基于ARM嵌入式系统设计并实现了MPEG-2 TS流的音视频解码和同步播放系统.在该系统中,由于ARM处理器内嵌了硬件视频解码器,为充分利用该资源,采用硬件MFC(multi-format codec)解码器对视频数据进行解码,同时采用开源的Mad(libmad)库对音...基于ARM嵌入式系统设计并实现了MPEG-2 TS流的音视频解码和同步播放系统.在该系统中,由于ARM处理器内嵌了硬件视频解码器,为充分利用该资源,采用硬件MFC(multi-format codec)解码器对视频数据进行解码,同时采用开源的Mad(libmad)库对音频数据进行解码.进一步利用V4L2(Video for Linux 2)驱动接口和ALSA(advanced Linux sound architecture)库实现视频和音频的播放.由于视频帧播放周期和硬件处理时延不一致,系统对音视频数据操作存在时间差,从而造成音视频播放不同步.于是采用将视频播放同步到音频播放流的方法实现音视频的播放同步.测试结果表明,设计的音视频解码和同步播放系统可以实现对音视频数据进行解码与同步播放.展开更多
A four-rod radio frequency quadruple (RFQ) accelerator is designed,manufactured,installed and commissioned for the Peking University Neutron Imaging Facility (PKUNIFTY).This 2699.6-mm-long RFQ accelerator with the mea...A four-rod radio frequency quadruple (RFQ) accelerator is designed,manufactured,installed and commissioned for the Peking University Neutron Imaging Facility (PKUNIFTY).This 2699.6-mm-long RFQ accelerator with the mean aperture radius of 3.88mm is operating at 201.5MHz in pulse mode.An inter-electrode voltage of 70kV is needed to accelerate the injected 50keV 40mA D+ ions up to 2MeV.We present the rf system,high rf power feeder design,lowver rf measurements and higher rf power test.Especially,the rf commissioning was carried out with rf power up to ~280 k W and duty factor of 4%.The measured x-ray spectrum shows that the rf inter-electrode voltage reaches 70.7 kV.It is found that the specific shunt impedance of the RFQ cavity reaches 52.7kΩ.m.展开更多
A 104-MHz ladder interdigital-H radio frequency quadrupole accelerator(T-IH-RFQ)is developed for applying RFQs to heavy ion implantation and accelerator-based mass spectroscopy in recent years at the Institute of Heav...A 104-MHz ladder interdigital-H radio frequency quadrupole accelerator(T-IH-RFQ)is developed for applying RFQs to heavy ion implantation and accelerator-based mass spectroscopy in recent years at the Institute of Heavy Ion Physics,Peking University.It could accelerate ions with a mass-to-charge ratio of less than 14,from 2.9 keV/u to 35.7 keV/u within a length of 1.1 m.The T-IH-RFQ cavity operating at H21(0)mode was constructed successfully.Based on a well designed rf power feeding system,the cavity was cold measured and tested with high rf power.In the case of cold measurement,the rf properties were obtained using a vector network analyzer with the help of a perturbation capacitor.During a high power test,the inter−electrode voltage was derived from the energy spectrum of x-rays measured by a high purity Ge detector.The results show that the specific shunt impedance of the T-IH-RFQ cavity reaches 178 kΩm,which could meet the requirements of beam dynamics design.展开更多
文摘基于ARM嵌入式系统设计并实现了MPEG-2 TS流的音视频解码和同步播放系统.在该系统中,由于ARM处理器内嵌了硬件视频解码器,为充分利用该资源,采用硬件MFC(multi-format codec)解码器对视频数据进行解码,同时采用开源的Mad(libmad)库对音频数据进行解码.进一步利用V4L2(Video for Linux 2)驱动接口和ALSA(advanced Linux sound architecture)库实现视频和音频的播放.由于视频帧播放周期和硬件处理时延不一致,系统对音视频数据操作存在时间差,从而造成音视频播放不同步.于是采用将视频播放同步到音频播放流的方法实现音视频的播放同步.测试结果表明,设计的音视频解码和同步播放系统可以实现对音视频数据进行解码与同步播放.
基金Supported by the National Natural Science Foundation of China under Grant Nos 11079001 and 10775009.
文摘A four-rod radio frequency quadruple (RFQ) accelerator is designed,manufactured,installed and commissioned for the Peking University Neutron Imaging Facility (PKUNIFTY).This 2699.6-mm-long RFQ accelerator with the mean aperture radius of 3.88mm is operating at 201.5MHz in pulse mode.An inter-electrode voltage of 70kV is needed to accelerate the injected 50keV 40mA D+ ions up to 2MeV.We present the rf system,high rf power feeder design,lowver rf measurements and higher rf power test.Especially,the rf commissioning was carried out with rf power up to ~280 k W and duty factor of 4%.The measured x-ray spectrum shows that the rf inter-electrode voltage reaches 70.7 kV.It is found that the specific shunt impedance of the RFQ cavity reaches 52.7kΩ.m.
基金by the National Natural Science Foundation of China under Grant Nos 10775009 and 11079001.Y.C.Nie would like to thank the China Scholarship Council(CSC)for financial support when he was in Frankfurt.
文摘A 104-MHz ladder interdigital-H radio frequency quadrupole accelerator(T-IH-RFQ)is developed for applying RFQs to heavy ion implantation and accelerator-based mass spectroscopy in recent years at the Institute of Heavy Ion Physics,Peking University.It could accelerate ions with a mass-to-charge ratio of less than 14,from 2.9 keV/u to 35.7 keV/u within a length of 1.1 m.The T-IH-RFQ cavity operating at H21(0)mode was constructed successfully.Based on a well designed rf power feeding system,the cavity was cold measured and tested with high rf power.In the case of cold measurement,the rf properties were obtained using a vector network analyzer with the help of a perturbation capacitor.During a high power test,the inter−electrode voltage was derived from the energy spectrum of x-rays measured by a high purity Ge detector.The results show that the specific shunt impedance of the T-IH-RFQ cavity reaches 178 kΩm,which could meet the requirements of beam dynamics design.
