107 research outputs found
Convolutional Autoencoder for the Spatiotemporal Latent Representation of Turbulence
No full textTurbulence is characterised by chaotic dynamics and a high-dimensional state space, which make this phenomenon challenging to predict. However, turbulent flows are often characterised by coherent spatiotemporal structures, such as vortices or large-scale modes, which can help obtain a latent description of turbulent flows. However, current approaches are often limited by either the need to use some form of thresholding on quantities defining the isosurfaces to which the flow structures are associated or the linearity of traditional modal flow decomposition approaches, such as those based on proper orthogonal decomposition. This problem is exacerbated in flows that exhibit extreme events, which are rare and sudden changes in a turbulent state. The goal of this paper is to obtain an efficient and accurate reduced-order latent representation of a turbulent flow that exhibits extreme events. Specifically, we employ a three-dimensional multiscale convolutional autoencoder (CAE) to obtain such latent representation. We apply it to a three-dimensional turbulent flow. We show that the Multiscale CAE is efficient, requiring less than 10% degrees of freedom than proper orthogonal decomposition for compressing the data and is able to accurately reconstruct flow states related to extreme events. The proposed deep learning architecture opens opportunities for nonlinear reduced-order modeling of turbulent flows from data.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Aerodynamic
Eurozona e debito pubblico: gli eurobond come strumento di integrazione politico-istituzionale
No full textGli eurobond non sono un tema nuovo. Sono presenti nella letteratura economica, meno in quella giuridica, da oltre trent’anni, con denominazioni che spesso mutano a seconda delle formulazioni proposte. Rientrano in quella categoria di idee che hanno valore non solo sotto il profilo della tecnica finanziaria o della finanza pubblica, ma anche perché rappresentano un primo passo verso la realizzazione di un’unione politica dell’Europa. I favorevoli vedono in questo tipo di proposte non solo una risposta alla crisi attraverso il finanziamento degli investimenti pubblici, ma anche la costruzione di una politica fiscale europea da affiancare a quella monetaria della Banca centrale europea. Gli scettici pongono, invece, l’accento sui tempi troppo lunghi che tali proposte richiederebbero per essere attuate e sul consenso non unanime che esse riscuotono da parte dei Paesi dell’Eurozona. L’introduzione degli eurobond presenta, infatti, ostacoli legali e distributivi. Quelli legali hanno a che fare, in particolare, con l’articolo 125 del Trattato sul Funzionamento dell’Unione europea (TFUE), che dispone il divieto di salvataggio da parte dell’Unione a favore di un Paese membro in difficoltà e, in particolare, vieta a ciascuno Stato membro di rispondere o di subentrare nei debiti di altri Stati membri (cosiddetta “clausola di no bail out”). Gli ostacoli distributivi sono legati alle modalità di partecipazione dei Paesi membri alle emissioni congiunte dei titoli del debito europeo in termini di risorse finanziarie e ai timori dei Paesi virtuosi del Nord Europa di dover fornire un contributo maggiore rispetto ai Paesi meno virtuosi del Sud Europa.
La tesi affronta, innanzitutto, il tema della fragilità della costruzione europea, che dipende essenzialmente dall’aver creato – contrariamente a quanto avvenuto nella storia dei popoli – “una moneta senza Stato”. Questa circostanza ha condotto, alla fine del 2009, alla crisi dell’euro e dei debiti sovrani. Per rimediare a tale fragilità istituzionale, bisognerebbe por mano a una serie di riforme come il rafforzamento del ruolo della Banca centrale europea come prestatore di ultima istanza, il completamento dell’unione bancaria, l’approfondimento dell’unione del mercato dei capitali, l’allargamento del bilancio europeo e l’accentramento delle politiche fiscali nazionali. Tra queste riforme rientra anche quella di dar vita all’emissione congiunta di debito sovrano a livello di Eurozona, o, in alternativa, a schemi che non prevedono la mutualizzazione del debito. Al riguardo, la ricerca prende in esame l’esistenza di eventuali basi giuridiche per emettere un debito federale dell’Unione europea, distinto dal debito degli Stati membri o, in alternativa, per procedere alla mutualizzazione dei debiti degli Stati membri.
La tesi passa, poi, in rassegna le varie proposte avanzate in tema di eurobond, classificandole in due gruppi principali, a seconda che prevedano o meno la mutualizzazione del debito. Nell’ambito delle proposte che si basano sulla mutualizzazione del debito rientrano gli eurobond in senso stretto, gli union bond, gli stability bond, le obbligazioni blu e rosse. Tali proposte, in quanto fondate sulla mutualizzazione del debito, non sono compatibili con l’articolo 125 del TFUE e richiederebbero pertanto la sua modifica. Nel secondo gruppo di proposte – che non contemplano la mutualizzazione del debito e pertanto non richiedono la modifica del TFUE – rientrano il programma PADRE (Politically Acceptable Debt Restructuring in Europe), il Fondo di ammortamento del debito a livello europeo (European Redemption Fund), gli European Safe Bond - ESB (acronimo inglese di “Titoli europei sicuri”), i Sovereign Bond Backed Securities - SBBS (acronimo inglese di “Titoli garantiti da obbligazioni sovrane”).
La ricerca esplora i possibili approcci alla prosecuzione del progetto europeo: la via della riduzione del rischio (risk-reduction), la via della condivisione del rischio (risk-sharing), la via della sintesi tra riduzione e condivisione del rischio. Quest’ultima via appare a chi scrive come l’unica politicamente percorribile. La stessa unione monetaria si è realizzata come combinazione tra i due approcci: il processo di convergenza delle finanze pubbliche (risk reduction) ha condotto alla creazione di un’unica banca centrale con il compito di mettere in atto un’unica politica monetaria e del cambio (risk sharing). Vi è però la necessità per l’Italia di fare la propria parte invertendo la traiettoria del rapporto debito-Pil attraverso un serio e rigoroso piano pluriennale di rientro dal debito (risk reduction), per acquisire, agli occhi dei principali partner europei, quella credibilità necessaria per convincerli a dar vita a un vero e proprio debito federale europeo (risk sharing). Gli eurobond non sono l’unico mezzo per raggiungere la finalità di una unificazione politica dell’Europa ma hanno il pregio di mettere insieme l’approccio funzionalista dei passi graduali con quello federalista della meta finale. Analogamente a quanto avvenuto nella storia di alcuni popoli (in particolare negli Stati Uniti d’America) in cui il processo di unificazione dei debiti ha segnato la nascita dello Stato, anche nel vecchio continente l’europeizzazione del debito degli Stati membri, al di là della valenza in termini di finanza pubblica, potrebbe assurgere a un vero e proprio atto “costitutivo” di un futuro Stato federale europeo.
Sotto il profilo metodologico, la ricerca è stata condotta attraverso la strumentazione propria dell’analisi economica del diritto, nella consapevolezza che il mercato – vale a dire il meccanismo economico che orienta il comportamento di individui e gruppi – da solo non è sufficiente ma ha bisogno di regole per poter funzionare. Anzi, se ben regolato, il mercato può essere fattore di sviluppo e di benessere. Questo ragionamento vale anche per il mercato comune e per la moneta unica europea, che da soli non bastano più. Come si è tentato di mostrare in questo lavoro, anche l’Eurozona, per poter sopravvivere e progredire, ha bisogno di un adeguamento delle proprie istituzioni che passa anche attraverso l’emissione congiunta di debito sovrano. Coerentemente con tale impostazione, l’indagine cerca di avere un approccio critico al tema degli eurobond, tentando di analizzarne i singoli aspetti con indipendenza di giudizio. La stesura dei capitoli e dei singoli paragrafi è stata preceduta da un lavoro di documentazione e consultazione di testi, riviste specializzate e articoli. Le conoscenze teoriche acquisite e le idee maturate sono state verificate sul campo, grazie ad un confronto diretto con i dirigenti che, nell’ambito del Dipartimento del Tesoro del Ministero dell’Economia e delle Finanze, hanno la responsabilità dell’emissione e della gestione del debito pubblico italiano. Chi scrive lavora presso la direzione del Debito pubblico del Dipartimento del Tesoro; cionondimeno, le opinioni che qui esprime sono personali e non rappresentano o impegnano in alcun modo l’amministrazione di appartenenza.
Alla luce delle considerazioni svolte, si ritiene che davvero gli eurobond possano spingere l’Eurozona verso una maggiore integrazione politico-istituzionale. L’analisi economica e giuridica può dare il proprio contributo alla comprensione della questione, ma la scelta dei passi da compiere in concreto spetta alle leadership politiche europee in quanto investite del consenso popolare. Il ricercatore può esporre gli effetti che derivano dall'adozione di una particolare misura o di uno specifico strumento. Oltre non può andare.Eurobonds are not a new topic. They have been present in the economic literature, less in the legal literature, for thirty years, with denominations which change according to the proposed formulations. They are relevant not only in terms of financial economics or public finance, but also because they represent a first step towards the realization of a political union of Europe. Those in favor look at eurobonds not only as a response to the crisis through the financing of public investments, but also as a tool to build up a European fiscal policy in addition to the monetary policy of the European Central Bank. On the contrary, the skeptics underline the fact that such proposals would require too mach time to be implemented and the fact that they have short consent in the Eurozone countries. The introduction of eurobonds presents legal and distributive barriers. The legal barriers are linked to the Article 125 of the Treaty on the Functioning of the European Union (TFEU), which provides for so-colled “no bail out clause” (“A Member State shall not be liable for or assume the commitments of central governments, regional, local or other public authorities, other bodies governed by public law, or public under¬ takings of another Member State”). The distributive obstacles, on the other hand, are linked to the way in which Member States could participate in joint issuance of European debt securities. In particular, the virtuous countries of Northern Europe are afraid that they would pay a greater share than the less virtuous countries of the Southern Europe.
First of all, the thesis analyzes the fragility of the European institutions, which depends essentially on having created – contrary to what has happened in the history of peoples – “a currency without a State”. In the end of 2009, this fragility led Europe to the crisis of euro and sovereign debts. To face this fragility, some institutional reforms should be carried out, such as the strengthening of the role of the European Central Bank as a lender of last resort, the completion of the banking union, the deepening of the capital market, the enlargement of the European budget and the centralization of national fiscal policies. These reformes also include the joint issuance of sovereign debts of Eurozone Member States. In this regard, the research examines the existence of possible legal bases for issuing a federal debt of the European Union, different from the debt of the Member States or, alternatively, for joint issuing the debt securities of the Member States.
Secondly, the thesis examines the various proposals of eurobonds, classifying them in two main groups. The first group, based on the joint issuance of debt, includes eurobonds in the strict sense, union bonds, stability bonds, blue and red bonds. These proposals, being based on the joint issuance of debt, are contrary to Article 125 of the TFEU and therefore would require its modification. The second group of proposals – which do not contemplate the joint issuance of debt and therefore do not require the modification of the TFEU – include the PADRE program (Politically Acceptable Debt Restructuring in Europe), the European Redemption Debt Fund, the European Safe Bonds, the Sovereign Bond Backed Securities.
Thirdly, the research explores the possible approaches to the continuation of the European project: the risk-reduction path, the risk-sharing path, the synthesis between risk reduction and risk sharing. This third path seems to be the only politically feasible. As we know, also the monetary union was realized as a combination of the two approaches: the process of convergence of public finances (risk reduction) led to the creation of a single central bank with the task of managing a single monetary policy (risk sharing). However, Italy has to reverse the trend of the debt-to-GDP ratio through a serious and rigorous long-term debt reduction plan (risk reduction), in order to convince the main European partners to issue European federal debt (risk sharing). Eurobonds are not the only tool to achieve the goal of a political unification of Europe but they have the merit of putting together the functionalist approach based on the gradual steps with the federalist approach based on the final goal. Similarly to what has happened in the history of some peoples, such as the United States of America, where the process of unification of debt of the single States has marked the birth of the federal State, even in Europe the consolidation of debt of the Member States might be a constitutive act of the United States of Europe.
Methodologically, the research is based on the economic analysis of law. According to this view, market – the economic mechanism which guides the behavior of individuals and groups – is not enough but needs good regulation. Indeed, if it is well regulated, market may be a factor of development and welfare. This way of thinking is also valid for the European single market and for the euro, which are no longer enough. As we have tried to show in this work, also the Eurozone institutions need a deep reform – including the joint issuance of sovereign debt – for their surviving and progress.
This work tries to have a critical approach to the topic of eurobonds. The theoretical knowledge and ideas have been checked thanks to a direct dialogue with managers who, within the Treasury Department of the Ministry of the Economy and Finance, are responsible for issuance and management of the Italian public debt. The author of this research works in the Public Debt Directorate at Treasury Department; nevertheless his opinions are personal and do not represent the Treasury Department.
For these considerations, eurobonds might really push the Eurozone towards a greater political and institutional integration. The economic and legal analysis may give its contribution to the debate, but the actual choices are up to the European policy-makers
Social Robot Co-Design Canvases: A Participatory Design Framework
No full textFunding Information: This project was funded by Futurice. M.A. acknowledges a grant from the project AMIGOS:PTDC/EEISII/7174/2014, and the Osk. Huttunen Foundation, and EP/T517847/1 (EPSRC). R.O. also acknowledges a grant by Fundação para a Ciência e a Tecnologia: (FCT) from the project AMIGOS:PTDC/EEISII/7174/2014 and a Ph.D. grant with the following reference: PD/BD/150570/2020. The work of M. R. and V. K. was partially financially supported by Academy of Finland Strategic Research Council project ROSE, 314180. Authors’ addresses: M. Axelsson, University of Cambridge, Department of Computer Science and Technology, The Computer Laboratory, William Gates Building, 15 JJ Thomson Avenue, Cambridge CB3 0FD; email: minja.axelsson@ cl.cam.ac.uk; R. Oliveira, Group on Artificial Intelligence for People and the Society (GAIPS), INESC-ID, Iscte-University Institute of Lisbon (CIS-IUL), Av. das Forças Armadas, 1649-026, Lisbon, Portugal; M. Racca, Idiap Research Institute, Rue Marconi 19, CH - 1920, Martigny, Switzerland; email: [email protected]; V. Kyrki, Aalto University, Department of Electrical Engineering and Automation, Maarintie 8, 02130 Espoo, Finland; email: [email protected]. Publisher Copyright: © 2021 Copyright held by the owner/author(s).Design teams of social robots are often multidisciplinary, due to the broad knowledge from different scientific domains needed to develop such complex technology. However, tools to facilitate multidisciplinary collaboration are scarce. We introduce a framework for the participatory design of social robots and corresponding canvas tool for participatory design. The canvases can be applied in different parts of the design process to facilitate collaboration between experts of different fields, as well as to incorporate prospective users of the robot into the design process. We investigate the usability of the proposed canvases with two social robot design case studies: a robot that played games online with teenage users and a librarian robot that guided users at a public library. We observe through participants' feedback that the canvases have the advantages of (1) providing structure, clarity, and a clear process to the design; (2) encouraging designers and users to share their viewpoints to progress toward a shared one; and (3) providing an educational and enjoyable design experience for the teams.Peer reviewe
Numerical solutions for lunar orbits
No full textStarting from a variational formulation based on Hamilton’s Principle, the paper exploits the finite element technique in the time domain in order to solve orbital dynamic problems characterised by constrained boundary value rather than initial value problems. The solution is obtained assembling a suitable number of finite elements inside the time interval of interest, imposing the desired constraints, and solving the resultant set of non-linear algebraic equations by means of Newton-Raphson method. In particular, in this work this general solution strategy is applied to periodic orbits determination. The effectiveness of the approach in finding periodic orbits in the unhomogeneous gravity field of the Moon is assessed by means of relevant examples, and the results are compared with those obtained by standard time marching techniques as well as with analytical results
Solar sail capture trajectories at Mercury
No full textMercury is an ideal environment for future planetary exploration by solar sail since it has proved difficult to reach with conventional propulsion and hence remains largely unexplored. In addition, its proximity to the Sun provides a solar sail acceleration of order ten times the sail characteristic acceleration at 1 AU. Conventional capture techniques are shown to be unsuitable for solar sails and a new method is presented. It is shown that capture is bound by upper and lower limits on the orbital elements of the approach orbit and that failure to be within limits results in a catastrophic collision with the planet. These limits are presented for a range of capture inclinations and sail characteristic accelerations. It is found that sail hyperbolic excess velocity is a critical parameter during capture at Mercury, with only a narrow allowed band in order to avoid collision with the planet. The new capture methodis demonstrated for a Mercury sample return mission
Biochemical and physiological parameters associated with Trypanosoma evansi prevalence in wild capybaras
No full textParasites can be detrimental to the health of wildlife populations and may negatively affect several aspects of the life history of their hosts. Investigating host health, therefore, is key to understanding important mechanisms of the host-parasite interaction at the individual and population levels. Recently, we reported a prevalence of 10% of Trypanosoma evansi (Steel 1884) in a population of capybaras (Hydrochoerus hydrochaeris Linnaeus 1766) from Esteros del Iberรก, Argentina; however, the impact of T. evansi infection in capybaras is unknown. The aim of this study was to explore associations between T. evansi infection and biochemical and physiological parameters in wild capybaras using blood samples (n=60) from a managed population of free-ranging capybaras from Esteros del Iberรก. Infection by T. evansi was negatively associated with body condition, albumin, alpha-2 globulin concentrations, albumin:globulin ratio and eosinophil counts, and it was positively associated with spleen index and gamma-globulin concentrations. These results suggest that T. evansi infection may pose significant impact on the health of wild capybaras.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author
Displaced geostationary orbits using hybrid low-thrust propulsion
No full textIn this paper, displaced geostationary orbits using hybrid low-thrust propulsion, a complementary combination of Solar Electric Propulsion (SEP) and solar sailing, are investigated to increase the capacity of the geostationary ring that is starting to become congested. The SEP propellant consumption is minimized in order to maximize the mission lifetime by deriving semi-analytical formulae for the optimal steering laws for the SEP and solar sail accelerations. By considering the spacecraft mass budget, the performance is also expressed in terms of payload mass capacity. The analyses are performed both for the use of pure SEP and hybrid low-thrust propulsion to allow for a comparison. It is found that hybrid low-thrust control outperforms the pure SEP case both in terms of payload mass capacity and mission lifetime for all displacements considered. Hybrid low-thrust propulsion enables payloads of 255 to 487 kg to be maintained in a 35 km displaced orbit for 10 to 15 years. Adding the influence of the J2 and J22 terms of the Earth’s gravity field has a small effect on this lifetime, which becomes almost negligible for small values of the sail lightness number. Finally, two SEP transfers that allow for an improvement in the performance of hybrid low-thrust control are optimized for the propellant consumption by solving the accompanying optimal control problem using a direct pseudospectral method. The first type of transfer enables a transit between orbits displaced above and below the equatorial plane, while the second type of transfer enables customized service for which a spacecraft is transferred to a Keplerian parking orbit when geostationary coverage is not needed. While the latter requires a modest propellant budget, the first type of transfer comes at the cost of an almost negligible SEP propellant consumption
High frequency thermal emission from the lunar surface and near surface temperature of the Moon from Chang'E-2 microwave radiometer
No full textNear surface temperature of the Moon and thermal behaviors of the lunar regolith can provide important information for constraining thermal and magmatic evolution models of the Moon and engineering constrains for in situ lunar exploration system. In this study, China's Chang'E-2 (CE-2) microwave radiometer (MRM) data at high frequency channels are used to investigate near surface temperature of the Moon given the penetration ability of microwave into the desiccated and porous lunar regolith. Factors that affect high frequency brightness temperature (TB), such as surface slope, solar albedo and dielectric constant, are analyzed first using a revised Racca's temperature model. Radiative transfer theory is then used to model thermal emission from a semi-infinite regolith medium, with considering dielectric constant and temperature profiles within the regolith layer. To decouple the effect of diurnal temperature variation in the uppermost lunar surface, diurnal averaged brightness temperatures at high frequency channels are used to invert mean diurnal surface and subsurface temperatures based on their bilinear profiles within the regolith layer. Our results show that, at the scale of the spatial resolution of CE-2 MRM, surface slope of crater wall varies typically from about 20 degrees to 30 degrees, and this causes a variation in TB about 10-15 K. Solar albedo can give rise to a TB difference of about 5-10 K between maria and highlands, whereas a similar to 2-8 K difference can be compensated by the dielectric constant on the other hand. Inversion results indicate that latitude (phi) variations of the mean diurnal surface and subsurface temperatures follow simple rules as cos(030) phi and cos(0.36) phi, respectively. The inverted mean diurnal temperature profiles at the Apollo 15 and 17 landing sites are also compared with the Apollo heat flow experiment data, showing an inversion uncertainty <4 K for surface temperature and <1 K for subsurface temperature. (C) 2014 Elsevier Inc. All rights reserved.Astronomy & AstrophysicsSCI(E)[email protected]
- …
