Search results for " solution"

Effect of several electrolytes on the rheopectic behaviour of concentrated soy lecithin dispersions

2005

Abstract Concentrated dispersions of soy lecithin (60 g/L) prepared by sonication-freezing–unfreezing method show a non-newtonian behaviour and a significant rheopexy. Shear stress versus shear rate plots shows a loop hysteresis area, which have been studied in soy lecithin dispersions prepared with aqueous solutions of various electrolytes (NaCl, CaCl2, MgCl2 and AlCl3) with concentrations in the range 10−5 to 10−2 mol/L. Also we have studied the effect of different pH on soy lecithin dispersions. The results have revealed a very sensitive influence of nature, valence and concentration of the respective cations and the pH value on the loop hysteresis area values. It seems to indicate that …

Probabilistic response of linear structures equipped with nonlinear dampers devices (PIS method)

2008

Passive control introducing energy absorbing devices into the structure has received considerable attention in recent years. Unfortunately the constitutive law of viscous fluid dampers is highly nonlinear, and even supposing that the structure behaves linearly, the whole system has inherent nonlinear properties. Usually the analysis is performed by a stochastic linearization technique (SLT) determining a linear system equivalent to the nonlinear one, in a statistical sense. In this paper the effect of the non-Gaussianity of the response due to the inherent nonlinearity of the damper device will be studied in detail via the Path Integral Solution (PIS) method. A systematic study is conducted…

Secondary Chemical Equilibria in Reversed-Phase Liquid Chromatography

2013

The addition of reagents to an RPLC mobile phase enables the separation of ionizable compounds, inorganic anions, and metal ions using conventional instrumentation, silica-based materials, and hydro-organic mixtures, thanks to a variety of secondary equilibria. This gives rise to several chromatographic modes, whose main features are outlined in this chapter. The effect of the mobile phase pH on the retention of ionizable compounds is described, together with the recommended experimental practice. The mechanism of adsorption of amphiphilic anions or cations on the stationary phase to attract analytes with opposite charge or suppress the silanol activity is discussed. Different reagents, suc…

Multiarm cyclam-grafted mesoporous silica: a strategy to improve the chemical stability of silica materials functionalized with amine ligands

2009

We have explored in this work the stability and the reactivity of multiarm cyclam-grafted mesoporous silica samples in aqueous solution. A series of hybrid materials have been prepared by grafting silylated cyclam molecules bearing one, two, or four silyl groups onto both amorphous silica gel (K60) and ordered mesoporous silica (SBA15). Under these conditions, cyclam moieties are attached to the silica walls via one, two, or four arms. Various physicochemical techniques have been applied to characterize the functionalized solids (elemental analysis, 1H-29Si and 1H-13C CPMAS NMR, and N2 adsorption-desorption isotherms). The interest in two and four arms for improving the chemical stability i…

Green synthesis of silver nanoparticles mediated by Pulicaria glutinosa extract

2013

Mujeeb Khan,1 Merajuddin Khan,1 Syed Farooq Adil,1 Muhammad Nawaz Tahir,2 Wolfgang Tremel,2 Hamad Z Alkhathlan,1 Abdulrahman Al-Warthan,1 Mohammed Rafiq H Siddiqui1 1Department of Chemistry, College of Science, King Saud University, Riyadh, Kingdom of Saudi Arabia; 2Institute of Inorganic and Analytical Chemistry, Johannes Gutenberg-University of Mainz, Mainz, Germany Abstract: The green synthesis of metallic nanoparticles (NPs) has attracted tremendous attention in recent years because these protocols are low cost and more environmentally friendly than standard methods of synthesis. In this article, we report a simple and eco-friendly method for the synthesis of silver NPs using an aqueous…

Bioprospective of Sorbus aucuparia leaf extract in development of silver and gold nanocolloids

2010

At the present time the bioprospective field is a dynamic area of research. The rapid biosynthesis of silver and gold nanoparticles without using toxic chemicals is reported here. Sorbus aucuparia is omnipresent in Europe. The aqueous leaves extract of the plant were used as reducing agent for the synthesis of silver and gold nanoparticles from their salt solutions. The synthesized nanoparticles were spherical, triangular and hexagonal in shape with an average size of 16 and 18nm for silver and gold, respectively. Different extract quantities, metal concentrations, temperatures and contact times were investigated to find their effect on nanoparticles synthesis. The resulting silver and gold…

Laser-Ablation-Induced Synthesis of SiO2-Capped Noble Metal Nanoparticles in a Single Step

2010

Here we describe a simple, powerful technique based on the laser ablation of a target immersed in a water solution of a metal salt. With this method, nanoparticles of different metals and alloys can be processed very quickly. Both the target and the salt solution can be chosen to produce metal nanoparticles of different sizes, surface-oxidized nanoparticles (silica-silver, for example), or even more complex structures to be defined by the researcher on one or more steps because the technique combines the advantages of both physical and chemical methods. We have applied this technique to the fabrication of inert silica-metal (silver, gold, and silver-gold) nanoparticles with a strong surface…

Geometric Singular Perturbation Theory Beyond Normal Hyperbolicity

2001

Geometric Singular Perturbation theory has traditionally dealt only with perturbation problems near normally hyperbolic manifolds of singularities. In this paper we want to show how blow up techniques can permit enlarging the applicability to non-normally hyperbolic points. We will present the method on well chosen examples in the plane and in 3-space.

New solvability conditions for the Neumann problem for ordinary singular differential equations

2000

A mathematical approach to predicting the percutaneous absorption enhancing effect of sodium lauryl sulphate.

2003

A study has been made of the effect of sodium lauryl sulphate (SLS) at several concentrations from 0.24 to 5% (w/w) on skin permeability. Seven model drugs were selected for this study on the basis of their lipophilicity as represented by their logP(oct) values (from -0.95 to 4.2). Skin pre-treatment with aqueous solutions of SLS does not increase the permeability coefficient of the most lipophilic compounds (logP(oct)> or =3). For the other compounds assayed the increase in the permeability coefficients depends on the concentration of SLS used in the skin pre-treatment, and on the lipophilicity of the compounds tested.The correlation between the inverse of SLS efficacy as an enhancer (1/ER…