Amplitude of the NMR signal

In the absence of magnetic field gradients and neglecting spin relaxation, the amplitude of the NMR signal depends on a correlation of spin location over the interval of measurement as... 

Figure 10 The spin-echo RF pulse sequence (A) and its result on the amplitude of the NMR signal (B) when applied to com samples.

NMR cryoporometry fill the pores with a liquid, freeze it, then measure the amplitude of the NMR signal from the liquid component as the sample is warmed, until all the liquid is melted. 

The relaxation curve is then probed point-bypoint by switching the field up to the detection field level and by acquiring the NMR signal using a RF pulse or an echo RF pulse sequence. The detection field is chosen as high as possible, and is the same for all experiments. This is the field to which the RF console is tuned. The amplitude of the NMR signal represents the magnetization at the end of the evolution interval, in which relaxation takes place. Thus... 

What is not commonly known outside the NMR community is the relative difficulty in making accurate relative density measurements by NMR/MRI compared, for example, with making velocity measurements by NMR/MRI. This is because density measurements rely on the signal strength, which can be affected by any number of factors. In contrast, the most common way to measure flow velocity by NMR/MRI is to use the phase of the NMR signal rather than the amplitude, which vastly reduces its sensitivity to amplitude variations. 

Because the amplitude of a NMR signal Is proportional to the amount of hydrogen present. In the data analyses described below maceral contents which are determined on a volume basis (denoted by vol%) have been converted to a wt% hydrogen basis (denoted by H-wt%) by the method of Lynch et al. (27). In practice, the changes produced In the maceral content values are small except for the coals richest In llptlnlte. 

The J-modulated spin-echo technique " and the DEPT technique " are pulse sequences, which transform the information of the CH signal multiplicity and of spin-spin coupling into phase relationships (positive and negative amplitudes) of the C signals in the proton decoupled C NMR spectra. The DEPT technique benefits from a polarisation transfer which increases the sensitivity by up to a factor of 4. For... 

NMR spectrometers of the late 1960s did not permit the detection of higher spin orders for sensitivity reasons, so no new name was coined for them the term used today is "higher multiplet effects". More importantly, with the cw instruments ubiquitous at that time a separation of different spin orders n was principally impossible. The advent of pulsed and Fourier transform spectrometers reduced that to a trivial task Because for a weakly coupled spin system the amplitude of the detectable signal is proportional to sim cos i , one simply has to acquire spectra with different flip angles i9 and form suitable linear combinations (e.g. one- and two-spin orders are separated by adding and subtracting two spectra acquired with = 45° and = 135°). ... 

The kind of NMR data required (e.g. signal amplitudes, relaxation information or chemical shift information with limited spectral resolution) plays a significant role in defining the design criteria for both hardware and software components. In common practice, in low-resolution NMR the concern is with the analysis of the NMR signal in the time domain (FID) and the characterisation of the physical structure of the bulk sample. The global characterisation of the sample in terms of molecular dynamics is key to successful use of low-field NMR. Relaxation information should provide rapid, reliable quantitative information for improved process control. The relaxation behaviour can provide extremely useful information on various aspects of mobile phases, e.g. moisture determination. 

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