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排序方式: 共有1858条查询结果,搜索用时 15 毫秒
61.
Adnane Hamiaz Rudy Klein Xavier Ferrieres Olivier Pascal Jean-Pierre Boeuf Jean-Rene Poirier 《Computer Physics Communications》2012,183(8):1634-1640
The modelling of plasma formation during microwave breakdown is a difficult task because of the strong non-linear coupling between Maxwell?s equations and plasma equations, and of the large plasma density gradients that form during breakdown. An original Finite Volume Time Domain (FVTD) method has been developed to solve Maxwell?s equations coupled with a simplified fluid plasma model and is described in this paper. This method is illustrated with the study of the shielding of a metallic aperture by the plasma generated by an incident high power electromagnetic wave. Typical results obtained with the FVTD method for this shielding problem are shown. 相似文献
62.
The paper presents a novel control-oriented, first-principle model of a three-way catalytic converter (TWC). The model accurately predicts the air–fuel ratio downstream of the catalyst and provides insights into the relative oxygen level (ROL) profile along the catalyst. The reaction mechanism of the TWC model is simplified to only two reactions, with oxygen being the only species stored on the active surface of the catalyst. All the information about the gas composition is taken from the upstream wide-range oxygen sensor. Additional model inputs are the exhaust gas temperature and the exhaust mass flow. The model is parameterized with only a few measurements from an engine test bench. Exact values of gas concentrations are not needed at any point.The ROL profile is a good indicator for the condition of the TWC. It can therefore be used to derive optimal TWC depletion strategies after fuel cut-off phases. Since the model is real-time capable, the ROL profile can even be used for on-line control strategies. Based thereon, a causal strategy is proposed with results that match those of the non-causal strategies found in off-line optimizations. 相似文献
63.
Discrete element methods (DEMs) provide new numerical means to study the behavior of soil-inclusion systems. In some cases, however, the classic DEM fails to model specific aspects of the inclusions. That is why a model based on spar elements is introduced, designed specifically for inclusions. In this model, the movement of the inclusion is considered as a dynamic process and is computed step by step in the same way as in the DEM. The model can be coupled with a DEM code, thus enabling one to simulate the interaction between an inclusion and a disk assembly. Contact laws at the contacts between disks and spar elements describe the interface constitutive behavior. Finally, the results obtained by simulating a geosynthetic anchorage in two different ways are reported. In the first case the inclusion is represented by disks, while in the last case it is represented by spar elements. The comparison shows that spar elements are much more versatile and can simplify the calibration of the discrete models used to simulate soil-inclusion systems. 相似文献
64.
The TORE SUPRA Tokamak was built by EURATOM-CEA association. The NbTi conductor of superconducting coils is inserted in a tight enclosure filled with pressurized superfluid helium of 0.125 MPa at 1.8 K. The thick casing is cooled to 4.5 K by 1.8 MPa in 4.5 K supercritical helium circulation. Around this thick casing, a 80 K thermal shield protects the parts at very low temperatures from the thermal radiation, which is cooled by pressurized helium at 80 K and 1.8 MPa. A new measurement method for helium mass flow rate of 80 K shield and 4.5 K casing is described in this paper. The commissioning was done on the two helium loops of the cryoplant: the supercritical 4.5 K thick casing and 80 K shields. The purpose is to improve control of the 4.5 K and 80 K refrigeration loops. 相似文献
65.
Pascal Matthieu Vronique Jean-Bernard Christian 《Sensors and actuators. A, Physical》2004,110(1-3):130-135
This paper describes a cantilever-based microsystem that permits the deposition of picoliter biological samples using a contact or non-contact method. Arrays of silicon-based cantilevers have been used to produce DNA microarrays. An electrowetting-on-dielectric (EWOD) principle is applied for the loading of the liquid by controlling surface tension. Deposition is achieved by direct contact between cantilevers and the surface by capillary transport. A non-contact deposition method has also been developed. It consists in an electric-field applied between the cantilevers and a conductive surface. The results obtained demonstrate that our system meets the need for producing high-density DNA, protein and cell chips. 相似文献
66.
David Teller Pascal Zimmer Daniel Hirschkoff 《International Journal of Information Security》2004,2(3-4):126-144
Current software and hardware systems, being parallel and reconfigurable, raise new safety and reliability problems, and the resolution of these problems requires new methods. Numerous proposals aim at reducing the threat of bugs and preventing several kinds of attacks. In this paper, we develop an extension of the calculus of mobile ambients, named controlled ambients, that is suited for expressing such issues, specifically denial of service attacks. We present a type system for controlled ambients, which makes static resource control possible in our setting, and enhance it with a rich notion of resources . 相似文献
67.
The aim of this paper is to propose new regularization and filtering techniques for dense and sparse vector fields, and to focus on their application to non-rigid registration. Indeed, most of the regularization energies used in non-rigid registration operate independently on each coordinate of the transformation. The only common exception is the linear elastic energy, which enables cross-effects between coordinates. Cross-effects are yet essential to give realistic deformations in the uniform parts of the image, where displacements are interpolated.In this paper, we propose to find isotropic quadratic differential forms operating on a vector field, using a known theorem on isotropic tensors, and we give results for differentials of order 1 and 2. The quadratic approximation induced by these energies yields a new class of vectorial filters, applied numerically in the Fourier domain. We also propose a class of separable isotropic filters generalizing Gaussian filtering to vector fields, which enables fast smoothing in the spatial domain. Then we deduce splines in the context of interpolation or approximation of sparse displacements. These splines generalize scalar Laplacian splines, such as thin-plate splines, to vector interpolation. Finally, we propose to solve the problem of approximating a dense and a sparse displacement field at the same time. This last formulation enables us to introduce sparse geometrical constraints in intensity based non-rigid registration algorithms, illustrated here on intersubject brain registration. 相似文献
68.
69.
Pascal J. Frey 《International journal for numerical methods in engineering》2004,60(6):1049-1074
Fast and accurate scanning devices are nowadays widely used in many engineering and biomedical fields. The resulting discrete data is usually directly converted into polygonal surface meshes, using ‘brute‐force’ algorithms, often resulting in meshes that may contain several millions of polygons. Simplification is therefore required in order to make storage, computation and display possible if not efficient. In this paper, we present a general scheme for mesh simplification and optimization that allows to control the geometric approximation as well as the element shape and size quality (required for numerical simulations). Several examples ranging from academic to complex biomedical geometries (organs) are presented to illustrate the efficiency and the utility of the proposed approach. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
70.
In this paper we aim at extending the non-derivable condensed representation in frequent itemset mining to sequential pattern mining. We start by showing a negative example: in the context of frequent sequences, the notion of non-derivability is meaningless. Therefore, we extend our focus to the mining of conjunctions of sequences. Besides of being of practical importance, this class of patterns has some nice theoretical properties. Based on a new unexploited theoretical definition of equivalence classes for sequential patterns, we are able to extend the notion of a non-derivable itemset to the sequence domain. We present a new depth-first approach to mine non-derivable conjunctive sequential patterns and show its use in mining association rules for sequences. This approach is based on a well known combinatorial theorem: the Möbius inversion. A performance study using both synthetic and real datasets illustrates the efficiency of our mining algorithm. These new introduced patterns have a high-potential for real-life applications, especially for network monitoring and biomedical fields with the ability to get sequential association rules with all the classical statistical metrics such as confidence, conviction, lift etc. 相似文献