Downward shift of infrared conductivity spectral weight at the DDW transition: role of anisotropy

We consider the motion of conductivity spectral weight at a finite-temperature phase transition at which $d_{x^2-y^2}$ density-wave (DDW) order develops. We show that there is a shift of spectral weight to higher frequencies if the quasiparticle lifetime is assumed to be isotropic, but a shift to lower frequencies if the quasiparticle lifetime is assumed to be anisotropic. We suggest that this is consistent with recent experiments on the pseudogap phase of the cuprate superconductors and, therefore, conclude that the observation of a downward shift in the spectral weight at the pseudogap temperature does not militate against the DDW theory of the pseudogap.Comment: 8 pages, 7 figures. Added reference

Staphylinids (Coleoptera, Staphylinidae) of Ukrainian metropolises

During hundreds of years, in large cities man has been forming a specific urban environment with original species composition of insect communities, including the most diverse group of predatory beetles – Staphylinidae family. Kyiv, Kharkiv, Dnipro are the three most populated cities of Ukraine. In the urban cenoses of these cities, over 140 species from 66 genera of Staphylinidae have been recorded. The total of 69 species (43 genera) were recorded in Kyiv, 67 (39 genera) in Dnipro and 66 (37 genera) in Kharkiv. Among them, , eight species in the catalogue of Palearctic staphylinds had not been previously recorded for Ukraine: Arpedium quadrum Grav., Atheta laticeps Thomson, Medon apicalis Kraatz, Ocalea rivularis Müll., Philonthus salinus Kiesenwetter, Quedius invreae Gridelli, Tasgius pedator Grav. and Xantholinus gallicus Coiffait. By number, common species accounted for 29 in Dnipro, 21 in Kyiv and 19 in Kharkiv. In all the metropolises, two species (Staphylinus caesareus Cederhjelm and Drusilla canaliculata (F.)) were identified as eudominants. Dominants and subdominants comprised 18–25 species. Almost two thirds of the fauna of staphylinids of the cities was classified as rare species. The lowest faunistic similarity was seen between the staphylinids of the urban cenoses of Dnipro and those in Kyiv and Kharkiv (15.3% and 17.5%), similarity was higher for Staphylinidae of Kyiv and Kharkiv (36.0%). Similarity by common species of staphylinids for Kyiv and Kharkiv equaled 73.9%, 28.2% for Dnipro and Kyiv and 37.1% for Dnipro and Kharkiv. The article offers a review of species diversity, number and ecological structure (biotopic confinedness, hygrothermal preference) of typical species of staphylinids in different urban cenoses of Kharkiv. Differences in qualitative-quantitative and ecological structures of staphylinids are related to the diversity of the conditions in a particular urban cenoses. The commonest representatives of the family in the metropolises were polytopic mesophilous carnivorous species