43,137 research outputs found
The Heliocentric Distance Where the Deflections and Rotations of Solar Coronal Mass Ejections Occur
Understanding the trajectory of a coronal mass ejection (CME), including any
deflection from a radial path, and the orientation of its magnetic field is
essential for space weather predictions. Kay et al. (2015b) developed a model,
Forecasting a CME's Altered Trajectory (ForeCAT), of CME deflections and
rotation due to magnetic forces, not including the effects of reconnection.
ForeCAT is able to reproduce the deflection of observed CMEs (Kay et al.
2015a). The deflecting CMEs tend to show a rapid increase of their angular
momentum close to the Sun, followed by little to no increase at farther
distances. Here we quantify the distance at which the CME deflection is
"determined," which we define as the distance after which the background solar
wind has negligible influence on the total deflection. We consider a wide range
in CME masses and radial speeds and determine that the deflection and rotation
of these CMEs can be well-described by assuming they propagate with constant
angular momentum beyond 10 Rs. The assumption of constant angular momentum
beyond 10 Rs yields underestimates of the total deflection at 1 AU of only 1%
to 5% and underestimates of the rotation of 10%. Since the deflection from
magnetic forces is determined by 10 Rs, non-magnetic forces must be responsible
for any observed interplanetary deflections or rotations where the CME has
increasing angular momentum.Comment: accepted in ApJ Letter
State Transfer and Spin Measurement
We present a Hamiltonian that can be used for amplifying the signal from a
quantum state, enabling the measurement of a macroscopic observable to
determine the state of a single spin. We prove a general mapping between this
Hamiltonian and an exchange Hamiltonian for arbitrary coupling strengths and
local magnetic fields. This facilitates the use of existing schemes for perfect
state transfer to give perfect amplification. We further prove a link between
the evolution of this fixed Hamiltonian and classical Cellular Automata,
thereby unifying previous approaches to this amplification task.
Finally, we show how to use the new Hamiltonian for perfect state transfer in
the, to date, unique scenario where total spin is not conserved during the
evolution, and demonstrate that this yields a significantly different response
in the presence of decoherence.Comment: 4 pages, 2 figure
Forecasting a Coronal Mass Ejection's Altered Trajectory: ForeCAT
To predict whether a coronal mass ejection (CME) will impact Earth, the
effects of the background on the CME's trajectory must be taken into account.
We develop a model, ForeCAT (Forecasting a CME's Altered Trajectory), of CME
deflection due to magnetic forces. ForeCAT includes CME expansion, a three-part
propagation model, and the effects of drag on the CME's deflection. Given the
background solar wind conditions, the launch site of the CME, and the
properties of the CME (mass, final propagation speed, initial radius, and
initial magnetic strength), ForeCAT predicts the deflection of the CME. Two
different magnetic backgrounds are considered: a scaled background based on
type II radio burst profiles and a Potential Field Source Surface (PFSS)
background. For a scaled background where the CME is launched from an active
region located between a CH and streamer region the strong magnetic gradients
cause a deflection of 8.1 degrees in latitude and 26.4 degrees in longitude for
a 1e15 g CME propagating out to 1 AU. Using the PFSS background, which captures
the variation of the streamer belt position with height, leads to a deflection
of 1.6 degrees in latitude and 4.1 degrees in longitude for the control case.
Varying the CME's input parameters within observed ranges leads to the majority
of CMEs reaching the streamer belt within the first few solar radii. For these
specific backgrounds, the streamer belt acts like a potential well that forces
the CME into an equilibrium angular position.Comment: 57 pages, 12 figures, accepted for publication in ApJ, fixed the
overflow of text in Fig. 3 captio
Self-energy flows in the two-dimensional repulsive Hubbard model
We study the two-dimensional repulsive Hubbard model by functional RG
methods, using our recently proposed channel decomposition of the interaction
vertex. The main technical advance of this work is that we calculate the full
Matsubara frequency dependence of the self-energy and the interaction vertex in
the whole frequency range without simplifying assumptions on its functional
form, and that the effects of the self-energy are fully taken into account in
the equations for the flow of the two-body vertex function. At Van Hove
filling, we find that the Fermi surface deformations remain small at fixed
particle density and have a minor impact on the structure of the interaction
vertex. The frequency dependence of the self-energy, however, turns out to be
important, especially at a transition from ferromagnetism to d-wave
superconductivity. We determine non-Fermi-liquid exponents at this transition
point.Comment: 48 pages, 18 figure
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