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  • 1
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    Water scarcity and climate change [Sustainability Science] (2014)
    National Academy of Sciences
    Details
    Publication Date: 2014-03-05
    Description: Water scarcity severely impairs food security and economic prosperity in many countries today. Expected future population changes will, in many countries as well as globally, increase the pressure on available water resources. On the supply side, renewable water resources will be affected by projected changes in precipitation patterns, temperature, and...
    Keywords: Global Climate Impacts: A Cross-Sector, Multi-Model Assessment Special Feature, Sustainability Science
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
    Published by National Academy of Sciences
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  • 2
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    Discovery of a high state AM CVn binary in the Galactic Bulge Survey (2016)
    Oxford University Press
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    Publication Date: 2016-08-10
    Description: We report on the discovery of a hydrogen-deficient compact binary (CXOGBS J175107.6-294037) belonging to the AM CVn class in the Galactic Bulge Survey. Deep archival X-ray observations constrain the X-ray positional uncertainty of the source to 0.57 arcsec, and allow us to uniquely identify the optical and UV counterpart. Optical spectroscopic observations reveal the presence of broad, shallow He i absorption lines while no sign of hydrogen is present, consistent with a high state system. We present the optical light curve from Optical Gravitational Lensing Experiment monitoring, spanning 15 yr. It shows no evidence for outbursts; variability is present at the 0.2 mag level on time-scales ranging from hours to weeks. A modulation on a time-scale of years is also observed. A Lomb–Scargle analysis of the optical light curves shows two significant periodicities at 22.90 and 23.22 min. Although the physical interpretation is uncertain, such time-scales are in line with expectations for the orbital and superhump periods. We estimate the distance to the source to be between 0.5 and 1.1 kpc. Spectroscopic follow-up observations are required to establish the orbital period, and to determine whether this source can serve as a verification binary for the eLISA gravitational wave mission.
    Print ISSN: 1745-3925
    Electronic ISSN: 1745-3933
    Topics: Physics
    Published by Oxford University Press
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  • 3
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    Deep radio imaging of 47 Tuc identifies the peculiar X-ray source X9 as a new black hole candidate (2015)
    Oxford University Press
    Details
    Publication Date: 2015-09-16
    Description: We report the detection of steady radio emission from the known X-ray source X9 in the globular cluster 47 Tuc. With a double-peaked C  iv emission line in its ultraviolet spectrum providing a clear signature of accretion, this source had been previously classified as a cataclysmic variable. In deep ATCA (Australia Telescope Compact Array) imaging from 2010 and 2013, we identified a steady radio source at both 5.5 and 9.0 GHz, with a radio spectral index (defined as S α ) of α = –0.4 ± 0.4. Our measured flux density of 42 ± 4 μJy beam –1 at 5.5 GHz implies a radio luminosity ( L ) of 5.8  x  10 27  erg s –1 , significantly higher than any previous radio detection of an accreting white dwarf. Transitional millisecond pulsars, which have the highest radio-to-X-ray flux ratios among accreting neutron stars (still a factor of a few below accreting black holes at the same L X ), show distinctly different patterns of X-ray and radio variability than X9. When combined with archival X-ray measurements, our radio detection places 47 Tuc X9 very close to the radio/X-ray correlation for accreting black holes, and we explore the possibility that this source is instead a quiescent stellar-mass black hole X-ray binary. The nature of the donor star is uncertain; although the luminosity of the optical counterpart is consistent with a low-mass main-sequence donor star, the mass transfer rate required to produce the high quiescent X-ray luminosity of 10 33  erg s –1 suggests the system may instead be ultracompact, with an orbital period of order 25 min. This is the fourth quiescent black hole candidate discovered to date in a Galactic globular cluster, and the only one with a confirmed accretion signature from its optical/ultraviolet spectrum.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 4
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    Deep radio imaging of 47 Tuc identifies the peculiar X-ray source X9 as a new black hole candidate (2015)
    Oxford University Press
    Details
    Publication Date: 2015-09-27
    Description: We report the detection of steady radio emission from the known X-ray source X9 in the globular cluster 47 Tuc. With a double-peaked C  iv emission line in its ultraviolet spectrum providing a clear signature of accretion, this source had been previously classified as a cataclysmic variable. In deep ATCA (Australia Telescope Compact Array) imaging from 2010 and 2013, we identified a steady radio source at both 5.5 and 9.0 GHz, with a radio spectral index (defined as S α ) of α = –0.4 ± 0.4. Our measured flux density of 42 ± 4 μJy beam –1 at 5.5 GHz implies a radio luminosity ( L ) of 5.8  x  10 27  erg s –1 , significantly higher than any previous radio detection of an accreting white dwarf. Transitional millisecond pulsars, which have the highest radio-to-X-ray flux ratios among accreting neutron stars (still a factor of a few below accreting black holes at the same L X ), show distinctly different patterns of X-ray and radio variability than X9. When combined with archival X-ray measurements, our radio detection places 47 Tuc X9 very close to the radio/X-ray correlation for accreting black holes, and we explore the possibility that this source is instead a quiescent stellar-mass black hole X-ray binary. The nature of the donor star is uncertain; although the luminosity of the optical counterpart is consistent with a low-mass main-sequence donor star, the mass transfer rate required to produce the high quiescent X-ray luminosity of 10 33  erg s –1 suggests the system may instead be ultracompact, with an orbital period of order 25 min. This is the fourth quiescent black hole candidate discovered to date in a Galactic globular cluster, and the only one with a confirmed accretion signature from its optical/ultraviolet spectrum.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 5
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    Impact of reservoirs on river discharge and irrigation water supply during the 20th century (2011)
    Wiley
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    Publication Date: 2011-03-06
    Description: This paper presents a quantitative estimation of the impact of reservoirs on discharge and irrigation water supply during the 20th century at global, continental, and river basin scale. Compared to a natural situation the combined effect of reservoir operation and irrigation extractions decreased mean annual discharge to oceans and significantly changed the timing of this discharge. For example, in Europe, May discharge decreased by 10%, while in February it increased by 8%. At the end of the 20th century, reservoir operations and irrigation extractions decreased annual global discharge by about 2.1% (930 km3 yr−1). Simulation results show that reservoirs contribute significantly to irrigation water supply in many regions. Basins that rely heavily on reservoir water are the Colorado and Columbia River basins in the United States and several large basins in India, China, and central Asia (e.g., in the Krishna and Huang He basins, reservoirs more than doubled surface water supply). Continents gaining the most are North America, Africa, and Asia, where reservoirs supplied 57, 22, and 360 km3 yr−1 respectively between 1981–2000, which is in all cases 40% more than the availability in the situation without reservoirs. Globally, the irrigation water supply from reservoirs increased from around 18 km3 yr−1 (adding 5% to surface water supply) at the beginning of the 20th century to 460 km3 yr−1 (adding almost 40% to surface water supply) at the end of the 20th century. The analysis is performed using a newly developed and validated reservoir operation scheme within a global-scale hydrology and vegetation model (LPJmL).
    Print ISSN: 0043-1397
    Electronic ISSN: 1944-7973
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 6
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    Gemini spectroscopy of Galactic Bulge Sources: a population of hidden accreting binaries revealed? (2015)
    Oxford University Press
    Details
    Publication Date: 2015-02-26
    Description: We present Gemini spectroscopy for 21 candidate optical counterparts to X-ray sources discovered in the Galactic Bulge Survey (GBS). For the majority of the 21 sources, the optical spectroscopy establishes that they are indeed the likely counterparts. One of the criteria we used for the identification was the presence of an Hα emission line. The spectra of several sources revealed an Hα emission line only after careful subtraction of the F or G stellar spectral absorption lines. In a subclass of three of these sources, the residual Hα emission line is broad ( 400 km s –1 ) which suggests that it is formed in an accretion disc, whereas in other cases the line width is such that we currently cannot determine whether the line emission is formed in an active star/binary or in an accretion disc. GBS source CX377 shows this hidden-accretion behaviour most dramatically. The previously identified broad Hα emission of this source is not present in its Gemini spectra taken ~1 yr later. However, broad emission is revealed after subtracting an F6 template star spectrum. The Gemini spectra of three sources (CX446, CX1004, and CXB2) as well as the presence of possible eclipses in light curves of these sources suggest that these sources are accreting binaries viewed under a high inclination.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 7
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    On the coexistence of stellar-mass and intermediate-mass black holes in globular clusters (2014)
    Oxford University Press
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    Publication Date: 2014-08-14
    Description: In this paper, we address the question: what is the probability of stellar-mass black hole (BH) binaries co-existing in a globular cluster with an intermediate-mass black hole (IMBH)? Our results suggest that the detection of one or more BH binaries can strongly constrain the presence of an IMBH in most Galactic globular clusters. More specifically, the detection of one or more BH binaries could strongly indicate against the presence of an IMBH more massive than 10 3 M in roughly 80 per cent of the clusters in our sample. To illustrate this, we use a combination of N -body simulations and analytic methods to weigh the rate of formation of BH binaries against their ejection and/or disruption rate via strong gravitational interactions with the central (most) massive BH. The eventual fate of a sub-population of stellar-mass BHs (with or without binary companions) is for all BHs to be ejected from the cluster by the central IMBH, leaving only the most massive stellar-mass BH behind to form a close binary with the IMBH. During each phase of evolution, we discuss the rate of inspiral of the central BH–BH pair as a function of both the properties of the binary and its host cluster.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 8
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    Integrated crop water management might sustainably halve the global food gap (2016)
    Institute of Physics (IOP)
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    Publication Date: 2016-02-16
    Description: As planetary boundaries are rapidly being approached, humanity has little room for additional expansion and conventional intensification of agriculture, while a growing world population further spreads the food gap. Ample evidence exists that improved on-farm water management can close water-related yield gaps to a considerable degree, but its global significance remains unclear. In this modeling study we investigate systematically to what extent integrated crop water management might contribute to closing the global food gap, constrained by the assumption that pressure on water resources and land does not increase. Using a process-based bio-/agrosphere model, we simulate the yield-increasing potential of elevated irrigation water productivity (including irrigation expansion with thus saved water) and optimized use of in situ precipitation water (alleviated soil evaporation, enhanced infiltration, water harvesting for supplemental irrigation) under current and projected f...
    Print ISSN: 1748-9318
    Electronic ISSN: 1748-9326
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering
    Published by Institute of Physics (IOP)
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  • 9
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    Recent decline in the global land evapotranspiration trend due to limited moisture supply (2010)
    Nature Publishing Group (NPG)
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    Publication Date: 2010-10-12
    Description: More than half of the solar energy absorbed by land surfaces is currently used to evaporate water. Climate change is expected to intensify the hydrological cycle and to alter evapotranspiration, with implications for ecosystem services and feedback to regional and global climate. Evapotranspiration changes may already be under way, but direct observational constraints are lacking at the global scale. Until such evidence is available, changes in the water cycle on land-a key diagnostic criterion of the effects of climate change and variability-remain uncertain. Here we provide a data-driven estimate of global land evapotranspiration from 1982 to 2008, compiled using a global monitoring network, meteorological and remote-sensing observations, and a machine-learning algorithm. In addition, we have assessed evapotranspiration variations over the same time period using an ensemble of process-based land-surface models. Our results suggest that global annual evapotranspiration increased on average by 7.1 +/- 1.0 millimetres per year per decade from 1982 to 1997. After that, coincident with the last major El Nino event in 1998, the global evapotranspiration increase seems to have ceased until 2008. This change was driven primarily by moisture limitation in the Southern Hemisphere, particularly Africa and Australia. In these regions, microwave satellite observations indicate that soil moisture decreased from 1998 to 2008. Hence, increasing soil-moisture limitations on evapotranspiration largely explain the recent decline of the global land-evapotranspiration trend. Whether the changing behaviour of evapotranspiration is representative of natural climate variability or reflects a more permanent reorganization of the land water cycle is a key question for earth system science.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Jung, Martin -- Reichstein, Markus -- Ciais, Philippe -- Seneviratne, Sonia I -- Sheffield, Justin -- Goulden, Michael L -- Bonan, Gordon -- Cescatti, Alessandro -- Chen, Jiquan -- de Jeu, Richard -- Dolman, A Johannes -- Eugster, Werner -- Gerten, Dieter -- Gianelle, Damiano -- Gobron, Nadine -- Heinke, Jens -- Kimball, John -- Law, Beverly E -- Montagnani, Leonardo -- Mu, Qiaozhen -- Mueller, Brigitte -- Oleson, Keith -- Papale, Dario -- Richardson, Andrew D -- Roupsard, Olivier -- Running, Steve -- Tomelleri, Enrico -- Viovy, Nicolas -- Weber, Ulrich -- Williams, Christopher -- Wood, Eric -- Zaehle, Sonke -- Zhang, Ke -- England -- Nature. 2010 Oct 21;467(7318):951-4. doi: 10.1038/nature09396.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Max Planck Institute for Biogeochemistry, 07745 Jena, Germany. mjung@bgc-jena.mpg.de〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/20935626" target="_blank"〉PubMed〈/a〉
    Keywords: Artificial Intelligence ; Atmosphere/*chemistry ; Fresh Water/*analysis ; *Global Warming/statistics & numerical data ; History, 20th Century ; History, 21st Century ; Humidity ; Plant Transpiration/*physiology ; Reproducibility of Results ; Seasons ; Soil/analysis ; Uncertainty ; Volatilization ; *Water Cycle
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Nature Publishing Group (NPG)
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  • 10
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    SUSTAINABILITY. Response to Comment on "Planetary boundaries: Guiding human development on a changing planet" (2015)
    American Association for the Advancement of Science (AAAS)
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    Publication Date: 2015-06-13
    Description: Jaramillo and Destouni claim that freshwater consumption is beyond the planetary boundary, based on high estimates of water cycle components, different definitions of water consumption, and extrapolation from a single case study. The difference from our analysis, based on mainstream assessments of global water consumption, highlights the need for clearer definitions of water cycle components and improved models and databases.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Gerten, Dieter -- Rockstrom, Johan -- Heinke, Jens -- Steffen, Will -- Richardson, Katherine -- Cornell, Sarah -- New York, N.Y. -- Science. 2015 Jun 12;348(6240):1217. doi: 10.1126/science.aab0031. Epub 2015 Jun 11.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Research Domain of Earth System Analysis, Potsdam Institute for Climate Impact Research, 14473 Potsdam, Germany. gerten@pik-potsdam.de. ; Stockholm Resilience Centre, Stockholm University, 10691 Stockholm, Sweden. ; Research Domain of Earth System Analysis, Potsdam Institute for Climate Impact Research, 14473 Potsdam, Germany. International Livestock Research Institute, Nairobi, 00100 Kenya. Commonwealth Scientific and Industrial Research Organization, St. Lucia, QLD 4067, Australia. ; Stockholm Resilience Centre, Stockholm University, 10691 Stockholm, Sweden. Fenner School of Environment and Society, The Australian National University, Canberra, ACT 2601, Australia. ; Center for Macroecology, Evolution, and Climate, University of Copenhagen, Natural History Museum of Denmark, 2100 Copenhagen, Denmark.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/26068844" target="_blank"〉PubMed〈/a〉
    Keywords: *Biological Evolution ; *Climate Change ; *Earth (Planet) ; Humans ; *Ozone Depletion
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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