2,207 research outputs found
The interconnection between galaxy mergers, AGN activity and rapid quenching of star formation in simulated post-merger galaxies
No full textWe investigate the role of galaxy mergers on supermassive black hole (SMBH)
accretion and star formation quenching in three state-of-the-art cosmological
simulations with contrasting physics models: EAGLE, Illustris and IllustrisTNG.
We find that recently coalesced 'post-mergers' in all three simulations have
elevated SMBH accretion rates by factors of ~2-5. However, rapid (within 500
Myr of coalescence) quenching of star formation is rare, with incidence rates
of 0.4% in Illustris, 4.5% in EAGLE and 10% in IllustrisTNG. The rarity of
quenching in post-mergers results from substantial gas reservoirs that remain
intact after the merger. The post-mergers that do successfully quench tend to
be those that had both low pre-merger gas fractions as well as those that
experience the largest gas losses. Although rare, the recently quenched
fraction of post-mergers is still elevated compared to a control sample of
non-mergers by factors of two in IllustrisTNG and 11 in EAGLE. Conversely,
quenching is rarer in Illustris post-mergers than in their control. Recent
observational results by Ellison et al. have found rapid quenching to be at
least 30 times more common in post-mergers, a significantly higher excess than
found in any of the simulations. Our results, therefore, indicate that whilst
merger-induced SMBH accretion is a widespread prediction of the simulations,
its link to quenching depends sensitively on the physics models, and that none
of the subgrid models of the simulations studied here can fully capture the
connection between mergers and rapid quenching seen in observations.Comment: This article has been accepted for publication in Monthly Notices of
the Royal Astronomical Societ
An optically accessible pyrolysis microreactor
No full textWe report an optically accessible pyrolysis micro-reactor suitable for \textit{in situ} laser spectroscopic measurements. A radiative heating design allows for completely unobstructed views of the micro-reactor along two axes. The maximum temperature demonstrated here is only 1300 K (as opposed to 1700 K for the usual SiC micro-reactor) because of the melting point of fused silica, but alternative transparent materials will allow for higher temperatures. Laser induced fluorescence measurements on nitric oxide are presented as a proof of principle for spectroscopic characterization of pyrolysis conditions. (This work has been published in J.~H. Baraban, D.~E. David, G.~B. Ellison, and J.~W. Daily. An Optically Accessible Pyrolysis Micro-Reactor. {\em Review of Scientific Instruments}, 87(1):014101, 2016.)Made available in DSpace on 2017-01-26T21:38:49Z (GMT). No. of bitstreams: 3
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Previous issue date: 2016-06-2
Diuretic Therapy for Patients With Heart Failure JACC State-of-the-Art Review
No full textExpansion of extracellular fluid volume is central to the pathophysiology of heart failure. Increased extracellular fluid leads to elevated intracardiac filling pressures, resulting in a constellation of signs and symptoms of heart failure referred to as congestion. Loop diuretics are one of the cornerstones of treatments for heart failure, but in contrast to other therapies, robust clinical trial evidence to guide the use of diuretics is sparse. A nuanced understanding of renal physiology and diuretic pharmacokinetics is essential for skillful use of diuretics in the management of heart failure in both the inpatient and outpatient settings. Diuretic resistance, defined as an inadequate quantity of natriuresis despite an adequate diuretic regimen, is a major clinical challenge that generally portends a poor prognosis. In this review, the authors discuss the fundamental mechanisms and physiological principles that underlie the use of diuretic therapy and the available data on the optimal use of diuretics.Felker, GM (reprint author), Duke Clin Res Inst, 200 Morris St, Durham, NC 27705 USA.
[email protected]
Interacting galaxies in the IllustrisTNG simulations -- IV: Enhanced Supermassive Black Hole Accretion Rates in Post-Merger Galaxies
No full textWe present an analysis of the instantaneous supermassive black hole (SMBH)
accretion rates in a collection of 1563 post-merger galaxies drawn from the
IllustrisTNG simulation. Our sample consists of galaxies that have experienced
a merger in the last simulation snapshot (within ~160 Myrs of coalescence) in
the redshift range 01:10 and post-merger
stellar masses > . We find that, on average, the accretion
rates of the post-mergers are ~1.7 times higher than in a control sample and
that post-mergers are 3-4 times more likely to experience a luminous active
galactic nuclei (AGN) phase than isolated galaxies. SMBH accretion rate
enhancements persist for ~2 Gyrs after coalescence, significantly exceeding the
~500 Myr lifetime of star formation rate enhancements. We find that the
presence of simultaneous enhancements in both the star formation and SMBH
accretion rates depends on both the mass ratio of the merger and on the gas
mass of the post-merger galaxy. Despite these accretion rate enhancements, only
~35% of post-mergers experience a luminous AGN ( erg/s) within
500 Myrs after coalescence, and fewer than 10\% achieve a luminosity in excess
of erg/s. Moreover, only ~10\% of the highest luminosity
( erg/s) AGN in the IllustrisTNG galaxy sample are recent
mergers. Our results are therefore consistent with a picture in which mergers
can (but don't always) trigger AGN activity, but where the majority of galaxies
hosting high luminosity AGN are not recent mergers.Comment: This article has been accepted for publication in Monthly Notices of
the Royal Astronomical Societ
Interacting galaxies in the IllustrisTNG simulations - III. (The rarity of) quenching in post-merger galaxies
No full textGalaxy mergers are traditionally one of the favoured mechanisms for the transformation of spiral galaxies to spheroids and for quenching star formation. To test this paradigm in the context of modern cosmological simulations, we use the IllustrisTNG simulation to investigate the impact of individual merger events on quenching star formation [i.e. star formation rate (SFR) at least 3σ below the star-forming main sequence] within 500 Myr after the coalescence phase. The rate of quenching amongst recently merged galaxies is compared with a control sample that is matched in redshift, stellar mass, SFR, black hole mass, and environment. We find quenching to be uncommon among the descendants of post-merger galaxies, with only ∼5 per cent of galaxies quenching within 500 Myr after the merger. Despite this low absolute rate, we find that quenching occurs in post-mergers at twice the rate of the control galaxies. The fraction of quenched post-merger descendants 1.5 Gyr after the merger become statistically indistinguishable from that of non-post-mergers, suggesting that mergers could speed up the quenching process in those post-mergers whose progenitors had physical conditions able to sustain effective active galactic nuclei (AGN) kinetic feedback, thus capable of removing gas from galaxies. Our results indicate that although quenching does not commonly occur promptly after coalescence, mergers none the less do promote the cessation of star formation in some post-mergers. We find that, in IllustrisTNG, it is the implementation of the AGN kinetic feedback that is responsible for quenching post-mergers, as well as non-post-merger controls. As a result of the released kinetic energy, galaxies experience gas loss and eventually they will quench. Galaxies with an initially low gas fraction show a preferable pre-disposition towards quenching. The primary distinguishing factor between quenched and star-forming galaxies is gas fraction, with a sharp boundary at fgas ~ 0.1 in TNG
Puppets
No full textHousehold words contributors Dudley Costello and W. H. Wills begin their brief historical survey of the puppet arts, 'The Pedigree of Puppets' (1852), by airily dispensing with the need to cover their 'tedious' origins in the ancient world.1 Anyone attempting a related survey of Dickens and puppets would be unwise to emu- te this selective approach. Puppets are simply too rarely encountered in Dickens's work to leave anything out.No Full Tex
Magic on the Internet--experimental tests of auction theory
No full textThesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Economics, 1996.Includes bibliographical references.by David H.L. Reiley.Ph.D
1918 Bureau of Standards personnel negative set 90
No full text(top row) E. W. Roberts; David H. Goren; Ellison S. Purington; Ellison S. Purington
(middle row) Kirk H. Logan; Paul E. Dahm; William E. Congdon; G. R. Wait
(bottom row) Miss Katherine R. Keeler; Miss E. R. Durfee; Miss Jane Campbell; Charles Reitell
This item is part of the Bureau of Standards Personnel 1918 collection
Turbulent stratified shear flow experiments: Length scale comparison
No full textStratified shear flows are ubiquitous in geophysical systems such as oceanic overflows, wind-driven thermoclines, and atmo- spheric inversion layers. The stability of such flows is governed by the Richardson Number Ri which represents a balance between the stabilizing influence of stratification and the destabilizing influence of shear. For a shear flow with velocity difference U, density difference ∆ρ and characteristic length H, one has Ri = g(∆ρ/ρ)H/U^2 which is often used when detailed information about the flow is not available. A more precise definition is the gradient Richardson Number Rig = N^2/S^2 where the buoyancy frequency N = ((g/ρ)∂ρ/∂z)^{1/2}, the mean strain S = ∂U/∂z in which z is parallel to gravity and suitable ensemble or time averages define the gradients. We explore the stability and mixing properties of a wall-bounded shear flow over a range 0.1< Rig <1 using simultaneous planar measurements of density and velocity fields using Planar Laser-Induced Fluorescence (PLIF) and Particle Image Velocimetry (PIV), respectively. The flow, confined from the top by glass horizontal boundary, is a lighter alcohol-water mixture injected from a nozzle into quiescent heavier salt-water fluid with velocity between 5 and 10 cm/s and with a relative fractional density difference of 0.0026 or 0.0052. The injected flow is turbulent with Taylor Reynolds number between 50 and 100. We compare a set of length scales that characterize the mixing properties of our turbulent stratified shear flow including the Thorpe Length L_T, the Ozmidov Length L_o, the Ellison Length L_E, and turbulent mixing lengths L_m and L_ρ
"Competitiveness Strategies, Resource Struggles and National Interest In the New Europe"
No full textThe New Member States face considerable challenges as members of the New Europe. This paper analyzes the economic development interests of these countries both in the context of their pre-membership strategies and of the evolving EU policy framework. While previous strategies involved the extensive use of investment promotion schemes and innovative forms of corporate taxation, EU membership constrains these practices in significant ways. Based primarily on the case of Hungary, this paper questions the advantages of EU membership for these states and further questions the ability of the EU policy framework to appropriately address their development needs. In many respects, the advantages of the enlargement appear better suited to appease Western interests in reducing the degree of competition over resources. As such, this paper predicts a persistent division of interests in the New Europe along what one might call a developmental divide, with less advanced states promoting more interventionist strategies and advanced states ultimately promoting a re-nationalization of EU redistributional spending
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