Mühendislik Fakültesi

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Differential Algebraic Equations in Primal Dual Interior Point Optimization Methods
(Amer inst Physics, 2004) Kasap, S; Kasap, Suat; Trafalis, TB; Endüstri Mühendisliği
Primal dual Interior Point Methods (IPMs) generate points that lie in the neighborhood of the central trajectory. The key ingredient of the primal dual IPMs is the parameterization of the central trajectory. A new approach to the parameterization of the central trajectory is presented. Instead of parameterizing the central trajectory by the barrier parameter, it is parameterized by the time by describing a continuous dynamical system. Specifically, a new update rule based on the solution of an ordinary differential equation for the barrier parameter of the primal dual IPMs is presented. The resulting ordinary differential equation combined with the first order Karush-Kuhn-Tucker (KKT) conditions, which are algebraic equations, are called differential algebraic equations (DAEs). By solving DAEs, we find an optimal solution to the given problem.
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
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: 1
Citation - Scopus: 1
Fmml: a Feature Model Markup Language
(Amer inst Physics, 2011) Nabdel, Leili; Karatas, Ahmet Serkan; Oguztuzun, Halit; Dogru, Ali
Feature modeling is a common way of representing commonality and variability in Software Product Line Engineering. Alternative notations are available to represent feature models. Compared with graphical notations, text-based notations can be more amenable to automated processing and tool interoperability. In this paper, we propose an XML-based feature modeling language to represent extended feature models with complex relationships.
Citation - WoS: 11
Citation - Scopus: 10
H(D) → D(H)+cu Collision System: Molecular Dynamics Study of Surface Temperature Effects
(Amer inst Physics, 2011) Vurdu, Can D.; Guvenc, Ziya B.
All the channels of the reaction dynamics of gas-phase H (or D) atoms with D (or H) atoms adsorbed onto a Cu(111) surface have been studied by quasiclassical constant energy molecular dynamics simulations. The surface is flexible and is prepared at different temperature values, such as 30 K, 94 K, and 160 K. The adsorbates were distributed randomly on the surface to create 0.18 ML, 0.28 ML, and 0.50 ML of coverages. The multi-layer slab is mimicked by a many-body embedded-atom potential energy function. The slab atoms can move according to the exerted external forces. Treating the slab atoms non-rigid has an important effect on the dynamics of the projectile atom and adsorbates. Significant energy transfer from the projectile atom to the surface lattice atoms takes place especially during the first impact that modifies significantly the details of the dynamics of the collisions. Effects of the different temperatures of the slab are investigated in this study. Interaction between the surface atoms and the adsorbates is modeled by a modified London-Eyring-Polanyi-Sato (LEPS) function. The LEPS parameters are determined by using the total energy values which were calculated by a density functional theory and a generalized gradient approximation for an exchange-correlation energy for many different orientations, and locations of one-and two-hydrogen atoms on the Cu(111) surface. The rms value of the fitting procedure is about 0.16 eV. Many different channels of the processes on the surface have been examined, such as inelastic reflection of the incident hydrogen, subsurface penetration of the incident projectile and adsorbates, sticking of the incident atom on the surface. In addition, hot-atom and Eley-Rideal direct processes are investigated. The hot-atom process is found to be more significant than the Eley-Rideal process. Furthermore, the rate of subsurface penetration is larger than the sticking rate on the surface. In addition, these results are compared and analyzed as a function of the surface temperatures. (c) 2011 American Institute of Physics. [doi:10.1063/1.3583811]
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
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.

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