394 research outputs found

    Deep Thermoacoustic Imaging Using Scanning Electron Acoustic Microscopy

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    There has developed over the past few years some controversy [1] over the meaning and use of terms such as “thermal wave imaging” vs. “thermoacoustic imaging” or “Thermal Wave Microscopy” as opposed to “Scanning Electron Acostic Microscopy” (SEAM). The issue in question is the extent of the role played by acoustics directly on the imaging. In the present work, SEAM studies of a prepared test standard are presented which show that macroscopic elastic properties can play an important role in imaging. The SEAM technique uses Coordinate Modulation (CM) of the electron beam [2] rather than the more commonly used intensity modulation via beam blanking. Defects as deep as 26 thermal diffusion lengths in stainless steel have been clearly imaged with this technique. This work strongly supports the Jackson -Amer thermal bending model [3] for low frequency (up to approximately 100kHz in small specimens) acoustic detection in the solid as compared to the theory of Opsal and Rosencwaig [4] which does not incorporate total specimen response to the thermal source. This problem has more recently been theoretically investigated by Favro [5,6], who has developed a more general theory encompasing both the Opsal-Rosencwaig short wavelength limit and the Jackson-Amer long wavelength limit. Favro’s theory also accounts for features in the image shown

    Chain-store pricing and the structure of retail markets

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    This paper examines competition between chain-stores and independent retailers in the UK retail opticians' market. We demonstrate that the pricing policy adopted by chain-stores can determine the impact their entry has on independent retailers. Crucially, in this market the chain-store retailers set an identical national price across all local markets. Our results suggest that this pricing strategy lessens the detrimental effect competition from chain-stores has on independent retailers

    Understanding childhood asthma in focus groups: perspectives from mothers of different ethnic backgrounds

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    BACKGROUND: Diagnosing childhood asthma is dependent upon parental symptom reporting but there are problems in the use of words and terms. The purpose of this study was to describe and compare understandings of childhood 'asthma' by mothers from three different ethnic backgrounds who have no personal experience of diagnosing asthma. A better understanding of parents' perceptions of an illness by clinicians should improve communication and management of the illness. METHOD: Sixty-six mothers living in east London describing their ethnic backgrounds as Bangladeshi, white English and black Caribbean were recruited to 9 focus groups. Discussion was semi-structured. Three sessions were conducted with each ethnic group. Mothers were shown a video clip of a boy with audible wheeze and cough and then addressed 6 questions. Sessions were recorded and transcribed verbatim. Responses were compared within and between ethnic groups. RESULTS: Each session, and ethnic group overall, developed a particular orientation to the discussion. Some mothers described the problem using single signs, while others imitated the sound or made comparisons to other illnesses. Hereditary factors were recognised by some, although all groups were concerned with environmental triggers. Responses about what to do included 'normal illness' strategies, use of health services and calls for complementary treatment. All groups were concerned about using medication every day. Expectations about the quality of life were varied, with recognition that restrictions may be based on parental beliefs about asthma, rather than asthma itself. CONCLUSION: Information from these focus groups suggests mothers know a great deal about childhood asthma even though they have no personal experience of it. Knowledge of how mothers from these ethnic backgrounds perceive asthma may facilitate doctor – patient communication with parents of children experiencing breathing difficulties
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