Phd Degree / Doktora

Permanent URI for this collectionhttps://hdl.handle.net/11147/2869

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Author: search.filters.author.Savacı, Ferit AcarLanguage: search.filters.language.en

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  • Doctoral Thesis
    Markov Olmayan Ortamlar ile Etkileşimdeki Süperiletken Transmon Kübitlerin Kesirli Dinamiği
    (01. Izmir Institute of Technology, 2025) Savacı, Ferit Acar; Erdoğan, Ruha Uğraş; Savacı, Ferit Acar
    Bu tezde, literatürde ilk defa olmak üzere, Mittag-Leffler (ML) tipi ilintilerin Markov bir çevre ile etkileşimde olan transmon kübitlerin eşfazlılık sürelerinin iyileştirilmesine olan etkisini irdeledik. Tez kapsamında gerçekleştirdiğimiz ikinci çalışmada, literatürde ilk defa, amorf bir çevre içindeki kusur ile etkileşimde olan transmon kübitin zaman dinamiğini analiz ettik. Markov karakteristiğine sahip gürültü eksenine dik uygulanan ML ilintili gürültüye ait karakteristik üstelin (KÜ), eşfazlılık süresine ve kubit durum dağılımına etkisini analiz ettik. Bu kapsamda yayıngan ve rastsal telegraf gürültüsünün kesirli genelleştirilmesinden inşaa ettiğimiz iki tip ML ilintili gürültü kullandık. Eşfazlılık süresinin KÜ ile ifade edilen hafızaya bağlı olarak arttığını gözlemledik. Transmon kübit ve üzerinde üretim aşamasında oluşan amorf kaplamadaki tek bir kusur arasında Gaussian olmayan karakteristiğe sahip enerji yayılımına sebep olabilecek, aynı zamanda etkileşimdeki sistem dinamiğinde uzun süreli hafızaya sebep olabilecek ağır kuyruklu Lévy tipi enerji salınımlarını irdeledik. Çevrenin güç tayfı yoğunluğunun zaman bağımlı olma durumunu zamana bağlı kesirli üstel ile betimledik. Bu ifadeye bağlı olarak, transmon kübitin zaman dinamiğini değişken mertebeli kesirli ana denklem ile ifade ettik; zamana bağlı KÜ ile betimlenen ortamın, kübit eşfazlılık süresine etkisinin, açık kuantum sistemlerinde ilk olmak üzere, bilgisayar benzetimlerini gerçekleştirdik.
  • Doctoral Thesis
    Stability Analysis of Nonlinear Dynamical Systems With Lévy Typeperturbations
    (01. Izmir Institute of Technology, 2023) Tamcı, Ege; Batal, Ahmet; Savacı, Ferit Acar
    In order to model the noise in power networks, generally, normal distribution is used. However, normal distribution is not convenient in modelling noise which has sudden peaks. Instead, combination of a continuous process and a jump processes is much more suitable. With this idea in mind, in this thesis, the stability and control of two equations used in modeling power grids is analyzed, under the assumption that they are exposed to Lévy process noise which includes jumps. These equations are the swing equation and the Kuramoto Model. The swing equation is used to model the single machine infinite bus system (SMIBS). Kuramoto Model is used when a large number of generators are considered as a network of coupled oscillators with their own natural frequencies. In our stability control study in the SMIBS, the noise in the system has sudden and finite changes is assumed and therefore should be modelled with a modified tempered α-stable process obtained by adding a finite jump condition on the tempered α-stable process when α < 1. The control functions depending on the mechanical power input and damping parameters are designed in order to make the system stable in probability and exponential stable at its equilibrium point. These theoretical results are supported by numerical studies. For Kuromato model, assuming that the power network consists of two layers, namely oscillator, and control layers and that is affected with a general Lévy process which has finite jumps, functions which provide the stability of phase and frequencies are obtained, depending on oscillator and coupling strengths. In the light of the numerical studies, the control of frequency and phase synchronization up to a certain noise intensity level can be evaluated, but it is not possible beyond that level is concluded.
  • Doctoral Thesis
    Stability Analysis and Control of Stochastic Power Systems
    (Izmir Institute of Technology, 2019) Yılmaz, Serpil; Savacı, Ferit Acar
    Increase of the electricity generation and the growth of global electricity consumption lead to an increase in the power fluctuations. In this dissertation, we have proposed a novel approach by modeling these fluctuations as alpha-stable Levy processes. We have focused on the stability analysis and control for stochastic single machine infinite bus system with an emphasis on (1) understanding the effect of impulsive and asymmetric power fluctuations on the rotor angle stability, and (2) developing control rule for synchronism in the presence of Wiener and alpha-stable Levy type power fluctuations. We have investigated the basin stability over the parameter space of mechanical power and damping parameters in the presence of alpha-stable Levy type load fluctuations. The probabilities of returning to the stable equilibrium point have been calculated for different characteristic exponent and skewness parameters of alpha-stable Levy motion to see the effect of impulsive and asymmetric load fluctuations. It has been shown that the impulsiveness and/or asymmetry in the distributions of the load fluctuations can cause the instability of the rotor angle. Hence, the synchronism is lost and the rotor angle despite being stable in the sense of probability, might not be stable in the mean square sense. Furthermore, we have studied the control of the rotor angle stability of single machine infinite bus power system in the presence of Wiener type stochastic fluctuations by minimizing the stochastic sensitivity function. We have also derived an analytical expression for the rotor angle dispersion of single machine infinite bus system in the presence of alpha-stable Levy type power fluctuations. The control rule for the minimization of the rotor angle dispersion has been achieved.
  • Doctoral Thesis
    Random Communication Systems Based on Alpha-Stable Processes
    (Izmir Institute of Technology, 2018) Ahmed, Areeb; Savacı, Ferit Acar; Ahmed, Areeb; Savacı, Ferit Acar
    This thesis presents alpha-stable carrier based random communication systems (RCSs) as an alternate way to perform covert transmission. The first objective is to develop an optimized model of RCS which consists of a receiver that requires less computational complexity and outperforms the previously proposed receivers. Next, in order to solve the existing synchronization issue in RCSs, the general behavior of fractional lower-order covariance method in α-stable noise environments has been evaluated to establish synchronization in RCSs. An optimized range of values for the associated parameters of α-stable carrier has also been presented to optimize the proposed synchronization method. The second objective is to establish criteria for evaluating and quantifying the security and covertness of RCSs. Therefore, the first security performance tradeoff characteristics (SPTC) have been proposed to compare the security of different RCSs. Moreover, the proposed optimized model of RCS has also been analyzed with respect to the developed security scale, i.e. SPTC. Secondly, the criterion to quantify the covertness of RCSs has also been developed to analyze the proposed RCS. Thirdly, an attack for RCS has also been proposed which highlights the potential vulnerabilities of RCSs. However, the counter-measure guidelines have been prescribed to further enhance the security of RCSs. An inverse system approach has been adopted to propose α-stable noise driven linear time invariant system based transmitter and its corresponding inverse system based receiver as a third objective. It can be considered as the most secure model for αstable noise carrier based RCS till now.
  • Doctoral Thesis
    Automatic Transcription of Traditional Turkish Art Music Recordings: a Computational Ethnomusicology Appraoach
    (Izmir Institute of Technology, 2012) Gedik, Ali Cenk; Savacı, Ferit Acar
    Music Information Retrieval (MIR) is a recent research field, as an outcome of the revolutionary change in the distribution of, and access to the music recordings. Although MIR research already covers a wide range of applications, MIR methods are primarily developed for western music. Since the most important dimensions of music are fundamentally different in western and non-western musics, developing MIR methods for non-western musics is a challenging task. On the other hand, the discipline of ethnomusicology supplies some useful insights for the computational studies on nonwestern musics. Therefore, this thesis overcomes this challenging task within the framework of computational ethnomusicology, a new emerging interdisciplinary research domain. As a result, the main contribution of this study is the development of an automatic transcription system for traditional Turkish art music (Turkish music) for the first time in the literature. In order to develop such system for Turkish music, several subjects are also studied for the first time in the literature which constitute other contributions of the thesis: Automatic music transcription problem is considered from the perspective of ethnomusicology, an automatic makam recognition system is developed and the scale theory of Turkish music is evaluated computationally for nine makamlar in order to understand whether it can be used for makam detection. Furthermore, there is a wide geographical region such as Middle-East, North Africa and Asia sharing similarities with Turkish music. Therefore our study would also provide more relevant techniques and methods than the MIR literature for the study of these non-western musics.