differential rotation
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Author(s):  
Panagiotis Iosif ◽  
Nikolaos Stergioulas

Abstract The emergence of novel differential rotation laws that can reproduce the rotational profile of binary neutron star merger remnants has opened the way for the construction of equilibrium models with properties that resemble those of remnants in numerical simulations. We construct models of merger remnants, using a recently introduced 4-parameter differential rotation law and three tabulated, zero-temperature equations of state. The models have angular momenta that are determined by empirical relations, constructed through numerical simulations. After a systematic exploration of the parameter space of merger remnant equilibrium sequences, which includes the determination of turning points along constant angular momentum sequences, we find that a particular rotation law can reproduce the threshold mass to prompt collapse to a black hole with a relative difference of only $\sim 1\%$ with respect to numerical simulations, in all cases considered. Furthermore, our results indicate a possible correlation between the compactness of equilibrium models of remnants at the threshold mass and the compactness of maximum-mass nonrotating models. Another key prediction of binary neutron star merger simulations is a relatively slowly rotating inner region, where the angular velocity Ω (as measured by an observer at infinity) is mostly due to the frame dragging angular velocity ω. In our investigation of the parameter space of the adopted differential rotation law, we naturally find quasi-spherical (Type A) remnant models with this property. Our investigation clarifies the impact of the differential rotation law and of the equation of state on key properties of binary neutron star remnants and lays the groundwork for including thermal effects in future studies.


2021 ◽  
Vol 61 (7) ◽  
pp. 940-948
Author(s):  
I. Zhivanovich ◽  
A. A. Solov’ev ◽  
V. I. Efremov

2021 ◽  
Vol 2078 (1) ◽  
pp. 012055
Author(s):  
Lintao Hu

Abstract This article mainly introduces the intelligent lifebuoy based on machine vision. The design uses the OpenMv camera to identify the drowning person. OpenMV sends the collected position information of the person to the MCU. If the drowning person is on the left or right side of the lifebuoy, the MCU controls the motor drive module. Control the differential rotation of the motor behind the lifebuoy so that the lifebuoy is facing the drowning person. If the drowning person is directly in front of the lifebuoy, the MCU controls the motor drive module to control the rotation of the motor behind the lifebuoy to make the lifebuoy gradually approach the drowning person, which can save life. Blue balloons was used instead of drowning people to conduct rescue experiments on the lake. The smart lifebuoy successfully recognized the blue balloon and swam near the blue balloon. Furthermore, a perfect solution is proposed for the shortcomings of the intelligent lifebuoy.


2021 ◽  
Vol 203 ◽  
pp. 114113
Author(s):  
Banglong Fu ◽  
Junjun Shen ◽  
Uceu F.H.R. Suhuddin ◽  
Ting Chen ◽  
Jorge F. dos Santos ◽  
...  

2021 ◽  
Vol 2 (5) ◽  
pp. 198
Author(s):  
Janosz W. Dewberry ◽  
Christopher R. Mankovich ◽  
Jim Fuller ◽  
Dong Lai ◽  
Wenrui Xu

2021 ◽  
Author(s):  
Hachem Dhouib ◽  
Stéphane Mathis ◽  
Florian Debras ◽  
Aurélie Astoul ◽  
Clément Baruteau

<p>Gaseous giant planets (Jupiter and Saturn in our solar system and hot Jupiters around other stars) are turbulent rotating magnetic objects that have strong and complex interactions with their environment (their moons in the case of Jupiter and Saturn and their host stars in the case of hot Jupiters/Saturns). In such systems, the dissipation of tidal waves excited by tidal forces shape the orbital architecture and the rotational dynamics of the planets.</p> <p>During the last decade, a revolution has occurred for our understanding of tides in these systems. First, Lainey et al. (2009, 2012, 2017) have measured tidal dissipation stronger by one order of magnitude than expected in Jupiter and Saturn. Second, unexplained broad diversity of orbital architectures and large radius of some hot Jupiters are observed in exoplanetary systems. Finally, new constraints obtained thanks to <em>Kepler</em>/K2 and TESS indicate that tidal dissipation in gaseous giant exoplanets is weaker than in Jupiter and in Saturn (Ogilvie 2014, Van Eylen et al. 2018, Huber et al. 2019).</p> <p>Furthermore, the space mission JUNO and the grand finale of the CASSINI mission have revolutionized our knowledge of the interiors of giant planets. We now know, for example, that Jupiter is a very complex planet: it is a stratified planet with, from the surface to the core, a differentially rotating convective envelope, a first mixing zone (with stratified convection), a uniformly rotating magnetised convective zone, a second magnetized mixing zone (the diluted core, potentially in stratified convection) and a solid core (Debras & Chabrier 2019). So far, tides in these planets have been studied by assuming a simplified internal structure with a stable rocky and icy core (Remus et al. 2012, 2015) and a deep convective envelope surrounded by a thin stable atmosphere (Ogilvie & Lin 2004) where mixing processes, differential rotation and magnetic field were completely neglected.</p> <p>Our objective is thus to predict tidal dissipation using internal structure models, which agree with these last observational constrains. In this work, we build a new ab-initio model of tidal dissipation in giant planets that coherently takes into account the interactions of tidal waves with their complex stratification induced by the mixing of heavy elements, their zonal winds, and (dynamo) magnetic fields. This model is a semi-global model in the planetary equatorial plane. We study the linear excitation of tidal magneto-gravito-inertial progressive waves and standing modes. We take into account the buoyancy, the compressibility, the Coriolis acceleration (including differential rotation), and the Lorentz force. The tidal waves are submitted to the different potential dissipative processes: Ohmic, thermal, molecular diffusivities, and viscosity. We here present the general formalism and the potential regimes of parameters that should be explored. The quantities of interest such as tidal torque, dissipation, and heating are derived. This will pave the way for full 3D numerical simulations that will take into account complex internal structure and dynamics of gaseous giant (exo-)planets in spherical/spheroidal geometry.</p> <p> </p>


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