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Some Algorithmic Problems for the Web Economy
No full textThis thesis investigates algorithmic problems arising in the context of the Web economy, focusing on two central themes: learning Random Utility Models (RUMs) and Online Bipartite Matching. Both problems are motivated by modern digital platforms---RUMs model user choice behavior in online platforms, while Online Bipartite Matching captures core challenges in online advertising allocation.
The first part of the thesis considers platforms that host vast catalogs of items but interact with users only through small subsets of options (``slates''). This setting reflects practical constraints faced by real-world systems, such as the ten blue links of web search or a movie shelf on Prime Video or Netflix. Modeling user behavior through Random Utility Models---the gold standard in Economics for discrete choice problems---we establish sharp bounds on the slate size required to predict user preferences across all possible subsets of items. We present improved algorithms and strong impossibility results for this problem. These impossibility results, which are further supported by empirical assessments on real-world datasets of moderate size, reveal a significant gap in the ability of current recommendation platforms to infer global preferences from limited interactions.
The second part addresses Online Bipartite Matching, a fundamental abstraction for online ad allocation. We derive a new impossibility bound showing that no online algorithm can achieve a competitive ratio better than 1 - e^{1 - e}. Our result, based on a simple and analytically tractable construction, currently stands as the best-known upper bound for many variants of stochastic online bipartite matching, including the famous randomly-permuted-adversarial-graph variant, improving the long-standing 0.823 bound of Manshadi, Oveis Gharan, and Saberi (SODA, 2011) after 14 years.
Overall, this thesis advances the state of the art on two fundamental problems at the intersection of algorithms and economics, highlighting both the algorithmic possibilities and the intrinsic limitations of large-scale online systems
Journeys through the Aniene Valley. A Guide to the Routes of the Sacred
No full textShaped by water and enclosed between the Prenestini, Ruffi, Simbruini and Lepini mountains, the Aniene Valley boasts a landscape of extraordinary complexity, where nature and history intertwine in a continuous process of transformation. Between Rome, Tivoli and Subiaco lies a territory that, along the seventy kilometres of the Via Tiburtina, showcases ancient and recent anthropic traces, capable of restoring the memory of a never-ending dialogue between man and the environment.
This guide offers a new interpretation of the Valley through interdisciplinary scientific contributions that describe sacred spaces and highlight a living, fragile and precious landscape: a threshold between the Ager Tiburtinus and the mountains, to be rediscovered with a new and mindful gaze
I soci nella crisi dell'impresa bancaria
No full textIl quadro normativo di gestione del dissesto dell’impresa bancaria costruito in sede eurounitaria all’esito della grande crisi finanziaria globale degli anni 2007-2011 ha sollevato l’emersione di rilevanti tensioni tra autonomia privata e interesse pubblico alla stabilità del sistema. La posizione dell’azionista di società bancaria appare invero caratterizzata da una compressione delle prerogative connesse alla partecipazione sociale, sotto il profilo patrimoniale e amministrativo, più accentuata di quella risultante dalla gestione della crisi dell’impresa comune e associata alla nota rischiosità del titolo azionario. Muovendo da tale prospettiva, la ricerca ha inteso comprendere le specificità del trattamento del socio nel contesto della crisi, verificando la coerenza della disciplina con i principi generali del diritto concorsuale e con le garanzie riconosciute dalle Carte costituzionali nazionali e sovranazionali ai diritti fondamentali. L’indagine è sviluppata attraverso un itinerario che coniuga un’analisi storico-sistematica con l’esame della disciplina di diritto positivo, europea e nazionale. Il lavoro, considerata la medesimezza di problematiche suscettibili di porsi in entrambi i modelli di gestione della crisi sotto il profilo della tutela di diritti fondamentali del singolo, giunge infine alla valutazione delle criticità emerse sotto quest’angolo di visuale. In particolare, nella più ampia ottica della tutela del valore della partecipazione azionaria si sono esaminate, individuando criticità e possibili soluzioni, da un lato, le questioni proprietarie direttamente connesse alla titolarità del bene-azione; dall’altro quelle correlate alla possibilità di recupero di una parte del valore della partecipazione sociale, perduto per effetto dell’esercizio del potere autoritativo, attraverso la cumulabilità di una duplicità di posizioni in capo al medesimo soggetto, quale socio e creditore risarcitorio dell’ente, danneggiato dalla violazione della disciplina in materia di prestazione di servizi di investimento (cd. mis-selling). In quest’ultima direzione, l’interesse alla ricerca di un bilanciamento che non si risolva in una aprioristica prevalenza del valore della stabilità finanziaria, cui risulta funzionale il framework di gestione della crisi, trova la sua ragione, tra le altre, nella considerazione per cui la disciplina in materia di prestazione di servizi di investimento risulta funzionale alla tutela non solo dell’interesse individuale dell’investitore, ma anche, attraverso questa, alla garanzia della integrità del mercato, in cui le stesse banche operano
System Thermal-Hydraulic Analyses Supporting the Development of Lead-cooled Fast Reactors
No full textThe urgent need to decarbonize the global energy system, in response to the climate crisis, has revitalized interest in nuclear power as a reliable, low-carbon, and dispatchable energy source. Nuclear energy, already a major contributor to carbon-free electricity generation, has the potential to play a central role in achieving deep decarbonization targets. To this end, the Generation IV International Forum (GIF) has promoted the development of advanced reactor concepts that aim to overcome the limitations of current technologies. Among these, Lead-cooled Fast Reactors (LFRs) have emerged as one of the most promising options. LFRs operate in a fast neutron spectrum by relying on liquid lead or lead-bismuth eutectic as the primary coolant and the deployment of advanced fuel types such as Mixed (MOX) fuel, typically composed of plutonium oxide blended with depleted or natural uranium oxide, allows for the recycling of plutonium recovered from spent nuclear fuel, thereby reducing the accumulation of fissile material in storage and supporting non-proliferation and sustainability goals. Additionally, operating in a fast neutron spectrum allows LFRs to
enhance the fuel utilization enabling the use of fertile isotopes such as Uranium-238 and Thorium-232 for breeding fissile material (respectively Plutonium-239 and Uranium-233). This capability extends the energy extracted per unit of natural uranium and reducing the need for fresh uranium mining. Moreover, the fast spectrum is particularly effective in transmuting long-lived minor actinides (such as neptunium, americium, and curium) into shorter-lived or stable isotopes through fission. This transmutation process significantly reduces the long-term radiotoxicity and heat load of nuclear waste, addressing one of the key challenges facing nuclear energy in terms of public acceptance and repository requirements. The choice of Heavy Liquid Metals (HLM) as reactor coolant offers a series of heat transfer and chemical advantages over traditional coolants. Their extremely high boiling point (around 1740 °C for lead and 1670 °C for LBE) permits reactor operation at atmospheric pressure, eliminating the need for pressurized vessels and reducing the risk of pressure-induced failures. The good thermophysical properties of HLMs namely the high density and thermal conductivity enhance passive heat removal capabilities and enable compact core designs with efficient heat transfer. The employment of HLMs enables operation at higher temperatures, improving the thermodynamic efficiency and contributing to the performances of LFRs. Additionally, HLMs are chemically inert with respect to air and water, eliminating the potential for violent reactions such as hydrogen generation, which is a major concern in Sodium-cooled Fast Reactors (SFRs) or Light Water Reactors (LWRs) designs. Despite their many advantages, the use HLMs as primary coolants introduces a series of technical challenges that must be carefully addressed to ensure safe and reliable reactor operation. One of the most critical issues is corrosion: at high temperatures, lead and LBE are chemically aggressive toward structural materials, particularly steels, leading to progressive degradation of components exposed to the coolant. The formation of protective oxide layers on the surface of steels can mitigate corrosion, but their stability is highly sensitive to the oxygen concentration in the coolant. Maintaining a precise and stable oxygen level is therefore essential, requiring the implementation of robust oxygen control and monitoring systems. A related concern is erosion and mass transfer, especially in regions of high flow velocity or thermal gradients, where protective oxide layers may be mechanically removed, further accelerating material degradation. Another major challenge involves coolant activation and polonium production, particularly for LBE, which contains Bismuth-209 that can be transmuted into Polonium-210 under neutron irradiation. Polonium-210 is a highly radiotoxic alpha emitter with a relatively short half-life (~138 days), posing significant radiological hazards during maintenance, operation, and decommissioning. This issue demands stringent containment strategies and remote handling capabilities. Pure lead avoids the polonium problem but remains heavier and has higher melting and freezing points, which introduces its own operational constraints. Moreover, the opacity of HLMs complicates flow visualization, instrumentation, and refuelling operations. Moreover, HLM Thermal-Hydraulics (TH) involves complex phenomena such as transition from forced to natural circulation, pool thermal stratification and freezing. Coolant freezing is also a considerable concern: lead freezes at around 327 °C and LBE at about 125 °C, necessitating continuous heating of the coolant and system components even during shutdown or maintenance phases to prevent solidification and blockages. This imposes complexity to decay heat removal systems, which must be designed to operate reliably across a
wide range of temperatures. Finally, the TH behaviour and simulation of HLMs presents unique modelling difficulties. Their high density and low Prandtl number result in flow and heat transfer characteristics that differ significantly from those of water, requiring significant efforts in Research and Development (R&D) activities. In the absence of full-scale operational reactors, the design and safety assessment of LFRs must rely heavily on high-fidelity numerical simulations supported by data from scaled experimental facilities. The qualification of numerical models and System Thermal-Hydraulic (STH) codes, and the validation of safety systems under representative conditions, remain critical steps in the development of this reactor class. This doctoral research contributes to the advancement of LFR technology through an extensive campaign of system-level TH analyses aimed at supporting the design, qualification, and safety demonstration of several LFR concepts under development in the world. The primary simulation tool used throughout the work is RELAP5, a STH code validated primarily for LWRs. The thesis is articulated around three key projects: ALFRED, the Westinghouse-LFR (WEC-LFR), and MYRRHA. In the case of ALFRED, a series of in-depth studies—including a Phenomena Identification and Ranking Table (PIRT) analysis—were performed to pinpoint the main technical challenges and to guide the prioritization of R&D activities. To assess reactor behaviour under both normal and accidental conditions, coupled Neutron Kinetic (NK) and TH simulations were conducted, focusing on unprotected transients. Particular attention was devoted to ALFRED’s innovative Decay Heat Removal (DHR) system, which relies on degradation of condensation mechanisms affected by the presence of non-condensable gases. This approach aims to conjugate two competing objectives: efficient decay heat removal and maintaining the primary coolant above its freezing point. To support and evaluate this concept, the SIRIO facility was involved in this work performing both experimental and numerical TH analyses. Additional extensive investigations were carried out to study the condensation process—both in pure conditions and with non-condensable—and to validate the TH models and correlations implemented in RELAP5. The work on the WEC-LFR involved two major facilities. The PHRF which is dedicated to study and test the Passive Heat Removal System (PHRS) of the WEC-LFR. The PHRS is based on water-to-air transition heat transfer regime causing the decreasing of heat removal. The PHRF was modelled and deeply analysed. The other experimental facility involved within this framework is the VLF, representing the Reactor Cooling System (RCS), was analysed performing a pre-test analysis to gain enough understanding of this facility both in nominal and accidental conditions. Furthermore, the inclusion of key components of the WEC-LFR’s RCS within the VLF experimental facility prompted detailed stand-alone analyses of two critical elements: the Primary Heat Exchanger (PHE) and the Fuel Pin Bundle Simulator (FPBS). The PHE, an innovative microchannel heat exchanger, represents a novel solution for which limited experience and literature exist within the nuclear industrial. As such, a comparative study was carried out using both a STH code (RELAP5) and a Computational Fluid Dynamics (CFD) tool (Ansys CFX) to better understand its behaviour. The FPBS, on the other hand, is a representative model of the WEC-LFR Fuel Assembly. To evaluate its performance, a subchannel analysis was performed using the DASSH code, followed by a comparative assessment between DASSH and RELAP5 to verify modelling consistency and identify code-specific limitations. Finally, for the MYRRHA reactor, a PIRT analysis has
been performed in parallel with ALFRED, in the framework of R&D activities supporting the development of LFRs in Europe. Next, the research focused on the secondary cooling system, investigated through the HEXACOM experimental facility. This work primarily aimed at applying and refining a qualification procedure for STH numerical models of experimental facilities, with the goal of enhancing modelling accuracy and supporting future licensing processes. A comprehensive RELAP5 model of the system was developed, calibrated, and validated using both experimental data and nominal design specifications. The simulation results offered important insights into the behaviour of the water loop and played a key role in the qualification of the thermal-hydraulic model. Future work should focus on extending the validation domain of STH codes through additional high-quality experimental data, particularly under transient and accident conditions. The coupling of STH codes with high-fidelity tools such as CFD or subchannel analysis codes should be further explored to improve the resolution of local phenomena within critical components. Moreover, the integration of multi-physics approaches—including structural, NK and TH feedback—will be essential to enhance the accuracy of safety assessments. On the experimental side, additional test campaigns on advanced facilities such as SIRIO, PHRF, VLF, and HEXACOM are necessary to refine modelling strategies and reduce uncertainties in design-relevant conditions. These future directions are expected to contribute significantly to the qualification and licensing of LFRs, ultimately supporting their safe and sustainable deployment in future nuclear energy systems
MOTUM. A system for motion online tracking under MRI
No full textAttempts to implement realistic body-environment interactions during functional magnetic resonance imaging (fMRI) experiments have developed expensive, hardly reproducible, and task-specific setups. Here, we introduce MOTUM (Motion Online Tracking Under MRI), a novel system that combines real-time kinematic tracking with immersive virtual reality, enabling participants to perform naturalistic movements inside the scanner. As a proof-of-concept, we tested MOTUM during a reach-to-grasp task with and without visual feedback of one's hand (N = 7). The system achieved high-fidelity motion tracking, induced an intense immersive experience, evoked expected sensorimotor brain activations, and maintained high fMRI data quality. Standard fMRI control metrics were below the critical threshold in 99% of volumes, indicating that participants' arm movements had minimal impact on head motion and data quality. Direct artifactual effects of arm and hand motion were also modest and well below critical limits. Critically, MOTUM allowed us to extract rich kinematic measures and link them to brain activity on a trial-by-trial basis. Parametric modulation analyses revealed that natural variations in movement dynamics significantly influenced neural responses in parietal, frontal, and occipital regions. In sum, MOTUM is a robust method to study motor control and beyond, enabling a new class of fMRI experiments that bridge ecological realism and experimental control, pushing current neuroimaging research toward real-life neuroscience
Exploiting two-layer redundancy: control and task allocation for heterogeneous multi-agent systems
No full textIn multirobot multitask scenarios, redundancy is a fundamental feature arising both from the presence of more agents than tasks and from surplus input resources relative to the controlled variables. This redundancy gives rise to two interrelated problems. First, determining which agent should execute which task to collectively achieve a global objective defines the {\it task allocation problem}. This requires accounting for the heterogeneous nature of agents and the constraints associated with task execution. Second, input redundancy enables the {\it control allocation problem}, which seeks to exploit extra degrees of freedom to fulfill secondary objectives, such as minimizing power consumption or enhancing fault tolerance. In practice, however, control allocation must account for input constraints that may give rise to the windup problem.
This thesis develops a comprehensive framework to simultaneously address task and control allocation in heterogeneous redundant multi-agent systems. The proposed cascaded architecture integrates input redundancy within the task allocation process, enabling the exploitation of surplus degrees of freedom to mitigate windup effects while executing tasks collaboratively.
The first part introduces a decentralized dynamic control allocation approach for weakly redundant multi-agent systems. This method is based on a dynamic output invisible allocator composed of an optimizer and an annihilator, designed to overcome saturation conditions and recover intended behavior. The allocation policy relies solely on local information, ensuring scalability.
The second part develops an optimization-based task allocation framework for heterogeneous redundant multi-agent systems. This framework leverages input redundancy information to assign tasks to the most capable and redundant agents, enabling cooperative task execution. The allocation problem is formulated as a Mixed-Integer Linear Program (MILP), enabling the systematic handling of agent heterogeneity and execution constraints. This leads to a fully decentralized control and task allocation framework for heterogeneous redundant systems.
The final part presents two independent applications of the proposed task allocation framework. First, task allocation is applied to autonomous collaborative ship collision avoidance, integrating maritime traffic regulations within the allocation policy. Second, task allocation is applied to Earth observation operations in multi-satellite systems, extending the formulation to support secondary objectives such as maximizing coverage of areas of interest and minimizing data latency to ground stations. These case studies demonstrate the framework’s capability to handle real-world complexities, such as dynamic operational constraints in maritime navigation and communication limitations in multi-satellite coordination
Quale futuro per i musei universitari
No full textIl testo affronta il ruolo e le potenzialità dei musei universitari nella museografia contemporanea, intesi come luoghi di restituzione di un sapere in continua evoluzione, capaci di coniugare conservazione, ricerca, didattica e divulgazione. In Italia, nonostante una crescente attenzione maturata negli ultimi decenni e rafforzata dagli obiettivi della Terza Missione universitaria, il quadro appare ancora complesso e frammentato. La creazione di sistemi e poli museali rappresenta un tentativo di valorizzazione, ma permangono criticità organizzative, comunicative e strutturali, aggravate dall’assenza di un coordinamento nazionale come quello svolto in passato dalla Commissione Musei della CRUI. Il contributo individua alcune linee strategiche per l’innovazione dei musei universitari: migliorare la comunicazione verso pubblici diversificati, recuperare l’unità delle collezioni, superare approcci disciplinari settoriali, riqualificare spazi e apparati tecnologici, rafforzare le relazioni con i sistemi museali territoriali e rilanciare il ruolo delle collezioni nella ricerca e nella didattica. La ricerca, di cui il testo è la presentazione, ha analizzato il panorama nazionale, valorizzando pratiche virtuose, in particolare i casi di Padova e Firenze, e ha approfondito il Polo Museale della Sapienza, con una mappatura dei musei e studi progettuali sui musei archeologici. L’esperienza internazionale di Maputo condotta da un gruppo di docenti della Sapienza, dimostra infine come competenze e progettualità possano favorire una reale integrazione tra università e società.The text examines the role and potential of university museums in contemporary museography, understood as places where constantly evolving knowledge is shared and made accessible, and as institutions capable of combining conservation, research, teaching, and public engagement.
In Italy, despite the growing attention paid to this field in recent decades and further strengthened by the objectives of the universities’ Third Mission, the overall situation still appears complex and fragmented. The creation of museum systems and hubs represents an attempt to enhance and promote this heritage, yet significant organizational, communicative, and structural challenges remain. These are further compounded by the lack of a national coordinating body such as the CRUI Museums Commission, which previously played this role.
The contribution identifies several strategic directions for innovation in university museums: improving communication with diverse audiences; restoring the unity of collections; overcoming narrow, discipline-based approaches; upgrading spaces and technological infrastructures; strengthening relationships with local and regional museum networks; and revitalizing the role of collections in research and teaching.
The research presented in the text analyses the national landscape, highlighting best practices—particularly the cases of Padua and Florence—and offers an in-depth study of the Sapienza Museum Hub, including a mapping of its museums and design-oriented studies focusing on archaeological museums. Finally, the international experience in Maputo, carried out by a group of Sapienza faculty members, demonstrates how expertise and project-based initiatives can foster genuine integration between universities and society
Prevenire il suicidio assistito è un interesse costituzionale
No full textL’articolo esamina la sentenza n. 204/2025 della Corte costituzionale, che ha dichiarato in larga parte illegittima la legge della Regione Toscana sul suicidio medicalmente assistito, riaffermando i limiti delle competenze regionali e la centralità del legislatore statale nelle materie civile e penale. La Corte ha escluso che il suicidio assistito possa configurarsi come un diritto, valorizzando l’interesse costituzionale alla prevenzione e il dovere di tutela della vita umana. Dopo la pronuncia, della legge toscana resta solo quanto già desumibile dalla sentenza n. 242/2019, con una sostanziale uniformità della disciplina sul territorio nazionale e spazi normativi regionali estremamente ridotti. La decisione solleva infine rilevanti interrogativi sull’opportunità e sui rischi di un intervento legislativo statale di dettaglio.This article examines Constitutional Court ruling no. 204/2025, which declared the Tuscany Region's law on physician-assisted suicide largely unconstitutional, reaffirming the limits of regional jurisdiction and the centrality of state legislature in civil and criminal matters. The Court ruled out the possibility of physician-assisted suicide being a right, highlighting the constitutional interest in prevention and the duty to protect human life. Following the ruling, only what can be deduced from ruling no. 242/2019 remains of the Tuscan law, with substantial uniformity of legislation across the country and extremely limited regional regulatory space. Finally, the decision raises significant questions about the opportunities and risks of detailed state legislative interventio
Existence and non-existence phenomena for nonlinear elliptic equations with data and singular reactions
No full textWe study existence and non-existence of solutions for singular elliptic boundary value problems as
\begin{equation}\label{eintro}\begin{cases}\tag{1}
\displaystyle -\Delta_p u+ \frac{a(x)}{u^{\gamma}}=\mu f(x) \ &\text{ in }\Omega,\\
u>0&\text{ in }\Omega,\\
u = 0 \ &\text{ on }
\partial\Omega,
\end{cases}
\end{equation}
where is a smooth bounded open subset of \re^N (), is the -Laplacian with p>1, 0<\gamma\leq 1, and is bounded and non-trivial. For any positive we show that problem \eqref{eintro} is solvable for any \mu >\mu_0>0, for some large enough. As a reciprocal outcome we also show that no finite energy solution exists if 0<\mu<\mu_{0*}, for some small .
This paper extends the celebrated one of J. I. Diaz, J. M. Morel and L. Oswald (\cite{DMO}) to the case . Our result is also new for provided the singular term has a critical growth near zero (i.e. )
Charge density wave and fluctuations in KV3Sb5 kagome superconductor studied by V K-edge X-ray absorption spectroscopy
No full textThe local structure of the KV3Sb5 kagome superconductor has been studied using X-ray absorption spectroscopy. Extended X-ray absorption fine structure (EXAFS) analysis reveals significant temperature-dependent changes in the local environment around vanadium (V) atoms. Notably, the V-Sb bond distance exhibits a distinct alteration in thermal expansion behavior at temperatures far exceeding the charge density wave (CDW) transition temperature (∼78 K). Additionally, mean square relative displacements of V-V pairs show excess distortions across the CDW transition, suggesting direct coupling between the CDW and local lattice distortions. X-ray absorption near-edge structure (XANES) measurements further demonstrate an unusual electronic response, providing evidence of a fluctuating CDW state. These findings highlight the complex interplay between structural and electronic degrees of freedom in KV3Sb5. The results advance our understanding of local structural dynamics during CDW formation in kagome materials and offer critical insights into the mechanisms driving quantum phases in these systems