Diffuse opaque

Consider, for example, the arrangement in Fig. 8-61. The two diffuse opaque surfaces are separated by a specular-diffuse transmitting and reflecting plane. For this example all planes are assumed to be infinite in extent. The specular-transmitted exchange between surfaces 1 and 3 may be calculated immediately with... 

The net rate of radiation transfer between any two gray, diffuse, opaque surfaces that form an enclosure is given by... 

Approximate Geometric, Layered Model. Using geometric optics (radiation size parameter OCr, larger than about five) and the concept of view factor, the emission, transmission, and reflection of periodically arranged, diffuse, opaque particles has been modeled by Mazza et... 

Boundary conditions to Eq. (8.6) depend on the kind of the boundary. Diffuse opaque (crucible wall) ... 

For opaque materials, the reflectance p is the complement of the absorptance. The directional distribution of the reflected radiation depends on the material, its degree of roughness or grain size, and, if a metal, its state of oxidation. Polished surfaces of homogeneous materials reflect speciilarly. In contrast, the intensity of the radiation reflected from a perfectly diffuse, or Lambert, surface is independent of direction. The directional distribution of reflectance of many oxidized metals, refractoiy materials, and natural products approximates that of a perfectly diffuse reflector. A better model, adequate for many calculational purposes, is achieved by assuming that the total reflectance p is the sum of diffuse and specular components p i and p. ... 

Many inorganic solids lend themselves to study by PL, to probe their intrinsic properties and to look at impurities and defects. Such materials include alkali-halides, semiconductors, crystalline ceramics, and glasses. In opaque materials PL is particularly surface sensitive, being restricted by the optical penetration depth and carrier diffusion length to a region of 0.05 to several pm beneath the surface. 

Fig. 18 Finite element modeling of steady-state concentration profiles in the human eye[241] from a hypothetical device that releases from one side only, (a) Device releases towards the front (b) device releases towards the back. Arbitrary concentration units (scale, inset a) highest concentration marked x. Contours are shown for x-z plane and for x-y plane through the center, x-z portion of finite element mesh displayed (inset b) device (opaque to diffusion) represented by voided region. (Adapted from Ref. 244.)... 

For IR sensing, three transducer principles are standard classical transmission for (sufficiently) transparent samples, (diffuse) reflection for opaque samples, in particular solids and strongly turbid liquids and attenuated total reflection (ATR), in particular for strongly absorbing samples and fluids with varying amounts of suspended solids or gas bubbles. 

With the exception of single-crystal transmission work, most solids are too opaque to permit the conventional use of ultraviolet/visible (UV/VIS) electronic spectroscopy. As a result, such work must be performed through the use of diffuse reflection techniques [8-10]. Important work has been conducted in which UV/VIS spectroscopy has been used to study the reaction pathways of various solid state reactions. Other applications have been made in the fields of color measurement and color matching, areas which can be of considerable importance when applied to the coloring agents used in formulations. 

The Kubelka-Munk theory treats the diffuse reflectance of infinitely thick opaque layers [4], a situation achieved in practice for UV/VIS spectroscopy through the use of powder path lengths of at least several millimeters. In this instance, the Kubelka-Munk equation has the form... 

Opaque minerals like iron oxides are frequently examined in the reflectance mode - and usually give diffuse reflectance spectra. Reflectance spectra provide information about the scattering and absorption coefficients of the samples and hence their optical properties. The parameters of reflectance spectra may be described in four different ways (1) by the tristimulus values of the CIE system (see 7.3.3) (2) by the Kubelka-Munk theory and (3) by using the derivative of the reflectance or remission function (Kosmas et al., 1984 Malengreau et ak, 1994 1996 Scheinost et al. 1998) and, (4) more precisely, by band fitting (Scheinost et al. 1999). 

The coalescence of atoms into clusters may also be restricted by generating the atoms inside confined volumes of microorganized systems [87] or in porous materials [88]. The ionic precursors are included prior to irradiation. The penetration in depth of ionizing radiation permits the ion reduction in situ, even for opaque materials. The surface of solid supports, adsorbing metal ions, is a strong limit to the diffusion of the nascent atoms formed by irradiation at room temperature, so that quite small clusters can survive. 

The lowering of the conductivity is not attributed to a change in the degree of ionization of the soln., but rather to the decreased mobility of the anions during the change from I to I3. At 25°, the mobility of the T-ion is 76 5 and of the I3 -ion, 410. The diffusion constant of I3 -ions, according to E. Brunner, is 0 9 per sq. cm. per day at 20°, that is, approximately the same as that of free iodine. When iodine dissolves in potassium iodide soln., W. C. Bray and G. M. J. McKay calculate that there is an expansion of 0 2376 c.c. per gram of iodine or 60 31 c.c. per mol. of iodine per litre of soln. The colour of dil. soln. of potassium tri-iodide is yellowish-brown which with increased cone, becomes very dark blue, almost opaque, in thin layers dark red. 

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