Correlation studies on an RC frame shaking-table specimen

This paper presents the correlation of the results of a new model for the dynamic analysis of reinforced concrete (RC) frames with the experimental time history of a two storey RC frame shaking-table specimen. The frame member model consists of separate subelements that describe the deformations due to flexure, shear and bond slip in RC structural elements. The subelements are combined by superposition of flexibility matrices to form the frame element. A non-linear solution method which accounts for the unbalance of internal forces between different subelements during a given load increment is used with the model. The ability of the proposed model to describe the dynamic response of frame structures under earthquake excitations is evaluated by comparing the analytical results with experimental evidence from a two-storey, one bay reinforced concrete frame tested on the shaking-table. The model parameters for the shaking-table specimen are derived from available experimental evidence and first principles of reinforced concrete. The effect of reinforcing bar slip on the local and global dynamic response of the test structure is assessed. © 1997 John Wiley & Sons, Ltd.     

Comparing the performances of four stochastic optimisation methods using analytic objective functions, 1D elastic full‐waveform inversion,and residual static computation

We compare the performances of four stochastic optimisation methods using four analytic objective functions and two highly non‐linear geophysical optimisation problems: one‐dimensional elastic full‐waveform inversion and residual static computation. The four methods we consider, namely, adaptive simulated annealing, genetic algorithm, neighbourhood algorithm, and particle swarm optimisation, are frequently employed for solving geophysical inverse problems. Because geophysical optimisations typically involve many unknown model parameters, we are particularly interested in comparing the performances of these stochastic methods as the number of unknown parameters increases. The four analytic functions we choose simulate common types of objective functions encountered in solving geophysical optimisations: a convex function, two multi‐minima functions that differ in the distribution of minima, and a nearly flat function. Similar to the analytic tests, the two seismic optimisation problems we analyse are characterised by very different objective functions. The first problem is a one‐dimensional elastic full‐waveform inversion, which is strongly ill‐conditioned and exhibits a nearly flat objective function, with a valley of minima extended along the density direction. The second problem is the residual static computation, which is characterised by a multi‐minima objective function produced by the so‐called cycle‐skipping phenomenon. According to the tests on the analytic functions and on the seismic data, genetic algorithm generally displays the best scaling with the number of parameters. It encounters problems only in the case of irregular distribution of minima, that is, when the global minimum is at the border of the search space and a number of important local minima are distant from the global minimum. The adaptive simulated annealing method is often the best‐performing method for low‐dimensional model spaces, but its performance worsens as the number of unknowns increases. The particle swarm optimisation is effective in finding the global minimum in the case of low‐dimensional model spaces with few local minima or in the case of a narrow flat valley. Finally, the neighbourhood algorithm method is competitive with the other methods only for low‐dimensional model spaces; its performance sensibly worsens in the case of multi‐minima objective functions.     

Chemical defenses against generalist fish predators and fouling organisms in two invasive ahermatypic corals in the genus Tubastraea

The introduction of exotic marine species has caused considerable economic and ecological damage around the world. Some of these species possess adaptations such as secondary metabolites which facilitate their successful invasion into new areas. In this study we tested two hypotheses: (i) crude extracts produced by two invasive hard corals Tubastraea coccinea and Tubastraea tagusensis, introduced to the southwest Atlantic, inhibit predation by generalist fish; (ii) substances found in the crude extracts of both species reduce or enhance the settlement of other organisms. In an in situ palatability bioassay the extract of T. tagusensis reduced predation by generalist fish. The extracts of both species of coral showed species‐specific effects on fouling organisms in in situ gel plate bioassays. Control and extract plates had similar total cover, although plates with extracts had significantly fewer Cladophora sp., and Lithophyllum sp. was only detected on control gels. In contrast, a hydrozoan was only found on plates with extracts and overall community ordination demonstrated clear differences in the fouling communities between treatments. These results demonstrate that both coral species have chemical substances which can bring about a negative interaction with potential fish predators and competitors such as algal and invertebrate foulers and the advantage gained could explain their success in invading new regions to the detriment of local fauna and flora.     

Seismic markers of the Messinian salinity crisis in the deep Ionian Basin

We conduct the seismic signal analysis on vintage and recently collected multichannel seismic reflection profiles from the Ionian Basin to characterize the deep basin Messinian evaporites. These evaporites were deposited in deep and marginal Mediterranean sedimentary basins as a consequence of the “salinity crisis” between 5.97 and 5.33 Ma, a basin-wide oceanographic and ecological crisis whose origin remains poorly understood. The seismic markers of the Messinian evaporites in the deep Mediterranean basins can be divided in two end-members, one of which is the typical “trilogy” of gypsum and clastics (Lower Unit – LU), halite (Mobile Unit – MU) and upper anhydrite and marl layers (Upper Unit – UU) traced in the Western Mediterranean Basins. The other end-member is a single MU unit subdivided in seven sub-units by clastic interlayers located in the Levant Basin. The causes of these different seismic expressions of the Messinian salinity crisis (MSC) appear to be related to a morphological separation between the two basins by the structural regional sill of the Sicily Channel. With the aid of velocity analyses and seismic imaging via prestack migration in time and depth domains, we define for the first time the seismic signature of the Messinian evaporites in the deep Ionian Basin, which differs from the known end-members. In addition, we identify different evaporitic depositional settings suggesting a laterally discontinuous deposition. With the information gathered we quantify the volume of evaporitic deposits in the deep Ionian Basin as 500,000 km³ ± 10%. This figure allows us to speculate that the total volume of salts in the Mediterranean basin is larger than commonly assumed. Different depositional units in the Ionian Basin suggest that during the MSC it was separated from the Western Mediterranean by physical thresholds, from the Po Plain/Northern Adriatic Basin, and the Levant Basin, likely reflecting different hydrological and climatic conditions. Finally, the evidence of erosional surfaces and V-shaped valleys at the top of the MSC unit, together with sharp evaporites pinch out on evaporite-free pre-Messinian structural highs, suggest an extreme Messinian Stage 3 base level draw down in the Ionian Basin. Such evidence should be carefully evaluated in the light of Messinian and post-Messinian vertical crustal movements in the area. The results of this study demonstrates the importance of extracting from seismic data the Messinian paleotopography, the paleomorphology and the detailed stratal architecture in the in order to advance in the understanding of the deep basins Messinian depositional environments.     

A map-matching algorithm dealing with sparse cellular fingerprint observations

ABSTRACT

The widespread availability of mobile communication makes mobile devices a resource for the collection of data about mobile infrastructures and user mobility. In these contexts, the problem of reconstructing the most likely trajectory of a device on the road network on the basis of the sequence of observed locations (map-matching problem) turns out to be particularly relevant. Different contributions have demonstrated that the reconstruction of the trajectory of a device with good accuracy is technically feasible even when only a sparse set of GNSS positions is available. In this paper, we face the problem of coping with sparse sequences of cellular fingerprints. Compared to GNSS positions, cellular fingerprints provide coarser spatial information, but they work even when a device is missing GNSS positions or is operating in an energy saving mode. We devise a new map-matching algorithm, that exploits the well-known Hidden Markov Model and Random Forests to successfully deal with noisy and sparse cellular observations. The performance of the proposed solution has been tested over a medium-sized Italian city urban environment by varying both the sampling of the observations and the density of the fingerprint map as well as by including some GPS positions into the sequence of fingerprint observations.     

Pelagic primary production in the Algero-Provençal Basin by means of multisensor satellite data: focus on interannual variability and its drivers

In this work, we make use of satellite estimates of chlorophyll a, photosynthetically active radiation and sea surface temperatures, to compute regional estimates of primary production integrated throughout the euphotic layer for the Algero-Provençal Basin, by means of a modified version of the vertically generalized production model. The seasonal and interannual variability of the primary production has been analysed over the decade 1997–2007. Empirical orthogonal functions analysis has been applied to decompose the variability of the primary production dataset in orthogonal modes of variability. The seasonal signal is distributed between the two first modes of variability, temporally shifted each other and respectively related to the northern (early spring) and the southern (winter) part of the basin. We found a minimum of the annual production in 2003, when a summer heatwave strongly enhanced the stratification of surface waters, further limiting the injection of nutrients into the surface layers. Maxima in the annual series are found in 1999 and 2005, due to two particularly intense and extended (in space) spring-blooms in the northern part of the basin. These two maxima, clearly identified in space and time by EOF analysis (EOF1 and EOF3), are related to strong mistral-wind interannual events occurring during winters of 1999 and 2005, preceding the blooms by some few months. We found that these production maxima are due both to a more intense production in the usual blooming area (shown by EOF1–PC1) as well as to an exceptional local production in the eastern side of the basin, off the Corsica western coasts (EOF3–PC3). Previous observations of exceptional deep-water formation events in 1999 and 2005, with easterly spots close to the primary production-observed anomalies, and the meridional character of the mistral 1999 and 2005 peaks both support the idea that such eastern PP interannual maxima would be actually due to exceptional production more than to an easterly advection of biomass from the usual bloom area. Finally, the potential link of the observed features with large-scale atmospheric forcing is discussed, and a potential relation of such interannual events with the East Atlantic pattern is drawn.     

High precision tilt observation at Mt. Etna Volcano,Italy

In 2007–2008, we installed on Mt. Etna two deep tilt stations using high resolution, self-leveling instruments. These installations are a result of accurate instrument tests, site selection, drilling and sensor positioning that has allowed detecting variations related to the principal diurnal and semidiurnal tides for first time on Mt. Etna using tilt data.     

Deglaciation of the western margin of the Barents Sea Ice Sheet — A swath bathymetric and sub-bottom seismic study from the Kveithola Trough

Kveithola Trough, an E–W trending glacial trough in the NW Barents Sea, was surveyed for the first time during the EGLACOM cruise of R/V OGS-Explora in summer 2008. Swath bathymetry shows that the seafloor is characterized by E–W trending mega-scale glacial lineations (MSGL) that record a fast flowing ice stream draining the Svalbard/Barents Sea Ice Sheet (SBIS) during the Last Glacial Maximum (LGM). MSGL are overprinted by transverse sediment ridges about 15 km apart which give rise to a staircase axial profile of the trough. Such transverse ridges are interpreted to be grounding-zone wedges (GZWs) formed by deposition of subglacial till during episodic ice stream retreat. Sub-bottom (CHIRP) and multi-channel reflection seismic data show that the present-day morphology is largely inherited from the palaeo-seafloor topography at the time of deposition of the transverse ridges, overlain by a draping glaciomarine unit which in places is over 15 m thick. Our data allow the reconstruction of depositional processes which accompanied deglaciation of the Spitsbergen Bank area. The sedimentary drape deposited on top of the GZWs is suggested to have accumulated at a very high rate, (on average in the order of 1–1.5 m ka^?1) and therefore may potentially preserve a high-resolution palaeoclimatic record of deglaciation and post-glacial conditions in this sector of the Barents Sea.