14,253 research outputs found
Dietary variations in three co-occurring rockfish species off the Pacific Northwest during anomalous oceanographic events in 1998 and 1999
Stomach samples from three rockfish species, yellowtail
(Sebastes f lavidus), widow (S. entomelas), and canary (S. pinniger) rockfish, seasonally collected off the Pacific Northwest in 1998 and 1999, provided quantitative information on the food habits of these species during and after the 1997–98 El Niño event. Although euphausiids were the most common major prey of all three predators, gelatinous zooplankton and fishes were the most commonly
consumed prey items during some seasonal quarters. The influence of the El Niño event was evident in the diets. Anomalous prey items, including the southern euphausiid species Nyctiphanes simplex and juveniles of Pacific whiting (Merluccius productus) frequently appeared in the diets in the spring and summer of 1998. The results of stomach contents analyses, based on 905 stomach samples from 49 trawl hauls during seven commercial fishing trips and from 56 stations during research surveys, were consistent with the timing of occurrence and the magnitude of change in biomass of some zooplankton species reported
from zooplankton studies in the northern California Current during the 1997–98 El Niño. Our findings indicate that the observed variations of prey groups in some rockfish diets
may be a function of prey variability related to climate and environment changes
Effect of ferromagnetic contacts on spin accumulation in an all-metallic lateral spin-valve system: Semiclassical spin drift-diffusion equations
We study the effect of the ferromagnetic (FM) contacts on the spin
accumulation in the lateral spin valve system for the collinear magnetization
configurations. When an additional FM electrode is introduced in the
all-metallic lateral spin-valve system, we find that the transresistance can be
fractionally suppressed or very weakly influenced depending on the position of
the additional FM electrode, and relative magnitudes of contact resistance and
the bulk resistance defined over the spin diffusion length. Nonlocal spin
signals such as nonlocal voltage drop and leakage spin currents are independent
of the magnetization orientation of the additional FM electrode. Even when the
additional contact is nonmagnetic, nonlocal spin signals can be changed by the
spin current leaking into the nonmagnetic electrode.Comment: 13 pages, 1 figure, revised versio
Supermassive black holes as the regulators of star formation in central galaxies
We present a relationship between the black hole mass, stellar mass, and star
formation rate of a diverse group of 91 galaxies with dynamically-measured
black hole masses. For our sample of galaxies with a variety of morphologies
and other galactic properties, we find that the specific star formation rate is
a smoothly decreasing function of the ratio between black hole mass and stellar
mass, or what we call the specific black hole mass. In order to explain this
relation, we propose a physical framework where the gradual suppression of a
galaxy's star formation activity results from the adjustment to an increase in
specific black hole mass and, accordingly, an increase in the amount of
heating. From this framework, it follows that at least some galaxies with
intermediate specific black hole masses are in a steady state of partial
quiescence with intermediate specific star formation rates, implying that both
transitioning and steady-state galaxies live within this region known as the
"green valley." With respect to galaxy formation models, our results present an
important diagnostic with which to test various prescriptions of black hole
feedback and its effects on star formation activity.Comment: 15 pages, 4 figures, 2 tables. Accepted for publication in The
Astrophysical Journa
Electron and phonon band-structure calculations for the antipolar SrPtP antiperovskite superconductor: Evidence of low-energy two-dimensional phonons
SrPt3P has recently been reported to exhibit superconductivity with Tc = 8.4
K. To explore its superconducting mechanism, we have performed electron and
phonon band calculations based on the density functional theory, and found that
the superconductivity in SrPt3P is well described by the strong coupling
phonon-mediated mechanism. We have demonstrated that superconducting charge
carriers come from pd\pi-hybridized bands between Pt and P ions, which couple
to low energy (~ 5 meV) phonon modes confined on the ab in-plane. These
in-plane phonon modes, which do not break antipolar nature of SrPt3P, enhance
both the electron-phonon coupling constant \lambda and the critical temperature
Tc. There is no hint of a specific phonon softening feature in the phonon
dispersion, and the effect of the spin-orbit coupling on the superconductivity
is found to be negligible.Comment: 5 pages, 5 figures, 1 tabl
Curvature-induced spin-orbit coupling and spin relaxation in a chemically clean single-layer graphene
The study of spin-related phenomena in materials requires knowledge on the
precise form of effective spin-orbit coupling of conducting carriers in the
solid-states systems. We demonstrate theoretically that curvature induced by
corrugations or periodic ripples in single-layer graphenes generates two types
of effective spin-orbit coupling. In addition to the spin-orbit coupling
reported previously that couples with sublattice pseudospin and corresponds to
the Rashba-type spin-orbit coupling in a corrugated single-layer graphene,
there is an additional spin-orbit coupling that does not couple with the
pseudospin, which can not be obtained from the extension of the
curvature-induced spin-orbit coupling of carbon nanotubes. Via numerical
calculation we show that both types of the curvature-induced spin-orbit
coupling make the same order of contribution to spin relaxation in chemically
clean single-layer graphene with nanoscale corrugation. The spin relaxation
dependence on the corrugation roughness is also studied.Comment: 8 pages, 4 figure
Tree-level electron-photon interactions in graphene
Graphene's low-energy electronic excitations obey a 2+1 dimensional Dirac
Hamiltonian. After extending this Hamiltonian to include interactions with a
quantized electromagnetic field, we calculate the amplitude associated with the
simplest, tree-level Feynman diagram: the vertex connecting a photon with two
electrons. This amplitude leads to analytic expressions for the 3D angular
dependence of photon emission, the photon-mediated electron-hole recombination
rate, and corrections to graphene's opacity and dynamic
conductivity for situations away from thermal equilibrium, as
would occur in a graphene laser. We find that Ohmic dissipation in perfect
graphene can be attributed to spontaneous emission.Comment: 5 pages, 3 figure
Magnetoelectric effects due to elastic coupling in ferroelectric/ferromagnetic multilayers
Author name used in this publication: C. H. Woo2007-2008 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishe
Curie temperature and critical thickness of ferroelectric thin films
Author name used in this publication: C. H. Woo2004-2005 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishe
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