Publications without Fulltext
Permanent URI for this collectionhttps://hdl.handle.net/20.500.14288/3
Browse
137 results
Filters
Advanced Search
Filter by
Settings
Search Results
Publication Metadata only Microfluidic pulse shaping methods for molecular communications(Elsevier, 2023) Department of Electrical and Electronics Engineering; Kahvazi Zadeh, Maryam; Bolhassan, Iman Mokari; Kuşcu, Murat; Department of Electrical and Electronics Engineering; Graduate School of Sciences and Engineering; College of EngineeringMolecular Communication (MC) is a bio-inspired communication modality that utilizes chemical signals in the form of molecules to exchange information between spatially separated entities. Pulse shaping is an important process in all communication systems, as it modifies the waveform of transmitted signals to match the characteristics of the communication channel for reliable and high-speed information transfer. In MC systems, the unconventional architectures of components, such as transmitters and receivers, and the complex, nonlinear, and time-varying nature of MC channels make pulse shaping even more important. While several pulse shaping methods have been theoretically proposed for MC, their practicality and performance are still uncertain. Moreover, the majority of recently proposed experimental MC testbeds that rely on microfluidics technology lack the incorporation of programmable pulse shaping methods, which hinders the accurate evaluation of MC techniques in practical settings. To address the challenges associated with pulse shaping in microfluidic MC systems, we provide a comprehensive overview of practical microfluidic chemical waveform generation techniques that have been experimentally validated and whose architectures can inform the design of pulse shaping methods for microfluidic MC systems and testbeds. These techniques include those based on hydrodynamic and acoustofluidic force fields, as well as electrochemical reactions. We also discuss the fundamental working mechanisms and system architectures of these techniques, and compare their performances in terms of spatiotemporal resolution, selectivity, system complexity, and other performance metrics relevant to MC applications, as well as their feasibility for practical MC applications.Publication Metadata only Boosting methylene blue adsorption capacity of an industrial waste-based geopolymer by depositing graphitic carbon nitride onto its surface: towards sustainable materials for wastewater treatment(Pergamon-Elsevier Science Ltd, 2024) Kaya-Ozkiper, Kardelen; Soyer-Uzun, Sezen; Department of Chemical and Biological Engineering; Uzun, Alper; Department of Chemical and Biological Engineering; Koç University Tüpraş Energy Center (KUTEM) / Koç Üniversitesi Tüpraş Enerji Merkezi (KÜTEM); Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); College of EngineeringSurface characteristics of a geopolymer (GP) from an industrial waste, red mud (RM), and metakaolin (MK), were tuned by depositing urea-derived graphitic carbon nitride (g-C3N4) onto its surface. Methylene blue (MB) adsorption measurements demonstrated that the resulting g-C3N4/RM-MK-GP offers an excellent MB uptake capacity of 170.9 mg g-1, much higher than those of either the GP or the g-C3N4. Kinetics measurements revealed that chemisorption has an important effect on adsorption. The regenerability of g-C3N4/RM-MK-GP was studied for up to four consecutive cycles. Differences between the adsorption capacities of g-C3N4 and g-C3N4/RM-MKGP were investigated by combining the power of various characterization tools. Results pointed out that surface functional groups associated with g-C3N4, surface hydroxyl and silanol groups of RM-MK-GP, together with exchangeable charge balancing cations of geopolymeric framework provide a unique structure for g-C3N4/RMMK-GP. This study presents a versatile route to produce a sustainable, efficient, and cheap adsorbent for wastewater treatment.Publication Metadata only The digital twin synchronization problem: framework, formulations, and analysis(Taylor & Francis Inc, 2023) Matta, Andrea; Department of Business Administration; Tan, Barış; Department of Business Administration; College of Administrative Sciences and EconomicsAs the adoption of digital twins increases steadily, it is necessary to determine how to operate them most effectively and efficiently. In this article, the digital twin synchronization problem is introduced and defined formally. Frequent synchronizations would increase cost and data traffic congestion, whereas infrequent synchronizations would increase the bias of the predictions and yield wrong decisions. This work defines the synchronization problem variants in different contexts. To discuss the problem and its solution, the problem of determining when to synchronize an unreliable production system with its digital twin to minimize the average synchronization and bias costs is formulated and analyzed analytically. The state-independent, state-dependent, and full-information solutions have been determined by using a stochastic model of the system. Solving the synchronization problem using simulation is discussed, and an approximate policy is proposed. Our results show that the performance of the state-dependent policy is close to the optimal solution that can be obtained with full information and significantly better than the performance of the state-independent policy. Furthermore, the approximate periodic state-dependent policy yields near-optimal results. To operate digital twins more effectively, the digital twin synchronization problem must be considered and solved to determine the optimal synchronization policy.Publication Metadata only Optical whispering gallery mode resonators: analysing thermo-optic tuning in a silicon sphere(Taylor and Francis Asia Pacific, 2024) Khan, Haseeb Ahmad; Ma, Li; Khan, Adnan Daud; Azeem, Farhan; Chaudhry, Muhammad Rehan; Anwar, Muhammad Sohail; Graduate School of Sciences and EngineeringIn this work, we discuss and experimentally investigate the whispering gallery modes (WGMs) in a 500 μm radius silicon sphere. We begin by reviewing the basics of WGM resonators, followed by simulations and experimental results obtained with the aforementioned silicon spherical WGM resonator. The recorded WGM signatures in the transmission and scattering spectra excited, in the near-infrared (near-IR) region, agree well with the simulations. Thermo-optic tuning of these WGMs is achieved by introducing a pump laser in the violet-blue region. Red-shifts in wavelength are observed, which increase with the increase in the pump power. A shift of 0.63 nm is observed at a pump power of 6.32 mW. We also study switching by analysing the transient response of the WGM spectra. The measured WGMs exhibit high quality factors ((Formula presented.)), which along with the aforesaid tunability, demonstrates the potential of spherical silicon resonator as a platform for photonic applications, e.g. sensing and communication. In summary, this work contributes towards the understanding of the fundamental physics of WGMs and provides insights into silicon WGM resonators.Publication Metadata only Development of a lunar vehicle with a hybrid rocket engine produced using lunar resources(Springer, 2024) Yalcintas, Ali; Department of Mechanical Engineering; Yelken, Ümit; Karabeyoğlu, Mustafa Arif; Department of Mechanical Engineering; Graduate School of Sciences and Engineering; College of EngineeringThis article presents a comprehensive study on the innovative use of in-situ lunar resources for the development of a hybrid rocket engine utilizing magnesium (Mg) and aluminium (Al), which are abundantly available in lunar regolith. The primary focus is on the feasibility and sustainability of using these metal oxides as primary fuels in propulsion systems specifically designed for lunar missions. The research encompasses the design phases of a lunar lander, highlighting the application of these metals in the engine design to facilitate efficient space travel between research stations on the Moon's surface. Detailed discussions cover the extraction and processing of Mg and Al directly on the lunar surface through adapted electrolysis processes suitable for the Moon's environment. The article also explores the engineering of a cryogenic tank system using native lunar materials to address the challenges posed by the Moon's extreme temperature fluctuations. A key component of the study is the simulation of simple trajectory calculations for travel between lunar research locations using the newly designed hybrid rocket engine. Theoretical analyses suggest that this metal-based propulsion technology could significantly enhance the logistical capabilities of lunar exploration missions, offering a viable solution for both crewed and uncrewed missions. The development of such technologies not only aims to reduce Earth dependence by utilizing lunar resources but also sets a precedent for future interplanetary travel infrastructure.Publication Metadata only A novel approach to tube design via von Mises probability distribution(Taylor and Francis Ltd., 2024) Subay, Şehmuz Ali; Department of Mechanical Engineering; Oral, Atacan; Subaşı, Ömer; Öztürk, Çağlar; Lazoğlu, İsmail; Department of Mechanical Engineering; Manufacturing and Automation Research Center (MARC); Graduate School of Sciences and Engineering; College of EngineeringDischarge tube is a critical component in a reciprocating compressor that carries the refrigerant. It also transmits vibrations from compressor body to housing, making the design of tube a complex engineering problem combining static, modal and flow behaviour. This study proposes a novel design algorithm for discharge tube, to decrease the dependency on the trial-and-error approach commonly used by manufacturers. The computational approach creates a tube that connects the inlet and outlet using von Mises probability distribution. The created geometries are checked for static and dynamic properties using FEA. The algorithm continues until a candidate design passes the imposed thresholds. The candidate designs perform similarly to benchmark in evaluated aspects, demonstrating promising results. The presented algorithm is successful in generating alternative tube designs from scratch and can accommodate varying requirements. The main novelty of this study is the development of a comprehensive decision algorithm that considers multiple engineering parameters simultaneously. © 2022 Informa UK Limited, trading as Taylor & Francis Group.Publication Metadata only Kirchhoff meets Johnson: in pursuit of unconditionally secure communication(WILEY, 2024) Department of Electrical and Electronics Engineering; Başar, Ertuğrul; Department of Electrical and Electronics Engineering; College of EngineeringNoise: an enemy to be dealt with and a major factor limiting communication system performance. However, what if there is gold in that garbage? In conventional engineering, our focus is primarily on eliminating, suppressing, combating, or even ignoring noise and its detrimental impacts. Conversely, could we exploit it similarly to biology, which utilizes noise-alike carrier signals to convey information? In this context, the utilization of noise, or noise-alike signals in general, has been put forward as a means to realize unconditionally secure communication systems in the future. In this tutorial article, we begin by tracing the origins of thermal noise-based communication and highlighting one of its significant applications for ensuring unconditionally secure networks: the Kirchhoff-law-Johnson-noise (KLJN) secure key exchange scheme. We then delve into the inherent challenges tied to secure communication and discuss the imperative need for physics-based key distribution schemes in pursuit of unconditional security. Concurrently, we provide a concise overview of quantum key distribution schemes and draw comparisons with their KLJN-based counterparts. Finally, extending beyond wired communication loops, we explore the transmission of noise signals over-the-air and evaluate their potential for stealth and secure wireless communication systems.Publication Metadata only Equipment selection for coupling a microgrid with a power-to-gas system in the context of optimal design and operation(Elsevier Ltd, 2024) Akülker, Handan; Department of Chemical and Biological Engineering; Aydın, Erdal; Department of Chemical and Biological Engineering; Koç University Tüpraş Energy Center (KUTEM) / Koç Üniversitesi Tüpraş Enerji Merkezi (KÜTEM); College of EngineeringThis study proposes a one-layer deterministic Mixed-Integer Nonlinear Programming to design and schedule a PTG-integrated microgrid. The key contribution is that optimal equipment selection, design, and scheduling, considering the PTG system at the core of the problem, are determined just in a single formulation. Scenarios based on different carbon dioxide taxes and natural gas prices are investigated. Only one wind turbine farm is chosen when the carbon dioxide tax is increased from 50 $/ton to 100 $/ton. On the other hand, when the natural gas price is increased from 1.548 $/m3 to 1.72 $/m3, two wind turbine farms are selected. Solar panel arrays are not chosen in all the scenarios. Generated power by solar panels is not enough for installation despite their much lower carbon dioxide emissions and negligible operational costs. Consequently, the optimal equipment selections may change linked to the natural gas price and carbon dioxide tax.Publication Metadata only Mesoporous graphitic carbon nitride-supported binary MPt (M: Co, Ni, Cu) nanoalloys as electrocatalysts for borohydride oxidation and hydrogen evolution reaction(Elsevier, 2020) Oliveira, Raisa C. P.; Sevim, Melike; Sljukic, Biljana; Sequeira, Cesar A. C.; Santos, Diogo M. F.; Department of Chemistry; Metin, Önder; Faculty Member; Department of Chemistry; College of Sciences; 46962In this work, binary MPt (M = Co, Ni, Cu) nanoalloys and mesoporous carbon nitride (mpg-C3N4) as support material are prepared, and then gathered together by liquid phase self-assembly in order to produce MPt/mpg-C3N4 electrocatalysts. The yielded electrocatalysts are characterized by TEM, ICP-MS and XRD techniques in order to determine their morphology, composition and textural properties. Evaluation of MPt/mpg-C3N4 (<3 wt.% of Pt) electrocatalysts performance for hydrogen evolution reaction (HER) and borohydride oxidation reaction (BOR) is carried out. Pt/mpg-C3N4 is also studied to better understand the alloying effect on the electrocatalysts' performance, being concluded that it clearly increases the catalytic activity while decreasing the necessary Pt metal amount. For HER, CoPt/mpg-C3N4 was found to be the best catalyst, presenting a Tafel slope of 109 mV dec(-1) at 65 degrees C. Regarding BOR, CuPt/mpg-C3N4 demonstrated the best catalytic activity with average activation energy and reaction order with respect to BH4- of 29.4 kJ mol(-1) and 0.87, respectively.Publication Metadata only Gap metric concept and implications for multilinear model-based controller design(Amer Chemical Soc, 2003) Galan, O.; Romagnoli, J.A.; Palazoglu, A.; Department of Chemical and Biological Engineering; Arkun, Yaman; Faculty Member; Department of Chemical and Biological Engineering; College of Engineering; 108526The gap metric concept is used within the context of multilinear model-based control. The concept of distance between dynamic systems is used as a criterion for selecting a set of models that can explain the nonlinear plant behavior in a given operating range. The case studies presented include a CSTR and a pH neutralization reactor. The gap metric is used to analyze the relationships among candidate models, resulting in a reduced model set that provides enough information to design multilinear controllers. The simulation and experimental results indicate good performance and stability features.