IMPROVED MULTIPLE BIRDSONG TRACKING WITH DISTRIBUTION DERIVATIVE METHOD AND MARKOV RENEWAL PROCESS CLUSTERING

DS & MP are supported by an EPSRC Leadership Fellowship EP/G007144/1

Field induced transitions and interlayer interactions in intermediate smectic phases.

A series of liquid crystal mixtures displaying wide three- and four-layer intermediate phases are reported. The mixtures are formed from a selenium-containing antiferroelectric material combined with up to 9% (by weight) of a chiral dopant. We describe physical properties including spontaneous polarization, layer spacing and tilt for mixtures including up to 9% concentration of the chiral dopant. Such measurements offer an insight into the factors that affect the stability of the intermediate smectic phases. However, a quantitative measure of the interlayer interaction strength can be obtained from analysis of field-temperature phase diagrams. Therefore, the field-temperature phase diagrams are also determined in the intermediate phase regime of the mixtures containing up to 5% w/w concentration of the chiral dopant and compared with theoretical predictions. Excellent agreement with the theory is observed for the pure material, though for mixtures with increasing concentrations of chiral dopant, deviations from the theory are recorded, in particular in the nature of the transition from the four-layer structure to the three-layer structure. Quantitative measurements of the interlayer interaction constants are deduced from the gradients of the field thresholds, and the interlayer pairing is found to reduce significantly with an increasing concentration of chiral dopant. An interlayer interaction constant of 147 ± 13 N m-2 K-1 is found in the pure material, reducing to 21 ± 4 N m-2 K-1 in the mixture with concentration of chiral dopant of 5%. Measurement of the interlayer interaction constants from the field-temperature phase diagrams is shown to give a quantitative understanding of the importance of the interlayer interaction, which is only indicated qualitatively by other measurements. Finally, some evidence is presented for an additional field-induced transition observed in temperature regions close to a triple point on the field-temperature phase diagram

Fluctuation - induced forces in critical fluids

The current knowledge about fluctuation - induced long - ranged forces is summarized. Reference is made in particular to fluids near critical points, for which some new insight has been obtained recently. Where appropiate, results of analytic theory are compared with computer simulations and experiments.Comment: Topical review, 24 pages RevTeX, 6 figure

Bulk and Boundary Critical Behavior at Lifshitz Points

Lifshitz points are multicritical points at which a disordered phase, a homogeneous ordered phase, and a modulated ordered phase meet. Their bulk universality classes are described by natural generalizations of the standard $\phi^4$ model. Analyzing these models systematically via modern field-theoretic renormalization group methods has been a long-standing challenge ever since their introduction in the middle of the 1970s. We survey the recent progress made in this direction, discussing results obtained via dimensionality expansions, how they compare with Monte Carlo results, and open problems. These advances opened the way towards systematic studies of boundary critical behavior at $m$-axial Lifshitz points. The possible boundary critical behavior depends on whether the surface plane is perpendicular to one of the $m$ modulation axes or parallel to all of them. We show that the semi-infinite field theories representing the corresponding surface universality classes in these two cases of perpendicular and parallel surface orientation differ crucially in their Hamiltonian's boundary terms and the implied boundary conditions, and explain recent results along with our current understanding of this matter.Comment: Invited contribution to STATPHYS 22, to be published in the Proceedings of the 22nd International Conference on Statistical Physics (STATPHYS 22) of the International Union of Pure and Applied Physics (IUPAP), 4--9 July 2004, Bangalore, Indi

Taming Liquid Crystal Self-Assembly: The Multifaceted Response of Nematic and Smectic Shells to Polymerization.

By photopolymerizing liquid crystal shells, their rich variety of self-assembled structures can be rendered permanent and the lifetime extended from days to months, without removing the characteristic responsiveness. If polymerization is carried out close to either boundary of the nematic phase, the process triggers the transition into the adjacent phase, to higher or to lower degree of order

Self-assembly of colloid-cholesteric composites provides a possible route to switchable optical materials

Colloidal particles dispersed in liquid crystals can form new materials with tunable elastic and electro-optic properties. In a periodic `blue phase' host, particles should template into colloidal crystals with potential uses in photonics, metamaterials, and transformational optics. Here we show by computer simulation that colloid/cholesteric mixtures can give rise to regular crystals, glasses, percolating gels, isolated clusters, twisted rings and undulating colloidal ropes. This structure can be tuned via particle concentration, and by varying the surface interactions of the cholesteric host with both the particles and confining walls. Many of these new materials are metastable: two or more structures can arise under identical thermodynamic conditions. The observed structure depends not only on the formulation protocol, but also on the history of an applied electric field. This new class of soft materials should thus be relevant to design of switchable, multistable devices for optical technologies such as smart glass and e-paper.Comment: Manuscript with 3 figures plus supporting text and figure

Ferroelectric Liquid-Crystals - from the Plane-Wave to the Multisoliton Limit

Contains fulltext : 27864.pdf (publisher's version ) (Open Access

Slow mode of the smectic-A-smectic-C-alpha(*) phase transition

Contains fulltext : 92658.pdf (publisher's version ) (Open Access