Molecules in the disk orbiting the twin young suns of V4046 Sgr

We report the results of a mm-wave molecular line survey of the nearby (D ~ 70 pc), 12 Myr-old system V4046 Sgr -- a tight (9 R_sun separation), short-period (2.42 day) binary with nearly equal component masses of ~0.9 M_sun -- conducted with the 30 m telescope of the Institut de Radio Astronomie Millimetrique (IRAM). We detected rotational transitions of 12CO 13CO, HCN, CN, and HCO+. The double-peaked CO line profiles of V4046 Sgr are well fit by a model invoking a Keplerian disk with outer radius of ~250 AU that is viewed at an inclination i = 35 degrees. We infer minimum disk gas and dust masses of ~13 and ~20 Earth masses from the V4046 Sgr CO line and submm continuum fluxes, respectively. The actual disk gas mass could be much larger if the gas-phase CO is highly depleted and/or 13CO is very optically thick. The overall similarity of the circumbinary disk of V4046 Sgr to the disk orbiting the single, ~8 Myr-old star TW Hya -- a star/disk system often regarded as representative of the early solar nebula -- indicates that gas giant planets are likely commonplace among close binary star systems. Given the relatively advanced age and proximity of V4046 Sgr, these results provide strong motivation for future high-resolution imaging designed to ascertain whether a planetary system now orbits its twin suns.Comment: 5 pages, 3 figures; to appear in Astronomy & Astrophysic

High-content assays for evaluating cellular and hepatic diacylglycerol acyltransferase activity

Acyl-CoA:diacylglycerol acyltransferase (DGAT) catalyzes the terminal step in triglyceride (TG) synthesis using diacylglycerol (DAG) and fatty acyl-CoA as substrates. In the liver, the production of VLDL permits the delivery of hydrophobic TG from the liver to peripheral tissues for energy metabolism. We describe here a novel high-content, high-throughput LC/MS/MS-based cellular assay for determining DGAT activity. We treated endogenous DGAT-expressing cells with stable isotope-labeled [13C18]oleic acid. The [13C18]oleoyl-incorporated TG and DAG lipid species were profiled. The TG synthesis pathway assay was optimized to a one-step extraction, followed by LC/MS/MS quantification. Further, we report a novel LC/MS/MS method for tracing hepatic TG synthesis and VLDL-TG secretion in vivo by administering [13C18]oleic acid to rats. The [13C18]oleic acid-incorporated VLDL-TG was detected after one-step extraction without conventional separation of TG and recovery by derivatizing [13C18]oleic acid for detection. Using potent and selective DGAT1 inhibitors as pharmacological tools, we measured changes in [13C18]oleoyl-incorporated TG and DAG and demonstrated that DGAT1 inhibition significantly reduced [13C18]oleoyl-incorporated VLDL-TG. This DGAT1-selective assay will enable researchers to discern differences between the roles of DGAT1 and DGAT2 in TG synthesis in vitro and in vivo

Evolution of sandstone peak-forest landscapes - insights from quantifying erosional processes with cosmogenic nuclides

The sandstone peak-forest landscape in Zhangjiajie UNESCO Global Geopark of Hunan Province, China, is characterized by \u3e 3000 vertical pillars and peak walls of up to 350 m height, representing a spectacular example of sandstone landform variety. Few studies have addressed the mechanisms and timescales of the longer-term evolution of this landscape, and have focused on fluvial incision. We use in situ cosmogenic nuclides combined with GIS analysis to investigate the erosional processes contributing to the formation of pillars and peak-forests, and discuss their relative roles in the formation and decay of the landscape. Model maximum-limiting bedrock erosion rates are the highest along the narrow fluvial channels and valleys at the base of the sandstone pillars (~83-122 mm kyr -1 ), and lowest on the peak wall tops (~2.5 mm kyr -1 ). Erosion rates are highly variable and intermediate along vertical sandstone peak walls and pillars (~30 to 84 mm kyr -1 ). Catchment-wide denudation rates from river sediment vary between ~26 and 96 mm kyr -1 and are generally consistent with vertical wall retreat rates. This highlights the importance of wall retreat for overall erosion in the sandstone peak-forest. In combination with GIS-derived erosional volumes, our results suggest that the peak-forest formation in Zhangjiajie commenced in the Pliocene, and that the general evolution of the landscape followed our sequential refined model: (i) slow lowering rates following initial uplift; (ii) fast plateau dissection by headward knickpoint propagation along joints and faults followed by; (iii) increasing contribution of wall retreat in the well-developed pillars and peak-forests and a gradual decrease in overall denudation rates, leading to; (iv) the final consumption of pillars and peak-forests. Our study provides an approach for quantifying the complex interplay between multiple geomorphic processes as required to assess the evolutionary pathways of other sandstone peak-forest landscapes across the globe