scholarly journals Revisiting migration in a disc cavity to explain the high eccentricities of warm Jupiters

2020 ◽  
Vol 500 (2) ◽  
pp. 1621-1632
Author(s):  
Florian Debras ◽  
Clément Baruteau ◽  
Jean-François Donati
Keyword(s):  
Numerical Simulations ◽  
Working Mechanism ◽  
High Eccentricity ◽  
A Value

ABSTRACT The distribution of eccentricities of warm giant exoplanets is commonly explained through planet–planet interactions, although no physically sound argument favours the ubiquity of such interactions. No simple, generic explanation has been put forward to explain the high mean eccentricity of these planets. In this paper, we revisit a simple, plausible explanation to account for the eccentricities of warm Jupiters: migration inside a cavity in the protoplanetary disc. Such a scenario allows to excite the outer eccentric resonances, a working mechanism for higher mass planets, leading to a growth in the eccentricity while preventing other, closer resonances to damp eccentricity. We test this idea with diverse numerical simulations, which show that the eccentricity of a Jupiter-mass planet around a Sun-like star can increase up to ∼0.4, a value never reached before with solely planet–disc interactions. This high eccentricity is comparable to, if not larger than, the median eccentricity of warm Saturn- to Jupiter-mass exoplanets. We also discuss the effects such a mechanism would have on exoplanet observations. This scenario could have strong consequences on the disc lifetime and the physics of inner disc dispersal, which could be constrained by the eccentricity distribution of gas giants.

scholarly journals Revisiting migration in a disc cavity to explain the high eccentricities of warm Jupiters

2020 ◽  
Author(s):  
Florian Debras ◽  
Clément Baruteau ◽  
Jean-François Donati
Keyword(s):  
Numerical Simulations ◽  
Working Mechanism ◽  
High Eccentricity ◽  
A Value

<p>The distribution of eccentricities of warm giant exoplanets is commonly explained through planet--planet interactions, although no physically sound argument favours the ubiquity of such interactions. No simple, generic explanation has been put forward to explain the high mean eccentricity of these planets.</p> <p>In this talk, I will present a simple, plausible explanation to account for the eccentricities of warm Jupiters: migration inside a cavity in the protoplanetary disc. Such a scenario allows to excite the outer eccentric resonances, a working mechanism for higher mass planets, leading to a growth in the eccentricity while preventing the drag from non-corotating eccentric gas to damp eccentricity. This idea is tested with diverse numerical simulations, which show that the eccentricity of a Jupiter-mass planet around a Sun-like star can increase up and settle to $\sim 0.4$, a value never reached before with solely planet--disc interactions. This high eccentricity is comparable to, if not larger than, the median eccentricity of warm Saturn- to Jupiter-mass exoplanets.</p> <p>I will finally discuss the effects such a scenario would have on observations, notably on the discs lifetime and the physics of inner disc dispersal.</p>

Multi-state voter model on weighted social networks with committed agents

2014 ◽  
Vol 25 (07) ◽  
pp. 1450022 ◽  
Author(s):  
Saijun Chen ◽  
Haibo Hu ◽  
Jun Chen ◽  
Zhigao Chen
Keyword(s):  
Social Networks ◽  
Numerical Simulations ◽  
Opinion Dynamics ◽  
The Other ◽  
Voter Model ◽  
Scaling Exponent ◽  
Dynamics Model ◽  
Topological Structures ◽  
A Value ◽  
Dynamics Models

There exist scaling correlations between the edge weights and the nodes' degrees in weighted social networks. Based on the empirical findings, we study a multi-state voter model on weighted social networks where the weight is given by the product of agents' degrees raised to a power θ and there exist persistent individuals whose opinions are independent of those of their friends. We find that the fraction of each opinion will converge to a value which only relates to the degrees of initial committed agents and the scaling exponent θ. The analytical predictions are verified by numerical simulations. The model indicates that agents' degrees and scaling exponent can significantly influence the final coexistence or consensus state of opinions. We also study the influence of degree mixing characteristics on the dynamics model by numerical simulations and discuss the relation between the model and the other related opinion dynamics models on social networks with different topological structures and initial configurations.

Direct numerical simulations of rotating turbulent channel flow

2008 ◽  
Vol 598 ◽  
pp. 177-199 ◽  
Author(s):  
OLOF GRUNDESTAM ◽  
STEFAN WALLIN ◽  
ARNE V. JOHANSSON
Keyword(s):  
Numerical Simulations ◽  
Channel Flow ◽  
Rotation Number ◽  
Turbulent Channel Flow ◽  
Shear Velocity ◽  
Direct Numerical Simulations ◽  
A Value ◽  
Rotation Numbers ◽  
Wall Shear ◽  
Two Sides

Fully developed rotating turbulent channel flow has been studied, through direct numerical simulations, for the complete range of rotation numbers for which the flow is turbulent. The present investigation suggests that complete flow laminarization occurs at a rotation number Ro = 2Ωδ/Ub ≤ 3.0, where Ω denotes the system rotation, Ub is the mean bulk velocity and δ is the half-width of the channel. Simulations were performed for ten different rotation numbers in the range 0.98 to 2.49 and complemented with earlier simulations (done in our group) for lower values of Ro. The friction Reynolds number Reτ = uτδ/ν (where uτ is the wall-shear velocity and ν is the kinematic viscosity) was chosen as 180 for these simulations. A striking feature of rotating channel flow is the division into a turbulent (unstable) and an almost laminarized (stable) side. The relatively distinct interface between these two regions was found to be maintained by a balance where negative turbulence production plays an important role. The maximum difference in wall-shear stress between the two sides was found to occur for a rotation number of about 0.5. The bulk flow was found to monotonically increase with increasing rotation number and reach a value (for Reτ = 180) at the laminar limit (Ro = 3.0) four times that of the non-rotating case.

Effect of the Circulation Number on the Stratification Coefficient for Solar Heating Systems

1991 ◽  
Vol 113 (4) ◽  
pp. 250-256
Author(s):  
Rajesh N. Dave
Keyword(s):  
Numerical Simulations ◽  
Analytical Model ◽  
General Expression ◽  
Entire Range ◽  
Solar Heating ◽  
Previous Model ◽  
Heating Systems ◽  
A Value ◽  
Air Heating ◽  
Definition Of

The effect of the circulation number (the number of times the entire storage mass is circulated through the system each day) on the stratification coefficient is investigated. An earlier model ignored the effect of the circulation number, assuming that a large value (a value > 2) did not have any effect. In this paper, an analytical model is developed to consider the effect of low circulation number. This model is combined with the previous model and a general expression for the stratification coefficient is developed that is valid for the entire range of circulation number. The extended analytical model is verified through numerical simulations. The results are valid for liquid-based as well as air heating systems. Clarifications are made regarding the definition of the stratification coefficient by introducing a concept of an instantaneous stratification coefficient.

scholarly journals The Obliquity of HIP 67522 b: A 17 Myr Old Transiting Hot, Jupiter-sized Planet

2021 ◽  
Vol 922 (1) ◽  
pp. L1
Author(s):  
Alexis Heitzmann ◽  
George Zhou ◽  
Samuel N. Quinn ◽  
Stephen C. Marsden ◽  
Duncan Wright ◽  
...  
Keyword(s):  
Surface Brightness ◽  
Planet Formation ◽  
Giant Planet ◽  
Young Stars ◽  
Global Model ◽  
High Eccentricity ◽  
A Value ◽  
Special Place ◽  
Migration History ◽  
Formation And Evolution

Abstract HIP 67522 b is a 17 Myr old, close-in (P orb = 6.96 days), Jupiter-sized (R = 10 R ⊕) transiting planet orbiting a Sun-like star in the Sco–Cen OB association. We present our measurement of the system’s projected orbital obliquity via two spectroscopic transit observations using the CHIRON spectroscopic facility. We present a global model that accounts for large surface brightness features typical of such young stars during spectroscopic transit observations. With a value of ∣ λ ∣ = 5.8 − 5.7 + 2.8 ° it is unlikely that this well-aligned system is the result of a high-eccentricity-driven migration history. By being the youngest planet with a known obliquity, HIP 67522 b holds a special place in contributing to our understanding of giant planet formation and evolution. Our analysis shows the feasibility of such measurements for young and very active stars.

scholarly journals Transit and residence times in the surface Adriatic Sea as derived from drifter data and Lagrangian numerical simulations

2013 ◽  
Vol 10 (1) ◽  
pp. 197-217 ◽  
Author(s):  
P.-M. Poulain ◽  
S. Hariri
Keyword(s):  
Numerical Simulations ◽  
Residence Time ◽  
Adriatic Sea ◽  
The Other ◽  
Residence Times ◽  
A Value ◽  
Advection Diffusion ◽  
Surface Circulation ◽  
Long Time ◽  
Adriatic Basin

Abstract. Statistics of transit and residence times in the surface Adriatic Sea, a semi-enclosed basin of the Mediterranean, are estimated from drifter data and Lagrangian numerical simulations. The results obtained from the drifters are generally underestimated given their short operating lifetimes (half life of ~ 40 days) compared to the transit and residence times. This bias can be removed by considering a large amount of numerical particles whose trajectories are integrated over a long time (750 days) with a statistical advection-diffusion model of the Adriatic surface circulation. Numerical particles indicate that the maximum transit time to exit the basin is about 216–260 days for objects released near the northern tip of the Adriatic, and that a particle entering on the eastern Otranto Channel will typically exit on the other side of the Channel after 170–185 days. A value of 150–168 days is estimated for the residence time in the Adriatic basin.

scholarly journals Barrel Instability in Binary Asteroids

2021 ◽  
Vol 2 (6) ◽  
pp. 231
Author(s):  
Matija Ćuk ◽  
Seth A. Jacobson ◽  
Kevin J. Walsh
Keyword(s):  
Numerical Simulations ◽  
Rotational State ◽  
Large Set ◽  
Binary Asteroids ◽  
High Eccentricity ◽  
Earth Asteroid ◽  
Prolate Shape ◽  
Planetary Satellites ◽  
Synchronous Rotation ◽  
Secondary Line

Abstract Most close-in planetary satellites are in synchronous rotation, which is usually the stable end-point of tidal despinning. Saturn’s moon Hyperion is a notable exception by having a chaotic rotation. Hyperion’s dynamical state is a consequence of its high eccentricity and its highly prolate shape. As many binary asteroids also have elongated secondaries, chaotic rotation is expected for moons in eccentric binaries, and a minority of asteroidal secondaries may be in that state. The question of secondary rotation is also important for the action of the binary Yarkovsky–O’Keefe–Radzievskii–Paddack (BYORP) effect, which can quickly evolve orbits of synchronous (but not nonsynchronous) secondaries. Here we report results of a large set of short numerical simulations which indicate that, apart from synchronous and classic chaotic rotation, close-in irregularly shaped asteroidal secondaries can occupy an additional, intermediate rotational state. In this “barrel instability” the secondary slowly rolls along its long axis, while the longest axis is staying largely aligned with the primary–secondary line. This behavior may be more difficult to detect through lightcurves than a fully chaotic rotation, but would likewise shut down BYORP. We show that the binary’s eccentricity, separation measured in secondary’s radii and the secondary’s shape are all important for determining whether the system settles in synchronous rotation, chaotic tumbling, or barrel instability. We compare our results for synthetic asteroids with known binary pairs to determine which of these behaviors may be present in the near-Earth asteroid binary population.

scholarly journals A Magnetic Betelgeuse? Numerical Simulations of Non-Linear Dynamo Action

2004 ◽  
Vol 219 ◽  
pp. 656-660
Author(s):  
S. B. F. Dorch
Keyword(s):  
Magnetic Field ◽  
Numerical Simulations ◽  
Related Question ◽  
Surface Structures ◽  
Irregular Surface ◽  
Linear Regime ◽  
Dynamo Action ◽  
Convective Envelope ◽  
A Value ◽  
Non Linear

Betelgeuse is an example of a cool supergiant displaying brightness fluctuations and irregular surface structures. Simulations by Freytag, Steffen, & Dorch (2002) of the convective envelope of the star have shown that the fluctuations in the star's luminosity may be caused by giant cell convection. A related question regarding the nature of Betelgeuse and supergiants in general is whether these stars may be magnetically active. If so, that may in turn also contribute to their variability. By performing detailed numerical simulations, I find that both linear kinematic and non-linear dynamo action are possible and that the non-linear magnetic field saturates at a value somewhat below equipartition: in the linear regime there are two modes of dynamo action.

Observations of the Thermal Decomposition of Brucite

1968 ◽  
Vol 26 ◽  
pp. 446-447
Author(s):  
P. L. Burnett ◽  
W. R. Mitchell ◽  
C. L. Houck
Keyword(s):  
Thermal Decomposition ◽  
Magnesium Oxide ◽  
Basal Plane ◽  
Magnesium Ions ◽  
A Value ◽  
Reaction Proceeds

Natural Brucite (Mg(OH)2) decomposes on heating to form magnesium oxide (MgO) having its cubic ﹛110﹜ and ﹛111﹜ planes respectively parallel to the prism and basal planes of the hexagonal brucite lattice. Although the crystal-lographic relation between the parent brucite crystal and the resulting mag-nesium oxide crystallites is well known, the exact mechanism by which the reaction proceeds is still a matter of controversy. Goodman described the decomposition as an initial shrinkage in the brucite basal plane allowing magnesium ions to shift their original sites to the required magnesium oxide positions followed by a collapse of the planes along the original <0001> direction of the brucite crystal. He noted that the (110) diffraction spots of brucite immediately shifted to the positions required for the (220) reflections of magnesium oxide. Gordon observed separate diffraction spots for the (110) brucite and (220) magnesium oxide planes. The positions of the (110) and (100) brucite never changed but only diminished in intensity while the (220) planes of magnesium shifted from a value larger than the listed ASTM d spacing to the predicted value as the decomposition progressed.

Field-assisted ionization theory for microscopists

1994 ◽  
Vol 52 ◽  
pp. 820-821
Author(s):  
Patrick P. Camus
Keyword(s):  
Electric Field ◽  
Electron Tunneling ◽  
Ionization Probability ◽  
Critical Distance ◽  
Tunneling Probability ◽  
Field Ionization ◽  
Radius Of Curvature ◽  
Field Evaporation ◽  
A Value ◽  
Ion Emission

The theory of field ion emission is the study of electron tunneling probability enhanced by the application of a high electric field. At subnanometer distances and kilovolt potentials, the probability of tunneling of electrons increases markedly. Field ionization of gas atoms produce atomic resolution images of the surface of the specimen, while field evaporation of surface atoms sections the specimen. Details of emission theory may be found in monographs.Field ionization (FI) is the phenomena whereby an electric field assists in the ionization of gas atoms via tunneling. The tunneling probability is a maximum at a critical distance above the surface,xc, Fig. 1. Energy is required to ionize the gas atom at xc, I, but at a value reduced by the appliedelectric field, xcFe, while energy is recovered by placing the electron in the specimen, φ. The highest ionization probability occurs for those regions on the specimen that have the highest local electric field. Those atoms which protrude from the average surfacehave the smallest radius of curvature, the highest field and therefore produce the highest ionizationprobability and brightest spots on the imaging screen, Fig. 2. This technique is called field ion microscopy (FIM).

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