Atılım Akademik Arşivi
Atılım Academic Archive
Atılım Akademik Arşivi; hakemli makaleleri, teknik raporları, çalışma raporlarını, yüksek lisans / doktora tezlerini ve daha fazlasını içeren Atılım Üniversitesi araştırma ekosistemi için oluşturulmuş bir dijital açık arşivdir.
Atılım Academic Archive; It is a digital open archive created for the Atılım University research ecosystem, which includes peer-reviewed articles, technical reports, study reports, master's / doctoral theses and more.
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Recent Submissions
Towards mmWave Altimetry for UAS: Exploring the Potential of 77 GHz Automotive Radars
(Drones, 2024-03-11) Awan, Maaz Ali; Dalveren, Yaser; Kara, Ali; Derawi, Mohammad
Precise altitude data are indispensable for flight navigation, particularly during the au tonomous landing of unmanned aerial systems (UASs). Conventional light and barometric sensors
employed for altitude estimation are limited by poor visibility and temperature conditions, respec tively, whilst global positioning system (GPS) receivers provide the altitude from the ean sea level (MSL) marred with a slow update rate. To cater to the landing safety requirements, UASs necessitate precise altitude information above ground level (AGL) impervious to environmental conditions. Radar altimeters, a mainstay in commercial aviation for at least half a century, realize these requirements through minimum operational performance standards (MOPSs). More recently, the proliferation of 5G technology and interference with the universally allocated band for radar altimeters from 4.2 to 4.4 GHz underscores the necessity to explore novel avenues. Notably, there is no dedicated MOPS tailored for radar altimeters of UASs. To gauge the performance of a radar al timeter offering for UASs, existing MOPSs are the de facto choice. Historically, frequency-modulated continuous wave (FMCW) radars have been extensively used in a broad spectrum of ranging ap plications including radar altimeters. Modern monolithic millimeter wave (mmWave) automotive radars, albeit designed for automotive applications, also employ FMCW for precise ranging with a
cost-effective and compact footprint. Given the technology maturation with excellent size, weight, and power (SWaP) metrics, there is a growing trend in industry and academia to explore their efficacy beyond the realm of the automotive industry. To this end, their feasibility for UAS altimetry remains largely untapped. While the literature on theoretical discourse is prevalent, a specific focus on mmWave radar altimetry is lacking. Moreover, clutter estimation with hardware specifications of a pure look-down mmWave radar is unreported. This article argues the applicability of MOPSs for commercial aviation for adaptation to a UAS use case. The theme of the work is a tutorial based on a simplified mathematical and theoretical discussion on the understanding of performance metrics and inherent intricacies. A systems engineering approach for deriving waveform specifications from operational requirements of a UAS is offered. Lastly, proposed future research directions and insights are included.
A Radio Frequency Fingerprinting-Based Aircraft Identification Method Using ADS-B Transmissions
(Aerospace, 2024-03-17) Gürer, Gürsu; Dalveren, Yaser; Kara, Ali; Derawi, Mohammad
The automatic dependent surveillance broadcast (ADS-B) system is one of the key components of the next generation air transportation system (NextGen). ADS-B messages are transmitted in unencrypted plain text. This, however, causes significant security vulnerabilities, leaving the system open to various types of wireless attacks. In particular, the attacks can be intensified by simple hardware, like a software-defined radio (SDR). In order to provide high security against such attacks, radio frequency fingerprinting (RFF) approaches offer reasonable solutions. In this study, an RFF method is proposed for aircraft identification based on ADS-B transmissions. Initially, 3480 ADS-B samples were collected by an SDR from eight aircrafts. The power spectral density (PSD) features were then extracted from the filtered and normalized samples. Furthermore, the support vector machine (SVM) with three kernels (linear, polynomial, and radial basis function) was used to identify the aircraft. Moreover, the classification accuracy was demonstrated via varying channel signal-to-noise ratio (SNR) levels (10–30 dB). With a minimum accuracy of 92% achieved at lower SNR levels (10 dB), the proposed method based on SVM with a polynomial kernel offers an acceptable
performance. The promising performance achieved with even a small dataset also suggests that the proposed method is implementable in real-world applications.
Revealing photoluminescence and nonlinear optical absorption characteristics of PbMo0.75W0.25O4 single crystal for optical limiting applications
(Physica Scripta, 2024-04-18) Doğan, Anıl; Karatay, Ahmet; Işık, Mehmet; Akhüseyin Yıldız, Elif; Gasanly, Nizami Mamed; Elmalı, Ayhan
Nonlinear absorption properties of PbMo0.75W0.25O4 single crystal fabricated by the Czochralski method were studied. The band gap energy of the crystal was determined as 3.12 eV. Urbach energy which represents the defect states inside the band gap was found to be 0.106 eV. PbMo0.75W0.25O4 single crystal has a broad photoluminescence emission band between 376 and 700 nm, with the highest emission intensity occurring at 486 nm and the lowest intensity peak at 547 nm, depending on the defect states. Femtosecond transient absorption measurements reveal that the lifetime of localized defect states is found to be higher than the 4 ns pulse duration. Open aperture (OA) Z-scan results demonstrate that the PbMo0.75W0.25O4 single crystal exhibits nonlinear absorption (NA) that includes two-photon absorption (TPA) as the dominant mechanism at the 532 nm excitations corresponding to 2.32 eV energy. NA coefficient (βeff) increased from 7.24 × 10−10 m W−1 to 8.81 × 10−10 m W−1 with increasing pump intensity. At higher intensities βeff tends to decrease with intensity increase. This decrease is an indication that saturable absorption (SA) occurred along with the TPA, called saturation of TPA. The lifetime of the defect states was measured by femtosecond transient absorption spectroscopy. Saturable absorption behavior was observed due to the long lifetime of the localized defect states. Closed aperture (CA) Z-scan trace shows the sign of a nonlinear refractive index. The optical limiting threshold of PbMo0.75W0.25O4 single crystal at the lowest intensity was determined as 3.45 mJ/cm2. Results show that the PbMo0.75W0.25O4 single crystal can be a suitable semiconductor material for optical limiting applications in the visible region.
Temperature-dependent tuning of band gap of Fe3O4 nanoparticles for optoelectronic applications
(Chemical Physics Letters, 2024-02-19) Delice, Serdar; Işık, Mehmet; Gasanly, Nizami Mamed
We have investigated structural, morphological and temperature dependent absorption characteristics of Fe3O4 nanoparticles. X-ray diffraction pattern exhibited six diffraction peaks belonging to the cubic phase structure with lattice parameter of a = 8.1602 Å. Spectral variation of absorption coefficient were utilized to achieve Tauc and spectral derivative analyses providing the band gap of the Fe3O4 at varying temperature. The band gap of Fe3O4 nanoparticles was found around 2.08 eV at 300 K and around 2.14 eV at 10 K. The band gap variation with applied temperatures between 10 and 300 K were also investigated using Varshni relation.
Dissident women’s organizations as a counter-hegemonic actor in Turkey
(Turkish Studies, 2023-05-02) Gündüz, Melisa; Gençoğlu, Funda
Could the Turkish women’s movement, which has a strong reaction mechanism, be a constituent actor of counter-hegemony? The main reasons behind this question are the women’s movement’s deep-rooted history and its openness to combine theory with practice/action. When looked from the Chantal Mouffe and Ernesto Laclau’s perspective of radical democracy theory, the women’s movement appears to have a considerable potential of deciphering the existing hegemony and articulating the social demands which exclude and are excluded by the present-day hegemony in Turkey. This article tries to understand how women’s movement in Turkey conceptualizes the existing power relations that constitute the neoliberal religio-conservative hegemony and how it responds to it.
Structural and Optical Properties of Interfacial InSe Thin Film
(ACS Omega, 2024-02-09) Emir, Cansu; Tataroğlu, Adem; Coşkun, Emre; Ocak, Sema Bilge
This study presents a comprehensive investigation of the optical and structural characteristics of the indium selenide (InSe) film prepared on a glass substrate. The structural characteristics of the InSe film were analyzed using characterization techniques including X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy while the UV–vis spectrophotometry method was used in the spectral range between 500 and 1000 nm to examine the optical characteristics. Thus, the UV–vis spectroscopic data were used to extract several optical parameters including extinction coefficient (k), optical band gap (Eg), refractive index (n), absorption coefficient (α), and optical conductivity (σopt). The optical transition of InSe was found as a direct transition. However, the optical analysis of this study has revealed that the InSe film has the potential to be used in various optoelectronic and photovoltaic applications.
On relations between transportation cost spaces and ℓ1
(Journal of Mathematical Analysis and Applications, 2020-11-15) Ostrovska, Sofiya; Ostrovskii, Mikhail I.
The present paper deals with some structural properties of transportation cost spaces, also known as Arens-Eells spaces, Lipschitz-free spaces and Wasserstein spaces. The main results of this work are: (1) A necessary and sufficient condition on an infinite metric space M, under which the transportation cost space on M contains an isometric copy of ℓ1.The obtained condition is applied to answer the open questions asked by Cúth and Johanis (2017) concerning several specific metric spaces. (2) The description of the transportation cost space of a weighted finite graph G as the quotient ℓ1(E(G))/Z(G), where E(G) is the edge set and Z(G) is the cycle space of G.
Real-Time Learning and Monitoring System in Fighting against SARS-CoV-2 in a Private Indoor Environment
(Sensors, 2022-11-15) Erişen, Serdar
The SARS-CoV-2 virus has posed formidable challenges that must be tackled through scientific and technological investigations on each environmental scale. This research aims to learn and report about the current state of user activities, in real-time, in a specially designed private indoor environment with sensors in infection transmission control of SARS-CoV-2. Thus, a real-time learning system that evolves and updates with each incoming piece of data from the environment is developed to predict user activities categorized for remote monitoring. Accordingly, various experiments are conducted in the private indoor space. Multiple sensors, with their inputs, are analyzed through the experiments. The experiment environment, installed with microgrids and Internet of Things (IoT) devices, has provided correlating data of various sensors from that special care context during the pandemic. The data is applied to classify user activities and develop a real-time learning and monitoring system to predict the IoT data. The microgrids were operated with the real-time learning system developed by comprehensive experiments on classification learning, regression learning, Error-Correcting Output Codes (ECOC), and deep learning models. With the help of machine learning experiments, data optimization, and the multilayered-tandem organization of the developed neural networks, the efficiency of this real-time monitoring system increases in learning the activity of users and predicting their actions, which are reported as feedback on the monitoring interfaces. The developed learning system predicts the real-time IoT data, accurately, in less than 5 milliseconds and generates big data that can be deployed for different usages in larger-scale facilities, networks, and e-health services.
Emergency response, and community impact after February 6, 2023 Kahramanmaraş Pazarcık and Elbistan Earthquakes: reconnaissance findings and observations on affected region in Türkiye
(Bulletin of Earthquake Engineering, 2024-02-07) Şenol Balaban, Meltem; Doğulu, Canay; Akdede, Nil; Akoğlu, Haldun; Karakayalı, Onur; Yılmaz, Sarper; Yılmaz, Serkan; Ajobiewe, Tolulope; Güzel, Selin; İkizer, Gözde; Akın, Müge; Ünal, Yeşim; Karancı, Ayşe Nuray
Türkiye has a long history of devastating earthquakes, and on February 6, 2023, the region experienced two major earthquakes with magnitudes of 7.7 and 7.6, striking Pazarcık and Elbistan, Kahramanmaraş, respectively, on the East Anatolian Fault Zone. These earthquakes resulted in significant loss of life and property, impacting multiple cities across 11 cities, and leaving a lasting impact on the country. The 2023 Kahramanmaraş Earthquakes rank among the deadliest and most damaging earthquakes in Türkiye, alongside the historical significance of the 1939 Erzincan Earthquake and the 1999 Marmara Earthquake. Despite reforms following the 1999 Marmara Earthquake in disaster policy and preparedness, the scale of damage from the February 6 earthquakes has been shocking, necessitating further insights and lessons for future earthquake management. This paper presents the outcomes of immediate response efforts organized after the 2023 Kahramanmaraş earthquakes to elucidate emergency response activities and their impacts on communities, considering the substantial size and severity of the damages. The study focuses on evaluating the emergency response provided within the first 24 h, 3 days, and 2 weeks after the earthquakes, aiming to promptly identify the nature and effectiveness of these responses, as well as the conditions that hindered their efficacy. By shedding light on the specific experiences and challenges faced during these crucial timeframes, the research aims to offer valuable insights and lessons learned. These findings contribute to improved preparedness strategies and more efficient emergency response measures needed in responding to future disaster scenarios. Ultimately, this study provides a useful resource for all stakeholders involved in emergency response and disaster management, offering valuable guidance to enhance resilience and preparedness in the face of seismic hazards.
Computational insight of lithium adsorption and intercalation in bilayer TiC3
(Electrochimica Acta, 2024-02-10) Park, Jongee; Fatima, Syeda Afrinish
Lithium-ion batteries (LIBs) have gained significant attention owing to their long lifespan. However, these batteries offer unmatched energy storage capacity and suffer from restricted lithium-ion mobility within the electrodes. Here, we employ first-principles calculation to investigate the two-dimensional TiC3 bilayer material. The results exhibit a remarkably high specific capacity of 1277 mAh/g and a low diffusion energy barrier of 0.12 eV. The TiC3 bilayer is anticipated to show high electrical conductivity, maintaining its metallicity due to strong bonding with four Li atoms. Additionally, its high thermal and dynamic stabilities are expected to significantly enhance the battery performance. Notably, the AB stacking bilayer TiC3 experiences a mere 6.01 % increase in volume, considerably smaller compared to the 28 % increase observed in the SiC bilayer. This suggests that TiC3 bilayers remain intact even at the highest concentration of lithium adsorptions. We also explored the solid-electrolyte interface (SEI) formation at the outset of battery operation using reactive force field molecular dynamics simulation. The reactive products of SEI are nicely matched with previous experimental and theoretical findings. All these intriguing properties position the TiC3 bilayer as an exceptionally promising material for use in LIBs.