13,610 research outputs found
Spatial variability of soil properties and soil erodibility in the Alqueva reservoir watershed
The aim of this work is to investigate how the spatial variability of soil properties and soil erodibility (K factor) were affected by the changes in land use allowed by irrigation with water from a reservoir in a semiarid area. To this end, three areas representative of different land uses (agroforestry grassland, lucerne crop and olive orchard) were studied within a 900 ha farm. The interrelationships between variables were analyzed by multivariate techniques and extrapolated using geostatistics. The results confirmed differences between land uses for all properties analyzed, which was explained mainly by the existence of diverse management practices (tillage, fertilization and irrigation), vegetation cover and local soil characteristics. Soil organic matter, clay and nitrogen content decreased significantly, while the K factor increased with intensive cultivation. The HJ-Biplot methodology was used to represent the variation of soil erodibility properties grouped in land uses. Native grassland was the least correlated with the other land uses. The K factor demonstrated high correlation mainly with very fine sand and silt. The maps produced with geostatistics were crucial to understand the current spatial variability in the Alqueva region. Facing the intensification of land-use conversion, a sustainable management is needed to introduce protective measures to control soil erosion
Mass Generation from Lie Algebra Extensions
Applied to the electroweak interactions, the theory of Lie algebra extensions
suggests a mechanism by which the boson masses are generated without resource
to spontaneous symmetry breaking. It starts from a gauge theory without any
additional scalar field. All the couplings predicted by the Weinberg-Salam
theory are present, and a few others which are nevertheless consistent within
the model.Comment: 11 pages; revtex; title and PACS have been changed; comments included
in the manuscrip
Importance of Granular Structure in the Initial Conditions for the Elliptic Flow
We show effects of granular structure of the initial conditions (IC) of
hydrodynamic description of high-energy nucleus-nucleus collisions on some
observables, especially on the elliptic-flow parameter v2. Such a structure
enhances production of isotropically distributed high-pT particles, making v2
smaller there. Also, it reduces v2 in the forward and backward regions where
the global matter density is smaller, so where such effects become more
efficacious.Comment: 4 pages, 5 figure
Fluctuation of the Initial Conditions and Its Consequences on Some Observables
We show effects of the event-by-event fluctuation of the initial conditions
(IC) in hydrodynamic description of high-energy nuclear collisions on some
observables. Such IC produce not only fluctuations in observables but, due to
their bumpy structure, several non-trivial effects appear. They enhance
production of isotropically distributed high-pT particles, making v2 smaller
there. Also, they reduce v2 in the forward and backward regions where the
global matter density is smaller, so where such effects become more
efficacious. They may also produce the so-called ridge effect in the two
large-pT particle correlation.Comment: 6 pages, 6 figures, presented at the IV Workshop on Particle
Correlations and Femtoscopy (WPCF2008), Krakow, Poland, 11-14 Sep 200
Memory effects on the statistics of fragmentation
We investigate through extensive molecular dynamics simulations the
fragmentation process of two-dimensional Lennard-Jones systems. After
thermalization, the fragmentation is initiated by a sudden increment to the
radial component of the particles' velocities. We study the effect of
temperature of the thermalized system as well as the influence of the impact
energy of the ``explosion'' event on the statistics of mass fragments. Our
results indicate that the cumulative distribution of fragments follows the
scaling ansatz , where is
the mass, and are cutoff parameters, and is a scaling
exponent that is dependent on the temperature. More precisely, we show clear
evidence that there is a characteristic scaling exponent for each
macroscopic phase of the thermalized system, i.e., that the non-universal
behavior of the fragmentation process is dictated by the state of the system
before it breaks down.Comment: 5 pages, 8 figure
Gravitation and Duality Symmetry
By generalizing the Hodge dual operator to the case of soldered bundles, and
working in the context of the teleparallel equivalent of general relativity, an
analysis of the duality symmetry in gravitation is performed. Although the
basic conclusion is that, at least in the general case, gravitation is not dual
symmetric, there is a particular theory in which this symmetry shows up. It is
a self dual (or anti-self dual) teleparallel gravity in which, due to the fact
that it does not contribute to the interaction of fermions with gravitation,
the purely tensor part of torsion is assumed to vanish. The ensuing fermionic
gravitational interaction is found to be chiral. Since duality is intimately
related to renormalizability, this theory may eventually be more amenable to
renormalization than teleparallel gravity or general relativity.Comment: 7 pages, no figures. Version 2: minor presentation changes,
references added. Accepted for publication in Int. J. Mod. Phys.
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