Estimation of the Longitudinal Dispersion Coefficient Using the Velocity Profile in Natural Streams

In this study, a theoretical method for predicting the longitudinal dispersion coefficient is developed based on the transverse velocity distribution in natural streams. Equations of the transverse velocity profile for irregular cross sections of the natural streams are analyzed. Among the velocity profile equations tested in this study, the beta distribution equation, which is a probability density function, is considered to be the most appropriate model for explaining the complex behavior of the transverse velocity structure of irregular natural streams. The new equation for the longitudinal dispersion coefficient that is based on the beta function for the transverse velocity profile is developed. A comparison of the proposed equation with existing equations and the observed longitudinal dispersion coefficient reveals that the proposed equation shows better agreement with the observed data compared to other existing equations.     

Effects of the Source on Wave Propagation in Pile Integrity Testing

One-dimensional stress wave theory is widely used to analyze quantitatively the reflections in low-strain integrity testing of piles. However, a point or disk loading produces body and Rayleigh waves near the pile top. The multireflections of these waves from the lateral surface of a pile are present in the wave field near the pile top. Effects of three-dimensional waves on the near field responses are obvious. These effects can be interpreted erroneously by an inexperienced user as “noises” or “pile anomalies.” To investigate wave propagation in the longitudinal direction, the behavior of the waves in the far field (some distance below the pile top) is studied by theoretical analysis of the longitudinal modes in free cylinders and numerical simulations. The wave pattern at the pile top is analyzed based on the response of an elastic half-space to a harmonic disk loading. The results show that when the ratio of the characteristic length of an impact pulse to the cylinder radius is large enough, the components of Rayleigh waves in the wave field at the pile top are diminished; the waves in the far field behave approximately as plane waves; the responses at positions between 1/2R and 3/4R from the pile axis are less affected by the multireflections. The results from numerical simulations support the practical recommendation to use a ratio of characteristic wavelength to pile radius larger than four. Under this condition, the reflections from the far field (say deeper than two pile diameters) can be analyzed from the responses at receiver positions about 0.6R from the pile axis based on one-dimensional stress wave theory.     

Source–receptor relationships for heavy metals in the European atmosphere

Atmospheric concentrations of heavy metals (HMs), in particular As, Cd, Cu, Pb and Zn, were studied in an effort to contribute to the understanding of European source-receptor relationships. A comparison was made between the ambient concentrations measured at 11 background aerosol monitoring stations (in Denmark, the Czech Republic, Finland, Norway and Sweden) and the corresponding HM concentrations estimated by the Heavy Metals Eulerian Transport (HMET) meteorological dispersion model. The collected samples were analysed with Particle Induced X-ray Emission analysis (PIXE) except the Finnish samples which were analysed with Inductively Coupled Plasma – Mass Spectrometry (ICP-MS). The available data covers the period 1985–1994. The comparison showed that the European emissions of As, Cd and Pb seem to be fairly well estimated. On the other hand, the European Zn emissions are underestimated by a factor of 3 or more, while the Cu emissions appear to be slightly overestimated. The HMET dispersion model also made it possible to select occasions for which the sampling sites had a substantial contribution of HM from the highly polluted “Black Triangle” region (on the borders between the Czech Republic, Poland and Germany). The time evolution of the sources of HMs within this source region could be studied by applying various statistical receptor models on the extensive data set from two Danish stations, Keldsnor and Tange, covering the period 1985–1994. Four source types were clearly discerned throughout the 10 year time period. These sources were: soil dust; sea spray; general combustion and oil combustion. The strong time-dependence observed for the contribution from the Black Triangle region emphasizes the importance of keeping the emission inventories continuously updated if HMs deposition calculations and HMs emissions reduction protocols are to be based on dispersion modelling approaches.     

某待建滨海核电厂厂址年均大气扩散因子计算模式与参数的实验研究

本文在某待建滨海核电厂厂趣现场野外实验基础上提出了计算该核电厂年均大气扩散因子的计算模型。此模型既考虑了向岸流与离岸流的差别,又考虑了混合层与热内边界层,混合释放与扩散参数随陆距变化等因素的综合影响。模型中所需要的各类参数,包括在１９９５,１９９６年间在该厂趣野外大气试验中获取的百米气象铁塔４个不同高度上的风,温逐时三维联合频率;湍流测量结合风洞实验获取的离岸流与向岸流的扩散参数。     

数字电视时代1550光纤传输技术及应用

详细探讨了数字电视时代数字电视联网的需求及比较,结果表明:1 550光纤传输技术结合光色散补偿技术,在数字电视联网应用中有很强的技术和成本等综合竞争优势。对1 550光纤传输技术在数字电视联网应用中出现的问题以及是否需要色散补偿的问题进行了分析,得出1 550光纤传输技术在数字电视联网应用中色散补偿是很有必要的。最后介绍了1 550数模混合传输网络应用设计实例。     

无机填料分散技术在覆铜板制造中的应用

文章通过介绍复合材料中无机填料的分散,填料表面处理,分散设备技术应用等内容,阐述了填料分散技术在覆铜板制造的应用。     

40Gb/s(STM-2 5 6)高速时分复用传输技术前景展望

随着技术的发展 ,4 0 Gb/ s(STM- 2 5 6 )作为 10 Gb/ s(STM- 6 4)传输业务颗粒的后续者 ,开始逐渐为业界熟悉。就 4 0 Gb/ s这一新兴技术的市场推动因素、应用场合以及影响 4 0 Gb/ s传输的一些关键技术作了介绍 ,并对其将来的应用前景作出展望     

单模光纤传输系统的扩容

综述最近几年来在扩大单模光纤传输容量方面的进展,包括密集波分复用,光纤有效截面与色散斜率的优化,第四、第五窗口的应用等;还介绍了几个光纤制造厂在这些方面所推出的新型单模光纤;最后对我国今后扩充光纤网络方面提出几点建议。     

脊加载环板行波管的理论与实验研究

脊加载环板行波管是一种频带相对较宽的大功率行波管 ,本文对脊加载环板慢波系统及其改进型进行了研究 ,理论与实验良好符合 ,实验表明脊加载环板慢波系统的改进型比脊加载环板慢波系统具有更宽的频带 ;同时对慢波系统采用等效线路模型 ,电子注采用二维圆环模型 ,研究了脊加载环板行波管的大信号特性 ,讨论了注波互作用的非线性效应。本文的结果将为脊加载环板行波管的设计提供理论基础。     

Conducting polyaniline composite: From syntheses in waterborne systems to chemical sensor devices

The development of a conducting composite from its one-step synthesis in aqueous dispersed medium to the characterization of its chemical sensor performance is detailed. Composite films of polyaniline and polyacrylate were processed from the crude dispersion with no need for post-formulation. The synthesis has been optimized to be as simple, cheap and transferable as possible. The composite composition is tunable, i.e. the nature of the dopant was varied and its effect on kinetic parameters was observed. Ab initio calculations have been performed on a series of six ionic systems to gain a deeper insight into the contribution of both the stability of the anilinium salts in the composite polymerization. The conductivities of all composites were recorded from room temperature to 150 °C and the thermal stability versus dopant highlighted. The conducting films were then studied as active layers in a chemical sensor. The results showed that these composites, easily synthesized and processed, are ammonia sensitive and exhibit a fast response when exposed to air pollution.