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991.
992.
993.
Ohne Zusammenfassung 相似文献
994.
Optimal and superoptimal approximations of a complex square matrix by polynomials in a normal basis matrix are considered.
If the unitary transform associated with the eigenvectors of the basis matrix is computable using a fast algorithm, the approximations
may be utilized for constructing preconditioners. Theorems describing how the parameters of the approximations could be efficiently
computed are given, and for special cases earlier results by other authors are recovered. Also, optimal and superoptimal approximations
for block matrices are determined, and the same type of theorems as for the point case are proved.
This research was supported by the Swedish National Board for Industrial and Technical Development (NUTEK) and by the U.S.
National Science Foundation under grant ASC-8958544. 相似文献
995.
5-Methylenolether derivatives of pyrrolo[3,4-a]carbazoles were obtained from cycloadditions between 3-(1-methoxyvinyl)-1-tosylindole and N-substituted maleimides. They
were transformed into the hydroxy derivatives by treatment with H2SO4, selectively reduced to the ether by H2/Pd–C, and in the imide moiety by L-Selectride?. From the analogous BOC protected indole derivative the parent α,β-unsaturated ketones were obtained, which were transformed into hydroxyimino compounds,
and which could be deprotected by heating to the melting point. Deprotection of the tosyl derivatives was not successful.
The imide part of the molecule was hydrolyzed using methanolic NaOH. The stereochemistry of all products was elucidated mainly
by spectroscopic methods, and compared with results of calculations. 相似文献
996.
997.
Otto Stern 《Zeitschrift für Physik A Hadrons and Nuclei》1926,39(10-11):751-763
998.
999.
Otto Schwelb 《Optics Communications》2007,271(2):424-429
A systematic approach to the design of extended free spectral range (FSR) series coupled microring multiplexers is described. The aim is to achieve large extension ratios and adequate suppression of the spurious interstitial modes, while moderating radiation enhancing ring diameter reduction as much as possible. Computer simulated results of the transmission and group delay characteristics are presented together with a universal plot for spurious mode suppression vs. relative ring diameter reduction. The significance of closely spaced twin resonances in the extended stopband is recognized. The effect of loss on filter performance, in the passband and in the extended stopband, is also briefly discussed. 相似文献
1000.
The fluorescence of ortho-hydroxycinnamic acid was studied in aqueous solution over the pH 0-14 range and in methanol. At pH values above 9.7, intense anion fluorescence is observed. In the pH 4-9 range emissions are from both the monoanion (albeit weakly) and from the dianion due to photodissociation. In the pH 0-4 range a blue and a green fluorescence was found, which is attributed to emissions from the unchanged molecule and from an unusual excited state tautomer respectively. The latter is assumed to be the phenolate anion of cinnamic acid and represents a tautomer with no equivalent in the electronic ground state. It is assumed to be formed by adiabatic photodissociation during the lifetime of the first excited singlet state. 相似文献