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Dilatational motions in the shape of travelling wave packets have been identified recently to be dynamically significant in hypersonic turbulent boundary layers. The present study investigates the mechanisms of their generation and their association with the solenoidal motions, especially the well-recognized near-wall self-sustaining process of the regeneration cycle between the velocity streaks and quasi-streamwise vortices. By exploiting the direct numerical simulation databases and orchestrating numerical experiments, we explore systematically the near-wall flow dynamics in the processes of the formation and transient growth of low-speed streaks. We conclude via theoretical ansatz that the nonlinearity related to the parallel density and pressure gradients close to the wall due to the restriction of the isothermal boundary condition is the primary cause of the generation of the dilatational structures at small scales. In fully developed turbulence, the formation and the existence of healthy dilatational travelling wave packets require the participation of the turbulence at scales larger than those of the near-wall regeneration cycles, especially the occurrence of the bursting events that generate vortex clusters. This is proven by the less intensified dilatational motions in the numerical experiments in which the Orr mechanism is alleviated and the vortical structures and turbulent bursts are weakened.
We compute steady planar incompressible flows and wall shapes that maximize the rate of heat transfer ($Nu$) between hot and cold walls, for a given rate of viscous dissipation by the flow ($Pe^2$), with no-slip boundary conditions at the walls. In the case of no flow, we show theoretically that the optimal walls are flat and horizontal, at the minimum separation distance. We use a decoupled approximation to show that flat walls remain optimal up to a critical non-zero flow magnitude. Beyond this value, our computed optimal flows and wall shapes converge to a set of forms that are invariant except for a $Pe^{-1/3}$ scaling of horizontal lengths. The corresponding rate of heat transfer $Nu \sim Pe^{2/3}$. We show that these scalings result from flows at the interface between the diffusion-dominated and convection-dominated regimes. We also show that the separation distance of the walls remains at its minimum value at large $Pe$.
The Canadian Judicial Council is primarily responsible for regulating misconduct among federally appointed judges. Over the last decade, the Council has faced some highly publicized challenges to its authority when judges facing misconduct complaints commenced judicial review proceedings pursuant to the Federal Courts Act. In response to these challenges, the Council sought to immunize itself from judicial review, first by pleading its case in court and then by pressing for legislative changes in the form of Bill C-9. The new legislation, which exempts the Council from almost all external judicial oversight, was driven by the Council and assented to by a government willing to delegate its power to judicial elites. The legislation not only fails to provide adequate checks on the Council's power as an administrative decision maker, it represents a high-water mark in judicialized politics, pointing to a judicialization of governance in the area of judicial discipline.
Motivated by insurance applications, we propose a new approach for the validation of real-world economic scenarios. This approach is based on the statistical test developed by Chevyrev and Oberhauser ((2022) Journal of Machine Learning Research, 23(176), 1–42.) and relies on the notions of signature and maximum mean distance. This test allows to check whether two samples of stochastic processes paths come from the same distribution. Our contribution is to apply this test to a variety of stochastic processes exhibiting different pathwise properties (Hölder regularity, autocorrelation, and regime switches) and which are relevant for the modelling of stock prices and stock volatility as well as of inflation in view of actuarial applications.
We show that there is a set $S \subseteq {\mathbb N}$ with lower density arbitrarily close to $1$ such that, for each sufficiently large real number $\alpha $, the inequality $|m\alpha -n| \geq 1$ holds for every pair $(m,n) \in S^2$. On the other hand, if $S \subseteq {\mathbb N}$ has density $1$, then, for each irrational $\alpha>0$ and any positive $\varepsilon $, there exist $m,n \in S$ for which $|m\alpha -n|<\varepsilon $.
A partition is finitary if all its members are finite. For a set A, $\mathscr {B}(A)$ denotes the set of all finitary partitions of A. It is shown consistent with $\mathsf {ZF}$ (without the axiom of choice) that there exist an infinite set A and a surjection from A onto $\mathscr {B}(A)$. On the other hand, we prove in $\mathsf {ZF}$ some theorems concerning $\mathscr {B}(A)$ for infinite sets A, among which are the following:
(1) If there is a finitary partition of A without singleton blocks, then there are no surjections from A onto $\mathscr {B}(A)$ and no finite-to-one functions from $\mathscr {B}(A)$ to A.
(2) For all $n\in \omega $, $|A^n|<|\mathscr {B}(A)|$.
(3)$|\mathscr {B}(A)|\neq |\mathrm {seq}(A)|$, where $\mathrm {seq}(A)$ is the set of all finite sequences of elements of A.
This paper extends the work of Tamano & Morinishi (J. Fluid Mech., vol. 548, 2006, pp. 361–373) by simulating supersonic turbulent channel flow with asymmetric thermal walls using a larger computational domain and a finer mesh. Direct numerical simulation is carried out for four cases with different thermal wall boundaries at the top wall at fixed $Ma=1.5$, $Re=6000$ and $Pr=0.72$, while the bottom wall is maintained at a constant temperature of $T_L$ equal to the reference temperature. These cases are referred to as the adiabatic case TAd, where the top wall is adiabatic; the pseudo-adiabatic case T32, where the top wall is isothermal with temperature $T_{w,t}=T_A$; the sub-adiabatic case T25, with $T_{w,t}=0.77T_A$; and the super-adiabatic case T40, with $T_{w,t}=1.24T_A$. Here, $T_A=3.234$ is the mean temperature at the adiabatic wall in the TAd case. The objective of this study is to compare and contrast the TAd case with its corresponding T32 case, and to investigate the effect of the wall temperature difference between the two isothermal walls. Comparisons of the basic turbulent statistics, the heat transfer between the Favre-averaged mean-flow kinetic energy, the Favre-averaged turbulent kinetic energy and the Favre-averaged mean internal energy, as well as the wall heat transfer properties, indicate that the TAd case and its corresponding T32 case are generally equivalent. The only discernible difference is in the region very close to the top wall for the temperature-fluctuation-related quantities. The analysis reveals that the asymmetry of the thermal walls causes asymmetry in the flow and thermal fields. In addition, the transfer of the heat generated by the pressure dilatation and the viscous stress is facilitated by the turbulent heat flux term and the mean molecular heat flux term.
Central Europe is an area of high diversity for the Talpidae (Eulipotyphla, Mammalia) during the Late Miocene. The assemblages from Slovakia (Borský Svätý Jur, Krásno, Pezinok, Šalgovce, Studienka, Triblavina) are no exception with their abundant material representing eleven species. The uropsiline Desmanella is represented by D. rietscheli and D. dubia. Desmanini fossils are attributed to Archaeodesmana vinea, Archaeodesmana dissona new species, Gerhardstorchia biradicata, and Gerhardstorchia sp. The scalopines Proscapanus minor and P. austriacus are well recorded in the Vallesian localities and support the emergence of P. austriacus before the MN9/10 transition. Talpini and Urotrichini are especially rare and only represented by Talpa cf. T. minuta and Urotrichini gen. sp. indet. Finally, we identified the youngest occurrence of Desmanodon in Europe, D. cf. D. fluegeli, at the MN9 locality of Borský Svätý Jur. The high diversity in the Late Miocene Central European is partly explained by the co-occurrence of the competing Scalopini and Talpini during the Vallesian, indicating high resource environments. The decline of these tribes, followed by the success of the desmans during the Turolian, appears as a consequence of regional environmental changes.
The central role of Gold Coast societies, ports, and cities in the emerging Atlantic circuit is critical to understanding the history of the Atlantic world. The study of the causes and effects of Gold Coast societies’ transition from African polities and economies to transatlantic entrepots and trading emporiums and their subsequent impact on the Americas has been the hallmark of Ray Kea's scholarship. Since the beginning of his career, Kea has been a significant contributor to the study of the African Atlantic, and the field's various debates and disciplinary evolutions. While many scholars of the Gold Coast recognize Kea's work as foundational to scholarship on the Gold Coast, engagement with his work has not been rigorous. Kea is often cited in bibliographies and aspects of his work have served as benchmarks for other forays into Gold Coast histories. However, there is a need to go beyond an appreciation for Kea as a trailblazer, passing reference of his scholarship, and bibliographic citation of his work to a more thorough and consistent discourse with his major ideas and propositions. Kea has been, for example, adept at integrating innovations and ideas in various disciplinary arenas. He dexterously applies Marxist and postmodernist theories, diverse historiographies of the Atlantic world, and conceptual tools to traditional archival and oral historical data in his analyses of Gold Coast and diasporic societies. This review essay argues for Kea's importance and the need for a deeper engagement with his work in the field by putting his work into conversation with both classic Atlantic historiographies and recent scholarship that has built off Kea's.
The 2022 Russian invasion of Ukraine was a watershed moment in European politics. The invasion prompted a massive influx of refugees into Central Europe, a region in which immigration has proven highly contentious and politically salient in recent decades. We study public opinion toward refugees in Hungary, a highly exclusionary political environment in which anti-migrant and anti-refugee sentiments are commonly invoked by the ruling government. Combining historical public opinion data from the past decade with two rounds of original survey data from 2022, we demonstrate that the Ukrainian refugee crisis was accompanied by a large increase in tolerance for refugees, reversing what had previously been one of the most anti-refugee public opinion environments in Europe. To explain this reversal, we use a series of survey experiments coupled with detailed settlement-level demographic data to investigate how conflict proximity and racial, religious, and national identity shape openness to refugees. We find that the distinguishing feature of the 2022 refugee crisis was that refugees were mostly white European Christians driven from their home country by conflict. We discuss the implications of our argument for Hungary, for European politics in times of crisis, and for the politics of public opinion in competitive authoritarian regimes.
In this study the authors examine the impact of social incomes on social inequalities and social integration in the post-2010 populist welfare system in Hungary. A detailed quantitative analysis reveals the structure and distribution of social incomes among different groups in contemporary Hungarian society. This analysis includes factors such educational attainment, demographic structure and income of households, number of children, and deprivation index. The results of the research show that welfare redistribution has lost its ability to reduce inequalities and instead serves as a means of perpetuating social disparities.
Shock-tube experiments and theoretical studies have been performed to highlight mode-coupling in an air–SF$_6$–air fluid layer. Initially, the two interfaces of the layer are designed as single mode with different basic modes. It is found that as the two perturbed interfaces become closer, interface coupling induces a different mode from the basic mode on each interface. Then mode coupling further generates new modes. Based on the linear model (Jacobs et al., J. Fluid Mech., vol. 295, 1995, pp. 23–42), a modified model is established by considering the different accelerations of two interfaces and the waves’ effects in the layer, and provides good predictions to the linear growth rates of the basic modes and the modes generated by interface coupling. It is observed that interface coupling behaves differently to the nonlinear growth of the basic modes, which can be characterized generally by the existing or modified nonlinear model. Moreover, a new modal model is established to quantify the mode-coupling effect in the layer. The mode-coupling effect on the amplitude growth is negligible for the basic modes, but is significant for the interface-coupling modes when the initial wavenumber of one interface is twice the wavenumber of the other interface. Finally, amplitude freeze-out of the second single-mode interface is achieved theoretically and experimentally through interface coupling. These findings may be helpful for designing the target in inertial confinement fusion to suppress the hydrodynamic instabilities.
Let $\mathfrak {F}_n$ be the set of all cuspidal automorphic representations $\pi$ of $\mathrm {GL}_n$ with unitary central character over a number field $F$. We prove the first unconditional zero density estimate for the set $\mathcal {S}=\{L(s,\pi \times \pi ')\colon \pi \in \mathfrak {F}_n\}$ of Rankin–Selberg $L$-functions, where $\pi '\in \mathfrak {F}_{n'}$ is fixed. We use this density estimate to establish: (i) a hybrid-aspect subconvexity bound at $s=\frac {1}{2}$ for almost all $L(s,\pi \times \pi ')\in \mathcal {S}$; (ii) a strong on-average form of effective multiplicity one for almost all $\pi \in \mathfrak {F}_n$; and (iii) a positive level of distribution for $L(s,\pi \times \widetilde {\pi })$, in the sense of Bombieri–Vinogradov, for each $\pi \in \mathfrak {F}_n$.
The debate over home state responsibility for human rights has focused on how home states might use accountability mechanisms to promote respect for human rights among their businesses abroad. However, a set of activists and researchers have opened a new front on the question of home state responsibility by focusing on the activities of Canadian diplomats providing advice and consular services to extractive firms abroad. This work documents how home states can be directly implicated in business and human rights controversies and how home state diplomats can put human rights defenders at increased risk. This paper outlines the growing body of research on the hidden influence of Canadian economic diplomacy in human rights controversies, suggesting a troubling disregard for corporate social responsibility and human rights concerns in these contexts, and making the case for robust accountability mechanisms to influence the conduct of both corporate actors and diplomatic officials.
An improved version of the non-equilibrium theory of non-homogeneous turbulence of Chen & Vassilicos (J. Fluid Mech., vol. 938, 2022, A7) predicts that an intermediate range of length scales exists where the interscale turbulence transfer rate, the two-point interspace turbulence transport rate and the two-point pressure gradient velocity correlation term in the two-point small-scale turbulent energy equation are all proportional to the turbulence dissipation rate and independent of length scale. Particle image velocimetry measurements in a field of view under the turbulence-generating impellers in a baffled water tank support these predictions and show that the measured small-scale turbulence is significantly non-homogeneous. The particle image velocimetry measurements also suggest that the rate with which large scales lose energy to the small scales in the two-point large-scale turbulent energy equation also appears to be approximately proportional to the turbulence dissipation rate and independent of length scale in the same intermediate range and that this rate may not balance the interscale turbulence transfer rate in the two-point small-scale turbulent energy equation because of turbulent energy transport caused by the non-homogeneity.