Mühendislik Fakültesi

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Genişbant Erişim Telekomünikasyon Sistemlerinin Kullanım Kriterleri
(1) Küçükoğlu, Afşin; Baykal, Yahya; 7812; 06.03. Elektrik-Elektronik Mühendisliği; 06. Mühendislik Fakültesi; 01. Çankaya Üniversitesi
Hızla artan bilgisayar ağı ihtiyacını gidermek ve yüksek hızı son kullanıcı noktalarına ulaştırabilmek amacıyla geliştirilmiş olan genişbant erişim sistemlerinin (access systems) teknolojik son durumu incelendi. Herhangi bir erişim uygulamasında kullanılması gereken tercih nedenleri karşılaştırıldı. Bu karşılaştırmayı sistematik olarak yapan internet tabanlı bir yazılım geliştirildi. Yazılımda, sistem kullanıcısının ihtiyacı ve mevcut altyapı faktörleri doğrultusunda hangi erişim sisteminin kullanıcı tarafından tercih edilmesi gerektiği kararına optimum olarak varılabilmesi hedeflendi. Çalışmamız, xDSL (x Digital Subscriber Line) ile Fiber Optic erişimlerini kapsayan kablolu ve LMDS (Local Multipoint Distribution Services) ile FSO (Free Space Optics) erişimlerini kapsayan kablosuz sistemleri içermektedir. Yazılım tarafından istenilen sorular ihtiyaç doğrultusunda cevaplandırıldığında, tüm sistemler bir ana karşılaştırma tablosunda toplanmakta, sistem maliyetleri de göz önüne alınarak bir karşılaştırma yapılmakta, sonuçta ise teknik ve ekonomik olarak uygulanabilir çözümler ve optimum çözüm önerilmektedir.
Contribution of Intelligent Repeat Engine in Mobile Learning for Enhancing Students’ Learning in Industrial Engineering Education
(1) Saran, Murat; Güleç, Ulaş; 17753; 06.01. Bilgisayar Mühendisliği; 06. Mühendislik Fakültesi; 01. Çankaya Üniversitesi
A Petri Net-Based Inference Network for Design Automation Under Nondeterminism Applied To Mechatronic Systems
(Pergamon Press Ltd, 1998) Erden, Z; Erkmen, AM; Erden, A; 06.04. Endüstri Mühendisliği; 06. Mühendislik Fakültesi; 01. Çankaya Üniversitesi
This paper introduces the completed part of an ongoing research, in which a Petri Net-based design inference network is developed for the representation and analysis of the functions and their interrelationships through information flow for the conceptual design stage of mechatronic systems in order to facilitate design automation. The theoretical framework behind the network is based on transition of Hybrid Automata into Petri Nets and application of this framework is introduced by a mechatronic design example.
Fragmentation of a Non-Rotating Ni19 Cluster: A Molecular Dynamics Study
(1999) Avcı, Halil; Çivi, Mehmet; Güvenç, Ziya Burhanettin; Jellinek, Julius; 06.01. Bilgisayar Mühendisliği; 06. Mühendislik Fakültesi; 01. Çankaya Üniversitesi
Collisionless fragmentation of a non-rotating Ni19 cluster is studied using constant-energy molecular dynamics computer simulations. The cluster is modelled by an embedded atom model (EAM) energy surface. Distribution of the channel-specific fragmentation probabilities, and global rate constants are computed and analyzed as functions of the internal energy of the cluster. The results are compared with those obtained using the RRK statistical approach, and also compared with the other multi-channel fragmentation work.
D2 +Nin(T), n=7 and 9, Collision System
(1999) Böyükata, Mustafa; Durmuş, Perihan; Özçelik, Süleyman; Güvenç, Ziya Burhanettin; Jellinek, Julius; 06.01. Bilgisayar Mühendisliği; 06. Mühendislik Fakültesi; 01. Çankaya Üniversitesi
In this study the kinetics of reactions of Nin n=7 and 9, clusters with a deuterium D2 molecule are studied via quasiclassical molecular dynamics. Dissociative chemisorption probabilities as functions of impact parameters, collision energies, and a rovibrational state of a molecule are calculated. And the corresponding reactive cross sections are evaluated. Resonance formation in the low collision energy region is discussed.
Citation - WoS: 8
Citation - Scopus: 7
Sputtering Yield and Dynamical Analysis of Ni(100) Surface: a Comparison of Four Different Ar-Surface Interaction Potentials
(Elsevier Science Bv, 2000) Güvenç, ZB; Hundur, Y; Hippler, R; 06.01. Bilgisayar Mühendisliği; 06. Mühendislik Fakültesi; 01. Çankaya Üniversitesi
The sputtering process of the Ar + Ni(100) collision system is investigated by means of constant energy molecular dynamics simulations. The Ni(100) is mimicked by an embedded-atom potential, and the interaction between the projectile and the surface is modelled by using four different screened Coulomb type potentials. The Ni atom emission from the lattice is analysed over the range of 10-40 eV collision energy. The maximum penetration depths of Ar, probability distributions of kinetic energy of the reflected Ar, and energy of the Ar and sputtered Ni atoms in the same collision events are evaluated as functions of the impact energy and sputtering time. Further, angular distributions of the scattered Ar are obtained. The calculated sputtering yields are compared with the available theoretical and experimental data. (C) 2000 Elsevier Science B.V. All rights reserved.
Citation - WoS: 12
Citation - Scopus: 14
Reactions of Small Ni Clusters With a Diatomic Molecule: Md Simulation of D2+nin (n=7-10) Systems
(Elsevier Science Bv, 2000) Durmus, P; Böyükata, M; Özçelik, S; Güvenç, ZB; Jellinek, J; 06.01. Bilgisayar Mühendisliği; 06. Mühendislik Fakültesi; 01. Çankaya Üniversitesi
The kinetics of the reactions of nickel clusters with a deuterium molecule are studied, Dissociative chemisorption probabilities of the D(2) molecule on the small Ni(n) (n=7-10) clusters are computed by a quasi-classical molecular dynamics computer simulation technique. Structures of the clusters are obtained by an embedded-atom potential, and the interaction between the D(2) and Ni(n) is modelled by an LEPS (London-Eyring-Polanyi-Sato) function (energy surface). This analysis includes the chemisorption probabilities as functions of the impact parameter and of the relative translational energy of the D(2). The corresponding reactive cross-sections for the ground state of the molecule are calculated as functions of the collision energy and the size of the cluster. The role of the size of the clusters is examined. An indirect mechanism to the reaction, which involves formation of molecular adsorption as precursors to dissociative adsorption in the low collision energy region (less than 0.1eV), is observed. Results are discussed by comparing with the other similar theoretical and experimental studies. (C) 2000 Elsevier Science B.V. All rights reserved.
Citation - WoS: 8
Citation - Scopus: 8
Dynamics of the D2+ni(100) Collision System: Analysis of the Reactive and Inelastic Channels
(Wiley-blackwell, 2001) Böyükata, M; Güvenç, ZB; Jackson, B; Jellinek, J; 06.01. Bilgisayar Mühendisliği; 06. Mühendislik Fakültesi; 01. Çankaya Üniversitesi
The reactive and scattering channels of the D(2)(v, j) + Ni(100) collision system are studied using quasiclassical molecular dynamics simulations. The interaction between the D(2) and the atoms of the surface is modeled by a LEPS (London-Eyring-Polani-Sato) potential energy function. The molecule is aimed at three different impact sites (atop, bridge, and center) of a rigid Ni(100) surface along the normal direction with various collision energies less than or equal to1.0 eV. Dissociative chemisorption probabilities are computed for different rotational states of the molecule. Probability distributions of the final rovibrational states of the ground-state Dp molecule scattered from those impact sites are also computed as a function of the collision energy. Higher collision energy results in excitation of higher rotational and/or vibrational states of the scattered molecule. At collision energies below 0.1 eV an indirect dissociation mechanism (through molecular adsorption) dominates the reaction. (C) 2001 John Wiley & Sons, Inc.
Citation - WoS: 21
Citation - Scopus: 20
Structure and Reactivity of Nin (n=7-14, 19) Clusters
(Wiley, 2001) Böyükata, M; Güvenç, ZB; Özçelik, S; Durmus, P; Jellinek, J; 06.01. Bilgisayar Mühendisliği; 06. Mühendislik Fakültesi; 01. Çankaya Üniversitesi
Results of a computer simulation study of Ni-n (n = 7-14, 19) clusters, their structures, energetics, and reactivity with a D-2 molecule are presented. The clusters are described by an embedded atom potential, whereas the interaction between the molecule and the clusters is modeled by an LEPS (London-Eyring-Polanyi-Sato) potential energy function. The focus is on structures of the dusters and their reactive channels. The total numbers of stable isomers of the clusters are obtained by sampling their phase space, and the isomers' energy spectra are determined. On the reactive side, dissociative chemisorptions cross sections and decay-rate constants are calculated. (C) 2001 John Wiley & Sons, Inc.
Citation - WoS: 7
Citation - Scopus: 8
Fragmentation of Water Clusters: Molecular-Dynamics Simulation Study
(Springer-verlag, 2001) Erkoç, S; Kökten, H; Güvenç, Z; 06.01. Bilgisayar Mühendisliği; 06. Mühendislik Fakültesi; 01. Çankaya Üniversitesi
The fragmentation of water clusters, [(H2O)(n): n = 2-8], have been investigated by using molecular-dynamics simulation method. In the simulations a polarizable-dissociable potential energy function for water has been used. Particular attention has been paid to investigate the effect of structural properties and cluster size of the fragmentation.
Citation - WoS: 3
Citation - Scopus: 3
Finite Size Scaling by Using Scaling Functions in Two-Dimensional Q=2 and 7 State Potts Models
(World Scientific Publ Co Pte Ltd, 2001) Seferoglu, N; Aydin, M; Gündüç, Y; Demirtürk, S; 01. Çankaya Üniversitesi; 02.02. Matematik; 02. Fen-Edebiyat Fakültesi
The scaling behaviors of the percolation cumulant and the surface renormalization are studied on q = 2 and 7 state Potts models. The results show that the scaling functions can be safely used to determine infinite lattice transition points and the thermal and magnetic exponents indicating that these functions have very small correction to scaling contributions.
Citation - WoS: 41
Citation - Scopus: 42
Eley-Rideal and Hot Atom Reactions Between Hydrogen Atoms on Ni(100): Electronic Structure and Quasiclassical Studies
(Amer inst Physics, 2001) Guvenc, ZB; Sha, XW; Jackson, B; 06.01. Bilgisayar Mühendisliği; 06. Mühendislik Fakültesi; 01. Çankaya Üniversitesi
The reactions of gas-phase H (or D) atoms with D (or H) atoms adsorbed onto a Ni(100) surface are studied. Electronic structure calculations based on density functional theory are used to examine the interaction of H atoms with the Ni(100) surface, as well as the interactions between two H atoms near the metal surface. A model potential-energy surface based on ideas from effective medium theory is fit to the results of these electronic structure calculations. Quasiclassical trajectory methods are used to simulate the interaction of low energy H and D atom beams with H and D-covered Ni(100) surfaces. It is found that hot-atom processes dominate the formation of molecular hydrogen. The distribution of energy in the product molecules is examined with regard to the various pathways available for reaction. The initial adsorbate coverage is varied and is shown to control the relative amounts of reflection, reaction, sticking, and subsurface penetration. Our results are compared with those from similar studies on Cu(111) and available experimental data for Ni(100). (C) 2001 American Institute of Physics.
Citation - WoS: 36
Citation - Scopus: 30
Structures and Energetics of Pdn (n=2-20) Clusters Using an Embedded-Atom Model Potential
(Elsevier Science Bv, 2002) Karabacak, M; Özçelik, S; Güvenç, ZB; 06.01. Bilgisayar Mühendisliği; 06. Mühendislik Fakültesi; 01. Çankaya Üniversitesi
We have studied the structure and energetics of the stable isomers of Pd(n) (n = 2-20) clusters by using molecular dynamics and slow-quenching techniques. Cohesion of the clusters is modeled by an embedded-atom potential due to Voter and Chen, which contains many-body atomic interactions. The isomers' statistics are obtained from 10000 independent initial configurations, which have been generated along a high-energy trajectory (the chosen energy value is high enough to melt the cluster). The internal kinetic energy of these initial conditions is removed slowly. Because of this slow minimization process the locally stable isomers are separated from those meta-stable ones. Probabilities belonging to sampling the basins of attractions of each isomer are computed, and compared with each other. Furthermore, the spectrum, which is formed by isomers' energies, is analyzed. (C) 2002 Published by Elsevier Science B.V.
Head Modeling With Camera Auto-Calibration and Deformation
(Akademische verlagsgesellsch Aka Gmbh, 2002) Hassanpour, R; Hassanpour, Reza; Atalay, V; Yazılım Mühendisliği; 06.09. Yazılım Mühendisliği; 06. Mühendislik Fakültesi; 01. Çankaya Üniversitesi
A 3D head modeling method from a sequence of 2D images is described. The views from which the input images are acquired are not calibrated., Therefore, an auto-calibration method for a sequence of images with small rotations and translation is developed. For this purpose, we have modified an already existing auto-calibration algorithm to incorporate known aspect ratio and skew values to make it applicable for small rotation around a single axis. We apply this auto-calibration technique to head (face) modeling. Three dimensional positions of known facial features computed from two dimensional images are used to. deform a generic head model by using a spring based energy minimization method.
Citation - WoS: 46
Kinetic Model for Eley-Rideal and Hot Atom Reactions Between H Atoms on Metal Surfaces
(Amer inst Physics, 2002) Jackson, B; Sha, XW; Guvenc, ZB; 06.01. Bilgisayar Mühendisliği; 06. Mühendislik Fakültesi; 01. Çankaya Üniversitesi
A simple kinetic model is used to describe the interaction of H and D atomic beams with H- and D-covered metal surfaces. The atoms incident from the gas phase can have a direct Eley-Rideal reaction with an adsorbate, reflect, penetrate into the bulk, knock an adsorbate out of its binding site, or trap to form a hot atom. These hot mobile atoms can go on to react with other adsorbates, or eventually relax and stick. A coarse-graining approach, which takes advantage of the large difference between the time scales for the kinetics experiments and the reaction dynamics, allows us to derive relatively simple kinetic equations for reaction rates and coverages. The approach is similar to a kinetic random walk model developed by Kuppers and co-workers [J. Phys. Chem. 109, 4071 (1998)] except that our equations can be used to derive analytical expressions for saturation coverages, rates, and yields. The model is applied to the case of H atom reactions on a Ni(100) surface, and a detailed comparison is made with both experimental and quasiclassical studies. (C) 2002 American Institute of Physics.
Citation - WoS: 27
Citation - Scopus: 31
The Effects of Lattice Motion on Eley-Rideal and Hot Atom Reactions: Quasiclassical Studies of Hydrogen Recombination on Ni(100)
(Amer Chemical Soc, 2002) Guvenc, ZB; Sha, XW; Jackson, B; 06.01. Bilgisayar Mühendisliği; 06. Mühendislik Fakültesi; 01. Çankaya Üniversitesi
Quasiclassical methods are used to simulate the interactions of H or D atom beams with D- or H-covered Ni(100) surfaces. The Ni substrate is treated as a multilayer slab, and the Ni atoms are allowed to move. The model potential energy surface is fit to the results of detailed total-energy calculations based on density functional theory. Most of the incident atoms trap to form hot atoms, which can eventually react with an adsorbate, or dissipate their energy and stick. The incident atom is found to lose several tenths of an eV of energy into the metal, upon initially colliding with the surface. This limits reflection to a few percent, at all coverages, and secondary reactions between adsorbates are significantly lowered. Long time hot atom reactions are also found to be damped out by the inclusion of lattice motion, leading to increased sticking, even at high coverages where dissipation into the adsorbates should be the primary energy loss mechanism. Overall, the inclusion of lattice motion is found to improve agreement with experiment.
Head Modeling with Camera Autocalibration and Deformation.
(2002) Hassanpour, Reza; Atalay, Mehmet Volkan; 06.09. Yazılım Mühendisliği; 06. Mühendislik Fakültesi; 01. Çankaya Üniversitesi
Citation - Scopus: 10
O(N) Algorithms in Tight-Binding Molecular-Dynamics Simulations of the Electronic Structure of Carbon Nanotubes
(2003) Dereli, G.; Özdoǧan, C.; 09.01. Ortak Dersler Bölümü; 09. Rektörlük; 01. Çankaya Üniversitesi
The O(N) and parallelization techniques have been successfully applied in tight-binding moleculardynamics simulations of single-walled carbon nanotubes (SWNT's) of various chiralities. The accuracy of the O(N) description is found to be enhanced by the use of basis functions of neighboring atoms (buffer). The importance of buffer size in evaluating the simulation time, total energy, and force values together with electronic temperature has been shown. Finally, through the local density of state results, the metallic and semiconducting behavior of (10 X 10) armchair and (17 X 0) zigzag SWNT's, respectively, has been demonstrated.
Citation - WoS: 73
Citation - Scopus: 69
Energetics and Structures of Small Clusters: Ptn, N=2-21
(Elsevier, 2003) Sebetci, A; Güvenç, ZB; 05.01. İç Mimarlık; 06.01. Bilgisayar Mühendisliği; 06. Mühendislik Fakültesi; 05. Mimarlık Fakültesi; 01. Çankaya Üniversitesi
The Voter and Chen version of an embedded-atom model, derived by fitting to experimental data of both diatomic molecule and bulk platinum simultaneously, has been applied to study the locally stable structures, energies and growth patterns of small platinum clusters in the size range of N = 2-21. Using molecular dynamics and thermal quenching simulations, the global minima and the other locally stable structures have been distinguished from those stationary structures that correspond to saddle points of the potential energy surface. Ten thousand independent initial configurations generated at high temperatures (about 2600 K) were used to obtain the number of isomers and the probabilities of sampling different basins of attractions, for each size of the clusters. Their energy spectra have been analyzed. Comparisons have been made with the results of previous calculations using electronic structure and empirical potential methods. Although many of the lowest energy structures correspond to icosahedral growth, a number of new structures have been identified for N = 15, 16, 17, 18, 20 and 21. It has been found that the lowest energy structures are not always the most probable isomers for each size. (C) 2002 Elsevier Science B.V. All rights reserved.
Comparison of physical optics integral and exact solutions for cylinder problem
(2003) Umul, Yusuf Ziya; Yengel, Emre; Aydın, Ayhan; 06.02. Elektronik ve Haberleşme Mühendisliği; 06.03. Elektrik-Elektronik Mühendisliği; 06.01. Bilgisayar Mühendisliği; 06. Mühendislik Fakültesi; 01. Çankaya Üniversitesi
The sound source composition of the urban sound environment varies depending on the geography and socio-cultural context. Current sound taxonomies in the literature categorize urban sound sources by their source types (e.g., human-made, natural, electromechanical) and respective semantic attributes. This study aims to add another taxonomical layer to the existing urban sound source categorization methods. The additional layer is a recently proposed sound source classification framework (CLIC). The CLIC framework identifies sound sources based on their Diegesis and Intention parametric attributes. The former parametric attribute, diegesis, was derived from film sound design. The geographical and socio-cultural context of the built environment can be considered as its narrative; hence, every event that happens within the functional context can be called diegetic, while the events that do not belong to that specific place can be called nondiegetic. The latter parametric attribute, intention, was derived from product design. One of the prominent sound source categorization methods in product sound design is to group the product emitted sounds as consequential and intentional. Combining these two parametric attributes with the existing taxonomies, the CLIC framework outputs a place-specific design guideline, clearly dictating the actions a sound designer should take. The two parametric attributes group the sound sources under four distinct areas, which dictates the degree of influence of designers on the specific sound source. The four zones are defined as the creation zone, limitation zone, isolation zone, and control zone. Each zone dictates step-by-step sound design instructions for the sound designer. This study consists of two main phases: field recordings and web-based listening tests. The sound sources present in the urban sound environment were identified in the field recordings phase. Later, in the web-based listening tests phase, the identified sound sources were evaluated based on the CLIC framework, and hence, their respective zones on the model were identified. The outcomes of the study propose clear step-by-step design guidelines and present action suggestions for environmental sound designers.

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