514 research outputs found
Kinetic Energy Density Study of Some Representative Semilocal Kinetic Energy Functionals
There is a number of explicit kinetic energy density functionals for
non-interacting electron systems that are obtained in terms of the electron
density and its derivatives. These semilocal functionals have been widely used
in the literature. In this work we present a comparative study of the kinetic
energy density of these semilocal functionals, stressing the importance of the
local behavior to assess the quality of the functionals. We propose a quality
factor that measures the local differences between the usual orbital-based
kinetic energy density distributions and the approximated ones, allowing to
ensure if the good results obtained for the total kinetic energies with these
semilocal functionals are due to their correct local performance or to error
cancellations. We have also included contributions coming from the laplacian of
the electron density to work with an infinite set of kinetic energy densities.
For all the functionals but one we have found that their success in the
evaluation of the total kinetic energy are due to global error cancellations,
whereas the local behavior of their kinetic energy density becomes worse than
that corresponding to the Thomas-Fermi functional.Comment: 12 pages, 3 figure
Robust control of the distributed solar collector field ACUREX using MPC for tracking
17th IFAC World Congress 2008. Seoul (Korea). 06/07/2008This paper presents the application of a robust model predictive control for tracking of piece-wise constant references (RMPCT) to a distributed collector field, ACUREX, at the solar power plant of PSA (Solar Plant of Almería). The main characteristic of a solar power plant is that the primary energy source, solar radiation, cannot be manipulated. Solar radiation varies throughout the day, causing changes in plant dynamics and strong disturbances in the process. The real plant is assumed to be modeled as a linear system with additive bounded uncertainties on the states. Under mild assumptions, the proposed RMPCT can steer the uncertain system in an admissible evolution to any admissible steady state, that is, under any change of the set point. This allows us to reject constant disturbances compensating the effect of then changing the setpoint
Theoretical study of electronic transport through a small quantum dot with a magnetic impurity
We model a small quantum dot with a magnetic impurity by the Anderson
Hamiltonian with a supplementary exchange interaction term. The transport
calculations are performed by means of the Green functions within the equation
of motion scheme, in which two decoupling procedures are proposed, for high and
low temperatures, respectively. The paper focuses on the charge fluctuations
for such a system, aspect not addressed before, as well as on the Kondo
resonance. We show a specific role of the excited state, which can be observed
in transport and in spin-spin correlations. Our studies show on a new many-body
feature of the phase shift of transmitted electrons, which is manifested in a
specific dip. In the Kondo regime, our calculations complement existing
theoretical results. The system shows three Kondo peaks in the density of
states: one at the Fermi energy and two side peaks, at a distance corresponding
to the singlet-triplet level spacing. The existence of the central peak is
conditioned by a degenerate state (the triplet) below the Fermi energy.Comment: 12 pages, 4 figure
Coulomb effects on the transport properties of quantum dots in strong magnetic field
We investigate the transport properties of quantum dots placed in strong
magnetic field using a quantum-mechanical ' approach based on the 2D
tight-binding Hamiltonian with direct Coulomb interaction and the
Landauer-B\"{u}ttiker (LB) formalism. The electronic transmittance and the Hall
resistance show Coulomb oscillations and also prove multiple addition
processes. We identify this feature as the 'bunching' of electrons observed in
recent experiments and give an elementary explanation in terms of spectral
characteristics of the dot. The spatial distribution of the added electrons may
distinguish between edge and bulk states and it has specific features for
bunched electrons. The dependence of the charging energy on the number of
electrons is discussed for strong and vanishing magnetic field. The crossover
from the tunneling to quantum Hall regime is analyzed in terms of dot-lead
coupling.Comment: 17 pages,8 figures,Revtex,submitted to Physical Review
Agrupaciones de modelos locales con descripción externa. Aplicación a una planta de frío solar
En este artículo se presenta y analiza un método de creación de modelos formados por
agrupaciones de submodelos locales lineales. La principal novedad es que la ponderación empleada
con los submodelos no es la habitual, basada en el estado o parte del mismo sino que se toman
exclusivamente señales instantáneas de entrada y salida del sistema. Esta elección simplifica algunos
aspectos de la creación del modelo, manteniendo intacta la capacidad de representación, siendo ´esta
comparada con otras técnicas. La simplificación aludida es importante pues acerca el método a la
práctica industrial del control de procesos. La técnica de identificación resultante se ilustra mediante
dos casos prácticos: un sistema simulado propuesto por Narendra y el sistema de captación de una
planta real de producción de frío a partir de energía solar. En ambos casos se muestran los errores de
generalización para la predicción a un paso y para la simulación usando gran cantidad de situaciones.
Los resultados indican que es factible el uso del método propuesto como técnica simplificada aplicable
en la industria.Comisión de la Comunidad Europea Proyecto de investigación HYCON FP6-51136
Un modelo de potencialidad climática para la trufa negra (Tuber melanosporum) en Teruel (España)
Black truffle (Tuber melanosporum) is an edible ectomycorrhizal mushroom whose cultivation is an economically-viable alternative in rural areas affected by depopulation. In the province of Teruel (Spain), truffle plantations occupy nowadays more than 4,500 ha, but no land use planning guidelines have been available. Species distribution models are tools that allow managers, farmers and foresters to plan ahead and make decisions with a scientific basis. The territory climatically suitable for T. melanosporum in Teruel has been predicted using a method based on the ecology field theory, previously tested in the development of distribution models for forest species. A dataset of 924 locations where black truffle has been collected in the Catalano-Aragonesa ecoregion and eight climatic parameters deeply influencing the presence and fructification of the black truffle have been considered and their corresponding habitats have been built. The distribution model, corrected under lithological criteria, has identified more than 8,000 km² as suitable for black truffle fructification in Teruel, almost 55% of the province, belonging 3,000 of them to the optimal class. This land is mainly distributed over the regions of Gúdar-Javalambre, Comunidad de Teruel and Maestrazgo. A further correction based on land-use criteria has identified more than 4,000 km² as suitable for truffle plantations, being 1,150 of them optimal. The model here presented will help to a proper planning for truffle cultivation in the province of Teruel.La trufa negra (Tuber melanosporum) es un hongo ectomicorrícico comestible cuyo cultivo supone en la actualidad una alternativa económica viable para zonas rurales afectadas gravemente por la despoblación. En la provincia de Teruel (España) hay más de 4.500 ha de plantaciones truferas, instaladas sin ningún proceso de planificación orientado a alcanzar un territorio rural ordenado. Los modelos territoriales de potencialidad o aptitud para las especies son herramientas que permiten a los gestores, agricultores y selvicultores desarrollar dicha planificación y tomar decisiones fundamentadas en un conocimiento científico lo más riguroso posible.
Utilizando un método basado en la teoría de campos aplicada a la ecología, habitual para elaborar las áreas potenciales de especies forestales vegetales, se ha determinado el territorio climáticamente apto para T. melanosporum en la provincia Teruel. Para construir este modelo se han utilizado 924 localizaciones de la ecorregión Catalano-Aragonesa. Elaborando ocho parámetros climáticos trascendentes para la fructificación de la trufa negra, se han construido sus correspondientes hábitats.
El modelo de potencialidad climática elaborado, completado con una corrección litológica, ha permitido identificar algo más de 8.000 km2 como aptos para la recolección de la trufa negra en Teruel, casi el 55% de la provincia, de los cuales 3.000 corresponden a la clase óptima y están distribuidos por las comarcas de Gúdar-Javalambre, Comunidad de Teruel y Maestrazgo. La adaptación del modelo ha permitido identificar más de 4.000 km2 como aptos para la instalación de plantaciones truferas, 1.150 de los cuales tienen potencialidad óptima.
El modelo generado en el presente trabajo permitirá la adecuada planificación territorial de la truficultura en la provincia de Teruel
Towards semantic knowledge mapping: an extension of compendium with semantic knowledge representation
Compendium is a knowledge mapping application equipped with graphical representations of ideas and
arguments. Extension of the processes in Compendium with Semantic Web technologies can be beneficial
for the intelligent searching of concepts or ideas, and supporting decision making process. This paper
presents the extended Compendium which exploits the Semantic Web for knowledge representation and
user interaction. The result evaluated by the experts and users showed that the extension eases and
streamlines the decision making process
Managing Information to Support the Decision Making Process
Decision-making is a crucial activity during the planning, design and operation of artefacts. To make a decision several alternatives must be evaluated and compared, which are tasks that require information, knowledge and expertise. A system that organises and manages the knowledge associated with every alternative and links ideas, arguments and issues can greatly improve and facilitate the decision making process. This paper presents how an Issue Based Information System (IBIS) implemented in Compendium (http://compendium.open.ac.uk) has been extended with new functionalities such as access to a toolkit of Multi-Criteria Decision Methods (MCDM), the ability to propagate values throughout the decision records and to perform sensitivity analysis of the recommended decisions with respect to a parameter. These additional functionalities enable the applicability of the system in the support of decisions that require not only argumentation, but also numerical evaluation of the properties of the alternatives such as those proposed during the design, planning and operation of engineering artefacts. </jats:p
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