Abstract This thesis studies the factors that govern transverse cracking during continuous casting of low carbon, niobium microalloyed and boron microalloyed steels. Crack susceptibility in the thick slab, billet and thin slab casting processes are compared by using typical conditions in laboratory hot ductility tests. There is limited published literature on hot ductility in aluminium-killed and siliconkilled boron microalloyed steels and the proposed mechanisms of failure by transverse cracking are contradictory. Few published papers specifically compare hot ductility behaviour of any steels between thick slab, billet and thin slab continuous casting processes. Thus, the basis of this research is to assess the influence of casting parameters and compositional variations on hot ductility behaviour in low carbon steels, niobium microalloyed steels, aluminium-killed boron microalloyed steels and silicon-killed, boron microalloyed steels. The typical temperature ranges, cooling rate and strain rate conditions of the continuous casting processes were used in reheated and in situ melted hot tensile tests performed on steel specimens. Solidification, transformation and precipitation temperatures were calculated using solubility equations and modelled using the Thermo-CalcTM thermodynamics program. Scanning electron microscopy and transmission electron microscopy were used to determine the modes of failure in the tested specimens. In the low carbon steels, hot ductility was improved by increasing the strain rate; by calcium treatment, which minimises copper sulphide and iron sulphide formation; and by maintaining a nickel to copper ratio of 1:1. It was shown that thin slab casting conditions provided the best hot ductility results for the low carbon steels. All the niobium steels showed poor ductility in the single-phase austenite temperature region, indicating that intergranular precipitation of fine niobium carbonitrides was the cause of the poor ductility. It was shown that the hot ductility was greatly improved by calcium treatment, by decreasing the cooling rate and by increasing the strain rate. Slow iv thin slab and thick slab casting conditions provided the best hot ductility results for the niobium steels. Hot ductility was substantially improved in the aluminium-killed boron steels by increasing the boron to nitrogen ratio from 0.19 to 0.75. The results showed that, at cooling rates generally associated with thick slab, bloom and slow thin slab casting, a boron to nitrogen ratio of ≥0.47 was sufficient to avoid a ductility trough altogether. However, under conditions typically experienced in fast thin slab and billet casting, a boron to nitrogen ratio of 0.75 was required to provide good hot ductility. The mechanism of the ductility improvement with increasing boron to nitrogen ratio was found to be enhanced precipitation of boron nitride, leading to a decrease in nitrogen available for aluminium nitride precipitation. In the silicon-killed boron steels, it was found that the boron to nitrogen ratio had the overriding influence on hot ductility and hence on crack susceptibility. Excellent hot ductility was found for boron to nitrogen ratios above 1. Additionally, analysis of industrial casting data showed that the scrap percentage due to transverse cracking increased significantly at manganese to sulphur ratios below fourteen. An exponential decay relationship between the manganese to sulphur ratio and the average scrap percentage due to transverse cracking was determined as a tool to predict scrap levels in the casting plant.

A Amazônia brasileira apresenta grande importância no processo de ciclagem de carbono na atmosfera, pois representa uma significativa parcela das florestas tropicais remanescentes. Porém, nos últimos 50 anos a Amazônia Legal Brasileira passou por intenso processo de mudança no uso da terra, fato que ocasionou aumento do desflorestamento na região. No Estado do Pará, o município de Paragominas foi considerado um dos principais responsáveis pelo desflorestamento até o ano de 2007. Tal cenário foi modificado após iniciativas de instituições públicas e empreendedores ligados ao setor rural do município, que em ações conjuntas modificaram a produção agropecuária de Paragominas, implantando sistemas produtivos mais eficientes. Atualmente o município é reconhecido como pólo de produção agropecuário sustentável na Amazônia. Neste trabalho, objetivou-se avaliar a dinâmica do carbono no solo sob diferentes usos, em uma cronossequência, no município de Paragominas. O solo da área de estudo é classificado como LATOSSOLO AMARELO Distrófico de textura argilosa. A pesquisa foi realizada na Fazenda Vitória, Paragominas - PA, onde foram avaliadas duas cronossequências distintas: (i) floresta natural (em 1992)-floresta secundária (em 1992, com 16 anos)-floresta secundária (em 2013, com 37 anos); (ii) floresta natural-pastagem degradada (em 1992, com 23 anos)-pastagem em sistema agrossilvipastoril com plantio direto (em 2013, com 4 anos). Na segunda cronossequência também foram avaliados dados de um sistema lavoura-pecuária sem plantio direto conduzido na área entre 2005 e 2008. Foram avaliados os teores de carbono e nitrogênio, a relação C:N, a densidade do solo, os estoques de carbono e nitrogênio e a composição isotópica do solo das áreas de estudo, nas camadas 0-10, 10-20, 20-30, 30-40, 40-60, 60-80, 80-100 cm. Observou-se que a floresta secundária, em pousio há 37 anos, apresentou os maiores incrementos de C e N, sendo superior ao encontrado no solo sob floresta nativa. Na mesma área, mesmo após 44 anos de condução de pastagem na mesma área, mais de 70% do carbono ainda era oriundo de plantas de ciclo fotossintético do tipo C3. A reforma da pastagem proporcionou alterações positivas nas características edáficas, pois houve aumento no estoque de carbono no solo após o manejo em sistema agrossilvipastoril com plantio direto na palha, também foi observado diminuição da densidade do solo neste período. Conclui-se que a adoção de técnicas agropecuárias, que fazem uso racional dos recursos naturais, são viáveis e ambientalmente corretas, pois observou-se que após a mudança no manejo da área ocorreu aumento do estoque de carbono no solo, sendo este um indicador de sustentabilidade em agropecuária de baixa emissão de carbono no Brasil. / The Amazon region plays a great role in the process of cycling carbon within the atmosphere because it represents a significant portion of the remaining tropical forests. However, in the last 50 years, several municipalities have passed through changes in land-use management which led to a significant increase in deforestation. In 2007, the municipality of Paragominas was considered one of the main areas responsible of the deforestation of the State of Para, Brazil. After many joint actions of public institutions and agricultural entrepreneurs, Paragominas went through a process of change of the scenario in its agricultural production system. Today this municipality is recognized as a responsible agricultural and livestock production center in the Amazon. The aim of this study was to assess the dynamics of soil carbon under different land-use management systems in a chronosequence. The soil of the site is classified as a clayey oxisol (dystrophic yellow Latosols, in the Brazilian classification system). The study was carried out in the ranch \"Fazenda Vitoria\", where, two distinct chronosequences were assessed: (i) a native forest (in 1992) - a secondary forest (16 year old in 1992) - a secondary forest (37 year old in 2013); and (ii) a native forest converted to degraded pasture (23 year old in 1992) - pasture in a no-till silvopastoral agroforestry system (4 year old in 2013). In the second chronosequence, data from a no-till crop-livestosk system was also assessed, which was carried out from 2005 to 2008. Soil carbon and nitrogen contents and stocks, C:N ratio, soil bulk density and their isotopic composition were evaluated. The secondary forest fallowed for 37 years, had the highest increments of C and N contents, with higher values than those found in the soil under native forest. It was observed that after 44 years of grazing on the same area more than 70% of carbon was originated from C3-phostosynthetic type plants. Pasture recovery led to positive changes in soil properties, as an increase in carbon stock associated to the reduction of soil bulk density after the implement of the no-till silvopastoral management system. Decrease in soil bulk density was also observed in this period. According to the results obtained in the evaluated production unit, it was observed that the adoption of agricultural techniques that make a rational use of natural resources is sustainable and environmentally friendly. It was observed that the change in management of the area induced an increase in carbon storage in the soil, this being an indicator of agricultural sustainability in relation to low-carbon management.

By August 2016, 180 countries have signed the Paris Agreement and committed to holding the increase in the global average temperature to well below 2degC above pre-industrial levels. Abiding by the agreement will require a substantial reduction of emissions over the next few decades and near zero emissions of CO2 and other long-lived greenhouse gases by the end of this century. In this context, the decarbonisation of the global power sector is of strategic importance, because low-carbon electricity has system-wide benefits that go beyond the electricity sector, enabling significant reductions of CO2 emissions in the industry, transport and buildings sectors. To make the necessary changes depends partly on improving the analysis and estimates of the economics of climate change, and for that there is an urgent need for a new generation of models that give a more accurate picture of the potential decarbonisation pathways. The technological transition towards a low carbon power sector depends on many uncertain factors, such as policy efficiency, renewable energy investment and availability of energy resources. The knowledge about how these uncertain factors interact, and the impacts on the technological evolution of the energy sector, are the key to creating successful policies for driving the economy towards a cleaner, low carbon society. In this context, the work presented here provides decarbonisation scenarios of the global power sector, under uncertain drivers of technological change, and in doing so, enables a better understanding of technology diffusion process in the power sector. The scenarios are created using the FTT:Power model, a representation of global power systems based on market competition, induced technological change and natural resource use and depletion. The scenarios analysed in this dissertation are focused on four drivers of technological change: energy policy, energy resource availability, learning and investment. The influence of uncertainty on each of these drivers is analysed in detail, through endogenous emission scenarios of the global power sector between 2016 and 2050. Emission pathways with uncertainty ranges, as well as policy recommendations, are presented as a result of the modelling exercise.

A importância das mudanças climáticas no cenário econômico-político internacional é crescente e os esforços para a geração e utilização de tecnologias de baixa emissão de carbono vêm se ampliando. Neste sentido que o Plano ABC é implementado nas propriedades rurais através de linha de Crédito Rural denominada Programa ABC. Os estados e municípios brasileiros possuem grandes disparidades econômicas e edafoclimáticas, apresentando adoção heterogênea de tecnologia no meio rural. Deste modo, o presente trabalho visa analisar a execução e distribuição dos recursos do Plano e Programa ABC, avaliando a aplicação destes de modo a atender os objetivos do projeto. Serão utilizadas informações dos empréstimos do Programa ABC de 2013 a 2016 obtidos através do SICOR, variáveis de desempenho da agropecuária obtidas com o IBGE e classificação de aptidão agrícola predominante nos municípios realizada por Sparovek (2015) para a obtenção de estatísticas e correlação de Spearman. Os resultados demonstram que as linhas de financiamento do ABC Recuperação, ABC Plantio Direto, ABC Florestas e ABC Integração correspondem à parcela superior a 98% do volume de crédito concedido. A maioria dos recursos é absorvida pelo Centro-Oeste e Sudeste. As regiões Norte e Nordeste possuem maior carência em produtividade agropecuária, portanto, os empréstimos do ABC nestas regiões resultariam em maiores impactos de mitigação de GEE, mas o volume de recursos destinado para as mesmas é baixo. Os resultados mostram que os recursos são destinados em sua maioria a municípios que possuem maior aptidão agrícola e assim devem propiciar menores efeitos de mitigação de GEE. Calculou-se que os empréstimos são mais fortemente relacionados com o rebanho bovino do que com as pastagens degradadas. Além disto, os investimentos realizados nas regiões de aptidão agrícola mais elevada possuem maior correlação com características econômicas. Para ampliar a eficiência da execução e distribuição dos recursos do Plano e Programa ABC, alterações que contemplem a possibilidade de aderência a múltiplos sistemas produtivos e a diferenciação de incentivos conforme definições de áreas prioritárias poderiam ser realizadas. / The importance of climate change in the international economic and political scenario is growing, and efforts for the generation and use of low-carbon technologies have been expanding. In this sense, the ABC Plan is implemented in rural properties through the rural crédit line called the ABC Program. The brazilian states and municipalities have great economic and edaphoclimatic disparities, presenting heterogeneous adoption of technology in rural areas. Thus, the present work aims to analyze the execution and distribution of resources of the ABC Plan and Program, evaluating their application in order to meet the project objectives. Information from the ABC Program loans from 2013 to 2016 obtained through SICOR, agricutural performance variables obtained with the IBGE and the calssification of predominant agricultural aptitude in the municipalities by Sparovek (2015) will be used to obtain statistics and Spearman correlation. Results show that the loans of ABC Recovery, ABC Direct Planting, ABC Forests and ABC Integration correspond up to 98% of the volume of credit granted. Most of the resources are absorbed by the Midwest and Southeast regions. The North and Northeast regions have greater deficiencies in agricultural productivity, therefore, the ABC loans in these regions would result in greater impacts of GHG mitigation, but the volume of resources allocated to them is low. Results show also that resources are mostly destined to municipalities that have greater agricultural aptitude and thus should provide less mitigation effects of GHG. Loans were estimated to be more strongly correlated to the cattle herd than to degraded pastures. In addition, investments made in regions with the highest agricultural aptitude have a higher correlation with economic characteristics. In order to increase the efficiency of the execution and distribution of the resources of the ABC Plan and Program, changes that contemplate the possibility of adherence to multiple productive systems and the differentiation of incentives according to definitions of priority areas could be realized.

Global warming and the energy crisis are two of the greatest challenges on which mankind is currently focused. This has forced governments and other organisations to think how to protect the environment and how to reduce fuel costs. A variety of new and exciting technologies are being investigated to address the energy problem. Alternative energy sources such as solar power, fuel cells, wind power and tidal waves are active areas of commercial and scientific pursuit. A major area of current research is moving towards the hydrogen economy and hydrogen based energy systems. Hydrogen can be produced in many ways, most commonly by steam reforming of hydrocarbon (70% to 85% thermal efficiency) but the downside is that it releases carbon mono oxide (CO)), compared with commercial PEM electrolysers where performance has been reported to be 56 -73% at normal temperature pressure(NTP) with zero carbon emission. Electrochemical production of hydrogen has several advantages: (i) It gives pure hydrogen. (ii) It allows portability (e.g. Solar energy could be used to power the electrochemical cell). (iii) It can be produced on demand. The generation of Hydrogen via electrolysis has been the subject of many studies over the last two hundred years. However, there is still room for further work to improve both the efficiency of the process and methods of storage of the gas. The cleanest method at present is to produce hydrogen by electrolysis, and the main focus of this research is to design and develop such a green energy fuel cell for on-demand application. The aim of the work presented in this thesis was to further investigate the electrolysis method for hydrogen production. An Electrochemical fuel cell contains a minimum of two electrodes: the positively charged electrode called the anode where oxygen bubble will form, and the second negatively charged electrode called the cathode, where hydrogen bubbles will form during a chemical reaction caused by applying electrical current between these electrode. The project was initiated with the objective of finding a low cost solution for on-demand hydrogen generation. To establish a starting point, the first cell (cell-1) design was based on the work of Stephen Barrie Chambers (see chapter 3) to check the performance levels. The fabrication of the cell-1 design resulted in a mixture of hydrogen and oxygen in the same chamber, which means the cell-1 design, has a possible fire and explosion hazard. The device also has the drawback of lower performance of hydrogen production; columbic efficiency is between 40% to 46% at 1 amp to 3 amp current in 30% KOH alkaline solution. However, the advantage of reproducing Stephen’s innovation is that it allowed a quick and deep understanding of hydrogen generation. This thesis presents recent work on the fabrication of low cost electrolysis cells containing continuous flow alkaline (KOH, up to 30%) electrolyte using low cost electrodes (stainless steel 316) and membranes based on ultrahigh molecular weight polyethylene (UHMW PE) to produce hydrogen without the hazard of fire and explosion. In this research an On-Demand Hydrogen Generation cell-3 achieved a 95% hydrogen generation coulombic efficiency, which is about 49% efficiency improvement as compared to the stainless steel electrode, and was 22% better than the nano structured electrode. The typical cell voltage is 2.5 V at current flow ranging from 30 to 120 mA cm-2 in 30% KOH electrolyte. The achievement here of such high efficiencies paves the way for more research in the areas of space management, electrode surface structure and flow control (based on the application requirement). This invention can be used for aeronautic, marine and automotive application as well as in many other areas.

Since various public and private actors at the international, supranational, national and subnational levels started to adopt long-term targets for reducing greenhouse gas emissions, low-carbon scenario analyses have flourished. Literature reveals an increasing number of analyses envisioning and exploring alternative images of low-carbon futures, as well as their adjacent transition pathways. Scenario approaches or “foresight” is intended to help policy-makers to navigate the maelstrom of confusion and conflicts associated with highly complex societal challenges such as climate change – i.e. the “super-wicked” problems. Typical scenario exercises aim at coping with uncertainty and conflicting values, and hence are often claimed as a suitable approach for knowing and governing super-wicked problems. When reviewing the scenario literature published over the recent years, we observe significant methodological developments, in particular at the level of the calculus or data-sets. These contributions have generated an increasing technical sophistication of scenario building methods, and contrast with the relative absence of social sciences research on scenarios. Scenario analyses have received little academic attention from social sciences, whether they are political science, sociology, philosophy of science or science and technology studies. By providing a SHS-analysis of low-carbon scenarios, the present thesis contributes to bridge this research gap. Scenarios are here understood as “boundary objects” linking different social worlds: science and policy, but also natural and social sciences. This thesis aspires to create an enhanced understanding on how scenario analyses perform such “boundary work”. More specifically, the following analysis of low-carbon scenarios is based on a twofold perspective focusing, on the one hand, on the interactions between low-carbon scenarios and governance (i.e. link between science and policy), and, on the other hand, on the making of knowledge about governance in low-carbon scenarios (i.e. link between natural and social sciences). In other words, it explores “scenarios in governance” and “governance in scenarios”. The thesis project includes three research axes, each based on its particular empirics. A first study explores the interactions between low-carbon scenarios and governance on the basis of a multiple case study analysing the role of four energy foresight studies in policy-making. The other two studies focus on the making of knowledge about governance in low-carbon scenarios. One of them provides an assessment of the knowledge needed to steer the low-carbon transition. The other one aims at contributing to the debate on the relations between quantitative modelling and social sciences by exposing a critical review of socio-technical energy transition models. The objective of the present thesis thus consists in providing an empirical contribution to social sciences research on low-carbon scenarios. / Doctorat en Sciences / info:eu-repo/semantics/nonPublished

Higher atmospheric concentration of greenhouse gases (GHG) such as carbon dioxide and methane has contributed to an increase in Earth's mean surface air temperature and caused climate changes. This largely reflects the increase in global energy consumption, which is heavily dependent on oil, natural gas, and coal. If not controlled, the combustion of these fossil fuels can also produce high levels of nitrogen oxides (NOx) and soot emissions, which adversely affect the air quality. New and extremely challenging fuel efficiency and exhaust emissions regulations are driving the development and optimisation of powertrain technologies as well as the use of low carbon fuels to cost-effectively meet stringent requirements and minimise the transport sector's GHG emissions. In this framework, the dual-fuel combustion has been shown as an effective means to maximise the utilisation of renewable liquid fuels such as ethanol in conventional diesel engines while reducing the levels of NOx and soot emissions. This research has developed strategies to optimise the use of ethanol as a substitute for diesel fuel and improve the effectiveness of dual-fuel combustion in terms of emissions, efficiency, and engine operational cost. Experimental investigations were performed on a single cylinder heavy-duty diesel engine equipped with a high pressure common rail injection system, cooled external exhaust gas recirculation, and a variable valve actuation system. A port fuel injection system was designed and installed, enabling dual-fuel operation with ethanol energy fractions up to 0.83. At low engine loads, in-cylinder control strategies such as the use of a higher residual gas fraction via an intake valve re-opening increased the combustion efficiency (from 87.7% to 95.9%) and the exhaust gas temperature (from 468 K to 531 K). A trade-off between operational cost and NOx reduction capability was assessed at medium loads, where the dual-fuel engine performance was less likely to be affected by combustion inefficiencies and in-cylinder pressure limitations. At high load conditions, a Miller cycle strategy via late intake valve closing decreased the in-cylinder gas temperature during the compression stroke, delaying the autoignition of the ethanol fuel and reducing the levels of in-cylinder pressure rise rate. This allowed for the use of high ethanol energy fractions of up to 0.79. Finally, the overall benefits and limitations of optimised ethanol-diesel dual-fuel combustion were compared against those of conventional diesel combustion. Higher net indicated efficiency (by up to 4.4%) combined with reductions in NOx (by up to 90%) and GHG (by up to 57%) emissions can help generate a viable business case of dual-fuel combustion as a technology for future high efficiency and clean heavy-duty engines.

Natural gas is currently an attractive substitute for diesel fuel in the Heavy-Duty (HD) diesel transportation sector. This is primarily attributed to its cost effectiveness, but also its ability to reduce the amount of CO2 and harmful engine pollutants emitted into the atmosphere. Lean-burn dual-fuel engines substitute natural gas in place of diesel but typically suffer from high engine-out methane (CH4) emissions, particularly under low load operation. In response to this issue, this work set out to improve upon the efficiency and emissions of a lean-burn dual-fuel combustion system in an HD diesel/natural gas engine. Thermodynamic experimental engine testing was performed at various steady-state operating points in order to identify the most effective methods and technologies for improving emissions and efficiency. Low Temperature Combustion (LTC) along with several valvetrain and injection strategies were evaluated for benefits, with special attention paid to low load operating conditions. LTC was proven to be a useful method for decreasing methane emissions while simultaneously improving engine efficiency. The benefits of LTC were a function of load with the greatest advantages experienced under medium load operation. Additionally, the low load strategies tested were determined to be effective techniques for reducing methane emissions and could possibly extend the dual-fuel operating regime to lighter load conditions. Overall, no operating condition tested throughout the engine map resulted in a brake engine-out methane emissions level of less than 0.5 g/kWh at gas substitutions greater than approximately 75%. It is suggested that the limits of this particular lean-burn dual-fuel design were reached, and that it would likely require improvements to either the combustion system or exhaust after-treatment if Euro VI emissions levels for methane were to be achieved.

A Amazônia brasileira apresenta grande importância no processo de ciclagem de carbono na atmosfera, pois representa uma significativa parcela das florestas tropicais remanescentes. Porém, nos últimos 50 anos a Amazônia Legal Brasileira passou por intenso processo de mudança no uso da terra, fato que ocasionou aumento do desflorestamento na região. No Estado do Pará, o município de Paragominas foi considerado um dos principais responsáveis pelo desflorestamento até o ano de 2007. Tal cenário foi modificado após iniciativas de instituições públicas e empreendedores ligados ao setor rural do município, que em ações conjuntas modificaram a produção agropecuária de Paragominas, implantando sistemas produtivos mais eficientes. Atualmente o município é reconhecido como pólo de produção agropecuário sustentável na Amazônia. Neste trabalho, objetivou-se avaliar a dinâmica do carbono no solo sob diferentes usos, em uma cronossequência, no município de Paragominas. O solo da área de estudo é classificado como LATOSSOLO AMARELO Distrófico de textura argilosa. A pesquisa foi realizada na Fazenda Vitória, Paragominas - PA, onde foram avaliadas duas cronossequências distintas: (i) floresta natural (em 1992)-floresta secundária (em 1992, com 16 anos)-floresta secundária (em 2013, com 37 anos); (ii) floresta natural-pastagem degradada (em 1992, com 23 anos)-pastagem em sistema agrossilvipastoril com plantio direto (em 2013, com 4 anos). Na segunda cronossequência também foram avaliados dados de um sistema lavoura-pecuária sem plantio direto conduzido na área entre 2005 e 2008. Foram avaliados os teores de carbono e nitrogênio, a relação C:N, a densidade do solo, os estoques de carbono e nitrogênio e a composição isotópica do solo das áreas de estudo, nas camadas 0-10, 10-20, 20-30, 30-40, 40-60, 60-80, 80-100 cm. Observou-se que a floresta secundária, em pousio há 37 anos, apresentou os maiores incrementos de C e N, sendo superior ao encontrado no solo sob floresta nativa. Na mesma área, mesmo após 44 anos de condução de pastagem na mesma área, mais de 70% do carbono ainda era oriundo de plantas de ciclo fotossintético do tipo C3. A reforma da pastagem proporcionou alterações positivas nas características edáficas, pois houve aumento no estoque de carbono no solo após o manejo em sistema agrossilvipastoril com plantio direto na palha, também foi observado diminuição da densidade do solo neste período. Conclui-se que a adoção de técnicas agropecuárias, que fazem uso racional dos recursos naturais, são viáveis e ambientalmente corretas, pois observou-se que após a mudança no manejo da área ocorreu aumento do estoque de carbono no solo, sendo este um indicador de sustentabilidade em agropecuária de baixa emissão de carbono no Brasil. / The Amazon region plays a great role in the process of cycling carbon within the atmosphere because it represents a significant portion of the remaining tropical forests. However, in the last 50 years, several municipalities have passed through changes in land-use management which led to a significant increase in deforestation. In 2007, the municipality of Paragominas was considered one of the main areas responsible of the deforestation of the State of Para, Brazil. After many joint actions of public institutions and agricultural entrepreneurs, Paragominas went through a process of change of the scenario in its agricultural production system. Today this municipality is recognized as a responsible agricultural and livestock production center in the Amazon. The aim of this study was to assess the dynamics of soil carbon under different land-use management systems in a chronosequence. The soil of the site is classified as a clayey oxisol (dystrophic yellow Latosols, in the Brazilian classification system). The study was carried out in the ranch \"Fazenda Vitoria\", where, two distinct chronosequences were assessed: (i) a native forest (in 1992) - a secondary forest (16 year old in 1992) - a secondary forest (37 year old in 2013); and (ii) a native forest converted to degraded pasture (23 year old in 1992) - pasture in a no-till silvopastoral agroforestry system (4 year old in 2013). In the second chronosequence, data from a no-till crop-livestosk system was also assessed, which was carried out from 2005 to 2008. Soil carbon and nitrogen contents and stocks, C:N ratio, soil bulk density and their isotopic composition were evaluated. The secondary forest fallowed for 37 years, had the highest increments of C and N contents, with higher values than those found in the soil under native forest. It was observed that after 44 years of grazing on the same area more than 70% of carbon was originated from C3-phostosynthetic type plants. Pasture recovery led to positive changes in soil properties, as an increase in carbon stock associated to the reduction of soil bulk density after the implement of the no-till silvopastoral management system. Decrease in soil bulk density was also observed in this period. According to the results obtained in the evaluated production unit, it was observed that the adoption of agricultural techniques that make a rational use of natural resources is sustainable and environmentally friendly. It was observed that the change in management of the area induced an increase in carbon storage in the soil, this being an indicator of agricultural sustainability in relation to low-carbon management.

Este trabalho, realizado em cooperação com a Gerdau Riograndense, tem por finalidade avaliar o comportamento do aço GG1013-M, um aço baixo teor de carbono microligado com vanádio e manganês, na laminação a quente no que tange a sua resistência à deformação, possibilitando assim a tomada de decisão em relação a modificações no processo. Foram realizados testes em simulador termomecânico Gleeble™ para determinação das temperaturas a serem usadas no teste prático no laminador, onde testou-se lotes que cobrissem toda a amplitude da faixa de composição química da qualidade do aço em estudo. No teste prático no laminador, foram retiradas amostras para os ensaios mecânicos, onde identificou-se, por intermédio do tratamento de dados em software estatístico, a influência da variação dentro da faixa da composição química sobre os limites de escoamento e resistência. Como resultado, conseguiu-se determinar a faixa de temperatura mais provável, onde a resistência a deformação a quente é menor, minimizando ou eliminando as conseqüências da redução de ductilidade a quente por conta do endurecimento da matriz por precipitação dos elementos de liga em forma de compostos. / This work was conducted in cooperation with Gerdau Riograndense aiming at the evaluation of the hot rolling behavior of a low carbon steel microalloyed with manganese and vanadium (internally GG1013-M steel).The deformation resistance was evaluated, allowing for the decision in relation to changes in the process. A thermomechanical simulator GleebleTM was used to determine the temperatures to be used in practical tests in the rolling mill, where it was tested different material batches covering the large range of chemical compositions for this kind of steel. Mechanical tests were performed on samples taken from the practical tests in the rolling mill. From this tests the influence of chemical composition variation on the yeld strength and maximum stress was studied. As a result, we were able to determine the most likely range of temperatures for a minimization of hot strentgh, therefore also minimizing or eliminating the consequences of the reduction in the hot ductility due precipitation hardening of the matrix.