Mühendislik Fakültesi

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Phase-Synchronized Fluidic Oscillator Pair
(AMER INST AERONAUTICS ASTRONAUTICS, 1801 ALEXANDER BELL DRIVE, STE 500, RESTON, VA 22091-4344 USA, 2019) Tomac, Mehmet N; Gregory, James W.
The relative phase of oscillating jets from a pair of fluidic oscillators was synchronized in this work. The means for this synchronization was mutual interaction through a shared feedback channel between the two oscillators. Flow visualization and hot-wire measurements indicated a strong correlation and phase synchronization between the two oscillators. A numerical analysis offered better understanding of the internal flow physics that led to the synchronization phenomenon. A portion of the output jet from one fluidic oscillator was redirected and crossed over into the adjacent oscillator, leading to momentum transfer between the two oscillators. A portion of this cross-oscillator flow was directed into the shared feedback channel and constituted the main feedback flow. In this process, one of the shared feedback channel outlets was blocked by a vortex, allowing only one oscillator to receive feedback flow. The primary mechanism for in-phase synchronization was the cross-oscillator flow, which was divided into phase-modulated momentum injection to the primary jet and modulated flow input to the shared channel feedback channel.
Structure Health Monitoring Using Wireless Sensor Networks on Structural Elements (vol 82, pg 68, 2019)
(ELSEVIER, RADARWEG 29, 1043 NX AMSTERDAM, NETHERLANDS, 2020) Ayyildiz, Cem; Erdem, H. Emre; Dirikgil, Tamer; Dugenci, Oguz; Kocak, Taskin; Altun, Fatih; Gungor, V. Cagri
This paper presents a system that monitors the health of structural elements in Reinforced Concrete (RC), concrete elements and/or masonry buildings and warn the authorities in case of physical damage formation. Such rapid and reliable detection of impairments enables the development of better risk management strategies to prevent casualties in case of earthquake and floods. Piezoelectric (PZT) sensors with lead zirconate titanate material are the preferred sensor type for fracture detection. The developed sensor mote hardware triggers the PZT sensors and collects the responses they gather from the structural elements. It also sends the collected data to a data center for further processing and analysis in an energy-efficient manner utilizing low-power wireless communication technologies. The access and the analysis of the collected data can be remotely performed via a web interface. Performance results show that the fractures serious enough to cause structural problems can be successfully detected with the developed system.
Citation - WoS: 251
Citation - Scopus: 263
Surface-Enhanced Raman Spectroscopy (SERS): An Adventure from Plasmonic Metals to Organic Semiconductors as SERS Platforms
(Royal Soc Chemistry, 2018) Demirel, Gokhan; Usta, Hakan; Yilmaz, Mehmet; Celik, Merve; Alidagi, Husniye Ardic; Buyukserin, Fatih; Demirel, Gokhan; Usta, Hakan; Yilmaz, Mehmet; Celik, Merve; Alidagi, Husniye Ardic; Buyukserin, Fatih
The quantitative determination and identification of bio-/chemical molecules at ultra-low concentrations is a hot topic in several fields including medical diagnostics, environmental science, and homeland security. Molecular detection techniques are conventionally based on optical, electrochemical, electronic, or gravimetric methodologies. Among these methods, surface-enhanced Raman spectroscopy (SERS) is considered as one of the most reliable, sensitive and selective techniques for non-destructive molecular analysis through the amplification of electromagnetic fields and/or creation of charge-transfer states between the chemisorbed analyte molecule and SERS active platform. Unfortunately, the applicability of SERS is rather limited, which is mainly due to the lack of highly sensitive SERS platforms with good stability and reproducibility. In line with this, metal nanoparticles (e.g., Au, Ag, and Cu) have been extensively exploited as SERS active platforms. Although the utilization of metallic nanoparticles in SERS is simple and cost-effective, the poor controllability of the structures and limited formation of hot spots in the detection zone leads to discrepancy in the resulting SERS signals. For these reasons, in the past few years, researchers have focused on fabricating 3-dimensional (3D) SERS platforms, which increase the adsorption of analyte molecules and facilitate hot spot formation in all three dimensions. However, the fabrication of 3D SERS platforms is mostly expensive and technologically demanding. Therefore, the discovery of non-metal alternative approaches is of great interest not only to widen SERS applications but to further elucidate fundamental questions. Considering recent developments on the fabrication and application of SERS active platforms, this review is structured in 3 main directions; (1) implementation of the plasmonic nanoparticles having different shapes into SERS-active platforms, (2) highlighting recent developments in the fabrication and application of 3D SERS-active platforms, and (3) examination of recent novel inorganic and organic semiconductor based platforms for SERS applications. At the end, we conclude with the promises and challenges for the future evolution of SERS.
Citation - WoS: 8
Citation - Scopus: 8
Low Velocity Oblique Impact Behavior of Adhesively Bonded Single Lap Joints
(Taylor & Francis Ltd, 2019) Atahan, M. Gokhan; Apalak, M. Kemal; Atahan, M. Gokhan; Apalak, M. Kemal
This article addresses the low velocity oblique impact behavior of adhesively bonded single lap joints, and the effects of adherend strength and plastic ductility, impact energy, overlap length and oblique impact angle on the damage initiation and propagation in the adhesive layer. The experimental contact force-time, contact force-central displacement variations, axial separation lengths through the adhesive layer and permanent central deflections of overlap region, adhesive fracture surfaces were evaluated in detail. In the explicit finite element analyses, the adhesive layer was divided into three zones: upper and lower adhesive interfaces and the adhesive layer between these interfaces. The adhesive interfaces were modeled with cohesive zone approach to predict the failure initiation and propagation along both upper and lower adhesive-adherend interfaces, whereas the elastic-plastic material model was implemented for the middle adhesive region between the upper and lower adhesive interfaces. The proposed finite element model predicted reasonably the damage initiation and propagation through the adhesive layer, and the contact force-time/central displacement variations. Especially, the test and analysis results were compared with those of the adhesively bonded single lap joints under a normal transverse impact load. Increasing oblique impact angle resulted in lower peak contact forces, shorter contact durations and earlier damage initiation and propagation through the adhesive layer. The peak contact forces increased, the contact duration decreased with increasing impact energy. The strength and plastic deformation capability of adherend materials also affected the damage initiation and propagation through the adhesive layer as well as the after-impact joint geometry.
Citation - WoS: 11
Citation - Scopus: 11
Biogas Intake Pressure and Port Air Swirl Optimization to Enhance the Diesel RCCI Engine Characteristics for Low Environmental Emissions
(Elsevier, 2024) Dalha, Ibrahim B.; Koca, Kemal; Said, Mior A.; Rafindadi, Aminu D.
Exhaust emission and combustion control in RCCI (reactivity-controlled compression ignition) focused mainly on the direct-injected fuel parameters, urging to investigate the advantages of port-fuel intake parameters. The engine was modified for port injection of Biogas at the valve and RCCI mode. The influence of port swirl ratio (PSR, 0 - 80%) and biogas injection pressure (BIP, 1 - 4 bar) on the diesel RCCI combustion and emissions was tested and optimized at varied loads and 1600 rpm in a port injection at the valve (PIVE) approach. Established kinetic mechanisms were combined with multi-objective optimization to further investigate, predict, and analyze emissions occurrence and trade-offs for reduced environmental impacts. The results show that the radiation absorption triggered by increased CO2 lowers combustion temperature, resulting in prolonged ignition. Setting the airflow to swirl lowers the in-cylinder pressure at elevated BIP while raising the heat generated across the BIPs. Increasing the PSR slows the combustion while BIP speeds up the process. BIP and PSR show great trade-off reduction ability among all emission parameters. The optimum unburned hydrocarbon, nitrogen oxide, particulate, and carbon monoxide emissions for the injection at the valve were found to be 109.58, 0.577, and 2.336 ppm, and 0.103%, respectively, at low-load, low-BIP, and high-PSR. The emissions were lowered by 6.58, 91.26, 80.65, and 13.45% compared to the premixed RCCI mode, respectively. Therefore, introducing lowpressure biogas amid high swirling air at the valve elevates the in-cylinder condition while lowering the emissions, mitigating their environmental implications.
Citation - WoS: 5
Node-Level Error Control Strategies for Prolonging the Lifetime of Wireless Sensor Networks
(IEEE-Inst Electrical Electronics Engineers Inc, 2021) Tekin, Nazli; Yildiz, Huseyin Ugur; Gungor, Vehbi Cagri
In Wireless Sensor Networks (WSNs), energy-efficiency and reliability are two critical requirements for attaining a long-term stable communication performance. Using error control (EC) methods is a promising technique to improve the reliability of WSNs. EC methods are typically utilized at the network-level, where all sensor nodes use the same EC method. However, improper selection of EC methods on some nodes in the network-level strategy can reduce the energy-efficiency, thus the lifetime of WSNs. In this study, a node-level EC strategy is proposed via mixed-integer programming (MIP) formulations. The MIP model determines the optimum EC method (i.e., automatic repeat request (ARQ), forward error correction (FEC), or hybrid ARQ (HARQ)) for each sensor node to maximize the network lifetime while guaranteeing a pre-determined reliability requirement. Five meta-heuristic approaches are developed to overcome the computational complexity of the MIP model. The performances of the MIP model and meta-heuristic approaches are evaluated for a wide range of parameters such as the number of nodes, network area, packet size, minimum desired reliability criterion, transmission power, and data rate. The results show that the node-level EC strategy provides at least 4.4% prolonged lifetimes and 4.0% better energy-efficiency than the network-level EC strategies. Furthermore, one of the developed meta-heuristic approaches (i.e., extended golden section search) provides lifetimes within a 3.9% neighborhood of the optimal solutions, reducing the solution time of the MIP model by 89.6%.
Citation - WoS: 18
Citation - Scopus: 20
A Simulation-Based Approximate Dynamic Programming Approach to Dynamic and Stochastic Resource-Constrained Multi-Project Scheduling Problem
(Elsevier, 2024) Satic, U.; Jacko, P.; Kirkbride, C.
We consider the dynamic and stochastic resource -constrained multi -project scheduling problem which allows for the random arrival of projects and stochastic task durations. Completing projects generates rewards, which are reduced by a tardiness cost in the case of late completion. Multiple types of resource are available, and projects consume different amounts of these resources when under processing. The problem is modelled as an infinite -horizon discrete -time Markov decision process and seeks to maximise the expected discounted long -run profit. We use an approximate dynamic programming algorithm (ADP) with a linear approximation model which can be used for online decision making. Our approximation model uses project elements that are easily accessible by a decision -maker, with the model coefficients obtained offline via a combination of Monte Carlo simulation and least squares estimation. Our numerical study shows that ADP often statistically significantly outperforms the optimal reactive baseline algorithm (ORBA). In experiments on smaller problems however, both typically perform suboptimally compared to the optimal scheduler obtained by stochastic dynamic programming. ADP has an advantage over ORBA and dynamic programming in that ADP can be applied to larger problems. We also show that ADP generally produces statistically significantly higher profits than common algorithms used in practice, such as a rule -based algorithm and a reactive genetic algorithm.
Citation - WoS: 44
Citation - Scopus: 52
CBI4.0: A Cross-Layer Approach for Big Data Gathering for Active Monitoring and Maintenance in the Manufacturing Industry 4.0
(Elsevier, 2021) Faheem, Muhammad; Butt, Rizwan Aslam; Ali, Rashid; Raza, Basit; Ngadi, Md Asri; Gungor, Vehbi Cagri
Industry 4.0 (I4.0) defines a new paradigm to produce high-quality products at the low cost by reacting quickly and effectively to changing demands in the highly volatile global markets. In Industry 4.0, the adoption of Internet of Things (IoT)-enabled Wireless Sensors (WSs) in the manufacturing processes, such as equipment, machining, assembly, material handling, inspection, etc., generates a huge volume of data known as Industrial Big Data (IBD). However, the reliable and efficient gathering and transmission of this big data from the source sensors to the floor inspection system for the real-time monitoring of unexpected changes in the production and quality control processes is the biggest challenge for Industrial Wireless Sensor Networks (IWSNs). This is because of the harsh nature of the indoor industrial environment that causes high noise, signal fading, multipath effects, heat and electromagnetic interference, which reduces the transmission quality and trigger errors in the IWSNs. Therefore, this paper proposes a novel cross-layer data gathering approach called CBI4.0 for active monitoring and control of manufacturing processes in the Industry 4.0. The key aim of the proposed CBI4.0 scheme is to exploit the multi-channel and multi-radio architecture of the sensor network to guarantee quality of service (QoS) requirements, such as higher data rates, throughput, and low packet loss, corrupted packets, and latency by dynamically switching between different frequency bands in the Multichannel Wireless Sensor Networks (MWSNs). By performing several simulation experiments through EstiNet 9.0 simulator, the performance of the proposed CBI4.0 scheme is compared against existing studies in the automobile Industry 4.0. The experimental outcomes show that the proposed scheme outperforms existing schemes and is suitable for effective control and monitoring of various events in the automobile Industry 4.0.
Fusion and Analysis of PET and CT Images of Patients With Non-Small Cell Lung Cancer
(Springer, 2016) Ayyildiz, O.; Yilmaz, B.; Karacavus, S.; Kayaalti, O.; Eset, K.; Gazeloglu, C.; Kaya, E.
Citation - WoS: 10
Citation - Scopus: 11
Structurally Colored Physically Unclonable Functions With Ultra-Rich and Stable Encoding Capacity
(Wiley-VCH Verlag GmbH, 2025) Esidir, Abidin; Ren, Miaoning; Pekdemir, Sami; Kalay, Mustafa; Kayaci, Nilgun; Gunaltay, Nail; Onses, Mustafa Serdar
Identity security and counterfeiting assume a critical importance in the digitized world. An effective approach to addressing these issues is the use of physically unclonable functions (PUFs). The overarching challenge is a simultaneous combination of extremely high encoding capacity, stable operation, practical fabrication, and a widely available readout mechanism. Herein this challenge is addressed by designing an optical PUF via exploiting the thickness-dependent structural color formation in nanoscopic films of ZnO. The structural coloration ensures authentication using widely available bright-field-based optical readout, whereas the metal oxide provides a high degree of structural stability. True physical randomness in spatial position is achieved by physical vapor deposition of ZnO through stencil masks that are fabricated by pore formation in polycarbonate membranes via photothermal processing of stochastically positioned plasmonic nanoparticles. Structural coloration emerges from thin film interference as confirmed via simulation studies. The rich color variation and stochastic definition of domain size and geometry result in chaotic features with an encoding capacity that approaches (6.4 x 105)(2752x2208). Deep learning-based authentication is further demonstrated by transforming these chaotic features into unbreakable codes without field limitations. This ultra-rich encoding capacity, coupled with outstanding thermal and chemical stability, forms a new cutting edge for state-of-the-art PUF-based encoding systems.
Prognostic Significance of the Texture Features Determined Using Three Dimensional 18F-FDG PET Images: New Potential Biomarkers
(Soc Nuclear Medicine inc, 2016) Karacavus, Seyhan; Yilmaz, Bulent; Kayaalti, Omer; Tasdemir, Arzu; Kaya, Eser; Icer, Semra; Asyali, Musa
Citation - WoS: 49
Citation - Scopus: 53
Comprehensive Experimental Analysis of the Effects of Elevated Temperatures in Geopolymer Concretes With Variable Alkali Activator Ratios
(Elsevier, 2023) Ozbayrak, Ahmet; Kucukgoncu, Hurmet; Aslanbay, Huseyin Hilmi; Aslanbay, Yuksel Gul; Atas, Oguzhan
By growing population and rapid urbanization, demand for concrete increases exponentially. Researches on use of fly ash material in waste product class for concrete production are important to produce concrete more environmentally friendly. However, there is a need for more research to use geopolymer concrete (GPC) in every field where ordinary Portland cement concrete (OPC) is used. Therefore, it is crucial to experimentally investigate thermal properties as well as me-chanical properties of geopolymer concrete. As investigated thermal properties, the main factor affecting strength development of GPC is alkali activator ratios. In this study, GPC prism samples with nine different compositions, produced by various alkali ratios. After flexural strength tests, they were cut into cubes and exposed to 400 degrees C, 600 degrees C and 800 degrees C, then they were subjected to compressive strength tests. Results obtained from different AA/FA and SS/SH ratios were eval-uated as mechanical properties at ambient temperature and physical, mechanical and micro-structural properties at elevated temperature. An empirical formula, which considers the effect of activator ratios, was proposed to calculate flexural strength depending on compressive strength of samples at ambient temperature. As an increase of SS/SH and AA/FA ratios, compressive strength increased, while flexural strength decreased. The increase in AA/FA ratio decreased compressive strength of samples exposed to high temperatures, while increase in SS/SH ratio did not deter-mine at elevated temperatures. There is an inverse change with AA/FA ratio and parallel change with SS/SH ratio between compressive strengths of samples at ambient temperature and exposed to high temperature.
Citation - WoS: 11
Citation - Scopus: 14
Detection of Movement Intention in EEG-Based Brain-Computer Interfaces Using Fourier-Based Synchrosqueezing Transform
(World Scientific Publ Co Pte Ltd, 2021) Karakullukcu, Nedime; Yilmaz, Bulent
Patients with motor impairments need caregivers' help to initiate the operation of brain-computer interfaces (BCI). This study aims to identify and characterize movement intention using multichannel electroencephalography (EEG) signals as a means to initiate BCI systems without extra accessories/methodologies. We propose to discriminate the resting and motor imagery (MI) states with high accuracy using Fourier-based synchrosqueezing transform (FSST) as a feature extractor. FSST has been investigated and compared with other popular approaches in 28 healthy subjects for a total of 6657 trials. The accuracy and f-measure values were obtained as 99.8% and 0.99, respectively, when FSST was used as the feature extractor and singular value decomposition (SVD) as the feature selection method and support vector machines as the classifier. Moreover, this study investigated the use of data that contain certain amount of noise without any preprocessing in addition to the clean counterparts. Furthermore, the statistical analysis of EEG channels with the best discrimination (of resting and MI states) characteristics demonstrated that F4-Fz-C3-Cz-C4-Pz channels and several statistical features had statistical significance levels, p, less than 0.05. This study showed that the preparation of the movement can be detected in real-time employing FSST-SVD combination and several channels with minimal pre-processing effort.
Citation - WoS: 3
Citation - Scopus: 3
Excitonic Interaction Amongst InP/ZnS Salt Pellets
(Royal Soc Chemistry, 2017) Altintas, Yemliha; Yazici, Ahmet Faruk; Unlu, Miray; Dadi, Seyma; Genc, Sinan; Mutlugun, Evren
Salt matrix has recently been introduced as a promising robust platform for embedding colloidal quantum dots to provide them with photo stability for versatile applications. This work demonstrates the excitonic interaction amongst high efficiency colloidal InP/ZnS quantum dots embedded in a KCl salt matrix. By varying the donor acceptor ratio within the solid platform, 65% Forster Resonance Energy Transfer (FRET) efficiency was attained. Optimizing the donor : acceptor ratio, we demonstrated the first FRET-enabled Cd-free pellets for white light generation possessing a color rendering index (CRI) of 84.7, correlated color temperature (CCT) of 5347.5 K, and a high luminous efficacy of optical radiation value (LER) of 324.3 lm/W-opt. Our study of excitonic interactions within quantum dot-loaded salt matrices will open new possibilities for future versatile optoelectronic applications.
Citation - WoS: 3
Citation - Scopus: 3
High Pressure Modifications in Amorphous Boron Suboxide: An Ab Initio Study
(Elsevier Sci Ltd, 2020) Durandurdu, Murat; Durandurdu, Murat
Using constant pressure ab initio calculations, we probe the high-pressure modifications in amorphous boron suboxide (B6O) consisting of glassy boron trioxide (B2O3) and boron (B) domains up to a theoretical pressure of 100 GPa. At this pressure, the structure remains amorphous. We find a steady increase in the average coordination of both B and oxygen (O) atoms. O atoms mostly attain threefold coordination as in B2O3 glass at high pressures. On the other hand, the mean coordination number of B-atoms reaches six at high pressures and the structural changes in B-rich regions are perceived to be quite analogous to those of amorphous B. B-12 clusters are found to persevere during the pressurizing process and the high-pressure modifications occur predominantly around O-atoms and the regions that connect the pentagonal pyramid-like motifs to each other. Upon pressure release, some high-pressure configurations persist in the model and another noncrystalline structure being about 10% denser than the original state is recovered, suggesting a permanent densification and a possible irreversible amorphous-to-amorphous phase transformation in B6O. The recovered network shows slightly better mechanical properties than the uncompressed model. During the compression and decompression processes, amorphous B6O remains semiconducting. The delocalization of some band tail states is seen at high pressures.

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