The maximum covering/shortest path problem: A multiobjective network design and routing formulation

In this paper the authors introduce the maximum covering/shortest path problem and the maximum population/shortest path problem, a special case of the former model. Both models are formulated as two objective integer programs. A summary of the results of a sample problem for the latter formulation is given. Possible modifications to, and extensions and applications of both models are also presented. With these formulations the authors extend the concept of ‘coverage’ from facility location analysis to network design and routing analysis.     

A Lagrangian relaxation-based heuristic for the vehicle routing with full container load

We address a problem of vehicle routing that arises in picking up and delivering full container load from/to an intermodal terminal. The substantial cost and time savings are expected by efficient linkage between pickup and delivery tasks, if the time of tasks and the suitability of containers for cargo allow. As this problem is NP-hard, we develop a subgradient heuristic based on a Lagrangian relaxation which enables us to identify a near optimal solution. The heuristic consists of two sub-problems: the classical assignment problem and the generalized assignment problem. As generalized assignment problem is also NP-hard, we employ an efficient solution procedure for a bin packing based problem, which replaces the generalized assignment problem. The heuristic procedure is tested on a wide variety of problem examples. The test results demonstrate that the procedure developed here can efficiently solve large instances of the problem.     

Column chromatography fractionation of complex waste water sample extracts for measurement of ppt levels of 2,3,7,8-tetrachlorodibenzo-p-dioxin

The novel application of azulene as a visual monitor of column chromatography performance during fractionation of complex waste water extracts for measurement of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) at part-per-trillion concentrations is described. TCDD elutes directly behind azulene, the blue visual aid, in the 6% ethyl ether/hexane fraction during Florisil column chromatography.     

A Multiobjective Approach to Design Franchise Outlet Networks

The economic goals and the resulting locational objectives of a franchisor and its individual franchisees are frequently in conflict. For example, one goal of the franchisor is to maximize system-wide market coverage, while the corresponding goal of the franchisee is to maximize his or her individual market share. Consequently, the optimal facility siting scheme from one perspective may be suboptimal from the other. That is, the facility siting scheme which maximizes system-wide coverage will not necessarily maximize the market shares of the individual franchises which make up the system. In this paper we introduce a multiobjective integer programming model to design franchise networks. The model selects franchise locations and identifies individual franchise market areas. Constraints in the formulation guarantee that all franchise locations are assigned at least a minimal threshold market area with sufficient demand to ensure economic survival. An underlying assumption of the model is that a rationing mechanism exists to assign demand to various franchise locations. Consequently, the model is most appropriate for service delivery franchises in which the franchisor can define and enforce exclusive franchise territories for the various franchise outlets. The purpose of this model is to generate alternative siting configurations which demonstrate the inherent trade-offs between the objectives of the franchisor and the individual franchisees. Given these various location alternatives, it is expected that the franchisor will then evaluate them in terms of other criteria such as the likelihood of the individual franchisee's success, pricing strategies for the various sites, total costs, total profit, and the effects of the response of competitors. Consequently, the proposed model should be viewed as an aid for one aspect of the decision process, i.e. the generation of alternative courses of action.     

Dielectrophoresis-based programmable fluidic processors

Droplet-based programmable processors promise to offer solutions to a wide range of applications in which chemical and biological analysis and/or small-scale synthesis are required, suggesting they will become the microfluidic equivalents of microprocessors by offering off-the-shelf solutions for almost any fluid based analysis or small scale synthesis problem. A general purpose droplet processor should be able to manipulate droplets of different compositions (including those that are electrically conductive or insulating and those of polar or non-polar nature), to control reagent titrations accurately, and to remain free of contamination and carry over on its reaction surfaces. In this article we discuss the application of dielectrophoresis to droplet based processors and demonstrate that it can provide the means for accurately titrating, moving and mixing polar or non-polar droplets whether they are electrically conductive or not. DEP does not require contact with control surfaces and several strategies for minimizing surface contact are presented. As an example of a DEP actuated general purpose droplet processor, we show an embodiment based on a scaleable CMOS architecture that uses DEP manipulation on a 32 x 32 electrode array having built-in control and switching circuitry. Lastly, we demonstrate the concept of a general-purpose programming environment that facilitates droplet software development for any type of droplet processor.     

The Maximum Utilization Subtree Problem

A number of network design problems can be built on the following premise: Given a tree network, T, containing node set, V, identify a single subtree, t, containing nodes, v, so that the subtree is located optimally with respect to the remaining, unconnected nodes {V–v}. Distances between unconnected nodes and nodes in the subtree t can be defined on travel paths that are restricted to lie in the larger tree T (the travel-restricted case), or can be defined on paths in an auxiliary complete graph G (the travel-unrestricted case).This paper presents the Maximum Utilization Subtree Problem (MUSP), a bicriterion problem that trades off the cost of a subtree, t, against the utilization of the subtree by the sum of the populations at nodes connected to the subtree, plus the distance-attenuated population that must travel to the subtree from unconnected nodes. The restricted and unrestricted cases are formulated as a two objective integer programs where the objectives are to maximize utilization of the subtree and minimize the cost of the subtree. The programs are tested using linear programming and branch and bound to resolve fractions.The types of problems presented in this paper have been characterized in the existing literature as structure location or extensive facility location problems. This paper adds two significant contributions to the general body of location literature. First, it draws explicit attention to the travel-restricted and travel-unrestricted cases, which may also be called limited-access and general-access cases, respectively. Second, the distance-attenuated demands represent a new objective function concept that does not appear in the location literature.     

The onset of coulomb explosions in polyatomic molecules

With the development of high intensity femtosecond lasers, the ionisation and dissociation dynamics of molecules has become an area of considerable interest. Using the technique of femtosecond laser mass spectrometry (FLMS), the molecules carbon disulphide, pyrimidine, toluene, cyclohexanone and benzaldehyde are studied with pulse widths of 50 fs in the near infrared (IR) wavelength region (790 nm). Results are presented and contrasted for laser beam intensities around 10(15) and 10(16) W cm(-2). For the lower intensities, the mass spectra yield dominant singly charged parent ions. Additionally, the appearance of doubly charged parent ions is evident for carbon disulphide, toluene and benzaldehyde with envelopes of doubly charged satellite species existing in these local regions. Carbon disulphide also reveals a small triply charged component. Such atomic-like features are thought to be a strong fingerprint of FLMS at these intensities. However, upon increasing the laser intensity to approximately 10(16) W cm(-2), parent ion dominance decreases and the appearance of multiply charged atomic species occurs, particularly carbon. This phenomenon has been attributed to Coulomb explosions in which the fast absorption of many photons may produce transient highly ionised parent species which can subsequently blow apart. Copyright 1999 John Wiley & Sons, Ltd.     

Uniform molecular analysis using femtosecond laser mass spectrometry

The potential of femtosecond laser time-of-flight mass spectrometry (FLMS) for uniform quantitative analysis of molecules has been investigated. Various samples of molecular gases and vapours have been studied, using ultra-fast ( approximately 50 fs) laser pulses with very high intensity (up to 1.6 x 10(16) Wcm(-2)) for non-resonant multiphoton ionisation/tunnel ionisation. Some of these molecules have high ionisation potentials, requiring up to ten photons for non-resonant ionisation. The relative sensitivity factors (RSF) have been determined as a function of the laser intensity and it has been demonstrated that for molecules with very different masses and ionisation potentials, uniform ionisation has been achieved at the highest laser intensities. Quantitative laser mass spectrometry of molecules is therefore a distinct possibility. Copyright 1999 John Wiley & Sons, Ltd.     

The hub location and network design problem with fixed and variable arc costs: formulation and dual-based solution heuristic

Many air, less-than-truck load and intermodal transportation and telecommunication networks incorporate hubs in an effort to reduce total cost. These hubs function as make bulk/break bulk or consolidation/deconsolidation centres. In this paper, a new hub location and network design formulation is presented that considers the fixed costs of establishing the hubs and the arcs in the network, and the variable costs associated with the demands on the arcs. The problem is formulated as a mixed integer programming problem embedding a multi-commodity flow model. The formulation can be transformed into some previously modelled hub network design problems. We develop a dual-based heuristic that exploits the multi-commodity flow problem structure embedded in the formulation. The test results indicate that the heuristic is an effective way to solve this computationally complex problem.