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The formation of large woody debris (LWD) 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 > 0.1m 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 m3 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 m3). Piles were larger in the seasonal and ephemeral flood frequency zones (mean = 54 m 3 and 55 m3) than piles in the active zone (c. 2 m3). 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.

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

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 Ql 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 HST. The light curve and timings are consistent with an ejection velocity for the plume material of v≃ 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 ∼ 7 min after the initial maximum, the cause of which is unclear.

We have shown previously that there is a good correlation between the degree of microtubule disassembly by methylmercury (MeHg) and the extent of inhibition of DNA replication in Concanavalin A (Con A)-stimulated mouse splenic lymphocytes. The purpose of this study was to determine if these two events are causally related and to examine the effects of MeHg-induced microtubule disassembly on earlier events of the stimulation process. We show that early steps constituting the activation pathway, such as the Con A-induced increase in Ca2+ influx and the expression of interleukin 2 receptor, are not inhibited by concentrations of MeHg that disassemble microtubules. RNA synthesis is not affected by short-term (3 h) treatment with MeHg, but longer treatment (24 h) inhibits RNA synthesis. In contrast, DNA synthesis is effectively inhibited by a 3-h treatment with MeHg. In lymphocytes treated with taxol, microtubules are not disassembled by MeHg; however, the inhibition of RNA and DNA synthesis persists. We conclude that the inhibition of nucleic acid synthesis by MeHg is not causally related to MeHg-induced microtubule disassembly.

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

We examined the distribution of nonlamin nuclear matrix antigens during the mitotic cell cycle in mouse 3T3 fibroblasts. Four monoclonal antibodies produced against isolated nuclear matrices were used to characterize antigens by the immunoblotting of isolated nuclear matrix preparations, and were used to localize the antigens by indirect immunofluorescence. For comparison, lamins and histones were localized using human autoimmune antibodies. At interphase, the monoclonal antibodies recognized non-nucleolar and nonheterochromatin nuclear components. Antibody P1 stained the nuclear periphery homogeneously, with some small invaginations toward the interior of the nucleus. Antibody I1 detected an antigen distributed as fine granules throughout the nuclear interior. Monoclonals PI1 and PI2 stained both the nuclear periphery and interior, with some characteristic differences. During mitosis, P1 and I1 were chromosome-associated, whereas PI1 and PI2 dispersed in the cytoplasm. Antibody P1 heavily stained the periphery of the chromosome mass, and we suggest that the antigen may play a role in maintaining interphase and mitotic chromosome order. With antibody I1, bright granules were distributed along the chromosomes and there was also some diffuse internal staining. The antigen to I1 may be involved in chromatin/chromosome higher-order organization throughout the cell cycle. Antibodies PI1 and PI2 were redistributed independently during prophase, and dispersed into the cytoplasm during prometaphase. Antibody PI2 also detected antigen associated with the spindle poles.

Let Λ (n) be the arithmetic function usually so denoted, which is zero unless n is a prime power pm (m ≥ 1), when it is log p. We write as usualandwhere the dash denotes that if x is an integer the last term Λ (x) of the sum is to be taken with a factor ½. We wrute further

We have used immunofluorescence staining with antibodies to tubulin and electron microscopy to examine the effects of microtubule assembly-promoting drug taxol on the organization of microtubules in unstimulated and in mitogen stimulated mouse splenic lymphocytes. A 4-h exposure to 10 microM taxol of unstimulated or stimulated cells results in an extensive reorganization of the microtubule system to form one to a few large bundles of microtubules which extend from the centrosome. Concomitantly, the centrosome is displaced from the normal position near the nucleus to a position near the plasma membrane. The Golgi apparatus is not disrupted by this treatment and also appears to be displaced in association with the centrosome. We then examined the capacity of lymphocytes with taxol-reorganized microtubules to respond to stimulation by the mitogen concanavalin A. The taxol-induced reorganization of microtubules has no effect on the increase in cell size (blastogenesis), the changes in structure of the nucleus and cytoplasm, or on the DNA replication that occurs in response to mitogen. The stimulated cells, however, do not proliferate and appear to accumulate in mitosis with the appearance of multiple asters. We conclude that all of the major events of mitogenic stimulation up to the first mitosis can occur in the presence of a highly reorganized microtubule system. Our results suggest that taxol will be a useful drug in determining those lymphocyte functions that are dependent on the presence of normal microtubule organization.