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排序方式: 共有892条查询结果,搜索用时 31 毫秒
811.
The paper presents some aspects about the dynamic response of the human body subjected to the vertical vibration in the travel inside the auto vehicle. There is a model presented in the specialized literature. This is transformed for the given study because was necessary to realize the vertical vibration along the human body. There are two different studies: using a linear lumped parameter systems seat - human body model; using a nonlinear lumped parameter systems seat-human body model. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
812.
Simona Cosco Veronica Ambrogi Pellegrino Musto Cosimo Carfagna 《Macromolecular Symposia》2006,234(1):184-192
In this work urea-formaldehyde microcapsules containing an epoxy resin are prepared by in situ polymerization of monomers in an oil-in-water emulsion. Scanning electronic microscopy (SEM) was performed to investigate on microcapsule size and surface morphology. Calorimetric and spectroscopic analyses were carried out with the aim of evaluate the encapsulation yield and the shell features. Factors determining the microencapsulability of the core material were described. In particular, our interest was devoted to a better understanding of the influence of the reaction parameters on the microcapsule properties. It was found that the encapsulation yield as well as the extent of urea-formaldehyde polymerization depends on the reaction temperature and the stirring speed. 相似文献
813.
Dissociation Energy Computations for Saline Bonds Implied in Interactions Mediated by Peptidoglicans
Simona Muntean Ludovic Kurunczi Cristian Bologa Gheorghe Ilia Zeno Simon 《Macromolecular Symposia》2006,235(1):215-219
Summary: Dissociation energy and hydration energy calculations, in water solution, are presented for saline bonds mediated by Ca2+ and Mg2+ ions with Brőnstedt type bases ( COO , OSO3 , OH). A computationally intensive method, Polarisable Continuum Model (PCM) using 6-31G* basis set, was applied. Hydration energies were computed by various methods, as well as dissociation energies of some L2M complexes. L2Ca complexes result as more stable against dissociation than L2Mg complexes. Hydration energy calculation results, for some of the methods, here used, seem rather reliable as compared to experimental results. 相似文献
814.
Cingolani A Galli S Masciocchi N Pandolfo L Pettinari C Sironi A 《Journal of the American Chemical Society》2005,127(17):6144-6145
A new polycrystalline vapochromic polymorph of the one-dimensional copper bispyrazolate polymer reversibly and selectively absorbs a number of small molecules; the crystal structures of the anhydrous and fully hydrated species, determined by powder diffraction methods, are markedly different despite their simple, fast, and reversible interconversion. 相似文献
815.
Matteo Manfredini Andrea Marchetti Simona Sighinolfi Lorenzo Tassi Alessandro Ulrici Moris Vignali Claudia Zucchi 《Journal of solution chemistry》2002,31(3):235-252
Kinematic viscosities of the binary 2-butanone (1) + 1,2-propanediol (2) solvent system have been measured for mixtures covering the whole miscibility range expressed by 0 x
i 1, at 19 temperatures in the range –10 t/°C 80. The measured values have been used to test empirical equations that express the kinematic viscosities as functions of the composition and temperature. Excess kinematic viscosities (E) have also been calculated. Sign and magnitude of these quantities are discussed in terms of type and nature of specific intermolecular interactions. Furthermore, derived quantities such as thermodynamic parameters of viscous flow (G, H and S), are analyzed on the basis of Eyring's model. All the investigated excess mixing properties indicate the probable existence of stable two-component adducts in this binary solvent system. 相似文献
816.
817.
Dondoni A Massi A Minghini E Sabbatini S Bertolasi V 《The Journal of organic chemistry》2003,68(16):6172-6183
A novel and versatile strategy for the synthesis of heterocyclic alpha-amino acids has been described. The use of components (aldehyde or beta-ketoester) bearing a masked glycinyl moiety in Biginelli and Hantzsch cyclocondensations allowed access to the 4-dihydropyrimidinyl-alpha-glycines, 4-dihydropyrimidinyl-alpha-alanines, 4-pyridyl-alpha-alanines, and 2-pyridyl-alpha-alanines classes. Dihydropyrimidinyl-amino acids were obtained as a mixture of diastereoisomers due to the formation of the stereocenter at C4 of the dihydropyrimidinone ring. Individual stereoisomers were isolated as pure compounds and their structures were assigned with the aid of X-ray crystallography and chiroptical properties. The enantiomeric purity of a representative selection of the above amino acids was greater than 96% as verified by derivatization to the corresponding Mosher's amides and subsequent (1)H and (19)F NMR spectroscopy. Incorporation of the 4-pyridyl-alpha-alanine derivative into a peptide chain is also described. 相似文献
818.
The use of bisindenyl zirconium dimethyl in the synthesis of the corresponding dihalides is described. The synthesis of Ind2ZrCl2 has been carried out, cleanly and quantitatively, by chlorination of Ind2ZrMe2 (2) with a variety of inorganic chlorides, including BCl3, SCl2 in either toluene or methylene chloride, and HCl in Et2O. The latter method is the preferred one, since it produces methane as the only byproduct, and the formed Ind2ZrCl2 precipitates quantitatively from the Et2O solvent: a simple filtration then gives the analytically pure product in quantitative yield. Ind2ZrBr2 and Ind2ZrI2 are obtained by reacting 2 with Br2 and I2, respectively. The ‘inverse’ synthesis of metallocene dichlorides by chlorination of their dimethyl ‘derivatives’ has advantages compared to the classic method: first, Ind2ZrCl2 is obtained in higher yield (90-96%); second, it is easier to purify (at the dimethyl stage) and is obtained free from LiCl. Five bisindenyl zirconium complexes with different sigma ligands have been investigated in solution propylene polymerizations: it is found that the σ-ligands have no relevant influence on the catalyst activity, nor on the polymer properties. 相似文献
819.
CuO based catalysts dispersed on silica-alumina supports at low (0.56 wt.%) and high (13 wt.%) Al(2)O(3) content were prepared by adsorption method with or without ultrasound treatment. The catalysts obtained were studied in their bulk (atomic absorption, X-ray diffraction, temperature programmed reduction) and surface (N(2) adsorption and X-ray photoelectron spectroscopy) properties. Significant differences between the series of catalysts prepared over the two supports in terms of size of the CuO aggregates and of their redox properties were evidenced. All the catalysts were tested in the selective catalytic reduction of NO(x) using C(2)H(4) as reducing species (HC-SCR process) in highly oxidant atmosphere. The CuO-catalysts prepared using ultrasounds were the most active. Moreover, they displayed a peculiar activity being able to activate NO both by reducing it to N(2), in larger extent, and by oxidizing it to NO(2). 相似文献
820.
Synthetic and natural polymers have complex dynamic behavior with distinct motions taking place on a wide range of time and length scales. For poly(dimethyl siloxane) we show that, at temperatures above the melting point, the reorientation of the CH3 groups provides a non-negligible contribution to the incoherent dynamic structure factor. Analysis of the quasielastic neutron scattering data is carried out using a model function that includes fast rotational motion of the CH3 groups and local conformational transitions between isomeric states. By using this model, detailed comparison between experimental data and theoretical predictions at distances where deviations from the traditional Rouse model are expected becomes possible. 相似文献