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  • 02 engineering and technology
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  • Archivio istituzionale della ricerca - Alma Mater Studiorum Università di Bologna

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  • Closed Access English
    Authors: 
    Renzo Nesti; E. Orsi; Giuseppe Pelosi; L. Possenti; Stefano Selleri;
    Publisher: Institute of Electrical and Electronics Engineers Inc.
    Country: Italy

    This paper presents the electromagnetic design of part of a receiver passive front-end at C band (4.2–5.6 GHz) to be used for radio astronomy applications. The front-end devices here shown are a circular corrugated horn, a differential phase shifter and an orthomode transducer, which are required to study the circular polarization content of the sky signal. All of these components are developed in waveguide technology, best suited for high sensitivity receivers. Design and fabrication aspects are presented and test results discussed.

  • Open Access English
    Authors: 
    Maria Alessandra Ancona; Lisa Branchini; A. De Pascale; Francesco Melino;
    Publisher: American Institute of Physics Inc.
    Country: Italy

    The new goals towards efficiency increase, pollutant emissions and fossil fuel reduction had led to an increasing diffusion of district heating networks. New generations of district heating had introduced the concept of smart thermal grids, consisting in the bidirectional thermal energy exchange between network and final users and aiming at replicating the concept of electric smart grid in the heat sector. With this purpose, the integration between district heating networks and distributed generation systems becomes essential and the optimization of the utility substations is a key point. This study aims at the elaboration of possible solutions for the conversion of an existing utility substation in order to enable a bidirectional thermal energy exchange. Two different configurations will be proposed and analyzed, considering different distributed generation systems to be installed at the final user. The operation model of these cases will be defined with the purpose of optimizing the thermal exchange. Furthermore, the actions required for the conversion of the existing utility substation will be evaluated through a technical analysis, in order to define the novel substation potentialities. Based on the obtained results, the preliminary technical schematic of the converted utility substations have been designed and discussed.The new goals towards efficiency increase, pollutant emissions and fossil fuel reduction had led to an increasing diffusion of district heating networks. New generations of district heating had introduced the concept of smart thermal grids, consisting in the bidirectional thermal energy exchange between network and final users and aiming at replicating the concept of electric smart grid in the heat sector. With this purpose, the integration between district heating networks and distributed generation systems becomes essential and the optimization of the utility substations is a key point. This study aims at the elaboration of possible solutions for the conversion of an existing utility substation in order to enable a bidirectional thermal energy exchange. Two different configurations will be proposed and analyzed, considering different distributed generation systems to be installed at the final user. The operation model of these cases will be defined with the purpose of optimizing the thermal exchange. Fu...

  • Restricted English
    Authors: 
    Pietro Mercati; Andrea Bartolini; Francesco Paterna; Tajana Simunic Rosing; Luca Benini;
    Publisher: Institute of Electrical and Electronics Engineers Inc.
    Country: Italy
    Project: EC | MULTITHERMAN (291125), EC | MULTITHERMAN (291125)

    Reliability is a major concern in multiprocessors. Dynamic Reliability Management (DRM) aims at trading off processor performance with lifetime. The state-of-the-art publications study only the theory supported by simulation. This paper presents the first complete software implementation, working on a real hardware, of a low-overhead, Android-compatible workload-aware DRM Governor for mobile multiprocessors. We discuss the design challenges and the run-time overhead involved. We show the effectiveness of our governor in guaranteeing the predefined target lifetime and show that it achieves up to 100% of lifetime improvement with respect to traditional governors, while providing comparable performance for critical applications.

  • Publication . Conference object . Preprint . Article . 2019
    Open Access English
    Authors: 
    Anna Guerra; Davide Dardari; Petar M. Djuric;
    Country: Italy
    Project: EC | AirSens (793581)

    In this paper, we propose a distributed solution to the navigation of a population of unmanned aerial vehicles (UAVs) to best localize a static source. The network is considered heterogeneous with UAVs equipped with received signal strength (RSS) sensors from which it is possible to estimate the distance from the source and/or the direction of arrival through ad-hoc rotations. This diversity in gathering and processing RSS measurements mitigates the loss of localization accuracy due to the adoption of low-complexity sensors. The UAVs plan their trajectories on-the-fly and in a distributed fashion. The collected data are disseminated through the network via multi-hops, therefore being subject to latency. Since not all the paths are equal in terms of information gathering rewards, the motion planning is formulated as a minimization of the uncertainty of the source position under UAV kinematic and anti-collision constraints and performed by 3D non-linear programming. The proposed analysis takes into account non-line-of-sight (NLOS) channel conditions as well as measurement age caused by the latency constraints in communication. 5 pages, 3 figures, conference

  • Publication . Conference object . Contribution for newspaper or weekly magazine . 2019
    Open Access English
    Authors: 
    Tommaso Cappello; Corrado Florian; Alberto Santarelli; Zoya Popovic;
    Publisher: IEEE
    Countries: United Kingdom, Italy

    This paper describes the linearization of a base-station L-band 500-W GaN Doherty high power amplifier (HPA) driven by OFDM signals. Pre-pulsing characterization is used to extract the gain dispersion of the carrier and peaking PAs due to trap-induced degradation of GaN-on-SiC transistors. Peak drain voltages reached by PA load-lines mainly set the trap states of the carrier and peaking PAs, while the recovery is longer with a dominant time constant of 100µs for this specific GaN technology. When the peak occurrences are below this dominant time constant of 100µs, such as for symbol periods of 16.7 to 66.7µs (i.e., LTE/5G OFDM), the HPA trap-state remains approximately constant in the time interval between voltage peaks, allowing low-complexity linearization of the HPA. With a 10-MHz OFDM signal with peak-to-peak intervals shorter than 100µs, a memory-less digital pre-distortion (DPD) is shown to improve ACLR by 4dB and NRMSE by 1.6 percentage points, as compared to peak-to-peak intervals longer than 100µs when significant trap recovery takes place.

  • Closed Access English
    Authors: 
    Krittika D'Silva; Anastasios Noulas; Mirco Musolesi; Cecilia Mascolo; Max Sklar;
    Publisher: ACM
    Country: Italy

    Estimating revenue and business demand of a newly opened venue is paramount as these early stages often involve critical decisions such as first rounds of staffing and resource allocation. Traditionally, this estimation has been performed through coarse measures such as observing numbers in local venues. The advent of crowdsourced data from devices and services has opened the door to better predictions of temporal visitation patterns for locations and venues. In this paper, using mobility data from the location-based service Foursquare, we treat venue categories as proxies for urban activities and analyze how they become popular over time. The main contribution of this work is a prediction framework able to use characteristic temporal signatures of places together with k-nearest neighbor metrics capturing similarities among urban regions to forecast weekly popularity dynamics of a new venue establishment. Our evaluation shows that temporally similar areas of a city can be valuable predictors, decreasing error by 41%. Our findings have the potential to impact the design of location-based technologies and decisions made by new business owners.

  • Open Access English
    Authors: 
    N. Terranova; O Serot; Pascal Archier; Cyrille De Saint Jean; Marco Sumini;
    Publisher: HAL CCSD
    Countries: France, Italy

    Fission product yields (FY) are fundamental nuclear data for several applications, including decay heat, shielding, dosimetry, burn-up calculations. To be safe and sustainable, modern and future nuclear systems require accurate knowledge on reactor parameters, with reduced margins of uncertainty. Present nuclear data libraries for FY do not provide consistent and complete uncertainty information which are limited, in many cases, to only variances. In the present work we propose a methodology to evaluate covariance matrices for thermal and fast neutron induced fission yields. The semi-empirical models adopted to evaluate the JEFF-3.1.1 FY library have been used in the Generalized Least Square Method available in CONRAD (COde for Nuclear Reaction Analysis and Data assimilation) to generate covariance matrices for several fissioning systems such as the thermal fission of U235, Pu239 and Pu241 and the fast fission of U238, Pu239 and Pu240. The impact of such covariances on nuclear applications has been estimated using deterministic and Monte Carlo uncertainty propagation techniques. We studied the effects on decay heat and reactivity loss uncertainty estimation for simplified test case geometries, such as PWR and SFR pin-cells. The impact on existing nuclear reactors, such as the Jules Horowitz Reactor under construction at CEA-Cadarache, has also been considered.

  • Closed Access English
    Authors: 
    Paolo Burgio; Robin Danilo; Andrea Marongiu; Philippe Coussy; Luca Benini;
    Publisher: HAL CCSD
    Countries: Italy, France

    Modern designs for embedded many-core systems increasingly include application-specific units to accelerate key computational kernels with orders-of-magnitude higher execution speed and energy efficiency compared to software counterparts. A promising architectural template is based on heterogeneous clusters, where simple RISC cores and specialized HW units (HWPU) communicate in a tightly-coupled manner via L1 shared memory. Efficiently integrating processors and a high number of HW Processing Units (HWPUs) in such an system poses two main challenges, namely, architectural scalability and programmability. In this paper we describe an optimized Data Pump (DP) which connects several accelerators to a restricted set of communication ports, and acts as a virtualization layer for programming, exposing FIFO queues to offload “HW tasks” to them through a set of lightweight APIs. In this work, we aim at optimizing both these mechanisms, for respectively reducing modules area and making programming sequence easier and lighter.

  • Publication . Article . Other literature type . Conference object . 2017
    Open Access English
    Authors: 
    Ruggero Caravita; Stefano Aghion; Claude Amsler; Germano Bonomi; R. S. Brusa; Massimo Caccia; Fabrizio Castelli; Giovanni Cerchiari; Daniel Comparat; Giovanni Consolati; +51 more
    Countries: Italy, Italy, France
    Project: EC | ANGRAM (748826)

    International audience; Positronium (Ps), the unstable bound state of electron and positron, is a valuable system for neutral antimatter spectroscopic studies and for antihydrogen production. Forming a pulsed beam cold antihydrogen using charge-exchange with the Rydberg Ps is the goal of the AEgIS Collaboration, which aims to measure gravity on neutral antimatter. Recent results achieved in producing, manipulating and studying Ps are summarized. Ps has been first produced with mesoporous silica targets in a reflection geometry. Spectroscopy of Ps n = 3 state has been conducted, yielding as a byproduct an independent estimate of the produced Ps temperature. Efficient laser excitation to the Rydberg levels was then achieved, validating the proof-of-concept of AEgIS. Subsequently, production of Ps from a new class of transmission targets was also achieved, opening the possibility for future experiments.

  • Publication . Part of book or chapter of book . Conference object . 2019
    Open Access English
    Authors: 
    Federico Ruggiero; Michael Lucchi; Marco Lorenzini; Paolo Valdiserri; Daniele Fattini;
    Publisher: AIP Conference Proceedings
    Country: Italy

    Cogeneration is an often viable and efficient solution to cover combined demands of electric and thermal power, especially when the demand of the latter remains fairly constant over time. The efficient use of energy and the economic advantages that are associate to it have made cogeneration the solution of choice in many industrial applications, among which paper mills represent a significant share. The heat recovery steam generator often has an auxiliary burner to ensure full coverage of the thermal load in all operating conditions. In order to reduce installation and conduction costs, the combustion chamber may lack an extraction fan, which has the drawback that pressure varies according to changes in the loads, and this affects the stability of the flame adversely. In order to ensure constant pressure in the combustion chamber, application of a gate valve downstream of the heat recovery steam generator is proposed. A lumped-parameter model is set up in Simulink® and the feedback loop tested for to sudden variations in the thermal power required by the paper mill, mainly due to variations in the number of operating machines, and to failure of the internal combustion engine. It is demonstrated that the gate valve is necessary and that the use of a PID feedback control system ensures a constant pressure in the combustion chamber.

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