Design and implementation of spectrum sensing for cognitive radios with a frequency-hopping primary system

In this work, spectrum sensing for cognitive radios is considered in the presence of multiple Primary Users (PU) using frequency-hopping communication over a set of frequency bands. The detection performance of the Fast Fourier Transform (FFT) Average Ratio (FAR) algorithm is obtained in closed-form, for a given FFT size and number of PUs. The effective throughput of the Secondary Users (SU) is formulated as an optimization problem with a constraint on the maximum allowable interference on the primary network. Given the hopping period of the PUs, the sensing duration that maximizes the SU throughput is derived. The results are validated using Monte Carlo simulations. Further, an implementation of the FAR algorithm on the Lyrtech (now, Nutaq) small form factor software defined radio development platform is presented, and the performance recorded through the hardware is observed to corroborate well with that obtained through simulations, allowing for implementation losses.     

A short recollection on the paper entitled "A common sense approach to peak picking in two-, three-, and four-dimensional spectra using automatic computer analysis of contour diagrams" by D.S. Garrett, R. Powers, A.M. Gronenborn, and G.M. Clore [J. Magn. Reson. 95 (1991) 214-220

The Contour Approach to Peak Picking was developed to aid in the analysis and interpretation and of multidimensional NMR spectra of large biomolecules. In essence, it comprises an interactive graphics software tool to computationally select resonance positions in heteronuclear, 3- and 4D spectra.     

Comprehensive mathematical simulation of functional magnetic resonance imaging time series including motion-related image distortion and spin saturation effect

There has been vast interest in determining the feasibility of functional magnetic resonance imaging (fMRI) as an accurate method of imaging brain function for patient evaluations. The assessment of fMRI as an accurate tool for activation localization largely depends on the software used to process the time series data. The performance evaluation of different analysis tools is not reliable unless truths in motion and activation are known. Lack of valid truths has been the limiting factor for comparisons of different algorithms. Until now, currently available phantom data do not include comprehensive accounts of head motion. While most fMRI studies assume no interslice motion during the time series acquisition in fMRI data acquired using a multislice and single-shot echo-planar imaging sequence, each slice is subject to a different set of motion parameters. In this study, in addition to known three-dimensional motion parameters applied to each slice, included in the time series computation are geometric distortion from field inhomogeneity and spin saturation effect as a result of out-of-plane head motion. We investigated the effect of these head motion-related artifacts and present a validation of the mapping slice-to-volume (MSV) algorithm for motion correction and activation detection against the known truths. MSV was evaluated, and showed better performance in comparison with other widely used fMRI data processing software, which corrects for head motion with a volume-to-volume realignment method. Furthermore, improvement in signal detection was observed with the implementation of the geometric distortion correction and spin saturation effect compensation features in MSV.     

对于具有一定宽度的光束通过展宽器的色散误差的评价

利用光线追踪法计算了具有一定宽度的光束通过Martinez展宽器时的色散误差.结果表明,通常的无宽度理想光线的展宽器模型有足够的精确度.但是如果将光束反转后再送入展宽器,将得到更加完美的色散误差补偿 关键词： 飞秒激光放大器 展宽器 压缩器 色散补偿     

风机盘管设计与仿真软件开发及实验验证

介绍了风机盘管设计与仿真软件,通过合理的计算逻辑,实现风机盘管的设计和性能分析。在设计模块中不仅可以按照最常见的设计条件进行产品开发,而且提出了另外两种设计形式。仿真模块中,可以进行单点和多点的变工况变结构性能分析,自动绘制曲线。并通过实验数据与仿真结果数据的比较,结果吻合较好,且变化趋势一致。软件大大提高了设计效率,并为盘管的性能优化提供预测。     

MS-Windows software for space groups: Application to domain structure symmetry analysis

An integrated package of programs has been developed for IBM-Compatible PCs to investigate the structures and representations of crystallographic space groups. The package is implemented as a Microsoft Windows application using Borland Delphi with user code in Object-Pascal.

Parts of this software have been adapted to assist in the symmetry analysis of domain structures. For a given phase transition the software identifies all domain states and finds, e.g. (i) symmetry groups of all domain states, (ii) all operations that transform a given domain state into another domain state, (iii) classes of crystallographically equivalent domain pairs with similar domain distinction, (iv) symmetries of ordered and unordered domain pairs, (v) twinning groups of domain pairs and associated minimal permutable sets of domain states, (vi) intermediate groups of the inverse twinning problem.

As an illustrative example of the use of the software we consider the symmetry analysis of domain structures in the 2H polytype TaSe₂.     

基于活性顺序图的形式化验证方法及工具研究

近年来,形式化验证方法在软件开发过程的作用越来越大。如何充分利用形式化验证方法提高软件系统的可靠性已成为软件开发者及使用者主要关注的问题。总结了近年来基于活性顺序图的形式化验证方法的研究进展,首先介绍活性顺序图的语言及其表达能力与复杂性,然后深入分析现有的基于活性顺序图的形式化验证的关键技术及其典型应用,最后实现一种基于活性顺序图的运行时验证工具,实验证明使用本验证工具进行形式化验证的可行性。     

Research on total-dose hardening for H-gate PD NMOSFET/SIMOX by ion implanting into buried oxide

In this work,we investigate the back-gate I-V characteristics for two kinds of NMOSFET/SIMOX transistors with H gate structure fabricated on two different SOI wafers.A transistors are made on the wafer implanted with Si+ and then annealed in N2,and B transistors are made on the wafer without implantation and annealing.It is demonstrated experimentally that A transistors have much less back-gate threshold voltage shift AVth than B transistors under X-ray total dose irradiation.Subthreshold charge separation technique is employed to estimate the build-up of oxide charge and interface traps during irradiation,showing that the reduced △Vth for A transistors is mainly due to its less build-up of oxide charge than B transistors.Photoluminescence (PL) research indicates that Si implantation results in the formation of silicon nanocrystalline (nanocluster) whose size increases with the implant dose.This structure can trap electrons to compensate the positive charge build-up in the buried oxide during irradiation,and thus reduce the threshold voltage negative shift.     

相敏光放大器对光纤偏振模色散进行补偿的探讨

根据耦合非线性薛定谔方程,在考虑偏振模色散的情况下,采用数值方法仿真了含有相敏光放大器的高速光纤传输系统性能,获得了一组优化参量.仿真结果表明,相敏光放大器对于光纤偏振模色散的影响有一定的补偿作用.     

同步水声跟踪定位系统软件抗距离模糊技术研究

同步水声跟踪定位系统通过时延测量进行定位,当信号传播时延大于脉冲重复周期时,就会出现距离模糊。距离模糊是远程高帧率定位系统不可避免的问题。以往多采用硬件方法抗模糊,使得系统趋于复杂。本文提出了两种软件抗模糊方法:举手表决法和参考位置标示法,前者利用真解的一致性抗模糊,无需任何先验信息;后者利用目标的参考位置抗模糊,需要目标初始就位点这一先验信息。文中给出了算法原理和适用条件。软件抗模糊方法简化了系统设备,海试结果验证了算法的有效性。