Ba~(2+)对Sr(NO_3)_2晶体生长的影响

寻找固态Raman激光器中的变频材料并使其能够满足科学研究和实际应用的需要已变得越来越重要。研究表明 ,含有NO3 基团的分子晶体应有很强的受激Raman散射效应。由于Ba(NO3 ) 2 晶体的NO3 基团在 1 0 47cm-1有一个很强的Raman活性峰 ,它能将Nd∶YAG激光器发出的波长为 1 .31 8～ 1 .338μm的激光变频到对人眼睛安全的波长为 1 .5 35～ 1 .5 5 6 μm的激光 ,转换效率达到 48%。但在我们的实验过程中发现 ,要生长出大晶体比较困难 ,而Sr(NO3 ) 2 晶体生长起来则较为容易。Sr(NO3 ) 2 和Ba(NO3 ) 2 为类质同构晶体 ,Sr(NO3 ) 2 晶体中的NO3 基团在 1 0 5 5 .6cm 1也有一个很强的Raman活性峰。所以 ,Sr(NO3 ) 2 晶体应该是一种很有前景的Raman激光变频材料。为此 ,我们研究了Sr(NO3 ) 2 晶体的生长以及Ba2 +离子掺入后的影响。Sr(NO3 ) 2 晶体用降温和蒸发溶剂两种方法生长。蒸发溶剂的生长温度固定在 5 0℃ ;降温生长的起始温度为 40℃。配制Sr(NO3 )...

Analysis on characteristics of 1-D apodized and chirped photonic crystals containing negative refractive materials

Using transfer matrix method,the optical transmission properties of 1-D photonic crystals composed partially of negative refraction media are analyzed. The transmission spectra of periodic photonic crystal,chirped photonic crystal and apodized photonic crystal are numerically simulated respectively. By contrast with optical transmission properties of ordinary photo-nic crystals made of positive refraction media,the transmission spectra of apodized photonic crystal become unregular,the Bragg flat-headed area recurs but the peak of transmission does not change significantly. Futhermore,the band gap range of chirped photonic crystal diminishes gradually.

Diagnosis of Seasonal Variations of Tropical Cyclogenesis over the South China Sea Using a Genesis Potential Index

This study examines the seasonal variations of tropical cyclogenesis over the South China Sea (SCS) using a genesis potential (GP) index developed by Emanuel and Nolan. How different environmental factors (including low-level vorticity, mid-level relative humidity, vertical wind shear, and potential intensity) contribute to these variations is investigated. Composite anomalies of the GP index are produced for the summer and winter monsoons separately. These composites replicate the observed seasonal variations of the observed frequency and location of tropical cyclogenesis over the SCS. The degree of contribution by each factor in different regions is determined quantitatively by producing composites of modified indices in which only one of the contributing factors varies, with the others set to climatology. Over the northern SCS, potential intensity makes the largest contributions to the seasonal variations in tropical cyclogenesis. Over the southern SCS, the low-level relative vorticity plays the primary role in the seasonal modulation of tropical cyclone (TC) genesis frequency, and the vertical wind shear plays the secondary role. Thermodynamic factors play more important roles for the seasonal variations in tropical cyclogenesis over the northern SCS, while dynamic factors are more important in the seasonal modulation of TC genesis frequency over the southern SCS.

Monitoring the Modal Frequency and Velocity Variations of Bridges under Ambient Excitation

We conducted a long-term monitoring experiment on the Lutuanxilu Bridge located in Changping District of Beijing, employing our recently developed real-time bridge monitoring system based on the Guralp CMG-6TD broadband seismometer. We identified the modal parameters with the stochastic subspace identification( SSI) algorithm,and continuously monitored the temporal velocity variation with coda wave interferometry.The results show that:( 1) the highly sensitive Guralp CMG-6TD broadband seismometer,which records the three-component vibration signal within broad frequency range,is well suited for long-term bridge health monitoring.( 2) With the continuous vibration signal from ambient excitation,the stochastic subspace algorithm can robustly identify the low-order modal parameters and the coda wave interferometry can accurately monitor the tiny velocity variation.( 3) The elastic modulus of bridge materials changes significantly associated with varying temperature,leading to diurnal velocity variation with amplitude of approximately 1%. The velocity variation shows strong negative correlation with temperature fluctuation. Meanwhile,the modal frequencies remain quite stable,suggesting that the velocity variation may be a more sensitive quantitative damage index.( 4) While the modal frequencies reflect the integrated health status of the bridge,the velocity variation can be utilized to monitor the local elastic modulus. Therefore,it is crucial for bridge health monitoring to continuously monitor the two key damage indexes under ambient excitation.

Modeling and parameter identification of amplitude- and frequency-dependent rubber isolator

A model to describe the hysteresis damping characteristic of rubber material was presented.It consists of a parallel spring and damper,whose coefficients change with the vibration amplitude and frequency.In order to acquire these relations,force decomposition was carried out according to some sine vibration measurement data of nonlinear forces changing with the deformation of the rubber material.The nonlinear force is decomposed into a spring force and a damper force,which are represented by the amplitude-and frequency-dependent spring and damper coefficients,respectively.Repeating this step for different measurements gives different coefficients corresponding to different amplitudes and frequencies.Then,the application of a parameter identification method provides the requested approximation functions over amplitude and frequency.Using those formulae,as an example,the dynamic characteristic of a hollow shaft system supported by rubber rings was analyzed and the acceleration response curve in the centroid position was calculated.Comparisons with the sine vibration experiments of the real system show a maximal inaccuracy of 8.5%.Application of this model and procedure can simplify the modeling and analysis of mechanical systems including rubber materials.

激光器

SPIE-Vol.3492(1)00161181998年 SPIE 会议录,卷3492(1):第3届国际惯性限制聚变用的固态激光器会议=1998 proceedings ofSPIE,Vol.3492(1):third international conference onsolid state lasers for application to inertial confinement fu-sion[会,英]/SPIE-the International Society for OpticalEngineering.—1998.—535P.(PC)本会议录分二部分。本书为第1部分,共收录了于1998年6月7～12日在美国加州蒙特里召开的第3届国际惯性限制聚变用的固态激光器会议上发表的58篇论文。内容主要涉及未来的装置,平滑与偏转,脉冲生成,电/光元件,光学损伤,薄膜涂层,系统试验,大型激光器系统的光学设计,变频材料和技术,衍射光学,非线性光学以及空间滤波器孔等。