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1.
The gravitational Szekeres differential system is completely integrable with two rational first integrals and an additional analytical first integral. We describe the dynamics of the Szekeres system when one of these two rational first integrals is negative, showing that all the orbits come from the infinity of and go to infinity. 相似文献
2.
Juan Luis García Guirao Jaume Llibre Wei Gao 《Journal of Difference Equations and Applications》2020,26(2):203-208
The objective of this work is to present sufficient conditions for having positive topological entropy for continuous self-maps defined on a closed surface by using the action of this map on the homological groups of the closed surface. 相似文献
3.
Nucleophilic β‐Carbon Activation of Propionic Acid as a 3‐Carbon Synthon by Carbene Organocatalysis 下载免费PDF全文
Dr. Zhenqian Fu Prof. Dr. Jaume Torres Pengcheng Zheng Prof. Dr. Song Yang Prof. Dr. Bao‐An Song Prof. Dr. Yonggui Robin Chi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(26):9360-9363
Direct β‐carbon activation of propionic acid (C2H5CO2H) by carbene organocatalysis has been developed. This activation affords the smallest azolium homoenolate intermediate (without any substituent) as a 3‐carbon nucleophile for enantioselective reactions. Propionic acid is an excellent raw material because it is cheap, stable, and safe. This approach provides a much better solution to azolium homoenolate synthesis than the previously established use of acrolein (enal without any substituent), which is expensive, unstable, and toxic. 相似文献
4.
5.
Daniel Zaragoza-Puchol Javier E. Ortiz Alejandro A. Orden Marianela Sanchez Jorge Palermo Alejandro Tapia Jaume Bastida Gabriela E. Feresin 《Molecules (Basel, Switzerland)》2021,26(1)
Plants in the Amaryllidaceae family synthesize a diversity of bioactive alkaloids. Some of these plant species are not abundant and have a low natural multiplication rate. The aims of this work were the alkaloids analysis of a Habranthus cardenasianus bulbs extract, the evaluation of its inhibitory activity against cholinesterases, and to test several propagation strategies for biomass production. Eleven compounds were characterized by GC-MS in the alkaloid extract, which showed a relatively high proportion of tazettine. The known alkaloids tazettine, haemanthamine, and the epimer mixture haemanthidine/6-epi-haemanthidine were isolated and identified by spectroscopic methods. Inhibitory cholinesterases activity was not detected. Three forms of propagation were performed: bulb propagation from seed, cut-induced bulb division, and micropropagated bulbs. Finally, different imbibition and post-collection times were evaluated in seed germination assays. The best propagation method was cut-induced bulb division with longitudinal cuts into quarters (T1) while the best conditions for seed germination were 0-day of post-collection and two days of imbibition. The alkaloids analyses of the H. cardenasianus bulbs showed that they are a source of anti-tumoral alkaloids, especially pretazettine (tazettine) and T1 is a sustainable strategy for its propagation and domestication to produce bioactive alkaloids. 相似文献
6.
Jaume Llibre Paulo R. da Silva Marco A. Teixeira 《Journal of Dynamics and Differential Equations》2007,19(2):309-331
Singular perturbations problems in dimension three which are approximations of discontinuous vector fields are studied in
this paper. The main result states that the regularization process developed by Sotomayor and Teixeira produces a singular
problem for which the discontinuous set is a center manifold. Moreover, the definition of sliding vector field coincides with
the reduced problem of the corresponding singular problem for a class of vector fields.
相似文献
7.
Homothetic solutions of the n-body problem can be seen as heteroclinic orbits when the dynamical variables are changed via the McGehee blow-up and the time is suitably scaled. Transversality of the invariant asymptotic manifolds which contain the heteroclinic orbits is related to some structural stability. We fully characterize the cases in which such transversality is obtained for the n-body problem in any dimension. 相似文献
8.
Periodic Solutions of the Duffing Differential
Equation Revisited via the Averaging Theory 下载免费PDF全文
We use three different results of the averaging theory of first order for studying the existence of new periodic solutions in the two Duffing differential equations $\ddot y+ a \sin y= b \sin t$ and $\ddot y+a y-c y^3=b\sin t$, where $a$, $b$ and $c$ are real parameters. 相似文献
9.
Jaume Llibre 《Acta Appl Math》2016,142(1):123-125