1,443 research outputs found
Calculation of renormalized viscosity and resistivity in magnetohydrodynamic turbulence
A self-consistent renormalization (RG) scheme has been applied to nonhelical
magnetohydrodynamic turbulence with normalized cross helicity and
. Kolmogorov's 5/3 powerlaw is assumed in order to compute the
renormalized parameters. It has been shown that the RG fixed point is stable
for . The renormalized viscosity and resistivity
have been calculated, and they are found to be positive for all
parameter regimes. For and large Alfv\'{e}n ratio (ratio of
kinetic and magnetic energies) , and . As
is decreased, increases and decreases, untill where both and are approximately zero. For large ,
both and vary as . The renormalized parameters for
the case are also reported.Comment: 19 pages REVTEX, 3 ps files (Phys. Plasmas, v8, 3945, 2001
Starbursts in multiple galaxy mergers
We numerically investigate stellar and gaseous dynamical evolution of mergers
between five identical late-type disk galaxies with the special emphasis on
star formation history and chemical evolution of multiple galaxy mergers. We
found that multiple encounter and merging can trigger repetitive massive
starbursts (typically 100 ) owing to the
strong tidal disturbance and the resultant gaseous dissipation during merging.
The magnitude of the starburst is found to depend on initial virial ratio
(i.e., the ratio of total kinematical energy to total potential energy) such
that the maximum star formation rate is larger for the merger with smaller
virial ratio. Furthermore we found that the time interval between the epochs of
the triggered starbursts is longer for the merger with the larger virial ratio.
The remnant of a multiple galaxy merger with massive starbursts is found to
have metal-poor gaseous halo that is formed by tidal stripping during the
merging. We accordingly suggest that metal-poor gaseous halo in a field
elliptical galaxy is a fossil record of the past multiple merging events for
the galaxy.Comment: 23 pages 16 figures,2000,ApJ,545 in press. For all ps figures, see
http://newt.phys.unsw.edu.au/~bekki/res.dir/paper.dir/mul.dir/fig.tar.g
Electromagnetic gyrokinetic turbulence in finite-beta helical plasmas
A saturation mechanism for microturbulence in a regime of weak zonal flow generation isinvestigated by means of electromagnetic gyrokinetic simulations. The study identifies a newsaturation process of the kinetic ballooning mode (KBM) turbulence originating from the spatial structure of the KBM instabilities in a finite-beta Large Helical Device (LHD) plasma.Specifically, the most unstable KBM in LHD has an inclined mode structure with respect to the mid-plane of a torus, i.e., it has a finite radial wave-number in flux tube coordinates, in contrast to KBMs in tokamaks as well as ion-temperature gradient modes in tokamaks and helical systems. The simulations reveal that the growth of KBMs in LHD is saturated by nonlinear interactions of oppositely inclined convection cells through mutual shearing as well as by the zonal flow. The saturation mechanism is quantitatively investigated by analysis of the nonlinear entropy transfer that shows not only the mutual shearing but also a self-interaction with an elongated mode structure along the magnetic field line
Effect of the curvature and the {\beta} parameter on the nonlinear dynamics of a drift tearing magnetic island
We present numerical simulation studies of 2D reduced MHD equations
investigating the impact of the electronic \beta parameter and of curvature
effects on the nonlinear evolution of drift tearing islands. We observe a
bifurcation phenomenon that leads to an amplification of the pressure energy,
the generation of E \times B poloidal flow and a nonlinear diamagnetic drift
that affects the rotation of the magnetic island. These dynamical modifications
arise due to quasilinear effects that generate a zonal flow at the onset point
of the bifurcation. Our simulations show that the transition point is
influenced by the \beta parameter such that the pressure gradient through a
curvature effect strongly stabilizes the transition. Regarding the modified
rotation of the island, a model for the frequency is derived in order to study
its origin and the effect of the \beta parameter. It appears that after the
transition, an E \times B poloidal flow as well as a nonlinear diamagnetic
drift are generated due to an amplification of the stresses by pressure
effects
Gyrokinetic Turbulence Simulations of High-beta Tokamak and Helical Plasmas with Full-kinetic and Hybrid Models
Influence of transport and ocean ice extent on biogenic aerosol sulfur in the Arctic atmosphere
The recent decline in sea ice cover in the Arctic Ocean could affect the regional radiative forcing via changes in sea ice-atmosphere exchange of dimethyl sulfide (DMS) and biogenic aerosols formed from its atmospheric oxidation, such as methanesulfonic acid (MSA). This study examines relationships between changes in total sea ice extent north of 70 degrees N and atmospheric MSA measurement at Alert, Nunavut, during 1980-2009; at Barrow, Alaska, during 1997-2008; and at Ny-Alesund, Svalbard, for 1991-2004. During the 1980-1989 and 1990-1997 periods, summer (July-August) and June MSA concentrations at Alert decreased. In general, MSA concentrations increased at all locations since 2000 with respect to 1990 values, specifically during June and summer at Alert and in summer at Barrow and Ny-Alesund. Our results show variability in MSA at all sites is related to changes in the source strengths of DMS, possibly linked to changes in sea ice extent as well as to changes in atmospheric transport patterns. Since 2000, a late spring increase in atmospheric MSA at the three sites coincides with the northward migration of the marginal ice edge zone where high DMS emissions from ocean to atmosphere have previously been reported. Significant negative correlations are found between sea ice extent and MSA concentrations at the three sites during the spring and June. These results suggest that a decrease in seasonal ice cover influencing other mechanisms of DMS production could lead to higher atmospheric MSA concentrations
Hybrid Method of Semi-Lagrangian and Additive Semi-implicit Runge-Kutta Schemes for Gyrokinetic Vlasov Simulations
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