The interiors of type-M4 stars or later (masses of \sim 0.35M_\odot or less) are convectively unstable from their nuclear-burning cores to the photosphere. Despite the relative simplicity of their internal structure, we know very little about the internal processes that drive their magnetic dynamos. Only a limited number of simulations have studied global-scale dynamo processes in M-dwarfs (e.g., Browning 2008; Yadav et al. 2015a, 2015b, 2016). Worse, all of these have suffered a fundamental limitation: heretofore it has only been possible to simulate spherical shells, with the coordinate singularity at r = 0 avoided by making a "cutout" in the middle of the simulation.
Dynamo Studio 2015 with x-force keygen 2015
It is surprising that the mean fields of these fully convective dynamos generally occupy one hemisphere or the other, but not both. In rapidly rotating solar-type stars with convection-zone shells fields typically symmetrically fill both hemispheres (e.g., Brown et al. 2010, 2011; Augustson et al. 2013, 2015; Nelson et al. 2013). Importantly, all previous M-dwarf dynamo simulations in deep shells also find two-hemisphere solutions. Those simulations have either found mean fields symmetrically in both hemispheres (e.g., Yadav et al. 2015a, 2016) or have built mean fields that do not undergo very many reversals (Browning 2008).
The convective flows fill the interior, as visible in Figure 3. Here we show entropy fluctuations in a cut at the equator. Cold, low-entropy plumes (blue) fall from the near-surface regions. The core comprises rising warm, high-entropy plumes (red). The center at r = 0 is a region of vigorous dynamics, and plumes frequently cross the origin. Convective enthalpy transport (Lh) dominates the radial luminosity balance, except in the upper boundary layer where thermal diffusion takes over (LQ). Though these simulations are stratified, the kinetic energy flux (LKE) is small, similar to rotationally constrained simulations of solar-type stars (e.g., Brown et al. 2008). The sum of the luminosities closely matches the nuclear source derived from MESA (L_ \mathcal S ), indicating that these models are in proper thermal equilibrium. This convection drives a robust differential rotation, shown by the mean angular velocity, \langle \rm\Omega \rangle, with a fast equator and slow polar and core regions. The gradients of angular velocity are strong in both radius and latitude. These gradients likely build the mean toroidal field \langle B_\phi \rangle via shear induction (a.k.a the "Ω-effect"). Correlations in the fluctuating flows and fields maintain the polar field. The latitudinal contrast in \langle \rm\Omega \rangle is about 10%, and the mean magnetic fields coexist with this shearing flow. This is similar to results from rapidly rotating simulations of solar-type stars (Brown et al. 2011), but markedly different from the results of Browning (2008) or Yadav et al. (2015a), where the fields strongly quench the differential rotation. Whether differential rotation and fields can coexist likely depends on the Rossby number regimes of the dynamos, as discussed in Yadav et al. (2016).
Gissinger (2009) presented results of numerical simulations of VKS using a kinematic code, which by taking into account both the axisymmetric mean of the flow and its non-axisymmetric components could generate either an axial dipole or axial quadrupole. The competition between these two modes could then result in reversals of the dipole field when the symmetry of the system was broken (by having the two impellers counter-rotate at different rates). This model thus reproduced the axial dipole found in the experiment, including the stationary field in the case of impellers counter-rotating at the same frequency and an oscillating field with reversals in the case of different rotation frequencies. In order to investigate the role of the ferromagnetic discs, Nore et al. (2015) put forth a tentative model of dynamo action in VKS. According to this model, dynamo action in VKS is the result of a three-step process. First, toroidal energy accumulates in the disks (due to their large permeability); second, poloidal field is produced in the blade region of the impellers due to the interaction of recirculating fluid flow in between the blades with the toroidal field that accumulates in the disks; and finally, the bulk flow transports this poloidal field throughout the vessel, where the ω effect can then create toroidal field (which in turn accumulates in the disks, thus closing the loop). Thus, the ferromagnetic impellers are critical for supplying a localized α effect to enable the dynamo. The authors also note that this model shares similarities with the flux transport dynamo mechanism proposed for the solar dynamo, in that the conversion of poloidal to toroidal field occurs in a different location from the conversion of toroidal to poloidal field, thus requiring the intermediate transport of flux for the dynamo to operate. This could help to explain why MDE did not achieve a dynamo using VKS-type soft-iron impellers. If the dynamo were purely the result of local dynamo action at the site of the impellers, one would expect MDE to achieve a dynamo as well. If however the global transport of field is also an integral part of the dynamo mechanism, then differences in the flow patterns resulting from the different vessel geometries may help to explain the different outcomes with respect to dynamo action. Further investigation is needed to sort out these issues.
We recently published a paper on Spark SQL that will appear in SIGMOD 2015 (co-authored with Davies Liu, Joseph K. Bradley, Xiangrui Meng, Tomer Kaftan, Michael J. Franklin, and Ali Ghodsi). In this blog post we are republishing a section in the paper that explains the internals of the Catalyst optimizer for broader consumption.
A new Armor Wars mini-series appears as part of the 2015 Secret Wars storyline. The Battleworld domain associated with this mini-series is called Technopolis where its inhabitants are forced to wear Iron Man armors due to a disease and will have that area's Tony Stark and Arno Stark as rival manufacturers.[5] 2ff7e9595c
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