scholarly journals Explaining the low luminosity of Uranus: a self-consistent thermal and structural evolution

2020 ◽  
Vol 633 ◽  
pp. A50 ◽  
Author(s):  
Allona Vazan ◽  
Ravit Helled
Keyword(s):  
Energy Content ◽  
Structural Evolution ◽  
Initial Energy ◽  
Planetary Science ◽  
Composition Gradient ◽  
Internal Cooling ◽  
Composition Distribution ◽  
Convective Mixing ◽  
Deep Interior ◽  
Composition Gradients

The low luminosity of Uranus is a long-standing challenge in planetary science. Simple adiabatic models are inconsistent with the measured luminosity, which indicates that Uranus is non-adiabatic because it has thermal boundary layers and/or conductive regions. A gradual composition distribution acts as a thermal boundary to suppress convection and slow down the internal cooling. Here we investigate whether composition gradients in the deep interior of Uranus can explain its low luminosity, the required composition gradient, and whether it is stable for convective mixing on a timescale of some billion years. We varied the primordial composition distribution and the initial energy budget of the planet, and chose the models that fit the currently measured properties (radius, luminosity, and moment of inertia) of Uranus. We present several alternative non-adiabatic internal structures that fit the Uranus measurements. We found that convective mixing is limited to the interior of Uranus, and a composition gradient is stable and sufficient to explain its current luminosity. As a result, the interior of Uranus might still be very hot, in spite of its low luminosity. The stable composition gradient also indicates that the current internal structure of Uranus is similar to its primordial structure. Moreover, we suggest that the initial energy content of Uranus cannot be greater than 20% of its formation (accretion) energy. We also find that an interior with a mixture of ice and rock, rather than separated ice and rock shells, is consistent with measurements, suggesting that Uranus might not be “differentiated”. Our models can explain the luminosity of Uranus, and they are also consistent with its metal-rich atmosphere and with the predictions for the location where its magnetic field is generated.

scholarly journals Jupiter’s evolution with primordial composition gradients

2018 ◽  
Vol 610 ◽  
pp. L14 ◽  
Author(s):  
Allona Vazan ◽  
Ravit Helled ◽  
Tristan Guillot
Keyword(s):  
Heavy Element ◽  
Bulk Composition ◽  
Outer Part ◽  
Early Evolution ◽  
Composition Gradient ◽  
Outer Envelope ◽  
Deep Interior ◽  
Higher Temperature ◽  
The One ◽  
Composition Gradients

Recent formation and structure models of Jupiter suggest that the planet can have composition gradients and not be fully convective (adiabatic). This possibility directly affects our understanding of Jupiter’s bulk composition and origin. In this Letter we present Jupiter’s evolution with a primordial structure consisting of a relatively steep heavy-element gradient of 40 M⊕. We show that for a primordial structure with composition gradients, most of the mixing occurs in the outer part of the gradient during the early evolution (several 107 yr), leading to an adiabatic outer envelope (60% of Jupiter’s mass). We find that the composition gradient in the deep interior persists, suggesting that ~40% of Jupiter’s mass can be non-adiabatic with a higher temperature than the one derived from Jupiter’s atmospheric properties. The region that can potentially develop layered convection in Jupiter today is estimated to be limited to ~10% of the mass.

Probing Convective Mixing in Stellar Interiors with α Centauri A and B

2017 ◽  
Vol 14 (S339) ◽  
pp. 308-308
Author(s):  
M. Joyce ◽  
B. Chaboyer
Keyword(s):  
Optical Observations ◽  
Frequency Separation ◽  
Composition Gradient ◽  
Small Frequency ◽  
Convective Mixing ◽  
Important Constraint ◽  
The Mean ◽  
Stellar Interiors ◽  
Large Frequency ◽  
Better Than

AbstractThe bright nearby binary α Centauri constitutes an excellent laboratory for testing stellar evolution models. The mass, radius, and luminosity of α Cen A and B are known to better than 1% accuracy thanks to recent interferometric and adaptive optical observations, and p-mode oscillations have been observed in both stars. We present new stellar models which fit simultaneously the classical and seismic observations, with particular emphasis on the convective mixing length parameter MLT – the adaptivity of which is necessary to fit the models to observations. The oscillation data provide an important constraint on the models, as the small frequency separation is sensitive to the composition gradient in the core of the stars, while the large frequency separation constrains the mean density of the stars, providing an independent check on the mass and radius.

scholarly journals Magnetically driven jets and winds from weakly magnetized accretion discs

2019 ◽  
Vol 490 (3) ◽  
pp. 3112-3133 ◽  
Author(s):  
J Jacquemin-Ide ◽  
J Ferreira ◽  
G Lesur
Keyword(s):  
Numerical Simulations ◽  
Energy Content ◽  
Initial Energy ◽  
Accretion Discs ◽  
Analytical Models ◽  
Magnetorotational Instability ◽  
New Class ◽  
Analytical Criterion ◽  
First Time

Abstract Semi-analytical models of disc outflows have successfully described magnetically driven, self-confined super-Alfvénic jets from near-Keplerian accretion discs. These jet-emitting discs (JEDs) are possible for high levels of disc magnetization μ defined as μ = 2/β, where beta is the usual plasma parameter. In near-equipartition JEDs, accretion is supersonic and jets carry away most of the disc angular momentum. However, these solutions prove difficult to compare with cutting-edge numerical simulations, for the reason that numerical simulations show wind-like outflows but in the domain of small magnetization. In this work, we present for the first time self-similar isothermal solutions for accretion–ejection structures at small magnetization levels. We elucidate the role of magnetorotational instability-like (MRI) structures in the acceleration processes that drive this new class of solutions. The disc magnetization μ is the main control parameter: Massive outflows driven by the pressure of the toroidal magnetic field are obtained up to μ ∼ 10−2, while more tenuous centrifugally driven outflows are obtained at larger μ values. The generalized parameter space and the astrophysical consequences are discussed. We believe that these new solutions could be a stepping stone in understanding the way astrophysical discs drive either winds or jets. Defining jets as self-confined outflows and winds as uncollimated outflows, we propose a simple analytical criterion based on the initial energy content of the outflow, to discriminate jets from winds. We show that jet solution is achieved at all magnetization levels, while winds could be obtained only in weakly magnetized discs that feature heating.

The utilization of the dietary energy of pangola and setaria by young growing beef cattle

1982 ◽  
Vol 98 (2) ◽  
pp. 395-404 ◽  
Author(s):  
G. D. Tudor ◽  
D. J. Minson
Keyword(s):  
Protein Content ◽  
Dry Matter ◽  
Production Systems ◽  
Energy Content ◽  
Live Weight ◽  
Initial Energy ◽  
Metabolizable Energy ◽  
Net Energy ◽  
Lower Efficiency ◽  
Tropical Grasses

SUMMARYThe net energy values for growth and fattening of two artificially dried tropical grasses-, pangola (Digitaria decumbens) and setaria (S. sphacelata var. sericea cv. Nandi), of similar estimated metabolizable energy content (8·07 and 7·96 MJ/kg D.M.) were determined with cattle using a slaughter technique. Growing cattle with a mean initial weight of 175 kg were given equal quantities of dry matter of the two grasses at each of three planes of nutrition above maintenance for a period of 152 days.The initial energy, fat and protein content of the total body of the 24 test animals was estimated from regressions relating fasted live weight to theśe components, derived from 12 similar cattle slaughtered at the beginning of the feeding period. The final energy, fat and protein content of the test animals was determined directly by chemical analysis. The metabolizable energy (ME) content of the grasses was estimated from the level of digestible energy (DE) determined with eight cattle, assuming that ME = 0·815 DE.The cattle fed pangola gained more live weight, empty-body weight, fat, protein and energy than animals fed similar quantities of setaria. The net energy value for growth and fattening (NEf) was determined using regressions relating energy retention to the quantity of dry matter eaten. NEf in MJ/kg dry matter was 2·27 for pangola and 1·31 for setaria.Efficiency of utilization of ME for growth and fattening (kf) was.27·7% for pangola and 16·9% for setaria. These values for tropical grasses are lower than any values reported for temperate pasture species. Thus the lower efficiency of utilization of ME may cause the lower production of cattle which graze tropical grasses.It was concluded that as the kf values of different tropical grasses are not constant, kf values should be measured on a wider range of tropical grasses so that this factor can be taken into account when evaluating grasses in animal production systems.

scholarly journals Control of Lateral Composition Distribution in Graded Films of Soluble Solid Systems A1−xBx by Partitioned Dual-Beam Pulsed Laser Deposition

Coatings ◽  
2020 ◽  
Vol 10 (6) ◽  
pp. 540
Author(s):  
Joe Sakai ◽  
José Manuel Caicedo Roque ◽  
Pablo Vales-Castro ◽  
Jessica Padilla-Pantoja ◽  
Guillaume Sauthier ◽  
...  
Keyword(s):  
Pulsed Laser Deposition ◽  
Ambient Pressure ◽  
Thickness Distribution ◽  
Pulsed Laser ◽  
Laser Deposition ◽  
Composition Gradient ◽  
Composition Distribution ◽  
Dual Beam ◽  
Soluble Solid ◽  
Characteristic Features

Lateral compositionally-graded thin films are powerful media for the observation of phase boundaries as well as for high-throughput materials exploration. We herein propose a method to prepare epitaxial lateral compositionally-graded films using a dual-beam pulsed laser deposition (PLD) method with two targets separated by a partition. Tuning the ambient pressure and the partition—substrate gap makes it possible to control of the gradient length of the deposits at the small sizes (≤ 10 mm) suitable for commercial oxide single crystal substrates. A simple Monte Carlo simulation qualitatively reproduced the characteristic features of the lateral thickness distribution. To demonstrate this method, we prepared (1−x)PbTiO3—xPbZrO3 and (1−x)LaMnO3—xLa0.6Sr0.4MnO3 films with lateral composition gradient widths of 10 and 1 mm, respectively, with the partitioned dual PLD.

scholarly journals Bowen–York model solution redux

2021 ◽  
Vol 81 (4) ◽  
Author(s):  
Emel Altas ◽  
Bayram Tekin
Keyword(s):  
Energy Content ◽  
Analytical Form ◽  
Initial Energy ◽  
Model Solution ◽  
Linear Momentum ◽  
Hamiltonian Constraint ◽  
Initial Value ◽  
Relativistic Case ◽  
Stationary Part ◽  
Dynamical Time

AbstractInitial value problem in general relativity is often solved numerically; with only a few exceptions one of which is the “model” solution of Bowen and York where an analytical form of the solution is available. The solution describes a dynamical, time-asymmetric, gravitating system with mass and linear momentum. Here we revisit this solution and correct an error which turns out to be important for identifying the energy-content of the solution. Depending on the linear momentum, the ratio of the non-stationary part of the initial energy to the total ADM energy takes values between [0, 0.592). This non-stationary part is expected to be turned into gravitational waves during the evolution of the system to possibly settle down to a black hole with mass and linear momentum. In the ultra-relativistic case (the high momentum limit), the maximum amount of gravitational wave energy is 59.2% of the total ADM energy. We also give a detailed account of the general solution of the Hamiltonian constraint.

scholarly journals The challenge of forming a fuzzy core in Jupiter

2020 ◽  
Vol 638 ◽  
pp. A121 ◽  
Author(s):  
Simon Müller ◽  
Ravit Helled ◽  
Andrew Cumming
Keyword(s):  
Gravity Data ◽  
Heavy Elements ◽  
Material Transport ◽  
Current State ◽  
Deep Interior ◽  
Fuzzy Core ◽  
Gas Accretion ◽  
Composition Gradients ◽  
Gaseous Envelope

Recent structure models of Jupiter that match Juno gravity data suggest that the planet harbours an extended region in its deep interior that is enriched with heavy elements: a so-called dilute or fuzzy core. This finding raises the question of what possible formation pathways could have lead to such a structure. We modelled Jupiter’s formation and long-term evolution, starting at late-stage formation before runaway gas accretion. The formation scenarios we considered include both primordial composition gradients, as well as gradients that are built as proto-Jupiter rapidly acquires its gaseous envelope. We then followed Jupiter’s evolution as it cools down and contracts, with a particular focus on the energy and material transport in the interior. We find that none of the scenarios we consider lead to a fuzzy core that is compatible with interior structure models. In all the cases, most of Jupiter’s envelope becomes convective and fully mixed after a few million years at most. This is true even when we considered a case where the gas accretion leads to a cold planet, and large amounts of heavy elements are accreted. We therefore conclude that it is very challenging to explain Jupiter’s dilute core from standard formation models. We suggest that future works should consider more complex formation pathways as well as the modelling of additional physical processes that could lead to Jupiter’s current-state internal structure.

scholarly journals Energy and protein nutrition of early-weaned pigs. 1. effect of energy intake and energy: protein on growth, efficiency and nitrogen utilization of pigs between 8–32 d

1980 ◽  
Vol 43 (2) ◽  
pp. 289-304 ◽  
Author(s):  
K. J. McCracken ◽  
S. M. Eddie ◽  
W. G. Stevenson
Keyword(s):  
Least Squares Method ◽  
Energy Content ◽  
Skim Milk ◽  
Nitrogen Retention ◽  
Growth Efficiency ◽  
Initial Energy ◽  
Feed Conversion ◽  
Response Curves ◽  
Protein Levels ◽  
Rate Of Increase

1. The effect of energy and protein intake on the growth, food efficiency and nitrogen retention of artificially-reared pigs was studied over three 8 d periods between 8–32 d of age in an experiment employing a 5×3×2 factorial design. The factors were initial energy: N value (I; 250, 355, 460, 565 or 670 kJ/g N), rate of increase of 1 at 8 d intervals (0, 12.5 or 25%) and plane of nutrition (three times daily to appetite or 75% of this intake).2. The range of energy: N values was obtained by formulating five diets based on dried skim milk, lactose and casein and feeding appropriate combinations of two diets. The diets, which were pelleted, contained 100 g maize oil/kg and the gross energy content was approximately 20 MJ/kg.3. N digestibility was high at all three age intervals, reaching 0.99 on the diet containing the highest dietary crude protein (N × 6.25) level. Metabolic faecal N excretion was found to be 1.1 g/kg dry matter (DM) intake.4. Growth rate, feed conversion ratio (kg food intake/kg wt gain; FCR), N retention (NR) and the proportion of digested N retained (NR:apparent digested N (ADN)) were significantly (P < 0.001) affected by I values at all age intervals and the responses were quadratic. Response curves were calculated by the least squares method and optimum values of I determined for each of the criteria.A constant energy:N value of approximately 400 kJ/g N was indicated by growth, FCR and NR optima but the NR:ADN value fell from 0.77 for the 8–16 d period to 0.60 for the 24–32 d period at this I value. It is concluded that a suitable compromise would be an I value of 470 kJ/g N increasing by 10%/week.5. There was a significant interaction between plane of nutrition and I values on FCR between 16–24 d (P < 0.001) and 8–32 d (P < 0.01) indicating that FCR was better at high protein levels and worse at low protein levels when the diets were fed on the lower plane of nutrition.

Effect of Internal Electromagnetic Stirrings DC Casting on Grain Refinement and Segregation of Large-Sized Billet of 2219 Alloy

2021 ◽  
Vol 1035 ◽  
pp. 227-234
Author(s):  
Hao Dong Zhao ◽  
Zhi Feng Zhang ◽  
Bao Li ◽  
Ming Wei Gao ◽  
Yue Long Bai
Keyword(s):  
Grain Refinement ◽  
Process Condition ◽  
Electromagnetic Stirring ◽  
Coarse Grain ◽  
Internal Cooling ◽  
Composition Distribution ◽  
Mean Grain Size ◽  
Engineering Problems ◽  
The Mean ◽  
Dc Casting

An advanced method called internal electromagnetic stirring (I-EMS) was investigated to resolve the engineering problems like coarse-grain, inhomogeneous structure and macrosegregation. The electromagnetic stirrer functioned with internal-cooling was inserted in the melt during DC casting. In this study, a round billet of 2219 alloy DC cast with a diameter of 880mm under I-EMS process condition was produced, and its structure and composition distribution were comparatively characterized. The results show that the mean grain size decreased from the range of 872, 1023, 332 μm to the range of 317, 438, 271 μm at different billet positions with I-EMS. I-EMS consequently produce superior grain refinement and homogeneity. The effect of I-EMS on the grain-refinement and macrosegregation was also discussed.

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