低气压直流放电金属铜等离子体

在原子蒸气激光同位素分离技术中用直流电源实现原子化和激发电离过程,低气压下使用焊锡短路阴、阳极得到了金属铜等离子体稳定射流。在气压10^-3Pa、功率0.9kW下,测得稳定放电的伏安特性曲线和光谱强度图。通过计算得到电子密度在10⁹cm^-3左右、电子温度在0.69eV左右。     

SN-分子离子的势能函数和光谱常数研究

采用耦合簇CCSD(T)方法结合系列相关一致基组aug-cc-pVXZ (X=D,T,Q,5) 对基态SN^-分子离子(X³∑^-) 进行了结构优化和单点能扫描计算. 用四种方法进行基组外推得到该体系的平衡核间距R_e=0.15852 nm, 谐振频率ω_e=948.05 cm^-1, 离解能D_e=3.934 eV均与实验数据符合得很好. 对单点能扫描结果用9参数Murrell-Sorbie势能函数进行了最小二乘拟合, 得到了体系的解析势能函数表达式, 并进一步推导出了体系的力常数和光谱常数. 拟合所得势能曲线准确地再现了SN^-分子离子的离解能和平衡结构特征. 通过求解核运动的径向薛定谔方程, 得到了无转动SN^- (X³∑^-) 的全部振动态, 并进一步计算出了各振动能级相应的分子常数. 与实验结果及其他理论研究结果的对比表明, 本文关于SN^-分子离子平衡常数和光谱常数的计算结果达到了较高的精度, 能为进一步的实验探测和理论研究提供参考依据. 关键词： 势能曲线 解析势能函数 光谱常数 振动能级     

Influence of the surface morphology on the melting of polymer crystals. I. Loops of random length and adjacent reentry

A polymer crystal with a noncrystalline surface layer formed by chain loops of different lengths is considered. It is assumed that the length of each loop can be changed by longitudinal diffusion of the molecule through the crystal lattice. From the condition that the free energy of the system is minimum, the loop length distribution and the average loop length as function of temperature are calculated. In contrast to the results for loops of equal length, for the present model, a substantial thickness of the noncrystalline surface layer and a broad melting range is obtained also for the case of adjacent reentry. In order to get this result one has to take into account that even an “ideal fold” consists of at least four rigidly arranged CH2 groups in energetically unfavored conformation.     

High P–T Brillouin scattering study of H2O melting to 26 GPa

The properties of solid and liquid phases of H₂O at high pressure and temperature remain an active area of research. In this study, Brillouin spectroscopy has been used to determine the temperature dependence of sound velocities in H₂O as a function of pressure up to 26 GPa through the phase field of ice VII and into the liquid to a maximum temperature of 1200 K. The Brillouin shift of the quasi-longitudinal acoustic mode moves to lower frequencies upon melting at each pressure. As a test of the method, measurements of the melting of Ar by Brillouin scattering at several pressures show a similar behavior for the acoustic mode, and measured melting points are consistent with previous results. The results of H₂O melting are consistent with previously reported melting curves below 20 GPa. The data at higher pressure indicate that ice melts at a higher temperature than a number of previous studies have indicated.     

BLENDS OF STYRENE-BUTADIENE-STYRENE TRIBLOCK COPOLYMER AND ISOTACTIC POLYPROPYLENE. REINFORCING EFFECT OF POLYPROPYLENE AT HIGH TEMPERATURES

Blends of styrene-butadiene-styrene (SBS) triblock copolymer with isotactic polypropylene (iPP) or maleic anhydride–grafted polypropylene (MAP) were prepared in a twin-screw extruder. Static and dynamic experiments at room temperature in previous works showed that the added homopolymers have a significant influence in the improvement of the general mechanical properties of the SBS when the homopolymer is the dispersed phase. Our aim was to study the reinforcing effect as a function of temperature. When the glass transition of the polystyrene blocks in the SBS is approached (40°C–50°C in static experiments), there is a significant worsening of the failure properties, as well as a profile change in the stress-strain plot. If a reinforcing hard phase is added, these changes can be decreased. The temperature dependence of the reinforcing effect of the added homopolymer was evaluated with the analysis of tensile experiments in terms of various theoretical models. A modified activation energy model with temperature-dependent parameters was used to describe the nonlinear regime and quantitatively compare the properties of the different blends with those of pure SBS.     

Solvable models of temporally correlated random walk on a lattice

We seek the conditional probability functionP(m,t) for the position of a particle executing a random walk on a lattice, governed by the distributionW(n, t) specifying the probability ofn jumps or steps occurring in timet. Uncorrelated diffusion occurs whenW is a Poisson distribution. The solutions corresponding to two different families of distributionsW are found and discussed. The Poissonian is a limiting case in each of these families. This permits a quantitative investigation of the effects, on the diffusion process, of varying degrees of temporal correlation in the step sequences. In the first part, the step sequences are regarded as realizations of an ongoing renewal process with a probability densityψ(t) for the time interval between successive jumps.W is constructed in terms ofψ using the continuous-time random walk approach. The theory is then specialized to the case whenψ belongs to the class of special Erlangian density functions. In the second part,W is taken to belong to the family of negative binomial distributions, ranging from the geometric (most correlated) to the Poissonian (uncorrelated). Various aspects such as the continuum limit, the master equation forP, the asymptotic behaviour ofP, etc., are discussed.     

Nonequilibrium fluctuations in μ space

The properties of fluctuations in space in or outside thermal equilibrium are obtained by solving hierarchies of equations derived either from the Liouville or the Master equation. In particular we study the one-, two-, etc., time correlation functions that describe the spatial and temporal behavior of the fluctuations in space. Explicit solutions are obtained for a dilute gas. The Langevin approach is briefly discussed. Our results are compared with those obtained in the extensive literature, which is reviewed in some detail.     

基于简单MOPA结构实现3.08 kW全光纤窄线宽线偏振激光输出

基于简单的主振荡功率放大结构,演示了一种高功率窄线宽线性偏振全光纤激光器,其最大输出功率为3.08 kW,3 dB线宽为0.2 nm。在整个功率缩放过程中,偏振消光比约为94%,光束质量M ²约为1.4。这是国内外首次实现3 kW全保偏光纤激光输出,与基于相位调制的窄线宽激光器相比,该激光器可实现近似的线宽,同时具有受激布里渊散射阈值高、系统结构简单、成本低等特点。     

基于科赫曲线分形结构太赫兹带通滤波器

太赫兹滤波器是太赫兹通信、太赫兹成像和太赫兹检测等太赫兹应用系统中不可或缺的功能器件。按照不同的分类方式,滤波器有不同的种类,常见的按照选频功能可分为高通滤波器、低通滤波器、带阻滤波器和带通滤波器。为了实现在太赫兹波段的滤波效果,世界各地的研究人员利用不同的结构、材料和控制方式实现了功能各异的太赫兹滤波器,但是考虑到设计的器件要应用到太赫兹系统中,成本低廉、结构简单、性能优越的太赫兹滤波器一直是研究人员的追求。分形概念自提出以来在很多研究领域都有了快速发展,但是在太赫兹波段的应用还不是很常见,特别是应用于太赫兹功能器件的设计。引入分形中科赫曲线的概念设计并制备了一种新型的太赫兹带通滤波器,该滤波器是在金属薄膜上刻蚀出科赫曲线分形结构,当太赫兹波垂直入射到该滤波器时候实现了在太赫兹波段的窄带滤波。在滤波器的设计过程中,追求理论与实验相结合,首先在电磁仿真软件中建立科赫曲线分形结构滤波器模型进行计算,探究分形结构应用于太赫兹波段进行滤波的可行性,在进行多次计算之后得到优化后的尺寸和结构,然后根据优化后的尺寸加工出科赫曲线分形结构太赫兹滤波器样品,并且将样品放在太赫兹时域光谱系统中进行实验测量,得到实验数据后与仿真结果进行比较。在仿真中利用了时域有限差分法模拟科赫曲线分形结构太赫兹带通滤波器的传输特性,优化后的仿真结果表明:滤波器的谐振频率为0.715 THz,透射系数能够达到0.92,-3 dB带宽为21.9 GHz,将仿真得到的散射参数进行S参数反演得到了太赫兹滤波器样品的电磁参数,这在理论上分析了太赫兹波在谐振点处产生透射增强的原因。利用飞秒激光微加工系统制备了尺寸优化后的科赫曲线分形结构太赫兹带通滤波器样品,然后使用太赫兹时域光谱系统对样品的传输特性进行测试,对实验得到的时域数据进行快速傅里叶变换之后得到频域数据,再把频域数据进行归一化处理后与之前的电磁仿真结果进行对比,发现实验测得的结果与电磁软件仿真得到的结果较为吻合。