Cycles zone refining

Zone refining uses repeated melting and freezing cycles to purify materials through crystallization. 

Water frozen slowly will be free of dissolved organic and inorganic compounds. The freeze-thaw cycle is used to purify semiconductors by the process called zone refining. Fog and dew have also been used as sources of freshwater. 

Zone refining is a purification process in which a rod of material is subjected to successive melting and freezing cycles. Impurities are swept by a moving molten zone to the end of the rod, which is cut off. 

The uranyl heavy atom parameters were then used to calculate Fj and Fj two sets of phases for the protein were calculated - one for each possible heavy atom enantiomorph - by the method of single isomorphous replacement with the inclusion of anomalous scattering data. The value of E" was initially calculated from the r.m.s. error in the least squares refinement for the centric zone, and E" was made equal to E/3. The phases, were used to compute difference Fouriers with coefficients (Fp - Fp exp.iap for the other derivatives. The phases calculated from uranyl positions gave a clear indication of the heavy atom positions of other derivatives which agreed well with those positions determined from the Patterson functions. The enantiomorphic set of uranyl positions gave no clear indication of the heavy atom positions. Thus, the correct enantio-morphs and relative origins for derivatives were established. We then carried out a series of phase refinement cycles (16,17). 

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