Samo Kralj

Bio: Samo Kralj is an academic researcher from University of Maribor. The author has contributed to research in topics: Liquid crystal & Phase transition. The author has an hindex of 31, co-authored 198 publications receiving 3370 citations. Previous affiliations of Samo Kralj include University of Ljubljana & Eindhoven University of Technology.

Stochastic resonance in a locally excited system of bistable oscillators

Abstract: Stochastic resonance is studied in a one-dimensional array of overdamped bistable oscillators in the presence of a local subthreshold periodic perturbation. The system can be treated as an ensemble of pseudospins tending to align parallel which are driven dynamically by an external periodic magnetic field. The oscillators are subjected to a dynamic white noise as well as to a static topological disorder. The latter is quantified by the fraction of randomly added long-range connections among ensemble elements. In the low connectivity regime the system displays an optimal global stochastic resonance response if a small-world network is formed. In the mean-field regime we explain strong changes in the dynamic disorder strength provoking a maximal stochastic resonance response via the variation of fraction of long-range connections by taking into account the ferromagnetic-paramagnetic phase transition of the pseudospins. The system size analysis shows only quantitative power-law type changes on increasing number of pseudospins.

Defect-enhanced nematic surface order reconstruction.

Abstract: Within the Landau-de Gennes phenomenological theory, we study the influence of an applied electric field with average strength E{a} on the position of a nematic line defect with topological charge M=+/-1/2 in a hybrid cell We explore the biaxial structure of the defect core and we describe its expulsion from the cell upon increasing E{a} We show that prior to the expulsion the defect core displays dramatic changes for strong enough surface anchorings At a critical value of E{a}, the core broadens and merges into a surface layer with a large biaxiality This transition corresponds to the reconstruction of the nematic order already observed in the bulk in response to an applied electric field A similar order reconstruction could take place even in the absence of defects, but at a higher threshold

Molecular dynamics study of nematic structures confined to a cylindrical cavity

Abstract: Molecular dynamics is used to simulate nematic liquid crystal structures confined to a submicron cylindrical cavity. Molecules, fixed at the lattice points, are set to interact via a modified induced-dipole--induced-dipole type coupling. Stability regions of characteristic nematic structures are determined as functions of the cylinder radius, homeotropic anchoring strength, and degree of the interaction anisotropy. A connection linking elastic and microscopic approaches is established. Results confirm most of the predictions of the elastic free energy deep in the submicron regime.

Finite-size effects on order reconstruction around nematic defects.

Abstract: By use of the Landau\char21{}de Gennes phenomenological theory, we study the texture of a nematic liquid crystal confined within a hybrid cell. Precisely, we consider cylindrically symmetric solutions containing topological defects dictated by appropriate boundary conditions. We focus our attention on cells whose dimensions are comparable with the biaxial correlation length ${\ensuremath{\xi}}_{b}$. For such severe confinements the order reconstruction (OR) configuration could be stable. Its structural details reflect the balance among boundary-enforced frustration, elastic penalties, and finite-size effects. In particular, we analyze the interplay between finite-size effects and topological defects. We show that defects are always pinned to the negatively (planar) uniaxial sheet of the OR structure. The presence of a ring defect can dramatically increase the critical threshold below which the OR structure is stable.

Confinement-induced orientational order in a ferroelectric liquid crystal containing dispersed aerosils.

Abstract: The study of the smectic-A to chiral smectic-C(*) phase transition of the liquid crystal S-(+)-[4-(2(')-methyl butyl) phenyl 4(')-n-octylbiphenyl-4-carboxylate] (CE8) containing dispersed hydrophilic aerosils reveals novel properties, important to understanding quenched disorder and confinement in ferroelectric liquid crystals. Smectic layer compression leads to a distribution of transition temperatures inducing smearing of the macroscopic data across the transition. A pronounced confinement-induced pretransitional tilted order is observed.

Phase separation in confined systems

Abstract: We review the current state of knowledge of phase separation and phase equilibria in porous materials. Our emphasis is on fundamental studies of simple fluids (composed of small, neutral molecules) and well-characterized materials. While theoretical and molecular simulation studies are stressed, we also survey experimental investigations that are fundamental in nature. Following a brief survey of the most useful theoretical and simulation methods, we describe the nature of gas‐liquid (capillary condensation), layering, liquid‐liquid and freezing/melting transitions. In each case studies for simple pore geometries, and also more complex ones where available, are discussed. While a reasonably good understanding is available for phase equilibria of pure adsorbates in simple pore geometries, there is a need to extend the models to more complex pore geometries that include effects of chemical and geometrical heterogeneity and connectivity. In addition, with the exception of liquid‐liquid equilibria, little work has been done so far on phase separation for mixtures in porous media.

Effects of confinement on freezing and melting.

Abstract: We present a review of experimental, theoretical, and molecular simulation studies of confinement effects on freezing and melting We consider both simple and more complex adsorbates that are confined in various environments (slit or cylindrical pores and also disordered porous materials) The most commonly used molecular simulation, theoretical and experimental methods are first presented We also provide a brief description of the most widely used porous materials The current state of knowledge on the effects of confinement on structure and freezing temperature, and the appearance of new surface-driven and confinement-driven phases are then discussed We also address how confinement affects the glass transition

Liquid-crystal materials find a new order in biomedical applications.

Abstract: With the maturation of the information display field, liquid-crystal materials research is undergoing a modern-day renaissance. Devices and configurations based on liquid-crystal materials are being developed for spectroscopy, imaging and microscopy, leading to new techniques for optically probing biological systems. Biosensors fabricated with liquid-crystal materials can allow label-free observations of biological phenomena. Liquid-crystal polymers are starting to be used in biomimicking colour-producing structures, lenses and muscle-like actuators. New areas of application in the realms of biology and medicine are stimulating innovation in basic and applied research into these materials.