We present a new filter scheme for magnetocardiogram （MCG） signal processing based on the quasi-periodic characteristic of the signals. The key points of this scheme are to determine the exact numbers of data points...We present a new filter scheme for magnetocardiogram （MCG） signal processing based on the quasi-periodic characteristic of the signals. The key points of this scheme are to determine the exact numbers of data points in each cardiac cycle by using electrocardiogram （ECG） data acquired simultaneously with the MCG signal and to normalize the MCG data sequence in each cycle into an identical length. Compared with conventional filters, the scheme has the advantage of more powerful noise suppression with less signal distortion. The desire for having high quality output signals from raw MCG data acquired in a simple shielded room or even in unshielded environment may be realized with the scheme.展开更多
We fabricated direct-current superconducting quantum interference device magnetometers with single layer epi-taxial Tl_(2)Ba_(2)CaCu_(2)O_(x) films on 36.8° SrTiO_(3) bicrystal substrates.The white Aux noise and ...We fabricated direct-current superconducting quantum interference device magnetometers with single layer epi-taxial Tl_(2)Ba_(2)CaCu_(2)O_(x) films on 36.8° SrTiO_(3) bicrystal substrates.The white Aux noise and the field-flux transformation coefficient of the devices are 1.5 × 10^(-5)Φ0/√Hz and 40 nT/Φ0,respectively.The magnetometers can work in unshielded environment.展开更多
Considering the properties of slow change and quasi-periodicity of magnetocardiography （MCG） signal, we use an integrated technique of adaptive and low-pass filtering in dealing with two-channel MCG data measured by...Considering the properties of slow change and quasi-periodicity of magnetocardiography （MCG） signal, we use an integrated technique of adaptive and low-pass filtering in dealing with two-channel MCG data measured by high Tc SQUIDs. The adaptive filter in the time domain is based on a noise feedback normalized least-mean-square （NLMS） algorithm, and the low-pass filter with a cutoff at 100Hz in the frequeucy domain characterized by Caussian functions is combined with a notch at the power line frequency. In this way, both relevant and irrelevant noises in original MCG data are largely eliminated. The method may also be useful for other slowly varying quasi-periodical signals.展开更多
Based on the results of explicit forms of free energy density for each possible arrangement of magnetization fluxes in large-scale two-dimensional （2D） square π-loop arrays given by Li et al [2007 Chin. Phys. 16 14...Based on the results of explicit forms of free energy density for each possible arrangement of magnetization fluxes in large-scale two-dimensional （2D） square π-loop arrays given by Li et al [2007 Chin. Phys. 16 1450], the field-cooled superconducting phase transition is further investigated by analysing the free energy of the arrays with a simplified symmetrical model. Our analytical result is exactly the same as that obtained in Li＇s paper by means of numerical calculations. It is shown that the phase transition splits into two branches with either ferromagnetic or anti-ferromagnetic flux ordering, which depends periodically on the strength of external magnetic flux φe through each loop and monotonically on the screen parameter β of the loops in the arrays. In principle, the diagram of the phase branches is similar to that of its one-dimensional counterpart. The influence of thermal fluctuation on the flux ordering during the transition from normal to superconducting states of the π-loop arrays is also discussed.展开更多
Quasiparticle dynamics of an optimally doped Bi2Sr2 CaCu2 O8＋δ single crystal is investigated by the femtosecond pump-probe technique. Temperature dependences of amplitude of the photoinduced differential reflectivi...Quasiparticle dynamics of an optimally doped Bi2Sr2 CaCu2 O8＋δ single crystal is investigated by the femtosecond pump-probe technique. Temperature dependences of amplitude of the photoinduced differential reflectivity and the relaxation time show the evidence of strong phonon bottleneck. The experimental results are analysed by the Rothwarf-Taylor model.展开更多
Josephson effects have been observed in Nb/YBa_(2)Cu_(3)O_(7-δ) point contacts and YBa_(2)Cu_(3)O_(7-δ) break junctions.When the junctions are exposed to a microwave field,the I-V characteristics show constant volta...Josephson effects have been observed in Nb/YBa_(2)Cu_(3)O_(7-δ) point contacts and YBa_(2)Cu_(3)O_(7-δ) break junctions.When the junctions are exposed to a microwave field,the I-V characteristics show constant voltage steps,the heights of which follow the Bessel function behavior.Obvious asymmetry about zero bias has been observed in YBCO break junctions which,we suggest,may possibly result from flux trapping in the complicated weak link structure of the system.Micrmave-induced sub-steps have also been found in YBCO break junctions.All experiments were conducted at liquid helium temperature.展开更多
The crystal structure and superconductivity of the compound Ba_(2)YCu_(3)O_(9-x) are orted in this paper.The compound has an orthorhombic distorted perovskite structure cell with a=3.892Å,b=3.824Åand c=11.64...The crystal structure and superconductivity of the compound Ba_(2)YCu_(3)O_(9-x) are orted in this paper.The compound has an orthorhombic distorted perovskite structure cell with a=3.892Å,b=3.824Åand c=11.64Å.The temperature at the middle point of superconducting transition is 93.6K.展开更多
In this paper, we have developed an algorithm based on singular value decomposition （SVD） for matrix. And the novel SVD algorithm with normalized period of cardiac cycles is presented. The results from real magnetoc...In this paper, we have developed an algorithm based on singular value decomposition （SVD） for matrix. And the novel SVD algorithm with normalized period of cardiac cycles is presented. The results from real magnetocardiography （MCG） data processing show that the new algorithm is better than the standard one not only in suppressing noises, but also in providing high-fidelity MCG signals.展开更多
We present a new least-mean-square algorithm of adaptive filtering to improve the signal to noise ratio for magneto-cardiography data collected with high-temperature SQUID-based magnetometers. By frequently adjusting ...We present a new least-mean-square algorithm of adaptive filtering to improve the signal to noise ratio for magneto-cardiography data collected with high-temperature SQUID-based magnetometers. By frequently adjusting the adaptive parameter a go systematic optimum values in the course of the programmed procedure, the convergence is accelerated with a highest speed and the minimum steady-state error is obtained simultaneously. This algorithm may be applied to eliminate other non-steady relevant noises as well.展开更多
We study the microwave response of surface intrinsic Josephson junctions on Bi2Sr2 CaCu2O8＋δ, in which bending pancake vortex lines are introduced in a controllable way. It is found that the bending vortices can gre...We study the microwave response of surface intrinsic Josephson junctions on Bi2Sr2 CaCu2O8＋δ, in which bending pancake vortex lines are introduced in a controllable way. It is found that the bending vortices can greatly influence the response. In some cases, typical Shapiro steps that lie far above the quasiparticle branch are observed, with the step interval satisfying the Josephson relation and their amplitude versus the square root of microwave power following the Bessel function behaviour. In the other cases, current steps that lie on the quasiparticle branch are observed, but only one or two steps appear at the same time under the variation of the microwave power.展开更多
An economical magnetocardiogram （MCG） system is built in our laboratory. It mainly consists of a MCG data acquisition stage equipped with two high-To superconducting quantum interference device （SQUID） magnetomete...An economical magnetocardiogram （MCG） system is built in our laboratory. It mainly consists of a MCG data acquisition stage equipped with two high-To superconducting quantum interference device （SQUID） magnetometers, a data processing stage with digital filtering and a one-layer μ-metal magnetically shielded room in conjunction with a high-Tc SQUID based active compensation. Experimental results show that a noise level of pico-tesla in MCG profiles, which is necessary for clinical applications, may be achieved with the system. Moreover, stable and convenient operations of the system are demonstrated with simulating MCG measurements.展开更多
文摘We present a new filter scheme for magnetocardiogram （MCG） signal processing based on the quasi-periodic characteristic of the signals. The key points of this scheme are to determine the exact numbers of data points in each cardiac cycle by using electrocardiogram （ECG） data acquired simultaneously with the MCG signal and to normalize the MCG data sequence in each cycle into an identical length. Compared with conventional filters, the scheme has the advantage of more powerful noise suppression with less signal distortion. The desire for having high quality output signals from raw MCG data acquired in a simple shielded room or even in unshielded environment may be realized with the scheme.
基金Supported by the National Center for R&D on Superconductivity and the Ministry of Science and Technology of China(NKBRSF-G19990646).
文摘We fabricated direct-current superconducting quantum interference device magnetometers with single layer epi-taxial Tl_(2)Ba_(2)CaCu_(2)O_(x) films on 36.8° SrTiO_(3) bicrystal substrates.The white Aux noise and the field-flux transformation coefficient of the devices are 1.5 × 10^(-5)Φ0/√Hz and 40 nT/Φ0,respectively.The magnetometers can work in unshielded environment.
文摘Considering the properties of slow change and quasi-periodicity of magnetocardiography （MCG） signal, we use an integrated technique of adaptive and low-pass filtering in dealing with two-channel MCG data measured by high Tc SQUIDs. The adaptive filter in the time domain is based on a noise feedback normalized least-mean-square （NLMS） algorithm, and the low-pass filter with a cutoff at 100Hz in the frequeucy domain characterized by Caussian functions is combined with a notch at the power line frequency. In this way, both relevant and irrelevant noises in original MCG data are largely eliminated. The method may also be useful for other slowly varying quasi-periodical signals.
基金Project supported by the State Key Development Program for Basic Research of China (Grant No 2006CB601007)the National Natural Science Foundation of China(Grant Nos 10474129 and 10534060)
文摘Based on the results of explicit forms of free energy density for each possible arrangement of magnetization fluxes in large-scale two-dimensional （2D） square π-loop arrays given by Li et al [2007 Chin. Phys. 16 1450], the field-cooled superconducting phase transition is further investigated by analysing the free energy of the arrays with a simplified symmetrical model. Our analytical result is exactly the same as that obtained in Li＇s paper by means of numerical calculations. It is shown that the phase transition splits into two branches with either ferromagnetic or anti-ferromagnetic flux ordering, which depends periodically on the strength of external magnetic flux φe through each loop and monotonically on the screen parameter β of the loops in the arrays. In principle, the diagram of the phase branches is similar to that of its one-dimensional counterpart. The influence of thermal fluctuation on the flux ordering during the transition from normal to superconducting states of the π-loop arrays is also discussed.
基金Supported by the National Natural Science Foundation of China under Grants Nos 10574155 and 10774185.
文摘Quasiparticle dynamics of an optimally doped Bi2Sr2 CaCu2 O8＋δ single crystal is investigated by the femtosecond pump-probe technique. Temperature dependences of amplitude of the photoinduced differential reflectivity and the relaxation time show the evidence of strong phonon bottleneck. The experimental results are analysed by the Rothwarf-Taylor model.
文摘Josephson effects have been observed in Nb/YBa_(2)Cu_(3)O_(7-δ) point contacts and YBa_(2)Cu_(3)O_(7-δ) break junctions.When the junctions are exposed to a microwave field,the I-V characteristics show constant voltage steps,the heights of which follow the Bessel function behavior.Obvious asymmetry about zero bias has been observed in YBCO break junctions which,we suggest,may possibly result from flux trapping in the complicated weak link structure of the system.Micrmave-induced sub-steps have also been found in YBCO break junctions.All experiments were conducted at liquid helium temperature.
文摘The crystal structure and superconductivity of the compound Ba_(2)YCu_(3)O_(9-x) are orted in this paper.The compound has an orthorhombic distorted perovskite structure cell with a=3.892Å,b=3.824Åand c=11.64Å.The temperature at the middle point of superconducting transition is 93.6K.
文摘In this paper, we have developed an algorithm based on singular value decomposition （SVD） for matrix. And the novel SVD algorithm with normalized period of cardiac cycles is presented. The results from real magnetocardiography （MCG） data processing show that the new algorithm is better than the standard one not only in suppressing noises, but also in providing high-fidelity MCG signals.
文摘We present a new least-mean-square algorithm of adaptive filtering to improve the signal to noise ratio for magneto-cardiography data collected with high-temperature SQUID-based magnetometers. By frequently adjusting the adaptive parameter a go systematic optimum values in the course of the programmed procedure, the convergence is accelerated with a highest speed and the minimum steady-state error is obtained simultaneously. This algorithm may be applied to eliminate other non-steady relevant noises as well.
基金Supported by the National Natural Science Foundation of China under Grant Nos 10474129 and 10534060, and the National Key Basic Research Programme of China under Grant Nos 2006CB601007 and 2006CB921107.
文摘We study the microwave response of surface intrinsic Josephson junctions on Bi2Sr2 CaCu2O8＋δ, in which bending pancake vortex lines are introduced in a controllable way. It is found that the bending vortices can greatly influence the response. In some cases, typical Shapiro steps that lie far above the quasiparticle branch are observed, with the step interval satisfying the Josephson relation and their amplitude versus the square root of microwave power following the Bessel function behaviour. In the other cases, current steps that lie on the quasiparticle branch are observed, but only one or two steps appear at the same time under the variation of the microwave power.
文摘An economical magnetocardiogram （MCG） system is built in our laboratory. It mainly consists of a MCG data acquisition stage equipped with two high-To superconducting quantum interference device （SQUID） magnetometers, a data processing stage with digital filtering and a one-layer μ-metal magnetically shielded room in conjunction with a high-Tc SQUID based active compensation. Experimental results show that a noise level of pico-tesla in MCG profiles, which is necessary for clinical applications, may be achieved with the system. Moreover, stable and convenient operations of the system are demonstrated with simulating MCG measurements.
