Photoacoustic spectroscopy for remote detection of liquid contamination

The remote detection and identification of liquid chemical contamination is a difficult problem for which no satisfactory solution has yet been found. We have investigated a new technique, pulsed indirect photoacoustic spectroscopy (PIPAS), and made an assessment of its potential for operation at stand-off ranges of order 10m. The method involves optical excitation of the liquid surface with a pulsed laser operating in the 9-11μm region. Pulse lengths are of order 3μs, with energy ∼300μJ and repetition rates ∼200Hz. Rapid heating of the liquid by the laser pulse produces acoustic emission at the surface, and this is detected by a sensitive directional microphone to increase the signal-to-noise ratio and reduce background clutter. The acoustic pulse strength is related to the liquid's absorption coefficient at the laser wavelength; tuning allows spectroscopic investigation and a means of chemical identification. Maximum coverage rates have been examined, and further experiments have examined the specificity of the technique, allowing a preliminary assessment of false-alarm and missed-signal rates. The practical aspects of applying the technique in a field environment have been assessed

EAACI guidelines on the diagnosis of IgE-mediated food allergy

This European Academy of Allergy and Clinical Immunology guideline provides recommendations for diagnosing IgE-mediated food allergy and was developed using the Grading of Recommendations, Assessment, Development and Evaluations (GRADE) approach. Food allergy diagnosis starts with an allergy-focused clinical history followed by tests to determine IgE sensitization, such as serum allergen-specific IgE (sIgE) and skin prick test (SPT), and the basophil activation test (BAT), if available. Evidence for IgE sensitization should be sought for any suspected foods. The diagnosis of allergy to some foods, such as peanut and cashew nut, is well supported by SPT and serum sIgE, whereas there are less data and the performance of these tests is poorer for other foods, such as wheat and soya. The measurement of sIgE to allergen components such as Ara h 2 from peanut, Cor a 14 from hazelnut and Ana o 3 from cashew can be useful to further support the diagnosis, especially in pollen-sensitized individuals. BAT to peanut and sesame can be used additionally. The reference standard for food allergy diagnosis is the oral food challenge (OFC). OFC should be performed in equivocal cases. For practical reasons, open challenges are suitable in most cases. Reassessment of food allergic children with allergy tests and/or OFCs periodically over time will enable reintroduction of food into the diet in the case of spontaneous acquisition of oral tolerance

Photoacoustic spectroscopy for the remote detection of condensed phase chemicals

This thesis presents an. investigation of the feasibility of exploiting the pulsed indirect photoacoustic spectroscopy (pIPAS) with respect to the remote detection and identification of hazardous liquid chemical species at ranges up to 10m. 2 / Modelling of the pulsed photoacoustic generation mechanism relevant to the case of its generation by pulsed laser irradiation of liquid samples at locations remote from the laser source and acoustic detection equipment was conducted to provide insight into the efficiency of the photoacoustic mechanism and the principle factors which determine the photoacoustic signal magnitude. The peak-to-peak pressure of the photoacoustic signal has been shown to be l.inearly dependent on the absorption coefficient of the sample and the laser pulse energy, and to vary inversely with the distance from the sampie to the detector. The duration of the photoacoustic signal is also dependent on a temporal characteristic which is defmed in terms of a combination of the laser pulse ,.-/ length and microphone impulse response. To demonstrate the feasibility of this method as a remote technique implemented outside the confmes of a photoacoustic cell, it has been necessary to produce a significant enhancement in the photoacoustic signal magnitude over that demonstrated in preliminary 'short range' laboratory experiments. Modifications to the experimental system design were observed to produce an increase in the photoacoustic signal by a factor of -10 and the detector sensitivity by a factor of -30, which together were sufficient to allow the laser-generated acoustic signal to be measurable over ranges of several metres. Using a pulsed C02 laser, tunable from 9.2 - 1O.9J.lm, the photoacoustic spectrum of simulant hazardous liquid chemicals has been measured at ranges up to 8m in the laboratory. Excellent agreement was obtained between the photoacoustic spectrum obtained using the PIPAS technique and the spectrum measured using a conventional transmission spectrometer. Using these system enhancements, positive identification of simulant liquids and unambiguous discrimination between the spectrum of typical background materials and simulant hazardous liquids has been demonstrated repeatedly and reliably.EThOS - Electronic Theses Online ServiceGBUnited Kingdo