CAM后置处理研究

分析了数控加工后置处理技术的特征、面临的问题和当前的发展趋势,介绍了应用通用后置处理器开发定制专用后置处理器的实践。     

基于DSP和FPGA的GPS伪随机码并行快速捕获方案设计

讨论了高动态下GPS伪随机码并行搜索的基本原理,以及自适应门限确定方法与搜索过程中应注意的问题。提出了一种基于高速DSP和FPGA的全数字解扩接收机方案,阐述了工作流程,并给出了系统的结构框图,经测试验证实现了伪随机码并行快速捕获的功能。     

圆柱度误差最小区域评定方法述评

本文简介圆柱度误差评定的常用数学模型，并对用最小区域法评定圆柱度误差的几种近似方法及其优缺点展开讨论。     

颈动脉内血流动力学特征受向前加速度影响的数值模拟

人们在日常或某些特殊条件下常会面临方向和大小发生迅速变化的加速度环境,已有研究发现加速度环境会影响心血管系统生理、病理特征。利用计算机模拟方法详细研究了向前加速度环境下人体颈动脉内的血流动力学参数变化规律。结果表明:加速度会对颈动脉内压力、压力梯度、壁面剪切应力等与血管生理、病理现象密切相关的血流动力学参数产生显著影响。研究结果为加速度环境下颈动脉生理、病理研究提供了一定的理论依据,也为航空航天领域加速度环境下人员防护提供参考。      

Simulation and analysis of chemical release in the ionosphere

Ionospheric inhomogeneous plasma produced by single point chemical release has simple space-time structure, and cannot impact radio wave frequencies higher than Very High Frequency (VHF) band. In order to produce more complicated ionospheric plasma perturbation structure and trigger instabilities phenomena, multiple-point chemical release scheme is presented in this paper. The effects of chemical release on low latitude ionospheric plasma are estimated by linear instability growth rate theory that high growth rate represents high irregularities, ionospheric scintillation occurrence probability and high scintillation intension in scintillation duration. The amplitude scintillations and the phase scintillations of 150?MHz, 400?MHz, and 1000?MHz are calculated based on the theory of multiple phase screen (MPS), when they propagate through the disturbed area.     

Experimental and numerical investigation on surface quality for two-point incremental sheet forming with interpolator

The unsatisfied surface quality seriously impedes the wide application of incremental sheet forming (ISF) in industrial field. As a novel approach, the interpolator method is a promising strategy to enhance the surface quality in ISF. However, the mechanism for the improvement of surface quality and the influence of interpolator properties on surface roughness are not well understood. In this paper, the influences of process variables (i.e. tool diameter, step size and thickness of interpolators) on the forming process (e.g. surface roughness, forming force and geometric error) are investigated through a systematic experimental approach of central composite design (CCD) in two-point incremental sheet forming (TPIF). It is obtained that the increase in thickness of interpolators decreases the surface roughness in direction vertical to the tool path while increases the surface roughness in direction horizontal to the tool path. Nevertheless, the combined influence between thickness of interpolators and process parameters (tool diameter and step size) is limited. Meanwhile, the placement of interpolator has little influence on the effective forming force of blank. In addition, the geometric error enlarges with the increase of step size and thickness of interpolator while decreases firstly and then increase with an increase in tool diameter. Finally, the influencing mechanism of the interpolator method on surface quality can be attributed to the decrease of the contact pressure due to the increase of contact area with the unchanged contact force. Meanwhile, the interpolator method eliminates the sliding friction on the surface of blank due to the stable relative position between the blank and the interpolator.     

装备激励约束定价模式机理对比分析与设计

激励约束定价模式能够极大调动承包商积极性，是控制装备成本的一种重要方法。通过深入分析美军激励约束定价模式和我军激励约束定价模式的设计机理，提出了承包商的期望利润和军方期望价格的计算方法，并通过对比不同定价模式的特点，在借鉴2种激励约束定价模式优点基础上，设计了一种新的激励约束定价策略，提出了指导装备激励约束定价模式改革的对策建议。最后，通过算例对本文方法进行了解释，同时验证了本文方法的有效性。     

非圆等距型面轮廓X-C轴联动高速磨削试验北大核心CSCD

针对非圆等距型面轮廓磨削加工存在表面质量差的问题,建立基于恒磨除率X-C轴联动磨削理论模型。选用陶瓷CBN砂轮进行三弧段非圆等距型面轮廓的高速磨削正交试验,探究砂轮线速度、工件速度和磨削深度对磨削比能、切向磨削力、磨削温度、表面粗糙度的影响规律。分析表明,砂轮线速度对切向磨削力、表面形貌的影响最大,磨削深度对磨削比能、磨削温度、表面粗糙度的影响最大。进行表面形貌观测未探测到明显的磨削烧伤区域,证明恒磨除率X-C轴联动磨削方式可用于非圆等距型面轮廓磨削加工。     

Plane wave spectrum and boresight error of radome-enclosed antennas

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线性分组码限距离译码器的性能分析

为了提高自动重传请求(ARQ)系统的通过率,在混合ARQ系统中,使用限距离译码器改善系统的性能。在限距离译码时,线性分组码纠正重量t的错误图样。纯纠错译码器和纯检错译码器都是限距离译码器的特例。本文首先介绍了Krautchouk多项式的几个重要性质,然后,用线性分组码及其对偶码的重量分布,分别导出了两种形式的错误译码概率的简化计算公式。由于生成函数方法的使用,成功地得到了重复码、汉明码和扩展汉明码的错误译码概率的解析公式,最后,讨论了Golay码和某些本原BCH码错误译码概率的计算方法。