How to calculate R Values for op amp circuit

epcole

I need help calculating the R values for this circuit from the following article:

AN HIGH RESOLUTION RESISTIVE PROBE FOR NONLINEAR ANALYSIS OF TWO-PHASE FLOWS
L. Cantelli, A. Fichera, A. Pagano

This is only a section of the circuit, there is more but I'm only interested in this part of it. I want to rectify a sinusoid and also to maintain a gain of 1. Has anyone come across something like this? There is an instrumentation amplifier before this but I'm not dealing with that in my project.

Thanks.