310 research outputs found
How large are present-day heat flux variations across the surface of Mars?
©2016. American Geophysical UnionThe first in situ Martian heat flux measurement to be carried out by the InSight Discoveryâclass mission will provide an important baseline to constrain the presentâday heat budget of the planet and, in turn, the thermochemical evolution of its interior. In this study, we estimate the magnitude of surface heat flux heterogeneities in order to assess how the heat flux at the InSight landing site relates to the average heat flux of Mars. To this end, we model the thermal evolution of Mars in a 3âD spherical geometry and investigate the resulting surface spatial variations of heat flux at the present day. Our models assume a fixed crust with a variable thickness as inferred from gravity and topography data and with radiogenic heat sources as obtained from gamma ray measurements of the surface. We test several mantle parameters and show that the presentâday surface heat flux pattern is dominated by the imposed crustal structure. The largest surface heat flux peakâto peak variations lie between 17.2 and 49.9 mW mâ2, with the highest values being associated with the occurrence of prominent mantle plumes. However, strong spatial variations introduced by such plumes remain narrowly confined to a few geographical regions and are unlikely to bias the InSight heat flux measurement. We estimated that the average surface heat flux varies between 23.2 and 27.3 mW mâ2, while at the InSight location it lies between 18.8 and 24.2 mW mâ2. In most models, elastic lithosphere thickness values exceed 250 km at the north pole, while the south pole values lie well above 110 km
Mercury's lowâdegree geoid and topography controlled by insolationâdriven elastic deformation
©2015. American Geophysical UnionMercury experiences an uneven insolation that leads to significant latitudinal and longitudinal variations of its surface temperature. These variations, which are predominantly of spherical harmonic degrees 2 and 4, propagate to depth, imposing a longâwavelength thermal perturbation throughout the mantle. We computed the accompanying density distribution and used it to calculate the mechanical and gravitational response of a spherical elastic shell overlying a quasiâhydrostatic mantle. We then compared the resulting geoid and surface deformation at degrees 2 and 4 with Mercury's geoid and topography derived from the MErcury, Surface, Space ENvironment, GEochemistry, and Ranging spacecraft. More than 95% of the data can be accounted for if the thickness of the elastic lithosphere were between 110 and 180 km when the thermal anomaly was imposed. The obtained elastic thickness implies that Mercury became locked into its present 3:2 spin orbit resonance later than about 1 Gyr after planetary formation
Present-day Mars' seismicity predicted from 3-D thermal evolution models of interior dynamics
©2018. American Geophysical UnionThe Interior Exploration using Seismic Investigations, Geodesy and Heat Transport mission, to be launched in 2018, will perform a comprehensive geophysical investigation of Mars in situ. The Seismic Experiment for Interior Structure package aims to detect global and regional seismic events and in turn offer constraints on core size, crustal thickness, and core, mantle, and crustal composition. In this study, we estimate the presentâday amount and distribution of seismicity using 3âD numerical thermal evolution models of Mars, taking into account contributions from convective stresses as well as from stresses associated with cooling and planetary contraction. Defining the seismogenic lithosphere by an isotherm and assuming two endâmember cases of 573 K and the 1073 K, we determine the seismogenic lithosphere thickness. Assuming a seismic efficiency between 0.025 and 1, this thickness is used to estimate the total annual seismic moment budget, and our models show values between 5.7 Ă 1016 and 3.9 Ă 1019 Nm
The thermal state and interior structure of Mars
©2018. American Geophysical UnionThe presentâday thermal state, interior structure, composition, and rheology of Mars can be constrained by comparing the results of thermal history calculations with geophysical, petrological, and geological observations. Using the largestâtoâdate set of 3âD thermal evolution models, we find that a limited set of models can satisfy all available constraints simultaneously. These models require a core radius strictly larger than 1,800âkm, a crust with an average thickness between 48.8 and 87.1âkm containing more than half of the planet's bulk abundance of heat producing elements, and a dry mantle rheology. A strong pressure dependence of the viscosity leads to the formation of prominent mantle plumes producing melt underneath Tharsis up to the present time. Heat flow and core size estimates derived from the InSight (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) mission will increase the set of constraining data and help to confine the range of admissible models.DFG, 280637173, FOR 2440: Materie im Inneren von Planeten - Hochdruck-, Planeten- und Plasmaphysi
The habitability of a stagnant-lid Earth
Plate tectonics is a fundamental component for the habitability of the Earth.
Yet whether it is a recurrent feature of terrestrial bodies orbiting other
stars or unique to the Earth is unknown. The stagnant lid may rather be the
most common tectonic expression on such bodies. To understand whether a
stagnant-lid planet can be habitable, i.e. host liquid water at its surface, we
model the thermal evolution of the mantle, volcanic outgassing of HO and
CO, and resulting climate of an Earth-like planet lacking plate tectonics.
We used a 1D model of parameterized convection to simulate the evolution of
melt generation and the build-up of an atmosphere of HO and CO over 4.5
Gyr. We then employed a 1D radiative-convective atmosphere model to calculate
the global mean atmospheric temperature and the boundaries of the habitable
zone (HZ). The evolution of the interior is characterized by the initial
production of a large amount of partial melt accompanied by a rapid outgassing
of HO and CO. At 1 au, the obtained temperatures generally allow for
liquid water on the surface nearly over the entire evolution. While the outer
edge of the HZ is mostly influenced by the amount of outgassed CO, the
inner edge presents a more complex behaviour that is dependent on the partial
pressures of both gases. At 1 au, the stagnant-lid planet considered would be
regarded as habitable. The width of the HZ at the end of the evolution, albeit
influenced by the amount of outgassed CO, can vary in a non-monotonic way
depending on the extent of the outgassed HO reservoir. Our results suggest
that stagnant-lid planets can be habitable over geological timescales and that
joint modelling of interior evolution, volcanic outgassing, and accompanying
climate is necessary to robustly characterize planetary habitability
Sheet-like and plume-like thermal flow in a spherical convection experiment performed under microgravity
We introduce, in spherical geometry, experiments on electro-hydrodynamic driven Rayleigh-BĂ©nard convection that have been performed for both temperature-independent (âGeoFlow I') and temperature-dependent fluid viscosity properties (âGeoFlow II') with a measured viscosity contrast up to 1.5. To set up a self-gravitating force field, we use a high-voltage potential between the inner and outer boundaries and a dielectric insulating liquid; the experiments were performed under microgravity conditions on the International Space Station. We further run numerical simulations in three-dimensional spherical geometry to reproduce the results obtained in the âGeoFlow' experiments. We use Wollaston prism shearing interferometry for flow visualization - an optical method producing fringe pattern images. The flow patterns differ between our two experiments. In âGeoFlow I', we see a sheet-like thermal flow. In this case convection patterns have been successfully reproduced by three-dimensional numerical simulations using two different and independently developed codes. In contrast, in âGeoFlow II', we obtain plume-like structures. Interestingly, numerical simulations do not yield this type of solution for the low viscosity contrast realized in the experiment. However, using a viscosity contrast of two orders of magnitude or higher, we can reproduce the patterns obtained in the âGeoFlow II' experiment, from which we conclude that nonlinear effects shift the effective viscosity rati
How large are present-day heat flux variations across the surface of Mars?
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A multimeasure approach to investigating affective appraisal of social information in Williams syndrome
People with Williams syndrome (WS) have been consistently described as showing heightened sociability, gregariousness, and interest in people, in conjunction with an uneven cognitive profile and mild to moderate intellectual or learning disability. To explore the mechanisms underlying this unusual socialâbehavioral phenotype, we investigated whether individuals with WS show an atypical appraisal style and autonomic responsiveness to emotionally laden images with social or nonsocial content. Adolescents and adults with WS were compared to chronological age-matched and nonverbal mental age-matched groups in their responses to positive and negative images with or without social content, using measures of self-selected viewing time (SSVT), autonomic arousal reflected in pupil dilation measures, and likeability ratings. The participants with WS looked significantly longer at the social images compared to images without social content and had reduced arousal to the negative social images compared to the control groups. In contrast to the comparison groups, the explicit ratings of likeability in the WS group did not correlate with their SSVT; instead, they reflected an appraisal style of more extreme ratings. This distinctive pattern of viewing interest, likeability ratings, and autonomic arousal to images with social content in the WS group suggests that their heightened social drive may be related to atypical functioning of reward-related brain systems reflected in SSVT and autonomic reactivity measures, but not in explicit ratings
Aplicacion del silicato tricalcico como una alternativa biocompatible.
El seleccionar un adecuado material para la obturaciĂłn apical es un acto fundamental para la resoluciĂłn de un caso con una lesiĂłn periapical persistente; los principales factores que deberĂĄ tener este material es su biocompatibilidad y el crear un sellado hermĂ©tico para evitar filtraciĂłn; deberĂĄ poseer capacidad para inducir osteogĂ©nesis y reparaciĂłn, no desarrollar toxicidad, ser radiopaco y bacteriostĂĄtico. El Biodentine es un material recientemente introducido al mercado (2011), principalmente compuesto de silicato tricĂĄlcico. Es usado para tratamientos de reparaciĂłn en corona y raĂz, reparando perforaciones, resorciones, empleado para apexificaciones y como material de retroobturaciĂłn; tambiĂ©n puede ser utilizado como un sustituto de dentina en caries demasiado extensas.
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Interpretation of ambiguous situations: evidence for a dissociation between social and physical threat in Williams syndrome
There is increasing evidence that Williams syndrome (WS) is associated with elevated anxiety that is non-social in nature, including generalised anxiety and fears. To date very little research has examined the cognitive processes associated with this anxiety. In the present research, attentional bias for non-social threatening images in WS was examined using a dot-probe paradigm. Participants were 16 individuals with WS aged between 13 and 34 years and two groups of typically developing controls matched to the WS group on chronological age and attentional control ability respectively. The WS group exhibited a significant attention bias towards threatening images. In contrast, no bias was found for group matched on attentional control and a slight bias away from threat was found in the chronological age matched group. The results are contrasted with recent findings suggesting that individuals with WS do not show an attention bias for threatening faces and discussed in relation to neuroimaging research showing elevated amygdala activation in response to threatening non-social scenes in WS
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