Steady-state flows in a visco-resistive magnetohydrodynamic model of tokamak plasmas with inhomogeneous heating

The axisymmetric visco-resistive magnetohydrodynamic steady states allowing flows (i.e. non-vanishing velocity fields) are computed for a toroidal JET-like geometry. It is shown that a spatially inhomogeneous heating of moderate magnitude leads to an increase of typical toroidal speeds with respect to the situation with uniform temperature with identical mean Hartmann numbers. A symmetry argument is introduced to capture the symmetry breaking, induced by the temperature gradient, that produces a net toroidal plasma flow.

Psychopaths and Symmetry: A Reply to Nelkin

An agent is morally competent if she can respond to moral considerations. There is a debate about whether agents are open to moral blame only if they are morally competent, and Dana Nelkin’s “Psychopaths, Incorrigible Racists, and the Faces of Responsibility” is an important contribution to this debate. Like others involved in this dispute, Nelkin takes the case of the psychopath to be instructive. This is because psychopaths are similar to responsible agents insofar as they act deliberately and on judgments about reasons, and yet psychopaths lack moral competence. Nelkin argues that, because of their moral incompetence, vices such as cruelty are not attributable to psychopaths. It follows that psychopaths are not open to moral blame since their behavior is only seemingly vicious. I have three aims in this reply to Nelkin. First, I respond to her claim that psychopaths are not capable of cruelty. Second, I respond to the related proposal—embedded in Nelkin’s “symmetry argument”—that a “pro-social psychopath” would not be capable of kindness. My responses to these claims are unified: even if the psychopath is not capable of “cruelty,” and the pro-social psychopath is not capable of “kindness,” the actions of these agents can have a significance for us that properly engages our blaming and praising practices. Finally, I argue that Nelkin’s strategy for showing that moral competence is required for cruelty supports a stronger conclusion than she anticipates: it supports the conclusion that blameworthiness requires not just moral competence, but actual moral understanding.

A note on deterministic updating and van Fraassen’s symmetry argument for conditionalization

In a recent paper, Pettigrew (Philos Stud, 2019. https://doi.org/10.1007/s11098-019-01377-y) argues that the pragmatic and epistemic arguments for Bayesian updating are based on an unwarranted assumption, which he calls deterministic updating, and which says that your updating plan should be deterministic. In that paper, Pettigrew did not consider whether the symmetry arguments due to Hughes and van Fraassen make the same assumption (Hughes and van Fraassen in: Proceedings of the Biennial Meeting of the Philosophy of Science Association. pp. 851–869, 1984; van Fraassen in: Rescher N (ed) Scientific inquiry in philosophical perspective. University Press of America, Lanham, pp. 183–223, 1987). In this note, I show that they do.

Instability of pulses in gradient reaction–diffusion systems: a symplectic approach

In a scalar reaction–diffusion equation, it is known that the stability of a steady state can be determined from the Maslov index, a topological invariant that counts the state’s critical points. In particular, this implies that pulse solutions are unstable. We extend this picture to pulses in reaction–diffusion systems with gradient nonlinearity. In particular, we associate a Maslov index to any asymptotically constant state, generalizing existing definitions of the Maslov index for homoclinic orbits. It is shown that this index equals the number of unstable eigenvalues for the linearized evolution equation. Finally, we use a symmetry argument to show that any pulse solution must have non-zero Maslov index, and hence be unstable. This article is part of the theme issue ‘Stability of nonlinear waves and patterns and related topics’.

Objections to Jeremy Simon’s Response to Lucretius’s Symmetry Argument

The first century B.C. poet Lucretius put forth an argument for why death is not bad for the person who has died. This argument is commonly referred to as Lucretius’s “symmetry argument” because of its assumption that the period before we were born is symmetrical to the period after we die. Jeremy Simon objects to the symmetry argument, claiming that the two periods are not relevantly symmetrical: being born earlier than we actually are born would not guarantee us more life, whereas extending our lifespan past the time we actually would die would guarantee us more life. Simon believes this difference between the two time periods also explains why it is reasonable for people to wish for a later death but not for an earlier birth. We raise several objections to Simon’s response. Our main objection is that insofar as people do not wish for an earlier birth, it is not because they fear losing more life, but rather is a result of being concerned about losing what is important about life, namely its unique content.

Perturbative matching of continuum and lattice quasi-distributions

Matching of the quasi parton distribution functions between continuum and lattice is addressed using lattice perturbation theory specifically withWilson-type fermions. The matching is done for nonlocal quark bilinear operators with a straightWilson line in a spatial direction. We also investigate operator mixing in the renormalization and possible O(a) operators for the nonlocal operators based on a symmetry argument on lattice.