No description available.

This thesis describes the development of a Mach-Zehnder interferometric filter based planar Doppler velocimetry (MZI-PDV) flow measurement technique. The technique uses an entirely new optical system, an unbalanced MZI incorporating glass blocks for wavefront-matching, to replace the iodine cell currently used in conventional PDV. The free spectral range of the interferometric filter can be selected by adjusting the optical path difference of the MZI. This allows the velocity measurement range, sensitivity and resolution to be varied. This system offers no restricts to the choice of laser wavelength of operation which is not the case with most techniques. Two techniques to process the interference fringe images are presented. The first uses the shift of the fringe pattern to determine the Doppler frequency shift along profiles. The second provides a full-field measurement by normalising the received light intensity at each pixel in the image. With the single camera MZI-PDV scheme, exact alignment of the two output images on the active area of the camera is automatic. This eliminates the pixel-matching problem in conventional two camera PDV systems. The technique allows the measurement of up to three components of the flow velocity across a plane defined by a laser light sheet. The construction of a single velocity component MZI-PDV system that incorporates a phase-locking system designed to stabilise the filter is described. Measurements are made on the velocity field of a rotating disc with maximum velocities of ~±70ms-1 and an axis-symmetric air jet (with a nozzle diameter of 20mm) with an exit velocity of ~85ms-1. Standard deviations in the measured velocities were found to be about 2.9 and 2ms-1 for the two processing methods respectively. The system was then modified to make 3-component velocity measurements using imaging fibre bundles to port multiple views to a single detector head, and the standard deviation of the velocity error is around ±3ms-1 for a maximum velocity of ~±30ms-1 in the field of view. The factors that will affect the quality of the interference fringe image are investigated including polarisation sensitivity of the two beam splitters and flatness of the optical components. The inclination angle and the optical path deviation have little effect on the contrast of the interference fringes since collimated light beams, rather than divergent ones, are used in the interferometer.

Sharp crested rectangular weirs used for discharge measurement purposes in open channel hydraulics are investigated experimentally. A series of experiments were conducted by measuring discharge and head over the weir for different weir heights for full width weir. It is seen that after a certain weir height, head and discharge relation does not change. Hence a constant weir height is determined. For that height / discharge and head over the weir are measured for variable weir width, starting from the full width weir to slit weir. Description of the discharge coefficient valid for the full range of weir widths and an empirical expression involving dimensionless flow variables is aimed. Experimental data obtained for this purpose and the results of the regression analysis performed are represented.

Orifices are essential devices for measurement and control of flow. It is important to define the flow field and understand the flow characteristics behind an orifice for the sake of reliability measures in many hydraulic engineering applications. Since analytical and experimental solutions are restricted, a numerical solution is obtained using volume of fluid (VOF) method with the CFD solver, FLUENT, for sharp crested orifices, orifice tubes and slots. The results are compared to the available data in the literature / also a large spectrum of data collection has been achieved.

The response of slotted plate, Venturi meter and standard orifice to the presence of two phase, three phase and low differential flows was investigated. Two mixtures (air-water and air-oil) were used in the two-phase analysis while a mixture of air, water and oil was employed in the three-phase case. Due to the high gas void fraction (α>0.9), the mixture was considered wet gas. A slotted plate was utilized in the low differential pressure analysis and the discharge coefficient behavior was analyzed. Assuming homogeneous flow, an equation with two unknowns was obtained for the multi-phase flow analysis. An empirical relation and the differential response of the meters were used to estimate the variables involved in the equation. Good performance in the gas mass flow rate estimation was exhibited by the slotted and standard plates for the air-water flow, while poor results were obtained for the air-oil and air-water oil flows. The performance of all the flow meter tested in the analysis improved for differential pressures greater than 24.9 kPa (100 in_H2O). Due to the tendency to a zero value for the liquid flow, the error of the estimation reached values of more than 500% at high qualities and low differential pressures. Air-oil and air-water-oil flows show that liquid viscosity influences the response of the differential pressure meters. The best results for high liquid viscosity were obtained in the Venturi meter using the recovery pressure for the gas flow estimation at differential pressures greater than 24.9 kPa (100 in_H2O). A constant coefficient Cd was used for the low differential pressure analysis and results did show that for differential pressure less than 1.24 kPa (5 inH2O) density changes are less than 1% making possible the incompressible flow assumption. The average of the computed coefficients is the value of Cd.

Mehr und mehr werden neue und dabei zunehmend multimediale Anwendungen fuer das Internet entwickelt und eingesetzt. In gleichem Masze wachsen auch die Qualitaetsanforderungen an diese Dienste. So gibt sich heute niemand mehr mit reiner ASCII--Text--Uebertragung von Informationen zufrieden. E-Mails werden mit MIME--Attachments versendet, Web--Seiten mit unzaehligen Grafiken ansehnlicher gemacht, und Konferenzen in Datennetzen erheben den Anspruch auf Audio-- und Video--Uebertragung in Echtzeit. Fuer Provider stellt sich hier nun das Problem der Finanzierung. Gegenstand dieser Arbeit ist es, anhand des Szenarios des Internet--Service--Providers ¨Freie Presse Online¨ ein Tarifmodell zu entwickeln, welches mittels Ressourcensteuerung arbeitet. Es soll ein Anreizsystem etabliert werden, um eine effizientere Ausnutzung der Ressourcen zu erzielen. Die finanzielle Grundlage bildet Prepayment. Die Einflusznahme geschieht nicht mittels veraenderlicher Entgelte, sondern direkt auf die dem Nutzer zur Verfuegung gestellten Ressourcen (Bandbreite, Verzoegerungszeit). Fuer den Entwurf des Modells werden Anleihen bei artverwandten Modellen genommen, so zum Beispiel bei der Tarifierung von elektrischer Energie, da die beiden Ressourcen Bandbreite (in Datennetzen) und Energie (in Stromnetzen) markante Aehnlichkeiten aufweisen. Weiterhin wird eine Analyse des Verhaltens der Nutzer im Bezug auf die Dauer und Tageszeit der Nutzung, Datenvolumen und Lastkurven durchgefuehrt. Die Analyse und das Accounting werden mittels der von der Real Time Flow Measurement Group vorgeschlagenen Architektur realisiert. Konkret kommt die Referenz-- Implementation NeTraMet zum Einsatz.

No description available.

Transcutaneous oxygen pressure measurement (TCp02) using a miniaturised Clarke electrode and a heating thermistor was developed independently by Huch et al and Eberhardt et al in 1972. After its initial use to non invasively monitor arterial partial pressure (Pa02) in neonates it was proposed as a useful test of skin blood flow and possibly amputation wound healing level selection in patients with peripheral vascular disease. Unfortunately a wide range of predictive values emerged with some authors reporting amputations healing when the TCp02 value was 0 mmHg. The investigation, while still considered useful, has not gained widespread support. This study investigates the use of TCp02, establishes a value for the use of the TCp02 Index to predict amputation wound healing potential and examines the hypothesis that the use of the TcpO Index to select amputation level can reduce patient morbidity and mortality. The literature is reviewed and a series of studies evaluating TCp02 use, undertaken in the Durban Metropolitan Vascular Service Non-Invasive Laboratories, are presented. TCp02 measurements were performed in a standardised manner with the subject supine breathing room air. Measurements were taken at fixed sites, on the mid dorsum of the foot (Foot), 10 cm distal to the tibial tuberosity and 2 cm lateral to the anterior tibial margin (BKA), 10 cm proximal to the patella in the midline (AKA) and on the chest in the mid-clavicular line. A TCp02 Index, the limb to chest ratio was defined. TCp02 data derived from control subjects asymptomatic of peripheral vascular disease were shown to be similar to age matched pooled data derived from the literature. In patients with peripheral vascular disease, absolute TCp02 and the TCp02 Index were shown to fall from proximal to distal sites and again were no different to pooled data derived from the literature. Based on presenting symptoms, the fall in TCp02 and the TCp02 Index was significant from proximal to distal sites. The reduction in absolute TCp02 and the TCp02 was also related to the most distal pulse present. TCp02 values were found to be no different in patients with peripheral vascular disease with or without diabetes. When comparing TCp02 and the TCp02 Index with Doppler pressure measurements at the Popliteal artery and at the foot, and the Doppler ankle brachial index (ABI), Doppler derived data were significantly higher in diabetic patients than in non-diabetic patients. No differences were noted in TCp02 data. TCp02 was compared with the 133Xe radio-isotope skin washout test. The best correlation was (r = 0.46) was obtained with a logarithmic curve y = 10.862Ln(x) + 38.751. TCp02 was compared with antibiotic concentrations (Cefoxitin) in muscle obtained from the site of amputation and the Cefoxitin Index, the ratio of muscle antibiotic concentration to plasma concentration, as an indication of the relationship of skin TCp02 to muscle blood flow. A significant correlation was shown between the Cefoxitin Index and TCp02 (r = 0.67, p = 0.035) and the TCp02 Index (r = 0.64, P = 0.045), suggesting that skin oxygen delivery may reflect muscle antibiotic delivery and hence blood flow. TCp02 and the TCp02 Index were compared with heated and unheated laser Doppler fluxmetry (LDF) in 35 patients undergoing amputation wound healing assessment. Significant correlations were shown between heated LDF, heated LDF Index and the TCp02 Index (r = 0.63 and r = 0.69, P < 0.0001). TCp02 Index values of 0.5 and 0.55 showed an accuracy of 96.2 % in predicting amputation outcome while LDF values of 3, 4 and 5 arbitrary units gave an accuracy of 88.5 %. Using receiver operator curves, a TCp02 Index of 0.55 was shown to be the best test. Over the years 1987 and 1988, TCp02 data were gathered on 193 patients undergoing lower limb amputation for peripheral vascular disease. Information on the outcome of the amputation was available for 152 amputations. Circumstances which might result in a reduced pre-operative TCp02 reading were identified and criteria were set for the use of TCp02 to predict amputation wound healing potential. 122 amputations which met the defined entry criteria were available for evaluation. A TCp02 Index of 0.50 gave a definitive predictive value below which no amputation healed. Similarly no amputation with an absolute TCp02 of less than 27 mmHg healed. Receiver operator characteristic curves showed the TCp02 Index to be a better test than absolute TCp02. A TCp02 Index of 0.55 was shown to have the best sensitivity of96.7 %, with a specificity of79.8 % and an accuracy of 90.2 %. When introduced to clinical practice, correct use of the TCp02 Index of 0.55 resulted in a reduction in amputation revision rate from 40.3 % in 1987, to 8.2 % in 1990. Initially some surgeons felt that the TCp02 Index predicted amputation wound failure at distal sites at which healing could be expected on clinical criteria, and chose amputate at sites with a TCp02 Index value less than 0.55. These amputations failed to heal. As surgeons gained confidence in the test, they chose to follow the TCp02 data more often and the percentage of amputations performed at sites predicted by the TCp02 Index to fail , fell from 35.5 % in 1987 to 6.6 % in 1990. Over a 15 year period at King Edward VIII Hospital, the amputation revision rate has fallen from an average of 32.7 % in the first five years when Tcp02 data were not available to the surgeon, to 21.4 % and 22.9 % in the two subsequent 5 year periods when Tcp02 data were available. The mortality rates were unchanged. The decline in revision rates was less than expected and relates to the fact that approximately only 42 % of patients requiring amputation undergo the test. This is because it is time consuming and available only during weekday office hours. These studies have confirmed the usefulness of Tcp02 measurement in the non-invasive vascular laboratory. The index is shown to be superior to absolute Tcp02 as a predictive test of amputation wound healing. The introduction of several criteria to define when Tcp02 use is appropriate has refined the investigation and made it clinically useful in our setting. A Tcp02 Index of 0.55 in the appropriate patient is a useful test to predict amputation wound healing and its use has resulted in reduced patient morbidity and mortality, confirming the hypothesis tested. / Thesis (M.D.)-University of Natal, 2001.

The pattern of mucosal blood flow in normal human stomachs, and benign gastric ulcers was assesed with laser Doppler flowmetry and the relationship between a single determination of ulcer blood flow and the systemic level of growth factors was investigated. A significant ascending gradient in mucosal blood flow from the antrum to fundus was demonstrated. Different levels of cellular activity in the regions of the stomach may explain this gradient. In the gastric ulcers that healed on standard medical therapy mucosal blood flow was significantly increased in comparison to normal stomachs. In the ulcers that were refractory to standard medical therapy mucosal blood flow was significantly lower than in normal stomachs and healing ulcers. Higher systemic levels of the growth factor bFGF were demonstrated in healing ulcers compared to non-healing ulcers. Gastric mucosal blood flow can increase in response to the increased metabolic demands of healing, however impairment of this response may be an important factor preventing healing of benign gastric ulcers. It would appear that non-healing of gastric ulcers can be predicted at initial diagnosis by reduced peri-ulcer gastric mucosal blood flow and low blood levels of bFGF. / Thesis (M.Med.Sc.)-University of Natal, Durban, 1999.

No description available.