Rigid and Finite Type Geometric Structures

Rigid geometric structures on manifolds, introduced by Gromov, are characterized by the fact that their infinitesimal automorphisms are determined by their jets of a fixed order. Important examples of such structures are those given by an H-reduction of the first order frame bundle of a manifold, where the Lie algebra of H is of finite type; in fact, for structures given by reductions to closed subgroups of first order frame bundles, finite type implies rigidity. The goal of this paper is to generalize this to geometric structures defined by reductions of frame bundles of arbitrary order, and to give an algebraic characterization of the property of being rigid in terms of a suitable notion of finite type.     

Inter-channel de-correlation for perceptual audio coding

Sound reproduction is evolving towards multi-channel systems with a growing number of channels. Consequently, high quality multi-channel codecs are required. Last generation perceptual audio codecs, represented by MPEG advanced audio coder (AAC), can efficiently code typical surround multi-channel material but may benefit from a previous block of inter-channel de-correlation, for certain audio recordings. These recordings present high correlation between non-symmetric channels, or correspond to loudspeaker arrangements different from surround, such as linear loudspeaker arrays. In order to valuate the advantages of this new coding approach, a multi-channel perceptual quality measure is developed.     

Markov approximations of chains of infinite order

We consider chains whose transition probabilities depend on the whole past, with summable continuity rates. We show that Ornstein's -distance between one such chain and its canonical Markov approximations of different orders is at worst proportional to the continuity rate of the chain. The result generalizes previous bounds obtained by X. Bressaud and ourselves, while relying on a similar coupling argument. Received: 9 April 2002     

Geometric phases and the informational completeness of quantum frames

The basic results on geometric phases are rederived by using infinite dimensional coordinate charts in line bundles, in Hopf bundles, and in projective Hilbert spaces. The determination of a quantum state can be then geometrically described as the measurement of Fubini-Study distances from that state to the elements of informationally complete quantum frames. The basic geometric features of such quantum frames are formulated, and their relationships to corresponding classical frames are analyzed.     

基于FPGA和单片机的多路信号光纤传输系统设计

基于FPGA和单片机技术,设计了多路信号光纤传输系统,利用单片机实现了模拟数据的高精度采集和通信信号的双向传输,利用FPGA实现了多路复杂信号的处理与传输。实验证明：该系统不仅能传输多路模拟与数字信号,以及低速数字信号与高速脉冲信号,还能实现双向CAN通信。与现有光纤传输系统相比,多路信号光纤传输系统不仅实现了多路复杂信号的采集,而且使用一根光纤实现了大容量多数据的双向传输,一方面减小了产品体积,另一方面降低了产品成本。     

Multivalued maps as a tool in modeling and rigorous numerics

Applications of the fixed point theory of multivalued maps can be classified into several areas: (1) Game theory and mathematical economics; (2) Discontinuous differential equations, differential inclusions, and optimal control; (3) Computing homology of maps; (4) Computer assisted proofs in dynamics; (5) Digital imaging. We give an overview of the most classical and well developed areas of applications (1) and (2), where a multivalued map is used as a generalization of a single-valued continuous map, and we survey more recent applications (3), (4), and (5), where multivalued maps play the role of a numerical tool. Dedicated to Felix Browder on his 80th birthday     

SEISMIC PERFORMANCE OF STEEL STRUCTURES WITH REDUCED BEAM SECTION CONNECTIONS

采用有限元方法对翼缘削弱型节点钢结构的抗震性能进行了研究,通过模态分析和动力时程分析,详细分析了框架的周期、结构动内力、动应力以及塑性变形区的发展规律等,并和普通节点框架的计算结果进行对比. 研究结果表明：在小震下,翼缘削弱型节点的抗震性能并不理想,但在大震下,表现出了良好的抗震性能,塑性变形出现在梁端削弱处,塑性应变增加,柱底剪力和顶层位移均比普通节点框架的小,建议在强震区推广使用翼缘削弱型节点.     

一种宽带多通道合成孔径雷达系统幅相特性测量与校正方法

多通道技术可以用来提高系统的频带宽度,是实现分辨率优于0.1 m的超高分辨率机载合成孔径雷达(SAR)系统的一种有效的技术途径。该文针对实际雷达系统中采用的单通道宽带信号发射、8通道下变频接收来完成宽带信号收发的方案,提出一种对该收发系统的幅相误差进行测量和校正的方法,该方法采用空间闭环辐射提取宽带收发通道的幅相误差,采取具有频偏误差修正的矢量网络分析技术完成多通道接收单元中各子通道幅相误差的提取,将两者结合用于补偿整个系统误差对信号合成和成像处理所带来的影响。实际测试数据和外场飞行试验结果验证了该系统测量和校正方法的有效性和可行性。     

基于多通道合成的优于0.1m分辨率的机载SAR系统

针对合成孔径雷达(SAR)高分辨率成像的应用需求,该文给出一种基于单通道发射、多通道并行接收的新的高分辨率SAR系统实现方案。SAR系统共有8个接收通道,信号带宽达到3.2 GHz,具有高分辨率成像、InSAR干涉成像以及全极化成像功能。文中提出一种新的采用空间辐射测量和频偏误差修正测量的分段测量与综合补偿的通道传递误差测量补偿方法,有效解决了高分辨率SAR宽频带收发系统中关键的多通道接收幅度相位误差校正问题,并在国内首次获得了优于0.1 m分辨率的SAR图像。文中详细介绍了系统的组成方案以及主要技术性能指标,重点探讨和分析了多通道系统的频带合成、系统幅度相位误差测量补偿、运动误差补偿和成像处理等实现技术,给出了测量、补偿和成像的试验结果。通过实际飞行试验,验证了高分辨率SAR系统的技术及方案的有效性和可行性。