Extinction factor

Sabine, R.B. Von Dreele, and J.E. Jorgensen, Extinction in time-of-flight neutron powder diffractometry, Acta Cryst. A44, 374 (1988) T.M. Sabine, A reconciliation of extinction theories, Acta Cryst. A44,368 (1988). 

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The authors [1259] managed to determine the position of the absorption maximum of 4-nitro-2,l,3-benzothiadiazole however, because of poor solubility of the substance (n-hexane) its concentration and extinction factor remained unknown. 

Multiplying each ordinate by d, or Jy, gives the area or volume of distribution. A full solution is generated if the extinction factor is introduced into the equation. 

The conclusion drawn from equation (8.56) is at odds with published data on polystyrene lattices and silver bromide, in which a volume proportionality is found [37,38]. However these distributions w ere narrow, and with narrow distributions the difference between volume and surface distributions is small. The conclusion is also at variance with data published on BCR 66 quartz powder, ranging in size from 0.3 to 3 pm. In this case, the median for the attenuation curve was 1.52 pm which reduced to 1.14 pm with extinction factor correction [39] and a correction of this magnitude could hide the effect. 

Ehki is the extinction multiplier, which accounts for deviations from the kinematical diffraction model. In powders, these are quite small and the extinction factor is nearly always neglected. 

Lp is the Lorentz polarization factor, A and E are absorption and extinction factors, and IF /1 the absolute magnitude of the structure factor. The sign or phase of the structure factor, a /, is not directly determinable from the diffraction experiment. 

Following HPLC separation of different folate forms, a number of detection systems can be used including UV, fluorometric, or electrochemical activity (65). Due to its sensitivity and selectivity, fluorescence detection is most commonly used, particularly for reduced folate forms (86). Quantitation is usually based on external standard methods, although an internal method using a stable isotope label has been recently reported (see below) (87). More cumbersome identification and quantifications are needed in methods in which folates are eluted in clusters (69). It is important that the actual concentrations of folate calibration solutions are determined using known extinction factors (30) because most commercially available folate calibrants are of variable purity (7). 

Suspended particles are the most important factor in visibility reduction. In most instances, the visual quality of air is controlled by partide scattering and is characterized by the extinction coeffident The size of particles plays a crucial role in their interaction with light. Other factors are the refractive index and shape of the particles, although their effect is harder to measure and is less well understood. If we could establish these properties, we could calculate the amount of light scattering and absorption. Alternatively, the extinction coeffident associated with an aerosol can be measured directly. 

The fraction of black-body radiation actually emitted by flames is called emissivity. Emissivity is determined first by adsorption of radiation by combustion products (including soot) in flames and second by radiation wavelength. These factors make emissivity modeling complicated. By assuming that a fire radiates as a gray body, in other words, that extinction coefficients of the radiation adsorption are independent of the wavelength, a fire s emissivity can be written as... 

Similarly, widespread control of prairie dogs has been a major factor in the near-extinction of the black-footed ferret. 

One factor which should be noted for palladium, which also applies to the observation of the transition metals Is that not all crystallites have the same efficiency for diffracting electrons, l.e., as the atomic number decreases, the extinction distance for the crystallite Increases (13). Thus one would anticipate Chat as the mean atomic number decreases, the crystallites will have Co be progressively larger to enable visual observation on a support such as alumina. 

In an attempt to resolve the discrepancy between calculated and measured extinction coefficients, one can consider the possible contributing factors which follow ... 

The accuracy of experimentally determined structure factors is limited by various error sources, which may be introduced by the experimental method itself or during the data reduction stage. A reduction of those errors is expected by the use of high-energy synchrotron radiation (E(/ ) > 100 keV) as primary beam source, because absorption and extinction corrections are negligible in most practical cases. 

Before going further, it may be noted that the flipping ratio does not depend either on the Lorentz factor or on absorption in the sample. Certain instrumental parameters such as the polarisation of the neutron beam for the two spin states, the half wavelength contamination of the neutron beam and the dead-time detector can readily be taken into account when analysing the data. On the other hand, the extinction which may occur in the scattering process is not so easy to assess, but must also be included [14]. Sometimes, it is even possible to determine the magnetisation density of twinned crystals [15]. 

For a typical monomolecular coverage, T — 10 10 mol/cm2, an electrode roughness factor r = 1000 and an extinction coefficient ads = 107 cm2/mol, the light-harvesting efficiency is, in comparison to the preceding case, very high, intimate contact with the semiconductor surface, hence the conditions for charge injection from S into the semiconductor are almost ideal (q9j—>100 per cent). 

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