Structural and Catalytic Differences between Two FADH(2)-Dependent Monooxygenases: 2,4,5-TCP 4-Monooxygenase (TftD) from Burkholderia cepacia AC1100 and 2,4,6-TCP 4-Monooxygenase (TcpA) from Cupriavidus necator JMP134

2,4,5-TCP 4-monooxygenase (TftD) and 2,4,6-TCP 4-monooxygenase (TcpA) have been discovered in the biodegradation of 2,4,5-trichlorophenol (2,4,5-TCP) and 2,4,6-trichlorophenol (2,4,6-TCP). TcpA and TftD belong to the reduced flavin adenine dinucleotide (FADH(2))-dependent monooxygenases and both use 2,4,6-TCP as a substrate; however, the two enzymes produce different end products. TftD catalyzes a typical monooxygenase reaction, while TcpA catalyzes a typical monooxygenase reaction followed by a hydrolytic dechlorination. We have previously reported the 3D structure of TftD and confirmed the catalytic residue, His289. Here we have determined the crystal structure of TcpA and investigated the apparent differences in specificity and catalysis between these two closely related monooxygenases through structural comparison. Our computational docking results suggest that Ala293 in TcpA (Ile292 in TftD) is possibly responsible for the differences in substrate specificity between the two monooxygenases. We have also identified that Arg101 in TcpA could provide inductive effects/charge stabilization during hydrolytic dechlorination. The collective information provides a fundamental understanding of the catalytic reaction mechanism and the parameters for substrate specificity. The information may provide guidance for designing bioremediation strategies for polychlorophenols, a major group of environmental pollutants.     

蜗形凸轮的误差分析

运用坐标变换和包络原理对蜗形凸轮进行误差分析,提出了一种加工误差的计算方法,为保证蜗形凸轮的加工精度具有一定的意义。     

植物病毒RNA在片检测方法的建立研究

报道了一种检测植物病毒核糖核酸（RNA）的新方法——RNA玻片杂交法。这种方法把互补脱氧核糖核酸（cDNA）芯片技术与RNA斑点杂交技术相结合,将植物样品的总RNA直接固定在玻片上,用荧光标记的病毒特异探针与芯片杂交后分析杂交信号以确定相应的样品有无该病毒侵染。参照膜杂交的方法,我们设计了一系列实验,对芯片的制备和检测条件进行了摸索,基本建立了在玻片上杂交检测RNA病毒和类病毒的方法。     

遗传算法优化区熔铈的再分配过程

在本研究中,通过冷坩埚感应区熔提纯铈以避免坩埚材料的污染。溶质再分配数值模型结合遗传算法搜寻优化区熔参数以提高溶质的再分配效率,并考虑变溶质分配系数对计算结果的影响。15次区熔后的化学结果分析显示,具有相近分配系数的Fe和Ni在试棒中部分别降低50%和90%,主要差别为初始含量不同。实验结果和计算结果的主要差别源于后续区熔实验过程中较窄熔区的不稳定。研究结果表明,GA是一种获得最优熔区长度的有力工具,但是需要采取有效办法获得稳定的熔区以促使杂质顺利迁移,另外杂质的初始含量应尽可能降低以获得好的提纯效果。     

Synthesis and characterization of BZSM-5 and its catalytic performance in the methanol to hydrocarbons reaction

Five kinds of BZSM-5 molecular sieve with different Si/B ratio and a SiZSM-5 molecular sieve were prepared by hydrothermal synthesis method followed by acid exchange and pelletization.The samples were characterized by XRD,SEM,FT-IR,ICP,low temperature N_2 physical adsorption and desorption,NH3-TPD and Py-IR.The catalytic performance in the reaction of methanol to hydrocarbons was evaluated in the fixed bed reactor.Compared with SiZSM-5,the amount and strength of Bronsted(B) acid were enhanced by introducing skeleton boron and the activity of the catalyst was greatly improved.The characterization and evaluation results indicated that the BZSM-5 catalyst synthesized from the gel of SiO_2/B_2 O_3 20 with Si/B ratio 74.48 had modest acidity strength,acid amount of 0.18 mmol NH_3·g~(-1) and large mesopore volume of 0.23 cm~3·g~(-1).The B acid ratio was higher and the acid strength of BZSM-5 was weaker than that of AIZSM-5,which could inhibit the deep coke formation and increase the activity stability.B-2 had the best lifetime which could reach 672 h under the same evaluation reaction conditions,due to the best matching of moderate acidity and good diffusion properties.     

Experimental study on compaction-induced anisotropic mechanical property of rockfill material

The anisotropy of rockfill materials has a significant influence on the performance of engineering structures. However, relevant research data are very limited, because of the difficulty with preparing specimens with different inclination angles using traditional methods. Furthermore, the anisotropy test of rockfill materials is complex and complicated, especially for triaxial tests, in which the major principal stress plane intersects with the compaction plane at different angles. In this study, the geometric characteristics of a typical particle fraction consisting of a specific rockfill material were statistically investigated, and the distribution characteristics of particle orientation in specimens prepared via different compaction methods were examined. For high-density rockfill materials, a set of specimen preparation devices for inclined compaction planes was developed, and a series of conventional triaxial compression tests with different principal stress direction angles were conducted. The results reveal that the principal stress direction angle has a significant effect on the modulus, shear strength, and dilatancy of the compacted rockfill materials. Analysis of the relationship between the principal stress direction angles, change in the stress state, and change in the corresponding dominant shear plane shows that the angle between the compacted surface and dominant shear plane is closely related to interlocking resistance associated with the particle orientation. In addition, different principal stress direction angles can change the extent of the particle interlocking effect, causing the specimen to exhibit different degrees of anisotropy.     

莫斯科城市规划理念的变迁

本文对16世纪以来莫斯科城市建设活动的几个基本发展阶段进行了概括和总结,在此基础上,重点对十月革命后莫斯科的城市规划思想、前苏联解体后新的城市规划理念、各历史阶段的特点及思想变迁进行了分析和评价。     

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本文通过实验及理论分析,探讨了川东地区水套加热炉烟筒遭受严重腐蚀破坏的主要原因,为水套炉烟筒防腐材料的研制工作提供了依据。     

Comparison of emission signals for different polarizations in femtosecond laser-induced breakdown spectroscopy

In this study, a femtosecond laser was focused to ablate brass target and generate plasma emission in air. The influence of lens to sample distance(LTSD) on spectral emission of brass plasma under linearly and circularly polarized pulses with different pulse energies was investigated. The results indicated that the position with the strongest spectral emission moved toward focusing lens with increasing the energy. At the same laser energy, the line emission under circularly polarized pulse was stronger compared with linearly polarized pulse for different LTSDs. Next, electron temperature and density of the plasma were obtained with Cu(Ⅰ) lines,indicating that the electron temperature and density under circularly polarized pulse were higher compared to that under linearly polarized pulse. Therefore, changing the laser polarization is a simple and effective way to improve the spectral emission intensity of femtosecond laserinduced plasma.