Reflection diffuse

Cahbration with standard reflectance and transmittance samples should be routinely used for optimum results in spectrophotometry and colorimetry. Cahbration of the wavelength (32) and photometric (33) scales is also advisable. The cahbration of a white reflectance standard in terms of the perfect reflecting diffuse, T, has been discussed (34), as have diagnostic tiles for tristimulus colorimetry (35). A collaborative reference program is available on instmment performance (36). 

Sampling reflectance reflectance diffuse integrating diffuse 180°... 

The electronic approximation switch NAHE was especially developed for devices at which it is necessary to start an electrical equipment without touching. The sensor is based on the opto-electronic principle. The beam of a transmitter is reflected diffusely on a target (e.g. hands) and registered by a receiver. The switching distance of 140... 190 mm can be adjusted according io customer s specification The switching on load ls S A/230 VAC or 1 A/l20 VAC. 

Many techniques are based on this principle and can be used for the analysis of all types of samples. The spectrum obtained from reflected light is not identical to that obtained by transmittance. The spectral composition of the reflected beam depends on the variation of the refractive index of the compound with wavelength. This can lead to specular reflection, diffuse reflection or attenuated total reflection. Each device is designed to favour only one of the above. The recorded spectrum must be corrected using computer software. 

A large number of partially oxidized divalent cation salts of the bis(oxalato)platinates have been reported (see Table 2).63 Only the series Mx[Pt(C204)]-6H20 (MOP where M = Fe, Co, Ni, Zn, Mg and 0.80 < x < 0.85) has been extensively studied.68 83 For most of these salts detailed studies have been made of their crystal structures and optical reflectivity at room temperature, and the variation of superlattice reflections, diffuse X-ray scattering, thermopower and DC electrical conductivity with temperature. 

The parameter Tr is the temperature corresponding to the half-range Maxwellian distribution of the particles reflected diffusively. The temperature 7 r is related to the temperature of the reflecting surface through the thermal accommodation coefficient E, defined as... 

When a light beam passes a matter the different phenomena are observed, which are schematically illustrated in Figure 2.2. These encompass reflection, diffusion, transmission, refraction, scattering, absorption, and luminescence. 

The wall section reflects diffusely in all directions, and only a fraction of the light coming from this area reaches the detector, giving the flux onto the detector as follows ... 

Equation (8-77) expresses the diffuse radiation leaving 1 which arrives at 2 and which may contribute to a diffuse radiosity of surface 2. The factor 1 - ps represents the fraction absorbed plus the fraction reflected diffusely. The inclusion of this factor is most important because we are considering only diffuse direct exchange, and thus must leave out the specular-reflection contribution... 

To analyze specular reflections we utilize a technique presented in Refs. 12 and 13. Consider the enclosure with four long surfaces shown in Fig. 8-51. Surfaces 1, 2, and 4 reflect diffusely, while surface 3 has both a specular and a diffuse component of reflection. The dashed lines represent mirror images of the surfaces 1, 2, and 4 in surface 3. (A specular reflection produces a mirror image ) The nomenclature 2(3) designates the mirror image of surface 2 in mirror 3. 

Under nonequilibrium conditions, [Mo] will be a lower, generally unknown value varying from site to site. Treatment of data reflecting diffusion control... 

The basic definition of reflectance, as used in colorimetry, is the ratio of the light flux reflected from a material to the light flux incident on the material. Reflectance involves accounting for all of the visible radiation in the system. This is in contrast to a reflectance factor, which is defined as the ratio of the light flux reflected from a material to light flux reflected from a standard material [23], Material standards of reflectance and transmittance are difficult to obtain. Reflectance, in particular, is difficult since the primary standard of reflectance is the perfect reflecting diffuser,... 

The magnitude of the solar heating is indicated by the so-called solar constant. In space, at the radius of the earth s orbit, the solar constant is about 443 Btu/(h)(ft2) (1396 W/m2). However, solar radiation is attenuated by passage through the atmosphere it is also reflected diffusely by the atmosphere, which itself varies greatly in composition. Table 7.2 provides representative values of the solar constant for use at ground level, as well as of the apparent daytime temperature of the sky for radiation purposes. 

It is also necessary to take sky radiation into account, that is, sunlight scattered by the atmosphere and reflected diffusely and which reaches all surfaces of the tank, including those not hit by direct sunlight because they are in shadow. This diffuse radiation Gs varies greatly but is generally small, between about 2.2 Btu/(h)(ft2) (6.93 W/m2) on a clear day and 44.2 Btu/(h)(ft2) (139 W/m2) on a cloudy day. For the day as described, assume that Gs is 25 Btu/(h)(ft2). This value must be added to all surfaces, including those in shadow. 

Evaluation of the A9 s that characterize an enclosure involves solution of a system of radiation balances on the surfaces. If the assumption is made that all the zones of the enclosure are gray and emit and reflect diffusely, then the direct-exchange area ij, as evaluated for the black-surface pair A and Ap applies to emission and reflections between them. If at a surface the total leaving-flux density, emitted plus reflected, is denoted by W (and called by some the radiosity and by others the exitance), radiation balances take the form ... 

Here we allow for the possibility of diffusion control in the barrier-crossing process [cf) in contrast to the intertial rate constant (c) generally assumed for passage from activated reactants to products in the TST model [84, 87]. The activation a) or deactivation (A) rate constants may also be diffusive. The occurrence of k < 1 reflects diffusive recrossings of the system in the TS region. In the absence of diffusional bottlenecks cf = c h), k becomes unity (i.e., the TST limit). 

Figure 21 Plot of Li concentration versus distance across a large quartz porphyroclast from the Santa Catalina mylonite zone, California. Solid symbols are parallel to the c-axis open symbols are perpendicular to it. The systematic decrease in Li content towards rim is interpreted to reflect diffusive loss to an intergranular fluid that was depleted in Li. Inset shows sketch of quartz grain in thin section and analyses C and arrows indicate crystallographic orientation of c-axis (source Hervig and Peacock, 1989).

For real surfaces, some molecules reflect diffusively and some reflect specularly. In other words, a portion of the momentum of the incident molecules is lost to the wall and a typically smaller portion is retained by the reflected molecules. This coefficient depends on the fluid, the solid and the surface finish, and has been determined experimentally to be in the range 0.2-0.8. The lower limit is for exceptionally smooth surfaces, while the upper limit is typically for most practical surfaces. 

As the pathways between two large, flat plates drawn schematically in Fig. 5.67 show, the radiation emitted by plate 1 always strikes plate 2 and continues to be reflected between the plates until it has been completely absorbed. The same is true for the radiation emitted by plate 2. The heat transfer is not different from that by diffuse reflection and equation (5.169) for the heat flux holds, regardless of whether one or both walls reflect diffusely or mirrorlike. The relevant relationship (5.170) for the heat flux with N radiation shields is applied without any changes for mirrorlike reflection. It is also valid when only the shields reflect mirrorlike and the plates diffusely. 

The size of the outer area 2 is immaterial for radiative exchange. Eq. (5.173) also holds if the inner surface 1 reflects diffusely. 

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