A Provably Efficient Option-Based Algorithm for both High-Level and Low-Level Learning

Hierarchical Reinforcement Learning (HRL) approaches have shown successful results in solving a large variety of complex, structured, long-horizon problems. Nevertheless, a full theoretical understanding of this empirical evidence is currently missing. In the context of the option framework, prior research has devised efficient algorithms for scenarios where options are fixed, and the high-level policy selecting among options only has to be learned. However, the fully realistic scenario in which both the high-level and the low-level policies are learned is surprisingly disregarded from a theoretical perspective. This work makes a step towards the understanding of this latter scenario. Focusing on the finite-horizon problem, we present a meta-algorithm alternating between regret minimization algorithms instanced at different (high and low) temporal abstractions. At the higher level, we treat the problem as a Semi-Markov Decision Process (SMDP), with fixed low-level policies, while at a lower level, inner option policies are learned with a fixed high-level policy. The bounds derived are compared with the lower bound for non-hierarchical finitehorizon problems, allowing to characterize when a hierarchical approach is provably preferable, even without pre-trained options

Green vs fossil-based energy vectors: A comparative techno-economic analysis of green ammonia and LNG value chains

This study conducts a comparative techno-economic assessment on the value chains of ammonia, as a green energy vector, and Liquefied Natural Gas (LNG), representing the benchmark energy vector, for long-distance energy transportation from Middle East to Europe. The value chain involves production from resources, conversion to an energy vector, storage and transport and reconversion of the energy vector to a suitable fuel. For comparison purposes, an electric power output of 400 MW is assumed to be produced by a power plant that utilizes either green or fossil fuels delivered to it. The adopted parameter for this comparison is the Levelized Cost of Energy (LCoE). Greenhouse gas emissions are economically penalized through the Social Cost of Carbon (SCC). Considering a SCC of 0.100 euro/kg, the LCoE of the LNG value chain is 59.19 euro/MWh, while that of ammonia is 231.71 euro/MWh. Since the cost of producing green hydrogen and purified natural gas strongly affects the results, a sensitivity analysis is performed to assess the impact of the assumed values. The SCC required to break even the LCoE of the two value chains is: 0.183 euro/MWh when considering the most favorable scenario for the green energy vector (low green hydrogen and high purified natural gas production costs) and 1.731 euro/kg when considering the most unfavorable one. This study highlights the cost-effectiveness of LNG in the current economic and regulatory landscape. However, the break-even range for the SCC indicates the potential for green ammonia to gain economic viability under higher carbon pricing scenarios

LA FALSIFICAZIONE DI STRUMENTI MUSICALI. UN'INDAGINE STORICO-CRITICA.

Falsificare significa attribuire a un manufatto un\u2019identit\ue0 che non gli appartiene con lo scopo di ottenere un beneficio a proprio vantaggio o a danno di altri soggetti. Nel corso dei secoli la falsificazione ha interessato reperti paletnologici, sculture d\u2019arte contemporanea, ritrovamenti archeologici, documenti, arredi, dipinti, reliquie e altro ancora. Gli strumenti musicali certamente non sono stati risparmiati dal fenomeno, che, anzi, si \ue8 dimostrato una vera e propria costante nella storia di questi prodotti. Dai casi pi\uf9 antichi conosciuti risalenti alla met\ue0 del Cinquecento, fino a quelli pi\uf9 recenti al principio del nuovo millennio, non si sono registrate pause nella realizzazione di esemplari fasulli e la presenza di contraffazioni, plagi o alterazioni ha interessato pressoch\ue9 tutti i continenti. La falsificazione ha potuto prosperare perch\ue9 ha sempre svolto la funzione essenziale di facilitare la reperibilit\ue0 di opere molto ricercate ma, per motivi economici o per scarsit\ue0 di modelli esistenti, difficilmente raggiungibili. In particolare \ue8 stata in grado di sfruttare la domanda diffusa di strumenti dalle elevate qualit\ue0 tecnico-sonore, di reperti antichi provenienti dalle passate civilt\ue0 musicali e di beni in cui investire ingenti capitali, concentrando gli interventi sui parametri fondamentali di uno strumento, ossia la sua et\ue0, il suo luogo d\u2019origine e l\u2019identit\ue0 del suo autore. Dalla comparsa quarant\u2019anni fa del primo studio sistematico sulla figura di Leopoldo Franciolini, l\u2019organologia ha associato la creazione di falsi strumenti musicali a questo antiquario fiorentino in maniera tanto automatica quanto eccessiva. Molti infatti sono stati i responsabili delle pratiche fraudolente in questo settore oltre a Franciolini, attivi prima di lui, dopo di lui e contemporaneamente a lui. Alcuni nomi possono essere citati, come Isaac Ehe, i fratelli Voller, Herny Werro, o Yuko Kanda, ma la verit\ue0 \ue8 che la maggior parte dei falsari \ue8 rimasta nell\u2019anonimato. Infine, se da un lato la falsificazione di strumenti musicali ha conosciuto storicamente un\u2019indubbia espansione, dall\u2019altro per\uf2 l\u2019interpretazione della natura di falso non pu\uf2 n\ue9 deve essere forzata. L\u2019inautenticit\ue0 di uno strumento, difatti, non \ue8 garanzia di falsit\ue0 senza che sia accompagnata dal riconoscimento dell\u2019intento programmatico d\u2019ingannare. Cos\uec come la mancata paternit\ue0 individuale riscontrata per uno strumento non rappresenta un criterio valido per ravvisarne e stabilirne la sofisticazione.Faking is an act through which an object is provided with an identity not belonging to it, in order to deceive and to benefit from somebody\u2019s detriment. Faking concerned archaeological finds, contemporary art sculptures, documents, furniture, paintings, relics and so on. Musical instruments were not spared by this phenomenon, which in contrast was a standard feature in the history of those artifacts. From the most ancient known cases in the middle of the 16th century until the most recent ones at the beginning of the new millennium, musical instruments\u2019 forgery has never ceased and counterfeited, plagiarized and altered products were spread nearly in every continent. This kind of falsification flourished as it eased the availability of very sought-after works, which otherwise were scarcely achievable because of economic reasons or shortage of specimens. Namely it was able to exploit the widespread demand for high performing musical instruments, for evidences of early musical cultures and for goods to invest in. Therefore its actions were focused on the most important parameters of an instrument: age, place of origin and maker\u2019s identity. When the first detailed research into the Florentine antique dealer Leopoldo Franciolini was published forty years ago, organology began to link his name with musical instruments\u2019 forgery as automatically as excessively. Indeed several other forgers operated before, at the same time and after Franciolini. Some of them may be mentioned, for instance Isaac Ehe, the Voller brothers or Yuko Kanda. Yet most of the fakers remained anonymous. Finally, on the one hand faking musical instruments was undoubtedly a common practice, but on the other hand detecting the nature of the fake must not be forced. If the purposeful intention of deceiving cannot be observed, then an unauthentic instrument \u2013 for example a replica \u2013 cannot be consequently judged to be false. In the same way, if the building of a musical instrument cannot be associated with one individual maker, it doesn\u2019t necessarily mean it is not genuine

Dynamic models for Large Eddy Simulation of compressible flows with a high order DG method

The impact of dynamic models for applications to LES of compressible flows is assessed in the framework of a numerical model based on high order discontinuous finite elements. The projections onto lower dimensional subspaces associated with lower degree basis functions are used as LES filter, along the lines proposed in Variational Multiscale templates. Comparisons with DNS results available in the literature for plane and constricted channel flows at Mach numbers 0.2, 0.7 and 1.5 show clearly that the dynamic models are able to improve the prediction of most key features of the flow with respect to the Smagorinsky models employed so far in a VMS-DG context