Browsing by Author "Gulsen, Mehmet"

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An Algorithmic Approach To Portfolio Construction: A Turkish Stock Market Case
(BORSA ISTANBUL REVIEW, 2024-11) Gulsen, Mehmet; Yildiz, Burak
The goal of building a diversified portfolio is to mitigate risks and manage risk-reward tradeoffs. Diversification is also crucial for ensuring the long-term success of a portfolio. Although passive investment has been on the rise in most developed markets, it has not gained wider acceptance in some emerging markets, such as T & uuml;rkiye. This study proposes an approach to construct a diversified portfolio that serves as a passive investment tool in the context of the Turkish stock market. Despite the long history of equity markets in T & uuml;rkiye, almost all available passive investment alternatives are prohibitively expensive, unlike those in developed markets. We design a simple methodology that addresses the essential components of building a successful portfolio while avoiding excessive fees. Additionally, we propose a dynamic balancing strategy that algorithmically adjusts the weight of each stock in the portfolio. We test this approach with historical data, demonstrating that it can achieve reasonable returns with minimal effort. Even when its performance does not beat the benchmark, the percentage deviation is still below the management fees charged for alternative investments.
Application of Cellular Manufacturing and Simulation Approaches for Performance Improvement in an Aerospace Company's Manufacturing Activities
(2019) Ic, Yusuf Tansel; Yurdakul, Mustafa; Gulsen, Mehmet; Dalcan, Gizem; Kirdar, Didem; Kale, Meric; Altinkaya, Zeynep; Aktas, Dogukan; https://orcid.org/0000-0001-9274-7467; AGE-3003-2022
This paper presents performance improvement studies performed in manufacturing activities of an aerospace company. Cellular Manufacturing (CM) and simulation approaches are used to improve performance in the factory of the company. In the application of CM, reorganization of machines in the machining section as manufacturing cells is performed by using Rank Order Clustering (ROC) algorithm and Hollier method. The performance improvement provided by CM application is measured in terms of the total material handling distances travelled by the parts. On the other hand, a simulation model in SIMAN is developed for panel production section of the factory. Based on the performance outputs of the simulation model, various recommendations are proposed in the operation rules and numbers of resources in the panel production section. The results show that both approaches provide considerable performance improvement in the manufacturing activities of the factory.
Decomposition Based Extended Project Scheduling for Make-To-Order Productiona
(2021) Turkgenci, Arda; Guden, Huseyin; Gulsen, Mehmet
Project scheduling has a critical function for many companies. Although there is a vast literature dedicated to the development of solution methodologies, the real-life applications of those techniques are few and often require over-simplification of the real-life problem. This study deals with the implementation of a project scheduling routine for a "make-to-order" machinery manufacturer. Although the problem is very similar to a resource-constrained project scheduling problem (RCPSP), which is a well-known and well-studied problem in the literature, it has multi-project and multi-mode components which make the project planning more challenging. Because of the multi-dimensional complexity of the problem, it is called a "Rich Project Scheduling Problem". Our approach employs two techniques to deal with the issue of complexity. The first one is regarding calculation of the latest start time for each activity in the project. The second one is the decomposition method that includes breaking down the big problem into small manageable pieces. The approach was tested on real-life problems of a machine-building company. We also built more complex test cases from the real projects for testing purposes. Our approach produced high-quality solutions to the complex project scheduling problems within reasonable time limits. This work contributes to current research in several ways. An extension to the RCPSP formulation to include multi-project and multi-mode problems is introduced and successfully used for solving real-life problems. Additionally, activities of an RCPSP can be split into multiple sub-activities. Doing so is called preemption. The proposed formulation permits mode-switching during the execution of an activity, and it uses an alternative methodology to calculate latest activity start times.
Double-row facility layout with replicate machines and split flows
(2019) Gulsen, Mehmet; Murray, Chase C.; Smith, Alice E.
This paper presents a new variant of the double row layout problem (DRLP) that features types of capacitated machines. This variant dramatically improves the fidelity with which the DRLP represents the complex production alternatives in many production environments, especially in the microcomputer industry. The problem consists of placing different classes of machines, each with multiple replicates, on either side of a central aisle. This is a common type of layout problem observed in many production and service environments. This work extends the DRLP literature by utilizing machine replicates in the layout. Multiple replicates of the same machine allow the product flow to split into multiple branches, each representing a parallel flow line. Flow splitting can improve machine utilization and reduces the number of machines needed. We also introduce machine sharing, which lets different products use the same machine. This eliminates the need for dedicated assignments of products to machines, which is a common assumption in the current literature. The consideration of re-entrant product flow, whereby each product can visit the same machine multiple times, represents another unique aspect of this research. The problem is formulated as a nonlinear mixed integer program. Due to the computational complexity of this problem a hierarchical optimization approach is developed and evaluated on test problems of various sizes. Computational results show that the proposed method produces consistent and high quality solutions across problem sizes. (C) 2019 Elsevier Ltd. All rights reserved.
The effect of combined preconditioning strategies on isokinetic strength in well trained kickboxers
(2018) Yilmaz, Atakan; Gurses, V.V.; Gulsen, Mehmet; 0000-0002-8826-8524
Purpose: The use of preconditioning strategies (PconSt) alone has a positive impact on performance. However, it is thought that there will be more impact on the performance of the combined preconditioning strategies, and this is the first work to prove it. This study was to examine the effect of combined preconditioning strategies on isokinetic strength in well-trained kickboxers. Material: The following preconditioning strategies were combined: morning resistance exercise (MRE), ischemic preconditioning (IP), active warm-up (AW-U), hormonal preconditioning (HP) and post-activation potentiation (PAP). Fifteen well-trained male kickboxers (age: 22.38 +/- 4.01years, height: 182.23 +/- 1.05cm, body mass: 77.67 +/- 8.01kg) volunteered for this study. Peak isokinetic knee extension and flexion moment were determined at 60 degrees/s, 180 degrees/s and 240 degrees/s bilaterally. All participants performed the pre-test and then were randomly divided into Sham and PconSt groups on separate days. For the PconSt group, MRE, IP, AW-U, HP and PAP were implemented sequentially before test. Results: The findings indicated significant increase in strength after combined training in the PconSt groups for right leg flexion at 180 degrees/s flexion (p < 0.05). The average percentage strength difference between sham and PconSt groups was 4.12 +/- 8.95%. Conclusions: This study showed that a combined preconditioning strategy increased isokinetic strength.
Incorporating Bill of Materials in Bottom-Up Demand Forecasting
(2018) Gulsen, Mehmet
In a manufacturing environment, the final product includes sub-assemblies and elementary parts that are put together hierarchically. By using hierarchy information in the bill of materials (BOM), demand forecasts for sub-assemblies and elementary parts can be generated from the final product. If an elementary part is used in multiple products, there will be several forecasts for the same part. The volatility of the aggregate forecast is expected to be higher as each product has its own independent demand pattern. An alternative approach is to reverse the process: first aggregate the historical data, then generate the forecasts. Hierarchical information from the bill of materials can be used for aggregation.
Smart Water Metering Implementation For The City Of Ankara
(2021) Gulsen, Mehmet; Barutcu, Burcu
Freshwater scarcity in urban centers is a major concern for municipalities. Expanding urbanization and increasing population place pressure on limited resources. Water conservation and effective water use seem to be the only feasible route to avoid impending water crises. This study analyzes water prospects for the city of Ankara. The current situation is evaluated, and issues related to water shortage are discussed. An action plan that focuses on conservation and efficient use of existing resources is presented. The installation of a smart metering system that started in 2019 is also discussed in this study. The benefits of such systems are reviewed from the perspectives of both the customer and the provider.