Mode coupling in two-dimensional magnetohydrodynamic flows

The spectrum of incompressible waves and instabilities of two-dimensional plasma geometries with background flow is calculated. The equilibrium is solved numerically by the recently developed program FLow Equilibrium Solver (FLES). The spectra of the equilibria are computed by means of another ne vcr program, the INcompressible 2-dimensional FLow Eigenvalue Solver (IN2FLES). Magnetic instabilities and instabilities driven by the the two-dimensionality and the flow are found. For linear equilibria, the eigenvalues for elliptical geometries remain close to the curves on which the eigenvalues for circular geometries lie. These curves may be found for unbounded domains by a calculation in Fourier space [see Lifschitz, A. In: Proceedings of 1995 International Workshop on Operator Theory and Applications (ed. R. Mennicken and C. Tretter), pp. 97-117, Birkhauser, Boston, 1998]. Here the relation between a new continuous spectrum of unbounded domains and the discrete spectrum of bounded domains is investigated. Finally, it is found that the two-dimensionality and the background flow may lead to an overstable cluster point

The spectrum of MHD flows about X-points.

A recently proposed method to calculate the spectrum of linear, incompressible, unbounded plasma flows is applied to magnetohydrodynamic flows about X points. The method transforms the two-dimensional spectral problem in physical space into a one-dimensional problem in Fourier space. The latter problem is far easier to solve. application of this method to X-point plasma flows results in two kinds of essential spectra. One kind corresponds to stable perturbations and the other one to perturbations that become overstable whenever the square of the poloidal Alfven Mach number becomes larger than 1. Apart from these two spectra, no other spectral values were found

Magnetohydrodynamics spectrum of gravitating plane plasmas with flow.

The ideal magnetohydrodynamic spectrum of gravitating plane plasmas with equilibrium flow is investigated. Flow makes the spectral problem non-self-adjoint, so that the spectrum can become overstable. The criteria for cluster spectra to appear are derived analytically and both stable and unstable sides of the spectrum are examined numerically. Above certain critical values of the shear flow at the resonant surface, the gravitating interchange modes disappear However, the local extrema of the continua can then take over the cluster spectrum

Microglia morphotyping in the adult mouse CNS using hierarchical clustering on principal components reveals regional heterogeneity but no sexual dimorphism

Microglia are the resident macrophages of the central nervous system (CNS) and play a pivotal role in immune surveillance and CNS homeostasis. Morphological transitions in microglia are indicative for local changes in the CNS microenvironment and serve as a proxy for the detection of alterations in the CNS, both in health and disease. Current strategies to ‘measure’ microglia combine advanced morphometrics with clustering approaches to identify and categorize microglia morphologies. However, these studies are labor intensive and clustering approaches are often subject to relevant feature selection bias. Here, we provide a morphometrics pipeline with user-friendly computational tools for image segmentation, automated feature extraction and morphological categorization of microglia by means of hierarchical clustering on principal components (HCPC) without the need for feature inclusion criteria. With this pipeline we provide new and detailed insights in the distribution of microglia morphotypes across sixteen CNS regions along the rostro-caudal axis of the adult C57BL/6J mouse CNS. Although regional variations in microglia morphologies were evident, we found no evidence for male–female dimorphism at any CNS region investigated, indicating that - by and large - microglia in adult male and female mice are morphometrically indistinguishable. Taken together, our newly developed pipeline provides valuable tools for objective and unbiased identification and categorization of microglia morphotypes and can be applied to any CNS (disease) model.</p

The Meta VCI Map consortium for meta-analyses on strategic lesion locations for vascular cognitive impairment using lesion-symptom mapping: design and multicenter pilot study

Introduction: The Meta VCI Map consortium performs meta-analyses on strategic lesion locations for vascular cognitive impairment using lesion-symptom mapping. Integration of data from different cohorts will increase sample sizes, to improve brain lesion coverage and support comprehensive lesion-symptom mapping studies. Methods: Cohorts with available imaging on white matter hyperintensities or infarcts and cognitive testing were invited. We performed a pilot study to test the feasibility of multicenter data processing and analysis and determine the benefits to lesion coverage. Results: Forty-seven groups have joined Meta VCI Map (stroke n = 7800 patients; memory clinic n = 4900; population-based n = 14,400). The pilot study (six ischemic stroke cohorts, n = 878) demonstrated feasibility of multicenter data integration (computed tomography/magnetic resonance imaging) and achieved marked improvement of lesion coverage. Discussion: Meta VCI Map will provide new insights into the relevance of vascular lesion location for cognitive dysfunction. After the successful pilot study, further projects are being prepared. Other investigators are welcome to join

Spectrum and stability of a rigidly rotating compressible plasma.

We consider the spectrum and stability of a compressible, rigidly rotating plasma column with constant magnetic pitch. It is found tl-lat when the pressure on axis is zero, a continuous spectrum arises, which may become unstable. When the pressure on axis is finite or a conducting core is included, the spectrum is discrete, but may still be unstable. The instability is due to the poloidal magnetic field and/or the rotation of the cylinder in combination with the density profile. It is found numerically that the pressure stabilizes both types of instabilities