Frequency and time domain comparison of selective polynomial filters with corrected phase characteristics

Two solutions to the polynomial filter’s transfer function synthesis problem are considered for comparison in the frequency and time domain: the broad class of filters with a critical monotonic amplitude characteristic (CMAC) in the passband and filters which use Chebyshev (C) polynomials. To complete the synthesis procedure for linear phase applications, group delay correctors are considered, for which a convenient approximation procedure is proposed here. Comparisons of the original functions and the corrected ones are performed in the frequency and time domain. It is shown that when CMAC and C are compared as such, the latter is by no means preferable from the selectivity point of view, while the opposite stands when the comparison is based on passband amplitude distortions. When phase-corrected filtering functions are compared, based on circuit complexity and time domain performance, the CMAC are shown to be preferable.     

校正梯形公式的推广

对数值积分中的校正梯形公式作出推广并讨论了中间值的渐近性.     

Finite element analysis of flow and heat transfer with moving free surface using fixed grid system

A numerical study was performed on flow and heat transfer involving moving free surfaces that occurs in mold filling processes such as casting and injection molding. In these problems, the calculation domain changes continuously and the numerical treatment of the moving interface tends to cause artificial diffusion. Among the solution algorithms based on the Eulerian method, the volume-of-fluid (VOF) method was used because the method is simple and efficient in handling the complex flow patterns inside the cavity. To solve the transport equation of free surface without artificial smearing of the interface the baby-cell method was employed in the geometric reconstruction of the free surface. Furthermore, a predictor–corrector method was adopted in the time integration of volume-of-fluid (VOF) transport equation to increase the accuracy. The proposed scheme was verified through several benchmark problems. In order to show the capability of the proposed method, several three-dimensional mold filling processes were solved. The current algorithm was applied to the floating body problem. Three-dimensional floating body problems were tested.     

Corrector estimates in homogenization of a nonlinear transmission problem for diffusion equations in connected domains

This paper is devoted to the homogenization of a nonlinear transmission problem stated in a two-phase domain. We consider a system of linear diffusion equations defined in a periodic domain consisting of two disjoint phases that are both connected sets separated by a thin interface. Depending on the field variables, at the interface, nonlinear conditions are imposed to describe interface reactions. In the variational setting of the problem, we prove the homogenization theorem and a bidomain averaged model. The periodic unfolding technique is used to obtain the residual error estimate with a first-order corrector.     

Determination of Pb in airborne particulate matter with a heavy matrix of silicon by SR-ETAAS

A study is undertaken to monitor Pb levels in airborne particulate matter collected on ash-free glass-fibre filters from urban and industrial areas of Argentina by electrothermal atomic absorption spectrometry with self-reversal background correction. For this sample with a heavy matrix of silicon, a simple acid treatment with aqua regia and HF is proposed aimed to minimize contamination and reduce sample treatment steps. Ultrasonic agitation was employed for sample homogenization. To overcome the problem of the high amounts of Si, main analytical variables including acid pretreatment conditions, temperature program of the graphite furnace and spectroscopic conditions were carefully studied and optimized. Continuum source and self-reversal methods for background correction were compared in order to avoid non-specific and spectral interferences due to the matrix. After optimization, synthetic acid solutions of Pb were employed for calibration. Calibration was linear within the range 1–40 µg L^{− 1} (correlation coefficient of 0.9995) when the 283.3 analytical line was used. Using optimized conditions limits of detection (3σ) of 0.6 µg L^{− 1} were achieved. The repeatability between injections (S_r%) was evaluated and was better than 4.2%. The precision (%RSD) for Pb determination in a single sample was estimated by analyzing three strips of the same filter. In all cases the RSD was better than 6.9%. For checking accuracy, an aliquot of a Standard Reference Material (NIST 2709, San Joaquin Soil) was subject to the same sample treatment and included in the overall analytical process. This method was successfully applied to the determination of Pb in airborne particulate matter collected in Buenos Aires city.     

Study of matrix effects and spectral interferences in the determination of lead in sediments, sludges and soils by SR-ETAAS using slurry sampling

An interference-free, fast, and simple method is proposed for Pb determination in environmental solid samples combining slurry sampling and electrothermal atomic absorption spectrometry. Samples were ground to an adequate particle size and slurries were prepared by weighing from 0.05 g to 0.20 g of dry sediment, adding nitric acid, and a solution containing 0.1% Triton X-100. Ultrasonic agitation was employed for slurries homogenization. Analytical variables including acid pre-treatment conditions, particle size, slurry stability, temperature program of the graphite furnace, and type and concentration of the chemical modifier were studied. The undesirable effects of potential non-specific and spectral interferences on Pb signal were also taken into account. Continuum source and self-reversal methods for background correction were evaluated and compared. For calibration, synthetic acid solutions of Pb were employed. Calibration was linear within the range 1-30 μg L⁻¹ and 5-30 μg L⁻¹ when the 217.0 nm and 283.3 nm analytical lines were used. Correlation coefficients of 0.9992 and 0.9997 were obtained. Using optimized conditions, limits of detection (3σ) of 0.025 μg g⁻¹ and 0.1 μg g⁻¹ were achieved for the 217.0 nm and 283.3 nm analytical lines, respectively. The method was successfully applied to the determination of lead in soil, contaminated soil, municipal sludge, and sediment samples. The accuracy was assessed by the analysis of two certified reference materials: municipal sludge (QC MUNICIPAL SLUDGE A) and lake sediment (TRAP-LRM from IJS).     

Runge–Kutta–Nyström‐type parallel block predictor–corrector methods

This paper describes the construction of block predictor–corrector methods based on Runge–Kutta–Nyström correctors. Our approach is to apply the predictor–corrector method not only with stepsize h, but, in addition (and simultaneously) with stepsizes a _i h, i = 1 ...,r. In this way, at each step, a whole block of approximations to the exact solution at off‐step points is computed. In the next step, these approximations are used to obtain a high‐order predictor formula using Lagrange or Hermite interpolation. Since the block approximations at the off‐step points can be computed in parallel, the sequential costs of these block predictor–corrector methods are comparable with those of a conventional predictor–corrector method. Furthermore, by using Runge–Kutta–Nyström corrector methods, the computation of the approximation at each off‐step point is also highly parallel. Numerical comparisons on a shared memory computer show the efficiency of the methods for problems with expensive function evaluations.     

一种固定下降沿的高精度时钟占空比调整电路

提出了一种基于连续时间积分器的高精度占空比调整电路，利用积分电压控制倒相器上升沿延迟，并进一步通过触发器合成50％占空比时钟。电路采用CMOS0．35μ m2P4M混合电路工艺实现。后仿结果表明，该电路能将30％～70％占空比的输入时钟自动调整至50％±0．2％。电路结构简单，芯片面积约为0．18mm×0．12mm，仿真功耗仅为0．2～0．4mW。该调整方法本身受电路、工艺失配影响小，且调整过程中保持调整前后下降沿对齐，便于与锁相环或延迟锁相环结合，进一步在调整占空比的同时，改善输出时钟的其他性能。     

某些半线性波动方程均匀化的矫正

本文处理具有H_0~1初值的半线性热方程均匀化的矫正问题．     

对MODIS—N扫描方式的讨论

在以摆镜为穿航迹扫描的光机扫描仪中,卫星航向运动的补偿使扫描频率降低一倍,并使扫描效率提高一倍,从而具有很高的实用价值。本文重点讨论了MODIS-N的扫描补偿方案,并对它的适用性进行了评价。