Double cyclometalation via carbon-silicon bond cleavage by palladium(II) acetate. X-ray structure of a cationic 1,4-dipalladated benzene ring and selective synthesis of heterobimetallic 1,4-phenylene-bridged platinum(II)-palladium(II) complexes

The disilylated compound 1,4-bis(trimethylsilyl)-2,3,5,6-tetrakis((dimethylamino)methyl)benzene, (Me(3)Si)(2)C2N4, 4, can be electrophilically palladated selectively at the C-Si bonds to afford the neutral 1,4-bis(palladium) complex [(AcOPd)(2)(C2N4)], from which the dicationic [(LPd)(2)(C2N4)](2+) (L = MeCN) organometallic species are accessible. The monosilylated species (Me(3)Si)(H)C2N4, 5, can be used for the preparation of the dicationic heterodinuclear platinum(II)-palladium(II) species [(LPd)(LPt)(C2N4)](2+) (L = MeCN) via a sequence of transmetalation of the organolithium derivative of 5 with [PtCl2(SEt(2))(2)], followed by a C-Si bond palladation reaction.

Synthesis of a tri(organoplatinum) complex via the double directed lithiation of a mono(organoplatinum) precursor

The new diarylplatinum complex Cis-[Pt(PEt(3))(2){C6H3(CH(2)NMe(2))(2)-3,5}(2)] 1, containing four free amine coordination sites, undergoes directed lithiation with Bu(t)Li and subsequent transmetallation with [PtCl2(SEt(2))(2)] to give a triplatinum species 3 which reductively eliminates the diplatinum complex[ClPt{2,6-(Me(2)NCH(2))(2)C6H2-C6H2(CH(2)NMe(2))(2)-2,6}PtCl] 4.

The effects of temperature on the performance of electrochemical double layer capacitors

An electrochemical double layer capacitor test cell containing activated carbon xerogel electrodes and ionic liquid electrolyte was tested at 15, 25 and 40 OC to examine the effect of temperature on electrolyte resistance (RS) and equivalent series resistance (ESR) measured using impedance spectroscopy and capacitance using charge/discharge cycling. A commercial 10F capacitor was used as a comparison. Viscosity, ionic self-diffusion coefficients and differential scanning calorimetry measurements were used to provide an insight into the behaviour of the 1,2-dimethyl-3-propylimdazolium electrolyte. Both RS and ESR decreased with increasing temperature for both capacitors. Increasing the temperature also increased the capacitance for both the test cell and the commercial capacitor but proportionally more for the test cell. An increase in temperature decreased the ionic liquid electrolyte viscosity and increased the self diffusion coefficients of both the anion and the cation indicating an increase in dissociation and increase in ionic mobility.

Different rooms, different voices: double-breasting, multi-channel representation and the managerial agenda

Double-breasting has been identified as where companies run union voice and non-union voice mechanisms across different plants. While research has focused on the incidence of such arrangements, there is a dearth of evidence into the dynamics of it. This article seeks to complement existing research by examining the contours of double-breasting in a case study organisation. The findings suggest that more research is necessary into the dynamics of double-breasting in terms of how voice in sites affects each other and the extent to which running different regimes affects the managerial agenda.

SuperWASP observations of pulsating Am stars

We have studied over 1600 Am stars at a photometric precision of 1 mmag with SuperWASP photometric data. Contrary to previous belief, we find that around 200 Am stars are pulsating d Sct and ? Dor stars, with low amplitudes that have been missed in previous, less extensive studies. While the amplitudes are generally low, the presence of pulsation in Am stars places a strong constraint on atmospheric convection, and may require the pulsation to be laminar. While some pulsating Am stars have been previously found to be d Sct stars, the vast majority of Am stars known to pulsate are presented in this paper. They will form the basis of future statistical studies of pulsation in the presence of atomic diffusion. An extended version of Table 1 containing all the detected frequencies and amplitudes is only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/535/A3

A search for line intensity enhancements in the far-UV spectra of active late-type stars arising from opacity

Context. Radiative transfer calculations have predicted intensity enhancements for optically thick emission lines, as opposed to the normal intensity reductions, for astrophysical plasmas under certain conditions. In particular, the results are predicted to be dependent both on the geometry of the emitting plasma and the orientation of the observer. Hence in principle the detection of intensity enhancement may provide a way of determining the geometry of an unresolved astronomical source.
Aims. To investigate such enhancements we have analysed a sample of active late-type stars observed in the far ultraviolet spectral region.
Methods. Emission lines of O vi in the FUSE satellite spectra of ϵ Eri, II Peg and Prox Cen were searched for intensity enhancements due to opacity.
Results. We have found strong evidence for line intensity enhancements due to opacity during active or flare-like activity for all three stars. The O vi 1032/1038 line intensity ratios, predicted to have a value of 2.0 in the optically thin case, are found to be up to ~30% larger during several orbital phases.
Conclusions. Our measurements, combined with radiative transfer models, allow us to constrain both the geometry of the O vi emitting regions in our stellar sources and the orientation of the observer. A spherical emitting plasma can be ruled out, as this would lead to no intensity enhancement. In addition, the theory tells us that the line-of-sight to the plasma must be close to perpendicular to its surface, as observations at small angles to the surface lead to either no intensity enhancement or the usual line intensity decrease over the optically thin value. For the future, we outline a laboratory experiment, that could be undertaken with current facilities, which would provide an unequivocal test of predictions of line intensity enhancement due to opacity, in particular the dependence on plasma geometry.

Early-type stars observed in the ESO UVES Paranal Observatory Project - III. Sub-parsec and AU-scale structure in the interstellar medium

UVES interstellar observations from the Paranal Observatory Project are presented for early-type stars located in the line of sight to the nearby open clusters IC 2391 (Omni Vel) and NGC 6475 (M7), with spectroscopic resolution R similar to 80 000 and signal-to-noise ratios in the Ti II (3383 angstrom), Ca II K, CH+ (4232 angstrom), Na I D and K I (7698 angstrom) lines of several hundred. The sightlines are a mixture of cluster and non-cluster objects. A total of 22 early-type stars (A and B type) are present in our sample towards IC 2391, with 21 towards NGC 6475/M7, and enable us to probe for differences in column density on scales from similar to 0.07 to 7.3 and similar to 0.05 to 4.9 pc in the respective clusters. Additionally, towards Praesepe the Na I D interstellar variation only is probed towards 13 sightlines and transverse scales of similar to 0.16-10.7 pc at R = 70 000. Towards IC 2391 variations are found in Ti II, Ca II K and Na I D column density in different sightlines of up to 0.7, 1.0 and 1.8 dex (excluding one star), respectively. This kind of variability correlates well with the Hipparcos parallax of the objects, and probes structure within the Local Bubble. For cluster-only objects the variations are 0.3, 0.3 and 0.5 dex, respectively. For the field of view towards NGC6475 the corresponding maximum variations are somewhat smaller, being 0.5, 0.3, 0.8 and 1.0 dex for Ti II, Ca II K, Na I and K I, respectively, for all objects and 0.4, 0.2, 0.6 and 0.7 dex for the cluster-only objects. These are uncorrelated with parallax, and again demonstrate that Ca II K tends to be more smoothly distributed than Na I D. A few likely cluster sightlines show evidence for CH+ and variations in this molecular species of a factor of 10 in equivalent width over sub-pc scales. Towards Praesepe variation in interstellar Na I D is small, being a maximum of only similar to 0.4 dex (including measurement errors), but with fewer sightlines studied. Overall, the scatter in the data is similar for the singly ionized species Ti II and Ca II, lending more support to the hypothesis that these two species sample similar parts of the interstellar medium (ISM). This also appears to be the case for the neutral species Na I D and K I in the one cluster studied. Finally, multiple-epoch observations from a variety of archive sources are used to search for astronomical unit (au) scale structure in the ISM towards 46 sightlines. There are tentative indications of structure on scales of tens to thousands of au for three sightlines. Future observations will confirm the veracity or otherwise of the time-variable components and others presented.

The VLT-FLAMES survey of massive stars: Nitrogen abundances for Be-type stars in the Magellanic Clouds

Aims. We compare the predictions of evolutionary models for early-type stars with atmospheric parameters, projected rotational velocities and nitrogen abundances estimated for a sample of Be-type stars. Our targets are located in 4 fields centred on the Large Magellanic Cloud cluster: NGC 2004 and the N 11 region as well as the Small Magellanic Cloud clusters: NGC 330 and NGC 346.

Optimization of double pulse pumping for Ni-like Sm x-ray lasers

We report a systematic study of double pulse pumping of the Ni-like Sm x-ray laser at 73 Angstrom, currently the shortest wavelength saturated x-ray laser. It is found that the Sm x-ray laser output can change by orders of magnitude when the intensity ratio of the pumping pulses and their relative delay are varied. Optimum pumping conditions are found and interpreted in terms of a simple model. (C) 1999 American Institute of Physics. [S0021-8979(99)07102-9].

Massive stars exploding in a He-rich circumstellar medium - I. Type Ibn (SN 2006jc-like) events

We present new spectroscopic and photometric data of the Type Ibn supernovae 2006jc, 2000er and 2002ao. We discuss the general properties of this recently proposed supernova family, which also includes SN 1999cq. The early-time monitoring of SN 2000er traces the evolution of this class of objects during the first few days after the shock breakout. An overall similarity in the photometric and spectroscopic evolution is found among the members of this group, which would be unexpected if the energy in these core-collapse events was dominated by the interaction between supernova ejecta and circumstellar medium. Type Ibn supernovae appear to be rather normal Type Ib/c supernova explosions which occur within a He-rich circumstellar environment. SNe Ibn are therefore likely produced by the explosion of Wolf-Rayet progenitors still embedded in the He-rich material lost by the star in recent mass-loss episodes, which resemble known luminous blue variable eruptions. The evolved Wolf-Rayet star could either result from the evolution of a very massive star or be the more evolved member of a massive binary system. We also suggest that there are a number of arguments in favour of a Type Ibn classification for the historical SN 1885A (S-Andromedae), previously considered as an anomalous Type la event with some resemblance to SN 1991bg.