基于经验模式分解的滤波去噪法及其在GPS多路径效应中的应用

经验模式分解(Empirical Mode Decomposition,EMD)是一种新的信号处理技术,它是基于数据本身的,且能在空间域中将信号进行分解,从而可以区分噪声和有用信号。根据EMD分解白噪声而得到的本征模式函数(IMF)分量的能量密度与其平均周期的乘积为一常量这一特性,建立一种新的基于EMD滤波去噪方法,并将该方法应用于GPS多路径效应的研究中。通过对模拟数据与GPS实测数据的处理分析,得出以下主要结论:①EMD滤波去噪法与小波方法都能最大限度地削弱测量的随机误差,但EMD滤波去噪法比小波方法更直接,且不受测不准原理及小波函数选择的影响;②相比小波方法,EMD能够更有效地剔除瞬时强噪声,从而能够提取更精确的多路径效应重复性误差改正模型。     

Method for assessing the chronic toxicity of marine and estuarine sediment-associated contaminants using the amphipod Corophium volutator

Acute sediment toxicity tests do not test key life stage events such as moulting and reproduction and therefore do not reveal the longer-term effects of contaminant exposure. A laboratory method is described for determining the chronic toxicity of contaminants associated with whole sediments. The test is conducted using neonates of the estuarine amphipod Corophium volutator at 15 degrees C, salinity 25 psu and a 12 h light:12 h dark photoperiod. The endpoints are survival and growth after 28 days and survival, growth and reproduction of amphipods upon termination of test i.e. reproduction within all control vessels (ca 75 days). The sediment chronic toxicity test was used to investigate the effects of sediments spiked with environmentally relevant preparations of slightly weathered Alaskan North Slope crude oil, including a water-accommodated-fraction (WAF) and a chemically-dispersed (Corexit 9527) WAF. Sediment oil concentrations were quantified using ultra-violet fluorescence. The amphipods exposed to chemically dispersed oil had higher mortality and lower growth rates than control-, Corexit 9527- and WAF-exposed organisms, resulting in reduced reproduction. The described method supplements the standard acute sediment test and would be particularly useful when long-term ecological effects are suspected but acute tests reveal no significant mortality. The sediment chronic test reported herein has shown that sediment that was not evidently toxic during 10-day acute tests could have population-level effects on sediment-dwelling amphipods.     

微塑料在海洋中的分布、生态效应及载体作用

微塑料通常被定义为最大尺寸小于5 mm的塑料碎片.受人类活动的影响,微塑料在海洋环境中广泛存在,引起了人们对其潜在影响的关注.由于粒径较小,微塑料可以通过多种途径进入水生生物体内,沿着食物链迁移、传递,影响海洋生态系统的健康与稳定.在海洋中长期停留的微塑料会吸附环境中的重金属、有机污染物和微生物等,加剧微塑料对海洋生物的毒性作用.本文综述了海洋环境中微塑料的污染特征,微塑料对海洋生物行为、生理等的影响,以及微塑料与微生物、其他污染物的相互作用和复合效应,并对微塑料对海洋环境及生物影响的研究进行了展望.     

抗浮设防水位的推断及其作用分析

建议设立建设工程抗浮设防标准作为勘察设计的规范性技术依据,通过归纳抗浮设防水位推断计算公式,阐述了最不利条件下各影响因素的涵义,明确其中的地下水位最大年季节性变幅应采用统计分析的上限分位标准值,同时提出组合效应的分析思路;依据地层的水力连续性原理及实际的工程技术条件,分析了弱透水性土层中基础浮托力折减的风险性;强调抗浮分析和设计中应将结构重力按抗力条件取值,并对抗浮设防水位应发挥的功用给予了一些说明。     

Galaxy evolution in clusters

The galaxy populations in present-day clusters are distinctly different from those of the field, indicating that environment plays a strong role in galaxy evolution. This review discusses some of the recent observations of moderate to high redshift clusters. A consistent picture of galaxy evolution in clusters appears to be emerging, which includes a population of galaxies which formed early in the cluster history, as well as field galaxies which have had their star formation truncated upon falling into the cluster potential. Galaxy interactions probably play an important role in exhausting star formation in some of these galaxies. However, there is significant variation in the populations of different cluster samples, with substantial evidence that some galaxies have their star formation terminated more gradually. This suggests that different mechanisms may dominate in different clusters, perhaps because of the recent merging history of the clusters. We also present a recent analysis of population gradients in clusters which suggests that the observed evolution in cluster populations is consistent with a scenario where changing infall rates drive the fraction of star forming galaxies in clusters, rather than a changing physical mechanism within the cluster. Thus, galaxy populations may provide a fundamental measure of the growth of large scale structure. This revised version was published online in July 2006 with corrections to the Cover Date.     

A finite element porothermoelastic model for dual-porosity media

An existing dual-porosity finite element model has been extended to include thermo-hydro-mechanical coupling in both media. The model relies on overlapping distinct continua for the fluid and solid domains. In addition, conductive and convective heat transfers are incorporated using a single representative thermodynamics continuum. The model is applied to the problem of an inclined borehole drilled in a fractured formation subjected to a three-dimensional state of stress and, a temperature gradient between the drilling fluid and the formation. A sensitivity analysis has been carried out to study the impact of thermal loading, effect of heat transport by pore fluid flow and, the effect of parameters of the secondary medium used to represent the fractures. Copyright © 2004 John Wiley & Sons, Ltd.     

Comparison between Different Models of Galactic Tidal Effects on Cometary Orbits

Different models of the action of the galactic tide are compared. Each model is a substitute for direct numerical integrations allowing a drastic decrease of the computation time. The models are built using two different techniques, (i) averaging of the fast variable (the mean anomaly) over one cometary period and (ii) fixing the comet in its aphelion direction. Moreover, we consider two different formalisms (Lagrangian and Hamiltonian) and also two different sets of variables. As expected, we find that the model results are independent of the formalism and the set of variables considered, and are highly accurate, whereas mathematical technique leads to poor results. In order to further reduce the computation time, mappings are built from the development of the solution of the models. We show that for these mappings, the set of variables giving the most accurate results is strongly dependent on the cometary eccentricity, e, and semimajor axis, a.     

Degradation due to Quantization Noise in Radio Astronomy Phased Arrays

In this article, a model is developed for determining the probability distribution of the output of a digital adder in case of 2-, 3- and 4-level quantization before summation. This probability distribution is then used to determine the efficiency of a system which determines the total power of the signal at the output of the digital adder.The sum-signal is also used in a VLBI correlation mode where the sum-signal is correlated with the signal from a VLBI partner. The efficiency, expressed in so-called Degradation Factors, is determined for 1- and 2-bit correlation and 2-, 3- and 4-level quantization before summation.Furthermore, the application of the calculated values (Total Power Detector Efficiencies and Degradation Factors) is illustrated.