Lehigh University

About: Lehigh University is a education organization based out in Bethlehem, Pennsylvania, United States. It is known for research contribution in the topics: Catalysis & Fracture mechanics. The organization has 12684 authors who have published 26550 publications receiving 770061 citations.

Oxidation of sulfur dioxide to sulfur trioxide over supported vanadia catalysts

Abstract: The objectives of this research are to establish the fundamental kinetics and mechanism of sulfur dioxide oxidation over supported vanadia catalysts and use these insights to facilitate the design of SCR DeNOx catalysts with minimal sulfur dioxide oxidation activity. A series of supported vanadia catalysts were prepared on various metal-oxide supports: ceria, zirconia, titania, alumina and silica. Raman spectroscopy was used to determine the coordination of surface species. At low vanadia loadings, vanadia preferentially exists on oxide support surfaces as isolated tetrahedrally coordinated (M‐O)3V a5 aO species. At higher vanadia loadings, the isolated (M‐O)3V a5 aO species polymerize on the oxide support surface breaking two V‐O‐M bonds and forming two V‐O‐V bridging bonds. The turnover frequency for sulfur dioxide oxidation was very low, 10 ˇ4 to 10 ˇ6 s ˇ1 at 4008C, and was independent of vanadia coverage suggesting that only one vanadia site is required for the oxidation reaction. As the support was varied, sulfur dioxide oxidation activity of the supported vanadia catalysts varied by one order of magnitude (Ce>Zr, Ti>Al>Si). The basicity of the bridging V‐O‐M oxygen appears to be responsible for influencing the adsorption and subsequent oxidation of the acidic sulfur dioxide molecule. Over the range of conditions studied, the rate of sulfur dioxide oxidation is zero-order in oxygen, first-order in sulfur dioxide and inhibited by sulfur trioxide. The turnover frequency for sulfur dioxide oxidation over WO3/TiO2 was an order of magnitude lower than that found for V2O5/TiO2, and no redox synergism between the surface vanadia and tungsten oxide species was evident for a ternary V2O5/ WO3/TiO2 catalyst. This suggests that WO3 promoted catalysts may be suitable for low-temperature SCR where minimal sulfur dioxide oxidation activity is required. # 1998 Elsevier Science B.V. All rights reserved.

The morphology of martensite in iron alloys

Abstract: Light and electron microscopy have been used to determine the main structural differences between the two major types of martensite in ferrous alloys. In the martensite that forms in dilute alloys of iron, the basic transformation unit takes the shape of a lath, and hence the term lath martensite is appropriate for identifying this morphology. Each lath is the result of a homogeneous shear, and successive shears produce a packet of parallel laths containing a high density of tangled dislocations. The other type, plate martensite, differs in the shape taken by a transformation unit and its transformation sequence is characterized by nonparallel plate formation. Investigation of a large number of binary ferrous systems shows that alloy composition and the transformation temperature influence the transition from lath to plate martensite. These two factors are discussed in terms of their possible effects on the plastic deformation mechanisms which must occur in the parent austenite and product martensite during transformation.

A study of hairpin vortices in a laminar boundary layer. Part 2. Hairpin vortices generated by fluid injection

Abstract: It has been suggested that hairpin vortices are a major sustaining flow structure involved in the perpetuation of turbulent boundary layers, although their origin within the boundary layer is unclear. One hypothesis is that hairpin structures are formed by the breakdown of the low-speed streak structures which develop adjacent to the surface beneath turbulent boundary layers. To examine this hypothesis, a water-channel study has been done which utilizes injection through surface slots in a flat plate to create artificial low-speed streak-type regions beneath a laminar boundary layer. Under appropriate conditions, these synthesized low-speed streaks develop a three-dimensional, shear-layer instability which breaks down to form a hairpin-vortex street. Employing both flow visualization and anemometry measurements, the characteristics of these hairpin structures and the parameters influencing their generation have been examined. The hairpin streets were determined to develop in a very periodic and repeatable manner within a definite range of flow parameters. Detailed flow patterns obtained using dye and hydrogen bubbles, both individually and collectively, indicate a remarkable similarity with previously observed patterns in the near-wall region of turbulent boundary layers. In addition, the development of the hairpin structures is observed to be quite sensitive to external forcing, as well as exhibiting a tendency for organized development of larger, more complex structures through a pairing-type process. Velocity measurements indicate the initial presence of strong inflexional profiles which evolve rapidly to velocity and turbulence-intensity profiles commensurate with those associated with turbulent boundary layers, but which do not exhibit the marked spreading associated with turbulence.

MIPLIB 2010 - Mixed Integer Programming Library version 5

Abstract: This paper reports on the fifth version of theMixed Integer Programming Library. The miplib 2010 is the first miplib release that has been assembled by a large group from academia and from industry, all of whom work in integer programming. There was mutual consent that the concept of the library had to be expanded in order to fulfill the needs of the community. The new version comprises 361 instances sorted into several groups. This includes the main benchmark test set of 87 instances, which are all solvable by today’s codes, and also the challenge test set with 164 instances, many of which are currently unsolved. For the first time, we include scripts to run automated tests in a predefined way. Further, there is a solution checker to test the accuracy of provided solutions using exact arithmetic.