Active galactic nucleus feedback in clusters of galaxies

Observations made during the last ten years with the Chandra X-ray Observatory have shed much light on the cooling gas in the centers of clusters of galaxies and the role of active galactic nucleus (AGN) heating. Cooling of the hot intracluster medium in cluster centers can feed the supermassive black holes found in the nuclei of the dominant cluster galaxies leading to AGN outbursts which can reheat the gas, suppressing cooling and large amounts of star formation. AGN heating can come in the form of shocks, buoyantly rising bubbles that have been inflated by radio lobes, and the dissipation of sound waves.Comment: Refereed review article published in Chandra's First Decade of Discovery Special Feature edition of the Proceedings of the National Academy of Science

Inside the Bondi radius of M87

Chandra X-ray observations of the nearby brightest cluster galaxy M87 resolve the hot gas structure across the Bondi accretion radius of the central supermassive black hole, a measurement possible in only a handful of systems but complicated by the bright nucleus and jet emission. By stacking only short frame-time observations to limit pileup, and after subtracting the nuclear PSF, we analysed the X-ray gas properties within the Bondi radius at 0.12-0.22 kpc (1.5-2.8 arcsec), depending on the black hole mass. Within 2 kpc radius, we detect two significant temperature components, which are consistent with constant values of 2 keV and 0.9 keV down to 0.15 kpc radius. No evidence was found for the expected temperature increase within ~0.25 kpc due to the influence of the SMBH. Within the Bondi radius, the density profile is consistent with $\rho\propto r^{-1}$. The lack of a temperature increase inside the Bondi radius suggests that the hot gas structure is not dictated by the SMBH's potential and, together with the shallow density profile, shows that the classical Bondi rate may not reflect the accretion rate onto the SMBH. If this density profile extends in towards the SMBH, the mass accretion rate onto the SMBH could be at least two orders of magnitude less than the Bondi rate, which agrees with Faraday rotation measurements for M87. We discuss the evidence for outflow from the hot gas and the cold gas disk and for cold feedback, where gas cooling rapidly from the hot atmosphere could feed the cirumnuclear disk and fuel the SMBH. At 0.2 kpc radius, the cooler X-ray temperature component represents ~20% of the total X-ray gas mass and, by losing angular momentum to the hot gas component, could provide a fuel source of cold clouds within the Bondi radius.Comment: 14 pages, 8 figures, accepted by MNRA

Farm-gate nitrogen balances on intensive dairy farms in the south west of Ireland

peer-reviewedNitrogen management and farm-gate N balances were evaluated on 21 intensive dairy farms in the south west of Ireland for each of four years (2003 to 2006). The mean annual stocking density was equivalent to 202 kg/ha (s.d. 29.6) of N excreted by livestock on the farm. The mean annual farm-gate N surplus (imports – exports) declined between 2003 and 2006 (277 to 232 kg/ha, s.e. 6.8; P < 0.001) due to a decline in annual N imports (fertilizer, feed and imported manures; 335 to 288 kg/ha, s.e. 6.9; P < 0.001). Overall annual fertilizer N use on the farms decreased during the study period (266 to 223 kg/ha, s.e. 6.5; P < 0.001) mainly due to lower inputs for the first application in spring and for the production of first-cut silage. These decreases were partly offset by applying more slurry in spring for early grazing and for first-cut silage. The introduction of white clover resulted in lower N imports on four farms. Export of N from farms was unaffected by reductions in N imports. The mean efficiency of N use tended to increase over time (0.18 in 2003 to 0.20 in 2006). The large variation in quantities of fertilizer N applied on farms with similar stocking densities suggests potential for further improvements in the efficiency of N use. In terms of fertilizer N use, complying with S.I. No. 378 of 2006 did not require major changes in the N management practiceson 19 of the farms.This project was part-funded by the European Research and Development Fund under INTERREG IIIB: Green Dairy Project N° 100 and partly by the Dairy Levy. Financial support for post-graduate students involved in this study was provided by the Teagasc Walsh Fellowship Scheme

Homogeneous cooling of rough, dissipative particles: Theory and simulations

We investigate freely cooling systems of rough spheres in two and three dimensions. Simulations using an event driven algorithm are compared with results of an approximate kinetic theory, based on the assumption of a generalized homogeneous cooling state. For short times $t$, translational and rotational energy are found to change linearly with $t$. For large times both energies decay like $t^{-2}$ with a ratio independent of time, but not corresponding to equipartition. Good agreement is found between theory and simulations, as long as no clustering instability is observed. System parameters, i.e. density, particle size, and particle mass can be absorbed in a rescaled time, so that the decay of translational and rotational energy is solely determined by normal restitution and surface roughness.Comment: 10 pages, 10 eps-figure

Singing for adults with chronic obstructive pulmonary disease (COPD)

Background Singing is a complex physical activity dependent on the use of the lungs for air supply to regulate airflow and create large lung volumes. In singing, exhalation is active and requires active diaphragm contraction and good posture. Chronic obstructive pulmonary disease (COPD) is a progressive, chronic lung disease characterised by airflow obstruction. Singing is an activity with potential to improve health outcomes in people with COPD. Objectives To determine the effect of singing on health-related quality of life and dyspnoea in people with COPD. Search methods We identified trials from the Cochrane Airways Specialised Register, ClinicalTrials.gov, the World Health Organization trials portal and PEDro, from their inception to August 2017. We also reviewed reference lists of all primary studies and review articles for additional references. Selection criteria We included randomised controlled trials in people with stable COPD, in which structured supervised singing training of at least four sessions over four weeks’ total duration was performed. The singing could be performed individually or as part of a group (choir) facilitated by a singing leader. Studies were included if they compared: 1) singing versus no intervention (usual care) or another control intervention; or 2) singing plus pulmonary rehabilitation versus pulmonary rehabilitation alone. Data collection and analysis Two review authors independently screened and selected trials for inclusion, extracted outcome data and assessed risk of bias. We contacted authors of trials for missing data. We calculated mean differences (MDs) using a random-effects model. We were only able to analyse data for the comparison of singing versus no intervention or a control group

Emerging Investigators Series: Pyrolysis Removes Common Microconstituents Triclocarban, Triclosan, and Nonylphenol from Biosolids

Reusing biosolids is vital for the sustainability of wastewater management. Pyrolysis is an anoxic thermal degradation process that can be used to convert biosolids into energy rich py-gas and py-oil, and a beneficial soil amendment, biochar. Batch biosolids pyrolysis (60 minutes) revealed that triclocarban and triclosan were removed (to below quantification limit) at 200 °C and 300 °C, respectively. Substantial removal (\u3e90%) of nonylphenol was achieved at 300 °C as well, but 600 °C was required to remove nonylphenol to below the quantification limit. At 500 °C, the pyrolysis reaction time to remove \u3e90% of microconstituents was less than 5 minutes. Fate studies revealed that microconstituents were both volatilized and thermochemically transformed during pyrolysis; microconstituents with higher vapor pressures were more likely to volatilize and leave the pyrolysis reactor before being transformed than compounds with lower vapor pressures. Reductive dehalogenation products of triclocarban and suspected dehalogenation products of triclosan were identified in py-gas. Application of biosolids-derived biochar to soil in place of biosolids has potential to minimize organic microconstituents discharged to the environment provided appropriate management of py-gas and py-oil

Effects of Velocity Correlation on Early Stage of Free Cooling Process of Inelastic Hard Sphere System

The free cooling process in the inelastic hard sphere system is studied by analysing the data from large scale molecular dynamics simulations on a three dimensional system. The initial energy decay, the velocity distribution function, and the velocity correlation functions are calculated to be compared with theoretical predictions. The energy decay rate in the homogeneous cooling state is slightly but distinctively smaller than that expected from the independent collision assumption. The form of the one particle velocity distribution is found not to be stationary. These contradict to the predictions of the kinetic theory based on the Enskog-Boltzmann equation and suggest that the velocity correlation is already important in the early stage of homogeneous cooling state. The energy decay rate is analysed in terms of the velocity correlation.Comment: 9 pages (figures included). To be published in J. Phys. Soc. Jpn. Vol. 73 No. 1 (2004) Added two references and removed one. Changed the name of T_{L}. Added unit constants in Sec. 5 and

X-ray Supercavities in the Hydra A Cluster and the Outburst History of the Central Galaxy's Active Nucleus

A 227 ksec Chandra Observatory X-ray image of the hot plasma in the Hydra A cluster has revealed an extensive cavity system. The system was created by a continuous outflow or a series of bursts from the nucleus of the central galaxy over the past 200-500 Myr. The cavities have displaced 10% of the plasma within a 300 kpc radius of the central galaxy, creating a swiss-cheese-like topology in the hot gas. The surface brightness decrements are consistent with empty cavities oriented within 40 degrees of the plane of the sky. The outflow has deposited upward of 10^61 erg into the cluster gas, most of which was propelled beyond the inner ~100 kpc cooling region. The supermassive black hole has accreted at a rate of approximately 0.1-0.25 solar masses per year over this time frame, which is a small fraction of the Eddington rate of a ~10^9 solar mass black hole, but is dramatically larger than the Bondi rate. Given the previous evidence for a circumnuclear disk of cold gas in Hydra A, these results are consistent with the AGN being powered primarily by infalling cold gas. The cavity system is shadowed perfectly by 330 MHz radio emission. Such low frequency synchrotron emission may be an excellent proxy for X-ray cavities and thus the total energy liberated by the supermassive black hole.Comment: 8 pages, 3 figures; Submitted to ApJ, revised per referee's suggestion