John A. Gardner

PAC analysis of defect motion by Blume's stochastic model forI=5/2 electric quadrupole interactions

Using Blumes stochastic model and the approach of Winkler and Gerdau, we have computed time-dependent effects on perturbed angular correlation (PAC) spectra due to defect motion in solids in the case ofI=5/2 electric quadrupole interactions. We report detailed analysis for a family of simple models: “XYZ+Z” models, in which the symmetry axis of an axial EFG is allowed to fluctuate among orientations alongx, y, andz axes, and a static axial EFG oriented along thez axis is added to the fluctuating EFGs. When the static EFG is zero, this model is termed the “XYZ” model. Approximate forms are given forG2(t) in the slow and rapid fluctuation regimes, i.e. suitable for the low and high temperature regions, respectively. Where they adequately reflect the underlying physical processes, these expressions allow one to fit PAC data for a wide range of temperatures and dopant concentrations to a single model, thus increasing the uniqueness of the interpretation of the defect properties. Application of the models is illustrated with data from a PAC study of tetragonal zirconia.

Scientific diagrams made easy with IVEO TM

Virtually all modern scientific documents and textbooks use graphical illustrations and/or data displays. The ViewPlus IVEOTM technology, based on Scalable Vector Graphics (SVG) is being developed to permit scientists to publish such graphics in a form fully usable by all people. The first release of IVEOTM was designed to make simple graphics accessible. Development of the second release, which includes improved text accessibility, linking, and interactivity, is described in this paper. We also discuss new research to expand accessibility of quantitative data in IVEOTM documents by using non-speech audio

Designing Media for Visually-Impaired Users of Refreshable Touch Displays: Possibilities and Pitfalls

This paper discusses issues of importance to designers of media for visually impaired users. The paper considers the influence of human factors on the effectiveness of presentation as well as the strengths and weaknesses of tactile, vibrotactile, haptic, and multimodal methods of rendering maps, graphs, and models. The authors, all of whom are visually impaired researchers in this domain, present findings from their own work and work of many others who have contributed to the current understanding of how to prepare and render images for both hard-copy and technology-mediated presentation of Braille and tangible graphics.

Stability of monoclinic and tetragonal zirconia at low oxygen partial pressure

We have found that both tetragonal and monoclinic zirconia annealed at temperaturess in the range of 1100 to 1300 °C in atmospheres of low oxygen partial pressures (down to 10 −26 Pa) transform slowly to an apparently cubic phase. The transformation can be reversed by increasing the oxygen partial pressure sufficiently, i.e., exposing the sample to air again. These observations were made by 111 In/Cd perturbed angular correlation (PAC) measurements of undoped zirconia samples. Upon annealing under various reducing atmospheres PAC spectra show a steadily increasing fraction of Cd probe atoms in a locally cubic environment with the fraction of probe atoms in tetragonal or monoclinic sites decreasing accordingly.

Total energy calculations for ZrO2

Abstract Total energy calculations are presented for zirconia in its tetragonal and cubic structure. The results show that the phase transition from tetragonal to cubic is driven by the thermal motion of the oxygen atoms. The theoretical value of the cohesive energy is in good agreement with experiment. The electric field gradients are in agreement with the experimental values obtained from Perturbed Angular Correlation measurements. This indicates that the lattice distortion around the probe tantalum nucleaus is small.

Energy and entropy of bond-breaking in liquid chalcogenides

Abstract From static magnetic susceptibility studies, we find that the energy to create a paramagnetic center in liquid sulfur at temperatures above 550°C is approximately 0.79 eV and the associated entropy is 4.4 k B . The bonding energies and entropies for a number of SSe alloys obtained from data reported here are similar to those of the pure materials. We also give magnetic susceptibility data for liquid S doped with Te and Tl which are compared to previous results for liquid Se.

Making journals accessible to the visually impaired: the future is near.

The American Physical Society (APS) has been a leader in using markup languages for publishing. ViewPlus has led development of innovative technologies for graphical information accessibility by people with print disabilities. APS, ViewPlus, and other collaborators in the Enhanced Reading Project are working together to develop the necessary technology and infrastructure for APS to publish its journals in the DAISY (Digital Accessible Information SYstem) eXtended Markup Language (XML) format, in which all text, math, and figures would be accessible to people who are blind or have other print disabilities. The first APS DAISY XML publications are targeted for late 2010.

Microcomputer‐controlled perturbed angular correlation spectrometer

A four‐detector time‐differential perturbed angular correlation spectrometer controlled by an inexpensive microcomputer is described. The use of twin‐single‐channel analyzers permits each detector to identify both gamma rays in the cascade. An improved gating logic system reduces the MCA/computer deadtime and allows larger sample activity and faster data accumulation. The twin‐single‐channel analyzer and gating circuit additions also permit simultaneous accumulation of two statistically independent sets of four‐channel spectra. The spectrometer provides on‐line display of raw data and the perturbation function derived from either set of four‐channel spectra.

Directly accessible mainstream graphical information

Plain text in well-authored electronic documents of nearly any format is accessible to a blind person who knows how to use a computer and screen reader. A great deal of common information is generally not presented as plain text however. Charts, diagrams, and graphs are common in business, scientific, and most professional literature. Maps and geographically-oriented data such as weather maps and complex census information would be virtually impossible to present in words. Until recently it has not been possible for authors of mainstream literature to present graphical information of these kinds in a format that could be accessed directly by blind people. In this paper, a new technology is described that does permit blind people to have direct access to most object-oriented graphical information. This new technology is possible because of two recent developments. One is the emergence of the mainstream SVG (Scalable Vector Graphics) language. The second is the Tiger technology for embossing tactile graphics.

Zirconia dynamics studied by PAC spectroscopy

Abstract Relaxation of 181 Ta nuclei due to diffusion of oxygen vacancies in cubic zirconia/yttria has been measured by perturbed angular correlation spectroscopy. The activation energy of the vacancy jump rate is found in a temperature range above 750°C and is in reasonable agreement with the activation energy of ionic conduction. Preliminary results of a 111 In/ 111 Cd perturbed angular correlation investigation of high-temperature monoclinic and tetragonal zirconia are also reported.