211,115 research outputs found
Catalytic P-H activation by Ti and Zr catalysts
No full textCatalytic dehydrocoupling of phosphines was investigated using the anionic zirconocene trihydride salts [Cp*Zr-2(mu-H)(3)Li](3) (1a) or [Cp*Zr-2(mu-H)(3)K(thf)(4)] (1b), and the metallocycles [CpTi(NPtBu3)(CH2)(4)] (6) and [Cp*M(NPtBu3)(CH2)(4)] (M = Ti 20, Zr 21) as catalyst precursors. Dehydrocoupling of primary phosphines RPH2 (R = Ph, C6H2Me3, Cy, C10H7) gave both dehydrocoupled dimers RP(H)P(H)R or cyclic oligophosphines (RP)(n) (n = 4, 5) while reaction of tBu(3)C(6)H(2)PH(2) gave the phosphaindoline tBu(2)(Me2CCH2)C6H2PH (9). Stoichiometric reactions of these catalyst precursors with primary phosphines afforded [Cp*Zr-2((PR)(2))H][K(thf)(4)] (R = Ph 2, Cy 3, C6H2Me3 4), [Cp*Zr-2((PPh)(3))H] [K(thf)(4)] (5), [CpTi(NPtBu3)(PPh)(3)] (7) and [CpTi(NPtBu3)(mu-PHPh)](2) (8), while reaction of 6 with (C(6)H(2)tBu3)PH2 in the presence of PMe3 afforded [CpTi(NPtBu3)(PMe3)(p(C(6)H(2)tBu(3))] (10). The secondary phosphines Ph2PH and (PhHPCH2)(2)CH2 also undergo dehydrocoupling affording (Ph2P)(2) and (PhPCH2)(2)CH2. The bisphosphines (CH2PH2)(2) and C6H4(PH2)(2) are dehydrocoupled to give (PCH2CH2PH)(2) (12) and (C6H4P(PH))(2) (13) while prolonged reaction of 13 gave (C6H4P2)(8) (14). The analogous bisphosphine Me2C6H4(PH)(2) (17) was prepared and dehydrocoupling catalysis afforded (Me2C6H2P(PH))(2) (18) and subsequently [(Me2C6H2P2)(2)(mu-Me2C6H2P2)](2) (19). Stoichiometric reactions with these bisphosphines gave [Cp*Zr-2(H)(PH)(2)C6H4] [Li(thf)(4)] (22), [Cp*Ti(NPtBu3)(PH)(2)C6H4](2) (23) and [Cp*Ti(NPtBu3)(PH)(2)C6H4] (24). 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Denophoelus Stephan 1989
No full textDenophoelus Stephan, 1989 (Fig. 24)Published as part of Ivie, Michael A., Lord, Nathan P., Foley, Ian A. & Ślipiński, S. Adam, 2016, Colydiine Genera (Coleoptera: Zopheridae: Colydiinae) of the New World: A Key and Nomenclatural Acts 30 Years in the Making, pp. 755-788 in The Coleopterists Bulletin 70 (4) on page 775, DOI: 10.1649/0010-065X-70.4.75
Selective sweep in the Flotillin-2 region of European Drosophila melanogaster.
No full textLocalizing genes that are subject to recent positive selection is a major goal of evolutionary biology. In the model organism Drosophila melanogaster many attempts have been made in recent years to identify such genes by conducting so-called genome scans of selection. These analyses consisted in typing a large number of genetic markers along the genomes of a sample of individuals and then identifying those loci that harbor patterns of genetic variation, which are compatible with the ones generated by a selective sweep. In this study we conduct an in-depth analysis of a genomic region located on the X chromosome of D. melanogaster that was identified as a potential target of recent positive selection by a previous genome scan of selection. To this end we re-sequenced 20 kilobases around the Flotillin-2 gene (Flo-2) and conducted a detailed analysis of the allele frequencies and linkage disequilibria observed in this new dataset. The results of this analysis reveal eight genetic novelties that are specific to temperate populations of D. melanogaster and that may have arisen during the expansion of the species outside its ancestral sub-Saharan habitat since about 16,000 years ago
Non-invasive study of Early Medieval wall paintings in the churches of St. Stephan in Chur and St. Martin in Disentis (Switzerland)
No full textThe Early Medieval wall paintings preserved in historical sites of the ancient Raetia Curiensis region (today’s Swiss Canton of Grisons and parts of Northern Italy and Austria) provide a rare testimony of the art
of this period.
This contribution presents the results of the non-invasive scientific campaigns carried out in the
churches of St. Stephan in Chur and St. Martin in Disentis/Mustér (Canton of Grisons, Switzerland). In the
church of St. Stephan, the investigations were performed in-situ on the surviving wall paintings of the
crypt and on several painted plaster fragments (crypt and upper church), while in Disentis a selection
of painted stucco fragments was studied. All the painted surfaces were firstly examined with technical
photography in visible, infrared, and ultraviolet ranges, followed by portable spectroscopic point analyses
(i.e. HH-XRF, FORS, and FTIR). The findings revealed the composition of most pigments such as iron-based
pigments (yellow and red ochres, green earth) and lead-based pigments (i.e., lead white and red lead).
In addition, for the St. Stephan’s site, the Visible Induced IR Luminescence (VIL) images combined with
point analyses, allowed for the identification of Egyptian blue (EB). Furthermore, the presence of zinc in
the wall paintings of the crypt of St. Stephan and the absence of this element in those referable to the
upper church, suggested differences in the procurement of copper for the manufacture of EB. The presence of arsenic and lead in iron-bearing pigments detected in the wall paintings of the crypt and their
negligible amount in those of the upper church, suggested that these pigments come from a different
sourcing area.
In the church of St. Martin, the use of different pigments for the execution of the incarnate of the
figures, the extraordinary state of conservation of minium, and the absence of green and blue pigments
are remarkable features of the stucco decoration paintings
A 2 h periodic variation in the low-mass X-ray binary Ser X-1
No full textSpectroscopy of the low-mass X-ray binary Ser X-1 using the Gran Telescopio Canarias have revealed a ?2 h periodic variability that is present in the three strongest emission lines. We tentatively interpret this variability as due to orbital motion, making it the first indication of the orbital period of Ser X-1. Together with the fact that the emission lines are remarkably narrow, but still resolved, we show that a main-sequence K dwarf together with a canonical 1.4 M? neutron star gives a good description of the system. In this scenario, the most likely place for the emission lines to arise is the accretion disc, instead of a localized region in the binary (such as the irradiated surface or the stream-impact point), and their narrowness is due instead to the low inclination (?10°) of Ser X-1
Nostalgia shapes and potentiates the future
No full textNostalgia is “a sentimental longing or wistful affection for the past” (Pearsall, 1998, p. 1266). This dictionary definition aligns well with lay conceptions (i.e., prototype analysis; cf. Rosch, 1978). Laypeople (Hepper, Ritchie, Sedikides, & Wildschut, 2012) across 18 cultures (Hepper et al., 2014) think of the construct “nostalgia” as encompassing fond, rose-colored, and personally important (i.e., self-defining) memories of one’s childhood or relationships, but also as encompassing pining and wishing for momentary returns to the past. They think of it, then, as a bittersweet (albeit more positive than negative) emotion that is relevant to the self and close others. Both content analyses of nostalgic narratives (Abeyta, Routledge, Roylance, Wildschut, & Sedikides, 2015; Holak & Havlena, 1998; Wildschut, Sedikides, Arndt, & Routledge, 2006, Studies 1-2) and in vivo manipulations of nostalgia (Baldwin, Biernat, & Landau, 2015; Wildschut et al., 2006, Studies 5-7; Stephan, Sedikides, & Wildschut, 2012) have corroborated these properties of the emotion.</p
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Correlated-gauge invariant calculations of nuclear magnetic shielding constants using the continuous transformation of the origin of the current density approach. II. Coupled cluster and density-functional theory results for eight small molecules
No full textThe quantum mechanical current density induced in a molecule by an external magnetic field isinvariant to translations of the coordinate system. This fundamental symmetry is exploited toformally annihilate the diamagnetic contribution to the current density via the approach of“continuous transformation of the origin of the current density-diamagnetic zero” CTOCD-DZ.The relationships obtained by this method for the magnetic shielding at the nuclei are intrinsicallyindependent of the origin of the coordinate system for any approximate computational schemerelying on the algebraic approximation. The authors report for the first time an extended series oforigin-independent estimates of nuclear magnetic shielding constants using the CTOCD-DZapproach at the level of density functional theory DFT with four different types of functionals andunrelaxed coupled cluster singles and doubles linear response CCSD-LR theory. The resultsobtained indicate that in the case of DFT the procedure employed is competitive with currentlyadopted computational methods allowing for basis sets of gauge-including atomic orbitals, whereaslarger differences between CTOCD-DZ and common origin CCSD-LR results are observed due tothe incomplete fulfillment of hypervirial relations in standard CCSD-LR theory. It was foundfurthermore that the unrelaxed CCSD-LR calculations predict larger correlation corrections for theshielding constants of almost all nonhydrogen atoms in their set of molecules than the usual relaxedenergy derivative CCSD calculations. Finally the results confirm the excellent performance of Kealand Tozer’s third functional, in particular, for the multiply bonded systems with a lot of electroncorrelation, but find also that the simple local density functional gives even better results for the fewsingly bonded molecules in their study where correlation effects are small
Microstructural study of zirconium oxide grown on a zirconium alloy substrate for orthopaedic applications
No full textThesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1998.Includes bibliographical references (leaves 93-95).by Stephan P. Mangin.Ph.D
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