Acoustic emission transducers--development of a facility for traceable out-of-plane displacement calibration.

Acoustic emission (AE) is a widely used technique that has been employed for the integrity testing of a range of vessels and structures for many years. The last decade has seen advances in signal processing, such that the reliability of AE technology is now being recognised by a wider range of industries. Furthermore, the need for quality control at the manufacturing stage, and requirements of in-service testing, is encouraging the issue of traceable measurements to be addressed. Currently, no independent calibration service for acoustic emission transducers is available within Europe. The UKs National Physical Laboratory (NPL) is undertaking work to develop a measurement facility for the traceable calibration of AE sensors. Such calibrations can contribute to greater acceptance of AE techniques in general, by meeting quality system and other traceability requirements. In this paper the key issues surrounding the development of such a facility are reviewed, including the need to establish repeatable AE sources, select suitable test blocks and to understand the limitations imposed by AE sensors themselves. To provide an absolute measurement of the displacement on the surface of a test block, laser interferometry is employed. In this way the output voltage of an AE sensor can be directly related to the displacement detected at the block surface. A possible calibration methodology is discussed and preliminary calibration results are presented for a commercially available AE sensor, showing its response to longitudinal wave modes.

The experience of the intensive care unit in a British Army field hospital during the 2003 Gulf conflict.

Over the last few years the Surgeon General's Department has overseen a major update in equipment scales for medical units in the field; anaesthesia and intensive care. This is to meet the aspiration of the Defence Chiefs, that injured servicemen on active service should receive the same standard of care as available in the United Kingdom. This paper discusses the experiences of the Intensive Care Unit operating within a Field Hospital both during the initial war fighting phase and subsequent peace keeping phase of the 2003 Gulf conflict (OP TELIC). Observations are made on patient activity, treatment strategy, and equipment adequacy.

The effect of temperature on the performance of audiometric mechanical coupler systems.

Measurements of mechanical coupler performance have been made over the temperature range 13 degrees C to 33 degrees C to investigate the change of force sensitivity level and mechanical impedance level with temperature for frequencies in the range 125 Hz to 5000 Hz. In addition, the temperature dependence of the voltage output of the mechanical coupler system has been measured for a coupler driven by a Radioear type B-71 bone vibrator, to investigate the net effect of these changes on an audiometer calibration. Very clear dependence on temperature has been found for all three parameters at some frequencies. In particular, coefficients approaching 0.6 dB/degrees C have been found for the rate of change of force sensitivity level at higher frequencies, and when driven by a bone vibrator coefficients around 0.5 dB/degrees C have been measured for the voltage output, again at the higher frequencies. This strong dependence of the performance of the mechanical coupler on temperature has implications for all those working in audiometric calibration, and especially for those involved in providing calibrations of audiometers in situ, where the mechanical coupler is transported from site to site and may well be exposed to extremes of temperature during transportation.

The performance and calibration of TDH39 earphones fitted with Model 51 and MX41/AR cushions.

Coupler measurements were made to compare the performances of new-style Model 51 cushions and old-style MX41/AR cushions fitted to TDH39 earphones. In addition, the calibration, using an artificial ear, of TDH39 earphones fitted with Model 51 cushions was compared with the calibration, using a reference coupler, of the same earphones fitted with MX41/AR cushions. It is concluded that the two cushion types can be taken as identical when fitted to TDH39 earphones, except at 6 kHz where differences in earphone sensitivity of up to 2.8 dB were observed. Likewise, output hearing levels of TDH39 earphones measured using a reference coupler and an artificial ear were found to be similar, except at 6 kHz where differences of up to 6.4 dB were observed. The data support the decision by ISO to declare the Model 51 equivalent to the MX41/AR cushion, thereby requiring TDH39 earphones to be calibrated using a reference coupler whichever cushion is fitted. However, they also highlight once again the ill-defined performance of TDH39 earphones at 6 kHz.

A comparison of nalbuphine with fentanyl for postoperative pain relief following termination of pregnancy under day care anaesthesia.

A double-blind investigation was undertaken to compare the efficacy of nalbuphine and fentanyl in the prevention of pain after day case termination of pregnancy. Forty patients were allocated randomly to receive nalbuphine 0.25 mg/kg or fentanyl 1.5 micrograms/kg immediately before induction of anaesthesia. The patients completed scores for pain and nausea, and performed a reaction time test to assess recovery. An observer assessed patient appearance at 1, 2 and 4 hours postoperatively. Patients who received nalbuphine had significantly lower pain scores at 1 hour (p less than 0.01) and 2 hours (p less than 0.05) and required significantly (p less than 0.05) less postoperative analgesia. No significant differences were found between the groups for incidence of nausea or for observer assessment of appearance. There was some evidence of psychomotor impairment at 2 hours in the nalbuphine group. Freedom from Controlled Drug Act regulations and improved analgesia with nalbuphine, render it more satisfactory for day case surgery than the more commonly used fentanyl.