LARGE-EDDY SIMULATION OF FLOW AROUND CYLINDER ARRAYS AT A SUBCRITICAL REYNOLDS NUMBER

The complex three-dimensional turbulent flows around a cylinder array with four cylinders in an in-line square configuration at a subcritical Reynolds number of 1.5 × 10^4 with the spacing ratio at L/D = 1.5 and 3.5 were investigated using the Large Eddy Simulation （LES）. The full field vorticity and velocity distributions as well as turbulent quantities were calculated in detail and the near wake structures were presented. The results show that the bi-stable flow nature was observed at L/D = 1.5 and distinct vortex shedding of the upstream cylinders occurred at L/D = 3.5 at Re = 1.5 × 10^4. The techniques of Laser Doppler Anemometry （LDA） and Digital Particle Image Velocimetry （DPIV） are also employed to validate the present LES method. The results show that the numerical predictions are in excellent agreement with the experimental measurements. Therefore, the full field instantaneous and mean quantities of the flow field, velocity field and vorticity field can be extracted from the LES results for further study of the complex flow characteristics.     

2008年奥运会对北京通信行业发展的影响研究

本文侧重于分析2008年奥运会对北京通信行业在基础设施建设，技术发展水平，电信消费、创造品牌形象和提升行业整体实力等方面的影响及作用。     

FRESH-DFE: A New Structure for Interference Cancellation

This paper proposes a new structure of decision feedback equalizer that exploits the cyclostationary properties of digitally modulated signals to mitigate interference. In the proposed structure, the forward filter of the conventional DFE is replaced by a cyclic filter. It is assumed that the desired and the interference signals use some mutually different signaling attributes, for example symbol rates, centre frequency etc. The resulting structure is evaluated in the presence of up to six strong interfering signals, a scenario that is typically found in wireless cellular systems. The proposed structure provides performance gains for some modulation formats but it reduces to the conventional DFE for other signal formats.     

Hash channels

It is believed that in authentication protocols where no random numbers are involved, it is hard to introduce subliminal channels. In this paper we show that subliminal channels exist in digital signature schemes where no random numbers are used. The source where the subliminal channels exist is widely acceptable hash functions with their outputs being of some randomness. Because the subliminal channels are established by using hash functions, the subliminal channels are called hash channels in this paper. This indicates that there exist subliminal channels in any authentication protocols that use hash functions.     

辗环机数字控制系统

介绍了某辗环机数字控制系统的研制，提出了采用定值反馈闭环控制方法跟踪目标值曲线。设备安全保护时间继电器参数可根椐实际工况自动设置，整个系统实际使用效果良好。     

数字孪生丹江口工程水质安全“四预”平台研发及应用

丹江口水库的水质安全关系到南水北调中线供水的保障，数字孪生丹江口是国内首个以水利工程水质安全为业务需求之一的数字孪生工程。针对丹江口水库水体水深大、范围大、污染来源分散和类型多，以及丹库与汉库水动力交换复杂、水质呈现分区分层等特点，研发高效高精度水动力水质机理模型、水质在线动态推演技术、水质浓度场三维仿真技术，首次实现水库全域水质浓度场时空演变全过程的在线推演和三维立体仿真展示，通过海量多源异构数据的科学解析、模型集成与多业务有机融合，实现水质在线推演、预警分析、安全态势预演、预案比选决策的水质安全“四预”功能。水质安全“四预”功能已成功应用于丹江口水质安全管理，为中线水源工程供水水质保障管理提供有力支撑。     

矿井交流提升机全数字电控技术在我矿的应用

介绍了矿井交流提升机全数字电控技术在深部铜矿主井电控技术改造中的应用情况，它的应用实现了矿井交流提升机提升系统的操作运行、检测、监视和安全保护等的高度自动化，且节能效果显著。     

Remediating Knowledge-Making Spaces in the Graduate Curriculum: Developing and Sustaining Multimodal Teaching and Research

Functional, critical, and rhetorical training in multimodal teaching and research must span all aspects of professional development within the graduate curriculum in order to best prepare emerging professionals for success in the age of digital media. The authors call upon multiple perspectives of their home program and offer a range of benchmarks for other programs that want to promote digital teaching and research as integral, sustainable components of their knowledge-making spaces.     

Digital redesign of uncertain interval systems based on time-response resemblance via particle swarm optimization

In this paper, a particle swarm optimization (PSO) based approach is proposed to derive an optimal digital controller for redesigned digital systems having an interval plant based on time-response resemblance of the closed-loop systems. Because of difficulties in obtaining time-response envelopes for interval systems, the design problem is formulated as an optimization problem of a cost function in terms of aggregated deviation between the step responses corresponding to extremal energies of the redesigned digital system and those of their continuous counterpart. A proposed evolutionary framework incorporating three PSOs is subsequently presented to minimize the cost function to derive an optimal set of parameters for the digital controller, so that step response sequences corresponding to the extremal sequence energy of the redesigned digital system suitably approximate those of their continuous counterpart under the perturbation of the uncertain plant parameters. Computer simulations have shown that redesigned digital systems incorporating the PSO-derived digital controllers have better system performance than those using conventional open-loop discretization methods.     

Design of a selective digital filter using the decimation technique

The implementation of an Intermediate Frequency (IF) filter in Digital Audio-VIsual Council (DAVIC) compliant modems is a particularly complex task. In previous works, we compared the performance of different designs (analog and digital) for the radio-frequency stage in a modem application. These designs have been evaluated for a particular case defined in the DAVIC recommendation. The design limits that were pointed out are mainly due, in the digital approach, to the high frequencies at which the IF stage must operate, and to the variation of the sampling frequency.

In this paper, we propose a digital implementation of the IF filter based on the decimation technique. The evaluation of the performance has been performed using the PTOLEMY software from the Berkeley University.