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Publication Metadata only A novel hybrid frost detection and defrosting system for domestic refrigerators(Elsevier, 2020) N/A; N/A; N/A; Department of Mechanical Engineering; Malik, Anjum Naeem; Khan, Shaheryar Atta; Lazoğlu, İsmail; PhD Student; PhD Student; Faculty Member; Department of Mechanical Engineering; Manufacturing and Automation Research Center (MARC); Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; N/A; 179391The frosting is a phenomenon most detrimental to the efficiency of refrigeration systems. The accumulation of frost blocks the airflow, deteriorating the cooling capacity and the coefficient of performance. The commercially available refrigeration systems use a blind and periodic defrosting cycle without any quantification of frost, which leads to lower efficiencies. Considering the new and tougher energy regulations in the refrigerators, nowadays increasing the efficiencies of the refrigerators becomes more critical. In this article, a new hybrid frost detection - defrosting system (HFDDS) is proposed that comprises of a novel photo-capacitive sensing technique and a dual-purpose additively manufacturable sensor and defrosting heater. The HFDDS can detect the formation of frost, measures the thickness of frost from 1.3 to 8 mm with a 5% margin of error, and triggers a defrosting response once a critical frost thickness is attained. The HFDDS is targeted to provide a defrosting on-demand instead of the inefficient blind and periodic defrosting cycles.Publication Metadata only A solution method for linear and geometrically nonlinear MDOF systems with random properties subject to random excitation(Elsevier, 1998) Micaletti, RC; Çakmak, Ahmet Ş.; Nielsen, Søren R.K.; Department of Mathematics; Köylüoğlu, Hasan Uğur; Teaching Faculty; Department of Mathematics; College of Sciences; N/AA method for computing the lower-order moments of response of randomly excited multi-degree-of-freedom (MDOF) systems with random structural properties is proposed. The method is grounded in the techniques of stochastic calculus, utilizing a Markov diffusion process to model the structural system with random structural properties. The resulting state-space formulation is a system of ordinary stochastic differential equations with random coefficients and deterministic initial conditions which are subsequently transformed into ordinary stochastic differential equations with deterministic coefficients and random initial conditions, This transformation facilitates the derivation of differential equations which govern the evolution of the unconditional statistical moments of response. Primary consideration is given to linear systems and systems with odd polynomial nonlinearities, for in these cases there is a significant reduction in the number of equations to be solved. The method is illustrated for a five-story shear-frame structure with nonlinear interstory restoring forces and random damping and stiffness properties. The results of the proposed method are compared to those estimated by extensive Monte-Carlo simulation.Publication Metadata only A theory of thin lamellar eutectic growth with anisotropic interphase boundaries(Elsevier, 2012) Akamatsu Silvere; Bottin-Rousseau Sabine; Faivre Gabriel; Department of Mechanical Engineering; Şerefoğlu, Melis; Researcher; Department of Mechanical Engineering; College of Engineering; 44888We present a semiempirical theory of the effects of an orientation dependence of the surface free energy of interphase boundaries (interphase boundary anisotropy) on lamellar eutectic growth in thin samples. We show that, to a good approximation, thin lamellar eutectic patterns with a strong interphase boundary anisotropy travel along the growth front at such a velocity - or, equivalently, at such an inclination angle of the lamellae left behind in the solid - that the surface tension force of the interphase boundary is nearly parallel to the applied thermal gradient. This explains, among other things, the crystallographic locking of lamellar eutectic patterns that occurs in those eutectic grains, which have CUSP singularities in the Wulff plot of the interphase boundary. Based on this theory, we show that the rotating directional solidification method, by which a thin sample is rotated with respect to a fixed unidirectional thermal gradient, must yield eutectic lamellae whose trajectories are nearly homothetic to the two-dimensional Wulff form of the interphase boundary. This opens up new possibilities for the experimental study of interphase boundary anisotropy in eutectic alloys.Publication Metadata only Analysis of solenoid based linear compressor for household refrigerator(Elsevier Sci Ltd, 2017) N/A; N/A; Department of Mechanical Engineering; Bijanzad, Armin; Hassan, Adnan; Lazoğlu, İsmail; PhD Student; PhD Student; Faculty Member; Department of Mechanical Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; N/A; 179391This article presents the analytical modeling of an oil-free solenoid actuator based linear compressor used in household refrigerators. The stator coil was excited with the pulse width modulated signal which caused linear oscillations in the armature using helical spring. Dynamic characteristics of the linear compressor were studied analytically considering the nonlinearity of the gas and electromagnetic force. The system dynamic models were validated with the finite element simulation as well as a specially designed experimental setup. Frequency response functions of stroke to current as well as pressure to current ratios were generated to evaluate the effect of excitation frequency on the compressor performance. The higher efficiency of the solenoid actuator was achieved when excited at the natural frequency. The results show that the natural frequency of the designed system is around 19 Hz and the work done in a cycle is approximately 1.3 J. Additionally, 47% isentropic and 87% electrical efficiency were achieved. (C) 2016 Elsevier Ltd and IIR. All rights reserved.Publication Metadata only Development of a new moving magnet linear compressor. Part B: performance analysis(Elsevier, 2020) Kerpicci, H.; N/A; N/A; Department of Mechanical Engineering; Bijanzad, Armin; Hassan, Adnan; Lazoğlu, İsmail; PhD Student; PhD Student; Faculty Member; Department of Mechanical Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; N/A; 179391This article is a continuation of the preceding article and focuses on the performance evaluation of an oil-free linear compressor prototype. The article introduces performance analysis parameters for a linear compressor along with their analytical attributes. Initially, the kinetic and kinematic analysis at resonance excitation frequency is performed with the help of a specially designed experimental setup. Furthermore, the frequency response functions of output to input parameters is presented to particularly monitor the shift in resonance frequency in the presence of refrigerant. Four different gases are used to quantify the shift and relating them with the physical properties of the refrigerant. Additionally, the pressure-volume curves for all these gases are presented and analysed. In the end, the motor and overall isentropic efficiencies of the prototype are measured at different input parameters. Additionally, the connection between the pressure output and volumetric efficiency is also discussed. (C) 2020 Elsevier Ltd and IIR. All rights reserved.Publication Metadata only Exact linearization of one-dimensional jump-diffusion stochastic differential equations(Springer, 2008) Ünal, Gazanfer; Sanver, Abdullah; N/A; İyigünler, İsmail; Master Student; Graduate School of Sciences and Engineering; N/ANecessary and sufficient conditions for the linearization of the one-dimensional Ito jump-diffusion stochastic differential equations (JDSDE) are given. Stochastic integrating factor has been introduced to solve the linear JDSDEs. Exact solutions to some linearizable JDSDEs have been provided.Publication Metadata only Feedrate scheduling strategies for free-form surfaces(Elsevier Sci Ltd, 2006) N/A; Department of Mechanical Engineering; N/A; Erdim, Hüseyin; Lazoğlu, İsmail; Öztürk, Burak; PhD Student; Faculty Member; N/A; Department of Mechanical Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; N/A; 179391; N/AFree-form machining is one of the commonly used manufacturing processes for several industries such as automobile, aerospace, die and mold industries. In 3D complicated free-form surfaces, it is critical, but often difficult, to select applicable cutting conditions to achieve high productivity while maintaining high quality of parts. It is essential to optimize the feedrate in order to improve the machining efficiency of the ball-end milling. Conservative constant feedrate values have been mostly used up to now since there was a lock of physical models and optimization tools for the machining processes. The common approach used in feedrate scheduling is material removal rate (MRR) model. In the MRR based approach, feedrate is inversely proportional to either average or instantaneous volumetric removal rate. Commonly used CAM programs and NC code generators based on only the geometric and volumetric analysis, but they do not concern the physics of the free-form machining process yet. The new approach that is also introduced in this paper is based on the mechanics of the process. In other words, the force-based models in which feedrate is set to values which keep either average or instantaneous machining forces to prescribed values. In this study, both feedrate scheduling strategies are compared theoretically and experimentally for 3D ball-end milling of free-form surfaces. It is shown that MRR based feedrate strategy outputs higher feedrate values compared to force based feedrate strategy. High feedrate values of the MRR strategy increase the cutting forces extensively which can be damaging to the part quality and to the CNC Machine. When the new force based feedrate-scheduling strategy introduced in this paper is used, it is shown that the machining time can be decreased significantly along the tool path. The force-based feedrate scheduling strategy is tested under various cutting conditions and some of the results are presented in the paper. (C) 2005 Elsevier Ltd. All rights reserved.Publication Metadata only Forces and hole quality in drilling(Elsevier Sci Ltd, 2005) N/A; Department of Mechanical Engineering; Department of Mechanical Engineering; Pirtini, Müge; Lazoğlu, İsmail; Resercher; Faculty Member; Department of Mechanical Engineering; Manufacturing and Automation Research Center (MARC); College of Engineering; College of Engineering; N/A; 179391Drilling is one of the most commonly used machining processes in various industries such as automotive, Aircraft and aerospace, dies/molds, home appliance, medical and electronic equipment industries. Due to the increasing competitiveness in the market, cycle times of the drilling processes must be decreased. Moreover, tight geometric tolerance requirements in designs demand that drilled hole precision must be increased in production. in this research, A new mathematical model based on the mechanics and dynamics of the drilling process is developed for the prediction of cutting forces and hole quality. a new method is also proposed in order to obtain cutting coefficients directly from a set of relatively simple calibration tests. the model is able to simulate the cutting forces for various cutting conditions in the process planning stage. in the structural dynamics module, measured frequency response functions of the spindle and tool system are integrated into the model in order to obtain drilled hole profiles. therefore, in addition to predicting the forces, the new model allows the determination and visualization of drilled hole profiles in 3D and to select parameters properly under the manufacturing and tolerance constraints. an extensive number of experiments is performed to validate the theoretical model outputs with the measured forces and CMM hole profiles. It is observed that model predictions agree with the force and CMM measurements. Some of the typical calibration and validation results are presented in this paper.Publication Metadata 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 EngineeringThis 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.Publication Metadata only Lamellar eutectic growth with anisotropic interphase boundaries: experimental study using the rotating directional solidification method(Elsevier, 2012) Akamatsu Silvere; Bottin-Rousseau Sabine; Faivre Gabriel; Department of Mechanical Engineering; Şerefoğlu, Melis; Researcher; Department of Mechanical Engineering; College of Engineering; 44888We report on an experimental study of the effects of interphase boundary anisotropy on eutectic microstructures using a new methodology called rotating directional solidification (RDS), which consists of rotating a thin sample with respect to a fixed unidirectional thermal gradient. The systems used are thin, large eutectic grains of the CBr 4-C 2Cl 6 and In-In 2Bi lamellar eutectic alloys. The shape of the observed RDS lamellar trajectories turns out to be a reproducible eutectic-grain-dependent feature, in agreement with the theoretical prediction that these trajectories are approximately homothetic to the Wulff form of the interphase boundary in the sample plane. We show that different modes of lamellar growth, ranging from quasi-isotropic to (crystallographically) locked, exist in different eutectic grains of the two alloys studied. A detailed characterisation of these modes is given, with particular attention to the as-yet poorly understood aspects of locked lamellar growth.