Theoretical and experimental study of Chen chaotic system with notch filter feedback control

Since the past two decades, the time delay feedback control method has attracted more and more attention in chaos control studies because of its simplicity and efficiency compared with other chaos control schemes. Recently, it has been proposed to suppress low-dimensional chaos with the notch filter feedback control method, which can be implemented in a laser system. In this work, we have analytically determined the controllable conditions for notch filter feedback controlling of Chen chaotic system in terms of the Hopf bifurcation theory. The conditions for notch filter feedback controlled Chen chaoitc system having a stable limit cycle solution are given. Meanwhile, we also analysed the Hopf bifurcation direction, which is very important for parameter settings in notch filter feedback control applications. Finally, we apply the notch filter feedback control methods to the electronic circuit experiments and numerical simulations based on the theoretical analysis. The controlling results of notch filter feedback control method well prove the feasibility and reliability of the theoretical analysis.     

HLS横向反馈系统研制中的关键技术

较为全面地介绍了合肥光源横向模拟反馈系统研制过程中, 所涉及的部分关键问题, 如矢量运算模块的开发, Notch滤波器研制, 基于Hilbert变换进行相空间重建、模式分析, 反馈Kicker腔的研制.     

复合材料切口应力奇性指数计算

提出一种计算广义平面应交状态下复合材料切口应力奇性指数的新方法.在切口尖端的位移幂级数渐近展开式被引入正交各向异性材料的物理方程后,将用位移表示的应力分量代入切口端部柱状邻域的线弹性理论控制方程,切口应力奇性指数的计算被转化为常微分方程组特征值的求解.采用插值矩阵法求解该常微分方程组,可一次性地获取切口尖端多阶应力奇性指数.本法适合平面和反平面应力场耦合或解耦的情形,并可退化计算裂纹或各向同性材料切口的应力奇性指数.算例表明,所提方法对分析复合材料切口应力奇性指数是一种准确有效的手段.     

基于V型腔光反馈法的半导体激光器线宽压窄和频率锁定初步研究

线宽压窄和频率锁定是提高激光器（特别是半导体激光器）性能的重要手段。在理论分析光反馈时的半导体激光器线宽压窄和频率锁定机理的基础上,建立了一套基于高品质V型光学谐振腔的半导体激光器线宽压窄实验系统,并利用该系统开展了初步实验研究。通过对比无有光反馈情况下的V型腔的透射光扫描线形,初步验证了V型腔用于半导体激光器线宽压窄和频率锁定的可行性,为后续研究奠定了基础。     

Modeling of aortic valve dynamics in a lumped parameter model of left ventricular-arterial coupling

A lumped parameter model of the sub-system of left ventricle, aortic valve, systemic arteries, systemic capillaries and systemic veins was considered during systole. A model of aortic valve dynamics based solely on geometrical and kinematical consideration is defined. The model is described by two geometrical parameters of aortic valve and a few kinematical relationships. The proposed model mimics the incisures in the aortic flow and aortic pressure very well. We showed that the dicrotic notch could be explained by aortic valve closing in terms of a lumped parameter model, without a need for any wave reflection theory. According to the proposed model the effects of aortic valve dynamics on the aortic flow and pressure are mainly limited to the valve opening and closing periods. The model offers a new paradigm for defining a more realistic left ventricle model.      

Simulation of a turbulent premixed open V-shaped flame using contour advection with surgery

Despite its capability of high spatial resolution, simulation of turbulent flows with traditional Lagrangian (front tracking) scheme is often discouraged by numerical instability caused by clustering of marker nodes and topological changes of fronts. Contour advection surgery (CAS), being a robust front tracking scheme, can limit the growth of front complexity during simulation without jeopardizing accuracy or efficiency. This allows it to open up an advantage over traditional front-tracking schemes. It has already been demonstrated that CAS, with incorporation of the reaction sheet model, can accurately simulate the propagation and advection of a turbulent premixed V-shaped flame. In this study, it is further tested with 10 values of vortex circulation. A range of upstream turbulence levels of 1.8–19.8% was obtained. Results indicate that upstream turbulence increase the average flame length, flame zone area and the overall burning rate. Flame surface density Σ was also estimated. Maximum values of Σ obtained lie in the range 0.1–1.4 mm⁻¹. Skewness towards the burnt region was observed in all profiles of Σ. Similar to results from laboratory experiments, it was found that Σ values decreases with upstream turbulence. From this study, the ability of CAS to cope with intense turbulence is demonstrated and a better quantitative understanding on the scheme has also been acquired.     

V形固体激光腔的动力学分析与改进

对通用的V形固体激光腔进行了全面的动力学分析，指出了它的优缺点，它的致命缺点是在动力学因子1ft≈1l1-f附近出现高损耗的运行区，激光器无法运行.为了克服这一缺点，在一种改进的V形腔基础上提出了一种更为紧凑的V形改进腔. 关键词： 固体激光腔 V形固体激光腔 改进的V形腔     

Molecular field theory for polar,biaxial bent-core nematics

We have studied a polar, biaxial nematic liquid crystal formed from bent-core molecules using molecular field theory. The model includes a simple Heisenberg-form dipolar intermolecular interaction in addition to the usual quadrupolar nematic interaction, and mimics a system consisting of nematogenic bent-core molecules with a large transverse dipole along the bisector of the two molecular arms. Such systems are regarded as good candidates for biaxial nematic liquid crystals. In principle, the molecular dipoles can align, thus stabilising the ordering of the minor axes. Our calculations predict that, for suitable values of the bent-core interarm angle, the biaxial nematic phase can be stabilised at higher temperatures than in the absence of the transverse dipole. In general, the transverse macroscopic polar order stabilises the biaxial nematic phase. In particular, for a large enough dipolar interaction, the Landau point in the pure biaxial nematic develops into a line of first-order polar biaxial nematic-to-isotropic phase transitions.     

Co−MOFs with 1,1′-(5-methyl-1,3-phenylene)bis(1H-imidazole) and aromatic carboxylates as coligands: synthesis,structure, and spectroscopic and thermal characterizations

Four cobalt(II) compounds, [Co(Bim)(IA)(H₂O)₂]_n·0.5nH₂O (1), [Co(Bim)(MA)(H₂O)₂]_n (2), [Co₂(Bim)₂(MA)₂]_n·nH₂O (3), and [Co₃(Bim)₄(TA)₂(H₂O)₂]_n·2.5nH₂O (4), have been synthesized by solvothermal reactions of cobalt(II) salts with 1,1′-(5-methyl-1,3-phenylene)bis(1H-imidazole) [Bim] and aromatic polycarboxylic acids (H₂IA = isophthalic acid, H₂MA = 5-methylisophthalic acid, and H₃TA = trimesic acid) as coligands. The four complexes were characterized by IR and UV?vis spectra, elemental analyses, X-ray powder and single-crystal diffractions, and thermogravimetric analyses (TGAs). 1 features a zigzag polymeric macrocycle chain containing a nanotubular channel, which is constructed by bridging the folded 20-membered macrocyclic [Co₂(Bim)₂] subunits with IA ligands. 2 represents a double-chain structure containing 18-membered macrocyclic [Co₂(Bim)(MA)] subunits. Both 3 and 4 are 2-D porous coordination polymers but have different architectures. In 3, cage-like [Co₄(Bim)₂(MA)₄] subunits are 4-connected nodes that are further bridged by another half-set of Bim ligands to form a 2-D helical structure containing one-dimensional achiral channels and alternately arranged left- and right-handed helical tubular channels. In 4, Bim ligands bridge three crystallographically independent Co centers into sharply distorted left- and right-handed helices which are further connected by TA ligands to form a meso layer about 3.0 nm monolayer thickness with a unique (3,4)-connected topology. The structural diversities of coordination polymers 1–4 are tuned by the flexible coordination number of Co and coligand polycarboxylates. Thermal analyses show that the main frameworks of all compounds remain stable to 352 °C. Moreover, the interesting color changes of crystals 1–4, varying from pink to purple and dark blue, result from the d → d* transitions of chromophoric Co²⁺ in different coordination geometries as determined by the UV–vis spectra in combination with crystal structure analyses.     

Small-scale fracture toughness of ceramic thin films: the effects of specimen geometry,ion beam notching and high temperature on chromium nitride toughness evaluation

For the implementation of thin ceramic hard coatings into intensive application environments, the fracture toughness is a particularly important material design parameter. Characterisation of the fracture toughness of small-scale specimens has been a topic of great debate, due to size effects, plasticity, residual stress effects and the influence of ion penetration from the sample fabrication process. In this work, several different small-scale fracture toughness geometries (single-beam cantilever, double-beam cantilever and micro-pillar splitting) were compared, fabricated from a thin physical vapour-deposited ceramic film using a focused ion beam source, and then the effect of the gallium-milled notch on mode I toughness quantification investigated. It was found that notching using a focused gallium source influences small-scale toughness measurements and can lead to an overestimation of the fracture toughness values for chromium nitride (CrN) thin films. The effects of gallium ion irradiation were further studied by performing the first small-scale high-temperature toughness measurements within the scanning electron microscope, with the consequence that annealing at high temperatures allows for diffusion of the gallium to grain boundaries promoting embrittlement in small-scale CrN samples. This work highlights the sensitivity of some materials to gallium ion penetration effects, and the profound effect that it can have on fracture toughness evaluation.