Yıldız Technical University
Recent publications
This study examined the impact of psychological capital—comprising hope, optimism, resilience, and self-efficacy—on comprehensive mental health, defined by the dual criteria of the absence of psychopathological symptoms and the presence of positive functioning. The participants of the study included 429 (65.5% female) Turkish adolescents, ranging in age from 13 to 18 years (M = 16.17 ± 0.83), and completed self-report measures of psychological capital, mental health, and well-being. Hierarchical regression analysis revealed that hope and optimism showed significant effects on internalizing problems, externalizing problems, perceived stress, emotional well-being, social well-being, and psychological well-being, even after accounting for the influence of age and gender. Additionally, resilience and self-efficacy demonstrated significant effects on psychological well-being. These results suggest the important role of psychological capital in enhancing psychological functioning and provide further evidence of its impact on the mental health and well-being of adolescents.
In the present study, dispersive solid phase extraction – hydride generation integrated with micro–sampling gas–liquid separator – flame atomic absorption spectrometry was proposed to determine lead in lake water samples taken in the Horseshoe Island, Antarctica. In scope of this study, microwave assisted NiFe2O4 nanoparticles were synthesized, and the characterization of nanoparticles were carried out by FT-IR, XRD and SEM. All influential parameters of dispersive solid phase extraction and hydride generation were optimized to enhance signal intensity belonging to the analyte. System analytical performance studies were performed, and limit of detection and limit of quantitation were calculated as 2.16 µg kg–1 and 7.19 µg kg–1, respectively. Recovery studies were conducted to the spiked lake water samples and two different calibration strategies were applied. Percent recovery results were calculated between 102.0 and 169.5% by external calibration strategy while matrix matching calibration strategy provided recovery results in the range of 78.8–142.9%.
In this study, the effects of adding Cu(NO 3 ) 2 and AgNO 3 metal salts to the polymerization medium on the electrochemical and spectroelectrochemical properties of poly(o-phenylenediamine) (PoPD) were investigated. It was observed that the presence of Cu(NO 3 ) 2 or AgNO 3 during polymerization increased the rate of current peak growth, indicating an acceleration of the polymerization process in the presence of metal ions. The cyclic voltammetry responses of the metal/polymer composites differed significantly from those of the pure polymer, confirming the formation of metal/polymer composites. FTIR and UV–vis absorption spectra were analyzed to explore the chemical structure of PoPD, PoPD/Cu, and PoPD/Ag polymer films. SEM and AFM analyses revealed distinct morphological differences between the polymer synthesized in the presence of metal salts and the pure polymer. Spectroelectrochemical analyses demonstrated that the polymer films exhibited reversible color changes from light copper to green, with distinct optical intensities in the UV–vis spectra. The absorbance and current values changed reversibly with the applied potential, with response times of approximately 10 s. Colorimetric analysis based on the CIE system showed unique variations in brightness (L), magnitude (a), and intensity (b) for PoPD, PoPD/Ag, and PoPD/Cu, confirming distinct colorimetric shifts during redox transitions. This study highlights the impact of Cu and Ag salts on the spectroelectrochemical and electrochromic performance of PoPD, revealing potential applications for PoPD composites in advanced electrochromic devices.
Lung and colon cancer are among the most commonly diagnosed and fatal cancer types in the world. Due to their metastatic properties, they complicate the treatment process and pose a great threat to human health. These aggressive types of cancer are resistant to chemotherapy drugs. Therefore, it is extremely important to investigate the therapeutic effects of natural compounds. In our previous study, effective doses of Royal Jelly (RJ) (100 mg/mL) and Aloe vera (AVE) (20 µg/mL) were determined and tested separately and in combination on lung and colorectal cancer cells. Glycolytic capacities were determined using the Seahorse XFe24 Analyzer, total transcriptome profiles were sequenced using NovaSeq 6000, and BAX and BCL-2 gene levels were determined using RT-qPCR. It was seen that RJ and RJ + AVE affected glycolytic capacity and more genes in lung cancer cells. In HT29, AVE alone was seen to reduce glycolytic capacity and RJ + AVE combination was seen to reduce the expression level of genes related to cell proliferation and cycle. After RJ + AVE treatments, the apoptotic process which is triggered via MAPK pathway was found in lung cancer. Moreover, BAX levels increased and BCL-2 levels decreased both lung and colorectal cancer cells. It was observed that the combination of RJ and AVE affected the glycolysis process, cell cycle, proliferation and apoptosis on lung and colorectal cancer. In particular, the combination of RJ + AVE was found to be more effective on lung cancer.
In this work, we study the relative compactness of subsets of separable subspaces Xs(Ω)X_{s} \left( \Omega \right) of so-called additive Banach function spaces X(Ω)X \left( \Omega \right) , which include the rearrangement-invariant spaces defined on the bounded domain ΩRn\Omega \subset R^{n}. We choose Xs(Ω)X_{s} \left( \Omega \right) such that the infinitely differentiable functions are dense in it. Moreover, we define the Banach–Sobolev spaces WXsm(Ω)W_{X_{s} }^{m} \left( \Omega \right) generated by the above subspaces and we study the compactness of embedding between such spaces. The obtained results are used to establish the equivalent norms on these spaces. These results allow us to prove the Poincaré and Friedrichs-type inequalities for such Sobolev spaces.
Floods have emerged as a critical global issue due to climate change, leading to increased research interest across various fields. However, the complex relationship between floods and geological factors remains insufficiently explored in the literature. This bibliometric analysis addresses this gap by examining the intellectual structure of research on floods and geology through a systematic review of 71 articles published between 1989 and 2024. The study reveals that environmental science dominates the field (44%), followed by earth and planetary sciences (16%), engineering (12%), and computer sciences (7%). Analysis of research terms demonstrates the field's breadth, with hydrology-related keywords comprising 58.4% of total terms, while flood-related and geology-related terms represent 21.9% and 19.7%, respectively. This study was conducted using data from the Scopus database, and co-word, co-citation, and co-author network analysis were performed through VOSviewer software. Key topics, influential publications, citation patterns, and international collaborations were identified and visualized using VOSviewer. The United States leads with 22 publications and 771 citations, followed by China with 15 publications and 117 citations. The analysis identified seven distinct international collaboration clusters, highlighting the global nature of flood research while also revealing geographical disparities in coverage. Notably, previous research demonstrates that integrating geological layers into hydrological models yields results closely matching real flood measurements, even in basins lacking measurement stations. This finding emphasizes the significance of understanding lithological characteristics for enhanced flood risk assessment. The analysis highlights an increasing application of advanced technologies, such as remote sensing, GIS, and machine learning, particularly in post-2020 studies, marking a shift toward data-driven approaches.
Objectives This study aims to present a systematic approach for designing, fabricating and characterizing ultrasonic transducers for thermoplastic sheet welding capable of operating in longitudinal–torsional (L&T) hybrid vibration modes at 20 kHz, driven by an axially poled piezoceramic stack. Methods Multiple horn models featuring circumferential deep helical grooves were designed to generate longitudinal and torsional vibratory displacements. Modal analyses were conducted to determine the appropriate dimensions for the desired mode shape and resonance frequency. The selected horn geometries were integrated with transducer bodies in a CAD environment to build 3D models of ultrasonic transducers. Modal and harmonic analyses were performed to evaluate their mode shapes, resonance frequencies, and displacement amplitudes under various excitation conditions. Prototypes of the optimized designs were fabricated using predetermined materials and geometries and characterized experimentally for resonance frequencies and tip displacements. The experimental results were compared with numerical analyses to validate the approach. Results The developed transducers demonstrated successful operation in L&T hybrid vibration modes at the targeted frequency, with displacement amplitudes and resonance frequencies aligning well with the numerical predictions. Combining exponential area reduction and helical grooves in the horn appears to be a highly effective method for achieving longitudinal-torsional vibration from a longitudinally vibrating transducer. Finite element analysis proved to be a valuable design tool, facilitating accurate dimensional optimization of the horns to achieve the desired L & T hybrid vibrational mode shapes. The apparent longitudinal and torsional (spring) stiffness of the horn significantly influences the longitudinal displacement amplitude and angular displacement at the horn tip. The resonance frequency of the transducers shifted to higher frequencies with increasing excitation voltage. Conclusion This research provides a comprehensive and validated framework for designing ultrasonic transducers capable of operating in hybrid vibration modes. The methodology reliably achieved the desired vibratory performance, with prototype results aligning closely with design objectives.
With the increase in the population of cities, the need for new constructions increases. In meeting this need, the recycling of buildings that are close to the end of their service life is a priority. When the quality of old buildings is examined, it is seen that the majority of them have low strength quality (< 20 MPa). Therefore, the use of demolition wastes with low concrete strength quality as recycled aggregate has a great potential to protect natural resources. In addition, the use of industrial wastes together with low-strength quality demolition wastes is an issue that needs to be investigated to produce more sustainable concrete. In this experimental study, cement was substituted with silica fume and fly ash mineral admixtures at 5% and 10% in concrete production. For coarse aggregates, recycled aggregates obtained from the demolition wastes of two buildings identified as risky within the scope of the Buyukcekmece Municipality Urban Transformation Project were used instead of those obtained from natural sources. The coarse aggregates obtained from these two separate buildings were divided into low (5 MPa) and intermediate (15 MPa) classes according to the strength of the source concrete and replaced with natural aggregates at 0%, 50%, and 100% to produce concrete mixes with no mineral additive, 5%, 10% mineral admixture. In order to investigate the reusability of recycled low and intermediate-strength aggregates obtained from construction demolition wastes in concrete production, mechanical tests such as compressive and splitting tensile strengths of concrete were determined on the 28th day. According to the test results, the fact that the aggregates obtained from low and intermediate strength quality are approximately the same value in terms of water absorption capacity (~ 7.5%) directly affected the concrete compressive strength and provided concrete production in the same strength class. According to the concrete compressive strength results of the series without mineral admixtures, the strength decreases as the RCA ratio increases, regardless of the parent concrete quality. Both strength quality classes without mineral admixtures successfully met the C30/37 concrete class at a 50% replacement ratio and the C20/25 concrete class at a 100% replacement ratio. This paper emphasizes that aggregates obtained from parent concrete with 5 MPa and 15 MPa strength can be considered in the same low-strength quality class and have similar properties in terms of use.
Traditional taxis have an important place in urban mobility because taxis provide flexible, comfortable and door-to-door service to passengers. However, for the continuity of traditional taxi services, profitability analyzes were needed despite the sharing economy. For this reason, the focus of this study is traditional taxis. This study aims to analyze the profitability of traditional taxi services in the urban arteries of Istanbul. For this purpose, a survey was conducted with 35 taxis and 70 taxi drivers. Then a model was then developed consisting of the independent variables number of trips (TRP), total trip distance (DST) and efficiency (EFF) that affect the profitability of taxi services. Additionally, contour plots were used to more accurately evaluate the effect of independent variables. As a result, it was concluded that the most important variable affecting the profitability of traditional taxi services is the efficiency (EFF) independent variable.
This study focuses on the synthesis of fluorohydroxyapatite (FHA), and the realization of scaffolds by 3D printing using polylactic acid (PLA) as polymer and graphene oxide (GO). The synthesis of FHA was carried out by the usual sol–gel method. The realization of the 3D scaffold was achieved with the 3D printing method. Four scaffolds were printed with PLA: the first was made with FHA and PLA (FHA/PLA), the second was made with GO in addition to FHA and PLA (FHA/PLA/GO), and the third and fourth ones were the FHA/PLA and FHA/PLA/GO scaffolds coated with electrosprayed hydrogel solution of doxorubicin (DOX) and polyvinyl alcohol (PVA): FHA/PLA/DOX/PVA and FHA/PLA/GO/DOX/PVA. The FHA and GO powders were characterized using Fourier transform infrared analysis and X‐ray diffraction analysis. A dissolution study was carried out with different contents of PVA (2.5%, 3% and 4%) to identify the scaffold with the best drug release profile. The 3% w/w PVA hydrogel solution was the best, so the drug release kinetics and drug release mechanism were studied using the most famous mathematical models: zero‐order model, Higuchi's model and Korsmeyer–Peppas model (power law model). The porosity of the 3D printed scaffolds was assessed by SEM and, finally, the cellular response of each scaffold on the viability of CDD human fibroblast cells was evaluated using the 3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide (MTT) assay. The sol–gel synthesis produces FHA, used in the realization of the scaffolds. The scaffolds have mixed porosity (macropores and micropores) promoting cell adhesion and proliferation, as shown by the results of the MTT assay. The addition of GO decreases the cell viability but keeps the scaffolds still biocompatible, and adding both DOX and GO to the FHA/PLA scaffolds has a negative impact on cell viability because DOX and GO remain toxic at the given percentages. © 2025 Society of Chemical Industry.
Family relationships and family life are important protective factors for psychological health. Establishing healthy communication between members of a family is important for the happiness of individuals. There are several cross-sectional findings regarding family communication in the literature. A longitudinal design was used to examine the mediating effect of cognitive flexibility in the relationship between family communication and happiness, taking into consideration the limitations of the cross-sectional design. In this study, data from the Turkish adult sample (N = 277) was collected in two waves at four-month intervals. The ages of the sample group [195 (70.4%) female and 82 (29.6%) male] are between 20 and 55. The average age was calculated as 29.66 (SD = 8.27). We used the cross-lagged panel model for the half-longitudinal mediation model for testing mediation with two time points at four-month intervals. The findings revealed that the variables of the study had significant longitudinal associations, and cognitive flexibility played a longitudinal mediating role in the relationship between family communication and happiness. The current results prove the importance of healthy relationships among family members and highlight the significant influence of family communication and cognitive flexibility on happiness.
Optimizing controllable parameters is crucial to milli-channel cooling system design. This study investigates the heat transfer and hydrodynamic properties of a novel annular flow boiling process of water in milli-channels with better pulsation that passes through a rectangular cross section at a constant temperature. By optimizing system operating parameters and vapor and liquid recirculation, the main novelty in this suggested approach is the achievement of continuous thin-film (micron-sized) annular flow conditions. The 3D simulation model created by a 1D simulation technique has certain boundary restrictions to guarantee the existence of a thin layer of annular flow across the boiler’s whole surface. In Taguchi analysis, the signal-to-noise ratio is determined by using the following input parameters: the Reynolds number, the heated surface temperature, and the pulsatile character of fluid flow. According to the findings, the vapor quality in pulsatile flow is estimated to be 2% to 3% greater than in continuous flow. As thin-film thickness increases, wall temperature declines toward flow. Moreover, there is an approximate 2.5% increase in the mean heat transfer coefficients for pulsatile flow cases compared to continuous flow cases. Furthermore, the average vapor velocity in pulsatile flow is lower than that in continuous flow, according to an analysis of the velocity distributions for each reference zone. The average surface temperature at specified planes in pulsatile flow scenarios is ~ 0.5 K higher than continuous flow situations.
Fatigue, arising from repetitive loading and unloading cycles, often leads to material failure, typically driven by stress concentrations. This study investigates the fatigue failure analysis of torsion springs used in wooden kitchen furniture hinges, where each hinge contains at least one spring responsible for controlled door movements. The research combines experimental and theoretical approaches, utilizing two distinct experimental setups: one conforming to TS EN 15570:2008 standards for door simulation and another optimized for efficiency. The experimental phase examines various scenarios, including the transition to EN 10270-1 SH material and modifications in spring geometry, such as square cross sections and spiral interval adjustments. A comprehensive finite element model using ANSYS is developed to predict fatigue behavior and validate experimental results. The model successfully identifies critical stress locations, which confirms the actual failure points observed during testing. The study incorporates the Goodman mean stress correction method and considers multiple modifying factors to generate accurate S-N curves for fatigue life prediction. Results demonstrate that while material changes to EN 10270-1 SH showed improved fatigue performance, geometric modifications done in the study primarily altered the location of maximum stress rather than reducing it. The research concludes that accurate finite element modeling at the design stage, combined with experimental validation, is crucial for predicting and optimizing spring fatigue life in practical applications.
Introduction In this study, the contents of essential and non-essential elements in the sugary and sugar-free varieties of aromatic coffees produced in Turkey were decided, and the effect of sugar addition was examined. Method For this purpose, essential (Mg, Se, B, Na, Ca, K, Co, Cr, Fe, Cu, Mn, Mo, P and Zn) and non-essential (As, Ba, Al, Cd, Ti, Ni, Sb and Pb) element contents of the aromatic coffees (sugary and sugar-free) (Classic, Gum Mastic, Gum Mastic Turkish Coffee, Hazelnut, Caramel and Turkish Coffee) supplied from a single brand were detected by using ICP-OES. The effects of the elements taken into the body by the consumption of coffee varieties on health and how much of an individual’s daily requirements are met were investigated. Thus, the place and importance of coffee consumption in nutrition have been determined. For coffee consumption of 3 cups, the intake amounts of selected elements were calculated. Furthermore, a risk assessment study was performed by utilizing the non-essential element concentrations of selected coffees. Results Experimental results showed that K is the most ample essential element in all types of coffee, and it has been proven that K ingestion encounters the daily requirement of 1% to 2% for adults. Conclusion According to the risk assessment results, the hazard index was calculated for 3 cups of each coffee type intake as less than 1, and these coffees may be classified in the low-risk group.
Rapid advances in the development of nanotechnology in recent years have led to functional magnetic nanoparticle types (MNPs) with different properties. The diverse applications of these nanoparticles make them a desirable candidate for use in biomedical areas due to their exclusive chemical and physical properties. The present work is conducted to study the in vitro biocompatibility of CoFe2O4@shell with different surface coatings (shell: ascorbic acid (AA), dextran (DEX), and polyethyleneimine (PEI). The cytotoxicity of coated nanoparticles is screened toward the glioma cancer line (C6) and fibroblast cell line (L929) using an MTT assay. CoFe2O4 NPs are synthesized using the co‐precipitation method together with hydrothermal synthesis and characterized regarding their structural and magnetic properties using state‐of‐the‐art techniques. Results showed the particles are consistent with the crystal structure of CoFe2O4 and the average crystallite size in the range of 16–18 nm. For the coated NPs, only a slight increase in the Hc is found except for the CoFe2O4@PEI NPs. The comparative analysis of the cytotoxic effects of CoFe2O4@shell NPs on L929 fibroblast and glioma cells shows that the cytotoxicity of samples is much more specific in brain tumor cells, especially it also indicates the significant efficacy of CoFe2O4@PEI in cancer cells.
The research aims to illustrate the effectiveness of Atmospheric Pressure Plasma Treatment (APLT) activation in enhancing durability in achieving high performance for Carbon Fiber Reinforced Polymer (CFRP) adhesively bonded joints. The study addresses several crucial aspects, encompassing the surface characterization of different treated CFRP surfaces and durability Wedge Test performance assessments under severe environmental conditions for 576h. To attain this objective, the parameters of APLT were examined alongside chemical isopropanol cleaning and peel-ply methods, considering chemical surface characteristics, as well as the performance of joints under environmental conditions. Observations have indicated that APLT facilitates the formation of polar functional groups with increased oxygen content, improving wettability, and leading to substantial enhancements in durability. Finally, findings from the Wedge Test revealed that APLT demonstrates remarkable endurance under elevated temperature/wet aging conditions. It displayed superior resistance to crack formation and limited propagation, thereby preserving higher fracture toughness energy.
Institution pages aggregate content on ResearchGate related to an institution. The members listed on this page have self-identified as being affiliated with this institution. Publications listed on this page were identified by our algorithms as relating to this institution. This page was not created or approved by the institution. If you represent an institution and have questions about these pages or wish to report inaccurate content, you can contact us here.
16,214 members
Bulent Bayram
  • Department of Geomatics Enginering
Osman Sagdic
  • Department of Food Engineering
Banu Mansuroglu (Mansour Karaman)
  • Department of Molecular Biology and Genetics Department
Tufan Demirel
  • Department of Industrial Engineering
Huseyin ELÇİÇEK
  • Department of Marine Engineering Operations
Information
Address
Istanbul, Turkey
Head of institution
Prof. Dr. Tamer Yılmaz