We explore the dependence of the incidence of moderate-luminosity (L0.5−8 keV = 1041.9−43.7 erg s-1) active galactic nuclei (AGNs) and the distribution of their accretion rates on host color at 0.5 ...<z < 2.5. Based on the deepest X-ray and UV-to-far-infrared data in the two The Great Observatories Origins Deep Survey (GOODS) fields, we identify 221 AGNs within a mass-complete parent galaxy sample down to M∗ > 1010 M⊙. We use extinction-corrected rest-frame U−V colors to divide both AGN hosts and non-AGN galaxies into red sequence (red), green valley (green), and blue cloud (blue) populations. We find that the fraction of galaxies hosting an AGN at fixed X-ray luminosity increases with stellar mass and redshift for all the three galaxy populations, independent of their colors. However, both the AGN fraction at fixed stellar mass and its evolution with redshift are clearly dependent on host colors. Most notably, red galaxies have the lowest AGN fraction (~5%) at z ~ 1 yet with most rapid evolution with redshift, increasing by a factor of ~5 (24%) at z ~ 2. Green galaxies exhibit the highest AGN fraction across all redshifts, which is most pronounced at z ~ 2 with more than half of them hosting an AGN at M∗ > 1010.6 M⊙. Together with the high AGN fraction in red galaxies at z ~ 2, this indicates that (X-ray) AGNs could be important in both transforming (quenching) star-forming galaxies into quiescent ones and subsequently maintaining their quiescence at high redshift. Furthermore, consistent with previous studies at lower redshifts, we show that the probability of hosting an AGN for the total galaxy population can be characterized by a universal Eddington ratio (as approximated by LX/M∗) distribution (p(λEdd) ~ λEdd-0.4), which is independent on host mass. Yet consistent with their different AGN fractions, galaxies with different colors appear to also have different p(λEdd) with red galaxies exhibiting more rapid redshift evolution compared with that for green and blue galaxies. Evidence for a steeper power-law distribution of p(λEdd) in red galaxies (p(λEdd) ~ λEdd-0.6) is also presented, though larger samples are needed to confirm. These results suggest that the AGN accretion or the growth of supermassive black holes is related to their host properties, and may also influence their hosts in a different mode dependent on the host color.
A novel amorphous composite coating was synthesized successfully on low carbon steel by laser cladding FeCrCoNiSiB high-entropy self-fluxed alloy powder. The combination of impact wear and XRD was ...adopted as a novel method to observe the crystalline phases of the coating. The research focused on the microstructure and high-temperature wear behavior of the two characteristic layers in the fabricated coatings. The amorphous/crystalline layer as the upper layer was composed of amorphous phase and face-centered cubic γ(Fe, Ni) phase, while body-centered cubic (Co, Fe) solid solution phases with carbides and borides precipitates preferred to appear in the bottom layer. The volume fraction of amorphous phase was approximately 49% in the upper layer, which gave birth to a novel wear mechanism and remarkably improve the wear resistance in high-temperature service environment.
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•Amorphous matrix coating was obtained with FeCrCoNiSiB high-entropy alloy powder.•The amorphous phase accounted for 49% of the amorphous/crystalline layer.•The wear mechanism of the amorphous layer and the dendritic layer was revealed.•The combination of impact wear and XRD was adopted to study the phase composition.
The effects of systematic variation of Mg and Cu contents (Mg: ~1.5, 2.0, and 2.5, Cu: ~1.5, 2.0, 2.5, and 2.9wt%) on the microstructures and mechanical properties of high-Zn (8.5wt%) Al–Zn–Mg–Cu ...alloys are investigated. Fracture toughness is experimentally approached by the Kahn tear test. Results showed that, under same ageing condition, the conductivity, hardness, strength and toughness of the designed alloys are primarily determined by Mg content: the higher the Mg content, the higher the hardness and strength, but the lower the conductivity and toughness. Increasing Cu content can produce a similar phenomenon, but with weak effects compared with Mg. The experiments and thermodynamic/kinetic simulation indicate that, increasing Mg/Cu content can improve the volume fraction of matrix precipitates, so as to improve the strength and hardness, and the effects of Mg are stronger than Cu. Additionally, increasing Mg content can somewhat reduce the sizes of the matrix precipitates especially in overaged condition, which is also good for the strength and hardness. However, with increasing Mg content the area fraction of the grain boundary precipitates (GBPs) and the yield stress contrast between grain interiors and precipitate free zones (PFZs) at grain boundary can be increased greatly, consequently promoting intergranular fracture and decreasing toughness. For the alloys with low/middle Mg content (e.g., 1.5/2.0wt%), increasing Cu content will improve the yield stress contrast between grain interiors and PFZs as well as the recrystallization degree, so that intergranular fracture will be promoted for toughness reduction. For the alloys with high Mg content (e.g., 2.5wt%), the increased undissolved phases induced by high Cu content will promote fracture at/near coarse constituent particles, favoring further toughness reduction.
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•Amorphous matrix coating was obtained with CoCrBFeNiSi high-entropy alloy powder.•The amorphous phase accounted for over 85% of the amorphous/crystalline layer.•The wear mechanism of ...the amorphous layer and the dendritic layer was revealed.
Amorphous coating was successfully fabricated on low carbon steel substrates with one-step laser cladding method using CoCrNiSiBFe high-entropy alloy powder. The microstructure and high-temperature wear mechanism of the fabricated coating was investigated. The coating exhibited layered microstructure including the columnar dendrites as the bottom layer and the amorphous-matrix layer with β-Co phase as the minor phase. The content of amorphous phase in the upper surface was up to 85.1%. Different high temperature wear mechanism was exhibited by the two layers leading to a remarkable decrease of wear mass loss and thus a much better wear resistance in the amorphous layer.
Highlights • κ opioid receptor activation induced significant conditioned place aversion in mice. • p38 MAPK activated in the amygdala after U50,488H pairing. • Intra-amygdala injection of SB203580 ...blocked U50,488H-induced conditioned place aversion.
Abstract
We present a new exploration of the cosmic star formation history and dust obscuration in massive galaxies at redshifts 0.5 < z < 6. We utilize the deepest 450- and 850-μm imaging from ...SCUBA-2 CLS, covering 230 arcmin2 in the AEGIS, COSMOS and UDS fields, together with 100–250 μm imaging from Herschel. We demonstrate the capability of the t-phot deconfusion code to reach below the confusion limit, using multiwavelength prior catalogues from CANDELS/3D-HST. By combining IR and UV data, we measure the relationship between total star formation rate (SFR) and stellar mass up to z ∼ 5, indicating that UV-derived dust corrections underestimate the SFR in massive galaxies. We investigate the relationship between obscuration and the UV slope (the IRX–β relation) in our sample, which is similar to that of low-redshift starburst galaxies, although it deviates at high stellar masses. Our data provide new measurements of the total SFR density (SFRD) in $M_{\ast }>10^{10}\,\textrm{M}_{\odot }$ galaxies at 0.5 < z < 6. This is dominated by obscured star formation by a factor of >10. One third of this is accounted for by 450-μm-detected sources, while one-fifth is attributed to UV-luminous sources (brighter than $L_{\rm UV}^\ast$), although even these are largely obscured. By extrapolating our results to include all stellar masses, we estimate a total SFRD that is in good agreement with previous results from IR and UV data at z ≲ 3, and from UV-only data at z ∼ 5. The cosmic star formation history undergoes a transition at z ∼ 3–4, as predominantly unobscured growth in the early Universe is overtaken by obscured star formation, driven by the build-up of the most massive galaxies during the peak of cosmic assembly.
A kind of hydrofoil, which is especially for use by helical vertical axis turbine for power generation from marine current, has been optimized by means of traditional genetic algorithms combined with ...hierarchical fair competition model. Bezier curve is used to parameterize the hydrofoils and numerical analysis is also introduced to evaluate hydrodynamic performance. Special fitness function as well as modified total lift–drag ratio is discussed in detail. Turbine performance tests and flow visualization experiments by PIV are conducted in order to draw a comparison between the optimized and two other competitive hydrofoils. The experimental results demonstrate that the optimized is more suitable to marine condition and beneficial to turbine efficiency improvement, and can be expected to act as a prospective hydrofoil for helical vertical axis turbine.
ABSTRACT
GW190814 was reported during LIGO’s and Virgo’s third observing run with the most asymmetric component masses (an ∼23 M⊙ black hole and an ∼2.6 M⊙ compact object). Under the assumption that ...this event is a binary black hole (BBH) merger formed through the isolated binary evolution channel, we reanalyse the publicly released data of GW190814 with the modified astrophysical priors on the effective spin χeff, and further explore its formation history using detailed binary modelling. We show that GW190814 is likely to have been formed through the classical common envelope channel. Our findings show that the properties inferred using the modified astrophysical priors are consistent with those inferred by the uniform priors. With the newly inferred properties of GW190814, we perform detailed binary evolution of the immediate progenitor of the BBH (namely a close binary system composed of a BH and a helium star) in a large parameter space, taking into account mass-loss, internal differential rotation, supernova kicks, and tidal interactions between the helium star and the BH companion. Our findings show that GW190814-like events could be formed in limited initial conditions just after the common envelope phase: an ∼23 M⊙ BH and a helium star of MZamsHe ∼ 8.5 M⊙ at solar metallicity (∼ 7.5 M⊙ at 10 per cent solar metallicity) with an initial orbital period at around 1.0 d. Additionally, the inferred low spin of the secondary indicates that the required metallicity for reproducing GW190814-like events should not be too low (e.g. Z ≳ 0.1 Z⊙).
GSN 069 is an optically identified very low-mass active galactic nuclei (AGN) that shows supersoft X-ray emission. The source is known to exhibit a huge X-ray outburst, with flux increased by more ...than a factor of ∼240 compared to the quiescence state. We report its long-term evolution in the X-ray flux and spectral variations over a timescale of ∼decade, using both new and archival X-ray observations from the XMM-Newton and Swift. The new Swift observations detected the source in its lowest level of X-ray activity since the outburst, a factor of ∼4 lower in the 0.2-2 keV flux than that obtained with the XMM-Newton observations nearly eight years ago. Combining with the historical X-ray measurements, we find that the X-ray flux is decreasing slowly. There seemed to be spectral softening associated with the drop of X-ray flux. In addition, we find evidence for the presence of a weak, variable, hard X-ray component, in addition to the dominant thermal blackbody emission reported before. The long decay of X-ray flux and spectral evolution, as well as the supersoft X-ray spectra, suggest that the source could be a tidal disruption event (TDE), though a highly variable AGN cannot be fully ruled out. Further continued X-ray monitoring would be required to test the TDE interpretation, by better determining the flux evolution in the decay phase.
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