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Gazi University Journal of Science
Number of Followers: 0  

  This is an Open Access Journal Open Access journal
ISSN (Online) 2147-1762
Published by Gazi Üniversitesi Homepage  [9 journals]
  • Genotoxicity of Two Nanoparticles: Titanium Dioxide and Zinc Oxide

    • Authors: Fatma ÜNAL; Funda DEMIRTAŞ KORKMAZ, Zekiye SULUDERE, Özlem EROL, Deniz YÜZBAŞIOĞLU
      Abstract: Nanoparticles (NPs) and nanoparticle-based materials have been increasingly used in various consumer and medical applications. However, investigations have disclosed that some NPs may generate toxic effects in different cell types and organisms. In this study, the cytotoxic and genotoxic potential of titanium dioxide (TiO2) and zinc oxide (ZnO) NPs were examined by using four genotoxicity tests, chromosome aberrations-CAs, sister chromatid exchange-SCE, micronucleus-MN, and comet, in human lymphocytes in vitro. The results showed that both NPs significantly increased the frequency of aberrant cells, CA/Cell, SCE, and DNA damage, and decreased mitotic index in some treatments. These results demonstrated that TiO2 and ZnO NPs induce genotoxic effects. Therefore, more detailed in vitro and in vivo experiments should be conducted for the safe usage of both NPs.
      PubDate: Wed, 01 Dec 2021 00:00:00 +030
  • Measuring the Efficiency of Turkish State Universities Based on a
           Two-Stage DEA Model

    • Authors: Emre KOÇAK; H. Hasan ÖRKCÜ
      Abstract: According to the efficiency scores obtained by Data Envelopment Analysis (DEA), the main problem for inefficient decision-making units (DMU) is the factors that cause inefficiency. To deal with this problem, various studies have been handled, such as decomposing the total efficiency score, and two-stage DEA which can divide the whole process into two parts has been developed. In this study, independent models where the whole process is called a black box and related models where the series relationship is established in the whole process are discussed comparatively. These models are used to measure graduate education performances and scientific and technological research competency performances of state universities in Turkey. When the overall performances of universities are examined; Gebze Technical, Hacettepe, İstanbul Technical, İzmir Institute of Technology and Middle East Technical have been determined as efficient universities both in terms of overall performances of universities and in terms of independent model and related model. İstanbul, Ankara, Boğaziçi and Gazi, have beendetermined as efficient universities only in terms of independent model. Furthermore, this study is consistent with the research universities determined by the Council of Higher Education through certain criteria.
      PubDate: Wed, 01 Dec 2021 00:00:00 +030
  • Preparation, Characterization and Antibacterial Activity of Malva
           Sylvestris L. Seed Extract Containing Novel Electrospun PVA Nanofibers

    • Authors: Kübra TURAN; Muharrem AKCAN, Orhan Murat KALFA
      Abstract: Medicinal plants have been a great source for pharmaceutical agents. However, prossessing these raw sources to turn into therapeutic drugs requires highly complex technologies and expensive methods. Malva sylvestris L. is a commonly used vegetable in traditional and ethnoveterinary medicine because of its antimicrobial and anti-inflammatory properties. Therefore, in this study we used PVA/M. sylvestris L. seed (MSs) extract biocomposites to produce nanofibers with electrospun technique. M. sylvestris L. seed extracts were prepared and divided into fractions with 20% ACN. The metabolites in MSs extract characterized by Q-TOF LC-MS. Biocomposites with different ratios of both polymer and extract were prepared for nanofiber production. Bionanofibers have been produced from these biocomposites with optimized electrospinning conditions and their morphological analysis has been performed using SEM and FTIR techniques. Nanofibers had average diameters within the range of ∼180–244 nm. They were also found to have antibacterial activity against several microorganisms including Gram-negative (P.aeruginosa and E.coli) and Gram-positive (S.aureus and E.faecalis) bacteria. These newly generated bionanofibers with antibacterial properties hold great potential to be used in medical applications and food packaging.
      PubDate: Wed, 01 Dec 2021 00:00:00 +030
  • Various Mechanical Properties of Denture Liners Combined with Zirconium
           Oxide Nanoparticles

    • Authors: Gulfem ERGUN; Ayşe Seda ATAOL, Ferhan EGİLMEZ, Rükan GENC ALTURK, Zeynep ŞAHİN
      Abstract: Debonding from the denture base, poor resistance to tearing, and increase in hardness are some of the problems with denture liners. This research purposed to analyze the changes in mechanical characteristics of the tissue conditioner and the denture liner concerning the interaction of the material with the zirconium oxide nanoparticles (ZrO2-NPs). The surface functionalization of ZrO2-NPs was done using a silane coupling agent as a modifier for better integration of them into the denture liners. Then, they were added into acrylic- and silicone-based denture liner in two different percentages (0.5% and 1% by weight; respectively). The performed tests were tear strength, tensile bond strength, and hardness (Shore A). 0.5% and 1% of ZrO2-NPs added tissue conditioner test groups displayed statistically significantly lower tensile bond strength values than tissue conditioners without ZrO2-NPs (p < 0.001). However, the tensile bond strength results of all subgroups for soft denture liner were statistically similar (p = 0.239). In all of the test groups of tissue conditioner and soft lining material, the highest tear strength values were obtained in 0.5% ZrO2-NPs added test groups (tissue conditioner; 0.58±0.11 N and soft denture liner; 4.10±0.58 N). The shore A hardness results of both tested groups determined no meaningful differences (p = 0.100). All subgroups of the tested silicone-based denture liners had satisfactory and clinically adequate bonding strength to the base of the prosthetic. 
      PubDate: Wed, 01 Dec 2021 00:00:00 +030
  • A Terahertz Metamaterial Absorber-Based Temperature Sensor Having Nine
           Resonance Peaks

    • Authors: Fulya BAĞCI
      Abstract: Design and investigation of a polarization-insensitive nine-band tunable metamaterial absorber at THz frequencies with equal to or more than 90% absorption ratio in all of the bands are reported. The tunable metamaterial absorber consists of four isosceles triangle patches with four U-shaped cut paths on top of an indium antimonide substrate, which has a fully metallic ground plane at the backside. Numerical analyses show that the metamaterial absorber has wide-angle characteristics under transverse-electric and transverse-magnetic modes. The permittivity of indium antimonide is highly dependent on temperature variations due to its temperature-dependent intrinsic carrier density, leading to shift of nine absorption peak frequencies upon change of environment temperature. Broadband switching of nine absorption peak frequencies with maximum 71.5% shift ratio between 190 K and 230 K is obtained. Temperature sensing performance of the metamaterial absorber is further evaluated and the sensitivities are found to be 11.5 GHz/K, 9.2 GHz/K, 8.3 GHz/K, 7.6 GHz/K, 7.0 GHz/K, 6.2 GHz/K, 5.3 GHz/K, 4.5 GHz/K and 4.2 GHz/K, from the first to ninth absorption band, respectively. Therefore, the proposed nine-band metamaterial absorber sensor has great potential in sensitive and accurate temperature measurement, absorption tuning in optoelectronic applications and as frequency selective thermal emitters.
      PubDate: Wed, 01 Dec 2021 00:00:00 +030
  • Estimation of Parameters of Topp-Leone Inverse Lomax Distribution in
           Presence of Right Censored Samples

    • Authors: Amal SOLİMAN; Doaa ISMAİL
      Abstract: In this paper, we deal with a three-parameter inverse Lomax cited as the Topp-Leone inverse Lomax (TLIL) distribution depend on Topp-Leone-G family. Expressions of its density and distribution functions are explored. The structure properties of suggested model are provided like quantile function, moments, incomplete moments and Rényi entropy. Maximum likelihood estimators of the TLIL distribution parameters along with reliability estimator are worked out via complete and type II censored samples. To investigate the statistical properties of estimates we present numerical illustration along with two real data.
      PubDate: Wed, 01 Dec 2021 00:00:00 +030
  • Optical Properties of Gaas/Alxga1-xas Superlattice Under E-Field for
           Quantum Cascade Laser Application

    • Authors: Behçet Özgür ALAYDİN
      Abstract: Optical properties of GaAs/AlxGa1-xAs superlattice are studied dependent on quantum well thickness of gain region and doping density of injector layers underperformed electric field. Conduction band alignment of the superlattice is obtained by using effective mass approximation. 1d-Schrodinger formula is solved by using FDM. Intersubband transition energies, linear (nonlinear and total) absorption coefficients and linear (nonlinear and total) refractive index changes are plotted under applied electric field intensity. Intersubband transition energy of electron from second excited state to first excited state shows 147 meV. It is found that -45 kV/cm electric field intensity and 5 nm layer thickness of last quantum well of the gain region are the best values for studied structure. After that, linear absorption coefficient is investigated dependent on carrier number in the injector region under electric field. It is found that carrier number over 5 𝑥 1016 𝑐𝑚−2 can causes huge internal absorption of the radiative emission obtained in gain region due to increase in linear absorption coefficient by factor 10. As a conclusion, total absorption coefficient and total refractive index change are calculated for optimized parameters.
      PubDate: Wed, 01 Dec 2021 00:00:00 +030
  • Thermodynamic Analysis of Industrial Cooling Systems with the Usage of
           Different Types of Evaporators: Experimental Study

    • Authors: Süleyman ERTEN; Meltem KOŞAN, Furkan İŞGEN, Esra DEMİRCİ, Mustafa AKTAŞ
      Abstract: Energy efficiency and the amount of refrigerant in heat exchangers used in cooling systems has recently been an important research subject. In this study, in order to compare and analyze different types of evaporators, industrial refrigerators were designed and in this context, test setups in accordance with TS EN ISO 23953-2 standard were produced. R290 (propane) was used as the refrigerant in the designed system. During the experiment, temperature-pressure measurements were taken at a certain point in the cooling system equipment of the products, which were cooled every minute, and test data were recorded. As a result of the data obtained from the experimental results, while the temperature difference of the air entering and leaving the evaporators was 6.797 ℃ in the first system using ½” tube diameter evaporator, it was calculated as 7.052 ℃ in the corrugated and hydrophilic coated second system using 3/8” tube diameter. In the experimental setups, the energy consumed in the first and second systems and the masses of R-290 refrigerant were measured as 24.64 kWh, 23.39 kWh and 700 grams, 430 grams, respectively. Consequently, it was calculated that the second system was 5.073% and 38.57% more efficient in terms of energy efficiency and the refrigerant mass used. Coefficient of performance values for the first and second systems were found as 2.807 and 3.013, respectively.
      PubDate: Wed, 01 Dec 2021 00:00:00 +030
  • Modelling Wind Energy Potential in Different Regions with Different

    • Authors: Mehmet DAŞ; Ebru AKPINAR, Sinan AKPINAR
      Abstract: Processing a lot of data is a very difficult and laborious task. In order to save time and ease the process, computational intelligence method is a very practical method for data processing. In the present study, the potential of wind energy in different regions of Turkey based on the hourly wind speed data in the years 2008-2017 were analysed statistically. Wind power density values have been examined mathematically and statistically and modelled using artificial intelligence methods. During the statistical analysis, maximum wind speed, average wind speed, wind power density, and standard deviation of wind speed have been determined. The cumulative Weibull function was used to determine wind power density and wind speed distribution on an annual basis using hourly wind speed data. Predictive models have been created by using machine learning algorithms which are computational intelligence method for the obtained wind power density values. Decision tree (DT) algorithm and multilayer perceptron (MLP) algorithm have been chosen as machine learning algorithms. Four different error analyses have been performed for DT and MLP estimates. In the machine algorithms used to estimate wind power values, the DT algorithm performed approximately 35% more accurate than the MLP algorithm. As a result, wind power densities for certain regions have been determined by using both mathematical model and computational intelligence methods.
      PubDate: Wed, 01 Dec 2021 00:00:00 +030
  • Flow and Heat Transfer in a Trapezoidal Cross-Sectional Microchannel Heat
           Sink Using Nanofluid

    • Authors: Faraz EGE; Oğuz TURGUT, Emre Aşkın ELİBOL
      Abstract: In this study, the effects of microchannel number, volume concentration, Reynolds number, and nanofluid type on heat transfer and flow characteristics in the heat sink consisting of trapezoidal microchannels are investigated numerically. Governing equations are solved by assuming three-dimensional, incompressible, steady and laminar flow. The channel material is chosen as copper, and a constant heat flux boundary condition is defined on the upper wall of heat sink. For two different nanofluids, CuO-water and Al2O3-water, investigated parameters are the number of trapezoidal channels (n=3-5) in the heat sink, Reynolds number (Re=200-1500), and volume concentration (=0-4%). Results show that using nanoparticles in base fluid causes to increase both heat transfer coefficient and pressure drop. Heat transfer coefficient increases with increasing number of trapezoidal cross-sectional channel in the heat sink, nanofluid volume concentration and Reynolds number. Pressure drop enhances with enhancing Reynolds number and microchannel number in the heat sink. The nanofluid type and volume concentration do not importantly affect the friction factor. According to the performance index, it is seen that adding CuO nanoparticles in water is convenient, but Al2O3 nanoparticles in water is not appropriate. It is observed that volume concentration for CuO-water nanofluid affects the thermal performance, but volume concentration for Al2O3-water nanofluid does not affect.
      PubDate: Wed, 01 Dec 2021 00:00:00 +030
  • Effect of Waste Titanium Chips Addition Into the Aluminum Alloys on Their

    • Authors: Gökhan ÖZER; Serhat ACAR, Alptekin KISASÖZ, Kerem Altuğ GÜLER
      Abstract: In the present study, turning chips were preferred to add titanium into liquid aluminum. Although being easy to reach and cheap, the chips were thought to be effective in minor titanium addition with their large surface area. Experimental studies have been carried out with A356 casting alloy and commercial purity aluminum. The effects of different process parameters were investigated on titanium transfer efficiency, microstructural and microhardness properties of the formed phases. The processes were carried out between 740 - 820 °C, for 2, 4, and 6 h, with the amount of added chips 5 and 10 wt.% (3 and 6 vol.%). The experiments were conducted with both commercially pure Al and A356 alloy. The microstructural investigations and microhardness measurements were carried out on the formed Al3Ti and (Al, Si)3Ti phases. The first noticeable result was that titanium transfer was more efficient in pure aluminum than in the A356 alloy. Also, it was observed that this difference became more significant with an increase in wt.% addition. The measured microhardness values were also differentiated depending on the Si content of the formed Al3Ti compound. Due to the presence of high Si content in A356 alloy, transference efficiencies of Ti were found highly limited compared to pure aluminum as the silicon enrichment in the Al3Ti compound reduces the diffusion of titanium and the growth rate of Al3Ti particles. Maximum transference efficiency was found 47.05% with 10 %wt. chip addition in commercially pure aluminum at the processing conditions of 780 °C for 4 h.   
      PubDate: Wed, 01 Dec 2021 00:00:00 +030
  • Some Properties of a Third Order Partial Recurrence Relation

    • Authors: Anthony G. SHANNON; Ömür DEVECİ
      Abstract: This paper explores a connection between third order recursive sequences and generalized continued fractions by analogy with second order recursive sequences and ordinary two-dimensional continued fractions. It does this with a partial recurrence relation which is related to the original third order recurrence relation, and raises a related conjecture.
      PubDate: Wed, 01 Dec 2021 00:00:00 +030
  • Scattering Function and The Resolvent of The Impulsive Boundary Value

    • Authors: Elgiz BAYRAM; Güler Başak ÖZNUR
      Abstract: The purpose of this study is to examine the properties of scattering solutions and the scattering function of an impulsive Sturm-Liouville boundary value problem on the semi axis. By using Jost solutions, we obtain the scattering function, asymptotic representation of Jost function and resolvent operator. Finally, we study scattering solutions and scattering function of an unperturbated impulsive equation.
      PubDate: Wed, 01 Dec 2021 00:00:00 +030
  • Prediction of Breast Cancer through Tolerance-based Intuitionistic
           Fuzzy-rough Set Feature Selection and Artificial Neural Network

    • Authors: Naiyer Mohammadi LANBARAN; Ercan ÇELİK
      Abstract: The importance of diagnosing breast cancer is one of the most significant issues in medical science. Diagnosing whether the cancer is benign or malignant is extremely essential in ascertaining the type of cure, moreover, to bringing down bills. This study aims to use the tolerance-based intuitionistic fuzzy-rough set approach to pick attributes and data processing with help of machine learning for the classification of breast cancer. The main purpose of selecting a feature is to make a subset of input variables by removing irrelevant variables or variables that lack predictive information. This study shows how to eliminate redundant data in big data and achieve more efficient results. Rough set theory has already been used successfully to set down attributes, but this theory is insufficient to reduce the properties of a real- value dataset because it will possibly drop knowledge through the decomposition procedure. and this prevents us from getting the right results. In this study, we used the tolerance based intuitive fuzzy rough method for attribute selection. In this technique, lower and upper approaches are used to intuitive fuzzy sets from rough sets to remove uncertainty due to having simultaneous membership, non-membership, and hesitation degrees and obtain better results. The used method is demonstrated to be better performing in the shape of chosen attributes.
      PubDate: Wed, 01 Dec 2021 00:00:00 +030
  • A new DoE-MTOPSIS based prediction model suggestion to capture potential
           SARS-CoV-2 reactivated patients

    • Authors: Yusuf Tansel İÇ
      Abstract: Difficulties to use convenient data during the Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) pandemic outbreak and complexities of the problem attitude crucial challenges in infectious disease modelling studies. Motivated by the on-going reach to predict a potential reactivated SARS-CoV-2 (COVID-19), we suggest a prediction model that beyond the clinical characteristics based evaluation approaches. In particular, we developed a possibly available and more efficient prediction model to predict a potential reactivated SARS-CoV-2 (COVID-19) patient. Our paper aims to explore the applicability of a modified Technique for Order Preference by Similarity to Ideal Solutions (MTOPSIS) integrated Design of Experiment (DoE) method to predict a potential reactivated COVID-19 patient in real-time clinical or laboratory applications. The presented novel model may be of interest to the readers studying similar research areas. We illustrate MTOPSIS integrated DoE method by applying it to the COVID-19 pandemic real clinical cases from Wuhan/China-based data. Despite the small sample size, our study provides an encouraging preliminary model framework. Finally, a step by step algorithm is suggested in the study for future research perspectives.
      PubDate: Wed, 01 Dec 2021 00:00:00 +030
  • Turkish Speech Recognition Techniques and Applications of Recurrent Units
           (LSTM and GRU)

    • Authors: Burak TOMBALOĞLU; Hamit ERDEM
      Abstract: A typical solution of Automatic Speech Recognition (ASR) problems is realized by feature extraction, feature classification, acoustic modeling and language modeling steps. In classification and modeling steps, Deep Learning Methods have become popular and give more successful recognition results than conventional methods. In this study, an application for solving ASR problem in Turkish Language has been developed. The data sets and studies related to Turkish Language ASR problem are examined. Language models in the ASR problems of agglutative language groups such as Turkish, Finnish and Hungarian are examined. Subword based model is chosen in order not to decrease recognition performance and prevent large vocabulary. The recogniton performance is increased by Deep Learning Methods called Long-Short Term Memory (LSTM) Neural Networks and Gated Recurrent Unit (GRU) in the classification and acoustic modeling steps. The recognition performances of systems including LSTM and GRU are compared with the the previous studies using traditional methods and Deep Neural Networks. When the results were evaluated, it is seen that LSTM and GRU based Speech Recognizers performs better than the recognizers with previous methods. Final Word Error Rate (WER) values were obtained for LSTM and GRU as 10,65% and 11,25%, respectively. GRU based systems have similar performance when compared to LSTM based systems. However, it has been observed that the training periods are short. Computation times are 73.518 and 61.020 seconds respectively. The study gave detailed information about the applicability of the latest methods to Turkish ASR research and applications.
      PubDate: Wed, 01 Dec 2021 00:00:00 +030
  • Comparative Analysis of Optical Multicarrier Modulations: An Insight into
           Machine Learning-based Multicarrier Modulation

    • Authors: Augustus IBHAZE; Frederick EDEKO, Patience ORUKPE
      Abstract: The performances of various optical multicarrier modulation schemes have been investigated in this work by comparatively analyzing the bit error rate response relative to the signal to noise ratio metric. The machine learning-based multicarrier modulation (MLMM) approach was proposed and adopted as a method to improve the bit error rate response of the conventional schemes. The results showed performance enhancement as the proposed machine learning approach outperformed the conventional schemes. This proposition is therefore recommended for adoption in the implementation of optical multicarrier modulation-based solutions depending on the spectral and energy efficiency requirements of the intended application.
      PubDate: Wed, 01 Dec 2021 00:00:00 +030
  • Color and COD Removal from Real Textile Wastewater using Nanoscale
           Zero-Value Iron (nZVI)

    • Authors: Özlem TEPE; Müslün Sara TUNÇ, Özge HANAY
      Abstract: Nanoscale zero-value iron (nZVI) has a high specific surface area and significant abilities to reduce contaminants. In this study, the removal of color and COD from real textile wastewater was studied by nZVI particles. A series of experiments were conducted to evaluate the effect of operational parameters such as solution pH, nZVI dosage and temperature on color and COD removal. The results showed that the color and COD removals mainly depend on solution pH. The color removal efficiencies were 96.3% at 436 nm, 97.8% at 525 nm and 98.0% at 620 nm, respectively at nZVI dosage of 0.3 g/L and initial pH of 3 after 180 minutes of reaction time at 25 ○C. Moreover, the maximum COD removal efficiency obtained under these conditions was 86%.
      PubDate: Wed, 01 Dec 2021 00:00:00 +030
  • Morphology and Ultrastructure of the Nymphal Malpighian Tubules of
           Conocephalus fuscus fuscus (Fabricius, 1793) (Orthoptera, Tettigoniidae)

    • Authors: Irmak POLAT
      Abstract: Malpighian tubules are the main osmoregulatory structures in insects. The primary task of the insects’ Malpighian tubules is to remove the nitrogenous wastes and other remained of metabolites. In this study, the nymphal Malpighian tubules of Conocephalus fuscus fuscus were studied with optical and transmission electron microscopy. The wall of each Malpighian tubule is comprised of a single layer of cells. The Malpighian tubules in nymphal C. fuscus fuscus have 3 types of epithelial cells. The first group of the cells outnumbers the other groups of cells and they have long microvilli at the apical side of the plasma membrane. The second group of the cells has electron-dense cytoplasm. The microvilli of the second group of the cells are shorter than those of the first group of the cells. The cytoplasm of the epithelial cells of the third group is so electron-lucent. These significant differences in the fine structure of the tubule cells were compared with the other Hexapoda orders. The general composition of the Malpighian tubules of the nymphal C. fuscus fuscus is generally similar, despite some histological differences compared to those of other species.
      PubDate: Wed, 01 Dec 2021 00:00:00 +030
  • A new natural hybrid of Verbascum L. (Scrophulariacae) from Turkey

    • Authors: Hayri DUMAN; Erkan UZUNHİSARCIKLI, Funda ÖZBEK
      Abstract: Verbascum × aytachii nothosp. nov. H. Duman & Uzunh. (sect. Bothrospermae) is described and illustrated as a new natural hybrid from the Orhaneli (Bursa Region) area in Western Anatolia, Turkey. This species is identified to have some intermediate morphological and palynological characteristics that place it between the parents which are V. ekicii and V. basivelatum. A comprehensive description, ecology, a distribution map and a detailed illustration are provided. Furthermore, pollen morphological properties of V. × aytachii and its parents are compared via light (LM) and scanning electron microscopes (SEM).
      PubDate: Wed, 01 Dec 2021 00:00:00 +030
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