油藏渗流与应力耦合分析

基于岩石力学与渗流力学理论，考虑到油藏中多相渗流的特点以及渗流与应力的耦合效应，建立了油藏多相渗流与应力耦合分析模型，研究了渗流与应力的耦合规律，给出了实现耦合分析的方法与步骤，最后通过算例检验了耦合分析的有效性和实用价值。

Numerical Simulation of 3D-Thermal Field with Phase Transformation

以激光熔凝表面强韧化处理为背景,应用空间的弹塑性有限单元和高精度的数值算法、同时考虑材料组织性能的变化来模拟材料的温度场。主要研究激光熔凝加工中瞬时温度场数值模拟,同时考虑相变潜热的影响,为第二步热应力场及残余应力的数值模拟做准备。最后用算例验证了模型的正确性,并给出了不同时刻温度场的分布。

近圆弧位形的约束无力场

<正> 太阳磁场在大气中常常被描述为无力场,无力场的理论模型常常考虑成延伸至无穷远,或者人为地截止至有限的区域。事实上,太阳大气中的磁场往往被约束在有限的空间,通过一间断面与大气交接。

Orientation preference and fractal character of short fatigue cracks in a weld metal

Short fatigue crack behaviour in a weld metal has been further investigated. The Schmid factor and the fractal dimension of short cracks on iso-stress specimens subjected to reversed bending have been determined and then applied to account for the distribution and orientation characteristics of short fatigue cracks. The result indicates that the orientation preference of short cracks is attributed to the large values of Schmid factor at relevant grains. The Schmid factors of most slip systems, which produced short cracks, are less than or equal to 0.4. Crack length measurements reveal that short crack path, compared to that of long crack, possesses a more stable and relatively larger value of fractal dimension. This is regarded as one of the typical features of short cracks.

砂土地基中吸力式沉箱的极限沉贯深度分析

吸力式沉箱是广泛应用于离岸结构物中的新型基础形式,贯入分析方法的研究是很重要的课题.分析了砂性土地基吸力贯入过程中的渗流状况,得出了筒内壁的压降比率与贯入深径比的关系公式,分析评估了抽吸作用对筒内壁压降比率的影响,提出了砂土地基中吸力贯入阻力和地基极限吸力的简便计算方法,给出了砂土地基中极限贯入深径比的计算公式,分析了各种砂土地基中的吸力贯入极限深径比.不计简体自重和抽吸效应影响时,这一比值介于2.1～2.5之间.

负啁啾高强度飞秒脉冲在正常色散材料中传输特性研究

利用块状正常色散材料作非线性介质，实验研究了负啁啾强激光飞秒脉冲在正常色散材料的传输过程中，脉冲波形及频谱随入射脉冲能量的变化特性．实验发现，负啁啾脉冲经过材料后激光光谱在被整形和压缩的同时，脉冲宽度也被压缩．实验获得的压缩脉冲宽度短于相等光谱宽度下的双曲正割转换极限脉冲宽度。数值模拟结果显示，在实验条件下模拟结果具有同样的变化特性．

Self-compression of femtosecond pulses in argon with a power close to the self-focusing threshold

Self-compression of femtosecond pulses in noble gases with an input power close to the self-focusing threshold has been investigated experimentally and theoretically. It is demonstrated that either multiphoton ionization (MPI) or space time focusing and self-steepening effects can induce pulse shortening, but they predominate at different beam intensities during the propagation. The latter effects play a key role in the final pulse self-compression. By choosing an appropriate focusing parameter, action distance of the space time focusing and self-steepening effects can be lengthened, which can promote a shock pulse structure with a duration as short as two optical cycles. It is also found that, for our calculation cases in which an input pulse power is close to the self-focusing threshold, either group velocity dispersion (GVD) or multiphoton absorption (MPA) has a negligible influence on pulse characteristics in the propagation process.

体布拉格光栅外腔半导体激光器光谱特性研究

用体布拉格光栅(VBG)作为反馈元件与瓦级半导体激光器(LD)以及快轴准直柱透镜构成一个可以将半导体激光器的工作波长稳定在体布拉格光栅布拉格波长处的外腔激光器。测量了体布拉格光栅外腔激光器的波长稳定性与其工作电流、热汇温度、激光束准直装置等因素的关系。分析了波长稳定效果与半导体激光器增益谱特性、外腔结构参量等因素的关系。研究表明,在相同的工作电流、热汇温度下,当准直柱透镜直径为0.4 mm时的波长稳定效果较好;在此情况下,当热汇温度控制在30 ℃,工作电流从0.5 A增加到1.5 A的测量范围内,以及当工

Polarization analysis and experimental implementation of PLZT electro-optical switch using fiber Sagnac interferometers

The polarization characteristics of electro-optical (EO) switches using fiber Sagnac interferometer (FSI) structures are theoretically investigated. Analytical solutions of output fields are presented when the twists and birefringence in a Sagnac loop are considered. Numerical calculations show that the twists of fiber, the orientation of the inserted phase retarder, and the splitting ratio of the coupler will influence both the output intensity and the output polarization properties of the proposed switch. A polarization-independent EO switch based on a Sagnac interferometer and a PUT bar was experimentally implemented, which showed good coincidence with the analytical results. The experiment showed a switch with 22 dB extinction ratio and less than 31.1 ns switching time. (c) 2006 Optical Society of America.

Upconversion properties of TM3+/Yb3+ codoped fluorophosphate glasses with low phonon density of states

Fluorophosphate glasses codoped with Tm3+ and Yb3+ were prepared and their thermal stability, phonon states, and upconversion properties were studied. It is found that the increment of phosphate content is good for the thermal stability but increases the phonon density of states. However, the phonon density of states of these fluorophosphate glasses is very low due to the low phosphate content in their composition. The upconversion luminescence spectra were measured under excitation of 970 nm laser diode, and the intense blue (476 nm) and near infrared (794 nm) emission were simultaneous obtained at room temperature. The sensitizing mechanisms of Yb3+ to Tm3+ for blue and red emission contain both sequential and cooperative sensitization. The near infrared emission is a two-photon upconversion process. These researches suggest that when the phosphate content in the composition is low enough, fluorophosphate glass can be suitable host material of Tm3+ codoped with Yb3+ for blue and near infrared upconversion luminescence. (c) 2005 Elsevier B.V All rights reserved.

Characterization of LaF3 coatings prepared at different temperatures and rates

LaF3 thin films were prepared by thermal boat evaporation at different substrate temperatures and various deposition rates. X-ray diffraction (XRD), Lambda 900 spectrophotometer and X-ray photoelectron spectroscopy (XPS) were employed to study crystal structure, transmittance and chemical composition of the coatings, respectively. Laser-induce damage threshold (LIDT) was determined by a tripled Nd:YAG laser system with a pulse width of 8 ns. It is found that the crystal structure became more perfect and the refractive index increased gradually with the temperature rising. The LIDT was comparatively high at high temperature. In the other hand, the crystallization status also became better and the refractive index increased when the deposition rate enhanced at a low level. If the rate was super rapid, the crystallization worsened instead and the refractive index would lessen greatly. On the whole, the LIDT decreased with increasing rate. (C) 2007 Elsevier B.V. All rights reserved.