Non-equilibrium concentration fluctuations in binary liquids with realistic boundary conditions

Because of the spatially long-ranged nature of spontaneous fluctuations in thermal non-equilibrium systems, they are affected by boundary conditions for the fluctuating hydrodynamic variables. In this paper we consider a liquid mixture between two rigid and impervious plates with a stationary concentration gradient resulting from a temperature gradient through the Soret effect. For liquid mixtures with a large Lewis number, we are able to obtain explicit analytical expressions for the intensity of the non-equilibrium concentration fluctuations as a function of the frequency $\omega$ and the wave number $q$ of the fluctuations. In addition we elucidate the spatial dependence of the intensity of the non-equilibrium fluctuations responsible for a non-equilibrium Casimir effect.Comment: 9 pages, 2 figure

Violation of action--reaction and self-forces induced by nonequilibrium fluctuations

We show that the extension of Casimir-like forces to fluctuating fluids driven out of equilibrium can exhibit two interrelated phenomena forbidden at equilibrium: self-forces can be induced on single asymmetric objects and the action--reaction principle between two objects can be violated. These effects originate in asymmetric restrictions imposed by the objects' boundaries on the fluid's fluctuations. They are not ruled out by the second law of thermodynamics since the fluid is in a nonequilibrium state. Considering a simple reaction--diffusion model for the fluid, we explicitly calculate the self-force induced on a deformed circle. We also show that the action--reaction principle does not apply for the internal Casimir forces exerting between a circle and a plate. Their sum, instead of vanishing, provides the self-force on the circle-plate assembly.Comment: 4 pages, 1 figure. V2: New title; Abstract partially rewritten; Largely enhanced introductory and concluding remarks (incl. new Refs.

An evaluation of management strategies for Atlantic tuna stocks

International agreements for the International Commission for the Conservation of Atlantic Tunas (ICCAT) convention area imply that Atlantic tuna stocks should be managed by strategies based on maximum sustainable yield (MSY); however, there is concern whether this will actually ensure sustainability with sufficiently high probability consistent with the principals of the precautionary approach. Therefore, the performance of MSY management strategies based on current assessment procedures was evaluated using a computer simulation framework. The framework includes the data collection, assessment, prediction, and management processes, as well as the implementation of management regulations. It therefore provides an integrated way to evaluate the relative importance of and the interactions between each component of the system with regard to the overall success of the management strategy. The study elucidates guidelines about assessment and management that are general enough to be applied to all tunas in the Atlantic Ocean. It does so by comparing different hypotheses about management and assessment for three stocks (North Atlantic albacore, Atlantic bigeye and East Atlantic skipjack), which are representative of the variety encountered (i.e. from data rich to poor and tropical to temperate waters) in ICCAT stocks. Management performance was especially sensitive to the carrying capacity of the stock. The type of proxy used for MSY was more important to the success of the procedure than the frequency of assessment or the number of indices used in the assessment. Whilst the procedure was successful at achieving the management objectives for albacore, it was only partially successful for bigeye and was too conservative for skipjack.No disponibl

Cinco modelos de mujer en el teatro de Alejandro Casona

Los personajes femeninos ocupan un papel esencial en el teatro de Alejandro Casona (1903-1965), dramaturgo asturiano parcialmente vinculado a la Generación del 27. Ellas, sean o no las protagonistas, son las agentes responsables de provocar el conflicto dramático y, generalmente, las únicas capaces de solucionarlo. Este artículo explora el planteamiento, la construcción y la materialización de cinco modelos de mujer (mujer evasora, educadora, sufridora, amante y sustituta) en diez personajes femeninos de tantas otras obras. Se trata de un análisis del carácter del personaje, su evolución y una reflexión acerca de los motivos del uso de este arquetipo. El estudio también explora la vida y la producción artística de Casona, las transformaciones sociales, culturales y políticas que vivieron las mujeres del segundo tercio del siglo XX y los rasgos del teatro del momento.Female characters have an essential role in Alejandro Casona’s (1903- 1965) theatre, an Asturian playwright, usually linked to the Generation of ’27. Although they may not be the main characters of the play, they are in charge of provoking the dramatic conflict and they usually are the ones destined to solve it. This article explores the approach, the construction and materialization of five female archetypes (evader woman, teacher, suffering woman, lover and substitute woman) in ten female characters from ten plays by Casona. This project studies each character’s behaviour, her evolution and Casona’s purpose for the use of that archetype. The text also analyses the author’s life and artistic work, the social, cultural and political transformations involving women that took place in the second third of the XXth century and the features of that era’s theatre

Boltzmann equation and hydrodynamic fluctuations

We apply the method of invariant manifolds to derive equations of generalized hydrodynamics from the linearized Boltzmann equation and determine exact transport coefficients, obeying Green-Kubo formulas. Numerical calculations are performed in the special case of Maxwell molecules. We investigate, through the comparison with experimental data and former approaches, the spectrum of density fluctuations and address the regime of finite Knudsen numbers and finite frequencies hydrodynamics.Comment: This is a more detailed version of a related paper: I.V. Karlin, M. Colangeli, M. Kroger, PRL 100 (2008) 214503, arXiv:0801.2932. It contains comparison between predictions and experiment, in particular. 11 pages, 6 figures, 2 table

Evaluation of different flow stress laws coupled with a physical based ductile failure criterion for the modelling of the chip formation process of Ti-6Al-4V under broaching conditions

During the machining of Ti-6Al-4V the changing deformation mechanisms produce a complex microstructure of segmented chips, which directly influenced tool-wear and process stability. Numerical simulation could give an insight into the physical phenomena involved in chip segmentation, but its accuracy is directly related to the reliability of the input parameters. In this work, therefore, three different flow stress law were evaluated coupled with a physical based ductile failure criterion, which depends on stress triaxiality and temperature. To this end, the flow stress laws were implemented in the finite element software AdvantEdge by programming user-defined subroutines. The resulting FEM models were compared with orthogonal cutting experimental tests (tubular/linear), analyzing different fundamental outputs (machining forces, temperatures in the workpiece and chip morphology). All the FEM models showed good agreement with the experimental results

NPS pollution analysis in groundwater and streams of rural watersheds in western and southeastern Pampas, Argentina

Non-point source water pollution is a key question in rural watersheds and it needs to be studied in order to prevent damages to ground and surface water quality. The main goal of this study is to analyze nutrient and chemical loads in groundwater and streams in Pampa region, Argentina. For studying groundwater loads, a set of 19 observation wells were installed in 2011, in western Buenos Aires. The wells were located at three landscape positions (upper, middle and lower hill) in seven agricultural fields and groundwater samples were monthly collected. As for surface water, two watersheds located in southeastern Buenos Aires, were chosen: Napaleofu creek Watershed (34.000 hectares) and Quequen Grande River watershed (938.000 hectares). Daily water samples were taken from the main stream from October 2011 to May 2013, at both watersheds. Water Samples collected from wells and streams, were analyzed to determine N, and chemical loads. A group of 11 herbicides and one insecticide frequently used by farmers in the watershed were chosen for the study. Nitrogen and chemical concentrations were analyzed considering rainfall events and also compared to critical limits. Preliminary results are presented from a subset of samples since remaining samples are currently being processed in laboratory. As for NO3-N concentration, most of wells presented variable concentration depending on monthly precipitation and landscape position. Considering 10 mg/L NO3-N as a standard limit, 52% of the observations exceed this value mostly related to unusual precipitations events at winter 2012. Nitrate-Nconcentration in streamflow at Quequen Grande River and Napaleofu creek were on average 5 ppm. NPS Pollution modeling is a second goal of this on-going research. SWAT validation results are also presented for one of the watersheds under study

Numerical Methods for the Stochastic Landau-Lifshitz Navier-Stokes Equations

The Landau-Lifshitz Navier-Stokes (LLNS) equations incorporate thermal fluctuations into macroscopic hydrodynamics by using stochastic fluxes. This paper examines explicit Eulerian discretizations of the full LLNS equations. Several CFD approaches are considered (including MacCormack's two-step Lax-Wendroff scheme and the Piecewise Parabolic Method) and are found to give good results (about 10% error) for the variances of momentum and energy fluctuations. However, neither of these schemes accurately reproduces the density fluctuations. We introduce a conservative centered scheme with a third-order Runge-Kutta temporal integrator that does accurately produce density fluctuations. A variety of numerical tests, including the random walk of a standing shock wave, are considered and results from the stochastic LLNS PDE solver are compared with theory, when available, and with molecular simulations using a Direct Simulation Monte Carlo (DSMC) algorithm

The Phononic Casimir Effect: An Analog Model

We discuss the quantization of sound waves in a fluid with a linear dispersion relation and calculate the quantum density fluctuations of the fluid in several cases. These include a fluid in its ground state. In this case, we discuss the scattering cross section of light by the density fluctuations, and find that in many situations it is small compared to the thermal fluctuations, but not negligibly small and might be observable at room temperature. We also consider a fluid in a squeezed state of phonons and fluids containing boundaries. We suggest that the latter may be a useful analog model for better understanding boundary effects in quantum field theory. In all cases involving boundaries which we consider, the mean squared density fluctuations are reduced by the presence of the boundary. This implies a reduction in the light scattering cross section, which is potentially an observable effect.Comment: 8 pages, 1 figure, talk presented at "60 Years of Casimir Effect", Brasilia, Brazil, June 200