8,730 research outputs found
Physics of relativistic shocks
Relativistic shocks are usually thought to occur in violent astrophysical
explosions. These collisionless shocks are mediated by a plasma kinetic
streaming instability, often loosely referred to as the Weibel instability,
which generates strong magnetic fields "from scratch" very efficiently. In this
review paper we discuss the shock micro-physics and present a recent model of
"pre-conditioning" of an initially unmagnetized upstream region via the
cosmic-ray-driven Weibel-type instability.Comment: Subm. to proceedings of the Annual International Astrophysics
Conference (AIAC-8), Hawaii, 200
Phase slip in a superfluid Fermi gas near a Feshbach resonance
In this paper, we study the properties of a phase slip in a superfluid Fermi
gas near a Feshbach resonance. The phase slip can be generated by the phase
imprinting method. Below the superfluid transition temperature, it appears as a
dip in the density profile, and becomes more pronounced when the temperature is
lowered. Therefore the phase slip can provide a direct evidence of the
superfluid state. The condensation energy of the superfluid state can be
extracted from the density profile of the phase slip, due to the unitary
properties of the Fermi gas near the resonance. The width of the phase slip is
proportional to the square root of the difference between the transition
temperature and the temperature. The signature of the phase slip in the density
profile becomes more robust across the BCS-BEC crossover.Comment: 5 pages, 2 figures, the density profile of a phase slip under
experimental conditions was calculate
Motion of Vacancies in a Pinned Vortex Lattice: Origin of the Hall Anomaly
Physical arguments are presented to show that the Hall anomaly is an effect
of the vortex many-body correlation rather than that of an individual vortex.
Quantitatively, the characteristic energy scale in the problem, the vortex
vacancy formation energy, is obtained for thin films. At low temperatures a
scaling relation between the Hall and longitudinal resistivities is found, with
the power depending on sample details. Near the superconducting transition
temperature and for small magnetic fields the Hall conductivity is found to be
proportional to the inverse of the magnetic field and to the quadratic of the
difference between the measured and the transition temperatures.Comment: minor change
Molecular Gas and Star formation in ARP 302
We present the Submillimeter Array observation of the CO J=2-1 transition
towards the northern galaxy, ARP 302N, of the early merging system, ARP 302.
Our high angular resolution observation reveals the extended spatial
distribution of the molecular gas in ARP 302N. We find that the molecular gas
has a very asymmetric distribution with two strong concentrations on either
side of the center together with a weaker one offset by about 8 kpc to the
north. The molecular gas distribution is also found to be consistent with that
from the hot dust as traced by the 24 micro continuum emission observed by the
Spitzer. The line ratio of CO J=2-1/1-0 is found to vary strongly from about
0.7 near the galaxy center to 0.4 in the outer part of the galaxy. Excitation
analysis suggests that the gas density is low, less than 10 cm, over
the entire galaxy. By fitting the SED of ARP 302N in the far infrared we obtain
a dust temperature of =26-36 K and a dust mass of M=2.0--3.6 M. The spectral index of the radio
continuum is around 0.9. The spatial distribution and spectral index of the
radio continuum emission suggests that most of the radio continuum emission is
synchrotron emission from the star forming regions at the nucleus and
ARP302N-cm. The good spatial correspondance between the 3.6 cm radio continuum
emission, the Spitzer 8 & 24 m data and the high resolution CO J=2-1
observation from the SMA shows that there is the asymmetrical star forming
activities in ARP 302N.Comment: 19 pages, 8 figures, accepted by A
Tunneling of a Quantized Vortex: Roles of Pinning and Dissipation
We have performed a theoretical study of the effects of pinning potential and
dissipation on vortex tunneling in superconductors. Analytical results are
obtained in various limits relevant to experiment. In general we have found
that pinning and dissipation tend to suppress the effect of the vortex velocity
dependent part of the Magnus force on vortex tunneling.Comment: Latex, 12 page
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