Rugged modules: The opposite of flatness

Relative notions of flatness are introduced as a mean to gauge the extent of the flatness of any given module. Every module is thus endowed with a flatness domain and, for every ring, the collection of flatness domains of all of its modules is a lattice with respect to class inclusion. This lattice, the flatness profile of the ring, allows us, in particular, to focus on modules which have a smallest flatness domain (namely, one consisting of all regular modules.) We establish that such modules exist over arbitrary rings and we call them Rugged Modules. Rings all of whose (cyclic) modules are rugged are shown to be precisely the von Neumann regular rings. We consider rings without a flatness middle class (i.e., rings for which modules must be either flat or rugged.) We obtain that, over a right Noetherian ring every left module is rugged or flat if and only if every right module is poor or injective if and only if R = S×T, where S is semisimple Artinian and T is either Morita equivalent to a right PCI-domain, or T is right Artinian whose Jacobson radical properly contains no nonzero ideals. Character modules serve to bridge results about flatness and injectivity profiles; in particular, connections between rugged and poor modules are explored. If R is a ring whose regular left modules are semisimple, then a right module M is rugged if and only if its character left module M⁺ is poor. Rugged Abelian groups are fully characterized and shown to coincide precisely with injectively poor and projectively poor Abelian groups. Also, in order to get a feel for the class of rugged modules over an arbitrary ring, we consider the homological ubiquity of rugged modules in the category of all modules in terms of the feasibility of rugged precovers and covers for arbitrary modules.     

一种SC-FDE散射通信系统的MIMO技术方案

在使用2付发射天线、2付接收天线和2个发射频率的传统散射通信系统基础上,提出了一种应用于单载波频域均衡(SC-FDE)散射通信系统的多输入多输出(MIMO)技术方案,可以在保证4重分集的情况下提供2倍的数据传输速率。提出的MIMO技术方案只需在发射端增加2部发射机,不需改变接收机的射频支路结构,具有实现简单的优点。仿真表明,提出的MIMO技术方案在无信道编译码时的误比特率(BER)性能比相应的传统分集系统性能恶化约1.9dB,在进行(64,57)(64,57)Turbo乘积码编译码时的性能恶化只有1.6dB,因此,与使用单独的2套传统分集系统提供2倍的数据传输速率相比,分别具有1.1dB和1.4dB的功率增益,而且具有体积小、成本低的优点。     

多用户OFDM系统的测距定时同步算法

在OFDMA系统中,上行链路的定时误差主要来自远近效应,导致用户间符号到达时刻不一致,因此,同步过程主要依靠测距来完成同步参数估计,再通过反馈机制予以调整。通过对OFDMA几种测距定时同步算法的研究,仿真分析了各自性能及运算复杂度,并在此基础上提出了一种联合同步方案,将3种算法结合应用于不同用户量的接入环境,以满足性能及复杂度的平衡需求。     

Low Fatigue in Epitaxial Pb(Zr<Subscript>0.2</Subscript>Ti<Subscript>0.8</Subscript>)O<Subscript>3</Subscript> on Si Substrates with LaNiO<Subscript>3</Subscript> Electrodes by RF Sputtering

Epitaxial PZT (001) thin films with a LaNiO₃ bottom electrode were deposited by radio-frequency (RF) sputtering onto Si(001) single-crystal substrates with SrTiO₃/TiN buffer layers. Pb(Zr_0.2Ti_0.8)O₃ (PZT) samples were shown to consist of a single perovskite phase and to have an (001) orientation. The orientation relationship was determined to be PZT(001)[110]∥LaNiO₃(001)[110]∥SrTiO₃ (001)[110]∥TiN(001)[110]∥Si(001)[110]. Atomic force microscope (AFM) measurements showed the PZT films to have smooth surfaces with a roughness of 1.15 nm. The microstructure of the multilayer was studied using transmission electron microscopy (TEM). Electrical measurements were conducted using both Pt and LaNiO₃ as top electrodes. The measured remanent polarization P _r and coercive field E _c of the PZT thin film with Pt top electrodes were 23 μC/cm² and 75 kV/cm, and were 25 μC/cm² and 60 kV/cm for the PZT film with LaNiO₃ top electrodes. No obvious fatigue after 10¹⁰ switching cycles indicated good electrical endurance of the PZT films using LaNiO₃ electrodes, compared with the PZT film with Pt top electrodes showing a significant polarization loss after 10⁸ cycles. These PZT films with LaNiO₃ electrodes could be potential recording media for probe-based high-density data storage.     

DSSS/CDMA系统窄带干扰抑制技术概述

 窄带干扰(NBI,Narrow-Band Interference)作为一类常见的共道干扰对扩频系统的影响不容忽视,虽然扩频系统本身具备一定的NBI对抗能力,但有效的NBI抑制技术可以显著提高系统性能.在过去的30年中,扩频系统NBI抑制技术的关注重心由单用户直扩(DSSS,Direct Sequence Spread Spectrum)系统扩展到多用户码分多址(CDMA,Code-Division Multiple-Access)系统.文章从预测技术、变换域技术、码辅助技术的角度对DSSS和CDMA系统NBI抑制技术的研究现状、分类比较以及发展趋势进行了全面概述.     

基于自适应窗口固定及传播的 多尺度纹理图像分割

 本文提出一种基于自适应窗口固定及传播的多尺度纹理图像分割方法,在小波域隐马尔科夫树模型(WHMT)的初始分割基础上,根据分割粗尺度上的区域一致性好,细尺度上的边缘准确的特点,利用上下尺度像素之间以及本层邻域像素的马尔科夫性,标记出图像的一致性区域和边缘区域,将一致性区域固定,类标直接下传到下一尺度,边缘区域则利用邻域信息确定出上文权值背景传播到下一尺度,与下尺度一起共同指导图像分割,从而很好的保持了区域均匀性和边缘准确性.同时根据纹理图像区域聚集性的特性,利用基于多项式展开和置信区间交叉(LPA_-ICI)方法找出各类区域聚集的物理位置中心,融入上下文权值背景中,使得指导分割策略能够更好的进行.实验表明,对于合成纹理图像来说,本文提出的多尺度融合算法在均匀区域内部及区域边界都大为改善,而且无须进行参数的训练,使算法快速的完成.     

Parallel Smoothed Aggregation Multilevel Schwarz Preconditioned Newton-Krylov Algorithms for Poisson-Boltzmann Problems

We study a multilevel Schwarz preconditioned Newton-Krylov algorithm to solve the Poisson-Boltzmann equation with applications in multi-particle colloidal simulation. The smoothed aggregation-type coarse mesh space is introduced in collaboration with the one-level Schwarz method as a composite preconditioner for accelerating the convergence of a Krylov subspace method for solving the Jacobian system at each Newton step. The important feature of the proposed solution algorithm is that the geometric mesh information needed for constructing the multilevel preconditioner is the same as the one-level Schwarz method on the fine mesh. Other components, such as the definition of the coarse mesh, all the mesh transfer operators, and the coarse mesh problem, are taken care of by the Trillinos/ML packages of the Sandia National Laboratories in the United States. After algorithmic parameter tuning, we show that the proposed smoothed aggregation multilevel Newton-Krylov-Schwarz (NKS) algorithm numerically outperforms than smoothed aggregation multigrid method and one-level version of the NKS algorithm with satisfactory parallel performances up to a few thousand cores. Besides, we investigate how the electrostatic forces between particles for the separation distance depend on the radius of spherical colloidal particles and valence ratios of cation and anion in a cubic system.     

The communication model for real‐time web service in telecom domain

Development of services that span over the Internet and Telecom networks is driving significant efforts towards the integration of services offered by Telecom operators. The telecommunications R&D community also starts adapting and developing similar service delivery platforms to offer a wide range of new value‐added services faster and more cost efficiently inspired by the success of Web service technologies for the development and deployment of IT services. In this paper, we have an analysis for Telecom Web services communication requirements and also propose Telecom Web services communication model considering the specific characteristics as state, asynchronous, event‐driven communications in Telecom domain. We focus on the design and implementation details for real‐time Web service communication model in Telecom domain, and as the framework of communication model for Telecom Web services, the enhanced state machine design and implementation, and the messages dispatching design and implementation for Telecom Web services communication model, and also illustrate the third party end call control scenarios. Finally, we give the conclusion and future essential work. Copyright © 2009 John Wiley & Sons, Ltd.     

Development and analysis of Crank‐Nicolson scheme for metamaterial Maxwell's equations on nonuniform rectangular grids

In this paper, we develop a fully implicit scheme on staggered grids to solve the Maxwell's equations when Drude metamaterial is involved. Unconditional stability and optimal error estimate of the scheme are proved. Numerical results are provided to support the theoretical analysis, and used to demonstrate the applicability of the scheme to simulate the complicated backward wave propagation phenomenon occurring in metamaterials.