Although lymphatic vessel behavior is analogous to hearts (e.g. systole and diastole) and blood vessels (e.g. basal tone), hearts and blood vessels have fundamentally different contractile properties. While summation during contraction is minimized in the heart, summation is necessary for tonic contraction in blood vessels. Because lymphatic vessel behavior mimics cardiac and vascular behavior, we hypothesized that above a critical contraction frequency there is significant summation, evidenced by significantly increased diastolic active tension (i.e. basal tone). We used an isovolumic, controlled-flow preparation to examine the interaction of contraction cycle-time with contraction frequency. Using segments of isolated lymphatic vessels (~1 cm in length and 3-4 mm in diameter) from bovine mesentery, we measured transmural pressure and diameter for end-diastole and end-systole during spontaneous contractions for 10 volume steps. We found time between contractions (beat-to-beat period) decreases with increasing diameter, and total contraction time (vessel twitch length, 11.08 ± 1.54 s) slightly increases with increasing diameter. At the intersection of these relationships, there is a critical period, below which the vessel does not have time to fully relax. Above the diameter at the critical period, diastolic active tension (end-diastolic minus passive vessel tension) significantly increases with increases in diameter (309 to 562% change in slope, p<0.0001), and, below the critical period, diastolic active tension increases with decreases in beat-to-beat period (712 to 2208% change in slope, p<0.0014). Because this transition occurs within a physiological range, it suggests summation may be crucial for lymphatic vessel function as a pump and a conduit.

Mechanische Beanspruchungen verändern bei nahezu jeder Zelle ihre Funktion und ihre Form. Wir interessieren uns besonders für die durch mechanische Beanspruchungen hervorgerufene Effekte im Blutgefäßsystem, dessen Innenseite von den sogenannten Endothelzellen ausgekleidet ist, die eine Permeabilitätsbarriere zwischen Blut und Gewebe darstellen. Durch den Blutstrom sind diese Zellen permanent einer erheblichen mechanischen Beanspruchung ausgesetzt, die nicht nur ihre Form, sondern auch ihre Funktionen wesentlich verändert. Wir haben in unserem Labor einen experimentellen Aufbau entwickelt, mit dem wir erstmalig zeigen konnten, dass laminare Strömungen zu einer Verstärkung der endothelialen Barrierefunktion führen und so vermutlich der Entwicklung der Gefäßverkalkung entgegenwirken. Neben diesen Experimenten wird das neue System auch zur dynamischen Untersuchung der Zellhaftung auf Biomaterialien verwendet. / Mechanical loads change the function and morphology of nearly every cell. We are particularly interested in the effects of mechanical loads on the endothelial cells which line the inner surface of blood vessels and control the exchange of water and solutes between blood and tissue (barrier function). These cells are exposed permanently to mechanical forces from the blood stream, which induces changes not only in cell morphology but also in function. We have developed an experimental setup which allows the endothelial barrier function to be measured under defined flow conditions. We have demonstrated for the first time that laminar shear stress enhances the endothelial barrier function, and thus a possible explanation for the anti-arteriosclerotic effect. Importantly, our setup can also be used to dynamically test the adhesion of cells on biomaterials.

Endothelzellen bilden eine monozellulare Grenzschicht in Blutgefäßen. Ihre Migration ist ein kritischer Teilschritt bei der Gefäßbildung, zum Beispiel während der Wundheilung. Obwohl bereits eine Reihe der dafür relevanten Mediatoren und pathogenen Determinanten bekannt sind, fehlt bisher eine quantitative Analyse der molekularen Mechanismen der Gefäßbildung und Zellmigration. Voraussetzung dafür sind Verfahren zur automatisierten Bestimmung von Zelltrajektorien in Sequenzen von Mikroskopaufnahmen migrierender Zellverbände. Dazu wurde ein statistisches Modell entwickelt, welches die Segmentierung und Verfolgung von Zellen in Bildsequenzen ermöglicht. Im vorliegenden Beitrag stellen wir dieses Modell vor, diskutieren die sich daraus ergebenden Lern- und Erkennungsalgorithmen und präsentieren erste Resultate. / Mechanical loads change the function and morphology of nearly every cell. We are particularly interested in the effects of mechanical loads on the endothelial cells which line the inner surface of blood vessels and control the exchange of water and solutes between blood and tissue (barrier function). These cells are exposed permanently to mechanical forces from the blood stream, which induces changes not only in cell morphology but also in function. We have developed an experimental setup which allows the endothelial barrier function to be measured under defined flow conditions. We have demonstrated for the first time that laminar shear stress enhances the endothelial barrier function, and thus a possible explanation for the anti-arteriosclerotic effect. Importantly, our setup can also be used to dynamically test the adhesion of cells on biomaterials.

Microvascular transport is strongly influenced by the nonuniform partitioning of red blood cells at diverging microvessel bifurcations, where blood flows from one mother vessel into two daughter vessels. In such bifurcations, the volume fractions of red blood cells in the blood entering each daughter vessel typically differ significantly from the volume fraction in the mother vessel. This phenomenon is caused, to a first approximation, by nonuniform distribution of red blood cells in the cross-section of the mother vessel and the tendency of red blood cells to follow background fluid streamlines. In smaller vessels, however, red blood cell trajectories can deviate significantly from fluid streamlines. In this dissertation, the mechanical reasons for these deviations and their contributions to nonuniform partitioning are analyzed.A two-dimensional model is used to simulate the motion and deformation of flexible particles as they travel alone through a diverging microvessel bifurcation. Deviations of particle trajectories from background fluid streamlines result from migration towards the mother vessel centerline upstream of the bifurcation and flow perturbations caused by cell obstruction in the bifurcation region. Cell migration, which arises because of flexibility, causes more nonuniform partitioning while cell obstruction causes more uniform partitioning. Bifurcations with differently sized daughter vessels experience, on average, a higher red blood cell flux into the smaller branch. Partitioning is unaffected by daughter branching angles.The motion of two interacting cells is also considered. In diverging bifurcations several types of interactions were found, in which the presence of a nearby cell causes a cell to enter a different branch than it would have otherwise. The net effect of these interactions is to cause more uniform partitioning. In wall-bounded linear shear flow, a two-dimensional swapping interaction was identified, in which two cells on different background fluid streamlines approach each other, slowly move onto their partner's streamline, and then move away from each other.The simulations produced by this two-dimensional model provide insight into the effects of red blood cell deformability, bifurcation geometry and volume fraction of red blood cells on red blood cell partitioning and on the resultant distribution and transport of materials in the microvasculature.

A numerical model that predicts high temperature pressure vessel rupture was developed. The finite element method of analysis was used to determine the effects that various parameters had on pressure vessel failure. The work was concerned with 500, 1000 and 33000 US gallon pressure vessels made of SA 455 steel. Experimental pressure vessel fire tests have shown that vessel rupture in a fully engulfing fire can occur in less than 30 minutes. This experimental work was used both to validate the numerical results as well as to provide important vessel temperature distribution information. Due to the fact that SA 455 steel is not meant for high temperature applications, there was little published high temperature material data. Therefore, elevated temperature tensile tests and creep rupture tests were performed to measure needed material properties. Creep and creep damage constants were calculated from SA 455 steel’s creep rupture data. The Kachanov One-State Variable technique and the MPC Omega method were the creep damage techniques chosen to predict SA 455 steel’s high temperature time-dependent behaviour. The specimens used in the mechanical testing were modeled to numerically predict the creep rupture behaviour measured in the lab. An extensive comparison between the experimental and numerical uniaxial creep rupture results revealed that both techniques could adequately predict failure times at all tested conditions; however, the MPC Omega method was generally more accurate at predicting creep failure strains. The comparison also showed that the MPC Omega method was more numerically stable than the One-State Variable technique when analyzing SA 455 steel’s creep rupture. The creep models were modified to account for multiaxial states of stress and were used to analyze the high temperature failure of pressure vessels. The various parameters considered included pressure vessel dimensions, fire type (fully engulfing or local impingement), peak wall temperature and internal pressure. The objective of these analyses was to gain a better understanding of the structural failure of pressure vessels exposed to various accidental fire conditions. The numerical results of rupture time and geometry of failure region were shown to agree with experimental fire tests. From the fully engulfing fire numerical analyses, it was shown that pressure vessels with a smaller length to diameter ratio and a larger thickness to diameter ratio were inherently safer. It was also shown that as the heated area was reduced, the failure time increased for the same internal pressure and peak wall temperature. Therefore, fully engulfing fires produced more structurally unstable conditions in pressure vessels then local fire impingements. / Thesis (Master, Mechanical and Materials Engineering) -- Queen's University, 2008-07-04 10:55:32.008

No description available.

A proposed hybrid electric marine vehicle was modeled in MATLAB Simulink and SimPowerSystems. Models for each of the individual propulsion components were developed and incorporated into a complete hybrid electric propulsion model. A vessel resistance model was created to support vessel performance and energy requirement evaluation. The model incorporates data based on the ship principal parameters and hull form. A rule-based supervisory controller for the proposed vessel was constructed. It is an amalgamation of control strategies of three vehicle architectures: electric vehicle, fuel cell electric vehicle, and hybrid electric vehicle (HEV). The complete model of the hybrid electric propulsion, control, and resistance subsystems was simulated on a dSPACE hardware-in-the-loop platform. For each simulation, the energy storage system (ESS) state of charge, station keeping/cruising mode, HEV assist, Beaufort number, current speed, true wind angle, and hotel load were specified. From the simulations, it was demonstrated that using a 30% ESS assisted HEV mode results in reduced emissions and fuel consumption as compared to a conventional vessel powertrain mode, supporting the case for plug-in hybrid electric vessels. A larger capacity ESS has the potential to reduce emissions and fuel consumption further, depending on ship usage. The basic rule-based supervisory controller proved functional for facilitating adequate power flows; however, further development is needed to improve efficiency and the mode selection process. / Graduate / 0548

In this work a cooling system connected to a reactor pressure vessel has been studied using the CFD method for the purpose of investigating the strengths and shortcomings of using CFD as a tool in similar fluid flow problems within nuclear power plants. The cooling system is used to transport water of 288K (15°C) into a nuclear reactor vessel filled with water of about 555K (282°C) during certain operating scenarios. After the system has been used, the warm water inside the vessel will be carried into the cooling system by buoyancy forces. It was of interest to investigate how quickly the warm water moves into the cooling system and how the temperature field of the water changes over time. Using the open source CFD code OpenFOAM 2.3.x and the LES turbulence modelling method, a certain operating scenario of the cooling system was simulated. A simplified computational domain was created to represent the geometries of the downcomer region within the reactor pressure vessel and the pipe structure of the cooling system. Boundary conditions and other domain properties were chosen and motivated to represent the real scenario as good as possible. For the geometry, four computational grids of different sizes and design were generated. Three of these were generated using the ANSA pre-processing tool, and they all have the same general structure only with different cell sizes. The fourth grid was made by the OpenFOAM application snappyHexMesh, which automatically creates the volume mesh with little user input. It was found that for the case at hand, the different computational grids produced roughly the same results despite the number of cells ranging from 0,14M to 3,2M. A major difference between the simulations was the maximum size of the time steps which ranged from 0,3ms for the finest ANSA mesh to 2ms for the snappy mesh, a difference which has a large impact on the total time consumption of the simulations. Furthermore, a comparison of the CFD results was made with those of a simpler 1D thermal hydraulic code, Relap5. The difference in time consumption between the two analyses were of course large and it was found that although the CFD analysis provided more detailed information about the flow field, the cheaper 1D analysis managed to capture the important phenomena for this particular case. However, it cannot be guaranteed that the 1D analysis is sufficient for all similar flow scenarios as it may not always be able to sufficiently capture phenomena such as thermal shocks and sharp temperature gradients in the fluid. Regardless of whether the CFD method or a simpler analysis is used, conservativeness in the flow simulation results needs to be ensured. If the simplifications introduced in the computational models cannot be proved to always give conservative results, the final simulation results need to be modified to ensure conservativeness although no such modifications were made in this work.

The motivation of this study lies in the necessity for a microfocal therapy to specifically target diseased areas in vascular pathologies such as age-related macular degeneration (AMD). AMD is the most common cause of legal blindness among people over the age of 60 in developed countries. This degenerative condition affects the macula, the central region of the retina, severely impairing detailed vision and hindering everyday activities. Worldwide, 25-30 million people live with some form of AMD. Among them, ~10% suffer from the more advanced and damaging form, wet-AMD, which causes rapid and severe loss of central vision. To date, there is no cure or long-term alternative for this degenerative disease despite intensive research efforts. With recent developments in biophysical tools and experimental procedures, in this study, we demonstrate a highly-localized therapeutic option: two-photon (2-photon) photodynamic therapy (PDT) that could be advantageous for the cure of wet-AMD, either alone or in combination with recently discovered anti-angiogenic therapies. This new approach offers selective targeting of the diseased area, thus minimizing damage to the surrounding sensitive healthy eye tissues, which is a major concern with the clinically-used, standard wide-beam, one-photon (1-photon) PDT. The objective of the research was to test the feasibility of microfocal 1-photon and the inherently localized 2-photon PDT, their optimization and also to evaluate the efficacy of existing 1-photon and novel 2-photon photosensitizers. In this thesis, I illustrated the in vitro (endothelial cell monolayer) and in vivo (window chamber mouse (WCM)) models that can be used to quantitatively compare the 2-photon efficiency of photosensitizers. Using the in vitro model, I compared the 2-photon efficacy of clinically used 1-photon PDT drugs Photofrin and Visudyne, and showed that the Visudyne is an order of magnitude better 2-photon photosensitizer than Photofrin. With the WCM model, I demonstrated a novel designer 2-photon photosensitizer is 20 times more efficient than Visudyne for single vessel occlusion. I also generated the drug and light dose reciprocity curve for localized single-vessel microfocal PDT. This is a necessary step towards applying the method to the relevant ocular models of AMD, which is the next phase for this research.

Thesis (doctoral)--Lund University, 1993. / Added t.p. with thesis statement inserted.