Browsing by Author "Pekcan, Onder"

Now showing 1 - 13 of 13

Citation Count: 2
3D self-assemble formation of molybdenum disulfide (MoS2)-doped polyacrylamide (PAAm) composite hydrogels
(Tubitak Scientific & Technological Research Council Turkey, 2022) Durmaz, Sumeyye; Yildiz, Ekrem; Uysal, Bengu Ozugur; Pekcan, Onder
Polyacrylamide (PAAm), a renowned member of the hydrogel class, has many uses throughout a wide range of industrial processes, including water absorbed diapers, contact lenses, wastewater treatment, biomedical applications such as drug delivery vehicles and tissue engineering because of its physical stability, durability, flexibility easier shaping, and so on. PAAm also provides new functionalities after the incorporation of inorganic structures such as molybdenum disulfide (MoS2). During the copolymerization process, the transmittance of all samples reduced significantly after a particular time, referred to as the gel point. Microgels form a tree above the gel point as projected by Flory-Stockmayer classical theory. Because of microgels positioned at the junction points of the Cayley tree, the addition of MoS2 results in strong intramolecular crosslinking and looser composites. Moreover, fractal geometry provides a quantitative measure of randomness and thus permits characterization of random systems such as polymers. Fractal dimension of these polymer composites is calculated from power-law-dependent scattered intensity. It was also confirmed that a hydrogel rapidly formed within a few seconds, indicating a 3D network formation inside the gel. These materials may have a great potential for application in wearable and implantable electronics due to this highly desired 3D self-assemble feature.
Citation Count: 0
CHAOTIC - DETERMINISTIC OR RANDOM NATURE OF EARTHQUAKES: A PHASE SPACE ANALYSIS
(Symmetrion, 2023) Arsan, Taner; Arsan, Taner
Using the phase space approach, time series analysis of high EV1 and low EV2 intense two different earthquakes that occurred at the nearly same precise spot, at different times, and were measured with the same sensor of a broadband station were studied. Time series data of strong, large (EV1) and weak, small (EV2) two earthquake events were analyzed by dividing them into three different regions. Fractal dimensions of the EV1 and EV2 were produced using the box-counting algorithm for east-west (BHE), north-south (BHN), and vertical (BHZ) components. The small, weak earthquake, EV2, created a larger fractal dimension in phase space by implying its random nature in all regions. However, EV1 is a strong, large earthquake that presents deterministic oscillatory behavior at a long-time region. Oscillatory behavior can be named surface wave. EV2 exhibits weak, high-frequency ground oscillations similar to fibrillation before and after the earthquake in the long-term areas.
Composite Hydrogel of Polyacrylamide/Starch as a Novel Amoxicillin Delivery System
(Mdpi, 2024) Poyraz, Yagmur; Baltaci, Nisa; Hassan, Gana; Alayoubi, Oubadah; Uysal, Bengu Ozugur; Pekcan, Onder
This study investigates the development and characterization of a novel composite hydrogel composed of polyacrylamide (PAAm), starch, and gelatin for use as an amoxicillin delivery system. The optical properties, swelling behavior, and drug release profile of the composite hydrogel's were studied to evaluate its efficacy and potential applications. UV-visible spectroscopy was employed to determine the optical properties, revealing significant transparency in the visible range, which is essential for biomedical applications. The incorporation of starch and gelatin into the polyacrylamide matrix significantly enhanced the hydrogel's swelling capacity and biocompatibility. Studies on drug delivery demonstrated a sustained release profile of amoxicillin in simulated gastrointestinal fluids, which is essential for maintaining therapeutic levels for a prolonged amount of time. The results indicate that the composite hydrogel of PAAm/starch/gelatin has good swelling behavior, appealing optical characteristics, and a promising controlled drug release mechanism. These results point to this hydrogel's considerable potential as a drug delivery method, providing a viable path toward enhancing the medicinal effectiveness of amoxicillin and maybe other medications.
Citation Count: 0
Decoding compositional complexity: Identifying composers using a model fusion-based approach with nonlinear signal processing and chaotic dynamics
(Pergamon-elsevier Science Ltd, 2024) Baykaş, Tunçer; Hekimoğlu, Mustafa; Hekimoglu, Mustafa; Pekcan, Onder; Tuncay, Gonul Pacaci
Music, a universal medium that effortlessly transcends the confines of language and culture, serves as a vessel for the distinctive expression of a composer's ingenuity, particularly palpable through the elaborate symphony of melodies, harmonies, and rhythms. This phenomenon is acutely observable in the realm of Turkish Classical Music, where the identification of individual composers poses a formidable challenge due to a confluence of diverse stylistic expressions and sophisticated techniques. Shaped by centuries of cultural interchanges, this genre is celebrated for its convoluted rhythmic frameworks and deep melodic modes, often exhibiting fractal characteristics that compound the complexity of composer classification based on mere audio signals. In response to these complexities, this study introduces an advanced analytical paradigm that amalgamates Multi-resolution analysis, spectral entropy assessments, and a spectrum of multidimensional chaotic and statistical descriptors. By invoking chaos theory, the research delineates distinct patterns and features inherent to musical compositions, subsequently deploying these discoveries for composer categorization. Employing a model fusion-based strategy, the approach utilizes esteemed base estimators for section-level probabilistic determinations, subsequently amalgamated at the song level through a Long Short-Term Memory (LSTM) neural network model to classify a corpus of 380 compositions from 15 distinct composers. The results of this study not only highlight the efficacy of chaos-based approaches in Musical Information Retrieval but also provide a nuanced understanding of the unique characteristics of Turkish Classical Music, thus advancing the boundaries of how musicological data is scrutinized and conceptualized within scholarly discourse.
Citation Count: 0
The Effect of Pyranine and MoS₂ Content on the Optical Properties of Polyacrylamide-MoS₂ Composite Gels
(Taylor & Francis inc, 2024) Uysal, Bengu Ozugur; Osma, Busra; Evingur, Gulsen Akin; Pekcan, Onder
The most favorable members of the class of two-dimensional (2D) materials, molybdenum sulfide (MoS2), graphene, and tungsten disulfide (WS2) have become a thriving research frontier for many applications, ranging from catalysis to optoelectronic devices, due to their superior electronic behavior and mechanical properties. Making a new, smart, hydrogel when incorporating MoS2 into basic hydrogels can change their optical, electronic, and mechanical properties. In this work, MoS2-doped polyacrylamide (PAAm) gels were prepared via the free radical crosslinking copolymerization technique at room temperature without pyranine which is often used for crosslinking PAAm. The optical properties of PAAm-MoS2 composite gels were investigated, and they were analyzed using ultraviolet (UV) and fluorescence spectroscopy. The absorbance was measured before and after diffusion of MoS2-doped PAAm, and after the release of pyranine in and out of the composite gel, respectively. The shift of the absorption edge toward shorter wavelengths was seen when the quantity of MoS2 in the PAAm composite gels was decreased. The constituents included in the polymer composites exhibited notable photon energy absorption within the visible and ultraviolet spectra. This absorption phenomenon induced electron transitions to states of elevated energy. Parameters, such as refractive index and extinction coefficient, were analyzed with respect to the content of MoS2. When the MoS2 amount was increased in the gels, the percentage of reflectance increased. The extinction coefficient increased at longer wavelength and it decreased in the UV range, the shorter wavelength region. The results suggested that MoS2-doped PAAm composite gels show promising optoelectronic properties for developing optoelectronic devices.
Citation Count: 29
Efficient Photocatalytic Degradation of Methylene Blue Dye from Aqueous Solution with Cerium Oxide Nanoparticles and Graphene Oxide-Doped Polyacrylamide
(Amer Chemical Soc, 2023) Kalaycioglu, Zeynep; Uysal, Bengu Ozugur; Pekcan, Onder; Erim, F. Bedia
A cerium oxide nanoparticles (CeO2-NPs)/graphene oxide (GO)/polyacrylamide (PAM) ternary composite was synthesized through free-radical polymerization of acrylamide in the presence of CeO2 nanoparticles and GO in an aqueous system. The synthesized composite material was characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and energy-dispersive X-ray (EDX) spectroscopy techniques and applied for the photocatalytic degradation of methylene blue (MB) dye from an aqueous solution. Tauc's model for direct transition was used to model for the optical band gap. The key operating parameters such as the amounts of CeO2-NPs and GO, pH, initial MB concentration, type of light irradiation, and contact time have been optimized to achieve the highest MB degradation percentage. The photocatalysis process was pH-dependent, and the optimum pH value was found to be 12.0. Under UV-A light, 90% dye degradation occurred in 90 min. The degradation of MB was also specified in terms of total organic carbon (TOC) and chemical oxygen demand (COD). Free-radical capture experiments were also performed to determine the role of radical species during the photocatalytic oxidation process. The photocatalytic process showed that the equilibrium data is in good agreement with the Langmuir-Hinshelwood kinetic model. A rate constant of 0.0259 min-1 was obtained. The hydrogel was also tested to assess its reusability, which is an important key factor in practical wastewater treatment. The photocatalytic activity only decreased to 75% after nine uses.
Citation Count: 0
Epidemic Models for Chemical Gel Phase Transformation: Effect of Optical Measurements with Different Wavelengths
(Taylor & Francis Inc, 2023) Bilge, Ayşe Hümeyra; Bilge, Ayse Humeyra; Pekcan, Onder; Incegul, Metehan
In our previous work we characterized the sol-gel transition of chemical and physical gels in terms of epidemic models which describe the spread of a disease in a society. We have shown that gelation in chemical gels can be represented by the Susceptible-Infected-Recovered (SIR) model, while the gelation mechanism of physical gels can be represented by the Susceptible-Infected-Susceptible (SIS) model. These studies were based on optical measurements at a single wavelength. In the present work we studied the gelation mechanism for chemical gels obtained from experiments that have been carried out with acrylamide (AAm) and N,N0-methylenebis (acrylamide) (Bis) as base materials for chemical gel formation in water and with cross-linker. The transmitted light intensity was measured for various wavelengths from 440 nm to 690 nm during the gelation process. The data are modeled by the epidemic SIR process. The results indicate that the gelation processes obtained from the same Bis and water contents observed at different wavelengths obey different SIR models. This observation is explained by the scattering of light of different wavelengths depending on the sizes of the micro-gels formed.
Citation Count: 0
Kinetics models for polyacrylamide-graphene oxide composites as antifoulant
(Wiley, 2023) Osma, Busra; Pekcan, Onder; Evinguer, Gulsen Akin
Antifouling paints are used to protect the surface against these organisms such as algae, sea squirts, and barnacles. According to previous research, fish and seaweeds do not adhere to submerged surfaces using wet and soft hydrogels. The aim of this study is to investigate the temperature effect on the performance of antifouling composites to develop new useful antifouling composites for shipping sector. In this swelling experiment, the behavior of hydrogels produced from polyacrylamide (PAAm) and graphene oxide (GO) was investigated at different temperatures. Free-radical cross-linking copolymerization formed composite, using acrylamide, ammonium persulfate, N, N & PRIME;-methylenebisacrylamide (BIS, Merck), and graphene oxide with various contents. The steady-state fluorescence technique was used for studying the swelling of PAAm-GO composites at various temperatures in pure water. When pyranine fluorescence intensity, I was measured, it decreased until swelling equilibrium was achieved. After the swelling experiment was started, the fluorescence emission (I-em) and scattering light intensities, I-sc from different GO content hydrogels were observed by real-time monitoring at various temperatures. Li-Tanaka and Fickian models were used to determine the diffusion coefficients for the swelling experiments in distilled and Marmara Sea Water for 8 and 50 mu l of GO content hydrogels, respectively. According to literature, PAAm is utilized as a surface coating material to reduce biofouling, for this reason, this research will show a way to be able to use PAAm inside antifouling paints material for the marine industry.
Citation Count: 1
Optical and mechanical properties of PNIPAm-MWCNTs and PNIPAm-GO composites
(Wiley, 2023) Unver, Batuhan; Pekcan, Onder; Evingur, Gulsen Akin
The aim of this study is to investigate drying, swelling, elastic properties, and to produce optical band gap energies on the performance of Poly (N-Isopropyl acrylamide) - Multi walled carbon nanotubes (PNIPAm - MWCNTs) and Poly (N-Isopropyl acrylamide)- Graphene Oxide (PNIPAm-GO) composites, respectively. The composites were prepared by free radical crosslinking copolymerization. Drying and swelling of PNIPAm-MWCNTs and PNIPAm- GO composites were performed by using steady state fluorescence technique. Firstly, the desorption coefficients of the composites were modeled by using Fick's Law. Cooperative diffusion coefficients were calculated by employing Li-Tanaka Model. When composite doped with 10 wt% of MWCNTs has a higher desorption coefficient than composite doped with the same amount of GO, 40wt% of GO content in the PNIPAm has a higher diffusion coefficient than the composite that has 40wt% of MWCNTs content in the swelling process. Secondly, the composite that has 40wt% of MWCNTs content has a higher modulus before swelling than the composite that has the same amount of GO contents. Lastly, optical band gap energies were calculated by using Tauc's approach, and Urbach's relation by using the data performed UV Spectroscopy. We found that PNIPAm -GO has a much narrower band gap value.
Citation Count: 3
Optical, Mechanical, and Electrical Properties of Polymer Composites Doped by Multiwalled Carbon Nanotubes
(Intechopen, 2016) Evingur, Gulsen Akin; Pekcan, Onder
Three-dimensional networks can be hydrophilic and/or hygroscopic. Optical, mechanical, and electrical properties of these materials encompass many fields of technology. Composites of carbon nanotubes (CNTs) in polymeric materials have attracted considerable attention in the research and industrial communities due to their unique optical, mechanical, and electrical properties. CNT polymer nanocomposites possess high stiffness, high strength, and good electrical conductivity at relatively low concentrations of CNT filler. Here, in this chapter, we survey the optical, mechanical, and electrical mechanisms for various polymeric systems. Composite gels and films were prepared with various molar percentages of multiwalled carbon nanotubes (MWCNTs). The optical, mechanical, and electrical behaviors of various composite gels doped by MWCNT are also discussed in the each sections of the chapter. The optical behaviors of the composites were performed by the UV-Vis spectroscopy and fluorescence spectroscopy in the first part of the chapter. On the other hand, compressive testing technique and rheological measurements were employed to determine the variations of mechanical properties of the composites in the second part of the chapter. Lastly, we review the electrical properties of the composites improved significantly by addition of MWCNTs researches.
Citation Count: 3
Polyacrylamide mediated polyvinyl pyrrolidone composites incorporated with aligned molybdenum disulfide
(Wiley, 2022) Uysal, Bengu Ozugur; Evingur, Gulsen Akin; Pekcan, Onder
In this study, we aimed to design a mechanically durable material consisting of Molybdenum disulfide (MoS2) as 2D material and polyvinyl pyrrolidone (PVP) enhanced Polyacrylamide (PAAm) composites. Composites containing different amounts of MoS2 were synthesized via a free-radical crosslinking copolymerization method. They were characterized using UV-visible spectroscopy, fluorescence, and mechanical techniques to illuminate band gap energy, absorption, slow release kinetics, and modulus of the composites. Furthermore, the effect of swelling on the elasticity of the composites was investigated. It was observed that the elasticity exhibited similar band gap energies with respect to the MoS2 content. The results demonstrated that the MoS2 content strongly influences the optical and mechanical properties of the composites and consequently physical parameters of the composites have been correlated with the various amounts of MoS2.
Citation Count: 0
A Quartz Crystal Microbalance (QCM) Study on the Formation of Aqueous ?-Carrageenan-Chitosan Composite Bilayers with NaCl and Graphene Oxide
(Taylor & Francis Inc, 2023) Kara, Selim; Arda, Ertan; Dolastir, Fahrettin; Pekcan, Onder; Evingur, Gulsen Akin
Biomaterials and thin biofilms play a fundamental role in the medical, food and pharmaceutical industries. The Quartz crystal microbalance (QCM) measurement technique is one of the attractive techniques which have been used for monitoring the thin-film formation process. In the current work described here, kappa-carrageenan and chitosan solutions were used for the layer-by-layer (LBL) deposition of polyelectrolyte multilayers (PEMs) on the gold surface of a 5 MHz AT-cut (thickness-shear mode) quartz crystal in a flow module. A sensitive QCM system was designed to detect 0.1 Hz differences in the resonance frequency (Delta f) and 10(-7) changes in the energy dissipation (Delta D) values, which are the measures of the deposited mass and the film rigidity, respectively. Negatively charged carrageenan and positively charged chitosan biomolecules in the solutions were used to build up sequential and very thin bilayers on the modified gold surface. The effects of NaCl and graphene oxide (GO) addition on the mass of the deposited films were also investigated. Intermolecular interactions between the biopolymer chains, Na+ cations and GO sheets were explained by interactions between molecules, such as electrostatic forces and hydrogen bondings.
Citation Count: 0
Residual LSTM neural network for time dependent consecutive pitch string recognition from spectrograms: a study on Turkish classical music makams
(Springer, 2023) Baykaş, Tunçer; Hekimoğlu, Mustafa; Baykas, Tuncer; Hekimoglu, Mustafa; Pekcan, Onder
Turkish classical music, characterized by 'makam', specific melodic configurations delineated by sequential pitches and intervals, is rich in cultural significance and poses a considerable challenge in identifying a musical piece's particular makam. This identification complexity remains an issue even for experienced musical experts, emphasizing the need for automated and accurate classification techniques. In response, we introduce a residual LSTM neural network model that classifies makams by leveraging the distinct sequential pitch patterns discerned within various audio segments over spectrogram-based inputs. This model's design uniquely merges the spatial capabilities of two-dimensional convolutional layers with the temporal understanding of one-dimensional convolutional and LSTM mechanisms embedded within a residual framework. Such an integrated approach allows for detailed temporal analysis of shifting frequencies, as revealed in logarithmically scaled spectrograms, and is adept at recognizing consecutive pitch patterns within segments. Employing stratified cross-validation on a comprehensive dataset encompassing 1154 pieces spanning 15 unique makams, we found that our model demonstrated an accuracy of 95.60% for a subset of 9 makams and 89.09% for all 15 makams. Our approach demonstrated consistent precision even when distinguishing makam pairs known for their closely related pitch sequences. To further validate our model's prowess, we conducted benchmark tests against established methodologies found in current literature, providing a comparative assessment of our proposed workflow's abilities.