A dimensional analysis of supersaturated total dissolved gas dissipation

Elevated levels of total dissolved gas (TDG) may occur downstream of dam discharges, leading to increased incidence of gas bubble disease in fish. Accelerating the dissipation of supersaturated TDG in the downstream river can mitigate this negative problem. However, developing effective mitigation techniques is hampered by limitations in present models of TDG dissipation processes. Furthermore, data useful for modelling the dissipation of supersaturated TDG through the free surface in natural rivers are limited. Past studies indicated that the TDG dissipation process is quantitatively different from the reaeration process, and TDG behavior is quantitatively different from dissolved oxygen. However, a correct parameterization of the TDG dissipation process is still missing. The paper presents a novel dimensional analysis of the dissipation of supersaturated TDG. This approach can provide a relationship between the TDG dissipation coefficient and some classical fluid mechanics index-numbers. This dimensional analysis considers some key parameters for the dissipation process both water and TDG properties as well as flow characteristics, including turbulence. These parameters are water kinematic viscosity, TDG molecular diffusivity and vertical turbulent diffusivity, and channel width. The application of dimensional analysis pointed out that the TDG dissipation coefficient is a function of the Schmidt number, the aspect ratio of the channel, and the shear Reynolds number. The dimensional analysis was then verified using both field data collected in some large natural rivers and reservoirs in Sichuan and experimental data in laboratory flume at State Key Laboratory of Hydraulics and Mountain River Engineering of Sichuan University. The analysis revealed the key role of turbulence in controlling the TDG dissipation while the importance of gas/water characteristics remains still unclear and needs further investigations

La visión socio-política sobre el mundo primitivo en el pensamiento de Giambattista Vico

El presente ensayo pone de relieve cómo Vico fue uno de los pensadores modernos que se planteó el objetivo de reconstruir la historia del mundo primitivo. A diferencia de varios autores que le precedieron y de otros contemporáneos, el filósofo napolitano mostró que el mundo originario, en lugar de idílico, se hallaba afligido por el miedo, la angustia y las necesidades básicas. Sin embargo, lo que ante todo define a Vico es el hecho de representar el mundo primitivo no como un bloque fijo y unitario, sino como un mundo constituido en diferentes fases históricas y por conflictos sociales y de clase. Al carecer de documentos escritos, Vico elaboró una reconstrucción de la historia basada en una nueva y revolucionaria teoría de mitos que, al fundarse en la creatividad inducida por la fantasía, son denominados “universali fantastici” (universales fantásticos).This essay emphasizes how Vico was one of the modern philosophers to set himself the goal to reconstruct the history of the primitive world. Differently from several authors who preceded him and also other contemporary thinkers, the Neapolitan philosopher showed that the world of the origin wasn’t idyllic, but it was affected by fear, anguish and basic needs. What mainly characterizes Vico, however, is the fact that he represented the primitive world not as a unitary and fixed block, but as a world made of different historical phases and of class and social conflicts. As there were no written documents, Vico elaborated a reconstruction of history, basing it on a new and revolutionary theory of myths which, being based on creativity induced by fantasy, are called “universali fantastici” (fantastic universals)

Testing the black hole "no-hair" hypothesis

Black holes in General Relativity are very simple objects. This property, that goes under the name of "no-hair," has been refined in the last few decades and admits several versions. The simplicity of black holes makes them ideal testbeds of fundamental physics and of General Relativity itself. Here we discuss the no-hair property of black holes, how it can be measured in the electromagnetic or gravitational window, and what it can possibly tell us about our universe.Comment: Commissioned by Classical and Quantum Gravit