The Experts below are selected from a list of 69 Experts worldwide ranked by ideXlab platform
Xiang Zhang - One of the best experts on this subject based on the ideXlab platform.
-
experimental demonstration of in plane Negative Angle refraction with an array of silicon nanoposts
Nano Letters, 2015Co-Authors: Yuan Wang, Zhen Sheng, Shichang Zou, Fuwan Gan, Xiang Zhang, Xi WangAbstract:Controlling an optical beam is fundamental in optics. Recently, unique manipulation of optical wavefronts has been successfully demonstrated by metasurfaces. However, these artificially engineered nanostructures have thus far been limited to operate on light beams propagating out-of-plane. The in-plane operation is critical for on-chip photonic applications. Here, we demonstrate an anomalous Negative-Angle refraction of a light beam propagating along the plane, by designing a thin dielectric array of silicon nanoposts. The circularly polarized dipoles induced by the high-permittivity nanoposts at the scattering resonance significantly shape the wavefront of the light beam and bend it anomalously. The unique capability of a thin line of the nanoposts for manipulating in-plane wavefronts makes the device extremely compact. The low loss all-dielectric structure is compatible with complementary metal-oxide semiconductor technologies, offering an effective solution for in-plane beam steering and routing for on...
-
optical Negative refraction by four wave mixing in thin metallic nanostructures
Nature Materials, 2012Co-Authors: Stefano Palomba, Xiang Zhang, Shuang Zhang, Yongshik Park, Guy Bartal, Xiaobo YinAbstract:the newly generated frequency emerges at a Negative Angle relative to the exciting wave. The ratio between the sines of the incidence and nonlinearly refracted Angles remains a Negative constant and depends only on the wavelength ratio, which therefore rigorously fulfils Snell’s law, extending the phenomenon of Negative refraction into the nonlinear regime. Furthermore, we use a metamaterial constructed from Au=SiO2=Au nanodisk structures to enhance the nonlinear efficiency by means of localized plasmon resonance 23 . The enhanced nonlinearity gives rise to excellent efficiency in spite of the ultra-small thickness of the nonlinear film, enabling for the first time the realization of optical nonlinear Negative refraction, which cannot be obtained in bulk dielectrics because of strict phasematchingconditions.Wefurtherobservedthatthisnonlinear Negative refraction can be realized with evanescent waves. The
Broadhurst, Matt K. - One of the best experts on this subject based on the ideXlab platform.
-
Effects of knot orientation on the height and drag of a penaeid trawl
'Elsevier BV', 2017Co-Authors: Broadhurst, Matt K., Sterling, David J., Balash Cheslav, Miller, Russell B., Matsubara ShinsukeAbstract:The knots used to make fishing nets are asymmetric which, in most cases for trawls, means they present either a positive or Negative Angle of attack (AOA) in horizontal panels, producing hydrodynamic side forces and changes in system geometry. The extent of associated displacement and drag were quantified in a flume tank using four, full-scale penaeid (shrimp/prawn) trawls with the same generic design, but with all possible combinations of knot orientation in the top and bottom panels. All four trawls had the same distance between the footrope and flume-tank floor at the wing end during a flow of 1.2 ms−1, but the trawl with both panels at a positive AOA had a significantly greater footrope height at the centre (by up to 13 mm). Further, compared to both trawls with their top panels orientated to have a positive AOA, the two with their top panels producing a Negative AOA had up to 27% lower headlines and 10% less total drag. Differences were also observed among vertically partitioned drag at the wing ends—depending on knot orientation in the bottom panel, which led to greater force on the headline or footrope when at Negative or positive AOAs, respectively. The magnitudes of observed variations in footrope and headline heights and drag are likely to affect the catching and engineering performances of penaeid trawls, and so knot orientation should be considered during attempts at improving selectivity and reducing drag. The results also reiterate a need for consistency among knot orientations to avoid confounding effects during fishery-dependant/independent surveys. © 2016 Elsevier B.V
-
Confounding effects of knot orientation in penaeid trawls
'Elsevier BV', 2016Co-Authors: Broadhurst, Matt K., Sterling, David J., Millar, Russell B.Abstract:This study assessed the potential for confounding engineering and/or catching effects due to different knot ('sheet bend') orientations (and therefore positive or Negative hydrodynamic lift) in the principal horizontal panels of a penaeid trawl. During 24 paired comparisons, orientating all meshes in the top and bottom belly panels of a trawl to produce a Negative Angle of attack (AOA) for all knots resulted in greater wing-end spread, and lower catches of school prawns, Metapenaeus macleayi per hectre trawled (means reduced by up to 26%) and three key species of schooling fish (by up to 67%), but more debris (4×) than when the meshes were orientated to produce a positive AOA. By comparison, catches of two other benthic fish remained unaffected by knot orientation. These catch differences were attributed to the Negative-AOA trawl potentially assuming a considerably lower position in the water column (and species-specific orientations). The results demonstrate that it is essential to maintain consistency in knot orientation in penaeid trawls when testing gear modifications and/or during fishery-dependent or -independent surveys
Millar, Russell B. - One of the best experts on this subject based on the ideXlab platform.
-
Confounding effects of knot orientation in penaeid trawls
'Elsevier BV', 2016Co-Authors: Broadhurst, Matt K., Sterling, David J., Millar, Russell B.Abstract:This study assessed the potential for confounding engineering and/or catching effects due to different knot ('sheet bend') orientations (and therefore positive or Negative hydrodynamic lift) in the principal horizontal panels of a penaeid trawl. During 24 paired comparisons, orientating all meshes in the top and bottom belly panels of a trawl to produce a Negative Angle of attack (AOA) for all knots resulted in greater wing-end spread, and lower catches of school prawns, Metapenaeus macleayi per hectre trawled (means reduced by up to 26%) and three key species of schooling fish (by up to 67%), but more debris (4×) than when the meshes were orientated to produce a positive AOA. By comparison, catches of two other benthic fish remained unaffected by knot orientation. These catch differences were attributed to the Negative-AOA trawl potentially assuming a considerably lower position in the water column (and species-specific orientations). The results demonstrate that it is essential to maintain consistency in knot orientation in penaeid trawls when testing gear modifications and/or during fishery-dependent or -independent surveys
Paul Eglin - One of the best experts on this subject based on the ideXlab platform.
-
breakdown of aerodynamic interactions for the lateral rotors on a compound helicopter
Aerospace Science and Technology, 2020Co-Authors: T C A Stokkermans, L L M Veldhuis, Bambang Soemarwoto, Raphael Fukari, Paul EglinAbstract:Abstract Auxiliary lift and/or thrust on a compound helicopter can introduce complex aerodynamic interactions between the auxiliary lift and thrust components and the main rotor. In this study high-fidelity computational fluid dynamics analyses were performed to capture the various aerodynamic interactions which are occurring for the Airbus RACER compound helicopter, featuring a box-wing design for auxiliary lift in cruise and wingtip-mounted lateral rotors in pusher configuration for auxiliary thrust in cruise and counter-torque in hover. Although the study was limited to a specific geometry, the effects and phenomena are expected to be to some extent applicable in general for compound helicopters and wingtip-mounted rotors in pusher configuration. A quantitative indication of the aerodynamic interaction effects could be established by leaving away different airframe components in the simulations. The downwash of the main rotor was found to cause a small Negative Angle of attack in cruise for the wings and lateral rotors and impinged directly on the lateral rotors in hover, resulting in moderate to very significant sinusoidally varying blade loading. The wing increased lateral rotor propulsive efficiency in cruise through its wingtip rotational flowfield and to a lesser extent through its wake. An upstream effect of the lateral rotors on the wing loading was also found. In hover the wing caused a net increase in left lateral rotor thrust as the deflection of the main rotor flow towards the rotor resulted in a local thrust decrease and the low momentum inflow to the rotor from the wake of the wing resulted in a local thrust increase. A small thrust decrease for the right lateral rotor was found due to the wing disturbing its slipstream as this rotor produced reversed thrust. In general, very significant aerodynamic interaction effects can be expected when a main rotor, lateral rotors and wing are in proximity to each other.
Eglin Paul - One of the best experts on this subject based on the ideXlab platform.
-
Breakdown of aerodynamic interactions for the lateral rotors on a compound helicopter
'Elsevier BV', 2020Co-Authors: Stokkermans T.c.a., Veldhuis L.l.m., Soemarwoto Bambang, Fukari Raphaël, Eglin PaulAbstract:Auxiliary lift and/or thrust on a compound helicopter can introduce complex aerodynamic interactions between the auxiliary lift and thrust components and the main rotor. In this study high-fidelity computational fluid dynamics analyses were performed to capture the various aerodynamic interactions which are occurring for the Airbus RACER compound helicopter, featuring a box-wing design for auxiliary lift in cruise and wingtip-mounted lateral rotors in pusher configuration for auxiliary thrust in cruise and counter-torque in hover. Although the study was limited to a specific geometry, the effects and phenomena are expected to be to some extent applicable in general for compound helicopters and wingtip-mounted rotors in pusher configuration. A quantitative indication of the aerodynamic interaction effects could be established by leaving away different airframe components in the simulations. The downwash of the main rotor was found to cause a small Negative Angle of attack in cruise for the wings and lateral rotors and impinged directly on the lateral rotors in hover, resulting in moderate to very significant sinusoidally varying blade loading. The wing increased lateral rotor propulsive efficiency in cruise through its wingtip rotational flowfield and to a lesser extent through its wake. An upstream effect of the lateral rotors on the wing loading was also found. In hover the wing caused a net increase in left lateral rotor thrust as the deflection of the main rotor flow towards the rotor resulted in a local thrust decrease and the low momentum inflow to the rotor from the wake of the wing resulted in a local thrust increase. A small thrust decrease for the right lateral rotor was found due to the wing disturbing its slipstream as this rotor produced reversed thrust. In general, very significant aerodynamic interaction effects can be expected when a main rotor, lateral rotors and wing are in proximity to each other.Flight Performance and Propulsio
