Air invasion in a granular layer immersed in a fluid: Morphology and dynamics

We investigate the morphology and dynamics of the region invaded by air injected at the bottom of an immersed granular bed. Previous experimental results point out the formation of a fluidized zone with a parabolic shape which does not depend, in the stationary regime, on the injection flow-rate. By tilting the experiment, we can tune the effective gravity in the system. We show that it does not affect significantly the morphology either. A numerical study made it possible to access the typical height and width of the structure, which are governed by the relative effects of gravity and capillarity. After a brief review on this subject, we propose first, new experimental observations on the air invasion regimes and on the morphology of the fluidized zone, in particular its growth dynamics; then, we complement the previous numerical study by considering the influence of the bottom boundary condition. In particular, we quantify the morphology of the invaded region when the gas is injected in the bulk, thus when air is likely to propagate downwards. These results are of practical importance in the prediction of the morphology of gas invasion in soils, from CO2 sequestration to pollutant propagation

Dynamics of crater formation in immersed granular materials

We report the formation of a crater at the free surface of an immersed granular bed, locally crossed by an ascending gas flow. In 2D, the crater consists of two piles which develop around the location of the gas emission. We observe that the typical size of the crater increases logarithmically with time, independently of the gas emission dynamics. We describe the related granular flows and give an account of the influence of the experimental parameters, especially of the grain size and of the gas flow

Flow and fracture in water-saturated, unconstrained granular beds

International audienceSpecialty section: This article was submitted to Interdisciplinary Physics, a section of the journal Frontiers in Physics The injection of gas in a liquid-saturated granular bed gives rise to a wide variety of invasion patterns. Many studies have focused on constrained porous media, in which the grains are fixed in the bed and only the interstitial fluid flows when the gas invades the system. With a free upper boundary, however, the grains can be entrained by the ascending gas or fluid motion, and the competition between the upward motion of grains and sedimentation leads to new patterns. We propose a brief review of the experimental investigation of the dynamics of air rising through a water-saturated, unconstrained granular bed, in both two and three dimensions. After describing the invasion pattern at short and long time, a tentative regime-diagram is proposed. We report original results showing a dependence of the fluidized zone shape, at long times, on the injection flow rate and grain size. A method based on image analysis makes it possible to detect not only the fluidized zone profile in the stationary regime, but also to follow the transient dynamics of its formation. Finally, we describe the degassing dynamics inside the fluidized zone, in the stationary regime. Depending on the experimental conditions, regular bubbling, continuous degassing, intermittent regime or even spontaneous flow-to-fracture transition are observed

Morphology of air invasion in an immersed granular layer

International audienceWe report a study of the paths formed by a finite volume of air gently injected at the base of an immersed granular material. A two-dimensional model, based on experimental observations, shows that the typical height and width of the region explored by the branched path depends not only on the injected volume V , but also on a dimensionless parameter χ which accounts for the relative effects of the gravity and capillarity. For a given injected volume V , larger gravity effects lead to taller and narrower structures; for a given χ , the typical height and width of the structure scale like V 1/2 and V 1/4 , respectively, while the typical gaseous fraction in the corresponding region increases accordingly like V 1/4 . Such results can be of practical importance: For instance, gas can be trapped on purpose in an underground natural container below a granular slurry. Our results can help in predicting if the gas is likely to reach the free surface and escape the system if the container presents a defect (hole or fracture)

Gas-induced fluidization of mobile liquid-saturated grains

International audienceGas invasion in liquid-saturated sands exhibits different morphologies and dynamics. For mobile beds, the repeated rise of gas through the layer leads to the growth of a fluidized zone, which reaches a stationary shape. Here, we present experimental results characterizing the evolution of the fluidized region as a function of the gas-flow rate and grain size. We introduce a new observable, the flow density, which quantifies the motion of the grains in the system. The growth of the fluidized zone is characterized by a spatiotemporal analysis, which provides the stabilization time, τ_s. In the stationary regime, we report two main contributions to motion in the fluidized region: the central gas rise and a convective granular motion. Interestingly, a static model with a fixed porous network accounts for the final shape of the invasion zone. We propose an explanation where the initial gas invasion weakens the system and fixes since the early stage the morphology of the fluidized zone

Venting dynamics of an immersed granular layer

6 pagesInternational audienceAir is injected locally at the base of an immersed granular bed. The gas, which is forced to flow gently through thematerial, creates several paths between the grains.We observe that the latter gas venting results in the emission of bubbles in a localized region at the free surface. Additional experiments, performed in two dimensions, permit a direct visualization of the paths, and a theoretical approach shows that the typical size of the region at the free surface can be accounted for by a diffusionlike process. The diffusion coefficient is expressed as a function of the system parameters

Visualizing the entrepreneur’s journey: Synchronic, iterative, and linear representations

In this paper, we draw from entrepreneurship literature to develop a typology of visual genres representing “journey”-related aspects of entrepreneurship. We identify and characterize iterative, linear, and synchronic representations of the entrepreneur’s journey, providing examples of each from the entrepreneurship literature, and we discuss how these visual genres collectively help neophyte entrepreneurs understand different aspects of their entrepreneurial journey. Finally, we draw implications for entrepreneurship communication and for professional communication more generally.Writin

Análisis de regresión lineal: codificación e interpretación

[ES] Desde los trabajos de Fisher de principios del pasado siglo se utiliza el análisis de varianza, aunque no siempre con pleno sentido. Dado que el análisis de varianza (ANOVA) y el de regresión (ANREG) son diferentes aplicaciones del modelo lineal general (MLG), en este trabajo se expone cómo se abordan los diseños experimentales clásicos desde la perspectiva del ANREG. Esto implica la codificación del factor, o los factores, en los distintos diseños. También se analizan las ventajas de este enfoque, sobre todo su flexibilidad y la cantidad y calidad de información que proporcionan. Se revisan ejemplos concretos con el software Jamovi. [ENG] Since Fisher's works in the early twentieth century, analysis of variance has been used, although not always with full comprehension. Given that analysis of variance (ANOVA) and regression analysis (ANREG) are different applications of the general linear model (GLM), this paper explains how classical experimental designs are approached from the perspective of ANREG. This involves the encoding of the factor, or factors, in different designs. The advantages of this approach are also analyzed, particularly its flexibility and the quantity and quality of information it provides. Concrete examples are reviewed using the software Jamovi

El informe de arbitraje según la recomendación de publicación y la productividad de los evaluadores

El informe de arbitraje de artículos de investigación es un género en el que se cristaliza una parte del proceso colectivo de construcción del conocimiento. Debido a su carácter confidencial, existen muy pocos trabajos que aborden empíricamente este género. A su vez, esos pocos estudios tienen una serie de limitantes, como la falta de definición de la unidad de análisis y la falta de integración de los datos discursivos con los datos sociales de quienes los producen. En este trabajo, presentamos un modelo que busca superar limitantes. Aplicamos este modelo para describir cómo varía el informe de arbitraje según dos atributos extralingüísticos, la recomendación de publicación (aceptar, condicionar o rechazar) y el número de artículos publicados por los evaluadores. Los resultados muestran que ambos atributos extralingüísticos se asocian a cambios específicos del discurso de este género, siendo la recomendación de publicación más determinante que la productividad de los evaluadores.The referee report of research articles is a discursive genre in which a part of the collective process of building knowledge is crystalized. Given its confidentiality, there is little empirical work on this genre. Among these few contributions, a series of limitations can be identified, such as the lack of definition of the unit of analysis or the lack of integration between discursive and sociometric data. In this article, we present a model that contributes to overcoming these limitations. The model was applied with the purpose of analyzing the variation of referee reports according to two extralinguistic variables, i.e., publication recommendation (accepted, conditioned, rejected) and referee's number of published articles. The results showed that both extralinguistic attributes were associated with specific discourse variations, of which publication recommendation was more decisive than referee's academic productivity