Search results for "Function"
showing 10 items of 14432 documents
The 'power' of tourism in Portugal
2012
The author analyses the upper tail of the distribution of tourism supply in Portugal from 2002 to 2009, using data from the Instituto Nacional de Estatística database. Tourism supply is defined in terms of the lodging capacity of hotel establishments in about 250 tourist destinations. The paper shows that the empirical distribution of tourism supply in Portugal is heavy-tailed and consistent with a power law behaviour in its upper tail. Such behaviour seems to be stable over the years, provided that, for the time horizon covered by the data sets, the scaling parameter is always close to the value of two. The power law hypothesis is tested positively through the use of graphical and analyti…
Y:BaZrO3 Perovskite Compounds I: DFT Study on the Unprotonated and Protonated Local Structures
2011
Y-doped BaZrO(3) derivatives were studied by density functional theory (DFT) to investigate the local arrangements of the octahedral sites in Pm3m cubic frameworks. Single- and double substitution of zirconium by yttrium were considered, including in the presence of a nearby oxygen vacancy. Although the structural symmetry of undoped barium zirconate was not modified after yttrium doping, the presence of yttrium induced several differences in the oxygen sites around it, according to the local geometrical arrangement of yttrium in the host matrix. As an example, the differences between such oxygen sites were shown in the presence of a proton. In this case, different stabilization energies ch…
Towards a Novel Approach to Multimedia Data Mixed Fragmentation
2009
International audience; Distributed multimedia applications have emerged at an increasing rate during the last decade in several domains (video conferencing, e-health, virtual meeting rooms, etc). This has created several new challenging problems related to the data integration and fragmentation, user-oriented and adaptive interfaces, real time and network performances, etc. In this paper, we focus on the problem of data(base) fragmentation in a multimedia context. We recall in this respect that data fragmentation consists of reducing irrelevant data accesses by grouping data frequently accessed together in dedicated segments. We mainly address the issue of query and predicate implication r…
Detecting Inference Channels in Private Multimedia Data via Social Networks
2009
International audience; Indirect access to protected information has been one of the key challenges facing the international community for the last decade. Providing techniques to control direct access to sensitive information remain insufficient against inference channels established when legitimate data reveal classified facts hidden from unauthorized users. Several techniques have been proposed in the literature to meet indirect access prevention. However, those addressing the inference problem when involving multimedia objects (images, audio, video, etc.) remain few and hold several drawbacks. In essence, the complex structure of multimedia objects makes the fact of detecting indirect a…
Reasoning with Vague Spatial Information from Upper Mesopotamia (2000BC)
2015
International audience; Concepts such as near, far, south of, etc., are by its own nature vague. However, they are quite common in human language. In the case of historical records, these concepts are often the only source of information regarding the position of ancient places whose exact location has been lost. In our research, we use digitized written records from Upper Mesopotamia (2000BC) from the HIGEOMES project. Our goal is to provide better understanding of the location of places, based on the analysis of spatial statements. In our approach, we analyse cardinal statements between places with known location. Using this information we construct a probabilistic function representing t…
Model Free Control for muscular force by Functional Electrical Stimulation using pulse width modulation
2016
International audience; Functional Electrical Stimulation (FES) is a useful technique for restoring functions for patients with neurological disorders. Muscle activities can be artificially driven through delivery of electrical pulses to skeletal muscles. Typically, muscles are activated by using constant stimulation train with a fixed parameters (amplitude, frequency and pulse width). In addition, the FES systems do not adapt the parameters stimulation to obtain a desired force response during the rehabilitation session. The purpose of this study is to investigate a real-time FES system for adapting automatically the stimulation parameters (stimulation pulse width) to track a desired force…
Fractional half-tangent of a curve described by Iterated Function Systems.
2009
International audience; The deterministic fractal curves and surfaces find many applications in modeling of rough objects. However, these curves and surfaces are nowhere differentiable. Without notion of tangent, we can not determine the relative orientation of two fractal shapes, to join them with a "natural" aspect. Various works proposed a generalization of the concept of derivative by introducing the fractional derivative. In this paper we apply this concept of fractional derivative to the curves described by Iterated Function Systems. We show that if the fractional derivative exists at boundary points of the curve, the direction of the fractional half-tangent is necessarily the eigenve…
OPTIMIZATIONS FOR TENSORIAL BERNSTEIN–BASED SOLVERS BY USING POLYHEDRAL BOUNDS
2010
The tensorial Bernstein basis for multivariate polynomials in n variables has a number 3n of functions for degree 2. Consequently, computing the representation of a multivariate polynomial in the tensorial Bernstein basis is an exponential time algorithm, which makes tensorial Bernstein-based solvers impractical for systems with more than n = 6 or 7 variables. This article describes a polytope (Bernstein polytope) with a number of faces, which allows to bound a sparse, multivariate polynomial expressed in the canonical basis by solving several linear programming problems. We compare the performance of a subdivision solver using domain reductions by linear programming with a solver using a c…
A Constrained Band Selection Method Based on Information Measures for Spectral Image Color Visualization
2011
International audience; We present a new method for the visualization of spectral images, based on a selection of three relevant spectral channels to build a Red-Green-Blue composite. Band selection is achieved by means of information measures at the first, second and third orders. Irrelevant channels are preliminarily removed by means of a center-surround entropy comparison. A visualization-oriented spectrum segmentation based on the use of color matching functions allows for computational ease and adjustment of the natural rendering. Results from the proposed method are presented and objectively compared to four other dimensionality reduction techniques in terms of naturalness and informa…
An Impulse Response Model for the 60 Ghz Channel Based on Spectral Techniques of alpha-stable Processes
2007
International audience; In order to make realistic simulations of the radio propagation mechanism in ultra-wide band channels, an appropriate model is needed. In this paper we propose a new technique to model the impulse response of the 60 Ghz channel. This new approach is based on the spectral analysis of alpha-stable processes. Our new model presents many advantages: firstly, the channel is characterized only by a one deterministic function (spectral density) in the place of four parameters. Secondly, the estimations procedure deals directly with the measured transfer functions which avoids loosing information in data pretreatment. Finally, an estimation of the spectral measure permits to…