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Viscous tilting and production of vorticity in homogeneous turbulence
Viscous depletion of vorticity is an essential and well known property of turbulent flows, balancing, in the mean, the net vorticity production associated with the vortex stretching mechanism. In this letter, we, however, demonstrate that viscous effects are not restricted to a mere destruction process, but play a more complex role in vorticity dynamics that is as important as vortex stretching. Based on the results from three dimensional particle tracking velocimetry experiments and direct numerical simulation of homogeneous and quasi-isotropic turbulence, we show that the viscous term in the vorticity equation can also locally induce production of vorticity and changes of the orientation of the vorticity vector (viscous tilting)
High-pressure study of the basal-plane anisotropy of the upper critical field of the topological superconductor SrxBi2Se3
We report a high-pressure transport study of the upper-critical field,
, of the topological superconductor SrBiSe ( K). was measured for magnetic fields directed along two
orthogonal directions, and , in the trigonal basal plane. While
superconductivity is rapidly suppressed at the critical pressure
GPa, the pronounced two-fold basal-plane anisotropy at K, recently reported at ambient pressure (Pan et al., 2016), is
reinforced and attains a value of at the highest pressure (2.2 GPa).
The data reveal that the unconventional superconducting state with broken
rotational symmetry is robust under pressure
Small scale aspects of flows in proximity of the turbulent/non-turbulent interface
The work reported below is a first of its kind study of the properties of
turbulent flow without strong mean shear in a Newtonian fluid in proximity of
the turbulent/non-turbulent interface, with emphasis on the small scale
aspects. The main tools used are a three-dimensional particle tracking system
(3D-PTV) allowing to measure and follow in a Lagrangian manner the field of
velocity derivatives and direct numerical simulations (DNS). The comparison of
flow properties in the turbulent (A), intermediate (B) and non-turbulent (C)
regions in the proximity of the interface allows for direct observation of the
key physical processes underlying the entrainment phenomenon. The differences
between small scale strain and enstrophy are striking and point to the definite
scenario of turbulent entrainment via the viscous forces originating in strain.Comment: 4 pages, 4 figures, Phys. Fluid
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