Studio di fenomeni d'instabilità gravitativa sui fondali marini, con particolare riferimento all'isola di Stromboli

In the last decade the interest for submarine instability grew up, driven by the increasing exploitation of natural resources (primary hydrocarbons), the emplacement of bottom-lying structures (cables and pipelines) and by the development of coastal areas, whose infrastructures increasingly protrude to the sea. The great interest for this topic promoted a number of international projects such as: STEAM (Sediment Transport on European Atlantic Margins, 93-96), ENAM II (European North Atlantic Margin, 96-99), GITEC (Genesis and Impact of Tsunamis on the European Coast 92-95), STRATAFORM (STRATA FORmation on Margins, 95-01), Seabed Slope Process in Deep Water Continental Margin (Northwest Gulf of Mexico, 96-04), COSTA (Continental slope Stability, 00-05), EUROMARGINS (Slope Stability on Europe’s Passive Continental Margin), SPACOMA (04-07), EUROSTRATAFORM (European Margin Strata Formation), NGI's internal project SIP-8 (Offshore Geohazards), IGCP-511: Submarine Mass Movements and Their Consequences (05-09) and projects indirectly related to instability processes, such as TRANSFER (Tsunami Risk ANd Strategies For the European region, 06-09) or NEAREST (integrated observations from NEAR shore sourcES of Tsunamis: towards an early warning system, 06-09). In Italy, apart from a national project realized within the activities of the National Group of Volcanology during the framework 2000-2003 “Conoscenza delle parti sommerse dei vulcani italiani e valutazione del potenziale rischio vulcanico”, the study of submarine mass-movement has been underestimated until the occurrence of the landslide-tsunami events that affected Stromboli on December 30, 2002. This event made the Italian Institutions and the scientific community more aware of the hazard related to submarine landslides, mainly in light of the growing anthropization of coastal sectors, that increases the vulnerability of these areas to the consequences of such processes. In this regard, two important national projects have been recently funded in order to study coastal instabilities (PRIN 24, 06-08) and to map the main submarine hazard features on continental shelves and upper slopes around the most part of Italian coast (MaGIC Project). The study realized in this Thesis is addressed to the understanding of these processes, with particular reference to Stromboli submerged flanks. These latter represent a natural laboratory in this regard, as several kind of instability phenomena are present on the submerged flanks, affecting about 90% of the entire submerged areal and often (strongly) influencing the morphological evolution of subaerial slopes, as witnessed by the event occurred on 30 December 2002. Furthermore, each phenomenon is characterized by different pre-failure, failure and post-failure mechanisms, ranging from rock-falls, to turbidity currents up to catastrophic sector collapses. The Thesis is divided into three introductive chapters, regarding a brief review of submarine instability phenomena and related hazard (cap. 1), a “bird’s-eye” view on methodologies and available dataset (cap. 2) and a short introduction on the evolution and the morpho-structural setting of the Stromboli edifice (cap. 3). This latter seems to play a major role in the development of largescale sector collapses at Stromboli, as they occurred perpendicular to the orientation of the main volcanic rift axis (oriented in NE-SW direction). The characterization of these events and their relationships with successive erosive-depositional processes represents the main focus of cap.4 (Offshore evidence of large-scale lateral collapses on the eastern flank of Stromboli, Italy, due to structurally-controlled, bilateral flank instability) and cap. 5 (Lateral collapses and active sedimentary processes on the North-western flank of Stromboli Volcano), represented by articles accepted for publication on international papers (Marine Geology). Moreover, these studies highlight the hazard related to these catastrophic events; several calamities (with more than 40000 casualties only in the last two century) have been, in fact, the direct or indirect result of landslides affecting volcanic flanks, as observed at Oshima-Oshima (1741) and Unzen Volcano (1792) in Japan (Satake&Kato, 2001; Brantley&Scott, 1993), Krakatau (1883) in Indonesia (Self&Rampino, 1981), Ritter Island (1888), Sissano in Papua New Guinea (Ward& Day, 2003; Johnson, 1987; Tappin et al., 2001) and Mt St. Augustine (1883) in Alaska (Beget& Kienle, 1992). Flank landslide are also recognized as the most important and efficient mass-wasting process on volcanoes, contributing to the development of the edifices by widening their base and to the growth of a volcaniclastic apron at the foot of a volcano; a number of small and medium-scale erosive processes are also responsible for the carving of Stromboli submarine flanks and the transport of debris towards the deeper areas. The characterization of features associated to these processes is the main focus of cap. 6; it is also important to highlight that some small-scale events are able to create damage to coastal areas, as also witnessed by recent events of Gioia Tauro 1978, Nizza, 1979 and Stromboli 2002. The hazard potential related to these phenomena is, in fact, very high, as they commonly occur at higher frequency with respect to large-scale collapses, therefore being more significant in terms of human timescales. In the last chapter (cap. 7), a brief review and discussion of instability processes identified on Stromboli submerged flanks is presented; they are also compared with respect to analogous processes recognized in other submerged areas in order to shed lights on the main factors involved in their development. Finally, some applications of multibeam data to assess the hazard related to these phenomena are also discussed.

In-situ and real time scanning probe microscopy of organic ultra thin films

In recent decades, Organic Thin Film Transistors (OTFTs) have attracted lots of interest due to their low cost, large area and flexible properties which have brought them to be considered the building blocks of the future organic electronics. Experimentally, devices based on the same organic material deposited in different ways, i.e. by varying the deposition rate of the molecules, show different electrical performance. As predicted theoretically, this is due to the speed and rate by which charge carriers can be transported by hopping in organic thin films, transport that depends on the molecular arrangement of the molecules. This strongly suggests a correlation between the morphology of the organic semiconductor and the performance of the OTFT and hence motivated us to carry out an in-situ real time SPM study of organic semiconductor growth as an almost unprecedent experiment with the aim to fully describe the morphological evolution of the ultra-thin film and find the relevant morphological parameters affecting the OTFT electrical response. For the case of 6T on silicon oxide, we have shown that the growth mechanism is 2D+3D, with a roughening transition at the third layer and a rapid roughening. Relevant morphological parameters have been extracted by the AFM images. We also developed an original mathematical model to estimate theoretically and more accurately than before, the capacitance of an EFM tip in front of a metallic substrate. Finally, we obtained Ultra High Vacuum (UHV) AFM images of 6T at lying molecules layer both on silicon oxide and on top of 6T islands. Moreover, we performed ex-situ AFM imaging on a bilayer film composed of pentacene (a p-type semiconductor) and C60 (an n-type semiconductor).

The VIMOS-VLT Deep Survey: the evolution of type-1 AGN

Quasars and AGN play an important role in many aspects of the modern cosmology. Of particular interest is the issue of the interplay between AGN activity and formation and evolution of galaxies and structures. Studies on nearby galaxies revealed that most (and possibly all) galaxy nuclei contain a super-massive black hole (SMBH) and that between a third and half of them are showing some evidence of activity (Kormendy and Richstone, 1995). The discovery of a tight relation between black holes mass and velocity dispersion of their host galaxy suggests that the evolution of the growth of SMBH and their host galaxy are linked together. In this context, studying the evolution of AGN, through the luminosity function (LF), is fundamental to constrain the theories of galaxy and SMBH formation and evolution. Recently, many theories have been developed to describe physical processes possibly responsible of a common formation scenario for galaxies and their central black hole (Volonteri et al., 2003; Springel et al., 2005a; Vittorini et al., 2005; Hopkins et al., 2006a) and an increasing number of observations in different bands are focused on collecting larger and larger quasar samples. Many issues remain however not yet fully understood. In the context of the VVDS (VIMOS-VLT Deep Survey), we collected and studied an unbiased sample of spectroscopically selected faint type-1 AGN with a unique and straightforward selection function. Indeed, the VVDS is a large, purely magnitude limited spectroscopic survey of faint objects, free of any morphological and/or color preselection. We studied the statistical properties of this sample and its evolution up to redshift z 4. Because of the contamination of the AGN light by their host galaxies at the faint magnitudes explored by our sample, we observed that a significant fraction of AGN in our sample would be missed by the UV excess and morphological criteria usually adopted for the pre-selection of optical QSO candidates. If not properly taken into account, this failure in selecting particular sub-classes of AGN could, in principle, affect some of the conclusions drawn from samples of AGN based on these selection criteria. The absence of any pre-selection in the VVDS leads us to have a very complete sample of AGN, including also objects with unusual colors and continuum shape. The VVDS AGN sample shows in fact redder colors than those expected by comparing it, for example, with the color track derived from the SDSS composite spectrum. In particular, the faintest objects have on average redder colors than the brightest ones. This can be attributed to both a large fraction of dust-reddened objects and a significant contamination from the host galaxy. We have tested these possibilities by examining the global spectral energy distribution of each object using, in addition to the U, B, V, R and I-band magnitudes, also the UV-Galex and the IR-Spitzer bands, and fitting it with a combination of AGN and galaxy emission, allowing also for the possibility of extinction of the AGN flux. We found that for 44% of our objects the contamination from the host galaxy is not negligible and this fraction decreases to 21% if we restrict the analysis to a bright subsample (M1450 <-22.15). Our estimated integral surface density at IAB < 24.0 is 500 AGN per square degree, which represents the highest surface density of a spectroscopically confirmed sample of optically selected AGN. We derived the luminosity function in B-band for 1.0 < z < 3.6 using the 1/Vmax estimator. Our data, more than one magnitude fainter than previous optical surveys, allow us to constrain the faint part of the luminosity function up to high redshift. A comparison of our data with the 2dF sample at low redshift (1 < z < 2.1) shows that the VDDS data can not be well fitted with the pure luminosity evolution (PLE) models derived by previous optically selected samples. Qualitatively, this appears to be due to the fact that our data suggest the presence of an excess of faint objects at low redshift (1.0 < z < 1.5) with respect to these models. By combining our faint VVDS sample with the large sample of bright AGN extracted from the SDSS DR3 (Richards et al., 2006b) and testing a number of different evolutionary models, we find that the model which better represents the combined luminosity functions, over a wide range of redshift and luminosity, is a luminosity dependent density evolution (LDDE) model, similar to those derived from the major Xsurveys. Such a parameterization allows the redshift of the AGN density peak to change as a function of luminosity, thus fitting the excess of faint AGN that we find at 1.0 < z < 1.5. On the basis of this model we find, for the first time from the analysis of optically selected samples, that the peak of the AGN space density shifts significantly towards lower redshift going to lower luminosity objects. The position of this peak moves from z 2.0 for MB <-26.0 to z 0.65 for -22< MB <-20. This result, already found in a number of X-ray selected samples of AGN, is consistent with a scenario of “AGN cosmic downsizing”, in which the density of more luminous AGN, possibly associated to more massive black holes, peaks earlier in the history of the Universe (i.e. at higher redshift), than that of low luminosity ones, which reaches its maximum later (i.e. at lower redshift). This behavior has since long been claimed to be present in elliptical galaxies and it is not easy to reproduce it in the hierarchical cosmogonic scenario, where more massive Dark Matter Halos (DMH) form on average later by merging of less massive halos.

Diencephalic asymmetries: morphological, immunohistochemical and ultrastructural analysis of habenular nuclei in elasmobranchs and teleosts

The habenular nuclei are diencephalic structures present in Vertebrates and they form, with the associated fiber systems, a part of the system that connects the telencephalon to the ventral mesencephalon (Concha M. L. and Wilson S. W., 2001). In representative species of almost all classes of Vertebrates the habenular nuclei are asymmetric, both in terms of size and of neuronal and neurochemical organization, although different types of asymmetry follow different evolutionary courses. Previous studies have analyzed the spread and diversity of the asymmetry in species for which data are not clear (Kemali M. et al., 1980). Notwithstanding that, it’s still not totally understood the evolution of the phenomenon, and the ontogenetic mechanisms that have led to the habenular asymmetry development are not clear (Smeets W.J. et al., 1983). For the present study 14 species of Elasmobranchs and 15 species of Teleostean have been used. Brains removed from the animals have been fixed using 4% paraformaldehyde in phosphate buffer; brains have been analyzed with different tecniques, and I used histological, immunohistochemical and ultrastructural analysis to describe this asymmetry. My results confirm data previously obtained studying other Elasmobranchs species, in which the left habenula is larger than the right one; the Teleostean show some slightly differences regarding the size of the habenular ganglia, in some species, in which the left habenular nucleus is larger than the right. In the course of studies, a correlation between the habits of life and the diencephalic asymmetry seems to emerge: among the Teleostean analyzed, the species with benthic life (like Lepidorhombus boscii, Platichthys flesus, Solea vulgaris) seem to possess a slight asymmetry, analogous to the one of the Elasmobranchs, while in the other species (like Liza aurata, Anguilla anguilla, Trisopterus minutus) the habenulae are symmetrical. However, various aspects of the neuroanatomical asymmetries of the epithalamus have not been deepened in order to obtain a complete picture of the evolution of this phenomenon, and new searches are needed to examine the species without clear asymmetry, in order to understand the spread and the diversity of the asymmetry among the habenulae between the Vertebrates.

Mediterranean brachiopods: morphological, ecological and phylogenetic aspects

The Brachiopoda of the Marine Protected Area “Secche di Tor Paterno”, Central Tyrrhenian Sea, have been investigated in order to give a first glance of the diversity of the brachiopods of this area and provide a new report on the Mediterranean Brachiopod fauna. Four species were reported: Novocrania anomala (Müller, 1776), Megathiris detruncata (Gmelin, 1790), Joania cordata (Risso,1826) and Argyrotheca cuneata (Risso,1826). For all the four species a morphological analysis was carried out. For the two most abundant species, J.cordata and A. cuneata, a morphometric study, based on thickness/width and length/width scattergrams, was carried out, in order to investigate their variability. Size-frequency distributions relative to the three dimensions of the shell were also computed, aimed at a evaluation of population dynamics of these two species. The results showed that, for both species, the parameters which most determine the rise of the shell during the growth of animal are width and length and that frequency distributions are mainly bi- or plurymodal and that they are difficult to interpret, as reported by other studies. Analysis of drill holes found on the shell of some specimens of the two same species revealed a predatory origin and that three different predators are responsible for them. Partial sequences of two different genetic markers, the Internal Transcribed Spacer 1 (ITS1) and the cytochrome oxidase subunit 1 (COI), were used to investigate the phylogenetic relationship between two populations of the eurybathic brachiopod species Gryphus vitreus (Born,1778) across the strait of Gibraltar. This represents the first genetic population study on brachiopods. Results from AMOVA and Bayesian analysis performed on 31 specimens highlighted no genetic differentiation indicating a likely panmixia, dispite the lecitotrophic development of the species.

Environmental influence on the phenotype: Morphological variation in human dentition

This work is about the role that environment plays in the production of evolutionary significant variations. It starts with an historical introduction about the concept of variation and the role of environment in its production. Then, I show how a lack of attention to these topics may lead to serious mistakes in data interpretation. A statistical re-analysis of published data on the effects of malnutrition on dental eruption, shows that what has been interpreted as an increase in the mean value, is actually linked to increase of variability. In Chapter 3 I present the topic of development as a link between variability and environmental influence, giving a review of the possible mechanisms by which development influences evolutionary dynamics. Chapter 4 is the core chapter of the thesis; I investigated the role of environment in the development of dental morphology. I used dental hypoplasia as a marker of stress, characterizing two groups. Comparing the morphology of upper molars in the two groups, three major results came out: (i) there is a significant effect of environmental stressors on the overall morphology of upper molars; (ii) the developmental response increases morphological variability of the stressed population; (iii) increase of variability is directional: stressed individuals have increased cusps dimensions and number. I also hypothesized the molecular mechanisms that could be responsible of the observed effects. In Chapter 5, I present future perspectives for developing this research. The direction of dental development response is the same direction of the trend in mammalian dental evolution. Since malnutrition triggers the developmental response, and this particular kind of stressor must have been very common in our class evolutionary history, I propose the possibility that environmental stress actively influenced mammals evolution. Moreover, I discuss the possibility of reconsidering the role of natural selection in the evolution of dental morphology.

Late Quaternary geological evolution of the Montenegro and Northern Albania continental margins

The object of this work has been the analysis of natural processes controlling the geological evolution of the Montenegro and Northern Albania Continental Margin (MACM) during the Late Quaternary. These include the modern sediment dispersal system and oceanographic regime, the building and shaping of the shelf margin at the scale of 100 kyr and relative to the most recent transition between glacial and interglacial periods. The analysis of the new data shows that the MACM is a shelf-slope system formed by a suite of physiographic elements, including: an inner and an outer continental shelf, separated by two tectonically-controlled morphological highs; a lobated drowned mid-shelf paleodelta, formed during the last sea level fall and low stand; an upper continental slope, affected by gravity-driven instability and a system of extensional faults with surficial displacement, featuring an orientation coherent with the regional tectonics. The stratigraphic study of the MACM shows a clear correspondence between the Late Pleistocene/Holocene mud-wedge and the low reflectivity sectors of the inner shelf. Conversely, most of the outer shelf and part of the continental slope expose deposits from the last sea level low stand, featuring a general sediment starving condition or the presence of a thin postglacial sediments cover. The MACM shows uplift in correspondence of the Kotor and Bar ridges, and subsidence in the outer shelf and upper slope sectors. In fact, seaward of these tectonic ridges, the sparker seismic profile show the presence of four well-defined seismo-stratigraphic sequences, interpreted as forced regression deposits, formed during the last four main glacial phases. In this way, the MACM records the 100 kyr scale sea level fluctuations on its seismo-stratigraphic architecture over the last 350 kyr. Over such time range, through the identification of the paleoshoreline deposits, we estimated an average subsidence rate of about 1.2 mm/yr.