Processing phase correction

At the end of the 2D experiment, we will have acquired a set of N FIDs composed of quadrature data points, with N /2 points from channel A and points from channel B, acquired with sequential (alternate) sampling. How the data are processed is critical for a successful outcome. The data processing involves (a) dc (direct current) correction (performed automatically by the instrument software), (b) apodization (window multiplication) of the <2 time-domain data, (c) Fourier transformation and phase correction, (d) window multiplication of the t domain data and phase correction (unless it is a magnitude or a power-mode spectrum, in which case phase correction is not required), (e) complex Fourier transformation in Fu (f) coaddition of real and imaginary data (if phase-sensitive representation is required) to give a magnitude (M) or a power-mode (P) spectrum. Additional steps may be tilting, symmetrization, and calculation of projections. A schematic representation of the steps involved is presented in Fig. 3.5. 

Phasing A process of phase correction that is carried out by a linear combination of the real and imaginary sections of a 1D spectrum to produce signals with pure absorption-mode peak shapes. 

Phasing The process of correcting the phase of a spectrum (either manually or under automation). 

The answer to the argument as to whether the mechanism of the induction of polymers is related to the nucleation process (as predicted in CNT [1-4]) or to the phase separation process [19,32] is that the nucleation process is correct in the case of melt crystallization. 

In this summary, the local thermal equilibrium model has been used to derive the energy equation. This model is much simpler than the two-phase model however, the local thermal equilibrium model is most likely not adequate to describe the transport of energy when the temperature of the fluid and solid are undergoing extremely rapid changes. Although such extremely rapid temperature changes are not expected, in most RTM, IP, and AP processes the correctness of the local thermal equilibrium assumption can be verified by following the procedure discussed by Whitaker [28]. 

The basic processing of ID and 2D data requires obligatory processing steps for transforming the raw data (FID) into a "readable spectrum, i.e. Fourier transformation and phase correction to produce a spectrum with absorptive lineshapes. Finally, a few additional step.s (calibration, peak picking, integration) as discussed in chapter 4 are required before the spectrum is eventually plotted. 

With the Autom. Phase Correction option selected from the Process pull-down menu (Fig. 5.4) a fully automatic phase correction can be performed. 

With the command Phase Correction in the Process pull-down menu the button panel is switched into Phase mode (Fig. 5.4) and a semi-automatic or fully manual phase correction may be performed. 

Fig. 5.4 Button panel for phase correction (left) opened by choosing the Phase Correction option in the Process pull-down menu (right).

Load the raw data of the ID H experiment measured for peracetylated glucose D NMRDATA GLUCOSE 1D H GH 002001.FID and perform a Fourier transformation. Use either the FT button in the button panel or from the Process pull-down menu choose the FT option. In the DC Correction dialog box click on the No button. Note that the calculated spectrum is incorrectly phased. Use the dual display option to compare this spectrum, showing the ring protons, with the correctly phased spectrum D NMRDATA GLUCOSE 1 D H GH 002999.l R. Exit the dual display and from the Process pull-down menu choose the Phase Correction option. The... 

For 2D data which need no phase correction the PHmod parameter in FI, available in the General parameter setup dialog box opened via the Process pull-down menu, must be set to me if a magnitude, or to ps if a power spectrum should be calculated. Use the Help tool for more informations. 

For 2D spectra to be displayed in phased mode, choose the Manual phase correction option from the Process pull-down menu of 2D WIN-NMR. This will also change the info field of the button panel and disable some of the panel buttons (Fig. 5.7). 

Fig. 5.7 Buttons accessible with the Manual phase correction option in the Process pull-down menu of 2D WIN- NMR (left). Additional button panel for adjusting the reference point and for switching the 2D display off (right).

Load the raw data obtained for peracetylated glucose with the 2D TOCSY experiment D NMRDATA GLUCOSE 2D HH GHHTO 001001.SER and perform a 2D FT following the guidelines given above. Enter the Manual phase correction option in the Process pull-down menu and perform a phase correction in F2 and Ft according to the procedure outlined above. Try to phase all peaks to positive absorption and store the spectrum (... 001001. RR). 

Correction, Window Function (Exponential LB = 1.0 Hz) and FT. In the frequency domain select Phase Correction (6th Order), Peak Picking (positive Peaks only X Range whole Spectrum) of the whole region. Save Spectrum (set Processing Number Increment = 1) and Plot Spectrum (set the plot parameters according to your preferences). Execute the automatic processing and if you are satisfied with the result, store this job for processing 1D C raw data as C.JOB. 

The data processing can be divided into three phases. Phase 1 is the removal of poor quality spectra with an automated routine. Phase 2 is the data preprocessing of the spectra, which passed the quality test. This usually entails some type of baseline correction and normalization process. Phase 3 is multivariate image reconstruction where the spectra are classified and reproduced as color points... 

For both the OVPO process and the MCVD process the correct temperature setting during the course of the respective process steps has an important bearing on the quality of the final preform. The reason is that both processes consist of a first step where reactions in the gas phase lead to soot particles which settle out afterwards, and of a second step where the soot is melted to a transparent glass. In the first step the efficiency for oxide formation critically depends on the temperature of the gas and differs from one oxide to another11. The second step is sensitive to temperature... 

The hardware and data-processing details of ID NMR data were discussed in Chapter 3 data sampling in the ADC, quadrature detection, the spectral window, weighting (window) functions, and phase correction. We will have to revisit each of these topics in the second (t, F ) dimension and some of them will take on added signihcance. 

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