The capacitated multiple allocation hub location problem: Formulations and algorithms

In this paper we consider and present formulations and solution approaches for the capacitated multiple allocation hub location problem. We present a new mixed integer linear programming formulation for the problem. We also construct an efficient heuristic algorithm, using shortest paths. We incorporate the upper bound obtained from this heuristic in a linear-programming-based branch-and-bound solution procedure. We present the results of extensive computational experience with both the heuristic and the exact methods.     

An upwinded state approximate Riemann solver

Stability is achieved in most approximate Riemann solvers through ‘flux upwinding’, where the flux at the interface is arrived at by adding a dissipative term to the average of the left and right flux. Motivated by the existence of a collapsed interface state in the gas‐kinetic Bhatnagar–Gross–Krook (BGK) method, an alternative approach to upwinding is attempted here; an interface state is arrived at by taking an upwinded average of left and right states, and then the flux is calculated as a function of this ‘collapsed’ interface state. This so called ‘state‐upwinding’ approach gives rise to a new scheme called the linearized Riemann solver for the Euler and Navier–Stokes equations. The scheme is shown to be closely associated with the Roe scheme. It is, however, computationally less expensive and gives qualitatively comparable results over a wide range of problems. Most importantly, this scheme is found to preserve stationary contacts while not exhibiting the carbuncle phenomenon which plagues the Roe and other contact‐preserving schemes. The scheme is therefore motivated as a new starting point to analyze the origin of the carbuncle phenomenon. Copyright © 2011 John Wiley & Sons, Ltd.     

Effect of wire diameter and overheat ratio near a conducting wall

The influence on several hot wire measurements of the diameter d and overheat ratio a of a wire placed near a conducting wall in a turbulent boundary layer is investigated. These measurements include the mean velocity and second, third and fourth order moments of the longitudinal velocity fluctuation u. A decrease in either d or a reduces the departure of the measured mean velocity from the expected linear sublayer value. The measured influence of d and a precludes the use of a universal correction for the mean velocity. There is no influence of a on the rms, skewness and flatness factors of u. Only a small increase is found in the skewness and flatness factors of u when d is decreased.     

A comparison of two methods for solving 0–1 integer programs using a general purpose simulated annealing algorithm

0–1 problems are often difficult to solve. Although special purpose algorithms (exact as well as heuristic) exist for solving particular problem classes or problem instances, there are few general purpose algorithms for solving practical-sized instances of 0–1 problems. This paper deals with a general purpose heuristic algorithm for 0–1 problems. In this paper, we compare two methods based on simulated annealing for solving general 0–1 integer programming problems. The two methods differe in the scheme used for neighbourhood transitions in the simulated annealing framework. We compare the performance of the two methods on the set partitioning problem.     

Inventory with service time and transfer of customers and/inventory

An inventory system with two parallel service facilities is considered. A certain number of customers are transferred from longer to shorter queue whenever their difference reaches a prescribed quantity. Along with this customer transfer, a certain quantity of inventory is also transferred, depending on availability. Further, if one of the queues has customers, but has no inventoried items whereas the other has at least one inventoried item to spare, then exactly one item is taken to the former and service begins thereby enhancing the efficiency of the system. Stability of the system is analysed. Several performance measures that helps in efficient design of such systems, are computed. Some numerical results are provided.     

Synthesis and characterization of monosubstituted and disubstituted poly(3,4‐propylenedioxythiophene) derivatives with high electrochromic contrast in the visible region

Monosubstituted and disubstituted 3,4‐propylenedioxythiophenes were synthesized and polymerized by both chemical and electrochemical methods. All the monomers were characterized for their molecular structures, and the polymers were characterized for their electrochemical properties. The disubstituted derivatives showed higher contrast than the corresponding monoalkyl derivatives. The highest electrochromic contrast of 89% was exhibited by a dibenzyl derivative, but the derivative was insoluble. On the other hand, the electrochemically polymerized dihexyl‐ and didodecyl‐substituted poly(3,4‐propylenedioxythiophene)s exhibited 74 and 77% electrochromic contrast, respectively, and were soluble. The molecular weights of the chemically and electrochemically synthesized polymers were analyzed by gel permeation chromatography. The chemically synthesized polymers showed higher molecular weights. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 419–428, 2005     

Crystallographic report: Dibenzyl(dichloro)(1,10‐phenanthroline)tin (IV) chloroform solvate

The monomeric title compound features a distorted octahedral tin (IV) centre within a C₂Cl₂N₂ donor set with two cis Cl atoms and two trans benzyl groups. Copyright © 2005 John Wiley & Sons, Ltd.