Line pair

Fig. 3 Image of the line pair te.st pattern after integration and enhancement...

Figure 2.6. The tetrahedral structures of ice (a), (fc) are planes through sheets of selected oxygen nuclei (open circles), hydrogen nuclei (shotm in the insert as solid circles) are not shown in the main drawing. The insert illustrates the overlap of oxygen line pairs and the hydrogen nuclei, thus forming the hydrogen bonds (dotted lines)...

We are now ready to derive an expression for the intensity pattern observed with the Young s interferometer. The correlation term is replaced by the complex coherence factor transported to the interferometer from the source, and which contains the baseline B = xi — X2. Exactly this term quantifies the contrast of the interference fringes. Upon closer inspection it becomes apparent that the complex coherence factor contains the two-dimensional Fourier transform of the apparent source distribution I(1 ) taken at a spatial frequency s = B/A (with units line pairs per radian ). The notion that the fringe contrast in an interferometer is determined by the Fourier transform of the source intensity distribution is the essence of the theorem of van Cittert - Zemike. 

The fundamental quantity for interferometry is the source s visibility function. The spatial coherence properties of the source is connected with the two-dimensional Fourier transform of the spatial intensity distribution on the ce-setial sphere by virtue of the van Cittert - Zemike theorem. The measured fringe contrast is given by the source s visibility at a spatial frequency B/X, measured in units line pairs per radian. The temporal coherence properties is determined by the spectral distribution of the detected radiation. The measured fringe contrast therefore also depends on the spectral properties of the source and the instrument. 

A way out of this dilemma is to perform an NMR-type experiment on the paramagnetic centre. NMR provides an inherently higher resolution than EPR, since only one line pair at frequences v is obtained for each nucleus (or set of magnetically equivalent nuclei). The lines appear, to first order, symmetrically spaced around the Larmor frequency v of the respective nucleus for nuclei with I = i and a hfc A the resonance condition is... 

Image Quality. Resolution of screens were measured at 50 KV peak x-ray exposures at film densities of 1.0 using standard lead resolution grids with sets of etched lines about I line pair per mm up to 15 line pairs per mm. The results are reported as the maximum set of line pairs resolved per mm. 

Particle Relative Size Blue APD Film Speeds Green Film Resolution, Line Pairs Per mm Signal Noise... 

The Hanawalt method is relatively straightforward for unknowns which are nearly single phase. For multiphase mixtures the identification becomes tedious. Consider the data for a white powder given in Table 4 (7). Again the search is begun with the two most intense lines, 2.41 A and 3.04 A, but no match is found for this line-pair. Now a new line-pair must be chosen and the first and third most intense lines seem likely. Searching the Hanawalt manual with the pair 2.41 A and 1.70 A yields the possibilities 7-TaH, CaO, and NaYOa. Only the four lines of the CaO standard pattern lines match the lines in the unknown pattern. 

A number of compounds of the p-block elements containing two bidentate ligands can be considered to be five-coordinate and trigonal bipyramidal if a non-bonding pair of electrons occupies one of the equatorial sites, for example [Sn(S2CNR2)2(lone pair)] and [Pb(RCOCH-COR)2(lone pair)].4 The greater repulsion observed from this line pair implies R(lone pair/bidentate) values of 0.6 for sulfur(IV) compounds, decreasing to 0.4 for selenium(IV) and 0.2 for tellurium(IV), antimony(III), tin(II) and lead(II).4... 

The quadrUpole interaction of the quadrupole moment of the I — 3/2 excited isomeric state of 57Fe with an electric field gradient at the nuclear position produces a characteristic line pair in Mossbauer spectra as shown in Fig. 2. The energy difference is called the quadrupole splitting... 

Chloroprotohemin in pyridine solution shows a different behavior two quadrupole fine pairs replace the single quadrupole fine pair for chloroprotohemin in aqueous solution. The wide quadrupole splitting (1.8 mm/S) of the new line pair is more characteristic of Mossbauer spectra obtained for methemoglobin these spectra will be discussed in the next section, but it suffices to point out here that the pyridine coordination produces an environment more nearly like the hexacoordinated environment of the iron in the hemoproteins (78). 

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