This portfolio details the design, construction and testing of three high accuracy digital pressure indicators. A discussion of old and contemporary pressure measurement technologies is included, as well as a comprehensive market survey of electronic pressure measurement instruments currently available. An integrated design strategy is adopted for the three separate digital pressure instruments, namely a battery - powered stand alone unit, a retransmitting version and an intrinsically safe version of the battery powered unit. Their implementation takes into account many design issues including ease of manufacturing, low power circuit design and electromagnetic compatibility. Novel features available upon all three instruments resulting from the design strategy adopted are high accuracy measurements, typically ±0.2% of full scale, a battery life of over 12 months, push button zeroing and linearisation, electromagnetic compliance with minimum design changes and an intrinsically safe power supply design that may be used not only in the instrument for which it was designed but for future instruments. Individual design issues with respect to each instrument are in the three project sections which complete this portfolio.

The work reported here is a proton magnetic resonance investigation of some polyatomic gases. Pulsed nuclear magnetic resonance techniques were used throughout. Little systematic work on gases using this technique has been reported hitherto, and the present study clearly indicates the potentialities of nuclear magnetic resonance experiments for the investigation of certain physical processes occurring in gases. The gases studied were hydrogen (H₂), methane (CH₄), ethane (C₂H₆) and ethylene (C₂H₄). A spectrometer and ancilliary equipment have been constructed enabling measurements to be made at 30 Mc/s, over a temperature range from 35K° to 300K° using gas pressures up to 200 atmospheres. In hydrogen, the spin-lattice relaxation time, T₁, was studied as a function of the density, temperature and ortho-para concentration of the gas. In the "dilute" gas region, T₁ was found to increase linearly with density at fixed temperature, indicating that the relaxation process is of intra-molecular origin and that studies of T₁ are able to yield valuable information on the asymmetric part of the intermolecular interaction. The temperature dependence of T₁ (at fixed density) was studied in the "dilute" gas between 35K° and 300K°, and quantum effects were discovered at low temperatures. In the dense gas, at low temperatures, T₁ was found to be a very rapidly increasing function of density at fixed temperature. In the dilute gas, T₁, at fixed density and temperature, was found to increase with increasing ortho-hydrogen concentration, indicating that the cross-section for a reorientation collision of two orthohydrogen molecules is greater than that for a collision between an ortho-molecule and a paramolecule. Diffusion measurements in hydrogen were carried out, at 78K°, as a function of density in the "dilute" gas, and it has been shown that the coefficient of self-diffusion is inversely proportional to density. The spin-spin relaxation time, T₂, for hydrogen at 78K° has been found to vary linearly with density, in the "dilute" gas, and T₂ = 0.8 T₁. In all the hydrocarbon gases studied, the relaxation process was governed by a single exponential function of time, thus enabling a unique relaxation time T₁ to be defined. In the "dilute" gas, T₁ was found to vary linearly with density. An estimate has been made of the mean square angle of rotation of a methane molecule and of an ethylene molecule per collision, with a view to examining the applicability of a rotational diffusion model for molecular reorientation in these gases. In methane, T₁ has been studied as a function of density just above the critical point for this gas and at room temperature. The effect of traces of oxygen on the relaxation process ("impurity relaxation") in the "dilute" and "dense" gas regions has been studied also. T₁ has been studied in ethane above and below the critical point, and in ethylene above the critical point, in the "dilute" and "dense" gas regions. The oxygen impurity effects have been found to be very marked indeed in the case of ethylene. In the course of this work, a n.m.r. method has also been evolved for the measurement of the compressibility of a gas. A programme of future n.m.r. work on gases, suggested by the results obtained and experience gained in this work, is outlined. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

An apparatus designed after the fashion of Young and of Kay has been constructed and assembled for the determination of the pressure - volume - temperature relationships of pure compounds up to 200 atmosphere and 360°C. Pressure measurement depends on the known characteristics of pure nitrogen, and auxiliary apparatus has been assembled for the production and use of this. Constant temperatures are obtained by boiling under a constant pressure the following compounds: carbon disulfide, chlorobenzene, bromobenzene, aniline, methyl salicylate, 1-bromonaphthalene, and mercury. These compounds have all been purified and have been used to calibrate a thermocouple for use in the apparatus. Normal-butanol has been carefully purified for insertion into the apparatus and determination of its pressure - volume - temperature relations and its vapor-pressure. The theoretical utilization of such data has been discussed. / Applied Science, Faculty of / Chemical and Biological Engineering, Department of / Graduate

A high-frequency surge and stall sensing fore-aft probe was developed at the Turbomachinery Research Laboratory at Virginia Tech. The probe was designed to detect surge and stall based on changes in large regions of flow behind a turbofan engine compressor fan. The probe exhibited excellent frequency response capabilities and can accurately measure data with response well above anticipated surge frequencies. A CFD analysis was performed in order to gain more understanding about the flow around the probe. The results of the CFD analysis and the experimental testing were analyzed and presented. The probe worked as expected when the flow was aligned with the upstream pressure transducer. Thus, it can be used to determine the onset of surge and stall. However, the probe was found to be extremely sensitive to off-axis flows. Design improvements are suggested in order to increase its capabilities. / Master of Science

This is the first time that electrical impedance studies have been performed on the pregnant cervix. In this thesis the following has been demonstrated: 1. An inter-observer variability in resistivity readings, initially of the order of 20%, but decreasing to 1% once proficiency with the technique was established. 2. An intra-observer variability in resistivity readings of less than 15% in 94% of cases using the 5.5mm probe and 90% when using the 8mm probe. 3. A degree of heterogeneity in the pregnant cervix as attested to by the differences in resistivity measurements on different sites on the cervix. Some of these changes were partly due to technical difficulties. Nevertheless there appeared to be an increase in extracellular resistivity measurements between the anterior and posterior lips of the external cervical os. 4. A positive correlation between the resistivity measurements and gestational age using the 5.5mm probe. No significant correlations were identified between resistivity readings and both parity and maternal age. 5. A statistically significant difference in resistivity readings when comparing the non-pregnant and pregnant cervix. The change in readings was in a direction which reflected the increase in tissue hydration described by others. 6. A statistically significant difference between readings for ripe and unripe cervices at the time of induction of labour, with a fall in extracellular resistivity with increasing favourability as assessed by the Bishop score. This was accompanied by an increase in intracellular resistivity with increasing cervical favourability. The effect of prostaglandin administration on the pregnant cervix demonstrated a decrease in extracellular resistivity and an increase in intracellular resistivity associated with the cervical ripening process. Whilst the results were neither of statistical nor of clinical significance, they were nevertheless in the direction predicted. 7. A statistically significant correlation between extracellular resistivity and interval to delivery using the 8mm probe. 8. A new investigative modality that had high patient acceptability. To date the findings demonstrated in this thesis conceptually agree with the literature on the pregnant cervix. Thus it is imperative to continue with further studies of this new investigative modality.

Thesis (Ph.D.)--University of Nebraska-Lincoln, 2006. / Title from title screen (site viewed on August 28, 2006). PDF text of dissertation: 116 p. : ill. ; 1.29Mb. UMI publication number: AAT 3208122. Includes bibliographical references. Also available in microfilm, microfiche and paper format.

Typescript, etc. / Digitized by Kansas State University Libraries

Typescript, etc. / Digitized by Kansas State University Libraries

Typescript, etc. / Digitized by Kansas State University Libraries

Call number: LD2668 .T4 1949 O4 / Master of Science