High Sensitivity Array Observations of the z=4.4z = 4.4 QSO BRI 1335-0417

We present sensitive phase-referenced VLBI results on the radio continuum emission from the $z=4.4$ QSO BRI 1335--0417. The observations were carried out at 1.4 GHz using the High Sensitivity Array (HSA). Our sensitive VLBI image at $189 \times 113$ mas ($1.25 \times 0.75$ kpc) resolution shows continuum emission in BRI 1335--0417 with a total flux density of $208 \pm 46 \mu$Jy, consistent with the flux density measured with the VLA. The size of the source at FWHM is $255 \times 138$ mas ($1.7 \times 0.9$ kpc) and the derived intrinsic brightness temperature is $\sim 3.5\times 10^4$ K. No continuum emission is detected at the full VLBI resolution ($32 \times 7$ mas, $211 \times 46$ pc), with a 4$\sigma$ point source upper limit of 34 $\mu$Jy beam$^{-1}$, or an upper limit to the intrinsic brightness temperature of $5.6\times 10^5$ K. The highest angular resolution with at least a 4.5$\sigma$ detection of the radio continuum emission is $53 \times 27$ mas ($0.35 \times 0.18$ kpc). At this resolution, the image shows a continuum feature in BRI 1335--0417 with a size of $64 \times 35$ mas ($0.42 \times 0.23$ kpc) at FWHM, and intrinsic brightness temperature of $\sim 2\times 10^5$ K. The extent of the observed continuum sources at 1.4 GHz and the derived brightness temperatures show that the radio emission (and thus presumably the far-infrared emission) in BRI 1335--0417 is powered by a major starburst, with a massive star formation rate of order a few thousand M_{\odot} {\rm yr}^{-1}$. Moreover, the absence of any compact high-brightness temperature source suggests that there is no radio-loud AGN in this$z=4.4$ QSO.Comment: 13 pages, 3 figures, AJ accepte

eBank UK: linking research data, scholarly communication and learning

This paper includes an overview of the changing landscape of scholarly communication and describes outcomes from the innovative eBank UK project, which seeks to build links from e-research through to e-learning. As introduction, the scholarly knowledge cycle is described and the role of digital repositories and aggregator services in linking data-sets from Grid-enabled projects to e-prints through to peer-reviewed articles as resources in portals and Learning Management Systems, are assessed. The development outcomes from the eBank UK project are presented including the distributed information architecture, requirements for common ontologies, data models, metadata schema, open linking technologies, provenance and workflows. Some emerging challenges for the future are presented in conclusion

Application and Evaluation of a Snowmelt Runoff Model in the Tamor River Basin, Eastern Himalaya Using a Markov Chain Monte Carlo (MCMC) Data Assimilation Approach

Previous studies have drawn attention to substantial hydrological changes taking place in mountainous watersheds where hydrology is dominated by cryospheric processes. Modelling is an important tool for understanding these changes but is particularly challenging in mountainous terrain owing to scarcity of ground observations and uncertainty of model parameters across space and time. This study utilizes a Markov Chain Monte Carlo data assimilation approach to examine and evaluate the performance of a conceptual, degree-day snowmelt runoff model applied in the Tamor River basin in the eastern Nepalese Himalaya. The snowmelt runoff model is calibrated using daily streamflow from 2002 to 2006 with fairly high accuracy (average Nash-Sutcliffe metric approx. 0.84, annual volume bias <3%). The Markov Chain Monte Carlo approach constrains the parameters to which the model is most sensitive (e.g. lapse rate and recession coefficient) and maximizes model fit and performance. Model simulated streamflow using an interpolated precipitation data set decreases the fractional contribution from rainfall compared with simulations using observed station precipitation. The average snowmelt contribution to total runoff in the Tamor River basin for the 2002-2006 period is estimated to be 29.7+/-2.9% (which includes 4.2+/-0.9% from snowfall that promptly melts), whereas 70.3+/-2.6% is attributed to contributions from rainfall. On average, the elevation zone in the 4000-5500m range contributes the most to basin runoff, averaging 56.9+/-3.6% of all snowmelt input and 28.9+/-1.1% of all rainfall input to runoff. Model simulated streamflow using an interpolated precipitation data set decreases the fractional contribution from rainfall versus snowmelt compared with simulations using observed station precipitation. Model experiments indicate that the hydrograph itself does not constrain estimates of snowmelt versus rainfall contributions to total outflow but that this derives from the degree-day melting model. Lastly, we demonstrate that the data assimilation approach is useful for quantifying and reducing uncertainty related to model parameters and thus provides uncertainty bounds on snowmelt and rainfall contributions in such mountainous watersheds

Constrained Spacecraft Relative Motion Planning Exploiting Periodic Natural Motion Trajectories and Invariance

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/143124/1/1.G002914.pd

Spectra and Light Curves of Failed Supernovae

Astronomers have proposed a number of mechanisms to produce supernova explosions. Although many of these mechanisms are now not considered primary engines behind supernovae, they do produce transients that will be observed by upcoming ground-based surveys and NASA satellites. Here we present the first radiation-hydrodynamics calculations of the spectra and light curves from three of these "failed" supernovae: supernovae with considerable fallback, accretion induced collapse of white dwarfs, and energetic helium flashes (also known as type .Ia supernovae).Comment: 33 pages, 14 figure

Towards smallholder food and water security: Climate variability in the context of multiple livelihood hazards in Nicaragua

Climate variability and change affect both food and water security, as do other hazards, such as shifting food prices, plant pathogens, and political economic changes. Although household food and water insecurity affect billions, most studies analyze them separately. This article develops a relational approach to explaining household access to food and water in a multi-hazard context. We identify pathways linking hazards to livelihood vulnerability and assess the relative importance of climate-related hazards. Analyzing longitudinal data collected from two surveys of the same 311 smallholder households in northern Nicaragua, conducted in 2014 and again in 2017, we find that peak seasons of food and water stress are asynchronous across the agricultural calendar, resulting in a total of five to six months of food and/or water stress. Across households, we find a significant positive relationship between water and food insecurity, even after adjusting for household fixed effects. Households experienced less food and water insecurity in 2017 than in 2014, due in part to the end of a severe drought in 2016, but remained concerned about damage from a severe coffee leaf rust outbreak and unfavorable agrifood prices that reduce income and threaten food security. Higher incomes and larger farm areas correlated with improved food and water security. We propose a generalizable approach for the joint assessment of household food and water security, which foregrounds the influence of seasonality and climate variability in the context of multiple hazards. This approach and our findings can contribute to developing integrated risk reduction strategies, building resilient livelihoods, and informing policy changes and partnerships with organized smallholders to improve resource access and sovereignty

Sensitive VLBI Observations of the z = 4.7 QSO BRI 1202-0725

We present sensitive phase-referenced VLBI results on the radio continuum emission from the z=4.7 double source BRI 1202-0725. The observations were carried out at 1425 MHz using the Very Long Baseline Array (VLBA), the phased Very Large Array (VLA), and the Green Bank Telescope (GBT). Our sensitive VLBI images of BRI 1202-0725 at 0.25 x 0.14 arcsec resolution show a continuum structure in each of its two components. Fitting Gaussian models to these continuum structures yield total flux densities of 315 +/- 38 and 250 +/- 39 microJy, for the northern and the southern components, respectively. The estimated intrinsic brightness temperatures of these continuum structures are about 2 x 10^4 K. Neither component is detected at the full VLBI resolution (29 mas x 7 mas), with a 4 sigma point source upper limit of 40 microJy/beam, or an upper limit to the intrinsic brightness temperature of 6.7 x 10^5 K. The highest angular resolution with at least a 4sigma detection is about 85 mas. At this resolution, the images reveal a single continuum feature in the northern component of BRI 1202-0725, and two continuum features in the southern component, separated by 320 mas. This is similar to the structures seen in the high resolution images of the CO emission. The extent of the observed continuum sources at 1.4 GHz and the derived brightness temperatures are consistent with nuclear starbursts. Moreover, the absence of any compact high-brightness temperature source suggests that thereis no radio-loud AGN in BRI 1202-0725.Comment: 19 pages, 5 figures. Accepted for publication in A

Final Results From the Circumarctic Lakes Observation Network (CALON) Project

Since 2012, the physical and biogeochemical properties of ~60 lakes in northern Alaska have been investigated under CALON, a project to document landscape-scale variability of Arctic lakes in permafrost terrain. The network has ten nodes along two latitudinal transects extending inland 200 km from the Arctic Ocean. A meteorological station is deployed at each node and six representative lakes instrumented and continuously monitored, with winter and summer visits for synoptic assessment of lake conditions. Over the 4-year period, winter and summer climatology varied to create a rich range of lake responses over a short period. For example, winter 2012-13 was very cold with a thin snowpack producing thick ice across the region. Subsequent years had relatively warm winters, yet regionally variable snow resulted in differing gradients of ice thickness. Ice-out timing was unusually late in 2014 and unusually early in 2015. Lakes are typically well–mixed and largely isothermal, with minor thermal stratification occurring in deeper lakes during calm, sunny periods in summer. Lake water temperature records and morphometric data were used to estimate the ground thermal condition beneath 28 lakes. Application of a thermal equilibrium steady-state model suggests a talik penetrating the permafrost under many larger lakes, but lake geochemical data do not indicate a significant contribution of subpermafrost groundwater. Biogeochemical data reveal distinct spatial and seasonal variability in chlorophyll biomass, chromophoric dissolved organic carbon (CDOM), and major cations/anions. Generally, waters sampled beneath ice in April had distinctly higher concentrations of inorganic solutes and methane compared with August. Chlorophyll concentrations and CDOM absorption were higher in April, suggesting significant biological/biogeochemical activity under lake ice. Lakes are a positive source of methane in summer, and some also emit nitrous oxide and carbon dioxide. As part of the Indigenous Knowledge component,76 Iñupiat elders, hunters and berry pickers have been interviewed and over 75 hours of videotaped interviews produced. The video library and searchable interview logs are archived with the North Slope community. All field data is archived at ACADIS, and further information is at www.arcticlakes.org