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排序方式: 共有491条查询结果,搜索用时 15 毫秒
61.
Mohamed Cheriet Reza Farrahi Moghaddam Rachid Hedjam 《Computer Vision and Image Understanding》2013,117(3):269-280
Almost all binarization methods have a few parameters that require setting. However, they do not usually achieve their upper-bound performance unless the parameters are individually set and optimized for each input document image. In this work, a learning framework for the optimization of the binarization methods is introduced, which is designed to determine the optimal parameter values for a document image. The framework, which works with any binarization method, has a standard structure, and performs three main steps: (i) extracts features, (ii) estimates optimal parameters, and (iii) learns the relationship between features and optimal parameters. First, an approach is proposed to generate numerical feature vectors from 2D data. The statistics of various maps are extracted and then combined into a final feature vector, in a nonlinear way. The optimal behavior is learned using support vector regression (SVR). Although the framework works with any binarization method, two methods are considered as typical examples in this work: the grid-based Sauvola method, and Lu’s method, which placed first in the DIBCO’09 contest. The experiments are performed on the DIBCO’09 and H-DIBCO’10 datasets, and combinations of these datasets with promising results. 相似文献
62.
A simple procedure for model reduction based upon a Schur decomposition of a given system is presented. The obtained partitioned system allows the combination of singular perturbation and aggregation approaches 相似文献
63.
64.
Ricotti Yann Ducret Damien El Guerjouma Rachid Franciosi Patrick 《Mechanics of materials : an international journal》2006,38(12):1143-1158
Measured elasticity moduli of a highly (68%) glass-fiber reinforced epoxy matrix for different amounts of fiber/matrix interface weakening and debonding, due to different hygrothermal ageing stages, are compared to estimated ones. Ultrasonic measurements provide seven of the nine elasticity moduli of the orthotropic material samples, including all the moduli significantly affected by damage. Theoretical estimates combine homogenization modeling techniques and Finite Element (FE) calculations, the latter when the effect of observed partial debonding on effective moduli is to be specified. These estimates are performed under different assumptions for the composite structure, with special attention to the existence of a fiber–matrix interphase. Analytical comparisons for the undamaged composite establish that matching US measurements with estimates cannot be obtained, regardless of the chosen model, without the assumption of an interphase layer of modified resin coating the fibers. This coating resin, when in relevant concentration with regard to literature data about fiber coating thickness, typically conserves the epoxy moduli transversally to the fiber orientation, while, in the fiber direction its moduli approach those of the fibers. The comparison of the US measurements on damaged samples to FE calculations assuming progressive one-directional debonding shows that most of the composite stiffness loss can preferentially be due to an initial interphase weakening, while the fiber/matrix debonding seems more likely delayed to long H-ageing times. This is consistent with physical interpretation of damage by water pooling through silane bridges bonding epoxy to glass. The calculations also provide the effective stiffness, at different damage stages, of the “Undamaged Equivalent Inhomogeneity” for this damaged inclusion type. 相似文献
65.
Ahmed El Oualkadi Jean-Marie Paillot Herv Guegnaud Rachid Allam 《AEUE-International Journal of Electronics and Communications》2005,59(6):352-358
A new RF switched capacitor bandpass filter and its command circuit made up of a ring voltage controlled oscillator with ‘XOR’ gates are proposed. Implemented in a standard CMOS technology, this circuit is intended to be used in a subset of professional mobile phone applications [380–520 MHz]. Experiments carried out on a prototype show a tunable center frequency range of 260 MHz [240–500 MHz], with a quality factor that can be as high as 300. 相似文献
66.
In an effort to establish a more reliable set of optical cross sections for a variety of chemical and biological aerosol simulants, we have developed a flow-through photoacoustic system that is capable of measuring absolute, mass-normalized extinction and absorption cross sections. By employing a flow-through design we avoid issues associated with closed aerosol photoacoustic systems and improve sensitivity. Although the results shown here were obtained for the tunable CO2 laser waveband region, i.e., 9.20-10.80 microm, application to other wavelengths is easily achievable. The aerosols considered are categorized as biological, chemical, and inorganic in origin, i.e., Bacillus atrophaeus endospores, dimethicone silicone oil (SF-96 grade 50), and kaolin clay powder (alumina and silicate), respectively. Results compare well with spectral extinction measured previously by Fourier-transform infrared spectroscopy. Comparisons with Mie theory calculations based on previously published complex indices of refraction and measured size distributions are also presented. 相似文献
67.
Carcaillon LI Salmi LR;Atout-Route Evaluation Group 《Accident; analysis and prevention》2005,37(6):1049-1055
The aim of this study was to evaluate the impact of a prevention program called “Atout-Route”, based on the concept of commitment. The program was implemented in March 2000, to reduce the number of drivers under the age of 25 years involved in motor-vehicle collisions in the county of Landes (southwestern France). Using data from the regional observatory of road safety, we defined a target and three control groups similar on age or location. We used Poisson and quasi-Poisson regression to estimate whether the observed evolution of motor-vehicle collisions, after the program was implemented, was different in the targeted group than in the three control groups. The number of motor-vehicle collisions decreased everywhere and in every age group. The effect of the prevention program was not statistically significant (relative risk = 0.89; 95% confidence interval 0.74–1.07). Our results are compatible with a positive effect of the program. The possible dilution of its effect by national road safety actions implemented since 2000, and our early assessment are possible reasons for the non-significant observation. 相似文献
68.
We address the problem of the segmentation of cerebral white matter structures from diffusion tensor images (DTI). A DTI produces, from a set of diffusion-weighted MR images, tensor-valued images where each voxel is assigned with a 3 x 3 symmetric, positive-definite matrix. This second order tensor is simply the covariance matrix of a local Gaussian process, with zero-mean, modeling the average motion of water molecules. As we will show in this paper, the definition of a dissimilarity measure and statistics between such quantities is a nontrivial task which must be tackled carefully. We claim and demonstrate that, by using the theoretically well-founded differential geometrical properties of the manifold of multivariate normal distributions, it is possible to improve the quality of the segmentation results obtained with other dissimilarity measures such as the Euclidean distance or the Kullback-Leibler divergence. The main goal of this paper is to prove that the choice of the probability metric, i.e., the dissimilarity measure, has a deep impact on the tensor statistics and, hence, on the achieved results. We introduce a variational formulation, in the level-set framework, to estimate the optimal segmentation of a DTI according to the following hypothesis: Diffusion tensors exhibit a Gaussian distribution in the different partitions. We must also respect the geometric constraints imposed by the interfaces existing among the cerebral structures and detected by the gradient of the DTI. We show how to express all the statistical quantities for the different probability metrics. We validate and compare the results obtained on various synthetic data-sets, a biological rat spinal cord phantom and human brain DTIs. 相似文献
69.
Salima Nadia Nasreddine Naima Rachid 《AEUE-International Journal of Electronics and Communications》2008,62(5):395-400
This article presents a set of accurate closed-form formulas for the electromagnetic parameters (inductance (L), capacitance (C) and characteristic impedance (Zc)) for squared coaxial lines with circular and square inner conductor. The analytical expressions, deduced from rigorous analysis by the finite element method (FEM), method of moments (MoM) and curves fitting techniques, can be easily implemented in CAD simulation tools, to design components for wireless communication. This study presents accurate and suitable general expressions for all squared coaxial lines with a wide range of outer to inner conductors ratio between 1.2 and 10. As an application, we present the design of 60 GHz branch line couplers. 相似文献
70.
Stripping methods studies for HVOF WC-10Co-4Cr coating removal 总被引:1,自引:0,他引:1
Richard Menini Nihad Ben Salah Rachid Nciri 《Journal of Materials Engineering and Performance》2004,13(2):185-194
The use of high-velocity oxyfuel (HVOF) cermet coatings is considered to be a valuable and innovative alternative technology
to replace Cr(VI) electroplating. Among others, a WC-10Co-4Cr coating is one of the best choices for landing gear components
due to its excellent tribology and corrosion properties. The stripping process of such a cermet coating was studied due to
its importance for the repair and overhaul of landing gear components. Stripping solutions fulfill the following criteria:
keep substrate integrity; exhibit a high strip rate (SR); lead to uniform dissolution; show no galvanic corrosion; and be
environmentally friendly. Three different high-strength steel substrates (4340, 300M, and Aermet100) were studied. Five different
stripping solutions were selected for the electrochemical study. Only three met the targeted criteria: the meta-nitrobenzane
sulfonate-sodium cyanide solution; the Rochelle salt; and a commercial nickel stripper. It was found that the process must
be electrolytic, and that ultrasonic agitation is needed to enhance the overall mass transport and removal of WC particles
and metallic matrix residues. When choosing the most efficient solution and conditions, the SR was found to be as high as
162 μm h−1, which is a very acceptable SR for productivity sake. 相似文献