Attenuation index

Attenuation Index (a ) can be defined in terms of the observed trans-mittancy, the cell length, and the concentration of total sugar solids as follows. 

In the absence of scattering, a = a and this quantity becomes independent of concentration but dependent on wave length. In the absence of absorption, a is a measure of the scattering, and is dependent on concentration and wave length. When both absorption and scattering are present, a defines the value of the attenuation index at a given concentration. 

Fig. 3.—Dependence of Attenuation Index on Concentration, Calculated at Various Values of k/s, with si = 0.1 cm.2/g.

An equation for the attenuation index can readily be obtained from the above considerations. In anticipation of a comparison with the results... 

The practical value of the attenuation index is evident from the above considerations. Because of the linear dependence, any transmittancy data on commercial sugar liquors can now be reported as attenuation indices at some reference concentration. This need not be the concentration actually used in making the measurement. It appears that either a or a can be used for this purpose. 

It is important to appreciate that particular values for the wavelength exponent, n, and the attenuation index, a, at some one wave length will characterize the entire transmittancy curve in the visible spectrum of the sugar solution. When a sugar liquor is treated with a solid adsorbent, the changes in the spectrophotometric curves in the visible spectrum are adequately defined by changes in the values of n and a (see Table I). This procedure promises to be an effective tool, both in research and in applications.31... 

The study of macromolecular adsorption on thin polymer films should also be feasible. Adsorption isotherms can be obtained on any nonfluorescing polymer that can be deposited in thin-film form on quartz. The only limitation is that the film be nonabsorbing at the excitation wavelength and exhibit minimal fluorescence. Thin films of depth d can be studied if [2ird/X] <0.1 and if the film attenuation index k is less than 0.1 (10). Thin films on quartz substrates can then be characterized by other surface analytical techniques. 

Fiber/parameter Wavelength (pm) Attenuation index, core temperature (°C)... 

Among the advanced HCC tumors, the typical expansive type of HCC is a sharply demarcated lesion that may be unifocal or multifocal, lypical features of expansive type HCC include tumor capsule and internal mosaic architecture. Most expansive HCC lesions have a well-developed fibrous capsule. The fibrous capsule is demonstrated by CT as a hypoattenuating rim which enhances in the delayed phase (Karahan et al. 2003 Ros et al. 1990). Internal mosaic architecture is characterized by components separated by thin fibrous septa. The different components may show various attenuation indexes on CT images, particularly if areas of well-differentiated tumor with different degrees of fatty metamorphosis are present. Internal septa show delayed enhancement, similar to that of the fibrous capsule (Fig. 13.9) (Yoshikawa et al. 1992). The infiltrative type HCC is characterized by an irregular and indistinct tumor-nontumor boundary. This type is demonstrated as a mainly uneven hypodense area with unclear mar-... 

In an early study, Greenleaf et al. [4] reported reconstructions of ultrasonic velocity from time-of-flight profiles. Since then there has been periodic activity in using ultrasound to determine the transmission properties attenuation or refractive index. 

A much better way would be to use phase contrast, rather than attenuation contrast, since the phase change, due to changes in index of refraction, can be up to 1000 times larger than the change in amplitude. However, phase contrast techniques require the disposal of monochromatic X-ray sources, such as synchrotrons, combined with special optics, such as double crystal monochromatics and interferometers [2]. Recently [3] it has been shown that one can also obtain phase contrast by using a polychromatic X-ray source provided the source size and detector resolution are small enough to maintain sufficient spatial coherence. 

Up to this point, we have calculated the linear response of the medium, a polarization oscillating at the frequency m of the applied field. This polarization produces its own radiation field that interferes with the applied optical field. Two familiar effects result a change in tlie speed of the light wave and its attenuation as it propagates. These properties may be related directly to the linear susceptibility The index of... 

The attenuated total reflectance (ATR) technique is used commonly in the near-infrared for obtaining absorption spectra of thin Aims and opaque materials. The sample, of refractive index i, is placed in direct contact with a material which is transparent in the region of interest, such as thallium bromide/thallium iodide (known as KRS-5), silver chloride or germanium, of relatively high refractive index so that Then, as Figure 3.f8... 

Attenuated total reflection, on which atr—ftir is based, occurs when the rarer medium is absorbing and is characterized by a complex refractive index (40). The absorbing characteristics of this medium allow coupling to the evanescent field such that this field is attenuated to an extent dependent on k. The critical angle in the case of attenuated total reflection loses its meaning, but internal reflection still occurs. Thus, if the internally reflected beam is monitored, its intensity will reflect the loss associated with the internal reflection process at the interface with an absorbing medium. 

Fig. 24. Attenuated total reflectance of thin film of thickness d and refractive index on a substrate of refractive index at the surface of internal reflection element (IRE) of refractive index Decay of evanescent field beyond thickness of thin film indicated.

Source sampling of particulates requites isokinetic removal of a composite sample from the stack or vent effluent to determine representative emission rates. Samples are coUected either extractively or using an in-stack filter EPA Method 5 is representative of extractive sampling, EPA Method 17 of in-stack filtration. Other means of source sampling have been used, but they have been largely supplanted by EPA methods. Continuous in-stack monitors of opacity utilize attenuation of radiation across the effluent. Opacity measurements are affected by the particle size, shape, size distribution, refractive index, and the wavelength of the radiation (25,26). 

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