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841.
Jaume Giné 《理论物理通讯》2021,73(1):15201-67
We use the generalized uncertainty principle to compute the first correction to the Hawking temperature associated to Hawking effect.From this value we obtain a new evaporation time and entropy of any Schwarzschild black hole analyzing their expressions and consequences. 相似文献
842.
The cyclicity of the period annulus of reversible quadratic Hamiltonian systems under quadratic perturbations was studied by several authors for different cases by using different methods. In this paper, we study this problem in a unified way. 相似文献
843.
844.
Prof. Dr. Mercedes Amat Elena Ghirardi Dr. Laura Navío Dr. Rosa Griera Dr. Núria Llor Dr. Elies Molins Prof. Dr. Joan Bosch 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(47):16044-16049
Up to four stereocenters with a well‐defined configuration are generated in a single synthetic step by the cyclocondensation of (R)‐phenylglycinol or (1S,2R)‐1‐amino‐2‐indanol with stereoisomeric mixtures (racemates, meso forms, diastereoisomers) of cyclohexanone‐based δ‐keto‐acid and δ‐keto‐diacid derivatives in enantio‐ and diastereoconvergent processes that involve dynamic kinetic resolution and/or desymmetrization of enantiotopic groups. A detailed analysis of the stereochemical outcome of this process is presented. This method provides easy access to enantiopure 8‐ and 6,8‐substituted cis‐decahydroquinolines, including alkaloids of the myrioxazine family. 相似文献
845.
This paper provides the classification of the phase portraits in the Poincaré disc of all piecewise linear continuous differential systems with two zones separated by a straight line having a unique finite singular point which is a node or a focus. The sufficient and necessary conditions for existence and uniqueness of limit cycles are also given. 相似文献
846.
Chideraa I. Nwachukwu Leanna J. Patton Nathan P. Bowling Eric Bosch 《Acta Crystallographica. Section C, Structural Chemistry》2020,76(5):458-467
The potential of pyrimidines to serve as ditopic halogen‐bond acceptors is explored. The halogen‐bonded cocrystals formed from solutions of either 5,5′‐bipyrimidine (C8H6N4) or 1,2‐bis(pyrimidin‐5‐yl)ethyne (C10H6N4) and 2 molar equivalents of 1,3‐diiodotetrafluorobenzene (C6F4I2) have a 1:1 composition. Each pyrimidine moiety acts as a single halogen‐bond acceptor and the bipyrimidines act as ditopic halogen‐bond acceptors. In contrast, the activated pyrimidines 2‐ and 5‐{[4‐(dimethylamino)phenyl]ethynyl}pyrimidine (C14H13N3) are ditopic halogen‐bond acceptors, and 1:1 halogen‐bonded cocrystals are formed from 1:1 mixtures of each of the activated pyrimidines and either 1,2‐ or 1,3‐diiodotetrafluorobenzene. A 1:1 cocrystal was also formed between 2‐{[4‐(dimethylamino)phenyl]ethynyl}pyrimidine and 1,4‐diiodotetrafluorobenzene, while a 2:1 cocrystal was formed between 5‐{[4‐(dimethylamino)phenyl]ethynyl}pyrimidine and 1,4‐diiodotetrafluorobenzene. 相似文献
847.
Symmetry‐Guided Synthesis of Highly Porous Metal–Organic Frameworks with Fluorite Topology
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Muwei Zhang Ying‐Pin Chen Mathieu Bosch Thomas Gentle III Kecheng Wang Dawei Feng Dr. Zhiyong U. Wang Prof. Dr. Hong‐Cai Zhou 《Angewandte Chemie (International ed. in English)》2014,53(3):815-818
Two stable, non‐interpenetrated MOFs, PCN‐521 and PCN‐523, were synthesized by a symmetry‐guided strategy. Augmentation of the 4‐connected nodes in the fluorite structure with a rigid tetrahedral ligand and substitution of the 8‐connected nodes by the Zr/Hf clusters yielded MOFs with large octahedral interstitial cavities. They are the first examples of Zr/Hf MOFs with tetrahedral linkers. PCN‐521 has the largest BET surface area (3411 m2 g‐1), pore size (20.5×20.5×37.4 Å) and void volume (78.5%) of MOFs formed from tetrahedral ligands. This work not only demonstrates a successful implementation of rational design of MOFs with desired topology, but also provides a systematic way of constructing non‐interpenetrated MOFs with high porosity. 相似文献
848.
849.
Jaume Haro 《International Journal of Theoretical Physics》2006,45(2):410-424
The quantum back-reaction problem in scalar QED is studied, in the semiclassical approximation, for nonstationary external electric fields. Using a model proposed in [Cooper, F., Mottola, E. (1989). Quantum back reaction in scalar QED as an initial-value problem. Physical Review D40(2), 456–464], based in a Hartree-type equation, we calculate, until order ħ, the induced current density and the induced electromagnetic field. Once we have computed the induced electromagnetic field, we obtain, until order ħ, the effective Lagrangian and the average density of produced pairs taking into account the back-reaction. 相似文献
850.