Stability of Volterra diffusion equations with time delays

This paper is concerned with asymptotic stability of a system of reaction-diffusion equations which is expressed in terms of Volterra integrals, under homogeneous Dirichlet boundary conditions. The effect of diffusion and delays on the stability of the system are analyzed, and sufficient conditions are given for the existence of positive solutions of the corresponding steady-state problem. Their global attraction with respect to nonnegative solutions of the time-dependent system is discussed. The main tools are Lyapunov functionals, positive definite kernels, and Laplace transforms.     

Theoretical studies of the band structure and optoelectronic properties of ZnOxS1−x

In the present article, we have revisited the electronic band gap nature of ZnO_xS_1?x (0 ≤ x ≤ 1) with the recently developed modified Becke and Johnson exchange potential and the calculated band gaps are found consistent with the experimental results. We expect that the band gap bowing parameter obtained in the present work will be close to the experimental one. As the optical properties of ZnO_xS_1?x (0 ≤ x ≤ 1) are very important, therefore different optical parameters like dielectric functions, refractive index and reflectivity are also calculated. The results are illustrated in terms of band structures, band gap energy as a function of oxygen composition, total and partial density of states. © 2012 Wiley Periodicals, Inc.     

Singular integral operators on product domains along twisted surfaces

We introduce a class of singular integral operators on product domains along twisted surfaces.We prove that the operators are bounded on L^p provided that the kernels satisfy weak conditions.     

Determination of zinc by square-wave adsorptive stripping voltammetry using alizarin as a chelating agent

The adsorptive collection of zinc(II) complex with alizarin ligand, coupled with the square-wave voltammetric technique at the hanging mercury drop electrode, yields a very sensitive electroanalytical procedure for the determination of zinc. The optimized experimental conditions include: supporting electrolyte (carbonate buffer), pH (11), alizarin concentration (1 × 10^?6 mol l^?1), accumulation time (60 s), accumulation potential (?0.1 V), scan rate (700 mV s^?1), pulse amplitude (0.06 V) and SW frequency (80 Hz). The monitored stripping voltammetric current was linear over the range of 5 × 10^?8 – 4 × 10^?7 mol l^?1 and the detection limit was 1 × 10^?8 mol l^?1. The relative standard deviation was calculated as 1.3% (n = 10) for 1 × 10^?8 mol l^?1 Zn(II) and the obtained electrochemical signal was stabile for up to 60 min. Possible interferences by either co-existing metal ions or other chelating agents were also investigated. The applicability of the proposed SW-AdSV method to the analysis of foodstuff was assessed by the determination of zinc content in instant coffee samples. The accuracy of the obtained voltammetric analytical results was validated by comparing with that obtained by atomic absorption spectrometric method and conducting the necessary statistical evaluation.     

Effect of ionic conductivity of a PAN–PC–LiClO<Subscript>4</Subscript> solid polymeric electrolyte on the performance of a TiO<Subscript>2</Subscript> photoelectrochemical cell

A nanoparticle TiO₂ solid-state photoelectrochemical cell has been fabricated. The effect of ionic conductivity of a solid electrolyte of polyacrylonitrile (PAN)–propylene carbonate (PC)–lithium perchlorate (LiClO₄) on the performance of a photoelectrochemical cell of indium tin oxide (ITO)/TiO₂/PAN–PC–LiClO₄/graphite has been investigated. A nanoparticle TiO₂ film was deposited onto ITO-covered glass substrate by controlled hydrolysis technique. A solid electrolyte of PAN–LiClO₄ with PC plasticizer prepared by solution casting technique was used as a redox couple medium. The room temperature conductivity of the electrolyte was determined by AC impedance spectroscopy technique. A graphite electrode was prepared onto a glass slide by electron beam evaporation technique. The device shows a photovoltaic effect under illumination. The short-circuit current density, J _sc, and open-circuit voltage, V _oc, vary with the conductivity of the electrolyte. The highest J _sc of 2.82 μA cm⁻² and V _oc of 0.56 V were obtained at the conductivity of 4.2 × 10⁻⁴ Scm⁻¹ and at the intensity of 100 mW cm⁻².     

Evaluation of glued-diaphragm fibre optic pressure sensors in a shock tube

Glued-diaphragm fibre optic pressure sensors that utilize standard telecommunications components which are based on Fabry–Perot interferometry are appealing in a number of respects. Principally, they have high spatial and temporal resolution and are low in cost. These features potentially make them well suited to operation in extreme environments produced in short-duration high-enthalpy wind tunnel facilities where spatial and temporal resolution are essential, but attrition rates for sensors are typically very high. The sensors we consider utilize a zirconia ferrule substrate and a thin copper foil which are bonded together using an adhesive. The sensors show a fast response and can measure fluctuations with a frequency up to 250 kHz. The sensors also have a high spatial resolution on the order of 0.1 mm. However, with the interrogation and calibration processes adopted in this work, apparent errors of up to 30% of the maximum pressure have been observed. Such errors are primarily caused by mechanical hysteresis and adhesive viscoelasticity. If a dynamic calibration is adopted, the maximum measurement error can be limited to about 10% of the maximum pressure. However, a better approach is to eliminate the adhesive from the construction process or design the diaphragm and substrate in a way that does not require the adhesive to carry a significant fraction of the mechanical loading.      

Fibril formation of lysozyme upon interaction with sodium dodecyl sulfate at pH 9.2

Fibril formation seems to be a general property of all proteins. Its occurrence in hen or human lysozyme depends on certain conditions, namely acidic pHs or the presence of some additives. This paper studies the interaction of lysozyme with sodium dodecyl sulfate (SDS) at pH 9.2, using UV-visible spectrophotometry, circular dichroism (CD) spectropolarimetry, electron microscopy (EM) and chemometry. Based on observations such as the strange increase in absorbance at 650nm (pH 9.2) and the presence of intermediates, it is assumed that lysozyme fibrils have been formed at pH 9.2 in the presence of SDS as an anionic surfactant. Thioflavin T emission fluorescence and an EM image confirmed this assumption. beta-cyclodextrin was then used as a turbidity inhibitor to establish its effect on the distribution of intermediates that participate in fibril formation.     

Xanthine oxidase inhibiting flavonol glycoside from Amberboa ramosa

A new flavonol glycoside (1) has been isolated from the ethyl acetate soluble fraction of Amberboa ramosa and assigned the structure 5,7,4'-trihydroxy-3,8-dimethoxylflavone 5-O-beta-D-gluco-pyranoside (1). In addition, 6,4'-dihydroxy-3,5,7-trimethoxyflavone (2), 5,7-dihydroxy-4'-methoxyflavone (3) and (23R)-5alpha-cycloart-24-ene-3beta,21,23-triol (4) have also been reported for the first time from this species. The structures were deduced on the basis of 1D and 2D NMR techniques. The compounds 1-3 displayed weak to moderate inhibition against the xanthine oxidase enzyme.     

Efficient photodegradation of resorcinol with Ag2O/ZnO nanorods heterostructure under a compact fluorescent lamp irradiation

Ag₂O/ZnO heterostructure has been recently synthesized using a facile chemical-precipitation method. X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy, and energy dispersive X-ray spectroscopy results confirmed the Ag₂O nanoparticles loading on ZnO nanorods. The Ag₂O addition increased the visible light absorption ability and a red shift for Ag₂O/ZnO heterostructure appeared when compared to pure ZnO. Photoluminescence spectra showed lower emission yield on the Ag₂O/ZnO heterostructure than on pure ZnO. Such a decrease in the emission yield represents the fraction of the excited state Ag₂O sensitizer involved in the charge injection process. Under compact fluorescent lamp irradiation, the Ag₂O/ZnO heterostructure demonstrated higher photocatalytic activity than pure ZnO in the degradation of resorcinol, which can be attributed to the high separation efficiency of the photogenerated electron-hole pairs based on the cooperative roles of Ag₂O loading on ZnO nanarods. All these characteristics represent a significant contribution of the Ag₂O/ZnO heterostructure to the practical applications in indoor environmental remediation.