Sürdürülebilir Kalkınma Amaçları
Yazarlar
- Araz, Onur(15)
- Ozturk, Samet(14)
- Ozyurt, E.(9)
- Turk, Veysel(9)
- Reis, Hatice Catal(7)
- Beder, Murat(6)
- Erdogdu, Ferruh(6)
- Peker, Iskender(6)
- Erol, Ismail(5)
- Kaygusuz, Abdullah(5)
- Ozturk, Kasif Furkan(5)
- Wang, Y.C.(5)
- Akpinar, Adem(4)
- Akçay, Serhatcan Berk(4)
- Coskun, Eda(4)
- Kankal, Murat(4)
- Kaya, Selim(4)
- Liu, Shuxiang(4)
- Ozden, Talat(4)
- Seferoğlu, Mehmet Tevfik(4)
- Varol, Temel(4)
- Öztürk, Serkan(4)
- Akinoglu, Bulent G.(3)
- Alemdag, Selcuk(3)
- Arslan, Mehmet(3)
- Cakir, Tufan(3)
- Gurocak, Zulfu(3)
- Gücer, Mehmet Ali(3)
- Günen, Mehmet Akif(3)
- Kaya, Ali(3)
- Mert, Behic(3)
- Mızrak, Sefa(3)
- Saydam Eker, Çiğdem(3)
- Tasci, Caner(3)
- Çelik, Necati(3)
- Ünlü, Ramazan(3)
- Şan, Murat(3)
- Akpinar, A.(2)
- Akpinar, Merve(2)
- Aksa, Hüseyin Can(2)
Yayınlar
- MakaleYalnız künye2021Static resistance of axially loaded multiplanar gap KK-joints of Circular Hollow sections at elevated temperatures
Wang, Y.C.; Ozyurt, E.
This paper presents the results of a numerical investigation of the behaviour, and proposes a method to calculate the static resistance of axially loaded Circular Hollow Section Double K-joints (DKK) at elevated temperatures. This type of joints is widely used in building construction, but currently, there is no method to calculate their static resistance at elevated temperatures. The numerical investigations of this paper cover a wide range of design parameters, including brace axial load combination, joint temperature, angles between brace members, longitudinal and transverse gap sizes, chord diameter to thickness ratio and brace diameter to chord diameter ratio. The results of this paper indicate that the ratio of joint elevated temperature resistance to ambient temperature resistance may be lower than the reduction factor for the yield strength of steel at elevated temperatures. There are two joint failure modes, one for small and one for large transverse gap. These failure modes and the demarcation between small and large gaps are independent of joint temperature. For joints with large gap, the ratio of joint resistance at elevated temperature to that at ambient temperature is close to the average of steel yield strength and Young's modulus reduction factors at elevated temperature. For joints with small gap, the joint resistance ratio follows the steel Young's modulus factor variation at elevated temperature if all four braces are under compression, but the trend changes to the average ratio of steel Young's modulus and yield strength reduction factors if the axial brace loads are balanced (compression in two brace members equal to tension force in the other two brace members). Linear interpolation can be applied between these two different loading cases.
- MakaleYalnız künye2020Analysis of ionospheric TEC anomalies for global earthquakes during 2000-2019 with respect to earthquake magnitude (Mw≥6.0)
Ulukavak, Mustafa; Yalçınkaya, Mualla; Kayıkçı, Emine Tanır; Öztürk, Serkan; Kandemir, Raif; Karslı, Hakan
In this work, a relationship between ionospheric TEC anomalies and different earthquake magnitude groups before the main shocks was investigated. For this purpose, 2942 global earthquakes with Mw≥6 from 2000 to 2019 and possible ionospheric TEC anomalies that occurred before earthquakes were examined by considering 13 different index values of space weather conditions (geomagnetic storm indices and solar activity indices). Anomalies of ionospheric TEC changes were defined for 15-days before and 4-days after the earthquakes by using 15-days moving median method with the length of 15 days. Earthquakes were first grouped according to their magnitudes, and then negative and positive TEC anomalies in quiet days before the earthquakes were detected. These anomalies were observed as ∼5–13, ∼5-10, ∼5-15, ∼3-13, ∼7-15, ∼1 and ∼5-8 days ago for the earthquakes of 6.0 ≤ Mw<6.5, 6.5 ≤ Mw<7.0, 7.0 ≤ Mw<7.5, 7.5 ≤ Mw<8.0, 8.0 ≤ Mw<8.5, 8.5 ≤ Mw<9.0, and 9.0 ≤ Mw<9.5, respectively. Mean of changes in TEC anomalies of these groups is 44.2 % TECU and we detected that the number of positive anomalies in each group is larger than the number of negative anomalies. Consequently, these analyses clearly show that the day-to-day changes in TEC anomalies may supply significant precursors prior to the global earthquakes (M ≥ 6) in the short-term earthquake prediction for main shocks.
- MakaleAçık Erişim2020One-year performance evaluation of two newly developed back-contact solar modules in two different climates
Ozden, Talat; Carr, Anna J.; Geerligs, Bart (L.J.); Turan, Rasit; Akinoglu, Bulent G.
To a certain extent, the photovoltaics industry is well developed, and the performance and expected yield of standard photovoltaic modules are well documented and researched. However, newer more efficient photovoltaic cell and module technologies are being developed all over the world. Outdoor testing of new photovoltaic technologies is very important to understand and validate their reliability and performance under different environmental conditions. For the first time, one year of monitored performance data is presented and analyzed for two high efficiencies interdigitated back contact prototype mini-modules at different locations, having different climates. The test results of a commercial heterojunction with intrinsic thin-layer” module are also presented for comparison. The results showed that the two mini-modules remained stable for the duration of the test period, and showed no signs of degradation. They did perform significantly differently due to the different climatic conditions. The results also show that the combination of ambient temperature difference together with relative humidity impacts the performance of the modules. Calculated outdoor yearly efficiencies are 19.05% and 18.36% for two integrated back contact mini-modules tested in Petten-Netherland and Ankara-Turkey, respectively. The temperature coefficients of the modules are also calculated and compared with two commercial photovoltaic modules.
- MakaleYalnız künye2020A novel billing approach for fair and effective demand side management: Appliance level billing (AppLeBill)
Çakmak, Recep; Altaş, İsmail Hakkı
Demand side management (DSM) is an important part of smart electrical grid studies due to high energy efficiency it provides. Effective DSM techniques are hinged on participation level of the customers and control manner of their loads so if there is no fair and appropriate management, customers will not embrace demand side management applications. Besides, the customers might not participate to the demand response process willingly if their comforts are not considered. Therefore, the DSM systems must consider fairness and customer's comfort as well as distribution system objectives. Multifarious DSM systems have been proposed in the literature, however, the fair billing has not included as a parameter in most of these studies. This paper introduces a novel billing approach based upon appliance level billing (AppLeBill) for fair and effective demand side management. The proposed AppLeBill idea offers a billing strategy such that time-shiftable appliances (TSAs) in a residence may have a separate billing rate rather than a single billing rate for total electricity usage. The proposed AppLeBill concept includes three different schemes which are explained and simulated in order to compare each other in terms of their potential benefits.
- MakaleYalnız künye2020An EEG-based stereoscopic research of the PSD differences in pre and post 2D&3D movies watching
Manshouri, Negin; Maleki, Masoud; Kayikcioglu, Temel
Despite knowing the reality of three-dimensional (3D) technology in the form of eye fatigue, this technology continues to be retained by people (especially the young community). To check the influences of the human brain's power spectrum density (PSD) pre and post a 2D and 3D movie watching, a five-member test group was arranged. In this study, electroencephalogram (EEG) was used as a neuroimaging method. EEG recordings of five individuals were taken both before and after watching 2D and 3D movies. The main framework of this study was to analyze the effects of power spectrum density (PSD) of the human brain by testing all EEG frequency bands before and after 2D and 3D movie watching, also to determine effective brain lobes, and consequently, EEG channels. After 2D/3D EEG recording, this record was divided into three stages for analysis. These stages consisted of Relax, Watching, and Rest. This benchmarking analysis included I) before and after watching the 2D movie (R2b and R2a), II) before and after watching the 3D movie (R3b and R3a), and III) after watching the 2D/3D movie (R2a and R3a). In the Relax and Rest stages, the 2D/3D EEG power differences in all channels of brain regions for the five EEG bands, including delta (δ), theta (θ), alpha (α), beta (β), and gamma (γ), were analyzed and compared. The PSD based on short-time Fourier transform (STFT) was used to select the dominant bands in this study. Feature extraction was performed on the preprocessed EEG signals using STFT and discrete wavelet transform (DWT). In the 2D analysis, δ, θ, α, and β acted as dominant bands, in 3D, δ, θ, and α were dominant bands, and in 2D/3D, δ and α were selected as meaningful and dominant bands. Partial least-squares regression (PLSR) and support vector machine (SVM) classification algorithms were considered in order to classify the obtained R2a and R3a EEG signals. After the dominant band selection, the correct choice of effective channel combinations in these bands resulted in the percentage of high success of classifiers for Stage III. Taking into account the optimum number of channels, the best percentage of classification accuracy for the average of PLSR and SVM classification results by considering the best channels of SVM and DWT feature extraction method is 91.83% and 80.73% respectively.
- MakaleYalnız künye2020Evaluating the feasibility of blockchain in logistics operations: A decision framework
Ar, Ilker Murat; Erol, Ismail; Peker, Iskender; Ozdemir, Ali Ihsan; Medeni, Tunc Durmus; Medeni, Ihsan Tolga
The main purpose of this study is to investigate the feasibility of blockchain technology in logistics industry using a quantitative approach. To this end, a decision framework is proposed based on a multi-criteria decision structure that incorporates AHP into VIKOR under Intuitionistic Fuzzy Theory. This integration presents different solutions and rankings based on different decision-making strategies and also captures uncertainty in the evaluation process. While Intuitionistic Fuzzy AHP calculates the importance weights of the proposed criteria indicated as scalability, privacy, interoperability, audit, latency, visibility, trust, and security, Fuzzy VIKOR ranks the logistics operations demonstrated as materials handling, warehousing, order processing, transportation, packaging, fleet management, labeling, vehicle routing and product returns management. The proposed decision framework was applied in a large-scale logistics company located in Turkey. The findings of this study suggest that while the most important criteria are security, visibility and audit, the most feasible logistics operations proved to be transportation, materials handling, warehousing, order processing and fleet management in a possible blockchain implementation. The decision framework in this study may enable decision makers to evaluate the feasibility of blockchain in logistics operations, which is one of the main research gaps in the current blockchain research. Furthermore, this is the first study that integrates AHP and VIKOR methods under Intuitionistic Fuzzy Theory in the context of blockchain.
- MakaleYalnız künye2020Development of a healthy corn-based snack with sage (Salvia officinalis L.) seed
Yuksel, Ferhat; Ilyasoglu, Huri; Baltaci, Cemalettin
A healthy corn-based snack was developed from the corn flour and sage (Salvia officinialis L.) seed flour. The effects of the process variables (sage seed flour: 0–15%, frying temperature: 170–190 °C, and frying time: 40–60 s) on the nutritional properties, fatty acid composition and oxidative stability of the snack chips were evaluated via Response Surface Methodology (RSM). The response models explaining 72–96% variability in the responses were obtained. Only sage seed flour presented significant effects on the nutritional properties (p < 0.05). The interaction term of sage seed flour and frying temperature showed significant effects on the fatty acid composition (p < 0.05). The sage seed flour could decrease total starch and in vitro glycemic index and increase total dietary fiber. The snack chips contained unsaturated fatty acids more than 60%, and their oils had acceptable peroxide value. The fortification of corn-based snack with sage seed enhanced the nutritional value.
- MakaleYalnız künye2020Temporal, geochemical and geodynamic evolution of the Late Cretaceous subduction zone volcanism in the eastern Sakarya Zone, NE Turkey: Implications for mantle-crust interaction in an arc setting
Aydin, Faruk; Oğuz Saka, Simge; Şen, Cüneyt; Dokuz, Abdurrahman; Aiglsperger, Thomas; Uysal, İbrahim; Kandemir, Raif; Karslı, Orhan; Sarı, Bilal; Başer, Rasim
The Late Cretaceous Artvin volcanic rocks (LCAVs) from the eastern Sakarya zone (ESZ) of NE Turkey are composed of mafic/basaltic (S1-Çatak and S2-Çağlayan) and felsic/acidic (S1-Kızılkaya and S2-Tirebolu) rock types that occurred in two successive stages: (i) first stage (S1: Turonian–Early Santonian) and (ii) second stage (S2: Late Santonian–Campanian). Clinopyroxene thermobarometric results point that the S2-Çağlayan basaltic rocks have crystallised at higher temperatures and under deeper crustal conditions than those of the S1-Çatak basaltic rocks. The LCAVs show a wide compositional spectrum, ranging from tholeiite to calc-alkaline/shoshonite and are typically represented by a geochemical composition resembling subduction-related arc rocks although the 87Sr/86Sr(i) (0.7044–0.7071) and ɛNd(i) values (−0.63 to + 3.47) as well as 206Pb/204Pb(i) (18.07–18.56), 207Pb/204Pb(i) (15.57–15.62) and 208Pb/204Pb(i) (37.12–38.55) ratios show very limited variation. The parent magmas of the S1-Çatak and S2-Çağlayan mafic volcanic rocks were derived from underplated basaltic melts that originated by partial melting of metasomatised spinel lherzolite and spinel-garnet lherzolite, respectively. It is proposed that the compositions of the S1-Kızılkaya (mainly dacitic) and S2-Tirebolu (rhyolitic to trachytic) felsic rocks were particularly controlled by metasomatised mantle–crust interaction and MASH zone + shallow crustal fractionation processes. Our data, together with data from previous studies, suggest that the S1- and S2-mafic and felsic rocks of the LCAVs (~95–75 Ma) are the products of two-stage volcanic event that took place during the northward subduction of the northern Neotethys Ocean (NNO).
- MakaleYalnız künye2020Hollow porous gold nanoparticle/reduced graphene oxide composite films for electrochemical supercapacitor applications
Bahar, Necmiye; Ekinci, Duygu
Here, we report the synthesis of hollow porous gold nanoparticles-decorated reduced graphene oxide (HPAuNPs/RGO) nanocomposites and their electrochemical performances as active electrode material for supercapacitors. Accordingly, the HPAuNPs were first prepared using a simple solution phase template method according to the modified literature procedure, and the size control of hollow porous gold particles was achieved by varying the concentration of hydroquinone used as the reducing agent. Then, the surface of the RGO nanosheets was decorated with HPAuNPs through the self-assembly approach. The structural and morphological features of synthesized nanoparticles and nanocomposites were evaluated by spectroscopic and morphologic methods. Also, the electrochemical supercapacitive performances of the HPAuNPs/RGO/GC nanocomposite electrodes as both cathode and anode materials were analyzed in Na2SO4 solution using electrochemical methods. As a control sample, the RGO/GC electrode was also examined under identical experimental conditions. The results indicate that the composite materials display higher specific capacitances (107–325 F/g) compared with bare RGO (55 and 37 F/g) at a potential scan rate of 20 mV/s. Furthermore, it is obtained that the specific capacitances of the composite electrodes based on hollow porous gold nanoparticles are larger than those of previously reported supercapacitors with spherical gold nanoparticles/graphene as electrode materials. The improved electrochemical properties of the HPAuNPs/RGO/GC nanocomposite electrodes can be ascribed to the hollow and porous structure of the gold particles on RGO sheets.
- MakaleYalnız künye2020Optimization of ultrafast laser parameters for 3D micromachining of fused silica
Dogan, Yusuf; Madsen, Christi K.
We present an optimization study on laser parameters for 3D micromachining of fused silica to achieve critical goals for practical applications including high surface quality, high volume production, and complex surfaces by ultrafast laser direct writing assisted chemical etching. We conducted experiments on laser pulse width of 300 fs and 1 ps, pulse energy ranging from 0.1 µJ to 1.6 µJ, three different polarizations (circular, parallel and perpendicular) and number of overlapped pulses from 3 to 10,000 at 1030 nm with up to 2 MHz repetition rate to investigate their effect on nanogratings and one dimensional (1D) channel and two dimensional (2D) planar surface selective etching on 1 mm thick fused silica. In one configuration, we achieved 21.8 nm RMS surface roughness with 80 µm Gaussian filtering and in another configuration, we estimated the maximum writing speed to be 1.25 m/s for given 2 MHz repetition rate with less than 400 nm filtered root mean square (RMS) surface roughness at a 1 mm2 area which covers the thickness of the glass.
- MakaleYalnız künye2020The effect of expressed breast milk, swaddling and facilitated tucking methods in reducing the pain caused by orogastric tube insertion in preterm infants: A randomized controlled trial
Apaydin Cirik, Vildan; Efe, Emine
Background: Orogastric tube feeding is used to support the nutrition of preterm infants. Although nonpharmacological methods are effective in reducing the pain caused by orogastric tube insertion, only limited studies have been found addressing this pain. No study has used combined nonpharmacological methods to reduce this orogastric tube insertion pain. Objective: This randomized controlled study aims to compare the effects of expressed breast milk, swaddling, facilitated tucking, expressed breast milk+swaddling, expressed breast milk+facilitated tucking and routine care methods on preterm infant pain and the physiological parameters (i.e., heart rate, oxygen saturation) before, during and after orogastric tube insertion procedures. Design: Randomised controlled trial. Setting: Three level III neonatal intensive care units in Turkey. Method: Preterm infants born at 32–34 weeks gestation were randomly assigned to six groups: routine care (n = 33), swaddling (n = 30), facilitated tucking (n = 32), expressed breast milk (n = 31), swaddling+expressed breast milk group (n = 30), and facilitated tucking+expressed breast milk group (n = 31). Orogastric tube insertion included four phases: baseline (the last one minute of 30 min without stimuli), the insertion, recovery (one minute after insertion), and recovery (two minutes after insertion). The four phases were videotaped. Premature infant pain profile score, heart rate and oxygen saturation were assessed by two independent evaluators who were blinded to the purpose of the study. Data were assessed by analysis of variance for the multiple repeated measurements, bonferroni and generalised estimating equation logistic regression. Results: There was a significant main effect of the intervention groups for all the pain and physiological parameters (heart rate: F = 3.99, p = 0.001; oxygen saturation: F = 5.22, p<0.001; pain profile 1 score: F = 9.55, p<0.001; pain profile 2 score: F = 9.74, p<0.001). The use of the nonpharmacological methods combined or alone was more effective in reducing infants’ pain profile score and physiological variables than routine care. Infants receiving swaddling+expressed breast milk had significantly lower pain profile scores during the insertion (phase2) (5.2 ± 1.7) than those receiving routine care (9.5 ± 3.6), swaddling (8.8 ± 2.9), facilitated tucking (7.2 ± 3.2), expressed breast milk (7.9 ± 2.6), facilitated tucking+expressed breast milk (6.6 ± 2.3) (p<0.001). The breast milk group had 6.195 times more pain than the swaddling+expressed breast milk, while the facilitated tucking group had 6.301, the facilitated tucking+expressed breast milk group had 3.107, the control group had 13.015, and the swaddling group had 7.892 times more pain. Conclusion: The swaddling+expressed breast milk method is clinically better pain relief nonpharmalogical option and is the recommended method to nurses for the orogastric tube insertion procedures, preterm infants.
- MakaleYalnız künye2020Finite element study on axially loaded reinforced Square Hollow Section T-joints at elevated temperatures
Ozyurt, E.
This study numerically investigates the elevated temperature resistance of collar plate and doubler plate reinforced Square Hollow Section (SHS) T-joints subjected to brace axial compressive load. The extensive numerical simulations were performed to examine the effects of the geometrical parameters of main members and reinforcing plate on the fire resistance of reinforced SHS T-joints after verification of the numerical models based on the available test results. The corresponding unreinforced joints were also analysed as reference resistance at five different temperature levels (20 °C, 400 °C, 500 °C, 600 °C, and 700 °C). Results indicate that the elevated temperature capacity of SHS T-joints can be significantly increased by using a collar plate or a doubler plate. Although the initial stiffness of the doubler plate reinforced joints was higher than the collar plate reinforced joints, their capacity was similar to each other. Also, the fire resistance of the reinforced joints mainly depended on the brace-to-chord width ratio and reinforcing plate thickness to chord wall thickness ratio. However, there was no beneficial effect on the fire resistance of reinforced joints when the thickness of the reinforcing plate was greater than 1.5 times the chord wall thickness. Moreover, there was an insignificant effect of half-width to thickness ratio of the chord, reinforcing length and reinforcing type as long as the required limit values of the reinforcing length and width were used based on the Eurocode 3 EN 1993-1-8. It is worth mentioning that modifying the steel yield strength in the ambient temperature design method to calculate the capacity of the reinforced SHS T-joints at elevated temperatures may be unsafe. A new design method was developed to predict the capacity of a collar plate and doubler plate reinforced SHS T-joints subjected to brace compressive load in fire.
- MakaleYalnız künye2020Dynamic properties of sand-bitumen mixtures as a geotechnical seismic isolation material
Kuvat, Ahmet; Sadoglu, Erol
Geotechnical seismic isolation (GSI) has been emerged as an economical and alternative method in recent years that reduces earthquake that will affect the superstructure. Crumb rubber-granular soil mixtures (SRM) are generally used as damping geomaterial in this method. However, the major disadvantage of SRM is that the addition of rubber leads to significant reduction in stiffness of the granular soil. In this study, dynamic properties (secant shear modulus (Gsec) and damping ratio (D)) of sand and bitumen mixtures (SB) which can be used as damping materials in GSI systems were determined by cyclic triaxial tests. In addition, monotonic triaxial tests were performed to determine the pre- and post-cyclic behavior of the mixtures. In the cyclic tests, the effect of bitumen penetration and content on the energy absorption capacity of the bituminous specimens was examined depending on cyclic stress ratio (CSR), cell pressure and loading frequency. According to the findings, it was determined that higher bitumen penetration and (CSR) result in decrease of Gsec and increase of D, yet the increase in confining pressure and the increase in loading frequency have the opposite effect. For the specimens prepared with both bitumen types, it was specified that the D increased depending on the increase of bitumen content, and the highest Gsec value was observed to be bitumen content of 8%. Moreover, the findings obtained from the monotonic triaxial tests showed that after a high number of cyclic loading, the peak deviatoric stresses of the SB samples increase slightly.
- MakaleYalnız künye2020Symbiotic Organisms Search Algorithm for multilevel thresholding of images
Küçükuğurlu, Büşranur; Gedikli, Eyüp
Thresholding is a frequently used method in image processing because of its consistency and low computational cost. Otsu's and Kapur's methods are two important techniques that were proved to be best thresholding methods. However, they have high computational complexity when extended to multilevel thresholding because of their exhaustively search. Recently, meta-heuristic algorithms have been successfully applied for thresholding problems. In this study, six different meta-heuristic algorithms based on Otsu's and Kapur's functions; Particle Swarm Optimization (PSO), Firefly Algorithm (FA), Symbiotic Organisms Search (SOS), Artifical Bee Colony (ABC), Genetic Algorithm (GA) and grey Wolf Optimizer (GWO) were used for multilevel thresholding problem and compared. Experimental results suggest that SOS, PSO and FA algorithms often have higher fitness values than other algorithms. Especially when more than two threshold values are determined, SOS algorithm mostly gives higher fitness values. PSNR and SSIM results of the algorithms are similar. In terms of computational complexity, the GWO algorithm has the fastest convergence. For standard deviations of objective functions; more stable results were obtained with SOS based on Kapur's function, SOS and PSO based on Otsu's function. Also, SOS based on Kapur's function was found to be the most successful algorithm in the Friedman test. As a result, although the GWO approached faster, the SOS algorithm produced more consistent results for both objective functions.
- MakaleYayıncıda açık erişim2019An experimental study on the compressive response of CFRP honeycombs with various cell configurations
Pehlivan, Levent; Baykasoğlu, Cengiz
The experimental investigation on the compressive response of carbon fiber reinforced polymer (CFRP) honeycombs with various cell configurations was carried out in the present work. The CFRP honeycomb specimens were manufactured by corrugation technique, in which the prepreg CFRP sheets were first corrugated into the certain shape using corrugated aluminum moulds under heat and pressure, and then the corrugated CFRP sheets were glued and stacked to construct honeycomb specimens. Twenty-seven groups of specimens were experimentally tested to examine the effects of cell geometry (i.e., square, circular, and hexagonal), cell wall thickness and height on the quasi-static out-of-plane crushing performance of the honeycombs. The square, circular, and hexagonal honeycomb specimen groups were designed to have almost the same weights. The results showed that the cell wall thickness is an significant parameters on the overal crushing response of the CFRP honeycombs while the out-of-plane compressive strenght of the honeycombs is generally independent of the height. It is observed that the hexagonal specimen groups have generally superior crushing performance in comparison with the square and circular counterparts due to their large double foil bonding surfaces. The experimental results also revealed that the crushing properties of the honeycomb structures with the core densities of 157–282 kg/m 3 could be increased more than two times with the appropriate selection of cell configurations.
- MakaleAçık Erişim2019Experimental and numerical studies on axially loaded reinforced square hollow section T-joints
Ozyurt, E.; Das, S.
This paper presents outcomes of experimental and numerical studies completed on unreinforced, collar plate reinforced and doubler plate reinforced Square Hollow Section (SHS)T-joints subjected to axial compressive loading on the brace member. A total of nine full-scale SHS T-joint specimens were fabricated and tested, in which six specimens were reinforced with collar plate and doubler plate. Non-linear finite element (FE)models were developed using finite element code, ABAQUS. Test data was used to validate these FE models. Subsequently, validated FE models were used to conduct an extensive parametric study to investigate the effect of various geometrical parameters of main members and reinforcement plates on the ultimate capacity of reinforced SHS T-joints. The parametric study found that use of both collar and doubler plate reinforcements significantly increase the ultimate capacity of SHS T-joints. Thickness of the reinforcing plate has a positive effect if the thickness of the reinforcing plate is limited to twice the thickness of the chord member. This study, however, found that the capacity of a reinforced SHS T-joint is not dependent on the type of reinforcing plate. The study concludes that the maximum capacity that can be achieved from a reinforced joint is about double the capacity of a similar unreinforced joint. It was found that the Eurocode EN 1993-1-8 overestimates the capacity of reinforced SHS T-joints. Therefore, a new design method for predicting the ultimate capacity of the collar plate and doubler plate reinforced SHS T-joints was developed and this new design method is presented in this paper.
- MakaleYalnız künye2019A new use of the ant system algorithm for the max-mean dispersion problem
Cura, Tunchan; Özdemir, Muhlis
This study addresses an NP-hard problem known as the max-mean dispersion problem (MaxMeanDP), which belongs to a well-known class of diversity problems. In view of the increasing importance of parallel computing, this study proposes an ant system (AS) approach to the MaxMeanDP in which ants execute the search process in parallel. Moreover, by proposing a rather different use of the pheromone trail and visibility compared to the original AS, a new AS algorithm is introduced that runs in parallel. Our analysis indicates that the new use of the pheromone trail and visibility significantly contributes to the quality of the solution. The results show that the proposed method is effective, efficient and comparable to other approaches.
- MakaleYalnız künye2019U-Pb geochronology, bulk-rock geochemistry and petrology of Late Cretaceous syenitic plutons in the Gölköy (Ordu) area (NE Turkey): Implications for magma generation in a continental arc extension triggered by slab roll-back
Temizel, İrfan; Arslan, Mehmet; Yücel, Cem; Yazar, Emel Abdioğlu; Kaygusuz, Abdullah; Aslan, Zafer
Late Cretaceous felsic plutons in the Eastern Pontides orogenic belt of Turkey are found in varying ages, sizes and compositions. The Late Cretaceous syenitic bodies, namely Direkli and Yeniköy Tepe plutons in the Ordu area, intruded into the Late Cretaceous volcanics and volcanoclastics, and compositionally consist of syenite and minor quartz-syenite with mainly granular and rarely porphyric, poikilitic and perthitic textures. The studied plutons contain K-feldspar, plagioclase, quartz, clinopyroxene, biotite and minor hornblende, and Fe-Ti oxide, apatite, and zircon. Mineral thermobarometer estimations imply that the syenitic plutons were crystallized in P-T conditions representing mid to shallow crustal levels. Petrochemically, these syenitic plutons show I-type, metaluminous-peraluminous transitional (A/CNK = 0.85–1.04) and shoshonitic features. LA-ICP-MS U-Pb zircon dating on the syenitic plutons yielded weighted mean ages of 78.5–72 Ma. Primitive mantle-normalized trace element patterns of the studied plutons are characterized by negative anomalies of Ba, Sr, Nb, Ta and Ti, and enrichment in Rb, Th, K, Ce and La. The chondrite-normalized rare earth element (REE) plots of the studied plutons show moderately enriched concave-shaped patterns (La N /Lu N = 10.3–10.7 for the Direkli pluton; La N /Lu N = 6.8–11.7 for the Yeniköy Tepe pluton) with negative Eu anomalies. The plutons have 87 Sr/ 86 Sr ratios (0.705368–0.706954), 143 Nd/ 144 Nd ratios (0.512600–0.512672), 206 Pb/ 204 Pb ratios (19.29–19.52) and 207 Pb/ 204 Pb ratios (15.65–15.67). The geochemical data, as well as regional geology, suggest that the Late Cretaceous syenitic plutons have formed in an extensional continental arc setting triggered by slab roll-back. The parental magma of syenitic plutons was derived from melts of lower crustal materials (metabasalt/metaandesite) and lithospheric mantle component.
- MakaleAçık Erişim2019Application of multi pass high pressure homogenization to improve stability, physical and bioactive properties of rosehip (Rosa canina L.) nectar
Saricaoglu, Furkan T.; Atalar, Ilyas; Yilmaz, Volkan A.; Odabas, Halil I.; Gul, Osman
The effect of high pressure homogenization (HPH) on physical and bioactive properties of rosehip nectar was investigated. Rosehip nectar has a sedimentation problem while waiting on the market shelf during the sale, for solving this problem, nectars were passed 1, 2 and 3 times through 75, 100 and 125 MPa pressures. Mean particle size decreased as pressure and pass number increased (p < 0.05), whereas zeta potential did not change (p > 0.05). Microstructural images revealed that HPH treatment disrupted the cells and caused to release of cell materials to serum. HPH treatment increased the ΔE values (from 2.48 to 6.03). HPH treated samples showed no sedimentation during storage for 15 days. All samples showed shear thinning behavior and were characterized as weak gel network (G′ > G″). Total phenolic content and ascorbic acid results were decreased by HPH treatments due to increasing outlet temperatures of product, however, antioxidant capacity of nectars increased after treatment due to increasing total carotenoid content. This study indicated that HPH treatment could solve the sedimentation problem during shelf life with minimally affecting bioactive and physical properties of rosehip nectar.
- MakaleAçık Erişim2019A numerical investigation of static resistance of welded planar steel tubular joints under in-plane and out-of-plane bending at elevated temperatures
Ozyurt, E.; Wang, Y.C.
This study presents the results of a numerical investigation on static resistance of welded planar steel tubular joints under in-plane and out-of-plane bending moments at elevated temperatures. The numerical simulations were carried out using the commercial finite Element software ABAQUS v6.14-1 and the simulation model was validated by comparing against test results for CHS joints under brace in-plane bending at elevated temperatures. Extensive numerical parametric simulations were performed for CHS/SHS/EHS joints under in-plane and out-of-plane bending at elevated temperatures, to establish a database of results covering a wide range of geometrical parameters, including brace to chord diameter ratio, the angle between brace to chord members, and chord diameter to twice chord thickness ratio. The ratios of joint elevated temperature resistance to ambient temperature resistance were compared to the steel yield strength reduction factor, the steel Young's modulus reduction factor, and the average of the above these reduction factors at different elevated temperatures. Based on the comparisons, it has been found that using the reduction factor for the yield strength of steel to modify the ambient temperature equations will overestimate the resistance of joints at elevated temperatures. As a simplified and safe recommendation, the ambient temperature joint resistance equations can be modified by the average reduction factors for the Young's modulus and yield strength at elevated temperatures. This modification factor can be increased to the yield strength reduction factor when the brace and chord widths/diameters are the same.