A unified model for the feedback and ballooning instabilities in the magnetosphere‐ionosphere (M‐I) coupling is developed by means of the reduced magnetohydrodynamic and two‐fluid equations, ...involving the local current closure and the ionospheric conductivity change in a scale of auroral fine structures, self‐consistently. In a low pressure gradient case, the Alfvén harmonics are destabilized through the feedback mechanism, while the ballooning instability appears if the magnetospheric pressure gradient exceeds a critical value. Transition of the dominant instability between the feedback and ballooning modes is brought by change of the normalized pressure gradient or the convection electric field in the magnetosphere. The obtained results imply a variety of appearance of auroral arcs and beads in the M‐I coupling system.
Plain Language Summary
A novel explanation on generation of arc and beading structures of auroras is provided by means of theoretical analysis based on the first principle of plasma physics. The theory predicts competition of two different types of perturbation growth, leading to a variety of auroral appearance.
Key Points
A new magnetosphere‐ionosphere coupling model is derived, where the feedback and ballooning instabilities are simultaneously described
Transition of dominant instability mode is brought by change of pressure gradient or convection electric field in the magnetosphere
The magnetosphere‐ionosphere coupling theory predicts a novel scenario on the auroral beading and preexisting arcs
To establish an appropriate steroid treatment regimen for autoimmune pancreatitis (AIP).
A retrospective survey of AIP treatment was conducted in 17 centres in Japan. The main outcome measures were ...rate of remission and relapse.
Of 563 patients with AIP, 459 (82%) received steroid treatment. The remission rate of steroid-treated AIP was 98%, which was significantly higher than that of patients without steroid treatment (74%, 77/104; p<0.001). Steroid treatment was given for obstructive jaundice (60%), abdominal pain (11%), associated extrapancreatic lesions except the biliary duct (11%), and diffuse enlargement of the pancreas (10%). There was no relationship between the period necessary to achieve remission and the initial dose (30 mg/day vs 40 mg/day) of prednisolone. Maintenance steroid treatment was given in 377 (82%) of 459 steroid-treated patients, and steroid treatment was stopped in 104 patients. The relapse rate of patients with AIP on maintenance treatment was 23% (63/273), which was significantly lower than that of patients who stopped maintenance treatment (34%, 35/104; p = 0.048). From the start of steroid treatment, 56% (55/99) relapsed within 1 year and 92% (91/99) relapsed within 3 years. Of the 89 relapsed patients, 83 (93%) received steroid re-treatment, and steroid re-treatment was effective in 97% of them.
The major indication for steroid treatment in AIP is the presence of symptoms. An initial prednisolone dose of 0.6 mg/kg/day, is recommend, which is then reduced to a maintenance dose over a period of 3-6 months. Maintenance treatment with low-dose steroid reduces but dose not eliminate relapses.
Gyrokinetic turbulence simulations are applied for the first time to the cross-scale interactions of microtearing modes (MTMs) and electron-temperature-gradient (ETG) modes. The investigation of the ...fluctuation response in a multiscale simulation including both types of instabilities indicates that MTMs are suppressed by ETG turbulence. A detailed analysis of nonlinear mode coupling reveals that radially localized current-sheet structures of MTMs are strongly distorted by fine-scale E×B flows of ETG turbulence. Consequently, electron heat transport caused by the magnetic flutter of MTMs is significantly reduced and ETG turbulence dominates electron heat transport.
Multiscale gyrokinetic turbulence simulations with the real ion-to-electron mass ratio and β value are realized for the first time, where the β value is given by the ratio of plasma pressure to ...magnetic pressure and characterizes electromagnetic effects on microinstabilities. Numerical analysis at both the electron scale and the ion scale is used to reveal the mechanism of their cross-scale interactions. Even with the real-mass scale separation, ion-scale turbulence eliminates electron-scale streamers and dominates heat transport, not only of ions but also of electrons. Suppression of electron-scale turbulence by ion-scale eddies, rather than by long-wavelength zonal flows, is also demonstrated by means of direct measurement of nonlinear mode-to-mode coupling. When the ion-scale modes are stabilized by finite-β effects, the contribution of the electron-scale dynamics to the turbulent transport becomes non-negligible and turns out to enhance ion-scale turbulent transport. Damping of the ion-scale zonal flows by electron-scale turbulence is responsible for the enhancement of ion-scale transport.
This paper presents modeling of a coal gasification reaction, and prediction of gasification performance for an entrained flow coal gasifier. The purposes of this study are to develop an evaluation ...technique for design and performance optimization of coal gasifiers using a numerical simulation technique, and to confirm the validity of the model. The coal gasification model suggested in this paper is composed of a pyrolysis model, char gasification model, and gas phase reaction model. A numerical simulation with the coal gasification model is performed on the CRIEPI 2
tons/day (T/D) research scale coal gasifier. Influence of the air ratio on gasification performance, such as a per pass carbon conversion efficiency, amount of product char, a heating value of the product gas, and cold gas efficiency is presented with regard to the 2
T/D gasifier. Gas temperature distribution and product gas composition are also presented. A comparison between the calculation and experimental data shows that most features of the gasification performance were identified accurately by the numerical simulation, confirming the validity of the current model.
This article gives a review of the entanglement dynamics of flexible polymer chains from theoretical and experimental points of view. The global motion of the entangled chains determines ...viscoelastic, dielectric, and diffusion properties in long time scales. The current tube models for this motion, incorporating the concepts of reptation, contour length fluctuation, arm retraction, constraint release, and tube dilation, are summarized. A summary is also made for extensive data for these properties. The model predictions are compared with those data, and the validity and limitation of the models are discussed. In particular, the models are critically examined for detailed dynamic features revealed from comparison of the viscoelastic and dielectric data (e.g. coherence in the submolecule motion), and the theoretical, as well as experimental, challenges remaining for future work are explained.
A linear eigenmode analysis of the magnetosphere‐ionosphere coupling shows that the feedback instability leading to spontaneous formation of auroral arc structures remains unstable even in a case ...with strong vertical shear of horizontal ion flows induced by ion‐neutral collisions in the E layer. For low‐order Alfvén harmonics, the linear frequency and growth rate obtained by means of a height‐resolved model of the ionosphere are comparable to those resulted from the height‐integrated one, where fine vertical structures of the ionospheric density and magnetic field perturbations are well resolved in the former. The present result confirms validity of the height‐integrated ionosphere model in the long parallel wavelength limit, as assumed in previous studies on the feedback instability.
Plain Language Summary
Spontaneous formation of auroral arcs can be explained in terms of a plasma instability in the magnetosphere‐ionosphere coupling. The present study confirms validity and robustness of the basic instability theory even in cases with inhomogeneous profiles of the ionospheric parameters such as the ion‐neutral collision.
Key Points
Feedback instability in the magnetosphere‐ionosphere coupling is unstable even in a case with strong vertical flow shear in the E layer
The linear eigenmode analysis captures entire profiles of the electromagnetic fields and the density perturbations along a field line
A conventional magnetosphere‐ionosphere coupling model with a height‐integrated ionosphere remains valid in a low‐frequency regime
•A contour dynamics method is applied to the Vlasov-Poisson system.•An efficient implementation of the periodic boundary condition is proposed.•The new method is benchmarked for the linear and ...nonlinear Landau damping.•Energy and particle conservation is examined for the benchmark test.•Particle trapping process is well captured by the contour dynamics method.
We revisit the contour dynamics (CD) simulation method which is applicable to large deformation of distribution function in the Vlasov-Poisson plasma with the periodic boundary, where contours of distribution function are traced without using spatial grids. Novelty of this study lies in application of CD to the one-dimensional Vlasov-Poisson plasma with the periodic boundary condition. A major difficulty in application of the periodic boundary is how to deal with contours when they cross the boundaries. It has been overcome by virtue of a periodic Green's function, which effectively introduces the periodic boundary condition without cutting nor reallocating the contours. The simulation results are confirmed by comparing with an analytical solution for the piece-wise constant distribution function in the linear regime and a linear analysis of the Landau damping. Also, particle trapping by Langmuir wave is successfully reproduced in the nonlinear regime.
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