720 research outputs found
Live–virtual–constructive simulation for testing and evaluation of air combat tactics, techniques, and procedures, Part 1: assessment framework
Statistical properties of substorm auroral onset beads/rays
Auroral substorms are often associated with optical ray or bead structures during initial brightening (substorm auroral onset waves). Occurrence probabilities and properties of substorm onset waves have been characterized using 112 substorm events identified in Time History of Events and Macroscale Interactions during Substorms (THEMIS) all-sky imager data and compared to Rice Convection Model–Equilibrium (RCM-E) and kinetic instability properties. All substorm onsets were found to be associated with optical waves, and thus, optical waves are a common feature of substorm onset. Eastward propagating wave events are more frequent than westward propagating wave events and tend to occur during lower-latitude substorms (stronger solar wind driving). The wave propagation directions are organized by orientation of initial brightening arcs. We also identified notable differences in wave propagation speed, wavelength (wave number), period, and duration between westward and eastward propagating waves. In contrast, the wave growth rate does not depend on the propagation direction or substorm strength but is inversely proportional to the wave duration. This suggests that the waves evolve to poleward expansion at a certain intensity threshold and that the wave properties do not directly relate to substorm strengths. However, waves are still important for mediating the transition between the substorm growth phase and poleward expansion. The relation to arc orientation can be explained by magnetotail structures in the RCM-E, indicating that substorm onset location relative to the pressure peak determines the wave propagation direction. The measured wave properties agree well with kinetic ballooning interchange instability, while cross-field current instability and electromagnetic ion cyclotron instability give much larger propagation speed and smaller wave period
New Insights into Dissipation in the Electron Layer During Magnetic Reconnection
Detailed comparisons are reported between laboratory observations of
electron-scale dissipation layers near a reconnecting X-line and direct
two-dimensional full-particle simulations. Many experimental features of the
electron layers, such as insensitivity to the ion mass, are reproduced by the
simulations; the layer thickness, however, is about 3-5 times larger than the
predictions. Consequently, the leading candidate 2D mechanism based on
collisionless electron nongyrotropic pressure is insufficient to explain the
observed reconnection rates. These results suggest that, in addition to the
residual collisions, 3D effects play an important role in electron-scale
dissipation during fast reconnection.Comment: 17 pages, 4 figure
Growth rates of the Weibel and tearing mode instabilities in a relativistic pair plasma
We present an algorithm for solving the linear dispersion relation in an
inhomogeneous, magnetised, relativistic plasma. The method is a generalisation
of a previously reported algorithm that was limited to the homogeneous case.
The extension involves projecting the spatial dependence of the perturbations
onto a set of basis functions that satisfy the boundary conditions (spectral
Galerkin method). To test this algorithm in the homogeneous case, we derive an
analytical expression for the growth rate of the Weibel instability for a
relativistic Maxwellian distribution and compare it with the numerical results.
In the inhomogeneous case, we present solutions of the dispersion relation for
the relativistic tearing mode, making no assumption about the thickness of the
current sheet, and check the numerical method against the analytical
expression.Comment: Accepted by PPC
Barbicidal overdose
Acute severe methemoglobinaemia is an uncommon but life-threatening condition caused by a variety of oxidizing agents commonly used in both health care and industrial settings. Thus, recognition is important as it is readily treatable. The oxygen transport is compromised as a result of abnormal levels of oxidized haemoglobin, and this leads to skin discolouration and a variety of symptoms. Diagnostic confusion occurs as the oxygen saturations (SpO2) on the pulse oximeter are unreliable (Sharma V, Haber A. Acquired methaemoglobinaemia: a case report of benzocaine-induced methaemoglobinaemia and a review of the literature. Clin Pul Med. 2002;9(1):53–8). A case of severe methaemoglobinaemia due to self poisoning with barbicide is presented with a brief discussion of the patho-physiology and an overview of the treatment. A barbicidal overdose has never been reported before
Simulating open quantum systems: from many-body interactions to stabilizer pumping
In a recent experiment, Barreiro et al. demonstrated the fundamental building
blocks of an open-system quantum simulator with trapped ions [Nature 470, 486
(2011)]. Using up to five ions, single- and multi-qubit entangling gate
operations were combined with optical pumping in stroboscopic sequences. This
enabled the implementation of both coherent many-body dynamics as well as
dissipative processes by controlling the coupling of the system to an
artificial, suitably tailored environment. This engineering was illustrated by
the dissipative preparation of entangled two- and four-qubit states, the
simulation of coherent four-body spin interactions and the quantum
non-demolition measurement of a multi-qubit stabilizer operator. In the present
paper, we present the theoretical framework of this gate-based ("digital")
simulation approach for open-system dynamics with trapped ions. In addition, we
discuss how within this simulation approach minimal instances of spin models of
interest in the context of topological quantum computing and condensed matter
physics can be realized in state-of-the-art linear ion-trap quantum computing
architectures. We outline concrete simulation schemes for Kitaev's toric code
Hamiltonian and a recently suggested color code model. The presented simulation
protocols can be adapted to scalable and two-dimensional ion-trap
architectures, which are currently under development.Comment: 27 pages, 9 figures, submitted to NJP Focus on Topological Quantum
Computatio
The Diffusion Region in Collisionless Magnetic Reconnection
A review of present understanding of the dissipation region in magnetic reconnection is presented. The review focuses on results of the thermal inertia-based dissipation mechanism but alternative mechanisms are mentioned as well. For the former process, a combination of analytical theory and numerical modeling is presented. Furthermore, a new relation between the electric field expressions for anti-parallel and guide field reconnection is developed
3D Magnetic Reconnection with a spatially confined X-line extent -- Implications for Dipolarizing Flux Bundles and the Dawn-Dusk Asymmetry
Using 3D particle-in-cell (PIC) simulations, we study magnetic reconnection
with the x-line being spatially confined in the current direction. We include
thick current layers to prevent reconnection at two ends of a thin current
sheet that has a thickness on an ion inertial (di) scale. The reconnection rate
and outflow speed drop significantly when the extent of the thin current sheet
in the current direction is < O(10 di). When the thin current sheet extent is
long enough, we find it consists of two distinct regions; an inactive region
(on the ion-drifting side) exists adjacent to the active region where
reconnection proceeds normally as in a 2D case. The extent of this inactive
region is ~ O(10 di), and it suppresses reconnection when the thin current
sheet extent is comparable or shorter. The time-scale of current sheet thinning
toward fast reconnection can be translated into the spatial-scale of this
inactive region; because electron drifts inside the ion diffusion region
transport the reconnected magnetic flux, that drives outflows and furthers the
current sheet thinning, away from this region. This is a consequence of the
Hall effect in 3D. While this inactive region may explain the shortest possible
azimuthal extent of dipolarizing flux bundles at Earth, it may also explain the
dawn-dusk asymmetry observed at the magnetotail of Mercury, that has a global
dawn-dusk extent much shorter than that of Earth.Comment: 9 pages, 9 figures, submitted to JGR on 01/23/201
The effects of the guide field on the structures of electron density depletions in collisionless magnetic reconnection
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