Production of super-high strength aluminum alloy billets by low frequency electromagnetic casting

The effects of low frequency electromagnetic field on the macro-physical fields in the semi-continuous casting process of aluminum alloys and the microstructure and crack in the billets were studied and analyzed by the numerical and experimental methods.Comparison of the results for the macro-physical fields in the low frequency electromagnetic casting（LFEC） process with the conventional DC casting process indicates the following characters due to the application of electromagnetic field：an entirely changed direction and remarkably increased velocity of melt flow;a uniform distribution and a decreased gradient of temperature;elevated isothermal lines;a reduced sump depth;decreased stress and plastic deformation.Further,the microstructure of the billets is refined remarkably and the crack in the billets is eliminated in LFEC process because of modification of the macro-physical fields induced by the application of low frequency electromagnetic field.

Cosntruction of the physical map of yeast（Saccharomyces cerevisiae）chromosome V^1

There are about 17 chromosomes in yeast Saccharomycescerevisiae.A middle sized chromosome,chromosome V,waschosen in this work for studying and constructing the physi-cal maps.Chromosome V from strain A364a was isolatedby pulsed-field gradient gel electrophoresis(PFGE).Gelslices containing chromosome V DNA were digestedwith two rare cutting enzymes,NotⅠand SfiⅠ,and three6-Nt recognizing enzymes,SmaⅠ,SstⅡ and ApaⅠ.Several strategies-partial or complete digestions,digestion with different sets of two enzymes,and hybrid-ization with cloned genetically mapped probes(CAN1,URA3,CEN5,PRO3,CHO1,SUP19,RAD51,RAD3)——were used to align the restriction fragments.There are 9,9,15,17,and 20 sites for NotⅠ,SfiⅠ,SmaⅠ,SstⅡ and ApaⅠrespectively in the map of the A364a chromosome V.Itstotal length was calculated to be 620 Kb(Kilo-bases).Thedistributions of the cutting sites for these five enzymesthrough the whole chromosome are not uniform.A comp-arison between the physical map and the genetic map wasalso made.