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971.
A general method for the synthesis of the title compounds by employing the reagent methyl -(dicarbomethoxymethyl)methanimidate is described. The preparation, properties and reactions of the reagent are also reported. 相似文献
972.
Benjamin R. Smith 《Graphs and Combinatorics》2007,23(6):691-711
A k-cycle decomposition of a complete multipartite graph is said to be gregarious if each k-cycle in the decomposition has its vertices in k different partite sets. Equipartite 3-cycle systems are 3-GDDs (and so are automatically gregarious), and necessary and sufficient
conditions for their existence are known. The cases of equipartite gregarious 4-, 6- and 8-cycle systems have also been dealt
with (using techniques that could be applied in the case of any even length cycle). Here we give necessary and sufficient conditions for the existence of a gregarious 5-cycle decomposition of
the complete equipartite graph Km(n) (in effect the first odd length cycle case for which the gregarious constraint has real meaning). In doing so, we also define some general cyclic
constructions for the decomposition of certain complete equipartite graphs into gregarious p-cycles (where p is an odd prime). 相似文献
973.
974.
Benjamin Arazi 《Designs, Codes and Cryptography》2006,38(3):399-415
Emerging standards specify a communication rate between a contactless smartcard and a terminal that is of the same order of
magnitude as the internal clock rate in the card. This gives a natural ground for the known card-terminal communication-computation
trade-off, where non-secure operations should rather be performed by the terminal and not in the card. In this paper we treat
an implementation of Elliptic Curve Digital Signature Algorithm (ECDSA), the most cost effective digital signature algorithm,
which has a potential of being executed under the heavy constraints imposed by a contactless smartcard environment. This algorithm
heavily relies on numerous calculations of modular multiplicative inverses. It is shown in this paper that, based on communicating
with the terminal, each modular inverse operation needed to be executed in the card during ECDSA signature generation requires only two modular
multiplications in the card. Each modular inverse operation performed during signature verification requires only one modular
multiplication in the card. A complete ECDSA implementation over integers or over GF(2n) is then treated in detail
AMS Classification: 94A62 相似文献
975.
976.
977.
978.
The pre-coloring extension problem consists, given a graph G and a set of nodes to which some colors are already assigned, in finding a coloring of G with the minimum number of colors which respects the pre-coloring assignment. This can be reduced to the usual coloring problem
on a certain contracted graph. We prove that pre-coloring extension is polynomial for complements of Meyniel graphs. We answer
a question of Hujter and Tuza by showing that “PrExt perfect” graphs are exactly the co-Meyniel graphs, which also generalizes
results of Hujter and Tuza and of Hertz. Moreover we show that, given a co-Meyniel graph, the corresponding contracted graph
belongs to a restricted class of perfect graphs (“co-Artemis” graphs, which are “co-perfectly contractile” graphs), whose
perfectness is easier to establish than the strong perfect graph theorem. However, the polynomiality of our algorithm still
depends on the ellipsoid method for coloring perfect graphs.
C.N.R.S.
Final version received: January, 2007 相似文献
979.
Hend Ben Ameur Martin Burger Benjamin Hackl 《Mathematical Methods in the Applied Sciences》2007,30(6):625-647
The aim of this paper is an analysis of geometric inverse problems in linear elasticity and thermoelasticity related to the identification of cavities in two and three spatial dimensions. The overdetermined boundary data used for the reconstruction are the displacement and temperature on a part of the boundary. We derive identifiability results and directional stability estimates, the latter using the concept of shape derivatives, whose form is known in elasticity and newly derived for thermoelasticity. For numerical reconstructions we use a least‐squares formulation and a geometric gradient descent based on the associated shape derivatives. The directional stability estimates guarantee the stability of the gradient descent approach, so that an iterative regularization is obtained. This iterative scheme is then regularized by a level set approach allowing the reconstruction of multiply connected shapes. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
980.
Jagerman David L. Balcıoglu Barış Altıok Tayfur Melamed Benjamin 《Queueing Systems》2004,46(3-4):481-506
It is known that correlations in an arrival stream offered to a single-server queue profoundly affect mean waiting times as compared to a corresponding renewal stream offered to the same server. Nonetheless, this paper uses appropriately constructed GI/G/1 models to create viable approximations for queues with correlated arrivals. The constructed renewal arrival process, called PMRS (Peakedness Matched Renewal Stream), preserves the peakedness of the original stream and its arrival rate; furthermore, the squared coefficient of variation of the constructed PMRS equals the index of dispersion of the original stream. Accordingly, the GI/G/1 approximation is termed PMRQ (Peakedness Matched Renewal Queue). To test the efficacy of the PMRQ approximation, we employed a simple variant of the TES+ process as the autocorrelated arrival stream, and simulated the corresponding TES +/G/1 queue for several service distributions and traffic intensities. Extensive experimentation showed that the proposed PMRQ approximations produced mean waiting times that compared favorably with simulation results of the original systems. Markov-modulated Poisson process (MMPP) is also discussed as a special case. 相似文献