2024 Cilt 29 Sayı 1

Permanent URI for this collectionhttps://hdl.handle.net/11452/41289

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The effect of different dielectric materials on radiation features of slotted patch antennas for 6g communication systems
(Bursa Uludağ Üniversitesi, 2024-03-18) Hakanoğlu, Barış Gürcan
In this study, patch antenna structures with rhombic shaped slots have been investigated for 6G communication systems. Four different dielectric materials, such as arlon, polyamide, polyimide, and silicon, have been selected for antennas with the same design procedure. In this way, the effects of slots on frequency responses for different dielectric substrates have been searched. The slots are parametrically analyzed in terms of edge size and location, and the designs are completed for values with the lowest return loss levels. The amount of return loss reduction in slotted antennas is 38% and 42% for arlon and polyamide, respectively, while the reduction is 28% and 8% for polyimide and silicon, respectively. In addition, bandwidth increases in slotted antennas vary according to the dielectric substrate material. The bandwidth increases have been 0.05 GHz, 0.426 GHz, 0.839 GHz, and 0.475 GHz for arlon, polyamide, polyimide, and silicon substrates, respectively. With these results, the study will give an insight to the researchers who will design antennas in 6G bands in terms of the effects of materials on antenna characteristics and will give inspiration for new designs.
The effect of essential oil on fiber morphology and surface properties in coaxial nanofibers
(Bursa Uludağ Üniversitesi, 2024-02-15) Avcı, Nursema Pala; Yılmaz, Nebahat Aral; Nergis, Fatma Banu
In this study, core-shell nanofibers were produced by using hydrophilic polyvinylpyrrolidone (PVP) polymer in the core and hydrophobic poly(e-caprolactone) (PCL) polymer in the shell. Essential oil added nanofiber structures were developed by adding thyme oil (TEO) and borage oil (BO) in the PVP core part by using Triton X 100 (TX-100) as the surfactant. 8% PVP-8% PCL nanofibers were produced by adding TEO, BO and a 1:1 volume/volume mixture of these two (TEO:BO) to the PVP solution. Addition of essential oil and surfactant to the solutions resulted in different conductivity and viscosity values. SEM images were analyzed and it was observed that nanofiber diameters increased when essential oil and surfactant were added to the core of the coaxial nanofibers. Pristine, TEO-added, TEO:BO added and BOadded nanofibers were calculated as 145 ± 66, 233 ± 150, 245 ± 165 and 300 ± 124 nm, respectively. Besides, water contact angle measurements showed that TX-100 and essential oil additives caused high hydrophilization of nanofiber by changing the hydrophobic nature of PCL. While the contact angle of the 8% PVP-8% PCL sample without additives were 98°, the contact angle of the oil and surfactant containing samples were measured as 0°. In conclusion, it was observed that the nanofiber morphology and surface properties changed when different essential oils and surfactant were added to the core-shell nanofibers.
Fractional order analysis of the 4-dimensional hyperchaotic pang system and its adaptive synchronization
(Bursa Uludağ Üniversitesi, 2024-01-09) Yılmaz, Gülnur; Günay, Enis
Fractional calculus is an effective method used to analyze the dynamics of nonlinear systems and provide more precise results. In this study, firstly, the 4-dimensional Pang system is introduced and its dynamic analyses demonstrating the hyperchaotic structure are given. Then, fractional-order calculations of the system are presented and the dynamics of the system for different fraction orders are investigated. At this point, according to the results obtained from Lyapunov exponents and phase-space representation, the Pang system exhibits periodic, chaotic, and hyperchaotic behaviors in different fractional orders. The results obtained at the end of this study present that the system is hyperchaotic for the fractional order of 3.52 and it is also confirmed that more accurate results are obtained than the integer-order analysis. In the next part of the study, adaptive synchronization of the fractional-order system is performed. Three different cases are examined and it is demonstrated that synchronization is achieved in all cases.
Increasing robustness of I-vectors via masking: A case study in synthetic speech detection
(Bursa Uludağ Üniversitesi, 2024-03-15) Aydın, Barış; Dişken, Gökay
Ensuring security in speaker recognition systems is crucial. In the past years, it has been demonstrated that spoofing attacks can fool these systems. In order to deal with this issue, spoof speech detection systems have been developed. While these systems have served with a good performance, their effectiveness tends to degrade under noise. Traditional speech enhancement methods are not efficient for improving performance, they even make it worse. In this research paper, performance of the noise mask obtained via a convolutional neural network structure for reducing the noise effects was investigated. The mask is used to suppress noisy regions of spectrograms in order to extract robust i-vectors. The proposed system is tested on the ASVspoof 2015 database with three different noise types and accomplished superior performance compared to the traditional systems. However, there is a loss of performance in noise types that are not encountered during training phase.
Investigation and analysis of new fiber from allium fistulosum L. (Scallion) plant’s tassel and its suitability for fiber-reinforced composites
(Bursa Uludağ Üniversitesi, 2024-03-08) Eryılmaz, Oğuz; Ovalı, Sabih
Eco-friendly materials receive more attention due to the necessity of addressing pollution and resource depletion in the face of exponential industrial expansion. Natural fibers provide a sustainable substitution, especially in green composites. This study investigated the feasibility of Allium fistulosum L. (Scallion) as a fiber resource for composite applications by using its tassel. Allium fistulosum L. is derived from a widely available plant and its waste tassels of the plant provide fiber properties and have the potential to be a reinforcing component in composites. The investigation involves characterizing Allium fistulosum L. (AfL) fibers through various analyses. The density of the AfL was determined approximately 1.35 – 1.45 g/ cm3 . The percentages of lignin, hemicellulose, and cellulose were found to be 24.31%, 29.73%, and 38.36%, respectively. FTIR and XRD analysis affirm AfL's cellulose, hemicellulose, and lignin presence. SEM images indicate a rough surface, necessitating modification for better matrix compatibility. TGA shows suitable thermal stability, majorly degrading beyond 267°C. Tensile testing demonstrates a tensile strength of 22.19 ±3.75 MPa and 0.87 ±0.16 GPa modulus, exceeding some natural fibers like aerial banyan tree roots and Cordia dichotoma. Results show promising features, indicating the viability of AfL fibers in composites with reduced environmental impact and economic benefits.
Microstrip patch antenna design with enhanced radiation efficiency for 5g 60 GHZ millimeter-wave systems
(Bursa Uludağ Üniversitesi, 2024-02-22) Irıqat, Sanaa; Yenikaya, Sibel; Uludağ Üniversitesi/Mühendislik Fakültesi/Elektrik-Elektronik Mühendisliği Bölümü.; 0000-0002-8360-1500; 0000-0002-9423-1752
In this paper, a wideband, high-gain microstrip patch antenna design for 60 GHz applications is presented. The chosen substrate material is Rogers RT 5880, with a thickness of 1.6 mm, a relative permittivity of 2.2, and a loss tangent of 0.0009. Initially, a simple rectangular patch antenna is designed. To address the challenges of low gain and low radiation efficiency, two rectangular parasitic elements are introduced. These parasitic elements interact with the main radiator, resulting in improved gain and radiation efficiency. In the final step, an extended ground plane structure is adopted to further enhance return loss, radiation efficiency, and gain. The proposed antenna achieves a high gain of 13.10 dBi and a maximum radiation efficiency of 90% with a compact size of 13.6 × 10.6 mm2 . For bandwidth calculations, given that the 60 GHz frequency band is known for its challenging propagation environment, the -15 dB criteria is chosen instead of the commonly used -10 dB criterion. According to this -15 dB criterion, the antenna exhibits wideband behavior spanning from 55 to 65 GHz, offering an impressive impedance bandwidth of 10 GHz. This design demonstrates significant potential for 60 GHz applications.
Parallel meshless radial basis function collocation method for neutron diffusion problems
(Bursa Uludağ Üniversitesi, 2024-02-27) Tanbay, Tayfun; Tayfun
The meshless global radial basis function (RBF) collocation method is widely used to model physical phenomena in science and engineering. The method produces highly accurate solutions with an exponential convergence rate. However, due to the global approximation structure of the method, dense node distributions lead to long computation times and hinder the applicability of the technique. In order to overcome this issue, this study proposes a parallel meshless global RBF collocation algorithm. The algorithm is applied to 2-D neutron diffusion problems. The multiquadric is used as the RBF. The algorithm is developed with Mathematica and eight virtual processors are used in calculations on a multicore computer with four physical cores. The method provides accurate numerical results in a stable manner. Parallel speedup increases with the number of processors up to five and seven processors for external and fission source problems, respectively. The speedup values are limited by the constrained resource sharing of the multicore computer’s memory. On the other hand, significant time savings are achieved with parallel computation. For the four-group fission source problem, when 4316 interpolation nodes are employed, the utilization of seven processors instead of sequential computation decreases the computation time of the meshless approach by 716 s.
PI controller design for time delay systems using different model order reduction methods
(Bursa Uludağ Üniversitesi, 2024-01-04) İrgan, Hilal; Tan, Nusret
This study focuses on designing PI controllers for time-delay systems using various model order reduction techniques to reduce complexity. The stability boundary locus method was used to determine PI parameters that stabilizing reduced order models. After the PI parameters have been determined using the weighted geometric center method, the calculated controller parameters have been implemented in the original system. In this way, the efficiency of the controller design is effectively demonstrated through the reduction techniques. In addition, the study investigated the effectiveness of reduction methods with increasing time delay and adding an integrator to the system. The importance of these results is that they demonstrate the use of model order reduction techniques in the design of controllers for time-delay systems and reveal the advantages of these methods.
The effect of graphite addition on the friction coefficient and wear behavior of glass fiber reinforced composites
(Bursa Uludağ Üniversitesi, 2024-03-08) Demir, Mehmet Emin
The use of fillers in fiber-reinforced epoxy matrix composites to enhance the wear performance of the composite is a widely employed method nowadays. In this study, the effect of incorporating graphite filler into a glass fiber-reinforced composite structure on the tribological properties of the composite was investigated. Composite materials produced using the hand lay-up method with three different levels of graphite filler were compared to unfilled composites in terms of wear behavior under different loads (7 N, 10 N, 15 N) and sliding distances (200 m, 400 m). The influence of load, filler content, and sliding distance on the friction coefficient and wear rate was discussed. When the results are examined, the significant effects of graphite filler on wear volume and friction coefficient are clearly observed. In the composite containing 12% graphite, the wear volume has decreased by almost 96%; this ratio has been around 93% for the composite with 4% graphite filler. As the reinforcement of graphite and force increase, the friction coefficient decreases, whereas with the increase in sliding distance, the friction coefficient declines. Microstructural analysis revealed that the filled composites exhibited less abrasion compared to the unfilled composites, and the surface porosity and craters were shallower.
Trends and future directions of risk management approaches applied in modular construction projects: Systematic review and meta-analysis
(Bursa Uludağ Üniversitesi, 2024-02-13) Khodabocus, Sabah; Seyis, Senem
In modular construction, given the different undertakings compared to conventional construction, the latter deems less risky. However, the current industry is faced with malpractices which are loopholes disabling full capacity performance. There is a noticeable lack of studies specifically analyzing the risk management approaches. This study aims to vigorously analyze all risk management approaches applied in previous projects by compiling qualitative and quantitative content for the eased risk assessment of modular projects. By performing a systematic literature review and meta-analysis, 175 documents were finalized and manually analyzed. Synthesis of the literature was carried out to generate graphs, illustrations, and tabularized content, followed by critical explanation for relevant risk management approaches identified according to risk category and project criteria. Risk management approaches for modular construction were showcased in terms of yearly trends, geographic involvement, keywords mostly encountered, and universities and institutions involvement. Classified risk management approaches were tabularized alongside a research domain targeting technical risk management approaches. Future work scopes were suggested with percentage initiations from analyzed studies. This study is a fundamental steppingstone in broadening knowledge on risk management approaches of modular construction and will aid both academicians and practitioners to get direct insights on current trends with project-oriented results showcased.
A wireless power transfer system design for charging of intra-body implant devices
(Bursa Uludağ Üniversitesi, 2024-01-09) Büyüktuna, Edanur; Dilek, Elif; Yorgancılar, Fatma Nur; Çetin, Ramazan; Ağçal, Ali
Wireless power transfer (WPT) presents numerous possibilities for recharging electronic devices in challenging environments. Charging of biomedical devices within the body is among the available opportunities. Inductively coupled WPT is a dependable and effective solution for powering these devices. Energy is transferred from the transmitter to the receiver in the inductively coupled WPT system through the use of coils and magnetic coupling. A WPT system was designed for this study, with dimensions of 4 cm by 4 cm, power output of 1 mW, and a frequency of 13.56 MHz. Series-Series (SS) topology was selected for its ease of handling and simple architecture. A square coil was selected as the receiver and transmitter coil structure due to its higher coupling factor than circular coils. ANSYS® Maxwell 3D was used to design the coils and perform magnetic analysis. In the ANSYS® HFSS program, the WPT system was placed inside the male human model and the electromagnetic exposure of the WPT on humans was examined. The magnetic scattering of the WPT system was within the safe values specified by IEEE and ICNIRP standards.

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