Large eddy simulation and PIV measurements of unsteady premixed flames accelerated by obstacles

In gas explosions, the unsteady coupling of the propagating flame and the flow field induced by the presence of blockages along the flame path produces vortices of different scales ahead of the flame front. The resulting flame/vortex interaction intensifies the rate of flame propagation and the pressure rise. In this paper, a joint numerical and experimental study of unsteady premixed flame propagation around three sequential obstacles in a small scale vented explosion chamber is presented. The modelling work is carried out utilising Large Eddy Simulation (LES). In the experimental work, previous results [Patel, S.N.D.H., Jarvis, S., Ibrahim, S.S., Hargrave, G.K., Proceedings of the Combustion Institute 29, 1849-1854 (2002)] are extended to include simultaneous flame and Particle Image Velocimetry (PIV) measurements of the flow field within the wake of each obstacle. Comparisons between LES predictions and experimental data show a satisfactory agreement in terms of shape of the propagating flame, flame arrival times, spatial profile of the flame speed, pressure time history and velocity vector fields. Computations through the validated model are also performed to evaluate the effects of both large scale and sub-grid scale (sgs) vortices on the flame propagation. The results obtained demonstrate that the large vortical structures dictate the evolution of the flame in qualitative terms (shape and structure of the flame, succession of the combustion regimes along the path, acceleration-deceleration step around each obstacle, pressure time trend). Conversely, the sgs vortices do not affect the qualitative trends. However, it is essential to model their effects on the combustion rate to achieve quantitative predictions for the flame speed and the pressure peak

Evolution of faint radio sources in the VIDEO-XMM3 field

© 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical SocietyIt has been speculated that low-luminosity radio-loud active galactic nuclei (AGN) have the potential to serve as an important source of AGN feedback, and may be responsible for suppressing star formation activity in massive elliptical galaxies at late times. As such the cosmic evolution of these sources is vitally important to understand the significance of such AGN feedback processes and their influence on the global star formation history of the Universe. In this paper, we present a new investigation of the evolution of faint radio sources out to z ~ 2.5. We combine a 1 square degree Very Large Array radio survey, complete to a depth of 100 μJy, with accurate 10 band photometric redshifts from the following surveys: Visible and Infrared Survey Telescope for Astronomy Deep Extragalactic Observations and Canada-France-Hawaii Telescope Legacy Survey. The results indicate that the radio population experiences mild positive evolution out to z ~ 1.2 increasing their space density by a factor of ~3, consistent with results of several previous studies. Beyond z = 1.2, there is evidence of a slowing down of this evolution. Star-forming galaxies drive the more rapid evolution at low redshifts, z 1.2. The evolution is best fitted by pure luminosity evolution with star-forming galaxies evolving as (1 + z)2.47 ± 0.12 and AGN as (1 + z)1.18 ± 0.21M.Peer reviewe

Soil and crop management practices and the water regulation functions of soils: a qualitative synthesis of meta-analyses relevant to European agriculture

Adopting soil and crop management practices that conserve or enhance soil structure is critical for supporting the sustainable adaptation of agriculture to climate change, as it should help maintain agricultural production in the face of increasing drought or water excess without impairing environmental quality. In this paper, we evaluate the evidence for this assertion by synthesizing the results of 34 published meta-analyses of the effects of such practices on soil physical and hydraulic properties relevant for climate change adaptation in European agriculture. We also review an additional 127 meta-analyses that investigated synergies and trade-offs or help to explain the effects of soil and crop management in terms of the underlying processes and mechanisms. Finally, we identify how responses to alternative soil–crop management systems vary under contrasting agro-environmental conditions across Europe. This information may help practitioners and policymakers to draw context-specific conclusions concerning the efficacy of management practices as climate adaptation tools.Our synthesis demonstrates that organic soil amendments and the adoption of practices that maintain “continuous living cover” result in significant benefits for the water regulation function of soils, mostly arising from the additional carbon inputs to soil and the stimulation of biological processes. These effects are clearly related to improved soil aggregation and enhanced bio-porosity, both of which reduce surface runoff and increase infiltration. One potentially negative consequence of these systems is a reduction in soil water storage and groundwater recharge, which may be problematic in dry climates. Some important synergies are reductions in nitrate leaching to groundwater and greenhouse gas emissions for nonleguminous cover crop systems. The benefits of reducing tillage intensity appear much less clear-cut. Increases in soil bulk density due to traffic compaction are commonly reported. However, biological activity is enhanced under reduced tillage intensity, which should improve soil structure and infiltration capacity and reduce surface runoff and the losses of agro-chemicals to surface water. However, the evidence for these beneficial effects is inconclusive, while significant trade-offs include yield penalties and increases in greenhouse gas emissions and the risks of leaching of pesticides and nitrate.Our synthesis also highlights important knowledge gaps on the effects of management practices on root growth and transpiration. Thus, conclusions related to the impacts of management on the crop water supply and other water regulation functions are necessarily based on inferences derived from proxy variables. Based on these knowledge gaps, we outlined several key avenues for future research on this topic

NOACs added to WHO’s essential medicines list: recommendations for future policy actions

The introduction of non-vitamin K antagonists oral anticoagulants, a class of medicines which includes dabigatran, apixaban, edoxaban and rivaroxaban, has resulted in improvements in the safety and efficacy of non valvular atrial fibrillation treatment for stroke prevention, with significant reductions in stroke, intracranial haemorrhage, and mortality. For these reasons, a team of World Heart Federation Emerging Leaders led efforts to add non-vitamin K antagonists oral anticoagulants to the World Health Organization’s Model List of Essential Medicines in 2019. Following the inclusion of this class of medicines in the Essential Medicines List, this editorial proposes several recommendations to improve the accessibility, affordability and acceptability of non-vitamin K oral anticoagulants, especially in low- and middle-income settings, in order to successfully manage non-valvular atrial fibrillation and to lower the risk of stroke

[O III] Equivalent Width and Orientation Effects in Quasars

The flux of the [OIII] line is considered to be a good indicator of the bolometric emission of quasars. The observed continuum emission from the accretion disc should instead be strongly dependent on the inclination angle theta between the disc axis and the line of sight. Based on this, the equivalent width (EW) of [OIII] should provide a direct measure of theta. Here we analyze the distribution of EW([OIII]) in a sample of ~6,000 SDSS quasars, and find that it can be accurately reproduced assuming a relatively small intrinsic scatter and a random distribution of inclination angles. This result has several implications: 1) it is a direct proof of the disc-like emission of the optical continuum of quasars; 2) the value of EW([OIII]) can be used as a proxy of the inclination, to correct the measured continuum emission and then estimate the bolometric luminosity of quasars; 3) the presence of almost edge-on discs among broad line quasars implies that the accretion disc is not aligned with the circumnuclear absorber, and/or that the covering fraction of the latter is rather small. Finally, we show that a similar analysis of EW distributions of broad lines (Hbeta, Mg II, C IV) provides no evidence of inclination effects, suggesting a disc-like geometry of the broad emission line region.Comment: 8 pages, 5 figures. Accepted for publication in MNRA

Superconformal operators in Yang-Mills theories on the light-cone

We employ the light-cone superspace formalism to develop an efficient approach to constructing superconformal operators of twist two in Yang-Mills theories with N=1,2,4 supercharges. These operators have an autonomous scale dependence to one-loop order and determine the eigenfunctions of the dilatation operator in the underlying gauge theory. We demonstrate that for arbitrary N the superconformal operators are given by remarkably simple, universal expressions involving the light-cone superfields. When written in components field, they coincide with the known results obtained by conventional techniques.Comment: 29 pages, Late

P2X receptors (version 2019.4) in the IUPHAR/BPS Guide to Pharmacology Database

P2X receptors (nomenclature as agreed by the NC-IUPHAR Subcommittee on P2X Receptors [46, 134]) have a trimeric topology [118, 132, 177] with two putative TM domains, gating primarily Na+, K+ and Ca2+, exceptionally Cl-. The Nomenclature Subcommittee has recommended that for P2X receptors, structural criteria should be the initial criteria for nomenclature where possible. X-ray crystallography indicates that functional P2X receptors are trimeric and three agonist molecules are required to bind to a single receptor in order to activate it [132, 88, 96, 161]. Native receptors may occur as either homotrimers (e.g. P2X1 in smooth muscle) or heterotrimers (e.g. P2X2:P2X3 in the nodose ganglion [251], P2X1:P2X5 in mouse cortical astrocytes [146], and P2X2:P2X5 in mouse dorsal root ganglion, spinal cord and mid pons [50, 207]. P2X2, P2X4 and P2X7 receptors have been shown to form functional homopolymers which, in turn, activate pores permeable to low molecular weight solutes [229]. The hemi-channel pannexin-1 has been implicated in the pore formation induced by P2X7 [188], but not P2X2 [38], receptor activation

Performance Improvement of a Sequencing Batch Reactor for Treating Tannery Wastewaters

[EN] Tannery wastewater has a high environmental impact due to its low biodegradability. Sequencing batch reactors (SBRs) are an established method for treating highly polluted wastewater. To minimize the hydraulic retention time (HRT) of the SBRs, various HRT values were tested and the best value was chosen according to the removal efficiency of the soluble chemical oxygen demand (COD). A series of experiments was then carried out with two cationic polyelectrolytes added to the system in two different modes to improve the effluent quality. Both modes were evaluated in terms of the soluble COD, suspended solid concentration, and turbidity of the final effluent. The results showed that reducing the HRT to two days did not diminish the COD removal efficiencies.This work was supported by the Universitat Politecnica de Valencia (Project Ref.: PAID-06-10-2269).Balaguer-Arnandis, E.; Cuartas Uribe, BE.; Bes-Piá, M.; Mendoza Roca, JA.; Galiana Aleixandre, MV. (2017). Performance Improvement of a Sequencing Batch Reactor for Treating Tannery Wastewaters. Chemical Engineering & Technology. 40(9):1666-1673. https://doi.org/10.1002/ceat.201600410S1666167340

Star formation in high-redshift quasars: excess [O II] emission in the radio-loud population

We investigate the [O II] emission line properties of 18,508 quasars at z<1.6 drawn from the Sloan Digital Sky Survey (SDSS) quasar sample. The quasar sample has been separated into 1,692 radio-loud and 16,816 radio-quiet quasars (RLQs and RQQs hereafter) matched in both redshift and i'-band absolute magnitude. We use the [O II]\lambda3726+3729 line as an indicator of star formation. Based on these measurements we find evidence that star-formation activity is higher in the RLQ population. The mean equivalent widths (EW) for [O II] are EW([O II])_RL=7.80\pm0.30 \AA, and EW([O II])_RQ=4.77\pm0.06 \AA, for the RLQ and RQQ samples respectively. The mean [O II] luminosities are \log[L([O II])_RL/W]=34.31\pm0.01 and \log[L([O II])_RQ/W]=34.192\pm0.004 for the samples of RLQs and RQQs respectively. Finally, to overcome possible biases in the EW measurements due to the continuum emission below the [O II] line being contaminated by young stars in the host galaxy, we use the ratio of the [O II] luminosity to rest-frame i'-band luminosity, in this case, we find for the RLQs \log[L([O II])_RL/L_opt]=-3.89\pm0.01 and \log[L([O II])_RQ/L_opt]=-4.011\pm0.004 for RQQs. However the results depend upon the optical luminosity of the quasar. RLQs and RQQs with the same high optical luminosity \log(L_opt/W)>38.6, tend to have the same level of [O II] emission. On the other hand, at lower optical luminosities \log(L_opt/W)<38.6, there is a clear [O II] emission excess for the RLQs. As an additional check of our results we use the [O III] emission line as a tracer of the bolometric accretion luminosity, instead of the i'-band absolute magnitude, and we obtain similar results. Radio jets appear to be the main reason for the [O II] emission excess in the case of RLQs. In contrast, we suggest AGN feedback ensures that the two populations acquire the same [O II] emission at higher optical luminosities.Comment: 12 pages, 9 figures, accepted for publication in MNRA

The role of black hole mass in quasar radio activity

We use a homogeneous sample of about 300, 0.3 <~ z <~ 3, radio-loud quasars drawn from the FIRST and 2dF QSO surveys to investigate a possible dependence of radio activity on black-hole mass. By analyzing composite spectra for the populations of radio-quiet and radio-loud QSOs -- chosen to have the same redshift and luminosity distribution -- we find with high statistical significance that radio-loud quasars are on average associated with black holes of masses ~10^{8.6} M_sun, about twice as large as those measured for radio-quiet quasars (~10^{8.3} M_sun). We also find a clear dependence of black hole mass on optical luminosity of the form log (M_BH/M_sun)_{RL}= 8.57(\pm 0.06) - 0.27(\pm 0.06) (M_B + 24.5) and log (M_BH/M_sun)_{RQ}= 8.43(\pm 0.05) -0.32(\pm 0.06) (M_B + 24.5), respectively for the case of radio-loud and radio-quiet quasars. It is intriguing to note that these two trends run roughly parallel to each other, implying that radio-loud quasars are associated to black holes more massive than those producing the radio-quiet case at all sampled luminosities. On the other hand, in the case of radio-loud quasars, we find evidence for only a weak (if any) dependence of the black hole mass on radio power. The above findings seem to support the belief that there exists -- at a given optical luminosity -- a threshold black hole mass associated with the onset of significant radio activity such as that of radio-loud QSOs; however, once the activity is triggered, there appears to be very little connection between black hole mass and level of radio output.Comment: 10 pages, 10 figures, minor changes to match the accepted versio