Structural optimization and segregation behavior of quaternary alloy nanoparticles based on simulated annealing algorithm

Alloy nanoparticles exhibit higher catalytic activity than monometallic nanoparticles, and their stable structures are of importance to their applications. We employ the simulated annealing algorithm to systematically explore the stable structure and segregation behavior of tetrahexahedral Pt–Pd–Cu–Au quaternary alloy nanoparticles. Three alloy nanoparticles consisting of 443 atoms, 1417 atoms, and 3285 atoms are considered and compared. The preferred positions of atoms in the nanoparticles are analyzed. The simulation results reveal that Cu and Au atoms tend to occupy the surface, Pt atoms preferentially occupy the middle layers, and Pd atoms tend to segregate to the inner layers. Furthermore, Au atoms present stronger surface segregation than Cu ones. This study provides a fundamental understanding on the structural features and segregation phenomena of multi-metallic nanoparticles.     

Compensation of body shake errors in terahertz beam scanning single frequency holography for standoff personnel screening

In the terahertz(THz) band, the inherent shake of the human body may strongly impair the image quality of a beam scanning single frequency holography system for personnel screening. To realize accurate shake compensation in imaging processing, it is quite necessary to develop a high-precision measure system. However, in many cases, different parts of a human body may shake to different extents, resulting in greatly increasing the difficulty in conducting a reasonable measurement of body shake errors for image reconstruction. In this paper, a body shake error compensation algorithm based on the raw data is proposed. To analyze the effect of the body shake on the raw data, a model of echoed signal is rebuilt with considering both the beam scanning mode and the body shake. According to the rebuilt signal model, we derive the body shake error estimated method to compensate for the phase error. Simulation on the reconstruction of point targets with shake errors and proof-of-principle experiments on the human body in the 0.2-THz band are both performed to confirm the effectiveness of the body shake compensation algorithm proposed.     

激光解吸电离技术在线测量苯水相二次有机气溶胶

利用气溶胶激光飞行时间质谱仪激光解吸电离技术开展了苯水相二次有机气溶胶在线测量研究。实验结果表明,苯水相光氧化反应形成的二次有机气溶胶粒子粒径小于1.0μm,激光解吸电离质谱中存在醛类m/z 29(CHO~+)、57(CHOCO~+),羧酸m/z 44(COO~+),苯环m/z 77(C_6H~+_5)、65(C_5H~+_5)和酚类化合物m/z 93(C_6H_5O~+)特征裂解碎片峰。醛类、羧酸和酚类化合物是苯水相SOA粒子的化学组分,各类型组分含量大小关系为:醛类化合羧酸酚类化合物。气溶胶激光飞行时间质谱仪激光解吸电离技术能够用于水相SOA粒子化学组分的在线测量,可用于水相SOA形成机理和过程的研究。     

Cu-bipy-BTC衍生碳基材料的制备及其氧还原电催化性能

制备高效、廉价的氧还原(ORR)电催化剂是燃料电池的技术关键. 本文采用水热法制备出前驱体金属有机骨架化合物（MOF：Cu-bipy-BTC,bipy=2,2′-联吡啶,BTC=均苯三甲酸）后,再高温煅烧得到碳基材料MOF-800. 采用扫描电镜、X射线衍射、红外光谱、氮气吸附/脱附等温线和X射线光电子谱表征了材料的形貌和结构特征;采用线性扫描伏安曲线、i-t曲线等考察了材料的氧还原催化性能. 结果表明,与前驱体Cu-bipy-BTC相比,MOF-800含有大量的微孔(0.5 ~ 1.3 nm),为铜、氮掺杂多孔碳. MOF-800的电荷转移阻抗为10.6 Ω,比Cu-bipy-BTC降低了97.2%,具有优良的导电性. MOF-800具有优异的ORR催化性能,其起始电位约为-0.04 V(vs. Ag/AgCl),其电子转移数接近4. 铜、氮掺杂的多孔碳结构导电性好,高含量的吡啶氮、吡咯氮和石墨氮提供了大量催化活性位点(C-N, Cu-N_x),是MOF-800具有高氧还原电催化性能的主要原因. 本研究可为煅烧Cu-bipy-BTC制备碳基材料用于燃料电池修饰阴极提供技术支撑与理论依据.     

极坐标激光直写系统原点定位的实验研究

分析了旋转线性光栅法对准光轴与旋转机械轴中心的理论准确度,实验研究了极坐标激光直写系统的原点定位.在极坐标激光直写系统下进行了圆环线条写入实验,得出了原点定位的准确度,原点定位准确度优于0.5 μm,实验与理论定位准确度基本一致.     

用157 nm激光制作的光子晶体光纤法布里-珀罗传感器

157nm准分子激光用于微加工具有单光子能量高,峰值功率高,材料吸收系数高,分辨率高等优点。利用157nm激光微加工的方法,在光子晶体光纤上融切出微小矩形孔,从而构成腔长为45.6μm的微光纤法布里-珀罗干涉腔,得到的干涉条纹平滑,衬比度约为26dB,并从激光与石英材料的相互作用上分析了形成较好干涉条纹的原因。把这种微腔应用于应变测量,在550μm范围内,腔长增量相对于应变的灵敏度为0.32nm/μm,线形度达0.9994。实验证明该微腔对温度不敏感,800℃范围内腔长变化仅20nm。157nm准分子激光加工光纤法布里-珀罗腔方法简单,一次成型,具有较高的加工效率和精度,有望实现光纤法布里-珀罗腔的规模化批量制造,具有较好的应用前景。     

A Darboux Transformation for the Coupled Kadomtsev--Petviashvili Equation

The coupled Kadomtsev-Petviashvili equation is considered. It is shown that a Darboux transformation can be constructed by means of an elementary approach.     

Microstructure and Optical Properties of AgxO Prepared by Direct-Current Magnetron-Sputtering Method

Two series of AgxO films are prepared on glass substrates by dc magnetron-sputtering method at room temperature and 90℃ under different oxygen to argon gas ratio （OAR） conditions. The mierostrueture is investigated by XRD and SEM in order to obtain the information on the component evolution of AgO＋Ag2O to Ag2O. Its optical properties are investigated by reflectance and absorption spectroscopy to extract the information on metallic and dielectric behaviour evolution of Ag2O, AgO and silver particles and the interband transition. The results indicate that the AgxO film prepared at room temperature is mainly made up of AgO and Ag2 O clusters while Ag2O is the primary component of AgxO prepared at 90℃. The AgxO film mainly consisting of the primary component shows indirect interband transition structure occurring at 2.89eV. Combination of increasing OAR and substrate temperature is an effective method to lower the threshold of thermal decomposition temperature of AgxO and to deal with the bottleneck of short-wavelength optical and magneto-optieM storage.     

两球形颗粒间横向毛细力的格子Boltzmann研究

采用以Shan-Chen多组分模型为基础的格子Boltzmann-伪固体模型对两颗粒间的浮体和浸润横向毛细力展开数值模拟研究,其中流体-固体间的相互作用及颗粒润湿性质在介观层次上采用简单形式得以充分考虑．三维测试表明,与已有理论解相比,成功再现了横向毛细力与颗粒间距的“1/L”关系,并确认了浸润横向毛细力与表面张力间的线性关系．这表明可进一步应用该模型研究横向毛细力作用下的颗粒自聚集等现象.     

Study of a millimeter-wave squint indirect holographic algorithm suitable for imaging with large field-of-view

In this paper a millimeter-wave （MMW） squint indirect holographic method is presented, which is suitable for imaging with a large field-of-view. The proposed system employs the squint operation mode to remove the background and twin- image interferences, which achieves a similar effect to off-axis holography but leaves out the large-aperture quasi-optical component. The translational scanning manner enables a large field of view and ensures the image uniformity, which is difficult to realize in off-axis holography. In addition, a corresponding imaging algorithm for the presented scheme is developed to reconstruct the image from the recorded hologram. Some imaging results on typical objects, obtained with electromagnetic simulation, demonstrate good performance of the imaging scheme and validate the effectiveness of the image reconstruction algorithm.