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  • Wiley  (61)
  • American Geophysical Union
  • American Institute of Physics (AIP)
  • Canadian Science Publishing
  • 2010-2014  (39)
  • 2000-2004  (38)
  • 1
    Electronic Resource
    Electronic Resource
    Computer simulation of void growth dynamics under the action of electromigration and capillary forces in narrow thin interconnects (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 90 (2001), S. 1564-1572 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A comprehensive picture of void dynamics in connection with the critical morphological evolution has been developed in order to understand the conditions under which premature failure of metallic thin interconnects occurs. Our mathematical model on the mass flow and accumulation on void surfaces, under the action of applied electrostatic and elastostatic force fields, and capillary effects, follows an irreversible but discrete thermodynamic formulation of interphases and surfaces. This formalism also takes into account in a natural way the mass transfer process (the void growth), between bulk phase and the void region in multi-component systems, in terms of the normalized local values of Gibbs free energy of transformation with respect to the specific surface Gibbs free energy, in addition to the contribution due to local curvature of the advancing reaction front, rather rigorously. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1382835
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  • 2
    Electronic Resource
    Electronic Resource
    Simulation of dislocation damping spectra associated with the collective motion of point defects and kink chain subjected to bulk segregation (2002)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 91 (2002), S. 1860-1870 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A theory of interactive and completely coupled systems of dislocations and mobile point defects is presented. The computer simulations yield an accurate prediction of experimental spectral data in terms of dislocation induced Cottrell relaxation and its gradual conversion into a Cottrell–Koster relaxation peak at high concentrations of spherical point defect. The bulk segregation of point defects to the kinked-dislocation line is also accounted for. Excellent results are obtained in computer simulations of aging, peaking, and finally the stabilization behavior of transient dislocation damping peaks. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1429769
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  • 3
    Electronic Resource
    Electronic Resource
    Dynamics of hierarchical folding on energy landscapes of hexapeptides (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 115 (2001), S. 10533-10547 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In this paper we apply the master equation approach to study the effects of the energy landscape topology and topography on the kinetics of folding, and on kinetic transitions of three alanine-hexapeptides analogs which involve polypeptides with neutral and charged groups and a cyclized polypeptide. We rely on the potential-energy landscapes of these molecular systems, which have been constructed using both a topological mapping analysis and a principal component analysis. It was found that the different topology and topography of the energy landscapes result in different "folding" time scales and that the systems with geometrical constraints (cyclization and opposite charges at the termini) "fold" more slowly than the unconstrained peptide. In addition, for each of the three polypeptide systems, the kinetics is nonexponential at the temperature range 400–600 K. The relaxation kinetics is characterized by logarithmic oscillations, which indicate hierarchical dynamics characterized by multiple time scales of fast (few ps) and slow (few μs) events. At higher temperatures, successive relaxation channels with similar characteristic time scales collapse into a single relaxation channel. While the kinetics of the unconstrained peptide at 600 K can be reasonably well described by a single exponential time scale, the kinetics of the constrained hexapeptides are inherently hierarchical and featured by multiple time scales even at high temperatures. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1415444
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  • 4
    Electronic Resource
    Electronic Resource
    Energy landscapes of conformationally constrained peptides (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 114 (2001), S. 993-1009 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Conformation constraints are known to affect the flexibility and bioactivity of peptides. In this study we analyzed the effect of conformation constraints on the topography of the energy landscapes of three analogous hexapeptides. The three analogs vary in the degree of constraint imposed on their conformational motion: linear alanine hexapeptide with neutral terminals (Ala6), linear alanine hexapeptide with charged terminals (chrg-Ala6), and cyclic alanine hexapeptide (cyc-Ala6). It was found that significantly different energy landscapes characterize each of the three peptides, leading to different folding behaviors. Since all three analogs would be encoded by the same gene, these results suggest that nongenomic post-translational modifications may play an important role in determining the properties of proteins as well as of their folding pathways. In addition, the present study indicates that the complexity of those energy landscapes that are dominated by funnel topography can be captured by one or two reaction coordinates, such as conformational similarity to the native state. However, for more complex landscapes characterized by multiple basins such a description is insufficient. This study also shows that similar views of the landscape topography were obtained by principal component analysis (based only on local minima) and by topological mapping analysis (based on minima and barrier information). Both methods were able to resolve the complex landscape topographies for all three peptides. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1329646
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  • 5
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    Estimating maximum mean canopy stomatal conductance for use in models (2001)
    Canadian Science Publishing
    Details
    Publication Date: 2001-02-01
    Description: Fertilized (F) and irrigated and fertilized (IF) stands of Pinus taeda L. produced twice the leaf area index of irrigated (I) and control (C) stands. Based on sap flux-scaled mean stomatal conductance (GS), we found that stomatal conductance in F was half that in other treatments. During the growing season, GS was related to vapor pressure deficit (D) and soil moisture. During the cooler season, soil moisture was high and light accompanied D in controlling GS. Under all conditions and treatments, the rate of decrease in GS with D was proportional to GS at low D (= 1 kPa). We evaluated whether GS can be used as an input to growth models and used a simple growth model (3-PG), which also predicts stand transpiration (EC), to compare with direct EC measurements in the four stands. Model predictions of monthly EC based on Penman-Montieth equation parameterized with maximum GS (GSmax) estimated under highest "native" soil moisture (0.07 m3·m3) produced long-term values within 10% of measured EC. When the model was parameterized with GSmax estimated under experimentally raised soil moisture, or with porometrically measured conductance, EC values were consistently overpredicted from 12 to 33%. Thus, sap-flux scaled mean canopy stomatal conductance obtained under non limiting light conditions, low D, and highest native soil moisture, is the most appropriate parameter value for certain single-leaf type of models.
    Print ISSN: 0045-5067
    Electronic ISSN: 1208-6037
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Published by Canadian Science Publishing
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  • 6
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    Estimating ma×imum mean canopy stomatal conductance for use in models (2001)
    Canadian Science Publishing
    Details
    Publication Date: 2001-01-01
    Print ISSN: 0045-5067
    Electronic ISSN: 1208-6037
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Published by Canadian Science Publishing
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  • 7
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    Sustained effects of atmospheric [CO2] and nitrogen availability on forest soil CO2 efflux (2013)
    Wiley
    Details
    Publication Date: 2013-10-01
    Description: Soil CO 2 efflux ( F soil ) is the largest source of carbon from forests and reflects primary productivity as well as how carbon is allocated within forest ecosystems. Through early stages of stand development, both elevated [CO 2 ] and availability of soil nitrogen (N; sum of mineralization, deposition, and fixation) have been shown to increase gross primary productivity, but the long-term effects of these factors on F soil are less clear. Expanding on previous studies at the Duke Free Air CO 2 Enrichment (FACE) site, we quantified the effects of elevated [CO 2 ] and N fertilization on F soil using daily measurements from automated chambers over 10 years. Consistent with previous results, compared to ambient-unfertilized plots, annual F soil increased under elevated [CO 2 ] (~17%) and decreased with N (~21%). N fertilization under elevated [CO 2 ] reduced F soil to values similar to untreated plots. Over the study period, base respiration rates increased with leaf productivity but declined after productivity saturated. Despite treatment-induced differences in aboveground biomass, soil temperature and water content were similar among treatments. Inter-annually, low soil water content decreased annual F soil from potential values – estimated based on temperature alone assuming non-limiting soil water content – by ~0.7% per 1.0% reduction in relative extractable water. This effect was only slightly ameliorated by elevated [CO 2 ]. Variability of soil N availability among plots accounted for the spatial variability of F soil , showing a decrease of ~114 g C m -2 y -1 per 1 g m -2 increase in soil N availability, with consistently higher F soil in elevated [CO 2 ] plots ~127 g C per 100 ppm [CO 2 ] over the +200 ppm enrichment. Altogether, reflecting increased belowground carbon partitioning in response to greater plant nutritional needs, the effects of elevated [CO 2 ] and N fertilization on F soil in this stand are sustained beyond the early stages of stand development and through stabilization of annual foliage production. This article is protected by copyright. All rights reserved.
    Print ISSN: 1354-1013
    Electronic ISSN: 1365-2486
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Published by Wiley
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  • 8
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    Real-time beamforming using high-speed FPGAs at the Allen Telescope Array (2011)
    Wiley
    Details
    Publication Date: 2011-02-24
    Description: The Allen Telescope Array (ATA) at the Hat Creek Radio Observatory (HCRO) is a wide-field panchromatic radio telescope currently consisting of 42 offset-Gregorian antennas each with a 6 m aperture, with plans to expand the array to 350 antennas. Through unique back-end hardware, the ATA performs real-time wideband beamforming with independent subarray capabilities and customizable beam shaping. The beamformers enable science observations requiring the full gain of the array, time domain (nonintegrated) output, and interference excision or orthogonal beamsets. In this paper we report on the design of this beamformer, including architecture and experimental results. Furthermore, we address some practical considerations in large-N wideband beamformers implemented on field programmable gate array platforms, including device utilization, methods of calibration and control, and interchip synchronization.
    Print ISSN: 0048-6604
    Electronic ISSN: 1944-799X
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 9
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    Forest water use and water use efficiency at elevated CO2: a model-data intercomparison at two contrasting temperate forest FACE sites (2013)
    Wiley
    Details
    Publication Date: 2013-02-08
    Description: Predicted responses of transpiration to elevated atmospheric CO 2 concentration (eCO 2 ) are highly variable among process-based models. To better understand and constrain this variability among models, we conducted an intercomparison of 11 ecosystem models applied to data from two forest free-air CO 2 enrichment (FACE) experiments at Duke University and Oak Ridge National Laboratory. We analysed model structures in order to identify the key underlying assumptions causing differences in model predictions of transpiration and canopy water-use efficiency. We then compared the models against data to identify model assumptions that are incorrect or are large sources of uncertainty. We found that model-to-model and model-to-observations differences resulted from four key sets of assumptions, namely: (i) the nature of the stomatal response to elevated CO 2 (coupling between photosynthesis and stomata was supported by the data); (ii) the roles of the leaf and atmospheric boundary layer (models which assumed multiple conductance terms in series predicted more decoupled fluxes than observed at the broadleaf site); (iii) the treatment of canopy interception (large inter-model variability, 2-15 %); and (iv) the impact of soil moisture stress (process uncertainty in how models limit carbon and water fluxes during moisture stress). Overall, model predictions of the CO 2 effect on WUE were reasonable (inter-model μ = ~28 ± 10 %) compared to the observations (μ = ~30 ± 13 %) at the well-coupled coniferous site (Duke), but poor (inter-model μ = ~24 ± 6 %; observations μ = ~38 ± 7 %) at the broadleaf site (Oak Ridge). The study yields a framework for analysing and interpreting model predictions of transpiration responses to eCO 2 , and highlights key improvements to these types of models. © 2013 Blackwell Publishing Ltd
    Print ISSN: 1354-1013
    Electronic ISSN: 1365-2486
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Published by Wiley
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  • 10
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    Optical properties of the Dead Sea (2013)
    Wiley
    Details
    Publication Date: 2013-02-13
    Description: [1]  The Dead Sea, located in the rift valley between Jordan and Israel, is a hypersaline lake, resulting in unique biogeochemistry and optical properties. In the spring of 2004 we conducted two days of physical and optical measurements in the lake. Because of the significant effect of dissolved salts onthe optical propertiesof water,our analysis required a novel processing approach to obtain dissolved and total inherent optical properties from the measurements. In addition, we show that the lake's salinity can be estimated from measurements of hyper-spectral absorption or attenuation spectra in the red and infrared parts of the spectrum, using published values of specific absorption of dissolved NaCl, despite the fact that the lake's salt chemistry is complex. In situ observations demonstrated that the lake has a two-layer structure with a warm and more turbid layer at the top 20-30 m and a clearer colder layer below. Both the particulate and dissolved absorption are well approximated by exponentially decreasing functions with the spectral slope of the particulate absorption about half that of the dissolved fraction and consistent with other aquatic environments. Both have relatively low and similar magnitudes in the blue (O(0.15 m -1 )). Mean particle size was observed to increase with depth consistent with precipitating salt crystals (observed in past campaigns) shown here toplay a major role in the lake's optical properties.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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