Using wastewater and high-rate algal ponds for nutrient removal and the production of bioenergy and biofuels.

This paper projects a positive outcome for large-scale algal biofuel and energy production when wastewater treatment is the primary goal. Such a view arises partly from a recent change in emphasis in wastewater treatment technology, from simply oxidising the organic matter in the waste (i.e.

Stress and strain behaviour modelling of the carotid bifurcation.

Background: The aim of this study is to investigate the biomechanical stress and strain behaviour within the wall of the artery and its influence on plaque formation and rupture using computational fluid dynamics (CFD).

Methods: A three-dimensional finite-element model of the carotid bifurcation was generated to analyse the wall stress and strain behaviour. Both single-layer and multilayer models were created and structural analysis was compared between these two types of models.

Development of optimized vascular fractal tree models using level set distance function.

Using the concepts of fractal scaling and constrained constructive optimization (CCO), a branching tree model, which has physiologically meaningful geometric properties, can be constructed. A vascular branching tree model created in this way, although statistically correct in representing the vascular physiology, still does not possess a physiological correct arrangement of the major arteries. A distance-function based technique for "staged growth" of vascular models has been developed in this work to address this issue.

Experimental measurement and mathematical modeling of pulsatile forces on a symmetric, bifurcated endoluminal stent graft model.

The objective of this study was to measure the pulsatile forces acting on a symmetric, bifurcated endoluminal stent graft to validate a computational fluid dynamics (CFD) and analytic model so that they can be used for various graft dimensions. We used a load cell to measure the force owing to the movement of an acrylic model of a bifurcated stent graft under pulsatile flow. This was then simulated with a CFD and analytic model.

Type II endoleaks: when is intervention indicated and what is the index of suspicion for types I or III?

One of the principal reasons for failure of endovascular aneurysm repair (EVAR) is the occurrence of endoleaks, which regardless of size or type can transmit systemic pressure to the aneurysm sac. There is little debate that type I endoleaks (poor proximal or distal sealing) are associated with continued risk of aneurysm rupture and require treatment. Similarly, with type III endoleak, there is agreement that the defect in the device needs to be addressed; however, what to do with type II endoleaks and their effect on long-term outcome are not so clear.

Dynamics of pulsatile flow in fractal models of vascular branching networks.

Efficient regulation of blood flow is critically important to the normal function of many organs, especially the brain. To investigate the circulation of blood in complex, multi-branching vascular networks, a computer model consisting of a virtual fractal model of the vasculature and a mathematical model describing the transport of blood has been developed. Although limited by some constraints, in particular, the use of simplistic, uniformly distributed model for cerebral vasculature and the omission of anastomosis, the proposed computer model was found to provide insights into blood circulation in the cerebral vascular branching network plus the physiological and pathological factors which may affect its functionality.

Modeling of antegrade and retrograde flow into a branch artery of the aorta: implications for endovascular stent-grafting and extra-anatomical visceral bypass.

Purpose: To compare antegrade and retrograde flow characteristics in a branch of a conduit under typical pulsatile pressure and flows, seeking an answer to the question: "Does it matter whether inflow to a branch vessel is antegrade or retrograde?"

Methods: A model was built to simulate an abdominal aorta with a branch designed to approximate a typical renal artery. Experiments were conducted to measure the flow rates from 40- and 200-mm-long inflow conduit tubes simulating a branch with antegrade and retrograde inflow configurations. For the base case with a flush origin of the branch, the pressure difference between the main conduit and branch vessel was adjusted so that the average branch flow rate was 1.

Movement and dislocation of modular stent-grafts due to pulsatile flow and the pressure difference between the stent-graft and the aneurysm sac.

Purpose: To investigate the stability and movement of modular aortic stent-grafts subjected to oscillating forces from pulsatile blood flow, with particular reference to the thoracic aorta.

Methods: Analytical mathematical modeling was used to understand the forces on modular grafts. In a benchtop experiment, a transparent acrylic box was filled with water to mimic an aneurysm.

Experimental force measurements on a bifurcated endoluminal stent graft model: comparison with theory.

The goal of this study was to experimentally validate a steady-state mathematical model, which can be used to compute the forces acting on a bifurcated endoluminal stent graft. To accomplish this task, an acrylic model of a bifurcated graft was used for the force measurements. The graft model was connected to the inlet piping with a flexible rubber membrane that allowed the graft model to move.

Suprarenal fixation: effect on blood flow of an endoluminal stent wire across an arterial orifice.

Purpose: To investigate what effect, if any, the presence of a stent wire in front of a renal artery has on the volume flow rate of blood through the renal artery.

Methods: Experimental, numerical, and analytical modeling methods were used to test 4 separate stent wire configurations: a stent wire across the center of an artery orifice, an off-center wire placed at one-quarter the arterial diameter, a V-shaped wire with its vertex at the center, and 2 stent wires at one-third-diameter spacing.

Results: For all the configurations studied, the presence of stent wires has a minimal effect on the blood flow rate into an artery of >/=3-mm diameter, with most flow rates decreasing by around 1%.

Measurement of particle motions within tumbling granular flows.

Flowing granular materials are complex, industrially important, and scientifically provocative. In this paper we report measurements of granular transport in 3-dimensional tumbling containers. We use magnetic resonance imaging techniques for direct tracking of particles and measure the interior flows of granular materials.

Analytical modeling and numerical simulation of forces in an endoluminal graft.

Purpose: To utilize mathematical analysis and computational fluid dynamics (CFD) to investigate the forces acting within the pressurized aorta and upon a stent-graft and how these forces may affect the ongoing performance of the stent-graft.

Methods: Analytical force balance analysis and CFD simulations using the Fluent code were used to mimic blood flow through a bifurcated stent-graft in a person at rest. Steady-state blood flow was assumed in which the inlet pressure approximated the mean blood pressure (100 mm Hg) and the blood flow velocity was an approximation of the peak systolic flow rate (0.