Coupling of rotating water jets by surface waves

International audienceAbove a critical flow rate, a single jet impinging from below on a water-air interface oscillates while arrays of jets exhibit collective behaviors. The aim of the paper is to explain the physics governing such an array. First, a series of experiments shows that the instability mechanism leading to the oscillation of a single jet is due to a feedback effect between surface distortion and the unstable jet as in the ''jet-edge'' system and that several jets are coupled through surface waves. Then a modelization is proposed in which jets are considered as oscillators close to their limit cycle coupled by delayed action to take into account the wave propagation. A good agreement is obtained between the predictions of the model and experiments on sets of two or four jets. The long range of the surface waves and the large number of oscillators render this jet configuration very similar to idealized phase coupled nonlinear oscillators investigated in theoretical models but with a not instantaneous coupling ensured by traveling waves. This allows in particular the existence of various synchronization modes, which appear as geometrical pattern

Liquid Film Coating a Fiber as a Model System for the Formation of Bound States in Active Dispersive-Dissipative Nonlinear Media

We analyze the coherent-structure interaction and the formation of bound states in active dispersivedissipative nonlinear media using a viscous film coating a vertical fiber as a prototype. The coherent structures in this case are droplike pulses that dominate the evolution of the film.We study experimentally the interaction dynamics and show evidence for formation of bound states. A theoretical explanation is provided through a coherent-structures theory of a simple model for the flow

Influence of humidity on granular packings with moving walls

A significant dependence on the relative humidity H for the apparent mass (Mapp) measured at the bottom of a granular packing inside a vertical tube in relative motion is demonstrated experimentally. While the predictions of Janssen's model are verified for all values of H investigated (25%< H <80%), Mapp increases with time towards a limiting value at high relative humidities (H>60%) but remains constant at lower ones (H=25%). The corresponding Janssen length is nearly independent of the tube velocity for H>60% but decreases markedly for H=25%. Other differences are observed on the motion of individual beads in the packing. For H=25%, they are almost motionless while the mean particle fraction of the packing remains constant; for H>60% the bead motion is much more significant and the mean particle fraction decreases. The dependence of these results on the bead diameter and their interpretation in terms of the influence of capillary forces are discussed.Comment: 6 pages, 6 figure

Pulse dynamics in low-Reynolds-number interfacial hydrodynamics: Experiments and theory

a b s t r a c t We analyze interaction of nonlinear pulses in active-dispersive-dissipative nonlinear media. A particular example of such media is a viscous thin film coating a vertical fibre. Experiments for this system reveal that the interface evolves into a train of droplike solitary pulses in which numerous inelastic coalescence events take place. In such events, larger pulses catch up with smaller ones and annihilate them. However, for certain flow conditions and after a certain distance from the inlet, no more coalescence is observed and the flow is described by quasi-equilibrium solitary pulses interacting continuously with each other through attractions and repulsions, and, eventually they form bound states of groups of pulses in which the pulses travel with the same velocities as a whole. This experimental study represents the first evidence of formation of bound states in low-Reynolds-number interfacial hydrodynamics. To gain theoretical insight into the interaction of the pulses and formation of bound states, we derive a weakly nonlinear model for the flow, the generalized Kuramoto-Sivashinsky (gKS) equation, that retains the fundamental mechanisms of the wave evolution, namely, dominant nonlinearity, instability, stability and dispersion. Much like in the experiments, the spatio-temporal evolution of the gKS equation is dominated by quasistationary solitary pulses which continuously interact with each other through coalescence events or attractions/repulsions. To understand the latter case, we utilize a weak-interaction theory for the solitary pulses of the gKS equation. The theory is based on representing the solution of the equation as a superposition of the pulses and an overlap function and leads to a coupled system of ordinary differential equations describing the evolution of the locations of the pulses, or, alternatively, the evolution of the separation distances. By analyzing the fixed points of this system, we obtain bound states of interacting pulses. For two pulses, we provide a criterion for the existence of a countable infinite or finite number of bound states, depending on the strength of the dispersive term in the equation. The interaction theory and resulting bound states are corroborated by computations of the full equation. We also find qualitative agreement between the theory and the experiments

Structural anisotropy of directionally dried colloids

Aqueous colloidal dispersions of silica particles become anisotropic when they are dried through evaporation. This anisotropy is generated by a uniaxial strain of the liquid dispersions as they are compressed by the flow of water toward a solidification front. Part of the strain produced by the compression is relaxed, and part of it is stored and transferred to the solid. This stored elastic strain has consequences for the properties of the solid, where it may facilitate the growth of shear bands, and generate birefringence

The interplay of crack hopping, delamination and interface failure in drying nanoparticle films

Films formed through the drying of nanoparticle suspensions release the build-up of strain through a variety of different mechanisms including shear banding, crack formation and delamination. Here we show that important connections exist between these different phenomena: delamination depends on the dynamics of crack hopping, which in turn is influenced by the presence of shear bands. We also show that delamination does not occur uniformly across the film. As cracks hop they locally initiate the delamination of the film which warps with a timescale much longer than that associated with the hopping of cracks. The motion of a small region of the delamination front, where the shear component of interfacial crack propagation is believed to be enhanced, results in the deposition of a complex zig-zag pattern on the supporting substrate

Human amniotic membrane for myocutaneous dehiscence after a radical surgical treatment of vulvar cancer: A case report

Background: The application of the amniotic membrane could have a favourable effect on tissue repair and regeneration. We report the first case of implant of an amniotic membrane in a patient affected by myo-cutaneous dehiscence, after a radical surgical treatment for vulvar cancer. Methods: We describe a case of a 74-years-old patient affected by vulvar cancer. After radiotherapy, the patient underwent to an anterior pelvic exenteration with uretero-ileo-cutaneostomy by Wallace, bilateral pelvic lymphadenectomy, omental biopsies, omental flap, bilateral inguinal lymphadenectomy, resection of ulcerated left inguinal lesion, reconstruction with left gracilis muscle flap and locoregional V-Y advancement flap. The patient developed a myo-cutaneous dehiscence. Two months after the surgery, following an accurate curettage of the wound and negative pressure therapy, a patch of human amniotic membrane was implanted. Results: The surgical procedure was easy, feasible and did not require long operating room times. No intraoperative or postoperative complications occurred. The results obtained were encouraging with a marked improvement in the surgical wound. Conclusion: the use of amniotic membranes was safely and easily performed to promote the healing of complicated surgical wounds

Drying colloidal systems: laboratory models for a wide range of applications

The drying of complex fluids provides a powerful insight into phenomena that take place on time and length scales not normally accessible. An important feature of complex fluids, colloidal dispersions and polymer solutions is their high sensitivity to weak external actions. Thus, the drying of complex fluids involves a large number of physical and chemical processes. The scope of this review is the capacity to tune such systems to reproduce and explore specific properties in a physics laboratory. A wide variety of systems are presented, ranging from functional coatings, food science, cosmetology, medical diagnostics and forensics to geophysics and art

Impact of COVID-19 mitigation measures on patients with spine disease in Friuli Venezia Giulia

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