One-way dependent clusters and stability of cluster synchronization in directed networks

Cluster synchronization in networks of coupled oscillators is the subject of broad interest from the scientific community, with applications ranging from neural to social and animal networks and technological systems. Most of these networks are directed, with flows of information or energy that propagate unidirectionally from given nodes to other nodes. Nevertheless, most of the work on cluster synchronization has focused on undirected networks. Here we characterize cluster synchronization in general directed networks. Our first observation is that, in directed networks, a cluster A of nodes might be one-way dependent on another cluster B: in this case, A may remain synchronized provided that B is stable, but the opposite does not hold. The main contribution of this paper is a method to transform the cluster stability problem in an irreducible form. In this way, we decompose the original problem into subproblems of the lowest dimension, which allows us to immediately detect inter-dependencies among clusters. We apply our analysis to two examples of interest, a human network of violin players executing a musical piece for which directed interactions may be either activated or deactivated by the musicians, and a multilayer neural network with directed layer-to-layer connections.Comment: This is a preprint of an article published in Nature Communications. The final authenticated version is available online at: https://doi.org/10.1038/s41467-021-24363-7 or https://rdcu.be/cnya

Castle and Stairs to Learn Iteration: Co-Designing a UMC Learning Module with Teachers

This experience report presents a participatory process that involved primary school teachers and computer science education researchers. The objective of the process was to co-design a learning module to teach iteration to second graders using a visual programming environment and based on the Use-Modify-Create methodology. The co-designed learning module was piloted with three second-grade classes. We experienced that sharing and reconciling the different perspectives of researchers and teachers was doubly effective. On the one hand, it improved the quality of the resulting learning module; on the other hand, it constituted a very significant professional development opportunity for both teachers and researchers. We describe the co-designed learning module, discuss the most significant hinges in the process that led to such a product, and reflect on the lessons learned

ERICA: A multiparametric toxicological risk index for the assessment of environmental healthiness

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Programmare per imparare la crittografia al Liceo Matematico

Descriviamo un corso di introduzione alle “grandi idee” della crittografia, pensato per il secondo anno del Liceo Matematico. Sua caratteristica fondamentale è l’approccio “per scoperta”: viene proposta una successione di crittosistemi (dai classici ai più moderni), di ciascuno dei quali lo studente puó sperimentare caratteristiche, possibili attacchi e limi- ti, sentendo la necessità di scoprire il successivo. Abbiamo usato Snap! (un linguaggio di programmazione visuale a blocchi) sia per costruire dei playground (linguaggi di pro- grammazione task-specific, con una ridottissima selezione mirata di istruzioni) con cui spe- rimentare i diversi schemi, sia per guidare un’attività unplugged sul protocollo di Diffie- Hellman. Il lavoro presenta in dettaglio il percorso, le attività e il materiale, nonché una prima valutazione dell’intervento didattico, condotta dopo due edizioni (la prima online e la seconda in presenza)

Cryptography in Grade 10: Core Ideas with Snap! and Unplugged

International audienceWe report our experience of an extracurricular online intervention on cryptography in Grade 10. Our first goal is to describe how we taught some fundamental cryptography ideas by making students encounter a progression of representative cryptosystems, from classical to modern, and discover their characteristics and limitations. We used Snap! (a visual programming language) to realize hands-on activities: block-programming playgrounds (a form of task-specific programming languages) to experiment with cryptosystems, and an interactive app to support an unplugged (albeit remote) Diffie-Hellman key agreement. After experimenting with each system, the students were involved in a Socratic discussion on how to overcome the discovered limitations, motivating the introduction of the following system in our path. Our second goal is to evaluate the students' perceptions and learning of cryptography core ideas. They appreciated the course and felt that, despite being remote, it was fun and engaging. According to the students, the course helped them understand the role of cryptography, CS, and Math in society and sparked their interest in cryptography and CS. The final assessment showed that the students well understood the cryptography ideas addressed. Our third goal is to discuss what worked and areas of improvement. The "remote-unplugged" Diffie-Hellman, where the meeting chat was a metaphor for the public channel, engaged the students in understanding this groundbreaking protocol. Overall, they praised the activities as engaging, even when challenging. However, a strong "instructor blindness" induced by remote teaching often prevented us from giving the students the right amount of guidance during the exploration activities

A necessity-driven ride on the abstraction rollercoaster of CS1 programming

International audienceIntroductory programming courses (CS1) are difficult for novices. Inspired by Problem solving followed by instruction and Productive Failure approaches, we define an original "necessity driven" learning design. Students are put in an apparently well-known situation, but this time they miss an essential ingredient (the target concept) to solve the problem. Then, struggling to solve it, they experience the necessity of that concept. A direct instruction phase follows. Finally, students return to the problem with the necessary knowledge to solve it. In a typical CS1 learning path, we recognise a challenging "rollercoaster of abstraction". We provide examples of learning sequences designed with our approach to support students when the abstraction changes (both upward and downward) inside the programming language, for example, when a new construct (and the related syntactical, conceptual, and strategic knowledge) is introduced. Also, we discuss the benefits of our design in light of Informatics education literature