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141.
142.
Silver nanoparticles supported on ionic‐tagged magnetic hydroxyapatite as a highly efficient and reusable nanocatalyst for hydrogenation of nitroarenes in water 下载免费PDF全文
A novel chemically modified magnetic hydroxyapatite (MHAp) was prepared and used as support and stabilizer for the synthesis of silver nanoparticles. First, 1,4‐diazabicyclo[2.2.2]octane (DABCO) was successfully grafted onto the surface of MHAp, and then silver nanoparticles were homogeneously loaded on mesoporous MHAp‐DABCO (ionic‐tagged MHAp) nanocomposite by in situ chemical reduction of silver nitrate using sodium borohydride. The structure and properties of the resulting MHAp‐DABCO‐Ag nanocomposite were confirmed using various techniques. The catalytic activity of ionic‐tagged MHAp‐Ag nanocatalyst was investigated for the hydrogenation reaction of nitroarenes in aqueous media. The results reveal that the Ag‐containing inorganic–organic nanocomposite is highly efficient for the reduction of a wide range of aromatic nitro compounds under green conditions. The superparamagnetic nature of the nanocatalyst leads to its being readily removed from solution via application of a magnetic field, and it can be easily stored and reused. 相似文献
143.
石油沥青质在烃中的稳定性研究 总被引:2,自引:0,他引:2
石油是以沥青质为分散相的非水胶体体系[1,2 ] 。研究认为 ,石油中沥青质的沉淀和絮凝 ,对石油开采及输送有十分重要的影响 [3]。提高沥青质在石油中的胶体稳定性 ,可强化石油加工过程中的重油减压蒸馏、催化裂化、减粘裂化及延迟焦化等过程[1,2 ] ,是提高炼厂轻质油收率、改善产品质量、提高综合经济效益的重要途径。国外关于沥青质在烃类介质中的稳定性研究报道较多 ,大多侧重于胶质对沥青质的稳定作用。由于胶质和沥青质均为由多种复杂结构分子组成的混和物 ,探讨胶质对沥青质的稳定机理极端困难 ,Chia-Lu Chang[4 ]等定量讨论了沥青质… 相似文献
144.
Hydraulic permeability is studied in porous media consisting of randomly distributed monodisperse spheres by means of computational fluid dynamics (CFD) simulations. The packing of spheres is generated by inserting a certain number of nonoverlapping spherical particles inside a cubic box at both low and high packing fractions using proper algorithms. Fluid flow simulations are performed within the interparticulate porous space by solving Navier-Stokes equations in a low-Reynolds laminar flow regime. The hydraulic permeability is calculated from the Darcy equation once the mean values of velocity and pressure gradient are calculated across the particle packing. The simulation results for the pressure drop across the packing are verified by the Ergun equation for the lower range of porosities (<0.75), and the Stokes equation for higher porosities (∼1). Using the results of simulations, the effects of porosity and particle diameters on the hydraulic permeability are investigated. Simulations precisely specified the range of applicability of empirical or semi-empirical correlations for hydraulic permeability, namely the Carman-Kozeny, Rumpf-Gupte, and Howells-Hinch formulas. The number of spheres in the model is gradually decreased from 2000 to 20 to discover the finite-size effect of pores on the hydraulic permeability of spherical packing, which has not been clearly addressed in the literature. In addition, the scale dependence of hydraulic permeability is studied via simulations of the packing of spheres shrunk to lower scales. The results of this work not only reveal the validity range of the aforementioned correlations, but also show the finite-size effect of pores and the scale-independence of direct CFD simulations for hydraulic permeability. 相似文献
145.
Youcef Amirat Vladimir Shelukhin 《Journal of Mathematical Analysis and Applications》2008,342(2):1227-1245
By the homogenization approach we justify a two-scale model of ion transport in porous media for one-dimensional horizontal steady flows driven by a pressure gradient and an external horizontal electrical field. By up-scaling, the electroosmotic flow equations in horizontal nanoslits separated by thin solid layers are approximated by a homogenized system of macroscale equations in the form of the Poisson equation for induced vertical electrical field and Onsager's reciprocity relations between global fluxes (hydrodynamic and electric) and forces (horizontal pressure gradient and external electrical field). In addition, the two-scale approach provides macroscopic mobility coefficients in the Onsager relations. 相似文献
146.
P. Sigmund 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,12(1):111-116
Second-harmonic cross-correlation operates a selection in time-phase among the randomly de-phased contributions to an optical
field that propagated through a scattering medium. It can thus be used to selectively detect the weak contribution remaining
coherent with the incident field.
Received 7 May 1999 相似文献
147.
M. H. Saffouri 《Il Nuovo Cimento D》1986,7(2):175-194
Summary A treatment of transition radiation is presented. This is based on the fields produced by the polarization charges in the
radiation zone. These charges are extracted from the exact forms of the fields which were derived previously. A distinction
is found between the radiation in the forward and in the backward regions. This would call for experimental verification.
Comparison with other treatments shows similarity in the general features but important differences in the details.
Riassunto Si presenta una trattazione della radiazione transitoria. Essa è basata sui campi emessi nella regione asintotica dalle cariche di polarizzazione. Queste cariche sono estratte dalle forme esatte di campi che erano stati precedentemente derivati. Si verifica una distinzione chiara fra la radiazione nella direzione avanti e indietro. Questo neccesiterebbe una verifica sperimentale. Il confronto con altri trattamenti mostra una somiglianza nelle linee generali ma anche importanti differenze nei dettagli.相似文献
148.
L.Q. Cao 《Journal of Mathematical Analysis and Applications》2008,343(2):1103-1118
In this paper, we study the optimal control on the boundary for parabolic equations with rapidly oscillating coefficients arising from the heat transfer problems and the optimal control on the boundary of composite materials or porous media. The multiscale asymptotic expansion of the solution for the problem in the case without any constraints is presented. We derive the proofs of all convergence results. 相似文献
149.
Micelles,microemulsions.vesicles,etc.,areorganicmicroheterogeneousmedia.Useofthesemediainanalyticalreactionsfordevelopingnewkinetic-baseddeterminationsorimprovingpreviouslyestablishedkineticmethodshasbeenreported"2.Inrecentyears,amixedmicellarmediumc... 相似文献
150.
Moisture removal from a two-layer porous media in which air is circulated through one layer and moisture is removed from the second has not been well studied due to the emphasis given to single-layer systems. This two-layer configuration is common in natural and engineered systems and can be used as a means to create a barrier to downward migrating fluids and to remove liquids and gases that may be present in the finer layer. However, there is little data on moisture removal from a two-layer porous media in which air is circulated through one layer parallel to the interface and moisture is removed from the finer second layer by evaporation. A conceptual model of the moisture removal from a two-layer porous media system was developed and compared to experimental moisture removal rates from laboratory scale dry barriers. The limited experimental data agrees well with the results predicted by the conceptual model, providing an initial validation. 相似文献