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排序方式: 共有286条查询结果,搜索用时 187 毫秒
71.
72.
Radoslav Kefirov Elena Ivanova Konstantin Hadjiivanov Stanislaw Dzwigaj Michel Che 《Catalysis Letters》2008,125(3-4):209-214
Fe3+–OH groups of a Fe–H–BEA sample prepared by conventional ion-exchange method are characterized by an IR band at 3686–3684 cm?1. They exhibit a weak acidity: upon low-temperature CO adsorption the O–H stretching modes are blue shifted by 100 cm?1 and the respective carbonyl adducts are observed at 2158 cm?1. The Fe3+–OH groups are reduced at room temperature by NO to form Fe2+–NO species and NO+ groups in cationic positions. Desorption of pre-adsorbed NO at temperatures above 373 K regenerates the Fe3+–OH groups. The relation of the Fe3+–OH species to the so-called α-oxygen is discussed. 相似文献
73.
The aim of this study was investigation of changes in the modified near-surface layer on the NiTi shape memory alloy, caused by ion implantation as well as their influence on the mechanical and shape memory properties of this material. Surface of NiTi has been modified by nitrogen ion beam at several fluences 1 × 1017 cm?2, 1 × 1018 cm?2 and 2 × 1018 cm?2 at the energy 50 keV. The effect of implantation parameters on surface characteristics and wear properties was investigated using dry-sliding-wear test, depth sensing indentation test and scanning profilometry method. The experimental results have shown how the ion implantation treatment can change the original surface: reducing Ni content in the surface, increasing the surface hardness (furthermore, the hardness improvement extended to the regions much deeper than the implanted layer), and improving the sliding wear resistance. The experimental results of surface treatment conditions and mechanical properties of the modified NiTi alloys are compared, analyzed and discussed in this paper. 相似文献
74.
Dynamic bounds for power and efficiency of non-ideal energy converters under nonlinear transfer laws
We present a thermodynamic approach to simulation and modeling of nonlinear energy converters, in particular radiation engines. Novel results are obtained especially for dynamical engines when the temperature of the propelling medium decreases in time due to a continual decrease of the medium's internal energy caused by the power production. Basic thermodynamic principles determine the converter's efficiency and work limits in terms of the entropy production. The real work is a cumulative effect obtained in a system of a resource fluid, a sequence of engines, and an infinite bath. Nonlinear modeling involves dynamic optimization in which the classical expression for efficiency at maximum power is generalized to endoirreversible machines and nonlinear transfer laws. The primary result is a finite-rate generalization of the classical, reversible work potential (exergy). The generalized work function depends on thermal coordinates and a dissipation index, h, i.e. a Hamiltonian of the minimum entropy production problem. This generalized work function implies stronger bounds on work delivered or supplied than the reversible work potential. The role of the nonlinear analyses and dynamic optimization is shown especially for radiation engines. As an example of the kinetic work limit, generalized exergy of radiation fluid is estimated in terms of finite rates, quantified by the Hamiltonian h. 相似文献
75.
Mercury emissions to the atmosphere from anthropogenic sources in Europe in 2000 and their scenarios until 2020 总被引:1,自引:0,他引:1
Pacyna EG Pacyna JM Fudala J Strzelecka-Jastrzab E Hlawiczka S Panasiuk D 《The Science of the total environment》2006,370(1):147-156
The paper reviews the current state of knowledge regarding European emissions of mercury and presents estimates of European emissions of mercury to the atmosphere from anthropogenic sources for the year 2000. This information was then used as a basis for Hg emission scenario development until the year 2020. Combustion of coal in power plants and residential heat furnaces generates about half of the European emissions being 239 tonnes. The coal combustion is followed by the production of caustic soda with the use of the Hg cell process (17%). Major points of mercury emission generation in the mercury cell process include: by-product hydrogen stream, end box ventilation air, and cell room ventilation air. This technology is now being changed to other caustic soda production technologies and further reduction of Hg emissions is expected in this connection. The third category on the list of the largest Hg emitters in Europe is cement production (about 13%). The largest emissions were estimated for Russia (the European part of the country), contributing with about 27% to the European emissions, followed by Poland, Germany, Spain, Ukraine, France, Italy and the United Kingdom. Most of these countries use coal as a major source of energy in order to meet the electricity and heat demands. In general, countries in the Central and Eastern Europe generated the main part of the European emissions in 2000. Emission reductions between 20% and 80% of the 2000 emission amounts can be obtained by the year 2020, as estimated by various scenarios. 相似文献
76.
Multi‐objective design optimization of antennas for reflection,size, and gain variability using kriging surrogates and generalized domain segmentation 下载免费PDF全文
Cost‐efficient multi‐objective design optimization of antennas is presented. The framework exploits auxiliary data‐driven surrogates, a multi‐objective evolutionary algorithm for initial Pareto front identification, response correction techniques for design refinement, as well as generalized domain segmentation. The purpose of this last mechanism is to reduce the volume of the design space region that needs to be sampled in order to construct the surrogate model, and, consequently, limit the number of training data points required. The recently introduced segmentation concept is generalized here to allow for handling an arbitrary number of design objectives. Its operation is illustrated using an ultra‐wideband monopole optimized for best in‐band reflection, minimum gain variability, and minimum size. When compared with conventional surrogate‐based approach, segmentation leads to reduction of the initial Pareto identification cost by over 20%. Numerical results are supported by experimental validation of the selected Pareto‐optimal antenna designs. 相似文献
77.
Two problems involving the use of dynamic lists in Pascal are (1) the limited size of the heap and (2) the difficulty in creating copies of complex multi-linked structures. Both these problems can be solved by writing the appropriate segment of memory to a file on disk. The heap segment may then be released. To recover the structure during a later phase of processing, the contents of the file can be transferred back onto the heap. This paper presents an algorithm to implement this solution. 相似文献
78.
79.
80.
Tadeusz Biedron Krystyna Brzezinska Przemyslaw Kubisa Stanislaw Penczek 《Polymer International》1995,36(1):73-80
Macromonomers were obtained by cationic polymerization of propylene oxide and epichlorohydrin proceeding by the activated monomer mechanism with hydroxyethyl acrylate as initiator. Up to DP n ~ 15 for propylene oxide and DP n ~ 20 for epichlorohydrin, polymerization proceeds as a living process, giving with quantitative yields macromonomers with functionality equal to one, controlled molecular weight and narrow molecular weight distribution (M wM n<1.2) free of side products. In the higer molecular weight region, side reactions become increasingly noticeable. Propylene oxide macromonomers undergo radical homopolymerization. Homopolymerization of macromonomer with M n = 8×102 gives graft copolymers with M n up to 7.2×103 in copolymerization with styrene, completely soluble graft copolymers with M n ~ 2×104 were obtained. Radical copolymerization of epichlorohydrin macromonomers with styrene gives initially soluble products with M n ~ 6×104 were obtained. Radical copolymerization of epichlorohydrin macromonomers with styrene gives initially soluble products with Mn~ 6×104, which are converted in the later stages into insoluble gels, apparently due to the chain transfer to chloromethly groups of the polyepichlorohydrin chains. 相似文献