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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.
Herein, we report an approach to combat counterfeiting and storage of valuable information based on the solid‐state fluorescence switching behavior of isoniazid functionalized naphthalene diimide (ISO_NDI) in response to an external stimuli (i. e., HCl vapor). The unique feature of ISO_NDI is further utilized to develop an invisible ink (ISO_NDI‐PVA) with commercial polymer polyvinyl alcohol (PVA). A solid‐state fluorescence recovery was observed while loading with HCl vapors. This exclusive property of the material could be applied directly as a security ink for confidential data storage purpose. Based on above strategy, we successfully realized the rewritable application by using ISO_NDI‐PVA ink and confirm its practical efficacy on various substrates by creating different patterns. The solid‐state fluorescence switching behavior of ISO_NDI‐PVA ink exhibited reversible on/off signal for multiple cycles under the influence of HCl/NH3 vapors. Mechanistic investigation supports a clear participation of intermolecular charge transfer (ICT) phenomenon in the solid‐state fluorescence switching property. The ease of fabricating the ink with invisible to visible characteristics in response to HCl vapors provides new opportunities for exploring the application of ISO_NDI‐PVA as invisible ink for targeted security applications. 相似文献
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The theory of magnetization in a longitudinal magnetic field is developed for an easy-plane multisublattice antiferromagnet with a singlet ground state and a strong single-ion anisotropy exceeding the magnitude of exchange interaction. The magnetic-field-induced phase transition from the singlet (magnetically dis-ordered) state to a multisublattice antiferromagnetic state represents a displacive magnetic phase transition. At T=0, this transition proceeds continuously and belongs to second-order phase transitions, while at T ≠0, the behavior changes to jumplike and the process becomes the first-order phase transition. 相似文献
16.
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
17.
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
18.
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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E. A. Kalita 《Ukrainian Mathematical Journal》1992,44(10):1235-1245
For second-order elliptic systems with the natural energy space W2
1 solutions with an isolated singularity are considered. If the speed of growth of the solution is less than the limiting speed determined by the modulus of the elliptic system, it is proved that either the singularity is removable or its order coincides with the order of the singularity of the fundamental solution of Laplace's equation. Systems are also considered with positive nonlinear lowest terms, for which a complete classification is obtained of the possible orders of isolated singularities.Translated from Ukrainskii Matematicheskii Zhurnal, Vol. 44, No. 10, pp. 1349–1358, October, 1992. 相似文献