Crystalline morphology of poly(l-lactic acid) thin films

Crystalline morphologies of spin-coated poly(l-lactic acid) (PLLA) thin films under different conditions are investigated mainly with atomic force microscopy (AFM) technique. When PLLA concentration in chloroform is varied from 0.01 to 1% gradually, disordered structure, rod-shape and larger spheres aggregates are observed in thin films subsequently. Under different annealing temperature, such as at 78, 102, 122 °C, respectively, we can find most rod-like crystalline aggregates. Interestingly, we observed that nucleation sites locate at the edge of the holes at the original crystalline stage. Then, these holes developed to form chrysanthemum-like and rods subsequently with annealing time meanwhile the size and the shape of crystalline aggregate are changed. In addition, effect of substrate and solvent on morphology is also discussed. On the other hand, the possible mechanism of crystalline morphology evolution is proposed.     

Study on photoluminescence properties of oxyfluoride germanate Glass

The oxyfluoride germanate glass and glass-ceramics were prepared by the melting–annealing method. The composition of the glass was chosen as 45GeO2–30BaF2–5B2O3–15AL2O3–5R2O–xSm2O3 (R = Li, Na, and K. x = 1.5, 2.0, and 2.5, mol%). Differential thermal analysis, X-ray diffraction, and photoluminescence spectra were carried out to study the effects of the concentration of Sm ions, the kinds of alkali ions and heat treatment on the photoluminescence properties of Sm ion doped oxyfluoride germanate glass. The results showed that the luminescence intensity of the oxyfluoride germanate glass increased when x changed from 1.5 to 2.0 and then decreased when x changed from 2.0 to 2.5. Among various R2O, the Li2O included glass has the strongest luminescence intensity among all the glasses. Heat treatment at 660 °C for 4 h resulted in the formation of the Ba3AlF9 nanocrystal and enhanced the luminescence intensity of the sample. The mechanism of luminescence intensity increase was discussed.     

Oscillation criteria for second order linear matrix differential systems with damping

Using a generalization of Sturm’s comparison theorem, some new oscillation criteria are established for the matrix differential system with damping

(P(t)Y^′)^′+R(t)Y^′+Q(t)Y=0${\left(P\left(t\right)Y^{\prime }\right)}^{\prime }+R\left(t\right)Y^{\prime }+Q\left(t\right)Y=0$

Multiple positive solutions for a semilinear elliptic equation with critical Sobolev exponent

In this paper, we study a class of semilinear elliptic equations with Hardy potential and critical Sobolev exponent. By means of the Ekeland variational principle and Mountain Pass theorem, multiple positive solutions are obtained.     

A Surface Mounting Embedded Optical Transceiver with Bi-Directional Data Rate of Eight Channels × 10 Gbps

Abstract

The bi-directional data rate is investigated of an eight-channel × 10-Gbps optical transceiver with a size of 15 mm × 15 mm × 6 mm and ball grid array package form that was designed and fabricated. A passive optical coupling method is designed based on a coupling lens array, which is transformed to substrate through a carrier. This electrical performance is characterized through a 3D full wave simulation and shows great advantages compared with traditional pluggable optical transceivers. Experimental eye diagram measurement in loop-back mode via a 2-m-long multi-mode fiber array shows an eye width of 51.984 ps at a bit-error rate order of 10^?12, which proves the transceiver's ability for 10.3125-Gbps data transmission.     

Effects of sintering temperature on microstructure and property evolution of Fe81Cu2Nb3Si14 soft magnetic materials fabricated from amorphous melt-spun ribbons by spark plasma sintering technique

Bulk Fe₈₁Cu₂Nb₃Si₁₄ soft magnetic materials were fabricated by spark plasma sintering (SPS) of amorphous powder, which was prepared by ball milling of melt-spun ribbons. Effects of sintering temperature on the evolution of microstructure and related properties were systematically investigated. Results show that the as-milled powders exhibit similar microstructure and thermal property in comparison with the original melt-spun ribbons. With an increase in the sintering temperature, the relative density, microhardness and saturation magnetization of the sintered samples improved obviously, but the coercive force decreased at the beginning and then increased with the increase of sintering temperature. The sintered samples exhibit typical soft magnetic characteristic. The desirable soft magnetic property of the sintered samples was achieved by SPS at 630 °C. Meanwhile, microstructure and densification behaviors of the sintered samples were also investigated.     

Matroids and Graphs with Few Non-Essential Elements

An essential element of a 3-connected matroid M is one for which neither the deletion nor the contraction is 3-connected. Tutte's Wheels and Whirls Theorem proves that the only 3-connected matroids in which every element is essential are the wheels and whirls. In an earlier paper, the authors showed that a 3-connected matroid with at least one non-essential element has at least two such elements. This paper completely determines all 3-connected matroids with exactly two non-essential elements. Furthermore, it is proved that every 3-connected matroid M for which no single-element contraction is 3-connected can be constructed from a similar such matroid whose rank equals the rank in M of the set of elements e for which the deletion M\e is 3-connected.     

左手介质矩形波导导模和表面模的场分布

从麦克斯韦方程组出发,结合电磁场的边界条件,推导出介质矩形波导导模的一般色散方程.对普通介质矩形波导和左手介质矩形波导的导模场分布分别进行了数值模拟.通过对比两种介质矩形波导的导模场分布的模拟结果,发现左手介质矩形波导Ex22模的场分布比普通介质波导Ex00模的场更集中在波导中部.同时,根据处理普通介质矩形波导的Marcatili方法.类比得到左手介质矩形波导表面模的色散方程,并数值模拟了低阶模的场分布,结果表明,能量主要集中在波导的四个角区以及波导的边缘.     

加速溶剂萃取-气相色谱法测定土壤中的有机磷农药

采用加速溶剂萃取-气相色谱法测定土壤中有机磷农药。土壤样品与无水硫酸钠混合后,再加适量中性氧化铝和活性碳,用丙酮-二氯甲烷在加速溶剂萃取仪土于10．3MPa、60℃条件下提取10min,用FPD检测器进行分析：土壤中7种有机磷农药的回收率为85．5％～102．7％,测定结果的相对标准偏差为5．7％～13．0％（n=6）,检出限为0．03～0．07μg/kg。该法具有良好的分离效果、较宽的线性关系和较高的灵敏度。     

核／壳结构聚丙烯酸酯塑料增韧剂的制备与结构控制

核／壳结构聚丙烯酸酯塑料增韧剂的制备与结构控制张会轩戴英杨海东＊冯之榴（吉林工学院化工系长春１３００１２）（中国科学院长春应用化学研究所１３００２２）关键词聚丙烯酸酯，增韧剂，制备，种子乳液聚合１９９６－０８－２８收稿，１９９７－０１－０６修回国家自...