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21.
Summary. Let ( real) be a family of real by matrices. A value of is called a Hopf value if has a conjugate pair of purely imaginary eigenvalues , . We describe a technique for detecting Hopf values based on the evolution of the Schur complement of in a bordered extension of where varies along the positive imaginary axis of the complex plane. We compare the efficiency of this method with more obvious
methods such as the use of the QR algorithm and of the determinant function of as well as with recent work on the Cayley transform. In particular, we show the advantages of the Schur complement method
in the case of large sparse matrices arising in dynamical problems by discretizing boundary value problems. The Hopf values
of the Jacobian matrices are important in this setting because they are related to the Hopf bifurcation phenomenon where steady
state solutions bifurcate into periodic solutions.
Received September 15, 1994 / Revised version received July 7, 1995 相似文献
22.
Summary. Let be the set of all real -matrices of rank . We prove that for there are no continuous vector fields such that the bordered matrix is regular for all . This result has some relevance for the numerical analysis of steady state bifurcation.
As a by-product we show that there is no nonvanishing continuous vector field with for all , where is the set of all matrices of rank deficiency one. This implies that there is no singular value decomposition of depending continuously on in any matrix set which contains . As another application we prove that in general there is no global analytic singular value decomposition for analytic matrix
valued functions of more than one real variable.
Received October 6, 1993 / Revised version received July 18, 1994 相似文献
23.
J. Govaerts 《Zeitschrift fur Physik C Particles and Fields》1991,51(2):297-311
The coupling to abelian background gauge fields of closed bosonic strings compactified on a torus is considered. There exist specific field configurations for which the theory cannot be defined consistently, in spite of the fact that the field equations of motion are then solved exactly. This critical behaviour is related to a breakdown of local and global world-sheet symmetries, as well as of spacetime unitarity. A physical interpretation of this phenomenon is proposed. The issue of spacetime duality is also discussed. This symmetry is shown to be partially broken for generic background field configurations. 相似文献
24.
't Hooft's consistency equations for subconstituent models are generalized to supersymmetric theories and a few solutions are outlined. 相似文献
25.
The alkylation of alkali metal and N+Bu4 ethylacetoacetate énolates by means of ethyl iodide, bromide and tosylate has been studied in diméthoxyéthane, in order to measure the reactivity of the associated forms. C/O alkylation ratios, structures of O-alkylated products and rates of alkylation, have been determined. With ethyl tosylate, the amount of O-alkylated products does not increase in the generally observed order Li+ < Na+ < K+ < Cs+ but in the order Na+ < K+ < Li+ ≈ Cs+. Some aspects of the alkali ethylacetoacetate énolates reactivity in weakly polar medium such as DME are discussed. 相似文献
26.
W. Govaerts 《Acta Mathematica Hungarica》1979,33(3-4):235-238
27.
Multi-vector Spherical Monogenics, Spherical Means and Distributions in Clifford Analysis 总被引:2,自引:0,他引:2
Rred BRACKX Bram De KNOCK Hennie De SCHEPPER 《数学学报(英文版)》2005,21(5):1197-1208
New higher-dimensional distributions have been introduced in the framework of Clifford analysis in previous papers by Brackx, Delanghe and Sommen. Those distributions were defined using spherical co-ordinates, the "finite part" distribution Fp x+^μ on the real line and the generalized spherical means involving vector-valued spherical monogenics. In this paper, we make a second generalization, leading to new families of distributions, based on the generalized spherical means involving a multivector-valued spherical monogenic. At the same time, as a result of our attempt at keeping the paper self-contained, it offers an overview of the results found so far. 相似文献
28.
The structure and representations of the rotation reflection symmetry group of the four-dimensional cubic lattice are described. Their connections with the representations of the three-dimensional lattice rotation reflection group, and with the representations of the continuous O(3) and O(4) groups are given. 相似文献
29.
30.
Gabriele Laudadio Sebastian Govaerts Ying Wang Davide Ravelli Hannes F. Koolman Maurizio Fagnoni Stevan W. Djuric Prof. Timothy Noël 《Angewandte Chemie (International ed. in English)》2018,57(15):4078-4082
A mild and selective C(sp3)?H aerobic oxidation enabled by decatungstate photocatalysis has been developed. The reaction can be significantly improved in a microflow reactor enabling the safe use of oxygen and enhanced irradiation of the reaction mixture. Our method allows for the oxidation of both activated and unactivated C?H bonds (30 examples). The ability to selectively oxidize natural scaffolds, such as (?)‐ambroxide, pregnenolone acetate, (+)‐sclareolide, and artemisinin, exemplifies the utility of this new method. 相似文献