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71.
Lanthanum cobaltite oxide, LaCoO3, was prepared by the evaporation technique and the amorphous metal complex method. Powders were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and surface area measurements. The effect of the synthesis route on the phase purity, particle size, surface area, and morphology of the powders was studied. A single perovskite phase was synthesized at 700°C using the amorphous metal complex route. However, the evaporation technique required higher temperature for LaCoO3 crystallization. Based on the characterization results, low temperature formation of LaCoO3 was attributed to the homogeneity of the precursors. Such behavior also results in different microstructures. Powder synthesized by the amorphous metal complex method exhibited the highest surface area and the lowest particle size. 相似文献
72.
In this article we consider a class of first order nonlinear integro-differential equations with delay. We propose new approach for investigating local and global existence of the solutions of its Cauchy problem. This approach gives new results. 相似文献
73.
We study the backward problem for non-linear (semilinear) parabolic partial differential equations in Hilbert spaces. The problem is severely ill-posed in the sense of Hadamard. Under a weak a priori assumption on the exact solution, we propose a new Fourier truncated regularization method for stabilising the ill-posed problem. In comparison with previous studies on solving the nonlinear backward problem, our method shows a significant improvement. 相似文献
74.
Remon M. Zaki Adel M. Kamal El-Dean Shaban M. Radwan Mokhtar A. Abd ul-Malik 《中国化学会会志》2020,67(4):658-673
In the present investigation, a simple and straightforward methodology for the preparation of novel bifunctional thienopyrazolopyrazines 4a–d has been reported. Synthesis of thieno or furopyrazolopyrazines 5a , b , e , f was achieved by the reaction of o-amino-esters 4a , b , e , f with 2,5-dimethoxytetrahydrofuran. The latter pyrrolyl derivatives 5a , b , e , f were used as starting intermediates for the synthesis of new pyrimido, pyrido, and pyrazino heterocycles fused to the thieno or furopyrazolopyrazine moiety. Furthermore, alkaline hydrolysis of the o-amino-ester 4a followed by acidification afforded the corresponding o-amino carboxylic acid 15 , which was used as a versatile precursor for the synthesis of other heterocyclic compounds fused to the thienopyrazolopyrazine ring system, namely: pyrimidine, oxazine, oxazepine, and pyridine derivatives 16–23 . The chemical structures of the synthesized compounds were confirmed on the basis of elemental and spectral analyses (Fourier-transform infrared spectroscopy [FT-IR], 1H nuclear magnetic resonance [NMR], and mass spectroscopy [MS] in addition to 13C NMR for some of them). Moreover, from the biological screening, we found that most of the tested compounds exhibited promising antifungal, antibacterial, and anti-inflammatory activities compared with the corresponding reference drugs. 相似文献
75.
Mokhtar Mabrouk Sherin F. Hammad Mohamed A. Abdelaziz Fotouh R. Mansour 《Chemistry Central journal》2018,12(1):143
Ligand exchange method is introduced as an alternative to Job’s and mole ratio methods for studying the stoichiometry of relatively weak metal complexes in solutions. The method involves adding varying amounts of a ligand (L) to an excess constant amount of a colored complex (MX) with appropriate stability and molar absorptivity. The absorbance of each solution is measured at the λmax of the initial complex, MX, and plotted against the concentration of the studied ligand, L. If the newly formed complex ML does not absorb at the λmax of the initial complex, then attenuation of the absorbance of the initial complex on adding varying quantities of the investigational ligand gives an inverse calibration line that intersects with the calibration curve of initial complex at a given point. If a line parallel to the ordinate is drawn from this point to the x-axis, the ratio of the two parts of the x-axis to the left and to the right (α/β) gives the metal to ligand molar ratio in the complex formed, ML. The new method has been applied to the study of the composition of iron (III) complexes with three bisphosphonate drugs: alendronate, etidronate, and ibandronate. The mole ratio was found to be 1:1 with the three investigated bisphosphonates and results were further confirmed by Job’s and mole ratio methods. The ligand exchange method is simpler, quicker, easier to perform and more accurate than Job’s and mole ratio methods for studying weak and relatively weak complexes.
相似文献
76.
We consider the question of whether the simple random walk (SRW) on an infinite tree is transient or recurrent. For random-trees (all vertices of distancen from the root of the tree have degreed
n
, where {d
n
} are independent random variables), we prove that the SRW is a.s. transient if lim inf
n
n
E(log(d
n-1))>1 and a.s. recurrent if lim sup
n
n E(log(d
n-1))<1. For random trees in which the degrees of the vertices are independently 2 or 3, with distribution depending on the distance from the root, a partial classification of type is obtained.Research supported in part by NSF DMS 8710027. 相似文献
77.
On a nonlocal problem for the Laplace equation in the unit ball with fractional boundary conditions 下载免费PDF全文
Mokhtar Kirane Berikbol T. Torebek 《Mathematical Methods in the Applied Sciences》2016,39(5):1121-1128
In this paper, we investigate the correct solvability for the Laplace equation with a nonlocal boundary condition in the unit ball. The considered boundary operator is of fractional order. This problem is a generalization of the well‐known Bitsadze–Samarskii problem. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
78.
G. A. El-Shobaky Th. El-Nabarawy G. A. Fagal M. Mokhtar 《Journal of Thermal Analysis and Calorimetry》1996,46(5):1473-1481
V2O5/Al2O3 solids of varying compositions were prepared, dried at 100°C and calcined in air at 400–1000°C. The solid-solid interactions between the mixed oxides were investigated by means of DTA, TG and XRD techniques.The results revealed that ammonium metavanadate and aluminium hydroxide decomposed at 260 and 290°C, respectively, to yield an ammonium vanadium intermediate compound and Al2O3 as solids. The intermediate compound readily decomposed at 360°C to give V2O5.Solid V2O5 generally catalyses the crystallization of Al2O3 to an extent proportional to its amount present. The solid-solid interactions between Al2O3 and V2O3 to produce AlV2O4 and AlVO4 took place at 750 and 900°C. These solids decomposed entirely at 1000°C, producing V2O5 and alpha-corundum. The pure Al2O3 samples employed existed as amorphous solids even when heated in air at 750°C, but in the presence of V2O5 (7–18 wt.%) they crystallized to thetaalumina at 600°C. The pure solid alumina crystallized at 1000°C to a mixture of theta and kappa-alumina. In the presence of V2O5, alpha-corundum together with kappa and theta phases was obtained on heating at 900°C. 相似文献
79.
80.
A new mesoporous organic–inorganic nanocomposite was formulated and then used as stabilizer and support for the preparation of palladium nanoparticles (Pd NPs). The properties and structure of Pd NPs immobilized on prepared 1,4‐diazabicyclo[2.2.2]octane (DABCO) chemically tagged on mesoporous γ‐Fe2O3@hydroxyapatite (ionic modified (IM)‐MHA) were investigated using various techniques. The synergistic effects of the combined properties of MHA, DABCO and Pd NPs, and catalytic activity of γ‐Fe2O3@hydroxyapatite‐DABCO‐Pd (IM‐MHA‐Pd) were investigated for the Heck cross‐coupling reaction in aqueous media. The appropriate surface area and pore size of mesoporous IM‐MHA nanocomposite can provide a favourable hard template for immobilization of Pd NPs. The loading level of Pd in the nanocatalyst was 0.51 mmol g?1. DABCO bonded to the MHA surface acts as a Pd NP stabilizer and can also lead to colloidal stability of the nanocomposite in aqueous solution. The results reveal that IM‐MHA‐Pd is highly efficient for coupling reactions of a wide range of aryl halides with olefins under green conditions. The superparamagnetic nature of the nanocomposite means that the catalyst to be easily separated from solution through magnetic decantation, and the catalytic activity of the recycled IM‐MHA‐Pd showed almost no appreciable loss even after six consecutive runs. 相似文献