164 research outputs found
On subducting slab entrainment of buoyant asthenosphere
Laboratory and numerical experiments and boundary layer analysis of the entrainment of buoyant asthenosphere by subducting oceanic lithosphere implies that slab entrainment is likely to be relatively inefficient at removing a buoyant and lower viscosity asthenosphere layer. Asthenosphere would instead be mostly removed by accretion into and eventual subduction of the overlying oceanic lithosphere. The lower (hot) side of a subducting slab entrains by the formation of a âŒ10â30 km-thick downdragged layer, whose thickness depends upon the subduction rate and the density contrast and viscosity of the asthenosphere, while the upper (cold) side of the slab may entrain as much by thermal 'freezing' onto the slab as by mechanical downdragging. This analysis also implies that proper treatment of slab entrainment in future numerical mantle flow experiments will require the resolution of âŒ10â30 km-thick entrainment boundary layers
Prevalence and predictors of complementary and alternative medicine modalities in patients with chronic hepatitis B
Background & Aims
The use of complementary and alternative medicine (CAM) in patients with chronic hepatitis B (CHB) can interact with antiviral treatment or influence healthâseeking behaviour. We aimed to study the use of individual CAM modalities in CHB and explore determinants of use, particularly migrationârelated, socioâeconomic and clinical factors.
Methods
A total of 436 CHB outpatients who attended the Toronto Centre for Liver Disease in 2015â2016 were included in this crossâsectional study. Using the comprehensive IâCAM questionnaire and health records, data were collected on socioâdemographic and clinical variables and on usage of 16 CAM modalities in the last year.
Results
Sixty percent of patients were male, 74% were Asian and 46% were using antiviral treatment. Threeâhundred and nine (71%) patients used CAM. Vitamin/mineral preparations (45% of patients) were most commonly used. Overall CAM use and the specific use of potentially injurious CAM, such as green tea extract (9.2%) and St. John's wort (0.2%), were not associated with liver disease severity. Female sex, family history of CHB, lower serum HBV DNA, and higher socioâeconomic status were independently associated with bioâholistic CAM use, the clinically mostârelevant CAM group (P < 0.05); ethnicity, antiviral therapy use and liver disease severity were not.
Conclusions
CAM use among CHB patients was extensive, especially use of vitamin and mineral preparations, but without direct influence on liver disease severity. Bioâholistic CAM use appeared to be associated with socioâeconomic status rather than with ethnicity or liver disease severity. Despite the rare use of hepatotoxins, physicians should actively inquire about it
Gaia white dwarfs within 40Â pc I : spectroscopic observations of new candidates
We present a spectroscopic survey of 230 white dwarf candidates within 40 pc of the Sun from the William Herschel Telescope and Gran Telescopio Canarias. All candidates were selected from Gaia Data Release 2 (DR2) and in almost all cases had no prior spectroscopic classifications. We find a total of 191 confirmed white dwarfs and 39 main-sequence star contaminants. The majority of stellar remnants in the sample are relatively cool (ăTeffă = 6200 K), showing either hydrogen Balmer lines or a featureless spectrum, corresponding to 89 DA and 76 DC white dwarfs, respectively. We also recover two DBA white dwarfs and 9â10 magnetic remnants. We find two carbon-bearing DQ stars and 14 new metal-rich white dwarfs. This includes the possible detection of the first ultra-cool white dwarf with metal lines. We describe three DZ stars for which we find at least four different metal species, including one which is strongly Fe- and Ni-rich, indicative of the accretion of a planetesimal with core-Earth composition. We find one extremely massive (1.31 ± 0.01 Mâ) DA white dwarf showing weak Balmer lines, possibly indicating stellar magnetism. Another white dwarf shows strong Balmer line emission but no infrared excess, suggesting a low-mass sub-stellar companion. High spectroscopic completeness (>99%) has now been reached for Gaia DR2 sources within 40 pc sample, in the northern hemisphere (ÎŽ > 0 deg) and located on the white dwarf cooling track in the Hertzsprung-Russell diagram. A statistical study of the full northern sample is presented in a companion paper
Extreme events and predictability of catastrophic failure in composite materials and in the Earth
Despite all attempts to isolate and predict extreme earthquakes, these nearly always occur without obvious warning in real time: fully deterministic earthquake prediction is very much a âblack swanâ. On the other hand engineering-scale samples of rocks and other composite materials often show clear precursors to dynamic failure under controlled conditions in the laboratory, and successful evacuations have occurred before several volcanic eruptions. This may be because extreme earthquakes are not statistically special, being an emergent property of the process of dynamic rupture. Nevertheless, probabilistic forecasting of event rate above a given size, based on the tendency of earthquakes to cluster in space and time, can have significant skill compared to say random failure, even in real-time mode. We address several questions in this debate, using examples from the Earth (earthquakes, volcanoes) and the laboratory, including the following. How can we identify âcharacteristicâ events, i.e. beyond the power law, in model selection (do dragon-kings exist)? How do we discriminate quantitatively between stationary and non-stationary hazard models (is a dragon likely to come soon)? Does the system size (the size of the dragonâs domain) matter? Are there localising signals of imminent catastrophic failure we may not be able to access (is the dragon effectively invisible on approach)? We focus on the effect of sampling effects and statistical uncertainty in the identification of extreme events and their predictability, and highlight the strong influence of scaling in space and time as an outstanding issue to be addressed by quantitative studies, experimentation and models
Questions of presence
This article considers some of the ways in which âthe black womanâ as both representation and embodied, sentient being is rendered visible and invisible and to link these to the multiple and competing ways in which she is âpresentâ. The issues are engaged through three distinct but overlapping conceptualisations of âpresenceâ. âPresenceâ as conceived (and highly contested) in performance studies; âpresenceâ as conceived and worked with in psychoanalysis; and âpresenceâ as decolonising political praxis among indigenous communities. I use these conceptualisations of presence to consider the various ways in which the black woman as figure and as embodied/sentient subject has been made present/absent in different discursive registers. I also explore what is foreclosed and how this is itself linked to legacies of colonial âworldingâ. I end with consideration of alternative modes of black womenâs presence and how this offers a resource for new modes of sociality.
Keywords
Black women; presence; colonial violence; de-gendering; psychosocial; triangular spac
Efeito do nĂvel nutricional antes e apĂłs a ovulação sobre a taxa de gestação e a prolificidade em ovelhas Santa InĂȘs
Ecological restoration as a real-world experiment: designing robust implementation strategies in an urban environment
Long-Term Changes in Water Quality and Productivity in the Patuxent River Estuary: 1985 to 2003
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