Turbulent Dynamics in the Solar Convection Zone

Observations of the sun reveal highly complex flows and magnetic structures that must result from turbulent convection in the solar envelope. A remarkable degree of large-scale coherence emerges from the small-scale turbulent dynamics, as seen in the cycles of magnetic activity and in the differential rotation profile of this star. High-performance computing now permits numerical simulations of compressible turbulence and magnetohydrodynamics with sufficient resolution to show that compact structures of vorticity and magnetic fields can coexist with larger scales. Such structured turbulence is yielding transport properties for heat and angular momentum at considerable variance with earlier models. These simulations are elucidating the coupling of turbulent fluid motions with rotation and magnetic fields, which must control the interlinked differential rotation and magnetic dynamo action.

Differences in purine metabolism in patients with Down's syndrome

Three enzymes intervening in de novo purine synthesis, as well as cystathionine B-synthetase, have been mapped to chromosome 21. In order to gain a better understanding of purine synthesis anomalies in Down's syndrome, the present authors studied the variations in mitotic index of lymphocyte cultures to which various inhibitors or metabolites of purine synthesis had been added. In spite of common gene dosage effects, unexpected and highly significant differences were noted between Down's syndrome patients without complications and those presenting with additional psychotic features. In Down's syndrome patients without complications, a highly significant decrease in mitotic index was noted in the presence of exogenous inosine. A significant decrease in the presence of adenosine and guanosine was also noted. These findings are in keeping with the expected metabolic repercussions of genes mapped to chromosome 21. In Down's syndrome patients with psychotic complications, the in vitro reactions were quite different. A paradoxal increase in mitotic index was noted in the presence of inosine and of adenosine, but the response to guanosine did not differ from that observed in normal controls. These findings were unexpected and seem to indicate that, in spite of the gene dosage effect, psychotic Down's syndrome patients are unable to compensate abnormal purine synthesis and resulting imbalances. Furthermore, a marked difference in purine metabolic reactions was noted between Down's syndrome patients receiving supplemental folic/folinic acid and those on no therapy. This suggests that some modulation of the gene dosage effect may be possible.