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排序方式: 共有161条查询结果,搜索用时 15 毫秒
31.
Nanometer-thick conformal pore sealing of self-assembled mesoporous silica by plasma-assisted atomic layer deposition 总被引:1,自引:0,他引:1
Jiang YB Liu N Gerung H Cecchi JL Brinker CJ 《Journal of the American Chemical Society》2006,128(34):11018-11019
On a porous substrate, regular atomic layer deposition (ALD) not only takes place on top of the substrate but also penetrates into the internal porosity. Here we report a plasma-assisted process in which the ALD precursors are chosen to be nonreactive unless triggered by plasma, so that ALD can be spatially defined by the supply of plasma irradiation. Since plasma cannot penetrate within the internal porosity, ALD has been successfully confined to the immediate surface. This not only gives a possible solution for sealing of porous low dielectric constant films with a conformal layer of nm-scale thickness but also enables us to progressively reduce the pore size of mesoporous materials in a sub-A/cycle fashion for membrane formation. 相似文献
32.
Florencia A. Teppa Pannia Federico García Santiago E. Perez Bergliaffa Mariana Orellana Gustavo E. Romero 《General Relativity and Gravitation》2017,49(2):25
We analyse configurations of neutron stars in the so-called R-squared gravity in the Palatini formalism. Using a realistic equation of state we show that the mass–radius configurations are lighter than their counterparts in General Relativity. We also obtain the internal profiles, which run in strong correlation with the derivatives of the equation of state, leading to regions where the mass parameter decreases with the radial coordinate in a counter-intuitive way. In order to analyse such correlation, we introduce a parametrisation of the equation of state given by multiple polytropes, which allows us to explicitly control its derivatives. We show that, even in a limiting case where hard phase transitions in matter are allowed, the internal profile of the mass parameter still presents strange features and the calculated \(\mathrm{mass}-\mathrm{radius}\) configurations also yield neutron stars lighter than those obtained in General Relativity. 相似文献
33.
Summary The chromatographic behavior of zwitterions in Ion-interaction chromatography (IIC) is, investigated theoretically for the
first time. The modification of the stationary phase in the presence of Ion-interaction reagent (IIR), and adsorption competition
between test analytes and IIR for inner layer sites are shown theoretically to change the partition coefficient for zwitterions.
Experimental results from the literature concerning retention behavior of zwitterions in IIC, were used to test the new thermodynamic
theory. Very reasonable estimates of (i) ΔG
o values for the IIR adsorption onto the stationary phase (II) total ligand concentration, and (iii) dipolar moments validate
the present thermodynamic model for the IIC of zwitterionic analytes.
Retention equations are compared to those which can be obtained, if the net charge of the analyte is zero, from the most important
retention models in IIC. None of them is able to explain, even in a qualitative way, the retention behavior of zwitterions
in IIC whereas, the present model is quantitatively able to do this. 相似文献
34.
Matias E. G. Suburu Florencia Cecchi Norma D'Accorso Fabio Daniel Cukiernik 《Journal of polymer science. Part A, Polymer chemistry》2020,58(8):1163-1176
A series of main chain discotic liquid crystal polymers, synthesized following a new approach based on the incorporation of triphenylene units in both comonomers, show ordered columnar mesophases in a very wide thermal range, including room temperature. The introduction of branching points based on the same kind of triphenylene units increases their thermal range and gives rise to glassy low-temperature phases. Room temperature extrusion of these polymers yields fibers with molecules oriented perpendicular to the mechanical stress, and an orientational order parameter close to 0.5, which slightly increases for branched polymers. 相似文献
35.
Fabrizio Melani Lucia Cecchi Vittoria Colotta Giovanna Palazzino Guido Filacchioni 《Journal of heterocyclic chemistry》1988,25(5):1367-1371
By reacting 2-chloronicotinoyl chloride with acetyl or benzoyl acetate, ethyl 2-methyl- or 2-phenyl-4-oxopyrano[2,3-b]pyridine-3-carboxylates were prepared. The nucleophilic rearrangement of the latter with hydrazines gave rise to the title compounds. 相似文献
36.
Florencia C. Calaza Manuel F. Gomez Luis A. Arrua Osmar A. Ferretti María C. Abello 《Reaction Kinetics and Catalysis Letters》2004,81(2):259-264
Alumina supported molybdenum oxide was prepared using ammonium heptamolybdate and molybdenum acetate as different precursors.
The catalysts were characterized by BET, AAS, SEM-EDAX, XRD, TPR and surface acidity measurements. The characterization results
and the catalytic behavior in oxydehydrogenation of propane were similar irrespective of precursor.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
37.
Giovanna Palazzino Lucia Cecchi Vittoria Colotta Fabrizio Melani Guido Filacchioni 《Journal of heterocyclic chemistry》1989,26(1):71-75
The synthesis of 1,2,3,4-tetrahydropyrazolo[4,3-c][1]benzazepin-1-ones 1 and that of its 10-methyl derivative 2 is reported. The preparation of the latter from 3-(2-aminobenzyl)3-pyrazolin-5-one and triethyl ortho-formate gave as the main product a derivative of the new tricyclic ring system, pyrazolo[1,5-c][1,3]benzo-diazepine. The structures of the new compounds synthesized were assigned by means of a 13C nmr study. 相似文献
38.
Cecchi T 《Journal of chromatography. A》2005,1072(2):201-206
A method that champions the approaches of two independent research groups, to quantitate the chromatographic stationary phase surface available for lipophilic ion adsorption, is presented. For the first time the non-approximated expression of the electrostatically modified Langmuir adsorption isotherm was used. The non approximated Gouy-Chapman (G-C) theory equation was used to give the rigorous surface potential. The method helps model makers, interested in ionic interactions, determine whether the potential modified Langmuir isotherm can be linearized, and, accordingly, whether simplified retention equations can be properly used. The theory cultivated here allows the estimates not only of the chromatographically accessible surface area, but also of the thermodynamic equilibrium constant for the adsorption of the amphiphile, the standard free energy of its adsorption, and the monolayer capacity of the packing. In addition, it establishes the limit between a theoretical and an empirical use of the Freundlich isotherm to determine the surface area. Estimates of the parameters characterising the chromatographic system are reliable from the physical point of view, and this greatly validates the present comprehensive approach. 相似文献
39.
A 13C nmr study of a diazo, of two diazonium salts and of some other model pyrazole compounds is reported. It is found that the C-4 diazo carbon is more shielded than the normal sp2 pyrazole hybridized carbon, while its diazonium salt is more deshielded. The electron density on the C-4 of the diazopyrazole is probably due to the positive charge on the terminal nitrogen. Thus the 13C chemical shift values allowed us to understand the chemical behaviour of a compound of potential antitumor activity. 相似文献