A new mode renumbering algorithm for bandwidth reduction

A new algorithm is presented for automatic renumbering of systems of interconnected nodes so as to minimize the bandwidth of the connectivity matrix. This is necessary to reduce storage requirements for banded matrix solution techniques. The method is based on those due to Cuthill and McKee¹ and Gibbs, Poole and Stockmeyer.² Under test against several other algorithms on a range of 20 examples of various types it always performed at least as well as, and in most cases better than, the best of the other methods. Seven examples are given in the paper, comparing final bandwidths with those produced by seven other algorithms.     

Bandwidth reduction by simulated annealing

The method of Simulated Annealing (SA) is investigated in the concrete problem of bandwidth reductio. We develop a very efficient way to compute the transitions, and this allows long annealing sessions (Monte Carlo runs) in reasonable time, enabling meaningful experimenting. It is demonstrated (empirically) that the neighbourhood relation in the space of states of the system greatly influences the convergence of the annealing. A pure SA algorithm is developed and used to obtain new lower bounds for the bandwidth in the 30 Everstine problems used as a benchmark for testing bandwidth reduction algorithms. An hybrid algorithm is also developed to be used in practice. It consists of an annealing session (without previous melting) run in cascade after the Cuthill-McKee algorithm. The running times are of the same order as those of the deterministic algorithms now in use, and improvements of (typically) 20 per cent are obtained on the 30 Everstine problems.     

Some useful renumbering strategies for unstructured grids

Several renumbering strategies for unstructured grids are discussed. They lead to a minimization of eache-misses and an optimal grouping of elements for different computer platforms, from superscalar workstations to multiprocessor register-to-register vector machines. Timings for a typical computational fluid dynamics (CFD) code that employs these renumbering strategies indicate that CPU requirements may be halved by applying them. The renumbering strategies discussed are all of linear time complexity, making them ideally suited for applications requiring frequent mesh changes. Furthermore, these renumbering strategies are not only valid for element-based codes but carry over to edge-based or face-based field solvers.     

A three-step renumbering procedure for high-order finite element analysis

An efficient renumbering method for high-order finite element models is presented. The method can be used to reduce the profile and wavefront of a coefficient matrix arising in high-order finite element computation. The method indirectly performs node renumbering and involves three main steps. In the first step, nodes at corners of the elements are numbered using an existing renumbering algorithm. In the second step, elements are numbered in an ascending order of their least new corner node numbers. Finally, based on the new element numbers, both corner and non-corner nodes are renumbered using an algorithm that simulates the node elimination procedure in a frontal solution method. The method is compared to the algorithms that directly perform node renumbering. The numerical results indicate that the three-step algorithm presented here is an order of magnitude faster and the resulting renumbering produces excellent profile and wavefront characteristics of the coefficient matrix. © 1998 John Wiley & Sons, Ltd.     

Bandwidth reduction technique for multilayer wavelength division multiplexing (WDM) bandpass filters

The push to develop 100 GHz and smaller bandwidth WDM filters is at demanding levels. Currently, 200 GHz is the standard bandwidth for multilayer interference coatings with high efficiencies, and enormous processing effort is going into the development of standard 100 GHz filters. This paper outlines a simple design that will reduce bandwidth up to 40% when applied to 200 GHz bandpass filters. This design method can also be used in existing 100 GHz designs to achieve even smaller bandwidths.     

自适应光学系统时间带宽和空间带宽的匹配

自适应光学系统存在的时间带宽和空间带宽。为了有效地利用自适应光学系统的系统资源，必须使这两种带宽匹配。本文通过经系统校正后的剩余波前扰动相位的均方差与系统时间带宽和空间带宽的关系，研究了在不同条件下系统时间带宽和空间带宽的匹配问题。     

Bandwidth of Current Transformers

Bandwidth is one of the important performance parameters of current transformers. Transformers are required to have adequate bandwidth to regenerate the measured current, apart from uncertainties that are caused by the nonsinusoidal waveforms along with harmonics. An expression for the transresistance of the current transformer in terms of parasitic components is derived. Approximate expressions for lower cutoff frequency, upper cutoff frequency, and bandwidth are derived from the equivalent models of the current probe in the corresponding frequency range. The expressions are validated by experimental results for a current transformer using a Ferroxcube ferrite core 528T500-4C4. An overview of the effects of different parasitic components, such as magnetizing inductance, leakage inductance, and stray capacitance, on the bandwidth of a current transformer is presented.      

A method of fretting wear reduction in an automatic wheel set gauge change system

The SUW 2000 railway vehicle wheel set with an automatic gauge change system is especially exposed to fatigue wear due to the specific working conditions. Taking into consideration the role which a wheel set has in both vehicle handling on a track and providing safety of railway traffic, the wheel set damage is impermissible. It also applies to the sleeve–axle rotational connection. This article presents research into both finding new and low-cost materials for a slide sleeve in the wheel hub node and looking for cheaper technologies for improving the surface layer of the wheel set under-hub which would eliminate fretting wear. The research was conducted on a simplified physical model of a real connection between a wheel and an axle. The results of the conducted wear tests show that fretting wear can be effectively limited by applying a metallic layer in the form of molybdenum coating. Grease with the addition of molybdenum disulphide can also protect the co-operating surfaces against fretting wear. It also allows for sustaining proper working conditions of frictional pair elements. This solution, however, is onerous due to the limited maintainability of the connection node. The studies carried out show that there is a full possibility of using this solution in real exploitation.     

Bandwidth optimization of optical data links by use of error-control codes

A design approach to optimizing the bandwidth of optical data links while simultaneously decreasing the bit-error rate is proposed. Mathematical analysis indicates that bandwidth gains by factors of 10-60 with power gains of as much as 8.9 dB are possible. To achieve these performance levels requires several innovations. First, conventional forward error-correcting codes cannot be used because of their excessive hardware cost. A reasonably powerful multidimensional parity-based error-control code is proposed and analyzed. These codes offer excellent error detection and moderate error-correction capabilities. Most importantly, they can operate at the fast clock rates that are required. Second, a hybrid automatic-repeat-request protocol is exploited to correct complex error patterns. In thermal-noise-limited systems this unique combination allows the optical clock rate to be increased significantly, thereby resulting in large bandwidth increases. The proposed design approach can be used in optical data links in which propagation delays are moderate and is applicable to fibers that exploit wavelength-division multiplexing or time-division multiplexing, one-dimensional parallel-fiber ribbons, and two-dimensional optical data links that use free space or guided waves. Several design examples are illustrated.     

Contrast for Unidirectionally Integrated Speckles Formed by Light of Finite Bandwidth

Unidirectional averaging of polychromatic speckles has been considered in the far field of a gaussian diffuser. The expression for the contrast has been derived and the numerical results are given for the diffuser limited by a square aperture. The analysis is valid when fluctuations in the optical path are greater than the maximum wavelength of light.     

超材料结构单元轮廓法对吸波材料衰减吸收频带的拓宽与优化

设计了一个由金属谐振单元、FR4基板和金属背板构成的超材料吸波体,通过数值仿真软件对该吸波体在2~8GHz范围内的S参数以及吸收率特征进行了计算;对这个模型进行了取轮廓化的处理,通过计算发现这种处理对其谐振吸收基本上没有影响;在此基础上,通过在这个轮廓模型中加入其他谐振单元,实现了双频带范围的微波衰减吸收。通过激光刻蚀的方法,对所设计的模型进行了实验验证,发现计算结果和实验结果有很好的一致性,这就验证了超材料轮廓法拓宽吸波材料的技术思路,为宽频带超材料吸波体的研究提供了一个可行的技术途径。     

网络带宽自适应的远程视频监控系统

当前的远程视频监控系统在一定程度上不能很好地适应网络带宽的变化,无法在多种网络线路上传输视频流。为解决这一问题,本文提出了网络带宽自适应的监控系统结构模型,使用位率控制精度较高的编码器以适应网络带宽的变化,并对网络状况动态进行检测。完成了远程视频监控系统BHJK,该系统可在IP宽带网、电话线及其混和线路上传输视频流,提供基于视频分析的智能运动检测和异常报警。     

400MHZ带宽声表面波RAC器件

一、引言 声表面波线性调频脉冲压缩滤波器以其卓越的性能在雷达与微波辐射测量系统中得到了广泛应用,随着此类系统对观测目标成像分辨率、清晰度和稳定性要求的提高,宽频带高性能的声表面波线性调频脉冲压缩滤波器的研究工作就显得更为重要.本文介绍我们最新研制可用于雷达、微波辐射测量设备的宽频带声表面波沟槽反射栅脉冲压缩滤波器(简称声表面波RAC器件),其线性调频带宽可作到400MHz.     

Bandwidth efficient concatenated coding schemes

Concatenated coded modulation is a powerful method for constructing coding schemes with large coding gain and low decoding complexity. For the concatenated scheme, the outer code has redundancy and the overall transmission rate is reduced. The problem of bandwidth expansion can be overcome by two procedures. First, the code rate of inner codes is increased with a special coding design. Second, a two-level concatenated scheme is constructed to compensate the rate loss. This way, the low-complexity concatenated coded modulation schemes can be designed without bandwidth expansion as compared with the uncoded scheme.     

Drag reduction by riblets

The interaction of the overlying turbulent flow with riblets, and its impact on their drag reduction properties are analysed. In the so-called viscous regime of vanishing riblet spacing, the drag reduction is proportional to the riblet size, but for larger riblets the proportionality breaks down, and the drag reduction eventually becomes an increase. It is found that the groove cross section A(g)(+) is a better characterization of this breakdown than the riblet spacing, with an optimum A(g)(+1/2) ≈ 11. It is also found that the breakdown is not associated with the lodging of quasi-streamwise vortices inside the riblet grooves, or with the inapplicability of the Stokes hypothesis to the flow along the grooves, but with the appearance of quasi-two-dimensional spanwise vortices below y(+) ≈ 30, with typical streamwise wavelengths λ(x)(+) ≈ 150. They are connected with a Kelvin-Helmholtz-like instability of the mean velocity profile, also found in flows over plant canopies and other surfaces with transpiration. A simplified stability model for the ribbed surface approximately accounts for the scaling of the viscous breakdown with A(g)(+).     

Packaging reduction by design

German legislation on the avoidance of packaging waste has provoked German industry to reduce packaging in a number of ways. One of these is reducing the sensitivity of engineered products to transport conditions. The principle of designing such products for the minimisation of their packaging requirements should be supplemented to existing design principles and should be included within the conventional design process. Thereby, future savings of materials, energy and recycling would be ensured and the competitiveness of industry would be increased as a result of cost reductions.