气体火花开关电极烧蚀研究

采用Mo,WCu和W分别作为三种气体火花开关的主电极材料,进行放电条件下电极烧蚀实验,研究开关电极烧蚀率和烧蚀形貌,分析电极烧蚀特征。结果表明,Mo,WCu和W开关的主电极烧蚀率分别为3.32×10-2 C-1·m-2,2.63×10-2 C-1·m-2和1.74×10-2 C-1·m-2,W开关主电极烧蚀率最小。实验后开关的主电极中心烧蚀严重,呈现明显裂纹和烧蚀坑。Mo主电极表面呈现明显熔融态,阴极表面形成大量裂纹(宽度达10μm)和孔隙(孔径达10μm);WCu和W主电极表面形成少量圆球状W突起(粒径达20μm及以上)。开关外壳内壁沉积了喷溅颗粒。WCu开关外壳沉积颗粒较大(粒径达10μm),Mo开关外壳沉积颗粒居中(粒径为2μm),W开关外壳沉积颗粒最小(近1μm)。因此可优先选用具有优异抗烧蚀性能的W作为气体火花开关电极材料。     

4种鹭的繁殖生态

1999-2001年对池鹭、牛背鹭、白鹭、夜鹭混群的迁入状况、繁殖行为、雏鸟生长等进行了观察研究。结果表明：鹭鸟数量逐年增多，种类由2种增加到4种，4种鹭鸟在筑巢、取食和生活习性等方面具有一定的种群协调性。4种鹭鸟的食物组成存在一定差异。夜鹭以蛙类和鱼类为主；白鹭以鱼类和甲壳类为主，另有蛙类和昆虫类；牛背鹭的食物主要由昆虫类和蛙类组成；池鹭以鱼类为主。幼鸟体重生长率与成体体型大小成负相关，比较分析4种鹭鸟体重增长曲线，以池鹭和牛背鹭生长较快。     

一类具有弱奇异核的偏积分微分方程的Chebyshev小波数值方法（英文）

本文提出一种基于第四类Chebyshev小波配置法,求解了一类具有弱奇异核的偏积分微分方程数值解.利用第四类移位Chebyshev多项式,在Riemann-Liouville分数阶积分意义下,导出Chebyshev的分数次积分公式.通过利用分数次积分公式和二维的第四类Chebyshev小波结合配置法,将具有弱奇异核的偏积分微分方程转化为代数方程组求解.给出了第四类Chebyshev小波的收敛性分析.数值例子证明了本文方法的有效性.     

Clifford M\"{o}bius变换与Hypergenic函数

首先,在实Clifford代数空间Cl_n+1,0(R)中给出了与Clifford Mbius变换相关的一些定理.其次,证明了hypergenic函数与Clifford Mobius变换的复合可以得到一个加权的hypergenic函数.     

马尔可夫链及其在股市分析中的应用

本文运用马尔可夫链理论预测股票价格分析股市,提出了股价运行周期和投资收益的最大化理论,并建立其随机过程模型,使决策的长期效益趋于最优,通过实例检验,证明了此模型的可行性和实用性.     

Robustness measurement of scale-free networks based on motif entropy

As a classical complex network model, scale-free network is widely used and studied. And motifs, as a high-order subgraph structure, frequently appear in scale-free networks, and have a great influence on the structural integrity, functional integrity and dynamics of the networks. In order to overcome the shortcomings in the existing work on the robustness of complex networks, only nodes or edges are considered, while the defects of high-order structure in the network are ignored. From the perspective of network motif, we propose an entropy of node degree distribution based on motif to measure the robustness of scale-free networks under random attacks. The effectiveness and superiority of our method are verified and analyzed in the BA scale-free networks.     

Near-zero thermal expansion in β-CuZnV2O7 in a large temperature range

We report a new type of near-zero thermal expansion material β-CuZnV₂O₇ in a large temperature range from 173 K to 673 K. It belongs to a monoclinic structure (C2/c space group) in the whole temperature range. No structural phase transition is observed at atmospheric pressure based on the x-ray diffraction and Raman experiment. The high-pressure Raman experiment demonstrates that two structural phase transitions exist at 0.94 GPa and 6.53 GPa, respectively. The mechanism of negative thermal expansion in β-CuZnV₂O₇ is interpreted by the variations of the angles between atoms intuitively and the phonon anharmonicity intrinsically resorting to the negative Grüneisen parameter.     

Improving sound diffusion in a reverberation tank using a randomly fluctuating surface

Underwater reverberation environments that satisfy the conditions of uniformity and isotropy of the diffuse field can be used to measure the acoustic characteristics of underwater targets. This study combines two practical indicators — the standard deviation of the absolute sound pressure field (to indicate uniformity) and the analysis of the wavenumber spectrum in the spherical harmonics domain (to indicate isotropy) — for an accurate evaluation of the diffusion of the sound field in a reverberation tank. A method is proposed that can improve the narrow-band diffusion of the sound field by employing a randomly fluctuating surface. An acoustic experiment was performed in a reverberation water tank (1.2 m×1 m×0.8 m), where a randomly fluctuating surface was generated by making waves. The experimental results show that as the wave motion contributes effectively to the random reflection of sound rays in all directions, the uniformity and isotropy are improved significantly when the surface is fluctuating randomly. This work helps to ensure accurate measurements of the characteristics of underwater targets in reverberation tanks.     

高三复习代数训练题(一)

选择题 :本大题共 12小题 ,每小题 5分 ,共 60分 .在每小题给出的四个选项中 ,只有一项是符合题目要求的 .1　已知集合Ｍ ={ 0 ,1,2 ,3,4 ,5 } ,Ｎ ={ 1,2 ,3} ,满足条件Ｎ Ａ Ｍ的集合Ａ的个数是 (　　 )(Ａ) 64.　 (Ｂ) 63.　 (Ｃ) 8.　 (Ｄ) 7.2　若θ是第二象限的角 ,则必有 (　　 )(Ａ)ｔｇ θ2 >ｃｔｇ θ2 .　　 (Ｂ)ｔｇ θ2 <ｃｔｇ θ2 .(Ｃ)ｓｉｎ θ2 <ｃｏｓ θ2 . (Ｄ)ｓｉｎ θ2 >ｃｏｓ θ2 .3　设 ｆ(2 ｘ) =ｘ2 - 2ｘ - 1,那么 ｆ(0 .5 )等于(　　 )(Ａ) 2 .　 (Ｂ) - 2 .　 (Ｃ) 1.　 (Ｄ) - 74 .4　设ｃｏｓ3ｘ =- 12…     

利用分子烙印技术分离中草药活性组分

用非共价法,在极性溶剂中,以丙烯酰胺作功能单体,以强极性化合物槲皮素为模板 ,制备了分子烙印聚合物(MIP). 液相色谱实验表明, MIP 对槲皮素具有特异的亲合性.将此 MIP直接分离银杏叶提取物水解液, 得到主要含模板槲皮素及与槲皮素结构相似化合物山奈 酚两种黄酮的组分.研究证实了MIP技术用于直接分离、提取中草药中具有特定药效化合物的 可行性.