scholarly journals Toward a new paradigm for Type II migration

2018 ◽  
Vol 617 ◽  
pp. A98 ◽  
Author(s):  
C. M. T. Robert ◽  
A. Crida ◽  
E. Lega ◽  
H. Méheut ◽  
A. Morbidelli
Keyword(s):  
Migration Rate ◽  
Giant Planet ◽  
Central Star ◽  
Fundamental Principle ◽  
Type Ii ◽  
New Paradigm ◽  
Low Viscosity ◽  
Accretion Rates ◽  
Gap Opening

Context. Giant planets open gaps in their protoplanetary and subsequently suffer so-called type II migration. Schematically, planets are thought to be tightly locked within their surrounding disks, and forced to follow the viscous advection of gas onto the central star. This fundamental principle, however, has recently been questioned as migrating planets were shown to decouple from the gas’ radial drift. Aims. In this framework, we question whether the traditionally used linear scaling of migration rate of a giant planet with the disk’s viscosity still holds. Additionally, we assess the role of orbit-crossing material as part of the decoupling mechanism. Methods. We have performed 2D (r, θ) numerical simulations of point-mass planets embedded in locally isothermal α-disks in steady-state accretion, with various values of α. Arbitrary planetary accretion rates were used as a means to diminish or nullify orbit-crossing flows. Results. We confirm that the migration rate of a gap-opening planet is indeed proportional to the disk’s viscosity, but is not equal to the gas drift speed in the unperturbed disk. We show that the role of gap-crossing flows is in fact negligible. Conclusions. From these observations, we propose a new paradigm for type II migration: a giant planet feels a torque from the disk that promotes its migration, while the gap profile relative to the planet is restored on a viscous timescale, thus limiting the planet migration rate to be proportional to the disk’s viscosity. Hence, in disks with low viscosity in the planet region, type II migration should still be very slow.

scholarly journals Probing the impact of varied migration and gas accretion rates for the formation of giant planets in the pebble accretion scenario

2020 ◽  
Vol 501 (2) ◽  
pp. 2017-2028
Author(s):  
N Ndugu ◽  
B Bitsch ◽  
A Morbidelli ◽  
A Crida ◽  
E Jurua
Keyword(s):  
Semimajor Axis ◽  
Small Mass ◽  
Type I ◽  
Type Ii ◽  
Water Ice ◽  
Low Viscosity ◽  
Planetary Mass ◽  
Gap Opening ◽  
Gas Accretion ◽  
The Impact

ABSTRACT The final orbital position of growing planets is determined by their migration speed, which is essentially set by the planetary mass. Small mass planets migrate in type-I migration, while more massive planets migrate in type-II migration, which is thought to depend mostly on the viscous evolution rate of the disc. A planet is most vulnerable to inward migration before it reaches type-II migration and can lose a significant fraction of its semimajor axis at this stage. We investigated the influence of different disc viscosities, the dynamical torque, and gas accretion from within the horseshoe region as mechanisms for slowing down planet migration. Our study confirms that planets growing in low viscosity environments migrate less, due to the earlier gap opening and slower type-II migration rate. We find that taking the gas accretion from the horseshoe region into account allows an earlier gap opening and this results in less inward migration of growing planets. Furthermore, this effect increases the planetary mass compared to simulations that do not take the effect of gas accretion from the horseshoe region. Moreover, combining the effect of the dynamical torque with the effect of gas accretion from the horseshoe region, significantly slows down inward migration. Taking these effects into account could allow the formation of cold Jupiters (a > 1 au) closer to the water ice line region compared to previous simulations that did not take these effects into account. We, thus, conclude that gas accretion from within the horseshoe region and the dynamical torque play crucial roles in shaping planetary systems.

scholarly journals THE ROLE OF THE STUDENT TEACHER MUSYAWARAH (MGMP) IN IMPROVING THE UNDERSTANDING OF PKN TEACHERS ABOUT HUMAN RIGHTS (HAM)

2021 ◽  
Vol 5 (02) ◽  
pp. 132
Author(s):  
Aries Abbas ◽  
Marhamah Marhamah
Keyword(s):  
Character Education ◽  
Moral Education ◽  
Fundamental Principle ◽  
Educational Institutions ◽  
New Paradigm ◽  
Learning Program ◽  
National Education ◽  
Children’S Views ◽  
Education Process

Respecting children's views is a fundamental principle that relates to all aspects of the implementation and interpretation of other articles of the convention. Every child's views need to be considered in making decisions that will affect the child's life and development. Factors that can affect the understanding of Civics teachers, the existence of socialization with fellow Civics teachers, the existence of a two-way communication with MGMP members, the existence of shared perceptions in overcoming problematic students, the existence of collaboration when solving problems faced by students and cooperation can be carried out with teachers PAI, counseling teachers, Civics teachers must know or really understand the role and objectives of Civics learning, because Civics subjects have a role in education to develop character development through the role of Civics teachers. In accordance with one of the missions of the new paradigm Civics subject, namely as character education. Civics as one of the subjects that have content in moral education and nationalism, is a subject that is obliged to take part in the character education process through the role of Civics teachers. By applying appropriate teaching methods and supported by all levels of personnel at these educational institutions, Civics teachers can take the initiative to be the driving force for the character learning program. As the output of this Civics learning, there will be a generation with truly quality human resources in accordance with the goals of national education.

scholarly journals Type II migration strikes back – an old paradigm for planet migration in discs

2019 ◽  
Vol 492 (1) ◽  
pp. 1318-1328 ◽  
Author(s):  
Chiara E Scardoni ◽  
Giovanni P Rosotti ◽  
Giuseppe Lodato ◽  
Cathie J Clarke
Keyword(s):  
Initial Conditions ◽  
Giant Planet ◽  
Type Ii ◽  
Standard Type ◽  
Planet Migration ◽  
Theoretical Predictions ◽  
Gap Opening ◽  
Long Time ◽  
Flow Through ◽  
Good Agreement

ABSTRACT In this paper, we analyse giant gap-opening planet migration in proto-planetary discs, focusing on the type II migration regime. According to standard type II theory, planets migrate at the same rate as the gas in the disc, as they are coupled to the disc viscous evolution; however, recent studies questioned this paradigm, suggesting that planets migrate faster than the disc material. We study the problem through 2D long-time simulations of systems consistent with type II regime, using the hydrodynamical grid code fargo3d. Even though our simulations confirm the presence of an initial phase characterized by fast migration, they also reveal that the migration velocity slows down and eventually reaches the theoretical prediction if we allow the system to evolve for enough time. We find the same tendency to evolve towards the theoretical predictions at later times when we analyse the mass flow through the gap and the torques acting on the planet. This transient is related to the initial conditions of our (and previous) simulations, and is due to the fact that the shape of the gap has to adjust to a new profile, once the planet is set into motion. Secondly, we test whether the type II theory expectation that giant planet migration is driven by viscosity is consistent with our simulation by comparing simulations with the same viscosity and different disc masses (or vice versa). We find a good agreement with the theory, since when the discs are characterized by the same viscosity, the migration properties are the same.

scholarly journals Migration of gap-opening planets in 3D stellar-irradiated accretion disks

2020 ◽  
Vol 642 ◽  
pp. A219
Author(s):  
O. Chrenko ◽  
D. Nesvorný
Keyword(s):  
Major Axis ◽  
Temperature Inversion ◽  
Central Star ◽  
Giant Planets ◽  
Type Ii ◽  
Semi Major Axis ◽  
Numerical Studies ◽  
Temperature Excess ◽  
Gap Opening ◽  
Outward Migration

Context. The origin of giant planets at moderate separations ≃1–10 au is still not fully understood because numerical studies of Type II migration in protoplanetary disks often predict a decay of the semi-major axis that is too fast. According to recent 2D simulations, inward migration of a gap-opening planet can be slowed down or even reversed if the outer gap edge becomes heated by irradiation from the central star, and puffed up. Aims. Here, we study how stellar irradiation reduces the disk-driven torque and affects migration in more realistic 3D disks. Methods. Using 3D hydrodynamic simulations with radiation transfer, we investigated the static torque acting on a single gap-opening planet embedded in a passively heated accretion disk. Results. Our simulations confirm that a temperature inversion is established at the irradiated outer gap edge and the local increase of the scale height reduces the magnitude of the negative outer Lindblad torque. However, the temperature excess is smaller than assumed in 2D simulations and the torque reduction only becomes prominent for specific parameters. For the viscosity α = 10−3, the total torque is reduced for planetary masses ranging from 0.1 to 0.7 Jupiter mass, with the strongest reduction being by a factor of − 0.17 (implying outward migration) for a Saturn-mass planet. For a Jupiter-mass planet, the torque reduction becomes stronger with increasing α (the torque is halved when α = 5 × 10−3). Conclusions. We conclude that planets that open moderately wide and deep gaps are subject to the largest torque modifications and their Type II migration can be stalled due to gap edge illumination. We then argue that the torque reduction can help to stabilize the orbits of giant planets forming at ≳ 1 au.

scholarly journals Influence of planetary gas accretion on the shape and depth of gaps in protoplanetary discs

2020 ◽  
Vol 643 ◽  
pp. A133 ◽  
Author(s):  
C. Bergez-Casalou ◽  
B. Bitsch ◽  
A. Pierens ◽  
A. Crida ◽  
S. N. Raymond
Keyword(s):  
Accretion Rate ◽  
High Viscosity ◽  
Giant Planets ◽  
Low Viscosity ◽  
Aspect Ratios ◽  
Accretion Rates ◽  
Gap Opening ◽  
Hydrodynamical Simulations ◽  
Gas Accretion ◽  
Protoplanetary Discs

It is widely known that giant planets have the capacity to open deep gaps in their natal gaseous protoplanetary discs. It is unclear, however, how gas accretion onto growing planets influences the shape and depth of their growing gaps. We performed isothermal hydrodynamical simulations with the Fargo-2D1D code, which assumes planets accreting gas within full discs that range from 0.1 to 260 AU. The gas accretion routine uses a sink cell approach, in which different accretion rates are used to cope with the broad range of gas accretion rates cited in the literature. We find that the planetary gas accretion rate increases for larger disc aspect ratios and greater viscosities. Our main results show that gas accretion has an important impact on the gap-opening mass: we find that when the disc responds slowly to a change in planetary mass (i.e., at low viscosity), the gap-opening mass scales with the planetary accretion rate, with a higher gas accretion rate resulting in a larger gap-opening mass. On the other hand, if the disc response time is short (i.e., at high viscosity), then gas accretion helps the planet carve a deep gap. As a consequence, higher planetary gas accretion rates result in smaller gap-opening masses. Our results have important implications for the derivation of planet masses from disc observations: depending on the planetary gas accretion rate, the derived masses from ALMA observations might be off by up to a factor of two. We discuss the consequences of the change in the gap-opening mass on the evolution of planetary systems based on the example of the grand tack scenario. Planetary gas accretion also impacts stellar gas accretion, where the influence is minimal due to the presence of a gas-accreting planet.

INOVASI PEMBELAJARAN AKIDAH AKHLAK MENGGUNAKAN METODE ROLE PLAY DALAM MENINGKATKAN PRESTASI BELAJAR SISWA

2018 ◽  
Vol 2 (1) ◽  
pp. 52-63
Author(s):  
Ansori Ansori
Keyword(s):  
Data Reduction ◽  
Role Play ◽  
Learning Goals ◽  
New Paradigm ◽  
Learning Materials ◽  
Analysis Technique ◽  
Flexible Schedule ◽  
Using Data ◽  
Real Action

The use of various methods will greatly help students in achieving learning goals. As role play method is one way mastery of learning materials through the development of imagination and appreciation of students on learning materials. Data collection techniques in this study are observation, interviews, and documentation. To analyze the data in this research using data analysis technique of Miles and Huberman model that is data reduction (Data Reduction), data presentation (Data Display) and conclusion (Conclution Drawing / verification) The findings in this research is innovation of role play method can change paradigm to the new paradigm so that the role of the teacher is more as a facilitator, counselor, consultant, and comrade study Flexible schedule, open as needed Learning directed by students themselves Problem-based, project, real world, real action, and reflection Design and investigation. Computers as tools, and dynamic media presentations.

Role of hyperglucagonemia in maintenance of increased rates of hepatic glucose output in type II diabetics

Diabetes ◽  
1987 ◽  
Vol 36 (3) ◽  
pp. 274-283 ◽  
Author(s):  
A. D. Baron ◽  
L. Schaeffer ◽  
P. Shragg ◽  
O. G. Kolterman
Keyword(s):  
Type Ii ◽  
Hepatic Glucose Output ◽  
Hepatic Glucose ◽  
Type Ii Diabetics ◽  
Glucose Output

Role of lipid oxidation in pathogenesis of insulin resistance of obesity and type II diabetes

Diabetes ◽  
1987 ◽  
Vol 36 (11) ◽  
pp. 1341-1350 ◽  
Author(s):  
J. P. Felber ◽  
E. Ferrannini ◽  
A. Golay ◽  
H. U. Meyer ◽  
D. Theibaud ◽  
...  
Keyword(s):  
Insulin Resistance ◽  
Lipid Oxidation ◽  
Type Ii Diabetes ◽  
Type Ii

Hume’s System of Space and Time

2010 ◽  
Vol 13 (1) ◽  
pp. 76-89 ◽  
Author(s):  
Angela M. Coventry
Keyword(s):  
Fundamental Principle ◽  
Space And Time ◽  
The Relationship

Hume’s account of the origin and nature of our ideas of space and time is generally thought to be the least satisfactory part of his empiricist system of philosophy. The main reason is internal in that the account is judged to be inconsistent with Hume’s fundamental principle for the relationship between senses and cognition, the copy principle. This paper defends Hume against the inconsistency objection by offering a new systematic interpretation of Hume on space and time and illuminating more generally the role of the copy principle in his philosophy. Humes Theorie des Wesens und des Ursprungs unserer Vorstellungen von Raum und Zeit wird generell zu den am wenigsten befriedigenden Teilen seiner empiristischen Philosophie gezählt. Der Hauptgrund dafür ist werkimmanent: Die Raum- Zeit-Theorie einerseits und Humes „copy principle“ andererseits – d.h. dasjenige Fundamental-Prinzip, das die Relation zwischen unseren Sinnen und unserem Denken regelt – werden als miteinander inkonsistent erachtet. Dieser Beitrag bietet eine neue, systematische Interpretation der Raum-Zeit-Lehre Humes und eine umfassendere Darstellung der Rolle des „copy principles“ in seiner Philosophie an. Auf diese Weise wird Hume gegen den Vorwurf der Inkonsistenz verteidigt.

Sign in / Sign up

Export Citation Format

Share Document