Attributed Stream Hypergraphs: temporal modeling of node-attributed high-order interactions

Recent advances in network science have resulted in two distinct research directions aimed at augmenting and enhancing representations for complex networks. The first direction, that of high-order modeling, aims to focus on connectivity between sets of nodes rather than pairs, whereas the second one, that of feature-rich augmentation, incorporates into a network all those elements that are driven by information which is external to the structure, like node properties or the flow of time. This paper proposes a novel toolbox, that of Attributed Stream Hypergraphs (ASHs), unifying both high-order and feature-rich elements for representing, mining, and analyzing complex networks. Applied to social network analysis, ASHs can characterize complex social phenomena along topological, dynamic and attributive elements. Experiments on real-world face-to-face and online social media interactions highlight that ASHs can easily allow for the analyses, among others, of high-order groups' homophily, nodes' homophily with respect to the hyperedges in which nodes participate, and time-respecting paths between hyperedges.Comment: Submitted to "Applied Network Science

An exact approach to the dynamics of locally-resonant beams

Abstract This paper presents an exact analytical approach to calculate the dynamic response of elastic beams with periodically-attached resonators, generally referred to as locally-resonant beams. Showing that a typical resonator is equivalent to an external constraint, whose reaction force on the beam depends on the deflection of the application point through a pertinent frequency-dependent stiffness, the beam-resonators coupled system is handled using only the beam motion equation, with Dirac's deltas modelling the shear-force discontinuities associated with the reaction forces of the resonators. This is the basis to tackle the dynamics of infinite as well as finite beams, the first by a transfer matrix method to calculate frequency band gaps, the second by a generalized function approach. The dynamics of the finite beam is studied in frequency and time domains deriving the exact frequency response and the exact modal response, including modal frequency and impulse response functions. The proposed approach is formulated for arbitrary number of resonators and loads, and applies for both non-proportional and proportional damping

Redefining Event Types and Group Evolution in Temporal Data

Groups -- such as clusters of points or communities of nodes -- are fundamental when addressing various data mining tasks. In temporal data, the predominant approach for characterizing group evolution has been through the identification of ``events". However, the events usually described in the literature, e.g., shrinks/growths, splits/merges, are often arbitrarily defined, creating a gap between such theoretical/predefined types and real-data group observations. Moving beyond existing taxonomies, we think of events as ``archetypes" characterized by a unique combination of quantitative dimensions that we call ``facets". Group dynamics are defined by their position within the facet space, where archetypal events occupy extremities. Thus, rather than enforcing strict event types, our approach can allow for hybrid descriptions of dynamics involving group proximity to multiple archetypes. We apply our framework to evolving groups from several face-to-face interaction datasets, showing it enables richer, more reliable characterization of group dynamics with respect to state-of-the-art methods, especially when the groups are subject to complex relationships. Our approach also offers intuitive solutions to common tasks related to dynamic group analysis, such as choosing an appropriate aggregation scale, quantifying partition stability, and evaluating event quality

Stochastic response of a fractional vibroimpact system

The paper proposes a method to investigate the stochastic dynamics of a vibroimpact single-degree-of-freedom fractional system under a Gaussian white noise input. It is assumed that the system has a hard type impact against a one-sided motionless barrier, which is located at the system's equilibrium position; furthermore, the system under study is endowed with an element modeled with fractional derivative. The proposed method is based on stochastic averaging technique and overcome the particular difficulty due to the presence of fractional derivative of an absolute value function; particularly an analytical expression for the system's mean squared response amplitude is presented and compared with results obtained by numerical simulations

Proceedings of the 24th Paediatric Rheumatology European Society Congress: Part three

From Springer Nature via Jisc Publications Router.Publication status: PublishedHistory: collection 2017-09, epub 2017-09-0

Towards Attributed Stream-Hypernetwork Analysis: Structure, Features and Dynamics of Complex Social Systems

Graphs are simple, intuitive proxies that allow for an effective modeling of many complex systems. Although functional, however, such simplicity imposes strong constraints on the system's representation. Indeed, many real world phenomena present much more than a relational structure, such as a wide set of attributes characterizing the entities and/or time-varying topologies. Additionally, relations may involve more than two entities at once, whereas graphs are intrinsically limited to pairwise interactions. These are pivotal features of any complex systems – especially social ones – and must be taken into account in order to deploy understand the systems’ nature. In this work, an all-encompassing framework is proposed, namely the Attributed Stream-Hypergraph (ASH). Leveraging powerful and well-understood models such as hypergraphs and stream graphs, ASH frames systems as a stream of node-attributed multiadic interactions. By doing so, it is able to provide novel insights that the original models are not able to unveil independently. After discussing other augmented graph models concerning attributed, temporal, and high-order networks, ASH is presented along with its analytical peculiarities and measures. A Python implementation of the model is also discussed and compared to other hypergraph libraries, emphasizing pros and cons of each. Lastly, ASH is leveraged to study both online and offline complex social systems, including Reddit mental health and political discussion boards, and face-to-face interactions in primary and high schools

Attributed Stream Hypergraphs: temporal modeling of node-attributed high-order interactions

Abstract Recent advances in network science have resulted in two distinct research directions aimed at augmenting and enhancing representations for complex networks. The first direction, that of high-order modeling, aims to focus on connectivity between sets of nodes rather than pairs, whereas the second one, that of feature-rich augmentation, incorporates into a network all those elements that are driven by information which is external to the structure, like node properties or the flow of time. This paper proposes a novel toolbox, that of Attributed Stream Hypergraphs (ASHs), unifying both high-order and feature-rich elements for representing, mining, and analyzing complex networks. Applied to social network analysis, ASHs can characterize complex social phenomena along topological, dynamic and attributive elements. Experiments on real-world face-to-face and online social media interactions highlight that ASHs can easily allow for the analyses, among others, of high-order groups’ homophily, nodes’ homophily with respect to the hyperedges in which nodes participate, and time-respecting paths between hyperedges

Flexural behavior of external beam-column reinforced concrete assemblages externally strengthened with steel cages

In this paper, an experimental study referring to the flexural behavior of full-scale external beam-column joints externally strengthened with steel angles and strips and subjected to cyclic reversal loading is presented. One control specimen and five other specimens having the same characteristics as the control specimen but strengthened with steel angles and strips along beams and columns, and characterized by different configurations of strengthening in the critical regions, were tested. The control specimen was designed with a weak column and strong beam to reproduce the most common cases of old frame structures in the Mediterranean area, which were designed only for gravity loads and are in need of retrofitting to seismic standards. A detailed discussion of the strengthening technique used and of the mechanical properties of the specimens studied under cyclic loading is presented. It is highlighted that, referring to the case of external beam-column assemblages that are not yet extensively studied in the literature, the steel cage is an effective reinforcing technique to increase the flexural and shear strength of beams and columns, also increasing the energy capacity dissipation and reducing the stiffness degradation