Free-radical polymerisation (FRP) has been one of the most important techniques for producing materials used in a very wide variety of applications and has enhanced the lives of millions of people around the world. However, for many years a number of fundamental questions regarding the key kinetic processes involved in FRP have remained unresolved. In particular, an accurate description of the mechanism for diffusion-controlled bimolecular termination has proven elusive. As a result, conventional modelling tools for FRP have often proven unreliable. The aim of this thesis, therefore, was to accurately study the evolution of the bimolecular termination rate coefficient during free radical polymerisation using a new and more accurate methodology based on ‘controlled/living’ reversible addition-fragmentation chain transfer (RAFT) polymerisation. This was undertaken in order to develop a more precise understanding of bimolecular termination and thereby develop a more reliable modeling approach capable of predicting the rates of reaction and evolution of molecular weight distributions for a wide range of experimental conditions and a wide range of functional monomers. The RAFT-CLD-T (RAFT Chain-Length-Dependent Termination) Method was used to determine accurate values for the conversion and chain-length-dependent termination rate coefficient, kti,i(x), as a function of various parameters. These parameters included the chain size, i, polymer concentration (or conversion, x), chain length size distribution and chain architecture/structure. The accuracy of the RAFT-CLD-T Method was crucial to this work, therefore, an important part of this thesis was devoted to evaluating the reliability of this technique. Below 5 % conversion and above 80 % conversion the method was found to be unreliable due to the effects of chain-length-dependent propagation, high PDI’s and short-long termination. However, between 5 % and 80 % conversion it was found that the method is extremely robust and a series of easy-to-use experimental guidelines were determined for accurately applying the RAFT-CLD-T Method. The effects of chain size, chain size distribution, solution polymer concentration, and matrix architecture were examined for the RAFT-mediated polymerisations of methyl methacrylate (MMA), styrene (STY) and methyl acrylate (MA). It was found that four distinct scaling regimes of termination are observed: (1) a ‘short’ chain dilute solution regime, (2) a ‘long’ chain dilute solution regime, (3) a semi-dilute solution regime and (4) a concentrated solution regime. In dilute polymer solutions, chain-length-dependent power law exponents, ’s, determined during the polymerisation of MMA, STY and MA (where kti,i(x)  i-) indicated that termination follows two major scaling regimes with exponents of approximately ~0.5 to 0.6 for ‘short’ chains and and ~0.12 to 0.16 for ‘long’ chains. Importantly, these exponents are in excellent agreement with theoretical predictions for translational and segmental diffusion-controlled termination, respectively. At increasing polymer concentrations, kti,i(x) falls rapidly coinciding with the onset of the gel effect. By comparing results from the RAFT-mediated polymerisations of MMA, STY, MA, and vinyl acetate (VAc) with theoretical models, we found that the onset of the gel effect coincided closely with the theoretical onset of chain overlap. Considerable uncertainty has plagued the evaluation of this phenomenon, but using a difunctional RAFT agent we showed this uncertainty arises from the influence of broad MWD’s on chain overlap and short-long termination. Finally, critical tests of this theory involving the bimolecular termination of linear radicals in solutions of star polymer confirmed that the gel effect coincided with chain overlap. Beyond the gel effect termination slows enormously, passing through the ‘semi-dilute solution’ regime and into the ‘concentrated solution’. In semi-dilute solution, theoretical predictions based on scaling theory (i.e. the ‘blob’ model) were in excellent agreement with results for the polymerisation of PSTY in linear and star polymer solutions, indicating that the solvent quality diminished both with increasing chain length and through the addition of a star polymer matrix. In concentrated solutions, the chain-length-dependent power law exponent increased linearly with conversion. For example, for MMA the chain length dependence of kt in the gel regime scaled as gel = 1.8x + 0.056, suggesting that reptation alone does not describe termination in the concentrated solution. Values of gel for PSTY, MA, and VAc were in similar agreement, indicating that a mechanism intermediate between unentangled and entangled semi-dilute scaling laws applies in the concentrated solution regime. Interestingly, gel values for these monomers were found to decrease with increasing chain flexibility in the order gel(MMA)> gel(STY)> gel(VAc)> gel(MA), suggesting matrix mobility is rate determining in concentrated solutions. Similarly, gel values were also larger in star polymer solutions, coinciding with decreasing matrix mobility. Thus, although it has been commonly believed that polymer chains diffuse via reptation above the gel effect, these results show that this only occurs for solutions containing rigid and/or highly immobile macromolecules and in very high concentrations. To describe these behaviours, a semi-empirical ‘composite kt model’ was also developed to describe kti,i(x) as a function of i and x up to high conversions. We showed that the model is very simple to implement and accurate for modelling a wide range of functional monomers and experimental conditions. In particular, we showed the method was accurate for modelling RAFT-mediated polymerisations of a very wide range of monomers (MA, MMA, and PSTY) and was even accurate for modelling conventional FRP’s. Thus, the model provides a simple, flexible and accurate method for predicting the rate of reaction and evolution of molecular weight distributions across a range of experimental conditions based on accurate kti,i(x) values.

Free-radical polymerisation (FRP) has been one of the most important techniques for producing materials used in a very wide variety of applications and has enhanced the lives of millions of people around the world. However, for many years a number of fundamental questions regarding the key kinetic processes involved in FRP have remained unresolved. In particular, an accurate description of the mechanism for diffusion-controlled bimolecular termination has proven elusive. As a result, conventional modelling tools for FRP have often proven unreliable. The aim of this thesis, therefore, was to accurately study the evolution of the bimolecular termination rate coefficient during free radical polymerisation using a new and more accurate methodology based on ‘controlled/living’ reversible addition-fragmentation chain transfer (RAFT) polymerisation. This was undertaken in order to develop a more precise understanding of bimolecular termination and thereby develop a more reliable modeling approach capable of predicting the rates of reaction and evolution of molecular weight distributions for a wide range of experimental conditions and a wide range of functional monomers. The RAFT-CLD-T (RAFT Chain-Length-Dependent Termination) Method was used to determine accurate values for the conversion and chain-length-dependent termination rate coefficient, kti,i(x), as a function of various parameters. These parameters included the chain size, i, polymer concentration (or conversion, x), chain length size distribution and chain architecture/structure. The accuracy of the RAFT-CLD-T Method was crucial to this work, therefore, an important part of this thesis was devoted to evaluating the reliability of this technique. Below 5 % conversion and above 80 % conversion the method was found to be unreliable due to the effects of chain-length-dependent propagation, high PDI’s and short-long termination. However, between 5 % and 80 % conversion it was found that the method is extremely robust and a series of easy-to-use experimental guidelines were determined for accurately applying the RAFT-CLD-T Method. The effects of chain size, chain size distribution, solution polymer concentration, and matrix architecture were examined for the RAFT-mediated polymerisations of methyl methacrylate (MMA), styrene (STY) and methyl acrylate (MA). It was found that four distinct scaling regimes of termination are observed: (1) a ‘short’ chain dilute solution regime, (2) a ‘long’ chain dilute solution regime, (3) a semi-dilute solution regime and (4) a concentrated solution regime. In dilute polymer solutions, chain-length-dependent power law exponents, ’s, determined during the polymerisation of MMA, STY and MA (where kti,i(x)  i-) indicated that termination follows two major scaling regimes with exponents of approximately ~0.5 to 0.6 for ‘short’ chains and and ~0.12 to 0.16 for ‘long’ chains. Importantly, these exponents are in excellent agreement with theoretical predictions for translational and segmental diffusion-controlled termination, respectively. At increasing polymer concentrations, kti,i(x) falls rapidly coinciding with the onset of the gel effect. By comparing results from the RAFT-mediated polymerisations of MMA, STY, MA, and vinyl acetate (VAc) with theoretical models, we found that the onset of the gel effect coincided closely with the theoretical onset of chain overlap. Considerable uncertainty has plagued the evaluation of this phenomenon, but using a difunctional RAFT agent we showed this uncertainty arises from the influence of broad MWD’s on chain overlap and short-long termination. Finally, critical tests of this theory involving the bimolecular termination of linear radicals in solutions of star polymer confirmed that the gel effect coincided with chain overlap. Beyond the gel effect termination slows enormously, passing through the ‘semi-dilute solution’ regime and into the ‘concentrated solution’. In semi-dilute solution, theoretical predictions based on scaling theory (i.e. the ‘blob’ model) were in excellent agreement with results for the polymerisation of PSTY in linear and star polymer solutions, indicating that the solvent quality diminished both with increasing chain length and through the addition of a star polymer matrix. In concentrated solutions, the chain-length-dependent power law exponent increased linearly with conversion. For example, for MMA the chain length dependence of kt in the gel regime scaled as gel = 1.8x + 0.056, suggesting that reptation alone does not describe termination in the concentrated solution. Values of gel for PSTY, MA, and VAc were in similar agreement, indicating that a mechanism intermediate between unentangled and entangled semi-dilute scaling laws applies in the concentrated solution regime. Interestingly, gel values for these monomers were found to decrease with increasing chain flexibility in the order gel(MMA)> gel(STY)> gel(VAc)> gel(MA), suggesting matrix mobility is rate determining in concentrated solutions. Similarly, gel values were also larger in star polymer solutions, coinciding with decreasing matrix mobility. Thus, although it has been commonly believed that polymer chains diffuse via reptation above the gel effect, these results show that this only occurs for solutions containing rigid and/or highly immobile macromolecules and in very high concentrations. To describe these behaviours, a semi-empirical ‘composite kt model’ was also developed to describe kti,i(x) as a function of i and x up to high conversions. We showed that the model is very simple to implement and accurate for modelling a wide range of functional monomers and experimental conditions. In particular, we showed the method was accurate for modelling RAFT-mediated polymerisations of a very wide range of monomers (MA, MMA, and PSTY) and was even accurate for modelling conventional FRP’s. Thus, the model provides a simple, flexible and accurate method for predicting the rate of reaction and evolution of molecular weight distributions across a range of experimental conditions based on accurate kti,i(x) values.

Free-radical polymerisation (FRP) has been one of the most important techniques for producing materials used in a very wide variety of applications and has enhanced the lives of millions of people around the world. However, for many years a number of fundamental questions regarding the key kinetic processes involved in FRP have remained unresolved. In particular, an accurate description of the mechanism for diffusion-controlled bimolecular termination has proven elusive. As a result, conventional modelling tools for FRP have often proven unreliable. The aim of this thesis, therefore, was to accurately study the evolution of the bimolecular termination rate coefficient during free radical polymerisation using a new and more accurate methodology based on ‘controlled/living’ reversible addition-fragmentation chain transfer (RAFT) polymerisation. This was undertaken in order to develop a more precise understanding of bimolecular termination and thereby develop a more reliable modeling approach capable of predicting the rates of reaction and evolution of molecular weight distributions for a wide range of experimental conditions and a wide range of functional monomers. The RAFT-CLD-T (RAFT Chain-Length-Dependent Termination) Method was used to determine accurate values for the conversion and chain-length-dependent termination rate coefficient, kti,i(x), as a function of various parameters. These parameters included the chain size, i, polymer concentration (or conversion, x), chain length size distribution and chain architecture/structure. The accuracy of the RAFT-CLD-T Method was crucial to this work, therefore, an important part of this thesis was devoted to evaluating the reliability of this technique. Below 5 % conversion and above 80 % conversion the method was found to be unreliable due to the effects of chain-length-dependent propagation, high PDI’s and short-long termination. However, between 5 % and 80 % conversion it was found that the method is extremely robust and a series of easy-to-use experimental guidelines were determined for accurately applying the RAFT-CLD-T Method. The effects of chain size, chain size distribution, solution polymer concentration, and matrix architecture were examined for the RAFT-mediated polymerisations of methyl methacrylate (MMA), styrene (STY) and methyl acrylate (MA). It was found that four distinct scaling regimes of termination are observed: (1) a ‘short’ chain dilute solution regime, (2) a ‘long’ chain dilute solution regime, (3) a semi-dilute solution regime and (4) a concentrated solution regime. In dilute polymer solutions, chain-length-dependent power law exponents, ’s, determined during the polymerisation of MMA, STY and MA (where kti,i(x)  i-) indicated that termination follows two major scaling regimes with exponents of approximately ~0.5 to 0.6 for ‘short’ chains and and ~0.12 to 0.16 for ‘long’ chains. Importantly, these exponents are in excellent agreement with theoretical predictions for translational and segmental diffusion-controlled termination, respectively. At increasing polymer concentrations, kti,i(x) falls rapidly coinciding with the onset of the gel effect. By comparing results from the RAFT-mediated polymerisations of MMA, STY, MA, and vinyl acetate (VAc) with theoretical models, we found that the onset of the gel effect coincided closely with the theoretical onset of chain overlap. Considerable uncertainty has plagued the evaluation of this phenomenon, but using a difunctional RAFT agent we showed this uncertainty arises from the influence of broad MWD’s on chain overlap and short-long termination. Finally, critical tests of this theory involving the bimolecular termination of linear radicals in solutions of star polymer confirmed that the gel effect coincided with chain overlap. Beyond the gel effect termination slows enormously, passing through the ‘semi-dilute solution’ regime and into the ‘concentrated solution’. In semi-dilute solution, theoretical predictions based on scaling theory (i.e. the ‘blob’ model) were in excellent agreement with results for the polymerisation of PSTY in linear and star polymer solutions, indicating that the solvent quality diminished both with increasing chain length and through the addition of a star polymer matrix. In concentrated solutions, the chain-length-dependent power law exponent increased linearly with conversion. For example, for MMA the chain length dependence of kt in the gel regime scaled as gel = 1.8x + 0.056, suggesting that reptation alone does not describe termination in the concentrated solution. Values of gel for PSTY, MA, and VAc were in similar agreement, indicating that a mechanism intermediate between unentangled and entangled semi-dilute scaling laws applies in the concentrated solution regime. Interestingly, gel values for these monomers were found to decrease with increasing chain flexibility in the order gel(MMA)> gel(STY)> gel(VAc)> gel(MA), suggesting matrix mobility is rate determining in concentrated solutions. Similarly, gel values were also larger in star polymer solutions, coinciding with decreasing matrix mobility. Thus, although it has been commonly believed that polymer chains diffuse via reptation above the gel effect, these results show that this only occurs for solutions containing rigid and/or highly immobile macromolecules and in very high concentrations. To describe these behaviours, a semi-empirical ‘composite kt model’ was also developed to describe kti,i(x) as a function of i and x up to high conversions. We showed that the model is very simple to implement and accurate for modelling a wide range of functional monomers and experimental conditions. In particular, we showed the method was accurate for modelling RAFT-mediated polymerisations of a very wide range of monomers (MA, MMA, and PSTY) and was even accurate for modelling conventional FRP’s. Thus, the model provides a simple, flexible and accurate method for predicting the rate of reaction and evolution of molecular weight distributions across a range of experimental conditions based on accurate kti,i(x) values.

Thesis (M.S.) -- University of Montana, 2008. / Title from title screen. Description based on contents viewed May 5, 2009. Includes bibliographical references (p. 113-119).

Thesis (Ph.D.)--University of Alabama at Birmingham, 2007. / Title from first page of PDF file (viewed on June 25, 2009). Includes bibliographical references.

Environ un tiers des maladies humaines, héréditaires ou acquises, sont dues à la génération d’un codon stop prématuré (PTC). Le système de contrôle appelé dégradation des ARNm non-sens (NMD) permet de détecter puis de dégrader des ARNm contenant un PTC. Les facteurs principaux de la NMD : UPF1, UPF2 et UPF3 reconnaissent les PTCs en interagissant avec le complexe de terminaison de traduction contenant les ribosomes, les facteurs de terminaison eRF1, eRF3 et la protéine poly(A) binding (Pab1p en levure). Nous avons pu résoudre la structure d'un tel complexe en levure comprenant un ribosome en cours de traduction en présence d’un ARNt dans le site P et de facteurs de terminaisons dans le site A. Aucune densité n’a pu être observée pour Pab1p indiquant la flexibilité de l’interaction avec ce complexe. Nous avons aussi évalué l’impact des facteurs de la NMD sur la terminaison dans un système de traduction in vitro humain. UPF3B retarde la reconnaissance du codon stop et favorise la dissociation des sous-unités ribosomales. UPF2 abolit l’effet de UPF3B tandis que l’addition de UPF1 n’a pas d’influence dans la terminaison. Par in vivo et in vitro pulldowns, nous avons montré que UPF3B interagit avec eRF3a et UPF1 et pourrait constituer le lien manquant entre la terminaison et la NMD. Nos résultats illustrent la complexité des mécanismes de la terminaison et de la NMD. / Premature termination codons (PTCs) account for approximately one third of inherited and acquired diseases. A surveillance pathway called nonsense-mediated mRNA decay (NMD) detects and degrades PTC-containing transcripts. NMD core factors UPF1, UPF2 and UPF3 mediate the recognition of PTCs by associating with the terminating translation machinery composed of the ribosome, the release factors eRF1 and eRF3 and the poly(A) binding protein (Pab1p in yeast). Using electron cryo-microscopy, we solved such a complex in yeast and observed the translating ribosome, containing a P-site tRNA and an A-site density for the release factors but not for Pab1p indicating that Pab1p is flexibly bound. We also probed the function of NMD factors in mammalian termination using a reconstituted human in vitro translation system. Surprisingly, we found that UPF3B delayed stop codon recognition and promoted ribosomal dissociation. The addition of UPF2 could abolish UPF3B’s effect on translation termination. UPF1 had no influence in the termination process alone or in combination with UPF2. Using in vitro and in vivo pulldowns we found that UPF3B interacts with eRF3a and UPF1, indicating that UPF3B could be the missing link between termination and NMD. Our results point to a complex interplay between the NMD factors and the termination apparatus.

The study addresses the way, according to the author, in which must be resolved the problem of the concurrence of termination events in an administrative contract. It is common that parties attribute non-compliances to each other or the coexistence of termination events with different effects each of them. In these situations, the termination event which must be applied as a matter of priority with its corresponding associated effects must be determined. In this context, it should be pointed out the doctrine of the Spanish Council of the State according to which the termination event occurred before in time is applicable as a priority. However, the author considers that should be taken into account the priority in time regarding the invocation of the termination event («activación») rather than its appearance («aparición»). Thus, the general rule is that termination events may be used by the party of the contract which has not caused them. However, the aforementioned rule does not entail that the party which may invoke a termination event, actually does so (la active), even though the presence of a material circumstance that justifies the existence of the termination event.On this basis, the author concludes that it is the priority in time of the invocation of the termination event [«activación»] (and not of its mere appearance) [y no de la simple «aparición»] which determines the termination event applicable as a priority when several termination events concur. / El estudio aborda la forma en la que, a juicio del autor, hay que resolver el problema de laconcurrencia de causas de resolución sobre un mismo contrato administrativo. Es bastante habitual que las partes se imputen incumplimientos recíprocos, o que coexistan causas de resolución del contrato con efectos distintos cada una de ellas. En tales situaciones, hay que determinar la causa de resolución que debe aplicarse de manera prioritaria, con sus efectos anejos.En este contexto, se alude a la doctrina del Consejo de Estado español, relativa a considerar de aplicación prioritaria la causa de resolución que aparezca antes en el tiempo. Ahora bien, el autor considera que debe atenderse a la prioridad cronológica, no en la «aparición» de la causa de resolución, sino en su «activación». La regla general es que las causas de resolución sean de utilización potestativa por la parte en el contrato que no las provocó; ello se traduce en que aun cuando exista la circunstancia material que justifica la existencia de la causa de resolución, sin embargo ello no significa que quien puede hacerla valer efectivamente la ponga en funcionamiento (la active). Concluye por ello el autor que es la prioridad en el tiempo de la«activación» (y no de la simple «aparición») la que determina la causa de resolución del contratoque deberá aplicarse prioritariamente cuando concurran varias causas de resolución.

Submitted by Edileide Reis (leyde-landy@hotmail.com) on 2013-04-17T18:56:35Z No. of bitstreams: 1 Tercio Souza.pdf: 653424 bytes, checksum: 6d606e3ff997d71434d31fb919e56d1d (MD5) / Approved for entry into archive by Rodrigo Meirelles(rodrigomei@ufba.br) on 2013-05-09T17:41:15Z (GMT) No. of bitstreams: 1 Tercio Souza.pdf: 653424 bytes, checksum: 6d606e3ff997d71434d31fb919e56d1d (MD5) / Made available in DSpace on 2013-05-09T17:41:15Z (GMT). No. of bitstreams: 1 Tercio Souza.pdf: 653424 bytes, checksum: 6d606e3ff997d71434d31fb919e56d1d (MD5) Previous issue date: 2009 / A presente dissertação parte do pluralismo e da democracia nas relações de trabalho para identificar alguns contornos das relações coletivas no direito brasileiro. Digo que a eficácia da negociação coletiva encontra-se vinculada à melhoria das condições dos trabalhadores em bem-estar social. Digo ainda que em função dessa necessidade o “pleno emprego” impõe a adoção de todos os instrumentos cabíveis inclusive a possível extinção dos contratos de trabalho em vigor para o acesso de novos trabalhadores a um mesmo posto de trabalho; tudo para concluir que é possível negociação coletiva em que se imponha a extinção compulsória dos contratos de trabalho. / Salvador

O acordo de acionistas é instrumento que serve à adequação da disciplina societária aos interesses pessoais e patrimoniais dos acionistas. Tais acordos têm natureza jurídica contratual e parassocial, em razão de estarem intrinsecamente ligados aos pactos sociais. Em razão de serem contratos e, portanto, estarem submetidos à teoria geral dos contratos, e, ao mesmo tempo, estarem tão fortemente coligados à seara social, surgem dificuldades na resolução de questões limítrofes entre o direito civil e o direito societário. Esses problemas aparecem especialmente quando se trata da extinção por causa superveniente do acordo, existindo dúvidas na doutrina e na jurisprudência quanto à possibilidade de aplicação aos pactos parassociais das hipóteses de extinção aplicáveis aos contratos em geral. Com o objetivo de auxiliar na solução dessa questão, no presente estudo, são examinadas as causas supervenientes de extinção dos contratos, mais especificamente, as hipóteses de expiração de termo ou de implemento de condição resolutiva, de resilição, de resolução, por inadimplemento ou por onerosidade excessiva, de impossibilidade superveniente inimputável, de morte das partes, e, ainda, os cenários em que existe insolvência ou dissolução das partes ou da própria sociedade, os quais têm, após um exame genérico quanto a seus aspectos conceituais, verificada a sua aplicabilidade ao acordo de acionistas e os efeitos que produzem em sua esfera. São respeitados, contudo, os temperamentos necessários em decorrência de sua natureza parassocietária. / The shareholders’ agreement is an instrument that serves the adequacy of the corporate discipline to the shareholders’ personal and equity interests. Such agreements have the legal nature of contracts that are inserted in the companies’ corporate structure, being intrinsically connected to the bylaws and to the companies’ articles of associations. Because they are contracts, and therefore are subject to the general theory of contracts, and at the same time are so strongly linked to the corporate sphere, difficulties arise in solving border issues between Civil Law and Corporate Law. These problems appear especially when it comes to the termination of the agreements because of supervening causes, leaving scholars and courts in doubt as to the possibility of applying to the shareholders’ agreements the extinction hypotheses applicable to contracts in general. With the aim of assisting in the solution of this issue, the present study examines the supervening causes of termination of shareholders’ agreements, more specifically, the hypothesis of expiration of the term or implementation of a condition, terminations with and without cause, unenforceable supervening impossibility, death of the parties, and also the scenarios in which there is insolvency or dissolution of the parties in the agreement or of the company itself, which, after a general examination of their conceptual aspects, were submitted to a verification concerning their applicability to the shareholders' agreement and concerning the effects to be produced on such agreements, respecting, however, their nature as contracts inserted in the corporate structure.

Este trabalho relata observações e analises sobre como os detectores de defeitos influenciam as operação de consenso. O conceito dos detectores de defeitos é essencial para as operações de consenso em sistemas distribuídos assíncronos, uma vez que esses representam uma das (micas formas de sobrepujar as limitações impostas pela chamada Impossibilidade FLP (impossibilidade de diferenciar um processo falho de um processo mais lento). Enquanto os detectores de defeitos tem seu funcionamento bem definido através de duas propriedades, completeness e accuracy, Não há nenhuma restrição quanto a forma de implementá-los. Na literatura são encontrados vários modelos de detectores de defeitos, construídos com as mais variadas estratégias, mecanismos de comunicação e de detecção. No entanto, estes modelos não costumam ser acompanhados de uma comparação com os detectores já existentes; os autores limitam-se a apresentar as inovações dos mecanismos sugeridos. De toda literatura pesquisada, apenas um trabalho procurou comparar diferentes modelos de detectores de defeitos, e através de simulações, avaliou o impacto destes detectores sobre o tempo de terminação das operações de consenso. Entretanto, aquele trabalho era bem limitado, tanto nos modelos de detectores analisados quanto nos objetivos das observações. O presente trabalho procurou estender aquele experimento, incluindo mais modelos de detectores, e transportando-os para um ambiente prático de execução. As observações realizadas não ficaram limitadas as avaliações já realizadas por aquele trabalho, de tal forma que os modelos de detectores testados foram analisados sob diversas métricas, situações e parâmetros de operação. Essas avaliações possibilitaram verificar o comportamento dos detectores frente aos padrões de falhas mais significativos, avaliar o impacto de cada detector sobre as operações de consenso e a sua interação com os elementos do ambiente de execução. Essas avaliações permitiram fazer uma comparação dos detectores, possibilitando a identificação de suas limitações, suas situações de melhor desempenho e possíveis otimizações para serem realizadas em trabalhos futuros. / This work presents our observations and analysis on the influence of the failure detectors on the consensus algorithm. Failure detectors are essential to the consensus over an asynchronous distributed system, as they represent one of the few techniques that are able to circumvent the limitation imposed by the FLP Impossibility (the impossibility to distinguish a crashed process from a slow one, in asynchronous systems). While failure detectors are well defined through two properties, completeness and accuracy, there's no rule about their implementation. Thus, in the literature there are many models of failure detectors, each one implemented using different approaches to the communication and detection strategies. However, these detectors seldom compare themselves to the existing ones; their authors usually present only the advantages and innovations of the new model. Indeed, we only found one work that tried to compare different failure detectors. Using simulation techniques, that work evaluated the impact of the failure detectors on the consensus termination time. However, that research was very limited in the number of detectors analyzed and in the evaluation goals. The present work extended that experience, including more detectors in the analysis and evaluating them in a practical environment. Also, the observations were not restricted to those from the original paper, and the detectors were analyzed with more metrics, failure patterns and operational parameters. The evaluation allowed us to identify the behavior from the detectors in face of the most significant failure patterns, their influence on the consensus operation and their interaction with the execution environment. These evaluation also enabled us to compare the detectors, identifying their limitations, their best employment situations and possible optimizations to future developments.