A torsional oscillator has been used to study the flow of liquid 4He through silica aerogel. The tortuosity and dissipation of the flow in the fractal aerogel environment has been measured, for both capillary condensed films and a fully saturated cell. The scaling of tortuosity as a function of filling fraction has been investigated. We compare the results of our 88%-porous aerogel to a 92%-por...

We propose a robust and fully automatic method for the analysis of vessel tortuosity. Our method does not rely on pre-segmentation of vessels, but instead acts directly on retinal image data. The method is based on theory of best-fit exponential curves in the roto-translation group SE(2). We lift 2D images to 3D functions called orientation scores by including an orientation dimension in the do...

Prey animals use different strategies to avoid detection by predators and to flee once detected. Key issues are what aspects of movement prey change in response to predation risk and how differences in habitat affect escape movements. We answer these questions for snowshoe hares (Lepus americanus) in Montana, using an experimental manipulation and habitats for which annual mortality rates varie...

Physical characteristics critical to chromatography including geometric porosity and tortuosity within the packed column were analysed based upon three dimensional reconstructions of bed structure in-situ. Image acquisition was performed using two X-ray computed tomography systems, with optimisation of column imaging performed for each sample in order to produce three dimensional representation...

BACKGROUND Coronary tortuosity (CT) is a common coronary angiographic finding. Whether CT leads to an apparent reduction in coronary pressure distal to the tortuous segment of the coronary artery is still unknown. The purpose of this study is to determine the impact of CT on coronary pressure distribution by numerical simulation. METHODS 21 idealized models were created to investigate the inf...

TRANSVERSE ENLARGEMENT of vessels is well recognized' and is known to result in aneurysmal formation. Most often this condition coexists with arteriosclerotic degeneration of the aorta or the major arteries.2-4 Of equal importance and more frequently recognized is the clinical entity of elongation and tortuosity of the aorta and the major arteries, secondary to degenerative changes of the blood...

TRANSVERSE ENLARGEMENT of vessels is well recognized' and is known to result in aneurysmal formation. Most often this condition coexists with arteriosclerotic degeneration of the aorta or the major arteries.2-4 Of equal importance and more frequently recognized is the clinical entity of elongation and tortuosity of the aorta and the major arteries, secondary to degenerative changes of the blood...

It is commonly assumeda, 7,9 that the solution to the diffusion equation with point source, derived from the equivalent heat problem s , describes ion migration in the brain. We show both theoretically and experimentally that the above solution must be generalized for iontophoresis of ions which are confined to the extracellular space of the brain. We further show that K ÷ behaves anomalously a...

BACKGROUND AND AIMS Root soil penetration and path optimization are fundamental for root development in soil. We describe the influence of soil strength on root elongation rate and diameter, response to gravity, and root-structure tortuosity, estimated by average curvature of primary maize roots. METHODS Soils with different densities (1·5, 1·6, 1·7 g cm-3), particle sizes (sandy loam; coarse...

An ultrasonic reflectivity method is proposed for measuring porosity and tortuosity of porous materials having a rigid frame. Porosity is the relative fraction by volume of the air contained within a material. Tortuosity is a geometrical parameter which intervenes in the description of the inertial effects between the fluid filled the porous material and its structure at high frequency range. I...