A string of tracers, interacting elastically, in a turbulent flow is shown to have a dramatically different behaviour when compared to the non-interacting case. In particular, such an elastic chain shows strong preferential sampling of the turbulent flow unlike the usual tracer limit: an elastic chain is trapped in the vortical regions. The degree of preferential sampling and its dependence on the elasticity of the chain is quantified via the Okubo-Weiss parameter. The effect of modifying the deformability of the chain, via the number of links that form it, is also examined. PACS numbers: 47.27.Gs, 05.20.Jj The development of Lagrangian techniques, in experiments and theory, has lead to major advances in our understanding of the complexity of turbulent flows, especially at small scales [1][2][3]. What makes this possible is the use of tracer particles which uniformly sample the flow and hence access the complete phase space in which the dynamics resides. This feature of tracers depends, crucially, on the assumption that the particles remain inertia-less and point-like. When some of these assumptions are relaxed, it may lead to dissipative particle dynamics and preferential sampling of the structures in a flow [4][5][6][7][8][9][10]. This is, for instance, the case for heavy, inertial particles, which show small-scale clustering and concentrate away from vortical regions. Various phenomena can influence the properties of inertial clustering in turbulence, such as gravity [11,12], turbophoresis [13,14], or the non-Newtonian nature of the fluid [15]. Preferential sampling in turbulent flows may also emerge as a result of the motility of particles, as in the case of gyrotactic [16], interacting [17], or jumping [18] micro-swimmers.We now propose a novel mechanism for preferential sampling in turbulent flows which is induced by extensibility. A simple model of an extensible object which retains enough internal structure is a chain of tracers with an elastic coupling between the nearest neighbours. We show, remarkably, that turning on such elastic interactions amongst tracers leads to very different dynamics: unlike the case of non-interacting tracers, an elastic chain preferentially samples vortical regions of the flow. We perform a systematic study of this phenomenon and quantify, via the Okubo-Weiss parameter, the level of preferential sampling and its dependence on the elasticity and deformability of the chain.Harmonic chains have been at the heart of several important problems in the areas of equilibrium and nonequilibrium statistical physics. These have ranged from problems in crystalline to amorphous transitions [19], electrical and thermal transport both in and out-ofequilibrium [20], as well as understanding structural properties of disordered and random systems [21]. Given the ubiquity and usefulness of the elastic chain, it is sur-prising that the effect of a turbulent medium on long chains has not been studied as extensively as in other areas of non-equilibrium statistical physics.There is another reason...

We study two-dimensional (2D) binary-fluid turbulence by carrying out an extensive direct numerical simulation (DNS) of the forced, statistically steady turbulence in the coupled Cahn-Hilliard and Navier-Stokes equations. In the absence of any coupling, we choose parameters that lead (a) to spinodal decomposition and domain growth, which is characterized by the spatiotemporal evolution of the Cahn-Hilliard order parameter ϕ, and (b) the formation of an inverse-energy-cascade regime in the energy spectrum E(k), in which energy cascades towards wave numbers k that are smaller than the energy-injection scale kin j in the turbulent fluid. We show that the Cahn-Hilliard-Navier-Stokes coupling leads to an arrest of phase separation at a length scale Lc, which we evaluate from S(k), the spectrum of the fluctuations of ϕ. We demonstrate that (a) Lc ~ LH, the Hinze scale that follows from balancing inertial and interfacial-tension forces, and (b) Lc is independent, within error bars, of the diffusivity D. We elucidate how this coupling modifies E(k) by blocking the inverse energy cascade at a wavenumber kc, which we show is ≃2π/Lc. We compare our work with earlier studies of this problem.

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In quantum systems, signatures of multifractality are rare. They have been found only in the multiscaling of eigenfunctions at critical points. Here we demonstrate multifractality in the magnetic-field-induced universal conductance fluctuations of the conductance in a quantum condensed-matter system, namely, high-mobility single-layer graphene field-effect transistors. This multifractality decreases as the temperature increases or as doping moves the system away from the Dirac point. Our measurements and analysis present evidence for an incipient Anderson-localization near the Dirac point as the most plausible cause for this multifractality. Our experiments suggest that multifractality in the scaling behaviour of local eigenfunctions are reflected in macroscopic transport coefficients. We conjecture that an incipient Anderson-localization transition may be the origin of this multifractality. It is possible that multifractality is ubiquitous in transport properties of lowdimensional systems. Indeed, our work suggests that we should look for multifractality in transport in other low-dimensional quantum condensed-matter systems. * aveek@iisc.ac.in arXiv:1804.04454v1 [cond-mat.mes-hall]