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Partitioning of the total cross

Some partial photoionization cross sections, derived in this way for neon, are shown in Fig. 2.11 as a function of photon energy. The uppermost curve is the total absorption cross section. At the onset of the ionization thresholds for the ejection of Is, 2s and 2p electrons this quantity shows the corresponding absorption edges (see the discussion related to equ. (2.11)). The partition of the total cross section into partial contributions cr(i) clearly demonstrates that the dominant features are due to main photoionization processes described by the partial cross sections satellite transitions from multiple photoionization processes are also present. If these are related to a K-shell ionization process, they are called in Fig. 2.11 multiple KL where the symbol KLX indicates that one electron from the K-shell and X electrons from the L-shell have been released by the photon interaction. Similarly, multiple I/ stands for processes where X electrons from the L-shell are ejected. Furthermore, these two groups of multiple processes are classified with respect to ionization accompanied by excitation, (e, n), or double ionization, ( ,e). If one compares in Fig. 2.11 the magnitude of the partial cross sections for 2p, 2s and Is photoionization at 1253.6 eV photon energy (Mg Ka radiation) and takes into account the different... [Pg.68]

Raith, W., Sinapius, G. and Stauffer, A.D. (1987). Partitioning of the positron-helium total scattering cross section. J. Phys. B At. Mol. Phys. 20 3557-3570. [Pg.400]

In QSAR 54, LogP represents the olive oil/ water partition coefficient, MW is the molecular weight of the solute and defines its size, and Kfe is a crude approximation of the total number of hydrogen bonds for each molecule. The molecular weight descriptor has also been an omnipresent variable in QSAR studies pertaining to cross-resistance of various drugs in multidrug-resistant cell lines (169). was used because it most... [Pg.25]

A measurement table is different from a contingency table. The latter results from counting the number of objects that belong simultaneously to various categories of two measurements (e.g. molar refractivity and partition coefficient of chemical compounds). It is also called a two-way table or cross-tabulation, as the total number of objects is split up in two ways according to the two measurements that are crossed with one another. The analysis of contingency tables is dealt with specifically in Chapter 32. [Pg.88]

Ionisation determines the partitioning of drugs across membranes. Unionised molecules can easily cross and reach an equilibrium across a membrane, while the ionised form cannot cross. When the pH is different in the compartments separated by the membrane the total (ionised + unionised) concentration will be different on each side. An acidic drug will become concentrated in a compartment with a high pH and a basic drug in one with a low pH. This is known as ion-trapping, and occurs in the stomach, kidneys, and across the placenta. Urinary acidification accelerates the excretion of weak bases, such as pethidine, while alkalinisation increases the excretion of acidic drugs, such as aspirin. As an example consider pethidine (pKa 8.6) with an unbound plasma concentration of 100 (arbitrary units). At pH 7.4 only 6% of the pethidine will be unionised so that at equilibrium the concentration of unionised pethidine in the urine will be 6 units. In urine at pH 6.5 only 0.8% of the pethidine will be unionised so that the total concentration in the urine will be 744 units. [Pg.33]

Note that in Table III local (Sza), (S ), and (Sa Sb) expectation values for the [Fe2] cluster 1 are listed. As shown in Section V the local expressions for the Mayer and the Clark and Davidson decomposition schemes differ. Hence, different values for the (S ), e.g., for partitioning schemes. The same argument holds for the cross terms (Sa Sb), here (Spei Sk< 2)- The total spin expectation value (S2) is shown to illustrate that spin contamination is fairly low for most spin states. The reader should not be confused by the fact that summation over the local spin values at the iron centers (Spel), (Spe2>, and (Spei SFe2) does not yield the same value for Mayer and for Clark and Davidson data and that they do not sum up to (S2). The total spin expectation value (S2) is only obtained when summing all local spin values of all atoms of the [Fe2] cluster 1. [Pg.218]


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Partitioning of the total cross section

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