Predicting Homoclinic Bifurcations in Planar Autonomous Systems

An analytical method to predict the homoclinic bifurcation in a planar autonomous self-excited weakly nonlinear oscillator is presented. The method is mainly based on the collision between the periodic orbit undergoing the homoclinic bifurcation and the saddle fixed point. To illustrate the analytical predictive criteria, two typical examples are investigated. The results obtained in this work are then compared to Melnikov's technique and to a previous criterion based on the vanishing of the frequency. Numerical simulations are also provided.     

基于拓扑优化的新型蜂窝结构设计

可变体飞行器若要实现机翼后掠角、面积和前后缘弯度等参数的大幅度变化,机翼蒙皮需要具有光滑的气动外形、大变形、高承载以及驱动力小的特点。针对柔性蒙皮的需求,本文利用拓扑优化方法设计了一种新型零泊松比蜂窝结构,通过有限元仿真与U形蜂窝结构和余弦形蜂窝结构进行对比,验证其变形和承载等性能。以最大应变2%为基准,比较了三种蜂窝结构的变形能力。结果表明,新型蜂窝结构的拉伸变形量高达75%,分别是U形蜂窝结构和余弦形蜂窝结构的1.7倍和2.1倍。在最大位移量相同时,所需驱动力分别是U形蜂窝结构和余弦形蜂窝结构的0.51倍和0.28倍,表明新型蜂窝结构具有很大的易变形能力。当蜂窝结构的橡胶蒙皮受到相同压强载荷且处于初始未拉伸状态/拉伸状态时,新型蜂窝结构橡胶蒙皮的最大法向位移量分别是U形蜂窝橡胶蒙皮和余弦形蜂窝橡胶蒙皮的0.4倍/0.56倍和0.29倍/0.42倍,表明新型蜂窝结构具有良好的面外承载能力。另外,通过适当增加壁厚,可以提高新型蜂窝结构本身的抗弯曲能力。分析结果表明,本文设计的新型蜂窝结构具备大变形、高承载以及驱动力小的优点。     

Perfect Optical Nonreciprocity with Mechanical Driving in a Three-Mode Optomechanical System *

Nonreciprocal devices are indispensable for building quantum networks and ubiquitous in modern communication technology. Here, we study perfect optical nonreciprocity in a three-mode optomechanical system with mechanical driving.The scheme relies on the interference between optomechanical interaction and mechanical driving. We find perfect optical nonreciprocity can be achieved even though nonreciprocal phase difference is zero if we drive the system by a mechanical driving with a nonzero phase. We obtain the essential conditions for perfectoptical nonreciprocity and analyze properties of the optical nonreciprocal transmission. These results can be used to control optical transmission in quantum information processing.      

Study on autonomous navigation based on pulsar timing model

The basic principle of pulsar timing model was introduced, and the general relativistic corrections were analyzed when pulse time of arrival (TOA) was transferred to coordinate TOA at the Solar System Barycentre. Based on the shifting, an iterative method of autonomous position determination for spacecraft was developed. Accordingly, the linear form of the position offset equation was evolved. Using the initial estimated value of spacecraft’s position as the input of pulsar timing equation, through calculation of the offset between measured or transferred and predicted TOA, the position offset can be solved by Least Squares. At last, the main error sources including modeling error and parameters error were discussed. Supported by the National Defence Laboratory Foundation of China (Grant No. 9140C3601010901) and Science Foundation of Shaanxi Province (Grant No. 2007F12) and the Technology Specialism Foundation of Shaanxi Education Department of Shaanxi Province (Grant No. 07JK332), and the Innovative Research Plan of Xi’an University of Technology (Grant No. 105-210714)     

考虑驾驶方式改变的一维元胞自动机交通流模型

在一维元胞自动机交通流WWH模型和SDNS模型的基础上,建立了考虑驾驶方式改变的元胞自动机模型（Change-CA模型）.具体描述为驾驶员可根据交通环境选择不同的驾驶方式在道路上驾车行驶,以各自的演化规则进行状态更新,同时定义了驾驶方式更新原则.通过计算机数值模拟,发现驾驶方式可变时,模型模拟得到的混合交通流流量较大;保守型驾驶方式对交通流变化的影响随改变概率增大而减少.并且在演化过程中,驾驶方式改变频率的变化趋势与改变概率、安全概率密切相关.与NS模型和SDNS模型相比,Change-CA模型减少了车流 关键词： 交通流 元胞自动机 驾驶方式 计算机数值模拟     

离心力场下H2O和R12热驱动换热特性实验研究

本文实验研究了离心力场下细微封闭循环通道中,以H2O和氟利昂R12为热驱动介质的热驱动流动规律和换热特性,重点分析了热驱动换热效果随Ra数Ro数的变化规律以及冷却效果。实验结果表明:在热流密度和旋转速度相同的条件下,采用介质R12可以获得较高的平均换热系数,冷却效果也优于以H2O为介质的冷却效果。最后建立了两种介质条件下相应的准则关系式。     

Mass spectrometric approaches in impaired driving toxicology

Driving under the influence of prescribed or illegal drugs increases the risk of having road accidents, just like driving under the influence of alcohol. In forensic toxicology, an increasing number of blood samples must be analyzed for drugs. Immunoassays tailored for a limited number of drugs (of abuse) are usually applied as prescreening tests at the roadside and/or in the laboratory. However, many other common drugs, such as anesthetics, antidepressants, antiepileptics, antihistamines, newer designer drugs, herbal drugs, neuroleptics (antipsychotics), opioids, or sedative-hypnotics, can also impair drivers. Therefore, this paper reviews multianalyte single-stage and tandem gas or liquid chromatography–mass spectrometry (GC-MS or LC-MS) procedures for the screening, identification, and validated quantification of such drugs in blood that have been reported since 2003. Basic information about the biosample assayed, workup, chromatography, the mass spectral detection mode, and validation data is summarized in tables. The pros and cons of the reviewed procedures are critically discussed, particularly with respect to their probable usefulness in impaired driving toxicology. Parts of this review were presented as a plenary lecture at T2007, the joint meeting of the International Council on Alcohol, Drugs, and Traffic Safety (ICADTS) and The International Association of Forensic Toxicologists (TIAFT), Seattle (WA), August 26–30, 2007.     

A gravity driven micro flow injection wetting film extraction system on a polycarbonate chip

A micro flow injection wetting film liquid-liquid extraction system has been developed for trace analyte concentration and on-chip detection. A hydrophobic channel fabricated on a polycarbonate chip was used to support the wetting film, and hydrostatic pressure generated by the difference in liquid levels was employed to drive the fluids. Sequential injection of segments of aqueous sample solution and organic solvent was conducted by switching the sample- or solvent-containing vials to an on-chip sampling probe, and detection was performed by a co-focused, laser induced fluorescence detector. Using butyl rhodamine B as a model analyte and butanol as the solvent for both film-coating and elution, various experimental conditions such as hydrostatic pressure, coating time, channel length, sampling volume, and sample acidity were investigated. Under optimized conditions, a 24-fold enrichment factor was obtained with the consumption of about 3 μL sample solution, and a detection limit (3σ) of 6.0 × 10⁻⁹ M butyl rhodamine B was achieved at the sampling rate of 19 h⁻¹. Eleven consecutive runs of a 1.0 × 10⁻⁵ M butyl rhodamine B solution produced a relative standard deviation of 1.5% for the detected fluorescence signals.     

Sub- and Super-Luminal Phenomena in a Doubly Driven Four-Level System

With the occurrence of an adding driving field, the properties of the dispersion and the absorption of a four-level system are changed greatly. The system can produce the normal and anomalous dispersion regions with proper parameters. Here, the driving fields can be seemed as knobs to manipulate the groupvelocity of a weak probe field between subluminal and superluminal.     

一种基于加速度计和天文的卫星自主导航新方法

直接敏感地平是一种典型自主天文导航方法,该方法简单可靠,易于实现,但是由于常用卫星轨道动力学J2模型精度有限,地球敏感器精度较低,因此导航精度不高。加速度计是测量运载体线加速度的常用惯性导航设备,当航天器在轨运行时,星载加速度计能够测量航天器所受发散力。结合上述两种方法的特点,提出一种将加速度计和天文相结合的自主天文导航新方法。在常用卫星轨道动力学模型基础上,引入大气阻力和太阳光压系数模型作为自主导航系统状态方程的一部分,并建立近地空间环境下星载加速度计的测量模型,将其与直接敏感地平均作为导航系统观测方程。设计基于信息融合的自主导航滤波方法,通过对多种导航模式进行数值仿真及结果分析,结果表明所设计方法提高了系统定位精度62.8%和速度精度63.9%,增强了系统可靠性。