871 research outputs found
Solitary vortex couples in viscoelastic Couette flow
We report experimental observation of a localized structure, which is of a
new type for dissipative systems. It appears as a solitary vortex couple
("diwhirl") in Couette flow with highly elastic polymer solutions. A unique
property of the diwhirls is that they are stationary, in contrast to the usual
localized wave structures in both Hamiltonian and dissipative systems which are
stabilized by wave dispersion. It is also a new object in fluid dynamics - a
couple of vortices that build a single entity somewhat similar to a magnetic
dipole. The diwhirls arise as a result of a purely elastic instability through
a hysteretic transition at negligible Reynolds numbers. It is suggested that
the vortex flow is driven by the same forces that cause the Weissenberg effect.
The diwhirls have a striking asymmetry between the inflow and outflow, which is
also an essential feature of the suggested elastic instability mechanism.Comment: 9 pages (LaTeX), 5 Postscript figures, submitte
Stretching of polymers in a random three-dimensional flow
Behavior of a dilute polymer solution in a random three-dimensional flow with
an average shear is studied experimentally. Polymer contribution to the shear
stress is found to be more than two orders of magnitude higher than in a
laminar shear flow. The results indicate that the polymer molecules get
strongly stretched by the random motion of the fluid.Comment: 4 pages, 3 figure
Remote operations and interactions for systems of arbitrary dimensional Hilbert space: a state-operator approach
We present a systematic simple method for constructing deterministic remote
operations on single and multiple systems of arbitrary discrete dimensionality.
These operations include remote rotations, remote interactions and
measurements. The resources needed for an operation on a two-level system are
one ebit and a bidirectional communication of two cbits, and for an n-level
system, a pair of entangled n-level particles and two classical ``nits''. In
the latter case, there are possible distinct operations per one n-level
entangled pair. Similar results apply for generating interaction between a pair
of remote systems and for remote measurements. We further consider remote
operations on spatially distributed systems, and show that the number of
possible distinct operations increases here exponentially, with the available
number of entangled pairs that are initial distributed between the systems. Our
results follow from the properties of a hybrid state-operator object
(``stator''), which describes quantum correlations between states and
operations.Comment: 18 pages, 3 figures, typo correction
Attractive and repulsive cracks in a heterogeneous material
We study experimentally the paths of an assembly of cracks growing in
interaction in a heterogeneous two-dimensional elastic brittle material
submitted to uniaxial stress. For a given initial crack assembly geometry, we
observe two types of crack path. The first one corresponds to a repulsion
followed by an attraction on one end of the crack and a tip to tip attraction
on the other end. The second one corresponds to a pure attraction. Only one of
the crack path type is observed in a given sample. Thus, selection between the
two types appears as a statistical collective process.Comment: soumis \`a JSTA
Elastic turbulence in curvilinear flows of polymer solutions
Following our first report (A. Groisman and V. Steinberg, \sl Nature , 53 (2000)) we present an extended account of experimental observations of
elasticity induced turbulence in three different systems: a swirling flow
between two plates, a Couette-Taylor (CT) flow between two cylinders, and a
flow in a curvilinear channel (Dean flow). All three set-ups had high ratio of
width of the region available for flow to radius of curvature of the
streamlines. The experiments were carried out with dilute solutions of high
molecular weight polyacrylamide in concentrated sugar syrups. High polymer
relaxation time and solution viscosity ensured prevalence of non-linear elastic
effects over inertial non-linearity, and development of purely elastic
instabilities at low Reynolds number (Re) in all three flows. Above the elastic
instability threshold, flows in all three systems exhibit features of developed
turbulence. Those include: (i)randomly fluctuating fluid motion excited in a
broad range of spatial and temporal scales; (ii) significant increase in the
rates of momentum and mass transfer (compared to those expected for a steady
flow with a smooth velocity profile). Phenomenology, driving mechanisms, and
parameter dependence of the elastic turbulence are compared with those of the
conventional high Re hydrodynamic turbulence in Newtonian fluids.Comment: 23 pages, 26 figure
Statistical properties of fractures in damaged materials
We introduce a model for the dynamics of mud cracking in the limit of of
extremely thin layers. In this model the growth of fracture proceeds by
selecting the part of the material with the smallest (quenched) breaking
threshold. In addition, weakening affects the area of the sample neighbour to
the crack. Due to the simplicity of the model, it is possible to derive some
analytical results. In particular, we find that the total time to break down
the sample grows with the dimension L of the lattice as L^2 even though the
percolating cluster has a non trivial fractal dimension. Furthermore, we obtain
a formula for the mean weakening with time of the whole sample.Comment: 5 pages, 4 figures, to be published in Europhysics Letter
On the quantum, classical and total amount of correlations in a quantum state
We give an operational definition of the quantum, classical and total amount
of correlations in a bipartite quantum state. We argue that these quantities
can be defined via the amount of work (noise) that is required to erase
(destroy) the correlations: for the total correlation, we have to erase
completely, for the quantum correlation one has to erase until a separable
state is obtained, and the classical correlation is the maximal correlation
left after erasing the quantum correlations.
In particular, we show that the total amount of correlations is equal to the
quantum mutual information, thus providing it with a direct operational
interpretation for the first time. As a byproduct, we obtain a direct,
operational and elementary proof of strong subadditivity of quantum entropy.Comment: 12 pages ReVTeX4, 2 eps figures. v2 has some arguments clarified and
references update
Editorial: Remembering Natalya Nikolaevna Vygodskaya
As the Guest Editor I want to dedicate this Special Issue in memory of my university professor Natalya Nikolaevna Vygodskaya (Figure 1) [...
Faraday waves on a viscoelastic liquid
We investigate Faraday waves on a viscoelastic liquid. Onset measurements and
a nonlinear phase diagram for the selected patterns are presented. By virtue of
the elasticity of the material a surface resonance synchronous to the external
drive competes with the usual subharmonic Faraday instability. Close to the
bicriticality the nonlinear wave interaction gives rise to a variety of novel
surface states: Localised patches of hexagons, hexagonal superlattices,
coexistence of hexagons and lines. Theoretical stability calculations and
qualitative resonance arguments support the experimental observations.Comment: 4 pages, 4figure
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