Nonlinear dynamics of oscillators with bilinear hysteresis and sinusoidal excitation

The transient and steady-state response of an oscillator with hysteretic restoring force and sinusoidal excitation are investigated. Hysteresis is modeled by using the bilinear model of Caughey with a hybrid system formulation. A novel method for obtaining the exact transient and steady-state response of the system is discussed. Stability and bifurcations of periodic orbits are studied using Poincaré maps. Results are compared with asymptotic expansions obtained by Caughey. The bilinear hysteretic element is found to act like a ‘soft spring’. Several sub-harmonic resonances are found in the system, however, no chaotic behavior is observed. Away from the sub-harmonic resonance the asymptotic expansions and the exact steady-state response of the system are seen to match with good accuracy.     

Early stage expansion and time-resolved spectral emission of laser-induced plasma from polymer

In the nanosecond laser ablation regime, absorption of laser energy by the plasma during its early stage expansion critically influences the properties of the plasma and thus its interaction with ambient air. These influences can significantly alter spectral emission of the plasma. For organic samples especially, recombination of the plasma with the ambient air leads to interfering emissions with respect to emissions due to native species evaporated from the sample. Distinguishing interfering emissions due to ambient air represents a critical issue for the application of laser-induced breakdown spectroscopy (LIBS) to the analysis of organic materials. In this paper, we report observations of early stage expansion and interaction with ambient air of the plasma induced on a typical organic sample (nylon) using time-resolved shadowgraph. We compare, in the nanosecond ablation regime, plasmas induced by infrared (IR) laser pulses (1064 nm) and ultraviolet (UV) laser pulses (266 nm). Nanosecond ablation is compared with femtosecond ablation where the post-ablation interaction is absent. Subsequent to the early stage expansion, we observe for each studied ablation regime, spectral emission from CN, a typical radical for organic and biological samples. Time-resolved LIBS allows identifying emissions from native molecular species and those due to recombination with ambient air through their different time evolution behaviors.     

Microstructure, bonding strength and thermal shock resistance of ceramic coatings on steels prepared by plasma electrolytic oxidation

Ceramic coatings were successfully prepared on steel by plasma electrolytic oxidation (PEO) in aluminate electrolyte and silicate electrolyte, respectively. The microstructure of the coatings including surface morphology, phase and element composition were studied by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. The bonding strength between the ceramic coating and the substrate was tested using different methods including tensile tests and shearing tests. The thermal shock resistance of the coatings was also evaluated. The results indicated that coatings obtained in both electrolytes were porous and coarse. The average diameters of the pores were below 10 μm. PEO coatings obtained in aluminate electrolyte were composed of Fe₃O₄ and FeAl₂O₄, while those obtained in silicate electrolyte were in a noncrystal state. PEO coatings obtained in aluminate electrolyte showed similar change trend of tensile strength and shearing strength with increasing treating time, namely, a relatively high values with middle time treating and low value with short and long time treating. The best coating was the samples treated with 30 min, whose tensile strength was 20.6 MPa and shearing strength was 16 MPa. The tensile strength and shearing strength of coatings obtained in silicate electrolyte were not strongly influenced by the treating time, the values of which were range in 14 ± 2 MPa and 11 ± 2 MPa, respectively. Coatings obtained in both electrolytes showed the best thermal shock resistance with middle time treating. Coatings obtained in silicate electrolyte show a little better thermal shock resistance than those obtained in aluminate electrolyte.     

冲击加载下铝中氦泡和孔洞的塑性变形特征研究

通过分子动力学模拟研究了在相同冲击加载强度下单晶铝中氦泡和孔洞的塑性变形特征,结果发现氦泡和孔洞的塌缩是由发射剪切型位错环引起的,而没有观测到棱锥型位错环发射. 氦泡和孔洞周围的位错优先成核位置基本一致,但是氦泡周围发射的位错环数目比孔洞多,位错环发射速度明显比孔洞快. 且氦泡和孔洞被冲击波先扫过部分比后扫过部分发射位错困难. 通过滑移面上的分解应力分析发现,氦泡和孔洞周围塑性特征的差别是由于氦泡内压引起最大分解应力分布改变造成的. 氦泡和孔洞被冲击波先后扫过部分塑性不对称是因为冲击波扫过时引起形状变化, 关键词： 分子动力学 冲击波 氦泡 孔洞     

Nonlinear blood oxygen level-dependent responses for transient activations and deactivations in V1 - insights into the hemodynamic response function with the balloon model

We report studies of the nonlinear nature of blood oxygen level-dependent (BOLD) responses to short transient deactivations in human visual cortex. Both functional magnetic resonance imaging (fMRI) and near-infrared spectroscopy (NIRS) have been used to compare and contrast the hemodynamic response functions (HRFs) associated with transient activation and deactivation in primary visual cortex. We show that signal decreases for short duration deactivations are smaller than corresponding signal increases in activation studies. Moreover, the standard balloon model of BOLD effects may be modified to account for the observed nonlinear nature of deactivations by appropriate changes to simple hemodynamic parameters without recourse to new assumptions about the nature of the coupling between activity and oxygen use.     

Investigation on optimization design of equivalent water depth truncated mooring system

The oil industry is now increasingly concentrating their efforts and activities in connection with developing fields in deeper waters, ranging typically from 500 m to 3000 m worldwide. However, the modeling of a full-depth system has become difficult presently; no tank facility is sufficiently large to perform the testing of a complete FPS with compliant mooring in 1000 m to 3000 m depth, within reasonable limits of model scale. Until recently, the most feasible procedure to meet this challenge seems to be the so-called “hybrid model testing technique”. To implement this technique, the first and important step is to design the equivalent water depth truncated mooring system. In this work, the optimization design of the equivalent water depth truncated mooring system in hybrid model testing for deep sea platforms is investigated. During the research, the similarity of static characteristics between the truncated and full depth system is mainly considered. The optimization mathematical model for the equivalent water depth truncated system design is set up by using the similarity in numerical value of the static characteristics between the truncated system and the full depth one as the objective function. The dynamic characteristic difference between the truncated and full depth mooring system can be minished by selecting proper design rule. To calculate the static characteristics of the mooring system, the fourth order Runge-Kutta method is used to solve the static equilibrium equation of the single mooring line. After the static characteristic of the single mooring line is calculated, the static characteristic of the whole mooring system is calculated with Lagrange numerical interpolation method. The mooring line material database is established and the standard material name and the diameter of the mooring line are selected as the primary key. The improved simulated annealing algorithm for continual & discrete variables and the improved complex algorithm for discrete variables are employed to perform the optimization calculation. The C++ programming language is used to develop the computer program according to the object-oriented programming idea. To perform the optimization calculation with the two algorithms mentioned above respectively and the better result is selected as the final one. To examine the developed program, an example of equivalent water depth truncated mooring system optimum design calculation on a 100,000-t, turret mooring FPSO in water depth of 320 m are performed to obtain the conformation parameters of the truncated mooring system, in which the truncated water depth is 160 m. The model test under some typical environment conditions are performed for both the truncated and the full depth system with model scale factor λ=80. After comparing the corresponding results from the test of the truncated system with those from the full depth system test, it’s found that the truncated mooring system design in this work is successful. Supported by the National Natural Science Foundation of China (Grant Nos. 10602055 and 40776007) and the Natural Science Foundation of China Jiliang University (Grant No. XZ0501)     

事故地点对交通波的影响研究

利用唐等人提出的考虑事故概率的交通流模型［Tang T Q, Huang H J, Xu G 2008 Physica A 387 6845］研究事故发生地点对冲击波和稀疏波的影响,其数值计算结果表明,该模型可以如实地刻画事故对这两种交通波的影响,但这种影响与事故发生地点密切相关. 关键词： 交通事故 冲击波 稀疏波     

透反区响应时间相等的双盒厚透反液晶显示器

提出了一种透反区响应时间相等的双盒厚透反液晶显示器。该透反液晶显示器在透射区采用了强锚定能边界条件,以缩短其响应时间;在反射区采用了弱锚定能边界条件,以增加其响应时间;采用过压驱动技术,使透反区的响应时间相等。分析了该透反液晶显示器的结构和原理,设计了透射区和反射区的边界锚定能,计算了响应时间和电光特性,得到了透反区响应时间相等,且具有良好电光特性的双盒厚透反液晶显示器。     

Ion Acceleration in Laser-Plasma Interaction： Shock, Sheath, and Scaling

Some notes and comments on ion acceleration in laser-plasma interaction is given, in particular for the implication of shock, sheath and sealing. A simple model is proposed for ion acceleration by the combination of shock and sheath. The obtained scaling relations between the maximum ion energy and laser parameters （power, pulse duration） as well plasma parameter （plasma density）for example α PL 7/12 Eion,max α TL1/3 and Eion,max α ne2/3,are compared to the previous works. Some deficiencies and implications of model and results are discussed.     

Orbit response matrix analysis and lattice periodicity restoration of the SSRF storage ring

In this paper, we present numerically and experimentally the linear beam-optics distortion in the SSRF storage ring and the correction of optics by using a number of quadrupole magnets installed in the storage ring. The measured orbit-response matrices were fitted to the model-response matrices to obtain the β and the dispersion functions in the storage ring. By readjusting the currents of quadrupole-magnet power supplies, we were able to successfully restore the optics parameters to values very close to the design ones, with rms deviations around 1%. This periodicity restoration is verified with the β function measurement.