6,807 research outputs found
The MHD Kelvin-Helmholtz Instability III: The Role of Sheared Magnetic Field in Planar Flows
We have carried out simulations of the nonlinear evolution of the
magnetohydrodynamic (MHD) Kelvin-Helmholtz (KH) instability for compressible
fluids in -dimensions, extending our previous work by Frank et al
(1996) and Jones \etal (1997). In the present work we have simulated flows in
the x-y plane in which a ``sheared'' magnetic field of uniform strength
``smoothly'' rotates across a thin velocity shear layer from the z direction to
the x direction, aligned with the flow field. We focus on dynamical evolution
of fluid features, kinetic energy dissipation, and mixing of the fluid between
the two layers, considering their dependence on magnetic field strength for
this geometry. The introduction of magnetic shear can allow a Cat's Eye-like
vortex to form, even when the field is stronger than the nominal linear
instability limit given above. For strong fields that vortex is asymmetric with
respect to the preliminary shear layer, however, so the subsequent dissipation
is enhanced over the uniform field cases of comparable field strength. In fact,
so long as the magnetic field achieves some level of dynamical importance
during an eddy turnover time, the asymmetries introduced through the magnetic
shear will increase flow complexity, and, with that, dissipation and mixing.
The degree of the fluid mixing between the two layers is strongly influenced by
the magnetic field strength. Mixing of the fluid is most effective when the
vortex is disrupted by magnetic tension during transient reconnection, through
local chaotic behavior that follows.Comment: 14 pages including 9 figures (4 figures in degraded jpg format), full
paper with original quality figures available via anonymous ftp at
ftp://canopus.chungnam.ac.kr/ryu/mhdkh2d.uu, to appear in The Astrophysical
Journa
Tests of star formation metrics in the low metallicity galaxy NGC 5253 using ALMA observations of H30 line emission
We use Atacama Large Millimeter/submillimeter Array (ALMA) observations of
H30 (231.90 GHz) emission from the low metallicity dwarf galaxy NGC
5253 to measure the star formation rate (SFR) within the galaxy and to test the
reliability of SFRs derived from other commonly-used metrics. The H30
emission, which originates mainly from the central starburst, yields a
photoionizing photon production rate of (1.90.3)10 s
and an SFR of 0.0870.013 M yr based on conversions that
account for the low metallicity of the galaxy and for stellar rotation. Among
the other star formation metrics we examined, the SFR calculated from the total
infrared flux was statistically equivalent to the values from the H30
data. The SFR based on previously-published versions of the H flux that
were extinction corrected using Pa and Pa lines were lower than
but also statistically similar to the H30 value. The mid-infrared (22
m) flux density and the composite star formation tracer based on H
and mid-infrared emission give SFRs that were significantly higher because the
dust emission appears unusually hot compared to typical spiral galaxies.
Conversely, the 70 and 160 m flux densities yielded SFR lower than the
H30 value, although the SFRs from the 70 m and H30 data
were within 1-2 of each other. While further analysis on a broader
range of galaxies are needed, these results are instructive of the best and
worst methods to use when measuring SFR in low metallicity dwarf galaxies like
NGC 5253.Comment: 14 pages, 5 figures, accepted for publication in MNRA
AnĂĄlise e controle da qualidade de inoculantes microbianos de interesse agrĂcola: bactĂ©rias fixadoras de nitrogĂȘnio.
Ultrahigh-Field Hole Cyclotron Resonance Absorption in InMnAs Films
We have carried out an ultrahigh-field cyclotron resonance study of p-type
In1-xMnxAs films, with Mn composition x ranging from 0% to 2.5%, grown on GaAs
by low-temperature molecular-beam epitaxy. Pulsed magnetic fields up to 500 T
were used to make cyclotron resonance observable in these low-mobility samples.
The clear observation of hole cyclotron resonance is direct evidence of the
existence of a large number of itinerant, effective-mass-type holes rather than
localized d-like holes. It further suggests that the p-d exchange mechanism is
more favorable than the double exchange mechanism in this narrow gap InAs-based
dilute magnetic semiconductor. In addition to the fundamental heavy-hole and
light-hole cyclotron resonance absorption appearing near the
high-magnetic-field quantum limit, we observed many inter-Landau-level
absorption bands whose transition probabilities are stronglydependent on the
sense of circular polarization of the incident light.Comment: 8 pages, 10 Postscript figure
Soliton equations and the zero curvature condition in noncommutative geometry
Familiar nonlinear and in particular soliton equations arise as zero
curvature conditions for GL(1,R) connections with noncommutative differential
calculi. The Burgers equation is formulated in this way and the Cole-Hopf
transformation for it attains the interpretation of a transformation of the
connection to a pure gauge in this mathematical framework. The KdV, modified
KdV equation and the Miura transformation are obtained jointly in a similar
setting and a rather straightforward generalization leads to the KP and a
modified KP equation.
Furthermore, a differential calculus associated with the Boussinesq equation
is derived from the KP calculus.Comment: Latex, 10 page
Systematic analysis of pT -distributions in p + p collisions
A systematic analysis of transverse momentum distribution of hadrons produced
in ultra-relativistic p + p collisions is presented. We investigate the
effective temperature and the entropic parameter from the non-extensive
thermodynamic theory of strong interaction. We conclude that the existence of a
limiting effective temperature and of a limiting entropic parameter is in
accordance with experimental data.Comment: 9 pages, 5 figure
A New Nonlinear Liquid Drop Model. Clusters as Solitons on The Nuclear Surface
By introducing in the hydrodynamic model, i.e. in the hydrodynamic equations
and the corresponding boundary conditions, the higher order terms in the
deviation of the shape, we obtain in the second order the Korteweg de Vries
equation (KdV). The same equation is obtained by introducing in the liquid drop
model (LDM), i.e. in the kinetic, surface and Coulomb terms, the higher terms
in the second order. The KdV equation has the cnoidal waves as steady-state
solutions. These waves could describe the small anharmonic vibrations of
spherical nuclei up to the solitary waves. The solitons could describe the
preformation of clusters on the nuclear surface. We apply this nonlinear liquid
drop model to the alpha formation in heavy nuclei. We find an additional
minimum in the total energy of such systems, corresponding to the solitons as
clusters on the nuclear surface. By introducing the shell effects we choose
this minimum to be degenerated with the ground state. The spectroscopic factor
is given by the ratio of the square amplitudes in the two minima.Comment: 27 pages, LateX, 8 figures, Submitted J. Phys. G: Nucl. Part. Phys.,
PACS: 23.60.+e, 21.60.Gx, 24.30.-v, 25.70.e
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