Field—ion microscopy observation of single—walled carbon nanotubes

Field-ion microscopy(FIM),a tool for surface analysis with atomic resolution,has been employed to observe the end structure of single-walled carbon nanotubes(SWCNTs).FIM images revealed the existence of open SWCNT ends,Amorphous carbon atoms were also observed to occur around SWCNTs and traditional field evaporation failed to remove them.Heat treatment was found to be efficacious in altering the end structures of SWCNT bundles.Carbon and oxygen atoms released from heated tungsten filament are believed to be responsible for the decoration imposed on the SWCNT ends.     

Atomic force microscopy investigation of growth process of organic TCNQ aggregates on SiO2 and mica substrates

<正>Deposition patterns of tetracyanoquinodimethane(TCNQ) molecules on different surfaces are investigated by atomic force microscopy.A homemade physical vapour deposition system allows the better control of molecule deposition. Taking advantage of this system,we investigate TCNQ thin film growth on both SiO_2 and mica surfaces.It is found that dense island patterns form at a high deposition rate,and a unique seahorse-like pattern forms at a low deposition rate.Growth patterns on different substrates suggest that the fractal pattern formation is dominated by molecule-molecule interaction.Finally,a phenomenal "two-branch" model is proposed to simulate the growth process of the seahorse pattern.     

δ势垒对多臂量子环中持续电流的影响

提出了中臂弯曲的多臂量子环模型,且是上臂最短和下臂最长的不等臂量子环.研究发现：总磁通为零时,持续电流随半导体环增大发生非周期性振荡,并与电极的磁矩方向及隧穿电子的自旋方向相关,下臂因为最长而获得最小的平均持续电流.AB磁通增强时,持续电流会发生周期性振荡,各臂之间明显出现相互制约的现象.各臂持续电流之间的差异与臂长和磁通分布相关,Rashba自旋轨道耦合具有改变持续电流相位和相位差的效应.在一定条件下,两种波函数所对应的持续电流是可分离的.     

A phase field model for vesicle–substrate adhesion

In this paper, a phase field model is developed for vesicle adhesion involving complex substrate and vesicle geometries. The model takes into account an adhesion potential that depends on the distance of vesicle to the substrate. A variational problem is solved in a 3D computational domain by minimizing the contribution of bending elastic energy and the adhesion energy under the constraints of total surface area and volume, described via a phase function. An adaptive finite element method is used to efficiently compute the numerical solutions of the model. The computational results are validated through comparison of several axisymmetric shapes with the sharp-interface ODE solution. Moreover, we compute shapes for non-axisymmetric situations to support the observation that concave substrates favor adhesion.     

A roe-average algorithm for a granular-gas model with non-conservative terms

A Roe-average algorithm has been derived for a granular-gas model, proposed by Goldshtein and Shapiro [Goldshtein, Shapiro, Mechanics of collisional motion of granular materials: Part 1. General hydrodynamic equations, J. Fluid Mech. 282 (1995) 75–114], which contains non-conservative terms in the Euler-like hyperbolic governing equations apart from sink terms, which arise from inelastic collision of granules and are present only in the energy equation. The non-conservative terms introduce non-isentropic effects in acoustic-wave propagation within granular media and they also contribute to the Rankine–Hugoniot relations across a discontinuity. A Roe-average algorithm, based on the same granular-gas model, was derived in the literature [V. Kamenetsky, A. Goldshtein, M. Shapiro, D. Degani, Evolution of a shock wave in a granular gas, Phys. Fluids, 12 (2000) 3036–3049] which then required the implementation of a shock-fitting technique at a discontinuity. In the present work, Roe-averaged variables have been obtained from the Rankine–Hugoniot jump relations and the non-conservative terms have been incorporated in the numerical flux formula consistent with upwind principles associated with the granular speed of sound. Results for unsteady one-dimensional granular flows, colliding with a wall, demonstrate the capability of the proposed algorithm to capture strong shocks in addition to flow features not found in molecular gases, such as a fluidized region downstream of the shock and a compacted solid-block region adjacent to the wall.     

混沌时间序列的局域高阶Volterra滤波器多步预测模型

依据相空间邻近轨道演化相似性特点建立训练模式,提出了基于自适应高阶非线性Volterra滤波器（HONFIR）的混沌时间序列多步预测模型（MSP-HONFIR）;通过定义距离相似度、趋势相似度来衡量轨道演化相似度,提出了混沌吸引子邻近轨道判别的新方法;从模型训练充分性角度出发探讨了MSP-HONFIR滤波器模型训练集规模控制的依据.数值研究表明MSP-HONFIR滤波器模型的多步预测性能优于原有HONFIR滤波器模型. 关键词： 混沌 非线性自适应预测 Volterra滤波器模型 训练模式     

利用Hyperion数据进行环境星HSI红边参数真实性检验

针对我国新发射运行的HJ-1A星HSI数据,利用高光谱分辨率的Hyperion数据进行了HJ-1A星HSI的光谱模拟,提取了红谷位置、红边位置、红边斜率和红边振幅等4个主要的红边参数,对真实与模拟环境星HSI数据的红边参数进行了对比分析,从而以Hyperion数据为参照检验了环境星HSI红边参数的真实性。研究结果显示,环境星HSI与模拟HSI的红边范围光谱反射率平均相关系数为0.946,标准差为0.011,为极显著相关,两种数据在红边范围内的光谱反射率变化高度一致;4个红边参数的相关系数分别为0.414,0.543,0.808和0.802,并且随植被覆盖度的变化呈现出明显的规律性,模拟与真实红边参数差值标准差分别为5.75,1.86,5.7e-4和0.024,认为环境星HSI的红边参数可以较好反映该区域植被变化所造成的红边光谱特征差异。     

红外辐射在水雾中衰减计算的修正方法研究

水雾系统对红外光谱有着强烈的衰减作用,因此在军事目标的各种制导对抗中被予以高度的关注。以Mie散射理论为基础,分析了粒子对红外光谱前向散射的聚集特性,定义了近前向散射比,并确定了在应用朗伯比尔定律时需修正的粒子尺度和散射半角的范围。通过大量计算发现,单独将粒子尺度和散射半角的乘积作为独立变量计算的视消光系数不够精确。在中远红外波段,前向散射附近的小角度内散射强度积分与粒子尺度和散射角都成正比,若红外波长为定值,则与粒子半径成正比。最后根据前向散射规律给出了两个不单独以x.θ为变量的经验计算公式,使得对水雾消光的修正计算更加简便精确。     

The nonlinear theory of slow-wave electron cyclotron masers with inclusion of the beam velocity spread

The nonlinear theory of slow-wave electron cyclotron masers (ECM) with an initially straight electron beam is developed. The evolution equation of the nonlinear beam electron energy is derived. The numerical studies of the slow-wave ECM efficiency with inclusion of Gaussian beam velocity spread are presented. It is shown that the velocity spread reduces the interaction efficiency.     

Optimization of direct modulation rate for circular microlasers by adjusting mode Q factor

Semiconductor microcircular lasers have been investigated as potential light sources for photonic integrated circuits and optical interconnections for more than two decades. However, the direct modulation bandwidths of the circular microlasers remain a challenge, especially when being compared with other microlasers, such as photonic crystal lasers. In this paper, microcircular lasers connected to an output waveguide are investigated for high‐speed direct modulation with optimized mode Q factors. Small signal modulation with a resonance frequency of f_R = 12.5 GHz is realized for a AlGaInAs/InP circular microlaser with a radius of 10 µm at 290 K. Furthermore, clear eye diagrams are observed at 12.5 Gbit/s for a 15‐µm radius circular microlaser with f_R = 6.9 GHz.