M-type barium hexaferrite powders doped with titanium and/or cobalt have been synthesized according to the stochiometric formulations BaFe(12 &amp / #8211 / (4/3)x)TixO19, BaFe12-xCoxO19 , BaFe12-2xTixCoxO19 (x varying from 0 to 1.5 with an increment of 0.5) by the mixed oxide approach. The powders were used to manufacture small ceramic tiles by sintering each composition at 1250 &deg / C with soaking times ranging from 1 to 16 hours. XRD work revealed formation of the magnetoplumbite crystal structure in all ceramics. The variations in processing parameters led to differences in microstructure and various dielectric and magnetic properties of the ceramic tiles. The interaction of the ceramics with electromagnetic waves was characterized by using a vector network analyzer in the X and Ku bands. The results revealed that, undoped barium hexaferrite ceramics and those doped with low titanium exhibited good microwave absorption properties.

Electromagnetic wave absorbing properties of SiC-based and alumina ceramic woven fabrics have been investigated. Electrical conductivities of SiC-based ceramic woven fabrics were modified by heat treatment in air resulting in their oxidation. Surface properties of alumina woven fabrics were altered by gold-sputtering resulting in a high conductivity layer on the surface of the wovens. Electromagnetic wave interactions of single layer and double layered combinations of these ceramic woven fabrics were determined in 17-40 GHz frequency range using &ldquo / free-space&rdquo / method. Electromagnetic wave absorption potential of ceramic woven fabrics with different chemical compositions and woven types were correlated with their material properties by X-ray diffraction, scanning electron microscopy and electrical conductivity measurements. Effects of modifications and varying woven fabric arrangements in combinations on the electromagnetic wave absorption potential of the ceramic woven fabrics have been discussed. Various double layer combinations of SiC-based and alumina woven fabrics revealed a promising potential in terms of both reduced reflection and transmission resulting in more than ~95% absorption in millimeter wavelength range, which makes them powerful candidate materials for electromagnetic wave absorption applications.

The aim of this study is to investigate the bulk glass forming ability (BGFA) of Ti-based alloy systems. These investigations were carried out in two main parts that are complementary to each other: theoretical and experimental. For theoretical studies, which are based on electronic theory of alloys in pseudopotential approximation, Ti-Zr, Ti-Co and Ti-Cu alloys were chosen as the binary systems. Alloying element additions were performed to each binary for the investigation of the BGFA of multicomponent Ti-based alloys. Among the three studied binary systems, Ti-Cu was found to exhibit better BGFA, and Mn, Al and Ni elements were found to be suitable for improving the BGFA of Ti-Cu binary alloy system. BGFA of Ti-Cu binary and Ti-Cu-(Mn, Al, Ni) multicomponent alloys were investigated with the experimental studies that were carried out with performing arc melting and centrifugal casting operations. The characterizations of these alloys were done with scanning electron microscopy, X-ray diffraction analysis and differential scanning calorimetry. Ti60Cu35Mn5, Ti60Cu35Al5 and Ti60Cu35Ni5 alloys were produced and characterized as examples for ternary systems. Among them, Ti60Cu35Mn5 system was found to have better indications regarding to BGFA. Therefore, it was chosen as the main composition and multicomponent alloys of Ti59Cu35Mn5Al1, Ti59Cu35Mn5Ni1 and Ti58Cu35Mn5Al1Ni1 were synthesized and characterized.

The time/cost trade-off models in project management aim to compress the project completion time by accelerating the activity durations at an expense of additional resources. The budget problem in discrete time/cost trade-off scheduling selects the time/cost mode -among the discrete set of specified modes- for each activity so as to minimize the project completion time without exceeding the available budget. There may be alternative modes that solve the budget problem optimally, however each solution may have a different total cost value. In this study we aim to find the minimum cost solution among the optimal solutions of the budget problem. We analyze the structure of the problem together with its linear programming relaxation and derive some mechanisms for reducing the problem size. We solve the reduced problem by linear programming relaxation and branch and bound based approximation and optimization algorithms. We find that our branch and bound algorithm finds optimal solutions for medium-sized problem instances in reasonable times and the approximation algorithms produce high quality solutions. We also discuss the way our algorithms could be used to construct the time/cost trade-off curve.

The recovery characteristics of Bolu-Himmetoglu, Bolu-Hatildag, K&uuml / tahya- Seyit&ouml / mer, and Nigde-Ulukisla oil shale samples and Bati Raman, &Ccedil / amurlu, and Garzan crude oil samples were tested experimentally using retort and microwave heating techniques. Many parameters like heating time, porosity, water saturation were studied. To enhance the efficiency of the processes three different iron powders (i.e. / Fe, Fe2O3, and FeCl3) were added to the samples and the doses of the iron powders were optimized. While crude oil viscosities were measured to explain the fluid rheologies, since it is impossible to measure the shale oil viscosity at the laboratory conditions due to its very high viscosity, shale oil viscosities were obtained numerically by using the electrical heating option of a reservoir simulator (CMG, STARS 2007) by matching between the laboratory and numerical oil production and temperature distribution results. Then the field scale simulations for retorting of oil shale and crude oil fields were conducted. Since the microwave heating cannot be simulated by CMG, STARS, microwave heating was modeled analytically. In order to explain the feasibility of heating processes, an economic evaluation was carried out. The experimental, numerical, and analytical results show that field scale oil recovery from oil shales and heavy crude oils by electrical and electromagnetic heating could be economically viable. While microwave heating is advantageous from an operational point of view, retorting is advantageous if the technically feasibility of the study is considered.

Modified Ring specimens are of the shape of discs having a hole inside and flattened ends. These specimens are used for determination of Mode I fracture toughness. Finite element program, named ABAQUS, is used for numerical modeling for finding stress intensity factors. Varying disc geometries were used for the experiments and numerical modeling in which size of the flat ends, radius of the hole inside, and external radius of the specimen were varied. Experiments were done by using pink Ankara andesite. Effects of internal hole radius, external disc radius and size of the flat ends on both stress intensity factor and fracture toughness were studied. In order to compare the results, fracture tests with semi-circular specimens under three point bending (SCB) were also performed. From a similar previous study, fracture toughness values of gray andesite were recalculated and compared to the fracture toughness values of pink andesite for varying geometrical factors. Size effect studies were performed as well for varying diameter of core specimens.Fracture toughness values of andesite were found to increase with increasing specimen size. Fracture toughness of 100 mm specimens was determined as 1.11&plusmn / 0.07 MPa&amp / #8730 / m, whereas fracture toughness of 75 mm specimens was 0.96&plusmn / 0.08 MPa&amp / #8730 / m. 100 mm or larger diameter specimens were suggested for the fracture toughness determination with the modified ring tests.

Chatter is unwanted since it causes deteriorating effects on the milling process. Stability lobe diagrams are developed in order to determine the stable cutting conditions at which chatter-free machining can be made. The need of cutting away more chips to make milling operations quicker has brought the concept of high-speed milling. This increased the importance of estimating stability lobe diagrams of the milling process more accurately. The state-of-art chatter and spindle-toolholder-tool models predict the stability lobe diagram for milling process quite effectively. However, sometimes chatter might occur even at cutting conditions selected using theoretically obtained stability lobe diagrams. One of the reasons for that may be nonlinearities in the system. This being the motivation, in this work, nonlinearities at the bearings of spindle-toolholder-tool system are investigated. In this thesis, cubic nonlinearity is assumed to represent stiffness of a bearing in a spindle-toolholder-tool system. Effects of nonlinearity on stability lobe diagram of a milling process are studied by using the mathematical model developed for such a system. Frequency response function of spindle-toolholder-tool system without bearings is obtained using Timoshenko beam model. Then, bearings are modeled by using describing function theory and coupled to the dynamics of spindle-toolholder-tool modeled. Solution of the equations of motion of the system in frequency domain is obtained via Newton&#039 / s method with ALC. It is an effective frequency domain method in which turning points on frequency response function are traced. This is important for the system studied, as bearing nonlinearity may introduce turn backs in the response of the system. Case studies are carried out to study the effects of bearing nonlinearity on stability lobe diagram. The effects of the following factors are studied: Magnitude of cutting force, degree of nonlinearity and number of teeth on cutter. Displacement amplitude dependent stiffness of bearings affects the dynamic response due to rigid body modes of the system. It is observed that an increase in cutting force magnitude or in coefficient of bearing nonlinearity results in increase of natural frequencies, thus showing hardening behavior. Shifting of frequencies in the response curve shifts stability lobes related to the affected modes, to the right. For increased number of flutes on cutter, effect of nonlinearity at bearings on stability of the milling process becomes lower. Experimental studies to determine the changes in dynamics of a system during cutting are also carried out in this thesis. Inverse chatter analysis is conducted to obtain modal parameters of a single-degree-of-freedom system using the experiment data. Decrease in natural frequency is observed at high cutting speeds for the particular spindle used. This shift may be due to speed-dependent bearing dynamics and real time adjustment of preload on bearings.

Multiple Signal Classification (MUSIC) Algorithm based and Wigner Distribution-Principal Component Analysis (WD-PCA) based classification techniques are very recently suggested resonance region approaches for electromagnetic target classification. In this thesis, performances of these two techniques will be compared concerning their robustness for noise and their capacity to handle large number of candidate targets. In this context, classifier design simulations will be demonstrated for target libraries containing conducting and dielectric spheres and for dielectric coated conducting spheres. Small scale aircraft targets modeled by thin conducting wires will also be used in classifier design demonstrations.

Distributed generation (DG) is electricity generation by small generating units, which are interconnected at distribution level with capacity less than 50 MW. Environmental concerns and the idea of using cheap and domestic renewable resources increased the popularity of DG following the developments in equipment technology. In Turkey, interconnection of DG is realized through the distribution busbars of 154/36 kV substation. The interconnection of DG at 36 kV feeders is not allowed by distribution system authority. This thesis proposes an interconnection rule which includes technical analyses to be conducted before the permission of interconnection of DG at 36 kV feeders. Moreover, the protection functions and operational requirements needed for the proper and safe operation of distribution system in presence of DG are introduced. A sample distribution system with relevant parameters is used for the simulation studies in Digsilent software. In order to determine the operational reserve requirement against the variations in wind generation, a statistical method including Weibull distribution, standard deviation and monthly average wind speeds is used. Convenience of hydropower plants&rsquo / response for being backup generation against the fluctuations in wind generation is analyzed by a mid-term dynamic model of the power system. A secondary control mechanism for the integration of wind power is suggested. Finally, an economic comparison between the interconnection alternatives of hydropower and photovoltaic power plants at the distribution busbar of the 154/36 kV substation and the 36 kV feeder is done by present worth analysis using the up to date power plant costs and incentives.

Radar systems have been very effective in gathering information in a battlefield, so that the tactical actions can be decided. On the contrary, self-protection systems have been developed to break this activity of radars, for which radar signals must be intercepted to be able to take counter measures on time. Ideally, interception should be done in a certain time with a 100% probability, but in reality this is not the case. To intercept radar signals in shortest time with the highest probability, a search strategy should be developed for the receiver. This thesis studies the conditions under which the intercept time increases and the probability of intercept decreases. Moreover, it investigates the performance of the search strategy of Clarkson with respect to these conditions, which assumes that a priori knowledge about the radars that will be intercepted is available. Then, the study identifies the cases where the search strategy of Clarkson may be not desirable according to tactical necessities, and proposes a probabilistic search strategy, in which it is possible to intercept radar signals with a specified probability in a certain time.