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Rationale: Posterior scleritis is an ocular inflammatory disorder that can be associated with both infectious and non-infectious immune reactions. Behcet disease is a chronic, relapsing, multisystemic inflammatory disorder with uveitis. There are no reported cases of posterior scleritis with Bechet disease. Patient concerns: A 50-year-old man previously diagnosed with systemic Behcet disease presented with ocular pain and decreased vision in the left eye. Diagnosis: Posterior scleritis associated with Behcet disease was diagnosed based on optical coherence tomography showing choroidal folds, as well as contrast computed tomography and ultrasound sonography demonstrating thickening of the posterior sclera. Interventions: Treatment with systemic corticosteroids was initiated. Since inflammation relapsed during steroid tapering, anti-tumor necrosis factor-alpha (TNF-α) therapy was used in combination, and tapering of steroids was possible without recurrence of inflammation for 12 months. Outcomes: Posterior scleritis was resolved and visual acuity improved. With the continuation of TNF-α therapy, oral prednisolone was successfully tapered and discontinued. No relapse of inflammation was observed at follow-up 1 year after discontinuation of prednisolone. Lessons: Ophthalmologists should be aware of the possibility of rare manifestation of posterior scleritis in patients with Behcet disease, and that combined use of systemic steroids and anti-TNF-α therapy may resolve the scleritis without recurrence of inflammation.

We found that hot electron plasmas lead to the generation of Langmuir waves and the generated Langmuir waves can be converted to the electromagnetic waves (solar Type III radio bursts) through the linear direct mode conversion process. The second harmonic emission is generated with time delay and the amplitude larger than that of fundamental emission.

We found that strong proton acceleration leading to the complete magnetic reconnection where both poloideal and axial magnetic fields reconnect.

We apply the obtained simulationresults to the proton acceleration during solar flares.

We found that the electron Bernstein waves in the high density plasma are converted to the X-mode in the low density plasma through the linear mode conversion process due to the density inhomogeneity.

The counter-streaming instability in magnetized and positron (pair) plasmas is investigated by using two dimensional, electromagnetic, relativistic Particle-In-Cell (PIC) code. It is shown that the electrostatic waves are strongly generated by the counter-streaming instability in a strongly magnetized pair plasmas ( ωce/ωpe=2). It is also show that the high-frequency electromagnetic waves are generated in the saturated phase of the electrostatic waves. The plasma maser process that the electrostatic waves can be converted to the high frewquency electromagnetic waves could be a possible mechanism for the electromagnetic wave emission in the pulsar magnetosphere.

We investigate the plasma dynamics during coalescence of two parallel current loops by using a resistive MHD code. We investigate the orbit of many protons in the electromagnetic fields obitained from the MHD simunations. We investigate two cases of the coalescence precess: as the original loop current for both cases of co-helicity and counter-helicity.

We investigate a new model of single-loop flare based on the fact that a magnetic flux tube with axial current can be explosively sistupted during collision of two moving solitary magnetic kinks (MoSMaK), particulary paying attention to an acceleration mechanism of high energy protons. At this time, we investigate a model which flow cross-section is not same as the collision cross-section. By using three-dimensional electromagnetic fields obtained from a resistive three-dimensional MHD equations during the single-loop flare, we investigate the orbit of many protons to obtain their energy spectra. We found that the protons can be accelerated to γ-ray emitting energies. The protons are accelerated mainly in one direction along the loop by electric field produced near the three-dimensional localized current associated with the magnetic reconnection process in the disrupted loop.

We investigate sissipation process of magnetic field energy in collisionless electron-positron (pair) plasmas by using two-dimensional, fully relativistic, electromagnetic particle-in-cell code. We consider the force-free magnetic configuration with no current-driven Bunneman instability. A half of initial magnetic field energy dissipates by the tearing instability. The dissipated energy can be converted into plasma kinetic energy as well as plasma heating. The trowth rate of tearing instability is two times larger than the heory of elefcron-ion tearing instabilty.

The electromagnetic counterstreaming instability in unmagnetized pair (electron-positron) plasmas which is influenced by the external magnetic field paralled to the streaming direction is investigated numerically. The simulation show that the counterstreaming instability changes its character from magnetic to electrostatic nature. The electrostatic waves growing due to the electrostatic counterstreaming instability play an important role for producing fast electrons and positrons with energy of MeV. The process of high-energy particle production in relativistic shocks in magnetized pair plasmas may be applied to gamma-ray burst events.

We investigate the generation mechanism of magnetic fields by shear-flow instability in pair plasmas, by using a 2-dimensional particle-in-cell code. We also investigate the effeciency of the conversion of the flow energy to the magnetic field energy by changing the external magnetic field intensity. We found that the energy conversion is very efficient with about 20% for the moderate intensity of the external magnetic field.

We investigate the dynamics of the relativistic flow in pair plasmas with force-free magnetic configuration, using a three-dimensional fully relativistic electromagnetic particle-in-cell (PIC) code. We observed that three-dimensional Alfven waves with magnetic helical structures can be excited through complicated three-dimensional tearing instability triggered from the stresming instability. During these dynamical processed the pair plasma can be heated through the magnetic field dissipation and also the high-energy particles are generated.

We investigate the magnetohydrodynamic (MHD) instability of the magnetic loop in association with the solar flare. We use 'safety factor' q to describe the local twist of the magnetic loop where low q value means the strong twist, then it becomes more unstable for the MHD instability.We present the q profile on the equilibrium for two types which may correspond to small and large flare. One type corresponding to small flare is the slim cylindrical untwisted magnetic loop in initial stage. When the tube is twisted, low q region is localized around the axis of the center of the loop. We conclude that the localized low q region must be ring shaped. The energy release by MHD instability can be localized with the ring shaped region. The other type is barrel shaped untwisted magnetic loop which may correspond to the large flare. After the twist, low q region is wide along the axis. The MHD instability is caused on the whole magnetic loop, therefore the energy release is global.

We present a model for high-energy solar flare explosions driven by 3-dimensional X-type current loop coalescence. The 3-dimensional X-type loop coalescence, where two crossed fluxtubes interact in one point, is a fundamentally new process as compared to the 1-D and 2-D cases studied earlier. It is shown that, following the strong plasma collapse due to pinch effect, a point-like plasma explosion can be driven and also fast magnetosonic shock waves can be excited;We found that the conditions in the area producing the remarkable flare bursts of 21 May 1984 were indeed such that the many flare spikes could have been due to 3-D explosive X-type current loop coalescence. We also show, by studing the conding the conditions of shock formation in a Gamma ray flare, that the time delay of γ-rays from the impulsive phase could be the time needed for the shock formation in the flaring region.We draw some general conclusions on the question why certain flares do emit γ-rays in the Mev energy range, and why other, apparently important and large flares, do not. We accentuate the fact that a well-developed high-energy flare has three phases of particle acceleration.

We studied the acceleration conditions in the small but fairly energetic flare of May 21, 1984 at 13:26 UT. The most pronounced aspect of this flare was a series of 13 microwave / x-ray spikes, each lasting for about 0.1s. A previous study has shown that each of these was due to a series of successive sudden formations of small plasma knots of high energy particles. Each of these knots lost its energy in about 50 ms. In the present study we show that these knots can originate by the process of x-type (3-D) flux tube coalescence. The predicted rise time (30 to 50 ms) and energy are in good agreement with the observationally derived parameters.

The coronal explosion, discovered by De Jager and Boelee (1984), and interpreted by them as manifestations of plasma streaming out of the flare kernels, can also be interpreted as signatures of current loop coalesscence in the flaring region.

In this work we used Particle-In-Cell simulations to study the interaction of circularly polarised Alfv��n waves with one dimensional plasma density inhomogeneities transverse to the uniform magnetic field (phase mixing) in collisionless plasmas. In our preliminary work we reported discovery of a new electron acceleration mechanism, in which progressive distortion of the Alfv��n wave front, due to the differences in local Alfv��n speed, generates an oblique (nearly parallel to the magnetic field) electrostatic field. The latter accelerates electrons through the Landau resonance. Here we report a detailed study of this novel mechanism, including: (i) analysis of broadening of the ion distribution function due to the presence of Alfv��n waves and (ii) the generation of compressive perturbations due to both weak non-linearity and plasma density inhomogeneity. The amplitude decay law in the inhomogeneous regions, in the kinetic regime, is demonstrated to be the same as in the MHD approximation described by Heyvaerts and Priest (1983)., Final, accepted in Astron. Astrophys., version; Low resolution figures are included here; High resolution figure version is available from D. Tsiklauri upon request. Astron. Astrophys. (in press)

Performance of quanta having a finite coherence length ℓ c in a periodic structure is studied. Classification between wave and particle properties depends strongly on the magnitude of coupling constant K, determined by the quantum mass, periodic potential depth and wavenumber. It is found that if K increases in a periodic structure with a fixed length, then a transmitted quantum is inclined to show wave properties even if ℓ c is short. As ℓ c becomes short, more quanta transmit through the structure even in the stop band. Coherence and medium lengths play an equivalent role in transmission. Namely, transmittance is nearly identical even if medium and coherence lengths are exchanged. Many oscillations due to the wave properties appearing in the transmission temporal wave can be explained by the effective mode mismatch among many eigenmodes. The oscillation period is controllable by changing the periodic potential depth or the effective mass.

Double sub-peak structures in the quasi-periodic oscillations found in the time profiles of two solar flares on 1980 June 7 and 1982 November 26 are well explained in terms of the coalescence instability of two current loops. This interpretation is supported by the observations of two microwave sources and their interaction for the November 26 flare. The difference of both sub-peak structures and time scales between the two flares are discussed from the viewpoint of different plasma parameters in our computer simulations.

We investigate a dynamical model of prominence formation in a current sheet at the boundary between two regions of opposite magnetic polarity. Coupled nonlinear equations describing the temporal compression and condensation of plasma in the current sheet are set up as a natural extension of the usual equations for current sheet collapse (Imshennik and Syrovatskii, 1967). It is shown that under certain conditions the current sheet undergoes a nonlinear oscillation during the compression. The thermal instability with cooling is driven by a density enhancement produced during the current sheet formation stage.

The non-linear coalescence instability of current carrying solar loops can explain many of the characteristics of the solar flares such as their impulsive nature, heating and high energy particle acceleration, amplitude oscillations of electromagnetic emission as well as the characteristics of 2-D microwave images obtained during a flare. The plasma compressibility leads to the explosive phase of loop coalescence and its overshoot results in amplitude oscillations in temperatures by adiabatic compression and decompression. We note that the presence of strong electric fields and super-Alfvenic flows during the course of the instabilty paly an important role in the production of non-thermal particles. A qualitative explanation on the physical processes taking place during the non-linear stages of the instability is given.

Magnetohydrodynamic simulation of the explosive coalescence of magnetic islands is carried out. This result is in agreement with the electromagnetic particle simulation. A theoretical model to describe this process observed in our computer simulations is presented. The theory describes the magnetic collapse and is based on a self-similar solution to the two-fluid plasma equations, as the simulation exhibits temporal self-similarity. The master equation for the scale factor takes a from of the orbital equation in a Sagdeev potential.

The nonlinear coalescence instability of current carrying solar loops can explain many of the characteristics of the solar flares such as their impulsive nature, heating and high energy particle acceleration, amplitude oscillations of electromagnetic emission as well as the characteristics of 2-D microwave images obtained during a solar flare. The physical characteristics of the explosive coalescence of currents are presented in detail through computer simulation and theory.Canonical characteristics of the explosive coalescence are: (1) a large amount of impulsive increase of kinetic energies of electrons and ions, (2) simultaneous heating and acceleration of electrons and ions in high and low energy spectra, (3) ensuing quasi-periodic amplitude oscillations in fields and particle quantities, (4) the double peak (or triple peak) structure in these profiles, and (5) characteristic break in energy spectra of electrons and ions. A single pair of currents as well as multiple currents may participate in the coalescence process, yielding varieties of phenomena. These physical properties seem to underlie in some of impulsive solar flares.In particular, double sub-peak structures in the quasi-periodic oscillations found in the time profiles of two solar flares on June 7, 1980 and November 26, 1982 are well explained in terms of the coalescence instability of two current loops. This interpretation is supported by the observations of two microwave sources and their interaction for the November 26, 1982 flare.Some more details as well as a generalization of the present model to solar flares with the coalescence as an elementary process in the flare phenomenon are presented.

It is shown that ion streams across the magnetic field moving with electrons cause explosive transverse electrostatic field during magnetic collapse such as coalescence instability of current loops. The electrostatic field can explosively accelerate ions and electrons perpendicular both to the magnetic field and ion streams. Ions and electrons are almost simultaneously accelerated to the opposite direction, respectively. The results obtained here well explain the simulation results of collisionless coalescence instability of current loops. The simultaneous acceleration mechanism of ions and electrons is applied to the origin of explosive high energy varticles in cosmic plasmas.

Note: J. Geophys. Res., in press, 資料番号: SA8000565000

Forced magnetic reconnection induced by magnetohydrodynamic (MHD) waves may account for the triggering of explosive solar activities such as flares. Reconnection in a neutral sheet plasma can be driven by the ponderomotive force associated with nonlinear MHD waves accompanying plasma vortex motion. The nonlinear stage of forced reconnection by MHD waves is simulated with a MHDparticle-code: Some conditions for fast reconnection are discussed with applications to solar flares.

Particle simulations of collisionless tearing, reconnection and coalescence of magnetic fields for a sheet-pinch configuration show that reconnection is Sweet-Parker like in the tearing and island formation phase. It is much faster to explosive in the island coalescence stage. Island coalescence is the most energetic process arrl leads to large ion temperature increase and oscillations in the merged state. Similar phenomena have been observed in equivalent MHD simulations.Coalescence and its effects, as observed in our simulations, may explain many of the features of solar flares and coronal X-ray brightening.

An explosive reconnection process associated with the nonlinear evolution of the coalescence instability is found through studies of the electromagnetic particle simulation. The explosive coalescence is a process of magnetic collapse, in which we find the magnetic and electrostatic field energies and temperatures (ion temperature in the coalescing direction, in particular) explode toward the explosion time to as (t_0 - t)^, (t_0 - t)^, and (t_0 - t)^, respectively.Single-peak, double-peak, and triple-peak structures of magnetic energy, temperature, and electrostatic energy, respectively, are observed on the simulatton as overshoot amplitude oscillations and these features are theoretically explained. Rapid acceleration of particles binormal to the magnetic field and electric field becomes possible.