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PrSi crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. Pr4+ is bonded in a 7-coordinate geometry to seven equivalent Si4- atoms. There are a spread of Pr–Si bond distances ranging from 3.10–3.27 Å. Si4- is bonded in a 9-coordinate geometry to seven equivalent Pr4+ and two equivalent Si4- atoms. Both Si–Si bond lengths are 2.52 Å.
PrSI crystallizes in the orthorhombic Pbca space group. The structure is three-dimensional. Pr3+ is bonded in a 7-coordinate geometry to four equivalent S2- and three equivalent I1- atoms. All Pr–S bond lengths are 2.86 Å. There are a spread of Pr–I bond distances ranging from 3.28–3.49 Å. S2- is bonded to four equivalent Pr3+ atoms to form a mixture of distorted corner and edge-sharing SPr4 tetrahedra. I1- is bonded in a 3-coordinate geometry to three equivalent Pr3+ atoms.
The Backscratching optical correlation algorithm has been proposed for four degree of freedom tracking. In an alternating Cartesian and log-polar implementation, the tracked parameters are scale, rotation, and two-dimenisonal translation. The algorithm has a finite capture radius in the four-dimensional tracking space. The capture radius is dependent on the tracked object, the correlator architecture, and the method of filter computation. Some methods of extending the capture radius are discussed. One is a modification of matched filters, another is a careful consideration of log-polar transform center, and another is an operational method. Some simulations of the filter construction method, in which a larger capture radius is gained at the expense of precision in determining the four parameters are presented.