A weighted max-min model for fuzzy multi-objective supplier selection in a supply chain

Supplier selection is one of the most important activities of purchasing departments. This importance is increased even more by new strategies in a supply chain. Supplier selection is a multi-criteria decision making problem in which criteria have different relative importance. In practice, for supplier selection problems, many input information are not known precisely. The fuzzy set theories can be employed due to the presence of vagueness and imprecision of information. A weighted max-min fuzzy model is developed to handle effectively the vagueness of input data and different weights of criteria in this problem. Due to this model, the achievement level of objective functions matches the relative importance of the objective functions. In this paper, an analytic hierarchy process (AHP) is used to determine the weights of criteria. The proposed model can help the decision maker (DM) to find out the appropriate order to each supplier, and allows the purchasing manager(s) to manage supply chain performance on cost, quality and service. The model is explained by an illustrative example.     

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.     

Inequality and growth in the United States: is there asymmetric response at the state level?

A previous study that tried to assess the impact of economic growth on income inequality in the U.S. used state-level data and an ARDL panel model to conclude that economic growth worsens income inequality in the U.S. In this article, we use the same data set but an ARDL time-series model applied to each state in the U.S. to show that the above conclusion is only valid in 20 states. Additionally, we use a nonlinear ARDL approach to show that the effects are asymmetric in the short run as well as in the long run. Significant long-run asymmetric effects reveal that in 28 states both an increase and a decrease in real output have worsened income distribution.     

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.