Abstract: A method of calibrating a nuclear density meter used in the measurement of density of a sand/water/oil slurry flowing in a pipe, without sampling the slurry, is provided comprising determining a net attenuation coefficient for the slurry being measured and mitigating radiation buildup.

Abstract: A general-purpose method is provided for authenticating, i.e., verifying the claimed identity of, users of a computer system through the selection of a sequence of images from a displayed assembly of images. The method is based on the capability of computer systems to display and manipulate individual thumbnail images via a graphical user display interface. The method takes image sequences selected by a user and formulates a password that is dependent on both the sequence and style of their selection. To ease the users' burden of complying with organizational policy to change passwords after some period of time, the method allows the same image sequence to be used repeatedly in a password change dialogue, yet generate a completely different password value each time. A new method of “salting” passwords to make them less vulnerable is also provided.