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We study the viscous-fingering instability in a radial Hele-Shaw cell in which the top boundary has been replaced by a thin elastic sheet. The introduction of wall elasticity delays the onset of the fingering instability to much larger values of the injection flow rate. Furthermore, when the instability develops, the fingers that form on the expanding air–liquid interface are short and stubby, in contrast with the highly branched patterns observed in rigid-walled cells (Pihler-Puzović et al., Phys. Rev. Lett., vol. 108, 2012, 074502). We report the outcome of a comprehensive experimental study of this problem and compare the experimental observations to the predictions from a theoretical model that is based on the solution of the Reynolds lubrication equations, coupled to the Föppl–von-Kármán equations which describe the deformation of the elastic sheet. We perform a linear stability analysis to study the evolution of small-amplitude non-axisymmetric perturbations to the time-evolving base flow. We then derive a simplified model by exploiting the observations (i) that the non-axisymmetric perturbations to the sheet are very small and (ii) that perturbations to the flow occur predominantly in a small wedge-shaped region ahead of the air–liquid interface. This allows us to identify the various physical mechanisms by which viscous fingering is weakened (or even suppressed) by the presence of wall elasticity. We show that the theoretical predictions for the growth rate of small-amplitude perturbations are in good agreement with experimental observations for injection flow rates that are slightly larger than the critical flow rate required for the onset of the instability. We also characterize the large-amplitude fingering patterns that develop at larger injection flow rates. We show that the wavenumber of these patterns is still well predicted by the linear stability analysis, and that the length of the fingers is set by the local geometry of the compliant cell.
An attempt is made to provide a consistent, independently motivated metaphysics of the Trinity by invoking an ontology of substances, attributes, and modes in the spirit of Descartes and Spinoza. The Trinity comprises one substance, triply attributed, where distinctions among attributes are ‘of reasoned reason’ only, but ‘founded’ in the nature of the substance.
The injection of fluid into the narrow liquid-filled gap between a rigid plate and an elastic membrane drives a displacement flow that is controlled by the competition between elastic and viscous forces. We study such flows using the canonical set-up of an elastic-walled Hele-Shaw cell whose upper boundary is formed by an elastic sheet. We investigate both single- and two-phase displacement flows in which the localised injection of fluid at a constant flow rate is accommodated by the inflation of the sheet and the outward propagation of an axisymmetric front beyond which the cell remains approximately undeformed. We perform a direct comparison between quantitative experiments and numerical simulations of two theoretical models. The models couple the Föppl–von Kármán equations, which describe the deformation of the thin elastic membrane, to the equations describing the flow, which we model by (i) the Navier–Stokes equations or (ii) lubrication theory. We identify the dominant physical effects that control the behaviour of the system and critically assess modelling assumptions that were made in previous studies. The insight gained from these studies is then used in Part 2 of this work, where we formulate an improved lubrication model and develop an asymptotic description of the key phenomena.
We investigate the injection of inviscid gas into the narrow liquid-filled gap between a rigid base plate and an overlying elastic sheet. After an early-time transient in which the gas deflects the sheet into a large blister, the viscous liquid displaced by the expanding bubble starts to accumulate in a wedge which advances as the elastic sheet peels away from the base. We analyse theoretically the subsequent interaction between viscous forces, elastic (bending or tension) forces and capillary forces. Asymptotic expressions are derived for the speed of spreading of the bubble, which reveal that the effect of the capillary pressure drop at the bubble tip is to suck down the sheet over the liquid wedge and thereby reduce the speed. We show that the system passes through three different asymptotic regimes in sequence. At early times, capillary effects are weak and hence the spreading of the bubble is controlled dominantly by the viscous-peeling process at the wedge tip. The capillary forces grow in importance with time, and at late times they dominate viscous effects and balance with elastic forces, leading to quasi-static spreading. Finally, at very late times, the capillary suction generates a narrow bottleneck at the wedge tip, which pushes a large ridge of liquid ahead of it. These results hold in the framework of standard lubrication theory as well as with an improved lubrication model, which takes into account films of wetting liquid deposited behind the advancing bubble tip. The predictions of the model are shown to be in excellent agreement with the Navier–Stokes simulations and experimental results from Part 1 of this work.
As a reader of the Journal of the American Philosophical Association, you might have wondered what measures are in place to ensure that submissions are evaluated impartially. The Journal deploys a ‘triply anonymous’ reviewing process. Editors handling papers do not know the identity of authors, nor do referees, and authors are not given referees’ names. And referees? Referees are selected on the basis of their expertise, with an eye toward the promotion of diversity to the extent possible.
You hold in your hands—or perhaps are viewing online—the first of four issues of the inaugural volume of the Journal of the American Philosophical Association. The Journal was inspired by the idea that the time had come for the American Philosophical Association to sponsor a journal serving the interests of the philosophical community worldwide, a fully generalist journal dedicated to publishing philosophically compelling articles in a timely manner.
Intolleranza 1960, an ‘azione scenica in two parts based on an idea by Angelo Maria Ripellino, music by Luigi Nono’, was first performed on 13 April 1961 during the 24th International Contemporary Music Festival at the Teatro La Fenice in Venice. In the aftermath of the première, critics perceived a gap in the work's realization between intentions and results, a gap perceived mainly in political terms. An examination of the dramaturgical and compositional genesis of the work through the sketches suggests a gap of a very different nature. The work as originally announced was to have revolutionary potential, and the innovations were intended by Nono to affect the musical language, the staging, and the dramatic content. But many of these ideas and innovations remained unrealized in the final production, while the ambitious dramaturgical logic underpinning the compositional process – involving ‘character rows’ for each of the principal roles – was never fully implemented. Nono's first theatrical work proves to be the result of a singular compromise between intention and necessity, something quite different from the original project. Nevertheless, the compositional solutions forced on Nono, partly through pressures of time, were to prove decisive in later works, liberating the now ‘autonomous’ interval from parametric predetermination and classic serial grids. Moreover, the work, which had been envisaged as an ideal convergence of dramaturgical and technical principles, became an emblem not only of the new music theatre but of avant-garde theatre in general.
This chapter was originally written for an event honouring E. J. Lowe. The author considers Lowe a philosopher of the first rank, a philosopher who has resisted the idea that philosophical problems are to be addressed in ways that keep ontology at arm's length. Lowe's work is a fine example of what the Australians call ontological seriousness. The remarks presented in the chapter are meant less as objections to Lowe's 'four-category ontology' than as requests for clarification. Lowe and David Armstrong agree that universals depend on their instances; the instances are 'metaphysically prior' to the universals. The chapter presents Lowe's account of dispositionality. The discussion is concluded by mentioning three aspects of Lowe's view. First, according to Lowe kinds depend on attributes that characterize them. Second, Lowe tells us that kinds are characterized by attributes, properties, and relations regarded as universals. Third, is an instance of the salt kind.
The low masses of irregular galaxies change the behavior of their interstellar medium (ISM) compared to that of normal spirals, so the role of magnetic fields in the ISM in irregulars may be very different than in spirals. We present high-resolution and high-sensitivity observations of the magnetic fields of two irregular galaxies: NGC 4214 and NGC 1569.
Shepard provides an account of mechanisms underlying perceptual judgment or representation. Ought we to interpret the account as revealing principles on which those mechanisms operate or merely an account of principles to which their operation apparently conforms? The difference, invisible so long as we remain at a high level of abstraction, becomes important when we begin to consider implementation. [Shepard]
1 Thess 5.9–10 can be translated: ‘For God has not destined us for wrath but for possession of salvation through our Lord Jesus Christ who died for us, so that whether we may be awake or whether we may be asleep we may together live with him.’ Paul uses the same verb for ‘asleep’ (καθεύδωμεν) in 5.10 as he uses in 5.6–8 with the metaphorical sense of being ethically or spiritually negligent in contrast to being ‘awake’ and ‘sober’, that is, ethically or spiritually vigilant: ‘Let us not be asleep (καθεύδωμεν) like the rest but let us be awake and sober. For those who sleep (καθεύδοντες) sleep (καθεύδουσιν) at night and those who get drunk get drunk at night. Since we are of the day, let us be sober . . .’ In 4.13–15 Paul uses a different verb for ‘asleep’ (κοιμάομάι) to refer to those who are physically dead. Nevertheless, most commentators insist upon interpreting καθευδώ in 5.10, not with the meaning it has in 5.6–7, but with the same meaning as καιμαομαι in 4.13–15 – those who have physically died. This also requires that ‘awake’ (γρηγορωμεν) in 5.10 be interpreted as physically ‘alive’ rather than ethically or spiritually ‘vigilant’, the sense it has in 5.6.
In recent years, philosophers bent on defending physicalism have been attracted to the notion that apparently nonphysical features of our world supervene on its physical features. Mental and moral properties, for instance, though not perhaps identifiable with or reducible to physical properties, are thought nevertheless to depend on, and to be determined by, physical properties. More generally, supervenience claims are taken to range over collections or “families” of supervenient properties (A-properties) regarded as depending on distinct families of subvenient B-properties. I shall designate claims of this sort “A/B-supervenience” claims. Sometimes the supervenience relation is distilled into a pair of slogans: “No A-difference without a B-difference”; “Two objects identical with respect to their B-properties must be identical with respect to their A-properties.”
According to Richard Miller, appeals to supervenience on behalf of physicalism are empty; it is “trivially” true that “the nonphysical supervenes on the physical.” Worse,
it is equally true that the physical supervenes on the moral, the mental, and the aesthetic. “No difference without a physical difference” is an excellent slogan. The gist of this paper can also be summarized with slogans. “No difference without a moral difference,” “no difference without a mental difference,” and “no difference without an aesthetic difference,” are as (trivially) true as the physicalist slogan.
Miller advances a pair of interesting and important claims. First, the supervenience of the nonphysical on the physical is “trivial.” Second, the supervenience relation is invariably symmetrical: when As supervene on Bs, the supervenience of Bs on As is “all but guaranteed.”
Recent work in epistemology and the philosophy of mind suggests that we may at last be putting our Cartesian heritage behind us. The notion that knowledge demands certainty, and that empirical knowledge, in particular, requires an agent-centred core of indubitable propositions, is out of fashion. Dualism is nowadays rarely espoused, and the Cartesian picture of minds as spectators monitoring an inner world that mirrors an outer world is under revision. Earlier, in Chapter 2, we surveyed arguments purporting to show that the contents of thoughts are fixed in part by historical or contextual features of thinkers, that what an agent thinks is determined, at least in part, by that agent's circumstances and causal history. A conception of this sort turns Cartesian internalism inside out. To possess a mind is not to occupy the place of a detached onlooker, but to be engaged in the world.
Although I am prepared to take externalism seriously, I have not officially endorsed any particular externalist programme. I have suggested only that, in general, externalist accounts of the mind promise to solve the problem of intentionality in a way that meshes with our impression of the world as layered, its characteristics hierarchically arranged. In particular, these accounts fit with the notion that agents possess mental characteristics in virtue of their possession of certain physical characteristics.
An important component of our everyday conception of the mind began as a lively philosophical thesis and evolved into common sense. The philosophical thesis was spelled out by Descartes, and, without suggesting that Descartes was its sole author, I shall, for convenience, refer to it as the Cartesian conception. According to this conception, minds are entities, sentient organs on a par with hearts and livers. Whereas the heart circulates blood, and the liver regulates metabolism, the mind feels and thinks. Minds receive stimuli from bodily receptors via impulses born by nerves that connect receptors to the brain. According to official Cartesian doctrine, the mind and the brain are separate entities, and events occurring in the mind are distinct from events occurring in the brain. Descartes believed that the brain operated on exclusively mechanical principles, whereas the mind was governed by principles of reason. There was, he thought, no prospect of deriving the latter from the former; hence minds must be separate, nonphysical substances, and brains turn out to be physical modes. Even God could not build a sentient robot, a physical device with the capacity to feel or think. Feelings and thoughts require a nonphysical, mental basis.