Dynamical behaviour of fine binary mixtures in the presence of air

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Acute esophageal necrosis and low-flow state

Acute esophageal necrosis (AEN), also called black esophagus, is quite exceptional. Endoscopic findings show circumferential black discolouration of the esophagus with or without exudates. The etiology of AEN is presently unknown and is assumed to be multifactorial. Distal esophageal involvement with proximal extension ending sharply at the gastroesophageal junction is the most common presentation. The present case report describes the clinical and endoscopic evolution of black esophagus observed in a patient with significant peripheral vascular disease, who was presented to the intensive care unit at the Hopital Saint-Francois d’Assise (Quebec City, Quebec). Through an extensive review of the literature, common underlying clinical conditions of patients diagnosed with AEN have been identified

Spontaneous Air-Driven Separation in Vertically Vibrated Fine Granular Mixtures

We report the observation of the spontaneous separation of vertically vibrated mixtures of fine bronze and glass spheres of similar diameters. At low frequencies and at sufficient vibrational amplitudes, a sharp boundary forms between a lower region of glass and an upper region of the heavier bronze. The boundary undergoes various oscillations, including periodic tilting motion, but remains extremely sharp. At higher frequencies, the bronze separates as a mid-height layer between upper and lower glass regions, and the oscillations are largely absent. The mechanism responsible for the separation can be traced to the effect of air on the granular motion.</jats:p

Reversing the Brazil nut effect

We propose a lattice model for studying the Brazil Nut Effect (BNE), i.e. the phase segregation occuring when a granular material is vertically shaked. The model considers the tap intensity and the mobility mu of the grains as the main physical parameters. Different mobilities for different grain species lead to segregation (BNE) patterns, reverse segregation (RBNE) patterns, "sandwhich" layered structures or vertical domains. A phase diagram (decompaction chi, mobility difference between both species Delta mu) is obtained in which the different phases are emphasized. In a narrow region of the diagram, different phases coexist. It is shown that the BNE segregation could be reversed by increasing the tap intensity or the characteristics of the grains. Numerical results are compared with earlier experimental works