Search results for "Refinement"
showing 10 items of 114 documents
Highly Accurate Conservative Finite Difference Schemes and Adaptive Mesh Refinement Techniques for Hyperbolic Systems of Conservation Laws
2007
We review a conservative finite difference shock capturing scheme that has been used by our research team over the last years for the numerical simulations of complex flows [3, 6]. This scheme is based on Shu and Osher’s technique [9] for the design of highly accurate finite difference schemes obtained by flux reconstruction procedures (ENO, WENO) on Cartesian meshes and Donat-Marquina’s flux splitting [4]. We then motivate the need for mesh adaptivity to tackle realistic hydrodynamic simulations on two and three dimensions and describe some details of our Adaptive Mesh Refinement (AMR) ([2, 7]) implementation of the former finite difference scheme [1]. We finish the work with some numerica…
Adaptation based on interpolation errors for high order mesh refinement methods applied to conservation laws
2012
Adaptive mesh refinement is nowadays a widely used tool in the numerical solution of hyperbolic partial differential equations. The algorithm is based on the numerical approximation of the solution of the equations on a hierarchical set of meshes with different resolutions. Among the different parts that compose an adaptive mesh refinement algorithm, the decision of which level of resolution is adequate for each part of the domain, i.e., the design of a refinement criterion, is crucial for the performance of the algorithm. In this work we analyze a refinement strategy based on interpolation errors, as a building block of a high order adaptive mesh refinement algorithm. We show that this tec…
Interactive Gradually Generating Relevance Query Refinement Under the Human-Mediated Scenario in Multilingual Settings
2016
As opposed to query modelling, relevance generating interactive query refinement (QR) is a technique aimed at exploiting syntax variations of gradually extended, being removed or replaced with some other keywords query, which depending on the factors like e.g. the information resource, the database structure, or the keyword alignment, facilitates significantly the searching process. Therefore our motivation is to explore the dynamism of the precision trend depended upon the factors analyzed. For a couple of language pairs which constitute multilingual settings, we develop a user-centred framework that imposes distributed search optimization. Our data set contains variety of query types subm…
Iteratively reweighted least squares in crystal structure refinements
2011
The use of robust techniques in crystal structure multipole refinements of small molecules as an alternative to the commonly adopted weighted least squares is presented and discussed. As is well known, the main disadvantage of least-squares fitting is its sensitivity to outliers. The elimination from the data set of the most aberrant reflections (due to both experimental errors and incompleteness of the model) is an effective practice that could yield satisfactory results, but it is often complicated in the presence of a great number of bad data points, whose one-by-one elimination could become unattainable. This problem can be circumvented by means of a robust least-squares regression that…
Iterative Multiple Bounding-Box Refinements for Visual Tracking.
2022
Single-object visual tracking aims at locating a target in each video frame by predicting the bounding box of the object. Recent approaches have adopted iterative procedures to gradually refine the bounding box and locate the target in the image. In such approaches, the deep model takes as input the image patch corresponding to the currently estimated target bounding box, and provides as output the probability associated with each of the possible bounding box refinements, generally defined as a discrete set of linear transformations of the bounding box center and size. At each iteration, only one transformation is applied, and supervised training of the model may introduce an inherent ambig…
Analysing Student Performance using Sparse Data of Core Bachelor Courses
2015
Curricula for Computer Science (CS) degrees are characterized by the strong occupational orientation of the discipline. In the BSc degree structure, with clearly separate CS core studies, the learning skills for these and other required courses may vary a lot, which is shown in students' overall performance. To analyze this situation, we apply nonstandard educational data mining techniques on a preprocessed log file of the passed courses. The joint variation in the course grades is studied through correlation analysis while intrinsic groups of students are created and analyzed using a robust clustering technique. Since not all students attended all courses, there is a nonstructured sparsity…
Feature Selection for Ensembles of Simple Bayesian Classifiers
2002
A popular method for creating an accurate classifier from a set of training data is to train several classifiers, and then to combine their predictions. The ensembles of simple Bayesian classifiers have traditionally not been a focus of research. However, the simple Bayesian classifier has much broader applicability than previously thought. Besides its high classification accuracy, it also has advantages in terms of simplicity, learning speed, classification speed, storage space, and incrementality. One way to generate an ensemble of simple Bayesian classifiers is to use different feature subsets as in the random subspace method. In this paper we present a technique for building ensembles o…
X-ray powder diffraction study of the stability of solid solutions in LaO(Cl1−xBrx)
1997
Abstract The formation of solid solutions in the LaO(Cl 1− x Br x ) series was studied by X-ray powder diffraction (XPD), Rietveld profile refinement and bond valence calculations. The LaO(Cl 1− x Br x ) (0 ≤ x ≤ 1, step 0.2, and x = 0.5) powder samples were prepared by the solid state reaction between La 2 O 3 and a mixture of ammonium chloride and bromide. The X-ray powder diffraction patterns were collected at room temperature between 5 and 125° in 2Θ using Cu K α 1 radiation (λ = 1.5406 A). The XPD data between 20 and 90° were analyzed with the DBWS-9006PC Rietveld profile refinement program. All the LaO(Cl 1− x Br x ) phases studied crystallize in the tetragonal PbFCl-type structure wi…
Characterization of the non-stoichiometry in lanthanum oxyfluoride by FT-IR absorption, Raman scattering, X-ray powder diffraction and thermal analys…
1997
Abstract The FT-IR absorption, FT-Raman scattering, X-ray powder diffraction (XPD), and thermogravimetry were used to explore the non-stoichiometry in LaOF. The TGA-DTA analyses between 30 and 1500°C showed that the LaO1 − xF1 + 2x phases yielded the stoichiometric LaOF as an intermediate product. The temperature of formation of the LaOF and La2O3 increased with increasing excess of fluoride. The room temperature XPD data in 6.5 ⩽ 2θ ⩽ 121° range were analyzed by the Rietveld profile refinement method and subsequently by the bond valence calculations. All LaO1 − xF1 + 2x phases possess the tetragonal PbFCl-type structure (space group: P4/nmm; Z = 2) while the stoichiometric LaOF has the hex…
Stability of Rare-Earth Oxychloride Phases: Bond Valence Study
2002
Abstract The crystal structures of the tetragonal rare earth ( RE ) oxychlorides, RE OCl ( RE =La–Nd, Sm–Ho, and Y) were studied by X-ray powder diffraction measurements, Rietveld analyses, and bond valence calculations. The tetragonal structure (space group P 4/ nmm , No. 129, Z =2) is stable for all but Er–Lu oxychlorides, which possess a hexagonal structure. The tetragonal structure consists of alternating layers of ( RE O) n n + complex cations and X n − anions, where the rare earth is coordinated to four oxygens and four plus one chlorines in a monocapped tetragonal antiprism arrangement. The Rietveld analyses yielded a coherent series of structural parameters. Preferred orientation an…