Percorrer por autor "Cunha, T."
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- Combined experimental and theoretical studies on electron transfer in potassium collisions with CCl4Publication . Regeta, K.; Kumar, S.; Cunha, T.; Mendes, Mónica; Lozano Martínez, Ana Isabel; Pereira, Pedro; Garcia, G.; Moutinho, A. M. C.; Bacchus-Montabonel, Marie-Christine; LIMAO-VIEIRA, PNegative ion formation in electron transfer experiments from fast neutral potassium (K) atom collisions with neutral tetrachloromethane (CCl4) molecules has been investigated in the laboratory frame range of 8-1000 eV. Comprehensive calculations on the electronic structure were performed for CCl4 in the presence of a potassium atom and used to help analyze the lowest unoccupied molecular orbitals participating in the collision process. Additionally, K+ energy loss produced in the forward direction has served to further our knowledge on the electronic state spectroscopy of CCl4. A vertical electron affinity of -0.79 +/- 0.20 eV has been obtained and assigned to a purely repulsive transition from CCl4 ground state to the(2)T(2) state of the temporary negative ion yielding Cl- formation. Other features in the energy loss spectrum were observed for the first time and related to Cl-2(-), CCl2-, and CCl3- formation. Special attention is also given to the unresolved feature corresponding to a positive electron affinity of 0.24 +/- 0.2 eV, assigned to a vibrationally hot transition from CCl4 ground state into the triply degenerate T-2(2) excited state of the negative ion. The combined time-of-flight mass spectrometry together with K+ energy loss data represents the most comprehensive assignment of the tetrachloromethane anion yields and the role of CCl4 electronic states in collision induced dissociation to date.
- Energy savings in 3G using dynamic spectrum access and base station sleep modesPublication . Cunha, T.; Rodrigues, A.; Vieira, Pedro; Martins, A.; Silva, N.; Varela, L.The energy consumption and energy efficiency of mobile telecommunication networks are crucial factors for the sustainability of this industry. This paper targets the reduction of the energy consumption at a Base Station (BS) level through the adoption of sleep modes during the off-peak periods of the day and relying in the existence of co-located and overlaid frequency bands to provide the coverage and capacity backup for the switched-off cells. It relies on the Dynamic Spectrum Allocation (DSA) method to opportunely relocate users during the low-load periods while maintaining the service quality of service (QoS). For the input data, real traffic statistics were used. Using this strategy and the proposed algorithm it was possible to achieve savings of about 43% per-site. The results were furthered to the study of a Portuguese mobile operator case and it was concluded that savings of more than 1.25 million euros were easily achieved.
- Tsunamigenic earthquakes in the Gulf of Cadiz: fault model and recurrencePublication . Matias, L. M.; Cunha, T.; Annunziato, A.; Baptista, Maria Ana Carvalho Viana; Carrilho, F.The Gulf of Cadiz, as part of the Azores-Gibraltar plate boundary, is recognized as a potential source of big earthquakes and tsunamis that may affect the bordering countries, as occurred on 1 November 1755. Preparing for the future, Portugal is establishing a national tsunami warning system in which the threat caused by any large-magnitude earthquake in the area is estimated from a comprehensive database of scenarios. In this paper we summarize the knowledge about the active tectonics in the Gulf of Cadiz and integrate the available seismological information in order to propose the generation model of destructive tsunamis to be applied in tsunami warnings. The fault model derived is then used to estimate the recurrence of large earthquakes using the fault slip rates obtained by Cunha et al. (2012) from thin-sheet neotectonic modelling. Finally we evaluate the consistency of seismicity rates derived from historical and instrumental catalogues with the convergence rates between Eurasia and Nubia given by plate kinematic models.