Cross-correlation peaks

The two-dimensional 31P DQ spectrum of OCP is shown in Figure 7, in which there are eight sets of auto- and cross-correlation peaks. Although the 31P CSA of HPO42 is quite sizable,107 the relatively high intensity of the P5-P5/P5-P6 correlation peak demonstrates that the DQ excitation... 

Before we present the test results, we describe some general features of the cross-correlation technique. First, the velocity data obtained by this technique are typically derived from the maximum cross-correlation peak, which evidently differs from the actual average velocity over the pipe cross section because of the finite acoustic beam width. Thus there appears to be a meter factor that is due to the velocity profile. Second, in the cross-correlation system, we use two parallel sets of electronics any phase difference caused by the electronics will lead to an error in measurement. 

FIGURE 5-21 Slurry velocities obtained from cross-correlation peaks vs. velocities measured by flow diversion for coal/oil slurries. 

In a synchronous 2D map, the peaks located in the diagonal (autopeaks) correspond to changes in intensity induced in our case by temperature, and are always positive. The cross-correlation peaks indicate an in-phase relationship between the two bands involved. 

It is also possible to use p-PIV for temperature measurements. The technique is based on the precondition that Brownian motion will cause width-wise broadening of the cross-correlation peak. A correlation-based PIV algorithm detects the magnitude of Brownian particle motion and can be used to determine the temperature of the fluid [41]. 

F- F homonuclear interaction, which is averaged out by fast MAS, is reintroduced using the back-to-back (BABA) recoupling sequence [64]. In a 2D MAS DQ-SQ NMR spectrum, fluorine atomic proximities between inequivalent F sites are revealed by paired cross-correlation peaks appearing at the individual chemical shifts of the two dipolar-coupled nuclei in the SQ direct dimension and the sum of them in the indirect DQ dimension, while the proximity between two equivalent F sites is disclosed by a single auto-correlation peak located on the DQ diagonal (with a slope of 2) of the 2D spectrum... 

Figure 5.9 2D DQ-SQ MAS (30 kHz) NMR correlation spectrum of P-BaAlFs- Top spectrum is the full projection in the F SQ dimension, on which lines are labelled. The DQ diagonals (with a slope of 2) of the 2D spectrum on which autocorrelation peaks appear are indicated by the dash lines. Paired cross-correlation peaks are indicated by horizontal solid lines [57]. Phys. Chem. Chem. Phys., 77, 950-957 (2009). Reproduced by permission of the PCCP Owner Societies Copyright (2009) Royal Society of Chemistry...

The radial velocities have been computed with the low resolution set-up (more spectral lines, no telluric line), using a cross-correlation technique. When excluding the seven outliers, the peak in centered at 83.0 0.4kms 1 with a dispersion of 1.9 0.2kms 1. Lithium abundance is being determined using Li i 6707.8 A. We used the B — V index to determined the ([3]), and the curve of growth from [7] to derive AT(Li). 

The DD-CSA cross-correlated relaxation, namely that between 13C-1H dipole and 31P-CSA, can also be used to determine backbone a and C angles in RNA [65]. The experiment requires oligonucleotides that are 13C-labeled in the sugar moiety. First, 1H-coupled, / - DQ//Q-II CP spectra are measured. DQ and ZQ spectra are obtained by linear combinations of four subspectra recorded for each q-increment. Then, the cross-relaxation rates are calculated from the peak intensity ratios of the doublets in the DQ and ZQ spectra. The observed cross-correlation rates depend on the relative orientations of CH dipoles with respect to the components of the 31P chemical shift tensor. As the components of the 31P chemical shift tensor in RNA are not known, the barium salt of diethyl phosphate was used as a model compound with the principal components values of -76 ppm, -16 ppm and 103 ppm, respectively [106]. Since the measured cross-correlation rates are a function of the angles / and e as well, these angles need to be determined independently using 3/(H, P) and 3/(C, P) coupling constants. 

Then, each of the correlation peaks exhibits a doublet of doublet structure along co2 because of the evolution of the (H.N) and the 1J(Ca,Ha) coupling during t. The intensity of the individual multiplet lines is affected by the dipole, dipole cross-correlated relaxation rate rcHN c H as well as the sums of two dipole/CSA cross-correlated relaxation rates r°HN C + rcHN N and r°c H c + r°c H N. By forming the ratios... 

Therein, cross-correlated relaxation T qHj c h °f the double and zero quantum coherence (DQ/ZQ) 4HizCixCjj generated at time point a creates the DQ/ZQ operator 4HjzCjJCiy. In the second part of the experiment, the operator 4HJZCjxQy is transferred via a 90° y-pulse applied to 13C nuclei to give rise to a cross peak at an(i... 

As an example of the measurement of cross-correlated relaxation between CSA and dipolar couplings, we choose the J-resolved constant time experiment [30] (Fig. 7.26 a) that measures the cross-correlated relaxation of 1H,13C-dipolar coupling and 31P-chemical shift anisotropy to determine the phosphodiester backbone angles a and in RNA. Since 31P is not bound to NMR-active nuclei, NOE information for the backbone of RNA is sparse, and vicinal scalar coupling constants cannot be exploited. The cross-correlated relaxation rates can be obtained from the relative scaling (shown schematically in Fig. 7.19d) of the two submultiplet intensities derived from an H-coupled constant time spectrum of 13C,31P double- and zero-quantum coherence [DQC (double-quantum coherence) and ZQC (zero-quantum coherence), respectively]. These traces are shown in Fig. 7.26c. The desired cross-correlated relaxation rate can be extracted from the intensities of the cross peaks according to ... 

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