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排序方式: 共有198条查询结果,搜索用时 31 毫秒
81.
Kralj Slavko Rojnik Matija Kos Janko Makovec Darko 《Journal of nanoparticle research》2013,15(5):1-11
Electrode catalysts composed of carbon-supported PtRu nanoparticles (PtRu/C) for use as a direct methanol fuel cell anode were synthesized by the reduction of precursor ions in an aqueous solution via irradiation with a high-energy electron beam. The effect of pH control in the precursor solution on the PtRu mixing state and the methanol oxidation activity was studied in order to enhance the catalytic activity for methanol oxidation. The PtRu/C structures were characterized by transmission electron microscopy, inductively coupled plasma atomic emission spectrometry, X-ray fluorescence spectrometry, and X-ray diffraction and X-ray absorption fine structure techniques. The methanol oxidation activity was evaluated by linear sweep voltammetry. The initial pH of the precursor solution has little influence on the average grain size for the metal particles (approximately 3.5 nm) on the carbon particle supports, but the dispersibility of the metal particles, PtRu mixing state, and methanol oxidation activity differed. The maintenance of a low pH in the precursor solution gave the best dispersibility of the PtRu nanoparticles supported on the surface of the carbon particles, whereas, a high pH gave the best PtRu mixing state and the highest oxidation current although a low dispersibility of the PtRu nanoparticles supported on the surface of the carbon particles was obtained. The PtRu mixing state strongly correlated with the methanol oxidation current. In addition, a high pH was more effective for PtRu mixing when using an electron beam irradiation reduction method, because the complexation reaction of the chelating agents was improved, which resulted in an enhancement of the catalytic activity for methanol oxidation. 相似文献
82.
Let H be an infinite-dimensional complex Hilbert space and let B(H) be the algebra of all bounded linear operators on (H). In the paper the equivalent definition of the star partial order on B(H), using selfadjoint idempotent operators, is introduced. Also some properties of the generalized concept of order relations on B(H), defined with the help of idempotent operators, are investigated. 相似文献
83.
The gas‐phase proton affinities (PAs) for a set of molecules with vinamidine structure are considered and their basicities in acetonitrile. It is shown that introducing double bonds to the imidazoline rings at the proton attachment site resulted in decrease in PA of the parent vinamidine. The increase in PA can be obtained by inducing modifications to the imidazoline ring at the junction of two diazepinylium rings. Placing methyl and dimethylamino substituents on the perimeter of the molecule further increased their gas‐phase PAs. Studied vinamidine molecules are superbases, which possess PA values in the range between 261.0 and 284.2 kcal mol–1 in the gas phase and pKa values of 24.6–31.9 units in acetonitrile. Dismembering proton attachment site by opening the two diazepinylium and imidazoline rings resulted in the largest drop in PA values, indicating its importance in constraining the positions of imino nitrogen atoms in the neutral form of the molecule. Vinamidine molecules studied here present important pieces of the ladder of highly basic organic compounds for they possess accessible vinamidine molecular framework. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
84.
Janko?Lu?nik Janez?Pirnat Zvonko?Trontelj Toma??Apih Alan?Gregorovi? 《Applied magnetic resonance》2009,36(1):115-120
The field application of a 14N nuclear quadrupole resonance (NQR) detector needed for the detection of different explosives, including trinitrotoluene
(TNT), requires the examination of the distribution of 14N NQR lines stemming from the monoclinic and/or orthorhombic modifications of TNT, as well as from a mixture of both. In this
work, 30 different TNT samples up to 70 years old were measured. The main result of this study is that the measured 14N NQR spectrum is strongly influenced by the environmental conditions to which the explosive was subject during its history. 相似文献
85.
Janko Latschev 《manuscripta mathematica》2006,121(3):293-315
We describe a homological criterion for the existence of a closed form transverse to a foliation which is allowed to have certain tame singularities, generalizing results in the nonsingular case by Sullivan. As illustrations of the method, we derive results about the existence of singular symplectic forms and about the characterization of intrinsic harmonicity for forms. 相似文献
86.
87.
The influence ofγ 60 Co radiation on some of the electrical properties of single crystals of triglycinsulphate irradiated under various conditions was studied with special emphasis on the temperature autostabilization regime. The smallest changes in these properties occur with crystals whose temperature during irradiation is kept above the Curie temperature and which are at the same time exposed to the effects of a strong alternating electric field, and with crystals which are kept in the temperature autostabilization regime during irradiation. The changes caused by irradiation can be partly eliminated by additionally bringing the crystals into the autostabilization regime (renovation). 相似文献
88.
Janko Gravner 《Transactions of the American Mathematical Society》1996,348(11):4549-4559
This paper defines a general Euclidean growth model via a translation invariant, monotone and local transformation on Borel subsets of . The main result gives a geometric condition for the boundary curvature of the iterates to go to 0. Consequences include estimates for the speed of convergence to the asymptotic shape, and a result about survival of Euclidean deterministic forest fires.
89.
It is shown that the total SCF molecular energies are fairly well reproduced by the sum of electrostatic potentials exerted on the nuclei calculated in the point-charge approximation. Hence, there is a very simple relation between the total energies and formal atomic charges in molecules. The semiempirical SCC-MO charges have the same performance as the ab initio DZ ones. 相似文献
90.
Karla Saric Zvonimir Janovic Otto Vogl 《Journal of polymer science. Part A, Polymer chemistry》1983,21(7):1913-1928
The terpolymerization of acrylonitrile with styrene and 2,3-dibromopropyl acrylate in emulsion and dimethyl formamide solution was investigated. Polymerizations, when stopped at low conversions, yielded terpolymers that showed good agreement between experimental and theoretical copolymerization composition data, calculated from the Alfrey-Goldfinger equation. The relationship between monomer feed and terpolymer compositions is displayed on triangular coordinate graphs proposed by Slocombe. By using a computer program the lines of unique composition and binary azeotropic composition for both systems were established. In the case of emulsion polymerization the azeotropic ternary point was determined at a molar ratio for acrylonitrile/styrene/2,3-dibromopropyl acrylate of 0.27/0.61/0.12. The experimental results of emulsion terpolymerization fit the calculated curves satisfactorily over a wide range of monomer compositions up to high conversions. The influence of 2,3-dibromopropyl acrylate on the thermal and flammability characteristics of the terpolymers is described. 相似文献