Browsing by Author "Rocha, J."
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- 13C solid-state nuclear magnetic resonance and Fourier transform infrared studies of the thermal decomposition of corkPublication . Neto, C. Pascoal; Rocha, J.; Gil, A.; Cordeiro, N.; Esculcas, A.P.; Rocha, S.; Delgadillo, I.; De Jesus, J.D.Pedrosa; Correia, A.J.FerrerThe thermal decomposition of cork has been studied by Fourier transform infrared (FTIR) spectroscopy and 13C solid-state nuclear magnetic resonance (NMR) spectroscopy with cross-polarization and magic-angle spinning (CP-MAS), high-power ‘H decoupling (HPDEC) and cross-polarization depolarization-polarization (CPDP). Waxes and other soluble components of cork begin to decompose at ca. 150°C. This is accompanied by partial decomposi tion of suberin, probably initiated at the points of attachment to the cell wall. The carbohydrates begin to decompose at ca. 200°C. The decomposition of lignin begins at 250-3OO”C, while suberin undergoes further degradation. Significant amounts of coke are formed in the process. At 400°C cork has been transformed into coke with traces of partially decomposed suberin. The thermal decomposition of cork is dependent on the calcination time, particularly in the 200-350°C range.
- Signatures of the preagricultural peopling processes in sub-Saharan Africa as revealed by the phylogeography of early Y chromosome lineagesPublication . Batini, C.; Ferri, G.; Destro-Bisol, G.; Brisighelli, F.; Luiselli, D.; Sanchez-Diz, P.; Rocha, J.; Simonson, T.; Brehm, António; Montano, V.; Elwali, N. E.; Spedini, G.; D'Amato, M. E.; Myres, N.; Ebbesen, P.; Comas, D.; Capelli, C.The study of Y chromosome variation has helped reconstruct demographic events associated with the spread of languages, agriculture, and pastoralism in sub-Saharan Africa, but little attention has been given to the early history of the continent. In order to overcome this lack of knowledge, we carried out a phylogeographic analysis of haplogroups A and B in a broad data set of sub-Saharan populations. These two lineages are particularly suitable for this objective because they are the two most deeply rooted branches of the Y chromosome genealogy. Their distribution is almost exclusively restricted to sub-Saharan Africa where their frequency peaks at 65% in groups of foragers. The combined high-resolution single nucleotide polymorphism analysis with short tandem repeats variation of their subclades reveals strong geographic and population structure for both haplogroups. This has allowed us to identify specific lineages related to regional preagricultural dynamics in different areas of sub-Saharan Africa. In addition, we observed signatures of relatively recent contact, both among Pygmies and between them and Khoisan speaker groups from southern Africa, thus contributing to the understanding of the complex evolutionary relationships among African hunter-gatherers. Finally, by revising the phylogeography of the very early human Y chromosome lineages, we have obtained support for the role of southern Africa as a sink, rather than a source, of the first migrations of modern humans from eastern and central parts of the continent. These results open new perspectives on the early history of Homo sapiens in Africa, with particular attention to areas of the continent where human fossil remains and archaeological data are scant.