827 research outputs found

    Identification of a novel high molecular weight protein preferentially expressed by sinusoidal endothelial cells in normal human tissues

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    Mouse mAb MS-1, raised against human spleen, detects an endothelial cell antigen abundantly expressed by the sinusoidal endothelia of spleen, lymph node, liver, and adrenal cortex, but absent from nonsinusoidal continuous endothelia in these organs. Immunoelectron microscopy of splenic tissue demonstrates that the MS-1 antigen is predominantly deposited at zones of intercellular contact between adjacent sinusoidal endothelial cells. mAb MS-1 also reacts with a variable proportion of high endothelial venules in tonsil, but not in other lymphoid tissues, and with an interstitial dendritic cell population most abundant in placenta. mAb MS-1 does not react with cultured resting or mediator-activated human umbilical vein endothelial cells, dermal fibroblasts, peripheral blood mononuclear cells, or the cell lines U937, HL-60, K562 or Mo7E; it does react with the primitive myeloid cell line KG-1. mAb MS-1 immunoprecipitates a major protein of 215 kD and minor proteins of 320 and 120 kD from splenic extracts as analyzed by SDS-PAGE with reduction. These proteins are soluble in aqueous buffers. Immunoprecipitation from KG-1 cell lysates detects four proteins of 280, 300, 205, and 120 kD; the 300-, 205-, and 120-kD species, presumably corresponding to the 320-, 215-, and 120-kD species in spleen, respectively, are secreted into the media. Under nonreducing conditions, immunoprecipitates from KG-1 cell lysates or conditioned media contain one predominant 300-kD species; upon isolation and reduction, this 300-kD species separates into the previously observed 300-, 205-, and 120-kD species. Pulse-chase experiments and limited proteolysis peptide mapping suggest that the 280-kD species is a precursor of the mature 300-kD species which may be subsequently cleaved to yield the 205- and 120-kD species. Because of its size, solubility and expression pattern, the antigen recognized by mAb MS-1 is likely to be an extracellular matrix protein utilized by endothelial cells of contorted, large caliber, or leaky microvessels that lack a well-formed basement membrane

    Evidence for Inverted Spectrum 20 GHz Emission in the Galactic Plane

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    A comparison of a 19 GHz full-sky map with the WMAP satellite K band (23 GHz) map indicates that the bulk of the 20 GHz emission within 7 degrees of the Galactic plane has an inverted (rising) spectrum with an average spectral index alpha = 0.21 +/- 0.05. While such a spectrum is inconsistent with steep spectrum synchrotron (alpha ~ -0.7) and flat spectrum free-free (alpha ~ -0.1) emission, it is consistent with various models of electric dipole emission from thermally excited spinning dust grains as well as models of magnetic dipole emission from ferromagnetic dust grains. Several regions in the plane, e.g., near the Cygnus arm, have spectra with even larger alpha. While low signal to noise of the 19 GHz data precludes a detailed map of spectral index, especially off the Galactic plane, it appears that the bulk of the emission in the plane is correlated with the morphology of dust. Regions with higher 23 GHz flux tend to have harder spectra. Off the plane, at Galactic latitudes between 7 and 20 degree the spectrum steepens to alpha = -0.16 +/- 0.15.Comment: 11 page, 3 figure

    What Next-Generation 21 cm Power Spectrum Measurements Can Teach Us About the Epoch of Reionization

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    A number of experiments are currently working towards a measurement of the 21 cm signal from the Epoch of Reionization. Whether or not these experiments deliver a detection of cosmological emission, their limited sensitivity will prevent them from providing detailed information about the astrophysics of reionization. In this work, we consider what types of measurements will be enabled by a next-generation of larger 21 cm EoR telescopes. To calculate the type of constraints that will be possible with such arrays, we use simple models for the instrument, foreground emission, and the reionization history. We focus primarily on an instrument modeled after the 0.1 km2\sim 0.1~\rm{km}^2 collecting area Hydrogen Epoch of Reionization Array (HERA) concept design, and parameterize the uncertainties with regard to foreground emission by considering different limits to the recently described "wedge" footprint in k-space. Uncertainties in the reionization history are accounted for using a series of simulations which vary the ionizing efficiency and minimum virial temperature of the galaxies responsible for reionization, as well as the mean free path of ionizing photons through the IGM. Given various combinations of models, we consider the significance of the possible power spectrum detections, the ability to trace the power spectrum evolution versus redshift, the detectability of salient power spectrum features, and the achievable level of quantitative constraints on astrophysical parameters. Ultimately, we find that 0.1 km20.1~\rm{km}^2 of collecting area is enough to ensure a very high significance (30σ\gtrsim30\sigma) detection of the reionization power spectrum in even the most pessimistic scenarios. This sensitivity should allow for meaningful constraints on the reionization history and astrophysical parameters, especially if foreground subtraction techniques can be improved and successfully implemented.Comment: 27 pages, 18 figures, updated SKA numbers in appendi

    Gridded and direct Epoch of Reionisation bispectrum estimates using the Murchison Widefield Array

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    We apply two methods to estimate the 21~cm bispectrum from data taken within the Epoch of Reionisation (EoR) project of the Murchison Widefield Array (MWA). Using data acquired with the Phase II compact array allows a direct bispectrum estimate to be undertaken on the multiple redundantly-spaced triangles of antenna tiles, as well as an estimate based on data gridded to the uvuv-plane. The direct and gridded bispectrum estimators are applied to 21 hours of high-band (167--197~MHz; zz=6.2--7.5) data from the 2016 and 2017 observing seasons. Analytic predictions for the bispectrum bias and variance for point source foregrounds are derived. We compare the output of these approaches, the foreground contribution to the signal, and future prospects for measuring the bispectra with redundant and non-redundant arrays. We find that some triangle configurations yield bispectrum estimates that are consistent with the expected noise level after 10 hours, while equilateral configurations are strongly foreground-dominated. Careful choice of triangle configurations may be made to reduce foreground bias that hinders power spectrum estimators, and the 21~cm bispectrum may be accessible in less time than the 21~cm power spectrum for some wave modes, with detections in hundreds of hours.Comment: 19 pages, 10 figures, accepted for publication in PAS

    PAPER-64 Constraints On Reionization II: The Temperature Of The z=8.4 Intergalactic Medium

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    We present constraints on both the kinetic temperature of the intergalactic medium (IGM) at z=8.4, and on models for heating the IGM at high-redshift with X-ray emission from the first collapsed objects. These constraints are derived using a semi-analytic method to explore the new measurements of the 21 cm power spectrum from the Donald C. Backer Precision Array for Probing the Epoch of Reionization (PAPER), which were presented in a companion paper, Ali et al. (2015). Twenty-one cm power spectra with amplitudes of hundreds of mK^2 can be generically produced if the kinetic temperature of the IGM is significantly below the temperature of the Cosmic Microwave Background (CMB); as such, the new results from PAPER place lower limits on the IGM temperature at z=8.4. Allowing for the unknown ionization state of the IGM, our measurements find the IGM temperature to be above ~5 K for neutral fractions between 10% and 85%, above ~7 K for neutral fractions between 15% and 80%, or above ~10 K for neutral fractions between 30% and 70%. We also calculate the heating of the IGM that would be provided by the observed high redshift galaxy population, and find that for most models, these galaxies are sufficient to bring the IGM temperature above our lower limits. However, there are significant ranges of parameter space that could produce a signal ruled out by the PAPER measurements; models with a steep drop-off in the star formation rate density at high redshifts or with relatively low values for the X-ray to star formation rate efficiency of high redshift galaxies are generally disfavored. The PAPER measurements are consistent with (but do not constrain) a hydrogen spin temperature above the CMB temperature, a situation which we find to be generally predicted if galaxies fainter than the current detection limits of optical/NIR surveys are included in calculations of X-ray heating.Comment: companion paper to Ali et al. (2015), ApJ 809, 61; matches version accepted to ApJ; 11 pages, 7 figure
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