Research advance in safety analysis methods for high concrete dam

High tensile stresses occurred in high concrete dams and in their foundation lead to the growing importance of their safety with the increase of concrete dam height.Without any exiting specification or successful experiences of concrete dams up to 300 m at home and abroad for reference,experts feel obliged to figure out how to perform safety analysis on high concrete dam.This paper involves the main contents and mechanical features of the safety analysis on high concrete dam and shows the current state and progress of the analysis methods.For the insufficiency and problems existing in normative methods,study on modern numerical method such as finite element method must be strengthened to find out the stress control criterion which is in accordance with the methods.Two aspects of the safety analysis of high dam--local damage from material level and integral destruction from structure level--should be considered.For the local damage,we should consider the non-homogeneity of material and strengthen the research of meso-damage mechanics.While for integral destruction of the system of high dam and its foundation,a study on non-strength theory should receive enough concerns.Further,attention should be paid to the research on the failure modes and criterions of high concrete dam failure analysis and safety evaluation,and the effect of uncertainty and classification of safety should be considered too.     

5GHz0．18μm CMOS功率放大器设计

文中介绍了一个基于TSMC 0．18μm CMOS工艺,可应用于802．11a无线局域网标准的功率放大器设计。该电路采用三级全差分结构,驱动级采用电阻并联负反馈网络来保证稳定性。在3．3V电源电压下,增益为16dB,输出1dB压缩点为17dBm,电路功耗为0．8 W,效率为18．1%。芯片面积为1．2mm×1．1 mm。     

粗粒度可重构结构的性能估计方法

在设计初期,估计粗粒度可重构结构的性能,对粗粒度可重构结构设计具有指导意义.在考虑局部数据存储器结构以及局部数据存储器与可重构阵列的接口结构的情况下,建立了粗粒度可重构结构的参数模型,使用改进的螺旋形绑定策略将应用算法DFG(Data Flow Graph)中的算子绑定到可重构阵列的处理单元上,提出了一种粗粒度可重构结构的性能估计方法.应用实例表明,在设计初期,该方法能得到周期精确的估计结果,有效地指导粗粒度可重构结构的设计.     

基于局部频谱连续细化的高精度频率估计算法

针对噪声环境下多普勒频率的快速、精确估计问题，提出了一种基于局部频谱连续细化的高精度频率估计算法．该算法先采用快速傅里叶变换对信号进行粗略的频谱估计，获取到感兴趣的窄带频谱范围后，再进行频域细化分析．由于在细化过程中采取时、频域两次加窗技术，将噪声抑制与频谱分析有机地结合在一起，提高了估计精度和频域稳定性，降低了计算量．     

一种局部频率估计的区域生长相位展开方法

提出了一种干涉SAR相位展开算法,该方法假设局部展开相位为理想平面,利用最大似然频率估计器估计出局部频率,并结合已展开的相位,共同推测出局部区域中心像素的展开相位;该方法整体上采用区域生长策略,由高质量的区域逐步向低质量的区域进行相位展开,最大限度地减少了误差传递.     

局部火灾下变截面门式钢刚架结构温度场的数值模拟

采用有限元法对门式钢刚架结构中的变截面梁进行了数值模拟,分别得到其在ISO标准升温曲线和局部火灾下的温度场变化,考察了升温曲线及火源位置对变截面梁升温的影响.该方法可以为大空间局部火灾下相关结构的抗火设计方法的研究提供参考.     

基于改进LMD方法的电压骤降检测与分析

随着新能源并网技术的普及和发展,大量非线性装置接入电网对其电能质量产生了一定影响,因此有必要对电能质量进行检测和分析。针对现有检测识别方法存在抗噪性和精确性不足的问题,提出一种改进的LMD方法。该方法首先对自适应分解方法筛选过程的机理进行研究,分析了极值点拟合分布程度容易受到高频间断信号干扰,提出对原始信号先加入受控高斯白噪声再进行LMD分解。其次针对特征参数提取部分存在端点能量泄漏问题,提出采用经验调制分解方法对瞬时参数进行检测的方式。通过仿真实验表明所提方法可以有效抑制模态混叠和端点效应。最后搭建了电压骤降实验平台,运用实测数据验证了所提方法能够准确提取电压骤降的各个扰动参数,从而为电能质量扰动分析提供了一种新思路。     

西门岗传统骑楼街区的现状及改造策略

骑楼作为岭南城市的传统建筑形式,集交通、住宅、商业和娱乐于一体,富有浓郁的岭南地域特色,具有极高的人文价值和经济价值。随着城市的快速扩张,广东省云浮市罗定市旧城区西门岗传统骑楼街区的街道存在公共街道遭到占用、交通指示系统缺失、道路残旧不堪等问题,而街区建筑存在传统建筑与翻新建筑风貌迥异、现代建筑肆意而建等问题。针对这种现状,对西门岗街道的改造可采取整体性保护、原真性保护和科学性改造三大策略;对街区建筑的改造可采取拆除、保护与新建的策略:拆除不协调的现代建筑及违章建筑,以功能置换等方法对传统骑楼进行改建和保护,对由于城市扩张所需的新建建筑采用传统骑楼的形制。     

A local meshless method for Cauchy problem of elliptic PDEs in annulus domains

This paper is concerned with the development of a meshless local approach based on the finite collocation method for solving Cauchy problems of 2-D elliptic PDEs in annulus domains. In the proposed approach, besides the collocation of unknown solution, the governing equation is also enforced in the local domains. Moreover, to improve the accuracy, the method considers auxiliary points in local subdomains and imposes the governing PDE operator at these points, without changing the global system size. Localization property of the method reduces the ill-conditioning of the problem and makes it efficient for Cauchy problem. To show the efficiency of the method, four test problems containing Laplace, Poisson, Helmholtz and modified Helmholtz equations are given. A numerical comparison with traditional local RBF method is given in the first test problem.     

NEXAFS study of electronic and atomic structure of active layer in Al/indium tin oxide/TiO2 stack during resistive switching

We have studied the stability of the resistive switching process in the Al/(In₂O₃)_0.9(SnO₂)_0.1/TiO₂ assembly grown by atomic layer deposition. Besides electrical characterization the effect of electric field on the atomic electronic structure of the TiO₂ layer was studied using near edge X-ray absorption fine structure (NEXAFS) spectroscopy. The region of the current instability in the I-V characteristics was revealed. Presumably this current instability is supported by the amorphous structure of the TiO₂ film but is initiated by the surface morphology of the Al substrate. A formation of the O₂ molecules was established which occurs specifically in the region of the current instability that is a result of electrical Joule heating manifestation.