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Finite Size (finite + size)
Terms modified by Finite Size Selected AbstractsEffects of wetting and drying cycles on in situ soil particle mobilizationEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 2 2008S. Majdalani Summary Understanding particle mobilization and transport in soils is a major concern for environmental protection and water resource management as they can act as vectors for sorbing pollutants. In natural soils, the existence of a finite size and renewable pool of dispersible particles has been hypothesized. Even though freeze-thaw and wetting-drying cycles have been identified as possible mechanisms of pool replenishment between rainfall events, to date the underlying phenomena ruling the renewal of particle pools are still largely unexplored. We carried out a series of infiltration-drainage experiments to study systematically the effects of periods without rain (pauses) on in situ particle mobilization in undisturbed soil columns. We found that, for a given column, pause duration between two rainfall events has a major influence on subsequent particle mobilization: the mass of leached particles increases with pause duration until it reaches a maximum (mass for a 200-hours pause is 15 time greater than for a 1-hour pause), and then it decreases for even longer pauses. This behaviour was correlated with soil water content, and can be explained by soil matrix weakening due to differential capillary stresses during drying. The consequences of this finding are important because the 15-fold increase in mass of leached particles, when pause duration is changed from 1 hour to 4 days, might overwhelm variations caused by changes in other parameters such as the ionic strength of the incoming solution or the rainfall intensity. [source] Entanglement and symmetry effects in the transition to the Schrödinger cat regimeFORTSCHRITTE DER PHYSIK/PROGRESS OF PHYSICS, Issue 11-12 2009F. de Pasquale Abstract We study two-spin entanglement and order parameter fluctuations as a function of the system size in the XY model in a transverse field and in the isotropic XXX model. Both models are characterized by the occurrence of ground state degeneracy also when systems of finite size are considered. This is always true for the XXX model, but only at the factorizing field for the XY model. We study the size dependence of symmetric states, which, in the presence of degeneracy, can be expanded as a linear combination of broken symmetry states. We show that, while the XY model looses its quantum superposition content exponentially with the size N, a decrease of the order of 1 / N is observed when the XXX model is considered. The emergence of two qualitatively different regimes is directly related to the difference in the symmetry of the models. [source] Mathematical framework towards the analysis of a generic traffic markerINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 4 2007Nasser-Eddine Rikli Abstract DiffServ architecture has been widely adopted for the provision of QoS over the Internet. This makes the full understanding of its operation imperative. We believe that only mathematical analysis may have the power of such goal. As the heart of a DiffServ router is the token bucket algorithm, a generic one, with two-colours marking, is to be considered here. A mathematical framework will be first developed for its analysis. Then, assuming an input traffic with Poisson arrivals and Exponential packet lengths, and a memoryless token bucket system, the two types of generated streams will be statistically characterized through their distributions and averages. This analysis will be carried out for two types of buckets, one with infinite size and a second with finite size. It will be shown how the derived equations will allow the prediction of the output traffic streams for given bucket and input traffic stream parameters. The paper will be then complemented by conclusions and suggestions. Copyright © 2006 John Wiley & Sons, Ltd. [source] Systematic and statistical error in histogram-based free energy calculationsJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 12 2003Mark N. Kobrak Abstract A common technique for the numerical calculation of free energies involves estimation of the probability density along a given coordinate from a set of configurations generated via simulation. The process requires discretization of one or more reaction coordinates to generate a histogram from which the continuous probability density is inferred. We show that the finite size of the intervals used to construct the histogram leads to quantifiable systematic error. The width of these intervals also determines the statistical error in the free energy, and the choice of the appropriate interval is therefore driven by the need to balance the two sources of error. We present a method for the construction of the optimal histogram for a given system, and show that the use of this technique requires little additional computational expense. We demonstrate the efficacy of the technique for a model system, and discuss how the principles governing the choice of discretization interval could be used to improve extended sampling techniques. © 2003 Wiley Periodicals, Inc. J Comput Chem 24: 1437,1446, 2003 [source] Extending point pattern analysis for objects of finite size and irregular shapeJOURNAL OF ECOLOGY, Issue 4 2006THORSTEN WIEGAND Summary 1We use a grid- and simulation-based approach to extend point pattern analysis to deal with plants of finite size and irregular shape, and compare the results of our approach with that of the conventional point approximation. The plants are approximated by using an underlying grid and may occupy several adjacent grid cells depending on their size and shape. Null models correspond to that of point pattern analysis but need to be modified to account for the finite size and irregular shape of plants. 2We use a mapped area of a grass-shrub steppe in semi-arid Patagonia, Argentina, to show that the shrub community is essentially randomly structured, but that shrubs facilitate grasses in their immediate neighbourhood. 3The occurrence of this random spatial structure provides important new information on the biology of shrub populations. In general, previous data from semi-arid and arid ecosystems have shown that adult shrubs tend to show over-dispersed patterns, whereas juveniles are clumped. 4We find that the point approximation may produce misleading results (i) if plant size varies greatly, (ii) if the scale of interest is of the same order of magnitude as the size of the plants, and (iii) if the plants of a given pattern are constrained through competition for space by the presence of other plants. The point approximation worked well in all other cases, but usually depicted weaker significant effects than when the size and shape of plants were taken into account. 5Our approach to quantifying small-scale spatial patterns in plant communities has broad applications, including the study of facilitation and competition. Ecologists will be able to use the software available to take advantage of these methods. [source] Crystalline/Crystalline Phase Transitions in Polymer Systems Consisting of Finite-Size Crystals in Each Crystalline Phase: Generalized Gibbs-Thomson EquationMACROMOLECULAR THEORY AND SIMULATIONS, Issue 7 2010Matsuo Hirami Abstract For polymer systems of two crystalline phases of one polymer component, each phase being consisted of polymer crystals of a finite size, we derive the crystalline-crystalline phase transition relationship, i.e., generalized Gibbs-Thomson equation. Its application combined with the crystalline-liquid transition relationship (usual Gibbs-Thomson equation) to the phase behavior of PT phase diagram of polyethylene (PE) is investigated, where the orthorhombic-hexagonal phase transition of PE crystal under high pressure being involved. Comparison with experimental data leads to the estimates of the structural characteristics such as the ratios of (the end surface free energy of polymer crystal/crystal length) for the respective crystalline phases. [source] Aperture field reconstruction by calculated cylindrical near fieldMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 11 2008Alcino Castelo Boso Abstract A method for determining the aperture field distribution of an array antenna from near-field measurement over the surface of a right circular cylinder enclosing the antenna is applied here. The approach relies on the concept of information content of the field. The truncation problem is solved by picking up the information that is lost due to the finite size of scanning area, in points of the space reachable by the measurement system. In this article, we rebuild the field at the aperture from near-field cylindrical calculated on the surface of measure, with dependence on the variable phi, and without dependence on the variable phi. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 2849,2851, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23825 [source] 3D analysis of a quasi circular microstrip antenna by finite element methodMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 4 2006M. Bourry Abstract In this work a complementary study of an elliptical antenna circularly polarized designed on a glass substrate is proposed using a 3D finite-element method that takes into account the finite size of the substrate. This simulation type gave more reliable results in near- and far-field analyses that were performed using a compact-range measurement system. The parasitic effect of the feeding line is confirmed in simulations and in measurements. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 635,639, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21430 [source] Spatial averaging of ensemble-based background-error variancesTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 633 2008Laure Raynaud Abstract It is common to compute background-error variances from an ensemble of forecasts, in order to calculate either climatological or flow-dependent estimates. However, the finite size of the ensemble induces a sampling noise, which degrades the accuracy of the variance estimation. An idealized 1D framework is firstly considered, to show that the spatial structure of sampling noise is relatively small-scale, and is closely related to the background-error correlations. This motivates investigations on local spatial averaging, which is here applied to ensemble-based variance fields in this 1D context. It is shown that a spatial averaging, manually optimized, helps to significantly reduce the sampling noise. This provides estimates which are as accurate as those derived from a much bigger ensemble. The dependencies of this optimization on the error correlation length-scale and on the heterogeneity of the variance and length-scale fields are also illustrated. These results are next confirmed in a more realistic 2D problem, by considering the current operational version of the Arpège background-error covariance matrix. Finally, the possibility to objectively and automatically optimize the filtering is explored. The idea is to apply the usual linear estimation theory and to use signal/noise ratios in order to calculate an optimal filter. The efficiency of this objective filtering is illustrated in the idealized 1D framework. Copyright © 2008 Royal Meteorological Society [source] Continuum molecular electrostatics, salt effects, and counterion binding,A review of the Poisson,Boltzmann theory and its modificationsBIOPOLYMERS, Issue 2 2008Grochowski Abstract This work is a review of the Poisson,Boltzmann (PB) continuum electrostatics theory and its modifications, with a focus on salt effects and counterion binding. The PB model is one of the mesoscopic theories that describes the electrostatic potential and equilibrium distribution of mobile ions around molecules in solution. It serves as a tool to characterize electrostatic properties of molecules, counterion association, electrostatic contributions to solvation, and molecular binding free energies. We focus on general formulations which can be applied to large molecules of arbitrary shape in all-atomic representation, including highly charged biomolecules such as nucleic acids. These molecules present a challenge for theoretical description, because the conventional PB model may become insufficient in those cases. We discuss the conventional PB equation, the corresponding functionals of the electrostatic free energy, including a connection to DFT, simple empirical extensions to this model accounting for finite size of ions, the modified PB theory including ionic correlations and fluctuations, the cell model, and supplementary methods allowing to incorporate site-bound ions in the PB calculations. © 2007 Wiley Periodicals, Inc. Biopolymers 89: 93,113, 2008. This article was originally published online as an accepted preprint. The "Published Online" date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com [source] | ||||||||||||||||