Magnetic pressure support and accretion disk spectra

Stellar atmosphere models of ionized accretion disks have generally neglected the contribution of magnetic fields to the vertical hydrostatic support, although magnetic fields are widely believed to play a critical role in the transport of angular momentum. Simulations of magnetorotational turbulence in a vertically stratified shearing box geometry show that magnetic pressure support can be dominant in the upper layers of the disk. We present calculations of accretion disk spectra that include this magnetic pressure support, as well as a vertical dissipation profile based on simulation. Magnetic pressure support generically produces a more vertically extended disk atmosphere with a larger density scale height. This acts to harden the spectrum compared to models that neglect magnetic pressure support. We estimate the significance of this effect on disk-integrated spectra by calculating an illustrative disk model for a stellar mass black hole, assuming that similar magnetic pressure support exists at all radii.Comment: submitted to Ap

Factors affecting the digestibility of raw and gelatinized potato starches.

The enzymatic digestibilities of raw and gelatinized starches in various potato starches, as well as sweet potato, cassava, and yam starches, were estimated, along with other starch properties, such as the phosphorus content, median granule size, and rapid visco analyzer (RVA) pasting properties. Furthermore, correlation coefficients were calculated between the hydrolysis rates (HR) by amylase and other starch quality parameters. A larger granule size was closely associated with a lower HR in raw starch, while the HR in gelatinized starch did not correlate with the median granule size. An increase in phosphorus content resulted in a definitely lower HR in raw starch and tended to decrease the HR in gelatinized starch for the composite of potato and other starches. In contrast, no correlation coefficients of the phosphorus content with the HRs in raw and gelatinized starches were observed within potato starches. Starches with higher peak viscosity and breakdown showed a lower HR in raw starch, while few or no effects of these RVA parameters on the HR in gelatinized starch were observed for the composite of potato and other starches or among potato starches, respectively

Magnetically Driven Accretion Flows in the Kerr Metric II: Structure of the Magnetic Field

We present a detailed analysis of the magnetic field structure found in general relativistic 3D MHD simulations of accreting tori in the Kerr metric with different black hole spins. Among the properties analyzed are the field strength as a function of position and black hole spin, the shapes of field lines, the degree to which they connect different regions, and their degree of tangling. We investigate prior speculations about the structure of the magnetic fields and discuss how frequently certain configurations are seen in the simulations. We also analyze the distribution of current density, with a view toward identifying possible locations for magnetic energy dissipation.Comment: Submitted to ApJ. PDF and PostScript files with high-resolution figures are available at http://www.pha.jhu.edu/~shirose/GRMHD/PaperII

Altered dendritic spine plasticity in cocaine-withdrawn rats

金沢大学附属病院神経科精神科Chronic cocaine treatment is associated with changes in dendritic spines in the nucleus accumbens, but it is unknown whether this neuroplasticity alters the effect of a subsequent cocaine injection on spine morphology and protein content. Three weeks after daily cocaine or saline administration, neurons in the accumbens were filled with the lipophilic dye, DiI. Although daily cocaine pretreatment did not alter spine density compared with daily saline, there was a shift from smaller to larger diameter spines. During the first 2 h after an acute cocaine challenge, a bidirectional change in spine head diameter and increase in spine density was measured in daily cocainepretreated animals. In contrast, no change in spine diameter or density was elicited by a cocaine challenge in daily saline animals during the first 2 h after injection. However, spine density was elevated at 6 h after a cocaine challenge in daily saline-pretreated animals. The time-dependent profile of proteins in the postsynaptic density subfraction elicited by a cocaine challenge in daily cocaine-pretreated subjects indicated that the changes in spine diameter and density were associated with a deteriorating actin cytoskeleton and a reduction in glutamate signaling-related proteins. Correspondingly, the amplitude of field potentials in accumbens evoked by stimulating prefrontal cortex was reduced for up to 6 h after acute cocaine in daily cocaine-withdrawn animals. These data indicate that daily cocaine pretreatment dysregulates dendritic spine plasticity elicited by a subsequent cocaine injection. Copyright © 2009 Society for Neuro science

NMII Forms a Contractile Transcellular Sarcomeric Network to Regulate Apical Cell Junctions and Tissue Geometry

SummaryNonmuscle myosin II (NMII) is thought to be the master integrator of force within epithelial apical junctions, mediating epithelial tissue morphogenesis and tensional homeostasis [1–3]. Mutations in NMII are associated with a number of diseases due to failures in cell-cell adhesion [4–8]. However, the organization and the precise mechanism by which NMII generates and responds to tension along the intercellular junctional line are still not known. We discovered that periodic assemblies of bipolar NMII filaments interlace with perijunctional actin and α-actinin to form a continuous belt of muscle-like sarcomeric units (∼400–600 nm) around each epithelial cell. Remarkably, the sarcomeres of adjacent cells are precisely paired across the junctional line, forming an integrated, transcellular contractile network. The contraction/relaxation of paired sarcomeres concomitantly impacts changes in apical cell shape and tissue geometry. We show differential distribution of NMII isoforms across heterotypic junctions and evidence for compensation between isoforms. Our results provide a model for how NMII force generation is effected along the junctional perimeter of each cell and communicated across neighboring cells in the epithelial organization. The sarcomeric network also provides a well-defined target to investigate the multiple roles of NMII in junctional homeostasis as well as in development and disease