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81.
Physical and thermodynamic properties have been calculated and analyzed for the best and optimized geometries of the 3‐D clusters with N = 3 to N = 10 atoms and unit cells of three types of crystalline systems using ab initio RHF/6–31G** method. Dependence of the lattice binding energy on the cluster parameter, R, has been studied. Similar behavior observed for the binding energies for all clusters shows that probabilities of their existence in the condensed phase are more or less the same. In the next step, thermodynamic properties have been calculated and analyzed for He27 3‐D helium clusters with simple cubic, body centered cubic (bcc), trigonal and hexagonal (hcp) configurations. The results show that the hexagonal cluster is more favored over other clusters. It is found that these clusters are electronically stable over a limited range of the values for the lattice parameter. ΔfH is constant in this stability region and thus the ΔfG exactly follows the variations of TΔfS. Surface effects have been investigated by comparing the square and hexagonal He9 2‐D lattices with the cubic and hexagonal He27 3‐D lattices, respectively. The lattice parameters, densities and molar volumes calculated for the clusters with hcp and bcc configurations have satisfactory agreement with the available experimental values. Properties of the He13, He34 and He104 hcp clusters have also been calculated and analyzed. 相似文献
82.
We analyze the network of cross-border bank lending connections among countries from 1977 to 2018. The network includes core countries that lend money and peripheral countries that borrow money from core countries. In nowadays highly connected banking network, financial crisis that start from a country can spread to other countries very fast and cause global affects. We use principal component analysis (PCA) to find the influential lending (core) countries in this network over the years and clusters of borrowing (peripheral) countries related to these impactful core countries. We find three clusters of peripheral countries, with some constant and some changing members over time. This can be a sign of changes in the financial or political interactions among countries. The changes in the role of core countries and how these roles get affected by the important financial crisis in the past decades is investigated. Among 31 of core countries, 7 countries have a partially or constantly important role in the network including France, United Kingdom, United States, Japan, Germany, Chinese Taipei and Switzerland. 相似文献
83.
Majid Masteri-Farahani Faezeh Farzaneh Mehdi Ghandi 《Reaction Kinetics and Catalysis Letters》2008,95(2):379-384
The sythesis, characterization and catalytic activity of WO2pypr [N,N′-bis (2-pyrrolmethlidenaminopropyl) amine] complexed to MCM-41 surface in the epoxidation of some alkenes with excellent
selectivity toward the corresponding epoxides is described in this presentation. 相似文献
84.
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86.
Novel derivatives of pyrido-[2,3-d] pyrimidines were synthesized via an efficient and catalyst- free, one-pot, three-component reaction of 3-(1-methyl-1H-pyrrol-2-yl)-3-oxopropanenitrile, 6-amino-(ethylthio)pyrimidine-4(3H)-one, and arylaldehydes under ultrasonic irradiations. This practical method furnished the desired pyridopyrimidines in high yields (79–89%) and short reaction times (25–40 min). 相似文献
87.
In this work, the complex magnitude of the dielectric constant of a thin film of ZnO nano-particles has been obtained in the range of visible spectrum. Using this spectrum, the UV–visible absorptive spectrum of ZnO spherical nano-colloid is obtained using Mie theory. The absorption spectrum of ZnO nano-colloid has been related to the optical properties of the prepared thin film with a simulation model based on the Mie theory and the findings are corroborated by fitting with the experimental results. Based on this curve fitting, the volume fraction of nanoparticles in the nano-colloid is obtained and the diameter (and the Bohr radius) of the molecules contributing in a nanoparticle crystal structure has been obtained. In this paper, frequency dependence of the optical properties coefficients and also local field considerations are applied. Finally the precise magnitude of saturation intensity of ZnO nano-colloid is measured. 相似文献
88.
Hazeghi Farzaneh Mozaffari Samaneh Ghorashi Seyed Mohammad Bagher 《Journal of Solid State Electrochemistry》2020,24(6):1427-1438
Journal of Solid State Electrochemistry - Cu-Ni bimetallic organic frameworks were synthesized by a facile and stepwise solvothermal method, utilizing metal organic framework as precursor.... 相似文献
89.
As a result of this study, a new and simple method was proposed for the fabrication of an ultra sensitive, robust and reversible ammonia gas sensor. The sensing mechanism was based upon the change in electrical resistance of a graphene aerogel as a result of sensor exposing to ammonia. Three-dimensional graphene hydrogel was first synthesized via hydrothermal method in the absence or presence of various amounts of thiourea. The obtained material was heated to obtain aerogel and then it was used as ammonia gas sensor. The materials obtained were characterized using different techniques such as Fourier transform infra red spectroscopy (FT-IR), thermal gravimetric analysis (TGA), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The thiourea-treated graphene aerogel was more porous (389 m2 g−1) and thermally unstable and exhibited higher sensitivity, shorter response time and better selectivity toward ammonia gas, compared to the aerogel produced in the absence of thiourea. Thiourea amount, involved in the hydrogel synthesis step, was found to be highly effective factor in the sensing properties of finally obtained aerogel. The sensor response time to ammonia was short (100 s) and completely reversible (recovery time of about 500 s) in ambient temperature. The sensor response to ammonia was linear between 0.02 and 85 ppm and its detection limit was found to be 10 ppb (3S/N). 相似文献
90.