A fast computation method for time scale signal denoising

This paper presents a novel and fast scheme for signal denoising in the wavelet domain. It exploits the time scale structure of the wavelet coefficients by modeling them as superposition of simple atoms, whose spreading in the time scale plane formally is the solution of a couple of differential equations. In this paper, we will show how the numerical solution of such equations can be avoided leading to a speed up of the scale linking computation. This result is achieved through a suitable projection space of the wavelet local extrema, requiring just least squares and filtering operations. Intensive experimental results show the competitive performances of the proposed approach in terms of signal to noise ratio (SNR), visual quality and computing time.     

Temperature gradients,not food resource gradients,affect growth rate of migrating Daphnia mendotae in Lake Michigan

Zooplankton production plays a critical role in the Great Lakes ecosystem, and vertical migration, which is exhibited by many zooplankton species, could affect production. We examined the effects of water temperature and food resource gradients on the growth rate of zooplankton undergoing vertical migration in Lake Michigan. In three laboratory experiments, juvenile Daphnia mendotae, native herbivorous cladocerans, were incubated for 5 days at water temperatures associated with the epilimnion and deep chlorophyll maxima (DCM) of Lake Michigan and were fed food resources collected directly from these regions. Growth rate strongly depended on water temperature, as Daphnia incubated at the epilimnetic temperature (21 °C) grew 42% faster than those at the DCM temperature (8 °C). Growth rate of Daphnia that alternated between the two temperatures every 12 h (0.108 day^− 1) was similar to the arithmetic average growth rate of the two water temperature treatment extremes (0.110 day^− 1), suggesting fluctuating temperatures alone do not substantially influence Daphnia growth. In contrast, food resources derived from different depths did not affect growth rate, nor was there a significant interaction between food resource origin and water temperature effects. Our results indicate that vertical migration will reduce growth rate, and hence zooplankton production, through reduced temperature, not from changes in resources. Consideration of the effects of vertical migration, especially given the known variability in this behavior, may substantially improve zooplankton production estimates in the Great Lakes.     

基于小波分析和神经网络的井下电缆故障测距方法

针对现有的井下电缆故障测距方法存在可靠性差、精度低的问题,介绍了一种基于小波分析理论和神经网络的井下电缆故障测距方法,并比较了BP神经网络和RBF神经网络用于该方法的测距性能。该故障测距方法采用3次B样条半正交小波对暂态零序电流信号进行小波变换,得到特定频带内的暂态零序电流模极大值,并将该模极大值作为神经网络的输入信号,根据模极大值与故障点位置的映射关系实现故障定位。仿真结果表明,该故障测距方法能够较好地进行井下电缆故障测距,且RBF神经网络的测距误差及训练速度均优于BP神经网络。     

Characteristics of pulsed photo-stimulated luminescence and thermoluminescence for the identification of gamma irradiated poultry eggs

Pulsed photo-stimulated luminescence (PPSL) is a simple screening method that can be employed qualitatively at the spot for the detection of eggs treated with ionizing radiation.Due to the variations in the results during storage,the eggs of ostrich,duck,hen,and quail were irradiated to doses of 0,1,2,and 3 kGy.Most of the samples were incorrectly identified during storage after four months of irradiation.Thermoluminescence (TL) technique was also tried by using egg shells in order to confirm the irradiation treatment in eggs.TL glow curves were recorded between the temperatures 50℃to 400℃at the rate of 5°/s for all the control and irradiated samples.On the basis of integrated areas of first glow curves (TL1),the glow curve ratios (TL1/TL2) and the shapes of maxima of TL1, the irradiation treatment of all the eggs was confirmed.Furthermore,the presence of calcite and aragonite minerals that cause the TL signal in the egg shells were studied using X-ray diffraction spectrometry.     

一种基于小波分析的网络流量异常检测与定位方法

根据网络流量在大时间尺度上的自相似性,以及在小时间尺度上异常流量、Lipschitz正则性与小波变换模极大值三者之间的关系,提出基于小波分析的网络流量异常检测方法.设计了采用该方法检测网络流量异常的模型,解决了方法实现过程中小波选择、模极大值曲线衰减判断、Hurst指数与Lipschitz指数求解等一些关键问题.实验表明,提出的方法能够较好的发现网络流量异常事件并定位异常发生时刻.     

双极HVDC输电线路行波故障定位

为准确定位双极HVDC输电线路故障,介绍了基于小波模极大值理论的双端D型行波故障测距方法及该方法在双极HVDC输电系统中的应用并用PSCAD和MATLAB软件仿真分析双极HVDC系统,得到故障点初始行波波头分别到达整流侧母线和逆变侧母线的时刻,从而算出故障点到达两侧母线的距离,完成故障定位。该结果表明,小波变换的模极大值能够刻画出故障行波信号的奇异点和奇异性,用小波变换提取高频暂态信号可准确找出故障极线路,识别出故障极初始电流行波的波头,实现双极HVDC输电线路高度精确的故障定位。     

电磁式电压互感器暂态仿真及行波传变特性分析

传统上认为电磁式电压互感器(potential transformer, PT)不能有效传变高频行波信号,因此铁路自闭贯通线在利用既有设备进行双端电压行波测距时还需进行系统的研究。文章基于PSCAD/EMTDC建立了JDZ10-10型PT等效模型,并植入自闭贯通线路中进行系统的仿真研究,利用小波模极大值法检测线路故障时电压互感器一次侧和二次侧的电压行波波头。仿真研究发现,自闭贯通线上常用的JDZ10-10型PT在0~125 kHz的低频段有较好的传变特性,能准确、无时延地传变行波波头信号和极性;但故障后1~2 ms二次侧存在一个振荡过程,因此1个一次侧波头传变到二次侧会产生多个波头。在准确识别二次侧行波第1个波头的情况下,可利用电压行波进行自闭贯通线路故障测距。该结果证明电压行波测距原理在铁路自闭贯通线路中具有适应性。     

区域最大分割算法在色域边界描述中的应用

在基于样本测量值的基础上,为快速描述出设备的色域边界,拟合得到不同色相面的边界曲线,采用区域均匀分割算法,测量样本的L*a*b*值后,对CIE L*a*b*均匀颜色空间进行区域均匀分割,并对其中的空集区域插值,最后利用存储的色域边界描述矩阵中的点集信息拟合出边界曲线。插值后,矩阵点集信息更加完整,描述的色域边界连续性和平滑性增强。该算法在计算精度上可以实现色域剖面边界描述,经插值后,等色相面的边界拟合效果更好。