Determination of azinphos-methyl and parathion-methyl in honey by stripping voltammetry

An electrochemical method for the determination of azinphos-methyl and parathion-methyl in honey is presented. The determination is established by adsorptive stripping differential pulse voltammetry at hanging mercury working electrode.In contrast to the chromatographic methods for the determination of pesticide residues, the sample preparation of the proposed method is minimal; analytes were extracted from honey samples with a mixture of (acetone):(Britton-Robinson buffer) and then were analyzed without any additional pretreatment.The response of the analytes either individually or as a mixture was studied for a series of deposition time and molar ratio. Two quantitation protocols were compared, using either the external calibration or the standard addition method. Accuracy was tested with spiked honey samples obtaining good recovery values. The limit of detection for the honey sample (for deposition time of 10 s) was calculated 51.71 μg kg⁻¹ for MeP and 65.87 μg kg⁻¹ for AzMet.     

A coupled volume-of-fluid and level set (VOSET) method for computing incompressible two-phase flows

A coupled volume-of-fluid and level set (VOSET) method, which combines the advantages and overcomes the disadvantages of VOF and LS methods, is presented for computing incompressible two-phase flows. In this method VOF method is used to capture interfaces, which can conserve the mass and overcome the disadvantage of nonconservation of mass in LS method. An iterative geometric operation proposed by author is used to calculate the level set function ? near interfaces, which can be applied to compute the accurate curvature κ and smooth the discontinuous physical quantities near interfaces. By using the level set function ? the disadvantages of VOF method, inaccuracy of curvature and bad smoothness of discontinuous physical quantities near interfaces, can be overcome. Finally the computing results made with VOSET method are compared with those made with VOF and LS methods.     

Preparation and studies of transparent conductive monolayers of multiwall carbon nanotubes on quartz and flexible polymer with the use of modified Langmuir technique

An improved Langmuir method is described and applied to produce transparent, conductive and flexible single layer of multiwall carbon nanotubes. This paper presents properties of multiwall carbon nanotubes spread on water subphase and in a form of Langmuir–Schaefer layers on a quartz plate and on flexible polymeric foil. The results show very high homogeneity of the monolayers on a very large area obtained with the use of the proposed modified Langmuir method and indicate their relatively high radiation transmission and electrical conductivity. Laser scanning confocal and scanning electron microscopic images of the layers are presented. The microscopic visualization of the nanolayers is supported by spectroscopic studies (transmittance, photoacoustics) in the range from ultraviolet to mid-infrared. Moreover, electric measurements (current versus voltage characteristics) of the carbon material on the polymeric foil are presented.The obtained results of the investigated multiwall carbon nanotubes are discussed in a view of potential application in optoelectronics.     

慢走丝线切割单点放电温度场有限元分析

建立了慢走丝电火花线切割单脉冲放电模型,利用有限元分析了单脉冲放电温度场分布。计算出该条件下工件放电凹坑几何特征,与实际切割条件下的材料去除率进行了对比,并根据电火花线切割的加工特点进行了修正。讨论了不同峰值电流和脉冲宽度条件下,蚀除凹坑体积与材料去除率(MRR)的变化规律,并分析了峰值电流和脉冲宽度对MRR的交互作用。分析结果表明:考虑实际加工的相关因素,模拟的单脉冲放电的MRR经修正后可以近似表征实际连续切割时的MRR;单个凹坑的蚀除量随着电流和脉宽的增大而增大,并且电流和脉宽的交互作用随着它们取值的增大而更加明显。     

一种新的OFDM联合信道估计方法

OFDM（正交频分复用）作为一种高效可靠的传输方式,被广泛应用于无线通信系统中,近年来越来越受到人们的关注。文中主要研究基于导频的OFDM信道估计,在此基础上提出了一种采用最小二乘法的联合信道估计方法。这种方法能够将传送数据与导频结合起来进行更精确的信道估计,从而提高系统性能。仿真结果表明,文中方法优于经典的信道估计方法。     

OFDM系统中基于导频插入的信道估计技术

介绍了OFDM通信系统中用导频插入来进行信道估计的技术。根据导频插入的方法,信道估计可以分为基于集中式导频插入的信道估计和基于间隔式导频插入的信道估计。在描述OFDM系统信道估计模型的基础上详细阐述这两种方法,并利用多径Rayleigh衰落信道比较它们的性能。     

TD-LTE下行信道估计的DSP实现

根据项目选定的硬件,权衡DSP实现复杂度和性能给出了利用LS算法来进行信道估计的DSP实现方案。主要从内存分配、运行效率以及计算精度方面对信道估计关键模块的设计进行了描述。分析DSP运行周期并搭建物理基带信号处理链路对比BER性能,结果表明该方案定点运算的误差小,具有良好的实时处理性能。     

单矢量水听器二维DOA和频率联合估计算法

基于单矢量水听器,利用时延数据构造两个阵形相同的子阵,运用LS-ESPRIT方法,对信号数据矩阵进行特征值分解,提取其特征值和相应的特征向量中包含的频率和角度信息,从而实现单频窄带信号的二维DOA和频率的联合估计。具有较好的估计精度,无需搜索过程并且能够实现三维参数的自动配对。使用MATLAB进行仿真,与基于单矢量水听器的波达方向矩阵法和基于声压阵的LS-ESPRIT方法进行比较,结果表明,该方法具有较好估计性能。     

声源DOA估计中LS-SVR核函数选取研究

基于多通道到达时间差(TDOA)的定位方法是声源到达方向(DOA)估计中的重要方法。其中,由TDOA到DOA的映射是该方法的一个关键,目前广泛采用的映射方法为最小二乘法。然而最小二乘法存在诸如声源位于阵列端射方向时性能急剧下降的问题。为克服这一缺点,提出了基于最小二乘支持向量回归机(LS-SVR)的映射方法。在支持向量机技术中,核函数的选取直接影响着支持向量机的性能,但之前的工作仅讨论了径向基核函数。针对声源DOA估计中的TDOA映射问题,研究了径向基核、多项式核以及线性核函数构造的LS-SVR对声源DOA估计的影响。     

数字时钟电路的设计与仿真

数字时钟设计既是电子教学中最为典型的综合性实验之一,也在商业领域有着极为广泛地应用。文中介绍了一种以74LS190同步可预置的十进制可逆计数IC为主功能芯片,联合其他逻辑门器件共同实现数字时钟功能的电路。该电路包含4个子模块,分别是1Hz脉冲产生电路、计数电路、手动校时电路和整点报时电路。设计过程中利用EWB5.0软件仿真,既提高了设计效率,又节约了设计成本。经验证,该电路工作稳定可靠,达到了预期的效果。