The radar altimeter carried aboard the Pioneer Venus orbiter spacecraft has yielded a topographic map covering 93% of the Venus globe, with a linear surface resolution of better than 150 km. Vertical measurement accuracy exceeds 200 m. Extremes in relief (expressed as a center‐of‐mass‐to‐surface radius) extend from a low of 6049 km to a high of 6062 km. Only about 5% of the observed surface is elevated more than 2 km above the mean radius (6051.5 ±0.1 km). Although the elevated terrain comprises a number of separated components, it is dominated by a massive equatorial region the size of South America. Of the total surface, 60% lies within 500 m, and 20% within 125 m, of the modal radius (6051.1 km). The planetary polar ellipticity is nearly zero, with an upper bound of 4 × 10−5. In addition to the surface relief, the distribution of average meter‐scale surface slopes, in the observable range from 1° to 10°, is determined for the same regions, and at the same footprint resolution, as in the altimetric observations. Elevated areas have generally higher values of average slope; most features seen in the earth‐based images are also seen in the vertical‐incidence spacecraft observations, although a few exceptions are noted. Of interest are several very long (up to nearly 5000 km, in one case), thin, and relatively straight parallel features, not hitherto reported on Venus.

From earth‐based Doppler and interferometric radio observations we determined the paths, in three dimensions and as functions of time, taken by the Pioneer probes as they fell to the surface of Venus. From the motion of each probe below about 65‐km altitude we were able to infer the ambient wind velocity with an estimated uncertainty of about 1 m s−1 in each vector component. The magnitude of the velocity was about 1 m s−1 or less near the surface of the planet and about 100 m s−1 near 65‐km altitude at all four probe locations. Distinct strata of high wind shear were centered at altitudes of 15, 45, and 60 km, where the atmosphere is most stable against verticle motion. Except within a few kilometers of the surface, the wind velocity was always directed within a few degrees of due west. At the day and the night probe sites, which were separated by 100° in longitude and 3° in latitude, the altitude profiles of the westward velocity were virtually identical. Thus the dominant motion of the lower atmosphere seems to be a retrograde zonal rotation. Eddies appear to account for most of the instantaneous meridional velocity. However, in the radiatively heated middle cloud layer, between 50‐ and 55‐km altitude, equatorward flow of 1–7 m s−1 was observed for all four probes. These observations, coupled with other observations of ∼10 m s−1 poleward average meridional velocity for cloud top features at about 65‐km altitude, suggest that within the clouds a thermally driven mean meridional circulation is superimposed on the much more rapid zonal rotation.

Interfacial tension behavior of binary and ternary mixtures of partially miscible Lennard-Jones fluids: A molecular dynamics simulation A molecular dynamics study of macromolecules in good solvents: Comparison with dielectric spectroscopy experimentsWe consider a family of molecular liquids, each consisting of linear molecules with N covalent bonds, focusing specifically on Nϭ1 ͑diatomic liquid͒, Nϭ3 ͑four-atom molecular liquid͒, and Nϭ200 ͑macromolecular liquid͒. The bonded and nonbonded potentials, u b (r) and u nb (r), are the same for each system, with u b representing stiff linear springs and u nb corresponding to the repulsive portion of the Lennard-Jones potential. The relaxation of the stress difference , following a constant-volume elongation of the system, is determined in terms of interatomic interactions by nonequilibrium molecular dynamics simulations. It is found that the nonbonded interactions make the principal contribution to while the bonds make a negative contribution. For all systems studied it is found that, following a short induction period after the start of relaxation, ϭC͗͗P 2 ( b )͘͘, where ͗͗P 2 ( b )͘͘(t) is a measure of the individual bond orientation and the proportionality constant Cϭ3.5 within simulation accuracy, for Nу3. The principal difference between the behavior for small and large N is the rate at which ͗͗P 2 ( b )͘͘(t) decays. An explanation of the broad applicability of the relation ϭC͗͗P 2 ( b )͘͘ is presented in terms of the concepts of steric shielding, intrinsic interaction distributions, and intrinsic stresses. The failure of this relation during the short induction period is explained in terms of anisotropies in atom distributions present immediately after deformation.

We present a method of visualizing topological defects arising in numerical simulations of liquid crystals. The method is based on scientific visualization techniques developed to visualize second-rank tensor fields, yielding information not only on the local structure of the field but also on the continuity of these structures. We show how these techniques can be used to first locate topological defects in fluid simulations of nematic liquid crystals where the locations are not known a priori and then study the properties of these defects including the core structure. We apply these techniques to simulation data obtained by previous authors who studied a rapid quench and subsequent equilibration of a Gay-Berne nematic. The quench produces a large number of disclination loops which we locate and track with the visualization methods. We show that the cores of the disclination lines have a biaxial region and the loops themselves are of a hybrid wedge-twist variety.