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861.
Zayani Jaafar Othman Adel Matoussi Francesca Rossi Giancarlo Salviati 《Applied Physics A: Materials Science & Processing》2014,117(3):1515-1524
The present work investigates the structural and dielectric properties of Zn1?x Mg x O composites prepared by the standard sintering method at 1200 °C during 24 h and doped with different weight percentages of MgO (x = 0–40 %). For this purpose, the scanning electron microscopy (SEM) was used to study the effect of the magnesium’s proportion on the morphology and crystallinity of the obtained samples. The SEM observations have shown rougher surfaces of the samples covered by grains having prismatic shapes and different sizes. The dielectric properties of the ceramics were investigated by spectroscopic impedance at different temperatures and frequencies, thus showing a frequency-dependent dispersion of the permittivity constants and dielectric losses. From these measurements, the relaxation processes were identified and their activation energies extracted. Dielectric responses were correlated with the microstructure and chemical composition of the ZnMgO composites. The mechanisms of ac conductivity are controlled by the polaron hopping and the electron tunneling models. Concerning the tunneling model, two types corresponding to the overlapping large polaron tunneling model for the composites Zn0.9Mg0.1O and Zn0.8Mg0.2O and the small polaron tunneling model for the composites Zn0.64Mg0.36O (in the frequency range 1.7 × 104 Hz–1 MHz) and Zn0.6Mg0.4O were observed. Besides, one type of hopping model corresponding to the correlated barrier hopping for the composites ZnO and Zn0.64Mg0.36O (in the frequency range 6 × 102–1.7 × 104 Hz) was noted. 相似文献
862.
The optical properties of CdxZn1−xS thin films on glass substrate prepared by spray pyrolysis method
A series of CdxZn1−xS thin films have been deposited on glass substrates using spray pyrolysis technique. The crystallinity and microstructure of CdxZn1−xS thin films have been investigated by X-ray diffraction (XRD). Based on the results of Hall measurements, the films obtained were an n-type semiconductor. The X-ray data analysis of CdxZn1−xS thin films showed that the grain size of the CdxZn1−xS increased with increase in Cd composition. It is observed that the band gap increases as the Cd composition decreases. The results also showed a blue shift of absorption edge of optical transmission spectra is increases as Zn ratio increases. The effects of Cd composition on the structural and optical properties of CdxZn1−xS thin films were related to their grain size, stress and carrier concentration. 相似文献
863.
864.
We consider the task of design optimization where the constraint is a state equation that can only be solved by a typically rather slowly converging fixed point solver. This process can be augmented by a corresponding adjoint solver and based on the resulting approximate reduced derivatives also an optimization iteration which actually changes the design. To coordinate the three iterative processes, we use an exact penalty function of doubly augmented Lagrangian type. The main issue here is how to derive a design space preconditioner for the approximated reduced gradient which ensures a consistent reduction of the employed penalty function as well as significant design corrections. Some numerical experiments for an alternating approach where any combination and sequencing of steps are used to improve feasibility and optimality done on a variant of the Bratu problem are presented. 相似文献
865.
Adel Jawahdou 《Nonlinear Analysis: Theory, Methods & Applications》2011,74(18):7325-7332
In this paper, we study the existence of mild solutions for initial value problems for semilinear Volterra integrodifferential equations in a Banach space. The arguments are based on the concept of measure of noncompactness in Fréchet space and the Tikhonov fixed point theorem. 相似文献
866.
Mesoporous RuO2–TiO2 nanocomposites at different RuO2 concentrations (0–10 wt %) are prepared through a simple one‐step sol–gel reaction of tetrabutyl orthotitanate with ruthenium(III) acetylacetonate in the presence of an F127 triblock copolymer as structure‐directing agent. The thus‐formed RuO2–TiO2 network gels are calcined at 450 °C for 4 h leading to mesoporous RuO2–TiO2 nanocomposites. The photocatalytic CH3OH oxidation to HCHO is chosen as the test reaction to examine the photocatalytic activity of the mesoporous RuO2–TiO2 nanocomposites under UV and visible light. The photooxidation of CH3OH is substantially affected by the loading amount and the degree of dispersion of RuO2 particles onto the TiO2, which indicates the exclusive effect of the RuO2 nanoparticles on this photocatalytic reaction under visible light. The measured photonic efficiency ξ=0.53 % of 0.5 wt % RuO2–TiO2 nanocomposite for CH3OH oxidation is maximal and the further increase of RuO2 loading up to 10 wt % gradually decreases this value. The cause of the visible‐light photocatalytic behavior is the incorporation of small amounts of Ru4+ into the anatase lattice. On the other hand, under UV light, undoped TiO2 shows a very good photonic efficiency, which is more than three times that for commercial photocatalyst, P‐25 (Evonik–Degussa); however, addition of RuO2 suppresses the photonic efficiency of TiO2. The proposed reaction mechanism based on the observed behavior of RuO2–TiO2 photocatalysts under UV and visible light is explored. 相似文献
867.
Kandiel TA Ismail AA Bahnemann DW 《Physical chemistry chemical physics : PCCP》2011,13(45):20155-20161
Mesostructured TiO(2) nanocrystals have been prepared using Pluronic F127 as the structure-directing agent. Platinum nanoparticles at different contents (0.1-1.0 wt%) have been photochemically deposited onto the mesoporous TiO(2). TEM investigation of 0.2 wt% Pt/TiO(2) calcined at 450 °C reveals that the TiO(2) particles are quite uniform in size and shape with the particle sizes of TiO(2) and Pt being 10 and 3 nm, respectively. The photocatalytic activities of the Pt loaded TiO(2) have been assessed and compared with those of nonporous commercial Pt/TiO(2)-P25 by determining the rates and the photonic efficiencies of molecular hydrogen production from aqueous methanol solutions. The results show that the amount of hydrogen evolved on Pt/TiO(2)-450 at low Pt loading (0.2 wt%) is three times higher than that evolved on Pt/TiO(2)-P25 and twelve times higher than that evolved on Pt/TiO(2)-350. Despite the BET surface area of the TiO(2)-450 photocatalyst being 3.5 times higher than that of TiO(2)-P25, a 60% smaller amount of the Pt co-catalyst is required to obtain the optimum photocatalytic hydrogen production activity. The reduced Pt loading on the mesoporous TiO(2) will be important both from a commercial and an ecological point of view. 相似文献
868.
Mosa AI Emara AA Yousef JM Saddiq AA 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2011,81(1):35-43
A new series of stable transition metal complexes of the formula M(L)X·S, where M = Cu(II), Ni(II), Co(III), Cr(III) and Fe(III) and L is the deprotonated ligand of 4-hydroxy-coumarin-3-thiocarbohydrazone, X = Cl(-), NO(3)(-) or CH(3)COO(-) and S = H(2)O and/or EtOH. The HL ligand was prepared by the reaction of 3-formyl-4-hydroxy-coumarine with thiocarbohydrazide in the molar ratio 1:1. The HL ligand and its metal complexes were characterized by elemental analysis, (1)H NMR, IR and electronic spectra, and molar conductance and magnetic measurements and thermal gravimetric analysis (TGA). The HL ligand acts as a monobasic tridentate ONS donor in all metal complexes, and coordinated through the phenolic OH, azomethine nitrogen and thione sulfur. Electronic spectra with magnetic moments suggested varieties of geometries around the central metal atoms. Thermal gravimetric analysis indicates that the complexes are stable up to 300°C, and release the uncoordinated and/or coordinated H(2)O/solvent molecules, which is accompanied by a color change. The formed complexes after releasing the solvent were investigated and their structures are suggested to have square planar or octahedral arrangement. Pharmacodynamic of cobalt(III) complex on some biochemical parameters and histological studies in serum and heart tissue in rats have been studied. Although the complexes demonstrated a significant effect at low dose than the high dose, the ligand showed significant good effects in both high and low doses on the biochemical analysis in serum and heart tissue. Cobalt complex was screened in order to evaluate its antifungal activity against the filamentous fungi Aspergillus niger, Aspergillus fumigatus, and Aspergillus flavus, and antibacterial activity against the Candida albicans, Escherichia coli, Klebseilla pneumoniae and Pseudomonas aeruginosa. 相似文献
869.
López-Vallejo F Caulfield T Martínez-Mayorga K Giulianotti MA Nefzi A Houghten RA Medina-Franco JL 《Combinatorial chemistry & high throughput screening》2011,14(6):475-487
Virtual screening is increasingly being used in drug discovery programs with a growing number of successful applications. Experimental methodologies developed to speed up the drug discovery processes include high-throughput screening and combinatorial chemistry. The complementarities between computational and experimental screenings have been recognized and reviewed in the literature. Computational methods have also been used in the combinatorial chemistry field, in particular in library design. However, the integration of computational and combinatorial chemistry screenings has been attempted only recently. Combinatorial libraries (experimental or virtual) represent a notable source of chemically related compounds. Advances in combinatorial chemistry and deconvolution strategies, have enabled the rapid exploration of novel and dense regions in the chemical space. The present review is focused on the integration of virtual and experimental screening of combinatorial libraries. Applications of virtual screening to discover novel anticancer agents and our ongoing efforts towards the integration of virtual screening and combinatorial chemistry are also discussed. 相似文献
870.