内螺纹强化管传热和阻力特性

本文提供了7个内径为15.54mm的内螺纹粗糙管单相流动的传热和阻力数据,为当前商用粗糙管常用尺寸提供了一系列新的内部强化数据.螺纹管结构参数为螺纹数(18～45),螺旋角(25°～45°)、螺纹高(0.33mm至0.55 mm).测试管由于螺纹处流动分离及表面积的显著增加而得到强化.测试数据范围为5.08≤Pr≤6.29.利用两种关联式来预测不同几何变量和雷诺数下St和摩擦系数.多重回归传热关联式的平均差分别为2.9%和3.8%.传热和摩擦关联式基于粗糙表面热量-动量传输比拟,标准差为分别是1.4%和5.4%.关联式能够合理地预测商用螺纹粗糙管的传热和摩擦.     

Experimental implementation of an all-optical OFDM system based on time lenses

<正>Experimental implementations of continuous optical time domain Fourier transformation based on time lenses and optical orthogonal frequency-division multiplexing(OFDM) system are carried out.Such a system is verified through 100-km transmission of 10-Gb/s non-return-to-zero(NRZ) intensity-modulated direct-detection(IM-DD) without any dispersion compensation.The system's bit error rate(BER) and power penalty are 10~(-12) and 4 dBm,respectively.     

随机奇异积分的Привалов-Plemelj公式

在概率极限意义下,研究了随机奇异积分,得到了Привалов-Plemelj公式,并获得了有关随机奇异积分的性质,取得了一些有意义的成果.     

一种光纤通信系统中非线性克尔效应抑制新方法

本文从非线性薛定鄂方程出发,提出了一种全光学的相位预加重来抑制非线性克尔效应的新方法,通过在发射端将输入光脉冲的初始相位上叠加一个平方相位值,改变光脉冲的初始相位值,从而提高光脉冲在光纤传输中抗非线性克尔效应能力.通过理论研究,仿真分析以及实验验证了该方法的可行性,实验验证在接收端可以提高误码率2个数量级以上.在长距离大容量光纤通信系统中有很好的应用前景.     

Novel high-sensitivity coherent transceiver for optical DPSK/DQPSK signals based on heterodyne detection and electrical delay interferometer

We present a novel coherent transceiver for optical differential phase-shift keying/differential quadrature phase-shift keying （DPSK/DQPSK） signals based on heterodyne detection and electrical delay interferometer. A simulation framework is provided to predict a theoretical sensitivity level for the reported scheme. High sensitivity of -45.18 dBm is achieved for 2.5-Gb/s return-to-zero （RZ）-DPSK signal, and high sensitivities of -36.83 dBm （I tributary） and -35.90 dBm （Q tributary） are observed for 2.5-GBaud/s RZ-DQPSK signal in back-to-back configuration. Transmission for both signals over 100 km is also investigated. Experimental results are discussed and analyzed.     

Pulsewidth-tunable CSRZ-DQPSK signal generation using DPMZMs

This letter proposes and experimentally demonstrates a simple scheme for generating 40-GBaud carriersuppressed return-to-zero differential quadrature phase shift keying(CSRZ-DQPSK) modulation signals with tunable pulsewidths using two dual-parallel Mach-Zehnder modulators(DPMZMs).The duty cycle of the generated 40-GHz CSRZ-DQPSK pulse train is continuously tuned from 31% to 62%,with the full-width at half-maximum tuned from 7.8 to 15.5 ps,by electrically tuning the delay between the two sine-clock signals in one of the DPMZMs.Error-free performance is achieved after 320-km transmission.     

熔融Cu57团簇在急冷过程中弛豫和局域结构转变的分子动力学研究

采用基于嵌入原子方法的正则系综分子动力学研究熔融Cu₅₇团簇在急冷过程中的弛豫及其局域结构变化.通过对弛豫过程中均方位移、非相干中间散射函数和非Gauss参数三种函数和原子键对随急冷温度不同所发生变化的分析表明,在经过短时间的原子剧烈运动后,急冷温度极大地影响着团簇内原子结构弛豫过程.急冷温度较高时,原子在经历短时间剧烈运动的β弛豫后,进入α弛豫区后以扩散运动为主,随后原子运动表现为非扩散性的原子局域结构重排,团簇内没有出现明显的成核结构.随着温度的降低,原子局域结构的变化在经过短时间原子剧烈运动的β弛豫后,在α弛豫区原子运动表现为扩散性运动,并出现一定数量的不稳定二十面体结构.当急冷温度很低时,在进入α弛豫区后,团簇结构变化逐渐表现为非扩散性原子局域结构重排,形成相当数量的稳定成核二十面体结构.     

Coalescence between Cu57 and Cu58 clusters at a room temperature: molecular dynamics simulations

Three coalescence processes of Cu57-Cu57,Cu57-Cu58,and Cu58-Cu58 clusters at 300 K are investigated by employing molecular dynamics simulations.According to the evolutions of mean square displacement and local atom packing,the coalescence process can be separated into three stages including an approaching stage,a coalescing stage,and a coalesced stage.The simulations show that the coalescence processes and the formed products are sensitive to the respective initial structures of,and the relative configuration between,the two coalescing icosahedron-based clusters.     

Coalescence between Cu57 and Cu5s clusters at a room temperature： molecular dynamics simulations

Three coalescence processes of Cu57-Cu57, Cu57-Cu58, and Cu5s Cu58 clusters at 300 K are investigated by employing molecular dynamics simulations. According to the evolutions of mean square displacement and local atom packing, the coalescence process can be separated into three stages including an approaching stage, a coalescing stage, and a coalesced stage. The simulations show that the coalescence processes and the formed products are sensitive to the respective initial structures of, and the relative configuration between, the two coalescing icosahedron-based clusters.     

衬底温度对ZnO薄膜生长过程和微结构的影响

从原子尺度上去研究薄膜生长过程中温度对薄膜取向性、缺陷结构以及薄膜完整性的影响和作用规律, 对于解释薄膜生长的物理本质、控制生长条件、提高薄膜制备的质量具有重要意义. 本文应用基于反应力场的分子动力学方法研究了ZnO薄膜(000l)表面作为衬底的薄膜沉积生长过程, 初步讨论了衬底温度(200、500和800 K)变化对沉积较薄ZnO膜质量的影响, 部分结果与实验观察相符. 结果表明, 衬底温度在500 K左右时, 沉积原子结构径向分布函数曲线特征峰尖锐、明显, 有序度较高, 注入和溅射对薄膜完整性影响较小, 沉积形成的薄膜结构稳定而又致密. 在预置衬底表面平坦的情况下薄膜呈现一种链岛状的生长模式, 每原子层均具有两种生长取向, 导致其生长前锋交汇处形成了一种新的有序缺陷.