Broad-line producers

In the linear approximation there is a direct Fourier relationship between the FID and the spectrum and, in the great majority of experunents, the spectrum is produced by Fourier transfonnation of the FID. It is a tacit assumption that everything behaves in a linear fashion with, for example, imifonn excitation (or effective RF field) across the spectrum. For many cases this situation is closely approximated but distortions may occur for some of the broad lines that may be encountered in solids. The power spectrum P(v) of a pulse applied at Vq is given by a smc fiinction 18]... 

In the case that SWCNTs were produced by laser ablation with Co and Ni, a very weak and narrow signal was superposed on the main broad line. To confirm that this narrow line is associated with SWCNTs, the sample was vacuum-annealed at 1500°C to remove the remaining Co and Ni. 

The process of exponential multiplication just described produces a rapid decay of the FID and the production of broad lines suppressing the decay of the FID gives narrow lines and better resolution, with increased noise level. An alternative approach to resolution enhancement is to reduce the intensity of the earlier part of the FID. Ideally, we should use a function that reduces the early part of the FID, to give sharper lines, as well as reduces the tail of the FID, to give a better signal-to-noise ratio. 

Up to this point, we have ignored the effect of h during the rf pulses. Of course, if h << H], then the effect is negligible. But in the case of very broad lines where h for many of the nuclear moments in the sample, the effect becomes very significant. The analytical solution to Equation 1 under these conditions is very complicated. In effect, the pulse sequence described above still produces a spin echo (as can be seen in... 

Morris et al. (1991) obtained hematite of very small particle size ( 10 nm), termed nanophase by slow thermal decomposition in air of tri-Ee -acetato-hy-droxy-nitrate. XRD shows only two broad lines as in a 2-line ferrihydrite, but the magnetic hyperfine field at 4.2 K of 50.4 T appears to be more in agreement with poorly crystalline hematite. Well-crystalline hematite and Al-hematite were produced by decomposing Ee-Al-oxinates at 700 °C (da Costa et al. 2001). 

For the spectral interpretation, 71 and 72 can be conceived of as extensions of 63 with two, or three, terminal a-(l— 2)-linked Man groups, respectively. The spectral features of the core residues, GlcNAc-1 and -2, and Man-3, -4, and -4, in 71 and 72 are essentially identical with those of the corresponding residues in compounds 63 and 68-70 (see Table XXVI). Heterogeneity of the peptide moiety produces multiple resonances for the N-acetyl protons, and also relatively broad-lined, anomeric doublets of GlcNAc-1 and of GlcNAc-2. 

A paramagnetic ion produces a very short relaxation time in nuclei closely associated with it. This results in a broad line. The overall effect depends both on the relaxation and on the rate of exchange. The slower rate process is the one that is measured. 

At these low intensities each line produces some broad luminescent features which varied from exciting line to exciting line. One sharp feature was present at each exciting line and is displayed in Fig. 6. This peak though weak can be assigned in conjunction... 

O = orthorhombic, T = tetragonal. CuNiF produced by the spontaneous dissociation of CuNiF in aHF over - 1 week gave an almost identical broad-line pattern. The xenon reduction vras complete within a few minutes. 

The exploitation of cross-correlation effects in high magnetic fields has introduced a new form of NMR spectroscopy called transverse relaxation-optimised spectroscopy or TROSY. The cross-correlation of the optimised dipole-dipole (DD) and chemical shift anisotropy (CSA) relaxation mechanisms leads to differential transverse relaxation rates for the two components of the l5N- H doublet in undecoupled spectra of l5N-labelled proteins. For one component, DD and CSA relaxation constructively add to produce very efficient relaxation, leading to a broad line, whereas for the other component, the two relaxation mechanisms constructively interfere, leading to a narrow line when the two mechanisms are nearly equal. There is no optimum field where DD and CSA relaxation are equal for all amide bonds, because DD relaxation between the amide protons and other nearby protons differs for each residue.72 Clearly, the overall effectiveness of TROSY is optimized when the non-exchangeable protons in the macromolecule... 

The chief problem in determining particle size from line breadths is to determine B from the measured breadth fiv/ of the diffraction line. Of the many methods proposed, Warren s is the simplest. The unknown is mixed with a standard which has a particle size greater than 1000 A, and which produces a diffraction line near that line from the unknown which is to be used in the determination. A diffraction pattern is then made of the mixture in either a Debye camera or, preferably, a diffractometer. This pattern will contain sharp lines from the standard and broad lines from the unknown, assumed to consist of very fine particles. Let Bg be the measured breadth, at half-maximum intensity, of the line from the standard. Then B is given, not simply by the difference between B and B, but by the equation... 

The hardness curve and diffraction patterns of Fig. 9-3 illustrate these changes for an alpha brass, a solid solution of zinc in copper, containing 30 percent zinc by weight. The hardness remains practically constant, for an annealing period of one hour, until a temperature of 200°C is exceeded, and then decreases rapidly with increasing temperature, as shown in (a). The diffraction pattern in (b) exhibits the broad diffuse Debye lines produced by the cold-rolled, unannealed alloy. These lines become somewhat narrower for specimens annealed at 100° and 200°C, and the Ka. doublet becomes partially resolved at 250°C. At 250°, therefore, the re-... 

Since 14N has 1= 1 its relaxation is usually dominated by quad-rupolar interactions. These produce broad lines, both in the 14N NMR spectrum and in the spectra of nuclei spin-spin coupled to nitrogen, (la, 2a) The 13N nucleus has I =, thus in a diamagnetic, chemically stable molecule it is relaxed by one or more of several less efficient mechanisms. 

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