In the initial stage of SAD phasing, the essential point is to break the intrinsic phase ambiguity. The presence of two kinds of phase information enables the discrimination of phase doublets from SAD data prior to density modification. One is from the heavy atoms (anomalous scatterers), while the other is from the direct-methods phase relationships. The former can be expressed by the Sim distribution, while the latter can be expressed by the Cochran distribution. Typically, only the Sim distribution has been used to yield initial phases for subsequent density modification. However, it has been demonstrated that using direct-methods phases based on the product of the Sim and Cochran distributions can lead to improved initial phases. In this paper, the direct-methods phasing procedure OASIS has been improved and combined with the SOLVE/RESOLVE procedure. Experimental SAD data from three known proteins with expected Bijvoet ratios / in the range 1.4-7.0% were used as test cases. In all cases, the phases obtained using the program RESOLVE beginning with initial phases based on experimental phases plus Sim and direct-methods information were more accurate than those based on experimental plus Sim phase information alone.

The principle of dual-space phasing is used in dealing with protein SAD data. Four programs are involved in iterative dual-space fragment extension to improve automatic model building. OASIS-2004 is used to break the phase ambiguity intrinsic in the SAD experiment. In the initial cycle, discrimination of SAD phase doublets is performed by the direct method incorporating the known anomalous-scattering substructure. In subsequent cycles, discrimination is performed by the direct method incorporating both the known anomalous-scattering substructure and the partial protein structure obtained from model building in the preceding cycle. DM is used to improve direct-method phases via density modification. RESOLVE is used for initial model building and ARP/wARP is used to complete the structure. Case studies with three sets of difficult SAD data showed that the procedure is beneficial to high-throughput protein-structure determination and all of the four programs involved make their unique contribution to the process.

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Understanding tungsten melting behavior and its influence on plasma operation is one of the main concerns for ITER, which will be operated with a full tungsten divertor. Similar to ITER, actively cooled tungsten cassette modules have been successfully installed for the upper divertor in EAST for a stronger heat exhaust ability. However, an unexpected in situ tungsten melting phenomenon has been observed around the strike point area on both the inner and outer targets during recent EAST plasma campaigns. It was identified that such tungsten melting was caused by the leading edges, which leads to much high heat load on the protruded edges of the cassette modules. All tungsten melting occurred only at the edges of the cassette modules where larger misalignment up to millimeter scale was formed. The melted layer, which was mainly driven by the electromagnetic force, was moved either up or down under different conditions. Only a few bridge connections along the vertical direction could be formed. Such tungsten melting ejected a large number of droplets into the core plasma, and resulted in a sharp increase of tungsten impurity and power radiation and could eventually lead to disruptions. With droplet ejection and melted layer removal, the melted corner seems to form a moderate chamfer structure and thus may mitigate the temperature rise. Under current operation conditions, EAST can tolerate such melting to some extent. Several solutions to help avoid this kind of melting have been proposed according to the thermal analysis for future EAST operations.