17,373 research outputs found
Flux of nutrients from Russian rivers to the Arctic Ocean: Can we establish a baseline against which to judge future changes?
Climate models predict significant warming in the Arctic in the 21st century, which will impact the functioning of terrestrial and aquatic ecosystems as well as alter landâocean interactions in the Arctic. Because river discharge and nutrient flux integrate largeâscale processes, they should be sensitive indicators of change, but detection of future changes requires knowledge of current conditions. Our objective in this paper is to evaluate the current state of affairs with respect to estimating nutrient flux to the Arctic Ocean from Russian rivers. To this end we provide estimates of contemporary (1970sâ1990s) nitrate, ammonium, and phosphate fluxes to the Arctic Ocean for 15 large Russian rivers. We rely primarily on the extensive data archives of the former Soviet Union and current Russian Federation and compare these values to other estimates and to model predictions. Large discrepancies exist among the various estimates. These uncertainties must be resolved so that the scientific community will have reliable data with which to calibrate Arctic biogeochemical models and so that we will have a baseline against which to judge future changes (either natural or anthropogenic) in the Arctic watershed
MUSE observations of a changing-look AGN I: The re-appearance of the broad emission lines
Optical changing-look Active Galactic Nuclei (AGN) are a class of sources
that change type within a short timescale of years or decades. This change is
characterised by the appearance or disappearance of broad emission lines, often
associated with dramatic AGN continuum flux changes that are orders of
magnitude larger than those expected from typical AGN variability. In this work
we study for the first time the host galaxy of a changing-look AGN, Mrk 590,
using high spatial resolution optical and near-infrared observations. We
discover that after ~ 10 yr absence, the optical broad emission lines of Mrk
590 have reappeared. The AGN optical continuum flux however, is still ~ 10
times lower than that observed during the most luminous state in the 1990s. The
host galaxy shows a 4.5 kpc radius star-forming ring with knots of ionised and
cold molecular gas emission. Extended ionised and warm molecular gas emission
are detected in the nucleus, indicating that there is a reservoir of gas as
close as 60 pc from the black hole. We observe a nuclear gas spiral between
radii r ~ 0.5 - 2 kpc, which has been suggested as a dynamical mechanism able
to drive the necessary gas to fuel AGN. We also discover blue-shifted and high
velocity dispersion [O III] emission out to a radius of 1 kpc, tracing a
nuclear gas outflow. The gas dynamics in Mrk 590 suggest a complex balance
between gas inflow and outflow in the nucleus of the galaxy.Comment: Accepted for publication in MNRA
Subband Engineering Even-Denominator Quantum Hall States
Proposed even-denominator fractional quantum Hall effect (FQHE) states
suggest the possibility of excitations with non-Abelian braid statistics.
Recent experiments on wide square quantum wells observe even-denominator FQHE
even under electrostatic tilt. We theoretically analyze these structures and
develop a procedure to accurately test proposed quantum Hall wavefunctions. We
find that tilted wells favor partial subband polarization to yield Abelian
even-denominator states. Our results show that tilting quantum wells
effectively engineers different interaction potentials allowing exploration of
a wide variety of even-denominator states
Testing Multi-Field Inflation: A Geometric Approach
We develop an approach for linking the power spectra, bispectrum, and
trispectrum to the geometric and kinematical features of multifield
inflationary Lagrangians. Our geometric approach can also be useful in
determining when a complicated multifield model can be well approximated by a
model with one, two, or a handful of fields. To arrive at these results, we
focus on the mode interactions in the kinematical basis, starting with the case
of no sourcing and showing that there is a series of mode conservation laws
analogous to the conservation law for the adiabatic mode in single-field
inflation. We then treat the special case of a quadratic potential with
canonical kinetic terms, showing that it produces a series of mode sourcing
relations identical in form to that for the adiabatic mode. We build on this
result to show that the mode sourcing relations for general multifield
inflation are extension of this special case but contain higher-order covariant
derivatives of the potential and corrections from the field metric. In
parallel, we show how these interactions depend on the geometry of the
inflationary Lagrangian and on the kinematics of the associated field
trajectory. Finally, we consider how the mode interactions and effective number
of fields active during inflation are reflected in the spectra and introduce a
multifield consistency relation, as well as a multifield observable that can
potentially distinguish two-field scenarios from scenarios involving three or
more effective fields.Comment: 21 pages, 4 figures + tables. Revised to clarify several points and
reorganized Section III for pedagogical reasons. Error in one equation and
typos were corrected, as well as additional references adde
Testing Two-Field Inflation
We derive semi-analytic formulae for the power spectra of two-field inflation
assuming an arbitrary potential and non-canonical kinetic terms, and we use
them both to build phenomenological intuition and to constrain classes of
two-field models using WMAP data. Using covariant formalism, we first develop a
framework for understanding the background field kinematics and introduce a
"slow-turn" approximation. Next, we find covariant expressions for the
evolution of the adiabatic/curvature and entropy/isocurvature modes, and we
discuss how the mode evolution can be inferred directly from the background
kinematics and the geometry of the field manifold. From these expressions, we
derive semi-analytic formulae for the curvature, isocurvature, and cross
spectra, and the spectral observables, all to second-order in the slow-roll and
slow-turn approximations. In tandem, we show how our covariant formalism
provides useful intuition into how the characteristics of the inflationary
Lagrangian translate into distinct features in the power spectra. In
particular, we find that key features of the power spectra can be directly read
off of the nature of the roll path, the curve the field vector rolls along with
respect to the field manifold. For example, models whose roll path makes a
sharp turn 60 e-folds before inflation ends tend to be ruled out because they
produce strong departures from scale invariance. Finally, we apply our
formalism to confront four classes of two-field models with WMAP data,
including doubly quadratic and quartic potentials and non-standard kinetic
terms, showing how whether a model is ruled out depends not only on certain
features of the inflationary Lagrangian, but also on the initial conditions.
Ultimately, models must possess the right balance of kinematical and dynamical
behaviors, which we capture in a set of functions that can be reconstructed
from spectral observables.Comment: Revised to match accepted PRD version: Improved discussion of
background kinematics and multi-field effects, added tables summarizing key
quantities and their links to observables, more detailed figures, fixed typos
in former equations (103) and (117). 49 PRD pages, 11 figure
A survey of business education in the public high schools of New England
Thesis (Ed.M.)--Boston University
Variability of Fe II Emission Features in the Seyfert 1 Galaxy NGC 5548
We study the low-contrast Fe II emission blends in the ultraviolet
(1250--2200A) and optical (4000--6000A) spectra of the Seyfert 1 galaxy NGC
5548 and show that these features vary in flux and that these variations are
correlated with those of the optical continuum. The amplitude of variability of
the optical Fe II emission is 50% - 75% that of Hbeta and the ultraviolet Fe II
emission varies with an even larger amplitude than Hbeta. However, accurate
measurement of the flux in these blends proves to be very difficult even using
excellent Fe II templates to fit the spectra. We are able to constrain only
weakly the optical Fe II emission-line response timescale to a value less than
several weeks; this upper limit exceeds all the reliably measured emission-line
lags in this source so it is not particularly meaningful. Nevertheless, the
fact that the optical Fe II and continuum flux variations are correlated
indicates that line fluorescence in a photoionized plasma, rather than
collisional excitation, is responsible for the Fe II emission. The iron
emission templates are available upon request.Comment: 34 pages including 12 figures and 2 tables. Accepted for publication
by ApJ (tentatively in vol. 626 June 10, 2005
Intermediate resolution H-beta spectroscopy and photometric monitoring of 3C 390.3 I. Further evidence of a nuclear accretion disk
We have monitored the AGN 3C390.3 between 1995 and 2000.Two large amplitude
outbursts, of different duration, in continuum and H beta light were observed
ie.: in October 1994 a brighter flare that lasted about 1000 days and in July
1997 another one that lasted about 700 days were detected. The flux in the H
beta wings and line core vary simultaneously, a behavior indicative of
predominantly circular motions in the BLR.Important changes of the Hbeta
emission profiles were detected: at times, we found profiles with prominent
asymmetric wings, as those normaly seen in Sy1s, while at other times, we
observe profiles with weak almost symmetrical wings, similar to those seen in
Sy1.8s. We found that the radial velocity difference between the red and blue
bumps is anticorrelated with the light curves of H beta and continuum
radiation.e found that the radial velocity difference between the red and blue
bumps is anticorrelated with the light curves of H-beta and continuum
radiation. Theoretical H-beta profiles were computed for an accretion disk, the
observed profiles are best reproduced by an inclined disk (25 deg) whose region
of maximum emission is located roughly at 200 Rg. The mass of the black hole in
3C 390.3, estimated from the reverberation analysis is Mrev = 2.1 x 10^9 Msun,
ie. 5 times larger than previous estimatesComment: 18 pages, 13 figures, 4 tables. to appear in Astronomy and
Astrophysic
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