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  • 1
    Online Resource
    Online Resource
    Anatomically interpretable deep learning of brain age captures domain-specific cognitive impairment
    Proceedings of the National Academy of Sciences ; 2023
    In:  Proceedings of the National Academy of Sciences Vol. 120, No. 2 ( 2023-01-10)
    Details
    In: Proceedings of the National Academy of Sciences, Proceedings of the National Academy of Sciences, Vol. 120, No. 2 ( 2023-01-10)
    Abstract: The gap between chronological age (CA) and biological brain age, as estimated from magnetic resonance images (MRIs), reflects how individual patterns of neuroanatomic aging deviate from their typical trajectories. MRI-derived brain age (BA) estimates are often obtained using deep learning models that may perform relatively poorly on new data or that lack neuroanatomic interpretability. This study introduces a convolutional neural network (CNN) to estimate BA after training on the MRIs of 4,681 cognitively normal (CN) participants and testing on 1,170 CN participants from an independent sample. BA estimation errors are notably lower than those of previous studies. At both individual and cohort levels, the CNN provides detailed anatomic maps of brain aging patterns that reveal sex dimorphisms and neurocognitive trajectories in adults with mild cognitive impairment (MCI, N  = 351) and Alzheimer’s disease (AD, N  = 359). In individuals with MCI (54% of whom were diagnosed with dementia within 10.9 y from MRI acquisition), BA is significantly better than CA in capturing dementia symptom severity, functional disability, and executive function. Profiles of sex dimorphism and lateralization in brain aging also map onto patterns of neuroanatomic change that reflect cognitive decline. Significant associations between BA and neurocognitive measures suggest that the proposed framework can map, systematically, the relationship between aging-related neuroanatomy changes in CN individuals and in participants with MCI or AD. Early identification of such neuroanatomy changes can help to screen individuals according to their AD risk.
    Type of Medium: Online Resource
    ISSN: 0027-8424 , 1091-6490
    URL: Article
    DOI: 10.1073/pnas.2214634120
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    Language: English
    Publisher: Proceedings of the National Academy of Sciences
    Publication Date: 2023
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  • 2
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    Nitric Oxide Represses the Arabidopsis Floral Transition
    American Association for the Advancement of Science (AAAS) ; 2004
    In:  Science Vol. 305, No. 5692 ( 2004-09-24), p. 1968-1971
    Details
    In: Science, American Association for the Advancement of Science (AAAS), Vol. 305, No. 5692 ( 2004-09-24), p. 1968-1971
    Abstract: The correct timing of flowering is essential for plants to maximize reproductive success and is controlled by environmental and endogenous signals. We report that nitric oxide (NO) repressed the floral transition in Arabidopsis thaliana . Plants treated with NO, as well as a mutant overproducing NO ( nox1 ), flowered late, whereas a mutant producing less NO ( nos1 ) flowered early. NO suppressed CONSTANS and GIGANTEA gene expression and enhanced FLOWERING LOCUS C expression, which indicated that NO regulates the photoperiod and autonomous pathways. Because NO is induced by environmental stimuli and constitutively produced, it may integrate both external and internal cues into the floral decision.
    Type of Medium: Online Resource
    ISSN: 0036-8075 , 1095-9203
    URL: Article
    DOI: 10.1126/science.1098837
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    Language: English
    Publisher: American Association for the Advancement of Science (AAAS)
    Publication Date: 2004
    detail.hit.zdb_id: 128410-1
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  • 3
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    Multiple constraints cause positive and negative feedbacks limiting grassland soil CO 2 efflux under CO 2 enrichment
    Proceedings of the National Academy of Sciences ; 2021
    In:  Proceedings of the National Academy of Sciences Vol. 118, No. 2 ( 2021-01-12)
    Details
    In: Proceedings of the National Academy of Sciences, Proceedings of the National Academy of Sciences, Vol. 118, No. 2 ( 2021-01-12)
    Abstract: Terrestrial ecosystems are increasingly enriched with resources such as atmospheric CO 2 that limit ecosystem processes. The consequences for ecosystem carbon cycling depend on the feedbacks from other limiting resources and plant community change, which remain poorly understood for soil CO 2 efflux, J CO2 , a primary carbon flux from the biosphere to the atmosphere. We applied a unique CO 2 enrichment gradient (250 to 500 µL L −1 ) for eight years to grassland plant communities on soils from different landscape positions. We identified the trajectory of J CO2 responses and feedbacks from other resources, plant diversity [effective species richness, exp(H)], and community change (plant species turnover). We found linear increases in J CO2 on an alluvial sandy loam and a lowland clay soil, and an asymptotic increase on an upland silty clay soil. Structural equation modeling identified CO 2 as the dominant limitation on J CO2 on the clay soil. In contrast with theory predicting limitation from a single limiting factor, the linear J CO2 response on the sandy loam was reinforced by positive feedbacks from aboveground net primary productivity and exp(H), while the asymptotic J CO2 response on the silty clay arose from a net negative feedback among exp(H), species turnover, and soil water potential. These findings support a multiple resource limitation view of the effects of global change drivers on grassland ecosystem carbon cycling and highlight a crucial role for positive or negative feedbacks between limiting resources and plant community structure. Incorporating these feedbacks will improve models of terrestrial carbon sequestration and ecosystem services.
    Type of Medium: Online Resource
    ISSN: 0027-8424 , 1091-6490
    URL: Article
    DOI: 10.1073/pnas.2008284117
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    Language: English
    Publisher: Proceedings of the National Academy of Sciences
    Publication Date: 2021
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  • 4
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    Increased stray gas abundance in a subset of drinking water wells near Marcellus shale gas extraction
    Proceedings of the National Academy of Sciences ; 2013
    In:  Proceedings of the National Academy of Sciences Vol. 110, No. 28 ( 2013-07-09), p. 11250-11255
    Details
    In: Proceedings of the National Academy of Sciences, Proceedings of the National Academy of Sciences, Vol. 110, No. 28 ( 2013-07-09), p. 11250-11255
    Abstract: Horizontal drilling and hydraulic fracturing are transforming energy production, but their potential environmental effects remain controversial. We analyzed 141 drinking water wells across the Appalachian Plateaus physiographic province of northeastern Pennsylvania, examining natural gas concentrations and isotopic signatures with proximity to shale gas wells. Methane was detected in 82% of drinking water samples, with average concentrations six times higher for homes 〈 1 km from natural gas wells ( P = 0.0006). Ethane was 23 times higher in homes 〈 1 km from gas wells ( P = 0.0013); propane was detected in 10 water wells, all within approximately 1 km distance ( P = 0.01). Of three factors previously proposed to influence gas concentrations in shallow groundwater (distances to gas wells, valley bottoms, and the Appalachian Structural Front, a proxy for tectonic deformation), distance to gas wells was highly significant for methane concentrations ( P = 0.007; multiple regression), whereas distances to valley bottoms and the Appalachian Structural Front were not significant ( P = 0.27 and P = 0.11, respectively). Distance to gas wells was also the most significant factor for Pearson and Spearman correlation analyses ( P 〈 0.01). For ethane concentrations, distance to gas wells was the only statistically significant factor ( P 〈 0.005). Isotopic signatures (δ 13 C-CH 4 , δ 13 C-C 2 H 6 , and δ 2 H-CH 4 ), hydrocarbon ratios (methane to ethane and propane), and the ratio of the noble gas 4 He to CH 4 in groundwater were characteristic of a thermally postmature Marcellus-like source in some cases. Overall, our data suggest that some homeowners living 〈 1 km from gas wells have drinking water contaminated with stray gases.
    Type of Medium: Online Resource
    ISSN: 0027-8424 , 1091-6490
    URL: Article
    DOI: 10.1073/pnas.1221635110
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    Language: English
    Publisher: Proceedings of the National Academy of Sciences
    Publication Date: 2013
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  • 5
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    Noble gases identify the mechanisms of fugitive gas contamination in drinking-water wells overlying the Marcellus and Barnett Shales
    Proceedings of the National Academy of Sciences ; 2014
    In:  Proceedings of the National Academy of Sciences Vol. 111, No. 39 ( 2014-09-30), p. 14076-14081
    Details
    In: Proceedings of the National Academy of Sciences, Proceedings of the National Academy of Sciences, Vol. 111, No. 39 ( 2014-09-30), p. 14076-14081
    Abstract: Horizontal drilling and hydraulic fracturing have enhanced energy production but raised concerns about drinking-water contamination and other environmental impacts. Identifying the sources and mechanisms of contamination can help improve the environmental and economic sustainability of shale-gas extraction. We analyzed 113 and 20 samples from drinking-water wells overlying the Marcellus and Barnett Shales, respectively, examining hydrocarbon abundance and isotopic compositions (e.g., C 2 H 6 /CH 4 , δ 13 C-CH 4 ) and providing, to our knowledge, the first comprehensive analyses of noble gases and their isotopes (e.g., 4 He, 20 Ne, 36 Ar) in groundwater near shale-gas wells. We addressed two questions. ( i ) Are elevated levels of hydrocarbon gases in drinking-water aquifers near gas wells natural or anthropogenic? ( ii ) If fugitive gas contamination exists, what mechanisms cause it? Against a backdrop of naturally occurring salt- and gas-rich groundwater, we identified eight discrete clusters of fugitive gas contamination, seven in Pennsylvania and one in Texas that showed increased contamination through time. Where fugitive gas contamination occurred, the relative proportions of thermogenic hydrocarbon gas (e.g., CH 4 , 4 He) were significantly higher ( P 〈 0.01) and the proportions of atmospheric gases (air-saturated water; e.g., N 2 , 36 Ar) were significantly lower ( P 〈 0.01) relative to background groundwater. Noble gas isotope and hydrocarbon data link four contamination clusters to gas leakage from intermediate-depth strata through failures of annulus cement, three to target production gases that seem to implicate faulty production casings, and one to an underground gas well failure. Noble gas data appear to rule out gas contamination by upward migration from depth through overlying geological strata triggered by horizontal drilling or hydraulic fracturing.
    Type of Medium: Online Resource
    ISSN: 0027-8424 , 1091-6490
    URL: Article
    DOI: 10.1073/pnas.1322107111
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    Language: English
    Publisher: Proceedings of the National Academy of Sciences
    Publication Date: 2014
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  • 6
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    Elevated levels of diesel range organic compounds in groundwater near Marcellus gas operations are derived from surface activities
    Proceedings of the National Academy of Sciences ; 2015
    In:  Proceedings of the National Academy of Sciences Vol. 112, No. 43 ( 2015-10-27), p. 13184-13189
    Details
    In: Proceedings of the National Academy of Sciences, Proceedings of the National Academy of Sciences, Vol. 112, No. 43 ( 2015-10-27), p. 13184-13189
    Abstract: Hundreds of organic chemicals are used during natural gas extraction via high-volume hydraulic fracturing (HVHF). However, it is unclear whether these chemicals, injected into deep shale horizons, reach shallow groundwater aquifers and affect local water quality, either from those deep HVHF injection sites or from the surface or shallow subsurface. Here, we report detectable levels of organic compounds in shallow groundwater samples from private residential wells overlying the Marcellus Shale in northeastern Pennsylvania. Analyses of purgeable and extractable organic compounds from 64 groundwater samples revealed trace levels of volatile organic compounds, well below the Environmental Protection Agency’s maximum contaminant levels, and low levels of both gasoline range (0–8 ppb) and diesel range organic compounds (DRO; 0–157 ppb). A compound-specific analysis revealed the presence of bis(2-ethylhexyl) phthalate, which is a disclosed HVHF additive, that was notably absent in a representative geogenic water sample and field blanks. Pairing these analyses with ( i ) inorganic chemical fingerprinting of deep saline groundwater, ( ii ) characteristic noble gas isotopes, and ( iii ) spatial relationships between active shale gas extraction wells and wells with disclosed environmental health and safety violations, we differentiate between a chemical signature associated with naturally occurring saline groundwater and one associated with alternative anthropogenic routes from the surface (e.g., accidental spills or leaks). The data support a transport mechanism of DRO to groundwater via accidental release of fracturing fluid chemicals derived from the surface rather than subsurface flow of these fluids from the underlying shale formation.
    Type of Medium: Online Resource
    ISSN: 0027-8424 , 1091-6490
    URL: Article
    DOI: 10.1073/pnas.1511474112
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    Language: English
    Publisher: Proceedings of the National Academy of Sciences
    Publication Date: 2015
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  • 7
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    Large stocks of peatland carbon and nitrogen are vulnerable to permafrost thaw
    Proceedings of the National Academy of Sciences ; 2020
    In:  Proceedings of the National Academy of Sciences Vol. 117, No. 34 ( 2020-08-25), p. 20438-20446
    Details
    In: Proceedings of the National Academy of Sciences, Proceedings of the National Academy of Sciences, Vol. 117, No. 34 ( 2020-08-25), p. 20438-20446
    Abstract: Northern peatlands have accumulated large stocks of organic carbon (C) and nitrogen (N), but their spatial distribution and vulnerability to climate warming remain uncertain. Here, we used machine-learning techniques with extensive peat core data ( n 〉 7,000) to create observation-based maps of northern peatland C and N stocks, and to assess their response to warming and permafrost thaw. We estimate that northern peatlands cover 3.7 ± 0.5 million km 2 and store 415 ± 150 Pg C and 10 ± 7 Pg N. Nearly half of the peatland area and peat C stocks are permafrost affected. Using modeled global warming stabilization scenarios (from 1.5 to 6 °C warming), we project that the current sink of atmospheric C (0.10 ± 0.02 Pg C⋅y −1 ) in northern peatlands will shift to a C source as 0.8 to 1.9 million km 2 of permafrost-affected peatlands thaw. The projected thaw would cause peatland greenhouse gas emissions equal to ∼1% of anthropogenic radiative forcing in this century. The main forcing is from methane emissions (0.7 to 3 Pg cumulative CH 4 -C) with smaller carbon dioxide forcing (1 to 2 Pg CO 2 -C) and minor nitrous oxide losses. We project that initial CO 2 -C losses reverse after ∼200 y, as warming strengthens peatland C-sinks. We project substantial, but highly uncertain, additional losses of peat into fluvial systems of 10 to 30 Pg C and 0.4 to 0.9 Pg N. The combined gaseous and fluvial peatland C loss estimated here adds 30 to 50% onto previous estimates of permafrost-thaw C losses, with southern permafrost regions being the most vulnerable.
    Type of Medium: Online Resource
    ISSN: 0027-8424 , 1091-6490
    URL: Article
    DOI: 10.1073/pnas.1916387117
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    Language: English
    Publisher: Proceedings of the National Academy of Sciences
    Publication Date: 2020
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  • 8
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    Climate-driven risks to the climate mitigation potential of forests
    American Association for the Advancement of Science (AAAS) ; 2020
    In:  Science Vol. 368, No. 6497 ( 2020-06-19)
    Details
    In: Science, American Association for the Advancement of Science (AAAS), Vol. 368, No. 6497 ( 2020-06-19)
    Abstract: Forests have considerable potential to help mitigate human-caused climate change and provide society with many cobenefits. However, climate-driven risks may fundamentally compromise forest carbon sinks in the 21st century. Here, we synthesize the current understanding of climate-driven risks to forest stability from fire, drought, biotic agents, and other disturbances. We review how efforts to use forests as natural climate solutions presently consider and could more fully embrace current scientific knowledge to account for these climate-driven risks. Recent advances in vegetation physiology, disturbance ecology, mechanistic vegetation modeling, large-scale ecological observation networks, and remote sensing are improving current estimates and forecasts of the risks to forest stability. A more holistic understanding and quantification of such risks will help policy-makers and other stakeholders effectively use forests as natural climate solutions.
    Type of Medium: Online Resource
    ISSN: 0036-8075 , 1095-9203
    URL: Article
    DOI: 10.1126/science.aaz7005
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    Language: English
    Publisher: American Association for the Advancement of Science (AAAS)
    Publication Date: 2020
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    detail.hit.zdb_id: 2066996-3
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  • 9
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    The Global Stoichiometry of Litter Nitrogen Mineralization
    American Association for the Advancement of Science (AAAS) ; 2008
    In:  Science Vol. 321, No. 5889 ( 2008-08), p. 684-686
    Details
    In: Science, American Association for the Advancement of Science (AAAS), Vol. 321, No. 5889 ( 2008-08), p. 684-686
    Abstract: Plant residue decomposition and the nutrient release to the soil play a major role in global carbon and nutrient cycling. Although decomposition rates vary strongly with climate, nitrogen immobilization into litter and its release in mineral forms are mainly controlled by the initial chemical composition of the residues. We used a data set of ∼2800 observations to show that these global nitrogen-release patterns can be explained by fundamental stoichiometric relationships of decomposer activity. We show how litter quality controls the transition from nitrogen accumulation into the litter to release and alters decomposers' respiration patterns. Our results suggest that decomposers lower their carbon-use efficiency to exploit residues with low initial nitrogen concentration, a strategy used broadly by bacteria and consumers across trophic levels.
    Type of Medium: Online Resource
    ISSN: 0036-8075 , 1095-9203
    URL: Article
    DOI: 10.1126/science.1159792
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    Language: English
    Publisher: American Association for the Advancement of Science (AAAS)
    Publication Date: 2008
    detail.hit.zdb_id: 128410-1
    detail.hit.zdb_id: 2066996-3
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  • 10
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    Trading Water for Carbon with Biological Carbon Sequestration
    American Association for the Advancement of Science (AAAS) ; 2005
    In:  Science Vol. 310, No. 5756 ( 2005-12-23), p. 1944-1947
    Details
    In: Science, American Association for the Advancement of Science (AAAS), Vol. 310, No. 5756 ( 2005-12-23), p. 1944-1947
    Abstract: Carbon sequestration strategies highlight tree plantations without considering their full environmental consequences. We combined field research, synthesis of more than 600 observations, and climate and economic modeling to document substantial losses in stream flow, and increased soil salinization and acidification, with afforestation. Plantations decreased stream flow by 227 millimeters per year globally (52%), with 13% of streams drying completely for at least 1 year. Regional modeling of U.S. plantation scenarios suggests that climate feedbacks are unlikely to offset such water losses and could exacerbate them. Plantations can help control groundwater recharge and upwelling but reduce stream flow and salinize and acidify some soils.
    Type of Medium: Online Resource
    ISSN: 0036-8075 , 1095-9203
    URL: Article
    DOI: 10.1126/science.1119282
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    Language: English
    Publisher: American Association for the Advancement of Science (AAAS)
    Publication Date: 2005
    detail.hit.zdb_id: 128410-1
    detail.hit.zdb_id: 2066996-3
    detail.hit.zdb_id: 2060783-0
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