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Permanent URI for this collectionhttps://hdl.handle.net/20.500.14288/6
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Publication Open Access Dimerization of pyrrole(TÜBİTAK, 1998) Yurtsever, Mine; Department of Chemistry; Yurtsever, İsmail Ersin; Faculty Member; Department of Chemistry; College of Sciences; 7129Accurate ab-inito quantum mechanical calculations of pyrrole dimers are reported. The thermodynamical stabilities of dimers with alpha - alpha, alpha -beta, and beta - beta type linkages are compared in order to predict the possibilities of branching in polypyrroles. Calculations employing large basis sets and including electron correlation effects predict the alpha - alpha dimers as the most stable form. However, an alpha - beta type bonding requires only 1.5-2.0 kcal/mol, and the energy necessary to introduce a beta - beta type bond is 3.6-4.0 kcal/mol. These values show that a high degree of branching is possible even at room temperatures.Publication Open Access Photonic integrated circuit-assisted optical time-domain reflectometer system(TÜBİTAK, 2022) Department of Electrical and Electronics Engineering; Onbaşlı, Mehmet Cengiz; Faculty Member; Department of Electrical and Electronics Engineering; College of Engineering; 258783Optical time-domain reflectometers (OTDR) are photonic systems that consist of an interrogator, a receiver and a fiber optical cable and have applications in telecommunications, security, environmental monitoring, distributed temperature and strain sensing. Since OTDR systems are bulk optical setups that consume multiple Watts of power, have large mass and volume footprint and are vulnerable to thermal drift, deployment of OTDR systems in the field is expensive, complicated and may not necessarily yield accurate sensing results. Thus, a compact, low-power, inexpensive and thermal drift-free OTDR system needs to be developed for improving the accuracy and the viability of OTDR in the field. In this study, I present the design and modeling of a photonic integrated OTDR system design based on IMEC's iSiPP50G silicon integrated photonic process design kit. The photonic integrated circuit includes a photonic modulator and a photodetector. Photonic power link budgets and the corresponding electronic signal-to-noise ratios are analyzed for 5-110 km fiber optical OTDR systems and power-efficient OTDR system designs are presented for inexpensive multiproject wafer fabrication.Publication Open Access CO2 absorption into primary and secondary amine aqueous solutions with and without copper ions in a bubble column(TÜBİTAK, 2022) Güler, Cansu; Uzunlar, Erdal; Department of Chemical and Biological Engineering; Erkey, Can; Yousefzadeh, Hamed; Faculty Member; Researcher; Department of Chemical and Biological Engineering; College of Engineering; 29633; N/AChemical absorption of CO2 into aqueous amine solutions using a nonstirred bubble column was experimentally investigated. The performance of CO2 absorption of four different primary and secondary amines including monoethanolamine (MEA), piperazine (PZ), 2-piperidineethanol (2PE), and homopiperazine (HPZ) were compared. The effects of initial concentration of amine, the inlet mole fraction of CO2, and solution temperature on the rate of CO2 absorption and CO2 loading (mol CO2/mol amine) were studied in the range of 0.02–1 M, 0.10–0.15, and 25–40 °C, respectively. The effect of the presence of copper ions in the amine solution on CO2 loading was also studied. By comparison of the breakthrough curves of the amines at different operational conditions, it was revealed that the shortest and longest time for the appearance of the breakthrough point was observed for MEA and HPZ solutions, respectively. CO2 loading of MEA, 2PE, PZ, and HPZ aqueous solutions at 25 °C, 0.2 M of initial concentration of amine, and 0.15 of inlet mole fraction of CO2 were 1.06, 1.14, 1.13, and 1.18 mol CO2/mol amine, respectively. By decreasing the inlet mole fraction of CO2 from 0.15 to 0.10, CO2 loading slightly decreased. As the initial concentration of amine and temperature decreased, CO2 loading increased. Also, the presence of copper ions in the absorbent solution resulted in a decrease in the CO2 loading of MEA and HPZ aqueous solutions. In case of PZ and 2PE amines, adding copper ions led to precipitation even at low copper ion concentrations.Publication Open Access A systematic and efficient input selection method for artificial neural networks using mixed-integer nonlinear programming(Konya Teknik Üniversitesi, 2022) Şıldır, Hasan; Department of Chemical and Biological Engineering; Aydın, Erdal; Faculty Member; Department of Chemical and Biological Engineering; College of Engineering; 311745Selection of input variables of the empirical models has vital effect on the prediction performance, reduced overfitting and reduced computational load. Various trials and error and sequential methods in the literature to deal with input selection for artificial neural networks (ANNs). However, these methods are not considered as automatic and systematic. This study proposes a novel and efficient mixed integer nonlinear programming-based approach to handle optimal input selection and the ANN training simultaneously for classification problems. Such selection uses binary (0-1) variables to represent the presence of the input variables and trains traditional continuous network weights simultaneously. Two classification case studies are given to demonstrate the advantages by using widely used data sets and statistical measures. The first data set is related to the characterization of the type of a tumor related to breast cancer, the second data set is about predicting the type of a biotechnological product using different features, the last one is related to heart failure prediction. Results show that better test performance can be achieved with optimally selected inputs, resulting in reduced overfitting. The proposed approach delivers a significant advantage during the design and training of the ANNs and is also applicable to other empirical models. / Ampirik modellerin girdi değişkenlerinin seçimi, tahmin performansı, azaltılmış fazla uydurma ve hesaplama yükünün azaltılması üzerinde önemli etkiye sahiptir. Literatürde yapay sinir ağları (YSA) için girdi seçimi ile ilgili çeşitli deneme yanılma yöntemleri mevcuttur ancak bu metodlar sistematik ve otomatik olarak kabul edilmemektedir. Bu çalışma, sınıflandırma problemleri için optimal girdi seçimi ve YSA eğitimini aynı anda ele almak için yeni ve verimli bir karma tamsayılı doğrusal olmayan programlama tabanlı bir yaklaşım önermektedir. Bu seçim, girdi değişkenlerinin varlığını temsil etmek için ikili (0-1) değişkenleri kullanır ve geleneksel sürekli ağ ağırlıklarını veya parametrelerini aynı anda eğitir. Yaygın olarak kullanılan veri setleri ve istatistiksel ölçümler kullanarak avantajları göstermek amacıyla üç sınıflandırma vaka çalışması sunulmuştur. Birinci veri seti meme kanseri ile ilgili tümörün tipin-in karakterizasyonu ile ilgili olup, ikinci veri seti ise farklı özellikler kullanılarak bir biyoteknolojik ürünün tipinin tahmin edilmesi ile ilgilidir, son veri seti ise kalp sağlığı ile ilgilidir. Sonuçlar, optimal olarak seçilen girdiler ile düşük fazla uydurma sayesinde daha iyi test performansının elde edilebileceğini göstermektedir. Önerilen yaklaşım, YSA'ların tasarımı ve eğitimi sırasında önemli bir avantaj sağlar ve diğer ampirik modellere de uygulanabilir.Publication Open Access Crowd-shipping service network design problem(Pamukkale University / Pamukkale Üniversitesi, 2022) Department of Industrial Engineering; Yıldız, Barış; Faculty Member; Department of Industrial Engineering; College of Engineering; 258791With the rising concerns over the increasing costs and negative externalities of city logistics, the need for innovative approaches to come up with low-cost and environmentally friendly distribution systems is on the rise. One such innovative approach is crowd-shipping (CS). In this model, which aims to combine packet and passenger transfers to utilize redundant transportation capacity, the individuals who want to earn small compensations and/or help the environment are employed to carry out package transfers between service points on the paths of their already planned trips. In this study, we introduce the strategic level CS network design problem, which needs to be solved to determine the locations and the capacities of the service points in the urban area to establish an efficient CS delivery system. We propose a novel Benders Decomposition algorithm to solve this challenging problem that we model as a scenario-based two-stage stochastic integer program. The results of our comprehensive numerical experiments attest to the efficacy of the approach to solve practical size problem instances and provide significant managerial insights, showing that such a well-designed CS network can provide savings (in terms of both economic and environmental costs), even in the case of express package transfers with very stringent delivery lead time restrictions. In particular, our results show that by carefully choosing the locations and the capacities of the service points, it is possible to carry out a significant portion of express deliveries with the crowd provided delivery capacity (up to 56% in our experiments) without deploying a very large number of them (less than 60 in all our experiment) in the region, indicating the strong potential and applicability of the CS delivery systems in real world delivery operations. / Şehir içi dağıtım faaliyetlerinin artan maliyetleri ve neden olduğu sorunlar (trafik, çevre kirliliği, gürültü, araç kazaları, vb.) hakkında artan kaygılar, bu alanda yenilikçi yaklaşımlara olan ihtiyacı giderek artırmaktadır. Ön plana çıkan söz konusu yaklaşımlardan birisi de Kitle destekli dağıtım (KDD) modelidir. Yolcu ve paket taşımacılığını bütünleştirerek atıl araç kapasitelerinin faydalı bir şekilde kullanılmasını amaçlayan bu modelde, kişilerin küçük ekonomik kazançlar sağlamak ve/veya dağıtım faaliyetlerinin çevreye verdiği zararları azaltılmasına katkı sunmak amacıyla kendi seyahatleri sırasında yolları üzerindeki servis noktaları arasında paket taşımacılığı yapması öngörülmektedir. Bu çalışmada, KDD faaliyetlerinin etkin bir şekilde yürütebilmesi için gerekli olan servis noktalarının/paket otomatlarının şehrin hangi noktalarına hangi kapasiteler ile kurulması gerektiğini belirlemek için çözülmesi gereken stratejik seviye “KDD servis ağı tasarımı” problemini literatüre tanıtıyoruz. İki seviyeli, senaryo tabanlı belirsiz bir tamsayılı program olarak modellediğimiz problemin çözümü için etkin bir Benders Ayrıştırma algoritması önermekteyiz. Gerçekleştirdiğimiz geniş kapsamlı hesapsal çalışmalar geliştirdiğimiz çözüm yönteminin etkinliğini ortaya koymakta, önemli yönetimsel çıkarımlar sunmaktadır. Elde ettiğimiz sonuçlar, hızlı paket taşımacılığı gibi oldukça zorlu ve maliyetli (ekonomik ve çevresel) bir dağıtım faaliyeti için iyi tasarlanmış bir KDD modelinin önemli kazanımlar sağlayabileceğini göstermektedir. Nispeten küçük sayıda (çalıştığımız problem örneklerinde en fazla 60 adet) servis noktaları ile dağıtımların önemli bir kısmının (çalıştığımız problem örneklerinde %56’ya kadar) “kitle” tarafından yapıldığı etkin bir KDD sisteminin teşkil edilebileceğini gösteren bu sonuçlar, önerilen yenilikçi yaklaşımın uygulanabilirliği konusunda önemli ipuçları vermektedir.Publication Open Access Thermal stabilities of hydroxyalkyl terminated polydimethylsiloxane oligomers(TÜBİTAK, 1997) Department of Chemistry; Yılgör, Emel; Yılgör, İskender; Researcher; Faculty Member; Department of Chemistry; College of Sciences; 40527; 24181The thermal stabilities of alpha,omega-hydroxypropyl, alpha,omega-hydroxybutyl alpha,omega-2-hydroxypentyl and alpha,omega-hydroxyhexyl terminated polydimethylsiloxane oligomers were investigated. Hydroxypropyl and hydroxybutyl terminated polydimethylsiloxane oligomers showed degradation upon heating through the loss of functional end groups, as determined by FTIR spectroscopy and gel permeation chromatography. alpha,omega-Hydroxyhexyl and alpha,omega-2-hydroxypentyl terminated polydimethylsiloxane oligomers were stable under similar conditions. The instability of the end groups is due to the backbiting of the terminal silicon in the PDMS by the primary hydroxyl oxygen, leading to the formation of 5- and 6-membered stable, heterocylic compounds. Loss of end groups also resulted in a dramatic increase in the molecular weights of the oligomers produced, as determined by GPC.Publication Open Access Reaction network reduction with mixed-integer nonlinear programming(Konya Teknik Üniversitesi, 2021) Şıldır, Hasan; Ertürk, Emrullah; Department of Chemical and Biological Engineering; Aydın, Erdal; Faculty Member; Department of Chemical and Biological Engineering; College of Engineering; 311745In this study, a Mixed-Integer Nonlinear programming (MINLP) problem is formulated for reaction network model reduction. The MINLP problem introduces binary variables for the existence of rate constants in addition to traditional continuous variables to minimize the prediction error. Such binary variables are implemented through linking constraints. Both the impact of initial conditions and operating conditions are investigated on the model reduction. Commercial and free solver comparisons are also provided in terms of computational time and results. The methodology is implemented on an experimentally-derived reaction pathway from the literature. A significant network reduction is achieved under different operating temperatures and initial conditions. The reduced model provides a satisfactory prediction accuracy with significantly low number of reactions and parameters. / Bu çalışmada, reaksiyon ağı küçültmesi için tam sayılı ve kesikli bir optimizasyon (MINLP) problemi formüle edilmiştir. Bu problem, tahmin hatasını enküçüklemek için geleneksel sürekli değişkenlere ek olarak reaksiyon hız sabitlerinin mevcudiyeti için iki değerli değişkenler tanımlamaktadır. Bu iki değerli değişkenler bağlantı kısıtı ile uygulanmaktadır. Başlangıç koşulları ve çalışma koşullarının model küçültmeye olan etkisi araştırılmıştır. Bu bağlamda, ticari ve ücretsiz çözücü programların hesaplama süreleri ve sonuçları karşılaştırmalı olarak sunulmuştur. Önerilen yöntem literatürde bulunan deneysel olarak türetilmiş reaksiyon ağına uygulanmıştır. Farklı sıcaklık ve başlangıç konsantrasyonlarında kayda değer ağ küçültülmesi sağlanmıştır. Küçültülmüş model önemli ölçüde az reaksiyon ve parametre sayısı ile tatmin edici kestirim doğruluğu sunmaktadır.