Nonlinear regimes of forced magnetic reconnection
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Vekstein, G., E-mail: g.vekstein@manchester.ac.uk [JBCA, School of Physics and Astronomy, University of Manchester, Manchester M13 9PL (United Kingdom); STEL, Nagoya University, Nagoya, Aichi 464-8601 (Japan); Kusano, K. [STEL, Nagoya University, Nagoya, Aichi 464-8601 (Japan)
2015-09-15
This letter presents a self-consistent description of nonlinear forced magnetic reconnection in Taylor's model of this process. If external boundary perturbation is strong enough, nonlinearity in the current sheet evolution becomes important before resistive effects come into play. This terminates the current sheet shrinking that takes place at the linear stage and brings about its nonlinear equilibrium with a finite thickness. Then, in theory, this equilibrium is destroyed by a finite plasma resistivity during the skin-time, and further reconnection proceeds in the Rutherford regime. However, realization of such a scenario is unlikely because of the plasmoid instability, which is fast enough to develop before the transition to the Rutherford phase occurs. The suggested analytical theory is entirely different from all previous studies and provides proper interpretation of the presently available numerical simulations of nonlinear forced magnetic reconnection.
Reconnection Rate in Collisionless Magnetic Reconnection under Open Boundary Conditions
Institute of Scientific and Technical Information of China (English)
HUANG Jun; MA Zhi-Wei
2008-01-01
Collisionless magnetic reconnection is studied by using two-dimensional Darwin particle-in-cell simulations with different types of open boundary conditions.The simulation results indicate that reconnection rates are strongly dependent on the imposed boundary conditions of the magnetic field Bx in the inward side. Under the zerogradient Bx boundary condition,the reconnection rate quickly decreases after reaching its maximum and no steady-state is found.Under both electromagnetic and magnetosonic boundary conditions,the system can reach a quasi-steady state.However,the reconnection rate Er≈ 0.08 under the electromagnetic boundary condition is weaker than Er≈ 0.13 under the magnetosonic boundary condition.
Nonlinear Acceleration Mechanism of Collisionless Magnetic Reconnection
Hirota, M; Ishii, Y; Yagi, M; Aiba, N
2012-01-01
A mechanism for fast magnetic reconnection in collisionless plasma is studied for understanding sawtooth collapse in tokamak discharges. Nonlinear growth of the tearing mode driven by electron inertia is analytically estimated by invoking the energy principle for the first time. Decrease of potential energy in the nonlinear regime (where the island width exceeds the electron skin depth) is found to be steeper than in the linear regime, resulting in acceleration of the reconnection. Release of free energy by such ideal fluid motion leads to unsteady and strong convective flow, which theoretically corroborates the inertia-driven collapse model of the sawtooth crash [D. Biskamp and J. F. Drake, Phys. Rev. Lett. 73, 971 (1994)].
Nonlinear magnetic reconnection in low collisionality plasmas
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Ottaviani, M. [Commission of the European Communities, Abingdon (United Kingdom). JET Joint Undertaking; Porcelli, F. [Politecnico di Torino, Turin (Italy)
1994-07-01
The magnetic reconnection in collisionless regimes, where electron inertia is responsible for the decoupling of the plasma motion from that of the field lines, is discussed. Since the linear theory of m=1 modes breaks down for very small magnetic island widths, a non linear analysis is called for. Thus, the behaviour of a collisionless, 2-D fluid slab model in the limit {rho}/d -> 0, is analyzed. The main result is that, when the island size is larger than the linear layer but smaller than the equilibrium scale length, the reconnection rate exhibits a quasi-explosive time behaviour, during which a current density sub-layer narrower than the skin depth is formed. It is believed that the inclusion of the electron initial term in Ohm`s law opens the possibility to understand the rapidity of relaxation process observed in low collisionality plasmas. 7 refs., 6 figs.
New Expression for Collisionless Magnetic Reconnection Rate
Klimas, Alexander J.
2014-01-01
For 2D, symmetric, anti-parallel, collisionless magnetic reconnection, a new expression for the reconnection rate in the electron diffusion region is introduced. It is shown that this expression can be derived in just a few simple steps from a physically intuitive starting point; the derivation is given in its entirety and the validity of each step is confirmed. The predictions of this expression are compared to the results of several long-duration, open-boundary PIC reconnection simulations to demonstrate excellent agreement.
On the Value of the Reconnection Rate
Comisso, Luca
2016-01-01
Numerical simulations have consistently shown that the reconnection rate in certain collisionless regimes can be fast, on the order of $0.1 v_A B_u$, where $v_A$ and $B_u$ are the Alfv\\'en speed and the reconnecting magnetic field upstream of the ion diffusion region. This particular value has been reported in myriad numerical simulations under disparate conditions. However, despite decades of research, the reasons underpinning this specific value remain mysterious. Here, we present an overview of this problem and discuss the conditions under which the "0.1 value" is attained. Furthermore, we explain why this problem should be interpreted in terms of the ion diffusion region length.
Magnetic reconnection rate in space plasmas: a fractal approach.
Materassi, Massimo; Consolini, Giuseppe
2007-10-26
Magnetic reconnection is generally discussed via a fluid description. Here, we evaluate the reconnection rate assuming a fractal topology of the reconnection region. The central idea is that the fluid hypothesis may be violated at the scales where reconnection takes place. The reconnection rate, expressed as the Alfvén Mach number of the plasma moving toward the diffusion region, is shown to depend on the fractal dimension and on the sizes of the reconnection or diffusion region. This mechanism is more efficient than prediction of the Sweet-Parker model and even Petschek's model for finite magnetic Reynolds number. A good agreement also with rates given by Hall MHD models is found. A discussion of the fractal assumption on the diffusion region in terms of current microstructures is proposed. The comparison with in-situ satellite observations suggests the reconnection region to be a filamentary domain.
Beidler, M. T.; Cassak, P. A.; Jardin, S. C.; Ferraro, N. M.
2017-02-01
We diagnose local properties of magnetic reconnection during a sawtooth crash employing the three-dimensional toroidal, extended-magnetohydrodynamic (MHD) code M3D-C1. To do so, we sample simulation data in the plane in which reconnection occurs, the plane perpendicular to the helical (m,n)=(1,1) mode at the q = 1 surface, where m and n are the poloidal and toroidal mode numbers and q is the safety factor. We study the nonlinear evolution of a particular test equilibrium in a non-reduced field representation using both resistive-MHD and extended-MHD models. We find growth rates for the extended-MHD reconnection process exhibit a nonlinear acceleration and greatly exceed that of the resistive-MHD model, as is expected from previous experimental, theoretical, and computational work. We compare the properties of reconnection in the two simulations, revealing the reconnecting current sheets are locally different in the two models and we present the first observation of the quadrupole out-of-plane Hall magnetic field that appears during extended-MHD reconnection in a 3D toroidal simulation (but not in resistive-MHD). We also explore the dependence on toroidal angle of the properties of reconnection as viewed in the plane perpendicular to the helical magnetic field, finding qualitative and quantitative effects due to changes in the symmetry of the reconnection process. This study is potentially important for a wide range of magnetically confined fusion applications, from confirming simulations with extended-MHD effects are sufficiently resolved to describe reconnection, to quantifying local reconnection rates for purposes of understanding and predicting transport, not only at the q = 1 rational surface for sawteeth, but also at higher order rational surfaces that play a role in disruptions and edge-confinement degradation.
Does the Rate of Collisionless Magnetic Reconnection Depend on the Dissipation Mechanism?
Aunai, Nicolas; Hesse, Michael; Black, Carrie; Evans, Rebekah; Kuznetsova, Maria
2012-01-01
The importance of the electron dissipation effect on the reconnection rate is investigated in the general case of asymmetric collisionless magnetic reconnection. Contrary to the standard collisionless reconnection model, it is found that the reconnection rate, and the macroscopic evolution of the reconnecting system, crucially depend on the nature of the dissipation mechanism and that the Hall effect alone is not able to sustain fast reconnection.
The local dayside reconnection rate for oblique interplanetary magnetic fields
Komar, Colin M
2016-01-01
We present an analysis of local properties of magnetic reconnection at the dayside magnetopause for various interplanetary magnetic field (IMF) orientations in global magnetospheric simulations. This has heretofore not been practical because it is difficult to locate where reconnection occurs for oblique IMF, but new techniques make this possible. The approach is to identify magnetic separators, the curves separating four regions of differing magnetic topology, which map the reconnection X-line. The electric field parallel to the X-line is the local reconnection rate. We compare results to a simple model of local two-dimensional asymmetric reconnection. To do so, we find the plasma parameters that locally drive reconnection in the magnetosheath and magnetosphere in planes perpendicular to the X-line at a large number of points along the X-line. The global magnetohydrodynamic simulations are from the three-dimensional Block-Adaptive, Tree Solarwind Roe-type Upwind Scheme (BATS-R-US) code with a uniform resisti...
Finite Larmor radius effects in the nonlinear dynamics of collisionless magnetic reconnection
Energy Technology Data Exchange (ETDEWEB)
Del Sarto, D [Institut Jean Lamour, UMR 7198 CNRS-Nancy University, Campus Victor Grignard - BP 70239, 54506 Vandoeuvre-les-Nancy Cedex (France); Marchetto, C [Associazione EURATOM-ENEA sulla Fusione, IFP-CNR, Via R. Cozzi 53, 20125 Milano (Italy); Pegoraro, F; Califano, F, E-mail: daniele.delsarto@ijl.nancy-universite.fr, E-mail: marchetto@ifp.cnr.it, E-mail: pegoraro@df.unipi.it, E-mail: califano@df.unipi.it [Physics Department and CNISM, Pisa University, Largo Pontecorvo 3, 56127 Pisa (Italy)
2011-03-15
We provide numerical evidence of the role of finite Larmor radius effects in the nonlinear dynamics of magnetic field line reconnection in high-temperature, strong guide field plasmas in a slab configuration, in the large {Delta}' regime. Both ion and electron temperature effects introduce internal energy variations related to mechanical compression terms in the energy balance, thus contributing to regularize the gradients of the ion density with respect to the cold regimes. For values of the Larmor radii that are not asymptotically small, the two temperature effects are no longer interchangeable, in contrast to what is expected from linear theory, and the differences are measurable in the numerical growth rates and in the nonlinear evolution of the density layers. We interpret such differences in terms of the change, due to ion temperature effects, of the Lagrangian advection of the 'plasma invariants' that are encountered in the cold-ion, warm-electron regime. The different roles of the ion and ion-sound Larmor radii in the reconnection dynamics near the X- and O-points are evidenced by means of a local quadratic expansion of the fields.
Energy Technology Data Exchange (ETDEWEB)
Wendel, D. E.; Olson, D. K.; Hesse, M.; Kuznetsova, M.; Adrian, M. L. [NASA Goddard Space Flight Center, Greenbelt, Maryland 20771 (United States); Aunai, N. [Institute for Research in Astrophysics and Planetology, University Paul Sabatier, Toulouse (France); Karimabadi, H. [SciberQuest, Inc., Del Mar, California 92014 (United States); Department of Computer and Electrical Engineering, University of California, San Diego, La Jolla, California 92093 (United States); Daughton, W. [Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)
2013-12-15
We investigate the distribution of parallel electric fields and their relationship to the location and rate of magnetic reconnection in a large particle-in-cell simulation of 3D turbulent magnetic reconnection with open boundary conditions. The simulation's guide field geometry inhibits the formation of simple topological features such as null points. Therefore, we derive the location of potential changes in magnetic connectivity by finding the field lines that experience a large relative change between their endpoints, i.e., the quasi-separatrix layer. We find a good correspondence between the locus of changes in magnetic connectivity or the quasi-separatrix layer and the map of large gradients in the integrated parallel electric field (or quasi-potential). Furthermore, we investigate the distribution of the parallel electric field along the reconnecting field lines. We find the reconnection rate is controlled by only the low-amplitude, zeroth and first–order trends in the parallel electric field while the contribution from fluctuations of the parallel electric field, such as electron holes, is negligible. The results impact the determination of reconnection sites and reconnection rates in models and in situ spacecraft observations of 3D turbulent reconnection. It is difficult through direct observation to isolate the loci of the reconnection parallel electric field amidst the large amplitude fluctuations. However, we demonstrate that a positive slope of the running sum of the parallel electric field along the field line as a function of field line length indicates where reconnection is occurring along the field line.
The dependence of cusp ion signatures on the reconnection rate
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S. K. Morley
Full Text Available The interpretation of structure in cusp ion dispersions is important for helping to understand the temporal and spatial structure of magnetopause reconnection. "Stepped" and "sawtooth" signatures have been shown to be caused by temporal variations in the reconnection rate under the same physical conditions for different satellite trajectories. The present paper shows that even for a single satellite path, a change in the amplitude of any reconnection pulses can alter the observed signature and even turn sawtooth into stepped forms and vice versa. On 20 August 1998, the Defense Meteorological Satellite Program (DMSP craft F-14 crossed the cusp just to the south of Longyearbyen, returning on the following orbit. The two passes by the DMSP F-14 satellites have very similar trajectories and the open-closed field line boundary (OCB crossings, as estimated from the SSJ/4 precipitating particle data and Polar UVI images, imply a similarly-shaped polar cap, yet the cusp ion dispersion signatures differ substantially. The cusp crossing at 08:54 UT displays a stepped ion dispersion previously considered to be typical of a meridional pass, whereas the crossing at 10:38 UT is a sawtooth form ion dispersion, previously considered typical of a satellite travelling longitudinally with respect to the OCB. It is shown that this change in dispersed ion signature is likely to be due to a change in the amplitude of the pulses in the reconnection rate, causing the stepped signature. Modelling of the low-energy ion cutoff under different conditions has reproduced the forms of signature observed.
Key words. Ionosphere (particle precipitation Magnetospheric physics (energetic particles, precipitating, magnetopause, cusp and boundary layers
Why does steady-state magnetic reconnection have a maximum local rate of order 0.1?
Liu, Yi-Hsin; Guo, F; Daughton, W; Li, H; Cassak, P A; Shay, M A
2016-01-01
Simulations suggest collisionless steady-state magnetic reconnection of Harris-type current sheets proceeds with a rate of order 0.1, independent of dissipation mechanism. We argue this long-standing puzzle is a result of constraints at the magnetohydrodynamic (MHD) scale. We perform a scaling analysis of the reconnection rate as a function of the opening angle made by the upstream magnetic fields, finding a maximum reconnection rate close to 0.2. The predictions compare favorably to particle-in-cell simulations of relativistic electron-positron and non-relativistic electron-proton reconnection. The fact that simulated reconnection rates are close to the predicted maximum suggests reconnection proceeds near the most efficient state allowed at the MHD-scale. The rate near the maximum is relatively insensitive to the opening angle, potentially explaining why reconnection has a similar fast rate in differing models.
Multiple Spacecraft Study of the Impact of Turbulence on Reconnection Rates
Wendel, Deirdre; Goldstein, Melvyn; Figueroa-Vinas, Adolfo; Adrian, Mark; Sahraoui, Fouad
2011-01-01
Magnetic turbulence and secondary island formation have reemerged as possible explanations for fast reconnection. Recent three-dimensional simulations reveal the formation of secondary islands that serve to shorten the current sheet and increase the accelerating electric field, while both simulations and observations witness electron holes whose collapse energizes electrons. However, few data studies have explicitly investigated the effect of turbulence and islands on the reconnection rate. We present a more comprehensive analysis of the effect of turbulence and islands on reconnection rates observed in space. Our approach takes advantage of multiple spacecraft to find the location of the spacecraft relative to the inflow and the outflow, to estimate the reconnection electric field, to indicate the presence and size of islands, and to determine wave vectors indicating turbulence. A superposed epoch analysis provides independent estimates of spatial scales and a reconnection electric field. We apply k-filtering and a new method adopted from seismological analyses to identify the wavevectors. From several case studies of reconnection events, we obtain preliminary estimates of the spectral scaling law, identify wave modes, and present a method for finding the reconnection electric field associated with the wave modes.
A model of global magnetic reconnection rate in relativistic collisionless plasmas
Liu, Yi-Hsin; Guo, Fan; Daughton, William; Li, Hui
2016-01-01
A model of global magnetic reconnection rate in relativistic collisionless plasmas is developed and validated by the fully kinetic simulation. Through considering the force balance at the upstream and downstream of the diffusion region, we show that the global rate is bounded by a value $\\sim 0.3$ even when the local rate goes up to $\\sim O(1)$ and the local inflow speed approaches the speed of light in strongly magnetized plasmas. The derived model is general and can be applied to magnetic reconnection under widely different circumstances.
Magnetic Reconnection Rates and Energy Release in a Confined X-class Flare
Veronig, A M
2015-01-01
We study the energy-release process in the confined X1.6 flare that occurred on 22 October 2014 in AR 12171. Magnetic-reconnection rates and reconnection fluxes are derived from three different data sets: space-based data from the Atmospheric Imaging Assembly (AIA) 1600 {\\AA} filter onboard the Solar Dynamics Observatory (SDO) and ground-based H$\\alpha$ and Ca II K filtergrams from Kanzelh\\"ohe Observatory. The magnetic-reconnection rates determined from the three data sets all closely resemble the temporal profile of the hard X-rays measured by the Ramaty High Energy Solar Spectroscopic Imager (RHESSI), which are a proxy for the flare energy released into high-energy electrons. The total magnetic-reconnection flux derived lies between $4.1 \\times 10^{21}$ Mx (AIA 1600 {\\AA}) and $7.9 \\times 10^{21}$ Mx (H$\\alpha$), which corresponds to about 2 to 4% of the total unsigned flux of the strong source AR. Comparison of the magnetic-reconnection flux dependence on the GOES class for 27 eruptive events collected fr...
The Rate of Flux Pile-up Magnetic Reconnection in the Solar Corona
Litvinenko, Y. E.
2000-05-01
The rate of two-dimensional flux pile-up magnetic reconnection is known to be severely limited by gas pressure in a low-beta plasma of the solar corona. For a two-dimensional stagnation point flow with nonzero vorticity, for example, the rate cannot exceed the Sweet-Parker scaling. The limitation should be less restrictive, however, for three-dimensional flux pile-up. This paper examines the maximum rate of three-dimensional pile-up reconnection in the approximation of reduced magnetohydrodynamics (RMHD), which is valid in the solar coronal loops. Gas pressure effects are ignored in RMHD, but a similar limitation on the rate of magnetic merging exists. Both the magnetic energy dissipation rate and the reconnection electric field are shown to increase by several orders of magnitude in RMHD as compared with strictly two-dimensional pile-up. This is enough to explain small solar flares and slow coronal transients with energy release rates of order 1025 - 1026 erg s-1, as well as heating of quiet coronal loops. Notably, the reconnection electric field is several orders of magnitude greater than the Dreicer field, hence it can efficiently accelerate charged particles in flares. This work was supported by NSF grant ATM-9813933.
Electron self-reinforcing process of magnetic reconnection.
Wan, Weigang; Lapenta, Giovanni
2008-07-04
The growth of collisionless magnetic reconnection is discovered to be a nonlinear electron self-reinforcing process. Accelerated by the reconnection electric field, the small portion of energetic electrons in the vicinity of the X point are found to be the cause of the fast reconnection rate. This new mechanism explains that recent simulation results of different reconnection evolutions (i.e., steady state, quasisteady state, or nonsteady state) are essentially determined by the availability of feeding plasma inflows. Simulations are carried out with open boundary conditions.
Three-dimensional Spontaneous Magnetic Reconnection
Beresnyak, Andrey
2017-01-01
Magnetic reconnection is best known from observations of the Sun where it causes solar flares. Observations estimate the reconnection rate as a small, but non-negligible fraction of the Alfvén speed, so-called fast reconnection. Until recently, the prevailing pictures of reconnection were either of resistivity or plasma microscopic effects, which was contradictory to the observed rates. Alternative pictures were either of reconnection due to the stochasticity of magnetic field lines in turbulence or the tearing instability of the thin current sheet. In this paper we simulate long-term three-dimensional nonlinear evolution of a thin, planar current sheet subject to a fast oblique tearing instability using direct numerical simulations of resistive-viscous magnetohydrodynamics. The late-time evolution resembles generic turbulence with a ‑5/3 power spectrum and scale-dependent anisotropy, so we conclude that the tearing-driven reconnection becomes turbulent reconnection. The turbulence is local in scale, so microscopic diffusivity should not affect large-scale quantities. This is confirmed by convergence of the reconnection rate toward ∼ 0.015{v}{{A}} with increasing Lundquist number. In this spontaneous reconnection, with mean field and without driving, the dissipation rate per unit area also converges to ∼ 0.006ρ {v}{{A}}3, and the dimensionless constants 0.015 and 0.006 are governed only by self-driven nonlinear dynamics of the sheared magnetic field. Remarkably, this also means that a thin current sheet has a universal fluid resistance depending only on its length to width ratio and to {v}{{A}}/c.
Singh, Nagendra
2011-12-01
Despite the widely discussed role of whistler waves in mediating magnetic reconnection (MR), the direct connection between such waves and the MR has not been demonstrated by comparing the characteristic temporal and spatial features of the waves and the MR process. Using the whistler wave dispersion relation, we theoretically predict the experimentally measured rise time (τ(rise)) of a few microseconds for the fast rising MR rate in the Versatile Toroidal Facility at MIT. The rise time is closely given by the inverse of the frequency bandwidth of the whistler waves generated in the evolving current sheet. The wave frequencies lie much above the ion cyclotron frequency, but they are limited to less than 0.1% of the electron cyclotron frequency in the argon plasma. The maximum normalized MR rate R=0.35 measured experimentally is precisely predicted by the angular dispersion of the whistler waves.
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G. Chisham
2004-12-01
Full Text Available This study presents, for the first time, detailed spatiotemporal measurements of the reconnection electric field in the Northern Hemisphere ionosphere during an extended interval of northward interplanetary magnetic field. Global convection mapping using the SuperDARN HF radar network provides global estimates of the convection electric field in the northern polar ionosphere. These are combined with measurements of the ionospheric footprint of the reconnection X-line to determine the spatiotemporal variation of the reconnection electric field along the whole X-line. The shape of the spatial variation is stable throughout the interval, although its magnitude does change with time. Consequently, the total reconnection potential along the X-line is temporally variable but its typical magnitude is consistent with the cross-polar cap potential measured by low-altitude satellite overpasses. The reconnection measurements are mapped out from the ionosphere along Tsyganenko model magnetic field lines to determine the most likely reconnection location on the lobe magnetopause. The X-line length on the lobe magnetopause is estimated to be ~6–11 R_{E} in extent, depending on the assumptions made when determining the length of the ionospheric X-line. The reconnection electric field on the lobe magnetopause is estimated to be ~0.2mV/m in the peak reconnection region.
Key words. Space plasma physics (Magnetic reconnection – Magnetospheric physics (Magnetopause, cusp and boundary layers – Ionosphere (Plasma convection
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.
Boosting Magnetic Reconnection by Viscosity and Thermal Conduction
Minoshima, Takashi; Imada, Shinsuke
2016-01-01
Nonlinear evolution of magnetic reconnection is investigated by means of magnetohydrodynamic simulations including uniform resistivity, uniform viscosity, and anisotropic thermal conduction. When viscosity exceeds resistivity (the magnetic Prandtl number Prm > 1), the viscous dissipation dominates outflow dynamics and leads to the decrease in the plasma density inside a current sheet. The low-density current sheet supports the excitation of the vortex. The thickness of the vortex is broader than that of the current for Prm > 1. The broader vortex flow more efficiently carries the upstream magnetic flux toward the reconnection region, and consequently boosts the reconnection. The reconnection rate increases with viscosity provided that thermal conduction is fast enough to take away the thermal energy increased by the viscous dissipation (the fluid Prandtl number Pr < 1). The result suggests the need to control the Prandtl numbers for the reconnection against the conventional resistive model.
Potter, William J.
2017-02-01
We calculate the severe radiative energy losses which occur at the base of black hole jets using a relativistic fluid jet model, including in situ acceleration of non-thermal leptons by magnetic reconnection. Our results demonstrate that including a self-consistent treatment of radiative energy losses is necessary to perform accurate magnetohydrodynamic simulations of powerful jets and that jet spectra calculated via post-processing are liable to vastly overestimate the amount of non-thermal emission. If no more than 95 per cent of the initial total jet power is radiated away by the plasma travels as it travels along the length of the jet, we can place a lower bound on the magnetization of the jet plasma at the base of the jet. For typical powerful jets, we find that the plasma at the jet base is required to be highly magnetized, with at least 10 000 times more energy contained in magnetic fields than in non-thermal leptons. Using a simple power-law model of magnetic reconnection, motivated by simulations of collisionless reconnection, we determine the allowed range of the large-scale average reconnection rate along the jet, by restricting the total radiative energy losses incurred and the distance at which the jet first comes into equipartition. We calculate analytic expressions for the cumulative radiative energy losses due to synchrotron and inverse-Compton emission along jets, and derive analytic formulae for the constraint on the initial magnetization.
Magnetic Reconnection in Astrophysical Environments
Lazarian, A; Vishniac, E; Kowal, G
2014-01-01
Magnetic reconnection is a process that changes magnetic field topology in highly conducting fluids. Traditionally, magnetic reconnection was associated mostly with solar flares. In reality, the process must be ubiquitous as astrophysical fluids are magnetized and motions of fluid elements necessarily entail crossing of magnetic frozen in field lines and magnetic reconnection. We consider magnetic reconnection in realistic 3D geometry in the presence of turbulence. This turbulence in most astrophysical settings is of pre-existing nature, but it also can be induced by magnetic reconnection itself. In this situation turbulent magnetic field wandering opens up reconnection outflow regions, making reconnection fast. We discuss Lazarian \\& Vishniac (1999) model of turbulent reconnection, its numerical and observational testings, as well as its connection to the modern understanding of the Lagrangian properties of turbulent fluids. We show that the predicted dependences of the reconnection rates on the level of...
A Nonlinear Approach to Tunisian Inflation Rate
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Thouraya Boujelbène Dammak
2016-09-01
Full Text Available In this study, we investigated the properties and the macroeconomic performance of the nonlinearity of the Inflation Rate Set in Tunisia. We developed an inference asymptotic theory for an unrestricted two-regime threshold autoregressive (TAR model with an autoregressive unit root. We proposed two types of tests namely asymptotic and bootstrap-based. These tests as well as the distribution theory allow a joint consideration of nonlinear thresholds and non-stationary unit roots. Our empirical results reveal a strong evidence of a threshold effect. This makes clear the possibility of non stationary and nonlinear of the Monthly Inflation Rate in Tunisia for the 1994.01-2011.06 period. While the Perron test found a unit root, our TAR unit root tests are arguably significant. Then, the evidence is quite strong that the inflation rate is not a unit root process.
Reconnection dynamics with secondary tearing instability in compressible Hall plasmas
Energy Technology Data Exchange (ETDEWEB)
Ma, Z. W., E-mail: zwma@zju.edu.cn; Wang, L. C.; Li, L. J. [Institute for Fusion Theory and Simulation, Zhejiang University, Hangzhou 310027 (China)
2015-06-15
The dynamics of a secondary tearing instability is systematically investigated based on compressible Hall magnetohydrodynamic. It is found that in the early nonlinear phase of magnetic reconnection before onset of the secondary tearing instability, the geometry of the magnetic field in the reconnection region tends to form a Y-type structure in a weak Hall regime, instead of an X-type structure in a strong Hall regime. A new scaling law is found that the maximum reconnection rate in the early nonlinear stage is proportional to the square of the ion inertial length (γ∝d{sub i}{sup 2}) in the weak Hall regime. In the late nonlinear phase, the thin elongated current sheet associated with the Y-type geometry of the magnetic field breaks up to form a magnetic island due to a secondary tearing instability. After the onset of the secondary tearing mode, the reconnection rate is substantially boosted by the formation of the X-type geometries of magnetic field in the reconnection regions. With a strong Hall effect, the maximum reconnection rate linearly increases with the increase of the ion inertial length (γ∝d{sub i})
The Nonlinear Spatial Damping Rate in QGP
Jiarong, L
1998-01-01
The derivative expansion method has been used to solve the semiclassical kinetic equations of quark-gluon plasma (QGP). The nonlinear spatial damping rate, the imaginary part of the wave vector, for the longitudinal secondary color waves in the long wavelength limit has been calculated numerically.
A new magnetic reconnection paradigm: Stochastic plasmoid chains
Loureiro, Nuno
2015-11-01
Recent analytical and numerical research in magnetic reconnection has converged on the notion that reconnection sites (current sheets) are unstable to the formation of multiple magnetic islands (plasmoids), provided that the system is sufficiently large (or, in other words, that the Lundquist number of the plasma is high). Nonlinearly, plasmoids come to define the reconnection geometry. Their nonlinear dynamics is rather complex and best thought of as new form of turbulence whose properties are determined by continuous plasmoid formation and their subsequent ejection from the sheet, as well as the interaction (coalescence) between plasmoids of different sizes. The existence of these stochastic plasmoid chains has powerful implications for several aspects of the reconnection process, from determining the reconnection rate to the details and efficiency of the energy conversion and dissipation. In addition, the plasmoid instability may also directly bear on the little understood problem of the reconnection trigger, or onset, i.e., the abrupt transition from a slow stage of energy accumulation to a fast (explosive) stage of energy release. This talk will first provide a brief overview of these recent developments in the reconnection field. I will then discuss recent work addressing the onset problem in the context of a forming current sheet which becomes progressively more unstable to the plasmoid instability. Work partially supported by Fundação para a Ciência e Tecnologia via Grants UID/FIS/50010/2013 and IF/00530/2013.
Steady-state properties of driven magnetic reconnection in 2D electron magnetohydrodynamics.
Chacón, L; Simakov, Andrei N; Zocco, A
2007-12-07
We formulate a rigorous nonlinear analytical model that describes the dynamics of the diffusion (reconnection) region in driven systems in the context of electron magnetohydrodynamics (EMHD). A steady-state analysis yields allowed geometric configurations and associated reconnection rates. In addition to the well-known open X-point geometry, elongated configurations are found possible. The model predictions have been validated numerically with two-dimensional EMHD nonlinear simulations, and are in excellent agreement with previously published work.
Formation of plasmoid chains in magnetic reconnection.
Samtaney, R; Loureiro, N F; Uzdensky, D A; Schekochihin, A A; Cowley, S C
2009-09-04
A detailed numerical study of magnetic reconnection in resistive MHD for very large, previously inaccessible, Lundquist numbers (10(4) magnetic-island) chains. The plasmoid number scales as S(3/8) and the instability growth rate in the linear stage as S(1/4), in agreement with the theory by Loureiro et al. [Phys. Plasmas 14, 100703 (2007)]. In the nonlinear regime, plasmoids continue to grow faster than they are ejected and completely disrupt the reconnection layer. These results suggest that high-Lundquist-number reconnection is inherently time-dependent and hence call for a substantial revision of the standard Sweet-Parker quasistationary picture for S>10(4).
Directory of Open Access Journals (Sweden)
J. D. Nichols
2006-03-01
Full Text Available We make the first quantitative estimates of the magnetopause reconnection rate at Jupiter using extended in situ data sets, building on simple order of magnitude estimates made some thirty years ago by Brice and Ionannidis (1970 and Kennel and Coroniti (1975, 1977. The jovian low-latitude magnetopause (open flux production reconnection voltage is estimated using the Jackman et al. (2004 algorithm, validated at Earth, previously applied to Saturn, and here adapted to Jupiter. The high-latitude (lobe magnetopause reconnection voltage is similarly calculated using the related Gérard et al. (2005 algorithm, also previously used for Saturn. We employ data from the Ulysses spacecraft obtained during periods when it was located near 5AU and within 5° of the ecliptic plane (January to June 1992, January to August 1998, and April to October 2004, along with data from the Cassini spacecraft obtained during the Jupiter flyby in 2000/2001. We include the effect of magnetospheric compression through dynamic pressure modulation, and also examine the effect of variations in the direction of Jupiter's magnetic axis throughout the jovian day and year. The intervals of data considered represent different phases in the solar cycle, such that we are also able to examine solar cycle dependency. The overall average low-latitude reconnection voltage is estimated to be ~230 kV, such that the average amount of open flux created over one solar rotation is ~500 GWb. We thus estimate the average time to replenish Jupiter's magnetotail, which contains ~300-500 GWb of open flux, to be ~15-25 days, corresponding to a tail length of ~3.8-6.5 AU. The average high-latitude reconnection voltage is estimated to be ~130 kV, associated with lobe "stirring". Within these averages, however, the estimated voltages undergo considerable variation. Generally, the low-latitude reconnection voltage exhibits a "background" of ~100 kV that is punctuated by one or two
Fast Magnetic Reconnection: Bridging Laboratory and Space Plasma Physics
Energy Technology Data Exchange (ETDEWEB)
Bhattacharjee, Amitava [University New Hampshire- Durham
2012-02-16
Recent developments in experimental and theoretical studies of magnetic reconnection hold promise for providing solutions to outstanding problems in laboratory and space plasma physics. Examples include sawtooth crashes in tokamaks, substorms in the Earth’s Magnetosphere, eruptive solar flares, and more recently, fast reconnection in laser-produced high energy density plasmas. In each of these examples, a common and long-standing challenge has been to explain why fast reconnection proceeds rapidly from a relatively quiescent state. In this talk, we demonstrate the advantages of viewing these problems and their solutions from a common perspective. We focus on some recent, surprising discoveries regarding the role of secondary plasmoid instabilities of thin current sheets. Nonlinearly, these instabilities lead to fast reconnection rates that are very weakly dependent on the Lundquist number of the plasma.
Fragment Driven Magnetic Reconnection
Galsgaard, K
2004-01-01
In this paper, we investigate a simple model where two, initially unconnected, flux systems are forced to interact in response to the imposed boundary driving by solving the non-ideal 3D MHD equations numerically. The reconnection rate of the dynamical process is determined and compared with the corresponding rate for the potential evolution of the magnetic field. This shows that the dynamic reconnection rate is about a factor of two smaller than the potential (perfect, instantaneous) rate for realistic solar driving velocities demonstrating that this three-dimensional magnetic reconnection process is fast. The energy input for a fixed advection distance is found to be independent of the driving velocity. The Joule dissipation associated with the reconnection process is also found to be basically dependent on the advection distance rather than driving velocity. This implies that the timescale for the event determines the effect the heating has on the temperature increase. Finally, the numerical experiments in...
Hyper-resistive forced magnetic reconnection
Energy Technology Data Exchange (ETDEWEB)
Vekstein, G., E-mail: g.vekstein@manchester.ac.uk [Jodrell Bank Centre for Astrophysics, University of Manchester, Manchester M13 9PL (United Kingdom)
2016-02-15
We study Taylor's model of forced magnetic reconnection mediated by plasma hyper-resistivity. This includes both linear and nonlinear regimes of the process. It is shown how the onset of plasmoid instability occurs in the strongly nonlinear regime of forced reconnection.
Schep, T. J.
1994-01-01
This lecture deals with the concept of magnetic field lines and with the conservation of magnetic flux. In high temperature fusion devices like tokamaks flux conservation can be violated and reconnection can occur at closed magnetic field lines. Reconnection processes lead to changes in the global t
Cause of sudden magnetic reconnection in a laboratory plasma.
Choi, S; Craig, D; Ebrahimi, F; Prager, S C
2006-04-14
The cause for sudden reconnection in reversed field pinch plasmas is determined experimentally for two cases: large reconnection events (the sawtooth crash) and small reconnection events during improved confinement. We measure the term in the MHD equations which represents the driving (or damping) of edge tearing modes due to the axisymmetric magnetic field. The term is negative for large reconnection events (the modes are stable, implying that reconnection may be driven by nonlinear coupling to other modes) and positive for small reconnection events (modes are unstable, reconnection is spontaneous).
Reconnection of superfluid vortex bundles.
Alamri, Sultan Z; Youd, Anthony J; Barenghi, Carlo F
2008-11-21
Using the vortex filament model and the Gross-Pitaevskii nonlinear Schroedinger equation, we show that bundles of quantized vortex lines in He II are structurally robust and can reconnect with each other maintaining their identity. We discuss vortex stretching in superfluid turbulence and show that, during the bundle reconnection process, kelvin waves of large amplitude are generated, in agreement with the finding that helicity is produced by nearly singular vortex interactions in classical Euler flows.
Energy Technology Data Exchange (ETDEWEB)
Masaaki Yamada, Russell Kulsrud and Hantao Ji
2009-09-17
We review the fundamental physics of magnetic reconnection in laboratory and space plasmas, by discussing results from theory, numerical simulations, observations from space satellites, and the recent results from laboratory plasma experiments. After a brief review of the well-known early work, we discuss representative recent experimental and theoretical work and attempt to interpret the essence of significant modern findings. In the area of local reconnection physics, many significant findings have been made with regard to two- uid physics and are related to the cause of fast reconnection. Profiles of the neutral sheet, Hall currents, and the effects of guide field, collisions, and micro-turbulence are discussed to understand the fundamental processes in a local reconnection layer both in space and laboratory plasmas. While the understanding of the global reconnection dynamics is less developed, notable findings have been made on this issue through detailed documentation of magnetic self-organization phenomena in fusion plasmas. Application of magnetic reconnection physics to astrophysical plasmas is also brie y discussed.
On Lorentz invariants in relativistic magnetic reconnection
Yang, Shu-Di; Wang, Xiao-Gang
2016-08-01
Lorentz invariants whose nonrelativistic correspondences play important roles in magnetic reconnection are discussed in this paper. Particularly, the relativistic invariant of the magnetic reconnection rate is defined and investigated in a covariant two-fluid model. Certain Lorentz covariant representations for energy conversion and magnetic structures in reconnection processes are also investigated. Furthermore, relativistic measures for topological features of reconnection sites, particularly magnetic nulls and separatrices, are analyzed.
Shock formation and structure in magnetic reconnection with a streaming flow.
Wu, Liangneng; Ma, Zhiwei; Zhang, Haowei
2017-08-18
The features of magnetic reconnection with a streaming flow have been investigated on the basis of compressible resistive magnetohydrodynamic (MHD) model. The super-Alfvenic streaming flow largely enhances magnetic reconnection. The maximum reconnection rate is almost four times larger with super-Alfvenic streaming flow than sub-Alfvénic streaming flow. In the nonlinear stage, it is found that there is a pair of shocks observed in the inflow region, which are manifested to be slow shocks for sub-Alfvénic streaming flow, and fast shocks for super-Alfvénic streaming flow. The quasi-period oscillation of reconnection rates in the decaying phase for super-Alfvénic streaming flow is resulted from the different drifting velocities of the shock and the X point.
Simakov, Andrei N; Chacón, L
2008-09-05
Dissipation-independent, or "fast", magnetic reconnection has been observed computationally in Hall magnetohydrodynamics (MHD) and predicted analytically in electron MHD. However, a quantitative analytical theory of reconnection valid for arbitrary ion inertial lengths, d{i}, has been lacking and is proposed here for the first time. The theory describes a two-dimensional reconnection diffusion region, provides expressions for reconnection rates, and derives a formal criterion for fast reconnection in terms of dissipation parameters and d{i}. It also confirms the electron MHD prediction that both open and elongated diffusion regions allow fast reconnection, and reveals strong dependence of the reconnection rates on d{i}.
Transition to whistler mediated magnetic reconnection
Mandt, M. E.; Denton, R. E.; Drake, J. F.
1994-01-01
The transition in the magnetic reconnection rate from the resistive magnetohydrodynamic (MHD) regime where the Alfen wave controls reconnection to a regime in which the ions become unmagnetized and the whistler wave mediates reconnection is explored with 2-D hybrid simulations. In the whistler regime the electrons carry the currents while the ions provide a neutralizing background. A simple physical picture is presented illustrating the role of the whistler mediated reconnection is calculated analytically. The development of an out-of-plane component of the magnetic field is an observable signature of whistler driven reconnection.
Nonlinearity degree of short-term heart rate variability signal
Institute of Scientific and Technical Information of China (English)
BIAN Chunhua; NING Xinbao
2004-01-01
A nonlinear autoregressive (NAR) model is built to model the heartbeat interval time series and the optimum model degree is proposed to be taken to evaluate the nonlinearity degree of heart rate variability (HRV). A group of healthy persons are studied and the results indicate that this method can effectively get nonlinear information from short (6-7 min) heartbeat series and consequently reflect the degree of heart rate variability, which supplies convenience in clinical application. Finally, a comparison with the traditional time domain method shows that the NAR model method can reflect the complexity of the whole signal and lessen the influence of noise and instability in the signal.
Yang, Kai; Longcope, Dana; Guo, Yang; Ding, Mingde
2017-08-01
Numerous proposed coronal heating mechanisms have invoked magnetic reconnection in some role. Testing such a mechanism requires a method of measuring magnetic reconnection coupled with a prediction of the heat delivered by reconnection at the observed rate. In the absence of coronal reconnection, field line footpoints move at the same velocity as the plasma they find themselves in. The rate of coronal reconnection is therefore related to any discrepancy observed between footpoint motion and that of the local plasma — so-called slipping motion. We propose a novel method to measure this velocity discrepancy by combining a sequence of non-linear force-free field extrapolations with maps of photospheric velocity. We obtain both from a sequence of vector magnetograms of an active region (AR). We then propose a method of computing the coronal heating produced under the assumption the observed slipping velocity was due entirely to coronal reconnection. This heating rate is used to predict density and temperature at points along an equilibrium loop. This, in turn, is used to synthesize emission in EUV and SXR bands. We perform this analysis using a sequence of HMI vector magnetograms of a particular AR and compare synthesized images to observations of the same AR made by SDO. We also compare differential emission measure inferred from those observations to that of the modeled corona.
Nonlinear Control of Heart Rate Variability in Human Infants
Sugihara, George; Allan, Walter; Sobel, Daniel; Allan, Kenneth D.
1996-03-01
Nonlinear analyses of infant heart rhythms reveal a marked rise in the complexity of the electrocardiogram with maturation. We find that normal mature infants (gestation >= 35 weeks) have complex and distinctly nonlinear heart rhythms (consistent with recent reports for healthy adults) but that such nonlinearity is lacking in preterm infants (gestation parasympathetic-sympathetic interaction and function are presumed to be less well developed. Our study further shows that infants with clinical brain death and those treated with atropine exhibit a similar lack of nonlinear feedback control. These three lines of evidence support the hypothesis championed by Goldberger et al. [Goldberger, A. L., Rigney, D. R. & West, B. J. (1990) Sci. Am. 262, 43-49] that autonomic nervous system control underlies the nonlinearity and possible chaos of normal heart rhythms. This report demonstrates the acquisition of nonlinear heart rate dynamics and possible chaos in developing human infants and its loss in brain death and with the administration of atropine. It parallels earlier work documenting changes in the variability of heart rhythms in each of these cases and suggests that nonlinearity may provide additional power in characterizing physiological states.
NUMERICAL STUDIES OF WEAKLY STOCHASTIC MAGNETIC RECONNECTION
Directory of Open Access Journals (Sweden)
G. Kowal
2009-01-01
Full Text Available We study the e ects of turbulence on magnetic reconnection using three-dimensional numerical simulations.This is the rst attempt to test the model of fast magnetic reconnection proposed by Lazarian & Vishniac (1999, which assumes the presence of weak, small-scale magnetic eld structure near the current sheet. This a ects the rate of reconnection by reducing the transverse scale for reconnection ows and by allowing many independent ux reconnection events to occur simultaneously. We performed a number of simulations to test the dependencies of the reconnection speed, de ned as the ratio of the in ow velocity to the Alfv n speed, on the turbulence power, the injection scale and resistivity. Our results show that turbulence signi cantly a ects the topology of magnetic eld near the di usion region and increases the thickness of the out ow region. We con rm the predictions of the Lazarian & Vishniac model. In particular, we report the growth of the reconnection speed proportional to V 2 l , where Vl is the amplitude of velocity at the injection scale. It depends on the injection scale linj as (linj=L2=3, where L is the size of the system, which is somewhat faster but still roughly consistent with the theoretical expectations. We also show that for 3D reconnection the Ohmic resistivity is important in the local reconnection events only, and the global reconnection rate in the presence of turbulence does not depend on it.
Self-regulation of the reconnecting current layer in relativistic pair plasma reconnection
Zenitani, S
2008-01-01
We investigate properties of the reconnecting current layer in relativistic pair plasma reconnection. We found that the current layer self-regulates its thickness when the current layer runs out current carriers and so relativistic reconnection retains a fast reconnection rate. Constructing a steady state Sweet-Parker model, we discuss conditions for the current sheet expansion. Based on the energy argument we conclude that the incompressible assumption is invalid in relativistic Sweet-Parker reconnection. The guide field cases are more incompressible than the anti-parallel cases, and we find a more significant current sheet expansion.
Information mining in weighted complex networks with nonlinear rating projection
Liao, Hao; Zeng, An; Zhou, Mingyang; Mao, Rui; Wang, Bing-Hong
2017-10-01
Weighted rating networks are commonly used by e-commerce providers nowadays. In order to generate an objective ranking of online items' quality according to users' ratings, many sophisticated algorithms have been proposed in the complex networks domain. In this paper, instead of proposing new algorithms we focus on a more fundamental problem: the nonlinear rating projection. The basic idea is that even though the rating values given by users are linearly separated, the real preference of users to items between the different given values is nonlinear. We thus design an approach to project the original ratings of users to more representative values. This approach can be regarded as a data pretreatment method. Simulation in both artificial and real networks shows that the performance of the ranking algorithms can be improved when the projected ratings are used.
Magnetic Reconnection in a Compressible MHD Plasma
Hesse, Michael; Birn, Joachim; Zenitani, Seiji
2011-01-01
Using steady-state resistive MHD, magnetic reconnection is reinvestigated for conditions of high resistivity/low magnetic Reynolds number, when the thickness of the diffusion region is no longer small compared to its length. Implicit expressions for the reconnection rate and other reconnection parameters are derived based on the requirements of mass, momentum, and energy conservation. These expressions are solved via simple iterative procedures. Implications specifically for low Reynolds number/high resistivity are being discussed
Laboratory observations of spontaneous magnetic reconnection.
Egedal, J; Fox, W; Katz, N; Porkolab, M; Reim, K; Zhang, E
2007-01-05
Detailed measurements of spontaneous magnetic reconnection are presented. The experimental data, which were obtained in the new closed Versatile Toroidal Facility magnetic configuration, document the profile evolution of the plasma density, magnetic flux function, reconnection rate, and the current density during a spontaneous reconnection event in the presence of a strong guide magnetic field. The reconnection process is at first slow, which allows magnetic stress to build in the system while the current channel becomes increasingly narrow and intense. The onset of a fast reconnection event occurs as the width of the current channel approaches the ion-sound-Larmor radius rho s. During the reconnection event magnetically stored energy is channeled into energetic ion outflows and a rapid increase in the electron temperature.
Explosive Turbulent Magnetic Reconnection
Higashimori, Katsuaki; Yokoi, Nobumitsu; Hoshino, Masahiro
2013-01-01
We report simulation results for turbulent magnetic reconnection obtained using a newly developed Reynolds-averaged magnetohydrodynamics model. We find that the initial Harris current sheet develops in three ways, depending on the strength of turbulence: laminar reconnection, turbulent reconnection, and turbulent diffusion. The turbulent reconnection explosively converts the magnetic field energy into both kinetic and thermal energy of plasmas, and generates open fast reconnection jets. This ...
Directory of Open Access Journals (Sweden)
M. Lockwood
2005-12-01
Full Text Available Using data from the EISCAT (European Incoherent Scatter VHF and CUTLASS (Co-operative UK Twin-Located Auroral Sounding System HF radars, we study the formation of ionospheric polar cap patches and their relationship to the magnetopause reconnection pulses identified in the companion paper by Lockwood et al. (2005. It is shown that the poleward-moving, high-concentration plasma patches observed in the ionosphere by EISCAT on 23 November 1999, as reported by Davies et al. (2002, were often associated with corresponding reconnection rate pulses. However, not all such pulses generated a patch and only within a limited MLT range (11:00-12:00 MLT did a patch result from a reconnection pulse. Three proposed mechanisms for the production of patches, and of the concentration minima that separate them, are analysed and evaluated: (1 concentration enhancement within the patches by cusp/cleft precipitation; (2 plasma depletion in the minima between the patches by fast plasma flows; and (3 intermittent injection of photoionisation-enhanced plasma into the polar cap. We devise a test to distinguish between the effects of these mechanisms. Some of the events repeat too frequently to apply the test. Others have sufficiently long repeat periods and mechanism (3 is shown to be the only explanation of three of the longer-lived patches seen on this day. However, effect (2 also appears to contribute to some events. We conclude that plasma concentration gradients on the edges of the larger patches arise mainly from local time variations in the subauroral plasma, via the mechanism proposed by Lockwood et al. (2000.
Potter, William J
2016-01-01
We calculate the severe radiative energy losses which occur at the base of black hole jets using a relativistic fluid jet model, including in-situ acceleration of non-thermal leptons by magnetic reconnection. Our results demonstrate that including a self-consistent treatment of radiative energy losses is necessary to perform accurate MHD simulations of powerful jets and that jet spectra calculated via post-processing are liable to vastly overestimate the amount of non-thermal emission. If no more than 95% of the initial total jet power is radiated away by the plasma travels as it travels along the length of the jet, we can place a lower bound on the magnetisation of the jet plasma at the base of the jet. For typical powerful jets, we find that the plasma at the jet base is required to be highly magnetised, with at least 10,000 times more energy contained in magnetic fields than in non-thermal leptons. Using a simple power-law model of magnetic reconnection, motivated by simulations of collisionless reconnecti...
Diagnostics of solar flare reconnection
Directory of Open Access Journals (Sweden)
M. Karlický
2004-01-01
Full Text Available We present new diagnostics of the solar flare reconnection, mainly based on the plasma radio emission. We propose that the high-frequency (600-2000 MHz slowly drifting pulsating structures map the flare magnetic field reconnection. These structures correspond to the radio emission from plasmoids which are formed in the extended current sheet due to tearing and coalescence processes. An increase of the frequency drift of the drifting structures is interpreted as an increase of the reconnection rate. Using this model, time scales of slowly drifting pulsating structure observed during the 12 April 2001 flare by the Trieste radiopolarimeter with high time resolution (1 ms are interpreted as a radio manifestation of electron beams accelerated in the multi-scale reconnection process. For short periods Fourier spectra of the observed structure have a power-law form with power-law indices in the 1.3-1.6 range. For comparison the 2-D MHD numerical modeling of the multi-scale reconnection is made and it is shown that Fourier spectrum of the reconnection dissipation power has also a power-law form, but with power-law index 2. Furthermore, we compute a time evolution of plasma parameters (density, magnetic field etc in the 2-D MHD model of the reconnection. Then assuming a plasma radio emission from locations, where the 'double-resonance' instability generates the upper-hybrid waves due to unstable distribution function of suprathermal electrons, we model radio spectra. Effects of the MHD turbulence are included. The resulting spectra are compared with those observed. It is found, that depending on model parameters the lace bursts and the decimetric spikes can be reproduced. Thus, it is shown that the model can be used for diagnostics of the flare reconnection process. We also point out possible radio signatures of reconnection outflow termination shocks. They are detected as type II-like herringbone structures in the 200-700 MHz frequency range. Finally
Fast magnetic reconnection in laser-produced plasma bubbles
Fox, W.; Bhattacharjee, A.; Germaschewski, K.
2011-01-01
Recent experiments have observed magnetic reconnection in high-energy-density, laser-produced plasma bubbles, with reconnection rates observed to be much higher than can be explained by classical theory. Based on fully kinetic particle simulations we find that fast reconnection in these strongly driven systems can be explained by magnetic flux pile-up at the shoulder of the current sheet and subsequent fast reconnection via two-fluid, collisionless mechanisms. In the strong drive regime with ...
Explosive turbulent magnetic reconnection.
Higashimori, K; Yokoi, N; Hoshino, M
2013-06-21
We report simulation results for turbulent magnetic reconnection obtained using a newly developed Reynolds-averaged magnetohydrodynamics model. We find that the initial Harris current sheet develops in three ways, depending on the strength of turbulence: laminar reconnection, turbulent reconnection, and turbulent diffusion. The turbulent reconnection explosively converts the magnetic field energy into both kinetic and thermal energy of plasmas, and generates open fast reconnection jets. This fast turbulent reconnection is achieved by the localization of turbulent diffusion. Additionally, localized structure forms through the interaction of the mean field and turbulence.
Reconnection of Magnetic Fields
Birn, J.; Priest, E. R.
2007-01-01
Preface; Part I. Introduction: 1.1 The Sun E. R. Priest; 1.2 Earth's magnetosphere J. Birn; Part II. Basic Theory of MHD Reconnection: 2.1 Classical theory of two-dimensional reconnection T. G. Forbes; 2.2 Fundamental concepts G. Hornig; 2.3 Three-dimensional reconnection in the absence of magnetic null points G. Hornig; 2.4 Three-dimensional reconnection at magnetic null points D. Pontin; 2.5 Three-dimensional flux tube reconnection M. Linton; Part III. Basic Theory of Collisionless Reconnection: 3.1 Fundamentals of collisionless reconnection J. Drake; 3.2 Diffusion region physics M. Hesse; 3.3 Onset of magnetic reconnection P. Pritchett; 3.4 Hall-MHD reconnection A. Bhattacharjee and J. Dorelli; 3.5 Role of current-aligned instabilities J. Büchner and W. Daughton; 3.6 Nonthermal particle acceleration M. Hoshino; Part IV. Reconnection in the Magnetosphere: 4.1 Reconnection at the magnetopause: concepts and models J. G. Dorelli and A. Bhattacharjee; 4.2 Observations of magnetopause reconnection K.-H. Trattner; 4.3 On the stability of the magnetotail K. Schindler; 4.4 Simulations of reconnection in the magnetotail J. Birn; 4.5 Observations of tail reconnection W. Baumjohann and R. Nakamura; 4.6 Remote sensing of reconnection M. Freeman; Part V. Reconnection in the Sun's Atmosphere: 5.1 Coronal heating E. R. Priest; 5.2 Separator reconnection D. Longcope; 5.3 Pinching of coronal fields V. Titov; 5.4 Numerical experiments on coronal heating K. Galsgaard; 5.5 Solar flares K. Kusano; 5.6 Particle acceleration in flares: theory T. Neukirch; 5.7 Fast particles in flares: observations L. Fletcher; 6. Open problems J. Birn and E. R. Priest; Bibliography; Index.
The Nonlinear Landau Damping Rate of a Driven Plasma Wave
Energy Technology Data Exchange (ETDEWEB)
Benisti, D; Strozzi, D J; Gremillet, L; Morice, O
2009-08-04
In this Letter, we discuss the concept of the nonlinear Landau damping rate, {nu}, of a driven electron plasma wave, and provide a very simple, practical, analytic formula for {nu} which agrees very well with results inferred from Vlasov simulations of stimulated Raman scattering. {nu} actually is more complicated an operator than a plain damping rate, and it may only be seen as such because it assumes almost constant values before abruptly dropping to 0. The decrease of {nu} to 0 is moreover shown to occur later when the wave amplitude varies in the direction transverse to its propagation.
Lp-decay rates to nonlinear diffusion waves for p-system with nonlinear damping
Institute of Scientific and Technical Information of China (English)
ZHU Changjiang; JIANG Mina
2006-01-01
In this paper, we study the Lp (2 ≤ p ≤ +∞) convergence rates of the solutions to the Cauchy problem of the so-called p-system with nonlinear damping. Precisely, we show that the corresponding Cauchy problem admits a unique global solution (v(x,t),u(x,t)) and such a solution tends time-asymptotically to the corresponding nonlinear diffusion wave (-v(x, t), -u(x, t)) governed by the classical Darcy's law provided that the corresponding prescribed initial error function (w0(x), z0(x))lies in (H3 × H2) (R) and |v+ - v-| + ‖w0‖3 + ‖z0‖2 is sufficiently small.Furthermore, the Lp (2 ≤ p ≤ +∞) convergence rates of the solutions are also obtained.
Numerical Tests of Fast Reconnection in Weakly Stochastic Magnetic Fields
Kowal, G; Vishniac, E T; Otmianowska-Mazur, K
2009-01-01
We study the effects of turbulence on magnetic reconnection using 3D numerical simulations. This is the first attempt to test a model of fast magnetic reconnection in the presence of weak turbulence proposed by Lazarian & Vishniac (1999). This model predicts that weak turbulence, generically present in most of astrophysical systems, enhances the rate of reconnection by reducing the transverse scale for reconnection events and by allowing many independent flux reconnection events to occur simultaneously. As a result the reconnection speed becomes independent of Ohmic resistivity and is determined by the magnetic field wandering induced by turbulence. To quantify the reconnection speed we use both an intuitive definition, i.e. the speed of the reconnected flux inflow, as well as a more sophisticated definition based on a formally derived analytical expression. Our results confirm the predictions of the Lazarian & Vishniac model. In particular, we find that Vrec Pinj^(1/2), as predicted by the model. The...
Reconnection in thin current sheets
Tenerani, Anna; Velli, Marco; Pucci, Fulvia; Rappazzo, A. F.
2016-05-01
It has been widely believed that reconnection is the underlying mechanism of many explosive processes observed both in nature and laboratory, but the question of reconnection speed and initial trigger have remained mysterious. How is fast magnetic energy release triggered in high Lundquist (S) and Reynolds (R) number plasmas?It has been shown that a tearing mode instability can grow on an ideal timescale, i.e., independent from the the Lundquist number, once the current sheet thickness becomes thin enough, or rather the inverse aspect ratio a/L reaches a scale a/L~S-1/3. As such, the latter provides a natural, critical threshold for current sheets that can be formed in nature before they disrupt in a few Alfvén time units. Here we discuss the transition to fast reconnection extended to simple viscous and kinetic models and we propose a possible scenario for the transition to explosive reconnection in high-Lundquist number plasmas, that we support with fully nonlinear numerical MHD simulations of a collapsing current sheet.
Asymmetric magnetic reconnection with a flow shear and applications to the magnetopause
Doss, C E; Cassak, P A; Wilder, F D; Eriksson, S; Drake, J F
2015-01-01
We perform a theoretical and numerical study of anti-parallel 2D magnetic reconnection with asymmetries in the density and reconnecting magnetic field strength in addition to a bulk flow shear across the reconnection site in the plane of the reconnecting fields, which commonly occurs at planetary magnetospheres. We predict the speed at which an isolated X-line is convected by the flow, the reconnection rate, and the critical flow speed at which reconnection no longer takes place for arbitrary reconnecting magnetic field strengths, densities, and upstream flow speeds, and confirm the results with two-fluid numerical simulations. The predictions and simulation results counter the prevailing model of reconnection at Earth's dayside magnetopause which says reconnection occurs with a stationary X-line for sub-Alfvenic magnetosheath flow, reconnection occurs but the X-line convects for magnetosheath flows between the Alfven speed and double the Alfven speed, and reconnection does not occur for magnetosheath flows g...
On two-dimensional magnetic reconnection with nonuniform resistivity
Malyshkin, Leonid M.; Kulsrud, Russell M.
2010-12-01
In this paper, two theoretical approaches for the calculation of the rate of quasi-stationary, two-dimensional magnetic reconnection with nonuniform anomalous resistivity are considered in the framework of incompressible magnetohydrodynamics (MHD). In the first, 'global' equations approach, the MHD equations are approximately solved for a whole reconnection layer, including the upstream and downstream regions and the layer center. In the second, 'local' equations approach, the equations are solved across the reconnection layer, including only the upstream region and the layer center. Both approaches give the same approximate answer for the reconnection rate. Our theoretical model is in agreement with the results of recent simulations of reconnection with spatially nonuniform resistivity.
Helicity, Reconnection, and Dynamo Effects
Energy Technology Data Exchange (ETDEWEB)
Ji, Hantao
1998-11-01
The inter-relationships between magnetic helicity, magnetic reconnection, and dynamo effects are discussed. In laboratory experiments, where two plasmas are driven to merge, the helicity content of each plasma strongly affects the reconnection rate, as well as the shape of the diffusion region. Conversely, magnetic reconnection events also strongly affect the global helicity, resulting in efficient helicity cancellation (but not dissipation) during counter-helicity reconnection and a finite helicity increase or decrease (but less efficiently than dissipation of magnetic energy) during co-helicity reconnection. Close relationships also exist between magnetic helicity and dynamo effects. The turbulent electromotive force along the mean magnetic field (alpha-effect), due to either electrostatic turbulence or the electron diamagnetic effect, transports mean-field helicity across space without dissipation. This has been supported by direct measurements of helicity flux in a laboratory plasma. When the dynamo effect is driven by electromagnetic turbulence, helicity in the turbulent field is converted to mean-field helicity. In all cases, however, dynamo processes conserve total helicity except for a small battery effect, consistent with the observation that the helicity is approximately conserved during magnetic relaxation.
Resistive instabilities and field line reconnection
Energy Technology Data Exchange (ETDEWEB)
White, R.B.
1980-05-01
A review is given of the linear theory of reconnection for a plane current layer. The three basic modes are the Rippling Mode, the Gravitational Interchange Mode, and the Tearing Mode. A derivation is given of the magnetic field energy which provides the driving force for the tearing mode. The necessary concepts for the analysis of tearing modes in cylindrical geometry are introduced. The equations governing tearing mode evolution in a tokamak are expanded to lowest order in the inverse aspect ratio. The tearing mode in a toroidal device is closely related to the ideal magnetohydrodynamic kink mode, and this relationship is stressed in the derivations of the linear growth rates for modes with poloidal model number m > 2 and for the quite different m = 1 mode. The nonlinear theory of tearing mode development and the implications of this theory for the understanding of toroidal magnetic confinement devices is reviewed.
Magnetic reconnection from a multiscale instability cascade.
Moser, Auna L; Bellan, Paul M
2012-02-15
Magnetic reconnection, the process whereby magnetic field lines break and then reconnect to form a different topology, underlies critical dynamics of magnetically confined plasmas in both nature and the laboratory. Magnetic reconnection involves localized diffusion of the magnetic field across plasma, yet observed reconnection rates are typically much higher than can be accounted for using classical electrical resistivity. It is generally proposed that the field diffusion underlying fast reconnection results instead from some combination of non-magnetohydrodynamic processes that become important on the 'microscopic' scale of the ion Larmor radius or the ion skin depth. A recent laboratory experiment demonstrated a transition from slow to fast magnetic reconnection when a current channel narrowed to a microscopic scale, but did not address how a macroscopic magnetohydrodynamic system accesses the microscale. Recent theoretical models and numerical simulations suggest that a macroscopic, two-dimensional magnetohydrodynamic current sheet might do this through a sequence of repetitive tearing and thinning into two-dimensional magnetized plasma structures having successively finer scales. Here we report observations demonstrating a cascade of instabilities from a distinct, macroscopic-scale magnetohydrodynamic instability to a distinct, microscopic-scale (ion skin depth) instability associated with fast magnetic reconnection. These observations resolve the full three-dimensional dynamics and give insight into the frequently impulsive nature of reconnection in space and laboratory plasmas.
Pulsating Magnetic Reconnection Driven by Three-Dimensional Flux-Rope Interactions.
Gekelman, W; De Haas, T; Daughton, W; Van Compernolle, B; Intrator, T; Vincena, S
2016-06-10
The dynamics of magnetic reconnection is investigated in a laboratory experiment consisting of two magnetic flux ropes, with currents slightly above the threshold for the kink instability. The evolution features periodic bursts of magnetic reconnection. To diagnose this complex evolution, volumetric three-dimensional data were acquired for both the magnetic and electric fields, allowing key field-line mapping quantities to be directly evaluated for the first time with experimental data. The ropes interact by rotating about each other and periodically bouncing at the kink frequency. During each reconnection event, the formation of a quasiseparatrix layer (QSL) is observed in the magnetic field between the flux ropes. Furthermore, a clear correlation is demonstrated between the quasiseparatrix layer and enhanced values of the quasipotential computed by integrating the parallel electric field along magnetic field lines. These results provide clear evidence that field lines passing through the quasiseparatrix layer are undergoing reconnection and give a direct measure of the nonlinear reconnection rate. The measurements suggest that the parallel electric field within the QSL is supported predominantly by electron pressure; however, resistivity may play a role.
Fast magnetic reconnection in laser-produced plasma bubbles.
Fox, W; Bhattacharjee, A; Germaschewski, K
2011-05-27
Recent experiments have observed magnetic reconnection in high-energy-density, laser-produced plasma bubbles, with reconnection rates observed to be much higher than can be explained by classical theory. Based on fully kinetic particle simulations we find that fast reconnection in these strongly driven systems can be explained by magnetic flux pileup at the shoulder of the current sheet and subsequent fast reconnection via two-fluid, collisionless mechanisms. In the strong drive regime with two-fluid effects, we find that the ultimate reconnection time is insensitive to the nominal system Alfvén time.
Linear and Nonlinear Heart Rate Variability Indexes in Clinical Practice
Directory of Open Access Journals (Sweden)
Buccelletti Francesco
2012-01-01
Full Text Available Biological organisms have intrinsic control systems that act in response to internal and external stimuli maintaining homeostasis. Human heart rate is not regular and varies in time and such variability, also known as heart rate variability (HRV, is not random. HRV depends upon organism's physiologic and/or pathologic state. Physicians are always interested in predicting patient's risk of developing major and life-threatening complications. Understanding biological signals behavior helps to characterize patient's state and might represent a step toward a better care. The main advantage of signals such as HRV indexes is that it can be calculated in real time in noninvasive manner, while all current biomarkers used in clinical practice are discrete and imply blood sample analysis. In this paper HRV linear and nonlinear indexes are reviewed and data from real patients are provided to show how these indexes might be used in clinical practice.
Evolutions of nonsteady state magnetic reconnection
Energy Technology Data Exchange (ETDEWEB)
Wan, Weigang [Los Alamos National Laboratory; Lapenta, Giovanni [KATHOLIEKE UNIV
2008-01-01
The full evolutions of collisionless non-steady-state magnetic reconnection are studied with full kinetic particle-in-cell simulations. There are different stages of reconnection: the onset or early growing stage when the out-of-plane electric field (Ey) structure is a monopole at the X-point, the bipolar stage when the Ey structure is bipolar and the outer electron diffusion region (EDR) is being elongated over time, and the possible final steady-state stage when E{sub y} is uniform in the reconnection plane. We find the change of reconnection rate is not empowered or dependent on the length of the EDR. During the early growing stage, the EDR is elongated while the reconnection rate is growing. During the later stage, the reconnection rate may significantly decrease but the length of the inner EDR is largely stable. The results indicate that reconnection is not controlled by the downstream physics, but rather by the availability of plasma inflows from upstream. The physical mechanism of the EDR elongation is studied. The Hall current induced by the quadrupole magnetic field (B{sub y}) is discovered to play an important role in this process. The condition of forming an extended electron super-Alfvenic outflow jet structure in nature is discussed. The jet structure could be elongated during the bipolar stage, and remains stable during steady state. The sufficiency of the electron inflow is crucial for the elongation. Open boundary conditions are applied in the outflow direction.
Turbulent General Magnetic Reconnection
Eyink, Gregory L
2014-01-01
Plasma flows with an MHD-like turbulent inertial range, such as the solar wind, require a generalization of General Magnetic Reconnection (GMR) theory. We introduce the slip-velocity source vector, which gives the rate of development of slip velocity per unit arc length of field line. The slip source vector is the ratio of the curl of the non ideal electric field in the Generalized Ohm's Law and the magnetic field strength. It diverges at magnetic nulls, unifying GMR with magnetic null-point reconnection. Only under restrictive assumptions is the slip velocity related to the gradient of the quasi potential (integral of parallel electric field along field lines). In a turbulent inertial range the curl becomes extremely large while the parallel component is tiny, so that line slippage occurs even while ideal MHD becomes accurate. The resolution of this paradox is that ideal MHD is valid for a turbulent inertial-range only in a weak sense which does not imply magnetic line freezing. The notion of weak solution i...
Turbulent Plasmoid Reconnection
Widmer, Fabien; Yokoi, Nobumitsu
2016-01-01
The plasmoid instability may lead to fast magnetic reconnection through long current sheets(CS). It is well known that large-Reynolds-number plasmas easily become turbulent. We address the question whether turbulence enhances the energy conversion rate of plasmoid-unstable current sheets. We carry out appropriate numerical MHD simulations, but resolving simultaneously the relevant large-scale (mean-) fields and the corresponding small-scale, turbulent, quantities by means of direct numerical simulations (DNS) is not possible. Hence we investigate the influence of small scale turbulence on large scale MHD processes by utilizing a subgrid-scale (SGS) turbulence model. We verify the applicability of our SGS model and then use it to investigate the influence of turbulence on the plasmoid instability. We start the simulations with Harris-type and force-free CS equilibria in the presence of a finite guide field in the direction perpendicular to the reconnection plane. We use the DNS results to investigate the growt...
Relating magnetic reconnection to coronal heating.
Longcope, D W; Tarr, L A
2015-05-28
It is clear that the solar corona is being heated and that coronal magnetic fields undergo reconnection all the time. Here we attempt to show that these two facts are related--i.e. coronal reconnection generates heat. This attempt must address the fact that topological change of field lines does not automatically generate heat. We present one case of flux emergence where we have measured the rate of coronal magnetic reconnection and the rate of energy dissipation in the corona. The ratio of these two, [Formula: see text], is a current comparable to the amount of current expected to flow along the boundary separating the emerged flux from the pre-existing flux overlying it. We can generalize this relation to the overall corona in quiet Sun or in active regions. Doing so yields estimates for the contribution to coronal heating from magnetic reconnection. These estimated rates are comparable to the amount required to maintain the corona at its observed temperature.
Oxygen consumption of cycle ergometry is nonlinearly related to work rate and pedal rate.
Londeree, B R; Moffitt-Gerstenberger, J; Padfield, J A; Lottmann, D
1997-06-01
The purpose of the study was to develop an equation to predict the oxygen cost of cycle ergometry. Forty subjects performed an incremental cycle ergometer test on three occasions at 50, 70, or 90 rpm in a counterbalanced order. Work rate was incremented every 5 or 6 min when steady rate values were achieved. To ensure accurate work rates, ergometer resistance was calibrated and flywheel revolutions were electronically measured. Oxygen consumption was measured with a computer interfaced system which provided results every minute. Oxygen consumption (mL.min-1) was the dependent variable, and independent variables were work rate (WR in kgm.min-1), pedal rate (rpm), weight (Kg), and gender (males, 0; females, 1). The following nonlinear equation was selected; VO2 = 0.42.WR1.2 + 0.00061.rpm3 + 6.35.Wt + 0.1136.RPM50.WR-0.10144.RPM90-WR-52-Gender, R2 = 0.9961, Sy.x = 106 mL.min-1, where RPM50: 50 rpm = 1, and RPM90: 90 rpm = 1, else = 0. It was concluded that the oxygen cost of cycle ergometry is nonlinearly related to work rate and pedal rate, linearly related to weight, and that females use less oxygen for a particular work rate.
Reconnection at 3D Magnetic Null Points: Effect of Current Sheet Asymmetry
Wyper, Peter F
2013-01-01
Asymmetric current sheets are likely to be prevalent in both astrophysical and laboratory plasmas with complex three dimensional (3D) magnetic topologies. This work presents kinematic analytical models for spine and fan reconnection at a symmetric 3D null with asymmetric current sheets. Asymmetric fan reconnection is characterized by an asymmetric reconnection of flux past each spine line and a bulk flow of plasma across the null point. In contrast, asymmetric spine reconnection is inherently equal and opposite in how flux is reconnected across the fan plane. The higher modes of spine reconnection also include localized wedges of vortical flux transport in each half of the fan. In this situation, two definitions for reconnection rate become appropriate: a local reconnection rate quantifying how much flux is genuinely reconnected across the fan plane and a global rate associated with the net flux driven across each semi-plane. Through a scaling analysis it is shown that when the ohmic dissipation in the layer ...
Reconnection in a slow Coronal Mass Ejection
Directory of Open Access Journals (Sweden)
G. Poletto
2008-10-01
Full Text Available This paper aims at studying reconnection occurring in the aftermath of the 28 May 2004, CME, first imaged by the LASCO (Large Angle and Spectrometric Coronagraph C2 at 11:06 UT. The CME was observed in White Light and UV radiation: images acquired by the LASCO C2 and C3 coronagraphs and spectra acquired by UVCS (Ultraviolet Coronagraph Spectrometer allowed us to identify the level at which field lines, stretched outwards by the CME ejection, reconnect below the CME bubble. As the CME propagates outwards, reconnection occurs at increasingly higher levels. The process goes on at a low pace for several hours: here we give the profile of the reconnection rate vs. heliocentric distance over a time interval of ≈14 h after the CME onset, extending estimates of the reconnection rate to larger distances than previously inferred by other authors. The reconnection rate appears to decrease with time/altitude. We also calculate upper and lower limits to the density in the diffusion region between 4 and 7 R_{⊙} and conclude by comparing estimates of the classical and anomalous resistivity in the diffusion region with the value inferred from the data. The latter turns out to be ≥5 order of magnitudes larger than predicted by classical or anomalous theories, pointing to the need of identifying the process responsible for the observed value.
Activation of MHD reconnection on ideal timescales
Landi, S; Del Zanna, L; Tenerani, A; Pucci, F
2016-01-01
Magnetic reconnection in laboratory, space and astrophysical plasmas is often invoked to explain explosive energy release and particle acceleration. However, the timescales involved in classical models within the macroscopic MHD regime are far too slow to match the observations. Here we revisit the tearing instability by performing visco-resistive two-dimensional numerical simulations of the evolution of thin current sheets, for a variety of initial configurations and of values of the Lunquist number $S$, up to $10^7$. Results confirm that when the critical aspect ratio of $S^{1/3}$ is reached in the reconnecting current sheets, the instability proceeds on ideal (Alfv\\'enic) macroscopic timescales, as required to explain observations. Moreover, the same scaling is seen to apply also to the local, secondary reconnection events triggered during the nonlinear phase of the tearing instability, thus accelerating the cascading process to increasingly smaller spatial and temporal scales. The process appears to be ro...
Dissipation and reconnection in boundary-driven reduced magnetohydrodynamics
Energy Technology Data Exchange (ETDEWEB)
Wan, Minping; Rappazzo, Antonio Franco; Matthaeus, William H. [Bartol Research Institute and Department of Physics and Astronomy, University of Delaware, Newark, DE 19716 (United States); Servidio, Sergio [Dipartimento di Fisica, Università della Calabria, I-87036 Cosenza (Italy); Oughton, Sean [Department of Mathematics, University of Waikato, Hamilton 3240 (New Zealand)
2014-12-10
We study the statistics of coherent current sheets, the population of X-type critical points, and reconnection rates in a coronal loop geometry, via numerical simulations of reduced magnetohydrodynamic turbulence. Current sheets and sites of reconnection (magnetic X-points) are identified in two-dimensional planes of the three-dimensional simulation domain. The geometry of the identified current sheets—including area, length, and width—and the magnetic dissipation occurring in the current sheets are statistically characterized. We also examine the role of magnetic reconnection, by computing the reconnection rates at the identified X-points and investigating their association with current sheets.
CHAIN RECONNECTIONS OBSERVED IN SYMPATHETIC ERUPTIONS
Energy Technology Data Exchange (ETDEWEB)
Joshi, Navin Chandra; Magara, Tetsuya [School of Space Research, Kyung Hee University, Yongin, Gyeonggi-Do, 446-701 (Korea, Republic of); Schmieder, Brigitte; Aulanier, Guillaume [LESIA, Observatoire de Paris, PSL Research University, CNRS Sarbonne Universités, Univ. Paris 06, Univ. Paris Diderot, Sorbonne Paris Cité, 5 place Jules Jansson, F-92195 Meudon (France); Guo, Yang, E-mail: navin@khu.ac.kr, E-mail: njoshi98@gmail.com [School of Astronomy and Space Science, Nanjing University, 210023 Nanjing (China)
2016-04-01
The nature of various plausible causal links between sympathetic events is still a controversial issue. In this work, we present multiwavelength observations of sympathetic eruptions, associated flares, and coronal mass ejections (CMEs) occurring on 2013 November 17 in two close active regions. Two filaments, i.e., F1 and F2, are observed in between the active regions. Successive magnetic reconnections, caused for different reasons (flux cancellation, shear, and expansion) have been identified during the whole event. The first reconnection occurred during the first eruption via flux cancellation between the sheared arcades overlying filament F2, creating a flux rope and leading to the first double-ribbon solar flare. During this phase, we observed the eruption of overlying arcades and coronal loops, which leads to the first CME. The second reconnection is believed to occur between the expanding flux rope of F2 and the overlying arcades of filament F1. We suggest that this reconnection destabilized the equilibrium of filament F1, which further facilitated its eruption. The third stage of reconnection occurred in the wake of the erupting filament F1 between the legs of the overlying arcades. This may create a flux rope and the second double-ribbon flare and a second CME. The fourth reconnection was between the expanding arcades of the erupting filament F1 and the nearby ambient field, which produced the bi-directional plasma flows both upward and downward. Observations and a nonlinear force-free field extrapolation confirm the possibility of reconnection and the causal link between the magnetic systems.
Perspectives on magnetic reconnection
Yamada, Masaaki
2016-01-01
Magnetic reconnection is a topological rearrangement of magnetic field that occurs on time scales much faster than the global magnetic diffusion time. Since the field lines break on microscopic scales but energy is stored and the field is driven on macroscopic scales, reconnection is an inherently multi-scale process that often involves both magnetohydrodynamic (MHD) and kinetic phenomena. In this article, we begin with the MHD point of view and then describe the dynamics and energetics of reconnection using a two-fluid formulation. We also focus on the respective roles of global and local processes and how they are coupled. We conclude that the triggers for reconnection are mostly global, that the key energy conversion and dissipation processes are either local or global, and that the presence of a continuum of scales coupled from microscopic to macroscopic may be the most likely path to fast reconnection. PMID:28119547
Wilder, F. D.; Ergun, R. E.; Goodrich, K. A.; Goldman, M. V.; Newman, D. L.; Malaspina, D. M.; Jaynes, A. N.; Schwartz, S. J.; Trattner, K. J.; Burch, J. L.; Argall, M. R.; Torbert, R. B.; Lindqvist, P.-A.; Marklund, G.; Le Contel, O.; Mirioni, L.; Khotyaintsev, Yu. V.; Strangeway, R. J.; Russell, C. T.; Pollock, C. J.; Giles, B. L.; Plaschke, F.; Magnes, W.; Eriksson, S.; Stawarz, J. E.; Sturner, A. P.; Holmes, J. C.
2016-06-01
We show observations from the Magnetospheric Multiscale (MMS) mission of whistler mode waves in the Earth's low-latitude boundary layer (LLBL) during a magnetic reconnection event. The waves propagated obliquely to the magnetic field toward the X line and were confined to the edge of a southward jet in the LLBL. Bipolar parallel electric fields interpreted as electrostatic solitary waves (ESW) are observed intermittently and appear to be in phase with the parallel component of the whistler oscillations. The polarity of the ESWs suggests that if they propagate with the waves, they are electron enhancements as opposed to electron holes. The reduced electron distribution shows a shoulder in the distribution for parallel velocities between 17,000 and 22,000 km/s, which persisted during the interval when ESWs were observed, and is near the phase velocity of the whistlers. This shoulder can drive Langmuir waves, which were observed in the high-frequency parallel electric field data.
Magnetohydrodynamic simulation of reconnection in turbulent astrophysical plasmas
Energy Technology Data Exchange (ETDEWEB)
Widmer, Fabien
2016-07-19
Turbulence is ubiquitous at large-Reynolds-number astrophysical plasmas like in the Solar corona. In such environments, the turbulence is thought to enhance the energy conversion rate by magnetic reconnection above the classical model predictions. Since turbulence cannot be simulated together with the large scale behaviour of the plasma, magnetic reconnection is studied through the average properties of turbulence. A Reynolds-averaged turbulence model is explored in which turbulence is self-sustained and -generated by the large scales (mean-) field inhomogeneities. Employing that model, the influence of turbulence is investigated by large-scale MHD numerical simulations solving evolution equations of the energy and cross-helicity of the turbulence together with the MHD equations. Magnetic reconnection is found to be either rapidly enhanced or suppressed by turbulence depending on the turbulence timescale. If the turbulence timescale is self-consistently calculated, reconnection is always strongly enhanced. Since the solar corona bears strong guide magnetic fields perpendicular to the reconnecting magnetic fields, the influences of a strong guide field on turbulent reconnection is separately investigated. A slow down of reconnection, obtained in the presence of a finite guide field, can be understood by a finite residual helicity working against the enhancement of reconnection by the turbulence. The influence of turbulence on magnetic reconnection is further studied by means of high resolution simulations of plasmoid-unstable current sheets. These simulations revealed the importance of turbulence for reaching fast reconnection.
Turbulent magnetic fluctuations in laboratory reconnection
Von Stechow, Adrian; Grulke, Olaf; Klinger, Thomas
2016-07-01
The role of fluctuations and turbulence is an important question in astrophysics. While direct observations in space are rare and difficult dedicated laboratory experiments provide a versatile environment for the investigation of magnetic reconnection due to their good diagnostic access and wide range of accessible plasma parameters. As such, they also provide an ideal chance for the validation of space plasma reconnection theories and numerical simulation results. In particular, we studied magnetic fluctuations within reconnecting current sheets for various reconnection parameters such as the reconnection rate, guide field, as well as plasma density and temperature. These fluctuations have been previously interpreted as signatures of current sheet plasma instabilities in space and laboratory systems. Especially in low collisionality plasmas these may provide a source of anomalous resistivity and thereby contribute a significant fraction of the reconnection rate. We present fluctuation measurements from two complementary reconnection experiments and compare them to numerical simulation results. VINETA.II (Greifswald, Germany) is a cylindrical, high guide field reconnection experiment with an open field line geometry. The reconnecting current sheet has a three-dimensional structure that is predominantly set by the magnetic pitch angle which results from the superposition of the guide field and the in-plane reconnecting field. Within this current sheet, high frequency magnetic fluctuations are observed that correlate well with the local current density and show a power law spectrum with a spectral break at the lower hybrid frequency. Their correlation lengths are found to be extremely short, but propagation is nonetheless observed with high phase velocities that match the Whistler dispersion. To date, the experiment has been run with an external driving field at frequencies higher than the ion cyclotron frequency f_{ci}, which implies that the EMHD framework applies
Aspects of Collisionless Magnetic Reconnection in Asymmetric Systems
Hesse, Michael; Aunai, Nicolas; Zeitani, Seiji; Kuznetsova, Masha; Birn, Joachim
2013-01-01
Asymmetric reconnection is being investigated by means of particle-in-cell simulations. The research has two foci: the direction of the reconnection line in configurations with non-vanishing magnetic fields; and the question why reconnection can be faster if a guide field is added to an otherwise unchanged asymmetric configuration. We find that reconnection prefers a direction, which maximizes the available magnetic energy, and show that this direction coincides with the bisection of the angle between the asymptotic magnetic fields. Regarding the difference in reconnection rates between planar and guide field models, we demonstrate that a guide field can provide essential confinement for particles in the reconnection region, which the weaker magnetic field in one of the inflow directions cannot necessarily provide.
Leonardis, E; Chapman, S C; Daughton, W; Roytershteyn, V; Karimabadi, H
2013-05-17
Recent fully nonlinear, kinetic three-dimensional simulations of magnetic reconnection [W. Daughton et al., Nat. Phys. 7, 539 (2011)] evolve structures and exhibit dynamics on multiple scales, in a manner reminiscent of turbulence. These simulations of reconnection are among the first to be performed at sufficient spatiotemporal resolution to allow formal quantitative analysis of statistical scaling, which we present here. We find that the magnetic field fluctuations generated by reconnection are anisotropic, have nontrivial spatial correlation, and exhibit the hallmarks of finite range fluid turbulence: they have non-Gaussian distributions, exhibit extended self-similarity in their scaling, and are spatially multifractal. Furthermore, we find that the rate at which the fields do work on the particles, J · E, is also multifractal, so that magnetic energy is converted to plasma kinetic energy in a manner that is spatially intermittent. This suggests that dissipation in this sense in collisionless reconnection on kinetic scales has an analogue in fluidlike turbulent phenomenology, in that it proceeds via multifractal structures generated by an intermittent cascade.
Magnetic reconnection in two-dimensional magnetohydrodynamic turbulence.
Servidio, S; Matthaeus, W H; Shay, M A; Cassak, P A; Dmitruk, P
2009-03-20
Systematic analysis of numerical simulations of two-dimensional magnetohydrodynamic turbulence reveals the presence of a large number of X-type neutral points where magnetic reconnection occurs. We examine the statistical properties of this ensemble of reconnection events that are spontaneously generated by turbulence. The associated reconnection rates are distributed over a wide range of values and scales with the geometry of the diffusion region. Locally, these events can be described through a variant of the Sweet-Parker model, in which the parameters are externally controlled by turbulence. This new perspective on reconnection is relevant in space and astrophysical contexts, where plasma is generally in a fully turbulent regime.
Directory of Open Access Journals (Sweden)
Syed Zaki Hassan Kazmi
Full Text Available The dynamical fluctuations in the rhythms of biological systems provide valuable information about the underlying functioning of these systems. During the past few decades analysis of cardiac function based on the heart rate variability (HRV; variation in R wave to R wave intervals has attracted great attention, resulting in more than 17000-publications (PubMed list. However, it is still controversial about the underling mechanisms of HRV. In this study, we performed both linear (time domain and frequency domain and nonlinear analysis of HRV data acquired from humans and animals to identify the relationship between HRV and heart rate (HR. The HRV data consists of the following groups: (a human normal sinus rhythm (n = 72; (b human congestive heart failure (n = 44; (c rabbit sinoatrial node cells (SANC; n = 67; (d conscious rat (n = 11. In both human and animal data at variant pathological conditions, both linear and nonlinear analysis techniques showed an inverse correlation between HRV and HR, supporting the concept that HRV is dependent on HR, and therefore, HRV cannot be used in an ordinary manner to analyse autonomic nerve activity of a heart.
Influence of forced respiration on nonlinear dynamics in heart rate variability
DEFF Research Database (Denmark)
Kanters, J K; Højgaard, M V; Agner, E;
1997-01-01
of this study was to test whether the known nonlinear input from spontaneous respiration is a source for the nonlinearities in heart rate variability. Twelve healthy subjects were examined in supine position with 3-h electrocardiogram recordings during both spontaneous and forced respiration in accordance...... expressed as the nonlinear prediction error did not differ between spontaneous respiration, 32.3 +/- 3.4 ms, and forced respiration, 31.9 +/- 5.7. It is concluded that the origin of the nonlinear dynamics in heart rate variability is not a nonlinear input from the respiration into the cardiovascular...... oscillator. Additional studies are needed to elucidate the mechanisms behind the nonlinear dynamics in heart rate variability....
Short- and long-term variations in non-linear dynamics of heart rate variability
DEFF Research Database (Denmark)
Kanters, J K; Højgaard, M V; Agner, E;
1996-01-01
OBJECTIVES: The purpose of the study was to investigate the short- and long-term variations in the non-linear dynamics of heart rate variability, and to determine the relationships between conventional time and frequency domain methods and the newer non-linear methods of characterizing heart rate...... variability. METHODS: Twelve healthy subjects were investigated by 3-h ambulatory ECG recordings repeated on 3 separate days. Correlation dimension, non-linear predictability, mean heart rate, and heart rate variability in the time and frequency domains were measured and compared with the results from...... corresponding surrogate time series. RESULTS: A small significant amount of non-linear dynamics exists in heart rate variability. Correlation dimensions and non-linear predictability are relatively specific parameters for each individual examined. The correlation dimension is inversely correlated to the heart...
TURBULENT RECONNECTION IN RELATIVISTIC PLASMAS AND EFFECTS OF COMPRESSIBILITY
Energy Technology Data Exchange (ETDEWEB)
Takamoto, Makoto [Max-Planck-Institut für Kernphysik, Heidelberg (Germany); Inoue, Tsuyoshi [Division of Theoretical Astronomy, National Astronomical Observatory of Japan (Japan); Lazarian, Alexandre, E-mail: mtakamoto@eps.s.u-tokyo.ac.jp, E-mail: tsuyoshi.inoue@nao.ac.jp, E-mail: alazarian@facstaff.wisc.edu [Department of Astronomy, University of Wisconsin, 475 North Charter Street, Madison, WI 53706 (United States)
2015-12-10
We report on the turbulence effects on magnetic reconnection in relativistic plasmas using three-dimensional relativistic resistive magnetohydrodynamics simulations. We found that the reconnection rate became independent of the plasma resistivity due to turbulence effects similarly to non-relativistic cases. We also found that compressible turbulence effects modified the turbulent reconnection rate predicted in non-relativistic incompressible plasmas; the reconnection rate saturates, and even decays, as the injected velocity approaches to the Alfvén velocity. Our results indicate that compressibility cannot be neglected when a compressible component becomes about half of the incompressible mode, occurring when the Alfvén Mach number reaches about 0.3. The obtained maximum reconnection rate is around 0.05–0.1, which will be able to reach around 0.1–0.2 if injection scales are comparable to the sheet length.
Institute of Scientific and Technical Information of China (English)
GUO Qintao; ZHANG Lingmi; TAO Zheng
2008-01-01
Thin wall component is utilized to absorb impact energy of a structure. However, the dynamic behavior of such thin-walled structure is highly non-linear with material, geometry and boundary non-linearity. A model updating and validation procedure is proposed to build accurate finite element model of a frame structure with a non-linear thin-walled component for dynamic analysis. Design of experiments (DOE) and principal component decomposition (PCD) approach are applied to extract dynamic feature from nonlinear impact response for correlation of impact test result and FE model of the non-linear structure. A strain-rate-dependent non-linear model updating method is then developed to build accurate FE model of the structure. Computer simulation and a real frame structure with a highly non-linear thin-walled component are employed to demonstrate the feasibility and effectiveness of the proposed approach.
Collisionless Reconnection and Electron Demagnetization
Scudder, J. D.
Observable, dimensionless properties of the electron diffusion region of collisionless magnetic reconnection are motivated and benchmarked in two and three dimensional Particle In Cell (PIC) simulations as appropriate for measurements with present state of the art spacecraft. The dimensionless quantities of this paper invariably trace their origin to breaking the magnetization of the thermal electrons. Several observable proxies are also motivated for the rate of frozen flux violation and a parameter \\varLambda _{\\varPhi } that when greater than unity is associated with close proximity to the analogue of the saddle point region of 2D reconnection usually called the electron diffusion region. Analogous regions to the electron diffusion region of 2D reconnection with \\varLambda _{\\varPhi } > 1 have been identified in 3D simulations. 10-20 disjoint diffusion regions are identified and the geometrical patterns of their locations illustrated. First examples of associations between local observables based on electron demagnetization and global diagnostics (like squashing) are also presented. A by product of these studies is the development of a single spacecraft determinations of gradient scales in the plasma.
Cluster Spacecraft Observations of Magnetopause Reconnection at Multiple Scales
Retino, A.; Vaivads, A.; Chasapis, A.; Rossi, C.; Sahraoui, F.; Canu, P.; Nakamura, R.; Mozer, F.
2013-12-01
Magnetic reconnection is an inherently multi-scale process where the dynamics at small-scales strongly affect the large-scale evolution of the process. The microphysics of reconnection (i.e. the physics at proton scales and below) is particularly important. Key questions are reconnection onset, time evolution (rate) and ion and electron heating/acceleration around reconnection sites. The Earth's magnetopause is an excellent laboratory for studying reconnection, especially at subsolar point where is more steady and easier to study with spacecraft data. Despite of initially being a high-latitude mission, ESA/Cluster spacecraft have crossed the subsolar magnetopause starting from 2008. During such recent orbits two spacecraft were separated by ~10s km (sub-proton/electron scales) while being apart ~ 1000s km (fluid scales) from the others. This special configuration allows studying reconnection at multiple scales. Here we present a few examples of magnetopause reconnection from such recent Cluster multi-scale orbits. For one case of subsolar reconnection, the observation of jet reversals at large scales allows setting the position of the reconnection site in between the spacecraft. Two-point observations at sub-proton/electron scales are then used to identify a very thin rotational discontinuity (having a thickness of about 10 electron gyroradii) and study the microphysics therein. We also show a few other examples of magnetopause reconnection from the Cluster Guest Investigator campaign (2012), for which orbit, spacecraft configuration and instrument modes were tailored to study reconnection at multiple scales. We discuss the relevance of such recent Cluster measurements for the reconnection science of upcoming NASA/MMS and other multi-scale future missions.
Buechner, J.; Jain, N.; Sharma, A.
2013-12-01
The four s/c of the Magnetospheric Multiscale (MMS) mission, to be launched in 2014, will use the Earth's magnetosphere as a laboratory to study the microphysics of three fundamental plasma processes. One of them is magnetic reconnection, an essentially multi-scale process. While laboratory experiments and past theoretical investigations have shown that important processes necessary to understand magnetic reconnection take place at electron scales the MMS mission for the first time will be able to resolve these scales by in space observations. For the measurement strategy of MMS it is important to make specific predictions of the behavior of current sheets with a thickness of the order of the electron skin depth which play an important role in the evolution of collisionless magnetic reconnection. Since these processes are highly nonlinear and non-local numerical simulation is needed to specify the current sheet evolution. Here we present new results about the nonlinear evolution of electron-scale current sheets starting from the linear stage and using 3-D electron-magnetohydrodynamic (EMHD) simulations. The growth rates of the simulated instabilities compared well with the growth rates obtained from linear theory. Mechanisms and conditions of the formation of flux ropes and of current filamentation will be discussed in comparison with the results of fully kinetic simulations. In 3D the X- and O-point configurations of the magnetic field formed in reconnection planes alternate along the out-of-reconnection-plane direction with the wavelength of the unstable mode. In the presence of multiple reconnection sites, the out-of-plane magnetic field can develop nested structure of quadrupoles in reconnection planes, similar to the 2-D case, but now with variations in the out-of-plane direction. The structures of the electron flow and magnetic field in 3-D simulations will be compared with those in 2-D simulations to discriminate the essentially 3D features. We also discuss
Nonlinear Resistivity for Magnetohydrodynamical Models
Lingam, Manasvi; Pfefferlé, David; Comisso, Luca; Bhattacharjee, Amitava
2016-01-01
A nonlinear current-dependent resistivity that accurately accounts for the collisional electron-ion momentum transfer rate is derived. It is shown that the Spitzer resistivity overestimates the resistivity in certain observationally relevant regimes. The nonlinear resistivity computed herein is a strictly decreasing function of the current, in contrast to some notable previous proposals. The relative importance of the new expression with respect to the well-established electron inertia and Hall terms is also examined. The subtle implications of this current-dependent resistivity are discussed in the context of plasma systems and phenomena such as magnetic reconnection.
Plasmoid Instability in High-Lundquist-Number Magnetic Reconnection
Huang, Yi-Min
2013-01-01
Our understanding of magnetic reconnection in resistive magnetohydrodynamics has gone through a fundamental change in recent years. The conventional wisdom is that magnetic reconnection mediated by resistivity is slow in laminar high Lundquist ($S$) plasmas, constrained by the scaling of the reconnection rate predicted by Sweet-Parker theory. However, recent studies have shown that when $S$ exceeds a critical value $\\sim10^{4}$, the Sweet-Parker current sheet is unstable to a super-Alfv\\'enic plasmoid instability, with a linear growth rate that scales as $S^{1/4}$. In the fully developed statistical steady state of two-dimensional resistive magnetohydrodynamic simulations, the normalized average reconnection rate is approximately 0.01, nearly independent of $S$, and the distribution function $f(\\psi)$ of plasmoid magnetic flux $\\psi$ follows a power law $f(\\psi)\\sim\\psi^{-1}$. When Hall effects are included, the plasmoid instability may trigger onset of Hall reconnection even when the conventional criterion f...
Magnetic Reconnection Onset via Disruption of a Forming Current Sheet by the Tearing Instability.
Uzdensky, D A; Loureiro, N F
2016-03-11
The recent realization that Sweet-Parker current sheets are violently unstable to the secondary tearing (plasmoid) instability implies that such current sheets cannot occur in real systems. This suggests that, in order to understand the onset of magnetic reconnection, one needs to consider the growth of the tearing instability in a current layer as it is being formed. Such an analysis is performed here in the context of nonlinear resistive magnetohydrodynamics for a generic time-dependent equilibrium representing a gradually forming current sheet. It is shown that two onset regimes, single-island and multi-island, are possible, depending on the rate of current sheet formation. A simple model is used to compute the criterion for transition between these two regimes, as well as the reconnection onset time and the current sheet parameters at that moment. For typical solar corona parameters, this model yields results consistent with observations.
Bifurcated structure of the electron diffusion region in three-dimensional magnetic reconnection.
Liu, Yi-Hsin; Daughton, W; Karimabadi, H; Li, H; Roytershteyn, V
2013-06-28
Three-dimensional kinetic simulations of magnetic reconnection reveal that the electron diffusion region is composed of two or more current sheets in regimes with weak magnetic shear angles ϕ≲80°. This new morphology is explained by oblique tearing modes which produce flux ropes while simultaneously driving enhanced current at multiple resonance surfaces. This physics persists into the nonlinear regime leading to multiple electron layers embedded within a larger Alfvénic inflow and outflow. Surprisingly, the thickness of these layers and the reconnection rate both remain comparable to two-dimensional models. The parallel electric fields are supported predominantly by the electron pressure tensor and electron inertia, while turbulent dissipation remains small.
SIVS EPIDEMIC MODELS WITH INFECTION AGE AND NONLINEAR VACCINATION RATE
Institute of Scientific and Technical Information of China (English)
无
2010-01-01
Vaccination is a very important strategy for the elimination of infectious diseaVaccination is a very important strategy for the elimination of infectious diseases. A SIVS epidemic model with infection age and nonlinear vaccination has been formulated in this paper. Using the theory of differential and integral equation, we show the local asymptotic stability of the infection-free equilibrium and the endemic equilibrium under some assumptions.
Two-dimensional MHD model of the reconnection diffusion region
Directory of Open Access Journals (Sweden)
N. V. Erkaev
2002-01-01
Full Text Available Magnetic reconnection is an important process providing a fast conversion of magnetic energy into thermal and kinetic plasma energy. In this concern, a key problem is that of the resistive diffusion region where the reconnection process is initiated. In this paper, the diffusion region is associated with a nonuniform conductivity localized to a small region. The nonsteady resistive incompressible MHD equations are solved numerically for the case of symmetric reconnection of antiparallel magnetic fields. A Petschek type steady-state solution is obtained as a result of time relaxation of the reconnection layer structure from an arbitrary initial stage. The structure of the diffusion region is studied for various ratios of maximum and minimum values of the plasma resistivity. The effective length of the diffusion region and the reconnection rate are determined as functions of the length scale and the maximum of the resistivity. For sufficiently small length scale of the resistivity, the reconnection rate is shown to be consistent with Petschek's formula. By increasing the resistivity length scale and decreasing the resistivity maximum, the reconnection layer tends to be wider, and correspondingly, the reconnection rate tends to be more consistent with that of the Parker-Sweet regime.
Reconnection at the Heliopause
Nickeler, D H; Nickeler, Dieter H.; Fahr, Hans-Joerg
2005-01-01
In this MHD-model of the heliosphere, we assume a Parker-type flow, and a Parker-type spiral magnetic field, which is extrapolated further downstream from the termination shock to the heliopause. We raise the question whether the heliopause nose region may be leaky with respect to fields and plasmas due to nonideal plasma dynamics, implying a breakdown of the magnetic barrier. We analyse some simple scenarios to find reconnection rates and circumstances, under which the heliosphere can be an "open" or a "closed" magnetosphere. We do not pretend to offer a complete solution for the heliosphere, on the basis of nonideal MHD theory, but present a prescription to find such a solution on the basis of potential fields including the knowledge of neutral points. As an example we imitate the Parker spiral as a monopole with a superposition of homogeneous asymptotical boundary conditions. We use this toy model for x < -R where R = 100 AU is the distance of the termination shock to describe the situation in the nose ...
Energy Technology Data Exchange (ETDEWEB)
Reber, T. J.; Plumb, N. C.; Waugh, J. A.; Dessau, D. S. [Department of Physics, University of Colorado, Boulder, Colorado 80309-0390 (United States)
2014-04-15
Detector counting rate nonlinearity, though a known problem, is commonly ignored in the analysis of angle resolved photoemission spectroscopy where modern multichannel electron detection schemes using analog intensity scales are used. We focus on a nearly ubiquitous “inverse saturation” nonlinearity that makes the spectra falsely sharp and beautiful. These artificially enhanced spectra limit accurate quantitative analysis of the data, leading to mistaken spectral weights, Fermi energies, and peak widths. We present a method to rapidly detect and correct for this nonlinearity. This algorithm could be applicable for a wide range of nonlinear systems, beyond photoemission spectroscopy.
Multiscale structures of resistive magnetic reconnection at high magnetic Reynolds numbers
Miyoshi, Takahiro; Kusano, Kanya
Magnetic reconnection is the most important process of explosive phenomena in space plasmas. The magnetic Reynolds number for the space plasmas are extremely high in general since those plasmas are thought to be collisionless or semi-collisional. However, magnetic reconnection rate becomes low as magnetic Reynolds number increases within the framework of a stationary resistive MHD model. Thus, modern models of magnetic reconnection often include kinetic effects such as the Hall effect to explain realistic explosive magnetic reconnection. It is thought, on the other hand, that the MHD approximation is valid for the plasmas within a very wide range of scales since the scale gap between the macro-and micro-scale is quite large, e.g., in the solar corona, the ratio of the macro to micro will be more than 107 . Such multiscale structures of MHD with wide range of scales, however, have not been clarified so far. Therefore, in this paper, resistive magnetic reconnection at high magnetic Reynolds numbers are investigated using very high-resolution MHD simulations. Simulation results show that the magnetic energy at high magnetic Reynolds numbers is explosively released, while that at not-so-high magnetic Reynolds numbers is steadily dissipated. In the case of high magnetic Reynolds numbers, multiple small scale plasmoids are intermittently created and ejected via secondary tearing modes in a nonlinearly developed thin current sheet. It is revealed that a secondary plasmoid is not only accelerated up to a local magnetosonic speed toward the down-stream region but also perturbs the up-stream region. Thus, complicated multiscale structures appear around the magnetic field reversal layer. Perspective for the high-resolution simulation of extremely high magnetic Reynolds numbers will be also discussed.
Reconnection at three dimensional magnetic null points: Effect of current sheet asymmetry
Wyper, P. F.; Jain, Rekha
2013-05-01
Asymmetric current sheets are likely to be prevalent in both astrophysical and laboratory plasmas with complex three dimensional (3D) magnetic topologies. This work presents kinematic analytical models for spine and fan reconnection at a radially symmetric 3D null (i.e., a null where the eigenvalues associated with the fan plane are equal) with asymmetric current sheets. Asymmetric fan reconnection is characterized by an asymmetric reconnection of flux past each spine line and a bulk flow of plasma across the null point. In contrast, asymmetric spine reconnection is characterized by the reconnection of an equal quantity of flux across the fan plane in both directions. The higher modes of spine reconnection also include localized wedges of vortical flux transport in each half of the fan. In this situation, two definitions for reconnection rate become appropriate: a local reconnection rate quantifying how much flux is genuinely reconnected across the fan plane and a global rate associated with the net flux driven across each semi-plane. Through a scaling analysis, it is shown that when the ohmic dissipation in the layer is assumed to be constant, the increase in the local rate bleeds from the global rate as the sheet deformation is increased. Both models suggest that asymmetry in the current sheet dimensions will have a profound effect on the reconnection rate and manner of flux transport in reconnection involving 3D nulls.
Reconnection at three dimensional magnetic null points: Effect of current sheet asymmetry
Energy Technology Data Exchange (ETDEWEB)
Wyper, P. F.; Jain, Rekha [School of Mathematics and Statistics, University of Sheffield, Sheffield, South Yorkshire S3 7RH (United Kingdom)
2013-05-15
Asymmetric current sheets are likely to be prevalent in both astrophysical and laboratory plasmas with complex three dimensional (3D) magnetic topologies. This work presents kinematic analytical models for spine and fan reconnection at a radially symmetric 3D null (i.e., a null where the eigenvalues associated with the fan plane are equal) with asymmetric current sheets. Asymmetric fan reconnection is characterized by an asymmetric reconnection of flux past each spine line and a bulk flow of plasma across the null point. In contrast, asymmetric spine reconnection is characterized by the reconnection of an equal quantity of flux across the fan plane in both directions. The higher modes of spine reconnection also include localized wedges of vortical flux transport in each half of the fan. In this situation, two definitions for reconnection rate become appropriate: a local reconnection rate quantifying how much flux is genuinely reconnected across the fan plane and a global rate associated with the net flux driven across each semi-plane. Through a scaling analysis, it is shown that when the ohmic dissipation in the layer is assumed to be constant, the increase in the local rate bleeds from the global rate as the sheet deformation is increased. Both models suggest that asymmetry in the current sheet dimensions will have a profound effect on the reconnection rate and manner of flux transport in reconnection involving 3D nulls.
Asymmetric magnetic reconnection with a flow shear and applications to the magnetopause
Doss, C. E.; Komar, C. M.; Cassak, P. A.; Wilder, F. D.; Eriksson, S.; Drake, J. F.
2015-09-01
We perform a systematic theoretical and numerical study of antiparallel two-dimensional magnetic reconnection with asymmetries in the plasma density and reconnecting magnetic field strength in addition to a bulk flow shear across the reconnection site in the plane of the reconnecting fields, which commonly occurs at planetary magnetospheres. We analytically predict the speed at which an isolated X line is convected by the flow, the reconnection rate, and the critical flow speed at which reconnection no longer takes place for arbitrary reconnecting magnetic field strengths, densities, and upstream flow speeds, and we confirm the results with two-fluid numerical simulations. The predictions and simulation results counter the prevailing model of reconnection at Earth's dayside magnetopause which says reconnection occurs with a stationary X line for sub-Alfvénic magnetosheath flow, reconnection occurs but the X line convects for magnetosheath flows between the Alfvén speed and double the Alfvén speed, and reconnection does not occur for magnetosheath flows greater than double the Alfvén speed. In particular, we find that X line motion is governed by momentum conservation from the upstream flows, which are weighted differently in asymmetric systems, so the X line convects for generic conditions including sub-Alfvénic upstream speeds. For the reconnection rate, as with symmetric reconnection, it drops with increasing flow shear and there is a cutoff speed above which reconnection is not predominant. However, while the cutoff condition for symmetric reconnection is that the difference in flows on the two sides of the reconnection site is twice the Alfvén speed, we find asymmetries cause the cutoff speed for asymmetric reconnection to be higher than twice the asymmetric form of the Alfvén speed. The stronger the asymmetries, the more the cutoff exceeds double the asymmetric Alfvén speed. This is due to the fact that in asymmetric reconnection, the plasma with the
Nonlinear Stability of a SIRS Epidemic Model with Convex Incidence Rate
Buonomo, B.; Rionero, S.
2010-09-01
We study an epidemic model for infections with non permanent acquired immunity (SIRS). The incidence rate is assumed to be convex respect to the infective class. By using a peculiar Lyapunov function, we obtain necessary and sufficient conditions for the local nonlinear stability of equilibria. Conditions ensuring the global stability of the endemic equilibrium are also obtained. Our procedure allows to enlarge the class of incidence rates ensuring the Lyapunov nonlinear stability of the endemic equilibrium for SIRS models.
McNaughton, B H; Kopelman, R; Agayan, Rodney R.; Kopelman, Raoul; Naughton, Brandon H. Mc
2006-01-01
We report on a new technique which was used to detect single Escherichia coli that is based on the changes in the nonlinear rotation of a magnetic microsphere driven by an external magnetic field. The presence of one Escherichia Coli bacterium on the surface of a 2.0 micron magnetic microsphere caused an easily measurable change in the drag of the system and, therefore, in the nonlinear rotation rate. The straight-forward measurement uses standard microscopy techniques and the observed average shift in the nonlinear rotation rate changed by a factor of ~3.8.
Directory of Open Access Journals (Sweden)
Juan Bolea
2016-11-01
Full Text Available The purpose of this study is to characterize and attenuate the influence of mean heart rate (HR on nonlinear heart rate variability (HRV indices (correlation dimension, sample and approximate entropy as a consequence of being the HR the intrinsic sampling rate of HRV signal. This influence can notably alter nonlinear HRV indices and lead to biased information regarding autonomic nervous system (ANS modulation.First, a simulation study was carried out to characterize the dependence of nonlinear HRV indices on HR assuming similar ANS modulation. Second, two HR-correction approaches were proposed: one based on regression formulas and another one based on interpolating RR time series. Finally, standard and HR-corrected HRV indices were studied in a body position change database.The simulation study showed the HR-dependence of non-linear indices as a sampling rate effect, as well as the ability of the proposed HR-corrections to attenuate mean HR influence. Analysis in a body position changes database shows that correlation dimension was reduced around 21% in median values in standing with respect to supine position (p < 0.05, concomitant with a 28% increase in mean HR (p < 0.05. After HR-correction, correlation dimension decreased around 18% in standing with respect to supine position, being the decrease still significant. Sample and approximate entropy showed similar trends.HR-corrected nonlinear HRV indices could represent an improvement in their applicability as markers of ANS modulation when mean HR changes.
Fast reconnection in relativistic plasmas: the magnetohydrodynamics tearing instability revisited
Del Zanna, L.; Papini, E.; Landi, S.; Bugli, M.; Bucciantini, N.
2016-08-01
Fast reconnection operating in magnetically dominated plasmas is often invoked in models for magnetar giant flares, for magnetic dissipation in pulsar winds, or to explain the gamma-ray flares observed in the Crab nebula; hence, its investigation is of paramount importance in high-energy astrophysics. Here we study, by means of two-dimensional numerical simulations, the linear phase and the subsequent non-linear evolution of the tearing instability within the framework of relativistic resistive magnetohydrodynamics (MHD), as appropriate in situations where the Alfvén velocity approaches the speed of light. It is found that the linear phase of the instability closely matches the analysis in classical MHD, where the growth rate scales with the Lundquist number S as S-1/2, with the only exception of an enhanced inertial term due to the thermal and magnetic energy contributions. In addition, when thin current sheets of inverse aspect ratio scaling as S-1/3 are considered, the so-called ideal tearing regime is retrieved, with modes growing independently of S and extremely fast, on only a few light crossing times of the sheet length. The overall growth of fluctuations is seen to solely depend on the value of the background Alfvén velocity. In the fully non-linear stage, we observe an inverse cascade towards the fundamental mode, with Petschek-type supersonic jets propagating at the external Alfvén speed from the X-point, and a fast reconnection rate at the predicted value {R}˜ (ln S)^{-1}.
Exchange Rates and Monetary Fundamentals: What Do We Learn from Linear and Nonlinear Regressions?
Directory of Open Access Journals (Sweden)
Guangfeng Zhang
2014-01-01
Full Text Available This paper revisits the association between exchange rates and monetary fundamentals with the focus on both linear and nonlinear approaches. With the monthly data of Euro/US dollar and Japanese yen/US dollar, our linear analysis demonstrates the monetary model is a long-run description of exchange rate movements, and our nonlinear modelling suggests the error correction model describes the short-run adjustment of deviations of exchange rates, and monetary fundamentals are capable of explaining exchange rate dynamics under an unrestricted framework.
Quantitative study of guide-field effects on Hall reconnection in a laboratory plasma.
Tharp, T D; Yamada, M; Ji, H; Lawrence, E; Dorfman, S; Myers, C E; Yoo, J
2012-10-19
The effect of guide field on magnetic reconnection is quantitatively studied by systematically varying an applied guide field in the Magnetic Reconnection Experiment (MRX). The quadrupole field, a signature of two-fluid reconnection at zero guide field, is altered by a finite guide field. It is shown that the reconnection rate is significantly reduced with increasing guide field, and this dependence is explained by a combination of local and global physics: locally, the in-plane Hall currents are reduced, while globally guide field compression produces an increased pressure both within and downstream of the reconnection region.
Reconnection of Colliding Cosmic Strings
Hanany, A; Hanany, Amihay; Hashimoto, Koji
2005-01-01
For vortex strings in the Abelian Higgs model and D-strings in superstring theory, both of which can be regarded as cosmic strings, we give analytical study of reconnection (recombination, inter-commutation) when they collide, by using effective field theories on the strings. First, for the vortex strings, via a string sigma model, we verify analytically that the reconnection is classically inevitable for small collision velocity and small relative angle. Evolution of the shape of the reconnected strings provides an upper bound on the collision velocity in order for the reconnection to occur. These analytical results are in agreement with previous numerical results. On the other hand, reconnection of the D-strings is not classical but probabilistic. We show that a quantum calculation of the reconnection probability using a D-string action reproduces the nonperturbative nature of the worldsheet results by Jackson, Jones and Polchinski. The difference on the reconnection -- classically inevitable for the vortex...
Interchange Reconnection Alfven Wave Generation
Lynch, B J; Li, Y
2014-01-01
Given recent observational results of interchange reconnection processes in the solar corona and the theoretical development of the S-Web model for the slow solar wind, we present further analysis of the 3D MHD simulation of interchange reconnection by Edmondson et al. (Astrophys. J. 707, 1427, 2009). Specifically, we analyze the consequences of the dynamic streamer belt jump that corresponds to flux opening by interchange reconnection. Information about the magnetic field restructuring by interchange reconnection is carried throughout the system by Alfven waves propagating away from the reconnection region, distributing the shear and twist imparted by the driving flows, including shedding the injected stress-energy and accumulated magnetic helicity along newly-open field lines. We quantify the properties of the reconnection-generated wave activity in the simulation. There is a localized high frequency component associated with the current sheet/reconnection site and an extended low frequency component associ...
First Principles Modeling of Nonlinear Incidence Rates in Seasonal Epidemics
2011-01-01
In this paper we used a general stochastic processes framework to derive from first principles the incidence rate function that characterizes epidemic models. We investigate a particular case, the Liu-Hethcote-van den Driessche's (LHD) incidence rate function, which results from modeling the number of successful transmission encounters as a pure birth process. This derivation also takes into account heterogeneity in the population with regard to the per individual transmission probability. We...
Stark, A; Fox, W; Egedal, J; Grulke, O; Klinger, T
2005-12-02
Observations in space and laboratory plasmas suggest magnetic reconnection as a mechanism for ion heating and formation of non-Maxwellian ion velocity distribution functions (IVDF). Laser-induced fluorescence measurements of the IVDF parallel to the X line of a periodically driven reconnection experiment are presented. A time-resolved analysis yields the evolution of the IVDF within a reconnection cycle. It is shown that reconnection causes a strong increase of the ion temperature, where the strongest increase is found at the maximum reconnection rate. Monte Carlo simulations demonstrate that ion heating is a consequence of the in-plane electric field that forms around the X line in response to reconnection.
Abreu, P
2001-01-01
The preliminary results on the search of colour reconnection effects (CR) from the four experiments at LEP, Aleph, Delphi, L3 and Opal, are reviewed. Extreme models are excluded by studies of standard variables, and on going studies of a method first suggested by L3, the particle flow method, are yet inconclusive.
First principles modeling of nonlinear incidence rates in seasonal epidemics.
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José M Ponciano
2011-02-01
Full Text Available In this paper we used a general stochastic processes framework to derive from first principles the incidence rate function that characterizes epidemic models. We investigate a particular case, the Liu-Hethcote-van den Driessche's (LHD incidence rate function, which results from modeling the number of successful transmission encounters as a pure birth process. This derivation also takes into account heterogeneity in the population with regard to the per individual transmission probability. We adjusted a deterministic SIRS model with both the classical and the LHD incidence rate functions to time series of the number of children infected with syncytial respiratory virus in Banjul, Gambia and Turku, Finland. We also adjusted a deterministic SEIR model with both incidence rate functions to the famous measles data sets from the UK cities of London and Birmingham. Two lines of evidence supported our conclusion that the model with the LHD incidence rate may very well be a better description of the seasonal epidemic processes studied here. First, our model was repeatedly selected as best according to two different information criteria and two different likelihood formulations. The second line of evidence is qualitative in nature: contrary to what the SIRS model with classical incidence rate predicts, the solution of the deterministic SIRS model with LHD incidence rate will reach either the disease free equilibrium or the endemic equilibrium depending on the initial conditions. These findings along with computer intensive simulations of the models' Poincaré map with environmental stochasticity contributed to attain a clear separation of the roles of the environmental forcing and the mechanics of the disease transmission in shaping seasonal epidemics dynamics.
First principles modeling of nonlinear incidence rates in seasonal epidemics.
Ponciano, José M; Capistrán, Marcos A
2011-02-01
In this paper we used a general stochastic processes framework to derive from first principles the incidence rate function that characterizes epidemic models. We investigate a particular case, the Liu-Hethcote-van den Driessche's (LHD) incidence rate function, which results from modeling the number of successful transmission encounters as a pure birth process. This derivation also takes into account heterogeneity in the population with regard to the per individual transmission probability. We adjusted a deterministic SIRS model with both the classical and the LHD incidence rate functions to time series of the number of children infected with syncytial respiratory virus in Banjul, Gambia and Turku, Finland. We also adjusted a deterministic SEIR model with both incidence rate functions to the famous measles data sets from the UK cities of London and Birmingham. Two lines of evidence supported our conclusion that the model with the LHD incidence rate may very well be a better description of the seasonal epidemic processes studied here. First, our model was repeatedly selected as best according to two different information criteria and two different likelihood formulations. The second line of evidence is qualitative in nature: contrary to what the SIRS model with classical incidence rate predicts, the solution of the deterministic SIRS model with LHD incidence rate will reach either the disease free equilibrium or the endemic equilibrium depending on the initial conditions. These findings along with computer intensive simulations of the models' Poincaré map with environmental stochasticity contributed to attain a clear separation of the roles of the environmental forcing and the mechanics of the disease transmission in shaping seasonal epidemics dynamics.
Nonlinearity and fractional integration in the US dollar/euro exchange rate
Directory of Open Access Journals (Sweden)
Kiran Burcu
2012-01-01
Full Text Available This paper examines the nonlinear behavior and the fractional integration property of the US dollar/euro exchange rate over the period from January 1999 to August 2010 by extending the procedure of Peter M. Robinson (1994 to the case of nonlinearity. First, using the approach developed by Mehmet Caner and Bruce E. Hansen (2001, we investigate the possible presence of nonlinearity in the series through the estimation of a two-regime threshold autoregressive model. After finding nonlinearity, we also allow for disturbances to be fractionally integrated based on the different versions of Robinson (1994 tests. The findings show that the US dollar/euro exchange rate follows a stationary process with a weak evidence for long memory.
Forecasting RMB Exchange Rate Based on a Nonlinear Combination Model of ARFIMA, SVM, and BPNN
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Chi Xie
2015-01-01
Full Text Available There are various models to predict financial time series like the RMB exchange rate. In this paper, considering the complex characteristics of RMB exchange rate, we build a nonlinear combination model of the autoregressive fractionally integrated moving average (ARFIMA model, the support vector machine (SVM model, and the back-propagation neural network (BPNN model to forecast the RMB exchange rate. The basic idea of the nonlinear combination model (NCM is to make the prediction more effective by combining different models’ advantages, and the weight of the combination model is determined by a nonlinear weighted mechanism. The RMB exchange rate against US dollar (RMB/USD and the RMB exchange rate against Euro (RMB/EUR are used as the empirical examples to evaluate the performance of NCM. The results show that the prediction performance of the nonlinear combination model is better than the single models and the linear combination models, and the nonlinear combination model is suitable for the prediction of the special time series, such as the RMB exchange rate.
Kohler, Susanna
2016-05-01
Because the Sun is so close, it makes an excellent laboratory to study processes we cant examinein distant stars. One openquestion is that of how solar magnetic fields rearrange themselves, producing the tremendous releases of energy we observe as solar flares and coronal mass ejections (CMEs).What is Magnetic Reconnection?Magnetic reconnection occurs when a magnetic field rearranges itself to move to a lower-energy state. As field lines of opposite polarity reconnect, magnetic energy is suddenly converted into thermal and kinetic energy.This processis believed to be behind the sudden releases of energy from the solar surface in the form of solar flares and CMEs. But there are many different models for how magnetic reconnection could occur in the magnetic field at the Suns surface, and we arent sure which one of these reconnection types is responsible for the events we see.Recently, however, several studies have been published presenting some of the first observational support of specific reconnection models. Taken together, these observations suggest that there are likely several different types of reconnection happening on the solar surface. Heres a closer look at two of these recent publications:A pre-eruption SDO image of a flaring region (b) looks remarkably similar to a 3D cartoon for typical breakout configuration (a). Click for a closer look! [Adapted from Chen et al. 2016]Study 1:Magnetic BreakoutLed by Yao Chen (Shandong University in China), a team of scientists has presented observations made by the Solar Dynamics Observatory (SDO) of a flare and CME event that appears to have been caused by magnetic breakout.In the magnetic breakout model, a series of loops in the Suns lower corona are confined by a surrounding larger loop structure called an arcade higher in the corona. As the lower loops push upward, reconnection occurs in the upper corona, removing the overlying, confining arcade. Without that extra confinement, the lower coronal loops expand upward
Magnetic reconnection in Saturn's magnetotail: A comprehensive magnetic field survey.
Smith, A. W.; Jackman, C. M.; Thomsen, M. F.; Dougherty, M. K.
2015-10-01
Magnetic reconnection is a fundamental process throughout the solar system, significantly shaping and modulating the magnetospheres of the magnetized planets. Within planetary magnetotails reconnection can be responsible for energizing particles and potentially changing the total flux and mass contained within the magnetosphere. The Kronian magnetosphere is thought to be a middle ground between the rotationally dominated Jovian magnetosphere and the solar wind driven terrestrial magnetosphere. However, previous studies have not been able to find a statistical reconnection x-line, as has been possible at both Jupiter and Earth. Additionally the standard picture of magnetotail reconnection at Saturn, developed by Cowley et al. [2004], suggests a potential asymmetry between the dawn and dusk flanks, caused by different reconnection processes dominating. This work centers on the development of an algorithm designed to find reconnection related events in spacecraft magnetometer data, aiming to reduce the bias that manual searches could inherently introduce, thereby ensuring the validity of any statistical analysis. The algorithm primarily identifies the reconnection related events from deflections in the north-south component of the magnetic field, allowing an almost uninterrupted in-situ search (when the spacecraft is situated within the magnetotail). The new catalogue of candidate reconnection events, produced by the algorithm, enables a more complete statistical view of reconnection in the Kronian magnetotail. Well-studied data encompassing the deep magnetotail and dawn flank (particularly from orbits in 2006) were used to train the algorithm and develop reasonable criteria. The algorithm was then applied to data encompassing the dusk flank (including orbits from 2009, for which plasma data have been examined by Thomsen et al. [2014]). This combination enables a robust, and global, comparison of reconnection rates, signatures and properties in the Kronian magnetotail.
Results on stabilization of nonlinear systems under finite data-rate constraints
Persis, Claudio De
2004-01-01
We discuss in this paper a result concerning the stabilization problem of nonlinear systems under data-rate constraints using output feedback. To put the result in a broader context, we shall first review a number of recent contributions on the stabilization problem under data-rate constraints when
Kinetic simulations of secondary reconnection in the reconnection jet
Huang, S. Y.; Zhou, M.; Yuan, Z. G.; Fu, H. S.; He, J. S.; Sahraoui, F.; Aunai, N.; Deng, X. H.; Fu, S.; Pang, Y.; Wang, D. D.
2015-08-01
Magnetic reconnection, as one important energy dissipation process in plasmas, has been extensively studied in the past several decades. Magnetic reconnection occurring in the downstream of a primary X line is referred to as secondary reconnection. In this paper, we used kinetic simulations to investigate the secondary reconnection in detail. We found that secondary reconnection is reversed by the compression caused by the outflowing jet originating from the primary reconnection site, which results in the erosion of the magnetic island between the two X lines within ~3 ωci-1. We show the observational signatures expected in electromagnetic fields and plasma measurements in the Earth's magnetotail, associated with this mechanism. These simulation results could be applied to interpret the signatures associated with the evolution of earthward magnetic islands in the Earth's magnetotail.
Three-dimensional fast magnetic reconnection driven by relativistic ultraintense femtosecond lasers.
Ping, Y L; Zhong, J Y; Sheng, Z M; Wang, X G; Liu, B; Li, Y T; Yan, X Q; He, X T; Zhang, J; Zhao, G
2014-03-01
Three-dimensional fast magnetic reconnection driven by two ultraintense femtosecond laser pulses is investigated by relativistic particle-in-cell simulation, where the two paralleled incident laser beams are shot into a near-critical plasma layer to form a magnetic reconnection configuration in self-generated magnetic fields. A reconnection X point and out-of-plane quadrupole field structures associated with magnetic reconnection are formed. The reconnection rate is found to be faster than that found in previous two-dimensional Hall magnetohydrodynamic simulations and electrostatic turbulence contribution to the reconnection electric field plays an essential role. Both in-plane and out-of-plane electron and ion accelerations up to a few MeV due to the magnetic reconnection process are also obtained.
Effects of Hall Current in the Driven Reconnection with Various Scales
Institute of Scientific and Technical Information of China (English)
YANG Hong-Ang; JIN Shu-Ping
2004-01-01
In the driven reconnection process with various scales, the effect of Hall current is studied numerically using a Hall magnetohydrodynamics (MHD) code derived from a multi-step implicit scheme. In the cases with Lc/di ≤ 1.0 (Lcis the half-thickness of initial current layer, di is the ion inertial length), the features of Hall MHD reconnection are shown as follows: a quasi-steady single X-line reconnection is obtained, the By component with a quadrupolar structure is generated and the maximum reconnection rate is larger than 0.11. In the cases with Lc/di ＞ 1.0, the effect of Hall current on the reconnection dynamics weakens and Hall MHD reconnection is gradually transformed into resistive MHD reconnection as Lc/di increases.
Ion acceleration and heating by kinetic Alfvén waves associated with magnetic reconnection
Liang, Ji; Lin, Yu; Johnson, Jay R.; Wang, Zheng-Xiong; Wang, Xueyi
2017-10-01
Our previous study on the generation and signatures of kinetic Alfvén waves (KAWs) associated with magnetic reconnection in a current sheet revealed that KAWs are a common feature during reconnection [Liang et al. J. Geophys. Res.: Space Phys. 121, 6526 (2016)]. In this paper, ion acceleration and heating by the KAWs generated during magnetic reconnection are investigated with a three-dimensional (3-D) hybrid model. It is found that in the outflow region, a fraction of inflow ions are accelerated by the KAWs generated in the leading bulge region of reconnection, and their parallel velocities gradually increase up to slightly super-Alfvénic. As a result of wave-particle interactions, an accelerated ion beam forms in the direction of the anti-parallel magnetic field, in addition to the core ion population, leading to the development of non-Maxwellian velocity distributions, which include a trapped population with parallel velocities consistent with the wave speed. The ions are heated in both parallel and perpendicular directions. In the parallel direction, the heating results from nonlinear Landau resonance of trapped ions. In the perpendicular direction, however, evidence of stochastic heating by the KAWs is found during the acceleration stage, with an increase of magnetic moment μ. The coherence in the perpendicular ion temperature T⊥ and the perpendicular electric and magnetic fields of KAWs also provides evidence for perpendicular heating by KAWs. The parallel and perpendicular heating of the accelerated beam occur simultaneously, leading to the development of temperature anisotropy with T⊥>T∥ . The heating rate agrees with the damping rate of the KAWs, and the heating is dominated by the accelerated ion beam. In the later stage, with the increase of the fraction of the accelerated ions, interaction between the accelerated beam and the core population also contributes to the ion heating, ultimately leading to overlap of the beams and an overall
Radiative Magnetic Reconnection in Astrophysics
Uzdensky, Dmitri A
2015-01-01
I review a new rapidly growing area of high-energy plasma astrophysics --- radiative magnetic reconnection, i.e., a reconnection regime where radiation reaction influences reconnection dynamics, energetics, and nonthermal particle acceleration. This influence be may be manifested via a number of astrophysically important radiative effects, such as radiation-reaction limits on particle acceleration, radiative cooling, radiative resistivity, braking of reconnection outflows by radiation drag, radiation pressure, viscosity, and even pair creation at highest energy densities. Self-consistent inclusion of these effects in magnetic reconnection theory and modeling calls for serious modifications to our overall theoretical approach to the problem. In addition, prompt reconnection-powered radiation often represents our only observational diagnostic tool for studying remote astrophysical systems; this underscores the importance of developing predictive modeling capabilities to connect the underlying physical condition...
Magnetic Reconnection: Theoretical and Observational Perspectives: Preface
Lewis, W. S.; Antiochos, S. K,; Drake, J. F.
2011-01-01
Magnetic reconnection is a fundamental plasma-physical process by which energy stored in a magnetic field is converted, often explosively, into heat and the kinetic energy of the charged particles that constitute the plasma. It occurs in a variety of astrophysical settings, ranging from the solar corona to pulsar magnetospheres and winds, as well as in laboratory fusion experiments, where it is responsible for sawtooth crashes. First proposed by R.G. Giovanelli in the late I 940s as the mechanism responsible for solar flares, magnetic reconnection was invoked at the beginning of the space age to explain not just solar flares but also the transfer of energy, mass, and momentum from the solar wind to Earth's magnetosphere and the subsequent storage and release of the transferred energy in the magnetotai\\. During the half century or so that has followed the seminal theoretical works by J.W. Dungey, P.A. Sweet, E.N. Parker, and H.E. Petschek, in-situ measurements by Earth-orbiting satellites and remote-sensing observations of the solar corona have provided a growing body of evidence for the occurrence of reconnection at the Sun, in the solar wind, and in the near-Earth space environment. The last thirty years have also seen the development of laboratory reconnection experiments at a number of institutions. In parallel with the efforts of experimentalists in both space and laboratory plasma physics, theorists have investigated, analytically and with the help of increasingly powerful MHD, hybrid, and kinetic numerical simulations, the structure of the diffusion region, the factors controlling the rate, onset, and cessation of reconnection, and the detailed physics that enables the demagnetization of the ions and electrons and the topological reconfiguration of the magnetic field. Moreover, the scope of theoretical reconnection studies has been extended well beyond solar system and laboratory plasmas to include more exotic astrophysical plasma systems whose strong (10
Detailed discussion of the optimum baud rate of nonlinearity in WDM transmission
Wang, Wanli; Qiao, Yaojun; Yang, Lin
2017-01-01
Different numbers of sub-channels correspond to different baud rates per sub-channel when the total baud rate is fixed. The optimum baud rate of nonlinearity in WDM systems is investigated in this paper. We find that the phase matching effect produces an optimum baud rate of nonlinearity, which is related to the chromatic dispersion accumulation of a single span. Then other factors that influence the optimum baud rate are analyzed. By mathematical derivation and simulation verification, larger number of spans and larger spectrum gap between sub-channels both make the optimum value decrease. We also find that different modulation formats barely change the optimum baud rate if other system settings are the same and all sub-channels have the same modulation format.
Activation of MHD reconnection on ideal timescales
Landi, S.; Papini, E.; Del Zanna, L.; Tenerani, A.; Pucci, F.
2017-01-01
Magnetic reconnection in laboratory, space and astrophysical plasmas is often invoked to explain explosive energy release and particle acceleration. However, the timescales involved in classical models within the macroscopic MHD regime are far too slow to match the observations. Here we revisit the tearing instability by performing visco-resistive two-dimensional numerical simulations of the evolution of thin current sheets, for a variety of initial configurations and of values of the Lunquist number S, up to 107. Results confirm that when the critical aspect ratio of S 1/3 is reached in the reconnecting current sheets, the instability proceeds on ideal (Alfvénic) macroscopic timescales, as required to explain observations. Moreover, the same scaling is seen to apply also to the local, secondary reconnection events triggered during the nonlinear phase of the tearing instability, thus accelerating the cascading process to increasingly smaller spatial and temporal scales. The process appears to be robust, as the predicted scaling is measured both in inviscid simulations and when using a Prandtl number P = 1 in the viscous regime.
Plasmoid Instabilities Mediated Three-Dimensional Magnetohydrodynamic Turbulent Reconnection
Energy Technology Data Exchange (ETDEWEB)
Huang, Yi-min [Princeton University; Guo, Fan [Los Alamos National Laboratory
2015-07-21
After some introductory remarks on fast reconnection in resistive MHD due to plasmoid instability, oblique tearing modes in 3D, and previous studies on 3D turbulent reconnection, the subject is presented under the following topics: 3D simulation setup, time evolution of the 3D simulation, comparison with Sweet-Parker and 2D plasmoid reconnection, and diagnostics of the turbulent state (decomposition of mean fields and fluctuations, power spectra of energy fluctuations, structure function and eddy anisotropy with respect to local magnetic field). Three primary conclusions were reached: (1) The results suggest that 3D plasmoid instabilities can lead to self-generated turbulent reconnection (evidence of energy cascade and development of inertial range, energy fluctuations preferentially align with the local magnetic field, which is one of the characteristics of MHD turbulence); (2) The turbulence is highly inhomogeneous, due to the presence of magnetic shear and outflow jets (conventional MHD turbulence theories or phenomenologies may not be applicable – e.g. scale-dependent anisotropy as predicted by Goldreich & Sridhar is not found); (3) 3D turbulent reconnection is different from 2D plasmoid-dominated reconnection in many aspects. However, in fully developed state, reconnection rates in 2D and 3D are comparable — this result needs to be further checked in higher S.
Parallel Electric Fields Associated with Sub-Solar Reconnection: MMS Observations
Ergun, Robert; Goodrich, Katherine; Wilder, Frederick; Holmes, Justin; Stawarz, Julia; Sturner, Andrew; Eriksson, Stefan; Malaspina, David; Unsanova, Maria; Torbert, Roy; Lindqvist, Per-Arne; Khotyaintsev, Yuri; Burch, James; Strangeway, Robert; Russel, Christopher; Giles, Barbara; Pollock, Craig
2016-04-01
We present MMS observations of parallel electric fields associated with sub-solar magnetic reconnection and provide an early interpretation of their implications on the reconnection processes. The MMS satellites have observed many instances of large-amplitude parallel electric fields (10's to greater than 100 mV/m) that appear to lie on or near the magnetic reconnection separatrix, in particular, near a strong current layer on the magnetospheric-side separatrix. These parallel electric field events are directly associated with magnetic reconnection and, on most occasions, are recorded by more than one of the MMS spacecraft. We see several types of parallel electric fields. We interpret purely parallel electrostatic waves and the evolved nonlinear states of these waves as mixing of cold plasma with warm magnetosheath plasma on a freshly reconnected field line. Large-amplitude spikes associated with tangled magnetic fields represent possible secondary reconnection events. Whistler waves and evolved non-linear whistler waves are associated with associated with mixing of plasmas. These observations suggest that (1) magnetic reconnection is often "patchy" and results in tangled magnetic field lines and that (2) cold plasma (<10 eV) is often present in sub-solar reconnection.
Sub-ion scale plasmoids during collisionless reconnection on TREX
Olson, Joseph; Egedal, Jan; Myers, Rachel; Greess, Sam; Clark, Mike; Wallace, John; Forest, Cary; Wisconsin Plasma Astrophysics Laboratory Collaboration
2016-10-01
The Terrestrial Reconnection Experiment (TREX), operating at the Wisconsin Plasma Astrophysics Laboratory, is able to explore a collisionless regime inaccessible to previous reconnection experiments. To date, TREX has already achieved Lundquist numbers up to 104 where kinetic effects, such as electron pressure anisotropy, become important to the reconnection dynamics. During a recent run campaign in this collisionless regime, the spontaneous formation of magnetic islands (plasmoids) inside the ion diffusion region was observed. It is known that long current layers are susceptible to tearing, leading to the formation of plasmoids, and that these plasmoids have strong effects on the reconnection rate and particle energization. However, contrary to theoretical and numerical predictions, the TREX experiments show that the plasmoid instability is active even when the current layer is less than one di long. Analysis of these events shows that smaller plasmoids occur at a higher rate than larger ones, suggesting that magnetic islands could be seeded in plasmas more effectively than previously thought.
On the energization of charged particles by fast magnetic reconnection
Sharma, Rohit; Mitra, Dhrubaditya; Oberoi, Divya
2017-09-01
We study the role of turbulence in magnetic reconnection, within the framework of magnetohydrodynamics, using three-dimensional direct numerical simulations. For small turbulent intensity, we find that the reconnection rate obeys Sweet-Parker scaling. For large enough turbulent intensity, reconnection rate departs significantly from Sweet-Parker behaviour, becomes almost a constant as a function of the Lundquist number. We further study energization of test-particles in the same set-up. We find that the speed of the energized particles obeys a Maxwellian distribution, whose variance also obeys Sweet-Parker scaling for small turbulent intensity but depends weakly on the Lundquist number for large turbulent intensity. Furthermore, the variance is found to increase with the strength of the reconnecting magnetic field.
On the energisation of charged particles by fast magnetic reconnection
Sharma, Rohit; Oberoi, Divya
2016-01-01
We study the role of turbulence in magnetic reconnection, within the framework of magneto-hydrodynamics, using three-dimensional direct numerical simulations. For small turbulent intensity we find that the reconnection rate obeys Sweet-Parker scaling. For large enough turbulent intensity reconnection rate departs significantly from Sweet-Parker behaviour, becomes almost a constant as a function of the Lundquist number. We further study energisation of test-particles in the same setup. We find that the speed of the energised particles obeys a Maxwellian distribution, whose variance also obeys Sweet-Parker scaling for small turbulent intensity but depends weakly on the Lundquist number for large turbulent intensity. Furthermore, the variance is found to increase with the strength of the reconnecting magnetic field.
Effects of breathing patterns and light exercise on linear and nonlinear heart rate variability.
Weippert, Matthias; Behrens, Kristin; Rieger, Annika; Kumar, Mohit; Behrens, Martin
2015-08-01
Despite their use in cardiac risk stratification, the physiological meaning of nonlinear heart rate variability (HRV) measures is not well understood. The aim of this study was to elucidate effects of breathing frequency, tidal volume, and light exercise on nonlinear HRV and to determine associations with traditional HRV indices. R-R intervals, blood pressure, minute ventilation, breathing frequency, and respiratory gas concentrations were measured in 24 healthy male volunteers during 7 conditions: voluntary breathing at rest, and metronome guided breathing (0.1, 0.2 and 0.4 Hz) during rest, and cycling, respectively. The effect of physical load was significant for heart rate (HR; p effect of load and breathing pattern was evident. Correlations to traditional HRV indices were modest (r from -0.14 to -0.67, p exercise does not significantly affect short-time HRV nonlinear indices, respiratory activity has to be considered as a potential contributor at rest and during light dynamic exercise.
Geometry effect on energy transfer rate in a coupled-quantum-well structure: nonlinear regime
Salavati-fard, T.; Vazifehshenas, T.
2014-12-01
We study theoretically the effect of geometry on the energy transfer rate at nonlinear regime in a coupled-quantum-well system using the balance equation approach. To investigate comparatively the effect of both symmetric and asymmetric geometry, different structures are considered. The random phase approximation dynamic dielectric function is employed to include the contributions from both quasiparticle and plasmon excitations. Also, the short-range exchange interaction is taken into account through the Hubbard approximation. Our numerical results show that the energy transfer rate increases by increasing the well thicknesses in symmetric structures. Furthermore, by increasing spatial asymmetry, the energy transfer rate decreases for the electron temperature range of interest. From numerical calculations, it is obtained that the nonlinear energy transfer rate is proportional to the square of electron drift velocity in all structures and also, found that the influence of Hubbard local field correction on the energy transfer rate gets weaker by increasing the strength of applied electric field.
Collisionless magnetic reconnection under anisotropic MHD approximation
Hirabayashi, Kota; Hoshino, Masahiro
We study the formation of slow-mode shocks in collisionless magnetic reconnection by using one- and two-dimensional collisionless magneto-hydro-dynamic (MHD) simulations based on the double adiabatic approximation, which is an important step to bridge the gap between the Petschek-type MHD reconnection model accompanied by a pair of slow shocks and the observational evidence of the rare occasion of in-situ slow shock observation. According to our results, a pair of slow shocks does form in the reconnection layer. The resultant shock waves, however, are quite weak compared with those in an isotropic MHD from the point of view of the plasma compression and the amount of the magnetic energy released across the shock. Once the slow shock forms, the downstream plasma are heated in highly anisotropic manner and a firehose-sense (P_{||}>P_{⊥}) pressure anisotropy arises. The maximum anisotropy is limited by the marginal firehose criterion, 1-(P_{||}-P_{⊥})/B(2) =0. In spite of the weakness of the shocks, the resultant reconnection rate is kept at the same level compared with that in the corresponding ordinary MHD simulations. It is also revealed that the sequential order of propagation of the slow shock and the rotational discontinuity, which appears when the guide field component exists, changes depending on the magnitude of the guide field. Especially, when no guide field exists, the rotational discontinuity degenerates with the contact discontinuity remaining at the position of the initial current sheet, while with the slow shock in the isotropic MHD. Our result implies that the slow shock does not necessarily play an important role in the energy conversion in the reconnection system and is consistent with the satellite observation in the Earth's magnetosphere.
Nonlinear analysis of heart rate variability in patients with eating disorders
Vigo, Daniel E.; Castro, Mariana N.; Dorpinghaus, Andrea; Weidema, Hylke; Cardinali, Daniel P.; Siri, Leonardo Nicola; Rovira, Bernardo; Fahrer, Rodolfo D.; Nogues, Martin; Leiguarda, Ramon C.; Guinjoan, Salvador M.
2008-01-01
Patients with anorexia nervosa or bulimia nervosa often have signs of autonomic dysfunction potentially deleterious to the heart. The aim of this study was to ascertain the nonlinear properties of heart rate variability in patients with eating disorders. A group of 33 women with eating disorders (14
Minimal data rate stabilization of nonlinear systems over networks with large delays
Persis, Claudio De
2007-01-01
We consider the problem of designing encoders, decoders and controllers which stabilize feedforward nonlinear systems over a communication network with finite bandwidth and large delay. The control scheme guarantees minimal data-rate semi-global asymptotic and local exponential stabilizatioln of the
The Nonlinear Dynamic Relationship of Exchange Rates: Parametric and Nonparametric Causality testing
Bekiros, S.D.; Diks, C.
2007-01-01
The present study investigates the long-term linear and nonlinear causal linkages among six currencies, namely EUR/USD, GBP/USD, USD/JPY, USD/CHF, AUD/USD and USD/CAD. The prime motivation for choosing these exchange rates comes from the fact that they are the most liquid and widely traded, covering
Nonlinear analysis of heart rate variability in patients with eating disorders
Vigo, Daniel E.; Castro, Mariana N.; Dorpinghaus, Andrea; Weidema, Hylke; Cardinali, Daniel P.; Siri, Leonardo Nicola; Rovira, Bernardo; Fahrer, Rodolfo D.; Nogues, Martin; Leiguarda, Ramon C.; Guinjoan, Salvador M.
2008-01-01
Patients with anorexia nervosa or bulimia nervosa often have signs of autonomic dysfunction potentially deleterious to the heart. The aim of this study was to ascertain the nonlinear properties of heart rate variability in patients with eating disorders. A group of 33 women with eating disorders (14
Convergence rates for dispersive approximation schemes to nonlinear Schr\\"odinger equations
Ignat, Liviu I
2011-01-01
This article is devoted to the analysis of the convergence rates of several numerical approximation schemes for linear and nonlinear Schr\\"odinger equations on the real line. Recently, the authors have introduced viscous and two-grid numerical approximation schemes that mimic at the discrete level the so-called Strichartz dispersive estimates of the continuous Schr\\"odinger equation. This allows to guarantee the convergence of numerical approximations for initial data in L2(R), a fact that can not be proved in the nonlinear setting for standard conservative schemes unless more regularity of the initial data is assumed. In the present article we obtain explicit convergence rates and prove that dispersive schemes fulfilling the Strichartz estimates are better behaved for H^s(R) data if 0 < s < 1/2. Indeed, while dispersive schemes ensure a polynomial convergence rate, non-dispersive ones only yield logarithmic decay rates.
Hooker, John C.
1990-01-01
A preliminary study of the applicability of nonlinear dynamic systems analysis techniques to low body negative pressure (LBNP) studies. In particular, the applicability of the heart rate delay map is investigated. It is suggested that the heart rate delay map has potential as a supplemental tool in the assessment of subject performance in LBNP tests and possibly in the determination of susceptibility to cardiovascular deconditioning with spaceflight.
What do we know about real exchange rate non-linearities?
DEFF Research Database (Denmark)
Kruse, Robinson; Frömmel, Michael; Menkhoff, Lukas;
This research points to the serious problem of potentially misspecified alternative hypotheses when testing for unit roots in real exchange rates. We apply a popular unit root test against nonlinear ESTAR and develop a Markov Switching unit root test. The empirical power of these tests against co...... model performs clearly better. An empirical application of these tests suggests that real exchange rates may indeed be explained by Markov-Switching dynamics....
Non-linear and scale-invariant analysis of the Heart Rate Variability
Kalda, J; Vainu, M; Laan, M
2003-01-01
Human heart rate fluctuates in a complex and non-stationary manner. Elaborating efficient and adequate tools for the analysis of such signals has been a great challenge for the researchers during last decades. Here, an overview of the main research results in this field is given. The following question are addressed: (a) what are the intrinsic features of the heart rate variability signal; (b) what are the most promising non-linear measures, bearing in mind clinical diagnostic and prognostic applications.
Relativistic Magnetic Reconnection in Pair Plasmas in Three Dimensions
Kagan, Daniel; Spitkovsky, Anatoly
2012-01-01
We investigate guide-field magnetic reconnection and particle acceleration in relativistic pair plasmas with three-dimensional particle-in-cell (PIC) simulations of a kinetic-scale current sheet in a periodic geometry at low magnetizations. The tearing instability is the dominant mode in the current sheet for all guide field strengths, while the linear kink mode is less important even without guide field. Oblique modes seem to be suppressed entirely. In its nonlinear evolution, the reconnection layer develops a network of interconnected and interacting magnetic flux ropes. As smaller flux ropes merge into larger ones, the reconnection layer evolves toward a three-dimensional, disordered state in which the resulting flux rope segments contain magnetic substructure on plasma skin depth scales. Embedded in the flux ropes, we detect spatially and temporally intermittent sites of dissipation reflected in peaks in the parallel electric field. Magnetic dissipation and particle acceleration persist until the end of t...
Helicity, Topology and Kelvin Waves in reconnecting quantum knots
di Leoni, P Clark; Brachet, M E
2016-01-01
Helicity is a topological invariant that measures the linkage and knottedness of lines, tubes and ribbons. As such, it has found myriads of applications in astrophysics and solar physics, in fluid dynamics, in atmospheric sciences, and in biology. In quantum flows, where topology-changing reconnection events are a staple, helicity appears as a key quantity to study. However, the usual definition of helicity is not well posed in quantum vortices, and its computation based on counting links and crossings of vortex lines can be downright impossible to apply in complex and turbulent scenarios. We present a new definition of helicity which overcomes these problems. With it, we show that only certain reconnection events conserve helicity. In other cases helicity can change abruptly during reconnection. Furthermore, we show that these events can also excite Kelvin waves, which slowly deplete helicity as they interact nonlinearly, thus linking the theory of vortex knots with observations of quantum turbulence.
Laboratory observation of localized onset of magnetic reconnection.
Katz, Noam; Egedal, Jan; Fox, Will; Le, Ari; Bonde, Jeff; Vrublevskis, Arturs
2010-06-25
Magnetic reconnection is a fundamental process in plasmas that results in the often explosive release of stored magnetic energy, but the trigger for its onset is not well understood. We explore this trigger for fast reconnection in toroidal experiments using a magnetic x-type geometry in the strong guide-field regime. We find that the onset occurs asymmetrically: the reconnection begins on one side of the torus and propagates around approximately at the Alfvén speed. The fast reconnection occurs only in the presence of a global plasma mode, which breaks the axisymmetry and enables the current at the x line to decrease sharply. A simple semiempirical model is used to describe the onset's growth rate.
MESSENGER observations of magnetic reconnection in Mercury's magnetosphere.
Slavin, James A; Acuña, Mario H; Anderson, Brian J; Baker, Daniel N; Benna, Mehdi; Boardsen, Scott A; Gloeckler, George; Gold, Robert E; Ho, George C; Korth, Haje; Krimigis, Stamatios M; McNutt, Ralph L; Raines, Jim M; Sarantos, Menelaos; Schriver, David; Solomon, Sean C; Trávnícek, Pavel; Zurbuchen, Thomas H
2009-05-01
Solar wind energy transfer to planetary magnetospheres and ionospheres is controlled by magnetic reconnection, a process that determines the degree of connectivity between the interplanetary magnetic field (IMF) and a planet's magnetic field. During MESSENGER's second flyby of Mercury, a steady southward IMF was observed and the magnetopause was threaded by a strong magnetic field, indicating a reconnection rate ~10 times that typical at Earth. Moreover, a large flux transfer event was observed in the magnetosheath, and a plasmoid and multiple traveling compression regions were observed in Mercury's magnetotail, all products of reconnection. These observations indicate that Mercury's magnetosphere is much more responsive to IMF direction and dominated by the effects of reconnection than that of Earth or the other magnetized planets.
Three-dimensional shock formation in the spontaneous fast reconnection evolution
Kondoh, K.; Ugai, M.; Shimizu, T.
2011-12-01
Shock structure associated with magnetic reconnection is studied using three-dimensional magneto-hydro-dynamics simulations on the basis of the spontaneous fast reconnection model. In the two-dimensional reconnection, the angle between the slow shock pair (thickness of the plasma sheet) is smaller (thinner) in the region with higher reconnection rate. On the other hand, in the three-dimensional reconnection, the reconnection rate in the diffusion region is not uniform in the direction of sheet current, and the angle between the shock pair at the center of the diffusion region should be smallest. However, the profile of the angle in the direction of sheet current is not satisfied with this relationship. It is shown that this structure is caused by the inflow from the direction of the positive and negative sheet current and the inflow of the magnetic flux accompanied with it.
Fast magnetic reconnection supported by sporadic small-scale Petschek-type shocks
Energy Technology Data Exchange (ETDEWEB)
Shibayama, Takuya, E-mail: shibayama@stelab.nagoya-u.ac.jp; Nakabou, Takashi [Institute for Space-Earth Environmental Research, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8601 (Japan); Kusano, Kanya [Institute for Space-Earth Environmental Research, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8601 (Japan); Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Kanazawa-ku, Yokohama, Kanagawa 236-0001 (Japan); Miyoshi, Takahiro [Department of Physical Science, Graduate School of Science, Hiroshima University, Higashi-Hiroshima 739-8526 (Japan); Vekstein, Grigory [Jodrell Bank Centre for Astrophysics, University of Manchester, Manchester M13 9PL (United Kingdom)
2015-10-15
Standard magnetohydrodynamic (MHD) theory predicts reconnection rate that is far too slow to account for a wide variety of reconnection events observed in space and laboratory plasmas. Therefore, it was commonly accepted that some non-MHD (kinetic) effects play a crucial role in fast reconnection. A recently renewed interest in simple MHD models is associated with the so-called plasmoid instability of reconnecting current sheets. Although it is now evident that this effect can significantly enhance the rate of reconnection, many details of the underlying multiple-plasmoid process still remain controversial. Here, we report results of a high-resolution computer simulation which demonstrate that fast albeit intermittent magnetic reconnection is sustained by numerous small-scale Petschek-type shocks spontaneously formed in the current sheet due to its plasmoid instability.
Turbulent reconnection and its implications
Lazarian, A.; Eyink, G.; Vishniac, E.; Kowal, G.
2015-01-01
Magnetic reconnection is a process of magnetic field topology change, which is one of the most fundamental processes happening in magnetized plasmas. In most astrophysical environments, the Reynolds numbers corresponding to plasma flows are large and therefore the transition to turbulence is inevitable. This turbulence, which can be pre-existing or driven by magnetic reconnection itself, must be taken into account for any theory of magnetic reconnection that attempts to describe the process in the aforementioned environments. This necessity is obvious as three-dimensional high-resolution numerical simulations show the transition to the turbulence state of initially laminar reconnecting magnetic fields. We discuss ideas of how turbulence can modify reconnection with the focus on the Lazarian & Vishniac (Lazarian & Vishniac 1999 Astrophys. J. 517, 700–718 ()) reconnection model. We present numerical evidence supporting the model and demonstrate that it is closely connected to the experimentally proven concept of Richardson dispersion/diffusion as well as to more recent advances in understanding of the Lagrangian dynamics of magnetized fluids. We point out that the generalized Ohm's law that accounts for turbulent motion predicts the subdominance of the microphysical plasma effects for reconnection for realistically turbulent media. We show that one of the most dramatic consequences of turbulence is the violation of the generally accepted notion of magnetic flux freezing. This notion is a cornerstone of most theories dealing with magnetized plasmas, and therefore its change induces fundamental shifts in accepted paradigms, for instance, turbulent reconnection entails reconnection diffusion process that is essential for understanding star formation. We argue that at sufficiently high Reynolds numbers the process of tearing reconnection should transfer to turbulent reconnection. We discuss flares that are predicted by turbulent reconnection and relate this process to
Parazzini, Marta; Ravazzani, Paolo; Thuroczy, György; Molnar, Ferenc B; Ardesi, Gianluca; Sacchettini, Alessio; Mainardi, Luca Tommaso
2013-06-01
This study was designed to assess the nonlinear dynamics of heart rate variability (HRV) during exposure to low-intensity EMFs. Twenty-six healthy young volunteers were subjected to a rest-to-stand protocol to evaluate autonomic nervous system in quiet condition (rest, vagal prevalence) and after a sympathetic activation (stand). The procedure was conducted twice in a double-blind design: once with a genuine EMFs exposure (GSM cellular phone at 900 MHz, 2 W) and once with a sham exposure (at least 24 h apart). During each session, three-lead electrocardiograms were recorded and RR series extracted off-line. The RR series were analyzed by nonlinear deterministic techniques in every phase of the protocol and during the different exposures. The analysis of the data shows there was no statistically significant effect due to GSM exposure on the nonlinear dynamics of HRV.
Magnetic reconnection during magnetospheric substorms
Baker, Daniel N.
1996-01-01
The near earth reconnection model of substorms represents an attempt to place a broad range of observations into a consistent framework. The roles and requirements of reconnection are discussed. High speed plasma sheet flows, thin current sheet instability, substorm triggering, plasmoids and flux ropes in the distant tail, and magnetohydrodynamic simulations are discussed. Substorms are global, coherent sequences of processes involving solar wind/magnetosphere/ionosphere interaction. Magnetic reconnection is required to explain different dayside and polar cap phenomena, which required nightside reconnection. The modification and expansion of the standard near earth neutral line (NENL) model can integrate breakup arcs, current disruption, current wedge features, and localized plasma flows into the magnetic reconnection framework.
Separatrices: the crux of reconnection
Lapenta, Giovanni; Divin, Andrey; Newman, David; Goldman, Martin
2014-01-01
Reconnection is one of the key processes in astrophysical and laboratory plasmas: it is the opposite of a dynamo. Looking at energy, a dynamo transforms kinetic energy in magnetic energy while reconnection takes magnetic energy and returns is to its kinetic form. Most plasma processes at their core involve first storing magnetic energy accumulated over time and then releasing it suddenly. We focus here on this release. A key concept in analysing reconnection is that of the separatrix, a surface (line in 2D) that separates the fresh unperturbed plasma embedded in magnetic field lines not yet reconnected with the hotter exhaust embedded in reconnected field lines. In kinetic physics, the separatrices become a layer where many key processes develop. We present here new results relative to the processes at the separatrices that regulate the plasma flow, the energisation of the species, the electromagnetic fields and the instabilities developing at the separatrices.
Structures of magnetic null points in reconnection diffusion region: Cluster observations
Institute of Scientific and Technical Information of China (English)
HU YunHui; R.NAKAMURA; W.BAUMJOHANN; H.R'EME; C.M.CARR; DENG XiaoHua; ZHOU Meng; TANG RongXin; ZHAO Hui; FU Song; SU ZhiWen; WANG JingFang; YUAN ZhiGang
2008-01-01
Magnetic reconnection is a very important and fundamental plasma process in transferring energy from magnetic field into plasma. Previous theory, numerical simulations and observations mostly concen-trate on 2-dimensional (2D) model; however, magnetic reconnection is a 3-dimensional (3D) nonlinear process in nature. The properties of reconnection in 3D and its associated singular structure have not been resolved completely. Here we investigate the structures and characteristics of null points inside the reconnection diffusion region by introducing the discretized Poincaré index through Gauss integral and using magnetic field data with high resolution from the four satellites of Cluster mission. We esti-mate the velocity and trajectory of null points by calculating its position in different times, and compare and discuss the observations with different reconnection models with null points based on character-istics of electric current around null points.
Measurement of heart rate variability by methods based on nonlinear dynamics.
Huikuri, Heikki V; Mäkikallio, Timo H; Perkiömäki, Juha
2003-01-01
Heart rate (HR) variability has been conventionally analyzed with time and frequency domain methods, which measure the overall magnitude of R-R interval fluctuations around its mean value or the magnitude of fluctuations in some predetermined frequencies. Analysis of HR dynamics by methods based on chaos theory and nonlinear system theory has gained recent interest. This interest is based on observations suggesting that the mechanisms involved in cardiovascular regulation likely interact with each other in a nonlinear way. Furthermore, recent observational studies suggest that some indexes describing nonlinear HR dynamics, such as fractal scaling exponents, may provide more powerful prognostic information than the traditional HR variability indexes. In particular, short-term fractal scaling exponent measured by detrended fluctuation analysis method has been shown to predict fatal cardiovascular events in various populations. Approximate entropy, a nonlinear index of HR dynamics, which describes the complexity of R-R interval behavior, has provided information on the vulnerability to atrial fibrillation. There are many other nonlinear indexes, eg, Lyapunov exponent and correlation dimensions, which also give information on the characteristics of HR dynamics, but their clinical utility is not well established. Although concepts of chaos theory, fractal mathematics, and complexity measures of HR behavior in relation to cardiovascular physiology or various cardiovascular events are still far away from clinical medicine, they are a fruitful area for future research to expand our knowledge concerning the behavior of cardiovascular oscillations in normal healthy conditions as well as in disease states.
Fluctuation dynamo based on magnetic reconnections
Baggaley, A. W.; Shukurov, A.; Barenghi, C. F.; Subramanian, K.
2010-01-01
We develop a new model of the fluctuation dynamo in which the magnetic field is confined to thin flux ropes advected by a multi-scale flow which models turbulence. Magnetic dissipation occurs only via reconnections of flux ropes. The model is particularly suitable for rarefied plasma, such as the solar corona or galactic halos. We investigate the kinetic energy release into heat, mediated by dynamo action, both in our model and by solving the induction equation with the same flow. We find that the flux rope dynamo is more than an order of magnitude more efficient at converting mechanical energy into heat. The probability density of the magnetic energy released during reconnections has a power-law form with the slope -3, consistent with the solar corona heating by nanoflares. We also present a nonlinear extension of the model. This shows that a plausible saturation mechanism of the fluctuation dynamo is the suppression of turbulent magnetic diffusivity, due to suppression of random stretching at the location of the flux ropes. We confirm that the probability distribution function of the magnetic line curvature has a power-law form suggested by \\citet{Sheck:2002b}. We argue, however, using our results that this does not imply a persistent folded structure of magnetic field, at least in the nonlinear stage.
Onset of Fast Magnetic Reconnection via Subcritical Bifurcation
Directory of Open Access Journals (Sweden)
ZHIBIN eGUO
2015-04-01
Full Text Available We report a phase transition model for the onset of fast magnetic reconnection. By investigating the joint dynamics of streaming instability(i.e., current driven ion acoustic in this paper and current gradient driven whistler wave {color{blue} {prior to the onset of fast reconnection}}, we show that the nonlinear evolution of current sheet(CS can be described by a Landau-Ginzburg equation. The phase transition from slow reconnection to fast reconnection occurs at a critical thickness, $Delta_csimeq frac{2}{sqrt{pi}}left|frac{v_{the}}{v_c}right|d_e$, where $v_{the}$ is electron thermal velocity and $v_c$ is the velocity threshold of the streaming instability. For current driven ion acoustic, $Delta_c$ is $leq10d_e$. If the thickness of the CS is narrower than $Delta_c$, the CS subcritically bifurcates into a rough state, which facilitates breakage of the CS, and consequently initiates fast reconnection.
Reconnecting to the biosphere.
Folke, Carl; Jansson, Asa; Rockström, Johan; Olsson, Per; Carpenter, Stephen R; Chapin, F Stuart; Crépin, Anne-Sophie; Daily, Gretchen; Danell, Kjell; Ebbesson, Jonas; Elmqvist, Thomas; Galaz, Victor; Moberg, Fredrik; Nilsson, Måns; Osterblom, Henrik; Ostrom, Elinor; Persson, Asa; Peterson, Garry; Polasky, Stephen; Steffen, Will; Walker, Brian; Westley, Frances
2011-11-01
Humanity has emerged as a major force in the operation of the biosphere, with a significant imprint on the Earth System, challenging social-ecological resilience. This new situation calls for a fundamental shift in perspectives, world views, and institutions. Human development and progress must be reconnected to the capacity of the biosphere and essential ecosystem services to be sustained. Governance challenges include a highly interconnected and faster world, cascading social-ecological interactions and planetary boundaries that create vulnerabilities but also opportunities for social-ecological change and transformation. Tipping points and thresholds highlight the importance of understanding and managing resilience. New modes of flexible governance are emerging. A central challenge is to reconnect these efforts to the changing preconditions for societal development as active stewards of the Earth System. We suggest that the Millennium Development Goals need to be reframed in such a planetary stewardship context combined with a call for a new social contract on global sustainability. The ongoing mind shift in human relations with Earth and its boundaries provides exciting opportunities for societal development in collaboration with the biosphere--a global sustainability agenda for humanity.
Onset and Evolution of Magnetic Reconnection in Line-Tied Systems
Daughton, W. S.; Akcay, C.; Billey, Z.; Finn, J.; Zweibel, E.; Gekelman, W. N.
2014-12-01
In space and astrophysical plasmas, current sheets arise spontaneously from the interaction of large-scale flows or magnetic structures. As these current layers approach kinetic scales, they may become unstable to the collisionless tearing instability, resulting in the formation and interaction of magnetic flux ropes. While theoretical treatments of the tearing instability have largely focused on 1D equilibria with periodic boundary conditions, current sheets in nature have a finite spatial extent and are embedded within larger open systems. In many applications, the field boundary conditions are line-tied as in the case of flux ropes on the dayside magnetopause where the ionosphere acts as a conducting surface. To assess the applicability of existing tearing theory to these more realistic configurations, we consider a series of 3D kinetic simulations of initially force-free current layers with line-tied boundary conditions for the fields, and open boundaries for the particles. The geometry and plasma parameters are motivated by a new laboratory experiment on the Large Plasma Device at UCLA. For sufficiently long systems, we demonstrate that key aspects of the theory remain valid, and a threshold condition is derived for the onset of reconnection in line-tied systems. To gain additional insight into the nonlinear evolution, field-line mapping diagnostics are employed to characterize the 3D structure of the magnetic field, the nonlinear reconnection rate and the dominant non-ideal terms in the generalized Ohm's law.
Goldberg, Robert K.
2000-01-01
There has been no accurate procedure for modeling the high-speed impact of composite materials, but such an analytical capability will be required in designing reliable lightweight engine-containment systems. The majority of the models in use assume a linear elastic material response that does not vary with strain rate. However, for containment systems, polymer matrix composites incorporating ductile polymers are likely to be used. For such a material, the deformation response is likely to be nonlinear and to vary with strain rate. An analytical model has been developed at the NASA Glenn Research Center at Lewis Field that incorporates both of these features. A set of constitutive equations that was originally developed to analyze the viscoplastic deformation of metals (Ramaswamy-Stouffer equations) was modified to simulate the nonlinear, rate-dependent deformation of polymers. Specifically, the effects of hydrostatic stresses on the inelastic response, which can be significant in polymers, were accounted for by a modification of the definition of the effective stress. The constitutive equations were then incorporated into a composite micromechanics model based on the mechanics of materials theory. This theory predicts the deformation response of a composite material from the properties and behavior of the individual constituents. In this manner, the nonlinear, rate-dependent deformation response of a polymer matrix composite can be predicted.
Asymptotic solution of nonlinear moment equations for constant-rate aerosol reactors
Directory of Open Access Journals (Sweden)
B. D. Shaw
1998-01-01
Full Text Available Nonlinear evolution equations based upon moments of the aerosol size distribution function are solved asymptotically for constant-rate aerosol reactors (i.e., where condensible monomer is added at a constant rate operating in the free-molecular limit. The governing equations are nondimensionalized and a large parameter that controls nucleation behavior is identified. Asymptotic analyses are developed in terms of this parameter. Comparison of the asymptotic results with direct numerical integration of the governing equations is favorable. The asymptotic results provide a simplified analytical approach to estimating average particle sizes, particle number densities, and peak supersaturation values for constant-rate aerosol reactors.
Comparing Linear and Non-linear Benchmarks of Exchange Rate Forecasting
SJ Retief, M Pretorius and I Botha
2015-01-01
Throughout the past 3 decades, the random walk model served as exchange rate forecasting benchmark to verify that a model is able to outperform a random process. However, its application as forecasting benchmark is contradictory. Rather than serving as a benchmark that explains exchange rate behaviour, it serves as a benchmark of what we do not understand in exchange rate forecasting â€“ the random component. In order to accommodate for the observed mean reverting and non-linear patterns in e...
Fermi~I particle acceleration in converging flows mediated by magnetic reconnection
Bosch-Ramon, V
2012-01-01
Converging flows with strong magnetic fields of different polarity can accelerate particles through magnetic reconnection. If the particle mean free path is larger than the thickness of the reconnection layer, but much smaller than the entire reconnection structure, the particle will mostly interact with the incoming flows potentially with a very low escape probability. We explore, in general and also in some specific scenarios, the possibility of particles being accelerated in a magnetic reconnection layer by interacting only with the incoming flows. We characterize converging flows undergoing magnetic reconnection, and derive analytical estimates for the particle energy distribution, acceleration rate, and maximum energies achievable in these flows. We also discuss a possible scenario, based on jets dominated by magnetic fields of changing polarity, in which this mechanism may operate. The proposed acceleration mechanism operates if the thickness of the reconnection layer is much smaller than its transversa...
Reconnection current sheet structure in a turbulent medium
Directory of Open Access Journals (Sweden)
E. T. Vishniac
2012-11-01
Full Text Available In the presence of turbulence, magnetic field lines lose their dynamical identity and particles entrained on field lines diffuse through space at a rate determined by the amplitude of the turbulence. In previous work (Lazarian and Vishniac, 1999; Kowal et al., 2009; Eyink et al., 2011 we showed that this leads to reconnection speeds which are independent of resistivity. In particular, in Kowal et al. (2009 we showed that numerical simulations were consistent with the predictions of this model. Here we examine the structure of the current sheet in simulations of turbulent reconnection. Laminar flows consistent with the Sweet-Parker reconnection model produce very thin and well ordered currents sheets. On the other hand, the simulations of Kowal et al. (2009 show a strongly disordered state even for relatively low levels of turbulence. Comparing data cubes with and without reconnection, we find that large scale field reversals are the cumulative effect of many individual eddies, each of which has magnetic properties which are not very different from turbulent eddies in a homogeneous background. This implies that the properties of stationary and homogeneous MHD turbulence are a reasonable guide to understanding turbulence during large scale magnetic reconnection events. In addition, dissipation and high energy particle acceleration during reconnection events take place over a macroscopic volume, rather than being confined to a narrow zone whose properties depend on microscopic transport coefficients.
Chen, Pang-Chia
2013-01-01
This paper investigates multi-objective controller design approaches for nonlinear boiler-turbine dynamics subject to actuator magnitude and rate constraints. System nonlinearity is handled by a suitable linear parameter varying system representation with drum pressure as the system varying parameter. Variation of the drum pressure is represented by suitable norm-bounded uncertainty and affine dependence on system matrices. Based on linear matrix inequality algorithms, the magnitude and rate constraints on the actuator and the deviations of fluid density and water level are formulated while the tracking abilities on the drum pressure and power output are optimized. Variation ranges of drum pressure and magnitude tracking commands are used as controller design parameters, determined according to the boiler-turbine's operation range.
Fan, Kuangang; Zhang, Yan; Gao, Shujing; Wei, Xiang
2017-09-01
A class of SIR epidemic model with generalized nonlinear incidence rate is presented in this paper. Temporary immunity and stochastic perturbation are also considered. The existence and uniqueness of the global positive solution is achieved. Sufficient conditions guaranteeing the extinction and persistence of the epidemic disease are established. Moreover, the threshold behavior is discussed, and the threshold value R0 is obtained. We show that if R0 1, then the system remains permanent in the mean.
Observational Signatures of Magnetic Reconnection
Savage, Sabrina
2014-01-01
Magnetic reconnection is often referred to as the primary source of energy release during solar flares. Directly observing reconnection occurring in the solar atmosphere, however, is not trivial considering that the scale size of the diffusion region is magnitudes smaller than the observational capabilities of current instrumentation, and coronal magnetic field measurements are not currently sufficient to capture the process. Therefore, predicting and studying observationally feasible signatures of the precursors and consequences of reconnection is necessary for guiding and verifying the simulations that dominate our understanding. I will present a set of such observations, particularly in connection with long-duration solar events, and compare them with recent simulations and theoretical predictions.
Colour reconnection in WW events
D'Hondt, J
2003-01-01
Preliminary results are presented for a measurement of the kappa parameter used in the JETSET SK-I model of colour reconnection in W /sup +/W/sup -/ to qq'qq' events at LEP2. An update on the investigation of colour reconnection effects in hadronic decays of W pairs, using the particle flow in DELPHI is presented. A second method is based on the observation that two different m/sub W/ estimators have different sensitivity to the parametrised colour reconnection effect. Hence the difference between them is an observable with information content about kappa. (6 refs).
Non-linear direct effects of acid rain on leaf photosynthetic rate of terrestrial plants.
Dong, Dan; Du, Enzai; Sun, Zhengzhong; Zeng, Xuetong; de Vries, Wim
2017-09-12
Anthropogenic emissions of acid precursors have enhanced global occurrence of acid rain, especially in East Asia. Acid rain directly suppresses leaf function by eroding surface waxes and cuticle and leaching base cations from mesophyll cells, while the simultaneous foliar uptake of nitrates in rainwater may directly benefit leaf photosynthesis and plant growth, suggesting a non-linear direct effect of acid rain. By synthesizing data from literature on acid rain exposure experiments, we assessed the direct effects of acid rain on leaf photosynthesis across 49 terrestrial plants in China. Our results show a non-linear direct effect of acid rain on leaf photosynthetic rate, including a neutral to positive effect above pH 5.0 and a negative effect below that pH level. The acid rain sensitivity of leaf photosynthesis showed no significant difference between herbs and woody species below pH 5.0, but the impacts above that pH level were strongly different, resulting in a significant increase in leaf photosynthetic rate of woody species and an insignificant effect on herbs. Our analysis also indicates a positive effect of the molar ratio of nitric versus sulfuric acid in the acid solution on leaf photosynthetic rate. These findings imply that rainwater acidity and the composition of acids both affect the response of leaf photosynthesis and therefore result in a non-linear direct effect. Copyright © 2017 Elsevier Ltd. All rights reserved.
Nonlinear effect of dispersal rate on spatial synchrony of predator-prey cycles.
Fox, Jeremy W; Legault, Geoffrey; Legault, Geoff; Vasseur, David A; Einarson, Jodie A
2013-01-01
Spatially-separated populations often exhibit positively correlated fluctuations in abundance and other population variables, a phenomenon known as spatial synchrony. Generation and maintenance of synchrony requires forces that rapidly restore synchrony in the face of desynchronizing forces such as demographic and environmental stochasticity. One such force is dispersal, which couples local populations together, thereby synchronizing them. Theory predicts that average spatial synchrony can be a nonlinear function of dispersal rate, but the form of the dispersal rate-synchrony relationship has never been quantified for any system. Theory also predicts that in the presence of demographic and environmental stochasticity, realized levels of synchrony can exhibit high variability around the average, so that ecologically-identical metapopulations might exhibit very different levels of synchrony. We quantified the dispersal rate-synchrony relationship using a model system of protist predator-prey cycles in pairs of laboratory microcosms linked by different rates of dispersal. Paired predator-prey cycles initially were anti-synchronous, and were subject to demographic stochasticity and spatially-uncorrelated temperature fluctuations, challenging the ability of dispersal to rapidly synchronize them. Mean synchrony of prey cycles was a nonlinear, saturating function of dispersal rate. Even extremely low rates of dispersal (systems are sufficient to generate and maintain synchrony of cyclic population dynamics, at least when environments are not too spatially heterogeneous.
An SIR Epidemic Model with Time Delay and General Nonlinear Incidence Rate
Directory of Open Access Journals (Sweden)
Mingming Li
2014-01-01
Full Text Available An SIR epidemic model with nonlinear incidence rate and time delay is investigated. The disease transmission function and the rate that infected individuals recovered from the infected compartment are assumed to be governed by general functions F(S,I and G(I, respectively. By constructing Lyapunov functionals and using the Lyapunov-LaSalle invariance principle, the global asymptotic stability of the disease-free equilibrium and the endemic equilibrium is obtained. It is shown that the global properties of the system depend on both the properties of these general functions and the basic reproductive number R0.
Kur'yanova, E V; Teplyi, D L; Zhukova, Yu D; Zhukovina, N V
2015-12-01
The basic behavioral activity of nonlinear rats was evaluated from the sum of crossed peripheral and central squares and peripheral and central rearing postures in the open fi eld test. This index was low (30 episodes). Male rats with high score of orientation and exploratory activity were characterized by higher indexes of total heart rate variability than rats with low or intermediate activity. Specimens with a greater contribution of VLF waves into the total power spectrum of heart rate variability were shown to dominate among the rats with high behavioral activity. Our results are consistent with the notions of a suprasegmental nature of VLF waves.
Energy exchanges in reconnection outflows
Lapenta, Giovanni; Goldman, Martin V.; Newman, David L.; Markidis, Stefano
2017-01-01
Reconnection outflows are highly energetic directed flows that interact with the ambient plasma or with flows from other reconnection regions. Under these conditions the flow becomes highly unstable and chaotic, as any flow jets interacting with a medium. We report here massively parallel simulations of the two cases of interaction between outflow jets and between a single outflow with an ambient plasma. We find in both case the development of a chaotic magnetic field, subject to secondary reconnection events that further complicate the topology of the field lines. The focus of the present analysis is on the energy balance. We compute each energy channel (electromagnetic, bulk, thermal, for each species) and find where the most energy is exchanged and in what form. The main finding is that the largest energy exchange is not at the reconnection site proper but in the regions where the outflowing jets are destabilized.
Innes, Davina; Huang, YiMin; Bhattacharjee, Amitava
2015-01-01
Our understanding of the process of fast reconnection has undergone a dramatic change in the last 10 years driven, in part, by the availability of high-resolution numerical simulations that have consistently demonstrated the break-up of current sheets into magnetic islands, with reconnection rates that become independent of Lundquist number, challenging the belief that fast magnetic reconnection in flares proceeds via the Petschek mechanism that invokes pairs of slow-mode shocks connected to a compact diffusion region. The reconnection sites are too small to be resolved with images but these reconnection mechanisms, Petschek and the plasmoid instability, have reconnection sites with very different density and velocity structures and so can be distinguished by high-resolution line-profiles observations. Using IRIS spectroscopic observations we obtain a survey of typical line profiles produced by small-scale events thought to be reconnection sites on the Sun. Slit-jaw images are used to investigate the plasma h...
Intelligent modeling and control for nonlinear systems with rate-dependent hysteresis
Institute of Scientific and Technical Information of China (English)
MAO JianQin; DING HaiShan
2009-01-01
A new modeling approach for nonlinear systems with rate-dependent hysteresis is proposed. The ap-proach is used for the modeling of the giant magnetostrictive actuator, which has the rate-dependent nonlinear property. The models built are simpler than the existed approaches. Compared with the exper-intent result, the model built can well describe the hysteresis nonlinear of the actuator for Input signals with complex frequency. An adaptive direct inverse control approach is proposed based on the fuzzy tree model and Inverse learning and special learning that are used in neural network broadly. In this approach, the inverse model of the plant is identified to be the initial controller firstly. Then, the inverse model Is connected with the plant in series and the linear parameters of the controller are adjusted using the least mean square algorithm by on-line manner. The direct Inverse control approach based on the fuzzy tree model is applied on the tracing control of the actuator by simulation. The simulation results show the correctness of the approach.
Propagation and dispersion of whistler waves generated by fast reconnection onset
Singh, Nagendra
2013-02-01
The role of whistler mode during the onset of magnetic reconnection (MR) has been widely suggested, but the manifestations of its highly dispersive and anisotropic propagation properties in reconnection events remain largely unclear. Comparing results from a recently developed theoretical model for reconnection in terms of whistler's dispersive behavior with those reported from laboratory experiments on fast spontaneous magnetic reconnection, we demonstrate that the onset of fast reconnection in electron current layers (ECLs) emits whistler wave packets. The time scale of the explosively fast reconnection events are inversely related to the whistler mode frequencies at the lower end of the whistler frequency band. The wave packets in this frequency band have a characteristic angular dispersion, which marks the initial opening of the reconnection exhaust angle. The multidimensional propagation of the whistler for the reconnection with a strong guide magnetic field is investigated, showing that the measured propagation velocities of the reconnection electric field along the guide field in the Versatile Toroidal Facility at MIT quantitatively compare with the group velocities of the whistler wave packets. The whistler mode dispersive properties measured in laboratory experiments without a guide magnetic field in the magnetic reconnection experiments at Princeton also compare well with the theoretically predicted dispersion of the wave packets depending on the ECL width. Fast normalized reconnection rates extending to ˜0.35 at the MR onset in thin ECLs imply whistler wave propagation away from the onset location. We also present evidences for the whistler wave packets being emitted from reconnection diffusion region as seen in simulations and satellite observations.
Goldman, M V; Newman, D L; Lapenta, G; Andersson, L; Gosling, J T; Eriksson, S; Markidis, S; Eastwood, J P; Ergun, R
2014-04-11
Kinetic simulations of magnetotail reconnection have revealed electromagnetic whistlers originating near the exhaust boundary and propagating into the inflow region. The whistler production mechanism is not a linear instability, but rather is Čerenkov emission of almost parallel whistlers from localized moving clumps of charge (finite-size quasiparticles) associated with nonlinear coherent electron phase space holes. Whistlers are strongly excited by holes without ever growing exponentially. In the simulation the whistlers are emitted in the source region from holes that accelerate down the magnetic separatrix towards the x line. The phase velocity of the whistlers vφ in the source region is everywhere well matched to the hole velocity vH as required by the Čerenkov condition. The simulation shows emission is most efficient near the theoretical maximum vφ=half the electron Alfven speed, consistent with the new theoretical prediction that faster holes radiate more efficiently. While transferring energy to whistlers the holes lose coherence and dissipate over a few local ion inertial lengths. The whistlers, however, propagate to the x line and out over many 10's of ion inertial lengths into the inflow region of reconnection. As the whistlers pass near the x line they modulate the rate at which magnetic field lines reconnect.
Magnetic reconnection in Saturn's magnetotail: A comprehensive magnetic field survey
Smith, A. W.; Jackman, C. M.; Thomsen, M. F.
2016-04-01
Reconnection within planetary magnetotails is responsible for locally energizing particles and changing the magnetic topology. Its role in terms of global magnetospheric dynamics can involve changing the mass and flux content of the magnetosphere. We have identified reconnection related events in spacecraft magnetometer data recorded during Cassini's exploration of Saturn's magnetotail. The events are identified from deflections in the north-south component of the magnetic field, significant above a background level. Data were selected to provide full tail coverage, encompassing the dawn and dusk flanks as well as the deepest midnight orbits. Overall 2094 reconnection related events were identified, with an average rate of 5.0 events per day. The majority of events occur in clusters (within 3 h of other events). We examine changes in this rate in terms of local time and latitude coverage, taking seasonal effects into account. The observed reconnection rate peaks postmidnight with more infrequent but steady loss seen on the dusk flank. We estimate the mass loss from the event catalog and find it to be insufficient to balance the input from the moon Enceladus. Several reasons for this discrepancy are discussed. The reconnection X line location appears to be highly variable, though a statistical separation between events tailward and planetward of the X line is observed at a radial distance of between 20 and 30RS downtail. The small sample size at dawn prevents comprehensive statistical comparison with the dusk flank observations in terms of flux closure.
Three-Dimensional Turbulent Reconnection Induced by the Plasmoid Instability
Bhattacharjee, A.; Huang, Y. M.
2014-12-01
It has been established that the Sweet-Parker current layer in high-Lundquist-number reconnection is unstable to the super-Alfvenic plasmoid instability. Past two-dimensional magnetohydrodynamic simulations have demonstrated that the plasmoid instability leads to a new regime in which the Sweet-Parker current layer evolves into a chain of plasmoids connected by secondary current sheets and the averaged reconnection rate becomes nearly independent of the Lundquist number. In a three-dimensional configuration with a guide field, the additional degree of freedom allows plasmoid instabilities to grow at oblique angles [S. Baalrud et al. Phys. Plasmas 19, 022101 (2012)] and develop the complex dynamics of flux ropes which overlap, cause field-line stochasticization, and self-generate a turbulent state. Three-dimensional simulations in the high-Lundquist-number regime show the formation of cigar-shaped eddies elongated in the direction of the local magnetic field, which is a signature of anisotropic MHD turbulence. Furthermore, the energy fluctuation spectra are found to satisfy power laws in the inertial range. The averaged 3D reconnection rate in the self-generated turbulent state is of the order of a hundredth of the characteristic Alfven speed, which is an order of magnitude lower than the reconnection rate reported in recent studies of externally driven 3D turbulent reconnection. The physical reasons for these differences will be discussed.
Local Dynamics and Global Size Coupling during Magnetic Reconnection
Jacobson, C. M.; Breslau, J. A.; Jardin, S. C.; Ji, H.
2008-11-01
Magnetic reconnection is an important physical process not only in small systems such as laboratory plasmas, but also in large systems such as solar flares. The reconnection rate increases with resistivity η and decreases with the current sheet length L. Recent experimental results suggest that these parameters are not independent, but anti-correlate such that ηL is kept roughly constant; thus the reconnection rate is a function of both local dynamics and global size [1]. In order to verify these results and further extend the system size, a numerical MHD model [2] is used. This code allows simulation of either two-fluid or single-fluid resistive MHD reconnection of colliding flux tubes on a 2D grid. The resistivity and system size are systematically varied, and scalings of the ion skin depth, collisionality, and reconnection rate due to these quantities are presented. Results are compared to experimental data, and findings are projected to solar flare scales. [1] A. Kuritsyn et al. Geophys. Res. Lett. 34, L16106 (2007) [2] J. A. Breslau and S. C. Jardin, Comput. Phys. Commun. 151, 8 (2003)
Examining the reaction of monetary policy to exchange rate changes: A nonlinear ARDL approach
Manogaran, Lavaneesvari; Sek, Siok Kun
2017-04-01
Previous studies showed the exchange rate changes can have significant impacts on macroeconomic performance. Over fluctuation of exchange rate may lead to economic instability. Hence, monetary policy rule tends to react to exchange rate changes. Especially, in emerging economies where the policy-maker tends to limit the exchange rate movement through interventions. In this study, we seek to investigate how the monetary policy rule reacts to exchange rate changes. The nonlinear autoregressive distributed lag (NARDL) model is applied to capture the asymmetric effect of exchange rate changes on monetary policy reaction function (interest rate). We focus the study in ASEAN5 countries (Indonesia, Malaysia, Philippines, Thailand and Singapore). The results indicated the existence of asymmetric effect of exchange rates changes on the monetary reaction function for all ASEAN5 countries in the long-run. Where, in majority of the cases the monetary policy is reacting to the appreciation and depreciation of exchange rate by raising the policy rate. This affirms the intervention of policymakers with the `fear of floating' behavior.
Fluctuation dynamo based on magnetic reconnections
Baggaley, Andrew W; Shukurov, Anvar; Subramanian, Kandaswamy
2009-01-01
We develop a new model of the fluctuation dynamo in which the magnetic field is confined to thin flux ropes advected by a multi-scale flow which models turbulence. Magnetic dissipation occurs only via reconnections of flux ropes. The model is particularly suitable for rarefied plasma, such as the Solar corona or galactic halos. We investigate the kinetic energy release into heat, mediated by dynamo action, both in our model and by solving the induction equation with the same flow. We find that the flux rope dynamo is more than an order of magnitude more efficient at converting mechanical energy into heat. The probability density of the magnetic energy released during reconnections has a power-law form with the slope -3, consistent with the Solar corona heating by nanoflares. We also present a nonlinear extension of the model. This shows that a plausible saturation mechanism of the fluctuation dynamo is the suppression of turbulent magnetic diffusivity, due to suppression of random stretching at the location o...
Evidence for collisionless magnetic reconnection at Mars
Eastwood, J. P.; Brain, D. A.; Halekas, J. S.; Drake, J. F.; Phan, T. D.; Øieroset, M.; Mitchell, D. L.; Lin, R. P.; Acuña, M.
2008-01-01
Using data from Mars Global Surveyor (MGS) in combination with Particle-In-Cell (PIC) simulations of reconnection, we present the first direct evidence of collisionless magnetic reconnection at Mars. The evidence indicates that the spacecraft passed through the diffusion region where reconnection is initiated and observed the magnetic field signatures of differential electron and ion motion - the Hall magnetic field - that uniquely indicate the reconnection process. These are the first such in-situ reconnection observations at an astronomical body other than the Earth. Reconnection may be the source of Mars' recently discovered auroral activity and the changing boundaries of the closed regions of crustal magnetic field.
THE NONLINEAR CUSP-CATASTROPHE MODEL OF THE SEDIMENT TRANSPORT RATE
Institute of Scientific and Technical Information of China (English)
无
2002-01-01
In the catastrophe theory of nonlinear science,the intensity of water-flow and the coefficient of non-uniformsediment m are regarded as two bound variables, and the in-tensity of bed-load transport Φ as the state variable in the mo-tion of non-uniform sediment in cusp-catastrophe model.Based on the standard equation of the cusp-catastrophe theo-ry, the relation equation between the intensity of bed-loadtransport Φ and the intensity of water-flow has been derivedby used coordinate transform and topology transform. The e-quation of bed load transport rate was built on the cusp-catas-trophe theory of nonlinear science. The others are applied toverify this equation, that the results calculated by the cusp-ca-tastrophe equation agree well with the other equations. Thisindicates that the cusp-catastrophe equation is reasonable, and the results fully reflect the characteristics of threshold motionand transport of non-uniform sediment. The purpose of thispaper is to explore the incipient motion and transport laws ofnon-uniform sediment from the viewpoint of nonlinear science.
Magnetic Reconnection: A Fundamental Process in Space Plasmas
Hesse, Michael
2010-01-01
For many years, collisionless magnetic reconnect ion has been recognized as a fundamental process, which facilitates plasma transport and energy release in systems ranging from the astrophysical plasmas to magnetospheres and even laboratory plasma. Beginning with work addressing solar dynamics, it has been understood that reconnection is essential to explain solar eruptions, the interaction of the solar wind with the magnetosphere, and the dynamics of the magnetosphere. Accordingly, the process of magnetic reconnection has been and remains a prime target for space-based and laboratory studies, as well as for theoretical research. Much progress has been made throughout the years, beginning with indirect verifications by studies of processes enabled by reconnection, such as Coronal Mass Ejections, Flux Transfer Events, and Plasmoids. Theoretical advances have accompanied these observations, moving knowledge beyond the Sweet-Parker theory to the recognition that other, collisionless, effects are available and likely to support much faster reconnect ion rates. At the present time we are therefore near a break-through in our understanding of how collisionless reconnect ion works. Theory and modeling have advanced to the point that two competing theories are considered leading candidates for explaining the microphysics of this process. Both theories predict very small spatial and temporal scales. which are. to date, inaccessible to space-based or laboratory measurements. The need to understand magnetic reconnect ion has led NASA to begin the implementation of a tailored mission, Magnetospheric MultiScale (MMS), a four spacecraft cluster equipped to resolve all relevant spatial and temporal scales. In this presentation, we present an overview of current knowledge as well as an outlook towards measurements provided by MMS.
Impulsive reconnection: 3D onset and stagnation in turbulent paradigms
Energy Technology Data Exchange (ETDEWEB)
Sears, Jason A [Los Alamos National Laboratory; Intrator, Thomas P [Los Alamos National Laboratory; Weber, Tom [Los Alamos National Laboratory; Lapenta, Giovanni [KATHOLIEKE UNIV.; Lazarian, Alexander [UNIV OF WISCONSIN
2010-12-14
Reconnection processes are ubiquitous in solar coronal loops, the earth's magnetotail, galactic jets, and laboratory configurations such as spheromaks and Z pinches. It is believed that reconnection dynamics are often closely linked to turbulence. In these phenomena, the bursty onset of reconnection is partly determined by a balance of macroscopic MHD forces. In a turbulent paradigm, it is reasonable to suppose that there exist many individual reconnection sites, each X-line being finite in axial extent and thus intrinsically three-dimensional (3D) in structure. The balance between MHD forces and flux pile-up continuously shifts as mutually tangled flux ropes merge or bounce. The spatial scale and thus the rate of reconnection are therefore intimately related to the turbulence statistics both in space and in time. We study intermittent 3D reconnection along spatially localized X-lines between two or more flux ropes. The threshold of MHD instability which in this case is the kink threshold is varied by modifying the line-tying boundary conditions. For fast inflow speed of approaching ropes, there is merging and magnetic reconnection which is a well known and expected consequence of the 2D coalescence instability. On the other hand, for slower inflow speed the flux ropes bounce. The threshold appears to be the Sweet Parker speed v{sub A}/S{sup 1/2}, where v{sub A} is the Alfven speed and S is the Lundquist number. Computations by collaborators at University of Wisconsin, Madison, Katholieke Universiteit Leuven, and LANL complement the experiment.
The Dynamics of an Eco-Epidemiological Model with Nonlinear Incidence Rate
Directory of Open Access Journals (Sweden)
Raid Kamel Naji
2012-01-01
Full Text Available This paper treats the dynamical behavior of eco-epidemiological model with nonlinear incidence rate. A Holling type II prey-predator model with SI-type of disease in prey has been proposed and analyzed. The existence, uniqueness, and boundedness of the solution of the system are studied. The local and global dynamical behaviors are investigated. The conditions, which guarantee the occurring of Hopf bifurcation of the system, are established. Finally, further investigations for the global dynamics of the proposed system are carried out with the help of numerical simulations.
QUALITATIVE ANALYSIS OF AN SEIS EPIDEMIC MODEL WITH NONLINEAR INCIDENCE RATE
Institute of Scientific and Technical Information of China (English)
WANG La-di; LI Jian-quan
2006-01-01
By means of limit theory and Fonda's theorem, an SEIS epidemic model with constant recruitment and the disease-related rate is considered. The incidence term is of the nonlinear form, and the basic reproduction number is found. If the basic reproduction number is less than one, there exists only the disease-free equilibrium, which is globally asymptotically stable, and the disease dies out eventually. If the basic reproduction number is greater than one, besides the unstable disease-free equilibrium, there exists also a unique endemic equilibrium, which is locally asymptotically stable, and the disease is uniformly persistent.
Thermal-inertial effects on magnetic reconnection in relativistic pair plasmas.
Comisso, Luca; Asenjo, Felipe A
2014-07-25
The magnetic reconnection process is studied in relativistic pair plasmas when the thermal and inertial properties of the magnetohydrodynamical fluid are included. We find that in both Sweet-Parker and Petschek relativistic scenarios there is an increase of the reconnection rate owing to the thermal-inertial effects, both satisfying causality. To characterize the new effects we define a thermal-inertial number which is independent of the relativistic Lundquist number, implying that reconnection can be achieved even for vanishing resistivity as a result of only thermal-inertial effects. The current model has fundamental importance for relativistic collisionless reconnection, as it constitutes the simplest way to get reconnection rates faster than those accessible with the sole resistivity.
Analytical Model of Fast Magnetic Reconnection with a Large Guide Field
Simakov, Andrei N; Zocco, A
2010-01-01
Analytical theory of fast magnetic reconnection with a large guide field is presented for the first time. We confirm that two distinct reconnection regimes are possible depending on whether the diffusion region thickness $\\delta$ is larger or smaller than the sound gyroradius $\\rho_s$. The reconnection is slow or Sweet-Parker-like for $\\delta \\gtrsim \\rho_s$, and fast otherwise. In the fast regime, however, we find that ion viscosity $\\mu$ plays a critical role. In particular, for $\\delta < \\rho_s$ the diffusion region thickness is proportional to $Ha^{-1}$ with $Ha \\propto 1/\\sqrt{\\eta \\mu}$ the Hartmann number, and the reconnection rate is proportional to $Pr^{-1/2}$ with $Pr = \\mu/\\eta$ the Prandtl number and $\\eta$ the resistivity. If the perpendicular ion viscosity is employed for $\\mu$ the reconnection rate becomes independent of both plasma $\\beta$ and collision frequencies and therefore potentially fast.
BIDIRECTIONAL OUTFLOWS AS EVIDENCE OF MAGNETIC RECONNECTION LEADING TO A SOLAR MICROFLARE
Energy Technology Data Exchange (ETDEWEB)
Hong, Jie; Ding, M. D.; Li, Ying; Yang, Kai; Cheng, Xin; Fang, Cheng [School of Astronomy and Space Science, Nanjing University, Nanjing 210023 (China); Chen, Feng [Max-Plank-Institut für Sonnensystemforschung, D-37077, Göttingen (Germany); Cao, Wenda, E-mail: dmd@nju.edu.cn [Big Bear Solar Observatory, New Jersey Institute of Technology, 40386 North Shore Lane, Big Bear City, CA 92314-9672 (United States)
2016-03-20
Magnetic reconnection is a rapid energy release process that is believed to be responsible for flares on the Sun and stars. Nevertheless, such flare-related reconnection is mostly detected to occur in the corona, while there have been few studies concerning the reconnection in the chromosphere or photosphere. Here, we present both spectroscopic and imaging observations of magnetic reconnection in the chromosphere leading to a microflare. During the flare peak time, chromospheric line profiles show significant blueshifted/redshifted components on the two sides of the flaring site, corresponding to upflows and downflows with velocities of ±(70–80) km s{sup −1}, comparable with the local Alfvén speed as expected by the reconnection in the chromosphere. The three-dimensional nonlinear force-free field configuration further discloses twisted field lines (a flux rope) at a low altitude, cospatial with the dark threads in He i 10830 Å images. The instability of the flux rope may initiate the flare-related reconnection. These observations provide clear evidence of magnetic reconnection in the chromosphere and show the similar mechanisms of a microflare to those of major flares.
Fractal Reconnection in Solar and Stellar Environments
Shibata, Kazunari
2016-01-01
Recent space based observations of the Sun revealed that magnetic reconnection is ubiquitous in the solar atmosphere, ranging from small scale reconnection (observed as nanoflares) to large scale one (observed as long duration flares or giant arcades). Often the magnetic reconnection events are associated with mass ejections or jets, which seem to be closely related to multiple plasmoid ejections from fractal current sheet. The bursty radio and hard X-ray emissions from flares also suggest the fractal reconnection and associated particle acceleration. We shall discuss recent observations and theories related to the plasmoid-induced-reconnection and the fractal reconnection in solar flares, and their implication to reconnection physics and particle acceleration. Recent findings of many superflares on solar type stars that has extended the applicability of the fractal reconnection model of solar flares to much a wider parameter space suitable for stellar flares are also discussed.
Sano, T; Sano, Takayoshi; Inutsuka, Shu-ichiro
2001-01-01
The nonlinear evolution and the saturation mechanism of the magnetorotational instability (MRI) are investigated using three-dimensional resistive MHD simulations. A local shearing box is used for our numerical analysis and the simulations begin with a purely vertical magnetic field. We find that the magnetic stress in the nonlinear stage of the MRI is strongly fluctuating. The time evolution shows the quasi-periodic recurrence of spike-shape variations typically for a few orbits which correspond to the rapid amplification of the magnetic field by the nonlinear growth of a two-channel solution followed by the decay through magnetic reconnections. The increase rate of the total energy in the shearing box system is analytically related to the volume-averaged torque in the system. We find that at the saturated state this energy gain of the system is balanced with the increase of the thermal energy mostly due to the joule heating. The spike-shape time evolution is a general feature of the nonlinear evolution of t...
Magnetic flux array for spontaneous magnetic reconnection experiments.
Kesich, A; Bonde, J; Egedal, J; Fox, W; Goodwin, R; Katz, N; Le, A
2008-06-01
Experimental investigation of reconnection in magnetized plasmas relies on accurate characterization of the evolving magnetic fields. In experimental configurations where the plasma dynamics are reproducible, magnetic data can be collected in multiple discharges and combined to provide spatially resolved profiles of the plasma dynamics. However, in experiments on spontaneous magnetic reconnection recently undertaken at the Versatile Toroidal Facility at MIT, the reconnection process is not reproducible and all information on the plasma must be collected in a single discharge. This paper describes a newly developed magnetic flux array which directly measures the toroidal component of the magnetic vector potential, A(phi). From the measured A(phi), the magnetic field geometry, current density, and reconnection rate are readily obtained, facilitating studies of the three-dimensional dynamics of spontaneous magnetic reconnection. The novel design of the probe array allows for accurate characterization of profiles of A(phi) at multiple toroidal angles using a relatively small number of signal channels and with minimal disturbance of the plasma.
On the characterization of magnetic reconnection in global MHD simulations
Directory of Open Access Journals (Sweden)
T. V. Laitinen
2006-11-01
Full Text Available The conventional definition of reconnection rate as the electric field parallel to an x-line is problematic in global MHD simulations for several reasons: the x-line itself may be hard to find in a non-trivial geometry such as at the magnetopause, and the lack of realistic resistivity modelling leaves us without reliable non-convective electric field. In this article we describe reconnection characterization methods that avoid those problems and are practical to apply in global MHD simulations. We propose that the reconnection separator line can be identified as the region where magnetic field lines of different topological properties meet, rather than by local considerations. The global convection associated with reconnection is then quantified by calculating the transfer of mass, energy or magnetic field across the boundary of closed and open field line regions. The extent of the diffusion region is determined from the destruction of electromagnetic energy, given by the divergence of the Poynting vector. Integrals of this energy conversion provide a way to estimate the total reconnection efficiency.
A new fast reconnection model in a collisionless regime
Tsiklauri, David
2008-01-01
Based on the first principles (by balancing the advection with the electron pressure tensor in the generalised Ohm's law, and using the conservation of mass) a simple model of magnetic reconnection in a collisionless regime is formulated. In addition to its importance from the fundamental point of view, the collisionless reconnection model offers a much faster reconnection rate ($M_{c'less}={(d_i/2)}^{1/2}$) than Sweet-Parker's classical one ($M_{sp}=S^{-1/2}$). The width of the diffusion region (current sheet) in the collisionless regime is found to be $\\delta_{c'less}={(d_i/2)}^{1/2}L$, which is much larger than the Sweet-Parker width ($\\delta_{sp}=S^{-1/2}L$) for the space plasma conditions. Amongst other issues, this alleviates e.g. the problem of interpretation of solar flares by means of reconnection, as for the typical solar coronal parameters the obtained collisionless reconnection time can be $< 10$ minutes, as opposed to Sweet-Parker's equivalent value of $<$ year. The new theoretical reconnec...
Fast reconnection in relativistic plasmas: the magnetohydrodynamics tearing instability revisited
Del Zanna, L; Landi, S; Bugli, M; Bucciantini, N
2016-01-01
Fast reconnection operating in magnetically dominated plasmas is often invoked in models for magnetar giant flares, for magnetic dissipation in pulsar winds, or to explain the gamma-ray flares observed in the Crab nebula, hence its investigation is of paramount importance in high-energy astrophysics. Here we study, by means of two dimensional numerical simulations, the linear phase and the subsequent nonlinear evolution of the tearing instability within the framework of relativistic resistive magnetohydrodynamics, as appropriate in situations where the Alfven velocity approaches the speed of light. It is found that the linear phase of the instability closely matches the analysis in classical MHD, where the growth rate scales with the Lundquist number S as S^-1/2, with the only exception of an enhanced inertial term due to the thermal and magnetic energy contributions. In addition, when thin current sheets of inverse aspect ratio scaling as S^-1/3 are considered, the so-called "ideal" tearing regime is retriev...
Final Report: Laboratory Studies of Spontaneous Reconnection and Intermittent Plasma Objects
Energy Technology Data Exchange (ETDEWEB)
Egedal-Pedersen, Jan [Massachusetts Institute of Technology; Porkolab, Miklos [Massachusetts Institute of Technology
2011-05-31
The study of the collisionless magnetic reconnection constituted the primary work carried out under this grant. The investigations utilized two magnetic configurations with distinct boundary conditions. Both configurations were based upon the Versatile Toroidal Facility (VTF) at the MIT Plasma Science and Fusion Center and the MIT Physics Department. The NSF/DOE award No. 0613734, supported two graduate students (now Drs. W. Fox and N. Katz) and material expenses. The grant enabled these students to operate the VTF basic plasma physics experiment on magnetic reconnection. The first configuration was characterized by open boundary conditions where the magnetic field lines interface directly with the vacuum vessel walls. The reconnection dynamics for this configuration has been methodically characterized and it has been shown that kinetic effects related to trapped electron trajectories are responsible for the high rates of reconnection observed. This type of reconnection has not been investigated before. Nevertheless, the results are directly relevant to observations by the Wind spacecraft of fast reconnection deep in the Earth magnetotail. The second configuration was developed to be relevant to specifically to numerical simulations of magnetic reconnection, allowing the magnetic field-lines to be contained inside the device. The configuration is compatible with the presence of large current sheets in the reconnection region and reconnection is observed in fast powerful bursts. These reconnection events facilitate the first experimental investigations of the physics governing the spontaneous onset of fast reconnection. In the Report we review the general motivation of this work and provide an overview of our experimental and theoretical results enabled by the support through the awards.
An Intrinsically Three-Dimensional Magnetic Reconnection Process in a Generalized Harris Sheet
Zhu, Ping; Wang, Zechen; Bonofiglo, Phillip
2016-01-01
A magnetic reconnection process in the generalized Harris sheet has been revealed to be intrinsically three-dimensional both geometrically and dynamically despite the spatial invariance of the original current sheet in the equilibrium current direction. The spatial distribution and structure of the quasi-separatrix layers, as well as their temporal emergence and evolution, indicate that the associated magnetic reconnection can only occur in a three-dimensional geometry which is irreducible to a two-dimensional reconnection process. Such a three-dimensional reconnection process is induced by the nonlinear development of an ideal MHD ballooning instability in the generalized Harris sheet, which is itself an intrinsically three-dimensional dynamic process.
Observing the release of twist by magnetic reconnection in a solar filament eruption.
Xue, Zhike; Yan, Xiaoli; Cheng, Xin; Yang, Liheng; Su, Yingna; Kliem, Bernhard; Zhang, Jun; Liu, Zhong; Bi, Yi; Xiang, Yongyuan; Yang, Kai; Zhao, Li
2016-06-16
Magnetic reconnection is a fundamental process of topology change and energy release, taking place in plasmas on the Sun, in space, in astrophysical objects and in the laboratory. However, observational evidence has been relatively rare and typically only partial. Here we present evidence of fast reconnection in a solar filament eruption using high-resolution H-alpha images from the New Vacuum Solar Telescope, supplemented by extreme ultraviolet observations. The reconnection is seen to occur between a set of ambient chromospheric fibrils and the filament itself. This allows for the relaxation of magnetic tension in the filament by an untwisting motion, demonstrating a flux rope structure. The topology change and untwisting are also found through nonlinear force-free field modelling of the active region in combination with magnetohydrodynamic simulation. These results demonstrate a new role for reconnection in solar eruptions: the release of magnetic twist.
Observing the release of twist by magnetic reconnection in a solar filament eruption
Xue, Zhike; Yan, Xiaoli; Cheng, Xin; Yang, Liheng; Su, Yingna; Kliem, Bernhard; Zhang, Jun; Liu, Zhong; Bi, Yi; Xiang, Yongyuan; Yang, Kai; Zhao, Li
2016-06-01
Magnetic reconnection is a fundamental process of topology change and energy release, taking place in plasmas on the Sun, in space, in astrophysical objects and in the laboratory. However, observational evidence has been relatively rare and typically only partial. Here we present evidence of fast reconnection in a solar filament eruption using high-resolution H-alpha images from the New Vacuum Solar Telescope, supplemented by extreme ultraviolet observations. The reconnection is seen to occur between a set of ambient chromospheric fibrils and the filament itself. This allows for the relaxation of magnetic tension in the filament by an untwisting motion, demonstrating a flux rope structure. The topology change and untwisting are also found through nonlinear force-free field modelling of the active region in combination with magnetohydrodynamic simulation. These results demonstrate a new role for reconnection in solar eruptions: the release of magnetic twist.
Observing the release of twist by magnetic reconnection in a solar filament eruption
Xue, Zhike; Yan, Xiaoli; Cheng, Xin; Yang, Liheng; Su, Yingna; Kliem, Bernhard; Zhang, Jun; Liu, Zhong; Bi, Yi; Xiang, Yongyuan; Yang, Kai; Zhao, Li
2016-01-01
Magnetic reconnection is a fundamental process of topology change and energy release, taking place in plasmas on the Sun, in space, in astrophysical objects and in the laboratory. However, observational evidence has been relatively rare and typically only partial. Here we present evidence of fast reconnection in a solar filament eruption using high-resolution H-alpha images from the New Vacuum Solar Telescope, supplemented by extreme ultraviolet observations. The reconnection is seen to occur between a set of ambient chromospheric fibrils and the filament itself. This allows for the relaxation of magnetic tension in the filament by an untwisting motion, demonstrating a flux rope structure. The topology change and untwisting are also found through nonlinear force-free field modelling of the active region in combination with magnetohydrodynamic simulation. These results demonstrate a new role for reconnection in solar eruptions: the release of magnetic twist. PMID:27306479
"Ideally" unstable current sheets and the triggering of fast magnetic reconnection
Tenerani, Anna; Pucci, Fulvia; Landi, Simone; Rappazzo, Antonio Franco
2016-01-01
Magnetic reconnection is thought to be the dynamical mechanism underlying many explosive phenomena observed both in space and in the laboratory, though the question of how fast magnetic reconnection is triggered in such high Lundquist ($S$) number plasmas has remained elusive. It has been well established that reconnection can develop over timescales faster than those predicted traditionally once kinetic scales are reached. It has also been shown that, within the framework of resistive Magnetohydrodynamics (MHD), fast reconnection is achieved for thin enough sheets via the onset of the so-called plasmoid instability. The latter was discovered in studies specifically devoted to the Sweet-Parker current sheet, either as an initial condition or an apparent transient state developing in nonlinear studies. On the other hand, a fast tearing instability can grow on an ideal, i.e., $S$-independent, timescale (dubbed "ideal" tearing) within current sheets whose aspect ratio scales with the macroscopic Lundquist number...
Particle-in-Cell Simulations of Collisionless Magnetic Reconnection with a Non-Uniform Guide Field
Wilson, Fiona; Hesse, Michael; Harrison, Michael G; Stark, Craig R
2015-01-01
Results are presented of a first study of collisionless magnetic reconnection starting from a recently found exact nonlinear force-free Vlasov-Maxwell equilibrium. The initial state has a Harris sheet magnetic field profile in one direction and a non-uniform guide field in a second direction, resulting in a spatially constant magnetic field strength as well as a constant initial plasma density and plasma pressure. It is found that the reconnection process initially resembles guide field reconnection, but that a gradual transition to anti-parallel reconnection happens as the system evolves. The time evolution of a number of plasma parameters is investigated, and the results are compared with simulations starting from a Harris sheet equilibrium and a Harris sheet plus constant guide field equilibrium.
TURBULENT MAGNETOHYDRODYNAMIC RECONNECTION MEDIATED BY THE PLASMOID INSTABILITY
Energy Technology Data Exchange (ETDEWEB)
Huang, Yi-Min; Bhattacharjee, A., E-mail: yiminh@princeton.edu [Department of Astrophysical Sciences and Princeton Plasma Physics Laboratory, Princeton University, Princeton, New Jersey 08543 (United States)
2016-02-10
It has been established that the Sweet–Parker current layer in high Lundquist number reconnection is unstable to the super-Alfvénic plasmoid instability. Past two-dimensional magnetohydrodynamic simulations have demonstrated that the plasmoid instability leads to a new regime where the Sweet–Parker current layer changes into a chain of plasmoids connected by secondary current sheets, and the averaged reconnection rate becomes nearly independent of the Lundquist number. In this work, a three-dimensional simulation with a guide field shows that the additional degree of freedom allows plasmoid instabilities to grow at oblique angles, which interact and lead to self-generated turbulent reconnection. The averaged reconnection rate in the self-generated turbulent state is of the order of a hundredth of the characteristic Alfvén speed, which is similar to the two-dimensional result but is an order of magnitude lower than the fastest reconnection rate reported in recent studies of externally driven three-dimensional turbulent reconnection. Kinematic and magnetic energy fluctuations both form elongated eddies along the direction of the local magnetic field, which is a signature of anisotropic magnetohydrodynamic turbulence. Both energy fluctuations satisfy power-law spectra in the inertial range, where the magnetic energy spectral index is in the range from −2.3 to −2.1, while the kinetic energy spectral index is slightly steeper, in the range from −2.5 to −2.3. The anisotropy of turbulence eddies is found to be nearly scale-independent, in contrast with the prediction of the Goldreich–Sridhar theory for anisotropic turbulence in a homogeneous plasma permeated by a uniform magnetic field.
Linear and Non-Linear Associations of Gonorrhea Diagnosis Rates with Social Determinants of Health
Directory of Open Access Journals (Sweden)
Hazel D. Dean
2012-09-01
Full Text Available Identifying how social determinants of health (SDH influence the burden of disease in communities and populations is critically important to determine how to target public health interventions and move toward health equity. A holistic approach to disease prevention involves understanding the combined effects of individual, social, health system, and environmental determinants on geographic area-based disease burden. Using 2006–2008 gonorrhea surveillance data from the National Notifiable Sexually Transmitted Disease Surveillance and SDH variables from the American Community Survey, we calculated the diagnosis rate for each geographic area and analyzed the associations between those rates and the SDH and demographic variables. The estimated product moment correlation (PMC between gonorrhea rate and SDH variables ranged from 0.11 to 0.83. Proportions of the population that were black, of minority race/ethnicity, and unmarried, were each strongly correlated with gonorrhea diagnosis rates. The population density, female proportion, and proportion below the poverty level were moderately correlated with gonorrhea diagnosis rate. To better understand relationships among SDH, demographic variables, and gonorrhea diagnosis rates, more geographic area-based estimates of additional variables are required. With the availability of more SDH variables and methods that distinguish linear from non-linear associations, geographic area-based analysis of disease incidence and SDH can add value to public health prevention and control programs.
Jesudason, Christopher G
2011-01-01
The primary emphasis of this work on kinetics is to illustrate the a posteriori approach to applications, where focus on data leads to novel outcomes, rather than the a priori tendencies of applied analysis which imposes constructs on the nature of the observable. The secondary intention is the development of appropriate methods consonant with experimental definitions. By focusing on gradients, it is possible to determine both the average and instantaneous rate constants that can monitor changes in the rate constant with concentration changes as suggested by this theory. Here, methods are developed and discussed utilizing nonlinear analysis which does not require exact knowledge of initial concentrations. These methods are compared with those derived from standard methodology. These gradient methods are shown to be consistent with the ones from standard methods and could readily serve as alternatives for studies where there are limits or unknowns in the initial conditions, such as in the burgeoning fields of ...
Semrau, Daniel; Xu, Tianhua; Shevchenko, Nikita A; Paskov, Milen; Alvarado, Alex; Killey, Robert I; Bayvel, Polina
2017-01-01
Achievable information rates (AIRs) of wideband optical communication systems using a ∼40 nm (∼5 THz) erbium-doped fiber amplifier and ∼100 nm (∼12.5 THz) distributed Raman amplification are estimated based on a first-order perturbation analysis. The AIRs of each individual channel have been evaluated for DP-64QAM, DP-256QAM, and DP-1024QAM modulation formats. The impact of full-field nonlinear compensation (FF-NLC) and probabilistically shaped constellations using a Maxwell-Boltzmann distribution were studied and compared to electronic dispersion compensation. It has been found that a probabilistically shaped DP-1024QAM constellation, combined with FF-NLC, yields achievable information rates of ∼75 Tbit/s for the EDFA scheme and ∼223 Tbit/s for the Raman amplification scheme over a 2000 km standard single-mode fiber transmission.
Nonlinear Least-Squares Time-Difference Estimation from Sub-Nyquist-Rate Samples
Harada, Koji; Sakai, Hideaki
In this paper, time-difference estimation of filtered random signals passed through multipath channels is discussed. First, we reformulate the approach based on innovation-rate sampling (IRS) to fit our random signal model, then use the IRS results to drive the nonlinear least-squares (NLS) minimization algorithm. This hybrid approach (referred to as the IRS-NLS method) provides consistent estimates even for cases with sub-Nyquist sampling assuming the use of compactly-supported sampling kernels that satisfies the recently-developed nonaliasing condition in the frequency domain. Numerical simulations show that the proposed NLS-IRS method can improve performance over the straight-forward IRS method, and provides approximately the same performance as the NLS method with reduced sampling rate, even for closely-spaced time delays. This enables, given a fixed observation time, significant reduction in the required number of samples, while maintaining the same level of estimation performance.
Magnetic reconnection launcher
Cowan, M.
1987-04-06
An electromagnetic launcher includes a plurality of electrical stages which are energized sequentially in the launcher with the passage of a projectiles. Each stage of the launcher includes two or more coils which are arranged coaxially on either closed-loop or straight lines to form gaps between their ends. The projectile has an electrically conductive gap-portion that passes through all the gaps of all the stages in a direction transverse to the axes of the coils. The coils receive an electric current, store magnetic energy, and convert a significant portion of the stored magnetic energy into kinetic energy of the projectile moves through the gap. The magnetic polarity of the opposing coils is in the same direction, e.g. N-S-N-S. A gap portion of the projectile may be made from aluminum and is propelled by the reconnection of magnetic flux stored in the coils which causes accelerating forces to act upon the projectile and at the horizontal surfaces of the projectile near its rear. The gap portion of the projectile may be flat, rectangular and longer than the length of the opposing coils. The gap portion of the projectile permits substantially unrestricted distribution of the induced currents so that current densities are only high where the useful magnetic force is high. This allows designs which permit ohmic oblation from the rear surfaces of the gap portion of the projectile allowing much high velocities to be achieved. An electric power apparatus controls the electric power supplied to the opposing coils until the gap portion of the projectile substantially occupies the gap between the coils, at which time the coils are supplied with peak current quickly. 8 figs.
State Anxiety and Nonlinear Dynamics of Heart Rate Variability in Students
Dimitriev, Aleksey D.
2016-01-01
Objectives Clinical and experimental research studies have demonstrated that the emotional experience of anxiety impairs heart rate variability (HRV) in humans. The present study investigated whether changes in state anxiety (SA) can also modulate nonlinear dynamics of heart rate. Methods A group of 96 students volunteered to participate in the study. For each student, two 5-minute recordings of beat intervals (RR) were performed: one during a rest period and one just before a university examination, which was assumed to be a real-life stressor. Nonlinear analysis of HRV was performed. The Spielberger’s State-Trait Anxiety Inventory was used to assess the level of SA. Results Before adjusting for heart rate, a Wilcoxon matched pairs test showed significant decreases in Poincaré plot measures, entropy, largest Lyapunov exponent (LLE), and pointwise correlation dimension (PD2), and an increase in the short-term fractal-like scaling exponent of detrended fluctuation analysis (α1) during the exam session, compared with the rest period. A Pearson analysis indicated significant negative correlations between the dynamics of SA and Poincaré plot axes ratio (SD1/SD2), and between changes in SA and changes in entropy measures. A strong negative correlation was found between the dynamics of SA and LLE. A significant positive correlation was found between the dynamics of SA and α1. The decreases in Poincaré plot measures (SD1, complex correlation measure), entropy measures, and LLE were still significant after adjusting for heart rate. Corrected α1 was increased during the exam session. As before, the dynamics of adjusted LLE was significantly correlated with the dynamics of SA. Conclusions The qualitative increase in SA during academic examination was related to the decrease in the complexity and size of the Poincaré plot through a reduction of both the interbeat interval and its variation. PMID:26807793
State Anxiety and Nonlinear Dynamics of Heart Rate Variability in Students.
Directory of Open Access Journals (Sweden)
Dimitriy A Dimitriev
Full Text Available Clinical and experimental research studies have demonstrated that the emotional experience of anxiety impairs heart rate variability (HRV in humans. The present study investigated whether changes in state anxiety (SA can also modulate nonlinear dynamics of heart rate.A group of 96 students volunteered to participate in the study. For each student, two 5-minute recordings of beat intervals (RR were performed: one during a rest period and one just before a university examination, which was assumed to be a real-life stressor. Nonlinear analysis of HRV was performed. The Spielberger's State-Trait Anxiety Inventory was used to assess the level of SA.Before adjusting for heart rate, a Wilcoxon matched pairs test showed significant decreases in Poincaré plot measures, entropy, largest Lyapunov exponent (LLE, and pointwise correlation dimension (PD2, and an increase in the short-term fractal-like scaling exponent of detrended fluctuation analysis (α1 during the exam session, compared with the rest period. A Pearson analysis indicated significant negative correlations between the dynamics of SA and Poincaré plot axes ratio (SD1/SD2, and between changes in SA and changes in entropy measures. A strong negative correlation was found between the dynamics of SA and LLE. A significant positive correlation was found between the dynamics of SA and α1. The decreases in Poincaré plot measures (SD1, complex correlation measure, entropy measures, and LLE were still significant after adjusting for heart rate. Corrected α1 was increased during the exam session. As before, the dynamics of adjusted LLE was significantly correlated with the dynamics of SA.The qualitative increase in SA during academic examination was related to the decrease in the complexity and size of the Poincaré plot through a reduction of both the interbeat interval and its variation.
Magnetic reconnection by a self-retreating X line.
Oka, M; Fujimoto, M; Nakamura, T K M; Shinohara, I; Nishikawa, K-I
2008-11-14
Particle-in-cell simulations of collisionless magnetic reconnection are performed to study asymmetric reconnection in which an outflow is blocked by a hard wall while leaving sufficiently large room for the outflow of the opposite direction. This condition leads to a slow, roughly constant motion of the diffusion region away from the wall, the so-called "X-line retreat." The typical retreat speed is approximately 0.1 times the Alfvén speed. At the diffusion region, ion flow pattern shows strong asymmetry and the ion stagnation point and the X line are not collocated. A surprise, however, is that the reconnection rate remains the same unaffected by the retreat motion.
Magnetic Reconnection by a Self-Retreating X-Line
Oka, M; Nakamura, T K M; Shinohara, I; Nishikawa, K -I
2008-01-01
Particle-in-cell (PIC) simulations of collisionless magnetic reconnection are performed to study asymmetric reconnection in which an outflow is blocked by a hard wall while leaving sufficiently large room for the outflow of the opposite direction. This condition leads to a slow, roughly constant motion of the diffusion region away from the wall, the so-called `X-line retreat'. The typical retreat speed is ~0.1 times the Alfven speed. At the diffusion region, ion flow pattern shows strong asymmetry and the ion stagnation point and the X-line are not collocated. A surprise, however, is that the reconnection rate remains the same unaffected by the retreat motion.
Effects of electron inertia in collisionless magnetic reconnection
Energy Technology Data Exchange (ETDEWEB)
Andrés, Nahuel, E-mail: nandres@iafe.uba.ar; Gómez, Daniel [Instituto de Astronomía y Física del Espacio, CC. 67, suc. 28, 1428, Buenos Aires (Argentina); Departamento de Física, Facultad de Ciencias Exactas y Naturales, Univrsidad de Buenos Aires, Pabellón I, 1428, Buenos Aires (Argentina); Martin, Luis; Dmitruk, Pablo [Departamento de Física, Facultad de Ciencias Exactas y Naturales, Univrsidad de Buenos Aires, Pabellón I, 1428, Buenos Aires (Argentina)
2014-07-15
We present a study of collisionless magnetic reconnection within the framework of full two-fluid MHD for a completely ionized hydrogen plasma, retaining the effects of the Hall current, electron pressure and electron inertia. We performed 2.5D simulations using a pseudo-spectral code with no dissipative effects. We check that the ideal invariants of the problem are conserved down to round-off errors. Our numerical results confirm that the change in the topology of the magnetic field lines is exclusively due to the presence of electron inertia. The computed reconnection rates remain a fair fraction of the Alfvén velocity, which therefore qualifies as fast reconnection.
Turbulent reconnection of magnetic bipoles in stratified turbulence
Jabbari, Sarah; Mitra, Dhrubaditya; Kleeorin, Nathan; Rogachevskii, Igor
2016-01-01
We consider strongly stratified forced turbulence in a plane-parallel layer with helicity and corresponding large-scale dynamo action in the lower part and nonhelical turbulence in the upper. The magnetic field is found to develop strongly concentrated bipolar structures near the surface. They form elongated bands with a sharp interface between opposite polarities. Unlike earlier experiments with imposed magnetic field, the inclusion of rotation does not strongly suppress the formation of these structures. We perform a systematic numerical study of this phenomenon by varying magnetic Reynolds number, scale separation ratio, and Coriolis number. We also focus on the formation of the current sheet between bipolar regions where reconnection of oppositely oriented field lines occurs. We determine the reconnection rate by measuring either the inflow velocity in the vicinity of the current sheet or by measuring the electric field in the reconnection region. We demonstrate that for small Lundquist number, S1000, the...
Magnetic reconnection at 3D null points: effect of magnetic field asymmetry
Al-Hachami, A. K.; Pontin, D. I.
2010-03-01
Context. The magnetic field in many astrophysical plasmas, for example in the solar corona, is known to have a highly complex - and clearly three-dimensional - structure. Turbulent plasma motions in high-β regions where field lines are anchored, such as the solar interior, can store large amounts of energy in the magnetic field. This energy can only be released when magnetic reconnection occurs. Reconnection may only occur in locations where huge gradients of the magnetic field develop, and one candidate for such locations are magnetic null points, known to be abundant for example in the solar atmosphere. Reconnection leads to changes in the topology of the magnetic field, and energy being released as heat, kinetic energy and acceleration of particles. Thus reconnection is responsible for many dynamic processes, for instance flares and jets. Aims: The aim of this paper is to investigate the properties of magnetic reconnection at a 3D null point, with respect to their dependence on the symmetry of the magnetic field around the null. In particular we examine the rate of reconnection of magnetic flux at the null point, as well as how the current sheet forms and its properties. Methods: We use mathematical modelling and finite difference resistive MHD simulations. Results: It is found that the basic structure of the mode of magnetic reconnection considered is unaffected by varying the magnetic field symmetry, that is, the plasma flow is found to cross both the spine and fan of the null. However, the peak intensity and dimensions of the current sheet are dependent on the symmetry/asymmetry of the field lines. As a result, the reconnection rate is also found to be strongly dependent on the field asymmetry. Conclusions: The symmetry/asymmetry of the magnetic field in the vicinity of a magnetic null can have a profound effect on the geometry of any associated reconnection region, and the rate at which the reconnection process proceeds.
Fast magnetic reconnection in the plasmoid-dominated regime.
Uzdensky, D A; Loureiro, N F; Schekochihin, A A
2010-12-03
A conceptual model of resistive magnetic reconnection via a stochastic plasmoid chain is proposed. The global reconnection rate is shown to be independent of the Lundquist number. The distribution of fluxes in the plasmoids is shown to be an inverse-square law. It is argued that there is a finite probability of emergence of abnormally large plasmoids, which can disrupt the chain (and may be responsible for observable large abrupt events in solar flares and sawtooth crashes). A criterion for the transition from the resistive magnetohydrodynamic to the collisionless regime is provided.
Magnetic Reconnection at a Three-dimensional Solar Null Point
DEFF Research Database (Denmark)
Frederiksen, Jacob Trier; Baumann, Gisela; Galsgaard, Klaus
2012-01-01
-like). The MHD simulations start out from a potential magnetic field containing a null-point, obtained from a SOHO magnetogram extrapolation approximately 8 hours before a C-class flare was observed. The magnetic field is stressed with a boundary motion pattern similar to the horizontal motions observed by SOHO......Using a specific solar null point reconnection case studied by Masson et al (2009; ApJ 700, 559) we investigate the dependence of the reconnection rate on boundary driving speed, numerical resolution, type of resistivity (constant or numerical), and assumed stratification (constant density or solar...
Sun, Dajun D; Lee, Ping I
2015-04-06
The importance of rate of supersaturation generation on the kinetic solubility profiles of amorphous systems has recently been shown by us; however, the previous focus was limited to constant rates of supersaturation generation. The objective of the current study is to further examine the effect of nonlinear rate profiles of supersaturation generation in amorphous systems, including (1) instantaneous or infinite rate (i.e., initial degree of supersaturation), (2) first-order rate (e.g., from dissolution of amorphous drug particles), and (3) matrix diffusion regulated rate (e.g., drug release from amorphous solid dispersions (ASDs) based on cross-linked poly(2-hydroxyethyl methacrylate) (PHEMA) hydrogels), on the kinetic solubility profiles of a model poorly soluble drug indomethacin (IND) under nonsink dissolution conditions. The previously established mechanistic model taking into consideration both the crystal growth and ripening processes was extended to predict the evolution of supersaturation resulting from nonlinear rates of supersaturation generation. Our results confirm that excessively high initial supersaturation or a rapid supersaturation generation leads to a surge in maximum supersaturation followed by a rapid decrease in drug concentration owing to supersaturation-induced precipitation; however, an exceedingly low degree of supersaturation or a slow rate of supersaturation generation does not sufficiently raise the supersaturation level, which results in a lower but broader maximum kinetic solubility profile. Our experimental data suggest that an optimal area-under-the-curve of the kinetic solubility profiles exists at an intermediate initial supersaturation level for the amorphous systems studied here, which agrees well with the predicted trend. Our model predictions also support our experimental findings that IND ASD in cross-linked PHEMA exhibits a unique kinetic solubility profile because the resulting supersaturation level is governed by a matrix
Reconnectable Network with Limited Resources
Institute of Scientific and Technical Information of China (English)
史维更
1991-01-01
The reachability of a strongly connected network may be destroyed after link damage.Since many networks are directed or equivalent directed,connected by directed links with the potential for reversal.Therefore the reachability can be restored by reversing the direction of links.[1] has studied this matter under unlimited resources (transmitter and receiver) condition.In this paper the reconnectability of a network with limited number of receivers and transmitters is discussed.Also a linear time algorithm is given to find a reconnected reversal for limited receivers and transmitters.
Linear and nonlinear analysis of normal and CAD-affected heart rate signals.
Acharya, U Rajendra; Faust, Oliver; Sree, Vinitha; Swapna, G; Martis, Roshan Joy; Kadri, Nahrizul Adib; Suri, Jasjit S
2014-01-01
Coronary artery disease (CAD) is one of the dangerous cardiac disease, often may lead to sudden cardiac death. It is difficult to diagnose CAD by manual inspection of electrocardiogram (ECG) signals. To automate this detection task, in this study, we extracted the heart rate (HR) from the ECG signals and used them as base signal for further analysis. We then analyzed the HR signals of both normal and CAD subjects using (i) time domain, (ii) frequency domain and (iii) nonlinear techniques. The following are the nonlinear methods that were used in this work: Poincare plots, Recurrence Quantification Analysis (RQA) parameters, Shannon entropy, Approximate Entropy (ApEn), Sample Entropy (SampEn), Higher Order Spectra (HOS) methods, Detrended Fluctuation Analysis (DFA), Empirical Mode Decomposition (EMD), Cumulants, and Correlation Dimension. As a result of the analysis, we present unique recurrence, Poincare and HOS plots for normal and CAD subjects. We have also observed significant variations in the range of these features with respect to normal and CAD classes, and have presented the same in this paper. We found that the RQA parameters were higher for CAD subjects indicating more rhythm. Since the activity of CAD subjects is less, similar signal patterns repeat more frequently compared to the normal subjects. The entropy based parameters, ApEn and SampEn, are lower for CAD subjects indicating lower entropy (less activity due to impairment) for CAD. Almost all HOS parameters showed higher values for the CAD group, indicating the presence of higher frequency content in the CAD signals. Thus, our study provides a deep insight into how such nonlinear features could be exploited to effectively and reliably detect the presence of CAD. Copyright © 2013 Elsevier Ireland Ltd. All rights reserved.
Modelling nonlinear behavior of labor force participation rate by STAR: An application for Turkey
Directory of Open Access Journals (Sweden)
Sibel Cengiz
2014-04-01
Full Text Available The aim of this paper is to contribute to the understanding of the behavior of participation rates in terms of gender differences. We employed smooth autoregressive transition models for the quarterly Turkish labor force participation rates (LFPR data between 2000: Q1 - 2011: Q4 to present an asymmetric participation behavior. The smoothness parameter indicates a gradual transition from low to high regimes. It is higher for female workers compared to the male workers. Participation rates diminish during a recession but they increase smoothly during the periods of expansion. The estimation results of Enders et al. (1998 also verified the asymmetry and nonlinearity in participation rates. During periods of economic expansion, they are higher than the threshold but the low regime indicator function takes the value zero. The results of the paper have economic implications for policy makers. Due to the discouraged worker and added worker effects, LFPR should be observed with the unemployment rates while evaluating the tightness of the labor market.
Motulsky, Harvey J; Brown, Ronald E
2006-03-09
Nonlinear regression, like linear regression, assumes that the scatter of data around the ideal curve follows a Gaussian or normal distribution. This assumption leads to the familiar goal of regression: to minimize the sum of the squares of the vertical or Y-value distances between the points and the curve. Outliers can dominate the sum-of-the-squares calculation, and lead to misleading results. However, we know of no practical method for routinely identifying outliers when fitting curves with nonlinear regression. We describe a new method for identifying outliers when fitting data with nonlinear regression. We first fit the data using a robust form of nonlinear regression, based on the assumption that scatter follows a Lorentzian distribution. We devised a new adaptive method that gradually becomes more robust as the method proceeds. To define outliers, we adapted the false discovery rate approach to handling multiple comparisons. We then remove the outliers, and analyze the data using ordinary least-squares regression. Because the method combines robust regression and outlier removal, we call it the ROUT method. When analyzing simulated data, where all scatter is Gaussian, our method detects (falsely) one or more outlier in only about 1-3% of experiments. When analyzing data contaminated with one or several outliers, the ROUT method performs well at outlier identification, with an average False Discovery Rate less than 1%. Our method, which combines a new method of robust nonlinear regression with a new method of outlier identification, identifies outliers from nonlinear curve fits with reasonable power and few false positives.
Directory of Open Access Journals (Sweden)
Motulsky Harvey J
2006-03-01
Full Text Available Abstract Background Nonlinear regression, like linear regression, assumes that the scatter of data around the ideal curve follows a Gaussian or normal distribution. This assumption leads to the familiar goal of regression: to minimize the sum of the squares of the vertical or Y-value distances between the points and the curve. Outliers can dominate the sum-of-the-squares calculation, and lead to misleading results. However, we know of no practical method for routinely identifying outliers when fitting curves with nonlinear regression. Results We describe a new method for identifying outliers when fitting data with nonlinear regression. We first fit the data using a robust form of nonlinear regression, based on the assumption that scatter follows a Lorentzian distribution. We devised a new adaptive method that gradually becomes more robust as the method proceeds. To define outliers, we adapted the false discovery rate approach to handling multiple comparisons. We then remove the outliers, and analyze the data using ordinary least-squares regression. Because the method combines robust regression and outlier removal, we call it the ROUT method. When analyzing simulated data, where all scatter is Gaussian, our method detects (falsely one or more outlier in only about 1–3% of experiments. When analyzing data contaminated with one or several outliers, the ROUT method performs well at outlier identification, with an average False Discovery Rate less than 1%. Conclusion Our method, which combines a new method of robust nonlinear regression with a new method of outlier identification, identifies outliers from nonlinear curve fits with reasonable power and few false positives.
Nonlinear Methods to Assess Changes in Heart Rate Variability in Type 2 Diabetic Patients
Energy Technology Data Exchange (ETDEWEB)
Bhaskar, Roy, E-mail: imbhaskarall@gmail.com [Indian Institute of Technology (India); University of Connecticut, Farmington, CT (United States); Ghatak, Sobhendu [Indian Institute of Technology (India)
2013-10-15
Heart rate variability (HRV) is an important indicator of autonomic modulation of cardiovascular function. Diabetes can alter cardiac autonomic modulation by damaging afferent inputs, thereby increasing the risk of cardiovascular disease. We applied nonlinear analytical methods to identify parameters associated with HRV that are indicative of changes in autonomic modulation of heart function in diabetic patients. We analyzed differences in HRV patterns between diabetic and age-matched healthy control subjects using nonlinear methods. Lagged Poincaré plot, autocorrelation, and detrended fluctuation analysis were applied to analyze HRV in electrocardiography (ECG) recordings. Lagged Poincare plot analysis revealed significant changes in some parameters, suggestive of decreased parasympathetic modulation. The detrended fluctuation exponent derived from long-term fitting was higher than the short-term one in the diabetic population, which was also consistent with decreased parasympathetic input. The autocorrelation function of the deviation of inter-beat intervals exhibited a highly correlated pattern in the diabetic group compared with the control group. The HRV pattern significantly differs between diabetic patients and healthy subjects. All three statistical methods employed in the study may prove useful to detect the onset and extent of autonomic neuropathy in diabetic patients.
Role of Reconnection in AGN Jets
Lyutikov, M
2003-01-01
We discuss the possible role of reconnection in electro-magnetically dominated cores of relativistic AGN jets. We suggest that reconnection may proceed in a two-fold fashion: initial explosive collapse on the Alfven time-scale of a current-carrying jet (which is of the order of the light crossing time) and subsequent slow quasi-steady reconnection. Sites of explosive collapse are associated with bright knots, while steady-state reconnection re-energizes particles in the ``bridges'' between the knots. Ohmic dissipation in reconnection layers leads to particle acceleration either by inductive electric fields or by stochastic particle acceleration in the ensuing electro-magnetic turbulence.
Reconnection in Solar Flares: Outstanding Questions
Indian Academy of Sciences (India)
Hiroaki Isobe; Kazunari Shibata
2009-06-01
Space observations of solar flares such as those from Yohkoh, SOHO,TRACE, and RHESSI have revealed a lot of observational evidence of magnetic reconnection in solar flares: cusp-shaped arcades, reconnection inflows, plasmoids, etc. Thus it has been established, at least phenomenologically, that magnetic reconnection does occur in solar flares. However, a number of fundamental questions and puzzles still remain in the physics of reconnection in solar flares. In this paper, we discuss the recent progresses and future prospects in the study of magnetic reconnection in solar flares from both theoretical and observational points of view.
Zenteno, Efrain; Piazza, Roberto; M. R. Bhavani Shankar; Rönnow, Daniel; Ottersten, Björn
2015-01-01
A digital predistortion (DPD) scheme is presented for non-linear distortion mitigation in multi-carrier satellite communication channels. The proposed DPD has a multiple-input multiple-output architecture similar to data DPD schemes. However, it enhances the mitigation performance of data DPDs using a multi-rate processing algorithm to achieve spectrum broadening of non-linear operators. Compared to single carrier (single-input single-output) signal (waveform) DPD schemes, the proposed DPD ha...
Lainscsek, C.; Rowat, P.; Schettino, L.; Lee, D.; Song, D.; Letellier, C.; Poizner, H.
2012-03-01
Parkinson's disease is a degenerative condition whose severity is assessed by clinical observations of motor behaviors. These are performed by a neurological specialist through subjective ratings of a variety of movements including 10-s bouts of repetitive finger-tapping movements. We present here an algorithmic rating of these movements which may be beneficial for uniformly assessing the progression of the disease. Finger-tapping movements were digitally recorded from Parkinson's patients and controls, obtaining one time series for every 10 s bout. A nonlinear delay differential equation, whose structure was selected using a genetic algorithm, was fitted to each time series and its coefficients were used as a six-dimensional numerical descriptor. The algorithm was applied to time-series from two different groups of Parkinson's patients and controls. The algorithmic scores compared favorably with the unified Parkinson's disease rating scale scores, at least when the latter adequately matched with ratings from the Hoehn and Yahr scale. Moreover, when the two sets of mean scores for all patients are compared, there is a strong (r = 0.785) and significant (p <0.0015) correlation between them.
Study on Rail Profile Optimization Based on the Nonlinear Relationship between Profile and Wear Rate
Directory of Open Access Journals (Sweden)
Jianxi Wang
2017-01-01
Full Text Available This paper proposes a rail profile optimization method that takes account of wear rate within design cycle so as to minimize rail wear at the curve in heavy haul railway and extend the service life of rail. Taking rail wear rate as the object function, the vertical coordinate of rail profile at range optimization as independent variable, and the geometric characteristics and grinding depth of rail profile as constraint conditions, the support vector machine regression theory was used to fit the nonlinear relationship between rail profile and its wear rate. Then, the profile optimization model was built. Based on the optimization principle of genetic algorithm, the profile optimization model was solved to achieve the optimal rail profile. A multibody dynamics model was used to check the dynamic performance of carriage running on optimal rail profile. The result showed that the average relative error of support vector machine regression model remained less than 10% after a number of training processes. The dynamic performance of carriage running on optimized rail profile met the requirements on safety index and stability. The wear rate of optimized profile was lower than that of standard profile by 5.8%; the allowable carrying gross weight increased by 12.7%.
Model for Incomplete Reconnection in Sawtooth Crashes
Beidler, Matthew T
2011-01-01
A model for incomplete reconnection in sawtooth crashes is presented. The reconnection inflow during the crash phase of sawteeth self-consistently convects the high pressure core toward the reconnection site, raising the pressure gradient there. Reconnection shuts off if the diamagnetic drift speed at the reconnection site exceeds a threshold, which may explain incomplete reconnection. The relaxation of magnetic shear after reconnection stops may explain the destabilization of ideal interchange instabilities reported previously. Proof-of-principle two-fluid simulations confirm this basic picture. Predictions of the model compare favorably to data from the Mega Ampere Spherical Tokamak. Applications to transport modeling of sawteeth are discussed. The results should apply across tokamaks, including ITER.
Model for incomplete reconnection in sawtooth crashes.
Beidler, M T; Cassak, P A
2011-12-16
A model for incomplete reconnection in sawtooth crashes is presented. The reconnection inflow during the crash phase of sawteeth self-consistently convects the high pressure core toward the reconnection site, raising the pressure gradient there. Reconnection shuts off if the diamagnetic drift speed at the reconnection site exceeds a threshold, which may explain incomplete reconnection. The relaxation of magnetic shear after reconnection stops may explain the destabilization of ideal interchange instabilities reported previously. Proof-of-principle two-fluid simulations confirm this basic picture. Predictions of the model compare favorably to data from the Mega Ampere Spherical Tokamak. Applications to transport modeling of sawteeth are discussed. The results should apply across tokamaks, including ITER.
Computational Modelling and Optimal Control of Ebola Virus Disease with non-Linear Incidence Rate
Takaidza, I.; Makinde, O. D.; Okosun, O. K.
2017-03-01
The 2014 Ebola outbreak in West Africa has exposed the need to connect modellers and those with relevant data as pivotal to better understanding of how the disease spreads and quantifying the effects of possible interventions. In this paper, we model and analyse the Ebola virus disease with non-linear incidence rate. The epidemic model created is used to describe how the Ebola virus could potentially evolve in a population. We perform an uncertainty analysis of the basic reproductive number R 0 to quantify its sensitivity to other disease-related parameters. We also analyse the sensitivity of the final epidemic size to the time control interventions (education, vaccination, quarantine and safe handling) and provide the cost effective combination of the interventions.
Ge, Hao; Qian, Hong
2017-01-01
This paper studies a mathematical formalism of nonequilibrium thermodynamics for chemical reaction models with N species, M reactions, and general rate law. We establish a mathematical basis for J. W. Gibbs' macroscopic chemical thermodynamics under G. N. Lewis' kinetic law of entire equilibrium (detailed balance in nonlinear chemical kinetics). In doing so, the equilibrium thermodynamics is then naturally generalized to nonequilibrium settings without detailed balance. The kinetic models are represented by a Markovian jumping process. A generalized macroscopic chemical free energy function and its associated balance equation with nonnegative source and sink are the major discoveries. The proof is based on the large deviation principle of this type of Markov processes. A general fluctuation dissipation theorem for stochastic reaction kinetics is also proved. The mathematical theory illustrates how a novel macroscopic dynamic law can emerges from the mesoscopic kinetics in a multi-scale system.
Global stability for delay SIR and SEIR epidemic models with nonlinear incidence rate.
Huang, Gang; Takeuchi, Yasuhiro; Ma, Wanbiao; Wei, Daijun
2010-07-01
In this paper, based on SIR and SEIR epidemic models with a general nonlinear incidence rate, we incorporate time delays into the ordinary differential equation models. In particular, we consider two delay differential equation models in which delays are caused (i) by the latency of the infection in a vector, and (ii) by the latent period in an infected host. By constructing suitable Lyapunov functionals and using the Lyapunov-LaSalle invariance principle, we prove the global stability of the endemic equilibrium and the disease-free equilibrium for time delays of any length in each model. Our results show that the global properties of equilibria also only depend on the basic reproductive number and that the latent period in a vector does not affect the stability, but the latent period in an infected host plays a positive role to control disease development.
Evaluating non-linear models on point and interval forecasts: an application with exchange rates
Directory of Open Access Journals (Sweden)
Emanuela Marrocu
2005-01-01
Full Text Available The aim of this paper is to compare the forecasting performance of SETAR and GARCH models against a linear benchmark using historical data for the returns of the Japanese yen/US dollar exchange rate. The relative performance of the models is evaluated on point forecasts and on interval forecasts. Point forecasts evaluation over the whole forecast period indicates that the performance of the models, when distinguishable, tends to favour the linear models. However, we show that if the evaluation of point forecasts is conducted over distinct subsamples or specific regimes there is more evidence of forecasting gains, especially from the SETAR models. Moreover, when we evaluate the validity of interval forecasts, the results produce clear evidence of the superiority of the non-linear models, and tend to favour especially the GARCH models.
Abreu, P
2002-01-01
The preliminary results on the search of colour reconnection effects (CR) from the four experiments at LEP, ALEPH, DELPHI, L3 and OPAL, are reviewed. Extreme models are excluded by studies of standard variables, and on going studies of a method first suggested by L3, the particle flow method (D. Duchesneau, (2001)), are yet inconclusive. (22 refs).
Directory of Open Access Journals (Sweden)
Pisit Leeahtam
2011-10-01
Full Text Available The objectives of this study are to find the fitting model and dependence measures of both Thailand’s exchange rate and Malaysia’s exchange rate during, between, and after the World’s recent financial crises based on linear, nonlinear and empirical copula approaches.The results of the study confirm that the nonlinear model (NNTs is an appropriate model for Thailand’s exchange rate return in percentage during the periods of 2008-2011but not for Malaysia’s exchange rate return. Based on empirical copula approach, the dependence measures are very small between Thailand’s exchange and Malaysia’s exchange. This seems to suggest that when global economy is affected by World’s financial crisis, the nonlinear approach should be used to predict Thailand’s exchange rate return in percentage. In addition, it suggests that both the nonlinear and linear approaches should be used to predict the Malaysia’s exchange rate return in percentage. Moreover, the relationship between the exchange rate of Thailand and that of Malaysia is not strong.This is also true for the currencies of both countries.
Faes, Luca; Zhao, He; Chon, Ki H; Nollo, Giandomenico
2009-03-01
We propose a method to extend to time-varying (TV) systems the procedure for generating typical surrogate time series, in order to test the presence of nonlinear dynamics in potentially nonstationary signals. The method is based on fitting a TV autoregressive (AR) model to the original series and then regressing the model coefficients with random replacements of the model residuals to generate TV AR surrogate series. The proposed surrogate series were used in combination with a TV sample entropy (SE) discriminating statistic to assess nonlinearity in both simulated and experimental time series, in comparison with traditional time-invariant (TIV) surrogates combined with the TIV SE discriminating statistic. Analysis of simulated time series showed that using TIV surrogates, linear nonstationary time series may be erroneously regarded as nonlinear and weak TV nonlinearities may remain unrevealed, while the use of TV AR surrogates markedly increases the probability of a correct interpretation. Application to short (500 beats) heart rate variability (HRV) time series recorded at rest (R), after head-up tilt (T), and during paced breathing (PB) showed: 1) modifications of the SE statistic that were well interpretable with the known cardiovascular physiology; 2) significant contribution of nonlinear dynamics to HRV in all conditions, with significant increase during PB at 0.2 Hz respiration rate; and 3) a disagreement between TV AR surrogates and TIV surrogates in about a quarter of the series, suggesting that nonstationarity may affect HRV recordings and bias the outcome of the traditional surrogate-based nonlinearity test.
Observations of Magnetic Reconnection and Plasma Dynamics in Mercury's Magnetosphere
DiBraccio, Gina A.
Mercury's magnetosphere is formed as a result of the supersonic solar wind interacting with the planet's intrinsic magnetic field. The combination of the weak planetary dipole moment and intense solar wind forcing of the inner heliosphere creates a unique space environment, which can teach us about planetary magnetospheres. In this work, we analyze the first in situ orbital observations at Mercury, provided by the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft. Magnetic reconnection and the transport of plasma and magnetic flux are investigated using MESSENGER Magnetometer and Fast Imaging Plasma Spectrometer measurements. Here, we report our results on the effect of magnetic reconnection and plasma dynamics on Mercury's space environment: (1) Mercury's magnetosphere is driven by frequent, intense magnetic reconnection observed in the form of magnetic field components normal to the magnetopause, BN, and as helical bundles of flux, called magnetic flux ropes, in the cross-tail current sheet. The high reconnection rates are determined to be a direct consequence of the low plasma beta, the ratio of plasma to magnetic pressure, in the inner heliosphere. (2) As upstream solar wind conditions vary, we find that reconnection occurs at Mercury's magnetopause for all orientations of the interplanetary magnetic field, independent of shear angle. During the most extreme solar wind forcing events, the influence of induction fields generated within Mercury's highly conducting core are negated by erosion due to persistent magnetopause reconnection. (3) We present the first observations of Mercury's plasma mantle, which forms as a result of magnetopause reconnection and allows solar wind plasma to enter into the high-latitude magnetotail through the dayside cusps. The energy dispersion observed in the plasma mantle protons is used to infer the cross-magnetosphere electric field, providing a direct measurement of solar wind momentum
Hippotherapy acute impact on heart rate variability non-linear dynamics in neurological disorders.
Cabiddu, Ramona; Borghi-Silva, Audrey; Trimer, Renata; Trimer, Vitor; Ricci, Paula Angélica; Italiano Monteiro, Clara; Camargo Magalhães Maniglia, Marcela; Silva Pereira, Ana Maria; Rodrigues das Chagas, Gustavo; Carvalho, Eliane Maria
2016-05-15
Neurological disorders are associated with autonomic dysfunction. Hippotherapy (HT) is a therapy treatment strategy that utilizes a horse in an interdisciplinary approach for the physical and mental rehabilitation of people with physical, mental and/or psychological disabilities. However, no studies have been carried out which evaluated the effects of HT on the autonomic control in these patients. Therefore, the objective of the present study was to investigate the effects of a single HT session on cardiovascular autonomic control by time domain and non-linear analysis of heart rate variability (HRV). The HRV signal was recorded continuously in twelve children affected by neurological disorders during a HT session, consisting in a 10-minute sitting position rest (P1), a 15-minute preparatory phase sitting on the horse (P2), a 15-minute HT session (P3) and a final 10-minute sitting position recovery (P4). Time domain and non-linear HRV indices, including Sample Entropy (SampEn), Lempel-Ziv Complexity (LZC) and Detrended Fluctuation Analysis (DFA), were calculated for each treatment phase. We observed that SampEn increased during P3 (SampEn=0.56±0.10) with respect to P1 (SampEn=0.40±0.14, p<0.05), while DFA decreased during P3 (DFA=1.10±0.10) with respect to P1 (DFA=1.26±0.14, p<0.05). A significant SDRR increase (p<0.05) was observed during the recovery period P4 (SDRR=50±30ms) with respect to the HT session period P3 (SDRR=30±10ms). Our results suggest that HT might benefit children with disabilities attributable to neurological disorders by eliciting an acute autonomic response during the therapy and during the recovery period.
Nonlinear short-term heart rate variability prediction of spontaneous ventricular tachyarrhythmia
Institute of Scientific and Technical Information of China (English)
ZHUANG JianJun; NING XinBao; DU SiDan; WANG ZhenZhou; HUO ChengYu; YANG Xi; FAN AiHua
2008-01-01
As malign ventricular tachyarrhythmias triggering sudden cardiac death (SCD),both ventricular tachycardia (VT) and ventricular fibrillation (VF) are major causes of mortality.The most efficient ther-apy for SCD prevention is implantable cardioverter defibrillators (ICD).The ICD can accurately and ef-fectively identify the forthcoming of fatal ventricular tachyarrhythmias and deliver a shock in order to restore patients' normal sinus rhythm.In this study,two nonlinear complexity measures based on en-tropy:approximate entropy (ApEn) and sample entropy (SampEn) as well as two time linear indices:the mean RR interval (the average of time intervals between consecutive R-waves) and the standard devia-tion of RR intervals were used for short-term forecasting of VT-VF occurrence.The last small sections of interbeat intervals preceding 135 VT-VF episodes from 78 patients stored by the ICD were analyzed and compared with individually acquired control time series (CON series) from the same patients,which are normally intrinsic sinus rhythms.The results demonstrate that in addition to an obvious in-crease in heart rates of the patients,the values of two entropy measures are significantly smaller for VT-VF episodes than those for CON series.Conclusions can be drawn that when a ventricular tach-yarrhythmia approaches,the sympathetic tone of the patients is increased,and the complexity of their RR intervals immediately before the onset of VT-VF events is obviously lower than that of RR Intervals recorded during sinus rhythms.For a better separation,the optimal range of threshold r is determined for two algorithms.ApEn and SampEn measures might be the suitable nonlinear parameters for shod-term prediction of life-threatening ventricular tachyarrhythmias in the application of the cardioversion and defibrillation.
Collisionless reconnection: magnetic field line interaction
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R. A. Treumann
2012-10-01
Full Text Available Magnetic field lines are quantum objects carrying one quantum Φ_{0} = 2πh/e of magnetic flux and have finite radius λ_{m}. Here we argue that they possess a very specific dynamical interaction. Parallel field lines reject each other. When confined to a certain area they form two-dimensional lattices of hexagonal structure. We estimate the filling factor of such an area. Anti-parallel field lines, on the other hand, attract each other. We identify the physical mechanism as being due to the action of the gauge potential field, which we determine quantum mechanically for two parallel and two anti-parallel field lines. The distortion of the quantum electrodynamic vacuum causes a cloud of virtual pairs. We calculate the virtual pair production rate from quantum electrodynamics and estimate the virtual pair cloud density, pair current and Lorentz force density acting on the field lines via the pair cloud. These properties of field line dynamics become important in collisionless reconnection, consistently explaining why and how reconnection can spontaneously set on in the field-free centre of a current sheet below the electron-inertial scale.
Spatial distribution of Mercury's flux ropes and reconnection fronts: MESSENGER observations
Sun, W. J.; Fu, S. Y.; Slavin, J. A.; Raines, J. M.; Zong, Q. G.; Poh, G. K.; Zurbuchen, T. H.
2016-08-01
We perform a statistical study of flux ropes and reconnection fronts based on MErcury Surface, Space ENviroment, GEochemistry, and Ranging (MESSENGER) magnetic field and plasma observations to study the implications for the spatial distribution of reconnection sites in Mercury's near magnetotail. The results show important differences of temporal and spatial distributions as compared to Earth. We have surveyed the plasma sheet crossings between -2 RM and -3 RM downtail from the planet, i.e., the location of Near-Mercury Neutral Line (NMNL). Plasma sheets were defined to be regions with β ≥ 0.5. Using this definition, 39 flux ropes and 86 reconnection fronts were identified in the plasma sheet. At Mercury, the distributions of flux ropes and reconnection fronts show clear dawn-dusk asymmetry with much higher occurrence rate on the dawnside plasma sheet than on the duskside. This suggests that magnetic reconnection in Mercury's magnetotail occurs more frequently in the dawnside than in the duskside plasma sheet, which is different than the observations in Earth's magnetotail showing more reconnection signatures in the duskside plasma sheet. The distribution of plasma sheet thickness shows that plasma sheet near the midnight is the thinnest part and does not show obvious asymmetry. Thus, the reasons that cause magnetic reconnection to preferentially occur on the dawnside of the magnetotail at Mercury may not be the plasma sheet thickness and require further study. The peak occurrence rates of flux ropes and reconnection fronts in Mercury's plasma sheet are ~ 60 times higher than that of Earth's values, which we interpret to be due to the highly variable magnetospheric conditions at Mercury. Such higher occurrence rate of magnetic reconnection would generate more plasma flows in the dawnside plasma sheet than in the duskside. These plasma flows would mostly brake and initiate the substorm dipolarization on the postmidnight sector at Mercury rather than the
Institute of Scientific and Technical Information of China (English)
无
2008-01-01
Quasi-likelihood nonlinear models (QLNM) include generalized linear models as a special case.Under some regularity conditions,the rate of the strong consistency of the maximum quasi-likelihood estimation (MQLE) is obtained in QLNM.In an important case,this rate is O(n-1/2(loglogn)1/2),which is just the rate of LIL of partial sums for I.I.d variables,and thus cannot be improved anymore.
Chromospheric magnetic reconnection: Two-fluid simulations of coalescing current loops
Smith, P D
2008-01-01
Aims: To investigate magnetic reconnection rates during the coalescence of two current loops in the solar chromosphere, by altering the neutral-hydrogen to proton density ratio, ioniziation/recombination coefficients, collision frequency and relative helicity of the loops. Methods: 2.5D numerical simulations of the chromosphere were conducted using a newly developed two-fluid (ion-neutral) numerical code. Developed from the Artificial Wind scheme, the numerical code includes the effects of ion-neutral collisions, ionization/recombination, thermal/resistive diffusivity and collisional/resistive heating. Results: It was found that the rates of magnetic reconnection strongly depend on the neutral-hydrogen to proton density ratio; increasing the density ratio by a thousand-fold decreased the rate of magnetic reconnection by twenty-fold. This result implies that magnetic reconnection proceeds significantly faster in the upper chromosphere, where the density of ions (protons) and neutral-hydrogen is comparable, tha...
3D reconnection due to oblique modes: a simulation of Harris current sheets
Directory of Open Access Journals (Sweden)
G. Lapenta
2000-01-01
Full Text Available Simulations in three dimensions of a Harris current sheet with mass ratio, mi/me = 180, and current sheet thickness, pi/L = 0.5, suggest the existence of a linearly unstable oblique mode, which is independent from either the drift-kink or the tearing instability. The new oblique mode causes reconnection independently from the tearing mode. During the initial linear stage, the system is unstable to the tearing mode and the drift kink mode, with growth rates that are accurately described by existing linear theories. How-ever, oblique modes are also linearly unstable, but with smaller growth rates than either the tearing or the drift-kink mode. The non-linear stage is first reached by the drift-kink mode, which alters the initial equilibrium and leads to a change in the growth rates of the tearing and oblique modes. In the non-linear stage, the resulting changes in magnetic topology are incompatible with a pure tearing mode. The oblique mode is shown to introduce a helical structure into the magnetic field lines.
Time window for magnetic reconnection in plasma configurations with velocity shear.
Faganello, M; Califano, F; Pegoraro, F
2008-10-24
It is shown that the rate of magnetic field line reconnection can be clocked by the evolution of the large-scale processes that are responsible for the formation of the current layers where reconnection can take place. In unsteady plasma configurations, such as those produced by the onset of the Kelvin-Helmholtz instability in a plasma with a velocity shear, qualitatively different magnetic structures are produced depending on how fast the reconnection process develops on the external clock set by the evolving large-scale configuration.
Directory of Open Access Journals (Sweden)
David E. Allen
2016-03-01
Full Text Available This paper features an analysis of major currency exchange rate movements in relation to the US dollar, as constituted in US dollar terms. Euro, British pound, Chinese yuan, and Japanese yen are modelled using a variety of non-linear models, including smooth transition regression models, logistic smooth transition regressions models, threshold autoregressive models, nonlinear autoregressive models, and additive nonlinear autoregressive models, plus Neural Network models. The models are evaluated on the basis of error metrics for twenty day out-of-sample forecasts using the mean average percentage errors (MAPE. The results suggest that there is no dominating class of time series models, and the different currency pairs relationships with the US dollar are captured best by neural net regression models, over the ten year sample of daily exchange rate returns data, from August 2005 to August 2015.
Directory of Open Access Journals (Sweden)
Nadhem Selmi
2015-02-01
Full Text Available The aim of this paper is to study the dynamics of the real exchange rate deviations of G7 countries by capturing nonlinearity and long memory features. In this context, we used fractionally integrated STAR (FISTAR models proposed by Van Dijk et al. (2002 [Van Dijk, D., Franses, P.H., Paap, R., (2002, A nonlinear long-memory model with an application to US unemployment, Journal of Econometrics, 110, 135-165.] for a case with an exponential transition function. Indeed, this study can take into account procedures characterized by several dynamic regimes and persistence phenomena. Empirically, the elements of both fractional long memory and threshold non-linearity are present for the real exchange rates of the G-7 countries against the US, notably in the EU countries.
Martin, J; Schneider, F; Kowalewskij, A; Jordan, D; Hapfelmeier, A; Kochs, E F; Wagner, K J; Schulz, C M
2016-12-01
Excessive workload may impact the anaesthetists' ability to adequately process information during clinical practice in the operation room and may result in inaccurate situational awareness and performance. This exploratory study investigated heart rate (HR), linear and non-linear heart rate variability (HRV) metrics and subjective ratings scales for the assessment of workload associated with the anaesthesia stages induction, maintenance and emergence. HR and HRV metrics were calculated based on five min segments from each of the three anaesthesia stages. The area under the receiver operating characteristics curve (AUC) of the investigated metrics was calculated to assess their ability to discriminate between the stages of anaesthesia. Additionally, a multiparametric approach based on logistic regression models was performed to further evaluate whether linear or non-linear heart rate metrics are suitable for the assessment of workload. Mean HR and several linear and non-linear HRV metrics including subjective workload ratings differed significantly between stages of anaesthesia. Permutation Entropy (PeEn, AUC=0.828) and mean HR (AUC=0.826) discriminated best between the anaesthesia stages induction and maintenance. In the multiparametric approach using logistic regression models, the model based on non-linear heart rate metrics provided a higher AUC compared with the models based on linear metrics. In this exploratory study based on short ECG segment analysis, PeEn and HR seem to be promising to separate workload levels between different stages of anaesthesia. The multiparametric analysis of the regression models favours non-linear heart rate metrics over linear metrics. © The Author 2016. Published by Oxford University Press on behalf of the British Journal of Anaesthesia. All rights reserved. For Permissions, please email: journals.permissions@oup.com.
Two-spacecraft observations of reconnection at the magnetopause: Model results and data comparison
Penz, T.; Farrugia, C. J.; Ivanova, V. V.; Semenov, V. S.; Biernat, H. K.; Torbert, R.
We revisit an example of “quasi-steady” magnetic reconnection at the dayside magnetopause on February 11, 1998, observed by Equator-S and Geotail at the dawnside magnetopause. Phan et al. [Phan, T.D. et al., 2000. Extended magnetic reconnection at the Earth’s magnetopause from detection of bi-directional jets. Nature 404, 848 850.] reported oppositely directed jets at these spacecrafts and inferred a length of the reconnection line of about 38RE. Pinnock et al. [Pinnock, M., Chisham, G., Coleman, I.J., Freeman, M.P., Hairston, M., Villain, J.-P., 2003. The location and rate of dayside reconnection during an interval of southward interplanetary magnetic field. Ann. Geophys. 21, 1467 1482.] used measurements from SuperDARN radars to show that the reconnection electric field was variable. Here we complement this work by obtaining snapshots of the reconnection electric field from the in situ observations. To do this, we apply a reconstruction method based on a model of compressible Petschek-type magnetic reconnection. This independent method uses magnetic field observations as input data to calculate the reconnection electric field. We obtain average values of Erec in the range of 0.4 2.4 mV/m. Further we infer a distance perpendicular to the reconnection line of 0.4 0.6RE. The model results are compared with the two studies mentioned above. It thus appears that while the transfer of momentum for this event is indeed large-scale, the actual rate depends on the time it is measured.
A Reconnecting Flux Rope Dynamo
Baggaley, Andrew W; Shukurov, Anvar; Subramanian, Kandaswamy
2009-01-01
We develop a new model of the fluctuation dynamo in which the magnetic field is confined in thin flux ropes advected by a multi-scale flow modeling turbulence. Magnetic dissipation occurs only via reconnection of the flux ropes. We investigate the kinetic energy release into heat, mediated by the dynamo action, both in our model and by solving the induction equation with the same flow. We find that a flux rope dynamo is an order of magnitude more efficient at converting mechanical energy into heat. The probability density of the magnetic energy release in reconnections has a power-law form with the slope -3, consistent with the Solar corona heating by nanoflares.
Baggaley, Andrew W.; Barenghi, Carlo F.; Shukurov, Anvar; Subramanian, Kandaswamy
2009-11-01
We develop a model of the fluctuation dynamo in which the magnetic field is confined to thin flux ropes advected by a multiscale model of turbulence. Magnetic dissipation occurs only via reconnection of the flux ropes. This model can be viewed as an implementation of the asymptotic limit Rm→∞ for a continuous magnetic field, where magnetic dissipation is strongly localized to small regions of strong-field gradients. We investigate the kinetic-energy release into heat mediated by the dynamo action, both in our model and by solving the induction equation with the same flow. We find that a flux-rope dynamo is an order of magnitude more efficient at converting mechanical energy into heat. The probability density of the magnetic energy release in reconnections has a power-law form with the slope -3 , consistent with the solar corona heating by nanoflares.
Reconnecting flux-rope dynamo.
Baggaley, Andrew W; Barenghi, Carlo F; Shukurov, Anvar; Subramanian, Kandaswamy
2009-11-01
We develop a model of the fluctuation dynamo in which the magnetic field is confined to thin flux ropes advected by a multiscale model of turbulence. Magnetic dissipation occurs only via reconnection of the flux ropes. This model can be viewed as an implementation of the asymptotic limit R_{m}-->infinity for a continuous magnetic field, where magnetic dissipation is strongly localized to small regions of strong-field gradients. We investigate the kinetic-energy release into heat mediated by the dynamo action, both in our model and by solving the induction equation with the same flow. We find that a flux-rope dynamo is an order of magnitude more efficient at converting mechanical energy into heat. The probability density of the magnetic energy release in reconnections has a power-law form with the slope -3 , consistent with the solar corona heating by nanoflares.
Patchy Reconnection in the Solar Corona
Guidoni, Silvina E
2011-01-01
Supra-arcade downflows (SADs) and supra-arcade downflowing loops (SADLs) descending from reconnection regions toward solar post-flare arcades seem to be two different observational signatures of retracting, isolated reconnected flux tubes with irreducible three-dimensional geometries. This dissertation describes work in refining and improving a novel model of patchy reconnection, where only a small bundle of field lines is reconnected across a current sheet and forms a reconnected thin flux tube. Traditional models have not been able to explain why some of the observed SADs appear to be hot and relatively devoid of plasma. The present work shows that plasma depletion naturally occurs in flux tubes that are reconnected across nonuniform current sheets and slide trough regions of decreasing magnetic field magnitude. Moreover, through a detailed theoretical analysis of generalized thin flux tube equations, we show that the addition to the model of pressure-driven parallel dynamics, as well as temperature-depende...
Particle acceleration at a reconnecting magnetic separator
Threlfall, J; Parnell, C E; Oskoui, S Eradat
2014-01-01
While the exact acceleration mechanism of energetic particles during solar flares is (as yet) unknown, magnetic reconnection plays a key role both in the release of stored magnetic energy of the solar corona and the magnetic restructuring during a flare. Recent work has shown that special field lines, called separators, are common sites of reconnection in 3D numerical experiments. To date, 3D separator reconnection sites have received little attention as particle accelerators. We investigate the effectiveness of separator reconnection as a particle acceleration mechanism for electrons and protons. We study the particle acceleration using a relativistic guiding-centre particle code in a time-dependent kinematic model of magnetic reconnection at a separator. The effect upon particle behaviour of initial position, pitch angle and initial kinetic energy are examined in detail, both for specific (single) particle examples and for large distributions of initial conditions. The separator reconnection model contains ...
Nonlinear temperature effects on multifractal complexity of metabolic rate of mice
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Fabio A. Labra
2016-10-01
Full Text Available Complex physiological dynamics have been argued to be a signature of healthy physiological function. Here we test whether the complexity of metabolic rate fluctuations in small endotherms decreases with lower environmental temperatures. To do so, we examine the multifractal temporal scaling properties of the rate of change in oxygen consumption r(VO2, in the laboratory mouse Mus musculus, assessing their long range correlation properties across seven different environmental temperatures, ranging from 0 °C to 30 °C. To do so, we applied multifractal detrended fluctuation analysis (MF-DFA, finding that r(VO2 fluctuations show two scaling regimes. For small time scales below the crossover time (approximately 102 s, either monofractal or weak multifractal dynamics are observed depending on whether Ta 15 °C respectively. For larger time scales, r(VO2 fluctuations are characterized by an asymptotic scaling exponent that indicates multifractal anti-persistent or uncorrelated dynamics. For both scaling regimes, a generalization of the multiplicative cascade model provides very good fits for the Renyi exponents τ(q, showing that the infinite number of exponents h(q can be described by only two independent parameters, a and b. We also show that the long-range correlation structure of r(VO2 time series differs from randomly shuffled series, and may not be explained as an artifact of stochastic sampling of a linear frequency spectrum. These results show that metabolic rate dynamics in a well studied micro-endotherm are consistent with a highly non-linear feedback control system.
Nonlinear temperature effects on multifractal complexity of metabolic rate of mice
Bogdanovich, Jose M.; Bozinovic, Francisco
2016-01-01
Complex physiological dynamics have been argued to be a signature of healthy physiological function. Here we test whether the complexity of metabolic rate fluctuations in small endotherms decreases with lower environmental temperatures. To do so, we examine the multifractal temporal scaling properties of the rate of change in oxygen consumption r(VO2), in the laboratory mouse Mus musculus, assessing their long range correlation properties across seven different environmental temperatures, ranging from 0 °C to 30 °C. To do so, we applied multifractal detrended fluctuation analysis (MF-DFA), finding that r(VO2) fluctuations show two scaling regimes. For small time scales below the crossover time (approximately 102 s), either monofractal or weak multifractal dynamics are observed depending on whether Ta 15 °C respectively. For larger time scales, r(VO2) fluctuations are characterized by an asymptotic scaling exponent that indicates multifractal anti-persistent or uncorrelated dynamics. For both scaling regimes, a generalization of the multiplicative cascade model provides very good fits for the Renyi exponents τ(q), showing that the infinite number of exponents h(q) can be described by only two independent parameters, a and b. We also show that the long-range correlation structure of r(VO2) time series differs from randomly shuffled series, and may not be explained as an artifact of stochastic sampling of a linear frequency spectrum. These results show that metabolic rate dynamics in a well studied micro-endotherm are consistent with a highly non-linear feedback control system.
Colour Reconnection - Models and Tests
Christiansen, Jesper R
2015-01-01
Recent progress on colour reconnection within the Pythia framework is presented. A new model is introduced, based on the SU(3) structure of QCD and a minimization of the potential string energy. The inclusion of the epsilon structure of SU(3) gives a new baryon production mechanism and makes it possible simultaneously to describe hyperon production at both $e^+e^-$ and pp colliders. Finally, predictions for $e^+e^-$ colliders, both past and potential future ones, are presented.
Magnetotail Reconnection and Flux Circulation: Jupiter and Saturn Compared
Jackman, C. M.; Vogt, M. F.; Slavin, J. A.; Cowley, S. W. H.; Boardsen, S. A.
2011-01-01
The Jovian magnetosphere has been visited by eight spacecraft, and the magnetometer data have been used to identify dozens of plasmoids and 250 field dipolarizations associated with magnetic reconnection in the tail [e.g. Vogt et al., 2010]. Since the arrival of the Cassini spacecraft at Saturn in 2004, the magnetometer instrument has also been used to identify reconnection signatures. The deepest magnetotail orbits were in 2006, and during this time 34 signatures of plasmoids were identified. In this study we compare the statistical properties of plasmoids at Jupiter and Saturn such as duration, size, location, and recurrence period. Such parameters can be influenced by many factors, including the different Dungey cycle timescales and cross-magnetospheric potential drops at the two planets. We present superposed epoch analyses of plasmoids at the two planets to determine their average properties and to infer their role in the reconfiguration of the nightside of the magnetosphere. We examine the contributions of plasmoids to the magnetic flux transfer cycle at both planets. At Jupiter, there is evidence of an extended interval after reconnection where the field remains northward (analogous to the terrestrial post-plasmoid plasma sheet). At Saturn we see a similar feature, and calculate the amount of flux closed on average in reconnection events, leading us to an estimation of the recurrence rate of plasmoid release.
Study of Local Reconnection Physics in a Laboratory Plasma
Energy Technology Data Exchange (ETDEWEB)
Hantao Ji; Troy Carter; Scott Hsu; Masaaki Yamada
2001-06-11
A short review of physics results obtained in the Magnetic Reconnection Experiment (MRX) is given with an emphasis on the local features of magnetic reconnection in a controlled environment. Stable two-dimensional current sheets are formed and sustained by induction using two internal coils. The observed reconnection rates are found to be quantitatively consistent with a generalized Sweet-Parker model which incorporates compressibility, unbalanced upstream-downstream pressure, and the effective resistivity. The latter is significantly enhanced over its classical values in the low collisionality regime. Strong local ion heating is measured by an optical probe during the reconnection process, and at least half of the increased ion energy must be due to nonclassical processes, consistent with the resistivity enhancement. Characteristics of high-frequency electrostatic and electromagnetic fluctuations detected in the current sheet suggest presence of the lower-hybrid-drift-like waves with significant magnetic components. The detailed structures of the current sheet are measured and compared with Harris theory and two-fluid theory.
New electric field in asymmetric magnetic reconnection.
Malakit, K; Shay, M A; Cassak, P A; Ruffolo, D
2013-09-27
We present a theory and numerical evidence for the existence of a previously unexplored in-plane electric field in collisionless asymmetric magnetic reconnection. This electric field, dubbed the "Larmor electric field," is associated with finite Larmor radius effects and is distinct from the known Hall electric field. Potentially, it could be an important indicator for the upcoming Magnetospheric Multiscale mission to locate reconnection sites as we expect it to appear on the magnetospheric side, pointing earthward, at the dayside magnetopause reconnection site.
Identification of Colour Reconnection using Factorial Correlator
Institute of Scientific and Technical Information of China (English)
FU Jing-Hua; LIU Lian-Shou
2000-01-01
A new signal is proposed for the colour reconnection in the hadronic decay of W+ W- in e+e- collisions. Using Pythia Monte Carlo it is shown that factorial correlators for W+ and W- without colour reconnection are almost identical to unity, while those for the cases with colour reconnection fall down approximately linearly in the log log plot. This signal, being based on the factorial correlator, is more sensitive than the ones using only averaged quantities.
Numerical simulation of internal reconnection event in spherical tokamak
Energy Technology Data Exchange (ETDEWEB)
Hayashi, Takaya; Mizuguchi, Naoki; Sato, Tetsuya [National Inst. for Fusion Science, Toki, Gifu (Japan)
1999-07-01
Three-dimensional magnetohydrodynamic simulations are executed in a full toroidal geometry to clarify the physical mechanisms of the Internal Reconnection Event (IRE), which is observed in the spherical tokamak experiments. The simulation results reproduce several main properties of IRE. Comparison between the numerical results and experimental observation indicates fairly good agreements regarding nonlinear behavior, such as appearance of localized helical distortion, appearance of characteristic conical shape in the pressure profile during thermal quench, and subsequent appearance of the m=2/n=1 type helical distortion of the torus. (author)
Mendonca, Goncalo V; Heffernan, Kevin S; Rossow, Lindy; Guerra, Myriam; Pereira, Fernando D; Fernhall, Bo
2010-08-01
Women demonstrate greater RR interval variability than men of similar age. Enhanced parasympathetic input into cardiac regulation appears to be not only greater in women, but also protective during periods of cardiac stress. Even though women may have a more favorable autonomic profile after exercise, little research has been conducted on this issue. This study was designed to examine the cardiac autonomic response, in both male and female participants, during the early recovery from supramaximal exercise. Twenty-five individuals, aged 20 to 33 years (13 males and 12 females), performed a 30-s Wingate test. Beat-to-beat RR series were recorded before and 5 min after exercise, with the participants in the supine position and under paced breathing. Linear (spectral analysis) and nonlinear analyses (detrended fluctuation analysis (DFA)) were performed on the same RR series. At rest, women presented lower raw low frequency (LF) power and higher normalized high frequency (HF) power. Under these conditions, the LF/HF ratio of women was also lower than that of men (pheart rate variability (HRV) (pchange in LF/HF ratio and α1 than men from rest to recovery. This study demonstrates that the cardiac autonomic function of women is more affected by supramaximal exercise than that of men. Additionally, DFA did not provide additional information about sexual dimorphisms, compared with conventional spectral HRV techniques.
A high repetition rate experimental setup for quantum non-linear optics with cold Rydberg atoms
Busche, Hannes; Ball, Simon W.; Huillery, Paul
2016-12-01
Using electromagnetically induced transparency and photon storage, the strong dipolar interactions between Rydberg atoms and the resulting dipole blockade can be mapped onto light fields to realise optical non-linearities and interactions at the single photon level. We report on the realisation of an experimental apparatus designed to study interactions between single photons stored as Rydberg excitations in optically trapped microscopic ensembles of ultracold 87Rb atoms. A pair of in-vacuum high numerical aperture lenses focus excitation and trapping beams down to 1 μm, well below the Rydberg blockade. Thanks to efficient magneto-optical trap (MOT) loading from an atomic beam generated by a 2D MOT and the ability to recycle the microscopic ensembles more than 20000 times without significant atom loss, we achieve effective repetition rates exceeding 110 kHz to obtain good photon counting statistics on reasonable time scales. To demonstrate the functionality of the setup, we present evidence of strong photon interactions including saturation of photon storage and the retrieval of non-classical light. Using in-vacuum antennae operating at up to 40 GHz, we perform microwave spectroscopy on photons stored as Rydberg excitations and observe an interaction induced change in lineshape depending on the number of stored photons.
Study of Heart Rate Variability in bipolar disorder: linear and nonlinear parameters during sleep
Directory of Open Access Journals (Sweden)
Matteo eMigliorini
2012-01-01
Full Text Available In the present paper we propose a methodology for the assessment of the autonomic nervous system (ANS in patients affected by bipolar disorder. ANS was explored by means heart rate variability (HRV analysis carried out during night recordings through the evaluation of many different parameters in the time and in the frequency domain, linear and non-linear. The recording of the signals was performed by a wearable sensorized T-shirt. HRV with movement analysis allowed also sleep staging and the estimation of REM sleep percentage over the total sleep time. A group of 8 normal female constituted the control group, on which normality ranges were estimated. One pathologic subject was recorded during four different nights, at time intervals of at least one week, and during different phases of the disturbance. Some of the calculated parameters (MEANNN, SDNN, RMSSD confirmed reduced HRV in depression and bipolar disorder. REM sleep percentage was found to be increased. LZC (Lempel Ziv complexity and SampEn (Sample Entropy, on the other hand, seem to correlate with the depression level. Even if the number of examined subjects is small, and the results need further validation, the proposed methodology and the calculated parameters seem promising tools for the monitoring of mood changes in psychiatric disorders.
Slipping magnetic reconnection in coronal loops.
Aulanier, Guillaume; Golub, Leon; Deluca, Edward E; Cirtain, Jonathan W; Kano, Ryouhei; Lundquist, Loraine L; Narukage, Noriyuki; Sakao, Taro; Weber, Mark A
2007-12-07
Magnetic reconnection of solar coronal loops is the main process that causes solar flares and possibly coronal heating. In the standard model, magnetic field lines break and reconnect instantaneously at places where the field mapping is discontinuous. However, another mode may operate where the magnetic field mapping is continuous but shows steep gradients: The field lines may slip across each other. Soft x-ray observations of fast bidirectional motions of coronal loops, observed by the Hinode spacecraft, support the existence of this slipping magnetic reconnection regime in the Sun's corona. This basic process should be considered when interpreting reconnection, both on the Sun and in laboratory-based plasma experiments.
A laboratory study of asymmetric magnetic reconnection in strongly driven plasmas.
Rosenberg, M J; Li, C K; Fox, W; Igumenshchev, I; Séguin, F H; Town, R P J; Frenje, J A; Stoeckl, C; Glebov, V; Petrasso, R D
2015-02-04
Magnetic reconnection, the annihilation and rearrangement of magnetic fields in a plasma, is a universal phenomenon that frequently occurs when plasmas carrying oppositely directed field lines collide. In most natural circumstances, the collision is asymmetric (the two plasmas having different properties), but laboratory research to date has been limited to symmetric configurations. In addition, the regime of strongly driven magnetic reconnection, where the ram pressure of the plasma dominates the magnetic pressure, as in several astrophysical environments, has also received little experimental attention. Thus, we have designed the experiments to probe reconnection in asymmetric, strongly driven, laser-generated plasmas. Here we show that, in this strongly driven system, the rate of magnetic flux annihilation is dictated by the relative flow velocities of the opposing plasmas and is insensitive to initial asymmetries. In addition, out-of-plane magnetic fields that arise from asymmetries in the three-dimensional plasma geometry have minimal impact on the reconnection rate, due to the strong flows.
Mujica-Parodi, L R; Yeragani, Vikram; Malaspina, Dolores
2005-01-01
Heart rate variability (HRV) reflects functioning of the autonomic nervous system and possibly also regulation by the neural limbic system, abnormalities of which have both figured prominently in various etiological models of schizophrenia, particularly those that address patients' vulnerability to stress in connection to psychosis onset and exacerbation. This study provides data on cardiac functioning in a sample of schizophrenia patients that were either medication free or on atypical antipsychotics, as well as cardiac data on matched healthy controls. We included a medication-free group to investigate whether abnormalities in HRV previously reported in the literature and associated with atypical antipsychotics were solely the effect of medications or whether they might be a feature of the illness (or psychosis) itself. We collected 24-hour ECGs on 19 patients and 24 controls. Of the patients, 9 were medication free and 10 were on atypical antipsychotics. All subject groups were matched for age and gender. Patient groups showed equivalent symptom severity and type, as well as duration of illness. We analyzed the data using nonlinear complexity (symbolic dynamic) HRV analyses as well as standard and relative spectral analyses. For the medication-free patients as compared to the healthy controls, our data show decreased R-R intervals during sleep, and abnormal suppression of all frequency ranges, but particularly the low frequency range, which persisted even after adjusting the spectral data for the mean R-R interval. This effect was exacerbated for patients on atypical antipsychotics. Likewise, nonlinear complexity analysis showed significantly impaired HRV for medication-free patients that was exacerbated in the patients on atypical antipsychotics. Altogether, the data suggest a pattern of significantly decreased cardiac vagal function of patients with schizophrenia as compared to healthy controls, apart from and beyond any differences due to medication side
Nonlinear decline-rate dependence and intrinsic variation of typeIa supernova luminosities
Energy Technology Data Exchange (ETDEWEB)
Wang, Lifan; Strovink, Mark; Conley, Alexander; Goldhaber,Gerson; Kowalski, Marek; Perlmutter, Saul; Siegrist, James
2005-12-14
Published B and V fluxes from nearby Type Ia supernova are fitted to light-curve templates with 4-6 adjustable parameters. Separately, B magnitudes from the same sample are fitted to a linear dependence on B-V color within a post-maximum time window prescribed by the CMAGIC method. These fits yield two independent SN magnitude estimates B{sub max} and B{sub BV}. Their difference varies systematically with decline rate {Delta}m{sub 15} in a form that is compatible with a bilinear but not a linear dependence; a nonlinear form likely describes the decline-rate dependence of B{sub max} itself. A Hubble fit to the average of B{sub max} and B{sub BV} requires a systematic correction for observed B-V color that can be described by a linear coefficient R = 2.59 {+-} 0.24, well below the coefficient R{sub B} {approx} 4.1 commonly used to characterize the effects of Milky Way dust. At 99.9% confidence the data reject a simple model in which no color correction is required for SNe that are clustered at the blue end of their observed color distribution. After systematic corrections are performed, B{sub max} and B{sub BV} exhibit mutual rms intrinsic variation equal to 0.074 {+-} 0.019 mag, of which at least an equal share likely belongs to B{sub BV}. SN magnitudes measured using maximum-luminosity or cmagic methods show comparable rms deviations of order {approx}0.14 mag from the Hubble line. The same fit also establishes a 95% confidence upper limit of 486 km s{sup -1} on the rms peculiar velocity of nearby SNe relative to the Hubble flow.
The role of guide field in magnetic reconnection driven by island coalescence
Stanier, A; Simakov, Andrei N; Chacon, L; Le, A; Karimabadi, H; Ng, Jonathan; Bhattacharjee, A
2016-01-01
A number of studies have considered how the rate of magnetic reconnection scales in large and weakly collisional systems by the modelling of long reconnecting current sheets. However, this set-up neglects both the formation of the current sheet and the coupling between the diffusion region and a larger system that supplies the magnetic flux. Recent studies of magnetic island merging, which naturally include these features, have found that ion kinetic physics is crucial to describe the reconnection rate and global evolution of such systems. In this paper, the effect of a guide field on reconnection during island merging is considered. In contrast to the earlier current sheet studies, we identify a limited range of guide fields for which the reconnection rate, outflow velocity, and pile-up magnetic field increase in magnitude as the guide field increases. The Hall-MHD fluid model is found to reproduce kinetic reconnection rates only for a sufficiently strong guide field, for which ion inertia breaks the frozen-...
Electron cyclotron maser instability (ECMI in strong magnetic guide field reconnection
Directory of Open Access Journals (Sweden)
R. A. Treumann
2017-08-01
Full Text Available The ECMI model of electromagnetic radiation from electron holes is shown to be applicable to spontaneous magnetic reconnection. We apply it to reconnection in strong current-aligned magnetic guide fields. Such guide fields participate only passively in reconnection, which occurs in the antiparallel components to both sides of the guide-field-aligned current sheets with current carried by kinetic Alfvén waves. Reconnection generates long (the order of hundreds of electron inertial scales electron exhaust regions at the reconnection site X point, which are extended perpendicular to the current and the guide fields. Exhausts contain a strongly density-depleted hot electron component and have properties similar to electron holes. Exhaust electron momentum space distributions are highly deformed, exhibiting steep gradients transverse to both the reconnecting and guide fields. Such properties suggest application of the ECMI mechanism with the fundamental ECMI X-mode emission beneath the nonrelativistic guide field cyclotron frequency in localized source regions. An outline of the mechanism and its prospects is given. Potential applications are the kilometric radiation (AKR in auroral physics, solar radio emissions during flares, planetary emissions and astrophysical scenarios (radiation from stars and compact objects involving the presence of strong magnetic fields and field-aligned currents. Drift of the exhausts along the guide field maps the local field and plasma properties. Escape of radiation from the exhaust and radiation source region still poses a problem. The mechanism can be studied in 2-D particle simulations of strong guide field reconnection which favours 2-D, mapping the deformation of the electron distribution perpendicular to the guide field, and using it in the numerical calculation of the ECMI growth rate. The mechanism suggests also that reconnection in general may become a source of the ECMI with or without guide fields. This is
Shi, Ping; Yu, Hongliu
2014-04-01
Calculation of linear parameters, such as time-domain and frequency-domain analysis of heart rate variability (HRV), is a conventional method for assessment of autonomic nervous system activity. Nonlinear phenomena are certainly involved in the genesis of HRV. In a seemingly random signal the Poincaré plot can easily demonstrate whether there is an underlying determinism in the signal. Linear and nonlinear analysis methods were applied in the computer words inputting experiments in this study for physiological measurement. This study therefore demonstrated that Poincaré plot was a simple but powerful graphical tool to describe the dynamics of a system.
Walker, Christoph
2010-01-01
A parameter-dependent model involving nonlinear diffusion for an age-structured population is studied. The parameter measures the intensity of the mortality. A bifurcation approach is used to establish existence of positive equilibrium solutions.
FUZZY IDENTIFIER WITH EXPONENTIAL RATE OF CONVERGENCE FOR NONLINEAR DYNAMIC SYSTEMS
Institute of Scientific and Technical Information of China (English)
2000-01-01
In this paper,fuzzy systems are used as identifiers for unknown nonlinear dynamic systems.The fuzzy identifier can incorporate linguistic knowledge of nonlinear dynamic systems with input-output pairs directly into the design.In the case where there is the modelling error,a new identification algorithm is proposed.It is proved that the fuzzy identifier is globally stable and the identification error converges to zero exponentially fast.
Heart rate and blood pressure response to short-term head-down bed rest: a nonlinear approach.
Balocchi, R; Di Garbo, A; Michelassi, C; Chillemi, S; Varanini, M; Barbi, M; Legramante, J M; Raimondi, G; Zbilut, J P
2000-06-01
Although it is well-known that prolonged exposure to microgravity environment such as in space travel results in derangements of orthostasis, recent evidence suggests that even short-term exposure may have similar effects and parallels such common examples as prolonged bed rest. Whereas spectral analysis of heart rate and systolic blood pressure have been unable to detect changes, we hypothesized that nonlinear indexes may be better able to uncover such perturbations. Eighteen healthy subjects were exposed to 4-hour head-down tilt, and of these, 4 exhibited fainting. Two nonlinear indexes, mutual information and recurrence quantification were used to analyze the data. Only recurrence quantification was able to detect a "decoupling" of heart rate and systolic blood pressure at rest using discriminant analysis (p < 0.05). These results suggest that orthostatic intolerance may be due to a decoupling of heart rate from systolic blood pressure reflexive activity occurring at rest.
Non-linear properties of R-R distributions as a measure of heart rate variability
Energy Technology Data Exchange (ETDEWEB)
Irurzun, I.M.; Bergero, P.; Cordero, M.C.; Defeo, M.M.; Vicente, J.L.; Mola, E.E
2003-06-01
We analyze the dynamic quality of the R-R interbeat intervals of electrocardiographic signals from healthy people and from patients with premature ventricular contractions (PVCs) by applying different measure algorithms to standardised public domain data sets of heart rate variability. Our aim is to assess the utility of these algorithms for the above mentioned purposes. Long and short time series, 24 and 0.50 h respectively, of interbeat intervals of healthy and PVC subjects were compared with the aim of developing a fast method to investigate their temporal organization. Two different methods were used: power spectral analysis and the integral correlation method. Power spectral analysis has proven to be a powerful tool for detecting long-range correlations. If it is applied in a short time series, power spectra of healthy and PVC subjects show a similar behavior, which disqualifies power spectral analysis as a fast method to distinguish healthy from PVC subjects. The integral correlation method allows us to study the fractal properties of interbeat intervals of electrocardiographic signals. The cardiac activity of healthy and PVC people stems from dynamics of chaotic nature characterized by correlation dimensions d{sub f} equal to 3.40{+-}0.50 and 5.00{+-}0.80 for healthy and PVC subjects respectively. The methodology presented in this article bridges the gap between theoretical and experimental studies of non-linear phenomena. From our results we conclude that the minimum number of coupled differential equations to describe cardiac activity must be six and seven for healthy and PVC individuals respectively. From the present analysis we conclude that the correlation integral method is particularly suitable, in comparison with the power spectral analysis, for the early detection of arrhythmias on short time (0.5 h) series.
Kuznetsova, M. M.; Hesse, M.; Rastaetter, L.; Toth, G.; DeZeeuw, D. L.; Gombosi, T. I.
2008-01-01
Magnetotail current sheet thinning and magnetic reconnection are key elements of magnetospheric substorms. We utilized the global MHD model BATS-R-US with Adaptive Mesh Refinement developed at the University of Michigan to investigate the formation and dynamic evolution of the magnetotail thin current sheet. The BATSRUS adaptive grid structure allows resolving magnetotail regions with increased current density up to ion kinetic scales. We investigated dynamics of magnetotail current sheet thinning in response to southwards IMF turning. Gradual slow current sheet thinning during the early growth phase become exponentially fast during the last few minutes prior to nightside reconnection onset. The later stage of current sheet thinning is accompanied by earthward flows and rapid suppression of normal magnetic field component $B-z$. Current sheet thinning set the stage for near-earth magnetic reconnection. In collisionless magnetospheric plasma, the primary mechanism controlling the dissipation in the vicinity of the reconnection site is non-gyrotropic effects with spatial scales comparable with the particle Larmor radius. One of the major challenges in global MHD modeling of the magnetotail magnetic reconnection is to reproduce fast reconnection rates typically observed in smallscale kinetic simulations. Bursts of fast reconnection cause fast magnetic field reconfiguration typical for magnetospheric substorms. To incorporate nongyritropic effects in diffusion regions we developed an algorithm to search for magnetotail reconnection sites, specifically where the magnetic field components perpendicular to the local current direction approaches zero and form an X-type configuration. Spatial scales of the diffusion region and magnitude of the reconnection electric field are calculated self-consistently using MHD plasma and field parameters in the vicinity of the reconnection site. The location of the reconnection sites and spatial scales of the diffusion region are updated
Frontiers for Laboratory Research of Magnetic Reconnection
Energy Technology Data Exchange (ETDEWEB)
Ji, Hantao [Princeton University; Guo, Fan [Los Alamos National Laboratory
2015-07-16
Magnetic reconnection occcurs throughout heliophysical and astrophysical plasmas as well as in laboratory fusion plasmas. Two broad categories of reconnection models exist: collisional MHD and collisionless kinetic. Eight major questions with respect to magnetic connection are set down, and past and future devices for studying them in the laboratory are described. Results of some computerized simulations are compared with experiments.
Pseudo-reconnection in MHD numerical simulation
Institute of Scientific and Technical Information of China (English)
无
2000-01-01
A class of pseudo-reconnections caused by a shifted mesh in magnetohydrodynamics (MHD) simulations is reported. In terms of this mesh system, some non-physical results may be obtained in certain circumstances, e.g. magnetic reconnection occurs without resistivity. After comparison, another kind of mesh is strongly recommended.
The Pressure Limitations on Flux Pile-up Reconnection
Litvinenko, Yuri E.
1999-05-01
The problem of the plasma pressure limitations on the rapidity of flux pile-up magnetic reconnection is re-examined, following the claim made by Jardine and Allen (1998) that the limitations can be removed by relaxing the assumption of zero-vorticity two-dimensional plasma flows. It is shown that for a two-dimensional stagnation point flow with nonzero vorticity the magnetic merging rate cannot exceed the Sweet-Parker scaling in a low-beta plasma. The pressure limitation appears to be much less restrictive for weak three-dimensional flux pile-up, provided the perturbation length scale in the third dimension is much less than the global length scale. The actual reconnection rate in the latter case, however, is much lower than this upper estimate unless the current sheet width is also much less than the global scale.
Three-dimensional dynamics of collisionless magnetic reconnection in large-scale pair plasmas.
Yin, L; Daughton, W; Karimabadi, H; Albright, B J; Bowers, Kevin J; Margulies, J
2008-09-19
Using the largest three-dimensional particle-in-cell simulations to date, collisionless magnetic reconnection in large-scale electron-positron plasmas without a guide field is shown to involve complex interaction of tearing and kink modes. The reconnection onset is patchy and occurs at multiple sites which self-organize to form a single, large diffusion region. The diffusion region tends to elongate in the outflow direction and become unstable to secondary kinking and formation of "plasmoid-rope" structures with finite extent in the current direction. The secondary kink folds the reconnection current layer, while plasmoid ropes at times follow the folding of the current layer. The interplay between these secondary instabilities plays a key role in controlling the time-dependent reconnection rate in large-scale systems.
Dynamic non-null magnetic reconnection in three dimensions. I. Particular solutions
Wilmot-Smith, A., Hornig, G., Priest, E. R.
2006-10-01
A stationary model of three-dimensional magnetic reconnection in the absence of a null point is presented, with a non-ideal region that is localized in space. Analytical solutions to the resistive magnetohydrodynamic equations are obtained, with the momentum equation included so that the model is fully dynamic, and thus extends the previous kinematic solutions. A splitting of variables allows solutions to be written in terms of a particular non-ideal solution, on which ideal solutions may be superposed. For the non-ideal solution alone, it is shown that only the field lines linking the diffusion region are affected by the reconnection process, and counter-rotating flows above and below the diffusion region are present. It is only the dimensions of the diffusion region along the reconnection line that are important for the reconnection rate. Many features of the previous stationary kinematic model are also observed here.
Riverman, K. L.; Anandakrishnan, S.; Alley, R. B.; Peters, L. E.; Christianson, K. A.; Muto, A.
2013-12-01
Northeast Greenland Ice Stream (NEGIS) is the largest ice stream in Greenland, draining approximately 8.4% of the ice sheet's area. The flow pattern and stability mechanism of this ice stream are unique to others in Greenland and Antarctica, and merit further study to ascertain the sensitivity of this ice stream to future climate change. Geophysical methods are valuable tools for this application, but their results are sensitive to the structure of the firn and any spatial variations in firn properties across a given study region. Here we present firn data from a 40-km-long seismic profile across the upper reaches of NEGIS, collected in the summer of 2012 as part of an integrated ground-based geophysical survey. We find considerable variations in firn thickness that are coincident with the ice stream shear margins, where a thinner firn layer is present within the margins, and a thicker, more uniform firn layer is present elsewhere in our study region. Higher accumulation rates in the marginal surface troughs due to drift-snow trapping can account for some of this increased densification; however, our seismic results also highlight enhanced anisotropy within the firn and upper ice column that is confined to narrow bands within the shear margins. We thus interpret these large firn thickness variations and abrupt changes in anisotropy as indicators of firn densification dependent on the effective stress state as well as the overburden pressure, suggesting that the strain rate increases nonlinearly with stress across the shear margins. A GPS strain grid maintained for three weeks across both margins observed strong side shearing, with rapid stretching and then compression along particle paths, indicating large deviatoric stresses in the margins. This work demonstrates the importance of developing a high-resolution firn densification model when conducting geophysical field work in regions possessing a complex ice flow history; it also motivates the need for a more
Hadronisation Models and Colour Reconnection
Bierlich, Christian
2016-01-01
Enhanced production of hadrons with $s$-quark content has been observed in $pp$ collisions at LHC, and earlier in collisions of heavy nuclei. We review the string hadronisation formalism and correc- tions from rope hadronisation and colour reconnection, corrections that takes place in such dense environments, and are able to correctly describe data. Since such corrections are very sensitive to the modelling of transverse proton structure, we investigate two such models, and compare to final states. Finally we describe how such corrections can also give a possible explanation to collective phenomena observed in small systems.
A Reconnecting Flux Rope Dynamo
Baggaley, Andrew W.; Barenghi, Carlo F.; Shukurov, Anvar; Subramanian, Kandaswamy
2009-01-01
We develop a new model of the fluctuation dynamo in which the magnetic field is confined in thin flux ropes advected by a multi-scale flow modeling turbulence. Magnetic dissipation occurs only via reconnection of the flux ropes. We investigate the kinetic energy release into heat, mediated by the dynamo action, both in our model and by solving the induction equation with the same flow. We find that a flux rope dynamo is an order of magnitude more efficient at converting mechanical energy into...
Relativistic Magnetic Reconnection in the Laboratory
Raymond, A; McKelvey, A; Zulick, C; Alexander, N; Batson, T; Bhattacharjee, A; Campbell, P; Chen, H; Chvykov, V; Del Rio, E; Fitzsimmons, P; Fox, W; Hou, B; Maksimchuk, A; Mileham, C; Nees, J; Nilson, P M; Stoeckl, C; Thomas, A G R; Wei, M S; Yanovsky, V; Willingale, L; Krushelnick, K
2016-01-01
Magnetic reconnection is a fundamental plasma process involving an exchange of magnetic energy to plasma kinetic energy through changes in the magnetic field topology. In many astrophysical plasmas magnetic reconnection plays a key role in the release of large amounts of energy \\cite{hoshino1}, although making direct measurements is challenging in the case of high-energy astrophysical systems such as pulsar wind emissions \\cite{lyubarsky1}, gamma-ray bursts \\cite{thompson1}, and jets from active galactic nuclei \\cite{liu1}. Therefore, laboratory studies of magnetic reconnection provide an important platform for testing theories and characterising different regimes. Here we present experimental measurements as well as numerical modeling of relativistic magnetic reconnection driven by short-pulse, high-intensity lasers that produce relativistic plasma along with extremely strong magnetic fields. Evidence of magnetic reconnection was identified by the plasma's X-ray emission patterns, changes to the electron ene...
Simulated Navier-Stokes trefoil reconnection
Kerr, Robert M
2015-01-01
The evolution and self-reconnection of a perturbed trefoil vortex knot is simulated, then compared to recent experimental measurements (Scheeler et al. 2014a). Qualitative comparisons using three-dimensional vorticity isosurfaces and lines, then quantitative comparisons using the helicity. To have a single initial reconnection, as in the experiments, the trefoil is perturbed by 4 weak vortex rings. Initially there is a long period with deformations similar to the experiment during which the energy, continuum helicity and topological self-linking number are all preserved. In the next period, once reconnection has clearly begun, a Reynolds number independent fraction of the initial helicity is dissipated in a finite time. In contrast, the experimental analysis finds that the helicity inferred from the trajectories of hydrogen bubbles is preserved during reconnection. Since vortices reconnect gradually in a classical fluid, it is suggested that the essential difference is in the interpretation of the reconnectio...
Statistics of Reconnection-Driven Turbulence
Kowal, Grzegorz; Lazarian, Alex; Vishniac, Ethan T
2016-01-01
Magnetic reconnection is a process that changes magnetic field topology in highly conducting fluids. Within the standard Sweet-Parker model, this process would be too slow to explain observations (e.g. solar flares). In reality, the process must be ubiquitous as astrophysical fluids are magnetized and motions of fluid elements necessarily entail crossing of magnetic frozen-in field lines and magnetic reconnection. In the presence of turbulence, the reconnection is independent of microscopic plasma properties, and may be much faster than previously thought, as proposed in Lazarian & Vishniac (1999) and tested in Kowal et al. (2009, 2012). However, the considered turbulence in the Lazarian-Vishniac model was imposed externally. In this work we consider reconnection-driven magnetized turbulence in realistic three-dimensional geometry initiated by stochastic noise. We demonstrate through numerical simulations that the stochastic reconnection is able to self-generate turbulence through interactions between the...
Lessons on collisionless reconnection from quantum fluids
Directory of Open Access Journals (Sweden)
Yasuhito eNarita
2014-12-01
Full Text Available Magnetic reconnection in space plasmas remains a challenge in physics in that the phenomenon is associated with the breakdown of frozen-in magnetic field in a collisionless medium. Such a topology change can also be found in superfluidity, known as the quantum vortex reconnection. We give a plasma physicists' view of superfluidity to obtain insights on essential processes in collisionless reconnection, including discussion of the kinetic and fluid pictures, wave dynamics, and time reversal asymmetry. The most important lesson from the quantum fluid is the scenario that reconnection is controlled by the physics of topological defects on the microscopic scale, and by the physics of turbulence on the macroscopic scale. Quantum vortex reconnection is accompanied by wave emission in the form of Kelvin waves and sound waves, which imprints the time reversal asymmetry.
Bidirectional outflows as evidence of magnetic reconnection leading to a solar microflare
Hong, Jie; Li, Ying; Yang, Kai; Cheng, Xin; Chen, Feng; Fang, Cheng; Cao, Wenda
2016-01-01
Magnetic reconnection is a rapid energy release process that is believed to be responsible for flares on the Sun and stars. Nevertheless, such flare-related reconnection is mostly detected to occur in the corona, while there have been few studies concerning the reconnection in the chromosphere or photosphere. Here we present both spectroscopic and imaging observations of magnetic reconnection in the chromosphere leading to a microflare. During the flare peak time, chromospheric line profiles show significant blueshifted/redshifted components on the two sides of the flaring site, corresponding to upflows and downflows with velocities of $\\pm$(70--80) km s$^{-1}$, comparable with the local Alfv\\'{e}n speed as expected by the reconnection in the chromosphere. The three-dimensional nonlinear force-free field configuration further discloses twisted field lines (a flux rope) at a low altitude, cospatial with the dark threads in He I 10830 \\r{A} images. The instability of the flux rope may initiate the flare-related...
Kim, Daewook; Kim, Dojin; Hong, Keum-Shik; Jung, Il Hyo
2014-01-01
The first objective of this paper is to prove the existence and uniqueness of global solutions for a Kirchhoff-type wave equation with nonlinear dissipation of the form Ku'' + M(|A (1/2) u|(2))Au + g(u') = 0 under suitable assumptions on K, A, M(·), and g(·). Next, we derive decay estimates of the energy under some growth conditions on the nonlinear dissipation g. Lastly, numerical simulations in order to verify the analytical results are given.
MESSENGER Observations of Magnetic Reconnection in Mercury's Magnetosphere
Slavin. James A.
2009-01-01
During MESSENGER'S second flyby of Mercury on October 6,2008, very intense reconnection was observed between the planet's magnetic field and a steady southward interplanetary magnetic field (IMF). The dawn magnetopause was threaded by a strong magnetic field normal to its surface, approx.14 nT, that implies a rate of reconnection approx.10 times the typical rate at Earth and a cross-magnetospheric electric potential drop of approx.30 kV. The highest magnetic field observed during this second flyby, approx.160 nT, was found at the core of a large dayside flux transfer event (FTE). This FTE is estimated to contain magnetic flux equal to approx.5% that of Mercury's magnetic tail or approximately one order of magnitude higher fraction of the tail flux than is typically found for FTEs at Earth. Plasmoid and traveling compression region (TCR) signatures were observed throughout MESSENGER'S traversal of Mercury's magnetotail with a repetition rate comparable to the Dungey cycle time of approx.2 min. The TCR signatures changed from south-north, indicating tailward motion, to north-south, indicating sunward motion, at a distance approx.2.6 RM (where RM is Mercury's radius) behind the terminator indicating that the near-Mercury magnetotail neutral line was crossed at that point. Overall, these new MESSENGER observations suggest that magnetic reconnection at the dayside magnetopause is very intense relative to what is found at Earth and other planets, while reconnection in Mercury's tail is similar to that in other planetary magnetospheres, but with a very short Dungey cycle time.
Melillo, Paolo; Bracale, Marcello; Pecchia, Leandro
2011-11-07
This study investigates the variations of Heart Rate Variability (HRV) due to a real-life stressor and proposes a classifier based on nonlinear features of HRV for automatic stress detection. 42 students volunteered to participate to the study about HRV and stress. For each student, two recordings were performed: one during an on-going university examination, assumed as a real-life stressor, and one after holidays. Nonlinear analysis of HRV was performed by using Poincaré Plot, Approximate Entropy, Correlation dimension, Detrended Fluctuation Analysis, Recurrence Plot. For statistical comparison, we adopted the Wilcoxon Signed Rank test and for development of a classifier we adopted the Linear Discriminant Analysis (LDA). Almost all HRV features measuring heart rate complexity were significantly decreased in the stress session. LDA generated a simple classifier based on the two Poincaré Plot parameters and Approximate Entropy, which enables stress detection with a total classification accuracy, a sensitivity and a specificity rate of 90%, 86%, and 95% respectively. The results of the current study suggest that nonlinear HRV analysis using short term ECG recording could be effective in automatically detecting real-life stress condition, such as a university examination.
Directory of Open Access Journals (Sweden)
Melillo Paolo
2011-11-01
Full Text Available Abstract Background This study investigates the variations of Heart Rate Variability (HRV due to a real-life stressor and proposes a classifier based on nonlinear features of HRV for automatic stress detection. Methods 42 students volunteered to participate to the study about HRV and stress. For each student, two recordings were performed: one during an on-going university examination, assumed as a real-life stressor, and one after holidays. Nonlinear analysis of HRV was performed by using Poincaré Plot, Approximate Entropy, Correlation dimension, Detrended Fluctuation Analysis, Recurrence Plot. For statistical comparison, we adopted the Wilcoxon Signed Rank test and for development of a classifier we adopted the Linear Discriminant Analysis (LDA. Results Almost all HRV features measuring heart rate complexity were significantly decreased in the stress session. LDA generated a simple classifier based on the two Poincaré Plot parameters and Approximate Entropy, which enables stress detection with a total classification accuracy, a sensitivity and a specificity rate of 90%, 86%, and 95% respectively. Conclusions The results of the current study suggest that nonlinear HRV analysis using short term ECG recording could be effective in automatically detecting real-life stress condition, such as a university examination.
Magnetic Reconnection at a Three-dimensional Solar Null Point
Frederiksen, J. T.; Baumann, G.; Galsgaard, K.; Haugbølle, T.; Nordlund, Å.
2012-04-01
Using a specific solar null point reconnection case studied by Masson et al (2009; ApJ 700, 559) we investigate the dependence of the reconnection rate on boundary driving speed, numerical resolution, type of resistivity (constant or numerical), and assumed stratification (constant density or solar-like). The MHD simulations start out from a potential magnetic field containing a null-point, obtained from a SOHO magnetogram extrapolation approximately 8 hours before a C-class flare was observed. The magnetic field is stressed with a boundary motion pattern similar to the horizontal motions observed by SOHO during the period preceding the flare. The general behavior is nearly independent of driving speed and numerical resolution, and is also very similar in stratified and unstratified models, provided only that the boundary motions are slow enough.
The Pressure Limitations on Flux Pile-Up Magnetic Reconnection
Litvinenko, Y. E.
1999-05-01
Flux pile-up magnetic reconnection was thought to be able to provide fast energy dissipation a strongly magnetized plasma, for example, in solar flares. We examine the problem of the plasma pressure limitations on the rapidity of flux pile-up reconnection. It is shown that for a two-dimensional stagnation point flow with nonzero vorticity the magnetic merging rate cannot exceed the Sweet-Parker scaling in a low-beta plasma, which is too slow to explain flares. Moreover, the solution has some undesireable properties such as a diffusion layer at the external boundary and the massively increasing inflow speed. The pressure limitation appears to be somewhat less restrictive for three-dimensional flux pile-up. This work was supported by NSF grant ATM-9813933.
Secondary fast reconnecting instability in the sawtooth crash
Del Sarto, Daniele
2016-01-01
In this work we consider magnetic reconnection in thin current sheets with both resistive and electron inertia effects. When the current sheet is produced by a primary instability of the internal kink type, the analysis of secondary instabilities indicates that reconnection proceeds on a time scale much shorter than the primary instability characteristic time. In the case of a sawtooth crash, non-collisional physics becomes important above a value of the Lundquist number which scales like S ~ (R/d_e)^{12/5}, in terms of the tokamak major radius R and of the electron skin depth d_e. This value is commonly achieved in present day devices. As collisionality is further reduced, the characteristic rate increases, approaching Alfv\\'enic values when the primary instability approaches the collisionless regime.
Scaling of Magnetic Reconnection in Relativistic Collisionless Pair Plasmas
Liu, Yi-Hsin; Guo, Fan; Daughton, William; Li, Hui; Hesse, Michael
2015-01-01
Using fully kinetic simulations, we study the scaling of the inflow speed of collisionless magnetic reconnection in electron-positron plasmas from the non-relativistic to ultra-relativistic limit. In the anti-parallel configuration, the inflow speed increases with the upstream magnetization parameter sigma and approaches the speed of light when sigma is greater than O(100), leading to an enhanced reconnection rate. In all regimes, the divergence of the pressure tensor is the dominant term responsible for breaking the frozen-in condition at the x-line. The observed scaling agrees well with a simple model that accounts for the Lorentz contraction of the plasma passing through the diffusion region. The results demonstrate that the aspect ratio of the diffusion region, modified by the compression factor of proper density, remains approximately 0.1 in both the non-relativistic and relativistic limits.
Continuous magnetic reconnection at Earth's magnetopause.
Frey, H U; Phan, T D; Fuselier, S A; Mende, S B
2003-12-04
The most important process that allows solar-wind plasma to cross the magnetopause and enter Earth's magnetosphere is the merging between solar-wind and terrestrial magnetic fields of opposite sense-magnetic reconnection. It is at present not known whether reconnection can happen in a continuous fashion or whether it is always intermittent. Solar flares and magnetospheric substorms--two phenomena believed to be initiated by reconnection--are highly burst-like occurrences, raising the possibility that the reconnection process is intrinsically intermittent, storing and releasing magnetic energy in an explosive and uncontrolled manner. Here we show that reconnection at Earth's high-latitude magnetopause is driven directly by the solar wind, and can be continuous and even quasi-steady over an extended period of time. The dayside proton auroral spot in the ionosphere--the remote signature of high-latitude magnetopause reconnection--is present continuously for many hours. We infer that reconnection is not intrinsically intermittent; its steadiness depends on the way that the process is driven.
Magnetic reconnection as an element of turbulence
Directory of Open Access Journals (Sweden)
S. Servidio
2011-10-01
Full Text Available In this work, recent advances on the study of reconnection in turbulence are reviewed. Using direct numerical simulations of decaying incompressible two-dimensional magnetohydrodynamics (MHD, it was found that in fully developed turbulence complex processes of reconnection locally occur (Servidio et al., 2009, 2010a. In this complex scenario, reconnection is spontaneous but locally driven by the fields, with the boundary conditions provided by the turbulence. Matching classical turbulence analysis with a generalized Sweet-Parker theory, the statistical features of these multiple-reconnection events have been identified. A discussion on the accuracy of our algorithms is provided, highlighting the necessity of adequate spatial resolution. Applications to the study of solar wind discontinuities are reviewed, comparing simulations to spacecraft observations. New results are shown, studying the time evolution of these local reconnection events. A preliminary study on the comparison between MHD and Hall MHD is reported. Our new approach to the study of reconnection as an element of turbulence has broad applications to space plasmas, shedding a new light on the study of magnetic reconnection in nature.
A current filamentation mechanism for breaking magnetic field lines during reconnection.
Che, H; Drake, J F; Swisdak, M
2011-06-01
During magnetic reconnection, the field lines must break and reconnect to release the energy that drives solar and stellar flares and other explosive events in space and in the laboratory. Exactly how this happens has been unclear, because dissipation is needed to break magnetic field lines and classical collisions are typically weak. Ion-electron drag arising from turbulence, dubbed 'anomalous resistivity', and thermal momentum transport are two mechanisms that have been widely invoked. Measurements of enhanced turbulence near reconnection sites in space and in the laboratory support the anomalous resistivity idea but there has been no demonstration from measurements that this turbulence produces the necessary enhanced drag. Here we report computer simulations that show that neither of the two previously favoured mechanisms controls how magnetic field lines reconnect in the plasmas of greatest interest, those in which the magnetic field dominates the energy budget. Rather, we find that when the current layers that form during magnetic reconnection become too intense, they disintegrate and spread into a complex web of filaments that causes the rate of reconnection to increase abruptly. This filamentary web can be explored in the laboratory or in space with satellites that can measure the resulting electromagnetic turbulence.
MHD simulations of three-dimensional resistive reconnection in a cylindrical plasma column
Striani, E.; Mignone, A.; Vaidya, B.; Bodo, G.; Ferrari, A.
2016-11-01
Magnetic reconnection is a plasma phenomenon where a topological rearrangement of magnetic field lines with opposite polarity results in dissipation of magnetic energy into heat, kinetic energy and particle acceleration. Such a phenomenon is considered as an efficient mechanism for energy release in laboratory and astrophysical plasmas. An important question is how to make the process fast enough to account for observed explosive energy releases. The classical model for steady state magnetic reconnection predicts reconnection times scaling as S1/2 (where S is the Lundquist number) and yields time-scales several order of magnitude larger than the observed ones. Earlier two-dimensional MHD simulations showed that for large Lundquist number the reconnection time becomes independent of S (`fast reconnection' regime) due to the presence of the secondary tearing instability that takes place for S ≳ 1 × 104. We report on our 3D MHD simulations of magnetic reconnection in a magnetically confined cylindrical plasma column under either a pressure balanced or a force-free equilibrium and compare the results with 2D simulations of a circular current sheet. We find that the 3D instabilities acting on these configurations result in a fragmentation of the initial current sheet in small filaments, leading to enhanced dissipation rate that becomes independent of the Lundquist number already at S ≃ 1 × 103.
Generation of Alfvenic Waves and Turbulence in Magnetic Reconnection Jets
Hoshino, M.
2014-12-01
The magneto-hydro-dynamic (MHD) linear stability for the plasma sheet with a localized bulk plasma flow parallel to the neutral sheet is investigated. We find three different unstable modes propagating parallel to the anti-parallel magnetic field line, and we call them as "streaming tearing'', "streaming sausage'', and "streaming kink'' mode. The streaming tearing and sausage modes have the tearing mode-like structure with symmetric density fluctuation to the neutral sheet, and the streaming kink mode has the asymmetric fluctuation. The growth rate of the streaming tearing mode decreases with increasing the magnetic Reynolds number, while those of the streaming sausage and kink modes do not strongly depend on the Reynolds number. The wavelengths of these unstable modes are of the order of the thickness of plasma sheet, which behavior is almost same as the standard tearing mode with no bulk flow. Roughly speaking the growth rates of three modes become faster than the standard tearing mode. The situation of the plasma sheet with the bulk flow can be realized in the reconnection exhaust with the Alfvenic reconnection jet, and the unstable modes may be regarded as one of the generation processes of Alfvenic turbulence in the plasma sheet during magnetic reconnection.
Magnetic Reconnection in the Solar Chromosphere
Lukin, Vyacheslav S.; Ni, Lei; Murphy, Nicholas Arnold
2017-08-01
We report on the most recent efforts to accurately and self-consistently model magnetic reconnection processes in the context of the solar chromosphere. The solar chromosphere is a notoriously complex and highly dynamic boundary layer of the solar atmosphere where local variations in the plasma parameters can be of the order of the mean values. At the same time, the interdependence of the physical processes such as magnetic field evolution, local and global energy transfer between internal and electromagnetic plasma energy, radiation transport, plasma reactivity, and dissipation mechanisms make it a particularly difficult system to self-consistently model and understand. Several recent studies have focused on the micro-physics of multi-fluid magnetic reconnection at magnetic nulls in the weakly ionized plasma environment of the lower chromosphere[1-3]. Here, we extend the previous work by considering a range of spatial scales and magnetic field strengths in a configuration with component magnetic reconnection, i.e., for magnetic reconnection with a guide field. We show that in all cases the non-equilibrium reactivity of the plasma and the dynamic interaction among the plasma processes play important roles in determining the structure of the reconnection region. We also speculate as to the possible observables of chromospheric magnetic reconnection and the likely plasma conditions required for generation of Ellerman and IRIS bombs.[1] Leake, Lukin, Linton, and Meier, “Multi-fluid simulations of chromospheric magnetic reconnection in a weakly ionized reacting plasma,” ApJ 760 (2012).[2] Leake, Lukin, and Linton, “Magnetic reconnection in a weakly ionized plasma,” PoP 20 (2013).[3] Murphy and Lukin, “Asymmetric magnetic reconnection in weakly ionized chromospheric plasmas,” ApJ 805 (2015).[*Any opinion, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National
Directory of Open Access Journals (Sweden)
Ying-Ying Wang
2015-06-01
Full Text Available The identification difficulties for a dual-rate Hammerstein system lie in two aspects. First, the identification model of the system contains the products of the parameters of the nonlinear block and the linear block, and a standard least squares method cannot be directly applied to the model; second, the traditional single-rate discrete-time Hammerstein model cannot be used as the identification model for the dual-rate sampled system. In order to solve these problems, by combining the polynomial transformation technique with the key variable separation technique, this paper converts the Hammerstein system into a dual-rate linear regression model about all parameters (linear-in-parameter model and proposes a recursive least squares algorithm to estimate the parameters of the dual-rate system. The simulation results verify the effectiveness of the proposed algorithm.
Directory of Open Access Journals (Sweden)
Ying Wang
2014-01-01
Full Text Available We investigate the dynamical behaviors of a class of discrete SIRS epidemic models with nonlinear incidence rate and varying population sizes. The model is required to possess different death rates for the susceptible, infectious, recovered, and constant recruitment into the susceptible class, infectious class, and recovered class, respectively. By using the inductive method, the positivity and boundedness of all solutions are obtained. Furthermore, by constructing new discrete type Lyapunov functions, the sufficient and necessary conditions on the global asymptotic stability of the disease-free equilibrium and endemic equilibrium are established.
Magnetic reconnection in lower solar atmosphere
Institute of Scientific and Technical Information of China (English)
汪景琇
1995-01-01
Observations of vector magnetic field have provided the decisive constraint on the magnetic topology of solar active regions, thus offering an observational basis to identify various physical processes. Based on both magnetic field observations and theoretical discussions, it has been inferred that the magnetic flux cancellation, discovered from the line-of-sight magnetograms, reflects the interaction between magnetic loop systems and is most likely the slow magnetic reconnection in the lower solar atmosphere. This type of reconnections may affect the magnetic activities in the higher atmosphere by the way of transporting the magnetic energy and helicity and sometimes may cause fast reconnection in the corona, providing the necessary energy in solar flares.
Yan, Xuehua
2014-01-01
This paper is the further investigation of work of Yan and Liu, 2011, and considers the global practical tracking problem by output feedback for a class of uncertain nonlinear systems with not only unmeasured states dependent growth but also time-varying time delay. Compared with the closely related works, the remarkableness of the paper is that the time-varying time delay and unmeasurable states are permitted in the system nonlinear growth. Motivated by the related tracking results and flexibly using the ideas and techniques of universal control and dead zone, an adaptive output-feedback tracking controller is explicitly designed with the help of a new Lyapunov-Krasovskii functional, to make the tracking error prescribed arbitrarily small after a finite time while keeping all the closed-loop signals bounded. A numerical example demonstrates the effectiveness of the results. PMID:25276859
Positive Almost Periodic Solution on a Nonlinear Logistic Biological Model with Grazing Rates
Institute of Scientific and Technical Information of China (English)
NI Hua; TIAN Li-xin
2013-01-01
In this paper,we study the following nonlinear biological model dx(t)/dt =x(t)[a(t)-b(t)xα(t)] + f(t,xt),by using fixed pointed theorem,the sufficient conditions of the existence of unique positive almost periodic solution for the above system are obtained,by using the theories of stability,the sufficient conditions which guarantee the stability of the positive almost periodic solution are derived.
Reconnection experiments including 3D magnetic nulls
Le, A.; Egedal, J.; Vrublevskis, A.
2010-11-01
A rich collection of magnetic reconnection scenarios is possible in three dimensions depending on the topological and geometric structure of the magnetic field [1]. In recent experiments at the Versatile Toroidal Facility (VTF) three-dimensional effects were essential even in nearly axisymmetric plasmas with a non-vanishing toroidal field [2]. To explore reconnection in 3D geometries including magnetic null points, a new adjustable set of coils will be installed in the vacuum chamber of VTF. The range of vacuum magnetic field topologies attainable in VTF will be explored numerically. Plasma reconnection experiments will be run in these configurations, and measurements will be presented if available. [4pt] [1] CE Parnell, et al., (2009) ``Three-Dimensional Magnetic Reconnection, in Magnetic Coupling between the Interior and the Atmosphere of the Sun,'' eds. S.S. Hasan and R.J. Rutten, Springer-Verlag, Heidelberg, Berlin. [0ex] [2] Katz, N. et al., (2010) Phys. Rev. Lett. 104, 255004.
The Role of Geometry in Magnetic Reconnection
Hesse, Michael; Aunai, Nicholas; Birn, Joachim; Zenitani, Seiji
2012-01-01
Magnetic reconnection is arguably the most effective energy conversion and transport process in plasmas. Reconnection is subject to topological considerations in two ways. First, the process itself involves a change in topology of the combined plasma-magnetic field system. This change in topology transcends that of the magnetic field alone and accounts for flux transport relative to the motion of the plasma in the system under investigation. The second way topology is important to magnetic reconnection is through modifications of the diffUSion/dissipation physics brought about by the structure of the reconnecting system. This presentation will present an overview and summary of both past and recent results pertaining to both aspects.
The Inner Workings of Magnetic Reconnection
Hesse, Michael; Zenitani, S.
2007-01-01
Magnetic reconnection is arguably the most efficient transport and energy conversion mechanism in almost ideal plasmas. Reconnection controls the overall dynamics in space and astrophysics plasmas, as well as in many laboratory plasma systems. Reconnection operates by means of a localized diffusion region, where deviations from the plasma idealness condition generate electric fields and permit plasma transport even far away from the diffusion region itself. Recent advances in analytic theory and computer modeling have begun to shed light on the internal dynamics of the diffusion region. In particular, we begin to understand the delicate nature of the force balance in the inner diffusion region, where particles can become unmagnetized and where electric field forces are important. This presentation will provide a brief introduction of the reconnection process and its applications. This introduction will be followed by a detailed analysis of the current understanding of dissipation region physics, and by an outlook toward future research.
The Dissipation Mechanism of Magnetic Reconnection
Hesse, Michael
2008-01-01
Magnetic reconnection is arguably the most efficient transport and energy conversion mechanism in almost ideal plasmas. Reconnection controls the overall dynamics in space and astrophysics plasmas, as well as in many laboratory plasma systems. Reconnection operates by means of a localized diffusion region, where deviations from the plasma idealness condition generate electric fields and permit plasma transport even far away from the diffusion region itself. Recent advances in analytic theory and computer modeling have begun to shed light on the internal dynamics of the diffusion region. In particular, we begin to understand the delicate nature of the force balance in the inner diffusion region, where particles can become unmagnetized and where electric field forces are important. This presentation will provide a brief introduction of the reconnection process and its applications. This introduction will be followed by a detailed analysis of the current understanding of dissipation region physics, and by an outlook toward future research.
Resistive Magnetohydrodynamic Simulations of Relativistic Magnetic Reconnection
Zenitani, Seiji; Hesse, Michael; Klimas, Alex
2010-01-01
Resistive relativistic magnetohydrodynamic (RRMHD) simulations are applied to investigate the system evolution of relativistic magnetic reconnection. A time-split Harten-Lan-van Leer method is employed. Under a localized resistivity, the system exhibits a fast reconnection jet with an Alfv enic Lorentz factor inside a narrow Petschek-type exhaust. Various shock structures are resolved in and around the plasmoid such as the post-plasmoid vertical shocks and the "diamond-chain" structure due to multiple shock reflections. Under a uniform resistivity, Sweet-Parker-type reconnection slowly evolves. Under a current-dependent resistivity, plasmoids are repeatedly formed in an elongated current sheet. It is concluded that the resistivity model is of critical importance for RRMHD modeling of relativistic magnetic reconnection.
Magnetic Reconnection in Extreme Astrophysical Environments
Uzdensky, Dmitri A
2011-01-01
Magnetic reconnection is a basic plasma process of dramatic rearrangement of magnetic topology, often leading to a violent release of magnetic energy. It is important in magnetic fusion and in space and solar physics --- areas that have so far provided the context for most of reconnection research. Importantly, these environments consist just of electrons and ions and the dissipated energy always stays with the plasma. In contrast, in this paper I introduce a new direction of research, motivated by several important problems in high-energy astrophysics --- reconnection in high energy density (HED) radiative plasmas, where radiation pressure and radiative cooling become dominant factors in the pressure and energy balance. I identify the key processes distinguishing HED reconnection: special-relativistic effects; radiative effects (radiative cooling, radiation pressure, and Compton resistivity); and, at the most extreme end, QED effects, including pair creation. I then discuss the main astrophysical application...
Magnetic reconnection events in the interplanetary space
Institute of Scientific and Technical Information of China (English)
魏奉思; R.Schwenn; 胡强
1997-01-01
Magnetic field and plasma measurements in the period of 1975-1981 with 0. 18-h averages from Helios spacecrafts are analyzed. It is discovered that magnetic reconnection phenomena exist in the interplanetary space. By means of the reconstruction of magnetic field configuration in the azimuth angle plane, it is found that the magnetic reconnection event with time scale of the order of day is a significant form of magnetic reconnection phenomena in the interplanetary space, which consists of a mediate body (or a plasma bulk) and two magnetic separator lines. It could originate from coronal mass ejection event or magnetic cloud in the interplanetary space. Numerical simulation has reproduced the basic characteristics of the magnetic reconnection events.
Test particle acceleration in explosive magnetohydrodynamic reconnection
Ripperda, Bart; Xia, Chun; Keppens, Rony
2016-01-01
Magnetic reconnection is the mechanism behind many violent phenomena in the universe. We demonstrate that energy released during reconnection can lead to non-thermal particle distribution functions. We use a method in which we combine resistive magnetohydrodynamics (MHD) with relativistic test particle dynamics. Using our open-source grid-adaptive MPI-AMRVAC software, we simulate global MHD evolution combined with test particle treatments in MHD snapshots. This approach is used to evaluate particle acceleration in explosive reconnection. The reconnection is triggered by an ideal tilt instability in two-and-a-half dimensional (2.5D) scenarios and by a combination of ideal tilt and kink instabilities in three-dimensional (3D) scenarios. These instabilities occur in a system with two parallel, adjacent, repelling current channels in an initially force-free equilibrium, as a simplified representation of flux ropes in a stellar magnetosphere. The current channels undergo a rotation and a separation on Alfv\\'enic t...
Magnetic Reconnection in the Earth's Magnetosphere
Tsurutani, B. T.; Lakhina, G. S.
1997-01-01
The process of magnetic reconnection plays an important role during the interaction of the solar wind with the Earth's magnetosphere which leads to the exchange of mass, momentum, and energy between these two highly conducting plasmas.
Resistive Magnetohydrodynamic Simulations of Relativistic Magnetic Reconnection
Zenitani, Seiji; Klimas, Alex
2010-01-01
Resistive relativistic magnetohydrodynamic (RRMHD) simulations are applied to investigate the system evolution of relativistic magnetic reconnection. A time-split Harten--Lan--van Leer (HLL) method is employed. Under a localized resistivity, the system exhibits a fast reconnection jet with an Alfv\\'{e}nic Lorentz factor inside a narrow Petschek-type exhaust. Various shock structures are resolved in and around the plasmoid such as the post-plasmoid vertical shocks and the "diamond--chain" structure due to multiple shock reflections. Under a uniform resistivity, Sweet--Parker-type reconnection slowly evolves. Under a current-dependent resistivity, plasmoids are repeatedly formed in an elongated current sheet. It is concluded that the resistivity model is of critical importance for RRMHD modeling of relativistic magnetic reconnection.
Evidence for reconnection at Saturn's magnetopause
McAndrews, H. J.; Owen, C. J.; Thomsen, M. F.; Lavraud, B.; Coates, A. J.; Dougherty, M. K.; Young, D. T.
2008-04-01
Observations of Saturn's magnetopause by the Cassini Plasma Spectrometer (CAPS) and magnetometer have revealed clear instances of magnetic reconnection signatures, two of which are described here. Both encounters occurred at the equator in the prenoon sector as Cassini was exiting the magnetosphere. Evidence of heating in the electrons and ions is highly suggestive of energization comparable to that associated with the reconnection process at Earth. In one case, the fields are strongly antiparallel and the magnetic data indicate the presence of a locally open magnetic field. In the other example, magnetic data indicate a locally closed magnetic field compatible with the field lines being locally parallel, but the particle signatures lead to the conclusion of a distant reconnection site poleward of the cusps being active. The reconnection voltage for the first case is calculated to be 48 kV, which is of the same order as previous estimates at Saturn. This is lower than the corotational voltage but is not insignificant.
Perkins, Steven E; Jelinek, Herbert F; Al-Aubaidy, Hayder A; de Jong, Berverlie
2017-03-01
Recovery of cardiac autonomic modulation following exercise can be measured using heart rate variability. The objective of this study was to investigate and compare recovery of autonomic cardiac regulation over three days following a single session of high intensity interval training compared to endurance training. Nine untrained students completed two exercise protocols in a one-way crossover design. The endurance protocol consisted of 45min of moderate intensity cycling, and the high intensity interval protocol of six 30s sets of high intensity cycling. Cardiac autonomic activity recovery was measured over three days post-exercise for two hours immediately following each exercise session and each morning thereafter using linear and nonlinear heart rate variability analysis. Both linear and nonlinear measures were significantly decreased immediately following exercise indicating loss of vagal activity. Root mean sum of squared differences (p=0.031) and high frequency (p=0.031) were suppressed following the interval exercise only. The long term correlation of the heart rate applying detrended fluctuation analysis was decreased immediately following endurance training (p=0.039) and trended to increase immediately following the interval protocol (p=0.156). Sample entropy was decreased immediately following both the endurance (p=0.023) and interval (p=0.031) protocols. No exercise effects were noted from 24h post exercise onwards. High intensity interval training had a greater impact on neurocardiac activity than moderate intensity endurance training as indicated by both linear and nonlinear heart rate variability measures. Copyright © 2016 Sports Medicine Australia. Published by Elsevier Ltd. All rights reserved.
A multi-model plasma simulation of collisionless magnetic reconnection
Datta, I. A. M.; Shumlak, U.; Ho, A.; Miller, S. T.
2016-10-01
Collisionless magnetic reconnection is a process relevant to many areas of plasma physics in which energy stored in magnetic fields within highly conductive plasmas is rapidly converted to plasma energy. A full understanding of this phenomenon, however, is currently incomplete as models developed to date have difficulty explaining the fast reconnection rates often seen in nature, such as in the case of solar flares. Therefore, this behavior represents an area of much research in which various plasma models have been tested in order to understand the proper physics explaining the reconnection process. In this research, the WARPXM code developed at the University of Washington is used to study the problem using a hybrid multi-model simulation employing Hall-MHD and two-fluid plasma models. The simulation is performed on a decomposed domain where different plasma models are solved in different regions, depending on a trade-off between each model's physical accuracy and associated computational expense in each region. The code employs a discontinuous Galerkin (DG) finite element spatial discretization coupled with a Runge-Kutta scheme for time advancement and uses boundary conditions to couple the different plasma models. This work is supported by a Grant from the United States Air Force Office of Scientific Research.
Onset of Reconnection in the near Magnetotail: PIC Simulations
Liu, Yi-Hsin; Birn, Joachim; Daughton, William; Hesse, Michael; Schindler, Karl
2014-01-01
Using 2.5-dimensional particle-in-cell (PIC) simulations of magnetotail dynamics, we investigate the onset of reconnection in two-dimensional tail configurations with finite Bz. Reconnection onset is preceded by a driven phase, during which magnetic flux is added to the tail at the high-latitude boundaries, followed by a relaxation phase, during which the configuration continues to respond to the driving. We found a clear distinction between stable and unstable cases, dependent on deformation amplitude and ion/electron mass ratio. The threshold appears consistent with electron tearing. The evolution prior to onset, as well as the evolution of stable cases, are largely independent of the mass ratio, governed by integral flux tube entropy conservation as imposed in MHD (magnetohydrodynamics). This suggests that ballooning instability in the tail should not be expected prior to the onset of tearing and reconnection. The onset time and other onset properties depend on the mass ratio, consistent with expectations for electron tearing. At onset,we found electron anisotropies T?/ T? (bottom tail divided by parallel tail) equals 1.1-1.3, raising growth rates and wavenumbers. Our simulations have provided a quantitative onset criterion that is easily evaluated in MHD simulations, provided the spatial resolution is sufficient. The evolution prior to onset and after the formation of a neutral line does not depend on the electron physics, which should permit an approximation by MHD simulations with appropriate dissipation terms.
Sajedi, Salar; Kamal Asl, Alireza; Ay, Mohammad R; Farahani, Mohammad H; Rahmim, Arman
2013-06-01
Applications in imaging and spectroscopy rely on pulse processing methods for appropriate data generation. Often, the particular method utilized does not highly impact data quality, whereas in some scenarios, such as in the presence of high count rates or high frequency pulses, this issue merits extra consideration. In the present study, a new approach for pulse processing in nuclear medicine imaging and spectroscopy is introduced and evaluated. The new non-linear recursive filter (NLRF) performs nonlinear processing of the input signal and extracts the main pulse characteristics, having the powerful ability to recover pulses that would ordinarily result in pulse pile-up. The filter design defines sampling frequencies lower than the Nyquist frequency. In the literature, for systems involving NaI(Tl) detectors and photomultiplier tubes (PMTs), with a signal bandwidth considered as 15 MHz, the sampling frequency should be at least 30 MHz (the Nyquist rate), whereas in the present work, a sampling rate of 3.3 MHz was shown to yield very promising results. This was obtained by exploiting the known shape feature instead of utilizing a general sampling algorithm. The simulation and experimental results show that the proposed filter enhances count rates in spectroscopy. With this filter, the system behaves almost identically as a general pulse detection system with a dead time considerably reduced to the new sampling time (300 ns). Furthermore, because of its unique feature for determining exact event times, the method could prove very useful in time-of-flight PET imaging.
Fully kinetic simulations of magnetic reconnection in partially ionised gases
Innocenti, M. E.; Jiang, W.; Lapenta, G.; Markidis, S.
2016-12-01
Magnetic reconnection has been explored for decades as a way to convert magnetic energy into kinetic energy and heat and to accelerate particles in environments as different as the solar surface, planetary magnetospheres, the solar wind, accretion disks, laboratory plasmas. When studying reconnection via simulations, it is usually assumed that the plasma is fully ionised, as it is indeed the case in many of the above-mentioned cases. There are, however, exceptions, the most notable being the lower solar atmosphere. Small ionisation fractions are registered also in the warm neutral interstellar medium, in dense interstellar clouds, in protostellar and protoplanetary accreditation disks, in tokamak edge plasmas and in ad-hoc laboratory experiments [1]. We study here how magnetic reconnection is modified by the presence of a neutral background, i.e. when the majority of the gas is not ionised. The ionised plasma is simulated with the fully kinetic Particle-In-Cell (PIC) code iPic3D [2]. Collisions with the neutral background are introduced via a Monte Carlo plug-in. The standard Monte Carlo procedure [3] is employed to account for elastic, excitation and ionization electron-neutral collisions, as well as for elastic scattering and charge exchange ion-neutral collisions. Collisions with the background introduce resistivity in an otherwise collisionless plasma and modifications of the particle distribution functions: particles (and ions at a faster rate) tend to thermalise to the background. To pinpoint the consequences of this, we compare reconnection simulations with and without background. References [1] E E Lawrence et al. Physical review letters, 110(1):015001, 2013. [2] S Markidis et al. Mathematics and Computers in Simulation, 80(7):1509-1519, 2010. [3] K Nanbu. IEEE Transactions on plasma science, 28(3):971-990, 2000.
The Diffusion Region in Collisionless Magnetic Reconnection
Hesse, Michael; Neukirch, Thomas; Schindler, Karl; Kuznetsova, Masha; Zenitani, Seiji
2011-01-01
A review of present understanding of the dissipation region in magnetic reconnection is presented. The review focuses on results of the thermal inertia-based dissipation mechanism but alternative mechanisms are mentioned as well. For the former process, a combination of analytical theory and numerical modeling is presented. Furthermore, a new relation between the electric field expressions for anti-parallel and guide field reconnection is developed.
Rate of non-linearity in DMS aerosol-cloud-climate interactions
Directory of Open Access Journals (Sweden)
M. A. Thomas
2011-11-01
Full Text Available The degree of non-linearity in DMS-cloud-climate interactions is assessed using the ECHAM5-HAMMOZ model by taking into account end-to-end aerosol chemistry-cloud microphysics link. The evaluation is made over the Southern oceans in austral summer, a region of minimal anthropogenic influence. In this study, we compare the DMS-derived changes in the aerosol and cloud microphysical properties between a baseline simulation with the ocean DMS emissions from a prescribed climatology, and a scenario where the DMS emissions are doubled. Our results show that doubling the DMS emissions in the current climate results in a non-linear response in atmospheric DMS burden and subsequently, in SO_{2} and H_{2}SO_{4} burdens due to inadequate OH oxidation. The aerosol optical depth increases by only ~20 % in the 30° S–75° S belt in the SH summer months. This increases the vertically integrated cloud droplet number concentrations (CDNC by 25 %. Since the vertically integrated liquid water vapor is constant in our model simulations, an increase in CDNC leads to a reduction in cloud droplet radius of 3.4 % over the Southern oceans in summer. The equivalent increase in cloud liquid water path is 10.7 %. The above changes in cloud microphysical properties result in a change in global annual mean radiative forcing at the TOA of −1.4 W m^{−2}. The results suggest that the DMS-cloud microphysics link is highly non-linear. This has implications for future studies investigating the DMS-cloud climate feedbacks in a warming world and for studies evaluating geoengineering options to counteract warming by modulating low level marine clouds.
Multiscale Modeling of Solar Coronal Magnetic Reconnection
Antiochos, Spiro K.; Karpen, Judith T.; DeVore, C. Richard
2010-01-01
Magnetic reconnection is widely believed to be the primary process by which the magnetic field releases energy to plasma in the Sun's corona. For example, in the breakout model for the initiation of coronal mass ejections/eruptive flares, reconnection is responsible for the catastrophic destabilizing of magnetic force balance in the corona, leading to explosive energy release. A critical requirement for the reconnection is that it have a "switch-on' nature in that the reconnection stays off until a large store of magnetic free energy has built up, and then it turn on abruptly and stay on until most of this free energy has been released. We discuss the implications of this requirement for reconnection in the context of the breakout model for CMEs/flares. We argue that it imposes stringent constraints on the properties of the flux breaking mechanism, which is expected to operate in the corona on kinetic scales. We present numerical simulations demonstrating how the reconnection and the eruption depend on the effective resistivity, i.e., the effective Lundquist number, and propose a model for incorporating kinetic flux-breaking mechanisms into MHO calculation of CMEs/flares.
Test particle acceleration in torsional fan reconnection
Hosseinpour, M.
2014-12-01
Magnetic reconnection is understood to be a potential mechanism for particle acceleration in astrophysical and space plasmas, especially in solar flares. Torsional fan reconnection is one of the proposed mechanisms for steady-state three-dimensional (3D) magnetic reconnection. By using the magnetic and electric fields for `torsional fan reconnection', the features of test particle acceleration with input parameters for the solar corona are investigated numerically. We show that torsional fan reconnection is potentially an efficient particle accelerator and a proton can gain up to tens of MeV of kinetic energy within only a few milliseconds. Although the final kinetic energy of the accelerated particle depends on the injection position but there exists only one scenario for the particle's trajectory with different initial positions in which the particle is accelerated on the fan plane. Moreover, adopting either spatially uniform or non-uniform localized plasma resistivity does not much influence the features of trajectory. These results are compared with those of torsional spine reconnection.
Directory of Open Access Journals (Sweden)
T. G. Shepherd
2009-11-01
Full Text Available An analysis of the attribution of past and future changes in stratospheric ozone and temperature to anthropogenic forcings is presented. The analysis is an extension of the study of Shepherd and Jonsson (2008 who analyzed chemistry-climate simulations from the Canadian Middle Atmosphere Model (CMAM and attributed both past and future changes to changes in the external forcings, i.e. the abundances of ozone-depleting substances (ODS and well-mixed greenhouse gases. The current study is based on a new CMAM dataset and includes two important changes. First, we account for the nonlinear radiative response to changes in CO2. It is shown that over centennial time scales the radiative response in the upper stratosphere to CO2 changes is significantly nonlinear and that failure to account for this effect leads to a significant error in the attribution. To our knowledge this nonlinearity has not been considered before in attribution analysis, including multiple linear regression studies. For the regression analysis presented here the nonlinearity was taken into account by using CO2 heating rate, rather than CO2 abundance, as the explanatory variable. This approach yields considerable corrections to the results of the previous study and can be recommended to other researchers. Second, an error in the way the CO2 forcing changes are implemented in the CMAM was corrected, which significantly affects the results for the recent past. As the radiation scheme, based on Fomichev et al. (1998, is used in several other models we provide some description of the problem and how it was fixed.
Helicity, topology, and Kelvin waves in reconnecting quantum knots
Clark di Leoni, P.; Mininni, P. D.; Brachet, M. E.
2016-10-01
Helicity is a topological invariant that measures the linkage and knottedness of lines, tubes, and ribbons. As such, it has found myriads of applications in astrophysics, fluid dynamics, atmospheric sciences, and biology. In quantum flows, where topology-changing reconnection events are a staple, helicity appears as a key quantity to study. However, the usual definition of helicity is not well posed in quantum vortices, and its computation based on counting links and crossings of centerline vorticity can be downright impossible to apply in complex and turbulent scenarios. We present a definition of helicity which overcomes these problems and which gives the expected result in the large-scale limit. With it, we show that certain reconnection events can excite Kelvin waves and other complex motions of the centerline vorticity, which slowly deplete helicity as they interact nonlinearly, thus linking the theory of vortex knots with observations of quantum fluids. This process also results in the depletion of helicity in a fully turbulent quantum flow, in a way reminiscent of the decay of helicity in classical fluids.
DEFF Research Database (Denmark)
Kooths, Stefan; Mitze, Timo Friedel; Ringhut, Eric
2004-01-01
This paper compares the predictive power of linear econometric and non-linear computational models for forecasting the inflation rate in the European Monetary Union (EMU). Various models of both types are developed using different monetary and real activity indicators. They are compared according...... to a battery of parametric and non-parametric test statistics to measure their performance in one- and four-step ahead forecasts of quarterly data. Using genetic-neural fuzzy systems we find the computational approach superior to some degree and show how to combine both techniques successfully....
Muñoz, P. A.; Büchner, J.
2016-10-01
Non-Maxwellian electron velocity space distribution functions (EVDFs) are useful signatures of plasma conditions and non-local consequences of collisionless magnetic reconnection. In the past, EVDFs were obtained mainly for antiparallel reconnection and under the influence of weak guide-fields in the direction perpendicular to the reconnection plane. EVDFs are, however, not well known, yet, for oblique (or component-) reconnection in case and in dependence on stronger guide-magnetic fields and for the exhaust (outflow) region of reconnection away from the diffusion region. In view of the multi-spacecraft Magnetospheric Multiscale Mission (MMS), we derived the non-Maxwellian EVDFs of collisionless magnetic reconnection in dependence on the guide-field strength bg from small ( b g ≈ 0 ) to very strong (bg = 8) guide-fields, taking into account the feedback of the self-generated turbulence. For this sake, we carried out 2.5D fully kinetic Particle-in-Cell simulations using the ACRONYM code. We obtained anisotropic EVDFs and electron beams propagating along the separatrices as well as in the exhaust region of reconnection. The beams are anisotropic with a higher temperature in the direction perpendicular rather than parallel to the local magnetic field. The beams propagate in the direction opposite to the background electrons and cause instabilities. We also obtained the guide-field dependence of the relative electron-beam drift speed, threshold, and properties of the resulting streaming instabilities including the strongly non-linear saturation of the self-generated plasma turbulence. This turbulence and its non-linear feedback cause non-adiabatic parallel electron acceleration. We further obtained the resulting EVDFs due to the non-linear feedback of the saturated self-generated turbulence near the separatrices and in the exhaust region of reconnection in dependence on the guide field strength. We found that the influence of the self-generated plasma turbulence
Comparison of linear and nonlinear feedback control of heart rate for treadmill running
National Research Council Canada - National Science Library
Hunt, Kenneth J; Maurer, Roman R
2016-01-01
Heart rate can be used to define exercise intensity; feedback control systems for treadmills which automatically adjust speed to track arbitrary heart rate target profiles are therefore of interest...
Achieving Fast Reconnection in Resistive MHD Models via Turbulent Means
Lapenta, Giovanni
2011-01-01
Astrophysical fluids are generally turbulent and this preexisting turbulence must be taken into account for the models of magnetic reconnection which are attepmted to be applied to astrophysical, solar or heliospheric environments. In addition, reconnection itself induces turbulence which provides an important feedback on the reconnection process. In this paper we discuss both theoretical model and numerical evidence that magnetic reconnection gets fast in the approximation of resistive MHD. We consider the relation between the Lazarian & Vishniac turbulent reconnection theory and Lapenta's numerical experiments testifying of the spontaneous onset of turbulent reconnection in systems which are initially laminar.
Glocer, Alex; Dorelli, J.; Toth, G.; Komar, C. M.; Cassak, P. A.
2016-01-01
In this work, we demonstrate how to track magnetic separators in three-dimensional simulated magnetic fields with or without magnetic nulls, apply these techniques to enhance our understanding of reconnection at the magnetopause. We present three methods for locating magnetic separators and apply them to 3-D resistive MHD simulations of the Earth's magnetosphere using the Block-Adaptive-Tree Solar-wind Roe-type Upwind Scheme code. The techniques for finding separators and determining the reconnection rate are insensitive to interplanetary magnetic field (IMF) clock angle and can in principle be applied to any magnetospheric model. Moreover, the techniques have a number of advantages over prior separator finding techniques applied to the magnetosphere. The present work examines cases of high and low resistivity for two clock angles. We go beyond previous work examine the separator during Flux Transfer Events (FTEs). Our analysis of reconnection on the magnetopause yields a number of interesting conclusions: Reconnection occurs all along the separator even during predominately northward IMF cases. Multiple separators form in low-resistivity conditions, and in the region of an FTE the separator splits into distinct branches. Moreover, the local contribution to the reconnection rate, as determined by the local parallel electric field, drops in the vicinity of the FTE with respect to the value when there are none.
Chaos-induced resistivity of collisionless magnetic reconnection in the presence of a guide field
Shang, Meng; Wu, De-Jin; Chen, Ling; Chen, Peng-Fei
2017-01-01
One of the most puzzling problems in astrophysics is to understand the anomalous resistivity in collisionless magnetic reconnection that is believed extensively to be responsible for the energy release in various eruptive phenomena. The magnetic null point in the reconnecting current sheet, acting as a scattering center, can lead to chaotic motions of particles in the current sheet, which is one of the possible mechanisms for anomalous resistivity and is called chaos-induced resistivity. In many interesting cases, however, instead of the magnetic null point, there is a nonzero magnetic field perpendicular to the merging field lines, usually called the guide field, whose effect on chaos-induced resistivity has been an open problem. By use of the test particle simulation method and statistical analysis, we investigate chaos-induced resistivity in the presence of a constant guide field. The characteristics of particle motion in the reconnecting region, in particular, the chaotic behavior of particle orbits and evolving statistical features, are analyzed. The results show that as the guide field increases, the radius of the chaos region increases and the Lyapunov index decreases. However, the effective collision frequency, and hence the chaos-induced resistivity, reach their peak values when the guide field approaches half of the characteristic strength of the reconnection magnetic field. The presence of a guide field can significantly influence the chaos of the particle orbits and hence the chaos-induced resistivity in the reconnection sheet, which decides the collisionless reconnection rate. The present result is helpful for us to understand the microphysics of anomalous resistivity in collisionless reconnection with a guide field.
Magnetic reconnection at 3D null points: effect of magnetic field asymmetry
Al-Hachami, A K
2009-01-01
The aim of this paper is to investigate the properties of magnetic reconnection at a 3D null point, with respect to their dependence on the symmetry of the magnetic field around the null. In particular we examine the rate of flux transport across the null point with symmetric/asymmetric diffusion regions, as well as how the current sheet forms in time, and its properties. Mathematical modelling and finite difference resistive MHD simulations are used. It is found that the basic structure of the mode of magnetic reconnection considered is unaffected by varying the magnetic field symmetry, that is, the plasma flow is found cross both the spine and fan of the null. However, the peak intensity and dimensions of the current sheet are dependent on the symmetry/ asymmetry of the field lines. As a result, the reconnection rate is also found to be strongly dependent on the field asymmetry.
Flux pileup in collisionless magnetic reconnection: bursty interaction of large flux ropes.
Karimabadi, H; Dorelli, J; Roytershteyn, V; Daughton, W; Chacón, L
2011-07-08
Using fully kinetic simulations of the island coalescence problem for a range of system sizes greatly exceeding kinetic scales, the phenomenon of flux pileup in the collisionless regime is demonstrated. While small islands on the scale of λ ≤ 5 ion inertial length (d(i)) coalesce rapidly and do not support significant flux pileup, coalescence of larger islands is characterized by large flux pileup and a weaker time averaged reconnection rate that scales as √(d(i)/λ) while the peak rate remains nearly independent of island size. For the largest islands (λ = 100d(i)), reconnection is bursty and nearly shuts off after the first bounce, reconnecting ~20% of the available flux.
Influence of the Hall effect and electron inertia in collisionless magnetic reconnection
Andrés, Nahuel; Gómez, Daniel
2015-01-01
We study the role of the Hall current and electron inertia in collisionless magnetic reconnection within the framework of full two-fluid MHD. At spatial scales smaller than the electron inertial length, a topological change of magnetic field lines exclusively due to electron inertia becomes possible. Assuming stationary conditions, we derive a theoretical scaling for the reconnection rate, which is simply proportional to the Hall parameter. Using a pseudo-spectral code with no dissipative effects, our numerical results confirm this theoretical scaling. In particular, for a sequence of different Hall parameter values, our numerical results show that the width of the current sheet is independent of the Hall parameter while its thickness is of the order of the electron inertial range, thus confirming that the stationary reconnection rate is proportional to the Hall parameter.
Reconnection Processes in the Chromosphere and Corona
Shibata, Kazunari
2012-07-01
Magnetic reconnection is a fundamental key physical process in magnetized plasmas. Recent space solar observations revealed that magnetic reconnection is ubiquitous in the solar chromospheres and corona. Especially recent Hinode observations has found various types of tiny chromospheric jets, such as chromospheric anemone jets (Shibata et al. 2007), penumbral microjets (Katsukawa et al. 2007), light bridge jets from sunspot umbra (Shimizu et al. 2009), etc. It was also found that the corona is full of tiny X-ray jets (Cirtain et al. 2007). Often they are seen as helical spinning jets (Shimojo et al. 2007, Patsourakos et al. 2008, Pariat et al. 2009, Filippov et al. 2009, Kamio et al. 2010) with Alfvenic waves (Nishizuka et al. 2008, Liu et al. 2009) and there are increasing evidence of magnetic reconnection in these tiny jets. We can now say that as spatial resolution of observations become better and better, smaller and smaller flares and jets have been discovered, which implies that the magnetized solar atmosphere consist of fractal structure and dynamics, i.e., fractal reconnection. Bursty radio and hard X-ray emissions from flares also suggest the fractal reconnection and associated particle acceleration. Since magnetohydrodynamics (MHD) does not contain any characteristic length and time scale, it is natural that MHD structure, dynamics, and reconnection, tend to become fractal in ideal MHD plasmas with large magnetic Reynolds number such as in the solar atmosphere. We would discuss recent observations and theories related to fractal reconnection in the chromospheres and corona, and discuss possible implication to chromospheric and coronal heating.
Instability, Turbulence, and 3D Magnetic Reconnection in a Line-Tied, Zero Net Current Screw Pinch
Brookhart, Matthew I.; Stemo, Aaron; Zuberbier, Amanda; Zweibel, Ellen; Forest, Cary B.
2015-04-01
This Letter reports the first experimental investigation into a line-tied plasma with a reversed current profile. Discrete current sources create a cylindrical plasma equilibrium with an axial field and zero net current. Detailed magnetic measurements show that an internal m =1 mode with no external character grows exponentially. The nonlinear evolution of the mode drives 3D reconnection events that reorganize the plasma equilibrium. The plasma is turbulent and exhibits reconnection events on a range of scales. These data are consistent with recent simulations of coronal loops and the nanoflare coronal heating mechanism.
Instability, turbulence, and 3D magnetic reconnection in a line-tied, zero net current screw pinch.
Brookhart, Matthew I; Stemo, Aaron; Zuberbier, Amanda; Zweibel, Ellen; Forest, Cary B
2015-04-10
This Letter reports the first experimental investigation into a line-tied plasma with a reversed current profile. Discrete current sources create a cylindrical plasma equilibrium with an axial field and zero net current. Detailed magnetic measurements show that an internal m=1 mode with no external character grows exponentially. The nonlinear evolution of the mode drives 3D reconnection events that reorganize the plasma equilibrium. The plasma is turbulent and exhibits reconnection events on a range of scales. These data are consistent with recent simulations of coronal loops and the nanoflare coronal heating mechanism.
Tanev, George; Saadi, Dorthe B; Hoppe, Karsten; Sorensen, Helge B D
2014-01-01
Chronic stress detection is an important factor in predicting and reducing the risk of cardiovascular disease. This work is a pilot study with a focus on developing a method for detecting short-term psychophysiological changes through heart rate variability (HRV) features. The purpose of this pilot study is to establish and to gain insight on a set of features that could be used to detect psychophysiological changes that occur during chronic stress. This study elicited four different types of arousal by images, sounds, mental tasks and rest, and classified them using linear and non-linear HRV features from electrocardiograms (ECG) acquired by the wireless wearable ePatch® recorder. The highest recognition rates were acquired for the neutral stage (90%), the acute stress stage (80%) and the baseline stage (80%) by sample entropy, detrended fluctuation analysis and normalized high frequency features. Standardizing non-linear HRV features for each subject was found to be an important factor for the improvement of the classification results.
Wang, Shuoyang; Isobe, Hiroaki
2015-01-01
Using a three-dimensional magnetohydrodynamic model, we simulate the magnetic reconnection in a single current sheet. We assume a finite guide field, a random perturbation on the velocity field and uniform resistivity. Our model enhances the reconnection rate relative to the classical Sweet-Parker model in the same configuration. The efficiency of magnetic energy conversion is increased by interactions between the multiple tearing layers coexisting in the global current sheet. This interaction, which forms a positive-feedback system, arises from coupling of the inflow and outflow regions in different layers across the current sheet. The coupling accelerates the elementary reconnection events, thereby enhancing the global reconnection rate. The reconnection establishes flux tubes along each tearing layer. Slow-mode shocks gradually form along the outer boundaries of these tubes, further accelerating the magnetic energy conversion.Such positive-feedback system is absent in two-dimensional simulation, three-dime...
What Causes Electron Holes During Magnetic Reconnection and What Can We Learn From Them
Goldman, Martin V.; Newman, David L.; Lapenta, Giovanni; Divin, Andre; Califano, Francesco; Che, Haihong
2009-11-01
Weak bipolar electrostatic fields are commonly observed in association with magnetic reconnection. Recent attention has focused on their origin due to nonlinear evolution of electrostatic instabilities.footnotetextGoldman, M. V., D. L. Newman, and P. Pritchett, GRL, 35, doi:10.1029/2008GL035608 (2008).^,footnotetextNewman, D. L. and M. V. Goldman, SM31B-1735, AGU Fall Meeting (2008).^,footnotetextChe, H., J. F. Drake, M. Swisdak, and P. H. Yoon, PRL, 102, 145004 (2009). We present evidence from both older and new reconnection simulations for the SPATIAL dependence of electrostatically unstable electron distributions along the separatrix during guide-field magnetic reconection. Particle distributions further from the reconnection region tend to be Buneman (electron-ion) unstable, while distributions closer to the reconnection region tend to be two-stream (electron-electron) unstable. It may be possible to infer properties of the particle distributions from measurements of the speed, half-width, amplitude and aspect ratio of weak electron holes.
The Onset of Magnetic Reconnection: Tearing Instability in Current Sheets with a Guide Field
Daldorff, Lars K. S.; Klimchuk, James A.; Leake, James E.; Knizhnik, Kalman
2017-08-01
Magnetic reconnection is fundamental to many solar phenomena, ranging from coronal heating, to jets, to flares and CMEs. A poorly understood yet crucial aspect of reconnection is that it does not occur until magnetic stresses have built to sufficiently high levels for significant energy release. If reconnection were to happen too soon, coronal heating would be weak and flares would be small. As part of our program to study the onset conditions for magnetic reconnection, we have investigated the instability of current sheets to tearing. Surprisingly little work has been done on this problem for sheets that include a guide field, i.e., for which the field rotates by less than 180 degrees. This is the most common situation on the Sun. We present numerical 3D resistive MHD simulations of several sheets and show how the behavior depends on the shear angle (rotation). We compare our results to the predictions of linear theory and discuss the nonlinear evolution in terms of plasmoid formation and the interaction of different oblique tearing modes. The relevance to the Sun is explained.
Quantifying three dimensional reconnection in fragmented current layers
Energy Technology Data Exchange (ETDEWEB)
Wyper, P. F., E-mail: peter.f.wyper@nasa.gov; Hesse, M., E-mail: michael.hesse-1@nasa.gov [Goddard Space Flight Center, 8800 Greenbelt Rd, Greenbelt, Maryland 20771 (United States)
2015-04-15
There is growing evidence that when magnetic reconnection occurs in high Lundquist number plasmas such as in the Solar Corona or the Earth's Magnetosphere it does so within a fragmented, rather than a smooth current layer. Within the extent of these fragmented current regions, the associated magnetic flux transfer and energy release occur simultaneously in many different places. This investigation focusses on how best to quantify the rate at which reconnection occurs in such layers. An analytical theory is developed which describes the manner in which new connections form within fragmented current layers in the absence of magnetic nulls. It is shown that the collective rate at which new connections form can be characterized by two measures; a total rate which measures the true rate at which new connections are formed and a net rate which measures the net change of connection associated with the largest value of the integral of E{sub ||} through all of the non-ideal regions. Two simple analytical models are presented which demonstrate how each should be applied and what they quantify.
Reconnection and Spire Drift in Coronal Jets
Moore, Ronald; Sterling, Alphonse; Falconer, David
2015-04-01
It is observed that there are two morphologically-different kinds of X-ray/EUV jets in coronal holes: standard jets and blowout jets. In both kinds: (1) in the base of the jet there is closed magnetic field that has one foot in flux of polarity opposite that of the ambient open field of the coronal hole, and (2) in coronal X-ray/EUV images of the jet there is typically a bright nodule at the edge of the base. In the conventional scenario for jets of either kind, the bright nodule is a compact flare arcade, the downward product of interchange reconnection of closed field in the base with impacted ambient open field, and the upper product of this reconnection is the jet-outflow spire. It is also observed that in most jets of either kind the spire drifts sideways away from the bright nodule. We present the observed bright nodule and spire drift in an example standard jet and in two example blowout jets. With cartoons of the magnetic field and its reconnection in jets, we point out: (1) if the bright nodule is a compact flare arcade made by interchange reconnection, then the spire should drift toward the bright nodule, and (2) if the bright nodule is instead a compact flare arcade made, as in a filament-eruption flare, by internal reconnection of the legs of the erupting sheared-field core of a lobe of the closed field in the base, then the spire, made by the interchange reconnection that is driven on the outside of that lobe by the lobe’s internal convulsion, should drift away from the bright nodule. Therefore, from the observation that the spire usually drifts away from the bright nodule, we infer: (1) in X-ray/EUV jets of either kind in coronal holes the interchange reconnection that generates the jet-outflow spire usually does not make the bright nodule; instead, the bright nodule is made by reconnection inside erupting closed field in the base, as in a filament eruption, the eruption being either a confined eruption for a standard jet or a blowout eruption (as
Magnetic Reconnection in Different Environments: Similarities and Differences
Hesse, Michael; Aunai, Nicolas; Kuznetsova, Masha; Zenitani, Seiji; Birn, Joachim
2014-01-01
Depending on the specific situation, magnetic reconnection may involve symmetric or asymmetric inflow regions. Asymmetric reconnection applies, for example, to reconnection at the Earth's magnetopause, whereas reconnection in the nightside magnetotail tends to involve more symmetric geometries. A combination of review and new results pertaining to magnetic reconnection is being presented. The focus is on three aspects: A basic, MHD-based, analysis of the role magnetic reconnection plays in the transport of energy, followed by an analysis of a kinetic model of time dependent reconnection in a symmetric current sheet, similar to what is typically being encountered in the magnetotail of the Earth. The third element is a review of recent results pertaining to the orientation of the reconnection line in asymmetric geometries, which are typical for the magnetopause of the Earth, as well as likely to occur at other planets.
The Dissipation Mechanism in Collisionless Magnetic Reconnection
Hesse, Michael; Kuznetsova, M.; Birn, J.; Schindler, K.
2006-01-01
The dissipation mechanism of magnetic reconnection remains a subject of intense scientific interest. On one hand, one set of recent studies have shown that particle inertia-based processes, which include thermal and bulk inertial effects, provide the reconnection electric field in the diffusion region. On the other hand, a second set of studies emphasizes the role of wave-particle interactions in providing anomalous resistivity in the diffusion region. In this presentation, we present analytical theory results, as well as PIC simulations of guide-field magnetic reconnection. We will show that the thermal electron inertia-based dissipation mechanism, expressed through nongyrotropic electron pressure tensors, remains viable in three dimensions. We will demonstrate the thermal inertia effect through studies of electron distribution functions. Furthermore, we will show that the reconnection electric field provides a transient acceleration on particles traversing the inner reconnection region. This inertial effect can be described as a diffusion-like term of the current density, which matches key features of electron distribution functions.
Nonthermal Particle Acceleration in Magnetic Reconnection
Guo, Fan; Li, Hui; Zhang, Haocheng; Daughton, William; Liu, Yi-Hsin; Lloyd-Ronning, Nicole
2017-08-01
Magnetic reconnection is a leading mechanism for dissipating magnetic energy and accelerating nonthermal particles in Poynting-flux-dominated flows. In this study, we investigate nonthermal particle acceleration during magnetic reconnection in a magnetically dominated plasma using fully kinetic simulations. We have studied the magnetically dominated regime by varying σe = 103-105 and mass ratios. The results demonstrate that reconnection quickly establishes power-law energy distributions for both electrons and ions within several (2-3) light-crossing times. For the cases with periodic boundary conditions, the power-law index is 1 < p < 2 for both electrons and ions. We study particle acceleration in magnetic reconnection via large-scale 3D kinetic simulations to examine several effects that may be important, including pre-existing fluctuations, kink and secondary tearing instabilities, and open boundary conditions. The results show that particle acceleration in reconnection layers is surprisingly robust despite the development of 3D turbulence and instabilities. The main acceleration mechanism is a Fermi-like acceleration through the drift motions of charged particles. We discuss the implication of this study in the context of Poynting-flux dominated jets and pulsar winds, especially the applications for explaining nonthermal high-energy emissions.
Fluctuation dynamics in reconnecting current sheets
von Stechow, Adrian; Grulke, Olaf; Ji, Hantao; Yamada, Masaaki; Klinger, Thomas
2015-11-01
During magnetic reconnection, a highly localized current sheet forms at the boundary between opposed magnetic fields. Its steep perpendicular gradients and fast parallel drifts can give rise to a range of instabilities which can contribute to the overall reconnection dynamics. In two complementary laboratory reconnection experiments, MRX (PPPL, Princeton) and VINETA.II (IPP, Greifswald, Germany), magnetic fluctuations are observed within the current sheet. Despite the large differences in geometries (toroidal vs. linear), plasma parameters (high vs. low beta) and magnetic configuration (low vs. high magnetic guide field), similar broadband fluctuation characteristics are observed in both experiments. These are identified as Whistler-like fluctuations in the lower hybrid frequency range that propagate along the current sheet in the electron drift direction. They are intrinsic to the localized current sheet and largely independent of the slower reconnection dynamics. This contribution characterizes these magnetic fluctuations within the wide parameter range accessible by both experiments. Specifically, the fluctuation spectra and wave dispersion are characterized with respect to the magnetic topology and plasma parameters of the reconnecting current sheet.
Fast Reconnection of Weak Magnetic Fields
Zweibel, Ellen G.
1998-01-01
Fast magnetic reconnection refers to annihilation or topological rearrangement of magnetic fields on a timescale that is independent (or nearly independent) of the plasma resistivity. The resistivity of astrophysical plasmas is so low that reconnection is of little practical interest unless it is fast. Yet, the theory of fast magnetic reconnection is on uncertain ground, as models must avoid the tendency of magnetic fields to pile up at the reconnection layer, slowing down the flow. In this paper it is shown that these problems can be avoided to some extent if the flow is three dimensional. On the other hand, it is shown that in the limited but important case of incompressible stagnation point flows, every flow will amplify most magnetic fields. Although examples of fast magnetic reconnection abound, a weak, disordered magnetic field embedded in stagnation point flow will in general be amplified, and should eventually modify the flow. These results support recent arguments against the operation of turbulent resistivity in highly conducting fluids.
Density Enhancements and Voids following Patchy Reconnection
Guidoni, S E
2011-01-01
We show, through a simple patchy reconnection model, that retracting reconnected flux tubes may present elongated regions relatively devoid of plasma, as well as long lasting, dense central hot regions. Reconnection is assumed to happen in a small patch across a Syrovatski\\'i (non-uniform) current sheet (CS) with skewed magnetic fields. The background magnetic pressure has its maximum at the center of the CS plane, and decreases toward the edges of the plane. The reconnection patch creates two V-shaped reconnected tubes that shorten as they retract in opposite directions, due to magnetic tension. One of them moves upward toward the top edge of the CS, and the other one moves downward toward the top of the underlying arcade. Rotational discontinuities (RDs) propagate along the legs of the tubes and generate parallel super-sonic flows that collide at the center of the tube. There, gas dynamics shocks that compress and heat the plasma are launched outwardly. The descending tube moves through the bottom part of t...
We should be using nonlinear indices when relating heart-rate dynamics to cognition and mood
National Research Council Canada - National Science Library
Young, Hayley; Benton, David
2015-01-01
Both heart rate (HR) and brain functioning involve the integrated output of a multitude of regulatory mechanisms, that are not quantified adequately by linear approximations such as means and standard deviations...
Ruth, D. C. S.; Costa Rodriguez, F.
2015-12-01
The most active volcanoes on earth erupt in a yearly to decadal time scales, typically erupt mafic magmas and are open-vent systems with prominent degassing plumes (e.g. Mayon, Arenal, Llaima, Etna). Here we investigate the plumbing systems, dynamics, and processes that drive eruptions at these systems. These are key questions for improving hazard evaluation, and better understanding the unrest associated with these types of volcanoes. The petrology and geochemistry from six historical eruptions (1947-2006) of Mayon volcano (Philippines) shows that all lavas are basaltic andesite with phenocrysts of plagioclase + orthopyroxene (Opx) + clinopyroxene. Opx crystals show a variety of compositions and zoning patterns (reverse, normal or complex) with Mg# (= 100 *Mg/[Mg+Fe]) varying from 67 to 81. The simplest interpretation is that the low Mg# parts of the crystals resided on an upper crustal and crystal rich reservoir that was intruded by more primitive magmas from which the high Mg# parts of the crystals grew. Modelling Mg-Fe diffusion in Opx shows that times since magma injection and eruption range from a few days up to 3.5 years in all of the investigated eruptions. The longest diffusion times are shorter than the repose times between the eruptions, which implies that crystal recycling between eruptive events is negligible. This is a surprising result that shows that for each eruption a different part of the evolved crystal-rich plumbing system is activated. This can be due to random intrusion location or an irreversibility of the plumbing system that prevents multiple eruptions from the same crystal-rich part. Moreover, we find that the number of intrusions markedly increases before each eruption in a non-linear manner. Such an increased rate of intrusions with time might reflect non-linear rheological properties of the crystal-rich system, of the enclosing rocks, or the non-linear evolution of crystal-melt reaction-dissolution fronts during magma intrusions.
Quasi-Separatrix Layers and Line-tied Reconnection in Collisionless Plasmas
Billey, Zachary; Zweibel, Ellen; Finn, John; Daughton, William
2015-11-01
Many plasmas undergoing magnetic reconnection have boundaries that have constant magnetic flux on the dynamical timescales of the system, such as coronal loops and planetary magnetospheres. Systems where the boundary magnetic flux is constant are called line-tied systems. We conduct collisionless fully 3D particle-in-cell simulations in slab geometry to study how line-tying changes the dynamics relative non-tied systems. We confirm Quasi-Separatrix Layers (QSLs) as a model for predicting potential reconnection sites in 3D systems. Based on this theory, we use line-integrated diagnostics to investigate the collisionless physics relating to the parallel electric field. Here we find non-gyrotopic terms in the pressure tensor are important at the center of the reconnection layer. We investigate the effect of varying the length of the line-tied plasma on the growth rate and reconnection process and compare oblique modes with equivalent periodic systems. We discuss the extension into collisionless regimes of the geometric width vs tearing width theory, developed to explain line-tied suppression of tearing in MHD reconnection. Work supported by the NSF and U.S. DoE through CMSO.
Tanuma, S; Kudoh, T; Shibata, K; Tanuma, Syuniti; Yokoyama, Takaaki; Kudoh, Takahiro; Shibata, Kazunari
2001-01-01
We examine the magnetic reconnection triggered by a supernova (or a point explosion) in interstellar medium, by performing two-dimensional resistive magnetohydrodynamic (MHD) numerical simulations with high spatial resolution. We found that the magnetic reconnection starts long after a supernova shock (fast-mode MHD shock) passes a current sheet. The current sheet evolves as follows: (i) Tearing-mode instability is excited by the supernova shock, and the current sheet becomes thin in its nonlinear stage. (ii) The current-sheet thinning is saturated when the current-sheet thickness becomes comparable to that of Sweet-Parker current sheet. After that, Sweet-Parker type reconnection starts, and the current-sheet length increases. (iii) ``Secondary tearing-mode instability'' occurs in the thin Sweet-Parker current sheet. (iv) As a result, further current-sheet thinning occurs and anomalous resistivity sets in, because gas density decreases in the current sheet. Petschek type reconnection starts and heats interste...
Particle Demagnetization in Collisionless Magnetic Reconnection
Hesse, Michael
2006-01-01
The dissipation mechanism of magnetic reconnection remains a subject of intense scientific interest. On one hand, one set of recent studies have shown that particle inertia-based processes, which include thermal and bulk inertial effects, provide the reconnection electric field in the diffusion region. In this presentation, we present analytical theory results, as well as 2.5 and three-dimensional PIC simulations of guide field magnetic reconnection. We will show that diffusion region scale sizes in moderate and large guide field cases are determined by electron Larmor radii, and that analytical estimates of diffusion region dimensions need to include description of the heat flux tensor. The dominant electron dissipation process appears to be based on thermal electron inertia, expressed through nongyrotropic electron pressure tensors. We will argue that this process remains viable in three dimensions by means of a detailed comparison of high resolution particle-in-cell simulations.
Energy Technology Data Exchange (ETDEWEB)
He, Zhaoguo [Center for Space Science and Applied Research, Chinese Academy of Sciences, Beijing 100190 (China); University of Chinese Academy of Sciences, Beijing 100049 (China); Zong, Qiugang, E-mail: qgzong@gmail.com; Wang, Yongfu [Institute of Space Physics and Applied Technology, Peking University, Beijing 100871 (China); Liu, Siqing; Lin, Ruilin; Shi, Liqin [Center for Space Science and Applied Research, Chinese Academy of Sciences, Beijing 100190 (China)
2014-12-15
Resonant pitch angle scattering by electromagnetic ion cyclotron (EMIC) waves has been suggested to account for the rapid loss of ring current ions and radiation belt electrons. For the rising tone EMIC wave (classified as triggered EMIC emission), its frequency sweep rate strongly affects the efficiency of pitch-angle scattering. Based on the Cluster observations, we analyze three typical cases of rising tone EMIC waves. Two cases locate at the nightside (22.3 and 22.6 magnetic local time (MLT)) equatorial region and one case locates at the duskside (18MLT) higher magnetic latitude (λ = –9.3°) region. For the three cases, the time-dependent wave amplitude, cold electron density, and cold ion density ratio are derived from satellite data; while the ambient magnetic field, thermal proton perpendicular temperature, and the wave spectral can be directly provided by observation. These parameters are input into the nonlinear wave growth model to simulate the time-frequency evolutions of the rising tones. The simulated results show good agreements with the observations of the rising tones, providing further support for the previous finding that the rising tone EMIC wave is excited through the nonlinear wave growth process.
He, Zhaoguo; Zong, Qiugang; Liu, Siqing; Wang, Yongfu; Lin, Ruilin; Shi, Liqin
2014-12-01
Resonant pitch angle scattering by electromagnetic ion cyclotron (EMIC) waves has been suggested to account for the rapid loss of ring current ions and radiation belt electrons. For the rising tone EMIC wave (classified as triggered EMIC emission), its frequency sweep rate strongly affects the efficiency of pitch-angle scattering. Based on the Cluster observations, we analyze three typical cases of rising tone EMIC waves. Two cases locate at the nightside (22.3 and 22.6 magnetic local time (MLT)) equatorial region and one case locates at the duskside (18MLT) higher magnetic latitude (λ = -9.3°) region. For the three cases, the time-dependent wave amplitude, cold electron density, and cold ion density ratio are derived from satellite data; while the ambient magnetic field, thermal proton perpendicular temperature, and the wave spectral can be directly provided by observation. These parameters are input into the nonlinear wave growth model to simulate the time-frequency evolutions of the rising tones. The simulated results show good agreements with the observations of the rising tones, providing further support for the previous finding that the rising tone EMIC wave is excited through the nonlinear wave growth process.
Chughtai, Mohsan Niaz; Forzati, Marco; Mårtensson, Jonas; Rafique, Danish
2012-03-26
In this paper we numerically investigate nonlinear impairments in a WDM system with mixed PM (D)QPSK and OOK channels. First we analyze the dependence of XPM and XPolM on SOP and baud rate in absence of PMD. In this case we find that the nonlinear impairments are highly dependent on relative SOP between the PM (D)QPSK and neighbouring OOK channels. The dependence on relative SOP is more pronounced in differential detection than in coherent detection. However, with increasing values of PMD this dependence decreases, and non-linear tolerance improves.
Solar flare mechanism based on magnetic arcade reconnection and island merging
Energy Technology Data Exchange (ETDEWEB)
C.Z. Chen; G.S. Choe
2000-06-15
The authors propose a model describing physical processes of solar flares based on resistive reconnection of magnetic field subject to continuous increase of magnetic shear in the arcade. The individual flaring process consists of magnetic reconnection of arcade field lines, generation of magnetic islands in the magnetic arcade, and coalescence of magnetic islands. When a magnetic arcade is sheared (either by foot point motion or by flux emergence), a current sheet is formed and magnetic reconnection can take place to form a magnetic island. A continuing increase of magnetic shear can trigger a new reconnection process and create a new island in the under lying arcade below the magnetic island. The new born island rises faster than the preceding island and merges with it to form one island. Before completing the island merging process, the new born island exhibits two phases of rising motion: a first phase with a slower rising speed and a second phase with a faster rising speed. The flare plasma heating occurs mainly due to magnetic reconnection in the current sheet under the new born island. The new born island represents the X-ray plasma ejecta which shows two phases of rising motion observed by Yohkoh [Ohyama and Shibata (1997)]. The first phase with slower new born island rising speed corresponds to the early phase of reconnection of line-tied field in the underlying current sheet and is considered as the preflare phase. In the second phase, the island coalescence takes place, and the underlying current sheet is elongated so that the line-tied arcade field reconnection rate is enhanced. This phase is interpreted as the impulsive phase or the flash phase of flares. The obtained reconnection electric field is large enough to accelerate electrons to an energy level higher than 10 keV, which is necessary for observed hard X-ray emissions. After merging of the islands is completed, magnetic reconnection continues in the current sheet under the integrated island for
Directory of Open Access Journals (Sweden)
Ömer Öztürkoğlu
2017-07-01
Full Text Available This study focuses on identical parallel machine scheduling of jobs with deteriorating processing times and rate-modifying activities. We consider non linearly increasing processing times of jobs based on their position assignment. Rate modifying activities are also considered to recover the increase in processing times of jobs due to deterioration. We also propose heuristics algorithms that rely on ant colony optimization and simulated annealing algorithms to solve the problem with multiple RMAs in a reasonable amount of time. Finally, we show that ant colony optimization algorithm generates close optimal solutions and superior results than simulated annealing algorithm.
Sub-Grid-Scale Description of Turbulent Magnetic Reconnection in Magnetohydrodynamics
Widmer, Fabien; Yokoi, Nobumitsu
2015-01-01
Magnetic reconnection requires, at least locally, a non-ideal plasma response. In collisionless space and astrophysical plasmas, turbulence could permit this instead of the too rare binary collisions. We investigated the influence of turbulence on the reconnection rate in the framework of a single fluid compressible MHD approach. The goal is to find out, whether unresolved, sub-grid for MHD simulations, turbulence can enhance the reconnection process in high Reynolds number astrophysical plasma. We solve, simultaneously with the grid-scale MHD equations, evolution equations for the sub-grid turbulent energy and cross helicity according to Yokoi's model (Yokoi (2013)) where turbulence is self-generated and -sustained through the inhomogeneities of the mean fields. Simulations of Harris and force free sheets confirm the results of Higashimori et al. (2013) and new results are obtained about the dependence on resistivity for large Reynolds number as well as guide field effects. The amount of energy transferred f...
de la Cruz, Rolando; Fuentes, Claudio; Meza, Cristian; Núñez-Antón, Vicente
2016-07-08
Consider longitudinal observations across different subjects such that the underlying distribution is determined by a non-linear mixed-effects model. In this context, we look at the misclassification error rate for allocating future subjects using cross-validation, bootstrap algorithms (parametric bootstrap, leave-one-out, .632 and [Formula: see text]), and bootstrap cross-validation (which combines the first two approaches), and conduct a numerical study to compare the performance of the different methods. The simulation and comparisons in this study are motivated by real observations from a pregnancy study in which one of the main objectives is to predict normal versus abnormal pregnancy outcomes based on information gathered at early stages. Since in this type of studies it is not uncommon to have insufficient data to simultaneously solve the classification problem and estimate the misclassification error rate, we put special attention to situations when only a small sample size is available. We discuss how the misclassification error rate estimates may be affected by the sample size in terms of variability and bias, and examine conditions under which the misclassification error rate estimates perform reasonably well.
Nonlinear Evolution of Magnetic Islands in the Magnetopause Current Sheet
Institute of Scientific and Technical Information of China (English)
XianminWANG; ZuyinPU
1996-01-01
Nonlinear evolution of magnetic islands produced by time-dependent magnetic reconnection in the magnetopause current sheet is studied.It is shown that the magnetic islands are unstable against the interference from external disturbances.Their structure can be destroyed by medium and small-scale solar wind turbulences,leading to stochastic magnetic reconnection and the formation of irregular small0scale structures in magnetospheric boundary regions.
Reconnection experiments with 3D magnetic nulls
Vrublevskis, A.; Egedal, J.; Le, A.; Montag, P.
2011-10-01
Three-dimensional effects have been crucial in explaining experiments at the Versatile Toroidal Facility (VTF) even in nominal axisymmetric plasmas with a non-vanishing toroidal field. In general, depending on the topological and geometric structure of the magnetic field, a rich collection of magnetic reconnection scenarios is possible in three dimensions. The new adjustable set of coils in VTF allows exploring reconnection in 2D and 3D geometries including configurations with magnetic null points. We present results of a numerical and experimental investigation of magnetic field topologies attainable in VTF. This work was supported by NSF CAREER Award 0844620.
Yang, Huan; Liu, Yi; Zhuang, Chenggang; Shi, Junren; Yao, Yugui; Massidda, Sandro; Monni, Marco; Jia, Ying; Xi, Xiaoxing; Li, Qi; Liu, Zi-Kui; Feng, Qingrong; Wen, Hai-Hu
2008-08-01
We have measured the normal state temperature dependence of the Hall effect and magnetoresistance in epitaxial MgB2 thin films with variable disorders characterized by the residual resistance ratio RRR ranging from 4.0 to 33.3. A strong nonlinearity of the Hall effect and magnetoresistance have been found in clean samples, and they decrease gradually with the increase of disorders or temperature. By fitting the data to the theoretical model based on the Boltzmann equation and ab initio calculations for a four-band system, for the first time, we derived the scattering rates of these four bands at different temperatures and magnitude of disorders. Our method provides a unique way to derive these important parameters in multiband systems.
Energy Technology Data Exchange (ETDEWEB)
Oudalova, A.A.; Geras' kin, S.A.; Dikarev, V.G.; Nesterov, Y.B.; Dikareva, N.S
2002-07-01
The low dose region was evaluated for meristem cells of spring barley. A study of the cytogenetic damage in the low dose range was carried out to determine the genuine shape of the dose curve. The relationship between the frequency of aberrant cells and the absorbed dose is shown to be non-linear with a site at low doses within which the cytogenetic damage exceeds the control level significantly and does not depend on dose value. Within the tested exposure region, the aberrant cell frequency is found to decrease with increasing dose rate, but the shape of the dose curve remained invariable. The piecewise linear model fits the experimental data much better than the linear one. (author)
Laboratory study of ion and electron dynamics during asymmetric magnetic reconnection
Yoo, J.; Jara-Almonte, J.; Yamada, M.; Ji, H.; Fox, W. R., II; Chen, L. J.; Roytershteyn, V.; Na, B.
2015-12-01
Magnetic reconnection at the dayside magnetopause has a large density asymmetry across the current sheet. To study effects of the density asymmetry on the ion and electron dynamics, plasmas with a significant (~10) density asymmetry are created in the Magnetic Reconnection Experiment (MRX) [1]. The density asymmetry affects the ion flow pattern by changing the in-plane electrostatic field such that the potential decrease on the high-density side becomes much smaller than that on the low-density side [2]. The ion inflow stagnation point is shifted toward the low-density side and the maximum ion outflow velocity is observed on the low-density side. The density asymmetry also makes the electron temperature profile asymmetric, which has a higher temperature near the low-density-side separatrices. The bulk electron heating is proportional to the total incoming magnetic energy per particle. The electron energization process during asymmetric reconnection is studied via numerical simulations. By comparing 2D simulations with corresponding 3D simulations, we find that the overall energization process does not depend on variations along the third dimension. Where and how electrons are energized during asymmetric reconnection will be discussed by using data from 2D numerical simulations. Finally, the scaling of the reconnection rate and the ion outflow speed given by the Cassak and Shay 2007 [3] is tested by systematically varying the density ratio. The measured ion outflow speed is about 40% of the theoretical values and the measured reconnection rate agrees with the scaling only with the measured density in the exhaust region. [1] M. Yamada et al., Phys. Plasmas 4, 1936 (1997). [2] J. Yoo et al., Phys. Rev. Lett. 113, 095002 (2014). [3] P. Cassak and M. Shay, Phys. Plasmas 14, 102114 (2007).
Steward, David R.
2016-11-01
Recharge from surface to groundwater is an important component of the hydrological cycle, yet its rate is difficult to quantify. Percolation through two-dimensional circular inhomogeneities in the vadose zone is studied where one soil type is embedded within a uniform background, and nonlinear interface conditions in the quasilinear formulation are solved using Newton's method with the Analytic Element Method. This numerical laboratory identifies detectable variations in pathline and pressure head distributions that manifest due to a shift in recharge rate through in a heterogeneous media. Pathlines either diverge about or converge through coarser and finer grained materials with inverse patterns forming across lower and upper elevations; however, pathline geometry is not significantly altered by recharge. Analysis of pressure head in lower regions near groundwater identifies a new phenomenon: its distribution is not significantly impacted by an inhomogeneity soil type, nor by its placement nor by recharge rate. Another revelation is that pressure head for coarser grained inhomogeneities in upper regions is completely controlled by geometry and conductivity contrasts; a shift in recharge generates a difference Δp that becomes an additive constant with the same value throughout this region. In contrast, shifts in recharge for finer grained inhomogeneities reveal patterns with abrupt variations across their interfaces. Consequently, measurements aimed at detecting shifts in recharge in a heterogeneous vadose zone by deciphering the corresponding patterns of change in pressure head should focus on finer grained inclusions well above a groundwater table.
Magnetopause Reconnection Impact Parameters from Multiple Spacecraft Magnetic Field Measurements
Wendel, Deirdre E.; Reiff, Patricia H.
2009-01-01
We present a novel technique that exploits multiple spacecraft data to determine the impact parameters of the most general form of magnetic reconnection at the magnetopause. The method consists of a superposed epoch of multiple spacecraft magnetometer measurements that yields the instantaneous magnetic spatial gradients near a magnetopause reconnection site. The gradients establish the instantaneous positions of the spacecraft relative to the reconnection site. The analysis is well suited to evaluating the spatial scales of singular field line reconnection, which is characterized by a two-dimensional x-type topology adjacent and perpendicular to a reconnecting singular field line. Application of the method to Cluster data known to lie in the vicinity of a northward IMF reconnection site establishes a field topology consistent with singular field line reconnection and a normal magnetic field component of 20 nT. The corresponding current structure consists of a 130 km sheet possibly embedding a thinner. bifurcated sheet.
Chain Reconnections observed in Sympathetic Eruptions
Joshi, Navin Chandra; Magara, Tetsuya; Guo, Yang; Aulanier, Guillaume
2016-01-01
The nature of various plausible causal links between sympathetic events is still a controversial issue. In this work, we present multi-wavelength observations of sympathetic eruptions, associated flares and coronal mass ejections (CMEs) occurring on 2013 November 17 in two close-by active regions. Two filaments i.e., F1 and F2 are observed in between the active regions. Successive magnetic reconnections, caused by different reasons (flux cancellation, shear and expansion) have been identified during the whole event. The first reconnection occurred during the first eruption via flux cancellation between the sheared arcades overlying filament F2, creating a flux rope and leading to the first double ribbon solar flare. During this phase we observed the eruption of overlaying arcades and coronal loops, which leads to the first CME. The second reconnection is believed to occur between the expanding flux rope of F2 and the overlying arcades of the filament F1. We suggest that this reconnection destabilized the equi...
Applying Relativistic Reconnection to Blazar Jets
Nalewajko, Krzysztof
2016-01-01
Rapid and luminous flares of non-thermal radiation observed in blazars require an efficient mechanism of energy dissipation and particle acceleration in relativistic active galactic nuclei (AGN) jets. Particle acceleration in relativistic magnetic reconnection is being actively studied by kinetic numerical simulations. Relativistic reconnection produces hard power-law electron energy distributions N(gamma) = N_0 gamma^(-p) exp(-gamma/gamma_max) with index p -> 1 and exponential cut-off Lorentz factor gamma_max ~ sigma in the limit of magnetization sigma = B^2/(4 pi w) >> 1 (where w is the relativistic enthalpy density). Reconnection in electron-proton plasma can additionally boost gamma_max by the mass ratio m_p/m_e. Hence, in order to accelerate particles to gamma_max ~ 10^6 in the case of BL Lacs, reconnection should proceed in plasma of very high magnetization sigma_max >~ 10^3. On the other hand, moderate mean jet magnetization values are required for magnetic bulk acceleration of relativistic jets, sigma...
VINETA II: a linear magnetic reconnection experiment.
Bohlin, H; Von Stechow, A; Rahbarnia, K; Grulke, O; Klinger, T
2014-02-01
A linear experiment dedicated to the study of driven magnetic reconnection is presented. The new device (VINETA II) is suitable for investigating both collisional and near collisionless reconnection. Reconnection is achieved by externally driving magnetic field lines towards an X-point, inducing a current in the background plasma which consequently modifies the magnetic field topology. Owing to the open field line configuration of the experiment, the current is limited by the axial sheath boundary conditions. A plasma gun is used as an additional electron source in order to counterbalance the charge separation effects and supply the required current. Two drive methods are used in the device. First, an oscillating current through two parallel conductors drive the reconnection. Second, a stationary X-point topology is formed by the parallel conductors, and the drive is achieved by an oscillating current through a third conductor. In the first setup, the magnetic field of the axial plasma current dominates the field topology near the X-point throughout most of the drive. The second setup allows for the amplitude of the plasma current as well as the motion of the flux to be set independently of the X-point topology of the parallel conductors.
Scaling of Navier-Stokes trefoil reconnection
Kerr, Robert M
2016-01-01
The reconnection of a trefoil vortex knot is examined numerically to determine how its helicity and two of its vorticity norms behave. During an initial phase, the helicity is remarkably preserved, as reported in recent experiments (Scheeler et al. 2014a). In addition, the enstrophy ($Z$) has self-similar growth where all $\\sqrt{\
Magnetic reconnection as a chondrule heating mechanism
Lazerson, Samuel A.
2010-12-01
The origin of chondrules (sub-millimeter inclusions found in stony meteorites) remains today an open question despite over century of examination. The age of these proto-solar relics shows a well defined cutoff of around 4.5 billion years ago. This places them as the oldest solids in the solar system. Chemical examination indicates that they experienced heating events on the order of 5000 K/hr for periods of around 30 minutes, followed by extending periods of cooling. Additional examination indicates the presence of large magnetic fields during their formation. Most attempts to explain chondrule formation in the proto-solar nebula neglect the existence of a plasma environment, with even less mention of dust being a charge carrier (dusty plasma). Simulations of magnetic reconnection in a dusty plasma are forwarded as a mechanism for chondrule formation in the proto-solar nebula. Here large dust-neutral relative velocities are found in the reconnection region. These flows are associated with the dynamics of reconnection. The high Knudsen number of the dust particles allows for a direct calculation of frictional heating due to collisions with neutrals (allowing for the neglect of boundary layer formation around the particle). Test particle simulations produce heating equivalent to that recorded in the chondrule mineral record. It is shown that magnetic reconnection in a dusty plasma is of fundamental importance to the formation of the most primitive solids in the solar system.
Formation and Reconnection of Three-Dimensional Current Sheets in the Solar Corona
Edmondson, J. K.; Antiochos, S. K.; DeVore, C. R.; Zurbuchen, T. H.
2010-01-01
Current-sheet formation and magnetic reconnection are believed to be the basic physical processes responsible for much of the activity observed in astrophysical plasmas, such as the Sun s corona. We investigate these processes for a magnetic configuration consisting of a uniform background field and an embedded line dipole, a topology that is expected to be ubiquitous in the corona. This magnetic system is driven by a uniform horizontal flow applied at the line-tied photosphere. Although both the initial field and the driver are translationally symmetric, the resulting evolution is calculated using a fully three-dimensional magnetohydrodynamic (3D MHD) simulation with adaptive mesh refinement that resolves the current sheet and reconnection dynamics in detail. The advantage of our approach is that it allows us to apply directly the vast body of knowledge gained from the many studies of 2D reconnection to the fully 3D case. We find that a current sheet forms in close analogy to the classic Syrovatskii 2D mechanism, but the resulting evolution is different than expected. The current sheet is globally stable, showing no evidence for a disruption or a secondary instability even for aspect ratios as high as 80:1. The global evolution generally follows the standard Sweet- Parker 2D reconnection model except for an accelerated reconnection rate at a very thin current sheet, due to the tearing instability and the formation of magnetic islands. An interesting conclusion is that despite the formation of fully 3D structures at small scales, the system remains close to 2D at global scales. We discuss the implications of our results for observations of the solar corona. Subject Headings: Sun: corona Sun: magnetic fields Sun: reconnection
Diffusive Shock Acceleration and Reconnection Acceleration Processes
Zank, G. P.; Hunana, P.; Mostafavi, P.; Le Roux, J. A.; Li, Gang; Webb, G. M.; Khabarova, O.; Cummings, A.; Stone, E.; Decker, R.
2015-12-01
Shock waves, as shown by simulations and observations, can generate high levels of downstream vortical turbulence, including magnetic islands. We consider a combination of diffusive shock acceleration (DSA) and downstream magnetic-island-reconnection-related processes as an energization mechanism for charged particles. Observations of electron and ion distributions downstream of interplanetary shocks and the heliospheric termination shock (HTS) are frequently inconsistent with the predictions of classical DSA. We utilize a recently developed transport theory for charged particles propagating diffusively in a turbulent region filled with contracting and reconnecting plasmoids and small-scale current sheets. Particle energization associated with the anti-reconnection electric field, a consequence of magnetic island merging, and magnetic island contraction, are considered. For the former only, we find that (i) the spectrum is a hard power law in particle speed, and (ii) the downstream solution is constant. For downstream plasmoid contraction only, (i) the accelerated spectrum is a hard power law in particle speed; (ii) the particle intensity for a given energy peaks downstream of the shock, and the distance to the peak location increases with increasing particle energy, and (iii) the particle intensity amplification for a particular particle energy, f(x,c/{c}0)/f(0,c/{c}0), is not 1, as predicted by DSA, but increases with increasing particle energy. The general solution combines both the reconnection-induced electric field and plasmoid contraction. The observed energetic particle intensity profile observed by Voyager 2 downstream of the HTS appears to support a particle acceleration mechanism that combines both DSA and magnetic-island-reconnection-related processes.
Brando, Victoria; Castro-Zaballa, Santiago; Falconi, Atilio; Torterolo, Pablo; Migliaro, Eduardo R
2014-03-01
As a first step in a program designed to study the central control of the heart rate variability (HRV) during sleep, we conducted polysomnographic and electrocardiogram recordings on chronically-prepared cats during semi- restricted conditions. We found that the tachogram, i.e. the pattern of heart beat intervals (RR intervals) was deeply modified on passing from alert wakefulness through quiet wakefulness (QW) to sleep. While the tachogram showed a rhythmical pattern coupled with respiratory activity during non-REM sleep (NREM), it turned chaotic during REM sleep. Statistical analyses of the RR intervals showed that the mean duration increased during sleep. HRV measured by the standard deviation of normal RR intervals (SDNN) and by the square root of the mean squared difference of successive intervals (rMSSD) were larger during REM and NREM sleep than during QW. SD-1 (a marker of short- term variability) and SD-2 (a marker of long-term variability) measured by means of Poincaré plots increased during both REM and NREM sleep compared to QW. Furthermore, in the spectral analysis of RR intervals, the band of high frequency (HF) was larger in NREM and REM sleep in comparison to QW, whereas the band of low frequency (LF) was larger only during REM sleep in comparison to QW. The LF/HF ratio was larger during QW compared either with REM or NREM sleep. Finally, sample entropy analysis used as a measure of complexity, was higher during NREM in comparison to REM sleep. In conclusion, HRV parameters, including complexity, are deeply modified across behavioral states.
Park, H.; Ho, C. H.; Jeong, S. J.
2015-12-01
Understanding the changes in vegetation annual cycle is crucial for improving our knowledge about various interactions between the terrestrial ecosystem and climate. However, our understanding about the vegetation seasonality is mostly confined to some phenological timings such as spring emergence and fall senescence. This study assessed large-scale variations in the vegetation green-up rate (VGrate), which indicates the rate of canopy development from winter dormancy to summer maturity, and its relationship over Northern Hemisphere temperate and boreal forests for 1982-2011. VGrate and local temperature changes show a positive correlation over the region of interest, and it indicates that a temperature increase during green-up period leads to faster canopy development. The responses of VGrate tend to be more sensitive to positive temperature anomalies than negative anomalies despite same magnitude of the temperature changes. These nonlinear responsiveness of VGrate to local temperature change is clearly observed in deciduous broadleaf forests over Eurasia compared to woodlands over North America. These results suggest that anomalous warming in green-up period would make canopy developments faster over wide temperate and boreal forest areas.
Three-dimensional magnetic reconnection through a moving magnetic null
Directory of Open Access Journals (Sweden)
V. S. Lukin
2011-11-01
Full Text Available A computational study of three-dimensional magnetic reconnection between two flux ropes through a moving reconnection site is presented. The configuration is considered in the context of two interacting spheromaks constrained by a perfectly conducting cylindrical boundary and oriented to form a single magnetic field null at its center. The initial magnetic field configuration is embedded into a uniform thermal plasma and is unstable to tilting. As the spheromaks tilt, their magnetic fields begin to reconnect at the null, subsequently displacing both the null and the reconnection site. The motion of the reconnection region and the magnetic null are shown to be correlated, with stronger correlation and faster reconnection observed in plasmas with lower thermal to magnetic pressure ratio. It is also shown that ion inertial effects allow for yet faster reconnection, but do not qualitatively change the dynamics of the process. Implications of the coupling between moving magnetic nulls and reconnection sites, as well as of possible mechanisms for fast reconnection through a moving reconnection region, are discussed. The simulations are conducted using both single-fluid and Hall MHD plasma models within the HiFi multi-fluid modeling framework.
Three-dimensional magnetic reconnection through a moving magnetic null
Lukin, V. S.; Linton, M. G.
2011-11-01
A computational study of three-dimensional magnetic reconnection between two flux ropes through a moving reconnection site is presented. The configuration is considered in the context of two interacting spheromaks constrained by a perfectly conducting cylindrical boundary and oriented to form a single magnetic field null at its center. The initial magnetic field configuration is embedded into a uniform thermal plasma and is unstable to tilting. As the spheromaks tilt, their magnetic fields begin to reconnect at the null, subsequently displacing both the null and the reconnection site. The motion of the reconnection region and the magnetic null are shown to be correlated, with stronger correlation and faster reconnection observed in plasmas with lower thermal to magnetic pressure ratio. It is also shown that ion inertial effects allow for yet faster reconnection, but do not qualitatively change the dynamics of the process. Implications of the coupling between moving magnetic nulls and reconnection sites, as well as of possible mechanisms for fast reconnection through a moving reconnection region, are discussed. The simulations are conducted using both single-fluid and Hall MHD plasma models within the HiFi multi-fluid modeling framework.
Influence of Spontaneously Generated Turbulence on Magnetic Reconnection
Daughton, William; Roytershteyn, Vadim; Karimabadi, Homa
2012-10-01
The 3D dynamics of reconnection is examined for electron-positron plasmas within Harris sheet geometry with a guide field. This configuration is unstable to tearing modes at resonant surfaces across the layer, corresponding to oblique angles relative to 2D models. Vlasov theory predicts a spectrum of oblique modes which can destroy the flux surfaces and produce interacting flux ropes. These structures coalesce to larger scales leading to the continual formation and break-up of new current sheets and the generation of turbulence. The fluctuation spectrum is highly anisotropic and is characterized by two power-laws with a break at k di˜1, where di is the inertial length. In the large 3D simulations, the dissipation rate is reduced by ˜40% relative to small 2D cases which are steady and laminar. In both limits, the reconnection remains fast (i.e. Alfv'enic), is insensitive to the system size and ultimately occurs within inertial-scale current sheets. These results imply that the physics responsible for setting the time scale is not radically altered by the turbulence. However, the results indicate that a larger fraction of the magnetic energy is accessible in 3D and that many more particles are accelerated into the high energy tails due to the turbulence.
Turbulent transport in 2D collisionless guide field reconnection
Muñoz, P A; Kilian, P
2016-01-01
Transport in collisionless plasmas is usually called anomalous, being due to the interaction between the particles and the self-generated turbulence by their collective interactions. Because of its relevance for astrophysical and space plasmas, we explore the excitation of turbulence in current sheets prone to component- or guide-field reconnection, a process not well understood, yet. We analyze the anomalous transport properties by using 2.5D Particle-in-Cell (PiC) code simulations. We split off the mean, slow variation (in contrast to the fast turbulent fluctuations) of the macroscopic observables and determine the main transport terms of the generalized Ohm's law. We verify our findings by comparing with the independently determined slowing-down rate of the macroscopic currents and with the transport terms obtained by the first order correlations of the turbulent fluctuations. We find that the turbulence is most intense in the "low density" separatrix region of guide-field reconnection. It is excited by st...
Ergun, R. E.; Holmes, J. C.; Goodrich, K. A.; Wilder, F. D.; Stawarz, J. E.; Eriksson, S.; Newman, D. L.; Schwartz, S. J.; Goldman, M. V.; Sturner, A. P.; Malaspina, D. M.; Usanova, M. E.; Torbert, R. B.; Argall, M.; Lindqvist, P.-A.; Khotyaintsev, Y.; Burch, J. L.; Strangeway, R. J.; Russell, C. T.; Pollock, C. J.; Giles, B. L.; Dorelli, J. J. C.; Avanov, L.; Hesse, M.; Chen, L. J.; Lavraud, B.; Le Contel, O.; Retino, A.; Phan, T. D.; Eastwood, J. P.; Oieroset, M.; Drake, J.; Shay, M. A.; Cassak, P. A.; Nakamura, R.; Zhou, M.; Ashour-Abdalla, M.; André, M.
2016-06-01
We report observations from the Magnetospheric Multiscale satellites of large-amplitude, parallel, electrostatic waves associated with magnetic reconnection at the Earth's magnetopause. The observed waves have parallel electric fields (E||) with amplitudes on the order of 100 mV/m and display nonlinear characteristics that suggest a possible net E||. These waves are observed within the ion diffusion region and adjacent to (within several electron skin depths) the electron diffusion region. They are in or near the magnetosphere side current layer. Simulation results support that the strong electrostatic linear and nonlinear wave activities appear to be driven by a two stream instability, which is a consequence of mixing cold (plasma in the magnetosphere with warm (~100 eV) plasma from the magnetosheath on a freshly reconnected magnetic field line. The frequent observation of these waves suggests that cold plasma is often present near the magnetopause.
Borissov, A.; Kontar, E. P.; Threlfall, J.; Neukirch, T.
2017-09-01
The conversion of magnetic energy into other forms (such as plasma heating, bulk plasma flows, and non-thermal particles) during solar flares is one of the outstanding open problems in solar physics. It is generally accepted that magnetic reconnection plays a crucial role in these conversion processes. In order to achieve the rapid energy release required in solar flares, an anomalous resistivity, which is orders of magnitude higher than the Spitzer resistivity, is often used in magnetohydrodynamic (MHD) simulations of reconnection in the corona. The origin of Spitzer resistivity is based on Coulomb scattering, which becomes negligible at the high energies achieved by accelerated particles. As a result, simulations of particle acceleration in reconnection events are often performed in the absence of any interaction between accelerated particles and any background plasma. This need not be the case for scattering associated with anomalous resistivity caused by turbulence within solar flares, as the higher resistivity implies an elevated scattering rate. We present results of test particle calculations, with and without pitch angle scattering, subject to fields derived from MHD simulations of two-dimensional (2D) X-point reconnection. Scattering rates proportional to the ratio of the anomalous resistivity to the local Spitzer resistivity, as well as at fixed values, are considered. Pitch angle scattering, which is independent of the anomalous resistivity, causes higher maximum energies in comparison to those obtained without scattering. Scattering rates which are dependent on the local anomalous resistivity tend to produce fewer highly energised particles due to weaker scattering in the separatrices, even though scattering in the current sheet may be stronger when compared to resistivity-independent scattering. Strong scattering also causes an increase in the number of particles exiting the computational box in the reconnection outflow region, as opposed to along the
Space weather. Ionospheric control of magnetotail reconnection.
Lotko, William; Smith, Ryan H; Zhang, Binzheng; Ouellette, Jeremy E; Brambles, Oliver J; Lyon, John G
2014-07-11
Observed distributions of high-speed plasma flows at distances of 10 to 30 Earth radii (R(E)) in Earth's magnetotail neutral sheet are highly skewed toward the premidnight sector. The flows are a product of the magnetic reconnection process that converts magnetic energy stored in the magnetotail into plasma kinetic and thermal energy. We show, using global numerical simulations, that the electrodynamic interaction between Earth's magnetosphere and ionosphere produces an asymmetry consistent with observed distributions in nightside reconnection and plasmasheet flows and in accompanying ionospheric convection. The primary causal agent is the meridional gradient in the ionospheric Hall conductance which, through the Cowling effect, regulates the distribution of electrical currents flowing within and between the ionosphere and magnetotail.
Magnetic reconnection: from MHD to QED
Bulanov, S. V.
2017-01-01
The paper examines the prospects of using laser plasmas for studying novel regimes of the magnetic field line reconnection and charged particle acceleration. Basic features of plasma dynamics in the three-dimensional configurations relevant to the formation of current sheets in a plasma are addressed by analyzing exact self-similar solutions of the magneto-hydrodynamics and electron magneto-hydrodynamics equations. Then the magnetic field annihilation in the ultrarelativistic limit is considered, when the opposite polarity magnetic field is generated in collisionless plasma by multiple laser pulses, in the regime with a dominant contribution of the displacement current exciting a strong large-scale electric field. This field leads to the conversion of the magnetic energy into the kinetic energy of accelerated particles inside a thin current sheet. Charged particle acceleration during magnetic field reconnection is discussed when radiation friction and quantum electrodynamics effects become dominant.
Magnetic reconnection in the near Venusian magnetotail.
Zhang, T L; Lu, Q M; Baumjohann, W; Russell, C T; Fedorov, A; Barabash, S; Coates, A J; Du, A M; Cao, J B; Nakamura, R; Teh, W L; Wang, R S; Dou, X K; Wang, S; Glassmeier, K H; Auster, H U; Balikhin, M
2012-05-04
Observations with the Venus Express magnetometer and low-energy particle detector revealed magnetic field and plasma behavior in the near-Venus wake that is symptomatic of magnetic reconnection, a process that occurs in Earth's magnetotail but is not expected in the magnetotail of a nonmagnetized planet such as Venus. On 15 May 2006, the plasma flow in this region was toward the planet, and the magnetic field component transverse to the flow was reversed. Magnetic reconnection is a plasma process that changes the topology of the magnetic field and results in energy exchange between the magnetic field and the plasma. Thus, the energetics of the Venus magnetotail resembles that of the terrestrial tail, where energy is stored and later released from the magnetic field to the plasma.
Magnetic reconnection: from MHD to QED
Bulanov, S V
2016-01-01
The paper examines the prospects of using laser plasmas for studying novel regimes of the magnetic field line reconnection and charged particle acceleration. Basic features of plasma dynamics in the three-dimensional configurations relevant to the formation of current sheets in a plasma are addressed by analyzing exact self-similar solutions of the magneto-hydrodynamics and electron magneto-hydrodynamics equations. Then the magnetic field annihilation in the ultrarelativistic limit is considered, when the opposite polarity magnetic field is generated in collisionless plasma by multiple laser pulses, in the regime with a dominant contribution of the displacement current exciting a strong large-scale electric field. This field leads to the conversion of the magnetic energy into the kinetic energy of accelerated particles inside a thin current sheet. Charged particle acceleration during magnetic field reconnection is discussed when radiation friction and quantum electrodynamics effects become dominant.
Introduction to Plasma Dynamo, Reconnection and Shocks
Energy Technology Data Exchange (ETDEWEB)
Intrator, Thomas P. [Los Alamos National Laboratory
2012-08-30
In our plasma universe, most of what we can observe is composed of ionized gas, or plasma. This plasma is a conducting fluid, which advects magnetic fields when it flows. Magnetic structure occurs from the smallest planetary to the largest cosmic scales. We introduce at a basic level some interesting features of non linear magnetohydrodynamics (MHD). For example, in our plasma universe, dynamo creates magnetic fields from gravitationally driven flow energy in an electrically conducting medium, and conversely magnetic reconnection annihilates magnetic field and accelerates particles. Shocks occur when flows move faster than the local velocity (sonic or Alfven speed) for the propagation of information. Both reconnection and shocks can accelerate particles, perhaps to gigantic energies, for example as observed with 10{sup 20} eV cosmic rays.
Theory of magnetic reconnection in solar and astrophysical plasmas.
Pontin, David I
2012-07-13
Magnetic reconnection is a fundamental process in a plasma that facilitates the release of energy stored in the magnetic field by permitting a change in the magnetic topology. In this paper, we present a review of the current state of understanding of magnetic reconnection. We discuss theoretical results regarding the formation of current sheets in complex three-dimensional magnetic fields and describe the fundamental differences between reconnection in two and three dimensions. We go on to outline recent developments in modelling of reconnection with kinetic theory, as well as in the magnetohydrodynamic framework where a number of new three-dimensional reconnection regimes have been identified. We discuss evidence from observations and simulations of Solar System plasmas that support this theory and summarize some prominent locations in which this new reconnection theory is relevant in astrophysical plasmas.
Reconnection outflow generated turbulence in the solar wind
Vörös, Z; Semenov, V S; Zaqarashvili, T V; Bruno, R; Khodachenko, M
2014-01-01
Petschek-type time-dependent reconnection (TDR) and quasi-stationary reconnection (QSR) models are considered to understand reconnection outflow structures and the features of the associated locally generated turbulence in the solar wind. We show that the outflow structures, such as discontinuites, Kelvin-Helmholtz (KH) unstable flux tubes or continuous space filling flows cannot be distinguished from one-point WIND measurements. In both models the reconnection outflows can generate more or less spatially extended turbulent boundary layers (TBDs). The structure of an unique extended reconnection outflow is investigated in detail. The analysis of spectral scalings and break locations show that reconnection outflows can control the local field and plasma conditions which may play in favor of one or another turbulent dissipation mechanisms with their characteristic scales and wavenumbers.
Start-Time of Magnetic Reconnection in Interplanetary Space
Institute of Scientific and Technical Information of China (English)
范全林; 魏奉思; 冯学尚
2003-01-01
Start-time of magnetic reconnection under typical interplanetary parameters has been numerically simulated by using the two-dimensional compressible magnetohydrodynamic equations with a third-order compact upwind scheme. Magnetic reconnection would occur near the interplanetary current sheet impacted by a plasmoid.Its initiation is associated with the interplanetary plasma parameter β and the momentum of the plasmoid.The higher the β value is, the faster the reconnection takes place. Meanwhile the reconnection occurs earlier with increasing the plasmoid momentum, and increasing driving velocity is more effective in initializing the reconnection than that of the plasma density when the other factors are kept to be the same. The evolution of the reconnection with the heliocentric distance is also investigated.
Particle trajectories and acceleration during 3D fan reconnection
Dalla, S; 10.1051/0004-6361:200809771
2008-01-01
Context. The primary energy release in solar flares is almost certainly due to magnetic reconnection, making this a strong candidate as a mechanism for particle acceleration. While particle acceleration in 2D geometries has been widely studied, investigations in 3D are a recent development. Two main classes of reconnection regimes at a 3D magnetic null point have been identified: fan and spine reconnection Aims. Here we investigate particle trajectories and acceleration during reconnection at a 3D null point, using a test particle numerical code, and compare the efficiency of the fan and spine regimes in generating an energetic particle population. Methods. We calculated the time evolution of the energy spectra. We discuss the geometry of particle escape from the two configurations and characterise the trapped and escaped populations. Results. We find that fan reconnection is less efficent than spine reconnection in providing seed particles to the region of strong electric field where acceleration is possible...
Shocks and Thermal Conduction Fronts in Retracting Reconnected Flux Tubes
Guidoni, Silvina
2010-01-01
We present a model for plasma heating produced by time-dependent, spatially localized reconnection within a flare current sheet separating skewed magnetic fields. The reconnection creates flux tubes of new connectivity which subsequently retract at Alfv\\'enic speeds from the reconnection site. Heating occurs in gas-dynamic shocks which develop inside these tubes. Here we present generalized thin flux tube equations for the dynamics of reconnected flux tubes, including pressure-driven parallel dynamics as well as temperature dependent, anisotropic viscosity and thermal conductivity. The evolution of tubes embedded in a uniform, skewed magnetic field, following reconnection in a patch, is studied through numerical solutions of these equations, for solar coronal conditions. Even though viscosity and thermal conductivity are negligible in the quiet solar corona, the strong gas-dynamic shocks generated by compressing plasma inside reconnected flux tubes generate large velocity and temperature gradients along the t...
Observational Aspects of Magnetic Reconnection at the Earth's Magnetosphere
Souza, Vitor M.; Koga, Daiki; Gonzalez, Walter D.; Cardoso, Flavia R.
2017-08-01
Magnetic field reconnection has shown to be the dominant process in the solar wind-Earth's magnetosphere interaction. It enables mass, momentum, and energy exchange between different plasma regimes, and it is regarded as an efficient plasma acceleration and heating mechanism. Reconnection has been observed to occur in laboratory plasmas, at planetary magnetospheres in our Solar System, and the Sun. In this work, we focus on analyzing the characteristics of magnetic reconnection at the Earth's magnetosphere according to spaceborne observations in the vicinity of our planet. Firstly, the locations where magnetic field reconnection are expected to occur within the vast magnetospheric region are addressed, and is shown how they are influenced by changes in the interplanetary magnetic field direction. The main magnetic field and plasma signatures of magnetic reconnection are discussed from both theoretical and observational points of view. Spacecraft observations of ion inertial length scale reconnection are also presented.
Energy Technology Data Exchange (ETDEWEB)
Horiuchi, Ritoku; Sato, Tetsuya [Theory and Computer Simulation Center, National Inst. for Fusion Science, Toki, Gifu (Japan)
1999-06-01
Generation of anomalous resistivity and dynamical development of collisionless reconnection in the vicinity of a magnetically neutral sheet are investigated by means of a three-dimensional particle simulation. For no external driving source, two different types of plasma instabilities are excited in the current layer. The lower hybrid drift instability (LHDI) is observed to grow in the periphery of current layer in an early period, while a drift kink instability (DKI) is triggered at the neutral sheet in a late period as a result of the nonlinear deformation of the current sheet by the LHDI. A reconnection electric field grows at the neutral sheet in accordance with the excitation of the DKI. When an external driving field exists, the convective electric field penetrates into the current layer through the particle kinetic effect and collisionless reconnection is triggered by the convective electric field earlier than the DKI is excited. It is also found that the anisotropic ion distribution is formed through the anomalous ion heating by the DKI. (author)
Evidence for Solar Tether-cutting Magnetic Reconnection from Coronal Field Extrapolations
Liu, Chang; Lee, Jeongwoo; Wiegelmann, Thomas; Moore, Ronald L; Wang, Haimin
2013-01-01
Magnetic reconnection is one of the primary mechanisms for triggering solar eruptive events, but direct observation of its rapid process has been of challenge. In this Letter we present, using a nonlinear force-free field (NLFFF) extrapolation technique, a visualization of field line connectivity changes resulting from tether-cutting reconnection over about 30 minutes during the 2011 February 13 M6.6 flare in NOAA AR 11158. Evidence for the tether-cutting reconnection was first collected through multiwavelength observations and then by the analysis of the field lines traced from positions of four conspicuous flare 1700 A footpoints observed at the event onset. Right before the flare, the four footpoints are located very close to the regions of local maxima of magnetic twist index. Especially, the field lines from the inner two footpoints form two strongly twisted flux bundles (up to ~1.2 turns), which shear past each other and reach out close to the outer two footpoints, respectively. Immediately after the fl...
Existence of two MHD reconnection modes in a solar 3D magnetic null point topology
Pariat, Etienne; Antiochos, Spiro; DeVore, C. Richard; Dalmasse, Kévin
2012-07-01
Magnetic topologies with a 3D magnetic null point are common in the solar atmosphere and occur at different spatial scales: such structures can be associated with some solar eruptions, with the so-called pseudo-streamers, and with numerous coronal jets. We have recently developed a series of numerical experiments that model magnetic reconnection in such configurations in order to study and explain the properties of jet-like features. Our model uses our state-of-the-art adaptive-mesh MHD solver ARMS. Energy is injected in the system by line-tied motion of the magnetic field lines in a corona-like configuration. We observe that, in the MHD framework, two reconnection modes eventually appear in the course of the evolution of the system. A very impulsive one, associated with a highly dynamic and fully 3D current sheet, is associated with the energetic generation of a jet. Before and after the generation of the jet, a quasi-steady reconnection mode, more similar to the standard 2D Sweet-Parker model, presents a lower global reconnection rate. We show that the geometry of the magnetic configuration influences the trigger of one or the other mode. We argue that this result carries important implications for the observed link between observational features such as solar jets, solar plumes, and the emission of coronal bright points.
Ng, Jonathan; Hakim, Ammar; Bhattacharjee, Amitava; Stanier, Adam; Daughton, William; Wang, Liang; Germaschewski, Kai
2015-01-01
As modeling of collisionless magnetic reconnection in most space plasmas with realistic parameters is beyond the capability of today's simulations, due to the separation between global and kinetic length scales, it is important to establish scaling relations in model problems so as to extrapolate to realistic scales. Recently, large scale particle-in-cell (PIC) simulations of island coalescence have shown that the time averaged reconnection rate decreases with system size, while fluid systems at such large scales in the Hall regime have not been studied. Here we perform the complementary resistive MHD, Hall MHD and two fluid simulations using a ten-moment model with the same geometry. In contrast to the standard Harris sheet reconnection problem, Hall MHD is insufficient to capture the physics of the reconnection region. Additionally, motivated by the results of a recent set of hybrid simulations which show the importance of ion kinetics in this geometry, we evaluate the efficacy of the ten-moment model in re...
Impact of the Eulerian chaos of magnetic field lines in magnetic reconnection
Firpo, M.-C.; Ettoumi, W.; Lifschitz, A. F.; Retinò, A.; Farengo, R.; Ferrari, H. E.; García-Martínez, P. L.
2016-12-01
Stochasticity is an ingredient that may allow the breaking of the frozen-in law in the reconnection process. It will first be argued that the non-ideal effects may be considered as an implicit way to introduce stochasticity. Yet there also exists an explicit stochasticity that does not require the invocation of non-ideal effects. This comes from the spatial (or Eulerian) chaos of magnetic field lines that can show up only in a truly three-dimensional description of magnetic reconnection since the two-dimensional models impose the integrability of the magnetic field lines. Some implications of this magnetic braiding, such as the increased particle finite-time Lyapunov exponents and increased acceleration of charged particles, are discussed in the frame of tokamak sawteeth that forms a laboratory prototype of spontaneous magnetic reconnection. A justification for an increased reconnection rate with chaotic vs. the integrable magnetic field lines is proposed. Moreover, in 3D, the Eulerian chaos of the magnetic field lines may coexist with the Eulerian chaos of velocity field lines, that is more commonly named the turbulence.
Resistive magnetohydrodynamic simulations of X-line retreat during magnetic reconnection
Murphy, N A
2010-01-01
To investigate the impact of current sheet motion on the reconnection process, we perform resistive magnetohydrodynamic (MHD) simulations of two closely located reconnection sites which move apart from each other as reconnection develops. This simulation develops less quickly than an otherwise equivalent single perturbation simulation but eventually exhibits a higher reconnection rate. The unobstructed outflow jets are faster and longer than the outflow jets directed towards the magnetic island that forms between the two current sheets. The X-line and flow stagnation point are located near the trailing end of each current sheet very close to the obstructed exit. The speed of X-line retreat ranges from ~0.02-0.06 while the speed of stagnation point retreat ranges from ~0.03-0.07, in units of the initial upstream Alfven velocity. Early in time, the flow stagnation point is located closer to the center of the current sheet than the X-line, but later on the relative positions of these two points switch. Consequen...
Energy Technology Data Exchange (ETDEWEB)
Ng, Jonathan; Huang, Yi-Min; Hakim, Ammar; Bhattacharjee, A. [Center for Heliophysics, Princeton Plasma Physics Laboratory, Princeton, New Jersey 08540 (United States); Stanier, Adam; Daughton, William [Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Wang, Liang; Germaschewski, Kai [Space Science Center and Physics Department, University of New Hampshire, Durham, New Hampshire 03824 (United States)
2015-11-15
As modeling of collisionless magnetic reconnection in most space plasmas with realistic parameters is beyond the capability of today's simulations, due to the separation between global and kinetic length scales, it is important to establish scaling relations in model problems so as to extrapolate to realistic scales. Recently, large scale particle-in-cell simulations of island coalescence have shown that the time averaged reconnection rate decreases with system size, while fluid systems at such large scales in the Hall regime have not been studied. Here, we perform the complementary resistive magnetohydrodynamic (MHD), Hall MHD, and two fluid simulations using a ten-moment model with the same geometry. In contrast to the standard Harris sheet reconnection problem, Hall MHD is insufficient to capture the physics of the reconnection region. Additionally, motivated by the results of a recent set of hybrid simulations which show the importance of ion kinetics in this geometry, we evaluate the efficacy of the ten-moment model in reproducing such results.
Magnetic reconnection and stochastic plasmoid chains in high-Lundquist-number plasmas
Loureiro, N. F.
2012-04-13
A numerical study of magnetic reconnection in the large-Lundquist-number (S), plasmoid-dominated regime is carried out for S up to 10 7. The theoretical model of Uzdensky [Phys. Rev. Lett. 105, 235002 (2010)] is confirmed and partially amended. The normalized reconnection rate is Ẽ eff ∼ 0.02 independently of S for S ≫ 10 4. The plasmoid flux (ψ) and half-width (w x) distribution functions scale as f (ψ) ∼ - ψ -2 and f (w x) ∼ w x -2. The joint distribution of ψ and w x shows that plasmoids populate a triangular region w x ≲ψ/B 0, where B 0 is the reconnecting field. It is argued that this feature is due to plasmoid coalescence. Macroscopic "monster" plasmoids with w x ∼ 10 % of the system size are shown to emerge in just a few Alfvén times, independently of S, suggesting that large disruptive events are an inevitable feature of large-S reconnection. © 2012 American Institute of Physics.
CICART Center For Integrated Computation And Analysis Of Reconnection And Turbulence
Energy Technology Data Exchange (ETDEWEB)
Bhattacharjee, Amitava [Univ. of New Hampshire, Durham, NH (United States)
2016-03-27
CICART is a partnership between the University of New Hampshire (UNH) and Dartmouth College. CICART addresses two important science needs of the DoE: the basic understanding of magnetic reconnection and turbulence that strongly impacts the performance of fusion plasmas, and the development of new mathematical and computational tools that enable the modeling and control of these phenomena. The principal participants of CICART constitute an interdisciplinary group, drawn from the communities of applied mathematics, astrophysics, computational physics, fluid dynamics, and fusion physics. It is a main premise of CICART that fundamental aspects of magnetic reconnection and turbulence in fusion devices, smaller-scale laboratory experiments, and space and astrophysical plasmas can be viewed from a common perspective, and that progress in understanding in any of these interconnected fields is likely to lead to progress in others. The establishment of CICART has strongly impacted the education and research mission of a new Program in Integrated Applied Mathematics in the College of Engineering and Applied Sciences at UNH by enabling the recruitment of a tenure-track faculty member, supported equally by UNH and CICART, and the establishment of an IBM-UNH Computing Alliance. The proposed areas of research in magnetic reconnection and turbulence in astrophysical, space, and laboratory plasmas include the following topics: (A) Reconnection and secondary instabilities in large high-Lundquist-number plasmas, (B) Particle acceleration in the presence of multiple magnetic islands, (C) Gyrokinetic reconnection: comparison with fluid and particle-in-cell models, (D) Imbalanced turbulence, (E) Ion heating, and (F) Turbulence in laboratory (including fusion-relevant) experiments. These theoretical studies make active use of three high performance computer simulation codes: (1) The Magnetic Reconnection Code, based on extended two-fluid (or Hall MHD) equations, in an Adaptive Mesh
CICART Center For Integrated Computation And Analysis Of Reconnection And Turbulence
Energy Technology Data Exchange (ETDEWEB)
Bhattacharjee, Amitava [Univ. of New Hampshire, Durham, NH (United States)
2016-03-27
CICART is a partnership between the University of New Hampshire (UNH) and Dartmouth College. CICART addresses two important science needs of the DoE: the basic understanding of magnetic reconnection and turbulence that strongly impacts the performance of fusion plasmas, and the development of new mathematical and computational tools that enable the modeling and control of these phenomena. The principal participants of CICART constitute an interdisciplinary group, drawn from the communities of applied mathematics, astrophysics, computational physics, fluid dynamics, and fusion physics. It is a main premise of CICART that fundamental aspects of magnetic reconnection and turbulence in fusion devices, smaller-scale laboratory experiments, and space and astrophysical plasmas can be viewed from a common perspective, and that progress in understanding in any of these interconnected fields is likely to lead to progress in others. The establishment of CICART has strongly impacted the education and research mission of a new Program in Integrated Applied Mathematics in the College of Engineering and Applied Sciences at UNH by enabling the recruitment of a tenure-track faculty member, supported equally by UNH and CICART, and the establishment of an IBM-UNH Computing Alliance. The proposed areas of research in magnetic reconnection and turbulence in astrophysical, space, and laboratory plasmas include the following topics: (A) Reconnection and secondary instabilities in large high-Lundquist-number plasmas, (B) Particle acceleration in the presence of multiple magnetic islands, (C) Gyrokinetic reconnection: comparison with fluid and particle-in-cell models, (D) Imbalanced turbulence, (E) Ion heating, and (F) Turbulence in laboratory (including fusion-relevant) experiments. These theoretical studies make active use of three high-performance computer simulation codes: (1) The Magnetic Reconnection Code, based on extended two-fluid (or Hall MHD) equations, in an Adaptive Mesh
Dynamics of Quantized Vortices Before Reconnection
Andryushchenko, V. A.; Kondaurova, L. P.; Nemirovskii, S. K.
2016-12-01
The main goal of this paper is to investigate numerically the dynamics of quantized vortex loops, just before the reconnection at finite temperature, when mutual friction essentially changes the evolution of lines. Modeling is performed on the base of vortex filament method using the full Biot-Savart equation. It was discovered that the initial position of vortices and the temperature strongly affect the dependence on time of the minimum distance δ (t) between tips of two vortex loops. In particular, in some cases, the shrinking and collapse of vortex loops due to mutual friction occur earlier than the reconnection, thereby canceling the latter. However, this relationship takes a universal square-root form δ ( t) =√{( κ /2π ) ( t_{*}-t) } at distances smaller than the distances, satisfying the Schwarz reconnection criterion, when the nonlocal contribution to the Biot-Savart equation becomes about equal to the local contribution. In the "universal" stage, the nearest parts of vortices form a pyramid-like structure with angles which neither depend on the initial configuration nor on temperature.
Vortex tube reconnection at Re = 104
van Rees, Wim M.; Hussain, Fazle; Koumoutsakos, Petros
2012-07-01
We present simulations of the long-time dynamics of two anti-parallel vortex tubes with and without initial axial flow, at Reynolds number Re = Γ/ν = 104. Simulations were performed in a periodic domain with a remeshed vortex method using 785 × 106 particles. We quantify the vortex dynamics of the primary vortex reconnection that leads to the formation of elliptical rings with axial flow and report for the first time a subsequent collision of these rings. In the absence of initial axial flow, a -5/3 slope of the energy spectrum is observed during the first reconnection of the tubes. The resulting elliptical vortex rings experience a coiling of their vortex lines imparting an axial flow inside their cores. These rings eventually collide, exhibiting a -7/3 slope of the energy spectrum. Studies of vortex reconnection with an initial axial flow exhibit also the -7/3 slope during the initial collision as well as in the subsequent collision of the ensuing elliptical vortex rings. We quantify the detailed vortex dynamics of these collisions and examine the role of axial flow in the breakup of vortex structures.
Fermi Acceleration in Magnetic Reconnection Sites
de Gouveia Dal Pino, E. M.; Kowal, G.; Lazarian, A.
2014-09-01
The mechanisms that accelerate cosmic relativistic particles are not fully understood yet. A variety of processes has been investigated and the acceleration in magnetic reconnection sites has lately gained increasing attention from researchers not only for its potential importance in the solar system, but also beyond it, in astrophysical environments like compact stellar sources, AGNs and GRBs, and even in diffusive magnetized media as the interstellar medium (ISM) and the intergalactic medium (IGM). In this talk we review this process and, supported by three-dimensional MHD simulations with the injection of thousands of test particles, we show that they can be efficiently accelerated by magnetic reconnection through a first-order Fermi process within large scale magnetic current sheets, even in a collisional fluid (contrary to what was previously believed), especially when local turbulence is present which makes reconnection fast, the acceleration layer thicker and the overall process naturally three-dimensional. Tests of particle acceleration in pure MHD turbulent environments (i.e., without the presence of large scale current sheets), on the other hand, indicate that the dominant acceleration process is a second-order Fermi.
Shear-Driven Reconnection in Kinetic Models
Black, C.; Antiochos, S. K.; Germaschewski, K.; Karpen, J. T.; DeVore, C. R.; Bessho, N.
2015-12-01
The explosive energy release in solar eruptive phenomena is believed to be due to magnetic reconnection. In the standard model for coronal mass ejections (CME) and/or solar flares, the free energy for the event resides in the strongly sheared magnetic field of a filament channel. The pre-eruption force balance consists of an upward force due to the magnetic pressure of the sheared field countered by a downward tension due to overlying unsheared field. Magnetic reconnection disrupts this force balance; therefore, it is critical for understanding CME/flare initiation, to model the onset of reconnection driven by the build-up of magnetic shear. In MHD simulations, the application of a magnetic-field shear is a trivial matter. However, kinetic effects are dominant in the diffusion region and thus, it is important to examine this process with PIC simulations as well. The implementation of such a driver in PIC methods is challenging, however, and indicates the necessity of a true multiscale model for such processes in the solar environment. The field must be sheared self-consistently and indirectly to prevent the generation of waves that destroy the desired system. Plasma instabilities can arise nonetheless. In the work presented here, we show that we can control this instability and generate a predicted out-of-plane magnetic flux. This material is based upon work supported by the National Science Foundation under Award No. AGS-1331356.
On the location of dayside magnetic reconnection during an interval of duskward oriented IMF
Directory of Open Access Journals (Sweden)
J. A. Wild
2007-02-01
Full Text Available We present space- and ground-based observations of the signatures of magnetic reconnection during an interval of duskward-oriented interplanetary magnetic field on 25 March 2004. In situ field and plasma measurements are drawn from the Double Star and Cluster satellites during traversals of the pre-noon sector dayside magnetopause at low and high latitudes, respectively. These reveal the typical signatures of flux transfer events (FTEs, namely bipolar perturbations in the magnetic field component normal to the local magnetopause, enhancements in the local magnetic field strength and mixing of magnetospheric and magnetosheath plasmas. Further evidence of magnetic reconnection is inferred from the ground-based signatures of pulsed ionospheric flow observed over an extended interval. In order to ascertain the location of the reconnection site responsible for the FTEs, a simple model of open flux tube motion over the surface of the magnetopause is employed. A comparison of the modelled and observed motion of open flux tubes (i.e. FTEs and plasma flow in the magnetopause boundary layer indicates that the FTEs observed at both low and high latitudes were consistence with the existence of a tilted X-line passing through the sub-solar region, as suggested by the component reconnection paradigm. While a high latitude X-line (as predicted by the anti-parallel description of reconnection may have been present, we find it unlikely that it could have been responsible for the FTEs observed in the pre-noon sector under the observed IMF conditions. Finally, we note that throughout the interval, the magnetosphere was bathed in ULF oscillations within the solar wind electric field. While no one-to-one correspondence with the pulsed reconnection rate suggested by the ground-based observation of pulsed ionospheric flow has been demonstrated, we note that similar periodicity oscillations were observed throughout the solar wind-magnetosphere-ionosphere system. These
Self-Feeding Turbulent Magnetic Reconnection on Macroscopic Scales
Lapenta, Giovanni
2008-01-01
Within a MHD approach we find magnetic reconnection to progress in two entirely different ways. The first is well-known: the laminar Sweet-Parker process. But a second, completely different and chaotic reconnection process is possible. This regime has properties of immediate practical relevance: i) it is much faster, developing on scales of the order of the Alfv\\'en time, and ii) the areas of reconnection become distributed chaotically over a macroscopic region. The onset of the faster process is the formation of closed circulation patterns where the jets going out of the reconnection regions turn around and forces their way back in, carrying along copious amounts of magnetic flux.
Turbulent transport in 2D collisionless guide field reconnection
Muñoz, P. A.; Büchner, J.; Kilian, P.
2017-02-01
Transport in hot and dilute, i.e., collisionless, astrophysical and space, plasmas is called "anomalous." This transport is due to the interaction between the particles and the self-generated turbulence by their collective interactions. The anomalous transport has very different and not well known properties compared to the transport due to binary collisions, dominant in colder and denser plasmas. Because of its relevance for astrophysical and space plasmas, we explore the excitation of turbulence in current sheets prone to component- or guide-field reconnection, a process not well understood yet. This configuration is typical for stellar coronae, and it is created in the laboratory for which a 2.5D geometry applies. In our analysis, in addition to the immediate vicinity of the X-line, we also include regions outside and near the separatrices. We analyze the anomalous transport properties by using 2.5D Particle-in-Cell code simulations. We split off the mean slow variation (in contrast to the fast turbulent fluctuations) of the macroscopic observables and determine the main transport terms of the generalized Ohm's law. We verify our findings by comparing with the independently determined slowing-down rate of the macroscopic currents (due to a net momentum transfer from particles to waves) and with the transport terms obtained by the first order correlations of the turbulent fluctuations. We find that the turbulence is most intense in the "low density" separatrix region of guide-field reconnection. It is excited by streaming instabilities, is mainly electrostatic and "patchy" in space, and so is the associated anomalous transport. Parts of the energy exchange between turbulence and particles are reversible and quasi-periodic. The remaining irreversible anomalous resistivity can be parametrized by an effective collision rate ranging from the local ion-cyclotron to the lower-hybrid frequency. The contributions to the parallel and the perpendicular (to the magnetic
Jet deflection by very weak guide fields during magnetic reconnection.
Goldman, M V; Lapenta, G; Newman, D L; Markidis, S; Che, H
2011-09-23
Previous 2D simulations of reconnection using a standard model of initially antiparallel magnetic fields have detected electron jets outflowing from the x point into the ion outflow exhausts. Associated with these jets are extended "outer electron diffusion regions." New PIC simulations with an ion to electron mass ratio as large as 1836 (an H(+) plasma) now show that the jets are strongly deflected and the outer electron diffusion region is broken up by a very weak out-of-plane magnetic guide field, even though the diffusion rate itself is unchanged. Jet outflow and deflection are interpreted in terms of electron dynamics and are compared to recent measurements of jets in the presence of a small guide field in Earth's magnetosheath.
Directory of Open Access Journals (Sweden)
V.C. Kunz
2012-05-01
Full Text Available The objectives of this study were to evaluate and compare the use of linear and nonlinear methods for analysis of heart rate variability (HRV in healthy subjects and in patients after acute myocardial infarction (AMI. Heart rate (HR was recorded for 15 min in the supine position in 10 patients with AMI taking β-blockers (aged 57 ± 9 years and in 11 healthy subjects (aged 53 ± 4 years. HRV was analyzed in the time domain (RMSSD and RMSM, the frequency domain using low- and high-frequency bands in normalized units (nu; LFnu and HFnu and the LF/HF ratio and approximate entropy (ApEn were determined. There was a correlation (P < 0.05 of RMSSD, RMSM, LFnu, HFnu, and the LF/HF ratio index with the ApEn of the AMI group on the 2nd (r = 0.87, 0.65, 0.72, 0.72, and 0.64 and 7th day (r = 0.88, 0.70, 0.69, 0.69, and 0.87 and of the healthy group (r = 0.63, 0.71, 0.63, 0.63, and 0.74, respectively. The median HRV indexes of the AMI group on the 2nd and 7th day differed from the healthy group (P < 0.05: RMSSD = 10.37, 19.95, 24.81; RMSM = 23.47, 31.96, 43.79; LFnu = 0.79, 0.79, 0.62; HFnu = 0.20, 0.20, 0.37; LF/HF ratio = 3.87, 3.94, 1.65; ApEn = 1.01, 1.24, 1.31, respectively. There was agreement between the methods, suggesting that these have the same power to evaluate autonomic modulation of HR in both AMI patients and healthy subjects. AMI contributed to a reduction in cardiac signal irregularity, higher sympathetic modulation and lower vagal modulation.
Poor glycemic control impacts linear and non-linear dynamics of heart rate in DM type 2
Directory of Open Access Journals (Sweden)
Daniela Bassi
2015-08-01
Full Text Available INTRODUCTION: It is well known that type 2 diabetes mellitus (T2DM produces cardiovascular autonomic neuropathy (CAN, which may affect the cardiac autonomic modulation. However, it is unclear whether the lack of glycemic control in T2DM without CAN could impact negatively on cardiac autonomic modulation. Objective: To evaluate the relationship between glycemic control and cardiac autonomic modulation in individuals with T2DM without CAN. Descriptive, prospective and cross sectional study.METHODS: Forty-nine patients with T2DM (51±7 years were divided into two groups according to glycosylated hemoglobin (HbA1c: G1≤7% and G2>7.0%. Resting heart rate (HR and RR interval (RRi were obtained and calculated by linear (Mean iRR; Mean HR; rMSSD; STD RR; LF; HF; LF/HF, TINN and RR Tri, and non-linear (SD1; SD2; DFα1; DFα2, Shannon entropy; ApEn; SampEn and CD methods of heart rate variability (HRV. Insulin, HOMA-IR, fasting glucose and HbA1c were obtained by blood tests.RESULTS: G2 (HbA1c≤7% showed lower values for the mean of iRR; STD RR; RR Tri, TINN, SD2, CD and higher mean HR when compared with G1 (HbA1c > 7%. Additionally, HbA1c correlated negatively with mean RRi (r=0.28, p=0.044; STD RR (r=0.33, p=0.017; RR Tri (r=-0.35, p=0.013, SD2 (r=-0.39, p=0.004 and positively with mean HR (r=0.28, p=0.045. Finally, fasting glucose correlated negatively with STD RR (r=-0.36, p=0.010; RR Tri (r=-0.36, p=0.010; TINN (r=-0.33, p=0.019 and SD2 (r=-0.42, p=0.002.CONCLUSION: We concluded that poor glycemic control is related to cardiac autonomic modulation indices in individuals with T2DM even if they do not present cardiovascular autonomic neuropathy.
Pulsating Reconnection in the interaction of Two Magnetic Fux Ropes.
Gekelman, W. N.; DeHaas, T.; Daughton, W. S.; Van Compernolle, B.
2015-12-01
Two flux ropes (dia = 7 cm, ds= 3 cm, L = 10m, Irope = 300 A/rope) are generated by using a mask in front of a high emissivity cathode (n = 4X1012 cm3, Te-rope = 8.5 eV) in a background magnetoplasma (He, Boz= 330 G, n=1.0X1012 cm3, Te = 4 eV) in the LAPD device at UCLA. The ropes are kink unstable ( I > 250 A) but not violently so. All three components of the magnetic field were measured with small (1 mm dia) 3-axis probes sensitive to and the plasma potential measured with an emissive probe. These were measured at over 42,000 locations in the volume containing the ropes and 7000 time steps (δτ = .33 μs). The total electric field and parallel resistivity as well as the Quasi Seperatrix layer (QSL) were derived from the data. The flux ropes periodically collide as they rotate about when another and kink. Each time this happens a strong QSL (Q<400) forms and the resistivity jumps to over a hundred times the classical value at locations within the QSL and also on the gradient of the rope current. The QSL formation and 3D electric fields are presented as a function of space and time. The reconnection rate is directly evaluated by integrating the electric field along field lines as well as the energy deposition . The data indicate that there is more than one process causing the enhanced resistivity. The reconnection rate cannot be explained by conventional 2D theories.
Study of Lower Hybrid Frequency Turbulence in the Magnetic Reconnection Experiment (MRX)
Dorfman, S. E.; Ji, H.; Roytershteyn, V.; Yamada, M.; Daughton, W. S.; Yoo, J.; Oz, E.; Tharp, T.; Lawrence, E. E.; Myers, C.
2010-12-01
One of the key open questions in magnetic reconnection is the nature of the mechanism that governs the reconnection rate in real astrophysical and laboratory systems. Comparisons between fully kinetic 2-D simulations of the Magnetic Reconnection Experiment (MRX) and experimental data indicate that three-dimensional dynamics, such as current layer disruptions recently observed in MRX, may play a key role in resolving an important discrepancy in the reconnection rate and layer width [1,2,3]. These disruptions are often associated with fluctuations in the lower hybrid frequency range and a rapid local reconnection rate. Fluctuations are observed not only in MRX [4], but also in space [5] and 3-D kinetic simulations. Comparison of fluctuation characteristics between the three domains may shed light on the underlying physics. In both the simulation and the experiments, the fluctuations are related to density gradients across the layer. The frequency range is similarly broadband up to the lower hybrid range, and the phase velocities are comparable in appropriately normalized units. However, while the electron drift speed is comparable to the phase velocity at the layer center in the experiment (consistent with previous MRX results [4]), the drift speed in the simulations is considerably larger. Furthermore, the fluctuations observed in the experiment are fully turbulent with correlation lengths the same order as the wavelength while those observed in the simulations and in space are more coherent. Some discharges also display "O-point" signatures consistent with magnetic island like structures. The present research explores the relationship between the disruptions and fluctuations in the context of the reconnection rate problem. Experiments are ongoing to determine what physics is responsible for the broader current layers (and correspondingly smaller drift speeds) observed in the experiment. [1] Y. Ren, et al., Phys. Plasmas 15, 082113 (2008). [2] S. Dorfman, et al
Direct evidence for kinetic effects associated with solar wind reconnection.
Xu, Xiaojun; Wang, Yi; Wei, Fengsi; Feng, Xueshang; Deng, Xiaohua; Ma, Yonghui; Zhou, Meng; Pang, Ye; Wong, Hon-Cheng
2015-01-28
Kinetic effects resulting from the two-fluid physics play a crucial role in the fast collisionless reconnection, which is a process to explosively release massive energy stored in magnetic fields in space and astrophysical plasmas. In-situ observations in the Earth's magnetosphere provide solid consistence with theoretical models on the point that kinetic effects are required in the collisionless reconnection. However, all the observations associated with solar wind reconnection have been analyzed in the context of magnetohydrodynamics (MHD) although a lot of solar wind reconnection exhausts have been reported. Because of the absence of kinetic effects and substantial heating, whether the reconnections are still ongoing when they are detected in the solar wind remains unknown. Here, by dual-spacecraft observations, we report a solar wind reconnection with clear Hall magnetic fields. Its corresponding Alfvenic electron outflow jet, derived from the decouple between ions and electrons, is identified, showing direct evidence for kinetic effects that dominate the collisionless reconnection. The turbulence associated with the exhaust is a kind of background solar wind turbulence, implying that the reconnection generated turbulence has not much developed.
A Model for Patchy Reconnection in Three Dimensions
Linton, M G
2005-01-01
We show, theoretically and via MHD simulations, how a short burst of reconnection localized in three dimensions on a one-dimensional current sheet creates a pair of reconnected flux tubes. We focus on the post-reconnection evolution of these flux tubes, studying their velocities and shapes. We find that slow-mode shocks propagate along these reconnected flux tubes, releasing magnetic energy as in steady-state Petschek reconnection. The geometry of these three-dimensional shocks, however, differs dramatically from the classical two-dimensional geometry. They propagate along the flux tube legs in four isolated fronts, whereas in the two-dimensional Petschek model, they form a continuous, stationary pair of V-shaped fronts. We find that the cross sections of these reconnected flux tubes appear as teardrop shaped bundles of flux propagating away from the reconnection site. Based on this, we argue that the descending coronal voids seen by Yohkoh SXT, LASCO, and TRACE are reconnected flux tubes descending from a fl...
A Model for Patchy Reconnection in Three Dimensions
Linton, M. G.; Longcope, D. W.
2006-05-01
We show, theoretically and via MHD simulations, how a short burst of localized reconnection on a current sheet creates a pair of reconnected flux tubes. We focus on the post-reconnection evolution of these flux tubes, studying their velocities and shapes. We find that slow-mode shocks propagate along these reconnected flux tubes, releasing magnetic energy as in steady state Petschek reconnection. The geometry of these three-dimensional shocks, however, differs significantly from the classical two-dimensional geometry. They propagate along the flux tube legs in four isolated fronts, whereas in the two-dimensional Petschek model, they form a continuous, stationary pair of V-shaped fronts. We find that the cross sections of these reconnected flux tubes appear as teardrop-shaped bundles of flux propagating away from the reconnection site. Based on this, we argue that the descending coronal voids seen by Yohkoh SXT, LASCO, and TRACE are reconnected flux tubes descending from a flare site in the high corona, for example after a coronal mass ejection. In this model, these flux tubes would then settle into equilibrium in the low corona, forming an arcade of postflare coronal loops.
Sustained lobe reconnection in Saturn's magnetotail
Thomsen, M. F.; Jackman, C. M.; Mitchell, D. G.; Hospodarsky, G.; Kurth, W. S.; Hansen, K. C.
2015-12-01
The degree to which solar wind driving may affect Saturn's magnetosphere is not yet fully understood. We present observations that suggest that under some conditions the solar wind does govern the character of the plasma sheet in Saturn's outer magnetosphere. On 16 September 2006, the Cassini spacecraft, at a radial distance of 37 Rs near local midnight, observed a sunward flowing ion population for ~5 h, which was accompanied by enhanced Saturn Kilometric Radiation emissions. We interpret this beam as the outflow from a long-lasting episode of Dungey-type reconnection, i.e., reconnection of previously open flux containing magnetosheath material. The beam occurred in the middle of a several-day interval of SKR activity and enhanced lobe magnetic field strength, apparently caused by the arrival of a solar wind compression region with significantly higher than average dynamic pressure. The arrival of the high-pressure solar wind also marked a change in the composition of the plasma-sheet plasma, from water-group-dominated material clearly of inner-magnetosphere origin to material dominated by light-ion composition, consistent with captured magnetosheath plasma. This event suggests that under the influence of prolonged high solar wind dynamic pressure, the tail plasma sheet, which normally consists of inner-magnetospheric plasma, is eroded away by ongoing reconnection that then involves open lobe field lines. This process removes open magnetic flux from the lobes and creates a more Earth-like, Dungey-style outer plasma sheet dominantly of solar wind origin. This behavior is potentially a recurrent phenomenon driven by repeating high-pressure streams (corotating interaction regions) in the solar wind, which also drive geomagnetic storms at Earth.
Doss, C E; Swisdak, M
2016-01-01
We investigate magnetic reconnection in systems simultaneously containing asymmetric (anti-parallel) magnetic fields, asymmetric plasma densities and temperatures, and arbitrary in-plane bulk flow of plasma in the upstream regions. Such configurations are common in the high-latitudes of Earth's magnetopause and in tokamaks. We investigate the convection speed of the X-line, the scaling of the reconnection rate, and the condition for which the flow suppresses reconnection as a function of upstream flow speeds. We use two-dimensional particle-in-cell simulations to capture the mixing of plasma in the outflow regions better than is possible in fluid modeling. We perform simulations with asymmetric magnetic fields, simulations with asymmetric densities, and simulations with magnetopause-like parameters where both are asymmetric. For flow speeds below the predicted cutoff velocity, we find good scaling agreement with the theory presented in Doss et al., J.~Geophys.~Res., 120, 7748 (2015). Applications to planetary...
A 10-stage reconnection demonstration launcher
Energy Technology Data Exchange (ETDEWEB)
Cnare, E.C.; Widner, M.M.; Duggin, B.W.
1989-01-01
A small-scale, 10-stage cylindrical reconnection launcher has been designed, fabricated, and tested. Ten-gram projectiles are accelerated from rest to 317 m/s through the 0.44 m launcher assembly with a projectile kinetic energy to capacitor stored energy efficiency of 9%. Comparison of test results and computer code predictions will be presented. Results of these studies have substantiated launcher scaling at small size and have provided a useful test bed for launcher components and diagnostics. 5 refs., 6 figs.
Whistler Mode Waves in Collisionless Magnetic Reconnection
Institute of Scientific and Technical Information of China (English)
GUO Jun; LU Quan-Ming; WANG Shui; WANG Yu-Ming; DOU Xian-Kang
2004-01-01
A 21/2-dimensional electromagnetic particle-in-cell (PIC) simulation code is used to investigate the wave phenomena in the plasma sheet of collisionless magnetic reconnection. The results show that these waves have the following characteristics: they are right-hand circularity polarized, with propagation direction nearly parallel to local magnetic field, and frequency between 0.07 and 0.17 times of local electron cyclotron frequency. Therefore we conclude that such waves are Whistler waves, and their possible excitation mechanisms are also discussed.
Fluctuation dynamo based on magnetic reconnections
Baggaley, Andrew W.; Barenghi, Carlo F.; Shukurov, Anvar; Subramanian, Kandaswamy
2009-01-01
We develop a new model of the fluctuation dynamo in which the magnetic field is confined to thin flux ropes advected by a multi-scale flow which models turbulence. Magnetic dissipation occurs only via reconnections of flux ropes. The model is particularly suitable for rarefied plasma, such as the Solar corona or galactic halos. We investigate the kinetic energy release into heat, mediated by dynamo action, both in our model and by solving the induction equation with the same flow. We find tha...
Cluster observation of electron energization during the magnetospheric reconnection
Gurram, Harsha; Egedal, Jan
2016-10-01
In situ spacecraft measurements in the Earths magnetosphere have shown that magnetic reconnection energizes the electrons and a source of the suprathermal electrons. This study investigates the electron distribution functions and electron heating recorded by the Cluster Mission during the reconnection event on August 21, 2002 in the interval 0754 to 0825. This event exhibits a flow reversal with the characteristic isotropic flat-top distribution around the flow reversal namely near the X-line. The distribution function measurements near reconnection reveal the presence of cold beams directed towards the X-line while the energized electrons are seen to be moving away from the reconnection region. The electrons see an increase in their bulk energy by a factor of 100 from the inflow to exhaust. The observed beam like features are in good agreement with the kinetic simulations and confirm the model for electron energization in reconnection exhaust.
Cross-Scale Observational Signatures of Magnetic Reconnection
Savage, Sabrina; Malaspina, David
2014-01-01
Magnetic reconnection is a significant mechanism for energy release across many astrophysical applications. In the solar atmosphere, reconnection is considered a primary contributor of flare evolution and coronal heating. Directly observing reconnection occurring in the solar atmosphere, however, is not trivial considering that the scale size of the diffusion region is magnitudes smaller than the observational capabilities of current instrumentation, and coronal magnetic field measurements are not currently sufficient to capture the process. Meanwhile, reconnection occurring in the Earth's magnetosphere transfers energy from the solar wind through a comparable process, although on vastly different scales. Magnetospheric measurements are made in situ rather than remotely; ergo, comparison of observations between the two regimes allows for potentially significant insight into reconnection as a stochastic and possibly turbulent process. We will present a set of observations from long-duration solar events and compare them to in situ measurements from the magnetosphere.
Plasma compression in magnetic reconnection regions in the solar corona
Provornikova, Elena; Lukin, Vyacheslav S
2016-01-01
It has been proposed that particles bouncing between magnetized flows converging in a reconnection region can be accelerated by the first order Fermi mechanism. Analytical considerations of this mechanism have shown that the spectral index of accelerated particles is related to the total plasma compression within the reconnection region similarly to the case of diffusive shock acceleration mechanism. As a first step to investigate the efficiency of Fermi acceleration in reconnection regions in producing hard energy spectra of particles in the solar corona, we explore the degree of plasma compression that can be achieved at reconnection sites. In particular, we aim to determine the conditions for the strong compressions to form. Using a two-dimensional resistive MHD numerical model we consider a set of magnetic field configurations where magnetic reconnection can occur including a Harris current sheet, a force-free current sheet, and two merging flux ropes. Plasma parameters are taken to be characteristic of t...
Relativistic Reconnection: an Efficient Source of Non-Thermal Particles
Sironi, Lorenzo
2014-01-01
In magnetized astrophysical outflows, the dissipation of field energy into particle energy via magnetic reconnection is often invoked to explain the observed non-thermal signatures. By means of two- and three-dimensional particle-in-cell simulations, we investigate anti-parallel reconnection in magnetically-dominated electron-positron plasmas. Our simulations extend to unprecedentedly long temporal and spatial scales, so we can capture the asymptotic state of the system beyond the initial transients, and without any artificial limitation by the boundary conditions. At late times, the reconnection layer is organized into a chain of large magnetic islands connected by thin X-lines. The plasmoid instability further fragments each X-line into a series of smaller islands, separated by X-points. At the X-points, the particles become unmagnetized and they get accelerated along the reconnection electric field. We provide definitive evidence that the late-time particle spectrum integrated over the whole reconnection r...
Implications of RHESSI Flare Observations for Magnetic Reconnection Models
Holman, Gordon D.; Sui, Linhui; Dennis, Brian R.
2004-01-01
The Ramaty High Energy Solar Spectroscopic Imager (RHESSI) observations of the 2002 April 15 solar flare and related flares provide compelling evidence for the formation of a large-scale, reconnecting current sheet in at least some flares. We describe the observed evolution of the April 15 flare in terms of magnetic reconnection models. We argue that the flare most likely evolved through magnetic geometries associated with super-slow reconnection (early rise phase), fast reconnection (impulsive phase), and slow reconnection (gradual phase). We also provide evidence for X-ray brightenings within the evolving current sheet, possibly induced by the tearing mode instability. This work was supported in part by the RHESSI Program and NASA's Sun-Earth Connection Program. This work would not have been possible without the dedicated efforts of the entire RHESSI team.
The Acceleration of Ions in Solar Flares During Magnetic Reconnection
Knizhnik, Kalman; Drake, James F
2011-01-01
The acceleration of solar flare ions during magnetic reconnection is explored via particle-in-cell simulations that self-consistently follow the motions of both protons and $\\alpha$ particles. We demonstrate that the dominant ion heating during reconnection with a guide field (a magnetic component perpendicular to the reconnection plane) results from pickup behavior during the entry into reconnection exhausts. In contrast with anti-parallel reconnection, the temperature increment is dominantly transverse, rather than parallel, to the local magnetic field. The comparison of protons and alphas reveals a mass-to-charge ($M/Q$) threshold in pickup behavior that favors heating of high $M/Q$ ions over protons, which is consistent with impulsive flare observations.
Conservation of writhe helicity under anti-parallel reconnection
Laing, Christian E; Sumners, De Witt L
2014-01-01
Reconnection is a fundamental event in many areas of science, from the interaction of vortices in classical and quantum fluids, and magnetic flux tubes in magnetohydrodynamics and plasma physics, to the recombination in polymer physics and DNA biology. By using fundamental results in topological fluid mechanics, the helicity of a flux tube can be calculated in terms of writhe and twist contributions. Here we show that the writhe is conserved under anti-parallel reconnection. Hence, for a pair of interacting flux tubes of equal flux, if the twist of the reconnected tube is the sum of the original twists of the interacting tubes, then helicity is conserved during reconnection. Thus, any deviation from helicity conservation is entirely due to the intrinsic twist inserted or deleted locally at the reconnection site. This result has important implications for helicity and energy considerations in various physical contexts.
Energy Technology Data Exchange (ETDEWEB)
Graf von der Pahlen, J.; Tsiklauri, D. [School of Physics and Astronomy, Queen Mary University of London, London E1 4NS (United Kingdom)
2014-01-15
Works of Tsiklauri and Haruki [Phys. Plasmas 15, 102902 (2008); 14, 112905 (2007)] are extended by inclusion of the out-of-plane magnetic (guide) field. In particular, magnetic reconnection during collisionless, stressed X-point collapse for varying out-of-plane guide-fields is studied using a kinetic, 2.5D, fully electromagnetic, relativistic particle-in-cell numerical code. For zero guide-field, cases for both open and closed boundary conditions are investigated, where magnetic flux and particles are lost and conserved, respectively. It is found that reconnection rates, out-of-plane currents and density in the X-point increase more rapidly and peak sooner in the closed boundary case, but higher values are reached in the open boundary case. The normalized reconnection rate is fast: 0.10-0.25. In the open boundary case it is shown that an increase of guide-field yields later onsets in the reconnection peak rates, while in the closed boundary case initial peak rates occur sooner but are suppressed. The reconnection current changes similarly with increasing guide-field; however for low guide-fields the reconnection current increases, giving an optimal value for the guide-field between 0.1 and 0.2 times the in-plane field in both cases. Also, in the open boundary case, it is found that for guide-fields of the order of the in-plane magnetic field, the generation of electron vortices occurs. Possible causes of the vortex generation, based on the flow of decoupled particles in the diffusion region and localized plasma heating, are discussed. Before peak reconnection onset, oscillations in the out-of-plane electric field at the X-point are found, ranging in frequency from approximately 1 to 2 ω{sub pe} and coinciding with oscillatory reconnection. These oscillations are found to be part of a larger wave pattern in the simulation domain. Mapping the out-of-plane electric field along the central lines of the domain over time and applying a 2D Fourier transform reveal that
Makhal, Krishnandu; Mathur, Paresh; Maurya, Sidharth; Goswami, Debabrata
2017-02-01
Third order nonlinearities of Mn(III)-Phthalocyanine chloride in dimethyl-sulphoxide under 50 fs pulses, operating at 94 MHz, by eliminating cumulative thermal effects have been investigated and reported by us. Modifications were done in data acquisition during Z-scan experiment, which included recording of time evolution waveform traces in an oscilloscope and not collection of Z versus transmission and utilization of a chopper of a suitable duty cycle. Time evolution traces were further processed analytically through MatLab® programming, which yielded Z-scan traces similar to what was obtained with single shot 50 fs pulse. We observed reverse saturable absorption at 800 nm owing to excited state absorption. We show that the nonlinear refractive index (γ) and nonlinear absorption coefficient (β) are over estimated almost 100 times, when MHz pulses are used compared to a situation, where thermo-optical nonlinearities are accounted. Illumination and dark periods are carefully set in a way, so that the sample is able to completely recover its initial temperature before arrival of the next pulse. Magnitudes of γ and β were found to be -(6.5-4.9) × 10-16 m2/W and (5.4-6.2) × 10-10 m/W under the MHz condition, whereas they were -(0.18-2.2) × 10-18 m2/W and (9.5-15) × 10-12 m/W under the thermally managed condition, respectively. To reveal the associated fast nonlinearity, femtosecond transient absorption experiment was performed, which inferred excited state absorption and ground state bleaching across the 450-780 nm region. Dynamics associated with these processes are reported along with fluorescence lifetime obtained through the TCSPC technique. Structure optimization using TDDFT calculations and HOMO-LUMO gaps with orbital pictures are also shown.
Murphy, G C; Pelletier, Guy
2008-01-01
Magnetic reconnection plays a critical role in many astrophysical processes where high energy emission is observed, e.g. particle acceleration, relativistic accretion powered outflows, pulsar winds and probably in dissipation of Poynting flux in GRBs. The magnetic field acts as a reservoir of energy and can dissipate its energy to thermal and kinetic energy via the tearing mode instability. We have performed 3d nonlinear MHD simulations of the tearing mode instability in a current sheet. Results from a temporal stability analysis in both the linear regime and weakly nonlinear (Rutherford) regime are compared to the numerical simulations. We observe magnetic island formation, island merging and oscillation once the instability has saturated. The growth in the linear regime is exponential in agreement with linear theory. In the second, Rutherford regime the island width grows linearly with time. We find that thermal energy produced in the current sheet strongly dominates the kinetic energy. Finally preliminary ...
Reconnection brightenings in the quiet solar photosphere
Rouppe van der Voort, Luc H. M.; Rutten, Robert J.; Vissers, Gregal J. M.
2016-08-01
We describe a new quiet-Sun phenomenon which we call quiet-Sun Ellerman-like brightenings (QSEB). QSEBs are similar to Ellerman bombs (EB) in some respects but differ significantly in others. EBs are transient brightenings of the wings of the Balmer Hα line that mark strong-field photospheric reconnection in complex active regions. QSEBs are similar but smaller and less intense Balmer-wing brightenings that occur in quiet areas away from active regions. In the Hα wing, we measure typical lengths of less than 0.5 arcsec, widths of 0.23 arcsec, and lifetimes of less than a minute. We discovered them using high-quality Hα imaging spectrometry from the Swedish 1-m Solar Telescope (SST) and show that, in lesser-quality data, they cannot be distinguished from more ubiquitous facular brightenings, nor in the UV diagnostics currently available from space platforms. We add evidence from concurrent SST spectropolarimetry that QSEBs also mark photospheric reconnection events, but in quiet regions on the solar surface. The movies are available in electronic form at http://www.aanda.org
Reconnection brightenings in the quiet solar photosphere
van der Voort, Luc H M Rouppe; Vissers, Gregal J M
2016-01-01
We describe a new quiet-Sun phenomenon which we call "Quiet-Sun Ellerman-like Brightenings" (QSEB). QSEBs are similar to Ellerman bombs (EB) in some respects but differ significantly in others. EBs are transient brightenings of the wings of the Balmer H-alpha line that mark strong-field photospheric reconnection in complex active regions. QSEBs are similar but smaller and less intense Balmer-wing brightenings that occur in quiet areas away from active regions. In the H-alpha wing we measure typical lengths of less than 0.5 arcsec, widths of 0.21 arcsec, and lifetimes of less than a minute. We discovered them using high-quality H-alpha imaging spectrometry from the Swedish 1-m Solar Telescope (SST) and show that in lesser-quality data they cannot be distinguished from more ubiquitous facular brightenings, nor in the ultraviolet diagnostics currently available from space platforms. We add evidence from concurrent SST spectropolarimetry that QSEBs also mark photospheric reconnection events, but in quiet regions ...
Coherent Structures and Reconnection in Collisionless Turbulence
Roytershteyn, Vadim; Karimabadi, Homa
2014-10-01
The sub-proton range of collisionless turbulence has attracted considerable attention in the last decades due to its role in the dissipation of cascading energy and increased availability of high-quality measurements capable of constraining the relevant models. Coherent structures, such as current sheets, have long been considered important sites for the dissipation of energy. However, a self-consistent treatment of their formation and of the relevant collisionless dissipation mechanisms has only become possible recently. Here we discuss several examples from recent kinetic simulations of turbulence focusing on the role of current sheets and magnetic reconnection. In the 3D fully kinetic simulations with initial conditions relevant to solar wind turbulence, current sheets form over a large range of scales and are shown to be sites of increased energy transfer between fluctuating fields and particles. Moreover, depending on the initial conditions and the type of driving, other types of coherent structures are possible, such as magnetic holes. 2D and 3D global hybrid simulations of the interaction between solar wind and planetary magnetospheres demonstrate inherent connection between collisionless shocks, turbulence, and magnetic reconnection. Specifically, the interaction of foreshock turbulence driven by reflected ions with the shock itself leads to a variety of fascinating phenomena in the magnetosheath, seeding both small-scale turbulence and large-scale global perturbations.
Particle Acceleration and Heating by Turbulent Reconnection
Vlahos, Loukas; Pisokas, Theophilos; Isliker, Heinz; Tsiolis, Vassilis; Anastasiadis, Anastasios
2016-08-01
Turbulent flows in the solar wind, large-scale current sheets, multiple current sheets, and shock waves lead to the formation of environments in which a dense network of current sheets is established and sustains “turbulent reconnection.” We constructed a 2D grid on which a number of randomly chosen grid points are acting as scatterers (i.e., magnetic clouds or current sheets). Our goal is to examine how test particles respond inside this large-scale collection of scatterers. We study the energy gain of individual particles, the evolution of their energy distribution, and their escape time distribution. We have developed a new method to estimate the transport coefficients from the dynamics of the interaction of the particles with the scatterers. Replacing the “magnetic clouds” with current sheets, we have proven that the energization processes can be more efficient depending on the strength of the effective electric fields inside the current sheets and their statistical properties. Using the estimated transport coefficients and solving the Fokker-Planck (FP) equation, we can recover the energy distribution of the particles only for the stochastic Fermi process. We have shown that the evolution of the particles inside a turbulent reconnecting volume is not a solution of the FP equation, since the interaction of the particles with the current sheets is “anomalous,” in contrast to the case of the second-order Fermi process.
Liu, Li; Wan, Jieqiu
2012-12-01
This paper explores the co-movement of Shanghai stock market and China Yuan (CNY) exchange rates. First, we find that stock price and exchange rate are significantly cross-correlated. Second, employing a cointegration test allowing for a structural break, we find that the Shanghai Composite Index (SCI) is not cointegrated with the exchange rate of CNY/USD. The so-called “cointegration” found in previous studies is just caused by the shock of the recent financial crisis. Third, using linear and nonlinear Granger causality tests, we find no causality between stock prices and exchange rates during the period before the recent financial crisis. After the financial crisis, a unidirectional causality behavior running from exchange rates to stock index is present.
Zenitani, S; Hoshino, M
2005-08-26
The linear and nonlinear evolution of a relativistic current sheet of pair (e(+/-)) plasmas is investigated by three-dimensional particle-in-cell simulations. In a Harris configuration, it is obtained that the magnetic energy is fast dissipated by the relativistic drift kink instability (RDKI). However, when a current-aligned magnetic field (the so-called "guide field") is introduced, the RDKI is stabilized by the magnetic tension force and it separates into two obliquely propagating modes, which we call the relativistic drift-kink-tearing instability. These two waves deform the current sheet so that they trigger relativistic magnetic reconnection at a crossover thinning point. Since relativistic reconnection produces a lot of nonthermal particles, the guide field is of critical importance to study the energetics of a relativistic current sheet.
Medvedev, A P; Gavrilushkin, A P; Kiselev, S V; Shelepnev, A V; Smirnov, N A
2001-01-01
An examination of 39 patients with heart diseases was performed before and after operations by the method of geometrical analysis of the nonlinear chaos (fractal) variability of the cardiac rhythm on the basis of the apparatus-programmed complex "Poly-spectrum". Five-minute-long registrations of ECG were carried on. On the basis of the data of examination of 195 healthy volunteers the reference norm of this method parameters was determined. Reliably lower parameters were found in patients with the acquired valvular disease. A dynamic investigation of the geometrical nonlinear structure of the cardiac rhythm has shown the possibility to make a prognosis of early complications after prosthetics of the heart valves.
Chen, Chun-I.; Chen, Hong Long; Chen, Shuo-Pei
2008-08-01
The traditional Grey Model is easy to understand and simple to calculate, with satisfactory accuracy, but it is also lack of flexibility to adjust the model to acquire higher forecasting precision. This research studies feasibility and effectiveness of a novel Grey model together with the concept of the Bernoulli differential equation in ordinary differential equation. In this research, the author names this newly proposed model as Nonlinear Grey Bernoulli Model (NGBM). The NGBM is nonlinear differential equation with power index n. By controlling n, the curvature of the solution curve could be adjusted to fit the result of one time accumulated generating operation (1-AGO) of raw data. One extreme case from Grey system textbook is studied by NGBM, and two published articles are chosen for practical tests of NGBM. The results prove the novel NGBM is feasible and efficient. Finally, NGBM is used to forecast 2005 foreign exchange rates of twelve Taiwan major trading partners, including Taiwan.
Effects of Ion-to-Electron Mass Ratio on Electron Dynamics in Collisionless Magnetic Reconnection
Institute of Scientific and Technical Information of China (English)
GUO Jun; LU Quan-Ming
2007-01-01
A 21/2-dimensional electromagnetic particle-in-cell (PIC) simulation code is used to investigate electron behaviour in collisionless magnetic reconnection. The results show that the ion/electron mass ratio (mi/me) almost has no impact on the reconnection rate, however it can significantly affect electron behaviour in the diffusion region. For the case with larger mass ratio, the width of electron current sheet becomes smaller and the outflow region along the separatrix is smaller, hence the peak of the electron outflow speed is essentially larger. Density cavities and the parallel electric field E// along the separatrix can be found in the case with larger mass ratio, which may have significant influences on the acceleration and heating of the electrons near the X point.
Simulation of turbulent magnetic reconnection in the smallscale solar wind
Institute of Scientific and Technical Information of China (English)
魏奉思; 胡强; R.Schwen; 冯学尚
2000-01-01
Some observational examples for the possible occurrence of the turbulent magnetic reconnection in the solar wind are found by analysing Helios spacecraft’s high resolution data. The phenom-ena of turbulent magnetic reconnections in small scale solar wind are simulated by introducing a third order accuracy upwind compact difference scheme to the compressible two-dimensional MHD flow. Numerical results verify that the turbulent magnetic reconnection process could occur in small scale in-terplanetary solar wind, which is a basic feature characterizing the magnetic reconnection in high-mag-netie Peynolds number ( RM = 2 000-10 000) solar wind. The configurations of the magnetic reconnection could evolve from a single X-line to a multiple X-line reconnection, exhibiting a complex picture of the formation, merging and evolution of magnetic islands, and finally the magnetic reconnection would evolve into a low-energy state. Its life-span of evolution is about one hour order of magnitude. Various magnetic and f
First Reconnected Flux Tubes in the Near-Earth Tail
Andersson, L.; Lapenta, G.; Newman, D. L.; Spanswick, E. L.; Baker, J. B.; Clausen, L.; Larson, D. E.; Frey, H. U.; Singer, H. J.; Angelopoulos, V.; Ergun, R. E.; Bonnell, J. W.; McFadden, J. P.; Glassmeier, K.; Baumjohann, W.
2010-12-01
Following the onset of reconnection, the first reconnecting flux tubes move away from the reconnection site creating an over-dense region in front of their leading edge, with a low density region lagging behind. The initial front observed at the magnetic equator has a fairly well distinguishable magnetic signature, which in space observation constitute a sub category of a broader group classified as magnetic pile-up events (or, alternatively, as dipolarization events). The first reconnecting flux tubes at the magnetic equator do not form a classic shock, but are associated with lower hybrid drift instabilities and whistler waves. As has been shown in work by others, the first reconnecting flux tubes are associated with strong dissipation, especially ion dissipation. In the high density region, the electrons and ions are decelerated and redirected perpendicular to the ejected exhaust. Near the first reconnecting flux tubes the ions gain energy and the electrons consist of two populations, one bi-streaming and the other more energetic (warmer) in the perpendicular direction. One particular magnetospheric disturbance event will be presented form the THEMIS mission where good observations from ground assets exits. Aurora intensification, enhanced 30 keV electrons and ionospheric currents are associated with this event. The radar clearly demonstrate the changes in the convection pattern helping to understand the satellite observations from the THEMIS and the GOES satellites. This reconfiguration event occurs in discrete steps by separate reconnection events.
The use of the power density for identifying reconnection regions
Hamrin, M.; Andersson, L.; Vaivads, A.; Pitkänen, T.; Gunell, H.
2015-10-01
In the vicinity of magnetic reconnection, magnetic energy is transferred into kinetic energy. A reconnection region hence corresponds to a load, and it should manifest itself as large and positive values of the power density, E·J ≫ 0, where E is the electric field and J the current density. In this article we analyze Cluster plasma sheet data from 2001-2004 to investigate the use of the power density for identifying possible magnetic reconnection events from large sets of observed data. From theoretical arguments we show that an event with E·J≳20 pW/m3 in the Earth's magnetotail observed by the Cluster instruments (X potential reconnection regions, but selected events must be reviewed separately to confirm any possible reconnection signatures by looking for other signatures such as Hall electric and magnetic fields and reconnection jets. The power density can be computed from multispacecraft data, and we argue that the power density can be used as a tool for identifying possible reconnection events from large sets of data, e.g., from the Cluster and the Magnetospheric Multiscale missions.
The Roles of Reconnected Flux and Overlying Fields in CME Speeds
Deng, Minda; Welsch, Brian T.
2017-01-01
Researchers have reported i) correlations of coronal mass ejection (CME) speeds and the total photospheric magnetic flux swept out by flare ribbons in flare-associated eruptive events, and, separately, ii) correlations of CME speeds and more rapid decay, with height, of magnetic fields in potential-field coronal models above eruption sites. Here, we compare the roles of both ribbon fluxes and the decay rates of overlying fields in a set of 16 eruptive events. We confirm previous results that higher CME speeds are associated with both higher ribbon fluxes and more rapidly decaying overlying fields. We find the association with ribbon fluxes to be weaker than a previous report, but stronger than the dependence on the decay rate of overlying fields. Since the photospheric ribbon flux is thought to approximate the amount of coronal magnetic flux reconnected during the event, the correlation of speeds with ribbon fluxes suggests that reconnection plays some role in accelerating CMEs. One possibility is that reconnected fields that wrap around the rising ejection produce an increased outward hoop force, thereby increasing CME acceleration. The correlation of CME speeds with more rapidly decaying overlying fields might be caused by greater downward magnetic tension in stronger overlying fields, which could act as a source of drag on rising ejections.
FAST MAGNETIC RECONNECTION IN THE SOLAR CHROMOSPHERE MEDIATED BY THE PLASMOID INSTABILITY
Energy Technology Data Exchange (ETDEWEB)
Ni, Lei; Kliem, Bernhard; Lin, Jun [Yunnan Observatories, Chinese Academy of Sciences, Kunming 650011 (China); Wu, Ning, E-mail: leini@ynao.ac.cn [School of Tourism and Geography, Yunnan Normal University, Kunming 650031 (China)
2015-01-20
Magnetic reconnection in the partially ionized solar chromosphere is studied in 2.5 dimensional magnetohydrodynamic simulations including radiative cooling and ambipolar diffusion. A Harris current sheet with and without a guide field is considered. Characteristic values of the parameters in the middle chromosphere imply a high magnetic Reynolds number of ∼10{sup 6}-10{sup 7} in the present simulations. Fast magnetic reconnection then develops as a consequence of the plasmoid instability without the need to invoke anomalous resistivity enhancements. Multiple levels of the instability are followed as it cascades to smaller scales, which approach the ion inertial length. The reconnection rate, normalized to the asymptotic values of magnetic field and Alfvén velocity in the inflow region, reaches values in the range ∼0.01-0.03 throughout the cascading plasmoid formation and for zero as well as for strong guide field. The outflow velocity reaches ≈40 km s{sup –1}. Slow-mode shocks extend from the X-points, heating the plasmoids up to ∼8 × 10{sup 4} K. In the case of zero guide field, the inclusion of both ambipolar diffusion and radiative cooling causes a rapid thinning of the current sheet (down to ∼30 m) and early formation of secondary islands. Both of these processes have very little effect on the plasmoid instability for a strong guide field. The reconnection rates, temperature enhancements, and upward outflow velocities from the vertical current sheet correspond well to their characteristic values in chromospheric jets.
Collisionless magnetic reconnection via Alfvén eigenmodes.
Dai, Lei
2009-06-19
We propose an analytic approach to the problem of collisionless magnetic reconnection formulated as a process of Alfvén eigenmodes' generation and dissipation. Alfvén eigenmodes are confined by the current sheet in the same way that quantum mechanical waves are confined by the tanh;{2} potential. The dynamical time scale of reconnection is the system scale divided by the eigenvalue propagation velocity of the n = 1 mode. The prediction of the n = 1 mode shows good agreement with the in situ measurement of the reconnection-associated Hall fields.
New Measure of the Dissipation Region in Collisionless Magnetic Reconnection
Zenitani, Seiji; Hesse, Michael; Klimas, Alex; Kuznetsova, Masha
2012-01-01
A new measure to identify a small-scale dissipation region in collisionless magnetic reconnection is proposed. The energy transfer from the electromagnetic field to plasmas in the electron s rest frame is formulated as a Lorentz-invariant scalar quantity. The measure is tested by two-dimensional particle-in-cell simulations in typical configurations: symmetric and asymmetric reconnection, with and without the guide field. The innermost region surrounding the reconnection site is accurately located in all cases. We further discuss implications for nonideal MHD dissipation.
New 3D vision of magnetic reconnection revealed
Institute of Scientific and Technical Information of China (English)
无
2007-01-01
@@ An international consortium led by astronomers from CAS and Peking University recently made the first satellite observation of the full three-dimensional (3D) geometry structure of magnetic reconnection, a process whereby the lines of a complex magnetic field break and reconnect to alter its structure drastically. Their work was published in the September issue of Nature Physics. Experts say that this pioneering discovery will help construct theoretical models of magnetic reconnection, a universal phenomenon in space related to star formation, solar explosions and the entry of solar wind energy into the near-Earth environment.
Helicity conservation under quantum reconnection of vortex rings
Zuccher, Simone
2016-01-01
Here we show that under quantum reconnection, simulated by using the three-dimensional Gross- Pitaevskii equation, self-helicity of a system of two interacting vortex rings remains conserved. By resolving the fine structure of the vortex cores, we demonstrate that total length of the vortex system reaches a maximum at the reconnection time, while both writhe helicity and twist helicity remain separately unchanged throughout the process. Self-helicity is computed by two independent methods, and topological information is based on the extraction and analysis of geometric quantities such as writhe, total torsion and intrinsic twist of the reconnecting vortex rings.
Tomlinson, Sean
2016-04-01
The calculation and comparison of physiological characteristics of thermoregulation has provided insight into patterns of ecology and evolution for over half a century. Thermoregulation has typically been explored using linear techniques; I explore the application of non-linear scaling to more accurately calculate and compare characteristics and thresholds of thermoregulation, including the basal metabolic rate (BMR), peak metabolic rate (PMR) and the lower (Tlc) and upper (Tuc) critical limits to the thermo-neutral zone (TNZ) for Australian rodents. An exponentially-modified logistic function accurately characterised the response of metabolic rate to ambient temperature, while evaporative water loss was accurately characterised by a Michaelis-Menten function. When these functions were used to resolve unique parameters for the nine species studied here, the estimates of BMR and TNZ were consistent with the previously published estimates. The approach resolved differences in rates of metabolism and water loss between subfamilies of Australian rodents that haven't been quantified before. I suggest that non-linear scaling is not only more effective than the established segmented linear techniques, but also is more objective. This approach may allow broader and more flexible comparison of characteristics of thermoregulation, but it needs testing with a broader array of taxa than those used here.
Extended Magnetic Reconnection Across the Dayside Magnetopause
Dunlop, M. W.; Zhang, Q.-H.; Bogdanova, Y. V.; Lockwood, M.; Pu, Z.; Hasegawa, H.; Wang, J.; Taylor, M. G. G. T.; Berchem, J.; Lavraund, B.; Eastwood, J.; Volwerk, M.; Shen, C.; Shi, J.-K.; Constantinescu, D.; Frey, H.; Fazakerley, A. N.; Sibeck, D.; Escoubet, P.; Wild, J. A.; Liu, Z.-X.
2011-01-01
The extent of where magnetic reconnection (MR), the dominant process responsible for energy and plasma transport into the magnetosphere, operates across Earth's dayside magnetopause has previously been only indirectly shown by observations. We report the first direct evidence of X-line structure resulting from the operation of MR at each of two widely separated locations along the tilted, subsolar line of maximum current on Earth's magnetopause, confirming the operation of MR at two or more sites across the extended region where MR is expected to occur. The evidence results from in-situ observations of the associated ion and electron plasma distributions, present within each magnetic X-line structure, taken by two spacecraft passing through the active MR regions simultaneously.
Plasma Astrophysics, part II Reconnection and Flares
Somov, Boris V
2007-01-01
This well-illustrated monograph is devoted to classic fundamentals, current practice, and perspectives of modern plasma astrophysics. The first part is unique in covering all the basic principles and practical tools required for understanding and working in plasma astrophysics. The second part presents the physics of magnetic reconnection and flares of electromagnetic origin in space plasmas within the solar system; single and double stars, relativistic objects, accretion disks, and their coronae are also covered. This book is designed mainly for professional researchers in astrophysics. However, it will also be interesting and useful to graduate students in space sciences, geophysics, as well as advanced students in applied physics and mathematics seeking a unified view of plasma physics and fluid mechanics.
Electron Acceleration in Collisionless Magnetic Reconnection
Institute of Scientific and Technical Information of China (English)
GUO Jun; LU Quan-Ming; WANG Shui; FU Xiang-Rong
2005-01-01
@@ A 21/2-dimensional electromagnetic particle-in-cell (PIC) simulation code is used to investigate the electron acceleration in collisionless magnetic reconnection. The results show that the electrons are accelerated in the diffusion region near the X point, and the acceleration process can be roughly divided into two procedures: firstly the electrons are accelerated in the z direction due to the electric field in the negative z direction. Then the electrons gyrate surrounding the magnetic field with the action of the Lorentz force, through this procedure the electrons reach higher velocity in the x direction and then flow out of the diffusion region. After being accelerated away from the diffusion region, part of electrons is trapped near the O point, and the other part of electrons flows into plasma sheet boundary layer along the magnetic field.
Particle Acceleration and Heating by Turbulent Reconnection
Vlahos, Loukas; Isliker, Heinz; Tsiolis, Vassilios; Anastasiadis, Anastasios
2016-01-01
Turbulent flows in the solar wind, large scale current sheets, multiple current sheets, and shock waves lead to the formation of environments in which a dense network of current sheets is established and sustains "turbulent reconnection". We constructed a 2D grid on which a number of randomly chosen grid points are acting as {\\bf scatterers} (i.e.\\ magnetic clouds or current sheets). In particular, we study how test particles respond inside this collection of scatterers. We study the energy gain of individual particles, the evolution of their energy distribution, their escape time distribution and we determine the transport coefficients from the particle dynamics. We have shown that our model describes very well the second order Fermi energization of non relativistic plasmas in open or periodic numerical boxes, when using magnetic clouds as scatterers. Replacing the "magnetic clouds" with current sheets, we have proven that the processes are much more efficient and particle heating and acceleration depends on...
Cosmic rays and stochastic magnetic reconnection in the heliotail
Directory of Open Access Journals (Sweden)
P. Desiati
2012-06-01
Full Text Available Galactic cosmic rays are believed to be generated by diffusive shock acceleration processes in Supernova Remnants, and the arrival direction is likely determined by the distribution of their sources throughout the Galaxy, in particular by the nearest and youngest ones. Transport to Earth through the interstellar medium is expected to affect the cosmic ray properties as well. However, the observed anisotropy of TeV cosmic rays and its energy dependence cannot be explained with diffusion models of particle propagation in the Galaxy. Within a distance of a few parsec, diffusion regime is not valid and particles with energy below about 100 TeV must be influenced by the heliosphere and its elongated tail. The observation of a highly significant localized excess region of cosmic rays from the apparent direction of the downstream interstellar flow at 1–10 TeV energies might provide the first experimental evidence that the heliotail can affect the transport of energetic particles. In particular, TeV cosmic rays propagating through the heliotail interact with the 100–300 AU wide magnetic field polarity domains generated by the 11 yr cycles. Since the strength of non-linear convective processes is expected to be larger than viscous damping, the plasma in the heliotail is turbulent. Where magnetic field domains converge on each other due to solar wind gradient, stochastic magnetic reconnection likely occurs. Such processes may be efficient enough to re-accelerate a fraction of TeV particles as long as scattering processes are not strong. Therefore, the fractional excess of TeV cosmic rays from the narrow region toward the heliotail direction traces sightlines with the lowest smearing scattering effects, that can also explain the observation of a harder than average energy spectrum.
Self-feeding turbulent magnetic reconnection on macroscopic scales.
Lapenta, Giovanni
2008-06-13
Within a MHD approach we find magnetic reconnection to progress in two entirely different ways. The first is well known: the laminar Sweet-Parker process. But a second, completely different and chaotic reconnection process is possible. This regime has properties of immediate practical relevance: (i) it is much faster, developing on scales of the order of the Alfvén time, and (ii) the areas of reconnection become distributed chaotically over a macroscopic region. The onset of the faster process is the formation of closed-circulation patterns where the jets going out of the reconnection regions turn around and force their way back in, carrying along copious amounts of magnetic flux.
Observations of slow electron holes at a magnetic reconnection site.
Khotyaintsev, Yu V; Vaivads, A; André, M; Fujimoto, M; Retinò, A; Owen, C J
2010-10-15
We report in situ observations of high-frequency electrostatic waves in the vicinity of a reconnection site in the Earth's magnetotail. Two different types of waves are observed inside an ion-scale magnetic flux rope embedded in a reconnecting current sheet. Electron holes (weak double layers) produced by the Buneman instability are observed in the density minimum in the center of the flux rope. Higher frequency broadband electrostatic waves with frequencies extending up to f(pe) are driven by the electron beam and are observed in the denser part of the rope. Our observations demonstrate multiscale coupling during the reconnection: Electron-scale physics is induced by the dynamics of an ion-scale flux rope embedded in a yet larger-scale magnetic reconnection process.
Electron-scale measurements of magnetic reconnection in space.
Burch, J L; Torbert, R B; Phan, T D; Chen, L-J; Moore, T E; Ergun, R E; Eastwood, J P; Gershman, D J; Cassak, P A; Argall, M R; Wang, S; Hesse, M; Pollock, C J; Giles, B L; Nakamura, R; Mauk, B H; Fuselier, S A; Russell, C T; Strangeway, R J; Drake, J F; Shay, M A; Khotyaintsev, Yu V; Lindqvist, P-A; Marklund, G; Wilder, F D; Young, D T; Torkar, K; Goldstein, J; Dorelli, J C; Avanov, L A; Oka, M; Baker, D N; Jaynes, A N; Goodrich, K A; Cohen, I J; Turner, D L; Fennell, J F; Blake, J B; Clemmons, J; Goldman, M; Newman, D; Petrinec, S M; Trattner, K J; Lavraud, B; Reiff, P H; Baumjohann, W; Magnes, W; Steller, M; Lewis, W; Saito, Y; Coffey, V; Chandler, M
2016-06-03
Magnetic reconnection is a fundamental physical process in plasmas whereby stored magnetic energy is converted into heat and kinetic energy of charged particles. Reconnection occurs in many astrophysical plasma environments and in laboratory plasmas. Using measurements with very high time resolution, NASA's Magnetospheric Multiscale (MMS) mission has found direct evidence for electron demagnetization and acceleration at sites along the sunward boundary of Earth's magnetosphere where the interplanetary magnetic field reconnects with the terrestrial magnetic field. We have (i) observed the conversion of magnetic energy to particle energy; (ii) measured the electric field and current, which together cause the dissipation of magnetic energy; and (iii) identified the electron population that carries the current as a result of demagnetization and acceleration within the reconnection diffusion/dissipation region.
GRBs from Magnetic Reconnection: Variability and Robustness of Lightcurves
Granot, Jonathan
2016-01-01
The dissipation mechanism that powers gamma-ray bursts (GRBs) remains uncertain almost half a century after their discovery. The two main competing mechanisms are the extensively studied internal shocks and the less studied magnetic reconnection. Here we consider GRB emission from magnetic reconnection accounting for the relativistic bulk motions that it produces in the jet's bulk rest frame. Far from the source the magnetic field is almost exactly normal to the radial direction, suggesting locally quasi-spherical thin reconnection layers between regions of oppositely directed magnetic field. We show that if the relativistic motions in the jet's frame are confined to such a quasi-spherical uniform layer, then the resulting GRB lightcurves are independent of their direction distribution within this layer. This renders previous results for a delta-function velocity-direction distribution (Beniamini & Granot 2016) applicable to a much more general class of reconnection models, which are suggested by numerica...
Imaging coronal magnetic-field reconnection in a solar flare
Su, Yang; Holman, Gordon D; Dennis, Brian R; Wang, Tongjiang; Temmer, Manuela; Gan, Weiqun
2013-01-01
Magnetic-field reconnection is believed to play a fundamental role in magnetized plasma systems throughout the Universe1, including planetary magnetospheres, magnetars and accretion disks around black holes. This letter present extreme ultraviolet and X-ray observations of a solar flare showing magnetic reconnection with a level of clarity not previously achieved. The multi-wavelength extreme ultraviolet observations from SDO/AIA show inflowing cool loops and newly formed, outflowing hot loops, as predicted. RHESSI X-ray spectra and images simultaneously show the appearance of plasma heated to >10 MK at the expected locations. These two data sets provide solid visual evidence of magnetic reconnection producing a solar flare, validating the basic physical mechanism of popular flare models. However, new features are also observed that need to be included in reconnection and flare studies, such as three-dimensional non-uniform, non-steady and asymmetric evolution.
(Non)-universality of vortex reconnections in superfluids
Villois, Alberto; Proment, Davide
2016-01-01
An insight into vortex reconnections in superfluids is presented making use of analytical results and numerical simulations of the Gross--Pitaevskii model. Universal aspects of the reconnection process are investigated by considering different initial vortex configurations and making use of a recently developed tracking algorithm to reconstruct the vortex filaments. We show that about the reconnection event the vortex lines approach and separate always accordingly to the time scaling $ \\delta \\sim t^{-1/2} $ with pre-factors that depend on the vortex configuration. We also investigate the behavior of curvature and torsion close to the reconnection point, demonstrating analytically that the curvature can exhibit a self-similar behavior that might be broken by the development of shock-like structures in the torsion.
Physical Conditions in the Reconnection Layer in Pulsar Magnetospheres
Uzdensky, Dmitri A
2012-01-01
The magnetosphere of a rotating pulsar naturally develops a current sheet beyond the light cylinder (LC). Magnetic reconnection in this current sheet inevitably dissipates a nontrivial fraction of the pulsar spin-down power within a few LC radii. We develop a basic physical picture of reconnection in this environment and discuss its implications for the observed pulsed gamma-ray emission. We argue that reconnection proceeds in the plasmoid-dominated regime, via an hierarchical chain of multiple secondary islands/flux ropes. The inter-plasmoid reconnection layers are subject to strong synchrotron cooling, leading to significant plasma compression. Using the conditions of pressure balance across these current layers, the balance between the heating by magnetic energy dissipation and synchrotron cooling, and Ampere's law, we obtain simple estimates for key parameters of the layers --- temperature, density, and layer thickness. In the comoving frame of the relativistic pulsar wind just outside of the equatorial c...
Ion Bernstein waves in a magnetic reconnection region
Narita, Y.; Nakamura, R.; Baumjohann, W.; Glassmeier, K. H.; Motschmann, U.; Comisel, H.
2015-12-01
Four-dimensional energy spectra and a diagram for dispersion relations are determined for the first time in a magnetic reconnection region in the magnetotail using the four-point magnetometer data from the Cluster mission on a spatial scale of 200 km, about 0.1 ion inertial lengths. The energy spectra are anisotropic with an extension in the perpendicular direction and axially asymmetric with respect to the mean magnetic field. The dispersion diagram for the waves in the quasi-perpendicular directions in the plasma rest frame is in reasonably good agreement with the ion Bernstein waves particularly at the second harmonic of the proton gyro-frequency. Perpendicular-propagating ion Bernstein waves likely exist in an outflow region of magnetic reconnection. We discuss the causality of the Bernstein waves with magnetic reconnection with an estimate of the anomalous resistivity, and propose an observationally-driven model of turbulent magnetic reconnection.
How is the magnetic reconnection derived from magnetohydrodynamics equations?
Tashiro, Tohru
2012-01-01
We clarify how magnetic reconnection can be derived from magnetohydrodynamics (MHD) equations in a way that is easily understandable to university students. The essential mechanism governing the time evolution of the magnetic field is diffusion dynamics. The magnetic field is represented by two components. It is clarified that the diffusion of a component causes a generation of another component that is initially zero and, accordingly, that the magnetic force lines are reconnected. For this reconnection to occur correctly, the initial magnetic field must be directed oppositely in the two regions, e.g., $y>0$ and $y0$ ($y<0$); and must be saturated for $y$ far from the x axis, which would indicate the existence of the current sheet. It will be clear that our comprehension based on diffusion runs parallel to the common qualitative explanation about the magnetic reconnection.
Magnetic Reconnection and Intermittent Turbulence in the Solar Wind
Osman, K T; Gosling, J T; Greco, A; Servidio, S; Hnat, B; Chapman, S C; Phan, T D
2014-01-01
A statistical relationship between magnetic reconnection, current sheets and intermittent turbulence in the solar wind is reported for the first time using in-situ measurements from the Wind spacecraft at 1 AU. We identify intermittency as non-Gaussian fluctuations in increments of the magnetic field vector, $\\mathbf{B}$, that are spatially and temporally non-uniform. The reconnection events and current sheets are found to be concentrated in intervals of intermittent turbulence, identified using the partial variance of increments method: within the most non-Gaussian 1% of fluctuations in $\\mathbf{B}$, we find 87%-92% of reconnection exhausts and $\\sim$9% of current sheets. Also, the likelihood that an identified current sheet will also correspond to a reconnection exhaust increases dramatically as the least intermittent fluctuations are removed from the dataset. Hence, the turbulent solar wind contains a hierarchy of intermittent magnetic field structures that are increasingly linked to current sheets, which ...
Anisotropic Electron Tail Generation during Tearing Mode Magnetic Reconnection
DuBois, Ami M.; Almagri, Abdulgader F.; Anderson, Jay K.; Den Hartog, Daniel J.; Lee, John David; Sarff, John S.
2017-02-01
The first experimental evidence of anisotropic electron energization during magnetic reconnection that favors a direction perpendicular to the guide magnetic field in a toroidal, magnetically confined plasma is reported in this Letter. Magnetic reconnection plays an important role in particle heating, energization, and transport in space and laboratory plasmas. In toroidal devices like the Madison Symmetric Torus, discrete magnetic reconnection events release large amounts of energy from the equilibrium magnetic field. Fast x-ray measurements imply a non-Maxwellian, anisotropic energetic electron tail is formed at the time of reconnection. The tail is well described by a power-law energy dependence. The expected bremsstrahlung from an electron distribution with an anisotropic energetic tail (v⊥>v∥ ) spatially localized in the core region is consistent with x-ray emission measurements. A turbulent process related to tearing fluctuations is the most likely cause for the energetic electron tail formation.
Reconnection at the Heliopause: Predictions for Voyager 2
Fuselier, S. A.; Cairns, I. H.
2017-09-01
Predicted and observed properties of the inner and outer heliosheath were recently used to assess whether magnetic reconnection was occurring at the Voyager 1 crossing of the heliopause. It was concluded that reconnection may not have been occurring locally, but may have been occurring at a location remote from Voyager 1. Here observations of 37 to 70 keV electrons measured by the LECP instrument on Voyager 1 are interpreted as possible evidence for remote reconnection and the study is extended to the heliopause near the projected crossing location of Voyager 2, where the plasma depletion layer (PDL) should be significantly stronger. The predicted plasma properties are used to determine if local reconnection is possible at this projected heliopause crossing.
Evaluation of Geese Theatre's Re-Connect program: addressing resettlement issues in prison.
Harkins, Leigh; Pritchard, Cecilia; Haskayne, Donna; Watson, Andy; Beech, Anthony R
2011-06-01
This study examined the impact of Geese Theatre's Re-Connect program on a sample of offenders who attended it. This program used theatre performance, experiential exercises, skills practice role-plays, and metaphors such as the masks to invite a group of offenders to consider and explore issues connected with their release and reconnecting with a life outside prison. Pre- and postprogram psychometric tests, behavior ratings, and interviews were completed to assess the effectiveness of the program. Significant changes were observed from pre- to posttreatment in terms of self-efficacy, motivation to change, and improved confidence in skills (i.e., social and friendship, occupational, family and intimacy, dealing with authority, alternatives to aggression or offending, and self-management and self-control skills). Improved behavior and engagement within the program was observed over the 3 days of the program. Interviews also revealed the positive impact the program had on the participants. This provides evidence supporting the short-term effectiveness of the Re-Connect program.
Energy release and transfer in solar flares: simulations of three-dimensional reconnection
Energy Technology Data Exchange (ETDEWEB)
Birn, Joachim [Los Alamos National Laboratory; Fletches, L [UNIV OF GLASGOW; Hesse, M [HGSFC; Neukirch, T [UNIV OF ST. ANDREWS
2008-01-01
Using three-dimensional magnetohydrodynamic (MHD) simulations we investigate energy release and transfer in a three-dimensional extension of the standard two-ribbon flare picture. In this scenario reconnection is initiated in a thin current sheet (suggested to form below a departing coronal mass ejection) above a bipolar magnetic field. Two cases are contrasted: an initially force-free current sheet (low beta) and a finite-pressure current sheet (high beta). The energy conversion process from reconnect ion consists of incoming Poynting flux (from the release of magnetic energy) turned into up-and downgoing Poynting flux, enthalpy flux and bulk kinetic energy flux. In the low-beta case, the outgoing Poynting flux is the dominant contribution, whereas the outgoing enthalpy flux dominates in the high-beta case. The bulk kinetic energy flux is only a minor contribution, particularly in the downward direction. The dominance of the downgoing Poynting flux in the low-beta case is consistent with an alternative to the thick target electron beam model for solar flare energy transport, suggested recently by Fletcher and Hudson. For plausible characteristic parameters of the reconnecting field configuration, we obtain energy release time scales and and energy output rates that compare favorably with those inferred from observations for the impulsive phase of flares.
Energy Technology Data Exchange (ETDEWEB)
Takasao, Shinsuke; Shibata, Kazunari [Kwasan and Hida Observatories, Kyoto University, Yamashina, Kyoto 607-8471 (Japan); Asai, Ayumi; Isobe, Hiroaki, E-mail: takasao@kwasan.kyoto-u.ac.jp [Unit of Synergetic Studies for Space, Kyoto University, Yamashina, Kyoto 607-8471 (Japan)
2012-01-20
We report the simultaneous extreme-ultraviolet observation of magnetic reconnection inflow and outflow in a flare on 2010 August 18 observed by the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory. We found that during the rise phase of the flare, some plasma blobs appeared in the sheet structure above the hot loops. The plasma blobs were ejected bidirectionally along the sheet structure (outflow), at the same time as the threads visible in extreme-ultraviolet images moved toward the sheet structure (inflow). The upward and downward ejection velocities are 220-460 km s{sup -1} and 250-280 km s{sup -1}, respectively. The inflow speed changed from 90 km s{sup -1} to 12 km s{sup -1} in 5 minutes. By using these velocities, we estimated the nondimensional reconnection rate, which we found to vary during this period from 0.20 to 0.055. We also found that the plasma blobs in the sheet structure collided or merged with each other before they were ejected from the sheet structure. We hypothesize that the sheet structure is the current sheet and that these plasma blobs are plasmoids or magnetic islands, which could be important for understanding the dynamics of the reconnection region.
Reconnection layer bounded by switch-off shocks: Dayside magnetopause crossing by THEMIS D
Sonnerup, Bengt; Paschmann, Götz; Haaland, Stein; Phan, Tai; Eriksson, Stefan
2016-04-01
We discuss observations of reconnection, obtained by Time History of Events and Macroscale Interactions during Substorms (THEMIS) D during an outward bound traversal of the low-latitude dayside magnetopause. The reconnection signatures include high magnetic shear, a southward directed Alfvénic jet, bounded by slow-mode shocks near the switch-off limit (as in the symmetric Petschek geometry), a small, sunward directed normal magnetic field and plasma inflow into the jet from both sides. We conclude that cold, unmeasured ionospheric ions helped establish the symmetry. The effective ion mass, estimated from the switch-off condition, was 2.39 amu on the magnetospheric side, where the number density was inferred from the spacecraft potential, and 1.09 amu on the magnetosheath side. After a modest pressure correction in the magnetospheric shock, the MHD jump conditions for density, pressure, temperature, and entropy were well satisfied. The shock jumps were much larger on the magnetosphere side than on the magnetosheath side; we show this to be a plasma β effect. The main dissipation mechanism appears to be irreversible transfer between thermal motion parallel and perpendicular to the field, such that both shocks bring about approximate downstream temperature isotropy. Hall currents and electric fields were present, albeit in a strongly asymmetric configuration. The magnetospheric shock had longer duration than the magnetosheath one, possibly as a result of a nonconstant magnetopause speed. We infer an average earthward magnetopause speed (14 km/s), corresponding nominal shock thicknesses (12 and 6 λi), dimensionless reconnection rates (0.061-0.085), and reconnection wedge angles (5° between shocks; 13° between separatrices).
Three-dimensional magnetic reconnection through a moving magnetic null
Lukin, V. S.; Linton, M. G.
2011-01-01
A computational study of three-dimensional magnetic reconnection between two flux ropes through a moving reconnection site is presented. The configuration is considered in the context of two interacting spheromaks constrained by a perfectly conducting cylindrical boundary and oriented to form a single magnetic field null at its center. The initial magnetic field configuration is embedded into a uniform thermal plasma and is unstable to tilting. As the sphe...
Three-dimensional magnetic reconnection through a moving magnetic null
Lukin, V. S.; Linton, M. G.
2011-01-01
A computational study of three-dimensional magnetic reconnection between two flux ropes through a moving reconnection site is presented. The configuration is considered in the context of two interacting spheromaks constrained by a perfectly conducting cylindrical boundary and oriented to form a single magnetic field null at its center. The initial magnetic field configuration is embedded into a uniform thermal plasma and is unstable to tilting. As the spheromaks tilt, their magnetic fi...
The role of lateral magnetic reconnection in solar eruptive events
Directory of Open Access Journals (Sweden)
A. Soenen
2009-10-01
Full Text Available On 10–11 December 2005 a slow CME occurred in between two coronal streamers in the Western Hemisphere. SOHO/MDI magnetograms show a multipolar magnetic configuration at the photosphere consisting of a complex of active regions located at the CME source and two bipoles at the base of the lateral coronal streamers. White light observations reveal that the expanding CME affects both of the lateral streamers and induces the release of plasma within or close to them. These transient phenomena are possibly due to magnetic reconnections induced by the CME expansion that occurs either inside the streamer current sheet or between the CME flanks and the streamer. Our observations show that CMEs can be associated to not only a single reconnection process at a single location in the corona, but also to many reconnection processes occurring at different times and locations around the flux rope. Numerical simulations are used to demonstrate that the observed lateral reconnections can be reproduced. The observed secondary reconnections associated to CMEs may facilitate the CME release by globally decreasing the magnetic tension of the corona. Future CME models should therefore take into account the lateral reconnection effect.
The Role of Compressibility in Energy Release by Magnetic Reconnection
Birn, J.; Borovosky, J. E.; Hesse, M.
2012-01-01
Using resistive compressible magnetohydrodynamics, we investigate the energy release and transfer by magnetic reconnection in finite (closed or periodic) systems. The emphasis is on the magnitude of energy released and transferred to plasma heating in configurations that range from highly compressible to incompressible, based on the magnitude of the background beta (ratio of plasma pressure over magnetic pressure) and of a guide field in two-dimensional reconnection. As expected, the system becomes more incompressible, and the role of compressional heating diminishes, with increasing beta or increasing guide field. Nevertheless, compressional heating may dominate over Joule heating for values of the guide field of 2 or 3 (in relation to the reconnecting magnetic field component) and beta of 5-10. This result stems from the strong localization of the dissipation near the reconnection site, which is modeled based on particle simulation results. Imposing uniform resistivity, corresponding to a Lundquist number of 10(exp 3) to 10(exp 4), leads to significantly larger Ohmic heating. Increasing incompressibility greatly reduces the magnetic flux transfer and the amount of energy released, from approx. 10% of the energy associated with the reconnecting field component, for zero guide field and low beta, to approx. 0.2%-0.4% for large values of the guide field B(sub y0) > 5 or large beta. The results demonstrate the importance of taking into account plasma compressibility and localization of dissipation in investigations of heating by turbulent reconnection, possibly relevant for solar wind or coronal heating.
Analysis of Vortex Line Cutting and Reconnection by a Blade
Saunders, Curtis; Marshall, Jeffrey
2015-11-01
The essence of vortex reconnection involves the cutting of vortex lines originating from one region and reconnecting to vortex lines originating from another region via the diffusion-regulated annihilation of vorticity. Vortex cutting by a blade is a special case of the more general class of vortex reconnection problems, with an important difference being that vorticity is generated at the reconnection site. In this study, a series of Navier-Stokes simulations of orthogonal vortex cutting by a blade with different values of vortex strength are reported. The three phases of vortex reconnection identified in the literature are found to have counterparts for the vortex cutting problem. However numerous differences between the mechanics of vortex cutting and reconnection within each phase are discussed. In addition, comparisons are made between the temporal changes of the maximum and minimum components of vorticity for vortices of differing strength but still within the vortex cutting regime. The vortex cutting results are also compared with predictions of a simple analytical model that incorporates the key elements of a stretched vorticity field interacting with a solid surface, which is representative of the vortex cutting mechanism near the blade leading edge. Funded by National Science Foundation project DGE-1144388.
Electron Whistler Mode Waves Associated with Collisionless Magnetic Reconnection
Institute of Scientific and Technical Information of China (English)
GUO Jun; YU Bin; GUO Guang-Hai; ZHAO Bo
2011-01-01
@@ The results of particle-in-cell (PIC) simulations are presented on the evolution of the electron whistler waves during the collisionless magnetic reconnection.The simulation results show that the electron whistler waves with frequency higher than the lower hybrid frequency are found to occur in the electrons outflow region.Moreover, the present results indicate that these electron whistler waves with high-frequency in the region greater than an ion inertial scale of the x-line are irrelevant to the fast reconnection, but are generated as a result of the reconnection processes.%The results of particle-in-cell (PIC) simulations are presented on the evolution of the electron whistler waves during the collisionless magnetic reconnection. The simulation results show that the electron whistler waves with frequency higher than the lower hybrid frequency are found to occur in the electrons outflow region. Moreover,the present results indicate that these electron whistler waves with high-frequency in the region greater than an ion inertial scale of the x-line are irrelevant to the fast reconnection, but are generated as a result of the reconnection processes.
Critical Differences of Asymmetric Magnetic Reconnection from Standard Models
Nitta, S.; Wada, T.; Fuchida, T.; Kondoh, K.
2016-09-01
We have clarified the structure of asymmetric magnetic reconnection in detail as the result of the spontaneous evolutionary process. The asymmetry is imposed as ratio k of the magnetic field strength in both sides of the initial current sheet (CS) in the isothermal equilibrium. The MHD simulation is carried out by the HLLD code for the long-term temporal evolution with very high spatial resolution. The resultant structure is drastically different from the symmetric case (e.g., the Petschek model) even for slight asymmetry k = 2. (1) The velocity distribution in the reconnection jet clearly shows a two-layered structure, i.e., the high-speed sub-layer in which the flow is almost field aligned and the acceleration sub-layer. (2) Higher beta side (HBS) plasma is caught in a lower beta side plasmoid. This suggests a new plasma mixing process in the reconnection events. (3) A new large strong fast shock in front of the plasmoid forms in the HBS. This can be a new particle acceleration site in the reconnection system. These critical properties that have not been reported in previous works suggest that we contribute to a better and more detailed knowledge of the reconnection of the standard model for the symmetric magnetic reconnection system.
X-Point Reconnection from Shear Driving in Kinetic Simulations
Black, C.; Antiochos, S. K.; DeVore, C. R.; Germaschewski, K.; Bessho, N.; Karpen, J. T.
2014-12-01
The explosive energy release in solar eruptive phenomena such as CMEs/eruptive flares and coronal jets is believed to be due to magnetic reconnection. Magnetic free energy builds up slowly in the corona due to footpoint stressing by the photospheric motions. Along with the free energy, current sheets build up at coronal nulls, which eventually triggers fast reconnection and explosive energy release. This basic scenario has been modeled extensively by MHD simulations and applied to both CMEs/eruptive flares and jets, but the reconnection itself is well-known to be due to kinetic processes. Consequently, it is imperative that shear-driven X-point reconnection be modeled in a fully kinetic system so as to test and guide the MHD results. In MHD simulations, the application of a magnetic-field shear at the system boundary is a trivial matter, but this is definitely not the case for a kinetic system, because the electric currents need to be fully consistent with all the mass motions. We present the first results of reconnection in a 2D X-Point geometry due to a velocity shear driver perpendicular to the plane of reconnection. We compare the results to high-resolution MHD simulations and discuss the implications for coronal activity.
Ho, K. K.; Moody, G. B.; Peng, C. K.; Mietus, J. E.; Larson, M. G.; Levy, D.; Goldberger, A. L.
1997-01-01
BACKGROUND: Despite much recent interest in quantification of heart rate variability (HRV), the prognostic value of conventional measures of HRV and of newer indices based on nonlinear dynamics is not universally accepted. METHODS AND RESULTS: We have designed algorithms for analyzing ambulatory ECG recordings and measuring HRV without human intervention, using robust methods for obtaining time-domain measures (mean and SD of heart rate), frequency-domain measures (power in the bands of 0.001 to 0.01 Hz [VLF], 0.01 to 0.15 Hz [LF], and 0.15 to 0.5 Hz [HF] and total spectral power [TP] over all three of these bands), and measures based on nonlinear dynamics (approximate entropy [ApEn], a measure of complexity, and detrended fluctuation analysis [DFA], a measure of long-term correlations). The study population consisted of chronic congestive heart failure (CHF) case patients and sex- and age-matched control subjects in the Framingham Heart Study. After exclusion of technically inadequate studies and those with atrial fibrillation, we used these algorithms to study HRV in 2-hour ambulatory ECG recordings of 69 participants (mean age, 71.7+/-8.1 years). By use of separate Cox proportional-hazards models, the conventional measures SD (Psurvival over a mean follow-up period of 1.9 years; other measures, including ApEn (P>.3), were not. In multivariable models, DFA was of borderline predictive significance (P=.06) after adjustment for the diagnosis of CHF and SD. CONCLUSIONS: These results demonstrate that HRV analysis of ambulatory ECG recordings based on fully automated methods can have prognostic value in a population-based study and that nonlinear HRV indices may contribute prognostic value to complement traditional HRV measures.