講師：Prof. Victor Steinberg (Department of Physics of Complex Systems, The Weizmann Institute of Science, Rehovot 76100, Israel)
題目：Elastic stresses in turbulent flow with polymers: their role in turbulent drag reduction and ways to measure
For years the experimental and theoretical studies on turbulent drag reduction
were concentrated on extracting relevant information from structure and
statistics of velocity field measurements.
Only recently it was suggested to investigate also an elastic stress field,
which has direct relation to changes of turbulent flow by adding polymers.
Experimentally we study structure and statistics of the elastic stress field in a related elastic turbulent flow.
We found unexpected for this flow boundary layer for elastic stresses
and strongly non-uniform distribution of elastic stresses in the flow.
We are currently developing similar approach for turbulent drag reduction problem.
講師：Dr. Miha Ravnik (Universtiy of Oxford, United Kingdom, University of Ljubljana, Slovenia)
題目：Entangled nematic colloids: route for hierarchical self-assembly
Liquid crystal colloids are characterized by the orientational anisotropy of
liquid crystalline continuum phase and discrete ordering of dispersed
colloidal inclusions. The long-ranged orientational ordering of liquid
crystals generates structural forces between the inclusions which allows for
the assembly of complex colloidal composites. Such inherent effective
elasticity of liquid crystals permits structuring of inclusions based on
entanglement, hierarchical ordering, and self-assembly.
Here we present the assembly of entangled colloidal structures that can be
built in confined nematic liquid crystals. Our work is based on the
numerical minimization of the phenomenological Landau-de Gennes free energy.
In entangled colloidal structures, delocalized defect lines stabilize new
topological objects and effectively behave as elastic belts. We found
entangled defect configurations first in uniform nematic cells, yet true
entangling of particles becomes possible in a non-homogeneous configuration
of the nematic. Beside simple loops, i.e. unknots and unlinks, we find also
single and multiple defect loops which form knots and links, respectively.
Entanglement of particles is generalized to 2D crystalline colloidal
structures. Regular array of disclination lines in entangled structures
opens a route for the hierarchical assembly of colloidal structures.
講師： Dr. Harald Pleiner (Max Planck Institute for Polymer Research)
Inverse Lehmann effects can be used as a microscopic pump
For cholesteric and chiral smectic liquid crystals
a rotation of the helical superstructure can be induced for
suitable boundary conditions for external fields such as
temperature gradients and electric fields: the Lehmann effect.
Here we predict that the inverse effect can lead to a pump
for particles and ions on a length scale of microns:
when a spatial pattern such as a phase winding pattern or a
spiral is generated, for example, for a freely suspended
smectic C* film, a concentration current arises.
We also point out, that this concentration current
is, under suitable experimental conditions, accompanied
by a heat current and/or an electric current. Similar effects
are expected for cholesterics, smectic F* and I* as well as
for Langmuir monolayers, since all these systems share the
of macroscopic chirality.
講師：Prof. Turab Lookman (Theoretical Division, Los Alamos National Laboratory, Los Alamos, USA)
題目：Microstructure and glassy phenomena for ferroelastic transitions
in two and three dimensions using strain pseudo-spin models
I will discuss how heterogeneity in functional materials is important in determining their behavior.
I will illustrate how strain heterogeneity may be modeled using Landau theory
in a consistent framework and briefly compare different approaches.
I will subsequently show how simpler,
discrete models provide the means of understanding aspects such as microstructure.
Finally, I will illustrate how the addition of disorder
allows us to generate phase diagrams
that are qualitative similar to those obtained for ferroelastics (strain glass).
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