中国北方大气湍流中微波传播闪烁问题研究

从分析影响微波段大气折射率结构常数的因素人手,考虑了温度和相对湿度对这一波段大气折射率结构常数的影响,建立了我国北方地区微波段大气折射率结构常数C2n模型,并以此模型为基础分析和推导了K-Ka波段的平面波在湍流大气中水平和斜程传输时的闪烁指数.研究表明:温度和相对湿度对微波段大气折射率结构常数有一定的影响,但湿度影响相对较小;同时在其它条件不变的情况下,和光波段一样,湍流的内尺度、传播高度、路径天顶角对微波段闪烁指数均有一定的影响.     

一种MODIS遥感图像大气校正的快速算法

本文设计了基于大气辐射传输模型对MODIS遥感图像进行大气校正的一种新的快速算法。根据Kaufman气溶胶光学厚度反演方法的基本原理,建立了简化的气溶胶光学厚度反演模型,通过6S模型获取气溶胶光学厚度参数,利用经验公式计算大气反射率及大气透过率等参数,实现了MODIS遥感图像的快速大气校正。     

Mie散射理论测量粒子系复折射率的透射方法

粒子的光学常数并不等同于构成粒子材料的光学常数,而通过粒子光谱复折射率数据,研究粒子及聚集粒子系的辐射特性,不仅对辐射物性的研究具有较高的理论意义,而且具有广泛的实际应用价值。粒子的复折射率不能直接通过实验测量(没有直接测量的仪器),须由实验测定其他量,然后结合相应的理论模型反求,属反问题研究。用简化的Mie散射理论及Kramers-Kronig关系式,利用傅里叶红外光谱仪对Al2O3粒子及煤灰粒子进行透射率实验测量,结合相应的理论模型,反演Al2O3粒子及煤灰粒子的复折射率。并对透射率实验误差对反演结果的影响进行了分析。     

Extrapolating wind speed time series vs. Weibull distribution to assess wind resource to the turbine hub height: A case study on coastal location in Southern Italy

Increasing knowledge on wind shear models to strengthen their reliability appears as a crucial issue, markedly for energy investors to accurately predict the average wind speed at different turbine hub heights, and thus the expected wind energy output. This is particularly helpful during the feasibility study to abate the costs of a wind power project, thus avoiding installation of tall towers, or even more expensive devices such as LIDAR or SODAR.The power law (PL) was found to provide the finest representation of wind speed profiles and is hence the focus of the present study. Besides commonly used for vertical extrapolation of wind speed time series, the PL relationship between “instantaneous” wind profiles was demonstrated by Justus and Mikhail to be consistent with the height variation of Weibull distribution. Therefore, in this work a comparison is performed between these two different PL–based extrapolation approaches to assess wind resource to the turbine hub height: (i) extrapolation of wind speed time series, and (ii) extrapolation of Weibull wind speed distribution. The models developed by Smedman–Högström and Högström (SH), and Panofsky and Dutton (PD) were used to approach (i), while those from Justus and Mikhail (JM) and Spera and Richards (SR) to approach (ii). Models skill in estimating wind shear coefficient was also assessed and compared.PL extrapolation models have been tested over a flat and rough location in Apulia region (Southern Italy), where the role played by atmospheric stability and surface roughness, along with their variability with time and wind characteristics, has been also investigated. A 3-year (1998–2000) 1–h dataset, including wind measurements at 10 and 50 m, has been used. Based on 10–m wind speed observations, the computation of 50–m extrapolated wind resource, Weibull distribution and energy yield has been made. This work is aimed at proceeding the research issue addressed within a previous study, where PL extrapolation models were tested and compared in extrapolating wind resource and energy yield from 10 to 100 m over a complex–topography and smooth coastal site in Tuscany region (Central Italy). As a result, wind speed time series extrapolating models proved to be the most skilful, particularly PD, based on the similarity theory and thus addressing all stability conditions. However, comparable results are returned by the empirical JM Weibull distribution extrapolating model, which indeed proved to be preferable as being: (i) far easier to be used, as z₀–, stability–, and wind speed time series independent; (ii) more conservative, as wind energy is underpredicted rather than overpredicted.     

Influence of atmospheric pressure plasma jet on the structure of microcrystalline starch with different relative crystallinity

This study demonstrated the effect on microcrystalline starch (MS) with different relative crystallinity (RC) by atmospheric pressure plasma jet (APPJ) treatment for 1, 3, 5 or 7 min. The morphology of MS granules was destroyed according to Scanning electron microscopy (SEM) analysis. APPJ treatment did not change the crystalline type of MS, but obviously decreased the RC of MS. Short-range molecular order of MS was clearly decreased after APPJ treatment though the Fourier transform infrared (FTIR) and Raman spectroscopy. Notably, the effect of APPJ on crystalline and short-range order structure of MS was gradually increased with the increase of RC, which revealed that the crystalline region of MS might be destroyed by APPJ. Furthermore, the pH of MS was decreased while water binding capacity (WBC) and swelling volume (SV) of MS were increased. Therefore, the APPJ treatment could be used as an alternative physical technology for starch modification.     

Discharge characteristic of nanosecond-pulse DBD in atmospheric air using magnetic compression pulsed power generator

Dielectric barrier discharge driven by repetitive nanosecond pulses can offer highly efficient non-thermal plasma at atmospheric pressure and is widely used for plasma applications. In this paper, the discharge is generated using a compact pulsed power generator based on one-stage magnetic compression. The output pulse can be up to 30 kV with a rise time of about 40 ns and a full width at half maximum of 70 ns. The electrical characteristics of the discharge parameters are studied by the measurement of voltage and current waveforms. The effects of applied voltage amplitude, voltage polarity, pulse repetition frequency, and barrier dielectric on discharge characteristics are investigated, respectively. The experimental results show that the discharge current, discharge power and electron density increase with the increase of the applied voltage, and the pulse repetition frequency has a slight effect on the electrical parameters. Moreover, the discharge current is influenced by the dielectric barrier, but it is not varied with the polarity of applied pulses.     

Characterization by Stm and Electrical Conductivity of Single-Walled Carbon Nanotubes

Abstract

Single-walled carbon nanotubes (SWCNT) prepared by a DC-Arc-Discharge and purified by a hydrothermal treatment followed by several steps of procedures including heating, burning, extracting and acid-washing are investigated by a conventional STM technique morphologically and spectroscopically. The electical resistivities of compacted pellets (mats) of SWCNT are measured as a function of temperature in the range from the room-temperature to 1.5K. The behaviors seems to be essentially originated in the metallic nature of individual SWCNT.     

Bi-modal trend in the long-term corrosion of aluminium alloys

A wide range of literature data including in situ immersion, tidal, coastal atmospheric and industrial exposures is used to show that the trend for longer term corrosion of aluminium alloys is nearly always more consistent with a bi-modal model than with the classical power-law function. It is proposed the bi-modal characteristic results from the accumulation of corrosion products causing localised anoxic conditions. These permit a change from predominantly cathodic oxygen reduction to hydrogen ion reduction under anoxic autocatalytic conditions within pits. This mechanism is consistent with established theory for pitting corrosion in aluminium.     

PMetro: Measurement of urban aerosols on a mobile platform

PMetro is an innovative time/space resolved urban aerosol monitoring and data management system. The core of the monitoring system is a customized optical particle counter (OPC) integrated on a cabin of the metro urban transport system in Perugia (Central Italy). This peculiar arrangement and setup allow regular, real-time measurement of aerosol particles on a well defined path through the city all over the day. The performances of the prototype OPC system have been customized and finally inter-compared with those of similar commercial devices placed at fixed points along the metro line. Data from the mobile system are integrated with environmental measurements from fixed monitoring stations along the metro path in order to attain models of the evolution of urban aerosol pollutants.     

Measurement and optimization of atmospheric plasma sprayed CoMoCrSi coatings parameters on Ti-6Al-4V substrates affecting microstructural and properties using hybrid abductor induction mechanism

A hybrid artificial intelligence method (AIM) is used to optimize the atmospheric plasma spraying (APS) processing parameters for CoMoCrSi coatings deposited on Ti-6Al-4V substrates. In the proposed approach, the Taguchi design method is used to obtain an initial solution for the optimal set of APS parameters. The true optimal values of the spray distance, chamber pressure, current, argon gas flow rate and hydrogen gas flow rate are then obtained using an artificial neural network (ANN) and genetic algorithm (GA). The coatings deposited using the processing parameters determined using the Taguchi design method alone have a porosity of 8.5%. However, following the ANN/GA optimization procedure, the porosity reduces to just 5.6%. The XRD analysis results show that the as-sprayed coatings contain Cr₃Si phase as a result of the high-temperature plasma flame. In addition, it is shown that the structure of the Ti phase in the coating transforms from a α-Ti crystal structure (i.e., HCP) to a β-Ti crystal structure (i.e., BCC) during thermal treatment at temperatures to 1200 °C. Finally, it is shown that the hardness of the annealed coatings increases with both an increasing annealing time and an increasing annealing temperature. The higher hardness under higher temperature conditions is attributed to the precipitation of Cr₃Si phase. Overall, the coatings obtained in the present study using the optimal spray-coating parameters have a low porosity, a high hardness and a good thermal stability at high temperatures.