VLBI observations of a sample of 15 EGRET-detected AGNs at 5 GHz

We report VLBI observations of 15 EGRET-detected AGNs with European VLBI Network (EVN) at 5 GHz. All sources in the sample display core-jet structures.

黄河首曲湿地功能区“黑土滩”退化草甸恢复改良

采用样方法研究了首曲湿地功能区"黑土滩"退化草甸改良后3 a的群落特征变化,分析了围栏封育和补播"高寒1号"生态组合草种对退化草甸的恢复改良效果.结果显示:仅封育3 a后,"黑土滩"退化草甸群落的盖度、高度、地上生物量和可食牧草比例均显著提高,丰富度指数由0.55增加到0.75,多样性指数由0.07增加到了0.25;封育后补播"高寒1号"生态草种相对于封育前,使得退化草甸的盖度增加了56.00%,高度增加了11.74 cm,地上生物量增加了222.24 g/m~2,可食牧草比例增加了55.98%,物种数由5种/m~2增加到了15种/m~2,丰富度指数由0.55增加到了3.29,多样性指数由0.07增加到了1.85,均匀度指数由0.06增加到了0.27.相对围栏封育而言,封育后补播是一种更有效的"黑土滩"退化草甸改良恢复措施.围栏封育和补播配套实施可以显著改善"黑土滩"退化草地的群落貌相、草地生产力和组分结构状况.

铁体系催化丁二烯聚合的研究

本工作研究了以三氯化铁为主催化剂，三异丁基铝为助催化剂，吡啶、苯胺、丙烯腈、乙二胺、四甲基乙二胺、2,2'－联比啶和邻啡啰啉等含氮化合物为配位体的催化体系聚合丁二烯。发现邻啡啰啉做配位体时，该体系有很高的催化活性，Fe/BD为3.0 * 10~(-5)，Al/BD为2.0 * 10~(-3)时，聚合物收率可达90％以上。认为能与活性中心形成五圆或六圆螯合环的共轭含氮化合物做配位体，对聚合活性有非常显著的提高。而且共轭的程度愈高，活性愈高。故乙二胺、四甲基乙二胺、2,2'－联吡啶及邻啡啰啉虽然都能够与Fe形成五圆螯合物，但活性不一样：并用分子轨道理论进行了讨论。本文详细地研究了FeCl_3-Al(i-C_4H_9)_3-phen体系催化丁二烯聚合，考察了phen、Al(i-C_4H_9)_3的用量及聚合温度对催化活性、聚合物特性粘数及微观结构的影响。加入phen得到中乙烯基PBD(1,2-结构为40％－60％)，而不加入phen则得到顺式1,4－结构较高的PBD（顺式－1,4结构为74.4％）。该体系得到的PBD的特性粘数一般大于10，难以加工，故进行了分子量调节的尝试。体系中加入氯化正丁烷、溴代正丙烷、碘甲烷等卤代烷及三氯乙烯、氯代苯等卤代烃，均不能使PBD的分子量降低，而且用量较大时基本不影响聚合反应。卤代丙烯及氯代苄均可以降低PBD的分子量，其中氯丙烯的分子量调节效果最佳。若用量合适，可以使PBD的特性粘数从10以上降到4以下，而基本上不影响聚合物收率。PBD的分子量分布较窄，分布宽度指数为2.0左右，不随氯丙烯的用量而改变。从实验结果讨论了FeCl_3-AlCi-C_4H_9)_3-phen体系催化丁二烯聚合的机理及分子量调节剂的链传移机理。认为该体系催化丁二烯聚合的活性中心为：链转移是通过分子量调节剂对活性中心的氧化加成－还原消除反应进行的。在phen存在下，FeCl_3、Fe(acac)_3等与烷基铝作用，及(phen)_2FeCl_2与烷基铝作用，均可以生成烷基铁络合物：但只分离出(C_2H_5)_2Fe(phen)_2。(i_C_4H_9)_2(phen)_2及由氯化铁和(phen)_2FeCl_2合成的烷基铁络合物还未得到纯的产物，但从反应产物的易氧化性、水解产物的分析及红外光谱，证实产物中存在烷基铁。用元素分析、红外光谱、远红外光谱及气相色谱分析表征了(C_2H_5)_2Fe(phen)_2的结构。(C_2H_5)_2Fe(phen)_2单独使用不能使丁二烯聚合，需加少量的烷基铝，与其中一个配位体络合，使活性中心有供丁二烯配位的空轨道，聚合反应才能顺利进行：得到的PBD特性粘数为1.8～2.4左右，1,2－结构为40－60％，顺式－1,4结构为53～41％，反式－1,4结构很少。初步证明所提出的铁体系催化丁二烯聚合的机理基本上是正确的。初步表征了铁体系聚丁二烯硫化胶的性能，其抗张强度为203～205公斤／厘米~2，300％定伸强度为70～125公斤／厘米~2，伸长离为453～573％。

A NEW TYPE OF SILICON-ON-INSULATOR WITH A PERFECT SURFACE SILICON LAYER

A novel silicon structure consisting of a silicon-on-defect layer (SODL), with enhanced surface Hall mobility in the surface layer on a buried defect layer (DL), has been discovered [J. Li, Nucl. Instr. and Meth. B59/60 (1991) 1053]. SODL material was formed by using proton implantation and subsequent two-step annealing. The implantation was carried out with a Varian 350D ion implanter. Based on the discovery, a standard measurement method (current-voltage curve method) was adopted to measure the true resistivity value of the DL in order to replace the spreading resistivity measurement by which the true resistivity in seriously defective silicon cannot be obtained. By adopting the current-voltage current method, the true resistivity value of the DL is measured to be 4.2 x 10(9) OMEGA cm. The SODL material was proved to be a silicon-on-insulator substrate.

GSMBE growth and characterization of InxGa1-xAs/InP strained-layer MQWs in a P-i-N configuration

InxGa1-xAs/InP (0.39 less than or equal to x less than or equal to 0.68) strained-layer quantum wells having 20 wells with thickness of 50 Angstrom in a P-i-N configuration were grown by gas source molecular beam epitaxy (GSMBE). High-resolution X-ray diffraction rocking curves show the presence of up to seven orders of sharp and intense satellite reflection, indicative of the structural perfection of the samples. Low-temperature photoluminescence and low-temperature absorption spectra were used to determine the exciton transition energies as a function of strain. Good agreement is achieved between exciton transition energies obtained experimentally at low temperature with those calculated using the deformation potential theory.

Heteroepitaxial Growth of 3C-SiC Films on Maskless Patterned Silicon Substrates

Heteroepitaxial growth of 3C-SiC on patterned Si substrates by low pressure chemical vapor deposition (LPCVD) has been investigated to improve the crystal quality of 3C-SiC films. Si substrates were patterned with parallel lines, 1 to 10μm wide and spaced 1 to 10μm apart, which was carried out by photolithography and reactive ion etching. Growth behavior on the patterned substrates was systematically studied by scanning electron microscopy (SEM). An air gap structure and a spherical shape were formed on the patterned Si substrates with different dimensions. The air gap formed after coalescence reduced the stress in the 3C-SiC films, solving the wafer warp and making it possible to grow thicker films. XRD patterns indicated that the films grown on the maskless patterned Si substrates were mainly composed of crystal planes with (111) orientation.

A Numerical Method for Calculating Transmission Coefficients Across Arbitrary Potential Barriers with High Accuracy

We report a new method for calculating transmission coefficients across arbitrary potential barriers based on the Runge-Kutta method. A numerical solution of the Schrodinger equation is calculated using the Runge-Kutta method,and a new model is established to analyze the numerical results to find the transmission coefficient. This technique is applied to various cases, such as parabolic potential barrier and double-barrier structures. Transmission probability with high precision is obtained and discussed. The tunnelling current density through a MOS structure is also explored and the result coincides with the Fowler-Nordheim model,which indicates the applicability of our method.

光子存储单元的光伏效应

报道了光存储效应在一种特殊设计的光存储单元Ⅰ-Ⅴ特性上的响应.当单元偏置在光存储模式下,越过禁带的光激发会产生一个台阶状的电流阶跃.利用瞬态光电流测试装置测量电流阶跃处的瞬态响应,验证了"开→关"光电流下降沿主要反映了光照消失后原先被存储起来的电子、空穴的衰变过程.其时间常数是光存储时间的一种度量,而光照下所出现的台阶状电流阶跃则是光子存储效应在Ⅰ-Ⅴ特性的反映.

Fiber Optic Coupling of CW Linear Laser Diode Array

Based on a set of microoptics the output radiation from a continuous wave (CW) linear laser diode array is coupled into a multi-mode optical fiber of 400 ptm diameter. The CW linear laser diode array is a 1 cm laser diode bar with 19 stripes with 100 fxm aperture spaced on 500 (xm centers. The coupling system contains packaged laser diode bar, fast axis collimator, slow axis collimation array, beam transformation system and focusing system. The high brightness, high power density and single fiber output of a laser diode bar is achieved. The coupling efficiency is 65% and the power density is up to 1.03 * 10~4 W/cm~2.

Self-assembled InAs quantum wires on InP(001)

Self-assembled InAs quantum wires (QWRs) embedded in In0.52Al0.48As In0.53Ga0.47As, and (In0.52Al0.48As)(2)/(In(0.53)Ga(0.47)AS)(2)-short-period-lattice matrixes on InP (001) were fabricated with molecular beam epitaxy (MBE). These QWR lines are along [110], x4 direction in the 2x4 reconstructed (001) surface as revealed with high energy electron diffraction (RHEED). Alignment of quantum wires in a multilayer structure depends on the composition of spacer layers.