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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.

Application of Positron Annihilation Spectroscopy to the Study of Defects in Perovskite Type Materials

Grebennikov, Dmytro January 2007 (has links)
<p>Formation of defects in ceramics <em>BaA<sub>1/3</sub>Nb<sub>2/3</sub>O<sub>3</sub> </em>(where A=Mg, Co or Zn) suitable for microwave applications was analyzed by using positron annihilation spectroscopy and X-ray diffraction techniques. The dependence of the microwave properties of perovskite ceramics on the defect structure of <em>ANb<sub>2</sub>O<sub>6</sub></em> (A = Mg, Co or Zn ) that was used as a precursor during the sintering process prompted us to conduct positron analysis of<em> ANb<sub>2</sub>O<sub>6</sub></em> columbites as well.</p> <p>Positron lifetime experiments revealed only one defect type - grain boundaries- and demonstrated that the lifetime component originating from the annihilation in defects depends on the size of the grains contained in the materials. For perovskite samples where the grain sizes are smaller than those of columbite materials, the intensity of the defects' component is larger and varies within 28-40%. Results of coincidence Doppler broadening measurements confirmed the presence of only one type of defect in both materials, i.e. grain boundaries.</p> <p>Theoretical calculations for the <em>ANb<sub>2</sub>O<sub>6</sub></em> columbite system resulted in bulk lifetimes of <em>τ<sub>b</sub></em> = <em>177, 176, and 172psec</em>, respectively for magnesium, zinc and cobalt columbites and are in agreement with experimental values. The presence of second phases in nonstoichiometric <em>A</em><sub>1+x</sub><em>Nb<sub>2</sub>O<sub>6</sub></em> (A=Mg, Co, or Zn) columbites did not change the bulk lifetimes of the columbite material because of the small difference in bulk lifetimes of the host material and impurities.</p> <p>Ordering in perovskite type materials that influences the microwave properties in ceramics also changes the positron characteristics of perovskites. Theoretical simulations demonstrated that for the disordered cubic phase, <em>τ<sub>b </sub>≈</em> 190<em> p</em>sec and for the completely ordered hexagonal phase, <em>τ<sub>b </sub>≈</em> <em>240 p</em>sec. The bulk lifetime of the final perovskite material greatly depends on the presence of the second phases (Ba-rich and, possibly, Co-rich) as well as on the fractional part of the hexagonal phase. The influence of additional phases on rb is more significant than that of the "disorderedordered" transition and can be used to monitor changes in the concentration of the former ones.</p> / Master of Applied Science (MASc)

Annealed Proton-Exchanged LiNb03 Ridge Waveguides -- Simulation, Fabrication and Characterization

Sun, Jian January 2010 (has links)
<p>Although semiconductor optical waveguides are quite mature in industry productions, fabrication of high quality lithium niobate (LiNb0<sub>3</sub>) waveguides has always been a challenging topic over the past decades. Intense studies have been done, and various kinds of fabrication methods have been invented, however, existing technologies still cannot provide a satisfyng solution with both excellent performances and easy processing. Traditional ion doped optical waveguides have poor light confinement, while the newly emerged etching and precise machining techniques are still under developing. Searching for new fabrication methods for LiNbO<sub>3</sub> waveguide devices is a meaningful pursuit of both academic and practical value.</p> <p>In this study, a novel fabrication technique for LiNbO<sub>3</sub> waveguides has been proposed and realized. Through the combination of proton-exchange and precise diamond blade dicing, the annealed proton-exchanged (APE) LiNbO<sub>3</sub> ridge waveguides with low propagation loss and single transmission mode have been fabricated for both 1550 nm and 1064 nm wavelengths. The results have shown good agreements with theoretical simulation. Based on the obtained data, a nonlinear second harmonic generation (SHG) wavelength converter has been fabricated using the APE ridge waveguide built on periodically polled MgO:LiNbO<sub>3</sub> (PPMgLN) substrate. Test results have shown remarkable improvements comparing with traditional waveguide structures.</p> <p>Although there are remaining problems need to be solved, the fabricated waveguides have demonstrated great potentials for various optical applications. Based on this platform, mid-infrared generation by difference frequency generation (DFG), compact blue laser via SHG, high-speed optical modulators and many other useful devices can be built. Not all of them have been fully exploited yet.</p> / Master of Applied Science (MASc)

Sensitivity and Uncertainty Analysis of (Th, Pu)O2 Benchmark Experiments in ZED-2 Using TSUNAMI

Zhu, Ting 03 1900 (has links)
<p>In 1984, the ZED-2 research reactor was used to study five (Th, Pu)O<sub>2</sub> fuel bundles with the goal to provide both benchmark tests for future reactor code validation and experimental measurements for a possible thorium fuel cycle in CANDU. In this work, the neutronic models of these critical experiments were investigated by TSUNAMI, a sensitivity and uncertainty (S/U) analysis tool, part of the SCALE6 reactor physics package from the Oak Ridge National Laboratory.</p> <p>TSUNAMI consists of different modules that are capable of calculating the values of k<sub>eff</sub> and the uncertainties in k<sub>eff</sub> due to uncertainties in the nuclear data. It generates energy-dependent sensitivity coefficients from which the percentage change in k<sub>eff</sub> due to perturbations in nuclear data values can be determined. The calculated k<sub>eff</sub> has a bias which is the difference between calculation and measurement. Several sources of uncertainties are responsible for the observed k<sub>eff</sub> bias. But the most dominant and universal contributor is the uncertainties in the nuclear data. Because of the shared nature of nuclear data in all simulations, correlations among the calculated k<sub>eff</sub> values exist and can be measured in terms of the correlations in the nuclear data uncertainties. TSUNAMI provides a consistent and systematic approach to examine these correlations and their effect on k<sub>eff</sub> biases. It also offers an interesting application of the Generalized Linear Least Squares (GLLS) methodology which applies adjustments to the original nuclear data so that k<sub>eff</sub> biases are reduced.</p> <p>Using TSUNAMI, the computed k<sub>eff</sub> values agree with the experimental k<sub>eff</sub> up to a bias of 2.3mk or lower. It is also found that the list of top uncertainty contributors in k<sub>eff</sub> is identical among the simulations, confirming a high degree of correlation in the nuclear data uncertainties. An illustrative example demonstrated the application of TSUNAMI to coolant void reactivity. In this particular simulation, the coolant density was reduced to mimic the loss of coolant condition. Positive reactivity was induced as the simulation predicted. Through S/U analysis, the uncertainty in the computed reactivity was determined in a similar fashion as the k<sub>eff</sub> uncertainty. Top reactivity uncertainty contributors were also identified. Finally the GLLS procedure was explored using the coolant void example along with the experiments.</p> <p>Even though the results are not conclusive on the applicability of these (Th, Pu)O<sub>2</sub> ZED-2 benchmark experiments to future thorium CANDU reactors, they have called attention to the need for a larger number and better designs of relevant benchmark experiments. It is proposed that they should be designed to maximize the sensitivity information of thorium and plutonium in order to offer more meaningful S/U analysis and establish good confidence in the future investigation of (Th, Pu)O<sub>2</sub> fuel in CANDU reactors.</p> / Master of Applied Science (MASc)

Application of Ion Implantation Techniques to Anode Electrocatalyst Development for Use in Alkaline Water Electrolysis

Akano, Gbadebo Usman January 1980 (has links)
<p>The project is concerned with development of suitable anode electrodes for oxygen evolution in 30 w/o KOH solution at BO°C. Li ions (15 keV, 40 keV and 60 keV) at doses of 1 x 10<sup>15</sup> to 1.5 x 10<sup>16</sup> ions/cm<sup>2</sup>, He ions (15 keV, 40 keV) at 3 x 10<sup>15</sup> ions/cm<sup>2</sup> and Ag ion (50 keV) at 1 x 10<sup>16</sup> to 4 x 10<sup>16</sup> ions/cm<sup>2</sup> have been implanted into polycrystalline Ni and oxidized Ni at room temperature. Ag has also been recoil implanted into Ni and NiO. Current-potential measurements have been carried out using galvanostatic techniques with the implanted samples as the oxygen electrode in 30 w/o KOH solution at BO°C. The Ag-imp1anted electrodes show a substantial reduction in electrode potential at 1 A/cm<sup>2</sup> (~ 60% compared to polished Ni) and all implanted samples show a more uniform corrosion products on the surface. Dual Tafel slopes are observed for all electrodes and the higher slope at the higher current densities is thought to be due to the formation of nickel oxide on the electrodes. The Tafel slope and exchange current density, at low current densities are considered consistent with reported data. RBS analysis of the Ag-imp1anted electrodes indicates that no Ag is lost as a result of the electrochemical measurements.</p> / Master of Engineering (ME)

Stress-Strain Characteristics and Histological Studies of Canine Connective Tissues

Ahood, Abdul Latiff 05 1900 (has links)
<p>This project is Part I of a study aimed at determining the stress-strain characteristics of various collagenous canine tissues, and relating them to their structure (histology). In addition Part II involves the isolation of the collagenous structures by enzymolysis of mucopolysaccharides and elastin, which results in the phenomenological elastic moduli of collagen in the various tissues. The present study provides this through in vitro tensile experiments on various tissues from the dog in the native state, after elastin removal by enzymolysis, or after removal of collagen by autoclaving. The elastin component, which exhibits a linear stress-strain curve, determines the tensile modulus of the native tissue at low strain, while collagen determines the modulus at high strain. The removal of elastin significantly alters the moduli at low strain for most of the tissues, although the high-strain moduli remain essentially unchanged.</p> / Master of Engineering (ME)

Porosity studies and determination of elastin content in canine connective tissues

Ahood, Abdul Latiff January 1978 (has links)
<p>By means of porosity curves and diffusion equations solved by computer, the microvoid and macrovoid (hence elastin) content of various tissues from the dog are determined. The elastin content is correlated to the stress-strain characteristics of the respective tissues obtained previously (Project I) and the results are supported, to some extent, by histology. The area correction for microvoids are found to be essential for the cases of the abdominal skin and the cornea anly. The correction for macrovoids are essential for all the tissues except the Achilles tendon.</p> / Master of Engineering (MEngr)

Zone Controller and Detector Locations at Bruce B

Anastasiou, Ioannis A. January 1978 (has links)
<p>The objective of this study was to investigate the effectiveness of various arrangements of zone controller and detector locations in suppressing xenon induced spatial power oscillations. Using the SORGHUM code, which is a two-group neutron diffusion code, it was necessary to modify the cross sections set as taken from the more detailed CHEBY code. Then, the optimum axial location of the zone controllers was investigated with a three-dimensional study, while later a two-dimensional search in detail revealed the optimal radial locations of the zone controllers and the detectors associated with them.</p> / Master of Engineering (ME)

Study of Xenon Induced Power Oscillations with λ-Modes

Anastasiou, Ioannis A. January 1978 (has links)
<p>A large thermal reactor operating at sufficiently high flux levels is susceptible to oscillations in the power distribution that are associated with a periodic redistribution of xenon poison. The particular perturbation method, λ-mode approximation, is presented in this report. A detailed description of the λ-mode mathematical formalism and the computer program XIPOLML and its application to Pickering reactors are reported.</p> / Master of Engineering (ME)

The Role of Void Distributions on Void Fraction Measurements

Archer, Paul Henri 08 1900 (has links)
<p>The distribution of voids in a nuclear reactor is of great importance due to their effect on the neutron flux and on the reactor dynamic characteristics in addition to the well known thermohydraulic problems they create.</p> <p>The possibility of using scattered neutrons to measure voids in a liquid flow is investigated experimentally. The appealing property of a scattering technique as compared to the well known transmission method, is that multiple detectors could be used for additional information about the distribution of the voids as well as their void fraction.</p> <p>For this purpose a beam of neutrons has been extracted from the McMaster University 5MW pool type nuclear reactor. Cylindrical pieces of Lucite have been used to simulate a column of water; this material has neutron transport properties which are very similar to those of liquid water.</p> <p>The neutron diagnostic method of detection has the advantage of not disturbing the flow of the fluid like devices such as probes and isolating valves would do.</p> <p>A BF<sub>3</sub> detector mounted on an arm which rotates about the axis of the cylindrical samples was used as the experimental set up. Lucite samples of different void fractions and possessing different void distributions were prepared. Different numbers of circular holes and of different relative sizes were drilled in the samples providing the possibility of simulating many void distributions by simply rotating the samples. Counting times of the order of 100 seconds were used in order to provide sufficient statistical accuracy to observe the differences in counts.</p> / Master of Engineering (ME)

Design, Fabrication and Characterization of n-Channel InGaAsP-InP Based Inversion Channel Technology Devices (ICT) for Optoelectronic Integrated Circuits (OEIC): Double Heterojunction Optoelectronic Switches (DOES), Heterojunction Field-Effect Transistors (HFET), Bipolar Inversion Channel Field-Effect Transistors (BICFET) and Bipolar Inversion Channel Phototransistors (BICPT).

Tan, Eugene January 1998 (has links)
<p>This thesis demonstrates inversion channel technology (ICT) as a viable technique for realizing InGaAsP-InP based monolithic optoelectronic integrated circuits (OEIC). Inversion channel technology utilizes a common substrate and a common fabrication sequence to monolithically integrate electrical, optical and optoelectronic devices, therefore, requiring compatibility in both the device structure and fabrication sequence. This technology is demonstrated by designing, fabricating and characterizing four types of ICT devices, the DOES, HFET, BICFET and BICPT, on a common structure with a common fabrication sequence. These devices were selected because they are complementary in function and provide the circuit designer all the basic elements for building monolithic OIECs: optical emitter, optoelectronic switches, bipolar and unipolar transistors, and photodetectors. Device models for InGaAsP-InP based DOES, HFET, BICFET and BICPT are developed and used to design the four device structures used in this work. These models identify the effect of device structure on the performance of the devices. The device models are also used to predict the input, output and transfer characteristics of each type of device. This provides an understanding of device physics and operation, and a basis for comparison with experimental results. A common fabrication sequence and fabrication recipes for self-aligned n-channel InGaAsP-InP based DOES, HFET, BICFET and BICPT is designed, developed and demonstrated. This includes the photomask set for self-aligned ICT devices, SiO₂ masking for self-aligned contact formation, SiO₂ sidewall passivation of mesas for ion-implantation, high accuracy RIE etching with a an in-situ QMS, implant activation for n- and p-implants in InGaAsP-InP, and metallization over tall vertical mesa structures. The operation of the DOES, HFET, BICFET and BICPT is demonstrated experimentally. Complete sets of electrical, optical and optoelectronic measurements of the input, output and transfer characteristics of each type of device is performed. These characteristics are compared with the theoretical predictions made by the models to validate the operation of each type of device. This work demonstrates ICT as a technology for realizing OEICs in the InGaAsP-InP material system, and presents the technology required to design, fabricate and characterize these integrated devices.</p> / Doctor of Philosophy (PhD)

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