Theoretical Studies on the Binding Mode and Reaction Mechanism of TLP Hydrolase kpHIUH

In this work, we have investigated the binding conformations of the substrate in the active site of 5-HIU hydrolase kpHIUH and its catalytic hydrolysis mechanism. Docking calculations revealed that the substrate adopts a conformation in the active site with its molecular plane laying parallel to the binding interface of the protein dimer of kpHIUH, in which His7 and His92 are located adjacent to the hydrolysis site C6 and have hydrogen bond interactions with the lytic water. Based on this binding conformation, density functional theory calculations indicated that the optimal catalytic mechanism consists of two stages: (1) the lytic water molecule is deprotonated by His92 and carries out nucleophilic attack on C6=O of 5-HIU, resulting in an oxyanion intermediate; (2) by accepting a proton transferred from His92, C6–N5 bond is cleaved to completes the catalytic cycle. The roles of His7, His92, Ser108 and Arg49 in the catalytic reaction were revealed and discussed in detail.     

Infrared and Raman Spectra for Amino Group and C˭O Stretching Modes in Biomolecule 5‐Aminouracil

Abstract

Assuming planar geometry of 5‐aminouracil and C_s point group symmetry, it has been possible to assign all the 36 (25a′+11a″) normal modes of vibration. The two NH bonds of the NH₂ group appear to be non-equivalent as the NH₂ stretching frequencies and do not satisfy the empirical relation proposed for the two equivalent NH bonds of the NH₂ group due to their involvement and interaction with one hydrogen bond and the other adjacent oxygen atom of the parent molecule. The planar and nonplanar bending modes due to the C₄?O₈ bond are expected with have lower magnitude compared with those due to the C₂?O₇ bond.     

空间激光与单模光纤和光子晶体光纤的耦合效率

为了设计最优光纤耦合系统,利用高斯模场近似单模阶跃光纤的模场和大模面积光子晶体光纤的模场,推导出了理想情况下空间激光与这两种光纤的耦合效率解析表达式以及光纤端面相对于耦合系统存在横向偏移和端面倾斜时的耦合效率解析表达式。基于上述理论表达式计算了空间激光与光纤的耦合效率,并通过实验验证了此理论表达式的有效性。理论计算和实验均证实了单模阶跃光纤对于横向偏移更敏感,当横向偏移量等于单模光纤的纤芯半径时所对应的耦合效率只有20.25%,为理论最大值的1/4;而大模面积光子晶体光纤对于端面倾斜更加敏感,当端面倾斜2°时对应的耦合效率只有40.5%,为理论最大值的1/2。所提出理论表达式和实验方法完全可以为设计光纤耦合系统提供准确的参数。     

Effect of surface treatment condition on interfacial degradation behavior in GFRP under acidic conditions

Interfacial degradation behavior of E-glass cloth reinforced vinyl ester resin under acidic conditions has been investigated. Specimens with different surface treatment conditions were prepared. Mode I fracture toughness tests were performed using DCB specimen, and the effect of surface treatment condition and immersion time on the crack propagation behavior is discussed. The crack propagation behavior changes as a function of the condition of the silane coupling agent and the immersion time due to the degradation of the interphase. A technique is proposed to evaluate the interfacial property. The change of fracture toughness of interphase and resin as a function of immersion time is studied by the crack propagation behavior and the fracture toughness of interphase and resin evaluated by this technique. The fracture toughness of interphase decreases rapidly with immersion in acidic solution.     

噪声模态单元预判的经验模态分解脉冲星信号消噪

为了改善脉冲星辐射脉冲信号的消噪效果, 提出了一种基于噪声模态单元预判的经验模态分解(EMD) 消噪声方法. 该方法首先利用EMD将含噪辐射脉冲信号分解为一组内蕴模态函数(IMF), 根据IMF系数的统计特性采用局部均方误差准则进行噪声模态单元预判, 并将噪声模态单元置零; 然后对噪声模态单元预判处理后的IMF以模态单元为基本单位进行最优比例萎缩消噪, 从而达到抑制噪声、保留信号的目的. 实验结果表明: 与Sure Shrink小波阈值法、Bayes Shrink小波阈值法和EMD模态单元比例萎缩法相比, 基于噪声模态单元预判的EMD消噪方法可以更有效地去除脉冲辐射信号中的噪声, 同时更好地保留信号突变处的细节信息特征, 在信噪比、 均方误差、峰值相对误差、峰位误差和相位误差等方面都有一定程度的改善. 关键词： 脉冲星信号消噪 经验模态分解 噪声模态单元预判 局部均方误差     

偏分复用系统中偏振模色散补偿与偏分解复用一体化方案

本文建立了偏分复用系统中偏振模色散与信号偏振态变化引起信道串扰的数学模型, 分析了偏振模色散对偏分复用信道射频功率的影响, 并提出了适用于偏分复用系统的光域偏振模色散补偿与偏分解复用同时进行的方案: 用信道的射频功率作为反馈控制信号, 监测链路中偏振模色散和偏振态变化引起的信道串扰的大小, 用改进的粒子群优化算法对偏振控制器进行自适应控制, 同时完成偏振模色散补偿与偏分解复用. 在112 Gb/s偏分复用-差分正交相移键控(PDM-DQPSK)传输系统中仿真验证了该方案的有效性. 结果表明该方案可以使112 Gb/s-PDM-DQPSK传输系统完成自适应偏分解复用的同时, 在1 dB的光信噪比代价下, 使系统对偏振模色散的容忍度提高20 ps. 关键词： 偏分复用系统 信道串扰 偏振模色散 偏分解复用     

过模波导器件的迭代设计方法

从模式保留和转换的角度, 过模波导器件可分为模式转换器、模式保留器和模式综合器. 传统方法只解决其中一种器件的设计或者对器件的某个指标进行改进. 本文在深入分析耦合波理论之后, 提出了过模波导器件的迭代设计方法, 从原理上解决了过模波导器件的设计问题. 该方法能够统一设计三类过模波导器件, 通过添加不同的结构控制方法, 可得到转换效率更高、带宽更宽、结构更紧凑、满足不同工程需求的器件, 而且还能有效设计一些新型器件. 给出了两个设计实例: 双频TM₀₁–TE₁₁模式变换器和光壁馈源喇叭. 双频TM₀₁–TE₁₁模式变换器的两个工作频点为8.75 GHz和10.3 GHz, 波导半径为16 mm, 在两个频点转换效率为99%以上. 光壁馈源喇叭实现TE₁₁模式向高斯束的转换. CST仿真结果验证了这两个器件设计的正确性和有效性. 关键词： 耦合波理论 模式转换器 模式过渡器 迭代法     

Bi2ZnOB2O6单晶偏振拉曼光谱

本文通过分析不同几何配置下的偏振拉曼光谱对非线性光学晶体的晶格振动模式进行了研究. 首先根据因子群分析,将晶体的振动模按晶体对称群的不可约表示进行分类,其次测量了晶体在10–1600 cm^-1范围内,不同几何配置下的偏振拉曼光谱,并在此基础上指认了晶体的晶格振动模式. 300 cm^-1以下的振动峰,归结为晶体的外振动,来自[BiO₆],[ZnO₄],[BO₄]和[BO₃]原子基团的平动和转动;300cm^-1以上为晶体的内振动,主要与Bi-O,和Zn-O键振动有关. 晶体拉曼光谱中最高振动频率达到1407 cm^-1,被指认为[BO₃]三角形中B-O键的伸缩振动,体现了[BO₃]基团中高的电子非局域化程度. 关键词： 2ZnOB₂O₆单晶')" href="#">Bi₂ZnOB₂O₆单晶 偏振拉曼光谱 振动模式