21,112 research outputs found
Preliminary Results from the Caltech Core-Collapse Project (CCCP)
We present preliminary results from the Caltech Core-Collapse Project (CCCP),
a large observational program focused on the study of core-collapse SNe.
Uniform, high-quality NIR and optical photometry and multi-epoch optical
spectroscopy have been obtained using the 200'' Hale and robotic 60''
telescopes at Palomar, for a sample of 50 nearby core-collapse SNe. The
combination of both well-sampled optical light curves and multi-epoch
spectroscopy will enable spectroscopically and photometrically based subtype
definitions to be disentangled from each other. Multi-epoch spectroscopy is
crucial to identify transition events that evolve among subtypes with time. The
CCCP SN sample includes every core-collapse SN discovered between July 2004 and
September 2005 that was visible from Palomar, found shortly (< 30 days) after
explosion (based on available pre-explosion photometry), and closer than ~120
Mpc. This complete sample allows, for the first time, a study of core-collapse
SNe as a population, rather than as individual events. Here, we present the
full CCCP SN sample and show exemplary data collected. We analyze available
data for the first ~1/3 of the sample and determine the subtypes of 13 SNe II
based on both light curve shapes and spectroscopy. We discuss the relative SN
II subtype fractions in the context of associating SN subtypes with specific
progenitor stars.Comment: To appear in the proceedings of the meeting "The Multicoloured
Landscape of Compact Objects and their Explosive Origins", Cefalu, Italy,
June 2006, to be published by AIP, Eds. L. Burderi et a
Compaction and dilation rate dependence of stresses in gas-fluidized beds
A particle dynamics-based hybrid model, consisting of monodisperse spherical
solid particles and volume-averaged gas hydrodynamics, is used to study
traveling planar waves (one-dimensional traveling waves) of voids formed in
gas-fluidized beds of narrow cross sectional areas. Through ensemble-averaging
in a co-traveling frame, we compute solid phase continuum variables (local
volume fraction, average velocity, stress tensor, and granular temperature)
across the waves, and examine the relations among them. We probe the
consistency between such computationally obtained relations and constitutive
models in the kinetic theory for granular materials which are widely used in
the two-fluid modeling approach to fluidized beds. We demonstrate that solid
phase continuum variables exhibit appreciable ``path dependence'', which is not
captured by the commonly used kinetic theory-based models. We show that this
path dependence is associated with the large rates of dilation and compaction
that occur in the wave. We also examine the relations among solid phase
continuum variables in beds of cohesive particles, which yield the same path
dependence. Our results both for beds of cohesive and non-cohesive particles
suggest that path-dependent constitutive models need to be developed.Comment: accepted for publication in Physics of Fluids (Burnett-order effect
analysis added
Evidence of precursor superconductivity as high as 180 K from infrared spectroscopy
We show that a multilayer analysis of the infrared c-axis response of
RBa2Cu3O7-d (R=Y, Gd, Eu) provides important new information about the
anomalous normal state properties of underdoped cuprate high temperature
superconductors. Besides competing correlations which give rise to a pseudogap
that depletes the low-energy electronic states below T*>>Tc, it enables us to
identify the onset of a precursor superconducting state below Tons>Tc. We map
out the doping phase diagram of Tons which reaches a maximum of ~180 K at
strong underdoping and present magnetic field dependent data which confirm our
conclusions.Comment: 5 pages, 3 figure
Statistics of skyrmions in Quantum Hall systems
We analyze statistical interactions of skyrmions in the quantum Hall system
near a critical filling fraction in the framework of the Ginzburg-Landau model.
The phase picked up by the wave-function during an exchange of two skyrmions
close to is , where is the skyrmion's
spin. In the same setting an exchange of two fully polarized vortices gives
rise to the phase . Skyrmions with odd and even numbers of reversed
spins have different quantum statistics. Condensation of skyrmions with an even
number of reversed spins leads to filling fractions with odd denominators,
while condensation of those with an odd number of reversed spins gives rise to
filling fractions with even denominators.Comment: 6 pages in Latex. addendum - skyrmions with odd or even number of
reversed spins have different quantum statistics. They condense to form
respectively even or odd denominator filling fraction state
Anomalous Exponent of the Spin Correlation Function of a Quantum Hall Edge
The charge and spin correlation functions of partially spin-polarized edge
electrons of a quantum Hall bar are studied using effective Hamiltonian and
bosonization techniques. In the presence of the Coulomb interaction between the
edges with opposite chirality we find a different crossover behavior in spin
and charge correlation functions. The crossover of the spin correlation
function in the Coulomb dominated regime is characterized by an anomalous
exponent, which originates from the finite value of the effective interaction
for the spin degree of freedom in the long wavelength limit. The anomalous
exponent may be determined by measuring nuclear spin relaxation rates in a
narrow quantum Hall bar or in a quantum wire in strong magnetic fields.Comment: 4 pages, Revtex file, no figures. To appear in Physical Revews B,
Rapid communication
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