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Permanent URI for this collectionhttps://hdl.handle.net/20.500.14288/3
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Publication Metadata only Metric-bourbaki algebroids: cartan calculus for m-theory(Elsevier, 2024) Çatal-Özer, Aybike; Doğan, Keremcan; Department of Physics; Dereli, Tekin; Department of Physics; College of SciencesString and M theories seem to require generalizations of usual notions of differential geometry on smooth manifolds. Such generalizations usually involve extending the tangent bundle to larger vector bundles equipped with various algebroid structures such as Courant algebroids, higher Courant algebroids, metric algebroids, or G-algebroids. The most general geometric scheme is not well understood yet, and a unifying framework for such algebroid structures is needed. Our aim in this paper is to propose such a general framework. Our strategy is to follow the hierarchy of defining axioms for a Courant algebroid: almostCourant - metric - pre -Courant - Courant. In particular, we focus on the symmetric part of the bracket and the metric invariance property, and try to make sense of them in a manner as general as possible. These ideas lead us to define new algebroid structures which we dub Bourbaki and metric-Bourbaki algebroids, together with their almostand pre -versions. For a special case of metric-Bourbaki algebroids that we call exact, we construct a collection of maps which generalize the Cartan calculus of exterior derivative, Lie derivative and interior product. This is done by a kind of reverse -mathematical analysis of the Severa classification of exact Courant algebroids. By abstracting crucial properties of this collection of maps, we define the notion of Bourbaki calculus. Conversely, given an arbitrary Bourbaki calculus, we construct a metric-Bourbaki algebroid by building up a standard bracket that is analogous to the Dorfman bracket. Moreover, we prove that any exact metric-Bourbaki algebroid satisfying some further conditions has to have a bracket that is the twisted version of the standard bracket; a partly analogous result to Severa classification. We prove that many physically and mathematically motivated algebroids from the literature are examples of these new algebroids, and when possible we construct a Bourbaki calculus on them. In particular, we show that the Cartan calculus can be seen as the Bourbaki calculus corresponding to an exact higher Courant algebroid. We also point out examples of Bourbaki calculi including the generalization of the Cartan calculus on vector bundle valued forms. One straightforward generalization of our constructions might be done by replacing the tangent bundle with an arbitrary Lie algebroid A. This step allows us to define an extension of our results, A -version, and extend our main results for them while proving many other algebroids from the literature fit into this framework.Publication Metadata only Mesocarnivores den site selection in arid ecosystems; a case study of Rüppell's fox and sand cat in central Iran(Elsevier, 2024) Feizabadi, Hossein Akbari; Ashrafi, Sohrab; Hemami, Mahmoud R.; Ahmadi, Mohsen; Department of Physics; Naderi, Mortaza; Department of Physics; College of SciencesUnderstanding the relationships between species and their pattern of coexistence is essential in conservation planning. Ruppell's fox and sand cat are two poorly known species of desert areas that coexist in most parts of the desert belt of Africa and the Middle East. However, their habitat selection in many parts of their distribution are unknown. In this research, using the data collected from a three-year monitoring plan, we investigated the relationship between the den sites of Ruppell's fox and sand cat and habitat variables based on the generalized linear mixed model (GLMM) method. The results showed that for Ruppell's foxes, only the density of rodent burrows had a significant and positive effect. In the sand cat model, in addition to prey, vegetation density (P-value < 0.05) and vegetation height (P -value < 0.10) had significantly positive effects and elevation had a significantly negative effect (P-value < 0.10). We found that the sand cat is more specialized in habitat selection and depends more on the habitat cover. While the Ruppell's fox chose a more diverse range of soil and vegetation classes, the sand cat selected its den sites exclusively in sandy loam soils with the predominant cover of Haloxylon spp. and Caligonum spp. Acting as a generalist species, Ruppell's fox displayed a more pronounced response to human presence and selected dens with a broader view of their surroundings. These findings enhance our understanding of mesocarnivore coexistence in desert regions and provide valuable insights for the conservation planning of these species.Publication Metadata only Objective-free ultrasensitive biosensing on large-area metamaterial surfaces in the near-IR(AMER CHEMICAL SOC, 2024) Department of Physics; Ramazanoğlu, Serap Aksu; Öktem, Evren; Department of Physics; College of Sciences; Graduate School of Sciences and EngineeringPlasmonic metamaterials have opened new avenues in medical diagnostics. However, the transfer of the technology to the markets has been delayed due to multiple challenges. The need of bulky optics for signal reading from nanostructures patterned on submillimeter area limits the miniaturization of the devices. The use of objective-free optics can solve this problem, which necessitates large area patterning of the nanostructures. In this work, we utilize laser interference lithography (LIL) to pattern nanodisc-shaped metamaterial absorber nanoantennas over a large area (4 cm(2)) within minutes. The introduction of a sacrificial layer during the fabrication process enables an inverted hole profile and a well-controlled liftoff, which ensures perfectly defined uniform nanopatterning almost with no defects. Furthermore, we use a macroscopic reflection probe for optical characterization in the near-IR, including the detection of the binding kinematics of immunologically relevant proteins. We show that the photonic quality of the plasmonic nanoantennas commensurates with electron-beam-lithography-fabricated ones over the whole area. The refractive index sensitivity of the LIL-fabricated metasurface is determined as 685 nm per refractive index unit, which demonstrates ultrasensitive detection. Moreover, the fabricated surfaces can be used multiple times for biosensing without losing their optical quality. The combination of rapid and large area nanofabrication with a simple optical reading not only simplifies the detection process but also makes the biosensors more environmentally friendly and cost-effective. Therefore, the improvements provided in this work will empower researchers and industries for accurate and real-time analysis of biological systems.Publication Metadata only Temporal evolution of entropy and chaos in low amplitude seismic wave prior to an earthquake(Pergamon-Elsevier Science Ltd, 2023) Akilli, Mahmut; Ak, Mine; Department of Physics; Yılmaz, Nazmi; Department of Physics; College of SciencesThis study investigates the temporal changes of entropy and chaos in low-amplitude continuous seismic wave data prior to two moderate-level earthquakes. Specifically, we examine seismic signals before and during the Istanbul-Turkey earthquake of September 26, 2019 (M = 5.7), and the Duzce-Turkey earthquake of November 17, 2021 (M = 5.2), which occurred near the Marmara Sea region on the north-Anatolian fault line. We aim to identify changes in complexity and chaotic characteristics in the pre-earthquake seismic waves and explore the possibility of earthquake forecasting minutes before an earthquake. To accomplish this, we utilize windowed scalogram entropy and sample entropy methods and compared the results with Lyapunov exponents and windowed scale index. Our findings indicate that measuring the temporal change of entropy using windowed scalogram entropy is sensitive to the change in complexity due to the frequency shifts during the weak ground motion approaching an earthquake.On the other hand, Lyapunov exponents and sample entropy appear more effective in their response to the change in complexity and chaotic characteristics due to the change in the signal amplitude. Additionally, the windowed scale index can detect temporal fluctuations in the aperiodicity of the signal. Overall, our results suggest that all four methods can be valuable in characterizing complexity and chaos in short-time pre -earthquake seismic signals, differentiating earthquakes, and contributing to the development of earthquake forecasting techniques.Publication Metadata only Localized thermal emission from topological interfaces(American Association for the Advancement of Science, 2024) Ergöktaş, M. Said; Keçebaş, Ali; Despotelis, Konstantinos; Soleymani, Sina; Bakan, Gökhan; Principi, Alessandro; Rotter, Stefan; Özdemir, Şahin K.; Kocabaş, Coşkun; Department of Physics; Kocabaş, Aşkın; Department of Physics; College of SciencesThe control of thermal radiation by shaping its spatial and spectral emission characteristics plays a key role in many areas of science and engineering. Conventional approaches to tailoring thermal emission using metamaterials are hampered both by the limited spatial resolution of the required subwavelength material structures and by the materials' strong absorption in the infrared. In this work, we demonstrate an approach based on the concept of topology. By changing a single parameter of a multilayer coating, we were able to control the reflection topology of a surface, with the critical point of zero reflection being topologically protected. The boundaries between subcritical and supercritical spatial domains host topological interface states with near-unity thermal emissivity. These topological concepts enable unconventional manipulation of thermal light for applications in thermal management and thermal camouflage.Publication Metadata only Spontaneous scalarization(American Physical Society, 2024) Doneva, Daniela D.; Silva, Hector O.; Sotiriou, Thomas P.; Yazadjiev, Stoytcho S.; Department of Physics; Ramazanoğlu, Fethi Mübin; Department of Physics; College of SciencesScalarization is a mechanism that endows strongly self -gravitating bodies, such as neutron stars and black holes, with a scalar -field configuration. It resembles a phase transition in that the scalar configuration appears only when a certain quantity that characterizes the compact object, for example, its compactness or spin, is beyond a threshold. A critical and comprehensive review of scalarization, including the mechanism itself, theories that exhibit it, its manifestation in neutron stars, black holes and their binaries, potential extension to other fields, and a thorough discussion of future perspectives, is provided.Publication Metadata only Identifying connectivity for two sympatric carnivores in human-dominated landscapes in central Iran (vol 17, e0269179, 2022)(Public Library Science, 2023) Rezaei, Sahar; Mohammadi, Alireza; Bencini, Roberta; Rooney, Thomas; Department of Physics; Department of Physics; ; College of Sciences;The affiliation for the last author is incorrect. The correct affiliation for Morteza Naderi is Arak University. An additional affiliation is missing for the last author. Morteza Naderi is also affiliated with the Department of Molecular Biology and Genetics, Faculty of Sciences, Koc University, Istanbul, Turkey. © 2023 Rezaei et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.Publication Metadata only Loss of hyperbolicity and tachyons in generalized Proca theories(American Physical Society, 2023) ; Department of Physics; Ünlütürk, Kıvanç İbrahim; Coates, Andrew; Ramazanoğlu, Fethi Mübin; Department of Physics; ; Graduate School of Sciences and Engineering; College of Sciences;Various groups recently demonstrated that the time evolution of the simplest self-interacting vector fields, those with self-interaction potentials, can break down after a finite duration in what is called loss of hyperbolicity. We establish that this is not an isolated issue, and other generalizations of the Proca theory suffer from the same problem. Specifically, we show that vector field theories with derivative self-interactions have a similar pathology. For this, we derive the effective metric that governs the dynamics, and show that it can change signature during time evolution. We also show that, generalized Proca theories may suffer from tachyonic instabilities as well, which lead to another form of unphysical behavior. © 2023 American Physical Society.Publication Metadata only Crossing the singularity of a gravitational wave collision(American Physical Society, 2024) Gurtug, Ozay; Department of Physics; Ünlütürk, Kıvanç İbrahim; Dereli, Tekin; Department of Physics; ; Graduate School of Sciences and Engineering; College of Sciences;A reformulation of general relativity inspired by the Belinski-Khalatnikov-Lifshitz conjecture had been introduced by Ashtekar, Henderson, and Sloan which is based on variables closely related to the basic variables of loop quantum gravity, thereby providing a way of classically analyzing singularities that may be carried over to the quantum theory. It is reasonable to expect that these variables are regular at generic spacelike singularities. This has been shown on various examples-particularly, cosmological spacetimes. In this study we extend this analysis to the singularities of gravitational wave collision spacetimes, which are the result of the mutual focusing of the two waves. We focus on two specific examples and explicitly confirm that the said variables are regular at the singularity and can be smoothly continued beyond it.Publication Metadata only Defect-populated configurations in nematic solid tori and cylinders(American Physical Society, 2024) Rojo-Gonzalez, Javier; de la Cotte, Alexis; Hoffmann, Ludwig A.; Giomi, Luca; Fernandez-Nieves, Alberto; Department of Physics; Carenza, Livio Nicola; Department of Physics; ; College of Sciences;We make toroidal droplets of nematic liquid crystal and explore the defect -populated stable configurations that appear after heating to the isotropic phase and cooling back to the nematic phase. These configurations, as confirmed by simulations, are made of defect pairs where the positive/negative defect is located in the region of maximum positive/negative Gaussian curvature. Moreover, we demonstrate through experiments and simulations that these defect pairs also appear and are stable in cylinders, which have zero Gaussian curvature, highlighting the crucial role of bulk nematic elasticity in stabilizing these structures.