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271.
Chain microstructure and conformation of partially quaternized poly(dimethylaminoethyl methacrylate)
Virgil Barboiu Gabriela Liliana Ailiesei Anca Giorgiana Grigoras Elena Rusu Ecaterina Stela Dragan 《International Journal of Polymer Analysis and Characterization》2019,24(7):610-618
1H-NMR spectroscopy was used to establish the chain microstructure and conformation produced by the quaternization reaction of syndiotactic poly[2-(dimethylamino)ethyl methacrylate], a polymer with tertiary amino groups in the side chains. A chain microstructure with mini blocks of modified units was found by analyzing the N+CH3 signal that was proved to be split in accordance with the composition triads. The macromolecular backbone changes its form by quaternization, from a close to an expanded coil, was confirmed by light scattering measurements and NOE spectra modifications. The two linked processes, the block formation and chain expansion can be the key in developing a reaction mechanism explaining both positive and negative deviations from a second-order kinetic model. 相似文献
272.
Georghiou PE Tran AH Mizyed S Bancu M Scott LT 《The Journal of organic chemistry》2005,70(16):6158-6163
Pentakis(1,4-benzodithiino)corannulene (6) in CS2 formed the strongest 1:1 complexes with C60 and C70 of any corannulene derivative yet reported. The 1,3,5,7,9-pentakis(propylthio)corannulene (4b) formed weaker 1:1 complexes with C60 and C70 in CS2, whereas the decakis(propylthio)corannulene (5b) and unsubstituted corannulene (1) showed no evidence for complexation with either C60 or C70 in CS2. 相似文献
273.
A compact form for the universalR-matrix of U
q
(sl
n
) is derived and illustrated by simple applications. 相似文献
274.
The positions of acetyl groups introduced by Friedel-Crafts reactions into 2,3-diphenylbenzofuran and its derivatives monomethylated in the 5,6 and 7 positions and dimethylated in the 5,6 positions were determined by means of single and double resonance NMR spectra. It was found that the first acetyl group occupies position 6 for all 6-unmethylated compounds and position 5 for 6-methylated compounds. The next two acetyl groups enter the para positions (4′ and 4″) of the phenyl groups with the same probability. When positions 5 and 6 are methylated the acetyl group enters positions 7,4′ and 4″ which are found to be of almost equal reactivity. The NMR parameters of compounds studied are listed. 相似文献
275.
Ruben M Breuning E Barboiu M Gisselbrecht JP Lehn JM 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(1):291-299
The [M(4)(II)L(4)](8+) [2 x 2]-grid-type complexes 1-8 present a set of features of particular interest for potential applications. All complexes exhibit multiple reduction levels at low reduction potentials paired with rather high stability. The modulation of the reduction potentials is possible by introduction of appropriate substituents on the ligands. The Co(II)(4) complexes 1-5 present a remarkable regularity in the disposition of the reduction levels, indicating the ability of the Co(II) sites to transmit electronic interactions between reduced ligands. In general, all investigated molecular systems 1-8 show characteristics typical for multilevel supramolecular electronic devices. 相似文献
276.
Charged translation covariant states with finite energy are constructed in the Higgs phase of the ?2 gauge theory coupled to a ?2 matter field. 相似文献
277.
Fedor Muntyanu Mihail Onu Yurie Dubkovetsky Vitalie Kistol 《Czechoslovak Journal of Physics》1996,46(Z4):2039-2040
In stationary magnetic fields up to 18T alongside with investigation of Shubnikov-de Haas oscillations in monocrystal blocks
there were studied oscillations of transport phenomena, connected with the electron spectrum peculiarities in the transition
layer and with the interaction of carriers with the bicrystal boundary. 相似文献
278.
Li Xin Chen Hsinchun Dang Yan Lin Yiling Larson Catherine A. Roco Mihail C. 《Journal of nanoparticle research》2008,10(1):3-22
Nanotechnology research and applications have experienced rapid growth in recent years. We assessed the status of nanotechnology research worldwide by applying bibliographic, content map, and citation network analysis to a data set of about 200,000 nanotechnology papers published in the Thomson Science Citation Index Expanded database (SCI) from 1976 to 2004. This longitudinal study shows a quasi-exponential growth of nanotechnology articles with an average annual growth rate of 20.7% after 1991. The United States had the largest contribution of nanotechnology research and China and Korea had the fastest growth rates. The largest institutional contributions were from the Chinese Academy of Sciences and the Russian Academy of Sciences. The high-impact papers generally described tools, theories, technologies, perspectives, and overviews of nanotechnology. From the top 20 institutions, based on the average number of paper citations in 1976–2004, 17 were in the Unites States, 2 in France and 1 in Germany. Content map analysis identified the evolution of the major topics researched from 1976 to 2004, including investigative tools, physical phenomena, and experiment environments. Both the country citation network and the institution citation network had relatively high clustering, indicating the existence of citation communities in the two networks, and specific patterns in forming citation communities. The United States, Germany, Japan, and China were major citation centers in nanotechnology research with close inter-citation relationships. 相似文献
279.
Packing, Tiling, Orthogonality and Completeness 总被引:3,自引:0,他引:3
Let Rd be an open set of measure 1. An open set DRd is calleda tight orthogonal packing region for if DDdoes not intersect the zeros of the Fourier transform of theindicator function of , and D has measure 1. Suppose that isa discrete subset of Rd. The main contribution of this paperis a new way of proving the following result: D tiles Rd whentranslated at the locations if and only if the set of exponentialsE = {exp 2i, x: } is an orthonormal basis for L2(). (This resulthas been proved by different methods by Lagarias, Reeds andWang [9] and, in the case of being the cube, by Iosevich andPedersen [3]. When is the unit cube in Rd, it is a tight orthogonalpacking region of itself.) In our approach, orthogonality ofE is viewed as a statement about packing Rd withtranslates of a certain non-negative function and, additionally,we have completeness of E in L2() if and only if the above-mentionedpacking is in fact a tiling. We then formulate the tiling conditionin Fourier analytic language, and use this to prove our result.2000 Mathematics Subject Classification 52C22, 42B99, 11K70. 相似文献
280.
The patent citation networks are described using critical node, core network, and network topological analysis. The main objective
is understanding of the knowledge transfer processes between technical fields, institutions and countries. This includes identifying
key influential players and subfields, the knowledge transfer patterns among them, and the overall knowledge transfer efficiency.
The proposed framework is applied to the field of nanoscale science and engineering (NSE), including the citation networks
of patent documents, submitting institutions, technology fields, and countries. The NSE patents were identified by keywords
“full-text” searching of patents at the United States Patent and Trademark Office (USPTO). The analysis shows that the United
States is the most important citation center in NSE research. The institution citation network illustrates a more efficient
knowledge transfer between institutions than a random network. The country citation network displays a knowledge transfer
capability as efficient as a random network. The technology field citation network and the patent document citation network
exhibit a␣less efficient knowledge diffusion capability than a random network. All four citation networks show a tendency
to form local citation clusters. 相似文献