We study the hydrodynamic and acoustic fields of turbulent jets issuing from nozzles modified by the addition of cylindrical tabs on the inner surface, one diameter upstream of the exit. The tabs are designed to promote significant growth of steady streaks in the nozzle turbulent boundary layer. A baseline smooth nozzle is also studied for comparison. Acoustic measurements are made using an azimuthal array for Mach numbers in the range 0.4 $\leqslant M_{\kern-1pt j} \leqslant$ 0.9. The tabs are found to reduce the emitted sound levels by up to 3 dB/St. In terms of overall sound pressure levels, reductions of up to 3 dB are observed at all measured polar angles in the range 20° $\leqslant \theta \leqslant$ 90°. Time-resolved particle image velocimetry experiments are conducted to measure the three components of velocity for a series of cross-stream planes at $M_{\kern-1pt j} =$ 0.7. A Floquet-based Fourier decomposition is applied for the azimuthally periodic flow field, and spectral proper orthogonal decomposition is then employed to extract coherent structures. Comparison of the structures obtained for nozzles with and without tabs shows an enhancement of the streaky structures by the tabs and a damping of Kelvin–Helmholtz wavepackets. A linear model based on the one-way Navier–Stokes equations is employed to explore the underlying amplification mechanisms and how these are impacted by the tabs. The model reproduces the growth–attenuation mechanism observed in the data, showing that the changes in the mean flow induced by the streaks work to reduce the amplification of the noise-generating coherent structures associated with linear spatial growth mechanisms.

In different parts of the world the claim is increasingly being made that continuous confinement of pet cats (Felis catus) is beneficial for both wildlife conservation and cat welfare. The first part of the claim is almost incontrovertible, but the second is misleading. The assertion that confined animals have superior welfare is rooted in thinking pre-dating the 1960s that equates welfare with physical health. By contemporary accounts of animal welfare, confinement of animals presents major welfare risks, and this recognition has been a major driver of refinement in livestock industries, e.g. moves towards free-range systems. Yet, these risks have not been widely acknowledged in debates over pet cat management. We argue that the current pervasive rhetoric from conservationists and some regulators that cat confinement is beneficial for wildlife and cats is, at best, confusing health with welfare. At worst, it is a deliberate attempt to mislead the public through portraying a win-win scenario where, instead, a trade-off must be navigated. Failure to recognise this trade-off undermines conservation goals three-fold. First, it limits the efficacy of behaviour change interventions to increase confinement. Second, it erodes public trust in organisations perceived as knowingly misleading the public. Finally, it reduces the incentive to make the one decision yielding long-term benefits for both cats and ecosystems; ceasing to own cats at all. Policy-makers should be wary of the allure of false win-win narratives when tackling contentious issues that require trade-offs to be made.

We consider the vortex–wedge interaction problem, taking as a departure point Howe’s model of a point vortex interacting with a semi-infinite half-plane, where the vortex path is influenced by its image and a closed-form analytical solution is obtained for the sound field. We generalise Howe’s model to consider wedges of arbitrary angles and explore the influence of vortex circulation, distance from the edge and the wedge half-angle. The effect of wedge angle on sound emission involves a reduced amplitude of the latter as the former is increased. An extension of the model is proposed to account for convection effects by a non-zero ambient flow. We identify a non-dimensional parameter that characterises the vortex kinematics close to the edge and the associated acoustic effect: high and low values of the parameter correspond, respectively, to high- and low-amplitude sound emission of high and low frequency.

This paper presents an experimental application of reactive control to jet installation noise based on destructive interference. The work is motivated by the success of previous studies in applying this control approach to mixing layers (Sasaki et al. Theor. 2018b Comput. Fluid Dyn. 32, 765–788), boundary layers (Brito et al. 2021 Exp. Fluids 62, 1–13; Audiffred et al. 2023 Phys. Rev. Fluids 8, 073902), flow over a backward-facing step (Martini et al. 2022 J. Fluid Mech. 937, A19) and, more recently, to turbulent jets (Maia et al. 2021 Phys. Rev. Fluids 6, 123901; Maia et al. 2022 Phys. Rev. Fluids 7, 033903; Audiffred et al. 2024b J. Fluid Mech. 994, A15). We exploit the fact that jet–surface interaction noise is underpinned by wavepackets that can be modelled in a linear framework and develop a linear control strategy where piezoelectric actuators situated at the edge of a scattering surface are driven in real time by sensor measurements in the near field of the jet, the objective being to reduce noise radiated in the acoustic field. The control mechanism involves imposition of an anti-dipole at the trailing edge to cancel the scattering dipole that arises due to an incident wavepacket perturbation. We explore two different control strategies: (i) the inverse feed-forward approach, where causality is imposed by truncating the control kernel, and (ii) the Wiener–Hopf approach, where causality is optimally enforced in building the control kernel. We show that the Wiener–Hopf approach has better performance than that obtained using the truncated inverse feed-forward kernel. We also explore different positions of the near-field sensors and show that control performance is better for sensors installed for streamwise positions downstream in the jet plume, where the signature of hydrodynamic wavepacket is better captured by the sensors. Broadband noise reductions of up to 50 % are achieved.

This study presents an approach to investigate the role of eddy viscosity in linearized mean-field analysis of broadband turbulent flows. The procedure is based on spectral proper orthogonal decomposition (SPOD), resolvent analysis and the energy budget of coherent structures and is demonstrated using the example of a turbulent jet. The focus is on the coherent component of the Reynolds stresses, the nonlinear interaction term of the fluctuating velocity component in frequency space, which appears as an unknown in the derivation of the linearized Navier–Stokes equations and which is the quantity modelled by the Boussinesq approach. For the considered jet the coherent Reynolds stresses are found to have a mostly dissipative effect on the energy budget of the dominant coherent structures. Comparison of the energy budgets of SPOD and resolvent modes demonstrates that dissipation caused by nonlinear energy transfer must be explicitly considered within the linear operator to achieve satisfactory results with resolvent analysis. Non-modelled dissipation distorts the energy balance of the resolvent modes and is not, as often assumed, compensated for by the resolvent forcing vector. A comprehensive analysis, considering different predictive and data-driven eddy viscosities, demonstrates that the Boussinesq model is highly suitable for modelling the dissipation caused by nonlinear energy transfer for the considered flow. Suitable eddy viscosities are analysed with regard to their frequency, azimuthal wavenumber and spatial dependence. In conclusion, the energetic considerations reveal that the role of eddy viscosity is to ensure that the energy the structures receive from the mean-field is dissipated.

Guided-jet waves have been shown to close resonance loops in a myriad of problems such as screech and impingement tones in jets. These discrete, upstream-travelling waves have long been identified in linear-stability models of jet flows, but in this work they are instead considered in the context of an acoustic-scattering problem. It is shown that the guided-jet mode results from total internal reflection and transmission of acoustic waves, arising from the shear layer behaving like a duct with some given wall impedance. After total reflection, only discrete streamwise wavenumbers may be supported by the flow, with these wavenumbers dictated by the fact that the standing wave formed inside of the jet must fit between the two shear layers. Close to the sonic line, the transmission of this mode to the outside is maximum, leading to a net-energy flux directed upstream, which dictates the direction of propagation of this mode, providing a clear connection to the better understood soft-duct mode (Towne et al., J. Fluid Mech., vol. 825, 2017, pp. 1113–1152). The model also indicates that these waves are generated in the core of the flow and can only be efficiently transmitted to the quiescent region under certain conditions, providing an explanation as to why screech is only observed at conditions where the discrete mode is supported by the flow. The present results explain, for the first time, the nature and characteristics of the guided-jet waves.

We present an experimental study of reactive control of turbulent jets, in which we target axisymmetric coherent structures, known to play a key role in the generation of sound. We first consider a forced jet, in which coherent structures are amplified above background levels, facilitating their detection, estimation and control. We then consider the more challenging case of an unforced jet. The linear control targets coherent structures in the region just downstream of the nozzle exit plane, where linear models are known to be appropriate for description of the lowest-order azimuthal modes of the turbulence. The control law is constructed in frequency space, based on empirically determined transfer functions. And the Wiener–Hopf formalism is used to enforce causality and to provide an optimal controller, as opposed to the sub-optimal control laws provided by simpler wave-cancellation methods. Significant improvements are demonstrated in the control of both forced and unforced jets. In the former case, order-of-magnitude reductions are achieved; and in the latter, turbulence levels are reduced by up to 60 %. The results open new perspectives for the control of turbulent flow at high Reynolds number.

We present radio observations of the galaxy cluster Abell S1136 at 888 MHz, using the Australian Square Kilometre Array Pathfinder radio telescope, as part of the Evolutionary Map of the Universe Early Science program. We compare these findings with data from the Murchison Widefield Array, XMM-Newton, the Wide-field Infrared Survey Explorer, the Digitised Sky Survey, and the Australia Telescope Compact Array. Our analysis shows the X-ray and radio emission in Abell S1136 are closely aligned and centered on the Brightest Cluster Galaxy, while the X-ray temperature profile shows a relaxed cluster with no evidence of a cool core. We find that the diffuse radio emission in the centre of the cluster shows more structure than seen in previous low-resolution observations of this source, which appeared formerly as an amorphous radio blob, similar in appearance to a radio halo; our observations show the diffuse emission in the Abell S1136 galaxy cluster contains three narrow filamentary structures visible at 888 MHz, between $\sim$80 and 140 kpc in length; however, the properties of the diffuse emission do not fully match that of a radio (mini-)halo or (fossil) tailed radio source.

We study coherent structures in subsonic turbulent jets subject to a flight stream. A thorough characterisation of the effects of a flight stream on the turbulent field was recently performed by Maia et al. (Phys. Rev. Fluids, vol. 8, 2023, 063902) and fluctuation energy attenuations were observed over a broad range of frequencies and azimuthal wavenumbers. The Kelvin–Helmholtz, Orr and lift-up mechanisms were all shown to be weakened by the flight stream. Here we expand upon that study and model the changes in the dynamics of jets in flight using global resolvent analysis. The resolvent model is found to correctly capture the main effects of the flight stream on the dynamics of coherent structures, which are educed from a large-eddy simulation database using spectral proper orthogonal decomposition. Three modifications of note are: the damping of low-frequency streaky/Orr structures that carry most of the fluctuation energy; a degradation of the low-rank behaviour of the jet in frequencies where modal instability mechanisms are dominant; and a rank decrease at very low Strouhal numbers. The latter effect is underpinned by larger gain separations predicted by the resolvent analysis, due to a reduction in the wavelength of associated flow structures. This leads to a clearer relative dominance of streaky structures generated by the lift-up mechanism, despite the fact that the lift-up mechanism has been weakened with respect to the static jet.

A decline in routine vaccinations, attributed to vaccine hesitancy, undermines preventative healthcare, impacting health and exacerbating vaccine disparities. University-public health partnerships can improve vaccination services. This study describes and evaluates a university-public health use case employing social determinants of health (SDoH)-based strategies to address vaccination disparities. Guided by the Translational Science Benefits Logic Model, the partnership offered no-cost preventative vaccines at community-based organization (CBO) sites, collected CBO clientele’s vaccination interest, hesitancy, and demographic data, and conducted descriptive analyses. One hundred seven vaccination events were held, administering 3,021 vaccines. This partnership enhanced health outcomes by addressing disparities through co-located vaccination and SDoH services.

There is currently considerable interest in the guided-jet mode, as a result of recent works demonstrating it being the upstream component of various resonant systems in high-speed flows. For given jet operating conditions, the mode is known to exist over only a finite-frequency range that, for a twin-jet system, has been observed to vary with both jet separation and solution symmetry. Vortex-sheet and finite-thickness linear stability models are here employed to consider the behaviour of the guided-jet mode as the two jets are brought together, for both a planar and round twin-jet system. It is demonstrated that in both cases as the twin-jet system merges it forms a higher-order mode of an equivalent single-jet geometry. This then imposes a constraint on the guided-jet mode as the finite-frequency range must change to meet that of the equivalent geometry the system merges to, explaining the previously observed dependence on jet separation.

Linear stability theory (LST) is often used to model the large-scale flow structures in the turbulent mixing region and near pressure field of high-speed jets. For perfectly expanded single round jets, these models predict the dominance of azimuthal wavenumbers $m=0$ and $m = 1$ helical modes for the lower frequency range, in agreement with empirical data. When LST is applied to twin-jet systems, four solution families appear following the odd/even behaviour of the pressure field about the symmetry planes. The interaction between the unsteady pressure fields of the two jets also results in their coupling. The individual modes of the different solution families no longer correspond to helical motions, but to flapping oscillations of the jet plumes. In the limit of large jet separations, when the jet coupling vanishes, the eigenvalues corresponding to the $m=1$ mode in each family are identical, and a linear combination of them recovers the helical motion. Conversely, as the jet separation decreases, the eigenvalues for the $m=1$ modes of each family diverge, thus favouring a particular flapping oscillation over the others and preventing the appearance of helical motions. The dominant mode of oscillation for a given jet Mach number $M_j$ and temperature ratio $T_R$ depends on the Strouhal number $St$ and jet separation $s$. Increasing both $M_j$ and $T_R$ independently is found to augment the jet coupling and modify the $(St,s)$ map of the preferred oscillation mode. Present results predict the preference of two modes when the jet interaction is relevant, namely varicose and especially sinuous flapping oscillations on the nozzles’ plane.

The Five Domains model is influential in contemporary studies of animal welfare. It was originally presented as a conceptual model to understand the types of impact that procedures may impose on experimental animals. Its application has since broadened to cover a wide range of animal species and forms of animal use. However, it has also increasingly been applied as an animal welfare assessment tool, which is the focus of this paper. Several critical limitations associated with this approach have not been widely acknowledged, including that: (1) it relies upon expert or stakeholder opinion, with little transparency around the selection of these individuals; (2) quantitative scoring is typically attempted despite the absence of clear principles for aggregation of welfare measures and few attempts to account for uncertainty; (3) there have been few efforts to measure the repeatability of findings; and (4) it does not consider indirect and unintentional impacts such as those imposed on non-target animals. These deficiencies lead to concerns surrounding testability, repeatability and the potential for manipulation. We provide suggestions for refinement of how the Five Domains model is applied to partially address these limitations. We argue that the Five Domains model is useful for systematic consideration of all sources of possible welfare compromise and enhancement, but is not, in its current state, fit-for-purpose as an assessment tool. We argue for wider acknowledgment of the operational limits of using the model as an assessment tool, prioritisation of the studies needed for its validation, and encourage improvements to this approach.

Spatial linear stability analysis is used to study the axisymmetric screech tones generated by twin converging round nozzles at low supersonic Mach numbers. Vortex-sheet and finite-thickness models allow for identification of the different waves supported by the flow at different conditions. Regions of the frequency–wavenumber domain for which the upstream-propagating guided jet modes are observed to be neutrally stable are observed to vary as a function of solution symmetry, jet separation, $S$, and the velocity profile used. Screech-frequency predictions performed using wavenumbers obtained from both models agree well with experimental data. Predictions obtained from the finite-thickness model better align with the screech tones measured experimentally and so are seen to be an improvement on predictions made with the vortex sheet. Additionally, results from the finite-thickness model predict both symmetric and antisymmetric screech tones for low $S$ that are found in the vortex-sheet model only at greater $S$. The present results indicate that the feedback loop generating these screech tones is similar to that observed for single-jet resonance, with equivalent upstream and downstream modes.

White kidney bean extract (WKBE) is a nutraceutical often advocated as an anti-obesity agent. The main proposed mechanism for these effects is alpha-amylase inhibition, thereby slowing carbohydrate digestion and absorption. Thus, it is possible that WKBE could impact the gut microbiota and modulate gut health. We investigated the effects of supplementing 20 healthy adults with WKBE for 1 week in a randomised, placebo-controlled crossover trial on the composition of the gut microbiota, gastrointestinal (GI) inflammation (faecal calprotectin), GI symptoms, and stool habits. We conducted in vitro experiments and used a gut model system to explore potential inhibition of alpha-amylase. We gained qualitative insight into participant experiences of using WKBE via focus groups. WKBE supplementation decreased the relative abundance of Bacteroidetes and increased that of Firmicutes, however, there were no significant differences in post-intervention gut microbiota measurements between the WKBE and control. There were no significant effects on GI inflammation or symptoms related to constipation, or stool consistency or frequency. Our in vitro and gut model system analyses showed no effects of WKBE on alpha-amylase activity. Our findings suggest that WKBE may modulate the gut microbiota in healthy adults, however, the underlying mechanism is unlikely due to active site inhibition of alpha-amylase.

Archaeologists have traditionally framed the impacts of natural disasters in terms of societal collapse versus cultural resilience. The 7.3ka cal BP Kikai-Akahoya (K-Ah) ‘super-eruption’ in south-western Japan was among the largest volcanic events of the Holocene. Here, the authors deploy a multi-proxy approach to examine how K-Ah devastated Tanegashima Island. While local Jōmon populations were annihilated, surrounding communities survived and eventually returned, adjusting their subsistence base to survive in the damaged environment. The article concludes that neither ‘collapse’ nor ‘resilience’ fully capture the complex dynamics of this process and that more research is needed to understand how disasters shape cultural trajectories.