A semi-analytical model of the Galilean satellites' dynamics

The Galilean satellites' dynamics has been studied extensively during the last century. In the past it was common to use analytical expansions in order to get simple models to integrate, but with the new generation computers it became prevalent the numerical integration of very sophisticated and almost complete equations of motion. In this article we aim to describe the resonant and secular motion of the Galilean satellites through a Hamiltonian, depending on the slow angles only, obtained with an analytical expansion of the perturbing functions and an averaging operation. In order to have a model as near as possible to the actual dynamics, we added perturbations and we considered terms that in similar studies of the past were neglected, such as the terms involving the inclinations and the Sun's perturbation. Moreover, we added the tidal dissipation into the equations, in order to investigate how well the model captures the evolution of the system.Comment: In the new version of the paper I introduced the following main changes: 1. qualitative (new plots) and quantitative (new tables) comparison of the model with the JPL ephemerides JUP310 2. comparison with the results of Musotto et al. 2002 3. extension and small corrections of Section 7, about tidal dissipatio

The long-term evolution of known resonant trans-Neptunian objects

Aims. Numerous trans-Neptunian objects are known to be in mean-motion resonance with Neptune. We aim to describe their long-term orbital evolution (both past and future) by means of a one-degree-of-freedom secular model. In this paper, we focus only on objects with a semi-major axis larger than 50 astronomical units (au). Methods. For each resonant object considered, a 500 000-year numerical integration is performed. The output is digitally filtered to get the parameters of the resonant secular model. Their long-term (Giga-year) orbital evolution is then represented by the level curves of the secular Hamiltonian. Results. For the majority of objects considered, the mean-motion resonance has little impact on the long-term trajectories (the secular dynamics is similar to a non-resonant one). However, a subset of objects is strongly affected by the resonance, producing moderately-high-amplitude oscillations of the perihelion distance and/or libration of the argument of perihelion around a fixed centre. Moreover, the high perihelion distance of the object 2015 FJ345 is plainly explained by long-term resonant dynamics, allowing us to also deduce its orbital elements at the time of capture in resonance (at least 15 million years ago). The same type of past evolution is expected for 2014 FZ71.Comment: 9 pages, 7 figures, 1 tabl

La risonanza di Laplace e la missione spaziale Juice

La risonanza di Laplace è una condizione particolare che vige tra le velocità angolari orbitali (o moti medi) dei tre satelliti galileiani più interni: Io (1), Europa (2) e Ganimede (3). I moti medi (indicati con n_i) delle coppie Io-Europa e Europa-Ganimede sono vicini alla risonanza 2:1, cioè per ogni giro del secondo satellite della coppia, il primo ne compie circa due: la doppia risonanza implica che ad ogni giro completo di Ganimede, Europa ne compie circa 2 ed Io 4. Inoltre le quantità n_1-2*n_2 e n_2-2*n_3 sono uguali, e sono state osservate essere pari a 0.7395 gradi al giorno, che corrisponde esattamente all'opposto delle variazioni dei pericentri di Io ed Europa. Da questo segue che ci sono degli angoli che rimangano fissi (o meglio librano intorno a certi valori), uno dei quali è l'angolo caratteristico della risonanza di Laplace phi=lambda_1-3*lambda_2+2*lambda_3=180 gradi (con lambda_i le longitudini medie). L'evoluzione della risonanza di Laplace è fortemente dipendente dalle forze mareali, specialmente da quelle di Io che agiscono su Giove (che per reazione producono una coppia sull'orbita di Io), e quelle di Giove su Io (che dissipano energia all'interno di Io). Le prime producono una diminuzione del moto medio di Io, quindi un rallentamento, mentre le seconde aumentano la stessa quantità, portando ad un'accelerazione del moto lungo l'orbita. Processi simili sono validi anche tra le coppie Giove-Europa e Giove-Ganimede, ma con effetti molto minori. L'evoluzione del sistema, che sembra mantenere fissa la sua equazione caratteristica n_1-3*n_2+2*n_3=0 ed è caratterizzata dalla variazione di n_1-2*n_2$ e n_2-2*n_3, dipende dall'energia e dal momento angolare che Io guadagna ai danni della rotazione di spin di Giove e che invece perde dalla dissipazione interna. In più, grazie alla particolare condizione di risonanza, c'è una ridistribuzione di queste due quantità tra i satelliti, cosicché il calcolo della variazione dei moti medi di Io, Europa e Ganimede non è semplice. Un esempio possibile di questo calcolo è stato effettuato utilizzando le equazioni planetarie di Lagrange partendo da opportune funzioni di perturbazione, che descrivono l'interazione gravitazionale tra i satelliti. Esse portano ad un risultato interessante, in quanto sebbene l'effetto complessivo delle maree porti a un'accelerazione di Io, la ridistribuzione di energia e momento angolare permette ad Europa e Ganimede di aumentare il loro moto medio ai danni di Io, che risulterà quindi decelerare. Nonostante la risonanza tra le tre lune di Giove sia stato oggetto di studio per più di 200 anni (già da Laplace alla fine del 1700 e formalizzato agli inizi del 1900 da De Sitter), essa è uno dei grandi problemi aperti della meccanica celeste. In bibliografia infatti i valori delle variazioni dei moti medi dei tre satelliti sono vari e contrastanti, e dipendono dalla scelta del modello dinamico e dalle osservazioni (perlopiù telescopiche) a cui viene aggiustato. Una possibilità venuta fuori di recente è quella di utilizzare i dati della missione spaziale JUICE, il cui arrivo nel sistema di Giove per il 2030. In particolare, la grande precisione con cui si determinerà l'orbita della sonda JUICE durante la fase dedicata a Ganimede, permetterà di ottenere la posizione di quest'ultimo con una precisione altrettanto buona. Anche i due incontri ravvicinati con Europa e i tredici con Callisto (il quarto satellite galileiano) permetteranno di ottenere informazioni sull'orbita e sul campo gravitazionale di questi ultimi. La mancanza di incontri con Io, invece, non permetterà di ottenere dei risultati soddisfacenti con il solo tracking dello spacecraft. Sebbene Io sia la luna chiave del sistema, gli effetti sono ripartiti in maniera abbastanza equa tra i tre satelliti, se non con una predominanza per Ganimede; la possibilità di calcolare l'orbita di quest'ultimo è quindi altrettanto importante per riconoscere l'influenza della risonanza sul moto dei tre satelliti. Dopo aver descritto i passi necessari per effettuare un processo di determinazione (o di stima dei parametri), il modello matematico da utilizzare per calcolare i dati range (distanza) e range-rate (variazione di distanza) di JUICE, e le forze che agiranno sullo spacecraft, si è cercato di rispondere alla domanda se i dati di JUICE saranno sensibili agli effetti quadratici nel tempo agenti sulla posizione del baricentro di Ganimede, dovuti alla variazione secolare di moto medio. La grande accuratezza delle misure di JUICE permettono di rilevare tale variazione, ma alcuni termini a lungo periodo (come la librazione dell'angolo di risonanza phi) possono mascherare il risultato che stiamo cercando. Perciò è necessario utilizzare anche le osservazioni astrometriche per riconoscere gli effetti secolari, in quanto tali misure sono state raccolte lungo un esteso periodo di tempo. E' possibile comunque integrare i dati ricavati durante il periodo in orbita attorno a Ganimede, con altri ottenuti dalle telecamere e gli strumenti di JUICE, distribuiti lungo tutta la missione; in questo modo è possibile che i dati della missione conterranno un'informazione complessiva (per la determinazione dell'evoluzione della risonanza di Laplace) che eguaglia quella di un intero secolo di osservazioni telescopiche. English version: The Laplace resonance is a particular condition of the three inner Galilean satellites' motion: Io (1), Europa (2) and Ganymede (3). Mean motions of the couples Io-Europa and Europa-Ganymede are near 2:1 resonance; moreover the quantities n_1-2*n_2 and n_2-2*n_3 are equal and their value is 0.7395 degree per day, which corresponds also to the opposite of the rate of change of the pericenter arguments of Io and Europa. Therefore there are resonant angles and one of them is the Laplace resonance characteristic angle phi=lambda_1-3*lambda_2+2*lambda_3=180 degree (with lambda_i the mean longitudes). The evolution of the Laplace resonance is strongly dependent on tidal forces, especially from the tidal force of Io on Jupiter (which as reaction produces a torque on Io) and that of Jupiter on Io (that dissipates energy into Io). The first one makes Io's mean motion decrease, instead the second one makes it increase. Similar processes are also valid for Europa-Jupiter and Ganymede-Jupiter couples, with effects smaller of some orders of magnitude. Then the evolution of the system, which preserve the mean motions relation n_1-3*n_2+2*n_2 and which is characterized by the change of the quantities n_1-2*n_2 and n_2-2*n_3, depends on the angular momentum and energy that Io gains from the rotation of Jupiter and it loses from internal dissipation. However, thanks to the resonance there is a redistribution of mean motion between the satellites, so the variations of the angular velocities of Io, Europa and Ganymede aren't simple to calculate. A simplified example of calculation of the mean motions variations shows that, although Io's mean motion variation due to tidal forces is positive, the exchange of energy and momentum makes Io decelerate. Although the resonance amongst the Jupiter's moons has been studied since the end of the eighteenth century (thanks to Laplace) and it was formalized by De Sitter at the beginning of the twentieth century, it is still an open problem in celestial mechanics. In bibliography the values of the mean motions variations are various and this depends on the choice of the astrometric observations and on the model that is used for the equations of motion. The hope is that the JUICE space mission data make it possible to clear the real situation. In particular, Ganymede's orbit will be determined with a very good precision (level of meters or decimetres, during the dedicated phase), but the spacecraft isn't orbiting around Io (instead it is making 2 flybys of Europa, 13 flybys of Callisto, 12 flybys of Ganymede and also an orbiting phase around Ganymede), so its position will not be determined with the only JUICE radioscience data. Although Io's behaviour is very important for the theory of the resonance, the effects on the positions are distributed with a similar order of magnitude, perhaps greater in Ganymede's orbit than in the other two; then the opportunity of calculating the orbit of Ganymede is as important as that of Io. Subsequently in the thesis, after having described general steps of an orbit determination process, the mathematical model to calculate the range and range-rate observables, and the forces whichi is acting on the spacecraft, we try to understand if JUICE will manage to detect quadratic effects of the time in the barycentre position of Ganymede. The great precision of the JUICE measurements allow to find mean motion variation of Ganymede, but some long period terms (such as the libration of the resonance angle phi) may mask the result we are searching. Then it is necessary to use also astrometric observations to recognize secular effects, because they had been taken along a great time span. However it is also possible to get more data from the JUICE mission thanks its instruments and cameras, in particular in the phases before that around Ganymede. In this way the data of JUICE will contain a total information (for the determination of the Laplace resonance evolution) which is almost equal to that of a whole century of telescopic observations

Novel sol-immobilization catalysts for the hydrogenation of levulinic acid and spectroscopic valuation of metal nanoparticles accessibility using probe molecules.

Hydrogenation of levulinic acid to gamma-valerolactone has been studied with novel supported-ruthenium catalyst, achieving high conversion and selectivity in mild condition and using water as a green solvent. Sol immobilization has been applied successfully with the aim of increasing the turnover of the hydrogenation reaction per atom of ruthenium. This allows the preparation of supported metal catalysts with lower loading (1 wt.%) in comparison with the established commercial standard (5 wt.%). The study of the influence of the ruthenium precursor has been performed and the results obtained with the best catalyst have been compared with those obtained with different preparation methods. The catalysts were characterized through nitrogen sorption, temperature programmed reduction, CO hemisorption and X-ray diffraction to determine the structure and properties of the support and of the active phase and to make hypotheses regarding the structure-activity relationship. Reusability tests were performed to asses the industrial validity of this system, the result showing that though high performances are achieved with fresh catalysts, deactivation issues have still to be addressed. A deeper investigation of sol-immobilization catalysts and in particular of the role of the capping agent used in the preparation of the metal sol has been performed using titania-supported gold catalysts. The adsorption of carbon monoxide was monitored by the use of infrared and UV-vis spectroscopy on 1 wt.% Au/TiO2 prepared by sol immobilization using polyvinylalcohol and polyvinylpyrrolidone as stabilisers before and after treatments to remove the polymer from the surface. Comparison of spectroscopic results obtained on these catalysts with accessible deposition-precipitation-prepared catalyst allowed finding a relationship between the activity of the catalyst in CO oxidation and the accessibility of the surface. These newly developed tools allow for a easier characterization of the metal surface of supported gold catalysts

IMEX_SfloW2D 1.0: a depth-averaged numerical flow model for pyroclastic avalanches

Abstract. Pyroclastic avalanches are a type of granular flow generated at active volcanoes by different mechanisms, including the collapse of steep pyroclastic deposits (e.g., scoria and ash cones), fountaining during moderately explosive eruptions, and crumbling and gravitational collapse of lava domes. They represent end-members of gravity-driven pyroclastic flows characterized by relatively small volumes (less than about 1 Mm3) and relatively thin (1–10 m) layers at high particle concentration (10–50 vol %), manifesting strong topographic control. The simulation of their dynamics and mapping of their hazards pose several different problems to researchers and practitioners, mostly due to the complex and still poorly understood rheology of the polydisperse granular mixture and to the interaction with the complex natural three-dimensional topography, which often causes rapid rheological changes. In this paper, we present IMEX_SfloW2D, a depth-averaged flow model describing the granular mixture as a single-phase granular fluid. The model is formulated in absolute Cartesian coordinates (whereby the fluid flow equations are integrated along the direction of gravity) and can be solved over a topography described by a digital elevation model. The numerical discretization and solution algorithms are formulated to allow for a robust description of wet–dry conditions (thus allowing us to accurately track the front propagation) and an implicit solution to the nonlinear friction terms. Owing to these features, the model is able to reproduce steady solutions, such as the triggering and stopping phases of the flow, without the need for empirical conditions. Benchmark cases are discussed to verify the numerical code implementation and to demonstrate the main features of the new model. A preliminary application to the simulation of the 11 February pyroclastic avalanche at the Etna volcano (Italy) is finally presented. In the present formulation, a simple semi-empirical friction model (Voellmy–Salm rheology) is implemented. However, the modular structure of the code facilitates the implementation of more specific and calibrated rheological models for pyroclastic avalanches

The use of carbon monoxide as a probe molecule in spectroscopic studies for determination of exposed gold sites on TiO2

The sol immobilisation technique, in which a stabilising ligand (such as polyvinyl alcohol or polyvinyl pyridine) can be used to tune metal particle size and composition, has become a valuable method of making supported nanoparticle catalysts. An unfortunate consequence of the stabilising ligand is that often access of reactant molecules to the metal nanoparticle surface is impeded. Several methods have been proposed for the removal of these ligands, though determination of the degree of their success is difficult. Here, we demonstrate the use of in situ infrared and UV-Vis spectroscopy to elucidate the access of carbon monoxide to the surface of Au/TiO2 catalysts before and after various ligand removal treatments. These were contrasted with a catalyst prepared by deposition precipitation prepared in the absence of stabilising ligand as a control. Changes were observed in the infrared spectrum, with the wavenumber of carbon monoxide linearly bonded to Au for catalysts shifting before and after ligand removal, which correlated well with the activity of the catalyst for carbon monoxide oxidation. Also the extent of shifting of the Au surface resonance plasmon band on the addition of carbon monoxide, observed by UV-Vis, also correlated well with catalyst activity. These simple methods can be used to determine the quantity of exposed metal sites after a ligand removal treatment and so determine the treatments effectiveness

Tilting Uranus via the migration of an ancient satellite

Context. The 98{\deg}-obliquity of Uranus is commonly attributed to giant impacts that occurred at the end of the planetary formation. This picture, however, is not devoid of weaknesses. Aims. On a billion-year timescale, the tidal migration of the satellites of Jupiter and Saturn has been shown to strongly affect their spin-axis dynamics. We aim to revisit the scenario of tilting Uranus in light of this mechanism. Methods. We analyse the precession spectrum of Uranus and identify the candidate secular spin-orbit resonances that could be responsible for the tilting. We determine the properties of the hypothetical ancient satellite required for a capture and explore the dynamics numerically. Results. If it migrates over 10 Uranus' radii, a single satellite with minimum mass 4e-4 Uranus' mass is able to tilt Uranus from a small obliquity and make it converge towards 90{\deg}. In order to achieve the tilting in less than the age of the Solar System, the mean drift rate of the satellite must be comparable to the Moon's current orbital expansion. Under these conditions, simulations show that Uranus is readily tilted over 80{\deg}. Beyond this point, the satellite is strongly destabilised and triggers a phase of chaotic motion for the planet's spin axis. The chaotic phase ends when the satellite collides into the planet, ultimately freezing the planet's obliquity in either a prograde, or plainly retrograde state (as Uranus today). Spin states resembling that of Uranus can be obtained with probabilities as large as 80%, but a bigger satellite is favoured, with mass 1.7e-3 Uranus' mass or more. Yet, a smaller ancient satellite is not categorically ruled out, and there is room for improving this basic scenario in future studies. Interactions among several pre-existing satellites is a promising possibility.Comment: Accepted for publication in Astronomy and Astrophysic

Antimicrobial resistance among migrants in Europe: a systematic review and meta-analysis

BACKGROUND: Rates of antimicrobial resistance (AMR) are rising globally and there is concern that increased migration is contributing to the burden of antibiotic resistance in Europe. However, the effect of migration on the burden of AMR in Europe has not yet been comprehensively examined. Therefore, we did a systematic review and meta-analysis to identify and synthesise data for AMR carriage or infection in migrants to Europe to examine differences in patterns of AMR across migrant groups and in different settings. METHODS: For this systematic review and meta-analysis, we searched MEDLINE, Embase, PubMed, and Scopus with no language restrictions from Jan 1, 2000, to Jan 18, 2017, for primary data from observational studies reporting antibacterial resistance in common bacterial pathogens among migrants to 21 European Union-15 and European Economic Area countries. To be eligible for inclusion, studies had to report data on carriage or infection with laboratory-confirmed antibiotic-resistant organisms in migrant populations. We extracted data from eligible studies and assessed quality using piloted, standardised forms. We did not examine drug resistance in tuberculosis and excluded articles solely reporting on this parameter. We also excluded articles in which migrant status was determined by ethnicity, country of birth of participants' parents, or was not defined, and articles in which data were not disaggregated by migrant status. Outcomes were carriage of or infection with antibiotic-resistant organisms. We used random-effects models to calculate the pooled prevalence of each outcome. The study protocol is registered with PROSPERO, number CRD42016043681. FINDINGS: We identified 2274 articles, of which 23 observational studies reporting on antibiotic resistance in 2319 migrants were included. The pooled prevalence of any AMR carriage or AMR infection in migrants was 25·4% (95% CI 19·1-31·8; I2 =98%), including meticillin-resistant Staphylococcus aureus (7·8%, 4·8-10·7; I2 =92%) and antibiotic-resistant Gram-negative bacteria (27·2%, 17·6-36·8; I2 =94%). The pooled prevalence of any AMR carriage or infection was higher in refugees and asylum seekers (33·0%, 18·3-47·6; I2 =98%) than in other migrant groups (6·6%, 1·8-11·3; I2 =92%). The pooled prevalence of antibiotic-resistant organisms was slightly higher in high-migrant community settings (33·1%, 11·1-55·1; I2 =96%) than in migrants in hospitals (24·3%, 16·1-32·6; I2 =98%). We did not find evidence of high rates of transmission of AMR from migrant to host populations. INTERPRETATION: Migrants are exposed to conditions favouring the emergence of drug resistance during transit and in host countries in Europe. Increased antibiotic resistance among refugees and asylum seekers and in high-migrant community settings (such as refugee camps and detention facilities) highlights the need for improved living conditions, access to health care, and initiatives to facilitate detection of and appropriate high-quality treatment for antibiotic-resistant infections during transit and in host countries. Protocols for the prevention and control of infection and for antibiotic surveillance need to be integrated in all aspects of health care, which should be accessible for all migrant groups, and should target determinants of AMR before, during, and after migration. FUNDING: UK National Institute for Health Research Imperial Biomedical Research Centre, Imperial College Healthcare Charity, the Wellcome Trust, and UK National Institute for Health Research Health Protection Research Unit in Healthcare-associated Infections and Antimictobial Resistance at Imperial College London

Measurement of the top quark-pair production cross section with ATLAS in pp collisions at \sqrt{s}=7\TeV

A measurement of the production cross-section for top quark pairs(\ttbar) in $pp$ collisions at \sqrt{s}=7 \TeV is presented using data recorded with the ATLAS detector at the Large Hadron Collider. Events are selected in two different topologies: single lepton (electron $e$ or muon $\mu$) with large missing transverse energy and at least four jets, and dilepton ($ee$, $\mu\mu$ or $e\mu$) with large missing transverse energy and at least two jets. In a data sample of 2.9 pb-1, 37 candidate events are observed in the single-lepton topology and 9 events in the dilepton topology. The corresponding expected backgrounds from non-\ttbar Standard Model processes are estimated using data-driven methods and determined to be $12.2 \pm 3.9$ events and $2.5 \pm 0.6$ events, respectively. The kinematic properties of the selected events are consistent with SM \ttbar production. The inclusive top quark pair production cross-section is measured to be \sigmattbar=145 \pm 31 ^{+42}_{-27} pb where the first uncertainty is statistical and the second systematic. The measurement agrees with perturbative QCD calculations.Comment: 30 pages plus author list (50 pages total), 9 figures, 11 tables, CERN-PH number and final journal adde