Heterogeneous fragmentation of metallic liquid microsheet with high velocity gradient

Large-scale molecular dynamics simulations are performed to study the fragmentation of metallic liquid sheets with high velocity gradient. Dynamic fragmentation of the system involves the formation of a network of fragments due to the growth and coalescence of holes, decomposition of the network into filaments, and further breakup of the filaments into spherical clusters. The final size distribution of the fragmented clusters in the large volume limit is found to obey a bilinear exponential form, which is resulted from the heterogeneous breakup of quasi-cylindrical filaments. The main factors contributing to fragmentation heterogeneity are introduced, including strain rate inhomogeneity and matter distribution nonuniformity of fragments produced during decomposition of the network structure.     

多孔线性控制套筒致裂效果影响因素分析

针对坚硬难垮落顶板弱化问题,在分析多孔线性控制套筒致裂机理的基础上,建立700mm×300mm×400mm试块。通过套筒致裂压力及钻孔孔壁周围应变变化情况,分析孔壁周围应力大小、分布及应力集中现象,研究钻孔直径、孔间距、套筒致裂压力对应力集中现象的影响,同时分析这三者对裂纹扩展方向的影响,得出套筒致裂最优法。试验结果表明:(1)套筒致裂效果受钻孔直径、孔间距和套筒压力等综合因素影响,采用大直径、大间距的布孔方式可获得较好的致裂效果;(2)多孔线性控制致裂试验的张性裂缝扩展方向主要沿着各钻孔中心连线方向;(3)钻孔直径30mm、间距300mm的试块致裂压力为18.6MPa,远大于顶板岩体抗拉强度,将套筒致裂法应用于顶板弱化是可行的。本研究对解决采空区坚硬顶板大面积悬顶具有理论意义和应用价值。     

仿生超疏油材料在苛刻工况条件下的应用

超双疏兼备超疏水和超疏油两种极端不润湿现象,其中超疏油的实现难度更大,应用前景广阔。为了获得超疏油材料,通常采用仿生思路,在材料表面构建粗糙结构和以含氟低表面能物质修饰表面。表面粗糙结构在机械力学作用下易遭到破坏,例如摩擦和冲击。低表面能物质修饰层在光照条件下易分解,而诸多的太阳能装置如太阳能电池板,必须在室外工作。耐紫外的超疏油性可以帮助这些设施实现高效工作并延长使用期限,节约资源。更进一步,科研人员研究了超疏油材料在各种苛刻条件下的可靠性。本文应用新进展聚焦在超疏油材料在紫外线照射下的可靠性或可逆响应性;超疏油材料经过撞击之后的油滴接触角变化;在高温条件下超疏油材料的极端润湿性能保持能力;在冲击条件下的稳定性,甚至包括了多种复合苛刻条件下的超疏油材料的耐受性。由于大多的工业环境无法避开摩擦和腐蚀,因此本文着重从超疏油材料的耐摩擦性和抗腐蚀性两个方面讨论了其研究现状,同时也讨论了超疏油在其他工程应用方面的可靠性。最后,总结了各实验方案的优缺点、实验与工业化过程中存在的问题、有望突破的方向,以及作者对于在苛刻工况条件下提升超疏油材料可靠性的观点。     

Experimental demonstration of narrow-band rugate minus filters using rapidly alternating deposition technology

The design, fabrication and performance of narrow-band rugate minus filters are investigated in this paper. A method of fabricating graded-index coatings by rapidly alternating deposition of low(Si O2) and high(Al2 O3) refractive index materials is presented to fabricate a rugate structure. The narrow-band rugate minus filter design and fabrication approaches are discussed in detail. The experimental results, including transmittance spectrum, surface damage test and damage morphology investigated with a scanning electron microscope, demonstrate the high performance of the as-fabricated spatial filter and confirm the feasibility of the fabrication method for narrow-band rugate minus filters.     

光学薄膜激光预处理能量密度选取

采用Nd∶YAG三倍频激光对光学薄膜进行了预处理.实验发现三倍频激光预处理对薄膜的抗激光损伤能力有明显的影响,影响规律比较复杂,归纳得出合适激光预处理能量密度与测试激光能量密度有关.理论上借助杂质诱导薄膜损伤的概率统计模型,从激光预处理引起的激光微区退火以及形成微尺寸损伤两个主要方面着手,很好地解释了复杂的实验现象.总体上看,预处理激光能量密度低于激光退火所需临界能量密度时,预处理效果以负作用为主;预处理激光能量密度高于激光退火所需临界能量密度,且低于激光诱导薄膜微损伤所需临界能量密度时,预处理效果以改善薄膜抗激光损伤能力为主,预处理激光能量密度要尽量选在这个范围内;预处理激光能量密度高于激光诱导薄膜微损伤所需临界能量密度时,预处理效果同样以负作用为主.     

氧化钪/氧化硅反射薄膜的355 nm激光损伤特性

采用电子束蒸发法制备了Sc2O3单层薄膜和Sc2O3/SiO2多层反射膜.利用原子力显微镜、X射线衍射仪等方法对薄膜的表面和结构进行,研究.采用355 nm激光研究了Sc2O3/SiO2多层薄膜的损伤特性和预处理效应,并对Sc2O3的损伤原因进行了分析.实验发现,Sc2O3具有较宽的带隙,薄膜结构为立方相,影响Sc2O3/SiO2 多层反射膜抗损伤能力的主要因素足材料的纯度.     

Rapidity dependence of hadron PT spectra in central Au＋Au collisions at √^SNN = 200 GeV

The transverse momentum spectra for identified hadrons at different rapidities in central Au＋Au collisions at √^SNN= 200 GeV are studied in a quark combination model. The results for PT spectra of π^±, K^±, p（p^-） and for the p/π ratios in a broader PT range at midrapidity agree well with the data. The transverse momentum spectra of pions, protons and antiprotons at various rapidities y - 1, η= 2.2 and y ≈ 3.2 are calculated and compared with the data.     

Tunable Anisotropic Absorption of Ag-Embedded SiO2 Thin Films by Oblique Angle Deposition

Ag-embedded SiO2 thin films are prepared by oblique angle deposition. Through field emission scanning electron microscopy （SEM）, an orientated slanted columnar structure is observed. Energy-dispersive x-ray （EDX） analysis shows the Ag concentration is about 3% in the anisotropic SiO2 matrix. Anisotropic surface plasma resonance （SPR） absorption is observed in the Ag-embedded SiO2 thin films, which is dependent on polarization state and incidence angle of two orthogonal polarized lights and the deposition angle. This means that optical properties and anisotropic SPR absorption can be tunable in Ag-embedded SiO2 thin films. Broadband polarization splitting is also observed and the transmission ratio Tp/Ts between p- and s-polarized lights is up to 2.7 for thin films deposited at a = 70°, which means that Ag-embedded SiO2 thin films are a promising candidate for thin film polarizers.     

不同沉积参量下ZrO2薄膜的微结构和激光损伤阈值

ZrO2采用X射线衍射(XRD)技术分析了不同充氧条件和沉积温度对ZrO2溥膜组成结构的影响,并对不同工艺下制备的薄膜的表面粗糙度和激光损伤阈值进行了测量。结果发现随着氧压的升高,ZrO2溥膜将由单斜相多晶态逐渐转变为非晶态结构,而随着基片温度的增加,溥膜将由非晶态逐渐转变为单斜相多晶态。同时发现随着氧压升高晶粒尺寸减小,而随着沉积温度增加,晶粒尺寸增大。氧压增加时工艺对表面粗糙度有一定程度的改善,而沉积温度升高,工艺对表面粗糙度的改善不明显。晶粒尺寸大小变化与表面粗糙度变化存在对应关系。激光损伤测量表明,氧压条件和沉积温度对ZrO2薄膜的抗激光损伤能力有着较大影响。     

基于Berreman矩阵的双折射薄膜光谱响应特性计算

采用Berreman特征矩阵方法,通过数值计算研究了双折射薄膜的反射、透射等光谱响应特性。依据电磁场理论的电场分量、磁场分量的界面连续条件,推导了光波在各向异性双轴薄膜中的Berreman转移矩阵,用以分析含有各向异性介质层的复杂薄膜系统的光学性质。这些矩阵递推关系包含了界面处的多点反射,适用于一般的各向异性的多层膜系统,包括入射媒质或基底为各向异性的情况。在文中给出了各向同性入射媒质双轴各向异性膜层一各向同性基底薄膜系统的计算结果,验证了该计算方法的可行性,以此作为进一步研究各向异性薄膜和相关光学薄膜器件设计的理论基础。