The stars of the galactic center

We consider the origin of the so-called S stars orbiting the supermassive black hole at the very center of the Galaxy. These are usually assumed to be massive main-sequence stars. We argue instead that they are the remnants of low-to-intermediate mass red giants which have been scattered on to near-radial orbits and tidally stripped as they approach the central black hole. Such stars retain only low-mass envelopes and thus have high effective temperatures. Our picture simultaneously explains why S stars have tightly-bound orbits, and the observed depletion of red giants in the very center of the Galaxy.Comment: 9 pages, 1 figure, ApJ Letters, in pres

Industry-Science Connections in Agriculture: Do public science collaborations and knowledge flows contribute to firm-level agricultural research productivity?

Prior research identifies a direct positive link between the stock of public scientific knowledge and agricultural productivity; however, an indirect contribution to agricultural productivity is also possible when this stock facilitates private sector invention. This study examines how “connectedness” between the stock of public scientific knowledge and private firms influences firm-level research productivity. Bibliographic information identifies the nature and degree to which firms use public agricultural science through citations and collaborations on scientific papers. Fixed effects models show that greater citations and collaborations with university researchers are associated with greater agricultural research productivity.public science, research productivity, patents, citations, collaboration, R&D, Productivity Analysis, Research and Development/Tech Change/Emerging Technologies, Q16, O31,

The AGN-starburst connection, Galactic superwinds, and M_BH - sigma

Recent observations of young galaxies at redshifts z ~ 3 have revealed simultaneous AGN and starburst activity, as well as galaxy-wide superwinds. I show that there is probably a close connection between these phenomena by extending an earlier treatment of the M_BH - sigma relation (King, 2003). As the black hole grows, an outflow drives a shell into the surrounding gas. This stalls after a dynamical time at a size determined by the hole's current mass and thereafter grows on the Salpeter timescale. The gas trapped inside this bubble cools and forms stars and is recycled as accretion and outflow. The consequent high metallicity agrees with that commonly observed in AGN accretion. Once the hole reaches a critical mass this region attains a size such that the gas can no longer cool efficiently. The resulting energy-driven flow expels the remaining gas as a superwind, fixing both the M_BH - sigma relation and the total stellar bulge mass at values in good agreement with observation. Black hole growth thus produces starbursts and ultimately a superwind.Comment: ApJ, in press, 4 page

Superhumps in Low-Mass X-Ray Binaries

We propose a mechanism for the superhump modulations observed in optical photometry of at least two black hole X-ray transients (SXTs). As in extreme mass-ratio cataclysmic variables (CVs), superhumps are assumed to result from the presence of the 3:1 orbital resonance in the accretion disc. This causes the disc to become non-axisymmetric and precess. However the mechanism for superhump luminosity variations in low mass X-ray binaries (LMXBs) must differ from that in CVs, where it is attributed to a tidally-driven modulation of the disc's viscous dissipation, varying on the beat between the orbital and disc precession period. By contrast in LMXBs, tidal dissipation in the outer accretion disc is negligible: the optical emission is overwhelming dominated by reprocessing of intercepted central X-rays. Thus a different origin for the superhump modulation is required. Recent observations and numerical simulations indicate that in an extreme mass-ratio system the disc area changes on the superhump period. We deduce that the superhumps observed in SXTs arise from a modulation of the reprocessed flux by the changing area. Therefore, unlike the situation in CVs, where the superhump amplitude is inclination-independent, superhumps should be best seen in low-inclination LMXBs, whereas an orbital modulation from the heated face of the secondary star should be more prominent at high inclinations. Modulation at the disc precession period (10s of days) may indicate disc asymmetries such as warping. We comment on the orbital period determinations of LMXBs, and the possibility and significance of possible permanent superhump LMXBs.Comment: 6 pages, 1 encapsulated figure. MNRAS in press; replaced to correct typographical error

Industry-science connections in agriculture : do public science collaborations and knowledge flows contribute to firm-level agricultural research productivity?

Prior research shows long-run productivity growth in agriculture is associated with increases in the stock of public scientific knowledge and private patented inventions. However, private inventions may be a function of the stock of public knowledge. In this paper, we examine the possibility that public knowledge contributes to productivity through its relationship with private sector invention. Our analysis identifies connections between the stock of public knowledge and private firm R&D and examines whether the degree of “connectedness” to public science is associated with greater firm-level research productivity in agriculture. Bibliographic information identifies the nature and degree to which firms use public agricultural science through citations and collaborations on scientific papers. Fixed effects models show that greater citations and collaborations with university researchers are associated with greater private agricultural research productivity

Black Holes, Galaxy Formation, and the M_BH-sigma Relation

Recent X-ray observations of intense high-speed outflows in quasars suggest that supercritical accretion on to the central black hole may have an important effect on a host galaxy. I revisit some ideas of Silk and Rees, and assume such flows occur in the final stages of building up the black hole mass. It is now possible to model explicitly the interaction between the outflow and the host galaxy. This is found to resemble a momentum-driven stellar wind bubble, implying a relation M_BH = (f_g kappa/2 pi G^2) sigma^4 = 1.5 10^8 sigma_200^4 Msun between black hole mass and bulge velocity dispersion (f_g = gas fraction of total matter density, kappa = electron scattering opacity), without free parameters. This is remarkably close to the observed relation in both slope and normalization. This result suggests that the central black holes in galaxies gain most of their mass in phases of super-Eddington accretion, which are presumably obscured or at high redshift. Observed super-Eddington quasars are apparently late in growing their black hole masses.Comment: 8 pages, no figures Accepted for publication in ApJ Letters; typos and references correcte

Role of angiopoietin-like protein 3 in sugar-induced dyslipidemia in rhesus macaques: suppression by fish oil or RNAi.

Angiopoietin-like protein 3 (ANGPTL3) inhibits lipid clearance and is a promising target for managing cardiovascular disease. Here we investigated the effects of a high-sugar (high-fructose) diet on circulating ANGPTL3 concentrations in rhesus macaques. Plasma ANGPTL3 concentrations increased ∼30% to 40% after 1 and 3 months of a high-fructose diet (both P < 0.001 vs. baseline). During fructose-induced metabolic dysregulation, plasma ANGPTL3 concentrations were positively correlated with circulating indices of insulin resistance [assessed with fasting insulin and the homeostatic model assessment of insulin resistance (HOMA-IR)], hypertriglyceridemia, adiposity (assessed as leptin), and systemic inflammation [C-reactive peptide (CRP)] and negatively correlated with plasma levels of the insulin-sensitizing hormone adropin. Multiple regression analyses identified a strong association between circulating APOC3 and ANGPTL3 concentrations. Higher baseline plasma levels of both ANGPTL3 and APOC3 were associated with an increased risk for fructose-induced insulin resistance. Fish oil previously shown to prevent insulin resistance and hypertriglyceridemia in this model prevented increases of ANGPTL3 without affecting systemic inflammation (increased plasma CRP and interleukin-6 concentrations). ANGPTL3 RNAi lowered plasma concentrations of ANGPTL3, triglycerides (TGs), VLDL-C, APOC3, and APOE. These decreases were consistent with a reduced risk of atherosclerosis. In summary, dietary sugar-induced increases of circulating ANGPTL3 concentrations after metabolic dysregulation correlated positively with leptin levels, HOMA-IR, and dyslipidemia. Targeting ANGPTL3 expression with RNAi inhibited dyslipidemia by lowering plasma TGs, VLDL-C, APOC3, and APOE levels in rhesus macaques