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Kuantum bilgisayarlarda gerçekleştirilen ayrık zaman kristallerinin gürültü direnci
No full textDiscrete Time Crystals (DTCs) are a non-equilibrium phase of matter that breaks the time-translation symmetry. This manifests as robust oscillations observed in driven Hamiltonians. Realizing DTCs on current Noisy Intermediate-Scale Quantum (NISQ) computers can be challenging due to the environmental noise, decoherence of qubits and computational errors. This thesis investigates the resilience and robustness of DTC and examines recent developments, and possible improvements of DTC stabilization using current quantum processors. Generally, an externally driven many-body system is expected to heat up to an infinite temperature state. This process, which is called thermalization, prevents the time-crystalline order. The two primary mechanisms that protect time-crystalline order are many-body localization (MBL) which has a strong disorder that prevents the thermalization, and Floquet prethermalization where its high frequency driving prevents the thermalization. These two processes allow us to realize and investigate the time crystals before a quantum system thermalizes.Ayrık Zaman Kristalleri (DTC'ler), zaman-öteleme simetrisini kıran maddenin denge dışı bir fazıdır. Bu durum, sürülen Hamiltoniyenlerde gözlenen sağlam salınımlar olarak ortaya çıkar. Mevcut Gürültülü Orta Ölçekli Kuantum (NISQ) bilgisayarlarında DTC'lerin gerçekleştirilmesi, çevresel gürültü, kubitlerin uyumsuzluğu ve hesaplama hataları nedeniyle zorlu olabilir. Bu tez, DTC'lerin direncini ve sağlamlığını araştırmakta, son gelişmeleri ve mevcut kuantum işlemciler kullanılarak DTC stabilizasyonunun olası iyileştirmelerini inceler. Genel olarak, dışarıdan sürülen bir çok-kütleli sistemin sonsuz sıcaklık durumuna kadar ısınması beklenir. Termalizasyon olarak adlandırılan bu süreç, zaman-kristal düzenini engeller. Zaman-kristal düzenini koruyan iki temel mekanizma, termalizasyonu engelleyen güçlü düzensizliğe sahip çok-cisim lokalizasyonu (MBL) ve yüksek frekanslı sürmenin termalizasyonu engellediği Floquet ön-termalizasyonudur. Bu iki süreç, bir kuantum sistem termalize olmadan önce zaman kristallerini gerçekleştirmemize ve araştırmamıza olanak tanır.M.S. - Master of Scienc
Presenting predictions and performance of probabilistic models for clinical decision support in trauma care
No full textIntroduction: Both predictions and performance of clinical predictive models can be presented with various verbal and visual representations. This study aims to investigate how different risk and performance presentations for probabilistic predictions affect clinical users' judgement and preferences. Methods: We use a clinical Bayesian Network (BN) model that has been developed for predicting the risk of Trauma Induced Coagulopathy (TIC). Three patient scenarios with different levels of TIC risk were shown to trauma care clinicians. The prediction and discriminatory performance of TIC BN were shown with each scenario using different charts in a random order. Bar charts, icon arrays and gauge charts were used for presenting the prediction. Receiver operating characteristic curves, true and false positive rate curves and icon arrays were used for presenting the performance. Risk judgement for patient scenarios, perceived accuracy for the predictions and the model, and preferences for charts were elicited using an online survey. Results: A total of 25 clinicians evaluated 75 BN predictions. The choice of risk charts was associated with the risk score in the borderline medium-risk scenario. The choice of risk and performance charts interacts with the perceived accuracy of the predictions and model in the high and low-risk scenarios, respectively. The participants had varying but persistent preferences regarding risk presentation charts. Icon arrays were preferred for performance presentations. Conclusions: The choice of presenting predictions and the performance of predictive models can affect risk and performance interpretation. Clinical predictive models should offer the flexibility of presenting predictions with different illustrations
KANT’IN ARDINDAN HEGEL’İN ONTOLOJİK DÜŞÜNCESİ
No full textThis study examines Hegel’s ontological thinking in response to Kant’s critical philosophy. It begins with an examination of Hegel’s critique of Kant’s theoretical philosophy. I argue that this comprehensive critique overcomes the limitations of transcendental idealism and opens the possibility for a post-critical ontology. The next step is an exploration of Hegel’s Science of Logic as a presuppositionless project, examining its ontological character in conjunction with the problem of beginning and method. The study then turns to the Doctrine of Being, where the initial movement unfolds through the dialectic of being, nothing, and becoming. From determinate being to infinity, fundamental ontological categories such as reality, something, other, limit, finitude are examined through their logical movement. I argue that by the end of this process, the true infinite assumes a central role in Hegel’s thought. The study proceeds to undertake an inquiry into the Doctrine of Essence. Hegel’s conceptualization of essence as negativity and mediation is analyzed in its contrast to the immediacy of illusory being. I focus then on the concept of reflection as the negative movement of essence. Following the three forms of reflection (positing, external, determining), identity, difference and contradiction emerge as determinations of reflection. It is argued here that Hegel challenges the conventional understanding of these logical principles from an ontological standpoint. Finally, the study moves on to an examination of the ground and actuality, which serve to overcome the dualism of being and essence and thus provide Hegel’s transition to the Concept.Bu çalışma Hegel’in ontolojik düşüncesini Kant’ın eleştirel felsefesine bir yanıt olarak incelemektedir. Çalışma Hegel'in, Kant’ın teorik felsefesine yönelttiği eleştirinin incelenmesiyle başlamaktadır. Bu kapsamlı eleştirinin transandantal idealizmin sınırlamalarının üstesinden geldiğini ve Kant sonrası bir ontolojinin imkanını gösterdiğini öne sürüyorum. Bir sonraki adım Hegel'in Mantık Bilimi'nin önvarsayımsız bir proje olarak ele alınması ve ontolojik karakterininin başlangıç ve yöntem sorunuyla bağlantılı olarak incelenmesidir. Ardından ilk hareketin varlık, hiçlik ve oluş diyalektiği olarak ortaya çıktığı Varlık Doktrini'ne dönüyorum. Belirli varlıktan sonsuzluğa, gerçeklik, bir şey, öteki, sınır, sonluluk gibi temel ontolojik kategoriler mantıksal hareket aracılığıyla inceleniyor. Bu sürecin sonunda gerçek sonsuzluk kavramının Hegel'in düşüncesinde merkezi bir rol üstlendiğini iddia ediyorum. Çalışma daha sonra Öz Doktrini’ne dair bir sorgulamaya girişiyor. Hegel'in özü olumsuzluk ve dolayım olarak kavramsallaştırması, yanılsamalı varlığın dolaysızlığıyla karşıtlığı içinde analiz ediliyor. Sonrasında özün negatif hareketi olarak refleksiyon kavramına odaklanıyorum. Refleksiyonun üç biçimini (koyutlayıcı, dışsal, belirleyici) takiben özdeşlik, fark ve çelişki refleksiyonun belirlenimleri olarak ortaya çıkıyor. Hegel'in bu mantıksal ilkelerin geleneksel anlayışına ontolojik bir bakış açısıyla meydan okuduğunu iddia ediyorum. Son olarak çalışma, varlık ve öz düalizmini aşma işlevini gören ve böylece Hegel'in Kavram’a geçişini sağlayan zemin ve aktüellik kavramlarının incelenmesine geçiyor.Ph.D. - Doctoral Progra
Examination of EMT-Type Impedance Scanning Techniques for Small Signal Stability Assessment of Inverter Based Resources
No full textModern power grids that incorporate inverter-based resources (IBRs) may be vulnerable to persistent oscillations and instability incidents, which jeopardize the reliable operation of the system. Unstable operation conditions can be identified via impedance-based stability assessment (IBSA) methods, provided that accurate frequency-dependent impedance models of the system are available. A promising approach for obtaining such impedance models is to use time-domain simulation scanning techniques based on electromagnetic transient (EMT)-type software. This paper studies and compares five EMT-type impedance scanning methods in terms of their application procedures, analytical relationship between obtained impedances, IBSA accuracies, and computational burdens. Critical technical notifications and guidelines for the selection and application of these scanning methods, considering different types of instabilities, are provided. For accuracy assessment, the IBSA results are compared with EMT simulations on a practical test system
Gün öncesi çok amaçlı reaktif güç optimizasyonu
No full textTransmission system operators (TSOs) need to control voltages along the grid to have an economic and reliable system operation. The coordination between the voltage setpoints of power plants, transformer tap positions and switching of shunt elements may be defined as an optimum reactive dispatch problem. This thesis aims to develop an efficient algorithm for the optimum reactive power dispatch problem. The main objective of this problem is the minimization of transmission losses. Due to operational costs of switching equipment of shunt elements and transformer tap changers, TSOs also expect the number of switching of these devices to be minimized. In this study, the minimization of switching of shunt elements and transformer tap changes are included in the objective function. Hence, the problem is formulated as a multi-period and multi-objective optimization problem. The optimum reactive power dispatch problem is a nonlinear and non-convex optimization problem due to the nonlinear power balance constraints. In addition, since the switch statuses of shunt elements and transformer tap positions are integer variables, the problem becomes a mixed integer nonlinear optimization problem (MINLP). Execution time for MINLP problems for large systems become impractical. Moreover, there is no guarantee for convergence. The main difficulty is the integer variables. Hence, in the first stage of the algorithm, the switch statuses of the shunt elements will be determined. Although the transformer tap variables are integer variables, these variables can be linearized without any practical loss of information. In the second stage of the algorithm the problem becomes a nonlinear optimization problem which can be solved using nonlinear interior point algorithm. The developed algorithm has been tested on IEEE 118 bus test network and convergence performance and execution time of the algorithm is considered as applicable for day ahead reactive power optimization.İletim sistem operatörleri ekonomik ve güvenli bir sistem işletmesi için şebekede gerilimleri kontrol etme ihtiyacı duymaktadır. Santral gerilim ayar değerleri, trafo kademe değerleri ve şönt ekipman anahtarlamalarının koordinasyonu bir optimum reaktif güç tevzi problemi olarak tanımlanabilir. Bu tez, optimum reaktif güç tevzi problemi için bir etkin bir algoritma geliştirmeyi amaçlamaktadır. Bu problemin temel amacı iletim kayıplarının en aza indirilmesidir. Şönt elemanların anahtarlama ekipmanlarının ve trafo kademe değiştiricilerinin işletme maliyetleri nedeniyle, iletim sistemi operatörleri bu cihazların anahtarlama sayısının en aza indirilmesini beklemektedir. Bu çalışmada şönt elemanların anahtarlama sayıları ve trafo kademe değişimlerinin en aza indirilmesi amaç fonksiyonuna dahil edilmiştir. Bu nedenle, problem, çok dönemli ve çok amaçlı bir optimizasyon problemi olarak formüle edilmiştir. Optimum reaktif güç tevzi problemi, doğrusal olmayan güç dengesi kısıtları nedeniyle doğrusal olmayan ve dışbükey olmayan bir optimizasyon problemidir. Ayrıca, şönt elemanlarının anahtarlama durumları ve trafo kademe konumlarının tamsayı değişkenler olması sebebiyle, problem karışık tam sayılı doğrusal olmayan bir optimizasyon problem (MINLP) haline gelmektedir. Büyük sistemler için MINLP problemlerinin çözüm süresi uygulanamaz hale gelmektedir. Ayrıca, problemin yakınsama garantisi de olmamaktadır. Bu problemlerde başlıca zorluk tamsayı değişkenlerdir. Bu nedenle, ilk aşamada şönt elemanlarının anahtarlama durumları belirlenecektir. Trafo kademe değişkenleri tamsayı olmasına rağmen, bu değişkenler herhangi bir pratik bilgi kaybı olmadan doğrusallaştırılabilir. İkinci aşamada, problem interior point algoritması ile çözülebilen bir optimizasyon problemi haline gelir. Geliştirilen algoritma IEEE 118 bara test şebekesinde test edilmiş ve algoritmanın yakınsama performansı ve yürütme süresi, gün öncesi reaktif güç optimizasyonu için uygulanabilir olarak kabul edilmiştir.Ph.D. - Doctoral Progra
Stakeholder Perspectives on Rankings of Higher Education Institutions: A Structural Equation Modeling Analysis
No full textThis study analyzes the factors influencing the stakeholder perspectives on of Higher Education Institution (HEI) rankings, reporting data collected from 1232 participants through a survey method and employing the Unified Theory of Acceptance and Use of Technology (UTAUT2) model and complementary models for the analyses. Our primary focus was to identify the relationships between various predictor variables influencing the perception of HEI rankings. We analyzed how demographic variables, such as age, gender, job experience, and employment status, might moderate these relationships. The key findings show that certain model dimensions, such has Performance Expectancy, Price Value, Habit, Hedonic Motivation, Perceived Information Quality, Perceived Trust, and Awareness significantly influence participants’ behavioral intentions and actual use of the HEI rankings. Overall, this study provides a quantitative perspective to perception of HEI rankings from a stakeholders’ point of view, reflecting similarities and differences among various participants
Milling force estimation based on harmonic force model and acceleration feedback
No full textMonitoring milling forces is crucial as they directly reflect the milling process. Direct force measurement using a dynamometer is challenging for industrial applications. However, indirect force measurement can be achieved with efficient Kalman filter estimation algorithms and low-cost accelerometers that can be conveniently installed in machine tools. Existing research establishes the force-acceleration relationship through modal analysis of the frequency response function (FRF). High-order system models for acceleration response not only increase computational effort but also introduce tuning issues for the estimator. This paper introduces a novel and simple Kalman filter system model. In this approach, the cutting force coefficients are treated as unknown state variables, resulting in a 4×4 identity state transition matrix. The acceleration measurement is related to the estimated coefficient states by modeling the milling forces as a sum of tooth passing frequency harmonics. First, an analytical derivation of the force harmonics in the angular domain is presented. Then, utilizing the FRF gains and phases at the tooth passing frequency harmonics, the acceleration is expressed in terms of coefficient state variables and integrated into the output matrix of the Kalman filter. By updating the output matrix with the measured angular position of the tool, a linear time-varying system model of the cutting process is achieved. The proposed method is validated through real cutting tests conducted under various process parameters. Comparison with dynamometer measurements shows that the milling force can be estimated with an average RMS error of around 5
Linearly implicit methods for the nonlinear Klein–Gordon equation
No full textWe present energy-preserving linearly implicit integrators for the nonlinear Klein–Gordon equation, based on the polarization of the polynomial functions. They are symmetric, second-order accurate in time and space, and unconditionally stable. Instead of solving a nonlinear algebraic equation at every time step, the linearly implicit integrators only require solving a linear system, which reduces the computational cost. We propose three types of linearly implicit integrators for the nonlinear Klein–Gordon equation, that preserve the modified, polarized invariants, ensuring the stability of the solutions in long-time integration. Numerical results confirm the theoretical convergence orders and preservation of the Hamiltonians that guarantee the stability of the solutions in long-time simulation
State of the art modelling for the Black Sea ecosystem to support European policies
Full text linkThe Black Sea is affected by numerous anthropogenic pressures, such as eutrophication and pollution through coastal and river discharges, fisheries overexploitation, species invasions, and the impacts of climate change. Growing concerns regarding the cumulative effects of these pressures have necessitated the need for an ecosystem approach to assessing the state of this basin. In recent years, the European Commission-JRC has developed a scientific and modelling tool, the Blue2 Modelling Framework with the aim of exploring the consequences of EU management and policy options on marine ecosystems. This framework has been designed to provide information on specific ecological indicators set out in EU legislation. Here, we present the Blue2 framework for the Black Sea ecosystem. The model represented the mid-1990s’ conditions in the Black Sea ecosystem including trophic levels from primary producers to marine mammals and sea birds. The model simulations covered a period from 1995–2021. The results showed that gulls & cormorant seabirds, sprat, horse mackerel and mugilidae had structuring role in the food web. Fishing fleets had indirect negative impacts on marine mammals in addition to commercially exploited species. Analysis of the ecosystem indicators confirmed the overall temporal degradation of the Black Sea when comparing results with other Black Sea models, whilst the comparison with the Mediterranean Sea allowed us to identify comparable indicators between similar model structures. The spatial/temporal model successfully simulated the overall ongoing declining dynamics of the Black Sea ecosystem as the biomasses of the majority of the functional groups had significant observed decreasing trends during the simulation period. This model is the first attempt to represent the historical and current state of the Black Sea ecosystem spatially and temporally, serving as a reference baseline for evaluating policy scenarios and assisting policy makers in the evaluation of potential environmental impacts of management options
Yeni aktivite tabanlı model geliştirmeyi desteklemek için farklı kentsel alt bölgelerin seyahat davranış örüntülerinin incelenmesi
No full textTransportation plays a vital role in shaping mobility patterns and access to opportunities in cities; it is important to forecast the travel patterns, when planning a city and its transportation infrastructure. Compared to traditional Four-Step travel demand forecasting, nowadays Activity-Based Model (ABM) approaches are preferred more, as they can better capture real travel behaviour (such as touring, activity scheduling, etc.). In case of data availability problems, a simplistic rule-ABM aims defining travel decisions (i.e. travel making, departure time, destination distance, travel time, etc.), obtained from a household travel survey (HHTS) results, used for trip/activity pattern generation. For large metropolitan areas, a main problem is definition of modelling region(s) for rule generation, as subregions can show different characteristics (i.e. share of commute trips, departure times, mode choices, etc.). This study investigates the need for developing subregion-specific ABM rules in a city, as an alternative to general rules. To test the hypothesis, three subregions from the northern corridor of İzmir Functional Urban Area (FUA) are selected to study as i) Karşıyaka Vicinity subregion with city characteristics, ii) a transitional region of Menemen District, and iii) remotely located mono-centric subregion of Aliağa District. The findings reveal significant differences by region, especially in terms of departure times, trip lengths, mode preferences, and travel probabilities, which supports the need to develop ABM rules for different urban subregions to better represent the urban travel demand generation.Ulaşım, şehirlerdeki hareketlilik modellerini ve fırsatlara erişimi şekillendirmede hayati bir rol oynar; bir şehri ve ulaşım altyapısını planlarken seyahat modellerini tahmin etmek önemlidir. Geleneksel Dört Adımlı seyahat talebi tahminine kıyasla, günümüzde Aktivite Tabanlı Model (ABM) yaklaşımları daha çok tercih edilmektedir, çünkü gerçek seyahat davranışlarını (tur, aktivite planlama vb.) daha iyi yakalayabilmektedir. Veri kullanılabilirliği sorunları durumunda, basit bir kural-ABM, seyahat kararlarını (yani seyahat yapma, hareket saati, varış noktası mesafesi, seyahat süresi vb.) tanımlamayı amaçlar ve bu, seyahat/aktivite modeli oluşturmak için kullanılan bir hanehalkı seyahat anketi (HHTS) sonuçlarından elde edilir. Büyük metropol alanları için, ana sorun kural oluşturma için modelleme bölgesinin/bölgelerinin tanımlanmasıdır, çünkü alt bölgeler farklı özellikler gösterebilir (yani işe gidip gelme yolculuklarının payı, hareket saatleri, mod seçimleri vb.). Bu çalışma, genel kurallara alternatif olarak bir şehirde alt bölgeye özgü ABM kurallarının geliştirilmesi ihtiyacını araştırmaktadır. Hipotezi test etmek için, İzmir Fonksiyonel Kentsel Alanı'nın (FUA) kuzey koridorundan i) Kent özelliklerine sahip Karşıyaka Civarı alt bölgesi, ii) geçiş bölgesi olan Menemen İlçesi ve iii) uzakta tek merkezli alt bölgesi olan Aliağa İlçesi'nin üzere üç alt bölge incelenmek üzere seçilmiştir. Bulgular, özellikle hareket saatleri, seyahat uzunlukları, mod tercihleri ve seyahat olasılıkları açısından bölgelere göre önemli farklılıklar ortaya koymaktadır ve bu da kentsel seyahat talebi üretimini daha iyi temsil etmek için farklı kentsel alt bölgeler için ABM kurallarının geliştirilmesi ihtiyacını desteklemektedir.M.S. - Master of Scienc