Fabrication of mesoporous metal chalcogenide nanoflake silica thin films and spongy mesoporous CdS and CdSe

Mesoporous silica metal oxide (ZnO and CdO) thin films have been used as metal ion precursors to produce the first examples of mesoporous silica metal sulfide (meso-SiO(2) @ZnS, meso-SiO(2) @CdS) or silica metal selenide (meso-SiO(2) @ZnSe, meso-SiO(2) @CdSe) thin films, in which the pore walls are made up of silica and metal sulfide or metal selenide nanoflakes, respectively. A gentle chemical etching with a dilute HF solution of the meso-SiO(2) @CdS (or meso-SiO(2) @CdSe) produces mesoporous cadmium sulfide (meso-CdS) (or cadmium selenide, meso-CdSe). Surface modified meso-CdS displays bright blue photoluminescence upon excitation with a UV light. The mesoporous silica metal oxides are formed as metal oxide nanoislands over the silica walls through a self-assembly process of a mixture of metal nitrate salt-two surfactants-silica source followed by calcination step. The reactions, between the H(2) S (or H(2) Se) gas and solid precursors, have been carried out at room temperature and monitored using spectroscopy and microscopy techniques. It has been found that these reactions are: 1)?taking place through the diffusion of sulfur or selenium species from the top metal oxide layer to the silica metal oxide interface and 2)?slow and can be stopped at any stage to obtain mesoporous silica metal oxide metal sulfide or silica metal oxide metal selenide intermediate thin films.     

Bäcklund’s Theorem for n Dimensional Lorentzian Submanifold in the Minkowski Space {\mathbb{E}_1^2n-1}

In this paper, Bäcklund’s Theorem is introduced on the Lorentzian n-submanifold of the Minkowski space \({\mathbb{E}_{1}^{2n-1}}\) by using the method of moving frames. Also, we prove the Integrability Theorem for the Lorentzian n-submanifold of the Minkowski space \({\mathbb{E}_{1}^{2n-1}}\).     

Invariant optical soliton solutions to the Coupled-Higgs equation

Optical and Quantum Electronics - A series of barium zinc borophosphate glasses doped with copper oxide was prepared for optical filters. The phosphate network exhibited P–O bonds in...     

HPLC–based methods for the determination of levetiracetam in biological and pharmaceutical samples

Levetiracetam is one of the new generation anti–epileptic agents (also known as anticonvulsants or antiseizure drugs). Following its approval for marketing in 2000, levetiracetam has been widely used in the treatment of epilepsy due to its broad spectrum effects. One of the advantages of this antiseizure drug is its rapid and complete absorption after oral administration. It has also minimal drug–drug and food interactions, and shows more than 95% bioavailability. The determination of levetiracetam in various samples is carried out using several analytical methods including HPLC–based methods. HPLC–based methods are used for different pharmaceutical analyses and play an important role in drug monitoring during patient follow–ups. This review provides a summary of the HPLC–based methods used in the determination and quantification of levetiracetam in biological fluids and pharmaceutical preparations.     

Effects of mechanical activation on the non-isothermal kinetics of mullite formation from kaolinite

The non-isothermal kinetics of mullite formation from both non-activated and mechanically activated kaolinite have been studied by differential thermal analysis (DTA). Kaolinite was mechanically activated in a planetary mill, while amorphization in the structure was studied by X-ray diffraction analysis. It was established that the mechanical activation especially affected the loss of structural water. The activation energies depending on the conversion for mullite formation have been calculated from the DTA curves by using the non-isothermal method of Coats and Redfern at heating rates of 5, 10, 15, and 20 °C min⁻¹. The mechanical activation and amorphization of the kaolinite brings to the formation of mullite at a lower heating temperature.     

On the reactivity of μ2-acetylenes coordinated to cobalt : II. Regiospecifity of the carbonylation of internal acetylenes

The μ₂-carbonyl- μ₂-spiro(2,3-substituted-2-butene-4-olide-4-ylidene)bis(tricarbonylcobalt)(CoCo), Co₂(CO)₇(C₄O₂R¹R²), “lactone” complexes were prepared from internal acetylenes. It was found that the reaction is regiospecific; in the products from an asymmetric internal alkyne the sp carbon atom which had the higher value of the ¹³C NMR chemical shift (δ) occupied the 2-, while that with the lower δ value the 3-position of the lactone ring. fa]For Part I, see ref. 1. Some results or this work were presented at the Annual Meeting of the Hungarian Chemical Society (MKE Vegyészkonferencia), Aug. 23–26, 1977. Debrecen. Abstracts (Elöadások összefoglalói) p. 156     

Investigation of bacterial adherence to a non-precious alloy with radiolabeling method

Summary The objective of this study was to investigate the bacterial adherence to a non-precious alloy with radiolabeling method. S. mutans, E. coliand C. albicanswere labeled with ^99mTc by using stannous chloride and their radiolabeling yields were calculated. After the labeling procedure, metal disks (3 mm×10 mm) were treated with microorganisms. The amount of labeled microorganisms adhered on metal surfaces was determined by activity measurements. The labeling yields for S. mutans, E. coliand C. albicanswere 69.95±7.58%, 78.84±0.44% and 79.71±10.17%, respectively. The mean values for adherence for S. mutans, E. coliand C. albicanson metal samples were 7.02±2.18%, 0.96±0.49% and 8.80±8.24%, respectively. The radiolabeling method could be considered as safe and precise for determining the adherence of microorganisms.     

Electrochemical Oxidation of ds‐DNA on Polypyrrole Nanofiber Modified Pencil Graphite Electrode

Preparation of a polypyrrole nanofiber (PPyNF) modified pencil graphite (PG) electrode and its usage in the electrochemical DNA biosensors was investigated. The electrodes (PPyNF/PG1 and PPyNF/PG2) were prepared from a solution containing 0.1 M pyrrole, 0.1 M Na₂CO₃ and 0.1 M LiCIO₄ by using potentiostatic and potentiodynamic methods. PPyNF/PG2 electrodes which were prepared by potentiostatic procedure showed higher responses for the oxidation of ds‐DNA than the PPyNF/PG1 electrodes prepared by potentiodynamic methods. Immobilization of the ds‐DNA on PG and PPyNF/PG surfaces was performed at a constant potential, +0.5 V, for 300 s in 0.5 M ABS (pH 4.8) containing 15 μg mL^?1 ds‐DNA and 20 mM LiCIO₄. The oxidation peak potentials of the ds‐DNA bases, guanine and adenine, were shifted to more cathodic values by using PPyNF/PG electrodes. The oxidation signal of the guanine base of ds‐DNA was decreased in the presence of methylene blue.     

Forced convective heat transfer in porous medium of wire screen meshes

The hydrodynamic and heat transfer characteristics of a porous medium consisting of 20 wire screen meshes are examined theoretically and experimentally. The hydrodynamic experiments are conducted for the range of Reynolds number based on mean velocity and wire diameter from 1.5 to 12. The Ergun's constants and thermal dispersion coefficients are calculated in this range. Nusselt number variation is determined in both thermally developing and fully developed flows by the help of forced convection heat transfer experiments conducted for the uniform heat flux boundary condition. Correlation functions of Nusselt number in the range of fully developed and thermally developing, and of thermal entrance length are obtained from experimental data. Solutions of momentum and energy equations simulating the experimental model are obtained numerically with variable porosity and the anticipated thermal dispersion coefficients. The thermal dispersion coefficients well-adjusted to the experimental data are determined by numerical solution of the energy equation. Received on 22 November 1996