纳米SnO2-TiO2复合材料的氢敏性能及气敏机理

以钛酸正丁酯和SnCl4·5H2O为前驱体,采用溶胶-凝胶法制备了SnO2及Sn/Ti摩尔比为5/1的SnO2-TiO2复合纳米材料,并以此复合材料制备了旁热式气敏传感器,对两者的氢敏性能做了比较,利用第一性原理对其气敏机理进行了理论分析.结果表明,TiO2的掺杂使SnO2导带底部产生了掺杂能级,使SnO2元件电阻下降,并随温度的上升出现先快速下降后缓慢下降2个过程.SnO2-TiO2元件对H2的灵敏性明显优于SnO2元件.吸附H后的SnO2电子态密度变化较小,而SnO2-TiO2的电子态密度则有明显变化,并产生了掺杂能级,导带负移,促进了能带间的电子转移.     

Real-scale DEM simulations on the fault evolution process observed in sandbox experiments

The study of fault structures and stress states in accretionary prisms is important to elucidate the building and releasing of seismic energy as they control the generation of great earthquakes and tsunami. In this paper, we present the evolution process of three-dimensional fault structures performed in sandbox simulations using a discrete element method (DEM). To realize a real-scale sandbox simulation, we developed state-of-the-art techniques in high performance parallel computing for the DEM and performed the world’s largest DEM simulation using up to 1.9 billion particles with a similar grain size as real sand to identify the three-dimensional fault structure. The DEM simulations reproduced the undulation of fault structures, similar to those commonly found in nature. In addition, the characteristic grain motion was observed near the frontal fault before the commencement of the uplift event of the sand bed, which could be a precursor of tectonic events behind accretionary prism formation.     

Experimental investigation and numerical modelling of density-driven segregation in an annular shear cell

Granular materials segregate spontaneously due to differences in particle size, shape, density and flow behaviour. In this paper we experimentally investigate density-difference-driven segregation for a range of density ratios and a range of heavy particle concentrations. The experiments are conducted in an annular shear cell with rotating bumpy bottom that yields an exponential shear profile. The cell is initially filled with a layer of light particles and an upper layer of heavier grains and, on top, a load provides confinement. The segregation process is filmed through the transparent side-wall with a camera, and the evolution of particle concentration in space and time is evaluated by means of post-processing image analysis. We also propose a continuum-approach to model density-driven segregation. We use a segregation-diffusion transport equation, constitutive relations for effective viscosity and friction coefficient, and a segregation velocity analogous to the Stokes’ law. The model, which is validated by comparison with experimental findings, can successfully predict density-driven segregation at different density ratios and volumetric fraction.     

Design and analysis of multi-source multi-area deregulated power system for automatic generation control using quasi-oppositional harmony search algorithm

The present article focuses on the study of automatic generation control (AGC) of a realistic power system having a distinct combination of multi-area multi-source generating units in each control area under deregulated framework. An attempt is made in this paper to integrate reheat thermal, hydro and gas generating unit in a single control area and, then, extended this combination to five control areas. In this work, six reheat thermal, six hydro and three gas generating units are taken into account for the modeling of five-area power system. Some important physical constraints like time delay, governor dead band and generation rate constraint are imposed in the power system dynamics to get an accurate perception of the deregulated AGC subject. The highlighting features of the present work are to model, simulate, optimize and co-relate their inter-related dynamic performances for the purpose of AGC study. For such a complex AGC model, the vital role of the proposed quasi-oppositional harmony search (QOHS) algorithm, as an optimizing tool, is signified while solving the AGC problem in deregulated regime. The simplicity of the structure and acceptability of the responses of the well-known proportional–integral–derivative controller, inherently, enforces to employ in this work. The three classes of extensive deregulated cases (in the presence of load following and physical constraints) are demonstrated by examining the closed loop performance of the studied model. The simulation results show that the designed power system model may be a feasible one and the proposed QOHS algorithm may be a promising optimization technique under these circumstances.     

南京地区粉土的不排水三轴压缩试验

通过全自动三轴仪进行了南京地区粉土的三轴不排水的试验,研究了围压和干密度对应力-应变曲线、孔隙水压力曲线和有效主应力比曲线的影响.试验表明:高围压状态下粉土试样呈现出弱应变软化型,而低围压状态下呈现出应变稳定型;低围压下试样在加载初期产生正孔隙水压力,随后产生负孔隙水压力,其后基本保持稳定;干密度越大,主应力差峰值越大,表现出较大的剪胀性,孔隙水压力易出现负孔隙水压力;干密度值较高时,土样处于密实状态,表现出剪胀特性,有效主应力比-应变曲线近于应变软化型;围压较低、干密度较大时,试样易表现出软化特征,试样出现剪切带破坏,强度明显下降.     

双层石墨烯非对称波导中导模的色散关系

从具有能隙的双层石墨烯载流子所满足的哈密顿量出发,研究了非对称外势产生的波导结构中导模的存在性．在给定不同外势区域波函数的情况下,利用势垒边界处波函数的连续性条件,解析推导出了非对称波导中导模的色散关系,讨论了双层石墨烯的能隙对导模性质的影响．该研究为基于双层石墨烯波导器件的实际应用提供了理论依据．     

一种高增益多频带微带贴片单元的设计

设计了一种由圆、正八边形、矩形组合构成的微带贴片天线,其使用同轴线馈电。采用有限元法对所设计天线的电特性进行了仿真研究。同时也对天线在不同尺寸参数下的性能指标进行了对比分析。结果表明,天线兼具高增益和多频带的特性,在2.25~2.33GHz、3.51~3.7GHz、4.34~4.6GHz频带内,带内回波损耗全部小于-10d B,天线最高增益达到7.37d B,且天线的E面和H面辐射波束较好,半功率波束宽度约是60°;仿真结果证实了所设计的天线具有良好的性能指标。     

CYCLIC DEFORMATION BEHAVIOUR OF Cu SINGLE CRYSTALS ORIENTED FORDOUBLE SLIP Ⅱ. Persistent Slip Bands and Deformation Bands

用光学显微镜和扫描电镜研究了双滑移取向（［０３４］，［１１７］）Ｃｕ单晶循环饱和后的表面形貌，塑性分切应变幅（γｐｌ）低于１０~（－３）时，［０３４］晶体表面上要为主滑移系的驻留滑移带（ＰＳＢｓ）占据，次滑移只在边缘区域启动，其ＰＳＢｓ细窄（＜１μｍ），体积百分数在１％以下．γｐｌ＞１０~（－３）时，次滑移开始在试样的中部启动，同时，表面出现二种贯穿晶体的宏观形变带（ＤＢＩ，ＤＢＩＩ），滑移带在形变带内集中．［１１７］晶体在γｐｌ＝４．４×１０~（－４）时，双滑移现象已十分明显．γｐｌ＞１０~（－３）时，表面也形成与前者相似的形变带．ＤＢＩ的惯习面与主滑移面平行（［０３４］晶体）或接近（［１１７］晶体），ＤＢＩＩ的惯习面则与前者垂直，文章讨论了形变带形成的可能原因．     

Tuning fermi level and band gap in Li4Ti5O12 by doping and vacancy for ultrafast Li+ insertion/extraction

Li₄T_i5O₁₂ (LTO) attracts great interest due to the “zero strain” during cycles but the poor electronic and ionic conductivity critically impede the practical application. Herein, we report a synergy strategy of tuning localized electrons to shift Fermi level and band gap by Mg/Zr co-doping and oxygen vacancy incorporation, which significantly improves Li⁺ and electronic transport. More importantly, the intrinsic synergistic mechanism has been revealed by neutron diffraction, X-ray absorption spectra, and first-principles calculations. The “elastic effect” of lattice induced by Mg/Zr co-doping allows LTO to accommodate more oxygen vacancies to a certain degree without a severe lattice distortion, which largely improves the electronic conductivity. Mg/Zr co-doping and oxygen vacancy incorporation effectively enhanced the dynamic characteristics of LTO electrode, achieving the excellent rate performance (90 mAh/g at 20C) and cycle stability (96.9% after 500 cycles at 10C). First-principles calculations confirm Fermi level shifts to the conduction band, and the band gap becomes narrowed due to the synergistic modulation, and the intrinsic mechanism of the enhanced electronic and Li-ion conductivity is clarified. This study offers some insights into achieving the fast Li⁺ insertion/extraction by tuning the crystal and electronic structure with lattice doping and oxygen vacancy engineering.     

四进正交小波基在图像压缩上的应用

针对四进正交小波不同构造方法及其滤波器组结构的优化问题,提出一种仅改变符号和位置的构造方法。在相同约束条件下设计不同实例,对比图像分解一次后小波系数的稀疏度,基于SPIHT算法进行图像压缩性能对比测试。实验结果表明,与其他结构下的四进小波相比,该方法构造的小波滤波器组结构相对较优,更能提高压缩性能。