Monte Carlo simulations for a simple model liquid crystal are presented. The influence of flat walls on the phase behavior is analyzed for two different anchoring mechanisms, one favoring homeotropic alignment and one simulating a twisted nematic cell without external fields, e.g., two walls with different homogeneous planar alignment. The simulations are performed in the constant pressure ensemble. The box volume may change in the directions perpendicular to the wall normal. The isotropic-nematic phase transition in the bulk system is first studied for different isobars. For the weak first order transition we do not observe any hysteresis down to a temperature accuracy of deltaT=0.001. The isotherm T=1 is then studied in the bulk as well as in the confined geometries. The walls stabilize the positional order in the systems due to the formation of layers. The orientational order is weakly stabilized.

No abstract

The impact of electron heating on vertical electrical transport in superlattices is shown to cause an S-shaped current–voltage characteristic in addition to the conventional N type occurring at lower fields. Our calculations are supported by experimental data. The combination of S- and N-type instabilities leads to a modified structure of the high-field domains associated with self-generated GHz oscillations.

A direct method for the computation of the twist Frank elasticity coefficient of a nematic liquid crystal is presented. The method, suitable for numerical calculations, is tested and applied in Monte Carlo simulations for a model system. The dependence of the elasticity coefficient on the temperature and density and its relation to the nematic order parameter are analyzed and discussed.

Modeling of large fluid systems requires in-house (specialized) tools, since applicability of Modelica and existing environments is limited.Nevertheless Modelica is a very powerful and descriptive modeling language, which is best suited for physical modeling in a heterogeneous environment. Its object oriented approach, the built-in documentation and the availability of commercial and free libraries justifies the decision for Modelica as the preferred modeling language within Siemens Energy.For an appropriate analysis of transient power plant processes, there often are large fluid systems to be modeled, i.e. there can be several thousand states. For such plant models, we use our in-house tool Dynaplant (DP), which is specialized for large fluid systems. A comparison between DP and Dymola[1] reveals some deficiencies of the Modelica world concerning performance and plant model construction: Especially, successive initialization and sparse matrix solvers are important features in need.