排序方式: 共有15条查询结果,搜索用时 125 毫秒
1.
We present a line-integral approach for computing the impedance-matrix elements in the traditional Rao-Wilton-Glisson formulation of the moment method for electromagnetic problems. The line integral extends over the perimeter of a triangle and can be computed numerically using a Gauss-Legendre quadrature. We present the conversion of the surface integral to a line integral, and we perform calculations where we compare the present method to a surface quadrature approach. 相似文献
2.
We derive a pair of boundary integral equations for the problem of scattering of an electromagnetic wave by an indentation in a perfectly conducting screen. The wall of the indentation obeys a dyadic impedance boundary condition. The unknowns are the electric current density on the wall of the indentation and the total tangential magnetic field in the opening of the indentation. We also derive integral representations for the fields everywhere in free space, including the far-field region. In all cases, the integrals involved extend over finite surfaces only 相似文献
3.
Asvestas J. S. Yankovich S. P. Allen O. E. 《Antennas and Propagation, IEEE Transactions on》2010,58(2):479-487
4.
The physical optics fields due to an aperture on a perfectly conducting screen are expressed in terms of line integrals over the boundary of the aperture. These line-integral representations have the same properties as the ones in terms of surface integrals over the aperture; in particular, they admit arbitrary, source distributions, and are continuous everywhere in the source-free half-space, including the geometric optics shadow boundary. 相似文献
5.
Electromagnetic scattering by indented screens 总被引:2,自引:0,他引:2
The problem of three dimensional electromagnetic scattering from a perfectly conducting screen with a bounded indentation is formulated as a system of boundary integral equations for the electric current density on the cavity wall and the interface between the cavity and free space. It is shown how the fictitious current density on the interface may be eliminated resulting in an integral equation of the second kind for the current density on the cavity wall only, with no integration over the infinite screen. In addition, integral representations are derived that represent the field everywhere in space in terms of the current density on the cavity wall only. Furthermore, asymptotic expressions for the far field are also presented. The equations and representations simplify considerably in the two-dimensional scalar case and results are presented for both TE and TM polarization 相似文献
6.
7.
George K Matsopoulos Nikolaos A Mouravliansky Pantelis A Asvestas Konstantinos K Delibasis Kerstin Gr?ndahl Hans-G?ran Gr?ndahl 《IEEE transactions on information technology in biomedicine》2006,10(4):763-774
In this paper, a digital subtraction radiology scheme is presented based on a new method for the automatic registration of dental radiographs acquired with or without rigorous a priori standardization. The scheme is comprised of an automatic registration method and a subtraction process. The proposed registration method can be considered as an object-based registration method without imposing the prerequisite of image segmentation in order to detect the boundary of the objects of interest or the automatic detection of matching landmarks. This is achieved by augmenting the dimensionality of the problem from two-dimensional gray-level matching to three-dimensional surface matching using the process of lifting in combination with a surface-matching technique. The pseudo three-dimensional affine transformation that matches the lifted images incorporates advantageous characteristics including spatial alignment of the surfaces, anisotropic correction of brightness/contrast differences, and stable convergence of the similarity function to its optimal value. The performance of the proposed automatic registration method is assessed against a manual method based on the projective transformation. The qualitative and quantitative assessments of the experiments have shown advantageous performance of the proposed automatic registration method against the manual one. Finally, the proposed registration method has been further improved in terms of execution time by the implementation of a surface decimation process. 相似文献
8.
Matsopoulos GK Asvestas PA Mouravliansky NA Delibasis KK 《IEEE transactions on medical imaging》2004,23(12):1557-1563
In this paper, an automatic method for registering multimodal retinal images is presented. The method consists of three steps: the vessel centerline detection and extraction of bifurcation points only in the reference image, the automatic correspondence of bifurcation points in the two images using a novel implementation of the self organizing maps and the extraction of the parameters of the affine transform using the previously obtained correspondences. The proposed registration algorithm was tested on 24 multimodal retinal pairs and the obtained results show an advantageous performance in terms of accuracy with respect to the manual registration. 相似文献
9.
P. Asvestas G.K. Matsopoulos K.S. Nikita 《Journal of Visual Communication and Image Representation》1998,9(4):392-400
Fractal dimension has been used for texture analysis as it is highly correlated with the human perception of surface roughness. Several methods have been proposed for the estimation of the fractal dimension of an image. One of the most popular is via its power spectrum density, provided that it is modeled as a fractional Brownian function. In this paper, a new method, called the power differentiation method (PDM), for estimating the fractal dimension of a two-variable signal from its power spectrum density is presented. The method is first applied to noise-free data of known fractal dimension. It is also tested with noise-corrupted and quantized data. Particularly, in the case of noise-corrupted data, the modified power differentiation method (MPDM) is developed, resulting in more accurate estimation of the fractal dimension. The results obtained by the PDM and the MPDM are compared directly to those obtained using four other well-known methods of fractal dimension. Finally, preliminary results for the classification of ultrasonic liver images, obtained by applying the new method, are presented. 相似文献
10.
Markaki VE Asvestas PA Matsopoulos GK 《Computer methods and programs in biomedicine》2009,93(1):61-72
In this paper, an Automatic Iterative Point Correspondence (AIPC) algorithm towards image registration is presented. Given an image pair, distinctive points are extracted only in one of the images (reference image), and the corresponding points in the other image are obtained automatically by maximizing a similarity measure between regions of the two images with respect to the parameters of a local transformation. The maximization is accomplished by means of an iterative procedure, in which candidate solutions for the transformation parameters are tested at each iteration; these solutions are evaluated by the similarity measure between image regions. The detected point pairs by the application of the AIPC algorithm are then used to estimate the parameters of a global projective transformation for the registration of the image pair. The proposed AIPC algorithm was applied on 113 in vitro and in vivo dental image pairs providing improved registration accuracy against three widely used registration methods. 相似文献