466 research outputs found
Analisi dei cicli operativi ed identificazione di scenari di sviluppo per il terminal carbonifero di Civitavecchia
No full textOggetto del seguente studio è l’analisi dei cicli operativi del terminal carbonifero di Civitavecchia la cui finalità è l’identificazione di scenari di sviluppo che, realizzati, possano produrre una importante diminuzione dei tempi non operativi e il conseguente incremento dei tempi di produzione. Sono stati ipotizzati tre progetti costruttivi
riguardanti le infrastrutture: costruzione di una diga foranea per impedire al moto ondoso di entrare in porto; prolungamento della banchina esistente in modo tale da far scaricare due navi contemporaneamente; costruzione di un ulteriore dome per
aumentare la capacità di stoccaggio del carbone. Le tre ipotesi progettuali opportunamente combinate hanno determinato sette scenari, per ognuno dei quali è stata calcolata la diminuzione dei tempi non operativi e il relativo risparmio economico. I risultati così ottenuti possono rappresentare un punto di partenza per eventuali studi successivi, che potrebbero approfondire l’aspetto prettamente economico e finanziario degli interventi stessi.The purpose of this study is the analysis of the operational cycles of the coal terminal in the port of Civitavecchia in order to identify development scenarios that could bring a substantial decrease of unoperational times, thus increasing operational times. It has been hypothesized three projects regarding the infrastructures: the construction of a offshore breakwater preventing the wave motion in the port; the extension of the quay allowing the discharge of two ships at one time; the building of another dome in order to increase the coal stock capacity. The combination of these three projects have been achieved seven scenarios; for each scenario the decrease of unoperational times and the rise of the cost effectiveness have been calculated. The obtained results may be considered as a starting point
to future studies focused on the economic and financial aspects regarding different projects
Effetti delle dimensioni delle navi sulle emissioni delle flotte container e passeggeri // Effects of ships’ dimension on emissions of container and cruise fleets
No full textThe paper approaches freight and passengers fleets, affected by naval gigantism, to investigate its energetic and environmental effects. Among the emerging trends, we encounter the increase of the installed power and, more relevantly, of the transport capacity of the ships. The result is a decrease of the specific power, particularly in the last 20 years. In the same period, an increase of the performances of ships in terms of environmental and energetic sustainability is ongoing. A further acceleration in this direction could come from the introduction of less pollutant fuels and renewable energies. It is a pillar for the development of future sustainable fleets, with relevant emerging investigation needs. In this context, the paper proposes a synthetic approach, combining dimensions and environmental performances of ships, tested on container and cruises fleets in operation in selected worldwide most frequented locations. The results could be useful to check effective policies, basing on emerging technologies and implementation of new rules and regulation
On Concavity and Supermodularity
No full textConcavity and supermodularity are in general independent properties. A class of functionals defined on a lattice cone of a Riesz space has the Choquet property when it is the case that its members are concave whenever they are supermodular. We show that for some important Riesz spaces both the class of positively homogeneous functionals and the class of translation invariant functionals have the Choquet property. We extend in this way the results of Choquet [2] and Konig [5].Concavity, Supermodularity
Stellar feedback by radiation pressure and photoionization
No full textThe relative impact of radiation pressure and photoionization feedback from young stars on surrounding gas is studied with hydrodynamic radiative transfer (RT) simulations. The calculations focus on the single-scattering (direct radiation pressure) and optically thick regime, and adopt a moment-based RT-method implemented in the moving-mesh code arepo. The source luminosity, gas density profile and initial temperature are varied. At typical temperatures and densities of molecular clouds, radiation pressure drives velocities of the order of ∼20 km s−1 over 1–5 Myr; enough to unbind the smaller clouds. However, these estimates ignore the effects of photoionization that naturally occur concurrently. When radiation pressure and photoionization act together, the latter is substantially more efficient, inducing velocities comparable to the sound speed of the hot ionized medium (10–15 km s−1) on time-scales far shorter than required for accumulating similar momentum with radiation pressure. This mismatch allows photoionization to dominate the feedback as the heating and expansion of gas lowers the central densities, further diminishing the impact of radiation pressure. Our results indicate that a proper treatment of the impact of young stars on the interstellar medium needs to primarily account for their ionization power whereas direct radiation pressure appears to be a secondary effect. This conclusion may change if extreme boosts of the radiation pressure by photon trapping are assumed
Baryonic impact on the dark matter orbital properties of Milky Way-sized haloes
No full textWe study the orbital properties of dark matter haloes by combining a spectral method and cosmological simulations of Milky Way-sized Galaxies. We compare the dynamics and orbits of individual dark matter particles from both hydrodynamic and N-body simulations, and find that the fraction of box, tube and resonant orbits of the dark matter halo decreases significantly due to the effects of baryons. In particular, the central region of the dark matter halo in the hydrodynamic simulation is dominated by regular, short-axis tube orbits, in contrast to the chaotic, box and thin orbits dominant in the N-body run. This leads to a more spherical dark matter halo in the hydrodynamic run compared to a prolate one as commonly seen in the N-body simulations. Furthermore, by using a kernel-based density estimator, we compare the coarse-grained phase-space densities of dark matter haloes in both simulations and find that it is lower by ∼0.5 dex in the hydrodynamic run due to changes in the angular momentum distribution, which indicates that the baryonic process that affects the dark matter is irreversible. Our results imply that baryons play an important role in determining the shape, kinematics and phase-space density of dark matter haloes in galaxies
Risk, ambiguity, and the separation of utility and beliefs.
No full textWe introduce a general model of static choice under uncertainty, arguably the weakest model achieving a separation of cardinal utility and a unique representation of beliefs. Most of the non-expected utility models existing in the literature are special cases of it. Such separation is motivated by the view that tastes are constant, whereas beliefs change with new information. The model has a simple and natural axiomatization. Elsewhere (forthcoming) we show that it can be very helpful in the characterization of a notion of ambiguity aversion, as separating utility and beliefs allows to identify and remove aspects of risk attitude from the decision maker’s behavior. Here we show that the model allows to generalize several results on the characterization of risk aversion in betting behavior. These generalizations are of independent interest, as they show that some traditional results for subjective expected utility preferences can be formulated only in terms of binary acts.
Efficiency of gas cooling and accretion at the disc-corona interface
No full textIn star-forming galaxies, stellar feedback can have a dual effect on the circumgalactic medium both suppressing and stimulating gas accretion. The trigger of gas accretion can be caused by disc material ejected into the halo in the form of fountain clouds and by its interaction with the surrounding hot corona. Indeed, at the disc-corona interface, the mixing between the cold/metal-rich disc gas (T ≲ 104 K) and the hot coronal gas (T ≳ 106 K) can dramatically reduce the cooling time of a portion of the corona and produce its condensation and accretion. We studied the interaction between fountain clouds and corona in different galactic environments through parsec-scale hydrodynamical simulations, including the presence of thermal conduction, a key mechanism that influences gas condensation. Our simulations showed that the coronal gas condensation strongly depends on the galactic environment, in particular it is less efficient for increasing virial temperature/mass of the haloes where galaxies reside and it is fully ineffective for objects with virial masses larger than 1013 M⊙. This result implies that the coronal gas cools down quickly in haloes with low-intermediate virial mass (Mvir ≲ 3 × 1012 M⊙) but the ability to cool the corona decreases going from late-type to early-type disc galaxies, potentially leading to the switching off of accretion and the quenching of star formation in massive systems
Transport planning system and management: is it a common methodology to face any kind of exceptional event possible?
No full textCores of non-atomic market games
No full textWe study the cores of non-atomic market games, a class of transferable utility cooperative games introduced by Aumann and Shapley [2], and, more in general, of those games that admit a na-continuous and concave extension to the set of ideal coalitions, studied by Einy, Moreno, and Shitovitz [12]. We show that the core of such games is norm compact and we provide some representation results. We also give a Multiple Priors interpretation of some of our results.We study the cores of non-atomic market games, a class of transferable utility cooperative
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