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We present a model for the scaling of mixing in weakly rotating stratified flows characterized by their Rossby, Froude and Reynolds numbers $Ro,Fr$ , $Re$ . This model is based on quasi-equipartition between kinetic and potential modes, sub-dominant vertical velocity, $w$ , and lessening of the energy transfer to small scales as measured by a dissipation efficiency $\\unicode[STIX]{x1D6FD}=\\unicode[STIX]{x1D716}_{V}/\\unicode[STIX]{x1D716}_{D}$ , with $\\unicode[STIX]{x1D716}_{V}$ the kinetic energy dissipation and $\\unicode[STIX]{x1D716}_{D}=u_{rms}^{3}/L_{int}$ its dimensional expression, with $w,u_{rms}$ the vertical and root mean square velocities, and $L_{int}$ the integral scale. We determine the domains of validity of such laws for a large numerical study of the unforced Boussinesq equations mostly on grids of $1024^{3}$ points, with $Ro/Fr\\geqslant 2.5$ , and with $1600\\leqslant Re\\approx 5.4\\times 10^{4}$ ; the Prandtl number is one, initial conditions are either isotropic and at large scale for the velocity and zero for the temperature $\\unicode[STIX]{x1D703}$ , or in geostrophic balance. Three regimes in Froude number, as for stratified flows, are observed: dominant waves, eddy–wave interactions and strong turbulence. A wave–turbulence balance for the transfer time $\\unicode[STIX]{x1D70F}_{tr}=N\\unicode[STIX]{x1D70F}_{NL}^{2}$ , with $\\unicode[STIX]{x1D70F}_{NL}=L_{int}/u_{rms}$ the turnover time and $N$ the Brunt–Väisälä frequency, leads to $\\unicode[STIX]{x1D6FD}$ growing linearly with $Fr$ in the intermediate regime, with a saturation at $\\unicode[STIX]{x1D6FD}\\approx 0.3$ or more, depending on initial conditions for larger Froude numbers. The Ellison scale is also found to scale linearly with $Fr$ . The flux Richardson number $R_{f}=B_{f}/[B_{f}+\\unicode[STIX]{x1D716}_{V}]$ , with $B_{f}=N\\langle w\\unicode[STIX]{x1D703}\\rangle$ the buoyancy flux, transitions for approximately the same parameter values as for $\\unicode[STIX]{x1D6FD}$ . These regimes for the present study are delimited by ${\\mathcal{R}}_{B}=ReFr^{2}\\approx 2$ and $R_{B}\\approx 200$ . With $\\unicode[STIX]{x1D6E4}_{f}=R_{f}/[1-R_{f}]$ the mixing efficiency, putting together the three relationships of the model allows for the prediction of the scaling $\\unicode[STIX]{x1D6E4}_{f}\\sim Fr^{-2}\\sim {\\mathcal{R}}_{B}^{-1}$ in the low and intermediate regimes for high $Re$ , whereas for higher Froude numbers, $\\unicode[STIX]{x1D6E4}_{f}\\sim {\\mathcal{R}}_{B}^{-1/2}$ , a scaling already found in observations: as turbulence strengthens, $\\unicode[STIX]{x1D6FD}\\sim 1$ , $w\\approx u_{rms}$ , and smaller buoyancy fluxes together correspond to a decoupling of velocity and temperature fluctuations, the latter becoming passive.

Galaxies are surrounded by large reservoirs of gas, mostly hydrogen, that are fed by inflows from the intergalactic medium and by outflows from galactic winds. Absorption-line measurements along the lines of sight to bright and rare background quasars indicate that this circumgalactic medium extends far beyond the starlight seen in galaxies, but very little is known about its spatial distribution. The Lyman-α transition of atomic hydrogen at a wavelength of 121.6 nanometres is an important tracer of warm (about 10 4 kelvin) gas in and around galaxies, especially at cosmological redshifts greater than about 1.6 at which the spectral line becomes observable from the ground. Tracing cosmic hydrogen through its Lyman-α emission has been a long-standing goal of observational astrophysics 1 – 3 , but the extremely low surface brightness of the spatially extended emission is a formidable obstacle. A new window into circumgalactic environments was recently opened by the discovery of ubiquitous extended Lyman-α emission from hydrogen around high-redshift galaxies 4 , 5 . Such measurements were previously limited to especially favourable systems 6 – 8 or to the use of massive statistical averaging 9 , 10 because of the faintness of this emission. Here we report observations of low-surface-brightness Lyman-α emission surrounding faint galaxies at redshifts between 3 and 6. We find that the projected sky coverage approaches 100 per cent. The corresponding rate of incidence (the mean number of Lyman-α emitters penetrated by any arbitrary line of sight) is well above unity and similar to the incidence rate of high-column-density absorbers frequently detected in the spectra of distant quasars 11 – 14 . This similarity suggests that most circumgalactic atomic hydrogen at these redshifts has now been detected in emission. Lyman-α emission from atomic hydrogen shows the location of warm gas and is ubiquitous around galaxies between redshifts of 3 and 6, thereby covering nearly all the sky.

Whether net primary productivity in an aquatic ecosystem is limited by nitrogen (N), limited by phosphorus (P), or co-limited by N & P is determined by the relative supply of N and P to phytoplankton compared to their elemental requirements for primary production, often characterized by the “Redfield” ratio. The supply of these essential nutrients is affected by both external inputs and biogeochemical processes within the ecosystem. In this paper, we examine external sources of nutrients to aquatic systems and how the balance of N to P inputs influences nutrient limitation. For ocean subtropical gyres, a relatively balanced input of N and P relative to the Redfield ratio from deep ocean sources often leads to near co-limitation by N and P. For lakes, the external nutrient inputs come largely from watershed sources, and we demonstrate that on average the N:P ratio for these inputs across the United States is well above that needed by phytoplankton, which may contribute to P limitation in those lake that experience this average nutrient loading. Watershed inputs are also important for estuaries and coastal marine ecosystems, but ocean sources of nutrients are also significant contributors to overall nutrient loads. The ocean-nutrient sources of N and P are very often at or below the Redfield ratio of 16:1 molar, and can be substantially so, particularly in areas where the continental shelf is wide. This large input of coastal ocean nutrients with a low N:P ratio is one factor that may make N limitation more likely in many coastal marine ecosystems than in lakes.

Background Numerous studies of dental antibiotic prescribing show that overprescribing is a worldwide occurrence. The aim of this study was to assess prescribing practices of general dentists in Australia for antibiotics, analgesics and anxiolytics and to determine the extent to which prescribing is in accordance with current guidelines. Methods A structured questionnaire was sent to 1468 dentists in Victoria and Queensland in July–August 2018. The questionnaire covered demographics, clinical conditions where dentists prescribe antibiotics, non-clinical factors which influence prescribing, and medicines for anxiolysis and pain relief. Responses were scored using a system based on the current Australian therapeutic guidelines. Logistic regression was used to determine the relative importance of independent variables on inappropriate prescribing. Results Three hundred eighty-two responses were received. Overall, 55% of overprescribing of antibiotics was detected, with a range of 13–88% on a routine or occasional basis depending on the scenario. Between 16 and 27% of respondents inappropriately preferenced analgesics over anti-inflammatories for dental pain; 46% of those who prescribed anxiolytic medicines did so inappropriately, with varying regimens and choices outside the guidelines. Years of practice was the main demographic factor influencing prescribing, with recent graduates (0–5 years) generally scoring better than their colleagues for antibiotic prescribing ( p  < 0.05). Conclusions Future interventions could be directed towards the appropriate role and use of antibiotics, shortfalls in knowledge and appropriate choices of medicines for pain relief and anxiolysis. Given that the most overprescribing occurred for localised swellings (88%), this area could be focused on in continuing education as well as ensuring it is addressed in undergraduate teaching. Continuing education on the appropriate use of medicines can be targeted at more experienced dentists as well as patients, especially those who expect antibiotics instead of treatment. Trial registration University of Melbourne Human Ethics Sub-Committee; ID: 1750768.1 .

Vibrio fischeri, a marine bacterium and symbiont of the Hawaiian bobtail squid Euprymna scolopes, depends on biofilm formation for successful colonization of the squid's symbiotic light organ. Here, we investigated if culture conditions, such as nutrient and salt availability, affect biofilm formation by V. fischeri by testing the formation of wrinkled colonies on solid media. We found that V. fischeri forms colonies with more substantial wrinkling when grown on the nutrient-dense LBS medium containing NaCl relative to those formed on the more nutrient-poor, seawater-salt containing SWT medium. The presence of both tryptone and yeast extract was necessary for the production of \"normal\" wrinkled colonies; when grown on tryptone alone, the colonies displayed a divoting phenotype and were attached to the agar surface. We also found that the type and concentration of specific seawater salts influenced the timing of biofilm formation. Of the conditions assayed, wrinkled colony formation occurred earliest in LBS(-Tris) media containing 425 mM NaCl, 35 mM MgSO4, and 5 mM CaCl2. Pellicle formation, another measure of biofilm development, was also enhanced in these growth conditions. Therefore, both nutrient and salt availability contribute to V. fischeri biofilm formation. While growth was unaffected, these optimized conditions resulted in increased syp locus expression as measured by a PsypA-lacZ transcriptional reporter. We anticipate these studies will help us understand how the natural environment of V. fischeri affects its ability to form biofilms and, ultimately, colonize E. scolopes.

This paper investigates the impact of two non-technical speech feedback perturbations outside the auditory modality: topical application of commercially-available benzocaine to reduce somatosensory feedback from speakers’ lips and tongue tip, and the presence of a mirror to provide fully-detailed visual self-feedback. In experiment 1, speakers were recorded under normal quiet conditions (i.e., baseline), then again with benzocaine application plus auditory degradation, and finally with the addition of mirror feedback. Speech produced under normal and both feedback-altered conditions was assessed via naïve listeners’ intelligibility discrimination judgments. Listeners judged speech produced under bisensory degradation to be less intelligible than speech from the un-degraded baseline, and with a greater degree of difference than previously observed with auditory-only degradation. The introduction of mirror feedback, however, did not result in relative improvements in intelligibility. Experiment 2, therefore, assessed the effect of a mirror on speech intelligibility in isolation with no other sensory feedback manipulations. Speech was recorded at baseline and then again in front of a mirror, and relative intelligibility was discriminated by naïve listeners. Speech produced with mirror feedback was judged as less intelligible than baseline tokens, indicating a negative impact of visual self-feedback in the absence of other sensory manipulations. The results of both experiments demonstrate that relatively accessible manipulations of non-auditory sensory feedback can produce speech-relevant effects, and that those effects are perceptible to naïve listeners.

In this study we consider a freely decaying, stably stratified homogeneous magnetohydrodynamic turbulent plasma with a weak vertical background magnetic field (\\(\\boldsymbol {B}_0=B_0\\hat {\\boldsymbol {z}}),\\) aligned with the density gradient of strength \\(N\\) (i.e. Brunt–Väisälä frequency). Both linear theory and direct numerical simulations (DNS) are used to analyse the flow dynamics for a Boussinesq fluid with unitary magnetic and thermal Prandtl numbers. We implemented a normal mode decomposition emphasizing different types of motions depending on whether both the Froude \\(F_r\\) and Alfvén–Mach \\(M\\) numbers are small or only \\(F_r\\) is small but \\(M\\) is finite. In the former case, there is a non-propagating (NP) mode and fast modes: Alfvén waves with frequency \\(\\omega _a\\) and magnetogravity waves with frequency \\(\\omega _{ag}\\). In the latter case, there are fast gravity waves with frequency \\(\\omega _g\\) and slow modes: NP mode and slow Alfvén waves. The numerical simulations carried out are started from initial isotropic conditions with zero initial magnetic and density fluctuations, so that the initial energy of the NP mode is strictly zero, for \\(0< B_0/(L_iN)\\leqslant 0.12\\) and a weak mean magnetic field (\\(B_0=0.2\\) or \\(B_0=0.4),\\) where \\(L_i\\) denotes the isotropic integral length scale. The DNS results indicate a weak turbulence regime for which \\(F_r\\) is small and \\(M\\) is finite. It is found that the vertical magnetic energy as well as the energy of the NP mode are drastically reduced as \\(N\\) increases, while there is instead a forward cascade even for the magnetic field. The contribution coming from the energy of fast (gravity) waves does not exceed \\(50\\,\\%,\\) while that coming from the energy of the NP mode does not exceed \\(10\\,\\%.\\) Vertical motions are more affected by the effect of stratification than by the effect of the mean magnetic field, while it is the opposite for horizontal motions. We show that the spectrum of slow (Alfvén) waves and fast (gravity) waves tends to follow the power law \\(k_\\perp ^{-3}\\) for a wide range of time, \\(3< t<20\\). At high vertical (or horizontal) wavenumbers, the main contribution to total energy comes from the energy of slow Alfvén waves. At large and intermediate horizontal (or vertical) scales, the spectra of the energy of NP mode exhibit a flat shape.

An experiment is conducted in a rectangular channel obstructed by a transverse line of four inclined cylindrical rods. The pressure on the surface of a central rod and the pressure drop through the channel are measured varying the inclination angle of the rods. Three assemblies of rods with different diameters are tested. The measurements were analyzed applying momentum conservation principles and semi-empirical considerations. Several invariant dimensionless groups of parameters relating the pressure at key locations of the system with characteristic dimensions of the rods are produced. It was found that the independence principle holds for most of the Euler numbers characterizing the pressure at different locations, that is, the group is independent of the inclination angle provided that the inlet velocity projection normal to the rods is used to non-dimensionalize the pressure. The resulting semi-empirical correlations can be useful for designing similar hydraulic units.

We briefly review helicity dynamics, inverse and bidirectional cascades in fluid and magnetohydrodynamic (MHD) turbulence, with an emphasis on the latter. The energy of a turbulent system, an invariant in the nondissipative case, is transferred to small scales through nonlinear mode coupling. Fifty years ago, it was realized that, for a two‐dimensional fluid, energy cascades instead to larger scales and so does magnetic excitation in MHD. However, evidence obtained recently indicates that, in fact, for a range of governing parameters, there are systems for which their ideal invariants can be transferred, with constant fluxes, to both the large scales and the small scales, as for MHD or rotating stratified flows, in the latter case including quasi‐geostrophic forcing. Such bidirectional, split, cascades directly affect the rate at which mixing and dissipation occur in these flows in which nonlinear eddies interact with fast waves with anisotropic dispersion laws, due, for example, to imposed rotation, stratification, or uniform magnetic fields. The directions of cascades can be obtained in some cases through the use of phenomenological arguments, one of which we derive here following classical lines in the case of the inverse magnetic helicity cascade in electron MHD. With more highly resolved data sets stemming from large laboratory experiments, high‐performance computing, and in situ satellite observations, machine learning tools are bringing novel perspectives to turbulence research. Such algorithms help devise new explicit subgrid‐scale parameterizations, which in turn may lead to enhanced physical insight, including in the future in the case of these new bidirectional cascades. Plain Language Summary Turbulent flows are prevalent in Geophysics and Space Physics. They are complex and involve interactions between fluctuations at widely separated scales, with the energy expected in the general case to flow only to small scales where it is dissipated. It was found recently that, contrary to such expectations, energy can go in substantial amounts to both the small and large scales, in the presence of magnetic fields, as applicable to space plasmas, and for rotating stratified flows as encountered in the atmosphere and the oceans. This result implies that the amount of energy available for dissipation may differ from flow to flow, and simple scaling arguments allow for predictions that are backed up by results stemming from direct numerical simulations. One should incorporate this bidirectional cascade phenomenon in the turbulence models used for global computations of geophysical and astrophysical media. Furthermore, machine learning tools may prove useful in deriving such enhanced models in their capacity to interrogate the large data bases that already exist for such complex flows. Key Points Magnetic helicity displays an inverse cascade to large scales which, in electron MHD, can be justified with a simple phenomenological model Total energy in MHD or rotating stratified turbulence has constant‐flux cascades to small and large scales, affecting mixing and dissipation With these results, needed modifications to subgrid scale turbulence models will be enhanced using tools from big data and machine learning

Reactive oxygen species (ROS) may cause cellular damage and oxidative stress-induced cell death. Autophagy, an evolutionarily conserved intracellular catabolic process, is executed by autophagy (ATG) proteins, including the autophagy initiation kinase Unc-51-like kinase (ULK1)/ATG1. Although autophagy has been implicated to have both cytoprotective and cytotoxic roles in the response to ROS, the role of individual ATG proteins, including ULK1, remains poorly characterized. In this study, we demonstrate that ULK1 sensitizes cells to necrotic cell death induced by hydrogen peroxide (H 2 O 2 ). Moreover, we demonstrate that ULK1 localizes to the nucleus and regulates the activity of the DNA damage repair protein poly (ADP-ribose) polymerase 1 (PARP1) in a kinase-dependent manner. By enhancing PARP1 activity, ULK1 contributes to ATP depletion and death of H 2 O 2 -treated cells. Our study provides the first evidence of an autophagy-independent prodeath role for nuclear ULK1 in response to ROS-induced damage. On the basis of our data, we propose that the subcellular distribution of ULK1 has an important role in deciding whether a cell lives or dies on exposure to adverse environmental or intracellular conditions.