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,

Phosphate Fertilizer Reactions under Various Soil Conditions

Agronomy (Soils

Supermassive Black Hole Mass Estimates Using Sloan Digital Sky Survey Quasar Spectra at 0.7 < z < 2

We present MgII-based black hole mass estimates for 27,602 quasars with rest-frame UV spectra available in the Sloan Digital Sky Survey Data Release Three. This estimation is possible due to the existence of an empirical correlation between the radius of the broad line region and the continuum luminosity at 3000 Angstroms. We regenerate this correlation by applying our measurement method to UV spectra of low-redshift quasars in the HST/IUE databases which have corresponding reverberation mapping estimates of the Hbeta broad line region's radius. Our mass estimation method uses the line dispersion rather than the full width at half maximum of the low-ionization MgII emission line. We measure MgII line dispersions for quasars whose spectra have been reconstructed using the most significant eigenspectra produced through Principal Component Analysis. We have tested the reliability of using reconstructed spectra in black hole mass estimation using a Monte Carlo simulation and by comparing the results from original and reconstructed Data Release Three spectra. We show that using reconstructed spectra not only makes bias-free mass estimation possible for quasars with low spectroscopic signal-to-noise ratio, but also reduces the intrinsic scatter of the distribution of the black hole masses to lower than 0.15 dex.Comment: 38 Pages, 12 figures, 3 Tables, 1 hyperlink to catalogue data. Accepted for publication in ApJ

Black Hole Masses in Three Seyfert Galaxies

We analyze published reverberation mapping data for three Seyfert galaxies (NGC 3227, NGC 3516, and NGC 4593) to refine the mass estimate for the supermassive black hole in the center of each object. Treatment of the data in a manner more consistent with other large compilations of such masses allows us to more securely compare our results to wider samples of data, e.g., in the investigation of the M_bh-sigma relationship for active and quiescent galaxies.Comment: 14 pages, 4 figures. Accepted for publication in Ap

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

Black hole mass estimation from X-ray variability measurements in AGN

We propose a new method of estimation of the black hole masses in AGN based on the normalized excess variance, sigma_{nxs}^2. We derive a relation between sigma_{nxs}^2, the length of the observation, T, the light curve bin size, Delta t, and the black hole mass, assuming that (i) the power spectrum above the high frequency break, f_{bf}, has a slope of -2, (ii) the high frequency break scales with black hole mass, (iii) the power spectrum amplitude (in 'frequency x power' space) is universal and (iv) sigma_{nxs}^2 is calculated from observations of length T < 1/f_{bf}. Values of black hole masses in AGN obtained with this method are consistent with estimates based on other techniques such as reverberation mapping or the Mbh-stellar velocity dispersion relation. The method is formally equivalent to methods based on power spectrum scaling with mass but the use of the normalized excess variance has the big advantage of being applicable to relatively low quality data.Comment: 5 pages, 1 figure, 1 table, accepted for publication in MNRAS Letter. Added minor change on page 5 - corrected mistake (1/T 1/T > nu

Highly Ionized Collimated Outflow from HE 0238 - 1904

We present a detailed analysis of a highly ionized, multiphased and collimated outflowing gas detected through O V, O VI, Ne VIII and Mg X absorption associated with the QSO HE 0238 - 1904 (z_em ~ 0.629). Based on the similarities in the absorption line profiles and estimated covering fractions, we find that the O VI and Ne VIII absorption trace the same phase of the absorbing gas. Simple photoionization models can reproduce the observed N(Ne VIII), N(O VI) and N(Mg X) from a single phase whereas the low ionization species (e.g. N III, N IV, O IV) originate from a different phase. The measured N(Ne VIII)/N(O VI) ratio is found to be remarkably similar (within a factor of ~ 2) in several individual absorption components kinematically spread over ~ 1800 km/s. Under photoionization this requires a fine tuning between hydrogen density (nH) and the distance of the absorbing gas from the QSO. Alternatively this can also be explained by collisional ionization in hot gas with T > 10^{5.7} K. Long-term stability favors the absorbing gas being located outside the broad line region (BLR). We speculate that the collimated flow of such a hot gas could possibly be triggered by the radio jet interaction.Comment: Minor revision (accepted for publication in MNRAS letter