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地球范围内相对论效应下的时间转移与同步 被引量:8
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作者 张科 薛舜 吕梅柏 《电子与信息学报》 EI CSCD 北大核心 2014年第8期1992-1998,共7页
对于星载时间保持系统来说,相对论效应对时钟测量精度的影响不可忽视。该文运用相对论理论研究地球范围内大尺度时空转移引起的时钟测量误差问题。分析计算了星载时钟测量相对论效应误差组成和量级,验证了频率调整法和实时补偿法消除相... 对于星载时间保持系统来说,相对论效应对时钟测量精度的影响不可忽视。该文运用相对论理论研究地球范围内大尺度时空转移引起的时钟测量误差问题。分析计算了星载时钟测量相对论效应误差组成和量级,验证了频率调整法和实时补偿法消除相对论误差的有效性。研究了普遍类型的地球轨道卫星、航空器以及月球探测器与地面时钟的转移与同步,提出在星载时钟频率调整分辨率不足时,可采取定步长时钟频率调整、带误差限的时钟频率调整或"跳秒"的形式控制时钟测量相对论效应长期误差,提出在无法实时获得航天器位置和速度时,可以根据互相关法预估周期误差。仿真验证了这些方法能有效地减小误差,为未来深空探测自主导航过程中时钟与地面时间的同步提供了方案。 展开更多
关键词 卫星导航 相对论效应 时空转移 时间保持系统 月球探测
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Tracheobronchial Polyflex stents for the management of benign refractory hypopharyngeal strictures 被引量:2
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作者 Rui Almeida Silva Nuno Mesquita +3 位作者 Pedro Pimentel Nunes Elisabete Cardoso Ricardo Marcos Pinto Luís Moreira Dias 《World Journal of Gastroenterology》 SCIE CAS CSCD 2012年第6期551-556,共6页
AIM:To describe a modified technique for placement of a tracheobronchial self-expanding plastic stent(SEPS) in patients with benign refractory hypopharyngeal strictures in order to improve dysphagia and allow strictur... AIM:To describe a modified technique for placement of a tracheobronchial self-expanding plastic stent(SEPS) in patients with benign refractory hypopharyngeal strictures in order to improve dysphagia and allow stricture remodeling.METHODS:A case series of four consecutive patients with complex hypopharyngeal strictures after combinedtherapy for laryngeal cancer,previously submitted to multiple sessions of dilation without lasting improvement,is presented.All patients underwent placement of a small diameter and unflared tracheobronchial SEPS.Main outcome measurements were improvement of dysphagia and avoiding of repeated dilation.RESULTS:The modified introducer system allowed an easy and technically successful deployment of the tracheobronchial Polyflex stent through the stricture.All four patients developed complications related to stent placement.Two patients had stent migration(one proximal and one distal),two patients developed phanryngocutaneous fistulas and all patients with stents in situ for more than 8 wk had hyperplastic tissue growth at the upper end of the stent.Stricture recurrence was observed at 4 wk follow-up after stent removal in all patients CONCLUSION:Although technically feasible,placement of a tracheobronchial SEPS is associated with a high risk of complications.Small diameter stents must be kept in place for longer than 3 mo to allow adequate time for stricture remodeling. 展开更多
关键词 Larynx neoplasms HYPOPHARYNX STRICTURES DILATION STENTS
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