Parametric decay of oblique Alfvén waves in two-dimensional hybrid simulations.

Certain types of plasma waves are known to become parametrically unstable under specific plasma conditions, in which the pump wave will decay into several daughter waves with different wavenumbers and frequencies. In the past, the related plasma instabilities have been treated analytically for various parameter regimes and by use of various numerical methods, yet the oblique propagation with respect to the background magnetic field has rarely been dealt with in two dimensions, mainly because of the high computational demand. Here we present a hybrid-simulation study of the parametric decay of a moderately oblique Alfvén wave having elliptical polarization. It is found that such a compressive wave can decay into waves with higher and lower wavenumbers than the pump.

Clustering of additional autoimmunity behaves differently in Hashimoto's patients compared with Graves' patients.

OBJECTIVE: It is unclear whether Hashimoto's thyroiditis and Graves' disease (often referred to as autoimmune thyroid disease, AITD) cluster to the same extent with other autoimmune disorders. METHODS: We assessed adrenal, ß-cell, celiac and gastric antibodies in a cohort of 523 adult patients with Graves' disease and 359 patients with Hashimoto's disease and compared their clustering. RESULTS: Adrenal autoimmunity associated more often with Hashimoto's disease (9.0%) than with Graves' disease (3.3%, P=0.001). ß-cell autoimmunity was seen more frequently in Hashimoto's disease (25.4%) than in Graves' disease (15.6%, P=0.001) patients. We found low prevalences of celiac autoimmunity (1.2% for Graves' and 1.2% for Hashimoto's disease). Celiac and gastric autoimmunity were not statistically different in Hashimoto's and Graves' disease patients. Although gastric autoimmunity itself was equally prevalent (around 20%), Hashimoto's disease often showed significantly more clustering of adrenal autoimmunity with gastric autoimmunity (5.3%) than Graves' disease (1.2%, P=0.001). Similarly, clustering of adrenal autoimmunity was seen with ß-cell autoimmunity in Hashimoto's patients (3.2%), while such clustering was much less encountered in 359 Graves' patients (0.9%, P=0.029). CONCLUSION: In conclusion, Hashimoto's disease shows a markedly higher clustering of additional autoimmunity, especially with adrenal and ß-cell autoimmunity. Combined clustering of gastric and adrenal autoimmunity and combined clustering of adrenal and ß-cell autoimmunity were both seen more often in Hashimoto's patients. Clustering with celiac disease appears to be low. These findings indicate that Hashimoto's and Graves' disease differ in their clinical expression regarding additional autoimmunity, which argues against the indiscriminate use of AITD as an entity.

Preferential heating and acceleration of alpha particles by Alfvén-cyclotron waves.

Preferential heating and acceleration of heavy ions in the solar wind and corona represent a long-standing theoretical problem in space physics, and are distinct experimental signatures of kinetic processes occurring in collisionless plasmas. We show that fast and slow ion-acoustic waves (IAW) and transverse waves, driven by Alfvén-cyclotron wave parametric instabilities can selectively destroy the coherent fluid motion of different ion species and, in this way lead to their differential heating and acceleration. Trapping of the more abundant protons by the fast IAW generates a proton beam with drift speed of about the Alfvén speed. Because of their larger mass, alpha particles do not become significantly trapped and start, by conservation of total ion momentum, drifting relative to the receding bulk protons. Thus the resulting core protons and the alpha particles are differentially heated via pitch-angle scattering.