266 research outputs found
The Occurrence of Chestnut Lamprey (lchthyomyzon castaneus; Pisces: Petromyzontidae) in the Chariton River in South-Central Iowa
In the mid-1990s, Iowa Department of Natural Resources (IDNR) Fisheries Bureau biologists began receiving reports from anglers of a parasitic lamprey attached to fish taken immediately downstream from Rathbun Lake on the Chariton River in south-central Iowa; these reports have continued to present. In 2002, the IDNR received and identified a chestnut lamprey (Ichthyomyzon castaneus Girard) from an angler who removed the lamprey from a common carp (Cyprinus carpio Linnaeus) he captured. This record was the first for a lamprey from the Chariton River drainage in Iowa. Five additional specimens of chestnut lamprey have been collected and identified since this specimen was found, all from the same location. The Rathbun Lake tailrace is one of only a few locations on Iowa\u27s interior rivers and streams with verified records for chestnut lamprey
Preheated Advection Dominated Accretion Flow
All high temperature accretion solutions including ADAF are physically thick,
so outgoing radiation interacts with the incoming flow, sharing as much or more
resemblance with classical spherical accretion flows as with disk flows. We
examine this interaction for the popular ADAF case. We find that without
allowance for Compton preheating, a very restricted domain of ADAF solution is
permitted and with Compton preheating included a new high temperature PADAF
branch appears in the solution space. In the absence of preheating, high
temperature flows do not exist when the mass accretion rate mdot == Mdot c^2 /
L_E >~ 10^-1.5. Below this mass accretion rate, a roughly conical region around
the hole cannot sustain high temperature ions and electrons for all flows
having mdot >~ 10^-4, which may lead to a funnel possibly filled with a tenuous
hot outgoing wind. If the flow starts at large radii with the usual equilibrium
temperature ~10^4 K, the critical mass accretion rate is much lower, mdot
\~10^-3.7 above which level no self-consistent ADAF (without preheating) can
exist. However, above this critical mass accretion rate, the flow can be
self-consistently maintained at high temperature if Compton preheating is
considered. These solutions constitute a new branch of solutions as in
spherical accretion flows. High temperature PADAF flows can exist above the
critical mass accretion rate in addition to the usual cold thin disk solutions.
We also find solutions where the flow near the equatorial plane accretes
normally while the flow near the pole is overheated by Compton preheating,
possibly becoming, a polar wind, solutions which we designate WADAF.Comment: 41 pages with 10 postscript figures (aastex5). Submitted to Ap
Does the Slim-Disk Model Correctly Consider Photon-Trapping Effects?
We investigate the photon-trapping effects in the super-critical black hole
accretion flows by solving radiation transfer as well as the energy equations
of radiation and gas. It is found that the slim-disk model generally
overestimates the luminosity of the disk at around the Eddington luminosity
(L_E) and is not accurate in describing the effective temperature profile,
since it neglects time delay between energy generation at deeper inside the
disk and energy release at the surface. Especially, the photon-trapping effects
are appreciable even below L ~ L_E, while they appear above ~ 3L_E according to
the slim disk. Through the photon-trapping effects, the luminosity is reduced
and the effective temperature profile becomes flatter than r^{-3/4} as in the
standard disk. In the case that the viscous heating is effective only around
the equatorial plane, the luminosity is kept around the Eddington luminosity
even at very large mass accretion rate, Mdot>>L_E/c^2. The effective
temperature profile is almost flat, and the maximum temperature decreases in
accordance with rise in the mass accretion rate. Thus, the most luminous radius
shifts to the outer region when Mdot/(L_E/c^2) >> 10^2. In the case that the
energy is dissipated equally at any heights, the resultant luminosity is
somewhat larger than in the former case, but the energy-conversion efficiency
still decreases with increase of the mass accretion rate, as well. The most
luminous radius stays around the inner edge of the disk in the latter case.
Hence, the effective temperature profile is sensitive to the vertical
distribution of energy production rates, so is the spectral shape. Future
observations of high L/L_E objects will be able to test our model.Comment: 10 pages, 7 figures, accepted for publication in Ap
Spin correlations in pion production near threshold
A first measurement of longitudinal as well as transverse spin correlation
coefficients for the reaction was made using a
polarized proton target and a polarized proton beam. We report kinematically
complete measurements for this reaction at 325, 350, 375 and 400 MeV beam
energy. The spin correlation coefficients and the analyzing power as well as angular
distributions for and the polarization observables
were extracted. Partial wave cross sections for dominant
transition channels were obtained from a partial wave analysis that included
the transitions with final state angular momenta of . The measurements
of the polarization observables are compared
with the predictions from the J\"ulich meson exchange model. The agreement is
very good at 325 MeV, but it deteriorates increasingly for the higher energies.
At all energies agreement with the model is better than for the reaction
.Comment: Preprint, 21 pp, submitted to Phys. Rev. C. Keywords: Mesons,
Polarization, Spin Correlations, Few body system
Volumetric imaging of shark tail hydrodynamics reveals a three-dimensional dual-ring vortex wake structure
Understanding how moving organisms generate locomotor forces is fundamental to the analysis of aerodynamic and hydrodynamic flow patterns that are generated during body and appendage oscillation. In the past, this has been accomplished using two-dimensional planar techniques that require reconstruction of three-dimensional flow patterns. We have applied a new, fully three-dimensional, volumetric imaging technique that allows instantaneous capture of wake flow patterns, to a classic problem in functional vertebrate biology: the function of the asymmetrical (heterocercal) tail of swimming sharks to capture the vorticity field within the volume swept by the tail. These data were used to test a previous three-dimensional reconstruction of the shark vortex wake estimated from two-dimensional flow analyses, and show that the volumetric approach reveals a different vortex wake not previously reconstructed from two-dimensional slices. The hydrodynamic wake consists of one set of dual-linked vortex rings produced per half tail beat. In addition, we use a simple passive shark-tail model under robotic control to show that the three-dimensional wake flows of the robotic tail differ from the active tail motion of a live shark, suggesting that active control of kinematics and tail stiffness plays a substantial role in the production of wake vortical patterns
Analyzing Powers for pp → pnπ^+
This research was sponsored by the National Science Foundation Grant NSF PHY-931478
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Novel Silicon Carbide Detector for Active Inspections
The need to address increasingly challenging inspection requirements (such as large volume objects, very fast inspection throughputs, potentially significant shielding, etc.) for such items as nuclear materials and explosives will require the use of active interrogation technologies. While these active technologies can successfully address these challenges by inducing unique, temporal signatures, the inspection environment will also induce overall “background signals” that can be orders of magnitude larger than the induced signatures. Detectors that can successfully operate in these types of customized, inspection environments (pulsed and continuous) and successfully extract induced signature data are clearly needed and will effectively define the limitations of any active inspection system. A novel silicon carbide detector is now being investigated to successfully address both neutron- and photon/bremsstrahlung-type inspection applications. While this paper describes this detector and highlights efforts related to neutron inspection, it will focus on its neutron and gamma-ray/photon detection performance in neutron- and bremssstrahlung-type inspection applications
Dependence of pp->pp pi0 near Threshold on the Spin of the Colliding Nucleons
A polarized internal atomic hydrogen target and a stored, polarized beam are
used to measure the spin-dependent total cross section Delta_sigma_T/sigma_tot,
as well as the polar integrals of the spin correlation coefficient combination
A_xx-A_yy, and the analyzing power A_y for pp-> pp pi0 at four bombarding
energies between 325 and 400 MeV. This experiment is made possible by the use
of a cooled beam in a storage ring. The polarization observables are used to
study the contribution from individual partial waves.Comment: 6 pages, 1 table, 4 figures, corrected equations 2 and
Observation of strong final-state effects in pi+ production in pp collisions at 400 MeV
Differential cross sections of the reactions and have been measured at MeV by detecting the charged
ejectiles in the angular range . The
deduced total cross sections agree well with those published previously for
neighbouring energies. The invariant mass spectra are observed to be strongly
affected by production and final-state interaction. The data are
well described by Monte Carlo simulations including both these effects. The
ratio of and cross sections also compares
favourably to a recent theoretical prediction which suggests a dominance of
-production in the relative -state.Comment: 17 pages, 5 figure
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