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This work investigates the formation mechanism of the turbulent secondary vortex street (SVS) which appears in the far wake of bluff bodies, when the (primary) Kármán vortex street is absent. The turbulent wakes of four types of highly porous bluff bodies (plates/meshes) are characterised via time-resolved particle image velocimetry and large eddy simulations. The effect of ambient turbulence and initial conditions on SVS development is also examined, by installing a turbulence grid upstream of the bodies, and by varying the homogeneity of the bluff body porosity. Our results indicate that the SVS is a far-wake evolution of near-wake shear-layer vortices which, in the absence of the vortex shedding instability, continually grow and are finally arranged into alternating vortices. Free-stream turbulence and body inhomogeneity are found to significantly influence SVS development by amplifying mixing and attenuating the shear-layer instabilities of the near wake, which in turn lead to the formation of weaker and less coherent SVS structures further downstream.
It is well known that almost all graphs are canonizable by a simple combinatorial routine known as colour refinement, also referred to as the 1-dimensional Weisfeiler–Leman algorithm. With high probability, this method assigns a unique label to each vertex of a random input graph and, hence, it is applicable only to asymmetric graphs. The strength of combinatorial refinement techniques becomes a subtle issue if the input graphs are highly symmetric. We prove that the combination of colour refinement and vertex individualization yields a canonical labelling for almost all circulant digraphs (i.e., Cayley digraphs of a cyclic group). This result provides first evidence of good average-case performance of combinatorial refinement within the class of vertex-transitive graphs. Remarkably, we do not even need the full power of the colour refinement algorithm. We show that the canonical label of a vertex $v$ can be obtained just by counting walks of each length from $v$ to an individualized vertex. Our analysis also implies that almost all circulant graphs are compact in the sense of Tinhofer, that is, their polytops of fractional automorphisms are integral. Finally, we show that a canonical Cayley representation can be constructed for almost all circulant graphs by the more powerful 2-dimensional Weisfeiler–Leman algorithm.
This paper is concerned with Liouville-type theorems of positive weak solutions to elliptic $m$-Laplace equation and inequality with the logarithmic nonlinearity $u^q(\log u)^p (q,p\geqslant0)$. Using a direct Bernstein method we obtain a first range of values of $m,q,p$ in which all positive weak solutions of equation are constants, this holds in the following cases: (i) $1 \lt m \lt 2$, $m-1 \lt q \lt 1$, $0 \lt p \lt q$; (ii) $m \gt 1$, $q\geqslant1$, $0 \lt p \lt 1$. When $q=1$, the positive weak solutions are required to be bounded. Based on transformation of inequality and the utilization of suitable cut-off functions, we establish a Liouville-type theorem for positive weak solutions of inequality; this result also remains valid on complete noncompact Riemannian manifold.
Debates over the links between ethnicity and conflict often focus on the national level and take an ahistorical approach. This approach hides cases of ethnic conflict that arise at the subnational level and leaves unanswered questions over how ethnicity became a driver of conflict. This article explores these blind spots, using three cases in the African Great Lakes region. The cases reviewed here are the bipolar situations of Hema v. Lendu in Ituri (DRC), Banyarwanda/Banyamulenge v. ‘Autochthons’ in South and North Kivu (DRC), and Hima v. Iru in Ankole (Uganda). These cases suggest that polarisation is a more useful approach than fragmentation, but simple correlations between ethnic dyads and conflict obfuscate the nature and depths of the cleavages, as well as the mechanisms fuelling them. We elaborate on the pathways of escalation, highlighting how and when elite manipulations can activate deeply held identitarian norms. We conclude by emphasising the many lulls and moments of de-escalation, countering the portrayal of ethnic conflict as somehow inevitable.
After nearly two decades of documenting Ngũgĩ wa Thiong’o’s life and work, this reflection situates my conversations with him within a broader canvas—one that allows us to hear him in dialogue with fellow writers, activists, and global artists.
To what extent does refugee protection in Western Europe depend on the ethno-religious and gender identity of asylum seekers? This article examines how selective humanitarianism, shaped by the identity of asylum seekers and migrants, shapes their protection status. It offers an analysis of Germany’s response to Yezidi refugees, in comparison with that of France, in the wake of the genocidal campaign carried out by the Islamic State in 2014. Drawing on fieldwork that includes interviews with Yezidi refugees and stakeholders in Germany, we argue that contemporary asylum regimes operate through three interrelated mechanisms: the securitization of certain groups, selective humanitarian exceptions, and neoliberal selection criteria. The Yezidi experience illustrates how these mechanisms generate hierarchies of protection, wherein even recognized victims of genocide must meet increasingly economic thresholds to secure lasting refuge. While specialized programs for women survivors represent important humanitarian innovations, they often exclude male family members, thereby producing new forms of vulnerability. Struggling to align with dominant narratives of economically valuable migrants, Yezidis encounter a renewed form of liminality in Europe.
The January 2025 Los Angeles wildland-urban interface wildfires represent a significant environmental disaster, resulting in widespread evacuations. Beyond the immediate physical and economic devastation, wildfires can have profound and lasting impacts on the mental well-being of affected populations. This study compared mental health outcomes between Southern California residents who evacuated due to the fires and those who did not evacuate.
Methods
Southern California residents (N = 739) were surveyed 2-3 months after the January 2025 wildfires. Logistic regression models assessed the association of evacuation status with depression, anxiety, and PTSD, adjusting for demographics and baseline pre-fire levels of depression and anxiety.
Results
Evacuating was significantly associated with higher odds of depression (AOR = 1.75 [1.08-2.85]) and PTSD (AOR = 2.44 [1.36-4.35]), after controlling for pre-fire mental health status and other demographic covariates. Evacuation status was not associated with anxiety.
Conclusions
These findings support previous research linking wildfire exposure to adverse mental health outcomes and highlight the importance of targeted mental health screening and support for wildfire evacuees, who are at increased risk for depression and PTSD.
We investigate the evolution of an external particle jet in a dense particle bed subjected to a radially divergent air-blast. Both random and single-mode perturbations are considered. By analysing the particle dynamics, we show that the Rayleigh–Taylor instability (RTI), the Richtmyer–Meshkov instability (RMI) and large particle inertia contribute to the formation of the external jet. The external particle jet exhibits a spike-like structure at its top and a bubble-like structure near its bottom. As the expanding particle bed lowers the internal gas pressure, particles near the bubble experience strong inward coupling forces and undergo RTI with variable acceleration. Meanwhile, particles in the spike experience weak gas–particle coupling and collision forces due to large particle inertia and low particle volume fraction, respectively. Consequently, the particles in the spike retain a nearly constant velocity, in contrast to the accelerating spikes observed in cylindrical RTI. To investigate the contributions of RMI to the particle jet growth, we track the trough-near particles in the single-mode perturbation case. It is revealed that the trough-near particles accelerate under the perturbation-induced pressure gradient, overtaking the crest-near particles and inducing phase inversion, thereby resulting in an increase in jet length. We establish a linear-growth model for the jet length increment, similar to the planar Richtmyer–Meshkov impulsive model. Combined with the jet-length-increment model, we propose an external-particle-jet-length model that is consistent with both numerical and experimental results for diverse initial gas pocket central pressures and particle bed thicknesses.
Asymptotic flow states with limiting drag modification are explored via direct numerical simulations in a moderate-curvature viscoelastic Taylor–Couette flow of the FENE-P fluid. We show that asymptotic drag modification (ADM) states are achieved at different solvent-to-total viscosity ratios ($\beta$) by gradually increasing the Weissenberg number from 10 to 150. As $\beta$ decreases from 0.99 to 0.90, for the first time, a continuous transition pathway is realised from the maximum drag reduction to the maximum drag enhancement, revealing a complete phase diagram of the ADM states. This transition originates from the competition between Reynolds stress reduction and polymer stress development, namely, a mechanistic change in angular momentum transport. Reduced $\beta$ has been found to effectively enhance elastic instability, suppressing large-scale Taylor vortices while promoting the formation of small-scale elastic Görtler vortices. The enhancement and in turn dominance of small-scale structures result in stronger incoherent transport, facilitating efficient mixing and substantial polymer stress development that ultimately drives the AMD state transition. Further analysis of the scale-decomposed transport equation of turbulent kinetic energy reveals an inverse energy cascade in the gap centre, which is attributed to the polymer-induced energy redistribution: polymers extract more energy from large scales than they can dissipate, with the excess energy redirected to smaller scales. However, the energy accumulating at smaller scales cannot be dissipated immediately and is consequently transferred back to larger scales via nonlinear interactions, thereby unravelling a novel polymer-mediated cycle for the reverse energy cascade. Overall, this study unravels the challenging puzzle of the existence of distinct dynamically connected ADM states and paves the way for coordinated experimental, simulation and theoretical studies of transition pathways to desired ADM states.
Let $\Bbbk$ be a field, $H$ a Hopf algebra over $\Bbbk$, and $R = (_iM_j)_{1 \leq i,j \leq n}$ a generalized matrix algebra. In this work, we establish necessary and sufficient conditions for $H$ to act partially on $R$. To achieve this, we introduce the concept of an opposite covariant pair and demonstrate that it satisfies a universal property. In the special case where $H = \Bbbk G$ is the group algebra of a group $G$, we recover the conditions given in [7] for the existence of a unital partial action of $G$ on $R$.
Le nouveau réalisme développé par Maurizio Ferraris fait de Immanuel Kant son adversaire privilégié. Celui-ci aurait mis à distance le réel au travers de schèmes conceptuels et ouvert la postmodernité qui ne pense qu’à l’aune du corrélationisme et du constructivisme. Pourtant, Kant est essentiel à sa pensée et plus que d’une opposition, il s’agit pour Ferraris de renverser l’oeuvre kantienne en trouvant dans la Critique de la faculté de juger une ontologie naturelle émergentiste, et dans la Critique de la raison pure une ontologie sociale reposant sur la documentalité.