SUBSTRUCTURES IN PROTOPLANETARY DISCS - DUST AND GAS DYNAMICS

In this Thesis I have investigated a problem of great interest in the present star and planet formation research field: the characterization of substructures recently detected in protoplanetary discs. The goal of my work is to understand what physical processes induce the peculiar disc substructures observed to date in protoplanetary discs. In the first part of my work I investigate if the occurrence of local pressure maxima induced by gravitational instabilities can trap dust particles and explore the detectability of these inhomogeneities at near-infrared and (sub-) millimetre wavelengths. The observational predictions of the resulting models show that the resolution capabilities and sensitivity of current telescopes are sufficient to spatially resolve the peculiar spiral structure of gravitationally unstable discs. In the second part of my work I explore the dynamical clearing mechanism induced by forming protoplanets embedded in discs with the aim, on the one hand, of understanding the physics of dust gap opening and, on the other hand, of reproducing the gap-like structures observed in the disc around HL Tau. I provide a necessary and sufficient condition for the minimum planet mass able to carve a dust gap, as well as an estimate of the location of the outer edge of the dust gap, which can be useful to estimate the mass of the planet from high-resolution (sub-) millimetre observations. I apply my findings to the case of HL Tau, showing that the three gaps detected by ALMA can be described by the presence of sub-Jupiter mass planets. Finally, in the last part of my work, I investigate if the horseshoes observed at (sub-) millimetre wavelengths in transitional discs can be explained by the dynamics of gas and dust at the edge of the cavity carved by a binary object. I found that the cavities carved by binaries with large mass ratio becomes eccentric, leading to a horseshoe-like feature in the gas density and also in the dust surface density that can be detected with current telescopes. Although a variety of disc models can potentially reproduce the disc substructures observed to date in protoplanetary discs, the analysis performed in this Thesis shows that my models can accurately reproduce the observational results and can be useful for shedding light on the mechanism responsible for the disc substructures

All functions are (locally) ss-harmonic (up to a small error) - and applications

The classical and the fractional Laplacians exhibit a number of similarities, but also some rather striking, and sometimes surprising, structural differences. A quite important example of these differences is that any function (regardless of its shape) can be locally approximated by functions with locally vanishing fractional Laplacian, as it was recently proved by Serena Dipierro, Ovidiu Savin and myself. This informal note is an exposition of this result and of some of its consequences

On the origin of horseshoes in transitional discs

We investigate whether the rings, lopsided features and horseshoes observed at millimetre (mm) wavelengths in transitional discs can be explained by the dynamics of gas and dust at the edge of the cavity in circumbinary discs. We use 3D dusty smoothed particle hydrodynamics calculations to show that binaries with mass ratio q greater than or similar to 0.04 drive eccentricity in the central cavity, naturally leading to a crescent-like feature in the gas density, which is accentuated in the mm dust grain population with intensity contrasts in mm continuum emission of 10 or higher. We perform mock observations to demonstrate that these features closely match those observed by the Atacama Large Millimetre/Submillimetre Array, suggesting that the origin of rings, dust horseshoes and other non-axisymmetric structures in transition discs can be explained by the presence of massive companions

Enforcing dust mass conservation in 3D simulations of tightly coupled grains with the Phantom SPH code

We describe a new implementation of the one-fluid method in the SPH code PHANTOM to simulate the dynamics of dust grains in gas protoplanetary discs. We revise and extend previously developed algorithms by computing the evolution of a new fluid quantity that produces a more accurate and numerically controlled evolution of the dust dynamics. Moreover, by limiting the stopping time of uncoupled grains that violate the assumptions of the terminal velocity approximation, we avoid fatal numerical errors in mass conservation. We test and validate our new algorithm by running 3D SPH simulations of a large range of disc models with tightly and marginally coupled grains

Data-Driven Epidemic Intelligence Strategies Based on Digital Proximity Tracing Technologies in the Fight against COVID-19 in Cities

In a modern pandemic outbreak, where collective threats require global strategies and local operational defence applications, data-driven solutions for infection tracing and forecasting epidemic trends are crucial to achieve sustainable and socially resilient cities. Indeed, the need for monitoring, containing, and mitigating the ongoing COVID-19 pandemic has generated a great deal of interest in Digital Proximity Tracing Technology (DPTT) on smartphones, as well as their function and effectiveness and insights of population acceptance. This paper introduces and compares different Data-Driven Epidemic Intelligence Strategies (DDEIS) developed on DPTTs. It aims to clarify to what extent DDEIS could be effective and both technologically and socially suitable in reaching the objective of a swift return to normality for cities, guaranteeing public health safety and minimizing the risk of epidemic resurgence. It assesses key advantages and limits in supporting both individual decision-making and policy-making, considering the role of human behaviour. Specifically, an online survey carried out in Italy revealed user preferences for DPTTs and provided preliminary data for an SEIR (Susceptible–Exposed–Infectious–Recovered) epidemiological model. This was developed to evaluate the impact of DDEIS on COVID-19 spread dynamics, and results are presented together with an evaluation of potential drawbacks

MDA, oxypurines, and nucleosides relate to reperfusion in short-term incomplete cerebral ischemia in the rat

Short-term incomplete cerebral ischemia (5 min) was induced in the rat by the bilateral clamping of the common carotid arteries. Reperfusion was obtained by removing carotid clamping and was carried out for the following 10 min. Animals were sacrificed either at the end of ischemia or reperfusion. Controls were represented by a group of sham-operated rats. Peripheral venous blood samples were withdrawn from the femoral vein from rats subjected to cerebral reperfusion 5 min before ischemia, at the end of ischemia, and 10 min after reperfusion. Neutralized perchloric acid extracts of brain tissue were analyzed by a highly sensitive high-performance liquid chromatography (HPLC) method for the direct determination of malondialdehyde, oxypurines, nucleosides, nicotinic coenzymes, and high-energy phosphates. In addition, plasma concentrations of malondialdehyde, hypoxanthine, xanthine, inosine, uric acid, and adenosine were determined by the same HPLC technique. Incomplete cerebral ischemia induced the appearance of a significant amount (8.05 nmol/g w.w.; SD = 2.82) of cerebral malondialdehyde (which was undetectable in control animals) and a decrease of ascorbic acid. A further 6.6-fold increase of malondialdehyde (53.30 nmol/g w.w.; SD = 17.77) and a 18.5% decrease of ascorbic acid occurred after 10 min of reperfusion. Plasma malondialdehyde, which was present in minimal amount before ischemia (0.050 mumol/L; SD = 0.015), significantly increased after 5 min of ischemia (0.277 mumol/L; SD = 0.056) and was strikingly augmented after 10 min of reperfusion (0.682 mumol/L; SD = 0.094). A similar trend was observed for xanthine, uric acid, inosine, and adenosine, while hypoxanthine reached its maximal concentration after 5 min of incomplete ischemia, being significantly decreased after reperfusion. From the data obtained, it can be concluded that tissue concentrations of malondialdehyde and ascorbic acid, and plasma levels of malondialdehyde, oxypurines, and nucleosides, reflect both the oxygen radical-mediated tissue injury and the depression of energy metabolism, thus representing early biochemical markers of short-term incomplete brain ischemia and reperfusion in the rat. In particular, these results suggest the possibility of using the variation of malondialdehyde, oxypurines, and nucleosides in peripheral blood as a potential biochemical indicator of reperfusion damage occurring to postischemic tissues

Multi-wavelength observations of protoplanetary discs as a proxy for the gas disc mass

Recent observations of protoplanetary discs reveal disc substructures potentially caused by embedded planets. We investigate how the gas surface density in discs changes the observed morphology in scattered light and dust continuum emission. Assuming that disc substructures are due to embedded protoplanets, we combine hydrodynamical modelling with radiative transfer simulations of dusty protoplanetary discs hosting planets. The response of different dust species to the gravitational perturbation induced by a planet depends on the drag stopping time \u2013 a function of the generally unknown local gas density. Small dust grains, being stuck to the gas, show spirals. Larger grains decouple, showing progressively more axisymmetric (ring-like) substructure as decoupling increases with grain size or with the inverse of the gas disc mass. We show that simultaneous modelling of scattered light and dust continuum emission is able to constrain the Stokes number, St. Hence, if the dust properties are known, this constrains the local gas surface density, \u3a3gas, at the location of the structure, and hence the total gas mass. In particular, we found that observing ring-like structures in mm-emitting grains requires St 73 0.4 and therefore \u3a3gas 720.4gcm 122\u2060. We apply this idea to observed protoplanetary discs showing substructures both in scattered light and in the dust continuu

Presenza di Terre Rare in suoli in zone ad elevata attività industriale

Il presente lavoro riporta dati preliminari sulla potenziale tossicità di polveri o strati superficiali di suolo in organismi vegetali modello. Radici di Allium cepa, specie utilizzata per test preliminari di citotossicità, sono state trattate con sospensioni acquose di campioni di suolo e polveri provenienti da varie zone del territorio di Augusta e Priolo nei quali è stata misurata la concentrazione di terre rare (REE) e metalli, al fine di valutarne gli effetti sulla crescita e sull’attività mitotica. I trattamenti non hanno indotto significative alterazioni della struttura e della crescita in questa specie, ma un rilevante aumento delle aberrazioni mitotiche. I dati suggeriscono la necessità di condurre un periodico monitoraggio delle concentrazioni di questi elementi nell’ambiente e di eseguire periodicamente test di tossicità su vari tipi di organismi

Enforcing dust mass conservation in 3D simulations of tightly coupled grains with the Phantom SPH code

We describe a new implementation of the one-fluid method in the SPH code Phantom to simulate the dynamics of dust grains in gas protoplanetary discs. We revise and extend previously developed algorithms by computing the evolution of a new fluid quantity that produces a more accurate and numerically controlled evolution of the dust dynamics. Moreover, by limiting the stopping time of uncoupled grains that violate the assumptions of the terminal velocity approximation, we avoid fatal numerical errors in mass conservation. We test and validate our new algorithm by running 3D SPH simulations of a large range of disc models with tightly and marginally coupled grains