Alignment direction orientation

Fig. 8.2 Ori entations of an amide NH dipolar coupling bond-vector of the protein ubiquitin. Each cone of orientations is compatible with two different alignment directions adopted by the protein in two different alignment media. The central lines defining each cone correspond to the orientations obtained from the measured dipolar couplings. The outer lines include orientations that are possible if the dipolar coupling values are either increased or decreased by 1 Hz. The angle at which the two cones intersect is defined by ft. The solid dot at the cone intersection determines the orientation of the dipolar coupling vector. (Reproduced with permission from B. E. Ramirez and A. Bax, J. Am. Chem. Soc. 1998, 720, 9106-9107.)...

So far we have discussed various studies on the relaxation of the population bPo of excited state rovibrational levels in elastic and inelastic collisions. To this end the intensity of fluorescence was measured in one or the other way. If an analysis of the state of polarization of the radiation is performed, one may obtain information on the behavior of alignment and orientation of the molecular angular momenta in elastic and inelastic collisions. If we register, under collisional conditions, the polarization properties of a directly laser-induced rovibrational level of the molecule, then, according to (2.35) and (2.39), it is possible to determine the rates... 

The number of components in the relative permittivity tensor is limited by the sample symmetry. In axially oriented samples two independent components are found, parallel and perpendicular to the alignment direction (ey and e L or j and e2), since the sample is isotropic in the plane normal to the direction of orientation, i.e. ej = e2. 

Fig. 15. Schematic of polar and alignment disorder as measured by XRD and NMR. Upper line polar disorder with random up or down orientations of the direction of the molecules with equal probabilities to restore the inversion symmetry for X-ray, the two directions are possible with equal probabilities on each site NMR cannot measure polar disorder, all sites are equivalent. Lower line alignment disorder of the molecules characterized by a long correlation time as compared to the inverse Larmor frequency coL, and librational disorder represented by ellipses of thermal-induced rotations (with angular amplitude possibly larger than the corresponding disalignment) around the mean alignment direction of the molecules. The frequencies of librations 1 jx is much larger than the Larmor frequency. For X-ray, both orientational disorders are mixed up with a preponderant contribution of the high-frequency librations for NMR, only alignment disorder remains.

Fig. 3. The phase separation process in a nematic solvent. System composition liquid crystal, 98%wt silicone oil (Aldrich), 2%wt. a Some droplets form after the quench (picture 20 s after the quench), b The droplets diffuse randomly and coalesce in the initial stages of the phase separation (picture 42 s after the quench), c Coalescence stops once a critical size is reached. The droplets begin to form small linear aggregates oriented along the alignment direction of the liquid crystal (picture 55 s after the quench), d The chains grow as time evolves (picture 120 s after the quench). Scale bar 60 im...

The reason for the lower experimental value lies, of course, in the facts that not all chain segments are parallel to the direction of alignment and that the average number of chains crossing unit area normal to the alignment direction is less than the theoretical number. In the next section models for highly oriented polyethylene are described. A model that has been found particularly useful for understanding the moduli of oriented LCPs is considered in section 12.4.7. 

The mechanical properties of composite materials under the influence of "rule of mixtures". The alignment or orientation of the fibres in the composite materials can be divided on three type one-dimensional reinforcement, two-dimensional (planar) reinforcement and three-dimensional(random) reinforcement. The random orientation type of the isotropic but has greatly decreased reinforcing value(about one-third of the one-dimentional reinforced value). As the fibre orientation becomes more random, the mechanical properties in any one direction become lower. 

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