Performance analysis of dense wavelength division multiplexing secure communications with multiple chaotic optical channels

The performance of dense wavelength division multiplexing secure communications with multiple chaotic optical channels is numerically analyzed in this paper. Taking the multiplexing of three chaotic optical channels as an example, we investigate the effects of second-order dispersion coefficient and nonlinear coefficient of fiber, channel spacing, message amplitude and bit rates on chaotic synchronization and multiplexing communications. Chaotic synchronization quality and Q-factor of the recovered message decrease with the increasing fiber length. A 1.25 Gbits/s non-return-to-zero (NRZ) sequence can be securely transmitted up to 60 km under the influence of the other two chaotic optical channels. Compared with the fiber dispersion, the cross-phase modulation is the primary factor which deteriorates the quality of communications. The results also show that the quality of communications is unlimited to the channel spacing as long as chaotic synchronization can be maintained. In addition, the effect of the amplitude of encrypted message on Q-factor and the confidentiality is demonstrated.     

多光子反Jaynes-Cummings模型中混合态二能级原子的粒子数反转特性

利用多光子反Jaynes-Cummings模型研究了单模相干光场与混合态二能级原子相互作用时,二能级原子的粒子数反转特性.讨论了相干光场的平均光子数、跃迁光子数以及原子初始态的混合度等参量对粒子数反转的影响.结果表明：二能级原子的粒子数反转有周期性的崩塌和回复现象. 相干光场平均光子数和跃迁光子数的增加会改变原子的回复周期和崩塌的衰减时间;随相干光场平均光子数的增加粒子数反转的振荡频率增大;随着混合度的减少回复的周期性和崩塌的衰减时间不发生变化但粒子数反转的振荡幅度增大.     

Eu掺杂量对锐钛矿相TiO2电子寿命和吸收光谱影响的第一性原理研究

采用基于密度泛函理论框架下的第一性原理平面波超软赝势方法,建立了不同Eu掺杂量的锐钛矿相TiO₂超胞模型,计算了其态密度、差分电荷密度、能带结构和吸收光谱.结果发现:掺杂后Eu在TiO₂的禁带中产生杂质能级.通过对比两种不同Eu掺杂量(1.39at%和2.08at%)下的锐钛矿TiO₂的能带结构,发现掺杂量越高,杂质能级越向深能级方向移动,说明电子复合率随杂质浓度增加而增加,即电子寿命变小,同时吸收光谱红移越显著,强度越强.根据实际需要,可在锐钛矿TiO₂中适量掺杂Eu,在适当减少电子寿命情况下,使吸收光谱红移.     

一维六方准晶中带三条不对称裂纹的圆形孔口问题的解析解

利用复变函数方法,通过构造保角映射,研究了一维六方准晶中带不对称三裂纹的圆形孔口的反平面剪切问题,给出了Ⅲ型裂纹问题的应力强度因子,在极限情形下,不仅可以还原为已有的结果,而且求得一维六方准晶中L裂纹问题在裂纹尖端的应力强度因子.     

含铜MCM-48催化剂上糠醛选择性加氢制糠醇

 以MCM-48为载体,采用新颖的负载方法(有机官能团化法)制备了铜基负载型催化剂. 结果表明,活性组分以较高的负载量均匀地分散在载体MCM-48表面,且负载活性组分后,分子筛的结构未被明显破坏. 本文首次将采用此负载方法制备的铜基MCM-48催化剂用于糠醛选择性加氢制糠醇反应,并得到了较高的活性、稳定性及糠醇选择性,该催化剂可以与商业催化剂相比,具有潜在的工业应用价值. 与一维结构的MCM-41相比,三维孔道结构的MCM-48有效避免了孔堵塞,大大提高了催化剂的稳定性. 引入助剂镧有利于羰基加氢,明显提高了糠醛的转化率. 使用后的催化剂并未被氧化,催化剂失活的主要原因之一是积炭.     

A dual band CMOS VCO with a balanced duty cycle buffer

This paper proposes a dual band VCO with a standard 0.35 μm CMOS process to generate 1.07 and 2.07 GHz. The proposed VCO architecture with 50% duty cycle circuit and a half adder (HA) is able to produce a frequency two times higher than that of the conventional VCOs. The measurement results demonstrate that the gain of VCO and power dissipation are 561 MHz/V and 14.6 mW, respectively. The phase noises of the dual band VCO are measured to be −102.55 and −95.88 dBc/Hz at 2 MHz offset from 1.07 and 2.07 GHz, respectively.     

抛物量子点中强耦合磁双极化子内部激发态性质

基于Lee-Low-Pines幺正变换,采用Pekar类型变分法研究了抛物量子点中强耦合磁双极化子的内部激发态性质,当考虑自旋和外磁场影响时,推导出二维量子点中强耦合磁双极化子基态的能量E0,声子平均数ˉN0以及第一激发态的能量E1,声子平均数ˉN1随量子点受限强度ω0,介电常数比η,电子-声子耦合强度α和磁场的回旋共振频率ωC的变化规律.结果表明,磁双极化子的基态能量E0和第一激发态能量E1由两电子的单粒子能量E E,两电子间库仑相互作用能E C,电子自旋与磁场相互作用能E s和电子-声子相互作用能E e-ph四部分组成;单粒子"轨道"运动与磁场相互作用导致了第一激发态能级E1分裂为E(1+1)1,E(1-1)1两条,而电子自旋-磁场相互作用的效应又使基态和第一激发态的各能级均产生了三条"精细结构";ˉN0和ˉN1随ω0,α和ωc的增加而增大,E e-ph的取值总是小于零,其绝对值随α,ω0和ωc的增加而增大;电子-声子相互作用的效应是束缚态磁双极化子形成的有力因素,而限定势和电子之间的库仑排斥能的存在不利于束缚态磁双极化子的形成;能量为E(1-1)1的磁双极化子要比能量为E(1+1)1的磁双极化子更容易且更稳定地处于束缚态.     

离散时多元风险模型的破产概率

本文研究了离散时多元风险模型的破产概率问题.利用经典大偏差的方法,获得了有限水平的破产概率,推广了离散时一元风险模型的相应结论.     

Asymmetric synthesis of N-phenylethyl-2-phenyldecahydroquinolin-4-ones via Lewis acid catalyzed imino-Diels–Alder reaction

The asymmetric synthesis of N-phenylethyl-2-phenyldecahydroquinolin-4-ones was performed via a Lewis acid catalyzed imino-Diels–Alder reaction between the enantiopure (R)-N-phenylethylbenzylideneimine and the trimethylsilyl enol ether of acetylcyclohexene. The regio- and stereoselective formation of intermediary bicyclic enoxysilanes, followed by their stereoselective protonation was evidenced. The initial stereoselectivity was kept only if the reaction mixture was treated using controlled basic conditions. Three enantiopure title compounds were isolated with a 5–15% yield.     

Exchange bias in a generalized Meiklejohn–Bean approach

A generalized Meiklejohn–Bean model is considered in order to derive an analytic expression for the dependence of the exchange bias field on the layer thickness involved in ferromagnetic/antiferromagnetic heterosystems, on the orientation of the applied magnetic field with respect to the magnetic easy axes and on the quenched magnetization M_AF of the antiferromagnetic pinning layer. While M_AF is a well-known feature of field-cooled dilute antiferromagnets, it seems to occur quite generally also in pure AF pinning substrates. The new analytic expressions are successfully compared with recent experimental results and Monte Carlo investigations.