This study presents the results of an investigation to develop a novel sensor which would give a direct indication of the extent of impact damage in a composite. This was achieved by using glass reinforcing fibres to produce a light-guide, which was embedded within a composite laminate. The laminate was then subjected to impact events or bending stresses of sufficient magnitude to cause damage. The impact energies used in this study varied between 2 and 10 Joules, and the indentation depths varied between 0.125 and 1 mm, allowing damage propagation to be monitored. The fall-off in the transmitted light was used to monitor the level of damage, along with C-scanning and sectioning to provide reference data. The use of reinforcing fibres to produce the sensor meant that the strains required to cause failure in the fibres was realistically close to those of the composite constituents. Changes in the transmission characteristics of the sensor were found to correspond to real failure events occurring during impact.

This thesis is concerned with the development and laboratory assessment of an electrochemical sensor for the detection and measurement of the volatile inhalation anaesthetic, forane. Investigations were therefore based on the heterogeneous and homogeneous reduction of this agent in non-aqueous electrolyte. Preliminary experiments at a mercury and other rotating disc electrodes (RDEs) revealed that the direct reduction of forane was not possible and therefore the use of an electron transfer mediator was examined. To this end, the radical anion of the polyaromatic compound, fluoranthene, (F), was investigated as a possible electro-reduction catalyst and the mediated reduction of the anaesthetic, via a catalytic process, demonstrated. Theory was presented for the calculation of chronoamperometric and steady state responses at the RDE resulting from one electron transfer and coupled (catalytic) homogeneous kinetic processes. The latter enabled a precise mechanism to be assigned to the F + forane process, while a comparison of the former theory with experimental chronoamperometric results was used, in conjunction with AC impedance studies, to investigate the adsorption of F at the mercury/acetonitrile interface. A polymer modified electrode, based on the polymer poly-(11-vinylfluoranthene) was demonstrated to be effective in the heterogeneous reduction of forane but displayed only a limited lifetime. Therefore, a Clark-type membrane electrode was constructed and the detection and measurement of forane, in the absence of oxygen, demonstrated using this device. However, the sluggish response of this sensor, together with interference problems from oxygen encouraged the development of a device which utilised a channel electrode (ChE) sensing approach. Theory was presented for the deduction of steady state currents at the ChE resulting from coupled catalytic kinetics and this was used to demonstrate that the same mechanism for the F + forane system operated at the ChE as the RDE. The conventional ChE was then modified by the incorporation of a membrane and this sensor, which was shown to operate successfully in the presence of high concentrations of oxygen and nitrous oxide, responded linearly to forane, while displaying an excellent response time of under ten seconds. The device should find application in clinical monitoring.

No description available.

No description available.

No description available.

Gas sensitive semiconductors have been known for many years and applied in static gas alarm systems for the monitoring of hazardous gases, however, their application has been limited by a lack of selectivity. In this work a semiconducting gas sensor has been configured for use as a gas chromatographic detector thus combining the sensitivity of semiconductor sensors with the selectivity of gas chromatography. The study has been confined to tin oxide devices, more specifically the Taguchi gas sensor (TGS) . The majority of this work has concentrated on the TGS 813 although the use of other TGS is described. The development of suitable instrumentation is described and rigorous optimisation of the operating parameters e.g. heater voltage and column temperature has been performed using the variable step size simplex technique. Attention was concentrated on the response of the TGS 813 to hydrogen which was used as a test gas. A novel figure of merit, response multiplied by retention time and divided by skew factor was designed so that optimum response was obtained whilst maintaining adequate chromatographic separation. Optimum conditions were verified by univariate searches and the response was observed to be most dependant upon heater voltage. A limit of detection of 20 ppb v/v of hydrogen in a 1 ml sample was obtained at optimal conditions. Illustrative analyses of hydrogen were performed in human breath and laboratory air with results found to be in close agreement with literature values. Calibration was found to be linear over at least three orders of magnitude. The response of the TGS 813 to low molecular weight alkanes has also been investigated. It was observed that different heater voltage optima existed for each of the C1-C5 alkanes and that the sensor was relatively more sensitive to the higher molecular weight compounds. As with hydrogen linear response was obtained over at least three orders of magnitude and an illustrative analysis of natural gas showed excellent agreement with known levels. A compromise optimum heater voltage was used to study the response of the TGS 813 to alcohols, aldehydes, ketones and some Cs hydrocarbons. Capillary columns were used in this investigation and it was noted that they had potentially wider application than packed columns due to the use of an inert carrier with an air make-up flow to the detector. This replaced the air carrier gas used previously which might degrade certain stationary phases. Three different types of TGS: the 813; 822 and 831 were used in a study of the response and skew factor for the detection of halogen-containing compounds. Very high skew factors were often observed, although, for some compounds it appeared that symmetrical peaks could be obtained within narrow heater voltage ranges. Skewed response was observed to be dependant upon sensor type, heater voltage and halogen proportion and type. Analysis of the three sensor types was performed and differences in potential surface area and tin oxide additives observed. The presence of additives was observed to adversely affect sensor recovery.

No description available.

No description available.

Low cost, low power wireless sensors (motes) promise to revolutionize environmental data collection, but are they currently refined enough for widespread use by hydrologists? Their viability as a replacement for traditional data collection techniques was investigated in a 7 ha forested watershed in south-western British Columbia. The watershed included 41 instrument clusters measuring air and soil temperature, humidity, throughfall, soil moisture content, overland flow and groundwater head. The foundation of each cluster was a data box containing a MDA300 data acquisition board and a MICA2 processor board from Crossbow Technologies, Inc.™ that allowed for short range wireless data collection. The 41 motes each recorded data every 15 minutes from July, 2006, to April, 2007. In addition to reporting on the reliability of the motes and sensors during the 10 months deployment, the high spatial and temporal resolution data collected by this study gave the opportunity for many analyses of catchment processes. As soil moisture and throughfall are two influential processes in the exchange of water between the earth and the atmosphere, these were the focus of the data analysis. The first analysis was a resampling experiment on seven different events selected from the full data set. Comparing 100 different subsamples each of 5, 10 and 20 points for throughfall and soil moisture showed if increasing the sample size eventually produced diminishing returns in the ability to reproduce the true catchment mean. With significant differences in prediction ability for both soil moisture and throughfall at times of differing hydrologic activity, this analysis provides further support for the theories of changing moisture states of soil moisture and threshold values for throughfall. The second analysis described how the organization of soil moisture and throughfall changed during a range of weather conditions and timescales. Spatial representation of normalized values and Pearson correlation coefficients showed that there were distinct differences between wet and dry periods for soil moisture and between long and short analysis periods for throughfall.

Thesis (M.S.)--Oregon State University, 2010. / Printout. Includes bibliographical references (leaves 95-97). Also available on the World Wide Web.