Context. Powerful winds at accretion-disk scales have been observed in the past 20 years in many active galactic nuclei (AGN). These are the so-called ultrafast outflows (UFOs). Outflows are ...intimately related to mass accretion through the conservation of angular momentum, and they are therefore a key ingredient of most accretion disk models around black holes (BHs). At the same time, nuclear winds and outflows can provide the feedback that regulates the joint BH and galaxy growth. Aims. We reconsidered UFO observations in the framework of disk-wind scenarios, both magnetohydrodynamic disk winds and radiatively driven winds. Methods. We studied the statistical properties of observed UFOs from the literature and derived the distribution functions of the ratio ω̄ of the mass-outflow and -inflow rates and the ratio λ w of the mass-outflow and the Eddington accretion rates. We studied the links between ω̄ and λ w and the Eddington ratio λ = L bol / L Edd . We derived the typical wind-activity history in our sources by assuming that it can be statistically described by population functions. Results. We find that the distribution functions of ω̄ and λ w can be described as power laws above some thresholds, suggesting that there may be many wind subevents for each major wind event in each AGN activity cycle, which is a fractal behavior. We then introduced a simple cellular automaton to investigate how the dynamical properties of an idealized disk-wind system change following the introduction of simple feedback rules. We find that without feedback, the system is overcritical. Conversely, when feedback is present, regardless of whether it is magnetic or radiation driven, the system can be driven toward a self-organized critical state. Conclusions. Our results corroborate the hypothesis that AGN feedback is a necessary key ingredient in disk-wind systems, and following this, in shaping the coevolution of galaxies and supermassive BHs.
•High-T deformation experiments are performed on a trachybasaltic melt.•Effects of shear and cooling rate on the rheology are systematically investigated.•Two different crystallization regimes mark ...the melt rheological evolution.•An exponential function describes the effect of crystallization on viscosity.•Lava flow emplacement modeling can be refined by disequilibrium rheology datasets.
Magmas often experience severe disequilibrium conditions during their migration through the Earth's crust and the subsequent emplacement on its surface. During their transport, magmas are subjected to a wide range of cooling (q) and deformation rates (γ˙), generating physico-chemical perturbations in the magmatic system able to inhibit or promote crystallization processes. Quantifying the magnitude and timescale of kinetic effects is essential to correctly constrain the rheological evolution of magmas and their ability to flow. Here we present a suite of cooling deformation experiments (CDE) conducted on a basalt from Mt. Etna (Sicily, Italy) to disentangle and model the concurrent effects of q (from 1 to 10°C/min) and γ˙ (from 1 to 10 s−1) on the rheology of the system. The analysis of the temporal evolution of viscosity indicates that both q and γ˙ strongly affect the onset of crystallization and achievement of a rheological cut-off over time, which represents the steep viscosity increase responsible for inhibiting magma flow. Both these rheological thresholds occur at lower T and earlier in time with increasing q, as well as at higher T and earlier in time with increasing γ˙. To reproduce the observed effects of crystallization on the apparent viscosity, we adopt a stretched exponential function that identifies two main crystallization regimes: i) a first shear-induced crystallization regime, characterized by a gentle viscosity increase and ii) a second cooling-dominated regime, marked by a steeper viscosity increase. The relative extent of these crystallization regimes strictly depends on the interplay between q and γ˙ on the crystallization kinetics and suggest a first order control of q and a subordinate role of γ˙.
In active volcanic environments magmas that ascend within the conduit and erupt at the surface as lava flows experience physico-chemical perturbations related to temperature changes and variable ...degrees of deformation. We have conducted experimental investigations to examine the concurrent effects of undercooling and stirring on the crystallization kinetics of a leucite-bearing phonotephrite from Somma-Vesuvius (Italy). Two sets of undercooling experiments have been carried out within the same temperature range of 1300–1150 °C. The first set involved classical static undercooling (SU) experiments with no stirring applied to the melt, while the second set involved dynamic undercooling (DU) experiments with a shear strain rate of 1 s−1 applied. By comparing SU and DU results with previous data from literature obtained using the same experimental approach, we observe that the degree of crystallization and the textural evolution of leucite and clinopyroxene progress upon the effect of melt stirring by shortening the incubation time. As a result, the solidification process is markedly enhanced in DU experiments, accompanied by a substantial increase in the crystal nucleation density and growth rate. Thermorheological modeling indicates that stirring-induced crystallization increases the melt viscosity by a factor of ∼1.5–4.5 depending on the system temperature. At a given temperature, mass transport can therefore produce higher crystallinity and higher viscosity magmatic suspensions than static crystallization conditions. We document that if subsequent cooling occurs, the existing crystal cargo in such suspensions may promote the onset of non-Newtonian rheological response, causing a transition from homogeneous viscous flow to shear localization and magma/lava rupture.
•Static and dynamic undercooling experiments are carried out on a phonotephritic melt.•Melt stirring enhances leucite and clinopyroxene crystallization.•Nucleation density, nucleation and growth rate of crystals increase via melt stirring.•Shear-induced crystallization favors the onset of non-Newtonian behavior at higher T.
Within subvolcanic plumbing systems, along volcanic conduits and post-eruptive emplacement, mineral textures and compositions are governed by complex kinetic (undercooling) and dynamic (convective) ...processes that deviate from theoretical models and equilibrium criteria. In this perspective, we have investigated the partitioning of major and trace cations between clinopyroxene and phonotephritic melt under convective stirring conditions at high degrees of undercooling (−ΔTnominal = 30–60 °C) and atmospheric pressure. We have integrated this novel data set with conventional static (no physical perturbation) clinopyroxene-melt compositions obtained under interface- and diffusion-controlled growth regimes. Results show that clinopyroxene growth kinetics and diffusion boundary layers caused by melt supersaturation are partly mitigated by the homogenizing effects of stirring. Because of continuous supply of fresh melt to the advancing crystal surface, the partitioning of major and trace cations is governed by local equilibrium effects, which are interpreted as the extension of equilibrium thermodynamic principles to non-equilibrium bulk systems. Major cations are incorporated into the clinopyroxene structure via the coupled substitution M1Mg, TSi ↔ M1Ti, TAl and in conformity with the thermodynamic mixing properties of CaMgSiO2, CaAl2SiO6, and CaTiAl2O6 components. The complementary relationship between lattice strain (ΔGstrain) and electrostatic (ΔGelectrostatic) energies of heterovalent substitutions is the most appropriate thermodynamic description for the accommodation of trace cations in the clinopyroxene lattice site (i.e., ΔGpartitioning = ΔGstrain + ΔGelectrostatic). The excess energy of partitioning ΔGpartitioning changes principally with Al in tetrahedral coordination and determines the type and number of charge-balanced and -imbalanced configurations taking place in the structural sites of clinopyroxene. An important outcome from dynamic stirring experiments is that superimposition of convective mass transfer on melt supersaturation phenomena causes the formation of Cr-rich concentric zones under closed system crystallization conditions. However, these Cr-rich zones do not correlate with enrichment in other compatible elements and depletion in incompatible elements, as would be expected in natural open systems characterized by input of more primitive magmas. While the convective transport acts to reduce the diffusive length scale of chemical species in the experimental melt, fresh Cr cations are more easily incorporated into the concentric zones due to crystal field effects. Together, our findings reveal that during magma ascent and emplacement, convective stirring may promote clinopyroxene crystallization and minimize kinetic effects on clinopyroxene zoning.
•Kinetic partitioning of cations between clinopyroxene and phonotephrite is presented.•Element partitioning in sector-zoned crystals is controlled by convective stirring.•Incorporation of REE + Y and HFSE depends on lattice strain and electrostatic energies.•Cr-rich concentric zoning originates by convection and crystal field effects.
We present kinetic partitioning data for trace cations measured in zoned clinopyroxene crystals obtained from a variably cooled and decompressed olivine basalt erupted at Mt. Etna volcano in Italy. ...Supersaturation effects and compositional heterogeneities at the interface melt lead to the development of sector zoning, concentric zoning, and patchy zoning in clinopyroxene crystals. Apparent partition coefficients between compositionally different growth layers and adjacent melts (Di) for isovalent groups of trace elements are tested for internal consistency on the thermodynamic basis of lattice strain (ΔGstrain) and electrostatic (ΔGelec) energies of substitutions. The excess energy of partitioning (ΔGpartitioning) for trace cations in zoned crystals accounts for a kinetic incorporation control leading to large enthalpic effects through distortion of the lattice and changes in the electrostatic forces. ΔGpartitioning depends upon the complementary relationship between ΔGstrain and ΔGelec, which is the most appropriate thermodynamic description for the accommodation of rare earth elements and high field strength elements in the lattice site of zoned crystals. Polyhedral sectors, skeletal forms, and overgrowth zones have Di values settled by the number of charge-balanced and -imbalanced configurations taking place in the lattice site as a function of aluminium in tetrahedral coordination, and crystal structural changes produced by heterovalent cation substitutions. In an energetically unstable macroscopic system ruled by cooling and decompression, thermodynamic requirements for the crystallochemical control of Di encompass the attainment of local equilibrium at the crystal-melt interface via the establishment of small-volume reaction kinetics. The requisite of local interface equilibrium is however susceptible to the anisotropic growth velocity of each specific clinopyroxene surface, thereby giving reason to different energetic properties of the crystallographic site. This axiomatic control requires that transition metal cations partition also in consideration of electronic effects related to the crystal field stabilization energy. The overriding implication is that Di values for trace cations having different size, charge, and electronic configuration serve as sensitive probes of the different crystal growth mechanisms, surface incorporation sites, and arrangements of atoms at the lattice-scale. In this perspective, fractional crystallization modeling of 2011–2013 bulk rock data from lava fountains indicates that the compositional evolution of magmas erupted at Mt. Etna cannot be described by a unique equilibrium value of Di for a given clinopyroxene-melt interface. The leverage of interface kinetics is distinctively dominant along the subvolcanic plumbing system, thereby requiring that values of Di differ for structurally and compositionally distinct zones in clinopyroxene phenocrysts. To successfully interpret the trace element signature of Etnean magmas, the archetypal constancy of partition coefficient at bulk thermodynamic equilibrium must be in some measure reappraised in favor of the establishment of a local interface equilibrium upon highly dynamic crystallization and growth conditions.
We present Atacama large millimeter/submillimeter array (ALMA) and compact array (ACA) C i\({}^{3}{P}_{1}{-}^{3}{P}_{0}\) (C i(1–0)) observations of NGC 6240, which we combine with ALMA CO(2–1) and ...IRAM Plateau de Bure Interferometer CO(1–0) data to study the physical properties of the massive molecular (H2) outflow. We discover that the receding and approaching sides of the H2 outflow, aligned east–west, exceed 10 kpc in their total extent. High resolution (\(0\buildrel{\prime\prime}\over{.} 24\)) C i(1–0) line images surprisingly reveal that the outflow emission peaks between the two active galactic nuclei (AGNs), rather than on either of the two, and that it dominates the velocity field in this nuclear region. We combine the C i(1–0) and CO(1–0) data to constrain the CO-to-H2 conversion factor (\({\alpha }_{\mathrm{CO}}\)) in the outflow, which is on average \(2.1\pm 1.2\,{M}_{\odot }{({\rm{K}}\mathrm{km}{{\rm{s}}}^{-1}{\mathrm{pc}}^{2})}^{-1}\). We estimate that 60 ± 20% of the total H2 gas reservoir of NGC 6240 is entrained in the outflow, for a resulting mass-loss rate of \({\dot{M}}_{\mathrm{out}}=2500\pm 1200\,{M}_{\odot }\,{\mathrm{yr}}^{-1}\equiv 50\pm 30\) SFR. These energetics rule out a solely star formation-driven wind, but the puzzling morphology challenges a classic radiative-mode AGN feedback scenario. For the quiescent gas, we compute \(\langle {\alpha }_{\mathrm{CO}}\rangle =3.2\pm 1.8\,{M}_{\odot }{({\rm{K}}\mathrm{km}{{\rm{s}}}^{-1}{\mathrm{pc}}^{2})}^{-1}\), which is at least twice the value commonly employed for (ultra) luminous infrared galaxies ((U)LIRGs). We observe a tentative trend of increasing \({r}_{21}\equiv {L}_{\mathrm{CO}(2-1)}^{{\prime} }/{L}_{\mathrm{CO}(1-0)}^{{\prime} }\) ratios with velocity dispersion and measure r 21 > 1 in the outflow, whereas r 21 ≃ 1 in the quiescent gas. We propose that molecular outflows are the location of the warmer, strongly unbound phase that partially reduces the opacity of the CO lines in (U)LIRGs, hence driving down their global \({\alpha }_{\mathrm{CO}}\) and increasing their r 21 values.
Infections caused by the hepatitis C virus (HCV) are a significant world health problem for which novel therapies are in urgent demand. The NS5B polymerase of HCV is responsible for the replication ...of viral RNA and has been a prime target in the search for novel treatment options. We had discovered allosteric finger‐loop inhibitors based on a thieno3,2‐bpyrrole scaffold as an alternative to the related indole inhibitors. Optimization of the thienopyrrole series led to several N‐acetamides with submicromolar potency in the cell‐based replicon assay, but they lacked oral bioavailability in rats. By linking the N4‐position to the ortho‐position of the C5‐aryl group, we were able to identify the tetracyclic thienopyrrole 40, which displayed a favorable pharmacokinetic profile in rats and dogs and is equipotent with recently disclosed finger‐loop inhibitors based on an indole scaffold.
Infections caused by the hepatitis C virus (HCV) are a significant world health problem for which novel therapies are in urgent demand. We previously discovered allosteric inhibitors of the HCV NS5B polymerase based on a thieno3,2‐bpyrrole scaffold, exemplified by 4. X‐ray crystallography confirmed binding of thienopyrroles to the upper‐thumb domain of NS5B. Extensive structure–activity relationship studies around compound 4 identified the potent tetracyclic thienopyrrole 40, which displayed a favorable pharmacokinetic profile in rats and dogs.
•TiO2-doped spodumene glass is highly unstable against reheating.•TiO2-driven nucleation begins as soon as the glass transition is approached.•Raman spectroscopy can monitor the modification of the ...starting glass upon heating.•Inattentive near-Tg viscosity measurements can lead to inaccuracies by 2 log units.
A spodumene glass (LiAlSi2O6), doped with 4 mol% TiO2 as a nucleating agent, was synthesized by containerless melting. Its accurate viscosity characterization by micropenetration viscometry or calorimetry is shown to be very challenging in the vicinity of the glass transition, due to the unpreventable occurrence of thermally activated non-stoichiometric crystal nucleation, closely overlapping the relaxation into the liquid state. TiO2 crystal nucleation brings about a compositional modification of the residual melt, with an associated increase in measured viscosity by up to 2 log units. A careful experimental approach and a profound understanding of seed formation are essential to circumvent or at least minimize such inaccuracies, getting as close as possible to the viscosity of the parent homogeneous melt.
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![ALMA [C i]3P1–3P0 Observati...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/0004-637X/small "ALMA [C i]3P1–3P0 Observations of NGC 6240: A Puzzling Molecular Outflow, and the Role of Outflows in the Global αCO Factor of (U)LIRGs")
