Nuclear magnetic resonance flip-angle effects observability of multipole operators. II

General FTNMR sampling-pulse flip-angle dependencies of non diagonal multipole operators are derived and discussed. It is demonstrated that the efficiency of the polarization transferred between the multipole operator, [math], and the implicit observable [math] is uniquely related to the chosen flip-angle. The angle dependent efifciencies of other polarisation transfers are also considered. The formalism developed in this work is valid for spin systems of arbitrary dimension and character

Mise au point sur une nouvelle description des processus de relaxation en résonance magnétique nucléaire

Cet article fait le point sur les idées très récentes concernant les problèmes de la relaxation paramagnétique nucléaire à l’échelle macroscopique. La notion de modes de relaxation est introduite à partir de l’étude des systèmes très simples de spins 1/2 : A, AX, AMX. L’intervention des différents mécanismes de relaxation dans la factorisation en blocs de la matrice d’évolution du système des spins, l’utilisation des propriétés de symétrie et des représentations tensorielles irréductibles conduisent naturellement à la notion de « spins virtuels » de première et de deuxième espèce. En particulier, le rôle des différentes corrélations (auto et corrélation croisée) est précisé dans le couplage entre les différents modes de relaxation

Metáforas e imagens dos formadores de professores na área da informática aplicada à educação Teacher educators' metaphors and images in the field of computing applied to education

O ponto de partida desta pesquisa é a preocupação com a lacuna existente entre a formação dos professores na área da informática educativa (IE) e sua experiência ulterior. A hipótese principal é que existe, entre os formadores dos professores desta área, uma certa representação do modelo de formação que se transferiria automaticamente para a futura prática dos professores. Foi realizada uma enquete com 21 professores da disciplina "Informática e Educação", da Universidade Católica de Goiás, utilizando-se as técnicas de associação livre de palavras, entrevista semi-estruturada e grupo focal. O núcleo figurativo das representações identificadas mostra o computador como um instrumento gerador de transformações educacionais e a informática educativa como o agente promotor das transformações pedagógicas. Esta analogia torna-se uma referência importante que dá forma ao discurso dos formadores por meio de metáforas que constituem o seu imaginário.<br>The focus of this research is the gap between the formation of educational computing (EC) teachers and their further experience. The main hypothesis is that, among EC teacher formers, there is a certain representation of the educational model and a conception on the beneficial aspects of digital technologies that would be automatically transferred to the future teachers' practice. An investigation was carried out with the 21 teachers of the discipline "Computing and Education" at the Catholic University of Goiás, with the use of techniques of free word association, semi-structured interviews and focus groups. The nucleus of the identified representations shows the computer as a generator of educational changes, and educational computing as the agent of pedagogical changes. This analogy becomes an important reference that shapes formers' discourse by means of metaphors which constitute their imagination