Kooperativer Bibliotheksverbund

Berlin Brandenburg

and
and

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
Filter
Language
Year
  • 1
    Language: English
    In: Revue Africaine de la Recherche en Informatique et Mathématiques Appliquées, 2014, Vol.17, pp.93-117
    Description: We present in this paper the formulation of a non-dissipative arbitrary high order time domain scheme for the elastodynamic equations. Our approach combines the use of an arbitrary high order discontinuous Galerkin interpolation with centred...
    Keywords: Computer Science ; Mathematics ; Elastodynamic Equation ; Discontinuous Galerkin Method ; Leapfrog Scheme ; Centered Scheme ; Équation Élastodynamique, Méthode Galerkin Discontinu, Schéma Saute-Mouton, Flux Centré ; Computer Science ; Mathematics
    ISSN: 1638-5713
    Source: Hyper Article en Ligne (CCSd)
    Source: Hyper Article en Ligne Open Access (CCSd)
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 2
    Language: English
    In: Acta Biotheoretica, 2018, Vol.66(1), pp.17-60
    Description: Within the last decade, several approaches using quaternion numbers to handle and model multiband images in a holistic manner were introduced. The quaternion Fourier transform can be efficiently used to model texture in multidimensional data such as color images. For practical application, multispectral satellite data appear as a primary source for measuring past trends and monitoring changes in forest carbon stocks. In this work, we propose a texture-color descriptor based on the quaternion Fourier transform to extract relevant information from multiband satellite images. We propose a new multiband image texture model extraction, called FOTO++, in order to address biomass estimation issues. The first stage consists in removing noise from the multispectral data while preserving the edges of canopies. Afterward, color texture descriptors are extracted thanks to a discrete form of the quaternion Fourier transform, and finally the support vector regression method is used to deduce biomass estimation from texture indices. Our texture features are modeled using a vector composed with the radial spectrum coming from the amplitude of the quaternion Fourier transform. We conduct several experiments in order to study the sensitivity of our model to acquisition parameters. We also assess its performance both on synthetic images and on real multispectral images of Cameroonian forest. The results show that our model is more robust to acquisition parameters than the classical Fourier Texture Ordination model (FOTO). Our scheme is also more accurate for aboveground biomass estimation. We stress that a similar methodology could be implemented using quaternion wavelets. These results highlight the potential of the quaternion-based approach to study multispectral satellite images.
    Keywords: Discrete quaternion Fourier transform ; Quaternion-based texture indices ; Multiband satellite images ; Aboveground biomass ; Cameroon
    ISSN: 0001-5342
    E-ISSN: 1572-8358
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 3
    Language: English
    In: 2015 11th International Conference on Signal-Image Technology & Internet-Based Systems (SITIS), November 2015, pp.68-75
    Description: In recent years, first approaches using quaternion numbers to handle and model multi chromatic images in a holistic manner were introduced. By defining quaternion Fourier transform, multidimensional data such as color images can be efficiently and easily process. On the other hand, multi chromatic satellite data appear as a primary source for measuring past trends and monitoring changes in forest carbon stocks. Thus, the processing of these data represents a fundamental challenge. In this work, inspired by the quaternion Fourier transforms, we propose a texture-color descriptor to extract relevant information from multi chromatic satellite images. We also propose a quaternion-based texture model, named FOTO++, to address the aboveground biomass estimation issue. Our proposed model begins by removing noises in the multi chromatic data while preserving the edges of canopies. After that, color texture indices are extracted using discrete form of Quaternion Fourier Transform and finally support vector regression method is used to derive biomass estimation from texture indices. Our texture features are modeled by a vector composed by the radial spectrum coming from the amplitude of quaternion Fourier Transform. We conduct several experiments in order the study the sensitivity of our model to acquisition parameters. We also assess its performances both on synthetic images and on real multi chromatic images of Cameroonian forest. The results provided support that our model is more robust to acquisition parameters than the classical Fourier Texture Ordination model and it is more accurate for aboveground biomass estimates. We stress that similar methodology could be used with quaternion wavelets. These results highlight the potential of quaternion-based approach to study multi chromatic images.
    Keywords: Quaternions ; Fourier Transforms ; Biomass ; Satellites ; Biological System Modeling ; Estimation ; Color ; Discrete Quaternion Fourier Transform ; Color Image ; Color-Texture ; Multi Chromatic Satellite Image ; Aboveground Biomass
    Source: IEEE Conference Publications
    Source: IEEE Xplore
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 4
    Language: English
    In: 2017 13th International Conference on Signal-Image Technology & Internet-Based Systems (SITIS), December 2017, pp.261-268
    Description: Natural shapes have complex volume forms that are usually difficult to model using simple analytical equations. The complexity of the representation is due to the heterogeneity of the physical environment and the variety of phenomena involved. In this study we consider the representation of the porous media. Thanks to the technological advances in Computed Topography scanners, the acquisition of images of complex shapes becomes possible. However, and unfortunately, the image data is not directly usable for simulation purposes. In this paper, we investigate the modeling of such shapes using a piece wise approximation of image data by ellipsoids. We propose to use a split-merge strategy and a region growing algorithm to optimize a functional including an error term and a scale term. The input of our algorithm is voxel-based shape description and the result is a set of tangent or disjoint ellipsoids representing the shape in an intrinsic way. We apply our method to represent 3D soil pore space from CT volume images. Within this specific context, we validate our geometrical modelling by using it for water draining simulation in porous media.
    Keywords: Shape ; Ellipsoids ; Approximation Algorithms ; Computational Modeling ; Three-Dimensional Displays ; Fitting ; Media ; CT Scanner ; Tomography ; Complex Shape ; Piecewise Approximation ; Ellipsoïds ; Pore Space
    Source: IEEE Conference Publications
    Source: IEEE Xplore
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 5
    Language: English
    In: Computers and Geosciences, February 2019, Vol.123, pp.20-37
    Description: In recent years, technological advances have stimulated researchers to try to unravel the extremely complex microscale processes that control the activity of microorganisms in soils. In particular, significant work has been carried out on the development of models able to accurately predict the microscale distribution of water, and the location of air–water interfaces in pores. A comparison, by Pot et al. (2015), of two different modeling approaches with actual synchrotron-based tomography data, shows that a two-phase lattice Boltzmann model (LBM) is able to predict remarkably well the location of air–water interfaces but is extremely slow, whereas a morphological model (MOSAIC), representing the pore space as a collection of spherical balls, provides a reasonable approximation of the observed air–water interfaces when each ball is allowed to drain independently, but does so blazingly fast. Interfaces predicted by MOSAIC, however, tend to have nonphysical shapes. In that general context, the key objective of the research described in the present article, based on the same tomography data as Pot et al. (2015), was to find out to what extent the use of ellipsoids instead of spherical balls in MOSAIC could not appreciably speed up computations, or at least, at equal computational time, provide a quantitatively better approximation of water-air interfaces. As far as we know, this is the first time an ellipsoids-based approximation of the soil pore space is proposed. A secondary objective was to assess whether ellipsoids might yield smoother, more physical, interfaces. Simulation results indicate that the use of ellipsoids provides a sizeable increase in accuracy in the prediction of air-water interfaces, an approximately 6-fold drop in computation time, and much more realistic-looking interfaces, compared to what is obtained with spherical balls. These observations are encouraging for the use of models based on geometric primitives to describe a range of microscale processes, and to address the still daunting issue of upscaling to the macroscopic scale.
    Keywords: Pore Scale ; Synchroton X-Ray Micro Computed Tomography ; Soil Air-Water Interfaces ; Computational Geometry ; 3d Volume Segmentation ; Morphological Modeling ; Geology
    ISSN: 0098-3004
    E-ISSN: 1873-7803
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 6
    Language: English
    In: PLoS ONE, 01 January 2014, Vol.9(7), p.e101129
    Description: To describe the variation in household crowding and social mixing patterns in the African meningitis belt and to assess any association with self-reported recent respiratory symptoms.In 2010, the African Meningococcal Carriage Consortium (MenAfriCar) conducted cross-sectional surveys in urban...
    Keywords: Sciences (General)
    E-ISSN: 1932-6203
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 7
    Language: English
    Description: In this paper, we introduce a fourth-order leap-frog time scheme combined with a high-order discontinuous Galerkin method for the solution of the elastodynamic equations. The time discretization, obtained via a simple construction based...
    Keywords: Mathematics ; Analysis of Pdes ; High Order Method ; Leap-Frog Scheme ; Elastodynamic Equation ; Velocity-Stress Formulation ; Discontinuous Galerkin Method ; Mathematics
    Source: Hyper Article en Ligne (CCSd)
    Source: Hyper Article en Ligne Open Access (CCSd)
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 8
    Description: Le chrome dur, utilisé comme revêtement de tige d’actionneurs hydrauliques linéaires, a été interdit pour risque sanitaire (directive européenne REACH). A cet effet, un revêtement de WS2 a été sélectionné par Safran Landing Systems pour substituer le chrome dur comme revêtement de tige de piston de frein hydraulique. La démarche de sélection utilisée, est limitée par son incapacité à expliquer les performances observées et démontre le besoin d’une démarche de sélection d’autant plus appropriée que la notion d’étanchéité des actionneurs hydrauliques linéaires est « floue ». Comme, la tribologie n’a pas vocation à caractériser les revêtements de surface, parce que son plus petit objet d’étude est un triplet tribologique, cette étude propose l’évaluation de la compatibilité tribologique du revêtement de WS2, avec la fonction d’étanchéité. La démarche utilisée montre que l’étanchéité est régie, par un critère en pression, et par une vérification des caractéristiques tribologiques du système tige/joints requises pour la réalisation de l’étanchéité ; ce qui nécessite un piston hydraulique instrumenté. L’absence de ce piston est compensée par une « caractérisation tribologique approchée » du contact tige/joints, qui associe les expertises tribologiques de pistons hydrauliques d’essais de qualification, appuyées par un modèle éléments finis (EF) du piston hydraulique d’une part, et les résultats d’un essai de frottement piste/joints, conçus à cet effet à l’aide d’un modèle EF d’autre part. Les résultats montrent que le système tige/joints présente de bonnes caractéristiques tribologiques pour le facteur de frottement et l’usure, alors que la localisation de l’accommodation de vitesses dans le cas du contact tige/joint d’étanchéité, accélère le débit source du revêtement et limite sa durée de vie. Enfin, cette thèse comble un vide méthodologique en proposant, une démarche de sélection d’un revêtement pour une application tribologique, et une démarche de triboconception d’un actionneur hydraulique linéaire dans le cas d’un fonctionnement quasi-statique. Hard chromium used as rod coating in linear hydraulic actuators has been forbidden by the European Directive REACH. In this situation, a WS2 coating has been selected by Safran Landing Systems to replace the hard chromium coating on rod pistons actuators of landing gear braking systems. The selection method was unable to explain the observed performance, and shows the lack of an appropriate methodology for the rod coating selection, mainly because the sealing concept is rather vague. Since tribology is not intended to characterize surface coatings, because its smallest object of study is a tribological triplet, this study proposes the evaluation of the tribological compatibility of the WS2 coating with the sealing function of the hydraulic piston. The adopted approach shows that the sealing performance is governed by a rod/seal contact pressure criterion and by the verification of the tribological characteristics of the rod/seal contact required to achieve a sealing performance. This tribological characterization requires an instrumented hydraulic piston. The absence of this piston is compensated by an "approximate tribological characterization" of the rod/seal contact, which combines the tribological expert analysis of hydraulic pistons of qualification tests, supported by a finite elements model (FE) of the hydraulic piston, and the results of a plate rod/seal friction test, designed for this purpose using another FE model. The results show that the rod/seal contact exhibits good tribological characteristics for the friction factor and wear, whereas the location of the velocity accommodation in the case of the rod/anti-extrusion seal contact accelerates the 3rd body generation of the coating and limits its life expectancy. Finally, this thesis fills a methodological lack by proposing a method of selecting a coating for a tribological application and a triboconception method of a linear hydraulic actuator in the case of quasi-static operating conditions.
    Keywords: Tribologie Des Matériaux Énergétiques ; Revêtement De Surface ; Compatibilité Tribologique ; Caractéristiques Tribologiques ; Revêtement De Ws2 ; Etanchéité ; Actionneur Hydraulique ; Tribology ; Surface Coating ; Tribological Compatibility ; Tribological Characteristics ; Ws2 Coating ; Waterproofing ; Hydraulic Actuator ; 621.890 72
    Source: Networked Digital Library of Theses and Dissertations
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 9
    Language: English
    In: PLoS ONE, July 2, 2014, Vol.9(7)
    Description: Objectives To describe the variation in household crowding and social mixing patterns in the African meningitis belt and to assess any association with self-reported recent respiratory symptoms. Methods In 2010, the African Meningococcal Carriage Consortium (MenAfriCar) conducted cross-sectional surveys in urban and rural areas of seven countries. The number of household members, rooms per household, attendance at social gatherings and meeting places were recorded. Associations with self-reported recent respiratory symptoms were analysed by univariate and multivariate regression models. Results The geometric mean people per room ranged from 1.9 to 2.8 between Ghana and Ethiopia respectively. Attendance at different types of social gatherings was variable by country, ranging from 0.5 to 1.5 per week. Those who attended 3 or more different types of social gatherings a week (frequent mixers) were more likely to be older, male (OR 1.27, p0.001) and live in urban areas (OR 1.45, p0.001). Frequent mixing and young age, but not increased household crowding, were associated with higher odds of self-reported respiratory symptoms (aOR 2.2, p0.001 and OR 2.8, p0.001 respectively). A limitation is that we did not measure school and workplace attendance. Conclusion There are substantial variations in household crowding and social mixing patterns across the African meningitis belt. This study finds a clear association between age, increased social mixing and respiratory symptoms. It lays the foundation for designing and implementing more detailed studies of social contact patterns in this region.
    Keywords: Respiratory Symptoms – Analysis ; Meningitis – Analysis
    ISSN: 1932-6203
    Source: Cengage Learning, Inc.
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 10
    Language: English
    In: Lecture Notes in Computer Science, High Performance Computing: 4th International Symposium, ISHPC 2002 Kansai Science City, Japan, May 15–17, 2002 Proceedings, pp.449-456
    Description: This paper presents the OpenMP parallelization of the Finite Element code LAGAMINE. It is a non-linear great deformations code for solid mechanics. The parallelization approach uses coarse grain: for the element loop, to build the stiffness matrix and for the direct solver, to compute the LU factorisation. Application is proposed to a stamping simulation.
    Keywords: Computer Science ; Programming Techniques ; Software Engineering ; Computation By Abstract Devices ; Mathematics of Computing ; Data Structures ; Computer Science
    ISBN: 9783540436744
    ISBN: 354043674X
    Source: SpringerLink Books
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
Close ⊗
This website uses cookies and the analysis tool Matomo. Further information can be found on the KOBV privacy pages