Construction of the optical part of a time-of-flight detector prototype for the AFP detector.

We present the construction of the optical part of the ToF (time-of-flight) subdetector prototype for the AFP (ATLAS Forward Proton) detector. The ToF detector in conjunction with a 3D silicon pixel tracker will tag and measure protons originating in central exclusive interactions p + p → p + X + p, where the two outgoing protons are scattered in the very forward directions. The ToF is required to reduce so-called pileup backgrounds that arise from multiple proton interactions in the same bunch crossing at high luminosity. The background can fake the signal of interest, and the extra rejection from the ToF allows the proton tagger to operate at the high luminosity required for measurement of the processes. The prototype detector uses fused silica bars emitting Cherenkov radiation as a relativistic particle passes through it. The emitted Cherenkov photons are detected by a micro-channel plate multi-anode Photomultiplier Tube (MCP-PMT) and processed by fast electronics.

[Measurement of acetabular polyethylene wear of total hip replacement, using a universal measuring microscope. Characteristics of measurements]. / Merení oteru polyetylenových jamek TEP kycelního kloubu univerzálním mericím mikroskopem Charakteristika merení

PURPOSE OF THE STUDY: The aim of the study was to present our own method of measuring acetabular polyethylene wear in total hip arthroplasty, including assessment of basic measurement characteristics. It is a well known fact that, in total hip replacement, polyethylene liners wear out with use. The rate of acetabular polyethylene wear can then be related to clinical or demographic data. MATERIAL AND METHODS: Our method, using a universal measuring microscope, is based on the ability of exact identification of central positions of the head of total hip replacement before implantation and after prosthesis removal. The difference between the original and final positions allows us to calculate both linear and volumetric wear of polyethylene. During one month, the same components were repeatedly measured by two independent investigators and a total of 10 ABG 1 acetabular components were checked. The results of measurements were evaluated by a series of statistical tests, including correlation and regression analyses and analysis of variance. RESULTS: High correlations were found among individual measurements made by each observer (r = 0.998; r = 0.973) as well as between the mean values obtained from the two observers (r = 0.996). The reliability of measurements was proved by a high correlation of the regression curve of each measurement with the "ideal" line. With two exceptions, the differences between paired measurements were not significant. CONCLUSIONS: Our method facilitates an in vitro measurement of polyethylene wear with considerable accuracy and high reliability.