9,344 research outputs found
Three-dimensional simulations of the orientation and structure of reconnection X-lines
This work employs Hall magnetohydrodynamic (MHD) simulations to study the
X-lines formed during the reconnection of magnetic fields with differing
strengths and orientations embedded in plasmas of differing densities. Although
random initial perturbations trigger the growth of X-lines with many
orientations, at late time a few robust X-lines sharing an orientation
reasonably consistent with the direction that maximizes the outflow speed, as
predicted by Swisdak and Drake [Geophys. Res. Lett., 34, L11106, (2007)],
dominate the system. The existence of reconnection in the geometry examined
here contradicts the suggestion of Sonnerup [J. Geophys. Res., 79, 1546 (1974)]
that reconnection occurs in a plane normal to the equilibrium current. At late
time the growth of the X-lines stagnates, leaving them shorter than the
simulation domain.Comment: Accepted by Physics of Plasma
All-Electron Path Integral Monte Carlo Simulations of Warm Dense Matter: Application to Water and Carbon Plasmas
We develop an all-electron path integral Monte Carlo (PIMC) method with
free-particle nodes for warm dense matter and apply it to water and carbon
plasmas. We thereby extend PIMC studies beyond hydrogen and helium to elements
with core electrons. PIMC pressures, internal energies, and pair-correlation
functions compare well with density functional theory molecular dynamics
(DFT-MD) at temperatures of (2.5-7.5) K and both methods together
form a coherent equation of state (EOS) over a density-temperature range of
3--12 g/cm and 10--10 K
Test evaluation of fuel cell catalysts Quarterly report, 15 Feb. - 15 May 1967
Catalytic activity of iron compounds for fuel cell catalyst
A natural study of the efficacy of replacement medications for the treatment of clozapine-induced hypersalivation
Design Considerations for Unmagnetized Collisionless-shock Measurements in Homologous Flows
The subject of this paper is the design of practical laser experiments that can produce collisionless shocks mediated by the Weibel instability. Such shocks may be important in a wide range of astrophysical systems. Three issues are considered. The first issue is the implications of the fact that such experiments will produce expanding flows that are approximately homologous. As a result, both the velocity and the density of the interpenetrating plasma streams will be time dependent. The second issue is the implications of the linear theory of the Weibel instability. For the experiments, the instability is in a regime where standard simplifications do not apply. It appears feasible but non-trivial to obtain adequate growth. The third issue is collisionality. The need to keep resistive magnetic-field dissipation small enough implies that the plasmas should not be allowed to cool substantially.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/98554/1/0004-637X_749_2_171.pd
Diamond degradation in hadron fields
The energy dependence of the concentration of primary displacements induced
by protons and pions in diamond has been calculated in the energy range 50 MeV
- 50 GeV, in the frame of the Lindhard theory. The concentrations of primary
displacements induced by protons and pions have completely different energy
dependencies: the proton degradation is very important at low energies, and is
higher than the pion one in the whole energy range investigated, with the
exception of the delta33 resonance region. Diamond has been found,
theoretically, to be one order of magnitude more resistant to proton and pion
irradiation in respect to silicon.Comment: 7 pages, 3 figure
Hysteresis and competition between disorder and crystallization in sheared and vibrated granular flow
Experiments on spherical particles in a 3D Couette cell vibrated from below
and sheared from above show a hysteretic freezing/melting transition. Under
sufficient vibration a crystallized state is observed, which can be melted by
sufficient shear. The critical line for this transition coincides with equal
kinetic energies for vibration and shear. The force distribution is
double-peaked in the crystalline state and single-peaked with an approximately
exponential tail in the disordered state. A linear relation between pressure
and volume () exists for a continuum of partially and/or
intermittently melted states over a range of parameters
The different origins of magnetic fields and activity in the Hertzsprung gap stars, OU Andromedae and 31 Comae
Context: When crossing the Hertzsprung gap, intermediate-mass stars develop a
convective envelope. Fast rotators on the main sequence, or Ap star
descendants, are expected to become magnetic active subgiants during this
evolutionary phase. Aims: We compare the surface magnetic fields and activity
indicators of two active, fast rotating red giants with similar masses and
spectral class but diferent rotation rates - OU And (Prot=24.2 d) and 31 Com
(Prot=6.8 d) - to address the question of the origin of their magnetism and
high activity.
Methods: Observations were carried out with the Narval spectropolarimeter in
2008 and 2013.We used the least squares deconvolution technique to extract
Stokes V and I profiles to detect Zeeman signatures of the magnetic field of
the stars. We provide Zeeman-Doppler imaging, activity indicator monitoring,
and a precise estimation of stellar parameters. We use stellar evolutionary
models to infer the evolutionary status and the initial rotation velocity on
the main sequence.
Results: The detected magnetic field of OU And is a strong one. Its
longitudinal component Bl reaches 40 G and presents an about sinusoidal
variation with reversal of the polarity. The magnetic topology of OU And is
dominated by large scale elements and is mainly poloidal with an important
dipole component, and a significant toroidal component. The detected magnetic
field of 31 Com is weaker, with a magnetic map showing a more complex field
geometry, and poloidal and toroidal components of equal contributions. The
evolutionary models show that the progenitors of OU And and 31 Com must have
been rotat
Conclusions: OU And appears to be the probable descendant of a magnetic Ap
star, and 31 Com the descendant of a relatively fast rotator on the main
sequence.Comment: 16 pages, 12 figure
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