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First Principles (first + principle)
Terms modified by First Principles Selected AbstractsElectronic and Magnetic Properties of SrTiO3/LaAlO3 Interfaces from First PrinciplesADVANCED MATERIALS, Issue 26-27 2010Hanghui Chen Abstract A number of intriguing properties emerge upon the formation of the epitaxial interface between the insulating oxides LaAlO3 and SrTiO3. These properties, which include a quasi two-dimensional conducting electron gas, low temperature superconductivity, and magnetism, are not present in the bulk materials, generating a great deal of interest in the fundamental physics of their origins. While it is generally accepted that the novel behavior arises as a result of a combination of electronic and atomic reconstructions and growth-induced defects, the complex interplay between these effects remains unclear. In this report, we review the progress that has been made towards unraveling the complete picture of the SrTiO3/LaAlO3 interface, focusing primarily on present ab initio theoretical work and its relation to the experimental data. In the process, we highlight some key unresolved issues and discuss how they might be addressed by future experimental and theoretical studies. [source] Supramolecular Crystal Engineering at the Solid,Liquid Interface from First Principles: Toward Unraveling the Thermodynamics of 2D Self-AssemblyADVANCED MATERIALS, Issue 13 2009Carlos-Andres Palma Abstract The formation of highly ordered 2D supramolecular architectures self-assembled at the solid,solution interfaces is subject to complex interactions between the analytes, the solvent, and the substrate. These forces have to be mastered in order to regard self-assembly as an effective bottom-up approach for functional-device engineering. At such interfaces, prediction of the thermodynamics governing the formation of spatially ordered 2D arrangements is far from being fully understood, even for the physisorption of a single molecular component on the basal plane of a flat surface. Two recent contributions on controlled polymorphism and nanopattern formation render it possible to gain semi-quantitative insight into the thermodynamics of physisorption at interfaces, paving the way towards 2D supramolecular crystal engineering. Although in these two works different systems have been chosen to tackle such a complex task, authors showed that the chemical design of molecular building blocks is not the only requirement to fulfill when trying to preprogram self-assembled patterns at the solid,liquid interface. [source] ChemInform Abstract: Electronic Structure and Chemical Bonding within MgB2 and Related Borides from First PrinciplesCHEMINFORM, Issue 36 2008Samir F. Matar Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Predictions of the Properties of Water from First Principles.CHEMINFORM, Issue 22 2007Robert Bukowski Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Local Structure and Chemical Bonding of Protonated LixMn2O4 Spinels from First Principles.CHEMINFORM, Issue 20 2006C. M. Fang Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] First principles study of small palladium cluster growth and isomerizationINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 7 2007Chen Luo Abstract Structures and physical properties of small palladium clusters Pdn up to n = 15 and several selected larger clusters were studied using density functional theory under the generalized gradient approximation. It was found that small Pdn clusters begin to grow 3-dimensionally at n = 4 and evolve into symmetric geometric configurations, such as icosahedral and fcc -like, near n = 15. Several isomers with nearly degenerate average binding energies were found to coexist and the physical properties of these clusters were calculated. For several selected isomers, relatively moderate energy barriers for structural interchange for a given cluster size were found, implying that isomerization could readily occur under ambient conditions. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 [source] First principles study of 1,2-dichlorobenzene adsorption on metallic carbon nanotubesINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 13 2006Solange B. Fagan Abstract A systematic study of the structural and electronic properties of a 1,2-dichlorobenzene (DCB) molecule interacting with metallic single-wall carbon nanotubes is reported. The calculations were performed through ab initio methods using the SIESTA code. The interaction between DCB and nanotube is observed to depend on the diameter and it is larger for metallic nanotubes when compared with semiconducting. The binding energies are small thus suggesting that the interaction is through a physisorption process. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006 [source] First principles study of the decomposition processes of AlN in a hydrogen atmospherePHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 9 2008U. Panyukova Abstract The growth of AlN films by the hydrogen vapor phase epitaxy method is generally carried out at a high temperature over a hydrogen atmosphere. The difficulties concerned with the decomposition processes on the surface during the film growth result in necessity of computer modelling of that processes. First principles calculations of the decomposition processes of AlN in a hydrogen atmosphere are reported. The mechanism of desorption of atoms from the surface was determined. Al atoms desorb as AlH from (0001) surface and as Al from (000-1) surface of AlN. And N atoms desorb as NH3 from (0001) surface and as NH from (000-1) surface of AlN. The desorption of Al atoms is a rate limiting reaction. The calculation results correspond well with the experimental date published earlier. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] First principles approach to binding energies of excitons, trions and biexcitons in quantum wellsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 5 2003A. V. Filinov Abstract We present first-principle path integral Monte-Carlo (PIMC) studies of strongly correlated electron,hole complexes such as excitons, trions (charged excitons) and biexcitons in AlxGa1,xAs quantum-well structures. The correlation and binding energies are calculated as function of quantum well width L, for 10 Å , L , 250 Å and compared with available experimental [1] and theoretical [2,4] data. As in the experiments, we observe a maximum of the binding energies in GaAs/AlGaAs quantum well samples around L = 40 Å the physical reason of which is the non-monotonic dependence of the electron (hole) confinement on the well width. The developed method is a powerful tool for further systematic investigation of the influence of temperature and many-body effects on bound states in heterostructures (e.g. depedence on finite exciton, biexciton densities) and disorder (e.g. well-width fluctuations). [source] Energy release control for numerical simulations of failure in quasi-brittle solidsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 1 2004Miguel A. GutiérrezArticle first published online: 4 NOV 200 Abstract A path-following constraint is developed which is based on the energy release during failure. This makes it applicable to the simulation of quasi-brittle materials when no previous knowledge is available on the failure behaviour of a body and, consequently, indirect displacement control methods like CMOD cannot be applied. The constraint is derived from the first principle of thermodynamics for a finite-element discretization of a solid with a continuum damage model. The performance of the constraint is demonstrated by means of a bending test on a single-edge-notched beam. Copyright © 2003 John Wiley & Sons, Ltd. [source] A Unified Dynamic Model Formulation for Robotic Manipulator SystemsJOURNAL OF FIELD ROBOTICS (FORMERLY JOURNAL OF ROBOTIC SYSTEMS), Issue 10 2003Anjan Kumar Swain This paper addresses the problem of the formulation of a unified dynamic model for sundry robotic manipulator systems derived from the first principle of mechanics instead of the existing formulation based on linear separability principle. It provides a systematic derivation, evaluation, and subsequent conceptual interpretation of manipulator dynamics model. Further, it analyzes the generality of the unified model over a wide range of manipulator configurations. In addition, it describes the implementation aspects of the unified model. © 2003 Wiley Periodicals, Inc. [source] Core-level shifts in complex metallic systems from first principlePHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 11 2006Weine Olovsson Abstract We show that core-level binding energy shifts (CLS) can be reliably calculated within density functional theory. The scheme includes both the initial (electron energy eigenvalue) as well as final state (relaxation due to core-hole screening) effects in the same framework. The results include CLS as a function of composition in substitutional random bulk and surface alloys. Sensitivity of the CLS to the local chemical environment in the bulk and at the surface is demonstrated. A possibility to use the CLS for structural determination is discussed. Finally, an extension of the model is made for Auger kinetic energy shift calculations. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] FCCU simulation based on first principle and artificial neural network modelsASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 6 2009Maria Mihe Abstract A first principle model has been developed for the reactor,regenerator system based on construction and operating data from an industrial fluid catalytic cracking unit (FCCU). The first principle model takes into account the main FCCU subsystems: reactor riser, regenerator, stripper, catalyst circulation lines, air blower, wet gas compressor and main fractionator. A five-lump kinetic scheme has been considered for the reactions taking place in the reactor riser. Subsequently, an artificial neural network (ANN) model has been built for the complex FCCU system. The dynamic simulator, based on the previously developed first principle model, served as the source of reliable data for ANN design, training and testing. The ANN developed model was successfully trained and tested. Comparison between first principle and neural network based model leads to a very good match between the two models. Results show the substantial reduction of the computation time featured by the ANN model compared to the first principle model, demonstrating its potential use for real-time implementation in model-based control algorithms. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source] Towards using modern data assimilation and weather forecasting methods in solar physicsASTRONOMISCHE NACHRICHTEN, Issue 3-4 2007A. S. BrunArticle first published online: 7 MAR 200 Abstract We discuss how data assimilation and forecasting methods developed in Earth's weather prediction models could be used to improve our capability to anticipate solar dynamical phenomena and assimilate the huge amount of data that new solar satellites, such as SDO or Hinode, will provide in the coming years. We illustrate with some simple examples such as the solar magnetic activity cycle, the eruption of CMEs, the real potential of such methods for solar physics. We believe that we now need to jointly develop solar forecasting models, whose purpose are to assimilate observational data in order to improve our predictability power, with "first principle" solar models, whose purpose is to understand the underpinning physical processes behind the solar dynamics. These two complementary approaches should lead to the development of a solar equivalent of Earth's general circulation model. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] A Simple and reliable formula for assessment of maximum volumetric productivities in photobioreactorsBIOTECHNOLOGY PROGRESS, Issue 2 2009Jean-François Cornet Abstract This article establishes and discusses the consistency and the range of applicability of a simple but general and predictive analytical formula, enabling to easily assess the maximum volumetric biomass growth rates (the productivities) in several kinds of photobioreactors with more or less 15% of deviation. Experimental validations are performed on photobioreactors of very different conceptions and designs, cultivating the cyanobacterium Arthrospira platensis, on a wide range of volumes and hemispherical incident light fluxes. The practical usefulness of the proposed formula is demonstrated by the fact that it appears completely independent of the characteristics of the material phase (as the type of reactor, the kind of mixing, the biomass concentration,), according to the first principle of thermodynamics and to the Gauss-Ostrogradsky theorem. Its ability to give the maximum (only) kinetic performance of photobioreactors cultivating many different photoautotrophic strains (cyanobacteria, green algae, eukaryotic microalgae) is theoretically discussed but experimental results are reported to a future work of the authors or to any other contribution arising from the scientific community working in the field of photobioreactor engineering and potentially interested by this approach. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2009 [source] Synthesis of a Model for Life-Cycle Project ManagementCOMPUTER-AIDED CIVIL AND INFRASTRUCTURE ENGINEERING, Issue 1 2000Ali Jaafari The focus of this article is on life-cycle objective,based project management models in general. The model has been designed (1) to facilitate employment of life-cycle objective,based project management approaches and (2) to support concurrent engineering and construction, thus promoting greater integration of total processes under which projects are proposed and implemented. In order to synthesize the functions designed in the model, we undertook a detailed case study of a large capital project. This case study has been documented in separate articles; only the results of the study will be presented in this article. While this field research shed light on the actual needs and requirements, the design of the functions was approached from first principles. They incorporate the basic shift from the traditional objectives of cost, time, and quality to life-cycle objective functions, such as return on investment, facility operability, and life-cycle integration. This article describes the fundamental philosophy and framework for the development of life-cycle project management in general and contrasts this with the traditional project management models. [source] Electromagnetic Effects on Transport Barrier RelaxationsCONTRIBUTIONS TO PLASMA PHYSICS, Issue 1-3 2008G. Fuhr Abstract Results of transport barrier relaxations computed with a new 3D electromagnetic simulation code (EMEDGE3D) of resistive ballooning turbulence are presented. In these simulations, a barrier forms due to an imposed E × B shear flow. We report the first self-consistent electromagnetic simulations based on first principles which exhibit barrier relaxation cycles. This barrier relaxes intermittently on confinement time scales, even if fluctuations of the E × B flow are suppressed. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] General Gyrokinetic Equations for Edge PlasmasCONTRIBUTIONS TO PLASMA PHYSICS, Issue 7-9 2006H. Qin Abstract During the pedestal cycle of H-mode edge plasmas in tokamak experiments, large-amplitude pedestal build-up and destruction coexist with small-amplitude drift wave turbulence. The pedestal dynamics simultaneously includes fast time-scale electromagnetic instabilities, long time-scale turbulence-induced transport processes, and more interestingly the interaction between them. To numerically simulate the pedestal dynamics from first principles, it is desirable to develop an effective algorithm based on the gyrokinetic theory. However, existing gyrokinetic theories cannot treat fully nonlinear electromagnetic perturbations with multi-scale-length structures in spacetime, and therefore do not apply to edge plasmas. A set of generalized gyrokinetic equations valid for the edge plasmas has been derived. This formalism allows large-amplitude, time-dependent background electromagnetic fields to be developed fully nonlinearly in addition to small-amplitude, short-wavelength electromagnetic perturbations. It turns out that the most general gyrokinetic theory can be geometrically formulated. The Poincaré-Cartan-Einstein 1-form on the 7D phase space determines particles' worldlines in the phase space, and realizes the momentum integrals in kinetic theory as fiber integrals. The infinitesimal generator of the gyro-symmetry is then asymptotically constructed as the base for the gyrophase coordinate of the gyrocenter coordinate system. This is accomplished by applying the Lie coordinate perturbation method to the Poincaré-Cartan-Einstein 1-form. General gyrokinetic Vlasov-Maxwell equations are then developed as the Vlasov-Maxwell equations in the gyrocenter coordinate system, rather than a set of new equations. Because the general gyrokinetic system developed is geometrically the same as the Vlasov-Maxwell equations, all the coordinate-independent properties of the Vlasov-Maxwell equations, such as energy conservation, momentum conservation, and phase space volume conservation, are automatically carried over to the general gyrokinetic system. The pullback transformation associated with the coordinate transformation is shown to be an indispensable part of the general gyrokinetic Vlasov-Maxwell equations. As an example, the pullback transformation in the gyrokinetic Poisson equation is explicitly expressed in terms of moments of the gyrocenter distribution function, with the important gyro-orbit squeezing effect due to the large electric field shearing in the edge and the full finite Larmour radius effect for short wavelength fluctuations. The familiar "polarization drift density" in the gyrocenter Poisson equation is replaced by a more general expression. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] THE EVOLUTION OF DISPERSAL IN A LEVINS' TYPE METAPOPULATION MODELEVOLUTION, Issue 10 2007Vincent A.A. Jansen We study the evolution of the dispersal rate in a metapopulation model with extinction and colonization dynamics, akin to the model as originally described by Levins. To do so we extend the metapopulation model with a description of the within patch dynamics. By means of a separation of time scales we analytically derive a fitness expression from first principles for this model. The fitness function can be written as an inclusive fitness equation (Hamilton's rule). By recasting this equation in a form that emphasizes the effects of competition we show the effect of the local competition and the local population size on the evolution of dispersal. We find that the evolution of dispersal cannot be easily interpreted in terms of avoidance of kin competition, but rather that increased dispersal reduces the competitive ability. Our model also yields a testable prediction in term of relatedness and life-history parameters. [source] Universal Behavior and Electric-Field-Induced Structural Transition in Rare-Earth-Substituted BiFeO3ADVANCED FUNCTIONAL MATERIALS, Issue 7 2010Daisuke Kan Abstract The discovery of a universal behavior in rare-earth (RE)-substituted perovskite BiFeO3 is reported. The structural transition from the ferroelectric rhombohedral phase to an orthorhombic phase exhibiting a double-polarization hysteresis loop and substantially enhanced electromechanical properties is found to occur independent of the RE dopant species. The structural transition can be universally achieved by controlling the average ionic radius of the A-site cation. Using calculations based on first principles, the energy landscape of BiFeO3 is explored, and it is proposed that the origin of the double hysteresis loop and the concomitant enhancement in the piezoelectric coefficient is an electric-field-induced transformation from a paraelectric orthorhombic phase to the polar rhombohedral phase. [source] Facile Fabrication and Superparamagnetism of Silica-Shielded Magnetite Nanoparticles on Carbon Nitride NanotubesADVANCED FUNCTIONAL MATERIALS, Issue 14 2009Jung Woo Lee Abstract Using conventional methods to synthesize magnetic nanoparticles (NPs) with uniform size is a challenging task. Moreover, the degradation of magnetic NPs is an obstacle to practical applications. The fabrication of silica-shielded magnetite NPs on carbon nitride nanotubes (CNNTs) provides a possible route to overcome these problems. While the nitrogen atoms of CNNTs provide selective nucleation sites for NPs of a particular size, the silica layer protects the NPs from oxidation. The morphology and crystal structure of NP,CNNT hybrid material is investigated by transmission electron microscopy (TEM) and X-ray diffraction. In addition, the atomic nature of the N atoms in the NP,CNNT system is studied by near-edge X-ray absorption fine structure spectroscopy (nitrogen K-edge) and calculations of the partial density of states based on first principles. The structure of the silica-shielded NP,CNNT system is analyzed by TEM and energy dispersive X-ray spectroscopy mapping, and their magnetism is measured by vibrating sample and superconducting quantum interference device magnetometers. The silica shielding helps maintain the superparamagnetism of the NPs; without the silica layer, the magnetic properties of NP,CNNT materials significantly degrade over time. [source] Synthesis, Structure, and Properties of Boron- and Nitrogen-Doped GrapheneADVANCED MATERIALS, Issue 46 2009L. S. Panchakarla Boron- and nitrogen-doped graphenes are are prepared by the arc discharge between carbon electrodes or by the transformation of nanodiamond under appropriate atmospheres. Using a combination of experiment and theories based on first principles, systematic changes in the carrier-concentration and electronic structure of the doped graphenes are demonstrated. Stiffening of the G-band mode and intensification of the defect-related D-band in the Raman spectra are also observed. [source] A nonlinear atomization model for computation of drop size distributions and spray simulationsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 11 2005Hongbok Park Abstract A model has been developed to provide a comprehensive simulation of a spray formed by a high-speed liquid jet. The primary atomization process is simulated in a completely nonlinear fashion using the boundary element method under the assumption of axisymmetric, inviscid flow. The presence of the orifice boundary layer is simulated with a ring vortex whose strength and location are uniquely determined from boundary layer properties at the orifice exit plane. Droplet and axisymmetric ligament tracking models have been developed to provide more comprehensive spray simulations. The breakup of the axisymmetric ligaments shed from the parent surface is assessed both in a nonlinear fashion as well as using the linear stability analysis of Ponstein. Using this latter approach, drop size distributions have been generated from first principles and compared with the popular Rosin,Rammler model. Copyright © 2005 John Wiley & Sons, Ltd. [source] Periodic models in quantum chemical simulations of F centers in crystalline metal oxidesINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 14 2007Yuri F. Zhukovskii Abstract We present a survey of recent first principles simulations of the neutral oxygen vacancies (F centers) existing as native or radiation-induced point defects in various crystalline metal oxides in different forms (bulk, bare substrate surface, and on the interface with metal adsorbates). We mainly consider periodic models in calculations of point defects using the metal oxide supercell or cyclic clusters. We compare different formalisms of first principles calculations, mostly the Density Functional Theory (DFT) as implemented in the framework of either localized basis set of atomic orbitals or delocalized basis sets of plane waves. We analyze in detail the structural and electronic properties of F centers in binary oxides of light metals (MgO and Al2O3), and ternary metal oxides (SrTiO3, BaTiO3, PbTiO3, KNbO3, and PbZrO3 perovskites). When available, we compare results of ab initio periodic defect calculations with experimental data, results of the first principles cluster calculations (both embedded and molecular) as well as with semi-empirical calculations. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 [source] Next generation of ab initio energy density functionals: Thoughts and facts from solvable modelsINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 5 2005N. H. March Abstract After a brief summary of trends revealed in the presentations of this DFT Conference, especially on ab initio energy density functionals and potentials, some emphasis will be given to the likely "next generation" of first-principles energy density functionals. The Slater exchange potential V(r) then seems a natural starting point, being related to the Dirac exchange energy density ,x(r) and the ground-state density n(r) by V(r) = 2,x(r)/n(r). We then discuss various "corrections" to this Slater potential V(r). Although usually small compared with the exchange potential, the correlation contribution Vc(r) remains difficult to treat from first principles, but we refer to a few directions stemming from (generally two-electron) solvable models. Finally, we give some attention to the kinetic energy, especially the single-particle functional Ts[n] but also, again though from simple examples, to the correlation kinetic energy. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005 [source] Application of nonlinear time,scaling for robust controller design of reaction systemsINTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL, Issue 1 2002P. Moya Abstract Even though the basic mechanisms of operation of reaction systems are relatively simple the dynamical models obtained from first principles are complex and contain highly uncertain terms. To develop reliable model-based controllers it is therefore necessary to simplify the system dynamics preserving the features which are essential for control. Towards this end, co-ordinate transformations identifying the states which are dependent/independent of the reactions and flows have been reported in the literature. This has allowed, for instance, the design of observers which are insensitive to the (usually unknown) reaction functions. The main contribution of this paper is to show the utility of nonlinear state-dependent time-scaling to simplify the system dynamics, and consequently the controller design. In particular, we show that with time-scaling and an input transformation we can reveal the existence of attractive invariant manifolds, which allows us to reduce the dimension of the system. As an application we study the well-known fourth order baker's yeast fed-batch fermentation process model, whose essential dynamics is captured by a planar system perturbed by an exponentially decaying term. We then exploit this particular structure to design, with reduced control authority, a nonlinear asymptotically stabilizing control law which is robust with respect to the reaction function. Copyright © 2001 John Wiley & Sons, Ltd. [source] Hierarchical Models in Environmental ScienceINTERNATIONAL STATISTICAL REVIEW, Issue 2 2003Christopher K. Wikle Summary Environmental systems are complicated. They include very intricate spatio-temporal processes, interacting on a wide variety of scales. There is increasingly vast amounts of data for such processes from geographical information systems, remote sensing platforms, monitoring networks, and computer models. In addition, often there is a great variety of scientific knowledge available for such systems, from partial differential equations based on first principles to panel surveys. It is argued that it is not generally adequate to consider such processes from a joint perspective. Instead, the processes often must be considered as a coherently linked system of conditional models. This paper provides a brief overview of hierarchical approaches applied to environmental processes. The key elements of such models can be considered in three general stages, the data stage, process stage, and parameter stage. In each stage, complicated dependence structure is mitigated by conditioning. For example, the data stage can incorporate measurement errors as well as multiple datasets with varying supports. The process and parameter stages can allow spatial and spatio-temporal processes as well as the direct inclusion of scientific knowledge. The paper concludes with a discussion of some outstanding problems in hierarchical modelling of environmental systems, including the need for new collaboration approaches. Résumé Les systèmes environnementaux sont complexes. Ils incluent des processus spatio-temporels trés complexes, interagissant sur une large variété d'échelles. II existe des quantités de plus en plus grandes de données sur de tels processus, provenant des systèmes d'information géographiques, des plateformes de télédétection, des réseaux de surveillance et des modèles informatiques. De plus, il y a souvent une grande variété de connaissance scientifique disponible sur de tels systémes, depuis les équations différentielles partielles jusqu'aux enquétes de panels. II est reconnu qu'il n'est généralement pas correct de considerer de tels processus d'une perspective commune. Au contraire, les processus doivent souvent étre examinés comme des systèmes de modèles conditionnels liés de manière cohérente. Cet article fournit un bref aperçu des approches hiérachiques appliquées aux processus environnementaux. Les éléments clés de tels modèles peuvent étre examinés à trois étapes principales: l'étape des donnèes, celle du traitement et celle des paramètres. A chaque étape, la structure complexe de dépendance est atténuée par le conditionnement. Par exemple, le stade des données peut incorporer des erreurs de mesure ainsi que de multiples ensembles de données sous divers supports. Les stades du traitement et des paramétres peuvent admettre des processus spatiaux et spatio-temporels ainsi que l'inclusion directe du savoir scientifique. L'article conclut par une discussion de quelques problèmes en suspens dans la modélisation hiérarchique des systèmes environnementaux, incluant le besoin de nouvelles approches de collaboration. [source] Intraprotein electrostatics derived from first principles: Divide-and-conquer approaches for QM/MM calculationsJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 16 2003Pablo A. Molina Two divide-and-conquer (DAQ) approaches for building multipole-based molecular electrostatic potentials of proteins are presented and evaluated for use in QM/MM calculations. One approach is a further development of the neutralization method of Bellido and Rullmann (J Comput Chem 1989, 10, 479,487) while the other is based on removing part of the electron density before performing the multipole expansion. Both methods create systems with integer charges without using charge renormalization. To determine their performance in terms of location of cuts and distance to QM region, the new DAQ approaches are tested in calculations of the proton affinity of N, of Lys55 in the inhibitor turkey ovomucoid third domain. Finally, the two methods are used to build a variety of MM regions, applied to calculations of the pKa of Lys55, and compared to other computational methodologies in which force field charges are employed. © 2003 Wiley Periodicals, Inc. J Comput Chem 24: 1971,1979, 2003 [source] Forecasting new product trial in a controlled test market environmentJOURNAL OF FORECASTING, Issue 5 2003Peter S. Fader Abstract A number of researchers have developed models that use test market data to generate forecasts of a new product's performance. However, most of these models have ignored the effects of marketing covariates. In this paper we examine what impact these covariates have on a model's forecasting performance and explore whether their presence enables us to reduce the length of the model calibration period (i.e. shorten the duration of the test market). We develop from first principles a set of models that enable us to systematically explore the impact of various model ,components' on forecasting performance. Furthermore, we also explore the impact of the length of the test market on forecasting performance. We find that it is critically important to capture consumer heterogeneity, and that the inclusion of covariate effects can improve forecast accuracy, especially for models calibrated on fewer than 20 weeks of data.,Copyright © 2003 John Wiley & Sons, Ltd. [source] How light gets through periodically nanostructured metal films: a role of surface polaritonic crystalsJOURNAL OF MICROSCOPY, Issue 3 2003A. V. Zayats Summary The physical origin of the enhanced optical transmission of periodically structured films related to surface plasmon polaritons is discussed from first principles. The enhancement of transmission through smooth, randomly rough and periodically nanostructured films is considered. Analysis shows that any metal (or dielectric) nanostructured film can exhibit enhanced transmission in certain spectral ranges corresponding to surface plasmon (or phonon) polariton Bloch mode states on a periodic structure. Resonant tunnelling via these states is responsible for the transmission enhancement. The properties of surface polaritonic crystals are analogous to those of photonic crystals and can find numerous applications for scaling down optical devices to nanometric dimensions as well as for designing novel nanostructured materials whose optical properties are determined by surface polariton interaction in a periodic structure. [source] | ||||||||||||||||||||||||||||||||||||||||