1,220 research outputs found
The Impact of Ethanol Production on Spatial Grain Market Relationships
cointegration, ethanol, grain markets, spatial relationships, Agribusiness, Agricultural and Food Policy, Agricultural Finance, Demand and Price Analysis, Land Economics/Use, Production Economics, Productivity Analysis,
Long-Term Profile Variability of Double-Peaked Emmission Lines in AGNs
An increasing number of AGNs exhibit broad, double-peaked Balmer emission
lines, which arise from the outer regions of the accretion disk which fuels the
AGN. The line profiles vary on timescales of 5--10 years. Our group has
monitored a set of 20 double-peaked emitters for the past 8 years (longer for
some objects). Here we describe a project to characterize the variability
patterns of the double-peaked H alpha line profiles and compare with those of
two simple models: a circular disk with a spiral arm and an elliptical disk.Comment: 2 pages, 1 figure, to appear in the proceedings of "The Interplay
among Black Holes, Stars and ISM in Galactic Nuclei", IAU 222, eds. T.
Storchi Bergmann, L.C. Ho, and H.R. Schmit
Optical Spectral Properties of Swift BAT Hard X-ray Selected Active Galactic Nuclei Sources
The Swift Burst Alert Telescope (BAT) survey of Active Galactic Nuclei (AGN)
is providing an unprecedented view of local AGNs ( = 0.03) and their host
galaxy properties. In this paper, we present an analysis of the optical spectra
of a sample of 64 AGNs from the 9-month survey, detected solely based on their
14-195 keV flux. Our analysis includes both archived spectra from the Sloan
Digital Sky Survey and our own observations from the 2.1-m Kitt Peak National
Observatory telescope. Among our results, we include line ratio classifications
utilizing standard emission line diagnostic plots, [O III] 5007 A luminosities,
and H-beta derived black hole masses. As in our X-ray study, we find the type 2
sources to be less luminous (in [O III] 5007 A and 14-195 keV luminosities)
with lower accretion rates than the type 1 sources. We find that the optically
classified LINERs, H II/composite galaxies, and ambiguous sources have the
lowest luminosities, while both broad line and narrow line Seyferts have
similar luminosities. From a comparison of the hard X-ray (14-195 keV) and [O
III] luminosities, we find that both the observed and extinction-corrected [O
III] luminosities are weakly correlated with X-ray luminosity. In a study of
the host galaxy properties from both continuum fits and measurements of the
stellar absorption indices, we find that the hosts of the narrow line sources
have properties consistent with late type galaxies.Comment: 84 pages, 20 figures, 17 tables, accepted in Ap
The Radial Structure of SNR N103B
We report on the results from a Chandra ACIS observation of the young,
compact, supernova remnant N103B. The unprecedented spatial resolution of
Chandra reveals sub-arcsecond structure, both in the brightness and in spectral
variations. Underlying these small-scale variations is a surprisingly simple
radial structure in the equivalent widths of the strong Si and S emission
lines. We investigate these radial variations through spatially resolved
spectroscopy using a plane-parallel, non-equilibrium ionization model with
multiple components. The majority of the emission arises from components with a
temperature of 1 keV: a fully ionized hydrogen component; a high ionization
timescale (n_e*t > 10^12 s cm^-3) component containing Si, S, Ar, Ca, and Fe;
and a low ionization timescale (n_e*t ~ 10^{11} s cm^-3) O, Ne, and Mg
component. To reproduce the strong Fe Kalpha line, it is necessary to include
additional Fe in a hot (> 2 keV), low ionization (n_e*t ~ 10^10.8 s cm^-3)
component. This hot Fe may be in the form of hot Fe bubbles, formed in the
radioactive decay of clumps of 56Ni. We find no radial variation in the
ionization timescales or temperatures of the various components. Rather, the Si
and S equivalent widths increase at large radii because these lines, as well as
those of Ar and Ca, are formed in a shell occupying the outer half of the
remnant. A shell of hot Fe is located interior to this, but there is a large
region of overlap between these two shells. In the inner 30% of the remnant,
there is a core of cooler, 1 keV Fe. We find that the distribution of the
ejecta and the yields of the intermediate mass species are consistent with
model prediction for Type Ia events.Comment: 34 pages, including 7 tables and 7 figures, Accepted by Ap
Long-Term Profile Variability in Active Galactic Nuclei with Double-Peaked Balmer Emission Lines
An increasing number of Active Galactic Nuclei (AGNs) exhibit broad,
double-peaked Balmer emission lines,which represent some of the best evidence
for the existence of relatively large-scale accretion disks in AGNs. A set of
20 double-peaked emitters have been monitored for nearly a decade in order to
observe long-term variations in the profiles of the double-peaked Balmer lines.
Variations generally occur on timescales of years, and are attributed to
physical changes in the accretion disk. Here we characterize the variability of
a subset of seven double-peaked emitters in a model independent way. We find
that variability is caused primarily by the presence of one or more discrete
"lumps" of excess emission; over a timescale of a year (and sometimes less)
these lumps change in amplitude and shape, but the projected velocity of these
lumps changes over much longer timescales (several years). We also find that
all of the objects exhibit red peaks that are stronger than the blue peak at
some epochs and/or blueshifts in the overall profile, contrary to the
expectations for a simple, circular accretion disk model, thus emphasizing the
need for asymmetries in the accretion disk. Comparisons with two simple models,
an elliptical accretion disk and a circular disk with a spiral arm, are unable
to reproduce all aspects of the observed variability, although both account for
some of the observed behaviors. Three of the seven objects have robust
estimates of the black hole masses. For these objects the observed variability
timescale is consistent with the expected precession timescale for a spiral
arm, but incompatible with that of an elliptical accretion disk. We suggest
that with the simple modification of allowing the spiral arm to be fragmented,
many of the observed variability patterns could be reproduced.Comment: 74 pages, 4 tables, 35 figure
Effective Feedback to Improve Primary Care Prescribing Safety (EFIPPS) a pragmatic three-arm cluster randomised trial:designing the intervention (ClinicalTrials.gov registration NCT01602705)
Peer reviewedPublisher PD
The IeDEA Harmonist Data Toolkit: A Data Quality and Data Sharing Solution for a Global HIV Research Consortium.
We describe the design, implementation, and impact of a data harmonization, data quality checking, and dynamic report generation application in an international observational HIV research network. The IeDEA Harmonist Data Toolkit is a web-based application written in the open source programming language R, employs the R/Shiny and RMarkdown packages, and leverages the REDCap data collection platform for data model definition and user authentication. The Toolkit performs data quality checks on uploaded datasets, checks for conformance with the network's common data model, displays the results both interactively and in downloadable reports, and stores approved datasets in secure cloud storage for retrieval by the requesting investigator. Including stakeholders and users in the design process was key to the successful adoption of the application. A survey of regional data managers as well as initial usage metrics indicate that the Toolkit saves time and results in improved data quality, with a 61% mean reduction in number of error records in a dataset. The generalized application design allows the Toolkit to be easily adapted to other research networks
Not So Fast Kepler-1513: A Perturbing Planetary Interloper in the Exomoon Corridor
Transit Timing Variations (TTVs) can be induced by a range of physical
phenomena, including planet-planet interactions, planet-moon interactions, and
stellar activity. Recent work has shown that roughly half of moons would induce
fast TTVs with a short period in the range of two-to-four orbits of its host
planet around the star. An investigation of the Kepler TTV data in this period
range identified one primary target of interest, Kepler-1513 b. Kepler-1513 b
is a planet orbiting a late G-type dwarf at
AU. Using Kepler photometry, this initial analysis
showed that Kepler-1513 b's TTVs were consistent with a moon. Here, we report
photometric observations of two additional transits nearly a decade after the
last Kepler transit using both ground-based observations and space-based
photometry with TESS. These new transit observations introduce a previously
undetected long period TTV, in addition to the original short period TTV
signal. Using the complete transit dataset, we investigate whether a
non-transiting planet, a moon, or stellar activity could induce the observed
TTVs. We find that only a non-transiting perturbing planet can reproduce the
observed TTVs. We additionally perform transit origami on the Kepler
photometry, which independently applies pressure against a moon hypothesis.
Specifically, we find that Kepler-1513 b's TTVs are consistent with an exterior
non-transiting Saturn mass planet, Kepler-1513 c, on a wide orbit,
5 outside a 5:1 period ratio with Kepler-1513 b. This example
introduces a previously unidentified cause for planetary interlopers in the
exomoon corridor, namely an insufficient baseline of observations.Comment: 20 pages, 13 figures. Accepted to MNRAS. Code available at
https://github.com/dyahalomi/Kepler151
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