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Simulation and machine learning-integrated investigation of double-linker MOFs for the separation of CF4 from CH4 and N2
No full textOne of the most crucial problems of the modern world is to combat the emission of greenhouse gases as these lead to extreme weather conditions, droughts, etc., and endanger the global ecosystem. Among the various greenhouse gases, the removal of carbon tetrafluoride, CF4, from the atmosphere is of particular interest as its global warming potential is several orders of magnitude higher than that of many other greenhouse gases, including carbon dioxide, CO2. The separation of CF4 from methane, CH4, and nitrogen, N-2, which are present in the atmosphere alongside CF4, can be efficiently accomplished by adsorption- or membrane-based processes. Metal-organic frameworks (MOFs) offer a variety of possibilities for gas separation due to their large surface areas and tailored chemical and physical structures. In this work, the separation of CF4/CH4, CF4/N-2, and CF4/CH4/N-2 in a subset of MOFs, double-linker MOFs (DL-MOFs), is investigated by using molecular simulations and machine learning (ML) methods. Among similar to 500 MOFs, the best MOFs for adsorption-based CF4/CH4, CF4/N-2, and CF4/CH4/N-2 separation are determined by considering the adsorption selectivity, working capacity, and regenerability. The ML models developed for adsorption-based CF4/CH4, CF4/N-2, and CF4/CH4/N-2 separation have revealed that only one or two features (Henry's constant and/or surface area) are sufficient to establish models that can make accurate predictions of gas uptake. The membrane-based CF4/CH4 and CF4/N-2 separation performances of DL-MOFs have also been studied, and it was found that inverse selective MOFs preferring CH4 or N-2 over CF4 can exist. Overall, this study will open avenues for the design and development of novel MOF adsorbents and membranes for the separation of CF4 from CH4 and N-2 by providing atomistic insights into the adsorption and diffusion properties of DL-MOFs.TÜBİTAK ; National Center for High Performance Computing of Turkey UhemPublisher versio
Grid-connected five-level split-source packed U-cell inverter - A proof of concept
No full textThis paper proposes a grid-connected single-stage multilevel inverter topology as a proof of concept, which is based on the five-level packed U-cell (PUC5) and the split-source inverter (SSI) topologies. The distinctive feature of the proposed topology is that it can boost the input voltage without requiring a separate DC-DC converter, only by adding three passive components to the original PUC5: a capacitor, an inductor, and a diode. Moreover, despite the added passive components, the proposed topology can still benefit from the sensor-less voltage balancing technique originally introduced for PUC5 to balance the voltage of its flying capacitor without the need for an external controller. The voltage gain is affected by different system parameters due to discontinuous conduction mode operation. The simulation results obtained using MATLAB/Simulink verified the functionality and potential of the single-stage topology introduced.IEEE Industrial Electronics Society (IES
A look into the future: the impact of metaverse on traditional theories and thinking in international business
No full textLeaders' experience and the transition from populism to dictatorship
No full textA growing body of research shows that although populists draw on mass support to weaken executive constraints, they rarely transition to personalist autocracy. This raises the question of how and why only a few populist leaders have been able to leverage mass support to establish personal authoritarian rule? Whereas previous studies have addressed this in terms of deep social and economic crises or the durability of formal and informal democratic institutions, we focus on the agency of populist leaders themselves. Specifically, we theorize that more experienced leaders are better able to capture state institutions and ultimately establish authoritarian rule, particularly if they inherit more malleable institutions at entry into office. We present a newly enlarged dataset of populist rule, which confirms that the transition to full dictatorship is rare. We find that political experience has a robust positive association with full democratic reversals, while controlling for other factors. Moreover, this relationship is pronounced in contexts where institutional regulations are less rigid. However, we find little evidence of an independent effect of a priori institutional weakness on democratic survival. Our findings have implications for the literatures on populism, democratic backsliding, and political leadership.Australian National University, Department of Political Social ChangePublisher versio
Regime uncertainty, democratic erosion and resilience, and turkish opposition actors
No full textWhich peculiar uncertainties does democratic erosion (DE) pose to opposition actors? How have these uncertainties influenced the behavior of opposition actors during Turkey's autocratization since the early 2000s? What can we learn from this case regarding the links between DE and opposition behavior? The latter should be treated as an integral part of explaining DE-the gradual decline in the quality of multiple aspects of democracy under popularly elected governments. We argue that a contextual uncertainty, "regime uncertainty" (RU) challenged Turkish opposition actors, compounding the other and related uncertainties they faced such as institutional and strategic uncertainties and affecting their resilience against DE. RU concerns the ambivalence that DE's inherent qualities generate about what the regime is, or is becoming. The resulting intra-opposition divisions and indecisions raise the question of whether the primary context, frame and end of opposition politics should be issue- and party-based competitive politics or defending democracy against an imminent threat. Hence, RU generates recurring rifts over "normal" versus "extraordinary" politics. We analyze the Turkish experience and intra-opposition politics in four sub-periods (nascent DE, consolidation of erosive power, advanced DE, breakdown and post-breakdown opposition experimentation). Turkish opposition actors' RU perceptions and resulting behaviors evolved on highly non-linear paths. We offer novel analytical/theoretical tools and argue that the agency and capacity of oppositions to overcome RU in a country, alongside their ability to surmount other challenges, should be considered an integral part of democratic resilience against erosion
The effectiveness of inclusive design approaches in the transformation of public spaces: A study on the case of İstanbul.
No full textCities worldwide undergo various transformations influenced by local and global factors. The design approaches used in this process determine the interaction of urban spaces with their users and lead to qualitative urban changes through the reproduction of space [1][2][3][4][5]. According to Gehl (2010), qualified urban space is an environment that facilitates encounters, interaction, and urban life [6]. In this context, inclusive spatial design approaches that make space for multiple users have been observed to positively affect the quality of public life by providing a diverse environment [7][8][9]. The quality of life in urban areas is improving, leading to sustainable and healthy urban space uses [10]. In urban planning, public spaces are becoming increasingly important in terms of time, users, and power relations [11]. To offer a diversity of experiences, cities should program spaces with contemporary connections to local culture and society, which can help build a sense of social identity in a particular place [6][12]. As urban resilience develops, it may be possible to recreate and develop a sense of social identity in public spaces in Istanbul, a city that has undergone many changes. [13]. This thesis explores the development of inclusive design approaches in the literature and their reflection in local thesis research in Turkey. It also investigates the effectiveness of these approaches in transforming public spaces in Istanbul. The study begins with a literature review based on the keywords 'sustainability, urban space, and human-place relationship', which are broad concepts related to the city. The literature and local sources analyze the impact areas of the theories and concepts produced in the context of the inclusive design approach over the years. The subsequent identification of the theoretical and conceptual development of urban design movements that evolved with these phases follows. The distribution and concentration processes of the identified keywords and concepts were used to map their reflection in local theses. The study analyzed the strategy plans and master plans of Istanbul's central public administration published between 2020 and 2023 using the same methodology. Additionally, the effectiveness of the inclusive spatial design process in Istanbul was investigated by identifying two areas where inclusion-based phased strategies have been advanced to the implementation process. Surveys and interviews were conducted in Zümrütevler Square in Maltepe district and Ordu Street in Fatih district to measure their effectiveness. The discussions focused on the current transformations of these areas and how they relate to the evolution of current inclusive spatial design approaches in the local context. The thesis provides valuable insights for individuals and institutions interested in understanding the design of public spaces in Istanbul, the local evolution of inclusive design, progressive strategies for promoting healthy urban spaces, and commonalities in their use.Dünya üzerinde farklı kimliklere ve kültürel yapılara sahip olan kentler, yerel ve global etkiler ile çeşitli dönüşümler geçirmektedirler. Yapılan araştırmalar ve uygulamalar, bu süreçte kullanılan tasarım yaklaşımlarının, kentsel alanların kullanıcıları ile etkileşimini belirlerken, mekanın yeniden üretimi ile de niteliksel kentsel değişimlerin doğduğunu ortaya koymaktadır [1][2][3][4][5]. Gehl (2010), nitelikli kentsel mekanı, daha fazla karşılaşmayı, etkileşimi ve kent yaşamını sunan bir ortam olarak tanımlamaktadır [6]. Bu bağlamda yapılan çeşitli uygulama süreçlerinde, kapsayıcı mekansal tasarım yaklaşımları geliştirerek çoklu kullanıcılara yer açabilmenin, çeşitlilik ortamı sağlayarak, kamusal yaşam kalitesini olumlu yönde etkilediği gözlemlenmektedir [7][8][9]. Artan kentsel alanlardaki yaşam kalitesi de sürdürülebilir ve sağlıklı gelişen kentsel mekan kullanımlarını da beraberinde getirir [10]. Kentlerdeki dönüşümlerde, kamusal olan yer; zaman, kullanıcı ve güç ilişkileri bağlamları ile her geçen gün daha önemli hale gelmektedir [11]. Şehirlerdeki deneyim çeşitliliğine yönelik olarak mekanların yerel kültürle ve toplumla güncel bağlantılarıyla programlanması, bir 'yer'deki sosyal kimlik duygusunu inşa edilebilir [6][12]. Değişikliklerle başa çıkabilmek, onlara uyum sağlayabilmek ve hatta onları şekillendirebilmek anlamına gelen 'kentsel dirençlilik' geliştikçe de çok sayıda değişime ev sahipliği yapan İstanbul'daki kamusal alanlarda 'yeniden' yaratımın ve sosyal kimlik duygusunun gelişebilmesi mümkün olabilir. [13] Tez çalışmasında, kapsayıcı tasarım yaklaşımlarının alanyazın çalışmalarında nasıl geliştiği ve Türkiye'deki yerel tez araştırmalarına ne şekilde yansıdığı incelenerek bu yaklaşımın, İstanbul'daki kapsayıcılık temelli yaklaşımlar ile dönüştürülen kamusal alanlardaki etkinliği araştırılmaktadır. İlkin, kente ilişkin üst ölçek kavramlardan 'sürdürülebilirlik, kentsel mekan ve insan-yer ilişkisi' anahtar kelimelerinden yola çıkılarak alanyazın taraması yapılmıştır. Yıllar içinde kapsayıcı tasarım yaklaşımı bağlamında üretilen önde gelen kuramların ve kavramların alanyazın çalışmalarındaki ve yerel kaynaklardaki kronolojik etki alanları incelenmiştir. Ardından, bu evrelerle gelişen kentsel tasarım akımlarının, bu gelişim içindeki yerleri saptanmıştır. Taramalarda belirlenen anahtar kelimelerin ve kavramların, yerel tez araştırmalarına ne ölçüde yansıdıkları, kavramların dağılımı ile yoğunlaşma süreçleri ele alınarak haritalandırılmıştır. Diğer yandan, İstanbul merkezi kamu yönetiminin, 2020-2023 yılları arasında yayınlanan strateji planları ve ana planları bu çerçevede ve aynı yöntemle incelenmiştir. Son olarak, İstanbul'da kapsayıcı mekansal tasarım sürecinin etkinliğini araştırmak üzere, kapsayıcılık temelli aşamalı stratejilerle uygulama sürecine kadar ilerletilen iki kamusal alan tespit edilmiştir. Bu sürecin etkinliğin ölçülmesine yönelik temsili alanlar olarak seçilen Maltepe ilçesindeki Zümrütevler Meydanı ve Fatih ilçesindeki Ordu Caddesi'nde, anket ve görüşmeler gerçekleştirilmiş, mevcut dönüşümleri ve bunların yerel bağlamdaki güncel kapsayıcı mekânsal tasarım yaklaşımlarının evrimi ile nasıl ilişkilendiği ele alınmıştır. Tez çalışması, İstanbul'daki kamusal alanların tasarımı, kapsayıcı tasarımın yerel evrim süreci, sağlıklı kentsel mekanlar için aşamalı stratejiler ve kullanımda ortaklaşalık hakkında bilgi edinmek isteyen kişiler ve kurumlar için faydalı olabilir
On the damping performance and mechanical response of additive-manufactured and thermo-mechanical processed alsimg alloy
No full textRecent advancements in additive manufacturing (AM) fuel efforts for expanding the design envelopes for components obtained via this technology through continuous improvement in mechanical behavior. Damping properties can also be altered depending on the microstructure evolved during AM. Therefore, achieving enhanced monotonic mechanical response with better damping properties is highly sought-after. In this respect, thermo-mechanical processing via severe plastic deformation (SPD) and artificial aging is imparted on the additive-manufactured samples with the target of grain refinement and densification to further improve mechanical and damping properties. Employing microstructural characterizations and mechanical experiments, a multi-scale exploration is carried out to develop a relation between the evolved microstructure and the resulting behavior. It is concluded that introducing a refined microstructure decorated with well-distributed (Mg,Si)-rich phase and favorable dislocation substructure in AlSi10Mg positively affects the resulting mechanical behavior. Moreover, it is shown that artificial aging can be employed to improve the damping characteristics of severely deformed additive-manufactured AlSi10Mg alloy.BAGEP Award of Bilim Akademisi ; Ozyegin University ; TÜBİTAKPublisher versio
Comparative study of reconfigurable intelligent surfaces against relay systems: Amplify-and-forward and decode-and-forward approaches
No full textThe concept of reconfigurable intelligent surfaces (RISs) has emerged as a promising paradigm for manipulating the channel propagation environment to satisfy the targeted key performance indicators for future wireless communication systems. This paper investigates the performance of RISs in wireless communication systems compared to traditional relay-assisted systems with some specific scenarios. We employ detailed simulations to analyze the impact of RIS elements on system performance. Our findings demonstrate that increasing the number of RIS elements leads to significant improvements in key performance metrics, particularly for the bit error rate (BER) and the path-loss (PL) impact on the system. However, the study also reveals a critical circumstance that RIS-aided system performance can change dramatically when positioned at a specific location. This research also compares and shows performance divergences between RIS, amplify-and-forward (AF) and decode-and-forward (DF) relays at different positions for all systems
Correction: ProbC: Joint modeling of epigenome and transcriptome effects in 3D genome
No full textFollowing publication of the original article it was reported there was a missing declaration of funding in the Funding declaration. The updated Funding declaration with the newly added text in bold is given below. Ozyegin University Research Grant. This research was funded by TUBITAK (Scientific and Technological Research Council of Turkey) 3501 Project with grant number 122E706. The original article has been updated.TÜBİTAKPublisher versio
Investigating strategies of the european air transport network after covid-19: A complex network theory analysis
No full textThis study explores the new strategic planning of the airports in Europe after COVID-19 based on number of connections and passenger seat capacity. Complex network theory was applied to reveal the European airport network using the Official Airline Guide dataset between September 2021 and August 2022. This study aims to identify changes in the strategy of airports operating in Europe and variations in European hubs for passenger transport based on supply (seat capacity) in the year following the COVID-19 pandemic. 693 airports (nodes) and 10 333 routes (edges) were examined in 44 European countries. Centrality metrics have highlighted different airports as pivots. While London Stansted Airport came to the forefront with the highest degree centrality, Amsterdam Schiphol Airport emerged as leader by connecting to highly influential airports with the best eigenvector and strength centrality metrics. Betweenness centrality also demonstrated that Istanbul Airport served as a critical connector, facilitating efficient routes between other airports. Connectivity, efficiency, and organizational patterns were also examined to provide a comprehensive overview of the European airport network. Average degree, clustering coefficient, average path length, diameter, reciprocity, and assortativity were calculated in the scope of connectivity. Each airport in the network is connected to around 29 others. The average path length was calculated as 2.66 to demonstrate how many average flights are needed to travel from one airport to any other in the network