Chaotic cold accretion on to black holes in rotating atmospheres

Chaotic cold accretion (CCA) profoundly differs from classic black hole accretion models. Using 3D high-resolution simulations, we probe the impact of rotation on the hot and cold accretion flow in a typical massive galaxy. In the hot mode, with or without turbulence, the pressure-dominated flow forms a geometrically thick rotational barrier, suppressing the accretion rate to ~1/3 of the Bondi rate. When radiative cooling is dominant, the gas loses pressure support and quickly circularizes in a cold thin disk. In the more common state of a turbulent and heated atmosphere, CCA drives the dynamics if the gas velocity dispersion exceeds the rotational velocity, i.e., turbulent Taylor number < 1. Extended multiphase filaments condense out of the hot phase via thermal instability and rain toward the black hole, boosting the accretion rate up to 100 times the Bondi rate. Initially, turbulence broadens the angular momentum distribution of the hot gas, allowing the cold phase to condense with prograde or retrograde motion. Subsequent chaotic collisions between the cold filaments, clouds, and a clumpy variable torus promote the cancellation of angular momentum, leading to high accretion rates. The simulated sub-Eddington accretion rates cover the range inferred from AGN cavity observations. CCA predicts inner flat X-ray temperature and $r^{-1}$ density profiles, as recently discovered in M 87 and NGC 3115. The synthetic H{\alpha} images reproduce the main features of cold gas observations in massive ellipticals, as the line fluxes and the filaments versus disk morphology. Such dichotomy is key for the long-term AGN feedback cycle. As gas cools, filamentary CCA develops and boosts AGN heating; the cold mode is thus reduced and the rotating disk remains the sole cold structure. Its consumption leaves the atmosphere in hot mode with suppressed accretion and feedback, reloading the cycle.Comment: 18 pages, 21 figures, published in A&A; fully revised version with new major results related to H{\alpha} and X-ray observation

Spatial distribution of introduced brook trout Salvelinus fontinalis (Salmonidae) within alpine lakes: evidences from a fish eradication campaign

Brook trout Salvelinus fontinalis have been used worldwide to stock fishless alpine lakes, negatively affecting native biota. Understanding its spatial ecology in invaded ecosystems can provide information to interpret and contrast its ecological impact. We opportunistically used capture points of brook trout gillnetted during an eradication campaign to assess the distribution patterns of four unexploited populations inhabiting high-altitude lakes. The main eradication method implies the use of many gillnets with several mesh sizes, which are selective for different fish sizes. For each lake we drew six capture maps associated with as many different mesh sizes, and we tested whether the distance from the coastline (which in alpine lakes is a reliable proxy of the most important spatial gradients, e.g. depth, temperature, prey availability, lighting conditions) influences the proportion of captured fish belonging to different size classes and the number of fish captured by the nets with different mesh sizes. To interpret the results, we also provide a cartographic description of the lakes’ bathymetry and littoral microhabitats. We found (1) a negative relationship between brook trout distribution and the distance from the coastline in all of the size classes, lakes and mesh sizes; (2) that large brook trout can thrive in the lakes’ center, while small ones are limited to the littoral areas; and (3) that the distance from the coastline alone cannot explain all the differences in the catch densities in different parts of the lakes. As in their native range, introduced brook trout populations also have littoral habits. Microhabitats, prey availability and distance from the spawning ground are other likely factors determining the distribution patterns of brook trout populations introduced in alpine lakes. The obtained results also provide useful information on how to plan new eradication campaigns

Atmospheres of retail and the asceticism of civilized consumption

Abstract. During recent decades, consumption-oriented spaces of comfort and hospitality have proliferated – including, for instance, lounge shopping malls, food court plazas, spas, entertainment retail, visitor centres, and the development of ever larger pedestrian precincts. In this article we explore shopping malls as capitalist "domes" in Sloterdijk's sense. We observe atmospheric production, atmospheric management and atmospheric culture (which we propose to call atmoculture) inside such domes. Processes of retailization and mallification – whereby shopping malls and retail spaces absorb increasing economic and societal energies – can be regarded as correlative to the rise of an atmoculture of civilized consumption. Such atmoculture is visible for instance in stress-avoidance strategies and the production of a pleasurable experience in consumption-oriented public zones. The design of contemporary retail spaces seems to pivot around specific atmospheric strategies developed to promote and sustain civilized consumption. In this piece, we describe four different strategies of atmospheric production, identifying their possible shortcomings and failings. Finally, we advance the hypothesis that the atmospheric production of retail can also be analyzed with reference to Sloterdijk's theorization of asceticism as self-disciplination.</p

Urban animals – domestic, stray and wild: notes from a bear repopulation project in the alps

This piece explores “domesticity” as a social territory defined by its relationship with the conceptual and ecological space of “the wild,” and asks whether these spaces stand in opposition to each other or more subtle relations of co-implication are at play. As we look into the domestic and the wild, a conceptual map of notions emerges, including the public, the common, the civilized, and the barbarian. The paper suggests the domestic and the wild constitute two semiotic-ecological domains constantly stretching into each other without any stable or even clear boundary line, and it elaborates on a series of corollaries for studying non-human animals in urban contexts. As an illustrative case study, we follow the story of Daniza, a wild brown bear introduced in the Brenta Natural Park on the Italian Alps in the 2000s. Declared a “dangerous animal,” Daniza was accidentally, and controversially, killed by the public authorities in 2014.info:eu-repo/semantics/acceptedVersio

Meiofaunal ecology in harsh environments: refugia and stepping stones, a case study in a deglaciating Alpine area

Climate change and progressive glacier loss are leading to rapid ecological shifts in alpine aquatic systems. Rock glaciers and paraglacial features such as proglacial lakes, moraines, and taluses can alter the gradients of glacial influence along alpine river networks. Particularly relevant is the effect of rock glacial streams on invertebrates, although the hydrology and ecology of such high-elevation stream types is still scarcely known. We investigated the main meiofaunal component of benthic communities of different stream types in a deglaciating area of the Italian Alps, i.e., Crustacea Copepoda. We used an index of habitat mildness based on water temperature, channel stability, turbidity, and organic detritus, to measure the difference in community metrics over a gradient of habitat amelioration, driven by the mixing of distinct stream types (glacial, rock-glacial, snowmelt, mixed) and their interactions with paraglacial features. The composition of copepod communities of rock-glacial sites differed from the one of the other stream types, particularly it was very different from the kryal sites, and more similar to the rhithral and krenal ones. Under progressive deglaciation, rock glaciers and paraglacial features will increasingly influence the meiofaunal communities of alpine river networks. As they host a higher number of taxa and individuals than non-glacial locations, rock glacial streams may act as stepping stones facilitating colonization following glacier retreat. After glacier loss, rock glacial streams may represent climate refugia for cold adapted taxa and/or kryal specialists, because the slow thawing of their ice might sustain cold water conditions for a longer period of time

Baryonically Closed Galaxy Groups

Elliptical galaxies and their groups having the largest L_x/L_B lie close to the locus in the L_x,L_B diagram expected for closed systems with baryon fractions equal to the cosmic mean value, f_b = 0.16. The estimated baryon fractions for several of these galaxies/groups are also close to 0.16 when the gas density is extrapolated to the virial radius. Evidently they are the least massive baryonically closed systems. Gas retention in these groups implies that non-gravitational heating cannot exceed about 1 keV per particle, consistent with the heating required to produce the deviation of groups from the L_x - T correlation for more massive clusters. Isolated galaxies/groups with X-ray luminosities significantly lower than baryonically closed groups may have undermassive dark halos, overactive central AGNs, or higher star formation efficiencies. The virial mass and hot gas temperatures of nearly or completely closed groups correlate with the group X-ray luminosities and the optical luminosities of the group-centered elliptical galaxy, an expected consequence of their merging history. The ratio of halo mass to the mass of the central galaxy for X-ray luminous galaxy/groups is about 80.Comment: 7 pages; Accepted by ApJ Letter

A comparative experimental study on the impact of standard and torrefied wood pellets on the drive parameters of a stratified batch gasifier

In these last years gasification studies have mainly involved raw biomasses. Recently, torrefied lignocellulosic materials have become particularly attractive but the majority of the investigations regarding this thermal treatment have been limited to the characterization of the feedstocks submitted to a wide range of working conditions. Only a limited and well documented number of works specifically dedicated to gasification of torrefied biomasses have been till now published. Most of these works, indeed, report results refer to industrial or pilot plants working within limited range conditions. As a consequence, extended investigations of the impact of the guide parameters of this process on a wide working conditions spectrum are not so easy to found. This work presents the results of an extended experimental campaign carried out on a specific small gasifier designed for a batch configuration and using air as gasification agent. The peculiarity of this experimental study consists in an on line monitoring of the biomass loss during the gasification process and in a direct experimental determination of the main parameters of the process as: the productivity of the syngas, its heating value, the amount of the remaining char, the power of the gasifier and the cold efficiency of the process. In particular the role of the air flow rate as critical parameter and its impact on the cited quantities is highlighted. For this investigation the results obtained for gasification tests of both commercial pellet (CP) and torrefied pellet (TP) characterized by a Mass Yield close to 80% are presented. The adopted experimental device allows to select several air flow rate ranging from 15 to 30 Nl·min-1. The L.H.V. of the syngas reaches values in the range 3.51 \u3c L.H.V. \u3c 3.85 and 4.14 \u3c L.H.V. \u3c 4.31 for CP and TP respectively. The maximum power values set at 2.73 kW for CP and 3.53 kW for TP. Interesting results can be deduced by reporting the trend of the cited quantities Vs. the air flow rate. As general result, the use of torrefied material confirms a significant improvement of the performances of the gasification process compared to those involving conventional biomasses. Please click Additional Files below to see the full abstract

Galactic Outflows and the pollution of the Galactic Environment by Supernovae

We here explore the effects of the SN explosions into the environment of star-forming galaxies like the Milky Way. Successive randomly distributed and clustered SNe explosions cause the formation of hot superbubbles that drive either fountains or galactic winds above the galactic disk, depending on the amount and concentration of energy that is injected by the SNe. In a galactic fountain, the ejected gas is re-captured by the gravitational potential and falls back onto the disk. From 3D nonequilibrium radiative cooling hydrodynamical simulations of these fountains, we find that they may reach altitudes up to about 5 kpc in the halo and thus allow for the formation of the so called intermediate-velocity-clouds (IVCs) which are often observed in the halos of disk galaxies. The high-velocity-clouds that are also observed but at higher altitudes (of up to 12 kpc) require another mechanism to explain their production. We argue that they could be formed either by the capture of gas from the intergalactic medium and/or by the action of magnetic fields that are carried to the halo with the gas in the fountains. Due to angular momentum losses to the halo, we find that the fountain material falls back to smaller radii and is not largely spread over the galactic disk. Instead, the SNe ejecta fall nearby the region where the fountain was produced, a result which is consistent with recent chemical models of the galaxy. The fall back material leads to the formation of new generations of molecular clouds and to supersonic turbulence feedback in the disk.Comment: 10 pages, 5 figures; paper of invited talk for the Procs. of the 2007 WISER Workshop (World Space Environment Forum), Alexandria, Egypt, October 2007, Spa. Sci. Rev

Bidens pilosa L. (Asteraceae) control in sunflower with residual herbicides.

Abstract One of the most damaging species in sunflower crops in Brazil is the hairy beggartick (Bidens pilosa L). The large number of seeds, the various vegetative cycles during the year, the staggered germination and the scarcity of selective and effective herbicides to control this weed in sunflower are some of attributes that hinder the control of hairy beggartick populations. Two experiments were carried out to evaluate the control of hairy beggarticks, as well as sunflower tolerance to herbicides. The treatments were as follows: S-metolachlor (1,200 and 2,400 g ai ha-1), flumioxazin (60 and 120 g ai ha-1), and sulfentrazone (150 and 300 g ai ha-1) and two controls (weedy and weed-free check). The selectivity of the herbicides was higher at low doses. Flumioxazin and sulfentrazone caused injury to sunflowers at the highest doses and mainly in sandy soils. Although S-metolachlor did not cause visual symptoms of injury, the higher dose reduced sunflower yield. The herbicides sulfentrazone and flumioxazin provided satisfactory control of hairy beggartick plants in both types of soils. S-metolachlor presented medium control of hairy beggarticks in clay soil; however, its efficiency was slightly higher when applied in sandy soil. The most efficient herbicide for controlling hairy beggartick plants was flumioxazin, followed by sulfentrazone