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Source-initiated geographical data flow approach for wireless ad hoc and sensor networks
Full text linkTasarsız (ad hoc) ve duyarga (sensör) ağlar, altyapısız ağlar olduğu için altyapılı ağlarda bol miktarda bulunan enerji, işlemci, bellek, bandgenişliği gibi kaynaklar kısıtlıdır ve özenle tüketilmelidir. Ağ elemanlarının boyutlarının çok küçük olması, enerjiyi en kısıtlı kaynak yapmaktadır. Ancak, kaynak ile varış arasında veri akışının sağlanması için kullanılan yöntemler enerji tüketimini arttırmaktadır. Bu nedenle, literatürde enerji-etkin yönlendirme protokolleri sunulmuştur. Bu protokollerden, coğrafi yer bilgisine dayanarak yönlendirme yapan protokoller, diğerlerine göre daha yüksek başarıma ve performans değerlerine sahiptir. Bu çalışmada, Durumsuz Ağırlıklı Yönlendirme (DAY) isimli bir özgün kaynak-başlatmalı veri akış tekniği sunulmaktadır. Düğümler sadece kendi sanal coğrafi yer bilgilerini bilmekte, ağ topololoji bilgisine ihtiyaç duymamaktadır. Her düğüm kendi ağırlığını hesaplamaktadır. Başlangıçta bu değer varışa olan mesafedir. Düğümler kendilerine gelen paketlerin içindeki ağırlık bilgilerine bakarak paketi tekrar göndermeye veya düşürmeye karar vermektedir. Bu karşılaştırma işlemi durumsuz olma özelliğini sağlamaktadır. Ağırlık parametresi sadece yer bilgisini içerebildiği gibi düğümün kalan enerjisi gibi Servis Kalitesi parametre bilgisini de içerebilir. Servis Kalite bilgisi sistemin yaşamömrünü arttırmaya yöneliktir. Durumsuz olma özelliği ile de, yönlendirme tablosu tutulan algoritmalarda görülen iletişim yükü büyük oranda azalmaktadır. DAY, aynı zamanda, güvenirliği sağlayan ve gerçek-zamanlı veri için de gerekli olan çoklu-yollar veya örülü çoklu-yollar kullanır. Tekrar-gönderimlerde eşik değerlerinin kullanımı, sistemde esnek ve enerji etkin bir veri akışı sağlar. Aynı zamanda, DAY, MAC-katmanından bağımsız çalışan ilk durumsuz coğrafi yönlendirme tekniğidir. Anahtar Kelimeler: Kablosuz ağlar, gezgin ağlar, sensör ağlar, iletişim, yol atama, yönlendirme. Routing without tables can be achieved by using location information of the nodes retrieved from GPS (Global Positioning System) or by applying a localization algorithm. In geographic routing protocols, nodes know their actual or relative positions with respect to a reference point, and share this information with immediate neighbour nodes for routing process. Geographic routing protocols use only local topology information and do not have any update overhead. Therefore, they provide scalability in mobile networks with respect to conventional routing protocols. Geographic routing protocols use greedy scheme or beaconless scheme for routing. In greedy schemes, nodes select the best next node on the route by using the local topology information. Collecting local topology information in greedy schemes consumes more energy than beaconless schemes due to reduced transmissions in the latter one. On the other hand, beaconless routing protocols in the literature propose solutions to be implemented at the MAC (Medium Access Control) layer. In those solutions, RTS (Request To Send) and CTS (Clear To Send) packets are also used for implementing routing protocol that increases the complexity of the MAC layer. However, sorting routing problem at the MAC layer is against the well-defined communication architecture. Besides that, those solutions become dependent to the MAC layer they use. In this study, a novel stateless data flow approach and routing algorithm for wireless sensor networks is proposed which is completely MAC-layer independent. Nodes do not have to be aware of local or global topology information. Routing is achieved without keeping tables. Nodes geographical positions are sufficient for routing process. A new metric called weight that is derived from nodes own position is used in routing process. The position can be either geographical or relative to a reference point system wide. Instead of the position, the weight value of the transmitting node is inserted into the packet. Each node on the route involves in routing process by considering its weight and the information in the received packet. To limit the number of forwarding nodes, a threshold is set in terms of the weight metric. On a packet receive; a node broadcasts the packet if its weight is between the weights of the transmitting node and the destination node and if also its weight difference greater than the threshold value. Besides that, decision to transmit includes QoS parameters such as power-left at the node to keep energy-limited nodes out of the route. The threshold value can be adjusted to save energy by limiting the number of retransmitting nodes. The threshold value can also be adjusted for reliability. More relaying in number causes the data to flow over multiple paths. Data transportation over multiple paths provides reliability. Reliability requirements challenge with the energy saving requirements. Therefore, threshold value can be used to balance these requirements as needs. Thirdly, the threshold value can be adjusted for void recovery. In case of void detection, the transmitting node decreases the threshold value allowing more nodes to be in data flow algorithm. By this way, nodes that may circumvent the void are forced to relay the data packets. Fourthly, the threshold value should be adjusted according to the node density in the network. In dense networks, the threshold value can be set to be high by default to limit the retransmitting nodes. In non-dense networks, the threshold value can be set to be low. The proposed algorithm, SWR, has the followingproperties: SWR provides scalability by not using routing tables, and by not beaconing. SWR simplifies routing process by using a weight metric and designing an appropriate algorithm for routing. SWR decreases calculations, delay, and resource requirements (such as processor and memory) at nodes by using weight metric. SWR decreases energy consumption by not beaconing, by using position-based routing based on threshold and considering the energy levels of the nodes. SWR provides reliability by using multipaths. SWR executes routing process completely in network layer, independent from the MAC layer used below. Keywords: Wireless networks, mobile networks, sensor networks, communications, routing, network layer.
A brand choice model based on house-hold panel data: An empirical model of CSD choice in Turkey
Full text linkTüketici panelleri günümüzde gerek pazarlama yöneticileri gerekse marka tercih modelleri üzerinde çalışan akademisyenler tarafından yaygın olarak başvurulan bir veri kaynağı haline gelmiştir. Gelişmiş ülkelerde genellikle tarayıcı teknolojilerine dayalı olarak toplanan tüketim paneli verisi gelişmekte olan ülkelerde günlük tutma yöntemiyle elde edilmektedir. Bu yöntemle toplanan hane paneli verilerinin kapsam ve güvenilirliğinin tarayıcı teknolojisiyle elde edilen verilere göre daha sınırlı olduğu kabul edilmektedir. Bu çalışmanın amacı, alışveriş günlüğüne dayalı tüketici paneli verisiyle Türkiye’de, hızlı tüketim malları sektöründe, başarılı bir marka tercih modeli kurabilmenin mümkün olup olmadığını araştırmaktır. Bu amaçla, öncelikle, günlük tutma yöntemine dayalı panellerde doğrudan ulaşmanın mümkün olmadığı rakip markalara ait fiyat bilgilerini üretmeye yönelik dört aşamalı bir yöntem önerilmiştir. Daha sonra, Türkiye’de 2004 yılında 1632 hane tarafından yapılmış 26031 kolalı içecek alışverişinden yararlanılarak çeşitli çoklu probit ve lojit modelleri kurulmuş; modellerden elde edilen bulgular rassal olarak belirlenen 408 hanelik test örneklemine ait 6686 alışveriş gözlemi üzerinde sınanmıştır. Sonuçlar göreli fiyatlar, hane büyüklüğü, toplam harcama, bir önceki tercih ve sosyo-ekonomik statü açıklayıcı değişkenlerinin yüksek güven düzeylerinde anlamlı olduğunu ve kurulan modellerin gerek test gerekse model örneklemlerindeki hanelerin marka tercihlerini başarıyla tahmin ettiğini göstermektedir. Yapılan marjinal etki analizlerine seçilen modellerin verdiği tepkiler de teorik beklentilerle hassas bir uyum içindedir. Bu çalışma, Türkiye’de hane paneli verisi ile tüketicilerin bir sektördeki marka tercihlerini modellemeyi hedefleyen öncü çalışmalardan biri olması bakımından önem taşımaktadır. Anahtar Kelimeler: Tüketim paneli, marka tercih modeli, çoklu probit, Hızlı Tüketim Malları, alışveriş günlüğü.One of the major sources of consumer level brand consumption data in Fast Moving Consumer Goods (FMCG) sector is the household consumer panels maintained by individual organizations. Consumer panels are capable of keeping histories of purchases for a sample of households. Household panel data is collected via barcode scanner technologies in the developed countries. Data collected by the optical scanning of Universal Product Code permits researchers study the effects of marketing variables on customer choice among product alternatives since the mid-1980s and many dozens of papers are published on brand and retailer choice issues since then. Employing scanner technology, panel organizations does not require its members to record all the items they purchase in a shopping trip, as their panel ID cards are scanned during the payment process at checkout. Building cooperation with the retailer companies, scanner panels are able to provide price and promotion data for all the products (in a given product category) without the necessity of being purchased. On the other hand, due to the high levels of technology costs, the household level panel information in developing markets is primarily gathered using the diary mode. It is believed that, in this mode of data collection, both the reliability and the scope of information collected from the panellists are still scarce compared to their scanner type counterparts in more developed markets. One of the important problems of diary mode data is the lack of complete price information. In diary mode panel organizations, households only record the prices of the products they purchase. As it is impossible for a shopper to list the prices of all the products in the product categories (of which the shopping basket includes an item), diary mode household panels are not capable of conducting complete price data in a given product category. As the brand choice models literature using household panel data mostly stands upon the unit prices of the products purchased and their alternatives displayed on shelves, there is a gap of modelling research in the developing markets in which consumer panel measurements are made based on diary mode. The purpose of this study is to investigate whether it is possible to establish an efficient brand choice model based on diary mode household panel data from the Turkish carbonated soft drinks market. In order to accomplish this goal, firstly, a four staged method of price data generating is suggested. Suggested method basically generates artificial unit prices for the products which are present at the retailer during the shopping trip but not purchased. Secondly, employing this price data, different multinomial probit and logit models of brand choice are built based on 26031 purchase occasions of a model sample of 1632 households. Using relevant goodness of fit and specification tests (mostly depending on the number of choices that were made correctly), the performances of these six models are tested on the 6686 purchases of a randomly selected test sample of 408 households. The results show high significance for the explanatory variables of brand loyalty (previous brand purchased), relative prices and household specific features such as total/per capita FMCG spending, household size and socio-economical status. While the coefficients have expected signs, the models predict the share of purchases remarkably well in both the model and the test samples. All of the models are capable of predicting more than three thirds of the brand choices correctly. However, Hausman tests reveal that the Independence of Irrelevant Alternatives criteria does not hold for the multinomial logit models. Therefore, theoretically, it is not possible to use the multinomial logit method in modelling the Turkish carbonated soft drinks market, although it was useful in variable selection process. Hopefully, the goodness of fit measures and specification tests show that, there is no theoretical problem for the multinomial probit models of brand choice built in this study. Moreover, the reactions of the probit models to the marginal effect analyses are consistent with the theoretical expectations and the models are capable of predicting the monthly shares of purchases with the error range of 3% successfully. Employing diary based consumer panel data, this study is one of the pioneering attempts to integrate the consumption level data and consumer features towards developing a brand choice model in Turkey. Keywords: Consumer panel, brand choice model, multinomial probit, Fast Moving Consumer Goods (FMCG), diary mode panel data
Numerical analysis of umbrella-arch method performed in metro tunnels
Full text linkTünel tasarımcıları, zayıf zeminlerde projelenen tüneller için inşa sırasında işçi ve yapım güvenliği ve özellikle şehir içinde daha da önem taşıyan yüzey oturmaları gibi kritik konuları denetim altına almak durumundadır. Bu çalışmada, zayıf zeminlerdeki tünel inşaatlarında tünelin göçmeden açılabilmesi ve tünel içi (konverjans) ve yüzey deformasyonlarını denetim altına almak için uygulanan şemsiye-kemer (umbrella-arch) yönteminin, tünel içi ve arazide oluşturduğu iyileşmelerin etkileri parametrik olarak incelenmiştir. Sayısal hesaplamalarda sonlu elemanlar yöntemi ile çalışan Plaxis yazılımı kullanılmıştır. Sayısal analizlerde, zemin davranışını temsil etmek amacıyla elastoplastik Mohr-Coulomb zemin modeli kullanılmıştır. Hesaplamalar, 2 boyutlu düzlem-gerilme ortamında elastik mesnetlere oturan kiriş kabulleriyle yapılmıştır. Yapılan sayısal modellemeler sonucunda şemsiye borularının uzunluklarının (Lp) en büyük yüzey oturmalarına (smaks) etkisi için farklı her tünel derinliğinde (Z) geçerli olabilecek bir bağıntıdan söz etmek mümkün görülmemektedir. Ancak, şemsiye borularının boylarının (Lp) artırılmasının oturmaların yüzey dağılımı üzerinde olumlu bir etki yaparak yüzey oturma bölgesini daralttığı anlaşılmıştır. Şemsiye-kemer borularının uygulama açısının yataydan uzaklaşması (b≠0o) yüzey oturma dağılımına ve aynada oluşan eksenel deformasyonlara (dx) olumsuz etki yaptığı, uygulama açısını artırmanın daha yüksek eksenel deformasyonlar verdiği görülmektedir. Şemsiye borularına verilecek en elverişli açının tünel eksenine paralel olduğu (b=0o) ve uygulamada boruların mümkün olan en küçük açı ile imal edilmesinin uygun olacağı sonucuna ulaşılmıştır. Şemsiye-kemer boru boylarının (Lp) tünel tavanı düşey deformasyonlarını her kazı kademesi için azalttığı görülmüştür. Şemsiye-kemer borularının boylarının (Lp) ayna yatay deformasyonlarını olumlu yönde etkilediği ve daha uzun boru boyu kullanmanın ayna yatay deformasyonlarını azalttığı görülmüştür. Anahtar Kelimeler: Mohr-Coulomb, zemin modeli, şemsiye-kiriş, elastik-kiriş, sonlu elemanlar.As a result of rapid urbanization, complex transportation networks have been built to overcome the demand for public transport. In urban areas the surface settlements (which take place during tunnel construction and service life) should be within the tolerance limits and should not effect nearby the superstructures. The tunnel excavation and support system should provide an adequate tunnel wall and face stability for worker and equipment safety and should prevent a possible collapse. The umbrella-arch method can be defined as a reinforcement technique which involves installing pipes ahead of the tunnel face prior to the excavation in order to limit the deformations that occur in the crown, face and surface settlements, in order to provide a longer stand-up time and to excavate the tunnel in safety. Quantifying the level of improvement provided by the reinforcements would enhance the design stage. The media in which a tunnel is going to be excavated would usually expose heterogenous and unisotropic properties and the tunnel route possesses varying cross-sections such as stations, rail switches, service depots etc. Therefore, there is a need to use simple and flexible methods that are applicable to different underground conditions. In this study, the effects of umbrella arch pipe roofing method on limiting the aforementioned deformations are investigated by numerical methods. Modelling each umbrella pipe individually by using 3D methods is not very efficient in application projects for the reasons summarized below; There are too many parameters affecting the reinforcement behaviour in tunnel excavation. Software chosen should be capable of reflecting the real in situ behavior of the material (stress-strain, long/short term behavior, pore-water pressures and movements, interaction between the support material etc.) in a convenient manner. Commercial software avaliable on the market are usually not user-friendly and requires extensive training. These 3D analyses require special and expensive hardware setups. Solution times are unacceptably long for the conditions where a quick respond is needed. These points urge the engineer to use more practical 2D software applications capable of reflecting the real in situ behaviour within a reasonable accuracy. This study presents the results of over 100 parametric Finite Element analyses of umbrella arch tunnel roof reinforcing based on two dimensional plane strain conditions with the assumption of beam on elastic multi-supports inserted in elastoplastic medium. Therefore, the analyses performed are on the longitudinal profile. In the constitutive model, the soil is discretized as 15 noded triangular elements; the umbrella pipes are modelled as beam elements of 5 nodes each of which has three degrees of freedom; the steel sets are modelled as strut elements which are one node spring elements of constant spring stiffness (normal stiffness) which are fixed at one end at a predefined length. The lateral far boundaries are taken at least eight times the diameter of the tunnel in order to obtain more accurate Finite Element Method (FEM) results. The vertical boundary of the model changes by the depth of tunnel. The out-of-plane dimension is taken as unit width (1m), therefore, some modifications are applied on the stiffness properties of beams. The tunnel is assumed to be excavated in a cohesive medium. For practical reasons it is assumed that no ground water exists. Total excavation length is 10m which is achieved by ten steps of 1m long advances. The cover depth (C), the length of umbrella pipes (Lp), the length of overlapping of pipes (Lo) and the application angle of pipes are the main constituents of parametric study. The results of parametric study show that it is not possible to deduce a general expression which is valid for all tunnel depths that the length of pipes (Lp), have a positive effect on decreasing maximum surface settlements (smax). However, the length of pipes has a possitive effect on narrowing the settlement trough, and decreasing the crown settlements and lateral face deformations (dx). The increase in the thickness of pipe reinforcing provides lining stability and limits the tunnel and surface deformations. Deviation of the application angle of pipes from horizontal plane, negatively affects the settlement trough, and lateral face. However, because it is not possible to place the pipes laterally due to the space that is occupied by the overlap, smallest minimum angle should be applied in order to achieve the best benefit from the method. Keywords: Mohr-Coulomb, soil model, FEM, forepole umbrella, elastic support.
Two dimensional generalized edge detector
Full text linkBu çalışmada, daha önce Gökmen ve Jain (1997) tarafından geliştirilen -uzayında görüntü gösterimi ve ayrıt saptayıcı iki boyutlu uzaya genişletilmektedir. Bu genişletme özellikle iki açıdan önemlidir. Birinci olarak, görüntülerin -uzayındaki davranışları en iyi, iki boyutlu düzleştirme ve ayrıt saptama süzgeçleri ile modellenebilir. İkincisi, genelleştirilmiş ayrıt saptayıcı (GAS) ile bilinen başarılı birçok ayrıt saptayıcısını üretebildiğinden, iki boyutlu GAS ile bu süzgeçlerin iki boyutlu biçimleri oluşturulabilir. Düzleştirme problemi, zar ve levha modellerinin doğrusal bileşiminden oluşan iki boyutlu karma enerji fonksiyonelinin en aza indirgenmesi olarak tanımlanmıştır. Gökmen ve Jain (1997) karma fonksiyoneli en aza indirgeyen denklemi, ayrıştırılabilir olduğu varsayımı altında tek boyutlu kısmi diferansiyel denklem olarak çözmüşlerdir. Ancak mevcut ayrıştırılabilir çözüm iki boyutlu özgün denklemi sağlamamaktadır. Bu çalışmada, karma fonksiyoneli en aza indirgeyen denklem takımı iki boyutlu uzaydaki çözümü sunulmaktadır. Türetilen süzgeçler önceki süzgeçlerle birinci ve ikinci tür hata karakteristiklerine göre karşılaştırıldığında gürültüye daha az duyar olduğu gözlenmiştir. Gerçek ve yapay görüntüler üzerinde yapılan deneysel sonuçlarla ayrıt saptayıcının performansı ve -uzayındaki davranışı sunulmuştur. Ayrıt saptayıcılar ile çalışırken ayarlanması gereken çok sayıda parametre bulunmaktadır. Verilen bir imge için en iyi parametre kümesini bulmanın genel geçer bir yöntemi bulunmamaktadır. Gerçektende, bir imge için en iyilenen bir ayrıt saptayıcının parametreleri başka bir imge için en iyi olmayacaktır. Bu çalışmada, en iyi GAS parametreleri, verilen bir imge için hesaplanan, alıcı işletim eğrisi üzerinden belirlenmiştir. Burada amaç GAS'ın başarımının sınırlarını göstermektir. Anahtar Kelimeler: Ayrıt saptama, düzenlileştirme kuramı, ölçek-uzayı gösterilimi, yüzey kurma.The aim of edge detection is to provide a meaningful description of object boundaries in a scene from intensity surface. These boundaries are due to discontinuities manifesting themselves as sharp variations in image intensities. There are different sources for sharp changes in images which are created by structure (e.g. texture, occlusion) or illumination (e.g. shadows, highlights). Extracting edges from a still image is certainly the most significant stage of any computer vision algorithm requiring high accuracy of location in the presence of noise. In many contour-based vision algorithms, such as shape-based query, curved-based stereo vision, and edge-based target recognition, their performance is highly dependent on the quality of the detected edges. Therefore, edge detection is an important area of research in computer vision. Despite considerable work and progress made on this subject, edge detection is still a challenging research problem due to the lack of a robust and efficient general purpose algorithm. Most of the efforts in edge detection have been devoted to the development of an optimum edge detector which can resolve the tradeoff between good localization and detection performance. Furthermore, extracting edges at different scales and combining these edges have attracted a substantial amount of interest. In the course of developing optimum edge detectors that can resolve the tradeoff between localization and detection performances, several different approaches have resulted in either a Gaussian filter or a filter whose shape is very similar to a Gaussian. Furthermore, these filters are very suitable for obtaining scale space edge detection since the scale of the filter can be easily controlled by means of a single parameter. For instance, in classical scale-space the kernel is a Gaussian and the scale-space representation is obtained either by convolving the image by a Gaussian with increasing standard deviation or equivalently by solving the linear heat equation in time. This representation is causal, since the isotropic heat equation satisfies a maximum principle. However, the Gaussian scale-space suffers from serious drawbacks such as over-smoothing and location uncertainty along edges at large scales due to interactions between nearby edges and displacements. Although these filters are used widely, it is very difficult to claim that they can provide the desired output for any specific problem. For instance, there are some cases where the improved localization performance is the primary requirement. In these cases, a sub-optimum conditions filter which promotes the localization performance becomes more appropriate. It has been shown that the first order R-filter can deliver improved results on checkerboard and bar images as well as some real images for moderate values of signal-to-noise ratio (SNR). In many vision applications, there is a great demand for a general-purpose edge detector which can produce edge maps with very different characteristics in nature, so that one of these edge maps may meet the requirements of the problem under consideration. Detecting edges in images is one of the most challenging issues in computer vision and image processing due to lack of a robust detector. Gökmen (1997) obtained an edge detector called Generalized Edge Detector (GED), capable of producing most of the existing edge detectors. The original problem was formulated on two-dimensional Hybrid model comprised of the linear combination of membrane and thin-plate functionals. Smoothing problem was then reduced to the solution of two-dimensional partial differential equation (PDE). The filters were obtained for one dimensional case assuming a separable solution. This study extends edge detection of images in lt-space to two-dimensional space. Two-dimensional extension of the representation is important since the properties of images in the space are best modeled by two dimensional smoothing and edge detector filters. Also since GED filters encompass most of the well-known edge detectors, two-dimensional version of these filters could be obtained. The derived filters are more robust to noise when compared to the previous one dimensional scheme in the sense of missing and false alarm characteristics. There are several parameters to tune when dealing with edge detectors. Usually there is no easy way to find the optimal edge detector parameters for an image. In fact, one set of optimal parameters may not be optimal for another image. In this study, we find optimal GED parameters using receiver operator characteristics for an image when its ideal edges are available using exhaustive search to see how best it achieves. Keywords: Edge detection, regularization theory, scale-space representation, surface reconstruction
Modeling impacts of climate change scenario over Turkey
Full text linkBu çalışmada izlenen yöntem, Türkiye ve çevresi üzerinde, günümüz ve gelecek için NASA-Sonlu Hacim Genel Dolaşım Modeli (fvGCM) tarafından üretilen projeksiyonların, ICTP-Bölgesel İklim Modeli (RegCM3) kullanılarak dinamik olarak ölçek küçültülmesidir. Günümüz (1961-1990, RF) ve gelecek (2071-2100, A2) simülasyonları için, Hükümetlerarası İklim Değşikliği Paneli (IPCC) tarafından belirlenmiş sera gazları emisyon senaryoları dikkate alınmıştır. A2 ve RF simülasyonlarının sıcaklık ve yağış için yapılan mevsimsel analizleri Türkiye’nin iklimsel bölgeleri üzerinde alansal ortalama alınarak ayrı ayrı incelenmiştir. A2 simülasyonuna göre, Türkiye üzerinde sıcaklıklardaki en dramatik değişim yaz mevsiminde Ege Bölgesi üzerindeki 5 ila 6 °C’ler arasındaki artıştır. Kış ayları dışındaki mevsimlerde artış, 3-4 °C arasında değişmektedir. Gelecek simülasyonundaki minimum artış, kış mevsiminden 2-3 °C olarak hesaplanmıştır. Yine A2 simülasyonunda, Doğu Karadeniz dağları boyunca uzanan bölgede kış yağışlarıdaki artış, rüzgar paterninin değişmesiyle orografik etkinin güçlenmesine bağlıdır. Türkiye’nin güneyi üzerinde de rüzgar paterninin güneyli değişimine bağlı olarak kış yağışlarında çok ciddi azalmalar (% 34) model sonuçlarında ortaya çıkmıştır. Sonbahar meviminde ise Güneydoğu Anadolu Bölgesinde yağışlarda % 50’lere varan artışlar görülmüştür. Bu artışların ana nedeni değişen rüzgar akımlarının taşıdığı nem olabilir. Gelecek iklim senaryosunda Fırat ve Dicle su havzalarını kapsayan alandaki kış yağışlarında yaşanan azalmalarla, küresel ısınmaya paralel sıcaklık artışının buharlaşmaya etkisiyle birlikte değerlendirildiğinde, model sonuçlarının hidrolojik analizlerinin önemi daha çok ortaya çıkmaktadır. Anahtar Kelimeler: İklim değişimi, bölgesel iklim modellemesi, ölçek küçültme.The Earth's climate has changed many times and fluctuated between the glacial and the interglacial periods since its formed. These changes related to natural forcings like volcanic eruptions, intense tectonic activity, solar activity and variation of Earth's orbital parameters, were sometimes very dramatic. Today, the global change we face to is different than the natural changes occurred in the past. Human-induced climate change has been taken into consideration extensively within the last decade more than ever. Recent advances in both climate observing systems and methodologies to detect the climate change, as well as broader global coverage of observations help scientists to better understand the climate system. Scientific studies which are led by IPCC (Intergovernmental Panel on Climate Change) showed that dominance of anthropogenic effect on global warming is indisputable (IPCC, 2007). Regional climate change modeling has been applied to many different areas such as agriculture, seasonal forecasting, hydrology applications, paleoclimate and climate projections. Because of its ability to resolve sharp gradients and contrasts in the surface conditions, the regional climate modeling approach yields more accurate and spatially detailed information. In this study, the ICTP-Regional Climate Model version 3 (RegCM3) has been used to downscale present and future scenario simulations generated by the NASA-Finite Volume General Circulation Model (fvGCM) over Turkey and its surroundings. The present-day (1961-1990, RF) and the future climate change simulations (2071-2100, A2) are based on the IPCC Greenhouse Gases emissions, which are CO2, CH4, N2O, and CFC11- CFC12. Emission scenarios for these gases have been implemented into the radiation scheme for the simulations and, relatively high resolution of 30 km is adopted to resolve the complex topography of the domain. The role of the domain characteristics such as complex land-sea distribution determines the sub-regional climatic features and spatial climate variability. This diverse climatic structure of the region brings great challenge for regional climate modeling. Levantine Sea, Aegean Sea and Black Sea are main moisture sources of the Turkey and its surrounding regions. A2 simulation results which correspond future climate indicate that warming over Turkey's climatic zones is in the range of 2-5 °C. Summer temperature changes are more dominant in the A2 scenario. This pattern has also been observed for neighboring countries. Summer heat wave conditions over Aegean region (5 °C increase) are more obvious in the area averages than in the spatial pattern based model results. The difference between the summer and winter change is about 3 °C and it could play an important role in contributing to temporal shifts of the transition seasons. In addition, warming in winter over eastern and southeastern of Turkey which have higher altitudes are nearly 1 °C higher than for Marmara and Aegean regions which have lower altitudes. Autumn temperature changes for all regions are affected by the extension of the summer season extension due to the global warming. Most significant precipitation changes in A2 scenario have been occurred over the Mediterranean region of Turkey in winter and over the Southeastern of Turkey in autumn. Our analyses show a 34% decrease over Mediterranean region and it is related to the change in the atmospheric circulation which in turn causes reduced orographic forcing. The same circulation change also enhanced orographic forcing especially over the east of the Black Sea region and results in significant precipitation increase. Decreases over the Aegean and Southeastern regions are around 20% in winter. Autumn precipitation over Southeastern region increased as high as 48%. Flow pattern changes which also affected Iraq and Syria are consistent with enhanced moisture availability over this region which may account for the major precipitation increase. All precipitation changes in winter and autumn are also statistically significant. The amount of precipitation over Turkey in summer season is very little except eastern Black Sea region. Therefore, percent changes for summer precipitation over all of regions could not be meaningful to discuss. Analyses of A2 simulation show that combined effect of precipitation decrease and evapotranspiration increase related to temperature increase could play major role to reduce water resources over Turkey. Especially, there could be significant problems over Euphrates-Tigris basin because of the decreasing water availability in future scenario. Keywords: Climate change, regional climate modeling, downscaling scenarios
Quantum size effects on gas transport
Full text linkYarıiletken teknolojilerinde kullanılan mikro fabrikasyon tekniklerinin gelişimi, yeni fiziksel etkilerin gözlendiği sensörler, tıbbi cihazlar, güç üreten mikro makineler, ısı değiştiricileri, pompalar, valfler, mikro-nano pipetler ve mikro iticilerin üretilmesini de günümüzde mümkün kılmıştır. Nano sistemlerde termodinamik denge durumunda dahi yoğunluk dağılımı homojen olmamakta ve sınırlarda yoğunluğun azalarak sıfır değerine ulaştığı bir sınır tabaka oluşmaktadır. Sınır tabaka kalınlığı Planck sabiti ile orantılı olduğundan kuantum sınır tabakası olarak adlandırılır. Kuantum sınır tabakası nedeniyle gaz parçacıkları geometrik hacimden daha küçük olan etkin bir hacmi doldururlar. Kuantum sınır tabakasının kalınlığı ısıl de Broglie dalga boyu mertebesindedir ve sınırlar ile parçacıklar arasındaki uzaktan etkileşme sebebiyle parçacıklar sınırları ısıl de Broglie dalga boyu mesafesinde hissederler. Bundan dolayı, parçacıkların dalga karakterleri nedeniyle etkilendikleri potansiyel, tanecik karakterine sahip parçacıkların etkilendiği klasik potansiyelden farklıdır. Bu nedenle potansiyel, klasik potansiyele etkin kuantum potansiyel olarak adlandırılan bir başka potansiyelin eklenmesiyle temsil edilir. Bu çalışmada; dikdörtgen geometriler için relaksasyon zamanı yaklaşımı altında Maxwellian gazların transport katsayıları kuantum ölçek etkisi altında incelenmiştir. Parçacık-parçacık ve parçacık-duvar çarpışmaları sonucu meydana gelen transport süreçler ayrı ayrı incelenerek iletim, difüzyon ve termal iletkenlik katsayıları 3 boyutlu dikdörtgen geometriler için çıkarılmıştır. Transport katsayıların, kuantum ölçek etkileri nedeniyle, transport ortamının ölçek ve geometrisine bağlı olduğu görülmüştür. Ayrıca, evrensel bir yasa olan Wiedemann-Franz yasasının nano ölçekte kuantum ölçek etkileri nedeniyle evrenselliğini kaybettiği bulunmuştur. Anahtar Kelimeler: Kuantum ölçek etkisi, nano gaz transportu, kuantum potansiyel.Fabrication of micro and nano electromechanical systems have led to the possibility of small scales devices such as, sensors, actuators, biomedical devices, pumps, propulsion system and micro engines for power generation based on new physical effects. Therefore, it is important to understand the influence of new effects on transport properties of gases confined in small scale structures. In nano scale, quantum mechanical effects become important and the transport models based on the concepts of the classical mechanics must be modified by considering the quantum mechanical concepts. In nano-scale, even at thermodynamic equilibrium, density distribution is not uniform and there is a boundary layer near to the boundaries where the density goes to zero. This layer is called quantum boundary layer since the thickness of the layer is proportional to the Planck's constant. Due to quantum boundary layer, gas particles fill an effective volume which is less than the geometric one. Due to wave characteristics of particles, there is a non-local repulsive interaction between boundaries and particles. Therefore particles tend to accumulate in the inner part of the domain and it causes a higher local density than the classical one for the interior regions. Thickness of this boundary layer is in the order of thermal de Broglie wavelength of the particles and it defines a characteristic length scale. Therefore, quantum size effects appear when the size of the domain becomes comparable with the thickness of the boundary layer. Due to non-local interaction between boundaries and particles, particles feel the boundaries when the distance is in the order of thermal de Broglie wave length. Thus, the potential acting on the wave-like particles is different than the potential acting on the particle-like ones. The true potential can be represented by adding an effective quantum potential to the classical one. In an effective potential approach, one replaces the quantum distribution function by a classical distribution function with a modified potential. Thus, all the quantum effects on local density are modeled through the effective quantum potential. Transport behavior of gases confined in nano scale is considerably different than that in macro scale, due to different kinds of size effects. Classic scaling approaches generally assumes that physical constants and material properties remain independent of the scale. However, this assumption breaks down when the wave character of gas particles is considered or the length scale of the system approaches to the characteristic length scale of the mechanism that controls the property of interest. When the dimension of the system becomes very small in one direction, then the component of the wave vector of the particle in this direction becomes strongly quantized. Consequently, in nano scale,it is important to examine the quantum size effects on transport coefficients. In this study, conductivity, diffusion and thermal conductivity coefficients of a Maxwellian gas are derived by considering the quantum size effects and the Boltzmann transport equation under the relaxation time approximation for 3D rectangular geometry. The particle-particle and particle-boundary collisions based transport processes are examined individually. In the case of particle-boundary collisions dominated transport regime, it is shown that quantum size effects are stronger in comparison with those in particle-particle collisions dominated one. It is seen that quantum potential gradient can be a driving force for the transport processes. In a domain filled by a Maxwellian gas under a temperature gradient, the temperature dependence of quantum potential causes quantum potential gradient as a secondary driving force and these driving forces may cause a new type of convection which can be called quantum convection. Consequently, it is shown that conductivity; diffusion and thermal conductivity coefficients depend on size and geometry of the transport domain due to quantum size effects. Therefore, shape and size of the domain become additional control parameters on the transport processes. Because of these control parameters, new transport processes can be defined and new micro and nano engines can be designed by using the quantum size effects. Furthermore, it is shown that the universal Wiedemann-Franz law, which is the ratio of the thermal conductivity to the electrical conductivity, loses its universality in nano scale due to quantum size effects. Keywords: Quantum size effects, nano gas transport, quantum potential
Development of fuzzy process control charts: Direct fuzzy approach
Full text linkKlasik kontrol diyagramları, W.A. Shewhart tarafından 1920’lerde geliştirilmiş olmasına rağmen yeni uygulama alanları ile günümüzde hala gelişimini sürdürmektedir. Verilerin tam ve kesin olduğu durumlarda klasik kontrol diyagramlarının kullanılması uygundur; ancak subjektifliğin önemli bir rol oynadığı bazı durumlarda bu kadar kesin verilere sahip olmak neredeyse imkânsızdır. Belirsizlik altındaki durumlarda karar analizleri genellikle olasılık teorisi ve/veya bulanık kümeler teorisi kullanılarak yapılmaktadır. Bunlardan birincisi karar vermenin stokastik yapısını diğeri ise insanın düşüncesinin subjektifliğini temsil eder. Bulanık kümeler teorisi, ne rassal ne de stokastik olan insanın zihinsel yapısından kaynaklanan belirsizliğin modellenmesinde mükemmeldir. Belirsiz, kesin olmayan veya dilsel anlatımlar içeren durumlarda bulanık kümeler teorisinin kullanılması kaçınılmazdır. Bu çalışmada, bulanık kümeler teorisi kullanılarak belirsizlik içeren dilsel verilerle kontrol diyagramlarına yeni yaklaşımlar geliştirilmiştir. Belirsizlik içeren dilsel veriler, bulanık sayılarla ifade edilmiştir. Dilsel veriler için bulanık kontrol diyagramları α-kesim yaklaşımı kullanılarak geliştirilmiş ve bu suretle muayene sıklığı tanımlanmıştır. Veri ve kontrol limitlerinin temsili değerler ile klasik biçime (nümerik değerlere) dönüştürülmesi sonucu taşıdığı bilgiler yitirilmektedir. Bulanık kontrol diyagramlarının oluşturulmasında, bulanık verilerin taşıdığı bilgilerin kaybolmasını önlemek amacıyla “Direkt Bulanık Yaklaşım” geliştirilmiştir. Bu yaklaşımda veriler bulanık sayılarla ifade edilmiş ve temsili değerler kullanılmadan kontrol limitleri de bulanık sayılar olarak hesaplanmıştır. Kontrol altında, kontrol dışında kararlarına ek olarak kısmen kontrol altında, kısmen kontrol dışında gibi ara kararlar geliştirilmiştir. Anahtar Kelimeler: Bulanık proses kontrol diyagramları, bulanık kümeler, dilsel veriler, normal olmayan davranış analizi, belirsizlik. Control charts have been widely used for monitoring process stability and capability. Control charts are based on data representing one or several quality-related characteristics of the product or service. If these characteristics are measurable on numerical scales, then variable control charts are used. If the quality-related characteristics cannot be easily represented in numerical form, then attribute control charts are useful. Even though the first classical control chart was proposed during the 1920's by W.A. Shewhart, today they are still subject to new application areas that deserve further attention. Classical process control charts are suitable when the data are exactly known and precise; but in some cases, it is nearly impossible to have such strict data if human subjectivity plays an important role. It is not surprising that uncertainty exists in the human world. To survive in our world, we are engaged in making decisions, managing and analyzing information, as well as predicting future events. All of these activities utilize information that is available and help us try to cope with information that is not. A rational approach toward decision-making should take human subjectivity into account, rather than employing only objective probability measures. A research work incorporating uncertainty into decision analysis is basically done through the probability theory and/or the fuzzy set theory. The former represents the stochastic nature of decision analysis while the latter captures the subjectivity of human behavior. The fuzzy set theory is a perfect means for modeling uncertainty (or imprecision) arising from mental phenomena which is neither random nor stochastic. Many problems in scientific investigation generate nonprecise data incorporating nonstatistical uncertainty. A nonprecise observation of a quantitative variable can be described by a special type of membership function defined on the set of all real numbers called a fuzzy number or a fuzzy interval. A methodology for constructing control charts is proposed when the quality characteristics are vague, uncertain, incomplete or linguistically defined. The binary classification into conforming and nonconforming used in the p-chart might not be appropriate in many situations where product quality does not change abruptly from satisfactory to worthless, and there might be a number of intermediate levels. Without fully utilizing such intermediate information, the use of the p-chart usually results in poorer performance than that of the x-chart. This is evidenced by weaker detectability of process shifts and other abnormal conditions such as unnatural patterns. To supplement the binary classification, several intermediate levels may be expressed by using linguistic terms. For example, the quality of a product can be classified into the following terms: 'perfect', 'good', 'medium', 'poor', or 'bad' depending on its deviation from specifications. Then, the continuous functions selected appropriately can be used to describe the quality characteristic associated with each linguistic term. In this study, the control charts for number of nonconformities are handled. The type of available data is the imprecise number of nonconformities such as "between 5 and 8" or "approximately 6". The statistical model is based on the classical Shewhart control charts. In the literature, there exist few papers on fuzzy control charts, which use defuzziffication methods such as fuzzy mod, fuzzy midrange, fuzzy median, and fuzzy average in the early steps of their algorithms. The use of defuzziffication methods in the early steps of the algorithm makes it too similar to the classical analysis. Linguistic data in those works are transformed into numeric values before control limits are calculated. Thus both control limits as well as sample values become numeric. This transformation may cause biased results due to the loss of information included by the samples. For example, two fuzzy samples with the equal fuzzy mod may explain very different characteristics. A new approach called direct fuzzy approach to fuzzy control charts is modeled in order to prevent the loss of information of the fuzzy data during the construction of control charts. In this approach, linguistic or uncertain data are represented by means of triangular and/or trapezoidal fuzzy numbers. Using fuzzy arithmetics, control limits based on the fuzzy data are also determined as fuzzy numbers. The decision about the process control is based on the area measurement method. The proposed approach directly compares the linguistic data in fuzzy space without making any transformation. The percentage area of the fuzzy sample behind the fuzzy control limits is used in the decision and intermediate decision levels are defined. Keywords: Fuzzy control charts, fuzzy sets, linguistic data, unnatural pattern analysis, uncertainty.
Financial parameters selection for a forecasting system on Istanbul Stock Exchange
Full text linkFinansal piyasalara odaklanan ve farklı amaçlarla yürütülen bir çok araştırmada fiyat veya getiri tahminine yönelik yoğun bir ilgi görülmektedir. Bu ilginin temel nedeni finansal piyasaların dinamiğini tespit etmektir. Piyasa davranışının belirlenmesi; makro yatırım politikalarından bireysel tasarruflara kadar birikimlerin yönlendirilmesinde, portföy optimizasyonundan piyasa ekonomisinin işleyişine kadar bir çok konuda yol gösterici olacaktır. Başka bir deyişle hisse senedi fiyat hareketlerinin tahmin edilebilirliğinin araştırılması; akademisyenlerin etkin pazar kuramını sınamasına yardımcı olurken; rasyonel ilişkiler tespit edilirse, yatırım uzmanları güvenilir getiri sağlayan bir işlem sistemi oluşturulabileceklerdir. Bu çalışmanın amacı, İMKB-100 endeks hareketlerini tahmin etmede; gayrısafi milli hasıla, sanayi üretim endeksi gibi makro ekonomik değişkenlerin ve reel gösterge faiz oranı, döviz kurları gibi finansal verilerin kullanılabilirliğini araştırmaktır. Finansal piyasalarda fiyat tahminine yönelik bir çok modelleme çalışması yürütülmüş, ancak her dönem ve her piyasada kullanılabilir bir sistem oluşturulamamıştır. Zira hisse senedi fiyatları üzerinde, tümü tahmin modellemesinde kullanılamayacak kadar çok sayıda lokal ve global değişkenin (meteorolojik ve astrolojik değişkenlere kadar) etkisi söz konusudur. Ülkemizde de farklı istatistiksel çalışmalarda finansal göstergelerin, İMKB Hisse Senedi Piyasası’ndaki fiyat hareketleri ile ilişkisi araştırılmıştır. Ayrıca son yıllarda sözkonusu ilişkilerin analizi yerine, değişkenlerin doğrudan endeks tahmininde kullanılabilirliği incelenmektedir. Çalışmada girdiler, mevsimsel ve enflasyonist etkilerden arındırıldıktan sonra İMKB-100 Endeksi ile ilişkileri irdelenmiş ve son olarak İleri Beslemeli Geri Yayılımlı (İBGYYSA) bir ağ tipi için uygun normalizasyon yöntemi araştırılmıştır. Anahtar Kelimeler: Menkul değer piyasalarında tahminleme, yapay sinir ağları, finansal pazarlarda tahmin parametreleri.In the last decade, with the growth of computational facilities, there are many academic attempts about financial market prediction. Because of the huge sort of local and global data that may affect market trends, forecasting models developed until today have been only effective in few markets and for a limited period of time. Studies about Istanbul Stock Exchange (ISE) are limited. Determining the complex relationship between financial markets and economic parameters needs a chaotic approach. Chaos is a nonlinear deterministic process which only appears random because it cannot be easily expressed. Multivariate analytical techniques using both quantitative and qualitative variables have repeatedly been used to help form the basis of investor stock price expectations and hence, influence investment decision making. However, the performance of multivariate analytical techniques is often less than conclusive and needs to be improved to more accurately forecast stock price performance. A neural network (NN) method has demonstrated its capability of addressing complex problems. A neural network method may be able to enhance an investor's forecasting ability. There are several motivations for trying to predict stock market prices. But initial background needs of almost everyone is to investigate the market behavior, because each study about financial markets starts on that base. The most principal motivation is naturally financial gain. Finding any system that can consistently give greater revenue then the average return in the dynamic market place, is very important for the owner of the system, to give market players the impression of being trustworthy. Moreover, many investors are continually looking for this superior system which will yield them higher returns. Another motivation for researchers is the Efficient Market Hypothesis (EMH). It has been proposed in the EMH that markets are so efficient and profit opportunities are discovered so quickly that no one can catch superior performance. Hypothesis states that no system can continually beat the market because if this system becomes public, everyone will use it, thus negating its potential gain. There has been an ongoing debate on the validity of the EMH, some researchers use forecast results to validate their claims, other observers trying to demonstrate that the market is weak in efficiency. Validity of EMH is very important for the board managers point of view. If it can be proved that the market behavior is rational, while researchers evaluate the concept of a new efficient market, it would be possible to attract new resources to the market and create a new transaction system in which investors believe. No matter what the prediction purpose and methodology are the first step is to choose the parameters that really represent the market direction of movement and the level of variation. On the other hand, typical investors trading behaviors have been guided by two main perspectives; namely; Fundamental and technical analysis. While technical analysis uses only past market prices and volume, fundamental analysis is derived from external information which comes from the economic system encircling the market. This information consists of interest rates, prices and returns of other assets, and many other macro or micro economic variables. The aim of this study was to evaluate the effectiveness of using macroeconomic indicators such as; gross national product, industrial production level and financial data such as; real benchmark, currency exchange rates, in predicting movements in the ISE 100 Index (ISE-100). Availability of midterm economic and financial indicators to estimate the ISE-100 trends was investigated in this research. If the investigation findings show that these variables are efficient to explain the price movements in the ISE, then two basic judgments will be reached. Firstly, the EMH will be canceled or at least in a most optimistic view, a weak form efficiency in the market will be proven. Secondly, an investment decision support system based on NN estimates will be developed for investment advisors and investors. Also, the EMH is presented and contrasted with chaos theory and neural networks. This paper refutes the EMH based on previous neural network work. Finally, future directions for applying neural networks to the financial markets are discussed. Using statistical investigation we find causal relations between some indicators including macroeconomic, inflation, alternative financial instruments, and the Turkish Security Market. After adjusting seasonal and influationist impacts; input variable has been investigated their midterm relationship with ISE-100 Index. In the last section, appropriate normalization method for a backpropagation feedforward networks (BPNN) was researched. Keywords: Predicting stock indexes, artificial neural networks, financial markets forecasting parameters
Dynamic vibration analysis of ballastless track
Full text linkDemiryolu üstyapısında ray ile tekerlek arasındaki temas sırasında düzensizlik ve pürüzlülükler nedeniyle ek dinamik yükler ve titreşim ortaya çıkmaktadır. Özellikle, demiryolu taşıtının neden olduğu titreşimlerin frekansları ile sistemin doğal frekansları çakıştığında rezonans denilen dinamik fenomen ortaya çıktığı için, sonlu eleman modellerini kullanan nümerik analizlerin yapılması ve rezonans durumundaki dinamik etkilerin belirlenmesi gereklidir. Bu çalışmada, İstanbul’da bulunan Aksaray-Havaalanı arasında kalan hafif metro hattında çelik seletli balastsız (beton döşemeli) üstyapı, nümerik yöntemle ANSYS 9.0 sonlu eleman programı kullanılarak analiz edilmiştir. Bu analizde, demiryolu üstyapısı yol eksenine göre simetrik bir yapıya sahip olduğundan hesaplamada kolaylık sağlamak için tek ray ve çelik seletten oluşan yol sistemi modellenmiştir. ANSYS programı ile harmonik analiz yapılarak dinamik hesap sonuçları ve grafikleri elde edilmiştir. Harmonik tepki analizi, aracın devamlı dinamik davranışını, dolayısıyla, tasarımın rezonans, yorulma ve zorlanmış titreşimin diğer zararlı etkilerine başarıyla karşı koyup koyamayacağını belirleyebilmeyi sağlar. Harmonik tepki analizi lineer bir yapının zamanla sinüzoidal (harmonik) olarak değişen yüklere karşı sürekli durum tepkisini belirlemekte kullanılan bir tekniktir. Nümerik analizde, 0-1500 Hz frekans aralığı için değişik yol parametrelerinin dinamik davranışa etkisi hesaplanmıştır. Demiryolunun öz frekanslarını, dinamik tepki davranışını tespit etmek ve ölçüm sonuçlarına göre sonlu eleman modelini doğrulamak amacıyla arazi titreşim ölçümü yapılmıştır. Arazide ray mantarına çekiç darbe yükü uygulanarak, rayın ve mesnetin (çelik selet) frekans tepki davranışı ölçülmüş, çelik seletli balastsız hattın sonlu elemanlar modeli doğrulanmıştır. Anahtar Kelimeler: Dinamik, demiryolu titreşimi, nümerik analiz, çekiç darbe testi.Additional dynamic loads and friction emerge on the railroad superstructure due to irregularity and roughness that occur between the rails and the wheels. In particular, when the vibration frequencies of the railroad vehicle and natural frequencies of the system match, a dynamic phenomenon called resonance occurs. Therefore, numeric analyses that use finite element models need to be performed, and resonating dynamic effects need to be determined. Furthermore, field vibration surveys should be conducted, and the natural frequencies of the railroad should be measured to support and verify the dynamic analysis. In this study, a ballastless superstructure with a steel baseplate of light metro track, which lies between Aksaray and the Airport in Istanbul, was analyzed with a numerical method using ANSYS 9.0 finite element software. Since the railroad superstructure has a symmetric structure with respect to the track axis, a rail system that consists of a single rail and a steel baseplate was modeled to simplify the computations in this analysis. In the discrete supported track model, the rail was modeled as an Euler-Bernoulli beam and steel baseplate, and it was assumed to be a rigid mass. Dynamic computation results and graphs were determined by performing harmonic analysis with the aid of ANSYS software. Harmonic receptance analysis enables the continuous dynamic behavior of the vehicle to be determined; as a result, the ability of the design to successfully withstand resonance, fatigue, and other harmless effects of constrained vibration is revealed. Harmonic receptance analysis is a technique that is used to determine steady-state receptance against sinusoidal (harmonically) changing loads of a linear structure. The purpose of this analysis is to estimate the receptance of the structure at various frequencies and plot it. In the numerical analysis, the effect of various track parameters for the 0-1500 Hz interval on the dynamic behavior was calculated. When modeling with the finite elements method, the wheel load was applied both above the support and in the middle of two supports. A field vibration survey was conducted to determine the natural frequencies of the railroad and the dynamic receptance behavior, and to validate the finite element model according to the measurement results. The frequency receptance behavior of the rail and the support was measured by applying a hammer impact load on the rail head in the field, and the finite element model of the ballastless track with steel baseplate was verified. A single peak value is observed on the dynamic receptance graph based on measurement results, and this value indicates the track natural frequency. The natural frequency of the ballastless track varies depending on baseplate distance and the type of elastic layer under the baseplate. But it is difficult to identify the natural frequency of the rail. Survey results for the ballastless track were remarkably consistent with the finite elements model, and the natural frequency and dynamic receptance values for both of them were found to be very close to each other. This is because there are not any granular materials that have unknown dynamic properties, like the ballast and soil in this superstructure; only elastic layers under rails and steel baseplate are present. It is possible to establish dynamic properties fully consistent with measurements, particularly for ballastless track models. Consequently, there is a good chance of precisely determining the dynamic behavior of the track for vehicle and track parameters. This study is the first in Turkey that combines railroad dynamic analysis and modeling and surveying, and it can be considered as a significant development for urban railroad systems and high speed railroad projects, which have grown in the last several years. It is crucial to analyze the effect of various track parameters (rail type, elastic layer, support distance, etc.) on the dynamic behavior of the railroad, as the ballastless superstructure is preferred for urban rail systems (subway and tramway systems). It is possible to explicate with finite element models validated by field surveys. Deciding on the most fitting design in terms of vibration and determining the natural frequencies of the track during the planning stage is necessary to reduce the negative environmental effects of urban rail systems, which are located very close to areas sensitive to vibration and noise, such as historical structures, residences, hospitals, and schools. Furthermore, future studies should focus on determining the excitation frequencies caused by trains and natural frequencies of nearby buildings. Keywords: Dynamic, railway vibration, numerical analysis, hammer impact test.
Gradient-based object segmentation and recognition
Full text linkBu çalışmada, aktif çevrit nesne bölütleyici yöntemlerle birlikte kullanılabilecek yeni bir eşzamanlı şekil betimleme ve tanıma sistemi önerilmiştir. Aktif çevrit bölütleyici olarak Hızlı Yürüme (Fast Marching) algoritması kullanılmış, Hızlı Yürüme metodu için yeni bir hız işlevi tanımlanmış, ayrıca çevriti nesne sınırlarından geçtiği sırada durdurmayı amaçlayan özgün yaklaşımlar önerilmiştir. Çalışmanın en önemli katkılarından birisi yeni ortaya atılan Gradyan Temelli Şekil Betimleyicisi (GTŞB) dir (Çapar vd., 2009). GTŞB, aktif çevrit bölütleyicilerinin yapısına uygun, sınır tabanlı, hem ikili hem de gri-seviyeli görüntülerle rahatça kullanılabilecek başarılı bir şekil betimleyicidir. GTŞB nin araç plaka karakter veritabanı, MPEG-7 şekil veritabanı, Kimia şekil veritabanı gibi farklı şekil veritabanlarında elde ettiği başarılar diğer çok bilinen sınır tabanlı betimleyicilerle de karşılaştırılarak verilmiştir. Elde edilen sonuçlar GTŞB nin tüm veritabanlarında diğer yöntemlere göre daha başarılı olduğunu işaret etmektedir. Çalışmada ortaya atılan bir diğer önemli yaklaşım da Hızlı Yürüme çevritinin nesne sınırına yaklaşırken örneklenerek şeklin birden fazla defa betimlenmesine olanak veren yeni sınıflandırıcı yapıdır. Bu yaklaşım nesne tanımayı bir denemede sonuçlandıran geleneksel yöntemlerin bu sınırlamasını aşarak aynı nesneyi birçok kez tanıma olanağı sunmaktadır. Bu tanıma sonuçlarının tümleştirilmesiyle tek tanımaya göre daha yüksek başarılar elde edildiği çalışmanın ilgili bölümlerinde gösterilmektedir. Bu çalışmada görüntüde bulunan nesneleri bölütlerken aynı zamanda betimleyebilen tümleşik bir yöntem önerilmiştir. Anahtar Kelimeler: Şekil betimleyici, Fourier dönüşümü, hızlı yürüme, yönlendirilebilir süzgeçler.We proposed a gradient based shape description and recognition methodology to use with active contour based object segmentation systems. We selected Fast Marching method which is an active contour segmentation technique is assigned for object detection and segmentation. We proposed a new speed function using first and second order intensity derivatives. In order to obtain the shapes properly, the evolving front is asked to be stopped near real object boundaries. Nevertheless, it is impossible for ordinary Fast Marching systems because of the non-zero speed functions. One of the contributions of the thesis is providing a new FM contour stopping algorithm. The proposed algorithm uses first and second order derivatives of local image intensities to determine whether an evolving node should stop or not The proposed system is capable for both segmentation and identification of shapes simultaneously. Since we utilized an active contour based segmentation approach for detecting objects, we need a contour based shape descriptor. In this work, we proposed a contour-based shape description scheme, named Gradient Based Shape Descriptor (GBSD), using some rotated gradient filter responses along the object boundary. GBSD can be applied to both binary and grayscale images. The proposed algorithm utilizes gradient based features which are extracted along the object boundaries. We use two-dimensional steerable G-Filters to obtain gradient information at different orientations and scales, and then aggregate the gradients into a shape signature. The signature derived from the rotated object is circularly shifted version of the signature derived from the original object. This property is called the circular-shifting rule. The shape descriptor is defined as the Fourier transform of the signature. We also provide a distance measure for the proposed descriptor by taking the circular-shifting rule into account. The performance of the proposed descriptor is evaluated over two databases; one containing digits taken from vehicle license plates and the other containing MPEG-7 Core Experiment and Kimia shape data set. The experiments show that the devised method outperforms other well-known Fourier-based shape descriptors such as centroid distance and boundary curvature. When we combine the proposed shape descriptor GBSD with Fast Marching (FM) approach, we obtain a descriptor vector for each FM evolving iteration. That means we have more than one feature vectors for a single shape. Besides, each vector will be able to be fed into a classifier to obtain different decisions. Each decision result can be threaded as a different source of information and a decision fusion process can be applied to get final decision. This is another contribution of the thesis. The proposed system has following advantages comparing with other concurrent object segmentation-recognition approaches; In previous studies, the evolving front is always forced to have the prior shape. However, we stop the front near object boundaries. It is stated that, the proposed method does not work when the number of prior object classes is more than one (Paragios vd., 2002). However, our system is capable to segment and recognize different class of characters. Previous researchers obtained the shape statistics from the whole map of level set values; however we employ only the front itself for shape description. Previously proposed systems need high calculation power because they have two optimization stages, one is for minimization of image energies, and other is for minimizing shape similarity energies. On the other hand, our system has one optimization step for minimizing both energies. Misrecognitions mostly occur because of segmentation problems. An object cannot be easily recognized if we cannot extract it from the background properly. In this study, many segmentation results are employed as input of classifiers to reduce the segmentation effects on recognition. In traditional recognition systems only one recognition chance exists for a single object but we can obtain many decision results while the active contour is capturing the shape. We showed in Section 5.4 that voting among these results raises the recognition performance comparing with single decision cases. We have feedback mechanism between segmentation and description. This feedback provides better segmentation and recognition results. Keywords: Shape descriptors, fourier, fast marching, steerable filters
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