Characterisation of global flow and local fluctuations in 3D SPH simulations of protoplanetary discs

A complete and detailed knowledge of the structure of the gaseous component in protoplanetary discs is essential to the study of dust evolution during the early phases of pre-planetesimal formation. The aim of this paper is to determine if three-dimensional accretion discs simulated by the Smoothed Particle Hydrodynamics (SPH) method can reproduce the observational data now available and the expected turbulent nature of protoplanetary discs. The investigation is carried out by setting up a suite of diagnostic tools specifically designed to characterise both the global flow and the fluctuations of the gaseous disc. The main result concerns the role of the artificial viscosity implementation in the SPH method: in addition to the already known ability of SPH artificial viscosity to mimic a physical-like viscosity under specific conditions, we show how the same artificial viscosity prescription behaves like an implicit turbulence model. In fact, we identify a threshold for the parameters in the standard artificial viscosity above which SPH disc models present a cascade in the power spectrum of velocity fluctuations, turbulent diffusion and a mass accretion rate of the same order of magnitude as measured in observations. Furthermore, the turbulence properties observed locally in SPH disc models are accompanied by meridional circulation in the global flow of the gas, proving that the two mechanisms can coexist.Comment: Accepted for publication in Monthly Notices of the Royal Astronomical Society. 21 pages, 25 figure

Planet gaps in the dust layer of 3D proto-planetary disks: Observability with ALMA

Among the numerous known extrasolar planets, only a handful have been imaged directly so far, at large orbital radii and in rather evolved systems. The Atacama Large Millimeter/submillimeter Array (ALMA) will have the capacity to observe these wide planetary systems at a younger age, thus bringing a better understanding of the planet formation process. Here we explore the ability of ALMA to detect the gaps carved by planets on wide orbits.Comment: 2 pages, 2 figures, to appear in the Proceedings of IAU Symp. 299: Exploring the Formation and Evolution of Planetary Systems (Victoria, Canada

Growing dust grains in protoplanetary discs - I. Radial drift with toy growth models

In a series of papers, we present a comprehensive analytic study of the global motion of growing dust grains in protoplanetary discs, addressing both the radial drift and the vertical settling of the particles. Here we study how the radial drift of dust particles is affected by grain growth. In a first step, toy models in which grain growth can either be constant, accelerate or decelerate are introduced. The equations of motion are analytically integrable and therefore the grains dynamics is easy to understand. The radial motion of growing grains is governed by the relative efficiency of the growth and migration processes which is expressed by the dimensionless parameter Lambda, as well as the exponents for the gas surface density and temperature profiles, denoted p and q respectively. When Lambda is of order unity, growth and migration are strongly coupled, providing the most efficient radial drift. For the toy models considered, grains pile up when -p+q+1/2<0. Importantly, we show the existence of a second process which can help discs to retain their solid materials. For accelerating growth, grains end up their migration at a finite radius, thus avoiding being accreted onto the central star.Comment: 12 pages, 9 figures. Accepted for publication in MNRAS. v2: typos correcte

WInDI: a Warp-Induced Dust Instability in protoplanetary discs

We identify a new dust instability that occurs in warped discs. The instability is caused by the oscillatory gas motions induced by the warp in the bending wave regime. We first demonstrate the instability using a local 1D (vertical) toy model based on the warped shearing box coordinates and investigate the effects of the warp magnitude and dust Stokes number on the growth of the instability. We then run 3D SPH simulations and show that the instability is manifested globally by producing unique dust structures that do not correspond to gas pressure maxima. The 1D and SPH analysis suggest that the instability grows on dynamical timescales and hence is potentially significant for planet formation.Comment: Accepted for publication in MNRAS, 13 pages, 10 figure

Lichen-spruce woodland early indicators of ecological resilience following silvicultural disturbances in Québec’s closed-crown forest zone

Lichen woodlands (LW) located in the closed-crown boreal forest are not a successional stage moving towards a closed black spruce feathermoss stand (FM), but an alternative stable state, due to their previous forest history, and the occur- rence of LWs located nearby closed-crown FM stands. Therefore, afforestation in those LWs through site preparation and plantation could shift back LW into FM stands. We implemented an experimental design with different combina- tions of silvicultural treatments in both site types (LW, FM). We monitored the evolution of plant diversity and the physiology of three bio-indicators (Picea mariana, Kalmia angustifolia, Rhododendron groenlandicum) in different microsites created by the silvicultural treatments. The return to the initial composition was noticed only two years after treatments, especially in the LW stands, thus indicating a higher level of early ecosystem resilience in LWs compared to FM stands. Mean species cover, especially in the FM stands, decreased the most in the skid trails created by logging, probably due to a lack of acclimation of bryophytes to open stand conditions. Conversely, ericaceous shrubs and lichens found in the LWs were already acclimated to open stand conditions, which give to LWs a restructuring advantage com- pared to FM plant communities after silvicultural treatments. Overall, FM and LW short-term resilience was similar, indicating equally efficient ecosystem reorganization in both stands. The comparable early resilience in managed LW and FM stands, in terms of plant biodiversity, contradicts the presumed fragility of LW stands, especially in this case where LWs are assumed to be an alternative stable state created by compound disturbances. Silvicultural treatments maintained the functional group diversity in LWs, a key element for ecosystem resilience. Therefore, this study support the idea that plantation following site preparation in LWs could be a valuable management strategy to reach several objectives, such as increasing forest carbon sinks

The allocation between EU member states of seats in the European Parliament

This note contains the recommendation for a mathematical basis for the apportionment of the seats in the European Parliament between the Member States of the European Union. This is the unanimous recommendation of the Participants in the Cambridge Apportionment Meeting, held at the instigation of the Committee on Constitutional Affairs at the Centre for Mathematical Sciences, University of Cambridge, on 28–29 January 2011

Análisis participativo de las dinámicas socio-ecológicas en las cabeceras de cuenca de los ríos Cautín y Bio-Bio en Chile

This document presents an analysis of the Lonquimay and the Curacautin landscapes as a socio-ecological system. The two commune areas constitute the Araucarias of Alto Malleco Forest Model in Chile, respective headwaters of the Bio Bio and the Cautin rivers. The first section introduces the analysis, by presenting its context, the issue addressed and the objective of analyzing socio-ecological dynamics. The second section, Material and Methods, tells how the analysis was led in Lonquimay and in Curacautin, presenting the PARDI method (Problem-Actors-Resources-Dynamics-Interactions) and describing the fieldwork for building conceptual models that allow to visualize practices of land use and water management. The third section of the document presents results. They consist in the formulation of the water security problem that the people of Lonquimay and Curacautin considered a central and shared issue; in the characterization and location of actors and resources that are involved in this problem; and in the representation of the main dynamics and interactions that link those actors and resources. For each landscape, two conceptual models were built, from the biophysical and the legal standpoints. The discussion section deals with the possibility to integrate both standpoints; with the mere modelling process, and; with the cost elements of water access. Main uncertainties highlighted by the analysis are revised and the report concludes by summing up our major findings in this participatory investigation process on socio-ecological dynamics.Este documento presenta un análisis de los sistemas socio-ecológicos conformados por las comunas de Lonquimay y de Curacautín del Bosque Modelo Araucarias de Alto Malleco (BMAAM) en Chile, respectivamente las cabeceras de las cuencas del Imperial y del Bio Bio. La primera sección introduce el análisis, presentando su contexto, problemática y objetivo, siempre en el marco del proyecto de investigación-acción EcoAdapt. La segunda sección explica cómo se desarrolló el análisis de las dinámicas socio-ecológicas en las comunas de Lonquimay y de Curacautín. Presenta el método PARDI (Problemática, Actores, Dinámica e Interacciones) y el trabajo de campo realizado para llegar a la construcción de modelos conceptuales que permiten visualizar las prácticas en el uso del suelo y el manejo del agua. La tercera sección presenta los resultados. Incluyen la formulación de una problemática compartida de seguridad hídrica en los dos territorios del BMAAM; la caracterización y ubicación de los actores y recursos que conciernen a la problemática común y la representación de las principales dinámicas e interacciones que vinculan dichos actores y recursos. En cada territorio, se construyeron dos modelos: con enfoque biofísico y con enfoque legal. La sección de discusión reflexiona sobre la posibilidad de integrar ambos enfoques, sobre el proceso de modelación conceptual, y sobre elementos de costos para el acceso al agua. Se revisan las principales incertidumbres vislumbradas en el análisis y la conclusión del informe recapitula los hallazgos de la investigación llevada en un proceso participativo

3D SPH simulations of grain growth in protoplanetary disks

We present the first results of the treatment of grain growth in our 3D, two-fluid (gas+dust) SPH code describing protoplanetary disks. We implement a scheme able to reproduce the variation of grain sizes caused by a variety of physical processes and test it with the analytical expression of grain growth given by Stepinski & Valageas (1997) in simulations of a typical T Tauri disk around a one solar mass star. The results are in agreement with a turbulent growing process and validate the method. We are now able to simulate the grain growth process in a protoplanetary disk given by a more realistic physical description, currently under development. We discuss the implications of the combined effect of grain growth and dust vertical settling and radial migration on subsequent planetesimal formatio