An orienteering model for the search and rescue problem

In this paper, we propose a new model for the search and rescue problem. We focus on the case of a single airborne search asset through a connected space and continuous time with a maximum travel time \(T\) . The intent is to maximize the detection of a cooperative target (search and rescue). The proposed model is based on the assumption of existing a priori information (e.g., result of information fusion process) to establish a spatial distribution of probability of containment in possible geographic locations. The possibility area is defined using a cut threshold on the probability of containment and the search path as well as the allocation of the level of effort to each region in the search space is obtained based on an orienteering model. We illustrate the application of the proposed model on an empirical example.     

A model to optimize placement operations on dual-head placement machines

Dual-head placement machines are important in the assembly of circuit cards because they offer the capability to place large components accurately. This paper presents a novel column-generation approach for optimizing the placement operations of a dual-head placement machine with the ultimate goal of improving the efficiency of assembly operations. Research objectives are a model that reflects relevant, practical considerations; a solution method that can solve instances within reasonable run times; and tests to establish computational benchmarks. Test results demonstrate the efficacy of our optimization approach on problems of realistic size and scope.     

A dynamic multi-objective location-allocation model for search and rescue assets

This paper presents a dynamic multi-objective mixed integer linear programming model to optimize the location and allocation of search and rescue (SAR) boats and helicopters to enhance the performance of maritime SAR missions. Our model incorporates simulated incident scenarios to account for demand uncertainty and allows relocation of vessels seasonally. We define three objectives as responding to incidents within a critical time, generating a balanced workload distribution among vessels of various types, and minimizing costs associated with operations and vessel relocations. Implementing a goal programming approach, we solve the problem for various objective function term weights and compare the performance of each solution with respect to 10 different metrics. Using historical incident datasets for the Aegean Sea, we show that the proposed model and solution approach can significantly improve the SAR performance and provide decision support for planners in developing effective and efficient resource location-allocation schemes.     

An ILP model with logical constraints for mail sorting facility selection

This paper studies a facility selection problem which is generalised from the design of a mail sorting system with multiple input and output. The problem is formulated as a 0–1 integer linear programming (ILP) problem with logical constraints. We show how the logical constraints can be embedded into a ILP model. We compare three strategies for handling logical relations: (1) explicitly as added linear constraints; (2) implicitly as symbolic constraints; and (3) a combination of the two. The effectiveness of computations under different strategies are shown.     

An objective hyperplane search procedure for solving the general all-integer linear programming (ILP) problem

We describe an objective hyperplane search method for solving a class of integer linear programming (ILP) problems. We formulate the search as a bounded knapsack problem and develop requisite theory for formulating knapsack problems with composite constraints and composite objective functions that facilitate convergence to an ILP solution. A heuristic solution algorithm was developed and used to solve a variety of test problems found in the literature. The method obtains optimal or near-optimal solutions in acceptable ranges of computational effort.     

Applying neural network and scatter search to optimize parameter design with dynamic characteristics

Parameter design is critical to enhancing a system's robustness by identifying specific control factor set points (levels) that make the system least sensitive to noise. Engineers have conventionally applied Taguchi methods to optimize parameter design. However, Taguchi methods can only obtain the optimal solution among the specified control factor levels. They cannot identify the real optimum when the parameter values are continuous. This study proposes a hybrid procedure combining neural networks and scatter search to optimize the continuous parameter design problem. First, neural networks are used to simulate the relationship between the control factor values and corresponding responses. Second, scatter search is employed to obtain the optimal parameter settings. The desirability function is utilized to transform the multiple responses into a single response. A case with dynamic characteristics is carried out in blood glucose strip manufacturing in Taiwan to demonstrate the practicability of the proposed procedure.     

An approach to optimize block surgical schedules

We provide an approach to optimize a block surgical schedule (BSS) that adheres to the block scheduling policy, using a new type of newsvendor-based model. We assume that strategic decisions assign a specialty to each Operating Room (OR) day and deal with BSS decisions that assign sub-specialties to time blocks, determining block duration as well as sequence in each OR each day with the objective of minimizing the sum of expected lateness and earliness costs. Our newsvendor approach prescribes the optimal duration of each block and the best permutation, obtained by solving the sequential newsvendor problem, determines the optimal block sequence. We obtain closed-form solutions for the case in which surgery durations follow the normal distribution. Furthermore, we give a closed-form solution for optimal block duration with no-shows.     

A simulation architecture to support intratheater sealift operations

A new architecture for simulating intratheater sealift operations is presented. Intratheater sealift operations refer to new strategies proposed for quickly deploying a military force to a theater of war when major seaports are not available. In this strategy, a self-deployable force is transported to a sea-based intermediate staging base (SISB) by conventional cargo transport ships. The SISB is a world-class seaport generally located within 800 miles of the theater of war. At the SISB, cargo is transferred to a new ship platform called the theater support vessel (TSV). TSVs are to be designed to access very small ports located at or near the theater of war. Simulation provides an efficient and cost-effective method for testing these strategies and for evaluating the required new logistics technologies. Should intratheater sealift operations prove viable, the simulation also provides a means to plan and rehearse an exercise. The new simulation architecture is described and example simulation case studies are conducted to demonstrate the capabilities and potential benefits of the approach.     

Development of a three-echelon SC model to optimize coordination costs

The purpose of this study is to suggest a conceptual framework for aligning the strategic issues and the structural issues of supply chain management, and also to disclose the effect of E-business application on such an alignment. The number of suppliers, number of tiers, the level of SC integration, order penetration point, lead time, and safety stock are defined as supply chain structural issues, and the characteristics of traded products and buyer–supplier relationship are set as key strategic issues for efficient construction of supply chain structure. E-business application is designed as a moderate variable for the alignment between the strategic issues and the structural issues of supply chain management. Such effort suggests a conceptual framework required for developing an advisable set of E-business application strategies for the efficiency improvement of overall supply chain management. The empirical research model proposed in this work may be used to establish an E-supply chain progression paradigm and a new dimensional manufacturing strategy framework in the E-business era.     

An integer programming approach to optimize Housing Benefit data retrieval

This article presents an integer programming approach to a practical problem faced by analysts in the Department for Work and Pensions working with Housing Benefit (HB) data. It shows how, using a simple modification of the set covering problem, the time required to retrieve HB data from the data server can be significantly decreased. Computational comparisons with two alternative, suboptimal approaches are also presented.     

An agent-based simulation model to evaluate alternative co-payment scenarios for contributing to health systems financing

Ageing populations, rapid technological progress and recent public budget cuts currently threaten the sustainability of public health systems. To meet growing needs with declining resources, decision-makers must identify new ways to avoid reducing the quality of services offered to citizens. This paper focuses on the so-called “co-payment” tools aimed to obtain additional resources for the public health budget directly from citizens. Whereas certain forms of co-payments have always been introduced within health systems to prevent moral hazard behaviours, other co-payment mechanisms are explicitly intended to help finance public healthcare systems. Literature and empirical findings do not agree about the final impact of such co-payment tools, particularly whether they can attain system sustainability and guarantee equitably delivered services. In this paper, we develop an agent-based simulation model which can be used by decision-makers as a decision support tool to compare different co-payment rules and evaluate their impact on the public budget and the health expense of different groups of citizens.     

An improved reservoir simulation model in the petroleum industry

Sensible prediction of petroleum production from a well reliesheavily on the accurate determination of reservoir constantsduring pressure drawdown or build-up tests. Models for simulatinga fractured reservoir have been developed to accommodate theslope changes in the measured pressure curves. This paper presentsa modification to Barenblatt et al.s (1960) prototype, suitablefor the simulation of a fractured reservoir. The modificationis intended to provide an improved interpretation of fluid flowin fractured porous media, as compared to the traditional conceptualization.The significant differences in terms of reservoir pressure predictionbetween this model and the one suggested by Warren & Root(1963) are identified and shown to depend on the compressibilitymagnitudes of fractures and matrix blocks. The analytical solutionsof this improved model have been obtained for both the caseof radial flow with quasi-steady matrix flow, and for the caseof one-dimensional linear flow where transient matrix flow isretained.     

An improved dynamic subgrid-scale model and its application to large eddy simulation of stratified channel flows

In the present paper, a new dynamic subgrid-scale (SGS) model of turbulent stress and heat flux for stratified shear flow is proposed. Based on our calculated results of stratified channel flow, the dynamic subgrid-scale model developed in this paper is shown to be effective for large eddy simulation (LES) of stratified turbulent shear flows. The new SGS model is then applied to the LES of the stratified turbulent channel flow to investigate the coupled shear and buoyancy effects on the behavior of turbulent statistics, turbulent heat transfer and flow structures at different Richardson numbers.     

整数线性规划投资组合模型的直接搜索算法求解

利用松弛最优邻近解临域整数点搜索法作过滤条件,建立求解整数规划的新方法——直接搜索算法,利用直接搜索算法并借助Matlab软件求解整数线性规划投资组合模型.数值结果表明了模型的建立与提出方法的有效性.     

An improved constitutive model for the numerical simulation of semi-solid thixoforming

In order to model thixoforming processes, previous papers presented a thermomechanical one-phase modelling. This first version of the constitutive model revealed several limitations: the model could not degenerate properly to pure solid or liquid behavior nor to free solid suspensions. The aim of this paper was to propose solutions to overcome these limitations.     

An extended queueing control model for facilities with front room and back room operations and mixed-skilled workers

Three related problems arising in retail facilities with front room and back room operations, and cross-trained workers, are considered. In the first problem, the goal is to determine an optimal policy for switching workers between the two rooms. In the second and third problems, the goal is to determine the minimum number of workers that should be hired by the facility such that a satisfactory switching policy exists. We analyze two questions arising from previous work on these problems. Firstly, we demonstrate that the previously proposed policy definition is sub-optimal and cannot represent a set of solutions that are reasonable in practice, and propose an alternative definition. Secondly, we examine the problem of finding the optimal combination of cross-trained and specialized workers under a complete set of assumptions regarding worker costs. This analysis shows that the structure of the optimal solution depends on the policy definition that is employed. Moreover, under some assumptions the cost of the ‘optimal’ solution with the original policy definition will be greater than the cost of the optimal solution with the new one.     

An age-structured model for the spread of epidemic cholera: Analysis and simulation

Occasional outbreaks of cholera epidemics across the world demonstrate that the disease continues to pose a public health threat. Traditional models for the spread of infectious diseases are based on systems of ordinary differential equations. Since disease dynamics such as vaccine efficacy and the risk for contracting cholera depend on the age of the humans, an age-structured model offers additional insights and the possibility of studying the effects of treatment options. The model investigated is given as a system of hyperbolic (first-order) partial differential equations in combination with ordinary differential equations. First, using a representation from the method of characteristics and a fixed point argument, we prove the existence and uniqueness of a solution to our nonlinear system. Then we present a finite difference approximation to the model and study the effect of high and low rates of shedding of cholera vibrios on the dynamics of the spread of the disease. The simulations demonstrate the explosive nature of cholera outbreaks that is observed in reality. The contrast of results for high and low rates of shedding of vibrios suggest a possible underlying cause for this effect.     

An activated sludge model which considers toxicant concentration: simulation and sensitivity analysis

A mathematical model has been developed which describes organics removal, oxygen utilization, ammonia-nitrogen removal, ortho-phosphate removal and biomass production in an aggregated microbial suspension. The suspension considered is of uniform floc size containing organics as a soluble biodegradable material and toxicants. The model is applicable to both steady-state and transient conditions as well as to systems experiencing only carbon oxidation or both carbon oxidation and nitrification. It comprises five partial differential equations and four ordinary differential equations, and takes into account the flow pattern in the reactor; intraparticle mass transport of oxygen, organics, ammonia-nitrogen and orthophosphate; biochemical reactions by the individual cells embedded in the floc; and toxicity effects on cellular reactions. In developing the model it was assumed that a lack of either organics, oxygen, ammonia-nitrogen, ortho-phosphate or any combination of these nutrients could limit the overall rate of the process and that the presence of toxicants could also limit the rate of the process. A sensitivity analysis performed on this model indicated that the single most important factor in determining model output (based on the effluent organics concentration) is the retention time in the reactor. The second most important factor is the floc radius.