排序方式: 共有19条查询结果,搜索用时 15 毫秒
1.
Popularized by Zassenhaus in the seventies, several algorithms for factoring polynomials use a so-called lifting and recombination scheme. Concerning bivariate polynomials, we present a new algorithm for the recombination stage that requires a lifting up to precision twice the total degree of the polynomial to be factored. Its cost is dominated by the computation of reduced echelon solution bases of linear systems. We show that our bound on precision is asymptotically optimal.
2.
M. Giusti G. Lecerf B. Salvy J.-C. Yakoubsohn 《Foundations of Computational Mathematics》2005,5(3):257-311
At the beginning of the 1980s, M. Shub and S. Smale developed a
quantitative analysis of Newton's method for multivariate analytic
maps. In particular, their α-theory gives an effective
criterion that ensures safe convergence to a simple isolated zero.
This criterion requires only information concerning the map at the
initial point of the iteration. Generalizing this theory to multiple
zeros and clusters of zeros is still a challenging problem. In this
paper we focus on one complex variable function. We study general
criteria for detecting clusters and analyze the convergence of
Schroder's iteration to a cluster. In the case of a multiple root,
it is well known that this convergence is quadratic. In the case of a
cluster with positive diameter, the convergence is still quadratic
provided the iteration is stopped sufficiently early. We propose a
criterion for stopping this iteration at a distance from the cluster
which is of the order of its diameter. 相似文献
3.
Dr. Matthieu Fonvielle Dénia Mellal Delphine Patin Maxime Lecerf Dr. Didier Blanot Dr. Ahmed Bouhss Dr. Marco Santarem Dr. Dominique Mengin‐Lecreulx Dr. Matthieu Sollogoub Dr. Michel Arthur Dr. Mélanie Ethève‐Quelquejeu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(4):1357-1363
Peptidyl–RNA conjugates have various applications in studying the ribosome and enzymes participating in tRNA‐dependent pathways such as Fem transferases in peptidoglycan synthesis. Herein a convergent synthesis of peptidyl–RNAs based on Huisgen–Sharpless cycloaddition for the final ligation step is developed. Azides and alkynes are introduced into tRNA and UDP‐MurNAc‐pentapeptide, respectively. Synthesis of 2′‐azido RNA helix starts from 2′‐azido‐2′‐deoxyadenosine that is coupled to deoxycytidine by phosphoramidite chemistry. The resulting dinucleotide is deprotected and ligated to a 22‐nt RNA helix mimicking the acceptor arm of Ala‐tRNAAla by T4 RNA ligase. For alkyne UDP‐MurNAc‐pentapeptide, meso‐cystine is enzymatically incorporated into the peptidoglycan precursor and reduced, and L ‐Cys is converted to dehydroalanine with O‐(mesitylenesulfonyl)hydroxylamine. Reaction of but‐3‐yne‐1‐thiol with dehydroalanine affords the alkyne‐containing UDP‐MurNAc‐pentapeptide. The CuI‐catalyzed azide alkyne cycloaddition reaction in the presence of tris[(1‐hydroxypropyl‐1H‐1,2,3‐triazol‐4‐yl)methyl]amine provided the peptidyl‐RNA conjugate, which was tested as an inhibitor of non‐ribosomal FemXWv aminoacyl transferase. The bi‐substrate analogue was found to inhibit FemXWv with an IC50 of (89±9) pM , as both moieties of the peptidyl–RNA conjugate contribute to high‐affinity binding. 相似文献
4.
Dr. Matthieu Fonvielle Dr. Inés Li de La Sierra‐Gallay Dr. Afaf H. El‐Sagheer Maxime Lecerf Delphine Patin Dr. Dénia Mellal Dr. Claudine Mayer Dr. Didier Blanot Dr. Nittaya Gale Dr. Tom Brown Dr. Herman van Tilbeurgh Dr. Mélanie Ethève‐Quelquejeu Dr. Michel Arthur 《Angewandte Chemie (International ed. in English)》2013,52(28):7278-7281
5.
Mathur S. Shen H. Lecerf N. Jilavi M.H. Cauniene V. Jørgensen J-E. Kareiva A. 《Journal of Sol-Gel Science and Technology》2002,24(1):57-68
Superconducting oxide ceramics of composition Y(Ba1–x
Sr
x
)2Cu4O8 (x = 0.00, 0.10, and 0.20) have been prepared by a simple sol-gel method based on the complexation of metal ions in aqueous medium, by chelating acetate and tartarate ligands. Homogeneous sols were obtained by complexing copper ions with tartaric acid, which prevented the flocculation of copper acetate during the gelation process. Single-phase bulk samples were obtained after firing the mixed-metal polymeric acetate-tartarate precursor to 835°C for 70 h in flowing oxygen atmosphere. Thermal decomposition of the gels was studied by thermogravimetry. Effect of strontium substitution on the properties of the compounds was studied by X-ray powder diffraction, electron microscopy, X-ray photoemission spectroscopy and resistivity measurements. These data indicate that nearly monophasic Y(Ba1–x
Sr
x
)2Cu4O8 superconducting samples were obtained for x < 0.30. The Sr-doping in the YBa2Cu4O8 (Y-124) phase shows a pronounced effect on the superconducting properties enhancing the critical temperature from 78 K (for the non-substituted sample) to 88 K (for Y(Ba1–x
Sr
x
)2Cu4O8). 相似文献
6.
7.
M. Giusti G. Lecerf B. Salvy J.-C. Yakoubsohn 《Foundations of Computational Mathematics》2007,7(1):1-58
Isolated multiple zeros or clusters of zeros of analytic maps with several variables are known to be difficult to locate and
approximate. This paper is in the vein of the α-theory, initiated by M. Shub and S. Smale in the beginning of the 1980s.
This theory restricts to simple zeros, i.e., where the map has corank zero. In this paper we deal with situations where the
analytic map has corank one at the multiple isolated zero, which has embedding dimension one in the frame of deformation theory.
These situations are the least degenerate ones and therefore most likely to be of practical significance. More generally,
we define clusters of embedding dimension one. We provide a criterion for locating such clusters of zeros and a fast algorithm
for approximating them, with quadratic convergence. In the case of a cluster with positive diameter
our algorithm stops at a distance of the cluster which is about its diameter. 相似文献
8.
Copper hydroxide Cu(OH)2 is metastable. It easily transforms into copper oxide CuO more stable, either in the solid state by a thermal dehydration or at room temperature, in aqueous basic solutions. In the solid state, the transformation is performed at a relatively low temperature, 423 K. It is a topotactic or a pseudomorphic transformation owing to clear relationships between axes of the two solids, in the three directions. The reacting process is described and the corresponding vectorial relations between crystal parameters are proposed. It is not the same case in aqueous basic solutions. Copper hydroxide gives rise to oxide through the formation of a complex anion, Cu(OH)42−, by a reconstructive transformation involving a dissolution reaction followed by a precipitation. 相似文献
9.
Sol-Gel Synthesis of Nano-Scaled BaTiO3, BaZrO3 and BaTi0.5Zr0.5O3 Oxides via Single-Source Alkoxide Precursors and Semi-Alkoxide Routes 总被引:2,自引:0,他引:2
Veith Michael Mathur Sanjay Lecerf Nicolas Huch Volker Decker Timo Beck Horst P. Eiser Wolfgang Haberkorn Robert 《Journal of Sol-Gel Science and Technology》2000,18(2):145-158
Sol-gel synthesis of nano-sized BaTiO3, BaZrO3 and BaTi0.5Zr0.5O3 ceramics using alkoxide and semi-alkoxide routes has been investigated and the pervoskites obtained have been compared with respect to crystallisation temperature, crystallite size and compositional purity. Heterometal alkoxides containing two (for BaTiO3 and BaZrO3) and three (for BaTi0.5Zr0.5O3) different metals were used as single-source precursors in the alkoxide route while semi-alkoxide synthesis was performed by reacting barium hydroxide or acetate with Ti and/or Zr alkoxides. Semi-alkoxide synthesis also produces stoichiometric and phase-pure oxides, however, at temperatures higher than 1000°C. At temperatures below 1000°C, BaCO3 and small amounts of other undesired phases (e.g., BaTi2O4) were present in the oxides derived from semi-alkoxide synthesis. Thermal behaviour, studied by TGA/DTA measurements, shows that thermal decomposition occurs in three major steps and depends on the educt composition and the synthesis route. Among alkoxide derived powders, crystalline BaTi0.5Zr0.5O3 phase is formed at 400°C while complete crystallisation of BaMO3 ceramics occurs around 600°C. The cubic to tetragonal phase transition for BaTiO3 is clearly observed at relatively low-temperature of 800°C. The stoichiometry and phase homogeneity of the obtained powders were demonstrated by energy dispersive X-ray analysis and powder diffractometry. The averaged crystallite size of the obtained nano-ceramics was evaluated using the FormFit programme. SEM and TEM observations revealed a high microstructural uniformity. 相似文献
10.
Lecerf 《Foundations of Computational Mathematics》2002,2(3):247-293
Newton's iterator is one of the most popular components of polynomial equation system solvers, either from the numeric or
symbolic point of view. This iterator usually handles smooth situations only (when the Jacobian matrix associated to the system
is invertible). This is often a restrictive factor. Generalizing Newton's iterator is still an open problem: How to design
an efficient iterator with a quadratic convergence even in degenerate cases? We propose an answer for an m -adic topology when the ideal m can be chosen generic enough: compared to a smooth case we prove quadratic convergence with a small overhead that grows
with the square of the multiplicity of the root. 相似文献