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In the face of budgetary limitations in organizations, identifying critical facilities for investing in quality improvement plans could be a sensible approach. In this paper, hierarchical facilities with specified covering radius are considered. If disruption happens to a facility, its covering radius will be decreased. For this problem, a bi-objective mathematical formulation is proposed. Critical facilities are equivalent to the facilities which attacking them causes the most reduction in the quality of the system performance. Consequently, this problem is studied in the interdiction problem framework. To solve the multi-objective model the weighting-sum approaches are applied. The first interdictor's objective function helps decision makers to identify the vulnerability of the system. Moreover, the second objective function may assist in minimizing the cost of applied quality improvement plans.

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The hub location problems (HLP) constitute an important class of facility location problems that have been addressed by numerous operations researchers in recent years. HLP is a strategic problem frequently encountered in designing logistics and transportation networks. Here, we address the competitive multiple allocation HLP in a duopoly market. It is assumed that an incumbent firm (the leader) is operating an existing hub network in a market and an entrant firm (the follower) tries to enter the market by locating its own hubs aiming at capturing as much flow as possible from the leader. The customers choose one firm based on the service level (cost, time, distance, etc.) provided by the firm. We formulate the problem from the entrant firm’s point of view and propose an efficient tabu search based solution algorithm to solve it. Computational experiments show the capability of the proposed solution algorithm to obtain the optimal solutions in short computing times.

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In this paper we describe the formal Lagrange-technique to optimize the production process of solid state crystals from a mixture crystal melt. After the construction of the adjoint equation system of the Boussinesq equation of the crystal melt the forward and backward problems (KKT-system) are discretized by a conservative finite volume method.

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The purpose of the present study was to determine the effect of education using mathematical games on learning and retention of third grade elementary students. This research in terms of purpose was conducted as an applied research. Also in terms of implementation and data collection method, the quasi-experimental method and pre-test-post-test design with a control group was used. The statistical population of the present study included all 6,500 female third grade elementary school students in District 1 of Mashhad- Iran. The sampling method in this study was in convenience form that included 60 students and were selected through convenience sampling method, thus two classes with 30 female students for each classroom were selected among the elementary girls' schools in District 1 of Mashhad- Iran. In order to collect data, two researcher-made tests of learning and retention were used, the validity of which was confirmed by experts and its reliability was calculated based on Cronbach's alpha equal to 0.81 and 0.83, respectively. Multivariate analysis of covariance (MANCOVA) was used in order to test the hypotheses inferential analysis. The results of data analysis showed that math games are effective on students math both learning and retention (P <0.01). Therefore, it can be concluded that education using math games is effective and has increased students' learning and retention.
 

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Abstract: This study developed a mathematical programming model in order to consider an SCND problem. In this model, the operational and financial decisions are simultaneously considered to design a supply chain network. It also paves the way for opening or closing facilities in order to adapt to fluctuations at market. Furthermore, an accounts payable policy is provided for the company managers because bank loans, liability repayment and new capital from shareholders are considered as decision variables in this model. The economic value added (EVA) index was also used besides the common operational objectives and constraints in order that the financial performance of supply chain and lower and / or upper limit value for financial rations to be measured. To demonstrate the efficiency of the proposed model, a test problem from the recent literature is used. And also, sensitivity analyses to evaluate the results are provided to obtain better insight and access to different aspects of the problem. The results illustrate that with appropriate financial decisions, creating more value for the company and its shareholders is achievable since the total created value by the proposed model with a new financial approach is able to improve the total created shareholder value as much as 21.05% and convince the decision-makers to apply it as an effective decision tool.