H. Y. Jing
,
L. X. Huo
,
Y. F. Zhang and F. Minami( 1) College of Material Science
,
Tianjin University
,
Tianjin 300072
,
China 2) Osaka University
,
Japan)
金属学报(英文版)
A computation framework for brittle fracture which incorporates weakest link statistics and a microme- chanics model reflecting reflecting local damage of the material is described.The Weibull stress W emerges as a probabilistic fracture parameter to define the condition leading material failure. Unstable crack propa- gation occurs at a critical value of W which may be attained paior to or following some amount of duc- tile crack extension. A realistic model of ductile crack growth using the computation cell methodology is used to define the evolution of near tip stress fields during crack extension. An application of proposed framework to predict the measured geometry and ductile tearing effects on the statistical distributio of fracture toughness for the pipe line steel welded joint is described.
关键词:
fracture toughness
,
null
,
null
赵洋
,
蔚辰刚
,
周强
,
吴周安
,
王树华
,
罗孟飞
应用化学
doi:10.3724/SP.J.1095.2014.30338
采用沉积沉淀法制备了Y-Mg-Al-F催化剂,应用XRD、NH3-TPD和Raman光谱等技术手段对催化剂进行表征,并与AlF3催化剂作比较,且将催化剂应用于四氟乙烷(HFC-134a)裂解制备三氟乙烯反应中.结果表明,1100℃焙烧的Y-Mg-Al-F催化剂具有较高的活性和反应稳定性.反应温度400℃时,四氟乙烷转化率大于25％.催化剂表面酸性和积碳是影响催化剂活性和稳定性的主要因素.
关键词:
四氟乙烷
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催化裂解
,
三氟乙烯
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沉积沉淀法
,
Y-Mg-Al
由芳田
,
黄世华
,
王大伟
,
黄艳
,
徐建华
中国稀土学报
利用水热方法合成出RbLn2F7(Ln=Gd,Y,Er,Yb和Lu),均为六方RbEr2F7型结构.掺杂Eu3+离子样品的光谱表明水热产物中氧杂质含量极低.在RbGd2F7:Eu3+(0.5mol%)的激发光谱中只观测到Gd3+离子f-f跃迁,Eu3+离子的激发跃迁很弱.激发Gd3+离子到6IJ能级后,观测到Eu3+离子的特征发射,Gd3+离子与Eu3+离子之间存在能量传递过程.Eu3+离子的5D0→7F1和5D0→7F2跃迁发射较强,表明稀土离子在六方RbLn2F7中处于非中心对称的格位.
关键词:
RbLn2F7
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水热合成
,
真空紫外(VUV)
,
氟化物
,
能量传递
,
稀土
罗湘宁
,
王晶
,
陈赓华
,
杨乾声
,
张利华
低温物理学报
doi:10.3969/j.issn.1000-3258.2000.01.003
本文采用偏置电流反转的频率与磁通调制频率相等的方案,研制了带偏置电流反转的dc SQUID测试系统,明显降低了YBCO双晶结dc SQUID的1/f噪声.在3Hz处,磁通噪声由静态偏置时的降低到.1/f噪声的角频率从1kHz下降到3Hz.前放的设计,采用低噪声集成电路,整个磁通锁定环置于测试杆顶端,简化了电路,提高了测试系统的稳定性.在白噪声区,测得最低磁通噪声为 .前放的噪声系数为1.1dB.
关键词:
Zhiyong Liu
材料科学技术（英文）
Here we report the fabrication and superconductivity of the iron-based arsenic oxide SmO1-xFxFeAs compound. X-ray diffraction (XRD) results prove that the lattice parameters a and c decrease systematically with increasing x in between 0<x≤0.35, but when x>0.35 the a and c increase with the decrease of x in
the SmO1-xFxFeAs. The critical temperature (Tc) increases with increasing x in between 0.15≤x≤0.3, while x>0.3 the Tc decreases with the increase of x. It is found that at x=0.3 SmO0.7F0.3FeAs has the highest onset resistivity transition temperature of 55.5 K. The critical current density (Jc) value at 10 K for the obtained SmO0.7F0.3FeAs is 1.3×105 A/cm2 (0 T). Meanwhile one can estimates Hc2(0) from the slope of the Hc2(T) curve at T=Tc (HC2 is the upper critical field), and for the 90% normal-state resistivity (ρn) criterion (Tc=55 K), Hc2(0) is determined to be ~253 T.
关键词:
SmO1-xFxFeAs compound
Superconductor Science & Technology
It is shown that the superconductivity in Ce(1-x)Gd(x)FeAsO(0.84)F(0.16) compounds can be modulated by internal (chemical) pressure. The internal pressure is induced by Gd substitution for Ce in CeFeAsO(0.84)F(0.16), which compresses the crystal lattice. The temperature dependences of resistivity and magnetization show that the superconducting-transition temperature T(c) is enhanced from 40 K for CeFeAsO(0.84)F(0.16) to 47.5 K for Ce(0.6)Gd(0.4)FeAsO(0.84)F(0.16). The increase and subsequent decrease of Tc upon application of external pressure, as observed previously in LaFeAsO(0.89)F(0.11), is entirely confirmed by the modulation of Tc of the Ce(1-x)Gd(x)FeAsO(0.84)F(0.16) superconductors by internal pressure.
关键词:
layered quaternary compound;43 k;iron
杨梅
,
刘其鹏
,
李东风
,
尤洪鹏
,
洪广言
中国稀土学报
以Y2O3,Yb2O3,Er2O3,NH4F等试剂为原料,采用水热法在180 ℃下保温10 h获得了NH4Y1.56Yb0.4Er0.04F7球形纳米粒子. 所获得的纳米粒子在氮气保护下400 ℃灼烧2 h,制备出Y0.78Yb0.2Er0.02F3纳米粒子. 利用Scherrer公式计算出NH4Y2F7:Yb3+,Er3+和YF3:Yb3+,Er3+的粒径分别为65.8和68.3 nm. TEM照片展示粒子近球形,其大小与Scherrer公式计算结果一致. TEM还揭示每个粒子上面应带有许多小孔. 氮气吸附脱附实验进一步证实了粒子上存在小孔. 在980 nm的红外激光激发下,NH4Y1.56Yb0.4Er0.04F7不发光,而Y0.78Yb0.2Er0.02F3发出明亮的绿光,表明所获得的Y0.78Yb0.2Er0.02F3具有强的上转换发光.
关键词:
NH4Y1.56Yb0.4Er0.04F7
,
Y0.78Yb0.2Er0.02F3
,
纳米粒子
,
水热法
,
上转换发光
,
稀土
李强
,
王其申
量子电子学报
doi:10.3969/j.issn.1007-5461.2007.01.002
针对淹没在1/f分形噪声中的有用信号恢复问题,提出了一种基于小波变换与Kalman滤波的多尺度滤波算法.首先将带有1/f分形噪声的信号分解成多尺度的子带信号,通过小波变换对1/f分形噪声的白化作用,消除了1/f分形噪声的自相似性和长程相关性.然后在小波域内,利用Kalman滤波实现了噪声和有用信号的分离,估计出了各子带中的有用信号.最后进行小波重构,较好地恢复出淹没在1/f分形噪声中的有用信号.仿真实验表明,使用多尺度Kalman滤波器能有效地抑制分形噪声,显著地提高了信噪比.
关键词:
图像处理
,
Kalman滤波
,
小波变换
,
1/f分形噪声
,
自相似性
