Apparent absorption coefficient

For determination of the number of protonic sites and Lewis acid sites on the surface, the integrated absorbances of the bands at 1450 cm-i (due to pyridine chemisorbed on Lewis acid sites, L-Py) and 1490 cm i (due to both the L-Py and pyridine chemisorbed on protonic acid sites, B-Py) were used with the tangent background for all samples. The values obtained were normalized to the weight of the sample wafer. To obtain the apparent absorption coefficients of the bands, a known amount of pyridine was adsorbed on the sample, and the absorbance of each band was measured. Then, a small quantity of water which is sufficient to convert all Lewis acid sites into protonic acid sites was introduced into the IR-... 

The first feature of interest is the variation of the peak height of the 3630 cm "3 (monomer) band with temperature and with concentration. Fig. 3 shows the apparent absorption coefficient, em, of the monomer band in ethanol as a function of concentration at several temperatures. The general decrease of em with increasing concentration is, of course, the result of depletion of monomer by formation of H-bonded species. Tt should be noted that the intercepts at zero concentration vary with temperature, with the highest value coming at the lowrest temperature. We reported this effect previously [10] and attributed it to interaction between alcohol monomers and the 0014 solvent, probably similar to weak H-bonding. Others have also noted this effect [11]. 

Figure V-10 shows the apparent absorption coefficients of NO in the region 1500 to 2300 A and Fig. V-10/> shows those in the region 1100 to 1500 A. Because of the lack of resolution of the monochromator, the absorption coefficient given in Fig. V-10a is a function of the slit width and the pressure of the gas (sec Section 1-8.1 for details). The true absorption coefficient may be obtained by computation from the oscillar strength and the assumed widths of the rotational lines. According to the computation by C ieslik and Nicolct (214) the true absorption coefficient of individual...

Similarly, the apparent absorption coefficient k can be defined from the normal—hemispherical transmittance T hj, as (Pilon et al., 2011)... 

Details are given of the determination of apparent absorption coefficients and optimal sample thickness of PE, PETP, cellulose, and cyclohexane by FT-Raman analysis. A relationship was developed that permits the optimal sample thickness for FT-Raman measurements to be determined by measuring the absorbance spectrum of a sample whose thickness is known. Results are discussed in the context of scattering theory, sampling considerations, and spectral artifacts. 9 refs. 

Overend [16] has pointed out that pressure-induced absorption can affect the apparent absorption coefficient value. The effect is attributed to intermolecular interaction. It is manifested in the slow rise of the apparent absorption coefficioit B as the pressure is increased. The phenomenon is clearly shown in Fig. 1.3. If such effects are present, the pressure-induced absorption has to be eliminated. This is achieved by extrapolating the linear part of the curve to zero pressure of the external gas for each B value determined. 

This is an important system in chemical processing. The effect of apparent density (liquid plus gas) as the fluid mixture enters the impeller is quite pronounced on the system horsepo ver. The horsepower falls off with increased gas flow which may lead to the danger of underpowering the unit. The absorption coefficient is a func-... 

It will be apparent that there is a relationship between the absorbance A, the transmittance T, and the molar absorption coefficient, since ... 

In our own studies to establish an in-house correlation between Caco-2 permeability and extent of drug absorption in humans, a set of 25 model drugs was used (Table 5.1). The importance of concentration and pH conditions were investigated and transport was studied both in apical to basolateral (absorptive) and basolateral to apical (secretory) directions. The apparent permeability coefficients were determined at concentrations of 10, 50, and 500 pM, and at two different settings of apical/basolateral pH values 6.5/7.4 and 7.4/7.4. The marker compounds represented a good diversity in molecular structure and transport properties and covered a range of low (<20%), moderate (20-80%) and high (>80%) extent of absorption in humans (Tab. 5.1). 

Fig. 14. The 1-H line at 6 K in n+ GaAsiSi implanted with a 500 nA current of 190 keV protons. The spectral resolution is 0.4 cm 1, (a) as implanted, (b) after 20 min. annealing at 200°C. (c) after additional 20 min. annealing at 400°C. The apparent increase of the absorption coefficient in (c) is due to the diffusion of hydrogen throughout the Si-doped layer. B. Pajot et al., Mat. Res. Soc. Symp. Proc, 104, 345 (1988). Materials Research Society.

Because phytate intakes were essentially constant, but calcium intake varied with caloric needs, a range of phytate/calcium molar ratios resulted with each phytate level. The correlation coefficient for apparent absorption and dietary phytate/zinc molar ratio was 0.62, P<0.01. The equation of the regression line was y =... 

Figure 10.2 Apparent permeability coefficients (Papp) observed in vitro across Calu-3 ( ) [62] and 16HBE14o- (o) [72] cell layers vs. in vivo rate constants (Ka) determined for absorption from the rat lung after intratracheal delivery of various molecules.

The exact absorption threshold of the absorption spectra was determined from the intercept of (crhv)2 versus hv plots (where absorption coefficient) for the direct band gap and was found to be 2.82-2.86 eV regardless of size. From a relationship between Eg and particle size of Agl after Meisel et al. (36), we found that the size of these particles was 6-7 nm. For the smallest particles, sample I, there is no peak in the spectra. Other than this finding, there is no apparent quantum confinement effect such as peak shift in the sample whose sizes are larger than 5 nm. 

It is apparent that Cr(C2C>4)3 3, m-Cr(OH2)2(0204)2 , and Cr(0H2)4C2044 react smoothly with cerium(IV) in acidic-sulfate media, 1 mole of oxalate being oxidized for each 2 moles of cerium(IV) consumed. The observations made are consistent with the view that the three reactions proceed, at least initially, according to the stoichiometries represented by the respective Reactions 3,1, and 2. The initial absorbances of reactant solutions (values obtained by extrapolation of measured absorbances to zero time) agree well with the values calculated, on the basis of Beer s law, from the absorptivity coefficients of the components. Further, as the reactions in 1.83Af sulfuric acid proceed, the absorbances of the solutions move toward the values expected for the assumed products at rates which demonstrate the reactions are first order in cerium(IV) and complex—see, for example, Figure 2. We thus find no indication that reaction intermediates contribute measurably to the absorbances of reactant solutions, or that reaction conditions cause the rapid equilibration of any of the oxalato complexes with other species... 

Predissociation is apparent below 3750 A. The absorption coefficients in the vacuum ultraviolet region 1300 to 1840 A have recently been measured by Basco and Morse (70). This is shown in Fig. VI 17. 

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