Ⅱ类变压器的绝缘要求和试验

依据标准 GB 19212.1—2003,对Ⅱ类变压器的绝缘要求和试验进行归纳总结,给出绝缘电阻、介电强度、爬电距离、电气间隙和穿过绝缘的距离的测试方法。     

一种新的基于遗传算法的参差MTI滤波器设计

提出一种新的搜索最优参差码的方法,该方法是以遗传算法为基础,在每一代群体中,执行完编码、复制、交叉、变异操作后,计算每一个体的适应度.然后每一个体按照一定的条件确定一组新的个体,随机抽取其中的一个个体,计算由其确定的适应度较原个体适应度的增量,决定是否由新抽取的个体代替原个体,达到终止条件时结束.该方法能够使得滤波器的第一零点尽可能地浅,是一种全局随机搜索算法,不依赖于初始种子都可以搜索到全局最优点,而且实现的个体平均适应度更高.     

Fountain码编译码算法结构的改进

在LT码的基础上对Raptor码进行了分析。根据IRA码的结构及其线性时间的编译码特性,提出了Raptor码和IRA码相结合的改进Fountain码结构。研究结果表明,该结构既保持了线性的编译码特性又能有效增强信元的恢复能力。利用其它编码技术与Raptor码相结合是今后进一步的研究方向。     

Truncated total least squares: a new regularization method for the solution of ECG inverse problems

The reconstruction of epicardial potentials (EPs) from body surface potentials (BSPs) can be characterized as an ill-posed inverse problem which generally requires a regularized numerical solution. Two kinds of errors/noise: geometric errors and measurement errors exist in the ECG inverse problem and make the solution of such problem more difficulty. In particular, geometric errors will directly affect the calculation of transfer matrix A in the linear system equation AX = B. In this paper, we have applied the truncated total least squares (TTLS) method to reconstruct EPs from BSPs. This method accounts for the noise/errors on both sides of the system equation and treats geometric errors in a new fashion. The algorithm is tested using a realistically shaped heart-lung-torso model with inhomogeneous conductivities. The h-adaptive boundary element method [h-BEM, a BEM mesh adaptation scheme which starts from preset meshes and then refines (adds/removes) grid with fixed order of interpolation function and prescribed numerical accuracy] is used for the forward modeling and the TTLS is applied for inverse solutions and its performance is also compared with conventional regularization approaches such as Tikhonov and truncated single value decomposition (TSVD) with zeroth-, first-, and second-order. The simulation results demonstrate that TTLS can obtain similar results in the situation of measurement noise only but performs better than Tikhonov and TSVD methods where geometric errors are involved, and that the zeroth-order regularization is the optimal choice for the ECG inverse problem. This investigation suggests that TTLS is able to robustly reconstruct EPs from BSPs and is a promising alternative method for the solution of ECG inverse problems.     

Charge Transportation and Chirality in Liquid Crystalline Helical Network Phases of Achiral BTBT-Derived Polycatenar Molecules

First examples of multichain (polycatenar) compounds, based on the π-conjugated [1]benzothieno[3,2-b]benzothiophene unit are designed, synthesized, and their soft self-assembly and charge carrier mobility are investigated. These compounds, terminated by the new fan-shaped 2-brominated 3,4,5-trialkoxybenzoate moiety, form bicontinuous cubic liquid crystalline (LC) phases with helical network structure over extremely wide temperature ranges (>200 K), including ambient temperature. Compounds with short chains show an achiral cubic phase with the double network, which upon increasing the chain length, is at first replaced by a tetragonal 3D phase and then by a mirror symmetry is broken triple network cubic phase. In the networks, the capability of bypassing defects provides enhanced charge carrier mobility compared to imperfectly aligned columnar phases, and the charge transportation is non-dispersive, as only rarely observed for LC materials. At the transition to a semicrystalline helical network phase, the conductivity is further enhanced by almost one order of magnitude. In addition, a mirror symmetry broken isotropic liquid phase is formed beside the 3D phases, which upon chain elongation is removed and replaced by a hexagonal columnar LC phase.     

基于路灯杆基站的规划建模研究

对路灯杆基站的应用场合原则、选址模型、天馈系统规划设计进行了详细的说明,并通过应用案例证明了关于路灯杆基站的规划设计方法在打造联通精品网络的工作中有着深远的推广意义。     

基于空间语义模型的高分辨率遥感图像目标检测方法

该文提出一种基于空间语义模型的方法,用于高分辨率遥感图像复杂场景中典型地物目标的自动检测。该方法通过分割获取图像对象,引入主题模型统计对象的多维特征,提高了对象特性描述的精度。在此基础上,对图像中有意义的地物目标及它们之间的空间关系建模表达和定量计算,通过获取场景的语义解析树,辅助实现对复杂地物目标的准确提取和定位。在测试数据集上的实验结果表明,该文方法具有较高的智能化程度和较强的稳定性。     

时分噪声调频干扰性能分析与验证

时分噪声调频干扰是一种常用的多目标干扰样式,对其性能的分析研究具有重要意义。构建了时分噪声调频干扰信号的产生模型,统计了不同的干扰重复周期、有效调制带宽和占空比下时分噪声调频干扰信号的功率和干扰带宽,分析出这些参数对时分噪声调频干扰信号功率和干扰带宽的影响,指出了关于脉冲信号带宽认识上的误区。对时分多目标干扰模拟设备生成的信号进行了测试,验证了相关结论。     

Hierarchical Ordered Dual‐Mesoporous Polypyrrole/Graphene Nanosheets as Bi‐Functional Active Materials for High‐Performance Planar Integrated System of Micro‐Supercapacitor and Gas Sensor

Planar integrated systems of micro‐supercapacitors (MSCs) and sensors are of profound importance for 3C electronics, but usually appear poor in compatibility due to the complex connections of device units with multiple mono‐functional materials. Herein, 2D hierarchical ordered dual‐mesoporous polypyrrole/graphene (DM‐PG) nanosheets are developed as bi‐functional active materials for a novel prototype planar integrated system of MSC and NH₃ sensor. Owing to effective coupling of conductive graphene and high‐sensitive pseudocapacitive polypyrrole, well‐defined dual‐mesopores of ≈7 and ≈18 nm, hierarchical mesoporous network, and large surface area of 112 m² g^?1, the resultant DM‐PG nanosheets exhibit extraordinary sensing response to NH₃ as low as 200 ppb, exceptional selectivity toward NH₃ that is much higher than other volatile organic compounds, and outstanding capacitance of 376 F g^?1 at 1 mV s^?1 for supercapacitors, simultaneously surpassing single‐mesoporous and non‐mesoporous counterparts. Importantly, the bi‐functional DM‐PG‐based MSC‐sensor integrated system represents rapid and stable response exposed to 10–40 ppm of NH₃ after only charging for 100 s, remarkable sensitivity of NH₃ detection that is close to DM‐PG‐based MSC‐free sensor, impressive flexibility with ≈82% of initial response value even at 180°, and enhanced overall compatibility, thereby holding great promise for ultrathin, miniaturized, body‐attachable, and portable detection of NH₃.     

Analysis of a secure conference scheme for mobile communication

Dynamic participation is a feature of the secure conference schemes that allows new conferees to join and the old conferees to leave. The conferees who have left should not be able to decrypt the secure conference communication anymore. A secure conference scheme with dynamic participation was proposed in M.S. Hwang and W.P. Yang (1995) and later it was modified with the self-encryption mechanism in K.F. Hwang and C.C. Chang (2003) for a better performance. In this paper we analyze both the original scheme and the modified version. We show that both of them are subject to the active and passive attacks presented in this paper. Our active attack works in the way that a colluding group of attackers can still obtain the conference key even after they all leave the conference. The passive attack does not need any attacker to ever participate the conference. The conference key can be compromised with a large probability as long as the number of conferees is large.