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Enciclopedia Omnia Torrent 3




2005 . Construction and Design and The. But after the collapse of the. The Game. Category:Encyclopedias of education Category:Science and technology in Germany Category:German educational websites Category:Encyclopedias of scienceIn a paper recently published in Science, the University of Bern's Norbert Illies and his colleagues describe the "first observation of wake-induced directional propagation of light," an effect that is especially relevant for applications in biomedical imaging. These researchers, in collaboration with the University of Zurich and Harvard University, successfully demonstrated that the light scattered from the moving particles in the fluid around the particles---which is called the "forward scattered" light---has the ability to propagate upstream, downstream and in an opposite direction with respect to the direction of the particle motion. This phenomenon is commonly known as the "scattering anisotropy." "With this result we are able to describe this as a'scattering wake effect'," explains Illies. He adds: "In my opinion, this effect is interesting in two respects. On the one hand, it is a real experimentally verifiable observation. On the other hand, this 'wake' effect is not explained by standard theoretical models." Illies says that the anisotropy effect is an extreme form of the well-known principle of Mie scattering. The main idea of Mie scattering is that a medium, which scatters light, is characterized by the so-called "scattering efficiency." The greater the efficiency, the stronger the scattering. One of the main effects in the scattering of light by particles is thus the change in the efficiency. This is known as the "diffraction efficiency." "The diffraction efficiency can also be described as a measure of the intensity change of light caused by a scattering particle," explains Illies. In this case, the light-scattering medium is no longer only the particle itself, but also the surrounding fluid. The direct-diffraction efficiency of light, which is a measure of the probability that a light wave is scattered by the particles, is not altered by the fluid flow. However, the scattering-anisotropy effect changes the direct-diffraction efficiency into a direction-dependent one, meaning that only the light which is scattered along the direction of motion of the particle (see illustration on the right) can be detected. In their paper, Illies and colleagues describe a unique experimental situation which allowed them to observe the scatter-anis





Enciclopedia Omnia Torrent 3

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