In memory of Delio Ruggiu (July 31st 1934 – August 8th 2004)

Delio Ruggiu, who died on August 8th 2004, was an outstanding colleague, but first and foremost a beloved and irreplaceable friend. We heard the news of his sudden and untimely death with immense sadness and a great sense of emptiness, along with a feeling of incredulity: he had got through apparently desperate times before, and none of us thought that this time he had come to the end. In the many years of our life at the Institute, Delio was always there to share so much of significance in the research activity, and his participation was invariably marked by a great sense of responsibility, intellectual rigour and enthusiasm.