Slab

About: Slab is a research topic. Over the lifetime, 31617 publications have been published within this topic receiving 318693 citations.

Magnetic superlens-enhanced inductive coupling for wireless power transfer

Abstract: We investigate numerically the use of a negative-permeability “perfect lens” for enhancing wireless power transfer between two current carrying coils. The negative permeability slab serves to focus the flux generated in the source coil to the receiver coil, thereby increasing the mutual inductive coupling between the coils. The numerical model is compared with an analytical theory that treats the coils as point dipoles separated by an infinite planar layer of magnetic material [Urzhumov et al., Phys. Rev. B 19, 8312 (2011)]. In the limit of vanishingly small radius of the coils, and large width of the metamaterial slab, the numerical simulations are in excellent agreement with the analytical model. Both the idealized analytical and realistic numerical models predict similar trends with respect to metamaterial loss and anisotropy. Applying the numerical models, we further analyze the impact of finite coil size and finite width of the slab. We find that, even for these less idealized geometries, the presence of the magnetic slab greatly enhances the coupling between the two coils, including cases where significant loss is present in the slab. We therefore conclude that the integration of a metamaterial slab into a wireless power transfer system holds promise for increasing the overall system performance.

Variable Impact of the Subducted Slab on Aleutian Island Arc Magma Sources: Evidence from Sr, Nd, Pb, and Hf Isotopes and Trace Element Abundances

Abstract: Major and trace element compositions and Sr, Nd, Pb, and Hf isotope ratios of Aleutian island arc lavas from Kanaga, Roundhead, Seguam, and Shishaldin volcanoes provide constraints on the composition and origin of the material transferred from the subducted slab to the mantle wedge. 40 Ar/ 39 Ar dating indicates that the lavas erupted mainly during the last � 400 kyr. Along-arc geochemical and isotopic variations are consistent with variable degrees of fluid input to the mantle wedge. Addition of bulk sediment, partially melted sediment, or a combination of sediment and fluid components may also explain the major and trace element and isotopic compositions of some Aleutian lavas. Mass-balance modeling suggests that the fluid is derived from subducted sediment (10–25%) and underlying oceanic crust (75–90%). Hf–Nd isotope data suggest that relative to Nd, little Hf is transferred to the mantle wedge via fluid. Lavas from Seguam Island in the central Aleutian arc have distinctly elevated B/La, U/Th, 87 Sr/ 86 Sr, and 207 Pb/ 204 Pb ratios, which probably reflect a large volume of fluid released from serpentinized oceanic crust plus the overlying layer of subducted sediment. We propose that the Amlia Fracture Zone, which was subducted beneath Seguam Island in the past 1 Myr, contains excess sediment and larger quantities of H2O-rich serpentine near the surface of the Pacific plate, and hence more fluid was available for transfer into the wedge in this section of the arc. The degree of partial melting of the mantle, modeled from the incompatible trace element contents of the lavas, correlates with the estimated mass of fluid fluxing of the mantle wedge. Seguam lavas, which show the largest quantity of fluid addition, have compositions that can be matched by a 22% partial melt of a fluid-modified mantle source, whereas Shishaldin and Roundhead lava compositions are consistent with an order of magnitude less partial melting of the mantle wedge.

Compositional mantle layering revealed by slab stagnation at ~1,000 km depth

Abstract: The stagnation of ~1000-km deep slabs indicates that dense basalt may be more abundant in the lower mantle than in the upper mantle. Improved constraints on lower-mantle composition are fundamental to understand the accretion, differentiation, and thermochemical evolution of our planet. Cosmochemical arguments indicate that lower-mantle rocks may be enriched in Si relative to upper-mantle pyrolite, whereas seismic tomography images suggest whole-mantle convection and hence appear to imply efficient mantle mixing. This study reconciles cosmochemical and geophysical constraints using the stagnation of some slab segments at ~1000-km depth as the key observation. Through numerical modeling of subduction, we show that lower-mantle enrichment in intrinsically dense basaltic lithologies can render slabs neutrally buoyant in the uppermost lower mantle. Slab stagnation (at depths of ~660 and ~1000 km) and unimpeded slab sinking to great depths can coexist if the basalt fraction is ~8% higher in the lower mantle than in the upper mantle, equivalent to a lower-mantle Mg/Si of ~1.18. Global-scale geodynamic models demonstrate that such a moderate compositional gradient across the mantle can persist can in the presence of whole-mantle convection.

Three‐dimensional structure of P‐wave anisotropy beneath the Tohoku district, northeast Japan

Abstract: [1] We retrieve three-dimensional structures of isotropic and anisotropic velocities of P-waves of the Tohoku district from first P-arrival time data, assuming azimuthal anisotropy to be caused by hexagonal symmetry axes distributed horizontally in the Earth. The results show that the high-velocity Pacific slab is clearly imaged in the isotropic velocity structure, even though the azimuthal anisotropy is taken into account. In addition, small-scale low-velocity regions and prominent low-velocity anomalies are found just below the active volcanoes and in the mantle wedge above the high-velocity Pacific slab, respectively. The fast propagation axis of P-waves is in mostly E-W direction in the upper crust, nearly N-S and E-W directions in the lower crust, E-W direction in the mantle wedge, and N-S direction in the descending Pacific slab. These features of the P-wave anisotropy structure are consistent with those of lateral variations of the fast polarization directions measured previously by shear-wave splitting observations. The plausible factor that causes the crust anisotropy is interpreted as being alignment or preferred orientation of microcracks and crust minerals. The mantle wedge anisotropy is attributed to lattice preferred orientation of the mantle minerals arising from present-day mantle process such as the mantle wedge convection and the plate motion. However, the fast propagation axis of P-waves in the slab is almost perpendicular to the magnetic lineation of the oceanic plate under the northwest Pacific, and thus the slab preserves the original anisotropic property that the Pacific plate gained when it formed.