Marjan Krašna

Symmetry breaking and structure of a mixture of nematic liquid crystals and anisotropic nanoparticles

Summary Orientational ordering of a homogeneous mixture of uniaxial liquid crystalline (LC) molecules and magnetic nanoparticles (NPs) is studied using the Lebwohl–Lasher lattice model. We consider cases where NPs tend to be oriented perpendicularly to LC molecules due to elastic forces. We study domain-type configurations of ensembles, which are quenched from the isotropic phase. We show that for large enough concentrations of NPs the long range uniaxial nematic ordering is replaced by short range order exhibiting strong biaxiality. This suggests that the impact of NPs on orientational ordering of LCs for appropriate concentrations of NPs is reminiscent to the influence of quenched random fields which locally enforce a biaxial ordering.

Aesthetics and creativity in e-learning material

We do know that new learning material must be interactive and actively involve students in the learning process. The idea is generally good but the implementation sometimes falls behind. During the analysis of e-learning materials that are publicly available, we discovered some noticeable and subtle flaws in the materials. The contemporary design paradigm of e-learning materials requires products that are didactically useful and aesthetically appropriate. The quality assured development of e-learning materials should be a part of education in all pedagogical studies. Students who study special didactical disciplines should acquire a critical view of the application of e-learning materials through their own prepared presentations. This article presents a discussion on the aesthetic conditions for designing of e-learning materials. The fundamental parameters for the assessment of aesthetically suitable e-learning materials will be reviewed as well as options for involving students in the learning process.

Sudden Isotropic-Nematic Phase Transition Within a Plan-Parallel Cell

ABSTRACT We study the nematic structure of a liquid crystal confined within a plan-parallel cell following the temperature driven isotropic-nematic phase transition quench. The Lebwohl-Lasher lattice model is used. The kinetics of the system is followed via Brownian molecular dynamics, enabling us to reach macroscopic time scales. In the simulation we assume that at one confining plate the nematic pattern becomes imprinted and frozen in after the phase transition. We study the main features of resulting nematic equilibrium structures.

Visualization of Nematic Director Field With the RGB Color System

The two-dimensional presentation of the three-dimensional nematic liquid crystal structure can be visualized in various ways: by oriented rotational ellipsoids, bricks, cylinders, or sticks, representing either individual molecules or nematic director field. Here, we give a different approach: the three axes of Cartesian coordinate system are assigned with three colors (red for x-axis, green for y-axis and blue for z-axis). We use the proportional mixing of these colors for various directions of the nematic director. Using this technique, different structures of nematic liquid crystals can be visualized clearly, particularly when combined with representation of nematic director field with sticks.

ICT support for promotion of nature park

Around the World and particularly in the Europe the conservation of the habitats becomes more important. For that reason, the project of connecting nature and people in Europe promotes the European Green Belt that stretch across 12500 km. A part of that European Green Belt is also the three state nature park (Goričko-Raab-Örség) spanning Slovenia, Austria and Hungary. Inhabitants the Goričko nature park are important factor for the parks the long time survival and preservation. But living in the park also presents multiple limitations and young people see them as hampering constraints of their life. Therefore, the activities for constant promotion and value of the park needs to become the daily routine. The old fashion promotional activities are not effective for the youngsters, which are accustomed to the fast life style and daily use of ICT. The study was made how to incorporate ICT into the promotion and daily life of the nature park and empower the activities to create visitors own footprint in the park and parks cyber space. The promotional activities, educational activities and competition between youngsters are covered in the article. The ICT is the backbone for the teamwork; individuals curiosity; and professionals.

Designing m-learning materials for language learning

There are hot debates if e-learning and m-learning are the same thing. This is a dilemma only for those who were now participate in the m-learning learning material production. From technical perspective we might see this just as viewport constraint. But those constraints have high implication into the background thinking processes. Classical windows navigation cannot be used and if we want m-learning materials to be successful we need to pay special attention to the just-in-time learning. Much effort needs to apply to the context when and where information is searched and displayed to statistically predict following user requests. Only such materials that are successful in prediction of users actions are successful as learning materials and do not becomes “digital rubbish” on mobile device. The article is focused on the design of m-learning for Slovene language on level A1 and A2 which is of paramount importance for further motivation for language learning.

Memory Effects in Mixtures of Liquid Crystals and Anisotropic Nanoparticles

For years there is a substantial interest on impact of disorder on condensed matter structural properties (Imry & Ma, 1975) (Bellini, Buscaglia, & Chiccoli, 2000) (Cleaver, Kralj, Sluckin, & Allen, 1996). Pioneering studies have been carried out in magnetic materials (Imry & Ma, 1975). In such system it has been shown that even relatively weak random perturbations could give rise to substantial degree of disorder. The main reason behind this extreme susceptibility is the existence of the Goldstone mode in the continuum field describing the orienational ordering of the system. This fluctuation mode appears unavoidably due to continuous symmetry breaking nature of the phase transition via which a lower symmetry magnetic phase was reached. For example, the Imry Ma theorem (Imry & Ma, 1975), one of the pillars of the statistical mechanics of disorder, claims, that even arbitrary weak random field type disorder could destroy long range ordering of the unperturbed phase and replace it with a short range order (SRO). Note that this theorem is still disputable because some studies claim that instead of SRO a quasi long order could be established (Cleaver, Kralj, Sluckin, & Allen, 1996). During last decades several studies on disorder have been carried out in different liquid crystal phases (LC) (Oxford University, 1996), which are typical soft matter representatives. These phases owe their softness to continuous symmetry breaking phase transitions via which these phases are reached on lowering the symmetry. In these systems disorder has been typically introduced either by confining soft materials to various porous matrices (e.g., aerogels (Bellini, Clark, & Muzny, 1992), Russian glasses (Aliev & Breganov, 1989), Vycor glass (Jin & Finotello, 2001), Control Pore Glasses (Kralj, et al., 2007) or by mixing them with different particles (Bellini, Radzihovsky, Toner, & Clark, 2001) (Hourri, Bose, & Thoen, 2001) of nm (nanoparticles) or micrometer (colloids) dimensions. It has been shown that the impact of disorder could be dominant in some measured quantities. In particular the validity of Imry-Ma theorem in LC-aerosil mixtures was proven (Bellini, Buscaglia, & Chiccoli, 2000). In our contribution we show that binary mixtures of LC and rod-like nanoparticles (NPs) could also exhibit random field-type behavior if concentration p of NPs is in adequate regime. Consequently, such systems could be potentially exploited as memory devices. The plan of the contribution is as follows. In Sec. II we present the semi-microscopic model used