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Istanbul, Turkey

Okan University is a private university in Istanbul, Turkey. Wikipedia.


Aptoula E.,Okan University
IEEE Transactions on Geoscience and Remote Sensing | Year: 2014

In this paper, we present the results of applying global morphological texture descriptors to the problem of content-based remote sensing image retrieval. Specifically, we explore the potential of recently developed multiscale texture descriptors, namely, the circular covariance histogram and the rotation-invariant point triplets. Moreover, we introduce a couple of new descriptors, exploiting the Fourier power spectrum of the quasi-flat-zone-based scale space of their input. The descriptors are evaluated with the UC Merced Land Use-Land Cover data set, which has been only recently made public. The proposed approach is shown to outperform the best known retrieval scores, despite its shorter feature vector length, thus asserting the practical interest of global content descriptors as well as of mathematical morphology in this context. © 1980-2012 IEEE. Source


Ozturk S.B.,Okan University | Toliyat H.A.,Texas A&M University
IEEE/ASME Transactions on Mechatronics | Year: 2011

In this paper, the position-sensorless direct torque and indirect flux control of brushless dc (BLDC) motor with nonsinusoidal back electromotive force (EMF) has been extensively investigated. In the literature, several methods have been proposed for BLDC motor drives to obtain optimum current and torque control with minimum torque pulsations. Most methods are complicated and do not consider the stator flux linkage control, therefore, possible high-speed operations are not feasible. In this study, a novel and simple approach to achieve a low-frequency torque ripple-free direct torque control (DTC) with maximum efficiency based on dq reference frame is presented. The proposed sensorless method closely resembles the conventional DTC scheme used for sinusoidal ac motors such that it controls the torque directly and stator flux amplitude indirectly using d-axis current. This method does not require pulsewidth modulation and proportional plus integral regulators and also permits the regulation of varying signals. Furthermore, to eliminate the low-frequency torque oscillations, two actual and easily available line-to-line back EMF constants (kba and kca) according to electrical rotor position are obtained offline and converted to the dq frame equivalents using the new line-to-line park transformation. Then, they are set up in the look-up table for torque estimation. The validity and practical applications of the proposed sensorless three-phase conduction DTC of BLDC motor drive scheme are verified through simulations and experimental results. © 2010 IEEE. Source


Akay O.,Okan University
Geosynthetics International | Year: 2016

Lightweight expanded polystyrene (EPS) geofoam (geofoam block) is used in slope remediation works as a soil substitute fill to reduce driving forces that can lead to global instability. On the other hand, the presence of seepage flow requires special attention because geofoam block slope systems are vulnerable to seepage-induced lateral forces. In this study, the effect of an internal drainage system on the alleviation of piezometric pressures within the back-slope of a geofoam block slope system was investigated. For this purpose, laboratory experiments were conducted using a small-scale lysimeter with dimensions of 60 cm height, 20 cm width, and 200 cm length. The slope was compacted with sand to obtain an overall dry unit weight of 14 kN/m3. The constant piezometric head boundary conditions of 25, 38 and 50 cm generated the necessary hydraulic energy gradient for the seepage flow directed from the water reservoir of the lysimeter to the 45° angle slope face. The slopes were remediated by using geofoam blocks assembled in an embankment-type configuration at the toe of the slope. The internal drainage system consisted of grooved geofoam blocks that formed the 10, 15 and 22.5 cm high embankments. Deep-seated failures of the non-remediated slope were prevented except for the experiments with 10 and 15 cm high embankments under 50 cm pressure head boundary conditions. In general, the internal drainage system alleviated the piezometric pressure conditions within the back-slope by lowering the phreatic surface using the active drainage channels observed during laboratory experiments. These drainage channels provided a convenient passageway for seepage flow. The coupled numerical variably saturated flow modelling and slope stability modelling predicted the factor of safety for global stability which confirmed the observed physical conditions in the laboratory. The use of the internal drainage system increased the factor of safety of the geofoam block slope system under seepage conditions. © 2015 Thomas Telford Ltd. Source


An arbitrary increase of rest masses input to the quantum mechanical description of an atomic or molecular object leads to the increase of the related total energy (i.e., the eigenvalue), and contraction of the size, associated with it. Furthermore, this occurrence, on the basis of the quantum mechanical description in consideration, yields the "invariance" of the quantity [total energy×mass×size2], framing a fundamental architecture, matter is made of. Henceforth, we will call this latter quantity "quantum-mechanical-description-scaling-invariance," or briefly quantummechanical-description-scaling-invariance (QMDSI). This leads, amongst other things, to a whole new systematic of diatomic molecules, in general polyatomic molecules. On the other hand, one can check that the quantity [total energy×mass×size2] happens to be a Lorentz invariant quantity, for one thing; dimensionally, it comes to the square of the action quantity or the square of Planck Constant (which is well Lorentz invariant). Thus, it appears that the QMDSI we disclose about [total energy×mass×size2] with regards to a hypothetical mass change in a quantum mechanical description, happens to work as the inherent mechanism of the end results of the Special Theory of Relativity, was the object in consideration, brought to a uniform translational motion. Or similarly, it comes to work as the innate machinery of the end results of the General Theory of Relativity, where this object is embedded in a gravitational field. In both cases, it is question of a "real, overall mass change," which in return can well be considered, as an input to the quantum mechanical description, in consideration, to investigate the related results. One can further show that the occurrence we unveil holds not only for a gravitational field but generally for all fields the object at hand interacts with. Note that, herein, we propose to use the word "field," in the sense of "effective surrounding." Indeed, in our approach, the related changes take place in the respective cores of the interacting bodies, and not, in a rather fuzzy way, in their environment. Next to the rest masses, there remains one other parameter one can alter in the given quantum mechanical description, of mainly (but without any loss of generality, really), atomistic and molecular objects: It is the product of electric charges, coming into play. Its arbitrary change, in fact, fully reflects the actual Lorentz transformation of electric forces, where the object is brought to a uniform translational motion. Herein, we provide principal mathematical proofs. In a subsequent article, we will disclose the related architecture, matter is made of. © 2013 Physics Essays Publication. Source


Ozer A.T.,Okan University
Geosynthetics International | Year: 2016

The use of expanded polystyrene geofoam (geofoam block) has been gaining momentum in roadway expansion projects. They are traditionally placed along the slope face of the existing roadway embankment as a side-hill fill. However, previous studies have shown the detrimental effects of seepage forces on the side-hill fill type of geofoam block configurations. In order to improve the performance of traditional embankment-widening configuration under seepage forces, an alternative geofoam block assembly is proposed. For this purpose, a lysimeter with dimensions of 60 cm high, 20 cm wide, and 200 cm long was constructed in the laboratory. Awater reservoir located at the end of the lysimeter provided three different constant pressure heads (25 cm-, 38 cm-, and 50 cm-H2O pressure) during the tests. An embankment-widening geofoam block assembly was placed along the slope face of marginally stable sandy embankment to investigate the effects of seepage on the stability of geofoam block assembly. The dimensions of the geofoam blocks used to construct the embankment-widening sections were 2.5 cm high, 5 cm wide, and 15 cm long. In addition to the laboratory physical testing, factors of safety against global stability and hydrostatic sliding failures were studied through coupled numerical modelling. Stability modelling comprised fully coupled variably saturated flow and conventional limit equilibrium analysis to quantify the performance of the lysimeter test against global stability failure. Factor of safety against hydrostatic sliding was quantified using fully coupled variably saturated flow and stress-deformation modelling. Both laboratory and numerical models showed that the proposed geofoam block configuration significantly improved the performance of traditional side-hill fill embankment-widening technique under seepage forces. © 2015 Thomas Telford Ltd. Source

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