Polytechnic University of Milan

About: Polytechnic University of Milan is a education organization based out in Milan, Italy. It is known for research contribution in the topics: Computer science & Finite element method. The organization has 18231 authors who have published 58416 publications receiving 1229711 citations. The organization is also known as: PoliMi & L-NESS.

Sequence-Aware Recommender Systems

Abstract: Recommender systems are one of the most successful applications of data mining and machine-learning technology in practice. Academic research in the field is historically often based on the matrix completion problem formulation, where for each user-item-pair only one interaction (e.g., a rating) is considered. In many application domains, however, multiple user-item interactions of different types can be recorded over time. And, a number of recent works have shown that this information can be used to build richer individual user models and to discover additional behavioral patterns that can be leveraged in the recommendation process.In this work, we review existing works that consider information from such sequentially ordered user-item interaction logs in the recommendation process. Based on this review, we propose a categorization of the corresponding recommendation tasks and goals, summarize existing algorithmic solutions, discuss methodological approaches when benchmarking what we call sequence-aware recommender systems, and outline open challenges in the area.

Reactivity of NO/NO2–NH3 SCR system for diesel exhaust aftertreatment: Identification of the reaction network as a function of temperature and NO2 feed content

Abstract: We present a systematic study of the NH3-SCR reactivity over a commercial V2O5–WO3/TiO2 catalyst in a wide range of temperatures and NO/NO2 feed ratios, which cover (and exceed) those of interest for industrial applications to the aftertreatment of exhaust gases from diesel vehicles. The experiments confirm that the best deNOx efficiency is achieved with a 1/1 NO/NO2 feed ratio. The main reactions prevailing at the different operating conditions have been identified, and an overall reaction scheme is herein proposed. Particular attention has been paid to the role of ammonium nitrate, which forms rapidly at low temperatures and with excess NO2, determining a lower N2 selectivity of the deNOx process. Data are presented which show that the chemistry of the NO/NO2–NH3 reacting system can be fully interpreted according to a mechanism which involves: (i) dimerization/disproportion of NO2 and reaction with NH3 and water to give ammonium nitrite and ammonium nitrate; (ii) reduction of ammonium nitrate by NO to ammonium nitrite; (iii) decomposition of ammonium nitrite to nitrogen. Such a scheme explains the peculiar deNOx reactivity at low temperature in the presence of NO2, the optimal stoichiometry (NO/NO2 = 1/1), and the observed selectivities to all the major N-containing products (N2, NH4NO3, HNO3, N2O). It also provides the basis for the development of a mechanistic kinetic model of the NO/NO2–NH3 SCR reacting system.

Off-grid systems for rural electrification in developing countries: Definitions, classification and a comprehensive literature review

Abstract: Access to electric power supply has always had a significant role in promoting improvements in all the society sectors, nevertheless nowadays 1.3 billion of people still do not have electricity access. Moreover, most of them live in rural areas of developing countries which are often isolated, scattered populated and characterized by poor infrastructure and services. In this situation, the growing consideration towards the target of universal access to energy has emphasized the role of rural electrification, and off-grid small-scale generation represents one of the most appropriate options. As a consequence, the scientific literature has devoted attention to this topic with a large number of papers. In this frame, the present analysis focuses on off-grid systems for rural electrification and provides a general framework to this topic and an analytical review of the literature. The work is based on the review of more than 350 papers mainly published from 2000 to 2014 within selected journals, and it is organized in two sections. In the first one we describe the role of small-scale generation systems throughout the process of electrification, the main features of rural areas and their typical energy uses, and we propose a new comprehensive taxonomy for off-grid systems for rural electrification. In the second one we develop an extensive review of the selected literature according to the proposed classification and to five main research areas: Technology: layout and components; Models and methods for simulation and sizing; Techno-economic feasibility analyses and sustainability analyses; Case studies analyses; Policy analyses. The work results in a comprehensive review which organizes and capitalizes the main fundamentals of the addressed topic and provides elements to get acquainted with the literature.