202 research outputs found
Smectic order, pinning, and phase transition in a smectic liquid crystal cell with a random substrate
We study smectic-liquid-crystal order in a cell with a heterogeneous
substrate imposing surface random positional and orientational pinnings.
Proposing a minimal random elastic model, we demonstrate that, for a thick
cell, the smectic state without a rubbed substrate is always unstable at long
scales and, for weak random pinning, is replaced by a smectic glass state. We
compute the statistics of the associated substrate-driven distortions and the
characteristic smectic domain size on the heterogeneous substrate and in the
bulk. We find that for weak disorder, the system exhibits a three-dimensional
temperature-controlled phase transition between a weakly and strongly pinned
smectic glass states akin to the Cardy-Ostlund phase transition. We explore
experimental implications of the predicted phenomenology and suggest that it
provides a plausible explanation for the experimental observations on polarized
light microscopy and x-ray scattering.Comment: 30 pages, 11 figures, Published in PRE, with minor typos correcte
Thermal phase diagrams of columnar liquid crystals
In order to understand the possible sequence of transitions from the
disordered columnar phase to the helical phase in hexa(hexylthio)triphenylene
(HHTT), we study a three-dimensional planar model with octupolar interactions
inscribed on a triangular lattice of columns. We obtain thermal phase diagrams
using a mean-field approximation and Monte Carlo simulations. These two
approaches give similar results, namely, in the quasi one-dimensional regime,
as the temperature is lowered, the columns order with a linear polarization,
whereas helical phases develop at lower temperatures. The helicity patterns of
the helical phases are determined by the exact nature of the frustration in the
system, itself related to the octupolar nature of the molecules.Comment: 12 pages, 9 figures, ReVTe
The Smectic - Phase Transition in Biaxial Disordered Environments
We study the smectic - phase transition in biaxial disordered
environments, e.g. fully anisotropic aerogel. We find that both the and
phases belong to the universality class of the "XY Bragg glass", and therefore
have quasi-long-ranged translational smectic order. The phase transition itself
belongs to a new universality class, which we study using an
expansion. We find a stable fixed point, which implies a continuous transition,
the critical exponents of which we calculate
First order isotropic - smectic-A transition in liquid crystal-aerosil gels
The short-range order which remains when the isotropic to smectic-A
transition is perturbed by a gel of silica nanoparticles (aerosils) has been
studied using high-resolution synchrotron x-ray diffraction. The gels have been
created \textit{in situ} in decylcyanobiphenyl (10CB), which has a strongly
first-order isotropic to smectic-A transition. The effects are determined by
detailed analysis of the temperature and gel density dependence of the smectic
structure factor. In previous studies of the continuous nematic to smectic-A
transition in a variety of thermotropic liquid crystals the aerosil gel
appeared to pin, at random, the phase of the smectic density modulation. For
the isotropic to smectic-A transition the same gel perturbation yields
different results. The smectic correlation length decreases more slowly with
increasing random field variance in good quantitative agreement with the effect
of a random pinning field at a transition from a uniform phase directly to a
phase with one-dimensional translational order. We thus compare the influence
of random fields on a \textit{freezing} transition with and without an
intervening orientationally ordered phase.Comment: 8 pages, 8 figure
Fluctuations and phase transitions in Larkin-Ovchinnikov liquid crystal states of population-imbalanced resonant Fermi gas
Motivated by a realization of imbalanced Feshbach-resonant atomic Fermi
gases, we formulate a low-energy theory of the Fulde-Ferrell and the
Larkin-Ovchinnikov (LO) states and use it to analyze fluctuations, stability,
and phase transitions in these enigmatic finite momentum-paired superfluids.
Focusing on the unidirectional LO pair-density wave state, that spontaneously
breaks the continuous rotational and translational symmetries, we show that it
is characterized by two Goldstone modes, corresponding to a superfluid phase
and a smectic phonon. Because of the liquid-crystalline "softness" of the
latter, at finite temperature the 3d state is characterized by a vanishing LO
order parameter, quasi-Bragg peaks in the structure and momentum distribution
functions, and a "charge"-4, paired Cooper-pairs, off-diagonal-long-range
order, with a superfluid-stiffness anisotropy that diverges near a transition
into a nonsuperfluid state. In addition to conventional integer vortices and
dislocations the LO superfluid smectic exhibits composite half-integer
vortex-dislocation defects. A proliferation of defects leads to a rich variety
of descendant states, such as the "charge"-4 superfluid and Fermi-liquid
nematics and topologically ordered nonsuperfluid states, that generically
intervene between the LO state and the conventional superfluid and the
polarized Fermi-liquid at low and high imbalance, respectively. The fermionic
sector of the LO gapless superconductor is also quite unique, exhibiting a
Fermi surface of Bogoliubov quasiparticles associated with the Andreev band of
states, localized on the array of the LO domain-walls.Comment: 56 pages, 21 figure
Attitudes Toward Organizational Change among Public Middle Managers
Positive attitudes toward change (PATC) are an important current issue in public
organizations facing profound financial and managerial reforms. This study aims to
identify social and organizational antecedents of PATC. The investigated population
is composed of middle managers working in Swiss public hospitals (N = 720), which
are currently being confronted by major reforms. Partial mediation effects of
organizational commitment (OC) in the relationships between independent variables
and PATC are also controlled. The findings show that perceived social support (work
relationships with colleagues and supervisors) as well as perceived organizational
support (employee voice and participation, information and communication, work-life
balance) are positively and significantly related to PATC. Stress perception is shown
to have a negative impact on PATC. This article provides valuable contributions with
respect to antecedents of attitudes toward change in a population of public middle
managers
âInteractive Technology Assessmentâ and Beyond: the Field Trial of Genetically Modified Grapevines at INRA-Colmar
International audienc
INDAGAĂĂES SOBRE AS NOVAS FORMAS DE FABRICAĂĂO DO HUMANO Ă LUZ DA NOĂĂO DE DĂDIVA DE MARCEL MAUSS
The meta-crisis of secular capitalism
The current global economic crisis concerns the way in which contemporary capitalism has turned to financialisation as a double cure for both a falling rate of profit and a deficiency of demand. Although this turning is by no means unprecedented, policies of financialisation have depressed demand (in part as a result of the long-term stagnation of average wages) while at the same time not proving adequate to restore profits and growth. This paper argues that the current crisis is less the ânormalâ one that has to do with a constitutive need to balance growth of abstract wealth with demand for concrete commodities. Rather, it marks a meta-crisis of capitalism that is to do with the difficulties of sustaining abstract growth as such. This meta-crisis is the tendency at once to abstract from the real economy of productive activities and to reduce everything to its bare materiality. By contrast with a market economy that binds material value to symbolic meaning, a capitalist economy tends to separate matter from symbol and reduce materiality to calculable numbers representing âwealthâ. Such a conception of wealth rests on the aggregation of abstract numbers that cuts out all the relational goods and the âcommonsâ on which shared prosperity depends
Small-angle neutron scattering from multilamellar lipid bilayers: Theory, model, and experiment
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