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As the surface conditions play a significant role on corona discharge and its related effects of the conductors,the influence of fine particulate matter on positive-polarity,direct-current conductors was studied experimentally in ...
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As the surface conditions play a significant role on corona discharge and its related effects of the conductors,the influence of fine particulate matter on positive-polarity,direct-current conductors was studied experimentally in this study.The surface morphologies of the conductor could be discovered from the experiments.The typical morphologies are the parallel chains of particles.To evaluate the surface condition quantitively,the surface roughness of the conductors is measured.It is found that the applied voltage and testing time have a great influence on the surface condition.After that,the corona characteristics of conductors are tested.It reveals that the total ground level electric field and ion flow density increases with the surface roughness growing.
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After having analyzed the requirement on the aerodynamic earth's surface roughness in two-dimensional distribution in the research field of interaction between land surface and atmosphere, this paper presents a new way to calculat...
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After having analyzed the requirement on the aerodynamic earth's surface roughness in two-dimensional distribution in the research field of interaction between land surface and atmosphere, this paper presents a new way to calculate the aerodynamic roughness using the earth's surface geometric roughness retrieved from SAR (Synthetic Aperture Radar) and TM thermal infrared image data. On the one hand, the SPM (Small Perturbation Model) was used as a theoretical SAR backscattering model to describe the relationship between the SAR backscattering coefficient and the earth's surface geometric roughness and its dielectric constant retrieved from the physical model between the soil thermal inertia and the soil surface moisture with the simultaneous TM thermal infrared image data and the ground microclimate data. On the basis of the SAR image matching with the TM image, the non-volume scattering surface geometric information was obtained from the SPM model at the TM image pixel scale, and the ground pixel surface's equivalent geometric roughness-height standard RMS (Root Mean Square) was achieved from the geometric information by the transformation of the typical topographic factors. The vegetation (wheat, tree) height retrieved from spectrum model was also transferred into its equivalent geometric roughness. A completely two-dimensional distribution map of the equivalent geometric roughness over the experimental area was produced by the data mosaic technique. On the other hand, according to the atmospheric eddy currents theory, the aerodynamic surface roughness was iterated out with the atmosphere stability correction method using the wind and the temperature profiles data measured at several typical fields such as bare soil field and vegetation field. After having analyzed the effect of surface equivalent geometric roughness together with dynamic and thermodynamic factors on the aerodynamic surface roughness within the working area, this paper first establishes a scale transformation model to calculate the aerodynamic surface roughness from surface equivalent geometric roughness. The final result retrieved from above series of models was validated using the filed measurements. It is concluded that the proposed approach is operational and feasible to derive the aerodynamic surface roughness at the pixel scale from a combination of the SAR and TM images.
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The observed surface wind speed(SWS)has declined across China over the last four decades,but the mechanisms responsible for this decline have been explored without reaching a consensus.In this study,we develop a physical method to...
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The observed surface wind speed(SWS)has declined across China over the last four decades,but the mechanisms responsible for this decline have been explored without reaching a consensus.In this study,we develop a physical method to quantify and adjust for the impact of urbanization around weather stations on the observed SWS over China from 1985 to 2017.The urbanization impact factor on the SWS is calculated based on Monin-Obukhov similarity theory,and the aerodynamic roughness length and zero-plane displacement height at each weather station are calculated yearly based on a 30-meter resolution satellite land cover product.The results show that urbanization around weather stations reduces the observed SWS by 11%on average over China.The urbanization impact on the observed SWS is the highest in southeastern China at 19%and the lowest over the Tibetan Plateau at 4%.Urbanization decreases the observed SWS by 9%over northwestern China and by 12%over northeastern China,northern China and southern China.More importantly,the proposed method can easily adjust for the urbanization impact on the observed SWS.After adjustment,the SWS appears to have started recovering during the 1990s,and the decreasing trend of SWS during the study period is nearly zero.The results shown here indicate that the observed decreasing trend of SWS from 1985 to 2017 over China is an observational local bias and does not reflect large-scale climatic variation.This inference is also consistent with geostrophic wind theory predictions;i.e.,SWS exhibits strong decadal variability,but its long-term trend is negligible.
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A general four-layer structure linear theory for predicting the effects of arbitrarilydistributed roughness change on the variations of wind speed and shear stress in the surfacelayer of3D and2D atmospheres was presented.The resul...
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A general four-layer structure linear theory for predicting the effects of arbitrarilydistributed roughness change on the variations of wind speed and shear stress in the surfacelayer of3D and2D atmospheres was presented.The results derived by the theory wereagreeable to the previous ones.
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As a Gaussian beam is incident upon a rough surface at low grazing angle, the Helmholts scalar wave equation may be replaced by the parabolic approximate equation. As the incident field is known, the scattered field and surface cu...
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As a Gaussian beam is incident upon a rough surface at low grazing angle, the Helmholts scalar wave equation may be replaced by the parabolic approximate equation. As the incident field is known, the scattered field and surface current give the Volterra integral equation.Surface roughness profile can be formulated by the integral equation of the surface currents. These two coupled equations are applied to invert the roughness profile of heterogeneous fractal surface.Using Monte Carlo method, the fractal rough surfaces with a band-limited Weistrass-Manderbrot function are numerically simulated and the scattered fields along a line parallel to the mean surface are solved. The Gaussian beam incidence and scattered fields are used to progressively invert the surface roughness profile. Reconstructed profile and its inverted fractal dimension,roughness variance and correlation length are well matched with the simulated surfaces.
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Three types of rough surface were processed by laser irradiation on the 3Cr2W8V material hot-work die steel surface.The wear experiments with smooth surface and rough surface samples were repeated on the pin-tray wear machine. Acc...
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Three types of rough surface were processed by laser irradiation on the 3Cr2W8V material hot-work die steel surface.The wear experiments with smooth surface and rough surface samples were repeated on the pin-tray wear machine. According to the wear results, we studied the regularity of wear resistance of different rough surface samples. The results indicated that bionic rough surface can improve the wear resistance of the material and the wear resistance can be increased 1 -2times, compared with the smooth surface. Also, the wear resistance of the rough surface was affected by laser current and duration of impulse. The bigger the laser current or the impulse duration, the better is the wear resistance. When the distance between the same kind of units which are distributed on the surfaces is changed, the wear resistance changes. The wear resistance of a bionic rough surface on which the grid units were distributed at spacing of 1 mm was the best. And we designed the wear models.
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The effect of microscale contact of rough surfaces on the adhesion and friction under negative normal forces was experimentally investigated. The adhesive force of single point contact - sapphire ball to flat polyurethane did not ...
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The effect of microscale contact of rough surfaces on the adhesion and friction under negative normal forces was experimentally investigated. The adhesive force of single point contact - sapphire ball to flat polyurethane did not vary with the normal force. With rough surface contact, which was assumed to be a great number of point contacts, the adhesive force increased logarithmically with the normal force. Under negative normal force adhesive state, the tangential force (more than hundred mN)were much larger than the negative normal force (several mN) and increased with the linear decrease of negative normal force.The results reveal why the gecko's toe must slide slightly on the target surface when it makes contact on a surface and suggest how a biomimetic gecko foot might be designed.
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