Ce travail présente une étude de la dynamique interfaciale de gouttes oscillantes dans une plage étendue de fréquences, en particulier dans le domaine des hautes fréquences. Nous avons développé une méthode de caractérisation de la dynamique des oscillations de gouttes, en présence d’un forçage externe imposé, sous la forme de variations de volume périodiques de faible amplitude sur une goutte attachée à l’extrémité d’un capillaire. Cette méthode permet d’identifier les modes d’oscillation des gouttes et d’en mesurer les fréquences et les taux d’amortissement. Cette méthode a été appliquée à différents systèmes liquide-liquide, en l’absence ou en présence de surfactants. Dans ce dernier cas, elle permet d’évaluer l’effet du comportement viscoélastique des interfaces sur la dynamique des oscillations. Ainsi 3 types d’interfaces ont été identifiés. Pour les interfaces de premier type (heptane/eau sans ajout de surfactant), chaque mode propre est modélisé par un oscillateur linéaire peu amorti. Les fréquences propres et les taux d’amortissement sont bien prédits par la théorie linéaire. Les interfaces de types 2 et 3 sont obtenues en ajoutant du pétrole brut à la phase dispersée. Les surfactants naturellement présents dans le pétrole (asphaltènes, résines) s’adsorbent à l’interface et lui confèrent des propriétés viscoélastiques. Pour les interfaces jeunes (type 2, moins de 20 minutes de vieillissement), les fréquences propres mesurées restent bien prédites par la théorie, qui considère des interfaces non contaminées, tandis que les taux d’amortissement sont de loin supérieurs aux valeurs théoriques. D’autre part, les interfaces vieillies (type 3) présentent des modes propres différents avec des fréquences de résonance supérieures à celles des interfaces jeunes. Dans ce cas, la dynamique de l’interface à haute fréquence est régie par l’élasticité du réseau formé par les espèces amphiphiles du pétrole brut. Les oscillations libres d’une goutte en ascension dans une phase externe stagnante, pour un système liquide-liquide sans ajout de surfactants, ont été étudiées. Les valeurs mesurées de la fréquence d’oscillation des 4 premiers modes sont en adéquation avec la théorie linéaire. Cependant les valeurs mesurées du taux d’amortissement sont très élevées par rapport aux valeurs théoriques, pour une interface non contaminée. En effet, des espèces résiduelles adsorbées à l’interface provoquent l’apparition d’un gradient de tension interfaciale par effet Marangoni et par suite une production de vorticité plus intense dans les couches-limites, ce qui conduit à l’augmentation de l’amortissement des oscillations. / We present an experimental study of oscillating drop interfacial dynamics at a wide frequency range, especially at high frequency. A characterization method of drops oscillation dynamics has been developed. The oscillations are generated by imposing low amplitude periodic variation of volume to a drop which is attached to a capillary tip. The present method is based on the identification of the drop eigenmodes and the determination of their frequencies and damping rates. It has been applied to characterize several liquid-liquid systems. Three types of interface have been identified. For interfaces of type 1 (heptane/water without added surfactant), each eigenmode is modelled by a weakly damped linear oscillator. Eigenfrequencies and damping rates are well predicted by the linear theory. Interfaces of Types 2 and 3 are obtained by adding crude oil to the disperse phase. Oil native surfactants (asphaltenes, resins) adsorb on the drop interface and provide the latter with viscoelastic behaviour. For young interfaces (type 2 with aging time below 20 minutes), eigenfrequencies remain well predicted by the theory, which deals with non contaminated interfaces, whereas the measured damping rates are significantly higher than the theoretical values. On the other hand, aged interfaces (type 3) exhibit different eigenmodes, of which eigenfrequencies are much higher than the resonance frequencies measured for the young interfaces. At high frequency, the dynamics of aged interfaces are governed by the elasticity of the network constituted by the crude oil amphiphilic species, while the dynamics of young interfaces are governed by interfacial tension. Freely decaying oscillations of a rising drop in a liquid at rest without added surfactant were also considered. Measured frequencies for the first four eigenmodes are in good agreement with the linear theory. However, measured damping rates are much higher than the theoretical rates for non contaminated interfaces. In fact, residual adsorbed species at the heptane/water interface induce Marangoni effects and thus gradients of interfacial tension. Therefore, vorticity production within the boundary layers is enhanced, which explains the observed increase of the oscillation damping rates.

This thesis deals with a Building Information Model (BIM) and its advanced use in construction practice. It focuses on the usage of BIM model in the determination of pressure drop in ventilation pipelines. An application able to calculate the pressure drop in a pipeline branch based on the geometrical parameters of the BIMs of structures was created within the work.

Povrchy inorganických materiálov, zvlášť kovov alebo kovových oxidov, ktoré sú často charakteristické vysokou povrchovou energiou, sú zvyčajne kontaminované adsorbovanými organickými molekulami. Tieto molekuly majú na povrchy zväčša nepriaznivý vplyv, do značnej miery napríklad ovplyvňujú funkcionalitu a výkonnosť polovodičov a znemožňujú, prípadne sťažujú prevedenie povrchových úprav na povrchoch kovov aj keramík. Taktiež majú nepriaznivý vplyv na priľnavosť. Adsorbované častice spôsobujú znižovanie hydrofilicity povrchu. Hydrofilicita, adhezivita a zmáčavosť povrchu sa veľmi dobre posudzujú prostredníctvom merania kontaktného uhlu. V tejto práci je značná pozornosť venovaná práve meraniu statického kontaktného uhlu. [10] Samotné meranie kontaktného uhlu je možné vykonať rôznymi spôsobmi, v tejto práci bol však použitý najvhodnejší prístup, a to metódou „sessile-drop“, teda pokladanej alebo depozitovanej kvapky na meraný povrch. K meraniu bol využitý klasický „sessile-drop goniometer“, teda aparatúra, ktorá pozostávala z nastaviteľného stojanu na vzorky, nad ktorým bol umiestnený zdroj svetla, a objektívu fotoaparátu, ktorý bol prepojený s kamerou zabudovaného smartfónu. Meranie prebiehalo tak, že kvapka s objemom 3L destilovanej superčistej vody bola depozitovaná na povrch substrátu pomocou mikroinjekčnej striekačky. Cieľom tejto práce bolo nielen stanoviť kontaktné uhly a porovnať ich hodnoty medzi rôznymi typmi materiálov navzájom a po upravách tepelného a/lebo chemického charakteru. Vyhodnotené údaje zachycovali zmeny, ku ktorým došlo na povrchoch daných keramických materiálov pri adsorpcii organických molekúl. Proces tepelnej úpravy (kalcinácia na teplote 800°C, následne pokles na teplotu 600°C, po celkovú dobu 16 hodín) bol aplikovaný na všetkých typoch vzoriek, kde niektoré sa medzi sebou líšili teplotou slinovania. Ihneď po kalcinácii boli vzorky podrobené meraniu kontaktných uhlov, z ktorého jasne vyplynulo, že hydrofilicita a zmáčavosť povrchu sa zvýšila. Tento jav bol pozorovaný na všetkých vzorkách, a na všetkých vzorkách sa hodnoty kontaktného uhlu líšili veľmi významne od hodnoty, ktorá bola získaná v tzv. primárnom meraní. Všetky detailné hodnoty a vyhodnotené výsledky sú posudzované v časti diskusia. Ďalšou úpravou povrchu, ktorá bola vykonaná na vybraných vzorkách, bolo čistenie povrchu etanolom. Proces bol opäť realizovaný na všetkých vzorkách. Potom, ako boli zrealizované všetky merania na kalcinovaných vzorkách, boli všetky tieto vzorky ponorené do etanolu na približne 2 hodiny. Po vybratí vzoriek a ich osušení na vzduchu boli uskutočnené ďalšie merania kontaktných uhlov. Výsledky priniesli opäť rozdielne hodnoty v porovnaní s predchádzajúcimi meraniami a sú rozvinuté v časti diskusia.

The diploma thesis deals with the issue of replacement of non-ecological refrigerant R22 according to the requirements of relevant juristic regulations and of subsequent influence of this replacement to the efficiency of air conditioning systems. The theoretical part is focused on proceeding processes in thermodynamic cycles and during heat transfer, then determines calculation of cooling and heating factor in context with experimental measurement. The experimental measurement utilizes to the assessment of operation of heat pump after refrigerant replacement and it is source for the composion of economical evaluation of alternative solutions due to the particular choice of refrigerant replacement.

The study is an investigation into the pathways of out-of-school youth and their re-entrance into the Education Training and Development (ETD) system or the labour market. In the study the pathways of youth who dropped out of school between grades 1 and 11 are traced as they seek re-entrance to the ETD system, or entrance into the labour market. Particular attention was given to the factors that determine the choices that dropouts make either in re-entering the ETD system or entering the labour market. An analysis of the experiences of the interviewed sample of dropouts is presented. The study employs a qualitative research methodology using interviews to elicit the experiences of dropouts and school managers. The participants (young people and three school principals) were selected through snowballing from a township south of Durban. Individual and focus group interviews were held. The findings provide evidence of the value of investing in education, as suggested by the youth. This is in line with the human capital theory framework that suggests that there are major benefits to investing in education. The study is concluded by suggesting the need for second chance education in South Africa. / Thesis (PhD)--University of Pretoria, 2011. / Education Management and Policy Studies / unrestricted

Le trafic dans les réseaux optiques est en constante augmentation depuis de nombreuses années. CISCO affirme qu'il devrait augmenter d'un facteur 13 en 2020. Ceci induit une augmentation de la consommation énergétique et de l'évolution de la taille des réseaux entrainant un accroissement de la complexité des réseaux. Dans ce contexte, pour répondre à l'augmentation du débit dans les réseaux et procure un réseau de télécommunications fiable, il faut prévoir une planification et une ingénierie de réseaux adaptées. Dans ce but, nous étudions dans cette thèse le design d'un nœud de commutation optique ROADM. nous considérons différentes architectures de nœud, composants et sous-systèmes utilisés dans les configurations de nœud RODM "Broadcast and Select" et "Route and Select". Diverses configurations de modules d'insertion/extraction sont analysées ("Colored/colorless, directional/directionless et contentional/contentionless"). Pour ce faire, nous avons développé un simulateur de nœud ROADM dans une plateforme de trafic dynamique et nous avons proposé une stratégie de gestion offline de la contention à l'intérieur du nœud. Nous avons obtenu une réduction du rapport de blocage intra noeud de l'ordre de 1.5. Ensuite, nous nous sommes focalisés sur la planification des futures générations de réseaux optiques métro cœur. Dans ce but, nous avons étudié la possibilité d'une transmission non cohérente à 100 Gb/s en utilisant le format de modulation PDM-DQPSK. Ensuite, nous avons considéré l'implémentation de la PDM-CS-DQPSK. La qualité de transmission de ces deux systèmes a finalement été évaluée / Traffic demand is exponentially increasing in recent years. Cisco forecast claims that by 2020, transport traffic will be 13 times of today's traffic transmission. This incremental traffic demand makes concerns about energy consumption and network scalability as well as increasing the network complexity. In this respect, to adresse the future traffic demand requirement and provide a reliable telecommunication network, precise network planning and engineering are needed. To this aim, we adress the problem of ROADM node design by presenting different architectures, components and subsystems to investigate the Broadcast and Select and Route and Select ROADM node architectures. Colored/colorless, directional/directionless and contentional/contentionless add/drop module configurations are studied. Futhermore, the problem of Intra Node Blocking is investigated by developing a node simulator in a dynamic network traffic platform. In this respect, we propose an offline contention management strategy for an ROADMnode in order to efficiently decrease the Intra Node blocking ration by more than 1.5 order of magnitude. Finally, we focus on network planning by investigating short and medium term network upgrades for metro-core optical network. To this goal, we investigate the possibility of non coherent signal transmission in metro-core segment of hierarchical layered optical network. Quality of transmission for 100 Gbit/s PDM-DQPSK-modulation format is investigated. Then, we propose the implementation of PDM-CS-DQPSK modulation format to transmit 100 Gbit/s signals in ROADM based optical transmission systems

Syfte Syftet med detta arbete var att ur före detta tävlings-fäktares perspektiv undersöka orsakerna bakom de omfattande avhopp som sker i övergången mellan ungdoms- och seniorklass i svensk fäktning, samt vad föreningar och förbund kunnat göra för att motverka dessa avhopp. Studien syftar även till att undersöka vilka åtgärder föreningar och förbund kan göra för att främja återupptagandet av tävlande enligt före detta tävlings-fäktare. Vilka orsaker ser före detta värj-fäktande ungdomar till varför de slutade tävla? Vilka åtgärder kunde föreningar och förbund vidtagit enligt före detta värjfäktare för att förhindra deras avhopp ifrån tävlande som ungdomar? Vilka åtgärder kan enligt före detta värjfäktare föreningar och förbund vidta för att främja återupptagande av tävlande? Metod Studiens teoretiska utgångspunkt är motivationsteorin self-determination theory (SDT) och är genomförd med en kvalitativ ansats. Sex semistrukturerade intervjuer har genomförts med före detta fäktare. Intervjuerna har analyserats med tematisk innehållsanalys. Resultat Respondenterna upplevde ett kompetensbekräftande genom tävlandet samt en stark känsla av tillhörighet och när dessa faktorer försvann eller minskade i omfattning ledde det till avhopp. Vidare framkom att avhoppen hade kunnat förhindrats. Därutöver framkom att fäktarna kan ställa sig positiva till att återuppta tävlandet som motionärer ifall det skulle finnas en attraktiv breddverksamhet vad gäller både tävlingar och träningar. I ett återupptagande av tävlandet hade det sociala sammanhanget varit högt prioriterat men också möjligheten att få mäta sig mot fäktare på liknande nivå som de själva i anpassade tävlingsformer. Slutsats Det fanns ett starkt samband mellan avhoppen och att de psykologiska behoven upphörde att uppfyllas av deltagande i sporten. Svensk fäktning kunde under ungdomsåren starkt uppfylla behoven kopplade till att känna samhörighet och kompetens och även i viss mån autonomi men misslyckades med att tillgodogöra de grundläggande psykologiska behoven när fäktarna blev äldre. Vidare visar detta vikten av att föreningar och förbund arbetar aktivt med att tillgodose de grundläggande psykologiska behoven för motivation ifall avhoppen ska minskas och för att främja till återupptagandet av tävlande. / Aim The aim of this study was to investigate, from the perspective of former competitive fencers, the reasons behind the high level of drop outs that occur in the transition between youth and senior levels in Sweden, as well as what clubs and federations could have done to counteract these drop outs. The study also aimed to investigate what measures clubs and federations can take to promote the resumption of competing according to former competitive fencers. - What reasons do former épée fencing youths give as why they stopped competing? - According to former épée fencers, what measures could clubs and federations have taken to prevent youth drop out? - According to former épée fencers, what measures can clubs and federations take to promote the resumption of competing? Method The study's theoretical framework was the self-determination theory (SDT) and the research body was qualitative. Six semi-structured interviews have been conducted with former fencers. The interviews have been analyzed using thematic content analysis. Results The results showed that the former fencers had experienced a confirmation of competence through competitions, as well as a strong sense of belonging to their teammates and friends in the sport. When these factors disappeared or decreased, it led to drop outs. It also emerged that these drop outs could have been prevented. In addition, it emerged that the fencers are positive about resuming competition recreationally if there is an wide range of activities in terms of both competitions and training targeted at recreational fencers. For the resumption of competing, social context has been identified as a high priority. Another high priority is the opportunity to compete against fencers of a similar level to themselves in adapted forms of competition. Conclusions There was a strong correlation between the drop out of youth fencers and their psychological needs not being fulfilled in the sport. During childhood of the respondents, participation in fencing strongly fulfilled the need for a sense of belonging and feeling of competence, and to a certain extent autonomy. Fencing in Sweden however failed to provide this as the fencers got older. Furthermore, if drop outs are to be reduced and the competing is to be resumed, the study demonstrates the importance of clubs and confederations working actively to meet the psychological needs of the athletes.

[pt] Sistemas líquido-líquido imiscíveis são amplamente encontrados na natureza e em processos industriais, abrangendo uma variedade de aplicações, incluindo adesão bacteriana, formação de biofilme, emulsificação, administração de medicamentos, injeção de água na recuperação de petróleo e remediação de solventes clorados em águas subterrâneas. Esses sistemas ocorrem quando dois líquidos não podem formar uma mistura homogênea devido a diferenças em suas propriedades moleculares, como polaridade ou densidade. Como resultado, os líquidos mantêm uma interface onde entram em contato, mas não se misturam, formando camadas distintas. Esse comportamento é influenciado pela tensão interfacial, uma força que minimiza a área de contato entre os dois líquidos e, assim, exerce uma influência significativa na estabilidade e no comportamento do sistema. Surfactantes, ou agentes tenso ativos (SSAs), são frequentemente usados para controlar as propriedades dessas interfaces. Esses compostos reduzem significativamente a tensão interfacial entre dois líquidos imiscíveis. Este estudo visa medir experimentalmente a tensão interfacial em um sistema líquido-líquido por meio de um método dinâmico in situ utilizando um reômetro equipado com sistema de microscopia. Este equipamento permite a observação e medição em tempo real do comportamento da interface dos fluidos sob várias condições. Dessa forma, a tensão interfacial é determinada com base nas teorias existentes de deformação de gotas, como o método de retração de gotas deformadas (DDRM). Investigamos o comportamento da tensão interfacial em um sistema composto por uma mistura de 95 por cento empeso de polidimetilsiloxano (PDMS) e hexadecano, uma solução de 80 por cento empeso de glicerol em água deionizada, e o surfactante não iônico lipofílico Twenn 80, com concentrações variando de 0,0005 por cento a 0,0500 por cento em peso. / [en] Immiscible liquid-liquid systems are widely found in nature and industrial processes, covering a variety of applications, including bacterial adhesion, biofilm formation, emulsification, drug delivery, water flooding in oil recovery, and remediation of chlorinated solvents in groundwater. These systems occur when two liquids cannot form a homogeneous mixture due to differences in their molecular properties, such as polarity or density. As a result, the liquids maintain an interface where they come into contact but do not mix, forming distinct layers. This behaviour is influenced by interfacial tension, a force that minimises the contact area between the two liquids and thus exerts a significant influence on the stability and behaviour of the system. Surfactants, or surface-active agents (SSAs), are often used to manage and manipulate the properties of these interfaces. These compounds significantly reduce the interfacial tension between two immiscible liquids. This study aims to experimentally measure the interfacial tension in a liquid-liquid system through a dynamic in situ method using the Rheo-Microscopy apparatus. This equipment allows real-time observation and measurement of fluid interface behaviour under various conditions. In this way, interfacial tension is determined based on existing drop deformation theories, such as the deformed drop retraction method (DDRM). We investigated the interfacial tension behaviour in a system composed of a 95 wt.percent polydimethylsiloxane (PDMS) hexadecane mixture, an 80 wt.percent glycerol solution in deionized water, and the lipophilic non-ionic surfactant Tween 80, with concentrations ranging from 0.0005 to 0.0500 wt.percent.

The wall effect is known to present difficulties when attempting to predict the pressure drop over randomly packed beds. The Nuclear Safety Standard Commission, “Kerntechnischer Auss-chuss" (KTA), made considerable efforts to develop an equation which predicts the pressure drop over cylindrical randomly packed beds consisting of mono-sized spheres. The KTA was able to estimate a limiting line, which defines the region for which the wall effect is negligible, however the theoretical basis for this line is unclear. The goal of this investigation was to determine the validity of the KTA limiting line, using an explicit approach. Packed beds were generated using Discrete Element Modelling (DEM), and the flow through the beds simulated using Computational Fluid Dynamics (CFD). STAR-CCM+R was used for both DEM and CFD operations, and the methods developed for this explicit approach were validated with empirical data. The KTA correlation predictions for friction factors were com- pared with the CFD results, as well as the predictions from a few other correlations. The KTA correlation predictions for friction factors did not correspond well with the CFD results at low aspect ratios and low modified Reynolds numbers, due to the influence of the wall effect. The KTA limiting line was found to be valid, but not exact. A new limiting line for the KTA correlation was suggested, however the new limiting line improved little on the existing line and was the result of some major assumptions. In order to improve the determination of the position of the KTA limiting line further, criteria need to be established which determine how small the error in predicted friction factor must be before the KTA correlation can be accepted as accurate. / MIng (Nuclear Engineering), North-West University, Potchefstroom Campus, 2014

The wall effect is known to present difficulties when attempting to predict the pressure drop over randomly packed beds. The Nuclear Safety Standard Commission, “Kerntechnischer Auss-chuss" (KTA), made considerable efforts to develop an equation which predicts the pressure drop over cylindrical randomly packed beds consisting of mono-sized spheres. The KTA was able to estimate a limiting line, which defines the region for which the wall effect is negligible, however the theoretical basis for this line is unclear. The goal of this investigation was to determine the validity of the KTA limiting line, using an explicit approach. Packed beds were generated using Discrete Element Modelling (DEM), and the flow through the beds simulated using Computational Fluid Dynamics (CFD). STAR-CCM+R was used for both DEM and CFD operations, and the methods developed for this explicit approach were validated with empirical data. The KTA correlation predictions for friction factors were com- pared with the CFD results, as well as the predictions from a few other correlations. The KTA correlation predictions for friction factors did not correspond well with the CFD results at low aspect ratios and low modified Reynolds numbers, due to the influence of the wall effect. The KTA limiting line was found to be valid, but not exact. A new limiting line for the KTA correlation was suggested, however the new limiting line improved little on the existing line and was the result of some major assumptions. In order to improve the determination of the position of the KTA limiting line further, criteria need to be established which determine how small the error in predicted friction factor must be before the KTA correlation can be accepted as accurate. / MIng (Nuclear Engineering), North-West University, Potchefstroom Campus, 2014