Lattice Kinetics of Diffusion-Limited Coalescence and Annihilation with Sources

We study the 1D kinetics of diffusion-limited coalescence and annihilation with back reactions and different kinds of particle input. By considering the changes in occupation and parity of a given interval, we derive sets of hierarchical equations from which exact expressions for the lattice coverage and the particle concentration can be obtained. We compare the mean-field approximation and the continuum approximation to the exact solutions and we discuss their regime of validity.Comment: 24 pages and 3 eps figures, Revtex, accepted for publication in J. Phys.

Keck Observatory Laser Guide Star Adaptive Optics Discovery and Characterization of a Satellite to the Large Kuiper Belt Object 2003 EL_(61)

The newly commissioned laser guide star adaptive optics system at Keck Observatory has been used to discover and characterize the orbit of a satellite to the bright Kuiper Belt object 2003 EL_(61). Observations over a 6 month period show that the satellite has a semimajor axis of 49,500 ± 400 km, an orbital period of 49.12 ± 0.03 days, and an eccentricity of 0.050 ± 0.003. The inferred mass of the system is (4.2 ± 0.1) × 10^(21) kg, or ~32% of the mass of Pluto and 28.6% ± 0.7% of the mass of the Pluto-Charon system. Mutual occultations occurred in 1999 and will not occur again until 2138. The orbit is fully consistent neither with one tidally evolved from an earlier closer configuration nor with one evolved inward by dynamical friction from an earlier more distant configuration

Metaproteomics of anaerobic microbial communities degrading long-chain fatty acids

The anaerobic conversion of long-chain fatty acids (LCFA), and specifically the difference between the degradation of unsaturated- and saturated-LCFA, is not fully understood. In this work, syntrophic degradation of stearate (C18:0) and oleate (C18:1) was studied. A comparative metaproteomics approach, in which proteins were analyzed by LC-MS/MS, was combined with 16S rRNA gene pyrosequencing. Saturated- and unsaturated-LCFA were converted to methane by the anaerobic consortia. 16S rRNA gene pyrosequencing revealed differences in the microbial composition of sludges incubated with stearate and oleate, separately. Abundance of microorganisms within Deltaproteobacteria and within Synergistia taxa was higher in stearate and oleate incubations, respectively. Methanosaeta was the most abundant methanogen in both conditions. Metaproteomics results were similar and comparable distributions of COG functional categories were found for both samples. Archaeal proteomes were much better identified than bacterial ones, with five times more proteins retrieved. Most of the proteins identified belong to Methanosaeta concilli and Syntrophobacter fumaroxidans, two organisms that have their genome sequenced. Syntrophobacter belongs to Deltaproteobacteria, however this group was not dominant in oleate incubation as determined by pyrosequencing results. Studying metaproteomes of complex microbial communities is still a big challenge especially because most of the genomes are not sequenced which hinders protein identification

Satellites of the largest Kuiper Belt objects

We have searched the four brightest objects in the Kuiper Belt for the presence of satellites using the newly commissioned Keck Observatory Laser Guide Star Adaptive Optics system. Satellites are seen around three of the four objects: Pluto (whose satellite Charon is well-known and whose recently discovered smaller satellites are too faint to be detected), 2003 EL61 (where a second satellite is seen in addition to the previously known satellite), and 2003 UB313 (where a satellite is seen for the first time). The object 2005 FY9, the brightest Kuiper Belt object (KBO) after Pluto, does not have a satellite detectable within 0".4 with a brightness of more than 1% of the primary. The presence of satellites around three of the four brightest KBOs is inconsistent with the fraction of satellites in the Kuiper Belt at large at the 99.2% confidence level, suggesting a different formation mechanism for these largest KBO satellites. The two satellites of 2003 EL61, and the one satellite of 2003 UB313, with fractional brightnesses of 5% and 1.5%, and 2%, of their primaries, respectively, are significantly fainter relative to their primaries than other known KBO satellites, again pointing to possible differences in their origin

Jupiter's visible aurora and Io footprint

Images obtained by the Galileo spacecraft's solid-state imaging (SSI) system represent the first survey of Jupiter's northern auroral emissions at visible wavelengths and on the nightside of the planet. These images captured the emissions with unprecedented spatial resolutions down to ∼26 km pixel^(−1). Four classes of emission were observed: (1) a continuous, primary arc associated with the middle/outer magnetosphere, (2) a variable secondary arc associated with the region just beyond Io's torus, (3) diffuse “polar cap” emission, and (4) a patch and tail associated with the magnetic footprint of Io. The primary arc emission occurs at an altitude 245±30 km above the 1-bar pressure level. Its horizontal width is typically a few hundred kilometers, and its total optical power output varied between ∼10^(10) and ∼10^(11) W in observations taken months apart. The location of the primary arc in planetary coordinates is similar to that on dayside images at other wavelengths and does not vary with local time. The morphology of the primary arc is not constant, changing from a multiply branched, latitudinally distributed pattern after dusk to a single, narrow arc before dawn. Emission from Io's ionospheric footprint is distinct from both the primary and secondary arcs. Measurements of its optical power output ranged from 2 to 7×10^8 W

Lithium isotopes in large rivers reveal the cannibalistic nature of modern continental weathering and erosion

The erosion of major mountain ranges is thought to be largely cannibalistic, recycling sediments that were deposited in the ocean or on the continents prior to mountain uplift. Despite this recognition, it has not yet been possible to quantify the amount of recycled material that is presently transported by rivers to the ocean. Here, we have analyzed the Li content and isotope composition (View the MathML source) of suspended sediments sampled along river depth profiles and bed sands in three of the largest Earth's river systems (Amazon, Mackenzie and Ganga–Brahmaputra rivers). The View the MathML source values of river-sediments transported by these rivers range from +5.3 to −3.6‰ and decrease with sediment grain size. We interpret these variations as reflecting a mixture of unweathered rock fragments (preferentially transported at depth in the coarse fraction) and present-day weathering products (preferentially transported at the surface in the finest fraction). Only the finest surface sediments contain the complementary reservoir of Li solubilized by water–rock interactions within the watersheds. Li isotopes also show that river bed sands can be interpreted as a mixture between unweathered fragments of igneous and sedimentary rocks. A mass budget approach, based on Li isotopes, Li/Al and Na/Al ratios, solved by an inverse method allows us to estimate that, for the large rivers analyzed here, the part of solid weathering products formed by present-day weathering reactions and transported to the ocean do not exceed 35%. Li isotopes also show that the sediments transported by the Amazon, Mackenzie and Ganga–Brahmaputra river systems are mostly sourced from sedimentary rocks (>60%) rather than igneous rocks. This study shows that Li isotopes in the river particulate load are a good proxy for quantifying both the erosional rock sources and the fingerprint of present-day weathering processes. Overall, Li isotopes in river sediments confirm the cannibalistic nature of erosion and weathering

Total Syntheses of Amphidinolide H and G

Eureka! The first conquest of the exceptionally potent cytotoxic agent amphidinolide H, which exhibits activity in the picomolar range against human epidermoid cancer cells, was long overdue. The successful route critically hinges upon the scrupulous optimization of the fragment-coupling events (see picture; RCM=ring-closing metathesis) and on the careful adjustment of the peripheral protecting-group pattern