No systematic effects of sampling direction on climate-growth relationships in a large-scale, multi-species tree-ring data set

Ring-width series are important for diverse fields of research such as the study of past climate, forest ecology, forest genetics, and the determination of origin (dendro-provenancing) or dating of archaeological objects. Recent research suggests diverging climate-growth relationships in tree-rings due to the cardinal direction of extracting the tree cores (i.e. direction-specific effect). This presents an understudied source of bias that potentially affects many data sets in tree-ring research. In this study, we investigated possible direction-specific growth variability based on an international (10 countries), multi-species (8 species) tree-ring width network encompassing 22 sites. To estimate the effect of direction-specific growth variability on climate-growth relationships, we applied a combination of three methods: An analysis of signal strength differences, a Principal Component Gradient Analysis and a test on the direction-specific differences in correlations between indexed ring-widths series and climate variables. We found no evidence for systematic direction-specific effects on tree radial growth variability in high-pass filtered ring-width series. In addition, direction-specific growth showed only marginal effects on climate-growth correlations. These findings therefore indicate that there is no consistent bias caused by coring direction in data sets used for diverse dendrochronological applications on relatively mesic sites within forests in flat terrain, as were studied here. However, in extremely dry, warm or cold environments, or on steep slopes, and for different life-forms such as shrubs, further research is advisable.</p

Characterization of the chemical-structure of sulfated glycosaminoglycans after enzymatic digestion - application of liquid-chromatography mass-spectrometry with an atmospheric-pressure interface

Pneumatically assisted electrospray was demonstrated to be a powerful ionization source for the analysis of oligosaccharides. A mass spectrometer was interfaced to an HPLC system, using this interface, to determine oligosaccharides from the enzymatic digestion of heparin separated on a reversed-phase column. To set up the technique, and particularly to clarify the ionization process, purified disaccharides, from enzymatic digestion of chondroitin sulphates, were measured. The use of a suitable counter ion in the mobile phase, tetrapropylammonium (TPA), to optimize the HPLC separation, gave, with sulphated di- and oligosaccharides, adducts [M + nTPA - (n + m)H]m-, which were unexpectedly stable to fragmentation; molecular ions [M - (n + 1)H]n-, in the presence of the counter ion, were observed only with desulphated or monosulphated disaccharides. The stability of the adducts and the use of a deuterated ion-pair reagent permitted an exact evaluation of the molecular masses of disaccharides and oligosaccharides of unknown structure. Spectra obtained in the absence of the counter ion contained singly or multiply charged molecular ions and fragmentation ions mainly from loss of the sulphate groups; under these ionization conditions the exact mass determination and interpretation of the spectra were difficult. After removal of the counter ion, tandem mass spectra could be obtained with some interesting data for the characterization of these molecules. Complete spectral analyses were performed with amounts of samples of 50 mug but, using microbore columns, one twentieth of this amount may give good spectra

O papel das interações sociais e de atividades propostas para o ensino-aprendizagem de conceitos químicos

Este trabalho teve como objetivo analisar o papel das interações sociais e de atividades didáticas propostas em aulas de Química. Apresenta discussões com base nas teorias sociointeracionistas de Vygotsky e Leontiev, suas implicações e abordagens nos diversos processos de construção de conceitos. O trabalho foi realizado em uma Escola Pública de Pernambuco, onde foram observados doze alunos, os quais participaram de diferentes tipos de atividade em sala de aula. Essas atividades, realizadas em pequenos grupos, sob a supervisão da professora, foram analisadas considerando-se como relevantes as oportunidades de interação e discussão que as mesmas possam ter possibilitado entre os alunos durante as aulas. Os resultados apontaram para a importância do planejamento de atividades que promovam um processo coletivo, cooperativo e interacionista de ensino e aprendizagem, reforçando o papel do outro na formação mais ampla dos alunos e contribuindo para uma melhor significação dos conceitos científicos