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Bounds on heat transfer have been the subject of previous studies concerning convection in the Boussinesq approximation: in the Rayleigh–Bénard configuration, the first result obtained by Howard (J. Fluid Mech., vol. 17, issue 3, 1963, pp. 405–432) states that the dimensionless heat flux $\textit {Nu}$ carried out by convection is such that $\textit {Nu} < (3/64 \ Ra)^{1/2}$ for large values of the Rayleigh number $Ra$, independently of the Prandtl number $Pr$. This is still the best-known upper bound, only with the prefactor improved to $\textit {Nu} -1 < 0.02634 \ Ra^{1/2}$ by Plasting & Kerswell (J. Fluid Mech., vol. 477, 2003, pp. 363–379). In the present paper, this result is extended to compressible convection. An upper bound is obtained for the anelastic liquid approximation, which is similar to an anelastic model used in astrophysics based on a turbulent diffusivity for entropy. The anelastic bound is still scaling as $Ra^{1/2}$, independently of $Pr$, but depends on the dissipation number $\mathcal {D}$ and on the equation of state. For monatomic gases and large Rayleigh numbers, the bound is $\textit {Nu} < 25.8\, Ra^{{1}/{2}} / (1-\mathcal {D}/2 )^{{5}/{2}}$.
Flows over a disc are studied in a wind tunnel over incidence angles between $0^\circ \text { and }36^\circ$, a Reynolds number of $2.7 \times 10^4$ and rotational speed ratios of $0\unicode{x2013}10$. Smoke-wire visualization, particle image velocimetry and hot-film anemometry are employed. Two vortex shedding modes originating from the upstream surface of the disc are observed. The first is dominant at incidence angles up to ${\sim }21^\circ$. Beyond $21^\circ$, the second mode dominates. It appears as a soliton on the vortices and has a shedding frequency nearly twice that of the first at the highest incidence angle. The Strouhal number monotonically increases with incidence angle from approximately 0.2 to 0.4. Spectral analysis of the hot-film measurements confirms the findings from flow visualization experiments. Flows over the spinning disc generally mimic the stationary disc flows; however, centrifugal forces lead to cross-stream instability features that may be attributed to spiral wave instabilities intrinsic to the boundary layers in rotating flows. Velocity measurements are used to construct streamline patterns to compare with the smoke streaklines. The unsteadiness of the flows results in large variances. Mean strain rates are extracted from velocity data, where the fixed disc case at normal incidence compares well with theoretical predictions. The unsteady boundary layer thickness over the fixed disc, however, is approximately twice that predicted by theory for steady flow, stemming from the dominance of large unsteady vortices. Limited comparisons are made of the Strouhal numbers from experiments and numerical calculations in the literature.
In this paper, we study random walks on groups that contain superlinear-divergent geodesics, in the line of thoughts of Goldsborough and Sisto. The existence of a superlinear-divergent geodesic is a quasi-isometry invariant which allows us to execute Gouëzel’s pivoting technique. We develop the theory of superlinear divergence and establish a central limit theorem for random walks on these groups.
Nancy Pelosi makes history. She was the first woman elected to a high-ranking position in the US House of Representatives when she became the Democratic Whip in 2001. She made more history as the first female Democratic Leader in 2003, and first woman elected as Speaker of the House in 2007. She made history by remaining the Democratic Leader even after losing the House majority. Pelosi made history yet again when she was again elected Speaker in 2019, joining Sam Rayburn as the only House leader to lose and then regain the Speakership.
This chapter seeks keywords and concepts that will enable us to grasp the contradictory and conflictive globality of the current moment and sharpen our analysis of equally contradictory and conflictive global pasts. In a plea to move beyond equating the global with openness, connection, and integration, I address the role of closure, boundaries, and limits in global history in a wider sense. For this purpose, I explore in an experimental and deliberately open-ended fashion how thinking about global spherescan be utilised fruitfully for the current practice of history writing. The first part explores the radically inclusive yet claustrophobic vision of the globe as a closed sphere from which there is no escape. Building on earlier closed-world and one-world discourses, this thinking gained prominence after the Second World War in the face of the threat of nuclear destruction and environmental degradation. I then move to think about the globe as composed of many bounded spheres – geopolitical but also social. Here, I take central examples from the realm of communication and language and discusses the public sphere as an exclusionary rather than inclusionary figure of thought.
The dimensional transition in turbulent jets of a shear-thinning fluid is studied via direct numerical simulations. Our findings reveal that under vertical confinement, the flow exhibits a unique mixed-dimensional (or 2.5-dimensional) state, where large-scale two-dimensional and small-scale three-dimensional structures coexist. This transition from three-dimensional turbulence near the inlet to two-dimensional dynamics downstream is dictated by the level of confinement: weak confinement guarantees turbulence to remain three-dimensional, whereas strong confinement forces the transition to two dimensions; the mixed-dimensional state is observed for moderate confinement and it emerges as soon as flow scales are larger than the vertical length. In this scenario, we observed that the mixed-dimensional state is an overall more energetic state, and it shows a multi-cascade process, where the direct cascade of energy at small scales and the direct cascade of enstrophy at large scales coexist. The results provide insights into the complex dynamics of confined turbulent flows, relevant in both natural and industrial settings.
In this article, I carry out an in-depth conceptualization of right-to-development governance to illustrate how, as a rights-based model suited to redressing the challenges that have held Africa back over the decades, it can leverage and accelerate the processes for development on the continent. I do so to provide clarity on the deficits in the understanding of the right to development and the dilemma of its implementation in Africa. Through a theoretical and qualitative socio-legal analysis, I frame the argument that Africa's development setbacks are largely generated and sustained by the lack of an operational model that can drive transformation on the continent. Besides having evolved as a claimable human right, the right to development is equally conceived as a model or paradigm for development which is yet to be fully explored to inform development thinking and practice on the continent, and thus enable shared prosperity and improved quality of life and standards of living for the peoples of Africa. The proposed right-to-development governance model is appropriately theorized in this article to provide the basis for its operationalization, which, as explained, entails a nuanced blend of nominal capitalism, communitarian socialism and contemporary culturalism.
After the Green Revolution successfully raised wheat and rice yields in more auspicious farming contexts, attention in agricultural development turned to crops that grew on poorer soils and in regions of indifferent rainfall. When Rockefeller Foundation agronomists reached out to India with an urge to establish an international center for research on such crops in the 1970s, they found eager hosts. The foundation’s agronomists had been active in India during the 1950s and 1960s and built a community of local collaborators. Indian scientists saw the proposal for an international center as offering the next frontier in crop development. The possibility of a center also met with considerable appeal among the political establishment in India. Two prime ministers from opposite political camps, Indira Gandhi and Chaudhary Charan Singh, came to support the eventual International Crops Research Institute for the Semi-Arid Tropics (ICRISAT) due to common ground in their respective politics of the poor and farmers’ politics. As the chapter shows, the circumstances of postcolonial India allowed for the emergence of institutionalized expertise outside the direct realm of the local state.
Distance is a central concern for global historians. It is a physical and external condition of social life that global processes bridge. Exchanges, encounters and conflicts between strangers are common themes of global historians. Distance is also a cultural and conceptual condition, one that defines relations between strangers far – and near. Mobility and the advent of new modes of transportation and communications had ambiguous effects of closing the gap between strangers while heightening social distances, the need to explain them and policies to redress them.
This article explores the importance of the Casa Sonzogno publishing house for the Italian operetta market from the second half of the nineteenth century until the eve of the First World War, including its offshoot company Casa musicale Lorenzo Sonzogno. The article focuses particularly on Casa Sonzogno’s policies of importation, translation and intermedial adaptation of foreign (mainly French) light music-theatre works, especially in the context of the wider social, economic and technological environment of Milan at the turn of the twentieth century, and considers Sonzogno’s concorsi for young composers. The article then addresses the experimental activities of the Casa musicale Lorenzo Sonzogno (1909–15), notably across opera, operetta and cinema. Casa Sonzogno’s centrality to the establishment of an Italian operetta market, I argue, both highlights the crucial role of publishers in the Italian operetta industry, and offers an alternative theatrical history to familiar narratives focused on Casa Ricordi and Italian opera.
This chapter explores the changing imaginaries of technological governance in the European Union (EU), on the basis of one increasingly significant element of the EU policy: ecodesign. The grounds for treating ecodesign as especially significant are at least twofold. First, ecodesign presents a success story in governmental steering of technological development in the EU. Remaining for the most part on the sidelines of public discussion, ecodesign has fundamentally impacted the daily life of all Europeans, making a very broad swathe of everyday products (vacuum cleaners, lamps, or washing machines) more energy efficient and longer lasting. Second, the expansion and deepening of ecodesign framework creates important background conditions for shaping technological futures. It sets the grounds for the conversation on how technology relates to a sustainable economy; what kind of technological advances are necessary; the desirable relation between production, distribution, and consumption; and finally, the distributive consequences of both technological and legal interventions. These questions will become ever more salient as the EU pursues sustainable futures, from the digital economy to the energy transition, from a more balanced transportation mix to sustainable food provision.