The local defect in rotating machine always gives rise to repetitive transients in the collected vibration signal. However, the transient signature is prone to be contaminated by strong background noises, thus it is a...The local defect in rotating machine always gives rise to repetitive transients in the collected vibration signal. However, the transient signature is prone to be contaminated by strong background noises, thus it is a challenging task to detect the weak transients for machine fault diagnosis. In this paper, a novel adaptive tunable Q-factor wavelet transform(TQWT) filter based feature extraction method is proposed to detect repetitive transients. The emerging TQWT possesses distinct advantages over the classical constant-Q wavelet transforms, whose Q-factor can be tuned to match the oscillatory behavior of different signals, but the parameter selection for TQWT heavily relies on prior knowledge. Within our adaptive TQWT filter algorithm, the automatic optimization techniques for three TQWT parameters are implemented to achieve an optimal TQWT basis that matches the transient components. Specifically, the decomposition level is selected according to a center frequency ratio based stopping criterion, and the Q-factor and redundancy are optimized based on the minimum energy-weighted normalized wavelet entropy.Then, the adaptive TQWT decomposition can be achieved in a sparse way and result in subband signals at various wavelet scales.Further, the optimum subband signal which carries transient feature information, is identified using a normalized energy to bandwidth ratio index. Finally, the single branch reconstruction signal from the optimum subband is obtained with transient signatures via inverse TQWT, and the frequency of repetitive transients is detected using Hilbert envelope demodulation. It has been verified via numerical simulation that the proposed adaptive TQWT filter based feature extraction method can adaptively select TQWT parameters and the optimum subband for repetitive transient detection without prior knowledge. The proposed method is also applied to faulty bearing vibration signals and its effectiveness is validated.展开更多
对HTTP Live Streaming深入研究之后,发现该协议在直播流媒体传输过程中存在视频流索引文件重复传送的问题。详细阐述了服务器与客户端之间的交互过程,并通过对网络监控软件的使用,检测到交互过程中服务器传输给客户端的视频流索引文件...对HTTP Live Streaming深入研究之后,发现该协议在直播流媒体传输过程中存在视频流索引文件重复传送的问题。详细阐述了服务器与客户端之间的交互过程,并通过对网络监控软件的使用,检测到交互过程中服务器传输给客户端的视频流索引文件存在较大的冗余,造成网络带宽开销增大。提出一种可行的改进方案,在.m3u8文件中添加一个#EXT-X-MEDIA-SEQUENCE-LAST标签,并使服务器和客户端都对该标签进行识别。通过对网络占用率的对比分析,改进后的方案对网络带宽的占用率明显减小,进而验证了该改进方案的可行性。展开更多
A novel ultra-broadband polarization splitter based on a dual-core photonic crystal fiber(DC-PCF)is designed.The full-vector finite element method and coupled-mode theory are employed to investigate the characteristic...A novel ultra-broadband polarization splitter based on a dual-core photonic crystal fiber(DC-PCF)is designed.The full-vector finite element method and coupled-mode theory are employed to investigate the characteristics of the polarization splitter.According to the numerical results,a graphene-filled layer not only broadens the working bandwidth but also reduces the size of the polarization splitter.Furthermore,the fluorine-doped region and the germanium-doped region can broaden the bandwidth.Also,the 4.78 mm long polarization splitter can achieve an extinction ratio of-98.6 d B at a wavelength of 1550 nm.When extinction ratio is less than-20 d B,the range of the wavelength is 1027 nm-1723 nm with a bandwidth of 696 nm.Overall,the polarization splitter can be applied to all-optical network communication systems in the infrared and near-infrared wavelength range.展开更多
A semiconductor optical amplifier gate based on tensile strained quasi bulk InGaAs is developed.At injection current of 80mA,a 3dB optical bandwidth of more than 85nm is achieved due to dominant band filling effect...A semiconductor optical amplifier gate based on tensile strained quasi bulk InGaAs is developed.At injection current of 80mA,a 3dB optical bandwidth of more than 85nm is achieved due to dominant band filling effect.Moreover,the most important is that very low polarization dependence of gain (<0 7dB),fiber to fiber lossless operation current (70～90mA) and a high extinction ratio (>50dB) are simultaneously obtained over this wide 3dB optical bandwidth (1520～1609nm) which nearly covers the spectral region of the whole C band (1525～1565nm) and the whole L band (1570～1610nm).The gating time is also improved by decreasing carrier lifetime.The wide band polarization insensitive SOA gate is promising for use in future dense wavelength division multiplexing (DWDM) communication systems.展开更多
This paper proposes a moving ratio test, which is a modified version of ratio test by involving a bandwidth parameter, to detect multiple changes in persistence, and to determine the direction of switch. The asymptoti...This paper proposes a moving ratio test, which is a modified version of ratio test by involving a bandwidth parameter, to detect multiple changes in persistence, and to determine the direction of switch. The asymptotic distribution as well as its consistency are established. In order to estimate the change points, the authors propose a two step estimate approach. Simulations illustrate the performance of the test and estimate procedures in finite samples. An application to the analysis of Sweden/US foreign exchange rate demonstrates the validity of the procedure in practice.展开更多
基金supported by the National Natural Science Foundation of China (Grant Nos. 51335006 & 51605244)
文摘The local defect in rotating machine always gives rise to repetitive transients in the collected vibration signal. However, the transient signature is prone to be contaminated by strong background noises, thus it is a challenging task to detect the weak transients for machine fault diagnosis. In this paper, a novel adaptive tunable Q-factor wavelet transform(TQWT) filter based feature extraction method is proposed to detect repetitive transients. The emerging TQWT possesses distinct advantages over the classical constant-Q wavelet transforms, whose Q-factor can be tuned to match the oscillatory behavior of different signals, but the parameter selection for TQWT heavily relies on prior knowledge. Within our adaptive TQWT filter algorithm, the automatic optimization techniques for three TQWT parameters are implemented to achieve an optimal TQWT basis that matches the transient components. Specifically, the decomposition level is selected according to a center frequency ratio based stopping criterion, and the Q-factor and redundancy are optimized based on the minimum energy-weighted normalized wavelet entropy.Then, the adaptive TQWT decomposition can be achieved in a sparse way and result in subband signals at various wavelet scales.Further, the optimum subband signal which carries transient feature information, is identified using a normalized energy to bandwidth ratio index. Finally, the single branch reconstruction signal from the optimum subband is obtained with transient signatures via inverse TQWT, and the frequency of repetitive transients is detected using Hilbert envelope demodulation. It has been verified via numerical simulation that the proposed adaptive TQWT filter based feature extraction method can adaptively select TQWT parameters and the optimum subband for repetitive transient detection without prior knowledge. The proposed method is also applied to faulty bearing vibration signals and its effectiveness is validated.
文摘对HTTP Live Streaming深入研究之后,发现该协议在直播流媒体传输过程中存在视频流索引文件重复传送的问题。详细阐述了服务器与客户端之间的交互过程,并通过对网络监控软件的使用,检测到交互过程中服务器传输给客户端的视频流索引文件存在较大的冗余,造成网络带宽开销增大。提出一种可行的改进方案,在.m3u8文件中添加一个#EXT-X-MEDIA-SEQUENCE-LAST标签,并使服务器和客户端都对该标签进行识别。通过对网络占用率的对比分析,改进后的方案对网络带宽的占用率明显减小,进而验证了该改进方案的可行性。
基金Project supported by the State Key Laboratory of Luminescence and Applications(Grant No.SKLA-2020-01)。
文摘A novel ultra-broadband polarization splitter based on a dual-core photonic crystal fiber(DC-PCF)is designed.The full-vector finite element method and coupled-mode theory are employed to investigate the characteristics of the polarization splitter.According to the numerical results,a graphene-filled layer not only broadens the working bandwidth but also reduces the size of the polarization splitter.Furthermore,the fluorine-doped region and the germanium-doped region can broaden the bandwidth.Also,the 4.78 mm long polarization splitter can achieve an extinction ratio of-98.6 d B at a wavelength of 1550 nm.When extinction ratio is less than-20 d B,the range of the wavelength is 1027 nm-1723 nm with a bandwidth of 696 nm.Overall,the polarization splitter can be applied to all-optical network communication systems in the infrared and near-infrared wavelength range.
文摘A semiconductor optical amplifier gate based on tensile strained quasi bulk InGaAs is developed.At injection current of 80mA,a 3dB optical bandwidth of more than 85nm is achieved due to dominant band filling effect.Moreover,the most important is that very low polarization dependence of gain (<0 7dB),fiber to fiber lossless operation current (70～90mA) and a high extinction ratio (>50dB) are simultaneously obtained over this wide 3dB optical bandwidth (1520～1609nm) which nearly covers the spectral region of the whole C band (1525～1565nm) and the whole L band (1570～1610nm).The gating time is also improved by decreasing carrier lifetime.The wide band polarization insensitive SOA gate is promising for use in future dense wavelength division multiplexing (DWDM) communication systems.
基金supported by the National Natural Science Foundation of China under Grant Nos.61065009 and 60972150
文摘This paper proposes a moving ratio test, which is a modified version of ratio test by involving a bandwidth parameter, to detect multiple changes in persistence, and to determine the direction of switch. The asymptotic distribution as well as its consistency are established. In order to estimate the change points, the authors propose a two step estimate approach. Simulations illustrate the performance of the test and estimate procedures in finite samples. An application to the analysis of Sweden/US foreign exchange rate demonstrates the validity of the procedure in practice.
