Horseshoe drag in three-dimensional globally isothermal disks

We study the horseshoe dynamics of a low-mass planet in a three-dimensional, globally isothermal, inviscid disk. We find, as reported in previous work, that the boundaries of the horseshoe region (separatrix sheets) have cylindrical symmetry about the disk´s rotation axis. We interpret this feature as arising from the fact that the whole separatrix sheets have a unique value of Bernoulli´s constant, and that this constant does not depend on altitude, but only on the cylindrical radius, in barotropic disks. We next derive an expression for the torque exerted by the horseshoe region on the planet, or horseshoe drag. Potential vorticity is not materially conserved as in two-dimensional flows, but it obeys a slightly more general conservation law (Ertel´s theorem) that allows an expression for the horseshoe drag identical to the expression in a two-dimensional disk to be obtained. Our results are illustrated and validated by three-dimensional numerical simulations. The horseshoe region is found to be slightly narrower than previously extrapolated from two-dimensional analyses with a suitable softening length of the potential. We discuss the implications of our results for the saturation of the corotation torque, and the possible connection to the flow at the Bondi scale, which the present analysis does not resolve.Fil: Masset, F. S.. Universidad Nacional Autónoma de México; MéxicoFil: Benítez Llambay, Pablo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Astronomía Teórica y Experimental. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de Astronomía Teórica y Experimental; Argentin

FARGO3D: A new GPU-oriented MHD code

We present the FARGO3D code, recently publicly released. It is a magnetohydrodynamics code developed with special emphasis on the physics of protoplanetary disks and planet-disk interactions, and parallelized with MPI. The hydrodynamics algorithms are based on finite-difference upwind, dimensionally split methods. The magnetohydrodynamics algorithms consist of the constrained transport method to preserve the divergence-free property of the magnetic field to machine accuracy, coupled to a method of characteristics for the evaluation of electromotive forces and Lorentz forces. Orbital advection is implemented, and an N-body solver is included to simulate planets or stars interacting with the gas. We present our implementation in detail and present a number of widely known tests for comparison purposes. One strength of FARGO3D is that it can run on either graphical processing units (GPUs) or central processing units (CPUs), achieving large speed-up with respect to CPU cores. We describe our implementation choices, which allow a user with no prior knowledge of GPU programming to develop new routines for CPUs, and have them translated automatically for GPUs.Fil: Benítez Llambay, Pablo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Astronomía Teórica y Experimental. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de Astronomía Teórica y Experimental; ArgentinaFil: Masset, Frédéric S.. Universidad Nacional Autónoma de México; Méxic

Carbon Sinks and Reservoirs: The Value of Permanence and Role of Discounting

Scientists are enthusiastic about storing carbon in terrestrial sinks and geological reservoirs in order to obviate the need for lifestyle-changing reductions in fossil-fuel use. Estimating relative costs of various options depends on how permanence is assessed and whether physical carbon is discounted. We demonstrate that, in carbon markets, terrestrial sinks credits cannot be traded one-for-one for emission reduction credits and the conversion factor would depend on how long sinks keep CO2 out of the atmosphere as compared with emission reductions and, discounting physical carbon. As a result, the authority could not determine a conversion factor and the market would be required to do so.climate change, carbon offset, carbon sinks, discounting physical carbon

Planet heating prevents inward migration of planetary cores

Planetary systems are born in the disks of gas, dust and rocky fragments that surround newly formed stars. Solid content assembles into ever-larger rocky fragments that eventually become planetary embryos. These then continue their growth by accreting leftover material in the disc. Concurrently, tidal effects in the disc cause a radial drift in the embryo orbits, a process known as migration. Fast inward migration is predicted by theory for embryos smaller than three to five Earth masses. With only inward migration, these embryos can only rarely become giant planets located at Earth's distance from the Sun and beyond, in contrast with observations. Here we report that asymmetries in the temperature rise associated with accreting infalling material produce a force (which gives rise to an effect that we call "heating torque") that counteracts inward migration. This provides a channel for the formation of giant planets and also explains the strong planet-metallicity correlation found between the incidence of giant planets and the heavy-element abundance of the host stars.Comment: 19 pages, 4 figure

Long-term and large-scale hydrodynamical simulations of migrating planets

We present a new method that allows long-term and large-scale hydrodynamical simulations of migrating planets over a grid-based Eulerian code. This technique, which consists in a remapping of the disk by tracking the planetary migration, enables runs of migrating planets over a time comparable to the age of protoplanetary disks. This method also has the potential to address efficiently problems related with migration of multi-planet systems in gaseous disks, and to improve current results of migration of massive planets by including global viscous evolution as well as detailed studies of the co-orbital region during migration. We perform different tests using the public code FARGO3D to validate this method and compare its results with those obtained using a classical fixed grid.Comment: Accepted for publication in ApJ. For a movie describing the method, see https://youtu.be/66o0Z2lX8N

Free-form optics for Fresnel-lens-based photovoltaic concentrators

The Concentrated Photovoltaics (CPV) promise relies upon the use of high-efficiency triple-junction solar cells (with proven efficiencies of over 44%) and upon high-performance optics that allow for high concentration concurrent with relaxed manufacturing tolerances (all key elements for low-cost mass production). Additionally, uniform illumination is highly desirable for efficiency and reliability reasons. All of these features have to be achieved with inexpensive optics containing only a few (in general no more than 2) optical elements. In this paper we show that the degrees of freedom using free-forms allow the introduction of multiple functionalities required for CPV with just 2 optical elements, one of which is a Fresnel lens

Conservation Payments under Risk: A Stochastic Dominance Approach

Conservation payments can be used to preserve forest and agroforest systems in developing countries. To explain landowners’ land-use decisions and determine the appropriate conservation payments, it is necessary to focus on risk associated with agricultural price and yield volatility. A theoretical framework is provided for assessing land-use allocation problems under risk and setting risk-efficient conservation payments when returns are not necessary normally distributed. Stochastic dominance rules are used to derive conditions for determining the conservation payments required to guarantee that the environmentally-preferred land use dominates, even when land uses are not considered to be mutually exclusive. An empirical application to shaded-coffee protection in the biologically important El Chocó region of West Ecuador shows that conservation payments required for preserving shaded-coffee areas are much higher than those calculated under the assumption of risk-neutrality. Further, the extant distribution of land has a strong impact on the required conservation payments.risk, conservation payments, land allocation, stochastic dominance, agroforest systems, portfolio diversification

Conservation Payments under Risk: A Stochastic Dominance Approach

Conservation payments can be used to preserve forest and agroforest systems. To explain landowners’ land-use decisions and determine appropriate conservation payments, it is necessary to focus on revenue risk. Marginal conditional stochastic dominance rules are used to derive conditions for determining the conservation payments required to guarantee that the environmentally-preferred land use dominates. An empirical application to shaded-coffee protection in the biologically important Chocó region of West-Ecuador shows that conservation payments required for preserving shaded-coffee areas are much higher than those calculated under risk-neutral assumptions. Further, the extant distribution of land has strong impacts on the required payments.agroforest systems, conservation payments, land allocation, portfolio diversification, risk, stochastic dominance

Desenvolvimento de habilidades condutuais maternas para promover a alfabetização inicial em crianças pré-escolares

The aim of this study was to test the effectiveness of a behavioral program aimed to mothers from low socio-cultural background in order to train them in conducting activities and strategies to promote language and pre-academic skills related to early literacy in their preschool children. The program was carried out focusing on two interactive contexts: joint reading of stories and puppet play. 20 women participated, with limited literacy practices whose preschool children showed low levels in pre-academic and linguistic skills. 10 mothers formed the experimental group, receiving the intervention program and 10 served as control group. There were three testing sessions (pretest, post-test and follow-up) and seven intervention sessions. The program was implemented in a group mode and it used techniques such as oral presentation, group discussion, modeling, role playing, feedback and reinforced practice. Results showed that the program was effective in developing some of the literacy practices in mothers. The main effects were observed in the interactive context of joint reading of stories. The results and limitations of the study are discussed and some recommendations are given for future programs.O objetivo do presente estudo foi provar a efetividade de um programa condutual (oficina) dirigido a mães de família de classe sociocultural baixa, para capacitá-las na realização de atividades e estratégias para promover em seus filhos pré-escolares habilidades linguísticas e pré-acadêmicas relacionadas com a alfabetização inicial. O programa enfocou-se em dois contextos específicos de interação: a leitura conjunta de contos e brincadeiras com marionetes. Participaram 20 mães, com práticas alfabetizadoras limitadas, cujos filhos pré-escolares mostraram poucas habilidades pré-acadêmicas e linguísticas. Dez mãe formaram o Grupo Experimental, recebendo o programa de intervenção e outras dez participaram como Grupo de Controle. Realizaram-se três sessões de avaliação (pré-teste, pós-teste e acompanhamento) e sete sessões de intervenção. O programa foi aplicado de maneira grupal e se utilizaram técnicas de exposição oral, discussão em grupo, modelagem, jogo de papéis, retroalimentação e prática reforçada. Os resultados mostraram que o programa foi eficaz para desenvolver algumas das práticas alfabetizadoras nas mães. Os maiores efeitos foram observados no contexto interativo de leitura conjunta de contos. Discutemse os resultados e limitações do estudo, e se derivam algumas sugestões para programas futuros.El objetivo del presente estudio fue probar la efectividad de un programa conductual (taller) dirigido a madres de familia de estrato sociocultural bajo, para capacitarlas en la realización de actividades y estrategias para promover en sus hijos preescolares habilidades lingüísticas y preacadémicas relacionadas con la alfabetización inicial. El programa se enfocó en dos contextos específicos de interacción: la lectura conjunta de cuentos y el juego con títeres. Participaron 20 madres, con prácticas alfabetizadoras limitadas, cuyos hijos preescolares mostraron pocas habilidades preacadémicas y lingüísticas. Diez madres conformaron el Grupo Experimental, recibiendo el programa de intervención y otras diez fungieron como Grupo Control. Se realizaron tres sesiones de evaluación (pre test, post test y seguimiento) y siete sesiones de intervención. El programa se aplicó de manera grupal y se utilizaron técnicas de exposición oral, discusión en grupo, modelamiento, juego de roles, retroalimentación y práctica reforzada. Los resultados mostraron que el programa fue eficaz para desarrollar algunas de las prácticas alfabetizadoras en las madres. Los mayores efectos se observaron en el contexto interactivo de lectura conjunta de cuentos. Se discuten los resultados y limitaciones del estudio, y se derivan algunas sugerencias para programas futuros