Slab

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

Hydrodynamic limit of the stationary Boltzmann equation in a slab

Abstract: We study the stationary solution of the Boltzmann equation in a slab with a constant external force parallel to the boundary and complete accommodation condition on the walls at a specified temperature. We prove that when the force is sufficiently small there exists a solution which converges, in the hydrodynamic limit, to a local Maxwellian with parameters given by the stationary solution of the corresponding compressible Navier-Stokes equations with no-slip boundary conditions. Corrections to this Maxwellian are obtained in powers of the Knudsen number with a controlled remainder.

Field Demonstration of Durable Link Slabs for Jointless Bridge Decks Based on Strain-Hardening Cementitious Composites

Abstract: The research presented herein describes the development of durable link slabs for jointless bridge decks based on strainhardening cementitious composite - engineered cementitious composite (ECC). Specifically the superior ductility of ECC was utilized to accommodate bridge deck deformations imposed by girder deflection, concrete shrinkage, and temperature variations, providing a cost-effective solution to a number of deterioration problems associated with bridge deck joints. Based on the findings within, the implementation of a durable ECC link slab is possible in a standard bridge deck reconstruction scenario. This report includes development of theoretical guidelines for compete design of an ECC link slab, example calculations, desk references, sample design drawings, material specifications, and contractual special provisions. In addition to these documents, the results of full scale mixing trials and demonstrations are summarized and recommendations are made along with batching sequences and mix designs for large scale mixing. A summary of construction practices and procedures is also included, followed by the results of full scale load testing on the completed ECC link slab demonstration bridge. Conclusions within the report reveal that with the aid of design documents provided within, the design of an ECC link slab element can be completed with little difficulty by Department of Transportation design engineers. The mixing of ECC material at commercial concrete plants can also produce a large scale version of the material similar in mechanical performance to laboratory grade material. The construction of an ECC link slab can be completed by a general contractor with some additional care when working with this new material. Finally, load tests conclude that the ECC link slab functions as designed under bending loads.

Mantle flow in subduction systems: The mantle wedge flow field and implications for wedge processes

Abstract: [1] The mantle wedge above subducting slabs is associated with many important processes, including the transport of melt and volatiles. Our understanding of mantle wedge dynamics is incomplete, as the mantle flow field above subducting slabs remains poorly understood. Because seismic anisotropy is a consequence of deformation, measurements of shear wave splitting can constrain the geometry of mantle flow. In order to identify processes that make first-order contributions to the pattern of wedge flow, we have compiled a data set of local S splitting measurements from mantle wedges worldwide. There is a large amount of variability in splitting parameters, with average delay times ranging from ~0.1 to 0.3 s up to ~1.0–1.5 s and large variations in fast directions. We tested for relationships between splitting parameters and a variety of parameters related to subduction processes. We also explicitly tested the predictions made by 10 different models that have been proposed to explain splitting patterns in the mantle wedge. We find that no simple model can explain all of the trends observed in the global data set. Mantle wedge flow is likely controlled by a combination of downdip motion of the slab, trench migration, ambient mantle flow, small-scale convection, proximity to slab edges, and slab morphology, with the relative contributions of these in any given subduction system controlled by the subduction kinematics and mantle rheology. There is also a likely contribution from B-type olivine and/or serpentinite fabric in many subduction zones, governed by the local thermal structure and volatile distribution.

What processes control the chemical compositions of arc front stratovolcanoes

Abstract: Arc front stratovolcanoes have global chemical systematics that constrain processes at convergent margins Positive correlations exist for arc averages among “fluid mobile,” “high field strength,” and “large ion lithophile” elements 143Nd/144Nd and 87Sr/86Sr from rear-arc lavas lacking subduction signature align with the oceanic “mantle array,” and correlate with arc front 143Nd/144Nd Most chemical parameters (but not isotopes) also correlate well with crustal thickness and slightly less well with the slab thermal parameter, but not with the depth of the slab nor model slab surface temperatures Successful models of arc volcanism should account for these global regularities Two distinct models can quantitatively account for the observations—different extents of melting of the mantle wedge caused by variations in wedge thermal structure, or varying contributions from the subducting slab owing to variations in the slab thermal structure Both successful model scenarios require a significant flux of melted ocean crust to the mantle source of all volcanic arcs The wedge melting model has constant contributions from ocean crust, sediment, and mantle wedge to lavas globally, while the slab model varies slab contributions with slab temperature The wedge melting model fit improves by incorporating convergence rate and slab dip, which should affect the wedge thermal structure; the slab model is not supported by a similar analysis The wedge model also more easily accommodates the isotope data The two models predict different primary H2O contents, with large variations in H2O for the wedge model, and relatively constant H2O for the slab model An evaluation of the effects of varying sediment compositions on arc lavas will benefit from considering the very different consequences of the two models