The Alignment of the Mean Wind and Stress Vectors in the Unstable Surface Layer   总被引：2，自引：1，他引：1  

M. Bernardes  N. L. Dias 《Boundary-Layer Meteorology》2010,134(1):41-59

A significant non-alignment between the mean horizontal wind vector and the stress vector was observed for turbulence measurements both above the water surface of a large lake, and over a land surface (soybean crop). Possible causes for this discrepancy such as flow distortion, averaging times and the procedure used for extracting the turbulent fluctuations (low-pass filtering and filter widths etc.), were dismissed after a detailed analysis. Minimum averaging times always less than 30 min were established by calculating ogives, and error bounds for the turbulent stresses were derived with three different approaches, based on integral time scales (first-crossing and lag-window estimates) and on a bootstrap technique. It was found that the mean absolute value of the angle between the mean wind and stress vectors is highly related to atmospheric stability, with the non-alignment increasing distinctively with increasing instability. Given a coordinate rotation that aligns the mean wind with the x direction, this behaviour can be explained by the growth of the relative error of the u–w component with instability. As a result, under more unstable conditions the u–w and the v–w components become of the same order of magnitude, and the local stress vector gives the impression of being non-aligned with the mean wind vector. The relative error of the v–w component is large enough to make it undistinguishable from zero throughout the range of stabilities. Therefore, the standard assumptions of Monin–Obukhov similarity theory hold: it is fair to assume that the v–w stress component is actually zero, and that the non-alignment is a purely statistical effect. An analysis of the dimensionless budgets of the u–w and the v–w components confirms this interpretation, with both shear and buoyant production of u–w decreasing with increasing instability. In the v–w budget, shear production is zero by definition, while buoyancy displays very low-intensity fluctuations around zero. As local free convection is approached, the turbulence becomes effectively axisymetrical, and a practical limit seems to exist beyond which it is not possible to measure the u-w component accurately.  相似文献   

UBV(RI)_C photometry of the open clusters Be 15, Be 80 and NGC 2192     

M. T. Tapia  W. J. Schuster  R. Michel  C. Chavarría-K.    W. S. Dias  R. Vázquez  A. Moitinho 《Monthly notices of the Royal Astronomical Society》2010,401(1):621-632

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The economics of mining seabed manganese nodules: A case study of the Indian Ocean nodule field     

Ranadhir Mukhopadhyay  Sankalp Naik  Shawn De Souza  Ozinta Dias  Sridhar D Iyer  Anil K Ghosh 《Marine Georesources & Geotechnology》2013,31(7):845-851

Abstract

Because of ever-growing demand for strategic metals, the focus of the international community has fallen on deep sea manganese nodules occurring at a water depth of more than 4500?m. We present an economic appraisal and strategy for mining of nodules from the Indian Ocean Nodule Field- one of the four economically potential areas in the world oceans. In contrast to the prevailing perception of non-viability of nodule mining, our analysis indicates a fair degree of economic feasibility and commercial sustainability to mine the deep-sea manganese nodules.  相似文献   

Estimating the Random Error in Eddy-Covariance Based Fluxes and Other Turbulence Statistics: The Filtering Method   总被引：1，自引：1，他引：0  

Scott T. Salesky  Marcelo Chamecki  Nelson L. Dias 《Boundary-Layer Meteorology》2012,144(1):113-135

A spatially local decomposition of turbulent fluxes based on properties of spatial filters is used to develop a new method of estimating random error in turbulent moments of any order. The proposed error estimation method does not require an estimate of the integral time scale, which can be highly sensitive to the method used to calculate it. The error estimation method is validated using synthetic flux data with a known ensemble mean and intercompared with existing methods using data from the Advection Horizontal Array Turbulence Study (AHATS). Typical errors for a 27.3-min block of data collected at a height of 8 m are found to be approximately 10% for the heat flux and 7–15% for variances. The error in the momentum flux increases rapidly with increasing atmospheric instability, reaching values of 40% or greater for unstable conditions. A new method based on filtering is also proposed to estimate integral time scales of turbulent quantities.  相似文献   

Obtaining Potential Virtual Temperature Profiles,Entrainment Fluxes,and Spectra from Mini Unmanned Aerial Vehicle Data     

N. L. Dias  J. E. Gonçalves  L. S. Freire  T. Hasegawa  A. L. Malheiros 《Boundary-Layer Meteorology》2012,145(1):93-111

We present a simple but effective small unmanned aerial vehicle design that is able to make high-resolution temperature and humidity measurements of the atmospheric boundary layer. The air model used is an adapted commercial design, and is able to carry all the instrumentation (barometer, temperature and humidity sensor, and datalogger) required for such measurements. It is fitted with an autopilot that controls the plane’s ascent and descent in a spiral to 1800 m above ground. We describe the results obtained on three different days when the plane, called Aerolemma-3, flew continuously throughout the day. Surface measurements of the sensible virtual heat flux made simultaneously allowed the calculation of all standard convective turbulence scales for the boundary layer, as well as a rigorous test of existing models for the entrainment flux at the top of the boundary layer, and for its growth. A novel approach to calculate the entrainment flux from the top-down, bottom-up model of Wynagaard and Brost is used. We also calculated temperature fluctuations by means of a spectral high-pass filter, and calculated their spectra. Although the time series are small, tapering proved ineffective in this case. The spectra from the untapered series displayed a consistent −5/3 behaviour, and from them it was possible to calculate a dimensionless dissipation function, which exhibited the expected similarity behaviour against boundary-layer bulk stability. The simplicity, ease of use and economy of such small aircraft make us optimistic about their usefulness in boundary-layer research.  相似文献   

Radiation-induced defects in euclase: formation of O<Superscript>−</Superscript> hole and Ti<Superscript>3+</Superscript> electron centers     

Lorena N. Dias  Maurício V. B. Pinheiro  Klaus Krambrock 《Physics and Chemistry of Minerals》2009,36(9):519-525

Irradiation techniques are often applied to gem minerals for color enhancement purposes. Natural green, blue and colorless specimens of rare gemological quality euclase, BeAlSiO₄(OH), from Brazil were irradiated with gamma rays in the dose range from 10 to 500 kGy. Although the colors of the different specimens were not strongly influenced, two different irradiation-induced paramagnetic defect centers were found by electron paramagnetic resonance (EPR). The first one is an O⁻ hole center interacting with one Al neighbor and the second is a Ti³⁺ electron center. The EPR angular rotation patterns of both irradiation-induced defects were measured and analyzed. The results suggest that O⁻ hole centers are formed by dissociation of the hydroxyl ions, similar as in topaz crystals. In euclase the OH⁻ ions interconnect distorted Al octahedra and Be tetrahedra in O₅ positions. During irradiation, the electrons are captured by titanium ions (Ti⁴⁺ + e⁻), leading to the formation of paramagnetic Ti³⁺ ions. From the EPR rotation patterns it is clear that these ions substitute for Al ions. The spin Hamiltonian parameters of the irradiation-induced defects are analyzed and compared to similar defect centers in other mineral specimens. Thermal annealing experiments show that the O⁻ hole centers and Ti³⁺ electron centers are directly connected through the radiation process.  相似文献   

中国、西班牙在莱斯诺德（LANZAROTE）岛的火山与地球动力学合作研究的首期结果     

蔡惟鑫  谭适龄  陈洪飞 《大地测量与地球动力学》1994,(4)

本文介绍中、西双方在西班牙莱斯诺德（ＬＡＮＺＡＲＯＴＥ）火山与地球动力学地下实验室共同进行静力水准仪、水平应变伸缩仪、岩体和空气测温计等仪器的合作研究实验以及分析所得的首批成果。  相似文献   

Factors affecting the productivity of manufacturing sector in Sri Lanka: a spatial analysis     

Sriyani Dias dr. 《GeoJournal》1991,23(2):113-120

Two indexes of productivity — labour productivity and capital productivity — have been employed to measure and map productivity patterns of manufacturing industries in Sri Lanka. There exist extensive regional differences in the levels of productivity. Regression results show that the spatial variation of labour productivity is positively related to capital intensity and the level of urbanization and is negatively related to the nature of enterprises. Capital intensity and level of urbanisation have a negative influence on the capital productivity. The selected five variables in the regression analyses explain 65% of the spatial variation of labour productivity and 39% of capital productivity.  相似文献   

Probabilistic comparative analysis between design rules of a shallow foundation safety     

S. Imanzadeh  D. Breysse  J. Baroth  D. Dias  N. Piegay  S.M. Elachachi 《Georisk: Assessment and Management of Risk for Engineered Systems and Geohazards》2020,14(2):128-141

ABSTRACT

A fact that is generally overlooked in many geotechnical uncertainty analyses is that input data of the model may be correlated. While this correlation may influence the system response, epistemic uncertainties i.e. lack of knowledge of this correlation appears as a risk factor. This paper discusses how a negative correlation between cohesion (c’) and friction angle (Ø’) with their associated uncertainties can influence both the bearing resistance of a shallow strip foundation footing and the estimation of its safety. A probabilistic approach that considers both the negative correlation and the uncertainty is used in this work as a reference. This method is compared to Eurocode 7 variants that do not for the correlation. These variants, resistance and material factoring methods appears to be more or less conservative depending on the negative correlation degree between (c’–Ø), their associated uncertainties and soil configurations. Finally, the proposed probabilistic comparison shows that the material factoring method is more conservative than the resistance one.  相似文献   

Uplift Capacity Prediction of Continuous Helix Piles in Cohesionless Soils Using Cone Penetrometer Tests     

Nait-Rabah  Ouahcène  Medjigbodo  Gildas  Salhi  Lakhdar  Roos  Christophe  Dias  Daniel 《Geotechnical and Geological Engineering》2021,39(7):4933-4946

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