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排序方式: 共有220条查询结果,搜索用时 15 毫秒
11.
Ze-Hun Cao Yu-Hao Wang Dr. Subarna Jyoti Kalita Dr. Uwe Schneider Prof. Dr. Yi-Yong Huang 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(5):1900-1906
Unprecedented phosphine-catalyzed [4+1] cycloadditions of allenyl imides have been discovered using various N-based substrates including methyl ketimines, enamines, and a primary amine. These transformations provide a one-pot access to cyclopentenoyl enamines and imines, or (chiral) γ-lactams through two geminal C−C bond or two C−N bond formations, respectively. Several P-based key intermediates including a 1,4-(bis)electrophilic α,β-unsaturated ketenyl phosphonium species have been detected by 31P NMR and HRMS analyses, which shed light on the postulated catalytic cycle. The synthetic utility of this new chemistry has been demonstrated through a gram-scaling up of the catalytic reaction as well as regioselective hydrogenation and double condensation to form cyclopentanoyl enamines and fused pyrazole building blocks, respectively. 相似文献
12.
Structural Chemistry - A Correction to this paper has been published: https://doi.org/10.1007/s11224-021-01788-w 相似文献
13.
In this paper, we propose a new methodology for numerically solving elliptic and parabolic equations with discontinuous coefficients and singular source terms. This new scheme is obtained by clubbing a recently developed higher‐order compact methodology with special interface treatment for the points just next to the points of discontinuity. The overall order of accuracy of the scheme is at least second. We first formulate the scheme for one‐dimensional (1D) problems, and then extend it directly to two‐dimensional (2D) problems in polar coordinates. In the process, we also perform convergence and related analysis for both the cases. Finally, we show a new direction of implementing the methodology to 2D problems in cartesian coordinates. We then conduct numerous numerical studies on a number of problems, both for 1D and 2D cases, including the flow past circular cylinder governed by the incompressible Navier–Stokes equations. We compare our results with existing numerical and experimental results. In all the cases, our formulation is found to produce better results on coarser grids. For the circular cylinder problem, the scheme used is seen to capture all the flow characteristics including the famous von Kármán vortex street. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
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15.
In this paper, we propose an implicit higher-order compact (HOC) finite difference scheme for solving the two-dimensional (2D) unsteady Navier–Stokes (N–S) equations on nonuniform space grids. This temporally second-order accurate scheme which requires no transformation from the physical to the computational plane is at least third-order accurate in space, which has been demonstrated with numerical experiments. It efficiently captures both transient and steady-state solutions of the N–S equations with Dirichlet as well as Neumann boundary conditions. The proposed scheme is likely to be very useful for the computation of transient viscous flows involving free and wall bounded shear layers which invariably contain spatial scale variation. Numerical results are presented and compared with analytical as well as established numerical data. Excellent comparison is obtained in all the cases. 相似文献
16.
Ajayan Vinu Pranjal Kalita Hamid Oveisi Ajayan Mano B.V. Subba Reddy 《Tetrahedron letters》2009,50(51):7132-1489
Here we demonstrate for the first time the synthesis of α-aminophosphonates through the three-component coupling reaction of aldehydes, amines, and diethyl phosphite by using highly acidic 3D mesoporous aluminosilicate nanocage catalyst, which gave excellent yield with a high selectivity in a short reaction time due to its high acidity, 3D pores, and a huge space in the nanocages. 相似文献
17.
Brajesh Pandey M. P. C. Kalita A. Perumal A. Srinivasan H. C. Verma 《Hyperfine Interactions》2008,183(1-3):147-153
Iron nitrides are attractive as they show excellent magnetic properties which can be utilized as recording and permanent magnetic materials for potential applications. Due to the high saturation magnetization and chemical stability, γ ′-Fe4N compound is widely investigated as a promising high density magnetic recording material. γ ′-Fe4N particles were synthesized by conventional gaseous nitriding in a heated atmosphere containing ammonia as a source of nitrogen. X-ray diffraction, 57Fe Mössbauer spectroscopy, vibrating sample magnetometer, scanning electron microscopy and transmission electron microscopy are used for the characterization of the as prepared sample. 相似文献
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19.
V. F. Shamrai A. E. Karpikhin V. P. Sirotinkin V. I. Kalita D. I. Komlev 《Crystallography Reports》2014,59(2):179-185
The structure of hydroxyapatite plasma coatings on a titanium substrate has been investigated by the X-ray Rietveld method. The hydroxyapatite crystal structure in plasma-deposited samples is characterized by strong distortions of its main element (tetrahedral PO4 cluster) and coordination calcium polyhedra, as well as calcium deficit in the Ca2 site; however, these features do not change the main motif of the hydroxyapatite structure. The bond distortions in PO4 clusters are estimated by the Bauer method. It is shown that hydrothermal treatment leads to the almost complete recovery of the hydroxyapatite structure. 相似文献
20.
The Ramanujan Journal - In this paper, we develop a finite field analogue for one of the Lauricella series, $$F^{(n)}_A$$ . Extending results of Greene, a finite field analogue for the multinomial... 相似文献