Parametric investigation of a transducer for guided wave applications

The use of dry-coupled thickness-shear piezoelectric transducers for the generation of ultrasonic guided waves in Non Destructive Testing is well established in industry. The control of guided waves can be supported by designing transducers that achieve a uniform excitation over frequency and contact area. It is necessary to control the wave modes generated such that only modes with characteristics useful for inspection are transmitted and received. Recent research has identified the need to improve the ultrasonic performance in terms of amplitude and signal-to-noise ratio of guided waves via the miniaturization of the transducers. The influence of the geometry of the transducer on the generation of guided waves needs to be investigated. It is well known that the geometry of the transducers influences the normal modes of the ultrasonic transducers, which in turn can influence their ability to excited ultrasonic guided waves. However, the influence of transducer geometry on ultrasonic performance is still not completely understood: mode coupling and the presence of satellite modes might be detrimental for the generation of guided waves. These requirements drive the testing of design changes in terms of geometry and shape of the electrodes to improve the ultrasonic performance of the aforementioned transducers. The transducer is analysed both numerically (by Finite Element Analysis) and experimentally (with Laser Vibrometry) to offer a characterisation of existing piezoelectric elements. It is shown that a change in the actuation area of the transducer leads to a significant difference in the ultrasonic output

Experimental and numerical analysis of a transducer for the generation of guided waves

Dry-coupled thickness-shear transducers represent one of the most common ways to excite guided waves for the inspection of tubular and plate-like structures. Although already established in industry, some features of these transducers need to be studied, i.e. the uniformity of vibration, the modes excitability and the transmission of ultrasonic energy into the inspected structure. In particular, due to the dispersive behaviour of guided waves and the mode coupling these transducers require a precise characterization to guarantee a uniform in-plane vibration. A numerical and experimental characterization of the assembly has been carried out to assess the influence of the elements of the assembly into the uniformity of vibration. The outcome of the results in terms of mode-shape, displacement pattern and resonance frequencies is discussed to predict useful design changes to enhance the ultrasonic performance of these transducers

Characterisation of the vibration of an ultrasonic transducer for guided wave applications

Dry-coupled thickness-shear piezoelectric transducers are typically used to excite guided waves in plate-like or tubular structures in the frequency range of 20-150 kHz. The dispersive behaviour of guided waves and the excitation of unwanted wave modes require a precise tuning of the excitation frequency to facilitate effective inspection. A natural frequency analysis of a typical piezoelectric transducer has been performed to identify the shape of vibration in the frequency range indicated. Moreover, an experimental analysis of the vibration of the piezoelectric element through a scanning laser Doppler Vibrometer has been conducted. The numerical and experimental results agree in indicating no longitudinal mode is present up to 94 kHz. Experiments also has shown that the higher the frequency the higher the longitudinal component of displacement

Reproductive success of Mariana Swiftlets (\u3ci\u3eAerodramus bartschi\u3c/i\u3e) on the Hawaiian island of O’ahu

Mariana Swiftlets (Aerodramus bartschi) are federally listed as endangered, with populations currently limited to just three islands in the Mariana Islands plus an introduced population on the Hawaiian island of O’ahu. Before efforts are made to reintroduce Mariana Swiftlets to other islands in the Mariana archipelago, additional information is needed concerning their breeding biology. Therefore, our objective was to examine the reproductive biology of Mariana Swiftlets over five annual cycles on the Hawaiian island of O’ahu. This introduced population used a human-made tunnel for roosting and nesting, and was studied as a surrogate to negate interference with endangered populations in the Mariana Islands. Active nests (N = 478) were observed in every month of the year, with peak nesting activity between May and September. All clutches consisted of one egg. Mean duration of incubation and nestling periods were 23.9 d (range = 18– 30 d, N = 233) and 55.0 d (range = 41–84 d, N = 228), respectively. Estimated nest success was 63%. Over half (52%) of nest failures were attributed to eggs found on the tunnel floor. Predation by rats (Rattus spp.) was also an important cause of nest failure and often resulted in the loss of most active nests. However, Mariana Swiftlets did re-nest after these predation events. Our results suggest that rat predation of both nests and adults may limit growth of the Mariana Swiftlet population on O’ahu, and could also affect the chances for successful establishment of relocated populations in the Mariana Islands. Another limiting factor on O’ahu is that only one nesting site is apparently available on the island. Current goals for downlisting Mariana Swiftlets from endangered to threatened include establishing populations on Guam, Rota, Aguiguan, and Saipan. To meet these goals, the population of Mariana Swiftlets on O’ahu can be important for testing reintroduction techniques, learning more about the natural history of these swiftlets, and providing individuals for reintroduction efforts in the Mariana Islands

How to Do Things Without Words: Infants, utterance-activity and distributed cognition

Clark and Chalmers (1998) defend the hypothesis of an ‘Extended Mind’, maintaining that beliefs and other paradigmatic mental states can be implemented outside the central nervous system or body. Aspects of the problem of ‘language acquisition’ are considered in the light of the extended mind hypothesis. Rather than ‘language’ as typically understood, the object of study is something called ‘utterance-activity’, a term of art intended to refer to the full range of kinetic and prosodic features of the on-line behaviour of interacting humans. It is argued that utterance activity is plausibly regarded as jointly controlled by the embodied activity of interacting people, and that it contributes to the control of their behaviour. By means of specific examples it is suggested that this complex joint control facilitates easier learning of at least some features of language. This in turn suggests a striking form of the extended mind, in which infants’ cognitive powers are augmented by those of the people with whom they interact

Integrating team science into interdisciplinary graduate education: an exploration of the SESYNC Graduate Pursuit

Complex socio-environmental challenges require interdisciplinary, team-based research capacity. Graduate students are fundamental to building such capacity, yet formal opportunities for graduate students to develop these capacities and skills are uncommon. This paper presents an assessment of the Graduate Pursuit (GP) program, a formal interdisciplinary team science graduate research and training program administered by the National Socio-Environmental Synthesis Center (SESYNC). Quantitative and qualitative assessment of the program’s first cohort revealed that participants became significantly more comfortable with interdisciplinary research and team science approaches, increased their capacity to work across disciplines, and were enabled to produce tangible research outcomes. Qualitative analysis of four themes—(1) discipline, specialization, and shared purpose, (2) interpersonal skills and personality, (3) communication and teamwork, and (4) perceived costs and benefits—encompass participants’ positive and negative experiences and support findings from past assessments. The findings also identify challenges and benefits related to individual personality traits and team personality orientation, the importance of perceiving a sense of autonomy and independence, and the benefit of graduate training programs independent of the university and graduate program environment

A compact system for intraoperative specimen imaging based on edge illumination x-ray phase contrast

A significant number of patients receiving breast-conserving surgery (BCS) for invasive carcinoma and ductal carcinoma in situ (DCIS) may need reoperation following tumor-positive margins from final histopathology tests. All current intraoperative margin assessment modalities have specific limitations. As a first step towards the development of a compact system for intraoperative specimen imaging based on edge illumination x-ray phase contrast, we prove that the system\u27s dimensions can be reduced without affecting imaging performance. We analysed the variation in noise and contrast to noise ratio (CNR) with decreasing system length using the edge illumination x-ray phase contrast imaging setup. Two-(planar) and three-(computed tomography (CT)) dimensional imaging acquisitions of custom phantoms and a breast tissue specimen were made. Dedicated phase retrieval algorithms were used to separate refraction and absorption signals. A \u27single-shot\u27 retrieval method was also used, to retrieve thickness map images, due to its simple acquisition procedure and reduced acquisition times. Experimental results were compared to numerical simulations where appropriate. The relative contribution of dark noise signal in integrating detectors is significant for low photon count statistics acquisitions. Under constant exposure factors and magnification, a more compact system provides an increase in CNR. Superior CNR results were obtained for refraction and thickness map images when compared to absorption images. Results indicate that the \u27single-shot\u27 acquisition method is preferable for a compact CT intraoperative specimen scanner; it allows for shorter acquisition times and its combination of the absorption and refraction signals ultimately leads to a higher contrast. The first CT images of a breast specimen acquired with the compact system provided promising results when compared to those of the longer length system

A compact system for intraoperative specimen imaging based on edge illumination x-ray phase contrast

“This is an author-created, un-copyedited version of an article accepted for publication/published in Physics in Medicine & Biology. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The Version of Record is available online at https://doi.org/10.1088/1361-6560/ab4912