102 research outputs found
Morphometric analysis of differently degraded simple craters on the moon
No full textThe main focus of this PhD research is the morphologic characterization of simple impact craters on lunar maria in order to find out a correlation between craters morphological degradation and absolute model ages of the surfaces where they were emplaced. Crater degradation can be indeed used to constrain the chronological evolution of planetary surfaces.
The crater degradation is usually retrieved through visual inspection by subdividing craters into 4 classes: C1 represents the freshest ones, C2 are the ones with the first evidence of degradation (smoothed rim), C3 and C4 are related to morphologies ranging from heavily eroded to totally flattened respectively [Arthur, 1963].
We firstly conducted a morphometric analysis of craters representative of the four classes starting from the freshest one represented by the Linné crater. Craters were chosen on a homogeneous geological unit, the S28 unit in mare Serenitatis, with an absolute model age of 2.84 Gy [Hiesinger et al., 2011]. This analysis allowed us to establish the thresholds of mean slope from craters inner wall, in order to constrain the morphometric characterization of the four degradation classes.
Successively we have extracted all impact craters (383) from a unique geological unit and we have defined the morphologic relationships among the degradation classes in function of the craters diameters.
Finally, we expanded our analysis to six lunar maria, considering six lunar maria with different average absolute model ages, in order to perform this analysis with the wider range of ages. For each mare we considered a unique surface (dataset) derived from the merging of geological units with similar absolute model ages within the basin, in order to guarantee the most homogeneous possible surfaces, both in terms of impact rheology and absolute age. From the six surfaces we have extracted inner wall mean slopes from over 1000 impact craters. The mean slope values of the inner walls have shown a relation between crater morphology and the absolute model ages of the geological units where they are located. Older basins are characterized by craters with lower mean slope values, suggesting a dominance of older craters in their population, whereas the younger units have shown higher mean slope values of their simple craters, suggesting a population dominated by recent impacts. This tendency is the expression of the morphological alteration strictly connected to the lunar maria age. Since the geomorphometry of impact craters is influenced by the absolute age of the target area, we have constrained potential isochrones by fixing absolute age thresholds based on the morphological variations of impact craters
Fundamental issues in antenna design for microwave medical imaging applications
No full textThis paper surveys the development of microwave medical imaging and the fundamental challenges associated with microwave antennas design for medical imaging applications. Different microwave antennas used in medical imaging applications such as monopoles, bow-tie, vivaldi and pyramidal horn antennas are discussed. The challenges faced when the latter used in medical imaging environment are detailed. The paper provides the possible solutions for the challenges at hand and also provides insight into the modelling work which will help the microwave engineering community to understand the behaviour of the microwave antennas in coupling media
Vivaldi's Four Seasons and the Globalization of Musical Taste
No full text"Vivaldi's Four Seasons, or at least parts of it, can be recognised by enormous numbers of people on this planet, and its sounds seem to come from almost every elevator shaft, mobile phone, restaurant and television advert in the world. It stands as the very epitome of a globalized artwork, and therefore it would be reasonable to suppose that globalization theories would be a great help in explaining its success. That this may not be the case is one of the main points of this paper -�� but before we get to that, there are two matters that have to be set in place. The first is to define the characteristics of the Four Seasons as a global commodity (note that I refer to it in the singular, since the four individual pieces come as a package); the second is to describe the main tenets of globalization theories and some of their chief generating ideas. Trying to map the characteristics of the work onto the assertions of the theories will be the main business of this paper, and this process is designed not only to illuminate the work, but also to test the theories." (Excerpt, introduction
Using satellite soil moisture and rainfall data for the monitoring and the prediction of natural hazards
No full textAn integrated model for prediction of shallow landslides at regional scale with the integration of satellite hydrological data
No full textEmpirical and Physically Based Thresholds for the Occurrence of Shallow Landslides in a Prone Area of Northern Italian Apennines
No full textRainfall thresholds define the conditions leading to the triggering of shallow landslides
over wide areas. They can be empirical, which exploit past rainfall data and landslide inventories, or
physicallybased, which integrate slope physical–hydrological modeling and stability analyses. In this
work, a comparison between these two types of thresholds was performed, using data acquired in
Oltrepò Pavese (Northern Italian Apennines), to evaluate their reliability. Empirical thresholds were
reconstructed based on rainfalls and landslides triggering events collected from 2000 to 2018. The same
rainfall events were implemented in a physicallybased model of a representative testsite, considering
dierent antecedent pore-water pressures, chosen according to the analysis of hydrological monitoring
data. Thresholds validation was performed, using an external dataset (August 1992–August 1997).
Soil hydrological conditions have a primary role on predisposing or preventing slope failures. In
Oltrepò Pavese area, cold and wet months are the most susceptible periods, due to the permanence of
saturated or close-to-saturation soil conditions. The lower the pore-water pressure is at the beginning
of an event, the higher the amount of rain required to trigger shallow failures is. physicallybased
thresholds provide a better reliability in discriminating the events which could or could not trigger
slope failures than empirical thresholds. The latter provide a significant number of false positives,
due to neglecting the antecedent soil hydrological conditions. These results represent a fundamental
basis for the choice of the best thresholds to be implemented in a reliable earlywarning system
Is the Linne' impact crater morphology influenced by the rheological layering on the Moon's surface? Insights from numerical modeling
No full textAbstract–Linne is a simple crater, with a diameter of 2.23 km and a depth of 0.52 km, located in northwestern Mare Serenitatis. Recent high-resolution data acquired by the Lunar Reconnaissance Orbiter Camera revealed that the shape of this impact structure is best described by an inverted truncated-cone. We perform morphometric measurements, including slope and profile curvature, on the Digital Terrain Model of Linne, finding the possible presence of three subtle topographic steps, at the elevation of +20, 100, and 200 m relative to the target surface. The kink at 100 m might be related to the interface between two different rheological layers. Using the iSALE shock physics code, we numerically model the formation of Linne crater to derive hints on the possible impact conditions and target physical properties. In the initial setup, we adopt a basaltic projectile impacting the Moon with a speed of 18 km s. For the local surface, we consider either one or two layers, in order to test the influence of material properties or composite rheologies on the final crater morphology. The one-layer model shows that the largest variations in the crater shape take place when either the cohesion or the friction coefficient is varied. In particular, a cohesion of 10 kPa marks the threshold between conical- and parabolic-shaped craters. The two-layer model shows that the interface between the two layers would be exposed at the observed depth of 100 m when an intermediate value (~200 m) for the upper fractured layer is set. We have also found that the truncated-cone morphology of Linne might originate from an incomplete collapse of the crater wall, as the breccia lens remains clustered along the crater walls, while the high-albedo deposit on the crater floor can be interpreted as a very shallow lens of fallout breccia. The modeling analysis allows us to derive important clues on the impactor size (under the assumption of a vertical impact and collision velocity equal to the mean value), and on the approximate, large-scale preimpact target properties. Observations suggest that these large-scale material properties likely include some important smaller scale variations, disclosed as subtle morphological steps in the crater walls. Furthermore, the modeling results allow advancing some hypotheses on the geological evolution of the Mare Serenitatis region where Linne crater is located (unit S14). We suggest that unit S14 has a thickness of at least a few hundreds of meters up to about 400 m
Collective Improvisation: The Practice and Vision of Ingemar Lindh
No full textIngemar Lindh's research on the principles of collective improvisation and performance conceived as process announce an important development in the 20th-century tradition of the actor's work. After early studies with Étienne Decroux and working collaborations with Jerzy Grotowski, Eugenio Barba, and Yves Lebreton, Lindh founded the first laboratory theatre in Sweden in 1971, the Institutet för Scenkonst. His practice of collective improvisation is viewed in light of postdramatic concerns such as its resistance to fixed scores, directorial montage, and choreography as an organizing principle
Comparison between mechanical and hydrological reinforcement effects of cultivated plants on shallow slope stability
No full textRoot reinforcement, provided by plants in soil, can be exerted by a mechanical effect, increasing soil shear strength for the presence of roots, or by a hydrological effect, induced by plant transpiration. No comparisons have been still carried out between mechanical and hydrological reinforcements on shallow slope stability in typical agroecosystems. This paper aims to compare these effects induced by sowed fields and vineyards and to assess their effects towards the shallow slope staibility. Root mechanical reinforcement has been assessed through Root Bundle Model-Weibull. Root hydrological reinforcement has been evaluated using an empirical relationship with monitored or modelled pore water pressure. Each reinforcement has been inserted in a stability model to quantify their impacts on susceptibility towards shallow landslides. Considering the same environment, corresponding to a typical agroecosystem of northern Italian Apennines, land use has significant effects on saturation degree and pore water pressure, influencing hydrological reinforcement. Root hydrological reinforcement effect is higher in summer, although rainfall-induced shallow landslides rarely occur in this period due to dry soil conditions. Instead, in wet and cold periods, when shallow landslides can develop more frequently, the stabilizing contribution of mechanical reinforcement is on average higher than the hydrological reinforcement. In vineyards, the hydrological reinforcement effect could be observed also during autumn, winter and spring periods, giving a contribution to slope stability also in these conditions. This situation occurs when plants uptake enough water from soil to reduce significantly pore water pressure, guaranteeing values of hydrological reinforcement of 1-3 kPa at 1 m from ground, in agreement with measured mechanical root reinforcement (up to 1.6 kPa). These results suggest that both hydrological and mechanical effects of vegetation deserve high regard in susceptibility towards shallow landslides, helping in selection of the best land uses to reduce probability of occurrence of these failures over large territories
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