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Edward J. Walsh - One of the best experts on this subject based on the ideXlab platform.
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numerical simulations and observations of surface wave fields under an extreme tropical cyclone
Journal of Physical Oceanography, 2009Co-Authors: Yalin Fan, Isaac Ginis, Tetsu Hara, Wayne C Wright, Edward J. WalshAbstract:Abstract The performance of the wave model WAVEWATCH III under a very strong, category 5, tropical cyclone wind forcing is investigated with different drag coefficient parameterizations and ocean current inputs. The model results are compared with field observations of the surface wave spectra from an airborne scanning radar altimeter, National Data Buoy Center (NDBC) time series, and satellite altimeter measurements in Hurricane Ivan (2004). The results suggest that the model with the original drag coefficient parameterization tends to overestimate the significant wave height and the Dominant Wavelength and produces a wave spectrum with narrower directional spreading. When an improved drag parameterization is introduced and the wave–current interaction is included, the model yields an improved forecast of significant wave height, but underestimates the Dominant Wavelength. When the hurricane moves over a preexisting mesoscale ocean feature, such as the Loop Current in the Gulf of Mexico or a warm- and co...
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numerical simulation of sea surface directional wave spectra under hurricane wind forcing
Journal of Physical Oceanography, 2003Co-Authors: Ilju Moon, Isaac Ginis, C.w. Wright, Hendrik L Tolman, Tetsu Hara, Edward J. WalshAbstract:Numerical simulation of sea surface directional wave spectra under hurricane wind forcing was carried out using a high-resolution wave model. The simulation was run for four days as Hurricane Bonnie (1998) approached the U.S. East Coast. The results are compared with buoy observations and NASA Scanning Radar Altimeter (SRA) data, which were obtained on 24 August 1998 in the open ocean and on 26 August when the storm was approaching the shore. The simulated significant wave height in the open ocean reached 14 m, agreeing well with the SRA and buoy observations. It gradually decreased as the hurricane approached the shore. In the open ocean, the Dominant Wavelength and wave direction in all four quadrants relative to the storm center were simulated very accurately. For the landfall case, however, the simulated Dominant Wavelength displays noticeable overestimation because the wave model cannot properly simulate shoaling processes. Direct comparison of the model and SRA directional spectra in all four quadrants of the hurricane shows excellent agreement in general. In some cases, the model produces smoother spectra with narrower directional spreading than do the observations. The spatial characteristics of the spectra depend on the relative position from the hurricane center, the hurricane translation speed, and bathymetry. Attempts are made to provide simple explanations for the misalignment between local wind and wave directions and for the effect of hurricane translation speed on wave spectra.
C E Grosch - One of the best experts on this subject based on the ideXlab platform.
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large eddy simulation of a coastal ocean under the combined effects of surface heat fluxes and full depth langmuir circulation
Journal of Physical Oceanography, 2016Co-Authors: Rachel Walker, Andres E Tejadamartinez, C E GroschAbstract:AbstractResults are presented from the large-eddy simulations (LES) of a wind-driven flow representative of the shallow coastal ocean under the influences of Langmuir forcing and surface heating and cooling fluxes. Langmuir (wind and surface gravity wave) forcing leads to the generation of Langmuir turbulence consisting of a wide range of Langmuir circulations (LCs) or parallel, counterrotating vortices that are aligned roughly in the direction of the wind. In unstratified, shallow coastal regions, the largest of the LCs reach the bottom of the water column. Full-depth LCs are investigated under surface waves with a significant wave height of 1.2 m and a Dominant Wavelength of 90 m and wave period of 8 s, for a wind speed of 7.8 m s−1 in a 15-m-deep coastal shelf region. Both unstable and stable stratification are imposed by constant surface heat fluxes and an adiabatic bottom wall. Simulations are characterized by Rayleigh and Richardson numbers representative of surface buoyancy forcing relative to wind...
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surface dynamics in les of full depth langmuir circulation in shallow water
Physica Scripta, 2013Co-Authors: Andres E Tejadamartinez, C E Grosch, Nityanand Sinha, Cigdem Akan, Guillaume MartinatAbstract:Large-eddy simulations (LES) of wind-driven shallow water flows with and without full-depth Langmuir circulation (LC) are described and near-surface dynamics analyzed. LC consists of parallel counter-rotating vortices or cells that are aligned roughly in the direction of the wind and are generated by the interaction of the wind-driven shear with the Stokes drift velocity induced by surface gravity waves. Simulations do not resolve surface waves; thus the top of the domain is taken as a non-deforming, free-slip, wind shear-driven surface. In the absence of resolved surface waves, the LC-generating mechanism is parameterized via the well-known Craik?Leibovich vortex force?(Craik and Leibovich 1976 J Fluid Mech. 73 401?26) appearing in the momentum equation. LES guided by the full-depth LC field measurements of?Gargett and Wells (2007 J Fluid Mech. 576 27?61) shows that this large-scale, downwind-elongated structure changes surface log-layer dynamics in terms of mean downwind velocity and budgets of turbulent kinetic energy (TKE). For example, in terms of mean velocity, the mixing due to LC leads to a deviation from the classical surface log-law profile that is exhibited by wind-driven flow without LC. Furthermore, LC leads to a deviation from the classical balance between production and dissipation rates of TKE in the log-layer. Two key parameters controlling the extent of surface log-layer disruption caused by LC are the Dominant Wavelength (?) of the surface waves generating LC and the turbulent Langmuir number, Lat, which is inversely proportional to wave forcing relative to wind forcing.
Klaus Lunau - One of the best experts on this subject based on the ideXlab platform.
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Spectral purity, intensity and Dominant Wavelength: Disparate colour preferences of two Brazilian stingless bee species.
PloS one, 2018Co-Authors: Sebastian Koethe, Sarah Banysch, Isabel Alves-dos-santos, Klaus LunauAbstract:Bees use floral colour as a major long distance orientation cue. While it is known for bumblebees and honeybees that Dominant Wavelength (≙ colour hue), colour contrast and spectral purity (≙ saturation) are crucial for flower detection and discrimination, only little is known about colour preferences in stingless bees (Meliponini). In this experiment freely flying workers of two Brazilian species of stingless bees-Partamona helleri and Melipona bicolor-were tested for colour preferences concerning the colour parameters Dominant Wavelength, spectral purity and intensity (≙ brightness). Each individual bee had to perform 57 tests, in which a definite series of dual choices between colour stimuli varying in intensity, spectral purity or Dominant Wavelength were presented. The results show that P. helleri chose colours of higher spectral purity and preferred bluish colours, while M. bicolor made generalized colour choices. Intensity did not influence the colour choice of any bee species. The results of P. helleri are consistent with findings for honeybees and bumblebees, while colour preferences in M. bicolor seem to be absent.
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colour is more than hue preferences for compiled colour traits in the stingless bees melipona mondury and m quadrifasciata
Journal of Comparative Physiology A-neuroethology Sensory Neural and Behavioral Physiology, 2016Co-Authors: Sebastian Koethe, Jessica Bossems, Adrian G Dyer, Klaus LunauAbstract:The colour vision of bees has been extensively analysed in honeybees and bumblebees, but few studies consider the visual perception of stingless bees (Meliponini). In a five-stage experiment the preference for colour intensity and purity, and the preference for the Dominant Wavelength were tested by presenting four colour stimuli in each test to freely flying experienced workers of two stingless bee species, Melipona mondury and Melipona quadrifasciata. The results with bee-blue, bee-UV-blue and bee-green colours offered in four combinations of varying colour intensity and purity suggest a complex interaction between these colour traits for the determination of colour choice. Specifically, M. mondury preferred bee-UV-blue colours over bee-green, bee-blue and bee-blue-green colours while M. quadrifasciata preferred bee-green colour stimuli. Moreover in M. mondury the preferences were different if the background colour was changed from grey to green. There was a significant difference between species where M. mondury preferred UV-reflecting over UV-absorbing bee-blue-green colour stimuli, whereas M. quadrifasciata showed an opposite preference. The different colour preferences of the free flying bees in identical conditions may be caused by the bees' experience with natural flowers precedent to the choice tests, suggesting reward partitioning between species.
Rongjun Xie - One of the best experts on this subject based on the ideXlab platform.
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synthesis and photoluminescent properties of la ca 3si6n11 ce3 fine powder phosphors for solid state lighting
ACS Applied Materials & Interfaces, 2011Co-Authors: Takayuki Suehiro, Naoto Hirosaki, Rongjun XieAbstract:We have developed a new Ce3+-activated nitride phosphor, (La,Ca)3Si6N11:Ce3+, using the gas-reduction−nitridation method. The synthesized (La,Ca)3Si6N11:Ce3+ possesses tunable yellow broadband emission with the Dominant Wavelength of 577−581 nm and the external quantum efficiency up to ∼42%, under an excitation of 450 nm. Precise steady-state and time-resolved photoluminescence analyses revealed that the only one type of Ce3+ center is active under the blue-light excitation. By combining the synthesized (La,Ca)3Si6N11:Ce3+ phosphors with the 450-nm InGaN chip, a broad range of white light with the correlated color temperatures of ∼2600−3800 K can be created, demonstrating their promising applicability to the warm-white light-emitting diodes.
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blue emitting lasi3n5 ce3 fine powder phosphor for uv converting white light emitting diodes
Applied Physics Letters, 2009Co-Authors: Takayuki Suehiro, Naoto Hirosaki, Rongjun Xie, Tsugio SatoAbstract:We have synthesized the pure ternary nitride phosphor, LaSi3N5:Ce3+ from the multicomponent oxide system La2O3–CeO2–SiO2, by using the gas-reduction-nitridation method. Highly pure, single-phase LaSi3N5:Ce3+ powders possessing particle sizes of ∼0.4–0.6 μm were obtained with the processing temperature ≤1500 °C. The synthesized LaSi3N5:Ce3+ exhibits tunable blue broadband emission with the Dominant Wavelength of 464–475 nm and the external quantum efficiency of ∼34%–67% under excitation of 355–380 nm. A high thermal stability of LaSi3N5:Ce3+ compared to the existing La–Si–O–N hosts was demonstrated, indicating the promising applicability as a blue-emitting phosphor for UV-converting white light-emitting diodes.
Takayuki Suehiro - One of the best experts on this subject based on the ideXlab platform.
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synthesis and photoluminescent properties of la ca 3si6n11 ce3 fine powder phosphors for solid state lighting
ACS Applied Materials & Interfaces, 2011Co-Authors: Takayuki Suehiro, Naoto Hirosaki, Rongjun XieAbstract:We have developed a new Ce3+-activated nitride phosphor, (La,Ca)3Si6N11:Ce3+, using the gas-reduction−nitridation method. The synthesized (La,Ca)3Si6N11:Ce3+ possesses tunable yellow broadband emission with the Dominant Wavelength of 577−581 nm and the external quantum efficiency up to ∼42%, under an excitation of 450 nm. Precise steady-state and time-resolved photoluminescence analyses revealed that the only one type of Ce3+ center is active under the blue-light excitation. By combining the synthesized (La,Ca)3Si6N11:Ce3+ phosphors with the 450-nm InGaN chip, a broad range of white light with the correlated color temperatures of ∼2600−3800 K can be created, demonstrating their promising applicability to the warm-white light-emitting diodes.
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blue emitting lasi3n5 ce3 fine powder phosphor for uv converting white light emitting diodes
Applied Physics Letters, 2009Co-Authors: Takayuki Suehiro, Naoto Hirosaki, Rongjun Xie, Tsugio SatoAbstract:We have synthesized the pure ternary nitride phosphor, LaSi3N5:Ce3+ from the multicomponent oxide system La2O3–CeO2–SiO2, by using the gas-reduction-nitridation method. Highly pure, single-phase LaSi3N5:Ce3+ powders possessing particle sizes of ∼0.4–0.6 μm were obtained with the processing temperature ≤1500 °C. The synthesized LaSi3N5:Ce3+ exhibits tunable blue broadband emission with the Dominant Wavelength of 464–475 nm and the external quantum efficiency of ∼34%–67% under excitation of 355–380 nm. A high thermal stability of LaSi3N5:Ce3+ compared to the existing La–Si–O–N hosts was demonstrated, indicating the promising applicability as a blue-emitting phosphor for UV-converting white light-emitting diodes.