Svensk Insektfauna Trettonde Steklar

Steklarne anses med skäl såsom de högst stående bland in-sekterna. De utmärka sig genom följande kännetecken: Hufvudet mycket rörligt med munöppningen vänd nedåt. Öfverkäkarne kraftigt utbildade, bitande; underkäkarne bilda tillsammans med underläppen en sug- eller slickapparat. Första mellankroppsleden är i allmänhet liten och ofvan oftast orörligt sammanväxt med andra leden, dess sido- och bröstplåtar äro alltid genom en !edgång rörligt förenade med ryggplåten {halsskölden), hvarigenom frambenen blifva mycket rörliga. Vingarne, som sällan saknas, äro fyra, tunna, nakna, hinnaktiga och endast försedda med ett ringa antal slutna vingfält; de bakre kortare och smalare än de främre. Förvandlingen är fullständig. Larverna hafva ett tydligt afsatt hufvud med bitande mundelar och tretton kroppsleder. Puppans kroppsdelar nästan fritt liggande

Svensk Insektfauna Steklar Gaddsteklar Andra Rofsteklar

Hufvudet medelmåttigt eller stort. Ögonen oftast nakna, mycket sällan håriga (Entomognathus), på insidan vanligen hela, sällan med en inskärning (Phila11thus, Trypoxylon); de äro oftast så stora, att de nå ned till mandiblernas rot, hvarigenom kinder komma att saknas; de stå antingen parallella eller närma sig hvarandra uppåt eller nedåt. Punktögonen tre ställda i trekant, vanligen halfklotformiga, de öfre sällan otydliga och långsträckta (T achytes). Öfverläppen är oftast liten och mer eller mindre dold under munskölden, sällan (Bembex) mycket stor och inslagen under mandiblern a. Mandiblerna äro vanligen skärformiga, enkla eller tandade. Underkäkarne och tungan äro korta och bilda således endast en föga utvecklad sug-eller slickapparat

First-principles study of the ferroelectric Aurivillius phase Bi2WO6

In order to better understand the reconstructive ferroelectric-paraelectric transition of Bi2WO6, which is unusual within the Aurivillius family of compounds, we performed first principles calculations of the dielectric and dynamical properties on two possible high-temperature paraelectic structures: the monoclinic phase of A2/m symmetry observed experimentally and the tetragonal phase of I4/mmm symmetry, common to most Aurivillius phase components. Both paraelectric structures exhibits various unstable modes, which after their condensation bring the system toward more stable structures of lower symmetry. The calculations confirms that, starting from the paraelectric A2/m phase at high temperature, the system must undergo a reconstructive transition to reach the P2_1ab ferroelectric ground state.Comment: added Appendix and two table

Electronic Structure and Valence Band Spectra of Bi4Ti3O12

The x-ray photoelectron valence band spectrum and x-ray emission valence-band spectra (Ti K _beta_5, Ti L_alpha, O K_alpha) of Bi4Ti3O12 are presented (analyzed in the common energy scale) and interpreted on the basis of a band-structure calculation for an idealized I4/mmm structure of this material.Comment: 6 pages + 7 PostScript figures, RevTex3.0, to be published in Phys.Rev.B52 (Oct.95). Figures also available via anonymous ftp at ftp://ftp.physik.uni-osnabrueck.de/pub/apostnik/BiTiO

Chemistry of layered d-metal pnictide oxides and their potential as candidates for new superconductors

Layered d-metal pnictide oxides are a unique class of compounds which consists of characteristic d-metal pnictide layers and metal oxide layers. More than 100 of these layered compounds, including the recently discovered Fe-based superconducting pnictide oxides, can be classified into 9 structure types. These structure types and the chemical and physical properties of the characteristic d-metal pnictide layers and metal oxide layers of the layered d-metal pnictide oxides are reviewed and discussed. Furthermore, possible approaches to design new superconductors based on these layered d-metal pnictide oxides are proposed.Comment: 29 pages including 6 tables and 2 figure

Electronic structure and ferroelectricity in SrBi2Ta2O9

The electronic structure of SrBi2Ta2O9 is investigated from first-principles, within the local density approximation, using the full-potential linearized augmented plane wave (LAPW) method. The results show that, besides the large Ta(5d)-O(2p) hybridization which is a common feature of the ferroelectric perovskites, there is an important hybridization between bismuth and oxygen states. The underlying static potential for the ferroelectric distortion and the primary source for ferroelectricity is investigated by a lattice-dynamics study using the Frozen Phonon approach.Comment: 17 pages, 7 figures. Phys. Rev. B, in pres

Deep-Sea Origin and In-Situ Diversification of Chrysogorgiid Octocorals

The diversity, ubiquity and prevalence in deep waters of the octocoral family Chrysogorgiidae Verrill, 1883 make it noteworthy as a model system to study radiation and diversification in the deep sea. Here we provide the first comprehensive phylogenetic analysis of the Chrysogorgiidae, and compare phylogeny and depth distribution. Phylogenetic relationships among 10 of 14 currently-described Chrysogorgiidae genera were inferred based on mitochondrial (mtMutS, cox1) and nuclear (18S) markers. Bathymetric distribution was estimated from multiple sources, including museum records, a literature review, and our own sampling records (985 stations, 2345 specimens). Genetic analyses suggest that the Chrysogorgiidae as currently described is a polyphyletic family. Shallow-water genera, and two of eight deep-water genera, appear more closely related to other octocoral families than to the remainder of the monophyletic, deep-water chrysogorgiid genera. Monophyletic chrysogorgiids are composed of strictly (Iridogorgia Verrill, 1883, Metallogorgia Versluys, 1902, Radicipes Stearns, 1883, Pseudochrysogorgia Pante & France, 2010) and predominantly (Chrysogorgia Duchassaing & Michelotti, 1864) deep-sea genera that diversified in situ. This group is sister to gold corals (Primnoidae Milne Edwards, 1857) and deep-sea bamboo corals (Keratoisidinae Gray, 1870), whose diversity also peaks in the deep sea. Nine species of Chrysogorgia that were described from depths shallower than 200 m, and mtMutS haplotypes sequenced from specimens sampled as shallow as 101 m, suggest a shallow-water emergence of some Chrysogorgia species