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  • 1
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 69 (1996), S. 1713-1715 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The correlation between trap density and leakage current of Pb(Zr53Ti47)O3 (PZT) capacitors is studied by examining the current–time (I–t) and the current–voltage (I–V) characteristics. The increase of leakage current after dc electrical field stress is correlated with the number of charges trapped inside the films. The spatial density distribution of trapped charges is calculated by analyzing the decay of discharging current after the application of dc stress. The discharging current is well fitted by a 1/t relationship where t is discharging time. This behavior can be explained by using the tunneling front model. A discharging process is proposed based on this consideration. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Lead–zirconate–titanate (PZT) is an interesting ferroelectric material for the application of DRAM and nonvolatile memory devices. In this work, metal-PZT-metal capacitors with Au and Pt as the top and the bottom electrodes are fabricated. The leakage current, time dependent dielectric breakdown (TDDB) lifetime and the correlation between them are studied. The leakage current is found to depend on the applied electric field in a power law relationship. The exponent in the power law relation is found to be 0.88 in the low field region (lower than 100 kV/cm) and 9.6 in the high field region (larger than 100 kV/cm). The TDDB of the PZT capacitors is measured. An extrapolation method is proposed to obtain the projected TDDB lifetime from the time to breakdown (tBD)data. The power law exponential extracted from the TDDB measurement in this method is found to be in good agreement with that obtained from the leakage current measurement. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1432-1939
    Keywords: Canopy structure ; Coordination ; Nitrogen allocation ; Optimization ; Photosynthesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract It has long been observed that leaf nitrogen concentrations decline with depth in closed canopies in a number of plant communities. This phenomenon is generally believed to be related to a changing radiation environment and it has been suggested by some researchers that plants allocate nitrogen in order to optimize total whole canopy photosynthesis. Although optimization theory has been successfully utilized to describe a variety of physiological and ecological phenomena, it has some shortcomings that are subject to criticism (e.g., time constraints, oversimplifications, lack of insights, etc.). In this paper we present an alternative to the optimization theory of plant canopy nitrogen distribution, which we term coordination theory. We hypothesize that plants allocate nitrogen to maintain a balance between two processes, each of which is dependent on leaf nitrogen content and each of which potentially limits photosynthesis. These two processes are defined as Wc, the Rubiscolimited rate of carboxylation, and Wj, the electron transport-limited rate of carboxylation. We suggest that plants allocate nitrogen differentially to, leaves in different canopy layers in such a way that Wc and Wj remain roughly balanced. In this scheme, the driving force for the allocation of nitrogen within a canopy is the difference between the leaf nitrogen content that is required to bring Wc and Wj into balance and the current nitrogen content. We show that the daily carbon assimilation of a canopy with a nitrogen distribution resulting from this internal coordination of Wc and Wj is very similar to that obtained using optimization theory.
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  • 5
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2015. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 120 (2015): 4028–4047, doi:10.1002/2014JC010425.
    Description: The interactions between waves, tidal currents, and bathymetry near New River Inlet, NC, USA are investigated to understand the effects on the resulting hydrodynamics and sediment transport. A quasi-3-D nearshore community model, NearCoM-TVD, is used in this integrated observational and modeling study. The model is validated with observations of waves and currents at 30 locations, including in a recently dredged navigation channel and a shallower channel, and on the ebb tidal delta, for a range of flow and offshore wave conditions during May 2012. In the channels, model skills for flow velocity and wave height are high. Near the ebb tidal delta, the model reproduces the observed rapid onshore (offshore) decay of wave heights (current velocities). Model results reveal that this sharp transition coincides with the location of the breaker zone over the ebb tidal delta, which is modulated by semidiurnal tides and by wave intensity. The modulation of wave heights is primarily owing to depth changes rather than direct wave-current interaction. The modeled tidally averaged residual flow patterns show that waves play an important role in generating vortices and landward-directed currents near the inlet entrance. Numerical experiments suggest that these flow patterns are associated with the channel-shoal bathymetry near the inlet, similar to the generation of rip currents. Consistent with other inlet studies, model results suggest that tidal currents drive sediment fluxes in the channels, but that sediment fluxes on the ebb tidal delta are driven primarily by waves.
    Description: Funding was provided by the Office of Naval Research (N00014-13-1–0120 and N00014-14-1-0586) and the Office of the Assistant Secretary of Defense for Research and Engineering.
    Description: 2015-12-07
    Keywords: Wave-current interaction ; Sediment transport ; New River ; Morphological evolution ; Tidal inlet
    Repository Name: Woods Hole Open Access Server
    Type: Article
    Format: application/pdf
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  • 6
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2018. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 123 (2018): 6779-6799, doi:10.1029/2017JC013625.
    Description: Observations of water levels, waves, currents, and bathymetry collected for a month at an unstratified tidal inlet with a shallow (1 to 2 m deep) ebb shoal are used to evaluate the asymmetry in flows and dynamics owing to inertia and waves. Along‐channel currents ranged from −1.5 to 0.6 m/s (positive inland) inside the main (3 to 5 m deep) channel crossing the ebb shoal. Net discharge is negligible, and ebb dominance of the channel flows is owing to inflow and outflow asymmetries near the inlet mouth. Offshore wave heights ranged from 0.5 to 2.5 m. During moderate to large wave events (offshore significant wave heights 〉1.2 m), wave forcing enhanced onshore mass flux near the shoal edge and inside the inlet, leading to reduced ebb flow dominance. Momentum balances estimated with the water depths, currents, and waves simulated with a quasi 3‐D numerical model reproduce the momentum balances estimated from the observations reasonably well. Both observations and simulations suggest that ebb‐dominant bottom stresses are balanced by the ebb‐dominant pressure gradient and the tidally asymmetric inertia, which is a sink (source) of momentum on flood (ebb). Simulations with and without waves suggest that waves drive local and nonlocal changes in the water levels and flows. Specifically, breaking waves at the offshore edge of the ebb shoal induce setup and partially block the ebb jet (local effects), which leads to a more onshore‐directed mass flux, changes to the advection across the ebb shoal, and increased water levels inside the inlet mouth (nonlocal effects).
    Description: WHOI Coastal Ocean Institute Student Research; Office of the Assistant Secretary of Defense for Research and Engineering; National Defense Science and Engineering; National Science Foundation; Office of Naval Research
    Description: 2019-03-22
    Keywords: Inlets ; Waves ; Inertia ; Tidal asymmetry ; Ebb shoal
    Repository Name: Woods Hole Open Access Server
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  • 7
    Publication Date: 2022-10-21
    Description: Delaware Bay is a large estuary with a deep, relatively narrow channel and wide, shallow banks, providing a clear example of a “channel-shoal” estuary. This numerical modeling study addresses the exchange flow in this channel-shoal estuary, specifically to examine how the lateral geometry affects the strength and mechanisms of exchange flow. We find that the exchange flow is exclusively confined to the channel region during spring tides, when stratification is weak, and it broadens laterally over the shoals during the more stratified neap tides, but still occupies a small fraction of the total width of the estuary. Exchange flow is relatively weak during spring tides, resulting from oscillatory shear dispersion in the channel augmented by weak Eulerian exchange flow. During neap tides, stratification and shear increase markedly, resulting in a strong Eulerian residual shear flow, with a net exchange flow roughly 5 times that of the spring tide. During both spring and neap tides, lateral salinity gradients generated by differential advection at the edge of the channel drive a tidally oscillating cross-channel flow, which strongly influences the stratification, along-estuary salt balance and momentum balance. The lateral flow also causes the phase variation in salinity that results in oscillatory shear dispersion during both spring and neap tides and is a significant advective momentum source driving the residual circulation. Thus, although the shoals make a negligible direct contribution to the exchange flow, the salinity gradients between the channel and the shoal are critical to the stratification and exchange flow within the estuarine channel.
    Description: National Science Foundation (NSF): OCE-1325136; National Science Foundation (NSF): OCE-1634490; National Science Foundation (NSF): Jia-Lin Chen OCE-1736539
    Keywords: Estuarine circulation ; Tidal dispersion ; Lateral circulation
    Repository Name: Woods Hole Open Access Server
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  • 8
    Publication Date: 2022-10-20
    Description: Author Posting. © American Geophysical Union, 2018. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Wave generation, dissipation, and disequilibrium in an embayment with complex bathymetry. Journal of Geophysical Research-Oceans, 123(11), (2018): 7856-7876, doi:10.1029/2018JC014381.
    Description: Heterogeneous, sharply varying bathymetry is common in estuaries and embayments, and complex interactions between the bathymetry and wave processes fundamentally alter the distribution of wave energy. The mechanisms that control the generation and dissipation of wind waves in an embayment with heterogeneous, sharply varying bathymetry are evaluated with an observational and numerical study of the Delaware Estuary. Waves in the lower bay depend on both local wind forcing and remote wave forcing from offshore, but elsewhere in the estuary waves are controlled by the local winds and the response of the wavefield to bathymetric variability. Differences in the wavefield with wind direction highlight the impacts of heterogeneous bathymetry and limited fetch. Under the typical winter northwest wind conditions waves are fetch‐limited in the middle estuary and reach equilibrium with local water depth only in the lower bay. During southerly wind conditions typical of storms, wave energy is near equilibrium in the lower bay, and midestuary waves are attenuated by the combination of whitecapping and bottom friction, particularly over the steep, longitudinal shoals. Although the energy dissipation due to bottom friction is generally small relative to whitecapping, it becomes significant where the waves shoal abruptly due to steep bottom topography. In contrast, directional spreading keeps wave heights in the main channel significantly less than local equilibrium. The wave disequilibrium in the deep navigational channel explains why the marked increase in depth by dredging of the modern channel has had little impact on wave conditions.
    Description: Funding was provided by National Science Foundation Coastal SEES: Toward Sustainable Urban Estuaries in the Anthropocene (OCE 1325136) and Ministry of Science and Technology (MOST 107‐2611‐M‐006‐004). We thank James Kirby, Fengyan Shi, and the two anonymous reviewers for their careful reading of our manuscript and their insightful comments. We thank Tracy Quirk for providing wave measurements in Bombay Hook, DE and Stow Creek, NJ. We thank Katie Pijanowski for compiling historical and modern bathymetric data for the estuary. Data supporting this study are posted to Zenodo (http://doi.org/10.5281/zenodo.1433055).
    Description: 2019-04-04
    Keywords: Estuarine hydrodynamics ; Wave energy ; Equilibrium wave ; Anthropogenic impact
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 9
    Publication Date: 2022-10-20
    Description: © The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Geyer, W. R., Ralston, D. K., & Chen, J. Mechanisms of exchange flow in an estuary with a narrow, deep channel and wide, shallow shoals. Journal of Geophysical Research: Oceans, 125(12), (2020): e2020JC016092, https://doi.org/10.1029/2020JC016092.
    Description: Delaware Bay is a large estuary with a deep, relatively narrow channel and wide, shallow banks, providing a clear example of a “channel‐shoal” estuary. This numerical modeling study addresses the exchange flow in this channel‐shoal estuary, specifically to examine how the lateral geometry affects the strength and mechanisms of exchange flow. We find that the exchange flow is exclusively confined to the channel region during spring tides, when stratification is weak, and it broadens laterally over the shoals during the more stratified neap tides but still occupies a small fraction of the total width of the estuary. Exchange flow is relatively weak during spring tides, resulting from oscillatory shear dispersion in the channel augmented by weak Eulerian exchange flow. During neap tides, stratification and shear increase markedly, resulting in a strong Eulerian residual shear flow driven mainly by the along‐estuary density gradient, with a net exchange flow roughly 5 times that of the spring tide. During both spring and neap tides, lateral salinity gradients generated by differential advection at the edge of the channel drive a tidally oscillating cross‐channel flow, which strongly influences the stratification, along‐estuary salt balance, and momentum balance. The lateral flow also causes the phase variation in salinity that results in oscillatory shear dispersion and is an advective momentum source contributing to the residual circulation. Whereas the shoals make a negligible direct contribution to the exchange flow, they have an indirect influence due to the salinity gradients between the channel and the shoal.
    Description: The ideas in this paper were influenced by discussions with Robert Chant. Funding was provided by National Science Foundation grants OCE‐1325136, OCE‐1634490, and OCE‐1736539.
    Description: 2021-04-29
    Keywords: Estuarine circulation ; Tidal dispersion ; Lateral circulation
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 10
    Publication Date: 1996-09-16
    Print ISSN: 0003-6951
    Electronic ISSN: 1077-3118
    Topics: Physics
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