Cavity ring-down spectroscopy has been used over the last twenty years as a highly sensitive absorption spectroscopic technique to measure light attenuation in gases, liquids, and solid samples. An optical cavity is used as a multi-pass cell, and the decay time of the light intensity in the cavity is measured, thereby rendering the techniques insensitive to light intensity fluctuations. Optical waveguides are used to build the optical cavities presented in this work. The geometries of such waveguides permit the use of very small liquid sample volumes while retaining the advantages of cavity ring-down spectroscopy. In this thesis cavity ring-down measurements are conducted, both, in the time domain and by measuring phase-shifts of sinusoidally modulated light, and the two methods are theoretically connected using a simple mathematical model, which is then experimentally confirmed. A new laser driver, that is compatible with high powered diode lasers, has to be designed to be able to switch from time domain to frequency domain measurements. A sample path length enhancement within the optical cavity is explored with the use of liquid core waveguides. The setup was optimised with respect to the matrix liquid, the geometrical matching of waveguide geometries, and the shape of liquid core waveguide ends. Additionally, a new technique of producing concave lenses at fibre ends has been developed and the output of a general fibre lens is simulated. Finally, liquid core waveguides are incorporated into a fibre-loop ring-down spectroscopy setup to measure the attenuation of two model dyes in a sample volume of <1 µL. The setup is characterized by measuring concentrations of Allura Red AC and Congo Red from 1 µM to a limit of detection of 5 nM. The performance of the setup is compared to other absorption techniques measuring liquid samples. / Thesis (Ph.D, Chemistry) -- Queen's University, 2013-04-23 14:08:16.33

INTRODUÇÃO: Apesar do índice de sucesso da cirurgia da ligadura ou cauterização da artéria esfenopalatina, para o tratamento da epistaxe severa, ser maior que 95%, a falha pode variar de 2% a 10%. Algumas variações anatômicas na parede lateral do nariz são relatadas, sendo referentes à localização do forame esfenopalatino (FEP), à presença de um forame acessório, à ramificação das artérias e à dimensão e morfologia do FEP. A variação anatômica dessa região assim como a escassez de estudos endoscópicos mostrando pontos de reparo para o encontro da artéria esfenopalatina e seus ramos podem justificar a falha cirúrgica em alguns casos, assim como a dificuldade técnica encontrada por alguns autores. OBJETIVO: Descrever a anatomia da região do FEP na parede lateral do nariz e as possíveis variações anatômicas, durante a dissecção endoscópica em cadáveres, e observar as possíveis diferenças entre os achados anatômicos, o gênero (masculino/feminino) e o grupo étnico/racial, assim como a simetria entre as fossas nasais. CASUÍSTICA E MÉTODOS: Estudo anatômico prospectivo realizado de setembro de 2006 a janeiro de 2007. A região do FEP de 61 cadáveres frescos (122 fossas nasais) foi cuidadosamente dissecada, sob visibilização endoscópica. Prevaleceram os cadáveres do sexo masculino (75%) e grupo étnico/racial pardo, seguidos de negros e brancos. Foram observados a presença da crista etmoidal da lâmina perpendicular do osso palatino, a localização dos forames esfenopalatino e acessório, o número de ramos arteriais emergentes pelos forames e a distância dos mesmos à espinha nasal anterior. Os dados foram analisados em relação ao gênero, grupo étnico/racial e simetria entre as fossas nasais do mesmo cadáver. Foi, ainda, avaliada a predição da presença do forame acessório em relação ao número de ramos arteriais emergentes através do FEP, à localização do FEP e à distância do FEP à espinha nasal anterior. RESULTADOS: A crista etmoidal esteve presente em 100% dos cadáveres, sendo anterior ao mesmo em 98,4% das vezes. A localização mais freqüente do FEP foi a região de transição do meato médio e meato superior (86,9%). A distância média do FEP e do forame acessório à espinha nasal anterior foi respectivamente de 66mm e 67mm, com desvio padrão de 5,3 e 4,7mm. O forame acessório esteve presente em 9,83% dos casos. Um único tronco arterial emergia através do FEP em 67,2% das vezes e em 100% dos forames acessórios. A análise da prevalência das variáveis estudadas em relação ao gênero e grupo étnico/racial não mostrou diferenças estatisticamente significantes (p<0,05). A análise da simetria mostrou concordância boa a excelente em relação à localização do FEP (índice Kappa 0,71/ p<0,001); concordância pobre em relação ao número de ramos arteriais emergentes através do FEP (índice Kappa 0,22/p=0,03) e ausência de concordância estatisticamente significante em relação à presença de forame acessório (p=0,53). Nenhuma das variáveis de interesse apresentou associação estatisticamente significante (p>0,05) que permita predizer a presença do forame acessório. CONCLUSÕES: Existem variações anatômicas na parede lateral do nariz que devem ser levadas em consideração para o sucesso do tratamento cirúrgico endoscópico da epistaxe severa. / INTRODUCTION: Even though the success rate of sphenopalatine ligation is greater than 95%, some authors have reported some difficulties in isolating those arteries during endoscopic surgical procedure. The failure rate of the sphenopalatine artery ligation or cauterization may vary from 2% to 10%. Some anatomical variations on the nose lateral wall are reported, with reference to the sphenopalatine foramen (SPF) location, the presence of an accessory foramen, arteries ramification and SPF dimension and morphology. Anatomical variation of the region, as well as scarcity of endoscopic studies showing landmarks to find the sphenopalatine artery and its branches may justify surgical failure. OBJECTIVE: The purpose of this study was to describe the anatomy of SPF region and possible anatomical variations, during the endoscopic cadaver dissection and to observe the symmetry between nasal sides and the relationship to gender and racial group. CASUISTICS AND METHODS: It is a prospective anatomical study developed from September, 2006 to January, 2007. The SPF of 61 fresh cadavers (122 nasal fossae) was carefully endoscopic dissected. Male (75%) and mixed race cadavers prevailed. Presence of ethmoidal crest, location of sphenopalatine and accessory foramens, number of arterial branches emerging through foramens and distances from the foramens to anterior nasal spine were observed. Data were analyzed in relation to gender, racial group and symmetry of the same cadaver. Prediction of the presence of accessory foramen was evaluated in relation to number of arterial branches emerging through SPF, SPF location and distance from the SPF to the anterior nasal spine. RESULTS: Ethmoidal crest was present in 100% of cadavers, being anterior to the SPF in 98.4% of times. The most frequent SPF location was the transition region of middle and superior meatus (86.9%). Mean distance from SPF and accessory foramen to anterior nasal spine was 6.6cm and 6.7cm, respectively. Accessory foramen was present in 9.83% of cases. A single arterial stem emerged through the SPF in 67.2% of times, and 100% through accessory foramens. The prevalence analyses showed no differences statistically significant (p>0,05) between gender and racial group. The symmetry analyses showed a strong conformity (Kappa index 0,71/p<0,01) between nasal fossae in relation to the SPF location; and a poor conformity (Kappa index 0,22/p=0,03) in relation to the number of arterial branches emerging through the SPF. There was no statistically significant conformity between nasal fossae and the presence of accessory foramen (p = 0,53). None of the variables of interest presents any statistically significant (p>0,05) association with the presence of the accessory foramen. CONCLUSIONS: Anatomical variations in the lateral nose wall exist, and should be taken into account, for a well-succeeded endoscopic surgical treatment of severe epistaxis.

INTRODUÇÃO: Apesar do índice de sucesso da cirurgia da ligadura ou cauterização da artéria esfenopalatina, para o tratamento da epistaxe severa, ser maior que 95%, a falha pode variar de 2% a 10%. Algumas variações anatômicas na parede lateral do nariz são relatadas, sendo referentes à localização do forame esfenopalatino (FEP), à presença de um forame acessório, à ramificação das artérias e à dimensão e morfologia do FEP. A variação anatômica dessa região assim como a escassez de estudos endoscópicos mostrando pontos de reparo para o encontro da artéria esfenopalatina e seus ramos podem justificar a falha cirúrgica em alguns casos, assim como a dificuldade técnica encontrada por alguns autores. OBJETIVO: Descrever a anatomia da região do FEP na parede lateral do nariz e as possíveis variações anatômicas, durante a dissecção endoscópica em cadáveres, e observar as possíveis diferenças entre os achados anatômicos, o gênero (masculino/feminino) e o grupo étnico/racial, assim como a simetria entre as fossas nasais. CASUÍSTICA E MÉTODOS: Estudo anatômico prospectivo realizado de setembro de 2006 a janeiro de 2007. A região do FEP de 61 cadáveres frescos (122 fossas nasais) foi cuidadosamente dissecada, sob visibilização endoscópica. Prevaleceram os cadáveres do sexo masculino (75%) e grupo étnico/racial pardo, seguidos de negros e brancos. Foram observados a presença da crista etmoidal da lâmina perpendicular do osso palatino, a localização dos forames esfenopalatino e acessório, o número de ramos arteriais emergentes pelos forames e a distância dos mesmos à espinha nasal anterior. Os dados foram analisados em relação ao gênero, grupo étnico/racial e simetria entre as fossas nasais do mesmo cadáver. Foi, ainda, avaliada a predição da presença do forame acessório em relação ao número de ramos arteriais emergentes através do FEP, à localização do FEP e à distância do FEP à espinha nasal anterior. RESULTADOS: A crista etmoidal esteve presente em 100% dos cadáveres, sendo anterior ao mesmo em 98,4% das vezes. A localização mais freqüente do FEP foi a região de transição do meato médio e meato superior (86,9%). A distância média do FEP e do forame acessório à espinha nasal anterior foi respectivamente de 66mm e 67mm, com desvio padrão de 5,3 e 4,7mm. O forame acessório esteve presente em 9,83% dos casos. Um único tronco arterial emergia através do FEP em 67,2% das vezes e em 100% dos forames acessórios. A análise da prevalência das variáveis estudadas em relação ao gênero e grupo étnico/racial não mostrou diferenças estatisticamente significantes (p<0,05). A análise da simetria mostrou concordância boa a excelente em relação à localização do FEP (índice Kappa 0,71/ p<0,001); concordância pobre em relação ao número de ramos arteriais emergentes através do FEP (índice Kappa 0,22/p=0,03) e ausência de concordância estatisticamente significante em relação à presença de forame acessório (p=0,53). Nenhuma das variáveis de interesse apresentou associação estatisticamente significante (p>0,05) que permita predizer a presença do forame acessório. CONCLUSÕES: Existem variações anatômicas na parede lateral do nariz que devem ser levadas em consideração para o sucesso do tratamento cirúrgico endoscópico da epistaxe severa. / INTRODUCTION: Even though the success rate of sphenopalatine ligation is greater than 95%, some authors have reported some difficulties in isolating those arteries during endoscopic surgical procedure. The failure rate of the sphenopalatine artery ligation or cauterization may vary from 2% to 10%. Some anatomical variations on the nose lateral wall are reported, with reference to the sphenopalatine foramen (SPF) location, the presence of an accessory foramen, arteries ramification and SPF dimension and morphology. Anatomical variation of the region, as well as scarcity of endoscopic studies showing landmarks to find the sphenopalatine artery and its branches may justify surgical failure. OBJECTIVE: The purpose of this study was to describe the anatomy of SPF region and possible anatomical variations, during the endoscopic cadaver dissection and to observe the symmetry between nasal sides and the relationship to gender and racial group. CASUISTICS AND METHODS: It is a prospective anatomical study developed from September, 2006 to January, 2007. The SPF of 61 fresh cadavers (122 nasal fossae) was carefully endoscopic dissected. Male (75%) and mixed race cadavers prevailed. Presence of ethmoidal crest, location of sphenopalatine and accessory foramens, number of arterial branches emerging through foramens and distances from the foramens to anterior nasal spine were observed. Data were analyzed in relation to gender, racial group and symmetry of the same cadaver. Prediction of the presence of accessory foramen was evaluated in relation to number of arterial branches emerging through SPF, SPF location and distance from the SPF to the anterior nasal spine. RESULTS: Ethmoidal crest was present in 100% of cadavers, being anterior to the SPF in 98.4% of times. The most frequent SPF location was the transition region of middle and superior meatus (86.9%). Mean distance from SPF and accessory foramen to anterior nasal spine was 6.6cm and 6.7cm, respectively. Accessory foramen was present in 9.83% of cases. A single arterial stem emerged through the SPF in 67.2% of times, and 100% through accessory foramens. The prevalence analyses showed no differences statistically significant (p>0,05) between gender and racial group. The symmetry analyses showed a strong conformity (Kappa index 0,71/p<0,01) between nasal fossae in relation to the SPF location; and a poor conformity (Kappa index 0,22/p=0,03) in relation to the number of arterial branches emerging through the SPF. There was no statistically significant conformity between nasal fossae and the presence of accessory foramen (p = 0,53). None of the variables of interest presents any statistically significant (p>0,05) association with the presence of the accessory foramen. CONCLUSIONS: Anatomical variations in the lateral nose wall exist, and should be taken into account, for a well-succeeded endoscopic surgical treatment of severe epistaxis.

Die vorliegende Arbeit beschreibt einen neuartigen Ablauf zur Herstellung eines Vibrationssensors auf Waferebene. Die Besonderheit des Sensors liegt in der Reduktion des Spaltmaßes der kapazitiven Elektroden im Anschluss an die Strukturerzeugung. Dies gelingt unter Nutzung des Mikroschweißprozess von Siliziumelementen. Hierbei sieht die innovative Fertigungstechnologie eine Strukturhöhe von 100 μm vor. Zusätzlich wird die Erarbeitung einer Struktur für die Durchführung eines Mikrozugversuchs auf Waferebene beschrieben. Dieser dient der Bestimmung der maximal ertragbaren Zugkraft mikromechanischer Schweißverbindungen und ermöglicht die fertigungsbegleitende Prozesskontrolle. Auf Basis der Messwerte lassen sich Rückschlüsse auf die Geometrie der Schweißstruktur ableiten als auch ein zerstörungsfreies Modell für die Vorhersage der Verbindungsfestigkeit entwickeln. Die Ergebnisbewertung umfasst die qualitative als auch quantitative Charakterisierung der Mikroschweißverbindung sowie die Bewertung des Vibrationssensors in Form eines Funktionsdemonstrators. / The Ph.D. thesis focuses on a novel approach for the fabrication of a MEMS accelerometer on wafer level. The technology relies on the micro welding process of silicon, which is utilized for fixing one component of the capacitive electrode system at a deflected position. Consequently, the gap width of the variable capacitor is reduced below 1 µm for a structure height of 100 µm. The silicon micro welding process is reviewed and investigated. By utilizing a micro tensile test, the maximum bearable load is deduced for different welding geometries. Following these results, a model for predicting the strength of the micro welding site is introduced, allowing for non destructive process monitoring. Finally, the characteristics of the MEMS accelerometer are measured on wafer level and chip level after hermetic packaging respectively.

Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: A reactor cavity cooling system (RCCS) is used in the PBMR to protect the concrete citadel surrounding the reactor from direct nuclear radiation impingement and heat. The speci ed maximum operating temperature of the concrete structure is 65 ±C for normal operating conditions and 125 ±C for emergency shut-down conditions. A conceptual design of an entirely passive RCCS suitable for the PBMR was done by using closed loop thermosyphon heat pipes (CLTHPs) to remove heat from a radiation heat shield over a horizontal distance to an annular cooling dam placed around the PBMR. The radiation shield is placed in the air space between the Reactor Pressure Vessel (RPV) and the concrete citadel, 180 mm from the concrete citadel. A theoretical heat transfer model of the RCCS was created. The theoretical model was used to develop a computer program to simulate the transient RCCS response during normal reactor operation, when the RCCS must remove the excess generated heat from the reactor cavity and during emergency shut-down conditions, when the RCCS must remove the decay heat from the reactor cavity. The main purpose of the theoretical model is to predict the surface temperature of the concrete citadel for di erent heat generation modes in the reactor core and ambient conditions. The theoretical model assumes a 1D geometry of the RCCS. Heat transfer by both radiation and convection from the RPV to the radiation heat shield (HS) is calculated. The heat shield is modelled as a n. The n e ciency was determined with the experimental work. Conduction through the n is considered in the horizontal direction only. The concrete structure surface is heated by radiation from the outer surface of the heat shield as well as by convection heat transfer from the air between the heat shield and the concrete structure surface. The modelling of the natural convection closed loop thermosyphon heat pipes in the RCCS is done by using the Boussinesq approximation and the homogeneous ow model. An experiment was built to verify the theoretical model. The experiment is a full scale model of the PBMR in the horizontal, or main heat transfer, direction, but is only a 2 m high section. The experiments showed that the convection heat transfer between the RPV and the HS cannot be modelled with simple natural convection theory. A Nusselt number correlation developed especially for natural convection in enclosed rectangles found in literature was used to model the convection heat transfer. The Nusselt number was approximately 3 times higher than that which classic convection theory suggested. An optimisation procedure was developed where 121 di erent combinations of n sizes and heat pipe sizes could be used to construct a RCCS once a cooling dam size was chosen. The purpose of the optimisation was to nd the RCCS with the lowest total mass. A cooling dam with a diameter of 50 m was chosen. The optimal RCCS radiation heat shield that operates with the working uid only in single phase has 243 closed loop thermosyphon heat pipes constructed from 62.72 mm ID pipes and 25 mm wide atbar ns. The total mass of the single phase RCCS is 225 tons. The maximum concrete structure temperature is 62.5 ±C under normal operating conditions, 65.8 ±C during a PLOFC emergency shut-down condition and 80.9 ±C during a DLOFC emergency shut-down condition. In the case where one CLTHP fails and the adjacent two must compensate for the loss of cooling capacity, the maximum concrete structure temperature for a DLOFC emergency shut-down will be 87.4 ±C. This is 37.6 ±C below the speci ed maximum temperature of 125 ±C. The RCCS design is further improved when boiling of the working uid is induced in the CLTHP. The optimal RCCS radiation heat shield that operates with the working uid in a liquid-vapour mixture, or two phase ow, has 338 closed loop thermosyphon heat pipes constructed from 38.1 mm ID pipes and 20 mm wide atbar ns. The total mass of the two phase RCCS is 198 tons, 27 tons less than the single phase RCCS. The maximum concrete structure temperature is 60 ±C under normal operating conditions, 2.5 ±C below that of the single phase RCCS. During a PLOFC emergency shut-down condition, the maximum concrete structure temperature is 62.3 ±C, 3.5 ±C below that of the single phase RCCS and still below the normal operating temperature of the single phase RCCS. By inducing two phase ow in the CLTHP, the maximum temperature of the working uid is xed equal to the saturation temperature of the working uid at the vacuum pressure. This property of water is used to limit the concrete structure temperature. This e ect is seen in the transient response of the RCCS where the concrete structure temperature increases until boiling of the working uid starts and then the concrete structure temperature becomes constant irrespective of the heat load on the RCCS. An increased heat load increases the quality of the working uid liquid-vapour mixture. Working uid qualities approaching unity causes numerical instabilities in the theoretical model. The theoretical model cannot capture the heat transfer to a control volume with a density lower than approximately 20 kg/m3. This limits the extent to which the two phase RCCS can be optimised. Recommendations are made relating to future work on how to improve the theoretical model in particular the convection modelling in the reactor cavities as well as the two phase ow of the working uid. Further recommendations are made on how to improve the basic design of the heat shield as well as the cooling section of the CLTHPs. / AFRIKAANSE OPSOMMING: 'n Reaktor lug spasie verkoelingstelsel (RLSVS) word in die PBMR gebruik om die beton wat die reaktor omring te beskerm teen direkte stralingskade en hitte. Die gespesi seerde maksimum temperatuur van die beton is 65 ±C onder normale bedryfstoestande en 125 ±C gedurende die noodtoestand afskakeling van die reaktor. 'n Konseptuele ontwerp van 'n geheel en al passiewe RLSVS geskik vir die PBMR is gedoen deur gebruik te maak van geslote lus termo-sifon (GLTSe) om hitte van die stralingskerm te verwyder oor a horisontale afstand na 'n ringvormige verkoelingsdam wat rondom die reaktor geposisioneer is. Die stralingskerm word in die lug spasie tussen die reaktor drukvat (RDV) en die beton geplaas, 180 mm vanaf die beton. 'n Teoretiese hitteoordrag model van die RLSVS was geskep. Die teoretiese model was gebruik vir die ontwikkeling van 'n rekenaar program wat die transiënte gedrag van die RLSVS sal simuleer gedurende normale bedryfstoestande, waar die oorskot gegenereerde hitte verwyder moet word vanuit die reaktor lug spasie, asook gedurende noodtoestand afskakeling van die reaktor, waar die afnemingshitte verwyder moet word. Die primêre doel van die teoretiese model is om the oppervlak temperatuur van die beton te voorspel onder verskillende bedryfstoestande asook verskillende omgewingstoestande. Die teoretiese model aanvaar 'n 1D geometrie van die RLSVS. Hitte oordrag d.m.v. straling asook konveksie vanaf die RDV na die stralingskerm word bereken. The stralingskerm word gemodelleer as 'n vin. Die vin doeltre endheid was bepaal met die eksperimente wat gedoen was. Hitte geleiding in die vin was slegs bereken in die horisontale rigting. Die beton word verhit deur straling vanaf die agterkant van die stralingskerm asook deur konveksie vanaf die lug tussen die stralingskerm en die beton. The modellering van die natuurlike konveksie GLTS hitte pype word gedoen deur om gebruik te maak van die Boussinesq benadering en die homogene vloei model. 'n Eksperiment was vervaardig om the teoretiese model te veri eer. Die eksperiment is 'n volskaal model van die PBMR in die horisontale, of hoof hitteoordrag, rigting, maar is net 'n 2 m hoë snit. Die eksperimente het gewys dat die konveksie hitte oordrag tussen die RDV en die stralingskerm nie met gewone konveksie teorie gemodelleer kan word nie. 'n Nusselt getal uitdrukking wat spesi ek ontwikkel is vir natuurlike konveksie in geslote, reghoekige luggapings wat in die literatuur gevind was, was gebruik om die konveksie hitteoordrag te modelleer. Die Nusselt getal was ongeveer 3 maal groter as wat klassieke konveksie teorie voorspel het. 'n Optimeringsprosedure was ontwikkel waar 121 verskillende kombinasies van vin breedtes en pyp groottes wat gebruik kan word om 'n RLSVS te vervaardig nadat 'n toepaslike verkoelingsdam diameter gekies is. Die doel van die optimering was om die RLSVS te ontwerp wat die laagste totale massa het. 'n Verkoelingsdam diameter van 50 m was gekies. Die optimale RLSVS stralingskerm, waarvan die vloeier slegs in die vloeistof fase bly, bestaan uit 243 GLTSe wat van 62.72 mm binne diameter pype vervaardig is met 25 mm breë vinne. The totale massa van die enkel fase RLSVS is 225 ton. Die maksimum beton temperatuur is 62.5 ±C vir normale bedryfstoestande, 65.8 ±C vir 'n PLOFC noodtoestand afskakeling en is 80.9 ±C vir 'n DLOFC noodtoestand afskakeling. In die geval waar een GLTS faal gedurende 'n DLOFC noodtoestand afskakeling en die twee naasgeleë GLTSe moet kompenseer vir die vermindering in verkoelings kapasiteit, is die maksimum beton temperatuur 87.4 ±C. Dit is 37.6 ±C laer as die gespesi seerde maksimum temperatuur van 125 ±C. Die RLSVS ontwerp kan verder verbeter word wanneer die vloeier in die GLTSe kook. Die optimale RLSVS stralingskerm met die vloeier wat kook, of in twee fase vloei is, bestaan uit 338 GLTSe wat van 38.1 mm binne diameter pype vervaardig is met 20 mm breë vinne. The totale massa van die twee fase vloei RLSVS is 198 ton, 27 ton ligter as die enkel fase RLSVS. Die maksimum beton temperatuur is 60 ±C vir normale bedryfstoestande, 2.5 ±C laer as die enkel fase RLSVS. Gedurende 'n PLOFC noodtoestand afskakeling is die maksimum beton temperatuur 62.3 ±C, 3.5 ±C laer as die enkel fase RLSVS en nogtans onder die maksimum beton temperatuur van die enkel fase RLSVS vir normale bedryfstoestande. Deur om koking te veroorsaak in die GLTS word die maksimum temperatuur van die vloeier vasgepen gelyk aan die versadigings temperatuur van die vloeier by die vakuüm druk. Hierdie einskap van water word gebruik om 'n limiet te sit op die maksimum temperatuur van die beton. Hierdie e ek kan gesien word in die transiënte gedrag van die RLSVS waar die beton temperatuur styg tot en met koking plaasvind en dan konstant raak ongeag van die hitte belasting op die RLSVS. 'n Toename in die hitte belasting veroorsaak net 'n toename in die kwaliteit van die vloeistof-gas mengsel. Mengsel kwaliteite van 1 nader veroorsaak numeriese onstabiliteite in die teoretiese model. The teoretiese model kan nie die hitteoordrag beskryf na 'n kontrole volume wat 'n digtheid het laer as ongeveer 20 kg/m3. Hierdie plaas 'n limiet op die optimering van die twee fase RLSVS. Aanbevelings was gemaak met betrekking tot toekomstige werk aangaande die verbetering van die teoretiese model met spesi eke klem op die modellering van konveksie in die reaktor asook die modellering van twee fase vloei. Verdere aanbevelings was gemaak aangaande die verbetering van die stralingskerm ontwerp asook die ontwerp van die verkoeling van die GLTSe.

Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: The feasibility of a closed loop thermosyphon for the Reactor Cavity Cooling System of the Pebble Bed Modular Reactor has been the subject of many research projects. Difficulties identified by previous studies include the hypothetical inaccuracies of heat transfer coefficient correlations available in literature. The aim of the research presented here is to develop inside-pipe heat transfer correlations that are specific to the current design of the RCCS. In order to achieve this, a literature review is performed which identifies reactors which employ closed loop thermosyphons and natural circulation. The literature review also explains the general one-dimensional two-fluid conservation equations that form the basis for numerical modelling of natural circulation loops. The literature review lastly discusses available heat transfer coefficient correlations with the aim of identifying over which ranges and under which circumstances these correlations are considered accurate. The review includes correlations commonly used in natural circulation modelling in the nuclear industry in aims of identifying correlations applicable to the modelling of the proposed RCCS. One of the objectives of this project is to design and build a one-third-height-scale model of the RCCS. Shortcomings of previous experimental models were assessed and, as far as possible, compensated for in the design of the model. Copper piping is used, eliminating material and surface property uncertainties. Several sight glasses are incorporated in the model, allowing for the visual identification of two-phase flow regimes. An orifice plate is used allowing for bidirectional flow measurement. The orifice plate, thermocouples and pipe-in-pipe heat exchangers are calibrated in-situ to minimize experimental error and aid repeatability. Twelve experiments are performed with data logging occurring every ten seconds. The results presented here are limited to selected single and two-phase flow operating mode results. Error analyses and repeatability of experimental measurements for single and two-phase operating modes as well as cooling water mass flow rates are performed, to show repeatability of experimental results. These results are used to mathematically determine the experimental inside-pipe heat transfer coefficients for both the evaporator and condenser sections. Trends in the heat transfer coefficient profiles are identified and the general behaviour of the profiles is thoroughly explained. The RCCS is modelled as a one-dimensional system. Correlations for the friction factor, heat transfer coefficient, void fraction and two-phase frictional multiplier are identified. The theoretical heat transfer coefficients are calculated using the mathematical model and correlations identified in the literature review. Fluid parameters are evaluated using experimentally determined temperatures and mass flow rates. The resulting heat transfer coefficient profiles are compared to experimentally determined profiles, to confirm the hypothesis that existing correlations do not accurately predict the inside-pipe heat transfer coefficients. The experimentally determined coefficients are correlated to 99% confidence intervals. These generated correlations, along with identified and established twophase heat transfer coefficient correlations, are used in a mathematical model to generate theoretical coefficient profiles. These are compared to the experimentally determined coefficients to show prediction accuracy. / AFRIKAANSE OPSOMMING: Die haalbaarheid van ‘n natuurlike sirkulasie geslote lus vir die Reaktor Holte Verkoeling Stelsel (RHVS) van die Korrelbed Modulêre Kern-Reaktor (KMKR) is die onderwerp van talle navorsings projekte. Probleme geïdentifiseer in vorige studies sluit in die hipotetiese onakkuraatheid van hitte-oordrag koëffisiënt korrelasies beskikbaar in literatuur. Die doel van die navorsing aangebied is om binne-pyp hitte-oordrag koëffisiënt korrelasies te ontwikkel spesifiek vir die huidige ontwerp van die RHVS. Ten einde dit te bereik, word ‘n literatuurstudie uitgevoer wat kern-reaktors identifiseer wat gebruik maak van natuurlike sirkulasie lusse. Die literatuurstudie verduidelik ook die algemene een-dimensionele twee-vloeistof behoud vergelykings wat die basis vorm vir numeriese modellering van natuurlike sirkulasie lusse. Die literatuurstudie bespreek laastens beskikbare hitte-oordrag koëffisiënt korrelasies met die doel om te identifiseer vir welke massavloei tempo waardes en onder watter omstandighede hierdie korrelasies as korrek beskou is. Die ontleding sluit korrelasies in wat algemeen gebruik word in die modellering van natuurlike sirkulasie in die kern industrie met die hoop om korrelasies vir gebruik in die modellering van die voorgestelde RHVS te identifiseer. Een van die doelwitte van die projek is om ‘n een-derde-hoogte-skaal model van die RHVS te ontwerp en te bou. Tekortkominge van vorige eksperimentele modelle is geidentifiseer en, so ver as moonlik, voor vergoed in die ontwerp van die model. Koper pype word gebruik wat die onsekerhede van materiaal en opperkvlak eindomme voorkom. Verkseie deursigtige polikarbonaat segmente is ingesluit wat visuele identifikasie van twee-fase vloei regimes toelaat. ‘n Opening plaat word gebruik om voorwaartse en terugwaartse vloeimeting toe te laat. Die opening plaat, termokoppels en hitte uitruilers is gekalibreer in plek om eksperimentele foute te verminder en om herhaalbaarheid te verseker. Twaalf eksperimente word uitgevoer en data word elke tien sekondes aangeteken. Die resultate wat hier aangebied word, is beperk tot geselekteerde enkel- en tweefase vloei meganismes van werking. Fout ontleding en herhaalbaarheid van eksperimentele metings, om die herhaalbaarheid van eksperimentele resultate te toon. Hierdie is gebruik om wiskundig te bepaal wat die eksperimentele binne-pyp hitte-oordrag koëffisiënte is vir beide die verdamper en kondenseerder afdelings. Tendense in die hitte-oordrag koëffisiënt profiele word geïdentifiseer en die algemene gedrag van die profiles is deeglik verduidelik. Die RHVS is gemodelleer as 'n een-dimensionele stelsel. Korrelasies vir die wrywing faktor, hitte-oordrag koëffisiënte, leegte-breuk en twee-fase wrywings vermenigvuldiger word geïdentifiseer. Die teoretiese hitte-oordrag koëffisiënte word bereken deur middle van die wiskundige model en korrelasies wat in literatuur geidentifiseer is. Vloeistof parameters is geëvalueer met eksperimenteel bepaalde temperature en massa-vloei tempos. Die gevolglike hitte-oordrag koëffisiënt profiles is vergelyk met eksperimentele profiele om die hipotese dat die bestaande korrelasies nie die binne-pyp hitte-oordrag koëffisiënte akkuraat voorspel nie, te bevestig. Die eksperimenteel bepaalde koëffisiënte is gekorreleer en die gegenereerde korrelasies, saam met geïdentifiseerde twee-fase hitte-oordrag koëffisiënt korrelasies, word gebruik in 'n wiskundige model om teoretiese koëffisiënt profiele te genereer. Dit word dan vergelyk met die eksperimenteel bepaalde hitteoordrag koëffisiënte om die akkuraatheid van voorspelling te toon. Tekortkominge in die teoretiese en eksperimentele model word geïdentifiseer en aanbevelings gemaak om hulle aan te spreek in die toekoms.

Thesis (MScEng)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: A high temperature reactor (HTR) generates heat inside of the reactor core through nuclear fission, from where the heat is transferred through the core and heats up the reactor pressure vessel (RPV). The heat from the RPV is transported passively through the reactor cavity, where it is cooled by the reactor cavity cooling system (RCCS), through the concrete confinement structure and ultimately into the environment. The concrete confinement structure can withstand temperatures of up to 65°C for normal operating conditions and temperatures of up to 125°C during an emergency. This project endeavours to research the heat transfer between an HTR’s RPV and the outside of the concrete confinement structure by utilising three investigative approaches: experimental, computational fluid dynamics (CFD) and analytical. The first approach, an experimental analysis, required the development of an experi- mental model. The model was used to perform experiments and gather temperature data that could be used to verify the accuracy of the CFD simulations. The second approach was a CFD analysis of the experimental model, and the external concrete temperatures from the simulation were compared with the temperatures measured with the experimen- tal model. Finally, an analytical analysis was performed in order to better understand CFD and how CFD solves natural convection-type problems. The experiments were performed successfully and the measurements taken were com- pared with the CFD results. The CFD results are in good agreement with the Dry experiments, but not with the Charged experiments. It was identified that the inaccurate results for the CFD simulations of the Charged experiments arose due to convective heat leakage through gaps in the heat shield and between the heat shield and the sides of the experimental model. A computer program was developed for the analytical analysis and it was established that the program could successfully solve the natural convection in a square cavity - as required. / AFRIKAANSE OPSOMMING: ’n Hoë temperatuur reaktor (HTR) genereer hitte binne die reaktor kern deur kernsplyting en die hitte word dan deur die kern versprei en verhit die reaktor se drukvat. Die hitte van die reaktor drukvat word dan passief deur die reaktorholte versprei, waar dit deur die reaktorholte se verkoelingstelsel afgekoel word, en deur die beton beskermingstruktuur gelei word en uiteindelik die omgewing bereik. Die beton beskermingstruktuur kan temperature van tot 65°C onder normale operasietoestande van die reaktor weerstaan, en temperature van tot 125°C tydens ’n noodgeval. Hierdie projek poog om die hitte-oordrag tussen ’n HTR-reaktor drukvat en die buitekant van die beton beskermingstruktuur te on- dersoek deur gebruik te maak van drie ondersoekbenaderings: eksperimenteel, numeriese vloei dinamika (NVD) en analities. Die eerste benadering, ’n eksperimentele analise, het die ontwikkeling van ’n eksper- imentele model vereis. Die model is gebruik om eksperimente uit te voer en temperatu- urmetings te neem wat gebruik kon word om die akkuraatheid van die NVD simulasies te bevestig. Die tweede benadering was ’n NVD-analise van die eksperimentele model, en die eksterne betontemperature verkry van die simulasies is vergelyk met die gemete temperature van die eksperimente. Uiteindelik is ’n analitiese analise uitgevoer ten einde NVD beter te verstaan en hoe NVD natuurlike konveksie-tipe probleme sal oplos. Die eksperimente is suksesvol uitgevoer en die metings is gebruik om die NVD resultate mee te vergelyk. Die NVD resultate van die Droë eksperimente het goeie akkuraatheid getoon. Dit was nie die geval vir die Gelaaide eksperimente nie. Daar is geïdentifiseer dat die verskille in resultate tussen die NVD en die eksperimente aan natuurlike konveksie hitte verliese deur gapings in die hitteskuld en tussen die hitteskuld en die kante van die eksperimentele model toegeskryf kan word. ’n Rekenaarprogram is geskryf vir die analitiese ontleding en die program kon suksesvol die natuurlike konveksie in ’n vierkantige ruimte oplos.

This dissertation has three parts which are distinctive from the perspective of their frequency regime of operation and from the nature of their contributions to the science and engineering communities. The first part describes work that was conducted on a vertical-external-cavity surface emitting-laser (VECSEL) in the optical frequency regime. We designed, fabricated, and tested a hybrid distributed Bragg reflector (DBR) mirror for a VECSEL sub-cavity operating at the laser emission wavelength of 1057 nm. The DBR mirror was terminated with a highly reflecting gold surface and integrated with an engineered pattern of titanium. This hybrid mirror achieved a reduction in half of the number of DBR layer pairs in comparison to a previously reported, successful VECSEL chip. Moreover, the output power of our VECSEL chip was measured to be beyond 4.0Wwith an optical-to-optical efficiency of 19.4%. Excellent power output stability was demonstrated; a steady 1.0 W output at 15.0 W pump power was measured for over an hour. The second part reports on an ultrafast in situ pump-probing of the nonequlibrium dynamics of the gain medium of a VECSEL under mode-locked conditions. We proposed and successfully tested a novel approach to measure the response of the inverted carriers in the active region of a VECSEL device while it was operating under passively mode-locked conditions. We employed the dual-frequency-comb spectroscopy (DFCS) technique using an asynchronous optical sampling (ASOPS) method based on modified time-domain spectroscopy (TDS) to measure the nonequilibrium dynamics of the gain medium of a phase-locked VECSEL that we designed and fabricated to operate at the1030 nm emission wavelength. Our spectroscopic studies used a probe pulse of 100 fs and an in situ pump pulse of 13 ps. We probed the gain medium of the VECSEL and recorded a depletion time of 13 ps, a fast recovery period of 17 ps, and 110 ps for the slow recovery time. Our scans thus demonstrated a 140 ps full depletion-recovery cycle in the nonequilibrium state. The third part discusses work in the microwave and millimeter wave frequency regimes. A new method to fabricate Luneburg lenses was proposed and demonstrated. This type of lens is well known; it is versatile and has been used for many applications, including high power radars, satellite communications, and remote sensing systems. Because the fabrication of such a lens requires intricate and time consuming processes, we demonstrated the design, fabrication and testing of a Luneburg lens prototype using a 3-D printing rapid prototyping technique both at the X and Ka-V frequency bands. The measured results were in very good agreement with their simulated values. The fabricated X-band lens had a 12 cm diameter and produced a beam having a maximum gain of 20 dB and a beam directivity (half-power beam width (HPBW)) ranging from 12° to 19°). The corresponding Ka-V band lens had a 7 cm diameter; it produced a beam with a HPBW about the same as the X-band lens, but with a maximum gain of more than 20 dB.

Nano-emitters are the new generation of laser devices. A photonic-crystal cavity, which highly confines light in small volumes, in combination with quantum-dots can enhance the efficiency and lower the threshold of this device. The practical realisation of a reliable, electrically pumped photonic-crystal laser at room-temperature is, however, challenging. In this project, a design for such a laser was established. Its properties are split up into electrical, optical and thermal tasks that are individually investigated via various device simulations. The resulting device performance showed that with our design the quantum-dots can be pumped in order to provide gain and to overcome the loss of the system. Threshold currents can be as low as 10’s of μA and Q-factors in the range of 1000’s. Gallium arsenide wafers were grown according to our specifications and their diode behaviour confirmed. Photonic-crystal cavities were fabricated through a newly developed process based on a TiOₓ hard-mask. Beside membraned cavities, also cavities on oxidised AlGaAs were fabricated with help to a unique hard-mask removal method. The cavities were measured with a self-made micro-photoluminescence setup with the highest Q-factor of 4000 for the membrane cavity and a remarkable 2200 for the oxide cavity. The fabrication steps, regarding the electrically pumped photonic-crystal laser, were developed and it was shown that this device can be fabricated. During this project, a novel type of gentle confinement cavity was developed, based on the adaption of the dispersion curve (DA cavity) of a photonic-crystal waveguide. Q-factors of as high as 600.000 were measured for these cavities made in Silicon.

In the past decade, great research effort was inspired by the need to realise active optical functionalities in silicon, in order to develop the full potential of silicon as a photonic platform. In this thesis we explore the possibility of achieving tunable delay and optical gain in silicon, taking advantage of the unique dispersion capabilities of photonic crystals. To achieve tunable optical delay, we adopt a wavelength conversion and group velocity dispersion approach in a miniaturised engineered slow light photonic crystal waveguide. Our scheme is equivalent to a two-step indirect photonic transition, involving an alteration of both the frequency and momentum of an optical pulse, where the former is modified by the adiabatic tuning possibilities enabled by slow light. We apply this concept in a demonstration of continuous tunability of the delay of pulses, and exploit the ultrafast nature of the tuning process to demonstrate manipulation of a single pulse in a train of two pulses. In order to address the propagation loss intrinsic to slow light structures, with a prospect for improving the performance of the tunable delay device, we also investigate the nonlinear effect of stimulated Raman scattering as a means of introducing optical gain in silicon. We study the influence of slowdown factors and pump-induced losses on the evolution of a signal beam along the waveguide, as well as the role of linear propagation loss and mode profile changes typical of realistic photonic crystal structures. We then describe the work conducted for the experimental demonstration of such effect and its enhancement due to slow light. Finally, as the Raman nonlinearity may become useful also in photonic crystal nanocavities, which confine light in very small volumes, we discuss the design and realisation of structures which satisfy the basic requirements on the resonant modes needed for improving Raman scattering.