On vertical variations of gas flow in protoplanetary disks and their impact on the transport of solids

A major uncertainty in accretion disk theory is the nature and properties of gas turbulence, which drives transport in protoplanetary disks. The commonly used viscous prescription for the Maxwell-Reynolds stress tensor gives rise to a meridional circulation where flow is outward near the midplane and inward away from it. This meridional circulation has been proposed as an explanation for the presence of high-temperature minerals (believed to be of inner solar system provenance) in comets. However, it has not been observed in simulations of magnetohydrodynamical (MHD) turbulence so far. In this study, we evaluate the extent to which the net transport of solids can be diagnostic of the existence of meridional circulation. To that end, we propose and motivate a prescription for MHD turbulence which has the same free parameters as the viscous one. We compare the effects of both prescriptions on the radial transport of small solid particles and find that their net, vertically integrated radial flux is actually quite insensitive to the flow structure for a given vertical average of the turbulence parameter $\alpha$, which we explain. Given current uncertainties on disk turbulence, one-dimensional models are thus most appropriate to investigate radial transport of solids. A corollary is that the presence of high-temperature material in comets cannot be considered an unequivocal diagnostic of meridional circulation. In fact, we argue that outward transport in viscous disk models is more properly attributed to turbulent diffusion rather than to the mean flows of the gas.Comment: 8 pages, 4 figures, accepted to Astronomy and Astrophysic

Optimal disability assistance when fraud and stigma matter

I study the optimal redistributive structure when individuals with distinct productivities also differ in disutility of work due to either disability or distaste for work. Taxpayers have resentment against inactive benefit recipients because some of them are not actually disabled but lazy. Therefore disabled people who take up transfers are stigmatized. Their stigma disutility increases with the number of non-disabled recipients. Tagging transfers according to disability characteristics decreases stigma. However, tagging is costly and imperfect. In this context, I show how the level of the per capita cost of monitoring relative to labour earnings of low-wage workers determines the optimality of tagging. Under mild conditions, despite their stigma disutility, inactive and disabled people get a strictly lower consumption than low-wage workers. The results are valid under a utilitarian criterion and a criterion which does not compensate for distaste for work.Tagging, Disability benefit, Fraud, Stigma

Take it or Leave it: Take-up, Optimal Transfer Programs, and Monitoring

This paper studies the optimal income redistribution and optimal monitoring when disability benefits are intended for disabled people but when some able agents with high distaste for work mimic them (type II errors). Labor supply responses are at the extensive margin and endogenous take-up costs may burden disabled recipients (because of either a reputational externality caused by cheaters or a snowball effect). Under paternalistic utilitarian preferences that do not compensate for distaste for work, inactive disabled recipients should obtain strictly lower consumption than disabled workers. The cost of monitoring supports adoption of an Earned Income Tax Credit. However, and surprisingly, with or without take-up costs, even if perfect monitoring is costless, it proves optimal to have type II errors. These results are robust to a utilitarian criterion. The paper provides numerical simulations calibrated on U.S. data.optimal income taxation, tagging, take-up, extensive margin

Optimal disability assistance when fraud and stigma matter

I study the optimal redistributive structure when individuals with distinct productivities also differ in disutility of work due to either disability or distase for work. Taxpayers have resentment against inactive benefit recipients because some of them are not actually disabled but lazy. Therefore, disabled people who take up transfers are stigmatized. Their stigma disutility increases with the number of non-disabled recipients. Tagging transfers according to disability characteristics decreases stigme. However, tagging is costly and imperfect. In this context, I show how the level of the per capital cost of monitoring relative to labor earnings of low-wage workers determines the optimality of tagging. Under mild conditions, despite their stigma disutility, inactive and disabled people get a strictly lower consumption than low-wage workers. The results are valid under a utilitarian criterion and a criterion which does not compensage for distate for work.Tagging, Disability, Benefit, Fraud, Stigma