Precession angle

Ni filtered Cu radiation 30° precession angle). Three layers of film (Kodak No-screen) were exposed simultaneously so that, if necessary, a longer range of intensities might be measured than with one. The films were chemically processed together. 

Figure 9.14. The hourly scan pattern of COBE, WMAP and Planck from left to right. In each panel the anti-solar direction is in the center, and plus signs denote the North and South ecliptic poles. An equiangular azimuthal projection is used. COBE scanned this area in one orbit of about 103 minutes, WMAP scans its pattern every hour, while Planck spends several hours integrating on one scan circle of radius 70° radius shown offset from anti-Sun by a 15° precession angle.

Figure 9.16. The path of the Planck scan circle center when the precession angle is 15° and the precession rate is 10 cycles per year. The difference between the Northern and Southern loops of the cycloid causes the asymmetry in the coverage pattern seen in Figure 9.15.

In the case of quasi-elastic neutron scattering, the total precession angle, q>, is a function of the energy transfer a> (p = cat. The detected intensity is the average of cos (p, weighted by the scattering function of the sample S Q,ca)... 

And what about optically uniaxial phases fti the case of a nematic, the molecular distribution is independent of the precession angle (O = const) but may depend on angle 4. For a smectic A, in the first approximation, the orientational distribution function is the same as for the nematic. However, there is some interaction between the translational and orientational degrees of freedom that can be taken into account as a correction to/(i9,0). At first, cmisider a distribution function for a uniaxial phase consisting of axially symmetric molecules [12]. 

The angle is usually called the nutation angle and the precession angle. The Euler angles can be expressed by the functions p, q T a P introduced above. By a direct calculation it can be found that... 

Precession (Buerger) Camera. In contrast to the Weissenberg camera, the crystal carrier is now coupled to the film cassette so that both move in exactly the same way while the pattern is being recorded (Fig. 23). A direction in the crystal pre-cesses (precession angle /<) about the incident X-ray beam, so that reciprocal lattice points lying in a plane perpendicular to this crystal direction cut the reflection sphere. A precession pattern represents the reciprocal lattice in undistorted form... 

Fig. 6. Orientational probability distribution of the N2 molecules in the disordered j5-phase of solid nitrogen, from Mean Field calculations [50]. This result, which would correspond to a nearly free precession of the molecules about the z-axis with a large spread in the precession angle, is thermodynamically unstable...

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