WoS İndeksli Yayınlar Koleksiyonu / WoS Indexed Publications Collection

Permanent URI for this collectionhttps://hdl.handle.net/11147/7150

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  • Article
    An Analysis of Vehicular Traffic Flow Using Langevin Equation
    (Faculty of Transport and Traffic Sciences, University of Zagreb, 2015) Koşun, Çağlar; Çelik, Hüseyin Murat; Özdemir, Serhan
    Traffic flow data are stochastic in nature, and an abundance of literature exists thereof. One way to express stochastic data is the Langevin equation. Langevin equation consists of two parts. The first part is known as the deterministic drift term, the other as the stochastic diffusion term. Langevin equation does not only help derive the deterministic and random terms of the selected portion of the city of Istanbul traffic empirically, but also sheds light on the underlying dynamics of the flow. Drift diagrams have shown that slow lane tends to get congested faster when vehicle speeds attain a value of 25 km/h, and it is 20 km/h for the fast lane. Three or four distinct regimes may be discriminated again from the drift diagrams; congested, intermediate, and free-flow regimes. At places, even the intermediate regime may be divided in two, often with readiness to congestion. This has revealed the fact that for the selected portion of the highway, there are two main states of flow, namely, congestion and free-flow, with an intermediate state where the noise-driven traffic flow forces the flow into either of the distinct regimes. © 2015, Faculty of Transport and Traffic Engineering. All rights reserved.
  • Article
    Citation - WoS: 21
    Citation - Scopus: 23
    Determination of Octane Number of Gasoline Using Near Infrared Spectroscopy and Genetic Multivariate Calibration Methods
    (Taylor and Francis Ltd., 2005) Özdemir, Durmuş
    The feasibility of rating the octane number of gasoline using near infrared (NIR) spectroscopy and three different genetic algorithm-based multivariate calibration methods was demonstrated. The three genetic multivariate calibration methods are genetic regression (GR), genetic classical least squares (GCLS), and genetic inverse least squares (GILS). The sample data set was obtained from the ftp address (ftp://ftp.clarkson.edu/pub/hopkepk/Chemdata/) with the permission of Professor. J. H. Kalivas. This data set contains the NIR spectra of 60 gasoline samples collected using diffuse reflectance as log (I / R) with known octane numbers and covers the range from 900 to 1700 nm in 2 nm intervals. Of these 60 spectra, 20 were used as the calibration set, 20 were used as the prediction set, and 20 were reserved for the validation purposes. Several calibration models were built with the three genetic algorithm-based methods, and the results were compared with the partial least squares (PLS) prediction errors reported in the literature. Overall, the standard error of calibration (SEC), standard error of prediction (SEP), and standard error of validation (SEV) values were in the range of 0.15-0.32 (in the units of motor octane number) for the GR and GILS, which are comparable with the literature. However, GCLS produced relatively large results (0.36 for SEC, 0.39 for SEP and 0.52 for SEV) when compared with the other two methods.
  • Article
    Citation - WoS: 10
    Citation - Scopus: 14
    Numerical Model for Sediment Transport Over Nonplanar, Nonhomogeneous Surfaces
    (American Society of Civil Engineers (ASCE), 2004) Tayfur, Gökmen; Singh, Vijay P.
    Sediment transport on surfaces with spatially variable microtopography, roughness, and infiltration was investigated using the diffusion wave equation. An implicit finite-difference scheme together with multivariate Newton's method was employed to solve the equation numerically. The simulation results showed that microtopography and roughness were the dominant factors causing significant spatial variations in sediment concentration. If the spatially varying microtopography was replaced by an average constant slope, the result was an overestimation of the sediment load. On the other hand, when the spatially varying roughness was replaced by the average roughness and the spatially varying infiltration rate by the average infiltration rate, the sediment discharge was not significantly affected. The sedimentograph reached an equilibrium much sooner when a constant infiltration rate was substituted for the time-varying infiltration rate.