1,130 research outputs found
INTERNAZIONALITA' E STORICITa' DEL PORTO FRANCO DI TRIESTE. Centro commerciale-emporiale-transitario globale.
No full textSpatio-Temporal Dynamics of Urban and Natural Areas in the Northern Littoral Zone of Rome: Land-Cover Change Analysis During the Last Thirty Years. Preliminary Results
No full textThe present study is focused on the littoral zone between Rome and Civitavecchia, where the spatio-temporal dynamics of the land cover has been analysed during the last thirty years, by means of Remote Sensing and GIS procedures. In a few decades, the coastal municipalities within the study area have considerably increased their inhabitants. Population and urban expansion have grown in parallel, at the expense of agricultural and natural areas, especially in the narrow coastal strip between the sea and the hills. Landsat satellite data from 1990 to 2019 have been processed and classified in order to describe and map the Land-Cover change (LCc). Maps have been suitable integrated with population data and other geospatial layers (transportation network). The results obtained allowed to understand the natural and rural land transformations, especially those related to the urban growth and expansion that are related to the proximity of Rome City
On dust evolution in planet-forming discs in binary systems-II. Comparison with Taurus and ρ Ophiuchus (sub-)millimetre observations: Discs in binaries have small dust sizes
No full textThe recently discovered exoplanets in binary or higher order multiple stellar systems sparked a new interest in the study of protoplanetary discs in stellar aggregations. Here, we focus on disc solids, as they make up the reservoir out of which exoplanets are assembled and dominate (sub-)millimetre disc observations. These observations suggest that discs in binary systems are fainter and smaller than in isolated systems. In addition, disc dust sizes are consistent with tidal truncation only if they orbit very eccentric binaries. In a previous study, we showed that the presence of a stellar companion hastens the radial migration of solids, shortening disc lifetime, and challenging planet formation. In this paper, we confront our theoretical and numerical results with observations: Disc dust fluxes and sizes from our models are computed at ALMA wavelengths and compared with Taurus and ρ Ophiuchus data. A general agreement between theory and observations is found. In particular, we show that the dust disc sizes are generally smaller than the binary truncation radius due to the combined effect of grain growth and radial drift: Therefore, small disc sizes do not require implausibly high eccentricities to be explained. Furthermore, the observed binary discs are compatible within 1σ with a quadratic flux-radius correlation similar to that found for single-star discs and show a close match with the models. However, the observational sample of resolved binary discs is still small and additional data are required to draw more robust conclusions on the flux-radius correlation and how it depends on the binary properties
On dust evolution in planet-forming discs in binary systems - I. Theoretical and numerical modelling: Radial drift is faster in binary discs
No full textMany stars are in binaries or higher order multiple stellar systems. Although in recent years a large number of binaries have been proven to host exoplanets, how planet formation proceeds in multiple stellar systems has not been studied much yet from the theoretical standpoint. In this paper, we focus on the evolution of the dust grains in planet-forming discs in binaries. We take into account the dynamics of gas and dust in discs around each component of a binary system under the hypothesis that the evolution of the circumprimary and the circumsecondary discs is independent. It is known from previous studies that the secular evolution of the gas in binary discs is hastened due to the tidal interactions with their hosting stars. Here, we prove that binarity affects dust dynamics too, possibly in a more dramatic way than the gas. In particular, the presence of a stellar companion significantly reduces the amount of solids retained in binary discs because of a faster, more efficient radial drift, ultimately shortening their lifetime. We prove that how rapidly discs disperse depends both on the binary separation, with discs in wider binaries living longer, and on the disc viscosity. Although the less-viscous discs lose high amounts of solids in the earliest stages of their evolution, they are dissipated slowly, while those with higher viscosities show an opposite behaviour. The faster radial migration of dust in binary discs has a striking impact on planet formation, which seems to be inhibited in this hostile environment, unless other disc substructures halt radial drift further in. We conclude that if planetesimal formation were viable in binary discs, this process would take place on very short time-scales
Encounters in star clusters and survival probabilities for planets
No full textThe stability of young planetary systems is strongly influenced by multiple factors, both internal and external. In this paper, we investigate the link between the environment in which young stars form and the possibility of having stable planetary systems around them. We analyze the robustness of such systems after an encounter with another star within the same stellar cluster. We employ a model for the star cluster to extract the encounter properties, such as the mass of the perturber star and its velocity. We perform numerical simulations on systems with a single planet perturbed by an external star, in order to calculate the emission probabilities of the planet. We also calculate analytically the stellar encounter rates in the cluster. We find that such probabilities are strongly dependent on the thermal velocity of the cluster. We also notice that these probabilities are generally quite small, below 3% for the systems tested by us
Effects of environment and multiplicity on planet formation
No full textStar formation does not take place in isolation, and young stars are subject to different kind of interactions with their natal environment. Dynamical encounters with other young stars and photoevaporation of the protostellar disc due to the intense UV field of neighbouring stars are just a couple of examples of how the environment affects star formation. Since planets are born during the star formation process, such effects may naturally affect also planet formation itself. The aim of this focus point is to define the state of the art of our knowledge in this particular field and to provide a few highlights of interesting new research avenues to pursue
The theory of kinks - I. A semi-analytic model of velocity perturbations due to planet-disc interaction
No full textA new technique to detect protoplanets is by observing the kinematics of the surrounding gas. Gravitational perturbations from a planet produce peculiar 'kinks' in channel maps of different gas species. In this paper, we show that such kinks can be reproduced using semi-analytic models for the velocity perturbation induced by a planet. In doing so we (i) confirm that the observed kinks are consistent with the planet-induced wake; (ii) show how to quantify the planet mass from the kink amplitude; in particular, we show that the kink amplitude scales with the square root of the planet mass for channels far from the planet velocity, steepening to linear as the channels approach the planet; and (iii) show how to extend the theory to include the effect of damping, which may be needed in order to have localized kinks
Modelling and Analysis of Base Isolated Structures with Friction Pendulum System considering Near Fault Events
No full textMaculare Pseudoforamenund Bestehen Hyaloider Arterien in Stark myelinisiertem retinalen Nervengewebe
No full text9-Anthroylacetone and its photodimer
No full text9-Anthroylacetone undergoes a head-to-tail [4π+4π] photo-dimerisation reaction that leads to the formation of 5,11-bis(1,3-diketobutyl)-5,6,11,12- tetrahydro-5,12,6,11-di-o-benzeno-dibenzo[a,e]cyclooctene both in solution and in the solid state when irradiated with different sources (sunlight, tungsten lamp, xenon lamp, UV laser beam 351-364 nm), the reaction being accompanied by a colour variation from bright yellow to colourless. Quantum yields >0.023 mol/Einstein are evaluated for the solid state reaction. Interestingly, the dimer dissociates to give 9-anthroylacetone, both thermally (T>130°C) and photochemically, by short UV wavelength irradiation. The single-crystal X-ray structure of 9-anthroylacetone and its dimer are reported. 9-Anthroylacetone undergoes a head-to-tail [4π+4π] photo-dimerisation reaction both in solution and in the solid state when irradiated with different sources; the dimer reversibly dissociates into 9-anthroylacetone, both thermally and photochemically
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