The emergence of multi-layer networking capabilities opens the path for the development of advanced network architectures and resilience concepts. In this dissertation we propose a novel resource-efficient homing sche...
详细信息
The emergence of multi-layer networking capabilities opens the path for the development of advanced network architectures and resilience concepts. In this dissertation we propose a novel resource-efficient homing scheme: dual homing with shared backup router resources. The proposed scheme realizes shared router-level redundancy, enabled by the emergence of control plane architectures such as generalized multi-protocol label switching. Additionally, virtualization schemes complement the proposed architecture. Different homing architectures are examined and compared under the prism of cost, availability, recovery time and energy efficiency. Multiple network layers are considered in Internet protocol over wavelength divi- sion multiplexing as well as Internet protocol over optical data unit settings - leading to the development of multi-layer optimization techniques. A generic multi-layer network design mathematical model, which can be applied to dif- ferent homing architecture considerations, is developed. The optimization objective can be adapted to either minimizing the cost for network equipment or the power consumption of the network. In order to address potential issues with regard to computational complexity, we develop a novel heuristic approach specifically targeting the proposed architecture. It is shown that significant cost savings can be achieved - even under extreme changes in the traffic demand volume, in the cost for different types of network equipment, as well as in the network topology characteristics. In order to evaluate occurring tradeoffs in terms of performance, we study the effects on availability and recovery time. We proceed to derive lower bounds on end-to-end availability for the different homing architectures. Additionally, an analytical recovery time model is developed and evaluated. We investigate how service-imposed maximum outage requirements have a direct effect on the setting of the proposed architecture.
This paper presents dynamic strategies for the integrated scheduling and runway assignment of both arrival and departure traffic over an airport. While a static scheduling scheme handles traffic over a specified plann...
详细信息
This paper presents dynamic strategies for the integrated scheduling and runway assignment of both arrival and departure traffic over an airport. While a static scheduling scheme handles traffic over a specified planning horizon simultaneously, sequential dynamic schedulers divide the planning horizon into a series of smaller scheduling windows and apply a static scheduling scheme sequentially over each window. Dynamic scheduling strategies are desirable for obtaining real-time solutions of continual traffic streams and for taking advantage of updated traffic information. In this paper, a multiple-point scheduling framework is used in which scheduling locations include runway thresholds as well as fixes over the terminal airspace and gates on the airport surface. Integrated static scheduling of both arrival and departure traffic is formulated as mixed-integerlinearprogramming. Solution variables include scheduled times of arrival at the multiple scheduling locations and aircraft sequences at merge points. Aircraft route assignments for both ground and airborne traffic are also included as discrete solution variables, from which optimal runway assignments can be determined. Then, different dynamic strategies with either overlapping or nonoverlapping scheduling windows are developed and compared. Induced constraints for ensuring sufficient separations among traffic in neighboring windows are discussed. The John F. Kennedy International Airport is used as the example in extensive numerical solutions to evaluate the computational speeds and scheduling performances of different dynamic strategies.
The multi-period multi-product (MPMP) production planning problems, generally, deal with matching production levels of individual products with fluctuated demands over planning horizon. The conventional MPMP optimisat...
详细信息
The multi-period multi-product (MPMP) production planning problems, generally, deal with matching production levels of individual products with fluctuated demands over planning horizon. The conventional MPMP optimisation models suffer from insufficient utilisation of available capacity of machines. This fallacy is due to inappropriate formulation of machine capacity and material handling constraints. In this study, a novel mathematical model is proposed to simultaneously optimise production quantities and provide information about managerial decisions such as subcontracting, carrying inventory/backordering, and also hiring/layoff personnel. The problem is then formulated as a mixed integer linear programming (MILP) model by applying appropriate linearisation of non-linear components. The objective is to minimise production costs comprising of production, storage, shortage, subcontracting costs and costs associated with hiring/dismissing labourers. Superiority of the proposed model over existing ones, has been initially evaluated by solving the case presented by Byrne and Bakir [Byrne, M. D. and Bakir, M. A., 1999. Production planning using a hybrid simulation-analytical approach. International Journal of Production Economics, 59 (1), 305-311], and then evaluated by comparing the results obtained from solving both the proposed and the conventional MPMP production planning models using a 100-randomly-generated-test-problem.
During the last decades there has been a consistent need for companies to manufacture 'green' products in order to contribute to environmental protection. The utilisation of used products (literally, the exten...
详细信息
During the last decades there has been a consistent need for companies to manufacture 'green' products in order to contribute to environmental protection. The utilisation of used products (literally, the extension of their useful life cycle) is an excellent, indirect way for companies to conform to this requirement and, at the same time, increase their profit. In this paper a mixed integer linear programming mathematical model is proposed, which can be used for the optimisation of procurement, remanufacturing, stocking and salvaging decisions. The model is flexible enough to incorporate multiple suppliers, several quality levels of returned products and multiple periods of time. The applicability of the model is demonstrated through the optimisation of alternative scenarios, the optimal solutions of which reveal the potential profitability of used products exploitation.
In this paper, the flexible flow shop sequence-dependent group scheduling problem (FFSDGS) with minimisation of makespan as the criterion (FFm vertical bar fmls, S-plk vertical bar C-max) is investigated. For the firs...
详细信息
In this paper, the flexible flow shop sequence-dependent group scheduling problem (FFSDGS) with minimisation of makespan as the criterion (FFm vertical bar fmls, S-plk vertical bar C-max) is investigated. For the first time a mathematical model for the proposed research problem is developed. Since the problem is shown to be NP-hard, six metaheuristic algorithms based on tabu search (TS) are developed to efficiently solve the problem. The proposed metaheuristics are different to the only available metaheuristic algorithm in the literature based on TS. By applying randomised complete block design and using available test problems in the literature, the best of the proposed TS algorithms in this research is identified. The performance of the best developed metaheuristic algorithm is then compared with the existing algorithm in the literature by solving the test problems, also available in the literature, ranging in size from small, medium, to large. A comparison based on paired t-test at 95% confidence interval, shows that the best proposed algorithm in this research has a better performance than the existing algorithm in the literature with an average percentage deviation of around 1.0% for medium and large size problems.
Many authors consider that production and marketing decisions should be integrated. In this paper, we discuss an aggregate planning problem that includes production, selling price, cash management and flexible capacit...
详细信息
Many authors consider that production and marketing decisions should be integrated. In this paper, we discuss an aggregate planning problem that includes production, selling price, cash management and flexible capacity (by means of hiring and firing and with the possibility of unlimited production subcontracting). The demand is considered to be a nonlinear function of the product selling price. The problem, which is modelled as a mixedintegerlinear program, can be solved using standard optimisation software. The results of a computational experiment and a numerical example are shown to illustrate the performance of the proposed model and obtain some managerial insights.
The problem we study in this paper arises from the washing step of hospital sterilisation services. Washers in the washing step are capable of handling more than one medical device set as long as their capacity is not...
详细信息
The problem we study in this paper arises from the washing step of hospital sterilisation services. Washers in the washing step are capable of handling more than one medical device set as long as their capacity is not exceeded. The medical device set sizes and arrival times to the sterilisation service may be different, but they all have the same washing duration. Thus, we model the washing step as a batch scheduling problem where medical device sets are treated as jobs with non-identical sizes and release dates, but equal processing times. The main findings we present in this paper are the following. First, we study two special cases for which polynomial algorithms are presented. We then develop a 2-approximation algorithm for the general problem. Finally, we develop a MILP model and compare it with another MILP model from the literature. Computational results show that our MILP model outperforms the model from the literature.
Pyruvate kinase-deficient Escherichia coli (PB25) is a low by-product-producing yet fast-growing mutant that has been shown to have technological potential. Determining the flux limits through finding the extreme poin...
详细信息
Pyruvate kinase-deficient Escherichia coli (PB25) is a low by-product-producing yet fast-growing mutant that has been shown to have technological potential. Determining the flux limits through finding the extreme point flux sets was previously reported to identify alternate metabolite trafficking scenarios. Previously, the extreme point flux sets were used to design tracer experiments;however, variation in extracellular measurements was not considered, and reaction reversibility was assumed to be low to moderate. In this study, we examined the utility of limiting the fluxes and predetermining the trafficking scenarios in PB25, including confirmation of quasi-linearity between extreme points to ensure sensitivity is maintained. The effects of variation in extracellular measurements and reaction reversibilities were also examined. Tightened flux limits reduced the nonlinearity between label distribution and fluxes. For low to moderate reversibility, contrast was also preserved. However, for highly reversible phosphoglucoisomerase activity, information from common analytes could lead to a flux solution that is biased towards one extreme point. Based on the PB25 model, some suggestions are provided for how predetermining flux limits and trafficking scenarios could enable flux identification in larger network problems.
This paper focuses on the flow shop sequence dependent group scheduling (FSDGS) problem with minimisation of total completion time as the criterion (Fm|f(mls), prmu, S-plk|Sigma C-j). The research problem is formulate...
详细信息
This paper focuses on the flow shop sequence dependent group scheduling (FSDGS) problem with minimisation of total completion time as the criterion (Fm|f(mls), prmu, S-plk|Sigma C-j). The research problem is formulated in form of two different mixed integer linear programming (MILP) models. Comparing with the latest MILP model for the proposed problem in the literature, the complexity size of the proposed models are significantly reduced. One of the proposed mathematical models is so effective that even medium-sized instances (problems up to 60 jobs in all groups) are solved to optimality in a reasonable amount of time. Moreover, a metaheuristic hybridising genetic and simulated annealing algorithm, called GSA, is proposed to solve the problems heuristically. All the results and analyses show the high performance of the proposed mathematical models as well as the proposed metaheuristic algorithm compared to the available ones in literature.
In the paper Li et al. [A robust branch-and-cut approach for the minimum-energy symmetric network connectivity problem. Omega 2012;40:210-7] it is claimed that a theoretical result appeared in Montemanni and Gambardel...
详细信息
In the paper Li et al. [A robust branch-and-cut approach for the minimum-energy symmetric network connectivity problem. Omega 2012;40:210-7] it is claimed that a theoretical result appeared in Montemanni and Gambardella [Exact algorithms for the minimum power symmetric connectivity problem in wireless networks. Computers and Operations Research 2005;32:2891-904] is wrong. In this note we show that the original result is correct, and that the counter-example used to prove the wrongness of the original result is incorrect. (C) 2012 Elsevier Ltd. All rights reserved.
暂无评论