Global view of Hopf bifurcations of a van der Pol oscillator with delayed state feedback

This paper presents both analytical and numerical studies on the global view of Hopf bifurcations of a van der Pol oscillator with delayed state feedback. Based on a detailed analysis of the stability switches of the trivial equilibrium of the system, the stability charts are given in a parameter space consisting of the time delay and the feedback gains. The center manifold reduction and the normal form method are used to study Hopf bifurcations with respect to the time delay. To gain an insight into the pe...     

双材料V型切口断裂研究

基于双材料V型切口理论,给出了新的双材料V型切口问题的应力强度因子定义,将单材料裂纹问题、双材料裂纹问题、V型切口问题的应力强度因子的定义相统一,进而得到应力外推法计算双材料V型切口K1的计算公式.以单向拉伸和三点弯曲模型为研究对象,研究了双材料中切口深度、泊松比、切口张角变化对应力奇异场的影响,得到了一些相关结论,为异体材料形成的V型切口在应力断料中应用时的参数选取提供了必要的理论依据.     

Capacity Reliability of Signalized Intersections with Mixed Traffic Conditions

The reliability of capacity of signalized intersections in mixed traffic conditions involving vehicles, bicycles, and pedestrians was investigated to complete the conventional, deterministic capacity calculations. Simulations using VISSIM provided estimates of capacity distributions, and demonstrated the effects of the analysis intervals on the distributions. With the random vehicle arrivals taken into account, a capacity reliability assessment method was given as a function. Assessments were also performed...     

定位组合调驱技术提高采收率实验研究

利用微观仿真模型和树脂胶结岩心,对定位组合调驱技术提高采收率机理、调剖及驱油效果进行了研究.分别进行了调剖剂的调剖实验和化学剂的驱油实验.研究结果表明,定位组合调驱技术提高采收率不只是调剖与驱油技术的简单加和,两者之间存在一定的协同作用,能够起到增强的效果.岩心调剖实验表明,选择顶替段塞时要保证其流变性和主段塞的流变性相同,对于非均质性严重、存在窜流通道的特定油藏,当调剖时机在含水率为90%左右、调剖深度为地层的1/3处时,调剖效果最好.对比分析认为,定位组合调驱技术提高采收率的效果很好.     

城镇土地评估系统发展特点及展望

从系统的标准化、开发模式、功能完整性、开发技术4个方面总结了城镇土地评估系统近15年的发展,并基于现阶段土地评估系统存在的问题,指出了新应用环境下系统发展的趋势.     

黄斑大蚊的喜湿性及其翅膀、腿表面的超疏水性

黄斑大蚊的翅膀、腿表面有很好的超疏水性, 水滴在其表面的静态接触角分别为150°,155°, 滚动角接近5°, 通过扫描电子显微镜观察发现, 在黄斑大蚊的翅膀、腿表面分布有大量呈规则排列的微纳米级复合凹槽、乳突, 复合结构及其表面的低表面能物质的协同作用使其表面具有良好的超疏水性, 这一特性使黄斑大蚊能在潮湿的环境中自由生存. 本文用 Cassie 理论对这种超疏水性进行了理论分析.     

δ~(13)C and water-use efficiency indicated by δ~(13)C of different plant functional groups on Changbai Mountains, Northeast China

Leaf δ13C of different plant functional groups (trees, shrubs and forbs; evergreen and deciduous; annual, biennial and perennial) were examined on the Changbai Mountains, China. Life form has a significant influence on plant δ13C, suggesting that leaf δ13C is also ideal for distinguishing functional groups species in temperate and frigid zones with high humidity. Additionally, the difference of water-use efficiency (WUE) is significant among different plant functional groups. δ13C and WUE are in the followi...     

荧光分光光度法测定两种中药对羟基自由基的清除作用

Fe2 EDTA在弱碱性介质中还原溶解氧生成超氧阴离子自由基(O 2·),O 2·进一步歧化为H2O2和氧分子,之后Fe2 EDTA与H2O2反应生成羟基自由基(·OH).·OH进攻对苯二甲酸产生唯一的强荧光羟基化产物2 羟基对苯二甲酸(HOTP).·OH清除剂加入体系后,与对苯二甲酸竞争结合·OH,导致对苯二甲酸的羟基化产物HOTP的生成量减少,从而导致体系荧光强度明显降低.我们首次成功地将以上原理运用于中药对·OH清除作用的研究,并于实验中首次发现中药白头翁和半支莲可以清除·OH,两种中药对·OH的清除具有负协同效应,同时测定了它们对·OH的清除率分别为白头翁IC50=1.80×10-2mg/mL;半支莲IC50=1.76×10-2mg/mL.     

Costate estimation for dynamic systems of the second order

The dynamics of a mechanical system in the Lagrange space yields a set of differential equations of the second order and involves much less variables and constraints than that described in the state space.This paper presents a so-called Legendre pseudo-spectral (PS) approach for directly estimating the costates of the Bolza problem of optimal control of a set of dynamic equations of the second order.Under a set of closure conditions,it is proved that the Karush-Kuhn-Tucker (KKT) multipliers satisfy the same...     

基于Alq3的有机发光二极管中的瞬时荧光与延迟荧光

制备了结构为ITO/CuPc/NPB/Alq3/LiF/Al的有机发光二极管, 并在100, 70, 40和15 K四个温度测量了器件在恒流偏置下电致发光随磁场的变化. 器件的电致发光包括瞬时荧光与延迟荧光两部分. 两者都可以受外加磁场影响, 但对磁场的依赖关系不同. 由此导出了在不同磁场强度时瞬时光强度与延迟光强度和总发光强度的关系. 基于对延迟光强度磁场效应的合理估计, 分别计算了器件在不同的温度、电流下瞬时光强度与延迟光强度的值, 和延迟光在器件总发光中的比重. 计算结果显示, 在15 K和160 μA时, 延迟光在器件总发光中的比重可超过20%. 对计算公式所基于的假设进行了分析, 并且探讨了这些假设对计算结果的影响.