https://ari.itu.edu.tr/index.php/ituari/issue/feed 2023-01-09T19:48:11+03:00 Ahmet GÜL ahmetg@itu.edu.tr Open Journal Systems <p>ARI – Bulletin of the Istanbul Technical University publishes:</p> <p>- Original research articles and short communications describing recent discoveries and developments in related fields.<br />- Review papers, dealing with emerging areas of basic, applied, natural sciences and engineering research.<br />- Special issues with guest editor(s) dedicated to relevant fundamental topics and to eminent scholars.</p> <p>All submitted articles will be peer reviewed based on anonymous refereeing.</p> <p>ARI – Bulletin of the Istanbul Technical University welcomes manuscripts spanning below fields of study, however, authors are encouraged to suggest relevant topics which might also be considered for a publication in the journal.</p> <p>| Basic Sciences | Physical Sciences | Engineering Sciences | Natural Sciences |</p> https://ari.itu.edu.tr/index.php/ituari/article/view/57 2023-01-09T19:34:52+03:00 A. Yalçın AKÖZ sil_dene@itu.edu.tr Mesut AKSOYDAN sil_dene@itu.edu.tr

In this study Timoshenko beams on elastic foundations are analyzed under arbitrary loading by transfer matrix method. The Winkler hypothesis adopted, because of its simplicity. The analytical approaches provide physical insight into the nature of the problem. It is observed that three distinct behavior of a structure of the beam exist depending on parameters. Therefore three types of transfer matrixes are derived by the spectral expansion method, in terms of the displacement, the rotation, the moment and the shear forces. Furthermore, three distinct stiffness matrixes are obtained. However, for engineering purposes only one of them has practical importance. The transfer matrix serves to derive the stiffness matrix, which is necessary to analyze the structural frames. For this purpose equivalent nodal forces are given for the concentrated and trapezoidal load distribution. The performance of the method is shown by the numerical examples.

2005-02-01T00:00:00+02:00 Copyright (c) 2005 ITU Press https://ari.itu.edu.tr/index.php/ituari/article/view/58 2023-01-09T19:34:54+03:00 Hamidreza KARIMI sil_dene@itu.edu.tr Amir BABAZADEH sil_dene@itu.edu.tr Parviz Jabedar MARALANI sil_dene@itu.edu.tr Behzad MOSHIRI sil_dene@itu.edu.tr Nejila PARSPOUR sil_dene@itu.edu.tr

This paper deals with the modeling and adaptive output tracking of a Transverse Flux Permanent Magnet Machine (TFPM) as a nonlinear system with unknown nonlinearities by utilizing high gain observer (HGO) and Radial Basis Function (RBF) networks. The technique of feedback linearization and H1 control are used to design an adaptive control law for compensating the unknown nonlinearity parts, such the effect of cogging torque, as a disturbance is decreased onto the rotor angle and angular velocity tracking performances. Finally, the capability of the proposed method is shown in the simulation results.

2005-02-01T00:00:00+02:00 Copyright (c) 2005 ITU Press https://ari.itu.edu.tr/index.php/ituari/article/view/59 2023-01-09T19:34:56+03:00 Cemal YILDIZ sil_dene@itu.edu.tr Pınar ÖNDER sil_dene@itu.edu.tr Emre BİROL sil_dene@itu.edu.tr Erkan ALCAN sil_dene@itu.edu.tr

The transport of monoenergetic neutrons in a bare homogeneous cylinder is studied. The transport equation is solved using FN method considering the pseudo-problem. Numerical values for the critical radius are obtained and tabulated for various c values. Numerical results indicate that the critical radius varies non-monotonically with forward scattering. Some selected illustrative results are compared with those already available in the literature. It is also shown that the FN method, though approximate, yields results accurate to at least three or four significant figures for the problem considered.

2005-02-01T00:00:00+02:00 Copyright (c) 2005 ITU Press https://ari.itu.edu.tr/index.php/ituari/article/view/60 2023-01-09T19:34:57+03:00 Muzaffer ERDOĞAN sil_dene@itu.edu.tr Orhan KAMER sil_dene@itu.edu.tr

We present a model to examine the infuence of various pinning regions on the magnetic hysteresis of a ferromagnetic amorphous wire by revealing the correlation between its magnetic hysteresis and pinning region configuration. Magnetization is performed with the motion of 180-degrees domain walls. Domain configuration in every stage of magnetization is traced by analyzing the total energy of domain-domain, domain wall-domain,domain wall-pinning center, and external magnetic field interactions. The predicted hysteresis loops obtained are found to be in good agreement with the experimental ones in literature.

2005-02-01T00:00:00+02:00 Copyright (c) 2005 ITU Press https://ari.itu.edu.tr/index.php/ituari/article/view/61 2023-01-09T19:34:58+03:00 Binnur KURT sil_dene@itu.edu.tr Muhittin GÖKMEN sil_dene@itu.edu.tr

An efficient contour based image coding scheme based on Centipede Model [1] is introduced in this paper. Unlike previous contour based models which presents discontinuities with various scales as a step edge of constant scale, the centipede model allows us to utilize the actual scales of discontinuities as well as location and contrast across them. The use of the actual scale of edges together with other properties enables us to reconstruct a better replica of the original image as compared to the algorithm lacking this feature. In this model, there is a centipede structure for each edge segment which lies along the edge segment and the gray level variation across an edge point is represented by a hybrid spline and distance between left and right feet of the centipede. The proposed model aims at reconstructing the closest intensity surface to the original one from the contour information. We first obtain edges by using the Generalized Edge Detector (GED) [2, 3] which controls the scale and shape of the filter, providing edges suitable to the application in hand. Then the detected edges are traced to produce the distinct contours. These contours are ranked by assigning a priority based on the weighted sum of contour length, mean contrast, contour density and mean contour curvature. In our scheme, the compression ratio is controlled by retaining the most significant segments and by adjusting the distance between the successive foot pairs. The original image is reconstructed from this sparse information by minimizing a hybrid energy functional which spans a space called lambdatau-space, where lambda represents the smoothness of the image and represents tau the continuity of the image. Since the GED filters are derived from this energy functional, we have utilized the same process both for detecting the edges and reconstructing the surface from them. The proposed model and the algorithm have been tested on both real and synthetic images. Compression ratio reaches to 180:1 for synthetic images while it ranges from 25:1 to 100:1 for real images. We have experimentally shown that the proposed model preserves perceptually important features even at the high compression ratios.

2005-02-01T00:00:00+02:00 Copyright (c) 2005 ITU Press https://ari.itu.edu.tr/index.php/ituari/article/view/62 2023-01-09T19:35:00+03:00 M. Cem GÜÇLÜ sil_dene@itu.edu.tr

At relativistic heavy ion colliders, electromagnetic fields of heavy nuclei are very strong and can produce a wide variety of leptons. We present recent results from CERN and RHIC on ultra-peripheral interactions, focusing on electron-positron pair production.

2005-02-01T00:00:00+02:00 Copyright (c) 2005 ITU Press https://ari.itu.edu.tr/index.php/ituari/article/view/63 2023-01-09T19:35:01+03:00 Fernando ALVARADO sil_dene@itu.edu.tr Hasan DAĞ sil_dene@itu.edu.tr

Incomplete LU factorization is a valuable preconditioning approach for sparse iterative solvers. An "ideal" but inffcient preconditioner for the iterative solution of Ax = b is A−1itself. This paper describes a preconditioner based on sparse approximations to partitioned representations of A−1, in addition to the results of implementation of the proposed method in a shared memory parallel environment. The partitioned inverses are normally somewhat sparse. Their sparsity can be enhanced with suitable ordering and partitioning algorithms. Sparse approximations to these partitioned inverse representations can be obtained either by discarding selected nonzero entries of these inverses or by precluding the creation of some inversion fills. Experimental results indicate that the use of these partitioned incomplete inverses as preconditioners results in excellent highly parallel preconditioners.

2005-02-01T00:00:00+02:00 Copyright (c) 2005 ITU Press https://ari.itu.edu.tr/index.php/ituari/article/view/64 2023-01-09T19:35:03+03:00 A. Burak GÖKTEPE sil_dene@itu.edu.tr Emine AĞAR sil_dene@itu.edu.tr A. Hilmi LAV sil_dene@itu.edu.tr

Nondestructive testing (NDT) is the integral part of the performance evaluation of exible pavements. In all NDT methods, Falling Weight Deectometer (FWD) is probably the most popular technique. Basically, it measures time-domain de ections from numerous road sections emerging by the applied impulse load. In order to characterize the structural integrity of considered pavement system, it is required to make an inversion for the calculation of mechanical pavement properties using a backcalculation tool covering both a forward pavement response model and an optimization algorithm. On the other hand, backcalculation problem can also be solved by an adaptive system using a supervised learning algorithm. In this manner, multilayer perceptron (MLP) and adaptive neuro-fuzzy system (ANFIS) methodologies, popular universal functional approximating techniques of Artificial Intelligence (AI), are appropriate for pavement backcalculation problem. Therefore, two-phased (forward and backward) structure of traditional backcalculation approaches is reduced into one step with the help of the supervised learning mechanisms of MLP and ANFIS. In this study, these methodologies are both employed to backcalculate mechanical properties of exible pavements and compared in terms of modeling precision, uncertainty handling, computational expense, and data requirements. Results indicated that, both techniques are valid and have certain advantages over each other and should be preferred with respect to quantity and quality of the data at hand. In addition, AI-based supervised nonlinear mapping techniques not only exhibit precise backcalculation results, but also enable real-time pavement analyzing abilities.

2005-02-01T00:00:00+02:00 Copyright (c) 2005 ITU Press https://ari.itu.edu.tr/index.php/ituari/article/view/65 2023-01-09T19:35:05+03:00 Zübeyde ÖZTÜRK sil_dene@itu.edu.tr

In this paper, optimum speed on high-speed railways is investigated according to total costs for the Istanbul-Ankara connection. This connection, whose feasibility studies are completed, will serve both passenger and freight traffic. The high-speed railway route, planned between Istanbul and Ankara, is a part of the TER project (The Trans- European North-South Railway). The total cost investigated for this route includes the traffic independent (constant) costs, traffic dependent (variable) costs and the social (environmental) costs. At the end of the study it was cocluded that the optimum speed at which costs are minimised is 200 km/h for passenger trains and 90 km/h for freight trains.

2005-02-01T00:00:00+02:00 Copyright (c) 2005 ITU Press https://ari.itu.edu.tr/index.php/ituari/article/view/66 2023-01-09T19:35:06+03:00 Kemal Selçuk ÖĞÜT sil_dene@itu.edu.tr

Various kinds of rail vehicles are running on a railway track such as; passenger vehicles, freight vehicles, mainline locomotives, shunting engines. The algebraic sum of the vehicle loads cannot give an accurate picture of the running load, because it does not take into account the way in which the load is applied, the running speed, so on. Therefore, a complex parameter giving an accurate estimate of the passing traffic load is necessary. Union Internationale de Chemins de Fer, UIC, proposed a method to calculate the theoretical traffic load for this purpose. In this study, initially, the theoretical traffic loads for Turkish Railway Network are calculated with the help of train loads, speeds and tonnage for 2003. At the second stage, the classification of lines for the purpose of track maintenance is made by using these traffic loads.

2005-02-01T00:00:00+02:00 Copyright (c) 2005 ITU Press https://ari.itu.edu.tr/index.php/ituari/article/view/67 2023-01-09T19:35:07+03:00 Ali NAZZAL sil_dene@itu.edu.tr Önder GÜLER sil_dene@itu.edu.tr Sermin ONAYGİL sil_dene@itu.edu.tr

The DGIN (New Daylight Glare Index) method was recently developed at University of Helsinki to respond the challenge of predicting discomfort glare from daylight mathematically. For daylit offices, the presence of windows with computer workstations introduces potential glare sources. This paper outlines a survey conducted in a daylit-computerized office to identify factors contributing to discomfort glare experience and test applicability of the new method. Results suggest that light distribution and presence of reflections correlate strongly with the discomfort experience, and the DGIN could be sufficiently predictive to serve as an aid to design because it shows reasonable correlation with the subjectively perceived discomfort.

2005-02-01T00:00:00+02:00 Copyright (c) 2005 ITU Press