Under clinical conditions,the major components of noises in human evoked potentialsare periodic impulses,such as power interferences, system oscillations. Reducing their effects by analogfilter is inevitably associate...Under clinical conditions,the major components of noises in human evoked potentialsare periodic impulses,such as power interferences, system oscillations. Reducing their effects by analogfilter is inevitably associated with the distortions of the signal of interest.In this paper,a new approachto suppress periodic noises is presented using time-domain operators which are applied on the individualdigitized responses before averaging.A new algorithm for real time processing is developed.The effectiveness of the algorithm in dealing with simulated as well as actual evoked responses is demonstrated.The results show that this algorithm has good performance in periodic noise suppression and has zerophase shift, thus it is very suitable to be implemented on biomedical instrumentations used inclinical setups.展开更多
Under clinical conditions,the major components of noises in human evoked potentialsare periodic impulses,such as power interferences, system oscillations. Reducing their effects by analogfilter is inevitably associate...Under clinical conditions,the major components of noises in human evoked potentialsare periodic impulses,such as power interferences, system oscillations. Reducing their effects by analogfilter is inevitably associated with the distortions of the signal of interest.In this paper,a new approachto suppress periodic noises is presented using time-domain operators which are applied on the individualdigitized responses before averaging.A new algorithm for real time processing is developed.The effectiveness of the algorithm in dealing with simulated as well as actual evoked responses is demonstrated.The results show that this algorithm has good performance in periodic noise suppression and has zerophase shift, thus it is very suitable to be implemented on biomedical instrumentations used inclinical setups.展开更多
For an over-damped linear system subjected to both parametric excitation of colored noise and external excitation of periodically modulated noise, and in the case that the cross-correlation intensity between noises is...For an over-damped linear system subjected to both parametric excitation of colored noise and external excitation of periodically modulated noise, and in the case that the cross-correlation intensity between noises is a time-periodic function, we study the stochastic resonance (SR) in this paper. Using the Shapiro-Loginov formula, we acquire the exact expressions of the first-order and the second-order moments. By the stochastic averaging method, we obtain the analytical expression of the output signal-to-noise ratio (SNR). Meanwhile, we discuss the evolutions of the SNR with the signal frequency, noise intensity, correlation rate of noise, time period, and modulation frequency. We find a new bona fide SR. The evolution of the SNR with the signal frequency presents periodic oscillation, which is not observed in a conventional linear system. We obtain the conventional SR of the SNR with the noise intensity and the correlation rate of noise. We also obtain the SR in a wide sense, in which the evolution of the SNR with time period modulation frequency presents periodic oscillation. We find that the time-periodic modulation of the cross-correlation intensity between noises diversifies the stochastic resonance phenomena and makes this system possess richer dynamic behaviors.展开更多
As one of the main error sources in high-precision Global Positioning System (GPS) data processing, higher-order ionospheric (HOI) delays cause significant effects on coordinate time series that cannot be ignored ...As one of the main error sources in high-precision Global Positioning System (GPS) data processing, higher-order ionospheric (HOI) delays cause significant effects on coordinate time series that cannot be ignored in analyses of long time series. Typically two geomagnetic models, DIPOLE model and Inter- national Geomagnetic Reference Field (IGRF) model, are used for calculating HOI corrections. This paper investigates the effects of HOI correction caused by the DIPOLE model on coordinate time series. GPS data from 104 globally distributed International GNSS Service (IGS) stations spanning from January, 1999 to December, 2003 were reprocessed following up-to-date processing strategies utilizing GAMIT and GLOBK software. Two coordinate time series solutions before and after applying HOI corrections using the DIPOLE model were derived for studying the effects in terms of seasonal variations and noise amplitudes. The results show that after applying the HOI corrections calculated with DIPOLE, the noise amplitudes of the coordinate time series increased, especially in the north and east directions, and the increased amplitudes of the flicker noise were larger than those of the white noise. Furthermore, spurious periodic signals that were probably introduced by the HOI corrections from the DIPOLE model were also found. Moreover, an apparent increase was confirmed for the power spectra of most of the stations, especially in the north direction, and the amplitudes of both the annual and semi-annual signals also increased in the north and east directions. It can be inferred that the quality of the external data sources such as the geomagnetic model might be the key factors that lead to the above results. The results also suggest that we should be very careful when the DIPOLE model is used for HOI corrections.展开更多
文摘Under clinical conditions,the major components of noises in human evoked potentialsare periodic impulses,such as power interferences, system oscillations. Reducing their effects by analogfilter is inevitably associated with the distortions of the signal of interest.In this paper,a new approachto suppress periodic noises is presented using time-domain operators which are applied on the individualdigitized responses before averaging.A new algorithm for real time processing is developed.The effectiveness of the algorithm in dealing with simulated as well as actual evoked responses is demonstrated.The results show that this algorithm has good performance in periodic noise suppression and has zerophase shift, thus it is very suitable to be implemented on biomedical instrumentations used inclinical setups.
文摘Under clinical conditions,the major components of noises in human evoked potentialsare periodic impulses,such as power interferences, system oscillations. Reducing their effects by analogfilter is inevitably associated with the distortions of the signal of interest.In this paper,a new approachto suppress periodic noises is presented using time-domain operators which are applied on the individualdigitized responses before averaging.A new algorithm for real time processing is developed.The effectiveness of the algorithm in dealing with simulated as well as actual evoked responses is demonstrated.The results show that this algorithm has good performance in periodic noise suppression and has zerophase shift, thus it is very suitable to be implemented on biomedical instrumentations used inclinical setups.
基金Project supported by the National Natural Science Foundation of China(Grant No.11171238)the Young Teacher Fund of Fujian Agriculture and Forestry Uninversity,China(Grant No.2011XJJ23)the Science and Technology Project of the Education Department of Sichuan Province,China(Grant No.14ZA0050)
文摘For an over-damped linear system subjected to both parametric excitation of colored noise and external excitation of periodically modulated noise, and in the case that the cross-correlation intensity between noises is a time-periodic function, we study the stochastic resonance (SR) in this paper. Using the Shapiro-Loginov formula, we acquire the exact expressions of the first-order and the second-order moments. By the stochastic averaging method, we obtain the analytical expression of the output signal-to-noise ratio (SNR). Meanwhile, we discuss the evolutions of the SNR with the signal frequency, noise intensity, correlation rate of noise, time period, and modulation frequency. We find a new bona fide SR. The evolution of the SNR with the signal frequency presents periodic oscillation, which is not observed in a conventional linear system. We obtain the conventional SR of the SNR with the noise intensity and the correlation rate of noise. We also obtain the SR in a wide sense, in which the evolution of the SNR with time period modulation frequency presents periodic oscillation. We find that the time-periodic modulation of the cross-correlation intensity between noises diversifies the stochastic resonance phenomena and makes this system possess richer dynamic behaviors.
文摘As one of the main error sources in high-precision Global Positioning System (GPS) data processing, higher-order ionospheric (HOI) delays cause significant effects on coordinate time series that cannot be ignored in analyses of long time series. Typically two geomagnetic models, DIPOLE model and Inter- national Geomagnetic Reference Field (IGRF) model, are used for calculating HOI corrections. This paper investigates the effects of HOI correction caused by the DIPOLE model on coordinate time series. GPS data from 104 globally distributed International GNSS Service (IGS) stations spanning from January, 1999 to December, 2003 were reprocessed following up-to-date processing strategies utilizing GAMIT and GLOBK software. Two coordinate time series solutions before and after applying HOI corrections using the DIPOLE model were derived for studying the effects in terms of seasonal variations and noise amplitudes. The results show that after applying the HOI corrections calculated with DIPOLE, the noise amplitudes of the coordinate time series increased, especially in the north and east directions, and the increased amplitudes of the flicker noise were larger than those of the white noise. Furthermore, spurious periodic signals that were probably introduced by the HOI corrections from the DIPOLE model were also found. Moreover, an apparent increase was confirmed for the power spectra of most of the stations, especially in the north direction, and the amplitudes of both the annual and semi-annual signals also increased in the north and east directions. It can be inferred that the quality of the external data sources such as the geomagnetic model might be the key factors that lead to the above results. The results also suggest that we should be very careful when the DIPOLE model is used for HOI corrections.