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| + | Afghanistan, Angola, the Democratic Republic of the Congo, Liberia, Rwanda, Sierra Leone and Sudan. Arms expert and longtime Bout critic Kathi Lynn Austin said "the verdict in the Viktor Bout trial closes the book on one of the most prolific enablers of war, mass atrocities and terrorism in the post Cold War era." | ||
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| + | Waves in composites and metamaterials,giuseppe zanotti<br><br>Basic Features of a Rainbow[edit]<br><br>A rainbow is a classic example of wave propagation in inhomogeneous media. In this case the medium is water droplets and air. The basic features of a rainbow are (see Figure 1):<br><br>The occurrence of a primary and a secondary rainbow,tn pas cher. The zenith of the primary rainbow is inclined at an angle of 42 to the line joining the sun and the antisolar point. The secondary rainbow is inclined at 51 to that line.<br><br>The sky is darker inside the Alexander's band that separates the primary and the second rainbows.<br><br>The colors in the primary and the secondary rainbows are in reverse order.<br><br>The speed of water droplets in the atmosphere is negligible compared to the speed of light,christian louboutin paris. We assume that the droplets are stationary.<br><br>The droplets are sufficiently far from each other that the effect of multiple scatter can be neglected.<br><br>It suffices to use geometric optics to explain rainbows.<br><br>A quick and easy explanation of the rainbow is that each droplet acts like a prism. This is true to the extent that the refractive index of water depends on the frequency of light and hence its color. However, the prism explanation is unsatisfactory because the surface of a droplet is curved and light gets refracted by a variety of angles. The key to understanding a rainbow is the dark band.<br><br>Recall Snell's law for refraction at an interface:<br><br>where is the angle of incidence, is the angle of refraction, is the refractive index of the incident material and is the refractive index of the refractive material. For air,tn requin pas cher homme, and for water (but depends on the frequency of the light). If the incident surface is curved, the light rays will be refracted at different angles and therefore different frequencies of light might overlap (unlike in a prism which has a planar interface).<br><br>The curvature of the water droplets causes some light rays to reach the observers whereas other rays are reflected away from the observer. This creates the darker Alexander's band (see Figure 2).<br><br>Consider rays of light getting refracted by and reflected inside a spherical water droplet (see Figure 3),air max one. The impact distance is defined as the distance between a ray and the equatorial plane of the raindrop (assuming that all rays are horizontal),nike tn. From the figure we can also see that the rays form a denser cluster at a certain impact distance,tn pas cher france. The cluster of rays at which this phenomenon occurs is called the rainbow ray because the intensity of the scattered light appears to be the brightest along this ray,louboutin homme. The primary rainbow is formed from rays that undergo one reflection inside the drop. The secondary rainbow is from rays that undergo two reflections.<br><br>The scattering angle is defined as the angle between the incident and the transmitted rays. For the primary rainbow,air jordan spizike, the scattering angle is the angle between the incident rays and the rays transmitted after one internal reflection. For the secondary rainbow,jordan femme, the scattering angle is the angle after two internal reflections. A plot of the scattering angle as a function of the impact parameter is shown in Figure 4. The scattering angle reaches a peak at a value of 180 42 for the primary rainbow and at an angle of 180 51 for the secondary rainbow.<br><br>The critical angle for the primary rainbow is given when = 2. The value is 42.5 below the equatorial plane of the droplet. For the secondary rainbow, the critical angle is 50.1 above the equatorial plane of the droplet.<br><br>The Descartes theory explains some of the observed phenomena. However,tn requin nike, the size of the droplet is not included in the computation. Neither are supernumerary arcs explained. But are they really spherical? The answer depends on the size (and therefore the velocity) of the raindrops. The motion of air around the raindrop leads to low pressure regions on the sides and for small raindrops conditions similar to Stokes flow exist. There is also a region of low pressure at the top of the raindrop due to flow separation at higher Reynolds numbers. As a result a raindrop evolves from a spherical shape to a bean shaped form and finally breaks apart at sizes above 5 mm (see Figure 7).<br><br>What about the reflected light from the lower half of the raindrop?[edit]<br><br>The reflected light does play a small role in the colors seen in a rainbow. However, the effect is small compared to the intensity of light observed at the rainbow angle due to reflection inside a raindrop.<br><br>Figure 8 shows the scattering of light in an air bubble inside water. Clearly the light is scattered away from the observer and a region of high intensity is not observed. Therefore fish will not be able to see bubblebows,tn requins.相关的主题文章： | ||
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Afghanistan, Angola, the Democratic Republic of the Congo, Liberia, Rwanda, Sierra Leone and Sudan. Arms expert and longtime Bout critic Kathi Lynn Austin said "the verdict in the Viktor Bout trial closes the book on one of the most prolific enablers of war, mass atrocities and terrorism in the post Cold War era." | Afghanistan, Angola, the Democratic Republic of the Congo, Liberia, Rwanda, Sierra Leone and Sudan. Arms expert and longtime Bout critic Kathi Lynn Austin said "the verdict in the Viktor Bout trial closes the book on one of the most prolific enablers of war, mass atrocities and terrorism in the post Cold War era." | ||
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