146 research outputs found
Dislocations in uniaxial lamellar phases of liquid crystals, polymers and amphiphilic systems
Dislocations in soft condensed matter systems such as lamellar systems of
polymers, liquid crystals and ternary mixtures of oil, water and surfactant
(amphiphilic systems) are described in the framework of continuum elastic
theory. These systems are the subject of studies of physics, chemistry and
biology. They also find applications in the industry. Here we will discuss in
detail the influence of dislocations on the bulk and surface properties of
these lamellar phases. Especially the latter properties have only been recently
studied in detail. We will present the experimental evidence of the existence
of screw and edge dislocations in the systems and study their static properties
such as: energy, line tension and core structure. Next we will show how does
the surface influence the equilibrium position of dislocations in the system.
We will give the theoretical predictions and present the experimental results
on thin copolymer films, free standing films of liquid crystals and smectic
droplets shapes. The surface is deformed by dislocations. These deformations
are known as edge profiles. Surface deformations induce elastic interactions
between edge dislocations. A new phenonenon discussed in our paper is the
fluctuations induced interactions between edge dislocations.At suitable
conditions edge dislocations can undergo an unbinding transition. Also a single
dislocation loop in a smectic freely suspended film can undergo an unbinding
transition. We shall also compute the equilibrium size of the loop contained
between two hard walls. Finally we will discuss the dynamical bulk properties
of dislocations such as: mobility (climb and glide),permeation, and helical
instability of screw dislocations. Lubrication theory will also be discussed.Comment: plain TeX, 65 pages, review for International Journal of Modern
Physics
Influence of the electric field on edge dislocations in smectics
The electric field applied perpendicularly to smectic layers breaks the
rotational symmetry of the system. Consequently, the elastic energy associated
with distortions induced by an edge dislocation diverges logarithmically with
the size of the system. In freely suspended smectic films the dislocations in
the absence of the electric field are located exactly in the middle of the
film. The electric field above a certain critical value can shift them towards
the surface. This critical field squared is a linear function of the surface
tension and is inversly proportional to the thickness of the film. The
equilibrium location of a dislocation in the smectic film subjected to the
field is also calculated.Comment: Tex, 13 pages, submitted to J. de Physique II. (permanent e-mail
address: [email protected]
From the Plateau problem to periodic minimal surfaces in lipids, surfactants and diblock copolymers
We present the novel method for generation of periodic surfaces based on the
simple Landau-Ginzburg model of microemulsion. We test the method on four
minimal surfaces (P,D,G, and I-WP), find two new surfaces of cubic symmetry,
show how to obtain periodic surfaces of high genus and n-tuply-continuous
phases. We point that the Landau model used here should be generic for all
systems characterized by internal interfaces, including the diblock copolymer
systems.Comment: 15 pages, Plain TeX , figures available on request or at
http://saka.ichf.edu.pl/WTGRH/surfaces.htm
Majority Model on a network with communities
We focus on the majority model in a topology consisting of two coupled
fully-connected networks, thereby mimicking the existence of communities in
social networks. We show that a transition takes place at a value of the
inter-connectivity parameter. Above this value, only symmetric solutions
prevail, where both communities agree with each other and reach consensus.
Below this value, in contrast, the communities can reach opposite opinions and
an asymmetric state is attained. The importance of the interface between the
sub-networks is shown.Comment: 4 page
Endo- vs. Exo-genous shocks and relaxation rates in book and music "sales"
In this paper, we analyze the response of music and book sales to an external
field and to buyer herding. We distinguish endogenous and exogenous shocks. We
focus on some case studies, whose data have been collected from ranking on
amazon.com. We show that an ensemble of equivalent systems quantitatively
respond in a similar way to a similar ''external shock'', indicating roads to
universality features. In contrast to Sornette et al. [Phys. Rev. Lett. {93},
228701 (2004)] who seemed to find power law behaviors, in particular at long
times, - a law interpreted in terms of an epidemic activity, we observe that
the relaxation process can be as well seen as an exponential one that saturates
toward an asymptotic state, itself different from the pre-shock state. By
studying an ensemble of 111 shocks, on books or records, we show that exogenous
and endogenous shocks are discriminated by their short-time behaviour: the
relaxation time seems to be twice shorter in endogenous shocks than in
exogenous ones. We interpret the finding through a simple thermodynamic model
with a dissipative force.Comment: to be published in physica
Ferromagnetic fluid as a model of social impact
The paper proposes a new model of spin dynamics which can be treated as a
model of sociological coupling between individuals. Our approach takes into
account two different human features: gregariousness and individuality. We will
show how they affect a psychological distance between individuals and how the
distance changes the opinion formation in a social group. Apart from its
sociological aplications the model displays the variety of other interesting
phenomena like self-organizing ferromagnetic state or a second order phase
transition and can be studied from different points of view, e.g. as a model of
ferromagnetic fluid, complex evolving network or multiplicative random process.Comment: 8 pages, 5 figure
Role of electrostatics in the texture of islands in free standing ferroelectric liquid crystal films
Curved textures of ferroelectric smectic C* liquid crystals produce space
charge when they involve divergence of the spontaneous polarization field.
Impurity ions can partially screen this space charge, reducing long range
interactions to local ones. Through studies of the textures of islands on very
thin free-standing smectic films, we see evidence of this effect, in which
materials with a large spontaneous polarization have static structures
described by a large effective bend elastic constant. To address this issue, we
calculated the electrostatic free energy of a free standing film of
ferroelectric liquid crystal, showing how the screened coulomb interaction
contributes a term to the effective bend elastic constant, in the static long
wavelength limit. We report experiments which support the main features of this
model
Shock waves in one-dimensional Heisenberg ferromagnets
We use SU(2) coherent state path integral formulation with the stationary
phase approximation to investigate, both analytically and numerically, the
existence of shock waves in the one- dimensional Heisenberg ferromagnets with
anisotropic exchange interaction. As a result we show the existence of shock
waves of two types,"bright" and "dark", which can be interpreted as moving
magnetic domains.Comment: 10 pages, with 3 ps figure
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