树形多体Hamilton系统的Lyapunov指数计算方法

研究了树形多体Hamilton系统Lyapunov指数的数值方法.利用多体Hamilton系统的正则方程和辛算法, 给出了多体Hamilton系统Lyapunov指数的计算方法,该算法具有较好的计算精度和通用性.利用该算法可对系统的运动稳定性进行分析.最后用算例说明了该算法的有效性.      

对称面圆周角对轴对称降落伞流场特性的影响

根据降落伞的特点,通过3点假设(伞衣薄膜、伞的轴对称和流场定常),将三维复杂流动问题转化成二维轴对称问题,以节约计算时间.定义对称面圆周角,保持伞衣幅底部直径和顶孔直径不变,选取对称面圆周角在80°~140°范围内变化,建立一系列轴对称降落伞的计算模型.利用数值模拟手段,求解RNG (Renormalization Group)k-epsilon湍流模型下的N-S方程组,获得与有关单位试验相吻合的计算结果.分析发现对称面圆周角和伞衣幅高度对降落伞阻力影响很小.算例中阻力随对称面圆周角的变化在±0.28%以内.对称面圆周角的变化对轴对称降落伞尾流区流场的拓扑结构没有影响.对称轴上存在2个鞍点,随着对称面圆周角的增大,第1个鞍点的位置几乎不变,第2个鞍点的位置向尾流方向推移.      

On the clustering of foF2 time series corresponding to disturbed ionospheric periods

This paper presents an analysis of a set of time series that represent foF2 disturbances during storm conditions, using clustering tools. The time series under study have been drawn from ionospheric observations obtained from eight European middle latitude ionosondes during a significant number of storm-time intervals and they are divided into eight groups according to the latitude (middle to low and middle to high) and the local time of the observation point at storm onset (afternoon, evening, morning, prenoon). The time series in each group have been analyzed using clustering-based methods. Specifically, each time series has been represented using two different ways of representation: the first is the raw representation while the second is through the parameters of the autoregressive (AR) model that best represents it. For each representation a hierarchy of clusterings is produced via the complete link algorithm. The two produced hierarchies are combined to a single one and the final clustering results are extracted from the produced hierarchy. The obtained results are in close agreement with the theoretical formulations concerning ionospheric storm effects at middle latitudes. In addition, they may be proved useful in the development of more accurate ionospheric forecasting methods.     

On mid-term periodicities of high-latitude solar activity

The mid-term periodicities of polar faculae are studied separately for the total disk, northern and southern hemispheres of the Sun for a time interval from 1951 August to 1998 December. Apart from the 11-year Schwabe cycle which is the fundamental period and is found in all of the three time series, the following prominent results are found: (1) the rotational periodicity of solar activity at high latitudes is approximately from 28 to 32 days; (2) a large number of quasi-periods appearing in low-latitude solar activity (annual variation, 1.3–1.7 years, quasi-biennial oscillation, and 4–5 years) also exist in polar faculae; (3) the periodicities on both hemispheres are not identical.     

模拟电子线路教学方法和教学手段改革与实践

模拟电子线路课程是工科院校最重要的专业基础课之一,基于当前高等教育对创新人才培养的迫切要求和国内高校教学条件不断改善的前提,从多年的教学实践出发,指出新形势下模拟电子线路教学方法和教学手段改革的必要性和具体实施办法.     

紧缩场超高频（UHF）天线测试方法的研究

针对CCR120／100紧缩场超高频（UHF）天线测试的问题，根据紧缩场的现有条件，给出了利用紧缩场进行UHF天线辐射特性测试的方法，以及进一步提高测试精度的方法，以满足卫星UHF频段天线辐射特性测试的需求。     

Investigating γ- and X-ray properties of GRBs using multivariate statistics

We propose to study the interrelation between the γ- (Fluence, 1sec Peakflux, duration) and X-ray (early X flux, 24 h X flux, X decay index, X spectral index, X HI column density) properties using the canonical correlation method. Computing the canonical correlations and variables we show that there is a significant interrelation between the γ- and X-ray data. Using the canonical variables from the analysis, we computed their correlations (canonical loadings) with the original ones. The canonical loadings revealed that the γ-ray fluence and the early X-ray flux give the strongest contribution to the correlation in contrast to the X-ray decay index and spectral index. An interesting new result appears to be the strong contribution of the HI column density to the correlation. Accepting the collapsar model of long GRBs this effect may be interpreted as an indication for the ejection of an HI envelope by the progenitor in the course of producing the GRB.     

Effects of Communication Methods on Communication Patterns and Performance in a Remote Spatial Orientation Task

Abstract

An experiment was conducted to examine the impact of communication methods (text-only, audio-only, and audio-plus-video) on communication patterns and effectiveness in a 2-person remote spatial orientation task. The task required a pair of participants to figure out the cardinal direction of a target object by communicating spatial information and perspectives. Results showed that overall effectiveness in the audio-only condition was better than the text-only and audio-plus-video conditions, and communication patterns were more predictive of errors than individual differences in spatial abilities. Discourse analysis showed that participants in the audio-plus-video condition performed less mental transformation of spatial information when communicating, which led to more interpretation errors by the listener. Participants in the text-only conditions performed less confirmation and made more errors by misreading their own display. Results suggested that speakers in the audio-plus-video condition minimized effort by communicating spatial information based on their own perspective but speakers in the audio-only and text-only conditions would more likely communicate transformed spatial information. Analysis of gestures in the audio-plus-video condition confirmed that iconic gestures tended to co-occur with spatial transformation. Iconic gesture rates were negatively correlated with transformation errors, indicating that iconic gestures more likely co-occurred with successful communication of spatial transformation. Results show that when visual interactive feedback is available, speakers tend to adopt egocentric spatial perspectives to minimize effort in mental transformation and rely on the feedback to ensure that the hearer correctly interprets the information. When visual interactive feedback is not available, speakers will put more effort in transforming spatial information to help the hearer to understand the information. The current result demonstrated that allowing two persons to see and communicate with each other during a remote spatial reasoning task can lead to more errors because of the use of a suboptimal communication strategy.     

传输型线阵测绘相机几何精度标定方法

分析了传统框幅式测绘相机几何精度评价和测试方法的局限性：不适用于以长焦距、小视场角为主的传输型线阵测绘相机。从传输型测绘相机原理出发。分析了以视主点作为传输型测绘相机主点评价指标的合理性和可行性。指出了同传统方法相比在几何精度标定过程中需要注意的问题并提出标定方法。