Externally applied stress sign and film elastic properties effects on brittle film fracture

Rectangular stainless steel samples with TiN film deposited on the front lateral surface were loaded in three-point bending to the maximum normal strain of 6%. Scanning electron microscopy showed that vertical cracks appeared in the tension zone when the tensile strain exceeded 1.5%, while horizontal cracks appeared in the compression zone when the compressive strain exceeded –2.9%. Film cracks in the compressive zone originate from the tensile stress imposed by the plastically deformed substrate due to the Poisson’s expansion. Taking plastic deformation and Poisson’s expansion of the substrate in compression into account, theoretical analysis of normal stress distribution along the cracked film segment in compression is presented. Substrate strain and film elastic properties affect film cracking in the compressive zone. At larger compressive strain, some transverse cracks along with buckling cause the film spallation. The presented method is useful for studying brittle film fracture with variable strain levels in a single sample.     

光谱编码成像系统的数据压缩技术

利用时间拉伸显微成像系统观察并记录非重复动态随机现象,在其超高成像速度和高空间分辨率下必定会产生大量的数据。一种基于差分检测和游程编码的数据压缩方法,可以有效地解决时间拉伸成像系统的数据存储问题。差分检测可以消除连续相同的信号,只检测出相邻信号的差异,从而提高游程编码算法的有效性。实验中,采用扫描频率为77.76 MHz的时间拉伸显微成像对分辨率板、人红细胞和人乳腺癌细胞线性扫描成像。实验结果表明,数据压缩比可以达到8.47,对比分析发现经过差分检测方法可以获得更高的压缩比。另外,通过计算重建后的图像与原图的结构相似性(SSIM)值发现,经过数据压缩后高质量的图像可以被重建。     

Topological nodal line semimetals predicted from first-principles calculations

Topological semimetals are newly discovered states of quantum matter, which have extended the concept of topological states from insulators to metals and attracted great research interest in recent years. In general, there are three kinds of topological semimetals, namely Dirac semimetals, Weyl semimetals, and nodal line semimetals. Nodal line semimetals can be considered as precursor states for other topological states. For example, starting from such nodal line states, the nodal line structure might evolve into Weyl points, convert into Dirac points, or become a topological insulator by introducing the spin–orbit coupling (SOC) or mass term. In this review paper, we introduce theoretical materials that show the nodal line semimetal state, including the all-carbon Mackay–Terrones crystal (MTC), anti-perovskite Cu₃PdN, pressed black phosphorus, and the CaP₃ family of materials, and we present the design principles for obtaining such novel states of matter.     

Renal Clearable Luminescent WSe2 for Radioprotection of Nontargeted Tissues during Radiotherapy

High‐energy ionizing radiation is widely used in medical diagnosis and cancer radiation therapy. However, high‐energy radiation can also impose significant damages in healthy tissues during medical treatments via direct DNA damages and indirect damages from production of reactive oxygen species (ROS). Therefore, it is urgent to develop highly effective radioprotectants with low toxicities that can meet the increasing needs for alleviating the adverse effects from cancer radiation therapy and nuclear emergency. In this work, strongly catalytic ultrasmall (sub‐5 nm) cysteine‐protected WSe₂ dots are employed to protect healthy tissues against radiation via diminishing radiation‐induced free radicals. The WSe₂ dots with high surface activities can recover radiation‐induced DNA damages and eliminate the excessive ROS generated from radiation. In vivo experiments confirm that the survival rate of mice treated with WSe₂ dots is significantly elevated with radiation damages postponed under exposure to high‐dose ionizing radiation. Furthermore, the free radicals in major organs and hematological system can be appreciably omitted, suggesting their unique role as free radical scavengers. These WSe₂ dots in ultrasmall size show rapid renal clearance of ≈74% injection dose via urine excretion in 24 h and do not cause any apparent toxicity in vivo for up to 30 d.     

Jacobi矩阵特征值反问题

研究如下一类Jacobi矩阵特征值反问题:问题IEP:给定两个互异实数λ,μ(λ<μ)和两个n维非零实向量x,y,求n阶Jacobi矩阵J,使得(λ,x),(μ,y)分别恰是J的第i,j(i≠j)个特征对。还分析了Jacobi矩阵的特征性质,给出了一个特征对恰是Jacobi矩阵J的第i个特征对的充分必要条件,由此导出了问题IEP有解的充分必要条件。     

S为1/2体系粉末或冷冻玻璃态电子自旋共振谱的模拟

本文较详细地介绍了模拟s为1/2体系粉末或冷冻玻璃态电子自旋共振谱的理论基础。给出了具体计算公式,利用这些公式完全可以在微机上进行计算机模拟电子自旋共振谱。     

Upconversion luminescence of Tm^3＋/Yb^3＋ codoped oxyfluoride glasses

Novel oxyfluoride glasses are developed with the composition of 30SiO2-15Al2O3-28PbF2-22CdF2-0.1TmF3 - xYbF3 - （4.9 - x） AlF3（x=0, 0.5, 1.0, 1.5, 2.0） in tool fraction, Furthermore, the upconversion luminescence characteristics under a 970nm excitation are investigated. Intense blue, red and near infrared luminescences peaked at 453nm, 476nm, 647nm and 789nm, which correspond to the transitions of Tm^3＋： ^1D2 →^3F4, ^1G4 →^3H6, ^1G4 →^3F4, and ^3H4 →^3H6, respectively, are observed. Due to the sensitization of Yb^3＋ ions, all the upconversion luminescence intensities are enhanced considerably with Yb^3＋ concentration increasing. The upconversion mechanisms are discussed based on the energy matching rule and quadratic dependence on excitation power. The results indicate that the dominant mechanism is the excited state absorption for those upconversion emissions.     

常压化学气相沉积技术生长ZnO:H薄膜的光学性质

采用常压金属有机物化学气相沉积技术(AP-MOCVD),以二乙基锌(DEZn)为Zn源,去离子水(H2O)为氧源,N2作载气,在外延ZnO薄膜的反应气氛中通入少量氢气,在c-Al2O3衬底上生长出了ZnO∶H薄膜。用X射线双晶衍射和光致发光谱对ZnO∶H薄膜的结晶性能和光学性质进行表征。结果表明,ZnO∶H薄膜(002)和(102)面的Ω扫描半峰全宽分别为46.1 mrad和81.4 mrad,表明该薄膜具有良好的结晶性能;室温下,ZnO∶H薄膜具有较强的紫外光发射(380 nm),在低温10 K光致发光谱中观测到位于3.3630 eV处与氢相关的中性施主束缚激子峰(I4)及其位于3.331 eV处的双电子卫星峰(TES)。采用退火的方法,通过观测I4峰的强度变化,研究了氢在ZnO∶H薄膜中的热稳定性。发现随着退火温度的升高,I4峰的强度逐渐减弱,表明在高温下退火,氢会从ZnO薄膜中逸出。