1,721,003 research outputs found
Monte Carlo study of slot-waveguide liquid crystal phase shifters
No full textWe present detailed Monte Carlo simulations of a simple model of a nematic liquid crystal slot waveguide shifter, investigating the effect of an applied electric external field. The simulations are based on the Lebwohl-Lasher lattice spin model with boundary conditions chosen to mimic the planar alignment as in Silicon Organic Hybrid waveguides and the homeotropic anchoring appropriate for Polydimethylsiloxane polymer walls. The external field is modeled by adding a term to the Hamiltonian which describes its coupling to the mesogenic molecules. We have investigated the effect of the external field on the optical transmission and the ordering across the cell
Lattice spin simulations of low power photonic liquid-crystal devices
No full textWe have performed a detailed Monte Carlo study of photonic devices based on nematic liquid crystal infiltrated in polydimethylsiloxane (PDMS) and in Silicon-Organic Hybrid (SOH) channels, to be used as waveguides. The simulations of a simple model of these slot waveguide shifters have shown the effect of an applied electric external field in two cases with different surface alignments, i.e. planar SOH and homeotropic PDMS. We have investigated the effect of the external field on the optical transmission and the ordering across the cell
Effect of Surface Anchoring on Creation of Defects in a Nematic Film. A Monte Carlo Simulation
No full textNematic systems confined to a bounded volume are particularly interesting because they present stable structure defects induced by the anchoring conditions on the surface. Here we present a Monte Carlo study of a hybrid nematic film with various strengths of coupling with the surfaces
GRAF-TYPE THEOREM FOR LAGUERRE AND LEGENDRE FUNCTIONS. COMPUTERS & MATHEMATICS WITH APPLICATIONS
No full textNematic liquid crystals in planar and cylindrical hybrid cells: Role of elastic anisotropy on the director deformations
No full textNematic samples filling a flat cell or the annular region between two concentric cylinders with hybrid anchoring conditions at the boundaries are investigated by setting up and minimizing their Frank elastic free energy. The coupling with the surfaces is taken to be strong on one side and weak on the other. The equations are numerically solved and the conditions for which the molecular organization inside the cell becomes uniform are analyzed. The classical calculation performed by G. Barbero and R. Barberi [J. Phys. 44, 609 (1983)] is reproduced and investigated from a different point of view, in order to compare the results of planar and cylindrical geometries. The results suggest that the cylindrical cell presents some unusual features deserving a more complete investigation. Although most part of the transitional phenomena are found for K-11 > K-33, a case not common for ordinary (lyotropic and thermotropic) liquid crystals, it is possible to find a completely uniform cell even for K-11 < K-33 in both the geometries considered here
Molecular organization of nematic liquid crystals between concentric cylinders: role of the elastic anisotropy, Phys. Rev. E, 91, 022501 (2015)
No full textThe orientational order in a nematic liquid crystal sample confined to an annular region between two concentric
cylinders is investigated by means of lattice Monte Carlo simulations. Strong anchoring and homeotropic
orientations, parallel to the radial direction, are implemented at the confining surfaces. The elastic anisotropy is
taken into account in the bulk interactions by using the pair potential introduced by Gruhn and Hess [T. Gruhn
and S. Hess, Z. Naturforsch. A 51, 1 (1996)] and parametrized by Romano and Luckhurst [S. Romano, Int. J.
Mod. Phys. B 12, 2305 (1998); Phys. Lett. A 302, 203 (2002); G. R. Luckhurst and S. Romano, Liq. Cryst. 26,
871 (1999)], i.e., the so-called GHRL potential. In the case of equal elastic constants, a small but appreciable
deformation along the cylinder axis direction is observed, whereas when the values of K11/K33 if K22 = K33 are
low enough, all the spins in the bulk follow the orientation imposed by the surfaces. For larger values of K11/K33,
spontaneous deformations, perpendicular to the polar plane, increase significantly. Our findings indicate that the
onset of these deformations also depends on the ratio K22/K33 and on the radius of the cylindrical surfaces.
Although expected from the elastic theory, no tangential component of the deformations was observed in the
simulations for the set of parameters analyzed
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Fourier expansions and multivariable Bessel functions concerning radiation problems
No full textThe link between generalized Bessel functions and other special functions is investigated using the Fourier series and the generalized Jacobi-Anger expansion. A new class of multivariable Hermite polynomials is then introduced and their relevance to physical problems discussed. As an example of the power of the method, applied to radiation physics, we analyse the role played by multi-variable Bessel functions in the description of radiation emitted by a charge constrained to a nonlinear oscillation
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