Signature Generality

Chemisorption is a process in which chemical bond forms and the valence electrons transport among the bonding constituent atoms. Processes of charge transport modify the valence band structure and introduce additional DOS features. The derived DOS features are detectable using STS (around Ep), PES (E Ep), and IPES (inverse PES, E Ep). 

STS measurements record the dlfdVi — Vi or the d(ln/t)/d(lnVt) — V curves, at a constant tip current, /(, and various tip voltages, Vp The features of an STS spectrum are associated with the on-site DOS of a few atoms at a surface [1, 2]. Features below Ep (tip negative bias) correspond to the occupied DOS at the surface, while features above Ep (tip positive) represent the allowed, yet unoccupied, DOS of the sample surface [3]. 

Relaxation of the Chemical Bond, Springer Series in Chemical Physics 108, DOI 10.1007/978-981-4585-21-7 4, Springer Science+Business Media Singapore 2014 

A set of PES profiles from an O-Cu(OOl) [18] surface shows three new DOS features around —1.45, —3.25, and —5.35 eV within the valence band (above — 7.04 eV) compared to that of a clean Cu(OOl) surface. The states around —1.45 eV (which coincide with the —1.4 eV STS feature in Rg. 4.1a) are anti-resonant, i.e., the intensity has no apparent change with varying incident beam energy. The anti-resonant DOS feature is the character of electrons that are strongly confined in one dimension such as molecular chains [19]. Thus, the anti-resonant DOS features around —1.45 eV can be related to the electron lone pairs that zigzag the 0 Cu 0 strings at the Cu(001)-0 surface. 

He-II (21.22 eV) PES revealed that with increasing the number of oxygen atoms on a polycrystalline Cu surface, oxidation takes place in three steps [9]  

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A frequency-domain vibration signature is generally used for the analysis because it is comprised of discrete peaks, each representing a specific vibration source. 

Actual time-domain vibration signatures are commonly referred to as time traces or time plots (see Figure 43.17). Theoretical vibration data are generally referred to as waveforms (see Figure 43.18). 

Table 44.6 is a vibration troubleshooting chart that identifies some of the common failure modes. This table provides general guidelines for interpreting the most common abnormal vibration profiles. These guidelines, however, do not provide positive verification or identification of machine-train problems. Verification requires an understanding of the failure mode and how it appears in the vibration signature. 

Ghosts are caused when two or more frequency components couple, or merge, to form another discrete frequency component in the vibration signature. This generally occurs with multiple-speed machines or a group of single-speed machines. 

Two point correlations We liave already mentioned several times that evolutions generally induce correlations between cell values at different sites indeed, the presence of correlations is a telltale signature of self-organization. The average density discussed above, however, is too crude a measure to capture these finer details. 

An alternative view presented by Reiners (2002), suggests that in general pyroxenites do not have more enriched signatures than peridotites in their trace element... 

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