3,462 research outputs found
The discontinuous Galerkin method for fractional degenerate convection-diffusion equations
We propose and study discontinuous Galerkin methods for strongly degenerate
convection-diffusion equations perturbed by a fractional diffusion (L\'evy)
operator. We prove various stability estimates along with convergence results
toward properly defined (entropy) solutions of linear and nonlinear equations.
Finally, the qualitative behavior of solutions of such equations are
illustrated through numerical experiments
The Radio Quiescence of Active Galaxies with High Accretion Rates
We present 6 cm Very Large Array observations of the Greene & Ho (2004)
sample of 19 low-mass active galaxies with high accretion rates. This is one of
the only studies of a uniform sample of narrow-line Seyfert 1 (NLS1) galaxies
with such high sensitivity and resolution. Although we detect only one source,
the entire sample is very radio-quiet down to strong limits. GH10 was found to
have a radio power of 8.5 x 10^21 W/Hz, and a ratio R = f(6 cm)/f(4400 A) of
2.8. The 3 sigma upper limits for the remaining nondetections correspond to
radio powers from 3 x 10^20 to 8 x 10^21 W/Hz and 0.47 < R <9.9. Stacking all
nondetections yields an even stronger upper limit of R < 0.27. An assessment of
existing observations in the literature confirms our finding that NLS1s are
consistently radio-quiet, with a radio-loud fraction of 0%-6%, which is
significantly lower than the 10%-20% observed in the general quasar population.
By analogy with stellar-mass black holes, we argue that AGNs undergo a state
transition at L_bol/L_Edd~0.01. Below this value a radiatively inefficient
accretion flow effectively drives an outflow, which disappears when the flow
turns into an optically thick, geometrically thin disk, or a radiation
pressure-dominated slim disk at still higher L_bol/L_Edd.Comment: To appear in ApJ; 8 pages, 3 figures; uses emulateapj5.st
Assessing the Challenges of SurfaceâLevel Aerosol Mass Estimates From Remote Sensing During the SEAC4RS and SEARCH Campaigns: Baseline Surface Observations and Remote Sensing in the Southeastern United States
The Studies of Emissions and Atmospheric Composition, Clouds and Climate Coupling by Regional Surveys (SEAC4RS) campaign conducted in the southeast United States (SEUS) during the summer of 2013 provided a singular opportunity to study local aerosol chemistry and investigate aerosol radiative properties and PM2.5 relationships, focusing on the complexities involved in simplifying the relationship into a linear regression. We utilize three Southeastern Aerosol Research and Characterization network sites and one Environmental Protection Agency Chemical Speciation Network station that afforded simultaneous Aerosol Robotic Network (AERONET) aerosol optical depth (AOD) and aerosol mass, chemistry, and light scattering monitoring. Prediction of AERONET AOD using linear regression of dailyâmean PM2.5 during the SEAC4RS campaign yielded r2 of 0.36â0.53 and highly variable slopes across four sites. There were further reductions in PM2.5 predictive skill using Moderate Resolution Imaging Spectroradiometer (MODIS) and Multiâangle Imaging SpetroRadiometer (MISR) AOD data, which have shorter correlation lengths and times relative to surface PM2.5. Longâterm trends in aerosol chemistry and optical properties in the SEUS are also investigated and compared to SEAC4RS period data, establishing that the SEUS experienced significant reduction in aerosol mass, corresponding with changes in both aerosol chemistry and optical properties. These changes have substantial impact on the PM2.5âAOD linear regression relationship and reinforce the need for longâterm aerosol observation stations in addition to concentrated field campaigns
Spin 1 inversion: a Majorana tensor force for deuteron alpha scattering
We demonstrate, for the first time, successful S-matrix to potential
inversion for spin one projectiles with non-diagonal yielding a
interaction. The method is a generalization of the
iterative-perturbative, IP, method. We present a test case indicating the
degree of uniqueness of the potential. The method is adapted, using established
procedures, into direct observable to potential inversion, fitting ,
, , and for d + alpha scattering over
a range of energies near 10 MeV. The interaction which we find is
very different from that proposed elsewhere, both real and imaginary parts
being very different for odd and even parity channels.Comment: 7 pages Revtex, 4 ps figure
Candidate Type II Quasars at 2 < z < 4.3 in the Sloan Digital Sky Survey III
At low redshifts, dust-obscured quasars often have strong yet narrow
permitted lines in the rest-frame optical and ultraviolet, excited by the
central active nucleus, earning the designation Type II quasars. We present a
sample of 145 candidate Type II quasars at redshifts between 2 and 4.3,
encompassing the epoch at which quasar activity peaked in the universe. These
objects, selected from the quasar sample of the Baryon Oscillation
Spectroscopic Survey of the Sloan Digital Sky Survey III, are characterized by
weak continuum in the rest-frame ultraviolet (typical continuum magnitude of i
\approx 22) and strong lines of CIV and Ly \alpha, with Full Width at Half
Maximum less than 2000 kms-1. The continuum magnitudes correspond to an
absolute magnitude of -23 or brighter at redshift 3, too bright to be due
exclusively to the host galaxies of these objects. Roughly one third of the
objects are detected in the shorter-wavelength bands of the WISE survey; the
spectral energy distributions (SEDs) of these objects appear to be intermediate
between classic Type I and Type II quasars seen at lower redshift. Five objects
are detected at rest frame 6\mu m by Spitzer, implying bolometric luminosities
of several times 10^46 erg s-1. We have obtained polarization measurements for
two objects; they are roughly 3% polarized. We suggest that these objects are
luminous quasars, with modest dust extinction (A_V ~ 0.5 mag), whose
ultraviolet continuum also includes a substantial scattering contribution.
Alternatively, the line of sight to the central engines of these objects may be
partially obscured by optically thick material.Comment: 26 pages, 13 figures, 10 tables, 4 machine readable tables. Accepted
for publication in MNRA
Re-Inventing Public Education:The New Role of Knowledge in Education Policy-Making
This article focuses on the changing role of knowledge in education policy making within the knowledge society. Through an examination of key policy texts, the Scottish case of Integrated Children Services provision is used to exemplify this new trend. We discuss the ways in which knowledge is being used in order to re-configure education as part of a range of public services designed to meet individuals' needs. This, we argue, has led to a 'scientization' of education governance where it is only knowledge, closely intertwined with action (expressed as 'measures') that can reveal problems and shape solutions. The article concludes by highlighting the key role of knowledge policy and governance in orienting education policy making through a re-invention of the public role of education
Black Holes in Pseudobulges and Spheroidals: A Change in the Black Hole-Bulge Scaling Relations at Low Mass
We investigate the relationship between black hole mass and host galaxy
properties for active galaxies with the lowest black hole masses currently
known in galaxy nuclei. Hubble Space Telescope imaging confirms that the host
galaxies have correspondingly low luminosity; they are ~1 mag below L*. In
terms of morphology, ~60% of the members of the sample are disk-dominated, and
all of these are consistent with containing a bulge or (more likely)
pseudobulge, while the remainder are compact systems with no discernible disk
component. In general the compact components of the galaxies do not obey the
fundamental plane of giant elliptical galaxies and classical bulges, but rather
are less centrally concentrated at a given luminosity, much like spheroidal
galaxies. Our results strongly confirm that a classical bulge is not a
requirement for a nuclear black hole. At the same time, the observed ratio of
black hole to bulge mass is nearly an order of magnitude lower in this sample
than that seen for classical bulges. While the M-sigma relation appears to
continue to low mass, it seems that black hole-galaxy scaling relations do
depend on galaxy structure.Comment: to appear in ApJ; 22 pages; 8 figures; original version available at
http://www.astro.princeton.edu/~jgreene/paper.pd
Putting the Bar Exam to the Test: An Examination of the Predictive Validity of Bar Exam Outcomes on Lawyering Effectiveness
How well does bar exam performance, on the whole, predict lawyering effectiveness? Is performance on some components of the bar exam more predictive? The current study, the first of its kind to measure the relationship between bar exam scores and a new lawyerâs effectiveness, evaluates these questions by combining three unique datasetsâbar results from the State Bar of Nevada, a survey of recently admitted lawyers, and a survey of supervisors, peers, and judges who were asked to evaluate the effectiveness of recently-admitted lawyers. We find that performance on both the Multistate Bar Examination (MBE) and essay components of the Nevada Bar have little relationship with the assessed lawyering effectiveness of new lawyers, calling into question the usefulness of these tests
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