Impacts of higher-order dispersions and saturable nonlinearities on modulation instability in negative-refractive metamaterials

On the basis of the standard linear stability analysis and Drude electromagnetic model,the impacts of higher-order dispersions and three kinds of typical saturable nonlinearities on modulation instability(MI) have been analyzed and calculated for negative-refractive metamaterials(MMs).Our results show that the MI gain spectra consist of only one spectral region instead of one or two regions in ordinary materials,which may be close to or far from the zero point.Particularly,the spectrum far from the zero point has a high cut-off frequency but a narrow spectral width,which is obviously beneficial to the generation of high-repetition-rate pulse trains.Moreover,MI characteristics here will vary with the normalized angular frequency which can be modified by adjusting the structures of negative-refractive MMs,signifying the controllability of bistable solitons and MI based applications.The effects of saturable nonlinearities are similar to those in ordinary materials.     

大气湍流对天文望远镜光电导行精度的影响

讨论了由大气湍流造成的望远镜导行误差,这一误差将给望远镜光电导行的精度带来较大影响。其中使用单点源目标的导行精度受限于大气相干长度和大气相干时间,而多点源目标及面源的导行精度还与湍流随高度的变化有关。通过分析和仿真(数值模拟)结果表明,现代天文观测必须考虑大气湍流对光电导行精度的影响。通过延长曝光时间可以有效降低湍流大气的影响,同时也降低了光电导行的反馈控制频率。当导行信标为多星或面源则可在一定程度上降低高层大气湍流带来的光电导行误差,从而可以适度减少光电导行曝光时间,提高其反馈控制频率。     

The ionic conductivity of Li6BaLa2M2O12 with coexisting Nb and Ta on the M sites

In a view to balancing cost and lithium ion conductivity, Li₆BaLa₂Nb _x Ta_2???x O₁₂ (x?=?0–2) was prepared by solid-state reaction, and its corresponding AC impedances were tested at temperatures ranging from 20 to 250 °C in air. Li₆BaLa₂Ta₂O₁₂ exhibits the highest conductivity, 8.77?×?10^?6?S/cm, and the second highest is Li₆BaLa₂Nb₂O₁₂ with 6.69?×?10^?6?S/cm. Partial replacement of Ta with Nb cannot bestow the advantages of cost saving or the enhancement of lithium ion conductivity. X-ray diffraction patterns revealed a gradual change as an increasing amount of Nb replaces Ta in Li₆BaLa₂Nb _x Ta_2???x O₁₂ (x?=?0–2), and it is thought that the trending of Nb and Ta to rest on the crystallographic planes is different.     

梯度计算的集合变分方案及其在大气Ekman层湍流系数反演中的应用

大气Ekman层湍流系数的准确计算对数值天气预报和污染物扩散计算有着重要的意义. 将集合计算和变分法结合起来, 提出了目标泛函梯度计算的集合变分方案, 并根据正演模式的线性化情况提出了两种计算流程. 利用这种集合变分梯度算法及两种流程对Ekman层湍流系数进行了反演试验, 结果表明这种算法实施简单、方便, 根据观测资料能够比较准确地反演湍流系数值. 关键词： 梯度计算 集合变分 湍流系数 反演     

利用多层膜生长技术制备纳米印章模板

在纳米印章技术中，为克服电子束刻蚀制备50nm以下线条的技术难点，利用等离子增强化学 气相沉积技术制备了a-Si/SiN_x多层膜，再利用选择性湿法腐蚀或干法腐蚀在横 截面上制备出浮雕型一维纳米级模板. 多层膜子层之间界面清晰陡峭，可以在纳米量级对子 层厚度进行控制，得到了侧壁在纳米尺度上平滑的模板. 通过控制多层膜子层的生长时间， 制备出线条宽度和槽状宽度均为20nm的等间距模板，品质优于电子束刻蚀技术制备的模板. 关键词： 纳米印章模板 多层膜生长技术     

Ising自旋体系的非平衡动态相变

在平均场理论架构下, 以含时金兹堡-朗道和Glauber动力学这两类动态模型为基础，研究 了受外场和温度共同驱动的Ising自旋体系的非平衡动态相变.确定了界定动态无序(动态顺 磁相P)和动态有序(动态铁磁相F)转变的动态相界.并根据动态序参量Q和Binder参数U随系统 温度t(r₀)、驱动外场频率ω和振幅h₀的变化规律，就上述两类模 型的动态相界上是否存在区分连续动态转变和非连续动态转变的三临界点这一引发争议的问 题做出了进一步分析说明. 关键词： Ising自旋体系 非平衡动态相变 含时金兹堡-朗道模型 Glauber 动力学模型     

X射线Kirkpatrick-Baez显微镜用超反射镜的研制

 介绍了一种可应用于X射线Kirkpatrick-Baez（KB）显微镜的光学元件—X射线超反射镜。选用的W和B₄C作为镀膜材料,膜对数为20,采用单纯型调优的方法实现了X射线超反射镜设计,用磁控溅射的方法在Si基片上完成了W/B₄C X射线超反射镜的制备。采用高分辨率X射线衍射仪（8 keV）测量了X射线超反射镜的反射特性。制备的X射线超反射镜在掠入射角分别为1.052°和1.143°处,反射角度带宽为0.3°,反射率达到20%,可满足KB型显微镜的要求。     

BROWNIAN MOTION MODEL OF THE FISSION PROCESS

Fission process is considered as a multidimensional Brownian motion. The Planck-Fokker equation is solved and the fission probability in the steady state approximationis calculated. The results is compared with the Bohr-Wheeler theory. Numerical cal-culations are performed for the fission of ²³⁶U and the results are discussed.     

Simultaneous two-way classical communication and measurement-device-independent quantum key distribution on oceanic quantum channels

Simultaneous two-way classical and quantum (STCQ) communication combines both continuous classical coherent optical communication and continuous-variable quantum key distribution (CV-QKD), which eliminates all detection-related imperfections by being measurement-device-independent (MDI). In this paper, we propose a protocol relying on STCQ communication on the oceanic quantum channel, in which the superposition-modulation-based coherent states depend on the information bits of both the secret key and the classical communication ciphertext. We analyse the encoding combination in classical communication and consider the probability distribution transmittance under seawater turbulence with various interference factors. Our numerical simulations of various practical scenarios demonstrate that the proposed protocol can simultaneously enable two-way classical communication and CV-MDI QKD with just a slight performance degradation transmission distance compared to the original CV-MDI QKD scheme. Moreover, the asymmetric situation outperforms the symmetric case in terms of transmission distance and optical modulation variance. We further take into consideration the impact of finite-size effects to illustrate the applicability of the proposed scheme in practical scenarios. The results show the feasibility of the underwater STCQ scheme, which contributes toward developing a global quantum communication network in free space.     

毫米波回旋速调管放大器的自洽非线性数值模拟

为了实现回旋速调管放大器的快速设计,基于经典的回旋管的稳态单模非线性理论方法,开展了回旋速调管放大器的束波作用效率的理论模拟研究。由于单模理论无法匹配回旋速调管放大器的输入腔、中间腔两端的突变边界条件,所以输入腔与中间腔都只能采用给定场法进行求解。回旋速调管的输出腔的功率输出端通常采用缓变结构,这种腔体可以采用单模自洽理论进行求解。对两腔毫米波回旋速调管放大器进行了理论模拟,并与商业粒子模拟软件的结果进行对比,验证了该数值理论模拟方法的有效性。