204 research outputs found
Colloidal particles at a nematic-isotropic interface: effects of confinement
When captured by a flat nematic-isotropic interface, colloidal particles can
be dragged by it. As a result spatially periodic structures may appear, with
the period depending on a particle mass, size, and interface
velocity~\cite{west.jl:2002}. If liquid crystal is sandwiched between two
substrates, the interface takes a wedge-like shape, accommodating the
interface-substrate contact angle and minimizing the director distortions on
its nematic side. Correspondingly, particles move along complex trajectories:
they are first captured by the interface and then `glide' towards its vertex
point. Our experiments quantify this scenario, and numerical minimization of
the Landau-de Gennes free energy allow for a qualitative description of the
interfacial structure and the drag force.Comment: 7 pages, 9 figure
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Maritime data integration and analysis: Recent progress and research challenges
The correlated exploitation of heterogeneous data sources offering very large historical as well as streaming data is important to increasing the accuracy of computations when analysing and predicting future states of moving entities. This is particularly critical in the maritime domain, where online tracking, early recognition of events, and real-time forecast of anticipated trajectories of vessels are crucial to safety and operations at sea. The objective of this paper is to review current research challenges and trends tied to the integration, management, analysis, and visualization of objects moving at sea as well as a few suggestions for a successful development of maritime forecasting and decision-support systems
Liquid crystal director fluctuations and surface anchoring by molecular simulation
We propose a simple and reliable method to measure the liquid crystal surface
anchoring strength by molecular simulation. The method is based on the
measurement of the long-range fluctuation modes of the director in confined
geometry. As an example, molecular simulations of a liquid crystal in slab
geometry between parallel walls with homeotropic anchoring have been carried
out using the Monte Carlo technique. By studying different slab thicknesses, we
are able to calculate separately the position of the elastic boundary
condition, and the extrapolation length
Measurement of azimuthal anchoring energy of nematic liquid crystal on photoaligning polymer surface
A method to determine the surface azimuthal anchoring energy of a nematic liquid crystal is proposed. The technique implies the measurement of the director deviation on the cell substrate as a function of strength and direction of the applied magnetic field. As an example, the dependence of the azimuthal anchoring coefficient on the exposure time is measured at the interface between the nematic K15 and polyvinylcinnamate film exposed by UV light. The analogous measurements performed in a wedge cell show that the method with magnetic field is more precise
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Scalable and privacy-respectful interactive discovery of place semantics from human mobility traces
Mobility diaries of a large number of people are needed for assessing transportation infrastructure and for spatial development planning. Acquisition of personal mobility diaries through population surveys is a costly and error-prone endeavour. We examine an alternative approach to obtaining similar information from episodic digital traces of people’s presence in various locations, which appear when people use their mobile devices for making phone calls, accessing the internet, or posting georeferenced contents (texts, photos, or videos) in social media. Having episodic traces of a person over a long time period, it is possible to detect significant (repeatedly visited) personal places and identify them as home, work, or place of social activities based on temporal patterns of a person’s presence in these places. Such analysis, however, can lead to compromising personal privacy. We have investigated the feasibility of deriving place meanings and reconstructing personal mobility diaries while preserving the privacy of individuals whose data are analysed. We have devised a visual analytics approach and a set of supporting tools making such privacy-preserving analysis possible. The approach was tested in two case studies with publicly available data: simulated tracks from the VAST Challenge 2014 and real traces built from georeferenced Twitter posts
Theory and simulation of the nematic zenithal anchoring coefficient
Combining molecular simulation, Onsager theory and the elastic description of
nematic liquid crystals, we study the dependence of the nematic liquid crystal
elastic constants and the zenithal surface anchoring coefficient on the value
of the bulk order parameter
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Increasing maritime situation awareness via trajectory detection, enrichment and recognition of events
The research presented in this paper aims to show the deployment and use of advanced technologies towards processing surveillance data for the detection of events, contributing to maritime situation awareness via trajectories’ detection, synopses generation and semantic enrichment of trajectories. We first introduce the context of the maritime domain and then the main principles of the big data architecture developed so far within the European funded H2020 datAcron project. From the integration of large maritime trajectory datasets, to the generation of synopses and the detection of events, the main functions of the datAcron architecture are developed and discussed. The potential for detection and forecasting of complex events at sea is illustrated by preliminary experimental results
Liquid crystal anchoring transitions on aligning substrates processed by plasma beam
We observe a sequence of the anchoring transitions in nematic liquid crystals
(NLC) sandwiched between the hydrophobic polyimide substrates treated with the
plasma beam. There is a pronounced continuous transition from homeotropic to
low tilted (nearly planar) alignment with the easy axis parallel to the
incidence plane of the plasma beam (the zenithal transition) that takes place
as the exposure dose increases. In NLC with positive dielectric anisotropy, a
further increase in the exposure dose results in in-plane reorientation of the
easy axis by 90 degrees (the azimuthal transition). This transition occurs
through the two-fold degenerated alignment characteristic for the second order
anchoring transitions. In contrast to critical behavior of anchoring, the
contact angle of NLC and water on the treated substrates monotonically declines
with the exposure dose. It follows that the surface concentration of
hydrophobic chains decreases continuously. The anchoring transitions under
consideration are qualitatively interpreted by using a simple phenomenological
model of competing easy axes which is studied by analyzing anchoring diagrams
of the generalized polar and non-polar anchoring models.Comment: revtex4, 18 pages, 10 figure
Entropic torque
Quantitative predictions are presented of a depletion-induced torque and
force acting on a single colloidal hard rod immersed in a solvent of hard
spheres close to a planar hard wall. This torque and force, which are entirely
of entropic origin, may play an important role for the key-lock principle,
where a biological macromolecule (the key) is only functional in a particular
orientation with respect to a cavity (the lock)
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