial ripples in magnetic or electric confinement fields in pure electron plasmas cause slow electrons to be trapped locally, and collisional diffusion across the trapping separatrix then causes surprisingly large trapped-particle-mediated (TPM) damping and transport effects. Here, we characterize TPM damping of m{theta} {ne} 0, mz = {+-}1 Trivelpiece-Gould (TG) plasma modes in large amplitude long-lived BGK states. The TPM damping gives {gamma}BGK/{omega} {approx} 10-4, and seems to dominate in regimes of weak collisions.
NASA Astrophysics Data System (ADS)
Severn, Greg; Green, Jonathan; Winters, Victoria; Yip, Chi-Shung; Hershkowitz, Noah; Schmitz, Oliver
2015-09-01
It is taken for granted that the usual Bohm criterion must be satisfied for weakly collisional, magnetized plasmas at the plasma-wall boundary for the case in which the magnetic field is normally incident on the boundary, but there is a paucity of experimental works that confirm it. Beyond this, theorists view the Bohm criterion as approximately true, holding only for collisionless plasmas. The question is whether Bohm's criterion really is satisfied in weakly collisional magnetized plasmas in the simplest case (n ∧ ∥ B /B, where n ∧ is the boundary surface normal vector) and how that criterion (the ions reaching a sonic point at the end of the presheath) is modified as collisionality rises. Experiments are conducted in a linear magnetized helicon plasma source at the University of Wisconsin, Madison, an upgraded version of MARIA (MARIA-Magnetized Anisot Ropic Ion-distribution Apparatus), in order to address these questions. Experimental results are discussed in light of relevant theoretical works. Work supported by NSF Grant Nos. PHY-1206421, CBET-0903783, and CBET-0903832, and MSN178461, and DOE Grant Nos. DE-FG02-97ER54437, DE FG02-03ER54728, and MSN170010.
Ambient tremors in a collisional orogenic belt
Chuang, Lindsay Yuling; Chen, Kate Huihsuan; Wech, Aaron G.; Byrne, Timothy; Peng, Wei
2014-01-01
Deep-seated tectonic tremors have been regarded as an observation tied to interconnected fluids at depth, which have been well documented in worldwide subduction zones and transform faults but not in a collisional mountain belt. In this study we explore the general features of collisional tremors in Taiwan and discuss the possible generation mechanism. In the 4 year data, we find 231 ambient tremor episodes with durations ranging from 5 to 30 min. In addition to a coseismic slip-induced stress change from nearby major earthquake, increased tremor rate is also highly correlated with the active, normal faulting earthquake swarms at the shallower depth. Both the tremor and earthquake swarm activities are confined in a small, area where the high attenuation, high thermal anomaly, the boundary between high and low resistivity, and localized veins on the surfaces distributed, suggesting the involvement of fluids from metamorphic dehydration within the orogen.
Dispersion relations in weakly degenerate plasmas
NASA Astrophysics Data System (ADS)
Rocchi, F.; Molinari, V. G.; Mostacci, D.; Sumini, M.
2001-06-01
From a quantum mechanical point of view, electrons in laser produced plasmas can be regarded as weakly degenerate. For instance, for a plasma with electron density of 10 22 cm -3 and electron temperature of 1 eV, Sommerfeld's parameter is between 1 and 2. Under these conditions the usual dispersion relations for waves in plasmas need be corrected to account for degeneracy. In the present work, starting from the transport equation with a simplified version of the Boltzmann-Uehling-Uhlenbeck collision kernel the propagation of waves impinging on a plasma with weakly degenerate electrons is investigated and dispersion relations accounting for degeneracy are derived. These dispersion relations give the classical ones in the limit for Sommerfeld's parameter approaching zero. A shift of the wavenumber value and a non-collisional damping due to degeneracy effects are predicted which render a weakly degenerate plasma more opaque to radiation than a non-degenerate one.
Collisional thulium vapour gas-discharge laser
Gerasimov, V A; Pavlinskii, A V
2004-01-31
A collisional laser on a system of atomic levels based on the principle proposed by Gould is built for the first time. The population of the upper laser level and relaxation of the lower level occur upon inelastic collisions of excited thulium atoms with helium atoms. The lower-level relaxation occurs in a reaction with an energy defect of > 13000 cm{sup -1}. (active media. lasers)
Collisional excitation of interstellar methyl cyanide
NASA Technical Reports Server (NTRS)
Green, Sheldon
1986-01-01
Theoretical calculations are used to determine the collisional excitation rates of methyl cyanide under interstellar molecular cloud conditions. The required Q(L,M) as a function of kinetic temperature were determined by averaging fixed energy IOS (infinite order sudden) results over appropriate Boltzmann distributions of collision energies. At a kinetic temperature of 40 K, rates within a K ladder were found to be accurate to generally better than about 30 percent.
Collisionally induced atomic clock shifts and correlations
Band, Y. B.; Osherov, I.
2011-07-15
We develop a formalism to incorporate exchange symmetry considerations into the calculation of collisional frequency shifts for atomic clocks using a density-matrix formalism. The formalism is developed for both fermionic and bosonic atomic clocks. Numerical results for a finite-temperature {sup 87}Sr {sup 1}S{sub 0} (F=9/2) atomic clock in a magic wavelength optical lattice are presented.
Collisional records in LL-chondrites
NASA Technical Reports Server (NTRS)
Graf, Thomas; Marti, Kurt
1994-01-01
One third of all the LL-chondrites have exposure ages of approx. 15 Ma and were exposed to cosmic rays following a collisional break-up. The probability that the 15-Ma peak represents a random signal is calculated to be less than 2%. Considerably lower probabilities are obtained if only LL5s or subgroups of high Ar-40 retention are used. Furthermore, we show that the peak shape agrees with statistical constraints obtained from multiple analyses of samples from the St. Severin LL6-chondrites. The frequency in and out of the 15-Ma peak varies significantly for different petrographic LL-types. The radiogenic Ar-40 retention systematics (most LL-chondrites retained Ar-40(sub rad) shows that no substantial heat pulse resulted in the 15-Ma collisional event. Interestingly, smaller exposure age clusters at approx. 28 Ma and approx. 40 Ma match up well with clusters in the histogram of L-chondrites. The distribution of LL-exposure ages is not consistent with that expected for a quasi-continuous injection of LL material into a resonance zone of the asteroid belt. The near absence of exposure ages shorter than 8 Ma either indicates a lack of recent collisional events or considerably longer transfer times than inferred from dynamical considerations.
Superfluorescence polarization: Signature of collisional redistribution
NASA Astrophysics Data System (ADS)
Kumarakrishnan, A.; Chudasama, S.; Han, X. L.
2003-09-01
We have studied effects of magnetic sublevel degeneracy on the polarization of superfluorescent pulses generated on the Ca 4s4p 1P1 3d4s 1D2 transition at 5.5 μm. These pulses were generated from a cell of length 50 cm by optically pumping calcium vapor on the 4s2 1S0 4s4p 1P1 transition in the presence of Ar gas. The axis of ellipticity of superfluorescence (SF) polarization is oriented parallel to the axis of the pump-laser polarization at large detunings, and undergoes an abrupt rotation through 90° for detunings close to resonance. The distribution of populations in the magnetic sublevels of the 1P1 state can be estimated using a simple model based on previously calculated cross sections for collisionally aided absorption in the presence of an intense (pump) field. For large detunings, these estimates are consistent with the polarized SF intensity measured in the experiment. A direct measurement of the populations of the 1P1 magnetic sublevels also supports the collisional redistribution predicted by the calculated cross sections. We therefore suggest that SF polarization can be a useful signature of collisional redistribution. However, the change in ellipticity is unexpected, and probable causes for this effect are discussed.
Collisional Behaviors of Astrophysical Collisionless Plasmas
NASA Astrophysics Data System (ADS)
Bret, A.
2015-12-01
In collisional fluids, a number of key processes rely on the frequency of binary collisions. Collisions seem necessary to generate a shock wave when two fluids collide fast enough, to fulfill the Rankine-Hugoniot (RH) relations, to establish an equation of state or a Maxwellian distribution. Yet, these seemingly collisional features are routinely either observed or assumed, in relation with collisionless astrophysical plasmas. This article will review our current answers to the following questions: How do colliding collisionless plasmas end-up generating a shock as if they were fluids? To which extent are the RH relations fulfilled in this case? Do collisionless shocks propagate like fluid ones? Can we use an equation of state to describe collisionless plasmas, like MHD codes for astrophysics do? Why are Maxwellian distributions ubiquitous in particle-in-cell simulations of collisionless shocks? Time and length scales defining the border between the collisional and the collisionless behavior will be given when relevant. In general, when the time and length scales involved in the collisionless processes responsible for the fluid-like behavior may be neglected, the system may be treated like a fluid.
NASA Astrophysics Data System (ADS)
Wang, G. Q.; Ma, J.; Weiland, J.; Zang, Q.
2013-10-01
We have made the first drift wave study of particle transport in the Experimental Advanced Superconducting Tokamak (Wan et al., Nucl. Fusion 49, 104011 (2009)). The results reveal that collisions make the particle flux more inward in the high collisionality regime. This can be traced back to effects that are quadratic in the collision frequency. The particle pinch is due to electron trapping which is not very efficient in the high collisionality regime so the approach to equilibrium is slow. We have included also the electron temperature gradient (ETG) mode to give the right electron temperature gradient, since the Trapped Electron Mode (TE mode) is weak in this regime. However, at the ETG mode number ions are Boltzmann distributed so the ETG mode does not give particle transport.
ACCRETION IN PROTOPLANETARY DISKS BY COLLISIONAL FUSION
Wettlaufer, J. S.
2010-08-10
The formation of a solar system such as ours is believed to have followed a multi-stage process around a protostar and its associated accretion disk. Whipple first noted that planetesimal growth by particle agglomeration is strongly influenced by gas drag, and Cuzzi and colleagues have shown that when midplane particle mass densities approach or exceed those of the gas, solid-solid interactions dominate the drag effect. The size dependence of the drag creates a 'bottleneck' at the meter scale with such bodies rapidly spiraling into the central star, whereas much smaller or larger particles do not. Independent of whether the origin of the drag is angular momentum exchange with gas or solids in the disk, successful planetary accretion requires rapid planetesimal growth to kilometer scales. A commonly accepted picture is that for collisional velocities V{sub c} above a certain threshold value, V {sub th{approx}} 0.1-10 cm s{sup -1}, particle agglomeration is not possible; elastic rebound overcomes attractive surface and intermolecular forces. However, if perfect sticking is assumed for all ranges of interparticle collision speeds the bottleneck can be overcome by rapid planetesimal growth. While previous work has dealt with the influences of collisional pressures and the possibility of particle fracture or penetration, the basic role of the phase behavior of matter-phase diagrams, amorphs, and polymorphs-has been neglected. Here, it is demonstrated for compact bodies that novel aspects of surface phase transitions provide a physical basis for efficient sticking through collisional melting/amorphization/polymorphization and subsequent fusion/annealing to extend the collisional velocity range of primary accretion to {Delta}V{sub c} {approx} 1-100 m s{sup -1} >> V {sub th}, which encompasses both typical turbulent rms speeds and the velocity differences between boulder-sized and small grains {approx}1-50 m s{sup -1}. Therefore, as inspiraling meter-sized bodies collide
Accretion in Protoplanetary Disks by Collisional Fusion
NASA Astrophysics Data System (ADS)
Wettlaufer, J. S.
2010-08-01
The formation of a solar system such as ours is believed to have followed a multi-stage process around a protostar and its associated accretion disk. Whipple first noted that planetesimal growth by particle agglomeration is strongly influenced by gas drag, and Cuzzi and colleagues have shown that when midplane particle mass densities approach or exceed those of the gas, solid-solid interactions dominate the drag effect. The size dependence of the drag creates a "bottleneck" at the meter scale with such bodies rapidly spiraling into the central star, whereas much smaller or larger particles do not. Independent of whether the origin of the drag is angular momentum exchange with gas or solids in the disk, successful planetary accretion requires rapid planetesimal growth to kilometer scales. A commonly accepted picture is that for collisional velocities Vc above a certain threshold value, V th~ 0.1-10 cm s-1, particle agglomeration is not possible; elastic rebound overcomes attractive surface and intermolecular forces. However, if perfect sticking is assumed for all ranges of interparticle collision speeds the bottleneck can be overcome by rapid planetesimal growth. While previous work has dealt with the influences of collisional pressures and the possibility of particle fracture or penetration, the basic role of the phase behavior of matter-phase diagrams, amorphs, and polymorphs—has been neglected. Here, it is demonstrated for compact bodies that novel aspects of surface phase transitions provide a physical basis for efficient sticking through collisional melting/amorphization/polymorphization and subsequent fusion/annealing to extend the collisional velocity range of primary accretion to ΔVc ~ 1-100 m s-1 Gt V th, which encompasses both typical turbulent rms speeds and the velocity differences between boulder-sized and small grains ~1-50 m s-1. Therefore, as inspiraling meter-sized bodies collide with smaller particles in this high velocity collisional fusion
State dependence of Rydberg interaction-induced collisional loss
NASA Astrophysics Data System (ADS)
Feng, Zhigang; Zhao, Kejia; Miao, Jingyuan; Li, Difei; Yang, Zhijun; Wu, Zhaochun; He, Zhao; Zhao, Jianming; Jia, Suotang
2016-09-01
We present a simple analytical formula from an existing theoretical model and theoretically investigate in detail the state dependence of interaction-induced collisional loss rate coefficients, and the various parameter effects on collisional loss rate. We also investigate the different mechanisms and corresponding effects on collisional loss by analyzing our previous experimental results using the present formula, and even investigate the time evolution of Rydberg atom number for different Rydberg states.
Missing Mass in Collisional Debris from Galaxies
NASA Astrophysics Data System (ADS)
Bournaud, Frédéric; Duc, Pierre-Alain; Brinks, Elias; Boquien, Médéric; Amram, Philippe; Lisenfeld, Ute; Koribalski, Bärbel S.; Walter, Fabian; Charmandaris, Vassilis
2007-05-01
Recycled dwarf galaxies can form in the collisional debris of massive galaxies. Theoretical models predict that, contrary to classical galaxies, these recycled galaxies should be free of nonbaryonic dark matter. By analyzing the observed gas kinematics of such recycled galaxies with the help of a numerical model, we demonstrate that they do contain a massive dark component amounting to about twice the visible matter. Staying within the standard cosmological framework, this result most likely indicates the presence of large amounts of unseen, presumably cold, molecular gas. This additional mass should be present in the disks of their progenitor spiral galaxies, accounting for a substantial part of the so-called missing baryons.
Collisional Drift Waves in Stellarator Plasmas
J.L.V. Lewandowski
2003-10-07
A computational study of resistive drift waves in the edge plasma of a stellarator with an helical magnetic axis is presented. Three coupled field equations, describing the collisional drift wave dynamics in the linear approximation, are solved as an initial-value problem along the magnetic field line. The magnetohydrodynamic equilibrium is obtained from a three-dimensional local equilibrium model. The use of a local magnetohydrodynamic equilibrium model allows for a computationally efficient systematic study of the impact of the magnetic field structure on drift wave stability.
Simulation of collisional fragmentation with explosives
NASA Technical Reports Server (NTRS)
Housen, Kevin
1993-01-01
For practical reasons, experimental studies of collisional fragmentation must at times rely on explosives to fragment a target body. For example, Housen et al., described experiments in which spheres were fragmented in a pressurized atmosphere. Explosives were used because impacts could not be performed in the pressure chamber. Explosives can also be used to study targets much larger than those which can be disrupted by conventional light-gas guns, thereby allowing size- and rate-effects to be investigated. The purpose of this study is to determine the charge burial depth required to simulate various aspects of collisions.
Ion closure theory for high collisionality revisited
Ji, Jeong-Young Held, Eric D.
2015-06-15
According to analytical calculations of the ion collision operator, the ion-electron collision terms could be larger than the ion-ion collision terms. In the previous work [J.-Y. Ji and E. D. Held, Phys. Plasmas 20, 042114 (2013)], the ion-electron collision effects are diminished by the ion temperature change terms introduced from unlikely assumptions. In this work, the high-collisionality closures for ions are calculated without the temperature change terms. The ion-electron collision terms significantly modify existing closure coefficients.
Electron parallel closures for arbitrary collisionality
Ji, Jeong-Young Held, Eric D.
2014-12-15
Electron parallel closures for heat flow, viscosity, and friction force are expressed as kernel-weighted integrals of thermodynamic drives, the temperature gradient, relative electron-ion flow velocity, and flow-velocity gradient. Simple, fitted kernel functions are obtained for arbitrary collisionality from the 6400 moment solution and the asymptotic behavior in the collisionless limit. The fitted kernels circumvent having to solve higher order moment equations in order to close the electron fluid equations. For this reason, the electron parallel closures provide a useful and general tool for theoretical and computational models of astrophysical and laboratory plasmas.
Wavepacket theory of collisional dissociation in molecules
Kulander, K.
1980-01-01
An explicit integration scheme is used to solve the time dependent Schroedinger equation for wavepackets which model collisions in the collinear H + H/sub 2/ system. A realistic LEPS-type potential energy surface is used. Collision energies considered are above the dissociation threshold and probabilities for collision induced dissociation are reported. Also quantum mechanical state-to-state transition probabilities are generated. These results are compared to extensive classical trajectory calculations performed on this same system. The time evolution of the wavepacket densities is studied to understand the dynamics of the collinear collisional dissociation process.
Triangularity effects on the collisional diffusion for elliptic tokamaks
NASA Astrophysics Data System (ADS)
Martín, Pablo; Castro, Enrique
2015-09-01
The effect of ellipticity and triangularity will be analyzed for axisymmetric tokamak in the collisional regime. Analytic forms for the magnetic field cross sections are taken from those derived recently by other authors. Analytic results can be obtained in elliptic plasmas with triangularity by using an special system of tokamak coordinates previously published. Our results show that triangularities smaller than 0.6 increase confinement for ellipticities in the range 1.2-2. This behavior happens for negative and positive triangularities, however this effect is stronger for negative than for positive triangularities. The maximum diffusion velocity is not obtained for zero triangularity, but for small negative triangularities. Ellipticity is also very important in confinement, but the effect of triangularity seems to be more important. High electric inductive fields increase confinement, though this field is difficult to modify once the tokamak has been built. The analytic form of the current produced by this field is like that of a weak Ware pinch with an additional factor, which weakens the effect by an order of magnitude. The dependence of the triangularity effect with the Shafranov shift is also analyzed.
Collisional Transfer of Population and Orientation in NaK
NASA Astrophysics Data System (ADS)
Wolfe, C. M.; Ashman, S.; Huennekens, J.; Beser, B.; Bai, J.; Lyyra, A. M.
2010-03-01
We report current work to study transfer of population and orientation in collisions of NaK molecules with argon and potassium atoms using polarization labeling (PL) and laser- induced fluorescence (LIF) spectroscopy. In the PL experiment, a circularly polarized pump laser excites a specific NaK A^1&+circ;(v'=16, J') <- X^1&+circ;(v''=0, J'±1) transition, creating an orientation (non-uniform MJ' level distribution) in both levels. The linearly polarized probe laser is scanned over various 3^1π(v, J'±1) <- A^1&+circ;(v'=16, J') transitions. The probe laser passes through a crossed linear polarizer before detection, and signal is recorded if the probe laser polarization has been modified by the vapor (which occurs when it comes into resonance with an oriented level). Using both spectroscopic methods, analysis of weak collisional satellite lines adjacent to these directly populated lines, as a function of argon buffer gas pressure and cell temperature, allows us to discern separately the effects collisions with argon atoms and potassium atoms have on the population and orientation of the molecule. In addition, code has been written which provides a theoretical analysis of the process, through a solution of the density matrix equations of motion for the system.
Archean collisional tectonics in SW Montana
Mogk, D.; Rickmond, D.; Salt, K.; Clark, M.; Mueller, P.; Lafrenze, D.; Wooden, J.; Henry, D.
1985-01-01
The Archean continental crust of SW Montana evolved through alternating cycles of stable platform sedimentation followed by crustal thickening through collisional tectonics. The ancient sialic crust in the Beartooth Mountains served as the nucleus for accretion of younger terranes to the west. The oldest orogenic cycle recognized in the Beartooth Mountains involves a 3.4 Ga old supracrustal sequence which was metamorphosed in the granulite facies (T=700-800/sup 0/C, P=6Kb, 35/sup 0/C/Km); deep burial is interpreted as the result of collisional tectonic thickening. The second orogenic cycle is subduction related and has produced 2.8 Ga old andesites, 2.75 Ga old calc-alkaline intrusives, upper amphibolite grade metamorphism, transcurrent faulting (in the North Snowy Block and Yankee Jim canyon at 2.8 Ga) and nappe emplacement. In the central Beartooths post-orogenic granites intrude pelitic schists (T=600/sup 0/C, P=8Kb, 25/sup 0/C/Km). West of the Beartooths the basement consists of 2.75-2.70 Ga old, tectonically telescoped coarse clastics (Gallatin, Madison Ranges) and stable platform sequences (Gravelly, Tobacco Root, Ruby Ranges). Nappe formation and granulite-migmatite (700-750/sup 0/C) associations are common, suggesting deep burial through tectonic thickening. A later-kinematic mesozonal (8Kb) qtz diorite-granodiorite batholithic complex is present in the northern Madison Range. Quartzofeldspathic paragneisses in the westernmost Archean basement are derived from either a continental or island arc source.
A COLLISIONAL ORIGIN FOR THE LEO RING
Michel-Dansac, Leo; Emsellem, Eric; Duc, Pierre-Alain; Bournaud, Frederic; Oosterloo, Tom; Morganti, Raffaella; Serra, Paolo; Ibata, Rodrigo
2010-07-10
Extended H I structures around galaxies are of prime importance for probing galaxy formation scenarios. The giant H I ring in the Leo group is one of the largest and most intriguing H I structures in the nearby universe. Whether it consists of primordial gas, as suggested by the apparent absence of any optical counterpart and the absence of an obvious physical connection to nearby galaxies, or of gas expelled from a galaxy in a collision is actively debated. We present deep wide field-of-view optical images of the ring region obtained with MegaCam on the CFHT. They reveal optical counterparts to several H I and UV condensations along the ring, in the g', r', and i' bands, which likely correspond to stellar associations formed within the gaseous ring. Analyzing the spectral energy distribution of one of these star-forming regions, we found it to be typical for a star-forming region in pre-enriched tidal debris. We then use simulations to test the hypothesis that the Leo ring results from a head-on collision between Leo group members NGC 3384 and M96. According to our model which is able to explain, at least qualitatively, the main observational properties of the system, the Leo ring is consistent with being a collisional ring. It is thus likely another example of extended intergalactic gas made-up of pre-enriched collisional debris.
Collisional-Radiative Kinetics in Monatomic Gases
NASA Astrophysics Data System (ADS)
Le, Hai; Karagozian, Ann
2012-11-01
A detailed model of electronic excited states is essential in capturing all the nonequilibrium processes of a partially ionized plasma by means of collisional and radiative interactions. This collisional-radiative (CR) model allows us to consider deviations from equilibrium distribution of the internal states, and is now more commonly used in the study of plasma discharges. Prior studies by Kapper and Cambier and Panesi et al. suggest that this level of detail is needed for an accurate prediction of the flow field, and it is particularly relevant to plasma-combustion interactions. The required number of excited states needed to be included in the CR model is often prohibitively large due to the nonequilibrium condition of the plasma. The consequence is a large system of ODE's which needs to be solved at each time step. A reduced mechanism for the CR model can be attained by grouping the upper states of the atomic state distribution (ASDF) into a pseudo-level in which the population is characterized either by a uniform distribution or a Boltzmann distribution. This talk presents both detailed and reduced models for an ionizing shock in Argon. Supported by the US Air Force/ERC, Inc. under subcontract RS111738.
Heat flux viscosity in collisional magnetized plasmas
Liu, C.; Fox, W.; Bhattacharjee, A.
2015-05-15
Momentum transport in collisional magnetized plasmas due to gradients in the heat flux, a “heat flux viscosity,” is demonstrated. Even though no net particle flux is associated with a heat flux, in a plasma there can still be momentum transport owing to the velocity dependence of the Coulomb collision frequency, analogous to the thermal force. This heat-flux viscosity may play an important role in numerous plasma environments, in particular, in strongly driven high-energy-density plasma, where strong heat flux can dominate over ordinary plasma flows. The heat flux viscosity can influence the dynamics of the magnetic field in plasmas through the generalized Ohm's law and may therefore play an important role as a dissipation mechanism allowing magnetic field line reconnection. The heat flux viscosity is calculated directly using the finite-difference method of Epperlein and Haines [Phys. Fluids 29, 1029 (1986)], which is shown to be more accurate than Braginskii's method [S. I. Braginskii, Rev. Plasma Phys. 1, 205 (1965)], and confirmed with one-dimensional collisional particle-in-cell simulations. The resulting transport coefficients are tabulated for ease of application.
Intense sediment transport: Collisional to turbulent suspension
NASA Astrophysics Data System (ADS)
Berzi, Diego; Fraccarollo, Luigi
2016-02-01
A recent simple analytical approach to the problem of steady, uniform transport of sediment by a turbulent shearing fluid dominated by interparticle collisions is extended to the case in which the mean turbulent lift may partially or totally support the weight of the sediment. We treat the granular-fluid mixture as a continuum and make use of constitutive relations of kinetic theory of granular gases to model the particle phase and a simple mixing-length approach for the fluid. We focus on pressure-driven flows over horizontal, erodible beds and divide the flow itself into layers, each dominated by different physical mechanisms. This permits a crude analytical integration of the governing equations and to obtain analytical expressions for the distribution of particle concentration and velocity. The predictions of the theory are compared with existing laboratory measurements on the flow of glass spheres and sand particles in water. We also show how to build a regime map to distinguish between collisional, turbulent-collisional, and fully turbulent suspensions.
Laser cooling by collisional redistribution of radiation.
Vogl, Ulrich; Weitz, Martin
2009-09-01
The general idea that optical radiation may cool matter was put forward 80 years ago. Doppler cooling of dilute atomic gases is an extremely successful application of this concept. More recently, anti-Stokes cooling in multilevel systems has been explored, culminating in the optical refrigeration of solids. Collisional redistribution of radiation has been proposed as a different cooling mechanism for atomic two-level systems, although experimental investigations using moderate-density gases have not reached the cooling regime. Here we experimentally demonstrate laser cooling of an atomic gas based on collisional redistribution of radiation, using rubidium atoms in argon buffer gas at a pressure of 230 bar. The frequent collisions in the ultradense gas transiently shift a highly red-detuned laser beam (that is, one detuned to a much lower frequency) into resonance, whereas spontaneous decay occurs close to the unperturbed atomic resonance frequency. During each excitation cycle, kinetic energy of order k(B)T-that is, the thermal energy (k(B), Boltzmann's constant; T, temperature)-is extracted from the dense atomic sample. In a proof-of-principle experiment with a thermally non-isolated sample, we demonstrate relative cooling by 66 K. The cooled gas has a density more than ten orders of magnitude greater than the typical values used in Doppler-cooling experiments, and the cooling power reaches 87 mW. Future applications of the technique may include supercooling beyond the homogeneous nucleation temperature and optical chillers. PMID:19727195
Collisional model for granular impact dynamics.
Clark, Abram H; Petersen, Alec J; Behringer, Robert P
2014-01-01
When an intruder strikes a granular material from above, the grains exert a stopping force which decelerates and stops the intruder. Many previous studies have used a macroscopic force law, including a drag force which is quadratic in velocity, to characterize the decelerating force on the intruder. However, the microscopic origins of the force-law terms are still a subject of debate. Here, drawing from previous experiments with photoelastic particles, we present a model which describes the velocity-squared force in terms of repeated collisions with clusters of grains. From our high speed photoelastic data, we infer that "clusters" correspond to segments of the strong force network that are excited by the advancing intruder. The model predicts a scaling relation for the velocity-squared drag force that accounts for the intruder shape. Additionally, we show that the collisional model predicts an instability to rotations, which depends on the intruder shape. To test this model, we perform a comprehensive experimental study of the dynamics of two-dimensional granular impacts on beds of photoelastic disks, with different profiles for the leading edge of the intruder. We particularly focus on a simple and useful case for testing shape effects by using triangular-nosed intruders. We show that the collisional model effectively captures the dynamics of intruder deceleration and rotation; i.e., these two dynamical effects can be described as two different manifestations of the same grain-scale physical processes. PMID:24580216
Heat flux viscosity in collisional magnetized plasmas
NASA Astrophysics Data System (ADS)
Liu, C.; Fox, W.; Bhattacharjee, A.
2015-05-01
Momentum transport in collisional magnetized plasmas due to gradients in the heat flux, a "heat flux viscosity," is demonstrated. Even though no net particle flux is associated with a heat flux, in a plasma there can still be momentum transport owing to the velocity dependence of the Coulomb collision frequency, analogous to the thermal force. This heat-flux viscosity may play an important role in numerous plasma environments, in particular, in strongly driven high-energy-density plasma, where strong heat flux can dominate over ordinary plasma flows. The heat flux viscosity can influence the dynamics of the magnetic field in plasmas through the generalized Ohm's law and may therefore play an important role as a dissipation mechanism allowing magnetic field line reconnection. The heat flux viscosity is calculated directly using the finite-difference method of Epperlein and Haines [Phys. Fluids 29, 1029 (1986)], which is shown to be more accurate than Braginskii's method [S. I. Braginskii, Rev. Plasma Phys. 1, 205 (1965)], and confirmed with one-dimensional collisional particle-in-cell simulations. The resulting transport coefficients are tabulated for ease of application.
Collisional population transfer in yterbium ions
Schauer, Martin Michael; Torgerson, Justin R; Danielson, Jeremy R; Zhao, Xinxin; Nguyen, Ahn - Tuan; Wang, Li - Bang
2009-01-01
Long-lived metastable states of Yb+ ions are used for atomic frequency standards, precision measurements, and quantum information research. The effect of population trapping and transfer in these states must be well understood. We report here the transfer of Yb+ ions into the long-lived {sup 2}F{sub 7/2} state by means of collisions between He buffer gas and Yb+ ions held in a linear Paul trap. Transfer rates were measured as functions of buffer-gas pressure and repump-laser power, and the collisional population transfer rates were extracted. The measured transfer rate coefficients are 8.32(75)x10-11 and 8.65(33)x10-11 cm3/s for the collisional processes {sup 2}P{sub 1/2}{yields}{sup 2}D{sub 5/2} and {sup 2}D{sub 3/2}{yields}{sup 2}F{sub 7/2}, respectively.
Maitra, Sarit; Banerjee, Gadadhar
2014-11-15
The influence of dust size distribution on the dust ion acoustic solitary waves in a collisional dusty plasma is investigated. It is found that dust size distribution changes the amplitude and width of a solitary wave. A critical wave number is derived for the existence of purely damping mode. A deformed Korteweg-de Vries (dKdV) equation is obtained for the propagation of weakly nonlinear dust ion acoustic solitary waves and the effect of different plasma parameters on the solution of this equation is also presented.
Polarization of fast particle beams by collisional pumping
Stearns, J. Warren; Kaplan, Selig N.; Pyle, Robert V.; Anderson, L. Wilmer; Ruby, Lawrence; Schlachter, Alfred S.
1988-01-01
Method and apparatus for highly polarizing a fast beam of particles by collisional pumping, including generating a fast beam of particles, and also generating a thick electron-spin-polarized medium positioned as a target for the beam. The target is made sufficiently thick to allow the beam to interact with the medium to produce collisional pumping whereby the beam becomes highly polarized.
Collisional effects on nonlinear ion drag force for small grains
Hutchinson, I. H.; Haakonsen, C. B.
2013-08-15
The ion drag force arising from plasma flow past an embedded spherical grain is calculated self-consistently and non-linearly using particle in cell codes, accounting for ion-neutral collisions. Using ion velocity distribution appropriate for ion drift driven by a force field gives wake potential and force greatly different from a shifted Maxwellian distribution, regardless of collisionality. The low-collisionality forces are shown to be consistent with estimates based upon cross-sections for scattering in a Yukawa (shielded) grain field, but only if non-linear shielding length is used. Finite collisionality initially enhances the drag force, but only by up to a factor of 2. Larger collisionality eventually reduces the drag force. In the collisional regime, the drift distribution gives larger drag than the shift distribution even at velocities where their collisionless drags are equal. Comprehensive practical analytic formulas for force that fit the calculations are provided.
Aeolian Sand Transport with Collisional Suspension
NASA Technical Reports Server (NTRS)
Jenkins, James T.; Pasini, Jose Miguel; Valance, Alexandre
2004-01-01
Aeolian transport is an important mechanism for the transport of sand on Earth and on Mars. Dust and sand storms are common occurrences on Mars and windblown sand is responsible for many of the observed surface features, such as dune fields. A better understanding of Aeolian transport could also lead to improvements in pneumatic conveying of materials to be mined for life support on the surface of the Moon and Mars. The usual view of aeolian sand transport is that for mild winds, saltation is the dominant mechanism, with particles in the bed being dislodged by the impact of other saltating particles, but without in-flight collisions. As the wind becomes stronger, turbulent suspension keeps the particles in the air, allowing much longer trajectories, with the corresponding increase in transport rate. We show here that an important regime exists between these two extremes: for strong winds, but before turbulent suspension becomes dominant, there is a regime in which in-flight collisions dominate over turbulence as a suspension mechanism, yielding transport rates much higher than those for saltation. The theory presented is based on granular kinetic theory, and includes both turbulent suspension and particle-particle collisions. The wind strengths for which the calculated transport rates are relevant are beyond the published strengths of current wind tunnel experiments, so these theoretical results are an invitation to do experiments in the strong-wind regime. In order to make a connection between the regime of saltation and the regime of collisional suspension, it is necessary to better understand the interaction between the bed and the particles that collide with it. This interaction depends on the agitation of the particles of the bed. In mild winds, collisions with the bed are relatively infrequent and the local disturbance associated with a collision can relax before the next nearby collision. However, as the wind speed increases, collision become more frequent
Collisional quenching of highly rotationally excited HF
NASA Astrophysics Data System (ADS)
Yang, B.; Walker, K. M.; Forrey, R. C.; Stancil, P. C.; Balakrishnan, N.
2015-06-01
Context. Collisional excitation rate coefficients play an important role in the dynamics of energy transfer in the interstellar medium. In particular, accurate rotational excitation rates are needed to interpret microwave and infrared observations of the interstellar gas for nonlocal thermodynamic equilibrium line formation. Aims: Theoretical cross sections and rate coefficients for collisional deexcitation of rotationally excited HF in the vibrational ground state are reported. Methods: The quantum-mechanical close-coupling approach implemented in the nonreactive scattering code MOLSCAT was applied in the cross section and rate coefficient calculations on an accurate 2D HF-He potential energy surface. Estimates of rate coefficients for H and H2 colliders were obtained from the HF-He collisional data with a reduced-potential scaling approach. Results: The calculation of state-to-state rotational quenching cross sections for HF due to He with initial rotational levels up to j = 20 were performed for kinetic energies from 10-5 to 15 000 cm-1. State-to-state rate coefficients for temperatures between 0.1 and 3000 K are also presented. The comparison of the present results with previous work for lowly-excited rotational levels reveals significant differences. In estimating HF-H2 rate coefficients, the reduced-potential method is found to be more reliable than the standard reduced-mass approach. Conclusions: The current state-to-state rate coefficient calculations are the most comprehensive to date for HF-He collisions. We attribute the differences between previously reported data and our results to differences in the adopted interaction potential energy surfaces. The new He rate coefficients can be used in a variety of applications. The estimated H2 and H collision rates can also augment the smaller datasets previously developed for H2 and electrons. Rate coefficient tables are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130
Collisional electron spectroscopy method for gas analysis
NASA Astrophysics Data System (ADS)
Stefanova, M. S.; Pramatarov, P. M.; Kudryavtsev, A. A.; Peyeva, R. A.; Patrikov, T. B.
2016-05-01
Recently developed collisional electron spectroscopy (CES) method, based on identification of gas impurities by registration of groups of nonlocal fast electrons released by Penning ionization of the impurity particles by helium metastable atoms, is verified experimentally. Detection and identification of atoms and molecules of gas impurities in helium at pressures of 14 - 90 Torr with small admixtures of Ar, Kr, CO2, and N2 are carried out. The nonlocal negative glow plasma of short dc microdischarge is used as most suitable medium. Records of the energy spectra of penning electrons are performed by means of an additional electrode - sensor, located at the boundary of the discharge volume. Maxima appear in the electron energy spectra at the characteristic energies corresponding to Penning ionization of the impurity particles by helium metastable atoms.
Wind enhanced planetary escape: Collisional modifications
NASA Technical Reports Server (NTRS)
Curtis, S. A.; Hartle, R. E.
1976-01-01
The problem of thermal escape is considered in which both the effects of thermospheric winds at the exobase and collisions below the exobase are included in a Monte Carlo calculation. The collisions are included by means of a collisional relaxation layer of a background gas which models the transition region between the exosphere and the thermosphere. The wind effects are considered in the limiting cases of vertical and horizontal flows. Two species are considered: terrestrial hydrogen and terrestrial helium. In the cases of terrestrial hydrogen the escape fluxes were found to be strongly filtered or throttled by collisions at high exospheric temperatures. The model is applied to molecular hydrogen diffusing through a methane relaxation layer under conditions possible on Titan. The results are similar to the case of terrestrial hydrogen with wind enhanced escape being strongly suppressed by collisions. It is concluded that wind enhanced escape is not an important process on Titan.
Collisional and Dynamical Evolution of Planetary Systems
NASA Technical Reports Server (NTRS)
Weidenschilling, Stuart J.
2004-01-01
Senior Scientst S. J. Weidenschilling presents his final administrative report in the research program entitled "Collisional and Dynamical Evolution of Planetary Systems," on which he was the Principal Investigator. This research program produced the following publications: 1) "Jumping Jupiters" in binary star systems. F. Marzari, S. J. Weidenschilling, M. Barbieri and V. Granata. Astrophys. J., in press, 2005; 2) Formation of the cores of the outer planets. To appear in "The Outer Planets" (R. Kallenbach, ED), ISSI Conference Proceedings (Space Sci. Rev.), in press, 2005; 3) Accretion dynamics and timescales: Relation to chondrites. S. J. Weidenschilling and J. Cuzzi. In Meteorites and the Early Solar System LI (D. Lauretta et al., Eds.), Univ. of Arizona Press, 2005; 4) Asteroidal heating and thermal stratification of the asteroid belt. A. Ghosh, S. J.Weidenschilling, H. Y. McSween, Jr. and A. Rubin. In Meteorites and the Early Solar System I1 (D. Lauretta et al., Eds.), Univ. of Arizona Press, 2005.
The complex correspondence between families and collisional events
NASA Astrophysics Data System (ADS)
Milani Comparetti, Andrea
2015-08-01
Asteroid families are identified as statistically significant concentrations of asteroids in the space of proper elements. The purpose of family classifications is meant to be the identification of the largest collisional events occurred during the history of the asteroid main belt. However, are the families as found in 1-1 correspondence with ancient collisional events? A recent analysis of larger classifications, based on larger and more accurate datasets of proper elements, indicates that this is not the case. There are multiple cratering events on the same parent body. There are collisional families split into two by the YORP effect. There are subfamilies arising from secondary collisions after the one forming a larger family, and this is not limited to recent events. There are families overlapping in proper elements space but with composition incompatible with a common parent body. There are cases not yet understood, but pointing to a complex collisional history. In total at least 10 cases of complex correpondence between families and collisional events have been identified, more are suspected but not yet supported by enough evidence. The disentagling of these complex collisional histories is an essential step towards the understanding of the asteroid collisional evolution.
Solar Wind Collisional Age from a Global Magnetohydrodynamics Simulation
NASA Astrophysics Data System (ADS)
Chhiber, R.; Usmanov, AV; Matthaeus, WH; Goldstein, ML
2016-04-01
Simple estimates of the number of Coulomb collisions experienced by the interplanetary plasma to the point of observation, i.e., the “collisional age”, can be usefully employed in the study of non-thermal features of the solar wind. Usually these estimates are based on local plasma properties at the point of observation. Here we improve the method of estimation of the collisional age by employing solutions obtained from global three-dimensional magnetohydrodynamics simulations. This enables evaluation of the complete analytical expression for the collisional age without using approximations. The improved estimation of the collisional timescale is compared with turbulence and expansion timescales to assess the relative importance of collisions. The collisional age computed using the approximate formula employed in previous work is compared with the improved simulation-based calculations to examine the validity of the simplified formula. We also develop an analytical expression for the evaluation of the collisional age and we find good agreement between the numerical and analytical results. Finally, we briefly discuss the implications for an improved estimation of collisionality along spacecraft trajectories, including Solar Probe Plus.
Dust charging and charge fluctuations in a weakly collisional radio-frequency sheath at low pressure
Piel, Alexander Schmidt, Christian
2015-05-15
Models for the charging of dust particles in the bulk plasma and in the sheath region are discussed. A new model is proposed that describes collision-enhanced ion currents in the sheath. The collisions result in a substantial reduction of the negative charge of the dust. Experimental data for the dust charge in the sheath can be described by this model when a Bi-Maxwellian electron distribution is taken into account. Expressions for the dust charging rate for all considered models are presented and their influence on the rise of the kinetic dust temperature is discussed.
NASA Astrophysics Data System (ADS)
Del Sarto, Daniele; Pucci, Fulvia; Tenerani, Anna; Velli, Marco
2016-03-01
This paper discusses the transition to fast growth of the tearing instability in thin current sheets in the collisionless limit where electron inertia drives the reconnection process. It has been previously suggested that in resistive MHD there is a natural maximum aspect ratio (ratio of sheet length and breadth to thickness) which may be reached for current sheets with a macroscopic length L, the limit being provided by the fact that the tearing mode growth time becomes of the same order as the Alfvén time calculated on the macroscopic scale. For current sheets with a smaller aspect ratio than critical the normalized growth rate tends to zero with increasing Lundquist number S, while for current sheets with an aspect ratio greater than critical the growth rate diverges with S. Here we carry out a similar analysis but with electron inertia as the term violating magnetic flux conservation: previously found scalings of critical current sheet aspect ratios with the Lundquist number are generalized to include the dependence on the ratio de2/L2, where de is the electron skin depth, and it is shown that there are limiting scalings which, as in the resistive case, result in reconnecting modes growing on ideal time scales. Finite Larmor radius effects are then included, and the rescaling argument at the basis of "ideal" reconnection is proposed to explain secondary fast reconnection regimes naturally appearing in numerical simulations of current sheet evolution.
Collisional Penrose process in a rotating wormhole spacetime
NASA Astrophysics Data System (ADS)
Tsukamoto, Naoki; Bambi, Cosimo
2015-05-01
In a collisional Penrose process, two particles coming from the asymptotically flat region collide in the ergosphere of a compact object. The collision produces two new particles, one with positive energy and one with negative energy. When the particle with positive energy escapes to infinity, the process extracts energy from the compact object. In this paper, we study the collisional Penrose process in a rotating wormhole spacetime. We consider the simple case of a head-on collision at the throat of a Teo wormhole. We find that the process of energy extraction from a Teo wormhole can be substantially more efficient than the collisional Penrose process in the Kerr black hole spacetime.
Field-free molecular alignment for probing collisional relaxation dynamics
NASA Astrophysics Data System (ADS)
Vieillard, Th.; Chaussard, F.; Billard, F.; Sugny, D.; Faucher, O.; Ivanov, S.; Hartmann, J.-M.; Boulet, C.; Lavorel, B.
2013-02-01
We report the experimental study of field-free molecular alignment in CO2 gas mixtures induced by intense femtosecond laser pulses in the presence of collisional processes. We demonstrate that the alignment signals exhibit specific features due to nontrivial collisional propensity rules that tend to preserve the orientation of the rotational angular momentum of the molecules. The analysis is performed with a quantum approach based on the modeling of rotational J- and M-dependent state-to-state transfer rates. The present work paves the way for strong-field spectroscopy of collisional dynamics.
Collisional coupling in counterstreaming laser-produced plasmas
NASA Technical Reports Server (NTRS)
Koopman, D. W.; Goforth, R. R.
1974-01-01
The collisional processes which transfer momentum between counterstreaming plasmas are reviewed and applied to the example of a laser-produced plasma expanding into a partially ionized background. Experimental measurements of the dependence of the ion flow field on collisional momentum transfer demonstrate the validity of the simplified treatment of collision processes which have been adopted. A numerical model which simulates the laser-plasma interaction with the background confirms the importance of collisions in previous experimental studies of momentum coupling, and provides some insight into the distinction between collisional and collisionless flow regimes.
Impact of collisionality on fluctuation characteristics of micro-turbulence
Vermare, L.; Hennequin, P.; Guercan, Oe. D.; Bourdelle, C.; Clairet, F.; Garbet, X.; Sabot, R.
2011-01-15
The influence of changing collisionality on density fluctuation characteristics is studied during dedicated {nu}* scaling experiments, using Doppler backscattering system. First, the repartition of fluctuation energy over different spatial scales, as represented by the wavenumber spectrum, is investigated and a modification of the shape of the perpendicular wavenumber spectrum in the low wavenumber part of the spectrum is observed when changing collisionality. In addition, a new procedure to evaluate the dispersion relation of micro-turbulence is presented. From the behavior of the perpendicular mean velocity of density fluctuations with the perpendicular wavenumber, different dispersion relations are obtained between low and high collisionality cases.
THE CREATION OF HAUMEA'S COLLISIONAL FAMILY
Schlichting, Hilke E.; Sari, Re'em E-mail: sari@tapir.caltech.edu
2009-08-01
Recently, the first collisional family was discovered in the Kuiper Belt. The parent body of this family, Haumea, is one of the largest objects in the Kuiper Belt and is orbited by two satellites. It has been proposed that the Haumea family was created from dispersed fragments that resulted from a giant impact. This proposed origin of the Haumea family is however in conflict with the observed velocity dispersion between the family members ({approx} 140 m s{sup -1}) which is significantly less than the escape velocity from Haumea's surface ({approx} 900 m s{sup -1}). In this paper we propose a different formation scenario for Haumea's collisional family. In our scenario the family members are ejected while in orbit around Haumea. This scenario, therefore, naturally gives rise to a lower velocity dispersion among the family members than expected from direct ejection from Haumea's surface. In our scenario Haumea's giant impact forms a single moon that tidally evolves outward until it suffers a destructive collision from which the family is created. We show that this formation scenario yields a velocity dispersion of {approx} 190 m s{sup -1} among the family members which is in good agreement with the observations. We discuss an alternative scenario that consists of the formation and tidal evolution of several satellites that are ejected by collisions with unbound Kuiper Belt objects. However, the formation of the Haumea family in this latter way is difficult to reconcile with the large abundance of Kuiper Belt binaries. We, therefore, favor forming the family by a destructive collision of a single moon of Haumea. The probability for Haumea's initial giant impact in today's Kuiper Belt is less than 10{sup -3}. In our scenario, however, Haumea's giant impact can occur before the excitation of the Kuiper Belt and the ejection of the family members afterward. This has the advantage that one can preserve the dynamical coherence of the family and explain Haumea's original
Particle Segregation in Collisional Shearing Flows
NASA Technical Reports Server (NTRS)
Jenkins, J. T.; Louge, M. Y.
1999-01-01
The size segregation of flowing or shaken grains is a commonly observed phenomenon in industrial processes and in nature. In systems that do not involve much agitation of the grains, several mechanisms that involve gravity have been identified as leading to such segregation. In highly agitated flows, there is a mechanism independent of gravity that is available to drive separation of different grains. This is associated with spatial gradients in the energy of their velocity fluctuations. Because collisions between grains inevitably dissipate energy, collisional granular shear flows are usually of limited extent in the direction transverse to the flow. One consequence of this is that shear flows are strongly influenced by their boundaries. Because grains, on average, slip relative to boundaries, a bumpy or frictional boundary can convert slip energy into fluctuation energy. However, because each collision between a grain and the boundary dissipates fluctuation energy, there is a competition between production and dissipation. In principle, it is possible to design the geometry of the boundary - for example, the size and spacing of the bumps - so that the boundary either produces or dissipates fluctuation energy. This permits the control of the component of the spatial gradient of the fluctuation energy that is normal to the boundary. The gradients in fluctuation energy established by such boundaries may be exploited to drive the separation by size or other properties in a binary mixture of spherical grains. Microgravity makes the visual observations possible by permitting us to employ moderate rates of shear. On earth, the effects of gravity can be minimized by shearing so rapidly that the particle pressure overwhelms gravity. However, in this event, separation takes place too rapidly for visual observation, buoyancy and/or condensation associated with the centripetal acceleration must be accounted for, and the particles can be severely damaged. Because, in the
Current driven instability in collisional dusty plasmas
NASA Astrophysics Data System (ADS)
Pandey, B. P.; Vladimirov, S. V.; Samarian, A.
2009-11-01
The current driven electromagnetic instability in a collisional, magnetized, dusty medium is considered in the present work. It is shown that in the presence of the magnetic field aligned current, the low-frequency waves in the medium can become unstable if the ratio of the current to the ambient field is larger than the light speed times the wave number. The growth rate of the instability depends upon the ratio of the Alfvén to the dust cyclotron frequency as well as on the ratio of the current density J to the dust charge density Zend, where Z is the number of electronic charge on the grain, e is the electron charge, and nd is the dust number density. The typical growth rate of this instability is on the order of Alfvén frequency which compares favorably with the electrostatic, cross-field current driven, Farley-Buneman instability and thus could play an important role in the Earth's ionosphere.
Collisional Ionization Equilibrium for Optically Thin Plasmas
NASA Technical Reports Server (NTRS)
Bryans, P.; Mitthumsiri, W.; Savin, D. W.; Badnell, N. R.; Gorczyca, T. W.; Laming, J. M.
2006-01-01
Reliably interpreting spectra from electron-ionized cosmic plasmas requires accurate ionization balance calculations for the plasma in question. However, much of the atomic data needed for these calculations have not been generated using modern theoretical methods and their reliability are often highly suspect. We have utilized state-of-the-art calculations of dielectronic recombination (DR) rate coefficients for the hydrogenic through Na-like ions of all elements from He to Zn. We have also utilized state-of-the-art radiative recombination (RR) rate coefficient calculations for the bare through Na-like ions of all elements from H to Zn. Using our data and the recommended electron impact ionization data of Mazzotta et al. (1998), we have calculated improved collisional ionization equilibrium calculations. We compare our calculated fractional ionic abundances using these data with those presented by Mazzotta et al. (1998) for all elements from H to Ni, and with the fractional abundances derived from the modern DR and RR calculations of Gu (2003a,b, 2004) for Mg, Si, S, Ar, Ca, Fe, and Ni.
Collisional Disruption of super-Earths
NASA Astrophysics Data System (ADS)
Marcus, Robert A.; Stewart, S. T.; Sasselov, D.; Hernquist, L. E.
2009-05-01
The late stages of planet formation are dominated by collisions between planetary embryos with masses on the order of one tenth the mass of the Earth in our solar system (e.g., Agnor et al. 1999). The dynamics of this stage determine the final configuration of planets in the system. In the solar system, there is evidence of possible late giant impacts in the histories of both Mercury (Benz et al. 1988, 2007) and the Earth (e.g., Canup 2004). Here we consider high energy collisions (near catastrophic disruption) between planets of initially terrestrial composition with a range of masses into the super-Earth regime. We derive the transition between collisional accretion and erosion for super-Earths, following the method of Stewart and Leinhardt (2009). We identify both a catastrophic disruption regime and grazing impact and bouncing regime, as found by Agnor and Asphaug (2004). In the disruption regime, we derive a scaling law for changing the bulk composition (iron to silicate ratio). We then discuss the observational implications for such missions as Kepler.
IONIZATION EQUILIBRIUM TIMESCALES IN COLLISIONAL PLASMAS
Smith, Randall K.; Hughes, John P. E-mail: jph@physics.rutgers.ed
2010-07-20
Astrophysical shocks or bursts from a photoionizing source can disturb the typical collisional plasma found in galactic interstellar media or the intergalactic medium. The spectrum emitted by this plasma contains diagnostics that have been used to determine the time since the disturbing event, although this determination becomes uncertain as the elements in the plasma return to ionization equilibrium. A general solution for the equilibrium timescale for each element arises from the elegant eigenvector method of solution to the problem of a non-equilibrium plasma described by Masai and Hughes and Helfand. In general, the ionization evolution of an element Z in a constant electron temperature plasma is given by a coupled set of Z + 1 first-order differential equations. However, they can be recast as Z uncoupled first-order differential equations using an eigenvector basis for the system. The solution is then Z separate exponential functions, with the time constants given by the eigenvalues of the rate matrix. The smallest of these eigenvalues gives the scale of the slowest return to equilibrium independent of the initial conditions, while conversely the largest eigenvalue is the scale of the fastest change in the ion population. These results hold for an ionizing plasma, a recombining plasma, or even a plasma with random initial conditions, and will allow users of these diagnostics to determine directly if their best-fit result significantly limits the timescale since a disturbance or is so close to equilibrium as to include an arbitrarily long time.
Cancellation of the Collisional Frequency Shift in Caesium Fountain Clocks
Szymaniec, K.; Chalupczak, W.; Tiesinga, E.; Williams, C. J.; Weyers, S.; Wynands, R.
2007-04-13
We have observed that the collisional frequency shift in primary caesium fountain clocks varies with the clock state population composition and, in particular, is zero for a given fraction of the |F=4,m{sub F}=0> atoms, depending on the initial cloud parameters. We present a theoretical model explaining our observations. The possibility of the collisional shift cancellation implies an improvement in the performance of caesium fountain standards and a simplification in their operation.
Effect of collisionality and diamagnetism on the plasma dynamo
Ji, H.; Yagi, Y.; Hattori, K.; Almagri, A.F.; Prager, S.C.; Hirano, Y.; Sarff, J.S.; Shimada, T.; Maejima, Y.; Hayase, K. ||
1995-08-07
Fluctuation-induced dynamo electric fields are measured over a wide range of electron collisionality in the edge of TPE-1RM20 reversed-field pinch (RFP). In the collisionless region the magnetohydrodynamic dynamo alone can sustain the parallel current, while in the collisional region a new dynamo mechanism resulting from the fluctuations in the electron diamagnetic drift becomes dominant. A comprehensive picture of the RFP dynamo emerges by combining with earlier results from MST and REPUTE RFPs.
The effect of collisionality and diamagnetism on the plasma dynamo
Ji, H.; Yagi, Y.; Hattori, K.; Hirano, Y.; Shimada, T.; Maejima, Y.; Hayase, K.; Almagri, A.F.; Prager, S.C.; Sarff, J.S.
1995-04-28
Fluctuation-induced dynamo forces are measured over a wide range of electron collisionality in the edge of TPE-1RM20 Reversed-Field Pinch (RFP). In the collisionless region the Magnetohydrodynamic (MHD) dynamo alone can sustain the parallel current, while in the collisional region a new dynamo mechanism resulting from the fluctuations in the electron diamagnetic drift becomes dominant. A comprehensive picture of the RFP dynamo emerges by combining with earlier results from MST and REPUTE RFPs.
Polarization of fast particle beams by collisional pumping
Stearns, J.W.; Kaplan, S.N.; Pyle, R.V.; Anderson, L.W.; Schlachter, A.S.; Ruby, L.
1984-10-19
The invention relates to method and apparatus for polarizing a fast beam of particles by collisional pumping, including generating a fast beam of particles, and generating a thick electron-spin-polarized medium positioned as a target for said beam, said medium being sufficiently thick to allow said beam to interact with said medium to produce collisional pumping whereby said particle beam becomes highly polarized.
Dependence of pedestal structure on collisionality at fixed beta in JT-60U
NASA Astrophysics Data System (ADS)
Urano, H.; Aiba, N.; Kamiya, K.; Kamada, Y.; the JT-60 Team
2016-01-01
The dependence of pedestal structure on collisionality at fixed beta has been investigated in JT-60U. In the ITER-relevant low collisionality regime, the pedestal width does not change with edge collisionality. In the high collisionality regime, the pedestal width broadens with increased edge collisionality. The pedestal pressure gradient and width are not significantly changed when the pedestal is close to an intermediate n peeling-ballooning mode boundary at low collisionality. The experimental result indicates that conventional pedestal models where the pedestal width is independent of collisionality and is determined by {β\\text{p}} at the pedestal is not a bad assumption in the ITER-relevant low collisionality regime. On the other hand, the pressure gradient decreases and the pedestal width increases at high collisionality. The pedestal broadening becomes significant when the pedestal is marginal to be unstable at the high n ballooning mode in the high collisionality regime.
Phase-Diffusion Dynamics in Weakly Coupled Bose-Einstein Condensates
Boukobza, Erez; Vardi, Amichay; Chuchem, Maya; Cohen, Doron
2009-05-08
We study the phase sensitivity of collisional phase diffusion between weakly coupled Bose-Einstein condensates, using a semiclassical picture of the two-mode Bose-Hubbard model. When weak coupling is allowed, zero relative phase locking is attained in the Josephson-Fock transition regime, whereas a {pi} relative phase is only locked in Rabi-Josephson point. Our analytic semiclassical estimates agree well with the numerical results.
Yip, Chi-Shung; Hershkowitz, Noah; Severn, Greg
2010-06-04
Recent experiments have shown that ions in weakly collisional plasmas containing two ion species of comparable densities nearly reach a common velocity at the sheath edge. A new theory suggests that collisional friction between the two ion species enhanced by two stream instability reduces the drift velocity of each ion species relative to each other near the sheath edge and finds that the difference in velocities at the sheath edge depends on the relative concentrations of the species. It is small when the concentrations are comparable and is large, with each species reaching its own Bohm velocity, when the relative concentration differences are large. To test these findings, ion drift velocities were measured with laser-induced fluorescence in argon-xenon plasmas. We show that the predictions are in excellent agreement with the first experimental tests of the new model.
Shikano, Yutaka
2011-03-28
I show that the weak value theory is useful from the viewpoints of the experimentally verifiability, consistency, capacity for explanation as to many quantum paradoxes, and practical advantages. As an example, the initial state in the Hardy paradox can be experimentally verified using the weak value via the weak measurement.
Magnetic reconnection in a weakly ionized plasma
Leake, James E.; Lukin, Vyacheslav S.; Linton, Mark G.
2013-06-15
Magnetic reconnection in partially ionized plasmas is a ubiquitous phenomenon spanning the range from laboratory to intergalactic scales, yet it remains poorly understood and relatively little studied. Here, we present results from a self-consistent multi-fluid simulation of magnetic reconnection in a weakly ionized reacting plasma with a particular focus on the parameter regime of the solar chromosphere. The numerical model includes collisional transport, interaction and reactions between the species, and optically thin radiative losses. This model improves upon our previous work in Leake et al.[“Multi-fluid simulations of chromospheric magnetic reconnection in a weakly ionized reacting plasma,” Astrophys. J. 760, 109 (2012)] by considering realistic chromospheric transport coefficients, and by solving a generalized Ohm's law that accounts for finite ion-inertia and electron-neutral drag. We find that during the two dimensional reconnection of a Harris current sheet with an initial width larger than the neutral-ion collisional coupling scale, the current sheet thins until its width becomes less than this coupling scale, and the neutral and ion fluids decouple upstream from the reconnection site. During this process of decoupling, we observe reconnection faster than the single-fluid Sweet-Parker prediction, with recombination and plasma outflow both playing a role in determining the reconnection rate. As the current sheet thins further and elongates, it becomes unstable to the secondary tearing instability, and plasmoids are seen. The reconnection rate, outflows, and plasmoids observed in this simulation provide evidence that magnetic reconnection in the chromosphere could be responsible for jet-like transient phenomena such as spicules and chromospheric jets.
Collisional energy transfer in highly excited molecules.
Houston, Paul L; Conte, Riccardo; Bowman, Joel M
2014-09-11
The excitation/de-excitation step in the Lindemann mechanism is investigated in detail using model development and classical trajectory studies based on a realistic potential energy surface. The model, based on a soft-sphere/line-of-centers approach and using elements of Landau-Teller theory and phase space theory, correctly predicts most aspects of the joint probability distribution P(ΔE,ΔJ) for the collisional excitation and de-excitation process in the argon-allyl system. The classical trajectories both confirm the validity of the model and provide insight into the energy transfer. The potential employed was based on a previously available ab initio intramolecular potential for the allyl fit to 97418 allyl electronic energies and an intermolecular potential fit to 286 Ar-allyl energies. Intramolecular energies were calculated at the CCSD(T)/AVTZ level of theory, while intermolecular energies were calculated at the MP2/AVTZ level of theory. Trajectories were calculated for each of four starting allyl isomers and for an initial rotational level of Ji = 0 as well as for Ji taken from a microcanonical distribution. Despite a dissimilarity in Ar-allyl potentials for fixed Ar-allyl geometries, energy transfer properties starting from four different isomers were found to be remarkably alike. A contributing factor appears to be that the orientation-averaged potentials are almost identical. The model we have developed suggests that most hydrocarbons should have similar energy transfer properties, scaled by differences in the potential offset of the atom-hydrogen interaction. Available data corroborate this suggestion. PMID:25116732
NASA Astrophysics Data System (ADS)
Mikkelsen, D. R.; Bitter, M.; Delgado-Aparicio, L.; Hill, K. W.; Greenwald, M.; Howard, N. T.; Hughes, J. W.; Rice, J. E.; Reinke, M. L.; Podpaly, Y.; Ma, Y.; Candy, J.; Waltz, R. E.
2015-06-01
Peaked density profiles in low-collisionality AUG and JET H-mode plasmas are probably caused by a turbulently driven particle pinch, and Alcator C-Mod experiments confirmed that collisionality is a critical parameter. Density peaking in reactors could produce a number of important effects, some beneficial, such as enhanced fusion power and transport of fuel ions from the edge to the core, while others are undesirable, such as lower beta limits, reduced radiation from the plasma edge, and consequently higher divertor heat loads. Fundamental understanding of the pinch will enable planning to optimize these impacts. We show that density peaking is predicted by nonlinear gyrokinetic turbulence simulations based on measured profile data from low collisionality H-mode plasma in Alcator C-Mod. Multiple ion species are included to determine whether hydrogenic density peaking has an isotope dependence or is influenced by typical levels of low-Z impurities, and whether impurity density peaking depends on the species. We find that the deuterium density profile is slightly more peaked than that of hydrogen, and that experimentally relevant levels of boron have no appreciable effect on hydrogenic density peaking. The ratio of density at r/a = 0.44 to that at r/a = 0.74 is 1.2 for the majority D and minority H ions (and for electrons), and increases with impurity Z: 1.1 for helium, 1.15 for boron, 1.3 for neon, 1.4 for argon, and 1.5 for molybdenum. The ion temperature profile is varied to match better the predicted heat flux with the experimental transport analysis, but the resulting factor of two change in heat transport has only a weak effect on the predicted density peaking.
Mikkelsen, D. R. Bitter, M.; Delgado-Aparicio, L.; Hill, K. W.; Greenwald, M.; Howard, N. T.; Hughes, J. W.; Rice, J. E.; Reinke, M. L.; Podpaly, Y.; Ma, Y.; Candy, J.; Waltz, R. E.
2015-06-15
Peaked density profiles in low-collisionality AUG and JET H-mode plasmas are probably caused by a turbulently driven particle pinch, and Alcator C-Mod experiments confirmed that collisionality is a critical parameter. Density peaking in reactors could produce a number of important effects, some beneficial, such as enhanced fusion power and transport of fuel ions from the edge to the core, while others are undesirable, such as lower beta limits, reduced radiation from the plasma edge, and consequently higher divertor heat loads. Fundamental understanding of the pinch will enable planning to optimize these impacts. We show that density peaking is predicted by nonlinear gyrokinetic turbulence simulations based on measured profile data from low collisionality H-mode plasma in Alcator C-Mod. Multiple ion species are included to determine whether hydrogenic density peaking has an isotope dependence or is influenced by typical levels of low-Z impurities, and whether impurity density peaking depends on the species. We find that the deuterium density profile is slightly more peaked than that of hydrogen, and that experimentally relevant levels of boron have no appreciable effect on hydrogenic density peaking. The ratio of density at r/a = 0.44 to that at r/a = 0.74 is 1.2 for the majority D and minority H ions (and for electrons), and increases with impurity Z: 1.1 for helium, 1.15 for boron, 1.3 for neon, 1.4 for argon, and 1.5 for molybdenum. The ion temperature profile is varied to match better the predicted heat flux with the experimental transport analysis, but the resulting factor of two change in heat transport has only a weak effect on the predicted density peaking.
Nonlinear coherent structures of Alfvén wave in a collisional plasma
NASA Astrophysics Data System (ADS)
Jana, Sayanee; Ghosh, Samiran; Chakrabarti, Nikhil
2016-07-01
The Alfvén wave dynamics is investigated in the framework of two-fluid approach in a compressible collisional magnetized plasma. In the finite amplitude limit, the dynamics of the nonlinear Alfvén wave is found to be governed by a modified Korteweg-de Vries Burgers equation (mKdVB). In this mKdVB equation, the electron inertia is found to act as a source of dispersion, and the electron-ion collision serves as a dissipation. The collisional dissipation is eventually responsible for the Burgers term in mKdVB equation. In the long wavelength limit, this weakly nonlinear Alfvén wave is shown to be governed by a damped nonlinear Schrödinger equation. Furthermore, these nonlinear equations are analyzed by means of analytical calculation and numerical simulation to elucidate the various aspects of the phase-space dynamics of the nonlinear wave. Results reveal that nonlinear Alfvén wave exhibits the dissipation mediated shock, envelope, and breather like structures. Numerical simulations also predict the formation of dissipative Alfvénic rogue wave, giant breathers, and rogue wave holes. These results are discussed in the context of the space plasma.
Hershkowitz, N.; Yip, C.-S.; Severn, G. D.
2011-05-15
Recent experiments have shown that ions in weakly collisional plasmas containing two ion species of comparable densities approximately reach a common velocity at the sheath edge equal to the bulk plasma ion sound velocity. A recent theory [S. D. Baalrud, C. C. Hegna, and J. D. Callen, Phys. Rev. Lett. 103, 205002 (2009)] suggests that this is a consequence of collisional friction between the two ion species enhanced by the two stream instability. The theory finds that the difference in velocities at the sheath edge depends on the relative concentrations of the two ions. The difference in velocities is small, with both species approaching to the bulk sound velocity, when the concentrations are comparable, and is large, with each species reaching its own Bohm velocity, when the relative concentration differences are large. To test these findings, drift velocities of Ar and Xe ions were measured with laser-induced fluorescence in Ar-Xe and He-Xe plasmas and combined with ion acoustic wave and plasma potential data. In addition, electron temperature was varied by a Maxwell demon [K. R. MacKenzie et al., App. Phys. Lett. 18, 529 (1971)]. The predictions were found to be in excellent agreement with the experimental data. The generalized Bohm criterion in two ion species plasmas is also verified in a wider variety of relative ion concentrations.
Collisional Effects on Nonlinear Ion Drag Force for Small Grains
NASA Astrophysics Data System (ADS)
Hutchinson, I. H.; Haakonsen, C. B.
2013-10-01
Ion drag force arising from plasma flow past an embedded grain in a plasma is a vital part of dusty plasma dynamics. Ion-neutral collisions are often significant for experimental dusty plasmas. They are here included self-consistently in properly nonlinear comprehensive drag calculations, for the first time. The ion drag on a spherical grain is calculated using particle in cell codes SCEPTIC and COPTIC. Using ion velocity ``drift'' distribution appropriate for flow driven by a force field gives wake potential and force greatly different from a shifted Maxwellian distribution, regardless of collisionality level. The low-collisionality forces are shown to be consistent with estimates based upon cross-sections for scattering in a Yukawa (shielded) grain field, but only if nonlinear shielding length is used. Finite collisionality initially enhances the drag force, but only by up to a factor of 2. Larger collisionality eventually reduces the drag force. In the collisional regime, the drift distribution gives larger drag than the shift distribution even at velocities where their collisionless drags are equal. Comprehensive practical analytic formulas for force that fit the calculations are provided. Partially supported by NSF/DOE Grant DE-FG02-06ER54982 and Science Graduate Fellowship Program DE-AC05-06OR23100.
Collisional activation with random noise in ion trap mass spectrometry
McLuckey, S.A.; Goeringer, D.E.; Glish, G.L.
1992-07-01
Random noise applied to the end caps of a quadrupole ion trap is shown to be an effective means for the collisional activation of trapped ions independent of mass/charge ratio and number of ions. This technique is compared and contrasted with conventional single-frequency collisional activation for the molecular ion of N,N-dimethylaniline, protonated cocaine, the molecular anion of 2,4,6-trinitrotoluene, and doubly protonated neuromedin U-8. Collisional activation with noise tends to produce more extensive fragmentation than the conventional approach due to the fact that product ions are also kinetically excited in the noise experiment. The efficiency of the noise experiment in producing detectable product ions relative to the conventional approach ranges from being equivalent to being a factor of 3 less efficient. Furthermore, discrimination against low mass/charge product ions is apparent in the data from multiply charged biomolecules. Nevertheless, collisional activation with random noise provides a very simple means for overcoming problems associated with the dependence of single-frequency collisional activation on mass/charge ratio and the number of ions in the ion trap. 45 refs., 7 figs.
Eulerian simulations of collisional effects on electrostatic plasma waves
NASA Astrophysics Data System (ADS)
Pezzi, Oreste; Valentini, Francesco; Perrone, Denise; Veltri, Pierluigi
2013-09-01
The problem of collisions in a plasma is a wide subject with a huge historical literature. In fact, the description of realistic plasmas is a tough problem to attack, both from the theoretical and the numerical point of view. In this paper, a Eulerian time-splitting algorithm for the study of the propagation of electrostatic waves in collisional plasmas is presented. Collisions are modeled through one-dimensional operators of the Fokker-Planck type, both in linear and nonlinear forms. The accuracy of the numerical code is discussed by comparing the numerical results to the analytical predictions obtained in some limit cases when trying to evaluate the effects of collisions in the phenomenon of wave plasma echo and collisional dissipation of Bernstein-Greene-Kruskal waves. Particular attention is devoted to the study of the nonlinear Dougherty collisional operator, recently used to describe the collisional dissipation of electron plasma waves in a pure electron plasma column [M. W. Anderson and T. M. O'Neil, Phys. Plasmas 14, 112110 (2007)]. Finally, for the study of collisional plasmas, a recipe to set the simulation parameters in order to prevent the filamentation problem can be provided, by exploiting the property of velocity diffusion operators to smooth out small velocity scales.
DBCC Software as Database for Collisional Cross-Sections
NASA Astrophysics Data System (ADS)
Moroz, Daniel; Moroz, Paul
2014-10-01
Interactions of species, such as atoms, radicals, molecules, electrons, and photons, in plasmas used for materials processing could be very complex, and many of them could be described in terms of collisional cross-sections. Researchers involved in plasma simulations must select reasonable cross-sections for collisional processes for implementing them into their simulation codes to be able to correctly simulate plasmas. However, collisional cross-section data are difficult to obtain, and, for some collisional processes, the cross-sections are still not known. Data on collisional cross-sections can be obtained from numerous sources including numerical calculations, experiments, journal articles, conference proceedings, scientific reports, various universities' websites, national labs and centers specifically devoted to collecting data on cross-sections. The cross-sections data received from different sources could be partial, corresponding to limited energy ranges, or could even not be in agreement. The DBCC software package was designed to help researchers in collecting, comparing, and selecting cross-sections, some of which could be constructed from others or chosen as defaults. This is important as different researchers may place trust in different cross-sections or in different sources. We will discuss the details of DBCC and demonstrate how it works and why it is beneficial to researchers working on plasma simulations.
Eulerian simulations of collisional effects on electrostatic plasma waves
Pezzi, Oreste; Valentini, Francesco; Perrone, Denise; Veltri, Pierluigi
2013-09-15
The problem of collisions in a plasma is a wide subject with a huge historical literature. In fact, the description of realistic plasmas is a tough problem to attack, both from the theoretical and the numerical point of view. In this paper, a Eulerian time-splitting algorithm for the study of the propagation of electrostatic waves in collisional plasmas is presented. Collisions are modeled through one-dimensional operators of the Fokker-Planck type, both in linear and nonlinear forms. The accuracy of the numerical code is discussed by comparing the numerical results to the analytical predictions obtained in some limit cases when trying to evaluate the effects of collisions in the phenomenon of wave plasma echo and collisional dissipation of Bernstein-Greene-Kruskal waves. Particular attention is devoted to the study of the nonlinear Dougherty collisional operator, recently used to describe the collisional dissipation of electron plasma waves in a pure electron plasma column [M. W. Anderson and T. M. O'Neil, Phys. Plasmas 14, 112110 (2007)]. Finally, for the study of collisional plasmas, a recipe to set the simulation parameters in order to prevent the filamentation problem can be provided, by exploiting the property of velocity diffusion operators to smooth out small velocity scales.
The Collisional Evolution of Debris Disks
NASA Astrophysics Data System (ADS)
Gáspár, A.; Rieke, G. H.; Psaltis, D.; Özel, F.; Balog, Z.
2014-03-01
With their discovery, debris disks gave the first proof of existence of extrasolar planetary systems (Aumann et al. 1984, Smith & Terrile 1984). Although extrasolar planets are now readily detected, the importance of debris disks in characterizing their host systems is not diminished. Debris disks are relatively easy to detect at infrared wavelengths, independent of their viewing angle; they enable the study of the dynamical evolution of their host systems; they are able to reveal the outer regions of the systems where planets are difficult to detect; and coronagraphic scattered light images show the active sites of major dust production within the systems. During their operational lifetime, the Spitzer Space Telescope and the Herschel Space Observatory have observed many hundreds of resolved and unresolved debris disks. These detections have helped us characterize the thermal emission and also location of the disks. The observations have also shown a general decay in the observed infrared luminosity of the debris disks as a function of system age and disk location. This evolution must be understood thoroughly before probing other parameters, such as their dependence on stellar metallicity or binarity. A second critical parameter is the shape of the particle size distribution, which can strongly influence conclusions from spectral energy distribution models. I will describe results obtained with our collisional cascade code, which has been optimized to study the time evolution of debris disk dust. I will show that the rate of the decay varies throughout the evolution of the disks, increasing its rate up to a certain point, which is followed by a leveling off to a value of Lir(t)~-0.6. This is slower than the ~-1 decay given by traditional analytic models. I will show how our numerical code can reproduce the fraction of detected debris disk sources within an extensive catalog of Spitzer and Herschel 24, 70, and 100 µm observations (Gaspar et al. 2013). I will also
Aperiodic Weak Topological Superconductors.
Fulga, I C; Pikulin, D I; Loring, T A
2016-06-24
Weak topological phases are usually described in terms of protection by the lattice translation symmetry. Their characterization explicitly relies on periodicity since weak invariants are expressed in terms of the momentum-space torus. We prove the compatibility of weak topological superconductors with aperiodic systems, such as quasicrystals. We go beyond usual descriptions of weak topological phases and introduce a novel, real-space formulation of the weak invariant, based on the Clifford pseudospectrum. A nontrivial value of this index implies a nontrivial bulk phase, which is robust against disorder and hosts localized zero-energy modes at the edge. Our recipe for determining the weak invariant is directly applicable to any finite-sized system, including disordered lattice models. This direct method enables a quantitative analysis of the level of disorder the topological protection can withstand. PMID:27391744
Aperiodic Weak Topological Superconductors
NASA Astrophysics Data System (ADS)
Fulga, I. C.; Pikulin, D. I.; Loring, T. A.
2016-06-01
Weak topological phases are usually described in terms of protection by the lattice translation symmetry. Their characterization explicitly relies on periodicity since weak invariants are expressed in terms of the momentum-space torus. We prove the compatibility of weak topological superconductors with aperiodic systems, such as quasicrystals. We go beyond usual descriptions of weak topological phases and introduce a novel, real-space formulation of the weak invariant, based on the Clifford pseudospectrum. A nontrivial value of this index implies a nontrivial bulk phase, which is robust against disorder and hosts localized zero-energy modes at the edge. Our recipe for determining the weak invariant is directly applicable to any finite-sized system, including disordered lattice models. This direct method enables a quantitative analysis of the level of disorder the topological protection can withstand.
Collisional evolution of asteroids - Populations, rotations, and velocities
NASA Technical Reports Server (NTRS)
Davis, D. R.; Chapman, C. R.; Greenberg, R.; Weidenschilling, S. J.; Harris, A. W.
1979-01-01
The collisional evolution of various initial populations of asteroids is simulated numerically and compared with the present asteroid size-frequency distribution to find those populations which collisionally relax to the present belt. Both orbital and size distributions are treated, as well as the simultaneous evolution of two collisionally interacting populations with different physical properties. If the initial belt distribution was a power law, the initial belt population at the time when the present high-collision speed was established was probably only modestly larger than the present population. However, other distributions allow a more massive early belt. The rotational evolution due to collisions of asteroids with power-law distributions is also examined and compared with observations, leading to conclusions generally in agreement with those of size evolution. The high-collision speed in the present belt is likely due to Jupiter. Gravitational stirring by massive Jupiter-scattered planetesimals or secular resonances sweeping through the belt are the most probable mechanisms.
Fundamentally distinct outcomes of asteroid collisional evolution: Itokawa and Eros
NASA Astrophysics Data System (ADS)
Cheng, A. F.; Barnouin-Jha, O.; Hirata, N.; Miyamoto, H.; Nakamura, R.; Yano, H.
2007-05-01
The outcomes of asteroid collisional evolution are presently unclear: are most asteroids larger than 1 km size gravitational aggregates reaccreted from fragments of a parent body that was collisionally disrupted, while much smaller asteroids are collisional shards that were never completely disrupted? The 16 km mean diameter S-type asteroid 433 Eros, visited by the NEAR mission, has surface geology consistent with being a fractured shard. The Hayabusa spacecraft visited an S-asteroid smaller than 1 km, namely 25143 Itokawa. Here we report the first comparative analyses of Itokawa and Eros geology. Itokawa lacks a global lineament fabric, and its blocks, craters, and regolith are inconsistent with formation and evolution as a fractured shard, unlike Eros. Itokawa is not a scaled-down Eros, but formed by a distinct process of catastrophic disruption and reaccumulation.
Symplectic integration for the collisional gravitational N-body problem
NASA Astrophysics Data System (ADS)
Hernandez, David M.; Bertschinger, Edmund
2015-09-01
We present a new symplectic integrator designed for collisional gravitational N-body problems which makes use of Kepler solvers. The integrator is also reversible and conserves nine integrals of motion of the N-body problem to machine precision. The integrator is second order, but the order can easily be increased by the method of Yoshida. We use fixed time step in all tests studied in this paper to ensure preservation of symplecticity. We study small N collisional problems and perform comparisons with typically used integrators. In particular, we find comparable or better performance when compared to the fourth-order Hermite method and much better performance than adaptive time step symplectic integrators introduced previously. We find better performance compared to SAKURA, a non-symplectic, non-time-reversible integrator based on a different two-body decomposition of the N-body problem. The integrator is a promising tool in collisional gravitational dynamics.
Collisional dynamics of perturbed particle disks in the solar system
NASA Technical Reports Server (NTRS)
Roberts, William W., Jr.
1989-01-01
Theoretical and computational studies were carried out on galactic and planetary disks. With the goal of addressing important open questions centered on galactic structure, the cloudy interstellar medium, giant molecular clouds, and star formation in galactic disks and the collisional dynamics of perturbed particulate matter in planetary disks, focus was largely on the self-gravitational effects, dissipative effects, and collisional dynamics of cloud-particle disks. N-body, 'cloud-particle' computational algorithms were developed for the purpose of isolating the role of gaseous self gravity from the roles of other dominant physical mechanisms and dynamical processes, e.g. the collisional dynamics and dissipative processes. The efforts focused largely on galactic disks show that observational constraints provide stringent tests of the numerical simulation techniques developed. Self gravitational effects of the galactic interstellar medium's gas clouds are included by means of Fourier Transform technique.
Transverse momentum diffusion and collisional jet energy loss in non-Abelian plasmas
Schenke, Bjoern; Strickland, Michael; Dumitru, Adrian; Nara, Yasushi; Greiner, Carsten
2009-03-15
We consider momentum broadening and energy loss of high-momentum partons in a hot non-Abelian plasma due to collisions. We solve the coupled system of Wong-Yang-Mills equations on a lattice in real time, including binary hard elastic collisions among the partons. The collision kernel is constructed such that the total collisional energy loss and momentum broadening are lattice-spacing independent. We find that the transport coefficient q corresponding to transverse momentum broadening receives sizable contributions from a power-law tail in the p{sub perpendicular} distribution of high-momentum partons. We establish the scaling of q and of dE/dx with density, temperature, and energy in the weak-coupling regime. We also estimate the nuclear modification factor R{sub AA} due to elastic energy loss of a jet in a classical Yang-Mills field.
Effects of Collisional Zonal Flow Damping on ITG turbulence
NASA Astrophysics Data System (ADS)
Lin, Zhihong
1999-11-01
In most previous transport studies, ion-ion collisions have been assumed to have little or no effect on the ion-temperature-gradient (ITG) turbulence, and tokamak core ion thermal transport have been considered ``collisionless''. However, recent transport scaling studies on DIII-D(C.C. Petty and T.C. Luce, Phys. Plasmas) 6, 909 (1999). core plasmas showed that effective thermal diffusivity strongly depends on collisionality in the H-mode, and is almost independent of collisionality in the L-mode. Here we report results of massively parallel gyrokinetic particle simulations which show that the ion thermal transport from electrostatic ITG turbulence depends on ion-ion collisions for representative tokamak core H-mode plasma parameters. The collisionality-dependence of the turbulent transport comes from the neoclassical damping of self-generated E × B zonal flows(Z. Lin, T.S. Hahm, W.W. Lee, W.M. Tang, and R.B. White, Science) 281, 1835 (1998). which regulate the turbulence. The results from our full torus gyrokinetic simulations with a momentum and energy conserving Fokker-Planck operator are consistent with the experimental observation that the collisional dependence of transport is much more pronounced in the enhanced confinement regime where turbulence is expected to be weaker than that of typical L-mode plasmas. Furthermore, the fluctuations and heat transport in these simulations exhibit bursting behavior with a period corresponding to the collisional damping time of poloidal flows. This is consistent with the observation in TFTR core plasmas(E. Mazzucato et al.), Phys. Rev. Lett. 77, 3145 (1996). of a density fluctuation bursting with a period ( ~ 3 ms) close to the collisional flow damping time calculated from experimental plasma parameters.
Radiative and collisional processes in CNA 2Π i
NASA Astrophysics Data System (ADS)
Halpern, Joshua B.; Huang, Yuhui; Titarchuk, Tatiana
1996-02-01
In the last four years we have carried out a number of studies on the radiative and collisional processes in theA 2Π i state of CN. Many of these of interest to those studying planetary atmospheres, comets and solar spectra are summarized in this paper. Data for CNA 2Π i fluorescence lifetimes and quenching rates, and collisional energy transfer between CNA 2Π i andX 2∑+ are reported. Detailed comparisons and a discussion of the results may be found in several already published papers.
Electron transport in a collisional plasma with multiple ion species
Simakov, Andrei N. Molvig, Kim
2014-02-15
A generalization of the Braginskii electron fluid description [S. I. Braginskii, Sov. Phys. JETP 6, 358 (1958)] to the case of an unmagnetized collisional plasma with multiple ion species is presented. A description of the plasma ions with disparate masses is also discussed.
Collisional Evolution Of The Populations Of Trans-Neptunian Objects
NASA Astrophysics Data System (ADS)
Campo Bagatin, Adriano; Benavidez, P. G.
2006-09-01
The Trans-Neptunian region is yet another example of a collisional system of small bodies in the Solar System. In the last decade the number of TNOs with reliable orbital elements is steadily increasing and we can begin to try and compare collisional evolution models to observed populations. We are developing a model that takes into account the known physics of the fragmentation of icy/rocky bodies, and that considers the different orbital characteristics of the Trans-Neptunian regions ("plutinos" or resonant objects, classical belt and scattered disk) and their mutual interactions. In the last few years it has been proposed that the outer planets, and in particular Neptune, have undergone a migration to their present location and that the TNO region may have experienced a similiar process. With this purpose we also mimick this migration and compare the corresponding outcomes with other possible scenarios. What was the primordial distribution in this region? Is the collisional cascade efficient enough to justify the loss of mass occurred in this region? Is the Trans-Neptunian belt collisionally relaxed? How did Neptune's migration affect the distribution of TNOs? These are some of the key questions regarding TNOs and the evolution of the outer Solar System that we try to help answering with this work. With aknowledgements to the spanish Ministerio de Educacion y Ciencia for financial support.
Comment on "Paleoclassical Transport in Low-Collisionality Toroidal Plasmas"
LoDestro, L L
2006-10-13
Paleoclassical transport [1] is a recently proposed fundamental process that is claimed to occur in resistive plasmas and to be missing in the collisional drift-kinetic equations (DKE) in standard use. In this Comment we raise three puzzles presented by paleoclassical transport as developed in [1], one to do with conservation and two concerning uniqueness.
The limits of the Bohm criterion in collisional plasmas
Valentini, H.-B.; Kaiser, D.
2015-05-15
The sheath formation within a low-pressure collisional plasma is analysed by means of a two-fluid model. The Bohm criterion takes into account the effects of the electric field and the inertia of the ions. Numerical results yield that these effects contribute to the space charge formation, only, if the collisionality is lower than a relatively small threshold. It follows that a lower and an upper limit of the drift speed of the ions exist where the effects treated by Bohm can form a sheath. This interval becomes narrower as the collisionality increases and vanishes at the mentioned threshold. Above the threshold, the sheath is mainly created by collisions and the ionisation. Under these conditions, the sheath formation cannot be described by means of Bohm like criteria. In a few references, a so-called upper limit of the Bohm criterion is stated for collisional plasmas where the momentum equation of the ions is taken into account, only. However, the present paper shows that this limit results in an unrealistically steep increase of the space charge density towards the wall, and, therefore, it yields no useful limit of the Bohm velocity.
Collisional diffusion in toroidal plasmas with elongation and triangularity
Martin, P.; Castro, E.; Haines, M. G.
2007-05-15
Collisional diffusion is analyzed for plasma tokamaks with different ellipticities and triangularities. Improved nonlinear equations for the families of magnetic surfaces are used here. Dimensionless average velocities are calculated as a function of the inductive electric field, elongation, triangularity, and Shafranov shift. Confinement has been found to depend significantly on triangularity.
Comets as collisional fragments of a primordial planetesimal disk
NASA Astrophysics Data System (ADS)
Morbidelli, A.; Rickman, H.
2015-11-01
Context. The Rosetta mission and its exquisite measurements have revived the debate on whether comets are pristine planetesimals or collisionally evolved objects. Aims: We investigate the collisional evolution experienced by the precursors of current comet nuclei during the early stages of the solar system in the context of the so-called Nice model. Methods: We considered two environments for the collisional evolution: (1) the transplanetary planetesimal disk, from the time of gas removal until the disk was dispersed by the migration of the ice giants; and (2) the dispersing disk during the time that the scattered disk was formed. We performed simulations using different methods in the two cases to determine the number of destructive collisions typically experienced by a comet nucleus of 2 km radius. Results: In the widely accepted scenario, where the dispersal of the planetesimal disk occurred at the time of the Late Heavy Bombardment about 4 Gy ago, comet-sized planetesimals have a very low probability of surviving destructive collisions in the disk. On the extreme assumption that the disk was dispersed directly upon gas removal, a significant fraction of the planetesimals might have remained intact. However, these survivors would still bear the marks of many nondestructive impacts. Conclusions: The Nice model of solar system evolution predicts that typical km-sized comet nuclei are predominantly fragments resulting from collisions experienced by larger parent bodies. An important goal for future research is to investigate whether the observed properties of comet nuclei are compatible with such a collisional origin.
Peculiarities of collisional excitation transfer with excited screened energy levels of atoms
Gerasimov, V. A.; Gerasimov, V. V.; Pavlinskiy, A. V.
2007-09-15
We report an experimental discovery of deviations from the known regularities in collisional excitation transfer processes for metal atoms. The collisional excitation transfer with excited screened energy levels of thulium and dysprosium atoms is studied. The selecting role of the screening 6s shell in collisional excitation transfer is shown.
DOE R&D Accomplishments Database
Lee, T. D.
1970-07-01
While the phenomenon of beta-decay was discovered near the end of the last century, the notion that the weak interaction forms a separate field of physical forces evolved rather gradually. This became clear only after the experimental discoveries of other weak reactions such as muon-decay, muon-capture, etc., and the theoretical observation that all these reactions can be described by approximately the same coupling constant, thus giving rise to the notion of a universal weak interaction. Only then did one slowly recognize that the weak interaction force forms an independent field, perhaps on the same footing as the gravitational force, the electromagnetic force, and the strong nuclear and sub-nuclear forces.
High-frequency electromagnetic surface waves in a semi-bounded weakly ionized plasma
Moaied, M.; Tyshetskiy, Yu.; Vladimirov, S. V.
2013-02-15
High-frequency electromagnetic surface waves (SWs) in a weakly ionized plasma half-space with Maxwellian electrons are studied taking into account elastic electron-neutral collisions. The SWs spectrum and damping rate are obtained numerically for a wide range of wavelengths, and the asymptotes of damping rate are analytically calculated in some limits. It is shown that the high-frequency SWs become strongly damped at wavelengths {lambda}<{lambda}{sub Min}, where {lambda}{sub Min} significantly depends on plasma parameters (e.g., electron temperature and electron and neutral atom density). The relative importance of collisional and Cherenkov (collisionless) damping of SWs is investigated and is graphically shown for a range of plasma parameters and SW wavelengths. The behavior of weakly ionized plasma with respect to the SW propagation has been recovered for the collisional parameter {eta}.
NASA Astrophysics Data System (ADS)
Chuang, S. Y.; Chang, F. H.; Bell, J. R.
Consideration is given to the development of a weak bond screening system which is based on the utilization of a high power ultrasonic (HPU) technique. The instrumentation of the prototype bond strength screening system is described, and the adhesively bonded specimens used in the system developmental effort are detailed. Test results obtained from these specimens are presented in terms of bond strength and level of high power ultrasound irradiation. The following observations were made: (1) for Al/Al specimens, 2.6 sec of HPU irradiation will screen weak bond conditions due to improper preparation of bonding surfaces; (2) for composite/composite specimens, 2.0 sec of HPU irradiation will disrupt weak bonds due to under-cured conditions; (3) for Al honeycomb core with composite skin structure, 3.5 sec of HPU irradiation will disrupt weak bonds due to bad adhesive or oils contamination of bonding surfaces; and (4) for Nomex honeycomb with Al skin structure, 1.3 sec of HPU irradiation will disrupt weak bonds due to bad adhesive.
NASA Technical Reports Server (NTRS)
Wilkes, B. J.; Mcdowell, J.
1994-01-01
Research into the optical, ultraviolet and infrared continuum emission from quasars and their host galaxies was carried out. The main results were the discovery of quasars with unusually weak infrared emission and the construction of a quantitative estimate of the dispersion in quasar continuum properties. One of the major uncertainties in the measurement of quasar continuum strength is the contribution to the continuum of the quasar host galaxy as a function of wavelength. Continuum templates were constructed for different types of host galaxy and individual estimates made of the decomposed quasar and host continua based on existing observations of the target quasars. The results are that host galaxy contamination is worse than previously suspected, and some apparent weak bump quasars are really normal quasars with strong host galaxies. However, the existence of true weak bump quasars such as PHL 909 was confirmed. The study of the link between the bump strength and other wavebands was continued by comparing with IRAS data. There is evidence that excess far infrared radiation is correlated with weaker ultraviolet bumps. This argues against an orientation effect and implies a probable link with the host galaxy environment, for instance the presence of a luminous starburst. However, the evidence still favors the idea that reddening is not important in those objects with ultraviolet weak bumps. The same work has led to the discovery of a class of infrared weak quasars. Pushing another part of the envelope of quasar continuum parameter space, the IR-weak quasars have implications for understanding the effects of reddening internal to the quasars, the reality of ultraviolet turnovers, and may allow further tests of the Phinney dust model for the IR continuum. They will also be important objects for studying the claimed IR to x-ray continuum correlation.
Atom-atom inelastic collisions and three-body atomic recombination in weakly ionized argon plasmas
NASA Technical Reports Server (NTRS)
Braun, C. G.; Kunc, J. A.
1989-01-01
A stationary collisional-radiative model including both inelastic electron-atom and atom-atom collisions is used to examine nonequilibrium weakly ionized argon plasmas with atomic densities 10 to the 16th to 10 to the 20th/cu cm, temperatures below 6000 K, and with different degrees of radiation trapping. It is shown that three-body atomic recombination becomes important at high particle densities. Comparison is made between the present approach and Thomson's theory for atomic recombination.
Ion-Atom and Atom-Atom Collisional Processes and Modeling of Stellar Atmospheres
NASA Astrophysics Data System (ADS)
Mihajlov, A. A.; Ignjatovic, Lj. M.; Sreckovic, V. A.; Dimitrijevic, M. S.; Dimitrijevic, M. S.
2015-09-01
We report the results obtained in our previous works on the influence of two groups of collisional processes (ion--atom and atom--atom) on the optical and kinetic properties of weakly ionised plasma. The first group includes radiative processes of the photodissociation/association type and radiative charge exchange, the second one -- chemi-ionisation/recombination processes. The effect of the radiative processed is assessed by comparing their intensities with those of the known competing processed in application to the solar photosphere and to the photospheres of DB white dwarfs. The studied chemi-ionisation/recombination processes are considered from the viewpoint of their influence on the populations of the excited states of the hydrogen atom (the Sun and an M-type red dwarf with an effective temperature of 3800~K) and helium atom (DB white dwarfs). The effect of these processes on the populations of the excited states of the hydrogen atom has been studied using the PHOENIX code, which generates the model of the considered atmosphere. The reported results demonstrate the unquestionable influence of the considered radiative and chemi- ionisation/recombination processes on the optical properties and on the kinetics of the weakly ionised layers in stellar atmospheres. It can be expected that the reported results will be a sufficient reason for including these processes in the models of stellar atmospheres.
NASA Technical Reports Server (NTRS)
Mcdowell, Jonathan C.; Elvis, Martin; Wilkes, Belinda J.; Willner, Steven P.; Oey, M. S.
1989-01-01
The recent emphasis on big bumps dominating the UV continuum of quasars has obscured the facts that bump properties vary widely and that there are objects in which no such component is evident. As part of a survey of quasar continuum spectra, a class of quasars is identified in which the optical-UV continuum big bump feature appears to be weak or absent, relative to both IR and X-ray. These weak bump quasars are otherwise normal objects and constitute a few percent of the quasar population.
NASA Technical Reports Server (NTRS)
Mcdowell, J. C.; Elvis, M.; Wilkes, B. J.
1992-01-01
Examples of quasars with anomalously weak IR emission are presented, and the effects of starlight subtraction on estimates of the UV and IR component strengths are discussed. Inferred model parameters are very sensitive to the position of the peak of the UV energy distribution. In many low redshift objects the peak is not seen; even in those objects where the turnover is clear, the turnover may not be intrinsic but instead due to reddening within the quasar host galaxy. The small number of unusual quasars with weak IR emission will be of utility as a probe of the quasar phenomenon in the absence of dominant dust reprocessing.
NASA Astrophysics Data System (ADS)
Hunter, John K.; Brio, Moysey
2000-05-01
We present numerical solutions of a two-dimensional inviscid Burgers equation which provides an asymptotic description of the Mach reflection of weak shocks. In our numerical solutions, the incident, reflected, and Mach shocks meet at a triple point, and there is a supersonic patch behind the triple point, as proposed by Guderley for steady weak-shock reflection. A theoretical analysis indicates that there is an expansion fan at the triple point, in addition to the three shocks. The supersonic patch is extremely small, and this work is the first time it has been resolved.
Localization of collisionally inhomogeneous condensates in a bichromatic optical lattice
NASA Astrophysics Data System (ADS)
Cheng, Yongshan; Adhikari, S. K.
2011-02-01
By direct numerical simulation and variational solution of the Gross-Pitaevskii equation, we studied the stationary and dynamic characteristics of a cigar-shaped, localized, collisionally inhomogeneous Bose-Einstein condensate trapped in a one-dimensional bichromatic quasiperiodic optical-lattice potential, as used in a recent experiment on the localization of a Bose-Einstein condensate [Roati , Nature (London)NATUAS0028-083610.1038/nature07071 453, 895 (2008)]. The effective potential characterizing the spatially modulated nonlinearity is obtained. It is found that the collisional inhomogeneity has influence not only on the central region but also on the tail of the Bose-Einstein condensate. The influence depends on the sign and value of the spatially modulated nonlinearity coefficient. We also demonstrate the stability of the stationary localized state by performing a standard linear stability analysis. Where possible, the numerical results are shown to be in good agreement with the variational results.
Collisional dynamics of perturbed particle disks in the solar system
NASA Technical Reports Server (NTRS)
Roberts, W. W.; Stewart, G. R.
1987-01-01
Investigations of the collisional evolution of particulate disks subject to the gravitational perturbation of a more massive particle orbiting within the disk are underway. Both numerical N-body simulations using a novel collision algorithm and analytical kinetic theory are being employed to extend our understanding of perturbed disks in planetary rings and during the formation of the solar system. Particular problems proposed for investigation are: (1) The development and testing of general criteria for a small moonlet to clear a gap and produce observable morphological features in planetary rings; (2) The development of detailed models of collisional damping of the wavy edges observed on the Encke division of Saturn's A ring; and (3) The determination of the extent of runaway growth of the few largest planetesimals during the early stages of planetary accretion.
Scaled Energy Spectroscopy of Collisionally Perturbed Potassium Rydberg States
NASA Astrophysics Data System (ADS)
Keeler, Matthew Len; Setzer, William
2010-03-01
We will present preliminary results on the recurrence spectroscopy (or scaled energy spectroscopy) of highly-excited potassium in the presence of collisional perturbations. Recurrence spectroscopy, with the aid of closed orbit theory, has produced useful insights into the semi-classical description of non-hydrogenic spectral features of excited atoms in external fields. We demonstrate how to apply recurrence spectroscopy to the Stark spectrum of potassium subject to collisional line-shift and line-broadening. When krypton gas is added to the system the absorption spectrum experiences line broadening, differential line shifts, and state mixing. With an appropriately modified energy scale, perturbations of the absorption spectrum become meaningful features within the scaled-energy spectrum. New features found within the recurrence spectra can then, with semi-classical closed orbit theory, be interpreted in terms of classical decoherence, elastic and inelastic collisions.
Collisional energy loss above the critical temperature in QCD
NASA Astrophysics Data System (ADS)
Lin, Shu; Pisarski, Robert D.; Skokov, Vladimir V.
2014-03-01
We compute the collisional energy loss for a heavy quark above the critical temperature in Quantum ChromoDynamics (QCD). We work in the semi Quark-Gluon Plasma, which assumes that this region is dominated by the non-trivial holonomy of the thermal Wilson line. Relative to the result of leading order in perturbation theory, at a fixed value of the coupling constant we generically find that collisional energy loss is suppressed by powers of the Polyakov loop, l<1. For small values of the loop, this suppression is linear when the heavy quark scatters off of light quarks, and quadratic when the heavy quark scatters off of gluons, or for Compton scattering.
Collisional effects on Rayleigh-Taylor-induced magnetic fields
Manuel, M. J.-E.; Flaig, M.; Plewa, T.; Li, C. K.; Séguin, F. H.; Frenje, J. A.; Casey, D. T.; Petrasso, R. D.; Hu, S. X.; Betti, R.; Hager, J.; Meyerhofer, D. D.; Smalyuk, V.
2015-05-15
Magnetic-field generation from the Rayleigh-Taylor (RT) instability was predicted more than 30 years ago, though experimental measurements of this phenomenon have only occurred in the past few years. These pioneering observations demonstrated that collisional effects are important to B-field evolution. To produce fields of a measurable strength, high-intensity lasers irradiate solid targets to generate the nonaligned temperature and density gradients required for B-field generation. The ablation process naturally generates an unstable system where RT-induced magnetic fields form. Field strengths inferred from monoenergetic-proton radiographs indicate that in the ablation region diffusive effects caused by finite plasma resistivity are not negligible. Results from the first proof-of-existence experiments are reviewed and the role of collisional effects on B-field evolution is discussed in detail.
Sheath formation under collisional conditions in presence of dust
Moulick, R. Goswami, K. S.
2014-08-15
Sheath formation is studied for collisional plasma in presence of dust. In common laboratory plasma, the dust acquires negative charges because of high thermal velocity of the electrons. The usual dust charging theory dealing with the issue is that of the Orbit Motion Limited theory. However, the theory does not find its application when the ion neutral collisions are significantly present. An alternate theory exists in literature for collisional dust charging. Collision is modeled by constant mean free path model. The sheath is considered jointly with the bulk of the plasma and a smooth transition of the plasma profiles from the bulk to the sheath is obtained. The various plasma profiles such as the electrostatic force on the grain, the ion drag force along with the dust density, and velocity are shown to vary spatially with increasing ion neutral collision.
Collisional shifts in optical-lattice atom clocks
Band, Y. B.; Vardi, A.
2006-09-15
We theoretically study the effects of elastic collisions on the determination of frequency standards via Ramsey-fringe spectroscopy in optical-lattice atom clocks. Interparticle interactions of bosonic atoms in multiply occupied lattice sites can cause a linear frequency shift, as well as generate asymmetric Ramsey-fringe patterns and reduce fringe visibility due to interparticle entanglement. We propose a method of reducing these collisional effects in an optical lattice by introducing a phase difference of {pi} between the Ramsey driving fields in adjacent sites. This configuration suppresses site-to-site hopping due to interference of two tunneling pathways, without degrading fringe visibility. Consequently, the probability of double occupancy is reduced, leading to cancellation of collisional shifts.
Cosmological evolution in f (R ,T ) theory with collisional matter
NASA Astrophysics Data System (ADS)
Baffou, E. H.; Houndjo, M. J. S.; Rodrigues, M. E.; Kpadonou, A. V.; Tossa, J.
2015-10-01
We study the evolution of the cosmological parameters, namely, the deceleration parameter q (z ) and the parameter of effective equation of state in a Universe containing, besides ordinary matter and dark energy, a self-interacting (collisional) matter, in the generalized f (R ,T ) theory of gravity, where R and T are the curvature scalar and the trace of the energy-momentum tensor, respectively. We use the generalized Friedmann-Robertson-Walker equations and the equation of continuity and obtain a differential equation in H (z ) , and we solve it numerically for studying the evolution of the cosmological parameters. Two f (R ,T ) models are considered. The results with collisional matter are compared with the ones of the Λ cold dark matter model, and also with the model where only noncollisional matter exists. The curves show that the models are acceptable because the values found for weff are consistent with observed data.
Gyrokinetic simulation of the collisional micro-tearing mode instability
NASA Astrophysics Data System (ADS)
Startsev, Edward; Lee, Wei-Li; Wang, Weixing
2015-11-01
An application of recently developed perturbative particle simulation scheme for finite- β plasmas in the presence of background inhomogeneities is presented. Originally, using similar scheme, we were able to simulate shear-Alfven waves, finite- β modified drift waves and ion temperature gradient modes using a simple gyrokinetic particle code based on realistic fusion plasma parameters. Recently, we have successfully used the scheme for simulation of linear tearing and drift-tearing modes, in both collisionless semi-collisional regimes in slab geometry with sheared magnetic field. Here, we present further development of this scheme for the simulation of linear semi-collisional micro-tearing mode driven by electron temperature gradient in high-aspect ratio cylindrical cross-section tokamak using the modified turbulence code GTS. Research supported by the U. S. Department of Energy.
Radiative and rovibrational collisional relaxation of sodium dimer
NASA Astrophysics Data System (ADS)
Bayram, Burcin; Horton, Tim; McFarland, Jacob
2016-05-01
Radiative and rovibrational collisional relaxation of sodium dimer of the A1Σu+ (8,30) state have been measured by direct observation of the decay fluorescence. Sodium molecular vapor is created in a heatpipe oven at 600 K and excited using a 6-ns pulsed dye laser pumped by a Nd:YAG, operating at 532 nm. The preliminary lifetime measurement was done by directly acquiring lifetime data through boxcar averager from the stored oscilloscope trace of the fluorescence. Analysis of the exponential decay of the fluorescence allows us to obtain the radiative lifetime. By introducing the argon buffer gas and varying the pressure of the heatpipe, a collisional cross section between excited sodium dimer and ground state argon atom collision can be extracted using Stern-Volmer relation.
Kinetic model for the collisionless sheath of a collisional plasma
NASA Astrophysics Data System (ADS)
Tang, Xian-Zhu; Guo, Zehua
2016-08-01
Collisional plasmas typically have mean-free-path still much greater than the Debye length, so the sheath is mostly collisionless. Once the plasma density, temperature, and flow are specified at the sheath entrance, the profile variation of electron and ion density, temperature, flow speed, and conductive heat fluxes inside the sheath is set by collisionless dynamics, and can be predicted by an analytical kinetic model distribution. These predictions are contrasted here with direct kinetic simulations, showing good agreement.
Collisional Radiative Models for non-Maxwellian plasmas
NASA Astrophysics Data System (ADS)
Hartgers, Bart; van Dijk, Jan; van der Mullen, Joost
1999-10-01
Collisional Radiative models are a useful tool for studying plasmas. In their simplest form, they are used to calculate an atomic state distribution function (ASDF) from given electron and neutral densities and an electron temperature. Additionally, global ionization and recombination coefficients can be calculated as a function of electron density and temperature. In turn, these coefficients are used as input for the general plasma model
Collisional Evolution of Edgeworth-Kuiper Belt Objects
NASA Astrophysics Data System (ADS)
Davis, D. R.; Farinella, P.
1997-01-01
The Edgeworth-Kuiper Belt contains a population of objects ≈10 3times that of the main asteroid belt, spread over a volume ≈10 3larger and with relative speeds ≈10 times lower. As for the asteroids, the size distribution of Edgeworth-Kuiper Belt objects has been modified by mutual impacts over Solar System history. We have modeled this collisional evolution process using a numerical code developed originally to study asteroid collisional evolution but modified to reflect collision rates in the Edgeworth-Kuiper Belt. Our numerical simulations show that collisional evolution is substantial in the inner part of the Edgeworth-Kuiper Belt, but its intensity decreases with increasing distance from the Sun. In the inner belt, objects with diameters D> 50-100 km are not depleted by disruptive collisions; hence they reflect the original (formative) population (many of them, however, may have been converted into "rubble piles"). On the other hand, smaller objects are mostly multigenerational fragments, although the original population must have contained a significant number of bodies down to at least a few tens of kilometers in size in order to initiate a collisional cascade. About 10 fragments, 1-10 km in size, are produced per year in the inner Edgeworth-Kuiper Belt, with a few percent of them inserted into chaotic resonant orbits. This is in rough agreement with the required influx rate of Jupiter-family comets. Both collisions and dynamical instabilities associated with resonances are processes that can inject comets into the "escape hatches," but our results indicate that most comets coming from the Edgeworth-Kuiper Belt would be fragments from larger parent bodies, rather than primitive planetesimals. However, this does not apply to Chiron-sized ( D> 100 km) objects, which must be primordial and delivered to the outer Solar System by either dynamical processes or nondisruptive collisions.
System and method for collisional activation of charged particles
Ibrahim, Yehia M; Belov, Mikhail E; Prior, David C
2013-09-24
A collision cell is disclosed that provides ion activation in various selective modes. Ion activation is performed inside selected segments of a segmented quadrupole that provides maximum optimum capture and collection of fragmentation products. The invention provides collisional cooling of precursor ions as well as product fragments and further allows effective transmission of ions through a high pressure interface into a coupled mass analysis instrument.
Collisional and dynamical processes in moon and planet formation
NASA Technical Reports Server (NTRS)
1979-01-01
The collisional and dynamical processes in moon and planet formation are discussed. A hydrodynamic code of collision calculations, the orbital element changes due to gravitational scattering, a validation of the mass shifting algorithm, a theory of rotations, and the origin of asteroids are studied. A numerical model of planet growth is discussed and a methodology to evaluate the rate at which megaregolith increases its depth as a function of total accumulate number of impacts on an initially smooth, coherent surface is described.
Kinetic simulation of a collisional shock wave in a plasma
Casanova, M.; Larroche, O. ); Matte, J. )
1991-10-14
The ion kinetic structure of a planar collisional shock front in a fully ionized plasma is investigated using a new Vlasov-Fokker-Planck code. The effects of ionic viscosity and ionic thermal conduction are found to be much larger than assumed in usual hydrodynamic plasma simulations with classical transport coefficients. This might have consequences on the numerical modeling of inertial-confinement fusion targets.
NASA Astrophysics Data System (ADS)
Steinberg, Aephraim; Feizpour, Amir; Rozema; Mahler; Hayat
2013-03-01
Quantum physics is being transformed by a radical new conceptual and experimental approach known as weak measurement that can do everything from tackling basic quantum mysteries to mapping the trajectories of photons in a Young's double-slit experiment. Aephraim Steinberg, Amir Feizpour, Lee Rozema, Dylan Mahler and Alex Hayat unveil the power of this new technique.
Weaknesses in Underperforming Schools
ERIC Educational Resources Information Center
van de Grift, Wim; Houtveen, Thoni
2007-01-01
In some Dutch elementary schools, the average performance of students over several years is significantly below the level that could be expected of them. This phenomenon is known as "underperformance." The most important identifiable weaknesses that go along with this phenomenon are that (a) learning material offered at school is insufficient to…
Venugopalan, Poothirikovil; Sivakumar, Puthuval; Ardley, Robert G.; Oates, Crispian
2012-01-01
We present an 11year-old boy with a weak right radial pulse, and describe the successful application of vascular ultrasound to identify the ulnar artery dominance and a thin right radial artery with below normal Doppler flow velocity that could explain the discrepancy. The implications of identifying this anomaly are discussed. PMID:22375269
NASA Astrophysics Data System (ADS)
Wittman, David M.; Jain, B.; Jarvis, M.; Knox, L.; Margoniner, V.; Takada, M.; Tyson, J.; Zhan, H.; LSST Weak Lensing Science Collaboration
2006-12-01
Constraining dark energy parameters with weak lensing is one of the primary science goals of the LSST. The LSST Weak Lensing Science Collaboration has been formed with the goal of optimizing the weak lensing science by optimizing the survey cadence; working with Data Management to insure high-quality pipeline processing which will meet our needs; developing the necessary analysis tools well before the onset of data-taking; participating in high-fidelity simulations to test the system end-to-end; and analyzing the real dataset as it becomes available. We review the major weak lensing probes, the twoand three-point shear correlations, and how they constrain dark energy parameters. We also review the possibility of going beyond dark energy models and testing gravity with the LSST data. To realize the promise of the awesome LSST statistical precision, we must ensure that systematic errors are kept under control. We review the major sources of systematics and our plans for mitigation. We present data that demonstrate that these sources of systematics can be kept to a level smaller than the statistical error.
An anomalous current drive mechanism in low collisionality plasmas
NASA Astrophysics Data System (ADS)
McDevitt, Chris; Tang, Xianzhu; Guo, Zehua
2013-10-01
Steady state tokamak operation requires non-inductive current drive, of which the neoclassical bootstrap current is the most economic option. Here we report a novel mechanism through which a bootstrap current may be driven even in a collisionless plasma. In analogy with the neoclassical mechanism, in which the collisional equilibrium established between trapped and passing electrons produces a steady state current, we show that resonant scattering of electrons by drift wave microturbulence provides an additional means of determining the equilibrium between trapped and passing electrons. The resulting collisionless equilibrium is shown to produce a mean current whose magnitude scales with the thermodynamic forces. Employing a linearized Fokker-Planck collision operator, the plasma current in the presence of both collisions and resonant electron scattering is computed as a function of collisionality. It is found that while the volume integrated electron current is only modestly affected by the turbulent fluctuations, the radial distribution of electron current is significantly modified in low collisionality plasmas. This work was supported by DOE OFES.
COLLISIONAL EVOLUTION OF ULTRA-WIDE TRANS-NEPTUNIAN BINARIES
Parker, Alex H.; Kavelaars, J. J.
2012-01-10
The widely separated, near-equal mass binaries hosted by the cold classical Kuiper Belt are delicately bound and subject to disruption by many perturbing processes. We use analytical arguments and numerical simulations to determine their collisional lifetimes given various impactor size distributions and include the effects of mass loss and multiple impacts over the lifetime of each system. These collisional lifetimes constrain the population of small (R {approx}> 1 km) objects currently residing in the Kuiper Belt and confirm that the size distribution slope at small size cannot be excessively steep-likely q {approx}< 3.5. We track mutual semimajor axis, inclination, and eccentricity evolution through our simulations and show that it is unlikely that the wide binary population represents an evolved tail of the primordially tight binary population. We find that if the wide binaries are a collisionally eroded population, their primordial mutual orbit planes must have preferred to lie in the plane of the solar system. Finally, we find that current limits on the size distribution at small radii remain high enough that the prospect of detecting dust-producing collisions in real time in the Kuiper Belt with future optical surveys is feasible.
Collisional ballooning mode dispersion relation in the banana regime
Zheng, L.; Tessarotto, M.
1995-08-01
Collisional ballooning mode theory in the banana regime is developed for tokamak configurations from the gyrokinetic formalism. A general dispersion relation is obtained, which in principle can deal with a collision operator of any type. However, investigation of an approximate Fokker--Planck collision operator developed in recent neoclassical transport theory is detailed. The most significant feature of the present theory as compared to the customary treatment lies in that the distinction between particle and fluid velocities is made in the ordering analyses. This reveals that the eigenfrequency of modes is determined by balancing the small-parallel-ion-velocity (SPIV) effect [L.-J. Zheng and M. Tessarotto, Phys. Plasmas {bold 1}, 3928 (1994)], instead of the fluid inertia one, with the instability drives. Since the parallel-electric-field effect is found to be negligible as compared to the SPIV effect, in contrast to the customary resistive ballooning mode picture, the leading collisional effect is demonstrated to be the modification of the SPIV effect instead of the relaxation of the frozen-in-law. The ion--ion collisions are the cause for this modification, while the electron collisional effect is shown to be negligible. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.
Tearing instabilities in the banana-plateau collisionality regime
Qu, W.X.; Callen, J.D.
1985-04-01
Starting from a resistive MHD set of equations and adding neoclassical currents (bootstrap, enhanced polarization and pinch type), we derive the eigenmode equation and relevant dispersion relation for ''neoclassical MHD'' tearing modes in the banana-plateau collisionality regime. The ballooning mode representation and a multiple length scale approximation are utilized. Analysis of the dispersion relation shows that the neoclassical effects on tearing modes are quite strong for ..sqrt..epsilon ..beta../sub p/(1 + nu/sub *//sub e/)/sup -1/ > S/sup -2/5/ (epsilon is the inverse aspect ratio, ..beta../sub p/ is the poloidal beta value, nu/sub *//sub e/ is the electron collisionality factor and S is the neoclassical MHD Reynolds number). The growth rate ..gamma.. and singular layer width deltax are increased typically by more than one order of magnitude from the usual values for epsilon ..beta../sub p/ approx. = 1. For our model, the changes in the tearing modes from the banana-plateau collisionality regime to the usual Pfirsch-Schlueter regime are very clear and natural.
Damping of Bernstein-Greene-Kruskal modes in collisional plasmas
NASA Astrophysics Data System (ADS)
Valentini, Francesco
2008-02-01
In this paper, the effect of Coulomb collisions on the stability of Bernstein-Greene-Kruskal (BGK) modes [I. B. Bernstein, J. M. Greene, and M. D. Krukal, Phys. Rev. 108, 546 (1957)] is analyzed by comparing the numerical results of collisional particle-in-cell (PIC) simulations with the theoretical predictions by Zakharov and Karpman [V. E. Zakharov and V. I. Karpman, Sov. Phys. JETP 16, 351 (1963)], for the collisional damping of nonlinear plasma waves. In the absence of collisions, BGK modes are undamped nonlinear electrostatic oscillations, solutions of the Vlasov-Poisson equations; in these structures nonlinearity manifests as the formation of a plateau in the resonant region of the particle distribution function, due to trapping of resonant particles, thus preventing linear Landau damping. When particle-particle Coulomb collisions are effective, this plateau is smoothed out since collisions drive the velocity distribution towards the Maxwellian shape, thus destroying the BGK structure. As shown by Zakharov and Karpman in 1963, under certain assumptions, an exponential time decay with constant damping rate is predicted for the electric field amplitude and a linear dependence of the damping rate on the collision frequency is found. In this paper, the theory by Zakharov and Karpman is revisited and the effects of collisions on the stability of BGK modes and on the long time evolution of nonlinear Landau damping are numerically investigated. The numerical results are obtained through a collisional PIC code that reproduces a physical phenomenology also observed in recent experiments with trapped pure electron plasmas.
Constraining Collisional Models of Planetesimals in Debris Disks
NASA Astrophysics Data System (ADS)
MacGregor, Meredith A.; Wilner, David J.; Hughes, A. Meredith; Steele, Amy; Ricci, Luca; Andrews, Sean M.; Chandler, Claire J.; Tahli Maddison, Sarah
2016-01-01
Debris disks around main-sequence stars are produced by the ongoing collisional erosion of planetesimals, analogous to Kuiper Belt Objects (KBOs) or comets in our own Solar System. Observations of these dusty belts offer a window into the physical and dynamical properties of planetesimals in extrasolar systems through the size distribution of dust grains. In particular, the millimeter/radio spectral index of thermal dust emission encodes information on the grain size distribution that can be used to test proposed collisional models of planetesimals. We have made sensitive Jansky Very Large Array (JVLA) observations of a sample of 7 nearby debris disks at 9 mm and combine these with archival Australia Telescope Compact Array (ATCA) observations of 8 additional debris disks at 7 mm. Using measurements at (sub)millimeter wavelengths from the literature, we place tight constraints on the millimeter spectral indices and thus grain size distributions of this sample of debris disks. Our analysis gives a weighted mean for the slope of the power-law grain distribution that is close to the classical prediction for a steady-state collisional cascade (q=3.5), but not consistent with the steeper distributions predicted by recent models that include more complex fragmentation processes. To interpret this result, we explore the effects of material strengths, velocity distributions, and small-size cutoffs on the steady-state grain size distribution.
NASA Astrophysics Data System (ADS)
Itonaga, K.; Motoba, T.
The recent theoretical studies of Lambda-hypernuclear weak decaysof the nonmesonic and pi-mesonic ones are developed with the aim to disclose the link between the experimental decay observables and the underlying basic weak decay interactions and the weak decay mechanisms. The expressions of the nonmesonic decay rates Gamma_{nm} and the decay asymmetry parameter alpha_1 of protons from the polarized hypernuclei are presented in the shell model framework. We then introduce the meson theoretical Lambda N -> NN interactions which include the one-meson exchanges, the correlated-2pi exchanges, and the chiral-pair-meson exchanges. The features of meson exchange potentials and their roles on the nonmesonic decays are discussed. With the adoption of the pi + 2pi/rho + 2pi/sigma + omega + K + rhopi/a_1 + sigmapi/a_1 exchange potentials, we have carried out the systematic calculations of the nonmesonic decay observables for light-to-heavy hypernuclei. The present model can account for the available experimental data of the decay rates, Gamma_n/Gamma_p ratios, and the intrinsic asymmetry parameters alpha_Lambda (alpha_Lambda is related to alpha_1) of emitted protons well and consistently within the error bars. The hypernuclear lifetimes are evaluated by converting the total weak decay rates Gamma_{tot} = Gamma_pi + Gamma_{nm} to tau, which exhibit saturation property for the hypernuclear mass A ≥ 30 and agree grossly well with experimental data for the mass range from light to heavy hypernuclei except for the very light ones. Future extensions of the model and the remaining problems are also mentioned. The pi-mesonic weak processes are briefly surveyed, and the calculations and predictions are compared and confirmed by the recent high precision FINUDA pi-mesonic decay data. This shows that the theoretical basis seems to be firmly grounded.
Weak Interactions and Instability Cascades.
Kadoya, Taku; McCann, Kevin S
2015-01-01
Food web theory states that a weak interactor which is positioned in the food web such that it tends to deflect, or mute, energy away from a potentially oscillating consumer-resource interaction often enhances community persistence and stability. Here we examine how adding other weak interactions (predation/harvesting) on the stabilizing weak interactor alters the stability of food web using a set of well-established food web models/modules. We show that such "weak on weak" interaction chains drive an indirect dynamic cascade that can rapidly ignite a distant consumer-resource oscillator. Nonetheless, we also show that the "weak on weak" interactions are still more stable than the food web without them, and so weak interactions still generally act to stabilize food webs. Rather, these results are best interpreted to say that the degree of the stabilizing effect of a given important weak interaction can be severely compromised by other weak interactions (including weak harvesting). PMID:26219561
The Dependence of H-mode Energy Confinement and Transport on Collisionality in NSTX
Kaye, S. M.; Gerhardt, S.; Guttenfelder, W.; Maingi, R.; Bell, R. E.; Diallo, A.; LeBlanc, B. P.; Podesta, M.
2012-11-27
Understanding the dependence of confi nement on collisionality in tokamaks is important for the design of next-step devices, which will operate at collisionalities at least one order of magnitude lower than in present generation. A wide range of collisionality has been obtained in the National Spherical Torus Experiment (NSTX) by employing two different wall conditioning techniques, one with boronization and between-shot helium glow discharge conditioning (HeGDC+B), and one using lithium evaporation (Li EVAP). Previous studies of HeGDC+B plasmas indicated a strong and favorable dependence of normalized con nement on collisionality. Discharges with lithium conditioning discussed in the present study gen- erally achieved lower collisionality, extending the accessible range of collisionality by almost an order of unity. While the confinement dependences on dimensional, engineering variables of the HeGDC+B and Li EVAP datasets differed, collisionality was found to unify the trends, with the lower collisionality lithium conditioned discharges extending the trend of increasing normalized confi nement time with decreasing collisionality when other dimension less variables were held as fi xed as possible. This increase of confi nement with decreasing collisionality was driven by a large reduction in electron transport in the outer region of the plasma. This result is consistent with gyrokinetic calculations that show microtearing and Electron Temperature Gradient modes to be more stable for the lower collisionality discharges. Ion transport, near neoclassical at high collisionality, became more anomalous at lower collisionality, possibly due to the growth of hybrid TEM/KBM modes in the outer regions of the plasma.
The Dependence of H-mode Energy Confinement and Transport on Collisionality in NSTX
Kaye, S. M.; Gerhardt, S.; Guttenfelder, W.; Maingi, R.; Bell, R. E.; Diallo, A.; LeBlanc, B. P.; Podesta, M.
2012-11-28
Understanding the dependence of confi nement on collisionality in tokamaks is important for the design of next-step devices, which will operate at collisionalities at least one order of magnitude lower than in present generation. A wide range of collisionality has been obtained in the National Spherical Torus Experiment (NSTX) by employing two different wall conditioning techniques, one with boronization and between-shot helium glow discharge conditioning (HeGDC+B), and one using lithium evaporation (Li EVAP). Previous studies of HeGDC+B plasmas indicated a strong and favorable dependence of normalized con nement on collisionality. Discharges with lithium conditioning discussed in the present study gen- erally achieved lower collisionality, extending the accessible range of collisionality by almost an order of unity. While the confinement dependences on dimensional, engineering variables of the HeGDC+B and Li EVAP datasets differed, collisionality was found to unify the trends, with the lower collisionality lithium conditioned discharges extending the trend of increasing normalized confi nement time with decreasing collisionality when other dimension less variables were held as fi xed as possible. This increase of confi nement with decreasing collisionality was driven by a large reduction in electron transport in the outer region of the plasma. This result is consistent with gyrokinetic calculations that show microtearing and Electron Temperature Gradient modes to be more stable for the lower collisionality discharges. Ion transport, near neoclassical at high collisionality, became more anomalous at lower collisionality, possibly due to the growth of hybrid TEM/KBM modes in the outer regions of the plasma
NASA Astrophysics Data System (ADS)
Pires, Sandrine; Starck, Jean-Luc; Leonard, Adrienne; Réfrégier, Alexandre
2012-03-01
This chapter reviews the data mining methods recently developed to solve standard data problems in weak gravitational lensing. We detail the different steps of the weak lensing data analysis along with the different techniques dedicated to these applications. An overview of the different techniques currently used will be given along with future prospects. Until about 30 years ago, astronomers thought that the Universe was composed almost entirely of ordinary matter: protons, neutrons, electrons, and atoms. The field of weak lensing has been motivated by the observations made in the last decades showing that visible matter represents only about 4-5% of the Universe (see Figure 14.1). Currently, the majority of the Universe is thought to be dark, that is, does not emit electromagnetic radiation. The Universe is thought to be mostly composed of an invisible, pressure less matter - potentially relic from higher energy theories - called "dark matter" (20-21%) and by an even more mysterious term, described in Einstein equations as a vacuum energy density, called "dark energy" (70%). This "dark" Universe is not well described or even understood; its presence is inferred indirectly from its gravitational effects, both on the motions of astronomical objects and on light propagation. So this point could be the next breakthrough in cosmology. Today's cosmology is based on a cosmological model that contains various parameters that need to be determined precisely, such as the matter density parameter Omega_m or the dark energy density parameter Omega_lambda. Weak gravitational lensing is believed to be the most promising tool to understand the nature of dark matter and to constrain the cosmological parameters used to describe the Universe because it provides a method to directly map the distribution of dark matter (see [1,6,60,63,70]). From this dark matter distribution, the nature of dark matter can be better understood and better constraints can be placed on dark energy
Weakly supervised glasses removal
NASA Astrophysics Data System (ADS)
Wang, Zhicheng; Zhou, Yisu; Wen, Lijie
2015-03-01
Glasses removal is an important task on face recognition, in this paper, we provide a weakly supervised method to remove eyeglasses from an input face image automatically. We choose sparse coding as face reconstruction method, and optical flow to find exact shape of glasses. We combine the two processes iteratively to remove glasses more accurately. The experimental results reveal that our method works much better than these algorithms alone, and it can remove various glasses to obtain natural looking glassless facial images.
Asymptotically Safe Weak Interactions
NASA Astrophysics Data System (ADS)
Calmet, Xavier
We emphasize that the electroweak interactions without a Higgs boson are very similar to quantum general relativity. The Higgs field could just be a dressing field and might not exist as a propagating particle. In that interpretation, the electroweak interactions without a Higgs boson could be renormalizable at the nonperturbative level because of a nontrivial fixed point. Tree-level unitarity in electroweak bosons scattering is restored by the running of the weak scale.
Suzuki, M.
1988-04-01
Dynamical mechanism of composite W and Z is studied in a 1/N field theory model with four-fermion interactions in which global weak SU(2) symmetry is broken explicitly by electromagnetic interaction. Issues involved in such a model are discussed in detail. Deviation from gauge coupling due to compositeness and higher order loop corrections are examined to show that this class of models are consistent not only theoretically but also experimentally.
Castner, E.W. Jr.; Chang, Y.J.; Melinger, J.S.; McMorrow, D.
1993-07-01
Recent work on the subject of solvation dynamics has concentrated on understanding the ultrafast dynamics of intermolecular interactions in strongly interacting, polar, and hydrogen-bonding solvents. In general, investigations into the effects of solvation dynamics on chemical reactions have concentrated on the highly polar liquids because it is in these solvents that the largest spectroscopic changes with solvent relaxation are observed. In these very polar liquids, however, the intermolecular dynamics are very complex, consisting of contributions from reorientational diffusion, inertially limited rotations, intermolecular vibrations involving both reorientational (librational) and translational degrees of freedom, and interaction-induced collisional effects. The role of collisional interaction-induced effects in shaping the intermolecular dynamics of molecular liquids has been a subject of considerable discussion. Molecular dynamics simulations have suggested that collisional effects can have a significant role in shaping the femtosecond dynamics and nonlinear-optical properties of molecular liquids. However, for anisotropic molecules, it is difficult to separate experimentally the collisional effects from other phenomena. In this paper the authors examine the intermolecular dynamics of the weakly interacting liquid carbon tetrachloride (CCl{sub 4}). Because carbon tetrachloride is a spherical top molecule (belonging to the T{sub d} point group), its intermolecular light-scattering spectrum is purely interaction-induced. By studying this purely collision-induced feature in CCl{sub 4}, the authors hope to gain insight on the lowest-frequency intermolecular vibrational behavior of more complex systems.
Breakdown of the Brillouin limit and classical fluxes in rotating collisional plasmas
Rax, J. M.; Fruchtman, A.; Gueroult, R.; Fisch, N. J.
2015-09-15
The classical collisionless analysis displaying the occurrence of slow and fast rigid body rotation modes in magnetized plasmas is extended to collisional discharges. Collisions speed up the fast mode, slow down the slow one, and break down the classical Brillouin limit. Rigid body rotation has a strong impact on transport, and a collisional radial transport regime, different from the classical Braginskii collisional flux, is identified and analyzed.
Fractionation of hydrogen and deuterium on Venus due to collisional ejection
NASA Technical Reports Server (NTRS)
Gurwell, Mark A.; Yung, Yuk L.
1993-01-01
The collisional ejection process for hydrogen on Venus is reanalyzed. Improved values for the efficiency of H and D escape as a function of the ionospheric temperature are reported. It is proposed that the reduction of the hydrogen flux for collisional ejection be reduced from 8 to 3.5 x 10 exp 6/sq cm/s, and a revised D/H fractional factor of 0.47 due to collisional ejection is suggested. The resulting deuterium flux is 3.1 x 10 exp 4/sq cm/s, roughly six times the flux due to charge exchange, making collisional ejection the dominant escape mechanism for deuterium on Venus.
Collisional Shift and Broadening of Iodine Spectral Lines in Air Near 543 nm
NASA Technical Reports Server (NTRS)
Fletcher, D. G.; McDaniel, J. C.
1995-01-01
The collisional processes that influence the absorption of monochromatic light by iodine in air have been investigated. Measurements were made in both a static cell and an underexpanded jet flow over the range of properties encountered in typical compressible-flow aerodynamic applications. Experimentally measured values of the collisional shift and broadening coefficients were 0.058 +/- 0.004 and 0.53 +/- 0.010 GHz K(exp 0.7)/torr, respectively. The measured shift value showed reasonable agreement with theoretical calculations based on Lindholm-Foley collisional theory for a simple dispersive potential. The measured collisional broadening showed less favorable agreement with the calculated value.
Fractionation of hydrogen and deuterium on Venus due to collisional ejection
NASA Astrophysics Data System (ADS)
Gurwell, M. A.; Yung, Y. L.
1993-02-01
The collisional ejection process for hydrogen on Venus is reanalyzed. Improved values for the efficiency of H and D escape as a function of the ionospheric temperature are reported. It is proposed that the reduction of the hydrogen flux for collisional ejection be reduced from 8 to 3.5 x 10 exp 6/sq cm/s, and a revised D/H fractional factor of 0.47 due to collisional ejection is suggested. The resulting deuterium flux is 3.1 x 10 exp 4/sq cm/s, roughly six times the flux due to charge exchange, making collisional ejection the dominant escape mechanism for deuterium on Venus.
NASA Astrophysics Data System (ADS)
Tallents, G. J.
2016-09-01
Collisional-radiative models enable average ionization and ionization populations, plus the rates of absorption and emission of radiation to be calculated for plasmas not in thermal equilbrium. At high densities and low temperatures, electrons may have a high occupancy of the free electron quantum states and evaluations of rate coefficients need to take into account the free electron degeneracy. We demonstrate that electron degeneracy can reduce collisional rate coefficients by orders-of-magnitude from values calculated neglecting degeneracy. We show that assumptions regarding the collisional differential cross-section can alter collisional ionization and recombination rate coefficients by a further factor two under conditions relevant to inertial fusion.
Weakly broken galileon symmetry
Pirtskhalava, David; Santoni, Luca; Trincherini, Enrico; Vernizzi, Filippo
2015-09-01
Effective theories of a scalar ϕ invariant under the internal galileon symmetryϕ→ϕ+b{sub μ}x{sup μ} have been extensively studied due to their special theoretical and phenomenological properties. In this paper, we introduce the notion of weakly broken galileon invariance, which characterizes the unique class of couplings of such theories to gravity that maximally retain their defining symmetry. The curved-space remnant of the galileon’s quantum properties allows to construct (quasi) de Sitter backgrounds largely insensitive to loop corrections. We exploit this fact to build novel cosmological models with interesting phenomenology, relevant for both inflation and late-time acceleration of the universe.
Grace, R.
1983-01-01
The Moby Dick spectrometer (at BNL) in coincidence with a range spectrometer and a TOF neutron detector will be used to study the weak decay modes of /sup 12/C. The Moby Dick spectrometer will be used to reconstruct and tag events in which specific hypernuclear states are formed in the reaction K/sup -/ + /sup 12/C ..-->.. ..pi../sup -/ + /sup 12/C. Subsequent emission of decay products (pions, protons and neutrons) in coincidence with the fast forward pion will be detected in a time and range spectrometer, and a neutron detector.
The collisional history of dwarf planet Ceres revealed by Dawn
NASA Astrophysics Data System (ADS)
Marchi, S.; Williams, D. A.; Mest, S. C.; Schenk, P.; O'Brien, D. P.; De Sanctis, M. C.; Ermakov, A.; Castillo, J. C.; Jaumann, R.; Neesemann, A.; Hiesinger, H.; Park, R. S.; Kneissl, T.; Schmedemann, N.; Raymond, C. A.; Russell, C. T.
2015-12-01
Impact craters are a ubiquitous feature of solid surfaces of celestial objects. Craters are oftentimes used to constrain the past evolution of their host objects, as well as to assess their crustal structures. The Dawn spacecraft, currently in orbit around the dwarf planet Ceres, has revealed a surface peppered with impact craters. Two important facts emerge from their global spatial distribution: i) significant longitudinal and latitudinal asymmetries in the crater areal density, ii) and the lack of well-preserved craters larger than 400 km in imaging data. Interestingly, most of the low crater density terrains are found in the vicinity of the three largest, well-preserved impact craters ranging from ~160 to ~290 km in diameter. These low crater areal density terrains expand over a greater distance than observed for large craters on rocky bodies and icy satellites, which typically are confined within one crater radius from the rim. To assess the collisional history of Ceres we developed a Monte Carlo model that tracks the timing, size and number of collisions throughout the history of the solar system. The model shows that Ceres' collisional evolution should have resulted typically in a factor of 10 more craters than observed, with some ~10 craters larger than 400 km expected to have formed over the last 4.5 Gyr ago. While small craters may have reached an equilibrium level, which does not allow then to further increase in number, the lack of evident large craters is a puzzle. A possibility is that the scars of large craters have been obliterated by topography relaxation due to an ice-rich crust. Here we will present an overview of the Ceres' crater spatial distribution and compare it to other siblings (such as the asteroid Vesta), and collisional evolution models. We will also discuss how these results pose important constraints on the internal structure of the dwarf planet in conjunction with surface composition and gravity data acquired by Dawn.
A Collisional Algorithm for Modeling Circumstellar Debris Disks
NASA Technical Reports Server (NTRS)
Nesvold, Erika; Kuchner, Marc
2011-01-01
Many planetary systems harbor circumstellar disks of dust and planetesimals thought to be debris left over from planet formation. These debris disks exhibit a range of morphological features which can arise from the gravitational perturbations of planets. Accurate models of these features, accounting for the interactions of the particles in a disk with each other and with whatever planets they contain, can act as signposts for planets in debris disks that otherwise could not be detected. Such models can also constrain the planet's mass and orbital parameters. Current models for many disks consider the gravitational and radiative effects of the star and planets on the disk, but neglect the morphological consequences of collisional interactions between the planetesimals. Many observed disk features are not satisfactorily explained by the current generation of models. I am developing a new kind of debris disk model that considers both the gravitational shaping of the disk by planets and the inelastic collisions between particles. I will use a hybrid N-body integrator to numerically solve the equations of motion for the particles and planets in the disk. To include the collisional effects, I begin with an algorithm that tests for collisions at each step of the orbit integration and readjusts the velocities of colliding particles. I am adapting this algorithm to the problem at hand by allowing each particle to represent a "swarm" of planetesimals with a range of masses. When the algorithm detects an encounter between swarms, two or three swarms are produced to approximate the range of possible trajectories of the daughter planetesimals. Here I present preliminary results from my collisional algorithm.
The Collisional Evolution of the Main Asteroid Belt
NASA Astrophysics Data System (ADS)
Bottke, W. F.; Brož, M.; O'Brien, D. P.; Campo Bagatin, A.; Morbidelli, A.; Marchi, S.
Collisional and dynamical models of the main asteroid belt allow us to glean insights into planetesimal- and planet-formation scenarios as well as how the main belt reached its current state. Here we discuss many of the processes affecting asteroidal evolution and the constraints that can be used to test collisional model results. We argue the main belt's wavy size-frequency distribution for diameter D < 100-km asteroids is increasingly a byproduct of comminution as one goes to smaller sizes, with its shape a fossil-like remnant of a violent early epoch. Most D > 100-km asteroids, however, are primordial, with their physical properties set by planetesimal formation and accretion processes. The main-belt size distribution as a whole has evolved into a collisional steady state, and it has possibly been in that state for billions of years. Asteroid families provide a critical historical record of main-belt collisions. The heavily depleted and largely dispersed "ghost families," however, may hold the key to understanding what happened in the primordial days of the main belt. New asteroidal fragments are steadily created by both collisions and mass shedding events via YORP spinup processes. A fraction of this population, in the form of D < 30 km fragments, go on to escape the main belt via the Yarkovsky/YORP effects and gravitational resonances, thereby creating a quasi-steady-state population of planet-crossing and near-Earth asteroids. These populations go on to bombard all inner solar system worlds. By carefully interpreting the cratering records they produce, it is possible to constrain how portions of the main-belt population have evolved with time.
s-Wave collisional frequency shift of a fermion clock.
Hazlett, Eric L; Zhang, Yi; Stites, Ronald W; Gibble, Kurt; O'Hara, Kenneth M
2013-04-19
We report an s-wave collisional frequency shift of an atomic clock based on fermions. In contrast to bosons, the fermion clock shift is insensitive to the population difference of the clock states, set by the first pulse area in Ramsey spectroscopy, θ(1). The fermion shift instead depends strongly on the second pulse area θ(2). It allows the shift to be canceled, nominally at θ(2)=π/2, but correlations perturb the null to slightly larger θ(2). The frequency shift is relevant for optical lattice clocks and increases with the spatial inhomogeneity of the clock excitation field, naturally larger at optical frequencies. PMID:23679589
A+M Collisional Databases in ALADDIN Format
ALADDIN (A Labelled Atomic Data Interface) is a database system developed in order to provide a standard and flexible format and interface for the exchange and management of atomic, molecular and plasma-material interaction data of interest to fusion research. As part of the Atomic and Molecular Data Information System (AMDIS), introduced by the IAEA Atomic and Molecular Data Unit, the ALADDIN interface is available on-line. Twelve databases from DOE and IAEA sources are available from the CFADC website under the heading A+M Collisional Databases.
Collisional width of giant resonances and interplay with Landau damping
Bonasera, A.; Burgio, G. F.; Di Toro, M.; Wolter, H. H.
1989-06-01
We present a semiclassical method to calculate the widths of giant resonances. We solve a mean-field kinetic equation (Vlasov equation) with collision terms treated within the relaxation time approximation to construct a damped strength distribution for collective motions. The relaxation time is evaluated from the time evolution of distortions in the nucleon momentum distribution using a test-particle approach. The importance of an energy dependent nucleon-nucleon cross section is stressed. Results are shown for isoscalar giant quadrupole and octupole motions. A quite important interplay between self-consistent (Landau) and collisional damping is revealed.
Zeeman degeneracy effects in collisional intense-field resonance fluorescence
NASA Technical Reports Server (NTRS)
Cooper, J.; Ballagh, R. J.; Burnett, K.
1980-01-01
Resonance fluorescence due to intense laser fields from a Zeeman degenerate atom being perturbed by collisional interactions is calculated in the impact regime by using the quantum-fluctuation-regression theorem. Various interesting effects are found. For example, the scattered intensity spectrum for a J = 0 to J = 1 transition for polarization parallel to the laser polarization is essentially an asymmetric triplet, whereas for a perpendicular polarization due to collisions the spectrum is essentially a doublet (whose frequencies do not correspond with any of those of the triplet). Further, the width of the fluorescent component (whose frequency is close to the unperturbed frequency) actually decreases with increasing laser power.
Using molecular alignment to track ultrafast collisional relaxation
NASA Astrophysics Data System (ADS)
Karras, G.; Hertz, E.; Billard, F.; Lavorel, B.; Hartmann, J.-M.; Faucher, O.
2014-06-01
Field-free molecular alignment has been used in order to track the collisional relaxation occurring in a molecular gas. CO2 molecules were initially irradiated by a short linearly polarized laser pulse resulting in the increase of their rotational energy. The evolution of the subsequent ultrafast relaxation process was optically probed after irradiating the sample with a second, weaker, short pulse leading to the alignment of the preheated molecules. Using classical molecular dynamic simulations, we were able to quantitatively reproduce the experimental shapes and amplitudes of the recorded revival transients for a time interval extending from 25 to 500 ps until thermalization of the gas sample is reached.
Comparison of Secondary Islands in Collisional Reconnection to Hall Reconnection
Shepherd, L. S.; Cassak, P. A.
2010-07-02
Large-scale resistive Hall-magnetohydrodynamic simulations of the transition from Sweet-Parker (collisional) to Hall (collisionless) magnetic reconnection are presented; the first to separate secondary islands from collisionless effects. Three main results are described. There exists a regime with secondary islands but without collisionless effects, and the reconnection rate is faster than Sweet-Parker, but significantly slower than Hall reconnection. This implies that secondary islands do not cause the fastest reconnection rates. The onset of Hall reconnection ejects secondary islands from the vicinity of the X line, implying that energy is released more rapidly during Hall reconnection. Coronal applications are discussed.
Elaboration of collisional-radiative models applied to Earth and Mars entry problems
NASA Astrophysics Data System (ADS)
Annaloro, Julien; Bultel, Arnaud; Omaly, Pierre
2014-11-01
Three Collisional-Radiative (CR) models are elaborated and tested in typical atmospheric entry conditions. The first CR model (CoRaM-AIR) is dedicated to the Earth atmospheric entry and is based on an electronically and vibrationally specific state-to-state description of N2-O2-Ar mixtures. The second CR model (CoRaM-MARS) is dedicated to the Mars atmospheric entry and treats the CO2-N2-Ar mixtures with a similar vibrationally and electronically specific approach. Since their implementation in a Computational Fluid Dynamics (CFD) code has not yet been performed, they are implemented in a 0D code giving the evolution in time of the excited states number density in constant pressure and temperature conditions similar to trajectory points at lower altitude. Nevertheless, such an implementation in a CFD code has been performed for a third CR model, specifically devoted to pure nitrogen flows (CoRaM-N2). The results show that the equilibrium is reached relatively slowly. In addition, the influence of radiation on the chemistry is weak.
Experimental measurements of the collisional absorption of XUV radiation in warm dense aluminium.
Kettle, B; Dzelzainis, T; White, S; Li, L; Dromey, B; Zepf, M; Lewis, C L S; Williams, G; Künzel, S; Fajardo, M; Dacasa, H; Zeitoun, Ph; Rigby, A; Gregori, G; Spindloe, C; Heathcote, R; Riley, D
2016-08-01
The collisional (or free-free) absorption of soft x rays in warm dense aluminium remains an unsolved problem. Competing descriptions of the process exist, two of which we compare to our experimental data here. One of these is based on a weak scattering model, another uses a corrected classical approach. These two models show distinctly different behaviors with temperature. Here we describe experimental evidence for the absorption of 26-eV photons in solid density warm aluminium (T_{e}≈1 eV). Radiative x-ray heating from palladium-coated CH foils was used to create the warm dense aluminium samples and a laser-driven high-harmonic beam from an argon gas jet provided the probe. The results indicate little or no change in absorption upon heating. This behavior is in agreement with the prediction of the corrected classical approach, although there is not agreement in absolute absorption value. Verifying the correct absorption mechanism is decisive in providing a better understanding of the complex behavior of the warm dense state. PMID:27627403
Experimental measurements of the collisional absorption of XUV radiation in warm dense aluminium
NASA Astrophysics Data System (ADS)
Kettle, B.; Dzelzainis, T.; White, S.; Li, L.; Dromey, B.; Zepf, M.; Lewis, C. L. S.; Williams, G.; Künzel, S.; Fajardo, M.; Dacasa, H.; Zeitoun, Ph.; Rigby, A.; Gregori, G.; Spindloe, C.; Heathcote, R.; Riley, D.
2016-08-01
The collisional (or free-free) absorption of soft x rays in warm dense aluminium remains an unsolved problem. Competing descriptions of the process exist, two of which we compare to our experimental data here. One of these is based on a weak scattering model, another uses a corrected classical approach. These two models show distinctly different behaviors with temperature. Here we describe experimental evidence for the absorption of 26-eV photons in solid density warm aluminium (Te≈1 eV). Radiative x-ray heating from palladium-coated CH foils was used to create the warm dense aluminium samples and a laser-driven high-harmonic beam from an argon gas jet provided the probe. The results indicate little or no change in absorption upon heating. This behavior is in agreement with the prediction of the corrected classical approach, although there is not agreement in absolute absorption value. Verifying the correct absorption mechanism is decisive in providing a better understanding of the complex behavior of the warm dense state.
Phantom crossing with collisional matter in f(T) gravity
NASA Astrophysics Data System (ADS)
Zubair, M.
2016-02-01
We study the late-time cosmological evolution of f(T) (where T is the torsion scalar) theories with matter contents consisting of collisional self-interacting matter and radiations. The power law, exponential and logarithmic f(T) models are considered to explore the evolution of Hubble parameter H(z), dark energy (DE) equation of state (EoS) ωDE and effective EoS parameter ωeff. We show that crossing of phantom divide line can be realized in the presence of collisional matter as compared to the results obtained for the choice of noncollisional matter [K. Bamba, C.-Q. Geng, C.-C. Lee and L.-W. Luo, J. Cosmol. Astropart. Phys. 01 (2011) 021; K. Bamba, C.-Q. Geng and C.-C. Lee, arXiv:1008.4036]. The evolutionary behavior of ωDE is consistent with the one developed in [P. Wu and H. Yu, Eur. Phys. J. C 71 (2011) 1552] and recent observational data [U. Alam, V. Sahni and A. A. Starobinsky, J. Cosmol. Astropart. Phys. 0406 (2004) 008; S. Nesseris and L. Perivolaropoulos, J. Cosmol. Astropart. Phys. 0701 (2007) 018; P. Wu and H. Yu, Phys. Lett. B 643 (2006) 315; U. Alam, V. Sahni and A. A. Starobinsky, J. Cosmol. Astropart. Phys. 0702 (2007) 011; H. K. Jassal, J. S. Bagla and T. Padmanabhan, Mon. Not. R. Astron. Soc. 405 (2010) 2639].
Ultrahigh-Energy Debris from the Collisional Penrose Process
NASA Astrophysics Data System (ADS)
Berti, Emanuele; Brito, Richard; Cardoso, Vitor
2015-06-01
Soon after the discovery of the Kerr metric, Penrose realized that superradiance can be exploited to extract energy from black holes. The original idea (involving the breakup of a single particle) yields only modest energy gains. A variant of the Penrose process consists of particle collisions in the ergoregion. The collisional Penrose process has been explored recently in the context of dark matter searches, with the conclusion that the ratio η between the energy of postcollision particles detected at infinity and the energy of the colliding particles should be modest (η ≲1.5 ). Schnittman [Phys. Rev. Lett. 113, 261102 (2014)] has shown that these studies underestimated the maximum efficiency by about 1 order of magnitude (i.e., η ≲15 ). In this work we show that particle collisions in the vicinity of rapidly rotating black holes can produce high-energy ejecta and result in high efficiencies under much more generic conditions. The astrophysical likelihood of these events deserves further scrutiny, but our study hints at the tantalizing possibility that the collisional Penrose process may power gamma rays and ultrahigh-energy cosmic rays.
GAP CLEARING BY PLANETS IN A COLLISIONAL DEBRIS DISK
Nesvold, Erika R.; Kuchner, Marc J. E-mail: Marc.Kuchner@nasa.gov
2015-01-10
We apply our 3D debris disk model, SMACK, to simulate a planet on a circular orbit near a ring of planetesimals that are experiencing destructive collisions. Previous simulations of a planet opening a gap in a collisionless debris disk have found that the width of the gap scales as the planet mass to the 2/7th power (α = 2/7). We find that gap sizes in a collisional disk still obey a power law scaling with planet mass, but that the index α of the power law depends on the age of the system t relative to the collisional timescale t {sub coll} of the disk by α = 0.32(t/t {sub coll}){sup –0.04}, with inferred planet masses up to five times smaller than those predicted by the classical gap law. The increased gap sizes likely stem from the interaction between collisions and the mean motion resonances near the chaotic zone. We investigate the effects of the initial eccentricity distribution of the disk particles and find a negligible effect on the gap size at Jovian planet masses, since collisions tend to erase memory of the initial particle eccentricity distributions. Finally, we find that the presence of Trojan analogs is a potentially powerful diagnostic of planets in the mass range ∼1-10 M {sub Jup}. We apply our model to place new upper limits on planets around Fomalhaut, HR 4796 A, HD 202628, HD 181327, and β Pictoris.
Early cosmochemical fractionation by collisional erosion during the Earth's accretion
NASA Astrophysics Data System (ADS)
Boujibar, A.; Andrault, D.; Bolfan-Casanova, N.; Bouhifd, M. A.
2014-12-01
Early in the Solar System history, planets grew through energetic collisions between planetesimals. Partial destruction of planetary embryos could have produce heterogeneous bodies, because of widespread internal chemical differentiation through core-segregation, partial melting of silicated mantles and fractional crystallization of magma oceans. On larger proto-planets, including the early Earth, meteoritic impacts have potentially induced erosion of part of the surface, which could have affected significantly the final chemical composition of terrestrial planets. Here we report that collisional erosion of 15-18% of the early Earth's surface reconciles the major apparent compositional differences between the known enstatite chondrites (EC) and the bulk Earth. We base our arguments on experimental measurements of the melting properties of an EC body at pressures between 1 bar and 25 GPa. At low degree of partial melting, the silicate melts are found highly enriched in SiO2, Al2O3 and Na2O and strongly depleted in MgO. Loss through collisional erosion of the surface of such differentiated planetesimal should ultimately raise its Mg/Si ratio and decrease its concentration in incompatible elements. We elaborate auto-coherent models of the Earth formation. Vaporization into space of the protocrusts could be a source of the Na-rich SiO gas that interacted with chondrules and explain the enrichments of enstatite chondrites in SiO2 and volatile lithophile elements.
A collisional origin to Earth's non-chondritic composition?
NASA Astrophysics Data System (ADS)
Bonsor, Amy; Leinhardt, Zoë M.; Carter, Philip J.; Elliott, Tim; Walter, Michael J.; Stewart, Sarah T.
2015-02-01
Several lines of evidence indicate a non-chondritic composition for bulk Earth. If Earth formed from the accretion of chondritic material, its non-chondritic composition, in particular the super-chondritic 142Nd /144Nd and low Mg/Fe ratios, might be explained by the collisional erosion of differentiated planetesimals during its formation. In this work we use an N-body code, that includes a state-of-the-art collision model, to follow the formation of protoplanets, similar to proto-Earth, from differentiated planetesimals (>100 km) up to isolation mass (>0.16 M⊕). Collisions between differentiated bodies have the potential to change the core-mantle ratio of the accreted protoplanets. We show that sufficient mantle material can be stripped from the colliding bodies during runaway and oligarchic growth, such that the final protoplanets could have Mg/Fe and Si/Fe ratios similar to that of bulk Earth, but only if Earth is an extreme case and the core is assumed to contain 10% silicon by mass. This may indicate an important role for collisional differentiation during the giant impact phase if Earth formed from chondritic material.
The Collisional Cascade Model For Saturn's Ring Spokes
NASA Astrophysics Data System (ADS)
Hamilton, D. P.; Jontof-Hutter, D.
2014-12-01
Dust particles are ubiquitous in the saturnian system, spewing forth from the geysers of Enceladus and lurking as mysterious wedge-shaped spokes in the planet's main rings. The smallest dust grains are strongly influenced by electromagnetic forces arising from the motions of charged dust particles relative to Saturn's rotating magnetic field while large dust grains follow Keplerian paths determined by the planet's gravity. The most interesting dynamics result when the two forces have similar strengths, typically for particles ~100 nanometer in size. Differences between the motions of dust grains and much larger ring particles provides a free energy source that powers spoke formation. Most observations of ongoing spoke formation can be understood in the context of a Collisional Cascade model in which a hail of rapidly-moving ~50nm dust grains rain down upon more massive ring particles. After leaving the ring plane en masse from the site of an initial disturbance, these mid-sized grains are accelerated by the magnetic field to high speeds relative to ring particles. When they return to the ring plane - nearly simultaneously over a large radial range - they strike dust-coated fluffy ring particles, freeing both visible 0.5 micron spoke particles and additional 50nm debris that goes on to continue the cascade. The Collisional Cascade model can account for the rapid onset of spokes, their hour-long active phases, and the propensity of spokes to prefer certain magnetic longitudes.
Quasi-collisional Magneto-optic Effects in Collisionless Plasmas
NASA Astrophysics Data System (ADS)
Keenan, Brett; Ford, Alex; Medvedev, Mikhail
2016-03-01
High-amplitude, chaotic/turbulent electromagnetic fluctuations are ubiquitous in astrophysical plasmas, where they can be excited by various kinetic-streaming and/or anisotropy-driven instabilities, such as the Weibel instability. These fields typically exist on ``sub-Larmor scales'' -- scales smaller than the electron Larmor radius. Electrons moving through such magnetic fields undergo small-angle stochastic deflections of their pitch-angles, thus establishing diffusive transport on long time-scales. We show that this behavior, under certain conditions, is equivalent to Coulomb collisions in collisional plasmas. The magnetic pitch-angle diffusion coefficient, which acts as an effective ``collision'' frequency, may be substantial in these, otherwise, collisionless environments. We show that this effect, colloquially referred to as the plasma ``quasi-collisionality'', may radically alter the expected radiative transport properties of candidate plasmas. We argue that the modified magneto-optic effects in these plasmas provide an attractive, novel radiative diagnostic tool for the exploration and characterization of small-scale magnetic turbulence.
Nonlinear transport processes in tokamak plasmas. I. The collisional regimes
Sonnino, Giorgio; Peeters, Philippe
2008-06-15
An application of the thermodynamic field theory (TFT) to transport processes in L-mode tokamak plasmas is presented. The nonlinear corrections to the linear ('Onsager') transport coefficients in the collisional regimes are derived. A quite encouraging result is the appearance of an asymmetry between the Pfirsch-Schlueter (P-S) ion and electron transport coefficients: the latter presents a nonlinear correction, which is absent for the ions, and makes the radial electron coefficients much larger than the former. Explicit calculations and comparisons between the neoclassical results and the TFT predictions for Joint European Torus (JET) plasmas are also reported. It is found that the nonlinear electron P-S transport coefficients exceed the values provided by neoclassical theory by a factor that may be of the order 10{sup 2}. The nonlinear classical coefficients exceed the neoclassical ones by a factor that may be of order 2. For JET, the discrepancy between experimental and theoretical results for the electron losses is therefore significantly reduced by a factor 10{sup 2} when the nonlinear contributions are duly taken into account but, there is still a factor of 10{sup 2} to be explained. This is most likely due to turbulence. The expressions of the ion transport coefficients, determined by the neoclassical theory in these two regimes, remain unaltered. The low-collisional regimes, i.e., the plateau and the banana regimes, are analyzed in the second part of this work.
Experimental observations of low-velocity collisional systems
NASA Astrophysics Data System (ADS)
Jorges, Jeffery; Dove, Adrienne; Colwell, Joshua
Low-velocity collisions in systems of centimeter-sized objects may result in particle growth by accretion, rebounding, or erosive processes that result in the production of additional smaller particles. Numerical simulations of these systems are limited by a need to understand the collisional parameters governing the outcomes of these collisions over a range of conditions. Here, we present the results from laboratory experiments designed to explore low-velocity collisions by conducting experiments in a vacuum chamber in our 0.8-sec drop tower apparatus. These experiments utilize a variety of impacting spheres, including glass, Teflon, aluminum, stainless steel, and brass. These spheres are either used in their natural state or are ``mantled'' - coated with a few-mm thick layer of a cohesive powder. A high-speed, high-resolution video camera is used to record the motion of the colliding bodies. These videos are then processed and we track the particles to determine impactor speeds before and after collision and the collisional outcome. We determine how the coefficient of restitution varies as a function of material type, morphology, and impact velocity. For impact velocities in the range from about 20-100 cm/s we observe that mantling of particles has the most significant effect, reducing the coefficients of restitution.
Gap Clearing by Planets in a Collisional Debris Disk
NASA Astrophysics Data System (ADS)
Nesvold, Erika R.; Kuchner, Marc J.
2015-01-01
We apply our 3D debris disk model, SMACK, to simulate a planet on a circular orbit near a ring of planetesimals that are experiencing destructive collisions. Previous simulations of a planet opening a gap in a collisionless debris disk have found that the width of the gap scales as the planet mass to the 2/7th power (α = 2/7). We find that gap sizes in a collisional disk still obey a power law scaling with planet mass, but that the index α of the power law depends on the age of the system t relative to the collisional timescale t coll of the disk by α = 0.32(t/t coll)-0.04, with inferred planet masses up to five times smaller than those predicted by the classical gap law. The increased gap sizes likely stem from the interaction between collisions and the mean motion resonances near the chaotic zone. We investigate the effects of the initial eccentricity distribution of the disk particles and find a negligible effect on the gap size at Jovian planet masses, since collisions tend to erase memory of the initial particle eccentricity distributions. Finally, we find that the presence of Trojan analogs is a potentially powerful diagnostic of planets in the mass range ~1-10 M Jup. We apply our model to place new upper limits on planets around Fomalhaut, HR 4796 A, HD 202628, HD 181327, and β Pictoris.
SELF-CONSISTENT SIZE AND VELOCITY DISTRIBUTIONS OF COLLISIONAL CASCADES
Pan, Margaret; Schlichting, Hilke E. E-mail: hilke@ucla.edu
2012-03-10
The standard theoretical treatment of collisional cascades derives a steady-state size distribution assuming a single constant velocity dispersion for all bodies regardless of size. Here we relax this assumption and solve self-consistently for the bodies' steady-state size and size-dependent velocity distributions. Specifically, we account for viscous stirring, dynamical friction, and collisional damping of the bodies' random velocities in addition to the mass conservation requirement typically applied to find the size distribution in a steady-state cascade. The resulting size distributions are significantly steeper than those derived without velocity evolution. For example, accounting self-consistently for the velocities can change the standard q = 3.5 power-law index of the Dohnanyi differential size spectrum to an index as large as q = 4. Similarly, for bodies held together by their own gravity, the corresponding power-law index range 2.88 < q < 3.14 of Pan and Sari can steepen to values as large as q = 3.26. Our velocity results allow quantitative predictions of the bodies' scale heights as a function of size. Together with our predictions, observations of the scale heights for different-sized bodies for the Kuiper belt, the asteroid belt, and extrasolar debris disks may constrain the mass and number of large bodies stirring the cascade as well as the colliding bodies' internal strengths.
Recombination and collisional x-ray lasers at LULI
NASA Astrophysics Data System (ADS)
Jamelot, Gerard; Jaegle, Pierre; Carillon, Antoine; Gauthe, Bernard; Goedtkindt, P.; Guennou, M.; Klisnick, Annie; Moeller, Clary; Rus, Bedrich; Sureau, Alain; Zeitoun, Philippe
1994-02-01
We present our recent efforts to produce X-ray lasers in the 200 angstroms range by using the moderate power drive of the LULI facility in Palaiseau. The 4 - 5 transitions of Li-like sulfur exhibit large gain-length products in recombining plasmas, and appear to be less sensitive to plasma non-uniformity than the 3 - 4 and 3 - 5 transitions previously studied. From numerical simulations this is likely due to smaller radiative and collisional excitation from 4f than from 3d levels. In collisional scheme, neon-like zinc gives analogous results to similar works on other elements for the 3p - 3s, J equals 2 yields 1 transitions, but the J equals 0 yields 1 transition shows a surprisingly large gain coefficient of 4.9 cm-1. From a detailed comparison of time-dependent intensities of the J equals 0 yields 1 and the J equals 2 yields 1 lines, we conclude that transitions from J equals 0 and from J equals 2 are not emitted in the same region of the plasma.
Multi-fluid plasma modeling with Braginskii collisional transport processes
NASA Astrophysics Data System (ADS)
Ho, A.; Shumlak, U.; Miller, S. T.
2015-11-01
Magnetohydrodynamics (MHD) works well where transport processes are primarily advective. Extensions of the MHD model are capable of capturing some collisional phenomena such as electrical resistivity, which are important in systems with mean free paths less than the characteristic length. However, MHD models have difficulties resolving systems where the Debye length cannot be assumed to approach zero. These systems arise in low density, hot plasmas. By modeling the ions and electrons as distinct fluids, the 5-moment multi-fluid plasma model is able to capture these short-range transport processes that are not accounted for in MHD. To model the transport processes the Braginskii transport terms are added to the 5-moment model, which introduces viscosity, heat conduction, and binary species interactions. These transport properties are affected by strong magnetic fields, resulting in anisotropic collisional effects. The multi-fluid equations are evolved explicitly and are coupled with Maxwell's equations. This research extends the University of Washington's WARPXM code to include the Braginskii terms with the 5-moment multi-fluid plasma model. The implementation is validated against theoretical results from a Hartmann flow benchmark problem. This work is supported by a grant from the United States Air Force Office of Scientific Research.
Dynamical and collisional evolution of Kuiper belt binaries
NASA Astrophysics Data System (ADS)
Brunini, Adrián; Zanardi, Macarena
2016-02-01
We present numerical simulations of the evolution of synthetic transneptunian binaries (TNBs) under the influence of the solar perturbation, tidal friction, and collisions with the population of classical Kuiper belt objects (KBOs). We show that these effects, acting together, have strongly sculpted the primordial population of TNBs. If the population of classical KBOs have a power-law size distribution as the ones that are inferred from recent observational surveys, the fraction of surviving binaries at present would be ˜70 per cent of the primordial population. The orbits of the surviving synthetic systems match reasonably well the observed sample. The collisional process excites the mutual orbital eccentricity of the binaries, acting against the effect of tides. Therefore only ˜10 per cent of the objects reach total orbital circularization (e ≤ 10-4). In addition, our results predict that the population of contact binaries in the transneptunian region should be small. Ultrawide binaries are naturally obtained by the combined action of Kozai cycles and tidal friction and collisional evolution, being the number and orbital distribution of them very similar to the ones of the observed population.
Collisional cooling investigation of THz rotational transitions of water
Dick, Michael J.; Drouin, Brian J.; Pearson, John C.
2010-02-15
An investigation of the pressure broadening by helium and hydrogen of six rotational transitions of water has been completed. The six transitions studied included two para water transitions (0{sub 00}-1{sub 11} and 1{sub 11}-2{sub 02}) and four ortho water transitions (1{sub 01}-1{sub 10}, 2{sub 21}-3{sub 12}, 3{sub 03}-3{sub 12} and 3{sub 12}-3{sub 21}) in the frequency region 0.55-1.17 THz. This survey was accomplished using the collisional cooling technique which allowed the broadening of each transition to be studied below the water condensation temperature. For each of the transitions studied, the temperature dependence of the pressure broadening by helium showed little dependence on temperature, while the broadening by hydrogen showed a sharp decrease at the lowest temperatures. This behavior was modeled, for each transition broadened by helium and hydrogen, with a power law, or a power law modified with a Boltzmann-like step function, and the results of these fits will be presented. In addition, an extensive investigation of the systematic error in the temperature of the water vapor in the collisional cooling experiment will be discussed. Finally, the impact of these new broadening measurements on models of star formation in the interstellar medium will be outlined.
Observation of anomalous field penetration in collisional, cylindrical ICP discharges
NASA Astrophysics Data System (ADS)
Evans, John D.; Chen, Francis F.; Arnush, Donald
2000-10-01
Measurements of the radial penetration of RF-generated B-fields are performed in a large diameter cylindrical ICP. A loop antenna surrounds a dome-shaped Pyrex top that sits on top of a magnetic bucket. Rtop=15cm height of top, Rbucket 18cm, bucket height 30cm, N 1011cm-3, Te 3eV, Prf < 1.4kW, Frf = 2-27.12MHz, Po 1-100mT. Field penetration (``skin") depths Lsd are measured in the outer plasma region (r > R/2) that are consistent with collisional skin depth theory. However, in the interior region (r < R/2), non-monotonic radial profiles and interference phenomena that resemble standing wave behavior (e.g. nodes) are observed, where no propagating waves are predicted to occur. Similar phenomena have been observed by other groups [1], but for chambers sizes such that R Lsd. Such observations were explained as manifestations of the anomalous skin effect (ASE), the electromagnetic analog of Debye shielding. However, these phenomena are more apparent as Po (and collisionality) is increased, in apparent contradiction to the predictions of ASE theory. Results of a detailed experimental investigation of interference phenomena under conditions that fall outside of the ASE regime will be presented, as well as a simple physical picture that resolves this apparent paradox. [1]. B. Joye and H. Schneider, Helv. Phys. Acta 51, 804 (1978).
Ultrahigh-Energy Debris from the Collisional Penrose Process.
Berti, Emanuele; Brito, Richard; Cardoso, Vitor
2015-06-26
Soon after the discovery of the Kerr metric, Penrose realized that superradiance can be exploited to extract energy from black holes. The original idea (involving the breakup of a single particle) yields only modest energy gains. A variant of the Penrose process consists of particle collisions in the ergoregion. The collisional Penrose process has been explored recently in the context of dark matter searches, with the conclusion that the ratio η between the energy of postcollision particles detected at infinity and the energy of the colliding particles should be modest (η≲1.5). Schnittman [Phys. Rev. Lett. 113, 261102 (2014)] has shown that these studies underestimated the maximum efficiency by about 1 order of magnitude (i.e., η≲15). In this work we show that particle collisions in the vicinity of rapidly rotating black holes can produce high-energy ejecta and result in high efficiencies under much more generic conditions. The astrophysical likelihood of these events deserves further scrutiny, but our study hints at the tantalizing possibility that the collisional Penrose process may power gamma rays and ultrahigh-energy cosmic rays. PMID:26197116
Weakly relativistic plasma expansion
Fermous, Rachid Djebli, Mourad
2015-04-15
Plasma expansion is an important physical process that takes place in laser interactions with solid targets. Within a self-similar model for the hydrodynamical multi-fluid equations, we investigated the expansion of both dense and under-dense plasmas. The weakly relativistic electrons are produced by ultra-intense laser pulses, while ions are supposed to be in a non-relativistic regime. Numerical investigations have shown that relativistic effects are important for under-dense plasma and are characterized by a finite ion front velocity. Dense plasma expansion is found to be governed mainly by quantum contributions in the fluid equations that originate from the degenerate pressure in addition to the nonlinear contributions from exchange and correlation potentials. The quantum degeneracy parameter profile provides clues to set the limit between under-dense and dense relativistic plasma expansions at a given density and temperature.
Abedi, Samira; Dorranian, Davoud; Abari, Mehdi Etehadi; Shokri, Babak
2011-09-15
In this paper, the effect of weakly relativistic ponderomotive force in the interaction of intense laser pulse with nonisothermal, underdense, collisional plasma is studied. Ponderomotive force modifies the electron density and temperature distribution. By considering the weakly relativistic effect and ohmic heating of plasma electrons, the nonlinear dielectric permittivity of plasma medium is obtained and the equation of electromagnetic wave propagation in plasma is solved. It is shown that with considering the ohmic heating of electrons and collisions, the effect of ponderomotive force in weakly relativistic regime leads to steepening the electron density profile and increases the temperature of plasma electrons noticeably. Bunches of electrons in plasma become narrower. By increasing the laser pulse strength, the wavelength of density oscillations decreases. In this regime of laser-plasma interaction, electron temperature increases sharply by increasing the intensity of laser pulse. The amplitude of electric and magnetic fields increases by increasing the laser pulse energy while their wavelength decreases and they lost their sinusoidal form.
On negative ion-drag force for dust in collisional plasmas
Patacchini, Leonardo; Hutchinson, Ian H.
2008-09-07
The ion-drag force on a dust particle in collisional plasmas is self-consistently calculated using the Particle In Cell code SCEPTIC in the entire range of charge-exchange collisionlality. It is shown that the ion-drag only reverses in the strongly collisional regime, where other forces are of much stronger magnitude than the ion-drag itself.
On negative ion-drag force for dust in collisional plasmas
NASA Astrophysics Data System (ADS)
Patacchini, Leonardo; Hutchinson, Ian H.
2008-09-01
The ion-drag force on a dust particle in collisional plasmas is self-consistently calculated using the Particle In Cell code SCEPTIC in the entire range of charge-exchange collisionlality. It is shown that the ion-drag only reverses in the strongly collisional regime, where other forces are of much stronger magnitude than the ion-drag itself.
NASA Technical Reports Server (NTRS)
Thaddeus, P.
1972-01-01
Investigation of the quantum mechanics of the collisional pumping process which Townes and Cheung (1969) propose as the cause of 'anomalous' formaldehyde absorption in diffuse dark nebulae discussed by Palmer et al. (1969). Quantum effects are taken into account in an attempt to determine whether such nebulae are likely to provide the physical conditions required for the collisional pumping process.
Collisionless Zonal Flow Saturation for Weak Magnetic Shear
NASA Astrophysics Data System (ADS)
Lu, Zhixin; Wang, Weixing; Diamond, Patrick; Ashourvan, Arash; Tynan, George
2015-11-01
The damping of the zonal flow, either collisional or collisionless, plays an important role in regulating the drift wave-zonal flow system, and can affect the transport and confinement. The tertiary instability, e.g., a generalized Kelvin-Helmholtz (KH) instability driven by flow shear, has been suggested theoretically as a possible damping mechanism [Rogers 2000 PRL, Diamond 2005 PPCF]. The sensitivity of the tertiary mode to magnetic shear has not been quantified, especially in weak magnetic shear regimes. In this work, parametric scans using gyrokinetic simulation demonstrate that the zonal electric field energy normalized by the turbulence electric field energy decreases as magnetic shear decreases. With ITG drive artificially eliminated, the time evolution of the zonal structure indicates that the zonal electric field damps more rapidly at weak shear. This suggests larger collisionless zonal flow damping or larger effective turbulent viscosity at weak magnetic shear. The effects of the zonal components of specific variables, e.g., the parallel shear flow and the radial electric field, on tertiary instability, are also studied. Quantitative studies on the magnetic shear scaling of tertiary instability excitation and the collisionless zonal flow saturation are ongoing.
Electromagnetic drift waves dispersion for arbitrarily collisional plasmas
Lee, Wonjae Krasheninnikov, Sergei I.; Angus, J. R.
2015-07-15
The impacts of the electromagnetic effects on resistive and collisionless drift waves are studied. A local linear analysis on an electromagnetic drift-kinetic equation with Bhatnagar-Gross-Krook-like collision operator demonstrates that the model is valid for describing linear growth rates of drift wave instabilities in a wide range of plasma parameters showing convergence to reference models for limiting cases. The wave-particle interactions drive collisionless drift-Alfvén wave instability in low collisionality and high beta plasma regime. The Landau resonance effects not only excite collisionless drift wave modes but also suppress high frequency electron inertia modes observed from an electromagnetic fluid model in collisionless and low beta regime. Considering ion temperature effects, it is found that the impact of finite Larmor radius effects significantly reduces the growth rate of the drift-Alfvén wave instability with synergistic effects of high beta stabilization and Landau resonance.
Cosmochemical fractionation by collisional erosion during the Earth's accretion
NASA Astrophysics Data System (ADS)
Boujibar, Asmaa; Andrault, Denis; Bolfan-Casanova, Nathalie; Bouhifd, Mohamed Ali; Monteux, Julien
2015-09-01
Early in the Solar System's history, energetic collisions of differentiated bodies affected the final composition of the terrestrial planets through partial destruction. Enstatite chondrites (EC) are the best candidates to represent the primordial terrestrial precursors as they present the most similar isotopic compositions to Earth. Here we report that collisional erosion of >15% of the early Earth's mass can reconcile the remaining compositional differences between EC and the Earth. We base our demonstration on experimental melting of an EC composition at pressures between 1 bar and 25 GPa. At low pressures, the first silicate melts are highly enriched in incompatible elements Si, Al and Na, and depleted in Mg. Loss of proto-crusts through impacts raises the Earth's Mg/Si ratio to its present value. To match all major element compositions, our model implies preferential loss of volatile lithophile elements and re-condensation of refractory lithophile elements after the impacts.
Collisional dynamics in a gas of molecular super-rotors.
Khodorkovsky, Yuri; Steinitz, Uri; Hartmann, Jean-Michel; Averbukh, Ilya Sh
2015-01-01
Recently, femtosecond laser techniques have been developed that are capable of bringing gas molecules to extremely fast rotation in a very short time, while keeping their translational motion relatively slow. Here we study collisional equilibration dynamics of this new state of molecular gases. We show that the route to equilibrium starts with a metastable 'gyroscopic stage' in the course of which the molecules maintain their fast rotation and orientation of the angular momentum through many collisions. The inhibited rotational-translational relaxation is characterized by a persistent anisotropy in the molecular angular distribution, and is manifested in the optical birefringence and anisotropic diffusion in the gas. After a certain induction time, the 'gyroscopic stage' is abruptly terminated by an explosive rotational-translational energy exchange, leading the gas towards the final equilibrium. We illustrate our conclusions by direct molecular dynamics simulation of several gases of linear molecules. PMID:26160223
Collisional-radiative modelling of an Ar helicon plasma discharge
NASA Astrophysics Data System (ADS)
Loch, Stuart
2005-10-01
We report on recent modelling results of emission observed from a helicon plasma, comparing theoretical and observed line intensities and line ratios of Ar, Ar^+ and Ar^2+. Our Helicon plasma is from the ASTRAL device at Auburn University, with spectral measurements from 275 nm through to 1015 nm. We concentrate on the Ar^+ ion stage, and present the results of a collisional-radiative model using various qualities of atomic data. In particular, we compare the modelling results using Plane-Wave Born, Distorted-Wave and R-matrix electron impact excitation data with those observed from the plasma. As part of the modelling work, we investigate the potential use of various lines as plasma diagnostic tools.
Cosmochemical fractionation by collisional erosion during the Earth's accretion
Boujibar, Asmaa; Andrault, Denis; Bolfan-Casanova, Nathalie; Bouhifd, Mohamed Ali; Monteux, Julien
2015-01-01
Early in the Solar System's history, energetic collisions of differentiated bodies affected the final composition of the terrestrial planets through partial destruction. Enstatite chondrites (EC) are the best candidates to represent the primordial terrestrial precursors as they present the most similar isotopic compositions to Earth. Here we report that collisional erosion of >15% of the early Earth's mass can reconcile the remaining compositional differences between EC and the Earth. We base our demonstration on experimental melting of an EC composition at pressures between 1 bar and 25 GPa. At low pressures, the first silicate melts are highly enriched in incompatible elements Si, Al and Na, and depleted in Mg. Loss of proto-crusts through impacts raises the Earth's Mg/Si ratio to its present value. To match all major element compositions, our model implies preferential loss of volatile lithophile elements and re-condensation of refractory lithophile elements after the impacts. PMID:26395157
Bohm's criterion in a collisional magnetized plasma with thermal ions
Hatami, M. M.; Shokri, B.
2012-08-15
Using the hydrodynamic model and considering a planar geometry, the modified Bohm's sheath criterion is investigated in a magnetized, collisional plasma consisting of electron and positive ions with finite temperature. It is assumed that the singly charged positive ions enter into the sheath region obliquely, i.e., their velocity at the sheath edge is not normal to the wall, and the electron densities obey Boltzmann relations. It is shown that there are both upper and lower limit for the Bohm entrance velocity of ions in this case and both of these limits depend on the magnitude and direction of the applied magnetic field. To determine the accuracy of our derived generalized Bohm's criterion, it reduced to some familiar physical condition. Also, using this generalized Bohm's criterion, the behavior of the electron and positive ion density distributions are studied in the sheath region.
Flexural extension of the upper continental crust in collisional foredeeps
Bradley, D.C.; Kidd, W.S.F.
1991-01-01
Normal faults on the outer slopes of trenches and collisional foredeeps reveal that high-amplitude lithospheric flexure can result in inelastic extensional deformation of the convex side of a flexed plate. This process, which we call "flexural extension', differs fundamentally from rifting in that the lower lithosphere contracts while the upper lithosphere extends. Structural evidence does not support common illustrations of flexural normal faults as planar-irrotational structures which simply die out at shallow crustal depths. Instead, the surface geology shows that flexural normal faulting must be rotational with respect to the enveloping surface of the flexed plate. This toppled domino geometry implies the presence at depth of a detachment or zone of distributed ductile simple shear where fault displacement and block rotation are accommodated. -from Authors
Collisional effects in the dynamics of a dipolar gas
NASA Astrophysics Data System (ADS)
Sykes, Andrew
2016-05-01
In this talk, we discuss the role of collisions in dipolar gases which are far from equilibrium. We compare and contrast collisional mechanisms with mean-field effects. We consider several cases of dynamical behaviour. We begin with cross-dimensional relaxation, where the time-scale of equilibration is studied following a quench in the trap parameters. We also discuss the damping of monopole and quadrupole excitations. Finally we discuss time-of-flight expansion dynamics. Our results demonstrate that collisions can play a significant role. We use these results to extract an estimate of the deca-heptuplet s-partial-wave scattering length of bosonic dysprosium, and to improve the accuracy of experimental time-of-flight expansion imaging. Financial support from the Marie Sklodowska-Curie H2020 framework program.
Self-focusing of electromagnetic pulsed beams in collisional plasmas
Faisal, Mohammad; Verma, M. P.; Sodha, Mahendra Singh
2008-10-15
In this paper, the self-focusing of an electromagnetic pulsed beam in a collisional plasma has been investigated in the paraxial approximation, following the formalism developed by Akhmanov. The energy balance equation for electrons, the equation expressing the equality of pressure gradient (of electrons and ions) to the force due to space charge field, and the equation for the beam width parameter f (obtained by following Akhmanov's approach) have been simultaneously solved for given initial (z=0) time profile of the pulse to obtain f as a function of {xi} (cz/{omega}r{sub 0}{sup 2}) and t{sup '}=t-z/V{sub g}, where V{sub g} is the group velocity. Both Gaussian and sine time profiles of the pulse have been investigated.
Collisional Processing of Comet Surfaces: Impact Experiments into Olivine
NASA Technical Reports Server (NTRS)
Lederer, S. M.; Jensen, E. A.; Cintala, M. J.; Smith, D. C.; Nakamura-Messenger, K.; Keller, L. P.; Wooden, D. H.; Fernandez, Y. R.; Zolensky, M. E.
2011-01-01
A new paradigm has emerged where 3.9 Ga ago, a violent reshuffling reshaped the placement of small bodies in the solar system (the Nice model). Surface properties of these objects may have been affected by collisions caused by this event, and by collisions with other small bodies since their emplacement. In addition, objects in the Kuiper Belt are believed to undergo extensive collisional processing while in the Kuiper Belt. Physical manifestations of shock effects (e.g., planar dislocations) in minerals typically found in comets will be correlated with spectral changes (e.g. reddening, loss and shift of peaks, new signatures) to allow astronomers to better understand geophysical impact processing that has occurred on small bodies. Targets will include solid and granular olivine (forsterite), impacted over a range of impact speeds with the Experimental Impact Laboratory at NASA JSC. Analyses include quantification of the dependence of the spectral changes with respect to impact speed, texture of the target, and temperature.
Test ion transport in a collisional, field-reversed configuration
NASA Astrophysics Data System (ADS)
Roche, T.; McWilliams, R.; Heidbrink, W. W.; Bolte, N.; Garate, E. P.; Morehouse, M.; Slepchenkov, M.; Wessel, F.
2014-08-01
Diffusion of test-ions in a flux-coil generated, collisional, field-reversed configuration is measured via time-resolved tomographic reconstruction of Ar+ optical emission in the predominantly nitrogen plasma. Azimuthal test ion diffusion across magnetic field lines is found to be classical during the stable period of the discharge. Test ion radial confinement is enhanced by a radial electric field, reducing the observed outward radial transport rate below predictions based solely on classical cross-field diffusion rates. Test ion diffusion is ˜500 m2 s-1 during the stable period of the discharge. The electric field inferred from plasma potential measurements and from equilibrium calculations is consistent with the observed reduction in argon transport.
Simulations of a molecular plasma in collisional-radiative nonequilibrium
NASA Technical Reports Server (NTRS)
Cambier, Jean-Luc; Moreau, Stephane
1993-01-01
A code for the simulation of nonequilibrium plasmas is being developed, with the capability to couple the plasma fluid-dynamics for a single fluid with a collisional-radiative model, where electronic states are treated as separate species. The model allows for non-Boltzmann distribution of the electronic states. Deviations from the Boltzmann distributions are expected to occur in the rapidly ionizing regime behind a strong shock or in the recombining regime during a fast expansion. This additional step in modeling complexity is expected to yield more accurate predictions of the nonequilibrium state and the radiation spectrum and intensity. An attempt at extending the code to molecular plasma flows is presented. The numerical techniques used, the thermochemical model, and the results of some numerical tests are described.
Collisional dynamics in a gas of molecular super-rotors
NASA Astrophysics Data System (ADS)
Khodorkovsky, Yuri; Steinitz, Uri; Hartmann, Jean-Michel; Averbukh, Ilya Sh.
2015-07-01
Recently, femtosecond laser techniques have been developed that are capable of bringing gas molecules to extremely fast rotation in a very short time, while keeping their translational motion relatively slow. Here we study collisional equilibration dynamics of this new state of molecular gases. We show that the route to equilibrium starts with a metastable `gyroscopic stage' in the course of which the molecules maintain their fast rotation and orientation of the angular momentum through many collisions. The inhibited rotational-translational relaxation is characterized by a persistent anisotropy in the molecular angular distribution, and is manifested in the optical birefringence and anisotropic diffusion in the gas. After a certain induction time, the `gyroscopic stage' is abruptly terminated by an explosive rotational-translational energy exchange, leading the gas towards the final equilibrium. We illustrate our conclusions by direct molecular dynamics simulation of several gases of linear molecules.
The acoustic instabilities in magnetized collisional dusty plasmas
Pandey, B. P.; Vladimirov, S. V.; Dwivedi, C. B.
2014-09-15
The present work investigates the wave propagation in collisional dusty plasmas in the presence of electric and magnetic field. It is shown that the dust ion-acoustic waves may become unstable to the reactive instability whereas dust-acoustic waves may suffer from both reactive and dissipative instabilities. If the wave phase speed is smaller than the plasma drift speed, the instability is of reactive type whereas in the opposite case, the instability becomes dissipative in nature. Plasma in the vicinity of dust may also become unstable to reactive instability with the instability sensitive to the dust material: dielectric dust may considerably quench this instability. This has implications for the dust charging and the use of dust as a probe in the plasma sheath.
Searching for Multiple Systems in Trojan Collisional Families and Centaurs
NASA Astrophysics Data System (ADS)
Marchis, Franck
2006-08-01
We propose to finalize our search for moonlet companions around Trojan asteroids using the Keck LGS AO capability at their opposition (Aug. for L5). We will focus on Trojans members of a collisional family to maximize the chance of detection, since recent study indicated than ~20% of the main-belt asteroid of the Koronis family are binary (Merline et al. 2005) and the discovery two moonlets orbiting around 87 Sylvia rubble-pile asteroid (Marchis et al. 2005) confirms that the collisions play a major role in the formation of binary systems. A search for binary Centaur asteroids, which may be connected to the Trojan family, will be initiated to complete the night.
Searching for Multiple Systems in L5-Trojan Collisional Families
NASA Astrophysics Data System (ADS)
Marchis, Franck
2007-02-01
After our successfull search for binary moonlet in the L4 Trojan swarm, leading to the discovery of a moonlet around 624 Hektor (Marchis et al., 2006), we propose to conduct the same program in the L5 Trojan population at opposition in Apr. 2007. We will focus also on Trojans members of a collisional family to maximize the chance of detection, since recent study indicated than ~20% of the main-belt asteroid of the Koronis family are binary (Merline et al. 2005) and the discovery two moonlets orbiting around 87 Sylvia rubble-pile asteroid (Marchis et al. 2005) confirms that the collisions play a major role in the formation of binary systems.
Collisionality dependence of the quasilinear particle flux due to microinstabilities
Fueloep, T.; Pusztai, I.; Helander, P.
2008-07-15
The collisionality dependence of the quasilinear particle flux due to the ion temperature gradient (ITG) and trapped electron mode (TEM) instabilities is studied by including electron collisions modeled by a pitch-angle scattering collision operator in the gyrokinetic equation. The inward transport due to ITG modes is caused mainly by magnetic curvature and thermodiffusion and can be reversed as electron collisions are introduced, if the plasma is far from marginal stability. However, if the plasma is close to marginal stability, collisions may even enhance the inward transport. The sign and the magnitude of the transport are sensitive to the form of the collision operator, to the magnetic drift normalized to the real frequency of the mode, and to the density and temperature scale lengths. These analytical results are in agreement with previously published gyrokinetic simulations. Unlike the ITG-driven flux, the TEM-driven flux is expected to be outwards for conditions far from marginal stability and inwards otherwise.
MODELING COLLISIONAL CASCADES IN DEBRIS DISKS: THE NUMERICAL METHOD
Gaspar, Andras; Psaltis, Dimitrios; Oezel, Feryal; Rieke, George H.; Cooney, Alan E-mail: dpsaltis@as.arizona.edu E-mail: grieke@as.arizona.edu
2012-04-10
We develop a new numerical algorithm to model collisional cascades in debris disks. Because of the large dynamical range in particle masses, we solve the integro-differential equations describing erosive and catastrophic collisions in a particle-in-a-box approach, while treating the orbital dynamics of the particles in an approximate fashion. We employ a new scheme for describing erosive (cratering) collisions that yields a continuous set of outcomes as a function of colliding masses. We demonstrate the stability and convergence characteristics of our algorithm and compare it with other treatments. We show that incorporating the effects of erosive collisions results in a decay of the particle distribution that is significantly faster than with purely catastrophic collisions.
Cosmochemical fractionation by collisional erosion during the Earth's accretion.
Boujibar, Asmaa; Andrault, Denis; Bolfan-Casanova, Nathalie; Bouhifd, Mohamed Ali; Monteux, Julien
2015-01-01
Early in the Solar System's history, energetic collisions of differentiated bodies affected the final composition of the terrestrial planets through partial destruction. Enstatite chondrites (EC) are the best candidates to represent the primordial terrestrial precursors as they present the most similar isotopic compositions to Earth. Here we report that collisional erosion of >15% of the early Earth's mass can reconcile the remaining compositional differences between EC and the Earth. We base our demonstration on experimental melting of an EC composition at pressures between 1 bar and 25 GPa. At low pressures, the first silicate melts are highly enriched in incompatible elements Si, Al and Na, and depleted in Mg. Loss of proto-crusts through impacts raises the Earth's Mg/Si ratio to its present value. To match all major element compositions, our model implies preferential loss of volatile lithophile elements and re-condensation of refractory lithophile elements after the impacts. PMID:26395157
Recombination and collisional X-UV lasers at ORSAY
Klisnick, A.; Carillon, A.; Dhez, P.; Goedtkindt, P.; Guennou, H.; Jamelot, G.; Jaegle, P.; Sureau, A.; Rus, B.; Zeitoun, P. ); Chenais-Popovics, C.; Renaudin, P.; Rancu, O.; Gauthier, J.C. ); Back, C.A. )
1995-01-10
In this paper we describe the progress achieved recently in our laboratory in the field of X-ray lasers. Both collisional excitation and recombination pumped systems are under investigation. We show that the 5g-4f transition in lithium-like ions could bring out a significant increase of the gain-length accessible with recombination X-ray lasers. We present preliminary results on an absorption spectroscopy experiment designed to probe the ionization state of recombination X-ray laser plasmas. Finally we report on the observation of a strong amplified signal at 212 A, the wavelength of a 3p-3s (J=0--1) in neon-like zinc. [copyright] 1995 [ital American] [ital Institute] [ital of] [ital Physics
Short-Period Comets: Primordial Bodies or Collisional Fragments?
Farinella; Davis
1996-08-16
Modeling results show that collisions among Edgeworth-Kuiper Belt Objects (EKOs), a vast swarm of small bodies orbiting beyond Neptune, have been a major process affecting this population and its progeny, the short-period comets. Most EKOs larger than about 100 kilometers in diameter survive over the age of the solar system, but at smaller sizes collisional breakup is frequent, producing a cascade of fragments having a power law size-frequency distribution. Collisions are also a plausible mechanism for injecting EKOs 1 to 10 kilometers in diameter into dynamical resonances, where they can be transported into the inner solar system to become short-period comets. The fragmental nature of these comets may explain their physical properties, such as shape, color, and strength. PMID:8688073
Signal Propagation in Collisional Plasma with Negative Ions
I. Kaganovich; S.V. Berezhnoi; C.B. Shin
2000-12-18
The transport of charged species in collisional currentless plasmas is traditionally thought of as a diffusion-like process. In this paper, it is demonstrated that, in contrast to two-component plasma, containing electrons and positive ions, the transport of additional ions in multi-species plasmas is not governed by diffusion, rather described by nonlinear convection. As a particular example, plasmas with the presence of negative ions have been studied. The velocity of a small perturbation of negative ions was found analytically and validated by numerical simulation. As a result of nonlinear convection, initially smooth ion density profiles break and form strongly inhomogeneous shock-like fronts. These fronts are different from collisionless shocks and shocks in fully ionized plasma. The structure of the fronts has been found analytically and numerically.
Collisional stabilization of van der Waals states of ozone
NASA Astrophysics Data System (ADS)
Ivanov, Mikhail V.; Babikov, Dmitri
2011-05-01
The mixed quantum-classical theory developed earlier [M. Ivanov and D. Babikov, J. Chem. Phys. 134, 144107 (2011)] is employed to treat the collisional energy transfer and the ro-vibrational energy flow in a recombination reaction that forms ozone. Assumption is that the van der Waals states of ozone are formed in the O + O2 collisions, and then stabilized into the states of covalent well by collisions with bath gas. Cross sections for collision induced dissociation of van der Waals states of ozone, for their stabilization into the covalent well, and for their survival in the van der Waals well are computed. The role these states may play in the kinetics of ozone formation is discussed.
A collisional-radiative average atom model for hot plasmas
Rozsnyai, B.F.
1996-10-17
A collisional-radiative `average atom` (AA) model is presented for the calculation of opacities of hot plasmas not in the condition of local thermodynamic equilibrium (LTE). The electron impact and radiative rate constants are calculated using the dipole oscillator strengths of the average atom. A key element of the model is the photon escape probability which at present is calculated for a semi infinite slab. The Fermi statistics renders the rate equation for the AA level occupancies nonlinear, which requires iterations until the steady state. AA level occupancies are found. Detailed electronic configurations are built into the model after the self-consistent non-LTE AA state is found. The model shows a continuous transition from the non-LTE to the LTE state depending on the optical thickness of the plasma. 22 refs., 13 figs., 1 tab.
The Violent Collisional History of Asteroid 4 Vesta
NASA Astrophysics Data System (ADS)
Marchi, S.; McSween, H. Y.; O'Brien, D. P.; Schenk, P.; De Sanctis, M. C.; Gaskell, R.; Jaumann, R.; Mottola, S.; Preusker, F.; Raymond, C. A.; Roatsch, T.; Russell, C. T.
2012-05-01
Vesta is a large differentiated rocky body in the main asteroid belt that accreted within the first few million years after the formation of the earliest solar system solids. The Dawn spacecraft extensively imaged Vesta’s surface, revealing a collision-dominated history. Results show that Vesta’s cratering record has a strong north-south dichotomy. Vesta’s northern heavily cratered terrains retain much of their earliest history. The southern hemisphere was reset, however, by two major collisions in more recent times. We estimate that the youngest of these impact structures, about 500 kilometers across, formed about 1 billion years ago, in agreement with estimates of Vesta asteroid family age based on dynamical and collisional constraints, supporting the notion that the Vesta asteroid family was formed during this event.
Species separation and kinetic effects in collisional plasma shocks
Bellei, C. Wilks, S. C.; Amendt, P. A.; Rinderknecht, H.; Zylstra, A.; Rosenberg, M.; Sio, H.; Li, C. K.; Petrasso, R.
2014-05-15
The properties of collisional shock waves propagating in uniform plasmas are studied with ion-kinetic calculations, in both slab and spherical geometry and for the case of one and two ion species. Despite the presence of an electric field at the shock front—and in contrast to the case where an interface is initially present [C. Bellei et al., Phys. Plasmas 20, 044702 (2013)]—essentially no ion reflection at the shock front is observed due to collisions, with a probability of reflection ≲10{sup −4} for the cases presented. A kinetic two-ion-species spherical convergent shock is studied in detail and compared against an average-species calculation, confirming effects of species separation and differential heating of the ion species at the shock front. The effect of different ion temperatures on the DT and D{sup 3}He fusion reactivity is discussed in the fluid limit and is estimated to be moderately important.
Collisional Time Scales in the Kuiper Disk and Their Implications
NASA Technical Reports Server (NTRS)
Stern, S. Alan
1995-01-01
We explore the rate of collisions among bodies in the present-day Kuiper Disk as a function of the total mass and population size structure of the disk. We find that collisional evolution is an important evolutionary process in the disk as a whole, and indeed, that it is likely the dominant evolutionary process beyond approx. 42 AU, where dynamical instability time scales exceed the age of the solar system. Two key findings we report from this modeling work are: that unless the disk's population structure is sharply truncated for radii smaller than approx. 1-2 km, collisions between comets and smaller debris are occurring so frequently in the disk, and with high enough velocities, that the small body (i.e., KM-class object) population in the disk has probably developed into a collisional cascade, thereby implying that the Kuiper Disk comets may not all be primordial, and that the rate of collisions of smaller bodies with larger 100 less R less 400 km objects (like 1992QB(sub 1) and its cohorts) is so low that there appears to be a dilemma in explaining how QB(sub 1)s could have grown by binary accretion in the disk as we know it. Given these findings, it appears that either the present-day paradigm for the formation of Kuiper Disk is failed in some fundamental respect, or that the present-day disk is no longer representative of the ancient structure from which it evolved. This in turn suggests the intriguing possibility that the present-day Kuiper Disk evolved through a more erosional stage reminiscent of the disks around the stars Beta Pictorus, alpha PsA, and alpha Lyr.
THE COLLISIONAL DIVOT IN THE KUIPER BELT SIZE DISTRIBUTION
Fraser, Wesley C.
2009-11-20
This paper presents the results of collisional evolution calculations for the Kuiper Belt starting from an initial size distribution similar to that produced by accretion simulations of that region-a steep power-law large object size distribution that breaks to a shallower slope at r approx 1-2 km, with collisional equilibrium achieved for objects r approx< 0.5 km. We find that the break from the steep large object power law causes a divot, or depletion of objects at r approx 10-20 km, which, in turn, greatly reduces the disruption rate of objects with r approx> 25-50 km, preserving the steep power-law behavior for objects at this size. Our calculations demonstrate that the roll-over observed in the Kuiper Belt size distribution is naturally explained as an edge of a divot in the size distribution; the radius at which the size distribution transitions away from the power law, and the shape of the divot from our simulations are consistent with the size of the observed roll-over, and size distribution for smaller bodies. Both the kink radius and the radius of the divot center depend on the strength scaling law in the gravity regime for Kuiper Belt objects. These simulations suggest that the sky density of r approx 1 km objects is approx10{sup 6}-10{sup 7} objects per square degree. A detection of the divot in the size distribution would provide a measure of the strength of large Kuiper Belt objects, and constrain the shape of the size distribution at the end of accretion in the Kuiper Belt.
Fluid-assisted melting in a collisional orogen
NASA Astrophysics Data System (ADS)
Berger, A.; Burri, T.; Engi, M.; Roselle, G. T.
2003-04-01
The Southern Steep Belt (SSB) of the Central Alps is the location of backthrusting during syn- to post-collisional deformation. From its metamorphic evolution and lithological contents the SSB has been interpreted as a tectonic accretion channel (TAC [1]). The central part of the SSB is additionally characterized by anatexites, leucogranitic aplites and pegmatites. Dehydration melting of muscovite is rare but did occurr locally. Moreover, no evidence of dehydration melting of biotite has been formed in that products of incongruent melting reactions (garnet, opx or cordierite) are missing. The melts are mainly produced by the infiltration of an external aqueous fluid. The fluids must have originated from the breakdown of hydrous minerals at temperatures below the water saturated solidus of the quartz-feldspar-system, such that the liberated fluids could not been trapped in the melt. Using the thermal modeling program MELONPIT [2] and assuming that solid fragments ascended in combination with tectonic accreated radioactive material, a complex thermal evolution inside the TAC has been derived. During subduction of the downgoing plate, isotherms were locally inverted, then subsequently relaxed, when subduction slowed down. At the collisional stage a small region develope, where the isotherms were still bent, and where temperatures increased during decompression. Assuming that dehydration reactions were followed by upward flow of fluids released from this region fluid present partial melting was triggered. The flow direction of the fluid was controlled by the pressure gradient and the steeply oriented foliations in the SSB. According to the model, the area of upward flowing fluids should be limited to the SSB. This is consistent with the observed regional distribution of leucosomes derived from in-situ melts. [1] Engi et al. (2001) Geology 29: 1143-1146 [2] Roselle et al. (2002) Am. J. Sci. 302: 381-409
Effects of Global Boundary and Local Collisionality on Magnetic Reconnection in a Laboratory Plasma
Kuritsyn, A.; Ji, H.; Gerhardt, S. P.; Ren, Y.; Yamada, M.
2007-07-24
The magnetic reconnection process is studied in a wide range of operating conditions in the well-controlled Magnetic Reconnection Experiment. The reconnection rate is observed to be a function of both global (i.e., system size) and local (collisionality) plasma parameters. When only local collisionality is lowered, the current sheet is shortened while effective resistivity is enhanced, both accelerating reconnection rates. At a fixed collisionality, the current sheet length increases with system size, resulting in the reduction of the reconnection rate. These results quantitatively agree with a generalized Sweet-Parker analysis.
CLMSZ, Garnet Mountain area, southern California: A collisionally generated contractional shear zone
Bracchi, K.A.; Girty, G.H.; Girty, M.S. . Dept. of Geological Sciences)
1993-04-01
The Harper Creek gneiss (HCg) and Oriflamme Canyon unit (OCu) underlie the central portion of the Cuyamaca Laguna Mountains shear zone (CLMSZ) in and around Garnet Mountain, Peninsular Ranges, California, and may have been deformed during Cretaceous arc-continent collision. U-Pb zircon work and petrological and geochemical analyses suggest that in the Garnet Mountain area, the 140 Ma HCg is derived from granite and granodiorite, whereas the 122 [+-] 1 Ma OCu is a protomylonite derived from a granite. Both units appear to be per aluminous calc-alkaline magmatic arc granitoids. Mineral assemblages suggest uppermost greenschist to lower amphibolite grade conditions during deformation. In the HCg, S-1hc is a mylonitic gneissosity with a mean attitude of N11W, 60 NE. A mineral streaking lineation lies within the plane of S-1hc and has a mean attitude of 61[degree] N76E. In the OCu, S-1oc strikes about N13W and dips 52 NE and contains a mineral streaking lineation with an attitude of 49 N52E. Dextral and sinistral shear bands, S-2d and S-2s (looking NW), transect S-1hc and S-1oc. S-2d and S-2s strike subparallel to S-1. In the HCg S-2s is weakly developed and dips about 32 NE, whereas S-2d is more dominant and dips about 76 NE. On the OCu these relationships are reversed. S-2d does not cross cut S-2s: hence, the two sets of shear bands are interpreted to be conjugates reflecting NE-SW contraction and subvertical extension during collisional development of the CLMSZ.
The Collisional and Radiative Processes of the Hydroxyl Radical
NASA Astrophysics Data System (ADS)
Steffens, Kristen Lisa
1995-01-01
The OH radical is an important species in the chemistry of atmospheric and combustion environments, where an understanding of OH concentration and chemistry is necessary to create and validate chemical models. Laser-induced fluorescence (LIF) is used with great success in OH detection, but OH LIF measurements require a vast knowledge of the collisional and spectroscopic properties of OH. Information is still lacking, especially concerning vibrational levels v^' > 0 of the rm A^2Sigma^+ electronic state. We investigate transition probabilities and collisional processes of these higher vibrational levels. Experimental vibrational band transition probabilities from v^' = 3 and 2 of OH rm A^2Sigma^+ are needed to determine the electronic transition moment for the rm A^2Sigma^+ -rm X^2Pi_{i } system to calculate a consistent set of rotational and vibrational dependent transition probabilities for uses including rm X^2Pi_ {i} temperature determinations and rm A^2Sigma^+ and rm X^2Pi_{i} nascent population determinations. Using LIF in a low -pressure CH_4/O_2 flame, we measured relative emission intensities for vibrational bands (3,0) through (3,5) and (2,0) through (2,6). Our emission intensities have been used in another study to determine the best rm A^2 Sigma^+-rm X^2 Pi_{i} electronic transition moment. For quantitative OH concentration measurements in high pressure flames exciting the predissociative v ^' = 3 level, one must account for vibrational energy transfer (VET). We measure the amounts of VET occurring from v^' = 3 in CH_4/O_2 , CH_4/air, and H _2/O_2 flames at pressures between 14 and 760 Torr. Significant amounts of VET occur in all flames and must be accounted for to get accurate OH concentrations. Stratospheric OH concentration measurement employs OH rm A^2Sigma^+v ^' = 1 excitation, which requires accurate VET and quenching cross sections for major colliders. We use LIF to measure the v^ ' = 1 VET and quenching cross sections for N_2, O_2 and CO_2
Collisional transfer of population and orientation in NaK.
Wolfe, C M; Ashman, S; Bai, J; Beser, B; Ahmed, E H; Lyyra, A M; Huennekens, J
2011-05-01
Collisional satellite lines with |ΔJ| ≤ 58 have been identified in recent polarization spectroscopy V-type optical-optical double resonance (OODR) excitation spectra of the Rb(2) molecule [H. Salami et al., Phys. Rev. A 80, 022515 (2009)]. Observation of these satellite lines clearly requires a transfer of population from the rotational level directly excited by the pump laser to a neighboring level in a collision of the molecule with an atomic perturber. However to be observed in polarization spectroscopy, the collision must also partially preserve the angular momentum orientation, which is at least somewhat surprising given the extremely large values of ΔJ that were observed. In the present work, we used the two-step OODR fluorescence and polarization spectroscopy techniques to obtain quantitative information on the transfer of population and orientation in rotationally inelastic collisions of the NaK molecules prepared in the 2(A)(1)Σ(+)(v' = 16, J' = 30) rovibrational level with argon and potassium perturbers. A rate equation model was used to study the intensities of these satellite lines as a function of argon pressure and heat pipe oven temperature, in order to separate the collisional effects of argon and potassium atoms. Using a fit of this rate equation model to the data, we found that collisions of NaK molecules with potassium atoms are more likely to transfer population and destroy orientation than collisions with argon atoms. Collisions with argon atoms show a strong propensity for population transfer with ΔJ = even. Conversely, collisions with potassium atoms do not show this ΔJ = even propensity, but do show a propensity for ΔJ = positive compared to ΔJ = negative, for this particular initial state. The density matrix equations of motion have also been solved numerically in order to test the approximations used in the rate equation model and to calculate fluorescence and polarization spectroscopy line shapes. In addition, we have measured
Reply to 'Comment on 'Collisional cooling investigation of THz rotational transitions of water''
Drouin, Brian J.; Pearson, John C.; Dick, Michael J.
2010-09-15
This response describes the authors' reaction to a critique of recent work on the ultracold physics of water. The possibility of spin-selective adsorption occurring in the context of the collisional cooling experiment is discussed.
NASA Astrophysics Data System (ADS)
Rosenberg, Claudio; Bellahsen, Nicolas
2016-04-01
The style of collision in the Alps varies along strike, reflecting different amounts and different modes of accommodation of collisional shortening. These differences control the patterns of exhumation during collision. Whereas the western Alps largely consist of a metamorphic complex formed during subduction and largely exhumed before the initiation of collision, the subduction nappe-stack of the Central and the Eastern Alps is strongly overprinted by collisional shortening and by Barrovian metamorphism. Based on compiled and new data we estimate amounts of collisional shortening along the strike of the chain and set it in relationship to the geometry of the collisional prism. The western Alpine collisional structures form a very large (in map view), but moderately shortened wedge, terminating in front of a poorly developed Molasse basin. Shortening of this wedge was mainly localized along its external parts, resulting in accretion of basement and cover units thrusted towards the foreland. Back-folding and back-thrusting are barely developed and no shortening takes place in the upper, Adriatic plate. In the Central Alps, the amount of collisional shortening is larger and it is distributed both in the lower and in the upper plate. The collisional prism is bivergent and partitioning of the amount of shortening between the upper and lower plates varies along strike, being most probably controlled by rheological, heterogeneities. The thickened accreted lower plate is strongly affected by Barrovian metamorphism where shortening is largest and localized within a confined area. A deep Molasse basin developed in front of the prism. In the Eastern Alps collisional kinematics vary from east to west, with orogen-parallel displacements dominating in the east and orogen-perpendicular ones in the West, where they culminate in the structural and metamorphic dome of the Tauern Window. Nowhere else in the Alps collisional shortening is so strongly localized in one and the same
Experimental investigations of weak definite and weak indefinite noun phrases
Klein, Natalie M.; Gegg-Harrison, Whitney M.; Carlson, Greg N.; Tanenhaus, Michael K.
2013-01-01
Definite noun phrases typically refer to entities that are uniquely identifiable in the speaker and addressee’s common ground. Some definite noun phrases (e.g. the hospital in Mary had to go the hospital and John did too) seem to violate this uniqueness constraint. We report six experiments that were motivated by the hypothesis that these “weak definite” interpretations arise in “incorporated” constructions. Experiments 1-3 compared nouns that seem to allow for a weak definite interpretation (e.g. hospital, bank, bus, radio) with those that do not (e.g. farm, concert, car, book). Experiments 1 and 2 used an instruction-following task and picture-judgment task, respectively, to demonstrate that a weak definite need not uniquely refer. In Experiment 3 participants imagined scenarios described by sentences such as The Federal Express driver had to go to the hospital/farm. The imagined scenarios following weak definite noun phrases were more likely to include conventional activities associated with the object, whereas following regular nouns, participants were more likely to imagine scenarios that included typical activities associated with the subject; similar effects were observed with weak indefinites. Experiment 4 found that object-related activities were reduced when the same subject and object were used with a verb that does not license weak definite interpretations. In Experiment 5, a science fiction story introduced an artificial lexicon for novel concepts. Novel nouns that shared conceptual properties with English weak definite nouns were more likely to allow weak reference in a judgment task. Experiment 6 demonstrated that familiarity for definite articles and anti- familiarity for indefinite articles applies to the activity associated with the noun, consistent with predictions made by the incorporation analysis. PMID:23685208
Fragmentation efficiencies of peptide ions following low energy collisional activation
NASA Astrophysics Data System (ADS)
Summerfield, Scott G.; Gaskell, Simon J.
1997-11-01
Low energy fragmentations of protonated peptides in the gas phase are generally attributed to charge-directed processes. The extent and location of peptide backbone fragmentation is accordingly influenced by the extent to which charge is sequestered on amino acid side-chains. We describe systematic studies of the efficiencies of decomposition of peptide ions to assess in particular the influence of the presence of basic amino acid residues and of the protonation state. In a set of analogues containing two arginine, two histidine or two lysine residues, the extent of fragmentation of [M + 2H]2+ ions decreases with increased basicity, reflecting decreased backbone protonation. The collisionally activated dissociation of multiply protonated melittin ions shows an increase in fragmentation efficiency with higher charge state (using activation conditions which are similar for each charge state). For a single charge state, acetylation of primary amine groups increases fragmentation efficiency, consistent with the reduction in basicity of lysine side-chains. Conversion of arginine residues to the less basic dimethylpyrimidylornithine, however, decreases fragmentation efficiency, suggesting more effective sequestering of ionizing protons; the effect may be attributable to a disfavouring of proton-bridged structures but this hypothesis requires further study. Preliminary data for the decompositions of [M- 2H]2- ions derived from peptides containing two acidic residues suggest that the sequestration of charge away from the backbone is again detrimental to efficient fragmentation. Apparently diagnostic cleavages adjacent to aspartic acid residues are observed.
Expansion of Collisional Radiative Model for Helium line ratio spectroscopy
NASA Astrophysics Data System (ADS)
Cinquegrani, David; Cooper, Chris; Forest, Cary; Milhone, Jason; Munoz-Borges, Jorge; Schmitz, Oliver; Unterberg, Ezekial
2015-11-01
Helium line ratio spectroscopy is a powerful technique of active plasma edge spectroscopy. It enables reconstruction of plasma edge parameters like electron density and temperature by use of suitable Collisional Radiative Models (CRM). An established approach is successful at moderate plasma densities (~1018m-3 range) and temperature (30-300eV), taking recombination and charge exchange to be negligible. The goal of this work is to experimentally explore limitations of this approach to CRM. For basic validation the Madison Plasma Dynamo eXperiment (MPDX) will be used. MPDX offers a very uniform plasma and spherical symmetry at low temperature (5-20 eV) and low density (1016 -1017m-3) . Initial data from MPDX shows a deviation in CRM results when compared to Langmuir probe data. This discrepancy points to the importance of recombination effects. The validated model is applied to first time measurement of electron density and temperature in front of an ICRH antenna at the TEXTOR tokamak. These measurements are important to understand RF coupling and PMI physics at the antenna limiters. Work supported in part by start up funds of the Department of Engineering Physics at the UW - Madison, USA and NSF CAREER award PHY-1455210.
Nonextensive statistics and the sheath criterion in collisional plasmas
Hatami, M. M.
2015-01-15
The Bohm criterion in an electropositive plasma containing nonextensively distributed electrons and warm ions is investigated by using a steady state two-fluid model. Taking into account the ion-neutral collisions and finite temperature of ions, a modified Bohm criterion is derived which limits both maximum and minimum allowable velocity of ions at the sheath edge (u{sub 0i}). It is found that the degree of nonextensivity of electrons (q) and temperature of positive ions (T{sub i}) affect only the lower limit of the entrance velocity of ions into the sheath while the degree of ion collisionality (α) influences both lower and upper limits of the ion velocities at the sheath edge. In addition, depending on the value of q, it is shown that the minimum velocity of positive ions at the sheath edge can be greater or smaller than its Maxwellian counterpart. Moreover, it is shown that, depending on the values of α and T{sub i}, the positive ions with subsonic velocity may enter the sheath for either q > 1 or −1 < q < 1. Finally, as a practical application, the density distribution of charged particles in the sheath region is studied for different values of u{sub 0i}, and it is shown that monotonical reduction of the positive ion density distribution occurs only when the velocity of positive ions at the sheath edge lies between two above mentioned limits.
On the inclusion of collisional correlations in quantum dynamics
Slama, N.; Reinhard, P.-G.; Suraud, E.
2015-04-15
We present a formalism to describe collisional correlations responsible for thermalization effects in finite quantum systems. The approach consists in a stochastic extension of time dependent mean field theory. Correlations are treated in time dependent perturbation theory and loss of coherence is assumed at some time intervals allowing a stochastic reduction of the correlated dynamics in terms of a stochastic ensemble of time dependent mean-fields. This theory was formulated long ago in terms of density matrices but never applied in practical cases because of its complexity. We propose here a reformulation of the theory in terms of wave functions and use a simplified 1D model of cluster and molecules allowing to test the theory in a schematic but realistic manner. We illustrate the performance in terms of several observables, in particular global moments of the density matrix and single particle entropy built on occupation numbers. The occupation numbers remain fixed in time dependent mean-field propagation and change when evaluating the correlations, then taking fractional values. They converge asymptotically towards Fermi distributions which is a clear indication of thermalization.
Collisional excitation of electron Landau levels in strong magnetic fields
NASA Technical Reports Server (NTRS)
Langer, S. H.
1981-01-01
The cross sections for the excitation and deexcitation of the quantized transverse energy levels of an electron in a magnetic field are calculated for electron-proton and electron-electron collisions in light of the importance of the cross sections for studies of X-ray pulsar emission. First-order matrix elements are calculated using the Dirac theory of the electron, thus taking into account relativistic effects, which are believed to be important in accreting neutron stars. Results for the collisional excitation of ground state electrons by protons are presented which demonstrate the importance of proton recoil and relativistic effects, and it is shown that electron-electron excitations may contribute 10 to 20% of the excitation rate from electron-proton scattering in a Maxwellian plasma. Finally, calculations of the cross section for electron-proton small-angle scattering are presented which lead to relaxation rates for the electron velocity distribution which are modified by the magnetic field, and to a possible increase in the value of the Coulomb logarithm.
Global, Collisional Model of High-Energy Photoelectrons
NASA Technical Reports Server (NTRS)
Khazanov, G. V.; Moore, T. E.; Liemohn, M. W.; Jordanova, V. K.; Fok, M.-C.
1996-01-01
A previously-developed colissional, interhemispheric flux tube model for photoelectrons (PE) has been extended to three dimensions by including transport due to vector E x vector B and magnetic gradient-curvature drifts. Using this model, initial calculations of the high-energy (greater then 50 eV) PE distribution as a function of time, energy, pitch angle, and spatial location in the equatorial plane, are reported for conditions of low geomagnetic activity. To explore both the dynamic and steady behaviors of the model, the simulation starts with the abrupt onset of photoelectron excitation, and is followed to steady state conditions. The results illustrate several features of the interaction of photoelectrons with typical magnetospheric plasmas and fields, including collisional diffusion of photoelectrons in pitch angle with flux tube filling, diurnal intensity and pitch angle asymmetries introduced by directional sunlight, and energization of the photoelectron distribution in the evening sector. Cross-field drift is shown to have a long time scale, taking 12 to 24 hours to reach a steady state distribution. Future applications of the model are briefly outlined.
Collisional Grooming Models of the Kuiper Belt Dust Cloud
NASA Technical Reports Server (NTRS)
Kuchner, Marc J.; Stark, Christopher C.
2010-01-01
We modeled the three-dimensional structure of the Kuiper Belt (KB) dust cloud at four different dust production rates, incorporating both planet-dust interactions and grain-grain collisions using the collisional grooming algorithm. Simulated images of a model with a face-on optical depth of approximately 10 (exp -4) primarily show an azimuthally- symmetric ring at 40-47 AU in submillimeter and infrared wavelengths; this ring is associated with the cold classical KB. For models with lower optical depths (10 (exp -6) and 10 (exp-7)), synthetic infrared images show that the ring widens and a gap opens in the ring at the location of Neptune; this feature is caused by trapping of dust grains in Neptune's mean motion resonances. At low optical depths, a secondary ring also appears associated with the hole cleared in the center of the disk by Saturn. Our simulations, which incorporate 25 different grain sizes, illustrate that grain-grain collisions are important in sculpting today's KB dust, and probably other aspects of the solar system dust complex; collisions erase all signs of azimuthal asymmetry from the submillimeter image of the disk at every dust level we considered. The model images switch from being dominated by resonantly trapped small grains ("transport dominated") to being dominated by the birth ring ("collision dominated") when the optical depth reaches a critical value of r approximately v/c, where v is the local Keplerian speed.
Effects of Collisional Dissipation on the "Colliding Beam Fusion Reactor "
NASA Astrophysics Data System (ADS)
Lampe, Martin; Manheimer, Wallace M.
1998-11-01
Rostoker, Binderbauer and Monkhorst have recently proposed a "colliding beam fusion reactor" (CBFR) for use with the p-B11 reaction. We have examined the various dissipative processes resulting from Coulomb collisions, and have concluded that the CBFR equilibrium cannot be sustained for long enough to permit net fusion gain. There are many collisional processes which occur considerably faster than fusion, and result in particle loss, energy loss, or detuning of the resonant energy for the p-B reaction. Pitch-angle scattering of protons off the boron beam, which occurs 100 times faster than fusion, isotropizes the proton beam and results in proton loss. Energy exchange between protons and boron, which is 20 times faster than fusion, detunes the resonance. Proton-proton scattering, which is faster than fusion for all CBFR scenarios, Maxwellianizes the protons and thus detunes the resonance. Ion-electron collisions lead indirectly to a friction between the two ion beams, which is typically fast compared to the fusion process. Results of Fokker-Planck analyses of each process will be shown.
Isotope Effects in Collisional VT Relaxation of Molecular Hydrogen
NASA Technical Reports Server (NTRS)
Bieniek, R. J.
2006-01-01
A simple exponential-potential model of molecular collisions leads to a two-parameter analytic expression for rates of collisionally induced vibrational-translation (VT) energy exchange that has been shown to be accurate over variations of orders of magnitude as a function of temperature in a variety of systems. This includes excellent agreement with reported experimental and theoretical results for the fundamental self-relaxation rate of molecular hydrogen H2(v = 1) + H2 yields H2(v = 0) + H2. The analytic rate successfully follows the five-orders-of-magnitude change in experimental values for the temperature range 50-2000 K. This approach is now applied to isotope effects in the vibrational relaxation rates of excited HD and D2 in collision with H2: HD(v = 1)+H2 yields HD(v = 0)+H2 and D2(v = 1)+H2 yields D2(v = 0)+H2. The simplicity of the analytic expression for the thermal rate lends itself to convenient application in modeling the evolving vibrational populations of molecular hydrogen in shocked astrophysical environments.
Evolution of a Gaussian laser beam in warm collisional magnetoplasma
NASA Astrophysics Data System (ADS)
Jafari, M. J.; Jafari Milani, M. R.; Niknam, A. R.
2016-07-01
In this paper, the spatial evolution of an intense circularly polarized Gaussian laser beam propagated through a warm plasma is investigated, taking into account the ponderomotive force, Ohmic heating, external magnetic field, and collisional effects. Using the momentum transfer and energy equations, both modified electron temperature and electron density in plasma are obtained. By introducing the complex dielectric permittivity of warm magnetized plasma and using the complex eikonal function, coupled differential equations for beam width parameter are established and solved numerically. The effects of polarization state of laser and magnetic field on the laser spot size evolution are studied. It is observed that in case of the right-handed polarization, an increase in the value of external magnetic field causes an increase in the strength of the self-focusing, especially in the higher values, and consequently, the self-focusing occurs in shorter distance of propagation. Moreover, the results demonstrate the existence of laser intensity and electron temperature ranges where self-focusing can occur, while the beam diverges outside of these regions; meanwhile, in these intervals, there exists a turning point for each of intensity and temperature in which the self-focusing process has its strongest strength. Finally, it is found that the self-focusing effect can be enhanced by increasing the plasma frequency (plasma density).
Hiding in the Shadows. II. Collisional Dust as Exoplanet Markers
NASA Astrophysics Data System (ADS)
Dobinson, Jack; Leinhardt, Zoë M.; Lines, Stefan; Carter, Philip J.; Dodson-Robinson, Sarah E.; Teanby, Nick A.
2016-03-01
Observations of the youngest planets (˜1-10 Myr for a transitional disk) will increase the accuracy of our planet formation models. Unfortunately, observations of such planets are challenging and time-consuming to undertake, even in ideal circumstances. Therefore, we propose the determination of a set of markers that can preselect promising exoplanet-hosting candidate disks. To this end, N-body simulations were conducted to investigate the effect of an embedded Jupiter-mass planet on the dynamics of the surrounding planetesimal disk and the resulting creation of second-generation collisional dust. We use a new collision model that allows fragmentation and erosion of planetesimals, and dust-sized fragments are simulated in a post-process step including non-gravitational forces due to stellar radiation and a gaseous protoplanetary disk. Synthetic images from our numerical simulations show a bright double ring at 850 μm for a low-eccentricity planet, whereas a high-eccentricity planet would produce a characteristic inner ring with asymmetries in the disk. In the presence of first-generation primordial dust these markers would be difficult to detect far from the orbit of the embedded planet, but would be detectable inside a gap of planetary origin in a transitional disk.
Constraining scalar fields with stellar kinematics and collisional dark matter
Amaro-Seoane, Pau; Barranco, Juan; Bernal, Argelia; Rezzolla, Luciano E-mail: jbarranc@aei.mpg.de E-mail: rezzolla@aei.mpg.de
2010-11-01
The existence and detection of scalar fields could provide solutions to long-standing puzzles about the nature of dark matter, the dark compact objects at the centre of most galaxies, and other phenomena. Yet, self-interacting scalar fields are very poorly constrained by astronomical observations, leading to great uncertainties in estimates of the mass m{sub φ} and the self-interacting coupling constant λ of these fields. To counter this, we have systematically employed available astronomical observations to develop new constraints, considerably restricting this parameter space. In particular, by exploiting precise observations of stellar dynamics at the centre of our Galaxy and assuming that these dynamics can be explained by a single boson star, we determine an upper limit for the boson star compactness and impose significant limits on the values of the properties of possible scalar fields. Requiring the scalar field particle to follow a collisional dark matter model further narrows these constraints. Most importantly, we find that if a scalar dark matter particle does exist, then it cannot account for both the dark-matter halos and the existence of dark compact objects in galactic nuclei.
Consistent analytic approach to the efficiency of collisional Penrose process
NASA Astrophysics Data System (ADS)
Harada, Tomohiro; Ogasawara, Kota; Miyamoto, Umpei
2016-07-01
We propose a consistent analytic approach to the efficiency of collisional Penrose process in the vicinity of a maximally rotating Kerr black hole. We focus on a collision with arbitrarily high center-of-mass energy, which occurs if either of the colliding particles has its angular momentum fine-tuned to the critical value to enter the horizon. We show that if the fine-tuned particle is ingoing on the collision, the upper limit of the efficiency is (2 +√{3 })(2 -√{2 })≃2.186 , while if the fine-tuned particle is bounced back before the collision, the upper limit is (2 +√{3 })2≃13.93 . Despite earlier claims, the former can be attained for inverse Compton scattering if the fine-tuned particle is massive and starts at rest at infinity, while the latter can be attained for various particle reactions, such as inverse Compton scattering and pair annihilation, if the fine-tuned particle is either massless or highly relativistic at infinity. We discuss the difference between the present and earlier analyses.
Potential around a dust grain in collisional plasma
Moulick, R. Goswami, K. S.
2015-04-15
The ion neutral collision can lead to interesting phenomena in dust charging, totally different from the expectations based on the traditional orbit motion limited theory. The potential around a dust grain is investigated for the collisional plasma considering the presence of ion neutral collisions. Fluid equations are solved for the one dimensional radial coordinate. It is observed that with the gradual increase in ion neutral collision, the potential structure around the dust grain changes its shape and is different from the usual Debye-Hückel potential. The shift however starts from a certain value of ion neutral collision and the electron-ion density varies accordingly. The potential variation is interesting and reconfirms the fact that there exists a region of attraction for negative charges. The collision modeling is done for the full range of plasma, i.e., considering the bulk and the sheath jointly. The potential variation with collision is also shown explicitly and the variation is found to cope up with the earlier observations.
Direct and Collisional Excitation of Automotive Fuel Components)
NASA Astrophysics Data System (ADS)
White, Allen R.; Wilson, Kyle; Sakai, Stephen; Devasher, Rebecca B.
2010-06-01
Adding energy directly into the vibrational modes of automotive fuel may reduce the threshold energy required for combustion, without raising the combustion charge temperature. This energy can be supplied either directly via incident laser radiation or indirectly through collision with directly excited molecules. The most common chemical in commercial gasoline, isooctane, does not absorb infrared radiation sufficiently at any wavelength for which an infrared laser is readily available. However, CO2 lasers are relatively cheap, and are available at wavelengths which are absorbed by isopropanol as well as ethanol, which is also a component of commercial gasoline. In this study, the infrared absorption of isopropanol and ethanol in balance isooctane were measured at three wavelengths (10.6 m, 10.2 m, and 9.3 m) of incident CO2 laser radiation. Additional time-resolved emission measurements were performed for these mixtures. The data support the existence of the proposed collisional pathway for energy transfer from ethanol and isopropanol to isooctane.
Collisional disruption of gravitational aggregates in the tidal environment
Hyodo, Ryuki; Ohtsuki, Keiji
2014-05-20
The degree of disruption in collisions in free space is determined by specific impact energy, and the mass fraction of the largest remnant is a monotonically decreasing function of impact energy. However, it has not been shown whether such a relationship is applicable to collisions under the influence of a planet's tidal force, which is important in ring dynamics and satellite accretion. Here we examine the collisional disruption of gravitational aggregates in the tidal environment by using local N-body simulations. We find that outcomes of such a collision largely depend on the impact velocity, the direction of impact, and the radial distance from the planet. In the case of a strong tidal field corresponding to Saturn's F ring, collisions in the azimuthal direction are much more destructive than those in the radial direction. Numerical results of collisions sensitively depend on the impact velocity, and a complete disruption of aggregates can occur even in impacts with velocity much lower than their escape velocity. In such low-velocity collisions, the deformation of colliding aggregates plays an essential role in determining collision outcomes, because the physical size of the aggregate is comparable to its Hill radius. On the other hand, the dependence of collision outcomes on impact velocity becomes similar to the case in free space when the distance from the planet is sufficiently large. Our results are consistent with Cassini observations of the F ring, which suggest ongoing creation and disruption of aggregates within the ring.
COLLISIONAL GROOMING MODELS OF THE KUIPER BELT DUST CLOUD
Kuchner, Marc J.; Stark, Christopher C. E-mail: starkc@umd.ed
2010-10-15
We modeled the three-dimensional structure of the Kuiper Belt (KB) dust cloud at four different dust production rates, incorporating both planet-dust interactions and grain-grain collisions using the collisional grooming algorithm. Simulated images of a model with a face-on optical depth of {approx}10{sup -4} primarily show an azimuthally symmetric ring at 40-47 AU in submillimeter and infrared wavelengths; this ring is associated with the cold classical KB. For models with lower optical depths (10{sup -6} and 10{sup -7}), synthetic infrared images show that the ring widens and a gap opens in the ring at the location of Neptune; this feature is caused by trapping of dust grains in Neptune's mean motion resonances. At low optical depths, a secondary ring also appears associated with the hole cleared in the center of the disk by Saturn. Our simulations, which incorporate 25 different grain sizes, illustrate that grain-grain collisions are important in sculpting today's KB dust, and probably other aspects of the solar system dust complex; collisions erase all signs of azimuthal asymmetry from the submillimeter image of the disk at every dust level we considered. The model images switch from being dominated by resonantly trapped small grains ('transport dominated') to being dominated by the birth ring ('collision dominated') when the optical depth reaches a critical value of {tau} {approx} v/c, where v is the local Keplerian speed.
A collisional family of icy objects in the Kuiper belt.
Brown, Michael E; Barkume, Kristina M; Ragozzine, Darin; Schaller, Emily L
2007-03-15
The small bodies in the Solar System are thought to have been highly affected by collisions and erosion. In the asteroid belt, direct evidence of the effects of large collisions can be seen in the existence of separate families of asteroids--a family consists of many asteroids with similar orbits and, frequently, similar surface properties, with each family being the remnant of a single catastrophic impact. In the region beyond Neptune, in contrast, no collisionally created families have hitherto been found. The third largest known Kuiper belt object, 2003 EL61, however, is thought to have experienced a giant impact that created its multiple satellite system, stripped away much of an overlying ice mantle, and left it with a rapid rotation. Here we report the discovery of a family of Kuiper belt objects with surface properties and orbits that are nearly identical to those of 2003 EL61. This family appears to be fragments of the ejected ice mantle of 2003 EL61. PMID:17361177
COLLISIONAL STRIPPING AND DISRUPTION OF SUPER-EARTHS
Marcus, Robert A.; Sasselov, Dimitar; Hernquist, Lars; Stewart, Sarah T.
2009-08-01
The final stage of planet formation is dominated by collisions between planetary embryos. The dynamics of this stage determine the orbital configuration and the mass and composition of planets in the system. In the solar system, late giant impacts have been proposed for Mercury, Earth, Mars, and Pluto. In the case of Mercury, this giant impact may have significantly altered the bulk composition of the planet. Here we present the results of smoothed particle hydrodynamics simulations of high-velocity (up to {approx}5v {sub esc}) collisions between 1 and 10 M {sub +} planets of initially terrestrial composition to investigate the end stages of formation of extrasolar super-Earths. As found in previous simulations of collisions between smaller bodies, when collision energies exceed simple merging, giant impacts are divided into two regimes: (1) disruption and (2) hit-and-run (a grazing inelastic collision and projectile escape). Disruption occurs when the impact parameter is near zero, when the projectile mass is small compared to the target, or at extremely high velocities. In the disruption regime, we derive the criteria for catastrophic disruption (when half the total colliding mass is lost), the transition energy between accretion and erosion, and a scaling law for the change in bulk composition (iron-to-silicate ratio) resulting from collisional stripping of a mantle.
Collisional energy transfer and quenching of electronic excitation
Lin, S. H.; Eyring, H.
1975-01-01
The purpose of this paper has been to explore in a preliminary way the nature and mechanism of collisional energy transfer and quenching of electronic excitation. For this purpose, the Born approximation has been used, and the triplet-triplet and singlet-singlet transfer, and the triplet-triplet and singlet-singlet quenching have been studied. It has been shown theoretically that (i) the singlet-singlet transfer constants (or cross sections) are always larger than the triplet-triplet transfer constants (or cross sections) for the same system of donor and acceptor; (ii) for the singlet-singlet transfer, the observed cross section varies linearly with respect to the spectral overlap between the donor emission and the acceptor absorption; (iii) the reason that the quenching constants (or cross sections) are always smaller than the energy transfer constants (or cross sections) is due to the fact that for the quenching the vibration of the acceptor hardly participates in accepting the electronic excitation and for the energy transfer only part of the excited electron energy of the donor is converted into the energy of nuclear motion; and (iv) the polar acceptor molecules are better quenchers than nonpolar acceptor molecules. PMID:16592281
Elimination of collisional dephasing by control laser fields
NASA Astrophysics Data System (ADS)
Sokolov, Alexei
2003-05-01
The perturbation of electronic states during a molecular collision results in an adiabatic shift of natural molecular frequencies. It is this frequency shift (integrated over the collision time) that produces an oscillation phase shift, and ultimately leads to dephasing of a molecular ensemble. However, the fact that during the collision all molecular levels shift in unison can be used to eliminate the shift of one selected transition, by applying a control laser field to an adjacent (control) transition. The amplitude and frequency of the control field can be adjusted such that the time-varying Stark shift produced by this field precisely compensates collisional frequency shift for the transition of interest, and as a result suppresses dephasing. This technique can possibly be extended to adiabatic atomic collisions, and to different types of inhomogeneous broadening. Earlier workers have demonstrated similar methods for Doppler width reduction, by utilizing velocity-dependent Stark shifts produced by control fields. There is also a relation of this proposal to electromagnetically induced transparency.
The radial gradients and collisional properties of solar wind electrons
NASA Technical Reports Server (NTRS)
Gilvie, K. W.; Scudder, J. D.
1977-01-01
The plasma instrument on Mariner 10 carried out measurements of electron density and temperature in the interplanetary medium between heliocentric distances of 0.85 and 0.45 AU. Due to the stable coronal configuration and low solar activity during the period of observation, the radial variations of these quantities could be obtained. The power-law exponent of the core temperature was measured to be -0.3 + or - 0.04, and the halo temperature was found to be almost independent of heliocentric distance. The exponent of the power law for the density variation was 2.5 + or - 0.2 and the extrapolated value at 1 AU was consistent with measured values during the same period. Calculations of the core electron self-collision time, and the core-halo equipartition time were made as a function of radial distance. These measurements indicate a macroscale picture of a Coulomb-collisional core and a collisionless isothermal halo. Extrapolating back to the sun, core and halo temperatures become equal at a radial distance of approx. 2-15 radii.
On collisional diffusion in a stochastic magnetic field
Abdullaev, S. S.
2013-08-15
The effect of particle collisions on the transport in a stochastic magnetic field in tokamaks is investigated. The model of resonant magnetic perturbations generated by external coils at the plasma edge is used for the stochastic magnetic field. The particle collisions are simulated by a random walk process along the magnetic field lines and the jumps across the field lines at the collision instants. The dependencies of the local diffusion coefficients on the mean free path λ{sub mfp}, the diffusion coefficients of field lines D{sub FL}, and the collisional diffusion coefficients, χ{sub ⊥} are studied. Based on these numerical data and the heuristic arguments, the empirical formula, D{sub r}=χ{sub ⊥}+v{sub ||}D{sub FL}/(1+L{sub c}/λ{sub mfp}), for the local diffusion coefficient is proposed, where L{sub c} is the characteristic length of order of the connection length l{sub c}=πqR{sub 0}, q is the safety factor, R{sub 0} is the major radius. The formula quite well describes the results of numerical simulations. In the limiting cases, the formula describes the Rechester-Rosenbluth and Laval scalings.
On collisional diffusion in a stochastic magnetic field
NASA Astrophysics Data System (ADS)
Abdullaev, S. S.
2013-08-01
The effect of particle collisions on the transport in a stochastic magnetic field in tokamaks is investigated. The model of resonant magnetic perturbations generated by external coils at the plasma edge is used for the stochastic magnetic field. The particle collisions are simulated by a random walk process along the magnetic field lines and the jumps across the field lines at the collision instants. The dependencies of the local diffusion coefficients on the mean free path λmfp, the diffusion coefficients of field lines DFL, and the collisional diffusion coefficients, χ⊥ are studied. Based on these numerical data and the heuristic arguments, the empirical formula, Dr=χ⊥+v||DFL/(1+Lc/λmfp), for the local diffusion coefficient is proposed, where Lc is the characteristic length of order of the connection length lc=πqR0, q is the safety factor, R0 is the major radius. The formula quite well describes the results of numerical simulations. In the limiting cases, the formula describes the Rechester-Rosenbluth and Laval scalings.
Collisional evolution - an analytical study for the non steady-state mass distribution.
NASA Astrophysics Data System (ADS)
Vieira Martins, R.
1999-05-01
To study the collisional evolution of asteroidal groups one can use an analytical solution for the self-similar collision cascades. This solution is suitable to study the steady-state mass distribution of the collisional fragmentation. However, out of the steady-state conditions, this solution is not satisfactory for some values of the collisional parameters. In fact, for some values for the exponent of the mass distribution power law of an asteroidal group and its relation to the exponent of the function which describes "how rocks break" the author arrives at singular points for the equation which describes the collisional evolution. These singularities appear since some approximations are usually made in the laborious evaluation of many integrals that appear in the analytical calculations. They concern the cutoff for the smallest and the largest bodies. These singularities set some restrictions to the study of the analytical solution for the collisional equation. To overcome these singularities the author performed an algebraic computation considering the smallest and the largest bodies and he obtained the analytical expressions for the integrals that describe the collisional evolution without restriction on the parameters. However, the new distribution is more sensitive to the values of the collisional parameters. In particular the steady-state solution for the differential mass distribution has exponents slightly different from 11/6 for the usual parameters in the asteroid belt. The sensitivity of this distribution with respect to the parameters is analyzed for the usual values in the asteroidal groups. With an expression for the mass distribution without singularities, one can evaluate also its time evolution. The author arrives at an analytical expression given by a power series of terms constituted by a small parameter multiplied by the mass to an exponent, which depends on the initial power law distribution. This expression is a formal solution for the
Resisting Weakness of the Will
Levy, Neil
2012-01-01
I develop an account of weakness of the will that is driven by experimental evidence from cognitive and social psychology. I will argue that this account demonstrates that there is no such thing as weakness of the will: no psychological kind corresponds to it. Instead, weakness of the will ought to be understood as depletion of System II resources. Neither the explanatory purposes of psychology nor our practical purposes as agents are well-served by retaining the concept. I therefore suggest that we ought to jettison it, in favour of the vocabulary and concepts of cognitive psychology. PMID:22984298
Reichenbach, H.; Kuhl, A.L.
1993-09-07
The purpose of this paper is to compare reflection factors for weak shocks from various surfaces, and to focus attention on some unsolved questions. Three different cases are considered: square-wave planar shock reflection from wedges; square-wave planar shock reflection from cylinders; and spherical blast wave reflection from a planar surface. We restrict ourselves to weak shocks. Shocks with a Mach number of M{sub O} < 1.56 in air or with an overpressure of {Delta}{sub PI} < 25 psi (1.66 bar) under normal ambient conditions are called weak.
Degenerate four-wave mixing and phase conjugation in a collisional plasma
Federici, J.F.; Mansfield, D.K.
1986-06-01
Although degenerate four-wave mixing (DFWM) has many practical applications in the visible regime, no successful attempt has been made to study or demonstrate DFWM for wavelengths longer than 10..mu..m. Recently, Steel and Lam established plasma as a viable DFWM and phase conjugation (PC) medium for infrared, far-infrared, and microwaves. However, their analysis is incomplete since collisional effects were not included. Using a fluid description, our results demonstrate that when collisional absorption is small and the collisional mean-free path is shorter than the nonlinear density grating scale length, collisional heating generates a thermal force which substantially enhances the phase conjugate reflectivity. When the collisional attenuation length becomes comparable to the length of the plasma, the dominant effect is collisional absorption of the pump waves. Numerical estimates of the phase conjugate reflectivity indicate that for modest power levels, gains greater than or equal to1 are possible in the submillimeter to centimeter wavelength range. This suggests that a plasma is a viable PC medium at those long wavelengths. In addition, doubly DFWM is discussed.
NASA Astrophysics Data System (ADS)
Oikonomou, V. K.; Karagiannakis, N.; Park, Miok
2015-03-01
We study some aspects of cosmological evolution in a universe described by a viable curvature corrected exponential F (R ) gravity model, in the presence of matter fluids consisting of collisional matter and radiation. Particularly, we express the Friedmann-Robertson-Walker equations of motion in terms of parameters that are appropriate for describing the dark energy oscillations and compare the dark energy density and the dark energy equation of state parameter corresponding to collisional and noncollisional matter. In addition to these, and owing to the fact that the cosmological evolution of collisional and noncollisional matter universes, when quantified in terms of the Hubble parameter and the effective equation of states parameters, is very much alike, we further scrutinize the cosmological evolution study by extending the analysis to the study of matter perturbations in the matter domination era. We quantify this analysis in terms of the growth factor of matter perturbations, in which case the resulting picture of the cosmological evolution is clear, since collisional and noncollisional universes can be clearly distinguished. Interestingly enough, since it is known that the oscillations of the effective equation of state parameter around the phantom divide are undesirable and unwanted in F (R ) gravities, when these are considered for redshifts near the matter domination era and before, in the curvature corrected exponential model with collisional matter that we study here there exist oscillations that never cross the phantom divide. Therefore, this rather unwanted feature of the effective equation of state parameter is also absent in the collisional matter filled universe.
Weak interactions and presupernova evolution
Aufderheide, M.B. State Univ. of New York . Dept. of Physics)
1991-02-19
The role of weak interactions, particularly electron capture and {beta}{sup {minus}} decay, in presupernova evolution is discussed. The present uncertainty in these rates is examined and the possibility of improving the situation is addressed. 12 refs., 4 figs.
Weak Deeply Virtual Compton Scattering
Ales Psaker; Wolodymyr Melnitchouk; Anatoly Radyushkin
2007-03-01
We extend the analysis of the deeply virtual Compton scattering process to the weak interaction sector in the generalized Bjorken limit. The virtual Compton scattering amplitudes for the weak neutral and charged currents are calculated at the leading twist within the framework of the nonlocal light-cone expansion via coordinate space QCD string operators. Using a simple model, we estimate cross sections for neutrino scattering off the nucleon, relevant for future high intensity neutrino beam facilities.
Weak ferromagnetism in the cuprates
NASA Astrophysics Data System (ADS)
Chovan, J.; Papanicolaou, N.
2001-02-01
An effective field theory that describes the low-frequency spin dynamics in the low-temperature orthorhombic phase of La 2CuO 4 is derived. The main features of the inherent covert weak ferromagnetism are thus accounted for in a straightforward manner but some of the finer theoretical predictions would require further experimental investigation. In particular, theory predicts the occurrence of magnetic stripes in undoped La 2CuO 4 which mediate the observed weak-ferromagnetic transition.
Measurements of ejection velocities in collisional disruption of ice spheres
NASA Astrophysics Data System (ADS)
Arakawa, Masahiko; Higa, Michiya
1996-09-01
Impact experiments are performed on ice spheres to measure the velocity field of ejected ice fragments and the conditions under which the fragments would reaccumulate during accretion in the outer solar system are considered. A single-stage light gas gun set in a cold room at -18°C and an image-converter camera running at 2 × 10 5-1 × 10 4 frames per second with a xenon flash lamp are used for observing the collisional phenomena. Spherical projectiles of ice ( mp = 1.5 g) collide head-on with spherical targets ( Mt = 1.5, 12, 172 g) at 150-690 m s -1. The ejection velocity is observed to vary with the initial position and ranges from 3 to 1/10 of the impact velocity ( Vi). The ejection velocity of fragments at the rear side of the target ( Ve) varies with distance from the impact point according to a power law relation, V e = V a( 1/D) -n, where Va is the antipodal velocity, l and D are the distance and the target diameter, and n = 1.5-2.0. Va depends on the specific energy ( Q) at a constant mass ratio ( m p/M t = 0.13 ) and the empirical dependence is written as Va = 0.35 × Q0.52. The ejection velocity of fine fragments formed by the jetting process near the impact point is determined to be 1.7-2.9 times as large as the impact velocity irrespective of the target size and the impact velocity.
Evolving Magnetic Reconnection in Well Confined Plasmas with Low Collisionalities*
NASA Astrophysics Data System (ADS)
Coppi, B.
2009-11-01
There are two kinds of modes, producing large scale magnetic islands in well confined plasmas with low degrees of collisionality. These have phase velocities of opposite signs and are expected to emerge following the excitation of other modes as they cannot be found to be linearly unstable. One type is the ``drift-tearing'' [1] mode with a phase velocity in the direction of the electron diamagnetic velocity (vde) and the other is classified as an ``inductive'' mode [2] with a phase velocity in the direction of vdi. The ``drift-tearing'' can be excited after a mode that has the effect of decreasing the ratio of the longitudinal to the transverse electron thermal conductivity, like the ``micro-reconnecting'' mode discussed in Ref. [3]. The second type requires the previous excitation of a pressure gradient driven mode [4] that has a flow velocity in the vdi direction. Moreover, a mode-particle resonance with a high energy particle population [1] is involved in the growth of both the primary and the secondary (reconnecting) mode. Recent experimental observations [4] are consistent with these conclusions. Sawtooth oscillations that involve periodic reconnection events and modes that are related to those described earlier are discussed. *Sponsored in part by the U.S. DoE. [1] B. Coppi, Phys. Fluids 8, 2273 (1965) [2] B. Coppi, Bull. Am. Phys. Soc 45, 366 (2000) [3] B. Coppi, in ``Collective Phenomena etc.'' pg. 59, Eds. G. Bertin et. al., Publ. World Scientific (2007) [4] P. Buratti et al. Paper 02.007, 2009 E.P.S. Conference
Collisional processes and transfer of mass among the planetary satellites
NASA Astrophysics Data System (ADS)
Marchi, S.; Dell'Oro, A.; Paolicchi, P.; Barbieri, C.
2001-08-01
Several pairs of planetary satellites may have been involved, during the history of the Solar System, in mutual mass transfer processes. Such processes can be triggered by catastrophic collisions of a satellite (parent body) with a third object. As a consequence, the collision fragments are injected into independent orbits that can cross the trajectory of the another satellite (target). These swarms of secondary impacts may be of some importance influencing the properties of the target body. Even the formation of the atmosphere around some giant satellites may have been triggered by the gas released after the impacts of fragments onto the target's surface. Moreover, the different albedos and the different surface density of impact craters within the same satellite system may be connected to peculiar collisional phenomena, such as those we are dealing with. A quantitative modelling of the role of mass transfer processes obviously requires an estimate of how much material the parent bodies are able to supply, and under what circumstances the process may take place. A general analysis of the various pairs throughout the major satellite systems present in the Solar System has been performed in the present paper. Our analysis uses a statistical algorithm, computing, as a function of the initial properties of the fragments (masses and ejection velocities from their parent body), the mean intrinsic probability of impact, and then the mean lifetime of a fragment before impacting the target, as well as the distribution of the relative velocity. For an order-of-magnitude estimate of the available amount of mass, some simple analytical equations have been derived to evaluate the fraction of fragments from the parent body that can reach the target. These formulae allow a preliminary discrimination of the interesting cases. The pair Hyperion-Titan and the Uranus system have been analyzed in detail.
On the Orbital and Collisional History of (433) Eros
NASA Astrophysics Data System (ADS)
Bottke, W. F.
2001-12-01
(433) Eros, a ~ 20 km S-type asteroid extensively explored by the NEAR spacecraft, has had a enigmatic collisional and dynamical history. Its orbital parameters (a = 1.46 AU, e = 0.22, and i = 10.8o) place it in the Near-Earth object (NEO) population, defined as those asteroid and comets having perihelia q < 1.3~AU and aphelia Q > 0.983 AU. NEOs, however, tend to be short-lived; typical residents have dynamical lifetimes of 10 Myr before they strike the Sun, a terrestrial planet, or are ejected out of the inner solar system via a close encounter with Jupiter. For this reason, we hypothesize that Eros has only recently evolved out of the main belt and that it has followed a complicated dynamical path to reach its current orbit. A plausible evolutionary scenario for Eros is the following: (1) A catastrophic disruption event liberates Eros from its parent body. Given Eros's relatively large size, it is likely that this event also produced an observable asteroid family (e.g., Maria family; Zappalà et al., 1997, Icarus 129, 1.). (2) The Yarkovsky effect, a radiation drag force, causes Eros to migrate towards a resonant "escape hatch" (e.g., 3:1 mean motion resonance with Jupiter). Typical drift rates for Eros-sized bodies are slow enough (da/dt ~ 5 x 10-6 AU Myr-1) that Eros could have taken billions of years to escape the main belt (Farinella and Vokrouhlický, 1999, Science 283, 1507). (3) Eros reaches its escape resonance and has its eccentricity pumped up high enough to enter the NEO region. (4) A combination of close encounters with the terrestrial planets and inner solar system resonances move Eros to its current orbital position. If this evolutionary history is correct, the cratering record of Eros is linked to its dynamical history, such that numerical modeling can begin to fill in the qualitative gaps discussed above. Integration results of test bodies evolving from the main belt (Bottke et al., 2001, Icarus, in press) suggest that Eros has a ~ 20% chance of
Laboratory Measurement of OH(υ = 2) Collisional Deactivation by Oxygen Atoms
NASA Astrophysics Data System (ADS)
Marschall, J.; Kalogerakis, K. S.; Copeland, R. A.
2001-05-01
Vibrationally excited hydroxyl radicals (υ = 6-9) are generated in the 80 to 100 km altitude range of the Earth's atmosphere by the reaction of atomic hydrogen with ozone. Low vibrational levels (υ < 5) are populated from the higher vibrational levels via collisions with molecular oxygen. For these low vibrational levels molecular oxygen relaxation is inefficient (1.3 - 17 x10-13 cm3-s-1 at room temperature [1]) and collisions with oxygen atoms may play an important role in the collisional lifetime in the atmosphere. Given the importance of O-atom collisions, we have developed an experimental approach and performed experiments on the collisional removal of OH(υ = 2) with O-atoms. In our experimental approach, we use the output of a pulsed excimer laser at 248 nm to photodissociate ozone in an O3/H2O/N2 mixture and the wavelength tunable output of a frequency-double Nd:YAG-pumped dye laser to probe the transient population of OH in the υ = 0, 1, and 2 vibrational levels using laser-induced fluorescence spectroscopy. Vibrationally excited OH molecules are produced, in vibrational levels up to and including υ = 2, through the exothermic reaction of O(1D) with water. By adjusting the composition of the O3/H2O/N2 mixture and by varying the 248 nm laser fluence to control the ozone dissociation fraction, the dominant relaxation partner can be varied systematically from ozone and water to atomic oxygen. We can dissociate > 90% of the ozone in the beam with easily obtainable laser fluences, generating copious amounts of O atoms. Using this method we obtained a preliminary rate constant of 4 \\pm 1 x10-11 cm3-s-1 for removal of OH(υ = 2) with O atoms. This rate constant is only slightly larger than the value of 3.3 \\pm 0.7 x10-11 cm3-s-1 for the reaction of OH(υ = 0) with O atoms to generate H atoms and oxygen molecules [2]. This weak dependence of OH loss rates on vibrational excitation is in contrast to previous measurements indicating a factor of 3 to 5 increase
... spine) Stroke MUSCLE DISEASES Becker muscular dystrophy Dermatomyositis Muscular dystrophy (Duchenne) Myotonic dystrophy POISONING Botulism Poisoning ( insecticides , nerve gas) Shellfish poisoning OTHER Anemia Myasthenia gravis Polio
Quantum discord with weak measurements
Singh, Uttam Pati, Arun Kumar
2014-04-15
Weak measurements cause small change to quantum states, thereby opening up the possibility of new ways of manipulating and controlling quantum systems. We ask, can weak measurements reveal more quantum correlation in a composite quantum state? We prove that the weak measurement induced quantum discord, called as the “super quantum discord”, is always larger than the quantum discord captured by the strong measurement. Moreover, we prove the monotonicity of the super quantum discord as a function of the measurement strength and in the limit of strong projective measurement the super quantum discord becomes the normal quantum discord. We find that unlike the normal discord, for pure entangled states, the super quantum discord can exceed the quantum entanglement. Our results provide new insights on the nature of quantum correlation and suggest that the notion of quantum correlation is not only observer dependent but also depends on how weakly one perturbs the composite system. We illustrate the key results for pure as well as mixed entangled states. -- Highlights: •Introduced the role of weak measurements in quantifying quantum correlation. •We have introduced the notion of the super quantum discord (SQD). •For pure entangled state, we show that the SQD exceeds the entanglement entropy. •This shows that quantum correlation depends not only on observer but also on measurement strength.
Analysis of Collisional Cross Sections of Rydberg nS and nD States of Ultracold Caesium Atoms
NASA Astrophysics Data System (ADS)
Feng, Zhigang; Miao, Jingyuan; Zhao, Kejia; Li, Difei; Yang, Zhijun; Wu, Fan; Wu, Zhaochun; Zhao, Jianming; Jia, Suotang
2016-05-01
We present a simple analytical formula derived from an existing theoretical model and a detailed theoretical investigation of effects of the van der Waals interaction and dipole–dipole interaction on collisional cross sections as functions of various parameters. We analyze the main mechanism leading to large collisional cross sections on the basis of our previous experimental results using the present formula and also analyze the effects of some other factors on collisional cross sections.
Warping the Weak Gravity Conjecture
NASA Astrophysics Data System (ADS)
Kooner, Karta; Parameswaran, Susha; Zavala, Ivonne
2016-08-01
The Weak Gravity Conjecture, if valid, rules out simple models of Natural Inflation by restricting their axion decay constant to be sub-Planckian. We revisit stringy attempts to realise Natural Inflation, with a single open string axionic inflaton from a probe D-brane in a warped throat. We show that warped geometries can allow the requisite super-Planckian axion decay constant to be achieved, within the supergravity approximation and consistently with the Weak Gravity Conjecture. Preliminary estimates of the brane backreaction suggest that the probe approximation may be under control. However, there is a tension between large axion decay constant and high string scale, where the requisite high string scale is difficult to achieve in all attempts to realise large field inflation using perturbative string theory. We comment on the Generalized Weak Gravity Conjecture in the light of our results.
Ion acoustic shock wave in collisional equal mass plasma
NASA Astrophysics Data System (ADS)
Adak, Ashish; Ghosh, Samiran; Chakrabarti, Nikhil
2015-10-01
The effect of ion-ion collision on the dynamics of nonlinear ion acoustic wave in an unmagnetized pair-ion plasma has been investigated. The two-fluid model has been used to describe the dynamics of both positive and negative ions with equal masses. It is well known that in the dynamics of the weakly nonlinear wave, the viscosity mediates wave dissipation in presence of weak nonlinearity and dispersion. This dissipation is responsible for the shock structures in pair-ion plasma. Here, it has been shown that the ion-ion collision in presence of collective phenomena mediated by the plasma current is the source of dissipation that causes the Burgers' term which is responsible for the shock structures in equal mass pair-ion plasma. The dynamics of the weakly nonlinear wave is governed by the Korteweg-de Vries Burgers equation. The analytical and numerical investigations revealed that the ion acoustic wave exhibits both oscillatory and monotonic shock structures depending on the frequency of ion-ion collision parameter. The results have been discussed in the context of the fullerene pair-ion plasma experiments.
Ion acoustic shock wave in collisional equal mass plasma
Adak, Ashish; Ghosh, Samiran; Chakrabarti, Nikhil
2015-10-15
The effect of ion-ion collision on the dynamics of nonlinear ion acoustic wave in an unmagnetized pair-ion plasma has been investigated. The two-fluid model has been used to describe the dynamics of both positive and negative ions with equal masses. It is well known that in the dynamics of the weakly nonlinear wave, the viscosity mediates wave dissipation in presence of weak nonlinearity and dispersion. This dissipation is responsible for the shock structures in pair-ion plasma. Here, it has been shown that the ion-ion collision in presence of collective phenomena mediated by the plasma current is the source of dissipation that causes the Burgers' term which is responsible for the shock structures in equal mass pair-ion plasma. The dynamics of the weakly nonlinear wave is governed by the Korteweg-de Vries Burgers equation. The analytical and numerical investigations revealed that the ion acoustic wave exhibits both oscillatory and monotonic shock structures depending on the frequency of ion-ion collision parameter. The results have been discussed in the context of the fullerene pair-ion plasma experiments.
NASA Astrophysics Data System (ADS)
Lucca Fabris, Andrea; Young, Chris V.; Cappelli, Mark A.; Plasma Physics Laboratory Team
2014-10-01
We study the evolution of the Xe I 6 s '[ 1 / 2 ] 1 - 6 p '[ 3 / 2 ] 2 (834.68 nm air) transition lineshape in a plasma discharge oscillating at 60 Hz using time-synchronized laser induced fluorescence (LIF) measurements and a collisional-radiative model. Two different time-synchronized LIF techniques based on phase sensitive detection of the fluorescence signal are applied, yielding consistent results. The maximum observed peak fluorescence intensity occurs at low values of the discharge current, although the peak intensity drops to zero at zero discharge current. The peak intensity also decreases at the discharge current maximum. A dynamic collisional-radiative model of the weakly ionized xenon discharge is also implemented, based on a set of rate equations. The proper electron impact cross-sections and radiative decay rates are identified from the literature and used to compute accurate rate coefficients with the Boltzmann solver Bolsig+, including the time-varying electric field. The time evolution of the probed excited state density predicted by the model shows good agreement with the experimental measurements. This work is sponsored by the U.S. Air Force Office of Scientific Research with Dr. Mitat Birkan as program manager. CVY acknowledges support from the DOE NNSA Stewardship Science Graduate Fellowship under Contract DE-FC52-08NA28752.
Cosmology and the weak interaction
Schramm, D.N. ):)
1989-12-01
The weak interaction plays a critical role in modern Big Bang cosmology. This review will emphasize two of its most publicized cosmological connections: Big Bang nucleosynthesis and Dark Matter. The first of these is connected to the cosmological prediction of Neutrino Flavours, N{sub {nu}} {approximately} 3 which is now being confirmed at SLC and LEP. The second is interrelated to the whole problem of galaxy and structure formation in the universe. This review will demonstrate the role of the weak interaction both for dark matter candidates and for the problem of generating seeds to form structure. 87 refs., 3 figs., 5 tabs.
Cosmology and the weak interaction
NASA Technical Reports Server (NTRS)
Schramm, David N.
1989-01-01
The weak interaction plays a critical role in modern Big Bang cosmology. Two of its most publicized comological connections are emphasized: big bang nucleosynthesis and dark matter. The first of these is connected to the cosmological prediction of neutrine flavors, N(sub nu) is approximately 3 which in now being confirmed. The second is interrelated to the whole problem of galacty and structure formation in the universe. The role of the weak interaction both for dark matter candidates and for the problem of generating seeds to form structure is demonstrated.
Late-time cosmological evolution in f (R ) theories with ordinary and collisional matter
NASA Astrophysics Data System (ADS)
Oikonomou, V. K.; Karagiannakis, N.
2015-04-01
We study the late-time cosmological evolution of f(R) theories of modified gravity, with the matter content of the Universe being that of collisional self-interacting matter. We assume that the Universe is described by a flat Friedmann-Lemaitre-Robertson-Walker metric and that it is matter and dark energy dominated. The results of our numerical analysis for a collisional matter f(R) theory are compared with those resulting from pressureless matter f(R) theory and from the Λ CDM model. As we shall demonstrate, the resulting picture can vary from model to model, indicating that the effect of collisional matter in f(R) theories is strongly model dependent. In all studied cases, the effective equation of state parameter does not cross the phantom divide, both in the collisional matter and pressureless matter f(R) theories. Finally, we thoroughly study the effects of collisional matter on one of the f(R) models that is known to provide a unified description of early time inflation and late-time acceleration. The overall picture of the evolution of the Universe is not drastically affected, apart from the matter era, which is further enhanced with an additional matter energy contribution. However, a fully consistent description of the Universe’s evolution requires the introduction of a dark energy compensate in the total energy density, a concept very well known from the literature.
Collisional modelling of the AU Microscopii debris disc
NASA Astrophysics Data System (ADS)
Schüppler, Ch.; Löhne, T.; Krivov, A. V.; Ertel, S.; Marshall, J. P.; Wolf, S.; Wyatt, M. C.; Augereau, J.-C.; Metchev, S. A.
2015-09-01
AU Microscopii's debris disc is one of the most famous and best-studied debris discs and one of only two resolved debris discs around M stars. We perform in-depth collisional modelling of the AU Mic disc including stellar radiative and corpuscular forces (stellar winds), aiming at a comprehensive understanding of the dust production and the dust and planetesimal dynamics in the system. Our models are compared to a suite of observational data for thermal and scattered light emission, ranging from the ALMA radial surface brightness profile at 1.3 mm to spatially resolved polarisation measurements in the visible. Most of the data are shown to be reproduced with dust production in a belt of planetesimals with an outer edge at around 40 au and subsequent inward transport of dust by stellar winds. A low dynamical excitation of the planetesimals with eccentricities up to 0.03 is preferred. The radial width of the planetesimal belt cannot be constrained tightly. Belts that are 5 au and 17 au wide, as well as a broad 44 au-wide belt, are consistent with observations. All models show surface density profiles that increase with distance from the star up to ≈40 au, as inferred from observations. The best model is achieved by assuming a stellar mass loss rate that exceeds the solar one by a factor of 50. The models reproduce the spectral energy distribution and the shape of the ALMA radial profile well, but deviate from the scattered light observations more strongly. The observations show a bluer disc colour and a lower degree of polarisation for projected distances <40 au than predicted by the models. These deviations may be reduced by taking irregularly shaped dust grains which have scattering properties different from the Mie spheres used in this work. From tests with a handful of selected dust materials, we favour mixtures of silicate, carbon, and ice of moderate porosity. We also address the origin of the unresolved central excess emission detected by ALMA and show that
Spoke Formation in Saturn's Ring: The Collisional Cascade Model
NASA Astrophysics Data System (ADS)
Hamilton, Douglas P.
2014-11-01
The mysterious wedge-shaped spokes in Saturn's main rings have defied explanation ever since their discovery during the Voyager flybys of the early 1980s. No earlier model can explain the three disparate timescales over which spokes evolve: i) the 10-minute formation time for a new spoke, ii) the hour-long period over which a spoke's radial edge remains active, and iii) the day-long timescale over which the magnetic longitude of earlier spoke activity is preferentially repopulated with subsequent spokes. This and other observations of ongoing spoke formation can be understood in the context of a Collisional Cascade model in which a hail of rapidly-moving submicron dust grains rain down upon more massive ring particles. Tiny ~0.1 micron grains leave the ring plane en masse from the site of an initial disturbance (likely a meteoroid impact) and are accelerated by the magnetic field to high speeds relative to more massive ring particles. When the dust returns to the ring plane -nearly simultaneously over a large radial range - they strike fluffy dust-coated ring particles at km/s speeds, freeing both visible 0.5 micron spoke particles and additional submicron debris. Differences between the motions of the 0.1 micron dust grains and the much larger ring particles provides a potent free energy source that powers spoke formation. The onset of this hail of tiny energetic impactors can account for the observed rapid formation of spokes and, as the hail continues to fall, for the hour-long active periods over which some spoke edges remains nearly radial. The hour-long timescale is controlled by differences in initial launch velocities and different grain charge-to-mass ratios which strongly affect vertical motions. Additional tiny grains liberated in the first hailstorm go on to continue the cascade, returning to strike the same magnetic longitude in the ring hours to days later and stirring up more micron-sized spoke particles. This continuing cascade nicely accounts for
Collisional Disruption of Gravity Dominated Bodies: New Data and Scaling
NASA Astrophysics Data System (ADS)
Movshovitz, N.; Nimmo, F.; Korycansky, D. G.; Asphaug, E. I.; Owen, M.
2015-12-01
We present data from a suite of 169 hydrocode simulations of collisions between planetary bodies with radii from 100 to 1000 km. The data is used to derive a simple scaling law for the threshold for catastrophic disruption, defined as a collision that leads to half the total colliding mass escaping the system post impact. For a target radius 100≤R_T≤1000 km and a mass MTM_T and a projectile radius r_p≤R_T and mass mpm_p we find that a head-on impact with velocity magnitude vv is catastrophic if the kinetic energy of the system in the center of mass frame, K=0.5{M_T}{m_p}/(M_T+m_p)v^2, exceeds K∗R_D=(3.3±0.6)U_R U_R where U_R=(3/5)G{M_T}^2/R_T + (3/5)G{m_p}^2/{r_p}+G{M_T}{m_p}/(M_T+{m_p}) is the gravitational binding energy of the system at the moment of impact; GG is the gravitational constant. Oblique impacts are catastrophic when the fraction of kinetic energy contained in the volume of the projectile intersecting the target at impact exceeds ˜1.9K∗_RD for 30° impacts and ˜3.5K∗_RD for 45deg; impacts. We compare predictions made with this scaling to those made with existing scaling laws in the literature extrapolated from numerical studies on smaller targets. We find significant divergence between predictions where in general our data suggest a lower threshold for disruption except for highly oblique impacts with r_p≪R_T. This result has implications for the efficiency of collisional grinding in the asteroid belt (Morbidelli, A., Bottke, W. F., Nesvorny, D., & Levison, H. F., 2009, Icarus, 204, 558-573), Kuiper belt (Greenstreet, S., Gladman, B., & McKinnon, W. B., 2015, Icarus, 258, 267-288), and early solar system accretion (Chambers, J. E., 2013, Icarus, 224, 43-56).
Graczyk, Krzysztof M.
2011-11-23
A short review of the Rein-Sehgal and isobar models is presented. The attention is focused on the nucleon-{Delta}(1232) weak transition form-factors. The results of the recent re-analyses of the ANL and BNL bubble chamber neutrino-deuteron scattering data are discussed.
Focal weakness following herpes zoster.
Cockerell, O C; Ormerod, I E
1993-01-01
Three patients presented with focal weakness of an arm which followed segmental herpes zoster affecting the same limb. Neurophysiological investigations suggest that the site of the lesion lay at the root, plexus, or peripheral nerve level. This reflects the various ways in which the virus may affect the peripheral nervous system. PMID:8410022
Cosmology with weak lensing surveys.
Munshi, Dipak; Valageas, Patrick
2005-12-15
Weak gravitational lensing is responsible for the shearing and magnification of the images of high-redshift sources due to the presence of intervening mass. Since the lensing effects arise from deflections of the light rays due to fluctuations of the gravitational potential, they can be directly related to the underlying density field of the large-scale structures. Weak gravitational surveys are complementary to both galaxy surveys and cosmic microwave background observations as they probe unbiased nonlinear matter power spectra at medium redshift. Ongoing CMBR experiments such as WMAP and a future Planck satellite mission will measure the standard cosmological parameters with unprecedented accuracy. The focus of attention will then shift to understanding the nature of dark matter and vacuum energy: several recent studies suggest that lensing is the best method for constraining the dark energy equation of state. During the next 5 year period, ongoing and future weak lensing surveys such as the Joint Dark Energy Mission (JDEM; e.g. SNAP) or the Large-aperture Synoptic Survey Telescope will play a major role in advancing our understanding of the universe in this direction. In this review article, we describe various aspects of probing the matter power spectrum and the bi-spectrum and other related statistics with weak lensing surveys. This can be used to probe the background dynamics of the universe as well as the nature of dark matter and dark energy. PMID:16286284
Insights on Continental Collisional Processes from GPS Data: Dynamics of the Peri-Adriatic Belts
NASA Astrophysics Data System (ADS)
Metois, Marianne; D'Agostino, Nicola; Avallone, Antonio; Chamot-Rooke, Nicolas; Rabaute, Alain; Duni, Llambro; Kuka, Neki; Koci, Rexhep; Georgiev, Ivan
2015-04-01
Recent advances in GPS technology and processing strategies make now spatial geodesy a suitable tool to image intra-continental slowly deforming areas such as collisional mountain belts and to get further insights on their kinematics and dynamics. Here, using the peri-Adriatic belts as a test case, we propose a methodology based on accurate GPS velocities to discriminate whether the current day deformation pattern over a mountain belt is controlled at the first order by gravity through gradients of gravitational potential energy. We calculate a new GPS velocity field covering the peri-Adriatic region and the entire Balkan Peninsula, taking advantage of newly available measurements coming from private networks operating since several years in this area. Based on these velocities, we derive the strain rate tensor and an interpolated velocity field using the method of Haines & Holt (1993). Opposite to the commonly accepted hypothesis considering the Balkans as part of the stable Eurasia, we show that the peninsula experiences significant compression across the Dinarides belt and extension toward the Aegean domain South of 44°N. We image a clockwise rotation of the entire peninsula around North Albania, and propose that the lithosphere under the old Scutari-Peck transform zone is weak and acts as a pivot point for this rotation since early Miocene. The Hellenic slab suction and the release of stress in the northern Hellenides subduction zone may favour the southwestward motion of the inner Balkan lithosphere, flowing between the rigid Apulia and Black sea blocks consequently. Because our velocity field is unusually dense in Slovenia and Austria, we picture the Eastern Alps deformation with great details and show that the Austrian Alps are moving eastward together with the Alpine foreland and Bohemian Promontory relative to stable Eurasia. Based on these new GPS data, we investigate the dynamics of the peri-Adriatic mountain belts, in particular of Albania and Eastern
NATIONAL HIGH MAGENTIC FIELD LABORATORY FEL INJECTOR DESIGN CONSIDERATION
Pavel Evtushenko; Stephen Benson; David Douglas; George Neil
2007-06-25
A Numerical study of beam dynamics was performed for two injector systems for the proposed National High Magnetic Field Laboratory at the Florida State University (FSU) Free Electron Laser (FEL) facility. The first considered a system consisting of a thermionic DC gun, two buncher cavities operated at 260 MHz and 1.3 GHz and two TESLA type cavities, and is very similar to the injector of the ELBE Radiation Source. The second system we studied uses a DC photogun (a copy of JLab FEL electron gun), one buncher cavity operated at 1.3 GHz and two TESLA type cavities. The study is based on PARMELA simulations and takes into account operational experience of both the JLab FEL and the Radiation Source ELBE. The simulations predict the second system will have a much smaller longitudinal emittance. For this reason the DC photo gun based injector is preferred for the proposed FSU FEL facility.
A multi-species 13-moment model for moderately collisional plasmas
NASA Astrophysics Data System (ADS)
Miller, S. T.; Shumlak, U.
2016-08-01
Fluid-based models of collisional transport in multi-species plasmas have typically been applied to parameter regimes where a local thermal equilibrium is assumed. While this parameter regime is valid for low temperature and/or high density applications, it begins to fail as plasmas enter the collisionless regime and kinetic effects dominate the physics. A plasma model is presented that lays the foundation for extending the validity of the collisional fluid regime using an anisotropic 13-moment fluid model derived from the Pearson type-IV probability distribution. The model explicitly evolves the pressure tensor and heat flux vector along with the density and flow velocity to capture dynamics usually restricted to kinetic models. Each particle species is modeled individually and collectively coupled through electromagnetic and collisional interactions.
Collisional stochastic ripple diffusion of alpha particles and beam ions on TFTR
Redi, M.H.; Zarnstorff, M.C.; White, R.B.; Budny, R.V.; Janos, A.C.; Owens, D.K.; Schivell, J.F.; Scott, S.D.; Zweben, S.J.
1995-07-01
Predictions for ripple loss of fast ions from TFTR are investigated with a guiding center code including both collisional and ripple effects. A synergistic enhancement of fast ion diffusion is found for toroidal field ripple with collisions. The total loss is calculated to be roughly twice the sum of ripple and collisional losses calculated separately. Discrepancies between measurements and calculations of plasma beta at low current and large major radius are resolved when both effects are included for neutral beam ions. A 20--30% reduction in alpha particle heating is predicted for q{sub a} = 6--14, R = 2.6 m DT plasmas on TFTR due to first orbit and collisional stochastic ripple diffusion.
Formation and evolution of vortices in a collisional strongly coupled dusty plasma
NASA Astrophysics Data System (ADS)
Jana, Sayanee; Banerjee, Debabrata; Chakrabarti, Nikhil
2016-07-01
Formation and evolution of vortices are studied in a collisional strongly coupled dusty plasma in the framework of a Generalized Hydrodynamic model (GH). Here we mainly present the nonlinear dynamical response of this strongly coupled system in presence of dust-neutral collisional drag. It is shown that the interplay between the nonlinear elastic stress and the dust-neutral collisional drag results in the generation of non-propagating monopole vortex for some duration before it starts to propagate like transverse shear wave. It is also found that the interaction between two unshielded monopole vortices having both same (co-rotating) and opposite (counter rotating) rotations result in the formation of two propagating dipole vortices of equal and unequal strength respectively. These results will provide some new understanding on the transport properties in such a strongly coupled system. The numerical simulation is carried out using a de-aliased doubly periodic pseudo-spectral code with Runge-Kutta-Gill time integrator.
New Regime of Low Ion Collisionality in the Neoclassical Equilibrium of Tokamak Plasmas
NASA Astrophysics Data System (ADS)
Ramos, J. J.
2015-11-01
The neoclassical description of an axisymmetric toroidal plasma equilibrium is formulated for an unconventionally low ordering of the collisionality that suits realistic thermonuclear fusion conditions. This requires a drift-kinetic analysis to the second order of the ion Larmor radius, which yields a new contribution to the leading solution for the non-Maxwellian part of the ion distribution function if the equilibrium geometry is not up-down symmetric. An explicit geometrical factor weighs this second Larmor-radius order, low-collisionality effect that modifies the neoclassical ion parallel flow and the ion contribution to the bootstrap current. For this low-collisionality neoclassical equilibrium solution, the pressure anisotropy part of the Chew-Goldberger-Low stress tensor is comparable to the gyroviscosity and their contributions to the flux-surface-averaged parallel momentum equation balance exactly. Work supported by the U.S. D.O.E.
Investigation of the Electron-Ion Hybrid Instability in a Collisional Environment
NASA Astrophysics Data System (ADS)
Tejero, E. M.; Enloe, L.; Sotnikov, V. I.; Amatucci, B.; Ganguli, G.
2013-12-01
The Electron-Ion Hybrid (EIH) instability, a transverse velocity shear-driven instability with frequency near the lower hybrid frequency, was previously predicted theoretically to explain the observation of lower hybrid waves in applications from the plasma sheet boundary layer to laser produced plasmas. The EIH instability has also been observed in the laboratory in scaled magnetospheric plasma conditions and in laser produced plasma expansion experiments across magnetic fields. In the work presented, we have expanded the theoretical framework to highly collisional plasmas for applications to the plasma region surrounding a hypersonic vehicle. In this collisional plasma layer, strongly sheared transverse flows can exist that can give rise to the EIH instability. We wish to study whether the resulting lower hybrid turbulence can impede communication to and from the hypersonic vehicle. Results from theory and a comparison from laboratory experiments on the generation of the EIH instability in a collisional plasma environment will be presented.
NASA Technical Reports Server (NTRS)
Vinolo, A. R.; Clarke, J. H.
1972-01-01
The gas dynamic structures of the transport shock and the downstream collisional relaxation layer are evaluated for partially ionized monatomic gases. Elastic and inelastic collisional nonequilibrium effects are taken into consideration. Three electronic levels are accounted for in the microscopic model of the atom. Nonequilibrium processes with respect to population of levels and species plus temperature are considered. By using an asymptotic technique the shock morphology is found on a continuum flow basis. The asymptotic procedure gives two distinct layers in which the nonequilibrium effects to be considered are different. A transport shock appears as the inner solution to an outer collisional relaxation layer in which the gas reaches local equilibrium. A family of numerical examples is displayed for different flow regimes. Argon and helium models are used in these examples.
Collisional pumping of water masers by species of particles at different temperatures
NASA Technical Reports Server (NTRS)
Anderson, Nels; Watson, William D.
1990-01-01
It has been reported that the extreme power of astrophysical water masers can be obtained from purely collisional pumping in environments with two kinetic temepratures. It is found that this pumping vanishes when the latest rates are utilized for the collisional excitation of H2O molecules by neutrals. Energetic ions must also be present under the conditions that have been proposed for such 'two-temperature' pumping, but they have been ignored in the past due to lack of information about the relevant cross sections. Quantal, multichannel calculations in the impact parameter approximation are performed to provide a basis for estimating these rates for the collisional excitation of H2O molecules by ions. Including the effects of these ions does not restore the inversion, but rather reduces the pumping for H2O masers in the proposed 'two-temperature' environments.
Collisional statistics and dynamics of two-dimensional hard-disk systems: From fluid to solid.
Taloni, Alessandro; Meroz, Yasmine; Huerta, Adrián
2015-08-01
We perform extensive MD simulations of two-dimensional systems of hard disks, focusing on the collisional statistical properties. We analyze the distribution functions of velocity, free flight time, and free path length for packing fractions ranging from the fluid to the solid phase. The behaviors of the mean free flight time and path length between subsequent collisions are found to drastically change in the coexistence phase. We show that single-particle dynamical properties behave analogously in collisional and continuous-time representations, exhibiting apparent crossovers between the fluid and the solid phases. We find that, both in collisional and continuous-time representation, the mean-squared displacement, velocity autocorrelation functions, intermediate scattering functions, and self-part of the van Hove function (propagator) closely reproduce the same behavior exhibited by the corresponding quantities in granular media, colloids, and supercooled liquids close to the glass or jamming transition. PMID:26382368
Superfluidlike Motion of an Absorbing Body in a Collisional Plasma
Vladimirov, S. V.; Khrapak, S. A.; Chaudhuri, M.; Morfill, G. E.
2008-02-08
Motion of a small charged absorbing body (micrograin) immersed in a stationary weakly ionized high pressure plasma environment is considered. It is shown that the total frictional (drag) force acting on the grain can be directed along its motion, causing the grain acceleration. At some velocity, the forces associated with different plasma components can balance each other, allowing free undamped superfluid motion of the grain. The conditions when such behavior can be realized and the possibility of a superconductive grain current are discussed in the context of complex (dusty) plasmas.
NASA Astrophysics Data System (ADS)
Thébault, P.
2012-01-01
Context. Debris discs are traditionally studied using two distinct types of numerical models: statistical particle-in-a-box codes to study their collisional and size distribution evolution, and dynamical N-body models to study their spatial structure. The absence of collisions in N-body codes is in particular a major shortcoming, as collisional processes are expected to significantly alter the results obtained from pure N-body runs. Aims: We present a new numerical model, to study the spatial structure of perturbed debris discs in both a dynamical and collisional steady-state. We focus on the competing effects of gravitational perturbations by a massive body (planet or star), the collisional production of small grains, and the radiation pressure placing these grains in possibly dynamically unstable regions. Methods: We consider a disc of parent bodies in a dynamical steady-state, from which small radiation-pressure-affected grains are released in a series of runs, each corresponding to a different orbital position of the perturber, where particles are assigned a collisional destruction probability. These collisional runs produce successive position maps that are then recombined, following a complex procedure, to generate surface density profiles for each orbital position of the perturbing body. Results: We apply our code to the case of a circumprimary disc in a binary. We find pronounced structures inside and outside the dynamical stability regions. For low eB, the disc's structure is time varying, with spiral arms in the dynamically "forbidden" region precessing with the companion star. For high eB, the disc is strongly asymmetric but time invariant, with a pronounced density drop in the binary's periastron direction.
Linear tearing mode stability equations for a low collisionality toroidal plasma
NASA Astrophysics Data System (ADS)
Connor, J. W.; Hastie, R. J.; Helander, P.
2009-01-01
Tearing mode stability is normally analysed using MHD or two-fluid Braginskii plasma models. However for present, or future, large hot tokamaks like JET or ITER the collisionality is such as to place them in the banana regime. Here we develop a linear stability theory for the resonant layer physics appropriate to such a regime. The outcome is a set of 'fluid' equations whose coefficients encapsulate all neoclassical physics: the neoclassical Ohm's law, enhanced ion inertia, cross-field transport of particles, heat and momentum all play a role. While earlier treatments have also addressed this type of neoclassical physics we differ in incorporating the more physically relevant 'semi-collisional fluid' regime previously considered in cylindrical geometry; semi-collisional effects tend to screen the resonant surface from the perturbed magnetic field, preventing reconnection. Furthermore we also include thermal physics, which may modify the results. While this electron description is of wide relevance and validity, the fluid treatment of the ions requires the ion banana orbit width to be less than the semi-collisional electron layer. This limits the application of the present theory to low magnetic shear—however, this is highly relevant to the sawtooth instability—or to colder ions. The outcome of the calculation is a set of one-dimensional radial differential equations of rather high order. However, various simplifications that reduce the computational task of solving these are discussed. In the collisional regime, when the set reduces to a single second-order differential equation, the theory extends previous work by Hahm et al (1988 Phys. Fluids 31 3709) to include diamagnetic-type effects arising from plasma gradients, both in Ohm's law and the ion inertia term of the vorticity equation. The more relevant semi-collisional regime pertaining to JET or ITER, is described by a pair of second-order differential equations, extending the cylindrical equations of Drake
Terahertz generation by beating two Langmuir waves in a warm and collisional plasma
Zhang, Xiao-Bo; Qiao, Xin; Cheng, Li-Hong; Tang, Rong-An; Zhang, Ai-Xia; Xue, Ju-Kui
2015-09-15
Terahertz (THz) radiation generated by beating of two Langmuir waves in a warm and collisional plasma is discussed theoretically. The critical angle between the two Langmuir waves and the critical wave-length (wave vector) of Langmuir waves for generating THz radiation are obtained analytically. Furthermore, the maximum radiation energy is obtained. We find that the critical angle, the critical wave-length, and the generated radiation energy strongly depend on plasma temperature and wave-length of the Langmuir waves. That is, the THz radiation generated by beating of two Langmuir waves in a warm and collisional plasma can be controlled by adjusting the plasma temperature and the Langmuir wave-length.
New regime of low ion collisionality in the neoclassical equilibrium of tokamak plasmas
NASA Astrophysics Data System (ADS)
Ramos, J. J.
2015-07-01
The neoclassical description of an axisymmetric toroidal plasma equilibrium is formulated for an unconventionally low ordering of the collisionality that suits realistic thermonuclear fusion conditions. This requires a drift-kinetic analysis to the second order of the ion Larmor radius, which yields a new contribution to the leading solution for the non-Maxwellian part of the ion distribution function if the equilibrium geometry is not up-down symmetric. An explicit geometrical factor weighs this second Larmor-radius order, low-collisionality effect that modifies the neoclassical ion parallel flow, and the ion contribution to the bootstrap current.
Collisional narrowing by polyatomic buffer gases in an optically pumped CH3F laser
NASA Technical Reports Server (NTRS)
Lawandy, N. M.; Koepf, G. A.
1980-01-01
The gain linewidth of an optically pumped CH3F molecular laser is observed with the addition of various polyatomic buffer gases. This is interpreted as collisional (Dicke) narrowing. The measurement is the first observation of collisional narrowing by polyatomic buffer gases. It is also the first observation of the effect in a laser oscillator. The effect was observed using a heterodyne mixing technique at the laser emission frequency of 604 GHz. Collision cross sections for SF6-CH3F and CS2-CH3F are obtained.
New regime of low ion collisionality in the neoclassical equilibrium of tokamak plasmas
Ramos, J. J.
2015-07-15
The neoclassical description of an axisymmetric toroidal plasma equilibrium is formulated for an unconventionally low ordering of the collisionality that suits realistic thermonuclear fusion conditions. This requires a drift-kinetic analysis to the second order of the ion Larmor radius, which yields a new contribution to the leading solution for the non-Maxwellian part of the ion distribution function if the equilibrium geometry is not up-down symmetric. An explicit geometrical factor weighs this second Larmor-radius order, low-collisionality effect that modifies the neoclassical ion parallel flow, and the ion contribution to the bootstrap current.
Exploring the collisional evolution of the asteroid belt
NASA Astrophysics Data System (ADS)
Bottke, W.; Broz, M.; O'Brien, D.; Campo Bagatin, A.; Morbidelli, A.
2014-07-01
The asteroid belt is a remnant of planet-formation processes. By modeling its collisional and dynamical history, and linking the results to constraints, we can probe how the planets and small bodies formed and evolved. Some key model constraints are: (i) The wavy shape of the main-belt size distribution (SFD), with inflection points near 100-km, 10--20-km, 1 to a few km, and ˜0.1-km diameter; (ii) The number of asteroid families created by the catastrophic breakup of large asteroid bodies over the last ˜ 4 Gy, with the number of disrupted D > 100 km bodies as small as ˜20 or as large as 60; (iii) the flux of small asteroids derived from the main belt that have struck the Moon over the last 3.5 Ga --- crater SFDs on lunar terrains with known ages suggest the D < 0.1 km projectile population has not varied appreciably over this interval; (iv) Vesta has an intact basaltic crust with two very large basins, but only two, on its surface. Fits to these parameters allow us to predict the shape of the initial main-belt SFD after accretion and the approximate asteroid disruption scaling law, with the latter consistent with numerical hydrocode simulations. Overall, we find that the asteroid belt probably experienced the equivalent of ˜6--10 Gy of comminution over its history. This value may seem strange, considering the solar system is only 4.56 Gy old. One way to interpret it is that the main belt once had more mass that was eliminated by early dynamical processes between 4--4.56 Ga. This would allow for more early grinding, and it would suggest the main belt's wavy-shaped SFD is a ''fossil'' from a more violent early epoch. Simulations suggest that most D > 100 km bodies have been significantly battered, but only a fraction have been catastrophically disrupted. Conversely, most small asteroids today are byproducts of fragmentation events. These results are consistent with growing evidence that most of the prominent meteorite classes were produced by young asteroid
Weak values and weak coupling maximizing the output of weak measurements
Di Lorenzo, Antonio
2014-06-15
In a weak measurement, the average output 〈o〉 of a probe that measures an observable A{sup -hat} of a quantum system undergoing both a preparation in a state ρ{sub i} and a postselection in a state E{sub f} is, to a good approximation, a function of the weak value A{sub w}=Tr[E{sub f}A{sup -hat} ρ{sub i}]/Tr[E{sub f}ρ{sub i}], a complex number. For a fixed coupling λ, when the overlap Tr[E{sub f}ρ{sub i}] is very small, A{sub w} diverges, but 〈o〉 stays finite, often tending to zero for symmetry reasons. This paper answers the questions: what is the weak value that maximizes the output for a fixed coupling? What is the coupling that maximizes the output for a fixed weak value? We derive equations for the optimal values of A{sub w} and λ, and provide the solutions. The results are independent of the dimensionality of the system, and they apply to a probe having a Hilbert space of arbitrary dimension. Using the Schrödinger–Robertson uncertainty relation, we demonstrate that, in an important case, the amplification 〈o〉 cannot exceed the initial uncertainty σ{sub o} in the observable o{sup -hat}, we provide an upper limit for the more general case, and a strategy to obtain 〈o〉≫σ{sub o}. - Highlights: •We have provided a general framework to find the extremal values of a weak measurement. •We have derived the location of the extremal values in terms of preparation and postselection. •We have devised a maximization strategy going beyond the limit of the Schrödinger–Robertson relation.
Tomography and weak lensing statistics
Munshi, Dipak; Coles, Peter; Kilbinger, Martin E-mail: peter.coles@astro.cf.ac.uk
2014-04-01
We provide generic predictions for the lower order cumulants of weak lensing maps, and their correlators for tomographic bins as well as in three dimensions (3D). Using small-angle approximation, we derive the corresponding one- and two-point probability distribution function for the tomographic maps from different bins and for 3D convergence maps. The modelling of weak lensing statistics is obtained by adopting a detailed prescription for the underlying density contrast that involves hierarchal ansatz and lognormal distribution. We study the dependence of our results on cosmological parameters and source distributions corresponding to the realistic surveys such as LSST and DES. We briefly outline how photometric redshift information can be incorporated in our results. We also show how topological properties of convergence maps can be quantified using our results.
Overdamping by weakly coupled environments
NASA Astrophysics Data System (ADS)
Esposito, Massimiliano; Haake, Fritz
2005-12-01
A quantum system weakly interacting with a fast environment usually undergoes a relaxation with complex frequencies whose imaginary parts are damping rates quadratic in the coupling to the environment in accord with Fermi’s “golden rule.” We show for various models (spin damped by harmonic-oscillator or random-matrix baths, quantum diffusion, and quantum Brownian motion) that upon increasing the coupling up to a critical value still small enough to allow for weak-coupling Markovian master equations, a different relaxation regime can occur. In that regime, complex frequencies lose their real parts such that the process becomes overdamped. Our results call into question the standard belief that overdamping is exclusively a strong coupling feature.
Overdamping by weakly coupled environments
Esposito, Massimiliano; Haake, Fritz
2005-12-15
A quantum system weakly interacting with a fast environment usually undergoes a relaxation with complex frequencies whose imaginary parts are damping rates quadratic in the coupling to the environment in accord with Fermi's 'golden rule'. We show for various models (spin damped by harmonic-oscillator or random-matrix baths, quantum diffusion, and quantum Brownian motion) that upon increasing the coupling up to a critical value still small enough to allow for weak-coupling Markovian master equations, a different relaxation regime can occur. In that regime, complex frequencies lose their real parts such that the process becomes overdamped. Our results call into question the standard belief that overdamping is exclusively a strong coupling feature.
Optimizing SNAP for Weak Lensing
NASA Astrophysics Data System (ADS)
High, F. W.; Ellis, R. S.; Massey, R. J.; Rhodes, J. D.; Lamoureux, J. I.; SNAP Collaboration
2004-12-01
The Supernova/Acceleration Probe (SNAP) satellite proposes to measure weak gravitational lensing in addition to type Ia supernovae. Its pixel scale has been set to 0.10 arcsec per pixel as established by the needs of supernova observations. To find the optimal pixel scale for accurate weak lensing measurements we conduct a tradeoff study in which, via simulations, we fix the suvey size in total pixels and vary the pixel scale. Our preliminary results show that with a smaller scale of about 0.08 arcsec per pixel we can minimize the contribution of intrinsic shear variance to the error on the power spectrum of mass density distortion. Currently we are testing the robustness of this figure as well as determining whether dithering yields analogous results.
NASA Astrophysics Data System (ADS)
Evans, John; Chen, Francis; Arnush, Donald
2000-10-01
Penetration of induced B-fields in unmagnetized and weakly magnetized ICPs is investigated in a large diameter cylindrical device. A loop antenna surrounds a dome-shaped Pyrex top on top of a magnetic bucket. Rtop=15cm ~ height of top, Rbucket ~ 18cm, bucket height ~ 30cm, N ~ 1011cm-3, Te ~ 3eV, Prf <1.4kW, Frf = 2-27MHz, Po ~1-100mT. Field penetration depths Lsd << Rtop are measured in the outer plasma region (r > Rtop/2) that agree with collisional skin depth theory, in the unmagnetized case. In the interior, non-monotonic radial profiles and interference phenomena are observed, where no propagating waves are predicted to occur. Similar observations by other groups have been attributed to the anomalous skin effect (ASE), the electromagnetic analog of Debye shielding. However, these phenomena are more apparent as Po (and hence collisionality) is increased, in apparent contradiction to ASE theory. A simple physical model will be presented that resolves this paradox. When a static Bo-field is applied, near-classical behavior is then recovered. Variations of Lsd with Bo yield good agreement between experiment and collisional theory in most cases. Coupling to a low-Bo helicon mode is expected when Lsd>=Rtop, characterized by a transition from evanescence to propagation.
Experimental observation of transition between strong and weak non-Markovianity
NASA Astrophysics Data System (ADS)
Bernardes, Nadja K.; Cuevas, Alvaro; Orieux, Adeline; Monken, Carlos H.; Mataloni, Paolo; Sciarrino, Fabio; Santos, Marcelo F.
2015-05-01
We experimentally observed in an optical setup and using full tomography process the so-called weak non-Markovian dynamics of a qubit [1]. This was done implementing the collisional model proposed in [2] to investigate the non- Markovian dynamics of an open quantum system interacting with a carefully controlled environment state. We also observed the transition from weak to strong (essentially) non-Markovianity. In our all-optical setup, a single photon system, initially entangled in polarization with an ancilla, is made to interact with a sequence of liquid crystal retarders driven by proper electric pulses, which simulates the environment. Depending on how the voltage is applied on each liquid crystal, it will work as a half-wave plate with different orientations. Then, by changing properly the parameters of the qubit-environment interactions, the system dynamics can suffer a transition from weak to strong non-Markovianity. In the strong regime, the full reconstruction of the entangled state was made by single entanglement witness between system and ancilla, showing a backflow of information, while, in the weak regime, given the contractive unital map feature, we can only measure the dynamics by a full process tomography analysis, searching for the violation of the divisibility completely positive map criterion, what was done successfully.
Competing weak localization and weak antilocalization in ultrathin topological insulators
NASA Astrophysics Data System (ADS)
Lang, Murong; He, Liang; Kou, Xufeng; Upadhyaya, Pramey; Fan, Yabin; Chu, Hao; Yeh, Nai-Chang; Wang, Kang
2013-03-01
We demonstrate the evidences of a surface gap opening in (Bi0.57Sb0.43)2 Te3 samples for film thickness below 6 quintuple layers, through magnetotransport and scanning tunneling spectroscopy measurements. By tuning Fermi level position relative to the gap, the striking crossover between weak antilocalization and weak localization is observed in nonmagnetic 4 and 5 QL films at low field region, a characteristic feature of quantum interferences competition, possibly owing to the change of net Berry phase. Furthermore, when the Fermi level is swept into the surface gap, the overall unitary behaviors are revealed at higher magnetic field, which are in contrast to the pure WAL signals obtained in thicker films. Besides, the surface bandgap of ultrathin film is also determined by low temperature STS measurements. Our findings show an exotic phenomenon characterizing the gapped TI surface states and point to the future realization of quantum spin Hall effect and dissipationless TI-based applications. This work was in part supported by Defense Advanced Research Projects Agency (DARPA), Focus Center Research Program-Center on Functional Engineered Nano Architectonics (FENA).
The Discovery and Modeling of O-Type-Like Collisional Ring Galaxies
NASA Astrophysics Data System (ADS)
Wu, Y.-T.; Jiang, I.-G.
2013-10-01
A new type of ring galaxies is discovered from the catalog of collisional ring galaxies in Madore et al. (2009). They are galaxies with axis-symmetric rings but originally classified as P-type collisional ring galaxies due to the existence of nearby companions. We call them O-Type-Like Collisional Ring Galaxies and model their formation through simulations of head-on galactic mergers. After head-on collisions by dwarf galaxies moving along the symmetric axis of disk galaxies, it was found that the simulations with smaller initial relative velocities between two galaxies, or the cases with heavier dwarf galaxies, could produce rings with higher density contrasts. There are more than one generation of rings in one collision and the lifetime of any generation of rings is about one dynamical time. We found that head-on penetrations could explain O-Type-Like Collisional Ring Galaxies well and the simulated rings resembling the observational images of rings are those at the early stage of one of the ring-generations.
COLLISIONAL ACTIVATION MASS SPECTRA OF M-. IONS OF AZO DYES CONTAINING 2-NAPHTHOL
Collisionally activated decomposition mass spectra of M- ions of azo dyes are presented. he compounds are of general structure Ar(l)-N=N-Ar(2), where Ar(l) is substituted phenyl and Ar(2) is 2-naphthol. Characteristic fragment ions observed include m/z 157, which corresponds to t...
Dusty Plasma Modeling of the Fusion Reactor Sheath Including Collisional-Radiative Effects
Dezairi, Aouatif; Samir, Mhamed; Eddahby, Mohamed; Saifaoui, Dennoun; Katsonis, Konstantinos; Berenguer, Chloe
2008-09-07
The structure and the behavior of the sheath in Tokamak collisional plasmas has been studied. The sheath is modeled taking into account the presence of the dust{sup 2} and the effects of the charged particle collisions and radiative processes. The latter may allow for optical diagnostics of the plasma.
Speed-dependent collisional effects on the 326.1-nm Cd line perturbed by Xe
Brym, S.; Ciuryl Trawinski, R.S.; Bielski, A.
1997-12-01
The experimental values of pressure broadening and shift parameters of the 326.1-nm Cd line perturbed by Xe are measured and compared with those calculated from the impact theory for different interaction potentials. The role of the correlations between collisional and Doppler broadening for the Cd-Xe system is discussed. {copyright} {ital 1997} {ital The American Physical Society}
NASA Technical Reports Server (NTRS)
Hoerz, Friedrich; Cintala, Mark; See, Thomas; Bernhard, Ronald; Cardenas, Frank; Davidson, William; Haynes, Jerry
1992-01-01
An experimental inquiry into the utility of discontinuous bumpers was conducted to investigate the collisional outcomes of impacts into single grid-like targets and to compare the results with more traditional bumper designs that employ continuous sheet stock. We performed some 35 experiments using 6.3 and 3.2 mm diameter spherical soda-lime glass projectiles at low velocities (less than 2.5 km/s) and 13 at velocities between 5 and 6 km/s, using 3.2 mm spheres only. The thrust of the experiments related to the characterization of collisional fragments as a function of target thickness or areal shield mass of both bumper designs. The primary product of these experiments was witness plates that record the resulting population of collisional fragments. Substantial interpretive and predictive insights into bumper performance were obtained. All qualitative observations (on the witness plates) and detailed measurements of displaced masses seem simply and consistently related only to bumper mass available for interaction with the impactor. This renders the grid bumper into the superior shield design. These findings present evidence that discontinuous bumpers are a viable concept for collisional shields, possibly superior to continuous geometries.
Collisional transport across the magnetic field in drift-fluid models
NASA Astrophysics Data System (ADS)
Madsen, J.; Naulin, V.; Nielsen, A. H.; Rasmussen, J. Juul
2016-03-01
Drift ordered fluid models are widely applied in studies of low-frequency turbulence in the edge and scrape-off layer regions of magnetically confined plasmas. Here, we show how collisional transport across the magnetic field is self-consistently incorporated into drift-fluid models without altering the drift-fluid energy integral. We demonstrate that the inclusion of collisional transport in drift-fluid models gives rise to diffusion of particle density, momentum, and pressures in drift-fluid turbulence models and, thereby, obviates the customary use of artificial diffusion in turbulence simulations. We further derive a computationally efficient, two-dimensional model, which can be time integrated for several turbulence de-correlation times using only limited computational resources. The model describes interchange turbulence in a two-dimensional plane perpendicular to the magnetic field located at the outboard midplane of a tokamak. The model domain has two regions modeling open and closed field lines. The model employs a computational expedient model for collisional transport. Numerical simulations show good agreement between the full and the simplified model for collisional transport.
NASA Technical Reports Server (NTRS)
Vinolo, A. R.; Clarke, J. H.
1973-01-01
The gas dynamic structures of the transport shock and the downstream collisional relaxation layer are evaluated for partially ionized monatomic gases. Elastic and inelastic collisional nonequilibrium effects are taken into consideration. In the microscopic model of the atom, three electronic levels are accounted for. By using an asymptotic technique, the shock morphology is found on a continuum flow basis. This procedure gives two distinct layers in which the nonequilibrium effects to be considered are different. A transport shock appears as the inner solution to an outer collisional relaxation layer. The results show four main interesting points: (1) on structuring the transport shock, ionization and excitation rates must be included in the formulation, since the flow is not frozen with respect to the population of the different electronic levels; (2) an electron temperature precursor appears at the beginning of the transport shock; (3) the collisional layer is rationally reduced to quadrature for special initial conditions, which (4) are obtained from new Rankine-Hugoniot relations for the inner shock.
THERMOSPRAY IONIZATION WITH REPELLER-INDUCED COLLISIONALLY ACTIVATED DISSOCIATION OF DYES
Thermospray ionization with repeller-induced collisionally activated dissociation (repeller-CAD) has been used to acquire mass spectra of a series of dyes. hese were obtained by applying a voltage of 400 V on the wire repeller. he mass spectra contained arge number of fragment io...
On collisionally enhanced laser pumping of supersonic jets of SF6
NASA Astrophysics Data System (ADS)
Bartell, L. S.; Goates, S. R.; Kacner, M. A.
1980-12-01
Electron-diffraction analyses of SF6 molecules in a microjet irradiated by a cw infrared laser are reported. Excitations of several photons per molecule are achieved in the collisional region extending for the order of a nozzle diameter before molecules become cold and dilute. A model accounting for results is proposed.
Collisional Evolution of High-Inclination Asteroids: Implications for Asteroid Strength
NASA Astrophysics Data System (ADS)
O'Brien, David P.; Michel, P.; Jutzi, M.
2009-09-01
Asteroids with inclinations larger than 20 degrees collide with one another, and with lower-inclination asteroids, with a velocity roughly twice as large as the average collisional velocity in the asteroid belt ( 10 km/sec for high-inclination bodies vs. 5 km/sec main belt average). Thus, their size distribution can potentially evolve differently than the main belt as a whole, for two reasons: 1) the larger collision velocity means that a smaller impactor can lead to their catastrophic disruption; and 2) the energy needed for catastrophic disruption is likely a function of collision velocity [1]. Using a collisional evolution model [2,3] modified to treat two interacting populations, as well as new velocity-dependent scaling laws for asteroid collisional disruption, we study the possible differences in the size distribution of high-inclination asteroids that may result from their increased collision velocity. Recent observations suggest that the size distribution of asteroids around a kilometer in diameter may be shallower for high-inclination asteroids than for low-inclination asteroids [4]. We will discuss the implications that such observational constraints have for the collisional properties of asteroids, namely their strength against catastrophic disruption and how it varies with impact velocity. References: [1] Benz and Asphaug (1999), Icarus 142, 5-20. [2] Bottke et al. (2005), Icarus 175, 111-140. [3] O'Brien (2009), Icarus, in press. [4] Terai and Itoh (2008), ACM 2008, abstract #8215.
Do the Pop II field blue stragglers have a collisional origin
Leonard, P.J.T.
1993-01-01
The hypothesis that the Pop II field blue stragglers have a collisional origin is considered. It appears unlikely that the majority of these stragglers were formed via collisions, but it is difficult to rule out the possibility that a small, but observable, fraction of them were.
Do the Pop II field blue stragglers have a collisional origin?
Leonard, P.J.T.
1993-03-01
The hypothesis that the Pop II field blue stragglers have a collisional origin is considered. It appears unlikely that the majority of these stragglers were formed via collisions, but it is difficult to rule out the possibility that a small, but observable, fraction of them were.
Investigation of collisional effects within the bending magnet region of a DIII-D neutral beamline
Kessler, D.N.; Hong, R.; Kellman, D.H.
1993-10-01
The region between the pole faces of the DIII-D neutral beamline residual ion bending magnets is an area of transient high gas pressure which may cause beam defocusing and increased heating of beamline internal components due to collisional effects. An investigation of these effects helps in understanding residual ion trajectories and in providing information for studying in the beamline capability for operation with increased pulse duration. Examination of collisional effects, and of the possible existence of space charge blow-up, was carried out by injecting deuterium gas into the region between the magnet pole faces with rates varying from 0 to 18 torr-{ell}/sec. Thermocouple and waterflow calorimetry data were taken to measure the beamline component heating and beam powder deposition on the magnet pole shields, magnet louvers, ion dump, beam collimators, and calorimeter. Data was also taken at gas flow rates varying from 0 to 25 torr-{ell}/sec into the neutralizer cell and is compared with the magnet region gas injection data obtained. Results show that both collisional effects and space charge blow-up play a role in magnet region component heating and that neutralizer gas flow sufficiently reduces component heating without incurring unacceptable power losses through collisional effects.
Weak lensing by galaxy troughs
NASA Astrophysics Data System (ADS)
Gruen, Daniel
2016-06-01
Galaxy troughs, i.e. underdensities in the projected galaxy field, are a weak lensing probe of the low density Universe with high signal-to-noise ratio. I present measurements of the radial distortion of background galaxy images and the de-magnification of the CMB by troughs constructed from Dark Energy Survey and Sloan Digital Sky Survey galaxy catalogs. With high statistical significance and a relatively robust modeling, these probe gravity in regimes of density and scale difficult to access for conventional statistics.
Detecting weakly interacting massive particles.
NASA Astrophysics Data System (ADS)
Drukier, A. K.; Gelmini, G. B.
The growing synergy between astrophysics, particle physics, and low background experiments strengthens the possibility of detecting astrophysical non-baryonic matter. The idea of direct detection is that an incident, massive weakly interacting particle could collide with a nucleus and transfer an energy that could be measured. The present low levels of background achieved by the PNL/USC Ge detector represent a new technology which yields interesting bounds on Galactic cold dark matter and on light bosons emitted from the Sun. Further improvements require the development of cryogenic detectors. The authors analyse the practicality of such detectors, their optimalization and background suppression using the "annual modulation effect".
Margaryan, A.; Hashimoto, O.; Kakoyan, V.; Knyazyan, S.; Tang, L.
2011-02-15
A new 'tagged-weak {pi} method' is proposed for determination of electromagnetic transition probabilities B(E2) and B(M1) of the hypernuclear states with lifetimes of {approx}10{sup -10} s. With this method, we are planning to measure B(E2) and B(M1) for light hypernuclei at JLab. The results of Monte Carlo simulations for the case of E2(5/2{sup +}, 3/2{sup +} {yields} 1/2{sup +}) transitions in {sub {Lambda}}{sup 7}He hypernuclei are presented.
Weak quasielastic production of hyperons
Singh, S. K.; Vacas, M. J. Vicente
2006-09-01
The quasielastic weak production of {lambda} and {sigma} hyperons from nucleons and nuclei induced by antineutrinos is studied in the energy region of some ongoing neutrino oscillation experiments in the intermediate energy region. The hyperon-nucleon transition form factors determined from neutrino-nucleon scattering and an analysis of high precision data on semileptonic decays of neutron and hyperons using SU(3) symmetry have been used. The nuclear effects due to Fermi motion and final state interaction effects due to hyperon-nucleon scattering have also been studied. The numerical results for differential and total cross sections have been presented.
Electromagnetic weak turbulence theory revisited
Yoon, P. H.; Ziebell, L. F.; Gaelzer, R.; Pavan, J.
2012-10-15
The statistical mechanical reformulation of weak turbulence theory for unmagnetized plasmas including fully electromagnetic effects was carried out by Yoon [Phys. Plasmas 13, 022302 (2006)]. However, the wave kinetic equation for the transverse wave ignores the nonlinear three-wave interaction that involves two transverse waves and a Langmuir wave, the incoherent analogue of the so-called Raman scattering process, which may account for the third and higher-harmonic plasma emissions. The present paper extends the previous formalism by including such a term.
Leucogranites of the Teton Range, Wyoming: A record of Archean collisional orogeny
NASA Astrophysics Data System (ADS)
Frost, Carol D.; Swapp, Susan M.; Frost, B. Ronald; Finley-Blasi, Lee; Fitz-Gerald, D. Braden
2016-07-01
Leucogranitic rocks formed by crustal melting are a prominent feature of collisional orogens of all ages. This study describes leucogranitic gneisses associated with an Archean collisional orogeny preserved in the Teton Range of northwestern Wyoming, USA. These leucogneisses formed at 2.68 Ga, and initial Nd isotopic compositions suggest they are derived from relatively juvenile sources. Two distinct groups of leucogneisses, both trondhjemitic, are identified on the basis of field relations, petrology, and geochemistry. The Webb Canyon gneiss forms large, sheet-like bodies of hornblende biotite trondhjemite and granodiorite. This gneiss is silica-rich (SiO2 = 70-80%), strongly ferroan, comparatively low in alumina, and is characterized by high Zr and Y, low Sr, and high REE contents that define "seagull"-shaped REE patterns. The Bitch Creek gneiss forms small sills, dikes, and plutons of biotite trondhjemite. Silica, Zr, Y, and REE are lower and alumina and Sr are higher than in the Webb Canyon gneiss. These differences reflect different melting conditions: the Webb Canyon gneiss formed by dehydration melting in which amphibole and quartz breaks down, accounting for the low alumina, high FeO, high silica content and observed trace element characteristics. The Bitch Creek gneiss formed by H2O-excess melting in which plagioclase breaks down leaving an amphibole-rich restite, producing magmas higher in alumina and Sr and lower in FeO and HREE. Both melt mechanisms are expected in collisional environments: dehydration melting accompanies gravitational collapse and tectonic extension of dramatically thickened crust, and water-excess melting may occur when collision places a relatively cool, hydrous lower plate beneath a hotter upper plate. The Archean leucogranitic gneisses of the Teton Range are calcic trondhjemites and granodiorites whereas younger collisional leucogranites typically are true granites. The difference in leucogranite composition reflects the
From pebbles to dust: experiments to observe low-velocity collisional outcomes
NASA Astrophysics Data System (ADS)
Dove, A.; Jorges, J.; Colwell, J. E.
2015-12-01
Particle size evolution in planetary ring systems can be driven by collisions at relatively low velocities (<1 m/s) occurring between objects with a range of sizes from very fine dust to decimeter-sized objects. In these complex systems, collisions between centimeter-sized objects may result in particle growth by accretion, rebounding, or erosive processes that result in the production of additional smaller particles. The outcomes of these collisions are dependent on factors such as collisional energy, particle size, and particle morphology. Numerical simulations are limited by a need to understand these collisional parameters over a range of conditions. We present the results of a sequence of laboratory experiments designed to explore collisions over a range of these parameters. We are able to observe low-velocity collisions by conducting experiments in vacuum chambers in our 0.8-sec drop tower apparatus. Initial experiments utilize a variety of impacting spheres, including glass, Teflon, aluminum, stainless steel, and brass. These spheres are either used in their natural state or are "mantled" - coated with a few-mm thick layer of a cohesive powder. A high-speed, high-resolution video camera is used to record the motion of the colliding bodies. These videos are then processed and we track the particles to determine impactor speeds before and after collision and the collisional outcome; in the case of the mantled impactors, we can assess how much of the powder was released in the collision. We also determine how the coefficient of restitution varies as a function of material type, morphology, and impact velocity. Impact velocities range from about 20-60 cm/s, and we observe that mantling of particles significantly reduces their coefficients of restitution. These results will contribute to an empirical model of collisional outcomes that can help refine our understanding of dusty ring system collisional evolution.
Charge on a weak polyelectrolyte
NASA Astrophysics Data System (ADS)
Wang, Shengqin; Granick, Steve; Zhao, Jiang
2008-12-01
Fluorescence measurements with single-molecule sensitivity are used to measure the hydrodynamic size and local pH of a weak polyelectrolyte, poly-2-vinyl pyridine end labeled with pH-sensitive dye, the polyelectrolyte having concentration so low (nanomolars) that molecular properties are resolvable only from fluorescence experiments and cannot be accessed by light scattering. We find that the local pH near the dye, inferred from its brightness, is consistently three orders of magnitude higher than the bulk pH. Upon varying the bulk pH, we measure the collapse point at which hydrophobic attraction overwhelms electrostatic repulsion between charged elements along the chain, and conclude that adding monovalent salt shifts this coil-to-globule collapse to higher pH than in the absence of salt. The influence of salt appears to shift the ionization equilibrium of this weak polyelectrolyte in the direction of the chain possessing enhanced electric charge at a given pH. Phenomenologically, this is opposite to the case for strong polyelectrolytes, although the mechanism differs.
Airway clearance in neuromuscular weakness.
Gauld, Leanne Maree
2009-05-01
Impaired airway clearance leads to recurrent chest infections and respiratory deterioration in neuromuscular weakness. It is frequently the cause of death. Cough is the major mechanism of airway clearance. Cough has several components, and assessment tools are available to measure the different components of cough. These include measuring peak cough flow, respiratory muscle strength, and inspiratory capacity. Each is useful in assessing the ability to generate an effective cough, and can be used to guide when techniques of assisting airway clearance may be effective for the individual and which are most effective. Techniques to assist airway clearance include augmenting inspiration by air stacking, augmenting expiration by assisting the cough, and augmenting both inspiration and expiration with the mechanical insufflator-exsufflator or by direct suctioning via a tracheostomy. Physiotherapists are invaluable in assisting airway clearance, and in teaching patients and their families how to use these techniques. Use of the mechanical insufflator-exsufflator has gained popularity in recent times, but several simpler, more economical methods are available to assist airway clearance that can be used effectively alone or in combination. This review examines the literature available on the assessment and management of impaired airway clearance in neuromuscular weakness. PMID:19379290
Weak lensing and cosmological investigation
NASA Astrophysics Data System (ADS)
Acquaviva, Viviana
2005-03-01
In the last few years the scientific community has been dealing with the challenging issue of identifying the dark energy component. We regard weak gravitational lensing as a brand new, and extremely important, tool for cosmological investigation in this field. In fact, the features imprinted on the Cosmic Microwave Background radiation by the lensing from the intervening distribution of matter represent a pretty unbiased estimator, and can thus be used for putting constraints on different dark energy models. This is true in particular for the magnetic-type B-modes of CMB polarization, whose unlensed spectrum at large multipoles (l ~= 1000) is very small even in presence of an amount of gravitational waves as large as currently allowed by the experiments: therefore, on these scales the lensing phenomenon is the only responsible for the observed power, and this signal turns out to be a faithful tracer of the dark energy dynamics. We first recall the formal apparatus of the weak lensing in extended theories of gravity, introducing the physical observables suitable to cast the bridge between lensing and cosmology, and then evaluate the amplitude of the expected effect in the particular case of a Non-Minimally-Coupled model, featuring a quadratic coupling between quintessence and Ricci scalar.
NASA Astrophysics Data System (ADS)
Hall, Lawrence J.; Pinner, David; Ruderman, Joshua T.
2014-12-01
The measured values of the weak scale, v, and the first generation masses, m u, d, e , are simultaneously explained in the multiverse, with all these parameters scanning independently. At the same time, several remarkable coincidences are understood. Small variations in these parameters away from their measured values lead to the instability of hydrogen, the instability of heavy nuclei, and either a hydrogen or a helium dominated universe from Big Bang Nucleosynthesis. In the 4d parameter space of ( m u , m d , m e , v), catastrophic boundaries are reached by separately increasing each parameter above its measured value by a factor of (1.4, 1.3, 2.5, ˜ 5), respectively. The fine-tuning problem of the weak scale in the Standard Model is solved: as v is increased beyond the observed value, it is impossible to maintain a significant cosmological hydrogen abundance for any values of m u, d, e that yield both hydrogen and heavy nuclei stability.
Weak antilocalisation in topological insulators
NASA Astrophysics Data System (ADS)
Bi, Xintao; Hankiewicz, Ewelina; Culcer, Dimitrie
2014-03-01
Topological insulators (TI) have changed our understanding of insulating behaviour. They are insulators in the bulk but conducting along their surfaces due to spin-orbit interaction. Much of the recent research focuses on overcoming the transport bottleneck, the fact that surface state transport is overwhelmed by bulk transport stemming from unintentional doping. The key to overcoming this bottleneck is identifying unambiguous signatures of surface state transport. This talk will discuss one such signature, which is manifest in the coherent backscattering of electrons. Due to strong spin-orbit coupling in TI one expects to observe weak antilocalisation rather than weak localisation, meaning that coherent backscattering increases the electrical conductivity. The features of this effect, however, are rather subtle, because in TI the impurities have strong spin-orbit coupling as well. I will show that spin-orbit coupled impurities introduce an additional time scale, which is expected to be shorter than the dephasing time, and the resulting conductivity has a logarithmic dependence on the carrier density, a behaviour hitherto unknown in 2D electron systems. The result we predict is observable experimentally and would provide a smoking gun test of surface transport.
The Computational Complexity of Weak Saddles
NASA Astrophysics Data System (ADS)
Brandt, Felix; Brill, Markus; Fischer, Felix; Hoffmann, Jan
We continue the recently initiated study of the computational aspects of weak saddles, an ordinal set-valued solution concept proposed by Shapley. Brandt et al. gave a polynomial-time algorithm for computing weak saddles in a subclass of matrix games, and showed that certain problems associated with weak saddles of bimatrix games are NP-complete. The important question of whether weak saddles can be found efficiently was left open. We answer this question in the negative by showing that finding weak saddles of bimatrix games is NP-hard, under polynomial-time Turing reductions. We moreover prove that recognizing weak saddles is coNP-complete, and that deciding whether a given action is contained in some weak saddle is hard for parallel access to NP and thus not even in NP unless the polynomial hierarchy collapses. Our hardness results are finally shown to carry over to a natural weakening of weak saddles.
NASA Astrophysics Data System (ADS)
Carbone, Emile; van Dijk, Jan; Kroesen, Gerrit
2015-04-01
In this paper, laser collisional induced fluorescence (LCIF) is used to probe resonant excitation transfers in an argon/hydrogen plasma resulting from heavy particle collisions. Different radiative transitions between the 1s and 2p states (in Paschen's notation) of argon are optically pumped by a nanosecond laser pulse. The spontaneous fluorescence and collisional responses of the argon and hydrogen systems are monitored by optical emission spectroscopy. A surfatron plasma source is used to generate an argon plasma with a few per cent hydrogen addition at pressures between 0.65 and 20 mbar. The electron density is measured independently by means of Thomson scattering. The overall response of the plasma due to optical pumping of argon is briefly discussed and an overview of the known heteronuclear excitation transfers in an argon/hydrogen plasma is given. The propagation of the shortcut in the Ar(1s) to H(n = 2) excitation transfer due to the optical pumping of the Ar(1s) states is seen in the atomic hydrogen LCIF responses. For the first time, we give direct experimental evidence of the existence of an efficient excitation transfer: Additionally, measurements are performed in order to estimate the resonant energy transfer between the resonant argon 1s states and hydrogen atoms: for which no previously measured cross sections could be found in the literature. These are extra quenching channels of argon 1s and 2p states that should be included in collisional-radiative modeling of argon-hydrogen discharges. The high repetition rate of the dye laser allows us to obtain a high sensitivity in the measurements. LCIF is shown to be a powerful tool for unraveling electron and also heavy particle excitation channels in situ in the plasma phase. The technique was previously developed for measuring electron or species densities locally in the plasma, but we show that it can be advantageously used to probe collisional transfers between very short-lived species which exist
NASA Astrophysics Data System (ADS)
Lenzer, Thomas; Luther, Klaus; Reihs, Karsten; Symonds, Andrew C.
2000-03-01
Complete and detailed experimental transition probability density functions P(E',E) have been determined for the first time for collisions between a large, highly vibrationally excited molecule, toluene, and several bath gases. This was achieved by applying the method of kinetically controlled selective ionization (KCSI) (Paper I [J. Chem. Phys. 112, 4076 (2000), preceding article]). An optimum P(E',E) representation is recommended (monoexponential with a parametric exponent in the argument) which uses only three parameters and features a smooth behavior of all parameters for the entire set of bath gases. In helium, argon, and CO2 the P(E',E) show relatively increased amplitudes in the wings—large energy gaps |E'-E|—which can also be represented by a biexponential form. The fractional contribution of the second exponent in these biexponentials, which is directly related to the fraction of the so-called "supercollisions," is found to be very small (<0.1%). For larger colliders the second term disappears completely and the wings of P(E',E) have an even smaller amplitude than that provided by a monoexponential form. At such low levels, the second exponent is therefore of practically no relevance for the overall energy relaxation rate. All optimized P(E',E) representations show a marked linear energetic dependence of the (weak) collision parameter α1(E), which also results in an (approximately) linear dependence of <ΔE> and of the square root of <ΔE2>. The energy transfer parameters presented in this study form a new benchmark class in certainty and accuracy, e.g., with only 2%-7% uncertainty for our <ΔE> data below 25 000 cm-1. They should also form a reliable testground for future trajectory calculations and theories describing collisional energy transfer of polyatomic molecules.
Heterogeneous, weakly coupled map lattices
NASA Astrophysics Data System (ADS)
Sotelo Herrera, M.^{a.} Dolores; San Martín, Jesús; Porter, Mason A.
2016-07-01
Coupled map lattices (CMLs) are often used to study emergent phenomena in nature. It is typically assumed (unrealistically) that each component is described by the same map, and it is important to relax this assumption. In this paper, we characterize periodic orbits and the laminar regime of type-I intermittency in heterogeneous weakly coupled map lattices (HWCMLs). We show that the period of a cycle in an HWCML is preserved for arbitrarily small coupling strengths even when an associated uncoupled oscillator would experience a period-doubling cascade. Our results characterize periodic orbits both near and far from saddle-node bifurcations, and we thereby provide a key step for examining the bifurcation structure of heterogeneous CMLs.
Weakly ionized cerium plasma radiography
NASA Astrophysics Data System (ADS)
Sato, Eiichi; Hayasi, Yasuomi; Germer, Rudolf; Koorikawa, Yoshitake; Murakami, Kazunori; Tanaka, Etsuro; Mori, Hidezo; Kawai, Toshiaki; Ichimaru, Toshio; Obata, Fumiko; Takahashi, Kiyomi; Sato, Sigehiro; Takayama, Kazuyoshi; Ido, Hideaki
2004-02-01
In the plasma flash x-ray generator, high-voltage main condenser of about 200 nF is charged up to 55 kV by a power supply, and electric charges in the condenser are discharged to an x-ray tube after triggering the cathode electrode. The flash x-rays are then produced. The x-ray tube is of a demountable triode that is connected to a turbo molecular pump with a pressure of approximately 1 mPa. As electron flows from the cathode electrode are roughly converged to a rod cerium target of 3.0 mm in diameter by electric field in the x-ray tube, the weakly ionized linear plasma, which consists of cerium ions and electrons, forms by target evaporating. At a charging voltage of 55 kV, the maximum tube voltage was almost equal to the charging voltage of the main condenser, and the peak current was about 20 kA. When the charging voltage was increased, weakly ionized cerium plasma formed, and the K-series characteristic x-ray intensities increased. The x-ray pulse widths were about 500 ns, and the time-integrated x-ray intensity had a value of about 40 μC/kg at 1.0 m from x-ray source with a charging voltage of 55 kV. In the angiography, we employed a film-less computed radiography (CR) system and iodine-based microspheres. Because K-series characteristic x-rays are absorbed easily by the microspheres, high-contrast angiography has been performed.
Statistical theory of electromagnetic weak turbulence
Yoon, Peter H.
2006-02-15
The weak turbulence theory as commonly found in the literature employs electrostatic approximation and is applicable to unmagnetized plasmas only. To this date, fully electromagnetic generalization of the existing weak turbulence theory based upon statistical mechanical approach remains largely incomplete. Instead, electromagnetic effects are incorporated into the weak turbulence formalism by means of the semiclassical approach. The present paper reformulates the fully electromagnetic weak turbulence theory from classical statistical mechanical (i.e., the Klimontovich) approach.
The Debris Disk of Vega: A Steady-state Collisional Cascade, Naturally
NASA Astrophysics Data System (ADS)
Müller, S.; Löhne, T.; Krivov, A. V.
2010-01-01
The archetypical debris disk around Vega has been observed intensively over the past 25 years. It has been argued that the resulting photometric data and images may be in contradiction with a standard, steady-state collisional scenario of the disk evolution. In particular, the emission in the mid-infrared (mid-IR) appears to be in excess of what is expected from a "Kuiper belt" at ~100 AU, which is evident in the submillimeter images and inferred from the majority of photometric points. Here we re-address the question of whether or not the Vega disk observations are compatible with a continuous dust production through a collisional cascade. Instead of seeking a size and spatial distribution of dust that provide the best fit to observations, our approach involves physical modeling of the debris disk "from the sources." We assume that dust is maintained by a belt of parent planetesimals, and employ our collisional and radiative transfer codes to consistently model the size and radial distribution of the disk material and then thermal emission of dust. In doing so, we vary a broad set of parameters, including the stellar properties, the exact location, extension, and dynamical excitation of the planetesimal belt, chemical composition of solids, and the collisional prescription. We are able to reproduce the spectral energy distribution in the entire wavelength range from the near-IR to millimeter, as well as the mid-IR and submillimeter radial brightness profiles of the Vega disk. Thus, our results suggest that the Vega disk observations are not in contradiction with a steady-state collisional dust production, and we put important constraints on the disk parameters and physical processes that sustain it. The total disk mass in lsim100 km-sized bodies is estimated to be ~10 Earth masses. Provided that collisional cascade has been operating over much of the Vega age of ~350 Myr, the disk must have lost a few Earth masses of solids during that time. We also demonstrate
THE DEBRIS DISK OF VEGA: A STEADY-STATE COLLISIONAL CASCADE, NATURALLY
Mueller, S.; Loehne, T.; Krivov, A. V.
2010-01-10
The archetypical debris disk around Vega has been observed intensively over the past 25 years. It has been argued that the resulting photometric data and images may be in contradiction with a standard, steady-state collisional scenario of the disk evolution. In particular, the emission in the mid-infrared (mid-IR) appears to be in excess of what is expected from a 'Kuiper belt' at approx100 AU, which is evident in the submillimeter images and inferred from the majority of photometric points. Here we re-address the question of whether or not the Vega disk observations are compatible with a continuous dust production through a collisional cascade. Instead of seeking a size and spatial distribution of dust that provide the best fit to observations, our approach involves physical modeling of the debris disk 'from the sources'. We assume that dust is maintained by a belt of parent planetesimals, and employ our collisional and radiative transfer codes to consistently model the size and radial distribution of the disk material and then thermal emission of dust. In doing so, we vary a broad set of parameters, including the stellar properties, the exact location, extension, and dynamical excitation of the planetesimal belt, chemical composition of solids, and the collisional prescription. We are able to reproduce the spectral energy distribution in the entire wavelength range from the near-IR to millimeter, as well as the mid-IR and submillimeter radial brightness profiles of the Vega disk. Thus, our results suggest that the Vega disk observations are not in contradiction with a steady-state collisional dust production, and we put important constraints on the disk parameters and physical processes that sustain it. The total disk mass in approx<100 km-sized bodies is estimated to be approx10 Earth masses. Provided that collisional cascade has been operating over much of the Vega age of approx350 Myr, the disk must have lost a few Earth masses of solids during that time. We
Analytic model of a magnetically insulated transmission line with collisional flow electrons
NASA Astrophysics Data System (ADS)
Stygar, W. A.; Wagoner, T. C.; Ives, H. C.; Corcoran, P. A.; Cuneo, M. E.; Douglas, J. W.; Gilliland, T. L.; Mazarakis, M. G.; Ramirez, J. J.; Seamen, J. F.; Seidel, D. B.; Spielman, R. B.
2006-09-01
We have developed a relativistic-fluid model of the flow-electron plasma in a steady-state one-dimensional magnetically insulated transmission line (MITL). The model assumes that the electrons are collisional and, as a result, drift toward the anode. The model predicts that in the limit of fully developed collisional flow, the relation between the voltage Va, anode current Ia, cathode current Ik, and geometric impedance Z0 of a 1D planar MITL can be expressed as Va=IaZ0h(χ), where h(χ)≡[(χ+1)/4(χ-1)]1/2-ln⌊χ+(χ2-1)1/2⌋/2χ(χ-1) and χ≡Ia/Ik. The relation is valid when Va≳1MV. In the minimally insulated limit, the anode current Ia,min=1.78Va/Z0, the electron-flow current If,min=1.25Va/Z0, and the flow impedance Zf,min=0.588Z0. {The electron-flow current If≡Ia-Ik. Following Mendel and Rosenthal [Phys. Plasmas 2, 1332 (1995)PHPAEN1070-664X10.1063/1.871345], we define the flow impedance Zf as Va/(Ia2-Ik2)1/2.} In the well-insulated limit (i.e., when Ia≫Ia,min), the electron-flow current If=9Va2/8IaZ02 and the flow impedance Zf=2Z0/3. Similar results are obtained for a 1D collisional MITL with coaxial cylindrical electrodes, when the inner conductor is at a negative potential with respect to the outer, and Z0≲40Ω. We compare the predictions of the collisional model to those of several MITL models that assume the flow electrons are collisionless. We find that at given values of Va and Z0, collisions can significantly increase both Ia,min and If,min above the values predicted by the collisionless models, and decrease Zf,min. When Ia≫Ia,min, we find that, at given values of Va, Z0, and Ia, collisions can significantly increase If and decrease Zf. Since the steady-state collisional model is valid only when the drift of electrons toward the anode has had sufficient time to establish fully developed collisional flow, and collisionless models assume there is no net electron drift toward the anode, we expect these two types
Collisional evolution - an analytical study for the nonsteady-state mass distribution
NASA Astrophysics Data System (ADS)
Martins, R. Vieira
1999-05-01
To study the collisional evolution of asteroidal groups we can use an analytical solutionfor the self-similar collision cascades. This solution is suitable to study the steady-state massdistribution of the collisional fragmentation. However, out of the steady-state conditions, thissolution is not satisfactory for some values of the collisional parameters. In fact, for some valuesfor the exponent of the mass distribution power law of an asteroidal group and its relation to theexponent of the function which describes how rocks break we arrive at singular points for theequation which describes the collisional evolution. These singularities appear since someapproximations are usually made in the laborious evaluation of many integrals that appear in theanalytical calculations. They concern the cutoff for the smallest and the largest bodies. Thesesingularities set some restrictions to the study of the analytical solution for the collisionalequation. To overcome these singularities we performed an algebraic computationconsidering the smallest and the largest bodies and we obtained the analytical expressions for theintegrals that describe the collisional evolution without restriction on the parameters. However,the new distribution is more sensitive to the values of the collisional parameters. In particular thesteady-state solution for the differential mass distribution has exponents slightly different from11⧸6 for the usual parameters in the Asteroid Belt. The sensitivity of this distribution with respectto the parameters is analyzed for the usual values in the asteroidal groups. With anexpression for the mass distribution without singularities, we can evaluate also its time evolution.We arrive at an analytical expression given by a power series of terms constituted by a smallparameter multiplied by the mass to an exponent, which depends on the initial power lawdistribution. This expression is a formal solution for the equation which describes the collisionalevolution
Kinetic theory of low-frequency cross-field instability in a weakly ionized plasma. II
Dimant, Y.S.; Sudan, R.N.
1995-04-01
The consistent kinetic approach developed in Paper I [Ya. S. Dimant and R. N. Sudan, Phys. Plasmas {bold 2}, 1157 (1995)] is applied to obtain the general dispersion relation of the two-stream {bold E}{times}{bold B} instability in collisionally dominated weakly ionized plasmas for wave frequencies small compared to the ion--neutral collision frequency. This dispersion relation covers the whole low-frequency band from the asymptotic short-wave limit studied in Paper I to the long-wave limit. Previous theories employing simplified kinetic theory or fluid equations for electron behavior are only correct in the long-wave limit. The principal new results are that the threshold conditions for this instability and the growth rates are altered from those predicted by earlier simplified theories. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.
Particle pinch and collisionality in gyrokinetic simulations of tokamak plasma turbulence
Angioni, C.; Candy, J.; Waltz, R. E.; Fable, E.; Maslov, M.; Weisen, H.; Peeters, A. G.
2009-06-15
The generic problem of how, in a turbulent plasma, the experimentally relevant conditions of a particle flux very close to the null are achieved, despite the presence of strong heat fluxes, is addressed. Nonlinear gyrokinetic simulations of plasma turbulence in tokamaks reveal a complex dependence of the particle flux as a function of the turbulent spatial scale and of the velocity space as collisionality is increased. At experimental values of collisionality, the particle flux is found close to the null, in agreement with the experiment, due to the balance between inward and outward contributions at small and large scales, respectively. These simulations provide full theoretical support to the prediction of a peaked density profile in a future nuclear fusion reactor.
Collisional processes in the O2 B 3Σu- state
NASA Astrophysics Data System (ADS)
Sick, Volker; Decker, Michael; Heinze, Johannes; Stricker, Winfried
1996-02-01
Collisional processes, which influence quantitative laser-induced fluorescence (LIF) measurements involving the B3Σ u- state of molecular oxygen, were investigated. Since the B state is strongly predissociating, these processes are though to be important only at higher pressure. However, we found that in LIF experiments in methane/air flames in the pressure range between atmospheric pressure and 40 bar collisional quenching and rotational energy transfer (RET) are important even at moderate pressures. Total quenching cross sections of 30(± 10) Å2for ν' = 2 and 100(± 30) Å2for ν = 0 and total RET cross sections of 40(± 16) Å2 were found. An upper limit of 0.7 Å 2 for the cross section for vibrational energy transfer (VET) out of ν' = 2 could be determined.
Improved modeling of relativistic collisions and collisional ionization in particle-in-cell codes
Perez, F.; Gremillet, L.; Decoster, A.; Drouin, M.; Lefebvre, E.
2012-08-15
An improved Monte Carlo collisional scheme modeling both elastic and inelastic interactions has been implemented into the particle-in-cell code CALDER[E. Lefebvre et al., Nucl. Fusion 43, 629 (2003)]. Based on the technique proposed by Nanbu and Yonemura [J. Comput. Phys. 145, 639 (1998)] allowing to handle arbitrarily weighted macro-particles, this binary collision scheme uses a more compact and accurate relativistic formulation than the algorithm recently worked out by Sentoku and Kemp [J. Comput. Phys. 227, 6846 (2008)]. Our scheme is validated through several test cases, demonstrating, in particular, its capability of modeling the electrical resistivity and stopping power of a solid-density plasma over a broad parameter range. A relativistic collisional ionization scheme is developed within the same framework, and tested in several physical scenarios. Finally, our scheme is applied in a set of integrated particle-in-cell simulations of laser-driven fast electron transport.
Collisional relaxation of bi-Maxwellian plasma temperatures in magnetized plasmas
NASA Astrophysics Data System (ADS)
Yoon, Peter H.
2016-07-01
In the literature, collisional processes are customarily discussed within the context of the Boltzmann-Balescu-Lenard-Landau type of collision integral, but such an equation is strictly valid for unmagnetized plasmas. For plasmas immersed in the ambient magnetic field, the foundational equation that describes binary collisions must be generalized to include the effects of magnetic field. The present paper makes use of such an equation in order to describe the collisional relaxation of temperatures under the assumption of bi-Maxwellian velocity distribution function. The formalism derived in the present paper may be useful for studying the effects of binary collisions on the isotropization of temperatures in the solar wind plasma, among possible applications.
Collisional excitation of HC3N by para- and ortho-H2
NASA Astrophysics Data System (ADS)
Faure, Alexandre; Lique, François; Wiesenfeld, Laurent
2016-08-01
New calculations for rotational excitation of cyanoacetylene by collisions with hydrogen molecules are performed to include the lowest 38 rotational levels of HC3N and kinetic temperatures to 300 K. Calculations are based on the interaction potential of Wernli et al. whose accuracy is checked against spectroscopic measurements of the HC3N-H2 complex. The quantum coupled-channel approach is employed and complemented by quasi-classical trajectory calculations. Rate coefficients for ortho-H2 are provided for the first time. Hyperfine resolved rate coefficients are also deduced. Collisional propensity rules are discussed and comparisons between quantum and classical rate coefficients are presented. This collisional data should prove useful in interpreting HC3N observations in the cold and warm ISM, as well as in protoplanetary discs.
Accurate Collisional Cross-Sections: Important Non-Lte Input Data
NASA Astrophysics Data System (ADS)
Mashonkina, L.
2010-11-01
Non-LTE modelling for a particular atom requires accurate collisional excitation and ionization cross-sections for the entire system of transitions in the atom. This review concerns with inelastic collisions with electrons and neutral hydrogen atoms. For the selected atoms, H i and Ca ii, comparisons are made between electron impact excitation rates from ab initio calculations and various theoretical approximations. The effect of the use of modern data on non-LTE modelling is shown. For most transitions and most atoms, hydrogen collisional rates are calculated using a semi-empirical modification of the classical Thomson formula for ionization by electrons. Approaches used to estimate empirically the efficiency of hydrogenic collisions in the statistical equilibrium of atoms are reviewed. This research was supported by the Deutsche Forschungsgemeinschaft with grant 436 RUS 17/13/07.
Collisional Transport in a Low Aspect Ratio Tokamak -- Beyond the Drift Kinetic Formalism
D.A. Gates; R.B. White
2004-01-28
Calculations of collisional thermal and particle diffusivities in toroidal magnetic plasma confinement devices order the toroidal gyroradius to be small relative to the poloidal gyroradius. This ordering is central to what is usually referred to as neoclassical transport theory. This ordering is incorrect at low aspect ratio, where it can often be the case that the toroidal gyroradius is larger than the poloidal gyroradius. We calculate the correction to the particle and thermal diffusivities at low aspect ratio by comparing the diffusivities as determined by a full orbit code (which we refer to as omni-classical diffusion) with those from a gyroaveraged orbit code (neoclassical diffusion). In typical low aspect ratio devices the omni-classical diffusion can be up to 2.5 times the calculated neoclassical value. We discuss the implications of this work on the analysis of collisional transport in low aspect ratio magnetic confinement experiments.
Model for collisional fast ion diffusion into Tokamak Fusion Test Reactor loss cone
Chang, C.S. |; Zweben, S.J.; Schivell, J.; Budny, R.; Scott, S.
1994-08-01
An analytic model is developed to estimate the classical pitch angle scattering loss of energetic fusion product ions into prompt loss orbits in a tokamak geometry. The result is applied to alpha particles produced by deutrium-tritium fusion reactions in a plasma condition relevant to Tokamak Fusion Test Reactor (TFTR). A poloidal angular distribution of collisional fast ion loss at the first wall is obtained and the numerical result from the TRANSP code is discussed. The present model includes the effect that the prompt loss boundary moves away from the slowing-down path due to reduction in banana thickness, which enables us to understand, for the first time. the dependence of the collisional loss rate on Z{sub eff}.
Collisional removal of HI from the inner disks of Virgo cluster galaxies
NASA Technical Reports Server (NTRS)
Valluri, Monica; Jog, Chanda J.
1990-01-01
There is sufficient observational evidence to show that many Virgo Cluster spirals are HI deficient in their inner disks (in addition to being HI deficient globally, as previously established). It is shown here that collisions between galaxies in a cluster can lead to the removal of HI gas from these galaxies while leaving the H2 gas, undisturbed. This follows directly from the application of the Spitzer-Baade collisional gas removal mechanism to galaxies consisting of stars and a two-component interstellar medium (ISM) consisting of HI and H2, with HI having the largest filling factor. This can account for both the observed HI deficiency in the inner regions and the normal H2 content of these galaxies. The frequency of galaxy collisions in the Virgo Cluster is shown to be large enough to make collisional gas removal a viable mechanism.
NASA Technical Reports Server (NTRS)
Liffman, Kurt
1990-01-01
The effects of catastrophic collisional fragmentation and diffuse medium accretion on a the interstellar dust system are computed using a Monte Carlo computer model. The Monte Carlo code has as its basis an analytic solution of the bulk chemical evolution of a two-phase interstellar medium, described by Liffman and Clayton (1989). The model is subjected to numerous different interstellar processes as it transfers from one interstellar phase to another. Collisional fragmentation was found to be the dominant physical process that shapes the size spectrum of interstellar dust. It was found that, in the diffuse cloud phase, 90 percent of the refractory material is locked up in the dust grains, primarily due to accretion in the molecular medium. This result is consistent with the observed depletions of silicon. Depletions were found to be affected only slightly by diffuse cloud accretion.
Progress in table-top transient collisional excitation x-ray lasers at LLNL
Da Silva, L B; Dunn, J; Li, Y; Nilsen, J; Osterheld, A; Shepherd, R; Shlyaptsev, V N
1999-02-07
We present progress in experiments for high efficiency Ne-like and Ni-like ion x-ray lasers using the transient collisional excitation scheme. Experimental results have been obtained on the COMET 15 TW table-top laser system at the Lawrence Livermore National Laboratory (LLNL). The plasma formation, ionization and collisional excitation of the x-ray laser have been optimized using two sequential laser pulses of 600 ps and 1 ps duration with an optional pre-pulse. We have observed high gains up to 55 cm{sup {minus}1} in Ne-like and Ni-like ion schemes for various atomic numbers. We report strong output for the 4d - 4p line in lower Z Ni-like ion sequence for Mo to Y, lasing from {approximately}190 {angstrom} to 240 {angstrom}, by pumping with less than 5 J energy on target.
Ion Collisional Transport Coefficients in the Solar Wind at 1 au
NASA Astrophysics Data System (ADS)
Hellinger, Petr
2016-07-01
Proton and alpha particle collisional transport coefficients (isotropization, relative deceleration frequencies, and heating rates) at 1 au are quantified using the Wind/Solar Wind Experiment data. In agreement with previous studies, the ion–ion Coulomb collisions are generally important for slow solar wind streams and tend to reduce the temperature anisotropies, the differential streaming, and the differences between the proton and alpha particle temperatures. In slow solar wind streams the Coulomb collisions between protons and alpha particles are important for the overall proton energetics, as well as the relative deceleration between the two species. It is also shown that ion temperature anisotropies and differential streaming need to be taken into account for evaluation of the collisional transport coefficients.
NASA Technical Reports Server (NTRS)
Providakes, Jason; Seyler, Charles E.
1990-01-01
A new mechanism is proposed for the source of energetic heavy ions (NO/+/, O2/+/, and O/+/) found in the magnetosphere. Simulations using a multispecies particle simulation code for resistive current-driven electrostatic ion cyclotron waves show transverse and parallel bulk heating of bottomside ionospheric heavy ion populations. The dominant mechanism for the transverse bulk heating is resonant ion heating by wave-particle ion trapping. Using a linear kinetic dispersion relation for a magnetized, collisional, homogenous, and multiion plasma, it is found that collisional electrostatic ion cyclotron waves near the NO(+), O2(+), and O(+) gyrofrequencies are unstable to field-aligned currents of 50 microA/sq m for a typical bottomside ionosphere.
Asteroid collisional evolution - An integrated model for the evolution of asteroid rotation rates
NASA Technical Reports Server (NTRS)
Farinella, P.; Davis, D. R.; Paolicchi, P.; Cellino, A.; Zappala, V.
1992-01-01
A comprehensive model for the changes in asteroid spin rates due to large collisions was developed by combining the theoretical results of Cellino et al. (1990) with previously published work on spin rate changes for cratering impacts (Harris, 1979; Dobrovolskis and Burns, 1984). The spin change algorithm, when incorporated into an existing simulation of collisional effects on asteroid sizes, produced an integrated model for studying the simultaneous evolution of asteroid sizes and spin rates over the solar system history. As a result of an analysis of 32 collisional scenarios with regard to the change in the spin rate as a function of asteroid size, it is concluded that the spin rates of all asteroids, except possibly the largest ones, have been significantly altered by collisions over the solar system history and that, in general, shattering impacts are much more important than cratering events in changing the spin of asteroids.
COLLISIONALLY EXCITED FILAMENTS IN HUBBLE SPACE TELESCOPE Hα AND Hβ IMAGES OF HH 1/2
Raga, A. C.; Castellanos-Ramírez, A.; Reipurth, B.; Chiang, Hsin-Fang; Bally, J.
2015-01-01
We present new Hα and Hβ images of the HH 1/2 system, and we find that the Hα/Hβ ratio has high values in ridges along the leading edges of the HH 1 bow shock and of the brighter condensations of HH 2. These ridges have Hα/Hβ = 4 → 6, which is consistent with collisional excitation from the n = 1 to the n = 3 and 4 levels of hydrogen in a gas of temperatures T = 1.5 → 10 × 10{sup 4} K. This is therefore the first direct evidence that the collisional excitation/ionization region of hydrogen just behind Herbig-Haro shock fronts is detected.
Propagation of surface waves on a semi-bounded quantum magnetized collisional plasma
Niknam, A. R.; Taheri Boroujeni, S.; Khorashadizadeh, S. M.
2013-12-15
The propagation of surface waves on a semi-bounded quantum plasma in the presence of the external magnetic field and collisional effects is investigated by using quantum magnetohydrodynamics model. A general analytical expression for the dispersion relation of surface waves is obtained by considering the boundary conditions. It is shown that, in some special cases, the obtained dispersion relation reduces to the results reported in previous works. It is also indicated that the quantum, external magnetic field and collisional effects can facilitate the propagation of surface waves on a semi-bounded plasma. In addition, it is found that the growth rate of the surface wave instability is enhanced by increasing the collision frequency and plasmonic parameter.
NASA Astrophysics Data System (ADS)
Abdoli-Arani, A.; Moghaddasi, M.
2016-07-01
Acceleration of an externally injected electron inside the collisional plasma-filled cylindrical waveguide during its motion in the fields of the ? mode excited by microwave radiation is studied. The effect of the electron collision frequency with background ions on the deflection angle and energy gain of electron, when it is injected along the direction of the mode propagation is investigated. The fields for the mode, the deflection angle of electron trajectory, due to these fields, and the electron energy gradient are obtained. The results for collisionless and collisional plasma are graphically presented. The numerical results illustrate that the presence of the electron collision term in the dielectric permittivity can reduce the electron's energy gain in the configuration.
Collisional tearing in a field-reversed sheet pinch assuming nonparallel propagation
NASA Technical Reports Server (NTRS)
Quest, K. B.; Coroniti, F. V.
1985-01-01
Linear tearing in a collisional reversed-field sheet pinch is examined assuming that the wave vector k is not parallel to the equilibrium magnetic field. Equilibrium and magnetic geometry are defined, and a set of perturbed moment equations is derived assuming quasi-parallel propagation. It is shown that the usual expression for collisional growth is recovered, assuming that k sub y = 0. It is shown that the y component of momentum balance requires the generation of nonzero dJ sub x well away from the null, and an interial coupling when z not equal to 0. The effects of k sub y not equal to 0 on the growth rate are discussed.
Nonextensive statistics and skin depth of transverse wave in collisional plasma
NASA Astrophysics Data System (ADS)
Hashemzadeh, M.
2016-05-01
Skin depth of transverse wave in a collisional plasma is studied taking into account the nonextensive electron distribution function. Considering the kinetic theory for charge particles and using the Bhatnagar-Gross-Krook collision model, a generalized transverse dielectric permittivity is obtained. The transverse dispersion relation in different frequency ranges is investigated. Obtaining the imaginary part of the wave vector from the dispersion relation, the skin depth for these frequency ranges is also achieved. Profiles of the skin depth show that by increasing the q parameter, the penetration depth decreases. In addition, the skin depth increases by increasing the electron temperature. Finally, it is found that in the high frequency range and high electron temperature, the penetration depth decreases by increasing the collision frequency. In contrast, by increasing the collision frequency in a highly collisional frequency range, the skin depth of transverse wave increases.
Protecting weak measurements against systematic errors
NASA Astrophysics Data System (ADS)
Pang, Shengshi; Alonso, Jose Raul Gonzalez; Brun, Todd A.; Jordan, Andrew N.
2016-07-01
In this work, we consider the systematic error of quantum metrology by weak measurements under decoherence. We derive the systematic error of maximum likelihood estimation in general to the first-order approximation of a small deviation in the probability distribution and study the robustness of standard weak measurement and postselected weak measurements against systematic errors. We show that, with a large weak value, the systematic error of a postselected weak measurement when the probe undergoes decoherence can be significantly lower than that of a standard weak measurement. This indicates another advantage of weak-value amplification in improving the performance of parameter estimation. We illustrate the results by an exact numerical simulation of decoherence arising from a bosonic mode and compare it to the first-order analytical result we obtain.
Efficient evaluation of collisional energy transfer terms for plasma particle simulations
NASA Astrophysics Data System (ADS)
Turrell, A. E.; Sherlock, M.; Rose, S. J.
2016-01-01
Particle-based simulations, such as in particle-in-cell (PIC) codes, are widely used in plasma physics research. The analysis of particle energy transfers, as described by the second moment of the Boltzmann equation, is often necessary within these simulations. We present computationally efficient, analytically derived equations for evaluating collisional energy transfer terms from simulations using discrete particles. The equations are expressed as a sum over the properties of the discrete particles.
Particle simulation model of transport in a bounded, Coulomb collisional plasma
Procassini, R.J.; Birdsall, C.K. )
1991-08-01
The transport of particles and energy in a fully ionized, collisional plasma is studied through the use of a kinetic transport model. A particle-in-cell (PIC) code has been coupled to a Monte Carlo, binary particle model of Coulomb collisions, to provide a fully kinetic, self-consistent description of transport and potential formation in a single spatial dimension and two velocity components (parallel and perpendicular to the spatial coordinate). The dependence of plasma transport on Coulomb collisionality is investigated by varying the normalized collision frequency within the range 10{sup {minus}2}{le}{nu}{sub *}{equivalent to}{nu}{sub {ital c}0}/{nu}{sub {ital be}0}{le}5, where {nu}{sub {ital c}0} is the average electron/ion collision frequency and {nu}{sub {ital be}0} is the frequency at which thermal electrons bounce between the collector sheath potential drops located adjacent to the absorbing plates at each end of the system. Collisions between charged-plasma and recycled-neutral particles are omitted in this study. For finite values of {nu}{sub *}, the heat conduction flux is found to be reduced from the value predicted by classical, hydrodynamic transport theory. The electron heat conduction flux is shown to lie between 12% and 21% of the free-streaming thermal flux {ital q}{sup {ital e}}{sub {ital fs}}{equivalent to}{ital n}{sub {ital e}v}{sub {parallel},{ital te}}{ital kT}{sub {ital e}}, where {ital n}{sub {ital e}}, {ital v}{sub {parallel},{ital te}}, and {ital kT}{sub {ital e}} are the steady-state values of the electron density, parallel thermal velocity, and temperature, respectively. The variation of several transport quantities with collisionality is presented, and the results are compared against those from other collisional plasma transport models.
The electromagnetic interchange mode in a partially ionized collisional plasma. [spread F region
NASA Technical Reports Server (NTRS)
Hudson, M. K.; Kennel, C. F.
1974-01-01
A collisional electromagnetic dispersion relation is derived from two-fluid theory for the interchange mode coupled to the Alfven, acoustic, drift and entropy modes in a partially ionized plasma. The fundamental electromagnetic nature of the interchange model is noted; coupling to the intermediate Alfven mode is strongly stabilizing for finite k sub z. Both ion viscous and ion-neutral stabilization are included, and it was found that collisions destroy the ion finite Larmor radius cutoff at short perpendicular wavelengths.
A study of the collisional dynamics for collisions of UF with atoms and molecules
NASA Astrophysics Data System (ADS)
Doverspike, L. D.; Champion, R. D.
1980-08-01
Absolute total cross sections for the collisional decomposition of the negative ion of uranium hexafluoride into its three lowest asymptotic channels in collisions with the rare gases were measured for collision energies ranging from below thresholds for decomposition up to a laboratory collision energy of 500 eV. The experimental results were found to be consistent with the predictions of a two step collision model where the unimolecular decomposition of the excited molecular negative ions is described with a statistical theory.
Gain Calculations for Inner-Shell Lasing by Electron Collisional Ionisation
NASA Astrophysics Data System (ADS)
Upcraft, L. M.
2002-11-01
Current high power femtosecond lasers have been shown to produce electron pulses which may be appropriate for the pumping of X-Ray lasers through collisional ionisation. Non-radiative Coster-Kronig type decay processes may be fast enough to form an inverted state and allow X-ray lasing within the biologically interesting "water window". Calculations of the atomic processes in metallic Ti, Mn and Cu are presented that potentially useable gains on the M1 - L3 transition.
Collisional Relaxation of a Strongly Magnetized, Two Isotope, Pure Ion Plasma
NASA Astrophysics Data System (ADS)
Chim, C. Y.; O'Neil, T. M.; Dubin, D. H. E.
2011-10-01
The collisional relaxation of a strongly magnetized pure ion plasmathat is composed of two species with slightly different mass is discussed. We have in mind two isotopes of the same singly ionized atom. Parameters are assumed to be ordered as Ωc 1, Ωc 2 >> |Ωc 1 -Ωc 2 | >> v / b , where Ωc 1 and Ωc 2 are the two cyclotron frequencies, v is the thermal velocity, and b is the classical distance of closest approach. For this ordering, the total cyclotron action for the two species, J1 =∑jɛ 1m1v⊥12 / 2Ωc 1 and J2 =∑jɛ 2m2v⊥j2 / 2Ωc 2 , are adiabatic invariants that constrain the collisional dynamics. On the time scale of a few collisions, entropy is maximized subject to the constancy of the total Hamiltonian H and the two actions J1 and J2, yielding a Gibbs distribution of the form exp [ - H / T -α1J1 -α2J2 ] . Collisional relaxation to the usual Gibbs distribution, exp [ - H / T ] , takes place on two time scales, each of which is exponentially longer than the usual collisional time scale. First, the two species share action so that α1 and α2 relax to a common value α. On an even longer time scale, the total action ceases to be a good constant of the motion and α relaxes to zero. Supported by NSF PHY-0903877 and DOE DE-SC0002451.
Stearns, J.W.; Burrell, C.F.; Kaplan, S.N.; Pyle, R.V.; Ruby, L.; Schlachter, A.S.
1985-04-01
Polarized beams at intensity levels heretofore not considered feasible have recently been proposed for heating and fueling fusion plasmas. Polarized-beam fueling could increase fusion rates by 50% as well as allow control of the directionality of the fusion products. A process which we have recently described, and called collisional pumping, promises to produce beams of polarized ions vastly more intense than producible by current methods.
OBSERVED BINARY FRACTION SETS LIMITS ON THE EXTENT OF COLLISIONAL GRINDING IN THE KUIPER BELT
Nesvorny, David; Vokrouhlicky, David; Bottke, William F.; Levison, Harold F.; Noll, Keith
2011-05-15
The size distribution in the cold classical Kuiper Belt (KB) can be approximated by two idealized power laws: one with steep slope for radii R > R* and one with shallow slope for R < R*, where R* {approx} 25-50 km. Previous works suggested that the size frequency distribution (SFD) rollover at R* can be the result of extensive collisional grinding in the KB that led to the catastrophic disruption of most bodies with R < R*. Here, we use a new code to test the effect of collisions in the KB. We find that the observed rollover could indeed be explained by collisional grinding provided that the initial mass in large bodies was much larger than the one in the present KB and was dynamically depleted. In addition to the size distribution changes, our code also tracks the effects of collisions on binary systems. We find that it is generally easier to dissolve wide binary systems, such as the ones existing in the cold KB today, than to catastrophically disrupt objects with R {approx} R*. Thus, the binary survival sets important limits on the extent of collisional grinding in the KB. We find that the extensive collisional grinding required to produce the SFD rollover at R* would imply a strong gradient of the binary fraction with R and separation, because it is generally easier to dissolve binaries with small components and/or those with wide orbits. The expected binary fraction for R {approx}< R* is {approx}<0.1. The present observational data do not show such a gradient. Instead, they suggest a large binary fraction of {approx}0.4 for R = 30-40 km. This may indicate that the rollover was not produced by disruptive collisions, but is instead a fossil remnant of the KB object formation process.
NASA Technical Reports Server (NTRS)
Lederer. S. M.; Jensen, E. A.; Wooden, D. H.; Lindsay, S. S.; Smith, D. C.; Cintala, M. J.; Nakamura-Messenger, K.; Keller, L. P.
2012-01-01
Impacts into forsterite and orthoenstatite at speeds typically encountered by comets demonstrate that shock imparted by collisions is detectable in the infrared signatures of their dust. The spectral signatures can be traced to physical alterations in their crystalline structures, as observed in TEM imaging and modeled using a dipole approximation. These results yield tantalizing insights into the collisional history of our solar system, as well as the history of individual comets and Trojan asteroids.
The Collisional Evolution of the Trans-Neptunian Object Size Distribution
NASA Astrophysics Data System (ADS)
O'Brien, D. P.; Greenberg, R.
2004-11-01
The HST survey of trans-Neptunian objects (TNOs) by Bernstein et al. [1] detected two distinct populations, `classical' and `excited', and found a deficit of smaller (≲100 km) TNOs relative to the power law found earlier for larger bodies. Using the analytical model of O'Brien and Greenberg [2] and a numerical collisional evolution model [3] with reasonable strength parameters for icy bodies [4], we find that the TNO populations likely started with shallow initial size distributions, and that bodies ≳ 10 km in diameter are likely not in a collisional steady state. If the initial size distributions were steeper than the current size distributions, collisional erosion could not remove enough bodies over the age of the solar system to match the observations. The size distribution of TNOs ≳ 10 km in diameter must therefore be primordial. We also use our numerical model to address the origin of Jupiter-family comets (JFCs). Comparing the `classical' and `excited' size distributions to the results of numerical simulations of the supply of JFCs, Bernstein et al. find that most JFCs are ˜1 km in diameter and come from the `excited' population. An upturn in the size distribution at sizes below their survey limit could increase the size of JFC precursors and possibly allow the `classical' population to contribute a significant number of JFCs. Our numerical simulations show that the collisional production of bodies below ˜10 km in diameter can create a small upturn in the `classical' and `excited' size distributions, but it is not able to substantially increase the contribution of JFCs from the `classical' population or increase the size of JFC precursors. [1] Bernstein et al., AJ, submitted (AstroPH/0308467 v.3). [2] O'Brien and Greenberg, Icarus 164, 2003. [3] O'Brien and Greenberg, in prep. [4] Benz and Asphaug, Icarus 142, 1999.
Coupling of an average-atom model with a collisional-radiative equilibrium model
Faussurier, G. Blancard, C.; Cossé, P.
2014-11-15
We present a method to combine a collisional-radiative equilibrium model and an average-atom model to calculate bound and free electron wavefunctions in hot dense plasmas by taking into account screening. This approach allows us to calculate electrical resistivity and thermal conductivity as well as pressure in non local thermodynamic equilibrium plasmas. Illustrations of the method are presented for dilute titanium plasma.
Weak percolation on multiplex networks.
Baxter, Gareth J; Dorogovtsev, Sergey N; Mendes, José F F; Cellai, Davide
2014-04-01
Bootstrap percolation is a simple but nontrivial model. It has applications in many areas of science and has been explored on random networks for several decades. In single-layer (simplex) networks, it has been recently observed that bootstrap percolation, which is defined as an incremental process, can be seen as the opposite of pruning percolation, where nodes are removed according to a connectivity rule. Here we propose models of both bootstrap and pruning percolation for multiplex networks. We collectively refer to these two models with the concept of "weak" percolation, to distinguish them from the somewhat classical concept of ordinary ("strong") percolation. While the two models coincide in simplex networks, we show that they decouple when considering multiplexes, giving rise to a wealth of critical phenomena. Our bootstrap model constitutes the simplest example of a contagion process on a multiplex network and has potential applications in critical infrastructure recovery and information security. Moreover, we show that our pruning percolation model may provide a way to diagnose missing layers in a multiplex network. Finally, our analytical approach allows us to calculate critical behavior and characterize critical clusters. PMID:24827287
Weakly Supervised Human Fixations Prediction.
Zhang, Luming; Li, Xuelong; Nie, Liqiang; Yang, Yi; Xia, Yingjie
2016-01-01
Automatically predicting human eye fixations is a useful technique that can facilitate many multimedia applications, e.g., image retrieval, action recognition, and photo retargeting. Conventional approaches are frustrated by two drawbacks. First, psychophysical experiments show that an object-level interpretation of scenes influences eye movements significantly. Most of the existing saliency models rely on object detectors, and therefore, only a few prespecified categories can be discovered. Second, the relative displacement of objects influences their saliency remarkably, but current models cannot describe them explicitly. To solve these problems, this paper proposes weakly supervised fixations prediction, which leverages image labels to improve accuracy of human fixations prediction. The proposed model hierarchically discovers objects as well as their spatial configurations. Starting from the raw image pixels, we sample superpixels in an image, thereby seamless object descriptors termed object-level graphlets (oGLs) are generated by random walking on the superpixel mosaic. Then, a manifold embedding algorithm is proposed to encode image labels into oGLs, and the response map of each prespecified object is computed accordingly. On the basis of the object-level response map, we propose spatial-level graphlets (sGLs) to model the relative positions among objects. Afterward, eye tracking data is employed to integrate these sGLs for predicting human eye fixations. Thorough experiment results demonstrate the advantage of the proposed method over the state-of-the-art. PMID:26168451
A Universe without Weak Interactions
Harnik, Roni; Kribs, Graham D.; Perez, Gilad
2006-04-07
A universe without weak interactions is constructed that undergoes big-bang nucleosynthesis, matter domination, structure formation, and star formation. The stars in this universe are able to burn for billions of years, synthesize elements up to iron, and undergo supernova explosions, dispersing heavy elements into the interstellar medium. These definitive claims are supported by a detailed analysis where this hypothetical ''Weakless Universe'' is matched to our Universe by simultaneously adjusting Standard Model and cosmological parameters. For instance, chemistry and nuclear physics are essentially unchanged. The apparent habitability of the Weakless Universe suggests that the anthropic principle does not determine the scale of electroweak breaking, or even require that it be smaller than the Planck scale, so long as technically natural parameters may be suitably adjusted. Whether the multi-parameter adjustment is realized or probable is dependent on the ultraviolet completion, such as the string landscape. Considering a similar analysis for the cosmological constant, however, we argue that no adjustments of other parameters are able to allow the cosmological constant to raise up even remotely close to the Planck scale while obtaining macroscopic structure. The fine-tuning problems associated with the electroweak breaking scale and the cosmological constant therefore appear to be qualitatively different from the perspective of obtaining a habitable universe.
Weak percolation on multiplex networks
NASA Astrophysics Data System (ADS)
Baxter, Gareth J.; Dorogovtsev, Sergey N.; Mendes, José F. F.; Cellai, Davide
2014-04-01
Bootstrap percolation is a simple but nontrivial model. It has applications in many areas of science and has been explored on random networks for several decades. In single-layer (simplex) networks, it has been recently observed that bootstrap percolation, which is defined as an incremental process, can be seen as the opposite of pruning percolation, where nodes are removed according to a connectivity rule. Here we propose models of both bootstrap and pruning percolation for multiplex networks. We collectively refer to these two models with the concept of "weak" percolation, to distinguish them from the somewhat classical concept of ordinary ("strong") percolation. While the two models coincide in simplex networks, we show that they decouple when considering multiplexes, giving rise to a wealth of critical phenomena. Our bootstrap model constitutes the simplest example of a contagion process on a multiplex network and has potential applications in critical infrastructure recovery and information security. Moreover, we show that our pruning percolation model may provide a way to diagnose missing layers in a multiplex network. Finally, our analytical approach allows us to calculate critical behavior and characterize critical clusters.
Collisional-radiative modeling of tungsten at temperatures of 1200–2400 eV
Colgan, James; Fontes, Christopher; Zhang, Honglin; Abdallah, Jr., Joseph
2015-04-30
We discuss new collisional-radiative modeling calculations of tungsten at moderate temperatures of 1200 to 2400 eV. Such plasma conditions are relevant to ongoing experimental work at ASDEX Upgrade and are expected to be relevant for ITER. Our calculations are made using the Los Alamos National Laboratory (LANL) collisional-radiative modeling ATOMIC code. These calculations formed part of a submission to the recent NLTE-8 workshop that was held in November 2013. This series of workshops provides a forum for detailed comparison of plasma and spectral quantities from NLTE collisional-radiative modeling codes. We focus on the LANL ATOMIC calculations for tungsten that were submitted to the NLTE-8 workshop and discuss different models that were constructed to predict the tungsten emission. In particular, we discuss comparisons between semi-relativistic configuration-average and fully relativistic configuration-average calculations. We also present semi-relativistic calculations that include fine-structure detail, and discuss the difficult problem of ensuring completeness with respect to the number of configurations included in a CR calculation.
Linear stability of low mode number tearing modes in the banana collisionality regime
Fitzpatrick, R. , Abingdon, OX14 3DB, England )
1989-12-01
The semicollisional layer equations governing the linear stability of small mode number tearing modes in a low beta, large aspect ratio, tokamak equilibrium are derived from an expansion of the gyrokinetic equation. In this analysis only the cases where the ion Larmor radius is either much less than, or much greater than, the layer width are considered. Both the electrons and the ions are assumed to lie in the banana collisionality regime. One interesting feature of the derived layer equations, in the limit of small ion Larmor radius, is a substantial reduction in the effective collisionality of the system due to neoclassical ion dynamics. Next, using a shooting code, a dispersion relation is obtained from the layer equations in the limits of small ion Larmor radius and a vanishingly small fraction of trapped particles. As expected, strong semicollisional stabilization of the mode is found, but, in addition, a somewhat weaker destabilizing effect is obtained in the transition region between the collisional and semicollisional regimes.
Effect of collisional heat transfer in ICRF power modulation experiment on ASDEX Upgrade
Tsujii, N.; D'Inca, R.; Bilato, R.; Bobkov, Vl. V.; Brambilla, M.; Schneider, P.; Noterdaeme, J.-M.; Van Eester, D.; Lerche, E. A.; Jaeger, E. F.; Collaboration: ASDEX Upgrade Team
2014-02-12
ICRF (ion cyclotron range of frequencies) heating experiments were performed in D-H plasmas at various H concentrations on ASDEX Upgrade. The rf power was modulated to measure the electron power deposition profile from electron temperature modulation. To minimize the contribution from indirect collisional heating and the effect of radial transport, the rf power was modulated at 50 Hz. However, peaking of electron temperature modulation was still observed around the hydrogen cyclotron resonance indicating collisional heating contribution. Time dependent simulation of the hydrogen distribution function was performed for the discharges, using the full-wave code AORSA (E.F. Jaeger, et al., Phys. Plasmas, Vol. 8, page 1573 (2001)) coupled to the Fokker-Planck code CQL3D (R.W. Harvey, et al., Proc. IAEA (1992)). In the present experimental conditions, it was found that modulation of the collisional heating was comparable to that of direct wave damping. Impact of radial transport was also analyzed and found to appreciably smear out the modulation profile and reduce the phase delay.
Neufeld, David A.
2010-01-01
An artificial neural network (ANN) is investigated as a tool for estimating rate coefficients for the collisional excitation of molecules. The performance of such a tool can be evaluated by testing it on a data set of collisionally induced transitions for which rate coefficients are already known: the network is trained on a subset of that data set and tested on the remainder. Results obtained by this method are typically accurate to within a factor of approx2.1 (median value) for transitions with low excitation rates and approx1.7 for those with medium or high excitation rates, although 4% of the ANN outputs are discrepant by a factor of 10 or more. The results suggest that ANNs will be valuable in extrapolating a data set of collisional rate coefficients to include high-lying transitions that have not yet been calculated. For the asymmetric top molecules considered in this paper, the favored architecture is a cascade-correlation network that creates 16 hidden neurons during the course of training, with three input neurons to characterize the nature of the transition and one output neuron to provide the logarithm of the rate coefficient.
NanoRocks: Experimental Study of Collisional Damping and Aggregation at Low Velocities
NASA Astrophysics Data System (ADS)
Colwell, Joshua E.; Brisset, Julie; Dove, Adrienne R.; Metzger, Jessica; Rascon, Allison
2015-11-01
The NanoRocks experiment on the International Space Station consists of 8 separate sample trays of particles from ~0.1 mm - 2.0 mm in diameter that undergo collisional evolution. The microgravity environment of the ISS allows collision speeds of less than 1 mm/s to be studied. At these speeds the experiment reproduces the velocity dispersion found in unperturbed regions of Saturn’s rings. Observations of the rings from Cassini instruments hint at aggregation and fragmentation of clumps depending on the local surface mass density, particle size distribution and velocity dispersion.The eight NanoRocks samples include plastic beads, copper, glass, and JSC-1 lunar regolith simulant. The samples are shaken at 1 minute intervals to provide initial collision velocities of a few cm/s, and video is recorded of the collisional evolution of the particle samples. We derive mean coefficients of restitution for the different samples based on the damping of the mean velocity dispersion as well as tracking of individual particle trajectories. The evolution of the velocity distribution is consistent with a uniform random distribution of the coefficient of restitution, independent of collision velocity. This is consistent with results of Heißelmann et al. (Icarus Vol. 206, pp. 424-430, 2010) using larger icy particles. We also find the onset of cluster formation at speeds of a few mm/s. We will present our results and discuss applications to models of the collisional evolution of Saturn’s rings.
Collisional-radiative modeling of tungsten at temperatures of 1200–2400 eV
Colgan, James; Fontes, Christopher; Zhang, Honglin; Abdallah, Jr., Joseph
2015-04-30
We discuss new collisional-radiative modeling calculations of tungsten at moderate temperatures of 1200 to 2400 eV. Such plasma conditions are relevant to ongoing experimental work at ASDEX Upgrade and are expected to be relevant for ITER. Our calculations are made using the Los Alamos National Laboratory (LANL) collisional-radiative modeling ATOMIC code. These calculations formed part of a submission to the recent NLTE-8 workshop that was held in November 2013. This series of workshops provides a forum for detailed comparison of plasma and spectral quantities from NLTE collisional-radiative modeling codes. We focus on the LANL ATOMIC calculations for tungsten that weremore » submitted to the NLTE-8 workshop and discuss different models that were constructed to predict the tungsten emission. In particular, we discuss comparisons between semi-relativistic configuration-average and fully relativistic configuration-average calculations. We also present semi-relativistic calculations that include fine-structure detail, and discuss the difficult problem of ensuring completeness with respect to the number of configurations included in a CR calculation.« less
NASA Technical Reports Server (NTRS)
Sembach, Kenneth R.; Savage, Blair D.; Jenkins, Edward B.
1994-01-01
We present Goddard High-Resolution Spectrograph observations at 3.5 km/s resolution and signal-to-noise ratios of 30 to 60 for the Al III, Si IV, and N V absorption lines in the far-ultraviolet spectrum of the O9.5 V star zeat Ophiuchi. The measurement reveal three types of highly ionized gas along the 140 pc line of sight. (1) Narrow components of Al III (b = 4.3 km/s, the mean value of (v(helio)) = -7.8 km/s; b = 3.2 km/s, the mean value of (v(sub helio)) = -14.4 km/s) and Si IV (b = 5.3 km/s, the mean value of (v(sub helio)) = -15.0 km/s) trace photionized gas in the expanding H II region surrounding zeta Oph. The observed magnitude and direction of the velocity offset between the Al III and Si IV profiles can be explained by models of H II regions that incorporate expansion. Narrow C IV absorption associated with the H II region is not detected. Predictions of the expected amounts of Si IV and C IV overestimate the column densities of these ions by factors of 30 and more than 10, respectively. The discrepancy may be due to the effects of elemental depletions in the gas and/or to the interaction of the stellar wind with surrounding matter. (2) Broad (b = 15 to 18 km/s) and weak Si IV and C IV absorption components are detected near the mean value of (v(sub helio)) = -26 km/s. The high-ionization species associated with these absorption components are probably produced by electron collisional ionization in a heated gas. This absorption may be physically related to the zeta Oph bow shock ot to a cloud complex situated within the local interstellar medium at d less than 60 pc. The C IV to Si IV column density ratio in this gas is 8, a factor of 6 less than conductive interface models predict, but this discrepancy may be removed by considering the effects of self-photoionization within the cooling gas in the model calculations. (3) A broad (b = 13 km/s) and weak C IV absorption feature detected at the mean value of (v(sub helio)) = -61 km/s is not seen in other
Pixelation Effects in Weak Lensing
NASA Technical Reports Server (NTRS)
High, F. William; Rhodes, Jason; Massey, Richard; Ellis, Richard
2007-01-01
Weak gravitational lensing can be used to investigate both dark matter and dark energy but requires accurate measurements of the shapes of faint, distant galaxies. Such measurements are hindered by the finite resolution and pixel scale of digital cameras. We investigate the optimum choice of pixel scale for a space-based mission, using the engineering model and survey strategy of the proposed Supernova Acceleration Probe as a baseline. We do this by simulating realistic astronomical images containing a known input shear signal and then attempting to recover the signal using the Rhodes, Refregier, and Groth algorithm. We find that the quality of shear measurement is always improved by smaller pixels. However, in practice, telescopes are usually limited to a finite number of pixels and operational life span, so the total area of a survey increases with pixel size. We therefore fix the survey lifetime and the number of pixels in the focal plane while varying the pixel scale, thereby effectively varying the survey size. In a pure trade-off for image resolution versus survey area, we find that measurements of the matter power spectrum would have minimum statistical error with a pixel scale of 0.09' for a 0.14' FWHM point-spread function (PSF). The pixel scale could be increased to 0.16' if images dithered by exactly half-pixel offsets were always available. Some of our results do depend on our adopted shape measurement method and should be regarded as an upper limit: future pipelines may require smaller pixels to overcome systematic floors not yet accessible, and, in certain circumstances, measuring the shape of the PSF might be more difficult than those of galaxies. However, the relative trends in our analysis are robust, especially those of the surface density of resolved galaxies. Our approach thus provides a snapshot of potential in available technology, and a practical counterpart to analytic studies of pixelation, which necessarily assume an idealized shape
Weak {}^* convergence of operator means
NASA Astrophysics Data System (ADS)
Romanov, Alexandr V.
2011-12-01
For a linear operator U with \\Vert U^n\\Vert \\le \\operatorname{const} on a Banach space X we discuss conditions for the convergence of ergodic operator nets T_\\alpha corresponding to the adjoint operator U^* of U in the {W^*O}-topology of the space \\operatorname{End} X^*. The accumulation points of all possible nets of this kind form a compact convex set L in \\operatorname{End} X^*, which is the kernel of the operator semigroup G=\\overline{\\operatorname{co}}\\,\\Gamma_0, where \\Gamma_0=\\{U_n^*, n \\ge 0\\}. It is proved that all ergodic nets T_\\alpha weakly {}^* converge if and only if the kernel L consists of a single element. In the case of X=C(\\Omega) and the shift operator U generated by a continuous transformation \\varphi of a metrizable compactum \\Omega we trace the relationships among the ergodic properties of U, the structure of the operator semigroups L, G and \\Gamma=\\overline{\\Gamma}_0, and the dynamical characteristics of the semi-cascade (\\varphi,\\Omega). In particular, if \\operatorname{card}L=1, then a) for any \\omega \\in\\Omega the closure of the trajectory \\{\\varphi^n\\omega, n \\ge 0\\} contains precisely one minimal set m, and b) the restriction (\\varphi,m) is strictly ergodic. Condition a) implies the {W^*O}-convergence of any ergodic sequence of operators T_n \\in \\operatorname{End} X^* under the additional assumption that the kernel of the enveloping semigroup E(\\varphi,\\Omega) contains elements obtained from the `basis' family of transformations \\{\\varphi^n, n \\ge 0\\} of the compact set \\Omega by using some transfinite sequence of sequential passages to the limit.
Pixelation Effects in Weak Lensing
NASA Astrophysics Data System (ADS)
High, F. William; Rhodes, Jason; Massey, Richard; Ellis, Richard
2007-11-01
Weak gravitational lensing can be used to investigate both dark matter and dark energy but requires accurate measurements of the shapes of faint, distant galaxies. Such measurements are hindered by the finite resolution and pixel scale of digital cameras. We investigate the optimum choice of pixel scale for a space-based mission, using the engineering model and survey strategy of the proposed Supernova Acceleration Probe as a baseline. We do this by simulating realistic astronomical images containing a known input shear signal and then attempting to recover the signal using the Rhodes, Refregier, & Groth algorithm. We find that the quality of shear measurement is always improved by smaller pixels. However, in practice, telescopes are usually limited to a finite number of pixels and operational life span, so the total area of a survey increases with pixel size. We therefore fix the survey lifetime and the number of pixels in the focal plane while varying the pixel scale, thereby effectively varying the survey size. In a pure trade-off for image resolution versus survey area, we find that measurements of the matter power spectrum would have minimum statistical error with a pixel scale of 0.09" for a 0.14" FWHM point-spread function (PSF). The pixel scale could be increased to ~0.16" if images dithered by exactly half-pixel offsets were always available. Some of our results do depend on our adopted shape measurement method and should be regarded as an upper limit: future pipelines may require smaller pixels to overcome systematic floors not yet accessible, and, in certain circumstances, measuring the shape of the PSF might be more difficult than those of galaxies. However, the relative trends in our analysis are robust, especially those of the surface density of resolved galaxies. Our approach thus provides a snapshot of potential in available technology, and a practical counterpart to analytic studies of pixelation, which necessarily assume an idealized shape
Collisional relaxation of a strongly magnetized two-species pure ion plasma
NASA Astrophysics Data System (ADS)
Chim, Chi Yung; O'Neil, Thomas M.; Dubin, Daniel H.
2014-04-01
The collisional relaxation of a strongly magnetized pure ion plasma that is composed of two species with slightly different masses is discussed. We have in mind two isotopes of the same singly ionized atom. Parameters are assumed to be ordered as Ω1,Ω2≫|Ω1-Ω2|≫v¯ij/b ¯ and v¯⊥j/Ωj≪b ¯, where Ω1 and Ω2 are two cyclotron frequencies, v¯ij=√T∥/μij is the relative parallel thermal velocity characterizing collisions between particles of species i and j, and b ¯=2 e2/T∥ is the classical distance of closest approach for such collisions, and v ¯⊥j/Ωj=√2T⊥j/mj /Ωj is the characteristic cyclotron radius for particles of species j. Here, μij is the reduced mass for the two particles, and T∥ and T⊥j are temperatures that characterize velocity components parallel and perpendicular to the magnetic field. For this ordering, the total cyclotron action for the two species, I1=∑i ∈1m1v⊥i2/(2Ω1) and I2=∑i∈2m2v⊥i2/(2Ω2) are adiabatic invariants that constrain the collisional dynamics. On the timescale of a few collisions, entropy is maximized subject to the constancy of the total Hamiltonian H and the two actions I1 and I2, yielding a modified Gibbs distribution of the form exp[-H /T∥-α1I1-α2I2]. Here, the αj's are related to T∥ and T⊥j through T⊥j=(1/T∥+αj/Ωj)-1. Collisional relaxation to the usual Gibbs distribution, exp[-H /T∥], takes place on two timescales. On a timescale longer than the collisional timescale by a factor of (b ¯2Ω12/v¯112)exp{5[3π(b¯|Ω1-Ω2|/v ¯12)]2/5/6}, the two species share action so that α1 and α2 relax to a common value α. On an even longer timescale, longer than the collisional timescale by a factor of the order exp {5[3π(v¯11)]2/5/6}, the total action ceases to be a good constant of the motion and α relaxes to zero.
Rheology of weakly vibrated granular materials
NASA Astrophysics Data System (ADS)
Dijksman, J. A.; Wortel, G.; van Hecke, M.
2009-06-01
We show how weak vibrations substantially modify the rheology of granular materials. We experimentally probe dry granular flows in a weakly vibrated split bottom shear cell—the weak vibrations modulate gravity and act as an agitation source. By tuning the applied stress and vibration strength, and monitoring the resulting strain as a function of time, we uncover a rich phase diagram in which non-trivial transitions separate a jammed phase, a creep flow case, and a steady flow case.
Spin effects in the weak interaction
Freedman, S.J. Chicago Univ., IL . Dept. of Physics Chicago Univ., IL . Enrico Fermi Inst.)
1990-01-01
Modern experiments investigating the beta decay of the neutron and light nuclei are still providing important constraints on the theory of the weak interaction. Beta decay experiments are yielding more precise values for allowed and induced weak coupling constants and putting constraints on possible extensions to the standard electroweak model. Here we emphasize the implications of recent experiments to pin down the strengths of the weak vector and axial vector couplings of the nucleon.
Ryutov, D. D.
2015-12-08
Part 1 of this note considered the kinematics of large-angle scattering (LAS) of the deuterons on the counter-streaming carbon ions, with both flows having the same velocity V. Due to a large mass ratio m_{C}/m_{D}, the backscattered deuterons have high velocity of up to (24/7)V. This significantly increases the cross-section for the neutron production in the collisions between the back-scattered and incoming deuterons and may provide significant contribution to the total neutron yield, despite the smallness of a large-angle Coulomb cross-section. This effect becomes particularly important when only one of the colliding streams is made of CD, whereas the other stream is made of CH. Part 1 evaluated the neutron yield produced by this mechanism and have found that its relative role increases for higher plasma densities and lower velocities. Part 2 discusses signatures of this effect which can be used to identify it experimentally and also discusses in some more detail its spatio-temporal characteristics. It goes without saying that a complete quantitative assessment should be based on numerical simulations accounting for the large-angle scattering.
Ryutov, D. D.
2015-12-01
Laser-generated interpenetrating plasma jets are widely used in the studies of collisionless interaction of counter-streaming plasmas in conjunction with possible formation of collisionless shocks. In a number of experiments of this type the plasma is formed on plastic targets made of CH or CD. The study of the DD neutron production from the interaction between two CD jets on the one hand and between a CD jet and a CH jet could serve as a qualitative indicator of the collisionless shock formation. The purpose of this memo is a discussion of the effect of collisions on the neutron generation in the interpenetrating CH and CD jets. First, the kinematics of the large-deflection collisions of the deuterons and carbon are discussed. Then the scattering angles are related with the corresponding Rutherford cross-section. After that expression for the number of the backscattered deuterons is provided, and their contribution to the neutron yield is evaluated. The results may be of some significance to the kinetic codes benchmarking and developing the neutron diagnostic.
CP Violation, Neutral Currents, and Weak Equivalence
DOE R&D Accomplishments Database
Fitch, V. L.
1972-03-23
Within the past few months two excellent summaries of the state of our knowledge of the weak interactions have been presented. Correspondingly, we will not attempt a comprehensive review but instead concentrate this discussion on the status of CP violation, the question of the neutral currents, and the weak equivalence principle.
On modeling weak sinks in MODPATH.
Abrams, Daniel; Haitjema, H; Kauffman, L
2013-01-01
Regional groundwater flow systems often contain both strong sinks and weak sinks. A strong sink extracts water from the entire aquifer depth, while a weak sink lets some water pass underneath or over the actual sink. The numerical groundwater flow model MODFLOW may allow a sink cell to act as a strong or weak sink, hence extracting all water that enters the cell or allowing some of that water to pass. A physical strong sink can be modeled by either a strong sink cell or a weak sink cell, with the latter generally occurring in low-resolution models. Likewise, a physical weak sink may also be represented by either type of sink cell. The representation of weak sinks in the particle tracing code MODPATH is more equivocal than in MODFLOW. With the appropriate parameterization of MODPATH, particle traces and their associated travel times to weak sink streams can be modeled with adequate accuracy, even in single layer models. Weak sink well cells, on the other hand, require special measures as proposed in the literature to generate correct particle traces and individual travel times and hence capture zones. We found that the transit time distributions for well water generally do not require special measures provided aquifer properties are locally homogeneous and the well draws water from the entire aquifer depth, an important observation for determining the response of a well to non-point contaminant inputs. PMID:23025655
Spin Seebeck effect in a weak ferromagnet
NASA Astrophysics Data System (ADS)
Arboleda, Juan David; Arnache Olmos, Oscar; Aguirre, Myriam Haydee; Ramos, Rafael; Anadon, Alberto; Ibarra, Manuel Ricardo
2016-06-01
We report the observation of room temperature spin Seebeck effect (SSE) in a weak ferromagnetic normal spinel Zinc Ferrite (ZFO). Despite the weak ferromagnetic behavior, the measurements of the SSE in ZFO show a thermoelectric voltage response comparable with the reported values for other ferromagnetic materials. Our results suggest that SSE might possibly originate from the surface magnetization of the ZFO.
Staggering towards a calculation of weak amplitudes
Sharpe, S.R.
1988-09-01
An explanation is given of the methods required to calculate hadronic matrix elements of the weak Hamiltonians using lattice QCD with staggered fermions. New results are presented for the 1-loop perturbative mixing of the weak interaction operators. New numerical techniques designed for staggered fermions are described. A preliminary result for the kaon B parameter is presented. 24 refs., 3 figs.
Fixing Employee Weaknesses: Addressing the Myth.
ERIC Educational Resources Information Center
Gilley, Jerry W.
2001-01-01
Suggests that human resources development professionals need to change their performance improvement focus and philosophy to embrace the importance of building on strengths and managing weaknesses. Identifies five characteristics indicative of employees' strengths. Describes seven strategies to help employees minimize their weaknesses while…
Crossing Institutional Boundaries: Writing Strengths and Weaknesses.
ERIC Educational Resources Information Center
Lumpkins, Julie
At any level, good writing requires an acknowledgment of writing strengths and weaknesses by both student and instructor. The four project collaborators/writing teachers outlined six specific areas on a teacher feedback sheet to note students' writing strengths and weaknesses; the areas of purpose, audience, thesis, development, organization, and…
Hieke, Andreas
2014-01-21
Unimolecular decay of sample ions imposes a limit on the usable laser fluence in matrix-assisted laser desorption/ionization (MALDI) ion sources. Traditionally, some modest degree of collisional sample ion cooling has been achieved by connecting MALDI ion sources directly to gas-filled radio frequency (RF) multipoles. It was also discovered in the early 1990s that gas-filled RF multipoles exhibit increased ion transmission efficiency due to collisional ion focusing effects. This unexpected experimental finding was later supported by elementary Monte Carlo simulations. Both experiments and simulations assumed a resting background gas with typical pressures of the order of 1 Pa. However, considerable additional improvements can be achieved if laser desorbed sample ions are introduced immediately after desorption, still within the ion source, in an axisymmetric rarefied supersonic gas jet with peak pressure of the order of 100 Pa and flow velocities >300 m/s, and under weak electric fields. We describe here the design principle and report performance data of an ion source coined “MALDI-2,” which incorporates elements of both rarefied aerodynamics and particle optics. Such a design allows superb suppression of metastable fragmentation due to rapid collisional cooling in <10 μs and nearly perfect injection efficiency into the attached RF ion guide, as numerous experiments have confirmed.
Hieke, Andreas
2014-01-21
Unimolecular decay of sample ions imposes a limit on the usable laser fluence in matrix-assisted laser desorption/ionization (MALDI) ion sources. Traditionally, some modest degree of collisional sample ion cooling has been achieved by connecting MALDI ion sources directly to gas-filled radio frequency (RF) multipoles. It was also discovered in the early 1990s that gas-filled RF multipoles exhibit increased ion transmission efficiency due to collisional ion focusing effects. This unexpected experimental finding was later supported by elementary Monte Carlo simulations. Both experiments and simulations assumed a resting background gas with typical pressures of the order of 1 Pa. However, considerable additional improvements can be achieved if laser desorbed sample ions are introduced immediately after desorption, still within the ion source, in an axisymmetric rarefied supersonic gas jet with peak pressure of the order of 100 Pa and flow velocities >300 m/s, and under weak electric fields. We describe here the design principle and report performance data of an ion source coined "MALDI-2," which incorporates elements of both rarefied aerodynamics and particle optics. Such a design allows superb suppression of metastable fragmentation due to rapid collisional cooling in <10 μs and nearly perfect injection efficiency into the attached RF ion guide, as numerous experiments have confirmed. PMID:25669372
Maximal Holevo Quantity Based on Weak Measurements
Wang, Yao-Kun; Fei, Shao-Ming; Wang, Zhi-Xi; Cao, Jun-Peng; Fan, Heng
2015-01-01
The Holevo bound is a keystone in many applications of quantum information theory. We propose “ maximal Holevo quantity for weak measurements” as the generalization of the maximal Holevo quantity which is defined by the optimal projective measurements. The scenarios that weak measurements is necessary are that only the weak measurements can be performed because for example the system is macroscopic or that one intentionally tries to do so such that the disturbance on the measured system can be controlled for example in quantum key distribution protocols. We evaluate systematically the maximal Holevo quantity for weak measurements for Bell-diagonal states and find a series of results. Furthermore, we find that weak measurements can be realized by noise and project measurements. PMID:26090962
Identical Quantum Particles and Weak Discernibility
NASA Astrophysics Data System (ADS)
Dieks, Dennis; Versteegh, Marijn A. M.
2008-10-01
Saunders has recently claimed that “identical quantum particles” with an anti-symmetric state (fermions) are weakly discernible objects, just like irreflexively related ordinary objects in situations with perfect symmetry (Black’s spheres, for example). Weakly discernible objects have all their qualitative properties in common but nevertheless differ from each other by virtue of (a generalized version of) Leibniz’s principle, since they stand in relations an entity cannot have to itself. This notion of weak discernibility has been criticized as question begging, but we defend and accept it for classical cases likes Black’s spheres. We argue, however, that the quantum mechanical case is different. Here the application of the notion of weak discernibility indeed is question begging and in conflict with standard interpretational ideas. We conclude that the introduction of the conceptual resource of weak discernibility does not change the interpretational status quo in quantum mechanics.
Persisting weakness after withdrawal of a statin.
Mygland, Åse; Ljøstad, Unn; Krossnes, Bård Kronen
2014-01-01
An 81-year-old woman treated with simvastatin for several years followed by atorvastatin for about 1 year presented with fatigue, weakness and unsteady gait. The finding of elevated creatine kinase (CK) and symmetric muscle weakness around shoulders and hips led to suspicion of a toxic statin-associated myopathy. Atorvastatin was withdrawn, but her weakness persisted. Owing to persisting weakness, an autoimmune myopathy (myositis) was suspected, but initially disregarded since a muscle biopsy showed necrotic muscle fibres without inflammatory cell infiltrates and myositis-specific autoantibodies were absent. After 18 months with slowly progressive weakness and increasing CK values, awareness of new knowledge about autoimmunity as a cause of necrotic myopathy, led to a successful treatment trial with intravenous immunoglobulines, followed by steroids and metothrexate. Antibodies to the target enzyme of statins (HMGCR (3-hydroksy-3-methylglutaryl-coenzyme A reductase)) were detected in her serum, and she was diagnosed with autoimmune necrotic myositis probably triggered by atorvastatin. PMID:24713712
Fully kinetic simulations of magnetic reconnction in semi-collisional plasmas
Daughton, William S; Roytershteyn, Vadim S; Albright, Brian J; Yin, Lin; Bowers, Kevin J; Karimabadi, Homa
2009-01-01
The influence of Coulomb collisions on the dynamics of magnetic reconnection is examined using fully kinetic simulations with a Monte-Carlo treatment of the Fokker-Planck collision operator. This powerful first-principles approach offers a bridge between kinetic and fluid regimes, which may prove useful for understanding the applicability of various fluid models. In order to lay the necessary groundwork, the collision algorithm is first carefully bench marked for a homogeneous plasma against theoretical predictions for beam-plasma interactions and electrical resistivity. Next, the collisional decay of a current layer is examined as a function of guide field, allowing direct comparisons with transport theory for the parallel and perpendicular resistivity as well as the thermoelectric force. Finally, the transition between collisional and collision less reconnection is examined in neutral sheet geometry. For modest Lundquist numbers S {approx}< 1000, a distinct transition is observed when the thickness of the Sweet-Parker layers falls below the ion inertia length {delta}{sub sp} {approx}< d,. At higher Lundquist number, deviations from the Sweet-Parker scaling are observed due to the growth of plasmoids (secondary-islands) within the elongated resistive layer. In certain cases, this instability leads to the onset of fast reconnection sooner than expected from {delta}{sub sp} {approx} d, condition. After the transition to fast reconnection, elongated electron current layers are formed which are unstable to the formation of new plasmoids. The structure and time-dependence of the electron diffusion region in these semi-collisional regimes is profoundly different than reported in two-fluid simulations.
Collisional evolution in the Eos and Koronis asteroid families - Observational and numerical results
NASA Technical Reports Server (NTRS)
Binzel, Richard P.
1988-01-01
The origin and evolution of the Eos and Koronis families are addressed by an analysis of Binzel's (1987) observational results. The Maxwellian distribution of the Eos family's rotation rates implies a collisionally-evolved population; these rates are also faster than those of the Koronis family and nonfamily asteroids. While the age of the Eos family may be comparable to the solar system's, that of the Koronis family could be considerably younger. Greater shape irregularity may account for the Koronis family's higher mean lightcurve amplitude.
Terahertz generation by two cross focused laser beams in collisional plasmas
Sharma, R. P. Singh, Ram Kishor
2014-07-15
The role of two cross-focused spatial-Gaussian laser beams has been studied for the high power and efficient terahertz (THz) radiation generation in the collisional plasma. The nonlinear current at THz frequency arises on account of temperature dependent collision frequency of electrons with ions in the plasma and the presence of a static electric field (applied externally in the plasma) and density ripple. Optimisation of laser-plasma parameters gives the radiated THz power of the order of 0.23 MW.
Collisional radiative model for heavy atoms in hot non-local-thermodynamical-equilibrium plasmas
NASA Astrophysics Data System (ADS)
Bar-Shalom, A.; Oreg, J.; Klapisch, M.
1997-07-01
A collisional radiative model for calculating non-local-thermodynamical-equilibrium (non-LTE) spectra of heavy atoms in hot plasmas has been developed, taking into account the numerous excited and autoionizing states. This model uses superconfigurations as effective levels with an iterative procedure which converges to the detailed configuration spectrum. The non-LTE opacities and emissivities may serve as a reliable benchmark for simpler on-line models in hydrodynamic code simulations. The model is tested against detailed configuration calculations of selenium and is applied to non-LTE optically thin plasma of lutetium.
Collisional Losses, Decoherence, and Frequency Shifts in Optical Lattice Clocks with Bosons
Lisdat, Ch.; Winfred, J. S. R. Vellore; Middelmann, T.; Riehle, F.; Sterr, U.
2009-08-28
We have quantified collisional losses, decoherence and the collision shift in a one-dimensional optical lattice clock on the highly forbidden transition {sup 1}S{sub 0}-{sup 3}P{sub 0} at 698 nm with bosonic {sup 88}Sr. We were able to distinguish two loss channels: inelastic collisions between atoms in the upper and lower clock state and atoms in the upper clock state only. Based on the measured coefficients, we determine the operation parameters at which a 1D-lattice clock with {sup 88}Sr shows no degradation due to collisions on the fractional uncertainty level of 10{sup -16}.
Spin waves and collisional frequency shifts of a trapped-atom clock.
Maineult, Wilfried; Deutsch, Christian; Gibble, Kurt; Reichel, Jakob; Rosenbusch, Peter
2012-07-13
We excite spin waves with spatially inhomogeneous Ramsey pulses and study the resulting frequency shifts of a chip-scale atomic clock of trapped 87Rb. The density-dependent frequency shifts of the hyperfine transition simulate the s-wave collisional frequency shifts of fermions, including those of optical lattice clocks. As the spin polarizations oscillate in the trap, the frequency shift reverses and it depends on the area of the second Ramsey pulse, exhibiting a predicted beyond mean-field frequency shift. Numerical and analytic models illustrate these observed behaviors. PMID:23030137
Broadening and collisional interference of lines in the IR spectra of ammonia. Theory
NASA Astrophysics Data System (ADS)
Cherkasov, M. R.
2016-06-01
The general theory of relaxation spectral shape parameters in the impact approximation (M. R. Cherkasov, J. Quant. Spectrosc. Radiat. Transfer 141, 73 (2014)) is adapted to the case of line broadening of infrared spectra of ammonia. Specific features of line broadening of parallel and perpendicular bands are discussed. It is shown that in both cases the spectrum consists of independently broadened singlets and doublets; however, the components of doublets can be affected by collisional interference. The paper is the first part of a cycle of studies devoted to the problems of spectral line broadening of ammonia.
NASA Technical Reports Server (NTRS)
Herman, R. M.
1983-01-01
A general theory of atomic dipole coherence under the influence of collisional phase changes, inelastic effects and optically active atom velocity changes, including those due to anisotropic interactions is presented. Velocity change effects are obtained in closed form. Line shapes appear as convolutions of standard pressure broadening contours with velocity-change contours. Width and shift parameters for the He-broadened Na D lines at 2 m bar pressure, 380 K are calculated, as are He-induced photon echo decay rates for these lines. Overall agreement with xperiment is reasonably good.
A one-dimensional collisional model for plasma-immersion ion implantation
Vahedi, V.; Lieberman, M.A.; Alves, M.V.; Verboncoeur, J.P.; Birdsall, C.K. )
1991-02-15
Plasma-immersion ion implantation (also known as plasma-source ion implantation) is a process in which a target is immersed in a plasma and a series of large negative-voltage pulses are applied to it to extract ions from the plasma and implant them into the target. A general one-dimensional model is developed to study this process in different coordinate systems for the case in which the pressure of the neutral gas is large enough that the ion motion in the sheath can be assumed to be highly collisional.
Campanell, M D; Khrabrov, A V; Kaganovich, I D
2012-06-01
A condition for sheath instability due to secondary electron emission (SEE) is derived for low collisionality plasmas. When the SEE coefficient of the electrons bordering the depleted loss cone in energy space exceeds unity, the sheath potential is unstable to a negative perturbation. This result explains three different instability phenomena observed in Hall thruster simulations including a newly found state with spontaneous ∼20 MHz oscillations. When instabilities occur, the SEE propagating between the walls becomes the dominant contribution to the particle flux, energy loss and axial transport. PMID:23003962
Diagnosing on plasma plume from xenon Hall thruster with collisional-radiative model
Yang Juan; Yokota, Shigeru; Kaneko, Ryotaro; Komurasaki, Kimiya
2010-10-15
The collisional-radiative model for xenon is used to calculate the electron density and temperature, and the atom population distribution in the plasma plume from a xenon Hall thruster. In the calculation, 173 levels of atom population are considered; only the processes of electron induced excitation and deexcitation, and spontaneous decay are simulated. The plasma plume is assumed to be optically thin. Consequently, the reasonable parameters of plasma plume along the outside center line of the thruster channel are obtained by making the calculated emission spectrum corresponding to measured ones and based on the atomic data available on site and by codes.
M.C. Campanell, A. Khrabrov and I Kaganovich
2012-05-11
A condition for sheath instability due to secondary electron emission (SEE) is derived for low collisionality plasmas. When the SEE coefficient of the electrons bordering the depleted loss cone in energy space exceeds unity, the sheath potential is unstable to a negative perturbation. This result explains three different instability phenomena observed in Hall thruster simulations including a newly found state with spontaneous ~20MHz oscillations. When instabilities occur, the SEE propagating between the walls becomes the dominant contribution to the particle flux, energy loss and axial transport.
Current-driven dust ion-acoustic instability in a collisional dusty plasma
Merlino, R.L.
1997-02-01
A fluid analysis of the excitation of dust ion-acoustic (DIA) waves in a collisional dusty plasma is presented. The DIA waves are excited by a relative drift of the electrons and ions produced by a steady-state electric field applied to the plasma. The DIA instability is more easily excited if the relative concentration of negatively charged dust is increased. The current interest in dusty plasmas is due to the realization of their importance in various astrophysical and geophysical environments (e.g., interstellar space, comet tails, planetary ring systems, and the polar mesosphere) as well as in industrial plasma processing devices used in semiconductor manufacturing.
A study of the collisional dynamics for collisions of UF6(-) atoms and molecules
NASA Astrophysics Data System (ADS)
Champion, R. L.; Doverspike, L. D.
1981-08-01
Absolute total cross sections for the collisional decomposition of the negative ion of Uranium Hexafluoride have been measured for laboratory collision energies up to 500 eV. The results have been analyzed with a statistical theory of unimolecular decomposition. By varying the temperature of the carbon surface upon which the negative ions are created, the average initial internal energy in the negative molecular ion can be selected. Experiments performed with 'hot' negative molecular ions indicate larger decomposition cross sections and lower energy thresholds when compared to results for 'cold' negative molecular ions.
NASA Astrophysics Data System (ADS)
Niknam, A. R.; Banjafar, M. R.; Jahangiri, F.; Barzegar, S.; Massudi, R.
2016-05-01
Terahertz (THz) radiation generation by the interaction of two co-propagating high intensity laser beams with a warm collisional inhomogeneous plasma is analytically investigated. By presenting the dielectric permittivity of plasma and taking into account the ponderomotive force, the nonlinear current at THz frequency is obtained. A secondary resonant enhancement of THz radiation is observed, in addition to that occurs at the plasma frequency, which can be tuned by plasma density and temperature. Moreover, we show that for each beat frequency, there exists an optimum temperature at which THz radiation is maximized. It is also shown that the power and efficiency of THz radiation decrease by increasing the collision frequency.
Kinetic approach for the ion drag force in a collisional plasma
Ivlev, A.V.; Zhdanov, S.K.; Khrapak, S.A.; Morfill, G.E.
2005-01-01
The linear kinetic approach to calculate the ion drag force in a collisional plasma is generalized. The model collision integral (for ion-neutral collisions) is discussed and employed to calculate the plasma response for arbitrary velocity of the plasma flow and arbitrary frequency of the collisions. The derived plasma response is used to calculate the self-consistent force on the test charged particle. The obtained results are compared to those of the traditional pair collision approach, and the importance of the self-consistent kinetic consideration is highlighted. In conclusion, the applicability of the proposed approach is discussed.
Dipolar vortices and collisional instability in rotating electron-positron-ion plasmas
Haque, Q.
2011-11-15
Linear dispersion relation of electrostatic waves is derived for rotating electron-positron-ion (e-p-i) plasmas. The role of the rotational plasma frequency on drift wave through Coriolis force in the pulsar magnetosphere is discussed. This wave can couple with acoustic mode. In the nonlinear regime, stationary solution in the form of dipolar vortices is obtained. At the end we have also found the collisional instability in the presence of neutral-ion collisions for this rotating e-p-i plasma. The importance of the study with respect to astrophysical plasmas is also pointed out.
Role of collisional broadening in Monte Carlo simulations of terahertz quantum cascade lasers
Matyas, Alpar; Lugli, Paolo; Jirauschek, Christian
2013-01-07
Using a generalized version of Fermi's golden rule, collisional broadening is self-consistently implemented into ensemble Monte Carlo carrier transport simulations, and its effect on the transport and optical properties of terahertz quantum cascade lasers is investigated. The inclusion of broadening yields improved agreement with the experiment, without a significant increase of the numerical load. Specifically, this effect is crucial for a correct modeling at low biases. In the lasing regime, broadening can lead to significantly reduced optical gain and output power, affecting the obtained current-voltage characteristics.
Asteroid 4 Vesta: Dynamical and collisional evolution during the Late Heavy Bombardment
NASA Astrophysics Data System (ADS)
Pirani, S.; Turrini, D.
2016-06-01
Asteroid 4 Vesta is the only currently identified asteroid for which we possess samples in the form of meteorites. These meteorites revealed us that Vesta is a differentiated body and that its differentiation produced a relatively thin basaltic crust that survived intact over its entire collisional history. The survival of the vestan basaltic crust has long been identified as a pivotal constraint in the study of the evolution of the asteroid belt and the Solar System but, while we possess a reasonably good picture of the effects of the last 4 Ga on such a crust, little is known about the effects of earlier events like the Late Heavy Bombardment. In this work we address this gap in our knowledge by simulating the Late Heavy Bombardment on Vesta in the different dynamical scenarios proposed for the migration of the giant planets in the broad framework of the Nice Model. The results of the simulations allowed us to assess the collisional history of the asteroid during the Late Heavy Bombardment in terms of produced crater population, surface saturation, mass loss and mass gain of Vesta and number of energetic or catastrophic impacts. Our results reveal that planet-planet scattering is a dynamically favorable migration mechanism for the survival of Vesta and its crust. The number of impacts of asteroids larger than about 1 km in diameter estimated as due to the LHB is 31 ± 5, i.e. about 5 times larger than the number of impacts that would have occurred in an unperturbed main belt in the same time interval. The contribution of a possible extended belt to the collisional evolution of Vesta during the LHB is quite limited and can be quantified in 2 ± 1 impacts of asteroids with diameter greater than or equal to 1 km. The chance of energetic and catastrophic impacts is less than 10% and is compatible with the absence of giant craters dated back to 4 Ga ago and with the survival of the asteroid during the Late Heavy Bombardment. The mass loss caused by the bombardment
Self-focusing of intense high frequency electromagnetic waves in a collisional magnetoactive plasma
Niknam, A. R.; Hashemzadeh, M.; Aliakbari, A.; Majedi, S.; Haji Mirzaei, F.
2011-11-15
The self-focusing of an intense electromagnetic beam in a collisional magnetoactive plasma has been investigated by the perturbation method. Considering the relativistic and ponderomotive nonlinearities and the first three terms of perturbation expansion for the electron density and velocity, the nonlinear wave equation is obtained. This wave equation is solved by applying the source dependent expansion method and the evolution of electromagnetic beam spot-size is discussed. It is shown that the laser spot-size decreases with increasing the collision frequency and external magnetic field strength.
1.8 Ga Svecofennian post-collisional shoshonitic magmatism in the Fennoscandian shield
NASA Astrophysics Data System (ADS)
Eklund, O.; Konopelko, D.; Rutanen, H.; Fröjdö, S.; Shebanov, A. D.
1998-12-01
At least 14 small (1-11 km across) 1.8 Ga Svecofennian post-collisional bimodal intrusions occur in southern Finland and Russian Karelia in a 600-km-long belt from the Åland Islands to the NW Lake Ladoga region. The rocks range from ultramafic, calc-alkaline, apatite-rich potassium lamprophyres to peraluminous HiBaSr granites, and form a shoshonitic series with K 2O+Na 2O>5%, K 2O/Na 2O>0.5, Al 2O 3>9% over a wide spectrum of SiO 2 (32-78%). Although strongly enriched in all rocks, the LILE Ba and Sr and the LREE generally define a decreasing trend with increasing SiO 2. Depletion is noted for HFSE Ti, Nb and Ta. Available isotopic data show overlapping values for lamprophyres and granites within separate intrusions and a cogenetic origin is thus not precluded. Initial magmas (Mg#>65) in this shoshonitic association are considered to be generated in an enriched lithospheric mantle during post-collisional uplift some 30 Ma after the regional Svecofennian metamorphic peak. However, prior to the melting episode, the lithospheric mantle was affected by carbonatite metasomatism; more extensively in the east than in the west. The melts generated in the more carbonate-rich mantle are extremely enriched in P 2O 5˜4%, F˜12,000 ppm, LILE: Ba˜9000 ppm, Sr˜7000 ppm, LREE: La˜600 ppm and Ce˜1000 ppm. The parental magma underwent 55-60% fractionation of biotite+clinopyroxene+apatite+magnetite+sphene whereupon intermediate varieties were produced. After further fractionation, 60-80%, of K-feldspar+amphibole+plagioclase±(minor magnetite, sphene and apatite), leucosyenites and quartz-monzonites were formed. In the west, where the source was less affected by carbonatite metasomatism, calc-alkaline lamprophyres (vogesites, minettes and spessartites) and equivalent plutonic rocks (monzonites) were formed. Removal of about 50% of biotite, amphibole, plagioclase, magnetite, apatite and sphene produced peraluminous HiBaSr granites. The impact of crustal assimilation is considered
Merritt, Elizabeth C. Adams, Colin S.; Moser, Auna L.; Hsu, Scott C. Dunn, John P.; Miguel Holgado, A.; Gilmore, Mark A.
2014-05-15
We report spatially resolved measurements of the oblique merging of two supersonic laboratory plasma jets. The jets are formed and launched by pulsed-power-driven railguns using injected argon, and have electron density ∼10{sup 14} cm{sup −3}, electron temperature ≈1.4 eV, ionization fraction near unity, and velocity ≈40 km/s just prior to merging. The jet merging produces a few-cm-thick stagnation layer, as observed in both fast-framing camera images and multi-chord interferometer data, consistent with collisional shock formation [E. C. Merritt et al., Phys. Rev. Lett. 111, 085003 (2013)].
Nonlinear Interaction of Elliptical Laser Beam with Collisional Plasma: Effect of Linear Absorption
NASA Astrophysics Data System (ADS)
Keshav, Walia; Sarabjit, Kaur
2016-01-01
In the present work, nonlinear interaction of elliptical laser beam with collisional plasma is studied by using paraxial ray approximation. Nonlinear differential equations for the beam width parameters of semi-major axis and semi-minor axis of elliptical laser beam have been set up and solved numerically to study the variation of beam width parameters with normalized distance of propagation. Effects of variation in absorption coefficient and plasma density on the beam width parameters are also analyzed. It is observed from the analysis that extent of self-focusing of beam increases with increase/decrease in plasma density/absorption coefficient.
Kinetic theory of low-frequency cross-field instability in a weakly ionized plasma. I
Dimant, Y.S.; Sudan, R.N.
1995-04-01
A consistent kinetic theory is developed for the description of electrons under conditions of a low-frequency two-stream {bold E}{times}{bold B} instability in collisionally dominated, weakly ionized plasmas. Starting from the Boltzmann collision integral, a simplified kinetic equation for the electron distribution function has been derived, which takes into account strong pitch-angle scattering of electrons by neutrals, velocity dependence of the electron--neutral collision frequency, etc. Linearized equations describing small oscillations of the electron distribution function and ion density are presented. For the asymptotic case of short waves, the dispersion relation of the {bold E}{times}{bold B} instability has been obtained and analyzed under conditions typical for the lower ionosphere. Under certain conditions, the rigorous kinetic consideration yields substantial changes in results compared to previous theories. The general approach may be applied to other linear and nonlinear low-frequency processes in a weakly ionized plasma. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.
Spectrum of Mathematical Weaknesses: Related Neuropsychological Correlates.
Perna, Robert; Loughan, Ashlee R; Le, Jessica; Hertza, Jeremy; Cohen, Morris J
2015-01-01
Math disorders have been recognized for as long as language disorders yet have received far less research. Mathematics is a complex construct and its development may be dependent on multiple cognitive abilities. Several studies have shown that short-term memory, working memory, visuospatial skills, processing speed, and various language skills relate to and may facilitate math development and performance. The hypotheses explored in this research were that children who performed worse on math achievement than on Full-Scale IQ would exhibit weaknesses in executive functions, memory, and visuoperceptual skills. Participants included 436 children (27% girls, 73% boys; age range = 5-17 years, M(age) = 9.45 years) who were referred for neuropsychological evaluations due to academic and/or behavioral problems. This article specifically focuses on the spectrum of math weakness rather than clinical disability, which has yet to be investigated in the literature. Results suggest that children with relative weakness to impairments in math were significantly more likely to have cognitive weaknesses to impairments on neuropsychological variables, as compared with children without math weaknesses. Specifically, the math-weak children exhibit a weakness to impairment on measures involving attention, language, visuoperceptual skills, memory, reading, and spelling. Overall, our results suggest that math development is multifaceted. PMID:25117216
Weak Measurements Destroy Too Much Quantum Correlation
NASA Astrophysics Data System (ADS)
Wu, Shao-xiong; Zhang, Jun; Yu, Chang-shui; Song, He-shan
2016-01-01
The quantum correlation under weak measurements is studied via skew information. For 2 × d-dimensional states, it can be given by a closed form which linearly depends on the quantum correlation [EPL. 107 (2014) 10007] determined by the strength of the weak measurement. It is found that the quantum correlation under weak measurements only captures partial quantumness of the state. In particular, the extraction of the residual quantumness by the latter measurements will inevitably destroy too much quantumness. To demonstration, the Werner state is given as an example.