We examine the linear stability of a shear flow driven by wind stress at the free surface and rotation at the lower boundary, mimicking oceanic flows influenced by surface winds and the Earth’s rotation. The linearised eigenvalue problem is solved using the Chebyshev spectral collocation method and a long-wave asymptotic analysis. Our results reveal new long-wave instability modes that emerge for non-zero rotational Reynolds numbers. It is observed that the most unstable mode, characterised by the lowest critical parameters, corresponds to long-wave spanwise disturbances with vanishing streamwise wavenumber. The asymptotic analysis, which shows excellent agreement with numerical results, analytically confirms the existence of this instability. Thus, the present study demonstrates the hitherto unreported combined influence of wind stress and the Earth’s rotation on ocean dynamics.

The Little Bustard Tetrax tetrax has experienced steep population declines across its range, with Sardinia now hosting the last remaining Italian population and the only island population worldwide. We conducted a systematic island-wide survey in 2023, based on 969 point-count data, analysed through robust distance sampling, to assess population density, spatial distribution, habitat associations, and the role of protected areas. We estimated a total density of 0.89 males/km², with 85% of individuals concentrated in two highland subpopulations, i.e. Ozieri and Abbasanta. Highest densities occurred in hay meadows and heterogeneous landscapes, while arable and fallow lands supported lower densities. Protected areas hosted five times higher densities of Little Bustard than unprotected land. Land-use changes over the past 13 years and current soil degradation showed no significant association with current densities, suggesting that declines may be linked to earlier landscape transformations. Our results underscore the critical importance of protected areas and traditional agropastoral systems for the conservation of the Little Bustard in Sardinia. Urgent conservation planning is needed to maintain existing habitats and mitigate emerging threats from land-use change and infrastructure expansion.

Rapid population declines of three species of Gyps vultures endemic to Asia were caused by unintentional poisoning by the non-steroidal anti-inflammatory drug (NSAID) diclofenac. Despite a ban on its veterinary use across South Asia, diclofenac has continued to be supplied for this purpose. Here, we report updated results from undercover pharmacy surveys, conducted between 2012 and 2024, in India, Nepal, Bangladesh, and Pakistan to investigate the availability and prevalence of veterinary NSAIDs. The purpose was to establish whether sales of diclofenac had continued and to determine which other veterinary NSAIDs were available. In India, the availability of diclofenac had declined in all Vulture Safe Zones (VSZs), but it was still readily available (up to 25% of sales) in Rajasthan where intensive conservation advocacy had not occurred. Elsewhere in the region, prevalence of diclofenac was low. The vulture-safe meloxicam continued to be the most commonly available veterinary NSAID throughout most of the region, especially in Nepal (85–100%), but still accounted for only 25–45% of products offered in other countries. In Bangladesh, the vulture-toxic ketoprofen was the most prevalent drug overall, but levels declined to a low level (<1% in 2024), following the nationwide ban on veterinary use of the drug in 2023. Fourteen different NSAIDs were recorded in our surveys, several of which are known or suspected to be toxic to vultures. Of special concern is a rapid increase in the prevalence of flunixin in Bangladesh. Flunixin has not been banned in any of the South Asian vulture range states. Conservation priorities should include awareness campaigns, stronger measures to implement current bans, safety-testing of other NSAIDs, especially flunixin, followed by bans on veterinary use of all NSAIDs found to be toxic to vultures. Prior evidence of safety to vultures should be a requirement for the licensing of all new veterinary NSAIDs.

Two-way diffusion equations arising in kinetic problems relating to electron scattering and in Brownian particle dynamics present singularities absent from conventional diffusion equations. Although calculations by Stein & Bernstein, and Fisch & Kruskal have revealed the formation of entry and exit slope discontinuities at the critical points where the velocity changes sign, the analytical structure of these discontinuities remains unclear. Here we fill this gap via a local similarity variable analysis, illustrated through the two-way diffusion equation $y \partial n/\partial x=\partial ^2 n/\partial y^2$ in $-1 \leq y \leq 1$; $0 \leq x \leq L$, with $n(x,\pm 1)=0$ with various entry conditions $n(0,y)_{y\gt 0}$, and the exit condition $n(L,y)_{y\lt 0}=0$. The similarity variable $\eta =y/x^{1/3}$ permits the analytical characterization of the entry discontinuity, except for constants determined by matching with numerical solutions obtained with two numerical schemes: separation of variables following the construction of Beals, or finite-difference discretization of the transient partial differential equation, which converges in time to a solution almost identical to the separation of variables solution. Although the slope discontinuity depends markedly on the initial condition $n(0,y)_{y\gt 0}$, a simple general similarity solution structure emerges empirically, always involving a spontaneous singular contribution $C |y|^{1/2}$ at $x=0,y\lt 0$. Slow convergence of both numerical solutions near $\{x,y\}=\{0,0\}$ is attributed to the poor eigenfunction representation of the ever-present singular solution component $|y|^{1/2}$. The similarity approach applies equally to other two-way diffusion equations when the coefficient of $\partial n/\partial x$ changes sign linearly with $y$. It can also be extended to situations where this coefficient is discontinuous at the critical points.

This study of red ochre in mortuary contexts in Neolithic to Iron Age sites in Thailand reveals regional and temporal variation. Used extensively at Neolithic Khok Phanom Di, often as body paint, the material was absent at contemporaneous inland sites. Its reappearance in the Bronze Age signalled a symbolic shift in practice, with pieces of ochre incorporated into elaborate funerary rituals. These patterns suggest differing cultural origins and evolving rituals. By the Iron Age, ochre use declined, coinciding with the spread of new mortuary ideologies. The authors highlight how ochre is a powerful marker of identity, belief and cultural change.

The convection velocity in high-Reynolds-number pipe flow was investigated using two-point correlations obtained from two laser Doppler velocimetry systems. The Reynolds number ranged from ${\textit{Re}}_{{\tau}}=3000$ to 20 800, and profiles were obtained from $y/R=0.002$ up to the pipe centre, where $R$ is the pipe radius. This study examines the scaling behaviour of convection velocity profiles derived from raw velocity signals, and the convection characteristics of very large-scale motions (VLSMs) and large-scale motions extracted via scale-separated or time-resolved velocity signals. The profiles show that convection velocities from raw signals exceed the local mean velocity near the wall and gradually approach it toward the centre. These profiles can be scaled using inner variables, namely $y^+$ and $\Delta x^+$, where $\Delta x^+$ represents the measurement distance. Scale-separated convection velocities for VLSM-scale structures – defined as those larger than $5R$ – were higher than the unfiltered values and remained nearly constant up to $y^+ \leq 2000$ at ${\textit{Re}}_{{\tau}} \approx 20\,000$. In this constant region, the convection velocity of VLSMs scaled well with the bulk velocity $U_{\textit{b}}$, taking values of approximately $0.85U_{\textit{b}}$. Furthermore, analysis of the time-resolved data highlights that, when applying Taylor’s frozen turbulence hypothesis, it is essential to consider both the scale dependence and the temporal fluctuations of the convection velocity, which reflect the underlying spatio-temporal dynamics of the flow structures. The present study provides valuable data for discussions on converting frequency-domain measurements into wavenumber space using Taylor’s hypothesis.

Surface roughness is often present in flight systems travelling at high speeds, but its interaction with compressible turbulence is not well understood. Using direct numerical simulations, we study how prism-shaped roughness influences supersonic turbulent boundary layers at a free-stream Mach number $M_\infty =2$. The dataset includes four simulations featuring cubic- and diamond-shaped elements in aligned and staggered configurations. All cases have an initial smooth region where a fully turbulent boundary layer transitions to a rough wall with positively skewed roughness elements relative to the smooth-wall zero plane. This causes a sudden boundary layer growth at the smooth-to-rough transition, generating an oblique shock wave. Individual roughness elements downstream do not generate shock or expansion waves, as they do not protrude into the supersonic region. For cubical elements, the staggered arrangement increases drag and produces more pronounced boundary layer growth than the aligned case. Rotating the cubes along their vertical axis further enhances these effects, yielding the highest drag. Interestingly, diamond-shaped elements in a staggered arrangement exhibit a dynamics similar to aligned cubes, producing lower drag than other cases. We explain the relative drag induced by each roughness shape by examining viscous and pressure drag components separately. The analysis reveals that, for staggered diamonds, the flow skims more easily over roughness, drastically reducing recirculation in troughs and gaps. In other cases, wake interactions are more prominent, causing spikes of highly positive and negative skin friction, a feature often neglected in reduced-order model formulations.