<p>The fuel assemblies used at the Swedish nuclear power plants contain typically between 100 and 300 fuel rods. An experimental technique has been demanded for determining the relative activities of specific isotopes in individual fuel rods without dismantling the assemblies. The purpose is to validate production codes, which requires an experimental relative accuracy of <2 % (1 σ).</p><p>Therefore, a new, non-destructive tomographic measurement technique for irradiated nuclear fuel assemblies has been developed. The technique includes two main steps: (1) the gamma-ray flux distribution around the assembly is recorded, and (2) the interior gamma-ray source distribution in the assembly is reconstructed. The use of detailed gamma-ray transport calculations in the reconstruction procedure enables accurate determination of the relative rod-by-rod source distribution.</p><p>To investigate the accuracy achievable, laboratory equipment has been constructed, including a fuel model with a well-known distribution of ¹³⁷Cs. Furthermore, an instrument has been constructed and built for in-pool measurements on irradiated fuel assemblies at nuclear power plants.</p><p>Using the laboratory equipment, a relative accuracy of 1.2 % was obtained (1 σ). The measurements on irradiated fuel resulted in a repeatability of 0.8 %, showing the accuracy that can be achieved using this instrument. The agreement between rod-by-rod data obtained in calculations using the POLCA–7 production code and measured data was 3.1 % (1 σ).</p><p>Additionally, there is a safeguards interest in the tomographic technique for verifying that no fissile material has been diverted from fuel assemblies, i.e. that no fuel rods have been removed or replaced. The applicability has been demonstrated in a measurement on a spent fuel assembly. Furthermore, detection of both the removal of a rod as well as the replacement with a non-active rod has been investigated in detail and quantitatively established using the laboratory equipment.</p>

<p>The present thesis deals with the application of <i>ab-initio</i> electronic structure calculations based on density functional theory for material design.</p><p>The correlation between magnetic properties and electronic structures has been investigated in detail for diluted magnetic semiconductors (DMS), which have promising application for spintronics devices. The point defects, acting as electron donor or electron acceptor, have been studied for their key role in mediating the long ranged ferromagnetic interaction between transition metal (TM) ions. The electron holes induced by electron acceptor are completely spin polarized in semiconductor and exhibit a very significant efficiency to the ferromagnetic coupling between TM ions. While the electron donor shows a negative effect to the ferromagnetism in the system. The common trend of magnetic interaction and electron charge transfer between TM ions and electron acceptors or electron donators have been outlined. The Coulomb correlation <i>U</i> of <i>d</i> electrons, which could change the energy levels of TM <i>d</i> band respective to the host semiconductor band, also shows a significant influence on the magnetic behavior in DMS. </p><p>The crystallography phase transition under high pressure has also been studied for the iron doped with light element, carbon. Our calculated results show that interstitial carbon defect has little effect on the iron's bcc to hcp phase transition under high pressure. The other carbon iron phases, like Fe₃C, has also been studied in a wide pressure range.</p><p>We also present a first-principles description on the temperature dependence of elastic constant for solids. The total temperature effects are approximated as a sum of two separated parts, the thermal expansion contribution, which gives the normal linearly decreasing effect on the elastic constant with increasing temperature, and the electronic band contribution, which could lead anomalous behavior for thermal elastic constants.</p>

The fuel assemblies used at the Swedish nuclear power plants contain typically between 100 and 300 fuel rods. An experimental technique has been demanded for determining the relative activities of specific isotopes in individual fuel rods without dismantling the assemblies. The purpose is to validate production codes, which requires an experimental relative accuracy of &lt;2 % (1 σ). Therefore, a new, non-destructive tomographic measurement technique for irradiated nuclear fuel assemblies has been developed. The technique includes two main steps: (1) the gamma-ray flux distribution around the assembly is recorded, and (2) the interior gamma-ray source distribution in the assembly is reconstructed. The use of detailed gamma-ray transport calculations in the reconstruction procedure enables accurate determination of the relative rod-by-rod source distribution. To investigate the accuracy achievable, laboratory equipment has been constructed, including a fuel model with a well-known distribution of 137Cs. Furthermore, an instrument has been constructed and built for in-pool measurements on irradiated fuel assemblies at nuclear power plants. Using the laboratory equipment, a relative accuracy of 1.2 % was obtained (1 σ). The measurements on irradiated fuel resulted in a repeatability of 0.8 %, showing the accuracy that can be achieved using this instrument. The agreement between rod-by-rod data obtained in calculations using the POLCA–7 production code and measured data was 3.1 % (1 σ). Additionally, there is a safeguards interest in the tomographic technique for verifying that no fissile material has been diverted from fuel assemblies, i.e. that no fuel rods have been removed or replaced. The applicability has been demonstrated in a measurement on a spent fuel assembly. Furthermore, detection of both the removal of a rod as well as the replacement with a non-active rod has been investigated in detail and quantitatively established using the laboratory equipment.

The present thesis deals with the application of ab-initio electronic structure calculations based on density functional theory for material design. The correlation between magnetic properties and electronic structures has been investigated in detail for diluted magnetic semiconductors (DMS), which have promising application for spintronics devices. The point defects, acting as electron donor or electron acceptor, have been studied for their key role in mediating the long ranged ferromagnetic interaction between transition metal (TM) ions. The electron holes induced by electron acceptor are completely spin polarized in semiconductor and exhibit a very significant efficiency to the ferromagnetic coupling between TM ions. While the electron donor shows a negative effect to the ferromagnetism in the system. The common trend of magnetic interaction and electron charge transfer between TM ions and electron acceptors or electron donators have been outlined. The Coulomb correlation U of d electrons, which could change the energy levels of TM d band respective to the host semiconductor band, also shows a significant influence on the magnetic behavior in DMS. The crystallography phase transition under high pressure has also been studied for the iron doped with light element, carbon. Our calculated results show that interstitial carbon defect has little effect on the iron's bcc to hcp phase transition under high pressure. The other carbon iron phases, like Fe3C, has also been studied in a wide pressure range. We also present a first-principles description on the temperature dependence of elastic constant for solids. The total temperature effects are approximated as a sum of two separated parts, the thermal expansion contribution, which gives the normal linearly decreasing effect on the elastic constant with increasing temperature, and the electronic band contribution, which could lead anomalous behavior for thermal elastic constants.

Crystal structure, morphology and crystallization kinetics of melt-crystallized polypropylene and poly(propylene-stat-ethylene) fractions with 2.7 to 11.0 mol% of ethylene were studied by differential scanning calorimeter, wide- and small-angle X-ray scattering, polarized light microscopy, transmission electron microscopy and infrared spectroscopy. With increasing ethylene content the poly(propylene-stat-ethylene) fractions showed unchanged crystallinity, increased unit cell volume and constant crystal thickness in combination with a shortened helix length. This indicated that a fraction of ethylene defects were incorporated into the crystal structure. During the isothermal crystallization both α- and γ-crystals could be formed. The γ-crystal fraction increased with increasing ethylene content and increasing crystallization temperature. For samples with α- and γ-crystal contents, multimodal melting was observed and a noticeable γ- to α-crystal conversion was observed on slow heating. The spherulitic structure of the copolymers was coarser than that for the homopolymer. The crystalline lamellae in copolymers exhibited profound curvature in contrast to the straighter cross-hatched α-crystals typical to the homopolymer. Area dependence of electrical breakdown strength was studied for thin polypropylene homopolymer films. The measurements were performed with an automatic measurement system equipped with a scanning electrode arm. Five different electrodes having areas between 0.045 cm2 and 9.3 cm2 were used and typically 40-80 breakdowns per sample and electrode area were collected. All measurements were performed on dry samples in air at room temperature. The data was analyzed statistically and the Weibull function parameters α and β, the first one related to 63% probability for the sample to break down and the second one to the width of the distribution were fitted to the obtained data. Different features concerning the measurement system and conditions, e.g. criteria for the automatic detection of the breakdowns, effect of electrode edge design, partial discharges, DC ramp speed and humidity were critically analyzed. It was concluded that the obtained α-parameter values were stable and repeatable over several years of time. The β-parameter values, however, varied ± 10-30%, more for the large than the small electrodes, and were also sensitive to the changes both in the sample itself and in the measurement conditions. Breakdown strengths of over 50 capacitor grade polypropylene films were analyzed. The obtained α-parameter values were between 450 and 850 V/μm, depending on the film grade and electrode area. In addition to the high breakdown strengths, reflected by the obtained α-values, another, sparse distribution consisting of low breakdown strengths was revealed when the amount of measurement points was high enough. This means that more than one Weibull distribution could be needed to describe the breakdown strength behavior of a polypropylene film. Breakdown values showed decreasing area dependence with decreasing electrode area. Breakdown strengths for larger sample areas were predicted from the small area data by area- and Weibull extrapolation. The area extrapolation led to predicted α-values 50% higher than measured at 4 m2 whereas the Weibull extrapolation showed an accuracy of ±15 % when predicted and measured values were compared. Breakdown strengths were also extrapolated for film areas similar to those in impregnated power capacitors. It turned out that the power capacitors, tested at the factory, performed much better than predicted by the extrapolation. However, a few weak spots with very low breakdown values were also found. For the poly(ethyelene terephtalate) dielectric, which is not swelled by the impregnation liquid, the large area breakdown strength was predictable. This indicates that for polypropylene film processing and impregnation led, in addition to the improved large area breakdown performance, also to sparse weak spots with low breakdown probabilities. Different Weibull distributions were responsible for the breakdown strengths for the processed and impregnated polypropylene than for the dry film samples. / QC 20101027

The structure and interactions of the defects in material on an atomistic scale ulti- mately determine the macroscopic behavior of that material. A fundamental understanding of how defects behave is essential for predicting materials failure; this is especially true in an irradiated environment, where defects are created at higher than average rates. In this work, we present two different atomistic scale computational studies of defects in body centered cubic (bcc) iron. First, the interaction energies between screw dislocations (line defects) and various kinds of point defects will be calculated, using anisotropic linear elastic theory and atomistic simulation, and compared. Second, the energetics and behavior of hydrogen and hydrogen-helium gas bubbles will be investigated.

Interactive handheld electronic displays use hydrogenated amorphous silicon (a-Si:H) thin film transistor (TFT) as a backplane and a Touch Screen Panel (TSP) on top as an input device. The low mobility and instability of a-Si:H TFT threshold voltage are major two issues for driving constant current as required for Active Matrix Organic Light Emitting Ddiode (AMOLED) displays. Low mobility is compensated by increasing transistor width or resorting to more expensive material TFTs. On the other hand, the ever increasing threshold voltage shift degrades the drain current under electrical operation causing OLED display to dim. Mutual capacitive TSP, the current cell phone standard, requires two layers of metals and a dielectric to be put in front of the display, further dimming the device and adding to visual noise due to sun reflection, not to mention increased integration cost and decreased yield. This thesis focuses on the aforementioned technological hurdles of a handheld electronic display by proposing a dual-gate TFT used as an OLED current driving TFT and a novel phase response readout scheme that can be applied to a one metal track TSP. Our dual-gate TFT has shown on average 20% increase in drive current over a single gate TFT fabricated in the same batch, attributed to the aid of a top channel to the convention bottom channel TFT. Furthermore the dual gate TFT shows three times the Poole-Frenkel current than the single gate TFT attributed to the increase in gate to drain overlap. The dual-gate TFT shows a 50% improvement in threshold voltage shift over a single gate TFT at room temperature, but only ~8% improvement under 75ºC. This is an important observation as it shows an accelerated threshold voltage shift in the dual-gate. This difference in the rate of threshold voltage change under varying temperature is attributed to the difference in interface states, supporting Libsch and Kanicki’s multi-level temperature dependant dielectric trapping model. The phase response TSP readout scheme requires IC only on one side of the display. Cadence Spectre simulation results showed that both touch occurrence and touch position can be obtained using only one metal layer.

Die vorliegende Arbeit befasst sich mit der Erzeugung und Detektion von Defekten im Halbleiter Zinkoxyd (ZnO). Der Fokus liegt dabei auf der Verwendung raumladungszonenspektroskopischer Techniken zur Detektion und Charakterisierung elektronischer Defektzustände. Es werden theoretische Aspekte von Raumladungszonen an Halbleitergrenzflächen und den darin enthaltenen elektronischen Defektzuständen behandelt. Das elektrische Potential in der Raumladungszone genügt einer nichtlinearen, eindimensionalen Poissongleichung, für die bekannte, näherungsweise Lösungen vorgestellt werden. Für eine homogen dotierte Raumladungszone gelang es, die exakte Lösung des Potentialverlaufs als Integral anzugeben und einen analytischen Ausdruck für die Kapazität der Raumladungszone zu berechnen. Desweiteren werden transiente und oszillatorische Lösungen der Differentialgleichung zur Beschreibung der Zeitentwicklung der Besetzungswahrscheinlichkeit von Defektzuständen für verschiedene experimentelle Bedingungen betrachtet. Sämtliche raumladungszonenspektroskopischen Experimente können durch geeignete Lösungen dieser beiden Differentialgleichungen beschrieben werden. Für die Fälle, für die keine analytischen Lösungen bekannt sind, wurde ein numerisches Modell entwickelt. Die Experimente wurden an ZnO Dünnfilmproben durchgeführt, welche mittels gepulster Laserablation auf Korundsubstraten abgeschieden wurden. Zur Erzeugung von Defekten wurden entweder Ionen in die Proben implantiert, die Proben mit hochenergetischen Elektronen bzw. Protonen bestrahlt oder einer thermischen Behandlung unterzogen. Die Raumladungszonen wurden durch Schottkykontakte realisiert. Durch die raumladungszonenspektroskopischen Verfahren, Kapazitäts-Spannungs Messungen, Admittanzspektroskopie, Deep-Level Transient Spectroscopy (DLTS), Minority Carrier Transient Spectroscopy, optische DLTS, Photokapazitäts- und Photostrommessungen, sowie der optischen Kapazitäts-Spannungs Messung konnten Defektzustände in der gesamten ZnO Bandlücke nachgewiesen werden. Durch Vergleiche der gemessenen Defektkonzentrationen in einer unbehandelten Referenzprobe mit denen in behandelten Proben konnten Aussagen über die experimentellen Bedingungen, unter denen intrinsische Defekte entstehen bzw. ausheilen, gewonnen und mit Stickstoff- bzw. Nickel- in Zusammenhang stehende Defekte identifiziert werden. Für eine Vielzahl untersuchter Defektzustände konnten die thermische Aktivierungsenergie der Ladungsträgeremission, Querschnitte für den Einfang freier Ladungsträger sowie die spektralen Photoionisationsquerschnitte bestimmt werden. Aus diesen Eigenschaften sowie den experimentellen Bedingungen unter denen der Defekt bevorzugt gebildet wird, wurden Rückschlüsse auf die mikroskopische Struktur einiger Defekte gezogen.

A new model of a critically-sized segmental femoral bone defect in rats was developed to enable in vivo imaging and facilitate post-mortem mechanical testing of samples. The critically-sized nature of the model was assessed and confirmed. The efficacy of sustained co-delivery of osteogenic (BMP-2 and TGF- Ò3) and angiogenic (VEGF) growth factors in promoting functional bone repair was assessed. Effects of scaffold modification in terms of geometry and composition were evaluated. The results indicated that co-delivery of BMP-2 and TGF- Ò3 resulted in a dose-dependent improvement in functional bone repair. Modification of the polylactide scaffold to include an absorbable ceramic component and a cored out geometry enhanced rate of union. Addition of VEGF to the scaffold treatment did not significantly impact revascularization of the defect site or functional repair of the bone defect. These data demonstrate that the complex environment of an acute bone defect requires different treatment strategies than simple ectopic models would suggest. A positive predictive correlation between bone repair parameters measured in vivo and mechanical functionality was established. The novel defect model demonstrated robustness and reproducibility. Implications for further research are discussed.

As a part of the quality management, product defectiveness prediction is vital for small software organizations as for instutional ones. Although for defect prediction there have been conducted a lot of studies, process enactment data cannot be used because of the difficulty of collection. Additionally, there is no proposed approach known in general for the analysis of process enactment data in software engineering. In this study, we developed a method to show the applicability of process enactment data for defect prediction and answered &ldquo / Is process enactment data beneficial for defect prediction?&rdquo / , &ldquo / How can we use process enactment data?&rdquo / and &ldquo / Which approaches and analysis methods can our method support?&rdquo / questions. We used multiple case study design and conducted case studies including with and without process enactment data in a small software development company. We preferred machine learning approaches rather than statistical ones, in order to cluster the data which includes process enactment informationsince we believed that they are convenient with the pattern oriented nature of the data. By the case studies performed, we obtained promising results. We evaluated performance values of prediction models to demonstrate the advantage of using process enactment data for the prediction of defect open duration value. When we have enough data points to apply machine learning methods and the data can be clusteredhomogeneously, we observed approximately 3% (ranging from -10% to %17) more accurate results from analyses including with process enactment data than the without ones. Keywords: