A novel non-intrusive microcell for sound-speed measurements in liquids. Speed of sound and thermodynamic properties of 2-propanone at pressures up to 160 MPa

A novel high-pressure, ultrasonic cell of extremely reduced internal dimensions ( 0.8 10 6 m3) and good precision for the determination of the speed of propagation of sound in liquids was conceived and built. It makes use of a non-intrusive methodology where the ultrasonic transducers are not in direct contact with the liquid sample under investigation. The new cell was used to carry out speed of sound measurements in 2-propanone (acetone) in broad ranges of temperature (265 < T =K < 340) and pressure (0:1 < p=MPa < 160). (p; q; T ) data for acetone were also determined but in a narrower T ; p range (298 to 333 K; 0.1 to 60 MPa). In this interval, several thermodynamic properties were thus calculated, such as: isentropic (js) and isothermal (jTÞ compressibility, isobaric thermal expansivity (ap), isobaric (cp) and isochoric (cv) specific heat capacity, and the thermal pressure coefficient (cv). Comparisons with values found in the literature generally show good agreement.info:eu-repo/semantics/publishedVersio

Thermophysical and thermodynamic properties of ionic liquids over an extended pressure range: [bmim][NTf2] and [hmim][NTf2]

The current study focuses on 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide, [bmim][NTf2], and 1-hexyl-3- methylimidazolium bis(trifluoromethylsulfonyl)amide, [hmim][NTf2]. The objective is to study the influence of pressure as well as that of the cation s alkyl chain length on several properties of this type of ionic liquids. Speed of propagation of ultrasound waves and densities in pure ionic liquids (ILs) as a function of temperature and pressure have been determined. Several other thermody namic properties such as compressibilities, expansivities and heat capacities have been obtained. Speed of sound measurements have been carried out in broad ranges of temperature (283 < T/K < 323) and pressure (0.1 < p/MPa < 150), using a non-intrusive micro cell. Density measurements have been performed at broad ranges of temperature (298 < T/K < 333) and pressure (0.1 < p/MPa < 60) using a vibrating tube densimeter. The pressure dependence of heat capacities, which is generally mild, is highly dependent on the curvature of the temperature dependence of density.info:eu-repo/semantics/publishedVersio

Função energia generalizada de controle para estabilização de sistemas não lineares

Neste trabalho, o conceito de função de Lyapunov de controle é estendido em duas direções principais. Na primeira direção, o conceito de função energia de controle (FEC) é proposto com o objetivo de não somente projetar leis de controle estabilizantes para sistemas não lineares mas também com o objetivo de fornecer uma estimativa da região de estabilidade do sistema em malha fechada. A FLC garante estabilidade local de um certo ponto de equilíbrio do sistema em malha fechada, mas usualmente não fornece estimativasótimas da região de estabilidade. O conceito de FEC é mais exigente que o conceito de FLC. Além de garantir estabilidade local do equilíbrio, a FEC fornece informações globais a respeito dos conjuntos limites e estimativas ótimas das regiões de estabilidade. A segunda direção está relacionada com o fato de que, em geral, é difícil encontrar FLC ou FEC para muitos sistemas não lineares. De forma a minimizar este problema e aplicar õ conceito de CEF em uma classe maior de sistemas, propõe-se neste artigo o conceito de função energia generalizada de controle (FEGC). A FEGC permite o projeto de controladores mesmo quando a derivada da função energia é positiva em algumas regiões limitadas do espaço de estados.extended in two main directions. In the first direction, the concept of control energy function (CEF) is proposed not only to design stabilizing feedback control laws but also to provide an estimate of the stability region of the closed-loopsystem. The CLF guarantees local stability of the closedloop- system but usually cannot provide optimal estimates of its stability region. The CEF concept is more restrict than the CLF concept. Beyond the guarantee of local stability, the CEF provides global information about limit sets and optimal estimates of stability region. The second direction is related to the fact that, in general, it is difficult to find a CLF or a CEF for many nonlinear systems. In order to overcome this problem and apply the concept of CEF for a larger class of systems, the concept of generalized control energy function (GCEF) is proposed in this paper. The GCEF allows the design of nonlinear controllers even when the derivative of the energy function is positive in some bounded regions of the state space