Search

Aims. We aim to determine the phase speed of an oscillation in a magnetic pore using only intensity images at one height. The observations were obtained using the CRisp Imaging SpectroPolarimeter at the Swedisch 1-m Solar Telescope and show variations in both cross-sectional area and intensity in a magnetic pore. Methods. We have designed and tested an observational method to extract the wave parameters that are important for seismology. We modelled the magnetic pore as a straight cylinder with a uniform plasma both inside and outside the flux tube and identify different wave modes. Using analytic expressions, we are able to distinguish between fast and slow modes and obtain the phase speed of the oscillations. Results. We found that the observed oscillations are slow modes with a phase speed around 5 km s-1. We also have strong evidence that the oscillations are standing harmonics. [ABSTRACT FROM AUTHOR]

Aims. We aim to calculate the kinetic, magnetic, thermal, and total energy densities and the flux of energy in axisymmetric sausage modes. The resulting equations should contain as few parameters as possible to facilitate applicability for different observations. Methods. The background equilibrium is a one-dimensional cylindrical flux tube model with a piecewise constant radial density profile. This enables us to use linearised magnetohydrodynamic equations to calculate the energy densities and the flux of energy for axisymmetric sausage modes. Results. The equations used to calculate the energy densities and the flux of energy in axisymmetric sausage modes depend on the radius of the flux tube, the equilibrium sound and Alfvén speeds, the density of the plasma, the period and phase speed of the wave, and the radial or longitudinal components of the Lagrangian displacement at the flux tube boundary. Approximate relations for limiting cases of propagating slow and fast sausage modes are also obtained. We also obtained the dispersive first-order correction term to the phase speed for both the fundamental slow body mode under coronal conditions and the slow surface mode under photospheric conditions. [ABSTRACT FROM AUTHOR]

Aims. We present a mathematical framework for the seismology of photospheric flux tubes using a uniform straight cylinder as a flux-tube model. In contrast to the earlier model of Fujimura & Tsuneta (2009, ApJ, 702, 1443), we also include a non-zero gas pressure; we do not use the thin tube approximation and we use an underdense region inside the flux tube. Methods. We used the linearised ideal magnetohydrodynamic equations to describe different wave modes in the photosphere. Using the wave mode polarisations we then obtained phase relations which represent different observables. Those phase relations were used to calculate phase differences and amplitude ratios. Finally we inverted these amplitude ratios to obtain plasma parameters which are not directly observable. Results. The mathematical framework results in phase differences that can be conveniently compared with observational data to distinguish between different wave modes. Once the wave mode has been identified, the inverted amplitude ratios can be used to either analytically or numerically estimate the magnitude of plasma parameters which are not directly observable, such as the vertical wavenumber. Artificial observations of different wave modes have shown that the framework mostly succeeds in identifying the correct wave mode and in reproducing the correct plasma parameters using the inverted amplitude ratios. [ABSTRACT FROM AUTHOR]

Mesenchymal stem cells (MSCs) are one of the most promising stem cell types due to their availability and relatively simple requirements for in vitro expansion and genetic manipulation. Besides the well-characterized MSCs derived from bone marrow, there is growing evidence suggesting that dental pulp and the umbilical cord matrix both contain a substantial amount of cells having properties similar to those of MSCs. In order to assess the potential of dental pulp-derived MSCs (DPSC) and umbilical cord-derived MSCs (UCSC) in future clinical applications, it is essential to gain more insight into their differentiation capacity and to evaluate the tissues formed by these cells. In the present study, the morphological and ultrastructural characteristics of DPSC and UCSC induced towards osteogenic, adipogenic, and chondrogenic lineages were investigated. Cultured DPSC and UCSC showed a similar expression pattern of antigens characteristic of MSCs including CD105, CD29, CD44, CD146, and STRO-1. Under appropriate culture conditions, both DPSC and UCSC showed chondrogenic and osteogenic potential. Adipogenesis could be only partially induced in DPSC resulting in the de novo expression of fatty acid binding protein (FABP), whereas UCSC expressed FABP combined with a very high accumulation of lipid droplets in the cytoplasm. Our results demonstrate, at the biochemical and ultrastructural level, that DPSC display at least bilineage potential, whereas UCSC, which are developmentally more primitive cells, show trilineage potential. We emphasize that transmission electron microscopical analysis is useful to elucidate detailed structural information and provides indisputable evidence of differentiation. These findings highlight their potential therapeutic value for cell-based tissue engineering. Copyright © 2010 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

Aims: Rapid and extensive activation of astrocytes occurs subsequent to many forms of central nervous system (CNS) injury. Recent studies have revealed that the expression profile of reactive astrocytes comprises antigens present during astrocyte development. Elevated levels of the injury-related cytokine transforming growth factor-beta 1 (TGF-β1) secreted by microglial cells and invading macrophages have been correlated with the reactive astrocyte phenotype and glial scar formation. Methods: In the present study, the expression profile of alpha-smooth muscle actin (α-SMA) and nestin, two cytoskeletal proteins expressed during astrocyte development, was studied in multiple sclerosis (MS) lesions. In addition, α-SMA and nestin organization and expression were analysed in rat primary astrocyte cultures in response to TGF-β1. Results: In active lesions and in the hypercellular margin of chronic active MS lesions, immunostaining for α-SMA revealed a subpopulation of reactive astrocytes, whereas the majority of reactive astrocytes expressed nestin. α-SMA and nestin expressing reactive astrocytes were in close relationship with TGF-β1 expressing macrophages or microglia. In addition, TGF-β1 expression within α-SMA or nestin expressing astrocytes was also detected. Our in vitro experiments showed that TGF-β1 regulated the organization and expression of α-SMA and nestin in astrocytes. Conclusions: Reactive astrocytes in active MS lesions re-express α-SMA and nestin. We suggest that the in vivo re-expression might be under regulation of TGF-β1. These results further clarify the regulation of astrocyte activity after CNS injury, which is important for the astroglial adaptation to pathological situations. [ABSTRACT FROM AUTHOR]