265 research outputs found
Parasites on parasites:Coupled fluctuations in stacked contact processes
We present a model for host-parasite dynamics which incorporates both vertical and horizontal transmission as well as spatial structure. Our model consists of stacked contact processes (CP), where the dynamics of the host is a simple CP on a lattice while the dynamics of the parasite is a secondary CP which sits on top of the host-occupied sites. In the simplest case, where infection does not incur any cost, we uncover a novel effect: a non-monotonic dependence of parasite prevalence on host turnover. Inspired by natural examples of hyperparasitism, we extend our model to multiple levels of parasites and identify a transition between the maintenance of a finite and infinite number of levels, which we conjecture is connected to a roughening transition in models of surface growth
Spatiotemporally Complete Condensation in a Non-Poissonian Exclusion Process
We investigate a non-Poissonian version of the asymmetric simple exclusion
process, motivated by the observation that coarse-graining the interactions
between particles in complex systems generically leads to a stochastic process
with a non-Markovian (history-dependent) character. We characterize a large
family of one-dimensional hopping processes using a waiting-time distribution
for individual particle hops. We find that when its variance is infinite, a
real-space condensate forms that is complete in space (involves all particles)
and time (exists at almost any given instant) in the thermodynamic limit. The
mechanism for the onset and stability of the condensate are both rather subtle,
and depends on the microscopic dynamics subsequent to a failed particle hop
attempts.Comment: 5 pages, 5 figures. Version 2 to appear in PR
The Circumnuclear Molecular Gas in the Seyfert Galaxy NGC4945
We have mapped the central region of NGC 4945 in the transition of
CO, CO, and CO, as well as the continuum at 1.3 mm, at an
angular resolution of 5\farc \times 3\farc with the Submillimeter Array. The
relative proximity of NGC 4945 (distance of only 3.8 Mpc) permits a detailed
study of the circumnuclear molecular gas and dust in a galaxy exhibiting both
an AGN (classified as a Seyfert 2) and a circumnuclear starburst in an inclined
ring with radius 2\farcs5 (50 pc). We find that all three molecular
lines trace an inclined rotating disk with major axis aligned with that of the
starburst ring and large-scale galactic disk, and which exhibits solid-body
rotation within a radius of 5\farc (95 pc). We infer an inclination
for the nuclear disk of , somewhat smaller than the
inclination of the large-scale galactic disk of . The
continuum emission at 1.3 mm also extends beyond the starburst ring, and is
dominated by thermal emission from dust. If it traces the same dust emitting in
the far-infrared, then the bulk of this dust must be heated by star-formation
activity rather than the AGN. We discover a kinematically-decoupled component
at the center of the disk with a radius smaller than 1\farcs4 (27 pc), but
which spans approximately the same range of velocities as the surrounding disk.
This component has a higher density than its surroundings, and is a promising
candidate for the circumnuclear molecular torus invoked by AGN unification
models.Comment: 13 pages, 10 figures,accepted by Ap
A Search for H2O Megamasers in High-z Type-2 AGNs
We report a search for H2O megamasers in 274 SDSS type-2 AGNs (0.3 < z <
0.83), half of which can be classified as type-2 QSOs from their [OIII] 5007
luminosity, using the Robert C. Byrd Green Bank Telescope (GBT) and the
Effelsberg 100-m radio telescope. Apart from the detection of the extremely
luminous water vapor megamaser SDSS J080430.99+360718.1, already reported by
Barvainis & Antonucci (2005), we do not find any additional line emission. This
high rate of non-detections is compared to the water maser luminosity function
created from the 78 water maser galaxies known to date and its extrapolation
towards the higher luminosities of "gigamasers" that we would have been able to
detect given the sensitivity of our survey. The properties of the known water
masers are summarized and discussed with respect to the nature of high-z type-2
AGNs and megamasers in general. In the appendix, we list 173 additional objects
(mainly radio galaxies, but also QSOs and galaxies) that were observed with the
GBT, the Effelsberg 100-m radio telescope, or Arecibo Observatory without
leading to the detection of water maser emission.Comment: 28 pages, 3 figures. Accepted for publication in the Astrophysical
Journa
Exact results for the zeros of the partition function of the Potts model on finite lattices
The Yang-Lee zeros of the Q-state Potts model are investigated in 1, 2 and 3
dimensions. Analytical results derived from the transfer matrix for the
one-dimensional model reveal a systematic behavior of the locus of zeros as a
function of Q. For 1<Q<2 the zeros in the complex plane lie
inside the unit circle, while for Q>2 they lie outside the unit circle for
finite temperature. In the special case Q=2 the zeros lie exactly on the unit
circle as proved by Lee and Yang. In two and three dimensions the zeros are
calculated numerically and behave in the same way. Results are also presented
for the critical line of the Potts model in an external field as determined
from the zeros of the partition function in the complex temperature plane.Comment: 15 pages, 6 figures, RevTe
Partition function zeros of the Q-state Potts model for non-integer Q
The distribution of the zeros of the partition function in the complex
temperature plane (Fisher zeros) of the two-dimensional Q-state Potts model is
studied for non-integer Q. On self-dual lattices studied (),
no Fisher zero lies on the unit circle in the complex
plane for Q<1, while some of the Fisher zeros lie
on the unit circle for Q>1 and the number of such zeros increases with
increasing Q. The ferromagnetic and antiferromagnetic properties of the Potts
model are investigated using the distribution of the Fisher zeros. For the
Potts ferromagnet we verify the den Nijs formula for the thermal exponent
. For the Potts antiferromagnet we also verify the Baxter conjecture for
the critical temperature and present new results for the thermal exponents in
the range 0<Q<3.Comment: 12 pages, 7 figures, RevTe
Human Exposure to Herpesvirus B–Seropositive Macaques, Bali, Indonesia
Herpesvirus B (Cercopithecine herpesvirus 1) has been implicated as the cause of approximately 40 cases of meningoencephalitis affecting persons in direct or indirect contact with laboratory macaques. However, the threat of herpesvirus B in nonlaboratory settings worldwide remains to be addressed. We investigated the potential for exposure to herpesvirus B in workers at a “monkey forest” (a temple that has become a tourist attraction because of its monkeys) in Bali, Indonesia. In July 2000, 105 workers at the Sangeh Monkey Forest in Central Bali were surveyed about contact with macaques (Macaca fascicularis). Nearly half of those interviewed had either been bitten or scratched by a macaque. Prevalence of injury was higher in those who fed macaques. Serum from 31 of 38 Sangeh macaques contained antibodies to herpesvirus B. We conclude that workers coming into contact with macaques at the Sangeh Monkey Forest are at risk for exposure to herpesvirus B
Molecular dynamics symulation of hydrogen diffusion in palladium
In the present work, the diffusion of hydrogen atoms in the crystal lattice of palladium was investigated using the molecular dynamics. The diffusion coefficients, activation energies and preexponential factors were determined for structures with different hydrogen concentration. It is determined that the diffusion coefficients decrease and the activation energy of diffusion grows with increasing concentrations of hydrogen
SMA CO(J=6-5) and 435 micron interferometric imaging of the nuclear region of Arp 220
We have used the Submillimeter Array (SMA) to make the first interferometric
observations (beam size ~1") of the 12CO J=6-5 line and 435 micron (690 GHz)
continuum emission toward the central region of the nearby ULIRG Arp 220. These
observations resolve the eastern and western nuclei from each other, in both
the molecular line and dust continuum emission. At 435 micron, the peak
intensity of the western nucleus is stronger than the eastern nucleus, and the
difference in peak intensities is less than at longer wavelengths. Fitting a
simple model to the dust emission observed between 1.3 mm and 435 micron
suggests that dust emissivity power law index in the western nucleus is near
unity and steeper in the eastern nucleus, about 2, and that the dust emission
is optically thick at the shorter wavelength. Comparison with single dish
measurements indicate that the interferometer observations are missing ~60% of
the dust emission, most likely from a spatially extended component to which
these observations are not sensitive. The 12CO J=6-5 line observations clearly
resolve kinematically the two nuclei. The distribution and kinematics of the
12CO J=6-5 line appear to be very similar to lower J CO lies observed at
similar resolution. Analysis of multiple 12CO line intensities indicates that
the molecular gas in both nuclei have similar excitation conditions, although
the western nucleus is warmer and denser. The excitation conditions are similar
to those found in other extreme environments, including M82, Mrk 231, and BR
1202-0725. Simultaneous lower resolution observations of the 12CO, 13CO, and
C18O J=2-1 lines show that the 13CO and C18O lines have similar intensities,
which suggests that both of these lines are optically thick, or possibly that
extreme high mass star formation has produced in an overabundance of C18O.Comment: 13 pages (emulateapj), 10 figures, Accepted for publication in Ap
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