Makale Koleksiyonu | Endüstri Mühendisliği Bölümü / Department of Industrial Engineering
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Öğe The impact of the COVID-19 pandemic on online grocery supply chain management: a case study in Istanbul(Gazi Üniversitesi, 2024-03) Javadi, Sonya; Keten, Olcay; Özer, A. İhsan; Alkan, R. ZeynepThe COVID-19 pandemic has already crippled normal life all over the world. Its negative impact not only changed the human health system tragically but also disrupted the global economic system. One negative result was ended up in the global food supply chain. As the lockdown times have suspended the manufacturing and logistic activities, therefore, the customers have experienced unimaginable chaos in the shopping markets. Moreover, the purchasing habit of the consumers has remarkably changed compared to pre-pandemic. To meet this new demand pattern, many grocery retailers have tried to adapt to the new normal. While before COVID-19 offline grocery purchasing was popular, after the pandemic, online service got tremendous attention in market. In this study, online grocery supply chain management during the COVID-19 in Istanbul is considered. The aim is to find out how online grocery companies will serve more efficiently during the pandemics and which factors have more effect on the customer’s satisfaction. To do so, first, three popular grocery retailers in Istanbul were selected. Then, a related survey was designed to understand the consumer experience as doing online grocery shopping in COVID-19. Unsurprisingly, a result shows that 60% of the respondents did online shopping every 3-4 days in one week, and the delivery time is the most important factor for the customers. Then, the SWOT analyses were performed accordingly, and the related strategies were summarized. Finally, several managerial implications were given to may improve the company’s online services in COVID-19 and post COVID-19 in Turkey.Öğe Sustainability via extended warranty contracts: design for a consumer electronics retailer(MDPI, 2024-01) Aksezer, Sezgin ÇağlarWarranty is one of the most important attributes of any product, from both manufacturer and consumer points of view. Although the retailers connect manufacturers to customers by selling goods, traditionally, they have isolated themselves from warranty-related matters such as customer complaints and maintenance costs. However, recent trends in consumer behavior toward extended warranty contracts have changed this approach. While retailers have started to generate considerable revenue from the sale of these contracts, sustainability is also achieved by longer product life cycles. This study analyzed the failure behavior of different classes of cell phone products and their related costs through a chain of consumer electronics retailer operating in Türkiye. To compete on pricing and customer service, a novel policy was designed for the retailer to honor the contracts in house rather than underwriting to a third party insurer as the industry standard. The maintenance records of 328 previous failures were analyzed to plot a failure model. Failure mode and effects analysis was carried out to identify failure classes and the respective costs for extended warranty design for cell phones. The expected warranty costs for coverage of the third, fourth, and fifth years of operation were determined. The results show that the retailer may achieve the same level of profit by increasing customer satisfaction along with the sustainability of the product through repair actions.Öğe Cargo company recommendation study based on probabilistic linguistic term set(Bitlis Eren Üniversitesi, 2023-12-28) Çoban, Veysel; Aksezer, Sezgin ÇağlarThe global economic structure is the main reason for changes in consumption habits and consumer behavior. Developing information technologies direct producers and consumers to e-commerce. Cargo services are an important link in the chain in the fast and effective operation of e-commerce. The growth in e-commerce has a driving force in the development of cargo services and cargo companies. Cargo companies can survive in global competition by being preferred by customers and increasing their number of customers. The change in the number of customers occurs by communicating the satisfaction or dissatisfaction with the cargo company to potential customers. This study deals with the preference levels of cargo companies serving in Turkey according to customer suggestions. The data obtained from the survey evaluations are processed and recommendation ranking calculations are made for cargo companies. Probabilistic Linguistic Term Sets (PLTS) are used to eliminate customer ambiguities in survey evaluations. Alternative cargo company recommendations are ranked based on the customers' past service experiences from cargo companies. Aras Cargo, MNG Cargo, PTT Cargo, Surat Cargo, UPS Cargo, Yurtiçi Cargo companies are evaluated according to price, personnel, speed, reliability and network attributes. The maximum deviation optimization method based on the Lagrangian function is used to calculate the weights of the cargo companies' attributes. The probabilistic linguistic cosine similarity method compares cargo companies pairwise under attributes and a similarity matrix is obtained for six cargo companies. The similarity matrix defines the alternative cargo company recommendation ranking based on customers' past experiences. UPS, SURAT and MNG cargo companies stand out as the most prioritized companies according to the evaluation results. The effects of attribute weights are observed by designing six different scenarios and it is observed that the differentiating attribute weights affect the recommendation ranking. Spearman correlation coefficient evaluation based on recommendation rankings indicates a high relationship between attributes.Öğe On computing the multivariate poisson probability distribution(Springer, 2023-06-20) Çekyay, Bora; Frenk, Johannes Bartholomeus Gerardus; Javadi, SonyaWithin the theory of non-negative integer valued multivariate infinitely divisible distributions, the multivariate Poisson distribution plays a key role. As in the univariate case, any non-negative integer valued infinitely divisible multivariate distribution can be approximated by a multivariate distribution belonging to the compound Poisson family. The multivariate Poisson distribution is an important member of this family. In recent years, the multivariate Poisson distributions also has gained practical importance, since they serve as models to describe counting data having a positive covariance structure. However, due to the computational complexity of computing the multivariate Poisson probability mass function (pmf) and its corresponding cumulative distribution function (cdf), their use within these counting models is limited. Since most of the theoretical properties of the multivariate Poisson probability distribution seem already to be known, the main focus of this paper is on proposing more efficient algorithms to compute this pmf. Using a well known property of a Poisson multivariate distributed random vector, we propose in this paper a direct approach to calculate this pmf based on finding all solutions of a system of linear Diophantine equations. This new approach complements an already existing procedure depending on the use of recurrence relations existing for the pmf. We compare our new approach with this already existing approach applied to a slightly different set of recurrence relations which are easier to evaluate. A proof of this new set of recurrence relations is also given. As a result, several algorithms are proposed where some of them are based on the new approach and some use the recurrence relations. To test these algorithms, we provide an extensive analysis in the computational section. Based on the experiments in this section, we conclude that the approach finding all solutions of a set of linear Diophantine equations is computationally more efficient than the approach using the recurrence relations to evaluate the pmf of a multivariate Poisson distributed random vector.Öğe Elections and stock market returns: evidence from Borsa Istanbul(Marmara Üniversitesi, 2023-06-22) Kayaçetin, Nuri VolkanStock prices may display predictable patterns around major political events, particularly in emerging market economies where political risk is a key component of asset risk premiums. One distinct event that would be expected to result in an abrupt increase in political risk is elections. Motivated by this notion, we study the returns for a set of indicator and sectoral indices of Borsa Istanbul stocks and the U.S. Dollar–Turkish Lira exchange rate around political elections held in Turkey over 2001–2020. Our tests reveal an accumulation of economically and statistically significant positive abnormal returns for all Borsa Istanbul stock indices and negative abnormal returns for the U.S. Dollar–Turkish Lira exchange rate over a window that starts as early as a month before the election date and extends for two weeks into the post-election period, with the effect being particularly strong in the week that immediately follows the election. Consistent with a political risk-based story, volatility of index returns starts increasing over the same period and plateaus out at a level that is roughly one-and-a-half to two-folds greater than its pre-election period average.
