640 research outputs found

    Warkworth 12-m VLBI Station: WARK12M

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    This report summarizes the geodetic VLBI activities in New Zealand in 2010. It provides geographical and technical details of WARK12M - the new IVS network station operated by the Institute for Radio Astronomy and Space Research (IRASR) of Auckland University of Technology (AUT). The details of the VLBI system installed in the station are outlined along with those of the collocated GNSS station. We report on the status of broadband connectivity and on the results of testing data transfer protocols; we investigate UDP protocols such as 'tsunami' and UDT and demonstrate that the UDT protocol is more efficient than 'tsunami' and 'ftp'. In general, the WARK12M IVS network station is fully equipped, connected and tested to start participating in regular IVS observational sessions from the beginning of 2011.Comment: 5 pages, 1 figure, Accepeted for the IVS 2010 Annual Repor

    The effects of velocities and lensing on moments of the Hubble diagram

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    We consider the dispersion on the supernova distance-redshift relation due to peculiar velocities and gravitational lensing, and the sensitivity of these effects to the amplitude of the matter power spectrum. We use the MeMo lensing likelihood developed by Quartin, Marra & Amendola (2014), which accounts for the characteristic non-Gaussian distribution caused by lensing magnification with measurements of the first four central moments of the distribution of magnitudes. We build on the MeMo likelihood by including the effects of peculiar velocities directly into the model for the moments. In order to measure the moments from sparse numbers of supernovae, we take a new approach using Kernel Density Estimation to estimate the underlying probability density function of the magnitude residuals. We also describe a bootstrap re-sampling approach to estimate the data covariance matrix. We then apply the method to the Joint Light-curve Analysis (JLA) supernova catalogue. When we impose only that the intrinsic dispersion in magnitudes is independent of redshift, we find σ8=0.440.44+0.63\sigma_8=0.44^{+0.63}_{-0.44} at the one standard deviation level, although we note that in tests on simulations, this model tends to overestimate the magnitude of the intrinsic dispersion, and underestimate σ8\sigma_8. We note that the degeneracy between intrinsic dispersion and the effects of σ8\sigma_8 is more pronounced when lensing and velocity effects are considered simultaneously, due to a cancellation of redshift dependence when both effects are included. Keeping the model of the intrinsic dispersion fixed as a Gaussian distribution of width 0.14 mag, we find σ8=1.070.76+0.50\sigma_8 = 1.07^{+0.50}_{-0.76}.Comment: 16 pages, updated to match version accepted in MNRA

    Observing the earliest moments of supernovae using strong gravitational lenses

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    We determine the viability of exploiting lensing time delays to observe strongly gravitationally lensed supernovae (gLSNe) from first light. Assuming a plausible discovery strategy, the Legacy Survey of Space and Time (LSST) and the Zwicky Transient Facility (ZTF) will discover \sim 110 and \sim 1 systems per year before the supernova (SN) explosion in the final image respectively. Systems will be identified 11.79.3+29.811.7^{+29.8}_{-9.3} days before the final explosion. We then explore the possibility of performing early-time observations for Type IIP and Type Ia SNe in LSST-discovered systems. Using a simulated Type IIP explosion, we predict that the shock breakout in one trailing image per year will peak at \lesssim 24.1 mag (\lesssim 23.3) in the BB-band (F218WF218W), however evolving over a timescale of \sim 30 minutes. Using an analytic model of Type Ia companion interaction, we find that in the BB-band we should observe at least one shock cooling emission event per year that peaks at \lesssim 26.3 mag (\lesssim 29.6) assuming all Type Ia gLSNe have a 1 M_\odot red giant (main sequence) companion. We perform Bayesian analysis to investigate how well deep observations with 1 hour exposures on the European Extremely Large Telescope would discriminate between Type Ia progenitor populations. We find that if all Type Ia SNe evolved from the double-degenerate channel, then observations of the lack of early blue flux in 10 (50) trailing images would rule out more than 27% (19%) of the population having 1 M_\odot main sequence companions at 95% confidence.Comment: 17 pages, 15 figures (including appendices). Accepted by MNRAS 3rd May 202

    First geodetic observations using new VLBI stations ASKAP-29 and WARK12M

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    We report the results of a successful 7 hour 1.4 GHz VLBI experiment using two new stations, ASKAP-29 located in Western Australia and WARK12M located on the North Island of New Zealand. This was the first geodetic VLBI observing session with the participation of these new stations. We have determined the positions of ASKAP-29 and WARK12M. Random errors on position estimates are 150-200 mm for the vertical component and 40-50 mm for the horizontal component. Systematic errors caused by the unmodeled ionosphere path delay may reach 1.3 m for the vertical component.Comment: 11 pages, 6 flgures, 4 table

    Endothelial colony-forming cells and pro-angiogenic cells: clarifying definitions and their potential role in mitigating acute kidney injury

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    Acute kidney injury (AKI) represents a significant clinical concern that is associated with high mortality rates and also represents a significant risk factor for the development of chronic kidney disease (CKD). This article will consider alterations in renal endothelial function in the setting of AKI that may underlie impairment in renal perfusion and how inefficient vascular repair may manifest post-AKI and contribute to the potential transition to CKD. We provide updated terminology for cells previously classified as ‘endothelial progenitor’ that may mediate vascular repair such as pro-angiogenic cells and endothelial colony-forming cells. We consider how endothelial repair may be mediated by these different cell types following vascular injury, particularly in models of AKI. We further summarize the potential ability of these different cells to mitigate the severity of AKI, improve perfusion and maintain vascular structure in pre-clinical studies

    Electrons in an eccentric background field

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    We present a description of electrons propagating in an elliptically polarized, plane wave background which includes circular and linear polarizations as special cases. We calculate, to all orders in the background field, the two point function and relate it to various expressions found in the literature. The background field induced mass shift of the electron is shown to be polarization independent in the full elliptic class. The matrix nature of this mass shift in the fermionic theory is discussed. The extent to which a momentum space description is possible for this system is clarified
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