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Observations of stable mainly dipolar magnetic fields at the surface of ~7% of single hot stars indicate that these fields are of fossil origin, i.e. they descend from the seed field in the molecular clouds from which the stars were formed. The recent results confirm this theory. First, theoretical work and numerical simulations confirm that the properties of the observed fields correspond to those expected from fossil fields. They also showed that rapid rotation does not modify the surface dipolar magnetic configurations, but hinders the stability of fossil fields. This explains the lack of correlation between the magnetic field properties and stellar properties in massive stars. It may also explain the lack of detections of magnetic fields in Be stars, which rotate close to their break-up velocity. In addition, observations by the BinaMIcS collaboration of hot stars in binary systems show that the fraction of those hosting detectable magnetic fields is much smaller than for single hot stars. This could be related to results obtained in simulations of massive star formation, which show that the stronger the magnetic field in the original molecular cloud, the more difficult it is to fragment massive cores to form several stars. Therefore, more and more arguments support the fossil field theory.
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.
It is now well established that a fraction of the massive (M > 8 M⊙) star population hosts strong, organised magnetic fields, most likely of fossil origin. The details of the generation and evolution of these fields are still poorly understood. The BinaMIcS project takes an important step towards the understanding of the interplay between binarity and magnetism during the stellar formation and evolution, and in particular the genesis of fossil fields, by studying the magnetic properties of close binary systems. The components of such systems are most likely formed together, at the same time and in the same environment, and can therefore help us to disentangle the role of initial conditions on the magnetic properties of the massive stars from other competing effects such as age or rotation. We present here the main scientific objectives of the BinaMIcS project, as well as preliminary results from the first year of observations from the associated ESPaDOnS and Narval spectropolarimetric surveys.
The Magnetism in Massive Stars (MiMeS) project represents the largest systematic survey of stellar magnetism ever undertaken. Based on a sample of over 550 Galactic B and O-type stars, the MiMeS project has derived the basic characteristics of magnetism in hot, massive stars. Herein we report preliminary results.
Titanium (IV) oxide, TiO2, has been the object of intense scrutiny for energy applications. TiO2 is inexpensive, non-toxic, and has excellent corrosion resistance when exposed to electrolytes. A major drawback preventing the widespread use TiO2 for photolysis is its relatively large band gap of ∼3eV. Only light with wavelengths shorter than 400 nm, which is in the ultraviolet portion of the spectrum, has sufficient energy to be absorbed. Less than 14 percent of the solar irradiation reaching the earth’s surface has energy exceeding this band gap. Adding dopants such as transition metals has long been used to reduce the gap and increase photocatalytic activity by accessing the visible part of the solar spectrum. The degree to which the band gap is reduced using transition metals depends in part on the overlap of the d-orbitals of the transition metals with the oxygen p-orbitals. Therefore, doping with anions such as nitrogen to modify the cation-anion orbital overlap is another approach to reduce the gap. Recent studies suggest that using a combination of transition metals and nitrogen as dopants is more effective at introducing intermediate states within the band gap, effectively narrowing it. Here we report the synthesis of mesoporous TiO2 spheres, co-doped with transition metals and nitrogen that exhibit a nearly flat absorbance response across the visible spectrum extending into the near infrared.
Buran-Kaya III is a rockshelter located in Crimea (Ukraine). It provides an exceptional stratigraphic sequence extending from the Middle Paleolithic to the Neolithic. Nine Paleolithic layers have been attributed to the Streletskaya or eastern Szeletian, Micoquian, Aurignacian, Gravettian, and Swiderian cultural traditions. Human remains from the richest Gravettian layer (6-1) are radiocarbon dated to 31.9 ka BP, and therefore represent, with Peştera cu Oase (Romania), one of the oldest anatomically modern humans in Europe. The aim of this study is to obtain a controlled stratigraphic sequence of Buran-Kaya III with new 14C dates from faunal and human bones, in their paleoenvironmental context. During our new excavations (2009–2011), sediments, bones, and teeth from the stratigraphical layers were sampled for sedimentological, geochemical, and 14C analyses. Fossil bones from the 2001 excavations were also analyzed. Accelerator mass spectrometry (AMS) 14C dating, including cross-dating, was performed at Groningen, Saclay/Gif-sur-Yvette, and Oxford. Biogeochemical analysis was used to test the integrity of the bone collagen. Dates were modeled using a Bayesian approach. The sedimentological, paleoenvironmental, and chronological data are mutually consistent and show that the Paleolithic human occupations at Buran-Kaya III range from the end of MIS 3 to early MIS 1. These results provide a new chronological and paleoenvironmental framework for the human settlements in eastern Europe during the late Middle and the Upper Paleolithic.
An energy resource is the first step in the chain that supplies energy services (for a definition of energy services, see Chapter 1). Energy services are largely ignorant of the particular resource that supplies them; however, often the infrastructures, technologies, and fuels along the delivery chain are highly dependent on a particular type of resource. The availability and costs of bringing energy resources to the market place are key determinants to affordable and accessible energy services.
Energy resources pose no inherent limitation to meeting the rapidly growing global energy demand as long as adequate upstream investment is forthcoming – for exhaustible resources in exploration, production technology, and capacity (mining and field development) and, by analogy, for renewables in conversion technologies.
Hydrocarbons and Nuclear
Occurrences of hydrocarbons and fissile materials in the Earth's crust are plentiful – yet they are finite. The extent of the ultimately recoverable oil, natural gas, coal, or uranium is the subject of numerous reviews, yet still the range of values in the literature is large (Table 7.1). For example, the range for conventional oil is between 4900 exajoules (EJ) for reserves to 13,700 EJ (reserves plus resources) – a range that sustains continued debate and controversy. The large range is the result of varying boundaries of what is included in the analysis of a finite stock of an exhaustible resource, e.g., conventional oil only or conventional oil plus unconventional occurrences, such as oil shale, tar sands, and extra-heavy oils.
Monitoring injecting drug users' (IDUs) health is challenging because IDUs form a difficult to reach population. We examined the impact of recruitment setting on hepatitis C prevalence. Individual datasets from 12 studies were merged. Predictors of HCV positivity were sought through a multilevel analysis using a mixed-effects logistic model, with study identifier as random intercept. HCV prevalence ranged from 21% to 86% across the studies. Overall, HCV prevalence was higher in IDUs recruited in drug treatment centres compared to those recruited in low-threshold settings (74% and 42%, respectively, P < 0·001). Recruitment setting remained significantly associated with HCV prevalence after adjustment for duration of injecting and recent injection (adjusted odds ratio 0·7, 95% confidence interval 0·6–0·8, P = 0·05). Recruitment setting may have an impact on HCV prevalence estimates of IDUs in Europe. Assessing the impact of mixed recruitment strategies, including respondent-driven sampling, on HCV prevalence estimates, would be valuable.
Schizophrenia patients demonstrate impairment on visual backward masking, a measure of early visual processing. Most visual masking paradigms involve two distinct processes, an early fast-acting component associated with object formation and a later component that acts through object substitution. So far, masking paradigms used in schizophrenia research have been unable to separate these two processes.
We administered three visual processing paradigms (location masking with forward and backward masking, four-dot backward masking and a cuing task) to 136 patients with schizophrenia or schizoaffective disorder and 79 healthy controls. A psychophysical procedure was used to match subjects on identification of an unmasked target prior to location masking. Location masking interrupts object formation, four-dot masking task works through masking by object substitution and the cuing task measures iconic decay.
Patients showed impairment on location masking after being matched for input threshold, similar to previous reports. After correcting for age, patients showed lower performance on four-dot masking than controls, but the groups did not differ on the cuing task.
Patients with schizophrenia showed lower performance when masking was specific to object substitution. The difference in object substitution masking was not due to a difference in rate of iconic decay, which was comparable in the two groups. These results suggest that, despite normal iconic decay rates, individuals with schizophrenia show impairment in a paradigm of masking by object substitution that did not also involve disruption of object formation.
We review the interaction in intermediate and high mass stars between their evolution and magnetic and chemical properties. We describe the theory of Ap-star ‘fossil’ fields, before touching on the expected secular diffusive processes which give rise to evolution of the field. We then present recent results from a spectropolarimetric survey of Herbig Ae/Be stars, showing that magnetic fields of the kind seen on the main-sequence already exist during the pre-main sequence phase, in agreement with fossil field theory, and that the origin of the slow rotation of Ap/Bp stars also lies early in the pre-main sequence evolution; we also present results confirming a lack of stars with fields below a few hundred gauss. We then seek which macroscopic motions compete with atomic diffusion in determining the surface abundances of AmFm stars. While turbulent transport and mass loss, in competition with atomic diffusion, are both able to explain observed surface abundances, the interior abundance distribution is different enough to potentially lead to a test using asterosismology. Finally we review progress on the turbulence-driving and mixing processes in stellar radiative zones.
Magnetic field and their related dynamical effects are thought to be important in stellar radiation zones. For instance, it has been suggested that a dynamo, sustained by a m = 1 MHD instability of toroidal magnetic fields (discovered by Tayler in 1973), could lead to a strong transport of angular momentum and of chemicals in such stable regions. We wish here to recall the different magnetic transport processes present in radiative zone and show how the dynamo can operate by recalling the conditions required to close the dynamo loop (BPol → BTor → BPol). Helped by high-resolution 3D MHD simulations using the ASH code in the solar case, we confirm the existence of the m = 1 instability, study its non-linear saturation, but we do not detect, up to a magnetic Reylnods number of 105, any dynamo action.
Magnetic field is an essential dynamical process in stellar radiation zones. Moreover, it has been suggested that a dynamo action, sustained by a MHD instability which affects the toroidal axisymmetric magnetic field, could lead to a strong transport of angular momentum and of chemicals in such regions. Here, we recall the different magnetic transport and mixing processes in radiative regions. Next, we show that the dynamo cannot operate as described by Spruit (2002) and recall the condition required to close the dynamo loop. We perform high-resolution 3D simulations with the ASH code, where we observe indeed the MHD instability, but where we do not detect any dynamo action, contrary to J. Braithwaite (2006). We conclude on the picture we get for magnetic transport mechanisms in radiation zones and the associated consequences for stellar evolution.
The use of chemical energy in the EAF has increased significantly in
recent years, both for enhancing productivity and reducing electricity
consumption. However, these tools are operated following pre-set
patterns, without any feedback information from the process. This
leads both to non-optimized operations and to occasional blowback
problems, resulting in damages to burners, lances, watercooled
panels and refractory lining. CRM has developed an on-line “distance-to-scrap” measurement
technique that can be fitted inside annular burners. This measurement
allows monitoring the melting of scrap in front of each burner,
and thus detecting blow-back occurrences before any damage is
created. This sensor was successfully tested in the Esch-Belval steel
plant of ArcelorMittal Profil Luxembourg. Industrial implementation is
With the first light of COROT, the preparation of KEPLER and the future helioseismology spatial projects such as GOLF-NG, a coherent picture of the evolution of rotating stars from their birth to their death is needed. We describe here the modelling of the macroscopic transport of angular momentum and matter in stellar interiors that we have undertaken to reach this goal. First, we recall in detail the dynamical processes that are driving these mechanisms in rotating stars and the theoretical advances we have achieved. Then, we present our new results of numerical simulations which allow us to follow in 2D the secular hydrodynamics of rotating stars, assuming that anisotropic turbulence enforces a shellular rotation law. Finally, we show how this work is leading to a dynamical vision of the Hertzsprung-Russel diagram with the support of asteroseismology and helioseismology, seismic observables giving constraints on the modelling of the internal transport and mixing processes. In conclusion, we present the different processes that should be studied in the near future to improve our description of stellar radiation zones.
The “airtight” technology allows energy savings but hinders direct
process observation inside the vessel and information on the unmelted
scrap volume and on possible skull formation at the furnace
walls. To overcome this difficulty, a new concept is proposed, based
on mounting a camera and an endoscope inside an existing burner.
This technique has been first implemented on the 155 tons DC furnace
in the PROFILARBED Esch-Belval plant. Typical images of the
melting phase are presented. Scrap movement mechanisms in the
burner produced cavity have been displayed in real time.
Operational benefits combine the appraisal of scrap basket charging
time and anticipation of abnormal melting behaviour.
The seismology and physics of localized structures beneath the surface of the Sun takes on a special significance with the completion in 2006 of a solar cycle of observations by the ground-based Global Oscillation Network Group (GONG) and by the instruments on board the Solar and Heliospheric Observatory (SOHO). Of course, the spatially unresolved Birmingham Solar Oscillation Network (BiSON) has been observing for even longer. At the same time, the testing of models of stellar structure moves into high gear with the extension of deep probes from the Sun to other solar-like stars and other multi-mode pulsators, with ever-improving observations made from the ground, the success of the MOST satellite, and the recently launched CoRoT satellite. Here we report the current state of the two closely related and rapidly developing fields of helio- and asteroseimology.
Research in roAp stars is being vigorously pursued, both theoretically and observationally by many groups. We report the discovery of a 21-min period, luminous roAp star, HD 116114. Longer periods for more luminous stars have been predicted theoretically and this is the first discovery of such a star. We discuss a model for the blue-to-red line profile variability observed in some roAp stars involving a shock wave high in the atmosphere of roAp stars, yet show that the H$\alpha$ line in 33 Lib has the blue-to-red-to-blue line profile variability expected for subsonic dipolar pulsation concentrated towards the pulsation pole. Further we report for 33 Lib unprecedented observations of the amplitudes and phases of its principal mode at 2.015 mHz and its first harmonic of that at 4.030 mHz.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html
We investigated the dependence of critical current density (Jc) on thickness of Yba2Cu3O7−δ (YBCO) films grown by pulsed laser deposition on (100) SrTiO3 (STO) and on rolling-assisted biaxially textured substrates (RABiTS). The thickness of YBCO films varied from 0.19 to 3 μm. The highest Jcs of 5.3 and 2.6 MA/cm2 at 77 K, self-field were obtained for 0.19-μm YBCO films on STO and RABiTS, respectively. Jc was found to decrease exponentially with YBCO thickness on both substrates. However, the results suggest different mechanisms are responsible for the Jc reduction in the two cases. On STO, growth of a-axis grains within c-axis films and broadening of the in-plane texture were observed in thick films. On RABiTS, degradation in cube texture as well as development of a porous surface morphology were found to correlate with film thickness.
A better control of the scrap basket charging operation by measuring the real scrap density,
a direct visualization device viewing inside the furnace to follow-up the melting progress,
an assessment of the liquid bath height by means of a gas blown through a porous brick:
three original techniques providing to the furnace operators new tools allowing an
optimization of the working practice are described.