Manifestation of biquadratic coupling in the smectic C* phase soft mode dielectric response

The soft mode dielectric response of three ferroelectric chiral smectic C* substances is studied in the vicinity of the smectic C*-smectic A* phase transition. For some substances the soft mode dielectric strength exhibits a pronounced anomaly in the C* phase just below the phase transition. We show how this anomaly can be systematically correlated with a corresponding anomaly in the experimentally determined ratio of spontaneous polarization over tilt. By comparing the experimental results with the theoretical predictions of an extended Landau model, we demonstrate how the crossover behaviour of the system can be interpreted as being the consequence of the presence of a biquadratic coupling between tilt and polarization in the Landau free-energy of the system.     

Determination of diazepam and nordazepam in milk and plasma in the presence of oxazepam and temazepam

For studies on the excretion of drugs into milk a sensitive high-performance liquid chromatographic assay was developed to quantitate diazepam and nordazepam in the milk and plasma of humans and rabbits in the presence of their major metabolites, oxazepam and temazepam. Flurazepam was used as an internal standard. The assay involves extractions with diethyl ether and an additional acid clean-up step. Chromatographic separation was achieved by a LiChrospher 60 RP-select B (5 microns) column and KH2PO4- acetonitrile (69:31, v/v) adjusted to pH 2.80 as a mobile phase. The same extraction and chromatographic conditions were suited to both types of samples, milk and plasma. The limits of determination using ultraviolet detection at 241 nm was for diazepam 20 ng/ml and for nordazepam 15 ng/ml. The absolute recoveries of diazepam, nordazepam and flurazepam in human milk were 84, 86 and 92% and in human plasma 97, 89 and 94%, respectively. The within- and between-day accuracy and precision for diazepam and nordazepam in milk and plasma at all concentrations tested (20-1500 ng/ml) were better than 8%. The high fat content which occurs in rabbit milk presented no limitation for the extraction of lipophilic diazepam: the method was successfully used to monitor milk and plasma concentrations of diazepam and nordazepam in lactating New Zealand White rabbits during 26-h infusions of diazepam (1.4 mg/h).     

Investigations of the structure of a cholesteric phase with a temperature induced helix inversion and of the succeeding Sc* phase in thin liquid crystal cells

Investigations of 4-[(S, S)-2, 3 epoxyhexyloxy]-phenyl-4-(decyloxy)-benzoate by polarizing microscopy, the Cano-Grandjean method, optical rotation dispersion and UV-VIS spectroscopy reveal a cholesteric phase with temperature induced reversal of the helical twist. Switching time experiments in the S_c* phase show that the intrinsic helix can be unwound reversibly and irreveribly by application of electric fields of different strengths.     

Experimental and theoretical study of the influence of a bias electric field on the dielectric properties of the chiral smectic A* phase

The influence of a bias electric field on the temperature and frequency dependence of the soft mode part of the complex dielectric constant of the chiral smectic A* phase has been studied experimentally. It was found that only close to T_S*CS*A does the bias field have any influence on the experimentally determined quantities. Here the relaxation frequency increased with increasing bias field, while the corresponding dielectric strength decreases. We also present a theoretical calculation of the influence of a bias field on the complex dielectric constant of the chiral smectic A* phase which, apart from minor details, is in accordance with the observed behaviour. Finally we discuss how the nature of the electroclinic effect can be correlated with the influence of the bias field on the smectic A* dielectric constant.     

Progressive, classical or balanced— A look at mathematical learning environments in Swiss-German lower-secondary schools

In a national supplement to TIMSS, lower-secondary school teachers (N=102) and their students (N=975) reported on mathematics instruction by means of a teacher questionnaire (teaching-learning methods, instructional sub-goals, facilitated student activities, achievement assessment, teacher role) and a student questionnaire (teachers' instructional proficiency, classroom climate). A cluster analysis performed on the ratings of teaching-learning methods yielded a solution with three clusters referred to as progressive, classical, and balanced learning environment. Cluster-related differences in facilitated student activities, achievement evaluation and preferred teacher role were found but not in instructional sub-goals. Students from different learning environments equally approved teachers' instructional proficiency and classroom climate and also had similar TIMSS mathematics scores. The results of this study provide empirical evidence that in addition to classical teacher-centered learning environments there seem to exist more diversified and studentcentered learning environments that address the needs for students to direct their own learning, communicate and work with others, and develop ways of dealing with complex problems. In line with the research literature it was also found that high mathematics achievement is not restricted to a certain type of learning environment.     

Micro-electromechanical Systems for Nano-science

Micro-electromechanical systems are ideal tools for nano-science because they bridge the gap between the nano- and the macro-world. Moreover, several of these instruments can be operated in parallel to either increase the throughput or to provide redundancy. The majority of the components of such a system have dimensions above the nanometer scale. Still, some require placement and pattern accuracy well below this limit. This will be highlighted in a short review of a few examples: Scanning optical near field microscope probe fabrication, where an aperture of 50 nm in diameter was incorporated at the probing tip; parallel scanning force microscope for measuring dust particles on Mars where redundancy is essential; and a miniaturized electron column for parallel electron beam lithography, where the throughput needs to be increased.     

Polarization and Viscosity Measurements in a Ferroelectric Liquid Crystal by the Field Reversal Method

With the aim to develop a standard method for measurements of the polarization of ferroelectric chiral smectic C liquid crystalline materials, we have studied thin, well-aligned samples of MBRA-8 using the field-reversal method. The method also provides an estimate for the rotational viscosity and for the response times.     

A pyroelectric liquid crystal polymer (PLCP) for second-harmonic generation

In order for a material to show a non-vanishing second order non-linear susceptibility, the material has to have a polar axis. This is hard to achieve in a liquid crystal system because of the strong quadrupolar order along the director. Electrostatic poling of polymers and polymer liquid crystals at high temperature and subsequent quenching to lower temperature only gives a small value of the polar order parameter and, in addition, results in materials which are not in thermodynamic equilibrium and therefore not stable over long times. Starting with a ferroelectric liquid crystal (which has polar order perpendicular to the director) we have succeeded in making a material with true polar order. It is not ferroelectric, although the ferroelectric properties of the starting and intermediate materials are basic for the procedure and for the final product which can be used for frequency doubling, of importance, for instance, in a wide area of optic communication applications.     

Smectic-A*-smectic-C* transition in a ferroelectric liquid crystal without smectic layer shrinkage

The smectic layer spacing of a nonfluorinated ferroelectric liquid crystal (FLC) compound with almost no shrinkage and only minor tendency to form zigzag defects was characterized by small angle x-ray diffraction. The material lacks a nematic phase. The smectic-A*-smectic-C* phase transition was studied by measuring the thermal and electric field response of the optical tilt and the electric polarization. These properties are described very well by a Landau expansion even without introduction of a higher-order Theta(6) term. This result suggests a pure second-order phase transition far from tricriticality and differs considerably from the typical behavior of the A*-C* transition in most FLC materials.