This work was carried out within the framework of the
" 2009 Italian-Egyptian Year of Science and Technology".

We thank
T. Hussein (President of the Egyptian National Academy of Science and Technology) and F. Porcelli (Scientific Attaché, Italian Embassy, Egypt) for diplomatic support;

the Egyptian Army for logistical support;

G. Negro for field assistance;

F. Speranza and P. Rochette for helpful discussion during the preparation of the field work;

the European Commission (through the Marie Curie Actions–RTNs ORIGINS project);

the Fondazione Cassa di Risparmio di Torino, the Banca Monte dei Paschi di Siena S.p.A.;

and Telespazio S.p.A. (in the framework of the ESA SSA program) for financial support.