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Zwanborn A.P.M. van den Berg P.M. 《Antennas and Propagation, IEEE Transactions on》1991,39(2):224-228
A number of electromagnetic field problems for planar structures can be formulated in terms of a hypersingular integral equation, in which a grad-div operator acts on a vector potential. The vector potential is a convolution of the free-space Green's function and some surface current density over the domain of interest. A weak form of this integral equation is obtained by testing it with subdomain basis functions defined over the plate domain only. As a next step, the vector potential is expanded in a sequence of subdomain basis functions and the grad-div operator is integrated analytically over the plate domain only. For the problem of electromagnetic scattering by a plate, the method shows excellent numerical performance. The numerical difficulties encountered in some previous conjugate gradient fast Fourier transform (CGFFT) methods have been eliminated 相似文献
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J. Clausen L. Damkilde L. Andersen 《International journal for numerical methods in engineering》2006,66(6):1036-1059
A new return method for implicit integration of linear isotropic yield criteria is presented. The basic idea is to perform all the manipulations in the principal stress space and thereby achieve very simple formulae for calculating the plastic corrector stresses, based on the constant gradient of such criteria. The return formulae are in closed form and no iteration is required. The method accounts for three types of stress return: return to a single yield plane, to a discontinuity line at the intersection of two yield planes and to a discontinuity point at the intersection between three or more yield planes. The infinitesimal and the consistent elastoplastic constitutive matrix are calculated for each type of stress return, as are the conditions to ascertain which type of return is required. The method is exemplified with the Mohr–Coulomb yield criterion. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
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We describe three case reports of hematomas in the abdominal wall muscles and discuss etiology, diagnostic findings and treatment. Abdominal wall hematomas are uncommon, and the condition is often misdiagnosed. One of our patients was laparotomised owing to suspected appendicitis, and one patient presented a tuberculous abscess that may have been an infected hematoma. Ultrasonographic examination or CT gives the correct diagnose. Conservative management is the treatment of choice unless bleeding is severe or the course is complicated by infection. 相似文献
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To check compliance with the maximum residue levels in foods and to monitor the residue levels to enable an evaluation of the exposure of the Danish population to pesticides, a monitoring programme for pesticides residues in fruit and vegetables was performed. Sampling plans were designed based on previous findings and on consumption data. Samples (n = 4404) of mainly fresh conventionally and organically grown fruit and vegetables were collected at wholesalers and importers and at food processing companies. Of the samples, 3% were frozen products and 5% organically grown. Of the samples, 34% were of Danish origin, with 66% from other countries. Two accredited laboratories performed analyses of the samples using capillary gas chromatography, liquid chromatography and a spectrophotometric method. Reporting levels were set at the lowest calibration level or at the limit of determination. Residues were found in 60% of the samples of fruit but in only 18% of the vegetable samples. Residues above the maximum residue levels were found in 6% of all samples of fruit and in 2% of the vegetable samples. 相似文献
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Maithripala D.H.S. Berg J.M. Dayawansa W.P. 《Automatic Control, IEEE Transactions on》2006,51(2):216-225
We present a general intrinsic tracking controller design for fully-actuated simple mechanical systems, when the configuration space is one of a general class of Lie groups. We first express a state-feedback controller in terms of a function-the "error function"-satisfying certain regularity conditions. If an error function can be found, then a general smooth and bounded reference trajectory may be tracked asymptotically from almost every initial condition, with locally exponential convergence. Asymptotic convergence from almost every initial condition is referred to as "almost-global" asymptotic stability. Error functions may be shown to exist on any compact Lie group, or any Lie group diffeomorphic to the product of a compact Lie group and R/sup n/. This covers many cases of practical interest, such as SO(n), SE(n), their subgroups, and direct products. We show here that for compact Lie groups the dynamic configuration-feedback controller obtained by composing the full state-feedback law with an exponentially convergent velocity observer is also almost-globally asymptotically stable with respect to the tracking error. We emphasize that no invariance is needed for these results. However, for the special case where the kinetic energy is left-invariant, we show that the explicit expression of these controllers does not require coordinates on the Lie group. The controller constructions are demonstrated on SO(3), and simulated for the axi-symmetric top. Results show excellent performance. 相似文献
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An efficient return algorithm for non-associated plasticity with linear yield criteria in principal stress space 总被引:1,自引:0,他引:1
An efficient return algorithm for stress update in numerical plasticity computations is presented. The yield criterion must be linear in principal stress space and can be composed of any number of yield planes. Each of these yield planes may have an associated or non-associated flow rule. The stress return and the formation of the constitutive matrix is carried out in principal stress space. Here the manipulations simplify and rely on geometrical arguments. The singularities arising at the intersection of yield planes are dealt with in a straightforward way also based on geometrical considerations. The method is exemplified on non-associated Mohr–Coulomb plasticity throughout the paper. 相似文献
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