EVALUATION OF COOL-SEASON ANNUALS EFFECT ON SOIL HEALTH IN WARM-SEASON PERENNIAL PASTURES IN SOUTHESTERN US.

Perennial grass crops represent approximately 8 million hectares of the land area of the humid lower southeastern United States. These forage crops receive high rates of fertilizer, especially nitrogen (N), and near monoculture remains have often been treated with repeated applications of herbicides. Pasture management is crucial to improve soil properties in pasturelands. Common pasture management practices include introducing cool-season multispecies in warm-season pasture systems and forage harvest frequency of pasture systems. It is known that cool-season multispecies in warm-season pasture systems ensure cattle feeding during winter season and have beneficial effects on soil microbial biomass, soil organic matter (SOM), and enzymatic activity. Forage harvest frequency is needed in pasturelands to regenerate after intensive grazing, contributing to soil nutrient returns and reduce soil compaction. In this study three sites were evaluated, two in Louisiana and one in central Mississippi to determine whether soil health is enhanced by overseeding different species of cool-season annual treatments in two warm season pastures bermudagrass (Cynodon dactylon (L.) Pers.) and bahiagrass (Paspalum notatum). For this, the evaluation of microecological and chemical properties of soil were included to analyze the impact of pastureland management practices and the impact of species on soil health. Harvest frequency rates were including in plots to evaluate two harvest frequency rates at 4-week, at 8-week, and a cool-season annual mulch. Samples were collected at two depths, 0-10cm and 10-20cm to evaluate how soil properties fluctuate through soil profile. The methods used to analyze microecological properties incorporate fatty acid methyl ester (FAMEs), and enzyme assays (β-glucosaminidase and β-glucosidase). The chemical properties measured included pH, total carbo (TC), total nitrogen (TN), nutrient concentrations, SOM, and inorganic N. Significant changes over time were observed in several soil properties, one of these was SOM, which changed over time in all sites. Depth significantly influenced majority of soil properties in this study, normally soil properties decreased when soil depth increased. Absolute abundance of fungi to bacteria ratio significantly increased under an 8-week harvest frequency treatment in 2020 in one site. Overseeding legumes, annual ryegrass, and grass increased potential β-glucosaminidase in soil in Louisiana. Relative abundance of arbuscular mycorrhiza fungi and Gram-negative bacteria increase in bottom depth of soil. General responses to harvest frequency treatments suggest that 8-week harvest frequency is more beneficial for most soil properties than 4-week harvest frequenc

Diffusive transport and self-consistent dynamics in coupled maps

The study of diffusion in Hamiltonian systems has been a problem of interest for a number of years. In this paper we explore the influence of self-consistency on the diffusion properties of systems described by coupled symplectic maps. Self-consistency, i.e. the back-influence of the transported quantity on the velocity field of the driving flow, despite of its critical importance, is usually overlooked in the description of realistic systems, for example in plasma physics. We propose a class of self-consistent models consisting of an ensemble of maps globally coupled through a mean field. Depending on the kind of coupling, two different general types of self-consistent maps are considered: maps coupled to the field only through the phase, and fully coupled maps, i.e. through the phase and the amplitude of the external field. The analogies and differences of the diffusion properties of these two kinds of maps are discussed in detail.Comment: 13 pages, 14 figure

GTC Spectra of z ~ 2.3 Quasars: Comparison with Local Luminosity Analogues

[Abridged] Context: The advent of 8-10m class telescopes makes possible for the first time detailed comparison of quasars with similar luminosity and very different redshifts. Aims: A search for z-dependent gradients in line emission diagnostics and derived physical properties by comparing, in a narrow bolometric luminosity range (log L ~ 46.1 +/- 0.4 [\ergss]), some of the most luminous local (z < 0.6) quasars with some of the lowest luminosity sources yet found at redshift z = 2.1 ~ 2.5. Method: Spectra for 22 high z sources were obtained with the 10.4m Gran Telescopio Canarias (GTC) while the HST (largely FOS) archive provides a low redshift control sample. Comparison is made in the context of the 4D Eigenvector 1 formalism meaning that we divide both source samples into high accreting Population A and low accreting Population B sources. Results: CIV 1549 shows very similar properties at both redshifts confirming at high redshift the CIV profile differences between Pop. A and B that are well established in local quasars. The CIV blueshift that appears quasi- ubiquitous in higher L sources is found in only half (Pop. A) of quasars observed in both of our samples. A CIV evolutionary Baldwin effect is certainly disfavored. We find evidence for lower metallicity in the GTC sample that may point toward a gradient with z. No evidence for a gradient in black hole mass or Eddington ratio is found. Conclusions: Spectroscopic differences established at low redshift are also present in much higher redshift quasars. Given that our samples involve sources with very similar luminosity the evidence for a systematic metallicity decrease, if real, points toward an evolutionary effect. Our samples appear representative of a slow evolving quasar population likely present at all redshifts.Comment: To appear in Astronomy & Astrophysic

Efficiency Centered Maintenance of Preheat Train of a Crude Oil Distillation Unit

Nowadays, maintenance is based on the synergistic integration of operational reliability and timely maintenance, which guarantees the required availability and optimal cost. Operational reliability implies producing more, better performance, longer life, and availability. Timely maintenance involves the least time out of service, fewer maintenance costs, fewer operating costs, and less money. In this work, we study the preheating train of a crude distillation unit of a refinery, which processes 994 m3/h, which presents a formation of a foulinglayer inside it. Among the impacts of fouling is the reduction in the effectiveness of heat transfer, the increase in fuel consumption, the increase in CO2 emissions, the increase in maintenance costs, and the decrease in the profit margin of process. An appropriate cleaning program of the surface of the heat exchanger network is necessary to preserve its key performance parameters, preferably close to design values. This paper presents the maintenance method centered on energy efficiency, to plan the intervention of the preheating train equipment maintenance, which considers the economic energy improvement and the cost of the type of maintenance. The method requires the calculation of the fouling evolution from which the global heat transfer coefficient is obtained, and the heat flux is determined as a function of time. It was observed that, as time passes, the resistance provided by fouling increases and that the overall heat transfer coefficient decreases. The energy efficiency centered maintenance has an indicator of economic justification (factor J) that relates the economic-energy improvement achieved when performing maintenance, taking into account the economic effort invested. Depending on the cost of the type of maintenance to be performed, a threshold should be chosen, from which the maintenance activity is justified. The effectiveness values of the heat exchanger (e) and the J indicator are used to form a criticality matrix, which allows prioritizing maintenance activities in each equipment. The planning of the implementation dates of the maintenance of each heat exchanger, from the maintenance method centered on energy efficiency applied to the crude distillation unit's, preheat train, constitutes a contribution in this specific field. The conceptual design of the maintenance method centered on energy efficiency presented in this work is feasible for other heat transfer equipment used in oil refineries and industry in general. The procedure developed uses real operation values, and with its implementation, a saving of 150000 US dollars was achieved. © 2020 ASME

Quasars: from the Physics of Line Formation to Cosmology

Quasars accreting matter at very high rates (known as extreme Population A [xA] or super-Eddington accreting massive black holes) provide a new class of distance indicators covering cosmic epochs from the present-day Universe up to less than 1 Gyr from the Big Bang. The very high accretion rate makes it possible that massive black holes hosted in xA quasars radiate at a stable, extreme luminosity-to-mass ratio. This in turns translates into stable physical and dynamical conditions of the mildly ionized gas in the quasar low-ionization line emitting region. In this contribution, we analyze the main optical and UV spectral properties of extreme Population A quasars that make them easily identifiable in large spectroscopic surveys at low-z (z < 1) and intermediate-z (2 < z < 2.6), and the physical conditions that are derived for the formation of their emission lines. Ultimately, the analysis supports the possibility of identifying a virial broadening estimator from low-ionization line widths, and the conceptual validity of the redshift-independent luminosity estimates based on virial broadening for a known luminosity-to-mass ratio.Comment: 13 pages, 5 figures. Invited lecture at SPIG 2018, Belgrade. To appear in Ato