Single‐phase flow in composite poroelastic media

The mathematical formulation and analysis of the Barenblatt–Biot model of elastic deformation and laminar flow in a heterogeneous porous medium is discussed. This describes consolidation processes in a fluid‐saturated double‐diffusion model of fractured rock. The model includes various degenerate cases, such as incompressible constituents or totally fissured components, and it is extended to include boundary conditions arising from partially exposed pores. The quasi‐static initial–boundary problem is shown to have a unique weak solution, and this solution is strong when the data are smoother. Copyright © 2002 John Wiley & Sons, Ltd.     

Ligand-mediated formation of Cu/metal oxide hybrid nanocrystals with tunable number of interfaces

Combining domains of different chemical nature within the same hybrid material through the formation of heterojunctions provides the opportunity to exploit the properties of each individual component within the same nano-object; furthermore, new synergistic properties will often arise as a result of unique interface interactions. However, synthetic strategies enabling precise control over the final architecture of multicomponent objects still remain scarce for certain classes of materials. Herein, we report on the formation of Cu/MO_x (M = Ce, Zn and Zr) hybrid nanocrystals with a tunable number of interfaces between the two domains. We demonstrate that the organic ligands employed during the synthesis play a key role in regulating the final configuration. Finally, we show that the synthesized nanocrystals serve as materials platforms to investigate the impact of the Cu/metal oxide interfaces in applications by focusing on the electrochemical CO₂ reduction reaction as one representative example.

We report on the formation of Cu/metal oxide hybrid nanocrystals with a tunable number of interfaces between the two domains. We demonstrate that the organic ligands employed during the synthesis play a key role in regulating the final configuration.     

Survey of segregation alteration of hydrogen-helium mixtures via structure factor

In this study, thermodynamic instabilities in hydrogen-helium fluid mixture have been analyzed. These kinds of investigations are inevitable for indicating hydrodynamic transitions in Hydrogen-Helium fluid mixture. Therefore, first we have derived equation of state of mixture via Barker-Henderson statistical perturbation theory. Moreover, we have used Yiping radial distribution function in calculating perturbed terms. Via equation of state, we have calculated excess Gibbs free energy and the Gibbs free energy in the long wavelength limit. By means of this energy in hand we could estimate degree of hetero-coordination and segregations of this mixture which is a measure for defining thermodynamic instabilities. At last, these measurements have made us capable of anticipating thermodynamic instabilities and coordination of mixture in different concentrations.     

Introduction of PEG-SANM nanocomposite as a new and highly efficient reagent for the promotion of the silylation of alcohols and phenols and deprotection of the silyl ethers

Poly (ethylene glycol)-sulfonated sodium montmorillonite (PEG-SANM) nanocomposite was prepared by a simple method and characterized using XRD, TGA, SEM, TEM, and FT-IR techniques. After preparation and characterization, this reagent was used as a highly efficient and reusable solid acid catalyst for the chemoselective silylation of alcohols and phenols and deprotection of the obtained silyl ethers. The method offers several advantages including high to excellent yields of the products, short reaction times, easy preparation of the catalyst and easy work-up procedure. In addition, the catalyst can be recycled and reused at least for five times without significant decrease in the catalytic activity.     

Green dispersive solid-phase microextraction of melamine using crosslinked beta-cyclodextrin with citric acid followed by high-performance liquid chromatography

In this research, a green approach for dispersive solid phase microextraction was introduced for the extraction and determination of melamine in various matrices such as infant formula and hot water in a melamine bowl. In this way, a natural polar polymer called ß-cyclodextrin has been cross-linked with citric acid to create a water-insoluble adsorbent. The extraction was carried out by dispersion of the sorbent into the sample solution. The effective parameters on the extraction efficiency of the melamine, including ion strength, extraction time, sample volume, amount of absorbent, pH, type of desorption solvent, desorption time, and desorption solvent volume were optimized by one variable at a time approach. Under the optimal conditions, the method showed a good linear dynamic range for melamine in the range of 1–1000 μg/L with a coefficient of determination of 0.9985. The obtained limit of detection was 0.3 μg/L. The intra-day and inter-day relative standard deviations (n = 3) were 3.1% and 3.2% respectively. Lastly, this technique was applied to extract and determine the analyte in a melamine bowl and infant formula with acceptable and satisfactory results.     

Flame atomic absorption spectrometric determination of μg amounts of Fe (III) ions after solid phase extraction using modified octadecyl silica membrane disks

A simple, rapid and reliable method has been developed to selectively separate and concentrate ultra trace amounts of Fe (III) ions from aqueous samples for the measurement by flame atomic absorption spectrometry (FAAS). By the passage of aqueous samples through an octadecyl silica membrane disk modified by a recently synthesized Schiff base (Bis-(4-nitro phenyl azo) salisilidine-1,3-diamino propane), Fe(III) ions adsorb quantitatively and most of matrix elements will pass through the disk to drain. The retained iron ions are then stripped from the disk by minimal amount of 0.1 mol l^− 1 sulfuric acid as eluent. Extraction efficiency and the influence of pH, flow rates, amount of ligand, type and least amount of stripping acid as eluent were evaluated. The recovery of the iron from aqueous solution on the membrane disk modified with 3 mg Schiff's base was quantitative over pH 2–4.5.