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1.
O. Hudec 《Mathematical Methods of Operations Research》1992,36(5):439-445
LetG=(V, E) be an undirected connected graph with positive edge lengths. The vertexp-center problem is to find the optimal location ofp centers so that the maximum distance to a vertex from its nearest center is minimized, where the centers may be placed at the vertices. Kariv and Hakimi have shown that this problem is NP-hard. We will consider two modifications of this problem in which each center may be located in one of two predetermined vertices. We will show the NP-completeness of their recognition versions. 相似文献
2.
This study examines the alkylation of diphenylamine (DPA) with nonene (NON) in a liquid phase catalyzed by acid-treated clay-based catalysts from commercial suppliers (Fulcat 22B, Nobelin MM, and Jeltar 300). Alkylations were conducted to achieve the highest possible selectivity of diisononyldiphenylamine (DNDPA), low selectivity of monoisononyldiphenylamine, and a maximum triisononyldiphenylamine yield of 4%. This study also examines the reaction conditions to selectively form dialkylated diphenylamine from DPA and NON in a batch reactor. Repeated use of the catalyst during the alkylation of DPA with NON was also investigated. Catalyst deactivation takes place during the alkylation of each batch and intensifies with repeated catalyst use, resulting in low DNDPA selectivity. The regenerated catalyst was sufficiently active only until the regeneration of the first and second batches. After the third batch, the catalyst’s selectivity for DNDPA was very low, and its reuse in the alkylation of DPA with NON was not efficient. Therefore, to achieve the maximum length of catalyst activity, the fresh catalyst was gradually added to the used catalyst from a previous batch, thus maintaining a high activity of eight batches. The reduction in catalyst activity was probably caused by the irreversible adsorption of substances on the surface, a loss of microporous structure, and a loss of surface acidity. DPA or alkylated products are adsorbed on the surface oxygen of the catalyst through nitrogen and form nitro formations. The fresh and regenerated catalysts were characterized by their surface area, surface acidity, pore size distribution, and pore volume. 相似文献
3.
A simple one-step synthesis of alkyl benzazol-2-carboxylates employing alkyl trialkoxyacetate is described. 相似文献
4.
Jesenák K. Kuchta L'. Hudec P. Fajnor V. Š. 《Journal of Thermal Analysis and Calorimetry》1999,55(3):773-777
Differences in mass loss occurring in the course of dynamic and isothermal heating of SiO2-aerogel and changes of specific surface and hydrophylicity during calcination were studied by thermal analysis. SiO2-aerogel was prepared from tetramethoxysilane (TMOS) hydrolyzed by ammonia solution at 0°C with molar ratio TMOS: H2O:NH4OH 4:1:0.01. Differences are caused mainly by oxidation of organic matter and by diffusion of products of the oxidation. Heat
transfer has none or little effect on the differences. Samples calcined at temperatures about 300°C reach maximum hydrophilicity
though they still contain small amounts of residual organic matter.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
5.
This study investigated the potential use of waste cooking oil (WCO) in the production of engine fuels and valuable chemicals via catalytic cracking. WCO was processed in its pure form and in a mixture with hydrotreated vacuum gas oil (HVGO). Catalytic cracking experiments were performed using a microactivity test (MAT) (simulation of the fluid catalytic cracking environment). In cracking over the standard fluid catalytic cracking equilibrium catalyst (FCC-ECAT), the oxygen contained in the feed was consumed in the formation of CO and CO2, water and into oxygenated organic compounds (phenolics, esters, carboxylic acids, etc.), which were found in the organic phase of the liquid product. In order to remove the unwanted organic oxygenates, the catalytic system based on pure FCC-ECAT was modified by addition of the ZSM-5-based FCC catalyst. By using the mixture containing FCC-ECAT and 10 mass % of FCC-ZSM-5, it was possible to reduce the amount of organic oxygenates to almost the feasible minimum when cracking pure WCO. The effect of the catalyst mixture on cracking the feed mixture of the vacuum gas oil with 10 vol. % of WCO was manifested in the practically zero formation of organic oxygenates and in a gasoline yield comparable with vacuum gas oil (VGO) cracking. 相似文献
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7.
Citral (I) is cyclized by UV irradiation1 to 2-isopropenyl-5-methylcyclopentane-carboxaldehyde (II), containing the carbon skeleton of the monoterpenes of ants and catmint. 1,6,6-Trimethylbicyclo[2,1,1]hexane-2-carboxaldehyde (XII, R = H), produced in lesser amount at the same time, was synthesized from camphor. The two photocitrals may, perhaps, come from a common intermediate containing the cyclopentane ring. 相似文献
8.
Jozef Krajovi Pavol Hudec Agáta Smieková Zdeno idek Mária Kubranová Ivan Horváth 《Reaction Kinetics and Catalysis Letters》1997,62(1):33-38
Acidic properties of Al-, Zr- and Cr- pillared montmorillonites prepared from Jelšovy Potok bentonite (Central Slovakia) have
been investigated using temperature-programmed desorption of ammonia. The number of acid sites varied with different interlayer
cations from 0.06 to 0.23 mmol g−1. The character of acid sites was similar in the case of Al- and Zr- forms. It is obvious that the chromium analogue contains
fewer acid sites, nevertheless, they seem to be stronger compared to Al- and Zr- pillared montmorillonites. 相似文献
9.
J. Ráhel’ M. Černák I. Hudec A. Brablec D. Trunec I. Chodák 《Czechoslovak Journal of Physics》2000,50(3):445
Effects of an atmospheric pressure surface discharge on a woven ultrahigh molecular weight polyethylene fabric were studied. Our results show that the surface discharge can be used to achieve a higher long-term wettability and improved adhesion properties of textile materials. 相似文献
10.
A knowledge-based fuzzy system for the purpose of municipalities classification is presented in this paper. It illustrates
how fuzzy systems can be used for municipalities classification and ranking tasks. The application of the system is explained
by the example of classification in one region in the Slovak Republic. The original problem of estimating and rough planning
of road maintenance requirements in winter was examined. The suggested methodology is supported by GIS technology for visualization
of the ranked municipalities to offer a better view on the territorial distribution of the obtained solution. A disadvantage
of fuzzy systems for the end user is in their complexity. This disadvantage has been analysed and a solution is suggested
to overcome it. The proposal deals with the integration of information system and self developed fuzzy system. This integration
enables creating the model, importing input data, processing rules and presenting results in tables and maps in one integrated
tool. 相似文献