Indirect determination of hexavalent chromium ion in complex matrices by adsorptive stripping voltammetry at a mercury electrode

A sensitive method for the determination of chromium ion(VI) in complex matrices such as crude oil and sludge is presented based on the decreasing effect of Cr(VI) on cathodic adsorptive stripping peak height of Cu-adenine complex. Under the optimum experimental conditions (pH 7.5 Britton-Robinson buffer, 5 × 10⁻⁵ M copper, 8 × 10⁻⁶ M adenine and accumulation potential −250 mV versus Ag/AgCl), a linear decrease of the peak current of Cu-adenine was observed, when the chromium(VI) concentration was increased from 5 μg L⁻¹ to 120 μg L⁻¹. Detection limit of 2 μg L⁻¹ was achieved for 120 s accumulation time. The relative standard deviations (R.S.D., %) were 1.8% and 4% for chromium(VI) concentrations of 18 μg L⁻¹ and 100 μg L⁻¹, respectively. The method was applied to the determination of chromium(VI) in the presence of high levels of chromium(III), in various real samples such as crude oil, crude oil tank button sludge, waste water and tap water samples. Effects of foreign ions and surfactants on the voltammetric peak and the influences of instrumental and analytical parameters were investigated in detail. The accuracy of the results was checked by ICP and/or AA.     

Morphology-dependent photonic circuit elements

We theoretically propose and experimentally demonstrate the design of a novel one-dimensional ringlike macroscopic optical circuit element. The similarity between morphologies of an optical planar waveguide and a whispering-gallery axially symmetric solid-state resonator is used.     

Transient response of laminated plates with arbitrary laminations and boundary conditions under general dynamic loadings

The dynamic analysis of laminated plates with various loading and boundary conditions is presented employing generalized differential quadrature (GDQ) method. The first-order shear deformation theory is considered to model the transient response of the plate. The GDQ technique together with Newmark integration scheme is employed to solve the system of transient equations governing dynamics of the plate. Different symmetric and asymmetric lamination sequences together with various combinations of clamped, simply supported, and free boundary conditions are considered. Particular interest of this study regards to asymmetric orthotropic plates having free edge and mixed boundary conditions. It is shown that the method provides reasonably accurate results with relatively small number of grid points. Comparison of the results with those of other methods demonstrates a very good agreement. It is also revealed that the present method offers similar order of accuracy for all variables including displacements and stress resultants.     

Lamb wave extraction of dispersion curves in micro/nano-plates using couple stress theories

In this paper, Lamb wave propagation in a homogeneous and isotropic non-classical micro/nano-plates is investigated. To consider the effect of material microstructure on the wave propagation, three size-dependent models namely indeterminate-, modified- and consistent couple stress theories are used to extract the dispersion equations. In the mentioned theories, a parameter called ‘characteristic length’ is used to consider the size of material microstructure in the governing equations. To generalize the parametric studies and examine the effect of thickness, propagation wavelength, and characteristic length on the behavior of miniature plate structures, the governing equations are nondimensionalized by defining appropriate dimensionless parameters. Then the dispersion curves for phase and group velocities are plotted in terms of a wide frequency-thickness range to study the lamb waves propagation considering microstructure effects in very high frequencies. According to the illustrated results, it was observed that the couple stress theories in the Cosserat type material predict more rigidity than the classical theory; so that in a plate with constant thickness, by increasing the thickness to characteristic length ratio, the results approach to the classical theory, and by reducing this ratio, wave propagation speed in the plate is significantly increased. In addition, it is demonstrated that for high-frequency Lamb waves, it converges to dispersive Rayleigh wave velocity.     

Improving anti-reflectivity and laser damage threshold of \hbox {SiO}_{2}/\hbox {ZrO}_{2} thin films by laser shock peening at 1064 nm

In this study, anti-reflection (AR) \(\hbox {SiO}_{2}/ \hbox {ZrO}_{2}\) thin films with 3-layers were designed and fabricated by the essential Macleod software and physical vapor deposition, respectively. In order to improve the optical and physical properties of the prepared samples, laser shock peening (LSP) technique was applied. For this purpose, an Argon Fluoride Excimer laser \((\lambda =193 \,\text {nm})\) with 110 and 240 mJ energies and 1 Hz frequency at different pulses was used. The effect of LSP method in improving transmissions and laser damage thresholds of the prepared samples was proved by using UV–Vis–IR spectroscopy in the wavelength range of 400–1200 nm and international standard ISO11254 at 1064 nm. In addition, scanning electron microscopy was used to check the effect of applying LSP.     

Determination of δ‐[L‐α‐aminoadipyl]‐L‐cysteinyl‐D‐valine in cell extracts of Penicillium chrysogenum using ion pair‐RP‐UPLC‐MS/MS

δ‐[L ‐α‐Aminoadipyl]‐L ‐cysteinyl‐D ‐valine (ACV) is a key intermediate in the biosynthesis pathway of penicillins and cephalosporins. Therefore, the accurate quantification of ACV is relevant, e.g. for kinetic studies on the production of these β‐lactam antibiotics. However, accurate quantification of ACV is a challenge, because it is an active thiol compound which, upon exposure to air, can easily react with other thiol compounds to form oxidized disulfides. We have found that, during exposure to air, the oxidation of ACV occurs both in aqueous standard solutions as well as in biological samples. Qualitative and quantitative determinations of ACV and the oxidized dimer bis‐δ‐[L ‐α‐aminoadipyl]‐L ‐cysteinyl‐D ‐valine have been carried out using ion pair reversed‐phase ultra high‐performance liquid chromatography, hyphenated with tandem mass spectrometry (IP‐RP‐UPLC‐MS/MS) as the analytical platform. We show that by application of tris(2‐carboxy‐ethyl)phosphine hydrochloride (TCEP) as the reducing reagent, the total amount of ACV can be determined, while using maleimide as derivatizing reagent enables to quantify the free reduced form only.     

Shellable quasi-forests and their h-triangles

In this paper we show that a quasi-forest is shellable if and only if its h-triangle satisfies ${h_{i,j}(\Delta)=0 \quad \forall i, \forall j >1 }$ . In addition, it will be shown that a quasi-forest is sequentially Cohen-Macaulay if and only if it is shellable.     

Polyampholytic Graft Copolymers as Matrix for TiO2/Eosin Y/[Mo3S13]2− Hybrid Materials and Light-Driven Catalysis

An effective strategy to enhance the performance of inorganic semiconductors is moving towards organic-inorganic hybrid materials. Here, we report the design of core–shell hybrid materials based on a TiO₂ core functionalized with a polyampholytic (poly(dehydroalanine)-graft-(n-propyl phosphonic acid acrylamide) shell (PDha-g-PAA@TiO₂). The PDha-g-PAA shell facilitates the efficient immobilization of the photosensitizer Eosin Y (EY) and enables electronic interactions between EY and the TiO₂ core. This resulted in high visible-light-driven H₂ generation. The enhanced light-driven catalytic activity is attributed to the unique core–shell design with the graft copolymer acting as bridge and facilitating electron and proton transfer, thereby also preventing the degradation of EY. Further catalytic enhancement of PDha-g-PAA@TiO₂ was possible by introducing [Mo₃S₁₃]²⁻ cluster anions as hydrogen-evolution cocatalyst. This novel design approach is an example for a multi-component system in which reactivity can in future be independently tuned by selection of the desired molecular or polymeric species.