Relative specular reflectance

Typical relative specular reflectance accessories are shown in Fig. 3. 

For this modality of measurements, when collecting the dark current we take the sample out interrupting the beam path by the lack of a reflecting element and for collecting the baseline, we use a known reflectance standard mirror. No standard mirror is perfect, so to calculate the absolute specular reflection of a sample, we need to take the true reflectance curve for the standard mirror used to acquire the baseline into account. For that reason, these accessories are called relative specular reflectance accessories. 

The modulation of surface electron density at Hg implied by Eq. (10) is manifested not only through changes of surface tension, but may be indirectly observed in the change of relative specular reflectivity (McIntyre and Peck, 1972 Gottesfeld et al., 1973) with electrode potential at Hg and at other metals under conditions not restricted to liquid state surfaces. 

Chemical polishing, yielding a surface of high specular reflectivity, exploits fully optimised bright dip solutions often achieved by the further addition of phosphoric acid at the expense of the residual water. Because phosphoric acid is relatively viscous at lower temperatures (e.g. less than 40°C) it can act as diffusion layer promoter (C), but its presence increases the chemical costs considerably. 

It should be pointed out that this particular derivation is valid only for weakly absorbing systems without significant contribution from specular reflectance. In addition, the particle size of the powdered sample must be relatively small (around 1 /Am). The theory for more complicated systems has been worked out, and the equations pertaining to a wide range of possibilities are available [4]. 

The mixture of these two types of light is what meets the eye, and the ratio of these two components affects the perceived depth of color. The higher the ratio of specular reflection, then the less the apparent color depth3. Additionally, any relatively large areas of specular reflection can generate visible points of light when oriented to reflect from point sources these cause the fibers or fabrics to glitter. 

Figure 6.85 Schematic illustration of specular reflection from a flat surface and diffuse reflection from a rough surface, both relative to the average surface. Reprinted, by permission, from J. F. Shackelford, Introduction to Materials Science for Engineers, 5th ed., p. 597. Copyright 2000 by Prentice-Hall, Inc.

Specular reflection is encountered when the reflecting medium is a smooth polished surface. The angle of reflection is identical to the incident angle of the radiation beam. If the surface is IR absorbent, the relative intensity of reflection is less for wavelengths that are absorbed than for wavelengths that are not. Thus, the plot of reflectance R, defined as the fraction of reflected incident radiant energy versus the wavelength (or wavenumber) appears similar to a transmission spectrum for the sample. 

Unlike classical analytical spectroscopy performed on liquids or dilute solutions of analytes, diffuse reflectance measurement in the near-infrared must deal with a composite effect of spectroscopic absorption and scattering from the analyte and the matrix in which it is found. Differences in refractive indices of the sample material, specular reflection and observance of relatively small differences are all dealt with in this technique. 

Compared to the PAS spectra of cotton cloth, in the Specular Reflectance spectra, the signal-to-noiae is higher and any noise is low enough to show clearly the spectral features described here. Even though there are differences due to the change in sampling conditions, the spectra can be compared for a one-to-one comparison and identification of absorption bands. Mote however that in the PAS spectrum relative intensities are displayed and that the Specular Reflectance spectra show an absolute response and measurement which leads to a better possibility for quantification and a more rigorous treatment of the data. 

Exposure of a Id and a 4a treated electrode to CO. An electrode treated with Id and 4a in the aforementioned manner was placed in a 50 mL 3-neck flask containing 30 mL of 0.1 M CH2C12 solution of Bu4NPF6. CO was then bubbled into the solution for 10 min and a cyclic voltammogram was subsequently recorded. The wave assigned to Id had shifted +120 mV relative to the 4a wave. Similarly, when a lxl cm2 Au electrode treated with Id and 4a was placed in a vial and purged with CO for 10 min, specular reflectance IR indicated surface conversion of Id to 2d. 

V-UV Application Specular Reflection by Crystal Faces. If one focuses the incoming beam 70 onto a single crystal face, the specular UV-vis reflectivity (and its polarization) can be measured. The crystal is mounted on a goniometer head the orientation of the crystal axes relative to the instrumental axes must be predetermined separately on an X-ray diffractometer. 

This holds for the diffuse reflecting outer cylinder. The heat flow has decreased significantly. The ratio Q(N = 1 )/Q(N = 0) has the value 0.487/2.368 = 0.206. With a mirrorlike reflecting outer cylinder d2 is replaced by dg. This then gives Q(N = 1 )/L = —0.480W/m and Q(N = 1 )/Q(N = 0) = 0.480/1.948 = 0.246. In specular reflection of the outer cylinder, the relative decrease of the heat flow caused by the protective shield is somewhat lower than that for a diffuse reflecting outer cylinder. However, the smallest absolute value of Q/L is yielded when both the shield and the outer cylinder reflect mirrorlike. 

Specular reflectance measurements are attractive for the evaluation of the optical constants of metals and other materials, particularly in the form of films, whose properties may differ markedly from those of bulk solids. The strength of the method is the rel-... 

With newer computational tools such as finite element and boundary element methods, conduction and convection in arbitrary three-dimensional geometries can be handled in a relatively straightforward manner. Some recent efforts have been made to link the FEM method (for ease in handling complex geometries) with alternative methods to evaluate view factors in order to predict thermal processing of complex shapes with specular surface radiative properties or specular reflection [177]. 

Predicted steady-state temperatures for the rod of Fig. 18.36 are shown in Fig. 18.37, based upon specification of pure diffuse reflection, as in Fig. 18.37a, or pure specular reflection, as in Fig. 18.37. As expected, the surfaces that face the heaters are at a high temperature, while those that are exposed to the cold openings are relatively cool. Local temperature differences of up to 100 K are evident when the diffuse and specular reflectivity predictions... 

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