Thickness-direction absorbance

Fig. 2.18. The thickness-direction absorbance may be obtained by tilting the sample at some angle, a, and determining the component in the z direction.

For freezing, A would be replaced by — A. Equivalently, A can be redefined as a dimensionless heat absorbed per unit mass during the phase change. Equation (235) is an exact expression for the melt thickness directly in terms of an integral of the melt temperature profile and the boundary conditions at the plate. It has the usual advantage of integral formula-... 

The X-ray depth dose distributions in a thick water absorber with large area beams are shown in Fig. 3. These distributions indicate that the attenuation is essentially exponential, and that the penetrating quality increases with the incident electron energy. Depth dose distributions for irradiating materials from opposite directions show the minimum dose in the middle of the material. The dose uniformity ratio (DUR), also known as the Dmax/Dmin dose ratio, increases with the thickness of the material, as shown in Fig. 4 (lower set of curves). For any thickness, the DUR decreases as the incident electron energy increases. 

When the press reaches bdc, the clutch must disengage the flywheel to remove the source of power. The brake then engages, holding the press ram stationary in the bdc position. Since the material shrinks in the thickness direction upon cooling, the pressure is reduced thus permitting the press ram to restock readily without excessive clutch wear on the flywheel face. Brake wear is also minimized since the plastic material acts as a shock absorber as it is contacted by the plunger. 

Attenuated total reflection (ATR) FTIR is one of the most useful tools for characterising the chemical composition and physical characteristics of polymer surfaces [53]. One useful application is the measurement of molecular orientation using polarised infrared ATR spectroscopy [54,55]. The polarised infrared ATR spectra normally include three-dimensional (e.g., machine, transverse, and thickness direction) orientational information in contrast to the polarised transmission infrared linear dichroism. In addition, band absorbance of less than 0.7 au is easily achieved, even with the strong absorption bands, because the penetration depth of ATR from sample surfaces can be adjusted to a few micrometers by changing the internal reflection element and/or the angle of incidence. If successful combination of the dynamic infrared spectroscopy and the ATR methods can be achieved, more useful dynamic orientational information can be obtained. 

Without absorbing water, these PEMs tend to be rather rigid and are poor ionic conductors. The ionic conductivity would dramatically increase with water content [78]. Therefore, ionic conductivity tests are mostly conducted in water or in water vapor with adequate related humidity. Two types of ionic conductivity for PEMs were used in-plane and through-plane conductivities. The former represents the conductivity along the membrane surface direction, and the latter refers to the conductivity across the membrane thickness direction. In addition, there are two methods for conductivity measurement two-point probe electrode and four-point probe electrode. The latter method is more accurate but the former uses a simpler device. Therefore, comparison of ionic conductivities between membranes must be of the same type and measured through the same method. The aforementioned conductivity measurements are suitable for both proton conductivity and anion conductivity. Proton conductivity (o) is calculated by the following equation [79-82] ... 

Slip casting of metal powders closely follows ceramic slip casting techniques (see Ceramics). SHp, which is a viscous Hquid containing finely divided metal particles in a stable suspension, is poured into a plaster-of-Paris mold of the shape desired. As the Hquid is absorbed by the mold, the metal particles are carried to the wall and deposited there. This occurs equally in all directions and equally for metal particles of all sizes which gives a uniformly thick layer of powder deposited at the mold wall. 

Since IR detector materials are direct bandgap materials (with no change in electron momentum required), they are very efficient absorbers (and emitters) of light - all IR photons are absorbed within the first few /rm of material. The reason that infrared detectors are 10 to 15 ptm thick is for structural and fabrication reasons, not for light absorption reasons. 

The short penetration depth of UV/blue photons is the reason that frontside CCD detectors have very poor QE at the blue end of the spectrum. The frontside of a CCD is the side upon which the polysilicon wires that control charge collection and transfer are deposited. These wires are 0.25 to 0.5 /xm thick and will absorb all UV/blue photons before these photons reach the photosensitive volume of the CCD. For good UV/blue sensitivity, a silicon detector must allow the direct penetration of photons into the photosensitive volume. This is achieved by turning the CCD over and thinning the backside until the photosensitive region (the epitaxial layer) is exposed to incoming radiation. 

Since natural Au consists solely of Au, the interface-selective enrichment technique cannot be applied in Au studies. The absorber thickness for Au is required to be large and therefore multilayered samples of Au layers/3r/ metal layers have to be prepared. The spectra for Au/Fe with varying Au-layer thickness are shown in Fig. 7.83 [437]. The results were interpreted as follows large magnetic hyperfine fields at Au sites exist only within two monolayers at the interface region, which are supposed to be induced by direct coupling with anti-ferromagnetically oriented Fe 3d atoms. 

Specular reflection IR spectroscopy has been used by Cole and coworkers to study the orientation and structure in PET films [36,37]. It has allowed characterizing directly very highly absorbing bands in thick samples, in particular the carbonyl band that can show saturation in transmission spectra for thickness as low as 2 pm. The orientation of different conformers could be determined independently. Specular reflection is normally limited to uniaxial samples because the near-normal incident light does not allow measuring Ay. However, it was shown that the orientation parameter along the ND can be indirectly determined for PET by using the ratio of specifically selected bands [38]. This approach was applied to the study of biaxially oriented PET bottles [39]. 

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