The unwinding of the short pitch helical smectic-C*alpha structure in an external electric field is studied within a discrete phenomenological model. It is found that the pitch increases quasicontinuously at low electric fields and is commensurate with the smectic layer thickness at any field. The sequence of stable structures recalls the once popular and then abandoned devil's staircase model. At larger fields the pitch grows discontinuously in steps of one smectic layer, forming a harmless staircase. Taking into account the achiral next-nearest-layer interactions the final transition to the unwound structure is found to be discontinuous.
Structures of various phases that appear in antiferroelectric liquid crystals can be described within a simple discrete phenomenological model of antiferroelectric liquid crystals, which for the smectic-C-alpha (SmC(alpha)) phase suggests a short-pitch helicoidal structure. In a paper presented here the same model is used to analyze theoretically free-standing films, formed by a finite number of smectic layers. In the bulk sample a transition from the smectic-A (SmA) phase is either to the ferroelectric SmC* phase, the SmC(*)(A) phase, or the antiferroelectric SmC(alpha) phase, as observed from experiments as well as comprehended in the model. However in free-standing films uniplanar structures, which in a bulk sample were not observed experimentally nor predicted by the model, are shown to appear immediately below the transition from the high-temperature SmA phase. In free-standing film uniplanar structure remains stable in a narrow temperature region between SmA and SmC(alpha) phase.
Three plain mirrors, perpendicular to each other, reflect a beam of light back into the direction it came from. An activity is suggested where pupils can employ this feature of perpendicular mirrors and make their own corner cube retroreflector-a kind of cat's eye.
Teaching quantum physics by the sum over paths approach and GeoGebra simulations
AbstractThe Slovene Science competition for primary school students aged between 6 and 12 years will be explained briefly. The competition is based on experiments, which should be done well in advance either at school or at home. An example of the proposed experiment for 11 and 12 year old students from the past year-a syphon-will be presented as well as the assessment questions referring to this particular experiment, which were posed at the competition. A fair proportion of the population took part in the competition. We will present a brief analysis of the obtained data, which offers an insight into the difficulty level of the questions.
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