On the Green function in visco‐elastic media obeying a frequency power‐law

In this work, we present an explicit expression for the Green function in a visco‐elastic medium. We choose Szabo and Wu's frequency power law model to describe the visco‐elastic properties and derive a generalized visco‐elastic wave equation. We express the ideal Green function (without any viscous effect) in terms of the viscous Green function using an attenuation operator. By means of an approximation of the ideal Green function, we address the problem of reconstructing a small anomaly in a visco‐elastic medium from wavefield measurements. Copyright © 2011 John Wiley & Sons, Ltd.     

A generic approach to measuring the machine flexibility of manufacturing systems

Despite extensive studies on the flexibility of manufacturing systems over the last two decades, a unified measurement approach has not been developed. To this end, we integrate two domains of machine flexibility models from the literature: operational capability-based machine flexibility and time and cost-based machine flexibility, and propose a generic model to measure machine flexibility with consideration of uncertainties in the system. Furthermore, in our approach we include part characteristics such as processing time and processing cost, the number of operations that a machine can perform, and uncertainties in demand and machine-part assignment. The resulting framework to measure machine flexibility is a two-stage model: a super efficiency Data Envelopment Analysis Model and a flexibility model. The results show that the marginal system machine flexibility does not always increase as the number of operations that a machine can perform increases, and the system machine flexibility depends on the demand uncertainty.     

Microstructure and properties of 3,3′,4,4′‐biphenyltetracarboxylic dianhydride (BPDA)‐p‐phenylene diamine (PDA) polyimide/poly(vinylsilsesquioxane) hybrid nanocomposite films

Hybrid nanocomposite films of poly(vinylsilsesquioxane) (PVSSQ) and polyimide (PI) (PI/PVSSQ) were prepared via sol‐gel process from triethoxyvinylsilane (VSSQ) and thermal imidization from 3,3′,4,4′‐biphenyltetracarboxylic dianhydride (BPDA)‐p‐phenylene diamine (PDA) polyamic acid (BPDA‐PDA PAA). We investigated the microstructure; interfacial interaction; and optical, thermal, dielectric, and mechanical properties of the hybrid films. The phase morphologies and degree of surface roughness were evaluated by scanning electron microscope (SEM) and atomic force microscope (AFM), respectively. It was found that the surface topography was influenced by the composition of PVSSQ. Hydrogen bonding interactions between polyimide (PI) matrix and PVSSQ domains were proved with FT‐IR spectroscopy. The transparency of the hybrid films was found to be dependent on the PVSSQ content. Incorporating of the PVSSQ in the hybrid composites increased the glass transition temperature of PI. Dielectric constants of the hybrid films were in the range of 2.37–3.59. Properties of the PI films were also significantly enhanced by adding 5–30 wt % of PVSSQ. For comparison, we also prepared the hybrid composites of PI and mixtures of VSSQ and tetraethoxysilane (TEOS) and the PI/silica hybrid composite containing 30 wt % of silica obtained from TEOS. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5189–5199, 2004     

Capillary electrophoresis for the analysis of antidepressant drugs: A review

Depression is a common mental disorder that may lead to major mental health problems, and antidepressant drugs have been used as a treatment of choice to mitigate symptoms of major depressive disorders by ameliorating the chemical imbalances of neurotransmitters in brain. Since abusing antidepressant drugs such as selective serotonin reuptake inhibitors and tricyclic antidepressant drugs can cause severe adverse effects, continuous toxicological monitoring of the parent compounds as well as their metabolites using numerous analytical methods appears pertinent. Among them, capillary electrophoresis has been popularly utilized since the method has a lot of advantages viz. using small amounts of sample and solvents, ease of operation, and rapid analysis. This review paper brings a survey of more than 30 papers on capillary electrophoresis of antidepressant drugs published approximately from 1999 until 2018. It focuses on the reported capillary electrophoresis techniques and their applications and challenges for determining antidepressant drugs and their metabolites. It is organized according to the commonly used capillary zone electrophoresis method, followed by non‐aqueous capillary electrophoresis and micellar electrokinetic chromatography, with details on breakthrough findings. Where available, information is given about the background electrolyte used, detector utilized, and sensitivity obtained.     

Ion chromatography on carbon clad zirconia modified by diazonium chemistry and functionalized latex particles

This work explores the potential of 3 μm carbon coated zirconia particles as a stationary phase for ion chromatography for the separation of organic acids and inorganic ions. A 4-phenylsulfonic acid functionality is introduced onto the carbon surface by reducing 4-phenylsulfonic acid diazonium chloride with borohydride in the presence of carbon clad zirconia particles. The elemental sulfur analysis gave 132 μeq-SO(3)H/g carbon clad zirconia and 2% S atomic concentration by XPS analysis. The -SO(3)(-) groups serve as electrostatic anchors for latex nanoparticles bearing quaternary triethylamine functional groups. The agglomeration step in 5 × 0.4 cm i.d. columns converts the packed particles into an anion exchanger. The breakthrough curves with nitrate indicate a capacity of 3 μeq/column. Separation of common organic acids and inorganic ions using carbonate eluent and suppressed conductivity detection yield plate heights (H) of 0.023-0.05 mm.     

Studies on the sensitivity of yttrium by electrothermal atomization from metallic and metal-carbide surfaces of a heated graphite atomizer in atomic absorption spectrometry

Atomization of yttrium in tube-type electrothermal atomizers was studied using various atomization surfaces: pyrocoated graphite surface, carbidized graphite surface and tantalum or tungsten metal surfaces. Carbidizing of pyrocoated graphite tubes with other carbide-forming metals (Ta, Zr or La) produces refractory metal-carbide surfaces thereby preventing the carbide-forming yttrium to come in physical contact with the reactive graphite surface. The result is an enhancement in the analytical sensitivity (peak height absorbance) of yttrium. The atomization of Y from a metal surface (Ta or W) gives better analytical sensitivity, lower atomization temperature, and negligible memory effect compared with those from metal-carbidized surfaces.