Screening surface intermediates

Material that remains on a given screening surface is the oversize or plus material, material passing through the screening surface is the undersize or minus material, and material passing one screening surface and retained on a subsequent surface is the intermediate material. 

Midrails, screens, mesh, intermediate vertical members, or equivalent intermediate structural members shall be installed between the top edge of the guardrail system and the walking/working surface when there is no wall or parapet wall at least 21 inches (53 cm) high. 

We should finally briefly discuss the calculation of spectra for the surface adsorbates which we will use to verify the theoretical models and to assign peaks in the spectra. The calculation of XES spectra has been discussed extensively previously [3]. Briefly we have shown that the ground state orbitals provide a balanced description of initial and final state and calculate the spectrum as the dipole transition between the valence orbitals and the selected Is core level [21]. The success of this approach relies on similar charge transfer screening in the core-ionized initial (or intermediate) state as for the valence-ionized levels. XES thus reflects the ground state molecular orbitals. 

If the d-band center is too far from the Fermi level, as in the case of PtjV and PtjTi, the intermediates and bind too weakly to the surface. For the PtjM systems, the experimental results (summarized in Fig. 3.6a) and componential screening of the same binary alloys (Fig. 3.6c) converge to the same optimal Pt to 3d ratio (e.g., PtjM) and the identity of the 3d element (e.g., Co or Ni). While it is tempting to conclude that the rationale for the variation in activity depends exclusively on the position of the metal d-states relative to the Fermi level. Fig. 3.6 clearly shows that for a similar position of the d-band center, a different activity is obtained on Pt-skin and Pt-skeleton surfaces. The relationships between the elec-trocatalytic activity of the ORR and the d-band center position were also recently demonstrated by Adzic and Mavrikakis [77, 78]. 

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