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961.
新型四倍频光生毫米波矢量信号调制技术 总被引:1,自引:0,他引:1
提出一种基于双并联马赫-曾德尔调制器(MZM)的新型四倍频光生毫米波技术,并用于矢量信号调制。传统的四倍频调制技术,由于数据信号同时调制到+2,-2阶边带上,拍频检测后两个边带上数据信号会产生相位叠加,只适用于不归零码(NRZ)等强度调制格式。提出的矢量信号调制技术将数据信号调制在一个-1阶边带上,另一个+3阶边带不携带数据,在拍频检测后幅度和相位信息被正确保留。同时,四倍频模块降低了传输过程中对电和光器件的带宽需求。理论分析和仿真结果表明,通过此方法产生的携带在60GHz载波上的6.25×108 symbol/s的四相相移键控(QPSK)信号,经过20km单模光纤传输后,误差向量幅度(EVM)损耗可以忽略。 相似文献
962.
Shang Quan Bu 《数学学报(英文版)》2012,28(1):37-44
We study the well-posedness of the equations with fractional derivative Dαu(t)=Au(t)+f(t)(0 ≤t≤2π),where A is a closed operator in a Banach space X,0α1 and Dα is the fractional derivative in the sense of Weyl.Although this problem is not always well-posed in Lp(0,2π;X) or periodic continuous function spaces Cper([0,2π];X),we show by using the method of sum that it is well-posed in some subspaces of L p(0,2π;X) or C per([0,2π];X). 相似文献
963.
We study the direct product decomposition of quantum many-valued algebras (QMV algebras) which generalizes the decomposition theorem of ortholattices (orthomodular lattices).In detail,for an idempo- tent element of a given QMV algebra,if it commutes with every element of the QMV algebra,it can induce a direct product decomposition of the QMV algebra.At the same time,we introduce the commutant C(S) of a set S in a QMV algebra,and prove that when S consists of idempotent elements,C(S) is a subalgebra of the QMV algebra.This also generalizes the cases of orthomodular lattices. 相似文献
964.
Yilun Shang 《Journal of statistical physics》2012,149(3):505-518
Many real-world networks belong to a particular class of structures, known as small-world networks, that display short distance between pair of nodes. In this paper, we introduce a simple family of growing small-world networks where both addition and deletion of edges are possible. By tuning the deletion probability q t , the model undergoes a transition from large worlds to small worlds. By making use of analytical or numerical means we determine the degree distribution, clustering coefficient and average path length of our networks. Surprisingly, we find that two similar evolving mechanisms, which provide identical degree distribution under a reciprocal scaling as t goes to infinity, can lead to quite different clustering behaviors and characteristic path lengths. It is also worth noting that Farey graphs constitute the extreme case q t ??0 of our random construction. 相似文献
965.
Yinnian He Yan Zhang Yueqiang Shang Hui Xu 《Numerical Methods for Partial Differential Equations》2012,28(5):1620-1642
A combination method of the Newton iteration and two‐level finite element algorithm is applied for solving numerically the steady Navier‐Stokes equations under the strong uniqueness condition. This algorithm is motivated by applying the m Newton iterations for solving the Navier‐Stokes problem on a coarse grid and computing the Stokes problem on a fine grid. Then, the uniform stability and convergence with respect to ν of the two‐level Newton iterative solution are analyzed for the large m and small H and h << H. Finally, some numerical tests are made to demonstrate the effectiveness of the method. © 2011 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2012 相似文献
966.
Ming-Chun Tang Shaoqiu Xiao Tianwei Deng Yan Wang Yanying Bai Changrong Liu Yuping Shang Jiang Xiong Bingzhong Wang 《Applied Physics A: Materials Science & Processing》2012,106(4):821-828
Compared with the traditional split-ring resonator reported by Pendry et al. (IEEE Trans. Microw. Theory Tech. 47:2075, 1999), the co-directional split-ring resonator, which has inherent low mutual coupling between its outer and inner rings, can
provide distinct dual-band magnetic resonances. In this paper, we analyzed and compared different types of split-ring resonator,
but selected the co-directional split-ring resonator for the tri-band magnetic resonator design because of its attractive
dual-band magnetic resonance characteristics. We then accommodated the rings’ resonant strengths in the co-directional split-ring
resonator to be nearly equal, and added an arm-loaded ring to design a new tri-band magnetic resonator. Finally, we designed
and experimentally demonstrated a broadband μ-negative planar material with low frequency dispersion, which consisted of three pairs of tri-band magnetic resonators with
slightly different dimensions. 相似文献
967.
The interfacial energies of three twin boundaries with low-index boundary planes: prismatic (101?0), basal O-terminated (0001), and basal Cr-terminated (0001), and the segregation energies of five doping elements (Ce, Hf, La, Y and Zr) have been calculated as a function of temperature. The static energies at 0 K were obtained through first-principles calculations and the energies at finite temperatures were derived based on the Debye model. The calculation results show that both the interfacial and segregation energies decrease as temperature increases and the segregation energies are found to be proportional to the ionic size mismatch and the interfacial energy. Our combined approaches suggest an efficient and less computationally intensive way to derive grain boundary energetics at finite temperatures. 相似文献
968.
The preparation, structures, and magnetic properties of a series of metal formate perovskites [CH3NH3][MnxZn1?x(HCOO)3] were investigated. The isostructural solid solution can be prepared in the complete range of x=0–1. The metal–organic perovskite structures consist of an anionic NaCl type [MnxZn1?x(HCOO)3?] framework with CH3NH3+ templates located in the nearly cubic cavities and forming hydrogen bonds to the framework. When the proportion of Mn increased (i.e., x changed from 0 to 1), the lattice dimensions and metal–oxygen and metal–metal distances show a slight, nonlinear increase because of the increased averaged metal ionic radius and the local structure distortion. Through the series, the magnetism changes from the long‐range ordering of spin‐canted antiferromagnetism for x≥0.40 to paramagnetism when x≤0.30, and the percolation limit was estimated to be xP=0.31(2) for this simple cubic lattice. In the low‐temperature region, enhancement of magnetization and the gradual decrease and final disappearance of coercive field, remnant magnetization, and spin‐flop field upon dilution were observed through this isotropic Heisenberg magnetic series. IR spectroscopic and thermal properties were also investigated. 相似文献
969.
970.
以醋酸锂、醋酸锰、硝酸镍、柠檬酸、乙二醇为原料,采用燃烧辅助合成锂离子电池正极材料LiNi0.05Mn1.95O4。采用X射线衍射、扫描电子显微镜、循环伏安、恒电流充放电等技术对合成产物进行物相、形貌及电化学性能分析与测试。结果表明:采用燃烧辅助合成LiNi0.05Mn1.95O4过程中,前驱体在空气中点燃后已形成单一尖晶石相,经750℃热处理4 h后得到的LiNi0.05Mn1.95O4粉末X射线衍射峰尖锐,结晶性好,晶粒尺寸均匀。该法合成的LiNi0.05Mn1.95O4粉末首次放电比容量为117.5 mAh.g-1,经50次充放电循环后的容量保持率为95.1%,合成的LiNi0.05Mn1.95O4粉末具有良好的电化学性能。 相似文献