[en] In this paper the author calculates the boson-soliton scattering amplitudes for various processes in the sine-Gordon model to obtain results in agreement with the prediction of no-particle production and equality of ingoing and outgoing sets of momenta. (Auth.)

[en] The ability to analyse the performance of complex structures has improved considerably over the last quarter-century, particularly with the availability of computers and the finite element system. This paper presents a series of finite element analyses undertaken as part of a programme of reassessment of a gas-cooled nuclear power station commissioned over 25 years ago. The aim of the analyses was to evaluate the general stress levels in the reactor shell and primary cooling circuit under various loading conditions and then to carry out more detailed studies of areas of particular interest, where high localised stresses were expected. The results for this 25 year old design were then assessed in the light of modern acceptable stress limits, and compared with anticipated values where possible, such as strain gauge readings for the initial proof testing of the vessel. Good agreement was obtained between the calculated and expected results and the code comparisons showed considerable redundancy in the original design. (orig.)

[en] The authors test the functional approach to tunnelling by using the sine-Gordon 'instanton' to calculate the second term in the asymptotic expansion of the width of the lowest band in a periodic potential. (Auth.)

[en] A software package is developed to perform explicit time domain finite element simulations of ultrasonic propagation on the graphical processing unit, using Nvidia’s CUDA. Of critical importance for this problem is the arrangement of nodes in memory, allowing data to be loaded efficiently and minimising communication between the independently executed blocks of threads. The initial stage of memory arrangement is partitioning the mesh; both a well established ‘greedy’ partitioner and a new, more efficient ‘aligned’ partitioner are investigated. A method is then developed to efficiently arrange the memory within each partition. The technique is compared to a commercial CPU equivalent, demonstrating an overall speedup of at least 100 for a non-destructive testing weld model

[en] Guided wave tomography offers a method to accurately quantify wall thickness losses in pipes and vessels caused by corrosion. This is achieved using ultrasonic waves transmitted over distances of approximately 1–2m, which are measured by an array of transducers and then used to reconstruct a map of wall thickness throughout the inspected region. To achieve accurate estimations of remnant wall thickness, it is vital that a suitable Lamb mode is chosen. This paper presents a detailed evaluation of the fundamental modes, S₀ and A₀, which are of primary interest in guided wave tomography thickness estimates since the higher order modes do not exist at all thicknesses, to compare their performance using both numerical and experimental data while considering a range of challenging phenomena. The sensitivity of A₀ to thickness variations was shown to be superior to S₀, however, the attenuation from A₀ when a liquid loading was present was much higher than S₀. A₀ was less sensitive to the presence of coatings on the surface of than S₀

[en] The finite element method solved with explicit time increments is a general approach which can be applied to many ultrasound problems. It is widely used as a powerful tool within NDE for developing and testing inspection techniques, and can also be used in inversion processes. However, the solution technique is computationally intensive, requiring many calculations to be performed for each simulation, so traditionally speed has been an issue. For maximum speed, an implementation of the method, called Pogo [Huthwaite, J. Comp. Phys. 2014, doi: 10.1016/j.jcp.2013.10.017], has been developed to run on graphics cards, exploiting the highly parallelisable nature of the algorithm. Pogo typically demonstrates speed improvements of 60-90x over commercial CPU alternatives. Pogo is applied to three NDE examples, where the speed improvements are important: guided wave tomography, where a full 3D simulation must be run for each source transducer and every different defect size; scattering from rough cracks, where many simulations need to be run to build up a statistical model of the behaviour; and ultrasound propagation within coarse-grained materials where the mesh must be highly refined and many different cases run

[en] Ferroelectric lead zirconate titanate (PZT) thin films have been analysed using electron backscatter diffraction (EBSD). Grain orientation mapping has been demonstrated, showing that features smaller than 100 nm may be successfully indexed. In conjunction with piezoresponse force microscopy (PFM), which was used to map and quantify the piezoelectric response from the same region of the films with a resolution of 10 nm, an analysis of the effects of grain orientation on the measured response at the nanoscale was possible. The microtexture of the film showed the presence of both mono- and multi-domains within grains exhibiting sizes of hundreds of nanometres.

[en] Spin-lattice relaxation times T₁ in ³He-⁴He solutions have been measured at temperatures between 1.5 and 3.3 K and for molar concentrations of 10%, 1%, and 0.1%. Little concentration dependence was observed. Below the lambda point, T₁ increases rapidly with increasing temperature; above, it is fairly constant. The data are well described by a wall relaxation mechanism, in which T₁ depends upon the time for the ³He spins to diffuse to the walls. We discuss a theory for diffusion in dilute solutions at high temperatures where the diffusion coefficient is primarily determined by ³He-roton scattering

[en] The safe operation of petrochemical plant requires screening of the pipework to ensure that there are no unacceptable levels of corrosion. Unfortunately, each plant has many thousands of metres of pipe, much of which is insulated or inaccessible. Conventional methods such as visual inspection and ultrasonic thickness gauging require access to each point of the pipe which is time consuming and very expensive to achieve. Extensional or torsional ultrasonic guided waves in the pipe wall provide an attractive solution to this problem because they can be excited at one location on the pipe and will propagate many metres along the pipe, returning echoes indicating the presence of corrosion or other pipe features. Guided Ultrasonics Ltd. have now commercialised the technique and this paper describes the basis of the method, together with examples of practical test results and typical application areas

[en] Texture in hexagonal close-packed (hcp) polycrystalline metals, often developed during thermomechanical processing, affects ultrasonic wave velocity. In this study, the relationship between bulk texture and ultrasonic wave velocity in aggregates of (predominantly) hcp grains is investigated using theoretical, numerical and experimental methods. A representative volume element methodology is presented, enabling the effects of texture on ultrasonic wave speed to be investigated in two-phase polycrystals, and is employed to examine the ultrasonic response of random polycrystals, textured polycrystals and macro-zones often observed in titanium alloys. Numerical results show that ultrasonic wave speed varies progressively with changing texture, over a range of ∼200 m s⁻¹, within bounds set by the two extreme single-crystal orientations. Experimental ultrasound studies and full electron backscatter diffraction (EBSD) characterization are conducted on unidirectionally rolled and cross-rolled Ti–6Al–4V samples in three orthogonal directions. In addition, the EBSD-determined textures are incorporated within the polycrystal model and predicted ultrasonic velocities compared directly with ultrasonic experiments. Good quantitative agreement is obtained and both the experimental and computed results demonstrate that ultrasonic velocity profiles exist for random, unidirectionally rolled and cross-rolled textures. The combined results indicate the possibility of the development of a methodology for bulk texture determination within Ti polycrystal components using ultrasound