氧化硅层中的锗纳米晶体团簇量子点

采用氧化和析出的方法在氧化硅中凝聚生成锗纳米晶体量子点结构. 其形成的锗晶体团簇没有突出的棱角和支晶结构，锗晶体团簇的轮廓较圆混，故可以用球形量子点模型来模拟实际的锗晶体团簇. 对比了在长时间退火氧化条件下和在短时间退火用激光照射氧化条件下所生成的锗纳米晶体结构的PL光谱和对应的锗纳米晶体团簇的尺寸分布. 短时间退火氧化条件下生成的锗纳米晶体较小(3.28—3.96nm)，长时间退火用激光照射氧化条件下所生成的锗纳米晶体较大(3.72—4.98nm)；其分布结构显示某些尺寸的锗纳米晶体团簇较稳定，适当的氧化条件可以得到尺寸分布范围较窄的锗纳米晶体团簇. 用量子点受限模型计算了锗纳米晶体团簇的能隙结构，用Monte Carlo方法模拟了PL光谱和对应的锗纳米晶体团簇的尺寸分布，分别与实验结果符合较好. 关键词： 锗晶体团簇 纳米晶体 量子点 激光照射     

C36团簇自组装的分子动力学研究

提出了利用C36团簇在气相条件下自组装制备新纳米团簇的设想，并利用分子动力学方法模 拟了包括真实氦气氛作用的碳团簇生长过程，发现环境气体温度是影响最后所生成的团簇结 构的关键因素：C36团簇在1000?K到2000?K的温度范围内，自组装形成保持C36线径特征的 蚕茧状新纳米团簇；在高于2000?K的温度下，最后形成的团簇趋于球状. 关键词： 分子动力学模拟 纳米碳团簇     

一种寻找团簇异构体的准动力学方法

建立了一套普遍适用的寻找团簇异构体的准动力学方法,该方法能够迅速给出在一般气相生长条件下形成概率较大的异构体.用该方法得到了C21的异构体谱,并采用分子动力学方法模拟了21个自由的碳原子在氦气氛中形成稳定团簇的过程,表明动力学过程中形成概率较大的异构体都已包含在该方法所得到的异构体谱中.所得到的C21最稳定结构的势能远低于采用遗传算法所得到的结果(Chem. Phys. Lett. 364 213,2002). 关键词： 团簇 异构体 最低势能 全局优化     

一种寻找团簇异构体的准动力学方法

建立了一套普遍适用的寻找团簇异构体的准动力学方法，该方法能够迅速给出在一般气相生长条件下形成概率较大的异构体.用该方法得到了C21的异构体谱，并采用分子动力学方法模拟了21个自由的碳原子在氦气氛中形成稳定团簇的过程，表明动力学过程中形成概率较大的异构体都已包含在该方法所得到的异构体谱中.所得到的C21最稳定结构的势能远低于采用遗传算法所得到的结果(Chem. Phys. Lett. 364 213，2002).     

纳米铜团簇在常温和升温过程中能量特征的分子动力学研究

采用分子动力学方法和F-S多体势函数，模拟研究纳米铜团簇常温下能量特征及其在升温直到熔化过程中的变化，确定了常温下纳米铜团簇的表面原子厚度和表面能，给出在不同温度下纳米铜团簇能量大小分布比例和能量的概率密度，细致描述了团簇升温过程团簇内部原子和表面原子之间不同的变化特征. 关键词： 铜团簇 分子动力学 能量特征 温度     

用扫描隧道显微镜操纵Cu亚表面自间隙原子

在超高真空环境下使用扫描隧道显微镜研究了吸附有双甘氨肽分子的Cu(001)表面.在一定的 偏压条件下，针尖在该表面扫描后会形成纳米尺度的Cu团簇，这些团簇可以根据意愿排列成 字母或图形.团簇的高度同偏压、隧道电流以及时间等条件有密切关系.在室温下可以稳定存 在的团簇为制造纳米器件提供了技术上的可能性.实验结果表明，形成团簇的Cu原子不是来 自Cu衬底表面或是针尖.化学吸附在Cu表面的双甘氨肽分子，受到隧道电场的作用会在Cu表 面形成张应变场，Cu亚表面自间隙原子在张应变场作用下迁移到表面是形成团簇的原因. 关键词： 扫描隧道显微镜 纳米尺度Cu团簇 自间隙原子     

Si(111)-(7×7)衬底上合成有序的IV族金属铅团簇阵列

文章作者在Si(111)(7×7)衬底上合成出位于同一主族的Pb的全同纳米团簇有序阵列.有趣的是,当衬底温度相对于最佳的生长温度范围发生微小的偏离时,Pb纳米团簇很容易转变为其他结构的团簇.结合实验结果和第一性原理总能量计算,文章作者揭示了几种Pb团簇的原子结构.这些结构都是以表面Pb和Si原子互换导致的混合模型为中心的衍生结构.Pb/Si(111)体系的这种边缘性质为研究表面幻数团簇的合成、分解等动力学过程提供了重要信息.     

分散良好的二氧化锡纳米团簇制备以及离子液体诱导金属绝缘相变调控研究（英文）

本文利用气相纳米团簇设备实现SnO_2纳米团簇的可控制备.高分辨透射电子显微镜用来分析SnO_2纳米团簇形貌及微观结构,结果表明制备的SnO_2纳米团簇分散良好,尺寸均匀(5～7 nm).通过门电压控制的离子液体实现对SnO_2纳米团簇金属绝缘转变的调控.结合第一性原理,从氧空位诱导电子占据角度系统分析了相应的调控机制.     

纳米团簇熔化过程的分子动力学模拟

本文采用分子动力学结合嵌入原子多体势,模拟了不同半径的Ni纳米团簇的升温熔化过程,研究团簇尺寸对熔点和表面能的影响.模拟结果表明:团簇的熔点显著低于体材料的熔点.团簇熔化的过程首先是在团簇的表面出现预熔,然后向团簇内部扩展,直到整个团簇完全熔为液态.在模拟的纳米尺度范围内,团簇的熔点与团簇尺寸基本成线性关系.团簇的表面能随着团簇尺寸的增大而减小,而且表面能均高于体材料的表面能.     

碱金属钠原子修饰硅原子团簇的结构及储氢性能研究

提出碱金属钠原子修饰笼形Si_6团簇的结构模型,采用密度泛函理论(DFT)研究钠原子修饰笼形Si_6团簇的结构及储氢性能.研究结果表明,氢分子与笼形Si_6团簇表面相互作用很弱,氢分子在其表面容易脱附.采用钠原子修饰笼形Si_6团簇后可有效避免氢分子的脱附,并且钠原子在笼形Si_6团簇的表面不发生团聚,有利于氢分子在其表面吸附和循环利用.研究发现在两个钠原子修饰笼形Si_6团簇的结构中,每个钠原子可以有效吸附六个氢分子.计算得到Na2Si_6团簇结构储氢的质量分数高达10.08 wt%,且氢分子的平均吸附能约为0.837 kcal/mol.可见,实现钠原子修饰笼形Si_6团簇结构在常温常压条件下储氢是有可能的.     

基于守恒高阶模型的动态交通分配建模与仿真

针对路网中的动态交通分配问题,采用高阶守恒模型（CHO）进行建模与数值研究,并推广高阶守恒模型二进二出路口的Riemann问题;同时将高阶守恒模型与动态网络加载（DNL）模型相结合,通过变分不等式对动态网络加载模型进行分析.数值模拟采用一阶有限体积法求解高阶守恒模型,同时采用梯度下降方法迭代求解动态网络加载模型的变分不等式问题,最终以动态用户最优条件为目标实现分配均衡.数值结果表明CHO模型与DNL模型结合解决动态交通分配问题是可行的,对传统模型的研究有一定的指导意义.     

具有大范围运动和非线性变形的空间柔性梁在非惯性坐标系下的动力学分析

本文针对具有大范围运动和非线性变形的空间柔性梁, 导出其在运动规律已知的非惯性坐标系下的动力学方程. 通过计算分析, 发现在本文精确模型下, 其各矩阵项较原来的一次耦合模型增加了两类耦合项. 通过仿真研究, 发现由于这两类耦合项的作用造成了附加刚度项K₁、动力刚度项K_d 的变化, 而刚度项对结构的动力学特性具有较大的影响.     

Dynamic analysis for a pair of spur gears with translational motion due to bearing deformation

In this study, the dynamic response of a pair of spur gears is analyzed when the gear set has translational motion due to bearing deformation. A new dynamic model for the gear set, considering translational motion, is proposed, in which the distance between the centers of a pinion and a gear varies with time. Therefore, the proposed model regards the pressure angle and the contact ratio as time-varying variables, while the previous model regards them as constants. After deriving nonlinear equations of motion for the gear set, the dynamic responses are computed by applying the Newmark time integration method. This paper claims that the new model produces more accurate dynamic responses in comparison to those of the previous model. Some dynamic response differences between the new and previous models are demonstrated, and the effects of damping and stiffness upon the dynamic responses are also investigated.     

Dynamic analysis of clamp band joint system subjected to axial vibration

Clamp band joints are commonly used for connecting circular components together in industry. Some of the systems jointed by clamp band are subjected to dynamic load. However, very little research on the dynamic characteristics for this kind of joint can be found in the literature. In this paper, a dynamic model for clamp band joint system is developed. Contact and frictional slip between the components are accommodated in this model. Nonlinear finite element analysis is conducted to identify the model parameters. Then static experiments are carried out on a scaled model of the clamp band joint to validate the joint model. Finally, the model is adopted to study the dynamic characteristics of the clamp band joint system subjected to axial harmonic excitation and the effects of the wedge angle of the clamp band joint and the preload on the response. The model proposed in this paper can represent the nonlinearity of the clamp band joint and be used conveniently to investigate the effects of the structural and loading parameters on the dynamic characteristics of this type of joint system.     

钢纤维混凝土板在冲击与爆炸荷载下的K&C模型

钢纤维混凝土(Steel fiber reinforced concrete,SFRC)具有优异的延性、韧性及能量吸收能力,被广泛应用于各类防护结构。K&C模型已成为研究普通混凝土构件动力响应的常用材料模型,但仍无法准确表征SFRC的动力特性。为了提高K&C模型在冲击及爆炸荷载作用下预测SFRC板动力响应的能力,对K&C模型进行了改进:基于大量三轴压缩实验数据,建立了新的失效强度面参数模型;采用反复试验法,建立了新的损伤演化模型,并校准了拉、压损伤参数;基于大量高应变率下SFRC的单轴压缩实验数据,建立了新的受压动力增强因子模型。通过LS-DYNA显式有限元动力分析软件模拟了SFRC板的动力响应,模拟结果验证了上述改进的有效性与可靠性。     

A new approach to design a control system for a FGR furnace using the combination of the CFD and linear system identification techniques

A new approach to design control systems for an industrial furnace with flue gas recirculation (FGR) is presented. To facilitate the control system design, a linear dynamic model is needed for the furnace. Full-scale computational fluid dynamics (CFD) simulations are used to generate the required small signal input and output data sets. Subsequently, a least squares based system identification technique is used to obtained the linear dynamic models. After model validation, feedback controller is designed based on these linear dynamic models. Finally, the performance of the designed closed-loop control system is also evaluated using both linear dynamic model and full-scale nonlinear CFD model. The comparison shows that the control system designed using the proposed approach can minimize the deviation of nitric oxides (NO) emission from the design point by minimize the dynamic NO formation, hence to prevent any excessive NO formation in the combustion process when the system subjects to disturbances.     

Dynamic characteristics of launch vehicle and spacecraft connected by clamp band

Spacecraft is usually fastened to the launch vehicle by clamp band in the aerospace industry. The application of clamp band joint brings local stiffness variation to the launch vehicle and spacecraft (LV/SC) system and affects the dynamic characteristics of the system. In this paper, the dynamic responses of the LV/SC system to the vibration and impact excitations were studied, where the effect of the clamp band joint was taken into account. Firstly, the mathematical model of the axial stiffness of the clamp band joint was derived. In the model, contact and slippage between the components were accommodated. Then the stiffness model was employed to construct the coupling dynamic model for the LV/SC system using the finite element software ANSYS. Finally, modal analysis and response analysis were carried out on the coupling dynamic model to investigate the dynamic characteristics of the LV/SC system; the simulation results were compared with those based on the dynamic model where the launch vehicle and the spacecraft were considered to be fixed together to explore the effect of the clamp band joint on the LV/SC system.     

Protein backbone dynamics from N-HN dipolar couplings in partially aligned systems: a comparison of motional models in the presence of structural noise

Residual dipolar couplings (RDCs) provide excellent probes for the exploration of dynamics in biomolecules on biologically relevant time-scales. Applying geometric motional models in combination with high-resolution structures to fit experimental RDCs allows the extraction of local dynamic amplitudes of peptide planes in proteins using only a limited number of data points. Here we compare the behaviour of three simple and intuitive dynamic modes: the Gaussian axial fluctuation model (1D-GAF), the two-site jump model, and a model supposing axially symmetric motion about a mean orientation. The requirement of a structural model makes this kind of methodology potentially very sensitive to structural imprecision. Numerical simulations of RDC dynamic averaging under different regimes show that the anisotropic motional models are more geometrically stringent than the axially symmetric model making it more difficult to alias structural noise as artificial dynamic amplitudes. Indeed, it appears that the model extracts accurate motional amplitudes even in the presence of significant structural error. We also show that a two-site jump model, also assuming the (alpha)C(i-1)-(alpha)C(i) as rotation axis, can only be distinguished from the previously developed GAF model beyond amplitude/jumps of around 40 degrees. The importance of appropriate estimation of the molecular alignment tensor for determination of local motional amplitudes is also illustrated here. We demonstrate a systematic scaling of extracted dynamic amplitudes if a static structure is assumed when determining the alignment tensor from dynamically averaged RDCs. As an example an artificial increase of 0.14 (0.85 compared to the expected 0.71) is observed in the extracted S2 if a pervasive 20 degrees GAF motion is present that is ignored in the tensor determination. Finally we apply a combined approach using the most appropriate motional model, to complete the analysis of dynamic motions from protein G.     

A biologically inspired spatiotemporal saliency attention model based on entropy value

A biologically inspired spatiotemporal saliency attention model based on entropy value is proposed in this paper. This model includes a dynamic attention phase and a static attention phase. In the dynamic attention phase, low-level visual features are extracted from current and some previous frames. Every feature map is resized into some different sizes. The feature maps in same size and same feature for all the frames are used to calculate the entropy value map. All the entropy maps are normalized and are fused into a dynamic saliency map. In the static attention phase, same features are extracted and form multi-scale feature maps by center-surround differences in current frame, and then those feature maps are transformed into conspicuity maps, which are linearly combined into a static saliency map. Our model decides salient regions based on a spatiotemporal saliency map which is generated by integration of the dynamic and the static saliency map. Experimental results indicate that: when there is noise among the frames or there is change of illumination among the frames, our model is excellent to Shi's model and Marat's model; when the moving objects do not belong to the static salient regions, our model is better than Ban's model.     

动态随机最短路径算法研究

静态最短路径问题已经得到很好解决, 然而现实中的网络大多具有动态性和随机性. 网络弧和节点的状态及耗费不仅具有不确定性且相互关联, 弧和节点的耗费都服从一定的概率分布, 因此把最短路径问题看作是一个动态随机优化问题更具有一般性. 文中分析了网络弧和节点的动态随机特性及其相互关系, 定义了动态随机最短路径; 给出了动态随机最短路径优化数学模型, 提出了一种动态随机最短路径遗传算法; 针对网络的拓扑特性设计了高效合理的遗传算子. 实验结果表明, 文中提出的模型和算法能有效地解决动态随机最短路径问题, 可以运用到交通、通信等网络的网络流随机优化问题中.