Spin echo decay curve

In an NMR analysis of the effects of /-irradiation induced degradation on a specific polyurethane (PU) elastomer system, Maxwell and co-workers [87] used a combination of both H and 13C NMR techniques, and correlated these with mechanical properties derived from dynamic mechanical analysis (DMA). 1H NMR was used to determine spin-echo decay curves for three samples, which consisted of a control and two samples exposed to different levels of /-irradiation in air. These results were deconvoluted into three T2 components that represented T2 values which could be attributed to an interfacial domain between hard and soft segments of the PU, the PU soft segment, and the sol... 

The methodology described in this procedure is limited to systems that do not contain free moisture. In cases when both oil and water signals are refocused after the second pulse (e.g., when free water is present), the spin-echo decay curve can be collected over varying x values. Log of the echo amplitudes versus x can be further analyzed to deconvolute the contribution of various components, in this example water and oil would result in a biexponential decay curve. Extrapolating each decay curve to X 0 gives the signals amplitudes due to the oil and the water fractions (A0 and Aw Fig. A1.3.4). 

Fig. 34. A plot of 1/T2G for Ni-doped YBCO7 against (a) T and (b) T/Tc.n The inset shows the spin echo decay curve at Tc values for x = 0 and 3%.

NMR relaxometry Free induction decay (T2 ) or solid echo Spin echo decay (T2) Magnetization recovery curve (7)) Eads (1998)... 

Fig. 2.18 Vector model for the reorientation of the spins by the microwave pulses. The sequence is employed to measure the phase-memory relaxation time from the decay of Hahn or primtiry echo signal and of anisotropic hypetfine and nuclear quadnrpole couplings observable as modulations on the echo decay curve. The latter is referred to as the ESEEM method...

DOSY is a technique that may prove successful in the determination of additives in mixtures [279]. Using different field gradients it is possible to distinguish components in a mixture on the basis of their diffusion coefficients. Morris and Johnson [271] have developed diffusion-ordered 2D NMR experiments for the analysis of mixtures. PFG-NMR can thus be used to identify those components in a mixture that have similar (or overlapping) chemical shifts but different diffusional properties. Multivariate curve resolution (MCR) analysis of DOSY data allows generation of pure spectra of the individual components for identification. The pure spin-echo diffusion decays that are obtained for the individual components may be used to determine the diffusion coefficient/distribution [281]. Mixtures of molecules of very similar sizes can readily be analysed by DOSY. Diffusion-ordered spectroscopy [273,282], which does not require prior separation, is a viable competitor for techniques such as HPLC-NMR that are based on chemical separation. 

NMR diffusometry Decay of spin echoes in the presence of a magnetic field gradient (echo attenuation curve) Price (1996, 1997, 1998a)... 

Fig. 7. T and T2 maps of the olfactory bulb of a young rabbit reconstructed directly from the noisy experimental images (a) and from the same images preliminary denoised by a quantitative multispectral non-linear edge-preserving filter (b). For Tx mapping, the recovery curve of a Spin-Echo sequence was sampled at n = 8 different repetition times, x = [500, 1000, 1500, 2000, 2500, 3000, 4000, 5000]T. For T2 mapping, the decay curve of the same Spin-Echo sequence was sampled at n = 5 different echo times, x = [10, 35, 60, 85, 110]T. For both, the model considers a single exponential term and the reconstruction is performed using LS approach.

Chang and Woessner, using the spin-echo technique, made and TU measurements on eletal muscle (115). While the curve Is cfbse to a single exponential decay, the T2 curve can be fitted with a double exponential function. The fast and slow (f,s) components have T values of 16 and 1.6 ms, respectively, for fresh muscle. The value for the same sample Is 18 ms. Hence, T. - Tg- < Tgg and Tgg = T. The reader will recall (Section 2 that T g depends upon the spectral density at twice the Larmor frequency, T depends on J((o whereas Tgf depends upon spectral densities at zero emd at Larmor frequency and Tgg depends upon the sum J(o) + J(2a>). Thus, the experimental results obtained by Chang emd Woessner Imply that J(0)>>J(o) ) = J(2oj ). This last equality. In turn. Indicates... 

The use of analytical models for spin dephasing in the solid state [39, 40] is not appropriate for the present case because they do not account for the specific distribution of nuclear spins around the electron spin. In order to consider the real matrix structure close to the chromophore we simulated the HE decay curves numerically by using the known crystal structure [9] and the nuclear flip-flop rate IE as a parameter. The echo decay is calculated as... 

The program has been used extensively in this laboratory with chemical relaxation and NMR-spin-echo experiments. A long test series has been performed either with computer generated data or by using a special electronic generator for three superimposed exponential decay curves with a precision in relaxation time and amplitude of about - 0.5 % [3]. The conclusions are ... 

The proton spin-spin relaxation times T2 and spin echo amplitude decay curves of concentrated solutions of maltose, sucrose, and glucose have been measured, and detailed n.m.r. data have been reported for trehalulose(l-0-a-D-glucopyranosyl-D-fructose, see Chapter 2). In D2O, the tautomers with -pyranose-, /3-furanose-, and a-furanose-configurated fructose moieties were present in 20 4 1 ratios. ... 

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