scholarly journals Internal-current Lorentz-force Heating of Astrophysical Objects

2021 ◽  
Vol 922 (2) ◽  
pp. L38
Author(s):  
Christopher F. Chyba ◽  
Kevin P. Hand
Keyword(s):  
Solar System ◽  
Lorentz Force ◽  
Ohmic Heating ◽  
Cross Product ◽  
Ohmic Dissipation ◽  
Tidal Dissipation ◽  
Radiogenic Heating ◽  
Astrophysical Objects ◽  
Out Of Plane ◽  
Close Distance

Abstract Two forms of ohmic heating of astrophysical secondaries have received particular attention: unipolar-generator heating with currents running between the primary and secondary, and magnetic induction heating due to the primary’s time-varying field. Neither appears to cause significant dissipation in the contemporary solar system. But these discussions have overlooked heating derived from the spatial variation of the primary’s field across the interior of the secondary. This leads to Lorentz-force-driven currents around paths entirely internal to the secondary, with resulting ohmic heating. We examine three ways to drive such currents, by the cross product of (1) the secondary’s azimuthal orbital velocity with the nonaxially symmetric field of the primary, (2) the radial velocity (due to nonzero eccentricity) of the secondary with the primary’s field, or (3) the out-of-plane velocity (due to nonzero inclination) with the primary’s field. The first of these operates even for a spin-locked secondary whose orbit has zero eccentricity, in strong contrast to tidal dissipation. We show that Jupiter’s moon Io today could dissipate about 600 GW (more than likely current radiogenic heating) in the outer 100 m of its metallic core by this mechanism. Had Io ever been at 3 Jovian radii instead of its current 5.9, it could have been dissipating 15,000 GW. Ohmic dissipation provides a mechanism that could operate in any solar system to drive inward migration of secondaries that then necessarily comes to a halt upon reaching a sufficiently close distance to the primary.

scholarly journals Testing the Vainshtein mechanism using stars and galaxies

2015 ◽  
Vol 24 (12) ◽  
pp. 1544021 ◽  
Author(s):  
Jeremy Sakstein ◽  
Kazuya Koyama
Keyword(s):  
General Relativity ◽  
Solar System ◽  
Main Sequence ◽  
Alternative Theories Of Gravity ◽  
The Novel ◽  
Main Sequence Stars ◽  
Cosmic Expansion ◽  
Astrophysical Objects ◽  
Theories Of Gravity ◽  
Alternative Theories

The Vainshtein mechanism is of paramount importance in many alternative theories of gravity. It hides deviations from general relativity (GR) in the solar system while allowing them to drive the acceleration of the cosmic expansion. Recently, a class of theories have emerged where the mechanism is broken inside astrophysical objects. In this essay, we look for novel probes of these theories by deriving the modified properties of stars and galaxies. We show that main-sequence stars are colder, less luminous and more ephemeral than GR predicts. Furthermore, the circular velocities of objects orbiting inside galaxies are slower and the lensing of light is weaker. We discuss the prospects for testing these theories using the novel phenomena presented here in light of current astrophysical surveys.

scholarly journals Nonlinear Dynamos

2010 ◽  
Vol 6 (S271) ◽  
pp. 297-303
Author(s):  
David Galloway
Keyword(s):  
Magnetic Field ◽  
Solar Cycle ◽  
Stokes Equation ◽  
Lorentz Force ◽  
Navier Stokes ◽  
Navier Stokes Equation ◽  
Direct Competition ◽  
Astrophysical Objects ◽  
Flow Domain ◽  
The Magnetic Field

AbstractThis paper discusses nonlinear dynamos where the nonlinearity arises directly via the Lorentz force in the Navier-Stokes equation, and leads to a situation where the Lorentz force and the velocity and the magnetic field are in direct competition over substantial regions of the flow domain. Filamentary and non-filamentary dynamos are contrasted, and the concept of Alfvénic dynamos with almost equal magnetic and kinetic energies is reviewed via examples. So far these remain in the category of toy models; the paper concludes with a discussion of whether similar dynamos are likely to exist in astrophysical objects, and whether they can model the solar cycle.

scholarly journals Frequency Modulated Magnetometer Using a Double-Ended Tuning Fork Resonator

Proceedings ◽  
2018 ◽  
Vol 2 (13) ◽  
pp. 1028 ◽  
Author(s):  
Eurico Esteves Moreira ◽  
João Gaspar ◽  
Luis Alexandre Rocha
Keyword(s):  
Lorentz Force ◽  
Tuning Fork ◽  
Force Transducer ◽  
Silicon On Insulator ◽  
Input Current ◽  
Experimental Characterization ◽  
Total Input ◽  
Out Of Plane ◽  
Sensor Configuration

A Lorentz force MEMS magnetometer based on a double-ended tuning fork (DETF) for out-of-plane sensing is presented here. A novel configuration using a hexagonal-shaped Lorentz force transducer is used, which simplifies the sensor configuration and improves its sensitivity. Frequency modulated devices were fabricated in an in-house process on silicon on insulator wafers (SOI) and then tested in vacuum. The final devices have a differential configuration and experimental characterization shows a sensitivity of 4.59 Hz/mT for a total input current (on the Lorentz bar) of 1.5 mA.

scholarly journals Ohmic Heating Effect on Magneto Hydrodynamic Marangoni Mixed Convection Boundary Layer Nanofluid Flow

2018 ◽  
Vol 7 (4.10) ◽  
pp. 666
Author(s):  
M. Srinivasu ◽  
Devulapalli R.V.S.R.K.Sastry ◽  
G. V.S.R.Deekshitulu
Keyword(s):  
Flat Surface ◽  
Marangoni Convection ◽  
Ohmic Heating ◽  
Flow Characteristics ◽  
Marangoni Effect ◽  
Immiscible Fluids ◽  
Convection Boundary Layer ◽  
Nanofluid Flow ◽  
Ohmic Dissipation ◽  
Convection Boundary

In surface driven flows, dissipative layers which occur along the surface of two immiscible fluids are known as marangoni boundary layers. Mixed connection takes place when buoyancy forces act beside marangoni effect. Consider a nanofluid flow along a flat surface experiencing marangoni convection with ohmic dissipation and magnetic field. Copper and Alumina are the nanoparticles with water as base fluid. The similarity equations are solved numerically by BVP solver ‘bcp4c”. The flow characteristics are analyzed graphically and discussed.  

scholarly journals Liquid water and organics in Comets: implications for exobiology

2009 ◽  
Vol 8 (4) ◽  
pp. 281-290 ◽  
Author(s):  
J.T. Wickramasinghe ◽  
N.C. Wickramasinghe ◽  
M.K. Wallis
Keyword(s):  
Solar System ◽  
Liquid Water ◽  
Indirect Evidence ◽  
Current Evidence ◽  
Carbonaceous Chondrites ◽  
Radiogenic Heating ◽  
Infrared Spectral ◽  
Solar Material ◽  
New Evidence ◽  
Modelling Data

AbstractLiquid water in comets, once considered impossible, now appears to be almost certain. New evidence has come from the discovery of clay minerals in comet Tempel 1, which compliments the indirect evidence in aqueous alteration of carbonaceous chondrites. Infrared spectral indication of clay is confirmed by modelling data in the 8–40 μm and 8–12 μm wavebands on the basis of mixtures of clays and organics. Radiogenic heating producing liquid water cores in freshly formed comets appears more likely on current evidence for solar system formation. A second possibility investigated here is transient melting in comets in the inner solar system, where thin crusts of asphalt-like material, formed due to solar processing and becoming hot in the daytime, can cause melting of sub-surface icy material a few centimetres deep. Supposing comets were seeded with microbes at the time of their formation from pre-solar material, there would be plenty of time for exponential amplification and evolution within the liquid interior and in the transient ponds or lakes formed as the outer layers are stripped away via sublimation.

Radiative and Viscous Ohmic Dissipation on MHD Tangent Hyperbolic Fluid over a Convectively Heated Sheet in a Suspension of Dust Particles

2018 ◽  
Vol 16 ◽  
pp. 177-190 ◽  
Author(s):  
S.U. Mamatha ◽  
Chakravarthula S.K. Raju ◽  
Mahesha ◽  
Oluwole Daniel Makinde
Keyword(s):  
Heat Transfer ◽  
Differential Equations ◽  
Ohmic Heating ◽  
Skin Friction Coefficient ◽  
Dust Particles ◽  
Stretching Surface ◽  
Ohmic Dissipation ◽  
Transfer Rates ◽  
Similarity Transformations ◽  
Tangent Hyperbolic Fluid

The present study deals with steady incompressible magneto hydrodynamic hyperbolic tangent fluid flow induced by a convectively heated stretching surface with the suspension of dust particles, Darcy-Forchheimer, thermal radiation, viscous dissipation and Ohmic heating. Similarity transformations were used to convert partial differential equations (PDEs) to a system of nonlinear ordinary differential equations (NODEs) which are solved numerically by Runge-Kutta Fehlberg method. The effect of pertinent parameters on velocity and temperature profiles of both fluid and dust phase within the boundary layer has been studied by considering various values of controlling parameters. Additionally, the skin friction coefficient and reduced heat transfer coefficient have been examined for various values of the governing parameters. It is found that Hartmann number and Forchheimer parameter reduce friction factor and heat transfer rates.

scholarly journals Highly sensitive low field Lorentz-force MEMS magnetometer

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Sofiane Ben Mbarek ◽  
Nouha Alcheikh ◽  
Hassen M. Ouakad ◽  
Mohammad I. Younis
Keyword(s):  
Lorentz Force ◽  
Beam Theory ◽  
Sensor Performance ◽  
Low Field ◽  
Highly Sensitive ◽  
Out Of Plane ◽  
Micro Sensor ◽  
Euler Bernoulli Beam ◽  
A Current ◽  
Good Agreement

AbstractWe present a highly sensitive Lorentz-force magnetic micro-sensor capable of measuring low field values. The magnetometer consists of a silicon micro-beam sandwiched between two electrodes to electrostatically induce in-plane vibration and to detect the output current. The method is based on measuring the resonance frequency of the micro-beam around the buckling zone to sense out-of-plane magnetic fields. When biased with a current of 0.91 mA (around buckling), the device has a measured sensitivity of 11.6 T−1, which is five orders of magnitude larger than the state-of-the-art. The measured minimum detectable magnetic field and the estimated resolution of the proposed magnetic sensor are 100 µT and 13.6 µT.Hz−1/2, respectively. An analytical model is developed based on the Euler–Bernoulli beam theory and the Galerkin discretization to understand and verify the micro-sensor performance. Good agreement is shown between analytical results and experimental data. Furthermore, the presented magnetometer is promising for measuring very weak biomagnetic fields.

scholarly journals On the equilibrium rotation of Hot Jupiters in eccentric and excited orbits

2010 ◽  
Vol 6 (S276) ◽  
pp. 287-294
Author(s):  
Alexandre C. M. Correia
Keyword(s):  
Solar System ◽  
Rotation Rate ◽  
Tidal Effects ◽  
Tidal Dissipation ◽  
Continuous Action ◽  
Hot Jupiters ◽  
Synchronous Motion ◽  
Eccentric Orbits ◽  
Synchronous Rotation ◽  
Probable Outcome

AbstractHot-Jupiters are a common sub-class of exoplanets, which are enough close to the star to undergo tidal dissipation. The continuous action of tides modify the rotation of the planets until an equilibrium situation is reached. It is often assumed that synchronous motion is the most probable outcome of tidal evolution, since synchronous rotation is observed for the majority of the satellites in the Solar System. This is true for circular orbits, but when the orbits are eccentric, tidal effects are stronger when the planets are closer to the star, and therefore, the rotation rate tends to equalize the orbital speed rate at the pericenter (which is faster than synchronous rotation). An additional complication arises if the eccentricity is not constant and undergoes periodic perturbations from an external companion. Here we obtain an expression for the equilibrium rotation of Hot-Jupiters undergoing tidal dissipation and planetary perturbations. We show that for these planets, the equilibrium rotation rate is faster than for non-perturbed eccentric orbits.

scholarly journals Magnetic-field evolution with large-scale velocity circulation in a neutron-star crust

2020 ◽  
Vol 494 (3) ◽  
pp. 3790-3798 ◽  
Author(s):  
Yasufumi Kojima ◽  
Kazuki Suzuki
Keyword(s):  
Magnetic Field ◽  
Neutron Star ◽  
Lorentz Force ◽  
Large Scale ◽  
Magnetic Energy ◽  
Fluid Motion ◽  
Navier Stokes Equation ◽  
Ohmic Dissipation ◽  
Neutron Star Crust ◽  
Field Evolution

ABSTRACT We examine the effects of plastic flow that appear in a neutron-star crust when a magnetic stress exceeds the threshold. The dynamics involved are described using the Navier–Stokes equation comprising the viscous-flow term, and the velocity fields for the global circulation are determined using quasi-stationary approximation. We simulate the magnetic-field evolution by taking into consideration the Hall drift, Ohmic dissipation, and fluid motion induced by the Lorentz force. The decrease in the magnetic energy is enhanced, as the energy converts to the bulk motion energy and heat. It is found that the bulk velocity induced by the Lorentz force has a significant influence in the low-viscosity and strong-magnetic-field regimes. This effect is crucial near magnetar surfaces.

scholarly journals Electron-Beam Evolution in Partially Ionized Hydrogenic Plasma with Return Currents

1994 ◽  
Vol 142 ◽  
pp. 729-734
Author(s):  
D. V. Syniavskii ◽  
V. V. Zharkova
Keyword(s):  
Electron Beam ◽  
Ohmic Heating ◽  
Plasma Heating ◽  
X Rays ◽  
Ohmic Dissipation ◽  
Lower Corona ◽  
Energetic Electrons ◽  
Coulomb Collisions ◽  
Ambient Plasma ◽  
X Ray

AbstractThis paper presents the kinetic equation solution for beam electrons injected during solar flares from the corona to the chromosphere, consisting of hydrogenic plasma with partial ionization. The electrons are considered to lose their energy both in collisional processes with the charged and neutral species of ambient plasma and in ohmic heating by return currents induced in the plasma by beam electrons. The evolution of the energy and angular distributions of energetic electrons is calculated as functions of the column density. The bulk of the electron-beam energy stored in low-energy electrons is shown to be lost in the ambient plasma heating, less via Coulomb collisions at the lower corona and more via ohmic dissipation at the upper chromosphere. More energetic electrons with energies above 120 keV can reach the chromospheric levels with a weak ionized plasma, where a decrease of the Coulomb collisions and the induced electric field of a return current produce beams as well directed as on the top boundary. The X-ray bremsstrahlung polarization is shown to be positive in the range 5%-10%. It is very sensitive to the emergent photon energies below 40 keV and to angles of view for all of the X-ray radiation range.Subject headings: acceleration of particles — plasmas — Sun: flares — Sun: X-rays, gamma rays

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