Parallel machine replacement under horizon uncertainty

Construction projects usually get delayed for several time periods. When the planning horizon of a project is extended, projections for purchase and salvage of machinery within the planning horizon become inaccurate and less beneficial and often lead to unexpected costs. In this article, we formulate a parallel machine replacement (PMR) problem as a two-stage stochastic program with an uncertain planning horizon. We consider renting as an alternative to purchasing and maintaining the machinery. We show the application of the model through a case study in construction projects. Through numerical analysis, we derive managerial implications and show the value of the stochastic model.     

On model selection in Bayesian regression

We discuss the problem of constructing a suitable regression model from a nonparametric Bayesian viewpoint. For this purpose, we consider the case when the error terms have symmetric and unimodal densities. By the Khintchine and Shepp theorem, the density of response variable can be written as a scale mixture of uniform densities. The mixing distribution is assumed to have a Dirichlet process prior. We further consider appropriate prior distributions for other parameters as the components of the predictive device. Among the possible submodels, we select the one which has the highest posterior probability. An example is given to illustrate the approach.     

Neyman–Pearson Lemma for Fuzzy Hypotheses Testing with Vague Data

In hypotheses testing, such as other statistical problems, we may confront imprecise concepts. One case is a situation in which both hypotheses and observations are imprecise. This paper tries to develop a new approach for testing fuzzy hypothesis when the available data are fuzzy, too. First, some definitions are provided, such as: fuzzy sample space, fuzzy-valued random sample, and fuzzy-valued random variable. Then, the problem of fuzzy hypothesis testing with vague data is formulated. Finally, we state and prove a generalized Neyman–Pearson Lemma for such problem. The proposed approach is illustrated by some numerical examples.     

The Emergence of Iran in the World Car Industry: An Estimation of its Export Potential

In the past 10 years Iran has been emerging as a major car producer in the world. However, due to delays in economic reforms, Iranian car exports have not increased as much as production. This paper presents a first estimation of the Iranian export potential in the car industry. Based on new theoretical developments of the gravity equation, an empirical bilateral trade model is proposed. It includes sectoral variables (car production, import tariffs), as well as other original variables, such as expectations and hysteresis. We then develop a dataset which includes the 40 major car‐exporting countries in the world, 34 importing countries, a 10‐year time period as well as four car production groups. The model is then estimated by using alternative panel data estimators, such as those of Hausman and Taylor and dynamic estimators as well as transformed variables estimators. Export potential is finally calculated from the residuals of the model. Results show that Iranian current car exports are about 100 times less than their fitted values. This indicates that there is a significant export potential for Iran, especially toward India, China, Russia, as well as smaller neighbours (Turkey, Pakistan, Central Asian countries). As a result, Iran could become the major auto supplier in the Middle East. However, this requires the completion and success of ongoing economic reforms.     

A production rate control policy for stochastic repair and remanufacturing systems

We consider the control of a manufacturing system responding to planned demand at the end of the expected life of each individual piece of equipment and unplanned demand triggered by a major equipment failure. The difficulty of controlling this type of production system resides in the variable nature of the remanufacturing process. In practice, remanufacturing operations for planned demand can be executed at different rates, referring to different component replacement and repair strategies. We formulate this problem as a multi-level control problem and propose a suboptimal control policy. The proposed control policy is described by inventory thresholds triggering the use of different execution modes. Determination of the control policy parameters is based on parameter optimization of analytical cost expressions. A numerical example based on a real case is presented. Our analysis demonstrates that the use of the proposed control approach can lead to a significant reduction in the total average cost, as compared to current practices.     

The dilemma of cheap food and self-sufficiency: The case of wheat in Iran

Self-sufficiency in wheat has been one of the major goals of Iranian agricultural policies since the Revolution of 1979. Even so, the country failed to achieve this goal by the early 2000s, despite a satisfactory growth in wheat production. This paper addresses this failure and the political difficulties in introducing reforms that would reduce the need for import. First, the production and consumption of wheat are examined. The conclusion is that the cheap-bread policy has mainly been responsible for the imbalances between domestic supply and demand, and the continued reliance on wheat imports. Moreover, the paper argues that the subsidy program is an expensive safety net for the needy and shows that the Iranian government has intended to reform the program since the early 1990s. However, subsidy reforms are politically sensitive, especially in developing countries where subsidies are considered very important, both for supporting the poor and for political stability. An analysis of the Iranian attempts at subsidy reform suggests that they have not yet succeeded, mainly due to such political considerations.     

Using Space Syntax to Assess the Built Environment for Physical Activity: Applications to Research on Parks and Public Open Spaces

The application of space syntax as a method for examining the role of spatial configuration on people's behavior has been widespread in several disciplines, such as urban design and architecture. However, the ideas and procedures of space syntax have rarely been applied in studies within the field of public health or leisure studies. This article briefly introduces the principles of space syntax and describes how space syntax can extend previous knowledge regarding associations between the built environment and physical activity with specific applications to research on parks and public open spaces.     

A study of economic efficiency of Iranian farmers in Ramjerd district: an application of stochastic programming

An extension of utility-efficient programming to the non-linear discrete stochastic programming method was developed and used in the analysis of the economic efficiency of a sample of farmers in Iran. The results indicate that it would be feasible to increase substantially farmers' total net revenue by increasing their economic efficiency in terms of technical and allocative efficiencies. The study further suggested that risk aversion plays an important role in farmers' behaviour. The sample farmers are risk averse and hence are likely to trade higher expected profits for lower risk. Understanding this characteristic is important for interventions intended to raise farm productivity and efficiency.     

Fuzzy Development of Multiple Response Optimization

This paper proposes a developed approach to Multiple Response Optimization (MRO) in two categories; responses without replicates and with some replicates based on fuzzy concepts. At first, the problem without any replicate in responses is investigated, and a fuzzy Decision Support System (DSS) is proposed based on Fuzzy Inference System (FIS) for MRO. The proposed methodology provides a fuzzy approach considering uncertainty in decision making environment. After calculating desirability of each response, total desirability of each experiment is measured by using values of each response desirability, applying membership function and fuzzy rules expressed by experts. Then Response Surface Methodology (RSM) is applied to fit a regression model between total desirability and controllable factors and optimize them. Next, a methodology is proposed for MRO with some replicates in responses which optimizes mean and variance simultaneously by applying fuzzy concepts. After introducing Deviation function based on robustness concept and using desirability function, a two objective problem is constituted. At last, a fuzzy programming is expressed to solve the problem applying degree of satisfaction from each objective. Then the problem is converted to a single objective model with the goals of increasing desirability and robustness simultaneously. The obtained optimum factor levels are fuzzy numbers so that a bigger satisfactory region could be provided. Finally, two numerical examples are expressed to illustrate the proposed methodologies for multiple responses without replicates and with some replicates.     

An Objective and Task Media Selection Decision Model and Advertising Cost Formula to Determine International Advertising Budgets

Abstract

A company needs to estimate the cost of media plans and advertising upon introducing a new or existing product into an unfamiliar environment such as a new international market. This article presents a conceptual framework for making media decisions and a method for estimating the cost of advertising in international markets. The objective and task method is used to build a working model in order to articulate the necessary steps leading to informed media decisions for budgeting an international advertising campaign. Methods of estimating product demand and a flow model for media selection are also presented.