Flow invariants in a channel obstructed by a line of inclined rods.

An experiment is conducted in a rectangular channel obstructed by a transverse line of four inclined cylindrical rods. The pressure on the surface of a central rod and the pressure drop through the channel are measured varying the inclination angle of the rods. Three assemblies of rods with different diameters are tested. The measurements were analyzed applying momentum conservation principles and semi-empirical considerations. Several invariant dimensionless groups of parameters relating the pressure at key locations of the system with characteristic dimensions of the rods are produced. It was found that the independence principle holds for most of the Euler numbers characterizing the pressure at different locations, that is, the group is independent of the inclination angle provided that the inlet velocity projection normal to the rods is used to non-dimensionalize the pressure. The resulting semi-empirical correlations can be useful for designing similar hydraulic units.

Tuning a lattice-Boltzmann model for applications in computational hemodynamics.

The interest in lattice-Boltzmann models in the computational hemodynamics realm has increased in recent years. In this context, the correct choice of numerical parameters for the appropriate simulation of blood flows in major arteries is a crucial aspect. For this reason, we present three parameter-tuning strategies that allow us to reproduce correctly the pulsatile time-dependent flow of an incompressible fluid under physiological regimes. These strategies are studied for a model based on a single-relaxation-time approach in combination with second order boundary conditions for both velocity and pressure, and proper equilibrium distributions that take care of the incompressible behavior exhibited by the fluid. The implementation is validated with the three-dimensional Womersley flow benchmark. As well, the simulation of blood flows in a curved artery, in an anastomosed vessel, in a patient specific vertebral artery and in an aneurysmal region are presented in order to show how the method and the setting of the numerical parameters are applied to different realistic hemodynamics problems.

Correcting magnetic probe perturbations on current density measurements of current carrying plasmas.

A method to infer the current density distribution in the current sheath of a plasma focus discharge from a magnetic probe is formulated and then applied to experimental data obtained in a 1.1 kJ device. Distortions on the magnetic probe signal caused by current redistribution and by a time-dependent total discharge current are considered simultaneously, leading to an integral equation for the current density. Two distinct, easy to implement, numerical procedures are given to solve such equation. Experimental results show the coexistence of at least two maxima in the current density structure of a nitrogen sheath.

A combined region growing and deformable model method for extraction of closed surfaces in 3D CT and MRI scans.

Image segmentation of 3D medical images is a challenging problem with several still not totally solved practical issues, such as noise interference, variable object structures and image artifacts. This paper describes a hybrid 3D image segmentation method which combines region growing and deformable models to obtain accurate and topologically preserving surface structures of anatomical objects of interest. The proposed strategy starts by determining a rough but robust approximation of the objects using a region-growing algorithm. Then, the closed surface mesh that encloses the region is constructed and used as the initial geometry of a deformable model for the final refinement. This integrated strategy provides an alternative solution to one of the flaws of traditional deformable models, achieving good refinements of internal surfaces in few steps. Experimental segmentation results of complex anatomical structures on both simulated and real data from MRI scans are presented, and the method is assessed by comparing with standard reference segmentations of head MRI. The evaluation was mainly based on the average overlap measure, which was tested on the segmentation of white matter, corresponding to a simulated brain data set, showing excellent performance exceeding 90% accuracy. In addition, the algorithm was applied to the detection of anatomical head structures on two real MRI and one CT data set. The final reconstructions resulting from the deformable models produce high quality meshes suitable for 3D visualization and further numerical analysis. The obtained results show that the approach achieves high quality segmentations with low computational complexity.

[Comparison of bacteriological and immunoenzyme methods for the serum determination of sisomicin. Pharmacokinetic application in the human]. / Comparaison des méthodes bactériologique et immuno-enzymatique pour le dosage sérique de la sisomicine. Application pharmacocinétique chez l'homme.

A modification of the serum gentamicin immunoenzymatic method (Syva- Biom erieux kit) for sisomicin assay is proposed and compared to the bacteriological reference method. It shows a higher sensitivity (0.1 mg.l-1) with a shortened time of analysis (less than 1 hour) and a good reproducibility (range: 4.7% to 1.6% for concentrations between 0.5 mg.l-1 and 10 mg.l-1) but the concentrations are 15 p. cent lower as compared to the bacteriological method. A pharmacokinetic study, performed in five patients, enables us to demonstrate the praticability of this method for the adaptation of the dosage regimen in renal insufficiency.