Frequency selective surface structure optimized by genetic algorithm

Frequency selective surface (FSS) is a two-dimensional periodic structure which has prominent characteristics of bandpass or bandblock when interacting with electromagnetic waves. In this paper, the thickness, the dielectric constant, the element graph and the arrangement periodicity of an FSS medium are investigated by Genetic Algorithm (GA) when an electromagnetic wave is incident on the FSS at a wide angle, and an optimized FSS structure and transmission characteristics are obtained. The results show that the optimized structure has better stability in relation to incident angle of electromagnetic wave and preserves the stability of centre frequency even at an incident angle as large as 80°, thereby laying the foundation for the application of FSS to curved surfaces at wide angles.     

Mean square exponential stability of uncertain stochastic delayed neural networks

This Letter concerns with the mean square exponential stability of uncertain stochastic delayed neural networks. By applying Lyapunov functional method, new delay-dependent/independent mean square exponential stability criteria are derived in terms of linear matrix inequalities. Two examples are presented which show our result are less conservative than the existing stability criteria.     

高能量高峰值功率激光系统的稳定性问题研究

针对高能量高峰值功率激光系统建立了相应的理论分析模型和计算程序,并针对放大系统的稳定性进行了分析,同时还对放大链路中的B积分、频谱漂移、泵浦光和信号光之间的时间同步抖动进行了模拟分析.分析结果表明：采用两级放大结构,有利于提高系统的稳定性;同时需要严格控制全系统B积分累积,建议全系统B积分的累积值小于2,超过2的B积分累积意味着更多的注入能量,如果泵浦光和信号光之间的同步时间抖动控制在±0.2 ns之内,输出稳定性可控制在rms2％之内.     

光纤陀螺SFS光源温度稳定性及驱动控制研究

随着光纤陀螺研究的不断进展,对陀螺光源的稳定性的要求也越来越高。SFS(超荧光光纤光源)正是应用于高精度陀螺要求的宽带光源,它的平均波长和功率的温度稳定性直接影响着光纤陀螺的性能。从SFS的特性分析对其驱动系统进行了设计,提出并实现了温度稳定性的控制方案。     

Fault tolerant synchronization of chaotic systems based on T-S fuzzy model with fuzzy sampled-data controller

In this paper the fault tolerant synchronization of two chaotic systems based on fuzzy model and sample data is investigated. The problem of fault tolerant synchronization is formulated to study the global asymptotical stability of the error system with the fuzzy sampled-data controller which contains a state feedback controller and a fault compensator. The synchronization can be achieved no matter whether the fault occurs or not. To investigate the stability of the error system and facilitate the design of the fuzzy sampled-data controller, a Takagi--Sugeno (T--S) fuzzy model is employed to represent the chaotic system dynamics. To acquire the good performance and produce less conservative analysis result, a new parameter-dependent Lyapunov--Krasovksii functional and a relaxed stabilization technique are considered. The stability conditions based on linear matrix inequality are obtained to achieve the fault tolerant synchronization of the chaotic systems. Finally, a numerical simulation is shown to verify the results.     

Effects of gain saturation on terahertz radiation via optical difference frequency generation

Numerical studies on stability of terahertz (THz) radiation generation based on difference frequency generation in nonlinear crystals are reported. When the gain saturation is achieved at a wavelength that corresponds to an optimal crystal length, the maximal output of THz radiation could be obtained. As a result of crystal absorption, the gain saturation region of THz radiation is unstable region for output. The stability of THz radiation is determined by the stability of pump in the stable region where behind of the gain saturation.     

Bandwidth and stability enhancement of optical parametric amplification using chirped ferroelectric superlattice

We report a theoretical analysis and numerical simulation of bandwidth and stability enhancement in optical parametric amplification (OPA) when using chirped periodically poled KTiOPO₄. Calculation results show that the bandwidth and stability are enhanced significantly by the use of a chirped grating. Temperature-gradient and fanned gratings are introduced and chirp factors of them are deduced and calculated. The use of a fanned grating flattens the Quasi-phase-matching response and improves the efficiency. Finally, we propose a method to reduce the instability induced by an unstable pump.     

CRT显示器稳定性实验研究

用屏幕色度计对一台SONY-G520显示器的显色特性进行了测量,研究了其开机稳定性和短、中、长期内的色差及色度偏差。实验结果表明,开机后,显示器的亮度Y和色度x,y分别可在2h,30min和1h达到相对稳定状态,且在达到相对稳定后,在短、中、长期内的平均色差分别为0.0611,0.1469和1.2536CIELAB色差单位;在中期内,Y,x,y,L,a,b的平均偏差分别为0.0663,0.0008,0.0015,0.0695,0.4740和0.1766。通过对显示器稳定性的测量,为在对比度敏感测量和色貌模型、图像质量、图像感知模型评价等研究领域中用显示器进行实验研究奠定了基础。     

MM工质热分解及其对ORC系统影响的研究

热稳定性是限制有机工质在有机朗肯循环(Organic Rankine Cycle,ORC)使用的重要因素。硅氧烷类工质具有低毒环保、化学性质稳定等优点,适用于150~350℃热源。本文研究了六甲基二硅氧烷(MM)工质热分解的特点及其对ORC系统的影响,结果表明,MM的热分解产物为硅氧烷类化合物及微量气态小分子碳氢化合物;热分解将导致系统性能下降,分解量足够大时,会出现蒸发器换热不充分导致膨胀机入口处工质干度低于1从而影响机组安全的问题。     

重频XeF蓝绿激光技术

利用表面放电光泵浦技术,研制了重频XeF(C-A)激光器,运行频率达到10 Hz。研究了运行频率、气体流量对激光输出能量稳定性的影响,分析了影响输出稳定性的主要因素,实验结果表明,提高气流量可有效改善重频输出能量的稳定性。同时,还给出了优化实验条件下不同运行频率连续20个脉冲较为理想的输出结果。运行频率分别为1,2,5 Hz时,输出能量稳定性较好,输出能量大于4.0 J;气流量大于53 L/s时,10 Hz重频运行的输出稳定性已显著提高,平均输出能量也达到1.8 J。     

Designing the mechanical properties of peptide-based supramolecular hydrogels for biomedical applications

Hydrogels are a class of special materials that contain a large amount of water and behave like rubber.These materials have found broad applications in tissue engineering,cell culturing,regenerative medicine etc.Recently,the exploration of peptide-based supramolecular hydrogels has greatly expanded the repertoire of hydrogels suitable for biomedical applications.However,the mechanical properties of peptide-based hydrogels are intrinsically weak.Therefore,it is crucial to develop methods that can improve the mechanical stability of such peptide-based hydrogels.In this review,we explore the factors that determine or influence the mechanical stability of peptide-based hydrogels and summarize several key elements that may guide scientists to achieve mechanically improved hydrogels.In addition,we exemplified several methods that have been successfully developed to prepare hydrogels with enhanced mechanical stability.These mechanically strong peptide-based hydrogels may find broad applications as novel biomaterials.It is still challenging to engineer hydrogels in order to mimic the mechanical properties of biological tissues.More hydrogel materials with optimal mechanical properties suitable for various types of biological applications will be available in the near future.     

芳香烃中位取代氟硼二吡咯的薄膜放大自发辐射稳定性研究

对苯基、萘基和蒽基在中位取代的氟硼二吡咯(BODIPY)衍生物薄膜的放大自发辐射(ASE)性能进行了研究,探讨了影响材料ASE稳定性的因素。首先,将3种BODIPY衍生物材料PhBOD、NaBOD和EnBOD掺入聚苯乙烯经溶液旋涂法制备成薄膜,接下来测试了吸收光谱和荧光光谱,然后在光泵浦条件下测量了3种样品的ASE性能,获得了材料的ASE阈值。进一步通过长时间泵浦、环境中长时间放置和高温环境下泵浦等方法研究了材料的光稳定性、ASE环境稳定性和热稳定性。最后使用Gaussian 09计算了分子基态性质。实验结果表明,PhBOD、NaBOD和EnBOD薄膜的初始阈值分别为12.4,4.55,3.4 k W/cm~2,其中PhBOD有较强的ASE稳定性。ASE稳定性差异可能与分子结构的共轭程度和化学稳定性相关。分子中各个基团的共轭程度较大、Mulliken电荷分布对称性较好的材料具有较好的ASE稳定性。     

New asymptotic stability criteria for neural networks with time-varying delay

The problem of delay-dependent asymptotic stability criteria for neural networks with time-varying delay is investigated. A new class of Lyapunov functional is constructed to derive some new delay-dependent stability criteria.The obtained criterion are less conservative because free-weighting matrices method and a convex optimization approach are considered. Finally, numerical examples are given to demonstrate the effectiveness of the proposed method.     

非晶态合金Fe80P20局域结构和性质的量子化学研究

利用原子簇模型Fe_4P简化了非晶态合金Fe_(80)P_(20)的局域结构,设计了四方锥、三角双锥、四面体及平面五边形等十几种构型,对其二、四重态分别进行密度泛函(DFT)优化计算,经过频率验证,获得五种稳定构型。从所得优化构型的键长和键级,可以发现原子簇Fe4P较好地反映了非晶态合金Fe_(80)P_(20)的局域结构。考察了各构型间的过渡转化情况,发现二重态构型的稳定性要好于四重态。分析各构型的能量、成键及电子转移情况,发现与P原子成键的Fe原子个数对这些性质影响较为明显。与P原子成键的Fe原子个数越多,体系的能量就越低,越容易存在；P原子的得电子能力随着与其成键Fe原子个数增多而减少,甚至会将失去自身电子转移到金属原子上。同时通过3d轨道布居数,讨论了原子簇的空穴数及磁学性质。     

碳纳米管/膨润土复合膜的附着性能及场发射性能

碳纳米管(CNT)阴极膜与基底的附着性能严重影响场发射的均匀性和稳定性.提出一种制作CNT/膨润土(BP)复合膜的方法.通过添加纳米尺度BP作为填料,使BP与CNT间产生插层效应,进而减小CNT膜的间隙势牟,改善CNT与基底间的接触性能.测试结果显示,CNT/BP复合膜与基底的附着性能得到明显改善,并且使场发射均匀性和...     

4,7-二(2-溴代噻吩-5-基)-2,1,3-苯并噻二唑-N-(1-辛基壬烷基)咔唑在ZnS(100)表面吸附的理论研究

采用密度泛函理论中的广义梯度近似(DFT/GGA)方法,在PW91/DNP水平上研究了4,7-二(2-溴代噻吩-5-基)-2,1,3-苯并噻二唑-N-(1-辛基壬烷基)咔唑(简称PC-DTBT)的低聚合物(PC-DTBT)n(n=1-5)的稳定性和化学活性.结果表明:随着聚合度增加,(PC-DTBT)n的稳定性降低,化学活性增强.采用密度泛函理论与周期性平板模型相结合的方法,研究了PC-DTBT单体在ZnS(100)表面的吸附,通过吸附前后化合物PC-DTBT的Mulliken charge和前线轨道分析表明:当PC-DTBT吸附在ZnS(100)表面时,ZnS(100)表面向PC-DTBT转移0.200 e电荷,前线轨道能隙变窄.理论预测的结果与实验值吻合.     

4,7-二(2-溴代噻吩-5-基)-2,1,3-苯并噻二唑-N-(1-辛基壬烷基)咔唑在ZnS(100)表面吸附的理论研究

采用密度泛函理论中的广义梯度近似(DFT/GGA)方法, 在PW91/DNP水平上研究了4,7-二(2-溴代噻吩-5-基)-2,1,3-苯并噻二唑-N-(1-辛基壬烷基)咔唑(简称PC-DTBT)的低聚合物(PC-DTBT)n(n=1-5)的稳定性和化学活性. 结果表明: 随着聚合度增加, (PC-DTBT)n的稳定性降低, 化学活性增强. 采用密度泛函理论与周期性平板模型相结合的方法, 研究了PC-DTBT单体在ZnS(100)表面的吸附, 通过吸附前后化合物PC-DTBT的Mulliken charge和前线轨道分析表明: 当PC-DTBT吸附在ZnS (100)表面时, ZnS(100)表面向PC-DTBT转移0.200 e电荷, 前线轨道能隙变窄. 理论预测的结果与实验值吻合.     

New delay-dependent stability criteria for neural networks with time-varying interval delay

The problem of stability analysis of neural networks with time-varying delay in a given range is investigated in this Letter. By introducing a new Lyapunov functional which uses the information on the lower bound of the delay sufficiently and an augmented Lyapunov functional which contains some triple-integral terms, some improved delay-dependent stability criteria are derived using the free-weighting matrices method. Numerical examples are presented to illustrate the less conservatism of the obtained results and the effectiveness of the proposed method.     

自组生长的硅纳米管的稳定性研究

文章作者的研究小组在世界上首次合成自组生长的硅纳米管（SiNTs）后,对它的稳定性研究又获得进展.采用5wt%的HF酸对自组生长的硅纳米管的稳定性进行了研究,研究表明HF酸可以去除硅纳米管的氧化物外层,只剩下晶体硅纳米管,说明所得到的硅纳米管是一种稳定结构,因而使其应用研究开发成为可能.研究表明,硅纳米管的稳定性与其生长形成过程密切相关.     

自组生长的硅纳米管的稳定性研究

文章作者的研究小组在世界上首次合成自组生长的硅纳米管（SiNTs）后,对它的稳定性研究又获得进展.采用5wt%的HF酸对自组生长的硅纳米管的稳定性进行了研究,研究表明HF酸可以去除硅纳米管的氧化物外层,只剩下晶体硅纳米管,说明所得到的硅纳米管是一种稳定结构,因而使其应用研究开发成为可能.研究表明,硅纳米管的稳定性与其生长形成过程密切相关。