14,723 research outputs found
A thorough analysis of the short- and mid-term activity-related variations in the solar acoustic frequencies
The frequencies of the solar acoustic oscillations vary over the activity
cycle. The variations in other activity proxies are found to be well correlated
with the variations in the acoustic frequencies. However, each proxy has a
slightly different time behaviour. Our goal is to characterize the differences
between the time behaviour of the frequency shifts and of two other activity
proxies, namely, the area covered by sunspots and the 10.7cm flux. We define a
new observable that is particularly sensitive to the short-term frequency
variations. We then compare the observable when computed from model frequency
shifts and from observed frequency shifts obtained with the Global Oscillation
Network Group (GONG) for cycle 23. Our analysis shows that on the shortest
time-scales the variations in the frequency shifts seen in the GONG
observations are strongly correlated with the variations in the area covered by
sunspots. However, a significant loss of correlation is still found. We verify
that the times when the frequency shifts and the sunspot area do not vary in a
similar way tend to coincide with the times of the maxima of the quasi-biennial
variations seen in the solar seismic data. A similar analysis of the relation
between the 10.7cm flux and the frequency shifts reveals that the short-time
variations in the frequency shifts follow even more closely those of the 10.7cm
flux than those of the sunspot area. However, a loss of correlation between
frequency shifts and 10.7cm flux variations is still found around the same
times.Comment: 7 pages, 6 figures, accepted for publication in MNRA
On the relation between activity-related frequency shifts and the sunspot distribution over the solar cycle 23
The activity-related variations in the solar acoustic frequencies have been
known for 30 years. However, the importance of the different contributions is
still not well established. With this in mind, we developed an empirical model
to estimate the spot-induced frequency shifts, which takes into account the
sunspot properties, such as area and latitude. The comparison between the model
frequency shifts obtained from the daily sunspot records and those observed
suggests that the contribution from a stochastic component to the total
frequency shifts is about 30%. The remaining 70% is related to a global,
long-term variation. We also propose a new observable to investigate the short-
and mid-term variations of the frequency shifts, which is insensitive to the
long-term variations contained in the data. On the shortest time scales the
variations in the frequency shifts are strongly correlated with the variations
in the total area covered by sunspots. However, a significant loss of
correlation is still found, which cannot be fully explained by ignoring the
invisible side of the Sun when accounting for the total sunspot area. We also
verify that the times when the frequency shifts and the sunspot areas do not
vary in a similar way tend to coincide with the times of the maximum amplitude
of the quasi-biennial variations found in the seismic data.Comment: 4 pages, 2 figures, proceedings of the Joint TASC2 - KASC9 Workshop -
SPACEINN - HELAS8 Conference "Seismology of the Sun and the Distant Stars
2016: Using Today's Successes to Prepare the Future". To be published by the
EPJ Web of Conference
The sedimentary geology of the “Serras d’Aire e Candeeiros” natural park (Portugal) : importance of the geological heritage
The main goal of this work is to contribute to the conservation and interpretation of the geological heritage of the Serras de Aires e Candeeiros Natural Park. The selection of the most relevant geosites took into account criteria of representation, exception, scientific importance, didactic clarity, accessibility, and exposure conditions
Influência da deformação cíclica de solos de fundação no desempenho de uma via-férrea de alta velocidade
É apresentada uma revisão teórica de alguns trabalhos anteriormente desenvolvidos
na definição das características de deformabilidade de solos sujeitos a carregamentos cíclicos.
Em função destas características foram definidas análises paramétricas para o estudo da influência do nível de deformação cíclica do solo de fundação no comportamento de uma viaférrea
de alta velocidade sujeita á passagem de um comboio Thalys a 314 km/h. Para o efeito
utilizaram-se modelos numéricos em estado plano de deformação.
Apresentam-se e discutem-se os resultados obtidos através destas análises.Fundação para a Ciência e a Tecnologia (FCT) - Projecto POCI/ECM/61114/2004
Tracking the relationship between euro area equities and sovereign bonds
This paper explores the relationship between stocks and sovereign bonds by means of the asymmetric detrended cross-correlation analysis (ADCCA). Drawing on data from 1999.01 to 2018.09 of the first wave of euro area countries, the full sample is divided into three subsets in accordance with economic and financial features. Some findings arise with striking implications for investors and policymakers. Firstly, empirical results show that cross-correlations differ from country to country, depending on the sub-period under analysis and on the time scale. Secondly, likewise within country estimates, cross-country linkages may point to fragmentation in the euro area with agents moving away from financial assets of lower-rated countries to invest in more robust economies in periods of turmoil. Thirdly, there is evidence of asymmetry since 'flight-to-quality' movements seem to be more relevant than 'flight-to-yield' episodes. Finally, while relationships were globally bidirectional until mid-2007, new causality patterns arose with the financial crisis.info:eu-repo/semantics/publishedVersio
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