Browsing by Subject "substitution"

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Open Access
EFL students' use of English articles at different proficiency levels : a comparison of context and task type
(2007) Önen, Serap
This study was designed to investigate the use of English articles by beginner, intermediate, and advanced level Turkish EFL students at Pamukkale University. It examined whether the accuracy of article use by the students varied with respect to the types of noun phrase (NP) contexts, and analyzed the types of errors committed by the students in using English articles. It also investigated whether the accuracy of article use varied with respect to the proficiency levels and the tasks that were given to the students. The data were collected through a multiple choice task and a written production task. The results of these tasks revealed that the accuracy of article use by students varies with respect to the types of NP contexts in the multiple choice task. However, there is no significant difference among the types in terms of the accuracy of article use in the written production task. Moreover, each proficiency level tended to omit or substitute the articles when they make a mistake. However, the variety and frequency of these errors depended on the proficiency level of the students, type of the NP contexts, and the tasks that were given to the students. The study also revealed that the accuracy of article use varied with respect to the proficiency levels, and the tasks that were given to the students.
Open Access
A first-principles study of defects and adatoms on silicon carbide honetcomb structures
(2009) Bekaroğlu, Erman
In this thesis a study of electronic and magnetic properties of two dimensional (2D), single layer of silicon carbide (SiC) in hexagonal structure and its quasi 1D armchair nanoribbons are presented by using first-principles plane wave method. In order to reveal dimensionality effects, a brief study of 3D bulk and 1D atomic chain of SiC are also included. The stability analysis based on the calculation of phonon mode frequencies are carried out for different dimensionalities. It is found that 2D single layer SiC in honeycomb structure and its bare and hydrogen passivated nanoribbons are ionic, non magnetic, wide band gap semiconductors. The band gap further increases upon self-energy corrections. Upon passivation of Si and C atoms at the edges of nanoribbon with hydrogen atoms, the edge states are discarded and the band gap increases. The effect of various vacancy defects, adatoms and substitutional impurities on electronic and magnetic properties in 2D single layer SiC and in its armchair nanoribbons are also investigated. Some of these vacancy defects and impurities, which are found to influence physical properties and attain magnetic moments, can be used to functionalize SiC honeycomb structures for novel applications.