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Thermoelectric properties of silicon doped germanium
Seebeck coeffcient is a property of material which shows the electrical potential difference created by the temperature difference. This electrical potential is useful in thermocouples and thermopower generation applications. Silicon doped germanium is a good material for thermopower generation applications. Moreover, in interface temperature measurement of bulk growth is possible with the thermoelectric property of Ge-Si alloy. Seebeck coeffcient measurements are made by the small ?T technique. In this technique, potential difference between two probes are measured and with changing the temperature of one probe potential difference change with respect to temperature can be calculated. Seebeck coeffcients of evaporation grade germanium, 5 atm% and 50 atm% silicon doped germanium has been measured. Moreover, electrical resistivity of 5-25 atm% silicon doped germanium at room temperature has been measured. Also, high temperature electrical resistivity measurements for 5 atm% and 50 atm% has been attempted.
A Novel system model implementation of network attacks and countermeasures
The Internet is an open and efficient TCP/IP protocol which is most widely usedin the world. As usage of the Internet and TCP/IP protocols increases, their lack ofbuilt-in security has become more and more problematic. Nowadays, network attacksare the most important and serious problem on the Internet. DoS attack is the oneof these network attacks which takes advantage of the lack of authenticity in the IPprotocol and stateless nature of the Internet.This thesis examines the TCP/IP architecture, general network structures andnetwork security mechanisms.Second, DDoS attacks and server system models are covered in this work. Newattack models are proposed and developed. These new models and also existing attackmodels are simulated. While generating dierent attacks, new proposed server model isalso designed and coded. This server is called \virtual server with a new perspective".Third, after generating the custom attacks against the custom server system,protection and warning mechanisms are required on the server side. In that case,custom intrusion detection and intrusion prevention system models are designed. Inaddition, numerous of simulation are completed.Finally, at the end of the research, many point of views about conutermeasuressystems are proposed, and their results are investigated.
Nutrient export coefficient modelling of the Melen watershed using estimated retention in the water body
The Melen Watershed provides fresh drinking water to most of Istanbul. According to The Ministry of Forest and Water Works of Turkey, regarding the pollution status, Melen River Basin should be primarily dealt with. Nutrient pollution such as nitrogen (N) and phosphorus (P) can cause water quality degradation in rivers, which are used as a source of drinking water. This situation raises the question of how the nutrients have moved depending on many factors such as land use and anthropogenic sources.Researchers developed several nutrient export coefficient models depending on aforementioned factors. For this purpose, statistical data includes a number of factors such as historical water quality data for the research field, land use, population and infrastructure were used. Nutrient export coefficients are estimates of the total load or mass of nitrogen (N) or phosphorus (P) exported from a watershed standardized to unit area and unit time (e.g., kg/km2/day). Almost no study has been conducted regarding this issue in Turkey.Within this study, nutrient export coefficients for the Melen Watershed were determined using the model that covers Frequentist and Bayesian approaches. River Retention Coefficient was determined and introduced into the model as an important variable. Frequently used hydrologic model, Soil & Water Assessment Tool (SWAT), was used as a tool for modeling of diffuse source pollution. As a brief recommendation, agricultural best management practices (BMP) were evaluated using SWAT model to determine the best management system to reduce nutrient loads in the Melen Watershed. This study is aimed to be an important precedent for other basins that are determined as in priority in terms of pollution by The Ministry of Forest and Water Works of Turkey.
Synthesis, HPLC and NMR studies on axially chiral pyridine compounds as potential bidentate N,N'-ligands
In this study, axially chiral enantiomeric and diastereomeric 2-arylimino-3-aryl-thiazolidine-4-ones have been synthesized and their stereostructures have been investigated. In these compounds, the rotation around N3-aryl bond is restricted resulting in axial chirality. Therefore, M and P enantiomers or RM, RP and SM, SP diastereomers exist. Enantiomeric and diastereomeric isomers of the compounds have been investigated by 1H-NMR and HPLC.In 3-(pyridin-2-yl)-2-(pyridin-2-ylimino)thiazolidine-4-one, it was found that the rotation around N3-aryl bond is too fast to make the enantiomeric isomer separation observable by enantioselective HPLC. On the other hand, the interconversion rate between the enantiomers of 3-(3-methylpyridin-2-yl)-2-(3-methylpyridin-2-ylimino)thiazolidine-4-one and the energy barrier for this compound have been determined by thermal racemization of the micropreparatively resolved enantiomers. Rotational barrier of the diastereomers of 5-methyl-3-(3-methylpyridin-2-yl)-2-(3-methylpyridin-2-ylimino) thiazolidine-4-one has also been determined by following the interconversion between the unequally populated diastereomers with time by HPLC. Also, 3-(3-methylpyridin-2-yl)-2-(3-methylpyridin-2-ylimino)thiazolidine-4-thione was synthesized by converting the C-4 carbonyl oxygen to a sulphur atom via the Lawesson Reagent.It was found that replacing one C-5 proton with a methyl group decreased the rotational barrier by 2.2 kJ/mol. On the other hand, replacing C-4 carbonyl oxygen with a sulphur atom increased the barrier by 18.3 kJ/mol.
Rehabilitation of damaged coasts usind beach nourishment and a case study in Izmit Bay
Part of Izmit Bay had been filled with excavation waste after the 1999 Earthquake causing beaches around the Bay to lose their natural form and usability. The main purpose of this study is to investigate the existing conditions of a typical fill area and find a feasible solution to reinstate a natural coast. After theoretical and experimental investigations, beach nourishment is proposed as a solution to rehabilitate the coasts of İzmit Bay by transforming them into recreational beaches. The geology, sediment properties, morphological structure and wave regime of the selected pilot site, Derince, is determined by field measurements, laboratory experiments and computer analysis. Along the coastal profile, sediment diameter differs from place to place, and especially in deeper zones, the rate of fine material (silt and clay) increases significantly. Bathymetric measurements indicate that the coastal profile is not in equilibrium. A physical model is established to examine the interaction between the native mixed soil and the granular nourishment sand. Laboratory experiments showed that there is no mixing between the native fine material and nourishment sand. Even after extreme storms, no silt and clay have been found on the nourished nearshore profile. Therefore, it is concluded that the predefined coasts can be rehabilitated using beach nourishment. Using the site specific parameters, alternative beach nourishment designs are developed including calculation of the required sand volumes and the project cost.
A comparison between students' mental models of atomic structure and visualizations in textbooks for the concept of atom
This study was designed for two major goals which are to describe students? mental models about atom concept from 6th to 11th grade and to compare students? mental models of atomic model with visual representations of atom in textbooks. in order to analyze the comparison of students? mental models from their drawings and textbook visuals Chi-square analyzes were used. Descriptive statistics were also used to describe students? mental models and textbook visual representations. The date was collected as qualitatively (Mental Model Atom Test) with 4 open ended questions including also drawings and quantitatively (Evaluation Rubric for Atomic Model Representations). The study was implemented in 2 elementary schools and 3 high schools with 180 students. in addition, 525 visuals from the Ministry of Education textbooks were evaluated in the study. The results indicated that Bohr?s Atomic Model were seen as the most frequent model in both the student? drawings and textbook atom visuals. The consistency with textbook visuals and students? drawings were not established statistically because of the 6th grade students and 10th grade students? drawings. The results obtained by qualitatively can show that motion was not seen frequently in students? drawings similarly textbooks visuals. Finally, the results stated that students are very stable to draw their previous model even though they can encounter with the new atom model.
Optimization of pigmented coatings for concentrating solar thermal applications
Spectrally selective coatings are used in absorbers of solar collectors to maximize efficiency of solar thermal energy systems. Desired coating should have high absorptance at solar wavelengths and low emittance at the wavelengths where absorber emits heat. This study focuses on pigmented coatings that consist of a binder and uniformly distributed nano-particles known as pigments that exhibit the desired spectrally selective behavior. Radiative behavior of coatings depends on coating thickness, pigment size, concentration, and the optical properties of binder and pigment materials. In order to understand the effect of these parameters, a unified radiative model of the pigmented coatings is developed, Lorentz-Mie theory in conjunction with Hartel theory to incorporate the multiple scattering effects is used to predict radiation properties for independent scattering, T-Matrix method is used to incorporate the dependent scattering and effective medium theory is used to handle cases with very small pigments. Through the solution of the radiative transfer equation by the four flux method, spectral reflectance is predicted. Design of such a coating is formulated as an inverse problem of estimating design variables such as pigment size, concentration and material to yield the desired spectral emittance of the ideal coating. The nonlinear problem is solved by optimization applying two methods; the Quasi Newton method and Nelder Mead simplex algorithm. While both algorithms are capable of providing the same solution, the convergence of Quasi Newton method is found to be superior to that of Nelder Mead simplex algorithm.
Knowledge extraction from experimental and computational data for selective CO oxidation and water gas shift reaction using data mining techniques
The objective of this dissertation is to apply various data mining techniques for knowledge extraction from experimental and computational data to improve catalyst design and testing conditions for selective CO oxidation and water gas shift reactions. First, the experimental data produced in our laboratory were analyzed in three parts: selective CO oxidation over Pt catalysts by neural networks, selective CO oxidation over Au catalysts by decision trees and neural networks, and water gas shift reaction over Pt catalysts by neural networks. In all these works, the models successfully established the effects and relative significances of the catalyst variables in a reasonable agreement with the literature. Then, the data generated by density functional theory for selective CO oxidation over Au nanoparticles were modeled using neural networks and logistic regression, both of which demonstrated that the relations between structural properties of the Au nanoparticles and adsorption energies of CO and O2 on these particles can be successfully established. Finally, the published data by the other investigators were modeled to assess the possibility of predicting the outcome of an experiment, which was not done yet, from the knowledge accumulated in the literature. First, the publications on selective CO oxidation over Cu based catalysts were modeled by neural networks. Then, the publications on the same reaction for noble metal-gold based catalysts were modeled by genetic algorithm supported clustering together with neural networks. In both works, the experimental CO conversions reported in each publication were successfully predicted by the neural networks trained using the data from the remaining publications. The relative significances of the input variables and the major trends associated with these variables were also successfully estimated. It was then concluded that the knowledge accumulated in the published data through years can be extracted using some suitable data mining tools to help the researchers in planning their future experimental works more effectively.
Ambient and forced vibration testing of a reinforced concrete building
The seismic performance of reinforced concrete buildings depends on their lateral stiffness and mass distribution, as well as their lateral load capacity and ductility characteristics. In recent decades, seismic strengthening of existing buildings has been commonly employed, for improving their performance under severe earthquake excitation. The results obtained from vibration tests and system identification methods specifically provide valuable information on the influence of seismic strengthening on the lateral stiffness attributes of the building, and help evaluate the effectiveness of the strengthing technique applied, in terms of improving the building?s vibration characteristics and seismic performance. In this study, ambient and forced vibration tests were conducted to evaluate the influence of the seismic strengthening on the vibration characteristics of the six-story reinforced concrete ET-B building, located on the Boğaziçi University Campus in Istanbul, Turkey. Modal vibration characteristics of the building were identified at various stages of strengthening. Ambient vibration tests were conducted on the building before and after its seismic strengthening. Forced vibration tests were conducted after seismic retrofit. Results of these tests enabled quantifing the changes, due to strengthening, in the modal characteristics (modal frequencies and mode shapes) of the building, and variation in the modal characteristics of the strenghened building with the intensity of shaking. In addition, simple finite element models of the building were generated, representing its structural configuration before and after seismic strengthening, also considering the impact of the brick-infill partition walls on its stiffness characteristics. The experimentally-identified modal vibration parameters of the building were compared with the results of the finite element model. The experimental and analytical results were found to be consistent in representing the pronounced influence of the structural walls on the lateral stiffness and thus the vibration characteristics of the building, as well as the relatively minor, yet noticeable influence of the brick-infill partition walls on its vibration characteristics.
Correlation and optimisation of thermodynamic model parameters with experimental data to predict emissions from a diesel engine
The biggest challenge in engine development is emission regulation today, which gets more stringent with time. Computer aided engineering (CAE) has also increasing importance together with increasing potential of processors for easy and quick calculations and also it is less expensive compared to conducting tests. Therefore it is highly important and challenging to predict emissions by using computer models and simulations precisely. For diesel engines, NOx and particle (soot) emissions have the highest importance. 3D CFD of combustion systems and phenomenological combustion models can provide such information. Phenomenological combustion models have the advantage of much lower runtimes compared to 3D CFD and can be used for wide variety of engine operating points for prediction. Such a phenomenological diesel combustion model is used and correlated with limited amount of test data for the prediction of emissions and is compared to a larger set of emission test data to see its performance. Assessments are made how well the emissions can be predicted by using such a model. The sensitivity of the model against different start of injection and exhaust gas recirculation values is tested. NOx model show good accuracy whereas soot model needs some modification. Both emission models can provide some insight in terms of direction (increase-decrease).