Stable H and O isotope variations reveal sources of recharge in Dhofar,Sultanate of Oman

Due to the ability of stable water isotopes to characterize the origin of water and connected processes of groundwater recharge, we used the isotope variations of hydrogen and oxygen in different water sources for assessing the recharge process in the Dhofar region. δ¹⁸O and δ²H of precipitation, spring water, and groundwater cover a range from ?10 to +2 and from ?70 to +7?‰ (vs Vienna Standard Mean Ocean Water), respectively, and correlate in a linear relationship close to the Global Meteoric Water Line. No obvious evaporation processes are detected. A clear signal of the recent precipitation is given by the annual monsoon. The monsoon signal is confirmed by several springs existing in the south at the foot of the Dhofar mountains and sources at Gogub above 450?m and Tawi Atir at 650?m above sea level. They occur here first in the form of water intercepted by trees as stemflow and throughflow. The isotope signature of groundwater in the Dhofar mountains reflects the climatic conditions at the time of recharge and the lithological features of the limestone matrix. To the north, the isotope patterns of the groundwater are continuously depleted from the monsoon signal along the outcropping aquifer D (Lower Umm Er Radhuma). Here, a more negative signature towards the wells in the Najd desert region was observed. Cyclone water that flooded wadis in the Dhofar region occasionally, as observed in November 2011, falls isotopically into the same range as we observed in the fossil groundwater. Taking into account the different sources of precipitation and groundwater and thus a clear distinction of the isotopic composition of the water sources, we conclude a recharge process divided into a southward and a northward component in the Dhofar region.     

基于弱粘接结构中谐振频率的研究

利用弹簧模型方法研究了铝-粘接剂-铝结构中波的反射和透射系数。首先利用粘接层界面的一次反射导出切向和法向刚度比表达式;其次,推导了粘接层界面存在多次反射和透射时刚度比、谐振频率及反射系数之间的关系,得到了弱粘接结构的反射系数随着不同刚度比的变化规律;最后求解了弱粘接层厚度的变化对谐振频率的影响。理论分析和数值计算的结果表明：反射系数取极大值时粘接层厚度与谐振频率的积成奇数倍的关系,反射系数极小值时粘接层厚度与谐振频率的积成整数倍的关系;随着刚度比的增加,谐振频率向高频方向漂移,随刚度比的减小,反射系数逐渐的趋近与1。     

三种不同型线柔性弹簧的有限元分析及对比研究

柔性弹簧对于低温制冷机的间隙密封及可靠性具有重要作用,文中在总结国内外柔性弹簧型线的基础上,针对用于低温制冷机的三种典型柔性弹簧,采用Ansys软件对其应力分布、径轴向刚度以及自然频率等特性进行了数值模拟和对比分析,该研究为探索具有优良性能的新型线结构的柔性弹簧指明了方向.     

非线性弹簧阻尼减振装置的探究

将汽车底盘减振装置简化为以非线性弹簧、阻尼器为主的被动阻尼式吸振器．利用Matlab软件对其在简谐力作用下的响应进行定量绘图分析,研究其振幅衰减、缓冲周期以及与由线性弹簧构成的简单模型进行比较,解释了减振装置具体的工作过程以及其中的基本工作原理．     

Spectral analysis for linear semi‐infinite mass‐spring systems

We study how the spectrum of a Jacobi operator changes when this operator is modified by a certain finite rank perturbation. The operator corresponds to an infinite mass‐spring system and the perturbation is obtained by modifying one interior mass and one spring of this system. In particular, there are detailed results of what happens in the spectral gaps and which eigenvalues do not move under the modifications considered. These results were obtained by a new tecnique of comparative spectral analysis and they generalize and include previous results for finite and infinite Jacobi matrices.     

探究弹簧自重对形变量的影响

在理论上,用2种方法研究了弹簧自重对形变量的影响,并用简单实验对该结论进行了论证,最终得出弹簧自身重力作用产生的形变量为x=G/2k的结论.应用该结论对习题进行了修正.     

基础水平运动的弹簧摆的周期解与稳定性

针对基础水平运动的弹簧摆的非线性动力学响应进行研究,利用拉格朗日方程建立了系统的动力学方程.将离散傅里叶变换、谐波平衡法以及同伦延拓方法相结合,对系统的周期响应进行求解,避免了传统方法计算中使用泰勒展开引起的小振幅的限制,与数值计算结果的对比表明该求解方法具有较高的精确度.利用Floquet理论分析了周期响应的稳定性,给出了基础运动振幅和频率对系统周期响应的影响.研究发现:对应某些基础频率和振幅,系统的周期响应可能发生Hopf分岔;利用数值计算研究了Hopf分岔后系统响应随基础频率和振幅的变化,发现系统出现了倍周期运动、拟周期运动和混沌等复杂的动力学行为.研究表明系统进入混沌的主要路径是拟周期环面破裂和阵发性.     

Engineering the optical spring via intra-cavity optical-parametric amplification

The ‘optical spring’ results from dynamical back-action and can be used to improve the sensitivity of cavity-enhanced gravitational-wave detectors. The effect occurs if an oscillation of the cavity length results in an oscillation of the intra-cavity light power having such a phase relation that the light's radiation pressure force amplifies the oscillation of the cavity length. Here, we analyse a Michelson interferometer whose optical-spring cavity includes an additional optical-parametric amplifier with adjustable phase. We find that the phase of the parametric pump field is a versatile parameter for shaping the interferometer's spectral density.