277 research outputs found

    Light-induced instabilities in photo-oriented liquid crystal cells

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    In a planar liquid crystal sample sandwiched between a photosensitive and a reference plate instabilities occurred, when the cell was illuminated from the reference side. The instabilities were induced both by polarized white light source and monochromatic laser beams. Static and dynamic regimes were found; for laser irradiation dynamic instability was found only in a range of polarization directions. A model, developed for monochromatic excitation, predicts that at certain thicknesses dynamic instability is forbidden. Experiments on a wedge-like cell confirmed this conclusion.Comment: to appear in Mol. Cryst. Liq. Crys

    Phase behaviors of binary mixtures composed of banana-shaped and calamitic mesogens

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    In this work, five mixtures with different concentrations of banana-shaped and calamitic compounds have been prepared and subsequently studied by polarizing optical microscopy, differential scanning calorimetry, and X-ray diffraction on non-oriented samples. The phase sequences and molecular parameters of the binary systems are presented

    European rodent on the edge: status and distribution of the Vojvodina blind mole rat

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    Recent research of blind mole rats of the species complex Nannospalax (superspecies leucodon) identified a small and fragmented population of these rodents on both sides of the Hungarian-Serbian border. Cytogenetic investigations proved that this population karyologically identical with the Vojvodina blind mole rat described earlier as Nannospalax (leucodon) montanosyrmiensis. Based on cytochrome b gene sequences obtained from three specimens originating from separate locations, these blind mole rats form a discrete phylogenetic clade which, with a difference of about 10%, is well separated from other blind mole rat taxa inhabiting the Carpathian Basin. The taxon has only two extant populations that are 150 km apart from each other. The combined occupied area is estimated to be less than 10 km(2), and the total estimated number of individuals is less than 300. These two remaining populations are heavily fragmented and under imminent threat by the establishment of tree plantations, small-scale and agro-industrial farms and land development. The situation is further aggravated by the fact that 80% of the individuals inhabit unprotected areas. A study of the landscape history of the wider area surrounding one of the populations - based on military maps spanning over the last 200 years - has shown a drastic decrease in the extent and quality of potential habitats. Based on our present knowledge, the Vojvodina blind mole rat is one of the most seriously threatened, rarest mammal in Europe, the remaining population of which can be wiped out within years unless immediate conservation action is taken. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1186/2193-1801-2-2) contains supplementary material, which is available to authorized users

    The Alcuin number of a graph and its connections to the vertex cover number

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    We consider a planning problem that generalizes Alcuin's river crossing problem to scenarios with arbitrary conflict graphs. This generalization leads to the so-called Alcuin number of the underlying conflict graph. We derive a variety of combinatorial, structural, algorithmical, and complexity theoretical results around the Alcuin number. Our technical main result is an NP-certificate for the Alcuin number. It turns out that the Alcuin number of a graph is closely related to the size of a minimum vertex cover in the graph, and we unravel several surprising connections between these two graph parameters. We provide hardness results and a fixed parameter tractability result for computing the Alcuin number. Furthermore we demonstrate that the Alcuin number of chordal graphs, bipartite graphs, and planar graphs is substantially easier to analyze than the Alcuin number of general graphs
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