热声系统中回热器特征阻抗与传播常数的研究

针对本实验室一台声驱动热声系统,采用传递函数法研究声驱动系统中回热器的特征阻抗和传播常数.通过调节谐振管长度,改变回热器表面的阻抗,从理论上分析了回热器网络传输方程中的声传播常数、特征阻抗与系统网络元件中的阻抗、导纳和流的关系.并且进一步讨论有无换热器以及不同的加热功率对回热器网络参数的影响.结论有利于进一步量化回热器的网络参数.     

低温液体流动沸腾数值计算中的相间传热模型

采用双流体模型预测了液氮在垂直管内的流动沸腾过程,着重考察和评价了五个常用的相间传热模型对数值计算结果的影响,找出了最优的相间传热模型;同时,研究还发现相间传热模型对流动压降的预测并无明显影响.     

氢吸附导致的SiC表面金属化

文章报道了最近对氢吸附导致β-SiC（001）-32表面金属化的研究结果.提出了β-SiC（001）-32表面金属化的一种新机制：通过形成氢桥键（Si-H-Si 复合结构）形成表面n型掺杂.该复合结构通过氢桥键增强了沟槽底部的弱结合的Si-Si二聚体,并向体系的导带提供电子.     

金属铈催化剂对单壁纳米碳管生长和结构的影响

研究了一种利用新型催化剂制备单壁纳米碳管（SWNTs）的工艺方法.将金属铈的氧化物（Ce O₂）与石墨粉按一定比例混合，填充到已打好孔的石墨棒中制成复合石墨电极 ，以其为阳 极在高温氦电弧中实施电弧放电.放电后的生成物经高分辨透射电子显微镜（HRTEM）和拉曼 光谱(Raman)的观察及分析表明：生成物中含有大量呈束状存在的单壁纳米碳管，管径均匀 ，平均直径为120—132nm. 关键词： 单壁纳米碳管 电弧放电 透射电镜分析     

连续变量量子离物传态的实验研究

利用单个Ⅱ类相位匹配OPA产生的双模压缩态实现连续变量压缩纠缠态，完成了连续变量量 子离物传态. Ⅱ类相位匹配OPA参量反放大过程可以实现正交振幅反关联、正交位相关联的 压缩纠缠态，这不同于一般运转于阈值以下的OPO产生的正交振幅关联、正交位相反关联的 压缩纠缠态，可以采用直接平衡测量的方法完成Bell态测量. 利用双KTP补偿非线性过程的 离散效应，获得了最大压缩大于2dB的双模压缩纠缠态，实现保真度06，考虑到探测效率 实际保真度为057. 这种方案简化了测量方法与纠缠光源产生装置，有利于进行量子通信 的实验研究与应用. 同时，讨论了探测过程中的一些非理想因素. 关键词： 量子离物传态 压缩纠缠态 Bell态测量     

超强激光与等离子体相互作用产生中子的计算

对超强激光与等离子体相互作用过程中发生的氘-氘反应的中子能谱进行了计算.并将计算结 果与实验结果相比较.采用麦克斯韦能量分布和高斯形式的角分布对实验结果进行拟合，从 而确定了入射氘离子的温度和角分布，为研究离子的加速机制提供了依据. 关键词： 中子能谱 激光与等离子体相互作用     

Directed segregation in compartmentalized bi-disperse granular gas

A bi-disperse granular gas in an asymmetrical two-compartment system is studied experimentally.The presence of asymmetry within the range of our experimental parameters results in a directed segregated state and a directed clustering state.This deterministic system does not depend on the initial conditions.A modified flux model based on Lohse’s flux model for bi-disperse granular gases is derived.The modified flux model explains qualitatively the experimental results.     

A 168-W high-power single-frequency amplifier in an all-fiber configuration

We present a high-power,single-frequency,narrow linewidth fiber amplifier based on master oscillator power amplification chains in an all-fiber configuration.The effect of the delivery fiber on the maximum output power is studied.A home-made 1064-nm seed laser with a 20-kHz linewidth is boosted to 129 W,and limited by stimulated Brillouin scattering(SBS) when the delivery fiber is 1.2 m long.By shortening the delivery fiber length to 0.7 m,the SBS threshold is increased efficiently and the maximum output power rises to 168 W with an 82.9% power conversion efficiency.The experimental results indicate that the output power can be further raised by shortening the delivery fiber length and increasing the pump power.     

Two-dimensional model of elastically coupled molecular motors

A flashing ratchet model of a two-headed molecular motor in a two-dimensional potential is proposed to simulate the hand-over-hand motion of kinesins.Extensive Langevin simulations of the model are performed.We discuss the dependences of motion and efficiency on the model parameters,including the external force and the temperature.A good qualitative agreement with the expected behavior is observed.     

Precise measurement of the line width of the photoassociation spectra of ultracold molecules by using a frequency shifter

We propose a technique to precisely measure the line width of the photoassociation spectra of the excited cesium molecule by using a frequency shifter to generate two laser beams with a precise frequency difference. A series of photoassociation (PA) spectra are recorded with two laser beam induced molecular lines, whose peak separation serves as an accurate frequency ruler to measure the line width of the PA spectra. The full width half maximum line width was studied as a function of PA laser intensity. The extrapolated value at zero laser intensity is (34.84 ± 0.22) MHz. By analyzing other broadening mechanisms, a value of (32.02 ± 0.70) MHz was deduced. It is shown that this scheme is inexpensive, simple, robust, and is promising for applications in a variety of other atomic species.