No description available.

The overall performance of a scramjet-powered vehicle not only depends on the performance of individual components but also on how the components interact with one another. Because scramjet engines must be integrated into the vehicle design, the optimization of the design of one component may detrimentally offset the performance of other components. This thesis addresses the optimization of the thrust nozzle of a scramjet-powered vehicle and shows how the optimization must include the integration of the nozzle into the overall vehicle design. The basic scramjet vehicle configuration chosen for the study is the somewhat conventional design of a vehicle with an axisymmetric centrebody, where fuel and payload may be stored, and a quasi-axisymmetric cowl. Six internal intake-combustor-nozzle modules are arranged around the centrebody. Paull et al. (1995) tested a configuration of this type (referred to as model 0) and demonstrated that, at some conditions, a net positive thrust could be produced. They suggest that the thrust nozzle of the vehicle has potential for design change that could lead to significantly improved performance. The main aim of the present study is to test this hypothesis. An important decision that was made early in the present project was that the research would focus on unfuelled operation of the vehicle design. This still allowed the influence of integration of the optimized nozzle to be studied but removed the complications introduced by combustion processes. In order to integrate optimization of design of the thrust nozzle, it was necessary to analyze the performance of the complete scramjet vehicle design. A simple analysis methodology that captures the important physical processes occurring in the flow through and around the vehicle is necessary so that rapid calculations can be made in an iterative optimization program. Therefore, the force prediction methodology that was developed used a combination of simple hypersonics theories and inviscid 3-D CFD modelling instead of using a full 3-D Navier-Stokes equation solver to minimize the calculation time. The pressure forces and viscous forces on the model were calculated separately for each component of the scramjet vehicle designs. The theory of van Driest (1956) for skin friction drag in turbulent boundary layers was found to produce best agreement with measurements. Therefore, it was employed to estimate the turbulent skin friction drag in the present research. To validate the current force prediction methodology, the net axial drag force on an unfuelled quasi-axisymmetric scramjet model derived from the design of Paull et al. (1995) and designed for operation at Mach 6 (model 1) was measured in the T4 Stalker tube at The University of Queensland using a single component Stress Wave Force Balance. (The design of Paull et al. (1995) is referred to here as model 0.) Tests were performed with Mach 6, Mach 8, and Mach 10 nozzles attached to the end of the shock tube. In order to get a wide range of flow conditions the nozzle-supply enthalpy was varied from 3 to 10 MJ/kg and the nozzle-supply pressure from 35 to 45 MPa. A reduction of the drag coefficient of model 1 was observed with decreasing nozzle-supply enthalpy for each of the tunnel nozzles tested. The performance of model 1 was analyzed using the force prediction methodology. Generally, the force prediction results were in good agreement with experimental results. The results indicate that the internal intakes provide 50% of the total drag. The skin friction drag in the combustion chambers and the nozzles account for 30% of the total drag. In order to investigate the influence on the overall performance of the vehicle obtained by improving the nozzle performance, optimization and parametric studies of quasi-axisymmetric scramjet nozzle designs were conducted. The vehicle which was optimized in this study is of a similar configuration to the model used in Paull et al. (1995). The vehicles are optimized for minimum fuel-off net axial drag for a design flight Mach number of 8 using the force prediction methodology and the Nelder and Mead (1965) optimization algorithm. The optimization studies focused on the combustion chamber and the nozzle. Therefore, the shape of the conical forebody and the intake were not changed. The external flow over the cowl was taken into account during the optimization studies. The results showed that a long nozzle with a large external cowl deflection angle, which allowed the nozzle area ratio to be increased, did not give better performance than a short nozzle with a smaller area ratio. This was due to the competing effects of increased external drag on the cowl and increased nozzle thrust as the nozzle area ratio increased. The optimum shape gave limited improvement compared with that of Paull et al. (1995). While fuelled performance of the vehicle was not the focus of the present investigation, a preliminary theoretical study of fuelled operation was performed. A parametric study to vary the nozzle length and external cowl deflection angle was performed for different flight Mach numbers. The results indicate a larger nozzle and higher external cowl deflection angle are appropriate for fuelled cases compared with unfuelled cases. The net axial force on a model with a geometry close to the optimum design (model 2) was measured in the T4 shock tunnel in order to check that the optimization procedure was valid. Model 2 showed generally better performance than other models experimentally. For the Mach 6 nozzle tests, although model 2 has some performance losses due to the spillage of flow around the intakes, model 2 shows approximately a 20% lower drag coefficient than model 1 and shows slightly better performance than model 0. For all test conditions, a break-down of the components of the drag coefficient indicates that the nozzle of model 2 produces approximately three times more thrust than the nozzle of model 0 and approximately twice more than that of model 1. For the Mach 8 nozzle tests, model 2 has approximately a 20% lower drag coefficient than model 1. However, for the Mach 10 nozzle tests, no significant differences between the models were observed in the measurements. Finally, the measurements and optimization study indicate that when model 2 is fuelled, it could be expected to be capable of cruise up to Mach 8 because of its very effective nozzle.

No description available.

Die selbständige, gerichtete Bewegung von biologischen Zellen ist eine der grundlegendsten und komplexesten Erscheinungen der Natur. In höher entwickelten Lebewesen spielt die Zellbewegung eine wichtige Rolle, z.B. bei der Entwicklung des Organismus, bei der Funktion des Immunsystems aber auch bei der Metastase von Krebszellen. Die physikalischen Prozesse die dieser Fähigkeit zugrunde liegen, sind im Fokus dieser Arbeit. Um besser zu verstehen welche Prozesse im Einzelnen und in welcher Kombination den Zellen erlauben sich gerichtet fortzubewegen, wurde in der vorliegenden Arbeit ein representatives Modellsystem von motilen Zellen untersucht. Fischkeratozyten bewegen sich in vitro regelmäßig und gleichförmig, relativ schnell über die Substratfläche, und stellen aus physikalischer Sicht eine optimierte, sich selbständig bewegende Polymermaschine dar. Um Kräfte in der Bewegungsebene der Zellen zu untersuchen, wurde in der vorliegenden Arbeit eine neuartige, auf dem Rasterkraftmikroskop (RKM) basierende Methode entwickelt. Zusätzlich wurden hochaufgelöste, mit dem Phasenkontrastmikroskop aufgenommene Bilderserien analysiert und die Geschwindigkeitsverteilung in der Zelle durch Korrelationsalgorithmen bestimmt. Die Struktur des Polymernetzwerkes wurde in mit Fluoreszenzfarbstoff markierten Zellen untersucht, und elastische Eigenschaften wurden mit rheologischen RKM-Messungen bestimmt. Traktionskraftmessungen an elastischen Substraten runden das umfassende Bild ab. Durch Veränderung der molekularen Strukturen mit verschiedenen Chemikalien, die unterschiedliche Prozesse im Gesamtsystem stören, konnte nun ein Phasenraum der Kraftgenerierungsprozesse untersucht und unterschiedliche Effekte verschiedenen Prozessen eindeutig zugeordnet werden. Es wurde somit erstmalig experimentell bewiesen, dass die Polymerisation von Aktin die treibende Kraft am vorderen Rand der Zelle ist. Darüber hinaus wurde das Verhalten des Kraftaufbaus mit einem Model beschrieben, das Aufschluss über die Funktionsweise der darunterliegenden Aktinpolymerstrukturens gibt. Desweiteren wurde in der Mitte der Zelle, zwischen vorderem Rand und Zellkörper, erstmalig eine rückwärtsgerichtete Kraft gemessen, die wichtig ist um ein Kräftegleichgewicht zu erstellen. Ein Model das auf entropischen Kräften im Polymersystem basiert, beschreibt diese kontraktilen Kräfte und ordnet sie der Depolymerisation von Aktin zu. Die Bewegung des Zellkörpers wiederum basiert auf dem Zusammenspiel dieser beiden Mechanismen, sowie der Kontraktion von Aktin und Aktinbündeln durch molekulare Motoren. Eine umfassendes Charakterisierung über verschiedene lokale Mechanismen und ihrer Wechselwirkungen konnte somit erstellt werden, und damit das Verständnis der Kraftgenerierung zur Zellbewegung vertieft.

In the present work, we experimentally study thrust generation from sinusoidally pitched rigid and flexible foils immersed in a uniform flow. The flexible foils are made by attaching a flexible flap of known flexural rigidity and flap length to the trailing edge of a rigid foil. For such thrust generating systems, a propulsive efficiency (η) may be defined as the ratio of the useful work done to the input energy requirement. In the present experiments, the propulsive efficiency (η) of the flapping foil can be determined from direct measurement of the unsteady forces and torque on the foil. The effects of systematic variation of the flexural rigidity of the foil, from highly flexible to rigid, on the thrust and efficiency characteristics of the foil are investigated. Studying such oscillating foils helps one to understand and mimic the efficient thrust generating mechanism in fishes and other creatures that use flapping to locomote themselves. A strain guage based loadcell is used to measure the forces normal to the foil (N) and forces along the chord of the foil (A). With a potentiometer, the instantaneous angular position (θ) is also measured, so that instantaneous lift (L) and thrust (T ) can be calculated. The measured moment (M) is used to calculate the instantaneous power input (P = Mθ˙). The foil is immersed in a uniform flow (u) set in a water tunnel, and the sinusoidal pitching (θ = θmaxsinωt) is provided by a servo motor. The Reynolds number (Re = uc/ν) in the present study is in the range of 103 to 104 . For the case of the rigid foil, the thrust and efficiency characteristics are presented for variation of the non-dimensional flapping frequency called the ‘reduced frequency’ (k = πfc/u), which is varied in the range of 1 to 10. At small reduced frequency (k < 3), the foil experiences a mean drag, while at k > 3, the foil experiences a mean thrust that grows rapidly as the reduced frequency (k) is increased. The thrust characteristics of the rigid foil are decided mainly by the normal force’s phase with respect to θ (φCN ) and its magnitude ([CN ]), as the chord-wise force is very small compared to the normal force (A << N). The measurements show that the non-dimensional mean thrust coefficient (CT ) scales as k2 and non-dimensional mean power (CP ) scales as k3 for k Ҳ 4. The maximum efficiency for rigid foils is found to be 8 % and it occurs at k 6. For the flexible foil case, the effect of making a portion of the total foil flexible by means of attaching a flexible flap of known flexural rigidity (EI) and flap length (cF ) to a rigid foil of length (cR) is studied. Unlike the rigid foils, the chordwise force (A) becomes an important factor in determining the thrust and efficiency characteristics of the flexible foils, due to the bending of the flap. We present results for a broad range of flexural rigidities from highly flexible flaps to stiff flaps, with the extent of flexibility fixed at cF /cR =0.8. We find that there is an optimal flexural rigidity for which the efficiency (η) reaches a maximum of 28 %. This represents a 250 % improvement compared to the rigid foil. The flexible foils with stiff flaps show a strange behavior with all the mean thrust coming from chordwise forces (A), unlike other flexible foils where the contribution to mean thrust come from both normal and chordwise forces. The effect of varying the extent of flexibility (cF/cR) with fixed flexural rigidity has also been studied. We define a non-dimensional flexibility parameter, R∗ = EI/(0.5ρu2sc3F ), which can combine the effect of variations in EI and cF /cR. Using this non-dimensional flexibility parameter (R∗), we find out that mean thrust and efficiency data for both the EI and cF/cR variation study collapse onto a single curve, indicating that R∗ can indeed be a single parameter characterizing flexibility. The present work shows that flexible foils can improve efficiency over rigid foils. Efficiency improvements can come in two ways depending on the R∗ of the flexible foil. Flexible foils with R∗ in the range of 10−2 to 100 show nearly 250% improvement in efficiency, accompanied by nearly 70 % loss in thrust compared to an entirely rigid foil of the same total chord. Flexible foils with R∗ in the range of 100 to 101 show nearly 50 % improvement in efficiency accompanied by nearly 100% increase in thrust.

No description available.

Aim  The purposes of this study were to investigate if the load-velocity (L-V) profile parameters – force capacity and efficiency - differ between swimmers of different performance level, and to investigate if efficiency is the key performance indicator between international elite and national elite level swimmers.  Method  Fifty-four swimmers (27 female and 27 male) of either regional level, national elite or international elite level, participated in this study. The swimmers performed three 25 m semi- tethered maximum effort swims with ascending loads (1 kg, 5% and 10% of body mass). Mean velocity during three stroke cycles mid-effort was calculated and plotted as a function of the external added load. A linear regression was established, expressing the relationship between load and velocity, with the intercepts between the axes and the regression line being defined as the theoretical maximum velocity (V0) and load (force capacity, L0). The slope of the regression line (slopeLV) serves as an index of efficiency. Results A statistically significant difference was found between the three performance levels for all L- V profile variables for front crawl: V0 (F [2, 51] = 7.76, p&lt;0.001), L0 (F [2, 51] = 5.18, p=0.009), and slopeLV (F [2, 51] = 3.36, p=0.043). A paired t-test revealed no difference in slopeLV between matched international elite and national elite level swimmers (t [9] = 1.42, p=0.188), but a near significant difference in L0 (t [9] = 2.11, p=0.064) . Both slopeLV and L0 for front crawl had a strong correlation with personal best in 100 m front crawl (PB100). Conclusion Efficiency was not found to be the key performance indicator between matched international elite and national elite swimmers in this study, and neither was force capacity. Nevertheless, a significant difference in all front crawl L-V profile parameters was found between performance level groups, but post hoc analyses indicated no difference between adjacent performance levels neither in L0 nor slopeLV. There was however a strong correlation between both slopeLV, and L0, to the swimmers’ PB100. All these findings imply that efficiency and force capacity seem to be of equal importance for high performance, but swimmers use different strategies to reach the high swim velocity. / Longitudinal development of performance determining factors in swimming (NIH)

Optical tweezers are a technique in which microscopic-sized particles, including living cells and bacteria, can be non-intrusively trapped with high accuracy solely using focused light. The technique has therefore become a powerful tool in the field of biophysics. Optical tweezers thereby provide outstanding manipulation possibilities of cells as well as semi-transparent materials, both non-invasively and non-destructively, in biological systems. In addition, optical tweezers can measure minute forces (&lt; 10-12 N), probe molecular interactions and their energy landscapes, and apply both static and dynamic forces in biological systems in a controlled manner. The assessment of intermolecular forces with force measuring optical tweezers, and thereby the biomechanical structure of biological objects, has therefore considerably facilitated our understanding of interactions and structures of biological systems. Adhesive bacterial organelles, so called pili, mediate adhesion to host cells and are therefore crucial for the initial bacterial-cell contact. Thus, they serve as an important virulence factor. The investigation of pili, both their biogenesis and their expected in vivo properties, brings information that can be of importance for the design of new drugs to prevent bacterial infections, which is crucial in the era of increased bacterial resistance towards antibiotics. In this thesis, an experimental setup of a force measuring optical tweezers system and the results of a number of biomechanical investigations of adhesive bacterial organelles are presented. Force measuring optical tweezers have been used to characterize three different types of adhesive organelles under various conditions, P, type 1, and S pili, which all are expressed by uropathogenic Escherichia coli. A quantitative biophysical force-extension model, built upon the structure and force response, has been developed. It is found, that this model describes the biomechanical properties for all three pili in an excellent way. Various parameters in their energy landscape, e.g., bond lengths and transition barrier heights, are assessed and the difference in behavior is compared. The work has resulted in a method that in a swift way allows us to probe different types of pili with high force and high spatial resolution, which has provided an enhanced understanding of the biomechanical function of these pili. / Optisk pincett är en teknik i vilken mikrometerstora objekt, inkluderande levande celler och bakterier, beröringsfritt kan fångas och förflyttas med hög noggrannhet enbart med hjälp av ljus. Den optiska pincetten har därmed blivit ett kraftfullt verktyg inom biofysiken, som möjliggör enastående precisions-manipulering av celler och semi-transparenta objekt. Dessutom kan denna manipulation göras intracellulärt, dvs. utan att fysiskt öppna eller penetrera cellernas membran. Den optiska pincetten kan även mäta mycket små krafter och interaktioner (&lt; 10-12 N) samt applicera både statiska och dynamiska krafter i biologiska system med utmärkt precision. Optisk pincett är därför en utmärkt teknik för mätning av intermolekylära krafter och för bestämning av biomekaniska strukturer och dess funktioner. Vissa typer av bakterier har specifika vidhäftningsorganeller som kallas för pili. Dessa förmedlar vidhäftningen till värdceller och är därför viktiga vid bakteriens första kontakt. En djupare förståelse av pilis uppbyggnad och biomekanik kan därmed ge information, som kan vara vital i framtagandet av nya mediciner som förhindrar bakteriella infektioner. Detta är av stor vikt i skenet av den ökande antibiotikaresistensen i vårt samhälle. I denna avhandling presenteras konstruktionen av en experimentell uppställning av kraftmätande optiskt pincett tillsammans med resultat från biomekaniska undersökningar av vidhäftande bakteriella organeller. Kraftmätande optisk pincett har använts för att karakterisera tre olika typer av pili, P, typ 1, och S pili, vilka kan uttryckas av uropatogena Escherichia coli. En kvantitativ biofysikalisk modell som beskriver deras förlängningsegenskaper under pålagd kraft har konstruerats. Modellen bygger på pilis strukturella uppbyggnad samt på dess respons som uppmäts med den kraftmätande optiska pincetten. Modellen beskriver de biomekaniska egenskaperna väl för alla tre pili. Dessutom kan ett antal specifika bindnings- och subenhetsparametrar bestämmas, t.ex. interaktionsenergier och bindningslängder. Skillnaden mellan dessa parametrar hos de tre pilis samt deras olika kraftrespons har jämförts. Detta arbete har dels resulterat i en förbättrad förståelse av pilis biomekaniska funktion och dels i en metod som, med hög noggrannhet, tillåter oss att bestämma ett antal biomekaniska egenskaper hos olika organeller på ett effektivt sätt.

Die selbständige, gerichtete Bewegung von biologischen Zellen ist eine der grundlegendsten und komplexesten Erscheinungen der Natur. In höher entwickelten Lebewesen spielt die Zellbewegung eine wichtige Rolle, z.B. bei der Entwicklung des Organismus, bei der Funktion des Immunsystems aber auch bei der Metastase von Krebszellen. Die physikalischen Prozesse die dieser Fähigkeit zugrunde liegen, sind im Fokus dieser Arbeit. Um besser zu verstehen welche Prozesse im Einzelnen und in welcher Kombination den Zellen erlauben sich gerichtet fortzubewegen, wurde in der vorliegenden Arbeit ein representatives Modellsystem von motilen Zellen untersucht. Fischkeratozyten bewegen sich in vitro regelmäßig und gleichförmig, relativ schnell über die Substratfläche, und stellen aus physikalischer Sicht eine optimierte, sich selbständig bewegende Polymermaschine dar. Um Kräfte in der Bewegungsebene der Zellen zu untersuchen, wurde in der vorliegenden Arbeit eine neuartige, auf dem Rasterkraftmikroskop (RKM) basierende Methode entwickelt. Zusätzlich wurden hochaufgelöste, mit dem Phasenkontrastmikroskop aufgenommene Bilderserien analysiert und die Geschwindigkeitsverteilung in der Zelle durch Korrelationsalgorithmen bestimmt. Die Struktur des Polymernetzwerkes wurde in mit Fluoreszenzfarbstoff markierten Zellen untersucht, und elastische Eigenschaften wurden mit rheologischen RKM-Messungen bestimmt. Traktionskraftmessungen an elastischen Substraten runden das umfassende Bild ab. Durch Veränderung der molekularen Strukturen mit verschiedenen Chemikalien, die unterschiedliche Prozesse im Gesamtsystem stören, konnte nun ein Phasenraum der Kraftgenerierungsprozesse untersucht und unterschiedliche Effekte verschiedenen Prozessen eindeutig zugeordnet werden. Es wurde somit erstmalig experimentell bewiesen, dass die Polymerisation von Aktin die treibende Kraft am vorderen Rand der Zelle ist. Darüber hinaus wurde das Verhalten des Kraftaufbaus mit einem Model beschrieben, das Aufschluss über die Funktionsweise der darunterliegenden Aktinpolymerstrukturens gibt. Desweiteren wurde in der Mitte der Zelle, zwischen vorderem Rand und Zellkörper, erstmalig eine rückwärtsgerichtete Kraft gemessen, die wichtig ist um ein Kräftegleichgewicht zu erstellen. Ein Model das auf entropischen Kräften im Polymersystem basiert, beschreibt diese kontraktilen Kräfte und ordnet sie der Depolymerisation von Aktin zu. Die Bewegung des Zellkörpers wiederum basiert auf dem Zusammenspiel dieser beiden Mechanismen, sowie der Kontraktion von Aktin und Aktinbündeln durch molekulare Motoren. Eine umfassendes Charakterisierung über verschiedene lokale Mechanismen und ihrer Wechselwirkungen konnte somit erstellt werden, und damit das Verständnis der Kraftgenerierung zur Zellbewegung vertieft.

No description available.