Adsorption of short-chain thiols and disulfides onto gold under defined mass transport conditions: coverage, kinetics, and mechanism

The adsorption of water-soluble alkane thiols and their corresponding disulfides onto gold was followed in real time using highly sensitive surface conductivity measurements. Particular attention was paid to producing clean surfaces and to the purity of the adsorbates. The rate of mass transport to the surface was constant, controlled, and measured, over the whole time course of the experiment (1-10(4) s), by convective diffusion. An adsorption rate equation derived for coupled steady state convective-diffusion mass transport and Langmuir kinetics shows that systems limited by mass transport must also be slowed by Langmuir kinetics. Thiols and disulfides adsorbed at the same rate, limited mainly by mass transport. The distinct slowdown in adsorption rate for longer alkanethiols, attributed to conformational transitions (lying down → standing up), was less evident for the neutral thiols/disulfides. The slower rate of charged thiol adsorption is thought to stem from steric interactions of large, hydrated tail groups, although calcium as a counterion accelerated monolayer formation. The adsorption kinetics of a charged thiol were almost the same under screened (by extra added salt) or unscreened conditions. Therefore, long-range electrostatic interactions appear to be less important than short-range steric ones in limiting adsorption rates at surfaces.     

Extended benzodifuran–furan derivatives as example of π-conjugated materials obtained from sustainable approach

The synthesis of extended benzodifuran–furan systems are described as an example of π-conjugated materials prepared by following a green approach with only water being produced as waste and using furan derivatives from renewable sources. Investigation of their optical and electrochemical properties shows that the new compounds present electronic properties compatible for application in organic electronics.     

Inversion formulas for the reznitskaya transform and stability of lipschitz type in determination of initial heat distribution

In the Reznitskaya transform combining the solutions of some general linear partial differential equations of hyperbolic type and parabolic type, isometrical identities and inversion formulas are established. Furthermore, stability of Lipschitz type in the determination of initial heat distribution is given as an application.     

Strobovideolaryngoscopic Findings in Singing Teachers

Professional voice users often present to otolaryngologists and laryngologists with specific voice complaints. The contributions of pathologic lesions to the patients' vocal complaints are not always clear on examination, and often, premorbid examinations of the larynx are not available for review. This study examines the incidence of laryngeal pathology among singing teachers. At a national convention of singing teachers, volunteers were recruited for a "free strobovideolaryngoscopic examination." All volunteers completed a detailed questionnaire of their vocal and medical history and underwent strobovideolaryngoscopic examination. Strobovideolaryngoscopic examinations were completed in 20 volunteers, 7 of whom had voice complaints and 13 of whom perceived their voices to be normal. Vocal fold masses were common among the asymptomatic singing teachers. Evidence of reflux laryngitis was a common finding among both symptomatic and asymptomatic singing teachers. Asymmetries in vocal fold hypomobility were more common among those with voice complaints than was the presence of vocal fold masses in the population studied.     

Comparison between homotopy analysis method and optimal homotopy asymptotic method for nth‐order integro‐differential equation

This paper presents general framework for solving the nth‐order integro‐differential equation using homotopy analysis method (HAM) and optimal homotopy asymptotic method (OHAM). OHAM is parameter free and can provide better accuracy over the HAM at the same order of approximation. Furthermore, in OHAM the convergence region can be easily adjusted and controlled. Comparison, via two examples, between our solution using HAM and OHAM and the exact solution shows that the HAM and the OHAM are effective and accurate in solving the nth‐order integro‐differential equation. Copyright © 2011 John Wiley & Sons, Ltd.