Longitudinal order

R i H is the longitudinal order auto-relaxation which may depend on all relaxation mechanisms affecting the spin system. We give below the dipolar and csa contributions... 

Figure 3 Creation of the longitudinal order by cross-correlation as a function of the mixing time fm which follows the inversion of a carbon-13 doublet (due to a./-coupling with a bonded proton). The read-pulse transforms the longitudinal polarization into an in-phase doublet and the longitudinal order into an antiphase doublet. The superposition of these two doublets leads to the observation of an asymmetric doublet.

These results suggest that the signals arise from dipole-dipole coupled protons. Kreis et al. confirmed this finding by measurements using one-dimensional zero- and double-quantum filtering, two-dimensional J-resolved spectroscopy, two-dimensional constant time COSY and longitudinal order separation... 

These equations involve additional parameters with respect to the classical Solomon equations (see (13)) which is the longitudinal order specific... 

Similarly to non-selective experiments, the first operation needed to perform experiments involving selective pulses is the transformation of longitudinal order (Zeeman polarization 1 ) into transverse magnetization or ly). This can be achieved by a selective excitation pulse. The first successful shaped pulse described in the literature is the Gaussian 90° pulse [1]. This analytical function has been chosen because its Fourier transform is also a Gaussian. In a first order approximation, the Fourier transform of a time-domain envelope can be considered to describe the frequency response of the shaped pulse. This amounts to say that the response of the spin system to a radio-frequency (rf) pulse is linear. An exact description of the... 

The constituent molecules of a cholesteric phase roust contain at least one center of chirality and frequently include a steroidal ring system. They are arranged with their long axes (directors) parallel, but without longitudinal order. A convenient description of a cholesteric arrangement (which is microscopically incorrect(3a)) places the molecules in nematic like "layers" which are very slightly twisted with respect to those above and below (Fig. 1). The angle and direction of... 

Meso phases can be recognized and evaluated by X-ray measurements. Three-dimensionally crystalline polymers have a meridian at the equator, and also exhibit sharp diffraction reflexes in all other directions (see Figure 5-6). Other polymers only give sharp diffraction reflexes at the meridian. Examples of this behavior are poly(trimethylene terephthalamide) and poly(oxydi-ethylene-4,4 -dibenzoate). Such behavior is caused by longitudinal order in the chain direction, and lateral disorder in both other dimensions the crystals have one-dimensional order and two-dimensional disorder, which is characteristic of nematic meso phases (Figure 5-29). Smectic and cholesterinic meso phases are other one-dimensional oriented ordered systems. 

On the other hand, considering the characteristic X-ray diffraction patterns of PAN fibers, Bohn et al. [40] suggested that the pseudo-hexagonal form of PAN presents only lateral order in the packing of chain axes, and no longitudinal order parallel to the chain axes. 

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