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Permanent URI for this collectionhttps://hdl.handle.net/20.500.14288/3
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Item Metadata only Cardiac magnetic resonance T2* mapping in patients with COVID-19 pneumonia is associated with serum ferritin level?(Springer Science and Business Media B.V., 2023) 0000-0001-7637-4445; 0000-0002-2176-5278; Ciftci, Hatice Ozge; Keles, Nursen; Karatas, Mesut; Parsova, Kemal Emrecan; Kahraman, Erkan; Durak, Furkan; Kocogulları, Cevdet Ugur; Yiyit, Nurettin; Department of Mechanical Engineering; N/A; Pekkan, Kerem; Özkök, Serçin; Faculty Member; PhD Student; College of Engineering; Graduate School of Sciences and Engineering; 161845; N/AThe coronavirus disease of 2019 (COVID-19)-related myocardial injury is an increasingly recognized complication and cardiac magnetic resonance imaging (MRI) has become the most commonly used non-invasive imaging technique for myocardial involvement. This study aims to assess myocardial structure by T2*-mapping which is a non-invasive gold-standard imaging tool for the assessment of cardiac iron deposition in patients with COVID-19 pneumonia without significant cardiac symptoms. Twenty-five patients with COVID-19 pneumonia and 20 healthy subjects were prospectively enrolled.Cardiac volume and function parameters, myocardial native-T1, and T2*-mapping were measured. The association of serum ferritin level and myocardial mapping was analyzed. There was no difference in terms of cardiac volume and function parameters. The T2*-mapping values were lower in patients with COVID-19 compared to controls (35.37 [IQR 31.67–41.20] ms vs. 43.98 [IQR 41.97–46.88] ms; p < 0.0001), while no significant difference was found in terms of native-T1 mapping value(p = 0.701). There was a positive correlation with T2*mapping and native-T1 mapping values (r = 0.522, p = 0.007) and negative correlation with serum ferritin values (r = − 0.653, p = 0.000), while no correlation between cardiac native-T1 mapping and serum ferritin level. Negative correlation between serum ferritin level and T2*-mapping values in COVID-19 patients may provide a non-contrast-enhanced alternative to assess tissue structural changes in patients with COVID-19. T2*-mapping may provide a non-contrast-enhanced alternative to assess tissue alterations in patients with COVID-19. Adding T2*-mapping cardiac MRI in patients with myocardial pathologies would improve the revealing of underlying mechanisms. Further in vivo and ex vivo animal or human studies designed with larger patient cohorts should be planned. © 2022, The Author(s), under exclusive licence to Springer Nature B.V.Item Metadata only Simplified top-down fabrication of sub-micron silicon nanowires(IOP Publishing Ltd, 2023) 0000-0002-2712-1908; N/A; N/A; 0000-0001-5931-8134; N/A; N/A; N/A; Department of Mechanical Engineering; Karimzadehkhouei, Mehrdad; Akıncı, Seçkin; Zare Pakzad, Sina; Alaca, Burhanettin Erdem; Researcher; Master Student; PhD Student; Faculty Member; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); n2STAR-Koç University Nanofabrication and Nanocharacterization Center for Scientifc and Technological Advanced Research; N/A; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; N/A; N/A; 115108Silicon nanowires are among the most promising nanotechnology building blocks in innovative devices with numerous applications as nanoelectromechanical systems. Downscaling the physical size of these devices and optimization of material functionalities by engineering their structure are two promising strategies for further enhancement of their performance for integrated circuits and future-generation sensors and actuators. Integration of silicon nanowires as transduction elements for inertial sensor applications is one prominent example for an intelligent combination of such building blocks for multiple functionalities within a single sensor. Currently, the efforts in this field are marred by the lack of batch fabrication techniques compatible with semiconductor manufacturing. Development of new fabrication techniques for such one-dimensional structures will eliminate the drawbacks associated with assembly issues. The current study aims to explore the limits of batch fabrication for a single nanowire within a thick Si layer. The objective of the current work goes beyond the state of the art with significant improvements to the recent viable approach on the monolithic fabrication of nanowires, which was based on a conformal side-wall coating for the protection of the nanoscale silicon line followed by deep etch of the substrate transforming the protected layer into a silicon nanowire. The newly developed fabrication approach eliminates side wall protection and thereby reduces both process complexity and process temperature. The technique yields promising results with possible improvements for future micro and nanofabrication processes.Item Metadata only Innovative MEMS stage for automated micromechanical testing(Institute of Electrical and Electronics Engineers Inc., 2023) 0000-0002-2712-1908; 0000-0003-2063-1566; N/A; 0000-0001-5931-8134; N/A; N/A; N/A; N/A; Department of Mechanical Engineering; N/A; Karimzadehkhouei, Mehrdad; Ali, Basit; Zare Pakzad, Sina; Alaca, Burhanettin Erdem; Çoban, Semih Berk; Researcher; PhD Student; PhD Student; Faculty Member; PhD Student; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); n2STAR-Koç University Nanofabrication and Nanocharacterization Center for Scientifc and Technological Advanced Research; N/A; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Engineering; Graduate School of Sciences and Engineering; N/A; N/A; N/A; 115108; N/AThis study introduces a comprehensive methodology for designing, fabricating, and testing a MEMS stage integrated into a commercial testing device, with a focus on enabling automated testing of multiple samples under in-plane loading conditions. Drawing inspiration from recent innovative MEMS stage designs, a new approach is developed to integrate micromanipulator tips into a commercial micro-mechanical testing machine, allowing for automated one-directional loading of micro-scale samples. To address challenges related to handling and alignment, a co-fabrication technique is employed, enabling the simultaneous fabrication of the micro-sample and MEMS stage within a single process flow. A novel fabrication method utilizing a silicon-on-insulator substrate is utilized. The calibration of testing method is conducted using both analytical and experimental methods to ensure accurate measurement of force and deflection within the in-plane testing protocol. The released micro-beam structures undergo repetitive loading to evaluate bending deformation. The developed approach is extended to multiple testing attempts on MEMS stage-micro-sample, combinations co-fabricated within a single chip, enabling precise statistical treatment of the measurements. © 2023 IEEE.Item Metadata only Nanomechanical modeling of the bending response of silicon nanowires(Amer Chemical Soc, 2023) 0000-0001-5931-8134; N/A; 0000-0002-0795-8970; Nasr Esfahani, Mohammad; Tasdemir, Zuhal; Wollschla''ger, Nicole; Li, Taotao; Li, XueFei; Leblebici, Yusuf; Alaca,; Department of Mechanical Engineering; N/A; N/A; Alaca, Burhanettin Erdem; Zare Pakzad, Sina; Yılmaz, Mustafa Akın; Faculty Member; PhD Student; PhD Student; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); n2STAR-Koç University Nanofabrication and Nanocharacterization Center for Scientifc and Technological Advanced Research; College of Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; 115108; N/A; N/AUnderstanding the mechanical behavior of silicon nanowiresis essentialfor the implementation of advanced nanoscale devices. Although bendingtests are predominantly used for this purpose, their findings shouldbe properly interpreted through modeling. Various modeling approachestend to ignore parts of the effective parameter set involved in therather complex bending response. This oversimplification is the mainreason behind the spread of the modulus of elasticity and strengthdata in the literature. Addressing this challenge, a surface-basednanomechanical model is introduced in this study. The proposed modelconsiders two important factors that have so far remained neglecteddespite their significance: (i) intrinsic stresses composed of theinitial residual stress and surface-induced residual stress and (ii)anisotropic implementation of surface stress and elasticity. The modelingstudy is consolidated with molecular dynamics-based study of the nativeoxide surface through reactive force fields and a series of nanoscalecharacterization work through in situ three-pointbending test and Raman spectroscopy. The treatment of the test datathrough a series of models with increasing complexity demonstratesa spread of 85 GPa for the modulus of elasticity and points to theorigins of ambiguity regarding silicon nanowire properties, whichare some of the most commonly employed nanoscale building blocks.A similar conclusion is reached for strength with variations of upto 3 GPa estimated by the aforementioned nanomechanical models. Preciseconsideration of the nanowire surface state is thus critical to comprehendingthe mechanical behavior of silicon nanowires accurately. Overall,this study highlights the need for a multiscale theoretical frameworkto fully understand the size-dependent mechanical behavior of siliconnanowires, with fortifying effects on the design and reliability assessmentof future nanoelectromechanical systems.Item Metadata only The role of native oxide on the mechanical behavior of silicon nanowires(Elsevier, 2023) 0000-0001-5931-8134; N/A; Esfahani, Mohammad Nasr; Department of Mechanical Engineering; N/A; Alaca, Burhanettin Erdem; Zare Pakzad, Sina; Faculty Member; PhD Student; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); n2STAR-Koç University Nanofabrication and Nanocharacterization Center for Scientifc and Technological Advanced Research; College of Engineering; Graduate School of Sciences and Engineering; 115108; N/AMolecular dynamics simulations are employed to study the effect of native oxide on the size-dependent mechanical properties of silicon nanowires. Despite their immense potential as essential building blocks in nanoelectromechanical systems, mechanical behavior of silicon nanowires still needs further attention for a full understanding. The leading source of ambiguity can be traced back to the fact that the presence of native oxide on silicon nanowire surfaces is ignored when interpreting nanomechanical test data, when it comes, for example, to converting force and deflection measurements to stress and strain. This problem needs immediate attention, because, first, nanowires have a significant surface area, and second, native oxide is the dominant surface state. With prior work reporting conflicting dimensional and computational viewpoints regarding the effect of native oxide on silicon nanowires properties, size dependence of nanowire mechanical properties is investigated here with great attention placed on critical size and atomistic simulation perspectives. For this purpose, Tersoff-Munetoh and modified Stillinger-Weber potentials are employed in this intensive computational study to address the influence of size and crystal orientation on nanowire elastic behavior and tensile strength. As a result, a striking set of differences is obtained. First, the presence of native oxide layer is observed to decrease both the modulus of elasticity and the ultimate strength. The reduction in the modulus of elasticity is observed to be as much as 30% and 40% for < 100 > and < 110 >-oriented nanowires, respectively. Similarly, the reduction in the ultimate strength is estimated to be as much as 20% using the modified Stillinger-Weber potential, which proved to be more suitable for strength analysis compared to Tersoff-Munetoh potential. Finally, the failure behavior is studied through the ductile failure probability calculations, where a higher size-dependent failure probability is observed for decreasing nanowire width upon oxidation. These results shed light on the background of existing inconsistencies between experimental and numerical findings in the literature, as opposing trends for silicon nanowire stiffness and strength were reported with decreasing size. The study provides a guideline to quantify the scale effect in silicon nanowire mechanical behavior as a combined outcome of oxide thickness, nanowire size and crystal orientation and thus to reduce the extent of uncertainties originating from inadequate interpretation of nanomechanical test data.Item Metadata only Biosensors for prostate cancer detection(Cell Press, 2023) 0000-0003-4604-217X; N/A; 0000-0002-5295-5701; 0000-0002-5693-350X; 0000-0003-2542-8110; Yetisen, Ali K.; Department of Mechanical Engineering; N/A; N/A; N/A; N/A; Taşoğlu, Savaş; Söylemez, Cansu; Sarabi, Misagh Rezapour; Nakhjavani, Sattar Akbar; Tokyay, Begüm Kübra; Faculty Member; PhD Student; PhD Student; Researcher; PhD Student; Koç University Research Center for Translational Medicine (KUTTAM) / Koç Üniversitesi Translasyonel Tıp Araştırma Merkezi (KUTTAM); KU Arçelik Research Center for Creative Industries (KUAR) / KU Arçelik Yaratıcı Endüstriler Uygulama ve Araştırma Merkezi (KUAR); College of Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; N/A; Graduate School of Sciences and Engineering; 291971; N/A; N/A; N/A; N/AProstate cancer (PC) is one of the most common tumors and a leading cause of mortality among men, resulting in similar to 375 000 deaths annually worldwide. Various analytical methods have been designed for quantitative and rapid detection of PC biomarkers. Electrochemical (EC), optical, and magnetic biosensors have been developed to detect tumor biomarkers in clinical and point-of-care (POC) settings. Although POC biosensors have shown potential for detection of PC biomarkers, some limitations, such as the sample preparation, should be considered. To tackle such shortcomings, new technologies have been utilized for development of more practical biosensors. Here, biosensing platforms for the detection of PC biomarkers such as immunosensors, aptasensors, genosensors, paper-based devices, microfluidic systems, and multiplex high-throughput platforms, are discussed.Item Metadata only A novel smart disinfection system using 3D-printed and electrically conductive composite hydrogel(Springernature, 2024) 0000-0002-8316-9623; 0000-0001-6624-3505; N/A; 0000-0002-3511-3887; 0000-0003-1600-7322; Gul, Seref; Department of Mechanical Engineering; Department of Chemical and Biological Engineering; N/A; N/A; N/A; Lazoğlu, İsmail; Kavaklı, İbrahim Halil; Velioğlu, Başak; Malik, Anjum Naeem; Khan, Shaheryar Atta; Faculty Member; Faculty Member; Researcher; PhD Student; PhD Student; Manufacturing and Automation Research Center (MARC); College of Engineering; College of Engineering; N/A; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; 179391; 40319; N/A; N/A; N/ASmart materials are ushering in the era of smart and adaptable products. Hydrogels are a distinct class of smart materials that can be 3D-printed to produce smart and active structures that can be used as sensors and actuators. The development and characterization of a 3D-printable and electrically conductive composite hydrogel, as well as its application in the development of a smart disinfection system, are discussed in this article. The developed composite hydrogel has a maximum electrical conductivity of 145 S.m-1, is stable up to 200 degrees C, and has a 3D printable rheology. Virtuous of its electrical conductivity, the composite hydrogel was used to create a smart disinfection system. Various disinfection systems have been adopted for the disinfection of contaminated surfaces; however, most of these systems require human evacuation from the surroundings due to the hazardous nature of the virucide. The proposed system is designed to disinfect contaminated surfaces on common-use equipment and is capable of real-time activation through user interaction. It employs a thermal disinfection process at 60 degrees C for 5 min and becomes ready for the next user once its temperature drops below 55 degrees C. This system consumes 1.64 Wh of energy per disinfection cycle and is suitable for scenarios with fewer than 60 user interactions in an 8-h work shift.Item Metadata only Tool flank wear prediction using high-frequency machine data from industrial edge device(Elsevier B.V., 2023) 0000-0002-8316-9623; N/A; N/A; N/A; Bilgili, Deniz; Burun, Gizem; Pehlivan, Toprak; Uresin, Ugur; Emekli, Engin (25621135500; Department of Mechanical Engineering; N/A; Department of Mechanical Engineering; N/A; Lazoğlu, İsmail; Beşirova, Cemile; Keçibaş, Gamze; Chehrezad, Mohammad Reza; Faculty Member; Master Student; Undergraduate Student; Researcher; College of Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; 179391; N/A; N/A; N/ATool flank wear monitoring can minimize machining downtime costs while increasing productivity and product quality. In some industrial applications, only a limited level of tool wear is allowed to attain necessary tolerances. It may become challenging to monitor a limited level of tool wear in the data collected from the machine due to the other components, such as the flexible vibrations of the machine, dominating the measurement signals. In this study, a tool wear monitoring technique to predict limited levels of tool wear from the spindle motor current and dynamometer measurements is presented. High-frequency spindle motor current data is collected with an industrial edge device while the cutting forces and torque are measured with a rotary dynamometer in drilling tests for a selected number of holes. Feature engineering is conducted to identify the statistical features of the measurement signals that are most sensitive to small changes in tool wear. A neural network based on the long short-term memory (LSTM) architecture is developed to predict tool flank wear from the measured spindle motor current and dynamometer signals. It is demonstrated that the proposed technique predicts tool flank wear with good accuracy and high computational efficiency. The proposed technique can easily be implemented in an industrial edge device as a real-time predictive maintenance application to minimize the costs due to manufacturing downtime and tool underuse or overuse. © 2023 Elsevier B.V.. All rights reserved.Item Metadata only Fractographic investigation of cryogenic temperature mode-II delamination behavior of filament Wound CFRP laminates with varied resin systems(MDPI, 2023) 0000-0002-5071-6133; Ufuk, Recep; Bilge, Kaan; Kiral, Baris Emre; Ereke, Murat; Department of Mechanical Engineering; Karabeyoğlu, Mustafa Arif; Faculty Member; College of Engineering; 114595This study investigates the mode-II delamination performance of filament-wound unidirectional composites with different types of epoxies as their matrix phase under room and cryogenic temperatures. A typical vacuum infusion resin, an aerospace-grade cold-curing resin and crack-resistant toughened resin systems were wet-wound with 12K carbon fiber tows to manufacture the composite samples. Test samples with a (0)16 ply sequence were tested according to ASTM D7905-19. The tested samples were investigated via microscopic analysis to assess the failure mechanisms associated with varying the matrix material and temperature. ENF tests at room temperature were found to be susceptible to the inherent variance in the fiber architectures along with resin-viscosity-driven fiber wetting. Cryogenic conditions induce a shift in the mode-II delamination behavior from a rather complex failure mechanism to a consistent fiber/matrix debonding mode with diminishing GIIc values except for the toughened resin system. The provided comprehensive fractographic analysis enables an understanding of the various causes of fracture, which determines the laminate performance. The combined evaluation of the distinctive damage modes reported in this study provides guidance on the conventional wet-winding process, which still remains a volumetrically dominant and viable option for cryogenic applications, particularly for vessels with limited operational durations like sounding rockets.Item Metadata only Rheological investigation of neonatal double-lumen cannula with and without deformable erythrocytes(Korean Soc Rheology, 2023) 0000-0002-3950-8798; Ullah, Minhaj; Cheema, Taqi Ahmad; Aleksey, Ni; Ahmad, Faiq; Lim, Hankwon; Department of Mechanical Engineering; Jamil, Muhammad; Researcher; College of EngineeringThe double-lumen cannula (DLC) is the most critical component of extracorporeal membrane oxygenation (ECMO) because of its narrow cross-section, thereby developing the highest shear stress in the entire ECMO circuit. To measure blood damage in a DLC, the Eulerian approach is generally used without contemplating exposure time or history of blood exposure to shear stresses. Alternatively, Lagrangian approach has also been recently employed for a Newtonian blood flow through a DLC, thereby leaving a research gap on the impact of variable shear rate in case of non-Newtonian blood flow. In the present study, the hemodynamic performance of DLC is investigated using different non-Newtonian models by applying Lagrangian approach. Moreover, the motion of RBC was tracked inside the cannula to predict its behavior during the motion. The results showed that the return lumen had higher pressure, velocity, and shear stress values than other parts of the DLC. In addition, recirculation was observed due to the mixing of blood coming from different inlets and found increase with increasing flow rate of blood. Moreover, it was found that the blood damage increased with increasing flow rate. There was more blood damage in the Newtonian model than in the other non-Newtonian models at higher flow rates. However, the Carreau model showed more blood damage at lower flow rates than the other models. The Cross model showed DLC's higher efficacy in delivering oxygenated blood to the tricuspid outlet because it showed the least blood damage among all other models. It was also concluded that the efficacy of the DLC to deliver oxygenated blood to the tricuspid outlet decreases with increasing blood flow rate.