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耳机的基本知识及选购 Q市面上耳机那么多,它们都有什么不同,又该如何选购呢?另外,好些耳机标称的低频下限都在20Hz以下,真有这么低?     

透过厂商的目光看广电市场 摩托罗拉——让我们的家连接起来!

从某种意义上说，产业首先是由技术推动的。当技术进入应用层面，并经过市场检验之后，有的被淘汰，有的则获得成功并根据业务需求不断改进与发展。技术的先进并不代表市场的成功。借着ICTC众多知名企业云集之机，本刊记者走访了摩托罗拉、思科、美国天河等几家公司的老总，把他们的新技术、新想法与新思路介绍给大家。企业家眼中的广电市场究竟怎样?这样的角度对我们广电人认识自身不无裨益。     

Experimental Research on Erbium-doped Superfluorescent Fiber Source

The effects of the variations in fiber length, fiber mirror reflectance on efficiency and output power are experimentally investigated for erbium-doped double pass backward superfluorescent fiber sources (SFSs). The influence of fiber length on mean wavelength stability (MWS) has also been demonstrated. By incorporating a short section of un-pumped erbium-doped fiber (EDF) at the output port, the pump power dependent on MWS becomes independent of pumped EDF length. This is a novel phenomenon that hasn‘t been reported up to now,and should be helpful to SFS fabrication and theory analysis. By using a fiber Michelson interferometer as spectrum slicing component,a multi-wavelength fiber source (MWFS) with ～20 channels (from 1542nm to 1559nm) is got. The MWFS has a channel spacing of ～0. 8 nm which satisfies ITUstandard. The intensity fluctuation among channels is less than 0.5dB,and the extinction ratio of all channels is above 14dB. This kind of MWFS should be useful to wavelength division multiplexing systems.     

扭杆弹簧预扭断裂原因分析

用化学分析、断口观察和金相检验等方法对预扭断裂的扭杆弹簧进行了分析。结果表明：淬火加热不足及原材料存在的内部裂纹是导致扭杆弹簧预扭断裂的主要原因。     

电站主蒸汽管道安全性检验与寿命评估

对超过设计寿命的主蒸汽管道进行了安全性检验,发现了管道存在的重大缺陷,并采取了相应的技术措施,在此基础上对主蒸汽管道进行了寿命评估。