Undulating membrane structure under mixed extensional-shear flow

We report on studies using a new X-ray extensional flow cell to examine, for the first time, the structure of undulating lamellar lyotropic liquid crystal systems under extensional flow. The extensional component of the flow profile produced within this cell causes the lamellae to orient. We find that, although the intermembrane spacing does not change at low flow rates, it suddenly decreases after a critical flow rate has been attained due to the stretching and straightening of the lamellae. The effects of the shear component of flow on this oriented system have been examined in the context of a theoretical model developed by Ramaswamy. Received 29 May 2001 and Received in final form 20 July 2001     

Spectroscopic, electrochemical, and computational aspects of the charge distribution in Ru(acac)2(R-o-benzoquinonediimine) complexes

The syntheses and properties are reported for five Ru(acac)2(R-bqdi) species where acac is acetylacetonate, and R-bqdi is the non-innocent ligand ortho-benzoquinonediimine substituted with R = H (1), 4,5-dimethyl (2), 4-Cl (3), or 4-NO2 (4), and N,N'-dimethylsulfonyl (5). Their identities and purities were confirmed by NMR, mass spectra, IR and analytical data. The large degree of metal-to-ligand pi-back-donation was analyzed by spectroscopic (UV/visible, IR, Raman) and electrochemical data, supported by molecular orbital composition computations using density functional theory (DFT), with the polarizable continuum model (PCM) to mimic the presence of solvent, and prediction of electronic spectra using time-dependent DFT methods. Extended charge decomposition analysis (ECDA) and natural population analysis (NPA) both produced a detailed picture of the bonding between the non-innocent bqdi ligand and the metal center, allowing correlations to be drawn between the nature of the R substituents and the quantitative extent of pi-back-donation and sigma-forward donation. In conclusion, the issue of whether these species are best regarded as Ru(II)(quinonediimine) or coupled Ru(III)(semiquinonediiminate) species is discussed.     

Heuristics for multi-period capacity expansion in local telecommunications networks

In this paper, different heuristics are devised to solve a multi-period capacity expansion problem for a local access telecommunications network with a tree topology. This expansion is done by installing concentrators at the nodes and cables on the links of the network. The goal is to find a least cost capacity expansion strategy over a number of periods to satisfy the demand. A local search heuristic is first proposed to improve previously reported results on problem instances based on different cost and demand structures. This heuristic is then integrated into a genetic algorithm to obtain further improvements.     

Titanium(IV) complexes of disulfide-linked Schiff bases

With the goal of preparing Ti(IV) complexes bearing a sulfur-based redox function of possible use in electrocatalytic oxidations of alcohols at electrode surfaces, a series of seven 2,2'-dithiodianiline Schiff-base derivatives, including two new variations, were tested in reactions with Ti(OR)(4) (R = (i)Pr, (t)Bu). Instead of the expected dimetallic products of general formula [LTi(OR)(2)](2), mononuclear species LTi(OR)(2) were obtained, confirmed by crystallographic determinations to have an unprecedented, symmetrical, and macrocyclic arrangement with four-point binding to the metal center and with the disulfide moieties remaining uncoordinated. Cyclic voltammetry performed in CH(2)Cl(2) displayed oxidations at potentials useful for fuel cells (+1.1-1.5 V vs Ag/AgCl), but despite the uncoordinated disulfide moieties, the complexes were reticent to engage in reduction processes.     

Complexes olefiniques du ruthenium: V. Structure cristalline et etude RMN de [RuClH(cod)(pyridine)2]

The complexes [RuClH(cod)(amine)₂] undergo amine exchange reactions with pyridine, γ-picoline or 4-(dimethylamino)pyridine. The crystalstructure of [RuClH(cod)(py)₂] has been determined from three-dimensional X-ray data. It crystallizes in space group P2₁/n of the monoclinic system; a 11.278(5); b 10.619(9); c 14.231(4) Å; β 90.34(3)°; Z = 4. The structure was solved by standard heavy atom methods and has been refined by least squares to a conventional R factor of 0.038 based on 5535 reflections. The coordination geometry around the ruthenium atom is octahedrally distorded with cis-aminepyridine ligands, the chloro and hydrido ligands being trans to each other and the cyclooctadiene moiety bound through the two double bonds. Principal bond lengths are: Ru-H 1.60(3); Ru-Cl 2.584(1), Ru-N 2.167(2) and 2.153(2) Å. ¹H and ¹³C NMR data are presented for the three complexes. The ¹³C NMR shifts of the olefin group indicate a large degree of π-back-bonding.     

Optimal fitting of computer model simulations to first transitcardiac radionuclide curves. II

A discrete-time, lumped-parameter mathematical model of the human cardiopulmonary circulation as it appears during a first-transit radionuclide study has been described. An optimal fitting process is used to match curves obtained from the model to curves obtained from first transit studies in order to estimate the parameters of the subject's heart. The development of the optimization technique is described in this paper. The results of testing the effects of overlapping compartments and errors in delay estimates are presented. A parameter determination analysis is performed by applying the optimization algorithm to simulated data. This analysis technique provides a method of estimating many parameters of heart function using a single, simple, rapid procedure. Results of clinical studies will be presented subsequently.     

Real-time decision problems: an operational research perspective

This paper is concerned with a class of dynamic and stochastic problems known as real-time decision problems. The objective is to provide responses of a required quality in a continuously evolving environment, within a prescribed time frame, using limited resources and information that is often incomplete or uncertain. Furthermore, the outcome of any particular decision may also be uncertain. This paper provides an overview of this class of problems, reviews the relevant Artificial Intelligence literature, proposes a dynamic programming framework, and assesses the potential usefulness of Operational Research approaches for their solution. Throughout the paper, a vehicle dispatching application illustrates the relevant concepts.     

Integration of AI and OR Techniques for Computer-Aided Algorithmic Design in the Vehicle Routing Domain

This paper shows how tools and techniques of artificial intelligence can be successfully integrated into a computer system working in the vehicle routing domain. The aim of this system, called ALTO, is to facilitate the development of routing algorithms for transportation vehicles. In this paper, we describe the general algorithmic framework and the rich interface provided by the system to the expert algorithm designer. We also introduce a methodology for acquiring useful knowledge in the domain, based on examples of successful and unsuccessful problem-solving strategies. With such knowledge, ALTO would then be capable of actively supporting the algorithm designer by suggesting good candidate algorithms for solving new problems.     

Tabu search with ejection chains for the vehicle routing problem with private fleet and common carrier

The problem reported in this paper is a variant of the classical vehicle routing problem, where customer requests for a transportation company can be served either by its private fleet of vehicles or assigned to an external common carrier. The latter case occurs if the demand exceeds the total capacity of the private fleet or if it is more economical to do so. Accordingly, the objective is to minimize the variable and fixed costs of the private fleet plus the costs charged by the common carrier. A tabu search heuristic with a neighbourhood structure based on ejection chains is proposed to solve this problem. It is empirically demonstrated that this algorithm outperforms the best approaches reported in the literature on a set of benchmark instances with both homogeneous and heterogeneous fleets.