Classification-tree models of software-quality over multiplereleases

This paper presents an empirical study that evaluates software-quality models over several releases, to address the question, “How long will a model yield useful predictions?” The classification and regression trees (CART) algorithm is introduced, CART can achieve a preferred balance between the two types of misclassification rates. This is desirable because misclassification of fault-prone modules often has much more severe consequences than misclassification of those that are not fault-prone. The case-study developed 2 classification-tree models based on 4 consecutive releases of a very large legacy telecommunication system. Forty-two software product, process and execution metrics were candidate predictors. Model 1 used measurements of the first release as the training data set; this model had 11 important predictors. Model 2 used measurements of the second release as the training data set; this model had 15 important predictors. Measurements of subsequent releases were evaluation data sets. Analysis of the models' predictors yielded insights into various software development practices. Both models had accuracy that would be useful to developers. One might suppose that software-quality models lose their value very quickly over successive releases due to evolution of the product and the underlying development processes. The authors found the models remained useful over all the releases studied     

Executive's guide to practical computer models

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Building accurate and robust HMM models for practical ASR systems

In this article the relevant training aspects for building robust and accurate HMM models for large vocabulary recognition system are discussed and adjusted, namely: speech features, training steps, and the tying options for context dependent (CD) phonemes. As the basis for building HMM models the well known MASPER training scheme is assumed. First the incorporation of the voicing information and its effect on the classical extraction methods like MFCC and PLP will be shown together with the derivative features, where the relative error reductions are up to 50%. Next the suggested enhancement of the standard training procedure by introducing garbled speech models will be presented and tested on real data. As it will be shown it brings more than a 5% drop in the error rate. Finally, the options for tying states of CD phonemes using decision trees and phoneme classification will be adjusted, tested, and explained.     

A practical electrode-array myoprocessor for surfaceelectromyography

A new myoprocessor is described which produces a relatively smooth and accurate measure of a muscle's electrical activity during both slow and rapid movements. This is achieved partly by spatial averaging of weakly correlated EMG signals from electrodes distributed over the surface of the muscle.     

A practical strategy for EMC design

The introduction of the European EMC Directive has made it very important that engineers design for EMC in their products from the start. The paper describes a strategy to ensure that EMC aspects of design are considered in a logical sequence during development. This strategy is discussed, checklists for EMC design are introduced and a number of important design areas highlighted     

Reconciling statistical models with practical experience of reverberation chambers

Presented are novel theoretical probability density functions (PDF) for the magnitude and phase of electromagnetic fields inside reverberation chambers (RC) operating in a `good-but-imperfect regime?. The derivation is based on considering two Gaussian random variables with mean values, variances and correlation between them that depart from the ideal assumptions. A multivariate approach using a complete joint Gaussian distribution of these variables is defined. Marginal distributions obtained by integration of this twodimensional joint PDF are compared with theoretical PDFs for ideal situations, and significantly lower rejection rates are experienced for field data measured in real RCs. Additionally, these novel marginal PDFs are highly general since they are able to describe both ideal and non-ideal stirred fields.     

一种实用的VCD文件处理方法

介绍了VCD(value change dump)文件在集成电路设计和测试相互结合的过程中所起到的重要作用,并对其特点进行了较为新颖全面的分析,在此基础上提出了一种非常实用的称为LYT(Li-Yang Translation)的中间格式,按照VCD文件的基本特点利用哈希表对关键词进行了分类压缩,把变化信息按照管脚进行了归类,并采用做差、合并的处理方法简化值变化信息的处理,实现了两者的相互转换。实际的测试表明:改进后的格式提高了VCD文件的处理速度。     

A practical dimensioning method for ATM systems

In this paper, a simplified practical method for dimensioning asynchronous transfer mode (ATM) systems is proposed. Packet switching services are classified into two categories: connection-oriented packet switching (COPS) with quality of service (QoS) guaranteed and connection-less packet switching (CLPS) on a best effort basis. A new control scheme is proposed for maintaining the cell-level QoS requirement for the COPS even in overload conditions. A dimensioning method is also proposed for the system where the COPS is served with nonpreemptive priority over the CLPS. The methods proposed are expected to contribute to the realization of robust and economical ATM systems     

A practical end-of-life model for semiconductor devices

The authors derive a model of active semiconductor device aging to predict end of mission life device parameters by extrapolating from early environmental and electrical test measurements. Beginning from mass action kinetics first principles, the model develops an envelope average of physico-chemical damage reaction kinetics of limited source amounts of contaminating reactants. Corroborating experimental and test data are included     

A reasonably practical XUV laser for applications

We describe a laboratory-scale 109 nm Xe Auger laser pumped by an all-commercial high-repetition-rate Nd:YAG laser system. The Xe laser provides pulse energies up to 1 μJ, and an average flux of 3×10 ¹² photons/s at 11.5 eV. Measurements of the gain, output energy, and output beam shape are reported, along with an investigation of the time dependence of the gain     

A practical approach for magnetic core-loss characterization

A practical approach for magnetic core-loss characterization up to a few megahertz is presented. An error analysis is for the first time performed, revealing that corrections are needed to compensate for errors introduced by the extra phase shift inherent in a measurement setup, and by shunt parasitic capacitance associated with an inductive device under test. A simple technique is then proposed to control the error so as to satisfy prescribed tolerances. Extensive measurements done on a TDK PC40 core yield results which support the analysis. Several sample cores are then characterized at a few megahertz     

DMT系统中一种易于实现的时域均衡器

总结了DMT系统中时域均衡器(TEQ)的主要设计方法，指出最大缩短信噪比(MSSNR)TEQ的最优设计方法很难实时实现。提出了一种MSSNR TEQ的次优设计方法，它首先估计出目标抽样窗的最优延迟，然后用分步求解法求出TEQ的抽头系数。和最优方法相比，次优方法的计算量大幅度减少，可实时实现，而其缩短信噪比的损失很小。仿真实验验证了次优方法的有效性。     

A practical RFID authentication mechanism for digital television

As information technology continuously progresses, more applied technologies are developed, such as radio frequency identification (RFID). In this paper, we propose a novel digital television (DTV) structure that uses RFID for encryption. RFID is widely used for various applications because of its advantages such as an extended lifetime and security, and it is less affected by environmental constraints. The proposed protocol uses RFID for encryption to withstand many attacks that the traditional system is vulnerable to, such as impersonation attack, replay attack and smart card cloning. Compared with other protocols, the proposed protocol is more secure and efficient. Thus, our proposed protocol makes the DTV framework more complete and secure.     

A practical technique for designing multiport coupling networks

A new technique is proposed for designing a passive lossless coupling network transforming any prescribed N by N symmetric immittance matrix into a corresponding N by N diagonal immittance matrix. A principal application of the technique is in the design of matching networks between N uncoupled resistive source impedances and planar antenna arrays. The technique is based upon repeated applications of Givens rotations, which can be implemented by a cascade connection of four-port directional couplers. Thus, both in the design technique and in the subsequent hardware implementation, our approach represents a significant departure from past design procedures. Existing synthesis methods involve the use of multiwinding transformers, which are impractical at microwave frequencies     

A practical optical modulator and link for antennas

This paper describes a practical application of a technique for coupling an antenna to a receiver using a passive fiber-optic link. This technique should avoid pickup and electromagnetic perturbations normally associated with the use of electrically conductive cables. Laser light (632.8 nm) is modulated at the antenna by an electrooptic lithium-tantalate crystal and is then transmitted with a fiber-optic cable to the receiver electronics. Using an avalanche photodiode, the amplitude modulated optical signal is converted to an electrical signal. The crystal is mounted directly on an antenna without amplifiers or other electrically powered components. Using a broad-band antenna with fields generated in an anechoic chamber and a standard TEM cell, the frequency response as measured dropped 3 dB per 1.0 GHz from 100 MHz to at least 2.0 GHz, with a signal-to-noise ratio of 5 dB with a 1.0-V/m field and a 1.0-kHz bandwidth. A dynamic range of at least 60 dB is shown.     

一种实用的稳压变压器

简要介绍一种实用的稳压变压器的原理、基本结构、设计、制造及优良性能。     

A practical method for obtaining prior distributions in reliability

In this paper, we propose a comprehensive methodology to specify prior distributions for commonly used models in reliability. The methodology is based on characteristics easy to communicate by the user in terms of time to failure. This information could be in the form of intervals for the mean and standard deviation, or quantiles for the failure-time distribution. The derivation of the prior distribution is done for two families of proper initial distributions, namely s-normal-gamma, and uniform distribution. We show the implementation of the proposed method to the parameters of the s-normal, lognormal, extreme value, Weibull, and exponential models. Then we show the application of the procedure to two examples appearing in the reliability literature, and . By estimating the prior predictive density, we find that the proposed method renders consistent distributions for the different models that fulfill the required characteristics for the time to failure. This feature is particularly important in the application of the Bayesian approach to different inference problems in reliability, model selection being an important example. The method is general, and hence it may be extended to other models not mentioned in this paper.     

一种实用的相控阵近场诊断新方法

提出了一种相控阵天线近场诊断的新方法.传统的方法要诊断出相控阵天线单元的激励,必须已知阵列单元的方向图和探头的方向图.文中基于相控阵天线的激励、单元方向图、探头方向图和近场测量数据之间的关系,得到了相控阵天线的激励和近场测量数据之间的耦合方程.利用多项式插值,在不必已知单元方向图和探头方向图的情况下,求解出相控阵天线的单元激励.     

一种实用的高分子材料样品制备方法

通常 ,要使得高分子材料 (指不填加无机填料的高分子共聚物或共混物 )适合于ＴＥＭ观察 ,需至少对样品进行如下 2步处理 :第一是样品的固化 ,进而实现超薄切片。对于一些弹性体如橡胶或橡塑共混物来说 ,固化更显得必要。实现这一步的最常规方法是在液氮冷冻下进行低温超薄切片 ;第二是样品的染色 ,因为高分子材料 ,无论橡胶或者塑料 ,均由Ｃ、Ｈ、Ｏ等轻元素组成 ,其对电子的散射能力相近 ,因而在用ＴＥＭ观察时没有反差。实现染色的最常规方法是采用ＯｓＯ4熏染切好的片 ,从而使橡胶相(通常含有双键 )显示深色 ,而塑料相显示浅色。因而在实…     

A practical method for friction identification in hydraulic actuators

Friction in hydraulic actuators can be described using nonlinear, velocity dependent models. In this paper, the friction is described by an exponential Stribeck friction model. An iterative algorithm is presented to identify the friction model parameters. The method fits two lines on the experimental data relating steady-state velocities to actuator pressure differentials. The parameters of the fitted lines are obtained using an iterative optimization technique. Based on the obtained parameters, the original nonlinear friction model parameters are completely reconstructed. The proposed method is validated by building a simulation model for a valve-controlled hydraulic system in which the friction is modeled based on the method described here. The proposed method can be used in practical situations, whereby fast and reliable identification of major parameters of the friction in hydraulic actuators is needed with easy to obtained pressure measurements.