Decentralized static output‐feedback H∞ controller design for buildings under seismic excitation

In this work, we present a new method in designing static output‐feedback H_∞ controllers suitable for vibrational control of buildings under seismic excitation. The method produces a Linear Matrix Inequality (LMI) formulation that allows obtaining static output‐feedback controllers with different information structure constraints by imposing a convenient zero–nonzero structure on the LMI variables. The application of the proposed methodology is illustrated by designing centralized and decentralized velocity‐feedback H_∞ controllers to mitigate the seismic response of a five‐story building. Copyright © 2011 John Wiley & Sons, Ltd.     

U–Pb zircon and 40Ar–39Ar K-feldspar dating of syn-sedimentary volcanism of the Neoproterozoic Maricá Formation: constraining the age of foreland basin inception and inversion in the Camaquã Basin of southern Brazil

New U–Pb zircon and ⁴⁰Ar–³⁹Ar K-feldspar data are presented for syn-sedimentary volcanogenic rocks from the Neoproterozoic Maricá Formation, located in the southern Brazilian shield. Seven (of nine) U–Pb sensitive high-resolution ion microprobe analyses of zircons from pyroclastic cobbles yield an age of 630.2±3.4 Ma (2σ), interpreted as the age of syn-sedimentary volcanism, and thus of the deposition itself. This result indicates that the Maricá Formation was deposited during the main collisional phase (640–620 Ma) of the Brasiliano II orogenic system, probably as a forebulge or back-bulge, craton-derived foreland succession. Thus, this unit is possibly correlative of younger portions of the Porongos, Brusque, Passo Feio, Abapã (Itaiacoca) and Lavalleja (Fuente del Puma) metamorphic complexes. Well-defined, step-heating ⁴⁰Ar–³⁹Ar K-feldspar plateau ages obtained from volcanogenic beds and pyroclastic cobbles of the lower and upper successions of the Maricá Formation yielded 507.3±1.8 Ma and 506.7±1.4 Ma (2σ), respectively. These data are interpreted to reflect total isotopic resetting during deep burial and thermal effects related to magmatic events. Late Middle Cambrian cooling below ca . 200 °C, probably related to uplift, is tentatively associated with intraplate effects of the Rio Doce and/or Pampean orogenies (Brasiliano III system). In the southern Brazilian shield, these intraplate stresses are possibly related to the dominantly extensional opening of a rift or a pull-apart basin, where sedimentary rocks of the Camaquã Group (Santa Bárbara and Guaritas Formations) accumulated.     

Effects of conspecifics on settling juveniles of the invasive golden mussel, Limnoperna fortunei

We conducted a field experiment to assess the influence of conspecific adults on recruitment success of the golden mussel Limnoperna fortunei. Tiles, 225 cm² surface area, were used as artificial substrates in four treatments: control (blank tiles), low (800 mussels m⁻²), medium (4,000 mussels m⁻²) and high (12,000 mussels m⁻²) density treatments. Results indicated that recruitment was strongly affected by the presence and density of conspecifics. After one and 3 months of exposure, numbers of recruits were significantly higher on tiles with conspecific adults than on blank tiles, and there was a positive and significant relationship between the number of recruits and the number of adults in the three treatments assayed. Also, after 3 months of exposure, recruits in all treatments with adults present were larger than recruits in the control treatment. Our results suggest that conspecific adults have a positive effect on recruitment success and growth of newly settled juveniles through factors that enhance larval settling or that contribute to the survival of settlers in areas colonized by adult conspecifics.     

Effect of coastal waves on sea level in Óbidos Lagoon,Portugal

This study reports the role of waves, tide, wind and freshwater discharges over the sea level in Óbidos Lagoon, a coastal system connected to the sea through a narrow and shallow mobile inlet. To address the hydrodynamic features of this coastal system, the relative importance of different physical forcings were evaluated. For this purpose, observations together with realistic and idealized numerical modeling were used. Both model and measurements show that the lagoon sea level remains above offshore sea level during storm wave periods. Hence, a simplified inlet-lagoon idealized model was described through mathematical expressions, to understand and highlight the physical processes responsible for sea-level elevation.     

Holocene evolution of a rock‐bounded barrier‐lagoon system,Cíes Islands,northwest Iberia

Coastal geomorphology results from the combined effects of contemporary dynamics, sea‐level rise and the inherited geological framework, yet the relative importance of these driving mechanisms may change throughout the evolutionary history of coastal deposits. In this contribution, we analyse the depositional history of the Cíes Islands barrier‐lagoon system, based on lithofacies, radiocarbon ages, and pollen analysis. Our results reveal a sedimentary sequence that provides evidence for striking changes in the dynamical functioning of this complex since the mid‐Holocene. The sedimentary sequence commenced about 7700 cal years bp by fresh‐water ponding of an upland depression located about 4 m below present mean sea‐level. Fresh‐water ponds were infilled by aeolian sediments following a gradual lowering of the water‐table 4000 cal years bp . Post‐3600 cal years bp sea‐level rise allowed water oscillations to reach the elevation of the bedrock causing the inundation of fresh‐water ponds and subsequent lagoonal and marine sedimentation. Subsequently, landward and upward migration of a sand‐barrier led to overwash and deposition of sand in the newly formed lagoon. The resultant sedimentary sequence suggests that climatic conditions played an important role controlling the sedimentation regime during the entire history of the basin; changing water‐table levels during early stages of evolution and increasing storminess during more recent times. In addition, background sea‐level rise related to the Holocene transgression was a key factor in controlling the evolution of the system, yet its influence depended to an extent on the relative elevation of the bedrock topography. Copyright © 2009 John Wiley & Sons, Ltd.     

Attenuation from microseismic datasets by the peak frequency method benchmarked with the spectral ratio method

Recently proposed peak-frequency method is used to estimate the P- and S-wave quality factors from microseismic events. We use a downhole monitoring dataset of 10 high signal-to-noise ratio microseismic events to calculate P- and S-wave effective attenuation of a carbonate reservoir. We benchmark these results with the spectral ratio method and obtain mutually consistent results. Additionally we develop and test two techniques of peak frequency determination. We show that the peak frequency method can be successfully used in the estimation of the quality factor and it provides precise measurements of attenuation.     

Magnetic Signatures and Curie Surface Trend Across an Arc–Continent Collision Zone: An Example from Central Philippines

Ground and aeromagnetic data are combined to characterize the onshore and offshore magnetic properties of the central Philippines, whose tectonic setting is complicated by opposing subduction zones, large-scale strike-slip faulting and arc–continent collision. The striking difference between the magnetic signatures of the islands with established continental affinity and those of the islands belonging to the island arc terrane is observed. Negative magnetic anomalies are registered over the continental terrane, while positive magnetic anomalies are observed over the Philippine Mobile Belt. Several linear features in the magnetic anomaly map coincide with the trace of the Philippine Fault and its splays. Power spectral analysis of the magnetic data reveals that the Curie depth across the central Philippines varies. The deepest point of the magnetic crust is beneath Mindoro Island at 32 km. The Curie surface shallows toward the east: the Curie surface is 21 km deep between the islands of Sibuyan and Masbate, and 18 km deep at the junction of Buruanga Peninsula and Panay Island. The shallowest Curie surface (18 km) coincides with the boundary of the arc–continent collision, signifying the obduction of mantle rocks over the continental basement. Comparison of the calculated Curie depth with recent crustal thickness models reveals the same eastwards thinning trend and range of depths. The coincidence of the magnetic boundary and the density boundary may support the existence of a compositional boundary that reflects the crust–mantle interface.