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991.
Jocelino Sato Vicente Francisco De Souza Neto 《Annals of Global Analysis and Geometry》2006,29(3):221-240
We classify the zero scalar curvature O(p+1)×O(q+1)-invariant hypersurfaces in the euclidean space ℝ
p+q+2, p,q > 1, analyzing whether they are embedded and stable. The Morse index of the complete hypersurfaces show the existence of embedded, complete and globally stable zero scalar curvature O(p+1)×O(q+1)-invariant hypersurfaces in ℝ
p+q+2, p+q≥ 7, which are not homeomorphic to ℝ
p+q+1. Such stable examples provide counter-examples to a Bernstein-type conjecture in the stable class, for immersions with zero scalar curvature.
Mathematics Subject Classifications (2000): 53A10, 53C42,49005. 相似文献
992.
The synthesis of 2-deoxy-α-DAH (2) is described based on the use of diazo chemistry as previously reported by us during the synthesis of the corresponding 2-deoxy-KDO. Initially, the
-arabino-aldehydo sugar derivative 3 was reacted with ethyl diazoacetate, using diethyl zinc as promoter. The corresponding β-hydroxy-α-diazo ester 4, obtained in very good yield, was transformed into the corresponding 2-diazo-3-deoxy-heptulosonate derivative 10, which was subjected to the action of rhodium(II). However, the major compound obtained in this reaction was the C-glycofuranoside 12 by the interaction of the benzyl protecting group employed at the OH of C-4 with the carbenoid generated at C-2. To avoid this undesired insertion reaction, aldehyde 13 was selected as a suitable starting material and, following the same chemistry than for 3, diazo 19 was efficiently synthesized. Finally, the intramolecular OH insertion mediated by rhodium(II) of 19 provided the targeted 2-deoxy-DAH derivative 21 in a reasonable good yield, which was finally transformed into the potassium salt of 2-deoxy-α-DAH 2. 相似文献
993.
Combretastatins A-4 and AVE-8062A have been synthesized by coupling 3,4,5-trimethoxyphenylacetylene with the corresponding iodomethoxyphenol and bromomethoxyaniline, followed by hydrolysis of the thermally-stable Ti(II)-alkyne complexes. 相似文献
994.
Marta Teijeira Yagamare Fall Francisco Santamarta Emilia Tojo 《Tetrahedron letters》2007,48(45):7926-7929
A new efficient and rapid experimental method and product isolation procedure as well as easy recyclable reaction media is expected to contribute to the development of a green strategy for the synthesis of furan diol from d-glucal. We determine the best conditions of reaction, minimizing the toxicity and finding an environmentally more acceptable process, using [Bmim][MSO4]/InCl3·3H2O as a new solvent system under extremely mild conditions, providing high yields with a dramatic enhancement of reaction rate. 相似文献
995.
Finite mixture modeling of censored and missing data using the multivariate skew-normal distribution
de Alencar Francisco H. C. Galarza Christian E. Matos Larissa A. Lachos Victor H. 《Advances in Data Analysis and Classification》2022,16(3):521-557
Advances in Data Analysis and Classification - Finite mixture models have been widely used to model and analyze data from a heterogeneous populations. Moreover, data of this kind can be missing or... 相似文献
996.
Cañizares-Carmenate Yudith Mena-Ulecia Karel MacLeod Carey Desmond Perera-Sardiña Yunier Hernández-Rodríguez Erix W. Marrero-Ponce Yovani Torrens Francisco Castillo-Garit Juan A. 《Molecular diversity》2022,26(3):1383-1397
Molecular Diversity - With the advancement of combinatorial chemistry and big data, drug repositioning has boomed. In this sense, machine learning and artificial intelligence techniques offer a... 相似文献
997.
Giacomo Quaranta Clara Argerich Martin Ruben Ibañez Jean Louis Duval Elias Cueto Francisco Chinesta 《Comptes Rendus Mecanique》2019,347(5):445-454
The present paper analyzes different integration schemes of solid dynamics in the frequency domain involving the so-called Proper Generalized Decomposition – PGD. The last framework assumes for the solution a parametric dependency with respect to frequency. This procedure allowed introducing other parametric dependences related to loading, geometry, and material properties. However, in these cases, affine decompositions are required for an efficient computation of separated representations. A possibility for circumventing such difficulty consists in combining modal and harmonic analysis for defining an hybrid integration scheme. Moreover, such a procedure, as proved in the present work, can be easily generalized to address nonlinear parametric dynamics, as well as to solve problems with non-symmetric stiffness matrices, always operating in the domain of low frequencies. 相似文献
998.
Juan Diego Pizarro Francisco Molina Dr. Manuel R. Fructos Prof. Dr. Pedro J. Pérez 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(45):10330-10335
A family of phosphine ligands containing a five-membered ring similar to the popular N-heterocyclic carbene ligands and an alkoxy third substituent has been developed. These alkoxydiaminophosphine ligands (ADAP) can be generated in one pot and reacted with a copper(I) source leading to the high yield isolation of complexes [(ADAP)CuX]2 (X=Cl, Br). The dinuclear nature of these compounds has been established by means of X-ray studies and DOSY experiments. A screening of the catalytic properties of these complexes toward carbene-transfer reactions from diazocompounds to C−H bonds (alkane, arene), olefins or N−H bonds, as well as in CuAAC or nitrene transfer reactions have shown a performance at least similar, if not better, than their (NHC)CuCl analogues, opening a new window in copper catalysis with these readily tunable ADAP ligands. 相似文献
999.
Francisco Gabriel Santos Silva Raildo Alves Fiuza Junior Jefferson Santos da Silva Carlos Magno S. R. de Brito Heloysa Martins Carvalho Andrade Jardel Pereira Gonçalves 《Journal of Thermal Analysis and Calorimetry》2014,116(1):287-293
The pozzolanic properties of the equilibrium catalyst (Ecat), an abundant waste from fluid catalytic cracking units of oil refineries, have been studied in cementitious matrices. The consumption of calcium hydroxide is usually taken as a means to assess the pozzolanicity of a material, ignoring the formation of C–S–H and other hydrates, the main product of the pozzolanic reaction. The use of thermal analysis methods allows the identification and quantification of the products of the hydration reaction, based on the loss of chemically combined water of phases present in a cementitious matrix. In the present study, TG/DTG techniques were used to quantify the amount of C–S–H + ettringite, C–A–S–H + C–A–H, and calcium hydroxide in cement–Ecat pastes, containing 0–40 % Ecat, aged for 1–28 days. The influence of the content of these phases on the mechanical properties of the resulting samples was also investigated by axial compression. The results further confirmed the pozzolanic activity of Ecat, so that the production of C–S–H and C–A–S–H increased with the aging time, but in a smaller amount than in the reference paste. The compressive strength test showed that the pastes containing 10 % Ecat, aged for 14 and 28 days, presented improved properties as compared to the corresponding references. 相似文献
1000.