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Open Access
3D-printed contact lenses: challenges towards translation and commercialization
(Future Medicine, 2022) Yetişen, Ali K.; Department of Mechanical Engineering; Taşoğlu, Savaş; Özdalgıç, Berin; Faculty Member; PhD Student; Department of Mechanical Engineering; KU Arçelik Research Center for Creative Industries (KUAR) / KU Arçelik Yaratıcı Endüstriler Uygulama ve Araştırma Merkezi (KUAR); Koç University Research Center for Translational Medicine (KUTTAM) / Koç Üniversitesi Translasyonel Tıp Araştırma Merkezi (KUTTAM); College of Engineering; Graduate School of Sciences and Engineering; 291971; 323683
NA
Open Access
3D-printed multi-stimuli-responsive mobile micromachines
(American Chemical Society (ACS), 2020) Lee, Yun-Woo; Ceylan, Hakan; Yasa, İmmihan Ceren; Department of Mechanical Engineering; Kılıç, Uğur; Sitti, Metin; Faculty Member; Department of Mechanical Engineering; School of Medicine; College of Engineering
Magnetically actuated and controlled mobile micromachines have the potential to be a key enabler for various wireless lab-on-a-chip manipulations and minimally invasive targeted therapies. However, their embodied, or physical, task execution capabilities that rely on magnetic programming and control alone can curtail their projected performance and functional diversity. Integration of stimuli-responsive materials with mobile magnetic micromachines can enhance their design toolbox, enabling independently controlled new functional capabilities to be defined. To this end, here, we show three-dimensional (3D) printed size-controllable hydrogel magnetic microscrews and microrollers that respond to changes in magnetic fields, temperature, pH, and divalent cations. We show two-way size-controllable microscrews that can reversibly swell and shrink with temperature, pH, and divalent cations for multiple cycles. We present the spatial adaptation of these microrollers for penetration through narrow channels and their potential for controlled occlusion of small capillaries (30 μm diameter). We further demonstrate one-way size-controllable microscrews that can swell with temperature up to 65% of their initial length. These hydrogel microscrews, once swollen, however, can only be degraded enzymatically for removal. Our results can inspire future applications of 3D- and 4D-printed multifunctional mobile microrobots for precisely targeted obstructive interventions (e.g., embolization) and lab- and organ-on-a-chip manipulations.
Open Access
A 2D MEMS stage for optical applications
(Society of Photo-optical Instrumentation Engineers (SPIE), 2006) Ataman, Çağlar; Petremand, Yves; Noell, Wilfried; Epitaux, Marc; de Rooij, Nico F.; Department of Electrical and Electronics Engineering; Ürey, Hakan; Faculty Member; Department of Electrical and Electronics Engineering; College of Engineering; 8579
A 2D MEMS platform for a microlens scanner application is reported. The platform is fabricated on an SOI wafer with 50/μm thick device layer. Entire device is defined with a single etching step on the same layer. Through four S-shaped beams, the device is capable of producing nonlinear 2D motion from linear ID translation of two pairs of comb actuator sets. The device has a clear aperture of 2mm by 2mm, which is hallowed from the backside for micro-optics assembly. In this paper, a numerical device model and its validation via experimental characterization results are presented. Integration of the micro-optical components with the stage is also discussed. Additionally, a new driving scheme to minimize the settling time of the device in DC operation is explored.
Open Access
A comparative study on GaSb epilayers grown on nominal and vicinal Si(100) substrates by molecular beam epitaxy
(Institute of Physics (IOP) Publishing, 2020) Arpapay, Burcu; Suyolcu, Y. Eren; van Aken, Peter A.; Gülgün, Mehmet Ali; Serincan, Uğur; Çorapçıoğlu, Gülcan; n2STAR-Koç University Nanofabrication and Nanocharacterization Center for Scientifc and Technological Advanced Research
The direct growth of GaSb buffer layers on Si substrates is attracting considerable interest in the integration of group III-Sb based device structures on lower-cost Si substrates. Here, we present the effect of various growth steps on the defect types and defect density that are crucial for advancing high crystal quality GaSb buffer layer on nominal/vicinal Si substrate. As a growth step, the applied thermal annealing at an intermediate step provided a decrease in the threading dislocation (TD) density down to 1.72 x 10(8) cm(-2), indicating a more effective method compared to post-growth annealing. Additionally, the importance of period number and position of GaSb/AlSb superlattice layers inserted in GaSb epilayers is demonstrated. In the case of the GaSb epilayers grown on vicinal substrates, the APB density as low as 0.06 mu m(-1) and TD density of 1.98 x 10(8) cm(-2) were obtained for the sample grown on 4 degrees miscut Si(100) substrate.
Open Access
A computational multicriteria optimization approach to controller design for pysical human-robot interaction
(Institute of Electrical and Electronics Engineers (IEEE), 2020) Tokatlı, Ozan; Patoğlu, Volkan; Department of Mechanical Engineering; Aydın, Yusuf; Başdoğan, Çağatay; Faculty Member; Department of Mechanical Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; 125489
Physical human-robot interaction (pHRI) integrates the benefits of human operator and a collaborative robot in tasks involving physical interaction, with the aim of increasing the task performance. However, the design of interaction controllers that achieve safe and transparent operations is challenging, mainly due to the contradicting nature of these objectives. Knowing that attaining perfect transparency is practically unachievable, controllers that allow better compromise between these objectives are desirable. In this article, we propose a multicriteria optimization framework, which jointly optimizes the stability robustness and transparency of a closed-loop pHRI system for a given interaction controller. In particular, we propose a Pareto optimization framework that allows the designer to make informed decisions by thoroughly studying the tradeoff between stability robustness and transparency. The proposed framework involves a search over the discretized controller parameter space to compute the Pareto front curve and a selection of controller parameters that yield maximum attainable transparency and stability robustness by studying this tradeoff curve. The proposed framework not only leads to the design of an optimal controller, but also enables a fair comparison among different interaction controllers. In order to demonstrate the practical use of the proposed approach, integer and fractional order admittance controllers are studied as a case study and compared both analytically and experimentally. The experimental results validate the proposed design framework and show that the achievable transparency under fractional order admittance controller is higher than that of integer order one, when both controllers are designed to ensure the same level of stability robustness.
Open Access
A DASH7-based power metering system
(Institute of Electrical and Electronics Engineers (IEEE), 2015) Çetinkaya, Oktay; Akan, Özgür Barış; Researcher; College of Engineering
Considering the inability of the existing energy resources to satisfy the current needs, the right and efficient. use of the energy has become compulsory. To make energy sustainability permanent, management and planning activities should be carried out by arranging the working hours and decreasing the energy wasting. For all these, power metering, managing and controlling systems or plugs has been proposed in recent efforts. Starting from this point, a new DASH7-based Smart Plug (D7SP) is designed and implemented to achieve a better structure compared to ZigBee equipped models and reduce the drawbacks of current applications. DASH7 technology reaches nearly 6 times farther distances in comparison with 2.4 GHz based protocols and provides multi-year battery life as a result of using limited energy during transmission. Performing in the 433 MHz band prevents the possible interference from overcrowded 2.4 GHz and the other frequencies which helps to gather a more reliable working environment. To shorten the single connection delays and human oriented failures, the MCU was shifted directly into the plug from the rear-end device. Working hours arrangement and standby power cutting off algorithms are implemented in addition to these energy saving targeted improvements to enhance more efficient systems. With the collaboration of the conducted hardware and software oriented adjustments and DASH7-based improvements, a more reliable, mobile and efficient system has been obtained in this work.
Open Access
A diversity combination model incorporating an inward bias for interaural time-level difference cue integration in sound lateralization
(Multidisciplinary Digital Publishing Institute (MDPI), 2020) N/A; Department of Computer Engineering; Mojtahedi, Sina; Erzin, Engin; Ungan, Pekcan; Faculty Member; Faculty Member; Department of Computer Engineering; Graduate School of Sciences and Engineering; College of Engineering; School of Medicine; N/A; 34503; N/A
A sound source with non-zero azimuth leads to interaural time level differences (ITD and ILD). Studies on hearing system imply that these cues are encoded in different parts of the brain, but combined to produce a single lateralization percept as evidenced by experiments indicating trading between them. According to the duplex theory of sound lateralization, ITD and ILD play a more significant role in low-frequency and high-frequency stimulations, respectively. In this study, ITD and ILD, which were extracted from a generic head-related transfer functions, were imposed on a complex sound consisting of two low- and seven high-frequency tones. Two-alternative forced-choice behavioral tests were employed to assess the accuracy in identifying a change in lateralization. Based on a diversity combination model and using the error rate data obtained from the tests, the weights of the ITD and ILD cues in their integration were determined by incorporating a bias observed for inward shifts. The weights of the two cues were found to change with the azimuth of the sound source. While the ILD appears to be the optimal cue for the azimuths near the midline, the ITD and ILD weights turn to be balanced for the azimuths far from the midline.
Open Access
A fast, accurate, and separable method for fitting a Gaussian function
(Institute of Electrical and Electronics Engineers (IEEE), 2019) Al-Nahhal Ibrahim; Dobre Octavia A.; Moloney Cecilia; Ikki Salama; Department of Electrical and Electronics Engineering; Başar, Ertuğrul; Faculty Member; Department of Electrical and Electronics Engineering; College of Engineering; 149116
Open Access
A machine learning approach for implementing data-driven production control policies
(Taylor _ Francis, 2021) Department of Business Administration; N/A; Tan, Barış; Khayyati, Siamak; Faculty Member; Department of Business Administration; College of Administrative Sciences and Economics; Graduate School of Sciences and Engineering; 28600; N/A
Given the extensive data being collected in manufacturing systems, there is a need for developing a systematic method to implement data-driven production control policies. For an effective implementation, first, the relevant information sources must be selected. Then, a control policy that uses the real-time signals collected from these sources must be implemented. We analyse the production control policy implementation problem in three levels: choosing the information sources, forming clusters of information signals to be used by the policy and determining the optimal policy parameters. Due to the search-space size, a machine-learning-based framework is proposed. Using machine learning speeds up optimisation and allows utilising the collected data with simulation. Through two experiments, we show the effectiveness of this approach. In the first experiment, the problem of selecting the right machines and buffers for controlling the release of materials in a production/inventory system is considered. In the second experiment, the best dispatching policy based on the selected information sources is identified. We show that selecting the right information sources and controlling a production system based on the real-time signals from the selected sources with the right policy improve the system performance significantly. Furthermore, the proposed machine learning framework facilitates this task effectively.
Open Access
A method for estimating stock-out-based substitution rates by using point-of-sale data
(Taylor _ Francis, 2009) Öztürk, Ömer Cem; Department of Business Administration; Tan, Barış; Karabatı, Selçuk; Faculty Member; Faculty Member; Department of Business Administration; College of Administrative Sciences and Economics; 28600; 38819
Empirical studies in retailing suggest that stock-out rates are quite high in many product categories. Stock-outs result in demand spillover, or substitution, among items within a product category. Product assortment and inventory management decisions can be improved when the substitution rates are known. In this paper, a method is presented to estimate product substitution rates by using only Point-Of-Sale (POS) data. The approach clusters POS intervals into states where each state corresponds to a specific substitution scenario. Then available POS data for each state is consolidated and the substitution rates are estimated using the consolidated information. An extensive computational analysis of the proposed substitution rate estimation method is provided. The computational analysis and comparisons with an estimation method from the literature show that the proposed estimation method performs satisfactorily with limited information.

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