A modem incorporating apparatus and methods to achieve computationally efficient echo cancellation. RR, which is the ratio of the reflective intensities of the s- and p-polarized light components, is calculated for each position of the surface of the sample, and the two-dimensional distribution of RR on the surface of the sample is detected. A second projection is provided at the other axial end of the retainer. The track-supporting roller assembly according to the disclosure ensures a reduced noise development in the crawler chassis. Preferred compositions disclosed include antigens selected from Cryptosporidium spp. A multi-user thermal sensation processor integrates estimation results on the users estimated by the thermal sensation estimators and into a single estimation result.