WoS İndeksli Yayınlar Koleksiyonu
Permanent URI for this collectionhttps://hdl.handle.net/20.500.12416/8653
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Article Vessel Segmentation in MRI Using a Variational Image Subtraction Approach(Tubitak Scientific & Technological Research Council Turkey, 2014) Nar, Fatih; Saran, Ayse Nurdan; Saran, MuratVessel segmentation is important for many clinical applications, such as the diagnosis of vascular diseases, the planning of surgery, or the monitoring of the progress of disease. Although various approaches have been proposed to segment vessel structures from 3-dimensional medical images, to the best of our knowledge, there has been no known technique that uses magnetic resonance imaging (MRI) as prior information within the vessel segmentation of magnetic resonance angiography (MRA) or magnetic resonance venography (MRV) images. In this study, we propose a novel method that uses MRI images as an atlas, assuming that the patient has an MRI image in addition to MRA/MRV images. The proposed approach intends to increase vessel segmentation accuracy by using the available MRI image as prior information. We use a rigid mutual information registration of the MRA/MRV to the MRI, which provides subvoxel accurate multimodal image registration. On the other hand, vessel segmentation methods tend to mostly suffer from imaging artifacts, such as Rician noise, radio frequency (RF) inhomogeneity, or partial volume effects that are generated by imaging devices. Therefore, this proposed method aims to extract all of the vascular structures from MRA/MRI or MRV/MRI pairs at the same time, while minimizing the combined effects of noise and RF inhomogeneity. Our method is validated both quantitatively and visually using BrainWeb phantom images and clinical MRI, MRA, and MRV images. Comparison and observer studies are also realized using the BrainWeb database and clinical images. The computation time is markedly reduced by developing a parallel implementation using the Nvidia compute unified device architecture and OpenMP frameworks in order to allow the use of the method in clinical settings.Article String Stable Cooperative Adaptive Cruise Control under Actuator Saturation(Pamukkale Univ, 2016) Schmidt, Klaus Werner; Cankaya, Erkam; Bingol, HilalCooperative adaptive cruise control (CACC) enables safe vehicle following in dense traffic based on distance measurements and communicated data via vehicle-to-vehicle communication. Existing CACC designs achieve the essential property of string stability but are limited to linear vehicle models. In this paper, we show that string stability is preserved when using a nonlinear vehicle model if the input signal of the leader vehicle does not saturate.Article Singular Dirac Systems in the Sobolev Space(Tubitak Scientific & Technological Research Council Turkey, 2017) Ugurlu, EkinIn this paper we construct Weyl's theory for the singular left-definite Dirac systems. In particular, we prove that there exists at least one solution of the system of equations that lies in the Sobolev space. Moreover, we describe the behavior of the solution belonging to the Sobolev space around the singular point.Article Reliability, Validity and Turkish Adaptation of Self-Directed Learning Scale (SDLS)(Ijate-INT Journal Assessment Tools Education, 2018) Demircioglu, Zeynep Isil; Cevik, Tugce; Ozcelik, Erol; Fucular, Emine Ezgi; Oge, Burak; Nazligul, Merve DenizciSelf-Directed Learning Scale (SDLS) developed by Lounsbury, Levy, Park, Gibson, and Smith (2009) was used for determining individuals' self-directed learning. The purpose of this study was to translate the SDLS into Turkish and to investigate its reliability and validity with a sample of 272 university students. The SDLS, the Modified Schutte Emotional Intelligence Scale (MSEIS), Self-Directed Learning Inventory (SDLI), and the Causal Uncertainty Scale (CUS) for determining convergent validity was applied to the participants. Factor analyses results verified the uni-dimensionality of the scale. The test-retest correlation of SDLS was 0.82, whereas Cronbach alpha coefficient of the scale was founded as 0.85 in the reliability analyses. Correlation coefficients representing for convergent validities varied from - 0.30 to 0.72 (p < .01) and criterion validity of the scale was determined as 0.236 when cumulative GPA was used as criterion in the assessment of concurrent validity. The findings suggest that the Turkish adaptation of SDLS is a valid and reliable tool to measure self-directed learning in Turkish samples.Article Outputs Bounds for Linear Systems with Repeated Input Signals: Existence, Computation and Application to Vehicle Platooning(Tubitak Scientific & Technological Research Council Turkey, 2018) Schmidt, Klaus Werner; Saglam, Harun BugraThis paper investigates the effect of repeated time-limited input signals on the output excursion of stable, linear time-invariant systems. It is first shown that the maximum norm of the output signal remains bounded if the repeated input signals are separated by a nonzero dwell time. Then a novel method for computing a tight bound on the output signal norm is proposed. The setting of the paper is motivated by a vehicle platooning application, where vehicles repeatedly open/close gaps in order to perform lane changes. The developed method analyzes driving safety by computing a bound on the spacing error between vehicles when performing repeated open/close gap maneuvers.Article Modeling and Analysis of a Microfluidic Capillary Valve(Gazi Univ, 2017) Yildirim, EnderHere, a numerical model for analysis of a capillary valve for use in microfluidic devices was presented. Capillary valves are preferred especially in passive microfluidic systems, where the capillary forces dominate the liquid motion, to manipulate the flow. The capillary valve in this work, was formed by the sudden expansion of a rectangular microchannel to an opening, whose depth and width are larger than the height and the width of the channel respectively. Noting that there was no available analytical model to determine the pressure capacity of such valves, a numerical model based on energy minimization was utilized. Free software Surface Evolver was used to solve the model. Dependence of the pressure capacity on the contact angle of the working liquid on the channel material was investigated. It was found that the pressure capacity of the valves would be maximum if the contact angle on all surfaces is 90 degrees. Accordingly, the valves could withstand approximately 2.5 kPa for 100 mu m x 100 mu m channels when the contact angle was 90 degrees. The model was verified by comparing the results with those available in the literature.Article Laminar Forced Convection Over An Inclined Flat Plate With Unheated Starting Length(Gazi Univ, 2019) Turgut, Oguz; Ozcan, Ahmet Cem; Turkoglu, HasmetTwo-dimensional laminar forced convection over an inclined flat plate with an unheated starting length was investigated numerically for both constant surface temperature and constant heat flux boundary conditions. The numerical study was implemented using the commercial software ANSYS Fluent 15.0. Air is used as working fluid. The influence of Reynolds number, inclination angle and the length of unheated plate on velocity and temperature distributions, surface temperature, surface heat flux and local Nusselt number was investigated. The results show that Reynolds number, inclination angle and the length of unheated region of plate play important role on heat transfer from the plate. It is seen that Nusselt number increases with increasing Reynolds number and inclination angle of inclined flat plate but decreases with increasing the length of unheated region of plate.Article Effects of Routing Algorithms on Novel Throughput Improvement of Mobile Ad Hoc Networks(Tubitak Scientific & Technological Research Council Turkey, 2012) Preveze, Barbaros; Safak, AyselA cognitive method called most congested access first (MCAF), minimizing the packet loss ratio and improving the throughput of a multihop mobile WiMAX network, is proposed. MCAF combines both the time division multiple access and the orthogonal frequency division multiple access methods. MCAF additionally uses spectral aid and buffer management methods, which air proposed in this paper, to manage both spectrum. access and packets in the buffers. By using these novel methods, real-time video and voice packet transmission is achieved, data packet loss rate is minimized, and the system throughput per node is improved. Effects of fastest path and ant colony routing algorithms on throughput improvement methods are investigated. It is shown that the fastest path routing algorithm, provides higher throughput values than the ant colony routing algorithm.Article Dissipative Operator and Its Cayley Transform(Tubitak Scientific & Technological Research Council Turkey, 2017) Ugurlu, Ekin; Tas, KenanIn this paper, we investigate the spectral properties of the maximal dissipative extension of the minimal symmetric differential operator generated by a second order differential expression and dissipative and eigenparameter dependent boundary conditions. For this purpose we use the characteristic function of the maximal dissipative operator and inverse operator. This investigation is done by the characteristic function of the Cayley transform of the maximal dissipative operator, which is a completely nonunitary contraction belonging to the class C-0. Using Solomyak's method we also introduce the self-adjoint dilation of the maximal dissipative operator and incoming/outgoing eigenfunctions of the dilation. Moreover, we investigate other properties of the Cayley transform of the maximal dissipative operator.Article Dirac Systems with Regular and Singular Transmission Effects(Tubitak Scientific & Technological Research Council Turkey, 2017) Ugurlu, EkinIn this paper, we investigate the spectral properties of singular eigenparameter dependent dissipative problems in Weyl's limit-circle case with finite transmission conditions. In particular, these transmission conditions are assumed to be regular and singular. To analyze these problems we construct suitable Hilbert spaces with special inner products and linear operators associated with these problems. Using the equivalence of the Lax-Phillips scattering function and Sz-Nagy-Foias characteristic functions we prove that all root vectors of these dissipative operators are complete in Hilbert spaces.