Tawa Inti Qocha, símbolo de la cosmología andina:concepcion q'ero del espacio

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Measuring the escape velocity and mass profiles of galaxy clusters beyond their virial radius

The caustic technique uses galaxy redshifts alone to measure the escape velocity and mass profiles of galaxy clusters to clustrocentric distances well beyond the virial radius, where dynamical equilibrium does not necessarily hold. We provide a detailed description of this technique and analyse its possible systematic errors. We apply the caustic technique to clusters with mass M_200>=10^{14}h^{-1} M_sun extracted from a cosmological hydrodynamic simulation of a LambdaCDM universe. With a few tens of redshifts per squared comoving megaparsec within the cluster, the caustic technique, on average, recovers the profile of the escape velocity from the cluster with better than 10 percent accuracy up to r~4 r_200. The caustic technique also recovers the mass profile with better than 10 percent accuracy in the range (0.6-4) r_200, but it overestimates the mass up to 70 percent at smaller radii. This overestimate is a consequence of neglecting the radial dependence of the filling function F_beta(r). The 1-sigma uncertainty on individual escape velocity profiles increases from ~20 to ~50 percent when the radius increases from r~0.1 r_200 to ~4 r_200. Individual mass profiles have 1-sigma uncertainty between 40 and 80 percent within the radial range (0.6-4) r_200. We show that the amplitude of these uncertainties is completely due to the assumption of spherical symmetry, which is difficult to drop. Alternatively, we can apply the technique to synthetic clusters obtained by stacking individual clusters: in this case, the 1-sigma uncertainty on the escape velocity profile is smaller than 20 percent out to 4 r_200. The caustic technique thus provides reliable average profiles which extend to regions difficult or impossible to probe with other techniques.Comment: MNRAS accepted, 20 page

Comparing Notes: Recording and Criticism

This chapter charts the ways in which recording has changed the nature of music criticism. It both provides an overview of the history of recording and music criticism, from the advent of Edison’s Phonograph to the present day, and examines the issues arising from this new technology and the consequent transformation of critical thought and practice

The 6dF Galaxy Survey: peculiar velocity field and cosmography

We derive peculiar velocities for the 6dF Galaxy Survey (6dFGS) and describe the velocity field of the nearby ($z<0.055$) southern hemisphere. The survey comprises 8885 galaxies for which we have previously reported Fundamental Plane data. We obtain peculiar velocity probability distributions for the redshift space positions of each of these galaxies using a Bayesian approach. Accounting for selection bias, we find that the logarithmic distance uncertainty is 0.11 dex, corresponding to $26\%$ in linear distance. We use adaptive kernel smoothing to map the observed 6dFGS velocity field out to $cz \sim 16,000$ \kms, and compare this to the predicted velocity fields from the PSCz Survey and the 2MASS Redshift Survey. We find a better fit to the PSCz prediction, although the reduced $\chi^2$ for the whole sample is approximately unity for both comparisons. This means that, within the observational uncertainties due to redshift independent distance errors, observed galaxy velocities and those predicted by the linear approximation from the density field agree. However, we find peculiar velocities that are systematically more positive than model predictions in the direction of the Shapley and Vela superclusters, and systematically more negative than model predictions in the direction of the Pisces-Cetus Supercluster, suggesting contributions from volumes not covered by the models.Comment: 22 pages, 14 figures, accepted for publication in MNRAS. Table 1 is available in its entirety as an ancillary file. Fully interactive 3D versions of Figures 11 and 12 are also available as ancillary files. A version of this paper with the 3D versions of Figs. 11 and 12 embedded within the pdf can also be accessed from http://www.6dfgs.net/vfield/veldata.pd

Investigating the cell biological mechanisms regulated by the cellular prion protein

Transmissible spongiform encephalopathies (TSEs) are rare, uniformly fatal neurodegenerative disorders that can affect many mammalian species, including humans. A hallmark of these diseases is the conversion of cellular prion protein (PrPC) into an abnormally folded form. This misfolded PrPC is infectious, since it can provide a template for pathogenic conversion of PrPC in a new host. In addition to any toxicity of the misfolded protein, loss of normal PrPC function could be involved in the neurodegenerative processes. However, the physiological role of PrPC is still poorly understood and this project has aimed to address that lack of knowledge. Out of the many putative functions ascribed to PrPC, the most commonly proposed is that it protects cells from stress. In contrast, I have found that stable transfection of the prion protein gene into SH-SY5Y neuroblastoma cells increases cell death in response to serum removal from the culture medium. Following treatment with several chemical toxins, two out of four stably transfected clones did, generally, display greater viability than untransfected cells that do not express detectable levels of PrPC. However, knockdown of PrPC expression by RNA interference had no effect on this stress resistance, indicating that it may not have been mediated directly by PrPC. Given the lack of robust stress protection afforded by PrPC transfection, proteomic analyses of the cells were carried out to identify alternative processes that were perturbed as a result of PrPC expression. The results obtained suggested roles for PrPC in cytoskeletal organisation and cell cycle regulation. Various proteins involved in cytoskeletal organisation were confirmed by western blotting to be differentially expressed in some or all of the stably transfected clones. Additionally, the expression changes to proteins involved in cell cycle regulation resulted in slower proliferation of the clones compared with untransfected cells, a difference that was reduced following RNA interference-mediated knockdown of PrPC. Taken together, these data suggested that specific growth factor-activated pathways were differentially regulated in the stably transfected clones. One candidate pathway was nerve growth factor (NGF) signalling, which promotes neuronal survival and differentiation as well as regulating various processes outside of the nervous system. PrPC-transfection resulted in altered expression of receptors for NGF, suggesting that the stably transfected clones were, indeed, responding differently to NGF stimulation. However, the molecular mechanism responsible for these expression changes remains to be determined, since co-immunoprecipitation experiments did not identify any physical interactions between PrPC and the NGF receptors. Nonetheless, a role for PrPC in modulating NGF signalling has the potential to explain many of the diverse phenotypic observations in PrPC-null mice and might indicate that loss of PrPC function is an important part of TSE pathogenesis

Wider Still and Wider: British Music Criticism since the Second World War

This chapter provides the first historical examination of music criticism in Britain since the Second World War. In the process, it also challenges the simplistic prevailing view of this being a period of decline from a golden age in music criticism

Tawa Inti Qocha, símbolo de la cosmología andina:concepcion q'ero del espacio

The article does not present a summary.El artículo no presenta resume