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991.
Reichert D Pascui O Bonagamba TJ Belton P Schmidt A deAzevedo ER 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2008,191(1):141-147
We present a minor but essential modification to the CODEX 1D-MAS exchange experiment. The new CONTRA method, which requires minor changes of the original sequence only, has advantages over the previously introduced S-CODEX, since it is less sensitive to artefacts caused by finite pulse lengths. The performance of this variant, including the finite pulse effect, was confirmed by SIMPSON calculations and demonstrated on a number of dynamic systems. 相似文献
992.
Marian Rauser Raphael Eckert Max Gerbershagen Meike Niggemann 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(20):6785-6789
A rare reductive coupling of nitro compounds with organohalides has been realized. The reaction is initiated by a partial reduction of the nitro group to a nitrenoid intermediate. Therefore, not only aromatic but also aliphatic nitro compounds are efficiently transformed into monoalkylated amines, with organohalides as the alkylating agent. Given the innate reactivity of the nitrenoid, a catalyst is not required, resulting in a high tolerance for aryl halide substituents in both starting materials. 相似文献
993.
Dr. Marian Olaru Daniel Duvinage Dr. Enno Lork Dr. Stefan Mebs Prof. Dr. Jens Beckmann 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(65):14758-14761
Fluoride abstraction from bis-m-terphenylelement fluorides (2,6-Mes2C6H3)2EF (E=P, As) generated the highly reactive phosphenium ion [(2,6-Mes2C6H3)2P]+ and the arsenium ion [(2,6-Mes2C6H3)2As]+, which immediately underwent intramolecular electrophilic substitution and formation of an 1,2,4-trimethyl-6-mesityl-5-m-terphenyl-benzo[b]phospholium ion and an 1,2,4-trimethyl-6-mesityl-5-m-terphenyl-benzo[b]arsolium ion, respectively. The formation of the latter involved a methyl group migration from the ortho-position of a flanking mesityl group to the meta-position. This reactivity of [(2,6-Mes2C6H3)2E]+ (E=P, As) is in sharp contrast to the related stibenium ion [(2,6-Mes2C6H3)2Sb]+ and bismuthenium ion [(2,6-Mes2C6H3)2Bi]+, which have been recently isolated and fully characterized (Angew. Chem. Int. Ed. 2018, 57 , 10080–10084). On the basis of DFT calculations, a mechanism for the rearrangement of the phosphenium and arsenium ions into the phospholium and arsolium ions is proposed, which is not feasible for the stibenium and bismuthenium ions. 相似文献
994.
Huang H Manciu M Ruckenstein E 《Langmuir : the ACS journal of surfaces and colloids》2005,21(1):94-99
Recent experiments on restabilization of protein-covered latex colloids at high ionic strengths reported by Lopez-Leon et al.(1) revealed strong specific anion effects. The same authors also emphasized that a recent polarization model, which involves both hydration and double layer forces, can account only for some of their experimental results but are in disagreement with other experimental results. The aim of the present paper is to show that most experimental results of ref 1 can be described, more than qualitatively, when the association equilibria for all the ions (with both the acidic and basic sites of the protein) are taken into account. As the traditional Poisson-Boltzmann approach, the polarization model neglects additional interactions between ions, and ions and surfaces, not included in the "mean field" electrical potential; therefore, a complete quantitative agreement should not be expected. While many of the discrepancies between calculations and experiment occur at low ionic strengths (10(-)(4)-10(-)(2) M), in the range of validity of the traditional DLVO theory, the latter can neither explain them. It is suggested that the structural modifications of the protein configuration induced by the electrolyte are responsible for some of the disagreements between experiment and calculations. 相似文献
995.
Marian Vâ jâ itu Alexandru Zaharescu 《Proceedings of the American Mathematical Society》2002,130(12):3447-3452
Let be a real number, a positive integer and a subset of . We give an upper bound for the number of distinct lengths of gaps between the fractional parts .
996.
We define the degree of nonclassicality of a one-mode Gaussian state of the quantum electromagnetic field in terms of the Bures distance between the state and the set of all classical one-mode Gaussian states. We find the closest classical Gaussian state and the degree of nonclassicality using a recently established expression for the Uhlmann fidelity of two single-mode Gaussian states. The decrease of nonclassicality under thermal mapping is carefully analyzed. Along the same lines, we finally present the evolution of nonclassicality during linear amplification. 相似文献
997.
Enhancement of two-photon emission in photonic crystals 总被引:1,自引:0,他引:1
Markowicz P Friend C Shen Y Swiatkiewicz J Prasad PN Toader O John S Boyd RW 《Optics letters》2002,27(5):351-353
We report the influence of photonic stopgaps on two-photon excited emission from highly efficient nonlinear chromophores infiltrated into high-quality photonic crystals. We have observed a sharp decrease (filter effect) in emission within the frequency range and direction of the stopgap as well as sharp enhancement of the two-photon excited emission associated with the stopgap's edge. This effect may be important for the development of low-threshold upconversion lasers. 相似文献
998.
Marian Grabowski 《Foundations of Physics》1989,19(7):923-930
The concept of generalized observable in the scheme of Hilbert quantum mechanics is discussed. We give an example of a possible ambiguity of this notion. The role of interpretation and the strong connection with concrete experimental procedures in the discussion of generalized observables are stressed to explain the above ambiguity.Dedicated to Professor Peter Mittelstaedt on the occasion of his 60th birthday.Humboldt fellow, on leave from the Institute of Physics, Nicholas Copernicus University, Torun, Poland. 相似文献
999.
1000.
On the basis of endospectral graphs, we present a graphical method for obtaining pairs of nonisomorphic graphs with identical atomic counts of self-returning walks. 相似文献