Search results for "approximation"
showing 10 items of 818 documents
A simple method to directly retrieve reference evapotranspiration from geostationary satellite images
2013
Abstract Application of FAO-56 methodology for the assessment of reference evapotranspiration, ET 0 , is challenging in areas of the world with sparse meteorological network stations. For this reason alternative procedures using remotely observed data have been proposed in the literature. In this work, a simplified version of the Makkink approach [J. Inst. Wat. Eng. 11: 277–288, 1957] was tested in a typical Mediterranean environment (Sicily, Italy). The implemented Makkink approach (MAK) uses remotely estimated solar radiation derived from Meteosat Second Generation (MSG) satellite data and in situ observations of air temperature to assess ET 0 at daily time scale. Alternatively, taking ad…
Fractional visco-elastic Timoshenko beam deflection via single equation
2015
This paper deals with the response determination of a visco-elastic Timoshenko beam under static loading condition and taking into account fractional calculus. In particular, the fractional derivative terms arise from representing constitutive behavior of the visco-elastic material. Further, taking advantages of the Mellin transform method recently developed for the solution of fractional differential equation, the problem of fractional Timoshenko beam model is assessed in time domain without invoking the Laplace-transforms as usual. Further, solution provided by the Mellin transform procedure will be compared with classical Central Difference scheme one, based on the Grunwald-Letnikov appr…
Flavor Release from i-Carrageenan Matrix: A Quantitative Structure-Property Relationships Approach
2006
International audience; We carried out a QSPR (quantitative structure-property relationships) approach to evaluate the influence of the chemical structure of aqueous matrixes over the partition coefficient between the gas phase and the matrix. The determination of the partition coefficient of flavor ingredients was performed by headspace analysis at equilibrium for both saline solution and -carrageenan gel. Starting from an initial list of 90 descriptors, we selected 10 descriptors to perform equation generation by the GFA (genetic function approximation) method available in the Cerius2 package. The best obtained equations involve only five descriptors, which encode electronic properties of…
On approximate system dynamic
1996
In this paper concepts and techniques from system theory are used to obtain state-space (Markovian ) models of dynamic economic processes instead of the usual VARMA models. In this respect the concept of state is reviewed as are Hankel norm approximations,and balanced realizations for stochastic models. We clarify some aspects of the balancing method for state space modelling of observed time series. This method may fail to satisfy the so-called positive real condition for stochastic processes. We us a state variance factorization algorithm which does not require us to solve the algebraic Riccati equation. We relate the Aoki-Havenner method to the Arun - Kung method.
Rapid acoustic boundary element method for solution of 3D problems using hierarchical adaptive cross approximation GMRES approach
2009
This paper presents a new solver for 3D acoustic problems called RABEM (Rapid Acoustic Boundary Element Method). The Adaptive Cross Approximation and a Hierarchical GMRES solver are used to generate both the system matrix and the right hand side vector by saving storage requirement, and to solve the system solution. The potential and the particle velocity values at selected internal points are evaluated using again the Adaptive Cross Approximation (ACA). A GMRES without preconditioner and with a block diagonal preconditioner are developed and tested for low and high frequency problems. Different boundary conditions (i.e. Dirichlet, Neumann and mixed Robin) are also implemented. Herein the p…
High-energy evolution to three loops
2018
The Balitsky-Kovchegov equation describes the high-energy growth of gauge theory scattering amplitudes as well as nonlinear saturation effects which stop it. We obtain the three-loop corrections to this equation in planar $\mathcal{N}=4$ super Yang-Mills theory. Our method exploits a recently established equivalence with the physics of soft wide-angle radiation, so-called non-global logarithms, and thus yields at the same time the three-loop evolution equation for non-global logarithms. As a by-product of our analysis, we develop a Lorentz-covariant method to subtract infrared and collinear divergences in cross-section calculations in the planar limit. We compare our result in the linear re…
Black hole evaporation in a thermalized final-state projection model
2007
4 pages, 1 figure.-- PACS nrs.: 04.70.Dy; 03.67.-a.-- ISI Article Identifier: 000245333600044.-- ArXiv pre-print available at: http://arxiv.org/abs/hep-th/0611152
Adiabatic regularization and particle creation for spin one-half fields
2013
The extension of the adiabatic regularization method to spin-$1/2$ fields requires a self-consistent adiabatic expansion of the field modes. We provide here the details of such expansion, which differs from the WKB ansatz that works well for scalars, to firmly establish the generalization of the adiabatic renormalization scheme to spin-$1/2$ fields. We focus on the computation of particle production in de Sitter spacetime and obtain an analytic expression of the renormalized stress-energy tensor for Dirac fermions.
A comparison of efficient methods for the computation of Born gluon amplitudes
2006
We compare four different methods for the numerical computation of the pure gluonic amplitudes in the Born approximation. We are in particular interested in the efficiency of the various methods as the number n of the external particles increases. In addition we investigate the numerical accuracy in critical phase space regions. The methods considered are based on (i) Berends-Giele recurrence relations, (ii) scalar diagrams, (iii) MHV vertices and (iv) BCF recursion relations.
Theory of ground state factorization in quantum cooperative systems.
2008
We introduce a general analytic approach to the study of factorization points and factorized ground states in quantum cooperative systems. The method allows to determine rigorously existence, location, and exact form of separable ground states in a large variety of, generally non-exactly solvable, spin models belonging to different universality classes. The theory applies to translationally invariant systems, irrespective of spatial dimensionality, and for spin-spin interactions of arbitrary range.