899 research outputs found
On-site approximation for spin-orbit coupling in LCAO density functional methods
We propose a computational method that simplifies drastically the inclusion
of spin-orbit interaction in density functional theory implemented on localised
atomic orbital basis sets. Our method is based on a well-known procedure for
obtaining pseudopotentials from atomic relativistic 'ab initio' calculations
and on an on-site approximation for the spin-orbit matrix elements. We have
implemented the technique in the SIESTA code, and we show that it provides
accurate results for the overall band structure and splittings of group IV and
III-IV semiconductors as well as for 5d metals.Comment: 8 pages, 4 figures. Published in J. Phys.: Condens. Matter 18
7999-8013, 2006. Some errata correcte
SEVERE ATTACK ON SUGARCANE AND GRASSES BY MOCIS LATIPES (GUENÉE), (LEPIDOPTERA: NOCTUIDAE) IN SOUTHWEST PUERTO RICO
SEVERE ATTACK ON SUGARCANE AND GRASSES BY MOCIS LATIPES (GUENÉE), (LEPIDOPTERA: NOCTUIDAE) IN SOUTHWEST PUERTO RIC
Comparative study of RPSALG algorithm for convex semi-infinite programming
The Remez penalty and smoothing algorithm (RPSALG) is a unified framework for penalty and smoothing methods for solving min-max convex semi-infinite programing problems, whose convergence was analyzed in a previous paper of three of the authors. In this paper we consider a partial implementation of RPSALG for solving ordinary convex semi-infinite programming problems. Each iteration of RPSALG involves two types of auxiliary optimization problems: the first one consists of obtaining an approximate solution of some discretized convex problem, while the second one requires to solve a non-convex optimization problem involving the parametric constraints as objective function with the parameter as variable. In this paper we tackle the latter problem with a variant of the cutting angle method called ECAM, a global optimization procedure for solving Lipschitz programming problems. We implement different variants of RPSALG which are compared with the unique publicly available SIP solver, NSIPS, on a battery of test problems.This research was partially supported by MINECO of Spain, Grants MTM2011-29064-C03-01/02
A comparative note on the relaxation algorithms for the linear semi-infinite feasibility problem
The problem (LFP) of finding a feasible solution to a given linear semi-infinite system arises in different contexts. This paper provides an empirical comparative study of relaxation algorithms for (LFP). In this study we consider, together with the classical algorithm, implemented with different values of the fixed parameter (the step size), a new relaxation algorithm with random parameter which outperforms the classical one in most test problems whatever fixed parameter is taken. This new algorithm converges geometrically to a feasible solution under mild conditions. The relaxation algorithms under comparison have been implemented using the extended cutting angle method for solving the global optimization subproblems.This research was partially supported by MICINN of Spain, Grant MTM2014-59179-C2-1-P and Sistema Nacional de Investigadores, Mexico
Improving a leaves automatic recognition process using PCA
In this work we present a simulation of a recognition process with
perimeter characterization of a simple plant leaves as a unique discriminating
parameter. Data coding allowing for independence of leaves size and orientation
may penalize performance recognition for some varieties. Border description
sequences are then used, and Principal Component Analysis (PCA) is applied in
order to study which is the best number of components for the classification task,
implemented by means of a Support Vector Machine (SVM) System. Obtained
results are satisfactory, and compared with [4] our system improves the
recognition success, diminishing the variance at the same time
Self-assembly and properties of a discrete water-soluble Prussian blue analogue FeII/CoIII cube: confinement of a water molecule in aqueous solution
Novel types of water-soluble anionic cubic cages, K4[{CoIII(Me3-Tacn)}4{FeII(CN)6}4] and Na4[{CoIII(Me3-Tacn)}4{FeII(CN)6}4] (Me3-Tacn = 1,4,7-trimethyl-1,4,7-triazacyclononane), were prepared by means of a mechanistically designed self-assembly process between [Co(Me3-Tacn)Cl3] and A4[FeII(CN)6] (M = Na or K), consisting of a rate-limiting outer-sphere redox step, followed by a fast substitution/inner-sphere redox reaction sequence. These compounds show remarkable stability in aqueous solution at different pH ranges, displaying neat protonation processes and reversible oxidation with peroxodisulfate to its neutral {FeIII4CoIII4} form. Furthermore, the cages behave as a robust and water-soluble molecular Prussian Blue analogue capable of encapsulating {Na-OH2}+ pairs and K+ cations in aqueous solution, with the cubic structure of the complex being preserved. Substitution of the {Na-OH2}+ pairs by K+ is easily accomplished, and the electrochemical properties of the sodium and potassium salts of the new cages have been found to be dramatically dependent on the encapsulated units
Bosonization on a lattice: The emergence of the higher harmonics
6 págs.; 2 figs.A general and transparent procedure to bosonize fermions placed on a lattice is presented. Harmonics higher than kF in the one-particle Green function are shown to appear due to the compact character of real electron bands. Quantitative estimations of the role of higher harmonics are made possible by this bosonization technique. © 1995 The American Physical Society.J.F. was supported by DEYCIT Project No. PB93-1248.Peer Reviewe
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