MNLS inverse discriminates between neuronal activity on oppositewalls of a simulated sulcus of the brain

The minimum-norm least-squares (MNLS) inverse for magnetic field measurements is applied to a representation of a sulcus of the human brain, where one or both walls have regions of neuronal activity. Simulations indicate that the magnetic source image (MSI) is largely confined to the appropriate wall of the sulcus, even for a depth of 4 cm where the distance between walls is only 3 mm. Two nearly oppositely oriented dipoles located 3 mm apart are found to be distinguished. Influences on the quality of the MSI by measurement noise and inaccuracy in determining the image surface are discussed in detail     

An FDTD/ray-tracing analysis method for wave penetration through inhomogeneous walls

A novel method of studying wave penetration through inhomogeneous walls using the hybrid technique based on combining finite-difference time-domain (FDTD) and ray tracing methods is presented . The FDTD method is used to analyze the transmission characteristics of inhomogeneous walls. Using the knowledge of the tangential electric and magnetic field distributions along the borders of the FDTD computation domain, rays are sent out to cover the rest of the environment so that prediction of signal coverage can be made more efficiently without compromising the accuracy. Numerical results of the method have been compared and shown to agree very well with those of measurement and those of full wave analysis. Examples have shown the inadequacy of the traditional ray tracing method in the presence of walls made of concrete blocks. However, the proposed method can accurately predict signal coverage by taking into account the scattered fields by the inhomogeneity inside the walls. The method does not add much to computational complexity. Reduction in computation time is even more significant when the incident waves can be approximated to be plane waves and the wall structure is periodic.     

Extended X-ray absorption fine structure studies of thulium doped GaN epilayers

The local structure of Tm³⁺ ions incorporated into GaN epilayers was studied by means of Extended X-ray Absorption Fine Structure. The samples were doped either in situ during growth by Molecular Beam Epitaxy or by ion implantation of layers grown by Metal Organic Chemical Vapour Deposition. The implantation was done at ion energy of 300 keV and different nominal fluences of 3×10¹⁵, 4×10¹⁵ cm⁻² and 5×10¹⁵ cm⁻². The concentration of Tm in the samples studied was measured by Wavelength Dispersive X-ray analysis. For the in situ doped sample with concentration of 0.5%, and for all of the implanted samples, Tm was found on the Ga site in GaN. The ion implanted sample and an in situ doped sample with a similar concentration of Tm showed the same local structure, which suggests that the lattice site occupied by Tm does not depend on the doping method. When the average Tm concentration for in situ doped samples is increased to 1.2% and 2.0%, Tm is found to occupy the Ga substitutional site and the presence of a substantial number of Tm ions in the second coordination sphere indicates dopant clustering in the films. The formation of pure TmN clusters was found in an in situ doped sample with a dopant concentration of 3.4%.     

一类含有非线性传染率的传染病模型的全局稳定性

讨论了一类带有非线性传染率的SIRS型传染病模型,得到了无病平衡点和地方病平衡点存在的阈值条件,借助构造Dulac函数和Liapunov函数,找到了两类平衡点全局渐近稳定的充要条件.     

HfOxNy的场发射特性

用直流溅射和高温退火相结合的方法制备了HfOxNy薄膜并测试了其场发射性能,发现其具有较低的开启电场、较大的发射电流密度以及很好的发射稳定性.高压"锻炼"对提高HfOxNy场发射性能起着关键作用,这与高压"锻炼"下薄膜内部结构和表面性质的改变有关.对场发射机理的研究表明,HfOxNy的场发射符合经典的FN隧穿理论.     

亚波长设计中的可制造性验证方法

描述了一种采用分辨率提高技术后用于可制造性设计的验证方法.该方法的目的是验证设计功能与设计目的是否一致,更精确地说,使刻印出来的图像与设计一致.还描述了这种基于模型的验证方法的过程建模,实例说明这种方法的性能.     

两种自主开发的图形外延SiGe工艺

使用清华大学微电子学研究所研发的UHV/CVD系统深入研究了图形外延SiGe工艺,分别选用单一的SiO2介质层和SiO2/P0ly-Si复合介质层,作为图形外延SiGe单晶材料的窗口屏蔽介质,开发出了不同的实用化图形外延SiGe工艺.     

计算机网络信息安全技术分析

本文论述了计算机网络面临的威胁和常见的黑客入侵技术，然后从信息加密技术、防火墙技术、入侵检测技术、系统容灾技术、网络安全管理策略等方面，分析了计算机网络信息安全的基本对策。     

基于"替换法"的汉字加、解密实现技术

文章讨论的基于“替换法”的汉字信息加、解密实现技术,改变了传统的汉字加密结果,使加密后的密文仍是可以识别和再利用的汉字,发送者可以在任何可编辑汉字的通讯设备上发送和接收密文,确保中文信息传输过程中的安全性。加、解密算法实现的代码语言为VFP6.0。     

静电驱动悬臂梁数模转换器设计、分析与模拟

提出了一种新型的微电子机械数模转换器 (MEMDAC)———静电驱动悬臂梁数模转换器 .与传统的静电驱动悬臂梁执行器相比 ,新的结构能更精确地控制梁的挠度 .文中给出了此MEMDAC的设计、分析和模拟过程 .有限元(FEA)分析表明此MEMDAC的最大输出位移为 1 5 1μm ,分辨率为 0 1μm ,其最大非线性误差为 0 0 3μm .