Surfaces diffuse, grey

The emissivity of a material is defined as the ratio of the radiation per unit area emitted from a real or from a grey surface (one for which the emissitivity is independent of wavelength) to that emitted by a black body at the same temperature. Emissivities of real materials are always less than unity and they depend on the type, condition and roughness of the material, and possibly on the wavelength and direction of the emitted radiation as well. For diffuse surfaces where emissivities are independent of direction, the emissivity, which represents an average over all directions, is known as the hemispherical emissivity. For a particular wavelength X this is given by ... 

The simple hopping mechanism, however, is not the only possible way for atoms to move on Cu(100). Figure 6.11 illustrates another possible diffusion process known as an exchange mechanism. In this mechanism, the adatom (shown in dark grey), replaces an atom that is initially a surface atom (shown in light grey) while the surface atom pops up onto the surface,... 

Figure 6.13 Schematic illustration of a lattice model for diffusion of Ag atoms on Pd doped Cu(100). The diagrams on the right show the fourfold surface sites in terms of the four surface atoms defining the site. The section of the surface shown on the left includes two well separated Pd atoms in the surface. The Pd atoms are located at the centers of the two grey squares in the diagram on the left.

After severe viral hepatitis had been overcome, we were able to use photolaparoscopy in many cases to document extensive parenchymal losses, particularly in the area of the left liver lobe. We found not only (1.) diffusely distributed scarred retractions and defects in the connective tissue on the liver surface, but also (2.) circumscribed, relatively clearly defined grey-white and sunken scar plates, and even (i.) a largely dystrophic loss of the left liver lobe. (s. figs. 21.10 22.15, 22.16)... 

When x = X(T), (diffuse and grey emitting surface), it holds that... 

Surfaces with low emissivities often exhibit approximately mirrorlike or specular reflection rather than diffuse reflection. We want to investigate how the assumption of mirrorlike reflection affects the heat transfer. The assumptions regarding the emission of diffuse and grey radiation remain unaltered. Grey Lambert radiators with mirrorlike reflection are therefore assumed. 

Fig. 13 Photo-induced processes occurring during photovoltaic energy conversion at the surface of the nanocrystalline titania films, 1 sensitizer (S) excitation by light, 2 radiative and nonradiative deactivation of the sensitizer, 3 electron injection in the conduction band followed by electron trapping and diffusion to the particle surface, 4 recapture of the conduction band electron by the oxidized sensitizer (S+), 5 recombination of the conduction band electrons with the oxidized form of the redox couple regenerating the sensitizer and transporting the positive charge to the counterelectrode. Grey spheres, titania nanoparticles, red dots, sensitizer, green and blue dots oxidized and reduced form of the redox couple. See Color Plates...

Given that the two redox reactions are opposite, the average concentration for each ion in the electrolyte remains equal to the initial value. As illustrated in figure A.26, this means that the average concentration value is found at the exact middle of the cell, at x= LI2. The grey surfaces have different areas because they no longer represent the amounts of substance consumed between two specific moments in time. This disparity observed at steady state is explained by the fact that Fe and Fe ions do not take the same time to reach steady state, because their diffusion coefficients are different. 

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