Japan is a world reference when it comes to video games. Nintendo, Sony, Sega... so many companies that have left their mark on contemporary popular culture. Fanny Barnabé knows this industry well. A lecturer at the Faculté Économie Management Communication sciencesPo (EMCP) and researcher at the CRIDS/NaDI research institute, she specializes in game studies, a field of research devoted to the study of games. After defending her doctoral thesis on videogame détournement in the fictional universe of Pokémon in 2017, she spent a year as a postdoctoral fellow at the Ritsumeikan Center For Game Studies (Ritsumeikan University, Kyoto), the archipelago's largest video game research center. Internationally recognized, the Center is fortunate to host an exceptional and unpublished archive, thanks to a donation from the giant Nintendo.

Many years and research work later, Fanny Barnabé visited Japan once again at the end of May, on an academic mission. The aim: to present the latest work being carried out at UNamur, particularly in edutainment or "serious game"and, she hopes, lay the foundations for new partnerships and student exchanges.

The Faculty of Informatics has long-standing links with the National Institute of Informatics (NII), an internationally recognized research institute located in the heart of Tokyo. Each year, Master's and PhD students from the faculty are hosted there for a period of four to six months to carry out internships and research projects, via a specific collaboration agreement (Memorandum Of Understanding agreement, or MOU). It's an experience much appreciated by students and PhD students alike, on both scientific and human levels.

Gilles Perrouin, researcher and chairman of the Faculty of Computer Science's Research Commission, guides these students through the presentation of their research topic, often focused in the fields of software engineering, artificial intelligence (AI) or, more recently, green AI. "These are research fields that are evolving very quickly", Gilles Perrouin points out. "There's a lot of debate right now around AI's energy consumption. It's a bit of an oxymoron to say that we can do green AI.But we're working on it via the exploration of smarter techniques when looking for promising solutions to avoid resorting to systematic training of the neural network, which is very costly in terms of energy"explains the researcher. The collaboration has led to the exploration of other areas of AI, such as sign language recognition (Professor Benoît Frénay), in addition to topics in formal methods and software engineering (Professors Pierre-Yves Schobbens and Xavier Devroey).

At the heart of the Mathematics Department, Alexandre Mauroy, professor and researcher at the Namur Institute for Complex Systems (naXys), is working with his long-time collaborator and friend Yoshihiko Susuki from the prestigious University of Kyoto on a project co-funded by F.N.R.S and JSPS (Japan) to study dynamical systems. "These are so-called 'non-linear' phenomena that do not respect the rules of proportionality. The equations are therefore very difficult, if not impossible, to solve in practice, explains Alexandre Mauroy. "To get around this problem, we mobilize techniques like operator theory, which we're studying as part of this project." This has the advantage of combining theoretical aspects with practical applications, particularly in the field of electrical distribution networks. "These are complex systems, with slow and fast dynamics. An interesting case for which mathematical tools need to be adapted", continues Alexandre Mauroy. This first positive partnership has already led to research visits between the two countries, and promises new collaborations in the future.

In a related field, Riccardo Muolo has been a postdoctoral fellow at the Institute of Science Tokyo since 2023, after completing a PhD thesis at UNamur under the supervision of Professor Timoteo Carletti. Building on the knowledge acquired during his PhD on network dynamics, Riccardo Muolo is now interested in network synchronization theory, a mathematical model that enables us to understand a wide variety of systems: from fireflies to electrical networks to the functioning of the human brain: "For example, in the brain, abnormal synchronization of neuronal networks is associated with pathologies such as epilepsy or Parkinson's. The recent power grid failure in Spain can also be analyzed through this theory", details the researcher.

Students wishing to spend part of their degree course in Japan have the opportunity to do so, thanks to the various agreements UNamur has signed with Japanese institutions. This is the case with the National Institute of Informatics (NII), but also with Soka University and Sophia University (Chiyoda), with which UNamur has signed framework agreements.

It all started with Nicolas Roy's trip to Stanford. Nicolas is a PhD student in the Department of Physics and a member of the NISM and NaXys Institutes. The purpose of the visit to Stanford was to develop expertise at UNamur on a new method of simulating twisted photonic crystals, recently published by the prestigious university. Following discussions during the stay at Stanford, avenues for collaboration emerged, notably that of continuing research related to one of their publications in order to try to make a device that allows the direction of the light beam to be manipulated as efficiently and compactly as possible.  The gamble paid off, as the theoretical study predicts a device measuring 6 microns (the size of a hair)!  What's more, it is very energy efficient.  In practical terms, it could be used to track satellites, for example, without moving the transmitter or receiver, which is complicated in a photonic circuit.  Another practical application is being studied for Meta, a company that wants to reduce the size of virtual reality headsets to a simple pair of glasses... 

During his PhD, and based on a Stanford team publication entitled "Theory for Twisted Bilayer Photonic Crystal Slabs", Nicolas reproduced the simulation method and developed an analytical model of the numerical simulations. The use of these inexpensive simulations has made it possible to find the photonic structures most capable of deflecting light in a controlled manner. The analytical model, in turn, provides an explanation for what has been observed, and thus a better understanding of what's going on. In short, it opens up prospects for simpler fabrication of future devices.

The research teams collaborating on this study are working on twisted photonic crystals, i.e. two-dimensional materials formed, for example, from two superimposed and structured layers of silicon, and their interaction with light. 

In designing an analytical model, Nicolas Roy also used a theory that has been known since the 1960s: lattice networks. A lattice network is a plane diffraction network with a sawtooth profile.  In concrete terms, it resembles the roofs of old factories.  The novelty he brought to this concept is that it allows us to understand the mechanism that controls the angle of the light beam's exit thanks to the twist between the two layers. In doing so, he identified that the system acted similarly to a lattice grating. The team, using meta-models, was able to concentrate the light in a very specific direction with 90% efficiency.

What is the purpose of this type of twisted structure? To control light and ultimately create systems that can slow it down or even stop it.

This twist technique therefore opens up many unexplored possibilities in photonics by adding a degree of control over light. The researchers are continuing their work in this area, continuing their fruitful collaboration with Professor Fan's team, Stanford University.  

It looks like there's no end in sight to the twisting at the University of Namur! 

The Belgian team

• Professor Michael Lobet (UNamur, Harvard University)
• Professor Alexandre Mayer (UNamur)
• Dr Nicolas Roy (UNamur)

The American team

• Professor Shanhui Fan (Stanford University)
• Dr Beicheng Lou

The researchers thank UNamur, and more specifically the Department of Physics and the NISM Institute for funding Nicolas Roy's trip, the Institut naXys for its support in this project, the PTCI technology platform, whose supercomputers made this study possible, as well as the FNRS for funding the research mandates of Michaël Lobet and Alexandre Mayer.

• Michaël Lobet, the physicist of the invisible who makes light twist
• Following in Einstein's footsteps: old theories, new perspectives
• Publication on light observation in Nature Communications

The study of complex systems published in Physical Reviews Letters supports a growing trend that focuses more on analyzing the collective behavior of a system rather than discovering the underlying mechanisms of interaction.

When we observe a flock of starlings swirling through the sky in perfect coordination - a phenomenon known as murmuration - we witness the elegant interplay of individual actions creating collective behavior. In trying to understand these fascinating patterns, researchers can isolate simple rules based on an individual bird's field of view and the distance separating it from its neighbors, but there's always the question of whether the model actually captures the processes driving interactions between birds (Fig. 1).

This is a general problem in complex systems research, which comes down to distinguishing mechanisms (the rules governing interactions) from behaviors (the observable patterns that emerge).

Representative networks of interacting individuals, or nodes, are a good way to study mechanisms versus behaviors. Until now, researchers have focused on pairwise interactions, but many systems also include higher-order interactions between several nodes. The impact of these higher-order mechanisms on behavior has not been clearly established. Thomas Robiglio, from the Central European University in Vienna, and his colleagues, including Maxime Lucas (CR FNRS - UNamur) addressed this question. They considered networks with higher-order interactions and evaluated the resulting behaviors in terms of statistical dependencies between node values.

The researchers identified higher-order behavioral signatures which, unlike their pairwise counterparts, reveal the presence of higher-order mechanisms. Their findings open up new avenues for distinguishing mechanisms and behaviors when studying complex systems - a distinction that is crucial for the study of inference in network science, neuroscience, the social sciences and beyond.

This study is also the subject of a "Featured in Physics" and "Editor's suggestion" article, and a "commentary" article at the journal's request, available on their website in English in full.

The study, entitled "Topology shapes dynamics of higher-order networks" proposes a theoretical framework specifically designed to understand complex higher-order networks where several agents interact at the same time and thus generalize networks with their interactions in pairs. More precisely, the study shows how topology shapes dynamics, how dynamics learns topology and how topology evolves dynamically.

The aim of this work is to introduce physicists, mathematicians, computer scientists and network scientists to this emerging research field, as well as to define future research challenges where discrete topology and nonlinear dynamics mix.

With the data in their possession, the researchers show that real-life complex systems such as the brain, chemical reactions and neural networks can be easily modeled as higher-order networks, characterized by multi-body connections indicating the fact that several elements of the system interact simultaneously.

This international team is convinced that the visibility of their work through this publication in Nature Physics will open the door to new collaborations with other disciplines that rely on network analysis to study real complex systems.

Kudos to the team for this publication!

After a Master's degree in physics (University of Florence, June 1995), Timoteo Carletti pursued his doctoral studies in Florence (Italy) and Paris (France) at IMCCE, finally defending his doctoral thesis in mathematics in February 2000.

He moved to Belgium in 2005, and was hired at the University of Namur as a lecturer, then as a professor (2008), and finally as a full professor (2011) in the Mathematics Department of the Faculty of Science. In 2010, he was one of the founders of the Namur Center for Complex Systems (now the Namur Institute for Complex Systems - naXys), which he headed until December 2014.