Influence of vertebrae and intervertebral disc on stresses in abdominal aortic aneurysms

Computational modelling of stress-strain states in Abdominal Aortic Aneurysms (AAAs) has become an important tool in assessment of their rupture risk in the last decades. As its application potential in clinical practice is increasing with every additional influencing factor considered in the model, many factors have been analysed already. Up-to-date models are based on patient-specific AAA geometry obtained typically from CT-A imaging under a known level of blood pressure. Mean arterial pressure (MAP) is used to create their unloaded geometry [1] which (with other additional features such as residual stresses) may increase the credibility of the results. Material behaviour is also a very important feature to be described correctly. Large deformations of the arterial wall and intraluminal thrombus (ILT) are mostly described using constitutive models based on mean population data gathered from mechanical testing of patient-specific specimens [3]. ILT can be taken into consideration not only for his poroelastic structure reducing the blood pressure on the AAA wall but also for its significant load-bearing contribution. Different mechanical properties across the ILT thickness. Can be considered as a significant feature too. ILT with large thickness also reduces oxygen supply into the AAA wall underneath and consequently changes its mechanical properties (strength)

Unification of New Zealand's local vertical datums: iterative gravimetric quasigeoid computations

New Zealand uses 13 separate local vertical datums (LVDs) based on normal-orthometric-corrected precise geodetic levelling from 12 different tide-gauges. We describe their unification using a regional gravimetric quasigeoid model and GPS-levelling data on each LVD. A novel application of iterative quasigeoid computation is used, where the LVD offsets computed from earlier models are used to apply additional gravity reductions from each LVD to that model. The solution converges after only three iterations yielding LVD offsets ranging from 0.24 m to 0.58 m with an average standard deviation of 0.08 m. The so-computed LVD offsets agree, within expected data errors, with geodetically levelled height differences at common benchmarks between adjacent LVDs. This shows that iterated quasigeoid models do have a role in vertical datum unification