Resolution performance analysis of cumulants-based rank reduction estimator in presence of unexpected modeling errors

Compared to the rank reduction estimator （RARE） based on second-order statistics （called SOS-RARE）, the RARE employing fourth-order cumulants （referred to as FOC-RARE） is capable of dealing with more sources and mitigating the negative influences of the Gaussian colored noise. However, in the presence of unexpected modeling errors, the resolution behavior of the FOC-RARE also deteriorate significantly as SOS-RARE, even for a known array covariance matrix. For this reason, the angle resolution capability of the FOC-RARE was theoretically analyzed. Firstly, the explicit formula for the mathematical expectation of the FOC-RARE spatial spectrum was derived through the second-order perturbation analysis method. Then, with the assumption that the unexpected modeling errors were drawn from complex circular Gaussian distribution, the theoretical formulas for the angle resolution probability of the FOC-RARE were presented. Numerical experiments validate our analytical results and demonstrate that the FOC-RARE has higher robustness to the unexpected modeling en＇ors than that of the SOS-RARE from the resolution point of view.     

TDOA localization with linear-correction in the presence of sensor position errors

This paper considers the problem of locating a source using time difference of arrival(TDOA) measurements obtained at spatially distributed sensors in the presence of sensor position errors. A linear-correction TDOA localization algorithm that involves closed-form weighted least squares(WLS) optimization only is developed. The proposed method first converts nonlinear TDOA equations into pseudo-linear ones by introducing an intermediate variable and obtains the initial source position estimate using the WLS technique. Then a linear-correction method is applied to improve the initial localization result by estimating and subtracting its positioning error. Simulation results demonstrate the good performance of the proposed method.     

非理想发射机情况下的QPSK性能分析

调制器的不均衡以及放大器的非线性对接收机的性能具有非常大的影响。由于不均衡对载波跟踪环路的稳态锁定点的影响,使得平均误比特率(BEP)的性能受到了的决定性影响。通过对调制器不均衡的模型讨论,深刻分析了调制器不均衡对载波跟踪环路稳态锁定点和平均BEP的影响。     

含同步误差的正交码CDMA系统性能分析

LS-95与WCDMA等正交码CDMA系统中均采用了相关接收机，所以只有在码元完全同步时才具有最优性能，但在实际接收机中，由于同步误差存在，会导致系统性能的下降。为此，文中着重分析了多径衰落信道中，存在同步误差与多址干扰时的正交码CDMA系统性能，推导了平均误比特率的计算公式，并在此基础上综合分析了信道特征、系统用户数、同步误差以及接收策略对系统性能的影响，为接收机的优化设计提供了理论依据和参考数据。     

Sensor array calibration for uniform rectangular array in presence of mutual coupling and sensor gain-and-phase errors

The sensor array calibration methods tailored to uniform rectangular array （URA） in the presence of mutual coupling and sensor gain-and-phase errors were addressed. First, the mutual coupling model of the URA was studied, and then a set of steering vectors corresponding to distinct locations were numerically computed with the help of several time-disjoint auxiliary sources with known directions. Then, the optimization modeling with respect to the array error matrix （defined by the product of mutual coupling matrix and sensor gain-and-phase errors matrix） was constructed. Two preferable algorithms （called algorithm I and algorithm II） were developed to minimize the cost function. In algorithm I, the array error matrix was regarded as a whole parameter to be estimated, and the exact solution was available. Compared to some existing algorithms with the similar computation framework, algorithm I can make full use of the potentially linear characteristics of URA＇s error matrix, thus, the calibration precision was obviously enhanced. In algorithm II, the array error matrix was decomposed into two matrix parameters to be optimized. Compared to algorithm I, it can further decrease the number of unknowns and, thereby, yield better estimation accuracy. However, algorithm II was incapable of producing the closed-form solution and the iteration operation was unavoidable. Simulation results validate the excellent performances of the two novel algorithms compared to some existing calibration algorithms.     

Relative efficiency appraisal of discrete choice modeling algorithms using small-scale maximum likelihood estimator through empirically tailored computing environment

Discrete choice models are widely used in multiple sectors such as transportation, health, energy, and marketing, etc., where the model estimation is usually carried out by using commercial software. Nonetheless, tailored computer codes offer modellers greater flexibility and control of unique modelling situation. Aligned with empirically tailored computing environment, this research discusses the relative performance of six different algorithms of a discrete choice model using three key performance measures: convergence time, number of iterations, and iteration time. The computer codes are developed by using Visual Basic Application (VBA). Maximum likelihood function (MLF) is formulated and the mathematical relationships of gradient and Hessian matrix are analytically derived to carry out the estimation process. The estimated parameter values clearly suggest that convergence criterion and initial guessing of parameters are the two critical factors in determining the overall estimation performance of a custom-built discrete choice model.

     

链条炉沼气再燃还原氮氧化物数值模拟与优化

为利用废弃沼气作为工业锅炉再燃燃料,实现对氮氧化物(NOx)的高效率还原,达到资源回收和NOx减排的目的.联用FLIC和FLUENT软件对工业锅炉床层及炉内燃烧特性进行了模拟,进而探究了CH4/NO摩尔比、沼气稀释比和沼气喷口布置形式对炉膛内NOx还原的影响.结果表明:CH4/NO摩尔比和两者混合程度是影响NOx还原两大主要因素,总体上NOx的还原率随着CH4/NO摩尔比和沼气稀释比的增大而升高;当CH4/NO摩尔比较小时,影响NOx还原率的主导因素是两者的混合程度;当沼气稀释到一定程度,其所具有的动量能够与主气流实现较好混合时,影响NOx还原率的主导因素是CH4/NO摩尔比;同时沼气稀释比的增大有利于减小气体不完全燃烧损失;为实现NOx高效率还原,再燃沼气喷口宜布置在前墙,但位置不宜过于偏下.本文能够为沼气在工业锅炉燃烧及NOx还原的工业应用提供一定的参考.     

精密机械热动态误差模糊神经网络建模研究

结合模糊逻辑与人工神经网络的优点,提出精密机械热动态误差的模糊神经网络模型,并在多变量模糊模型后件结构与参数辨识中提出了主分量分析建模的新方法.基于语言控制规则的模糊模型,采用模糊推理方法,建模的关键在于结构辨识和参数辨识. 采用主分量分析方法可有效地辨识模型后件的结构与参数.为克服建模用的有效数据量少于后件参数,而无法建立相应的模糊模型这一问题,采用一种多变量系统的模糊神经网络建模方法,利用神经网络具有学习的能力,通过使用适当数量的具有充分激励信息的优选数据组作为学习样本对神经网络进行训练,从而建立起模糊神经网络模型.当辨识的模型精度达不到要求时,可应用模糊神经网络的多次训练获取更高的模型精度.实测数据建模表明,模糊神经网络模型能有效地描述热动态误差.     

开槽结构中串扰的网络分析方法与低成本噪声抑制

提出一种可快速计算开槽结构中串扰特性的网络分析方法,该方法将返回平面开槽描述为槽线模式与微带线模式的相互耦合,进而将电路板结构分解为通过理想变压器连接的槽线结构和微带线结构模型.根据模型的级联特点,使用四端口传输矩阵进行分析.与全波仿真相比,此方法在保证准确度的前提下,可将分析时间从60min降低至30s.使用跨接于开槽两端的短路线来旁路槽线模式电磁场,从而改善传输特性,抑制串扰.仿真和实验测试表明,该方法可将近端串扰减小25dB,将远端串扰减小20dB.与传统的添加去耦电容方法相比,具有带宽大、布线方便、成本低等优点.     

多频干扰下混合DS—SFH／MSK扩频系统性能分析

分析了相干ＭＳＫ跳频调制的混合直接序列－慢跳频（ＤＳ－ＳＦＨ）扩频信号在部分频带多频干扰和加性白高期噪声下的性能。假调直接序列扩频后的信号带宽等于跳频频隙间隔,在此条件下推导了系统的误比特率公式,评价了在最恶劣干扰条件下系统的性能。分析中改变系统参数如ＤＳ／ＳＦＨ混合比、干扰频点数、信噪比及干信比,结果表明,在某些情况下,在慢跳频系统中加入直扩成分,在不增加系统总带宽的条件下,可以有效地改善系统对     

高等级公路圆曲线施工中的精确测设

随着公路等级的提高,对于道路中心线的精确性要求更高.因此,选择何种方法能够迅速、准确地测设曲线上各点位,是一个没有彻底解决的问题,通过对比圆曲线的多种测设方法,提出了极坐标法解算标定数据的新方法.     

高等数学考试中的一些错误分析

对高等数学考试中出现的一些错误进行了分析和归纳,并根据教学经验指出了学生在学习中的哪些因素可能导致这些错误,也分析了一些客观存在的因素,最后对改变这些现状进行了探讨,并提出了相应的建议。     

高等级公路圆曲线施工中的精确测设

随着公路等级的提高,对于道路中心线的精确性要求更高.因此,选择何种方法能够迅速、准确地测设曲线上各点位,是一个没有彻底解决的问题,通过对比圆曲线的多种测设方法,提出了极坐标法解算标定数据的新方法.     

Prediction of diameter errors compensation in bars turning

On the basis of analyzing the machine-workpiece-tool system, the main factors affecting diameter errors in bars turning are considered, and the mathematic models of the actual workpiece diameter at the cutting point are established according to the three usual methods of mounting workpieces on a turning machine. Further a predictionsystem for diameter errors is developed; a new method, called discrete nodes output, is presented and applied to expressing workpiece diameter errors at given points along the part axis, then off-line compensation is implemented according to the prediction values to diminish machining errors. The results indicate that the method can diminish diameter errors more than 70%, greatly improve the machining accuracy of bars.     

Prediction of diameter errors compensation in bars turning

On the basis of analyzing the machine-workpiece-tool system, the main factors affecting diameter errors in bars turning are considered, and the mathematic models of the actual workpiece diameter at the cutting point are established according to the three usual methods of mounting workpieces on a turning machine. Further a prediction system for diameter errors is developed; a new method, called discrete nodes output, is presented and applied to expressing workpiece diameter errors at given points along the part axis, then off-line compensation is implemented according to the prediction values to diminish machining errors. The results indicate that the method can diminish diameter errors more than 70%, greatly improve the machining accuracy of bars. Foundation item: Projects (50175081 and 50475117) supported by the National Natural Science Foundation of China; project (033181611) supported by the Tianjin Municipal Science and Technology Commission     

曲线运动切向加速度计算中的常见错误

在计算曲线运动的切向加速度时,经常出现用不同的方法得到不同结果的情形.为了解决这一问题,对计算曲线运动切向加速度的常用方法进行了研究,发现产生这一问题的原因是相当一部分大学物理教材中的切向加速度的计算公式是不正确的,这些教材中的公式是质点的加速度在轨迹曲线的切线方向上的投影等于质点的速率对时间的导数.其实正确的公式应该是质点的加速度在轨迹曲线的切线方向上的投影等于质点的速度在轨迹曲线的切线方向上的投影对时间的导数.     

AHP中几个保序定理的新证明

在ＡＨＰ的排序理论中，保序性是一个十分重要的问题．本文给出ＡＨＰ中几个保序定理新的、简单的证明     

东部温润季冻区公路三级自然区划方法

公路自然区划具有很强的模糊性,为了在区划工作中减少人为主观因素的影响,使所作的公路自然区划更具科学性,本文以模糊数学理论为基础,提出了以模糊聚类分区方法进行东部温润季冻区三级自然区划的分区思想.以鲁豫轻冻区(Ⅱ5)三级自然区划为例,提炼分区指标,建立指标权重向量,构建模糊相似矩阵,依据自然因素对公路工程综合影响的相近程度,采用直接聚类法进行聚类分区,并结合地理相关性分析法对模型分区结果进行适当调整,最终确定了鲁豫轻冻区(Ⅱ5)的三级自然区划方案.