Early evolution of clumps formed via gravitational instability in protoplanetary disks; precursors of Hot Jupiters?

Although it is fairly established that Gravitational Instability (GI) should occur in the early phases of the evolution of a protoplanetary disk, the fate of the clumps resulting from disk fragmentation and their role in planet formation is still unclear. In the present study we investigate semi-analytically their evolution following the contraction of a synthetic population of clumps with varied initial structure and orbits coupled with the surrounding disk and the central star. Our model is based on recently published state-of-the-art 3D collapse simulations of clumps with varied thermodynamics. Various evolutionary mechanisms are taken into account, and their effect is explored both individually and in combination with others: migration and tidal disruption, mass accretion, gap opening and disk viscosity. It is found that, in general, at least 50% of the initial clumps survive tides, leaving behind potential gas giant progenitors after ~10^5 yr of evolution in the disk. The rest might be either disrupted or produce super-Earths and other low mass planets provided that a solid core can be assembled on a sufficiently short timescale, a possibility that we do not address in this paper. Extrapolating to million year timescales, all our surviving protoplanets would lead to close-in gas giants. This outcome might in part reflect the limitations of the migration model adopted, and is reminiscent of the analogous result found in core-accretion models in absence of fine-tuning of the migration rate. Yet it suggests that a significant fraction of the clumps formed by gravitational instability could be the precursors of Hot Jupiters

Large grains can grow in circumstellar discs

We perform coagulation & fragmentation simulations to understand grain growth in T Tauri & brown dwarf discs. We present a physically-motivated approach using a probability distribution function for the collision velocities and separating the deterministic & stochastic velocities. We find growth to larger sizes compared to other models. Furthermore, if brown dwarf discs are scaled-down versions of T Tauri discs (in terms of stellar & disc mass, and disc radius), growth at the same location with respect to the outer edge occurs to similar sizes in both discs.Comment: Submitted to the conference proceedings of the IAU Symposium 299 - Exploring the formation and evolution of planetary systems. 2 pages; 2 figure

Large grains can grow in circumstellar discs

We perform coagulation & fragmentation simulations to understand grain growth in T Tauri & brown dwarf discs. We present a physically-motivated approach using a probability distribution function for the collision velocities and separating the deterministic & stochastic velocities. We find growth to larger sizes compared to other models. Furthermore, if brown dwarf discs are scaled-down versions of T Tauri discs (in terms of stellar & disc mass, and disc radius), growth at the same location with respect to the outer edge occurs to similar sizes in both disc

From dust to planetesimals: an improved model for collisional growth in protoplanetary disks

Planet formation occurs within the gas and dust rich environments of protoplanetary disks. Observations of these objects show that the growth of primordial sub micron sized particles into larger aggregates occurs at the earliest stages of the disks. However, theoretical models of particle growth that use the Smoluchowski equation to describe collisional coagulation and fragmentation have so far failed to produce large particles while maintaining a significant populations of small grains. This has been generally attributed to the existence of two barriers impeding growth due to bouncing and fragmentation of colliding particles. In this paper, we demonstrate that the importance of these barriers has been artificially inflated through the use of simplified models that do not take into account the stochastic nature of the particle motions within the gas disk. We present a new approach in which the relative velocities between two particles is described by a probability distribution function that models both deterministic motion and stochastic motion. Taking both into account can give quite different results to what has been considered recently in other studies. We demonstrate the vital effect of two "ingredients" for particle growth: the proper implementation of a velocity distribution function that overcomes the bouncing barrier and, in combination with mass transfer in high-mass-ratio collisions, boosts the growth of larger particles beyond the fragmentation barrier. A robust result of our simulations is the emergence of two particle populations (small and large), potentially explaining simultaneously a number of long-standing problems in protoplanetary disks, including planetesimal formation close to the central star, the presence of mm to cm size particles far out in the disk, and the persistence of micron-size grains for millions of years.Comment: Accepted for publication in ApJ. Additional appendix included. Minor changes from previous versions. 46 pages, 10 figure

DIAGNÓSTICOS EM PATOLOGIA VETERINÁRIA DE ANIMAIS DOMÉSTICOS ENCAMINHADOS AO INSTITUTO FEDERAL CATARINENSE CÂMPUS CONCÓRDIA

A produção animal apresenta participação significativa na economia catarinense. A região Oeste de Santa Catarina é a maior produtora de suínos, aves e bovinos de leite, assim como tem boa expressão na produção de bovinos de corte e pequenos ruminantes (IBGE, 2011). No entanto, a falta de conhecimento técnico-científico, aliado à carência de controle sanitário desses rebanhos, muitas vezes tem levado à diminuição da eficiência produtiva. O desconhecimento das enfermidades que afetam os rebanhos dificulta a tomada de decisões baseadas no controle e prevenção das enfermidades (RIET-CORREA et al., 2007)

Improving the grain growth model in the outer part of circumstellar disks

Observations of T-Tauri circumstellar discs show the presence of mm or cm size dust grains at large distances from the central star (r > 10s AU). There empirical data challenge the currently mainstream grain growth theory, that disfavours the formation of such large grains in the outer disc and, despite formation, predicts their rapid inward migration due to coupling with the gas on short timescales. In this work, we develop some improvements in the grain growth theory and implement them in GrOG (Growth Of Grains), a new numerical solver for the coagulation and fragmentation of grains inside a circumstellar disc. Our results revise conclusions from previous theoretical models, as we are able to growth particles of significantly larger size

Improving the grain growth model in the outer part of circumstellar disks

Observations of T-Tauri circumstellar discs show the presence of mm or cm size dust grains at large distances from the central star (r > 10s AU). There empirical data challenge the currently mainstream grain growth theory, that disfavours the formation of such large grains in the outer disc and, despite formation, predicts their rapid inward migration due to coupling with the gas on short timescales. In this work, we develop some improvements in the grain growth theory and implement them in GrOG (Growth Of Grains), a new numerical solver for the coagulation and fragmentation of grains inside a circumstellar disc. Our results revise conclusions from previous theoretical models, as we are able to growth particles of significantly larger size

Vascular endothelial growth factor receptor-3 activity is modulated by its association with caveolin-1 on endothelial membrane.

Vascular endothelial growth factor receptor-3 (VEGFR-3) is constitutively expressed in lymphatic vessels and transiently in endothelial cells of blood vessels during angiogenesis. Here we report that VEGFR-3 localizes in the caveolae membrane of endothelial cells and co-immunoprecipitates with caveolin-1. Caveolin-1 silencing or its depletion from the cell membrane by cholesterol increases VEGFR-3 autophosphorylation, suggesting that caveolin acts as a negative regulator of VEGFR-3 activity. Receptor activation induces caveolin-1 phosphorylation on tyrosine residues including tyrosine 14. Cell treatment with Src or Abl inhibitors PP2 or STI571, prior to receptor stimulation, affects caveolin-1 phosphorylation without affecting receptor autophosphorylation, suggesting that both Src and Abl are involved in VEGFR-3-dependent caveolin-1 phosphorylation. Caveolin-1 phosphorylation in Src/Fyn/Yes knockout cells demonstrated that Abl phosphorylates caveolin-1 independently from Src family members. These results suggest a functional interaction between VEGFR-3 and caveolin-1 to modulate endothelial cell activation during angiogenesis