2,667 research outputs found
Clinostomum marginatum metacercaria: Incidence in Smallmouth Bass from a North Arkansas Stream and in vitro Oxygen Consumption Studies
Small mouth bass (Micropterus dolomieui) captured from Crooked Creek (Marion Co., Arkansas) in the summers of 1977 and 1987 were found to have a high incidence of infection with the metacercaria of Clinostomum marginatum (yellow grub). Of 41 fish collected in 1977, 32 (78%) were found infected with metacercariae with some fish containing large numbers of parasites. The number of larvae per fish ranged from 1 to 184, with an average of 23.2 ± 38 per smallmouth. Eighty-six percent of the bass collected in 1987 were found positive for C. marginatum. The number of metacercariae per fish ranged from 1 to 227 with an average of 32.7 ± 54 per fish. Fish from both collection groups ranged in size from 12 to 34 cm. No significant correlation could be found between the number of metacercariae per fish and the length of the host. Using metacercariae removed from host tissue, the effect on oxygen consumption by glucose, serotonin and insulin, singularly or in combination, was measured by manometric methods. Glucose alone did not stimulate oxygen utilization, serotonin alone and with glucose was stimulatory, and insulin with glucose also increased oxygen consumption
Disc wind models for FU Ori objects
We present disc wind models aimed at reproducing the main features of the
strong Na I resonance line P-Cygni profiles in the rapidly-accreting pre-main
sequence FU Ori objects. We conducted Monte Carlo radiative transfer
simulations for a standard magnetocentrifugally driven wind (MHD) model and our
own "Genwind" models, which allows for a more flexible wind parameterisation.
We find that the fiducial MHD wind and similar Genwind models, which have flows
emerging outward from the inner disc edge, and thus have polar cavities with no
absorbing gas, cannot reproduce the deep, wide Na I absorption lines in FU Ori
objects viewed at low inclination. We find that it is necessary to include an
"inner wind" to fill this polar cavity to reproduce observations. In addition,
our models assuming pure scattering source functions in the Sobolev
approximation at intermediate viewing angles () do not yield sufficiently deep line profiles. Assuming complete
absorption yields better agreement with observations, but simple estimates
strongly suggest that pure scattering should be a much better approximation.
The discrepancy may indicate that the Sobolev approximation is not applicable,
possibly due to turbulence or non-monotonic velocity fields; there is some
observational evidence for the latter. Our results provide guidance for future
attempts to constrain FU Ori wind properties using full MHD wind simulations,
by pointing to the importance of the boundary conditions necessary to give rise
to an inner wind, and by suggesting that the winds must be turbulent to produce
sufficiently deep line profiles.Comment: 12 pages, 17 figures, accepted for publication in MNRA
Cosmic ray acceleration to ultrahigh energy in radio galaxies
The origin of ultrahigh energy cosmic rays (UHECRs) is an open question. In
this proceeding, we first review the general physical requirements that a
source must meet for acceleration to 10-100 EeV, including the consideration
that the shock is not highly relativistic. We show that shocks in the backflows
of radio galaxies can meet these requirements. We discuss a model in which
giant-lobed radio galaxies such as Centaurus A and Fornax A act as
slowly-leaking UHECR reservoirs, with the UHECRs being accelerated during a
more powerful past episode. We also show that Centaurus A, Fornax A and other
radio galaxies may explain the observed anisotropies in data from the Pierre
Auger Observatory, before examining some of the difficulties in associating
UHECR anisotropies with astrophysical sources.Comment: 6 pages, 4 figures. Proceedings of UHECR 2018, 8-12 October 2018,
Paris, Franc
Amplification of perpendicular and parallel magnetic fields by cosmic ray currents
Cosmic ray (CR) currents through magnetised plasma drive strong instabilities
producing amplification of the magnetic field. This amplification helps explain
the CR energy spectrum as well as observations of supernova remnants and radio
galaxy hot spots. Using magnetohydrodynamic (MHD) simulations, we study the
behaviour of the non-resonant hybrid (NRH) instability (also known as the Bell
instability) in the case of CR currents perpendicular and parallel to the
initial magnetic field. We demonstrate that extending simulations of the
perpendicular case to 3D reveals a different character to the turbulence from
that observed in 2D. Despite these differences, in 3D the perpendicular NRH
instability still grows exponentially far into the non-linear regime with a
similar growth rate to both the 2D perpendicular and 3D parallel situations. We
introduce some simple analytical models to elucidate the physical behaviour,
using them to demonstrate that the transition to the non-linear regime is
governed by the growth of thermal pressure inside dense filaments at the edges
of the expanding loops. We discuss our results in the context of supernova
remnants and jets in radio galaxies. Our work shows that the NRH instability
can amplify magnetic fields to many times their initial value in parallel and
perpendicular shocks.Comment: Published in MNRAS. 14 pages, 12 figures, 2 tables. Replacement
corrects some typesetting error
The Impact of Accretion Disk Winds on the Optical Spectra of Cataclysmic Variables
Many high-state non-magnetic cataclysmic variables (CVs) exhibit blue-shifted
absorption or P-Cygni profiles associated with ultraviolet (UV) resonance
lines. These features imply the existence of powerful accretion disk winds in
CVs. Here, we use our Monte Carlo ionization and radiative transfer code to
investigate whether disk wind models that produce realistic UV line profiles
are also likely to generate observationally significant recombination line and
continuum emission in the optical waveband. We also test whether outflows may
be responsible for the single-peaked emission line profiles often seen in
high-state CVs and for the weakness of the Balmer absorption edge (relative to
simple models of optically thick accretion disks). We find that a standard disk
wind model that is successful in reproducing the UV spectra of CVs also leaves
a noticeable imprint on the optical spectrum, particularly for systems viewed
at high inclination. The strongest optical wind-formed recombination lines are
H and He II . We demonstrate that a higher-density outflow
model produces all the expected H and He lines and produces a recombination
continuum that can fill in the Balmer jump at high inclinations. This model
displays reasonable verisimilitude with the optical spectrum of RW Trianguli.
No single-peaked emission is seen, although we observe a narrowing of the
double-peaked emission lines from the base of the wind. Finally, we show that
even denser models can produce a single-peaked H line. On the basis of
our results, we suggest that winds can modify, and perhaps even dominate, the
line and continuum emission from CVs.Comment: 15 pages, 13 figures. Accepted to MNRA
Particle acceleration in radio galaxies with flickering jets: GeV electrons to ultrahigh energy cosmic rays
Variability is a general property of accretion discs and their associated
jets. We introduce a semi-analytic model for particle acceleration and radio
jet/lobe evolution and explore the effect of Myr timescale jet variability on
the particles accelerated by an AGN jet. Our work is motivated by the need for
local powerful ultrahigh energy cosmic ray (UHECR) sources and evidence for
variability in AGN and radio galaxies. Our main results are: i) UHECR and
nonthermal radiative luminosities track the jet power but with a response set
by the escape and cooling times, respectively; ii) jet variability produces
structure in the electron, synchrotron and UHECR spectra that deviates from
that produced for a constant jet power - in particular, spectral hardening
features may be signatures of variability; iii) the cutoff in the integrated CR
spectrum is stretched out due to the variation in jet power (and, consequently,
maximum CR energy). The resulting spectrum is the convolution of the jet power
distribution and the source term. We derive an approximate form for a
log-normal distribution of powers; iv) we introduce the idea of GeV
'proxy electrons' that are cooling at the same rate that UHECRs of rigidity 10
EV are escaping from the source, and determine the corresponding photon
frequencies that probe escaping UHECRs. Our results demonstrate the link
between the history of an astrophysical particle accelerator and its particle
contents, nonthermal emission and UHECR spectrum, with consequences for
observations of radio galaxies and UHECR source models.Comment: 17 pages, 11 figures. Accepted to MNRA
Line-driven Disk Winds in Active Galactic Nuclei: The Critical Importance of Ionization and Radiative Transfer
Accretion disk winds are thought to produce many of the characteristic
features seen in the spectra of active galactic nuclei (AGN) and quasi-stellar
objects (QSOs). These outflows also represent a natural form of feedback
between the central supermassive black hole and its host galaxy. The mechanism
for driving this mass loss remains unknown, although radiation pressure
mediated by spectral lines is a leading candidate. Here, we calculate the
ionization state of, and emergent spectra for, the hydrodynamic simulation of a
line-driven disk wind previously presented by Proga & Kallman (2004). To
achieve this, we carry out a comprehensive Monte Carlo simulation of the
radiative transfer through, and energy exchange within, the predicted outflow.
We find that the wind is much more ionized than originally estimated. This is
in part because it is much more difficult to shield any wind regions
effectively when the outflow itself is allowed to reprocess and redirect
ionizing photons. As a result, the calculated spectrum that would be observed
from this particular outflow solution would not contain the ultraviolet
spectral lines that are observed in many AGN/QSOs. Furthermore, the wind is so
highly ionized that line-driving would not actually be efficient. This does not
necessarily mean that line-driven winds are not viable. However, our work does
illustrate that in order to arrive at a self-consistent model of line-driven
disk winds in AGN/QSO, it will be critical to include a more detailed treatment
of radiative transfer and ionization in the next generation of hydrodynamic
simulations.Comment: 13 pages, 10 figures - Accepted for publication in Ap
Clinostomum marginatum (Yellow Grub) Metacercaris in Black Bass From the Caddo River in West Arkansas
Seventy-two bass (Micropterus-spp.), mostly smallmouth, were collected from three areas of the Caddo River in west Arkansas and examined for the presence of Clinostomum marginatum metacercariae. Prevalence, mean abundance, and abundance for all fish were 68%, and 4.2 ±6.5, and 30, respectively. Fish from the upstream area near the headwaters were more heavily infested than those from further downstream. A gill/total body larval ratio of seven, was found for bass from another Arkansas stream, was examined as a predictor for total Clinostomum populations instream bass. Using the formula gill parasites X seven divided by N(72), a value of 3.3 was found for mean abundance. The gill/total body ratio for Caddo bass was found to be higher at 8.9 but the ratio of 7 gives a reasonable estimate of Clinostomum burdens in a stream bass population. Use of this ratio allows bass hosts to be examined without necropsy thus preserving the host population in its environment
Current and Future constraints on Very-Light Axion-Like Particles from X-ray observations of cluster-hosted Active Galaxies
We discuss our recent constraints on the coupling of Very-Light Axion-Like
Particles (of masses ) to electromagnetism from
observations of the cluster-hosted Active Galactic Nuclei (AGN)
H1821+643 and NGC1275. In both cases, the inferred high-quality AGN spectra
excluded all photon-ALP couplings at the level, respectively, based on
the non-detection of spectral distortions attributed to photon-ALP
inter-conversion along the cluster line-of-sight. Finally, we present the
prospects of tightening current bounds on such ALPs by up to a factor of 10
with next-generation X-ray observatories such as , and
given their improved spectral and spatial resolution and collecting area
compared to current missions.Comment: 4 pages, 1 figure. Accepted for publication to Memorie della SAIt for
the Proceedings of the European Astronomical Society 2022 (EAS 2022) Annual
Meeting Symposium S3 "The Dark matter multi-messenger challenge
Review and Investigation of Unsatisfactory Control Characteristics Involving Instability of Pilot-airplane Combination and Methods for Predicting These Difficulties from Ground Tests
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