Detection of multiple cracks using frequency measurements

A method for detection of multiple open cracks in a slender Euler-Bernoulli beams is presented based on frequency measurements. The method is based on the approach given by Hu and Liang [J. Franklin Inst. 330 (5) (1993) 841], transverse vibration modelling through transfer matrix method and representation of a crack by rotational spring. The beam is virtually divided into a number of segments, which can be decided by the analyst, and each of them is considered to be associated with a damage parameter. The procedure gives a linear relationship explicitly between the changes in natural frequencies of the beam and the damage parameters. These parameters are determined from the knowledge of changes in the natural frequencies. After obtaining them, each is treated in turn to exactly pinpoint the crack location in the segment and determine its size. The forward, or natural frequency determination, problems are examined in the passing. The method is approximate, but it can handle segmented beams, any boundary conditions, intermediate spring or rigid supports, etc. It eliminates the need for any symbolic computation which is envisaged by Hu and Liang [J. Franklin Inst. 330 (5) (1993) 841] to obtain mode shapes of the corresponding uncracked beams. The proposed method gives a clear insight into the whole analysis. Case studies (numerical) are presented to demonstrate the method effectiveness for two simultaneous cracks of size 10% and more of section depth. The differences between the actual and predicted crack locations and sizes are less than 10% and 15% respectively. The numbers of segments into which the beam is virtually divided limits the maximum number of cracks that can be handled. The difference in the forward problem is less than 5%.     

Vibrations of stretched damped beams under non-ideal boundary conditions

A simply supported damped Euler-Bernoulli beam with immovable end conditions are considered. The concept of non-ideal boundary conditions is applied to the beam problem. In accordance, the boundaries are assumed to allow small deflections and moments. Approximate analytical solution of the problem is found using the method of multiple scales, a perturbation technique.     

空爆毁伤地面机动目标扫描准则研究

文中主要针对多爆炸成型弹丸空爆战斗部,在分析区域识别和占空比识别两种不同扫描准则的基础上,应用蒙特卡洛方法计算了战斗部对目标的毁伤概率.通过仿真计算结果对比分析,获得了不同扫描准则对毁伤概率的影响,结果可为多爆炸成型弹丸空爆战斗部设计和选择使用扫描准则提供参考依据.     

数据录入约束与导航器

信息软件使用的方便性、易用性、安全性和稳定性在很大程度上取决于数据录入方式的优劣。分析了数据录入的约束规则，探讨了录入导航原理，并介绍了一种已在开目管理软件中普遍采用的数据录入导航器组件。     

数字加速度传感器ADXL210在轨检仪中的应用

介绍了一种轨道检测仪及其重要传感器数字加速度传感器ADXL210的工作原理、功能、应用，并给出了ADXL210与MCS－51单片机的接口硬件电路和软件程序。     

带有块间串扰MC-CDMA的时域信道估计和多用户检测

本文把带有IBI的MC-CDMA系统等效解释为特殊的直接序列码分多址（DS-CDMA）系统，并给出了相应的时域信道估计方法和时域线性最小均方误差（MMSE）多用户检测方法。仿真实验表明了本文方法的性能。     

震源延迟叠加技术及应用效果

延迟叠加爆炸是针对高分辨率和深层地震勘探而提出来的一种激发方式。这种激发方式能在保证地震分辨率的前提下有效提高地震波能量 ,在地震波的入射角范围内 ,有效克服非球形炸药激发引起的地震波传播的方向性。应用弹性波动力学对多级延迟爆炸进行理论研究 ,结合实际试验资料 ,研究了延迟爆炸情况下激发参数对地震波能量、主频、频宽等的影响。从几何地震学出发 ,分析了不同时间激发的地震波在地下空间中的干涉情况 ,对其能量传播的方向性进行了研究。理论分析和试验效果表明 ,延迟叠加震源与相同药量的普通震源相比 ,激发地震波的主频高 ,频带宽 ,增强了下传能量 ,降低了次生干扰 ,在高分辨率和深层地震勘探中具有明显的优势。     

低功耗反射式连续波雷达模拟源的设计

介绍了一种基于DDS的连续波雷达模拟源的设计方案。阐述了其工作原理,并详细介绍了组成该模拟源的主要部件的工作原理和技术指标。实践表明,其具有大动态功率输出范围、高频率稳定度和低功耗的特点,连续工作时间长,使用方便灵活。最后推导出了模拟源雷达截面的计算公式。     

On the Auditory Modality Superiority Effect in Serial Recall: Separating Input and Output Factors.

The modality effect in immediate recall refers to superior recall of the last few items within lists presented in spoken as opposed to printed form. The locus of this well-known effect has been unclear. N. Cowan, J. S. Saults, E. M. Elliott, and M. Moreno (2002) introduced a new method to distinguish between the effects of input serial position, output serial position, and the number of items yet to be recalled and found that large modality effects occurred only in conditions in which delay and interference at output (from items already recalled) was high. The authors replicated that finding, even when the response period included output interference acoustically similar to the spoken stimuli to be recalled. However, the authors found that output delay and interference act only by lowering the level of performance to a more sensitive range. The modality effect thus originates during encoding of the list to be recalled, not during output. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

论工艺参数对烧结产质量的影响及分析

本文论述了正确认识烧结工艺参数对搞好烧结生产的意义，介绍了烧结工艺参数其及相互关系，详述了烧结主要工艺参数对其产质量的影响，提出了烧结工艺参数认识的几点结论性意见。