Fluorescence of nitrobenzoxadiazole (NBD)-labeled lipids in model membranes is connected not to lipid mobility but to probe location

Nitrobenzoxadiazole (NBD)-labeled lipids are popular fluorescent membrane probes. However, the understanding of important aspects of the photophysics of NBD remains incomplete, including the observed shift in the emission spectrum of NBD-lipids to longer wavelengths following excitation at the red edge of the absorption spectrum (red-edge excitation shift or REES). REES of NBD-lipids in membrane environments has been previously interpreted as reflecting restricted mobility of solvent surrounding the fluorophore. However, this requires a large change in the dipole moment (Dm) of NBD upon excitation. Previous calculations of the value of Dm of NBD in the literature have been carried out using outdated semi-empirical methods, leading to conflicting values. Using up-to-date density functional theory methods, we recalculated the value of Dm and verified that it is rather small (B2 D). Fluorescence measurements confirmed that the value of REES is B16 nm for 1,2-dioleoyl-sn-glycero-3- phospho-L-serine-N-(NBD) (NBD-PS) in dioleoylphosphatidylcholine vesicles. However, the observed shift is independent of both the temperature and the presence of cholesterol and is therefore insensitive to the mobility and hydration of the membrane. Moreover, red-edge excitation leads to an increased contribution of the decay component with a shorter lifetime, whereas time-resolved emission spectra of NBD-PS displayed an atypical blue shift following excitation. This excludes restrictions to solvent relaxation as the cause of the measured REES and TRES of NBD, pointing instead to the heterogeneous transverse location of probes as the origin of these effects. The latter hypothesis was confirmed by molecular dynamics simulations, from which the calculated heterogeneity of the hydration and location of NBD correlated with the measured fluorescence lifetimes/REES. Globally, our combination of theoretical and experiment-based techniques has led to a considerably improved understanding of the photophysics of NBD and a reinterpretation of its REES in particular.

A aprendizagem da leitura : Concepções sobre a funcionalidade da linguagem escrita e o sucesso na leitura no final do 1º ano de escolaridade

A Aprendizagem da Leitura é um desafio para as crianças que iniciam o primeiro ano de escolaridade tomando-se, para algumas, difícil de alcançar e influenciando negativamente todo o seu percurso escolar. O objectivo deste estudo é procurar perceber qual a relação entre os conhecimentos/concepções que as crianças do primeiro ano de escolaridade possuem, no início do ensino básico, sobre os objectivos/funções da leitura e o sucesso na sua aprendizagem no final do ano lectivo. A amostra foi constituída por 59 crianças, de nacionalidade portuguesa, que no ano lectivo 2006/2007 frequentaram pela primeira vez o primeiro ano de escolaridade, nas Escolas Básicas do 1o Ciclo do Agrupamento de Escolas de Arraiolos e que ainda não saibam ler no início do ano lectivo. A recolha de dados foi feita em dois momentos: no início e no final do ano lectivo. No primeiro momento, em Setembro e Outubro de 2006, foi feita às crianças uma entrevista individual semi-directiva (Alves Martins, 2000), que permitiu conhecer as suas concepções funcionais da leitura e foi também aplicada a Prova de Linguagem Técnica da Leitura/Escrita (Alves Martins, Mata, Peixoto & Monteiro, 2000), para avaliar os conhecimentos de linguagem técnica das crianças; no segundo momento, em Junho de 2007, foi aplicada uma Prova de Leitura (Alves Martins, 2000), para avaliar o desempenho em leitura no final do ano lectivo. Para o tratamento dos dados, a metodologia que utilizámos combinou a análise qualitativa e a análise quantitativa Relativamente à entrevista recorremos à análise qualitativa - análise de conteúdo, quanto à Prova de Linguagem Técnica da Leitura/Escrita e à Prova de Leitura foi feita uma análise quantitativa, seguindo o tratamento estatístico a metodologia proposta pelos autores das provas. ABSTRACT; The Learning of the Reading is a challenge to children who begin the first school year, becoming, for some of them, difficult to achieve and influencing in a negative way their entire school itinerary. The purpose of this study is to try to understand what the relation is between the knowledge/conceptions children in the first school year possess, at the beginning of the elementary education, about the purposes/functions of reading and the success of their learning at the end of the school year. The sample was constituted by 59 children, of Portuguese nationality, that in the school year of 2006/2007 attended for the first time the first school year, in the Elementary Schools of the 1st Cycle of the Assemblage of Schools of Arraiolos and that could not read in the beginning of the school year. The joining of data was made in two moments: in the beginning and in the end of the school year. ln the first moment, in September and October 2006, an individual semi­directive interview (Alves Martins, 2000) was made to the children, which allowed to know their functional conceptions of reading and was also made the Proof of Technical Language of Reading/Writing (Alves Martins, Mata, Peixoto & Monteiro, 2000), in order to evaluate the children's knowledge of technical language; in the second moment, in June 2007, a Proof of Reading (Alves Martins, 2000) was made, to evaluate the performance in reading at the end of the school year. For data treatment, the method we used combined the qualitative analysis and the quantitative analysis. About the interview, we used the qualitative analysis-content analysis, about the Proof of Technical Language of Reading/Writing and the Proof of Reading was made a quantitative analysis, having the statistic treatment followed the method proposed by the authors of the proofs.

A finite-strain solid–shell using local Löwdin frames and least-squares strains

A finite-strain solid–shell element is proposed. It is based on least-squares in-plane assumed strains, assumed natural transverse shear and normal strains. The singular value decomposition (SVD) is used to define local (integration-point) orthogonal frames-of-reference solely from the Jacobian matrix. The complete finite-strain formulation is derived and tested. Assumed strains obtained from least-squares fitting are an alternative to the enhanced-assumed-strain (EAS) formulations and, in contrast with these, the result is an element satisfying the Patch test. There are no additional degrees-of-freedom, as it is the case with the enhanced-assumed-strain case, even by means of static condensation. Least-squares fitting produces invariant finite strain elements which are shear-locking free and amenable to be incorporated in large-scale codes. With that goal, we use automatically generated code produced by AceGen and Mathematica. All benchmarks show excellent results, similar to the best available shell and hybrid solid elements with significantly lower computational cost.

A finite-strain solid–shell using local Löwdin frames and least-squares strains

A finite-strain solid–shell element is proposed. It is based on least-squares in-plane assumed strains, assumed natural transverse shear and normal strains. The singular value decomposition (SVD) is used to define local (integration-point) orthogonal frames-of- reference solely from the Jacobian matrix. The complete finite-strain formulation is derived and tested. Assumed strains obtained from least-squares fitting are an alternative to the enhanced-assumed-strain (EAS) formulations and, in contrast with these, the result is an element satisfying the Patch test. There are no additional degrees-of-freedom, as it is the case with the enhanced- assumed-strain case, even by means of static condensation. Least-squares fitting produces invariant finite strain elements which are shear-locking free and amenable to be incorporated in large-scale codes. With that goal, we use automatically generated code produced by AceGen and Mathematica. All benchmarks show excellent results, similar to the best available shell and hybrid solid elements with significantly lower computational cost.