The TW Hya Disk at 870 microns: Comparison of CO and Dust Radial Structures

We present high resolution (0.3" = 16 AU), high signal-to-noise ratio Submillimeter Array observations of the 870 microns (345 GHz) continuum and CO J=3--2 line emission from the protoplanetary disk around TW Hya. Using continuum and line radiative transfer calculations, those data and the multiwavelength spectral energy distribution are analyzed together in the context of simple two-dimensional parametric disk structure models. Under the assumptions of a radially invariant dust population and (vertically integrated) gas-to-dust mass ratio, we are unable to simultaneously reproduce the CO and dust observations with model structures that employ either a single, distinct outer boundary or a smooth (exponential) taper at large radii. Instead, we find that the distribution of millimeter-sized dust grains in the TW Hya disk has a relatively sharp edge near 60 AU, contrary to the CO emission (and optical/infrared scattered light) that extends to a much larger radius of at least 215 AU. We discuss some possible explanations for the observed radial distribution of millimeter-sized dust grains and the apparent CO-dust size discrepancy, and suggest that they may be hallmarks of substructure in the dust disk or natural signatures of the growth and radial drift of solids that might be expected for disks around older pre-main sequence stars like TW Hya.Comment: ApJ, in press (fixed typo in Equation 4

Several stressors fail to reduce adult hippocampal neurogenesis

Neurogenesis in the dentate gyrus of the hippocampus of adult laboratory animals has been widely reported to be vulnerable to many psychological and physical stressors. However, we have found no effects of acute restraint stress, acute or subchronic tailshock stress, or acute, subchronic, or chronic resident-intruder stress on neural progenitor cell (NPC) proliferation, short or long term survival of newborn cells, or brain-derived neurotrophic factor (BDNF) mRNA expression in adult rats. In addition, we did not observe any effect of chronic resident-intruder stress on NPC proliferation in adolescent rats. A selectively bred stress-sensitive line was also found to exhibit no alterations in NPC proliferation following tailshock stress, although this line did exhibit a lower proliferation rate under baseline (unstressed) conditions when compared with non-selected rats. These results challenge the prevailing hypothesis that any stressor of sufficient intensity and duration has a marked negative impact upon the rate of hippocampal neurogenesis, and suggest that some yet unidentified factors related to stress and experimental conditions are crucial in the regulation of neurogenesis

Registered social landlords and development plans A report for the Housing Corporation and Devon and Cornwall Housing Association

SIGLEAvailable from British Library Document Supply Centre-DSC:f99/2284 / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Several stressors fail to reduce adult hippocampal neurogenesis

Neurogenesis in the dentate gyrus of the hippocampus of adult laboratory animals has been widely reported to be vulnerable to many psychological and physical stressors. However, we have found no effects of acute restraint stress, acute or subchronic tailshock stress, or acute, subchronic, or chronic resident-intruder stress on neural progenitor cell (NPC) proliferation, short or long term survival of newborn cells, or brain-derived neurotrophic factor (BDNF) mRNA expression in adult rats. In addition, we did not observe any effect of chronic resident-intruder stress on NPC proliferation in adolescent rats. A selectively bred stress-sensitive line was also found to exhibit no alterations in NPC proliferation following tailshock stress, although this line did exhibit a lower proliferation rate under baseline (unstressed) conditions when compared with non-selected rats. These results challenge the prevailing hypothesis that any stressor of sufficient intensity and duration has a marked negative impact upon the rate of hippocampal neurogenesis, and suggest that some yet unidentified factors related to stress and experimental conditions are crucial in the regulation of neurogenesis