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Search Results: 1 - 10 of 26942 matches for " mixed-control "
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The Concept of Mixed-Control Mechanisms and its Applicability to Paper Degradation Studies
A. Barański,J.M. ?agan,T. ?ojewski
E-Preservation Science , 2006,
Abstract: Analysis of kinetic data obtained during accelerated ageing of paper is frequently based on the use of Arrhenius equation for extrapolation of kinetic data. However this kind of analysis can be misleading if two or more concurrent processes occur simultaneously. In the case of paper degradation these are, most frequently, acidic hydrolysis and oxidation of cellulose. In such cases application of a mixed-control concept, for many years used in practical applications of chemical kinetics (especially in metallurgy) can be helpful. The present paper is an attempt of explaining the fundamental terminology and concepts connected with the kinetic equations of mixed-control type.
A Mixed-control Mechanism Model of Proeutectoid Ferrite Growth under Non-equilibrium Interface Condition in Fe-C Alloys
Ruiheng WU,Xueyu RUAN,Hongbing ZHANG,TYHsu,
T.Y.Hsu

材料科学技术学报 , 2004,
Abstract: By combining the α/γ interface migration and the carbon diffusion at the interface in Fe-C alloys, a mathematical model is constructed to describe the mixed-control mechanism for proeutectoid ferrite formation from austenite. In this model, the α/γ interface is treated as non-equilibrium interface, i.e., the carbon concentration of austenite at γ/α interface is obtained through theoretical calculation, instead of that assumed as the local equilibrium concentration.For isothermal precipitation of ferrite in Fe-C alloys, the calculated results show that the rate of interface migration decreases monotonically during the whole process, while the rate of carbon diffusion from γ/α interface into austenite increases to a peak value and then decreases. The process of ferrite growth may be considered as composed of three stages: the period of rapid growth, slow growth and finishing stage. The results also show that the carbon concentration of austenite at γ/α interface could not reach the thermodynamic equilibrium value even at the last stage of ferrite growth.
TEMPERATURE AND HUMIDITY CONSIDERATIONS FOR THE PRESERVATION OF ORGANIC COLLECTIONS - THE ISOPERM REVISITED
Tom Strang,David Grattan
E-Preservation Science , 2009,
Abstract: Since Sebera published his paper on Isoperms in 1994,much has changed. A significant amount of data has accumulatedon the mechanism of paper degradation, more activationenergies have been determined and there has been aconvergence of values. Assumptions about the relationshipbetween the relative humidity and the moisture content orthe rate of degradation of paper need no longer be made asnear complete theoretical descriptions are available. Themethod of modelling has therefore been revised and nowincorporates the Arrhenius equation and the moisture sorptionisotherm, which is best modelled by the Guggenheim-Anderson-deBoer (GAB) equation. This new method willallow direct experimental verification of the isoperm forcellulosic materials in museum collections. As the cost ofenergy usage for preser vation has now become an importantquestion, it is particularly critical to have access tomore accurate isoperms.
H control for uncertain Markovian jump systems with mode-dependent mixed delays
H∞ control for uncertain Markovian jump systems with mode-dependent mixed delays

Yingchun Wang,Huaguang Zhang,
Yingchun Wang
,Huaguang Zhang

自然科学进展 , 2008,
Abstract: We study the problem of H∞ control for a class of Markovian jump systems with norm-bounded parameter uncertainties and modedependent mixed delays including discrete delays and distributed delays in this paper. Our aim is to present a new delay-dependent control approach such that the resulting closed-loop system is robust mean-square (MS) exponentially stable and satis?es a prescribed H∞ performance level, irrespective of the parameter uncertainties. Such delay-dependent approach does not require system transformation or free-weighting matrix. A numerical example shows that the results are less conservative and more e?ective.
Effect of Weeds and Some Methods for their Control in Seed Production Stands of Sainfoin (Onobrychis viciifolia Scop.)
Tsvetanka Dimitrova
Pesticidi i Fitomedicina , 2010,
Abstract: During the 2007-2009 period in the experimental field of the Institute of Forage Cropsa study was conducted with the purpose of investigating the effect of weeds and somemethods for their control in seed production stands of sainfoin (Onobrychis viciifolia Scop.).The trial was carried out on a slightly leached chernozem on an area with a natural backgroundof weed infestation. As a result of the study it was found:Establishment of very uniform and productive seed production stands of sainfoinrequired effective weed control concentrated mainly in the first year when the degree ofweed infestation was the highest and reached to a number of 245 plants/m2 and the freshweed biomass to 1311 g/m2.The chemical control method showed the highest efficacy had the highest efficiencywhen, in the year of stand establishment at the stage of second-fourth true leaf of sainfoin,the treatment was conducted with imazamox 40g/l (Pulsar 40) at the dose of 48 g a.i./haor with the system of Bentazon 600 g/l (Basagran 600 SL) – 900 g a.i./ha – fluazifop-P-butylg/l (Fusilad Forte) – 120 g a.i./ha. In the years of seed production in spring at the beginningof vegetation, the treatment was conducted with imazamox 40 g/l (Pulsar 40) at the doseof 20 g a.i./ha + adjuvant DESH at the dose of 1000 ml/ha.An alternative to the chemical method is to sow sainfoin under cover of spring barleyachieving more complete use of the area in the first year, a weed suppressive and ecologicaleffect, but some negative residual effect on the crop was also observed;The pure stands of sainfoin with chemical control of weeds had the highest seed productivity,exceeding the zero check by 24 to 28%, followed by the stands with spring barleyas a cover crop with an increase of 12% and the mixed stands of sainfoin with crestedwheatgrass had the lowest productivity.
Automatic tuning of model predictive controllers based on multiobjective optimization
Francisco,M.; Vega,P.;
Latin American applied research , 2010,
Abstract: in this work a general procedure for tuning multivariable model predictive controllers (mpc) with constraints is presented. control system parameters are obtained by solving a multiobjective optimization problem. the set of objectives includes controllability aspects, in terms of the h∞ norms of some closed loop transfer functions of the system, and others related to the range of manipulated and controlled variables, expressed using the l1 norm. moreover, the use of multiple linearized models for tuning, allows for the specification of robust performance criteria through a set of constraints. the mathematical optimization for tuning all controller parameters is tackled in two iterative steps. first, integer parameters are obtained using a specific random search, and secondly a sequential programming based method is used to tune the real parameters. as a validation example, the tuning of the control system for the activated sludge process of a wastewater treatment plant has been selected.
DISCRIMINACIóN DE FUENTES DE CONTROL TEMPORAL EN PROGRAMAS DE REFORZAMIENTO DE INTERVALO
óscar García-Leal,Luis Alfaro-Hernández,Carlos A. Díaz-Lemus
Revista Colombiana de Psicología , 2009,
Abstract:
Automatic tuning of model predictive controllers based on multiobjective optimization
M. Francisco,P. Vega
Latin American applied research , 2010,
Abstract: In this work a general procedure for tuning multivariable model predictive controllers (MPC) with constraints is presented. Control system parameters are obtained by solving a multiobjective optimization problem. The set of objectives includes controllability aspects, in terms of the H∞ norms of some closed loop transfer functions of the system, and others related to the range of manipulated and controlled variables, expressed using the l1 norm. Moreover, the use of multiple linearized models for tuning, allows for the specification of robust performance criteria through a set of constraints. The mathematical optimization for tuning all controller parameters is tackled in two iterative steps. First, integer parameters are obtained using a specific random search, and secondly a sequential programming based method is used to tune the real parameters. As a validation example, the tuning of the control system for the activated sludge process of a wastewater treatment plant has been selected.
Mixed H 2 / H ∞ control of flexible structures
De Farias D. P.,De Oliveira M. C.,Geromel J. C.
Mathematical Problems in Engineering , 2000,
Abstract: This paper addresses the design of full order linear dynamic output feedback controllers for flexible structures. Unstructured H ∞ uncertainty models are introduced for systems in modal coordinates and in reduced order form. Then a controller is designed in order to minimize a given H 2 performance function while keeping the maximum supported H ∞ perturbation below some appropriate level. To solve this problem we develop an algorithm able to provide local optimal solutions to optimization problems with convex constraints and non-convex but differentiable objective functions. A controller design procedure based on a trade-off curve is proposed and a simple example is solved, providing a comparison between the proposed method and the usual minimization of an upper bound H 2 to the norm. The method is applied to two different flexible structure theoretical models and the properties of the resulting controllers are shown in several simulations.
Efeito da composi??o das correntes do conversor das unidades de FCC no desempenho catalítico de aditivos DESOx
Polato, Carla Maria Salerno;Monteiro, José Luiz Fontes;Henriques, Cristiane Assump??o;
Química Nova , 2009, DOI: 10.1590/S0100-40422009000100007
Abstract: hydrotalcite-like compounds having mg partially replaced by cu or mn were prepared and used as precursors for two mixed oxides (cu-om50 and mn-om50) that were evaluated for sox removal in the presence of o2, no and co. under so2/o2 reaction system, sox removal was slightly higher over cu-om50. the addition of co and no to the feed markedly hindered the so2 oxidation over cu-om50 while no significant effect was observed for mn-om50. for the regeneration step, the use of propane instead of h2 reduces regeneration capacity, mainly for cu-om50. mn-om50 was less affected by the feed composition, suggesting that it was a promising additive for sox removal.
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