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The term supercurrent relates to a macroscopic dissipation-free collective motion of a quantum condensate and is commonly associated with such famous low-temperature phenomena as superconductivity and superfluidity. Another type of motion of quantum condensates is second sound-a wave of the density of a condensate. Recently, we reported on an enhanced decay of a parametrically induced Bose-Einstein condensate (BEC) of magnons caused by a supercurrent outflow of the BEC phase from the locally heated area of a room temperature magnetic film. Here, we present the direct experimental observation of a long-distance spin transport in such a system. The condensed magnons being pushed out from the potential well within the heated area form a density wave, which propagates through the BEC many hundreds of micrometers in the form of a specific second sound pulse-Bogoliubov waves-and is reflected from the sample edge. The discovery of the long distance supercurrent transport in the magnon BEC further advances the frontier of the physics of quasiparticles and allows for the application of related transport phenomena for low-loss data transfer in perspective magnon spintronics devices.Supercurrent is a macroscopic quantum phenomenon when many bosons (real-or quasiparticles) being selfassembled in one quantum state with minimum energy and zero velocity-a Bose-Einstein condensate (BEC)[1-11]-move as a whole due to a phase gradient imposed on their joint wave function. This phenomenon being mostly associated with resistant-free electric currents of Cooper pairs [12] in superconductors and superfluidity of liquid Helium [13-17] is, however, much more widespread [18][19][20]. It is experimentally confirmed in the quantum condensates of diluted ultracold gases [21,22], of nuclear magnons in liquid 3 He [23-25], of polaritons in semiconductor microcavities [26] and, recently, of electron magnons in room-temperature ferrimagnetic films [27]. Supercurrents being topologically confined often manifest themselves in a form of quantum vortices [21,28,29].The quantum condensate supports another form of motion-second sound [15,30]. Second sound can be considered as elementary excitations of various types, which can propagate in continuous media with an almost linear dispersion law in the long-wavelength limit. The term second sound stems from an analogy with the ordinary sound waves or first sound-the wave oscillations of media density and mechanical momentum. The most well-known example of second sound is anti-phase oscillations of the densities ρ n and ρ s of the normal-fluid and superfluid components of superfluid 4 He, in which the total density ρ = ρ n + ρ s does not oscillate [15]. These oscillations can be associated with temperature waves, because the ratio ρ n /ρ s strongly depends on the local temperature, while ρ in 4 He is practically temperature independent. Some solid dielectrics represent another system type which supports the propagation of temperature waves at low temperatures [31][32][33][34]. In this case, the second soun...

We elucidate the mechanism of drag reduction by polymers in turbulent wall-bounded flows: while momentum is produced at a fixed rate by the forcing, polymer stretching results in the suppression of momentum flux to the wall. On the basis of the equations of fluid mechanics we develop the phenomenology of the "maximum drag reduction asymptote" which is the maximum drag reduction attained by polymers. Based on Newtonian information only we demonstrate the existence of drag reduction, and with one experimental parameter we reach agreement with the experimental measurements.

The quantization of vortex lines in superfluids requires the introduction of their density L(r, t) in the description of quantum turbulence. The space homogeneous balance equation for L(t), proposed by Vinen on the basis of dimensional and physical considerations, allows a number of competing forms for the production term P. Attempts to choose the correct one on the basis of time-dependent homogeneous experiments ended inconclusively. To overcome this difficulty we announce here an approach that employs an inhomogeneous channel flow which is excellently suitable to distinguish the implications of the various possible forms of the desired equation. We demonstrate that the originally selected form which was extensively used in the literature is in strong contradiction with our data. We therefore present a new inhomogeneous equation for L(r, t) that is in agreement with our data and propose that it should be considered for further studies of superfluid turbulence.

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