Ağca Aktunç, Esra

Ağca Aktunç, Esra

Name Variants

Ağca Aktunç, Esra
E.,Ağca Aktunç
E. Ağca Aktunç
Esra, Ağca Aktunç
Agca Aktunc, Esra
E.,Agca Aktunc
E. Agca Aktunc
Esra, Agca Aktunc
Aktunç, Esra Ağca
Aktunç, Esra Ağca
Aktunc, Esra Agca

Job Title

Dr. Öğr. Üyesi

Email Address

Esra.agca@khas.edu.tr

Full item page

Scholarly Output

7

Articles

3

Citation Count

0

Supervised Theses

3 Scholarly Output Search Results

Now showing 1 - 7 of 7

Multi-objective disaster relief logistics
(Kadir Has Üniversitesi, 2018) Samarah, Mahdi M; Agca Aktunc, Esra
Disaster relief logistics is one of the major fields of operations research. Deciding the locations of depots before the disaster by minimizing total costs and total distances between nodes of demands and these depots is the main purpose of this study. The efficiency of disaster relief logistics is expressed in terms of the total transportation cost. The other objective function is considering minimizing total accumulated time to represent efficacy to supply different number of pallets which include basic materials and necessary types of foods. Equity is represented by minimizing the percentage of unsatisfied demand achieved by balancing the capability to serve demand nodes and the ability to diminish number of pallets that would not reach the nodes. Dealing with uncertainty in both demands and distances create different scenarios for our study and the results explain how each objective function affects the logistics decisions for each scenario.
Multi-Objective Nurse Scheduling With Shift Preferences in a Surgical Suite
(Kadir Has Üniversitesi, 2017) Tekin, Elif; Aktunç, Esra Ağca
Hemşire çizelgelemesi, hastane personel çizelgelemesinin önemli bir parçasıdır. Optimum hemşire çizelgelemesi oluşturulurken göz önüne alınan adil iş yükü dağılımı ve iş memnuniyeti sağlık hizmetlerindeki kaliteyi doğrudan etkilemektedir. Bu tez projesinde, ameliyathane hemşire çizelgelemesi oluşturulurken önemli kısıtlar yasaların belirlediği çalışma saatleri, hastane yönetiminin gereksinimleri ve hemşire tercihleri dikkate alınmıştır Öncelikle, hemşireler, önem arz eden öncelikli günler için örneğin, kendi planlı ameliyatları, düğün günü veya doğum günleri gibi günleri belirleyebilirler. Ardından, vardiyalar diğer kısıtlamalara uygun olarak adil iş yükü sağlayacak şekilde tahsis edilir. Adil bir iş yükü dağılımını sağlayan ve izin günleri için hemşire tercihlerini karşılayan en uygun hemşire çizelgelerini oluşturmak için, GAMS programında tüm kısıtlamalara sahip çok amaçlı bir tamsayı programı oluşturuldu ve hedef programlama modeli ile CPLEX kullanılarak çözüldü. Projenin amacı hemşirelerin iş memnuniyetini arttırmak ve orantısız vardiya atamasının sonucunda ortaya çıkan yorgunluğun yol açtığı tıbbi hataları azaltmaktır. Böylece hemşire memnuniyeti arttırılarak hizmet kalitesinin de arttırılması beklenmektedir. Hemşire tercihleri değiştirilerek birbirinden farklı senaryolar için çizelgeler oluşturulmuştur ve hemşire tercihlerinin karşılanma oranları ile fazla mesailerin adil dağılımı gibi performans ölçütlerine bakılarak çizelgeler arasında kıyaslamalar yapılmıştır.
A Behavioral Study for Examining the Compliance of Pricing Models in Revenue Management Theory With the Decisions of Human Decision Makers
(Kadir Has Üniversitesi, 2020) Erkol, Cüneyt; Çavdaroğlu, Nur; Ağca Aktunç, Esra; Çavdaroğlu, Nur; Aktunç, Esra Ağca
This study involves four computer-based experiments based on different assumptions which are performed in a laboratory-setting. The behavior patterns of the subjects and the degree of deviation of these behaviors from optimal strategies are analyzed by various statistical methods. The common aim of the experiments examined in this thesis is to understand how successful Revenue Management theoretical models are in explaining real human behavior. In various cases, it has been possible to determine in which direction deviations from theoretical models occur and causes can be understood. In static competitor price treatment (in experiments 1 and 2), subjects exhibit a higher tendency to underprice. The "gambler's fallacy" bias is the dominant behavioral pattern observed in dynamic price setting. Humans consistently make pricing decisions below theoretical optimum, and only a small minority of the subjects are able to make optimum pricing decisions, supporting the presence of bounded rationality. Higher cognitive reflection skills help perform decisions closer to optimal, although not significantly better. Maximizing tendency does not show significance in meeting neither the optimum price, nor the potential revenue. Higher risk appetite makes better decisions in a dynamic competitor price setting. Neither the impact of learning effect, nor the demand-chasing bias is prevalent in the findings. Anchoring on the competitor price is observable in dynamic price setting. The study is useful in revealing the human factor issues that companies aiming to increase their profitability should pay attention to. Furthermore, the study can also be helpful in determining information to be provided to decision makers by an effective decision support system, and it proposes recommendations regarding the measures companies can take to improve human decision makers' decisions.
Citation Count: 6
Forecasting Models for Daily Natural Gas Consumption Considering Periodic Variations and Demand Segregation
(Elsevier Ltd, 2020) Yükseltan, Ergün; Yücekaya, Ahmet; Bilge, Ayşe Hümeyra; Ağca Aktunç, Esra
Due to expensive infrastructure and the difficulties in storage, supply conditions of natural gas are different from those of other traditional energy sources like petroleum or coal. To overcome these challenges, supplier countries require take-or-pay agreements for requested natural gas quantities. These contracts have many pre-clauses; even if they are not met due to low/high consumption or other external factors, buyers must completely fulfill them. A similar contract is then imposed on distributors and wholesale consumers. It is, thus, important for all parties to forecast their daily, monthly, and annual natural gas demand to minimize their risk. In this paper, a model consisting of a modulated expansion in Fourier series, supplemented by deviations from comfortable temperatures as a regressor is proposed for the forecast of monthly and weekly consumption over a one-year horizon. This model is supplemented by a day-ahead feedback mechanism for the forecast of daily consumption. The method is applied to the study of natural gas consumption for major residential areas in Turkey, on a yearly, monthly, weekly, and daily basis. It is shown that residential heating dominates winter consumption and masks all other variations. On the other hand, weekend and holiday effects are visible in summer consumption and provide an estimate for residential and industrial use. The advantage of the proposed method is the capability of long term projections, reflecting causality, and providing accurate forecasts even with minimal information.
Citation Count: 22
Demand Uncertainty and Inventory Turnover Performance an Empirical Analysis of the Us Retail Industry
(Emerald Group Publishing Limited, 2016) Hancerliogullari, Gulsah; Sen, Alper; Aktunç, Esra Ağca
Purpose - The purpose of this paper is to investigate the impact of demand uncertainty on inventory turnover performance through empirical modeling. In particular the authors use the inaccuracy of quarterly sales forecasts as a proxy for demand uncertainty and study its impact on firm-level inventory turnover ratios. Design/methodology/approach - The authors use regression analysis to study the effect of various measures on inventory performance. The authors use a sample financial data for 304 publicly listed US retail firms for the 25-year period from 1985 to 2009. Findings - Controlling for the effects of retail segments and year it is found that inventory turnover is negatively correlated with mean absolute percentage error of quarterly sales forecasts and gross margin and positively correlated with capital intensity and sales surprise. These four variables explain 73.7 percent of the variation across firms and over time and 93.4 percent of the within-firm variation in the data. Practical implications - In addition to conducting an empirical investigation for the sources of variation in a major operational metric the results in this study can also be used to benchmark a retailer's inventory performance against its competitors. Originality/value - The authors develop a new proxy to measure the demand uncertainty that a firm faces and show that this measure may help to explain the variation in inventory performance.
Citation Count: 8
Managing Natural Gas Demand for Free Consumers Under Uncertainty and Limited Storage Capacity
(Elsevier, 2020) Aktunç, Esra Ağca; Yükseltan, Ergün; Yücekaya, Ahmet; Bilge, Ayşe Hümeyra
Demand for energy sources depends on several factors such as population growth, urbanization, industrialization, and climate. Among fundamental energy sources, natural gas is characterized by storage limitations and take-or-pay contracts, which makes it especially critical to forecast the demand accurately for cost management policies. Suppliers of natural gas require take-or-pay contracts to ensure that consumers pay for any unused amount up front; and if the demand exceeds the agreed amount, they pay for over-use as well. Consumers with a demand above the eligible consumer limit are categorized as free consumers; and they have to specify their daily, monthly, and annual demand in these take-or-pay contracts. In residential areas, natural gas is used predominantly for heating, hence its consumption has a strong seasonality. In winter, the variability in the atmospheric temperature leads to fluctuations in the demand, while in summer, weekend effects dominate. In order to take these features into account, a demand forecasting model based on a modulated expansion in Fourier series, supplemented by deviations from comfortable temperatures, is used in this study to determine the threshold value for the onset of natural gas usage for heating purposes. The upper and lower bounds for consumption are obtained as a function of temperature only, after analyzing the details of the temperature-consumption relationship using historical data. Moreover, a temperature-based simulation methodology is proposed and simulation results that provide guidelines to manage the costs of storage under uncertainty are presented by suggesting the minimum storage capacity required and showing the distribution of the costs.
Citation Count: 9
Nurse Scheduling With Shift Preferences in a Surgical Suite Using Goal Programming
(Springer international Publishing Ag, 2018) Aktunc, Esra Agca; Tekin, Elif
Nurse scheduling is a crucial part of hospital personnel scheduling. For effective nurse scheduling, fair workload and job satisfaction should be taken into account, as these factors affect the quality of service in healthcare. In this study, monthly nurse scheduling constraints for a surgical suite are determined according to government regulations, hospital management requirements, and nurse preferences. A multi-objective integer program with hard and soft constraints is formulated and solved as a goal programming model to produce an optimal nurse schedule which provides fair workload and satisfies shift preferences of nurses. Our goal is improving job satisfaction of nurses as well as reducing medical errors caused by fatigue, a result of disproportional shift assignment. Resulting schedules for various shift preference scenarios are compared to show the improvement in the schedule quality in terms of performance measures such as distribution of preference violations among nurses.