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排序方式: 共有1809条查询结果,搜索用时 17 毫秒
21.
Significant progress has been made in recent years regarding the photooxidation of olefin copolymers, but questions still remain. This paper reviews the progress and probes the photooxidative chemistry of ethylene–propylene (EP) and ethylene/propylene/diene monomer (EPDM) copolymers. Both stabilized and unstabilized polymer plaques were irradiated in a xenon are and the surface chemistry followed using infra-red spectroscopy. Model compounds were used to help elucidate the chemistry caused by unique structural features present in the copolymers. Volatile products evolved during photooxidation were determined giving valuable insight into the degradation chemistry. 相似文献
22.
Ming Li Zbigniew Twardowski Felix Mok Norbert Tam 《Journal of Applied Electrochemistry》2007,37(4):499-504
Sodium dichromate is commonly used in sodium chlorate production to maintain high current efficiency; however, it is also
a well documented carcinogen. To reduce the environmental impact, identification of a suitable alternative with similar buffering
characteristics to dichromate and without adverse effect on the electrolytic performance of sodium chlorate production is
important; sodium molybdate is a good candidate. Molybdate ion and its conjugated acid work as a buffer pair at pH 5–6, a
lower and slightly narrower pH window than the typical buffer region of dichromate. Nonetheless, the molybdate buffer works
effectively during the electrolytic process by maintaining pH at 5.9. Although the use of molybdate buffer will lower the
overpotential of hydrogen evolution reaction (HER) by 100 mV, the average off-gas oxygen content is noticeably compromised
at 3.6–4.6%, measured using a pilot cell operated at 3 kA m−2and 80 °C during a 3-day trial. The resulting current efficiency of 91 92% is significantly lower than when dichromate is
employed as the process additive (> 96%). Mixtures of different dichromate and molybdate ratio were also investigated in terms
of the resulting cathode surface potential. 相似文献
23.
The various routes of synthesis of some methoxy- and acetylamino-9,10-dihydro-7H-imidazo[1,2-b]benz[d,e]isoquinolin-7-one derivatives are described. The mixtures of geometric isomers obtained were separated and the chemical constitution of individual isomers was confirmed by the u.v., i.r., n.m.r. and mass spectroscopy. The fluorescence properties of individual isomers were also determined. 相似文献
24.
The inter-relations between iron catalysts, recycle solvent composition and product yield and composition have been investigated in bench-scale (1–2 kg h?1) continuous hydrogenation of Australian coals at process severity of 21–22 MPa at 400–430°C. Products and recycle solvent are recovered in batch distillation (atmospheric and vacuum) and the distillate solvent is returned to slurry feed without further treatment. Successive samples of recycle solvent are analysed by g.c.-m.s., i.r. and titrimetry. The effect of adding iron catalysts in the form of red mud - sulphur mixtures or compounds after a short period of continuous operation without catalyst is demonstrated. Distillate yields from black coals increase from 24–34 wt% daf under non-catalytic conditions to 35–53 wt% daf by adding iron catalysts. The composition of the almost equilibrated recycle solvent also changes and a new equilibrium is approached after the iron catalyst is added. The effect of solvent composition on distillate yield can not be determined from these data. The ratio of hydroaromatic components to hydroaromatic plus aromatic components in the solvent increases from ≈0.2 at non-catalytic equilibrium to ≈0.5–0.6 at catalysed equilibrium after adding iron. Other compositional parameters in the recycle solvent do not show any clear responses to the addition of iron. Equilibrium solvent composition under constant operating conditions is attained at ≈10 passes at 1 kg h?1 throughput with total system holdup of ≈20 kg. Paraffins for the Queensland subbituminous coal equilibrated at 18–24% in the solvent, phenolics at 16–21%, basic nitrogen at ≈0.4% (as N), and the balance a mixture of aromatics and hydroaromatics. The total aromatics neglecting phenolics in the equilibrium recycle solvent consists of ≈40–50% each of two-and three-ring and 5–10% four-ring members. 相似文献
25.
A. F. Jankowski T. O. Wilford 《JOM Journal of the Minerals, Metals and Materials Society》1987,39(6):28-30
An increase in grain size during deposition occurs in physical vapor deposition. Columnar grain structures result as the coating thickens beyond the point of constant grain size (>25 μm). As the deposition is taking place, the grain size of the Ti coating increases from that on the order of 0.01 (Jim to that greater than 1.0 μm. At a certain critical thickness during deposition, tc, the grain size stabilizes. This study examines the minimum coating thickness required to produce the ultimate grain size. Then this investigation relates the critical thickness to the texture of the coating. 相似文献
26.
Norbert Koppenhagen Benjamin Mueller Alexander Maedche Ye Li Stephanie Hiller 《Information Systems and E-Business Management》2016,14(3):613-636
E-procurement and supplier-relationship management systems have helped to substantially advance process execution in supply management. However, current supply network systems still face challenges of high data integration efforts, as well as the decoupling of structured data and processes from the growing amount of digitalized unstructured interactions of supply management professionals. Inspired by the room for improvement posed by this challenges, our research proposes a design for a supply network artifact in supplier qualification that addresses these problems by enabling holistic integration of data, processes, and people. The artifact is developed following an action design research approach. Building on a set of meta-requirements derived from literature and practice explorations, we conceptualize two design principles and derive corresponding design decisions that have been implemented in an software artifact. Finally, we formulate testable hypotheses and evaluate the artifact and its design in the context of supplier qualification. Our results show that the proposed design reduces mental effort of supply management professionals and significantly increases efficiency when performing typical supply network tasks such as supplier qualification. 相似文献
27.
Paweł Jankowski Dominika Ogończyk Ladislav Derzsi Wojciech Lisowski Piotr Garstecki 《Microfluidics and nanofluidics》2013,14(3-4):597-604
Modification of the surfaces of polycarbonate (PC) with the use of a solution of tin (II) chloride renders them hydrophilic. The surface draping is stable against exposure to water and to alcohols. Exposure to alkanes reduces but does not diminish the effect. The method is compatible—in using the same solvent and temperature—with the hydrophobic modification of PC (Jankowski et al. in Lab Chip 11:1151–1156, 2011). The combination of these methods makes it possible to generate single and multiple monodisperse emulsions with the use of flow-focusing junctions in systems made in PC—a material that is suitable for fabrication of multilayer, high-throughput microfluidic devices. 相似文献
28.
Paweł Jankowski Dominika Ogończyk Ladislav Derzsi Wojciech Lisowski Piotr Garstecki 《Microfluidics and nanofluidics》2013,14(5):767-774
Modification of the surfaces of polycarbonate (PC) with the use of a solution of tin (II) chloride renders them hydrophilic. The surface draping is stable against exposure to water and to alcohols. Exposure to alkanes reduces but does not diminish the effect. The method is compatible—in using the same solvent and temperature—with the hydrophobic modification of PC Jankowski et al. ( Lab Chip 11:748–752, 2011). The combination of these methods makes it possible to generate single and multiple monodisperse emulsions with the use of flow-focusing junctions in systems made in PC—material that is suitable for fabrication of multilayer, high throughput microfluidic devices. 相似文献
29.
Structural damage identification by adding virtual masses 总被引:1,自引:0,他引:1
Jilin Hou Łukasz Jankowski Jinping Ou 《Structural and Multidisciplinary Optimization》2013,48(1):59-72
This paper presents a method for damage identification by adding virtual masses to the structure in order to increase its sensitivity to local damages. The main concept is based on the Virtual Distortion Method (VDM), which is a fast structural reanalysis method that employs virtual distortions or pseudo loads to simulate structural modifications. In this paper, the structure with an added virtual mass is called the virtual structure. First, the acceleration frequency response of the virtual structure is constructed numerically by the VDM using local dynamic data measured only by a single excitation sensor and a single acceleration sensor. Second, the value of the additional mass is determined via sensitivity analysis of the constructed frequency responses of the virtual structure with respect to damage parameters; only the natural frequencies with high sensitivity are selected. This process is repeated for all the considered placements of the virtual mass. At last, the selected natural frequencies of all the virtual structures are used together for damage identification of the real structure. A finite element (FE) model of a plane frame is used to introduce and verify the proposed method. The damage can be identified precisely and effectively even under simulated 5 % Gaussian noise pollution. 相似文献
30.
Norbert Kuhn Klaus Madlener Friedrich Otto 《Applicable Algebra in Engineering, Communication and Computing》1994,5(5):287-316
Algorithms for solving uniform decision problems for algebraic structures crucially depend on the chosen finite presentations for the structures under consideration. Rewriting techniques have been used very successfully to solve uniform decision problems, when the presentations considered involve finite, noetherian, and ()-confluent rewriting systems. Whenever the class of algebraic structures considered is closed under the operation of taking finitely generated substructures, then the algorithms for solving the uniform decision problems can be applied to the substructures as well. However, since these algorithms depend on the form of the presentations, this involves the task of constructing a presentation of a certain form for a substructure given a presentation of this form for the structure itself and a finite set of generating elements for the substructure.This problem, which has received a lot of attention in algebra, is here investigated from an algorithmic point of view. The structures considered are the following two classes of groups, which have been studied extensively before: the polycyclic groups and the context-free groups.Finitely generated context-free groups can be presented by finite, monadic, and -confluent string-rewriting systems. Due to their nice algorithmic properties these systems provide a way to effectively solve many decision problems for context-free groups. Since finitely generated subgroups of context-free groups are again contextfree, they can be presented in the same way. Here we describe a process that, from a finite, monadic, and -confluent string-rewriting system presenting a context-free groupG and a finite subsetU ofG, determines a presentation of this form for the subgroup U ofG that is generated byU. For finitely presented polycyclic groups we obtain an analogous result, when we use finite confluent PCP2-presentations to describe these groups.This work was performed while this author was visiting at the Fachbereich Informatik, Universität Kaiserslautern, during his sabbatical 1991/92 相似文献