Minimum heat flow from the core and thermal evolution of the Earth

The role of heat flow coming from the core is often overlooked or underestimated in simple models of Earth's thermal evolution. Throughout most of Earth's history, the mantle must have been extracting from the core at least the amount of heat that is required to operate the geodynamo. In view of recent laboratory measurements and theoretical calculations indicating a higher thermal conductivity of iron than previously thought, the above constraint has important implications for the thermal history of the Earth's mantle. In this work we construct a paramaterized mantle convection model that treats both the top and the core-mantle boundary heat fluxes according to the boundary layer theory, or alternatively employs the model of Labrosse (2015) to compute the thermal evolution of the Earth's core. We show that the core is likely to provide all the missing heat that is necessary in order to avoid the so-called “thermal catastrophe” of the mantle. Moreover, by analyzing the mutual feedback between the core and the mantle, we provide the necessary ingredients for obtaining thermal histories that are consistent with the petrological record and have reasonable initial conditions. These include a sufficiently high viscosity contrast between the lower and upper mantle, whose exact value is sensitive to the activation energy that governs the temperature dependence of the viscosity

A multiphase model of core formation

International audienceThe differentiation of solid planets with segregation of metal from silicates happens during the Hadean time while the planet is still growing by accretion. The separation of metal occurs when at least the metallic phase is liquid and proceeds by a combination of transport by diapiric instabilities and by more diffuse percolation flow. In this paper we develop a formalism derived from Bercovici et al. that can handle simultaneously two components, silicates and metal, and where the metal can be present both in solid and liquid states. The mechanical equations are non-Boussinesq as the lateral density variations are of the same order as the density itself. When the metal is solid, the metal and the silicates are locked together and we treat their mixture as a single-phase fluid where density is function of composition (iron-silicate proportions). When metal is liquid, it can separate from the silicates and the two phases interact through shear stress ( e. g. Darcy flow) and normal stress. The evolution of the volume proportion of liquid iron is controlled by the difference of pressure between the solid and liquid phases. The energy conservation equation takes into account the different mechanisms by which the gravitational energy is dissipated as heat. The 2-D Cartesian numerical code that we implemented to solve these equations makes use of numerical techniques that have not been previously used in geophysical two-phase modelling; we discuss the numerical aspects and benchmark the solutions. We present simulations of core-mantle differentiation showing that the first impact that melts the iron phase near the surface is potentially able to trigger the whole core-mantle segregation in a runaway phenomenon. The threshold of this instability in terms of the impactor and planetary size and the initial planetary temperature is investigated. The segregation of the metal occurs by a mechanism that was not suggested before and which is intermediate between the usual diapir instability and a porosity wave. Although we cannot explore the whole parameter space of our numerical model, we show various simulations that clarify the role of the most important parameters, such as the solid and metal viscosities or the depth dependence of gravit

Simultaneous melting and compaction in deformable two phase media

The definitive version is available at www.blackwell-synergy.comInternational audienceMelt generation and extraction are typically modeled using the two-phase equations developed by \cite{mckenzie:1984} or \cite{scott:1984}. Various approximations are often made to simplify the problem which may lead to some unphysical results (\eg, thermodynamically inconsistent conditions of melting and unrealistic porosity profiles). Here, we discuss a generalized version of the set of equations introduced by \cite{BRS1} that allows for mass transfer between the two phases and consider a self-consistent set of equations. In our description the two phases are submitted to individual pressure fields whose difference is related to the surface tension at the interfaces, changes in porosity and the melting rate. A kinetic relation for the melting rate arises from the second law of thermodynamics. The condition of chemical equilibrium corresponds to the usual univariant equality of the chemical potentials of each phase when the matrix and melt are motionless. In the most general form, phase equilibrium is influenced by both the Gibbs-Thomson effect that arises naturally from thermodynamic considerations on surface tension and by the viscous deformation of the phases. We apply these new equations to a steady state problem of pressure release melting in a univariant system. We treat melting and compaction simultaneously and observe several new effects including multiple boundary layers near the onset of melting that correspond to various force balances. A consequence of matrix compaction and melt expulsion (or matrix dilation and melt accumulation) is a pressure difference between melt and solid that facilitates (inhibits) melting. For parameters corresponding to mid-oceanic ridge magmatism, compaction induces melting to start as much as $\sim2$\,km below the standard solidus. Numerical solutions are necessary to determine the magnitude of the melt zone shift. Numerical results support the boundary layer solutions obtained analytically and suggest that in most of the melting zone the movement of melt and matrix should be close to the Darcy equilibrium where the buoyancy of melt is balanced by the viscous drag between the phases. The Darcy equilibrium follows an initial stage where the matrix viscous stresses balance Darcy drag. In all situations the steady state porosity profile remains a monotonous function of depth. The existence of a compaction layer following a melting zone where the porosity is maximum as described in various earlier publications has never been found

Thermal evolution and differentiation of planetesimals and planetary embryos

International audienceIn early Solar System during the runaway growth stage of planetary formation, the distribution of planetary bodies progressively evolved from a large number of planetesimals to a smaller number of objects with a few dominant embryos. Here, we study the possible thermal and compositional evolution of these planetesimals and planetary embryos in a series of models with increasing complexities. We show that the heating stages of planetesimals by the radioactive decay of now extinct isotopes (in particular 26Al) and by impact heating can occur in two stages or simultaneously. Depending on the accretion rate, melting occurs from the center outward, in a shallow outer shell progressing inward, or in the two locations. We discuss the regime domains of these situations and show that the exponent β that controls the planetary growth rate View the MathML source of planetesimals plays a crucial role. For a given terminal radius and accretion duration, the increase of β maintains the planetesimals very small until the end of accretion, and therefore allows radioactive heating to be radiated away before a large mass can be accreted. To melt the center of ∼500 km planetesimal during its runaway growth stage, with the value β = 2 predicted by astrophysicists, it needs to be formed within a couple of million years after condensation of the first solids. We then develop a multiphase model where the phase changes and phase separations by compaction are taken into account in 1-D spherical geometry. Our model handles simultaneously metal and silicates in both solid and liquid states. The segregation of the protocore decreases the efficiency of radiogenic heating by confining the 26Al in the outer silicate shell. Various types of planetesimals partly differentiated and sometimes differentiated in multiple metal-silicate layers can be obtained

Effects of Sunitinib and Other Kinase Inhibitors on Cells Harboring a PDGFRB Mutation Associated with Infantile Myofibromatosis

Infantile myofibromatosis represents one of the most common proliferative fibrous tumors of infancy and childhood. More effective treatment is needed for drug-resistant patients, and targeted therapy using specific protein kinase inhibitors could be a promising strategy. To date, several studies have confirmed a connection between the p.R561C mutation in gene encoding platelet-derived growth factor receptor beta (PDGFR-beta) and the development of infantile myofibromatosis. This study aimed to analyze the phosphorylation of important kinases in the NSTS-47 cell line derived from a tumor of a boy with infantile myofibromatosis who harbored the p.R561C mutation in PDGFR-beta. The second aim of this study was to investigate the effects of selected protein kinase inhibitors on cell signaling and the proliferative activity of NSTS-47 cells. We confirmed that this tumor cell line showed very high phosphorylation levels of PDGFR-beta, extracellular signal-regulated kinases (ERK) 1/2 and several other protein kinases. We also observed that PDGFR-beta phosphorylation in tumor cells is reduced by the receptor tyrosine kinase inhibitor sunitinib. In contrast, MAPK/ERK kinases (MEK) 1/2 and ERK1/2 kinases remained constitutively phosphorylated after treatment with sunitinib and other relevant protein kinase inhibitors. Our study showed that sunitinib is a very promising agent that affects the proliferation of tumor cells with a p.R561C mutation in PDGFR-beta

Pharmacokinetics of intramuscularly administered thermoresponsive polymers

Aqueous solutions of some polymers exhibit a lower critical solution temperature (LCST); that is, they form phase-separated aggregates when heated above a threshold temperature. Such polymers found many promising (bio)medical applications, including in situ thermogelling with controlled drug release, polymer-supported radiotherapy (brachytherapy), immunotherapy, and wound dressing, among others. Yet, despite the extensive research on medicinal applications of thermoresponsive polymers, their biodistribution and fate after administration remained unknown. Thus, herein, they studied the pharmacokinetics of four different thermoresponsive polyacrylamides after intramuscular administration in mice. In vivo, these thermoresponsive polymers formed depots that subsequently dissolved with a two-phase kinetics (depot maturation, slow redissolution) with half-lives 2 weeks to 5 months, as depot vitrification prolonged their half-lives. Additionally, the decrease of T-CP of a polymer solution increased the density of the intramuscular depot. Moreover, they detected secondary polymer depots in the kidneys and liver; these secondary depots also followed two-phase kinetics (depot maturation and slow dissolution), with half-lives 8 to 38 days (kidneys) and 15 to 22 days (liver). Overall, these findings may be used to tailor the properties of thermoresponsive polymers to meet the demands of their medicinal applications. Their methods may become a benchmark for future studies of polymer biodistribution

Safety and Outcome of Revascularization Treatment in Patients With Acute Ischemic Stroke and COVID-19: The Global COVID-19 Stroke Registry.

BACKGROUND AND OBJECTIVES COVID-19 related inflammation, endothelial dysfunction and coagulopathy may increase the bleeding risk and lower efficacy of revascularization treatments in patients with acute ischemic stroke. We aimed to evaluate the safety and outcomes of revascularization treatments in patients with acute ischemic stroke and COVID-19. METHODS Retrospective multicenter cohort study of consecutive patients with acute ischemic stroke receiving intravenous thrombolysis (IVT) and/or endovascular treatment (EVT) between March 2020 and June 2021, tested for SARS-CoV-2 infection. With a doubly-robust model combining propensity score weighting and multivariate regression, we studied the association of COVID-19 with intracranial bleeding complications and clinical outcomes. Subgroup analyses were performed according to treatment groups (IVT-only and EVT). RESULTS Of a total of 15128 included patients from 105 centers, 853 (5.6%) were diagnosed with COVID-19. 5848 (38.7%) patients received IVT-only, and 9280 (61.3%) EVT (with or without IVT). Patients with COVID-19 had a higher rate of symptomatic intracerebral hemorrhage (SICH) (adjusted odds ratio [OR] 1.53; 95% CI 1.16-2.01), symptomatic subarachnoid hemorrhage (SSAH) (OR 1.80; 95% CI 1.20-2.69), SICH and/or SSAH combined (OR 1.56; 95% CI 1.23-1.99), 24-hour (OR 2.47; 95% CI 1.58-3.86) and 3-month mortality (OR 1.88; 95% CI 1.52-2.33).COVID-19 patients also had an unfavorable shift in the distribution of the modified Rankin score at 3 months (OR 1.42; 95% CI 1.26-1.60). DISCUSSION Patients with acute ischemic stroke and COVID-19 showed higher rates of intracranial bleeding complications and worse clinical outcomes after revascularization treatments than contemporaneous non-COVID-19 treated patients. Current available data does not allow direct conclusions to be drawn on the effectiveness of revascularization treatments in COVID-19 patients, or to establish different treatment recommendations in this subgroup of patients with ischemic stroke. Our findings can be taken into consideration for treatment decisions, patient monitoring and establishing prognosis