185 research outputs found
Curved Herbig-Haro Jets: Simulations and Experiments
Herbig-Haro jets often show some degree of curvature along their path, in
many cases produced by the ram pressure of a side-wind. We present simulations
of both laboratory and astrophysical curved jets and experimental results from
laboratory experiments. We discuss the properties and similarities of the
laboratory and astrophysical flow, which show the formation of internal shocks
and working surfaces. In particular the results illustrate how the break-up of
the bow-shock and clumps in the flow are produced without invoking jet
variability; we also discuss how jet rotation reduces the growth of the
Rayleigh-Taylor instability in curved jets.Comment: 15 pages, 5 figure, accepted to be published in The Astrophysical
Journa
Asymmetries in the Value of Existence
According to asymmetric comparativism, it is worse for a person to exist with a miserable life than not to exist, but it is not better for a person to exist with a happy life than not to exist. My aim in this paper is to explain how asymmetric comparativism could possibly be true. My account of asymmetric comparativism begins with a different asymmetry, regarding the (dis)value of early death. I offer an account of this early death asymmetry, appealing to the idea of conditional goods, and generalize it to explain how asymmetric comparativism could possibly be true. I also address the objection that asymmetric comparativism has unacceptably antinatalist implications
Three-Dimensional Simulations of Jets from Keplerian Disks: Self--Regulatory Stability
We present the extension of previous two-dimensional simulations of the
time-dependent evolution of non-relativistic outflows from the surface of
Keplerian accretion disks, to three dimensions. The accretion disk itself is
taken to provide a set of fixed boundary conditions for the problem. The 3-D
results are consistent with the theory of steady, axisymmetric, centrifugally
driven disk winds up to the Alfv\'en surface of the outflow. Beyond the
Alfv\'en surface however, the jet in 3-D becomes unstable to non-axisymmetric,
Kelvin-Helmholtz instabilities. We show that jets maintain their long-term
stability through a self-limiting process wherein the average Alfv\'enic Mach
number within the jet is maintained to order unity. This is accomplished in at
least two ways. First, poloidal magnetic field is concentrated along the
central axis of the jet forming a ``backbone'' in which the Alfv\'en speed is
sufficiently high to reduce the average jet Alfv\'enic Mach number to unity.
Second, the onset of higher order Kelvin-Helmholtz ``flute'' modes (m \ge 2)
reduce the efficiency with which the jet material is accelerated, and transfer
kinetic energy of the outflow into the stretched, poloidal field lines of the
distorted jet. This too has the effect of increasing the Alfv\'en speed, and
thus reducing the Alfv\'enic Mach number. The jet is able to survive the onset
of the more destructive m=1 mode in this way. Our simulations also show that
jets can acquire corkscrew, or wobbling types of geometries in this relatively
stable end-state, depending on the nature of the perturbations upon them.
Finally, we suggest that jets go into alternating periods of low and high
activity as the disappearance of unstable modes in the sub-Alfv\'enic regime
enables another cycle of acceleration to super-Alfv\'enic speeds.Comment: 57 pages, 22 figures, submitted to Ap
Well-Being as Harmony
In this paper, I sketch out a novel theory of well-being according to which well-being is constituted by harmony between mind and world. The notion of harmony I develop has three aspects. First there is correspondence between mind and world in the sense that events in the world match the content of our mental states. Second there is positive orientation towards the world, meaning that we have pro-attitudes towards the world we find ourselves in. Third there is fitting response to the world. Taken together these three aspects make up an ideal of being attuned to, or at home in, the world. Such harmony between mind and world constitutes well-being. Its opposite â being disoriented, ill-at-ease in, or hostile to the world â makes a life go poorly. And, as we shall see, many of the things that intuitively contribute to well-being are instantiating one or more of the three aspects of harmony
Landscape configuration, organic management, and within-field position drive functional diversity of spiders and carabids
Abstract Agricultural management intensity and landscape heterogeneity act as the main drivers of biodiversity loss in agricultural landscapes while also determining ecosystem services. The trait-based functional diversity approach offers a way to assess changes in community functionality across agroecosystems. We focused on carabids and spiders, because they are an important component of crop field biodiversity and have significant biological control potential. We assessed the effect of small- vs. large-scale agricultural landscapes, organic farming, and within-field position on functional diversity of spiders and carabids. We sampled pairs of organic and conventional winter wheat fields in small-scale agricultural landscapes (former West Germany) and in neighbouring large-scale agricultural landscapes (former East Germany). We sampled arthropods with funnel traps in transects at field edges, field interiors (15 m from edge), and field centres. The gradient from field edges towards the centres played an important role: spider body size decreased; ballooning ability increased, and hunting strategy switched from active hunters to more web-builders?presumably, due to higher microhabitat stability in the field centre. Higher trait diversity of spiders in field edges suggested higher biocontrol potential in small-scale agriculture. In contrast, carabid feeding switched from herbivores to carnivores, presumably due to higher pest densities inside crop fields. Furthermore, small-scale agricultural landscapes and organic management supported larger, i.e., less dispersive carabids. Synthesis and applications. In our research, spiders were more sensitive to edge effects and less sensitive to management and landscape composition than carabids. Smaller fields and longer edges, as well as organic management increase carabid functional diversity, which may increase resilience to environmental change. Since many spider species are confined to field edges, the effect of within-field position on functional diversity is more important in small-scale agricultural landscapes with more edge habitat than in large-scale agricultural landscapes. Our findings suggest that European Union policy should acknowledge the high benefits of small-scale agriculture for the functional role of major predators such as spiders and carabid beetles, as the benefits are equal to those from a conversion to organic agriculture
Should Research Ethics Encourage the Production of Cost-Effective Interventions?
This project considers whether and how research ethics can contribute to the provision of cost-effective medical interventions. Clinical research ethics represents an underexplored context for the promotion of cost-effectiveness. In particular, although scholars have recently argued that research on less-expensive, less-effective interventions can be ethical, there has been little or no discussion of whether ethical considerations justify curtailing research on more expensive, more effective interventions. Yet considering cost-effectiveness at the research stage can help ensure that scarce resources such as tissue samples or limited subject popula- tions are employed where they do the most good; can support parallel efforts by providers and insurers to promote cost-effectiveness; and can ensure that research has social value and benefits subjects. I discuss and rebut potential objections to the consideration of cost-effectiveness in research, including the difficulty of predicting effectiveness and cost at the research stage, concerns about limitations in cost-effectiveness analysis, and worries about overly limiting researchersâ freedom. I then consider the advantages and disadvantages of having certain participants in the research enterprise, including IRBs, advisory committees, sponsors, investigators, and subjects, consider cost-effectiveness. The project concludes by qualifiedly endorsing the consideration of cost-effectiveness at the research stage. While incorporating cost-effectiveness considerations into the ethical evaluation of human subjects research will not on its own ensure that the health care system realizes cost-effectiveness goals, doing so nonetheless represents an important part of a broader effort to control rising medical costs
Hedonism and the experience machine
Money isnât everything, so what is? Many government leaders, social policy theorists, and members of the general public have a ready answer: happiness. This paper examines an opposing view due to Robert Nozick, which centres on his experience-machine thought experiment. Despite the example's influence among philosophers, the argument behind it is riddled with difficulties. Dropping the example allows us to re-version Nozick's argument in a way that makes it far more forceful - and less dependent on people's often divergent intutions about the experience machine
Ethics and âfrackingâ: A review of (the limited) moral thought on shale gas development
Whilst claims about the ethicality of shale gas development via hydraulic fracturing (âfrackingâ) are commonplace in everyday discourse, little scholarly attention has been afforded explicitly to this aspect of unconventional fossil fuel extraction. The limited research that speaks to ethical considerations largely describes ethical concerns associated with development â extremely few claims in research literature make an ethical case for development. The most common ethical concerns cited in research stem from issues of distributive justice, with procedural justice, the precautionary principle, exposure to involuntary risks, rights-based arguments, and changes in community character and way of life as next most common. Additional research hints implicitly at ethical dilemmas associated with shale gas development, but does not openly identify these issues as having moral implications. Many ethical considerations relate closely to concerns about water quality and the volume/supply of water available for other purposes. The limited scholarship in this area reveals the import of understanding the ways in which ethics permeate thoughts about shale gas development for designing policy that responds to constituent needs and concerns. Even more limited than research on ethical claims in association with shale gas development is well-reasoned scholarship that analyses the extent to which ethical claims about development are well justified and philosophically justifiable. A comprehensive and systematic analysis of the range of ethical claims potentially relevant to shale gas development and their usefulness for informing policy on this topic would contribute greatly to informed decision-making on this controversial issue â something that science alone cannot achieve
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