Ground-wave attenuation function for a Gaussian modulated carrier signal

The time-harmonic theory of ground-wave propagation is generalised to the time domain for a Gaussian modulated carrier signal. The model is a vertical electric dipole located on a flat imperfectly conducting earth. It is shown that the radiated field is characterised by a modified Sommerfeld-type attenuation function with a time-dependent `numerical distance?.     

Inverse random describing function

A solution to the problem of evaluating a nonlinearity that yields a given random describing function is given. Approximate methods are discussed for cases where the describing function is only known graphically.     

Survival probability of precipitations and rain attenuation in tropical and equatorial regions

This contribution presents a stochastic model useful for the generation of a long-term tropospheric rain attenuation time series for Earth space or a terrestrial radio link in tropical and equatorial heavy rain regions based on the well-known Cox–Ingersoll–Ross model previously employed in research in the fields of finance and economics. This model assumes typical gamma distribution for rain attenuation in heavy rain climatic regions and utilises the temporal dynamic of precipitation collected in equatorial Johor, Malaysia. Different formations of survival probability are also discussed. Furthermore, the correlation between these probabilities and the Markov process is determined, and information on the variance and autocorrelation function of rain events with respect to the particular characteristics of precipitation in this area is presented. The proposed technique proved to preserve the peculiarities of precipitation for an equatorial region and reproduce fairly good statistics of the rain attenuation correlation function that could help to improve the prediction of dynamic characteristics of rain fade events.     

Rain cell size statistics as a function of rain rate for attenuation modeling

Rain cell size statistics as a function of rain rate have been deduced by employing a radar data base of rain reflectivity data acquired over a three-year period at Wallops Island, VA. These cell statistics have important applications in slant path rain attenuation modeling and remote sensing of the earth's surface from space at frequencies above 10 GHz.     

Bayes estimation of reliability under a random environment governedby a Dirichlet prior

The reliability function of a component whose lifetime is exponentially distributed with a known parameter λ>0 is R (t|λ)=exp (-λt). If an environmental effect multiplies the parameter by a positive factor η, then the reliability function becomes R(t|η,λ)=exp(-ηλt). The authors assume that η itself is random, and its uncertainty is described by a Dirichlet process prior D(α) with parameter α=MG₀, where M>O represents an intensity of assurance in the prior guess, G₀, of the (unknown) distribution of η. Under squared error loss, the Bayes estimator of R(t|η,λ) is derived both for the no-sample problem and for a sample of size n. Using Monte Carlo simulation, the effects of n, M, G₀ on the estimator are studied. These examples show that: (a) large values of n lead to estimates where the data outweigh the prior, and (b) large values of M increase the contribution of the prior to the estimates. These simulation results support intuitive ideas about the effect of environment and lifetime parameters on reliability     

新颖的能量函数准则下的主分量分析算法

本文通过一个新颖的能量函数把Ｏｊａ规则与准确的梯度搜索联系起来,从而证明了Ｏｊａ规则可以通过梯度搜索而获得。推导了相应的梯度算法和递归最小二乘算法,根据Ｌｙａｐｕｎｏｖ稳定性原理和随机扰动理论分析了算法的全局渐近收敛性能。最后,给出了跟踪时变ＤＯＡ的计算机模拟结果。     

A geometric-process maintenance model for a deteriorating system under a random environment

This paper studies a geometric-process maintenance-model for a deteriorating system under a random environment. Assume that the number of random shocks, up to time t, produced by the random environment forms a counting process. Whenever a random shock arrives, the system operating time is reduced. The successive reductions in the system operating time are statistically independent and identically distributed random variables. Assume that the consecutive repair times of the system after failures, form an increasing geometric process; under the condition that the system suffers no random shock, the successive operating times of the system after repairs constitute a decreasing geometric process. A replacement policy N, by which the system is replaced at the time of the failure N, is adopted. An explicit expression for the average cost rate (long-run average cost per unit time) is derived. Then, an optimal replacement policy is determined analytically. As a particular case, a compound Poisson process model is also studied.     

Coherence function of interrelated periodically nonstationary random processes

A coherence function characterizing the correlation between harmonic components of two signals that are described by periodically correlated random processes has been proposed. Such function is shown to be invariant with regard to linear transformations of signals.Aformula for coherence function is concretized for the amplitude- and phase-modulated signals.     

The estimation of the optimum linear decision function with a sequential random method

This paper is concerned with the categorizing of patterns by means of linear decision functions,^{1}as developed by Highleyman [1], [2]. A new procedure for the estimation of the optimum linear decision function is developed. This procedure determines the minimum estimation of the loss function with a sequential random method. An application of the procedure to the same problem as discussed in [1] and [2] yields better results than the procedure developed by Highleyman.     

Improved method for determining the shear strength of chip component solder joints

In this paper an improved method has been presented to determine the solder joint shear strength of passive discrete surface mounted (SMD) chip components (like resistors and capacitors).To calculate the stress in a solder joint in the case of shear loading, the force applied should be measured and the amount of joined surface (wetted area of the component metallization) calculated.Using the method we suggest, we first measured the exact position of the chip component after soldering according to the guidelines set out in standard IPC 9850 (Institute for Interconnecting and Packaging Electronic Circuits). To determine the accurate value of the joined surface, a 3D profile calculation was carried out taking into account the exact position of chip components after soldering. The calculation of the profile was based on the principle of minimum energy. Then, the next stage was to determine the maximum force experimentally that the solder joint was able to withstand before failure in shear. The evaluation of the shear load results verified that the standard deviation coefficient of the results was lower when the shear strength of the solder is characterized by the maximum stress instead of maximum force. It was proved by our experiments and by simulations that the shear strength of misaligned components solder joints depends on the degree of component misalignment after reflow soldering.     

Componentwise coherence function of correlated periodically nonstationary random processes

In this paper we consider a novel componentwise coherence function, which is determined by the cross-spectral densities of stationary components of periodically nonstationary random processes i.e. stationary correlated random processes, which modulate their carrier harmonics. The properties of the introduced coherence function are specified for the amplitude- and phase-modulated signals. Its graphical frequency dependencies have been obtained for the specified signal parameters. The advantages of componentwise coherence function in comparison with previously suggested integral coherence function are shown. We present the method for the selection of stationary modulating components, which is based on the frequency shift and low-pass filtration. The properties of selected components for the cases of amplitude- and phase-modulated processes are analyzed.     

Sheet resistance component of series resistance in a solar cell as a function of grid geometry

Most photovoltaic solar cells use some type of light-transmitting grid electrode on the upper surface to reduce series resistance losses as the current is collected. The geometry of this grid is chosen through consideration of optical transparency and series resistance. A method of calculating the series resistance as a function of grid geometry is presented here with the following assumptions: (1) current generation is uniform over the area of the cell; (2) the thickness of the upper semiconductor layer is very much smaller than the lateral dimensions of the cell; (3) the resistance of the grid electrode is much less than the sheet resistance of the upper semiconductor layer, and (4) the current flow in the layer is ohmic. These assumptions will be satisfied for most solar cells of interest. The method is then applied to several representative grid geometries and the results are compared with previous calculations in the literature.     

On the longitudinal component of the Green's function dyadic

Discussion of the divergenceless property of the right-hand side of the dyadic-wave equation for the Green's dyad has centered on the inconsistency of expanding the Green's dyad only in terms of transverse-wave functions. By including the longitudinal functions in the Ohm-Rayleigh expansion of the dyad, a simple closed form expression for the longitudinal component is derived which yields the expected singular quasi-static field. The result is verified in a coordinate independent manner with the aid of the Helmholtz theorem.     

Techniques for estimating test length under random test

When a circuit is tested using random or pseudorandom patterns, it is essential to determine the amount of time (test length) required to test it adequately. We present a methodology for predicting different statistics of random pattern test length. While earlier methods allowed estimation only of upper bounds of test length and only for exhaustive fault coverage, the technique presented here is capable of providing estimates of all statistics of interest (including expected value and variance) for all coverage specifications.Our methodology is based on sampling models developed for fault coverage estimation [1]. Test length is viewed as awaiting time on fault coverage. Based on this relation we derive the distribution of test length as a function of fault coverage. Methods of approximating expected value and variance of test length are presented. Accuracy of these approximations can be controlled by the user. A practical technique for predicting expected test length is developed. This technique is based on clustering faults into equal detectability subsets. A simple and effective algorithm for fault clustering is also presented. The sampling model is applied to each cluster independently and the results are then aggregated to yield test lengths for the whole circuit. Results of experiments with several circuits (both ISCAS '85 benchmarks and other practical circuits) are also provided.This work was done while the author was with the Department of Electrical Engineering, Southern Illinois University, Carbondale, IL 62901.     

电力存量特种光缆风振环境下衰减特性研究

指出了开展风振环境下的衰减性能实验室测试的必要性,提出了风振条件下的衰减性能实验室测试方法,利用广东电网公司现存的备用OPGW(2盘)、ADSS光缆及ADL光缆样品在实验室进行风振环境模拟测试,通过实际测试,基于测试数据,总结分析了各存量光缆的衰减性能数据,得出了目前库存的OPGW、ADSS、ADL光缆线路衰减性能在风振环境下指标满足行业标准要求的结论.     

Reliability of single strength under n-stresses

In this paper we have considered the reliability of a system when n-stresses acted on a single strength component with probability distributions that were exponential, normal and gamma. We infer that when n-stresses act on a single strength component with an exponential distribution, the component has the same reliability as single stress and strength components which are connected in series, whereas normal and gamma distributions do not follow this rule.     

Multiple signal extraction by multiple interference attenuation in the presence of random noise in seismic array data

A vector of digital filters is derived for the multichannel processing of the signals acquired by an array of sensors with the objective of extracting multiple desired signals by the attenuation of multiple interferences and random noise. The signals and interferences are assumed to have arbitrary waveforms with no a priori knowledge of these waveforms. The time duration of the recorded array data is assumed to be long enough to incorporate all time delayed propagated waveforms at the sensors of the array. The derivation is for the general case of an arbitrary array geometric configuration and is not confined to the special case of a linear array of equispaced sensors. The rationale adopted in the derivation of the filters is to give first priority at each discrete frequency to passing the signals, a second priority to canceling the interferences, and a third priority to attenuating the random noise. This rationale well suits the case of seismic data that are dominantly corrupted by strong interferences rather than random noise. Solving a constrained minimization problem derives the vector of array filters. The computation of this vector requires the application of a powerful matrix decomposition technique for the detection of any redundant and/or inconsistent constraints at each discrete frequency. The simulation results demonstrate the extraction ability of the derived filters in both the multiple input single output and the multiple input multiple output processing schemes.