Real-time video correlator

Device provides two-dimensional correlation of video data. Operation is reliable, accurate, and predictable

Making chiral fermion actions (almost) gauge invariant using Laplacian gauge fixing

Straight foreward lattice descriptions of chiral fermions lead to actions that break gauge invariance. I describe a method to make such actions gauge invariant (up to global gauge transformations) with the aid of gauge fixing. To make this prescription unambiguous, Laplacian gauge fixing is used, which is free from Gribov ambiguities.Comment: 3 p., Latex, (proc. Lattice '93, Dallas), 2 figs. appended, UCSD/PTH 93-4

Ultrasonic metal sheet thickness measurement without prior wave speed calibration

Conventional ultrasonic mensuration of sample thickness from one side only requires the bulk wave reverberation time and a calibration speed. This speed changes with temperature, stress, and microstructure, limiting thickness measurement accuracy. Often, only one side of a sample is accessible, making in situ calibration impossible. Non-contact ultrasound can generate multiple shear horizontal guided wave modes on one side of a metal plate. Measuring propagation times of each mode at different transducer separations, allows sheet thickness to be calculated to better than 1% accuracy for sheets of at least 1.5 mm thickness, without any calibration

Shear horizontal (SH) ultrasound wave propagation around smooth corners

Shear horizontal (SH) ultrasound guided waves are being used in an increasing number of non-destructive testing (NDT) applications. One advantage SH waves have over some wave types, is their ability to propagate around curved surfaces with little energy loss; to understand the geometries around which they could propagate, the wave reflection must be quantified. A 0.83 mm thick aluminium sheet was placed in a bending machine, and a shallow bend was introduced. Periodically-poled magnet (PPM) electromagnetic acoustic transducers (EMATs), for emission and reception of SH waves, were placed on the same side of the bend, so that reflected waves were received. Additional bending of the sheet demonstrated a clear relationship between bend angles and the reflected signal. Models suggest that the reflection is a linear superposition of the reflections from each bend segment, such that sharp turns lead to a larger peak-to-peak amplitude, in part due to increased phase coherence

Deciding Joinability Modulo Ground Equations In Operational Type Theory

Operational Type Theory (OpTT) can be used to construct and check proofs related to programs, but the development of these proofs can be somewhat tedious. An algorithm is presented that can be used to automatically generate proofs of equality in OpTT. The algorithm takes as input a set of ground equations and two terms that should be tested for joinability modulo the supplied ground equations. The algorithm will equate the terms if and only if there exists an OpTT proof that can equate the two terms using only the proof rules related to evaluation under the operational semantics, symmetry, transitivity, and congruence with respect to the supplied ground equations. The description of this algorithm is accompanied by a proof that the algorithm is partially correct

Weld defect detection using PPM EMAT generated shear horizontal ultrasound

AbstractAustenitic welds are inspected using PPM EMAT generated shear horizontal (SH) waves. Results are compared to measurements taken using a 1D piezoelectric phased array using the total focusing method (TFM). For the first time there is clear experimental evidence of the SH wave method demonstrating higher sensitivity to defect detection. SH waves suffer less beam steering in a weld than either compression or SV waves, which can miss defects due to weld microstructure anisotropy and attenuation. All defects were identified from every side of the weld/plate using the SH waves, but this was not possible using the piezoelectric transducer

Manifestly Gauge Invariant Models of Chiral Lattice Fermions

A manifestly gauge invariant lattice action for nonanomalous chiral models is proposed which leads in the continuum limit to the theory free of doublers.Comment: 9 pages, LaTeX. Revised version with an extended discussion of the role of higher derivative regulators. Submitted to Phys.Lett.B. Preprint SMI-9-9

Time of flight diffraction and imaging (TOFDI)

Time of flight diffraction and imaging (TOFDI) is based on time of flight diffraction (TOFD), adding cross-sectional imaging of the sample bulk by exploiting the scattering of ultrasonic waves from bulk defects in metals. Multiple wave modes are emitted by a pulsed laser ultrasound ablative source, and received by a sparse array of receiving electromagnetic acoustic transducers (EMATs), for non-contact (linear) scanning, with mode-conversions whenever waves are scattered. Standard signal processing techniques, such as band-pass filters, reduce noise. A B-scan is formed from multiple data captures (A-scans), with time and scan position axes, and colour representing amplitude or magnitude. B-scans may contain horizontal lines from surface waves propagating directly from emitter to receiver, or via a back-wall, and angled lines after reflection off a surface edge. A Hough transform (HT), modified to deal with the constraints of a B-scan, can remove such lines. A parabola matched filter has been developed that identifies the features in the B-scan caused by scattering from point-like defects, reducing them to peaks and minimising noise. Multiple B-scans are combined to reduce noise further. The B-scan is also processed to form a cross-sectional image, enabling detection and positioning of multiple defects. The standard phase correlation technique applied to camera images, has been used to track the relative position between transducer and sample. Movement has been determined to sub-pixel precision, with a median accuracy of 0.01mm of linear movement (0.06 of a pixel), despite uneven illumination and the use of a basic low resolution camera. The prototype application is testing rough steel products formed by continuous casting, but the techniques created to facilitate operation of TOFDI are applicable elsewhere

The Chiral Extension of Lattice QCD

The chiral extension of Quantum Chromodynamics (XQCD) adds to the standard lattice action explicit pseudoscalar meson fields for the chiral condensates. With this action, it is feasible to do simulations at the chiral limit with zero mass Goldstone modes. We review the arguments for why this is expected to be in the same universality class as the traditional action. We present preliminary results on convergence of XQCD for naive fermions and on the methodology for introducing counter terms to restore chiral symmetry for Wilson fermions.Comment: 7 pages, LATTICE 94 talk by R. Brower: Latex file with 2 postscript figures for encapsulatio

Mode mixing in shear horizontal ultrasonic guided waves

SH guided waves are used increasingly for non-destructive testing (NDT) applications, particularly for pipes and pipe supports using circumferentially guided wave modes. In practical implementations, it is not always straightforward to ensure single-mode operation and this requires consideration when interpreting results. During shear horizontal (SH) wave generation or SH guided wave interaction with geometrical changes or defects, multiple SH guided wave modes may be produced, depending on the shear wave speed, the frequency of operation, the thickness of the sample and the transducer characteristics. This paper discusses the interference patterns created as the multiple SH modes mix (for both continuous tone generation and short bursts), and the problems caused by the interference patterns on applications such as NDT. In particular, the patterns can lead to defects being missed during an NDT inspection using SH waves, and a way to circumvent this problem is suggested