Dynamical problem of micropolar viscoelasticity

The dynamic problem in micropolar viscoelastic medium has been investigated by employing eigen value approach after applying Laplace and Fourier transformations. An example of infinite space with concentrated force at the origin has been presented to illustrate the application of the approach. The integral transforms have been inverted by using a numerical technique to obtain the displacement components, force stresses, couple stress and microrotation in the physical domain. The results for these quantities are given and illustrated graphically.     

Measurements of stratospheric chlorine monoxide (ClO) from groudbased FTIR observations

Infrared absorption features due to ClO in the lower stratosphere have been identified from groundbased solar absorption spectra taken from Aberdeen, U.K. (57° N, 2° W) on 20 January 1995. A vertical column abundance of 3.42 (±0.47)×10¹⁵ molec cm^-2 has been derived from 13 independent absorption features in the P and R branches of the (0–1) vibration-rotation band of ³⁵ClO, spanning the spectral region 817–855 cm^-1. The observed absorption features are consistent with very high levels of ClO (approximately 2.6 parts per billion by volume (ppbv)) in the altitude range 16–22 km. A comparison of this profile with a 3D chemical transport model profile indicates the observation was made inside the polar vortex and shows good qualitative agreement but the model underestimates the concentrations of ClO. Simultaneous measurements of other species were made including HCl, HF and ClONO₂. These columns yield a value for HCl+ClONO₂+ClO of 7.02±0.65×10¹⁵ molec cm^-2. This is lower than the total inorganic chlorine (ClO _y ) column of 10.7±1.6×10¹⁵ molec cm^-2 estimated from mean measured (HCl+ClONO₂)/HF ratios together with in-vortex HF measurements. The discrepancy is probably due to significant amounts of the ClO dimer (Cl₂O₂) in the lower part of the stratosphere. The measurements of highly elevated levels of ClO are used to estimate O₃ loss rates at the 400, 475 and 550 K levels making assumptions about the probable distribution of ClO and Cl₂O₂. These are compared with loss rates derived from ozone sonde data.     

Detection, excision and statistics of interference at the Mauritius radio telescope

A technique to detect man-made interference in the visibility data of the Mauritius Radio Telescope (MRT) has been developed. This technique is based on the understanding that the interference is generally ‘spiky’ in nature and has Fourier components beyond the maximum frequency which can arise from the radio sky and can therefore be identified. We take the sum of magnitudes of visibilities on all the baselines measured at a given time to improve detectability. This is then high-pass filtered to get a time series from which the contribution of the sky is removed. Interference is detected in the high-pass data using an iterative scheme. In each iteration, interference with amplitudes beyond a certain threshold is detected. These points are then removed from the original time series and the resulting data are high-pass filtered and the process repeated. We have also studied the statistics of the strength, numbers, time of occurrence and duration of the interference at the MRT. The statistics indicate that most often the interference excision can be carried out while post-integrating the visibilities by giving a zero weight to the interference points.     

On smoothing techniques for the removal of periodic noise of known period

This paper is concerned with the analysis of the linear modely(n)=X(n)+S(n)+(n) for the data sequencey(n) (n=1, 2, ..., N) whereX={x _IJ} is a knownJ × M matrix of full rankM. Here, the(n) are unknown vectors, which we wish to estimate for eachn; S(n) (n=1, 2, ..., N) is a periodic component (which we wish to estimate or remove) superimposed on the linear structureX(n); and(n) is an error vector which is specified as having zero expectation (with possible further properties). Such models commonly occur in geophysical data analysis.Modified from Technical Report No. 33, Computer Centre, The Australian National University.     

典型振动信号时-频分析方法研究

首先对比较简单的单分量信号和多分量信号进行时-频分析,对比了不同时-频分析方法(STFT、WD、Hilbert时-频谱分析、连续小波分析)的分析精度。结果表明对单分量信号和可以分解为若干单分量信号叠加的多分量信号,Hilbert时-频谱分析精度最好,WD和STFT次之,连续小波变换的精度最差;由于Hilbert时-频谱分析和WD方法要求信号为单分量信号或可以分解为若干单分量的信号,故其不适用于复杂信号的时-频分析;对多分量信号,STFT时-频谱较连续小波时-频谱精度高些。需要指出的是,当使用STFT方法时,取不同的窗参数,STFT的时-频分析精度相差很大,必须使用合适的窗参数,以取得较好的分析效果。此外还对El Centro波的两水平分量和人工合成的地震动进行了时-频分析,虽然STFT的时间分辨率和频率分辨率存在矛盾,但它对信号的适应性最强,对复杂信号的时-频分析精度一般可以满足需要,而连续小波变换进行信号的时-频分析时,时-频分辨精度最差,且对于大于30Hz的频率分量,随频率的增加,时-频分析的效果和精度迅速变差,说明小波变换并不适合于做时-频分析,尤其对于高频信号,用连续小波变换得到的时-频谱图看起来很粗糙,而且很难准确解释。进一步对比了真实地震动和人工地震动的时-频分布,认为用胡聿贤教授合成人工地震动的方法合成的地震动在时-频域上的分布和真实地震动相似。     

同时计算二维实序列的DFT和二维实序列的DFT的IDFT的新公式

利用二维离散傅里叶变换（DFT）的一些性质，将Gunther提出的关于同时计算一个N点实序列的DFT和另一个N点实序列的DFT的逆离散傅里叶变换（IDFT）的4个新的直接公式中的第1和第4个公式，以及他提出的关于同时计算2个N点实序列的DFT的新公式推广到了二维的情形，并给出了相关证明。这些结果在处理实信号时是非常有用的。     

傅立叶变换红外光谱联用技术在化石燃料分析中的应用

对傅立叶变换红外光谱联用技术在化石燃料分析中的应用进行了较全面的总结评述,重点介绍了气相色谱／红外光谱联机、高压液相色谱／红外光谱联机、薄层色谱／红外光谱联机、超临界流体色谱／红外光谱联机、裂解色谱／红外光谱联机、热重分析／红外光谱联机、气相色谱／红外光谱／质谱三机联用技术等在化石燃料的结构组分分析、成因机理研究及其勘探等诸方面的重要应用,尤其是在芳香族化合物和几何异构体的分离鉴定方面发挥出的突出功效。引用文献５９篇。     

A Single-Station Spectral Model of the Monthly Median foF2 and M(3000)F2

A new single-station model (SSM) for monthly median values of the ionospheric parameters foF2 and M(3000)F2 has been developed. Fourier analysis provides a tool for decomposing the time-varying ionospheric parameters. The 12–month smoothed sunspot number R ₁₂ was used as an external solar characteristic because of its availability and predictability. However, for the first time, the solar activity is described not only by R ₁₂ , but also by the linear coefficient K _R representing the tendency of the change of solar activity. A general non-linear approximation of the influence of the solar-cycle characteristics R ₁₂ and K _R and ionospheric parameters foF2 and M(3000)F2 was accepted. The new SSM is applied to several European stations and its statistical evaluation shows better results than the other two SSMs used in the paper. The approach described in the paper does not contradict the use of different synthetic ionospheric indices (as the T-index, MF2–index); the basic aim is to show only that using one additional new characteristic of the solar-cycle variations, such as K _R , improves the monthly median model.     

A new solution for a partially penetrating constant‐rate pumping well with a finite‐thickness skin

A mathematical model describing the constant pumping is developed for a partially penetrating well in a heterogeneous aquifer system. The Laplace‐domain solution for the model is derived by applying the Laplace transforms with respect to time and the finite Fourier cosine transforms with respect to vertical co‐ordinates. This solution is used to produce the curves of dimensionless drawdown versus dimensionless time to investigate the influences of the patch zone and well partial penetration on the drawdown distributions. The results show that the dimensionless drawdown depends on the hydraulic properties of the patch and formation zones. The effect of a partially penetrating well on the drawdown with a negative patch zone is larger than that with a positive patch zone. For a single‐zone aquifer case, neglecting the effect of a well radius will give significant error in estimating dimensionless drawdown, especially when dimensionless distance is small. The dimensionless drawdown curves for cases with and without considering the well radius approach the Hantush equation (Advances in Hydroscience. Academic Press: New York, 1964) at large time and/or large distance away from a test well. Copyright © 2007 John Wiley & Sons, Ltd.