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In this paper, we explore the hydrodynamics of spheroidal active particles in viscosity gradients. This work provides a more accurate modelling approach, in comparison to spherical particles, for anisotropic organisms such as Paramecium swimming through inhomogeneous environments, but more fundamentally examines the influence of particle shape on viscotaxis. We find that spheroidal squirmers generally exhibit dynamics consistent with their spherical analogues, irrespective of the classification of swimmers as pushers, pullers or neutral swimmers. However, the slenderness of the spheroids tends to reduce the impact of viscosity gradients on their dynamics; when a swimmer becomes more slender, the viscosity difference across its body is reduced, which leads to slower reorientation. We also derive the mobility tensor for passive spheroids in viscosity gradients, generalizing previous results for spheres and slender bodies. This work enhances our understanding of how shape factors into the dynamics of passive and active particles in viscosity gradients, and offers new perspectives that could aid the control of both natural and synthetic swimmers in complex fluid environments.
The growth with fetch of young wind waves under steady wind forcing that is commonly attributed to shear flow instability results in a spatially inhomogeneous wave field with a spectrum evolving along the tank. The present laboratory study accounts for multiple co-existing statistically stationary random frequency harmonics. Single-point synchronous measurements of the instantaneous surface elevation and of its along-wind slope component are performed by optical methods at numerous locations. Assuming exponential spatial growth, the phase shift between the surface elevation and surface slope at each frequency is related to the spatial growth rate of each harmonic. The validity of the assumption that the wave energy varies exponentially with fetch is examined in a separate set of experiments; the instantaneous surface elevation at various wind-forcing conditions is measured at multiple locations along the tank. The spatial variation of the energy of individual frequency harmonics is determined. It is found that, below the local peak frequency, the energy of each harmonic grows exponentially, while the evolution of waves at frequencies approaching and exceeding the local peak is strongly affected by sheltering by the dominant wave, as well as by nonlinear bound waves. The outcomes of two independent methods of determination of spatial growth rates at a range of young wave frequencies are compared. The accumulated data also enable quantitative analysis of the sheltering phenomenon. The essential difference between the spatial and the temporal wind-wave evolution cases is discussed.
This article presents new discoveries from a manuscript from the Collegiate Church of St Chad, Shrewsbury, with implications for the circulation of ecclesiastical music, particularly sequences, in twelfth- and thirteenth-century England. It begins with a brief examination of the twelfth-century musical contents of the manuscript, which are shown to hold close scribal affinities: in particular, a ‘winged’ neume shape is contextualised by contemporaneous musical inscriptions found in a manuscript probably written at Haughmond Abbey. The remainder of the article considers music, mostly sequences, inscribed in a palimpsest gathering at the back of the St Chad's manuscript in the thirteenth century. Two of these are compared for the first time with their concordances, one concordance newly discovered. Examination of the preservation and record of these musical entries (with discussion of contrafacture and marginalia) sheds light on creative practices of citation and intertextuality, performance traditions, and processes of reading and recording music at St Chad's, ultimately illuminating the role the church played within a creative network across England and northern Europe.
Perioperative immunisation administration surrounding congenital heart surgery is controversial. Delayed immunisation administration results in children being at risk of vaccine-preventable illnesses and is associated with failure to complete immunisation schedules. Among children with CHD, many of whom are medically fragile, vaccine-preventable illnesses can be devastating. Limited research shows perioperative immunisation may be safe and effective.
Methods:
We surveyed Pediatric Acute Care Cardiology Collaborative member centres and explored perioperative immunisation practices. We analysed responses using descriptive statistics.
Results:
Complete responses were submitted by 35/46 (76%) centres. Immunisations were deferred for any period prior to surgery by 23 (66%) centres and after surgery by 31 (89%) centres. Among those who deferred post-operative immunisation, 20 (65%) required deferral only for patients whose operations required cardiopulmonary bypass. Duration of deferral in the pre- and post-operative periods was variable. Many centres included exceptions to their policy for specific vaccine-preventable illnesses. Almost all (34, 97%) centres administer routine childhood immunisation to patients who remain admitted for prolonged periods.
Conclusions:
Most centres defer routine childhood immunisation for some period before and after congenital heart surgery. Centre specific practices vary. Immunisation deferral confers risk to patients and may not be warranted in this population. Further research would be necessary to understand the immunologic impact of these practices.
This article explores the times and datedness of new opera. When referring to an opera (20**) the bracketed number that follows the composition title usually refers to the date of composition or the first performance. When asked how many times an opera was played, its interpreters tend to refer to the number of performances, not the number of instances of rehearsal and individual practice. These times often remain unmentioned by performers, composers, production teams and institutions. But what do we make invisible when we exclude the main act of collective labour in the production of a new staged work? How do new operas structure their times and, in turn, how do these various times restructure new opera? I call for an inclusion of the rehearsal in the temporal narratives that new opera tells through its dates and times, emerging from collaborative processes in compound temporalities. With ethnographic glimpses into different operatic rehearsal studios, I examine the process that takes up most of new opera's time – rehearsal time – rather than audiences’ or performers’ lived experiences during the performance. This article maps the times inside rehearsal time – from daily schedules, call times and deep times of props to computational time and the timing of time itself – for better understanding new opera's ontology.
Over the past 40 years, no scholar has written so deeply or prolifically on the histories of Saint Domingue and the Haitian Revolution as David Geggus. Indeed, the scale of the research required to compile the population database of enslaved people in Saint Domingue across different labor sectors from 1770 to 1791 is a testament to years of work in French archives—I can think of no other scholar of Haiti who could make that heavy lift. As an outsider to the field of Haitian history, I am grateful for his intervention and to the editors of The Americas for giving me the opportunity to respond.
The presence of a dispersed phase can significantly modulate the drag in turbulent systems. We derived a conserved quantity that characterizes the radial transport of azimuthal momentum in the fluid–fluid two-phase Taylor–Couette turbulence. This quantity consists of contributions from advection, diffusion and two-phase interface, which are closely related to density, viscosity and interfacial tension, respectively. We found from interface-resolved direct numerical simulations that the presence of the two-phase interface consistently produces a positive contribution to the momentum transport and leads to drag enhancement, while decreasing the density and viscosity ratios of the dispersed phase to the continuous phase reduces the contribution of local advection and diffusion terms to the momentum transport, respectively, resulting in drag reduction. Therefore, we concluded that the decreased density ratio and the decreased viscosity ratio work together to compete with the presence of a two-phase interface for achieving drag modulation in fluid–fluid two-phase turbulence.
Deportations and the threat of removal are choreographic strategies of the nation-state's ever-growing monopoly of movement through border securitization and immigration enforcement, which persists into the twenty-first century. While literature and the visual arts have received critical and popular attention by considering forced family separations, dance remains overlooked. Analyzing dance performances that relate directly to deportation teaches us not only about the painful impact of forced removal: it instructs us to decode, move and maintain relationships as aliens and citizens amid the increasing control of motion in the United States and the cruel joke offered by a nation of immigrants.
The meaning of the verb ἀλληγορέω stands at the heart of the debate concerning Paul's hermeneutic in Galatians 4.21–31. If by using the term Paul means ‘I am interpreting these things allegorically’, then the question of Paul's interpretive procedure would be all but answered – he would likely be allegorising as the Greeks did before him and the early church fathers did after. However, if he does not mean this, then the question remains open. This article argues that the phrase ἅτινά ἐστιν ἀλληγορούμɛνα means ‘these things are symbolic’, which would indeed leave this question open. This rendering is best for two reasons: First, the majority of the uses of ἀλληγορέω available in the two hundred or so years surrounding the writing of Galatians mean ‘to speak symbolically’. Second, the contextual clues surrounding Paul's use of the term in Galatians itself, such as his call to hear the law in verse 21, strongly suggest such a reading. To prove this thesis, this article provides detailed exposition of the texts in which ἀλληγορέω occurred around the time Paul wrote Galatians before turning to Paul's own use of the term in Galatians 4.24.
We develop a dynamic model of debt contracts with adverse selection. Entrepreneurs borrow investment goods from lenders to run businesses whose returns depend on entrepreneurial productivity and common productivity. Entrepreneurial productivity is the entrepreneur’s private information, and lenders construct beliefs about entrepreneurial productivity based on the entrepreneur’s business operation history, common productivity history, and the terms of the contract. The model provides insights into the dynamic and cross-sectional relations between firm age and credit risk, persistency of the effects of a productivity shock, cyclical asymmetry of the business cycle, slow recovery after a crisis, and constructive and destructive economic downturns.
We consider a model in which the correlation between shocks to consumption and to expected future consumption growth is nonzero and varies over time. We validate this assumption empirically using the model’s implication that time variation in consumption growth persistence (CGP) drives the correlation between stock and bond returns. Our model implies that the stock–bond correlation is also related to the predictive relation between bond yields and future stock returns. Finally, we provide suggestive evidence that asset price fluctuations are the primary driver of changes in CGP.