Variation of added mass and its application to the calculation of amplitude response for a circular cylinder

In the present study, analyzed are the variation of added mass for a circular cylinder in the lock-in ( synchronization) range of vortex-induced vibration (VIV) and the relationship between added mass and natural frequency. A theoretical minimum value of the added mass coefficient for a circular cylinder at lock-in is given. Developed are semi-empirical formulas for the added mass of a circular cylinder at lock-in as a function of flow speed and mass ratio. A comparison between experiments and numerical simulations shows that the semi-empirical formulas describing the variation of the added mass for a circular cylinder at lock-in are better than the ideal added mass. In addition, computation models such as the wake oscillator model using the present formulas can predict the amplitude response of a circular cylinder at lock-in more accurately than those using the ideal added mass.

快速凝固/粉末冶金高阻尼铝合金挤压成形过程的数值模拟

采用有限元分析软件ANSYS,分析了快速凝固/粉末冶金(Rapidly Solidified/Powder Metallurgy,RS/PM)高阻尼铝合金FMS0714/10(Zn-30Al)的挤压成形过程,研究了模具与坯料间的摩擦条件和挤压比对阻尼铝合金成形过程的影响,探讨了挤压过程材料表面产生裂纹的机理,进行了成形工艺优化.研究结果表明:挤压过程中FMS0714/10(Zn-30Al)阻尼铝合金材料的流动与变形不均匀,导致了应力应变分布的不均匀:材料表面应力应变较大,芯部应力应变较小;表面过大的应变和轴向拉应力是表面裂纹的诱因;减小模具和坯料间的摩擦,增大挤压比,可以减小材料表面应力,使应变分布趋于均匀,从而减少材料表面损伤,优化材料表面质量,提高成品合格率.数值模拟的研究结果将为FMS0714/10(Zn-30Al)阻尼铝合金材料挤压工艺的制订以及新材料的设计和研制提供有益的参考.

器件韧性镀膜微划痕破坏机理研究

对硅基体上之韧性镀膜（铝膜）的粘结强度及破坏机理进行微划痕实验及理论研究，从实验中观察出该体系的破坏特征，进而测量出微划痕水平驱动力、划痕深度随划痕水平位移并伴随有界面脱胶发生时的变化规律。针对微划痕破坏特征，建立了双粘聚力模型，并对由微划痕引起的界面弹塑性脱胶进行了数值模拟，给出界面脱胶时能量释放率随其他材料参数变化的理论预测曲线，并将预测值与文中的铝／硅实验结果及与其他文献中关于铂／氧化镍的实验结果进行对比，达到基本符合，通过对韧性薄膜／脆性基体的微划痕实验研究和理论分析，获得如下主要结论：1.韧性膜的微划痕破坏特征为，当划刀尖端接近界面时，将突然发生薄膜沿界面的脱胶现象，并在界面附近脆性基一侧形成界面裂纹并扩展；微划痕的水平驱动力表征了整个薄膜脱胶体系的能量释放率；薄膜或涂层材料的塑性变形对微划痕过程有较强的抑制作用。2.界面的分离强度和材料的剪切强度对微划痕过程有重要的影响。3.划痕刀片的几何特征角对刻痕水平驱动力影响不大。

温压炸药爆炸抛撒的运动规律

采用高速运动分析系统观察了高能炸药、含铝炸药和温压炸药爆炸产物抛撒的过程;比较了这3种炸药的爆炸产物抛撒运动及后燃特点,通过比较直观地观察到温压炸药爆炸和后燃2个过程,以及后燃火球的成长历程,根据实验结果确定了温压炸药爆炸产物抛撒半径随时同变化的数学表达式.

TDLAS测量甲烷／空气预混平面火焰温度和H2O浓度

基于可调谐二极管激光器吸收光谱技术(TDLAS)建立了温度和H20浓度测量系统，利用光谱数据库Hi— tran2004在1393nm附近选择了在500～1300K有很高测温灵敏度的两条水吸收线：7168.437 cm- ，7185.597 cm- 。 在1kHz的扫描频率下，利用直接吸收一扫描波长法对甲烷／空气预混平面火焰进行测量，并进行边界层修正，与热电 偶的对比结果显示，在温度区间1100～1350K，两者最大相差80K(6.7％)；水蒸气组分浓度与计算值平均相差小于 O.02(10％)．

Coherent population transfer with chirped few-cycle laser pulses in an excited-doublet four-level system

The behavior of population transfer in an excited-doublet four-level system driven by linear polarized few-cycle ultrashort laser pulses is investigated numerically. It is shown that almost complete population transfer can be achieved even when the adiabatic criterion is not fulfilled. Moreover, the robustness of this scheme in terms of the Rabi frequencies and chirp rates of the pulses is explored.

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。

Computation of the ambiguity function for circularly symmetric pupils

A method of computing the ambiguity function (AF) for a circularly symmetric pupil function is presented. The AFs of a clear aperture and two shaded apertures are considered in detail and an explicit expression for the first of these AFs is given. We explain these results in the context of the well-known optical transfer function theory and show a primary application of these computations. A good analytic approximation is also introduced, providing an alternative method for calculating the AF, in a simpler way.

基于联合变换相关器的Dempster-Shafer理论计算

提出了用联合变换相关器（JTC）来实现证据理论概率分配函数正交和的光学计算，在理论上对于如何用联合变像相关器实现证据理论分配函数正交和作了详细的讨论，并作了相应的仿真测试，结果显示该方法是可行的。与John Caulfield提出的用声光器件矢量外积实现的正交和计算相比，在该结构中由于采用二进制编码的数值计算，因此其计算精度得到了提高，同时对联合变换相关器输入端二进制编码的数值空间位置的适当调整可以直接得到所需要的证据理论正交和矢量，在处理步骤上得到了简化。

放大自发辐射对全固态激光器调Q性能的影响

为定量分析放大自发辐射（ASE）对调Q激光器性能的影响，在调Q激光速率方程中引入放大自发辐射项。并在合理的近似下求解，给出了激光二极管（LD）端面抽运电光调Q运转的固体激光器反转粒子数的建立过程，分析了放大自发辐射对激光上能级储能效率的影响及考虑放大自发辐射时调Q激光器输出脉冲宽度和脉冲能量随抽运功率的变化关系。结果表明，由于放大自发辐射的存在，上能级储能效率降低，且在一定的抽运功率下，调Q输出脉冲宽度变宽，脉冲能量下降。用LGS（La3Ga5SiO14）晶体作电光调Q元件，在激光二极管抽运的Nd：YVO

飞秒激光辐照ZnO晶体

利用飞秒激光对ZnO晶体进行辐照，对辐照前后的晶体样品进行发光光谱及拉曼光谱检测。辐照后发光光谱的某些发光峰强度有明显增强，但未产生新的发光峰，表明没有新的缺陷结构产生，但晶体内锌空位、间隙位锌、间隙位缺陷浓度增加。拉曼光谱结果表明，辐照后ZnO晶体未产生相变，但随着辐照激光功率的增大，拉曼峰327 cm-1，437 cm-1强度明显减弱，表明在飞秒激光辐照作用下氧化锌的结晶程度下降。但574 cm-1峰值却随着辐照功率的增大而变大，分析表明该拉曼峰很可能是由于晶体内间隙位缺陷所致。同时实验过程中观察到飞

The spectroscopic properties of Er3(+)-doped TeO2-Nb2O5 glasses with high mechanical strength performance

(100 - x)TeO2 - xNb(2)O(5) (x=5-20) mobic tellurite glasses doped with 0.5 mol.% Er2O3 were synthesized, and their thermal, mechanical, and spectroscopic properties were measured and compared to the properties of the typical 75TeO(2)-20ZnO-5Na(2)O (TZN) tellurite glass. The refractive index (n(d)), density (p), and glass transition temperature (T-g) of bulk glasses increase with the Nb2O5 content. The Vickers microhardness (H-v) of bulk glass in niobic tellurite glasses also increases with the Nb2O5 content. The values (2.5-3.2 GPa) of H, in the niobic tellurite glasses are 47-88% larger than that (1.7 GPa) in TZN glass. The effect of Nb2O5 content on absorption spectra, the Judd-Ofelt parameters Omega(t) (t = 2, 4, 6), fluorescence spectra and the lifetimes of Er3+ :I-13/2 level were also investigated, and the stimulated emission crosssection was calculated from McCumber theory. With increasing Nb2O5 content in the glass composition, the Omega(t) (t = 2, 4, 6) parameters, fluorescence full width at half maximum (FWHM) Of I-13/2 of Er3+ increase, while the I-4(13/2) lifetimes of Er3+ decreases. Compared with TZN glass, the gain bandwidth properties of Er3+-doped TeO2-Nb2O5 glass is much larger than in tellurite glass based TeO2-ZnO-Na2O system, bismush-based glass, germanate, and silicate glasses, which indicates that TeO2-Nb2O5 glasses are better choice as a practical available host material for broadband Er3+-doped amplifier. (c) 2005 Elsevier B.V. All rights reserved.

Characteristics and optical spectra of V : YAG crystal grown in reducing atmosphere

A V:YAG single crystal was grown by the temperature gradient technique (TGT) with graphite-heating elements. The as-grown crystal has different colorations of light green and yellow brown in different parts. Distribution of vanadium in three samples with different colorations was determined by inductively coupled plasma-mass spectrometry. From the absorption spectrum of the yellow-brown part with peaks at 370, 820 and 1320nm, we can deduce that the reducing atmosphere of carbon diffused from the heating elements can increase the concentration of tetrahedral V3+ ions and induce F color centers. All three samples exhibited light-green color after annealing in vacuum or H-2 atmospheres. In the vacuum annealing process, the V3+ ions in tetrahedral positions were enhanced through two methods: one method is the exchanging of octahedral V3+ and tetrahedral Al3+ ions in neighboring sites under thermal excitation, the other is that F color centers were thoroughly eliminated and the escaped free electrons could be captured by V ions with higher valance states to further improve the concentration of tetrahedral V3+ ions. Besides the two mechanisms, the H-2 annealing process greatly improved the V-tetra(3+) ions through the reduction effect of H-2. (c) 2006 Elsevier B.V. All rights reserved.

Annealing effects on electron-beam evaporated Al2O3 films

The effects of post-deposited annealing on structure and optical properties of electron-beam evaporated Al2O3 single layers were investigated. The films were annealed in air for 1.5 h at different temperatures from 250 to 400 degrees C. The optical constants and cut-off wavelength were deduced. Microstructure of the samples was characterized by X-ray diffraction (XRD). Profile and surface roughness measurement instrument was used to determine the rms surface roughness. It was found that the cut-off wavelength shifted to short wavelength as the annealing temperature increased and the total optical loss decreased. The film structure remained amorphous even after annealing at 400 degrees C temperature and the samples annealed at higher temperature had the higher rms surface roughness. The decreasing total optical loss with annealing temperature was attributed to the reduction of absorption owing to oxidation of the film by annealing. Guidance to reduce the optical loss of excimer laser mirrors was given. (c) 2004 Elsevier B.V. All rights reserved.