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Notes: We report an unusual case occuring in a 25-year-old male of a balloon cell nevus which also showed clinical and pathological features of a halo nevus.

Notes: A physical-space eddy-damped quasinormal Markovian model for the two-point scalar correlation function is used to simulate wind tunnel experiments on scalar mixing. The simulations closely approximate experimentally observed trends of scalar variance and length scales in both heated-grid and heated-screen experiments. The simplicity of the model should enable its effective use in modeling the analogous turbulent mixing terms in the two-point scalar probability density function equations.

Notes: Abstract Transverse energy distributions have been measured for collisions of 10 GeV/nucleon Si with targets of Al, Cu and Pb using a combination of a NaI wall and a uranium based sampling calorimeter. The measured cross sectionsdσ/dE T anddE T /dη are consistent with full stopping and an increase, with increasing values ofE T , of energy flow into large angles.

Notes: Summary Negatively stained paracrystals of reconstituted thin filaments decorated with myosin subfragment 1 (S1), at high calcium concentrations (≥10−5 m), exhibitpgg plane group symmetry with component filaments having 28 subunits in 13 turns of the actin genetic helix. Isolated S1 decorated F-actin filaments trapped in a stain film were also observed to form spontaneously paracrystals withpgg plane group symmetry. We conclude that a favourable S1-S1 interaction must exist in order to stabilize these structures. Three-dimensional helical reconstructions, calculated from these paracrystals show S1 to be curved, 12 to 14 nm long and tilted with respect to the helical axis, in broad agreement with previous reconstructions calculated from isolated particles. Reconstructions of S1 and HMM decorated filaments that resolve actin show a principal myosin binding site located on the side of the actin subunit reported by Taylor & Amos [J. molec. Biol. 147, 297–324 (1981)] and a possible small interaction on the opposite side. The appearance, symmetry and helical reconstructions of iolated F-actin filaments decorated with heavy meromyosin (HMM) were similar to those of S1 decorated filaments, except at high radii where extra mass was observed. This probably arose from the connection between the two heads of HMM bound to the same long-pitch strand of actin. In contrast to most studies on thin filaments, which use reconstituted filaments, we present data on natural I-segments of muscle homogenates. Individual filaments exhibited actin helical symmetry which on reconstruction gave a two-domain motif oriented constitently with its long axis approximately perpendicular to the helical axis, but inclined towards the 5.9 nm genetic helix. Our original interpretation of these maps [Seymour & O'Brien,Nature, Lond. 283, 680–2 (1980)] depended upon reconstructions from F-actin paracrystals, which suggested actin was rather symmetrical in shape. New data from tw- and three-dimensional crystal studies and reconstructions of actin-tropomyosin filaments show that actin is rather elongated and consists of two domains. These results indicate that actin contributes towards both domains of our I-segment motif and are consistent with the monomer long axis lying approximately perpendicular to the helical axis. Although tropomyosin is not resolved, comparison of the actin-tropomyosin and I-segment reconstructions suggests that tropomyosin is strongly merged with the actin domain at a lower radius from the helical axis and that the domain at higher radius arises solely from actin.

Notes: Summary Crystals formed from a mixture of tropomyosin and troponin T have an open double-stranded lattice structure with a diamond-shaped repeat. In some regions the appearance in electron micrographs of negatively stained specimens changes from this double-diamond lattice to a more condensed banded crystal form. The double-diamond lattice has plane group symmetrycmm with unit cell 76.3 by 21.7nm. The molecules form continuous chains along the diagonal of the unit cell and the diagonal length (79.4 nm) is that expected for two tropomyosin molecules joined end-to-end. Computer filtering of the micrographs shows that the strands of the lattice are thicker from the acute vertex of the large diamond to a point about half-way along the side of the diamond, where there is a small blob of density. At the acute vertex of the diamond is a large blob of density which is accentuated, however, by being at the lattice node where strands cross each other, and which is much weaker in regions of the micrographs where the crystals have condensed laterally. The results indicate that troponin T is a long thin molecule running in contact with the tropomyosin strands over 40–50% of the tropomyosin molecular length. The small globular region may represent the end-to-end overlap of tropomyosin but is more likely to be a globular region at the C-terminal region of troponin T.