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Context. Very massive stars pass through the Wolf-Rayet (WR) stage before they finally explode. Details of their evolution have not yet been safely established, and their physics are not well understood. Their spectral analysis requires adequate model atmospheres, which have been developed step by step during the past decades and account in their recent version for line blanketing by the millions of lines from iron and iron-group elements. However, only very few WN stars have been re-analyzed by means of line-blanketed models yet. Aims. The quantitative spectral analysis of a large sample of Galactic WN stars with the most advanced generation of model atmospheres should provide an empirical basis for various studies about the origin, evolution, and physics of the Wolf-Rayet stars and their powerful winds. Methods. We analyze a large sample of Galactic WN stars by means of the Potsdam Wolf-Rayet (PoWR) model atmospheres, which account for iron line blanketing and clumping. The results are compared with a synthetic population, generated from the Geneva tracks for massive star evolution. Results. We obtain a homogeneous set of stellar and atmospheric parameters for the GalacticWN stars, partly revising earlier results. Conclusions. Comparing the results of our spectral analyses of the Galactic WN stars with the predictions of the Geneva evolutionary calculations, we conclude that there is rough qualitative agreement. However, the quantitative discrepancies are still severe, and there is no preference for the tracks that account for the effects of rotation. It seems that the evolution of massive stars is still not satisfactorily understood.
The new tetrathiacrown ethers maleonitrile-tetrathia-12-crown-4 (mn12S(4)) and maleonitrile-tetrathia-13-crown- 4 (mn13S(4)) have been prepared and characterised by X-ray crystallographic analysis. These crown ethers form 2:1, 3:2 and 1: 1 complexes with AgY (Y = BF4, PF6). The crystal structures of [Ag(mn12S(4))(2)]BF4 (3a), [Ag(mn13S(4))(2)]BF4 (4a) and [Ag-2(mn13S(4))(3)](PF6)(2) (6b) have been determined. Compound 3a contains the centrosymmetric sandwich complex cation [Ag(mn12S(4))(2)](+) where each mn12S(4) ligand is coordinated to the Ag centre in an endo manner through all four S atoms. The 2:1 complex [Ag(mn12S(4))(2)](+) is the first sandwich complex with a tetrathiacrown ether and the first complex with an octa(thioether) coordination sphere. The crystal structure of compound 4a also reveals a 2:1 complex. This complex, [Ag(mnl3S(4))(2)](+), exhibits a half-sandwich structure. One mn13S(4) ligand coordinates to Ag+ by all four S donor atoms and the other 13S(4) crown by only one S atom. Compound 6b contains a dinuclear Ag complex. The Ag complexes 3a,b-8a,b were also studied by electrospray ionisation mass spectrometry. Collision-induced dissociation (CID) was used to compare the relative stability of 2:1 complexes [AgL2]+ and 1:1 complexes [AgL](+) (L = mn12S(4), mn13S(4)). The C-13 NMR chemical shifts of 2:1 and 1:1 Ag complexes and their corresponding free ligands were also estimated and compared. The free energy of the barrier of ring inversion (Delta G(double dagger)) for [Ag(mn12S(4))(2)](+) was determined to be 64 kJmol(-1).
The estimation of minimum-misfit stochastic models from empirical ground-motion prediction equations
(2006)
In areas of moderate to low seismic activity there is commonly a lack of recorded strong ground motion. As a consequence, the prediction of ground motion expected for hypothetical future earthquakes is often performed by employing empirical models from other regions. In this context, Campbell's hybrid empirical approach (Campbell, 2003, 2004) provides a methodological framework to adapt ground-motion prediction equations to arbitrary target regions by using response spectral host-to-target-region-conversion filters. For this purpose, the empirical ground-motion prediction equation has to be quantified in terms of a stochastic model. The problem we address here is how to do this in a systematic way and how to assess the corresponding uncertainties. For the determination of the model parameters we use a genetic algorithm search. The stochastic model spectra were calculated by using a speed-optimized version of SMSIM (Boore, 2000). For most of the empirical ground-motion models, we obtain sets of stochastic models that match the empirical models within the full magnitude and distance ranges of their generating data sets fairly well. The overall quality of fit and the resulting model parameter sets strongly depend on the particular choice of the distance metric used for the stochastic model. We suggest the use of the hypocentral distance metric for the stochastic Simulation of strong ground motion because it provides the lowest-misfit stochastic models for most empirical equations. This is in agreement with the results of two recent studies of hypocenter locations in finite-source models which indicate that hypocenters are often located close to regions of large slip (Mai et al., 2005; Manighetti et al., 2005). Because essentially all empirical ground-motion prediction equations contain data from different geographical regions, the model parameters corresponding to the lowest-misfit stochastic models cannot necessarily be expected to represent single, physically realizable host regions but to model the generating data sets in an average way. In addition, the differences between the lowest-misfit stochastic models and the empirical ground-motion prediction equation are strongly distance, magnitude, and frequency dependent, which, according to the laws of uncertainty propagation, will increase the variance of the corresponding hybrid empirical model predictions (Scherbaum et al., 2005). As a consequence, the selection of empirical ground-motion models for host-to-target-region conversions requires considerable judgment of the ground-motion analyst
The Enigma of Arrival
(2006)
The empire in 1871 - 1914
(2006)
Receiver functions (RF) are used to investigate the upper mantle structure beneath the Eifel, the youngest volcanic area of Central Europe. Data from 96 teleseismic events recorded by 242 seismological stations from permanent and a temporary network has been analysed. The temporary network operated from 1997 November to 1998 June and covered an area of approximately 400 x 250 km(2) centred on the Eifel volcanic fields. The average Moho depth in the Eifel is approximately 30 km, thinning to ca. 28 km under the Eifel volcanic fields. RF images suggest the existence of a low velocity zone at about 60-90 km depth under the West Eifel. This observation is supported by P- and S-wave tomographic results and absorption (but the array aperture limits the resolution of the tomographic methods to the upper 400 km). There are also indications for a zone of elevated velocities at around 200 km depth, again in agreement with S-wave and absorption tomographic results. This anomaly is not visible in P-wave tomography and could be due to S-wave anisotropy. The RF anomalies at the Moho, at 60-90 km, and near 200 km depth have a lateral extent of about 100 km. The 410 km discontinuity under the Eifel is depressed by 15-25 km, which could be explained by a maximum temperature increase of +200 degrees C to +300 degrees C. In the 3-D RF image of the Eifel Plume we also notice two additional currently unexplained conversions between 410 and 550 km depth. They could represent remnants of previous subduction or anomalies due to delayed phase changes. The lateral extent of these conversions and the depression of the 410 km discontinuity is about 200 km. The 660 km discontinuity does not show any depth deviation from its expected value. Our observations are consistent with interpretation in terms of an upper mantle plume but they do not rule out connections to processes at larger depth
In this study the effect of phonotactic constraints concerning word-initial consonant clusters in children with delayed phonological acquisition was explored. Twelve German-speaking children took part (mean age 5;1). The spontaneous speech of all children was characterized by the regular appearance of the error patterns fronting, e.g., Kuh (cow) → /tu:/, or stopping, e.g., Schaf (sheep) → /ta:f/, which were inappropriate for their chronological age. The children were asked to produce words (picture naming task, word repetition task) with initial consonant clusters, in which the application of the error patterns would violate phonotactic sequence constraints. For instance, if fronting would apply in /kl-/, e.g., Kleid (dress), it would be realized as the phontactically illegal consonant cluster /tl-/. The results indicate that phonotactic constraints affect word production in children with delayed phonological developments. Surprisingly, we found that children with fronting produced the critical consonants correctly significantly more often in word-initial consonant clusters than in words in which they appeared as singleton onsets. In addition, the results provide evidence for a similar developmental trajectory of acquisition in children with typical development and in children with delayed phonological acquisition. Keywords: Children with delayed phonological acquisition, phonotactic constraints, word-initial consonant clusters, fronting, stopping.
A series of novel platinum-containing carbazole monomers and polymers was synthesized and fully characterized by UV-VIS absorption, luminescence, and photoinduced absorption studies. In these compounds, a carbazole unit is incorporated into the main chain via either a para- or a meta-linkage. We discuss the effects of linkage and polymerization on the energy levels of S-1, T-1, and T-n. The S-1-T-1 splitting observed for the meta-linked monomer (0.4 eV) is only half of that in the para-linked monomer (0.8 eV). Upon polymerization, the exchange energy in the para- linked compound reduces, yet still remains larger than in the meta-linked polymer. We attribute the difference in exchange energy to the difference in wave function overlap between electron and hole in these compounds. (c) 2006 American Institute of Physics
The crystal and molecular structures of sodium and barium complexes of dibenzo-24-crown-8 ether
(2006)
The sodium and barium isothiocyanate complexes of 6,7,9,10,12,13,20,21,23,24,26,27-dodecahydrodibenzo[b,n]- 1,4,7,10,13,16,19,22-octaoxacyclotetracosin (dibenzo-24-crown-8 ether = DB24C8) were synthesized and analyzed by X-ray diffraction. The sodium complex, [Na(DB24C8)(NCS)(H2O)] 1, crystallizes in the orthorhombic space group Fdd2 with 16 molecules in the unit cell. The coordination number of Na is 6 and the central ion is located in a distorted octahedric environment. Only four of the crown ether oxygen atoms are involved. The coordination polyhedron is completed by the isothiocanate anion and by a water molecule, which is stabilized by hydrogen bonds. The barium complex, [Ba(DB24C8)(NCS)(2)] 2, crystallizes in the trigonale space group P3(1)21 with 3 molecules in the unit cell. Crystallographic C-2 symmetry is observed for the complex. The coordination number of Ba is 10. Barium is coordinated with the eight oxygen atoms of the macrocyclic ligand and with two isothiocyanate anions. The absolute structure was estimated using the FLACK parameter
Relationships of annelid subtaxa are controversially discussed and additional markers are necessarily needed to get further insights into their evolution. Due to their high content of information, mitochondrial genomes have been proven very useful in phylogenetic analyses. Whereas many complete mitochondrial genomes of arthropods are available, lophotrochozoan taxa are only scarcely represented and this is especially true for annelids. Here we present the complete mitochondrial genome of the orbiniid polychaete Orbinia latreillii. The circular genome is 15,558 bp in size and contains the same 37 genes as found in most other metazoans. As in the case for all studied annelids all genes are transcribed from the same strand. Compared with the known data from other annelids at least five gene translocations must be hypothesized for O. latreillii. A comparison of the available data shows that gene translocations within Annelida seem to be less frequent than in molluscs, but more frequent as previously assumed. Phylogenetic analyses of mitochondrial DNA sequence data and amino acid data support an inclusion Of Sipuncula within Annelida and a closer relationship to orbiniids is recovered for this taxon.
The communicatory significance of localised defecation sites in bushbuck (Tragelaphus scriptus)
(2006)
Like several other mammals, bushbuck (Tragelaphus scriptus) deposit faeces in specific localised defecation sites (LDS). A previous study has ruled out a function of LDS in the context of parasite avoidance. In this study, we investigated the communicatory significance of LDS. In a free ranging population, we tested whether LDS serve to demarcate home ranges, and/or if LDS are used for communication in a non-territorial context. In both sexes, LDS increased significantly in number towards the periphery of individual home ranges. However, the distribution pattern of LDS, as revealed by a nearest-neighbour mapping technique (nearest distances between LDS), did not support the idea that LDS serve home range/territory-demarcation because LDS did not follow a pattern of minimal nearest-neighbour distances along the margins of home ranges. We found females to urinate more often in LDS than males. Notably, information transfer was most frequent between sending (urinating or defecating) females and receiving/responding males (urination or defecation at places where a female had previously signalled). Our results suggest that LDS mainly serve for inter- sexual communication in bushbuck
What is "Celtic"and what is universal in the "Celtic Englishes"? This was the central concern of the fourth and final Colloquium of studies on language contact between English and the Celtic languages at the University of Potsdam in September 2004. The contributions to this volume discuss the "Celtic" peculiarities of Standard English in England and in Ireland (North and South). They also examine the perceived "Celticity" of personal names in the "Celtic" countries (Ireland, Wales, Cornwall, Brittany). Moreover, they put emphasis on specific grammatical features such as the expression of perfectivity, relativity, intensification and the typological shift of verbal word formation from syntheticity to analycity as well as the emergence of universal contact trends shared by Celtic, African and Indian Englishes. Thus, the choice of contributors and the scope of their articles makes Celtic Englishes IV an invaluable handbook for scholarly work in the field of the English - Celtic relations.
We study the Cauchy problem for the oscillation equation of the couple-stress theory of elasticity in a bounded domain in R3. Both the displacement and stress are given on a part S of the boundary of the domain. This problem is densely solvable while data of compact support in the interior of S fail to belong to the range of the problem. Hence the problem is ill-posed which makes the standard calculi of Fourier integral operators inapplicable. If S is real analytic the Cauchy-Kovalevskaya theorem applies to guarantee the existence of a local solution. We invoke the special structure of the oscillation equation to derive explicit conditions of global solvability and an approximation solution.