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排序方式: 共有472条查询结果,搜索用时 46 毫秒
91.
Mircea Bulinski 《Molecules (Basel, Switzerland)》2021,26(10)
Polyvinyl alcohol is unique among polymers. Apart from its preparation, it is not built up in polymerization reactions from monomers, unlike most vinyl-polymers, and it is biodegradable in the presence of suitably acclimated microorganisms. It is an environmentally friendly material for a wide range of applications, from medical ones, based on its biocompatibility, to integrated optics. This paper reviews, in addition to the preparation and optimization of films of polyvinyl alcohol doped with different metal species, the role of dopants and doping technologies in the involved electronic mechanism. The optical properties were studied by UV-VIS-IR, Mössbauer spectroscopy, and other measurement techniques, with applications such as real-time holography, microlasers, optical sensors or nanophotonics in mind. 相似文献
92.
We report a novel Nb(V)−carboxylate cluster obtained from reaction of niobium(V) ethoxide and pivalic (trimethylacetic) acid. Single crystal X-ray diffraction data reveal a structure composed of 16 Nb(V) ions featuring oxo-, ethoxy- and pivalate moieties. The new cluster exhibits the highest nuclearity among structurally characterized niobium carboxylates reported to date. 相似文献
93.
94.
Najiba DoujaRaluca Malacea Mircea BanciuMichèle Besson Catherine Pinel 《Tetrahedron letters》2003,44(37):6991-6993
The diastereoselective hydrogenation of 2-methyl nicotinic acid covalently bound to proline ester or pyroglutamic ester over supported metallic catalyst yielded moderate diastereoselectivity (26%). The hydrogenation of the corresponding pyridinium salt was studied and similar de's were achieved. 相似文献
95.
Mircea I. Beciu 《General Relativity and Gravitation》1989,21(10):1013-1019
We consider the connection between the thermal effect of a black hole and the restoration of a broken symmetry. It appears that the second law of thermodynamics could be violated in a special circumstance. It is shown that this does not happen if we impose some constraints on the Higgs field.This essay recieved Honorable Mention from the Gravity Research Foundation—Ed. 相似文献
96.
Mihaela Mic Adrian Pîrnău Călin G. Floare Maria Miclăuș Irina Kacso Mariana Palage Mircea Bogdan 《Journal of inclusion phenomena and macrocyclic chemistry》2018,92(1-2):195-204
Spectroscopic investigation supported by molecular modeling methods has been used to describe the inclusion complex of β-cyclodextrin (β-CD) with 1-Methyl-1-({2-[4-(trifluoromethyl)phenyl]-1,3-thiazol-4-yl}methyl) piperidinium chloride (1MPTMPC) in solution and in solid state. The formation of inclusion complex between the β-CD and the 1MPTMPC has been investigated both in solution and in the solid state. Solution-state complexation between the 1MPTMPC and β-CD was established using 1H NMR spectroscopy and isothermal titration calorimetry (ITC). From the 1H NMR spectroscopic studies, 1:1 complex stoichiometry was deduced with an association constant (K) of 925 M?1. Using an independent binding model, the ITC technique provides a K value of the same order with the one determined by NMR and the thermodynamic parameters ΔH, ΔS and ΔG which reveals driving forces involved during complex formation. The formation of the solid inclusion compound was confirmed by X-ray powder diffraction and differential scanning calorimetry. The most probable conformation of the inclusion complex obtained through a molecular docking investigation corroborates well to ROESY experiment. 相似文献
97.
Potential Analysis - We introduce and study the unconstrained polarization (or Chebyshev) problem which requires to find an N-point configuration that maximizes the minimum value of its potential... 相似文献
98.
Giancarlo Bartolucci Mircea Dragoman Romolo Marcelli Fabrizio Pini 《International Journal of Infrared and Millimeter Waves》1995,16(10):1719-1732
A tunnel diode non-linear transmission line has been investigated for second and third harmonic generation purposes. Design criteria are given and performance predictions have been obtained simulating the single diode behavior by means of a polynomial expression. An optimization of the non-linear transmission line as a harmonic generator has been obtained as a function of the number of diodes, their separation distances and the bias voltage. 相似文献
99.
Habuchi S Cotlet M Gensch T Bednarz T Haber-Pohlmeier S Rozenski J Dirix G Michiels J Vanderleyden J Heberle J De Schryver FC Hofkens J 《Journal of the American Chemical Society》2005,127(25):8977-8984
Recently, it has been shown that the red fluorescent protein DsRed undergoes photoconversion on intense irradiation, but the mechanism of the conversion has not yet been elucidated. Upon irradiation with a nanosecond-pulsed laser at 532 nm, the chromophore of DsRed absorbing at 559 nm and emitting at 583 nm (R form) converts into a super red (SR) form absorbing at 574 nm and emitting at 595 nm. This conversion leads to a significant change in the fluorescence quantum yield from 0.7 to 0.01. Here we demonstrate that the photoconversion is the result of structural changes of the chromophore and one amino acid. Absorption, fluorescence, and vibrational spectroscopy as well as mass spectrometry suggest that a cis-to-trans isomerization of the chromophore and decarboxylation of a glutamate (E215) take place upon irradiation to form SR. At the same time, another photoproduct (B) with an absorption maximum at 386 nm appears upon irradiation. This species is assigned as a protonated form of the DsRed chromophore. It might be a mixture of several protonated DsRed forms as there is at least two ways of formation. Furthermore, the photoconversion of DsRed is proven to occur through a consecutive two-photon absorption process. Our results demonstrate the importance of the chromophore conformation in the ground state on the brightness of the protein as well as the importance of the photon flux to control/avoid the photoconversion process. 相似文献
100.
Sung Chul Hong Shijun Jia Mircea Teodorescu Tomasz Kowalewski Krzysztof Matyjaszewski Amy C. Gottfried Maurice Brookhart 《Journal of polymer science. Part A, Polymer chemistry》2002,40(16):2736-2749
Poly(n‐butyl acrylate)‐graft‐branched polyethylene was successfully prepared by the combination of two living polymerization techniques. First, a branched polyethylene macromonomer with a methacrylate‐functionalized end group was prepared by Pd‐mediated living olefin polymerization. The macromonomer was then copolymerized with n‐butyl acrylate by atom transfer radical polymerization. Gel permeation chromatography traces of the graft copolymers showed narrow molecular weight distributions indicative of a controlled reaction. At low macromonomer concentrations corresponding to low viscosities, the reactivity ratios of the macromonomer to n‐butyl acrylate were similar to those for methyl methacrylate to n‐butyl acrylate. However, the increased viscosity of the reaction solution resulting from increased macromonomer concentrations caused a lowering of the apparent reactivity ratio of the macromonomer to n‐butyl acrylate, indicating an incompatibility between nonpolar polyethylene segments and a polar poly(n‐butyl acrylate) backbone. The incompatibility was more pronounced in the solid state, exhibiting cylindrical nanoscale morphology as a result of microphase separation, as observed by atomic force microscopy. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2736–2749, 2002 相似文献