Bursting of rigid bubbles

We propose here a fluid dynamics video relating the bursting of soap rigid films.Comment: 4 pages and 2 videos included for the Gallery of Fluid Motion 201

Numerical Simulations of Dynamos Generated in Spherical Couette Flows

We numerically investigate the efficiency of a spherical Couette flow at generating a self-sustained magnetic field. No dynamo action occurs for axisymmetric flow while we always found a dynamo when non-axisymmetric hydrodynamical instabilities are excited. Without rotation of the outer sphere, typical critical magnetic Reynolds numbers $Rm_c$ are of the order of a few thousands. They increase as the mechanical forcing imposed by the inner core on the flow increases (Reynolds number $Re$). Namely, no dynamo is found if the magnetic Prandtl number $Pm=Rm/Re$ is less than a critical value $Pm_c\sim 1$. Oscillating quadrupolar dynamos are present in the vicinity of the dynamo onset. Saturated magnetic fields obtained in supercritical regimes (either $Re>2 Re_c$ or $Pm>2Pm_c$) correspond to the equipartition between magnetic and kinetic energies. A global rotation of the system (Ekman numbers $E=10^{-3}, 10^{-4}$) yields to a slight decrease (factor 2) of the critical magnetic Prandtl number, but we find a peculiar regime where dynamo action may be obtained for relatively low magnetic Reynolds numbers ($Rm_c\sim 300$). In this dynamical regime (Rossby number $Ro\sim -1$, spheres in opposite direction) at a moderate Ekman number ($E=10^{-3}$), a enhanced shear layer around the inner core might explain the decrease of the dynamo threshold. For lower $E$ ($E=10^{-4}$) this internal shear layer becomes unstable, leading to small scales fluctuations, and the favorable dynamo regime is lost. We also model the effect of ferromagnetic boundary conditions. Their presence have only a small impact on the dynamo onset but clearly enhance the saturated magnetic field in the ferromagnetic parts. Implications for experimental studies are discussed

Видавничі функції Науково-консультаційної ради Народного комісаріату земельних справ УСРР

У статті висвітлено видавничі функції Науково-консультаційної ради НКЗС УСРР (1927-1930 рр.), а саме, коротко розглянуті наукові видання, де друкувалися матеріали учених та організаторів сільськогосподарської науки того часу.В статье рассмотрены издательские функции Научно-консультационного совета НКНД УССР (1927-1930 гг.), а именно, коротко представлены научные издания, где печатались материалы ученых и организаторов сельскохозяйственного опытного дела того времени.The publishing functions of Scientific consultative council of the Public commissariat of agriculture of USSR in 1927–1930 are considered in the article, namely, briefly presented scientific journals, where printed materials scientists and organizers of agricultural experimental work at the time

Reaction-diffusion dynamics: confrontation between theory and experiment in a microfluidic reactor

We confront, quantitatively, the theoretical description of the reaction-diffusion of a second order reaction to experiment. The reaction at work is \ca/CaGreen, and the reactor is a T-shaped microchannel, 10 $\mu$m deep, 200 $\mu$m wide, and 2 cm long. The experimental measurements are compared with the two-dimensional numerical simulation of the reaction-diffusion equations. We find good agreement between theory and experiment. From this study, one may propose a method of measurement of various quantities, such as the kinetic rate of the reaction, in conditions yet inaccessible to conventional methods

Sr-Nd-Hf isotopes along the Pacific Antarctic Ridge from 41 to 53°S

International audienceMajor, trace element and Sr-Nd-Hf isotope data in basalts collected along the Pacific-Antarctic Ridge (PAR) axis between 53 and 41°S, far from any hotspot influence, reveal tight coherent geochemical variations within the depleted MORB mantle. All samples are located below the Pacific reference line defining two sub-oceanic mantle domains on each side of the Easter microplate. The data extend the PAR 66-53°S field towards more radiogenic Sr (0.70264), less radiogenic Nd (ɛ = 7.7) and Hf (ɛ = 11.4) values. The along ridge geochemical variability is closely related to the morphological segmentation of the ridge. Anomalous geochemical features are attributed to the atypical morphology of two segments due to the presence of off-axis magmatism. The first order ridge discontinuity defined by the Menard transform fault separates two slightly different mantle domains, each with its own history