225 research outputs found
Fluctuations of topological disclination lines in nematics: renormalization of the string model
The fluctuation eigenmode problem of the nematic topological disclination
line with strength is solved for the complete nematic tensor order
parameter. The line tension concept of a defect line is assessed, the line
tension is properly defined. Exact relaxation rates and thermal amplitudes of
the fluctuations are determined. It is shown that within the simple string
model of the defect line the amplitude of its thermal fluctuations is
significantly underestimated due to the neglect of higher radial modes. The
extent of universality of the results concerning other systems possessing line
defects is discussed.Comment: 6 pages, 3 figure
Nematic cells with defect-patterned alignment layers
Using Monte Carlo simulations of the Lebwohl--Lasher model we study the
director ordering in a nematic cell where the top and bottom surfaces are
patterned with a lattice of point topological defects of lattice
spacing . We find that the nematic order depends crucially on the ratio of
the height of the cell to . When the system is very
well--ordered and the frustration induced by the lattice of defects is relieved
by a network of half--integer defect lines which emerge from the point defects
and hug the top and bottom surfaces of the cell. When the
system is disordered and the half--integer defect lines thread through the cell
joining point defects on the top and bottom surfaces. We present a simple
physical argument in terms of the length of the defect lines to explain these
results. To facilitate eventual comparison with experimental systems we also
simulate optical textures and study the switching behavior in the presence of
an electric field
Two Experimental Tests of the Halperin-Lubensky-Ma Effect at the Nematic-Smectic-A Phase Transition
We have conducted two quantitative tests of predictions based on the
Halperin-Lubensky-Ma (HLM) theory of fluctuation-induced first-order phase
transitions. First, we explore the effect of an external magnetic field on the
nematic-smectic-A (NA) transition in a liquid crystal. Second, we examine the
dependence of the first-order discontinuity as a function of mixture
concentration in pure 8CB and three 8CB-10CB mixtures. We find the first
quantitative evidence for deviations from the HLM theory.Comment: 4 pages, 2 figure
Bulk and surface biaxiality in nematic liquid crystals
Nematic liquid crystals possess three different phases: isotropic, uniaxial,
and biaxial. The ground state of most nematics is either isotropic or uniaxial,
depending on the external temperature. Nevertheless, biaxial domains have been
frequently identified, especially close to defects or external surfaces. In
this paper we show that any spatially-varying director pattern may be a source
of biaxiality. We prove that biaxiality arises naturally whenever the symmetric
tensor \Sb=(\grad \nn)(\grad \nn)^T possesses two distinct nonzero
eigenvalues. The eigenvalue difference may be used as a measure of the expected
biaxiality. Furthermore, the corresponding eigenvectors indicate the directions
in which the order tensor \QQ is induced to break the uniaxial symmetry about
the director \nn. We apply our general considerations to some examples. In
particular we show that, when we enforce homeotropic anchoring on a curved
surface, the order tensor become biaxial along the principal directions of the
surface. The effect is triggered by the difference in surface principal
curvatures
Spatiotemporal rheochaos in nematic hydrodynamics
Motivated by the observation of rheochaos in sheared wormlike micelles
[Bandyopadhyay et al., Phys. Rev. Lett, 84 2022, (2000); Europhys. Lett. 56,
447 (2001); Pramana 53, 223 (1999)] we study the coupled nonlinear partial
differential equations for the hydrodynamic velocity and order parameter fields
in a sheared nematogenic fluid. In a suitable parameter range, we find
irregular, dynamic shear-banding and establish by decisive numerical tests that
the chaos we observe in the model is spatiotemporal in nature.Comment: Slight changes in text, references and Fig. 5 inset; 6 eps figures
(figs 2,3,4 at lower resolution to reduce file size; full files available on
request); accepted for publication in Phys Rev Let
Ring-Pattern Dynamics in Smectic-C* and Smectic-C_A* Freely Suspended Liquid Crystal Films
Ring patterns of concentric 2pi-solitons in molecular orientation, form in
freely suspended chiral smectic-C films in response to an in-plane rotating
electric field. We present measurements of the zero-field relaxation of ring
patterns and of the driven dynamics of ring formation under conditions of
synchronous winding, and a simple model which enables their quantitative
description in low polarization DOBAMBC. In smectic C_A* TFMHPOBC we observe an
odd-even layer number effect, with odd number layer films exhibiting order of
magnitude slower relaxation rates than even layer films. We show that this rate
difference is due to much larger spontaneous polarization in odd number layer
films.Comment: 4 RevTeX pgs, 4 eps figures, submitted to Phys. Rev. Let
Macroscopic Properties of Smectic C G Liquid Crystals
Abstract. We discuss the macroscopic behavior of smectic CG liquid crystals. Smectic CG is the most general tilted smectic phase that is fluid in the layers. It is characterized by global C1 symmetry. Consequently, it is ferroelectric, pyroelectric and piezoelectric, opening up a number of possible applications for such a phase. As smectic CG-phase has a macroscopic hand due to its structure, it is a natural candidate to explain the recent experimental observations of left and right-handed helices in a system composed of achiral molecules. We also discuss critically to what extent smectic CG could be important for liquid crystalline phases formed by banana-shaped molecules. Phase transitions involving a smectic CG phase and defects of its in-plane director are briefly discussed. PAC
X-Ray Diffraction Intensities of a Smectic-A Liquid Crystal
Higher-order diffraction from the smectic-A liquid-crystalline phase of cyanooctylbiphenyl (COB) has been measured. The dominant short-range disorder, described by the relative intensities, is in agreement with our estimate of the smectic order parameter based on McMillan's mean-field theory
'An Apotheosis of Well-Being': Durkheim on austerity and double-dip recessions
This article is an attempt to contribute a view on the economic crisis from classical sociology, a voice often missing from the sociological response to the crisis. The work of Émile Durkheim provides a unique perspective here centred on morality and inequality produced in a historical context akin to our neoliberal times. It is argued there are four key points to take from Durkheim’s work. Firstly, that the initial credit crunch can be more fully understood with reference to the economic anomie which Durkheim sees as ‘chronic’ in a time of marketization. Secondly, that this creates an antagonistic relationship between a supposedly self-dependent rich and lazy poor. Thirdly, this conception of self-dependency and individual initiative makes any attempt to regulate the economy akin to sacrilege. Finally, the state is unwilling to intervene due to the emergence of ‘pseudo-democracies’. Therefore, Durkheim’s theory accounts for the initial crisis, austerity and double-dip recessions in a sociological framework. The article concludes by returning to the centrality of morality to the crisis for Durkheim and highlighting the omission of this in contemporary debates
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