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61.
In this paper, a servomechanism problem is considered in which a stabilizing controller is to be chosen as the solution of a H 2-optimization problem with asymptotic tracking and (exact or approximate) decoupling constraints. The cost functional is made-up of terms which penalize the tracking error and control effort associated with a class of persistent reference signals. To solve the optimization problem with asymptotic tracking and exact decoupling constraints, an explicit parametrization is presented of all stabilizing controllers which satisfy these constraints. On the basis of this parametrization the problem in question is recast as an unconstrained H 2 problem and conditions on problem data are then stated under which there exists a unique solution. To handle the case of asymptotic tracking and approximate decoupling constraints, a parametrization of all stabilizing controllers which achieve asymptotic tracking is used to eliminate the tracking constraint; this leads to an H 2 optimization problem with several non-definite H 2 constraints. Approximate solutions to such a problem are obtained by means of a sequence of H 2 problems with a single non-definite H 2 constraint which, in turn, are solved by line search and spectral factorization. A numerical example is presented to illustrate the effect of the exact and approximate decoupling constraints on the attained optimal cost value and time responses. 相似文献
62.
63.
Beghi SP Santos JM Reis NC de Sá LM Goulart EV de Abreu Costa E 《Water science and technology》2012,66(10):2223-2228
Complaints from the Domingos Martins population about sewage odours in the city made the district attorney order an impact assessment of the odours emitted by the city wastewater treatment plant (WWTP). This study comprised various techniques, models and population surveys. In 2007, an odour emission model proved that the main hydrogen sulphide emitter was the aeration tank of the WWTP (13.5 g h(-1)) and such emissions, according to CALPUFF model, should be perceived in the whole Domingos Martins city centre area. In this area, 58% of those interviewed were annoyed by the WWTP odours. However, in 2009, the odour monitoring panel recorded few odour occurrences. A second population survey showed that hereafter only 20% of those interviewed were annoyed by the WWTP emissions. Odour emission and dispersion models run with 2010 data proved a drastic reduction of the WWTP aeration tank emissions and consequently the city centre was not bothered by WWTP emissions anymore. The odour emission reduction was due to the modification of the WWTP aeration tank system. Despite the odour emission reduction, houses located southeast of the WWTP were still annoyed by sewage odours. However, in this part of the town, other sources of sewage odours have been found. 相似文献
64.
Electrochemical corrosion of Pb–1 wt% Sn and Pb–2.5 wt% Sn alloys for lead-acid battery applications
The aim of this study was to compare the electrochemical corrosion behavior of as-cast Pb–1 wt% Sn and Pb–2.5 wt% Sn alloy samples in a 0.5 M H2SO4 solution at 25 °C. A water-cooled unidirectional solidification system was used to obtain the as-cast samples. Electrochemical impedance spectroscopy (EIS) diagrams, potentiodynamic polarization curves and an equivalent circuit analysis were used to evaluate the electrochemical corrosion response. It was found that a coarse cellular array has a better electrochemical corrosion resistance than fine cells. The pre-programming of microstructure cell size of Pb–Sn alloys can be used as an alternative way to produce as-cast components of lead-acid batteries with higher corrosion resistance associated with environmental and economical aspects. 相似文献
65.
This study focuses on the processing of vitrified floor tiles incorporated with a petroleum oily sludge. Floor tile formulations containing up to 5 wt% of the petroleum oily sludge in replacement of kaolin were prepared. The tile formulations were granulated by the dry process, pressed, and fired at temperatures between 1200 and 1250 °C using a fast-firing cycle. The specimens were characterized before and after firing. XRD was used to identify the crystalline phases present during sintering and SEM was used to show how the structure changes during densification. Three parameters were used to describe densification: linear shrinkage, water absorption, and flexural strength. The results showed that the petroleum oily sludge could be used as an alternative raw material in the floor tile formulations. The densification behavior of the floor tile pieces is influenced by the petroleum oily sludge addition and firing temperature. The vitrified floor tiles produced reached the technical characteristics of porcelain floor tiles, depending on petroleum oily sludge content and firing temperature. 相似文献
66.
This work focuses on the reuse of grits waste, from cellulose industry, as a raw material to replace traditional carbonate material in ceramic wall tiles. Wall tile formulations bearing up to 15?wt% of the grits waste were prepared for replacement of calcareous. The tile manufacturing route consisted of dry powder granulation, uniaxial pressing, and firing at temperatures ranging from 1100?°C to 1180?°C by using a fast-firing cycle. The wall tile specimens were tested to determine their physical and mechanical properties (linear shrinkage, water absorption, apparent porosity, apparent density, breaking strength, and flexural strength). The firing behavior, phase transformations, and microstructure were evaluated by dilatometry, XRD, and SEM. The results showed that the fired wall tile specimens are composed of anorthite and quartz, as major mineral phases, and mullite as a minor phase. It was found that the grits waste had a positive influence on the properties and microstructure of the wall tile specimens. The results also revealed that the grits waste from cellulose industry could be used as a total replacement of traditional calcareous material in wall tile formulations. 相似文献
67.
This is the first of two papers concerning conjugate transport in convective drying of multiparticle systems. In this study, a methodology for the solution of conjugate transport problems is proposed. The theoretical aspects and relevant assumptions are briefly discussed and the results for convective heat and mass transfer in assemblages of spheres are presented. It is shown that both heat and mass transfer rates for an assemblage of two spheres in tandem arragement are significantly different from those of a single sphere case, and that care should be taken when modeling multiparticle systems by means of single-particle analysis. 相似文献
68.
The grading of structural timber members allows for their greater efficiency and quality. This grading can be done by means of nondestructive methods that improve the evaluation process. Timber grading makes it possible to augment the k mod,3 coefficient, resulting in greater structural reliability. The purpose of this work was to calibrate the modification coefficient (k mod,3) of the Brazilian NBR 7190:2007 code for the Design of Timber Structures. The modification coefficients are numbers that govern the estimation of a property of a material as a function of phenomena that may occur permanently or during a certain period of the service life of the building, being that the coefficient k mod,3 leads in consideration if the wood is of first or second-class quality. The experimental procedure involved a study of structural members of Eucalyptus grandis and Pinus sp., which were graded by ultrasound and transverse vibration techniques to determine the dynamic modulus of elasticity (Ed). The members were visually graded and static bending tests (MOE) were conducted concomitantly. The results indicated that the transverse vibration technique yielded higher modification coefficient (k mod,3) values than the ultrasound technique, since it grades the material at values closer to those obtained in static bending. 相似文献
69.
Leandro C. Silva Valéria V. Murata Carla E. Hori Adilson J. Assis 《Optimization and Engineering》2010,11(3):441-458
In this work three mathematical models for methane steam reforming in membrane reactors were developed. The first one is a steady state, non isothermal, non isobaric and one dimensional model derived from material and energy balances and validated using experimental data from the literature. It is referred as full model. The influence of two different intrinsic kinetics available, as well as, the influence of five important parameters on methane conversion (XCH4_{mathrm{CH}_{4}}) and hydrogen recovery (YH2_{mathrm{H}_{2}}) were parametrically evaluated through simulations. The second model, referred as meta-model, was obtained though the response surface technique. This meta-model was included into a constrained optimization problem solved using NPSOL. The third model, referred as a simplified model, takes into account only mass balances from the full model. Using this model, a gradient based method (DIRCOL) was used to perform the optimization of the sum of methane conversion and hydrogen recovery. High methane conversions and hydrogen recoveries were reached through these methodologies. 相似文献
70.
Patrícia da Silva Malheiros Ctia Tavares dos Passos Letícia Sopea Casarin Leandro Serraglio Eduardo Cesar Tondo 《Food Control》2010,21(3):298-301
The growth of Staphylococcus aureus inoculated onto poultry meat was investigated under different incubation periods and temperature patterns. Transfer of this microorganism to surface materials and their disinfection was also evaluated. The evaluation of transfer was carried out by placing the contaminated meat cubes on stainless steel and polyethylene surfaces for 10 s and 10 min each, and the surfaces were disinfected with 0.5% chlorhexidine digluconate (CHXdG) for 1 and 10 min each. After 24 h, there was a significant increase of the bacteria count at 20 °C, but not at temperatures between 7 and 15 °C. Significant counts of S. aureus were transferred after a few seconds of contact of the cubes with both materials, and significant differences of transferred cell counts were not detected among the surface materials or durations of contact. The CHXdG solution was able to inactivate all the transferred cells after 10 min of exposure; however, the same result was not observed with 1-min exposure. The time of contact and the type of surface material did not influence the quantity of the transferred cells. The 0.5% CHXdG solution was effective for the disinfection of the contaminated surfaces without previous cleaning. 相似文献