Laser Stark saturation spectroscopy in methyl alcohol

The method of Lamb dip spectroscopy in Stark tuned molecular gases is discussed and applied to the experimental assignment of methyl alcohol infrared transitions in the ₅ C–O stretch band. Theoretical expressions for Stark Lamb dip patterns are derived for P, Q and R-branch transitions. Stark tuning results and transition quantum number assignments are presented for several 10m transitions, along with measured values of resonant frequencies, absorption coefficients and pressure broadening coefficients.Work supported by the Army Research Office, Durham, and the National Science Foundation.     

Dynamics of two vibro-impact nonlinear energy sinks in parallel under periodic and transient excitations

A linear oscillator (LO) coupled with two vibro-impact (VI) nonlinear energy sinks (NES) in parallel is studied under periodic and transient excitations, respectively. The objective is to study response regimes and to compare their efficiency of vibration control. Through the analytical study with multiple scales method, two slow invariant manifolds (SIM) are obtained for two VI NES, and different SIM that result from different clearances analytically supports the principle of separate activation. In addition, fixed points are calculated and their positions are applied to judge response regimes. Transient responses and modulated responses can be further explained. By this way, all analysis is around the most efficient response regime. Then, numerical results demonstrate two typical responses and validate the effectiveness of analytical prediction. Finally, basic response regimes are experimentally observed and analyzed, and they can well explain the complicated variation of responses and their corresponding efficiency, not only for periodic excitations with a fixed frequency or a range of frequency, but also for transient excitation. Generally, vibration control is more effective when VI NES is activated with two impacts per cycle, whatever the types of excitation and the combinations of clearances. This observation is also well reflected by the separate activation of two VI NES with two different clearances, but at different levels of displacement amplitude of LO.     

附加黏滞阻尼器减震结构基于性能的抗震设计方法

本文以位移设计方法的概念为主,结合能力谱法提出附加黏滞流体阻尼器结构基于位移的初步设计方法.首先讨论了减震结构基于性能设计方法的实现途径并加以比较;其次定量研究了使用加速度反应谱转换为位移反应谱的条件,分析指出真实位移反应谱(均值)与转换得到的位移反应谱随着场地特征周期的增大,两者之间的差值逐渐增大;在场地条件相同的情况下,阻尼比越大两者的差异也越大.最后结合我国抗震设计规范,给出了主体结构保持弹性状态时,非迭代法确定附加黏滞流体阻尼器的减震结构设计流程.非线性时程分析结果表明该设计方法实用、有效.     

Laser performance and thermal lens of diode-pumped Nd,Y-codoped:SrF_2 single crystals

We demonstrate the laser performances of Nd, Y：SrF2 crystals with Nd＇3＋ concentrations of 0.15 and 0.43 at.%. The sample with 0.43 at.% Nd3＋ concentration yields a maximum output power of 1.023 W at 1056.9 nm with a slope efficiency of 53%. The focal length of the thermal lens is analyzed for the 0.15 at.% Nd3＋-doped crystal sample. An improved cavity is designed considering the thermal lens. The maximum output power is 464 mW at 1056.9 nm, with a slope efficiency of 36.1%. The wavelength is tuned within the range of 1049.74-1059.13 nm.     

Modelling and identifying the parameters of a magneto-rheological damper with a force-lag phenomenon

In this study a model based on the Bouc–Wen–Baber–Noori (BWBN) method was proposed to describe the distorted hysteretic behaviour of a self-constructed magneto-rheological (MR) damper whose mechanical performance was measured with an Instron test machine. The experimental results indicated that the MR damper exhibited a force-lag phenomenon. The parameters of the modified BWBN model were identified with the MATLAB SIMULINK Design and Optimisation toolbox. A comparison between the experimental results and modelling predictions revealed that the proposed model could well present the force-lag phenomenon.     

激光自外差相干测量中分布反馈半导体激光器电流调谐非线性的补偿方法

半导体激光器的电流调谐非线性对自外差相干测量的精度影响很大.研究了分布反馈半导体(DFB) 激光器的电流调谐特性,据此提出一种数学模型补偿方法.利用已知光程差下的差拍频率,建立了动态调频 系数的数学模型.以此模型对DFB激光器的电流调谐非线性进行补偿,可以将差拍信号频率预测值的相对误差 减小约3%,提高了系统的测量精度.数学模型补偿方法简化了测量系统的结构,适用于高精度的电流调谐 激光在线测量系统.     

控制两相邻结构地震动响应的Maxwell模型流体阻尼器优化参数研究

运用被动连接单元减小相邻结构的振动被证明是一种行之有效的手段。将两相邻结构简化为两单自由度体系,用Maxwell模型模拟连接两相邻结构的流体阻尼器,分别导出了在地面白噪声激励下主结构平均振动能量最小或两相邻结构总平均振动能量最小这两个控制目标下流体阻尼器优化参数的一般表达式,该优化参数仅与两相邻结构的相对自振频率和相对质量有关,也讨论了两相邻结构的相对自振频率和相对质量对控制效果的影响。最后,运用具有不同相对参数的三类相邻结构在El Centro 1940 NS地震波作用下时域响应的数值结果说明了这种被动优化流体阻尼器能够非常有效地减小在地震作用下两相邻结构的振动响应。     

Enhancing suspension vibration reduction by diagonal inerter

Applied Mathematics and Mechanics - The diagonal inerter is integrated into a suspension vibration reduction system (SVRS). The dynamic model of the SVRS with diagonal inerter and damping is...     

Performance of Range Separated Density Functional in Solvent Continuum: Tuning Long-range Hartree–Fock Exchange for Improved Orbital Energies

Performance of the density functionals mainly depends on the proper approximation of exchange-correlation functionals. Modification of various parameters of such functionals, according to the demand of the system, has brought their accuracy level to a new height. Recent reports highlight that Long-range Corrected (LC) functionals are not encouraging in reproducing orbital energies in solvent. Therefore, in this article, we have proposed a tuning scheme for the LC functional for improved orbital energies. In this scheme, the optimized long-range HF exchange and the dielectric constant of the medium are included to modify the form of functionals. The proposed tuning is tested over a set of 103 molecules from IP131 database and fifteen solvent dielectrics. The tuned range separated functionals reproduce orbital eigenvalues in solvent continuum with good accuracy. More importantly, there is a consistency in the error for the tuned functional across the solvent media. © 2019 Wiley Periodicals, Inc.