Contributions to Loss Across the Magnetopause During an Electron Dropout Event.

Dropout events are dramatic decreases in radiation belt electron populations that can occur in as little as 30 minutes. Loss to magnetopause due to a combination of magnetopause shadowing and outward radial transport plays a significant role in these events. We examine the dropout of relativistic electron populations during the October 2012 geomagnetic storm using simulated electron phase space density, evaluating the contribution of different processes to losses across the magnetopause. We compare loss contribution from outward transport calculated using a standard empirical radial diffusion model that assumes a dipolar geomagnetic field to an event-specific radial diffusion model evaluated with a non-dipolar geomagnetic field. We additionally evaluate the contribution of Shabansky type 1 particles, which bounce along magnetic field lines with local equatorial maxima, to the loss calculated during this event. We find that the empirical radial diffusion model with a dipolar background field underestimates the contribution of radial diffusion to this dropout event by up to 10% when compared to the event-specific, non-dipolar radial diffusion model. We additionally find that including Shabansky type 1 particles in the initial electron phase space density, that is, allowing some magnetic field lines distorted from the typical single-minima configuration in drift shell construction, increases the calculated loss by an average of 0.75%. This shows that the treatment of the geomagnetic field significantly impacts the calculation of electron losses to the magnetopause during dropout events, with the non-dipolar treatment of radial diffusion being essential to accurately quantify the loss of outer radiation belt populations.

Autogenous and efficient acceleration of energetic ions upstream of Earth's bow shock.

Earth and its magnetosphere are immersed in the supersonic flow of the solar-wind plasma that fills interplanetary space. As the solar wind slows and deflects to flow around Earth, or any other obstacle, a 'bow shock' forms within the flow. Under almost all solar-wind conditions, planetary bow shocks such as Earth's are collisionless, supercritical shocks, meaning that they reflect and accelerate a fraction of the incident solar-wind ions as an energy dissipation mechanism1,2, which results in the formation of a region called the ion foreshock3. In the foreshock, large-scale, transient phenomena can develop, such as 'hot flow anomalies'4-9, which are concentrations of shock-reflected, suprathermal ions that are channelled and accumulated along certain structures in the upstream magnetic field. Hot flow anomalies evolve explosively, often resulting in the formation of new shocks along their upstream edges5,10, and potentially contribute to particle acceleration11-13, but there have hitherto been no observations to constrain this acceleration or to confirm the underlying mechanism. Here we report observations of a hot flow anomaly accelerating solar-wind ions from roughly 1-10 kiloelectronvolts up to almost 1,000 kiloelectronvolts. The acceleration mechanism depends on the mass and charge state of the ions and is consistent with first-order Fermi acceleration14,15. The acceleration that we observe results from only the interaction of Earth's bow shock with the solar wind, but produces a much, much larger number of energetic particles compared to what would typically be produced in the foreshock from acceleration at the bow shock. Such autogenous and efficient acceleration at quasi-parallel bow shocks (the normal direction of which are within about 45 degrees of the interplanetary magnetic field direction) provides a potential solution to Fermi's 'injection problem', which requires an as-yet-unexplained seed population of energetic particles, and implies that foreshock transients may be important in the generation of cosmic rays at astrophysical shocks throughout the cosmos.

Relativistic Electrons Produced by Foreshock Disturbances Observed Upstream of Earth's Bow Shock.

Charged particles can be reflected and accelerated by strong (i.e., high Mach number) astrophysical collisionless shock waves, streaming away to form a foreshock region in communication with the shock. Foreshocks are primarily populated by suprathermal ions that can generate foreshock disturbances-large-scale (i.e., tens to thousands of thermal ion Larmor radii), transient (∼5-10 per day) structures. They have recently been found to accelerate ions to energies of several keV. Although electrons in Saturn's high Mach number (M>40) bow shock can be accelerated to relativistic energies (nearly 1000 keV), it has hitherto been thought impossible to accelerate electrons beyond a few tens of keV at Earth's low Mach number (1≤M<20) bow shock. Here we report observations of electrons energized by foreshock disturbances to energies up to at least ∼300 keV. Although such energetic electrons have been previously observed, their presence has been attributed to escaping magnetospheric particles or solar events. These relativistic electrons are not associated with any solar or magnetospheric activity. Further, due to their relatively small Larmor radii (compared to magnetic gradient scale lengths) and large thermal speeds (compared to shock speeds), no known shock acceleration mechanism can energize thermal electrons up to relativistic energies. The discovery of relativistic electrons associated with foreshock structures commonly generated in astrophysical shocks could provide a new paradigm for electron injections and acceleration in collisionless plasmas.

Dynamical-systems approach to relativistic nonlinear wave-particle interaction in collisionless plasmas.

In this report, we present a dynamical systems approach to study the exact nonlinear wave-particle interaction in relativistic regime. We give particular attention to the effect of wave obliquity on the dynamics of the orbits by studying the specific cases of parallel (θ = 0) and perpendicular (θ = -π/2) propagations in comparison to the general case of oblique propagation θ =]-π/2,0[. We found that the fixed points of the system correspond to Landau resonance and that the dynamics can evolve from trapping to surfatron acceleration for propagation angles obeying a Hopf bifurcations condition. Cyclotron-resonant particles are also studied by the construction of a pseudo-potential structure in the Lorentz factor γ. We derived a condition for which Arnold diffusion results in relativistic stochastic acceleration. Hence, two general conclusions are drawn: (1) The propagation angle θ can significantly alter the dynamics of the orbits at both Landau and cyclotron-resonances. (2) Considering the short-time scales upon which the particles are accelerated, these two mechanisms for Landau and cyclotron resonant orbits could become potential candidates for problems of particle energization in collisionless space and cosmic plasmas.

Sweet's syndrome in a patient with rheumatoid arthritis, Sjögren's syndrome and lymph node tuberculosis.

Sweet's syndrome (SS) is an acute neutrophilic dermatosis characterised by abrupt onset of fever, leukocytosis and cutaneous eruption, with dermal neutrophilia on skin biopsy. Most cases are idiopathic but SS can be associated with various affections, especially neoplastic, inflammatory and infectious diseases. The authors report the case of an SS occurring in a patient with a known rheumatoid arthritis associated with a secondary Sjögren's syndrome, with incidental finding of concurrent lymph node tuberculosis. In case of SS, an associated disease (malignant, inflammatory or infectious diseases) must imperatively be searched for, knowing that two or more of these affections can coexist.

[Crohn's disease with isolated vulvar localization and pregnancy. A case report]. / Maladie de Crohn à localisation vulvaire isolée et grossesse. A propos d'un cas.

Extra-intestinal manifestations of Crohn's disease are well described. A very uncommon gynaecologic manifestation of this disease is vulvar involvement. Till now, sixteen cases have been reported in the literature. We report a case of a pregnant woman with isolated vulvar involvement, without bowel manifestations. The diagnosis have been clinically uncertain, but the histopathology goes with Crohn's disease. Discussion point out the difficulties in diagnosis and management of this vulvar condition, and of its association with pregnancy.