Deposition of ZnS thin film by ultrasonic spray pyrolysis: effect of thickness on the crystallographic and electrical properties

Zinc sulfide (ZnS) thin films have been deposited on Si (1 0 0) substrate using ultrasonic spray pyrolysis. X-ray diffraction (XRD) analysis revealed that the films are (0 0 2) preferentially oriented with c-axis-oriented wurtzite structure. The crystallinity has been found to improve with film thickness in the 180–6000 nm range. Film structure has been analyzed by XRD, scanning electron microscope, FTIR, and Raman spectroscopies, while the stoichiometry has been verified by energy-dispersive spectroscopy and particle-induced X-ray emission techniques. Electrical properties of the grown films were characterized by current–voltage and capacitance–voltage measurements where, the films show better conducting behavior at higher thickness.     

Solvent selection in ultrasonic-assisted emulsification microextraction: Comparison between high- and low-density solvents by means of novel type of extraction vessel

There are numerous published reports about dispersive liquid phase microextraction of the wide range of substances, however, till now no broadly accepted systematic and purpose oriented selection of extraction solvent has been proposed. Most works deal with the optimization of available solvents without adequate pre-consideration of properness. In this study, it is tried to compare the performances of low- and high-density solvents at the same conditions by means of novel type of extraction vessel with head and bottom conical shape. Extraction efficiencies of seven basic pharmaceutical compounds using eighteen common organic solvents were studied in this work. It was much easier to work with high-density solvents and they mostly showed better performances. This work shows that although exact predicting the performance of the solvents is multifaceted case but the pre-consideration of initial selection of solvents with attention to the physiochemical properties of the desired analytes is feasible and promising. Finally, the practicality of the method for extraction from urine and plasma samples was investigated.     

A facile approach to prepare water-soluble magnetic metal (oxide) frameworks based on Na,Ca alginate and maghemite

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Sloshing waves in a heated viscoelastic fluid layer in an excited rectangular tank

In this paper, we have investigated the motion of a heated viscoelastic fluid layer in a rectangular tank that is subjected to a horizontal periodic oscillation. The mathematical model of the current problem is communicated with the linearized Navier–Stokes equation of the viscoelastic fluid and heat equation together with the boundary conditions that are solved by means of Laplace transform. Time domain solutions are consequently computed by using Durbin's numerical inverse Laplace transform scheme. Various numerical results are provided and thereby illustrated graphically to show the effects of the physical parameters on the free-surface elevation time histories and heat distribution. The numerical applications revealed that increasing the Reynolds number as well as the relaxation time parameter leads to a wider range of variation of the free-surface elevation, especially for the short time history.     

Shock waves for the hyperbolic balance laws with discontinuous sources

In this paper, we are concerned with the behavior of shock waves in a 2 × 2 balance law with discontinuous source terms. We obtain the existence of a local shock wave solution of this problem and deduce that the discontinuous source terms create a weak discontinuity in this solution. Copyright © 2013 John Wiley & Sons, Ltd.     

A numerical analysis of a class of generalized Boussinesq‐type equations using continuous/discontinuous FEM

An improved class of Boussinesq systems of an arbitrary order using a wave surface elevation and velocity potential formulation is derived. Dissipative effects and wave generation due to a time‐dependent varying seabed are included. Thus, high‐order source functions are considered. For the reduction of the system order and maintenance of some dispersive characteristics of the higher‐order models, an extra O(μ²ⁿ⁺²) term (n ∈ ?) is included in the velocity potential expansion. We introduce a nonlocal continuous/discontinuous Galerkin FEM with inner penalty terms to calculate the numerical solutions of the improved fourth‐order models. The discretization of the spatial variables is made using continuous P₂ Lagrange elements. A predictor‐corrector scheme with an initialization given by an explicit Runge–Kutta method is also used for the time‐variable integration. Moreover, a CFL‐type condition is deduced for the linear problem with a constant bathymetry. To demonstrate the applicability of the model, we considered several test cases. Improved stability is achieved. Copyright © 2011 John Wiley & Sons, Ltd.     

Design,preparation and characterization of Cu/GA/Fe3O4@SiO2 nanoparticles as a catalyst for the synthesis of benzodiazepines and imidazoles

The synthesis and characterization of an efficient and reusable nanocatalyst, Cu/GA/Fe₃O₄@SiO₂, obtained by ultrasonic‐assisted grafting of guanidineacetic acid on modified Fe₃O₄@SiO₂ core–shell nanocomposite spheres and subsequent immobilization of Cu(II), are described. The catalyst was characterized by means of X‐ray diffraction, scanning and transmission electron microscopies, energy‐dispersive X‐ray spectroscopy, elemental analysis, thermogravimetric analysis, Fourier transform infrared spectroscopy, vibrating sample magnetometry and inductively coupled plasma optical emission spectrometry. The prepared nanocatalyst facilitated an efficient and straightforward friendly procedure for the synthesis of benzodiazepines and imidazoles in ethanol and under solvent‐free conditions, respectively. The nanocatalyst can be easily recovered using a magnet and reused several times without any significant loss of activity. Copyright © 2016 John Wiley & Sons, Ltd.     

哈佛大学有效提升物理教学质量的举措分析

深入探讨了哈佛大学提升物理课程教学质量的举措,诸如卓越的教学方法、全面的教师培养、科学的教学指导、高效的教学评价等.哈佛大学的这些全面、细致、具体、实用的举措对我国大学物理教学质量的提升具有一定的借鉴意义.     

Silica iodide catalyzed,ultrasound-promoted,one-pot four-component synthesis of novel 1,4,5,6-tetrahydropyridine-3-carboxylate derivatives

Silica iodide catalyzed, competent synthesis of 15 novel substituted-1,4,5,6-tetrahydropyridine-3-carboxylate derivatives was achieved by a one-pot four-component cyclocondensation of Meldrum's acid, aryl aldehydes, aromatic amines and ethyl acetoacetate under ultrasonic irradiation. In comparison to the conventional methods, our protocol is convenient, eco-friendly and offers several benefits such as: mild conditions, high yields, shorter reaction time and ease in product isolation.