Global ETD Search

1	Cellulose degradation in pulp fibers studied as changes in molar mass distributions Berggren, Rickard January 2003 (has links) In this thesis, size-exclusion chromatography (SEC) of woodpolymers dissolved in lithium chloride/N,N-dimethylacetamide(LiCl/DMAc) has been used to characterize the molar massdistributions (MMD) of wood polymers in pulp fibers afterchemical degradation. Characterization of birch kraft pulps subjected to ozonedegradation and acid hydrolysis, respectively, rendereddifferent changes in the MMD. Ozone degradation resulted inlarge redistributions of the original MMD, observed as thedevelopment of a distinct fraction of cellulose withintermediate molar mass. Acid hydrolysis resulted in minorchanges of the original MMD compared to ozonation. Fiberssubjected to acid hydrolysis were considerably weaker thanozonated fibers. These results indicated that there aredifferences in how the two chemicals degrade the fiber. The solubility of softwood kraft pulp fibers was enhanced byderivatization of the fiber polymers with ethyl-isocyanateduring simultaneous dissolution in LiCl/DMAc. Thederivatization made it possible to achieve reliable estimationsof the MMD, and hence molar masses, of softwood kraft pulps.The derivatization procedure made it possible to dissolve 90 %of softwood kraft pulps with kappa numbers over 50. Severe alkaline degradation of birch and Norway spruce woodchips was studied both by varying the pulping time and byvarying the initial alkali concentration. Differences werefound in the MMD of the two fiber types, and the alkalinedegradation was found to affect polymers in the entire MMD. Multi-angular laser light scattering (MALLS) was used as adetection technique with SEC on cellulosic samples. The MMD andaverage molar masses obtained through directstandardcalibration with commercial standards were compared with MMDand molar masses as obtained by MALLS-detection. Largediscrepancies were found, and two methods of correcting forthese discrepancies were developed. Theoretical simulations of polymer degradation wereperformed. Random, or homogeneous degradation was used as amodel for alkaline cellulose chain scission, and a resemblancewith experimental data was observed. End-wise depolymerizationof cellulose was also simulated and the results are discussedin the light of experimentally observed MMD. <b>Keywords:</b>cellulose, kraft pulp, birch, spruce,ozonation, acid hydrolysis, degradation, MMD, sizeexclusionchromatography, light scattering, molar mass, chainscission cellulose kraft pulp birch spruce ozonation acid hydrolysis degradation MMD size-exclusion chromatography light scattering molar mass chain scission
2	Cellulose degradation in pulp fibers studied as changes in molar mass distributions Berggren, Rickard January 2003 (has links) <p>In this thesis, size-exclusion chromatography (SEC) of woodpolymers dissolved in lithium chloride/N,N-dimethylacetamide(LiCl/DMAc) has been used to characterize the molar massdistributions (MMD) of wood polymers in pulp fibers afterchemical degradation.</p><p>Characterization of birch kraft pulps subjected to ozonedegradation and acid hydrolysis, respectively, rendereddifferent changes in the MMD. Ozone degradation resulted inlarge redistributions of the original MMD, observed as thedevelopment of a distinct fraction of cellulose withintermediate molar mass. Acid hydrolysis resulted in minorchanges of the original MMD compared to ozonation. Fiberssubjected to acid hydrolysis were considerably weaker thanozonated fibers. These results indicated that there aredifferences in how the two chemicals degrade the fiber.</p><p>The solubility of softwood kraft pulp fibers was enhanced byderivatization of the fiber polymers with ethyl-isocyanateduring simultaneous dissolution in LiCl/DMAc. Thederivatization made it possible to achieve reliable estimationsof the MMD, and hence molar masses, of softwood kraft pulps.The derivatization procedure made it possible to dissolve 90 %of softwood kraft pulps with kappa numbers over 50.</p><p>Severe alkaline degradation of birch and Norway spruce woodchips was studied both by varying the pulping time and byvarying the initial alkali concentration. Differences werefound in the MMD of the two fiber types, and the alkalinedegradation was found to affect polymers in the entire MMD.</p><p>Multi-angular laser light scattering (MALLS) was used as adetection technique with SEC on cellulosic samples. The MMD andaverage molar masses obtained through directstandardcalibration with commercial standards were compared with MMDand molar masses as obtained by MALLS-detection. Largediscrepancies were found, and two methods of correcting forthese discrepancies were developed.</p><p>Theoretical simulations of polymer degradation wereperformed. Random, or homogeneous degradation was used as amodel for alkaline cellulose chain scission, and a resemblancewith experimental data was observed. End-wise depolymerizationof cellulose was also simulated and the results are discussedin the light of experimentally observed MMD.</p><p><b>Keywords:</b>cellulose, kraft pulp, birch, spruce,ozonation, acid hydrolysis, degradation, MMD, sizeexclusionchromatography, light scattering, molar mass, chainscission</p> cellulose kraft pulp birch spruce ozonation acid hydrolysis degradation MMD size-exclusion chromatography light scattering molar mass chain scission
3	An Evaluation of Approaches for Generative Adversarial Network Overfitting Detection Tung Tien Vu (12091421) 20 November 2023 (has links) <p dir="ltr">Generating images from training samples solves the challenge of imbalanced data. It provides the necessary data to run machine learning algorithms for image classification, anomaly detection, and pattern recognition tasks. In medical settings, having imbalanced data results in higher false negatives due to a lack of positive samples. Generative Adversarial Networks (GANs) have been widely adopted for image generation. GANs allow models to train without computing intractable probability while producing high-quality images. However, evaluating GANs has been challenging for the researchers due to a need for an objective function. Most studies assess the quality of generated images and the variety of classes those images cover. Overfitting of training images, however, has received less attention from researchers. When the generated images are mere copies of the training data, GAN models will overfit and will not generalize well. This study examines the ability to detect overfitting of popular metrics: Maximum Mean Discrepancy (MMD) and Fréchet Inception Distance (FID). We investigate the metrics on two types of data: handwritten digits and chest x-ray images using Analysis of Variance (ANOVA) models.</p> Deep learning Statistical data science generative adversarial network (GANs) chest X-ray datasets frechet inception distance maximum mean discrepancy (MMD)
4	Contribution à l'analyse des effets de vieillissement de composants actifs et de circuits intégrés sous contraintes DC et RF en vue d'une approche prédictive / Contribution to the analysis of aging effects of active components and integrated circuits under DC and RF constraints for a predictive approach Lahbib, Insaf 13 December 2017 (has links) Les travaux de cette thèse portent sur la simulation de la dégradation des paramètres électriques des transistors MOS et bipolaires sous stress statiques et dynamiques. Cette étude a été menée à l’aide d’un outil de simulation de fiabilité développé en interne. Selon la technologie MOS ou bipolaire, les mécanismes étudiés ont été successivement : Hot Carrier Injection, Bias Temperature instability, Mixed Mode et Reverse base emitter bias. L’investigation a été aussi étendue au niveau circuit. Nous nous sommes ainsi intéressés à l’effet de la dégradation des transistors sur la fréquence d’un oscillateur en anneau et les performances RF d’un amplificateur faible bruit. Les circuits ont été soumis à des contraintes DC , AC et RF. La prédictibilité, établie de ces dégradations, a été validée par des essais de vieillissement expérimentaux sur des démonstrateurs encapsulés et montés sur PCB. Les résultats de ces études ont permis de valider la précision du simulateur et la méthode de calcul quasi-statique utilisée pour calculer les dégradations sous stress dynamiques. Ces travaux de recherche ont pour but d’inscrire cette approche prédictive dans un flot de conception de circuits afin d’assurer leur fiabilité. / The work of this thesis focuses on the simulation of the electrical parameters degradation of MOS and bipolar transistors under static and dynamic stresses. This study was conducted using an in-house reliability simulation tool. According to the MOS or bipolar technology, the studied mechanisms were successively: Hot Carrier Injection, Bias Temperature instability, Mixed Mode and Reverse base emitter bias. The investigation was then extended to circuit-level. The effect of transistors degradation on a ring oscillator frequency and the RF performances of a low noise amplifier were investigated. The circuits were subjected to DC, AC and RF constraints. Predictability of these degradations has been validated by experimental aging tests on encapsulated and PCB-mounted demonstrators. The results of these studies proved the accuracy of the simulator and validated the quasi-static calculation method used to predict the degradation under dynamic stress. The goal of this research is to embed this predictive approach into a circuit design flow to ensure its reliability. Prédiction de la dégradation Stress DC, Stress RF Dégradation des paramètres DC et RF Reliability simulation DC and RF parameters degradation Lifetime estimation Transistor-level reliability Circuit-level reliability Design for reliability
5	Influence of Fenugreek gum on bread and in vitro physiological effects Roberts, Keisha 18 May 2012 (has links) ABSTRACT Influence of fenugreek gum on bread and in vitro physiological effects Keisha T. Roberts Advisors: University of Guelph Dr. S.W. Cui Professor T.E. Graham This thesis examined the effect of fenugreek gum, from Canadian grown fenugreek on bread quality, when substituted for wheat flour at 5 % and 10 %, and the in vitro physiological effects of these breads, based on models of acute and long - term feeding. Study I determined bread could be produced with 10 % fenugreek gum, while maintaining quality parameters of volume and texture, comparable to a control. This was accomplished through the development of a novel bread production method, using the lamination procedure for puff pastry production. The behavior of fenugreek gum and starch (wheat flour) was determined by rapid visco analysis (RVA), farinograph and dynamic rheological measurement, while scanning electron microscopy of bread found fenugreek gum could be identified within the bread matrix. Study 2 in vitro starch digestion found fenugreek gum at 5 % and 10 % reduced glucose liberated from bread, with 10 % fenugreek gum causing a reduction of over 30 %. RVA of fenugreek breads highlighted differences in viscosity between breads and wheat flour substituted with the gum. This was substantial as viscosity measurements by RVA are conducted on raw ingredients and not the food as consumed, which reflects the possible reduction in viscosity with food processing. This study also determined extruding fenugreek gum may have caused morphological changes to the gum, which may possibly contribute to attenuation of glucose liberated in vitro. Study 3 evaluated the accumulation of short chain fatty acids (SCFA) from the fermentation of three substrates: Extruded fenugreek gum, bread with 10 % extruded gum and control bread, based on fecal microbiota from three donors. SCFA profiles varied with substrates and donors, with fenugreek gum having the highest accumulation of SCFA after 12 hours. Donors were a caucuasian Canadian, a black Jamaican and a black Trinidadian who was the only donor culturally exposed to fenugreek. This Trinidadian’s SCFA profiles were consistently higher for fenugreek gum than the other donors. These studies collectively showed fenugreek gum, though viscous could be successfully incorporated into bread and have potential as a functional food and nutraceutical.
6	選舉制度與結果的比例性偏差：以台灣立法委員選舉制度為例（1992-2008） / The disproportionality of electoral system: the case of legislative election in Taiwan (1992-2008) 張佑丞, Chang, Yu-Cheng Unknown Date (has links) 選舉制度的設計與評估，主要有兩方面的考量，一是可治理性；二是分配的比例性。以台灣的情況為例，新選制的選舉結果，理論上政府的運作將趨向穩定；相較之下，在制度替換的過程中，改革者通常只看見舊制度的缺失，舊制度本身所具有的優點－比例性，在改革過程中往往被忽視。本文的研究目的即是重拾對比例性的視野，透過Loosemore-Hanby D指數測量選制改革前後的比例性偏差程度，檢視1992至2008年間比例性偏差數值的變化，並從五個面向－選區規模、席次分配、法定門檻、席次總數、選票結構－解釋比例性偏差發生的原因，發現所有的選制設計皆不利於比例性，導致新選制的比例性偏差與舊制度產生極大的落差。此外，透過比較其他可能的比例性狀況可以發現，無論是聯立制的模擬或是票源模擬的結果，皆顯示有助於提升小黨的代表性；另一方面，同樣採用並立制的日本，四次的選舉經驗可以做為我國參考的對象，但是由於選舉制度的各項要素不盡相同，也使得兩國選舉結果的比例性和小黨代表性呈現差異性。最後，混合制固然同時融合了相對多數決制和比例代表制的特性，但是由於制度上選制要素以及非制度上國情與社會狀況的不同，很難期待一個完美的選舉制度出現，因此，我們只能尋求一個理想的選舉制度，且善用混合制所具有的彈性，做出適度的調整。 / Upon the evaluation of an electoral system, the main concerns are the governability and proportionality. In Taiwan’s case, the electoral system of Legislative Yuan altered from SNTV to mixed-member system; however, the reformers invariably accentuated the stability of governance but ignored the semi-proportionality of SNTV. Hence, the result of election in 2008 got unbalance between governability and proportionality. This article tends to measure the degree of disproportionality by Loosemore-Hanby index from 1992 to 2008 and tries to explain how disproportionality occurred from five dimensions－district magnitude, levels of seat allocation, threshold, number of total seats, and ballot structure. In addition, the results could be quite different when it compared with of other situations. According to this paper, the representation of small parties and the degree of proportionality will be enhanced while adopting MMP and redistributing the votes. Moreover, this paper is going to make a comparative study with Japan which have adopted MMM and have experienced four times elections since 1996. Finally, although mixed systems combine some features of both plurality and PR, there is still no perfect electoral system in the world. However, by making good use of flexibility of mixed systems, we might have an “ideal” system which can be regularly updated to suit changing needs and political conditions. 選舉制度杜瓦傑法則比例性偏差複席單記非讓渡投票制並立式混合制聯立式混合制 Electoral System Duverger’s Law Disproportionality SNTV-MMD MMM MMP
7	立法委員選舉制度變革對我國政黨體系之影響 / The impacts on Taiwan’s party systems from its’legislative members election reform 張家愷, Chang, Chia Kai Unknown Date (has links) 過去由於我國立法委員選舉所採用的「複數選區單記非讓渡投票制」，常造成選風敗壞、偏激取向、派系政治等諸多負面影響。有鑑於此，立法院於2004年8月23日通過「席次減半」及「單一選區兩票制」的修憲案，並於2005年6月7日經國民大會複決通過，自第七屆開始，立法委員任期改為4年，席次減半為113人。2008年1月12日第七屆立法委員選舉首次實施「單一選區兩票制」，而本文將檢視此次立委選舉結果相關資料，探討選制改變後對我國政黨體系之影響，並從過去的理論評析與實際運作層面相互驗證，探討理論與實務之間異同，及其可能之影響因素，然而，由於僅是一次實施的結果，因此相關後續發展仍須持續觀察。 / In the past, our national elections of members of Legislative Yuan adopted “multi-member-district, single non-transferable vote.” It usually caused negative influences such as deterioration of election, extreme trends, and faction politics. Therefore, Legislative Yuan passed constitution-amending bills “seats reduction in half” and “single-district two votes system” on August 23rd, 2004. These bills were passed by National Assembly on June 7th, 2005. The term of service for the seventh legislators was prolonged into four years and the seats were reduced in half to 113 seats. The seventh legislator election adopted “single-district two votes system” for the first time on January 12th, 2008. The essay will survey information related to the outcome of the legislator election, discussing the influence of changing election systems on the systems of political parties. Through the mutual demonstration between past theory criticism and practical operation, it discusses common and different points between theories and practices and finds out possible influential elements. However, it is just the outcome of single practice so it’s following development requires constant observations. 複數選區單記非讓渡投票制席次減半單一選區兩票制選舉制度政黨體系 SNTV-MMD seats reduction in half Single constituency / two-ballot system electoral system party system
8	Probabilistic Regression using Conditional Generative Adversarial Networks Oskarsson, Joel January 2020 (has links) Regression is a central problem in statistics and machine learning with applications everywhere in science and technology. In probabilistic regression the relationship between a set of features and a real-valued target variable is modelled as a conditional probability distribution. There are cases where this distribution is very complex and not properly captured by simple approximations, such as assuming a normal distribution. This thesis investigates how conditional Generative Adversarial Networks (GANs) can be used to properly capture more complex conditional distributions. GANs have seen great success in generating complex high-dimensional data, but less work has been done on their use for regression problems. This thesis presents experiments to better understand how conditional GANs can be used in probabilistic regression. Different versions of GANs are extended to the conditional case and evaluated on synthetic and real datasets. It is shown that conditional GANs can learn to estimate a wide range of different distributions and be competitive with existing probabilistic regression models. machine learning ml regression probabilistic distribution cgan gan conditional gan adversarial networks neural network deep learning f-gan f-cgan f-divergence adversarial training bimodal heteroskedastic mmd maximum mean discrepancy gmmn generative moment matching network conditional gmmn ipm kde cgan evaluation cgan regression gan regression cgan-regression regression using gan deep nn implicit generative conditional model complex noise aleatoric uncertainty dctd mdn heteroskedastic regression gp Other Computer and Information Science Annan data- och informationsvetenskap

Search results