Poletti M.A.,Callaghan Innovation |
Fazi F.M.,University of Southampton
Journal of the Acoustical Society of America | Year: 2015
An application of current interest in sound reproduction systems is the creation of multizone sound fields which produce multiple independent sound fields for multiple listeners. The challenge in producing such sound fields is the avoidance of interference between sound zones, which is dependent on the geometry of the zone and the direction of arrival of the desired sound fields. This paper provides a theoretical basis for the generation of two zones based on the creation of sound fields with nulls and the positioning of those nulls at arbitrary positions. The nulls are created by suppressing low-order mode terms in the sound field expansion. Simulations are presented for the two-dimensional case which shows that suppression of interference is possible across a broad frequency audio range. © 2015 Acoustical Society of America.
Long N.J.,Callaghan Innovation
Entropy | Year: 2013
Maximum entropy inference can be used to find equations for the critical currents (Jc) in a type II superconductor as a function of temperature, applied magnetic field, and angle of the applied field, θ or φ. This approach provides an understanding of how the macroscopic critical currents arise from averaging over different sources of vortex pinning. The dependence of critical currents on temperature and magnetic field can be derived with logarithmic constraints and accord with expressions which have been widely used with empirical justification since the first development of technical superconductors. In this paper we provide a physical interpretation of the constraints leading to the distributions for Jc(T) and Jc(B), and discuss the implications for experimental data analysis. We expand the maximum entropy analysis of angular Jc data to encompass samples which have correlated defects at arbitrary angles to the crystal axes giving both symmetric and asymmetric peaks and samples which show vortex channeling behavior. The distributions for angular data are derived using combinations of first, second or fourth order constraints on cot θ or cot φ. We discuss why these distributions apply whether or not correlated defects are aligned with the crystal axes and thereby provide a unified description of critical currents in superconductors. For J//B we discuss what the maximum entropy equations imply about the vortex geometry. © 2013 by the authors.
Ingham B.,Callaghan Innovation
Journal of Applied Crystallography | Year: 2014
Spotty diffraction rings arise when the size distribution of crystallites illuminated by the incident beam includes crystallites that are large compared with the size of the beam. In this article, several statistical measures are used in conjunction to quantify spottiness and relate it to a crystallite size distribution: the number of peaks, the normalized root mean square intensity variation and the fractal dimension. These are demonstrated by way of example using synchrotron X-ray diffraction patterns collected during in situ corrosion of mild steel in carbon dioxide-saturated aqueous brine. © 2014 International Union of Crystallography.
Callaghan Innovation and Southwest Scientific Editing & Consulting L.L.C. | Date: 2013-06-10
Callaghan Innovation | Date: 2012-11-30
An arm rehabilitation system for exercising a users arm. The system provides an arm support device moveable upon a support surface by a users first arm. The arm support device has a main body configured to movably engage the support surface on one side and has a hand support portion on an opposing side at or toward one end of the body for supporting a users hand of the first arm. A primary hand support formation protrudes from the hand support portion and a secondary hand support handle extends from the main body at or toward the periphery of the hand support portion. An adjustable switch support boom assembly is also mounted to the main body and has at least one operable user input component for generating an actuation signal in response to operation by the user. An onboard motion tracking system mounted to or within the main body is configured to sense motion of the main body to enable user interaction with an interactive computer system running an application program.