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Nomenclatura Unesco > (22) Física > (2213) Termodinámica
(2213.01) Cambios de estado (2213.02) Física de la transmisión del calor
(2213.03) Altas presiones (2213.04) Altas temperaturas
(2213.05) Teoría cinética (2213.06) Bajas temperaturas
(2213.07) Cambio de fase (2213.08) Técnicas de medida del calor
(2213.09) Equilibrios termodinámicos (2213.10) Relaciones termodinámicas
(2213.11) Fenómenos de transporte (2213.99) Otras (especificar)

Mostrando recursos 1 - 20 de 2,286

1. Dynamics of fluctuations in a fluid below the onset of Rayleigh-Benard convection - Ortiz de Zárate Leira, José María; Sengers, Jan V.; Ahlers, Guenter; Oh, Jaechul
We present experimental data and their theoretical interpretation for the decay rates of temperature fluctuations in a thin layer of a fluid heated from below and confined between parallel horizontal plates. The measurements were made with the mean temperature of the layer corresponding to the critical isochore of sulfur hexafluoride above but near the critical point where fluctuations are exceptionally strong. They cover a wide range of temperature gradients below the onset of Rayleigh-Benard convection, and span wave numbers on both sides of the critical value for this onset. The decay rates were determined from experimental shadowgraph images of the...

2. Comment on "Shear-induced quench of long-range correlations in a liquid mixture" - Ortiz de Zárate Leira, José María; Sengers, Jan V.
Recently, Wada [Phys. Rev. E 69, 031202 (2004)] presented an analysis of the long-range nature of concentration fluctuations in a binary liquid mixture subjected to a concentration gradient in a uniform shear flow as a function of the wave number k of the fluctuations. Specifically, he argued that the presence of a uniform shear causes the intensity of the concentration fluctuations to crossover from the well-known k(-4) dependence at large wave numbers to a k(-4/3) dependence for small wave numbers. The purpose of this comment is to point out that the wave-number dependence of the concentration fluctuations to be expected...

3. Long-wavelength nonequilibrium concentration fluctuations induced by the Soret effect - Ortiz de Zárate Leira, José María; Fornés, José Antonio; Sengers, Jan V.
In this paper we evaluate the enhancement of nonequilibrium concentration fluctuations induced by the Soret effect when a binary fluid layer is subjected to a stationary temperature gradient. Starting from the fluctuating Boussinesq equations for a binary fluid in the large-Lewis-number approximation, we show how one can obtain an exact expression for the nonequilibrium structure factor in the long-wavelength limit for a fluid layer with realistic impermeable and no-slip boundary conditions. A numerical calculation of the wave-number dependence of the nonequilibrium enhancement and of the corresponding decay rate of the concentration fluctuations is also presented. Some physical consequences of our...

4. Concentration fluctuations in nonisothermal reaction-diffusion systems - Ortiz de Zárate Leira, José María; Sengers, Jan V.; Bedeaux, Dick; Kjelstrup, Signe
In this paper a simple reaction-diffusion system, namely a binary fluid mixture with an association-dissociation reaction between the two components, is considered. Fluctuations at hydrodynamic spatiotemporal scales when a temperature gradient is present in this chemically reacting system are studied. First, fluctuating hydrodynamics when the system is in global equilibrium (isothermal) is reviewed. Comparing the two cases, an enhancement of the intensity of concentration fluctuations in the presence of a temperature gradient is predicted. The nonequilibrium concentration fluctuations are spatially long ranged, with an intensity depending on the wave number q. The intensity exhibits a crossover from a proportional to...

5. Transverse-velocity fluctuations in a liquid under steady shear - Ortiz de Zárate Leira, José María; Sengers, Jan V.
We present an analysis of the transverse-velocity fluctuations in an isothermal liquid layer with a uniform shear rate between two parallel horizontal boundaries as a function of the wave number and the Reynolds number. The results were obtained by solving a stochastic version of the Orr-Sommerfeld equation subject to no-slip boundary conditions in a second-order Galerkin approximation. We find that the spatial Fourier transform of the transverse-velocity fluctuations exhibits a maximum as a function of the (horizontal) wave number q(parallel to). This maximum is associated with a crossover from a q(parallel to)(-4) dependence for larger q(parallel to) to a q(parallel...

6. Nonequilibrium velocity fluctuations and energy amplification in planar Couette flow - Ortiz de Zárate Leira, José María; Sengers, Jan V.
In this paper we investigate intrinsic thermally excited nonequilibrium velocity fluctuations in laminar planar Couette flow. For this purpose we have complemented the solution of the stochastic Orr-Sommerfeld equation for the intensity of the fluctuations of the wall-normal velocity, presented in a previous publication, with a solution of the stochastic Squire equation for the intensity of the fluctuations of the wall-normal vorticity. We have obtained exact solutions of these equations without boundary conditions and solutions in a Galerkin approximation when appropriate boundary conditions are included. These results enable us to make a quantitative assessment of the intensity of these nonequilibrium...

7. Concentration fluctuations in non-isothermal reaction-diffusion systems. II. The nonlinear case - Ortiz de Zárate Leira, José María; Bedeaux, D.; Pagonabarraga, I.; Sengers, J. V.; Kjelstrup, S.
In this paper, we consider a simple reaction-diffusion system, namely, a binary fluid mixture with an association-dissociation reaction between two species. We study fluctuations at hydrodynamic spatiotemporal scales when this mixture is driven out of equilibrium by the presence of a temperature gradient, while still being far away from any chemical instability. This study extends the analysis in our first paper on the subject [J. M. Ortiz de Zarate, J. V. Sengers, D. Bedeaux, and S. Kjelstrup, J. Chem. Phys. 127, 034501 (2007)], where we considered fluctuations in a non-isothermal reaction-diffusion system but still close to equilibrium. The present extension...

8. Spatial correlations in nonequilibrium reaction-diffusion problems by the Gillespie algorithm - Ortiz de Zárate Leira, José María; Luis Hita, Jorge
We present a study of the spatial correlation functions of a one-dimensional reaction-diffusion system in both equilibrium and out of equilibrium. For the numerical simulations we have employed the Gillespie algorithm dividing the system into cells to treat diffusion as a chemical process between adjacent cells. We find that the spatial correlations are spatially short ranged in equilibrium but become long ranged in nonequilibrium. These results are in good agreement with theoretical predictions from fluctuating hydrodynamics for a one-dimensional system and periodic boundary conditions.

9. Revisão do modelo de miedema para formação de ligas metálicas - Stedile, Fernanda Chiarello
Resumo não disponível

10. Giant Casimir effect in fluids in nonequilibrium steady states - Ortiz de Zárate Leira, José María; Kirkpatrick, T. R.; Sengers, J. V.
In this Letter, we consider the fluctuation-induced force exerted between two plates separated by a distance L in a fluid with a temperature gradient. We predict that for a range of distances L, this nonequilibrium force is anomalously large compared to other Casimir forces. The physical reason is that correlations in a nonequilibrium fluid are generally of longer range than other correlations, even than those near an equilibrium critical point. This giant Casimir force is related to a divergent Burnett coefficient that characterizes an Onsager cross effect between the pressure and the temperature gradient. The predicted Casimir force should be...

11. Investigation of Fickian diffusion in the ternary mixture of 1,2,3,4-tetrahydronaphthalene, isobutylbenzene, and dodecane - Ortiz de Zárate Leira, José María; Mialdun, A.; Sechenyh, V.; Legros, J. C.; Shevtsova, V.
We present a comprehensive analysis of experimental results obtained for Fickian diffusion in the benchmark ternary liquid mixture of 1,2,3,4-tetrahydronaphthalene, isobutylbenzene, and dodecane (nC(12)) with equal mass fractions. Isothermal diffusion coefficients have been measured by two independent experimental methods: by Taylor dispersion technique, and by a counter flow cell fitted with an optical interferometry device. The experimental diffusion matrices have been critically analyzed regarding the Onsager reciprocal relations, for which we introduce a matrix asymmetry index S-2 that is independent of the frame of reference and the component order.

12. Fluctuation-induced pressures in fluids in thermal nonequilibrium steady states - Ortiz de Zárate Leira, José María; Kirkpatrick, T. R.; Sengers, J. V.
Correlations in fluids in nonequilibrium steady states are long range. Hence, finite-size effects have important consequences in the nonequilibrium thermodynamics of fluids. One consequence is that nonequilibrium temperature fluctuations induce nonequilibrium Casimir-like pressures proportional to the square of the temperature gradient. Hence, fluctuations cause a breakdown of the concept of local thermal equilibrium. Furthermore, transport coefficients become dependent on boundary conditions and on gravity. Thus nonequilibrium fluctuations affect some traditional concepts in nonequilibrium thermodynamics.

13. Resiliencia: ¿Es posible medirla e influir en ella? - Monroy Cortés, Brisa Gissel; Palacios Cruz, Lino
El objetivo de este trabajo es hacer una revisión acerca del concepto de resiliencia, sus aspectos biológicos, las formas en las que se puede intentar medirla y algunas posibles intervenciones. El término resiliencia es una castellanización de la palabra inglesa resilience o resiliency, que originalmente se usaba en la termodinámica. En las ciencias biológicas se define como «la capacidad de un ecosistema o de un organismo para regresar a la estabilidad al sufrir una alteración». En la investigación psicosocial, Rutter define a la resiliencia como «la resistencia relativa a las experiencias psicosociales de riesgo». Para que el proceso de resiliencia se pueda presentar, es necesario que el individuo se encuentre...

14. Aplicação de métodos de mecânica-quântica no estudo da degradação da atrazina - Zanlorenzi, Cristiano
Resumo: A atrazina é um dos herbicidas mais utilizados no mundo por atuar seletivamente no controle de plantas daninhas pré e pós-emergência em culturas agrícolas, principalmente de milho e de cana de açúcar. Com o intuito de degradar este herbicida, técnicas oxidativas avançadas, baseadas no radical hidroxila, são utilizadas. Porém, durante o processo de degradação da atrazina, muitos outros subprodutos são gerados, o que ocasiona muitas incertezas sobre o mecanismo desta reação. Nesta perspectiva, estudos teóricos foram dirigidos em calcular as energias e as geometrias moleculares correspondentes de alguns estados de transição selecionados, objetivando gerar curvas de energias potencial para a etapa de abstração de hidrogênio. A partir...

15. La chaleur, mode de mouvement / - Tyndall, John.
Mode of access: Internet.

16. On the possibility of stable regularities without fundamental laws - Filomeno, Aldo
Esta tesis doctoral investiga la noción de necesidad física. Concretamente, estudia si es posible explicar las regularidades no accidentales sin la asunción habitual de un conjunto preexistente de leyes que gobiernan la Naturaleza. Al dispensar de dicha asunción se pone del lado de las llamadas teorías deflacionistas sobre leyes de la Naturaleza, como la humeana o la antirealista. El propósito principal de la tesis es el de complementar dichas teorías con una explicación —ausente a día de hoy— sobre la apariencia de necesidad física. Para proveer dicha explicación, recurro a campos a los que no se había recurrido en la...

17. Nuevos compuestos de Mo y W conteniendo ligandos xantato, dinitrógeno, etileno e isonitrilo: estudio de su reactividad frente al CO2 - Galindo del Pozo, Agustín
Esta Memoria pretende efectuar una contribución al estudio de los compuestos de coordinación no clásicos y a los compuestos organometálicos de los elementos molibdeno y wolframio en diversos estados de oxidación, fundamentalmente cero, dos y cuatro. Los compuestos investigados se pueden agrupar para su estudio según la naturaleza de los ligandos, clasificación que es por otra parte habitual en Química Organometálica. Atendiendo a este criterio, la descripción de las especies estudiadas se efectuará en cada uno de los siguientes grupos: 1. Compuestos que contienen a ligando de tipo O-alquilditiocarbonato o xantato. 2. Derivados que contienen a los ligandos dinitrógenos o etileno coordinados. 3....

18. Estructura, estabilidad, morfología, y características reológicas de películas de emulsionantes alimentarios (lípidos y proteínas) esparcidas sobre la interfase aire-agua - Carrera Sánchez, Cecilio
Tradicionalmente, la formulación de productos alimenticios ha sido más un arte que una ciencia. Esto se debe a que muchos de los alimentos que se consumen habitualmente son el resultado de una larga y compleja historia. Sin embargo, la industrialización de la producción de alimentos, que ha tenido lugar en este siglo, ha creado una gran demanda de alimentos procesados, en los cuales es necesaria la incorporación de determinados ingredientes para facilitar su conservación, su producción a escala industrial, su distribución a grandes distancias y su almacenamiento. Muchos de estos alimentos, como es el caso de las emulsiones y espumas, son...

19. MODELOS TERMODINÁMICOS PARA EL EQUILIBRIO VAPOR LIQUIDO A BAJAS PRESIONES: FASE LIQUIDA, MODELO DE WILSON. - Ríos A, Luís Guillermo
This paper deals with the way in which the liquid � vapor temperature � composition Tyx phase diagram for a binary system at low pressures can be obtained. The system studied, the ethanol� water system, has an azeotrope which is a manifestation of a highly non ideal behavior. The procedure uses a computational method that combines the cubic equation of Redlich � Kwong (useful to get the fugacity coefficient of the component i of a gas mixture, i ) and the model proposed by Wilson (useful to get the activity coefficient of the component i in a liquid mixture, i ).

20. Fundamentos de termodinámica clásica - Hoyos Madrigal, Bibian Alonso; Mejía Laverde, Martha Cecilia

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