During seismic data acquisition, a high-sensitivity geophone with a high inherent frequency can increase high frequency energy by suppressing low frequency signals. This could cause a worse response at low frequencies...During seismic data acquisition, a high-sensitivity geophone with a high inherent frequency can increase high frequency energy by suppressing low frequency signals. This could cause a worse response at low frequencies. If the advantages of high-sensitivity data and conventional data are combined, the effective bandwidth will be broadened. Considering this, we propose a partial frequency band match filtering method which can combine the advantages of both high frequency and conventional frequency ranges. By introducing Ricker wavelets with different dominant frequencies and amplitudes, we established a theoretical model which possesses characteristics of both types of seismic data and demonstrates the feasibility of the partial frequency band match filtering method. A test using single shot records shows the effectiveness of this method for widening the effective frequency band.展开更多
Receiver ghost reflections adversely affect variable-depth streamer （VDS） data acquisition. In addition, the frequency notches caused by the interference between receiver ghosts and primary waves strongly affect sei...Receiver ghost reflections adversely affect variable-depth streamer （VDS） data acquisition. In addition, the frequency notches caused by the interference between receiver ghosts and primary waves strongly affect seismic data processing and imaging. We developed a high-resolution Radon transform algorithm and used it to predict receiver ghosts from VDS data. The receiver ghost reflections are subtracted and removed from the raw data. We propose a forward Radon transform operator of VDS data in the frequency domain and, based on the ray paths of the receiver ghosts, we propose an inverse Radon transform operator. We apply the proposed methodology to model and field data with good results. We use matching and subtracting modules of commercially available seismic data processing software to remove the receiver ghosts. The frequency notches are compensated and the effective frequency bandwidth of the seismic data broadens.展开更多
Aperture-dependent motion compensation is important for wide beam Synthetic Aperture Radar(SAR) data processing.This paper studies a wide beam motion compensation algorithm based on frequency division.It takes blocks ...Aperture-dependent motion compensation is important for wide beam Synthetic Aperture Radar(SAR) data processing.This paper studies a wide beam motion compensation algorithm based on frequency division.It takes blocks along azimuth dimension in frequency domain and applies an-gle-variant motion compensation in time domain.With this frequency division based motion com-pensation approach,the effects of aperture-dependent residual phase errors are corrected precisely.The rationale and procedure of this algorithm are introduced in detail.Point targets and images of a P-band airborne SAR with motion errors are simulated to validate this algorithm.Compared with the wide beam motion compensation algorithms based on time division,the proposed algorithm has better performance,especially in terms of high-frequency motion errors.展开更多
Space time coding can provide high data rate and performance gain for wireless communication system. Performance comparison of space time trellis codes and space time transmit diversity is carried out under the sam...Space time coding can provide high data rate and performance gain for wireless communication system. Performance comparison of space time trellis codes and space time transmit diversity is carried out under the same bandwidth efficiency in this paper. We also propose some optimum low rate space time trellis codes in quasi static Rayleigh fading chan￣nel. Performance analysis and simulation show that the low rate space time trellis codes outperform space time transmit diversity at the same bandwidth efficiency, and are more suitable for the power limited wireless communication system which has no strict requirement on bandwidth efficiency.展开更多
This paper presents an approach to calculate dispersion penalty for VSR-1 optical links.Based on parameters of a specific VSR-1 link,dispersion penalties are computed for various modal dispersion bandwidths respective...This paper presents an approach to calculate dispersion penalty for VSR-1 optical links.Based on parameters of a specific VSR-1 link,dispersion penalties are computed for various modal dispersion bandwidths respectively.The worst-case eye closure is expressed numerically by using the signal waveform at time 0,and the signal waveform is obtained in frequency domain through FFT algorithm.By this approach,the dispersion penalty is determined by the shape of transfer functions of the various components in the links.To simplify the derivation of multimode fiber link transfer function,a Gaussian form of normalized impulse response is used.This calculation approach can be used to estimate the worst-case dispersion penalty of VSR-1 links in the link budget analysis.展开更多
In our recent work [Phys. Chem. Chem. Phys. 11, 9149 （2009）], a molecular-mechanics force field-based amidc-Ⅰ vibration frequency map （MM-map） for peptides and proteins was constructed. In this work, the temperat...In our recent work [Phys. Chem. Chem. Phys. 11, 9149 （2009）], a molecular-mechanics force field-based amidc-Ⅰ vibration frequency map （MM-map） for peptides and proteins was constructed. In this work, the temperature dependence of the MM-map is examined based on high-temperature molecular dynamics simulations and infrared （IR） experiments. It is shown that the 298-K map works for up to 500-K molecular dynamics trajectories, which reasonably reproduces the 88 ℃ experimental IR results. Linear IR spectra are also simulated for two tripeptides containing natural and unnatural amino acid residues, and the results are in reasonable agreement with experiment. The results suggest the MM-map can be used to obtain the temperature-dependent amide-Ⅰ local mode frequencies and their distributions for peptide oligomers, which is useful in particular for understanding the IR signatures of the thermally unfolded species.展开更多
The relationship between global warming and the variation in tropical cyclone (TC) genesis frequency is analyzed using the data of the Tropical Cyclone Year Book by the China Meteorological Administration and the Nati...The relationship between global warming and the variation in tropical cyclone (TC) genesis frequency is analyzed using the data of the Tropical Cyclone Year Book by the China Meteorological Administration and the National Centers for Environmental Prediction (NCEP) reanalysis data from 1949 to 2007. The observational results indicate that the average sea surface temperature (SST) in the Intertropical Convergence Zone (ITCZ) region (10°N– 20°N, 100°E– 140°E) increases by 0.6°C against the background of global warming, while the frequency of tropical cyclone geneses in this region decreases significantly. Generally, the rise of SSTs is favorable for the genesis of tropical cyclones, but it is now shown to be contrary to the normal effect. Most of the tropical cyclones in the western North Pacific (WNP) are generated in the ITCZ. This is quite different from the case in the Atlantic basin in which the tropical cyclones are mostly generated from the easterly wave. Our research results demonstrate that the ITCZ has a weakening trend in strength, and it has moved much more equatorward in the past 40 years; both are disadvantageous to the formation of tropical cyclones. Furthermore, our study also found that the ridge of the subtropical high tends to shift slightly equatorward, which is another adverse mechanism for the formation of tropical cyclones.展开更多
With a live wire, line impedance could be measured by means of only passive elements such as inductors or resistors, whose techniques are well known. However, as the voltage and current used for the measurement are in...With a live wire, line impedance could be measured by means of only passive elements such as inductors or resistors, whose techniques are well known. However, as the voltage and current used for the measurement are increased, the size of the inductor or resistor being used also needs to be increased, so it would be virtually impossible to make an accurate measurement. Because of this, the authors have developed a novel measurement method for line impedance using LC resonance, which the authors describe first place. In the second place, the authors propose another line impedance. The novel method is that the rectangular wave with minimum voltage is injected into the distribution line system. By means of this method, the line capacitance and the line inductance can be measured. These proposals are confirmed by the simulation or experiment. Finally, the frequency response analysis method is to be examined, whose mechanism and results are to be presented and discussed.展开更多
In the prediction theory for the broadband noise generated from a multiblade fan, the vortices in the Karman vortex street was divided into n pieces. The frequency distribution of the noise was estimated so that the S...In the prediction theory for the broadband noise generated from a multiblade fan, the vortices in the Karman vortex street was divided into n pieces. The frequency distribution of the noise was estimated so that the Strouhal number could become constant even if the wake is spread by the diffusion. From the results of the measurement of the internal flow of the fan, it was found that the noise was related to the wake characteristics of the specific location in the scroll casing where the relative flow velocity was high. The noise operating in the vicinity of the maximum efficiency point of the fan was distributed over the domain from 500 Hz to 1250 Hz. It was experimentally proved that the influence of the Karman vortex street on the noise in the domains of high and low frequencies did not exist when the distribution of the estimated sound pressure level corresponded to the measured broadband noise.展开更多
基金financially supported by the National Natural Science Foundation of China(No.41104072)College Students Science and Technology Innovation Activity Plan in Zhejiang Province(No. 2012R401214)
文摘During seismic data acquisition, a high-sensitivity geophone with a high inherent frequency can increase high frequency energy by suppressing low frequency signals. This could cause a worse response at low frequencies. If the advantages of high-sensitivity data and conventional data are combined, the effective bandwidth will be broadened. Considering this, we propose a partial frequency band match filtering method which can combine the advantages of both high frequency and conventional frequency ranges. By introducing Ricker wavelets with different dominant frequencies and amplitudes, we established a theoretical model which possesses characteristics of both types of seismic data and demonstrates the feasibility of the partial frequency band match filtering method. A test using single shot records shows the effectiveness of this method for widening the effective frequency band.
文摘Receiver ghost reflections adversely affect variable-depth streamer （VDS） data acquisition. In addition, the frequency notches caused by the interference between receiver ghosts and primary waves strongly affect seismic data processing and imaging. We developed a high-resolution Radon transform algorithm and used it to predict receiver ghosts from VDS data. The receiver ghost reflections are subtracted and removed from the raw data. We propose a forward Radon transform operator of VDS data in the frequency domain and, based on the ray paths of the receiver ghosts, we propose an inverse Radon transform operator. We apply the proposed methodology to model and field data with good results. We use matching and subtracting modules of commercially available seismic data processing software to remove the receiver ghosts. The frequency notches are compensated and the effective frequency bandwidth of the seismic data broadens.
文摘Aperture-dependent motion compensation is important for wide beam Synthetic Aperture Radar(SAR) data processing.This paper studies a wide beam motion compensation algorithm based on frequency division.It takes blocks along azimuth dimension in frequency domain and applies an-gle-variant motion compensation in time domain.With this frequency division based motion com-pensation approach,the effects of aperture-dependent residual phase errors are corrected precisely.The rationale and procedure of this algorithm are introduced in detail.Point targets and images of a P-band airborne SAR with motion errors are simulated to validate this algorithm.Compared with the wide beam motion compensation algorithms based on time division,the proposed algorithm has better performance,especially in terms of high-frequency motion errors.
文摘Space time coding can provide high data rate and performance gain for wireless communication system. Performance comparison of space time trellis codes and space time transmit diversity is carried out under the same bandwidth efficiency in this paper. We also propose some optimum low rate space time trellis codes in quasi static Rayleigh fading chan￣nel. Performance analysis and simulation show that the low rate space time trellis codes outperform space time transmit diversity at the same bandwidth efficiency, and are more suitable for the power limited wireless communication system which has no strict requirement on bandwidth efficiency.
基金Supported by"863"Hi-Tech Research and Development Program(2005AA311030) and the National Natural Science Foundationof China(Grant No.60502005)
文摘This paper presents an approach to calculate dispersion penalty for VSR-1 optical links.Based on parameters of a specific VSR-1 link,dispersion penalties are computed for various modal dispersion bandwidths respectively.The worst-case eye closure is expressed numerically by using the signal waveform at time 0,and the signal waveform is obtained in frequency domain through FFT algorithm.By this approach,the dispersion penalty is determined by the shape of transfer functions of the various components in the links.To simplify the derivation of multimode fiber link transfer function,a Gaussian form of normalized impulse response is used.This calculation approach can be used to estimate the worst-case dispersion penalty of VSR-1 links in the link budget analysis.
基金This work was supported by the National Natural Science Foundation of China （No.30870591）, the National Basic Research Program of China （No.2007CB815205） and the Chinese Academy of Sciences （Hundred Talent Fund）. Chen Han thanks Dr. Kai-cong Cai for helpful discussions.
文摘In our recent work [Phys. Chem. Chem. Phys. 11, 9149 （2009）], a molecular-mechanics force field-based amidc-Ⅰ vibration frequency map （MM-map） for peptides and proteins was constructed. In this work, the temperature dependence of the MM-map is examined based on high-temperature molecular dynamics simulations and infrared （IR） experiments. It is shown that the 298-K map works for up to 500-K molecular dynamics trajectories, which reasonably reproduces the 88 ℃ experimental IR results. Linear IR spectra are also simulated for two tripeptides containing natural and unnatural amino acid residues, and the results are in reasonable agreement with experiment. The results suggest the MM-map can be used to obtain the temperature-dependent amide-Ⅰ local mode frequencies and their distributions for peptide oligomers, which is useful in particular for understanding the IR signatures of the thermally unfolded species.
基金Specialized Project on Climate Change by China Meteorological Administration 2008Natural Science Foundation of China (40730948)Typhoon foundation of 2004 (2004STB006) by Shanghai Typhoon Institute
文摘The relationship between global warming and the variation in tropical cyclone (TC) genesis frequency is analyzed using the data of the Tropical Cyclone Year Book by the China Meteorological Administration and the National Centers for Environmental Prediction (NCEP) reanalysis data from 1949 to 2007. The observational results indicate that the average sea surface temperature (SST) in the Intertropical Convergence Zone (ITCZ) region (10°N– 20°N, 100°E– 140°E) increases by 0.6°C against the background of global warming, while the frequency of tropical cyclone geneses in this region decreases significantly. Generally, the rise of SSTs is favorable for the genesis of tropical cyclones, but it is now shown to be contrary to the normal effect. Most of the tropical cyclones in the western North Pacific (WNP) are generated in the ITCZ. This is quite different from the case in the Atlantic basin in which the tropical cyclones are mostly generated from the easterly wave. Our research results demonstrate that the ITCZ has a weakening trend in strength, and it has moved much more equatorward in the past 40 years; both are disadvantageous to the formation of tropical cyclones. Furthermore, our study also found that the ridge of the subtropical high tends to shift slightly equatorward, which is another adverse mechanism for the formation of tropical cyclones.
文摘With a live wire, line impedance could be measured by means of only passive elements such as inductors or resistors, whose techniques are well known. However, as the voltage and current used for the measurement are increased, the size of the inductor or resistor being used also needs to be increased, so it would be virtually impossible to make an accurate measurement. Because of this, the authors have developed a novel measurement method for line impedance using LC resonance, which the authors describe first place. In the second place, the authors propose another line impedance. The novel method is that the rectangular wave with minimum voltage is injected into the distribution line system. By means of this method, the line capacitance and the line inductance can be measured. These proposals are confirmed by the simulation or experiment. Finally, the frequency response analysis method is to be examined, whose mechanism and results are to be presented and discussed.
文摘In the prediction theory for the broadband noise generated from a multiblade fan, the vortices in the Karman vortex street was divided into n pieces. The frequency distribution of the noise was estimated so that the Strouhal number could become constant even if the wake is spread by the diffusion. From the results of the measurement of the internal flow of the fan, it was found that the noise was related to the wake characteristics of the specific location in the scroll casing where the relative flow velocity was high. The noise operating in the vicinity of the maximum efficiency point of the fan was distributed over the domain from 500 Hz to 1250 Hz. It was experimentally proved that the influence of the Karman vortex street on the noise in the domains of high and low frequencies did not exist when the distribution of the estimated sound pressure level corresponded to the measured broadband noise.
