Alan Kenneth Head 1925 - 2010

Alan Head had many scientific interests. He was a mathematical physicist but was so widely read that he could turn his hand to almost anything that had a scientific basis. His contributions ranged from a design for a giant radio telescope to writing a computer program to simulate the diffraction of electrons as they pass through a crystalline specimen containing defects on an atomic scale and to calculate the images produced by these defects; from the elastic properties of engineering materials to the aberrations in aplanatic, non-spherical lens systems; from the causes of fracture in solid state materials to the patented design for a refrigerator that obtains its cooling power by selectively radiating electromagnetic radiation through a ?window' in the earth's atmosphere to outer space; from Galois theory to quantum computers. Perhaps his greatest success was the theory of fatigue in aluminium alloys used in the construction of jet aeroplanes. Not only was he able to establish the micro-mechanisms involved, his analysis was such that the time that the processes would take to produce a complete failure could be estimated. Without this analysis, commercial aviation as we know it today would have been totally unsafe, whereas knowing the effective lifetime of components and replacing them before the end of their lifetime meant that, provided the relevant maintenance was carried out diligently, travel by air could be safe. The project that gave Alan most pleasure was his understanding of Galois theory and his being the first person to apply it to a practical case concerning the elastic anisotropy of crystalline materials. These two examples epitomise the value Alan put on ?theory'. Theory was only good if it led to a practical, useful result. Alan Head had a brilliant career but his feet were always firmly on the ground. He was modest, quietly spoken and very approachable. He was a friend and mentor to many. There are more than ten scientific topics (including those mentioned above) described in this memoir and he made significant contributions to all of them.