Pullback attractors for a singularly nonautonomous plate equation

We consider the family of singularly nonautonomous plate equation with structural damping $$u_{tt} + a(t,x)u_{t} + (- \Delta) u_{t} + (-\Delta)^{2} u + \lambda u = f(u),$$ in a bounded domain $\Omega \subset \R^n$, with Navier boundary conditions. When the nonlinearity $f$ is dissipative we show that this problem is globally well posed in $H^2_0(\Omega) \times L^2(\Omega)$ and has a family of pullback attractors which is upper-semicontinuous under small perturbations of the damping $a$

Shelf-Ocean material exchange influencing the Atlantic chemical composition off NW Iberian margin since the last glaciation

Rivers are the main conduit of sediment to the shelf. The basin geology, the drainage area and the discharge rate are the major factors that determine their sediment load (Milliman and Syvistski, 1992). Besides suspended particles, dissolved components may also give some information on the eroded crust. Sr isotopes in carbonate shells of biological organisms have been used to study, in the geological record, the influence exerted by the chemical weathering of the continental crust on the seawater composition (Macdougall, 1991). In this work, Sr isotope ratios obtained in tests of foraminifera representing the last 40 ka are presented and discussed in the scope of the palaeogeographical evolution of NW Iberia. This work aims to present and discuss the results of Sr isotope analyses (performed, by TIMS, in the Isotope Geology Laboratory of the University of Aveiro) of tests of two species of foraminifera, from nine samples taken along the OMEX core KC 024-19 (181 cm; 42°08’98’’N, 10°29´96’’W, and 2765m), collected in the Galicia Bank area, off Galicia. Taking into account that Sr contained in the carbonate tests is usually considered as preserving the signature of the contemporaneous seawater, one planktonic species (Globigerina bulloides) and one benthic species (Cibicides wuellerstorfi) were selected in order to try to detect Sr isotope variations both through time and between two different levels of the water column. The core age model, which records the last 40 ka, is based on a combination of oxygen isotope stratigraphy, eight AMS 14C datings and the synchronisation of the last four Heinrich Events in the Iberian Margin sedimentary records. As a whole, the obtained 87Sr/86Sr ratios vary between 0.709209 and 0.709108, with a mean 2σ error of 0.000025. These values lie within the range of modern marine Sr isotope ratios (0.70910-0.70922), as previously defined using analyses of both seawater and marine carbonates (see compilation by Faure and Mensing, 2005). Despite their small variation, the 87Sr/86Sr ratios obtained in G. bulloides seem to indicate that Sr dissolved in seawater at the KC 024-19 core site became slightly less radiogenic after the Last Glacial Maximum (LGM). This decrease is concomitant with diminishing amounts of the detrital components in the sediments (Fig. 1). Therefore, both the composition of dissolved Sr, as revealed by results on tests of planktonic foraminifera, and the proportions of suspended terrigenous particulate material arriving at the KC 024-19 site point to a decreasing importance of the contribution of the erosion of the Iberian Variscan crust since the Last Glacial Maximum and in the Holocene. The 87Sr/86Sr ratios measured in tests of benthic foraminifera (C. wuellerstorfi) are more erratic and no correlation can be established with palaeogeographical/palaeoclimatic constraints. The difference between the behaviour of Sr compositions in G. bulloides and C. wuellerstorfi may indicate that whilst the planktonic foraminifera should reproduce very closely the seawater composition, the benthic organisms should, in addition to the major role of seawater, also be affected by some sort of interaction with the sediments. As such, planktonic foraminifera are probably more reliable indicators of seawater composition in studies involving very small periods and corresponding very slight variations of the 87Sr/86Sr ratios. Taking into account that G. bulloides is a common planktonic species (living mostly in the first 50m of the water column), whose tests seem to be in equilibrium with sea water composition, variations in its 87Sr/86Sr ratios can be related with changes in the chemical composition of the water of the Atlantic Ocean off NW Iberian Margin. The highest 87Sr/86Sr values are contemporaneous with a period of low sea level (about -140 m; Dias et al., 2000) during the LGM. According to Dias et al. (2000) at 18 ka BP the shoreline was close to the shelf break. The summital parts of the Gerês and Estrela mountains were covered by local glaciers and close to the coast freezing occurred frequently. The river catchments, which extended far to the shelf, received more rainfall due to a longer, compared to present day conditions, wet season, which promoted both physical and chemical weathering. Higher pluviosity combined with the effect of spring ice melting maintained high river discharge and consequently caused very important sediment supply to the coastal zone. The extremely narrow shelf was a very energetic environment due to sea bottom inclination and very limited long wave refraction. Therefore, at that time, a long wet season and very competent rivers should have caused important erosion of the Variscan basement in NW Iberia. Additionally, then, the shoreline was much closer to the KC 024-19 site. The combination of all these factors favoured an important deposition of terrigenous sediments and the local slight enrichment in radiogenic Sr of the seawater. With sea level rise, after the deglaciation and during the Holocene, the river estuaries became progressively far away from the shelf break. Their competence of transport also became progressively reduced and the offshore transport of detrital sediments became progressively lower. Conversely the biogenic carbonate proportion in the sediments increased, due to lower dilution by the terrigenous particles. Simultaneously, the values of 87Sr/86Sr in the seawater at the KC 024-19 site became lower, as a consequence of a complete homogenization with the ocean global composition, which was now more effective with the increasing distance towards shoreline

Tunable pseudogap Kondo effect and quantum phase transitions in Aharonov-Bohm interferometers

We study two quantum dots embedded in the arms of an Aharonov-Bohm ring threaded by a magnetic flux. The system can be described by an effective one-impurity Anderson model with an energy- and flux-dependent density of states. For specific values of the flux, this density of states vanishes at the Fermi energy, yielding a controlled realization of the pseudogap Kondo effect. The conductance and transmission phase shifts reflect a nontrivial interplay between wave interference and interactions, providing clear signatures of quantum phase transitions between Kondo and non-Kondo ground states.Comment: Published versio

Trace fossils from the Desejosa Formation (Schist and Greywacke Complex, Douro Group, NE Portugal): new Cambrian age constraints

Trace fossils from a new locality in the Desejosa Formation, Freixo de Espada à Cinta area, northeast Portugal, are described, including Teichichnus rectus and the first Cambrian record from Iberia of the ichnogenus Rosselia, identified as R. cf. socialis. A literary review of the Cambrian record of Rosselia reveals no occurrences older than Cambrian Age 3. The occurrence of Rosselia in the Desejosa Formation therefore adds evidence to that of earlier reports on trilobite remains from the upper part of the Desejosa Formation for a Cambrian age of this unit. Both Rosselia and Teichichnus are zindicative of the Cruziana ichnofacies, which is representative of a shallow-marine depositional environment, consistent with earlier interpretations for the depositional conditions of the upper part of the Desejosa Formation in this sector, and in the equivalent Cambrian units in Spain

Crimes contra o mercado de valores mobiliários

A presente dissertação tem como objetivo, a conclusão do Mestrado em Análise Financeira. O mercado de valores mobiliários tem um papel de suma importância na economia mundial. Com o advento da internet e o desenvolvimento tecnológico, as fronteiras, por onde o dinheiro transitava, deixaram de existir, o que facilita a prática de crimes contra o mercado, tornando-os mais sofisticados. Os órgãos supervisores, reguladores e fiscalizadores, assim como, a legislação dos diversos países têm que se adaptar para fazer face a esse novo cenário. Os crimes financeiros, nomeadamente, o abuso de informação e a manipulação de mercado abalam o regular funcionamento do mercado de valores mobiliários e geram a desconfiança entre os investidores. O caso do Grupo EBX, ocorrido no Brasil, ilustra o assunto muito bem, pois, enquadra-se nos dois tipos de crime financeiro. O caso ainda está a ser julgado

Hábitos Alimentares Durante a Gravidez em Mulheres com Parto Muito Pré-Termo: Uma Análise Exploradora

Introduction: Preterm birth is increasing worldwide, representing a major cause of death and long-term loss of human potential among survivors. Some morbidities during pregnancy are well-known risk factors for preterm labor, but it is not yet known whether deviations from adequate dietary patterns are associated with preterm delivery. Diet may be an important modulator of chronic inflammation, and pro-inflammatory diets during pregnancy were reported to be associated with preterm birth. The aim of this study was to assess the food consumption during pregnancy of Portuguese women giving birth very prematurely and the association between the food consumption and the major maternal morbidities during pregnancy related with preterm delivery. Material and methods: A single-center cross-sectional observational study including consecutive Portuguese women giving birth before 33 weeks of gestation was conducted. Recall of eating habits during pregnancy was obtained within the first week after delivery, using a semi quantitative food frequency questionnaire validated for Portuguese pregnant women. Results: Sixty women with a median age of 36.0 years were included. Of these, 35% were obese or overweight at the beginning of pregnancy, 41.7% and 25.0% gained excessive or insufficient weight during pregnancy, respectively. Pregnancy-induced hypertension was present in 21.7% of cases, gestational diabetes in 18.3%, chronic hypertension in 6.7%, and type 2 diabetes mellitus in 5.0%. Pregnancy-induced hypertension was significantly associated with increased daily consumption of pastry products (31.2 vs 10.0 g, p = 0.022), fast food (39.6 vs 29.7 g, p = 0.028), bread (90.0 vs 50.0 g, p = 0.005), pasta, rice and potatoes (225.7 vs 154.3 g, p = 0.012). In a multivariate analysis, only bread consumption maintained a significant, albeit weak, association (OR = 1.021; 1.003 - 1.038, p = 0.022). Conclusion: Pregnancy-induced hypertension was associated with increased consumption of pastry products, fast food, bread, pasta, rice, and potatoes, although only bread consumption had a weak but statistically significant association with pregnancy-induced hypertension in a multivariate analysis.info:eu-repo/semantics/publishedVersio

Complexity and predictability of daily precipitation in a semi-arid region: an application to Ceará, Brazil

International audienceComplexity and predictability of daily precipitation in a tropical semi-arid region (Ceará State, Brazil) is assessed by applying entropy concepts. Precipitation regimes in that region depend on several dynamical forcings, the most important being the displacement and activity of the Inter-tropical Convergence Zone in the Atlantic Ocean. Topography is another important factor that influences the spatial distribution of rainfall in the region. A hierarchical approach based on sequences of events of different lengths is used to estimate complexity of daily precipitation records. It is shown that precipitation in Ceará exhibit more random than periodic sequences, which indicates a large degree of complexity. Nevertheless, there is indication of potentially inherent rules in the precipitation time-series that could ultimately improve prediction on time-scales between 9?11 days. It is suggested that synoptic-scale disturbances (1?8 days) represent important sources of rules in the precipitation regimes in this region