یک مدل بهینه سازی مبتنی بر نظریه نمونه کارها برای استراتژی خرید بخار ذغال سنگ: مطالعه موردی شرکت برق تایوان  A portfolio theory based optimization model for steam coal purchasing strategy: A case study of Taiwan  Power Company

1. Introduction As the globalization of business activities accelerated, today’s supply chains span the globe with unprecedented complexities and uncertainties. These complexities and uncertainties not only increase risk, but also reduce visibility that, in turn, makes supply chain operations more vulnerable to unforeseen disruptions. Re- flecting growing concerns over supply chain disruptions, supply chain risk management (SCRM) has become an emerging research topic (Altay and Ramirez, 2010; Ellis et al., 2011; Manuj and Mentzer, 2008a, 2008b; Revilla and Sáenz, 2014; Schoenherr et al., 2012; Son and Orchard, 2013; Tang, 2006a; Whitney et al., 2014; Zsidisin and Wagner, 2010). One of the central themes of past SCRM research includes the definition and categorization of supply chain risks and identification of their sources. For instance, borrowing from investment portfolio concepts, Rao and Goldsby (2009) defined supply chain risk in two ways: First, risk is considered the manifestation of uncontrollability that may result in either positive or negative outcome. Second, risk refers to a form of negative outcomes that adversely affect organizational performance. Altay and Ramirez (2010) investigated how natural disaster such as earthquake, windstorms, floods, and fires affected firms in different business sectors. They observed that firms did not take disaster disruption management seriously due to their perceived low probability of disaster occurrence, despite the fact that natural disaster actually affected firm performances. Considering the potential connection between the firm’s perceived risk and risk mitigation actions, Ellis et al. (2011) identified individual, organizational, and environmental factors that affected the formation of risk perception and mitigation actions. Despite a variety of risk factors (sources) and their level of importance to mitigation actions, Revilla and Sáenz (2014) found the level of disruption management implementation to be universal all across the world. More recently, Ambulkar et al. (2015) identified three antecedents for enhancing the firm’s resilience to supply chain disruptions: (1) supply chain disruption orientation; (2) resource reconfiguration capabilities and (3) firm’s risk management infrastructure. They found that supply chain disruption affected the firm’s resilience level differently depending upon the firm’s resource configuration and risk management infrastructure. Focusing on the effectiveness of risk mitigation actions rather than the identification of risk sources, Whitney et al. (2014) noticed that multiple sourcing was often used as a temporary hedge to reduce supply chain disruption risks. However, they found that temporary multiple sourcing turned out to be ineffective in dealing with supply chain disruption, if product design and manufacturing methods for the disrupted items were complex. Supporting this finding, Bode and Wagner (2015) showed that horizontal, vertical, and spatial supply chain complexities increased the frequency of supply chain disruption and thus made a temporary hedge less efficient. In the presence of various supply chain risks illustrated above, this paper aims to develop risk mitigation action plans that help firms better control such risks, while assessing the impact of supply chain security and safety stock practices on supply chain disruption occurrence based on the empirical study. In particular, drawing upon the contingency theory, this paper introduces firm’s risk taking propensity as an antecedent, which may reflect the firm’s risk management behavior, proposes security compliance and safety stock plans, and identifies various types of supply chain disruption occurrence.