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Thermal analyses of samples of thorium dicarbide in equilibrium with graphite show arrests which indicate phase transitions at 1427 ± 21°C arid 1481 ± 28°C. These thermal effects have been observed on heating and cooling both in standard thermal analysis and in differential thermal analysis using graphite as a reference material. The microstructure of thorium dicarbide samples shows the characteristic “herringbone” pattern of a material which has undergone a martensitic-type transition.
A high-temperature X-ray investigation has revealed that the observed thermal arrests correspond to erystallographic transformations. The monodinic modification found at room temperature is stable to 1427°C, at which temperature a tetragonal modification with a0 = 4.235 ± 0.002Å and c0 = 5.408 ± 0.002Å is formed. At 1481°C, the tetragonal is transformed to cubic with a0 = 5.809 ± 0.002 Å. The best agreement between observed and calculated intensities has been obtained with C-C units of 1.5-Å assumed bond length in space groups P42/mmc and Pa3 for the tetragonal and cubic modifications, respectively.
An epitaxial NdFeAs(O,F) thin film of 90 nm thickness grown by molecular beam epitaxy on MgO single crystal with Tc = 44.2 K has been investigated regarding a possible vortex glass–liquid transition. The voltage–current characteristics show excellent scalability according to the vortex-glass model with a static critical exponent ν of around 1.35 and a temperature-dependent dynamic exponent z increasing from 7.8 to 9.0 for the investigated temperature range. The large and non-constant z values are discussed in the frame of 3D vortex glass, thermally activated flux motion, and inhomogeneity broadening.
Background: Worry is a common feature across many anxiety disorders. It is important to understand how and when worry presents from childhood to adolescence to prevent long-term negative outcomes. However, most of the existing studies that examine the relationship between worry and anxiety disorders utilize adult samples. Aims: The present study aimed to assess the level of worry in children and adolescents and how relationships between worry and symptoms of separation anxiety disorder (SAD) and social anxiety disorder (Soc) may present differently at different ages. Method: 127 children (age 8–12 years) and adolescents (age 13–18 years), diagnosed with any anxiety disorder, presenting at a child anxiety out-patient clinic, completed measures of worry, anxiety and depression. Results: Worry scores did not differ by age group. Soc symptoms were significantly correlated with worry in both age groups; however, SAD symptoms were only significantly correlated with worry in younger participants. After the inclusion of covariates, SAD symptoms but not Soc symptoms remained significant in the regression model with younger children, and Soc symptoms remained significant in the regression model with older children. Conclusions: The finding that worry was comparable in both groups lends support for worry as a stable construct associated with anxiety disorders throughout late childhood and early adolescence.
Rotation in massive stars has been studied on the main sequence and during helium burning for decades, but only recently have realistic numerical simulations followed the transport of angular momentum that occurs during more advanced stages of evolution. The results affect such interesting issues as whether rotation is important to the explosion mechanism, whether supernovae are strong sources of gravitational radiation, the star's nucleosynthesis, and the initial rotation rate of neutron stars and black holes. We find that when only hydrodynamic instabilities (shear, Eddington-Sweet, etc.) are included in the calculation, one obtains neutron stars spinning at close to critical rotation at their surface – or even formally in excess of critical. When recent estimates of magnetic torques (Spruit 2002) are added, however, the evolved cores spin about an order of magnitude slower. This is still more angular momentum than observed in young pulsars, but too slow for the collapsar model for gamma-ray bursts.
Classical studies of accreting white dwarfs have assumed spherical symmetry. However, it is believed that in close binary systems the transfered matter carries angular momentum to spin up the accreting star. Here, we present preliminary results of CO white dwarf models which accrete helium rich matter with effects of rotation considered, in the context of the Sub-Chandrasekhar mass scenario for Type Ia supernovae.
We discuss the first available binary evolution models which include up-to-date rotational physics for both components, as well as angular momentum accretion and spin-orbit coupling. These models allow a self-consistent computation of the mass transfer efficiency during Roche-lobe overflow phases, and a determination of the transition from quasi-conservative to non-conservative evolution. Applications to massive binary systems lead to predictions for the spin rates of compact objects in binaries, and for the occurrence of gamma-ray bursts from collapsars in binaries. Rotational effects in accreting white dwarfs are found to stabilise the shell burning and decrease the carbon abundance in progenitor models for Chandrasekhar-mass Type Ia supernovae, and to potentially avoid a detonation of the white dwarf within the sub-Chandrasekhar mass scenario.
The spectrum of the supergiant FG Sge has been studied from a series of high dispersion 120-in. coudé spectrograms obtained during the interval 1969–72, thus continuing the work of Herbig and Boyarchuk (1968). The star, of effective temperature about 6500 K in 1972, is cooling at the rate of 250 K yr-1; it is known to have ejected a still visible planetary nebula some 6000 years ago (Flannery and Herbig, 1973). Abnormally strong absorption lines of Y ii, Zr ii, Ce ii, La iiand other s-process species began to appear in the spectrum of the central star some time after 1967 and have progressively strengthened. Present abundances per gram of these elements are about 25 times the solar value. There is little doubt that the atmosphere of the star has been enriched in these elements during the past seven years, but the rate of enrichment now appears to be slowing down.
The B fields in OB stars (BOB) survey is an ESO large programme collecting spectropolarimetric observations for a large number of early-type stars in order to study the occurrence rate, properties, and ultimately the origin of magnetic fields in massive stars. As of July 2014, a total of 98 objects were observed over 20 nights with FORS2 and HARPSpol. Our preliminary results indicate that the fraction of magnetic OB stars with an organised, detectable field is low. This conclusion, now independently reached by two different surveys, has profound implications for any theoretical model attempting to explain the field formation in these objects. We discuss in this contribution some important issues addressed by our observations (e.g., the lower bound of the field strength) and the discovery of some remarkable objects.
Rotation is a key parameter in the evolution of massive stars, affecting their evolution, chemical yields, ionizing photon budget, and final fate. We determined the projected rotational velocity, υe sin i, of ~330 O-type objects, i.e. ~210 spectroscopic single stars and ~110 primaries in binary systems, in the Tarantula nebula or 30 Doradus (30 Dor) region. The observations were taken using VLT/FLAMES and constitute the largest homogeneous dataset of multi-epoch spectroscopy of O-type stars currently available. The most distinctive feature of the υe sin i distributions of the presumed-single stars and primaries in 30 Dor is a low-velocity peak at around 100 km s−1. Stellar winds are not expected to have spun-down the bulk of the stars significantly since their arrival on the main sequence and therefore the peak in the single star sample is likely to represent the outcome of the formation process. Whereas the spin distribution of presumed-single stars shows a well developed tail of stars rotating more rapidly than 300 km s−1, the sample of primaries does not feature such a high-velocity tail. The tail of the presumed-single star distribution is attributed for the most part – and could potentially be completely due – to spun-up binary products that appear as single stars or that have merged. This would be consistent with the lack of such post-interaction products in the binary sample, that is expected to be dominated by pre-interaction systems. The peak in this distribution is broader and is shifted toward somewhat higher spin rates compared to the distribution of presumed-single stars. Systems displaying large radial velocity variations, typical for short period systems, appear mostly responsible for these differences.
We present a mechanism for generating cosmological magnetic fields during the Epoch of Reionization, based on the photoionization of intergalactic hydrogen. A general formula is presented, together with an example numerical application which yields magnetic field strengths between 10−23 to 10−19 G on intersource scales. This mechanism, which operates all along Reionization around any ionizing source, participates to the premagnetization of the whole intergalactic medium. Also, the spatial configuration of these fields may help discriminate them from those produced by other mechanisms in future observations.
The enigmatic oxygen sequence Wolf-Rayet (WO) stars represent a very late stage in massive star evolution, although their exact nature is still under debate. The spectra of most of the WO stars have never been analysed through detailed modelling with a non-local thermodynamic equilibrium expanding atmosphere code. Here we present preliminary results of the first homogeneous analysis of the (apparently) single WOs.
In 2008, Granett et al. claimed a direct detection of the integrated Sachs-Wolfe (iSW) effect, through the stacking of CMB patches at the positions of identified superstructures. Additionally, the high amplitude of their measured signal was reported to be at odds with predictions from the standard model of cosmology. However, a closer inspection of these results prompts multiple questions, more specifically about the amplitude and significance of the expected signal. We propose here an original theoretical prediction of the iSW effect produced by such superstructures. We use simulations based on GR and the LTB metric to reproduce cosmic structures and predict their exact theoretical iSW effect on the CMB. The amplitudes predicted with this method are consistent with the signal measured when properly accounting the contribution of the non-negligible (and fortuitous) primordial CMB fluctuations to the total signal. It also highlights the tricky nature of stacking measurements and their interpretation.
The VLT-FLAMES Tarantula Survey is an ESO Large Program from which we have obtained multi-epoch optical spectroscopy of over 800 massive stars in the 30 Doradus region of the Large Magellanic Cloud. This unprecedented dataset is being used to address outstanding questions in how massive stars evolve from the early main sequence to their deaths as core collapse supernovae. Here we focus on the rotation properties of the population of presumably single O stars and use binary population synthesis predictions to show that the rapid rotators among this population likely are post-interaction binaries. The same type of population synthesis can be used to study the mass function of massive young clusters. We argue – on the basis of predictions for the Arches and Quintuplet clusters – that a sizable fraction of the very massive WNh stars in 30 Doradus may also have such a binary interaction history. We single out the WNh star discovered in the VFTS, VFTS 682, and discuss its properties.
The nearby red supergiant (RSG) Betelgeuse has a complex circumstellar medium out to at
least 0.5 parsecs from its surface, shaped by its mass-loss history within the past ≈ 0.1
Myr, its environment, and its motion through the interstellar medium (ISM). In principle
its mass-loss history can be constrained by comparing hydrodynamic models with
observations. Observations and numerical simulations indicate that Betelgeuse has a very
young bow shock, hence the star may have only recently become a RSG. To test this
possibility we calculated a stellar evolution model for a single star with properties
consistent with Betelgeuse. We incorporated the resulting evolving stellar wind into 2D
hydrodynamic simulations to model a runaway blue supergiant (BSG) undergoing the
transition to a RSG near the end of its life. The collapsing BSG wind bubble induces a bow
shock-shaped inner shell which at least superficially resembles Betelgeuse’s bow shock,
and has a similar mass. Surrounding this is the larger-scale retreating bow shock
generated by the now defunct BSG wind’s interaction with the ISM. We investigate whether
this outer shell could explain the bar feature located (at least in projection) just in
front of Betelgeuse’s bow shock.
Betelgeuse, the bright red supergiant (RSG) in Orion, is a runaway star. Its supersonic motion through the interstellar medium has resulted in the formation of a bow shock, a cometary structure pointing in the direction of motion. We present the first 3D hydrodynamic simulations of the formation and evolution of Betelgeuse’s bow shock. We show that the bow shock morphology depends substantially on the growth timescale for Rayleigh-Taylor versus Kelvin-Helmholtz instabilities. We discuss our models in light of the recent Herschel, GALEX and VLA observations. If the mass in the bow shock shell is low (~few × 10-3M⊙), as seems to be implied by the AKARI and Herschel observations, then Betelgeuse’s bow shock is very young and is unlikely to have reached a steady state. The circular, smooth bow shock shell is consistent with this conclusion. We further discuss the implications of our results, in particular, the possibility that Betelgeuse may have only recently entered the RSG phase.
The Dominion Radio Astrophysical Observatory (DRAO) is carrying out a survey as part of an international collaboration to image the northe, at a common resolution, in emission from all major constituents of the interstellar medium; the neutral atomic gas, the molecular gas, the ionised gas, dust and relativistic plasma. For many of these constituents the angular resolution of the images (1 arcmin) will be more than a factor of 10 better than any previous studies. The aim is to produce a publicly-available database of high resolution, high-dynamic range images of the Galaxy for multi-phase studies of the physical states and processes in the interstellar medium. We will sketch the main scientific motivations as well as describe some preliminary results from the Canadian Galactic Plane Survey/Releve Canadien du Plan Galactique (CGPS/RCPG).
The automatic implantable defibrillator is an electronic device designed to continuously monitor cardiac rhythm, identify ventricular fibrillation and deliver corrective defibrillatory discharges, when indicated. Physically similar to early pacemakers, it weights 250 grams and has a volume of 145 cc (Figure 1). All materials in contact with body tissue are biocompatible. The defibrillating electrodes are made from titanium and silicone rubber. One electrode, designed for placement in the superior vena cava near the right atrial junction, is located on the distal end of an intravascular catheter. The second electrode, in the form of a flexible rectangular patch, is placed extrapericardially over the apex of the heart. The outside surface of the apical electrode is insulated to achieve optimal current distribution.
The device is powered by lithium batteries having a projected monitoring life of approximately 3 years or a discharge capability of approximately 100 shocks. The sensing system detects ventricular fibrillation by monitoring a sampled probability density function of ventricular electrical activity.
Photochemical methods were developed to obtain a variation of the refractive index in aromatic polymer surfaces and a change in the photoluminescence characteristics of phenylene-vinylene-based polymers. Films of aromatic polymers, among them polystyrene (PS), poly(2-vinylnaphthalene) (PVN) and derivatives of poly(-phenylene-vinylene) (PPV) were UV irradiated in the presence of gaseous hydrazine (N2H4). The photoreaction led to a strongreduction of the refractive index of the polymers due to a hydrogenation of the aromatic units. In the case of PPV, we observed reductive photobleaching. This new technique was employed to produce photogenerated patterns in PPV. The results are compared to oxidative bleaching.
In-situ SEM electromigration studies were performed at
fully embedded via/line interconnect structures to visualize the
time-dependent void evolution in inlaid copper interconnects. Void
formation, growth and movement, and consequently interconnect degradation,
depend on both interface bonding and copper microstructure. Two phases are
distinguished for the electromigration-induced interconnect degradation
process: In the first phase, agglomerations of vacancies and voids are
formed at interfaces and grain boundaries, and voids move along weak
interfaces. In the second phase of the degradation process, they merge into
a larger void which subsequently grows into the via and eventually causes
the interconnect failure. Void movement along the copper line and void
growth in the via are discontinuous processes, whereas their step-like
behavior is caused by the copper microstructure. Directed mass transport
along inner surfaces depends strongly on the crystallographic orientation of
the copper grains. Electromigration lifetime can be drastically increased by
changing the copper/capping layer interface. Both an additional CoWP coating
and a local copper alloying with aluminum increase the bonding strength of
the top interface of the copper interconnect line, and consequently,
electromigration-induced mass transport and degradation processes are
A dual scaffold structure made of biodegradable polymers and seeded with neural stem cells has been developed to address the issues of spinal cord injury including axonal severance and the loss of neurons and glia. The general design of the scaffold is derived the structure of the spinal cord with an outer section which mimics the white matter with long axial pores to provide axonal guidance and an inner section seeded with neural stem cells to address the issues of cell replacement and mimic the general character of the gray matter. The seeded scaffold leads to improved functional recovery as compared with the lesion control or cells alone following spinal cord injury.