Photosensitive in wide spectral region composites based on polyphenylenevinylene

Optical and photovoltaic properties of polyphenylenevinylene derivative – poly(2-methoxy-5-(3-,7-dimethyl-octyloxy)-1,4-phenylenevinylene (MDMO-PPV) and its composites with high (40 %) concentration polymethine dyes (PD) – meso-Cl and hexaindoletricarbocyanine (HITC) films have been studied. Two H-aggregates of dyes with different energies that weakly depend on the molecular structure of dyes, is formed in MDMO-PPV with PD in composites films. The efficiency of photogeneration of charge carrier by these aggregates is greater than the efficiency of photogeneration of charge carriers by the quasi-isolated molecules of dye. It results in substantial expansion of the absorption region (in comparison with the absorption region of molecules in solution) and photosensitivity in the side of higher energies. The presence of PD aggregates in the films MDMO-PPV influences on their photosensitivity that depends on PD molecular structure. This dependence can be caused by interaction between the molecules of MDMO-PPV and dye. In composites MDMO-PPV/HITC, the value of interaction is low and practically does not influence the efficiency of photogeneration of charge carriers by MDMO-PPV molecules, which give a considerable contribution to formation of the photovoltage in 2-3 eV regions. The interaction of meso-Cl and MDMO-PPV molecules is stronger, and this, probably, results in considerable decrease of photovoltage in the region of the excitation of MDMO-PPV

Handstand Scent Marking in the Dwarf Mongoose (Helogale parvula)

Many mammal species adopt marking postures that elevate their scent deposits. The most extreme of these is handstand marking, in which an individual reverses against an upright object, flings its hind legs into the air above its back and balances bipedally on its fore feet. The resulting anogenital deposit is thus raised one full body length above ground level. It has been suggested that this energetically costly form of marking serves to provide conspecifics with information about the marker's body size and hence competitive ability. However, this explanation assumes that the height of an individuals' deposit does reflect accurately its body size, an assumption that has never been tested in any hand-standing species. This study investigated the relationship between body size and handstand mark height in a wild population of dwarf mongooses (Helogale parvula) in South Africa. We found that although body size and marking height were correlated positively for female dwarf mongooses, they were not related for males. Male dwarf mongooses (who are subject to intrasexual competition from outside their group) invested more heavily in anogenital range marking, marking at three times the female frequency and placing their deposits significantly higher than females (although they were not dimorphic). Males that were particularly vulnerable to rivals (i.e. those that were small for their age) tended to mark higher than more robust age-mates, in keeping with the predictions of Adams & Mesterton-Gibbons' (1995, J. Theor. Biol.175, 405-421). model of deceptive threat communication. These findings suggest strongly that the height of anogenital scent deposits is of social significance to dwarf mongooses. © 2012 Blackwell Verlag GmbH