Complexos derivados de 1,1-bis(difenilfosfina)ferroceno : sintese, caracterizacao e propriedades cataliticas

Uma parte importante da química de orgametálicos atual centra-se no estudo de compostos heterobimetálicos com o propósito de avaliar de que modo as possíveis interações entre os metais podem alterar a reatividade dos centros metálicos presentes na molécula. Os ligantes ferrocenilas tem sido bastante utilizados para obter-se compostos desta natureza. Dentro desta classe de ligantes destaca-se o 1,1'-bis(difenilfosfina)ferroceno(dppf). Muitos trabalhos surgiram na literatura nos últimos dez anos descrevendo a síntese, caracterização estrutural, no estado sólido ou em solução, de novos complexos metálicos derivados deste metaloligante, bem como o estudo de suas propriedades catalíticas. O objetivo deste trabalho foi sintetizar novos compostos derivados do 1,1'-bis(difenilfosfina) ferroceno (dppf) e estudá-los no estado sólido ou em solução. Desta forma, foram pela primeira vez sintetizados os compostos dppfFe(NO)2(1), [dppfCo(NO)2][SBf6](2) e dppfNicod(3) e [dppfNi(MeCN)4]2 (4) os quais foram caracterizados por espectroscopia na região do infravermelho, ressonância magnética nuclear de ¹H e ³¹P{¹H}, análise elementar de C,H e N, condutividade molar no caso do composto catiônico(2) e difração de Raios-X de monocristal, no caso do composto(1). A espectroscopia Mössbauer de 57Fe constitui-se uma técnica adequada para a análise deste metaligante, que contém um átomo de Fe na sua molécula, pois pode fornecer informações estruturais e evidenciar eventuais efeitos interativos que ocorram entre os centros metálicos quando o ligante encontra-se complexado a outros metais. Foram, então, estudados por espectroscopia Mössbauer, à baixa temperatura, os compostos (1),(2),(3),(4) e dppfFe(CO)3 (5) e os resultados obtidos comparados com os apresentados na literatura para compostos análogos contendo o ligante dppf. Os complexos derivados do dppf exibem um processo de oxidação centrado no ferroceno além dos processos de oxiredução presentes nos outros centros metálicos da molécula. O estudo das alterações que podem ocorrer neste processo devido à presença de um segundo metal de transição ou dos ligantes é importante pois pode fornecer informações sobre como modular o potencial redox centrado no ligante ferrocenila, permitindo assim um controle de sua reatividade. Sendo assim, neste trabalho foi realizado um estudo eletroquímico, por voltametria cíclica, dos compostos (1),(2) e (5). Compostos de Ni(0) ou Ni(II) são conhecidos catalisadores em reações de oligomerização e polimerização de olefinas e dienos. Compostos ferrodinitrosilas e cobaltodinitrosilas, na presença de redutores, apresentam alta seletividade em reações de ciclomerização de dienos. Nestes sistemas catalíticos a atividade e seletividade doscompostos está intimamente relacionada com a natureza dos ligantes unidos ao metal de transição do percussor catalítico. Devido às características dos compostos sintetizados e estudados neste trabalho, decidiu-se verificar a possível influência do ligante ddpf, na atividade e seletividade das reações com dienos, escolhendo-se o butadieno como substrato modelo. Estudou-se, então, a atividade catalítica dos compostos (1),(2),(3),(4),(5) e dppfNiCl2 (6) frente ao butadieno, na ausência e presença do cocatalisador, AlEt2Cl.

Nonparametric specification tests for conditional duration models

This paper deals with the testing of autoregressive conditional duration (ACD) models by gauging the distance between the parametric density and hazard rate functions implied by the duration process and their non-parametric estimates. We derive the asymptotic justification using the functional delta method for fixed and gamma kernels, and then investigate the finite-sample properties through Monte Carlo simulations. Although our tests display some size distortion, bootstrapping suffices to correct the size without compromising their excellent power. We show the practical usefulness of such testing procedures for the estimation of intraday volatility patterns.

A family of autoregressive conditional duration models

This paper develops a family of autoregressive conditional duration (ACD) models that encompasses most specifications in the literature. The nesting relies on a Box-Cox transformation with shape parameter λ to the conditional duration process and a possibly asymmetric shocks impact curve. We establish conditions for the existence of higher-order moments, strict stationarity, geometric ergodicity and β-mixing property with exponential decay. We next derive moment recursion relations and the autocovariance function of the power λ of the duration process. Finally, we assess the practical usefulness of our family of ACD models using NYSE transactions data, with special attention to IBM price durations. The results warrant the extra flexibility provided either by the Box-Cox transformation or by the asymmetric response to shocks.

A family of autoregressive conditional duration models

This paper develops a family of autoregressive conditional duration (ACD) models that encompasses most specifications in the literature. The nesting relies on a Box-Cox transformation with shape parameter λ to the conditional duration process and a possibly asymmetric shocks impact curve. We establish conditions for the existence of higher-order moments, strict stationarity, geometric ergodicity and β-mixing property with exponential decay. We next derive moment recursion relations and the autocovariance function of the power λ of the duration process. Finally, we assess the practical usefulness of our family of ACD models using NYSE price duration data on the IBM stock. The results warrant the extra flexibility provided either by the Box-Cox transformation or by the asymmetric response to shocks.

Oviposition preference hierarchy in Ceratitis capitata (Diptera, Tephritidae): influence of female age and experience

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Cidade e identidade: discursividades imagético-espaciais e a construção da identidade espacial do Recife, Veneza Brasileira

This treatise analyzes the identitary setting called Veneza Brasileira (Brazilian Venice) which is subscribed to the discoursive materialization related to the imagetic setting (literary and mediatic) produced about the city of Recife. The main investigation of this research is to examine the way how the identitary setting called Veneza Brasileira has been constructed in the imagetic setting practices about the city of Recife in the nineteenth and twentieth centuries. This study is subscribed to the Applied Linguistics and considers the theoretical perspectives that come from the Cultural Studies which investigation basis is focused on authors such as: Hall (2006); Bauman (1999; 2001;2005); Silva (2000); and Castells (2000) related to the discussion over identity, as well as the discussion over Urban Studies presented in Santos (1997; 1999); Ferrara (1998); and Pesavento (2001). Moreover it is also based on the theoretical basis found in Foucault (2004; 2006; 2007). Furthermore theoretical-methodological approaches rely on the French Discourse Analysis (DA) found in Orlandi (2001); Gregolin (2007); and Courtine (2006). On being so, this treatise aims to: analyze the meaning effects over the production of the identitary setting, especially the so-called Veneza Brasileira, in the imagetic setting discoursive practices (Poems, Post Cards and Touristic Guides) which are produced over the urban setting of the city of Recife. This research is characterized by being qualitative and interpretative and the theoretical analytical approaches contributed to the reading of both poetic and iconic images presented in the excerpts of poems from the nineteenth century and early twentieth century in: Manuel Bandeira s poems, Carlos Pena Filho s poems, and João Cabral de Melo Neto s poems which were produced in the early and late twentieth century. Moreover, this study observed some photographic images in Post Cards and Touristic Guides related to the visiting of historical sites in Recife. One could conclude that the imagetic setting discourse about Recife produced different identitary effects over the so-called Veneza Brasileira along these three centuries: in the nineteenth century, the poetry constructed the utopia city along with the meaning effect of identitary unit; as for the twentieth century, one observed an oscillation between a utopia/heteroutopia city meaning effect of both united and fragmented identity, the latter one is prevalent. As for the twenty-first century, the media reconstructed over again the utopia city, and consequently, produced meaning effect of identitary unit. These same meaning effects of identity either corroborate or contradict to/with the concepts of the postmodernism over identity along these three centuries. In other words, considering the imagetic setting, this oscillation occurs in the proportion of one finds an (ex) inclusion of social agents that construct these same identities.

Analysis of various conditions in order to measure electromyography of isometric contractions in water and on air

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Oviposition behavior of Ceratitis capitata wiedemann (Diptera: Tephritidae): Association between oviposition preference and larval performance in individual females

The oviposition preference and larval performance of females of Ceratitis capitata (Wiedemann) were examined. Wild or laboratory-reared females were tested for oviposition preference in relation to papaya fruit in different stages of ripeness, as well as to two different fruits: papaya and apple. The results demonstrated that both laboratory-reared and wild females preferred ripe papaya fruit compared to unripe fruit for oviposition, and that ripe papaya was the best for larval performance. When oviposition preference was tested with different fruits (papaya and apple), both wild and laboratory-reared larvae developed better in papaya. However, only wild females showed a preference for oviposition on papaya as opposed to apple. Laboratory-reared females showed no oviposition preference on fruits that resulted in better larval performance.

Descentralización fiscal en Venezuela

Incluye Bibliografía

An analysis of maritime transport and its costs for the Caribbean

Includes bibliography