Evaluation of the arterial kink point during flexion of the hip: A dynamic angiographic study in iliac endofibrosis patients.

PURPOSE: The aim of the study was to determine the flexion point's location of the ilio-femoral arterial axis and its angulation. MATERIALS AND METHODS: Thirty-seven dynamic digital subtraction angiographies were analyzed and were included in the current study. Different lengths were measured, based on specific anatomical landmarks: the origin of the external iliac artery, the inguinal ligament and the bifurcation of the femoral artery. These lengths were measured in extension and during flexion of the hip in order to determine the flexion point of the artery. RESULTS: In extension, some physiological angulations of the external iliac artery were measured. During flexion of the hip joint, the distance from the kink point to the bifurcation of the common iliac artery was respectively 82 ± 21 mm (range 48-116) on the right side and 95 ± 20 mm (range 59-132) on the left side. The distance from the kink point to the inguinal ligament was respectively 38 ± 40 mm (range 12-138) on the right side and 26 ± 23 mm (range 8-136) on the left side. The distance from the kink point to the bifurcation of the femoral artery was respectively 45 ± 29 mm (range 15-107) on the right side and 27 ± 12 mm (range 10-66) on the left side. During flexion, the angulation of the flexion point of the ilio-femoral axis was 114 ± 18° (range 81-136°). CONCLUSIONS: The flexion point was located cranially to the inguinal ligament and below the departure of the external iliac artery.

Anisotropic acoustic metafluid for underwater operation.

The paper presents a method to design and characterize mechanically robust solid acoustic metamaterials suitable for operation in dense fluids such as water. These structures, also called metafluids, behave acoustically as inertial fluids characterized by anisotropic mass densities and isotropic bulk modulus. The method is illustrated through the design and experimental characterization of a metafluid consisting of perforated steel plates held together by rubber coated magnetic spacers. The spacers are very effective at reducing the effective shear modulus of the structure, and therefore effective at minimizing the ensuing coupling between the shear and pressure waves inside the solid effective medium. Inertial anisotropy together with fluid-like acoustic behavior are key properties that bring transformation acoustics in dense fluids closer to reality.

Highly anisotropic elements for acoustic pentamode applications.

Pentamode metamaterials are a class of acoustic metafluids that are characterized by a divergence free modified stress tensor. Such materials have an unconventional anisotropic stiffness and isotropic mass density, which allow themselves to mimic other fluid domains. Here we present a pentamode design formed by an oblique honeycomb lattice and producing customizable anisotropic properties. It is shown that anisotropy in the stiffness can exceed 3 orders of magnitude, and that it can be realistically tailored for transformation acoustic applications.

Experimental Demonstration of Underwater Acoustic Scattering Cancellation.

We explore an acoustic scattering cancellation shell for buoyant hollow cylinders submersed in a water background. A thin, low-shear, elastic coating is used to cancel the monopole scattering from an air-filled, neutrally buoyant steel shell for all frequencies where the wavelength is larger than the object diameter. By design, the uncoated shell also has an effective density close to the aqueous background, independently canceling its dipole scattering. Due to the significantly reduced monopole and dipole scattering, the compliant coating results in a hollow cylindrical inclusion that is simultaneously impedance and sound speed matched to the water background. We demonstrate the proposed cancellation method with a specific case, using an array of hollow steel cylinders coated with thin silicone rubber shells. These experimental results are matched to finite element modeling predictions, confirming the scattering reduction. Additional calculations explore the optimization of the silicone coating properties. Using this approach, it is found that scattering cross-sections can be reduced by 20 dB for all wavelengths up to k0a = 0.85.

Investigations of human EEG response to viewing fractal patterns.

Owing to the prevalence of fractal patterns in natural scenery and their growing impact on cultures around the world, fractals constitute a common feature of our daily visual experiences, raising an important question: what responses do fractals induce in the observer? We monitored subjects' EEG while they were viewing fractals with different fractal dimensions, and the results show that significant effects could be found in the EEG even by employing relatively simple silhouette images. Patterns with a fractal dimension of 1.3 elicited the most interesting EEG, with the highest alpha in the frontal lobes but also the highest beta in the parietal area, pointing to a complicated interplay between different parts of the brain when experiencing this pattern.