The formation of large woody debris (LAID) piles has a profound impact on channel patterns and riparian succession in temperate rivers. The opportunity to study LWD along the Sabie River, a river in the semi-arid region of Kruger National Park, South Africa, arose in February 2000 after a significant flood (c. 100-year return interval) removed a large proportion of the fully mature riparian forest and other plant communities. Much of the uprooted vegetation was deposited as LWD piles (woody vegetation accumulations deposited on the ground >0.1 m(3)) throughout the riparian and upland zones. In this article we describe the spatial distribution patterns of LWD as related to geomorphic channel type and flood frequency zone, and assess pile composition characteristics six months after the flood. Within the areas surveyed there were 68 LWD piles per hectare, the median size of LWD piles was 4.6 m(3) but pile sizes (by volume) varied widely. Pool/rapid geomorphic channel types had the highest density of LWD piles (79 ha(-1)) and the largest piles (by volume) were in the bedrock anastomosing channels (mean = 124 m(3)). Piles were larger in the seasonal and ephemeral flood frequency zones (mean = 54 m(3) and 55 M) than piles in the active zone (c. 2 m(3)). The patterns of distribution and volume of LWD will affect the subsequent development of vegetation communities as debris piles form a mosaic of patches of surviving organisms and propagules that can strongly influence the initial trajectory of succession. The amount, distribution, and subsequent decomposition of LWD are different from that reported for temperate rivers, suggesting that the role of LWD may be different on non-floodplain rivers such as the Sabie in semi-arid South Africa. Copyright (C) 2004 John Wiley Sons, Ltd.

We present low-resolution photometric spectra in the wavelength range 407–907 μm of impact sites G, H, E, C, K, L, Q1, and W plus K together, arising from the collision of Comet D/Shoemaker–Levy 9 with Jupiter. The spectra were obtained from narrow band CCD images taken between July 15th and July 22nd using the 1-m Jacobus Kapteyn Telescope on La Palma. Our results indicate the impact debris to have low overall optical depths (τ < 1) which decrease with increasing wavelength for all individual sites observed. Our results also imply that mass absorption of sunlight is the dominant process occurring in the impact debris and that a decrease in optical depth with time is due to the material dissipating in the jovian atmosphere.

Collisions between small bodies (such as asteroids and comets) and the terrestrial planets are known to throw ejecta far beyond the point of impact. But until the fragments of comet Shoemaker-Levy 9 hit Jupiter in July 1994 (refs 1, 2), there had been no opportunity to study the effects of such collisions on gas-giant planets. Here we present optical spectra obtained during the collision of fragments L and Q(1), with Jupiter. We observed emission lines from sodium, magnesium, calcium, iron, manganese and chromium as the ejecta plume fell back onto Jupiter's atmosphere. All of these elements are expected to occur only very deep in Jupiter's atmosphere-considerably below the depth to which the fragments penetrated--, suggesting that the material responsible for the emissions originated almost entirely in the comet itself. The initial. phase of emission is associated with heating of the impact ejecta as it fell back onto the planet. A second, later phase of emission was also observed, which we associate with grains of silicate dust that condensed within the cooling fireball and subsequently re-entered, meteor-like, into Jupiter's atmosphere.

We report optical CCD imaging and photometry of the impact plume on Jupiter resulting from the destruction of fragment L of D/Shoemaker-Levy 9. The plume appears resolved in several frames, with the largest dimensions appearing similar to those of other plumes imaged by NST. The light curve and timings are consistent with an ejection velocity for the plume material of v similar or equal to 20 km s(-1). The plume itself was detected by reflected sunlight from dust grains, and the observed fluxes are consistent with an optically thick plume composed of silicates. A large flare in the light curve was observed similar to 7 min after the initial maximum, the cause of which is unclear.

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Final results from model atmosphere analyses of all blue stars in a similar to 325 square degree region of the Galactic halo are presented. A kinematic analysis reveals the presence of one star which cannot have been ejected from the disk according to contemporary theories. Ten other objects have, however, evolutionary times consistent with classification as disk runaway stars. Our results therefore imply the existence of some 200 stars in the Galaxy unexplainable in terms of disk ejection models, and set a lower limit of 10,000 runaway halo B-type stars.

High-resolution optical stellar and interstellar observations toward the halo star HD 203664 and six surrounding early-type stars have been combined with a 21 cm mapping of the region to investigate a 70 km s-1 high-velocity cloud (HVC). The distance of the HVC from the Galactic plane (z) has been constrained to lie between 200 and 1500 pc; upper limits to temperature and velocity dispersion of 4600 K and 2.2 km s-1 have been estimated; and a column density ratio N(Na II)/N(Ca II) congruent-to 0.32 has been deduced. These parameters are consistent with the material being shocked gas, possibly arising from an old supernova remnant. The N(Na I)/N(H I) and N(Ca II)/N(H I) ratios are anomalously large by factors of approximately 20 and 100, respectively, with respect to normal diffuse gas; several scenarios are presented as possible explanations of this phenomenon.

Infrared photometry of seventeen high latitude early-type stars, that have either been identified as post-AGB objects or are post-AGB candidates, has been obtained at JHKL and nbM wavelengths. This has been combined with optical and IRAS observations, and compared with LTE model atmosphere fluxes; infrared excesses are found for five stars. Of the known post-AGB stars, only the highest mass objects reveal an infrared excess, suggesting a correlation between the presence of circumstellar material and mass. This may be explained in terms of the very different transition times for high and low mass post-AGB stars from the AGB to becoming a planetary nebula.

From the UKST UBVRI survey, six high Galactic latitude stars have been previously identified which may be young hydrogen-burning objects. Using high-dispersion optical spectra, model atmosphere analyses are presented for these targets. Two, have normal or nearly normal Population I chemical compositions, one appears to be subluminous while the remaining three are possibly normal late B-type stars. A kinematic analysis indicates that one star having normal parameters is an excellent candidate for formation in the halo, having an evolutionary age an order of magnitude less than the time required for it to attain its current position following ejection from the Galactic disk. A preliminary analysis implies that there may currently be a few thousand normal B-type stars in the Galactic halo with z-distances from the plane of the Galaxy in the ran 3 < z < 22 k

Abstract An empirical equation for the prediction of the viscosity of several pure paraffin hydrocarbons and nitrogen is presented. It involves temperature, pressure and six constants of the material, and it applies reliably to both liquids and gases. The equation is similar in form to van der Waal's equation of state. For the paraffin hydrocarbons methane through n-hexane and nitrogen, an average absolute deviation of 1.9 percent was obtained on 1,006 data points described in the literature by 14 authors. When this equation is extended to complex, liquid hydrocarbon mixtures, a correlation was obtained with an average absolute deviation of 9.9 percent. Introduction Equations describing the flow of gas and liquid through porous media contain the viscosity coefficient of the fluid. If other pertinent variables remain constant, the volume rate of flow is inversely proportional to this coefficient. In dealing with condensate fluids and volatile oils, however, the compositional effects resulting from changing pressure materially affect the viscosity. The effect of compositional changes also may be significant in certain secondary recovery or pressure maintenance processes, notably miscible displacement or gas injection. Early attempts to describe the performance of reservoirs utilized a volumetric material balance method wherein gas and liquid in the reservoir were identified as produced gas and liquid at the surface. This method of analysis proved adequate for reservoirs at moderate temperature and pressure that contained gas with moderately low amounts of condensable materials. The volumetric material balance procedures for "black oil" reservoirs leave much to be desired when applied to condensate and volatile oil reservoirs because phase behavior and compositional changes the relatively more important in these cases. The alternative is a compositional material balance, which in turn, requires a correlation of properties of the reservoir fluid with composition. This paper supplies this correlation in regard to viscosity, for reservoir crude oils. REVIEW OF LITERATURE The literature contains many empirical equations describing the effects of composition, temperature and pressure on the viscosities of pure liquids and binary liquid mixtures. However, the applicability of a majority of these equations is limited to very low pressures and to a small number of systems. Most of the, when applied to complex hydrocarbon systems, are of little value. The lack of utility of the majority of equations results from the fact that they were developed to show the separate effect of temperature, pressure or composition on viscosity, but not to predict the viscosity as a function of all three variables. And with the few exceptions noted below, they were developed to apply to much simpler systems than hydrocarbon mixtures. P. 157ˆ