基于MDT/MasterCAM的金属型铸造模具CAD/CAM

以空调器压缩机气缸为例，介绍了如何用MDT和MasterCAM实现铸造模具的开发过程，对其几何外形造型设计和数控加工编程进行了详细的分析，实现了CAD／CAM技术在铸造模具中的应用。     

《喧嚣与骚动》中的意识流描写

从《喧嚣与骚动》中意识流的主体、小说中意识流的时间意义、小说中意识流的多视觉叙述等方面,分析了福克纳如何摹仿人的意识,表现瞬息万变的意识之流,精心设置时空转换的媒介,发掘意识间的互补机能,以多视觉叙述的形式,对使人迷惑不解的形像群体进行再整理,使读者深切地感受种种不同意识活动凝聚而成的整体悲剧氛围,清楚地把握整个形象体系的内在联系和在自然时空中的相互关系,理解引起情感震撼的生活本源。     

Efficient transmission based on RGB LED lamp for indoor visible light communication

We investigate the multilevel modulation for red-green-blue light emitting diode (RGB LED). A simple approach for extracting soft values from the modulation is proposed. The mapping way from bits to the modulated symbols for the multilevel modulation is also investigated. The modified modulation is obtained through the brute force. Based on the Monte Carlo simulations, the proposed approach and modified modulation are confirmed and better bit error rate (BER) performances are obtained.     

Temperature-dependent second harmonic generation process based on an MgO-doped periodically poled lithium niobate waveguide

The temperature dependency of a 5-mol% MgO-doped periodically poled lithium niobate waveguide was investigated in this paper. We started with the temperature-dependent refractive index equation for the waveguide. Secondly, the temperature dependency of the second harmonic generation effect was experimentally researched under different temperatures and pump powers. The quasi-phase matched wavelengths, efficiency bandwidths and peak efficiencies of the waveguide were measured. The experimental results agreed with theoretical simulations, which are indispensable in the following all-optical sampling studies based on the cascaded second harmonic generation/difference-frequency generation process in the current device.     

Impacts of operational parameters on nonlinear polarization rotation-based passively mode-locked fiber laser

The operational parameters including the polarization controlling and the pump power in a nonlinear polarization rotation-based passively mode-locked fiber laser are studied in this paper.The carrier rate equations of the activated erbium-doped fiber are first employed together with the nonlinear Shro¨dinger equations to reveal the relation between the operational parameters and the output state of the passively mode-locked fiber laser.The numerical and experimental results demonstrate that the output state of the mode-locked laser varies with the polarization controlling and the pump power.The periodicity of the polarization controlling is observed.With given pump power,there exists a set of polarization controlling under which the ultra-short pulse can be generated.With given polarization controlling,the mode-locked state can be maintained generally except for some particular values of pump power.Three shapes of the output optical spectra from the fiber cavity can be identified when the pump power changes.The results in this paper provide a comprehensive insight into the operation of the nonlinear polarization rotation-based passively mode-locked fiber laser.     

分数阶傅里叶变换及其在光通信中的应用

 分数阶傅里叶变换是传统傅里叶变换的一种扩展形式,它能够在介于时域和频域之间的分数域内分析和处理信号。由于分数阶傅里叶变换的一些独特的性质,已经被广泛应用于解微分方程、量子力学、图像处理和信号处理当中。本文介绍分数阶傅里叶变换,综述其在滤波器、神经网络、图像处理和无线通信等领域的应用;结合本课题组近年来的工作成果,重点介绍了其在光通信领域中的典型应用;展望了分数阶傅里叶变换在光通信中的发展趋势。     

高速光纤通信测量技术的发展趋势

 光纤通信单信道速率持续向100 Gbit/s甚至更高发展,对测量仪器的带宽提出了更高的要求。由于电子瓶颈的限制,传统的电示波器极限带宽在70～90 GHz。目前能够测量100 Gbit/s光通信信号的电示波器技术难度和成本越来越高。为了突破电子瓶颈的限制,需要采用新的采样机理对超高速光通信信号或超宽带光信号进行测量。介绍了光域采样的基本原理和相应的光采样示波器及光采样示波器研发的进展。随着信道速率的不断提高,光纤链路的物理损伤对信号的影响越来越显著,如何监测光纤链路的物理损伤成为超高速光通信网需要解决的问题。基于对光物理层损伤的研究,提出了采用分数阶傅里叶变换测量光纤链路色散和非线性效应的方法,并对高速光纤通信链路的测量技术发展作了展望。     

新闻英语词汇特性探析

新闻英语具有语速快、涉及词汇量大、相关目的语国家社会文化背景繁杂等特点,尤其是新闻英语词汇特性突出.分析新闻英语的词汇特性,能帮助英语学习者更好地掌握新闻英语词汇的特征和运用规律,准确地了解新闻英语的信息内容.     

可见光定位系统中扩展LED ID的双频率或运算调制方法北大核心CSCD

随着可见光通信的发展,室内可见光定位技术获得了广泛的关注。在以图像传感器为接收终端的见光定位系统中,针对单频率调制ID方案简单易实施,但受限于接收终端采集频率上限,可提供ID数量过少,难以满足实际较大面积场景的应用需要。提出了一种扩展ID方法,将两个不同频率的方波进行或运算,输出信号加载到驱动端作为LED ID标识。采用普通商用手机开展了实验研究,结果表明,与使用单一以频率作为LED ID相比,在本系统中可提供ID数量增加了6倍以上,可提供153种ID,且实验中识别ID准确率100%,在LED灯具被遮挡的面积达到1/3时,仍能正确识别出ID。     

印第安文学与多元文化的融合

印第安人作为北美最早的居民,创造了辉煌的印第安文学传统。当代美国印第安女作家路易丝·厄德里奇的《爱之药》探讨了回归印第安文化传统、追寻族裔文化身份的主题,这也是贯穿当代美国印第安作家作品的主题。《爱之药》分析了深受主流社会影响的当代印第安人困顿混乱的生活状态,为现代化进程中的印第安种族指出生存的必由之路,即维护族裔文化,回归部落传统,正视社会现实,融入多元文化。从印第安文学的复兴及其发展现状来看,美国印第安文学必将成为多元文化中重要的组成部分。