Magnetic energy fluxes in close-in star-planet systems

2015 ◽  
Vol 11 (S320) ◽  
pp. 403-408
Author(s):  
A. Strugarek ◽  
A. S. Brun ◽  
S. P. Matt ◽  
V. Réville
Keyword(s):  
Magnetic Energy ◽  
Three Dimensional ◽  
Magnetic Interaction ◽  
Magnetic Interactions ◽  
Energy Fluxes ◽  
Magnetic Topology ◽  
Poynting Flux ◽  
Order Of Magnitude ◽  
Ideal Magnetohydrodynamic ◽  
The Impact

AbstractMagnetic interactions between a close-in planet and its host star have been postulated to be a source of enhanced chromospheric emissions. We develop three dimensional global models of star-planet systems under the ideal magnetohydrodynamic (MHD) approximation to explore the impact of magnetic topology on the energy fluxes induced by the magnetic interaction. We conduct twin numerical experiments in which only the magnetic topology of the interaction is altered. We find that the Poynting flux varies by more than an order of magnitude when varying the magnetic topology from an aligned case to an anti-aligned case. This provides a simple and robust physical explanation for on/off enhanced chromospheric emissions induced by a close-in planet on time-scales of the order of days to years.

scholarly journals Planet migration and magnetic torques

2015 ◽  
Vol 11 (A29A) ◽  
pp. 14-18
Author(s):  
A. Strugarek ◽  
A. S. Brun ◽  
S. P. Matt ◽  
V. Reville
Keyword(s):  
Numerical Experiments ◽  
Three Dimensional ◽  
Magnetic Star ◽  
Magnetic Topology ◽  
Global Models ◽  
Planet Migration ◽  
Order Of Magnitude ◽  
Ideal Magnetohydrodynamic ◽  
The Impact ◽  
The Ideal

AbstractThe possibility that magnetic torques may participate in close-in planet migration has recently been postulated. We develop three dimensional global models of magnetic star-planet interaction under the ideal magnetohydrodynamic (MHD) approximation to explore the impact of magnetic topology on the development of magnetic torques. We conduct twin numerical experiments in which only the magnetic topology of the interaction is altered. We find that magnetic torques can vary by roughly an order of magnitude when varying the magnetic topology from an aligned case to an anti-aligned case. Provided that the stellar magnetic field is strong enough, we find that magnetic migration time scales can be as fast as ~100 Myr. Hence, our model supports the idea that magnetic torques may participate in planet migration for some close-in star-planet systems.

scholarly journals Modeling the elastic transmission of tidal stresses to great distances inland in channelized ice streams

2014 ◽  
Vol 8 (6) ◽  
pp. 2007-2029 ◽  
Author(s):  
J. Thompson ◽  
M. Simons ◽  
V. C. Tsai
Keyword(s):  
Three Dimensional ◽  
Hydrologic Model ◽  
Ice Streams ◽  
Ice Stream ◽  
Nonlinear Viscoelastic ◽  
Grounding Line ◽  
Dimensional Finite Element ◽  
Order Of Magnitude ◽  
Three Dimensional Finite Element ◽  
The Impact

Abstract. Geodetic surveys suggest that ocean tides can modulate the motion of Antarctic ice streams, even at stations many tens of kilometers inland from the grounding line. These surveys suggest that ocean tidal stresses can perturb ice stream motion at distances about an order of magnitude farther inland than tidal flexure of the ice stream alone. Recent models exploring the role of tidal perturbations in basal shear stress are primarily one- or two-dimensional, with the impact of the ice stream margins either ignored or parameterized. Here, we use two- and three-dimensional finite-element modeling to investigate transmission of tidal stresses in ice streams and the impact of considering more realistic, three-dimensional ice stream geometries. Using Rutford Ice Stream as a real-world comparison, we demonstrate that the assumption that elastic tidal stresses in ice streams propagate large distances inland fails for channelized glaciers due to an intrinsic, exponential decay in the stress caused by resistance at the ice stream margins. This behavior is independent of basal conditions beneath the ice stream and cannot be fit to observations using either elastic or nonlinear viscoelastic rheologies without nearly complete decoupling of the ice stream from its lateral margins. Our results suggest that a mechanism external to the ice stream is necessary to explain the tidal modulation of stresses far upstream of the grounding line for narrow ice streams. We propose a hydrologic model based on time-dependent variability in till strength to explain transmission of tidal stresses inland of the grounding line. This conceptual model can reproduce observations from Rutford Ice Stream.

scholarly journals Urca reactions during neutron star inspiral

2019 ◽  
Vol 486 (1) ◽  
pp. 1424-1436
Author(s):  
Phil Arras ◽  
Nevin N Weinberg
Keyword(s):  
Neutron Star ◽  
Chemical Potential ◽  
Fluid Motion ◽  
Three Dimensional ◽  
Reaction Rates ◽  
Heating Rates ◽  
Static Approximation ◽  
Oscillation Modes ◽  
Order Of Magnitude ◽  
The Impact

Abstract We study the impact of Urca reactions driven by tidally induced fluid motion during binary neutron star inspiral. Fluid compression is computed for low radial order oscillation modes through an adiabatic, time-dependent solution for the mode amplitudes. Optically thin neutrino emission and heating rates are then computed from this adiabatic fluid motion. Calculations use direct and modified Urca reactions operating in a $M=1.4\, \mathrm{ M}_\odot$ neutron star, which is constructed using the Skyrme Rs equation of state. We find that the energy pumped into low-order oscillation modes is not efficiently thermalized even by direct Urca reactions, with core temperatures reaching only T ≃ 108 K during the inspiral. Although this is an order of magnitude larger than the heating due to shear viscosity considered by previous studies, it reinforces the result that the stars are quite cold at merger. Upon excitation of the lowest order g mode, the chemical potential imbalance reaches $\beta \gtrsim 1\, \rm MeV$ at orbital frequencies $\nu _{\rm orb} \gtrsim 200\, \rm Hz$, implying significant charged-current optical depths and Fermi-blocking. To assess the importance of neutrino degeneracy effects, the neutrino transfer equation is solved in the static approximation for the three-dimensional density distribution, and the reaction rates are then computed including Fermi-blocking. We find that the heating rate is suppressed by a factor of a ∼2 for $\nu _{\rm orb} \gtrsim 200\, \rm Hz$. The spectrum of emitted νe and $\bar{\nu }_e$, including radiation transfer effects, is presented for a range of orbital separations.

scholarly journals The impact of progenitor asymmetries on the neutrino-driven convection in core-collapse supernovae

2020 ◽  
Vol 494 (4) ◽  
pp. 5360-5373 ◽  
Author(s):  
Rémi Kazeroni ◽  
Ernazar Abdikamalov
Keyword(s):  
Buoyant Density ◽  
Three Dimensional ◽  
Core Collapse ◽  
Wide Range ◽  
Order Of Magnitude ◽  
Post Shock ◽  
Nuclear Burning ◽  
Density Perturbations ◽  
Perturbation Parameters ◽  
The Impact

ABSTRACT The explosion of massive stars in core-collapse supernovae may be aided by the convective instabilities that develop in their innermost nuclear burning shells. The resulting fluctuations support the explosion by generating additional turbulence behind the supernova shock. It was suggested that the buoyant density perturbations arising from the interaction of the pre-collapse asymmetries with the shock may be the primary contributor to the enhancement of the neutrino-driven turbulent convection in the post-shock region. Employing three-dimensional numerical simulations of a toy model, we investigate the impact of such density perturbations on the post-shock turbulence. We consider a wide range of perturbation parameters. The spatial scale and the amplitude of the perturbations are found to be of comparable importance. The turbulence is particularly enhanced when the perturbation frequency is close to that of the convective turnovers in the gain region. Our analysis confirms that the buoyant density perturbations is indeed the main source of the additional turbulence in the gain region, validating the previous order-of-magnitude estimates.

scholarly journals Modeling the elastic transmission of tidal stresses to great distances inland in channelized ice streams

2014 ◽  
Vol 8 (2) ◽  
pp. 2119-2177 ◽  
Author(s):  
J. Thompson ◽  
M. Simons ◽  
V. C. Tsai
Keyword(s):  
Three Dimensional ◽  
Hydrologic Model ◽  
Ocean Tides ◽  
Ice Streams ◽  
Ice Stream ◽  
Nonlinear Viscoelastic ◽  
Grounding Line ◽  
Order Of Magnitude ◽  
Three Dimensional Finite Element ◽  
The Impact

Abstract. Geodetic surveys suggest that ocean tides can modulate the motion of Antarctic ice streams. Data from Whillans Ice Plain, Rutford Ice Stream, and other Antarctic ice streams show periodicity in flow velocity at periods similar to those of ocean tides at geodetic stations many tens of kilometers inland from the grounding line. These data suggest that ocean tidal stresses can perturb ice stream motion at distances about an order of magnitude farther inland than tidal flexure of the ice stream alone. Recent models exploring the role of tidal perturbations in basal shear stress are primarily two-dimensional, with the impact of the ice stream margins either ignored or parameterized. Here, we use two- and three-dimensional finite element modeling to investigate transmission of tidal stresses in ice streams and the impact of considering more realistic, three-dimensional ice stream geometries. Using Rutford Ice Stream as a real-world comparison, we demonstrate that the assumption that elastic tidal stresses in ice streams propagate large distances inland fails for channelized glaciers due to an intrinsic, exponential decay in the stress due to resistance at the ice stream margins. This behavior is independent of basal conditions beneath the ice stream and cannot be fit to observations using either elastic or nonlinear viscoelastic rheologies without nearly complete decoupling of the ice stream from its lateral margins. Our results suggest that a mechanism external to the ice stream is necessary to explain the tidal modulation of stresses far upstream of the grounding line for narrow ice streams. We propose a hydrologic model based on time-dependent variability in till strength to explain transmission of tidal stresses inland of the grounding line. This conceptual model reproduces observations from Rutford Ice Stream.

Bifurcations of magnetic topology by the creation or annihilation of null points

1996 ◽  
Vol 56 (3) ◽  
pp. 507-530 ◽  
Author(s):  
E. R. Priest ◽  
D. P. Lonie ◽  
V. S. Titov
Keyword(s):  
Magnetic Field ◽  
Magnetic Energy ◽  
Three Dimensional ◽  
Two Dimensions ◽  
Three Dimensions ◽  
Comprehensive Treatment ◽  
Global Changes ◽  
Magnetic Topology ◽  
Cylindrically Symmetric ◽  
Saddle Node

Linear null points of a magnetic field may come together and coalesce at a secondorder null, or vice versa a second-order null may form and split, giving birth to a pair of linear nulls. Such local bifurcations lead to global changes of magnetic topology and in some cases release of magnetic energy. In two dimensions the null points are of X or O type and the flux function is a Hamiltonian; the magnetic field may undergo addle-centre, pitchfork or degenerate resonant bifurcations. In three dimensions the null points and their creation or annihilation by bifurcations are considerably more complex. The nulls possess a skeleton consisting of a spine curve and a fan surface and are of radial-type (proper or improper) or spiral-type; the type of null and the inclination of spine and fan depend on the magnitudes of the current components along and normal to the spine. In cylindrically symmetric fields a comprehensive treatment is given of the various types of saddle-node, Hopf and saddle-node—Hopfbifurcations. In fully three-dimensional situations examples are given of saddle-node and degenerate bifurcations, in which generically two nulls are created or destroyed and are joined by a separator field line, which is the intersection of the two fans. Furthermore, global bifurcations can create chaotic field lines that could perhaps trigger energy release in, for example, solar flares.

scholarly journals Reconnection in substorms and solar flares: analogies and differences

2009 ◽  
Vol 27 (3) ◽  
pp. 1067-1078 ◽  
Author(s):  
J. Birn ◽  
M. Hesse
Keyword(s):  
Magnetic Flux ◽  
Solar Flares ◽  
Energy Transport ◽  
Magnetic Energy ◽  
Three Dimensional ◽  
Minor Role ◽  
Magnetospheric Substorms ◽  
Ohmic Dissipation ◽  
Current Sheets ◽  
Poynting Flux

Abstract. Magnetic reconnection is the crucial process in the release of magnetic energy associated with magnetospheric substorms and with solar flares. On the basis of three-dimensional resistive MHD simulations we investigate similarities and differences between the two scenarios. We address in particular mechanisms that lead to the onset of reconnection and energy release, transport, and conversion mechanisms. Analogous processes might exist in the motion of field line footpoints on the sun and in magnetic flux addition to the magnetotail. In both cases such processes might lead to a loss of neighboring equilibrium, characterized by the formation of a very thin embedded current sheet, which acts as trigger for reconnection. We find that Joule (or ohmic) dissipation plays only a minor role in the overall energy transfer associated with reconnection. The dominant transfer of released magnetic energy occurs to electromagnetic energy (Poynting) flux and to thermal energy transport as enthalpy flux. The former dominates in low-beta, specifically initially force-free current sheets expected for the solar corona, while the latter dominates in high-beta current sheets, such as the magnetotail. In both cases the outflow from the reconnection site becomes bursty, i.e. spatially and temporally localized, yet carrying most of the outflow energy. Hence an analogy might exist between bursty bulk flows (BBFs) in the magnetotail and pulses of Poynting flux in solar flares. Further similarities might exist in the role of collapsing magnetic flux tubes, as a consequence of reconnection, in the heating and acceleration of charged particles.

scholarly journals Stellar wind and supernova feedback from massive stars

2012 ◽  
Vol 10 (H16) ◽  
pp. 586-586
Author(s):  
Julian M. Pittard ◽  
Hazel Rogers
Keyword(s):  
Stellar Wind ◽  
Massive Star ◽  
Massive Stars ◽  
Three Dimensional ◽  
Energy Fluxes ◽  
Hydrodynamical Models ◽  
Stellar Cluster ◽  
Molecular Material ◽  
The Impact ◽  
Supernova Feedback

AbstractWe have constructed three-dimensional hydrodynamical models to simulate the impact of massive star feedback, via winds and SNe, on inhomogeneous molecular material left over from the formation of a massive stellar cluster. We are studying the timescales for the molecular material to be removed from the environment of a massive stellar cluster and the mass and energy fluxes into the wider environment.

Detection, Averaging, and 3D Reconstruction of Biological Specimens on Hypercubes (Transputer-based) Computers

1990 ◽  
Vol 48 (1) ◽  
pp. 454-455
Author(s):  
Jose-Maria Carazo ◽  
I. Benavides ◽  
S. Marco ◽  
J.L. Carrascosa ◽  
E.L. Zapata
Keyword(s):  
3D Reconstruction ◽  
3D Structure ◽  
Three Dimensional ◽  
Software Tools ◽  
Mapping Method ◽  
Computer Architectures ◽  
Parallel Computer ◽  
Reconstruction Process ◽  
Computing Power ◽  
Order Of Magnitude

Obtaining the three-dimensional (3D) structure of negatively stained biological specimens at a resolution of, typically, 2 - 4 nm is becoming a relatively common practice in an increasing number of laboratories. A combination of new conceptual approaches, new software tools, and faster computers have made this situation possible. However, all these 3D reconstruction processes are quite computer intensive, and the middle term future is full of suggestions entailing an even greater need of computing power. Up to now all published 3D reconstructions in this field have been performed on conventional (sequential) computers, but it is a fact that new parallel computer architectures represent the potential of order-of-magnitude increases in computing power and should, therefore, be considered for their possible application in the most computing intensive tasks.We have studied both shared-memory-based computer architectures, like the BBN Butterfly, and local-memory-based architectures, mainly hypercubes implemented on transputers, where we have used the algorithmic mapping method proposed by Zapata el at. In this work we have developed the basic software tools needed to obtain a 3D reconstruction from non-crystalline specimens (“single particles”) using the so-called Random Conical Tilt Series Method. We start from a pair of images presenting the same field, first tilted (by ≃55°) and then untilted. It is then assumed that we can supply the system with the image of the particle we are looking for (ideally, a 2D average from a previous study) and with a matrix describing the geometrical relationships between the tilted and untilted fields (this step is now accomplished by interactively marking a few pairs of corresponding features in the two fields). From here on the 3D reconstruction process may be run automatically.

Scanning-tunneling spectroscopy on conjugated polymer films

2003 ◽  
Vol 771 ◽  
Author(s):  
M. Kemerink ◽  
S.F. Alvarado ◽  
P.M. Koenraad ◽  
R.A.J. Janssen ◽  
H.W.M. Salemink ◽  
...  
Keyword(s):  
Polymer Films ◽  
Conjugated Polymer ◽  
Three Dimensional ◽  
Field Enhancement ◽  
Direct Consequence ◽  
Scanning Tunneling Spectroscopy ◽  
Tunneling Spectroscopy ◽  
Band Alignment ◽  
Scanning Tunneling ◽  
Order Of Magnitude

AbstractScanning-tunneling spectroscopy experiments have been performed on conjugated polymer films and have been compared to a three-dimensional numerical model for charge injection and transport. It is found that field enhancement near the tip apex leads to significant changes in the injected current, which can amount to more than an order of magnitude, and can even change the polarity of the dominant charge carrier. As a direct consequence, the single-particle band gap and band alignment of the organic material can be directly obtained from tip height-voltage (z-V) curves, provided that the tip has a sufficiently sharp apex.

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