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41.
This paper addresses the problem of designing controllers that are robust to a great uncertainty in a time constant of the plant. Plants must be represented by minimum phase rational transfer functions of an arbitrary order. The design specifications are: (1) a phase margin for the nominal plant, (2) a gain crossover frequency for the nominal plant, (3) zero steady state error to step commands, and (4) a constant phase margin for all the possible values of the time constant (T): 0<T<∞. We propose a theorem that defines the structure of the set of controllers that fulfil these specifications and show that it is necessary for these robust controllers to include a fractional-order PI term. Examples are developed for both stable and unstable plants, and the results are compared with a standard PI controller and a robust controller designed using the QFT methodology. 相似文献
42.
Fernando Soler-Toscano Fernando R. Velázquez-Quesada 《Journal of Logic, Language and Information》2014,23(2):141-168
Among the non-monotonic reasoning processes, abduction is one of the most important. Usually described as the process of looking for explanations, it has been recognized as one of the most commonly used in our daily activities. Still, the traditional definitions of an abductive problem and an abductive solution mention only theories and formulas, leaving agency out of the picture. Our work proposes a study of abductive reasoning from an epistemic and dynamic perspective. In the first part we explore syntactic definitions of both an abductive problem in terms of an agent’s information and an abductive solution in terms of the actions that modify the agent’s information. We look at diverse kinds of agents, including not only omniscient ones but also those whose information is not closed under logical consequence and those whose reasoning abilities are not complete. In the second part, we look at an existing logical framework whose semantic model allows us to interpret the previously stated formulas, and we define two actions that represent forms of abductive reasoning. 相似文献
43.
Diogo R. Ferreira Fernando Szimanski Célia G. Ralha 《Journal of Intelligent Information Systems》2014,43(2):379-407
While it is possible to analyze the run-time behavior of a business process through process mining techniques, in practice there is often a gap between the low-level nature of the events recorded in an event log and the high-level of abstraction at which the process is modeled. This makes it difficult to understand the recorded behavior in terms of the high-level activities in the process model. Also, it makes it difficult to improve the model based on run-time data about the process. In this work we present an approach to mine mappings between the events in the log and the activities in the model. These mappings can be used to generate suggestions of how the process model can be extended in order to capture the behavior recorded in the event log. Using a real-world and publicly available event log, we show how the approach can improve the model in a stepwise manner, until it covers all the behavior recorded in the event log. 相似文献
44.
Silphinene Sesquiterpenes as Model Insect Antifeedants 总被引:3,自引:0,他引:3
González-Coloma A Valencia F Martín N Hoffmann JJ Hutter L Marco JA Reina M 《Journal of chemical ecology》2002,28(1):117-129
Silphinene sesquiterpenes are established chrysomelid antifeedants. In this work, nine silphinene analogs, 11-acetoxy-5-angeloyloxysilphinen-3-one (1), 11-acetoxy-5-tigloyloxysilphinen-3-one (2), 11-acetoxy-5-iso- butyryloxysilphinen-3-one (3), 11-hydroxy-5-angeloyloxysilphinen-3-one (4), 11,5-dihydroxysilphinen-3-one (5), 11,5-diacetoxysilphinen-3-one (6), 5,11-diisobutyryloxysilphinen-3-one (7), silphinen-3,5,11-trione (8), and O-methyl-5-epicantabrenolic acid methyl ester (10), and a presilphiperfolane sesquiterpene (9) were tested against several divergent insect species, including the lepidopteran Spodoptera littoralis, the chrysomelid Leptinotarsa decemlineata, and five aphid species, and their antifeedant effects were compared with those of picrotoxinin, a GABA-antagonist, and thymol, an allosteric modulator for insect GABA receptors. All insects tested responded to at least one silphinene analog and/or GABA antagonist. Compound 3 and thymol were effective antifeedants against all species tested except S. littoralis, with varying potencies according to their feeding ecologies. The toxicity of these compounds was species-dependent and did not correlate with their antifeedant effect. 相似文献
45.
Fernando J. Beltrán 《臭氧:科学与工程》1997,19(1):13-38
Kinetics of competition between the ozone direct reaction with compounds in water, ozone-hydroperoxide ion reaction leading to free radicals in the O3/H2O2 process, and the photolysis of ozone in the O3/UV process are discussed in terms of diffusion and reaction times to establish conditions for these reactions to be competitive. Film theory and chemical kinetic concepts then are applied to estimate initial rates of ozone absorption and consumption, removal rates of compounds present in water, and the importance of the radical oxidation path versus direct ozone and/or photolysis reactions. 相似文献
46.
A series of fracture mechanics tests of a set of random and impact copolymers of polypropylene, in which the ethylene content was varied, is described. The plane strain toughness is found to change from the homopolymer value, but thereafter to be independent of ethylene content. The yield stress of the impact copolymers decreases markedly with ethylene content, while that for random copolymers increases only slightly. This is reflected in toughness values in tension. A comparison with the behavior of other rubber-modified materials is made and it is concluded that crazing is an important mechanism in polypropylene and is perhaps more rate and temperature sensitive than in acrylonitrile-butadiene-styrene (ABS). 相似文献
47.
Fernando A. Oliveira Neri Alves José A. Giacometti Carlos J. L. Constantino Luiz H. C. Mattoso Ana M. O. A. Balan Aldo E. Job 《应用聚合物科学杂志》2007,106(2):1001-1006
This work describes the preparation and characterization of composite materials obtained by the combination of natural rubber (NR) and carbon black (CB) in different percentages, aiming to improve their mechanical properties, processability, and electrical conductivity, aiming future applications as transducer in pressure sensors. The composites NR/CB were characterized through optical microscopy (OM), DC conductivity, thermal analysis using differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMA), thermogravimetry (TGA), and stress–strain test. The electrical conductivity varied between 10?9 and 10 S m?1, depending on the percentage of CB in the composite. Furthermore, a linear (and reversible) dependence of the conductivity on the applied pressure between 0 and 1.6 MPa was observed for the sample with containing 80 wt % of NR and 20% of CB. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007 相似文献
48.
This article reports the design and deployment of two optical‐fiber temperature sensors based on the fiber Fabry–Perot etalon. The first involved the use of an extrinsic fiber Fabry–Perot sensor, but in this instance, the coefficient of thermal expansion of the reflector and/or capillary was chosen to offer a mismatch. Hence, the cavity length could increase or decrease according to the coefficient of thermal expansion of the fiber and/or capillary. For comparison, single‐mode and multimode optical‐fiber Bragg gratings were also used as temperature sensors. The Fabry–Perot sensors operated from ?50 to 410°C. The accuracy of the measurements was up to ±0.5°C with a low‐cost charged‐coupling‐device spectrometer. The sensors also worked effectively in a microwave oven and in a composite panel in an autoclave. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 83–95, 2004 相似文献
49.
Beatriz Miranda Eva Díaz Salvador Ordez Fernando V. Díez 《Catalysis communications》2006,7(12):945-949
The performance of 0.5% Ru/Al2O3 for the deep oxidation of trichloroethene (1000–2500 ppmV, WHSV = 55 h−1) in air was studied in this work. Experiments were carried out both at dry and wet (20,000 ppmV of H2O) conditions. Catalytic performance was studied in terms of activity and selectivity for the different reaction products (CO2, HCl, Cl2, C2Cl4, CCl4 and CHCl3). Both the activity and the selectivity for total combustion are higher than other catalysts suggested in the literature for this process (especially Pd and Pt).The main organic by-products are CCl4 and CHCl3, whereas in all the other catalysts tested in the literature, tetrachloroethene is the main organic by-product. This fact suggests that the mechanism of the combustion reaction, involving a double-bond scission, is essentially specific for this catalyst.Kinetic data was fit to a pseudo-first order kinetic expression, providing fairly good fit. 相似文献
50.
Cecilia R. Lederhos Pablo C. L’Argentière Fernando Coloma-Pascual Nora S. Fígoli 《Catalysis Letters》2006,110(1-2):23-28
The 1-heptyne selective hydrogenation carried out at 150 kPa, and at 283 and 303 K using Ru/Al2O3 and Ru/C as catalysts, was studied. Catalysts were prepared by the incipient wetness impregnation technique using RuCl3 as precursor. Ru/Al2O3 was treated in hydrogen at 373 or 573 K and Ru/C only at the last temperature. Catalysts were characterized by hydrogen chemisorption,
TPR and XPS. Ru dispersion after treatment in hydrogen at the highest temperature is similar for both catalysts. Ru is present
as Ru0 in Ru/C, while Ru0 and Ru electron-deficient species are present on the catalysts surface after hydrogen treatment at the two temperatures using
Al2O3 as support. The best catalytic behavior was observed for the highest temperature of hydrogen treatment and for 303 K reaction
temperature. As a consequence of a shape selectivity effect of the C support, the best conversion is obtained with the alumina
supported catalyst. 相似文献