WoS İndeksli Yayınlar Koleksiyonu
Permanent URI for this collectionhttps://hdl.handle.net/20.500.12573/394
Browse
11 results
Search Results
Article Use of Laser-Induced Bubbles in Intraocular Pressure Measurement: A Preliminary Study(IOP Publishing Ltd, 2018-11-23) Altindis, Fatih; Ozdur, Ibrahim T.; Mutlu, Sait N.; Yilmaz, BulentThis work investigates the feasibility of a novel approach for measuring intraocular pressure (IOP) by analyzing micron-level laser-induced bubble characteristics in the intraocular fluid. We believe that this concept may be used as a non-invasive alternative for measuring a patient's IOP by analyzing the laser-induced bubble volume in the intraocular fluid in the anterior chamber of the eye. The behavior of laser-induced bubbles was examined under differing fluid pressure levels and at differing laser pulse energy levels. An intraocular medium-like environment was imitated and an imaging system was designed in order to capture laser-induced bubbles with their movements. The video recordings of the bubbles were processed using custom software, and the volume of the bubbles was estimated using three different approaches. The bubble volumes were estimated more accurately by using the rising velocity of the bubble rather than its direct radii appearances on the images. An inversely proportional relationship was observed between the laser-induced bubble volume and the fluid pressure. IOP can be measured with a non-invasive technique using laser-induced bubble volume. Deeper and detailed studies, including clinical studies, may lead to the use of lasers for measuring IOP.Conference Object Citation - Scopus: 1Three-Dimensional Imaging in Degraded Visual Field(IOP Publishing Ltd, 2016-04) Oran, A.; Ozharar, S.; Ozdur, I.Imaging at degraded visual environments is one of the biggest challenges in today's imaging technologies. Especially military and commercial rotary wing aviation is suffering from impaired visual field in sandy, dusty, marine and snowy environments. For example during landing the rotor churns up the particles and creates dense clouds of highly scattering medium, which limits the vision of the pilot and may result in an uncontrolled landing. The vision in such environments is limited because of the high ratio of scattered photons over the ballistic photons which have the image information. We propose to use optical spatial filtering (OSF) method in order to eliminate the scattered photons and only collect the ballistic photons at the receiver. OSF is widely used in microscopy, to the best of our knowledge this will be the first application of OSF for macroscopic imaging. Our experimental results show that most of the scattered photons are eliminated using the spatial filtering in a highly scattering impaired visual field. The results are compared with a standard broad area photo detector which shows the effectiveness of spatial filtering.Article Tapered Curved-Beam Hinges for Electret-Based Vibration Energy Harvesting Devices(IOP Publishing Ltd, 2024-12-01) Hah, DooyoungInterest in vibration energy harvesting have been growing recently for various applications. One of the major development goals for vibration energy harvesters has been improvement in energy conversion efficiency. To pursue that goal, one of the main approaches has been to broaden the spectra of harvesters. Employment of nonlinear springs, such as curved-beam hinges, has proven to be effective for that purpose. The main contribution of the current study is to introduce a lateral taper to the curved beam so as to further optimize the harvester performances. Via numerical analysis by using stochastic differential equations, the study shows that at 0.05g of vibration strength, tapered curved-beam hinges can result in higher electric power output than the non-tapered ones. Deformation-induced stress was taken into consideration as well, in reference to the fracture strength of the material (single-crystal silicon). At lower vibration strength (0.02g), spring nonlinearity becomes weaker, and as a result, the narrowest curved-beam hinge produces the highest output power. Overall, the current study demonstrates that tapering of the curved beam can be a useful addition in the vibration energy harvester design.Article Citation - WoS: 11Citation - Scopus: 13On the Detailed Mechanical Response Investigation of PHBV/PCL and PHBV/PLGA Electrospun Mats(IOP Publishing Ltd, 2019-03-29) Bal, Burak; Tugluca, Ibrahim Burkay; Koc, Nuray; Isoglu, Ismail AlperIn this study, electrospun mats of pristine poly(epsilon-caprolactone) (PCL), Poly(D, L-lactide-co-glycolide) (PLGA), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), as well as PHBV/PCL blends and PHBV/PLGA blends in different ratios (80:20, 75:25, 50:50, 25:75, 20:80, 10:90, 5:95%, w/w) and Centella Asiatica (CA) loaded (1, 5, 10%, w/v) PHBV/PCL and PHBV/PLGA polyester blends were prepared. Electrospun mats were characterized by scanning electron microscopy (SEM) in order to show uniform and bead and defect-free fiber structure with average diameter. The blend ratio and strain rate dependencies of mechanical behavior of these electrospun membranes were investigated under tensile loading. The tensile tests were conducted at an initial strain rates of 10(-1) s(-1), 10(-2) s(-1), 10(-3) s(-1) and 10(-4) s(-1) at room temperature and the best and worst combinations of PHBV/PLGA, PHBV/PCL blend ratios for both stress and ductility required applications were specified for each strain rate. The effects of blend ratios on the tensile strength and Young's modulus were also investigated. Moreover, the effects of Centella Asiatica on the electrospun membranes' mechanical behavior were demonstrated at different strain rates. Consequently, this study constitutes an important guideline for the selection and usage of the aforementioned electrospun membranes as a wound dressing material in terms of mechanical response at different loading scenarios.Article Citation - WoS: 12Citation - Scopus: 13Highly Luminescent ZnCdTeS Nanocrystals With Wide Spectral Tunability for Efficient Color-Conversion White-Light(IOP Publishing Ltd, 2021-09-28) Soheyli, Ehsan; Zargoush, Sirous; Yazici, Ahmet Faruk; Sahraei, Reza; Mutlugun, EvrenCdTe-based semiconductor nanocrystals (NCs) with size and composition-dependent efficient bandgap properties are historically mature nanomaterials for colloidal optoelectronic applications. In this work, we present the highly luminescent quaternary ZnCdTeS NCs with tunable emission across a wide visible spectrum from green to red spectral range. Prepared via a direct aqueous-based approach, a second capping agent of trisodium citrate (TSC) was used to enhance the photoluminescence (PL) emission efficiency, the chemical stability, and to spectrally widen the coverage of the emission spectra of ZnCdTeS NCs. Adding TCS created a remarkable blue shift from 572 nm in the absence of TSC, to 548 nm. On the other hand, upon optimization of experimental parameters, superior ZnCdTeS NCs with a narrow PL profile typically less than 50 nm, the high quantum efficiency of 76%, and tunable emission from 515-to-645 nm were synthesized in an aqueous solvent. The keynotes were the superior and reproducible luminescent properties for the core only NCs, without shell and using relatively low reaction temperatures. It was shown that in the suggested synthesis method, the high efficiency emitted color of ZnCdTeS NCs can be easily controlled from 515-to-650 nm with excellent stability against harsh conditions. The biexponential decay profiles of samples prepared at different reaction temperatures demonstrated that the average recombination lifetime is below 40 ns and increases with the growth of the ZnCdTeS NCs. Results reveal that the excitonic energy levels have the main role in the recombination process. Finally, to demonstrate the functional advantages of the prepared NCs in optoelectronics, the NCs were used to fabricate color-conversion white light-emitting diodes. The color coordinate of the device is recorded as (0.4951, 0.3647) with CRI of 91, CCT of 1954 K, and LER of 251 lm W-1 by employing only two distinct emitters for color conversion.Article Citation - WoS: 15Citation - Scopus: 18FRET Enabled Light Harvesting within Quantum Dot Loaded Nanofibers(IOP Publishing Ltd, 2018-01-24) Altintas, Yemliha; Kiremitler, Nuri Burak; Genc, Sinan; Onses, M. Serdar; Mutlugun, EvrenThe spatial control of the nano-emitters in novel light harvesting platforms offers great potential for the manipulation of the excitonic interaction amongst the donor-acceptor pairs of energy transferring agents. In this work, we report colloidal quantum dot loaded electrospun nanofibers as a light harvesting platform to study the excitonic interaction among them. The donor emission lifetime modified from 12.46 ns to 7.45 ns with the change in the ratio of green and red quantum dots in the nanofiber, as a result of confining acceptor quantum dots in close proximity. The spectrally narrow emitter luminescent nanofiber platforms have further been investigated for their potential of white light generation. The hybrid platform of blue LED integrated electrospun nanofibers has been shown to demonstrate a correlated color temperature of 3632.5 K, luminous efficacy of optical radiation value of 307.7 lm/W-opt along with color rendering index value of 60.Article Citation - WoS: 5Citation - Scopus: 5Experimental Investigation on Chloroprene and Acrylonitrile Butadiene Rubber Types Reinforced With Nano-Materials(IOP Publishing Ltd, 2019-05-31) Dogan, O.; Esat, V.; Bal, B.In this research, the effects of three different nano-materials (Nano-Carbon Black, Nano-ZnO, and Multi-Walled Carbon Nanotubes (MWNTs)) on two different rubber types (Chloroprene Rubber (CR), and Acrylonitrile Butadiene Rubber (NBR)) were experimentally investigated. In order to achieve this purpose, mechanical tests and detailed aging tests (in air, oil and fuel) were conducted conforming to international standards. Three different nano-materials were added to rubber with different combinations. A good dispersion of MWNTs within the polymer matrix was monitored by using field-emission Scanning Electron Microscopy (FE-SEM). It was observed that nano-materials both have positive and detrimental effects on hardness, tensile strength, ductility and aging tests performance. It was observed that nano-material reinforced rubber composites are thermally more stable than current products. Most significantly, it was seen that compression set value, which is a critical property for rubber grade, decreased with the addition of MWNTs. Therefore, rubber products with higher sealing capacity and longer service life can be obtained by adding MWNTs.Conference Object Citation - WoS: 1Estimation of Cohesion for Intact Rock Materials Using Regression and Soft Computing Analyses(IOP Publishing Ltd, 2024-01-01) Koken, E.; Strzalkowski, P.; Kazmierczak, U.; Strzałkowski, P.Shear strength parameters such as cohesion (c) and internal friction angle (phi) are among the most critical rock properties used in the geotechnical design of most engineering projects. However, the determination of these properties is laboring and requires special equipment. Therefore, this study introduces several predictive models based on regression and artificial intelligence methods to estimate the c of different rock types. For this purpose, a comprehensive literature survey is carried out to collect quantitative data on the shear strength properties of different rock types. Then, regression and soft computing analyses are performed to establish several predictive models based on the collected data. As a result of these analyses, five different predictive models (M1-M5) were established. Based on the performance of the established predictive models, the artificial neural network-based predictive model (model 5, M5) was the most suitable choice for evaluating the c for different rock types. In addition, mathematical expressions behind the M5 model are also presented in this study to allow users to implement it more efficiently. In this regard, the present study can be declared a case study showing the applicability of regression and soft computing analyses to evaluate the c of different rock types. However, the number of datasets used in this study should be increased to get more comprehensive predictive models in future studies.Article Citation - WoS: 10Citation - Scopus: 11Effect of the Shell Material and Confinement Type on the Conversion Efficiency of Core/Shell Quantum Dot Nanocrystal Solar Cells(IOP Publishing Ltd, 2018-04-20) Sahin, MehmetIn this study, the effects of the shell material and confinement type on the conversion efficiency of core/shell quantum dot nanocrystal (QDNC) solar cells have been investigated in detail. For this purpose, the conventional, i.e. original, detailed balance model, developed by Shockley and Queisser to calculate an upper limit for the conversion efficiency of silicon p-n junction solar cells, is modified in a simple and effective way to calculate the conversion efficiency of core/shell QDNC solar cells. Since the existing model relies on the gap energy (E-g) of the solar cell, it does not make an estimation about the effect of QDNC materials on the efficiency of the solar cells, and gives the same efficiency values for several QDNC solar cells with the same E-g. The proposed modification, however, estimates a conversion efficiency in relation to the material properties and also the confinement type of the QDNCs. The results of the modified model show that, in contrast to the original one, the conversion efficiencies of different QDNC solar cells, even if they have the same E-g, become different depending upon the confinement type and shell material of the core/shell QDNCs, and this is crucial in the design and fabrication of the new generation solar cells to predict the confinement type and also appropriate QDNC materials for better efficiency.Article Citation - WoS: 2Citation - Scopus: 2Cation Exchange Mediated Synthesis of Bright Au@ZnTe Core-Shell Nanocrystals(IOP Publishing Ltd, 2020-10-16) Sadeghi, Sadra; Melikov, Rustamzhon; Sahin, Mehmet; Nizamoglu, SedatThe synthesis of heterostructured core-shell nanocrystals has attracted significant attention due to their wide range of applications in energy, medicine and environment. To further extend the possible nanostructures, non-epitaxial growth is introduced to form heterostructures with large lattice mismatches, which cannot be achieved by classical epitaxial growth techniques. Here, we report the synthetic procedure of Au@ZnTe core-shell nanostructures by cation exchange reaction for the first time. For that, bimetallic Au@Ag heterostructures were synthesized by using PDDA as stabilizer and shape-controller. Then, by addition of Te and Zn precursors in a step-wise reaction, the zinc and silver cation exchange was performed and Au@ZnTe nanocrystals were obtained. Structural and optical characterization confirmed the formation of the Au@ZnTe nanocrystals. The optimization of the synthesis led to the bright nanocrystals with a photoluminescence quantum yield up to 27%. The non-toxic, versatile synthetic route, and bright emission of the synthesized Au@ZnTe nanocrystals offer significant potential for future bio-imaging and optoelectronic applications.