准单色近平行光束的X射线源

针对准单色近平行光束X射线背光成像诊断需求,提出了一种用球面弯晶进行X射线衍射选单从而获取准直光束的新方案.在神光Ⅱ装置上,设计了基于球面弯晶X射线衍射选单准直光束系统,完成了该系统的安装、调试和实验应用,获得了准单色(10~(-3)△λ/λ10~(-2))、小发散角(2 mrad)和大辐照匀斑(直径φ500 m)的X射线光源.同时基于衍射光学和球面镜成像理论,研究了不同布拉格角对球面弯晶X射线衍射光束发散角及其像散差的影响.结果表明,布拉格角会影响球面弯晶X射线衍射光束的发散角.用控制布拉格角范围的方法有望获得发散角优于1 mrad的近平行光束X射线光源.这种准单色、极小发散度和均匀角分布的X射线光源可应用于高分辨X射线成像诊断.     

Time-resolved shadowgraphs and morphology analyses of aluminum ablation with multiple femtosecond laser pulses

Aluminum ablation by multiple femtosecond laser pulses is investigated via time-resolved shadowgraphs and scanning electron microscope(SEM) images of the ablation spot. The spatial distribution of the ejected material and the radius of the shock wave generated during the ablation are found to vary with the increase in the number of pulses. In the initial two pulses, nearly concentric and semicircular stripes within the shock wave front are observed, unlike in subsequent pulses. Ablation by multiple femtosecond pulses exhibits different characteristics compared with the case induced by single femtosecond pulse because of the changes to the aluminum target surface induced by the preceding pulses.     

Preparation and Thermal Characterization of Diamond-Like Carbon Films

Diamond-like carbon （DLC） films are prepared on silicon substrates by microwave electron cyclotron resonance plasma enhanced chemical vapor deposition. Raman spectroscopy indicates that the films have an amorphous structure and typical characteristics. The topographies of the films are presented by AFM images. Effective thermal conductivities of the films are measured using a nanosecond pulsed photothermal reflectance method. The results show that thermal conductivity is dominated by the microstructure of the films.     

冻融后钢筋再生混凝土粘结性能研究

为了进一步了解冻融环境下再生混凝土的抗拉性能及钢筋与再生混凝土的粘结性能,以100％再生粗骨科取代天然碎石制作了再生混凝土劈裂抗拉试件以及以钢筋直径12mm、16mm和20mm为变动因素的钢筋再生混凝土中心拔出试件.采用快冻法将劈裂抗拉试件和中心拔出试件进行冻融循环后分别进行劈裂和拉拔试验,研究冻融循环下再生混凝土劈裂抗拉性能及钢筋与再生混凝土间粘结性能的变化规律.在总结试验结果的基础上,提出了遭受冻融后再生混凝土劈裂抗拉强度及钢筋与再生混凝土间粘结强度的计算表达式,可为我国冻融环境下再生混凝土结构的耐久性设计提供有益的参考.     

一种电磁带隙结构的快速分析方法

 使用直接传输方法分析有限周期Mushroom-like 电磁带隙结构的表面波带隙,与无限周期的电磁带隙结构表面波色散能带图相比,该方法能大大缩短分析时间。将电磁带隙结构放置于波导底面,通过计算波导的传输系数,分析了不同波导高度和电磁带隙结构周期数对带隙范围的影响。加工了Mushroom-like电磁带隙结构样品,并使用一对探针耦合的方法测量了电磁带隙结构的TE和TM表面波带隙,实验结果表明使用直接传输方法确定的表面波带隙与测量数据吻合良好,证明了此方法的有效性。     

A function cascade synchronization method with unknown parameters and applications

This paper investigates the function cascade synchronization of chaos system. Combining cascade synchronization scheme, parametric adaptive control and projective synchronization scheme, it proposes a new function cascade synchronization scheme to address a generalized-type synchronization problem of three famous chaotic systems: the Lorenz system, Liu system and R\"{o}ssler system, the states of two identical chaotic systems with unknown parameters can be asymptotically synchronized by choosing different special suitable error functions. Numerical simulations are used to verify the effectiveness of the proposed synchronization techniques.     

皮质骨断裂力学行为的实验研究

采用稳态裂纹扩展和疲劳裂纹扩展的实验, 研究了牛皮质骨横向和纵向裂纹扩展的断裂力学行为. 沿着两个方向制备了紧凑拉伸(CT)试件. 由于试件尺寸的限制,采用数值计算方法确定了裂纹尖端应力强度因子与裂纹长度的关系. 在实验中, 采用数字图像相关法精确测定裂纹尖端的位置. 由于裂纹沿横向扩展时有较大的偏斜, 将采用$J$积分测量其断裂韧性. 实验结果表明, 在裂纹扩展的一定范围内, 皮质骨的断裂韧度随着裂纹不断扩展而增大, 即表现出上升的阻力曲线(R-curve)性质.而皮质骨的横向裂纹扩展的断裂韧度要远远大于纵向裂纹扩展的断裂韧度, 表现出各向异性的阻力曲线行为. 在疲劳裂纹扩展中, 纵向疲劳裂纹扩展率要大于横向疲劳裂纹扩展率, 这说明皮质骨具有各向异性的疲劳裂纹扩展性质.      

碱性Al-H_2O_2半燃料电池Au/Ni阴极性能研究

以泡沫镍为基体,AuCl3为沉积液,应用快速自沉积法制备了泡沫镍负载的纳米Au/Ni电极.电化学方法测定AuCl3溶液的浓度和沉积时间对Au粒子的尺寸和分布以及以该电极作为Al-H2O2半燃料电池阴极对H2O2性能的影响.实验表明,泡沫镍经2mmol·L-1AuCl3溶液浸渍60s后,其表面完全被粒径小于100nm的Au粒子覆盖;以其为阴极的Al-H2O2半燃料电池,在0.4mol·L-1H2O2溶液中峰值功率达135mW·cm-2.     

A spin switch device based on a triple quantum dots superlattice using the Dicke effect

Spin-dependent transport in a triple quantum dots superlattice system with a bridge coupling to two leads is studied. There exists an odd-even parity oscillation of spin polarization at the central dot level εc = 0 due to the spin-dependent Fano and Dicke effects induced by the quantum interference and the Rashba spin-orbit interaction. In the case of even numbers of triple quantum dots, the device can be used as a spin switch by tuning the energy difference h between the energies of the central and the lateral dots. These results may be helpful to design and fabricate practical spintronic devices.     

灯盏花甲素、乙素等天然黄酮-7-O-糖苷的合成

灯盏花甲素(apigenin-7-O-β-D-glucuronide, 1)和乙素(scutellarin, scutellarein-7-O-β-D-glucuronide, 2)是灯盏花素(breviscapine)中的两种主要黄酮苷成分, 具有抗氧化、抗肿瘤和治疗老年痴呆等生理活性; 大波斯菊苷(apigetrin, 3)、车前子苷(plantaginin, 4)、apigenin 7-O-β-D-xylopyranoside (5)、apigenin 7-O-α-L-rhamnopyranoside (6)等黄酮-7-O-糖苷也具有相似的结构和生理活性. 本工作针对黄酮苷元(芹菜素7和野黄芩素8)溶解度差、7位羟基酸性强而亲核性较弱以及糖醛酸糖基化给体反应活性较弱的问题, 综合利用使苷元有效增溶的保护基策略、金(I)催化的糖苷化方法和后期糖醛酸氧化策略, 高效构建了黄酮-7-O-葡萄糖醛酸结构, 并经统一的保护基脱除完成了灯盏花甲素(1) (36%)和乙素(2) (7%)的合成. 采用相似的策略, 从苷元出发分别以4~7步完成了天然黄酮-7-O-糖苷3~6的合成.