Graduate School of Engineering and Science

Permanent URI for this collectionhttps://hdl.handle.net/11693/115678

Browse

Now showing 1 - 20 of 3469

Open Access
Design and implementation of a tool for teaching programming
(1988) Göktepe, Mesut
In this thesis, a survey on computer applications for teaching programming and some graphical programming tools together with their underlying environments has been carried out and a graphical Pascal teaching tool is designed and implemented. Graphical programming tools provide the user the ability to solve the problems through the use of icons and symbols allowing very little text. Here, a Pascal teaching tool is presented in a very user friendly environment to teach programming through the use of flowcharts in a visual manner.
Open Access
Electronic structure of Si/Ge semiconductor superlattices
(1988) Gülseren, Oğuz
A brief review about the two dimensional electron systems and especially band offsets is given. The electronic properties of the Si„/Ge„(001) strained superlattices as a function of the superlattice periodicity and the band misfit is investigated by using the empirical tight-binding method. The difference between the direct and indirect band gaps is reduced from 2.01 eV for bulk Si to 0.01 eV for n = 6. Consequently, the superlattice with n = 6 can be considered as quasi-direct, while it is at least 0.15 eV for n = 4 case. For the cases n=5,6, and 8, the band gap might become direct for large values of band misfit.
Open Access
Congestion control in interconnected computer networks
(1988) Ulusoy, Özgür
A computer network has a collection of resources shared by multiple users. The capacity of the resources is limited, and if the user demands exceed the capacity, the network becomes ’congested’. The congestion causes a degradation in system performance. In interconnected networks there are two classes of traffic within a network. One class is the local traffic that is generated and transmitted within the network. The other class is the internetwork traffic transmitted to or from other networks. In this thesis, the effect of internetwork traffic on the performance of a network is investigated. Computer simulation of an interconnected network model is provided in order to evaluate the effectiveness of a window-based congestion control mechanism on preventing congestion in gateways and in attached networks caused by the overload of internetwork traffic. Also two dynamic window congestion control algorithms are provided and studied. These algorithms provide further control to window mechanism by adjusting the window size in accordance with the availability of the network resources at the destination. Dynamic algorithms are evaluated comparing them with static window control.
Open Access
Secondary storage management in an object-oriented database management system
(1988) Karaorman, Murat
In this thesis, a survey on object-orientation and object-oriented database management systems has been carried out and a secondary storage management and indexing module is implemented for an object-oriented database management system prototype developed at Bilkent University. First, basic concepts, characteristics, and application areas of objectoriented approach are introduced, then, the designed prototype system is presented, the secondary storage management module is explained in detail and the functions of the other modules are summarized. Finally, the current research issues in the object-oriented database systems are introduced.
Open Access
Atomic theory of the scanning tunneling microscope
(1988) Tekman, Ahmet Erkan
The Scanning Tunneling Microscope is proven to be one of the most powerful tools for surface structure determination. Present theories are able to explain the operation of the microscope when the tip is far from the surface. For the small tip height case the atomic-scale interaction of the tip and the surface has to be included in the theory. The electronic structure of the combined system of the tip and the surface is calculated with an Empirical Tight Binding approach for graphite. It is found that in the vicinity of the tip some Tip Induced Localized States are formed. These states play an important role in the tunneling phenomenon. The contribution of these states to the tunneling current is calculated.
Open Access
An Object memory for an object-oriented database management system
(1988) Kesim, F. Nihan
Object-oriented paradigm is an approach that can be applied in various areas of computing. In this approach, each entity is represented by an object which captures the state and the behaviour of the entity. In this thesis, a focused survey of object-oriented paradigm in general and object-oriented database management systems in particular has been carried out and an object memory module is designed and implemented for an object-oriented database management system prototype. The object memory module handles the representation, access and manipulation of objects in the system and provides the primitive functions that are necessary in the development of the prototype.
Open Access
A Parallel Prolog emulator
(1988) Gürsoy, Attila
There are various parallel Prolog execution models proposed so far. In this study, an emulator has been developed to test the execution model PPEM. The emulator is used to collect data to evaluate the performance of the model. The underlying architecture is assumed to be a tightly coupled multiprocessor system. Some implementation difficulties faced, which are not apparent in the definition of PPEM are discussed, and performance results are presented.
Open Access
Design and analysis of just-in-time production systems
(1988) Oğuz, Ceyda
Just-in-Time (JIT) production systems have initially appeared in the Japanese manufacturing environment due to the scarcity of their critical resources. The main aim in JIT production systems is to eliminate waste. To achieve this objective, setup times, lead times, in-process inventories, and defective production must all be minimized. In the design process of a JIT production system, several factors such as lot size, number of kanbans, unit load size, and buffer capacities must be taken into account. In this study, a mathematical model is developed for a single-item, single-line, multi-stage, and multi-period JIT production system. The original model is nonlinear in both objective function and constraints. To reduce the computational difficulties, the nonlinear model is then approximated by a linear model. Next, a simulation model is developed to incorporate the stochastic nature of the demand. A sensitivity analysis is performed on unit load size and on buffer capacity under different demand patterns to examine their effects on the behavior of the model. The results show that thofee unit load size values exceeding 10 percent of the maximum demand in the planning horizon have no effect on the model.
Open Access
Message passing in an object-oriented database management system
(1988) Özelçi, Sibel M.
In this thesis, a focused survey on object-oriented database management systems and on object-orientation in general was carried out and a single- user object-oriented database management system prototype was designed and implemented. A command language was defined and a message passing scheme was proposed and implemented. A compiler for the language was developed. The developed language is computationally complete and aims at solving the impedance mismatch problem. It contains both data definition and data manipulation statements. The statements can be used interactively or in the form of methods. After compilation, the statements are translated into integer codes and these codes are used to perform the necessary operations.Since the developed prototype is a single-user system, the message passing passing scheme does not provide any concurrency control mechanisms and stacks are used to implement message passing and argument handling.
Open Access
Stabilization of multivariable systems with constrained control structure
(1988) Ünyelioğlu, Konur Alp
The following problem is considered: Given a multivariable system with m inputs and r outputs and an m x r matrix whose nonnegative (i,j)’th element represents the cost of setting up a feedback link from the j ’th output to the i’th input, find a set of feedback links with minimum total cost, which does not give rise to fixed modes. Utilizing the graph-theoretic characterization of structurally fixed modes, the problem is decomposed into two subproblems, which are then solved by using concepts and results from network theory. The combination of the optimum solutions of the subproblems provides a suboptimal solution to the original problem.
Open Access
Continuous processing of images through user sketched functional blocks
(1988) Kaya, Aydın
An object oriented user interface is developed for interacting with and processing images. The software prepared for this purpose includes image processing functions as well as user friendly interaction tools both of a lower level such as menus, panels, windows and a higher level such as a schematics. The lower level utilities provide direct interface with the available image processing functions. At the higher level, the nodes of the schematics serve as image processing function instantiations and the arcs are the paths through which processed images flow. By constructing such a schematics, a complex set of operations can be applied to images continuously.
Open Access
Text, image, graphics editor
(1988) Coşar, Ahmet
The editor proposed in this study can manipulate textual, graphics and image data in a unified way. Each data type can be edited individually or dependencies can be set up between various data items so that modifying one might propagate its effects on others. The system is developed by using new software tools and techniques such as object oriented programming, multi window workstations running with event selection principles and iconic interfacing. Facilities for data protection, such as journaling are provided. Data storage and editing principles are handled within guidelines of well established standards. However, where such definitions fall short, proposals for new techniques are made especially with respect to relation sets binding various data types
Open Access
Design and implementation of a general purpose median filter unit in VLSI
(1988-10) Karaman, Mustafa
The median of a group, containing an odd number of elements, is defined as the middle element, when the elements of the group are sorted. A median filter finds the median of a number of elements at its inputs. Median filters are frequently used in many signal and image processing applications for smoothing of the noisy signals and images while at the same time preserving the edge information. The required window size, speed, and the word length of the median filters vary depending on the applications. In order to meet these changing demands a general purpose median filter unit configuration is proposed. The unit consists of two single-chip median filters. One of the chips is designed for unlimited word-length and extensibility to larger window sizes whereas the other one is for real-time video applications. The networks of the chips are based on the odd/even transposition sorting. The chips are implemented in 3-mu m MsquareCMOS by using full-custom VLSI design techniques. For physical testing of the chips, the test vectors and the corresponding outputs of the chips are generated by using software tools written for this purpose. In this thesis, the algorithms, VLSI implementations, simulation results, testing, and applications of the chips are presented.
Open Access
Part family machine group formation problem in cellular manufacturing systems
(1989) Kandiller, Levent
The first and the most important stage in the design of Cellular Manufacturing (CM) systems is the Part Family Machine Group Formation (PF/MGF) problem. In this thesis, different approaches to the PF/MG-F problem are discussed. Initially, the design process of CM systems is overviewed. Heuristic techniques developed for the PF/MG-F problem are classified in a general framework. The PF/MG-F problem is defined and some efficiency indices designed to evaluate the PF/MG-F techniques are presented. One of the efficiency indices evaluates the inter-cell flows and inner-cell densities while another one measures the within-cell work-load balances. Another index measures the under-utilization levels of machines. A number of the most promising PF/MG-F techniques are selected for detailed analysis. These selected techniques are evaluated and compared in terms of the efficiency measures by employing randomly generated test problems. Finally, further research areas are addressed.
Open Access
A Run-time environment for an object-oriented database management system
(1989) Yengül, Can
In this thesis, an object-oriented query processor, a database language executer, and the protocols for the system- defined classes are designed and implemented. The designed and implemented database language completely fulfills the requirements of the object-oriented paradigm. Query processing functions are implemented through the message passing paradigm, which results in a uniform treatment of data manipulation and query processing functions. The run-time environment also supports the implementation of inheritance mechanism, class hierarchy maintenance, instance access and modification, and access to class definitions.
Open Access
Exact and approximate decoupling and noninteracting control problems
(1989) Akar, Nail
In this thesis, we consider “exact” and “approximate” versions of the disturbance decoupling problem and the noninteracting control problem for linear, time-invariant systems. In the exact versions of these problems, we obtain necessary and sufficient conditions for the existence of an internally stabilizing dynamic output feedback controller such that prespecified interactions between certain sets of inputs and certain sets of outputs are annihilated in the closed-loop system. In the approximate version of these problems we require these interactions to be quenched in the ‘Hoo sense, up to any degree of accuracy. The solvability of the noninteracting control problems are shown to be equivalent to the existence of a common solution to two linear matrix equations over a principal ideal domain. A common solution to these equations exists if and only if the equations each have a solution and a bilateral matrix equation is solvable. This yields a system theoretical interpretation for the solvability of the original noninteracting control problem.
Open Access
High Tc superconductivity
(1989) Gedik, M. Zafer
critical summary of the recent developments in high temperature superconductivity is given. Physical properties of the new materials are summarized. The new theories proposed to explain high Tc are reviewed. In the case of a special type anisotropic gap, the currents and conductivity for single particle tunneling in high Tc superconductor junctions are calculated. Tunneling is assumed to be specular. The position of the peak in the conductivity curve, is found to be determined by the shape of the Fermi surface. Two geometries are considered: tunneling paxallel and perpendicular to CuO^ planes. The order of the peaks for these two configurations turns out to be opposite to experimental results. It is concluded that, conventional one band theory of superconductivity is not enough to explain observed tunneling spectra of high Tc superconductors.
Open Access
Free-form solid modeling using deformations
(1989) Güdükbay, Uğur
One of the most important problems of available solid modeling systems is that the range of shapes generated is limited. It is not easy to model objects with free-form surfaces in a conventional solid modeling system. Such objects can be defined arl^itrarily but then operations on them are not transparent and complications occur. A method for achieving free-form effect is to define regular objects or surfaces, then deform them. This keeps various properties of the model intact while achieving the required visuaJ appearance. This thesis explains a number of geometric modeling techniques with deformations applied to them in attempts to combine various approaches developed so far. Regular deformations, which include twisting, bending, and tapering, and free-form deformation technique are combined as a new deformation method. This eliminates some of the disadvantages peculiar to each method and utilizes the advantages of both.
Open Access
Design and implementation of an object-oriented expert system shell
(1989) Toroslu, İsmail Hakkı
Expert systems represent a new opportunity in computing. An expert system is a computing system capable of representing and reasoning about some knowledge-rich domain with a view to solving problems and giving advice. Expert system shells are developed to create expert systems in an easy way. In recent years the object-oriented paradigm has been developed. The objectoriented approach has many advantages such as data abstraction, program modularity, and structural data representation. Therefore, we are developing an expert system shell which stores knowledge and data in object-oriented style. Also, an object-oriented DBMS part of our shell satisfy the needs of several expert systems rec|uiring large base of fcvcts. Such shells can be used to build expert systems by only adding the domain-specific knowledge.
Open Access
Knowledge base verification in an expert system shell
(1989) Polat, Faruk
An important part of an expert system is its knowledge base which contains domain dei^endent knowledge. Knowledge base verification is one of the important ¡problems of knowledge acquisition. It is the process of checking that a knowledge base is complete and consistent. An analysis of the rules can detect many potential problems that may exist in a knowledge base. The knowledge base may be incomplete, inconsistent, or even partly erroneous. Those problems unless identified and corrected may cause the inference engine to produce inconsistent results such as conflicting conclusions and sometimes to enter infinite loops. In order to be general, rules with certainty factors are preferred for knowledge representation. This is partly because rules are used in many applications and certainty factors are necessary when knowledge has probabilistic characteristics. Our approacli is to develop a knowledge base verification tool that can be used as a part of a rule-based expert system shell.