Thermal convection with non-Newtonian plates

The coupling between plate motions and mantle convection is investigated using a fully dynamic numerical model consisting of a thin non-Newtonian layer which is dynamically coupled to a thick Newtonian viscous layer. The non-Newtonian layer has a simple power-law rheology characterized by power-law index n and stiffness constant Μ p. A systematic investigation of steady, single cell configurations demonstrates that under certain conditions ( n > 7 being one of them) the non-Newtonian layer behaves like a mobile tectonic plate. Time-dependent calculations with multicellular configurations show the ability of the plate-mantle coupling model to adjust the number of plates and their sizes in accordance with the flow in the Newtonian layer. These calculations show that the geometry and number of plates do not necessarily resemble the planform of convection below.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/72550/1/j.1365-246X.1992.tb02109.x.pd

KRAS-mutation incidence and prognostic value are metastatic site-specific in lung adenocarcinoma: poor prognosis in patients with KRAS-mutation and bone metastasis

Current guidelines lack comprehensive information on the metastatic site-specific role of KRAS mutation in lung adenocarcinoma (LADC). We investigated the effect of KRAS mutation on overall survival (OS) in this setting. In our retrospective study, 500 consecutive Caucasian metastatic LADC patients with known KRAS mutational status were analyzed after excluding 32 patients with EGFR mutations. KRAS mutation incidence was 28.6%. The most frequent metastatic sites were lung (45.6%), bone (26.2%), adrenal gland (17.4%), brain (16.8%), pleura (15.6%) and liver (11%). Patients with intrapulmonary metastasis had significantly increased KRAS mutation frequency compared to those with extrapulmonary metastases (35% vs 26.5%, p=0.0125). In contrast, pleural dissemination and liver involvement were associated with significantly decreased KRAS mutation incidence (vs all other metastatic sites; 17% (p<0.001) and 16% (p=0.02) vs 33%, respectively). Strikingly, we found a significant prognostic effect of KRAS status only in the bone metastatic subcohort (KRAS-wild-type vs KRAS-mutant; median OS 9.7v 3.7 months; HR, 0.49; 95% CI, 0.31 to 0.79; p =0.003). Our study suggests that KRAS mutation frequency in LADC patients shows a metastatic site dependent variation and, moreover, that the presence of KRAS mutation is associated with significantly worse outcome in bone metastatic cases.(VLID)469049

Convective motions in the mantle

Key subjects related to the present status of mantle convection theory are reviewed in this paper. Rheology of the polycrystalline mantle material is known from laboratory experiments. Diffusion and dislocation creeps must predominate in the long-term deformation of the mantle at high temperatures; their effective viscosities can be estimated from measured creep parameters. Inhomogeneities in the chemical and phase composition of the mantle can influence the convective pattern considerably. Perhaps the most significant heterogeneities in this respect are those produced by the phase changes of the transition zone. The endothermic spinel-perovskite transition at 660 km depth can create an efficient obstacle to vertical flow. Available seismic tomographic images show clear signs of such an obstacle in some subduction zones, at other places however the downwellings seem to be unimpeded. The exact degree of flow layering caused by the 660 km discontinuity is not known, but some sort of flow stratification is strongly suggested by the isotopic and trace element geochemistry which shows that different chemical reservoirs must exist in the mantle on the geological time scale. Equations and the main governing forces are analyzed, and the basic structures of the convective flow are demonstrated in examples of numerical solutions. In particular, recent modelling results are discussed with regard to the plume forms allowed by a semi-permeable internal phase boundary. It is shown that three different kinds of plumes can reach the surface and produce hotspots: those arising from the internal phase boundary, those coming from the basal boundary layer of the mantle, and a recently described new plume type which breaks through the phase transition starting from a diffuse volume below the transition zone

The number of hotspots in three-dimensional numerical models of mantle convection

Thermal convection has been modelled in a 3D model box, in order to estimate the areal density of upwellings and compare it to the density of hotspots, assumed as surface imprints of the cylindrical upwellings of the mantle. The number of the hotspots of the Earth is 40 to 100. If this is translated to a nondimensional areal plume density, using the depth of the convecting layer as length unit, a value of 2-6 is obtained for whole-mantle convection, while this value is 0.04-0.10 for a separately convecting upper mantle. The nondimensional theoretical areal plume density has been found about 0.2-1.0 for reasonable numerical models of the mantle. The fact, that the theoretical value lies between the densities estimated for one- and two-layer mantle systems, supports the possibility of a mixed regime, where some of the plumes come from the base of the mantle, some others from the 660 km boundary