Abstract
The retail shelf space planning problem has long been addressed by Marketing and Operations Research (OR) professionals and researchers, with the first empirical studies tracing back to the 1960s and the first modelling approaches back to the 1970s. Due to this long history, this field presents a wide range of different mathematical modelling approaches that deal with the decisions surrounding a set of products and not only define their space assignment and related quantity, but also their vertical and horizontal positioning within a retail shelf. These decisions affect customer demand, namely in the form of space- and position-dependent demand and replenishment requirements. Current literature provides either more comprehensive decision models with a wide range of demand effects but limited practical applicability, or more simplistic model formulations with greater practical application but limited consideration of the associated demand. Despite the recent progress seen in this research area, no work has yet systematised published research with a clear focus on shelf space planning. As a result, there is neither any up-to-date structured literature nor a unique model approach, and no benchmark sets are available. This paper provides a description and a state-of-the-art literature review of this problem, focusing on optimisation models. Based on this review, a classification framework is proposed to systematise the research into a set of sub-problems, followed by a unified approach with a univocal notation of model classes. Future lines of research point to the most promising open questions in this field.

Abstract
The scant literature that addresses issues related to the Technology Balance of Payments (TBP) often refers that a surplus balance may correspond to a high degree of technological autonomy, a low level of technology imports, or an inability to assimilate foreign technologies. It is not clear, however, from this literature whether, and to what extent, the balance of the TBP is related to countries' international competitiveness. The purpose of this paper is to detail the evolution of the TBP for Southern European countries and to assess the extent to which it influences these countries' international competitiveness. Using static and dynamic panel data techniques on data for four Southern European countries (Greece, Italy, Portugal and Spain) between 2000 and 2017, our results highlight that a positive TBP significantly contributes to foster countries' international competitiveness.

Abstract
IIoT platforms are a digital enabler for the industrial digital transformation, allowing the organisations to have a clear vision over its current status, promoting flexibility for a fast adjustment to market changes. The development of such a complex technological environment raises a two-fold concern: to promote a simpler modular customisation, and to promote the domain expert's involvement in the process. This requires a new approach on the specification of IIoT architecture, where the conceptualisation phase is crucial. In this context, semantics might play an impacting role, accommodating the multidisciplinary knowledge of IIoT architectures in a technological artefact, at the service of both technological architects and companies' domain experts. This paper discusses a semantic model to represent IIoT components, its conceptual relations, and technical constraints in a common view, supporting the construction of both IIoT concept and platforms within organisations.

Abstract
The recent Bluetooth 5.1 specification introduced the use of Angle-of-Arrival (AoA) information which enables the design of novel low-cost indoor positioning systems. Existing approaches rely on multiple fixed gateways equipped with antenna arrays, in order to determine the location of an arbitrary number of simple mobile omni-directional emitters. In this paper, we instead present an approach where mobile receivers are equipped with antenna arrays, and the fixed infrastructure is composed of battery-powered beacons. We implement a simulator to evaluate the solution using a real-world data set of AoA measurements. We evaluated the solution as a function of the number of beacons, their transmission period, and algorithmic parameters of the position estimation. Sub-meter accuracy is achievable using 1 beacon per 15 m(2) and a beacon transmission period of 500 ms.

Abstract
Social networks are becoming larger and more complex as new ways of collecting social interaction data arise (namely from online social networks, mobile devices sensors, ...). These networks are often large-scale and of high dimensionality. Therefore, dealing with such networks became a challenging task. An intuitive way to deal with this complexity is to resort to tensors. In this context, the application of tensor decomposition has proven its usefulness in modelling and mining these networks: it has not only been applied for exploratory analysis (thus allowing the discovery of interaction patterns), but also for more demanding and elaborated tasks such as community detection and link prediction. In this work, we provide an overview of the methods based on tensor decomposition for the purpose of analysing time-evolving social networks from various perspectives: from community detection, link prediction and anomaly/event detection to network summarization and visualization. In more detail, we discuss the ideas exploited to carry out each social network analysis task as well as its limitations in order to give a complete coverage of the topic.

Abstract
Flipped Classroom approach was implemented in an Automation course with around 100 students. Videos focused on GRAFCET topics were given to students prior to class and problem-based challenges were solved in class by the students in a collaborative way. The teacher’s role was to guide students in their learning process. The goal was to identify students’ behavior regarding this learning approach, and the videos in particular, by using questionnaires. Result analysis shows a positive feedback from students motivating teachers to enlarge this learning approach to other courses. © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Switzerland AG 2021.