Detection of subsurface defects of fused silica optics by confocal scattering microscopy

<正>A non-destructive technique for subsurface measurements is proposed by combining light scattering method with laser confocal scanning tomography.The depth and distribution of subsurface defect layers are represented in term of scattered light intensity pattern,and three types of fused silica specimens are fabricated by different grinding and polishing processes to verify the validity and effectiveness.By using the direct measurement method with such technique,micron-scale cracks and scratches can be easily distinguished,and the instructional subsurface defect depths of 55,15,and 4μm are given in real time allowing for an in-process observation and detection.     

不同温度下二氧化硅纳米管的结构和振动性质的分子动力学模拟

采用三种势能模型, 利用分子动力学模拟研究了在300～1600 K内4、6和8元环的二氧化硅纳米管. 结果表明,三种纳米管的末端环的稳定性随温度的升高而降低. 通过振动态密度考察了二氧化硅纳米管的有效振动特性. 以及不同温度下二氧化硅纳米管的红外光谱.     

弹性撞击速度的激光分束测量技术

 研制了一个激光分束测速系统。它由一台4mW He-Ne激光器，一个将单束激光分成10束相互平行的等间距（间距为5 mm）激光的分光器，一个高灵敏度、工作状态自检、可进行波形合成、10路接受、一路输出的光电接收转换装置，一台数字存贮示波器，以及微型计算机组成。可进行弹性撞击速度的测量。     

An experimental and kinetic modeling study of a premixed nitromethane flame at low pressure

A premixed nitromethane/oxygen/argon flame at low pressure (4.67 kPa) has been investigated using tunable vacuum ultraviolet (VUV) photoionization and molecular-beam mass spectrometry. About 30 flame species including hydrocarbons, oxygenated and nitrogenous intermediates have been identified by measurements of photoionization efficiency spectra. Mole fraction profiles of the flame species have been determined by scanning burner position at some selected photon energies. The results indicate that N₂ and NO are the major nitrogenous products in the nitromethane flame. Compared with previous studies on nitromethane combustion, a number of unreported intermediates, including C₃H₄, C₄H₆, C₄H₈, C₂H₂O, C₂H₄O, CH₃CN, H₂CNHO, C₃H₃N and C₃H₇N, are observed in this work. Based on our experimental results and previous modeling studies, a detailed oxidation mechanism including 69 species and 314 reactions has been developed to simulate the flame structure. Despite some small discrepancies, the predictions by the modeling study are in reasonable agreement with the experimental results.     

Universal spin-dependent variable range hopping in wide-band-gap oxide ferromagnetic semiconductors

This paper proposes a universal spin-dependent variable range hopping theoretical model to describe various experimental transport phenomena observed in wide-band-gap oxide ferromagnetic semiconductors with high transition metal concentration. The contributions of the `hard gap' energy, Coulomb interaction, correlation energy, and exchange interaction to the electrical transport are considered in the universal variable range hopping theoretical model. By fitting the temperature and magnetic field dependence of the experimental sheet resistance to the theoretical model, the spin polarization ratio of electrical carriers near the Fermi level and interactions between electrical carriers can be obtained.     

Coherent control of negative refraction based on local-field enhancement and dynamically induced chirality

This paper studies the electromagnetic response of a coherently driven dense atomic ensemble to a weak probe.It finds that negative refraction with little absorption may be achieved in the presence of local-field enhanced interaction and dynamically induced chirality.The complex refractive index governing the probe refraction and absorption depends critically on the atomic density,the steady population distribution,the coherence dephasings,and the frequency detunings,and is also sensitive to the phase of the driving field because the photonic transition paths form a close loop.Thus,it can periodically tune the refractive index at a fixed frequency from negative to positive values and vice versa just by modulating the driving phase.Moreover,the optimal negative refraction is found to be near the probe magnetic resonance,which then requires the electric fields of the probe and the drive being on two-photon resonance due to the dipole synchronisation.     

铁电-铁磁多铁性脉冲形成线特性

对"多铁性"脉冲形成线输出特性进行了研究。利用镍锌铁氧体-钛酸钡陶瓷复合多铁性材料制作了脉冲形成线。在不同的磁回路条件下得到了不同脉冲宽度的电脉冲方波,其中以高磁导率材料组合成的闭合磁回路得到了脉冲宽度约201 ns的方波输出。推算出脉冲形成线的相对介电常数接近2 000,相对磁导率大于1.4。基于有效磁导率的概念,分析了多铁性脉冲形成线几何构型对脉冲输出特性的影响。分析表明:平板状"多铁性脉冲形成线"的有效磁导率不仅取决于平板介质的磁导率,还取决于周围介质的磁导率,因而有效磁导率通常较小,其输出表现出明显的铁电性而只有"弱"的铁磁性;相比之下,同轴结构的"多铁性脉冲形成线"具有更高的有效磁导率,其输出可同时表现出强的铁电性和铁磁性,即更明显的"多铁性"。"多铁性脉冲形成线"有可能在紧凑型脉冲功率系统中获得应用。     

Discrete gap breathers in a two-dimensional diatomic face-centered square lattice

In this paper we study the existence and stability of two-dimensional discrete gap breathers in a two-dimensional diatomic face-centered square lattice consisting of alternating light and heavy atoms, with on-site potential and coupling potential. This study is focused on two-dimensional breathers with their frequency in the gap that separates the acoustic and optical bands of the phonon spectrum. We demonstrate the possibility of the existence of two-dimensional gap breathers by using a numerical method. Six types of two-dimensional gap breathers are obtained, i.e., symmetric, mirror-symmetric and asymmetric, whether the center of the breather is on a light or a heavy atom. The difference between one-dimensional discrete gap breathers and two-dimensional discrete gap breathers is also discussed. We use Aubry's theory to analyze the stability of discrete gap breathers in the two-dimensional diatomic face-centered square lattice.     

基于多层膜技术的硬X射线Laue透镜衍射效率的理论研究

采用耦合波理论分析了X射线在多层膜Laue透镜中的传播,选择Cu的Kα线作X射线光源,计算了多层膜Laue透镜的衍射效率.材料为WSi2/Si,最外层宽度为10 nm,深度为8 500 nm的多层膜Laue透镜,倾斜情况下外层区域局部光栅的衍射效率可达59%,理论上证明了多层膜Laue透镜是实现X射线聚焦的有效手段.     

Thermodynamics, Conformation and Active Sites of the Binding of Zn–Nd Hetero-bimetallic Schiff Base to Bovine Serum Albumin

The interactions between N,N′-di(2-hydroxy-3-methyoxy-phenyl-1-methylene)-o-phenyldiamine-mone Zn(II), Nd(III) nitrate (2LZnNd) and bovine serum albumin (BSA) was investigated by various spectroscopic techniques under physiological conditions. It was proved that the fluorescence quenching of BSA by 2LZnNb was a result of the formation of a non-fluorescent complex with the binding constants of 3.15 × 10⁵; 2.72 × 10⁵ and 2.44 × 10⁵ M^–1 at 298 K, 304 K and 310 K, respectively. A marked increase in the fluorescence anisotropy in the proteinous environments indicates that BSA introduces motional restriction on the drug molecule. The corresponding thermodynamics parameters ΔH and ΔS were calculated to be –16.36 kJ mol^–1 and 43.48 J mol^–1 K^–1 via van’t Hoff equation. Moreover, the competitive probes experiment revealed that the binding location of 2LZnNb to BSA is in the hydrophobic pocket of site II. The effect of 2LZnNb on the conformation of BSA has been analyzed by means of CD spectrum and three-dimensional fluorescence spectra. The results indicate that the conformation of BSA molecules was changed in the presence of 2LZnNb Schiff base.