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Indexed at: search.filters.indexed.PubMedSubject: search.filters.subject.Mechanical engineering

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Now showing 1 - 4 of 4
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    PublicationOpen Access
    Adaptive Q control for tapping-mode nanoscanning using a piezoactuated bimorph probe
    (American Institute of Physics (AIP) Publishing, 2007) Department of Mechanical Engineering; Günev, İhsan; Varol, Aydın; Karaman, Sertaç; Başdoğan, Çağatay; Master Student; Faculty Member; Department of Mechanical Engineering; College of Engineering; N/A; N/A; N/A; 125489
    A new approach, called adaptive Q control, for tapping-mode atomic force microscopy (AFM) is introduced and implemented on a homemade AFM setup utilizing a laser Doppler vibrometer and a piezoactuated bimorph probe. In standard Q control, the effective Q factor of the scanning probe is adjusted prior to the scanning depending on the application. However, there is a trade-off in setting the effective Q factor of an AFM probe. The Q factor is either increased to reduce the tapping forces or decreased to increase the maximum achievable scan speed. Realizing these two benefits simultaneously using standard Q control is not possible. In adaptive Q control, the Q factor of the probe is set to an initial value as in standard Q control, but then modified on the fly during scanning when necessary to achieve this goal. In this article, we present the basic theory behind adaptive Q control, the electronics enabling the online modification of the probe's effective Q factor, and the results of the experiments comparing three different methods: scanning (a) without Q control, (b) with standard Q control, and (c) with adaptive Q control. The results show that the performance of adaptive Q control is superior to the other two methods.
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    PublicationOpen Access
    Haemodynamic recovery properties of the torsioned testicular Artery Lumen
    (Nature Publishing Group (NPG), 2017) Göktaş, Selda; Pişkin, Şenol; Çapraz, Can T.; Çakmak, Yusuf O.; N/A; Department of Mechanical Engineering; Yalçın, Özlem; Ermek, Erhan; Pekkan, Kerem; Other; Faculty Member; Department of Mechanical Engineering; School of Medicine; College of Engineering; 218440; 109991; 161845
    Testicular artery torsion (twisting) is one such severe vascular condition that leads spermatic cord injury. In this study, we investigate the recovery response of a torsioned ram testicular artery in an isolated organ-culture flow loop with clinically relevant twisting modes (90°, 180°, 270° and 360° angles). Quantitative optical coherence tomography technique was employed to track changes in the lumen diameter, wall thickness and the three-dimensional shape of the vessel in the physiological pressure range (10–50 mmHg). As a control, pressure-flow characteristics of the untwisted arteries were studied when subjected to augmented blood flow conditions with physiological flow rates up to 36 ml/min. Both twist and C-shaped buckling modes were observed. Acute increase in pressure levels opened the narrowed lumen of the twisted arteries noninvasively at all twist angles (at ∼22 mmHg and ∼35 mmHg for 360°-twisted vessels during static and dynamic flow experiments, respectively). The association between the twist-opening flow rate and the vessel diameter was greatly influenced by the initial twist angle. The biomechanical characteristics of the normal (untwisted) and torsioned testicular arteries supported the utilization of blood flow augmentation as an effective therapeutic approach to modulate the vessel lumen and recover organ reperfusion.
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    PublicationMetadata only
    Impedimetric antimicrobial peptide biosensor for the detection of human immunodeficiency virus envelope protein GP120
    (Cell Press, 2024) Department of Mechanical Engineering; Uygun, Zihni Onur; Taşoğlu, Savaş; Department of Mechanical Engineering; 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
    This study presents the design and implementation of an antimicrobial peptide -based electrochemical impedance spectroscopy (EIS) based biosensor system. The biosensor consists of a gold coated carbon electrode with MXene and silver nanoparticles (AgNPs) for the label -free detection of the human immunodeficiency virus (HIV) envelope protein gp120. Scanning electron microscopy was used to confirm the presence and distribution of MXene and AgNPs on the biosensor surface. The employment of the antimicrobial peptide on the electrode surface minimized the denaturation of the biorecognition receptor to ensure reliable and stable performance. The biosensor exhibited a linear range of 10-4000 pg mL-1 for gp120 detection, demonstrating good repeatability in real samples. The limit of detection (LOD) and limit of quantification (LOQ) were also calculated as 0.05 pg mL-1 and 0.14 pg mL-1, respectively. This biosensing platform has promising applications in the detection of HIV in clinical and point -of -care settings./Yönetim kurulu üyelerinin azlini zorlaştıran düzenlemeler, bir taraftan farklı bağlamlarda şirket tüzel kişiliğinin, azınlık pay sahiplerinin ve yönetim kurulu üyelerinin menfaatlerinin korunmasına hizmet edebilmekte; ayrıca ülkemizdeki gibi blok pay sahipliği yapısının yaygın olduğu hukuk sistemlerinde, çoğunluk ve azınlık pay sahipleri arasında kontrol paylaşımını da mümkün kılmaktadır. Diğer taraftan ise, genel kurulun yönetim kurulu üyelerini görevden alma konusundaki mutlak ve devredilemez yetkisini sınırlandırmakta; böylelikle yönetim kurulu üyesi ve şirket arasındaki güvenin sarsıldığı durumlarda ilgili üyenin görevine son verilebilmesi imkânını daraltmaktadır. Öte yandan Türk Hukukunda, genel kurulun yönetim kurulu üyelerini azil yetkisini sınırlandıran düzenlemelerin ortaklık düzeninde geçerli olup olmadığı hususunda bir belirsizlik vardır. Bu çalışmada esas sözleşmedeki bir düzenlemeyle, genel kurulun yönetim kurulu üyelerini görevden alma yetkisinin sınırlandırılmasının mümkün olup olmadığı konusunda iki soruya cevap aranmıştır: Bunlardan biri, böyle bir kararın alınmasının belirli bir süreye yahut haklı sebeplerin veya bazı şartların varlığına bağlanıp bağlanamayacağı; diğeri ise, genel kurul toplantısı ve kararı açısından, özel yetersayılar aranıp aranmayacağıdır. İlk soruya öğretide genellikle olumsuz cevap verilmesine karşılık, ikinci soruya verilen cevap ise olumlu yöndedir. Çalışmada savunduğumuz görüş çerçevesinde, yönetim kurulu üyelerinin azli imkânının haklı sebep, koşul, süre veya yaptırım gibi düzenlemelerle sınırlandırılması mümkün olmamalıdır. Benzer şekilde yönetim kurulu üyelerinin görevden alınması hususunda toplantı ve/veya karar yetersayılarının da kanuna göre ağırlaştırılması imkân dahilinde olmamalıdır. Anılan türdeki düzenlemelerin esas sözleşmeye eklenmesi hâlinde ise, bunların bâtıl olacağının kabulü gerekir.
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    Left atrial ligation in the avian embryo as a model for altered hemodynamic loading during early vascular development
    (Journal of Visualized Experiments, 2023) Department of Mechanical Engineering; Sevgin, Börteçine; Çoban, Merve Nur; Karataş, Faruk; Pekkan, Kerem; Department of Mechanical Engineering; Graduate School of Sciences and Engineering; College of Engineering
    Due to its four-chambered mature ventricular configuration, ease of culture, imaging access, and efficiency, the avian embryo is a preferred vertebrate animal model for studying cardiovascular development. Studies aiming to understand the normal development and congenital heart defect prognosis widely adopt this model. Microscopic surgical techniques are introduced to alter the normal mechanical loading patterns at a specific embryonic time point and track the downstream molecular and genetic cascade. The most common mechanical interventions are left vitelline vein ligation, conotruncal banding, and left atrial ligation (LAL), modulating the intramural vascular pressure and wall shear stress due to blood flow. LAL, particularly if performed in ovo, is the most challenging intervention, with very small sample yields due to the extremely fine sequential microsurgical operations. Despite its high risk, in ovo LAL is very valuable scientifically as it mimics hypoplastic left heart syndrome (HLHS) pathogenesis. HLHS is a clinically relevant, complex congenital heart disease observed in human newborns. A detailed protocol for in ovo LAL is documented in this paper. Briefly, fertilized avian embryos were incubated at 37.5 degrees C and 60% constant humidity typically until they reached Hamburger-Hamilton (HH) stages 20 to 21. The egg shells were cracked open, and the outer and inner membranes were removed. The embryo was gently rotated to expose the left atrial bulb of the common atrium. Pre-assembled micro-knots from 10-0 nylon sutures were gently positioned and tied around the left atrial bud. Finally, the embryo was returned to its original position, and LAL was completed. Normal and LALinstrumented ventricles demonstrated statistically significant differences in tissue compaction. An efficient LAL model generation pipeline would contribute to studies focusing on synchronized mechanical and genetic manipulation during the embryonic development of cardiovascular components. Likewise, this model will provide a perturbed cell source for tissue culture research and vascular biology.