Simulation of ultrasonic lamb wave generation, propagation and detection for a reconfigurable air coupled scanner

A computer simulator, to facilitate the design and assessment of a reconfigurable, air-coupled ultrasonic scanner is described and evaluated. The specific scanning system comprises a team of remote sensing agents, in the form of miniature robotic platforms that can reposition non-contact Lamb wave transducers over a plate type of structure, for the purpose of non-destructive evaluation (NDE). The overall objective is to implement reconfigurable array scanning, where transmission and reception are facilitated by different sensing agents which can be organised in a variety of pulse-echo and pitch-catch configurations, with guided waves used to generate data in the form of 2-D and 3-D images. The ability to reconfigure the scanner adaptively requires an understanding of the ultrasonic wave generation, its propagation and interaction with potential defects and boundaries. Transducer behaviour has been simulated using a linear systems approximation, with wave propagation in the structure modelled using the local interaction simulation approach (LISA). Integration of the linear systems and LISA approaches are validated for use in Lamb wave scanning by comparison with both analytic techniques and more computationally intensive commercial finite element/difference codes. Starting with fundamental dispersion data, the paper goes on to describe the simulation of wave propagation and the subsequent interaction with artificial defects and plate boundaries, before presenting a theoretical image obtained from a team of sensing agents based on the current generation of sensors and instrumentation.     

Proposed reaction mechanisms for selenium UV photolysis vapor generation by computational methods

The production of volatile analyte species by UV photolysis in the presence of low-molecular-weight organic acids as an alternative to chemical vapor generation has been of recent interest. The mechanism of this process is not well understood. Proposed mechanisms often involve photolytic cleavage of the organic acid as the initial step. Evidence suggests that this may not be the dominant route for UV photolysis vapor generation. In this work computational methods were applied to determine a possible alternative mechanism in the absence of free-radical production. The proposed mechanism specifically focused on selenium vapor generation. An energetically favored mechanism was found for UV photolysis of inorganic selenium in the presence of formic and acetic acids which is consistent with previously reported experimental results.     

A framework for identifying student blockages during transitions in the modelling process

In this article we present, illustrate, test and refine a framework developed by Galbraith, Stillman, Brown and Edwards (2006) for identifying student blockages whilst undertaking modelling tasks during transitions in the modelling process. The framework was developed with 14~15 year old students who were engaging in their first experiences of modelling at the secondary level.     

The keyskills agenda: exploring implications for mathematics

As part of a broader research objective concerned with identifying the range of employer defined skill profiles that characterize workplace performance, this paper examines skill contexts for Application of Number, one of six UK defined Key Skills similar to Australian defined Key Competencies. Following the construction of questionnaires, grounded in the Analytic Hierarchy Process, applications of the instrument in both the UK and in Australia produced a ratio scale of priorities within the Key Skills area. This enabled a specification of the relative balance between classical competencies, e.g. facility with pen and paper calculations and emerging competencies demanded by the effective use of ICT. Relevance to workplace learning, including the transition from school to employment, and related aspects of mathematics education are discussed. Among the research outcomes is that spreadsheets are assuming a pre-eminent position and that this is an overriding priority for each defined activity and at each job level.     

Effects of anharmonic splitting upon collisionless multiple-photon laser excitation of SF6

Qualitative agreement of the dependence of molecular excitation upon laser frequency, between non-perturbative quantum-mechanical calculations and experimental measurements of the collisionless multiple-photon excitation of a few vibrational quanta in SF₆ by a CO₂ laser, results when anharmonic splitting of the vibrational energy levels is taken into account.     

Identification of the SF6 transitions pumped by a CO2 laser

The quantum numbers (J values and octahedral symmetry types) of the SF₆ transitions from the ground state to v₃ = 1 that fall within ± 1.5 G Hz of the CO₂ P(14), P(18), and P(20) laser lines have been assigned. The SF₆ absorptions nearest these three laser frequencies are R(28) A⁰₂, P(33) A¹₂, and an F₂ component of P(59) or P(60), respectively.     

Two-centre Hartree-Fock problems

Explorative Hartree-Fock calculations based on the two-centre oscillator Hamiltonian with a contact type residual force are carried out for the light systems ${}^8\text{Be}\text{2}{}^{\mathrm{<mtext>4</mtext><mtext>He</mtext>}}$ and ${}^{24}\text{Mg}\text{2}{}^{12}\text{C}$. Preliminary contact with experiment is made for the HF ground-state energies after correction for Coulomb and c.m. fluctuation effects. The single-particle spectra of the combined systems, which occur for a centre separation of 3.6 fm (⁸Be) and 2.8 fm (²⁴Mg) are compared to one-centre results.     

Results from a set of low speed blade-vortex interaction experiments

The results of a Blade-Vortex Interaction (BVI) experiment are presented. The experiments were the second series to be carried out at Glasgow University (see Kokkalis and Galbraith 1986, 1987), and reflect improvement to the facility. These improvements have resulted in sufficient resolution to observe clear evidence of vortex passage and propagative disturbances caused by the BVI. Additionally the quality of the pressure data permitted a meaningful assessment of force and moment coefficients, and a clear correspondence between their detailed time histories was observed. The data obtained are also compared with the results of previous studies, and qualitative and quantitative similarities are discussed.