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931.
932.
The interaction of elastic waves with a planar array of periodically spaced cracks of equal length is investigated. The angle of incidence is arbitrary. By the use of Fourier series techniques, the mixed-boundary value problem for a typical strip is reduced to a singular integral equation, which is solved numerically. It is shown that the reflected and transmitted displacement fields are the superposition of an infinite number of homogeneous and inhomogeneous plane body-wave modes. The reflection and transmission coefficients, which correspond to the modes of order zero, are plotted versus the frequency for three angles of incidence. Sharp resonance and antiresonance effects are observed. A check of the accuracy of the computations is provided by the balance of rates of energies. 相似文献
933.
In this paper we study some questions related to the socle of a nondegenerate noncommutative Jordan algebra. First we show that elements of finite rank belong to the socle, and that every element in the socle is von Neumann regular and has finite spectrum. Next we show that for Jordan Banach algebras the socle coincides with the maximal von Neumann regular ideal. For a nondegenerate noncommutative Jordan algebra, the annihilator of its socle can be regarded as a radical which is, generally, larger than Jacobson radical. Moreover, a nondegenerate noncommutative Jordan algebra whose socle has zero annihilator is isomorphic to a subdirect sum of primitive algebras having nonzero socle (which were described in [4]). Finally, these results are specialized to the particular case of an alternative algebra.The authors wish to thank the referee for his suggestions for improving the presentation of the paper. 相似文献
934.
Casalderrey M Souto C Concheiro A Gómez-Amoza JL Martínez-Pacheco R 《Chemical & pharmaceutical bulletin》2004,52(4):398-401
This study compares the drug loading capacity of Cellactose and two excipients of similar composition and similar particle size, prepared by dry granulation and extrusion-spheronization respectively. The drugs evaluated were acetaminophen and furosemide. Acetaminophen did not significantly affect the flow properties of any of the excipients, whereas furosemide markedly worsened flow properties, eliminating the differences initially existing among the three excipients. For both drugs, tablet mechanical properties were clearly better with Cellactose than with the other excipients. Acetaminophen dissolution rate was very similar regardless of the excipient used, but furosemide dissolution rate was lower from Cellactose tablets than from tablets prepared with the other excipients. This important difference is discussed in terms of micropore structure, specific surface area, and wettability of tablets, and is attributable to the special structure of Cellactose particles. 相似文献
935.
The Rayleigh beam is a perturbation of the Bernoulli–Euler beam. We
establish convergence of the solution of the Exact Controllability Problem
for the Rayleigh beam to the corresponding solution of the Bernoulli–Euler
beam. Convergence is related to a Singular Perturbation Problem. The main
tool in solving this perturbation problem is a weak version of a lower bound
for hyperbolic polynomials. 相似文献
936.
Guerrero Julio Becerra; Rodriguez-Palacios Angel; Wood Geoffrey V. 《Bulletin London Mathematical Society》2003,35(2):218-224
An element u of a norm-unital Banach algebra A is said to beunitary if u is invertible in A and satisfies ||u|| = ||u1||= 1. The norm-unital Banach algebra A is called unitary if theconvex hull of the set of its unitary elements is norm-densein the closed unit ball of A. If X is a complex Hilbert space,then the algebra BL(X) of all bounded linear operators on Xis unitary by the RussoDye theorem. The question of whetherthis property characterizes complex Hilbert spaces among complexBanach spaces seems to be open. Some partial affirmative answersto this question are proved here. In particular, a complex Banachspace X is a Hilbert space if (and only if) BL(X) is unitaryand, for Y equal to X, X* or X** there exists a biholomorphicautomorphism of the open unit ball of Y that cannot be extendedto a surjective linear isometry on Y. 2000 Mathematics SubjectClassification 46B04, 46B10, 46B20. 相似文献
937.
The inter- and intramolecular addition of free radicals onto ketenimines is studied. All the attempts to add intermolecularly several silicon, oxygen or carbon centered radicals to N-(4-methylphenyl)-C,C-diphenyl ketenimine were unsuccessful. In contrast, the intramolecular addition of benzylic radicals, generated from xanthates, onto the central carbon of a ketenimine function with its N atom linked to the ortho position of the aromatic ring occurred under a variety of reaction conditions. These intramolecular cyclizations provide a novel radical-mediated synthesis of 2-alkylindoles. 相似文献
938.
Humet M Carbonell T Masip I Sánchez-Baeza F Mora P Cantón E Gobernado M Abad C Pérez-Payá E Messeguer A 《Journal of combinatorial chemistry》2003,5(5):597-605
A positional scanning library of N-alkylglycine trimers (peptoids) containing over 10 000 compounds has been synthesized on solid phase. The synthetic pathway involved the use of the submonomer strategy and a set of 22 commercially available primary amines as a chemical diversity source. The unbiased nature of the library allowed its screening against a variety of biological targets, leading to the identification of individual peptoids exhibiting remarkable biological activities (García-Martínez, C. et al. Proc. Natl. Acad. Sci. U.S.A. 2002, 99, 2374. Montoliu, et al. J. Pharm. Exp. Therap. 2002, 302, 29. Planells-Cases, R., et al. J. Pharm. Exp. Therap. 2002, 302, 163). In the present work, the screening of this library against a panel of Gram-positive and Gram-negative bacteria led to the identification of different compounds exhibiting antimicrobial activity. 相似文献
939.
940.
Fernández C Nieto O Fontenla JA Rivas E de Ceballos ML Fernández-Mayoralas A 《Organic & biomolecular chemistry》2003,1(5):767-771
Glucosyl dopamine (DA) derivatives may represent a new class of DA prodrugs that would interact with glucose transporter GLUT-1, present in the blood-brain barrier, and generate DA in the brain. Therefore, compounds bearing the sugar moiety linked to either the amino group or the catechol ring of DA through amide, ester, carbamate, peptide or glycosidic bonds were synthesized. The behavior of the compounds as prodrugs was monitored in different media and the affinity of the glycoconjugates for the glucose carrier GLUT-1 using human erythrocytes was also studied. Most of the compounds were markedly stable in buffer and plasma, and several compounds released DA when incubated with brain extracts and the rate was related to the bond linking DA with glucose. The new glucosyl conjugates substituted at the C-6 position of the sugar were more potent inhibitors of glucose transport when compared to C-1 and C-3 substituted derivatives. This work provides structure-activity information about the interaction of substituted glucose with the GLUT-1 transporter. 相似文献