740 research outputs found
NITROGEN CARRY-OVER IMPACTS IN IRRIGATED COTTON PRODUCTION, SOUTHERN HIGH PLAINS OF TEXAS
A dynamic optimization model which introduces an intertemporal nitrate-nitrogen residual function is used to derive and evaluate nitrogen fertilizer optimal decision rules for irrigated cotton production in the Southern High Plains of Texas. Results indicate that optimal nitrogen applications critically depend on initial nitrate-nitrogen levels and nitrogen-to-cotton price ratios. Also, the results indicate that single-year optimization leads to suboptimal nitrogen applications, which helps explain long-term cotton yield declines in the Southern High Plains of Texas; but single-year optimization does not significantly impact the net present value of returns of irrigated cotton operations.Crop Production/Industries,
Time Response of Water-based Liquid Scintillator from X-ray Excitation
Water-based liquid scintillators (WbLS) present an attractive target medium
for large-scale detectors with the ability to enhance the separation of
Cherenkov and scintillation signals from a single target. This work
characterizes the scintillation properties of WbLS samples based on LAB/PPO
liquid scintillator (LS). X-ray luminescence spectra, decay profiles, and
relative light yields are measured for WbLS of varying LS concentration as well
as for pure LS with a range of PPO concentrations up to 90 g/L. The
scintillation properties of the WbLS are related to the precursor LAB/PPO:
starting from 90 g/L PPO in LAB before synthesis, the resulting WbLS have
spectroscopic properties that instead match 10 g/L PPO in LAB. This could
indicate that the concentration of active PPO in the WbLS samples depends on
their processing.Comment: 6 pages, 7 figures, 2 tables. Submitted to Materials Advances, a
journal of the Royal Society of Chemistr
Validation of an ocean shelf model for the prediction of mixed-layer properties in the Mediterranean Sea west of Sardinia
The Regional Ocean Modeling System (ROMS) has been employed to
explore the sensitivity of the forecast skill of mixed-layer
properties to initial conditions, boundary conditions, and
vertical mixing parameterisations. The initial and lateral boundary
conditions were provided by the Mediterranean Forecasting System
(MFS) or by the MERCATOR global ocean circulation model via one-way
nesting; the initial conditions were additionally updated through the
assimilation of observations. Nowcasts and forecasts from the weather
forecast models COSMO-ME and COSMO-IT, partly melded with
observations, served as surface boundary conditions. The vertical
mixing was parameterised by the GLS (generic length scale)
scheme Umlauf and Burchard (2003) in four different set-ups. All ROMS
forecasts were validated against the observations which were taken during
the REP14-MED survey to the west of Sardinia. Nesting
ROMS in MERCATOR and updating the initial conditions through data
assimilation provided the best agreement of the predicted mixed-layer properties with the time series from a moored
thermistor chain. Further improvement was obtained by the usage of
COSMO-ME atmospheric forcing, which was melded with real observations,
and by the application of the k-ω vertical mixing scheme with
increased vertical eddy diffusivity. The predicted temporal
variability of the mixed-layer temperature was reasonably well
correlated with the observed variability, while the modelled
variability of the mixed-layer depth exhibited only agreement with the
observations near the diurnal frequency peak. For the forecasted
horizontal variability, reasonable agreement was found with
observations from a ScanFish section, but only for the mesoscale
wave number band; the observed sub-mesoscale variability was not
reproduced by ROMS
Reverberation Mapping Results from MDM Observatory
We present results from a multi-month reverberation mapping campaign
undertaken primarily at MDM Observatory with supporting observations from
around the world. We measure broad line region (BLR) radii and black hole
masses for six objects. A velocity-resolved analysis of the H_beta response
shows the presence of diverse kinematic signatures in the BLR.Comment: To appear in the Proceedings of the IAU Symposium No. 267:
Co-Evolution of Central Black Holes and Galaxies, Rio de Janeiro, 200
History of Hydrogen Reionization in the Cold Dark Matter Model
We calculate the reionization history in Cold Dark Matter (CDM) models. The
epoch of the end of reionization and the Thomson scattering optical depth to
the cosmic microwave background depend on the power spectrum amplitude on small
scales and on the ionizing photon emissivity per unit mass in collapsed halos.
We calibrate the emissivity to reproduce the measured ionizing background
intensity at z=4. Models in which all CDM halos have either a constant
emissivity or a constant energy emitted per Hubble time, per unit mass, predict
that reionization ends near z~6 and the optical depth is in the range 0.05 <
tau_e < 0.09, consistent with WMAP results at the 1 to 2 sigma level. If the
optical depth is as high as 0.17 (as suggested by WMAP), halos of velocity
dispersion ~ 3-30 km/s at z>15 must have ionizing emissivities per unit mass
larger by a factor >~ 50 compared to the more massive halos that produce the
ionizing emissivity at z=4. This factor increases to 100 if the CDM power
spectrum amplitude is required to agree with the Croft et al. (2002)
measurement from the Lyman alpha forest. If tau_e >~ 0.17 were confirmed, a
higher ionizing emissivity at z>15 compared to z=4 might arise from an enhanced
star formation rate or quasar abundance per unit mass and an increased escape
fraction for ionizing photons; the end of reionization could have been delayed
to z~6 because of the suppression of gas accretion and star formation in
low-mass halos as the medium was reionized.Comment: 19 pages, 4 figues, submitted to Ap
Tourette syndrome as a motor disorder revisited – Evidence from action coding
Because tics are the defining clinical feature of Tourette syndrome, it is conceptualized predominantly as a motor disorder. There is some evidence though suggesting that the neural basis of Tourette syndrome is related to perception–action processing and binding between perception and action. However, binding processes have not been examined in the motor domain in these patients. If it is particularly perception–action binding but not binding processes within the motor system, this would further corroborate that Tourette syndrome it is not predominantly, or solely, a motor disorder. Here, we studied N = 22 Tourette patients and N = 24 healthy controls using an established action coding paradigm derived from the Theory of Event Coding framework and concomitant EEG-recording addressing binding between a planned but postponed, and an interleaved immediate reaction with different levels of overlap of action elements. Behavioral performance during interleaved action coding was normal in Tourette syndrome. Response locked lateralized readiness potentials reflecting processes related to motor execution were larger in Tourette syndrome, but only in simple conditions. However, pre-motor processes including response preparation and configuration reflected by stimulus-locked lateralized readiness potentials were normal. This was supported by a Bayesian data analysis providing evidence for the null hypothesis. The finding that processes integrating different action-related elements prior to motor execution are normal in Tourette syndrome suggests that Tourette it is not solely a motor disorder. Considering other recent evidence, the data show that changes in “binding” in Tourette syndrome are specific for perception–action integration but not for action coding
Observational Limits on Type 1 AGN Accretion Rate in COSMOS
We present black hole masses and accretion rates for 182 Type 1 AGN in
COSMOS. We estimate masses using the scaling relations for the broad Hb, MgII,
and CIV emission lines in the redshift ranges 0.16<z<0.88, 1<z<2.4, and
2.7<z<4.9. We estimate the accretion rate using an Eddington ratio L_I/L_Edd
estimated from optical and X-ray data. We find that very few Type 1 AGN accrete
below L_I/L_Edd ~ 0.01, despite simulations of synthetic spectra which show
that the survey is sensitive to such Type 1 AGN. At lower accretion rates the
BLR may become obscured, diluted or nonexistent. We find evidence that Type 1
AGN at higher accretion rates have higher optical luminosities, as more of
their emission comes from the cool (optical) accretion disk with respect to
shorter wavelengths. We measure a larger range in accretion rate than previous
works, suggesting that COSMOS is more efficient at finding low accretion rate
Type 1 AGN. However the measured range in accretion rate is still comparable to
the intrinsic scatter from the scaling relations, suggesting that Type 1 AGN
accrete at a narrow range of Eddington ratio, with L_I/L_Edd ~ 0.1.Comment: Accepted for pulication in ApJ. 7 pages, 5 figures, table 1 available
on reques
Central Masses and Broad-Line Region Sizes of Active Galactic Nuclei. II. A Homogeneous Analysis of a Large Reverberation-Mapping Database
We present improved black hole masses for 35 active galactic nuclei (AGNs)
based on a complete and consistent reanalysis of broad emission-line
reverberation-mapping data. From objects with multiple line measurements, we
find that the highest precision measure of the virial product is obtained by
using the cross-correlation function centroid (as opposed to the
cross-correlation function peak) for the time delay and the line dispersion (as
opposed to full width half maximum) for the line width and by measuring the
line width in the variable part of the spectrum. Accurate line-width
measurement depends critically on avoiding contaminating features, in
particular the narrow components of the emission lines. We find that the
precision (or random component of the error) of reverberation-based black hole
mass measurements is typically around 30%, comparable to the precision attained
in measurement of black hole masses in quiescent galaxies by gas or stellar
dynamical methods. Based on results presented in a companion paper by Onken et
al., we provide a zero-point calibration for the reverberation-based black hole
mass scale by using the relationship between black hole mass and host-galaxy
bulge velocity dispersion. The scatter around this relationship implies that
the typical systematic uncertainties in reverberation-based black hole masses
are smaller than a factor of three. We present a preliminary version of a
mass-luminosity relationship that is much better defined than any previous
attempt. Scatter about the mass-luminosity relationship for these AGNs appears
to be real and could be correlated with either Eddington ratio or object
inclination.Comment: 61 pages, including 8 Tables and 16 Figures. Accepted for publication
in The Astrophysical Journa
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