Saturation of the signal

It has been observed that nuclei in the lower energy state undergo transitions to the higher energy state. The populations of the two states may approach equality, and if this situation arises no further net absorption of energy take place, and the observed NMR resonance signal will fade out. This particular situation is termed as saturation of the signal. 

It is pertinent to mention here that in a small NMR spectrum the populations in the two spin states never become equal, by virtue of the fact that higher energy nuclei are constantly returning to the lower energy spin state. 

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It is important to avoid saturation of the signal during pulse width calibration. The Bloch equations predict that a delay of 5 1] will be required for complete restoration to the equilibrium state. It is therefore advisable to determine the 1] values an approximate determination may be made quickly by using the inversion-recovery sequence (see next paragraph). The protons of the sample on which the pulse widths are being determined should have relaxation times of less than a second, to avoid unnecessary delays in pulse width calibration. If the sample has protons with longer relaxation times, then it may be advisable to add a small quantity of a relaxation reagent, such as Cr(acac) or Gkl(FOD)3, to induce the nuclei to relax more quickly. 

Steric interaction between the 1- and 9-positions in dibenzofurans has, however, been observed by NMR techniques. Thus saturation of the signal for the 1-methyl group in the H-NMR spectrum of 1,2,3,4-tetramethyl-dibenzofuran (11) produced a 38% nuclear Overhauser effect at the 9-H. This may be compared qualitatively with the 33% nuclear Overhauser effect produced on the 5-H in the spectrum of 1,2,3,4-tetramethylphenanthrene by... 

The nuclear Overhauser method has been used to demonstrate that in the dibenzofuranol 14 the position ortho to the hydroxy group is vacant. Saturation of the signal due to the benzylic protons of the benzyl group in the spectrum of the benzyl ether 15 gave a 39% nuclear Overhauser effect at the aromatic proton. 

EEG signals recorded by the signal conditioning system are filtered between 1 and 64 Hz and with a notch filter of 50 Hz. Amplification levels are adjusted to avoid saturation of the signal input to the computer. The differential output between the 2 cortical electrodes is digitized on-line at a sampling rate of 256 Hz/channel and the data stored in raw data files. 

The signal from PTCDA and DiMe-PTCDI internal modes remains visible even for a metal coverage of 43 nm, with higher intensity compared to the pure organic film. For Ag deposition onto DiMe-PTCDI no saturation of the signal intensity was observed up to a coverage of 263 nm. 

For sensor optimization, experiments were performed with different concentrations of the target oligonucleotide in the range 0.06-0.75 p.M and the results for the two different immobilization procedures were compared. The two sensors showed a similar behavior with a saturation of the signal for concentrations higher than 0.5 p.M. A 35% higher response was obtained... 

According to this model the amplitude of the oscillations and the decrease factor of the amplitude are the primary characteristics of the response that might be evaluated during a few periods of such response. Since these characteristics are directly related to the fundamental parameters characterising the surfaces and gas, it seems reasonable to suppose that the novel approach will increase the selectivity of the gas detection and decrease the detection time because the saturation of the signal is not required. 

Sometimes excess free rhodamine-azide may be present and it rnns at the bottom of the gel. We find it useful to run gels until the rhodamine azide band elutes from the gel this minimizes saturation of the signal when scanning the gel. 

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