2,649 research outputs found
Observation of explosive collisionless reconnection in 3D nonlinear gyrofluid simulations
The nonlinear dynamics of collisionless reconnecting modes is investigated,
in the framework of a three-dimensional gyrofluid model. This is the relevant
regime of high-temperature plasmas, where reconnection is made possible by
electron inertia and has higher growth rates than resistive reconnection. The
presence of a strong guide field is assumed, in a background slab model, with
Dirichlet boundary conditions in the direction of nonuniformity. Values of ion
sound gyro-radius and electron collisionless skin depth much smaller than the
current layer width are considered. Strong acceleration of growth is found at
the onset to nonlinearity, while at all times the energy functional is well
conserved. Nonlinear growth rates more than one order of magnitude higher than
linear growth rates are observed when entering into the small- regime
Gyrofluid simulations of collisionless reconnection in the presence of diamagnetic effects
The effects of the ion Larmor radius on magnetic reconnection are
investigated by means of numerical simulations, with a Hamiltonian gyrofluid
model. In the linear regime, it is found that ion diamagnetic effects decrease
the growth rate of the dominant mode. Increasing ion temperature tends to make
the magnetic islands propagate in the ion diamagnetic drift direction. In the
nonlinear regime, diamagnetic effects reduce the final width of the island.
Unlike the electron density, the guiding center density does not tend to
distribute along separatrices and at high ion temperature, the electrostatic
potential exhibits the superposition of a small scale structure, related to the
electron density, and a large scale structure, related to the ion
guiding-center density
Gyrofluid simulations of collisionless reconnection in the presence of diamagnetic effects
The effects of the ion Larmor radius on magnetic reconnection are
investigated by means of numerical simulations, with a Hamiltonian gyrofluid
model. In the linear regime, it is found that ion diamagnetic effects decrease
the growth rate of the dominant mode. Increasing ion temperature tends to make
the magnetic islands propagate in the ion diamagnetic drift direction. In the
nonlinear regime, diamagnetic effects reduce the final width of the island.
Unlike the electron density, the guiding center density does not tend to
distribute along separatrices and at high ion temperature, the electrostatic
potential exhibits the superposition of a small scale structure, related to the
electron density, and a large scale structure, related to the ion
guiding-center density
String cosmological model in the presence of a magnetic flux
A Bianchi type I string cosmological model in the presence of a magnetic flux
is investigated. A few plausible assumptions regarding the parametrization of
the cosmic string and magneto-fluid are introduced and some exact analytical
solutions are presented.Comment: 9 pages, 4 Figure
Cosmological Magnetogenesis driven by Radiation Pressure
The origin of large scale cosmological magnetic fields remains a mystery,
despite the continuous efforts devoted to that problem. We present a new model
of magnetic field generation, based on local charge separation provided by an
anisotropic and inhomogeneous radiation pressure. In the cosmological context,
the processes we explore take place at the epoch of the reionisation of the
Universe. Under simple assumptions, we obtain results (i) in terms of the order
of magnitude of the field generated at large scales and (ii) in terms of its
power spectrum. The amplitudes obtained (B ~ 8.10^(-6) micro-Gauss) are
considerably higher than those obtained in usual magnetogenesis models and
provide suitable seeds for amplification by adiabatic collapse and/or dynamo
during structure formation.Comment: 9 pages, 2 figure
A review of recent perspectives on biomechanical risk factors associated with anterior cruciate ligament injury
There is considerable evidence to support a number of biomechanical risk factors associated with non-contact anterior cruciate ligament (ACL) injury. This paper aimed to review these biomechanical risk factors and highlight future directions relating to them. Current perspectives investigating trunk position and relationships between strength, muscle activity and biomechanics during landing/cutting highlight the importance of increasing hamstring muscle force during dynamic movements through altering strength, muscle activity, muscle length and contraction velocity. In particular, increased trunk flexion during landing/cutting and greater hamstring strength are likely to increase hamstring muscle force during landing and cutting which have been associated with reduced ACL injury risk. Decision making has also been shown to influence landing biomechanics and should be considered when designing tasks to assess landing/cutting biomechanics. Coaches should therefore promote hamstring strength training and active trunk flexion during landing and cutting in an attempt to reduce ACL injury risk.Peer reviewe
Excitation of MHD waves in magnetized anisotropic cosmologies
The excitation of cosmological perturbations in an anisotropic cosmological
model and in the presence of a homogeneous magnetic field was studied, using
the resistive magnetohydrodynamic (MHD) equations. We have shown that
fast-magnetosonic modes, propagating normal to the magnetic field grow
exponentially and saturated at high values, due to the resistivity. We also
demonstrate that the jeans-like instabilities are enhanced inside a resistive
and the formation of condensations formed within an anisotropic fluid influence
the growing magnetosonic waves.Comment: 12 pages, RevTex, 5 figures ps, accepted for publication to Astronomy
and Astrophysic
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