激波在带扩容室的变截面管中传播和消波效果的数值分析

在利用实验结果验证程序的基础上，对激波在具有复杂结构管道内的传播特性进行了数值模拟，比较了不同入射激波条件和特征尺寸对扩容室消波效应的影响，并考虑了二维(轴对称、平面)模型和三维模型的影响。计算结果表明，同一尺寸的扩容室对不同马赫数人射激波的消波效果是相近的，扩容室特征尺寸不同则消波效果差别很大。

Friction and Wear Studies of Octadecyltrichlorosilane SAM on Silicon

A self-assembled monolayer of octadecyltrichlorosilane (OTS) was prepared on a single-crystal silicon wafer (111) and its tribological properties were examined with a one-way reciprocating tribometer. The worn surfaces and transfer film on the counterface were analyzed by means of scanning electron microscopy and X-ray photoelectron spectroscopy. The results show that, due to the wear of the OTS monolayer and the formation of the transfer film on the counterpart ball, the friction coefficient gradually increases from 0.06 to 0.13 with increasing sliding cycles and then keeps stable at a normal load of 0.5N. The transfer film is characterized by deposition, accumulation, and spalling at extended test duration. Though low friction coefficients of the monolayer in sliding against steel or ceramic counterfaces are recorded, poor load-carrying capacity and antiwear ability are also shown. Moreover, the monolayer itself or the corresponding transfer film on the counterface fails to lubricate even at a normal load of 1.0 N. Thus, the self-assembled monolayer of octadecyltrichlorosilane can be a potential boundary lubricant only at very low loads.

Ocean currents-induced pipeline lateral stability on sandy seabed

Unlike previous mechanical actuator loading methods, in this study, a hydrodynamic loading method was employed in a flow flume for simulating ocean currents induced submarine pipeline stability on a sandy seabed. It has been observed that, in the process of pipeline losing lateral stability in currents, there usually exist three characteristic times: (1) onset of sand scour; (2) slight lateral displacement of pipeline; and (3) breakout of pipeline. An empirical linear relationship is established between the dimensionless submerged weight of pipeline and Froude number for describing pipeline lateral stability in currents, in which the current-pipe-soil coupling effects are reflected. Scale effects are examined with the method of "modeling of models," and the sand particle size effects on pipeline stability are also discussed. Moreover, the pipeline stability in currents is compared with that in waves, which indicates that the pipeline laid directly upon the sandy seabed is more laterally stable in currents than in waves.

星系密度波的维持问题以及Waser机制的进一步数值研究

本文着眼于星系螺旋结构的维持问题,采用一种简化的星系模型,以数值解方法研究了密度波的各种有关的动力学特性。结果还进一步证实了作者用渐近分析方法所得到的Waser开关特性和共转圈势垒上的隧道效应。

One-dimensional improvement and two-dimensional and 3-dimensional treatments for stable oscillation condition, mode structure and power output in high-speed-flow lasers

For high-speed-flow lasers, the one-dimensional and first-order approximate treatment in[1] under approximation of geometrical optics is improved still within the scope of approx-imation of geometrical optics. The strict accurate results are obtained, and what is more,two- and three-dimensional treatments are done. Thus for two- and three-dimensional cases, thestable oscillation condition, the formulae of power output and analytical expression of modesunder approximation of geometrical optics (in terms of gain function) are derived. Accord-ing to the present theory, one-and two-dimensional calculations for the typical case of Gerry'sexperiment are presented. All the results coincide well with the experiment and are better thanthe results obtained in [1].In addition, the applicable scope of Lee's stable oscillation condition given by [1] is ex-panded; the condition for the approximation of gcometrical optics to be applied to mode con-structure in optical cavity is obtained for the first time and the difference between thiscondition and that for free space is also pointed out in the present work.

Tunable and efficient diode-pumped Yb3+: GYSO laser

Effective diode-pumped cw tunable laser action of a new alloyed crystal Yb:Gd(2(1-)x) Y2xSiO5 (Yb:GYSO, x = 0.5) is demonstrated for the first time. The alloyed crystal retains excellent laser properties of Gd2SiO5 (GSO), as well as the favorable growth properties and the desirable physical of Y2SiO5 (YSO). With a 5-at.% Yb: GYSO sample, we achieved 2.44 W output power at 1081.5 nm and a slope efficiency of 57%. And its laser wavelength could be tuned from 1030nm to 1089 nm. (c) 2006 Optical Society of America.

不同烧蚀条件下飞秒激光脉冲诱导ZnO纳米结构研究

烧蚀条件对飞秒激光脉冲诱导氧化锌纳米结构有重要影响。研究了800nm,150fs,250kHz的飞秒激光脉冲分别在空气中,去离子水中以及无水乙醇中垂直聚焦于氧化锌晶体表面,诱导形成不同形态的纳米结构。实验结果表明,在空气中利用飞秒激光脉冲辐照样品表面,形成了周期为180nm的纳米线;在去离子水中辐照诱导形成了由氧化锌纳米线聚集而成的"纳米球";在无水乙醇中形成出现分叉结构的纳米线。拉曼光谱分析辐照前后晶体晶相结果表明,形成的纳米结构相对于辐照前特征峰437cm-1强度有所下降,在570cm-1处的峰值则显著增强。分析了在各种烧蚀条件下诱导形成纳米结构的演化过程以及物理机理。

Structure and properties of amorphous thin film for optical data storage

In this paper the magnetic and magneto-optical properties of amorphous rare earth-transition metal (RE-TM) alloys as well as the magnetic coupling in the multi-layer thin films for high density optical data storage are presented. Using magnetic effect in scanning tunneling microscopy the clusters structure of amorphous RE-TM thin films has been observed and the perpendicular magnetic anisotropy in amorphous RE-TM thin films has been interpreted. Experimental results of quick phase transformation under short pulse laser irradiation of amorphous semiconductor and metallic alloy thin films for phase change optical recording are reported. A step-by-step phase transformation process through metastable states has been observed. The waveform of crystallization propagation in micro-size spot during laser recording in amorphous semiconductor thin films is characterized and quick recording and erasing mechanism for optical data storage with high performance are discussed. The nonlinear optical effects in amorphous alloy thin films have been studied. By photo-thermal effect or third order optical nonlinearity, the optical self-focusing is observed in amorphous mask thin films. The application of amorphous thin films with super-resolution near field structure for high-density optical data storage is performed. (c) 2007 Elsevier B.V. All rights reserved.

大模场面积光纤激光器79．4W单横模输出

abstract {A large-mode-area (LMA) multimode fiber before and after coiling was studied contrastively in the experiment. Single-transverse-mode output was achieved when the fiber laser was coiled around a mandrel of 65 mm radius. After coiling, beam quality factor of the laser dropped from 1.24 to 1.06 and slope efficiency dropped from 64.7% to 54.3%. When the launched pump power was 149 W, the corresponding output power was 94.7 W and 79.4 W, respectively. However, the brightness of the coiled fiber laser was 1.15 times that of the uncoiled. Coiled modal losses of different modes were also calculated for the fiber employed in the experiment. The measured results agree well with the calculated ones.}

A new Yb-doped oxyorthosilicate laser crystal: Yb : Gd2SiO5

A new Yb-doped oxyorthosilicate laser crystal, Yb:Gd2SiO5 (Yb:GSO), has been grown by the Czochralski (Cz) method. The crystal structure was determined by means of X-ray diffraction analysis. Room temperature absorption and fluorescence spectra of Yb3+ ions in GSO crystal were measured. Then. spectroscopic parameters of Yb:GSO were calculated and compared with those of another Yb-doped oxyorthosilicate crystal Yb:YSO. Results indicated that Yb:GSO crystal seemed to be a very promising laser gain media in generating ultra-pulses and tunable solid state laser applications. As expected, the output power of 2.72 W at 1089 nm was achieved in Yb:GSO crystal with absorbed power of only 4.22 W at 976 nm, corresponding to the slope efficiency of 71.2% through the preliminary laser experiment. (c) 2005 Elsevier Ltd. All rights reserved.

新型掺杂LiAlO2晶体衬底研究

本文系统研究了LiAlO2晶体及掺钛0．2％原子分数LiAlO2晶体的水解性能，用原子力显微镜对（100）晶片在不同水解时间下的表面形貌进行了观察，对比发现这两种晶体的（100）面均具有极性和易水解性。同时观察到掺钛LiAlO2晶体的抗水解性比纯LiAlO2晶体更好，因为掺钛LiAlO2晶体有更多的Li空位，水解的活性得到降低。

Yb：YAG透明陶瓷的制备和激光输出

制备了高质量的Yb：YAG透明陶瓷．Yb：YAG透明陶瓷的晶粒尺寸为10μm左右且分布均匀，晶界处和晶粒中没有杂质、气孔的存在．Yb：YAG样品中所有元素分布均匀，不同的晶粒间，晶粒和晶界间成分是一致的，没有出现成分的偏析．4mm厚样品的透过率为80％．LD泵浦获得了波长为1030nm，最大功率为268mW的连续激光输出．