Inversion-recovery filter

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. 7.2.1 Pulse sequences for T and related magnetization filters, typical evolution curves of filtered magnetization components, and schematic filter transfer functions applicable in the slow motion regime. Note that the axes of correlation times start at Tc = Wo (a) Saturation recovery filter, (b) Inversion recovery filter, (c) Stimulated echo filter.

A filtering effect similar to saturation recovery is obtained for the inversion recovery filter (Fig. 7.2.1(b), cf. Fig. 2.2.8(b)). The longitudinal magnetization is inverted before recovery during the filter time tf, so that the contrast range is doubled with respect to the saturation-recovery filter (cf. eqn (2.2.36)) and negative magnetization values are admitted,... 

Fig. 7.2.22 [Gutl] Pulse sequences for combined determination of T and T2 in inhomogeneous Bo fields, (a) Steady-state inversion recovery filter [Sezl). (b) Steady-state saturation recovery filter [Gutl]. (c) Train of echoes measured by sequence (b) which shows the magnetization build-up with T] and the decay with Ti of unfilled, cross-linked SBR.

Vanderveen et al. studied D2O in Nafion membranes using MQ-filtered deuteron experiments as a function of the hydration level. They evaluated the T2 relaxation times and interpreted the results in terms of a hydration model with two water domains. Ohkubo and co-workers studied Nafion, as well as sulfonated poly(ethersulfone) membranes. They used diffusion-weighted H inversion-recovery measurements followed by Laplace-trans-form analysis of the distribution of longitudinal relaxation times and were able to distinguish water molecules in larger and smaller channels. 

In previous sections we have seen how constraints of boundedness have enabled recovery of frequencies beyond the band limit of the observing instrument. Starting with the inverse-filter estimate... 

There are a number of methods, nearly all iterative, that treat the inverse problem of recovery and successfully (some quite imaginatively) deal with the noise problem. The straightforward inverse-filtered estimate was adhered to in this research because of the possibility of saving computational time in the overall restoration. In practice, only discrete data are taken. 

It is seen that in the case of flat top sampling, the sampled signal spectrum is a distorted version of X f) because of the factor T/sSinc(T/). If r < T, this distortion is small and the original signal can be recovered almost exactly. If not, the factor r/j sinc(T/) must be compensated for by an inverse filter having a frequency response of the form [sinc(r/)] before recovery of x t) takes place. 

From the stability of the inverse (or zero) dynamics motion (Eq. 15) and of the linear filter (Eq. 16b) (tuned sufficiently fast), the stability of the closed-loop system motion follows. The regulated-measured outputs (z, ) have quasi(q)LNPA tracking dynamics, and the unmeasured regulated outputs (Zf) have the Eb-stability property (7) of the ZD motion (Eq. 15). As the controller gain is tuned faster, the controller approaches the behavior of its feedforward counterpart (Eq. 14), and this feature in turn constitutes the behavior recovery target of the measurement -driven controller that will be developed next. 

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