Ti relaxation

Live oil with dissolved methane does not follow the above correlations as methane relaxes by a spin-rotation mechanism, even when dissolved in liquid hydrocarbons [13]. The Ti relaxation time as a function of rj/T is illustrated in Figure 3.6.2 for different gas/oil ratios expressed in units of m3 m-3 as a parameter. The solid line is the fit for zero gas/oil ratio and is given by Eq. (1). 

In CP MAS NMR studies of rhodopsin and their photoactivated state-metarhodopsin, Ahuja et al.70 have used the measurements of the Ti relaxation time. The Ti values measured for Cl8 (0.34 s for rhodopsin... 

Ti relaxation experiment (left side of the figure) as well as 19F T1 (right side of the figure). 

The optimal formulations were obtained using a statistical approach (D-optimal design) and the particles obtained with these formulations had high relaxivities (20-25 s mM ) and small particle sizes (80-100 nm). These formulations appeared to be highly stable in blood, since no change in Ti relaxivity was observed when they where mixed with whole blood. 

A NMR study of water adsorbed on silica gel has been made by Zimmerman el al. 18). Transverse (Ta) and longitudinal (Ti) relaxation times of various amounts of water adsorbed at 25° have been obtained with the use of the spin-echo technique and a two-phase behavior of both Ta and T relaxation times has been observed as illustrated in Figs. 10a and b. Generally only one T value is obtained, as for a single phase, except for x/m g HaO/g solid) values in the vicinity ol x/m = 0.126. Two values of Ta... 

Figure 4.19 Temperature dependence of the dipolar Ti relaxation time in semi logarithmic coordinates at the Larmor frequency coq- The dashed T i curve corresponds to a higher Larmor frequency. The regions with and 1 <<0)qT ...

The manner in which the RF pulse is applied is critical to NMR analysis. A very simplified pulse sequence is a combination of RF pulses, signals, and intervening periods of recovery, as illustrated in Figure 6.80. The main components of the pnlse sequence are the repetition time, TR, which is the time from the application of one RF pulse to the application of the next RF pulse (measured in milliseconds) and the echo time, TE. The repetition time determines the amount of relaxation that is allowed to occur between the end of one RF pulse and the application of the next. Therefore, the repetition time determines the amount of Ti relaxation that has occnrred. The echo time is the time from the application of the RF pnlse to the peak of the signal induced in the coil (also measured in milliseconds). The TE determines how much decay of transverse magnetization is allowed to occur before the signal is read. Therefore, TE controls the amount of T2 relaxation that has occnrred. 

An interesting new experimental approach has been taken in order to separate overlapping EPR spectra as they appear e.g. in the multi Fe/S centre containing complex I. Inversion- and saturation-recovery measurements which allow to measure Ti relaxation times are used in a inversion-recovery filter which is subsequently applied to separate EPR signals on account of their Trdifferences. In addition, this filter can be used in conjunction with high-resolution hyperfine measurements e.g. by ESEEM and thus the separated centres can be characterized in depth.211... 

Fig. 6. (a) Schematic representation of a simple slice-selective 2-D spin-echo pulse sequence. In this pulse sequence the magnetic field gradient (G, ) is varied for successive acquisitions of different rows of the k-space raster, (b) The corresponding k-space raster used to show how we interpret the pulse sequence. Following a sufficient Ti-relaxation period, the sequence is repeated to acquire a second row of the k-space raster. Acquisition of each row of k-space requires a separate r.f. excitation and application of a G,-gradient of different magnitude. 

Nanny, M. A., Bortiatynski, J. M., and Hatcher, P. G. (1997). Noncovalent interactions between acenaphthenone and dissolved fulvic acid as determined by 13C NMR Ti relaxation measurements—Response. Environ. Sci. Technol. 31, 3744-3745. 

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