A parallel finite element sliding mesh technique for the simulation of viscous flows in agitated tanks

A parallel sliding mesh algorithm for the finite element simulation of viscous fluid flows in agitated tanks is presented. Lagrange multipliers are used at the sliding interfaces to enforce the continuity between the fixed and moving subdomains. The novelty of the method consists of the coupled solution of the resulting velocity–pressure‐Lagrange multipliers system of equations by an ILU(0)‐QMR solver. A penalty parameter is introduced for both the interface and the incompressibility constraints to avoid pivoting problems in the ILU(0) algorithm. To handle the convective term, both the Newton–Raphson scheme and the semi‐implicit linearization are tested. A penalty parameter is introduced for both the interface and the incompressibility constraints to avoid the failure of the ILU(0) algorithm due to the lack of pivoting. Furthermore, this approach is versatile enough so that it allows partitioning of sliding and fixed subdomains if parallelization is required. Although the sliding mesh technique is fairly common in CFD, the main advantage of the proposed approach is its low computational cost due to the inexpensive and parallelizable calculations that involve preconditioned sparse iterative solvers. The method is validated for Couette and coaxial stirred tanks. Copyright © 2011 John Wiley & Sons, Ltd.     

Multi-criteria supplier segmentation using a fuzzy preference relations based AHP

One of the strategic activities of a firm is supplier segmentation, whereby a firm creates groups of suppliers to handle them differently. Existing literature provides several typologies of suppliers, each of which uses different dimensions/variables. In this paper, different typologies are combined by distinguishing two overarching dimensions, the capabilities and the willingness of suppliers to cooperate with a particular firm. These dimensions cover almost all the existing supplier segmentation criteria mentioned in existing literature. For each particular situation, these dimensions can be specified using a multi-criteria decision-making method. A methodology is proposed that includes a fuzzy Analytic Hierarchy Process (AHP) which uses fuzzy preference relations to incorporate the ambiguities and uncertainties that usually exist in human judgment. The proposed methodology is used to segment the suppliers of a broiler company. The result is a segmentation of suppliers based on two aggregated dimensions. Finally some strategies to handle different segments are discussed and concluding remarks and suggestions for future research are provided.     

Multifunctional,Defect‐Engineered Metal–Organic Frameworks with Ruthenium Centers: Sorption and Catalytic Properties

A mixed‐linker solid‐solution approach was employed to modify the metal sites and introduce structural defects into the mixed‐valence Ru^II/III structural analogue of the well‐known MOF family [M₃^II,II(btc)₂] (M=Cu, Mo, Cr, Ni, Zn; btc=benzene‐1,3,5‐tricarboxylate), with partly missing carboxylate ligators at the Ru₂ paddle‐wheels. Incorporation of pyridine‐3,5‐dicarboxylate (pydc), which is the same size as btc but carries lower charge, as a second, defective linker has led to the mixed‐linker isoreticular derivatives of Ru‐MOF, which display characteristics unlike those of the defect‐free framework. Along with the creation of additional coordinatively unsaturated sites, the incorporation of pydc induces the partial reduction of ruthenium. Accordingly, the modified Ru sites are responsible for the activity of the “defective” variants in the dissociative chemisorption of CO₂, the enhanced performance in CO sorption, the formation of hydride species, and the catalytic hydrogenation of olefins.     

A note on the parameterized EM method

We study and analyze the parameterized method in view of the acceleration of the EM algorithm. Some theoretical results and discussions on the choice of the step size improve the understanding of the method and its limits.     

Combinatorics of Free Cumulants

We derive a formula for expressing free cumulants whose entries are products of random variables in terms of the lattice structure of non-crossing partitions. We show the usefulness of that result by giving direct and conceptually simple proofs for a lot of results about R-diagonal elements. Our investigations do not assume the trace property for the considered linear functionals.     

Drawing Disconnected Graphs on the Klein Bottle

We prove that two disjoint graphs must always be drawn separately on the Klein bottle in order to minimize the crossing number of the whole drawing.