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Design optimization by employing thermal distrıbution in 3-phase induction motors
Get PDFBasit ve sağlam yapıları nedeniyle asenkron motorlar, endüstriyel uygulamalarda en yaygın elektrik motorlarıdır. Artan malzeme maliyetleri, elektrikli otomobiller ve beyaz eşya sektörü gibi alanlarda kompakt yapıda elektrik motorlarına duyulan ihtiyaç ve değişken hızlı tahriklerin yaygın kullanımı nedeniyle makinanın çeşitli kısımlarındaki sıcaklık artışının belirlenmesi büyük önem taşımaktadır. Bu çalışmada, asenkron motorlarda sürekli halde sıcaklık dağılımını ve ısıl geçici rejimi belirlemek üzere akım kaynaklı elektriksel devre benzeşimine dayanan bir ısıl model oluşturulmuştur. Isıl modeli oluşturmakta kullanılan kritik parametreler belirlenmiş ve bu parametrelerin hesabı incelenmiştir. Farklı yükleme durumları için elde edilen sonuçlar deneysel yolla elde edilen verilerle kıyaslanarak modelin doğruluğu gösterilmiştir. Asenkron motorun sürekli rejimdeki işletme büyüklüklerini hesaplayan bir tasarım programı yazılmıştır. Gerek imalatçı, gerek kullanıcı açısından motor performansının iyileştirilmesi ve maliyetin düşürülmesi büyük önem taşımaktadır. İşletme maliyetinin toplam maliyetin büyük bir kısmını oluşturması nedeniyle, işletme maliyetinin, motorda kullanılan aktif malzemelerin iyileştirilmesi ve motor tasarım değişkenlerinin optimizasyonu yoluyla azaltılması büyük önem taşır. Isıl model, asenkron motor tasarım programıyla birleştirilerek motor tasarım optimizasyonu için kullanılmıştır. Sabit güçte, mevcut tasarıma göre daha yüksek verimli, kompakt ve sıcaklık artışı minimumlaştırılmış bir motor tasarımı gerçekleştirilmiştir. Optimizasyon yöntemi olarak ısıl işlem benzeşimi kullanılmış ve asenkron motorun çok amaçlı tasarım optimizasyonu için basit ve verimli bir yapay ısıl işlem algoritması geliştirilmiştir. Anahtar Kelimeler: Isıl modelleme, yapay ısıl işlem benzeşimi, tasarım optimizasyonu, çok amaçlı optimizasyon.Induction motors are most common electric motors for industrial application due to their simple construction and robustness. Because of increased material costs, need of compactnes for many applications and extensive use of variable speed drives, the temperature rise should be investigated in various part of an induction motor. An useful method of thermal analysis is to use an equivalent electrical circuit. By electro-thermal analogy based on well-known Poison and Laplace equations, thermal behaviour of induction motor could represented through electrical elements, such as resistors, capacitors and independenet current sources. Induction motor can be geometrically divided to eight components which are connected to each other via thermal resistances. Each part has a bulk thermal storage. In the network, a node connotes the mean temperature of the component. All network parameters are derived from dimensional information of motor components, thermal properties of materials used in motor construction and several thermal constants such as thermal conduction and convection coefficents. Different operating power losses of motor form the current sources which represent the heat sources. The overall network can be represented as a linear set of 8 equations. A thermal model for estimating the steady-state temperature distribution and transient thermal behaviour of a 3-phase induction motor was developed in this study. Critical parameters of the model such as convection film coefficents of air gap, end cap air and frame, frame-stator yoke thermal contact coefficent were determined and their computations and experimental methods were discussed. The accuracy of the model for both steady state and transient cases was proven by comparing the calculated results that obtained from various load conditions with those of the experimental results. The temperatures at different points of motor stator and body were obtained using thermocuple sensors and infrared thermometer. The results were also verified by comparing a 2D finite element model. To show the sensivity of the model to its component, a sensivity analaysis was conducted. It is important to improve the performance and to reduce the cost of the machine from the both manufacturers and custormers point of view. Operating cost is the main part of the total cost. It is achieved by increasing motor efficiency through improving the materials and optimizing the motor design variable. The thermal model integrated with design program was used for induction motor design optimization. The aim of design optimization is to several objective functions F(x) reach their optimum values while keeping others in their acceptable limits. Si-mulated annealing was choosen as optimization method. This process is based on an analogy from thermodynamics where a system is slowly cooled in order to achieve its lowest energ state. Simulated annealing is an hill climbing iterative search in which sometimes the points corresponding to worse objective function values can be accepted in order to avoiding to trapped in a local minima. The algorithm employs a random search, which not only accepts changes that decrease objective function, f, but also some changes that increase it. The latter are accepted with a probability, where is the decrease in F and T is an independent control parameter that simulates the impact of thermodynamic temperature in physical annealing. A simple and efficient simulated annealing algorithm was developed to obtain multi-objective design optimization of the induction motor. The accuracy of algorithm was proven by optimizing some well-known optimization test functions. The algorithm was also tested by comparing it with the well known methods such as pattern search and adaptive simulated annealing. Some of the the selected objective functions are temperature, efficiency and weights of active parts such as stator and rotor magnetic circuits and windings. These objectives were optimized under several constraints such as start-up torque and current, nominal and pull off torques, magnetizing current, and power factor. The induction motor's steady state performance was calculated by a design program which was written as a part of this study. Only dominated solutions were accepted. A more efficient, more compact motor design with minimum temperature rise was achieved for constant power. Keywords: Thermal modelling, simulated annealing, design optimization, multi-objective optimization
A new behavior combining method for mobile robots
Get PDF Davranış Temelli Robotlarda karmaşık karar verme süreci, bir giriş bilgisine belirli şekilde yanıt veren basit davranışlar üzerine kurulmuştur. Her bir davranış o anki giriş bilgilerine göre yanıtını belirler, sonra bu yanıtlar birleştirilerek elde edilen sonuç robotun kararı olarak uygulamaya konulur. Her biri ayrı güdü ile hareket eden davranışlar her zaman paralel istemlerde bulunmayabilir; birbirlerine zıt istemlerde bile bulunabilirler. Dolayısıyla robotun vereceği kararın başarısı, yanıtların ne şekilde birleştirileceği ile yakından ilişkilidir. Davranış tanımından veya karar verme kurallarından dolayı sürecin içerdiği belirsizlikler problemi zorlaştırmaktadır. Bu makalede, davranışların koordinasyonu için Belirsizlik Matrisi kavramı çerçevesinde yeni bir yöntem önerilmektedir. Bir davranışın tüm yanıtları Belirsizlik Matrisi ile gösterilip birleştirilerek davranışın ana yanıtı, ardından bu şekilde bulunan değerler bir araya getirilerek karar verme sisteminin ortak yanıtı elde edilmektedir. Yöntemin sınanması için; ‘hedefe doğru git’, ‘engelden kaçın’, ‘gezin’ ve ‘doğru git’ şeklinde dört davranışı bulunan bir mobil robot ele alınmış ve engellerin bulunduğu bir ortamda hedef noktasına gitme problemi için bilgisayar ortamında simülasyon düzeneği oluşturulmuştur. Bu çalışmada önerilen yöntem, davranış seçme matrisine göre belirli bir davranışın yanıtını ana yanıt olarak kabul eden klasik yöntem ile karşılaştırılmış ve önerilen metot açısından olumlu sonuçlar elde edilmiştir. Farklı yerleşim düzenleri ile yapılan denemelerde, önerilen yöntemin, robotu hedefe daha kısa sürede ulaştırdığı, yol süresince robotu engellerden daha uzakta tuttuğu ve ardı ardına gelen çelişkili adımları azalttığı görülmüştür. Anahtar Kelimeler: Davranış temelli robotlar, belirsizlik matrisi, belirsiz bilgi.Because robots are becoming more complex every day, the decision-making system which determines how the robot shall act, also gets equally complicated, becoming more difficult to manage. These difficulties may be overcome by grouping all movements and tendencies of the robot as "behaviors". A behavior is a mechanism which describes the reaction and response corresponding to a stimulus. From this perspec-tive, decision-making systems are revised into behaviors and consequently simplified. In this approach, the problems of which behavior to consider and how to combine responses to get an optimum result, are critical factors for attaining success.Response of a behavior is independent of the global purposes of the robot; it always gives the same reaction to the same action. Therefore it should be managed with a higher-level layer so that the robot could accomplish its global purposes. The responses of behaviors are converted into action by evaluation according to a coordination mechanism and then necessary action is taken. The success of the behavioral robot is closely related to the coordination system. The most widely used coordination methods are as follows; (1) Arbitration: The behavior with the highest priority will be executed, (2) Action-Selected: The selected action depending on the conditions and preferences present at the time is executed, (3) Voting: The response winning the majority of the votes is taken into account and the rest is disregarded, (4) Collective: The responses of the active behaviors are collected and the necessary action is executed.The process of combining behaviors involves various types of uncertainties including (1) inputs used to determine responses of the behaviors, (2) rules regarding the type of response given by the "behavior" to these inputs, (3) if more than one behavior is considered, the rules to determine which one of these should be selected as the "dominant behavior." A tool is necessary to represent and process these uncertainties existing in the responses. Uncertainty matrix is able to fulfill this task.A new approach is proposed in this work that coordinates responses of all behaviors using Uncertainty Matrix. In this method, responses of each behavior are represented by Uncertainty Matrix and the combined response of the behavior is calculated. Then the main result is found with the same manner.The navigation problem of behavior-based robots to reach the target point while keeping away from the obstacles was simulated. The simulation environment consists of a 20 m × 30 m sized rectangular platform and one behavioral mobile robot placed in this, one unit of target point, three units of mobile or fixed obstacle blocks with a diameter of 1 m, and one unit of obstacle block with a diameter of 3 m. The robot has four behaviors, namely, move to goal, avoid obstacles, go ahead, and walk around. Two methods of behavior coordination are compared: (1) the classical approach that selects a behavior using behavior selection matrix and (2) the approach proposed in this work that coordinates responses of all behaviors using uncertainty matrix. In the second method, all responses of each behavior are represented by uncertainty matrix and the combined response is calculated. In cycles, 0.2 s each, the situation is reevaluated according to two methods and the robot moves on to the next point.In a typical starting position, the method proposed enables the robot to reach the goal in 61.2 s while the classical method reaches the goal in 78.2 s. The proposed method: (1) Makes the robot reach the goal in a shorter time, (2) Keeps the robot away from the obstacles. The method takes the nearest obstacle into account. Therefore the robot moves by keeping away from the obstacles, (3) Has less consequent contradictory steps, (4) Compared to classic methods, the resultant values obtained by using the uncertainty matrix are more meaningful. In this method, the probability value, that is "the certainty of selection of the angular value," is also obtained besides the angular value.Positive results have been achieved in the simulation of the method proposed for the combination of the uncertainty, represented by uncertainty matrix, in the responses of the behaviors related to the determination of direction in mobile robots. Improvements at other stages of the decision-making processes of the behavior-based robots are possible by using the concept of the uncertainty matrix. Keywords: Behavior based robots, uncertainty matrix, uncertain knowledge
Forecasting monthly precipitation for arid regions using conditional feed-forward backpropagation artificial neural network combined with Markov chain
Get PDFUnderstanding, modeling, prediction or forecasting of precipitation has always been important. Precipitation is the driven factor of hydrological cycle and is one of the main sources of water without which the humankind cannot survive. In particular, it becomes the unique source of water in arid regions where surface water courses are generally intermittent or ephemeral in nature. In such regions the main water income is from the groundwater storages that are again fed by precipitation. In such regions, therefore, precipitation becomes much more interesting than runoff to analyze as flow records are generally insufficient in length to obtain accurate estimations. Analysis of precipitation is evident not only because of that reason but also for agricultural and socio-economical activities, for increasing human and environmental demands as well as for planning and management of water resources. Precipitation changes both in time and space and affects on other components of the hydrological cycle; i.e. surface runoff, infiltration, groundwater, seepage, percolation, evaporation, transpiration, etc. Time variation comes from the seasonal climatological changes in the atmosphere whereas spatial change is due to the topographical heterogeneity on the earth surface. Precipitation amount should be predicted accurately for an affective water resources management and planning. Prediction of hydrometeorological time series is difficult because of uncertainty in the parameters which affect the time series. In literature, the applications of artificial neural networks to forecast arid-region precipitation are limited. Forecasting monthly precipitation in arid regions is investigated by means of the conditional feed-forward backpropagation artificial neural network combined with Markov chain. Amman meteorological station from the hilly region in Jordan is selected for application. Various homogeneity tests are used for the data, which is found homogeneous according to the results of the tests. The feed-forward backpropagation artificial neural networks, statistical, and stochastic methods provided negative approximations for some of the low precipitation (dry months) whereas Markov chain forecasts are bounded with zero as the lower limit. Prediction using Markov chain does not generate physically unexplainable results mainly because the forecasts of the feed-forward backpropagation combined with Markov chain method are bounded with the minimum (zero) precipitation. Antecedent monthly precipitation data are used as input to the model to predict the total precipitation in the next month. Selection of the inputs is based on the correlation coefficient. For the station analyzed, it is observed that precipitation in any month was highly correlated to its previous two months and its previous year record. A trial-and-error based construction for various artificial neural networks are tested. A total of 28 combinations of input variables are investigated. It is finally ended with an architecture that uses, as input variables, precipitation in two previous months and the previous year?s precipitation of the month to be forecasted. Also a periodical component is added into the input vector to simulate the existing periodicity in the monthly precipitation. Since the sigmoid function is used as the activation function for hidden and output layers, the model input and output are scaled appropriately to fall within the function limit (zero to one). Conditional feed-forward backpropagation artificial neural network combined with Markov chain is trained using the Levenberg-Marquardt training algorithm. After training is over, the weights are used to test the network performance on the test data. In conclusion, it is seen that the conditional model considerably improves the accuracy of the one month ahead precipitation forecasting compared to the unconditional model. Keywords: Monthly precipitation, arid region, artificial neural networks, feed-forward backpropagation, Markov chain, Jordan.Su kaynaklarının etkin bir şekilde planlanması ve yönetimi için yağışın doğru bir şekilde tahmin edilmesi büyük önem taşımaktadır. Hidrometeorolojik zaman serilerinin tahmini, zaman serisini etkileyen parametrelerin belirsizliğinden dolayı en zor işlerden biridir. Yapay sinir ağlarına dayalı kurak bölge yağış tahmin modelleri literatürde çok sınırlı sayıda bulunmaktadır. Bu çalışmada aylık toplam yağışın tahmini için Markov zincirleri eklenmiş koşullu ileri beslemeli geri yayılım yapay sinir ağları yöntemi kullanılmıştır. Uygulama için Ürdün’ün dağlık bölgesinden Amman meteoroloji istasyonu seçilmiştir. Çalışmada kullanılan veriler homojenlik testlerinden geçirilmiş, kullanılan testlere göre Ürdün’ün bu istasyonunun yağış verilerinin homojen olduğu belirlenmiştir. Bu çalışmada geliştirilen modeller, önceki aylara ait gözlenmiş yağış verilerini kullanarak gelecek ayın yağışının tahmin edilmesi prensibine dayanarak kurulmuştur. Deneme-yanılma yöntemi ile çok sayıda model seçeneği üretilmiştir. Girdi sayısı minimum olacak şekilde önce sadece bir önceki ayın yağışının girdi olarak kullanıldığı model seçeneği ile başlanmış, seçilen girdiler farklı hücre sayıları ile denenmiştir. Hücre sayısı girdi sayısı kadar seçilmiş, ampirik bir düşünce ile girdi sayısının iki katına kadar birer birer artırılmıştır. Periyodikliğin etkisinin görülmesi açısından periyodik bileşen de modellerde girdi olarak kullanılmıştır. Denenen her bir modelin performansı Ortalama Karesel Hata (OKH) ve belirlilik katsayısı (R2) ile ölçülmüştür. Markov zincirleri ile birleştirilmiş koşullu ileri beslemeli geri yayılım yapay sinir ağı modelinin kuru ayların belirlenmesinde, en yüksek yağış ve yağış tahmininde büyük başarı gösterdiği anlaşılmıştır. Anahtar Kelimeler: Aylık yağış, kurak bölge, yapay sinir ağları, ileri beslemeli geri yayılım, Markov zinciri, Ürdün
Bitümlü karışımların gerilme-şekil değiştirme davranışı
Get PDFBitümlü karışımların tasarımı için halen yaygın olarak kullanılmakta olan ampirik yöntemler, sıkıştırılmış karışımların gerçek malzeme özelliklerini tam olarak yansıtamamakta ve yalnızca kabul-red ölçütü olarak kullanılabilmektedir. Asfalt kaplama performanslarının tahminine yönelik tasarım yöntemlerinde kullanılan temel malzeme özelliklerinin belirlenmesine gereksinim duyulmaktadır. Üç Eksenli Kayma Mukavemeti (ÜKM) deneyi, özellikle zemin mekaniğinde kohezyonlu ve granüler malzemelerin davranışlarını belirlemekte halen yaygın olarak kullanılmaktadır. Marshall yönteminin yetersiz kaldığı günümüzde ÜKM deneyinin bitümlü karışımların deformasyon davranışının belirlenmesinde daha gerçekçi sonuçlar vereceği düşünülmüştür. Bu çalışmada, agrega gradasyonun ve bağlayıcı yüzdesinin bitümlü karışımların deformasyon davranışı üzerindeki etkileri ÜKM deneyi ile incelenmiştir. Kalıcı deformasyonların yüksek sıcaklıklarda oluştuğu dikkate alınarak deneyler 40, 50, ve 60 oC’lerde gerçekleştirilmiştir. Bu amaçla, 2006 yılında yayınlanan Karayolları Teknik Şartnamesinde yer alan üç farklı karışım tipi (Aşınma Tip-1, TMA Tip-1 ve TMA Tip-2) seçilmiştir. Tek tip bitümlü bağlayıcının (İzmit B 50-70) kullanıldığı çalışmada belirtilen karışım tipleri için Marshall ve statik sıkıştırma yöntemleri ile hazırlanan numuneler üzerinde Marshall tasarımları yapılmıştır. ÜKM deney numunelerinin hazırlanmasında çift taraflı statik sıkıştırma yöntemi kullanılmıştır. ÜKM deneyinden elde edilen gerilme-şekil değiştirme eğrileri, incelenen parametrelerin deformasyon direnci üzerindeki bilinen etkilerini çok iyi derecede açıklamaktadır. Marshall deneyi sonuçları Taş Mastik Asfalt (TMA) karışımların gerçek deformasyon direncini yansıtmazken, ÜKM deney sonuçları agrega gradasyonun deformasyon direncine olumlu etkisini açıkça ortaya koymaktadır. Bu sonuçlar, ÜKM deneyinin karışım tasarımında ve kalıcı deformasyon tahmininde kullanılabileceğini göstermektedir. Anahtar Kelimeler: Bitümlü karışımlar, deformasyon direnci, üç eksenli kayma mukavemeti deneyi, gerilme-şekil değiştirme ilişkisi, agrega gradasyonu, bitüm yüzdesi.All over the world, established and new hot-mix asphalt design methods may be classified as recipe, empirical, volumetric, performed-related and per-formed based. Simulation and fundamental test methods are generally carried out in recently developed performance-related and performance-based mix design methods since they give the best relations between the results obtained in-situ and laboratory. In addition to this, simulation and fundamental test methods measure the material response under various stress conditions. In the analytical design, the fundamental properties of materials of pavement layers are required to determine stress-strain curve of the structure. Well known empirical design methods such as Marshall do not reflect the material properties. On the other hand, Superior Performing Asphalt Pavements (Superpave) which is the cutting edge method in mix design requires complicated and expensive equipment. For this reason, economical and less complicated methods are investigated. The triaxial shear strength test is not new in concept and theoretical development. The triaxial shear strength test has been shown to be suitable for evaluating the strength of asphalt concrete mixtures. The triaxial test is widely used in soil mechanics in order to determine the shearing resistance and stress deformation behavior of cohesive and granular materials under various conditions of axial loadings and confining pressures and drainage conditions of test specimens. Asphalt concrete mixtures which are composed of aggregates, bitumen and air are some extend analogous to soils which are composed of soil solids, water and air. Thus it is logical to apply the theory for the triaxial testing developed in soil mechanic to asphalt concrete mixtures. However, the use of the triaxial test for testing asphaltic paving materials is slow in acceptance by pavement engineers mainly due to the complexity of the test and also the lack of a standard procedure. This is evident by the scarcity of published information on the use of the triaxial test for strength testing of asphalt concrete mixtures since the pioneering work of the Triaxial Institute in the early 1950’s. Research in this direction was discontinued due to the complexity of the laboratory triaxial tests, which are time consuming and the difficulties in relating the test results to field behavior of asphalt mixtures. In this study the deformation resistances of hot-mix asphalt mixtures were investigated by the means of triaxial shear strength test. Effects of grading, bitumen content and the temperature on the deformation resistance were investigated. For this purpose, three different asphalt mixtures (Wearing Course Type-1, SMA Type-1 and SMA Type-) were selected. The Marshall mix design (ASTM D 1559) were carried out on three different mixtures. Triaxial shear strength test was conducted on the specimens prepared by double-plunger static compression method. In total, 132 and 145 were tested for the Marshall Design, triaxial shear strength test, respectively. A preliminary study investigated the compaction energy for Wearing Course Type-1 and Stone Mastic Asphalt (SMA) by using the double-plunger compaction equipment as detailed in ASTM D 1074. Later, optimum bitumen contents of mixtures prepared utilizing both static and Marshall Compactor were determined by Marshall Design method. In experimental study, the effect of mixture gradation and the bitumen content on the deformation resistance were examined by the triaxial shear strength tests. For this purpose, İzmir B 50-70 bitumen were used in three different contents. The triaxial shear strength tests were conducted at temperatures of 40, 50 and 60 oC. According to the results, compared to deviator stress values between Wearing Course Type-1 and SMA mixtures for specimens tested at 40 oC, the discrepancy were relating high than the specimens tested at 50 oC and 60 oC. In addition, the deformation resistance of Wearing Course Type-1 was reduced more than that of SMA mixtures at 50 and 60 oC. It should also be noted that the stress-strain curves related to Wearing Course Type-1 were located under those related SMA mixtures. The results revealed that the effects of gradation on deformation resistance were positive at higher temperatures such as 50 and 60oC. The results revealed that gap grading is superior to continuous grading in terms of deformation resistant. The results revealed that gap grading is superior to continuous grading in terms of deformation resistant. More realistic results were obtained from the stress-strain curves showing the effects of above parameters on the deformation resistance. Keywords: Bituminous mixtures, deformation resistance, triaxial shear strength test, stress-strain, gradation of aggregate, bitumen content. 
Modeling of tsunami waves in the Sea of Marmara
Get PDFIstanbul is the most important city of Turkey in the view of economical, social and cultural aspects. Because of the active faults in the Sea of Marmara, there is always an expectation of an important earthquake that will be harmful for the city and also for the other big cities that are located around the Sea of Marmara such as Bursa, İzmit, Tekirdağ and Yalova. In addition to the earthquake, a tsunami which occurs in the Sea of Marmara can also be a very destructive hazard for Istanbul and other cities around the Sea of Marmara. There are many tsunamis that happened in the Sea of Marmara in the history. The main reason of these tsunamis is the slumps and the landslides that were triggered by an earthquake. One of the most important reasons of the tsunamis on the earth is the submarine landslides. Movement at the sea bottom stirs the above water mass. This causes tsunami waves and these waves damage the coastal areas seriously. The aim of this study is to find the maximum wave heights of possible tsunamis around Tuzla coasts using different scenarios. A submarine landslide that may be occurred after an earthquake or because of any other reason in the Sea of Marmara at the region near to northeast Marmara coasts is taken as the reason of the tsunami in the simulations that are performed in the study. As the solution method, one hybrid method was developed. The main objective of this method is to combine an analytical solution presenting near-field tsunami amplitudes above the submarine mass failure with a numerical solution indicating the tsunami amplitudes in the coastal regions. An analytical model that is frequently used in the literature was applied to find the amplitudes of tsunami waves at the surface of Sea of Marmara above the submarine landslide region. These tsunami waves will be directly affected from the water depth of the Sea of Marmara. It will be also affected by the shore profile when traveling to the coasts. Because of this reason, a computational fluid dynamics model which is based on finite elements method is used in the regions that are very close to the coasts. The model solves the Navier-Stokes equations. Analytical and numerical models were used together in this study. The analytical model is used from the submarine up to sea surface and the numerical model is used for modeling of the movement of the tsunami waves at the sea surfaces. In the border of two models the outputs of analytical model is used as the inputs of numerical model that means the initial and boundary conditions of numerical model is obtained from the analytical model. The output of the analytical model is the tsunami wave amplitudes for each minute of a 900 seconds period. The submarine landslide type that is named as Model2 in the literature was applied in this study. The model was applied to the submarine landslide region that is located between 400m and 800m depth of water surface around Tuzla coast. Time series of the wave amplitudes at the top of the water mass over the landslide region for the landslide model were calculated by using analytical model. These time series were used as inputs of the numerical model. Then the numerical model is performed for simulating the wave propagation in the shallow waters of shore of Tuzla. The simulations for 13 different landslide velocities are performed for the previously determined landslide model on the selected mesh. These velocities were ranging between Cr=10 m/s and Cr=300 m/s. As a result of this, the effects of landslide model and different landslide velocities to the amplitudes of the tsunami waves were observed clearly. In another stage the landslide type and submarine landslide velocities were taken as constant and the thickness and width of the sliding mass were changed. The results of these simulations show that there is a linear relation for the thicknesses and the widths with the wave heights. The equations used in numerical modeling were Saint Venant equations that are derived from Navier-Stokes equations. The equations used in numerical modeling were also changed in this study in order to see the effects of both dispersive and non-dispersive waves to the coast. Keywords: Analytical modeling, numerical modeling, submarine landslide, tsunami, Sea of Marmara.Bu çalışmada Marmara Denizi’nde Tuzla açıklarında bulunan heyelan bölgesindeki bir hareketlenme sonucunda sahilde seçilen belli noktalarda oluşan tsunami dalga yükseklikleri literatürde çok kullanılan bir denizaltı heyelan modeli ile analitik olarak modellenmiş ve heyelan bölgesinin üzerinden itibaren Tuzla kıyılarına kadar nümerik olarak modellenmiştir. Denizaltı heyelanının değişik hızlardaki hareketine göre Tuzla kıyılarındaki dalga yükseklikleri hesaplanmıştır. Çalışmada ele alınan heyelan bölgesi Tuzla açıklarında, 400 m ile 800 m’lik derinlikteki yamaçtadır. Seçilen heyelan modeli için heyelanın üzerindeki su kütlesi yüzeyinde oluşacak dalga genliklerine ait zaman serileri analitik yöntemlerle iki ve üç boyutlu olarak elde edilmiştir. Elde edilen zaman serileri sınırdaki hareketi modellemekte ve bu hareket nümerik yönteme zorlayıcı etki olarak eklenmiş ve kıyıya kadar taşınarak kıyıdaki dalga genlikleri bulunmuştur. Ayrıca çalışma alanında üç boyutlu olarak tsunami dalgalarının ilerleyişi görselleştirilerek tsunami dalgalarının çeşitli bölgelerdeki etkileri anlaşılmaya çalışılmıştır. Kıyıdaki kritik noktalarda oluşabilecek maksimum dalga yükseklikleri hesaplanmıştır. Proje sahası içerisinde seçilen lineer doğrultular boyunca Tsunami dalgalarının ilerleyişi gözlenerek batimetrinin dalga yüksekliği üzerindeki etkisi ortaya konulmuştur. Analitik model Cr=10 m/s ile Cr=300 m/s arasındaki farklı heyelan hızları için çalıştırılarak yüzeyde elde edilen dalga genlikleri nümerik modelde kullanılarak farklı heyelan hızlarında kıyıda meydana gelecek dalga yükseklikleri gözlemlenmiştir. Bu çalışmada dünya literatüründe yeni olduğu düşünülen, analitik yöntemle nümerik yöntemin birleştirilmesi gerçekleştirilmiştir. Anahtar Kelimeler: Analitik model, nümerik model, denizaltı heyelanı, tsunami, Marmara Denizi. 
Investigation of properties of macro defect free (MDF) cements prepared with different polyvinyl alcohol copolymers and alumina cements
Get PDFMacro-Defect Free (MDF) Cements, which are cement-polymer composites, had been developed and patented by the scientists from Imperial Chemical Industry (ICI) in order to increase especially the flexural strength of cementious materials by decreasing large voids at the early 1980?s in London. These new composite materials were produced by adding small amount of polymer and water into the cement and processed in a different method inspired by rubber production. The most important property of this composite is its unusually high flexural strength. Although, generally more than 80% (by weight) of this composite is cement, it has 20-30 times higher flexural strength than conventional cement paste. 150-300 MPa flexural strengths are easily achieved which are close to the strength of ordinary steel and it was a very important development if we compare it with ordinary cement paste which has only 5-10 MPa flexural strength. Inventors of the MDF cements attributed this high flexural strength to the elimination of macro voids in the material during processing and they thought that polymer was a rheological aid and inert filler. However, further studies have proved that crosslinking reactions between the ions of cement and polymer chains are also very important to obtain such high flexural strengths. In addition, pressing the material under moderate temperature after production is another reason for improving mechanical properties. Different cement and polymer types can be used for the production of this composite material. However, highest flexural strengths are always obtained when Calcium Alumina Cements (CAC) as cement and Poly (Vinyl alcohol) Acetate (PVAc) copolymers as polymer were used. On the other hand, this composite has serious durability problems under water effect. Significant amount of swelling are observed and the strength of this composite decreases in water storage even in very short time. In this study, MDF cements were produced by using CAC-PVAc copolymers and effects of ingredients on the water sensitivity were investigated. In the first part of the experimental studies, MDF cements were produced with different type of PVAcs which differ in their hydrolysis degrees. Secondly, MDF cements were also produced with four different types of CACs which differ in their Al2O3 content and their effects on water sensitivity were investigated. Biaxial flexural strength tests were conducted on the specimens after storing in both dry and humid conditions. Purpose of these tests was finding the most suitable PVAc and CAC type with respect to both mechanical and durability properties. Seven different types of PVAc were used in the first step. Their hydrolysis degrees were changing between 79.6 to 99.1%. MDF cements were successfully produced with 5 of 7 different PVAcs, except those with fully hydrolyzed PVAc (98.4%) or carboxylated PVAc (96.0%). All mixtures were affected from moisture in different rates between 45% and 80% depending on PVAc type. However, the PVAc at the lowest hydrolysis degree (79.6%) gave the lowest strength loss (45%). Increasing the degree of hydrolysis of PVAc increased the strength loss of MDF specimens stored in water.In the second step, MDF cements were produced with 4 different types of calcium alumina cement, which their alumina contents were changing between 42 to 79%. Water/cement ratio was changing between 0.09 and 0.19 while the polymer/cement ratio was kept constant at 0.07. Twenty five different batches were prepared in order to produce MDF cements, which differ in their water contents. Production was successful with all 4 different types of calcium alumina cements. The highest biaxial flexural strength was obtained as 257 MPa on CAC 70 composite, which was prepared by cement with 70% Al2O3 content and water/cement ratio of 0.15. The lowest biaxial flexural strength was 70 MPa and belongs to the CAC 79 composite, which was prepared with 79% Al2O3 content cement and water/cement ratio of 0.19. Although, the production of MDF becomes harder for highest level of Al2O3 (79%) than those with lower Al2O3 content there is a slight increase on properties with the increasing content of Al2O3 up to 70%. As conclusion, MDF cements, which were produced with low hydrolysis degrees PVAcs, and alumina cements, which have highest Al2O3 content up to 70%, showed higher flexural strength and better durability properties under water effect. Keywords: MDF cement, calcium alumina cement, polymer, polyvinyl alcohol acetate. composite.Literatürde Macro-Defect-Free (MDF) cement olarak adlandırılan büyük boşluklarından arındırılmış çimento-polimer kompozitleri veya kısaca MDF çimento olarak adlandırabileceğimiz malzeme 1980’li yılların başında çimento bazlı malzemelerin özellikle eğilme dayanımlarının artırılması amacıyla geliştirilmiştir. MDF çimentolar, ağırlıkça % 80’den fazla oranda çimentonun az miktarlarda polimer ve su ile karıştırılması ile elde edilir. Bu karışıma yüksek eğilme dayanımları elde edebilmek için kauçuk endüstrisinde de kullanılan kalenderleme işlemi uygulanmaktadır. Bu esnada çimento ve polimer arasında çapraz bağların olduğu düşünülmekte ve bu durum yüksek eğilme dayanımlarının temel sebebi olarak açıklanmaktadır. Ayrıca, bu malzemeyi üretimden sonra bir miktar basınç ve sıcaklık altında küre tabi tutmanın da eğilme dayanımının artırılmasında önemli etkisi vardır. Öyle ki normal çimento hamuru ile ancak 5-10 MPa eğilme dayanımı elde edilebilirken, MDF çimento ile 200 MPa’ı aşmak rahatlıkla mümkündür. Hatta bazı araştırmacılar 300 MPa’ın da üzerine ulaşarak çeliğin dayanımına yaklaşmışlardır. En yüksek dayanımlar alüminli çimento ve polivinil alkol-asetat (PVAc) kopolimerleri kullanılan kompozitlerde elde edilmektedir. Öte yandan, bu kompozitlerde çok önemli dürabilite problemleri söz konusudur. Özellikle bu malzemenin suyla temas etmesi halinde dayanımı büyük oranda düşmektedir. Bu çalışmada farklı PVAc ve alüminli çimentolar kullanılarak üretilen çimento-polimer kompozitlerinin dayanım ve dayanıklılık özellikleri incelenmiştir. Çalışmanın 1. bölümünde hidroliz dereceleri farklı PVAc’ların kullanılmasının MDF üzerindeki etkisi incelenirken, alüminli çimentoların Al2O3 yüzdesindeki değişimin etkilerinin incelenmesi 2. bölümü oluşturmaktadır. Bu sayede MDF çimento üretimi için en uygun malzemeler belirlenmeye çalışılmıştır. Anahtar Kelimeler: MDF çimento, alüminli çimento, polimer, polivinil alkol-asetat, kompozit
Factors effecting rutting in bituminous hot mixtures and suggestions to reduce rutting
Get PDFRutting is one of the important distress types that occur in flexible pavements. It is described as vertical permanent deformation in contact area between wheel and road surface along the way, longitudinally. Rutting causes transversely unevenness in road surface. A road of which transversely unevenness is over an acceptable limit reveals many problems in point of comfort and safety. The passengers in a vehicle may be disturbed and control of vehicle gets difficult during changing line, water accumulates in wheel path in rainy days, water accumulated causes icing in cold weather and aquaplaning, consequently, breaking distance gets longer. In this study, rutting mechanism, rutting types and effectual factors have been explained in detail. Densification (decrease in volume, compaction) and shear deformation play important roles in rutting mechanism of bituminous hot mixtures. Rutting mechanism consist of two stage. In the first stage, permanent deformation below the tires is greater than the one at the edge of wheel path. In this stage, compaction effect (densification) of traffic is more effectual than shear deformation. And then, decreasing volume below the tires gets approximately equal to increasing volume at the edge of wheel path. This case that is the initial of second stage indicates to complete the compaction of pavement under traffic. And so, the reason of further rutting is shear deformation without volume change. It is difficult to determine that how much part of rutting is resulting from densification or shear deformation. However, shear deformation plays more important role in the part near the surface than the lower part of pavement. In addition, many scientific researches have indicated that shear deformation is more influential parameter than compaction in deformation behavior in the greater part of life of pavement. There are four types of rutting formation based on different reasons. These are structural rutting, flow (instability) rutting, wear rutting and consolidation (compaction) rutting. Structural rutting is resulted from deformations in one or more layer beneath the bituminous pavement layer. Because of this type of rutting formation is that stresses occurred in pavement layers exceed the materials resistance. The material rising is not appeared at the edge of the wheel path in this type of the rutting formation. Flow rutting is resulted from deformations in the bituminous pavement layer or layers. Because of this type of rutting formation is that stresses occurred in bituminous pavement layer(s) due to loading exceed the bituminous materials resistance. The material rising is appeared at the edge of the wheel path in this type of the rutting formation. Shear deformation plays an important role rather than densification (compaction) in this type of rutting. Wear rutting, that is named surface rutting type, is resulted from wearing the aggregates on the surface of pavement by the using of studded tires in winter. This type of rutting formation appears especially in the north Europe countries using studded tires. The parameter to be considered in wear rutting formation is aggregate toughness. Fourth type of rutting formation is consolidation (compaction) rutting, that is named surface rutting type too. Consolidation rutting has a same cross - section with that of wear rutting. This type of rutting formation occurs because of laying the bituminous mixture in cold weather and (or) insufficient compaction of pavement. Factors effecting rutting formation in bituminous hot mixtures are into two groups named external factors and internal factors. External factors consist of vehicle factors (axle load, tires inflation pressure, loading time etc.), climatic conditions (temperature, raining, freezing and thawing etc.) and geometrical standards of road (gradient, curb radius etc.). Internal factors consist of aggregate (shape, roughness, size etc.), bituminous binder (penetration, softening point, etc), bituminous hot mixtures composition (air void, bitumen content, void in mineral aggregate, void filled with asphalt, etc.), and design and construction wrong (inappropriate pavement thickness, insufficient compaction, laying pavement in cold weather etc.) An agregate gradation of which nominal maximum agregate size and coarse agregate percent are high should be preferred for resistance to rutting in bituminous hot mixtures. For example, stone mastic asphalt (SMA) mixture of which nominal maximum agregate size is bigger than 12.7 mm, coarse agregate percent is high and binder is modified bitumen provides high performance for rutting resistance. In addition to this, SMA mixtures can be used in two-layer system that is preferred in France. In this system, while the upper thin layer provides durability, impermeability and skid resistance, the lower thick layer provides resistance to rutting and fatigue cracking. SMA mixture should be the lower layer of this system. Keywords: Rutting, permanent deformation, bituminous hot mixture.Tekerlek izi oluşumu (oluklanma), esnek yol üstyapılarında görülen önemli bozulma türlerinden biridir. Taşıt tekerleklerinin yola değdiği bölümlerde, yol boyunca oluşan düşey kalıcı deformasyonlar olarak tanımlanır. Tekerlek izi oluşumu yolun enine düzgünlüğünün bozulmasına neden olur. Enine düzgünlüğü kabul edilebilir bir sınırın üzerinde bozulan bir yol, konfor ve güvenlik yönünden büyük sorunlar ortaya çıkarır. Ağır taşıt sayılarındaki artış, bunların taşıma sistemlerinin değişmesi, dingil ağırlıklarının ve lastik iç basınçlarının artması gibi değişmelere bağlı nedenlerle, yollardaki bozulmalar hızla artmıştır. Yollarda görülen bozulma türleri; kalıcı deformasyonlar (tekerlek izi, çökme, kabarma, yığılma, ondülasyon), çatlamalar (yorulma ve termal) ve ayrılmalar (sökülme, soyulma)’dır. Bu bozulmalar arasında tekerlek izi oluşumu, son yıllarda dikkate alınması gereken en önemli sorun haline gelmiştir. Tekerlek izi oluşumuna neden olan başlıca faktörler, yukarıdaki gelişmelere ek olarak, ticari taşıtların yasal sınırın üzerinde yüklenmesi, bunların düşük hızla hareket etmesi, uzun süreli veya durağan yükler, aşırı yük tekrarı, trafik yüklerine ve iklim koşullarına uygun olmayan malzeme kullanımı, tasarım ve yapım hataları olarak sıralanabilir. Bu çalışmada, bitümlü sıcak karışımlardaki tekerlek izi oluşumunda etkili faktörler, dış faktörler ve iç faktörler olmak üzere iki grupta incelenmiştir. Dış faktörler; araç faktörleri, iklim koşulları ve yol geometrik parametreleridir. İç faktörler ise; agrega, bitümlü bağlayıcı, bitümlü sıcak karışım bileşimi ile tasarım ve yapım hatalarıdır. Çalışmanın sonunda tekerlek izi oluşumunu azaltmaya yönelik öneriler sunulmuştur. Anahtar Kelimeler: Tekerlek izi, kalıcı deformasyon, bitümlü sıcak karışım
Hydrogeochemical characteristics of Eskişehir-Sivrihisar-Günyüzü basin
Get PDFYeraltısuları Türkiyenin yarı kurak bölgelerinde çoğu zaman tek su kaynağıdır. Yarı kurak iklim özelliğindeki Günyüzü Havzası, Eskişehir-Sivrihisar ilçesi güneydoğusunda, Sakarya nehri ana drenaj alanı içerisinde yer almaktadır. Havzada, geçirimsiz ortam olarak sınıflandırılan metamorfik şistler, granitik kayaçlar ve diyabaz dayklarıyla sınırlanan Paleozoyik yaşlı mermerler, sıcak ve soğuk sular için ana rezervuar kayaç niteliğindedir. Aynı zamanda havza içindeki Neojen yaşlı kireçtaşları, konglomeralar ve Kuvaterner yaşlı alüvyonlar da diğer önemli akiferlerdir. Çalışma kapsamında 9 su noktasından kurak (Temmuz-Eylül 2005) ve yağışlı (Mart-Mayıs 2006) dönemlerde sistematik örnekler alınmıştır. Örneklerin analizleri kurak ve yağışlı dönemde suların Ca++>Mg++>Na+>K+ ve HCO3->SO4= >Cl- şeklinde bir iyon dizilimine sahip olduğunu göstermiştir. İncelenen sular içinde ortalama 35oC sıcaklık değeri ile termal su niteliğinde olan Çardak Hamamı kaynağı (K7) ise Ca++> Na+> Mg++>K+ ve HCO3->Cl->SO4= şeklinde bir dizilim sergilemiştir. Elde edilen tüm bu iyon dağılımı, bölgedeki karbonatlı kayaçların, suların ana bileşenlerinin oluşumunda belirleyici olduğu ve suların nispeten yüksek magnezyum içeriğinden dolayı da akifer kayaçların dolomitik bileşen içerdiğini işaret etmiştir. Sularda ölçülen δ18O (%o –11.2 - %o-8.9) ve δ2H (%o -79 - %o -60) izotop değerleri, suların atmosferik kökenli olduğunu, 3H (0 – 8 TU) değerleri ise suların sığ, (Musluk çeşmesi kaynağı (K2), Çukurçeşme kaynağı (K3), Atlas kaynağı (K6), Nasrettin Hoca kaynağı (K8), Babadat kaynağı (K9)) ve derin (Yeniçıkrı kaynağı (K1), Subaşı kaynağı (K5), 55886/A (K4), Çardak Hamamı kaynağı (K7)) dolaşımlı olduğunu ortaya koymuştur. Anahtar Kelimeler: Günyüzü havzası, hidrojeokimya, akifer, izotop.Groundwater is mostly the unique water source in semiarid regions of Turkey. The aim of this study is to define aquifer characteristics by using hydrogeochemical and hydrogeological data obtained from the Günyüzü Basin located in the Sakarya River catchment area at the SW of Eskişehir-Sivrihisar. The study area covers an area of 543 km2 with an annual average precipitation of 393 mm/year. The study area comprises Mesozoic metamorphic rocks, Eocene granite, Neogene sedimentary rocks and recent alluvium where different hydrogeological properties such as unconfined-confined-partly karstic, fractured and granular aquifers having thermal component can be observed. The metamorphic basement begins with radiolarite, serpantinite, splitic basalt and diabases which are overlain by micaschist, quartzite, calcschist and marble. The thickness of brown, beige, light gray marble is more than 100 meters and seen at the top of metamorphic series. The metamorphic series are cut by magmatic rocks, where the main marble aquifer is bordered by these impermeable intrusions at sides and by impermeable schists at the bottom within the studied area. The geological units in the study area are hydrogeologically classified as local rich, medium, poor aquifers and aquicludes. Paleozoic marbles have been jointed and faulted and evaluated as local permeable units. They contain and conduct significant amount of groundwater. According to data obtained from pumping tests at wells drilled in the marbles, the hydraulic conductivity ranges between 1.19 and 98.9 m/day and specific capacity is between 0.64 and 75 l/sec/m. Although these figures do not represent the whole aquifer, they provide an idea of the heterogeneity of the system. Most of the spring discharge from this aquifer. Marbles also play an important role on recharge of the basin, because the thickness of marbles is more than 100 meters and seen at the top of metamorphic series at higher altitudes of basin. Short and heavy rainfalls and snowmelts directly affect the recharge in this karstic area where response of these events has been observed in the spring discharges. Quaternary alluvium and Neogene conglomerates and limestones are secondary important aquifers. According to data obtained from the pumping experiments carried out at the wells drilled in the basin, the hydraulic conductivity of the Neogene limestones varies between 1.39 and 4.1 m/day and specific capacity varies between 1.8 and 2.9 l/sec/m. The hydraulic conductivity of the Neogene conglomerates varies between 0.27 and 0.39 m/day and specific capacity is between 0.38 and 0.55/sec/m. The ophiolite, schists of the metamorphic complex, Eocene granites, Neogene marl, clays and diabases are the other impermeable levels in basin. Samples obtained from springs and wells within the research area from 9 locations, choosen in order to represent aquifer characteristics, have been examined. The groundwaters have pH values ranging from 6.59 to7.56, and temperatures changes 14 - 35oC. Piper and Schoeller semilogaritmic diagrams are both used in order to specify the dominant lithology in the formation of chemical composition, and to classify water samples with respect to their chemical composition. Results indicate that they generally have Ca++>Mg++>Na+>K+ and HCO3->SO4-2>Cl- anions and cations which show that carbonate rocks are dominant in the formation of chemical composition. The chemical composition of water samples consist with the lithological properties of the researched area. Only Hamamkarahisar spring (K7) is characterized by Ca++> Na+> Mg++>K+ and HCO3->Cl->SO4-2. anions and cations. δ18O (‰–11.2 - %o-8.9) and δ2H (‰-79 - ‰-60) isotope values show that all water (thermal and cold) samples except for Çukurçeşme spring are located in between the Ankara meteoric line (d2H = 8.d18O + 14.5 ) and Global meteoric line (d2H = 8.d18O + 10) This shows that all waters (thermal and cold) are of meteoric in origin. The elevation- oxygen-18 plot of precipitation is found to be –0.32 ‰/ 100 m. The EC-Tritium relationship indicates the existence of groups with different origins. These groups that have high EC ( 590–1216 mg/l ) and low 3H (0 – 4 TU) values represent the deep circulating waters (K1, K4, K5, K7), low EC ( 309–440 mg/l ) and high 3H (4-10 TU) values represent the shallow circulating waters ( K2, K3, K6, K8, K9) where these waters mix in various proportions. Keywords: Günyüzü Basin, groundwater, hydrogeochemistry, aquifer, isotope
Nano-fiber yapılı sepiyolitin hazırlanması ve atomik kuvvet mikroskopu (AFM) ile boyut tayini
Get PDFSepiolite is a natural hydrated magnesium silicate clay mineral with microfiber structure and high surface area. Fibers are constructed by tetrahedral and octahedral structured oxides within half cell formula of Si12O30Mg8(OH,F)48H2O. Sepiolite has special futures like; high surface area, fiber structure, porosity, tunnel/channel composition, crystal morphology, surface activity and formation of stable high viscosity suspensions at low solid concentrations. This unique structure of sepiolite can be altered by heat and/or acid activations. It also exhibits severe sensitivity to any mechanical perturbations; any interference may result as structural changes which can enhance or deteriorate the characteristics of sepiolite. Cation exchange capacity, fiber dimensions (fiber length/fiber width) and the type and amount of accompanying impurities are the main factors identifying the reologic behavior of sepiolite pulps. If sepiolite fiber bundles are disintegrated in water with a mechanic impeller, these particles may form random structures in the form of networks and increase the apparent viscosity values. Better dispersion of these fibers leads to an enhancement of water sorption on the fiber surface and in turn in inner galleries, resulting in entrainment of water within the network and thus viscosity increase. In this study, the dimensions of sepiolite fibers after mechanical dispersion are investigated based on a technique described in the literature for monitoring the sizes of montmorillonite and smectite type clays by Atomic Force Microscope (AFM). Unlikely the previous studies where a sepiolite fiber sizes were measured with SEM technique; conducting AFM study to determine the difference in the sizes of sepiolite fibers is unique. The mechanical dispersion process is conducted as a function of time and stirring rate, and the results of rheological behavior is followed through viscosity. A Turkish sepiolite sample of 65 10% purity was obtained from Eskişehir region. Sepiolite suspensions were prepared at 3%solids by weight in pure water as described in the literature. As sepiolite suspensions are characterized by time dependent flow behavior, they exhibit thixotrophy. The viscosity measurements were taken at different spindle rates but particularly at 5 rpm spindle rate. The highest viscosity value was obtained with the suspensions prepared at the highest stirring rate of 21.000 rpm. The samples run at 1, 3, 5 min. and the corresponding viscosity values of 6400, 9600, 4800 cP respectively were collected for AFM investigations. Several techniques have been established to investigate platelet structured clays. For our special case, these procedures were overrun and modified to investigate the fiber structured sepiolite samples; this involves dropping of 1 ml dilute sepiolite suspension onto a clean mica surface. The drop is dried with nitrogen gas and the mica plate is stored in a Petri dish till AFM investigation to avoid any airborne impurities to settle on the surface. For AFM investigations, Nanoscope III model AFM set up was used at the tapping mode to produce 512*512 pixel graphics of sepiolite settled on the mica surface. The sample prepared for 1 minute stirring, represents bundles consisting of approximately 50-60 fibers. Ensuing sample of 3 minutes stirring was made with fiber groups of 5-10. Increase in apparent viscosity values upon increasing stirring time, indicates the presence of loosened bundles and thus better network. However, when the stirring period is increased to 5 minutes the viscosity value decreases and the AFM graphics, showed the failure in size uniformity with accompanying a weak networking. AFM graphics n-Surf 1.0 Beta visualizer program coupled with XYit program is used for numerical analysis of the fiber or bundle dimensions. Finally the collected data are averaged with Excel program. Investigating a total of 130 profiles, the average height*width of 1, 3 and 5 minute stirring is found as 514*50, 249*28 and 157*22 nm, respectively; the corresponding fiber or bundle lengths are 1643, 1126 and 1055 nm, respectively. As a result considering the average sizes, at the same percent solids, the number of fibers or groups in a suspension prepared at 3 minute stirring is 8 times more than that of 1 minute stirring, indicating a better network leading to higher viscosity. As opposed to this, further stirring at 5 minute stirring deteriorated the dimensions of fibers and the formation of network due to fracture of fibers. Keywords: Sepiolite, mechanic dispersion, size determination with AFM.Sepiyolit, mikrofiber yapılı ve yüksek yüzey alanına sahip doğal bir kil mineralidir. Yüksek yüzey alanı, lifsi yapısı, porozitesi, kristal morfolojisi ve kompozisyonu, yüzey aktivitesi, düşük konsantrasyonlarda yüksek viskoziteli duraylı süspansiyonlar oluşturma gibi sıra dışı özellikleri mevcuttur. Sepiyolitin yapısı, ısıl işlemlere, asitle muameleye ve ayrıca uygulanabilecek mekaniksel işlemlere karşı hassasiyeti sayesinde mineralin sahip olduğu sorptif, katalitik ve reolojik özellik gibi en faydalı özelliklerini değiştirmek mümkün olabilir. Sepiyoliti oluşturan lif demetleri suda bir mekanik karıştırıcı kullanılarak dağıtılırsa, bir ağ yapı içerisinde parçacık iç ve dış yüzeyleri artan lifler daha fazla su adsorplama ve parçacıklar arasında daha fazla su tutulmasını sağlayarak viskozitenin artırılmasına yardımcı olmaktadır. Bu çalışmada yapılan viskozite ölçümlerine göre; 21000 rpm hızda yüksek hızlı bir mekanik karıştırıcıda 3 dakika boyunca işleme tabi tutularak hazırlanan pülp ile 5 rpm spindle hızında ölçülen en yüksek görünür viskozite olarak 9600 cP elde edilmiştir. Karıştırma hızının düşmesi ile viskozite değerleri düşmektedir. Artan süreler ise kritik bir eşiğe kadar viskozite değerini artırdıktan sonra düşürmektedir. Nano boyutlara kadar serbestleşmesi beklenen sepiyolitin, birim liflere ayrılmasını teyit etmek ve bu ölçekte boyutlarının belirlenebilmesi nano ölçekli malzeme hazırlanabilmesi için önemli bir aşamadır. Bu nedenle daha önce smektit tipi killerle gerçekleştirilen Atomik Kuvvet Mikroskobu (AFM) çalışmalarına paralel olarak inceleme gerçekleştirilmiştir. Sepiyolit için AFM inceleme numunesi hazırlama yöntemi belirlenmiş ve ortalama olarak en iyi viskoziteyi veren pülpteki lif boyutları 249*29*1127 nm (genişlik*yükseklik*uzunluk) olarak tespit edilmiştir. Alınan görüntülerde 3 dakika mekanik dağıtma öncesinde liflerin demetler halinde olduğu, sonrasında sepiyolit liflerinin kırılarak parçalanmakta olduğu görülmüştür. Bu kırık lifler, boyutlarının küçüklüğü nedeniyle rastgele bir ağ yapı içerisinde kendilerine yer bulamayarak viskoziteyi düşürmeye neden olmaktadır. Anahtar Kelimeler: Sepiyolit, mekanik dağıtma, AFM ile boyut tayini
Determination of occurrence of fumonisin in dried figs
Get PDFBesleyici ve sağlıklı bir gıda olan kuru incir dünyada yaygın olarak üretilen meyvelerdendir. Fumonisinler, mısırda yaygın olarak bulunmakta olup Fusarium verticilloides ve F. proliferatum tarafından üretilmektedir. Bu çalışmada Ege Bölgesi’nden 2003 ve 2004 yıllarında 7 farklı yöreden kurutma aşamasından temin edilen kuru incir örneklerinde fumonisin varlığı ELISA yöntemi kullanılarak araştırılmıştır. ELISA yöntemiyle toplam fumonisin tayini ekstraksiyon, katı faz ekstraksiyon kolonuyla temizleme işlemlerinden sonra gerçekleştirilmiştir. İncir örneklerinin %81.8’inde 0.1 ppm’in üstünde fumonisin varlığı belirlenmiştir. Çalışmanın ikinci yılında örneklerde birinci yıla göre daha yüksek oranda fumonisin kontaminasyonu belirlenmiştir. Buna karşılık birinci yılda daha yüksek fumonisin düzeyleri belirlenmiştir. Her iki yılda da örneklerde fumonisin kontaminasyonu en fazla 1.0-5.0 ppm arasındadır. Kurutma aşamasından temin edilen kuru incirlerde ELISA yöntemiyle belirlenen toplam fumonisin değerleri HPLC yöntemi ile karşılaştırılmıştır. ELISA yöntemi ile HPLC yöntemine göre kuru incirde çok daha yüksek fumonisin değerleri elde edilmiştir. Örneklerin tamamında iki yöntemle elde edilen bulgular karşılaştırıldığında regresyon katsayısı 0.869 olarak hesaplanmıştır. HPLC yöntemiyle 1 ppm değerinin altındaki FB1 değerleri dikkate alındığında iki yöntem arasında ilişki belirlenmemiştir. 1 ppm’in üzerindeki değerler için iki yöntem arasında korelasyon belirlenmesine rağmen ELISA yöntemiyle elde edilen fumonisin miktarları HPLC yöntemine göre çok yüksektir. ELISA yöntemiyle 115 örneğin 11 adedinde yanlış pozitif sonuç belirlenmiştir. Elde edilen bulgulara göre kuru incirde fumonisin tayini için ELISA tarama amaçlı olarak kullanılabilecek bir yöntem olup sonuçların HPLC gibi başka bir yöntemle doğrulanması gerektiği düşünülmektedir. Anahtar Kelimeler: Kuru incir, fumonisin, ELISA.Dried fig, very nutritional and a healthy food, is one of the most widely produced fruits in the world. Dried figs can be consumed directly, or as fig paste in production of different desserts and candies. It is an important agricultural product following raisin and dried apricot among Turkish dried fruit exports. Turkey is ranked first in dried fig exporting countries with approximately 52600 tons of dried figs in 2005, equivalent to 52% of world´s dried fig exports. Dried figs are produced mainly in the Aegean Region in the western part of Turkey. Environmental conditions in the Aegean Region during ripening, harvesting and drying of figs seem favorable for mycotoxin production in infected fruits. Harvesting and sun-drying processes and water activity value of fig fruits during drying are also effective on mycotoxin formation. Fumonisins are produced by Fusarium verticilloides and Fusarium proliferatum, fungi that commonly contaminate maize. Fumonisins induce several diseases in animals such as Equine leukonencephalomalacia in horses, Porcine pulmonary oedema. A relationship between consumption of fumonisin containing maize and incidence of esophageal cancer by humans in certain areas of the world has been determined. With regard to the animal studies and epidemiological studies on humans, fumonisins have been classified as a possible human carcinogen (Group 2B) by IARC. Thin-layer chromatography (TLC) and liquid chromatographic (LC), mass spectroscopic (MS), gas chromatographic and immunochemical methods have been used for fumonisin analysis in foods. In this study, the total fumonisin incidence and levels were determined in the Turkish dried figs, collected from the drying stage in seven different districts located in the Aegean Region in 2003 and 2004. Occurrence of total fumonisin (FB1, FB2, FB3) in dried figs was investigated by Enzyme Linked Immunoassay (ELISA) after extraction with methanol: water and clean up with solid phase extraction cartridge. The results of the two years indicate that fumonisin presence is a potential risk in dried figs. Fumonisins were detected in 94 samples of the 115 naturally dried figs collected from orchards before any treatment. The total fumonisins in dried figs contamination were determined as 78.9% and 86.4 % in 2003 and 2004 samples, respectively. Although the lower contamination incidences were observed in 2003 than in 2004, higher total fumonisin content was determined in the first year of the study. The highest incidences of fumonisin positive samples were obtained within the range 1.0-5.0 ppm for each year. 19.7% and 11.4% of the dried fig samples had fumonisin level exceeding 20 ppm in 2003 and 2004, respectively. ELISA and High Performance Liquid Chromatography (HPLC) methods for the determination of fumonisins in dried figs were compared. Only occurrence of fumonisin B1 in dried figs was determined by HPLC. Among the fumonisin derivatives, FB1 is the most common one and constitutes about 70-80% of the total fumonisin content of F. verticilloides cultures and naturally contaminated foods. Fumonisin B2 accounts for 15-25% of the total fumonisin while fumonisin B3 accounts for % 3-8. Correlation between ELISA and HPLC methods was observed for all samples. However, no correlation between methods was recorded for samples below 1 ppm Fumonisin B1 level (obtained by HPLC). Regression coefficient was calculated as 0.820 for samples that contains above 1 ppm fumonisin B1. Although there was a correlation between methods for samples above 1 µg/gr, fumonisin levels obtained by ELISA were much higher than HPLC. False positive results were obtained by ELISA in 11 of 115 dried fig samples. Overestimation of the fumonisin content and false positive results in ELISA assays have been also reported previously. Although solid phase extraction cartridge was used for cleaning in the ELISA assay, higher fumonisin levels than HPLC were observed in dried fig samples because of the solvent effect of methanol. Hence, it was reported that solvent and matrix effect could be decreased by diluting the extract with phosphate buffer or distilled water. It is considered that ELISA assay can be used as a screening method to determine the occurence of fumonisin in dried figs after diluting the extracts. The mycotoxin concentrations in positive samples should be confirmed by a chromatographic methods such as HPLC to eliminate the false positive and false negative results. Keywords: Dried figs, fumonisin, ELISA
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