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Extended Systems (extended + system)
Selected AbstractsVariable structure robust state and parameter estimatorINTERNATIONAL JOURNAL OF ADAPTIVE CONTROL AND SIGNAL PROCESSING, Issue 2 2001Alex S. Poznyak Abstract The problem of simultaneous robust state and parameters estimation for a class of SISO non-linear systems under mixed uncertainties (unmodelled dynamics as well as observation noises) is addressed. A non-linear variable structure robust ,observer,identifier' is introduced to obtain the corresponding estimates. Lie derivative technique is used to obtain the observability conditions for the equivalent extended non-linear system. It is shown that, in general, the extended system can lose the global observability property and a special procedure is needed to work well in this situation. The suggested adaptive observer has the non-linear high-gain observer structure with adjusted parameters that provides ,a good' upper bound for the identification error performance index. The van der Monde transformation is used to derive this bound which turns out to be tight. Three examples dealing with a simple pendulum, the Duffing equation and the van del Pol oscillator are considered to illustrate the effectiveness of the suggested approach. Copyright © 2001 John Wiley & Sons, Ltd. [source] Modeling an industrial energy system: Perspectives on regional heat cooperationINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 9 2008S. Klugman Abstract Through energy efficiency measures, it is possible to reduce heat surplus in the pulp and paper industry. Yet pulp and paper mills situated in countries with a heat demand for residential and commercial buildings for the major part of the year are potential heat suppliers. However, striving to utilize the heat within the mills for efficient energy use could conflict with the delivery of excess heat to a district heating system. As part of a project to optimize a regional energy system, a sulfate pulp mill situated in central Sweden is analyzed, focusing on providing heat and electricity to the mill and its surrounding energy systems. An energy system optimization method based on mixed integer linear programming is used for studying energy system measures on an aggregated level. An extended system, where the mill is integrated in a regional heat market (HM), is evaluated in parallel with the present system. The use of either hot sewage or a heat pump for heat deliveries is analyzed along with process integration measures. The benefits of adding a condensing unit to the back-pressure steam turbine are also investigated. The results show that the use of hot sewage or a heat pump for heat deliveries is beneficial only in combination with extended heat deliveries to an HM. Process integration measures are beneficial and even increase the benefit of selling more heat for district heating. Adding a condensing turbine unit is most beneficial in combination with extended heat deliveries and process integration. Copyright © 2007 John Wiley & Sons, Ltd. [source] Modular solvers for image restoration problems using the discrepancy principleNUMERICAL LINEAR ALGEBRA WITH APPLICATIONS, Issue 5 2002Peter Blomgren Abstract Many problems in image restoration can be formulated as either an unconstrained non-linear minimization problem, usually with a Tikhonov -like regularization, where the regularization parameter has to be determined; or as a fully constrained problem, where an estimate of the noise level, either the variance or the signal-to-noise ratio, is available. The formulations are mathematically equivalent. However, in practice, it is much easier to develop algorithms for the unconstrained problem, and not always obvious how to adapt such methods to solve the corresponding constrained problem. In this paper, we present a new method which can make use of any existing convergent method for the unconstrained problem to solve the constrained one. The new method is based on a Newton iteration applied to an extended system of non-linear equations, which couples the constraint and the regularized problem, but it does not require knowledge of the Jacobian of the irregularity functional. The existing solver is only used as a black box solver, which for a fixed regularization parameter returns an improved solution to the unconstrained minimization problem given an initial guess. The new modular solver enables us to easily solve the constrained image restoration problem; the solver automatically identifies the regularization parameter, during the iterative solution process. We present some numerical results. The results indicate that even in the worst case the constrained solver requires only about twice as much work as the unconstrained one, and in some instances the constrained solver can be even faster. Copyright © 2002 John Wiley & Sons, Ltd. [source] Muffin-Tin Orbital Wannier-Like Functions for Insulators and MetalsCHEMPHYSCHEM, Issue 9 2005Eva Zurek Abstract Herein, we outline a method that is able to generate truly minimal basis sets that accurately describe either a group of bands, a band, or even just the occupied part of a band. These basis sets are the so-called NMTOs, muffin-tin orbitals of order N. For an isolated set of bands, symmetrical orthonormalization of the NMTOs yields a set of Wannier functions that are atom-centered and localized by construction. They are not necessarily maximally localized, but may be transformed into those Wannier functions. For bands that overlap others, Wannier-like functions can be generated. It is shown that NMTOs give a chemical understanding of an extended system. In particular, orbitals for the , and , bands in an insulator, boron nitride, and a semimetal, graphite, will be considered. In addition, we illustrate that it is possible to obtain Wannier-like functions for only the occupied states in a metallic system by generating NMTOs for cesium. Finally, we visualize the pressure-induced s,d transition. [source] Chemical bonding in ternary magnesium hydridesINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 3 2003Emilio Orgaz Abstract The electronic structure of various alkali and alkaline,earth magnesium-based hydrides was investigated in detail. These types of crystalline compounds show MgH4 or MgH6 units ordered within a light-metal framework. We investigated the nature of the chemical bonding in these units by means of quantum chemical calculations of several related clusters. The properties of the charge density of the clusters, within the framework of the theory of atoms in molecules, was analyzed. A further set of computations of the band structure of the solid hydrides was conducted using a state-of the-art density functional-based method and the mechanism of stabilization of the MgH units is discussed. It was found that the properties obtained at the molecular level correlate well with those of the solid crystals, indicating the molecular nature of the extended systems in which the units MgHx, x = 4, 6, are stabilized by means of MgH closed-shell interactions. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 94: 150,164, 2003 [source] The Role of Charge Localization in Current-Driven DynamicsISRAEL JOURNAL OF CHEMISTRY, Issue 1 2007Ryan Jorn We explore the role of charge localization in current-triggered, resonance-mediated, dynamical events in molecular junctions. To that end we use a simple model for a molecular rattle, a Li+C9H,9 zwitterion attached between two metal clusters. By varying the size of the metal clusters we systematically vary the degree of delocalization of the electronic orbitals underlying the resonant current, and thus can draw general conclusions regarding the effect of delocalization on dynamical processes induced by resonance inelastic current in molecular electronics. In the small cluster limit, we find interesting quantum dynamics in the nuclear subspace, corresponding to coherent tunneling of the wave packet through the barrier of an asymmetric double-well potential. These dynamics are rapidly damped with increasing charge delocalization in extended systems. [source] DIESEL-MP2: A new program to perform large-scale multireference-MP2 computations,JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 10 2006Patrick Musch Abstract This article presents a new MR-MP2 code (Multi- Reference Møller,Plesset 2nd order) suitable for the computation MR-MP2 energies of extended systems with strong near degeneracy effects (e.g., open shell systems). It is based on the DIESEL program package developed by Hanrath and Engels. Due to improved algorithms the new code is able to handle systems with 400,500 basis functions and more than 100 electrons. The code is made for parallel computers with distributed memory, but can also be run on local machines. It possesses two integral interfaces (MOLCAS, TURBOMOLE). The algorithms are briefly introduced and timings for the Neocarzinostatin chromophore are presented. The efficiencies of the codes obtained with Intel or GNU compilers are compared. © 2006 Wiley Periodicals, Inc. J Comput Chem 27: 1055,1062, 2006 [source] A multiple-scattering theory of circular and linear dichroism for photoemission and photoabsorptionJOURNAL OF SYNCHROTRON RADIATION, Issue 1 2002S. Di Matteo A unified treatment of circular dichroism, both natural and magnetic, in (spin-resolved) photoemission and photoabsorption from core levels is given, valid in the many-body case and for extended systems, together with an extension of the formalism to treat linear dichroism. The reduction of this scheme to a one-electron picture in the framework of multiple scattering theory is briefly discussed and shows the intimate connection of the two spectroscopies via a generalized optical theorem. Plausibility arguments are given that in correlated d -band systems screening and relaxation effects are not so drastic as in other cases, due to the autoscreening action of the excited photoelectron, so that the final density of states is much like the initial unperturbed one. It is shown how to exploit this point of view to obtain in favorables cases separated orbital and spin moment radial (surface) distribution maps from dichroic magnetic EXAFS spectra (photoelectron diffraction patterns) related to the ground state. Dichroic natural spectra, both in photoemission and absorption, are shown to be sensitive only to atoms in chiral geometry. [source] DFT/CCSD(T) Investigation of the Interaction of Molecular Hydrogen with Carbon NanostructuresCHEMPHYSCHEM, Issue 11 2009Miroslav Rube Abstract The interaction of molecular hydrogen with carbon nanostructures is investigated within the DFT/CC correction scheme. The DFT/CC results are compared with the benchmark calculations at the CCSD(T) level of theory for benzene and naphthalene, and at the MP2 level for the more extended systems. The DFT/CC method offers a reliable alternative to the highly correlated ab initio calculations at a cost comparable to the standard DFT method. The results for H2 adsorbed on graphene as well as single-wall carbon nanotubes (SWCNT) are presented. The DFT/CC binding energy on graphene of 5.4 kJ,mol,1 is in good agreement with experiment (5.00±0.05 kJ,mol,1). For (10,10)-SWCNT, the H2 molecule is mostly stabilized inside the tube with an estimated binding energy of 7.2 kJ,mol,1. [source] Minimum action method for the study of rare eventsCOMMUNICATIONS ON PURE & APPLIED MATHEMATICS, Issue 5 2004Weinan E The least action principle from the Wentzell-Freidlin theory of large deviations is exploited as a numerical tool for finding the optimal dynamical paths in spatially extended systems driven by a small noise. The action is discretized and a preconditioned BFGS method is used to optimize the discrete action. Applications are presented for thermally activated reversal in the Ginzburg-Landau model in one and two dimensions, and for noise induced excursion events in the Brusselator taken as an example of non-gradient system arising in chemistry. In the Ginzburg-Landau model, the reversal proceeds via interesting nucleation events, followed by propagation of domain walls. The issue of nucleation versus propagation is discussed and the scaling for the number of nucleation events as a function of the reversal time and other material parameters is computed. Good agreement is found with the numerical results. In the Brusselator, whose deterministic dynamics has a single stable equilibrium state, the presence of noise is shown to induce large excursions by which the system cycles out of this equilibrium state. © 2004 Wiley Periodicals, Inc. [source] | ||||||||||||||||