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991.
An intriguing aerobic oxidation of alkynes through copper catalysis is described, in which bis(pinacolato)diboron (B2pin2) played a dominant intermediary role in the formation 1,2-diketones. This novel protocol, which can be performed at room temperature, is versatile for various substituted alkynes, including diarylalkynes and arylalkylalkynes. The mechanism of this reaction was preliminarily investigated by control experiments.  相似文献   
992.
Underwater acoustics is of fundamental importance for marine science and technology. However, acoustic waves transmitted by state‐of‐the‐art underwater acoustic systems are not inherently phase locked, which hinders the development of underwater acoustic technology. For example, the precision of underwater distance measurement can only achieve centimeter level. As a versatile tool, optical frequency combs have enabled revolutionary progress in optical metrology and precision measurement. In parallel with optical frequency combs, here, the generation of fully stabilized, underwater acoustic frequency combs is reported, in which equidistant acoustic modes are produced via a hydroacoustic transducer. The precision of each individual acoustic mode is measured to be 10?9 at 1 s and 10?12 at 1000 s averaging times. Underwater distance measurements are carried out in an anechoic pool using a dual‐comb scheme. Comparison with reference values shows consistency within 50 µm (7 × 10?6 in relative). The relatively long‐duration experiments at 7 m distance yield an Allan deviation of 1.8 µm (2.6 × 10?7 in relative) at 1 s and further 480 nm (6.8 × 10?8 in relative) at 40 s averaging times. The approach to acoustic frequency comb generation offers a promising and powerful platform for future underwater distance measurement, positioning, and navigation.  相似文献   
993.
994.
基于密度泛函理论,系统研究了由两个La@Si_(16)组装而成的高度稳定的管状二聚体La_2@Si_(32)团簇.电子结构分析显示,内嵌La原子诱导的类sp~2杂化对于提高管状Si_(32)的稳定性至关重要.Mülliken布局分析显示,La_2@Si_(32)的总磁矩为2 μ_B,主要来源于两个La原子和第三、第六层的八个Si原子;电荷是由Si原子转移到了La原子上.此外,通过连接一系列La_2@Si_(32)单体而获得了一类组装的硅纳米线La@SiNW,研究结果显示La@SiNW具有金属导电特性,其总磁矩为2 μ_B.上述特征暗示具有磁性的La_2@Si_(32)和La@SiNW可能在自旋电子器件和高密度磁记录材料方面具有潜在的应用前景.  相似文献   
995.
康玲  项冰冰  翟素兰  鲍中奎  张海峰 《物理学报》2018,67(19):198901-198901
复杂网络多影响力节点的识别可以帮助理解网络的结构和功能,具有重要的理论意义和应用价值.本文提出一种基于网络区域密度曲线的多影响力节点的识别方法.应用两种不同的传播模型,在不同网络上与其他中心性指标进行了比较.结果表明,基于区域密度曲线的识别方法能够更好地识别网络中的多影响力节点,选中的影响力节点之间的分布较为分散,自身也比较重要.本文所提方法是基于网络的局部信息,计算的时间复杂度较低.  相似文献   
996.
Zhai  Cong  Wu  Weitiao 《Nonlinear dynamics》2018,93(4):2185-2199
Nonlinear Dynamics - In this paper, we propose an extension of the optimal velocity car-following model to consider explicitly the timid and aggressive driving behavior as well as the traffic jerk....  相似文献   
997.
In this work, we apply a principal component analysis (PCA) method with a kernel trick to study the classification of phases and phase transitions in classical XY models of frustrated lattices. Compared to our previous work with the linear PCA method, the kernel PCA can capture nonlinear functions. In this case, the Z2 chiral order of the classical spins in these lattices is indeed a nonlinear function of the input spin configurations. In addition to the principal component revealed by the linear PCA, the kernel PCA can find two more principal components using the data generated by Monte Carlo simulation for various temperatures as the input. One of them is related to the strength of the U(1) order parameter, and the other directly manifests the chiral order parameter that characterizes the Z2 symmetry breaking. For a temperature-resolved study, the temperature dependence of the principal eigenvalue associated with the Z2 symmetry breaking clearly shows second-order phase transition behavior.  相似文献   
998.
Interaction of a strong converging shock wave with an SF6 gas bubble is studied, focusing on the effects of shock intensity and shock shape on interface evolution. Experimentally, the converging shock wave is generated by shock dynamics theory and the gas bubble is created by soap film technique. The post-shock flow field is captured by a schlieren photography combined with a high-speed video camera. Besides, a three-dimensional program is adopted to provide more details of flow field. After the strong converging shock wave impact, a wide and pronged outward jet, which differs from that in planar shock or weak converging shock condition, is derived from the downstream interface pole. This specific phenomenon is considered to be closely associated with shock intensity and shock curvature. Disturbed by the gas bubble, the converging shocks approaching the convergence center have polygonal shapes, and the relationship between shock intensity and shock radius verifies the applicability of polygonal converging shock theory. Subsequently, the motion of upstream point is discussed, and a modified nonlinear theory considering rarefaction wave and high amplitude effects is proposed. In addition, the effects of shock shape on interface morphology and interface scales are elucidated. These results indicate that the shape as well as shock strength plays an important role in interface evolution.  相似文献   
999.
桁架结构重分析的一种新方法   总被引:3,自引:1,他引:3  
刘亮  翟宇毅 《计算力学学报》1998,15(2):149-153160
本文依据有限元的原理,建立了杆单元基本位移的计算方法,给出了在桁架结构拓扑优化重分析中的新方法,该方法将优化计算的结构设计变量与性态参数之间的关系以显式的形式表达出来,故在结构拓扑优化过程中,不需要再反复地用有限元方法对新产生的拓扑结构进行重分析,节省了大量的计算时间,同时,由于采用了相对基础结构的基本位移修正的方法,不仅减少计算的累积误差,也避免了由于可能出现的几何可变情况而使拓扑优化计算过程中  相似文献   
1000.
The magnetoelectric (ME) gyrator is a device that can convert not only active and reactive impedances, but also current and voltage. In this work, we have carried out research on three gyrators structures based on Terfenol-D/PZT/Terfenol-D, Metglas/PZT/Metglas and Nickel/PZT/Nickel. Detailed investigations of the ME gyrator based on these trilayer composite structures have been performed at the electromechanical resonance frequency.  相似文献   
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