Non-equilibrium Anisotropic Phases, Nucleation and Critical Behavior in a Driven Lennard-Jones Fluid

We describe short-time kinetic and steady-state properties of the non--equilibrium phases, namely, solid, liquid and gas anisotropic phases in a driven Lennard-Jones fluid. This is a computationally-convenient two-dimensional model which exhibits a net current and striped structures at low temperature, thus resembling many situations in nature. We here focus on both critical behavior and details of the nucleation process. In spite of the anisotropy of the late--time spinodal decomposition process, earlier nucleation seems to proceed by Smoluchowski coagulation and Ostwald ripening, which are known to account for nucleation in equilibrium, isotropic lattice systems and actual fluids. On the other hand, a detailed analysis of the system critical behavior rises some intriguing questions on the role of symmetries; this concerns the computer and field-theoretical modeling of non-equilibrium fluids.Comment: 7 pages, 9 ps figures, to appear in PR

German to Spanish translation of Einstein’s work on the formation of meanders in rivers

In 1926 Albert Einstein gave a clear explanation of the physical processes involved in the meander formation and evolution in open channels (Einstein, 1926). Although this work is far from being recognized as one of his greatest achievements, such as his annus mirabilis papers in 1905, he shows a truly remarkable didactic skills that make it easy to understand even to the non- specialist. In particular, a brilliant explanation of the tea leaf paradox can be found in this paper of 1926, presented as a simple experiment for clarifying the role of Earth rotation and flow curvature in the differential river banks erosion. This work deserves to be considered as a pioneering work that has laid a basic knowledge in currently very active research fields in fluvial geomorphology, estuarine physics, and hydraulic engineering. In response to the curiosity aroused and transmitted to the authors over the years by undergraduates and MSc. students, and also due to its historical and scientific significance, we present here the Spanish translation of Einstein’s original work published in German in 1926 in Die Naturwissenschaften (Einstein, 1926). Einstein’s drawings have not been interpreted, but just updated preserving their original spirit

Distribución espacial de salinidad y turbidez en el estuario del Guadalquivir

En esta contribución se analiza la variabilidad espacio-temporal a escala promediomareal de salinidad y la turbidez en el estuario del Guadalquivir. Se han determinado los flujos de concentración de sal y sólidos en suspensión a lo largo de todo el estuario

Effects of tidal-forcing variations on tidal properties along a narrow convergent estuary

A 1D analytical framework is implemented in a narrow convergent estuary that is 78 km in length (the Guadiana, Southern Iberia) to evaluate the tidal dynamics along the channel, including the effects of neap-spring amplitude variations at the mouth. The close match between the observations (damping from the mouth to ∼ 30 km, shoaling upstream) and outputs from semi-closed channel solutions indicates that the M2 tide is reflected at the estuary head. The model is used to determine the contribution of reflection to the dynamics of the propagating wave. This contribution is mainly confined to the upper one third of the estuary. The relatively constant mean wave height along the channel (< 10% variations) partly results from reflection effects that also modify significantly the wave celerity and the phase difference between tidal velocity and elevation (contradicting the definition of an “ideal” estuary). Furthermore, from the mouth to ∼ 50 km, the variable friction experienced by the incident wave at neap and spring tides produces wave shoaling and damping, respectively. As a result, the wave celerity is largest at neap tide along this lower reach, although the mean water level is highest in spring. Overall, the presented analytical framework is useful for describing the main tidal properties along estuaries considering various forcings (amplitude, period) at the estuary mouth and the proposed method could be applicable to other estuaries with small tidal amplitude to depth ratio and negligible river discharge.info:eu-repo/semantics/publishedVersio

Tide transformation in the Guadalquivir estuary (SW Spain) and process-based zonation

An edited version of this paper was published by AGU. Copyright (2012) American Geophysical Union.This study analyzes tide transformation in the Guadalquivir estuary (SW Spain). When fresh water discharges are less than 40 m3/s, the estuary is tidally-dominated (flood-dominated) and well mixed. Under such conditions, the estuary can be divided into three stretches, each characterized by a different tide propagation process. In the first stretch of 25 km, the dominant process is diffusion. In the next stretch, approximately over 35 km length, convergence and friction processes are in balance. At the head of the estuary, in the last stretch, the tidal motion is partially standing because of tidal reflection on the Alcalá del Río dam, located 110 km upstream from the estuary mouth. The reflection coefficient R varies with the frequency; for diurnal constituents its magnitude ∣RD∣ is 0.25; this value increases in the case of semi-diurnal (∣RS∣ ≈ 0.40), and quarter-diurnal constituents (∣RQ∣ ≈ 0.65), and reaches its minimum at the sixth-diurnal components (∣RX∣ ≈ 0.10). The tidal reflection can generate residual currents that have consequences in the bed morphology. Furthermore, when the fresh water discharges are greater than 400 m3/s, the estuary is fluvially-dominated and the water level can be calculated as the linear superposition of tide and river contributions. However, superposition arguments do not hold for currents at any point in the estuary.This research was funded by the Spanish Ministry of Science and Innovation (project CTM2009-10520/MAR) and by the Department of Innovation, Science and Business of the Andalusian Regional Government through the project P09-TEP-4630 and a research contract between the University of Granada and the CSIC (under the direction of the Port Authority of Seville).Peer reviewe

On the similarities and differences between lattice and off–lattice models of driven fluids

Microscopic modeling of complex systems by cellular automata, which deal with particles at lattice sites interacting via simple local rules, involves some arbitrariness besides a drastic simplification of nature. Here we briefly report on some recent work on the influence of dynamic details on the morphological and critical properties of one of such model systems. In particular, we discuss on the similarities and differences between a kinetic nonequilibrium Ising model—which is a prototype for nonequilibrium anisotropic phase transitions—and its off–lattice counterpart, namely, an analogue in which the spatial coordinates of the particles vary continuously. We also pay attention to a related driven lattice model with nearest-neighbor exclusion

Circulation and distribution of suspended mesozooplankton carcasses in a mid-latitude estuary

The coast of southern Chile, located between 37° and 41°S, has many estuaries, which, together with their wetlands, still comprise a region with high biological richness and a high ecosystem value. The Valdivia River Estuary (VRE) stands out due to its relative size and commercial importance. This study analyses time series of environmental forcings and idealized model output to identify estuarine regimes and the subtidal circulation, and its influence on the distribution of Suspended Meso-Zooplankton Carcasses (SMZC), which may affect the local labile organic carbon input. Field campaigns were conducted in 2014 and 2015, and time series of metocean forcings span from 2012 to 2018. The characteristic regimes of the estuary that control the seasonal suspended particulate matter distribution were identified as Normal, Extreme, Exceptional Rainy, and Exceptional Dry. When mapped on the Geyer & MacCready circulation-stratification diagram, they coincide with partially-mixed, strongly-stratified, salt-wedge, and well-mixed water column structures, respectively. The idealized numerical model allows determining the subtidal circulation patterns induced by the along-channel density gradient, river discharge, and wind. The equilibrium SMZC distribution within the VRE during Normal and Exceptional Dry regimes was determined from the modeled circulation patterns. Model results indicated that, during the austral autumn (April 2014; Normal regime), the SMZC distribution shows a maximum concentration as low as 128 individuals per m3 located near the head of the estuary. This suggests low residence times of suspended carcasses within the estuary. During the austral summer (January 2015; Exceptional Dry regime), the SMZC distribution exhibits its maximum value near the mouth, exceeding 15,000 ind. m−3. These results suggest a massive carcass-derived carbon export towards the estuary mouth during dry seasons. Remarkably, the cross-section where maximum SMZC was predicted during this regime matches the area where large beds of Tagelus dombeii have been reported. Overall, this study highlights the importance of circulation-stratification relationships on the control of SMZC trapping mechanisms and on the identification of hotspots of benthic biomass in mid-latitude estuaries. Other estuaries with similar relationships and regimes might experience similar shifts in suspended meso-zooplankton distribution patterns in response to seasonal changes in forcings. © 202