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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On the continuity in q of the family of the limit q-Durrmeyer operators
(Demonstratio Mathematica, 2024-04-25) Gürel Yılmaz, Övgü; Ostrovska, Sofiya; Turan, Mehmet
The present paper deals with the one-parameter family {Dq}q∈[0,1] of Bernstein-type operators introduced by Gupta, and called the limit q-Durrmeyer operators. The continuity of this family with respect to the parameter q is examined in two most important topologies of the operator theory, namely, the strong and uniform operator topologies. It is proved that {Dq}q∈[0,1] is continuous in the strong operator topology for all q ∈ [0, 1]. When it comes to the uniform operator topology, the continuity is preserved solely at q = 0, and fails at all q ∈ (0, 1]. In addition, a few estimates for the distance between two limit q-Durrmeyer operators have been derived in the operator norm on C[0, 1].
Quartz crystal microbalance–based aptasensor integrated with magnetic pre‑concentration system for detection of Listeria monocytogenes in food samples
(Microchimica Acta, 2024-04-03) Beyazıt, Fatma; Arıca, Mehmet Yakup; Açıkgoz‑Erkaya, İlkay; Özalp, Veli Cengiz; Bayramoğlu, Gülay
A fast and accurate identifcation of Listeria monocytogenes. A new quartz crystal microbalance (QCM) aptasensor was designed for the specific and rapid detection of L. monocytogenes. Before detection of the target bacterium from samples inthe QCM aptasensor, a magnetic pre-enrichment system was used to eliminate any contaminant in the samples. The preparedmagnetic system was characterized using ATR-FTIR, SEM, VSM, BET, and analytical methods. The saturation magnetizationvalues of the Fe3O4, Fe3O4@PDA, and Fe3O4@PDA@DAPEG particles were 57.2, 40.8, and 36.4 emu/g, respectively.The same aptamer was also immobilized on the QCM crystal integrated into QCM flow cell and utilized to quantitativelydetect L. monocytogenes cells from the samples. It was found that a specific aptamer-magnetic pre-concentration systemefficiently captured L. monocytogenes cells in a short time approximately 10 min). The Fe3O4@PDA@DA-PEG-Apt particlesprovided selective isolation of L. monocytogenes from the bacteria-spiked media up to 91.8%. The immobilized aptamercontent of the magnetic particles was 5834 μg/g using 500 ng Apt/mL. The QCM aptasensor showed a very high range ofanalytical performance to the target bacterium from 1.0 × 102and 1.0 × 107CFU/mL. The limit of detection (LOD) and limit of quantitation (LOQ) were 148 and 448 CFU/mL, respectively, from the feeding of the QCM aptasensor flow cell with the eluent of the magnetic pre-concentration system. The reproducibility of the aptasensor was more than 95%. The aptasensor was very specific to L. monocytogenes compared to the other Listeria species (i.e., L. ivanovii, L. innocua, and L. seeligeri) or other tested bacteria such as Staphylococcus aureus, Escherichia coli, and Bacillus subtilis. The QCM aptasensor was regenerated with NaOH solution, and the system was reused many times.
Aptamer decorated PDA@magnetic silica microparticles for bacteria purifcation
(Microchimica Acta, 2024-04-23) Kavruk, Murat; Babaie, Zahra; Kibar, Güneş; Çetin, Barbaros; Yeşilkaya, Hasan; Amrani, Yassine; Dursun, Ali Doğan; Özalp, Veli Cengiz
One significant constraint in the advancement of biosensors is the signal-to-noise ratio, which is adversely affected by the presence of interfering factors such as blood in the sample matrix. In the present investigation, a specific aptamer binding was chosen for its affinity, while exhibiting no binding affinity towards non-target bacterial cells. This selective binding property was leveraged to facilitate the production of magnetic microparticles decorated with aptamers. A novel assay was developed to effectively isolate S. pneumoniae from PBS or directly from blood samples using an aptamer with an affinity constant of 72.8 nM. The capture experiments demonstrated efficiencies up to 87% and 66% are achievable for isolating spiked S. pneumoniae in 1 mL PBS and blood samples, respectively.
Enhancing machining efficiency of Ti-6Al-4V through multi-axial ultrasonic vibration-assisted machining and hybrid nanofluid minimum quantity lubrication
(Journal of Manufacturing Processes, 2024-06-15) Namlu, Ramazan Hakkı; Lotfi, Bahram; Kılıç, S. Engin
Ti-6Al-4V offers a balance of good strength with lightweight properties. Yet, Ti-6Al-4V poses machining challenges, including low thermal conductivity, chemical adhesion to cutting tools, and chip removal difficulties. To improve machining efficiency, Ultrasonic Vibration-Assisted Machining (UVAM) has emerged as a promising approach. UVAM has demonstrated reduced tool wear, cutting forces, and improved surface quality compared to Conventional Machining (CM). Additionally, Minimum Quantity Lubrication (MQL) methods offer sustainable coolant alternatives, with recent research focusing on Nanofluid-MQL (NMQL) and Hybrid Nanofluid-MQL (HNMQL) for enhanced performance. Although there exists a body of literature showcasing the promising effects of UVAM and MQL methods individually, comprehensive investigations into the synergistic effects of these methodologies remain limited. This study addresses these critical research gaps by conducting a systematic examination of combined application of multi-axial UVAM and HNMQL. Specifically, it delves into the comparison of different vibration directions within UVAM, evaluates the effectiveness of UVAM when combined with cutting fluids incorporating Al2O3 and CuO nanoparticles in NMQLs and HNMQLs, and contrasts these novel approaches with conventional machining methods. The study unfolds in three distinct stages. The first stage examines the ultrasonic cutting mechanism and its combined application with the MQL technique. In the second stage, the study investigates the physical properties of the cutting fluids, including contact angle and surface tension. The final stage encompasses slot milling operations, where an array of parameters such as cutting forces, surface roughness, surface topography, surface texture, and the occurrence of burr formations are rigorously analyzed. The results demonstrate that the combination of multi-axial UVAM with HNMQL yields substantial advantages over traditional machining methods. Notably, it leads to a remarkable reduction in cutting forces (up to 37.6 %) and surface roughness (up to 37.4 %). Additionally, this combination engenders the production of highly homogeneous and uniform surface textures, characterized by minimal surface defects and a significantly diminished occurrence of burr formations. These findings underscore the potential of multi-axial UVAM combined with HNMQL as a promising approach in enhancing the machining of Ti-6Al-4V, thus offering a pathway to enhance the efficiency and precision of aerospace component manufacturing processes.
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.