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排序方式: 共有72条查询结果,搜索用时 15 毫秒
1.
2.
CV Tomy D Pal SS Banerjee S Ramakrishnan AK Grover S Bhattacharya MJ Higgins G Balakrishnan McK Paul 《Pramana》2002,58(5-6):925-935
The weakly pinned single crystals of the hexagonal 2H-NbSe2 compound have emerged as prototypes for determining and characterizing the phase boundaries of the possible order-disorder
transformations in the vortex matter. We present here a status report based on the ac and dc magnetization measurements of
the peak effect phenomenon in three crystals of 2H-NbSe2, in which the critical current densities vary over two orders of magnitude. We sketch the generic vortex phase diagram of
a weakly pinned superconductor, which also utilizes theoretical proposals. We also establish the connection between the metastability
effects and pinning. 相似文献
3.
G. A. Kachkovskii N. V. Andrushko S. Yu. Sheiko O. I. Kolodyazhnyi 《Russian Journal of General Chemistry》2005,75(11):1735-1743
Stereochemistry of addition of di- and trialkyl phosphites to C=N compounds was investigated. Reactions of achiral dialkyl phosphites with chiral aldimines as well as that of chiral di-(1R,2S,5R)-menthyl phosphite with achiral aldimines result in low diastereomeric enrichment of the addition compound. Reaction stereoselectivity increased when supplementary chiral inductor was introduced to the reaction system. Reaction of di-(1R,2S, 5R)-menthyl phosphite with (S)-α-methylbenzylbenzaldimine proceeds as concerted asymmetric induction to form practically one diastereomer of N-substituted aminophosphonic acid. However, reaction of di-(1R,2S, 5R)-menthyl phosphite with (R)-α-methylbenzylbenzaldimine proceeded as not concerted asymmetric induction, and diastereomeric enrichment of the product was low. By chemical extrapolation, absolute configuration of compounds formed was established. Tri-(1R,2S,5R)-menthyl phosphite reacts with C=N compounds in the presence of boron trifluoride etherate to form aminophosphonic acid derivatives with the absolute configuration opposite to that appearing in the reaction of di-(1R,2S,5R)-menthyl phosphite with the same C=N compounds. 相似文献
4.
R. V. Visgert S. G. Sheiko L. M. Korotkikh 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1-2)
Abstract Compounds 2,4-(CF3SO2)2C6H3X while X = C1 (I), SO2C1 (II), SO2F (III), SO2NHC6H5(IV), HNSO2Cc6H5(V) are synthesized with the aim of finding active arylating means. Kinetics of the interaction of these compounds with the nucleophylic reagents, the character of the leaving group and the properties of medium are investigated by the spectrophotometric method. 相似文献
5.
Guido W Vandermeulen Dariush Hinderberger Hui Xu Sergei S Sheiko Gunnar Jeschke Harm-Anton Klok 《Chemphyschem》2004,5(4):488-494
Herein we describe the structure and dynamics of self-assembled nano-objects generated from poly(ethylene glycol) based (PEG-ylated) coiled-coil hybrid block copolymers. Electron paramagnetic resonance (EPR) experiments on spin-labeled samples provided a strong indication for a parallel alignment of the peptide helices in at least the dimeric coiled-coil nano-object and indicated that the PEG chains are folded rather closely around the peptide core of the nano-objects. The EPR results were supported by AFM studies, which revealed the presence of discrete nanosized objects in thin, spin cast films of the block copolymers on mica substrates. Since their size and structure may be engineered via directed mutations in the amino acid sequence, these nano-objects may be interesting building blocks for the development of supramolecular materials with various potential applications. 相似文献
6.
Joji Tanaka Satu Hkkinen Parker T. Boeck Yidan Cong Sbastien Perrier Sergei S. Sheiko Wei You 《Angewandte Chemie (International ed. in English)》2020,59(18):7203-7208
An orthogonal combination of cationic and radical RAFT polymerizations is used to synthesize bottlebrush polymers using two distinct RAFT agents. Selective consumption of the first RAFT agent is used to control the cationic RAFT polymerization of a vinyl ether monomer bearing a secondary dormant RAFT agent, which subsequently allows side‐chain polymers to be grafted from the pendant RAFT agent by a radical‐mediated RAFT polymerization of a different monomer, thus completing the synthesis of bottlebrush polymers. The high efficiency and selectivity of the cationic and radical RAFT polymerizations allow both polymerizations to be conducted in one‐pot tandem without intermediate purification. 相似文献
7.
Lebedeva NV Sun FC Lee HI Matyjaszewski K Sheiko SS 《Journal of the American Chemical Society》2008,130(13):4228-4229
Adsorption-induced degradation of brushlike macromolecules was monitored through molecular imaging by atomic force microscopy. The rate constant for C-C bond cleavage was shown to be extremely sensitive to the substrate surface energy. A few percent increase in the surface energy from 69.2 to 71.2 mN/m led to an order of magnitude increase of the scission rate. The absolute values of the rupture forces ranging from 2.57 to 2.47 nN are in agreement with previously calculated and measured values for stretching surface-tethered molecules. 相似文献
8.
Effect of residual copper on stability of molecular brushes with poly(n-butyl acrylate) (PBA) side chains was studied. The brushes were prepared by atom transfer radical polymerization (ATRP) using the grafting-from approach. Although the copper concentration was decreased down to below ten ppm levels by passing through alumina column, further removal was required to prevent crosslinking reactions. Further removal was performed by dialysis or precipitation. 相似文献
9.
P.G. Khalatur A.R. Khokhlov S.A. Prokhorova S.S. Sheiko M. Möller P. Reineker D.G. Shirvanyanz N. Starovoitova 《The European physical journal. E, Soft matter》2000,1(1):99-103
Conformational properties of comb-like polymers strongly adsorbed on a flat solid surface were investigated using computer
simulation and scanning force microscopy. The computer simulation showed that the macromolecules with asymmetric distribution
of the side chains relatively to the backbone are effectively in a collapsed state even under conditions of a good solvent.
They formed peculiar helical superstructures which could be observed by scanning force microscopy of cylindrical brushes of
polymethylmethacrylate on mica.
Received 13 September 1999 相似文献
10.
In subnormal glow discharge under d.c. excitation at different pressure in a varying transverse magnetic field (0 to 30 G)
some measurements have been carried out for various initial average tube currents. The voltage across the discharge increases
and average tube current and residual current decreases in the magnetic field. With the help of Beckman’s expression [4] for
the axial field and the electron density distribution in a transverse magnetic field the observed variation of current and
voltage can be satisfactorily explained. The variation of axial electric field with transverse magnetic field can be represented
to a fair degree of accuracy by the derived equation. The behaviour of residual current with magnetic field has been observed
in these oscillations. 相似文献