Prototyping a robotic dental testing simulator.

A parallel robot based on the Stewart platform is being developed to simulate jaw motion and investigate its effect on jaw function to test the wearing away of dental components such as individual teeth, crowns, bridges, full set of dentures, and implant-supported overdentures by controlling chewing motion. The current paper only describes the comparison between an alternative configuration proposed by Xu and the Stewart platform configuration. The Stewart platform was chosen as an ideal structure for simulating human mastication as it is easily assembled, has high rigidity, high load-carrying capacity, and accurate positioning capability. The kinematics and singularities of the Stewart platform have been analysed and software developed to (a) test the control algorithms/strategy of muscle movement for the six degree of freedom of mastication cycle and (b) simulate and observe various design options to be able to make the best judgement in product development. The human replica skull has been analysed and reverse engineered with further simplification before integration with the Stewart platform computer-aided design (CAD) to develop the robotic dental testing simulator. Assembly modelling of the reproduced skull was critically analysed for good occlusion in CAD environment. A pulse-width modulation (PWM) circuit plus interface was built to control position and speed of the chosen actuators. A computer numerical control (CNC) machine and wire-electro-discharge machining (wire EDM) were used to manufacture the critical parts such as lower mandible, upper maxilla, and universal joints.

Fabrication of large-aperture lightweight diffractive lenses for use in space.

We describe the advantages of using diffractive (Fresnel) lenses on thin membranes over conventional optics for, among others, future space telescope projects. Fabrication methods are presented for lenses on two types of freestanding membrane up to 50 cm in size. The first is a Fresnel lens etched into a thin (380-microm) glass sheet, and the second is an approximately 50-microm-thick polymer membrane containing a Fresnel lens made by replication process from a specially made fused-silica master. We show optical performance analysis of all the lenses that are fabricated, including a diffraction-limited Airy spot from a 20-m- focal-length membrane lens in a diffractive telescope system.

Target-controlled remifentanil in combination with propofol for spontaneously breathing day-case patients.

Remifentanil is a new potent opioid with a very short duration of action irrespective of duration of infusion. It may have a role in day-case anaesthesia as part of a balanced total intravenous anaesthetic technique with propofol. We examined the respiratory depressant effects of remifentanil in 20 patients undergoing day-case anaesthesia. The target plasma concentration of remifentanil was varied while maintaining a constant target-controlled infusion of 4.5 microg x ml-1 propofol. In only 12 patients was satisfactory spontaneous respiration maintained. In these patients the median remifentanil target concentration was 1.6 ng x ml-1 and was achieved with a median infusion rate of 0.05 microg x kg-1 x min-1. The range of target concentrations associated with satisfactory spontaneous respiration was wide and varied over a 4.7-fold range from 0.6 to 2.8 ng x ml-1.

Eyeglass. 1. Very large aperture diffractive telescopes.

The Eyeglass is a very large aperture (25-100-m) space telescope consisting of two distinct spacecraft, separated in space by several kilometers. A diffractive lens provides the telescope s large aperture, and a separate, much smaller, space telescope serves as its mobile eyepiece. Use of a transmissive diffractive lens solves two basic problems associated with very large aperture space telescopes; it is inherently launchable (lightweight, packagable, and deployable) it and virtually eliminates the traditional, very tight surface shape tolerances faced by reflecting apertures. The potential drawback to use of a diffractive primary (very narrow spectral bandwidth) is eliminated by corrective optics in the telescope s eyepiece; the Eyeglass can provide diffraction-limited imaging with either single-band (Deltalambda/lambda approximately 0.1), multiband, or continuous spectral coverage.

Pressure changes over the anterior neck during tracheal and oesophageal intubation.

Pressure changes were measured on the skin over the cricoid and thyroid cartilages during intubation of the oesophagus or trachea in 21 consenting patients. A 100-ml bag of saline was firmly fixed to the anterior neck and the pressure changes in the bag recorded. Typical and distinctively different pressure patterns for tracheal and oesophageal intubation were recorded. Oesophageal intubation was accompanied by a statistically significantly higher and longer pressure rise and, most characteristically, by an obvious and sustained rise in baseline pressure. This method is, however, neither practical nor recommended for clinical use in detecting accidental oesophageal intubation. Capnography should always be used during tracheal intubation as an ongoing capnographic waveform provides the only guarantee of correct tracheal placement.

Detection of accidental oesophageal intubation. Role of the anaesthetic assistant.

Three situations in which an anaesthetic assistant might be able to detect accidental oesophageal intubation during or immediately after intubation were assessed. These were: firstly, whilst applying cricoid pressure, secondly, whilst applying gentle palpation over the trachea just above the suprasternal notch and, thirdly, after intubation by means of a 'roll test'. During cricoid pressure, tracheal intubation was correctly diagnosed in all of 10 cases. However, deliberate oesophageal intubation was only detected in six out of 10 cases. During suprasternal palpation, three cases out of 10 oesophageal and three cases out of 10 tracheal intubation were misdiagnosed. In the 'roll test', two out of 10 tracheal and five out of 10 oesophageal intubations were misdiagnosed. In conclusion, no method could be relied on entirely and may indeed give false reassurance. Nonetheless, any doubt expressed about the tracheal tube position by the assistant should be taken seriously and a careful check made.