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91.
Siqueira Iolanda Scheibe de Dweck Jo Toledo Filho Romildo Dias 《Journal of Thermal Analysis and Calorimetry》2020,142(4):1413-1428
Journal of Thermal Analysis and Calorimetry - The interest in the use of cellulose fibers of increasingly smaller sizes in cementitious materials has increased in recent years. This paper brings... 相似文献
92.
Dr. Juliana Arriel Torres Dr. Gelson T. S. T. Da Silva Dr. Fernando Barbosa de Freitas Silva Dr. Caue Ribeiro 《Chemphyschem》2020,21(21):2392-2396
Tin dioxide (SnO2) has intrinsic characteristics that do not favor its photocatalytic activity. However, we evidenced that surface modification can positively influence its performance for CO2 photoreduction in the gas phase. The hydroxylation of the SnO2 surface played a role in the CO2 affinity decreasing its reduction potential. The results showed that a certain selectivity for methane (CH4), carbon monoxide (CO), and ethylene (C2H4) is related to different SnO2 hydrothermal annealing. The best performance was seen for SnO2 annealed at 150 °C, with a production of 20.4 μmol g−1 for CH4 and 16.45 μmol g−1 for CO, while for SnO2 at 200 °C the system produced more C2H4, probably due to a decrease of surface −OH groups. 相似文献
93.
94.
QSAR modeling of flotation collectors using principal components extracted from topological indices 总被引:1,自引:0,他引:1
Natarajan R Nirdosh I Basak SC Mills DR 《Journal of chemical information and computer sciences》2002,42(6):1425-1430
Several topological indices were calculated for substituted-cupferrons that were tested as collectors for the froth flotation of uranium. The principal component analysis (PCA) was used for data reduction. Seven principal components (PC) were found to account for 98.6% of the variance among the computed indices. The principal components thus extracted were used in stepwise regression analyses to construct regression models for the prediction of separation efficiencies (Es) of the collectors. A two-parameter model with a correlation coefficient of 0.889 and a three-parameter model with a correlation coefficient of 0.913 were formed. PCs were found to be better than partition coefficient to form regression equations, and inclusion of an electronic parameter such as Hammett sigma or quantum mechanically derived electronic charges on the chelating atoms did not improve the correlation coefficient significantly. The method was extended to model the separation efficiencies of mercaptobenzothiazoles (MBT) and aminothiophenols (ATP) used in the flotation of lead and zinc ores, respectively. Five principal components were found to explain 99% of the data variability in each series. A three-parameter equation with correlation coefficient of 0.985 and a two-parameter equation with correlation coefficient of 0.926 were obtained for MBT and ATP, respectively. The amenability of separation efficiencies of chelating collectors to QSAR modeling using PCs based on topological indices might lead to the selection of collectors for synthesis and testing from a virtual database. 相似文献
95.
Chen X Sichelschmidt O Kleemann W Petracic O Binek Ch Sousa JB Cardoso S Freitas PP 《Physical review letters》2002,89(13):137203
The ac susceptibility of a superferromagnetic discontinuous multilayer [Co(80)Fe20(1.4 nm)/Al(2)O3(3 nm)](10) is measured as a function of temperature, frequency, and field amplitude and compared to static and dynamic hysteresis loops. Its properties are successfully mapped onto the predicted [T. Nattermann, V. Pokrovsky, and V. M. Vinokur, Phys. Rev. Lett. 87, 197005 (2001)]] dynamical phase transitions, which link the relaxation, creep, sliding, and switching regimes of pinned domain walls. 相似文献
96.
A. Petri Ch. Br uchle H. Leigeber A. Miller H. -P. Weitzel F. -H. Kreuzer 《Liquid crystals》1993,15(1):113-121
Photosensitive cholesteric polysiloxanes, which contain an azo dye, were irradiated with linearly polarized light. The cholesteric samples were oriented in the Grandjean texture. Before irradiation they reflected circularly polarized light in the near infrared region. For perpendicular incidence, only one order of reflection was observed. Upon irradiation with linearly polarized light, which is absorbed by the azo dye, additional reflection bands appeared in the visible part of the spectrum. It turned out that the additional reflection is caused by a new Bragg type grating which shows higher reflection orders. The formation of the grating is based on the periodic deformation of the helical ordering of the molecules. The deformation is periodic, as due to photoselection, only dye molecules in equidistant layers with a suitable orientation absorb radiation. For low exposure, the grating reflects linearly polarized light. After continued irradiation, the reflection bands disappear almost completely. High birefringence, strongly dichroic dye absorption and the loss of the reflecting properties prove that a planar nematic texture has developed. The formation of this texture from the Grandjean texture is a new example for photoinduced rotational diffusion. 相似文献
97.
Cholesteric polysiloxanes containing an azo dye were irradiated with linearly or circularly polarized laser light or with the unpolarized light from a HgXe lamp. Photoinduced rotational diffusion was observed leading to new textures with a completely different orientational distribution of the chromophoric and the mesogenic side chains. A broad variety of new structures was detected depending on the polarization state of the light, the helical arrangement of the azo dye and the optional application of an electrical d.c. field. The new structures were characterized by spectroscopy with polarized light. Co-operative reorientation of chromophoric and mesogenic side chains was proven. The formation of a Bragg grating upon short term irradiation with linearly polarized light was observed. Continued irradiation leads in most cases to a strongly birefringent texture with a high dichroic ratio of the azo dye resembling a planar nematic texture. With circularly polarized light or with unpolarized light, a uniaxial homeotropic texture appeared predominantly. The formation of the new textures occurred in the glassy state of the samples leading to new structures with good optical quality and an exceptionally good long-term stability. 相似文献
98.
Mme Maryvonne L. Martin M. Franois Lefevre Mme Denise Lapeyre M. Grard J. Martin M. Richard Mantione 《Magnetic resonance in chemistry : MRC》1969,1(1):19-26
Magnetic non-equivalence of methylenic protons in A? CH2? CH3 groups were studied for several types of compounds. Results are compared with respect (1) to the nature of heteroatom A:A = O and A = S and (2) to the structure of the local dissymmetry element: asymmetric carbon, ketal group and allenic system. Influence of substitution is discussed in relation to conformational problems. Furthermore a variation of the methylene geminal coupling constant with substituents of carbon α to OEt is observed. 相似文献
99.
100.
Wiecko M Girnt D Rastätter M Panda TK Roesky PW 《Dalton transactions (Cambridge, England : 2003)》2005,(12):2147-2150
The chiral phosphanylamido ligand, (N(CHMePh)(PPh2))-, has been introduced into co-ordination chemistry. As starting material the oily amines HN(R-*CHMePh)(PPh2)(1a) and HN(S-*CHMePh)(PPh2)(1b) were used. To reconfirm their absolute structure, 1b was oxidized with H2O2 in air to obtain HN(S-*CHMePh)(P(O)Ph2)(2) as a solid compound. The solid-state structure of 2 was established by single-crystal X-ray diffraction. The lithium salts of both enantiomers Li(N(R-*CHMePh)(PPh2))(3a) and Li(N(S-*CHMePh)(PPh2))(3b) were prepared by deprotonation reaction of 1a,b. Compounds 3a,b were further reacted with zirconocen dichloride to give the chiral metallocenes [(eta5-C5H5)2Zr(Cl)(eta2-N(R-*CHMePh)(PPh2))](4a) and [(eta5-C5H5)2Zr(Cl)(eta2-N(S-*CHMePh)(PPh2))](4b). In an alternative approach to give chiral zirconium compounds, the neutral amine 1b was reacted with [(PhCH2)4Zr] to give the enantiomeric pure complex [(PhCH2)3Zr(eta2-N(S-*CHMePh)(PPh2))](5). The solid-state structures of all zirconium complexes were determined by single-crystal X-ray diffraction. 相似文献