Ryan P. Haggerty

A Comparison of Two Probability Encoding Methods: Fixed Probability vs. Fixed Variable Values

We present the results of an experiment comparing two popular methods for encoding probability distributions of continuous variables in decision analysis: eliciting values of a variable, X , through comparisons with a fixed probability wheel and eliciting the percentiles of the cumulative distribution, F ( X ), through comparisons with fixed values of the variable. We show slight but consistent superiority for the fixed variable method along several dimensions such as monotonicity, accuracy, and precision of the estimated fractiles. The fixed variable elicitation method was also slightly faster and preferred by most participants. We discuss the reasons for its superiority and conclude with several recommendations for the practice of probability assessment.

A curved image-plate detector system for high-resolution synchrotron X-ray diffraction

The developed curved image plate (CIP) is a one-dimensional detector which simultaneously records high-resolution X-ray diffraction (XRD) patterns over a 38.7 degrees 2theta range. In addition, an on-site reader enables rapid extraction, transfer and storage of X-ray intensity information in </=30 s, and further qualifies this detector to study kinetic processes in materials science. The CIP detector can detect and store X-ray intensity information linearly proportional to the incident photon flux over a dynamical range of about five orders of magnitude. The linearity and uniformity of the CIP detector response is not compromised in the unsaturated regions of the image plate, regardless of saturation in another region. The speed of XRD data acquisition together with excellent resolution afforded by the CIP detector is unique and opens up wide possibilities in materials research accessible through X-ray diffraction. This article presents details of the basic features, operation and performance of the CIP detector along with some examples of applications, including high-temperature XRD.

CTEAS: A graphical-user-interface-based program to determine thermal expansion from high-temperature X-ray diffraction

The coefficient of thermal expansion analysis suite (CTEAS) has been developed to calculate and visualize thermal expansion properties of crystalline materials in three dimensions. The software can be used to determine the independent terms of the second-rank thermal expansion tensor using hkl values, corresponding dhkl listings and lattice constants obtained from powder X-ray diffraction patterns collected at different temperatures. Using CTEAS, a researcher can also visualize the anisotropy of this essential material property in three dimensions. In-depth understanding of the thermal expansion of crystalline materials can be a useful tool in understanding the dependence of the thermal properties of materials on temperature when correlated with the crystal structure.

Powder diffraction by fixed incident angle reflection using a curved position-sensitive detector

As curved position-sensitive detectors improve in angular resolution, the effects that fixed incident angle reflection have on X-ray diffraction peaks become more apparent. In this study the effects of sample transparency, incident beam height, detector resolution and sample displacement on the intensity, location, width and shape of powder diffraction peaks were examined. The functions describing each of these phenomena are presented and were successfully used to quantitatively model the diffraction peaks collected in this geometry. Three distinct regimes of diffraction peak resolution were identified from the phenomena that limit the peak variance. Pertinent criteria based on experimental parameters have been outlined to classify fixed incident angle reflection experiments into each regime. Guidelines for improvement of experimental resolution and for conducting analysis of data acquired using fixed incident angle reflection geometry and curved position-sensitive detectors are also provided.