3,215 research outputs found
SPH calculations of Mars-scale collisions: The role of the equation of state, material rheologies, and numerical effects
No full textWe model large-scale (≈ 2000 km) impacts on a Mars-like planet using a Smoothed Particle Hydrodynamics code. The effects of material strength and of using different Equations of State on the post-impact material and temperature distributions are investigated. The properties of the ejected material in terms of escaping and disc mass are analysed as well. We also study potential numerical effects in the context of density discontinuities and rigid body rotation. We find that in the large-scale collision regime considered here (with impact velocities of 4 km/s), the effect of material strength is substantial for the post-impact distribution of the temperature and the impactor material, while the influence of the Equation of State is more subtle and present only at very high temperatures
On the multiple generations of planetary embryos
No full textGlobal models of planet formation tend to begin with an initial set of
planetary embryos for the sake simplicity. While this approach gives valuable
insights on the evolution of the initial embryos, the initial distribution
itself is a bold assumption. Limiting oneself to an initial distribution may
neglect essential physics that precedes, or follows said initial distribution.
We wish to investigate the effect of dynamic planetary embryo formation on the
formation of planetary systems. The presented framework begins with an initial
disk of gas, dust and pebbles. The disk evolution, the formation of
planetesimals and the formation of planetary embryos is modeled consistently.
Embryos then grow by pebble, planetesimal and eventually gas accretion. Planet
disk interactions and N-body dynamics with other simultaneously growing embryos
is included in the framework. We show that the formation of planets can occur
in multiple consecutive phases. Earlier generations grow massive by pebble
accretion but are subject to fast type I migration and thus accretion to the
star. The later generations of embryos that form grow to much smaller masses by
planetesimal accretion, as the amount of pebbles in the disk has vanished. The
formation history of planetary systems may be far more complex than an initial
distribution of embryos could reflect. The dynamic formation of planetary
embryos needs to be considered in global models of planet formation to allow
for a complete picture of the systems evolution.Comment: 12 pages, 9 figures. Accepted for publication in Astronomy &
Astrophysic
Population study on MHD wind-driven disc evolution
No full textContext. Current research has established magnetised disc winds as a promising way of driving accretion in protoplanetary discs.
Aims. We investigate the evolution of large protoplanetary disc populations under the influence of magnetically driven disc winds as well as internal and external photoevaporation. We aim to constrain magnetic disc wind models through comparisons with observations.
Methods. We ran 1D vertically integrated evolutionary simulations for low-viscosity discs, including magnetic braking and various outflows. The initial conditions were varied and chosen to produce populations that are representative of actual disc populations inferred from observations. We then compared the observables from the simulations (e.g. stellar accretion rate, disc mass evolution, disc lifetime, etc.) with observational data.
Results. Our simulations show that to reach stellar accretion rates comparable to those found by observations (~10−8 M⊙ yr−1), it is necessary to have access not only to strong magnetic torques, but weak magnetic winds as well. The presence of a strong magnetic disc wind, in combination with internal photoevaporation, leads to the rapid opening of an inner cavity early on, allowing the stellar accretion rate to drop while the disc is still massive. Furthermore, our model supports the notion that external photoevaporation via the ambient far-ultraviolet radiation of surrounding stars is a driving force in disc evolution and could potentially exert a strong influence on planetary formation.
Conclusions. Our disc population syntheses show that for a subset of magnetohydrodynamic wind models (weak disc wind, strong torque), it is possible to reproduce important statistical observational constraints. The magnetic disc wind paradigm thus represents a novel and appealing alternative to the classical α-viscosity scenario
Planetary population synthesis and the emergence of four classes of planetary system architectures
No full textLa filosofía del derecho de Alexandre Kojève
No full textThis article is a presentation of Alexandre Kojève’s philosophy of law, exposed in his Esquisse d’une phénoménologie du droit (1981). Little attention has been paid to this work. So there is a gap that has to be filled with a critical reflection of its strengths. Among them, undoubtedly, we count the fact that Kojève is introducing a conception of international justice that casts a singular light on current debates about cosmopolitanism and globalization. According to this author, citizenship is the key element of the process of global expansion of the juridical sphere. In sum, Kojève’s philosophy is useful to reflect upon the contrast between the juridical and the political, which is the basis for all philosophy of law, in order to achieve world peace and international justice.Este artículo es una presentación de la filosofía del derecho de Alexandre Kojève contenida en su Esquisse d’une phénoménologie du droit (1981). La poca atención que dicha obra ha recibido es un vacío que debiera llenarse con una reflexión crítica de sus puntos fuertes. Entre ellos destaca una concepción de la justicia internacional que proyecta una luz muy singular sobre los actuales debates en torno a la globalización y el cosmopolitismo. A ojos de este autor, la ciudadanía es el elemento clave para aquilatar la expansión global de lo jurídico. En suma, Kojève aparece como un valioso referente en la labor de pensar la contraposición entre lo jurídico y lo político que está en la base de toda filosofía del derecho, con la aspiración al logro de la justicia internacional y la paz mundial en el horizonte
Effect of pebble flux-regulated planetesimal formation on giant planet formation
No full textContext. The formation of gas giant planets by the accretion of 100 km diameter planetesimals is often thought to be inefficient. A diameter of this size is typical for planetesimals and results from self-gravity. Many models therefore use small kilometer-sized planetesimals, or invoke the accretion of pebbles. Furthermore, models based on planetesimal accretion often use the ad hoc assumption of planetesimals that are distributed radially in a minimum-mass solar-nebula way.Aims. We use a dynamical model for planetesimal formation to investigate the effect of various initial radial density distributions on the resulting planet population. In doing so, we highlight the directive role of the early stages of dust evolution into pebbles and planetesimals in the circumstellar disk on the subsequent planet formation.Methods. We implemented a two-population model for solid evolution and a pebble flux-regulated model for planetesimal formation in our global model for planet population synthesis. This framework was used to study the global effect of planetesimal formation on planet formation. As reference, we compared our dynamically formed planetesimal surface densities with ad hoc set distributions of different radial density slopes of planetesimals.Results. Even though required, it is not the total planetesimal disk mass alone, but the planetesimal surface density slope and subsequently the formation mechanism of planetesimals that enables planetary growth through planetesimal accretion. Highly condensed regions of only 100 km sized planetesimals in the inner regions of circumstellar disks can lead to gas giant growth.Conclusions. Pebble flux-regulated planetesimal formation strongly boosts planet formation even when the planetesimals to be accreted are 100 km in size because it is a highly effective mechanism for creating a steep planetesimal density profile. We find that this leads to the formation of giant planets inside 1 au already by pure 100 km planetesimal accretion. Eventually, adding pebble accretion regulated by pebble flux and planetesimal-based embryo formation as well will further complement this picture.Open access articleThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]
Reconfiguração do consensualismo contratual: as ações tituladas nominativas e os limites à transmissão
No full textPartimos da evolução histórica do consensualismo contratual salientando os
principais carateres que, nos diversos momentos históricos, se foram evidenciando.
Numa segunda etapa exploramos os fundamentos dogmáticos do modelo de
transmissão contratual assumido pelo legislador e a sua viabilidade no sistema
jurídico global, em particular, no direito dos valores mobiliários. Constatamos a
crescente necessidade na prática mercantil e inevitabilidade no sistema jurídico
global da admissibilidade da existência de contratos de compra e venda de natureza
meramente obrigacional. Num terceiro momento desenvolvemos os principais
aspetos do regime jurídico aplicável às ações tituladas nominativas fora do mercado
regulado, em particular, os principais limites à transmissão, enquanto instrumentos/barreiras ao consensualismo contratual.We start from the historical evolution of contractual consensualism emphasizing the
main aspects that, in different historical moments, were showing up. In a second
stage we explore the dogmatic foundations of the transmission model contractual
assumed by the legislator and its viability in the global legal system, in particular, in
securities law. We note the growing need in commercial practice and inevitability in
the global legal system the admissibility of the existence of contracts of sale purely
obligatory. In the third stage we develop the main aspects of the legal regime
applicable to nominative titled actions outside the regulated market, in particular,
the main limits to the transmission, as instruments / barriers to contractual
consensualism
RV-detected planets around M dwarfs: Challenges for core accretion models
No full textPlanet formation is sensitive to the conditions in protoplanetary disks, for
which scaling laws as a function of stellar mass are known. We aim to test
whether the observed population of planets around low-mass stars can be
explained by these trends, or if separate formation channels are needed.
We address this question by confronting a state-of-the-art planet population
synthesis model with a sample of planets around M dwarfs observed by the HARPS
and CARMENES radial velocity (RV) surveys. To account for detection biases, we
performed injection and retrieval experiments on the actual RV data to produce
synthetic observations of planets that we simulated following the core
accretion paradigm.
These simulations robustly yield the previously reported high occurrence of
rocky planets around M dwarfs and generally agree with their planetary mass
function. In contrast, our simulations cannot reproduce a population of giant
planets around stars less massive than 0.5 solar masses. This potentially
indicates an alternative formation channel for giant planets around the least
massive stars that cannot be explained with current core accretion theories. We
further find a stellar mass dependency in the detection rate of short-period
planets. A lack of close-in planets around the earlier-type stars () in our sample remains unexplained by our model and
indicates dissimilar planet migration barriers in disks of different spectral
subtypes.
Both discrepancies can be attributed to gaps in our understanding of planet
migration in nascent M dwarf systems. They underline the different conditions
around young stars of different spectral subtypes, and the importance of taking
these differences into account when studying planet formation.Comment: Accepted for publication in A&A. 19 pages, 9 figure
“Era por Alexandre tod’esto demostrado”: ¿pruebas verídicas y pruebas engañosas en el Libro de Alexandre?
No full textEl Libro de Alexandre es un texto de s. XIII, que se escribió en la España medieval. En este escrito, el autor pretende demostrar que, en el Alexandre, algunas de las situaciones que se ponen a prueba son aceptadas, pero eso no significa que el macedonio gane la prueba. El articulo esta dividido en tres apartados. En el primero, el autor da cuenta de la historia textual de la obra y también dedica ciertas líneas al Estado de la cuestión del texto; mientras que, en la segunda parte, nos guía a conceptos etimológicos de los términos prueba, evidencia y demás. En el tercer apartado se centra en algunas pruebas expuestas en el Libro de Alexandre.The Libro de Alexandre is a literary work, written during the medieval Spain. In this paper, the author tries to demonstrate that, carefully reading the L.A, some of the situations that are set as proves are accepted, but it does not mean that Alexander can be a victor. This paper is divided in three sections: firstly, the author tells the textual history of the L.A and, then, tries to update the State of art: on the other hand, in the second part, the author offers meanings about terms as: prueba and evidencia. Finally, the author focuses on certain passages contained in the Libro de Alexandre that can be taken as failed proves
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