“Atomistic”, Quantum and Ballistic Effects in Nanoscale MOSFETs

In this paper we describe the effects of quantum confinement and ballistic transport in the channel on the dispersion of threshold voltage due to the discrete distribution of dopants. To this aim, a recently developed 3D Poisson-Schrödinger solver is used, along with a 2D solver of ballistic transport. The Schrödinger equation is solved with density functional theory, in the local density approximation. Results on statistically meaningful ensembles of devices show that both ballistic transport and quantum confinement lead to an increase of threshold voltage dispersion.     

融合多注意力机制与PointRCNN的三维点云目标检测

针对三维不规则的点云格式和密度不均匀的问题,提出了一种融合多注意力机制与PointRCNN网络用于三维点云目标检测。本实验主要对PointRCNN两阶段网络分别进行改进,首先,把通道注意力与空间注意力机制串行通过调节输入到第一阶段各网络层的分布,批量归一化进一步快速识别三维特征;其次,引入交叉位置注意力机制到第二阶段网络为了避免交叉路径出现位置偏差,从而进一步精细化三维目标位置以进行特征提取。在KITTI数据集上实验结果表明：相比于PointRCNN检测网络,改进的网络在小汽车和行人测试上平均均值精度(mAP)分别提高了1.2%、1.9%。因此改进的方法在解决了点云格式不规则和密度不均匀问题的同时还保证了检测精度。     

A 3D analytical modeling of tri-gate tunneling field-effect transistors

In this paper, a three-dimensional (3D) analytical solution of the electrostatic potential is derived for the tri-gate tunneling field-effect transistors (TG TFETs) based on the perimeter-weighted-sum approach. The model is derived by separating the device into a symmetric and an asymmetric double-gate (DG) TFETs and then solving the 2D Poisson’s equation for these structures. The subthreshold tunneling current expression is extracted by numerical integrating the band-to-band tunneling generation rate over the volume of the device. It is shown that the potential distributions, the electric field profile, and the tunneling current predicted by the analytical model are in close agreement with the 3D device simulation results without the need of fitting parameters. Additionally, the dependence of the tunneling current on the device parameters in terms of the gate oxide thickness, gate dielectric constant, channel length, and applied drain bias is investigated and also demonstrated its agreement with the device simulations.     

2D sense for faster 3D MRI

Sensitivity encoding in two spatial dimensions (2D SENSE) with a receiver coil array is discussed as a means of improving the encoding efficiency of three-dimensional (3D) Fourier MRI. it is shown that in Fourier imaging with two phase encoding directions, 2D SENSE has key advantages over one-dimensional parallel imaging approaches. By exploiting two dimensions for hybrid encoding, the conditioning of the reconstruction problem can be considerably improved, resulting in superior signal-to-noise behavior. As a consequence, 2D SENSE permits greater scan time reduction, which particularly benefits the inherently time-consuming 3D techniques. Along with the principles of 2D SENSE imaging, the properties of the technique are discussed and investigated by means of simulations. Special attention is given to the role of the coil configuration, yielding practical setups with four and six coils. The in vivo feasibility of the two-dimensional approach is demonstrated for 3D head imaging, permitting four-fold scan time reduction. Presented in parts at the 16th meeting of the ESMRMB, Sevilla, September, 1999.     

3D diffusion tensor imaging with 2D navigated turbo spin echo

A Cartesian two-dimensional navigator with variable orientation for online motion correction is introduced. It corrects for all possible zeroth- and first-order phase errors due to rigid-body motion of a subject during the diffusion-weighting preparation. The technique is developed for the application of three-dimensional (3D) imaging sequences, which offer the opportunity of high-resolution diffusion-weighted imaging, or diffusion tensor imaging (DTI) with isotropic voxel resolution. The navigator was applied to a displaced 3D turbo spin-echo sequence with an ECG-gated diffusion preparation to avoid phase errors due to gross brain pulsation. Online and offline corrected in vivo images acquired with this sequence are compared to investigate the advantages of online correction. Also eigenvector maps of the diffusion tensor are presented with an isotropic resolution of 1 mm³, which indicate that this new navigator technique is a promising approach for high-resolution DTI.     

基于EGWOEO算法的三维无线传感网络覆盖优化

针对三维随机部署无线传感网络节点出现的覆盖率低和节点不均现象，以覆盖率为适应度函数，提出一种基于EGWOEO算法的三维无线传感网络覆盖优化算法。首先，采用Tent混沌映射初始化种群，以增加种群多样性；其次，利用反向学习策略，以增加全局搜索能力；之后，融入双曲正切高斯策略，加强算法寻优能力；然后，提出一种正余弦函数的非线性收敛因子，以平衡全局与局部搜索；最后，改进种群位置更新方程，加快算法的收敛速度与精度。将改进的EGWOEO算法应用于三维WSN覆盖优化中，仿真结果表明，与GWO、PSOGWO、LGWO算法相比，EGWOEO算法的三维WSN覆盖率平均增量分别为11.023%、10.662%和12.401%,改善了节点分布不均现象，提高了节点利用率。     

特高压大跨越架空线路三维工频电场计算

1000kV特高压输电线路跨越江河时,线路的档距和弧垂均较大,为了解线路周围的电场确定线路最小对地高度,引入线性单元模拟电荷法,同时考虑铁塔的影响,根据悬链线方程建立了特高压大跨越线路的模型,采用三维电场的计算方法计算了线路周围的工频电场分布。三维电场方法与二维电场方法的计算和对比分析结果表明:对于特高压普通架空线路,采用二维电场方法与采用三维电场方法所得的计算结果基本相等,均可满足工程要求;对于特高压大跨越线路,采用三维电场方法计算可以更准确地反映大跨越线路的电场分布,提高工程的设计精度。     

三维恒定磁场的唯一性

本文首先说明用场量Ｂ，Ｈ或用向量磁住Ａ表述时，三维恒定磁场解答的唯一性；然后着重研究Ａ的向量泊蚣方程混合边值问题和Ａ的旋度旋度方程混合边值问题的唯一性，并进一步讨论了两者的等价性。     

Fast 3D thermal simulation of power module packaging

This paper presents a thermal model that uses a Fourier series solution to the heat equation to carry out transient 3D thermal simulation of power device packaging. The development and implementation of this physics‐based method is described. The method is demonstrated on a stacked 3D multichip module. The required aspects of 3D heat conduction are captured successfully by the model. Compared with previous thermal models presented in literature, it is fast, accurate and can be easily integrated with an inverter circuit simulator to model realistic converter load cycles. Copyright © 2012 John Wiley & Sons, Ltd.     

Numerical Analysis of Tunneling Between Stacked Quantum Wires with the Inclusion of the Effects from Effective Mass Discontinuities

A technique for the exact solution of the 3D Schrödinger equation in a structure with the effective mass varying in the direction transverse with respect to that of electron propagation is presented. Such a technique is applied to the study of the tunneling conductance between two stacked quantum wires as a function of the voltage applied to a top gate, whose action on the confinement potential is evaluated by means of a 3D Poisson solver. Results are then compared with those for an approximate model that allows separating the variables of the Schrödinger equation and with those for a simplified treatment of the gate action.     

三维非平稳车载信道建模及其空-时相关特性研究

针对车载(V2V)通信系统无线传播场景的非平稳特性且无线信号三维传播时俯仰角(EAs)与水平角(AAs)非独立的特点,提出一种基于规则几何的新型三维非平稳V2V信道参考模型及其相应的仿真模型。为了刻画信道的非平稳特性,考虑了信号收发车辆以任意方向和速度运动而引起的多时变参数。针对EAs、AAs角度谱服从VMF联合分布的情形推导了模型的部分统计特性,并深入研究了车辆行驶环境、非平稳性以及收发端行驶状态对信道空-时相关函数的影响。仿真结果表明,提出的信道模型可以捕捉车辆行驶方向变化对信道空-时相关性的影响,多普勒功率谱密度理论值与实测值的基本一致、仿真模型与参考模型统计特性的高度拟合验证了理论推导的正确性和模型的实用性。     

圆柱型锂离子电池三维分层热耦合模型研究

圆柱型锂离子电池的电芯由电池单元卷绕形成,其中电池单元由浸润在电解液中的正负极片、隔膜以及正负极耳组成。三维平均体积模型难以分析电池内部复杂的电化学系统,对此,针对实物的三维结构建立了考虑瞬态温度变化与电化学反应间相互影响的三维分层模型。通过实验验证了模型的准确性,基于模型结果详细分析了在不同放电倍率下电池内部电流密度和极化电压等电化学特征、焦耳热及反应热的产热速率和电池内部温度分布。研究结果有助于后续电池温度一致性及热管理技术的研究。     

横向磁通电机的三维磁场分析与计算

采用ANSYS有限元软件对横向磁通电机进行了三维磁场分析与计算,模拟了横向磁通电机定子铁心与磁体在不同相对位置下的磁密分布,找出了电机空载时定子轭部磁密的变化,求出了电机空载反电势,并绘制了相应的曲线,为横向磁通电机的优化设计奠定了基础。     

二维时变电磁场问题中涡流的约束

对于二维正弦电磁场问题,由于电源电流密度是一个未知的复常数,加上边界条件中向量磁位不易给定,因此需要对载流导体中的总电流进行约束,才能得到磁密和电密的唯一、正确解.本文对二维积分方程法和有限元法中涡流的约束方法进行了研究.对有限元法,根据问题的性质,又分成给定电流的多导体系统,串联约束和并联约束等三种情况,对每种情况都给出了定解方程和相应的离散格式.     

Effective Mass Approach for n-MOSFETs on Arbitrarily Oriented Wafers

The general theory for quantum simulation of cubic semiconductor n-MOSFETs is presented within the effective mass equation approach. The full three-dimensional transport problem is described in terms of coupled transverse subband modes which arise due to quantum confinement along the body thickness direction. Couplings among the subbands are generated for two reasons: due to spatial variations of the confinement potential along the transport direction, and due to non-alignment of the device coordinate system with the principal axes of the constant energy conduction band ellipsoids. The problem simplifies considerably if the electrostatic potential is separable along transport and confinement directions, and further if the potential variations along the transport direction are slow enough to prevent dipolar coupling (Zener tunneling) between subbands. In this limit, the transport problem can be solved by employing two unitary operators to transform an arbitrarily oriented constant energy ellipsoid into a regular ellipsoid with principal axes along the transport, width and confinement directions of the device.     

三维MUSIC近场噪声源识别算法仿真

为了识别三维空间内的噪声源,推导了三维MUSIC近场噪声源识别算法。在LabVIEW里进行三维MUSIC近场噪声源识别算法的仿真,仿真结果验证了该算法的有效性。针对三维MUSIC算法空间搜索计算量大的缺点,提出了改进的搜索方法:先设搜索半径为定值进行二维MUSIC谱搜索,得到噪声源的方向参数;然后确定2个方向参数进行一维MUSIC谱搜索,得到噪声源的半径参数;最后在前2次搜索确定的空间位置附近进行小范围的三维MUSIC谱搜索。改进的搜索方法使空间计算量大大减少的同时精度可以得到保证。     

Evaluation of Mixing Rules for Dielectric Constants of Composite Dielectrics by MC-FEM Calculation on 3D Cubic Lattice

Effective dielectric constants of diphase composite dielectrics are simulated by Monte Carlo-finite element method on three-dimensional lattice. Effective dielectric constants with coefficients of variation less than 5.5% are obtained for different ratios of dielectric constants of the two phases, ranging from 10 to 700. Various mixing rules and equations are fitted to these data and the accuracy and relevance of the fits are thoroughly examined. Modified logarithmic rule loses its physical basis when fitted to three-dimensional data. As the ratio of dielectric constants of the two phases increases, the parameters in general Lichterecker mixing rule, general Bruggeman's symmetric equation, general effective media equation and its modified form all increase or decrease monotonously. General effective media equation and its modified form give the best fits to the effective dielectric constants simulated. The simulation results for the dielectric constants of some composite systems are in good agreement with experimental data.     

用GALERKIN有限元法分析三维及准三维涡流场

本文采用Galerkin有限元法推导了三维,准三维涡流磁场的弱解形式.并利用所得结果,计算了一台三十万千瓦汽轮发电机端部磁场.     

Towards Fully Quantum Mechanical 3D Device Simulations

We present a simulator for calculating, in a consistent manner, the realistic electronic structure of three-dimensional heterostructure quantum devices under bias and its current density close to equilibrium. The electronic structure is calculated fully quantum mechanically, whereas the current is determined by employing a semiclassical concept of local Fermi levels that are calculated self-consistently. We discuss the numerical techniques employed and present illustrative examples that are compared with quantum transport calculations. In addition, the simulator has been used successfully to study shape-dependent charge localization effects in self-assembled GaAs/InGaAs quantum dots.