含持久生存数据模型的识别问题

混合和非混合模型被广泛地用于拟合含有持久生存者的生存数据．当添加有协变量时,这两类模型却都不具有比例危险率(PH)结构．“不正确”比例危险率模型能克服上述缺点．本文研究此模型的识别问题．同时也考虑“不正确”的可加危险率(AH)模型的识别问题．本文的结果对模型的参数估计有重要意义．     

从PISA到“面向未来”科学素养调查

PISA的评估具有前瞻性,它的焦点不在于评估学生对学校课程的掌握程度,而是着眼于真实生活的挑战。与PISA的评估重点有类似的精神实质,新课程也要求将学生科学素养发展的焦点从“知道什么”向“能做什么”转变。“面向未来”科学素养调查借鉴PISA的思路和方法,探索性地建立了评估科学素养发展的五能力模型和情景化测试的方法。调查的实践成功地描述了学生发展的现状,找到了问题所在,对科学教育提供了有价值的建议。调查证明,以“面向未来”为价值导向,以“能力”为评估对象,是评估学生科学素养发展和科学课程改革的可操作、有成效的评估方案。     

广义根方估计的效率

讨论了线性回归模型中未知参数最小二乘估计的改进,引入了一种估计的相对效率,证明了广义根方估计比狭义根方估计的效率较高。     

Parameter Estimation Accuracy of the Effort-Moderated Item Response Theory Model Under Multiple Assumption Violations

As low-stakes testing contexts increase, low test-taking effort may serve as a serious validity threat. One common solution to this problem is to identify noneffortful responses and treat them as missing during parameter estimation via the effort-moderated item response theory (EM-IRT) model. Although this model has been shown to outperform traditional IRT models (e.g., two-parameter logistic [2PL]) in parameter estimation under simulated conditions, prior research has failed to examine its performance under violations to the model’s assumptions. Therefore, the objective of this simulation study was to examine item and mean ability parameter recovery when violating the assumptions that noneffortful responding occurs randomly (Assumption 1) and is unrelated to the underlying ability of examinees (Assumption 2). Results demonstrated that, across conditions, the EM-IRT model provided robust item parameter estimates to violations of Assumption 1. However, bias values greater than 0.20 SDs were observed for the EM-IRT model when violating Assumption 2; nonetheless, these values were still lower than the 2PL model. In terms of mean ability estimates, model results indicated equal performance between the EM-IRT and 2PL models across conditions. Across both models, mean ability estimates were found to be biased by more than 0.25 SDs when violating Assumption 2. However, our accompanying empirical study suggested that this biasing occurred under extreme conditions that may not be present in some operational settings. Overall, these results suggest that the EM-IRT model provides superior item and equal mean ability parameter estimates in the presence of model violations under realistic conditions when compared with the 2PL model.     

Parameter estimation of an unstable system with a PID controller in a closed loop configuration

An essential part of the auto-tuning control involves parameter estimation of a suitable low order model. Since a common way to control an unstable system is via a PID controller, there is a growing interest in the application of new PID-based algorithms for the identification task. In this light the relative advantages of two recently published methods are investigated. The first method is based on typical data of the reaction curve and the time delay is measured directly from the initial portion of the curve. The second method utilizes a least-squares algorithm to get an equivalent time delay together with the values of the other parameters. Thus, the obtained time delay approximates not only the true delay but also part of the nonlinear and the higher order dynamics. This is an advantage when a PID auto-tuning is sought. Two examples are provided to demonstrate and compare between the results of the methods.     

运动补偿图像编码中的并行三步算法

本文提出了一种计算运动图像位移矢量Ｄ的新算法。这种新算法称为并行三步算法，模拟结果表明：这种新算法比现有的同类算法有更好的性能。     

基于对地观测数据的城镇人口估算方法研究（英文）

本文对对地观测数据支持下的城镇人口估算方法进行了研究。首先，将研究区的居民地划分为高密度区、中密度区和低密度区，并且通过解译IKONOS数据获取各类型居民地的面积；然后，通过线性相关分析，研究居民地面积与居民人口之间的相关关系，并建立了相关关系式；最后，应用训练数据对居民地面积与居民人口之间的关系式进行了检验，结果显示：应用对地观测数据进行城镇人口估算，在理论上可信、方法上可行，是城镇应急状态下进行人口估算的可取方法。     

A simple channel estimator for space-time coded OFDM systems in rapid fading channels

A simple channel estimator for space-time coded orthogonal frequency division multiplexing (OFDM) systems in rapid fading channels is proposed. The channels at the training bauds are estimated using the EM (expectation-maximization) algorithm, while the channels at the data bauds are estimated based on the method for modelling the time-varying channel as the linear combination of several time-invariant "Doppler channels". Computer simulations showed that this estimator outperforms the decision-directed tracking in rapid fading channels and that the performance of this method can be improved by iteration.     

基于遗传算法的阵列相位误差校正

针对声纳水听器阵列比较突出的相位误差,研究了一种基于遗传算法的阵列校正方法。该方法利用无相位误差时阵列协方差矩阵具有Toeplitz结构的特性构造代价函数,并以此作为遗传算法中进化个体的适应度函数,由算法搜索的最优个体得到阵元相位误差的估值。计算机仿真结果表明,该方法可以明显地减小阵列相位误差对MUSIC算法DOA估计结果的影响。