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  • 1
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    Hydraulic time constants for transpiration of loblolly pine at a free-air carbon dioxide enrichment site (2013)
    Oxford University Press
    Details
    Publication Date: 2013-02-21
    Description: The impact of stored water on estimates of transpiration from scaled sap flux measurements was assessed in mature Pinus taeda (L.) at the Duke Free-Air CO 2 Enrichment (FACE) site. We used a simple hydraulic model with measurements of sap flux ( J ) at breast height and the base of the live crown for 26 trees over 6 months to examine the effects of elevated CO 2 (eCO 2 ) and fertilization (N F ) treatments, as well as temporal variation in soil moisture ( M ( t ) ), on estimates of the hydraulic time constant (). At low M ( t ) , there was little (〈12%) difference in of different treatments. At high M ( t ) , differences were much greater, with reductions of 27, 52 and 34% in eCO 2 , N F and eCO 2 x N F respective to the control. Incorporating with these effects into the analysis of a larger data set of previous J measurements at this site (1998–2008) improved agreement between modeled and measured values in 92% of cases. However, a simplified calibration of that neglected treatment and soil moisture effects performed more dependably, improving agreement in 98% of cases. Incorporating had the effect of increasing estimates of reference stomatal conductance at 1 kPa vapor pressure deficit (VPD) and saturating photosynthetic active radiation (PAR) an average of 12–14%, while increasing estimated sensitivities to VPD and PAR. A computationally efficient hydraulic model, such as the one presented here, incorporated into a hierarchical model of stomatal conductance presents a novel approach to including hydraulic time constants in estimates of stomatal responses from long-term sap flux data sets.
    Print ISSN: 0829-318X
    Electronic ISSN: 1758-4469
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Published by Oxford University Press
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  • 2
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    The effects of elevated CO2 and nitrogen fertilization on stomatal conductance estimated from 11 years of scaled sap flux measurements at Duke FACE (2013)
    Oxford University Press
    Details
    Publication Date: 2013-02-21
    Description: In this study, we employ a network of thermal dissipation probes (TDPs) monitoring sap flux density to estimate leaf-specific transpiration ( E L ) and stomatal conductance ( G S ) in Pinus taeda (L.) and Liquidambar styraciflua L. exposed to +200 ppm atmospheric CO 2 levels (eCO 2 ) and nitrogen fertilization. Scaling half-hourly measurements from hundreds of sensors over 11 years, we found that P. taeda in eCO 2 intermittently (49% of monthly values) decreased stomatal conductance ( G S ) relative to the control, with a mean reduction of 13% in both total E L and mean daytime G S . This intermittent response was related to changes in a hydraulic allometry index ( A H ), defined as sapwood area per unit leaf area per unit canopy height, which decreased a mean of 15% with eCO 2 over the course of the study, due mostly to a mean 19% increase in leaf area ( A L ). In contrast, L. styraciflua showed a consistent (76% of monthly values) reduction in G S with eCO 2 with a total reduction of 32% E L , 31% G S and 23% A H (due to increased A L per sapwood area). For L. styraciflua , like P. taeda , the relationship between A H and G S at reference conditions suggested a decrease in G S across the range of A H . Our findings suggest an indirect structural effect of eCO 2 on G S in P. taeda and a direct leaf level effect in L. styraciflua . In the initial year of fertilization, P. taeda in both CO 2 treatments, as well as L. styraciflua in eCO 2 , exhibited higher G S with N F than expected from shifts in A H , suggesting a transient direct effect on G S . Whether treatment effects on mean leaf-specific G S are direct or indirect, this paper highlights that long-term treatment effects on G S are generally reflected in A H as well.
    Print ISSN: 0829-318X
    Electronic ISSN: 1758-4469
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Published by Oxford University Press
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  • 3
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    Hillslope Hydrology in Global Change Research and Earth System Modeling (2019)
    Wiley
    Details
    Publication Date: 2019
    Description: Abstract Earth System Models (ESMs) are essential tools for understanding and predicting global change, but they cannot explicitly resolve hillslope‐scale terrain structures that fundamentally organize water, energy, and biogeochemical stores and fluxes at subgrid scales. Here we bring together hydrologists, Critical Zone scientists, and ESM developers, to explore how hillslope structures may modulate ESM grid‐level water, energy, and biogeochemical fluxes. In contrast to the one‐dimensional (1‐D), 2‐ to 3‐m deep, and free‐draining soil hydrology in most ESM land models, we hypothesize that 3‐D, lateral ridge‐to‐valley flow through shallow and deep paths and insolation contrasts between sunny and shady slopes are the top two globally quantifiable organizers of water and energy (and vegetation) within an ESM grid cell. We hypothesize that these two processes are likely to impact ESM predictions where (and when) water and/or energy are limiting. We further hypothesize that, if implemented in ESM land models, these processes will increase simulated continental water storage and residence time, buffering terrestrial ecosystems against seasonal and interannual droughts. We explore efficient ways to capture these mechanisms in ESMs and identify critical knowledge gaps preventing us from scaling up hillslope to global processes. One such gap is our extremely limited knowledge of the subsurface, where water is stored (supporting vegetation) and released to stream baseflow (supporting aquatic ecosystems). We conclude with a set of organizing hypotheses and a call for global syntheses activities and model experiments to assess the impact of hillslope hydrology on global change predictions.
    Print ISSN: 8755-1209
    Electronic ISSN: 1944-9208
    Topics: Geosciences
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 4
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    Liquid crystal self-assembly of random-sequence DNA oligomers [Applied Physical Sciences] (2012)
    National Academy of Sciences
    Details
    Publication Date: 2012-01-25
    Description: In biological systems and nanoscale assemblies, the self-association of DNA is typically studied and applied in the context of the evolved or directed design of base sequences that give complementary pairing, duplex formation, and specific structural motifs. Here we consider the collective behavior of DNA solutions in the distinctly different regime where DNA base sequences are chosen at random or with varying degrees of randomness. We show that in solutions of completely random sequences, corresponding to a remarkably large number of different molecules, e.g., approximately 1012 for random 20-mers, complementary still emerges and, for a narrow range of oligomer lengths, produces a subtle hierarchical sequence of structured self-assembly and organization into liquid crystal (LC) phases. This ordering follows from the kinetic arrest of oligomer association into long-lived partially paired double helices, followed by reversible association of these pairs into linear aggregates that in turn condense into LC domains.
    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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  • 5
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    Chiral nanopore arrays [Applied Physical Sciences] (2014)
    National Academy of Sciences
    Details
    Publication Date: 2014-10-08
    Description: A series of simple hierarchical self-assembly steps achieve self-organization from the centimeter to the subnanometer-length scales in the form of square-centimeter arrays of linear nanopores, each one having a single chiral helical nanofilament of large internal surface area and interfacial interactions based on chiral crystalline molecular arrangements.
    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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  • 6
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    Hillslope Hydrology in Global Change Research and Earth System Modeling (2019)
    Wiley
    Details
    Publication Date: 2019
    Description: Abstract Earth System Models (ESMs) are essential tools for understanding and predicting global change, but they cannot explicitly resolve hillslope‐scale terrain structures that fundamentally organize water, energy, and biogeochemical stores and fluxes at subgrid scales. Here we bring together hydrologists, Critical Zone scientists, and ESM developers, to explore how hillslope structures may modulate ESM grid‐level water, energy, and biogeochemical fluxes. In contrast to the one‐dimensional (1‐D), 2‐ to 3‐m deep, and free‐draining soil hydrology in most ESM land models, we hypothesize that 3‐D, lateral ridge‐to‐valley flow through shallow and deep paths and insolation contrasts between sunny and shady slopes are the top two globally quantifiable organizers of water and energy (and vegetation) within an ESM grid cell. We hypothesize that these two processes are likely to impact ESM predictions where (and when) water and/or energy are limiting. We further hypothesize that, if implemented in ESM land models, these processes will increase simulated continental water storage and residence time, buffering terrestrial ecosystems against seasonal and interannual droughts. We explore efficient ways to capture these mechanisms in ESMs and identify critical knowledge gaps preventing us from scaling up hillslope to global processes. One such gap is our extremely limited knowledge of the subsurface, where water is stored (supporting vegetation) and released to stream baseflow (supporting aquatic ecosystems). We conclude with a set of organizing hypotheses and a call for global syntheses activities and model experiments to assess the impact of hillslope hydrology on global change predictions.
    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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  • 7
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    Suppression of cooling by strong magnetic fields in white dwarf stars (2014)
    Nature Publishing Group (NPG)
    Details
    Publication Date: 2014-10-21
    Description: Isolated cool white dwarf stars more often have strong magnetic fields than young, hotter white dwarfs, which has been a puzzle because magnetic fields are expected to decay with time but a cool surface suggests that the star is old. In addition, some white dwarfs with strong fields vary in brightness as they rotate, which has been variously attributed to surface brightness inhomogeneities similar to sunspots, chemical inhomogeneities and other magneto-optical effects. Here we describe optical observations of the brightness and magnetic field of the cool white dwarf WD 1953-011 taken over about eight years, and the results of an analysis of its surface temperature and magnetic field distribution. We find that the magnetic field suppresses atmospheric convection, leading to dark spots in the most magnetized areas. We also find that strong fields are sufficient to suppress convection over the entire surface in cool magnetic white dwarfs, which inhibits their cooling evolution relative to weakly magnetic and non-magnetic white dwarfs, making them appear younger than they truly are. This explains the long-standing mystery of why magnetic fields are more common amongst cool white dwarfs, and implies that the currently accepted ages of strongly magnetic white dwarfs are systematically too young.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Valyavin, G -- Shulyak, D -- Wade, G A -- Antonyuk, K -- Zharikov, S V -- Galazutdinov, G A -- Plachinda, S -- Bagnulo, S -- Machado, L Fox -- Alvarez, M -- Clark, D M -- Lopez, J M -- Hiriart, D -- Han, Inwoo -- Jeon, Young-Beom -- Zurita, C -- Mujica, R -- Burlakova, T -- Szeifert, T -- Burenkov, A -- England -- Nature. 2014 Nov 6;515(7525):88-91. doi: 10.1038/nature13836. Epub 2014 Oct 19.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Special Astrophysical Observatory of Russian Academy of Science, Nizhnij Arkhyz, Zelenchukskiy region, Karachai-Cherkessian Republic 369167, Russia. ; Institute for Astrophysics, Georg-August-University, Friedrich-Hund-Platz 1, D-37077, Gottingen, Germany. ; Department of Physics, Royal Military College of Canada, PO Box 17000 Station Forces, Kingston, Ontario, K7K 7B4, Canada. ; Crimean Astrophysical Observatory, Nauchny, Crimea 98409, Ukraine. ; Instituto de Astronomia, Observatorio Astronomico Nacional San Pedro Martir (SPM), Universidad Nacional Autonoma de Mexico, 22860 Ensenada, Baja California, Mexico. ; 1] Instituto de Astronomia, Universidad Catolica del Norte, Avenida Angamos 0610, Antofagasta, Chile [2] Pulkovo Observatory, Pulkovskoe Shosse 65/1, Saint-Petersburg 196140, Russia. ; Armagh Observatory, College Hill, Armagh BT61 9DG, UK. ; Korea Astronomy and Space Science Institute 776, Daedeokdae-ro, Yuseong-gu, Daejeon 305-348, South Korea. ; 1] Instituto de Astrofisica de Canarias, 38200, La Laguna, Tenerife, Spain [2] Departamento de Astrofisica, Universidad de La Laguna, 38206 La Laguna, Tenerife, Spain. ; Instituto Nacional de Astrofisica, Optica y Electronica, Apartado Postal 51 y 216, 72000 Tonantzintla, Pueblo, Mexico. ; European Southern Observatory, Alonso de Cordova 3107, Santiago, Chile.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/25327247" target="_blank"〉PubMed〈/a〉
    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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  • 8
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    Structural transitions and guest/host complexing of liquid crystal helical nanofilaments induced by nanoconfinement (2017)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2017-02-12
    Description: A lamellar liquid crystal (LC) phase of certain bent-core mesogenic molecules can be grown in a manner that generates a single chiral helical nanofilament in each of the cylindrical nanopores of an anodic aluminum oxide (AAO) membrane. By introducing guest molecules into the resulting composite chiral nanochannels, we explore the structures and functionality of the ordered guest/host LC complex, verifying the smectic-like positional order of the fluidic nematic LC phase, which is obtained by the combination of the LC organization and the nanoporous AAO superstructure. The guest nematic LC 4'- n -pentyl-4-cyanobiphenyl is found to form a distinctive fluid layered ordered LC complex at the nanofilament/guest interface with the host 1,3-phenylene bis[4-(4-nonyloxyphenyliminomethyl)benzoate], where this interface contacts the AAO cylinder wall. Filament growth form is strongly influenced by mixture parameters and pore dimensions.
    Electronic ISSN: 2375-2548
    Topics: Natural Sciences in General
    Published by American Association for the Advancement of Science (AAAS)
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  • 9
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    ALMA observations of the supergiant B[e] star Wd1-9 (2016)
    Oxford University Press
    Details
    Publication Date: 2016-10-17
    Description: Mass-loss in massive stars plays a critical role in their evolution, although the precise mechanism(s) responsible – radiatively driven winds, impulsive ejection and/or binary interaction – remain uncertain. In this Letter, we present Atacama Large Millimetre/Submillimeter Array line and continuum observations of the supergiant B[e] star Wd1-9, a massive post-main-sequence object located within the starburst cluster Westerlund 1 (Wd1). We find it to be one of the brightest stellar point sources in the sky at millimetre wavelengths, with (serendipitously identified) emission in the H41α radio recombination line. We attribute these properties to a low velocity (~100 km s –1  ) ionized wind, with an extreme mass-loss rate 6.4 x 10 –5 ( d /5 kpc) 1.5 M yr – 1 . External to this is an extended aspherical ejection nebula indicative of a prior phase of significant mass-loss. Taken together, the millimetre properties of Wd1-9 show a remarkable similarity to those of the highly luminous stellar source MWC349A. We conclude that these objects are interacting binaries evolving away from the main sequence and undergoing rapid case-A mass transfer. As such they – and by extension the wider class of supergiant B[e] stars – may provide a unique window into the physics of a process that shapes the life-cycle of ~70 per cent of massive stars found in binary systems.
    Print ISSN: 1745-3925
    Electronic ISSN: 1745-3933
    Topics: Physics
    Published by Oxford University Press
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  • 10
    Electronic Resource
    Electronic Resource
    When is a natural duality ‘good’? (1996)
    Springer
    Algebra universalis 35 (1996), S. 265-295 
    Details
    ISSN: 1420-8911
    Keywords: 08C05 ; 08C15 ; 18A40 ; Duality theory ; injective ; natural duality ; strong duality ; congruence distributivity ; near unanimity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract Building on the most current work in the theory of natural dualities, we continue the study of strong dualities for the quasi-variety generated by a finite algebra. We investigate ten different versions of what we would like to mean by a ‘good duality’. Each version concerns, among other things, a specific restriction on the type of the structures in the dual category which insures that the dual structures will in a useful sense be simple. Through each investigation we seek a theorem characterizing, in terms of finitely verifiable conditions, those finite algebras generating a quasi-variety which admits a strong duality meeting the given restrictions. Our study includes a careful treatment of coproducts, logarithmic dualities and strong dualities by various unary structures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01195501
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