Arama Sonuçları

Listeleniyor 1 - 10 / 17
  • Öğe
    An exergy analysis of a concentric tube heat exchanger using hBN-water nanofluids
    (Inder Science Publishers, 2021) Budak Ziyadanoğulları, Neşe; Perçin, Süleyman
    This study investigated the effects of using nanofluids prepared with hexagonal boron nitride (hBN) nanoparticles on the thermal performance and pressure drop of a concentric tube heat exchanger. Experiments were carried out with water-hBN nanofluids for stable, dispersed, 0.01%, 0.1% and 1% volume concentrations, at different flow rates and Reynolds numbers under parallel and counter-flow conditions. When the experimental results were examined, the exergy loss was higher in the parallel-flow heat exchanger compared to the counter-flow heat exchanger. The highest exergy loss value was obtained for distilled water at the highest Reynolds number (Re = 8,700) for parallel flow operation at 170 W. The exergy loss of water at the highest Reynolds number (Re = 8,700) for parallel flow operation increased by 15.7%, 24.8% and 49.8% for hBN-water concentrations of 0.01%, 0.1% and 1%, respectively. Exergy loss of water at the highest Reynold number (Re = 8,700) for counter flow operation increased by 11.3%, 17.3% and 29.2% for hBN-water concentrations of 0.01%, 0.1% and 1%, respectively. When evaluating the exergy analysis of the system, exergy losses due to pressure drops were negligible for both flows (parallel and counter).
  • Öğe
    Finite element analysis of the stress distributions in peri-implant bone in modified and standard-threaded dental implants
    (Taylor & Francis, 2016-01) Topkaya, Tolga; Dündar, Serkan; Solmaz, Murat Yavuz; Yaman, Ferhan; Atalay, Yusuf; Saybak, Arif; Asutay, Fatih; Çakmak, Ömer
    The aim of this study was to examine the stress distributions with three different loads in two different geometric and threaded types of dental implants by finite element analysis. For this purpose, two different implant models, Nobel Replace and Nobel Active (Nobel Biocare, Zurich, Switzerland), which are currently used in clinical cases, were constructed by using ANSYS Workbench 12.1. The stress distributions on components of the implant system under three different static loadings were analysed for the two models. The maximum stress values that occurred in all components were observed in FIII (300 N). The maximum stress values occurred in FIII (300 N) when the Nobel Replace implant is used, whereas the lowest ones, in the case of FI (150 N) loading in the Nobel Active implant. In all models, the maximum tensions were observed to be in the neck region of the implants. Increasing the connection between the implant and the bone surface may allow more uniform distribution of the forces of the dental implant and may protect the bone around the implant. Thus, the implant could remain in the mouth for longer periods. Variable-thread tapered implants can increase the implant and bone contact.
  • Öğe
    Experimental investigation of solar stills integrated with solar water heating collectors
    (Türk Isı Bilimi ve Tekniği Derneği, 2017-10-31) Argunhan, Zeki; El, Emin; Yıldız, Cengiz; Çakmak, Gülşah
    Solar still is a more practical way of obtaining clean water. In this study, we aimed to improve the efficiency of solar still systems and obtain distilled water at the same time. For this purpose, 5 different solar still systems were designed. Type 1; conventional solar still, Type 2; conventional solar still integrated with solar water heating collector and run via natural convection, Type 3; conventional solar still integrated with solar water heating collector and tubular heat exchanger and run via natural convection, Type 4; conventional solar still placed with plate heat exchanger and integrated with solar water heating collector and run via natural convection, Type 5; conventional solar still placed with plate heat exchanger and integrated with solar water heating collector and run via forced convection. In this study, the experiments were carried out on the parameters influencing the performance, the amount of distilled water obtained, and the efficiency of experiment settings designed in different types; and finally the results were presented. The amount of distilled water and efficiency of conventional solar still were 2389 ml and 51.47%, respectively. Maximum total amount of water and efficiency from natural convection systems were obtained from Type 4, and the values calculated were found as to be 5788 ml and 55.91%. Maximum amount of distilled water and the efficiency were obtained by utilizing forced convection system were found as to be 6068 ml and 58.99%, respectively.
  • Öğe
    Plantago major protective effects on antioxidant status after administration of 7,12-dimethylbenz(a)anthracene in rats
    (Asian Pacific Organization for Cancer Prevention, 2011) Oto, Gökhan; Ekin, Suat; Özdemir, Hülya; Demir, Halit; Yaşar, Semih; Levent, Abdulkadir; Berber, İsmet; Kaki, Barış
    Aim: The present study was designed to evaluate effects of Plantago major extract on oxidative status in Wistar albino rats administrated 7,12-dimethylbenz(a)anthracene (DMBA). Methods: Rats were divided into three equal groups of 6 animals each: Group 1 controls, group 2 treated with DMBA (100 mg/kg, single dose) and group 3 receiving the DMBA and the aqueous extract at 100 mg/kg/d for 60 days. Results: Significant decrease in catalase (P<0.05), carbonic anhydrase (p≤0.01), reduced glutathione (GSH) (P<0.01) and total protein (P<0.01) values was observed in the DMBA group compared with the healthy controls and DMBA + Plantago major groups. Conclusion: The results suggest preventive effects of Plantago major on DMBA induced oxidative damage in Wistar albino rats that might be due to decreased free radical generation.
  • Öğe
    A generalization of the Katzman-Zhang algorithm
    (Elsevier, 2021-03) Yeşil, Mehmet
    In this paper, we study the notion of special ideals. We generalize the results on those as well as the algorithm obtained for finite dimensional power series rings by Mordechai Katzman and Wenliang Zhang to finite dimensional polynomial rings.
  • Öğe
    A novel approach for extracting ideal exemplars by clustering for massive time-ordered datasets
    (TÜBİTAK, 2017-07-30) Ertuğrul, Ömer Faruk
    The number and length of massive datasets have increased day by day and this yields more complex machine learning stages due to the high computational costs. To decrease the computational cost many methods were proposed in the literature such as data condensing, feature selection, and filtering. Although clustering methods are generally employed to divide samples into groups, another way of data condensing is by determining ideal exemplars (or prototypes), which can be used instead of the whole dataset. In this study, first the efficiency of traditional data condensing by clustering approach was confirmed according to obtained accuracies and condensing ratios in 9 different synthetic or real batch datasets. This approach was then improved to be employed in time-ordered datasets. In order to validate the proposed approach, 23 different real time-ordered datasets were used in experiments. Achieved mean RMSEs were 0.27 and 0.29 by employing the condensed (mean condensed ratio was 97.17%) and the whole datasets, respectively. Obtained results showed that higher accuracy rates and condensing ratios were achieved by the proposed approach.
  • Öğe
    Electronic properties of Cu/n-InP metal-semiconductor structures with cytosine biopolymer
    (Polska Akademia Nauk, 2015-09) Güllü, Ömer; Türüt, Abdülmecit
    This work shows that cytosine biomolecules can control the electrical characteristics of conventional Cu/n-InP metal-semiconductor contacts. A new Cu/n-InP Schottky junction with cytosine interlayer has been formed by using a drop cast process. The current-voltage (I-V) and capacitance-voltage (C-V) characteristics of Cu/cytosine/n-InP structure were investigated at room temperature. A potential barrier height as high as 0.68 eV has been achieved for Cu/cytosine/n-InP Schottky diodes, which have good I-V characteristics. This good performance is attributed to the effect of interfacial biofilm between Cu and n-InP. By using C-V measurement of the Cu/cytosine/n-InP Schottky diode the diffusion potential and the barrier height have been calculated as a function of frequency. Also, the interface-state density of the Cu/cytosine/n-InP diode was found to vary from 2:24 × 1013 eV-1cm-2 to 5.56× 1012 eV-1 cm-2.
  • Öğe
    An artificial neural network model to predict the thermal properties of concrete using different neurons and activation functions
    (Hindawi, 2019-04-01) Fidan, Şehmus; Oktay, Hasan; Polat, Süleyman; Öztürk, Sarper
    Growing concerns on energy consumption of buildings by heating and cooling applications have led to a demand for improved insulating performances of building materials. The establishment of thermal property for a building structure is the key performance indicator for energy efficiency, whereas high accuracy and precision tests are required for its determination which increases time and experimental costs. The main scope of this study is to develop a model based on artificial neural network (ANN) in order to predict the thermal properties of concrete through its mechanical characteristics. Initially, different concrete samples were prepared, and their both mechanical and thermal properties were tested in accordance with ASTM and EN standards. Then, the Levenberg-Marquardt algorithm was used for training the neural network in the single hidden layer using 5, 10, 15, 20, and 25 neurons, respectively. For each thermal property, various activation functions such as tangent sigmoid functions and triangular basis functions were used to examine the best solution performance. Moreover, a cross-validation technique was used to ensure good generalization and to avoid overtraining. ANN results showed that the best overall R2 performances for the prediction of thermal conductivity, specific heat, and thermal diffusivity were obtained as 0.996, 0.983, and 0.995 for tansig activation functions with 25, 25, and 20 neurons, respectively. The performance results showed that there was a great consistency between the predicted and tested results, demonstrating the feasibility and practicability of the proposed ANN models for predicting the thermal property of a concrete.
  • Öğe
    A noninvasive time-frequency-based approach to estimate cuffless arterial blood pressure
    (TÜBİTAK, 2018-09-28) Ertuğrul, Ömer Faruk; Sezgin, Necmettin
    Arterial blood pressure (ABP) is one of the most vital signs in the prophylaxis and treatment of blood pressure-related diseases because raised blood pressure is the most significant cause of death and the second major cause of disability in the world. Higher ABP yields greater strain on arteries and these extra strains turn arteries into thicker, less flexible, and more narrow structures. This increases the possibility of having an artery busting or artery occlusion, which are the primary reasons for heart attacks, kidney disease, or strokes. In addition to its importance in monitoring cardiovascular homeostasis, measurement of ABP is imperative in surgical operations. In this study, a simple and effective approach was proposed to estimate ABP from electrocardiogram (ECG) and photoplethysmograph (PPG) signals by an extreme learning machine (ELM) and statistical properties of the ECG and/or PPG signals in the time-frequency domain. To evaluate and apply the proposed approach, the Cuffless Blood Pressure Estimation Dataset, which was published and shared by UCI, was employed. First, the statistical properties were extracted from ECG and PPG signals that were in the time-frequency domain. Later, extracted features were employed to estimate cuffless ABP for each subject by the ELM and some popular machine learning methods. Achieved results and reported results in the literature showed that the proposed approach can be successfully employed for estimating cuffless blood pressure (BP) from ECGs and/or PPGs. Additionally, with the proposed approach, the systolic BP, mean BP, and diastolic BP can be calculated simultaneously.
  • Öğe
    Electrooxidation of thiourea and its square-wave voltammetric determination using pencil graphite electrode
    (Walter de Gruyter, 2011-04-01) Levent, Abdulkadir; Keskin, Ertuğrul; Yardım, Yavuz; Şentürk, Zühre
    The electrochemical properties of thiourea (TU) were investigated in pH range 2.0-12.0 by cyclic and square-wave voltammetry. The compound was irreversibly oxidized at a pencil graphite electrode in one or two oxidation steps which are pH-dependent. Based on the voltammetric peak for the second oxidation process of TU in phosphate buffer at pH 12.0, a square-wave voltammetric method was proposed for the determination of the compound in the range 6.3-30μm, with a detection limit of 1.29μm. The applicability to direct assays of wastewaters was also tested.