Nitinol Embolic Protection Filters: Design Investigation by Finite Element Analysis

The widespread acceptance of carotid artery stenting (CAS) to treat carotid artery stenosis and its effectiveness compared with surgical counterpart, carotid endarterectomy (CEA), is still a matter of debate. Transient or permanent neurological deficits may develop in patients undergoing CAS due to distal embolization or hemodynamic changes. Design, development, and usage of embolic protection devices (EPDs), such as embolic protection filters, appear to have a significant impact on the success of CAS. Unfortunately, some drawbacks, such as filtering failure, inability to cross tortuous high-grade stenoses, malpositioning and vessel injury, still remain and require design improvement. Currently, many different designs of such devices are available on the rapidly growing dedicated market. In spite of such a growing commercial interest, there is a significant need for design tools as well as for careful engineering investigations and design analyses of such nitinol devices. The present study aims to investigate the embolic protection filter design by finite element analysis. We first developed a parametrical computer-aided design model of an embolic filter based on micro-CT scans of the Angioguard? XP (Cordis Endovascular, FL) EPD by means of the open source pyFormex software. Subsequently, we used the finite element method to simulate the deployment of the nitinol filter as it exits the delivery sheath. Comparison of the simulations with micro-CT images of the real device exiting the catheter showed excellent correspondence with our simulations. Finally, we evaluated circumferential basket-vessel wall apposition of a 4 mm size filter in a straight vessel of different sizes and shape. We conclude that the proposed methodology offers a useful tool to evaluate and to compare current or new designs of EPDs. Further simulations will investigate vessel wall apposition in a realistic tortuous anatomy.     

Elastic buckling analysis of pultruded FRP portal frames having semi-rigid connections

Presented in this paper are results for the elastic instability of Pultruded Fibre Reinforced Polymer (PFRP) portal frames with semi-rigid connections. The kinematical model used is based on a second-order displacement field, accounting for the shear strain influence on both non-uniform bending and torsion. A two-node locking-free finite element with seven degrees of freedom per node is adopted. Joint flexibility at member ends is included by means of a simple manipulation of the stiffness matrix to the finite element, such that the influence of joint behaviour on membrane, shear, bending and torsion deformations, as well as to cross-section warping, can easily be taken into account. Numerical examples are reported and discussed to illustrate the influence on elastic buckling loads of in-plane and out-of-plane moment-rotation behaviour of joints, as well as the role played by the base warping restraint and deformable lateral bracings.     

Enhanced electrical conductivities of N-doped carbon nanotubes by controlled heat treatment

The thermal stability of nitrogen (N) functionalities on the sidewalls of N-doped multi-walled carbon nanotubes was investigated at temperatures ranging between 1000 °C and 2000 °C. The structural stability of the doped tubes was then correlated with the electrical conductivity both at the bulk and at the individual tube levels. When as-grown tubes were thermally treated at 1000 °C, we observed a very significant decrease in the electrical resistance of the individual nanotubes, from 54 kΩ to 0.5 kΩ, which is attributed to a low N doping level (e.g. 0.78 at% N). We noted that pyridine-type N was first decomposed whereas the substitutional N was stable up to 1500 °C. For nanotubes heat treated to 1800 °C and 2000 °C, the tubes exhibited an improved degree of crystallinity which was confirmed by both the low R value (I(D)/I(G)) in the Raman spectra and the presence of straight graphitic planes observed in TEM images. However, N atoms were not detected in these tubes and caused an increase in their electrical resistivity and resistance. These partially annealed doped tubes with enhanced electrical conductivities could be used in the fabrication of robust and electrically conducting composites, and these results could be extrapolated to N-doped graphene and other nanocarbons.     

Compression and decompression of images with discrete fuzzy transforms

In foregoing papers we have used the compression/decompression method of images based on the concept of discrete fuzzy transform (and its inverse) of a function f defined on a real interval with respect to the fuzzy sets A₁,…,A_n forming a fuzzy partition of such interval. Here we make a detailed experimental comparison with the similar method based on the fuzzy transforms F^↑ and F^↓ of f defined via a continuous triangular norm and its corresponding residuum, respectively. We consider some images of sizes 256 × 256 (pixels) extracted from the well-known database Corel Galery (Arizona Directory). By using the same compression rate in both methods, we have that the PSNR (Peak Signal to Noise Ratio) obtained with the discrete fuzzy transform (and its inverse) of f is more higher than the PSNR determined with the operators F^↑ and F^↓ defined via the usual Lukasiewicz, product and minimum triangular norms. Moreover, we compare our results with the classical JPEG method for values of compression rate approximately equal to those used in the previous methods.