Continuous time control of make-to-stock production systems

Ankara : The Department of Industrial Engineering and the Institute of Engineering and Sciences of Bilkent University, 2010.Thesis (Ph. D.) -- Bilkent University, 2010.Includes bibliographical references leaves 117-120.We consider the problem of production control and stock rationing in a make-tostock production system with multiple servers –parallel production channels--, and several customer classes that generate independent Poisson demands. At decision epochs, in conjunction with the stock allocation decision, the control specifies whether to increase the number of operational servers or not. Previously placed production orders cannot be cancelled. We both study the cases of exponential and Erlangian processing times and model the respective systems as M /M /s and M /Ek /s make-to-stock queues. We characterize properties of the optimal cost function, and of the optimal production and rationing policies. We show that the optimal production policy is a state-dependent base-stock policy, and the optimal rationing policy is of state-dependent threshold type. For the M /M /s model, we also prove that the optimal ordering policy transforms into a bang-bang type policy when we relax the model by allowing order cancellations. Another model with partial ordercancellation flexibility is provided to fill the gap between the no-flexibility and the full-flexibility models. Furthermore, we propose a dynamic rationing policy for the systems with uncapacitated replenishment channels, i.e., exogenous supply systems. Such systems can be modeled by letting s --the number of replenishment channels-- go to infinity. The proposed policy utilizes the information on the status of the outstanding replenishment orders. This work constitutes a significant extension of the literature in the area of control of make-to-stock queues, which considers only a single server. We consider an arbitrary number of servers that makes it possible to cover the spectrum of the cases from the single server to the infinite servers. Hence, our work achieves to analyze both the exogenous and endogenous supply leadtimes.Bulut, ÖnderPh.D

On stock rationing policies for continuous review inventory systems

Cataloged from PDF version of article.Rationing is an inventory policy that allows prioritization of different demand classes. In this thesis, we analyze the stock rationing policies for continuous review systems. We clarify some of the ambiguities present in the current literature. Then, we propose a new method for the exact analysis of lot-for-lot inventory systems with backorders under rationing policy. We show that if such an inventory system is sampled at multiples of supply leadtime, the state of the system evolves according to a Markov chain. We provide a recursive procedure to generate the transition probabilities of the embedded Markov chain. It is possible to obtain the steady-state probabilities of interest with desired accuracy by considering a truncated version of the chain. Finally, we propose a dynamic rationing policy, which makes use of the information on the status of the outstanding replenishment orders. We conduct a simulation study to evaluate the performance of the proposed policy.Bulut, ÖnderM.S

The effect of dietary soybean meal on growth, nutrient utilization, body composition and some serum biochemistry variables of two banded seabream, Diplodus vulgaris (Geoffroy Saint-Hilaire, 1817)

This study was performed to determine the optimum level of soybean meal diets for two banded seabream for growth performance, nutrient utilization, body composition and serum biochemistry. Two banded seabream were fed five experimental diets which were formulated replace fish meal by soybean meal at 0, 20, 30, 40 and 50%. Up to 40% of dietary fish meal was successfully replaced with no growth depression. Whole body composition of two banded seabream was not affected by soybean meal inclusion level. Total protein, triglyceride and total cholesterol of fish fed the SM50 diets were significantly lower compared to fish fed the soybean free diet. On the other hand, serum glucose level significantly increased as dietary soybean meal inclusion increased. Results showed that 40% fish meal can be replaced in diets for the two banded seabream by defatted soybean meal. Further studies to determine the inclusion level of soybean meal more than 40% with amino acid or enzyme supplementation are needed

Does Platelet Mass Index Play a Role in Predicting Biochemical Recurrence in Localized Prostate Cancer?

Objective:The aim of this study is to investigate the association of preoperative platelet mass index (PMI) with tumor pathologic features and postoperative biochemical recurrence in patients undergoing radical prostatectomy due to localized prostate cancer.Materials and Methods:Data of 141 patients, who underwent radical prostatectomy for localized prostate cancer between April 2004 and April 2017, were retrospectively screened. Patient age, preoperative prostate-specific antigen (PSA) level, platelet count, mean platelet volume and PMI value, neutrophil-lymphocyte ratio (NLR), tumor grade, Gleason score, tumor volume, lymph node involvement, surgical margin positivity and biochemical recurrence at 3 months were all noted. The relationship of preoperative PMI value with age, PSA, pathologic parameters, surgical margin positivity and biochemical recurrence was evaluated.Results:The mean age of the patients was 61.79±5.98 years, the mean PSA value was 9.50±6.69 ng/mL, mean PMI was 2003.91±486.69, and the mean NLR was 2.79±2.06. There was no correlation of PMI value with PSA, pathological stage, Gleason score, lymph node involvement, tumor volume, surgical margin positivity, and biochemical recurrence. There was statistically significant negative correlation between PMI and Gleason score.Conclusion:In our study, we could not demonstrate preoperative PMI as a prognostic factor for early biochemical recurrence in patients undergoing radical prostatectomy for prostate cancer. To achieve a better conclusion that we can generalize, there is a need for prospective studies with larger patient series

Monte Carlo Simulation Studies in Item Response Theory with the R Programming Language

Monte Carlo simulation studies play an important role in operational and academic research in educational measurement and psychometrics. Item response theory (IRT) is a psychometric area in which researchers and practitioners often use Monte Carlo simulations to address various research questions. Over the past decade, R has been one of the most widely used programming languages in Monte Carlo studies. R is a free, open-source programming language for statistical computing and data visualization. Many user-created packages in R allow researchers to conduct various IRT analyses (e.g., item parameter estimation, ability estimation, and differential item functioning) and expand these analyses to comprehensive simulation scenarios where the researchers can investigate their specific research questions. This study aims to introduce R and demonstrate the design and implementation of Monte Carlo simulation studies using the R programming language. Three IRT-related Monte Carlo simulation studies are presented. Each simulation study involved a Monte Carlo simulation function based on the R programming language. The design and execution of the R commands is explained in the context of each simulation study

Optimization of Gluten-Free Tulumba Dessert Formulation Including Corn Flour: Response Surface Methodology Approach

Tulumba dessert is widely preferred in Turkey; however, it cannot be consumed by celiac patients because it includes gluten. The diversity of gluten-free products should be expanded so that celiac patients may meet their daily needs regularly. In this study, corn flour (CF) / potato starch (PS) blend to be used in the gluten-free tulumba dessert formulation was optimized using the Response Surface Methodology (RSM). Increasing ratio of PS in the CF-PS led to a decrease in hardness of the dessert and to an increase in expansion, viscosity, adhesiveness, yield of dessert both with and without syrup (P0.05), additionally these desserts had a much higher sensory score compared to the control sample in terms of the overall quality and pore structure (P<0.05)

A dynamic rationing policy for continuous-review inventory systems

Stock rationing is an inventory policy that allows differential treatment of customer classes without using separate inventories. In this paper, we propose a dynamic rationing policy for continuous-review inventory systems, which utilizes the information on the status of the outstanding replenishment orders. For both backordering and lost sales environments, we conduct simulation studies to compare the performance of the dynamic policy with the static critical level and the common stock policies and quantify the gain obtained. We propose two new bounds on the optimum dynamic rationing policy that enables us to tell how much of the potential gain the proposed dynamic policy realizes. We discuss the conditions under which stock rationing - both dynamic and static - is beneficial and assess the value of the dynamic policy.Multiple demand classes Rationing Dynamic rationing Simulation

Selenyum Dioksit ve Paklitaksel Kombinasyonunun MDA-MB-231 Meme Kanseri Hücre Hattı Üzerine Etkisinin Değerlendirilmesi

Amaç: Bu çalışmanın amacı, bitkisel kökenli bileşik olan selenyum dioksit (SEL) ile kemoterapötik ilaç olan paklitaksel’in (PTX) kombine uygulamasının MDA-MB-231 meme kanseri hücre hattı üzerine etkisinin belirlenmesidir. Gereç ve Yöntemler: Çalışmamızda öncelikle SEL’in yarı maksimal inhibitör konsantrasyonunun belirlenmesi amacıyla MTT testi yapıldı. Deney grupları SEL1, SEL2, SEL3, PTX, SEL1+PTX, SEL2+PTX ve SEL3+PTX şeklinde oluşturulduktan sonra apoptoz TUNEL metodu, NF-kB ekspresyonu immunofloresan boyama metodu ile hücre canlılığı ise MTT analizi ile gösterildi. Bulgular: SEL’in meme kanseri hücrelerinde hücre canlılığını azalttığı gösterildi. SEL1, SEL2, SEL3, PTX gruplarında kontrole göre apoptozun arttığı görüldü (p0,999, p>0,999, p=0,725). Sonuç: Mevcut çalışmada MDA-MB-231 meme kanseri hücre dizisinde SEL ve PTX’in antagonistik etkiye sahip oldukları belirlenmiştir.Aim: The aim of this study is to determine the effect of the combined application of the plant-derived compound selenium dioxide and the chemotherapeutic drug paclitaxel (PTX) on the MDA-MB-231 breast cancer cell line. Material and methods: In our study, first of all, the MTT test was performed to determine the semi-maximal inhibitory concentration of selenium dioxide. After the experimental groups were formed as SEL1, SEL2, SEL3, PTX, SEL1+PTX, SEL2+PTX, and SEL3+PTX, apoptosis was demonstrated by the TUNEL method, NF-kB expression was demonstrated by the immunofluorescent staining method, and cell viability was demonstrated by MTT analysis. Results: Selenium dioxide has been shown to decrease cell viability in breast cancer cells. Apoptosis was observed to be increased in SEL1, SEL2, SEL3, and PTX groups compared to control(