Slab

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

Leaky wave radiation from a periodically photoexcited semiconductor slab waveguide

Abstract: This paper presents investigations on leaky wave antennas that are modeled by periodical illumination of light on a grounded semiconductor slab waveguide using an asymptotic method of singular perturbation procedure based on multiple scales. Analytical results clearly show that the periodical illumination strongly affects the radiation characteristics such as efficiency and the radiation angle. The dominant effects are studied quantitatively and are outlined in the performance diagrams as a function of optically induced plasma density and the grating period. Initial experimental results at Q band using silicon slab guide under an array of 820-nm LED CW excitation are also reported and are in relatively good agreement with the theory. >

Temporal Evolution of the Mariana Arc: Mantle Wedge and Subducted Slab Controls Revealed with a Tephra Perspective

Abstract: Tephras recovered by deep-sea drilling from fore-arc to back-arc locations across the Mariana Volcanic Arc record the last 34 Myr of the system’s evolution. Major and trace element abundances and Sr–Nd–Pb–Hf isotope ratios have been determined for tephra with high temporal precision and an average inter-tephra layer interval of � 1 Myr. Temporal variations of source-sensitive radiogenic isotopes and large-ion lithophile elements (LILE) are mostly decoupled from unchanging modes observed in silica and, with the exception of K, other archetypical crust-forming major elements. Modeling confirms that the temporal isotopic and elemental abundance trends are controlled by subducted slab and mantle sources. The Pb and Sr fluxes can be linked to fluids from altered oceanic crust (AOC), and are influenced by contributions from the mantle wedge and slab partial melts, whereas Hf mostly derives from the sub-arc mantle. Most plausibly, a K2O increase and fluctuations at � 10 Ma can be linked to collision of the leading trace of the Cretaceous-aged Western Pacific Seamount Province with the arc. This is inferred to have arrived at the Mariana Trench at � 15–16 Ma, coincident with the termination of spreading in the Parece Vela back-arc basin. A short period of slab melting followed, possibly induced by slab rollback that peaked at � 8–9 Ma and ended with incipient rifting in the Mariana Trough at � 7 Ma. Each of the periods of arc formation (52–24, 22–11 and 10–0 Ma) is characterized by a distinctive mixture of source materials that is not repeated through time. Mariana Arc crustal growth has occurred through the addition of predominantly mafic and silicic melts formed during relatively short time intervals, traceable via their chemically distinctive subducted slab inputs.

Shear wave anisotropy in the Mariana Subduction Zone

Abstract: To determine the location, strength, and orientation of seismic anisotropy in the Mariana subduction zone beneath Guam, we evaluated shear wave splitting in local S, regional S and ScS, and teleseismic core phases such as SKS recorded at station GUMO. Fast directions from the local S phases have an average azimuth of −45°, and splitting times range from 0.1 s to 0.4 s. For local S phases from events within the southeastern half of the subducting slab, splitting parameters manifest minimal frequency dependence in both fast direction and splitting time. However, for the remaining local S phases in the data set, fast directions vary with frequency content. No well-constrained splitting parameters were obtained for the regional and teleseismic phases, but the particle motions of these unsplit phases are consistent with an average anisotropic fast direction of ∼−45°. Anisotropy due solely to olivine oriented by slab-entrained flow in the mantle wedge would produce local S fast directions at ∼−66°, and anisotropy due solely to fossil seafloor spreading in the subducting slab would yield fast directions at −20° to −30°. Neither of these predictions is consistent with the observed fast directions. However, the observed splitting, including the frequency-dependent fast directions, can be explained by models containing anisotropy in both the slab and wedge, and possibly (although not necessarily) anisotropy due to recent extension in the overriding Philippine sea plate.

Mathematical Heat Transfer Model Research for the Improvement of Continuous Casting Slab Temperature

Abstract: To improve the temperature of continuous casting slab, a mathematical heat transfer model simulating the solidification process of continuous casting slab was developed based on the technical conditions of the slab caster of Steelmaking plant of Wu-Han Iron and Steel Group Corp., by which the slab temperature distribution and shell thickness were computed. The adequacy of the model was compared with the measured slab surface temperature at the caster exit. The effects of the main operation parameters including casting speed, secondary cooling conditions, slab size and steel melt superheat on the solidification process were discussed and the means of enhancing the slab temperature was brought forward. Raising the casting speed from 1.0 or 1.1 to 1.3 m/min, controlling the flow rate of secondary cooling water and optimizing the spray pattern at the lower segments of secondary cooling zone could effectively improve the slab temperature. Whereas increasing the superheat is adverse to the production of slab with high temperature. The results of model research have been applied to plant operation at Steelmaking plant of Wu-Han Iron and Steel Group Corp. The slab surface temperature has risen from 900 to 1 250°C, and the slab are directly fed to the rolling mill after exiting caster.