用功、能增量方法研究压杆跳跃性屈曲

在微弯杆件平衡位置作准静态位移时,以任一点处的状态为参考态,建立的平衡位置有微位移时,用功、能增量平衡关系,可以直接导得相应突变模型的平衡方程来对杆跳跃式屈曲行为进行分析。该研究途径也可用于其他弹性体跳跃式屈曲问题。

混凝土收缩徐变分析的虚功增量方程及应用

为计算大跨柔性混凝土结构的力学响应,常需同时进行非线性与混凝土收缩徐变分析。基于非线性分析的虚功增量方程和混凝土收缩徐变的本构关系导出了用于非线性与收缩徐变耦合计算的混凝土收缩徐变分析的虚功增量方程,并将该虚功增量方程应用于杆系结构,结合拖动坐标法建立了非线性有限元格式的不平衡力的计算方法。通过算例表明,该文方法能够同时计算结构的非线性效应和收缩徐变效应,并且解的精度取与非线性的分析精度相同。

岩土塑性理论中功表达的近似性

对广义剪应力、广义剪应变的表达式作了说明,在给出其增量表达的同时,指出了在计算二者增量时可能产生的误解。在此基础上,分析比较由平均主应力、体积应变增量、广义剪应力、广义剪应变增量表述的功的增量以及由三向主应力与三向主应变增量表述的功的增量得出:两种表述在一般情况下并不一致。但在某些特殊情况下,例如等应力Lode角加载并满足应力全量Lode角与应变增量Lode角相等时,二者的表述一致。岩土塑性理论中塑性功增量存在与功的增量相同的问题,然而对于实际岩土材料,应力全量与塑性应变增量等Lode角的假定在一般情况下是不能满足的。因此在岩土塑性理论中,对于一般情况下的等应力Lode加载情况,用平均主应力、塑性体积应变增量、广义剪应力、塑性广义剪应变增量表述的塑性功增量也只是一种近似。

惯性矩二次变化变截面梁柱几何非线性分析

为研究考虑剪切变形的变截面梁杆结构几何非线性问题,应用Timoshenko梁理论,采用位移、转角独立插值的方法,获取考虑剪切影响的惯性矩二次变化变截面梁单元的形函数;从严格的虚功增量方程出发,建立同时考虑轴力、剪切、弯曲效应及其耦合项的平面变截面梁柱单元几何非线性增量平衡方程,得到惯性矩二次变化变截面梁单元大位移切线刚度阵;与经典算例进行对比,验证了本文方法的精确性与有效性.

狭窄煤柱岩爆的突变理论分析

基于简化的狭窄煤柱岩爆分析模型和功、能增量平衡关系,导得狭窄煤柱岩爆的突变模式属折迭突变模型。该突变模型的平衡方程和平衡路径所展示的全部性态,可对煤柱以岩爆形式破坏和渐进形式破坏过程中包括系统稳定性在内的所有主要行为作一一对应的描述。首次给出的岩梁弹性能变化(释放)率曲线包含了丰富的信息量,对理解岩梁-煤柱系统在各阶段的行为规律有着重要的作用。能量输入率0=J是系统失稳的临界条件,其表达式中蕴涵了Cook刚度判据,故可视为Cook判据能量形式的动态推广。

大挠度梁静态变形对动态特性影响分析

在经典梁理论基础上,引入剪切修正因子,采用U.L法,推导了新的空间大挠度梁的切线刚度矩阵;以三维连续体增量虚功原理为基础,建立了空间大挠度梁考虑剪切影响的静态分析模型和动态特性分析模型;首先根据所建立的模型进行了大挠度梁的静态特性分析,验证了模型的正确性;然后进行了大挠度梁的动态特性分析,揭示了悬臂梁静态大变形对动态特性的影响规律。指出悬臂梁在大载荷作用下,结构固有频率会因为梁的大变形而发生明显变化,基频变化尤为明显。

杆系结构几何非线性分析的有限元法(二)——空间问题

以三维连续体的虚功增量方程为基础,采用平动和转角位移分别插值的方法,导出了三维空间梁结构大位移、大转动问题内力分析的 UL 法(Updated Lagrangian FormuIation)。考虑轴向、剪切、弯曲和扭转效应,提出了新的几何刚度矩阵,并建立了描述大转动规律的坐标转换矩阵。算例表明,依本文方法编制的程序具有分析结构强几何非线性行为的能力;在满足本文假定(即每次加载增量中转角增量是小量)的条件下,可以描述任意大角度的刚体转动。

家族企业“创新致富”模式研究

中国的家族企业要实现可持续发展,需要进行致富模式的转型。中国经济的崛起和所处的转型阶段使“创新致富”成为一种极具竞争力的家族企业新型致富模式。家族企业无论采取哪种创新形式,基于整体观的“创新致富”模式价值边际分析都是必不可少的。其中企业创新价值增量分析和“创新致富”方案的优化,有利于实现家族企业致富模式的转型。

A continuous differentiable wavelet threshold function for speech enhancement

Enhanced speech based on the traditional wavelet threshold function had auditory oscillation distortion and the low signal-to-noise ratio (SNR). In order to solve these problems, a new continuous differentiable threshold function for speech enhancement was presented. Firstly, the function adopted narrow threshold areas, preserved the smaller signal speech, and improved the speech quality; secondly, based on the properties of the continuous differentiable and non-fixed deviation, each area function was attained gradually by using the method of mathematical derivation. It ensured that enhanced speech was continuous and smooth; it removed the auditory oscillation distortion; finally, combined with the Bark wavelet packets, it further improved human auditory perception. Experimental results show that the segmental SNR and PESQ (perceptual evaluation of speech quality) of the enhanced speech using this method increase effectively, compared with the existing speech enhancement algorithms based on wavelet threshold.

Study on HPM Power Measurement by Dipole Aatenna

In order to reduce the gain of a receiving antenna in HPM power measurement,especially in lower frequency, a low gain dipole antenna of L band is designed.By theoretical analysis and numerical simulation,the optimized results of the antenn are obtained:its central frequency is 1.75GHz,the variety of gain is less than 1.1dB in frequency band 1.70—1.80GHz,the estimated value of the power capacity of the antenna is 0.1MW,which can satisfy the demand of corresponding measurement.

Ion dynamics associated with substorm dipolarization fronts

We report where and how ions are accelerated in the proximity of earthward propagating dipolarization fronts （DFs） in the magnetotail during a magnetospheric substorm on February 15, 2008. Two DFs were observed by multiple THEMIS space- craft in the near-Earth magnetotail （-10 Re）. We studied the ion dynamics associated with these DFs by comparing observed results with large scale kinetic （LSK） simulation results. The LSK simulation reproduced the sudden ion energy flux enhance- ment concurrent with the arrival of the DF at the satellite locations. We found that ions can be accelerated to more than 100 keV energy at the DF. These ions were initially non-adiabatically accelerated near magnetic reconnection site and then still non-adiabatically accelerated at the DF structure.

Fangjihuangqi Tang improved lower urinary tract dysfunction in benign prostatic hyperplasia rats model

OBJECTIVE: To investigated the effect and mechanism of Fangjihuangqi Tang (FHT) on lower urinary tract dysfunction induced by benign prostatic hyperplasia (BPH) in rats. METHODS: Male rats were randomly divided into seven groups: normal, model, finasteride (0.5 mg/ kg), terazosin (0.5 mg/kg), and FHT (10, 5, 2.5 g/kg). Rats were administered testosterone (0.5 mg sc) for 6 weeks after orchiectomy, excluding the normal group. All rats were intragastrically administered assigned drugs for 4 weeks from the third week. Urodynamics were assessed in rats under anesthesia. Serum dihydrotestosterone (DHT) and prostatic acid phosphatase (PAP) were measured. The prostate index (PI), bladder index (BI), and pathological detection were evaluated. RESULTS: In the model group, the PI, BI, serum DHT, serum PAP, threshold pressure (TP), micturition pressure (MP), and residual urine volume (RV)were significantly higher. Moreover, inter-micturition duration (IMD) was significantly lower and the prostatic and bladder showed obvious pathological changes. The IMD was significantly higher, while BI, TP, MP, and RV were significantly lower and bladder pathological changes were alleviated in the FHT (10, 5 g/kg), finasteride, and terazosin groups. The PI, DHT, and PAP were significantly lower in the finasteride group, but they did not change significantly in the FHT (10, 5, 2.5 g/kg) and terazosin groups. CONCLUSION: FHT could relieve symptoms of lower urinary tract dysfunction in BPH rats but with no apparent effect on reducing the volume of the enlarged prostate itself.