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111.
Bowen Li Jianzhong Chen Zhenfeng Zhang Ilya D. Gridnev Wanbin Zhang 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(22):7407-7412
An efficient nickel‐catalyzed asymmetric hydrogenation of N‐tBu ‐ sulfonyl imines was developed with excellent yields and enantioselectivities using (R,R)‐QuinoxP* as a chiral ligand. The use of a much lower catalyst loading (0.0095 mol %, S/C=10500) represents the highest catalytic activity for the Ni‐catalyzed asymmetric hydrogenations reported so far. Mechanistic studies suggest that a coordination equilibrium exists between the nickel salt and its complex, and that excess nickel salt promotes the formation of the active Ni‐complex, and therefore improved the efficiency of the hydrogenation. The catalytic cycle was also investigated by calculations to determine the origin of the enantioselectivity. An extensive network of numerous weak attractive interactions was found to exist between the catalyst and substrate in the transition state and may also contribute to the high catalytic activity. 相似文献
112.
Aharon Gero Ilya Levin 《International Journal of Mathematical Education in Science & Technology》2019,50(5):779-787
The invention of the computer has led to the establishment of a new research paradigm, computation, which has recently become more and more popular in scientific exploration. However, computation is not well represented in high school and university curricula in science and engineering, although it applies to a wide range of disciplines beyond computer science and software engineering. In light of the increasing need to provide students with computational education, this paper presents a novel way to develop computational thinking among students. The proposed approach is based on the implementation of Papert's theory of constructionism in electronic spreadsheets. In this approach, students build their knowledge while constructing the difference equation that describes a physical (or engineering) phenomenon, based on specific cases investigated in the spreadsheet. The method does not require the students to write code or perform complex calculations in the spreadsheet and makes it possible to teach advanced subjects at a relatively early stage. The method is demonstrated through contents taken from the secondary and tertiary curricula in mechanics and electromagnetism. 相似文献
113.
Dmitri V. Konarev Alexey V. Kuzmin Salavat S. Khasanov Alexey A. Goryunkov Victor A. Brotsman Ilya N. Ioffe Akihiro Otsuka Hideki Yamochi Hiroshi Kitagawa Rimma N. Lyubovskaya 《化学:亚洲杂志》2019,14(11):1958-1964
Radical anion salt {cryptand[2.2.2] (K+)}2(bispheroid)2??3.5C6H4Cl2 ( 1 ) of the double‐caged fullerene C60 derivative, in which fullerene cages are linked by a cyclobutane bridging cycle and additionally by a pyrrolizidine moiety, was obtained. Each fullerene cage in this derivative accepts one electron on reduction, thus forming the (bispheroid)2? dianions with two interacting S=1/2 spins on the neighboring cages. Low‐temperature magnetic measurements reveal a singlet ground state of the bispheroid dianions whereas triplet contributions prevail at increased temperature. An estimated exchange interaction between two spins J/kB=?78 K in 1 indicates strong magnetic coupling between them, nearly two times higher than that (J/kB=?44.7 K) in previously studied (C60?)2 dimers linked via a cyclobutane bridge only. The enhancement of magnetic coupling in 1 can be explained by a shorter distance between the fullerene cages and, possibly, an additional channel for the magnetic exchange provided by a pyrrolizidine bridge. Quantum‐chemical calculations of the lowest electronic state of the dianions by means of multi‐configuration quasi‐degenerate perturbation theory support the experimental findings. 相似文献
114.
Aleksandr A. Lanin Artem S. Chebotarev Matvey S. Pochechuev Ilya V. Kelmanson Andrei B. Fedotov Vsevolod V. Belousov Aleksei M. Zheltikov 《Journal of Raman spectroscopy : JRS》2019,50(9):1296-1302
Within the past decade, nonlinear Raman microscopy has earned a well-deserved status of a gold-standard technology for chemically selective imaging. Even though second- and third-harmonic microscopy is much less demanding on a laser source and multifrequency beam arrangement, it is increasingly falling behind nonlinear Raman scattering as a method of bioimaging because it offers no mechanism whereby imaging could be made chemically specific. Here, we show, however, that such a mechanism does exist, helping harmonic-generation microscopy overcome its no-chemical-specificity handicap. We demonstrate that, with the laser wavelength tuned to a three-photon resonance with the Soret band of hemoglobin, third-harmonic generation provides a chemically specific method for a high-contrast imaging of red blood cells in a broad class of biological systems, including live brain. Moreover, third-harmonic generation imaging can be conveniently combined with second-harmonic microscopy on a compact laser platform, providing, as our experiments on rat brain show, a powerful resource for three-dimensional, cell-specific label-free deep-brain imaging. 相似文献
115.
A new approach to optimal maintenance of systems (networks) is suggested. It is applied to systems subject to two external independent shock processes. A system ‘consists’ of two parts, and each shock process affects only its own part. A new notion of bivariate signature is suggested and used for obtaining survival characteristics of a system and further optimization of the preventive maintenance actions. The preventive maintenance optimization is considered in the univariate discrete scale that counts the overall numbers of shocks of both types. An example of a transportation network is considered. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
116.
117.
Mirza I. Bichurin Oleg V. Sokolov Viktor S. Leontiev Roman V. Petrov Alexander S. Tatarenko Gennadiy A. Semenov Sergey N. Ivanov Andrei V. Turutin Ilya V. Kubasov Alexander M. Kislyuk Mikhail D. Malinkovich Yuriy N. Parkhomenko Andrei L. Kholkin Nikolai A. Sobolev 《physica status solidi b》2020,257(3):1900398
118.
Shridhar Manjunath Mingkai Liu Vidur Raj Rifat A. Aoni David A. Powell Ilya V. Shadrivov Mohsen Rahmani 《Advanced Optical Materials》2020,8(7)
Metamaterials are engineered structures designed to interact with electromagnetic radiation, whereby the frequency range in which metamaterials respond depends on their dimensions. In this paper, it is demonstrated that a metamaterial can be functional in more than one frequency region. An advanced metamaterial is demonstrated that can interact with both terahertz (THz) and near‐infrared (NIR) frequencies, concurrently. This work exploits meander line resonators with nanoscale linewidth distributed over microscale areas, and experimentally demonstrates that such a metamaterial can simultaneously interact with NIR and THz waves. The engineered metamaterial acts as a plasmonic grating in the NIR range and simultaneously acts as an array of electric resonators in the THz range. Moreover, the performance of the engineered metamaterial is polarization‐independent in both wavelength regions. Finally, a unique feature of the proposed metamaterial is that it enables resonant frequency tuning in the THz region without affecting the NIR response. All these novel advantages of dual‐band meander metamaterial make it an ideal alternative for cutting‐edge applications such as bi‐functional sensing, imaging, filtering, modulation, and absorption. 相似文献
119.
120.
Elena?F.?ShekaEmail author Ekaterina?A.?Nikitina Valentin?A.?Zayets Ilya?Ya.?Ginzburg Joop?Schoonman 《Journal of nanoparticle research》2005,7(2-3):171-186
The current paper presents results of a quantum-chemical study of the surface structure of nanoparticles of both rutile and anatase crystallographic modifications. Different stages of the surface relaxation are discussed. Water adsorption is considered. The calculations were performed in the spd-basis by using semi-empirical quantum-chemical codes, both sequential and parallel. The results are mainly addressed to the study of the interface formed by titania nanoparticles and a set of carboxylated species, namely, benzoic, bi-isonicotinic acids as well as tris-(2,2′-dcbipyridine) Fe(II) complex placed on the surface of either rutile or anatase polymorphs.This revised version was published online in August 2005 with a corrected issue number. 相似文献