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  • 1
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    Assimilating Along-Track Altimetric Observations through Local Hydrostatic Adjustment in a Global Ocean Variational Assimilation System (2012)
    American Meteorological Society
    Details
    Publication Date: 2017-04-03
    Description: A global ocean three-dimensional variational data assimilation system was developed with the aim of assimilating along-track sea level anomaly observations, along with in situ observations from bathythermographs and conventional sea stations. All the available altimetric data within the period October 1992–January 2006 were used in this study. The sea level corrections were covariated with vertical profiles of temperature and salinity according to the bivariate definition of the background-error vertical covariances. Sea level anomaly observational error variance was carefully defined as a sum of instrumental, representativeness, observation operator, and mean dynamic topography error variances. The mean dynamic topography was computed from the model long-term mean sea surface height and adjusted through an optimal interpolation scheme to account for observation minus first-guess biases. Results show that the assimilation of sea level anomaly observations improves the model sea surface height skill scores as well as the subsurface temperature and salinity fields. Furthermore, the estimate of the tropical and subtropical surface circulation is clearly improved after assimilating altimetric data. Nonnegligible impacts of the mean dynamic topography used have also been found: compared to a gravimeter-based mean dynamic topography the use of the mean dynamic topography discussed in this paper improves both the consistency with sea level anomaly observations and the verification skill scores of temperature and salinity in the tropical regions. Furthermore, the use of a mean dynamic topography computed from the model long-term sea surface height mean without observation adjustments results in worsened verification skill scores and highlights the benefits of the current approach for deriving the mean dynamic topography.
    Description: European Commission WP4 Fondazione Cassa di Risparmio di Bologna Cnes
    Description: Published
    Description: 738-754
    Description: 3.7. Dinamica del clima e dell'oceano
    Description: 4.6. Oceanografia operativa per la valutazione dei rischi in aree marine
    Description: 5.4. Banche dati di geomagnetismo, aeronomia, clima e ambiente
    Description: JCR Journal
    Description: partially_open
    Keywords: Data assimilation ; Satellite observations ; Ocean models ; Sea level ; In situ observations ; Variational analysis ; 03. Hydrosphere::03.01. General::03.01.01. Analytical and numerical modeling ; 03. Hydrosphere::03.01. General::03.01.03. Global climate models ; 03. Hydrosphere::03.01. General::03.01.04. Ocean data assimilation and reanalysis
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 2
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    Baroclinic Stationary Waves in Aquaplanet Models (2012)
    American Meteorological Society
    Details
    Publication Date: 2020-02-24
    Description: An aquaplanet model is used to study the nature of the highly persistent low-frequency waves that have been observed in models forced by zonally symmetric boundary conditions. Using the Hayashi spectral analysis of the extratropical waves, the authors find that a quasi-stationary wave 5 belongs to a wave packet obeying a well-defined dispersion relation with eastward group velocity. The components of the dispersion relation with k ≥ 5 baroclinically convert eddy available potential energy into eddy kinetic energy, whereas those with k 〈 5 are baroclinically neutral. In agreement with Green’s model of baroclinic instability, wave 5 is weakly unstable, and the inverse energy cascade, which had been previously proposed as a main forcing for this type of wave, only acts as a positive feedback on its predominantly baroclinic energetics. The quasi-stationary wave is reinforced by a phase lock to an analogous pattern in the tropical convection, which provides further amplification to the wave. It is also found that the Pedlosky bounds on the phase speed of unstable waves provide guidance in explaining the latitudinal structure of the energy conversion, which is shown to be more enhanced where the zonal westerly surface wind is weaker. The wave’s energy is then trapped in the waveguide created by the upper tropospheric jet stream. In agreement with Green’s theory, as the equator-to-pole SST difference is reduced, the stationary marginally stable component shifts toward higher wavenumbers, while wave 5 becomes neutral and westward propagating. Some properties of the aquaplanet quasi-stationary waves are found to be in interesting agreement with a low frequency wave observed by Salby during December–February in the Southern Hemisphere so that this perspective on low frequency variability, apart from its value in terms of basic geophysical fluid dynamics, might be of specific interest for studying the earth’s atmosphere.
    Description: Published
    Description: 1023–1040.
    Description: JCR Journal
    Description: restricted
    Keywords: Boundary conditions ; 03. Hydrosphere::03.02. Hydrology::03.02.99. General or miscellaneous
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 3
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    Quality Assessment of a 1985–2007 Mediterranean Sea Reanalysis (2012)
    American Meteorological Society
    Details
    Publication Date: 2020-02-24
    Description: A simulation and two reanalyses from 1985 to 2007 have been produced for the Mediterranean Sea using different assimilation schemes: a reduced-order optimal interpolation [System for Ocean Forecast and Analysis (SOFA)] and a three-dimensional variational scheme (OceanVar). The observational dataset consists of vertical temperature and salinity in situ profiles and along-track satellite sea level anomalies; daily mean fields of satellite sea surface temperature are used for correcting the air–sea fluxes. This paper assesses the quality of the reanalyses with respect to observations and the simulation. Both the SOFA and OceanVar schemes give very similar root-mean-square errors and biases for temperature and salinity fields compared with the assimilated observations. The largest errors are at the thermocline level and in regions of large eddy field variability. However, OceanVar gives 20% better results for sea level anomaly root-mean-square error.
    Description: Published
    Description: 569-59
    Description: JCR Journal
    Description: open
    Keywords: Mediterranean Sea ; 03. Hydrosphere::03.01. General::03.01.05. Operational oceanography
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 4
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    Parameterisation of the Sedimentation of Raindrops with Finite Maximum Diameter (2012)
    American Meteorological Society
    In:  EPIC3Monthly Weather Review., American Meteorological Society, 140(5), pp. 1589-1602
    Details
    Publication Date: 2014-04-17
    Repository Name: EPIC Alfred Wegener Institut
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  • 5
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    A comparison of methods for estimating Reynolds stress from ADCP measurements in wavy environments (2012)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2011. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Atmospheric and Oceanic Technology 28 (2011): 1539–1553, doi:10.1175/JTECH-D-11-00001.1.
    Description: Turbulent Reynolds stresses are now routinely estimated from acoustic Doppler current profiler (ADCP) measurements in estuaries and tidal channels using the variance method, yet biases due to surface gravity waves limit its use in the coastal ocean. Recent modifications to this method, including spatially filtering velocities to isolate the turbulence from wave velocities and fitting a cospectral model to the below-wave band cospectra, have been used to remove this bias. Individually, each modification performed well for the published test datasets, but a comparative analysis over the range of conditions in the coastal ocean has not yet been performed. This work uses ADCP velocity measurements from five previously published coastal ocean and estuarine datasets, which span a range of wave and current conditions as well as instrument configurations, to directly compare methods for estimating stresses in the presence of waves. The computed stresses from each were compared to bottom stress estimates from a quadratic drag law and, where available, estimates of wind stress. These comparisons, along with an analysis of the cospectra, indicated that spectral fitting performs well when the wave climate is wide-banded and/or multidirectional as well as when instrument noise is high. In contrast, spatial filtering performs better when waves are narrow-banded, low frequency, and when wave orbital velocities are strong relative to currents. However, as spatial filtering uses vertically separated velocity bins to remove the wave bias, spectral fitting is able to resolve stresses over a larger fraction of the water column.
    Description: J. Rosman acknowledges funding from the National Science Foundation (OCE-1061108).
    Keywords: Coastal flows ; Momentum ; Ocean circulation ; Waves, oceanic ; In situ observations ; Instrumentation/sensors
    Repository Name: Woods Hole Open Access Server
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  • 6
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    Turbulent kinetic energy dissipation in Barrow Canyon (2012)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2012. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 42 (2012): 1012–1021, doi:10.1175/JPO-D-11-0184.1.
    Description: Pacific Water flows across the shallow Chukchi Sea before reaching the Arctic Ocean, where it is a source of heat, freshwater, nutrients, and carbon. A substantial portion of Pacific Water is routed through Barrow Canyon, located in the northeast corner of the Chukchi. Barrow Canyon is a region of complex geometry and forcing where a variety of water masses have been observed to coexist. These factors contribute to a dynamic physical environment, with the potential for significant water mass transformation. The measurements of turbulent kinetic energy dissipation presented here indicate diapycnal mixing is important in the upper canyon. Elevated dissipation rates were observed near the pycnocline, effectively mixing winter and summer water masses, as well as within the bottom boundary layer. The slopes of shear/stratification layers, combined with analysis of rotary spectra, suggest that near-inertial wave activity may be important in modulating dissipation near the bottom. Because the canyon is known to be a hotspot of productivity with an active benthic community, mixing may be an important factor in maintenance of the biological environment.
    Description: ELS was supported as a WHOI Postdoctoral Scholar through the WHOI Ocean and Climate Change Institute.
    Description: 2012-12-01
    Keywords: Arctic ; Continental shelf/slope ; Mixing ; Small scale processes
    Repository Name: Woods Hole Open Access Server
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  • 7
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    Variability of the Atlantic meridional overturning circulation in CCSM4 (2012)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2012. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Climate 25 (2012): 5153–5172, doi:10.1175/JCLI-D-11-00463.1.
    Description: Atlantic meridional overturning circulation (AMOC) variability is documented in the Community Climate System Model, version 4 (CCSM4) preindustrial control simulation that uses nominal 1° horizontal resolution in all its components. AMOC shows a broad spectrum of low-frequency variability covering the 50–200-yr range, contrasting sharply with the multidecadal variability seen in the T85 × 1 resolution CCSM3 present-day control simulation. Furthermore, the amplitude of variability is much reduced in CCSM4 compared to that of CCSM3. Similarities as well as differences in AMOC variability mechanisms between CCSM3 and CCSM4 are discussed. As in CCSM3, the CCSM4 AMOC variability is primarily driven by the positive density anomalies at the Labrador Sea (LS) deep-water formation site, peaking 2 yr prior to an AMOC maximum. All processes, including parameterized mesoscale and submesoscale eddies, play a role in the creation of salinity anomalies that dominate these density anomalies. High Nordic Sea densities do not necessarily lead to increased overflow transports because the overflow physics is governed by source and interior region density differences. Increased overflow transports do not lead to a higher AMOC either but instead appear to be a precursor to lower AMOC transports through enhanced stratification in LS. This has important implications for decadal prediction studies. The North Atlantic Oscillation (NAO) is significantly correlated with the positive boundary layer depth and density anomalies prior to an AMOC maximum. This suggests a role for NAO through setting the surface flux anomalies in LS and affecting the subpolar gyre circulation strength.
    Description: The CCSM project is supported by NSF and the Office of Science (BER) of the U.S. Department of Energy. SGY and YOK were supported by the NOAA Climate Program Office under Climate Variability and Predictability Program Grants NA09OAR4310163 and NA10OAR4310202, respectively.
    Description: 2013-02-01
    Keywords: Meridional overturning circulation ; Coupled models ; Ocean models ; Oceanic variability
    Repository Name: Woods Hole Open Access Server
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  • 8
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    Energy transfer from high-shear, low-frequency internal waves to high-frequency waves near Kaena Ridge, Hawaii (2012)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2012. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 42 (2012): 1524–1547, doi:10.1175/JPO-D-11-0117.1.
    Description: Evidence is presented for the transfer of energy from low-frequency inertial–diurnal internal waves to high-frequency waves in the band between 6 cpd and the buoyancy frequency. This transfer links the most energetic waves in the spectrum, those receiving energy directly from the winds, barotropic tides, and parametric subharmonic instability, with those most directly involved in the breaking process. Transfer estimates are based on month-long records of ocean velocity and temperature obtained continuously over 80–800 m from the research platform (R/P) Floating Instrument Platform (FLIP) in the Hawaii Ocean Mixing Experiment (HOME) Nearfield (2002) and Farfield (2001) experiments, in Hawaiian waters. Triple correlations between low-frequency vertical shears and high-frequency Reynolds stresses, uiw∂Ui/∂z, are used to estimate energy transfers. These are supported by bispectral analysis, which show significant energy transfers to pairs of waves with nearly identical frequency. Wavenumber bispectra indicate that the vertical scales of the high-frequency waves are unequal, with one wave of comparable scale to that of the low-frequency parent and the other of much longer scale. The scales of the high-frequency waves contrast with the classical pictures of induced diffusion and elastic scattering interactions and violates the scale-separation assumption of eikonal models of interaction. The possibility that the observed waves are Doppler shifted from intrinsic frequencies near f or N is explored. Peak transfer rates in the Nearfield, an energetic tidal conversion site, are on the order of 2 × 10−7 W kg−1 and are of similar magnitude to estimates of turbulent dissipation that were made near the ridge during HOME. Transfer rates in the Farfield are found to be about half the Nearfield values.
    Description: This work was supported by the National Science Foundation and the Office of Naval Research.
    Description: 2013-03-01
    Keywords: Diapycnal mixing ; Energy transport ; Internal waves ; Nonlinear dynamics ; Ship observations ; Spectral analysis/models/distribution
    Repository Name: Woods Hole Open Access Server
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  • 9
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    Improving HF radar estimates of surface currents using signal quality metrics, with application to the MVCO high-resolution radar system (2012)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2012. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Atmospheric and Oceanic Technology 29 (2012): 1377–1390, doi:10.1175/JTECH-D-11-00160.1.
    Description: Estimates of surface currents over the continental shelf are now regularly made using high-frequency radar (HFR) systems along much of the U.S. coastline. The recently deployed HFR system at the Martha’s Vineyard Coastal Observatory (MVCO) is a unique addition to these systems, focusing on high spatial resolution over a relatively small coastal ocean domain with high accuracy. However, initial results from the system showed sizable errors and biased estimates of M2 tidal currents, prompting an examination of new methods to improve the quality of radar-based velocity data. The analysis described here utilizes the radial metric output of CODAR Ocean Systems’ version 7 release of the SeaSonde Radial Site Software Suite to examine both the characteristics of the received signal and the output of the direction-finding algorithm to provide data quality controls on the estimated radial currents that are independent of the estimated velocity. Additionally, the effect of weighting spatial averages of radials falling within the same range and azimuthal bin is examined to account for differences in signal quality. Applied to two month-long datasets from the MVCO high-resolution system, these new methods are found to improve the rms difference comparisons with in situ current measurements by up to 2 cm s−1, as well as reduce or eliminate observed biases of tidal ellipses estimated using standard methods.
    Description: 2013-03-01
    Keywords: Coastal flows ; Currents ; Data processing ; Data quality control ; In situ atmospheric observations ; Remote sensing
    Repository Name: Woods Hole Open Access Server
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  • 10
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    Cross-shelf and out-of-bay transport driven by an open-ocean current (2012)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2011. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 41 (2011): 2168–2186, doi:10.1175/JPO-D-11-08.1.
    Description: This paper studies the interaction of an Antarctic Circumpolar Current (ACC)–like wind-driven channel flow with a continental slope and a flat-bottomed bay-shaped shelf near the channel’s southern boundary. Interaction between the model ACC and the topography in the second layer induces local changes of the potential vorticity (PV) flux, which further causes the formation of a first-layer PV front near the base of the topography. Located between the ACC and the first-layer slope, the newly formed PV front is constantly perturbed by the ACC and in turn forces the first-layer slope with its own variability in an intermittent but persistent way. The volume transport of the slope water across the first-layer slope edge is mostly directly driven by eddies and meanders of the new front, and its magnitude is similar to the maximum Ekman transport in the channel. Near the bay’s opening, the effect of the topographic waves, excited by offshore variability, dominates the cross-isobath exchange and induces a mean clockwise shelf circulation. The waves’ propagation is only toward the west and tends to be blocked by the bay’s western boundary in the narrow-shelf region. The ensuing wave–coast interaction amplifies the wave amplitude and the cross-shelf transport. Because the interaction only occurs near the western boundary, the shelf water in the west of the bay is more readily carried offshore than that in the east and the mean shelf circulation is also intensified along the bay’s western boundary.
    Description: Y. Zhang acknowledges the support of the MIT-WHOI Joint Program in Physical Oceanography and NSF OCE-9901654 and OCE- 0451086. J. Pedlosky acknowledges the support of NSF OCE-9901654 and OCE-0451086.
    Keywords: Baroclinic flows ; Eddies ; Fronts ; Mass fluxes/transport ; Mesoscale processes ; Topographic effects
    Repository Name: Woods Hole Open Access Server
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  • 11
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    An equatorial ocean bottleneck in global climate models (2012)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2012. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Climate 25 (2012): 343–349, doi:10.1175/JCLI-D-11-00059.1.
    Description: The Equatorial Undercurrent (EUC) is a major component of the tropical Pacific Ocean circulation. EUC velocity in most global climate models is sluggish relative to observations. Insufficient ocean resolution slows the EUC in the eastern Pacific where nonlinear terms should dominate the zonal momentum balance. A slow EUC in the east creates a bottleneck for the EUC to the west. However, this bottleneck does not impair other major components of the tropical circulation, including upwelling and poleward transport. In most models, upwelling velocity and poleward transport divergence fall within directly estimated uncertainties. Both of these transports play a critical role in a theory for how the tropical Pacific may change under increased radiative forcing, that is, the ocean dynamical thermostat mechanism. These findings suggest that, in the mean, global climate models may not underrepresent the role of equatorial ocean circulation, nor perhaps bias the balance between competing mechanisms for how the tropical Pacific might change in the future. Implications for model improvement under higher resolution are also discussed.
    Description: KBK gratefully acknowledges the J. Lamar Worzel Assistant Scientist Fund. GCJ is supported by NOAA’s Office of Oceanic and Atmospheric Research. RM gratefully acknowledges the generous support and hospitality of the Divecha Centre for Climate Change and CAOS at IISc, Bangalore, and partial support by NASA PO grants.
    Description: 2012-07-01
    Keywords: Tropics ; Ocean circulation ; Ocean dynamics ; Climate models ; Coupled models ; Ocean models
    Repository Name: Woods Hole Open Access Server
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  • 12
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    The global subduction/obduction rates : their interannual and decadal variability (2012)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2012. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Climate 25 (2012): 1096–1115, doi:10.1175/2011JCLI4228.1.
    Description: Ventilation, including subduction and obduction, for the global oceans was examined using Simple Ocean Data Assimilation (SODA) outputs. The global subduction rate averaged over the period from 1959 to 2006 is estimated at 505.8 Sv (1 Sv ≡ 106 m3 s−1), while the corresponding global obduction rate is estimated at 482.1 Sv. The annual subduction/obduction rates vary greatly on the interannual and decadal time scales. The global subduction rate is estimated to have increased 7.6% over the past 50 years, while the obduction rate is estimated to have increased 9.8%. Such trends may be insignificant because errors associated with the data generated by ocean data assimilation could be as large as 10%. However, a major physical mechanism that induced these trends is primarily linked to changes in the Southern Ocean. While the Southern Ocean plays a key role in global subduction and obduction rates and their variability, both the Southern Ocean and equatorial regions are critically important sites of water mass formation/erosion.
    Description: This work was supported by the Key State Basic Research Program of China under Grant 2012CB417401, the National Natural Science Foundation of China (Grants 40906007, 40890152), and the Open Foundation of Physical Oceanography Laboratory, OUC, under Grant 200902.
    Description: 2012-08-15
    Keywords: Decadal variability ; Southern Ocean ; Trends ; Water masses ; Convergence ; Mixing
    Repository Name: Woods Hole Open Access Server
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  • 13
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    Horizontal density structure and restratification of the Arctic Ocean surface layer (2012)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2012. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 42 (2012): 659–668, doi:10.1175/JPO-D-11-0125.1.
    Description: Ice-tethered profiler (ITP) measurements from the Arctic Ocean’s Canada Basin indicate an ocean surface layer beneath sea ice with significant horizontal density structure on scales of hundreds of kilometers to the order 1 km submesoscale. The observed horizontal gradients in density are dynamically important in that they are associated with restratification of the surface ocean when dense water flows under light water. Such restratification is prevalent in wintertime and competes with convective mixing upon buoyancy forcing (e.g., ice growth and brine rejection) and shear-driven mixing when the ice moves relative to the ocean. Frontal structure and estimates of the balanced Richardson number point to the likelihood of dynamical restratification by isopycnal tilt and submesoscale baroclinic instability. Based on the evidence here, it is likely that submesoscale processes play an important role in setting surface-layer properties and lateral density variability in the Arctic Ocean.
    Description: Funding was provided by the National Science Foundation Office of Polar Programs Arctic Sciences Section under Awards ARC-0519899, ARC-0856479, and ARC-0806306. Support was also provided by the Woods Hole Oceanographic Institution Arctic Research Initiative.
    Description: 2012-10-01
    Keywords: Arctic ; Ocean dynamics
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  • 14
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    ENSO and Pacific decadal variability in the Community Climate System Model Version 4 (2012)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2012. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Climate 25 (2012): 2622–2651, doi:10.1175/JCLI-D-11-00301.1.
    Description: This study presents an overview of the El Niño–Southern Oscillation (ENSO) phenomenon and Pacific decadal variability (PDV) simulated in a multicentury preindustrial control integration of the NCAR Community Climate System Model version 4 (CCSM4) at nominal 1° latitude–longitude resolution. Several aspects of ENSO are improved in CCSM4 compared to its predecessor CCSM3, including the lengthened period (3–6 yr), the larger range of amplitude and frequency of events, and the longer duration of La Niña compared to El Niño. However, the overall magnitude of ENSO in CCSM4 is overestimated by ~30%. The simulated ENSO exhibits characteristics consistent with the delayed/recharge oscillator paradigm, including correspondence between the lengthened period and increased latitudinal width of the anomalous equatorial zonal wind stress. Global seasonal atmospheric teleconnections with accompanying impacts on precipitation and temperature are generally well simulated, although the wintertime deepening of the Aleutian low erroneously persists into spring. The vertical structure of the upper-ocean temperature response to ENSO in the north and south Pacific displays a realistic seasonal evolution, with notable asymmetries between warm and cold events. The model shows evidence of atmospheric circulation precursors over the North Pacific associated with the “seasonal footprinting mechanism,” similar to observations. Simulated PDV exhibits a significant spectral peak around 15 yr, with generally realistic spatial pattern and magnitude. However, PDV linkages between the tropics and extratropics are weaker than observed.
    Description: M. Alexander, A. Capotondi, and J. Scott’s participation was supported by a grant from the NSF Climate and Large-scale Dynamics Program. Y.-O. Kwon gratefully acknowledges support from a WHOI Heyman fellowship and a grant from the NSF Climate and Largescale Dynamics Program. The CESM project is supported by the National Science Foundation and the Office of Science (BER) of the U.S. Department of Energy.
    Description: 2012-10-15
    Keywords: Atmosphere-ocean interaction ; El Nino ; ENSO ; La Nina ; Pacific decadal oscillation ; Climate models
    Repository Name: Woods Hole Open Access Server
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  • 15
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    High-latitude contribution to global variability of air–sea sensible heat flux (2012)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2012. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Climate 25 (2012): 3515–3531, doi:10.1175/JCLI-D-11-00028.1.
    Description: The study examined global variability of air–sea sensible heat flux (SHF) from 1980 to 2009 and the large-scale atmospheric and ocean circulations that gave rise to this variability. The contribution of high-latitude wintertime SHF was identified, and the relative importance of the effect of the sea–air temperature difference versus the effect of wind on decadal SHF variability was analyzed using an empirical orthogonal function (EOF) approach. The study showed that global SHF anomalies are strongly modulated by SHF at high latitudes (poleward of 45°) during winter seasons. Decadal variability of global wintertime SHF can be reasonably represented by the sum of two leading EOF modes, namely, the boreal wintertime SHF in the northern oceans and the austral wintertime SHF in the southern oceans. The study also showed that global wintertime SHF is modulated by the prominent modes of the large-scale atmospheric circulation at high latitudes. The increase of global SHF in the 1990s is attributable to the strengthening of the Southern Hemisphere annular mode index, while the decrease of global SHF after 2000 is due primarily to the downward trend of the Arctic Oscillation index. This study identified the important effects of wind direction and speed on SHF variability. Changes in winds modify the sea–air temperature gradient by advecting cold and dry air from continents and by imposing changes in wind-driven oceanic processes that affect sea surface temperature (SST). The pattern of air temperature anomalies dominates over the pattern of SST anomalies and dictates the pattern of decadal SHF variability.
    Description: The study is supported by the NOAA Office of Climate Observations (OCO) and the WHOI Arctic Climate Initiative. X. Song acknowledges the support from the China Scholarship Council, National Natural Science Foundation of China (NSFC) (40930844, 40976004, and 40921004) and the Ministry of Education’s 111 Project (B07036).
    Description: 2012-11-15
    Keywords: Atmosphere-ocean interaction
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  • 16
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    On the response of a buoyant plume to downwelling-favorable wind stress (2012)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2012. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 42 (2012): 1083–1098, doi:10.1175/JPO-D-11-015.1.
    Description: Here, the response of a coastally trapped buoyant plume to downwelling-favorable wind forcing is explored using a simplified two-dimensional numerical model and a prognostic theory for the resulting width, depth, and density anomaly and along-shelf transport of the plume. Consistent with the numerical simulations, the analytical model shows that the wind causes mixing of the plume water and that the forced cross-shelf circulation can also generate significant deepening and surface narrowing, as well as increased along-shelf transport. The response is due to a combination of the purely advective process that leads to the steepening of the isopycnals and the entrainment of ambient water into the plume. The advective component depends on the initial plume geometry: plumes that have a large fraction of their total width in contact with the bottom (“bottom trapped”) suffer relatively small depth and width changes compared to plumes that have a large fraction of their total width detached from the bottom (“surface trapped”). Key theoretical parameters are Wγ/Wα, the ratio of the width of the plume detached from the bottom to the width of the plume in contact with it, and the ratio of the wind-generated mixed layer δe to the initial plume depth hp, which determines the amount of water initially entrained into the plume. The model results also show that the cross-shelf circulation can be strongly influenced by the wind-driven response in combination with the geostrophic shear of the plume. The continuous entrainment into the plume, as well as transient events, is also discussed.
    Description: This work has been supported by FONDECYT Grant 1070501. S. Lentz received support by theNational Science Foundation GrantOCE-0751554. C. Moffat had additional support from the National Science Foundation Office of Polar Programs through U.S. Southern Ocean GLOBEC Grants OPP 99-10092 and 06- 23223.
    Description: 2013-01-01
    Keywords: Baroclinic flows ; Boundary currents ; Coastal flows ; Upwelling/downwelling ; Wind ; Ocean models
    Repository Name: Woods Hole Open Access Server
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    ENSO’s impact on the gap wind regions of the eastern tropical Pacific Ocean (2012)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2012. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Climate 25 (2012): 3549–3565, doi:10.1175/JCLI-D-11-00320.1.
    Description: The recently released NCEP Climate Forecast System Reanalysis (CFSR) is used to examine the response to ENSO in the northeast tropical Pacific Ocean (NETP) during 1979–2009. The normally cool Pacific sea surface temperatures (SSTs) associated with wind jets through the gaps in the Central American mountains at Tehuantepec, Papagayo, and Panama are substantially warmer (colder) than the surrounding ocean during El Niño (La Niña) events. Ocean dynamics generate the ENSO-related SST anomalies in the gap wind regions as the surface fluxes damp the SSTs anomalies, while the Ekman heat transport is generally in quadrature with the anomalies. The ENSO-driven warming is associated with large-scale deepening of the thermocline; with the cold thermocline water at greater depths during El Niño in the NETP, it is less likely to be vertically mixed to the surface, particularly in the gap wind regions where the thermocline is normally very close to the surface. The thermocline deepening is enhanced to the south of the Costa Rica Dome in the Papagayo region, which contributes to the local ENSO-driven SST anomalies. The NETP thermocline changes are due to coastal Kelvin waves that initiate westward-propagating Rossby waves, and possibly ocean eddies, rather than by local Ekman pumping. These findings were confirmed with regional ocean model experiments: only integrations that included interannually varying ocean boundary conditions were able to simulate the thermocline deepening and localized warming in the NETP during El Niño events; the simulation with variable surface fluxes, but boundary conditions that repeated the seasonal cycle, did not.
    Description: This research was supported by grants from the NOAA office of Global Programs and the NSF Climate and Global Dynamics Division.
    Description: 2012-11-15
    Keywords: North Pacific Ocean ; Atmosphere-ocean interaction ; ENSO ; Thermocline circulation ; Waves, oceanic ; Ocean models
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    A surface mooring for air–sea interaction research in the Gulf Stream. Part I : mooring design and instrumentation (2012)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2012. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Atmospheric and Oceanic Technology 29 (2012): 1363–1376, doi:10.1175/JTECH-D-12-00060.1.
    Description: The design of a surface mooring for deployment in the Gulf Stream in the Mid-Atlantic Bight is described. The authors' goals were to observe the surface meteorology; upper-ocean variability; and air–sea exchanges of heat, freshwater, and momentum in and near the Gulf Stream during two successive 1-yr deployments. Of particular interest was quantifying these air–sea fluxes during wintertime events that carry cold, dry air from the land over the Gulf Stream. Historical current data and information about the surface waves were used to guide the design of the surface mooring. The surface buoy provided the platform for both bulk meteorological sensors and a direct covariance flux system. Redundancy in the meteorological sensors proved to be a largely successful strategy to obtain complete time series. Oceanographic instrumentation was limited in size by considerations of drag; and two current meters, three temperature–salinity recorders, and 15 temperature recorders were deployed. Deployment from a single-screw vessel in the Gulf Stream required a controlled-drift stern first over the anchor sites. The first deployment lasted the planned full year. The second deployment ended after 3 months when the mooring was cut by unknown means at a depth of about 3000 m. The mooring was at times in the core of the Gulf Stream, and a peak surface current of over 2.7 m s−1 was observed. The 15-month records of surface meteorology and air–sea fluxes captured the seasonal variability as well as several cold-air outbreaks; the peak observed heat loss was in excess of 1400 W m−2.
    Description: This work was funded by the National Science Foundation Grant OCE04-24536 as part of the CLIVAR Mode Water Dynamics Experiment (CLIMODE). The Vetlesen Foundation is also acknowledged for the early support of SB.
    Description: 2013-03-01
    Keywords: Buoy observations
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  • 19
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    The unpredictable nature of internal tides on continental shelves (2012)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2012. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 42 (2012): 1981–2000, doi:10.1175/JPO-D-12-028.1.
    Description: Packets of nonlinear internal waves (NLIWs) in a small area of the Mid-Atlantic Bight were 10 times more energetic during a local neap tide than during the preceding spring tide. This counterintuitive result cannot be explained if the waves are generated near the shelf break by the local barotropic tide since changes in shelfbreak stratification explain only a small fraction of the variability in barotropic to baroclinic conversion. Instead, this study suggests that the occurrence of strong NLIWs was caused by the shoaling of distantly generated internal tides with amplitudes that are uncorrelated with the local spring-neap cycle. An extensive set of moored observations show that NLIWs are correlated with the internal tide but uncorrelated with barotropic tide. Using harmonic analysis of a 40-day record, this study associates steady-phase motions at the shelf break with waves generated by the local barotropic tide and variable-phase motions with the shoaling of distantly generated internal tides. The dual sources of internal tide energy (local or remote) mean that shelf internal tides and NLIWs will be predictable with a local model only if the locally generated internal tides are significantly stronger than shoaling internal tides. Since the depth-integrated internal tide energy in the open ocean can greatly exceed that on the shelf, it is likely that shoaling internal tides control the energetics on shelves that are directly exposed to the open ocean.
    Description: This research was supported by ONR Grants N00014-05-1-0271, N00014-08-1-0991, N00014-04- 1-0146, and N00014-11-1-0194.
    Description: 2013-05-01
    Keywords: Internal waves ; Nonlinear dynamics ; Tides
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  • 20
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    Two configurations of the Western Arctic Shelfbreak Current in summer (2012)
    American Meteorological Society
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    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2012. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 42 (2012): 329-351, doi:10.1175/JPO-D-11-026.1.
    Description: Data from a closely spaced array of moorings situated across the Beaufort Sea shelfbreak at 152°W are used to study the Western Arctic Shelfbreak Current, with emphasis on its configuration during the summer season. Two dynamically distinct states of the current are revealed in the absence of wind, with each lasting approximately one month. The first is a surface-intensified shelfbreak jet transporting warm and buoyant Alaskan Coastal Water in late summer. This is the eastward continuation of the Alaskan Coastal Current. It is both baroclinically and barotropically unstable and hence capable of forming the surface-intensified warm-core eddies observed in the southern Beaufort Sea. The second configuration, present during early summer, is a bottom-intensified shelfbreak current advecting weakly stratified Chukchi Summer Water. It is baroclinically unstable and likely forms the middepth warm-core eddies present in the interior basin. The mesoscale instabilities extract energy from the mean flow such that the surface-intensified jet should spin down over an e-folding distance of 300 km beyond the array site, whereas the bottom-intensified configuration should decay within 150 km. This implies that Pacific Summer Water does not extend far into the Canadian Beaufort Sea as a well-defined shelfbreak current. In contrast, the Pacific Winter Water configuration of the shelfbreak jet is estimated to decay over a much greater distance of approximately 1400 km, implying that it should reach the first entrance to the Canadian Arctic Archipelago.
    Description: This work was supported by National Science Foundation GrantsOCE-0726640,OPP-0731928, and OPP-0713250.
    Description: 2012-09-01
    Keywords: Arctic ; Continental shelf/slope ; Boundary currents
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  • 21
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    Estuarine exchange flow quantified with isohaline coordinates : contrasting long and short estuaries (2012)
    American Meteorological Society
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    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2012. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 42 (2012): 748–763, doi:10.1175/JPO-D-11-086.1.
    Description: Isohaline coordinate analysis is used to compare the exchange flow in two contrasting estuaries, the long (with respect to tidal excursion) Hudson River and the short Merrimack River, using validated numerical models. The isohaline analysis averages fluxes in salinity space rather than in physical space, yielding the isohaline exchange flow that incorporates both subtidal and tidal fluxes and precisely satisfies the Knudsen relation. The isohaline analysis can be consistently applied to both subtidally and tidally dominated estuaries. In the Hudson, the isohaline exchange flow is similar to results from the Eulerian analysis, and the conventional estuarine theory can be used to quantify the salt transport based on scaling with the baroclinic pressure gradient. In the Merrimack, the isohaline exchange flow is much larger than the Eulerian quantity, indicating the dominance of tidal salt flux. The exchange flow does not scale with the baroclinic pressure gradient but rather with tidal volume flux. This tidal exchange is driven by tidal pumping due to the jet–sink flow at the mouth constriction, leading to a linear dependence of exchange flow on tidal volume flux. Finally, a tidal conversion parameter Qin/Qprism, measuring the fraction of tidal inflow Qprism that is converted into net exchange Qin, is proposed to characterize the exchange processes among different systems. It is found that the length scale ratio between tidal excursion and salinity intrusion provides a characteristic to distinguish estuarine regimes.
    Description: SNC is supported by a WHOI postdoctoral scholarship, a NSF Grant OCE-0926427, and a Taiwan National Science Council Grant NSC 100- 2199-M-002-028.WRGis supported byNSFGrantOCE- 0926427. JAL is supported by NSF Grant OCE-0452054.
    Description: 2012-11-01
    Keywords: Coastal flows
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  • 22
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    The role of advection, straining, and mixing on the tidal variability of estuarine stratification (2012)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2012. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 42 (2012): 855–868, doi:10.1175/JPO-D-10-05010.1.
    Description: Data from the Hudson River estuary demonstrate that the tidal variations in vertical salinity stratification are not consistent with the patterns associated with along-channel tidal straining. These observations result from three additional processes not accounted for in the traditional tidal straining model: 1) along-channel and 2) lateral advection of horizontal gradients in the vertical salinity gradient and 3) tidal asymmetries in the strength of vertical mixing. As a result, cross-sectionally averaged values of the vertical salinity gradient are shown to increase during the flood tide and decrease during the ebb. Only over a limited portion of the cross section does the observed stratification increase during the ebb and decrease during the flood. These observations highlight the three-dimensional nature of estuarine flows and demonstrate that lateral circulation provides an alternate mechanism that allows for the exchange of materials between surface and bottom waters, even when direct turbulent mixing through the pycnocline is prohibited by strong stratification.
    Description: The funding for this research was obtained from NSF Grant OCE-08-25226.
    Description: 2012-11-01
    Keywords: Mixing ; Ocean circulation ; Shear structure/flows ; Transport ; Turbulence
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  • 23
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    On the nature and variability of the east Greenland Spill Jet : a case study in Summer 2003 (2012)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2011. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 41 (2011): 2307–2327, doi:10.1175/JPO-D-10-05004.1.
    Description: Results from a high-resolution (~2 km) numerical simulation of the Irminger Basin during summer 2003 are presented. The focus is on the East Greenland Spill Jet, a recently discovered component of the circulation in the basin. The simulation compares well with observations of surface fields, the Denmark Strait overflow (DSO), and the hydrographic structure of typical sections in the basin. The model reveals new aspects of the circulation on scales of O(0.1–10) days and O(1–100) km. The model Spill Jet results from the cascade of dense waters over the East Greenland shelf. Spilling can occur in various locations southwest of the strait, and it is present throughout the simulation but exhibits large variations on periods of O(0.1–10) days. The Spill Jet sometimes cannot be distinguished in the velocity field from surface eddies or from the DSO. The vorticity structure of the jet confirms its unstable nature with peak relative and tilting vorticity terms reaching twice the planetary vorticity term. The average model Spill Jet transport is 4.9 ±1.7 Sv (1 Sv ≡ 106 m3 s−1) equatorward, about 2½ times larger than has been previously reported from a single ship transect in August 2001. Kinematic analysis of the model results suggests two different types of spilling events. In the first case (type I), a local perturbation results in dense waters descending over the shelf break into the Irminger Basin. In the second case (type II), surface cyclones associated with DSO deep domes initiate the spilling process. During summer 2003, more than half of the largest Spill Jet transport values are of type II.
    Description: The research is supported by the National Science Foundation Grants OCE-0726393 and OCI-0904640 (MGM and TWNH) and OCE-0726640 (RSP).
    Description: 2012-06-01
    Keywords: North Atlantic Ocean ; In situ observations ; Regional models
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    Subtropical mode water variability in a climatologically forced model in the northwestern Pacific Ocean (2012)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2012. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 42 (2012): 126–140, doi:10.1175/2011JPO4513.1.
    Description: A climatologically forced high-resolution model is used to examine variability of subtropical mode water (STMW) in the northwestern Pacific Ocean. Despite the use of annually repeating atmospheric forcing, significant interannual to decadal variability is evident in the volume, temperature, and age of STMW formed in the region. This long time-scale variability is intrinsic to the ocean. The formation and characteristics of STMW are comparable to those observed in nature. STMW is found to be cooler, denser, and shallower in the east than in the west, but time variations in these properties are generally correlated across the full water mass. Formation is found to occur south of the Kuroshio Extension, and after formation STMW is advected westward, as shown by the transport streamfunction. The ideal age and chlorofluorocarbon tracers are used to analyze the life cycle of STMW. Over the full model run, the average age of STMW is found to be 4.1 yr, but there is strong geographical variation in this, from an average age of 3.0 yr in the east to 4.9 yr in the west. This is further evidence that STMW is formed in the east and travels to the west. This is qualitatively confirmed through simulated dye experiments known as transit-time distributions. Changes in STMW formation are correlated with a large meander in the path of the Kuroshio south of Japan. In the model, the large meander inhibits STMW formation just south of Japan, but the export of water with low potential vorticity leads to formation of STMW in the east and an overall increase in volume. This is correlated with an increase in the outcrop area of STMW. Mixed layer depth, on the other hand, is found to be uncorrelated with the volume of STMW.
    Description: E.M.D. acknowledges support of the Doherty Foundation and National Science Foundation (OCE-0849808). S.R.J was sponsored by the National Science Foundation (OCE-0849808). Participation of S.P. and F.B. was supported by the National Science Foundation by its sponsorship of the National Center for Atmospheric Research.
    Description: 2012-07-01
    Keywords: Water masses ; Pacific Ocean ; Tracers ; Advection ; Forcing ; Interannual variuability
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  • 25
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    The modification of bottom boundary layer turbulence and mixing by internal waves shoaling on a barrier reef (2012)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2011. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 41 (2011): 2223–2241, doi:10.1175/2011JPO4344.1.
    Description: Results are presented from an observational study of stratified, turbulent flow in the bottom boundary layer on the outer southeast Florida shelf. Measurements of momentum and heat fluxes were made using an array of acoustic Doppler velocimeters and fast-response temperature sensors in the bottom 3 m over a rough reef slope. Direct estimates of flux Richardson number Rf confirm previous laboratory, numerical, and observational work, which find mixing efficiency not to be a constant but rather to vary with Frt, Reb, and Rig. These results depart from previous observations in that the highest levels of mixing efficiency occur for Frt 〈 1, suggesting that efficient mixing can also happen in regions of buoyancy-controlled turbulence. Generally, the authors find that turbulence in the reef bottom boundary layer is highly variable in time and modified by near-bed flow, shear, and stratification driven by shoaling internal waves.
    Description: Funding was provided by grants from the National Oceanic and Atmospheric Administration’s National Undersea Research Program, National Science Foundation Grants OCE-0622967 and OCE- 0824972 to SGM, and the Singapore Stanford Program. Kristen Davis was supported by a National Defense Science and Engineering Graduate Fellowship and an ARCS Foundation Fellowship.
    Keywords: Boundary layer ; Turbulence ; Bottom currents ; Mixing ; Internal waves
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    Resonant and near-resonant internal wave interactions (2012)
    American Meteorological Society
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    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2012. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 42 (2012): 669–691, doi:10.1175/2011JPO4129.1.
    Description: The spectral energy density of the internal waves in the open ocean is considered. The Garrett and Munk spectrum and the resonant kinetic equation are used as the main tools of the study. Evaluations of a resonant kinetic equation that suggest the slow time evolution of the Garrett and Munk spectrum is not in fact slow are reported. Instead, nonlinear transfers lead to evolution time scales that are smaller than one wave period at high vertical wavenumber. Such values of the transfer rates are inconsistent with the viewpoint expressed in papers by C. H. McComas and P. Müller, and by P. Müller et al., which regards the Garrett and Munk spectrum as an approximate stationary state of the resonant kinetic equation. It also puts the self-consistency of a resonant kinetic equation at a serious risk. The possible reasons for and resolutions of this paradox are explored. Inclusion of near-resonant interactions decreases the rate at which the spectrum evolves. Consequently, this inclusion shows a tendency of improving of self-consistency of the kinetic equation approach.
    Description: YL is supported by NSF DMS Grant 0807871 and ONR Award N00014-09-1-0515.
    Description: 2012-11-01
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  • 27
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    Mechanisms behind the temporary shutdown of deep convection in the Labrador Sea : lessons from the Great Salinity Anomaly years 1968–71 (2012)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2012. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Climate 25 (2012): 6743–6755, doi:10.1175/JCLI-D-11-00549.1.
    Description: From 1969 to 1971 convection in the Labrador Sea shut down, thus interrupting the formation of the intermediate/dense water masses. The shutdown has been attributed to the surface freshening induced by the Great Salinity Anomaly (GSA), a freshwater anomaly in the subpolar North Atlantic. The abrupt resumption of convection in 1972, in contrast, is attributed to the extreme atmospheric forcing of that winter. Here oceanic and atmospheric data collected in the Labrador Sea at Ocean Weather Station Bravo and a one-dimensional mixed layer model are used to examine the causes of the shutdown and resumption of convection in detail. These results highlight the tight coupling of the ocean and atmosphere in convection regions and the need to resolve both components to correctly represent convective processes in the ocean. They are also relevant to present-day conditions given the increased ice melt in the Arctic Ocean and from the Greenland Ice Sheet. The analysis herein shows that the shutdown was initiated by the GSA-induced freshening as well as the mild 1968/69 winter. After the shutdown had begun, however, the continuing lateral freshwater flux as well as two positive feedbacks [both associated with the sea surface temperature (SST) decrease due to lack of convective mixing with warmer subsurface water] further inhibited convection. First, the SST decrease reduced the heat flux to the atmosphere by reducing the air–sea temperature gradient. Second, it further reduced the surface buoyancy loss by reducing the thermal expansion coefficient of the surface water. In 1972 convection resumed because of both the extreme atmospheric forcing and advection of saltier waters into the convection region.
    Description: This research was funded by a grant from the NWO/SRON User Support Programme Space Research. FS acknowledges support from OCE- 0850416 and NOAA NA08OAR4310569.
    Description: 2013-04-01
    Keywords: Atmosphere-ocean interaction ; Intermediate waters ; Oceanic variability
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  • 28
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    Wavenumber–frequency spectra of inertia–gravity and mixed Rossby–gravity waves in the equatorial Pacific Ocean (2012)
    American Meteorological Society
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    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2012. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 42 (2012): 1859–1881, doi:10.1175/JPO-D-11-0235.1.
    Description: In the 1970s and 1980s, there was considerable interest in near-equatorial variability at periods of days to weeks associated with oceanic equatorial inertia–gravity waves and mixed Rossby–gravity waves. At that time, the measurements available for studying these waves were much more limited than today: most of the available observations were from scattered island tide gauges and a handful of short mooring records. More than a decade of the extensive modern data record from the Tropical Atmosphere Ocean (TAO)/Triangle Trans-Ocean Buoy Network (TRITON) mooring array in the Pacific Ocean is used to reexamine the internal-wave climate in the equatorial Pacific, with a focus on interpretation of the zonal-wavenumber/frequency spectrum of surface dynamic height relative to 500 decibars at periods of 3–15 days and zonal wavelengths exceeding 30° of longitude. To facilitate interpretation of the dynamic height spectrum and identification of equatorial wave modes, the spectrum is decomposed into separate spectra associated with dynamic height fluctuations that are symmetric or antisymmetric about the equator. Many equatorial-wave meridional modes can be identified, for both the first and second baroclinic mode. Zonal-wavenumber/frequency spectra of the zonal and meridional wind stress components are also examined. The observed wind stress spectra are used with linear theory of forced equatorial waves to provide a tentative explanation for the zonal-wavenumber extent of the spectral peaks seen in dynamic height. Examination of the cross-equatorial symmetry properties of the wind stress suggests that virtually all of the large-scale equatorial inertia–gravity and mixed Rossby–gravity waves examined may be sensitive to both zonal and meridional wind stress.
    Description: This research was funded by NASA Grant NNX10AO93G.
    Description: 2013-05-01
    Keywords: Inertia-gravity waves
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    The mean age of ocean waters inferred from radiocarbon observations : sensitivity to surface sources and accounting for mixing histories (2012)
    American Meteorological Society
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    Publication Date: 2022-05-26
    Description: Author Posting. © American Meteorological Society, 2012. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 42 (2012): 291–305, doi:10.1175/JPO-D-11-043.1.
    Description: A number of previous observational studies have found that the waters of the deep Pacific Ocean have an age, or elapsed time since contact with the surface, of 700–1000 yr. Numerical models suggest ages twice as old. Here, the authors present an inverse framework to determine the mean age and its upper and lower bounds given Global Ocean Data Analysis Project (GLODAP) radiocarbon observations, and they show that the potential range of ages increases with the number of constituents or sources that are included in the analysis. The inversion requires decomposing the World Ocean into source waters, which is obtained here using the total matrix intercomparison (TMI) method at up to 2° × 2° horizontal resolution with 11 113 surface sources. The authors find that the North Pacific at 2500-m depth can be no younger than 1100 yr old, which is older than some previous observational estimates. Accounting for the broadness of surface regions where waters originate leads to a reservoir-age correction of almost 100 yr smaller than would be estimated with a two or three water-mass decomposition and explains some of the discrepancy with previous observational studies. A best estimate of mean age is also presented using the mixing history along circulation pathways. Subject to the caveats that inference of the mixing history would benefit from further observations and that radiocarbon cannot rule out the presence of extremely old waters from exotic sources, the deep North Pacific waters are 1200–1500 yr old, which is more in line with existing numerical model results.
    Description: GG is supported by the J. Lamar Worzel Assistant Scientist Fund and the Penzance Endowed Fund in Support of Assistant Scientists. PJH is supported by NSF Award 0960787.
    Description: 2012-08-01
    Keywords: North Pacific Ocean ; Mass fluxes/transport ; Ocean circulation ; Tracers ; Optimization ; Variational analysis
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    The CCSM4 ocean component (2012)
    American Meteorological Society
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Meteorological Society, 2012. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Climate 25 (2012): 1361–1389, doi:10.1175/JCLI-D-11-00091.1.
    Description: The ocean component of the Community Climate System Model version 4 (CCSM4) is described, and its solutions from the twentieth-century (20C) simulations are documented in comparison with observations and those of CCSM3. The improvements to the ocean model physical processes include new parameterizations to represent previously missing physics and modifications of existing parameterizations to incorporate recent new developments. In comparison with CCSM3, the new solutions show some significant improvements that can be attributed to these model changes. These include a better equatorial current structure, a sharper thermocline, and elimination of the cold bias of the equatorial cold tongue all in the Pacific Ocean; reduced sea surface temperature (SST) and salinity biases along the North Atlantic Current path; and much smaller potential temperature and salinity biases in the near-surface Pacific Ocean. Other improvements include a global-mean SST that is more consistent with the present-day observations due to a different spinup procedure from that used in CCSM3. Despite these improvements, many of the biases present in CCSM3 still exist in CCSM4. A major concern continues to be the substantial heat content loss in the ocean during the preindustrial control simulation from which the 20C cases start. This heat loss largely reflects the top of the atmospheric model heat loss rate in the coupled system, and it essentially determines the abyssal ocean potential temperature biases in the 20C simulations. There is also a deep salty bias in all basins. As a result of this latter bias in the deep North Atlantic, the parameterized overflow waters cannot penetrate much deeper than in CCSM3.
    Description: NCAR is sponsored by the National Science Foundation. The CCSM is also sponsored by the Department of Energy. SGY was supported by the NOAA Climate Program Office under Climate Variability and Predictability Program Grant NA09OAR4310163.
    Description: 2012-09-01
    Keywords: Ocean circulation ; Climate models ; General circulation models ; Ocean models
    Repository Name: Woods Hole Open Access Server
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    Buoyancy arrest and shelf–ocean exchange (2012)
    American Meteorological Society
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Meteorological Society, 2012. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 42 (2012): 644–658, doi:10.1175/JPO-D-11-0143.1.
    Description: When steady flow in a stratified ocean passes between the continental slope and open ocean, its ability to cross isobaths is potentially limited by buoyancy arrest. If the bottom Ekman transport vanishes and there are no interior stresses, then steady linear flow on an f plane must be geostrophic and follow isobaths exactly. The influence of arrest on cross-shelf transport is investigated here to establish 1) whether there are substantial penetration asymmetries between cases with upwelling and downwelling in the bottom boundary layer; 2) over what spatial scales, hence in what parameter regime, buoyancy arrest is important; and 3) the effects of depth-dependent interior flow. The problem is approached using scalings and idealized numerical models. The results show that there is little or no asymmetry introduced by bottom boundary layer behavior. Further, if the stratification is weak or moderate, as measured by a slope Burger number s = αN/f (where α is the bottom slope, N is buoyancy frequency, and f is the Coriolis parameter), buoyancy arrest does not exert a strong constraint on cross-isobath exchange.
    Description: This research was supported by the National Science Foundation Physical Oceanography program through Grant OCE-0849498.
    Description: 2012-10-01
    Keywords: Coastal flows ; Ekman pumping/transport
    Repository Name: Woods Hole Open Access Server
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    Influences of precipitation on water mass transformation and deep convection (2012)
    American Meteorological Society
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Meteorological Society, 2012. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 42 (2012): 1684–1700, doi:10.1175/JPO-D-11-0230.1.
    Description: The influences of precipitation on water mass transformation and the strength of the meridional overturning circulation in marginal seas are studied using theoretical and idealized numerical models. Nondimensional equations are developed for the temperature and salinity anomalies of deep convective water masses, making explicit their dependence on both geometric parameters such as basin area, sill depth, and latitude, as well as on the strength of atmospheric forcing. In addition to the properties of the convective water, the theory also predicts the magnitude of precipitation required to shut down deep convection and switch the circulation into the haline mode. High-resolution numerical model calculations compare well with the theory for the properties of the convective water mass, the strength of the meridional overturning circulation, and also the shutdown of deep convection. However, the numerical model also shows that, for precipitation levels that exceed this critical threshold, the circulation retains downwelling and northward heat transport, even in the absence of deep convection.
    Description: This study was supported by the National Science Foundation underGrantsOCE-0850416, OCE-0959381, andOCE-0859381.
    Description: 2013-04-01
    Keywords: Boundary currents ; Deep convection ; Eddies ; Meridional overturning circulation ; Ocean dynamics ; Stability
    Repository Name: Woods Hole Open Access Server
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    The wavenumber–frequency content of resonantly excited equatorial waves (2012)
    American Meteorological Society
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Meteorological Society, 2012. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 42 (2012): 1834–1858, doi:10.1175/JPO-D-11-0234.1.
    Description: The theoretical resonant excitation of equatorial inertia–gravity waves and mixed Rossby–gravity waves is examined. Contrary to occasionally published expectations, solutions show that winds that are broadband in both zonal wavenumber and frequency do not in general produce peaks in the wavenumber–frequency spectrum of sea surface height (SSH) at wavenumbers associated with vanishing zonal group velocity. Excitation of total wave energy in inertia–gravity modes by broadband zonal winds is virtually wavenumber independent when the meridional structure of the winds does not impose a bias toward negative or positive zonal wavenumbers. With increasing wavenumber magnitude |k|, inertia–gravity waves asymptote toward zonally propagating pure gravity waves, in which the magnitude of meridional velocity υ becomes progressively smaller relative to the magnitude of zonal velocity u and pressure p. When the total wave energy is independent of wavenumber, this effect produces a peak in |υ|2 near the wavenumber where group velocity vanishes, but a trough in |p|2 (or SSH variance). Another consequence of the shift toward pure gravity wave structure is that broadband meridional winds excite inertia–gravity modes progressively less efficiently as |k| increases and υ becomes less important to the wave structure. Broadband meridional winds produce a low-wavenumber peak in total wave energy leading to a subtle elevation of |p|2 at low wavenumbers, but this is due entirely to the decrease in the forcing efficiency of meridional winds with increasing |k|, rather than to the vanishing of the group velocity. Physical conditions that might alter the above conclusions are discussed.
    Description: This research was funded by NASA Grant NNX10AO93G.
    Description: 2013-05-01
    Keywords: Inertia-gravity waves ; Ocean dynamics
    Repository Name: Woods Hole Open Access Server
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    Automatic Human Gait Imitation and Recognition in 3D from Monocular Video with an Uncalibrated Camera (2012)
    Hindawi
    Details
    Publication Date: 2012-03-09
    Description: A framework of imitating real human gait in 3D from monocular video of an uncalibrated camera directly and automatically is proposed. It firstly combines polygon-approximation with deformable template-matching, using knowledge of human anatomy to achieve the characteristics including static and dynamic parameters of real human gait. Then, these characteristics are processed in regularization and normalization. Finally, they are imposed on a 3D human motion model with prior constrains and universal gait knowledge to realize imitating human gait. In recognition based on this human gait imitation, firstly, the dimensionality of time-sequences corresponding to motion curves is reduced by NPE. Then, we use the essential features acquired from human gait imitation as input and integrate HCRF with SVM as a whole classifier, realizing identification recognition on human gait. In associated experiment, this imitation framework is robust for the object’s clothes and backpacks to a certain extent. It does not need any manual assist and any camera model information. And it is fitting for straight indoors and the viewing angle for target is between 60° and 120°. In recognition testing, this kind of integrated classifier HCRF/SVM has comparatively higher recognition rate than the sole HCRF, SVM and typical baseline method.
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    Swell and Wind-Sea Distributions over the Mid-Latitude and Tropical North Atlantic for the Period 2002–2008 (2012)
    Hindawi
    Details
    Publication Date: 2012-03-09
    Description: We present an analysis of wind-sea and swell fields for mid-latitude and tropical Atlantic for the period 2002–2008 using a combination of satellite data (altimeter significant wave height and scatterometer surface winds) and model results (spectrum peak wave period and propagation direction). Results show a dominance of swell over wind-sea regimes throughout the year. A small but clear decrease in swell energy and an associated increase in wind-sea potential growth were observed in the NE trade winds zone. A seasonal summertime increase in wind-sea energy in the Amazon River mouth and adjacent shelf region and in African coast was apparent in the results, probably associated to a strengthening of the alongshore trade winds in these regions. Albeit with a significantly smaller energy contribution of wind-seas as compared to swell energy, we could say that a kind of mixed seas is more evident in the trade winds region, with the remaining area being highly dominated by swell energy. An analysis of wave-age shows the absence of young-seas. Only ~2% of all data points was classified as wind-sea, a classification confirmed by a fit to a theoretical relation between wind speed, peak period, and significant wave height for fully developed wind-seas.
    Print ISSN: 1687-9406
    Electronic ISSN: 1687-9414
    Topics: Geosciences
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    Photocatalytic Water Splitting for Hydrogen Production with Novel M2YbSbO7 (M = In, Gd, Y) by Using Visible Light Photoenergy (2012)
    Hindawi
    Details
    Publication Date: 2012-02-24
    Description: Novel photocatalysts M2YbSbO7 (M=In, Gd, Y) were synthesized by solid state reaction method for the first time. A comparative study on the structural and photocatalytic properties of M2YbSbO7 M2YbSbO7 (M=In, Gd, Y) was reported. The results showed that In2YbSbO7, Gd2YbSbO7, and Y2YbSbO7 crystallized with the pyrochlore-type structure, cubic crystal system and space group Fd3m. For the photocatalytic water splitting reaction, H2 or O2 evolution was observed from pure water with In2YbSbO7, Gd2YbSbO7, or Y2YbSbO7 as the photocatalyst under visible light irradiation. (wavelength>420 nm). Moreover, under visible light irradiation (λ>420 nm), H2 and O2 were also evolved by using In2YbSbO7, Gd2YbSbO7, or Y2YbSbO7 as catalyst from CH3OH/H2O and AgNO3/H2O solutions respectively. The In2YbSbO7 photocatalyst showed the highest activity compared with Gd2YbSbO7 or Y2YbSbO7. At the same time, The Y2YbSbO7 photocatalyst showed higher activity compared with Gd2YbSbO7. The photocatalytic activities were further improved under visible light irradiation with In2YbSbO7, Gd2YbSbO7, or Y2YbSbO7 being loaded by Pt, NiO, or RuO2. The effect of Pt was better than that of NiO or RuO2 for improving the photocatalytic activity of In2YbSbO7, Gd2YbSbO7, or Y2YbSbO7.
    Print ISSN: 1110-662X
    Electronic ISSN: 1687-529X
    Topics: Electrical Engineering, Measurement and Control Technology , Energy, Environment Protection, Nuclear Power Engineering
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    Multipath Adaptive Tabu Search for a Vehicle Control Problem (2012)
    Hindawi
    Details
    Publication Date: 2012-02-24
    Description: Tabu search has become acceptable worldwide as one of the most efficient intelligent searches applied to various real-world problems. There have been different modifications made to the generic tabu search in recent years to achieve better performances. Among those reviewed in the introduction of this paper, the adaptive tabu search (ATS) has incorporated the backtracking and the adaptive search radius mechanisms that help accelerate the search and release it from a local solution lock. The paper explains an enhancement made to the ATS to accomplish multipath ATS (MATS) algorithms. Performances of the ATS and the MATS are evaluated using surface optimization problems, and results are presented in the paper. Finally, the MATS is applied to solve a real-world vehicle control problem.
    Print ISSN: 1110-757X
    Electronic ISSN: 1687-0042
    Topics: Mathematics
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    Multiple Periodic Solutions of Delayed Predator-Prey Systems with Type IV Functional Responses on Time Scales (2012)
    Hindawi
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    Publication Date: 2012-03-13
    Description: With the help of a continuation theorem based on Gaines and Mawhin's coincidence degree, easily verifiable criteria are established for the existence of multiple positive periodic solutions of delayed predator-prey systems with type IV functional responses on time scales. Our results not only unify the existing ones but also widen the range of applications.
    Print ISSN: 1026-0226
    Electronic ISSN: 1607-887X
    Topics: Mathematics
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    Eosin Yellowish Dye-Sensitized ZnO Nanostructure-Based Solar Cells Employing Solid PEO Redox Couple Electrolyte (2012)
    Hindawi
    Details
    Publication Date: 2012-03-13
    Description: ZnO nanostructures are synthesized by low-temperature methods, and they possess polycrystalline hexagonal wurtzite structure with preferential c-axial growth. Morphological study by SEM shows the presence of ~30 nm sized spherical-shaped ZnO nanoparticle, the branched flower-like ZnO composed of many nanorods (length: 1.2 to 4.2 μm and diameter: 0.3 to 0.4 μm), and ~50 nm diameter of individual ZnO nanorods. Reduction in photoemission intensity of nanorods infers the decrease in electron-hole recombination rate, which offers better photovoltaic performance. The dye-sensitized solar cell (DSSC) based on ZnO nanorods sensitized with Eosin yellowish dye exhibits a maximum optimal energy conversion efficiency of 0.163% compared to that of nanoparticles and nanoflowers, due to better dye loading and direct conduction pathway for electron transport.
    Print ISSN: 1110-662X
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    Topics: Electrical Engineering, Measurement and Control Technology , Energy, Environment Protection, Nuclear Power Engineering
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    A Generalized and Improved (G′/G)-Expansion Method for Nonlinear Evolution Equations (2012)
    Hindawi
    Details
    Publication Date: 2012-03-13
    Description: A generalized and improved (G′/G)-expansion method is proposed for finding more general type and new travelling wave solutions of nonlinear evolution equations. To illustrate the novelty and advantage of the proposed method, we solve the KdV equation, the Zakharov-Kuznetsov-Benjamin-Bona-Mahony (ZKBBM) equation and the strain wave equation in microstructured solids. Abundant exact travelling wave solutions of these equations are obtained, which include the soliton, the hyperbolic function, the trigonometric function, and the rational functions. Also it is shown that the proposed method is efficient for solving nonlinear evolution equations in mathematical physics and in engineering.
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    On the Dynamics of a Higher-Order Difference Equation (2012)
    Hindawi
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    Publication Date: 2012-03-16
    Description: This paper deals with the investigation of the following more general rational difference equation: yn+1=αyn/(β+γ∑i=0kyn-(2i+1)p∏i=0kyn-(2i+1)), n=0,1,2,…, where α,β,γ,p∈(0,∞) with the initial conditions x0,x-1,…,x-2k,x-2k-1∈(0,∞). We investigate the existence of the equilibrium points of the considered equation and then study their local and global stability. Also, some results related to the oscillation and the permanence of the considered equation have been presented.
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    Topics: Mathematics
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    Structural Heterogeneities in Southeast Tibet: Implications for Regional Flow in the Lower Crust and Upper Mantle (2012)
    Hindawi
    Details
    Publication Date: 2012-03-16
    Description: Our seismic study together with the MT analysis reveal a “R-shape” flow existing in both the lower crust and uppermost mantle, which suggests the crustal deformation along the deep, large sutures (such as the Longmen Shan fault and the Anninghe Fault) under the southeastern Tibetan Plateau is maintained by dynamic pressure from the regional flow intermingled with the hot upwelling asthenosphere. The material in the lower crust and uppermost mantle flowing outward from the center of the plateau is buttressed by the old, strong lithosphere that underlies the Sichuan basin, pushing up on the crust above and maintaining steep orogenic belt through dynamic pressure. We therefore consider that the “R-shape” regional flow played a key role in the crustal deformation along the deep suture zones of the Bangong-Nujiang, the Longmen-Shan faults, and other local heavily faulted zones beneath the southeastern Tibetan Plateau.
    Print ISSN: 1687-885X
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    Synchronization of Two Rank-One Chaotic Systems without and with Delay via Linear Delayed Feedback Control (2012)
    Hindawi
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    Publication Date: 2012-03-16
    Description: This paper illustrates the presence of chaos in rank-one chaotic systems with delay via a binary test (called 0-1 test) for chaos. Chaotic synchronization between two rank-one chaotic systems without and with delay is achieved by means of Lyapunov functional and linear delayed feedback control method. Numerical simulations are implemented to verify the effectiveness of the proposed chaos synchronization scheme.
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    On a Generalized Hyers-Ulam Stability of Trigonometric Functional Equations (2012)
    Hindawi
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    Publication Date: 2012-03-16
    Description: Let G be an Abelian group, let ℂ be the field of complex numbers, and let f,g:G→ℂ. We consider the generalized Hyers-Ulam stability for a class of trigonometric functional inequalities, |f(x-y)-f(x)g(y)+g(x)f(y)|≤ψ(y),  |g(x-y)-g(x)g(y)-f(x)f(y)|≤ψ(y), where ψ:G→ℝ is an arbitrary nonnegative function.
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    The Effect of Dissolved Humic Acids on Aluminosilicate Formation and Associated Carbon Sequestration (2012)
    Hindawi
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    Publication Date: 2012-03-16
    Description: Allophane and imogolite neogenesis in soils may occur in the presence of organic matter. To understand this process under conditions relevant to soils, the influence of dissolved organic carbon (DOC) as humic acid (HA), on aluminosilicate formation was studied at 25C∘, pH 6, and low-DOC concentrations. For solutions with initial Al/Si ratios of 1–2.1, and 0–6 mg/L DOC, precipitates recovered after 20 h had Al/Si ratios of 2.2–2.7. The formation of allophane, imogolite-like material, and aluminosilicate gel was confirmed by XRD, FTIR, and NMR. The effect of DOC was to produce a small, but systematic increase in imogolite-like Si in the precipitate, and a decrease in the formation of aluminosilicate gel. Results suggest that the presence of DOC as HA slows the otherwise rapid polymerization of Al and Si at low temperature, and may also promote the formation of imogolite. The high C content of these precipitates indicates that this process may facilitate the sequestration of organic matter, slowing C cycling in soils.
    Print ISSN: 1687-7667
    Electronic ISSN: 1687-7675
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
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    A Note on Some Identities of Frobenius-Euler Numbers and Polynomials (2012)
    Hindawi
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    Publication Date: 2012-03-16
    Description: The purpose of this paper is to give some identities on the Frobenius-Euler numbers and polynomials by using the fermionic p-adic q-integral equation on ℤp.
    Print ISSN: 0161-1712
    Electronic ISSN: 1687-0425
    Topics: Mathematics
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    A Hybrid Multiobjective Genetic Algorithm for Robust Resource-Constrained Project Scheduling with Stochastic Durations (2012)
    Hindawi
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    Publication Date: 2012-03-15
    Description: We study resource-constrained project scheduling problems with perturbation on activity durations. With the consideration of robustness and stability of a schedule, we model the problem as a multiobjective optimization problem. Three objectives—makespan minimization, robustness maximization, and stability maximization—are simultaneously considered. We propose a hybrid multiobjective evolutionary algorithm (H-MOEA) to solve this problem. In the process of the H-MOEA, the heuristic information is extracted periodically from the obtained nondominated solutions, and a local search procedure based on the accumulated information is incorporated. The results obtained from the computational study show that the proposed approach is feasible and effective for the resource-constrained project scheduling problems with stochastic durations.
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    Adaptive Modified Function Projective Synchronization between Two Different Hyperchaotic Dynamical Systems (2012)
    Hindawi
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    Publication Date: 2012-03-16
    Description: This work investigates modified function projective synchronization between two different hyperchaotic dynamical systems, namely, hyperchaotic Lorenz system and hyperchaotic Chen system with fully unknown parameters. Based on Lyapunov stability theory, the adaptive control law and the parameter update law are derived to achieve modified function projective synchronized between two diffierent hyperchaotic dynamical systems. Numerical simulations are presented to demonstrate the effectiveness of the proposed adaptive controllers.
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    Robust H∞ Filtering of 2D Roesser Discrete Systems: A Polynomial Approach (2012)
    Hindawi
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    Publication Date: 2012-03-15
    Description: The problem of robust H∞ filtering is investigated for the class of uncertain two-dimensional (2D) discrete systems described by a Roesser state-space model. The main contribution is a systematic procedure for generating conditions for the existence of a 2D discrete filter such that, for all admissible uncertainties, the error system is asymptotically stable, and the H∞ norm of the transfer function from the noise signal to the estimation error is below a prespecified level. These conditions are expressed as parameter-dependent linear matrix inequalities. Using homogeneous polynomially parameter-dependent filters of arbitrary degree on the uncertain parameters, the proposed method extends previous results in the quadratic framework and the linearly parameter-dependent framework, thus reducing its conservatism. Performance of the proposed method, in comparison with that of existing methods, is illustrated by two examples.
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    Stochastic ℋ∞ Finite-Time Control of Discrete-Time Systems with Packet Loss (2012)
    Hindawi
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    Publication Date: 2012-03-15
    Description: This paper investigates the stochastic finite-time stabilization and ℋ∞ control problem for one family of linear discrete-time systems over networks with packet loss, parametric uncertainties, and time-varying norm-bounded disturbance. Firstly, the dynamic model description studied is given, which, if the packet dropout is assumed to be a discrete-time homogenous Markov process, the class of discrete-time linear systems with packet loss can be regarded as Markovian jump systems. Based on Lyapunov function approach, sufficient conditions are established for the resulting closed-loop discrete-time system with Markovian jumps to be stochastic ℋ∞ finite-time boundedness and then state feedback controllers are designed to guarantee stochastic ℋ∞ finite-time stabilization of the class of stochastic systems. The stochastic ℋ∞ finite-time boundedness criteria can be tackled in the form of linear matrix inequalities with a fixed parameter. As an auxiliary result, we also give sufficient conditions on the robust stochastic stabilization of the class of linear systems with packet loss. Finally, simulation examples are presented to illustrate the validity of the developed scheme.
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    Static and Vibrational Analysis of Partially Composite Beams Using the Weak-Form Quadrature Element Method (2012)
    Hindawi
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    Publication Date: 2012-03-16
    Description: Deformation of partially composite beams under distributed loading and free vibrations of partially composite beams under various boundary conditions are examined in this paper. The weak-form quadrature element method, which is characterized by direct evaluation of the integrals involved in the variational description of a problem, is used. One quadrature element is normally sufficient for a partially composite beam regardless of the magnitude of the shear connection stiffness. The number of integration points in a quadrature element is adjustable in accordance with convergence requirement. Results are compared with those of various finite element formulations. It is shown that the weak form quadrature element solution for partially composite beams is free of slip locking, and high computational accuracy is achieved with smaller number of degrees of freedom. Besides, it is found that longitudinal inertia of motion cannot be simply neglected in assessment of dynamic behavior of partially composite beams.
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    Coupled Fixed-Point Theorems for Contractions in Partially Ordered Metric Spaces and Applications (2012)
    Hindawi
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    Publication Date: 2012-03-16
    Description: Bhaskar and Lakshmikantham (2006) showed the existence of coupled coincidence points of a mapping F from X×X into X and a mapping g from X into X with some applications. The aim of this paper is to extend the results of Bhaskar and Lakshmikantham and improve the recent fixed-point theorems due to Bessem Samet (2010). Indeed, we introduce the definition of generalized g-Meir-Keeler type contractions and prove some coupled fixed point theorems under a generalized g-Meir-Keeler-contractive condition. Also, some applications of the main results in this paper are given.
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    A New Optimization via Simulation Approach for Dynamic Facility Layout Problem with Budget Constraints (2012)
    Hindawi
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    Publication Date: 2012-03-16
    Description: A new efficient heuristic algorithm has been developed for the dynamic facility layout problem with budget constraint (DFLPB) using optimization via simulation technique. The heuristic integrates integer programming and discrete event simulation to address DFLPB. In the proposed algorithm, the nonlinear model of the DFLP has been changed to a pure integer programming (PIP) model. Then, the optimal solution of the PIP model has been used in a simulation model that has been designed in a similar manner as the DFLP for determining the probability of assigning a facility to a location. After a sufficient number of runs, the simulation model obtains near optimum solutions. Finally, to test the performance of the algorithm, several test problems have been taken from the literature and solved. The results show that the proposed algorithm is more efficient in terms of speed and accuracy than other heuristic algorithms presented in previous works.
    Print ISSN: 1687-5591
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    Topics: Computer Science , Technology
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    Spatial Variation in Bird Community Composition in Relation to Topographic Gradient and Forest Heterogeneity in a Central Amazonian Rainforest (2012)
    Hindawi
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    Publication Date: 2012-02-03
    Description: We investigated the effects of landscape features and forest structure on the avian community at the Reserva Florestal Adolpho Ducke near Manaus, in the Brazilian Amazon. We sampled the landscape and forest in 72 50 × 50 m plots systematically distributed in the reserve, covering an area of 6,400 ha. The avifauna was sampled using mist nets and acoustic surveys near the plots. We found no significant relationships between landscape features and forest components in the plots and the number of bird species and individuals sampled. Results of Principal Coordinate Analyses, however, showed that bird species composition changes along a topographic gradient (plateau-slope-valley), and also in relation to leaf litter depth and distance to forest streams. We also found compositional differences in the avian community on the eastern and western water basins that compose the reserve. Our results suggest that although most bird species occur throughout the reserve, many species track differences in the landscape and the forest structure.
    Electronic ISSN: 1687-9716
    Topics: Biology , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
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    Effect of Land Application of Phosphorus-Saturated Gypsum on Soil Phosphorus in a Laboratory Incubation (2012)
    Hindawi
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    Publication Date: 2012-02-07
    Description: Agricultural drainage ditches can deliver high loads of phosphorus (P) to surface water. Installation of filter structures containing P sorbing materials (PSMs), including gypsum, is an emerging practice that has shown promise to reduce these P loads. The objective of this study was to evaluate what effect soil amendment with gypsum would have on soil P concentrations and forms in a laboratory incubation experiment. Gypsum was saturated at two levels with P, and applied to a silt loam and a sandy loam at two rates. The treated soils were incubated in the laboratory at 25°C, and samples were collected on eight dates between 0 and 183 days after amendment. Spent gypsum application did not significantly increase soil water-extractable or Mehlich 3 P when applied at typical agronomic rates. This appears to be a viable strategy to remove P from agricultural drainage waters but does not appear to provide any additional P fertilizer value.
    Print ISSN: 1687-7667
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    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
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    On the Solution of Double-Diffusive Convective Flow due to a Cone by a Linearization Method (2012)
    Hindawi
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    Publication Date: 2012-02-08
    Description: The paper details the use of a nonperturbation successive linearization method to solve the coupled nonlinear boundary value problem due to double-diffusive convection from an inverted cone. Diffusion-thermo and thermal-diffusion effects have been taken into account. The governing partial differential equations are transformed into ordinary differential equations using a suitable similarity transformation. The SLM is based on successively linearizing the governing nonlinear boundary layer equations and solving the resulting higher-order deformation equations using spectral methods. The results are compared with the limited cases from previous studies and results obtained using the Matlab inbuilt bvp4c numerical algorithm and a shooting technique that uses Runge-Kutta-Fehlberg (RKF45) and Newton-Raphson schemes. These comparisons reveal the robustness and validate the usage of the linearisation method technique. The results show that the nonperturbation technique in combination with the Chebyshev spectral collocation method is an efficient numerical algorithm with assured convergence that serves as an alternative to numerical methods for solving nonlinear boundary value problems.
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    Subsurface Lateral Flow in Texture-Contrast (Duplex) Soils and Catchments with Shallow Bedrock (2012)
    Hindawi
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    Publication Date: 2012-02-09
    Description: Development-perched watertables and subsurface lateral flows in texture-contrast soils (duplex) are commonly believed to occur as a consequence of the hydraulic discontinuity between the A and B soil horizons. However, in catchments containing shallow bedrock, subsurface lateral flows result from a combination of preferential flow from the soil surface to the soil—bedrock interface, undulations in the bedrock topography, lateral flow through macropore networks at the soil—bedrock interface, and the influence of antecedent soil moisture on macropore connectivity. Review of literature indicates that some of these processes may also be involved in the development of subsurface lateral flow in texture contrast soils. However, the extent to which these mechanisms can be applied to texture contrast soils requires further field studies. Improved process understanding is required for modelling subsurface lateral flows in order to improve the management of waterlogging, drainage, salinity, and offsite agrochemicals movement.
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    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
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    Travel Time Model of Left-Turning Vehicles at Signalized Intersection (2012)
    Hindawi
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    Publication Date: 2012-02-09
    Description: The travel time of left-turning vehicles at signalized intersection was discussed. Under the assumption that the opposing through vehicles headway follows M3 distribution, the travel time model was established on the basis of gap theory and queue theory. Comparison was done with the common model based on the assumption that the opposing through vehicles headway follows negative exponential distribution. The results show that the model in this paper has stronger applicability and its most relative error is less than 15%. In addition, the sensitivity analysis was done. The results show that the opposing through flow rate has significant impact on travel time. The impact of left-turning flow rate and following headway is light when the opposing through flow rate is small, the threshold is about 0.18 veh/s. The model established in this paper can well calculate travel time of left-turning vehicles at intersection, and the methodology may provide reference to other occasions.
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    Axisymmetric Stagnation Flow of a Micropolar Nanofluid in a Moving Cylinder (2012)
    Hindawi
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    Publication Date: 2012-02-09
    Description: An analysis is carried out for axisymmetric stagnation flow of a micropolar nanofluid in a moving cylinder with finite radius. The coupled nonlinear partial differential equations of the problem are simplified with the help of similarity transformations and the resulting coupled nonlinear differential equations are solved analytically by homotopy analysis method (HAM). The features of the flow phenomena, inertia, heat transfer, and nanoparticles are analyzed and discussed.
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    Effects of Thermocapillarity and Thermal Radiation on Flow and Heat Transfer in a Thin Liquid Film on an Unsteady Stretching Sheet (2012)
    Hindawi
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    Publication Date: 2012-02-09
    Description: This paper examines the effects of thermocapillarity and thermal radiation on the boundary layer flow and heat transfer in a thin film on an unsteady stretching sheet with nonuniform heat source/sink. The governing partial differential equations are converted into ordinary differential equations by a similarity transformation and then are solved by using the homotopy analysis method (HAM). The effects of the radiation parameter, the thermocapillarity number, and the temperature-dependent parameter in this study are discussed and presented graphically via velocity and temperature profiles.
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    Energy-Efficient Multi-Job Scheduling Model for Cloud Computing and Its Genetic Algorithm (2012)
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    Publication Date: 2012-02-09
    Description: For the problem that the energy efficiency of the cloud computing data center is low, from the point of view of the energy efficiency of the servers, we propose a new energy-efficient multi-job scheduling model based on Google’s massive data processing framework. To solve this model, we design a practical encoding and decoding method for the individuals and construct an overall energy efficiency function of the servers as the fitness value of each individual. Meanwhile, in order to accelerate the convergent speed of our algorithm and enhance its searching ability, a local search operator is introduced. Finally, the experiments show that the proposed algorithm is effective and efficient.
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    Research on the Human Dynamics in Mobile Communities Based on Social Identity (2012)
    Hindawi
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    Publication Date: 2012-02-10
    Description: Through analyzing the data about the releases, comment, and forwarding of 120,000 microblog messages in a year, this paper finds out that the intervals between information releases and comment follow a power law; besides, the analysis of data in each 24 hours reveals obvious differences between microblogging and website visit, email, instant communication, and the use of mobile phone, reflecting how people use fragments of time via mobile internet technology. The paper points out the significant influence of the user's activity on the intervals of information releases and thus demonstrates a positive correlation between the activity and the power exponent. The paper also points out that user's activity is influenced by social identity in a positive way. The simulation results based on the social identity mechanism fit well with the actual data, which indicates that this mechanism is a reasonable way to explain people's behavior in the mobile Internet.
    Print ISSN: 1026-0226
    Electronic ISSN: 1607-887X
    Topics: Mathematics
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    MHD Flow of an Incompressible Viscous Fluid through Convergent or Divergent Channels in Presence of a High Magnetic Field (2012)
    Hindawi
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    Publication Date: 2012-02-10
    Description: The flow of an incompressible electrically conducting viscous fluid in convergent or divergent channels under the influence of an externally applied homogeneous magnetic field is studied both analytically and numerically. Navier-Stokes equations of fluid mechanics and Maxwell’s electromagnetism equations are reduced into highly non-linear ordinary differential equation. The resulting non-linear equation has been solved analytically using a very efficient technique, namely, differential transform method (DTM). The DTM solution is compared with the results obtained by a numerical method (shooting method, coupled with fourth-order Runge-Kutta scheme). The plots have revealed the physical characteristics of flow by changing angles of the channel, Hartmann and Reynolds numbers.
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    Hidden and Not So Hidden Symmetries (2012)
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    Publication Date: 2012-02-13
    Description: Hidden symmetries entered the literature in the late Eighties when it was observed that there could be gain of Lie point symmetry in the reduction of order of an ordinary differential equation. Subsequently the reverse process was also observed. Such symmetries were termed “hidden”. In each case the source of the “new” symmetry was a contact symmetry or a nonlocal symmetry, that is, a symmetry with one or more of the coefficient functions containing an integral. Recent work by Abraham-Shrauner and Govinder (2006) on the reduction of partial differential equations demonstrates that it is possible for these “hidden” symmetries to have a point origin. In this paper we show that the same phenomenon can be observed in the reduction of ordinary differential equations and in a sense loosen the interpretation of hidden symmetries.
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    Analytical and Semi-Analytical Treatment of the Satellite Motion in a Resisting Medium (2012)
    Hindawi
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    Publication Date: 2012-02-13
    Description: The orbital dynamics of an artificial satellite in the Earth's atmosphere is considered. An analytic first-order atmospheric drag theory is developed using Lagrange's planetary equations. The short periodic perturbations due to the geopotential of all orbital elements are evaluated. And to construct a second-order analytical theory, the equations of motion become very complicated to be integrated analytically; thus we are forced to integrate them numerically using the method of Runge-Kutta of fourth order. The validity of the theory is checked on the already decayed Indian satellite ROHINI where its data are available.
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    A Numerical Method for Lane-Emden Equations Using Hybrid Functions and the Collocation Method (2012)
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    Publication Date: 2012-02-13
    Description: A numerical method to solve Lane-Emden equations as singular initial value problems is presented in this work. This method is based on the replacement of unknown functions through a truncated series of hybrid of block-pulse functions and Chebyshev polynomials. The collocation method transforms the differential equation into a system of algebraic equations. It also has application in a wide area of differential equations. Corresponding numerical examples are presented to demonstrate the accuracy of the proposed method.
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    Statistical Behavior of a Financial Model by Lattice Fractal Sierpinski Carpet Percolation (2012)
    Hindawi
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    Publication Date: 2012-02-13
    Description: The lattice fractal Sierpinski carpet and the percolation theory are applied to develop a new random stock price for the financial market. Percolation theory is usually used to describe the behavior of connected clusters in a random graph, and Sierpinski carpet is an infinitely ramified fractal. In this paper, we consider percolation on the Sierpinski carpet lattice, and the corresponding financial price model is given and investigated. Then, we analyze the statistical behaviors of the Hong Kong Hang Seng Index and the simulative data derived from the financial model by comparison.
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    Less Conservative Control Design for Linear Systems with Polytopic Uncertainties via State-Derivative Feedback (2012)
    Hindawi
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    Publication Date: 2012-02-13
    Description: The motivation for the use of state-derivative feedback instead of conventional state feedback is due to its easy implementation in some mechanical applications, for example, in vibration control of mechanical systems, where accelerometers have been used to measure the system state. Using linear matrix inequalities (LMIs) and a parameter-dependent Lyapunov functions (PDLF) allowed by Finsler’s lemma, a less conservative approach to the controller design via state-derivative feedback, is proposed in this work, with and without decay rate restriction, for continuous-time linear systems subject to polytopic uncertainties. Finally, numerical examples illustrate the efficiency of the proposed method.
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    Robust Gene Expression Index (2012)
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    Publication Date: 2012-02-13
    Description: The frequentist gene expression index (FGX) was recently developed to measure expression on Affymetrix oligonucleotide DNA arrays. In this study, we extend FGX to cover nonnormal log expressions, specifically long-tailed symmetric densities and call our new index as robust gene expression index (RGX). In estimation, we implement the modified maximum likelihood method to unravel the elusive solutions of likelihood equations and utilize the Fisher information matrix for covariance terms. From the analysis via the bench-mark datasets and simulated data, it is shown that RGX has promising results and mostly outperforms FGX in terms of relative efficiency of the estimated signals, in particular, when the data are nonnormal.
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    Chaos and Control in Coronary Artery System (2012)
    Hindawi
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    Publication Date: 2012-02-14
    Description: Two types of coronary artery system N-type and S-type, are investigated. The threshold conditions for the occurrence of Smale horseshoe chaos are obtained by using Melnikov method. Numerical simulations including phase portraits, potential diagram, homoclinic bifurcation curve diagrams, bifurcation diagrams, and Poincaré maps not only prove the correctness of theoretical analysis but also show the interesting bifurcation diagrams and the more new complex dynamical behaviors. Numerical simulations are used to investigate the nonlinear dynamical characteristics and complexity of the two systems, revealing bifurcation forms and the road leading to chaotic motion. Finally the chaotic states of the two systems are effectively controlled by two control methods: variable feedback control and coupled feedback control.
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    Radar Waveform Design for Extended Target Recognition under Detection Constraints (2012)
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    Publication Date: 2012-02-15
    Description: We address the problem of radar phase-coded waveform design for extended target recognition in the presence of colored Gaussian disturbance. Phase-coded waveforms are selected since they can fully exploit the transmit power with sufficient variability. An important constraint, target detection performance, is considered to meet the practical requirements. The waveform is designed to achieve maximum recognition performance under a control on the achievable signal-to-noise ratio (SNR) of every possible target hypothesis. We formulate the code design in terms of a nonconvex, NP-hard quadratic optimization problem in the cases of both continuous and discrete phases. Techniques based on semidefinite relaxation (SDR) and randomization are proposed to approximate the optimal solutions. Simulation results show that the recognition performance and the detection requirements are well balanced and accurate approximations are achieved.
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    Specific Niche Characteristics Facilitate the Invasion of an Alien Fish Invader in Boreal Streams (2012)
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    Publication Date: 2012-02-17
    Description: We studied the ecological niche relations of native stream fish and an alien invader, brook trout (Salvelinus fontinalis), to examine if brook trout had located an underused environmental niche in our boreal study system. In both study years (1994 versus 2004), we found brook trout to have the most marginal niche position of all the fish species examined. The most important environmental variable affecting the distribution of brook trout was pH, with acid headwater sites being dominated by this species. Brown trout, in contrast, had relatively nonmarginal niche, occurring in average conditions across the sampled sites. Other fish species had niche positions between the two salmonids. Our results show that fish invasions may be strongly facilitated by the presence of suboptimally occupied environmental niche space in the recipient river system.
    Electronic ISSN: 1687-9716
    Topics: Biology , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
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    Implementation of a Differential Geometric Filter for Spacecraft Formation Orbit Estimation (2012)
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    Publication Date: 2012-02-17
    Description: The differential geometric filter is implemented to estimate the absolute and relative positions of the spacecraft in a formation. The extended Kalman Filter is also implemented as a benchmark for the differential geometric estimation. Only relative positions between the spacecraft are measured. Relative positions are measured using a wireless local positioning system (WLPS) installed in all spacecraft. Two different scenarios are studied: (1) the observations include WLPS measurements only and (2) the observations include WLPS measurements in addition to measurements for the absolute position of one spacecraft made by a radar that takes measurements from the earth’s surface. Results show that the differential geometric estimation has better stability performance and a faster convergence rate compared to the extended Kalman filter.
    Print ISSN: 1687-5966
    Electronic ISSN: 1687-5974
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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    Generalized Derivations in Semiprime Gamma Rings (2012)
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    Publication Date: 2012-02-17
    Description: Let M be a 2-torsion-free semiprime Γ-ring satisfying the condition aαbβc=aβbαc for all a,b,c∈M,  α,β∈Γ, and let D:M→M be an additive mapping such that D(xαx)=D(x)αx+xαd(x) for all x∈M,  α∈Γ and for some derivation d of M. We prove that D is a generalized derivation.
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    The Effects of Chemical Reaction, Hall, and Ion-Slip Currents on MHD Micropolar Fluid Flow with Thermal Diffusivity Using a Novel Numerical Technique (2012)
    Hindawi
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    Publication Date: 2012-02-17
    Description: The problem of magnetomicropolar fluid flow, heat, and mass transfer with suction through a porous medium is numerically analyzed. The problem was studied under the effects of chemical reaction, Hall, ion-slip currents, and variable thermal diffusivity. The governing fundamental conservation equations of mass, momentum, angular momentum, energy, and concentration are converted into a system of nonlinear ordinary differential equations by means of similarity transformation. The resulting system of coupled nonlinear ordinary differential equations is the then solved using a fairly new technique known as the successive linearization method together with the Chebyshev collocation method. A parametric study illustrating the influence of the magnetic strength, Hall and ion-slip currents, Eckert number, chemical reaction and permeability on the Nusselt and Sherwood numbers, skin friction coefficients, velocities, temperature, and concentration was carried out.
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    Existence of Solutions for the Evolution p(x)-Laplacian Equation Not in Divergence Form (2012)
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    Publication Date: 2012-02-17
    Description: The existence of weak solutions is studied to the initial Dirichlet problem of the equation ut=udiv(|∇u|p(x)−2∇u), with inf p(x)>2. We adopt the method of parabolic regularization. After establishing some necessary uniform estimates on the approximate solutions, we prove the existence of weak solutions.
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    Derivatives of Multivariate Bernstein Operators and Smoothness with Jacobi Weights (2012)
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    Publication Date: 2012-02-21
    Description: Using the modulus of smoothness, directional derivatives of multivariate Bernstein operators with weights are characterized. The obtained results partly generalize the corresponding ones for multivariate Bernstein operators without weights.
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    Note on the Choquet Integral as an Interval-Valued Aggregation Operators and Their Applications (2012)
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    Publication Date: 2012-02-21
    Description: The concept of an interval-valued capacity is motivated by the goal to generalize a capacity, and it can be used for representing an uncertain capacity. In this paper, we define the discrete interval-valued capacities, a measure of the entropy of a discrete interval-valued capacity, and, Choquet integral with respect to a discrete interval-valued capacity. In particular, we discuss the Choquet integral as an interval-valued aggregation operator and discuss an application of them.
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    Geodesic Effect Near an Elliptical Orbit (2012)
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    Publication Date: 2012-02-21
    Description: Using a differential geometric treatment, we analytically derived the expression for De Sitter (geodesic) precession in the elliptical motion of the Earth through the gravitational field of the Sun with Schwarzschild's metric. The expression obtained in this paper in a simple way, using a classical approach, agrees with that given in B. M. Barker and R. F. O'Connell (1970, 1975) in a different setting, using the tools of Newtonian mechanics and the Euler-Lagrange equations.
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    Three-Step Fixed Point Iteration for Generalized Multivalued Mapping in Banach Spaces (2012)
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    Publication Date: 2012-02-21
    Description: The convergence of three-step fixed point iterative processes for generalized multivalued nonexpansive mapping was considered in this paper. Under some different conditions, the sequences of three-step fixed point iterates strongly or weakly converge to a fixed point of the generalized multivalued nonexpansive mapping. Our results extend and improve some recent results.
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    (λ,μ)-Fuzzy Version of Ideals, Interior Ideals, Quasi-Ideals, and Bi-Ideals (2012)
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    Publication Date: 2012-02-21
    Description: We introduced (λ,μ)-fuzzy ideals, (λ,μ)-fuzzy interior ideals, (λ,μ)-fuzzy quasi-ideals, and (λ,μ)-fuzzy bi-ideals of an ordered semigroup and studied them. When λ=0 and μ=1, we meet the ordinary fuzzy ones. This paper can be seen as a generalization of Kehayopulu and Tsingelis (2006), Kehayopulu and Tsingelis (2007), and Yao (2009).
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    Periodic Points and Fixed Points for the Weaker (ϕ,φ)-Contractive Mappings in Complete Generalized Metric Spaces (2012)
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    Publication Date: 2012-02-21
    Description: We introduce the notion of weaker (ϕ,φ)-contractive mapping in complete metric spaces and prove the periodic points and fixed points for this type of contraction. Our results generalize or improve many recent fixed point theorems in the literature.
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    An Analytical Approach to the Analysis of Guard-Channel-Based Call Admission Control in Wireless Cellular Networks (2012)
    Hindawi
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    Publication Date: 2012-02-21
    Description: We develop an analytical approach to the performance analysis and optimization of wireless cellular networks for which different types of calls are prioritized based on a channel reservation scheme. We assume that the channel occupancy time differs for new and handover calls. We obtain simple formulas for calculating quality of service (QoS) metrics and solve some problems related to finding the optimal values of guard channels as well as present the results of numerical experiments.
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    Filtering-Based Fault Detection for Stochastic Markovian Jump System with Distributed Time-Varying Delays and Mixed Modes (2012)
    Hindawi
    Details
    Publication Date: 2012-12-26
    Description: The problem of fault detection for stochastic Markovian jump system is considered. The system under consideration involves discrete and distributed time-varying delays, Itô-type stochastic disturbance, and different system and delay modes. The aim of this paper is to design a fault detection filter such that the fault detection system is stochastically stable and satisfies a prescribed disturbance attenuation level. By using a novel Lyapunov functional, a mix-mode-dependent sufficient condition is formulated in terms of linear matrix inequalities. A numerical example is given to illustrate the effectiveness of the proposed main results.
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    Existence and Uniqueness of Homoclinic Solution for a Class of Nonlinear Second-Order Differential Equations (2012)
    Hindawi
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    Publication Date: 2012-12-26
    Description: The authors study the existence and uniqueness of a set with -periodic solutions for a class of second-order differential equations by using Mawhin's continuation theorem and some analysis methods, and then a unique homoclinic orbit is obtained as a limit point of the above set of -periodic solutions.
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    Integral Bifurcation Method together with a Translation-Dilation Transformation for Solving an Integrable 2-Component Camassa-Holm Shallow Water System (2012)
    Hindawi
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    Publication Date: 2012-12-26
    Description: An integrable 2-component Camassa-Holm (2-CH) shallow water system is studied by using integral bifurcation method together with a translation-dilation transformation. Many traveling wave solutions of nonsingular type and singular type, such as solitary wave solutions, kink wave solutions, loop soliton solutions, compacton solutions, smooth periodic wave solutions, periodic kink wave solution, singular wave solution, and singular periodic wave solution are obtained. Further more, their dynamic behaviors are investigated. It is found that the waveforms of some traveling wave solutions vary with the changes of parameter, that is to say, the dynamic behavior of these waves partly depends on the relation of the amplitude of wave and the level of water.
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    General Helices of AW(k)-Type in the Lie Group (2012)
    Hindawi
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    Publication Date: 2012-12-26
    Description: We study curves of AW(k)-type in the Lie group G with a bi-invariant metric. Also, we characterize general helices in terms of AW(k)-type curve in the Lie group G.
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    Numerical Oscillations Analysis for Nonlinear Delay Differential Equations in Physiological Control Systems (2012)
    Hindawi
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    Publication Date: 2012-12-26
    Description: This paper deals with the oscillations of numerical solutions for the nonlinear delay differential equations in physiological control systems. The exponential -method is applied to and it is shown that the exponential -method has the same order of convergence as that of the classical -method. Several conditions under which the numerical solutions oscillate are derived. Moreover, it is proven that every nonoscillatory numerical solution tends to positive equilibrium of the continuous system. Finally, the main results are illustrated with numerical examples.
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    A Trend-Switching Financial Time Series Model with Level-Duration Dependence (2012)
    Hindawi
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    Publication Date: 2012-12-26
    Description: The financial time series model that can capture the nonlinearity and asymmetry of stochastic process has been paid close attention for a long time. However, it is still open to completely overcome the difficult problem that motivates our researches in this paper. An asymmetric and nonlinear model with the change of local trend depending on local high-low turning point process is first proposed in this paper. As the point process can be decomposed into the two different processes, a high-low level process and an up-down duration process, we then establish the so-called trend-switching model which depends on both level and duration (Trend-LD). The proposed model can predict efficiently the direction and magnitude of the local trend of a time series by incorporating the local high-low turning point information. The numerical results on six indices in world stock markets show that the proposed Trend-LD model is suitable for fitting the market data and able to outperform the traditional random walk model.
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    Peristaltic Slip Flow of a Viscoelastic Fluid with Heat and Mass Transfer in a Tube (2012)
    Hindawi
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    Publication Date: 2012-12-26
    Description: The paper discusses the combined effect of slip velocity and heat and mass transfer on peristaltic flow of a viscoelastic fluid in a uniform tube. This study has numerous applications. It serves as a model for the chyme movement in the small intestine, by considering the chyme as a viscoelastic fluid. The problem is formulated and analysed using perturbation expansion in terms of the wave number as a parameter. Analytic solutions for the axial velocity component, pressure gradient, temperature distribution, and fluid concentration are derived. Also, the effects of the emerging parameters on pressure gradient, temperature distribution, concentration profiles, and trapping phenomenon are illustrated graphically and discussed in detail.
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    Finite-SNR Diversity-Multiplexing Tradeoff for Cooperative Transmissions with Opportunistic Network Coding (2012)
    Hindawi
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    Publication Date: 2012-12-26
    Description: We present a multiuser cooperative transmission scheme with opportunistic network coding (CTONC), which can improve system performance. In contrast to direct transmission and conventional cooperative transmission, the CTONC allows the relay node to decide whether or not to help do cooperation and employ network coding based on the limited feedback from the destinations. It will not help a transmission pair unless its direct transmission fails. This enables CTONC to make efficient use of the degrees of freedom of the channels. We derive and analyze the diversity-multiplexing tradeoff for the CTONC over Rayleigh fading channels at finite signal-to-noise ratios (SNRs). Theoretical analysis and numerical results show that the proposed scheme achieves better performance gain in terms of average mutual information, outage probability, and finite-SNR diversity-multiplexing tradeoff.
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    Highly Efficient Calculation Schemes of Finite-Element Filter Approach for the Eigenvalue Problem of Electric Field (2012)
    Hindawi
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    Publication Date: 2012-12-27
    Description: This paper discusses finite-element highly efficient calculation schemes for solving eigenvalue problem of electric field. Multigrid discretization is extended to the filter approach for eigenvalue problem of electric field. With this scheme one solves an eigenvalue problem on a coarse grid just at the first step, and then always solves a linear algebraic system on finer and finer grids. Theoretical analysis and numerical results show that the scheme has high efficiency. Besides, we use interpolation postprocessing technique to improve the accuracy of solutions, and numerical results show that the scheme is an efficient and significant method for eigenvalue problem of electric field.
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    Numerical Identification of Multiparameters in the Space Fractional Advection Dispersion Equation by Final Observations (2012)
    Hindawi
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    Publication Date: 2012-12-25
    Description: This paper deals with an inverse problem for identifying multiparameters in 1D space fractional advection dispersion equation (FADE) on a finite domain with final observations. The parameters to be identified are the fractional order, the diffusion coefficient, and the average velocity in the FADE. The forward problem is solved by a finite difference scheme, and then an optimal perturbation regularization algorithm is introduced to determine the three parameters simultaneously. Numerical inversions are performed both with the accurate data and noisy data, and several factors having influences on realization of the algorithm are discussed. The inversion solutions are in good approximations to the exact solutions demonstrating the efficiency of the proposed algorithm.
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    LMI Approach to Stability Analysis of Cohen-Grossberg Neural Networks with -Laplace Diffusion (2012)
    Hindawi
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    Publication Date: 2012-12-25
    Description: The nonlinear -Laplace diffusion () was considered in the Cohen-Grossberg neural network (CGNN), and a new linear matrix inequalities (LMI) criterion is obtained, which ensures the equilibrium of CGNN is stochastically exponentially stable. Note that, if , -Laplace diffusion is just the conventional Laplace diffusion in many previous literatures. And it is worth mentioning that even if , the new criterion improves some recent ones due to computational efficiency. In addition, the resulting criterion has advantages over some previous ones in that both the impulsive assumption and diffusion simulation are more natural than those of some recent literatures.
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    An -Firm Real-Time Aware Fault-Tolerant Mechanism in Wireless Sensor Networks (2012)
    Hindawi
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    Publication Date: 2012-12-25
    Description: Many real-time routing mechanisms have been proposed to support the newly developed wireless sensor networks (WSNs) applications such as the transmission and retrieval of multimedia traffic. However, the inherent source constraints of sensor network and instability of wireless communication set quite a problem for the existing routing mechanisms to meet the quality of service (QoS) requirements of some specific QoS-aware applications. Hence, real-time fault-tolerant schemes are highly desired for WSNs to address these challenges. In this paper, we propose an -firm-based real-time fault-tolerant mechanism, which helps routing mechanisms to achieve specific QoS requirement by employing a local status indicator (LSI) at each sensor node to monitor and evaluate the local conditions of node and network. Therefore, specific fault recovery mechanisms could be implemented for ensuring an acceptable QoS performance, according to the evaluated LSI values. By using this fault-tolerant scheme, each node dynamically adjusts its transmission capability to mitigate the performance degradation of real-time service caused by network faults and to maintain the desired reliability and timeliness. Simulation result shows that LSI cannot only help to reduce the effects of congestion, link failure, and void, but also reach higher successful transmission ratio and smaller transmission delay.
    Print ISSN: 1550-1329
    Electronic ISSN: 1550-1477
    Topics: Electrical Engineering, Measurement and Control Technology
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    Food versus Fuel: Toward a New Paradigm—The Need for a Holistic Approach (2012)
    Hindawi
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    Publication Date: 2012-12-25
    Description: A key objective of this paper is to provide an assessment of the current and future situation on the “food versus fuel” debate and to contribute to possible alternatives to minimise or avoid future conflict. The debate has centred on three main areas: (i) food versus biofuel production, (ii) their positive and negative effects (i.e., GHG, climate change, and the broader environment), and (iii) a socioeconomic impact. The debate has been controversial because it has largely been driven by politics, ethical/moral considerations, and vested interests rather than by science. The paper focuses on food prices, land competition, GHG, energy balance, and energy subsidies and concerns with the rapid expansion of bioenergy for electricity and heat, climatic changes, the role of agriculture as a key factor, the potential of biomass energy resources, and the various alternatives to minimize or avoid conflict between food and fuel production. Biomass for energy is both “part of the problem and part of the solution.” It proposes a holistic approach: a new paradigm that takes full account of the diverse and complex nature of biomass energy sources and states that the fundamental underlying causes are social injustice, inequality, waste, and so forth, rather than land competition for food and fuel.
    Print ISSN: 2090-7451
    Electronic ISSN: 2090-746X
    Topics: Energy, Environment Protection, Nuclear Power Engineering
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    Polynomials in Control Theory Parametrized by Their Roots (2012)
    Hindawi
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    Publication Date: 2012-12-25
    Description: The aim of this paper is to introduce the space of roots to study the topological properties of the spaces of polynomials. Instead of identifying a monic complex polynomial with the vector of its coefficients, we identify it with the set of its roots. Viète's map gives a homeomorphism between the space of roots and the space of coefficients and it gives an explicit formula to relate both spaces. Using this viewpoint we establish that the space of monic (Schur or Hurwitz) aperiodic polynomials is contractible. Additionally we obtain a Boundary Theorem.
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    Benzothiazine Dyes/2,4,6-Tris(trichloromethyl)-1,3,5-triazine as a New Visible Two-Component Photoinitiator System (2012)
    Hindawi
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    Publication Date: 2012-12-25
    Description: Novel photoinitiator systems working under visible radiation were studied. The photoredox pair constructed with dye derivatives of 12H-quinoxalino-[2,3-b][1,4]-benzothiazine (1–3) and 2,4,6-tris(trichloromethyl)-1,3,5-triazine (Tz) were found to be effective initiators for free radical polymerization of trimethylolpropane triacrylate (TMPTA) using VIS light. Photosensitization occurred through electron transfer, which was confirmed by the observation of a radical cation of the studied dyes. The 1•+ was also characterized in cryogenic matrices (mixture of CH2Cl2 and ionic liquid: 1-butyl-3-methylimidazolium hexafluorophosphate ( −)) and its reactivity was investigated by means of pulse radiolysis in solution at room temperature. In a halogenated solvent and in a mixture of CH2Cl2 and  −, the radical cation 1•+ underwent deprotonation to form a neutral radical 1•, which was stable in the second time scale. During photolysis of the 1/Tz photoredox pair in 1-methyl-2-pyrrolidone and monomer, the formation of a neutral radical 1• was not observed.
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    Topics: Electrical Engineering, Measurement and Control Technology , Energy, Environment Protection, Nuclear Power Engineering
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    A Tikhonov-Type Regularization Method for Identifying the Unknown Source in the Modified Helmholtz Equation (2012)
    Hindawi
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    Publication Date: 2012-12-25
    Description: An inverse source problem in the modified Helmholtz equation is considered. We give a Tikhonov-type regularization method and set up a theoretical frame to analyze the convergence of such method. A priori and a posteriori choice rules to find the regularization parameter are given. Numerical tests are presented to illustrate the effectiveness and stability of our proposed method.
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    Improved Polynomial Fuzzy Modeling and Controller with Stability Analysis for Nonlinear Dynamical Systems (2012)
    Hindawi
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    Publication Date: 2012-12-25
    Description: This study presents an improved model and controller for nonlinear plants using polynomial fuzzy model-based (FMB) systems. To minimize mismatch between the polynomial fuzzy model and nonlinear plant, the suitable parameters of membership functions are determined in a systematic way. Defining an appropriate fitness function and utilizing Taylor series expansion, a genetic algorithm (GA) is used to form the shape of membership functions in polynomial forms, which are afterwards used in fuzzy modeling. To validate the model, a controller based on proposed polynomial fuzzy systems is designed and then applied to both original nonlinear plant and fuzzy model for comparison. Additionally, stability analysis for the proposed polynomial FMB control system is investigated employing Lyapunov theory and a sum of squares (SOS) approach. Moreover, the form of the membership functions is considered in stability analysis. The SOS-based stability conditions are attained using SOSTOOLS. Simulation results are also given to demonstrate the effectiveness of the proposed method.
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