Made available in DSpace on 2014-06-12T18:04:23Z (GMT). No. of bitstreams: 2 arquivo213_1.pdf: 4056030 bytes, checksum: c7d78e098b753c3c2b6ce96fc5f9588a (MD5) license.txt: 1748 bytes, checksum: 8a4605be74aa9ea9d79846c1fba20a33 (MD5) Previous issue date: 2011 / Universidade Federal de Pernambuco / Nos últimos anos o biodiesel se tornou uma alternativa para a demanda crescente de combustível. O próximo passo é conseguir produzir um biodiesel economicamente competitivo com o diesel fóssil em um processo em nível industrial. Este trabalho visa estudar do ponto de vista computacional, uma planta piloto de biodiesel, simulando o processo desde a reação de transesterificação de óleos vegetais, chegando até a purificação do biodiesel, utilizando o APEN/HYSYS. Além disso, foi feito o estudo da viabilidade econômica preliminar da mesma, fazendo-se uso do custo anualizado total unitário CATU. Os resultados das simulações foram comparados com os resultados obtidos numa planta piloto montada em Pernambuco/Brasil. Em seguida, foi comparada a viabilidade econômica da planta piloto, com uma planta operando com uma coluna de destilação reativa para produção do referido combustível. Os resultados mostraram que a destilação reativa é um processo mais econômico para a produção do biodiesel do que em um processo em batelada

There has been recent concern regarding the regeneration and recruitment of aspen (Populus tremuloides) in the western United States. Forest management techniques have been employed in order to promote the regeneration and recruitment of aspen. We quantified aspen regeneration treatments in southern Utah, USA to better understand the factors driving aspen recruitment. Driving factors were identified by addressing two major research themes: (1) identify the primary ecological controls on aspen regeneration success; (2) assess the relative importance and influence of these controls on successful regeneration. Our definition of successful aspen regeneration requires the satisfaction of two criteria relating to height and density, respectively: (1) regeneration that has attained heights above the ungulate browsing threshold (e.g. >2m); and (2) regeneration that is occurring at a density that represents desired conditions for future stocking (e.g. ≥10,000 stems ha⁻¹). The primary ecological controls on regeneration success were identified using nonmetric multidimensional scaling, and Random Forests analysis was used to assess the relative importance and influence of regeneration controls. These analyses identified three primary factors that are responsible for regeneration success. These factors were (1) contemporary herbivory pressure, (2) site preparation technique, and (3) advance reproduction. Herbivory is the leading predictor of regeneration success, and has integral impacts on other primary regeneration drivers. We suggest considerations that can be made regarding regeneration drivers in order to enhance the effectiveness of aspen management in the future.

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Yes / This investigation reports the first study to predict natural gas hydrate formation using both Aspen HYSYS® and HydraFlash software for various gas compositions and thermodynamic inhibitors (monoethylene glycol [MEG] concentrations at 10, 20, 30, and 40 wt.% and methanol concentrations at 10 and 20 wt.%). The simulated predictions are compared with the results of the experimental data in the literature. It has been shown that HydraFlash software can accurately predict hydrate formation conditions for a given industrial case, without having to carry out costly experimental work. This work also evaluated the effect of inhibitors and it appears that inhibitor type and concentration are determined according to condition of gas composition. MEG is consequently selected as the most ideal hydrate inhibitor for the industrial case. This also was confirmed through COSMO-RS studies in which the sigma profile and sigma potential of the considered inhibitors were obtained and presented using density functional (DFT) calculations to verify the hydrogen bonding affinities of the inhibitors to water molecules. HydraFlash was utilized to predict the dissociation conditions of hydrates under the influence of a high concentration of MEG inhibition, reaching up to 40 wt.% at 313 K and a pressure of 311.1 bar. Finally, it is shown that both software packages are quite accurate and useful tools for the prediction of hydrate for simple systems. However, HydraFlash can simulate more complex systems, including different types of salts at higher pressures. Investigation results indicate insightful guidance for accurately predicting hydrate dissociation under simulated conditions. / The authors would also like to thank the Turkish National Agency for offering an Erasmus student grant for Mr. Nejmi Söyler under the Erasmus+ Program Action 1 throughout the training period.

Quaking aspen (Populus tremuloides Michx.) is the most widespread broadleaf tree species of North America. Increasing evidence shows that aspen has diverging ecological roles across its range as both “seral” and “stable” aspen community types. This leads us to believe that the successional pathway of aspen may not always lead to a climax conifer sere, but may in some cases consist of persisting stands of pure aspen. This study is an attempt to understand the relationship of aspen community types to climatic, physical, and biophysical variables by modeling patterns of aspen and conifer distribution using remote sensing and GIS technology. Study methodologies and results were specifically designed to aid land managers in identifying extent and status of aspen populations as well as prioritizing aspen restoration projects. Four study sites were chosen in order to capture the geographic and climatic range of aspen. Photointerpretation of NAIP color infrared imagery and linear unmixing of Landsat Thematic Mapper imagery were used to classify dominant forest cover. A Kappa analysis indicates photointerpretation methods to be more accurate (Khat=92.07%, N=85) than linear unmixing (Khat=51.05%, N=85). At each plot, variables were calculated and derived from DAYMET data, digital elevation models, and soil surveys, then assessed for precision and ability to model aspen and conifer distributions. A generalized linear model and discriminant analysis were used to assess habitat overlap between aspen and conifer and to predict areas where “stable” aspen communities are likely to occur. Results do not provide definitive evidence for a “stable” aspen niche. However, the model indicates 60 to 90 cm of total annual precipitation and topographic positions receiving greater than 4,500 Wh m‐2 d‐1 of solar radiation have a higher potential for “stable” aspen communities. Model predictions were depicted spatially within GIS as probability of conifer encroachment. In addition, prediction‐conditioned fallout rates and receiver operating characteristic curves were used to partition the continuous model output. Categorical maps were then produced for each study site delineating potential “stable” and “seral” aspen community types using an overlay analysis with landcover maps of aspen‐conifer forests.

The encroachment of woody species into grassland and savanna ecosystems has been well document since the early 1800s. Within the parkland ecoregion of western Canada, trembling aspen (Populus tremuloides Michx.) has been one of the key tree species increasing in dominance. Aspen encroachment is best explained not by single mechanism, but rather by a number of interacting ecological factors. In this study I examined the ecological consequences of the clonal biology in aspen as a means to explain persistence and observed tree-grass ratios within grassland savannas of western Canada. Results suggest that aspen stands cycle between a “stable” phase characterized by a dense mature canopy, and an “unstable” phase characterized by canopy breakup and increased regeneration from root suckers. It is during this unstable phase that clonal encroachment is likely to occur. Within these mature stands, different-aged ramets promote persistence by maximizing developmental variation. Such a mechanism overcomes the functional phenotypic uniformity of ramets within a single age-structured stand. Results from my study indicate that physiological integration is beneficial to the growth and survivorship of regenerating and encroaching aspen ramets. My results also suggest that the benefits of physiological integration are greatest in more stressful environments, and in recently established post-fire ramets. Finally, the consequences of variation in adaptive ecological relevant traits among individuals was examined by determining differences in vigor among aspen clones in relation to the production of secondary compounds (phenolic glycosides). My results demonstrate a high degree of variation in leaf phenolic glycosides production among clones. A significant amount of this variation was accounted for by differences in clone vigor (within population: individual susceptibility hypothesis), with a smaller amount related to environmental differences (among populations). In all instances, vigorous clones were significantly higher in levels of phenolic glycosides compared with dieback clones, suggesting that some individuals may be predisposed to undergo density-independent mortality. This has important ecological implications, because it implies that one of the key mechanisms regulating population dynamics, community interactions and biodiversity may be related to intrinsic adaptive differences in susceptibility among individuals.

The encroachment of woody species into grassland and savanna ecosystems has been well document since the early 1800s. Within the parkland ecoregion of western Canada, trembling aspen (Populus tremuloides Michx.) has been one of the key tree species increasing in dominance. Aspen encroachment is best explained not by single mechanism, but rather by a number of interacting ecological factors. In this study I examined the ecological consequences of the clonal biology in aspen as a means to explain persistence and observed tree-grass ratios within grassland savannas of western Canada. Results suggest that aspen stands cycle between a “stable” phase characterized by a dense mature canopy, and an “unstable” phase characterized by canopy breakup and increased regeneration from root suckers. It is during this unstable phase that clonal encroachment is likely to occur. Within these mature stands, different-aged ramets promote persistence by maximizing developmental variation. Such a mechanism overcomes the functional phenotypic uniformity of ramets within a single age-structured stand. Results from my study indicate that physiological integration is beneficial to the growth and survivorship of regenerating and encroaching aspen ramets. My results also suggest that the benefits of physiological integration are greatest in more stressful environments, and in recently established post-fire ramets. Finally, the consequences of variation in adaptive ecological relevant traits among individuals was examined by determining differences in vigor among aspen clones in relation to the production of secondary compounds (phenolic glycosides). My results demonstrate a high degree of variation in leaf phenolic glycosides production among clones. A significant amount of this variation was accounted for by differences in clone vigor (within population: individual susceptibility hypothesis), with a smaller amount related to environmental differences (among populations). In all instances, vigorous clones were significantly higher in levels of phenolic glycosides compared with dieback clones, suggesting that some individuals may be predisposed to undergo density-independent mortality. This has important ecological implications, because it implies that one of the key mechanisms regulating population dynamics, community interactions and biodiversity may be related to intrinsic adaptive differences in susceptibility among individuals.

[pt] A indústria da borracha sintética tem grande importância e está presente no cotidiano da sociedade mundial. A borracha de butadieno ou polibutadieno é um dos polímeros mais utilizados neste campo, principalmente na produção de pneus. Portanto, o controle das condições operacionais e das propriedades finais do polímero formado são pontos importantes a serem estudados, pois são um desafio para a indústria. Assim, o presente trabalho tem como foco simular a polimerização em solução de polibutadieno utilizando o software Aspen Plus, onde foram utilizados 1,3-butadieno, tetracloreto de titânio, trietilalumínio e hexano como monômero, catalisador, cocatalisador e solvente, respectivamente. Nesta parte do trabalho, obtiveram-se gráficos de distribuição de massa molar que apresentaram propriedades semelhantes aos polibutadienos comerciais e alguns polibutadienos sintetizados em escala de bancada encontrados na literatura. Além disso, em uma segunda parte do trabalho, estuda-se e explica-se a técnica de distribuição instantânea e como foi gerada uma base de dados para um modelo de aprendizagem de máquina chamado de XGBoost, onde pontos dos gráficos da MMD (molar mass distribution) do polímero serviram como entrada do modelo a fim de prever as constantes cinéticas da polimerização. Ambos os estudos e simulações mostram que três e quatro sítios de catalisadores ativos são capazes de sintetizar polímeros com propriedades semelhantes aos polibutadienos comerciais e em escala de bancada. / [en] The synthetic rubber industry is of great importance and is present in the daily life of world society. Butadiene rubber or polybutadiene is one of the most used polymers in this field, mainly in the production of tires. Therefore, controlling the operating conditions and the final properties of the polymer formed are important points to be studied, as they are a challenge for the industry. Thus, the present work focuses on simulating the polymerization in solution of polybutadiene using the Aspen Plus software, where 1,3-butadiene, titanium tetrachloride, triethylaluminum and hexane were used as monomer, catalyst, cocatalyst and solvent, respectively. From the work, molar mass distribution graphs were obtained that showed properties similar to commercial polybutadienes and some polybutadienes synthesized on a bench scale found in the literature. Furthermore, in a second part of the work, the instant distribution technique is studied and explained and how a database was generated for a machine learning model called XGBoost, where points from the MMD (molar mass distribution) graphs of the polymer served as input to the model in order to predict the kinetic constants of polymerization. Both studies and simulations show that three and four sites of active catalysts are able to synthesize polymers with properties similar to commercial and bench-scale polybutadienes.

This thesis includes two studies: The first examined developmental changes that take place in the physiology of aspen (Populus tremuloides Michx.) and to characterize developmental influences on patterns of phenotypic trait variation among different aged ramets within the aspen clones. We surveyed eight clones, each with 8 distinct age classes ranging from 1 to 170 yrs in age. Using regression analysis we examined the relationships between ramet age and expression of functional phenotypes. Eight of the phenotypic traits demonstrated a non-linear relationship in which large changes in phenotype occurred in the early stages of ramet development and stabilized thereafter. Water and nutrient concentration, leaf gas exchange and phenolic glycosides tended to decrease from early to late development, while sucrose and condensed tannin concentrations and water use efficiency increased with ramet age. We hypothesize that ontogenetically derived phenotypic variation leads to fitness differentials among different aged ramets, which may have important implications for clone fitness. Age-related increases in phenotypic diversity may partially underlie aspen's ability as a species to tolerate the large environmental gradients that span its broad geographical range. Fire is an essential component of many forest ecosystems and fire exclusion policies and other anthropogenic factors have significantly altered disturbance regimes, which has lead to increased aspen succession to conifers. The second study examined how post-fire aspen regeneration success is influenced by increasing conifer abundance under longer fire return intervals. 66 sites were selected from the Sanford prescribed fire complex located in the Dixie National Forest. Slope, aspect, sucker regeneration heights, soil samples, and post and prefire stand densities were measured. Results from this study demonstrated that pre-disturbance conifer abundance and aspen densities are good predictors of aspen sucker regeneration success. Results also found that although conifer densities don't change across aspects, aspen densities are different on north facing slopes. We hypothesize the high levels of aspen regeneration came from a large disturbance size which overwhelmed the high levels of herbivores.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1980. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Bibliography: leaves 114-115. / by Suphat Watanasiri. / M.S.