A method for sintering silicon nitride using microwave energy at 2.45 GHz is described. Sintering takes place in air, in times of between 30 and 120 minutes and has been scaled up to give isothermal conditions over a batch size of 150 mm diameter by 200 mm in height and weighs approximately 1.0 kg. Additions of 5% alumina and 5% yttria result in a sintered product density of approximately 97% of theoretical, with a density variation better than:±0.5% throughout the batch.It has been estimated that a load of 7.0 kg can be conventionally sintered using a 12 hour cycle and an energy consumption of 19.7 kWh/kg. In contrast with microwave energy, a batch of 540 g can be sintered in 120 minutes with an energy consumption of approximately 3.1 kWh/kg. This results in a possible energy savings of up to 78% for microwave heating.
Standard bandshift reactions (Fig. 3a) utilized 32 P-labelled`BH' probes that contained three CpG sites (underlined below) whose methylation/mismatch status was varied. The BH probes used in Fig. 3c were 59TCAGATTCGCGCZGGCTGCGATAAGCTGZGCGGATCCZGGGAATTCAGCT39 39AGTCTAAGCGCGGYCGACGCTATTCGACGYGCCTAGGGYCCTTAAGTCGA59 where Y C, m 5 C, T or U, and Z C or m 5 C (see underlined dinucleotides). The three CpG sites were identically modi®ed/mismatched within each probe. Binding reactions were carried out at room temperature for 30 min in 20 mM HEPES pH 7.9, 25 mM NaCl, 10 mM b-mercaptoethanol, 1 mM EDTA, 4% glycerol, 1% digitonin and 50 ng sonicated E. coli DNA. The glycosylase reaction does not occur under these conditions (data not shown). Complexes were electrophoresed through 6% polyacrylamide gels in 0:5 3 TBE at 4 8C. Complexes formed under conditions favourable to the glycosylase reaction (Fig. 3b, c) utilized the¯uorescent or 32 P-labelled JJ oligonucleotide (see above) as a probe. In standard gel-retardation reactions, 200 nM protein was incubated with 66 nM labelled oligonucleotide substrate and 333 nM unlabelled homoduplex oligonucleotide in 50 mM Tris±HCl pH 8.0, 1 mM DTT, 5% glycerol, 1 mM EDTA at 37 8C for 20 min. The samples were electrophoresed immediately through a 6% native 0:5 3 TBE polyacrylamide gel for 45 min at 100 V. A probe with an abasic site was generated by treatment of oligonucleotide JJ containing a MG×UG mismatch with the enzyme uracil DNA glycosylase.
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