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1.
Ralf Freund Christos Allagiannis Peter Schnholzer Karl Bernauer 《Helvetica chimica acta》1994,77(3):615-621
A crude hydrate 6 and a crystalline hemiacetal 7 of glyoxylamide 4 were prepared from crotonamide 5 (Scheme 2). Particularly hemiacetal 7 , but also 6 and the ‘dimer’ 8 (obtained from 7 ) may serve as homochiral auxiliaries. The structure of 8 was determined by X-ray analysis. By arenesulfonyl halides, tryptimines 12–14 of 4 were diastereoselectively transformed into spirotricycles 15–17 and 19 . 相似文献
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3.
Christos Kravvaritis Marilena Mitrouli Jennifer Seberry 《Linear and Multilinear Algebra》2007,55(5):471-490
In the present article we concentrate our study on the growth problem for the weighing matrix W(12,11) and show that the unique W(12,11) has three pivot structures. An improved algorithm for extending a k × k (0,+,-) matrix to a W(n,n-1), if possible, has been developed to simplify the proof. For the implementation of the algorithm special emphasis is given to the notions of data structures and parallel processing. 相似文献
4.
George Lagogiannis Christos Makris Athanasios Tsakalidis 《Journal of Discrete Algorithms》2006,4(1):106-141
We consider the problem of maintaining a dynamic ordered set of n integers in a universe U under the operations of insertion, deletion and predecessor queries. The computation model used is a unit-cost RAM, with a word length of w bits, and the universe size is |U|=2w. We present a data structure that uses O(|U|/log|U|+n) space, performs all the operations in O(loglog|U|) time and needs O(loglog|U|/logloglog|U|) structural changes per update operation. The data structure is a simplified version of the van Emde Boas' tree introducing, in its construction and functioning, new concepts, which help to keep the important information for searching along the path of the tree, in a more compact and organized way. 相似文献
5.
We show that between any two nodes of a cubic, planar, three-connected graph there are three paths whose lengths are 0, 1, and 2 modulo 3, respectively. The proof is by a rather extensive case analysis. Counterexamples show that all three hypotheses (i.e., planarity, degree-three, and three-connectivity) are necessary. 相似文献
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7.
Christos KaimakliotisAlbert J. Fry 《Tetrahedron letters》2003,44(31):5859-5861
Electrochemical reduction of oxygen in the presence of an alpha-dimethylsilyl ester results in removal of the dimethylsilyl group. The reaction presumably proceeds by a mechanism involving electrochemically-generated superoxide ion. 相似文献
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9.
Christos Faloutsos 《BIT Numerical Mathematics》1988,28(4):736-754
We design and analyze integrated ways of applying the signature file approach for text and attributes simultaneously. In traditional signature file methods, the records are stored sequentially in the main file; for every record, a hash-coded abstraction of it (record signature) is created and stored in the signature file (usually, sequentially). To resolve a query, the signature file is scanned; the signatures retrieved correspond to all the qualifying records, plus some false drops.Here, we extend some signature file methods, namely superimposed coding and disjoint coding, to handle text and attributes. We develop a mathematical model and derive formulas for the optimal choice of parameters. The proposed methods achieve significant performance improvements, because they can take advantage of the skewed distribution of the queries. Depending on the query frequencies, the false drop probability can be reduced 40–45 times ( 97% savings), for the same overhead.Also with the University of Maryland Institute for Advanced Computer Studies (U.M.I.A.C.S.). This research was sponsored partially by the National Science Foundation under the grant DCR-86-16833. 相似文献
10.
Constantinides CP Koutentis PA Schatz J 《Journal of the American Chemical Society》2004,126(49):16232-16241
Unrestricted density functional calculations in combination with the broken-symmetry approach and spin-projection methods have been employed to study a series of formally 4n pi antiaromatic linear and angular polyheteroacenes. Calculations show that the linear polyheteroacene molecules have either stable singlet zwitterionic 6-9 or singlet diradical 5 ground states because they sacrifice the aromaticity of the central arene to form two independent cyanines. The corresponding angular compounds 10-14 have robust triplet states, since they cannot create independent cyanines to escape their overall antiaromaticity. An analysis based on the SOMO-SOMO energy splittings, their spatial distributions, and the spin density populations for the triplet states is presented to clarify the factors that determine their ground state multiplicities. 相似文献