A new fractal image compression algorithm based on high frequency energy (HFE) partitioning andmatched domain block searching is presented to code synthetic aperture radar (SAR) imagery. In the hybridcoding algorithm,...A new fractal image compression algorithm based on high frequency energy (HFE) partitioning andmatched domain block searching is presented to code synthetic aperture radar (SAR) imagery. In the hybridcoding algorithm, the original SAR image is decomposed to low frequency components and high frequencycomponents by wavelet transform (WT). Then the coder uses HFE of block to partition and searchthe matched domain block for each range block to code the low frequency components. For the high frequencycomponents, a modified embedded zero-tree wavelet coding algorithm is applied. Experiment resultsshow that the proposed coder obtains about 0. 3dB gain when compared to the traditional fractal coderbased on the quadtree partition. Moreover, the subjective visual quality of the reconstructed SAR imageof the proposed coder outperforms that of the traditional fractal coders in the same compression ratio(CR).展开更多
Based on the Gauss linear frequency modulated wavelet transform, a new characteristic index is presented, namely time frequency energy attenuation factor which can reflect the difference features of waveform in earthq...Based on the Gauss linear frequency modulated wavelet transform, a new characteristic index is presented, namely time frequency energy attenuation factor which can reflect the difference features of waveform in earthquake focus mechanism, wave traveling path and its attenuation characteristics in focal area or near field. In order to test its validity, we select the natural earthquakes and explosion or collapse events whose focus mechanisms vary obviously,and some natural earthquakes located at the same site or in a very small area. The study indicates that the time frequency energy attenuation factors of the natural earthquakes are obviously different with that of explosion or collapse events, and the change of the time frequency energy attenuation factors is relatively stable for the earthquakes under the normal seismicity background. Using the above mentioned method, it is expected to offer a useful criterion for strong earthquake prediction by continuous earthquake observation.展开更多
Central nerve signal evoked by thoughts can be directly used to control a robot or prosthetic devices without the involvement of the peripheral nerve and muscles.This is a new strategy of human-computer interaction.A ...Central nerve signal evoked by thoughts can be directly used to control a robot or prosthetic devices without the involvement of the peripheral nerve and muscles.This is a new strategy of human-computer interaction.A method of electroencephalogram(EEG) phase synchronization combined with band energy was proposed to construct a feature vector for pattern recognition of brain-computer interaction based on EEG induced by motor imagery in this paper,rhythm and beta rhythm were first extracted from EEG by band pass filter and then the frequency band energy was calculated by the sliding time window;the instantaneous phase values were obtained using Hilbert transform and then the phase synchronization feature was calculated by the phase locking value(PLV) and the best time interval for extracting the phase synchronization feature was searched by the distribution of the PLV value in the time domain.Finally,discrimination of motor imagery patterns was performed by the support vector machine(SVM).The results showed that the phase synchronization feature more effective in4s-7s and the correct classification rate was 91.4%.Compared with the results achieved by a single EEG feature related to motor imagery,the correct classification rate was improved by 3.5 and4.3 percentage points by combining phase synchronization with band energy.These indicate that the proposed method is effective and it is expected that the study provides a way to improve the performance of the online real-time brain-computer interaction control system based on EEG related to motor imagery.展开更多
We study the energy scaling of terahertz (THz) emission through difference frequency generation of near-infrared pulses, and demonstrate that Gigawatt few-cycle THz transients at the central frequency of 30 THz are pr...We study the energy scaling of terahertz (THz) emission through difference frequency generation of near-infrared pulses, and demonstrate that Gigawatt few-cycle THz transients at the central frequency of 30 THz are produced from GaSe crystal pumped by two pulses at 1.65 and 1.95 micrometers, with the high quantum yield of 28%. Our analysis indicates that the high yield of DFG originates from the largely reduced group velocity mismatch as the long-wavelength pumping pulses are employed.展开更多
The femtosecond pulse shaping technique has been shown to be an effective method to control the multi-photon absorption by the light–matter interaction. Previous studies mainly focused on the quantum coherent control...The femtosecond pulse shaping technique has been shown to be an effective method to control the multi-photon absorption by the light–matter interaction. Previous studies mainly focused on the quantum coherent control of the multi-photon absorption by the phase, amplitude and polarization modulation, but the coherent features of the multi-photon absorption depending on the energy level structure, the laser spectrum bandwidth and laser central frequency still lack in-depth systematic research. In this work, we further explore the coherent features of the resonance-mediated two-photon absorption in a rubidium atom by varying the energy level structure, spectrum bandwidth and central frequency of the femtosecond laser field. The theoretical results show that the change of the intermediate state detuning can effectively influence the enhancement of the near-resonant part, which further affects the transform-limited （TL）-normalized final state population maximum. Moreover, as the laser spectrum bandwidth increases, the TL-normalized final state population maximum can be effectively enhanced due to the increase of the enhancement in the near-resonant part, but the TL-normalized final state population maximum is constant by varying the laser central frequency. These studies can provide a clear physical picture for understanding the coherent features of the resonance-mediated two-photon absorption, and can also provide a theoretical guidance for the future applications.展开更多
The present paper develops a new method for damage localization and severity estimation based on the employment of modal strain energy. This method is able to determine the damage locations and estimate their severiti...The present paper develops a new method for damage localization and severity estimation based on the employment of modal strain energy. This method is able to determine the damage locations and estimate their severities, requiring only the information about the changes of a few lower natural frequencies. First, a damage quantification method is formulated and iterative approach is adopted for determining the damage extent. Then a damage localization algorithm is proposed, in which a damage indicator is formulated where unity value corresponds to the true damage scenario. Finally, numerical studies and model tests are conducted to demonstrate the effectiveness of the developed algorithm.展开更多
The frequency in middle of magnon energy band in a five-layer ferromagnetic superlattice is studied by using the linear spin-wave approach and Green＇s function technique. It is found that four energy gaps and corresp...The frequency in middle of magnon energy band in a five-layer ferromagnetic superlattice is studied by using the linear spin-wave approach and Green＇s function technique. It is found that four energy gaps and corresponding four frequencie in middle of energy gaps exist in the magnon band along Kx direction perpendicular to the superlattice plane. The spin quantum numbers and the interlayer exchange couplings all affect the four frequencies in middle of the energy gaps. When all interlayer exchange couplings are same, the effect of spin quantum numbers on the frequency wg1 in middle of the energy gap Δw12 is complicated, and the frequency wg1 depends on the match of spin quantum numbers in each layer. Meanwhile, the frequencies wg2, wg3, and wg4 in middle of other energy gaps increase monotonously with increasing spin quantum numbers. When the spin quantum numbers in each layer are same, the frequencies wg1, wg2, wg3, and wg4 all increase monotonously with increasing interlayer exchange couplings.展开更多
The fiber reinforced concrete has good dynamic mechanical properties. But corresponding research lacks the dynamic damage characteristics of the polypropylene fiber（fiber of low elastic modulus） and steel fiber（fib...The fiber reinforced concrete has good dynamic mechanical properties. But corresponding research lacks the dynamic damage characteristics of the polypropylene fiber（fiber of low elastic modulus） and steel fiber（fiber of high elastic modulus） reinforced concrete under medium strain rate（10-6 s-1-10-4 s-1）. In order to study the effect of strain rate on the damage characteristics of fiber reinforced concrete during the full curve damage process, the real time dynamic acoustic emission（AE） technique was applied to monitor the damage process of fiber reinforced concrete at three strain rates. The AE wavelet energy spectrum in ca8 frequency band and average AE peak frequency at three strain rates were analyzed. With the accumulation of damage, the AE wavelet energy spectrum in ca8 frequency band increased first and then decreased, and the average AE peak frequency increased gradually. With the increase of strain rate, the AE wavelet energy spectrum in ca8 frequency band and average AE peak frequency decreased gradually. The polypropylene fiber content has more obvious effect on the Dynamic increase factor（DIF） of the peak stress than the steel fiber content. The theoretical basis was provided for the monitoring of dynamic damage of fiber reinforced concrete based on the AE technique.展开更多
In the process of oilfield water injection volume of injection allocation often appear with the pump displacement situation does not match, the widespread adoption of stator frequency technology allows the pump displa...In the process of oilfield water injection volume of injection allocation often appear with the pump displacement situation does not match, the widespread adoption of stator frequency technology allows the pump displacement and volume of injection allocation phase matching. But the technology in pump class load application speed range is limited, there is still a reflux valve control blind area,＂ turn off undead＂ problem. ＂ One-for-several＂ rotor frequency Technique in water injection station application, solved the control blind area problem, the full realization of the variable frequency close return voltage injection, at the same time, the successful implementation of the slip power efficient feedback. Stable water injection pressure of the system, and the electric energy is saved, satisfy the oilfield high efficiency, fine water needs, has a high application value.展开更多
This paper investigates a highly efficient and promising control method for forced vibration control of an axially moving beam with an attached nonlinear energy sink（NES）.Because of the axial velocity,external force...This paper investigates a highly efficient and promising control method for forced vibration control of an axially moving beam with an attached nonlinear energy sink（NES）.Because of the axial velocity,external force and external excitation frequency,the beam undergoes a high-amplitude vibration.The Galerkin method is applied to discretize the dynamic equations of the beam–NES system.The steady-state responses of the beams with an attached NES and with nothing attached are acquired by numerical simulation.Furthermore,the fast Fourier transform（FFT）is applied to get the amplitude–frequency responses.From the perspective of frequency domain analysis,it is explained that the NES has little effect on the natural frequency of the beam.Results confirm that NES has a great potential to control the excessive vibration.展开更多
The performance of the Mel-Frequency Cepstrum Coefficients (MFCC) may be affected by (1) the number of filters, (2) the shape of filters, (3) the way in which filters are spaced, and (4) the way in which the power spe...The performance of the Mel-Frequency Cepstrum Coefficients (MFCC) may be affected by (1) the number of filters, (2) the shape of filters, (3) the way in which filters are spaced, and (4) the way in which the power spectrum is warped. In this paper, several compar- ison experiments are done to find a best implementation. The traditional MFCC calculation excludes the 0th coefficient for the reason that it is regarded as somewhat unreliable. According to the analysis and experiments, the authors find that it can be regarded as the generalized frequency band energy (FBE) and is hence useful, which results in the FBE-MFCC. The au- thors also propose a better analysis, namely the auto-regressive analysis, on the frame energy, which outperforms its 1st and/or 2nd order differential derivatives. Experiments with the '863' Speech Database show that, compared with the traditional MFCC with its corresponding auto- regressive analysis coefficients, the FBE-MFCC and the frame energy with their corresponding auto-regressive analysis coefficients form the best combination, reducing the Chinese syllable er- ror rate (CSER) by about 10%, while the FBE-MFCC with the corresponding auto-regressive analysis coefficients reduces CSER by 2.5%. Comparison experiments are also done with a quite casual Chinese speech database, named Chinese Annotated Spontaneous Speech (CASS) corpus. The FBE-MFCC can reduce the error rate by about 2.9% on an average.展开更多
The frequency of based on the load pattern the power system varies of the consumers. With continuous increase in the load, the frequency of the system keeps decreasing and may reach its minimum allowable limits. Furth...The frequency of based on the load pattern the power system varies of the consumers. With continuous increase in the load, the frequency of the system keeps decreasing and may reach its minimum allowable limits. Further increase in the load will result in more frequency drop leading to the need of load shedding, if excess generation is not available to cater the need. This paper proposed a methodology in a hybrid thermal-hydro system for finding the required amount of load to be shed for setting the frequency of the system within its minimum allowable limits. The load shedding steps were obtained based on the rate of change of frequency with the increase in the load in both areas. The impact of superconducting magnetic energy storage （SMES） was obtained on load shedding scheme. The comparison of the results was presented on the two-area system.展开更多
Based on ECMWF objective analysis data, the relationships between tropical convective activi- ties and extratropical circulation, as well as the low frequency kinetic energy, have been investigat- ed by making use of ...Based on ECMWF objective analysis data, the relationships between tropical convective activi- ties and extratropical circulation, as well as the low frequency kinetic energy, have been investigat- ed by making use of diagnostic analysis methods on the intraseasonal time scale in winters of 1983/ 1984 and 1986/1987. From this study, it is found that the different intensities of the tropical con- vective activities may bring about both the different intraseasonal teleconnection wave trains be- tween the tropics and the extratropics and the different dispersions of the low frequency wave ener- gy. Moreover, the tropical convection can be an important junction factor for the teleconnection ef- fect of the tropical and extratropical circulations on the intraseasonal time scale.展开更多
基金Supported by the National Natural Science Foundation of China (No. 90304003)the President Fund of GUCAS (No. O85101HM03).
文摘A new fractal image compression algorithm based on high frequency energy (HFE) partitioning andmatched domain block searching is presented to code synthetic aperture radar (SAR) imagery. In the hybridcoding algorithm, the original SAR image is decomposed to low frequency components and high frequencycomponents by wavelet transform (WT). Then the coder uses HFE of block to partition and searchthe matched domain block for each range block to code the low frequency components. For the high frequencycomponents, a modified embedded zero-tree wavelet coding algorithm is applied. Experiment resultsshow that the proposed coder obtains about 0. 3dB gain when compared to the traditional fractal coderbased on the quadtree partition. Moreover, the subjective visual quality of the reconstructed SAR imageof the proposed coder outperforms that of the traditional fractal coders in the same compression ratio(CR).
文摘Based on the Gauss linear frequency modulated wavelet transform, a new characteristic index is presented, namely time frequency energy attenuation factor which can reflect the difference features of waveform in earthquake focus mechanism, wave traveling path and its attenuation characteristics in focal area or near field. In order to test its validity, we select the natural earthquakes and explosion or collapse events whose focus mechanisms vary obviously,and some natural earthquakes located at the same site or in a very small area. The study indicates that the time frequency energy attenuation factors of the natural earthquakes are obviously different with that of explosion or collapse events, and the change of the time frequency energy attenuation factors is relatively stable for the earthquakes under the normal seismicity background. Using the above mentioned method, it is expected to offer a useful criterion for strong earthquake prediction by continuous earthquake observation.
基金supported by the National Natural Science Foundation of China(81470084,61463024)the Research Project for Application Foundation of Yunnan Province(2013FB026)+2 种基金the Cultivation Program of Talents of Yunnan Province(KKSY201303048)the Focal Program for Education Department of Yunnan Province(2013Z130)the Brain Information Processing and Brain-computer Interaction Fusion Control of Kunming University Scienceand Technology(Fund of Discipline Direction Team)
文摘Central nerve signal evoked by thoughts can be directly used to control a robot or prosthetic devices without the involvement of the peripheral nerve and muscles.This is a new strategy of human-computer interaction.A method of electroencephalogram(EEG) phase synchronization combined with band energy was proposed to construct a feature vector for pattern recognition of brain-computer interaction based on EEG induced by motor imagery in this paper,rhythm and beta rhythm were first extracted from EEG by band pass filter and then the frequency band energy was calculated by the sliding time window;the instantaneous phase values were obtained using Hilbert transform and then the phase synchronization feature was calculated by the phase locking value(PLV) and the best time interval for extracting the phase synchronization feature was searched by the distribution of the PLV value in the time domain.Finally,discrimination of motor imagery patterns was performed by the support vector machine(SVM).The results showed that the phase synchronization feature more effective in4s-7s and the correct classification rate was 91.4%.Compared with the results achieved by a single EEG feature related to motor imagery,the correct classification rate was improved by 3.5 and4.3 percentage points by combining phase synchronization with band energy.These indicate that the proposed method is effective and it is expected that the study provides a way to improve the performance of the online real-time brain-computer interaction control system based on EEG related to motor imagery.
基金Supported by the National Natural Science Foundation of China under Grant Nos 11274326,61221064,61405222,11134010 and 11127901the Shanghai Sailing Program under Grant No 14YF1406200
文摘We study the energy scaling of terahertz (THz) emission through difference frequency generation of near-infrared pulses, and demonstrate that Gigawatt few-cycle THz transients at the central frequency of 30 THz are produced from GaSe crystal pumped by two pulses at 1.65 and 1.95 micrometers, with the high quantum yield of 28%. Our analysis indicates that the high yield of DFG originates from the largely reduced group velocity mismatch as the long-wavelength pumping pulses are employed.
基金Supported by the National Natural Science Foundation of China under Grant Nos 51132004,11474096 and 11604199the Science and Technology Commission of Shanghai Municipality under Grant No 14JC1401500the Higher Education Key Program of He'nan Province under Grant Nos 17A140025 and 16A140030
文摘The femtosecond pulse shaping technique has been shown to be an effective method to control the multi-photon absorption by the light–matter interaction. Previous studies mainly focused on the quantum coherent control of the multi-photon absorption by the phase, amplitude and polarization modulation, but the coherent features of the multi-photon absorption depending on the energy level structure, the laser spectrum bandwidth and laser central frequency still lack in-depth systematic research. In this work, we further explore the coherent features of the resonance-mediated two-photon absorption in a rubidium atom by varying the energy level structure, spectrum bandwidth and central frequency of the femtosecond laser field. The theoretical results show that the change of the intermediate state detuning can effectively influence the enhancement of the near-resonant part, which further affects the transform-limited （TL）-normalized final state population maximum. Moreover, as the laser spectrum bandwidth increases, the TL-normalized final state population maximum can be effectively enhanced due to the increase of the enhancement in the near-resonant part, but the TL-normalized final state population maximum is constant by varying the laser central frequency. These studies can provide a clear physical picture for understanding the coherent features of the resonance-mediated two-photon absorption, and can also provide a theoretical guidance for the future applications.
基金supported by the National Natural Science Foundation of China (50909088, 51010009)Science & Technology Development Project of Qingdao (09-1-3-18-jch)Program for New Century Excellent Talents in University (NCET-10-0762)
文摘The present paper develops a new method for damage localization and severity estimation based on the employment of modal strain energy. This method is able to determine the damage locations and estimate their severities, requiring only the information about the changes of a few lower natural frequencies. First, a damage quantification method is formulated and iterative approach is adopted for determining the damage extent. Then a damage localization algorithm is proposed, in which a damage indicator is formulated where unity value corresponds to the true damage scenario. Finally, numerical studies and model tests are conducted to demonstrate the effectiveness of the developed algorithm.
基金Supported by the Natural Science Foundation of Liaoning Province of China under Grant No. 20062040
文摘The frequency in middle of magnon energy band in a five-layer ferromagnetic superlattice is studied by using the linear spin-wave approach and Green＇s function technique. It is found that four energy gaps and corresponding four frequencie in middle of energy gaps exist in the magnon band along Kx direction perpendicular to the superlattice plane. The spin quantum numbers and the interlayer exchange couplings all affect the four frequencies in middle of the energy gaps. When all interlayer exchange couplings are same, the effect of spin quantum numbers on the frequency wg1 in middle of the energy gap Δw12 is complicated, and the frequency wg1 depends on the match of spin quantum numbers in each layer. Meanwhile, the frequencies wg2, wg3, and wg4 in middle of other energy gaps increase monotonously with increasing spin quantum numbers. When the spin quantum numbers in each layer are same, the frequencies wg1, wg2, wg3, and wg4 all increase monotonously with increasing interlayer exchange couplings.
基金Funded by the National Natural Science Foundation of China(No.51009058)Postdoctoral Science Foundation of China(No.2011M501160)+1 种基金the University Natural Science Research Project of Jiangsu Province(No.13KJD560002)the Doctoral Research Start-up Fund of Jinling Institute of Technology(No.Jit-b-201321)
文摘The fiber reinforced concrete has good dynamic mechanical properties. But corresponding research lacks the dynamic damage characteristics of the polypropylene fiber（fiber of low elastic modulus） and steel fiber（fiber of high elastic modulus） reinforced concrete under medium strain rate（10-6 s-1-10-4 s-1）. In order to study the effect of strain rate on the damage characteristics of fiber reinforced concrete during the full curve damage process, the real time dynamic acoustic emission（AE） technique was applied to monitor the damage process of fiber reinforced concrete at three strain rates. The AE wavelet energy spectrum in ca8 frequency band and average AE peak frequency at three strain rates were analyzed. With the accumulation of damage, the AE wavelet energy spectrum in ca8 frequency band increased first and then decreased, and the average AE peak frequency increased gradually. With the increase of strain rate, the AE wavelet energy spectrum in ca8 frequency band and average AE peak frequency decreased gradually. The polypropylene fiber content has more obvious effect on the Dynamic increase factor（DIF） of the peak stress than the steel fiber content. The theoretical basis was provided for the monitoring of dynamic damage of fiber reinforced concrete based on the AE technique.
文摘In the process of oilfield water injection volume of injection allocation often appear with the pump displacement situation does not match, the widespread adoption of stator frequency technology allows the pump displacement and volume of injection allocation phase matching. But the technology in pump class load application speed range is limited, there is still a reflux valve control blind area,＂ turn off undead＂ problem. ＂ One-for-several＂ rotor frequency Technique in water injection station application, solved the control blind area problem, the full realization of the variable frequency close return voltage injection, at the same time, the successful implementation of the slip power efficient feedback. Stable water injection pressure of the system, and the electric energy is saved, satisfy the oilfield high efficiency, fine water needs, has a high application value.
基金supported by the National Natural Science Foundation of China (project nos.11772205 , 11202140 , 11402151 , 11572182 , 51305421)the funding support from the Natural Science Foundation of Liaoning Province (201501708)
文摘This paper investigates a highly efficient and promising control method for forced vibration control of an axially moving beam with an attached nonlinear energy sink（NES）.Because of the axial velocity,external force and external excitation frequency,the beam undergoes a high-amplitude vibration.The Galerkin method is applied to discretize the dynamic equations of the beam–NES system.The steady-state responses of the beams with an attached NES and with nothing attached are acquired by numerical simulation.Furthermore,the fast Fourier transform（FFT）is applied to get the amplitude–frequency responses.From the perspective of frequency domain analysis,it is explained that the NES has little effect on the natural frequency of the beam.Results confirm that NES has a great potential to control the excessive vibration.
文摘The performance of the Mel-Frequency Cepstrum Coefficients (MFCC) may be affected by (1) the number of filters, (2) the shape of filters, (3) the way in which filters are spaced, and (4) the way in which the power spectrum is warped. In this paper, several compar- ison experiments are done to find a best implementation. The traditional MFCC calculation excludes the 0th coefficient for the reason that it is regarded as somewhat unreliable. According to the analysis and experiments, the authors find that it can be regarded as the generalized frequency band energy (FBE) and is hence useful, which results in the FBE-MFCC. The au- thors also propose a better analysis, namely the auto-regressive analysis, on the frame energy, which outperforms its 1st and/or 2nd order differential derivatives. Experiments with the '863' Speech Database show that, compared with the traditional MFCC with its corresponding auto- regressive analysis coefficients, the FBE-MFCC and the frame energy with their corresponding auto-regressive analysis coefficients form the best combination, reducing the Chinese syllable er- ror rate (CSER) by about 10%, while the FBE-MFCC with the corresponding auto-regressive analysis coefficients reduces CSER by 2.5%. Comparison experiments are also done with a quite casual Chinese speech database, named Chinese Annotated Spontaneous Speech (CASS) corpus. The FBE-MFCC can reduce the error rate by about 2.9% on an average.
文摘The frequency of based on the load pattern the power system varies of the consumers. With continuous increase in the load, the frequency of the system keeps decreasing and may reach its minimum allowable limits. Further increase in the load will result in more frequency drop leading to the need of load shedding, if excess generation is not available to cater the need. This paper proposed a methodology in a hybrid thermal-hydro system for finding the required amount of load to be shed for setting the frequency of the system within its minimum allowable limits. The load shedding steps were obtained based on the rate of change of frequency with the increase in the load in both areas. The impact of superconducting magnetic energy storage （SMES） was obtained on load shedding scheme. The comparison of the results was presented on the two-area system.
文摘Based on ECMWF objective analysis data, the relationships between tropical convective activi- ties and extratropical circulation, as well as the low frequency kinetic energy, have been investigat- ed by making use of diagnostic analysis methods on the intraseasonal time scale in winters of 1983/ 1984 and 1986/1987. From this study, it is found that the different intensities of the tropical con- vective activities may bring about both the different intraseasonal teleconnection wave trains be- tween the tropics and the extratropics and the different dispersions of the low frequency wave ener- gy. Moreover, the tropical convection can be an important junction factor for the teleconnection ef- fect of the tropical and extratropical circulations on the intraseasonal time scale.
