A new sensitive optical bulk test-system for thallium based on pyridylazo resorcinol

A color changeable optode for thallium(III) ions in aqueous solutions was prepared by physical inclusion of 4-(2-pyridylazo)-resorcinol into a plasticized PVC film. The increase in the absorbance of the optode at 524 nm is proportional to thallium(III) concentration. Different parameters effecting the sensitivity such as sample parameters and composition of the membrane were optimized. The response times of the prepared test-system are found to be 230, 210, and 180 s for 4.8 × 10^?6, 4.8 × 10^?5, and 4.8 × 10^?4 M Tl(III), respectively. The analytical performance of the optode was evaluated, obtaining a linear concentration range of two decades of concentration, 3.1 × 10^?6 ? 4.7 × 10^?4 M Tl(III), with a limit of detection of 1.8 × 10^?6 M Tl(III). Selectivity of the optode is also studied. Application of the optode to the determination of Tl(III) in some aqueous samples yields good results.     

A micro-discharge photoionization detector for micro-gas chromatography

We report on a small (20?×?10 mm) micromachined device for the detection of gases in micro-gas chromatography (GC). It incorporates a micro-discharge across a 20-μm gap, and a remote electrode in the micro cavity that generates an electrical signal corresponding to the photo-ionization of gaseous analytes in a stream of carrier gas. Multi-component mixtures were detected and the results compared to those obtained with a flame ionization detector. The minimum detectable limit is 350 pg.μL^?1 of n-octane in air when applying a 1.4 mW discharge. The combination of wet etching of glass (as used for microfluidic channels) with a lift-off process for detector electrodes by a robust batch process results in a universal, non-destructive, and sensitive microdetector for micro-GC.

Dilute magnetic semiconductor and half-metal behaviors in C-codoped BeO nanotubes: A first principles simulations

The geometric, electronic and magnetic properties of C-codoped single walled BeO nanotubes (SWBeONTs) are systematically explored by using ab-initio density functional theory calculations. We performed our calculations for C codoping BeO nanotube in two different chiralities: (8,0) and (5,5). In each case, two different configurations are considered, first the two oxygen atoms replaced by two carbon atoms are on first nearest neighbor sites in the plane of codoping and second they are far from each other. We found when C atoms are at the nearest-neighboring positions; the antiferromagnetism (AFM) phase is stable while increasing the distance between the two C atoms, the ferromagnetism stability increases. In the AFM phase the structures are nonmagnetic semiconductors, but in the FM phase all these systems are half-metallic systems with high magnetic moment and 100% spin polarization which can be used as magnetic nanostructure and possible future applications in permanent magnetism, magnetic recording, and spintronics.     

One-pot synthesis of organo-silica hybrids with high thermal properties via a simple sol–gel process

Journal of Thermal Analysis and Calorimetry - Organic–inorganic hybrid composites have received much attention of scientists in the recent years due to the notable improvement of thermal...     

Synthesis and Characterization of Co3O4 Nanoparticles by Thermal Treatment Process

The simple preparation of Co₃O₄ nanoparticles from a solid metallorganic molecular precursor [bis(salicylaldehydeato)cobal(II)]; [Co(sal)₂] has been achieved via two simple steps: firstly, the [Co(sal)₂] precursor was precipitated from the reaction of cobalt(II) acetate and salicylaldehyde; in propanol under nitrogen condition; then, cubic phase Co₃O₄ nanoparticles with the size of mostly 20–30 nm could be produced by thermal treatment of the [Co(sal)₂] in air at 500 °C for 5 h. The as-synthesized products were characterized by powder XRD, FT-IR, TEM and SEM. The results confirm that the resulting oxide was pure single-crystalline Co₃O₄ nanoparticles. The optical absorption spectrum indicates that the direct band gaps of Co₃O₄ nanoparticles are 1.53 and 2.02 eV. The optical property test indicates that the absorption peak of the nanoparticles shifts towards short wavelength, and the blue shift phenomenon might be ascribed to the quantum effect. The hysteresis loops of the obtained samples reveal the ferromagnetic behaviors the enhanced coercivity (H _c ) and decreased saturation magnetization (M _s ) in contrast to their respective bulk materials.     

Transient thermal stresses in two-dimensional functionally graded thick hollow cylinder with finite length

In this paper transient thermal stresses in a thick hollow cylinder with finite length made of two-dimensional functionally graded material (2D-FGM) based on classical theory of thermoelasticity are considered. The volume fraction distribution of materials, geometry and thermal load are assumed to be axisymmetric but not uniform along the axial direction. The finite element method with graded material properties within each element is used to model the structure. Temperature, displacements and stress distributions through the cylinder at different times are investigated. Also the effects of variation of material distribution in two radial and axial directions on the thermal stress distribution and time responses are studied. The achieved results show that using 2D-FGM leads to a more flexible design so that time responses of structure, maximum amplitude of stresses and uniformity of stress distributions can be modified to a required manner by selecting suitable material distribution profiles in two directions.     

Numerical Study of Ignition Process in Turbulent Shear-less Methane-air Mixing Layer

In this work, ignition process in a turbulent shear-less methane-air mixing layer is numerically investigated. A compressible large eddy simulation method with Smagorinsky sub-grid scale model is used to solve the flow field. Also, a thickened flame combustion model and DRM-19 reduced mechanism are used to compute species distribution and the heat release. Non-reacting mean and RMS axial velocity profiles and mean mixture fraction are validated against experimental data. Instantaneous mixture fraction contours show that the large bursts penetrate from the fuel stream into that of the oxidizer and vice versa and a random behaviour in the cross-stream direction. Flame kernel initiation, growth and propagation are analysed and compared with the experimental data. The ignition results show that the flame is not stable and blow-off occurs, but a more detailed investigation shows that local and short time flame stabilization exist during blow-off. During these local stabilization, heat release increased at the upstream edge of the flame. Most_upstream flame edge scalar analysis shows that the methane mass fraction has a dominant role in the local flame stabilization. OH, HO₂, CH₂O and heat release contours demonstration reveal that HO₂ and CH₂O mass fraction as well as the heat release reach a maximum on the border of the flame, but the maximum OH concentration is located in the middle of flame kernel.     

Force coefficients and Strouhal numbers of three circular cylinders subjected to a cross-flow

In this paper, wind tunnel experiments were conducted to measure the mean force coefficients and Strouhal numbers for three circular cylinders of equal diameters in an equilateral-triangular arrangement when subjected to a cross-flow. These experiments were carried out at five subcritical Reynolds numbers ranging from 1.26 × 10⁴ to 6.08 × 10⁴. The pressure distributions on the surface of the cylinders were measured using pressure transducers. Furthermore, the hot-wire anemometer was employed to measure the vortex shedding frequencies behind each cylinder. Six spacing ratios (l/d) varying from 1.5 to 4 were investigated. It is observed that for l/d > 2, the upstream cylinder experiences a lower mean drag coefficient compared with the downstream cylinders. The minimum values of the drag coefficient for the downstream cylinders occur at l/d = 1.5 and l/d = 2, because there is no vortex shedding from the foregoing cylinders. Also, the value of the pressure coefficient behind the upstream cylinder reduces by increasing l/d. Moreover, by decreasing the value of l/d, the Strouhal number for the upstream cylinder increases. It can be concluded that the flow pattern and aerodynamic coefficients are basically dependent on l/d; in other words, decreasing l/d results in an increase in the effects of the flow interference between the cylinders.     

Synthesis of cobalt nanoparticles from [bis(2-hydroxyacetophenato)cobalt(II)] by thermal decomposition

[Bis(2-hydroxyacetophenato)cobalt(II)] was used as a new precursor to prepare cobalt (Co) and tricobalt tetraoxide (Co₃O₄) nanoparticles of 15–25 nm in average diameter by thermal decomposition. The different combinations of triphenylphosphine, and oleylamine were added as surfactants to control the particle size. The products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and Fourier transform infrared (FT-IR) spectroscopy. Time-dependent FT-IR studies indicate that oxidation of the as-synthesized cobalt nanoparticles in air is slow. The valence change of cobalt from the nanoparticle sample is not observed after it is kept in hexane under air for 30 days. The magnetic property was studied with vibrating sample magnetometer (VSM). The hysteresis loops of the obtained samples reveal the soft magnet behaviors the enhanced coercivity (H_c) and decreased saturation magnetization (M_s) in contrast to their respective bulk materials.     

Thermal decomposition of [bis(salicylaldehydato)cadmium(II)] to CdS nanocrystals

The present investigation reports, the novel synthesis of nanocrystals CdS using thermal decomposition of [bis(salicylaldehydato)cadmium(II)], as a new precursor, and elemental sulfur in oleylamine. The as-synthesized CdS crystals have diameters about 10 nm. The products were characterized by X-ray diffraction (XRD) transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), ultraviolet–visible (UV–Vis) spectroscopy and Fourier transformed infrared (FT-IR) spectra. The results of this paper show that the shape and size of cadmium sulfide nanocrystals can be controlled systematically by adjusting certain reaction parameters, such as the reactant concentration, the reaction temperature and the reaction time. Cadmium sulfide nanoparticles and nanorods with different lengths have been successfully prepared.