6,234 research outputs found
Monopole clusters and critical dynamics in four-dimensional U(1)
We investigate monopoles in four-dimensional compact U(1) with Wilson action.
We focus our attention on monopole clusters as they can be identified
unambiguously contrary to monopole loops. We locate the clusters and determine
their properties near the U(1) phase transition. The Coulomb phase is
characterized by several small clusters, whereas in the confined phase the
small clusters coalesce to one large cluster filling up the whole system. We
find that clusters winding around the periodic lattice are absent within both
phases and during the transition. However, within the confined phase, we
observe periodically closed monopole loops if cooling is applied.Comment: 3 pages, Wuppertal preprint WUB 93-3
Study of nickel hydroxide electrodes. 2: Oxidation products of nickel (2) hydroxides
Pure phases of some oxidized Ni oxides were prepared galvanimetrically with the Ni(2) hydroxide electrode of an alkaline battery. The crystallographic data of these phases, their chemical behavior, and conditions of transition were studied
Monopoles in Compact U(1) -- Anatomy of the Phase Transition
We present evidence that the existence of a first order phase transition in
compact U(1) with Wilson action is not related to monopole loops wrapping
around the toroidal lattice, as has been previously suggested. Our analysis is
based on the suppression of such loops by `soft boundary conditions' that
correspond to an infinitely large chemical potential for the monopoles on the
boundary, during the updating process. It is observed that the double peak
structure characteristic for the first order phase transition reappears at
sufficiently large lattice sizes and separations from the lattice boundary.Comment: 8 pages, (color) ps-figures available via anonymous ftp at
ftp://wpts0.physik.uni-wuppertal.de/pub/monopoles/figures.u
New Record of \u3ci\u3eBrachycercus Maculatus\u3c/i\u3e Berner (Ephemeroptera: Caenidae) From New York and a Key to Larvae of Northeastern Species
Brachycercus maculatus, a member of a rare group of mayflies, is now recorded for the first time from New York State in the upper Hudson River. An illustrated key to the Brachycercus larvae of northeastern North America is provided to spur further study of the genus in the region
A Spitzer Survey of Novae in M31
We report the results of the first infrared survey of novae in the nearby
spiral galaxy, M31. Both photometric and spectroscopic observations of a sample
of 10 novae (M31N 2006-09c, 2006-10a, 2006-10b, 2006-11a, 2007-07f, 2007-08a,
2007-08d, 2007-10a, 2007-11d, and 2007-11e) were obtained with the Spitzer
Space Telescope. Eight of the novae were observed with the IRAC (all but M31N
2007-11d and 2007-11e) and eight with the IRS (all but 2007-07f and 2007-08a),
resulting in six in common between the two instruments. The observations, which
were obtained between ~3 and ~7 months after discovery, revealed evidence for
dust formation in two of the novae: M31N 2006-10a and (possibly) 2007-07f, and
[Ne II] 12.8 micron line emission in a third (2007-11e). The Spitzer
observations were supplemented with ground-based optical photometric and
spectroscopic data that were used to determine the speed classes and
spectroscopic types of the novae in our survey. After including data for
dust-forming Galactic novae, we show that dust formation timescales are
correlated with nova speed class in that dust typically forms earlier in faster
novae. We conclude that our failure to detect the signature of dust formation
in most of our M31 sample is likely a result of the relatively long delay
between nova eruption and our Spitzer observations. Indeed, the two novae for
which we found evidence of dust formation were the two "slowest" novae in our
sample. Finally, as expected, we found that the majority of the novae in our
sample belong to the Fe II spectroscopic class, with only one clear example of
the He/N class (M31N 2006-10b). Typical of an He/N system, M31N 2006-10b was
the fastest nova in our sample, not detected with the IRS, and just barely
detected in three of the IRAC bands when it was observed ~4 months after
eruption.Comment: 37 pages, 12 figures, accepted for publication in the Astrophysical
Journa
Robustness of Binary Black Hole Mergers in the Presence of Spurious Radiation
We present an investigation into how sensitive the last orbits and merger of
binary black hole systems are to the presence of spurious radiation in the
initial data. Our numerical experiments consist of a binary black hole system
starting the last couple of orbits before merger with additional spurious
radiation centered at the origin and fixed initial angular momentum. As the
energy in the added spurious radiation increases, the binary is invariably
hardened for the cases we tested, i.e. the merger of the two black holes is
hastened. The change in merger time becomes significant when the additional
energy provided by the spurious radiation increases the Arnowitt-Deser-Misner
(ADM) mass of the spacetime by about 1%. While the final masses of the black
holes increase due to partial absorption of the radiation, the final spins
remain constant to within our numerical accuracy. We conjecture that the
spurious radiation is primarily increasing the eccentricity of the orbit and
secondarily increasing the mass of the black holes while propagating out to
infinity.Comment: 12 pages, 12 figure
First-Order Signals in Compact QED with Monopole Suppressed Boundaries
Pure gauge compact QED on hypercubic lattices is considered with periodically
closed monopole currents suppressed. We compute observables on sublattices
which are nested around the centre of the lattice in order to locate regions
where translation symmetry is approximately recovered. Our Monte Carlo
simulations on -lattices give indications for a first-order nature of the
U(1) phase transition.Comment: 3 pages, uuencoded Z-compressed .tar file, to appear in proceedings
of lattice 9
Swift observations of the 2006 outburst of the recurrent nova RS Ophiuchi: III. X-ray spectral modelling
Following the Swift X-ray observations of the 2006 outburst of the recurrent
nova RS Ophiuchi, we developed hydrodynamical models of mass ejection from
which the forward shock velocities were used to estimate the ejecta mass and
velocity. In order to further constrain our model parameters, here we present
synthetic X-ray spectra from our hydrodynamical calculations which we compare
to the Swift data. An extensive set of simulations was carried out to find a
model which best fits the spectra up to 100 days after outburst. We find a good
fit at high energies but require additional absorption to match the low energy
emission. We estimate the ejecta mass to be in the range (2-5) x 10^{-7} solar
masses and the ejection velocity to be greater than 6000 km/s (and probably
closer to 10,000 km/s). We also find that estimates of shock velocity derived
from gas temperatures via standard model fits to the X-ray spectra are much
lower than the true shock velocities.Comment: 13 pages, 5 figures, Accepted for publication in Ap
Dynamical overlap simulations using HMC
We apply the Hybrid Monte Carlo method to the simulation of overlap fermions.
We give the fermionic force for the molecular dynamics update. We present early
results on a small dynamical chiral ensemble.Comment: Lattice2004(machines), 3 pages; references updated, minor changes to
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