13,181 research outputs found
Responses of Hyalella azteca and Ceridaphnia dubia to reservoir sediments following Chelated Copper Herbicide Applications
In response to nuisance growths of algae and vascular
plants, such as dioecious hydrilla (
Hydrilla verticillata
L.f.
Royle), copper formulations have been applied in lakes and
reservoirs for a number of years. Concerns have arisen regarding
the long-term consequences of copper applications
and those concerns have appropriately focused on sediment
residues. In this study, we evaluated the toxicity of sediments
from treated (for a decade) and untreated areas in Lake
Murray, South Carolina and estimated the capacity of those
sediments to bind additional copper. Two sentinel aquatic invertebrates,
Hyalella azteca
Saussure and
Ceriodaphnia dubia
Richard, were used to measure residual toxicity of treated
and untreated sediments from the field and after laboratory
amendments. (PDF has 5 pages.
The Binary Black Hole Model for Mrk 231 Bites the Dust
Mrk 231 is a nearby quasar with an unusually red near-UV-to-optical
continuum, generally explained as heavy reddening by dust (e.g., Leighly et al.
2014). Yan et al. 2015 proposed that Mrk~231 is a milli-parsec black-hole
binary with little intrinsic reddening. We show that if the observed FUV
continuum is intrinsic, as assumed by Yan et al. 2015, it fails by a factor of
about 100 in powering the observed strength of the near-infrared emission
lines, and the thermal near and mid-infrared continuum. In contrast, the line
and continuum strengths are typical for a reddened AGN spectral energy
distribution. We find that the HeI*/Pbeta ratio is sensitive to the spectral
energy distribution for a one-zone model. If this sensitivity is maintained in
general broad-line region models, then this ratio may prove a useful diagnostic
for heavily reddened quasars. Analysis of archival HST STIS and FOC data
revealed evidence that the far-UV continuum emission is resolved on size scales
of ~40 parsecs. The lack of broad absorption lines in the far-UV continuum
might be explained if it were not coincident with the central engine. One
possibility is that it is the central engine continuum reflected from the
receding wind on the far side of the quasar.Comment: Consistent with the accepted ApJ pape
Effect of edge transmission and elastic scattering on the resistance of magnetic barriers
Strong magnetic barriers are defined in two-dimensional electron gases by
magnetizing dysprosium ferromagnetic platelets on top of a Ga[Al]As
heterostructure. A small resistance across the barrier is observed even deep
inside the closed regime. We have used semiclassical simulations to explain
this behavior quantitatively in terms of a combined effect of elastic electron
scattering inside the barrier region and E x B drift at the intersection of the
magnetic barrier with the edge of the Hall bar.Comment: 7 pages 4 figure
Theory of phonon-drag thermopower of extrinsic semiconducting single-wall carbon nanotubes and comparison with previous experimental data
A theoretical model for the calculation of the phonon-drag thermopower,
, in degenerately doped semiconducting single-wall carbon nanotubes
(SWCNTs) is proposed. Detailed calculations of are performed as a
function of temperature, tube radius and position of the Fermi level. We derive
a simple analytical expression for that can be utilized to determine
the free carrier density in doped nanotubes. At low temperatures shows
an activated behavior characteristic of the one-dimensional (1D) character of
carriers. Screening effects are taken into account and it is found that they
dramatically reduce the magnitude of . Our results are compared with
previous published experimental data in bulk p-doped SWCNT materials. Excellent
agreement is obtained in the temperature range 10-200 K for a consistent set of
parameters. This is a striking result in view of the complexity of these
systems.Comment: 21 pages, 6 figures. This version has been accepted for publication
in Phys. Rev.
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