Publications with Fulltext
Permanent URI for this collectionhttps://hdl.handle.net/20.500.14288/6
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Publication Open Access CdTe quantum dot sensitized hexaniobate nanoscrolls and their photoelectrochemical properties(Royal Society of Chemistry (RSC), 2012) Department of Chemistry; Öztuna, Feriha Eylül Saraç; Akkaya, Ceren Yılmaz; Acar, Havva Funda Yağcı; Ünal, Uğur; PhD Student; Faculty Member; Department of Chemistry; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); College of Sciences; N/A; N/A; 178902; N/AWe have constructed hybrid quantum dot-layered niobate films with an electrophoretic deposition method. The structure and photoelectrochemical behaviour were demonstrated.Publication Open Access Investigation of hydrodynamic behavior of alginate aerogel particles in a laboratory scale Wurster fluidized bed(Multidisciplinary Digital Publishing Institute (MDPI), 2019) Department of Chemical and Biological Engineering; Erkey, Can; Akgün, Işık Sena; Faculty Member; Researcher; Department of Chemical and Biological Engineering; Graduate School of Sciences and Engineering; 29633; N/AThe effects of design and operating parameters on the superficial velocity at the onset of circulatory motion and the residence time of alginate aerogel particles in a laboratory scale Wurster fluidized bed were investigated. Several sets of experiments were conducted by varying Wurster tube diameter, Wurster tube length, batch volume and partition gap height. The superficial velocities for Wurster tube with 10 cm diameter were lower than the tube with 8 cm diameter. Superficial velocities increased with increasing batch volume and partition gap height. Moreover, increasing batch volume and partition gap height led to a decrease in the particle residence time in the Wurster tube. The results showed that there is an upper limit for each parameter in order to obtain a circulatory motion of the particles. It was found that the partition gap height should be 2 cm for proper particle circulation. Maximum batch volume for the tube with 10 cm diameter was found as 500 mL whereas maximum batch volume was 250 mL for the tube with 8 cm diameter. The fluidization behavior of the aerogel particles investigated in this study could be described by the general fluidization diagrams in the literature.Publication Open Access Understanding the link between inflammasome and apoptosis through the response of THP-1 cells against drugs using droplet-based microfluidics(American Chemical Society (ACS), 2022) Gençtürk, E.; Kasım, M.; Ülgen, K.O.; Department of Physics; Department of Electrical and Electronics Engineering; Kiraz, Alper; Morova, Berna; Faculty Member; Researcher; Department of Physics; Department of Electrical and Electronics Engineering; College of Sciences; College of Engineering; 22542; N/ADroplet-based microfluidic devices are used to investigate monocytic THP-1 cells in response to drug administration.Consistent and reproducible droplets are created, each of which acts as a bioreactor to carry out single cell experiments withminimized contamination and live cell tracking under an invertedfluorescence microscope for more than 2 days. Here, the effects ofthree different drugs (temsirolimus, rifabutin, and BAY 11-7082) on THP-1 are examined and the results are analyzed in the contextof the inflammasome and apoptosis relationship. The ASC adaptor gene tagged with GFP is monitored as the inflammasomereporter. Thus, a systematic way is presented for deciphering cell-to-cell heterogeneity, which is an important issue in cancertreatment. The drug temsirolimus, which has effects of disrupting the mTOR pathway and triggering apoptosis in tumor cells, causesTHP-1 cells to express ASC and to be involved in apoptosis. Treatment with rifabutin, which inhibits proliferation and initiatesapoptosis in cells, affects ASC expression byfirst increasing and then decreasing it. CASP-3, which has a role in apoptosis and isdirectly related to ASC, has an increasing level in inflammasome conditioning. Thus, the cell under the effect of rifabutin might befaced with programmed cell death faster. The drug BAY 11-7082, which is responsible for NF Kappa B inhibition, shows similar results totemsirolimus with more than 60% of cells having highfluorescence intensity (ASC expression). The microfluidic platform presentedhere offers strong potential for studying newly developed small-molecule inhibitors for personalized/precision medicine.Publication Open Access Introduction to noise radar and its waveforms(Multidisciplinary Digital Publishing Institute (MDPI), 2020) De Palo, Francesco; Galati, Gaspare; Pavan, Gabriele; Wasserzier, Christoph; Department of Electrical and Electronics Engineering; Savcı, Kubilay; Department of Electrical and Electronics Engineering; Graduate School of Sciences and EngineeringIn the system-level design for both conventional radars and noise radars, a fundamental element is the use of waveforms suited to the particular application. In the military arena, low probability of intercept (LPI) and of exploitation (LPE) by the enemy are required, while in the civil context, the spectrum occupancy is a more and more important requirement, because of the growing request by non-radar applications; hence, a plurality of nearby radars may be obliged to transmit in the same band. All these requirements are satisfied by noise radar technology. After an overview of the main noise radar features and design problems, this paper summarizes recent developments in "tailoring" pseudo-random sequences plus a novel tailoring method aiming for an increase of detection performance whilst enabling to produce a (virtually) unlimited number of noise-like waveforms usable in different applications.Publication Open Access An aging model of NH3 storage sites for predicting kinetics of NH3 adsorption, desorption and oxidation over hydrothermally aged Cu-chabazite(Multidisciplinary Digital Publishing Institute (MDPI), 2020) Şanlı, D.; Özener, B.; Hisar, G.; Department of Chemical and Biological Engineering; Bozbağ, Selmi Erim; Erkey, Can; Researcher; Faculty Member; Department of Chemical and Biological Engineering; College of Engineering; N/A; 29633A unified transient kinetic model which can predict the adsorption, desorption and oxidation kinetics of NH3 over hydrothermally aged Cu-chabazite was developed. The model takes into account the variation of fractional coverages of NH3 storage sites due to hydrothermal aging. In order to determine the fractional coverage of these sites, the catalyst was aged for various times at a certain temperature followed by NH3 adsorption, desorption and temperature-programmed desorption (TPD) experiments. TPD profiles were deconvoluted mainly into three peaks with centres at 317, 456 and 526 oC, respectively. Hydrothermal aging resulted in the progressive increase in the intensity of the peak at 317 oC and decrease in the intensity of the peaks at 456 and 526 oC, along with decreased NH3 oxidation at high temperatures. A model for hydrothermal aging kinetics of the fractional coverage of storage sites was developed using three reactions with appropriate rate expressions with parameters regressed from experimental data. The model was then incorporated into a multi-site kinetic model for the degreened Cu-Chabazite by the addition of aging reactions on each storage site. The effects of both aging time and temperature on the kinetics NH3 adsorption, desorption and oxidation were successfully predicted in the 155-540 oC range. This study is the first step towards the development of a hydrothermal aging-unified kinetic model of NH3-Selective Catalytic Reduction over Cu-chabazite.Publication 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/AA 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.Publication Open Access Finger-actuated microneedle array for sampling body fluids(Multidisciplinary Digital Publishing Institute (MDPI), 2021) Ahmadpour, Abdollah; Yetişen, Ali K.; Department of Mechanical Engineering; Taşoğlu, Savaş; Sarabi, Misagh Rezapour; Faculty Member; 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; N/AThe application of microneedles (MNs) for minimally invasive biological fluid sampling is rapidly emerging, offering a user-friendly approach with decreased insertion pain and less harm to the tissues compared to conventional needles. Here, a finger-powered microneedle array (MNA) integrated with a microfluidic chip was conceptualized to extract body fluid samples. Actuated by finger pressure, the microfluidic device enables an efficient approach for the user to collect their own body fluids in a simple and fast manner without the requirement for a healthcare worker. The processes for extracting human blood and interstitial fluid (ISF) from the body and the flow across the device, estimating the amount of the extracted fluid, were simulated. The design in this work can be utilized for the minimally invasive personalized medical equipment offering a simple usage procedure.Publication Open Access Silk-hydrogel lenses for light-emitting diodes(Nature Publishing Group (NPG), 2017) Melikov, Rustamzhon; Press, Daniel Aaron; Kumar, Baskaran Ganesh; Dogru, Itir Bakis; Sadeghi, Sadra; Chirea, Mariana; Department of Chemistry; Department of Electrical and Electronics Engineering; Yılgör, İskender; Nizamoğlu, Sedat; Faculty Member; Faculty Member; Department of Chemistry; Department of Electrical and Electronics Engineering; College of Sciences; College of Engineering; 24181; 130295Today the high demand for electronics leads to massive production of waste, thus green materials based electronic devices are becoming more important for environmental protection and sustainability. The biomaterial based hydrogels are widely used in tissue engineering, but their uses in photonics are limited. In this study, silk fibroin protein in hydrogel form is explored as a bio-friendly alternative to conventional polymers for lens applications in light-emitting diodes. The concentration of silk fibroin protein and crosslinking agent had direct effects on optical properties of silk hydrogel. The spatial radiation intensity distribution was controlled via dome- and crater-type silk-hydrogel lenses. The hydrogel lens showed a light extraction efficiency over 0.95 on a warm white LED. The stability of silk hydrogel lens is enhanced approximately three-folds by using a biocompatible/biodegradable poly(ester-urethane) coating and more than three orders of magnitude by using an edible paraffin wax coating. Therefore, biomaterial lenses show promise for green optoelectronic applications.Publication Open Access Automatic CNN-based Arabic numeral spotting and handwritten digit recognition by using deep transfer learning in Ottoman population registers(Multidisciplinary Digital Publishing Institute (MDPI), 2020) Department of History; Kabadayı, Mustafa Erdem; Can, Yekta Said; Faculty Member; Department of History; College of Social Sciences and Humanities; 33267; N/AHistorical manuscripts and archival documentation are handwritten texts which are the backbone sources for historical inquiry. Recent developments in the digital humanities field and the need for extracting information from the historical documents have fastened the digitization processes. Cutting edge machine learning methods are applied to extract meaning from these documents. Page segmentation (layout analysis), keyword, number and symbol spotting, handwritten text recognition algorithms are tested on historical documents. For most of the languages, these techniques are widely studied and high performance techniques are developed. However, the properties of Arabic scripts (i.e., diacritics, varying script styles, diacritics, and ligatures) create additional problems for these algorithms and, therefore, the number of research is limited. In this research, we first automatically spotted the Arabic numerals from the very first series of population registers of the Ottoman Empire conducted in the mid-nineteenth century and recognized these numbers. They are important because they held information about the number of households, registered individuals and ages of individuals. We applied a red color filter to separate numerals from the document by taking advantage of the structure of the studied registers (numerals are written in red). We first used a CNN-based segmentation method for spotting these numerals. In the second part, we annotated a local Arabic handwritten digit dataset from the spotted numerals by selecting uni-digit ones and tested the Deep Transfer Learning method from large open Arabic handwritten digit datasets for digit recognition. We achieved promising results for recognizing digits in these historical documents.Publication Open Access Minimum length scheduling for multi-cell full duplex wireless powered communication networks(Multidisciplinary Digital Publishing Institute (MDPI), 2021) Iqbal, M. S.; Sadi, Y.; Department of Electrical and Electronics Engineering; Ergen, Sinem Çöleri; Faculty Member; Department of Electrical and Electronics Engineering; College of Engineering; 7211Wireless powered communication networks (WPCNs) will be a major enabler of massive machine type communications (MTCs), which is a major service domain for 5G and beyond systems. These MTC networks will be deployed by using low-power transceivers and a very limited set of transmission configurations. We investigate a novel minimum length scheduling problem for multi-cell full-duplex wireless powered communication networks to determine the optimal power control and scheduling for constant rate transmission model. The formulated optimization problem is combinatorial in nature and, thus, difficult to solve for the global optimum. As a solution strategy, first, we decompose the problem into the power control problem (PCP) and scheduling problem. For the PCP, we propose the optimal polynomial time algorithm based on the evaluation of Perron– Frobenius conditions. For the scheduling problem, we propose a heuristic algorithm that aims to maximize the number of concurrently transmitting users by maximizing the allowable interference on each user without violating the signal-to-noise-ratio (SNR) requirements. Through extensive simulations, we demonstrate a 50% reduction in the schedule length by using the proposed algorithm in comparison to unscheduled concurrent transmissions.