In Memoriam Jean-Claude Dousse

‘Πάντα ῥεῖ’—‘everything flows’ A saying in Ancient Greek, attributed to the philosopher Heraclitus of Ephesus, states ‘τὰ πάντα ῥεῖ καὶ οὐδὲν μένει’. It may be translated to ‘everything flows, and nothing stays’. Late 2020, a few months after the passing of Prof. Dr. Jean-Claude Dousse, we published an editorial to commemorate his scientific carrier. In this short summary,1 we anticipated the launch of a special issue ‘In Memoriam Jean-Claude Dousse’. It took us time to put it together, to involve and give time to all colleagues who wanted to contribute to this special issue, especially in view of the recent COVID-19 pandemic, and we are happy to present it here. We truly believed that it was important that the Special Issue is seeing the light. Many scientists have contributed to this Special Issue, which will give the readers of Wiley X-Ray Spectrometry journal an overview of the fields of science in which the imprints and legacy of Jean-Claude Dousse may be found. We would like here to thank all the authors, the reviewers, the editorial team at X-ray Spectrometry, for their time, their work, for their will to contribute to this venture. We would also like to express our appreciation of the numerous expressions of support to this initiative, whether these were followed by a contribution or not. We also recall with a lot of emotions, the feedback received after the special session ‘In Memoriam Jean-Claude Dousse’ we organised during the European X-Ray Spectrometry (EXRS) 2022 Conference,2 under the auspices of EXSA3 and of its members part of the EXRS’ International Advisory Committee. This session, widely attended, has been the opportunity to elaborate on present scientific achievements in various fields of research linked to high-resolution X-ray spectroscopy, while grounding them into the past, and looking towards future developments. The common threads to all these works, were the impact that Jean-Claude's scientific journey had on the science, and that his generous personality, one that has forged trust, that has led to scientific respect he had on his colleagues, collaborators and alumni. A sentence was repeated by all speakers ‘I was one of the lucky persons who […]’ learnt, worked, collaborated, knew Jean-Claude. Indeed, the passion with which Jean-Claude was dealing with science, learning and acting on the world using his scientific imagination and curiosity while providing a heart-centred scientific education and collaboration to his pairs, shined during this session. It is mirrored in this Special Issue. Engraved in the trophy given to him in 2018 at the occasion of the attribution of his title of emeritus professor by the University of Fribourg, Switzerland, were these words: ‘X-Rays are forever’. Without doubt, the scientific legacy of Jean-Claude will be remembered in the X-ray Spectrometry community, and his works will continue to lay the foundations to many upcoming scientific breakthroughs. Science will keep providing advancement, and impacting our lives, while simultaneously, ‘Πάντα ῥεῖ’—‘everything flows’. But this XRS Special Issue will stay in the literature, and we hope that with it, together with all contributors, to have honoured Jean-Claude Dousse.