Abstract
We report the first large, systematic study of the dynamics and energetics of a representative sample of Fanaroff–Riley type II (FR II) radio galaxies with well-characterized group/cluster ...environments. We used X-ray inverse-Compton and radio synchrotron measurements to determine the internal radio-lobe conditions, and these were compared with external pressures acting on the lobes, determined from measurements of the thermal X-ray emission of the group/cluster. Consistent with previous work, we found that FR II radio lobes are typically electron dominated by a small factor relative to equipartition, and are overpressured relative to the external medium in their outer parts. These results suggest that there is typically no energetically significant proton population in the lobes of FR II radio galaxies (unlike for FR Is), and so for this population, inverse-Compton modelling provides an accurate way of measuring total energy content and estimating jet power. We estimated the distribution of Mach numbers for the population of expanding radio lobes, finding that at least half of the radio galaxies are currently driving strong shocks into their group/cluster environments. Finally, we determined a jet power–radio luminosity relation for FR II radio galaxies based on our estimates of lobe internal energy and Mach number. The slope and normalization of this relation are consistent with theoretical expectations, given the departure from equipartition and environmental distribution for our sample.
ABSTRACT
The effects of feedback from high luminosity radio-loud active galactic nuclei (AGN) have been extensively discussed in the literature, but feedback from low-luminosity radio-loud AGN is ...less well understood. The advent of high sensitivity, high angular resolution, large field-of-view telescopes such as LOFAR is now allowing wide-area studies of such faint sources for the first time. Using the first data release of the LOFAR Two Metre Sky Survey (LoTSS) we report on our discovery of a population of 195 radio galaxies with 150-MHz luminosities between 3 × 1022 and 1.5 × 1025 WHz−1 and total radio emission no larger than 80 kpc. These objects, which we term galaxy-scale jets (GSJ), are small enough to be directly influencing the evolution of the host on galaxy scales. We report upon the typical host properties of our sample, finding that 9 per cent are hosted by spirals with the remainder being hosted by elliptical galaxies. Two of the spiral-hosted GSJ are highly unusual with low radio luminosities and FRII-like morphology. The host properties of our GSJ show that they are ordinary AGN observed at a stage in their life shortly after the radio emission has expanded beyond the central regions of the host. Based on our estimates, we find that about half of our GSJ have internal radio lobe energy within an order of magnitude of the ISM energy so that, even ignoring any possible shocks, GSJ are energetically capable of affecting the evolution of the host. The current sample of GSJ will grow in size with future releases of LoTSS and can also form the basis for further studies of feedback from low-luminosity radio sources.
Composite ceramic coatings were formed on a magnesium alloy by AC plasma electrolytic oxidation using a phosphate-based electrolyte with α-Al2O3, monoclinic ZrO2 or CeO2 particles in suspension. ...Effects of particles concentration (2, 5 and 10g/L) on the electrical response, composition/morphology and corrosion behaviour of the coatings were investigated. Findings revealed successful incorporation of particles, which were preferentially located in the outer coating layer. Due to high temperatures at the locations of microdischarges, zirconia particles underwent transformation from monoclinic to tetragonal structure. The majority of alumina and ceria particles remained unaffected, although some of the alumina particles possibly formed MgAl2O4 by reaction with the substrate. Porosity and thickness of the coatings tended to decrease with increasing particles concentration in the electrolyte. Coatings formed in the electrolytes containing CeO2 particles revealed the best long-term corrosion performance in 0.5wt% NaCl solution.
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•PEO coatings were developed in electrolytes with α-Al2O3, ZrO2 or CeO2 particles.•Treatments with suspended particles show an early drop of the current.•Particles are preferentially incorporated into the outer PEO layer.•PEO coatings containing particles reveal superior anticorrosion properties.•CeO2 particle addition leads to a better long-term corrosion performance.
•A356 gravity-cast and rheocast pre-anodized aluminium alloys were coated by PEO.•Different sealing techniques were applied after the coating process.•Iron-rich constituents of the substrate occlude ...the continuity of the porous anodic film.•PEO coatings consisted of a mixture of α-Al2O3, γ-Al2O3 and mullite.•Post-treatments improved both hydrophobic and corrosion properties.
Voltage-controlled PEO coatings were developed on A356 aluminum alloys (gravity-cast and rheocast) with a pre-anodized layer. The influence of the alloy manufacturing process and the effect of Si-rich phase on the structure and composition of the oxide layers were evaluated using SEM, EDS and XRD. The pre-anodized oxide layer preserves the microstructure of the substrate due to the presence of secondary phases that have a different behavior relative to the matrix during anodizing. PEO coatings consisted of a mixture of α-Al2O3, γ-Al2O3 and mullite. The corrosion behavior and the effectiveness of different sealing techniques based on salts of nickel, cobalt, cerium and phosphonic acid were also studied. Post-treatments improved the hydrophobic properties of the coatings and showed a beneficial effect, significantly increasing the coating impedance and thereby reducing the susceptibility to corrosion.
Abstract
The relative positions of the high and low surface brightness regions of radio-loud active galaxies in the 3CR sample were found by Fanaroff and Riley to be correlated with their luminosity. ...We revisit this canonical relationship with a sample of 5805 extended radio-loud active galactic nuclei (AGN) from the LOFAR Two-Metre Sky Survey (LoTSS), compiling the most complete data set of radio-galaxy morphological information obtained to date. We demonstrate that, for this sample, radio luminosity does not reliably predict whether a source is edge-brightened (FRII) or centre-brightened (FRI). We highlight a large population of low-luminosity FRIIs, extending three orders of magnitude below the traditional FR break, and demonstrate that their host galaxies are on average systematically fainter than those of high-luminosity FRIIs and of FRIs matched in luminosity. This result supports the jet power/environment paradigm for the FR break: low-power jets may remain undisrupted and form hotspots in lower mass hosts. We also find substantial populations that appear physically distinct from the traditional FR classes, including candidate restarting sources and ‘hybrids’. We identify 459 bent-tailed sources, which we find to have a significantly higher SDSS cluster association fraction (at z < 0.4) than the general radio-galaxy population, similar to the results of previous work. The complexity of the LoTSS faint, extended radio sources not only demonstrates the need for caution in the automated classification and interpretation of extended sources in modern radio surveys, but also reveals the wealth of morphological information such surveys will provide and its value for advancing our physical understanding of radio-loud AGN.
In this study, the microstructure and corrosion behaviour of rheocast and gravity-cast A356 aluminium alloys were examined and compared. Scanning Kelvin probe force microscopy (SKPFM) results proved ...that large potential differences between iron-containing intermetallics and the alpha -Al matrix were responsible for the initiation of the attack at the intermetallics/ alpha -Al interfaces. For longer immersion times, corrosion attack proceeded through the eutectic areas. Semisolid processing refined the eutectic silicon and iron-intermetallics and reduced the potential difference between secondary phases and the matrix. This resulted in improved pitting corrosion resistance of the rheocast A356 aluminium alloy.
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•Electro- and chemical-polishing of Cuprovide similar adhesion of PVD Nb3Sn for - relevant to SRF Cu cavities.•Abrasion introduces coating defects: nodule compression, cracking, ...pitting, fragmentation, comminution, and detachment.•Coating degradation is similar for electropolished and chemically-polished Cu. Some coating remains attached to high loads.
The paper presents the first study of the abrasion resistance and degradation processes of magnetron-sputtered Nb3Sn coatings on electropolished (EP) or chemical polished (CP) copper substrates. The coating-substrate system is of interest for application in radio frequency superconducting cavities as an improvement on bulk niobium cavities. The microstructural and chemical properties of the substrates and coating were examined by scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDS), electron backscatter diffraction, X-ray diffraction, and focused ion beam cross-sectioning. The abrasion resistance was investigated by scratch testing under progressive loads up to 200 N, after which the scratched surfaces were characterised by SEM/EDS to determine the failure mechanisms of the coatings. Several stages of coating damage were identified, including nodule compression, cracking, pitting, fragmentation, comminution and detachment. Nevertheless, substantial amounts of fragmented and embedded coating remained attached to the copper up to the highest load. The findings indicated similar abrasion resistance behaviour for the EP and CP conditions.
In this work, corrosion and wear resistance of uncoated and PEO coated AZ91/SiC/0-10p composites manufactured by semisolid processing is evaluated by corrosion tests in saline solution and ...ball-on-disc tests. AZ91/SiC composites show a globular microstructure with SiC clusters located at the interglobular regions. PEO coatings reveal a trilayered structure with thicker, less porous and softer regions at the locations of SiC clusters. Corrosion rate increases with increasing the volume fraction of reinforcement, which shows a cathodic activity and disrupts the continuity of the β-phase network. PEO improves the corrosion resistance, but it is also negatively influenced by the presence of the reinforcement. Tribological tests show a positive effect of the reinforcement on uncoated materials, whereas an opposite effect is found on PEO coated materials, probably due to the detachment of SiC particles from the coating.
•AZ91/SiC/0-10p corrosion rate increases with the volume fraction of reinforcement.•PEO coatings improve corrosion resistance of AZ91/SiC/0-10p composites.•PEO coatings corrosion rate increases with the volume fraction of SiC.•Wear resistance increases with SiC content in non-coated materials.•Wear behaviour of PEO coated materials is negatively influenced by SiC clusters.
Abstract
The 2 Jy sample is a survey of radio galaxies with flux densities above 2 Jy at 2.7 GHz. As part of our ongoing work on the southern subset of 2 Jy sources, in paper I of this series we ...analysed the X-ray cores of the complete 2 Jy sample with redshifts 0.05 < z < 0.7. For this work we focus on the X-ray emission associated with the extended structures (jets, lobes, and environments) of the complete subset of 2 Jy sources with 0.05 < z < 0.2 that we have observed with Chandra. We find that hotspots and jet knots are ubiquitous in Fanaroff–Riley class II (FRII) sources, which also inhabit systematically poorer environments than the Fanaroff–Riley class I (FRI) sources in our sample. Spectral fits of the hotspots with good X-ray statistics invariably show properties consistent with synchrotron emission, and we show that inverse-Compton mechanisms underpredict the X-ray emission we observe by 1–2 orders of magnitude. Inverse-Compton emission is detected from many of the lobes in our sample, and we find that the lobes of the FRII sources show magnetic fields lower by up to an order of magnitude than expected from equipartition extrapolations. This is consistent with previous results, which show that most FRII sources have electron energy densities higher than minimum energy requirements.
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