Behavior of hot-pressed boron carbide at high temperatures. II. Strength

Translated from Poroshkovaya Metallurgiya, No. 6(318), pp. 77–82, June, 1989.     

Multicoil array for high resolution imaging of the breast

An RF multicoil array for high resolution imaging of the breast is presented. The RF multicoil is incorporated into a dedicated breast imaging apparatus that holds either breast in gentle compression during imaging. Simulations and imaging experiments demonstrate the high sensitivity and RF homogeneity of the multicoil array. Direct comparisons are made between the multicoil and a surface coil. In vivo images are presented to demonstrate the homogeneity of the RF field of the multicoil over the entire breast. An in vivo image of both high temporal and spatial resolution is shown, which demonstrates the sensitivity of the RF multicoil array that may be achieved in a practical imaging experiment.     

Three-dimensional structure of the plant photosystem II reaction centre at 8 A resolution

Photosystem II is a multisubunit enzyme complex involved in plant photosynthesis. It uses solar energy to catalyse the breakdown of water to reducing equivalents and molecular oxygen. Native photosystem II comprises more than 25 different subunits, and has a relative molecular mass of more than 600K. Here we report the three-dimensional structure of a photosystem II subcomplex, containing the proteins D1, D2, CP47 and cytochrome b-559, determined by electron crystallography. This CP47 reaction centre, which has a relative molecular mass of 160K, can perform light-mediated energy and electron-transfer reactions but is unable to oxidize water. The complex contains 23 transmembrane alpha-helices, of which 16 have been assigned to the D1, D2 and CP47 proteins. The arrangement of these helices is remarkably similar to that of the helices in the reaction centres of purple bacteria and of plant photosystem I, indicating a common evolutionary origin for these assemblies. The map suggests that redox cofactors in the D1-D2 complex are located in positions analogous to those in the bacterial reaction centre, but the distance between the chlorophylls corresponding to the bacterial 'special pair' is significantly larger.