Systematic TLM Measurements of NiSi and PtSi Specific Contact Resistance to n- and p-Type Si in a Broad Doping Range

We present the data on specific silicide-to-silicon contact resistance (ρc) obtained using optimized transmission-line model structures, processed for a broad range of various n- and p-type Si doping levels, with NiSi and PtSi as the silicides. These structures, despite being attractive candidates for embedding in the CMOS processes, have not been used for NiSi, which is the material of choice in modern technologies. In addition, no database for NiSi–silicon contact resistance exists, particularly for a broad range of doping levels. This letter provides such a database, using PtSi extensively studied earlier as a reference

Almost Contact Lagrangian Submanifolds of Nearly Kaehler 6-Sphere

For a Lagrangian submanifold M of S 6 with nearly Kaehler structure, we provide conditions for a canonically induced almost contact metric structure on M by a unit vector field, to be Sasakian. Assuming M contact metric, we show that it is Sasakian if and only if the second fundamental form annihilates the Reeb vector field ξ, furthermore, if the Sasakian submanifold M is parallel along ξ, then it is the totally geodesic 3-sphere. We conclude with a condition that reduces the normal canonical almost contact metric structure on M to Sasakian or cosymplectic structure

Gamma-Ray Bursts from tidally spun-up Wolf-Rayet stars?

The collapsar model requires rapidly rotating Wolf-Rayet stars as progenitors of long gamma-ray bursts. However, Galactic Wolf-Rayet stars rapidly lose angular momentum due to their intense stellar winds. We investigate whether the tidal interaction of a Wolf-Rayet star with a compact object in a binary system can spin up the Wolf-Rayet star enough to produce a collapsar. We compute the evolution of close Wolf-Rayet binaries, including tidal angular momentum exchange, differential rotation of the Wolf-Rayet star, internal magnetic fields, stellar wind mass loss, and mass transfer. The Wolf-Rayet companion is approximated as a point mass. We then employ a population synthesis code to infer the occurrence rates of the various relevant binary evolution channels. We find that the simple scenario -- i.e., the Wolf-Rayet star being tidally spun up and producing a collapsar -- does not occur at solar metallicity and may only occur with low probability at low metallicity. It is limited by the widening of the binary orbit induced by the strong Wolf-Rayet wind or by the radius evolution of the Wolf-Rayet star that most often leads to a binary merger. The tidal effects enhance the merger rate of Wolf-Rayet stars with black holes such that it becomes comparable to the occurrence rate of long gamma-ray bursts.Comment: 9 pages, 11 figures, accepted for publication in A&

HVS7: a chemically peculiar hyper-velocity star

Context: Hyper-velocity stars are suggested to originate from the dynamical interaction of binary stars with the supermassive black hole in the Galactic centre (GC), which accelerates one component of the binary to beyond the Galactic escape velocity. Aims: The evolutionary status and GC origin of the HVS SDSS J113312.12+010824.9 (HVS7) is constrained from a detailed study of its stellar parameters and chemical composition. Methods: High-resolution spectra of HVS7 obtained with UVES on the ESO VLT were analysed using state-of-the-art NLTE/LTE modelling techniques that can account for a chemically-peculiar composition via opacity sampling. Results: Instead of the expected slight enrichments of alpha-elements and near-solar Fe, huge chemical peculiarities of all elements are apparent. The He abundance is very low (<1/100 solar), C, N and O are below the detection limit, i.e they are underabundant (<1/100, <1/3 and <1/10 solar). Heavier elements, however, are overabundant: the iron group by a factor of ~10, P, Co and Cl by factors ~40, 80 and 440 and rare-earth elements and Hg even by ~10000. An additional finding, relevant also for other chemically peculiar stars are the large NLTE effects on abundances of TiII and FeII (~0.6-0.7dex). The derived abundance pattern of HVS7 is characteristic for the class of chemical peculiar magnetic B stars on the main sequence. The chemical composition and high vsini=55+-2km/s render a low mass nature of HVS7 as a blue horizontal branch star unlikely. Conclusions: Such a surface abundance pattern is caused by atomic diffusion in a possibly magnetically stabilised, non-convective atmosphere. Hence all chemical information on the star's place of birth and its evolution has been washed out. High precision astrometry is the only means to validate a GC origin for HVS7.Comment: 9 pages, 3 figure

Health-related quality of life (HRQoL) after different axillary treatments in women with breast cancer:a 1-year longitudinal cohort study

Purpose: As life expectancy continues to rise, post-treatment health-related quality of life (HRQoL) of breast cancer patients becomes increasingly important. This study examined the one-year longitudinal relation between axillary treatments and physical, psychosocial, and sexual wellbeing and arm symptoms. Methods: Women diagnosed with breast cancer who received different axillary treatments being axilla preserving surgery (APS) with or without axillary radiotherapy or full axillary lymph node dissection (ALND) with or without axillary radiotherapy were included. HRQoL was assessed at baseline, 6- and 12-months postoperatively using the BREAST-Q and the European Organization for Research and Treatment of Cancer QoL Questionnaire Breast Cancer Module (EORTC QLQ-BR23). Mixed regression models were constructed to assess the impact of axillary treatment on HRQoL. HRQoL at baseline was compared to HRQoL at 6- and at 12-months postoperatively. Results: In total, 552 patients were included in the mixed regressions models. Except for ALND with axillary radiotherapy, no significant differences in physical and psychosocial wellbeing were found. Physical wellbeing decreased significantly between baseline and 6- and 12-months postoperatively (p &lt; 0.001, p = 0.035) and psychosocial wellbeing decreased significantly between baseline and 12 months postoperatively (p = 0.028) for ALND with axillary radiotherapy compared to APS alone. Arm symptoms increased significantly between baseline and 6 months and between baseline and 12 months postoperatively for APS with radiotherapy (12.71, 13.73) and for ALND with radiotherapy (13.93, 16.14), with the lowest increase in arm symptoms for ALND without radiotherapy (6.85, 7.66), compared to APS alone (p &lt; 0.05). Conclusion: Physical and psychosocial wellbeing decreased significantly for ALND with radiotherapy compared to APS alone. Shared decision making and expectation management pre-treatment could be strengthened by discussing arm symptoms per axillary treatment with the patient.</p

Quantitative spectroscopy of Deneb

Quantitative spectroscopy of luminous BA-type supergiants offers a high potential for modern astrophysics. The degree to which we can rely on quantitative studies of this class of stars as a whole depends on the quality of the analyses for benchmark objects. We constrain the basic atmospheric parameters and fundamental stellar parameters as well as chemical abundances of the prototype A-type supergiant Deneb to unprecedented accuracy (Teff = 8525 +/- 75 K, log(g) = 1.10 +/- 0.05 dex, M_spec = 19 +/- 3 M_sun, L = 1.96 +/- 0.32 *10^5 L_sun, R = 203 +/- 17 R_sun, enrichment with CN-processed matter) by applying a sophisticated hybrid NLTE spectrum synthesis technique which has recently been developed and tested. The study is based on a high-resolution and high-S/N spectrum obtained with the Echelle spectrograph FOCES on the Calar Alto 2.2m telescope. Practically all inconsistencies reported in earlier studies are resolved. Multiple metal ionization equilibria and numerous hydrogen lines from the Balmer, Paschen, Brackett and Pfund series are brought into match simultaneously for the stellar parameter determination. Stellar wind properties are derived from H_alpha line-profile fitting using line-blanketed hydrodynamic non-LTE models. A self-consistent view of Deneb is thus obtained, allowing us to discuss its evolutionary state in detail by comparison with the most recent generation of evolution models for massive stars. (abridged)Comment: 17 pages, 12 figures. Accepted for publication in A&

Boron Abundances in Main Sequence B-type Stars: A Test of Rotational Depletion during Main Sequence Evolution

Boron abundances have been derived for seven main sequence B-type stars from HST STIS spectra around the B III 2066 A line. In two stars, boron appears to be undepleted with respect to the presumed initial abundance. In one star, boron is detectable but it is clearly depleted. In the other four stars, boron is undetectable implying depletions of 1 to 2 dex. Three of these four stars are nitrogen enriched, but the fourth shows no enrichment of nitrogen. Only rotationally induced mixing predicts that boron depletions are unaccompanied by nitrogen enrichments. The inferred rate of boron depletion from our observations is in good agreement with these predictions. Other boron-depleted nitrogen-normal stars are identified from the literature. Also, several boron-depleted nitrogen-rich stars are identified, and while all fall on the boron-nitrogen trend predicted by rotationally-induced mixing, a majority have nitrogen enrichments that are not uniquely explained by rotation. The spectra have also been used to determine iron-group (Cr, Mn, Fe, and Ni) abundances. The seven B-type stars have near solar iron-group abundances, as expected for young stars in the solar neighborhood. We have also analysed the halo B-type star, PG0832+676. We find [Fe/H] = -0.88 +/- 0.10, and the absence of the B III line gives the upper limit [B/H]<2.5. These and other published abundances are used to infer the star's evolutionary status as a post-AGB star.Comment: 31 pages, 14 figures. accepted to Ap

The VLT-FLAMES survey of massive stars: constraints on stellar evolution from the chemical compositions of rapidly rotating Galactic and Magellanic Cloud B-type stars

We have previously analysed the spectra of 135 early B-type stars in the LMC and found several groups of stars that have chemical compositions that conflict with the theory of rotational mixing. Here we extend this study to Galactic and SMC metallicities with the analysis of ~50 Galactic and ~100 SMC early B-type stars with rotational velocities up to ~300km/s. The surface nitrogen abundances are utilised as a probe of the mixing process. In the SMC, we find a population of slowly rotating nitrogen-rich stars amongst the early B type core-hydrogen burning stars, similar to the LMC. In the Galactic sample we find no significant enrichment amongst the core hydrogen-burning stars, which appears to be in contrast with the expectation from both rotating single-star and close binary evolution models. However, only a small number of the rapidly rotating stars have evolved enough to produce a significant nitrogen enrichment, and these may be analogous to the non-enriched rapid rotators previously found in the LMC sample. Finally, in each metallicity regime, a population of highly enriched supergiants is observed, which cannot be the immediate descendants of core-hydrogen burning stars. Their abundances are, however, compatible with them having gone through a previous red supergiant phase. Together, these observations paint a complex picture of the nitrogen enrichment in massive main sequence and supergiant stellar atmospheres, where age and binarity cause crucial effects. Whether rotational mixing is required to understand our results remains an open question at this time, but could be answered by identifying the true binary fraction in those groups of stars that do not agree with single-star evolutionary models (abridged).Comment: Accepted paper - 86 pages with tables and figure