AABS

This study is an optimization approach to the rectilinear interdiction problem by locating a line barrier. Interdiction problems study the eect of a limited disruption action on operations of a system. Network interdiction problems, where nodes and arcs of the network are susceptible to disruption actions, are extensively studied in the operations research literature. In this study, we consider a set of sink points on the plane that are being served by source points and our aim is to study the eect of locating a line barrier on the plane (as a disruption action) such that the total shortest distance between sink and source points is maximized. We compute the shortest distances after disruption using visibility concept and utilizing properties of our problem. The amount of disruption is limited by imposing constraints on the length of the barrier and also the total number of disrupted points. The suggested solution approaches are based on mixed-integer programming and a polynomial-time algorithm.

The aim of this study was to improve the mechanical properties &ldquo / Moplen&rdquo / EP300L which is a heterophase copolymer. Polymer blends and nanocomposites were prepared by melt compounding method in a twin screw extruder. Nanofil&reg / 5 (N5) and Nanofil&reg / 8(N8) were used as the organoclays, and maleic anhydride grafted polypropylene (M) was used as the compatibilizer. The effects of additive concentrations and types of organoclays on the morphology, mechanical and thermal properties were investigated. Organoclay loading over 2 wt% prevented the intercalation mechanism resulting in large aggregates of clay, thus the material properties became poor even in the presence of compatibilizer. Compatibilizer addition improved the intercalation ability of the polymer, however a substantial increase in mechanical properties was not obtained up to 6 wt % loading of the compatibilizer. XRD analysis revealed that intercalated structures were formed with the addition of compatibilizer and organoclay. The nanocomposites that were prepared with N5 type organoclay showed delaminated structures at 6 wt % compatibilizer loading. v Nanofill &reg / 5 exhibited the highest improvements in mechanical properties, since the degree of organoclay dispersion was better in Nanofill &reg / 5 containing nanocomposites in comparison to Nanofill &reg / 8 containing ones. The DSC analysis indicated a insignificant reduction in the melting temperature of the ternary nanocomposites.

In the present study,transint flow analyses of a long oil pipeline are performed.

This thesis analyzes the relationship between upper extremity musculoskeletal disorders and longtime computer usage. Firstly / maastricht upper extremity questionnaire is applied to Financial Control and Information Technology Departments of Turk Telekom. Results are analyzed by using spss 16.0 tool by conduction of ordinal logistic regression analysis to determine the significance between work environment and postural information and upper extremity musculoskeletal complaints. Then / development of a new tool, namely PACU (postural analysis of computer users), takes place aiming to determine the factors of disorders, by mainly focusing on work-related neck and upper limb disorders, for long time computer users of Financial Control and Information Technology Departments of Turk Telekom. Results of the PACU are analyzed by using the methods of correlation, chi square goodness of fit test, factor analysis, and ordinal logistic regression.

In this thesis, mechanical and elastic behaviour of anisotropic materials are inves- tigated in order to understand the optimum mechanical behaviour of them in selected directions. For an anisotropic material with known elastic constants, it is possible to choose the best set of e&curren / ective elastic constants and e&curren / ective eigen- values which determine the optimum mechanical and elastic properties of it and also represent the material in a speci.ed greater material symmetry. For this reason, bounds on the e&curren / ective elastic constants which are the best set of elastic constants and e&curren / ective eigenvalues of materials have been constructed symbollicaly for all anisotropic elastic symmetries by using Hill [4,13] approach. Anisotropic Hooke.s law and its Kelvin inspired formulation are described and generalized Hill inequalities are explained in detail. For di&curren / erent types of sym- metries, materials were selected randomly and data of elastic constants for them were collected. These data have been used to calculate bounds on the e&curren / ective elastic constants and e&curren / ective eigenvalues. Finally, by examining numerical results of bounds given in tables, it is seen that the materials selected from the same symmetry type which have larger interval between the bounds, are more anisotropic, whereas some materials which have smaller interval between the bounds, are closer to isotropy.

Structural properties of pristine and defected graphene nanoribbons have been investigated by stretching them under 5 percent and 10 percent uniaxial strain until fragmentation. The stretching process has been carried out by performing molecular dynamics simulations (MDS) at 1 K and 300 K to determine the temperature effect on the structure of the graphene nanoribbons. Results of the simulations indicated that temperature, edge shape of graphene nanoribbons and stretching speed have a considerable effect on structural properties, however they have a slight effect on the strain value. The maximum strain at which fracture occurs is found to be 46.41 percent whereas minimum strain value is calculated as 21.00 percent. On the other hand, the defect formation energy is strongly affected from temperature and edge shape of graphene nanoribbons. Stone-Wales formation energy is calculated as -1.60 eV at 1 K whereas -30.13 eV at 300 K for armchair graphene nanoribbon.

Many dynamical systems in nature and technology involve delays in the interaction of variables forming the system. Furthermore, many of such systems involve external inputs or perturbations which might force the system to have arbitrary initial function. The conventional way to model these systems is using delay differential equations (DDE). However, DDEs with arbitrary initial functions has serious problems for finding analytical and computational solutions. This fact is a strong motivation for considering abstractions and approximations for dynamical systems involving delay. In this thesis, the piecewise linear systems with delay on piecewise constant part which is a useful subclass of hybrid dynamical systems is studied. We introduced various representations of these systems and studied the state transition conditions. We showed that there exists fixed point and periodic stable solutions. We modelled the genomic regulation of fission yeast cell cycle. We discussed various potential uses including approximating the DDEs and finally we concluded.

A software GPS receiver is a functional GPS receiver in software. It has several advantages compared to its hardware counterparts. For instance, improvements in receiver architecture as well as GPS system structure can be easily adapted to it. Furthermore, interaction between nearby sensors can be coordinated easily. In this thesis, a SGR (software GPS receiver) is presented from a practical point of view. Major components of the SGR are implemented in Matlab environment. Furthermore, some alternative algorithms are implemented. SGR implementation is considered in two main sections namely a signal processing section and a navigation section. Signal processing section is driven by the raw GPS signal samples obtained from a GPS front-end of NordNavTM R-25 instrument. The conventional and the block adjustment of synchronizing signal (BAAS) processing methods are implemented and their performances are compared in terms of their speed and outputs. Signal processing section outputs raw GPS measurements and navigation data bits. Since the output data length is insufficient in our case, navigation section input is fed from AshtechTM GPS receiver for a moving platform and TrimbleTM GPS Receiver for a stationary platform. Satellite position computation, pseudorange corrections, Kalman filter and LSE (least squares estimation) are implemented in the navigation section. Kalman filter and LSE methods are compared in terms of positioning accuracy for a moving as well as a stationary platform. Results are compared with the commercial GPS outputs. This comparison shows that the software navigation section is equivalent to the commercial GPS in terms of positioning accuracy.