No abstract

Recent fieldwork on the island of Faial (Azores) led to the establishment of a detailed volcanic stratigraphic sequence, which is composed of five main geological formations. One of them, the Caldeira Formation, comprising mainly pumice fall and flow deposits, was judged to be Holocene in age. Organic materials were found preserved in or below some of the pyroclastic deposits from this formation. Wood, charcoal, peat and soil samples were radiocarbon dated, permitting correlation of deposits from different sequences and the establishment of a chronological framework for the Caldeira volcanic activity. These materials yielded ages from ca. 10–1 ka bp. The average dormant interval in the Caldeira pyroclastic activity from 4–1 ka ago is ca. 400 yr, with eruptions approximately every 200–800 yr. This frequency of activity indicates that the Caldeira volcano is an active, dangerous structure that should be closely monitored.

No abstract

The modelling of fractional linear systems through ARMA models is addressed. To perform this study, a new recursive algorithm for impulse response ARMA modelling is presented. This is a general algorithm that allows the recursive construction of ARMA models from the impulse response sequence. This algorithm does not need an exact order specification, as it gives some insights into the correct orders. It is applied to modelling fractional linear systems described by fractional powers of the backward difference and the bilinear transformations. The analysis of the results leads to propose suitable models for those systems. IntroductionPseudo-fractional auto-regressive moving average (ARMA) modelling is a pole-zero modelling of fractional linear systems. These are described by fractional differential equations in the continuous-time case or auto-regressive integrated moving average (ARIMA) models in the discrete-time case. The first case is based on the definition of fractional differintegration, whereas the second deals with the fractional differencing that is a fractional version of the well-known finite differences. These systems are characterised by having a long memory that cannot be explained by the usual linear systems that have short memory (exponential). The desire of finding a theoretical base for such systems led to the fractional calculus that has recently received a great deal of attention in the scientific literature, through the publication of books, special issues of journals, review articles, as well as a very large number of research papers. The interest in fractional calculus comes from the fact that it provides foundations for the understanding of several natural phenomena and the basic theory for building models for the systems underlying them. However, adoption of the fractional calculus by the physicists and engineering community was inhibited historically by the lack of clear experimental evidence for its need and by the difficulty in constructing simple models for simulation or even implementation of simple fractional systems. Fractional calculus is almost as old as the common calculus, but only since 30 years ago it has been a subject of specialised publications and conferences.The basic building block of this kind of systems is the non-integer order derivative and integral that have been approximated by fractional powers of the backward difference or the bilinear transformations -the former is exactly the building block of the fractional differencing, as said earlier. However, these approximations are described infinite impulse response (IIR) systems with nonrational transfer functions. For these, ARMA models are only approximations. However, the usefulness of ARMA models makes them very interesting when constructing discrete-time approximating models for fractional systems. In the last few years, a lot of attempts to obtain such models have been done [1 -5]. However, it is not clear how to perform such modelling and how to choose the most suitable orders, although there are a l...

Palaeomagnetic results and K-Ar age data for the Sintra and Sines intrusive complexes (W. Portugal), and further details on the palaeomagnetic structure of the Lisbon volcanics are reported. The Sintra complex consists of two main intrusive phases having been emplaced in the Upper Cretaceous at around 90 Ma and 75 Ma respectively. The radiometric results show that the Sines complex formed concurrently with the second Sintra magmatism. The early (main) Sintra pluton has a characteristic magnetization of D=358', I = 27' (ag5 = 3.3'). This remanence direction is defined by gabbros and diorites as the granitic rocks (constituting the bulk of the complex) are shown to possess stable secondary magnetization imposed during Quaternary weathering. The characteristic magnetization of the younger intrusive event, as defined by the Sines rocks, has a mean direction of D=041', I =41' (ag5 = 3.3'). These two Upper Cretaceous palaeomagnetic directions are significantly different at the 95 per cent probability level. The Lisbon volcanics show the presence of the '75 Ma' magnetization suggesting that also this volcanic complex dates from the Upper Cretaceous. In addition, the palaeomagnetic results from the Lisbon complex have given further substance to a previously reported magnetization component with shallow inclination and north-northwest declination, now defined by D = 333' 1 = 14' (ag5 = 7.4'). It is inferred that this magnetization which has a dual-polarity structure formed through low temperature oxidation in late Cretaceous to Lower Tertiary time. The declination difference between the '90 Ma' and

In this paper a new least-squares (LS) approach is used to model the discrete-time fractional differintegrator. This approach is based on a mismatch error between the required response and the one obtained by the difference equation defining the auto-regressive, moving-average (ARMA) model. In minimizing the error power we obtain a set of suitable normal equations that allow us to obtain the ARMA parameters. This new LS is then applied to the same examples as in

Rosmarinic acid (RA) is a phenolic compound with biological activity. The objective of the present study was to investigate whether this compound kept its biological activity in the presence of proteins. For this purpose, bovine serum albumin (BSA) was used as a model protein, and the capacity of the RA to inhibit acetylcholinesterase (AChE) and affect antioxidant activity was evaluated in the absence and presence of BSA. A mixture of phenolic compounds containing RA, obtained from a medicinal plant was added to this study. The AChE inhibitory activity of RA was reduced by ∼57% in the presence of BSA, while the antioxidant activity increased. These results lead to the investigation of the effect of RA on the BSA structure using Fourier transform infrared spectroscopy (FTIR). At 37°C and higher temperatures, RA caused a decrease in the temperature modifications on the protein structure. Furthermore, FTIR and native-gel analysis revealed that protein aggregation/precipitation, induced by temperature, was reduced in the presence of RA. The novelty of the present work resides in the study of the enzyme inhibitory activity and antioxidant capacity of polyphenols, such as RA, in the presence of a protein. The findings highlight the need to consider the presence of proteins when assessing biological activities of polyphenols in vitro and that enzyme inhibitory activity may be decreased, while the antioxidant capacity remains or even increases.

No abstract