硅单粒子位移损伤多尺度模拟研究

本文结合分子动力学方法和动力学蒙特卡罗方法, 研究了单个粒子入射硅引起的位移损伤缺陷的产生和演化过程; 基于Shockley-Read-Hall理论计算了单个粒子入射引起的位移损伤缺陷导致的泄漏电流增加及其演化过程, 比较了缺陷退火因子与泄漏电流退火因子之间的差异, 并将计算结果与实验值进行了对比. 结果表明, 计算泄漏电流时, 仅考虑一种缺陷的情况下缺陷退火因子与泄漏电流退火因子相同, 考虑两种缺陷类型情况下二者在数值上有所区别, 但缺陷退火因子仍能在一定程度上反映泄漏电流的退火行为. 分子动力学模拟中采用Stillinger-Weber势函数和Tersoff势函数时缺陷退火因子和泄漏电流退火因子与实验结果一致, 基于Stillinger-Weber势函数的计算结果与实验值更为接近.     

Electron-induced Ti-rich surface segregation on SrTiO3 nanoparticles

Atomic surface structures of nanoparticles are of interest in catalysis and other fields. Aberration-corrected HREM facilitates direct imaging of the surfaces of nanoparticles. A remaining concern of surface imaging arises from beam damage. It is important to identify the intrinsic surface structures and the ones created by electron beam irradiation in TEM. In this study, we performed aberration-corrected HREM and EELS to demonstrate that TiO and bcc type Ti islands form due to intense electron irradiation. The formation of Ti-rich islands is in agreement with previous high temperature annealing experiments on the surfaces of SrTiO₃ single crystals.     

Zeolites are no longer a challenge: Atomic resolution data by Aberration-corrected STEM

Transmission electron microscopy is undoubtedly an indispensable tool for materials characterization, which can currently reach sub-angstrom resolution down to the elemental building blocks of matter, isolated single atoms of most elements. In addition to the phenomenal image resolution, if the material is strong enough, it can be accompanied with chemical information, converting electron microscopy into a unique method for the analysis of a great variety of materials. Unfortunately, extracting all this valuable information is not simple as most materials in one way or another are affected by the strong and localized electron beam. Radiolysis is one kind of reaction between electrons and matter than can cause irreversible structural transformations in our materials. This effect is the predominant factor in zeolites, zeotypes and the majority of molecular sieves. In the present work some results, taken at high voltage (300 kV) and minimizing the exposure to the beam, are presented proving the feasibility of the technique to obtain unprecedented atomic resolution information of different zeolites and microporous solids.     

Quantitative analysis of oxidative DNA damage induced by high-voltage pulsed discharge with cavitation

Pulsed discharge is used for sterilization and disinfection, but the details of the molecular mechanisms remain largely unknown. Since pulsed discharge generates reactive oxygen species (ROS), we analyzed the oxidative DNA damages after pulsed discharge treatment to consider the involvement of ROS in the damaging process. We applied pulsed discharge with cavitation to plasmid DNA molecules and estimated the yields of the damages by agarose gel electrophoresis. The treated DNA contained various oxidative DNA damages, including single and double strand breaks and base lesions. The yields of the damages increased in response to the energy used for pulsed discharge. We also measured the yield of 8-hydroxyguanine (8-OH-G), one of the major oxidative base lesions, in the treated plasmid DNA by mass spectrometry quantitatively and found that the yield of the oxidative base lesion corresponded to the increment of the applied energy. In addition, we observed the involvement of mutM gene, which is responsible for repair of 8-OH-G, in the increased sensitivity of Escherichia coli to pulsed discharge. Therefore, ROS seem to mediate the sterilization ability of pulsed discharge.     

ECONOMICALLY OPTIMAL MARINE RESERVES WITHOUT SPATIAL HETEROGENEITY IN A SIMPLE TWO‐PATCH MODEL

Bioeconomic analyses of spatial fishery models have established that marine reserves can be economically optimal (i.e., maximize sustainable profit) when there is some type of spatial heterogeneity in the system. Analyses of spatially continuous models and models with more than two discrete patches have also demonstrated that marine reserves can be economically optimal even when the system is spatially homogeneous. In this note we analyze a spatially homogeneous two‐patch model and show that marine reserves can be economically optimal in this case as well. The model we study includes the possibility that fishing can damage habitat. In this model, marine reserves are necessary to maximize sustainable profit when dispersal between the patches is sufficiently high and habitat is especially vulnerable to damage.     

超光滑加工精磨过程中损伤层与余量匹配的研究

对超光滑加工散粒研磨工序中采用的三级精磨法,进行了实验研究,通过改进差分化学刻蚀实验测出各级损伤层的厚度,利用损伤层厚度对加工余量匹配进行了优化。研究表明损伤层厚度与砂粒的粒径和压载之积成线性关系,与研磨时长无关;实验测得W28、W10、W5号磨料在实验条件下研磨加工产生的损伤层厚度分别为12.4μm、8.2μm、5.8μm;并根据损伤层厚度提出了加工余量的匹配建议方案。损伤层的相关研究为超光滑加工中提高生产效率以及减少麻点产生几率的研究提供了参考。     

Molecular Characterization of DNA Double Strand Breaks with Tip‐Enhanced Raman Scattering

DNA double strand breaks (DSBs) are deadly lesions that can lead to genetic defects and cell apoptosis. Techniques that directly detect DNA DSBs include scanning electron microscopy, atomic force microscopy (AFM), and fluorescence based approaches. While these techniques can be used to identify DSBs they provide no information on the molecular events occurring at the break. Tip‐enhanced Raman scattering (TERS) can provide molecular information from DNA at the nanoscale and in combination with AFM provides a new way to visualize and characterize the molecular structure of DSBs. DSBs result from cleavage at the 3’‐ and 5’‐bonds of deoxyribose upon exposure to UVC radiation based on the observation of P? O? H and methyl/methylene deformation modes enhanced in the TERS spectra. It is hypothesized that strand fragments are hydrogen‐terminated at the lesion, indicating the action of free radicals during photon exposure.     

Evaluation of radiation damage behavior in polyimide aerogel by infrared camera and photoacoustic spectroscopy

In this work, the optical absorption and thermal properties of polyimide aerogel have been investigated by Infrared Camera, ultraviolet–visible and photoacoustic spectroscopy under low energy proton irradiation. The characterization method of the infrared camera can obtain the optical absorption ratio, and meanwhile get the information of specific heat capacity. Moreover, it can acquire the nature information of damaged area rather than the overall performance. The results show an increase in optical absorption after proton irradiation, which is in good coincidence with Ultraviolet–visible spectroscopy analysis. And the specific heat capacity decreased linearly with proton fluences, which can be attributed to the irradiation damage and carbonization in polyimide aerogel. The Raman spectra suggested the cleavage of chemical bonds and carbonization in polyimide aerogel. This work provides the novel, non-destructive and sensitive methods to characterize irradiation damage of aerogel.