Effects of radiation damping on Z-spectra

Radiation damping induced by the strong water magnetization in Z-spectroscopy experiments can be sufficient to perturb significantly the resultant Z-spectrum. With a probe tuned to exact electrical resonance the effects are relatively straightforward, narrowing the central feature of the Z-spectrum. Where, as is commonly the case, the probe is tuned sufficiently well to give optimum signal-to-noise ratio and radiofrequency field strength but is not at exact resonance, radiation damping introduces an unexpected asymmetry into the Z-spectrum. This has the potential to complicate the use of Z-spectrum asymmetry to study chemical exchange, for example in the estimation of pH in vivo.     

An investigation into the effects of electrostatic and squeeze-film non-linearities on the shock spectrum of microstructures

We present an investigation into the effects of some of the common microelectromechanical systems (MEMS) non-linearities on their shock response and shock spectrum. As a case study, a capacitive accelerometer is selected to investigate theoretically and experimentally the effect of non-linearities due to squeeze film damping (SQFD) and electrostatic actuation. For the theoretical investigation, a non-linear single-degree-of-freedom model is used to simulate the response of the device. It is shown that, in the case of light damping, the electrostatic forces soften the microstructure and raise its deflection significantly. Dynamic pull-in instability is predicted near the dynamic range zone of the shock spectrum. On the other hand, SQFD is found to highly suppress the deflection of the microstructure in the dynamic range, while it is of less effect in the quasi-static range. Experimentally, the capacitive accelerometer is powered with a DC load and then subjected to acceleration pulses generated by a shaker. Tests are conducted while the accelerometer is operated in air, where the squeeze film effect is significant, and while placed inside a vacuum chamber. Simulation results are compared to experimental data showing excellent agreement.     

Maxwell泥床上线性长波衰减的研究

用Maxwell模型作为非牛顿泥床本构,建立了一组新的Boussinesq型方程组,以描述波-泥相互作用下水波的传播. 基于该方程,解析给出了一维线性长波衰减率的表达式. 当泥层模型退化到牛顿流体时,该结果与前人文献的结果一致. 当无量纲松弛时间λ较大时,衰减率随泥深近似地出现周期性的极值现象,这些极值位置对应泥层中各阶模态的衰减率峰值.      

干摩擦支承边界梁的非线性振动分析

研究梁具有纵向干摩擦边界条件时非线性振动。干摩擦力本构关系分别为粘住—滑动状态、瞬态滑动状态、粘住状态三种情形描述。首先由Ｈａｍｉｌｔｏｎ原理建立梁的动力学方程及其干摩擦力的边界条件，然后借助于Ｇａｌｅｒｋｉｎ法转化得到非线性常微分方程。采用谐波平衡原理进行系统的基波稳态响应求解，并讨论解的稳定性条件。数值计算利用ｔｕｒｂｏ－Ｃ语言在微机上完成，由此得到摩擦力参数改变时几种典型的频响特性曲线。     

Maxwell-Lorentz Dynamics of Rigid Charges

We establish global existence and uniqueness of the dynamics of classical electromagnetism with extended, rigid charges and fields which need not to be square integrable. We also consider a modified theory of electromagnetism where no self-interaction occurs. That theory and our results are crucial for approaching the as yet unsolved problem of the general existence of dynamics of Wheeler-Feynman electromagnetism, which we shall address in the follow up paper. We conclude by discussing the energy conservation without self-interaction.     

Radiation damping in an anharmonic oscillator

The effect of radiation damping in an anharmonic oscillator has been calculated using the technique of Kryloff and Bogolituboff. It is found that the intensity distribution of the emitted spectral line is asymmetric about its intensity maximum. The index of asymmetry agree with the experimental data on x-rayK _{a 1,2}lines.     

Elastic waves in a Timoshenko beam with boundary damping

In this paper we consider a Timoshenko beam with a damping moment applied to one of the endpoints. The elastic waves that develop from two sets of localised initial disturbances in the beam, are simulated and it is shown that properties of the spectrum adequately explain the features of the waves. We also show, using energy calculations, that the boundary moment is significantly more effective in reducing vibrations in the beam in one of the cases under consideration. The so-called second spectrum of the Timoshenko beam plays a prominent part in explaining this phenomenon.     

Multicomponent latex IPN materials: 2. Damping and mechanical behavior

The integrals of the linear loss shear modulus vs. temperature (loss area, LA) and linear tan δ vs. temperature (tan δ area, TA) were characterized for various core/shell latex particles with synthetic rubber, poly(butadiene-stat-styrene) [P (Bd/S), 90/10], and interpenetrating polymer networks (IPN) as the cores. The IPN cores were composed of P(Bd/S) (T_g ≃ − 70°C) and an acrylate based copolymer (T_g around 10°C) for potential impact and damping improvement in thermoplastics. Poly(styrene-stat-acrylonitrile) (SAN, 72/28) was the shell polymer for all these polymers. Under the same loading, for both toughening and damping controls, among the IPN core/shell, blend of separate core/shell, and multilayered core/shell polymers, the IPN core/shell polymers were the best dampers. However, the other core/shell polymers also showed higher LA values than P(Bd/S)/SAN core/shell polymer. A comparison of LA values via a group contribution analysis method was made, the effect of particle morphology and phase continuity on damping being studied. Inverted core/shell latex particles (glassy polymer SAN was synthesized first) showed much higher LA and TA values than normal core/shell ones (rubbery polymer was synthesized first). Models for maximum LA and TA behavior are proposed. The damping property was essentially controlled by the phase miscibility and morphology of the core/shell latex particles. The LA values for each peak in these multiphase materials provided some indication of the several fractional phase volumes. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 1501–1514, 1997     

无穷维空间的牛顿法收敛域定理

本文对无穷维空间的映象给出了广义导数的概念,利用这种导数替代光滑映象的Frechet导数,给出了无穷维空间非光滑算子方程的阻尼牛顿法收敛域的一个定理。