We study theoretically the spectral intensity evolutions of the femtosecond Gaussian and parabolic pulses with different initial pulse energies and compare the nonlinear compressions of these pulses based on a meter-l...We study theoretically the spectral intensity evolutions of the femtosecond Gaussian and parabolic pulses with different initial pulse energies and compare the nonlinear compressions of these pulses based on a meter-long hollow-core fiber filled with neon for different initial pulse durations. The pulses are first coupled into gas-filled hollow-core fiber for spectrum broadening, then compressed by the optimal chirp compensation. The parabolic pulse possesses a shorter pulse duration, larger peak power, and cleaner wings than Gaussian pulse. The properties are useful for compressing the pulses and thus generating the high-energy, short-duration pulses.展开更多
This paper presents a novel view of the impact of electron collision off-axis positions on the dynamic properties and relativistic nonlinear Thomson inverse scattering of excited electrons within tightly focused, circ...This paper presents a novel view of the impact of electron collision off-axis positions on the dynamic properties and relativistic nonlinear Thomson inverse scattering of excited electrons within tightly focused, circularly polarized laser pulses of varying intensities. We examine the effects of the transverse ponderomotive force, specifically how the deviation angle and speed of electron motion are affected by the initial off-axis position of the electron and the peak amplitude of the laser pulse. When the laser pulse intensity is low, an increase in the electron's initial off-axis distance results in reduced spatial radiation power, improved collimation, super-continuum phenomena generation, red-shifting of the spectrum's harmonic peak, and significant symmetry in the radiation radial direction. However, in contradiction to conventional understandings,when the laser pulse intensity is relatively high, the properties of the relativistic nonlinear Thomson inverse scattering of the electron deviate from the central axis, changing direction in opposition to the aforementioned effects. After reaching a peak, these properties then shift again, aligning with the previous direction. The complex interplay of these effects suggests a greater nuance and intricacy in the relationship between laser pulse intensity, electron position, and scattering properties than previously thought.展开更多
The electromagnetic time-reversal(TR)technique has the characteristics of spatiotemporal focusing in a time-reversal cavity(TRC),which can be used for pulse compression,thus forming an electromagnetic pulse with high ...The electromagnetic time-reversal(TR)technique has the characteristics of spatiotemporal focusing in a time-reversal cavity(TRC),which can be used for pulse compression,thus forming an electromagnetic pulse with high peak power.A time-reversed pulse-compression method in a single channel has high pulse compression gain.However,single channel pulse compression can only generate limited gain.This paper proposes a novel TR power-combination method in a multichannel TRC to obtain higher peak power based on TR pulse-compression theory.First,the TR power-combination model is given,and the crosstalk properties of the associated channel and the influence of the reversal performance are studied.Then,the power-combination performances for the TR pulse compression,such as combined signal to noise ratio(SNR)and combined compression gain,are analyzed by numerical simulation and experimental methods.The results show that the proposed method has obvious advantages over pulse-compression methods using a single channel cavity,and is more convenient for power combination.展开更多
Geometrical nonlinearity of the soft soil and the deviation of water flow in the soft clay from Darcy's law have been well recognized in practice. However, the theory of consolidation, which can account for both t...Geometrical nonlinearity of the soft soil and the deviation of water flow in the soft clay from Darcy's law have been well recognized in practice. However, the theory of consolidation, which can account for both the geometrical nonlinearity and the non-Darcian flow, has not been reported so far. In this contribution, a model for the consolidation of soft clay which can allow for these two factors simultaneously is proposed. Utilizing the finite difference method, the numerical model for this problem is developed. With the numerical model, the effects of the geometrical nonlinearity and the non-Darcian flow on the consolidation of the soft soil are investigated. The results show that when the self-weight stress is calculated by the same method, the rate of the non-Darcian consolidation for the large-strain case is larger than that for the small-strain case, but the difference between them is limited. However, the difference between the consolidation rates caused by the non-Darcian and Darcian flows is significant. Therefore, when the geometrical nonlinearity of the soft clay is considered in calculating the consolidation settlement, due to the complexity of the large-strain assumption, the small-strain assumption can be used to replace it if the self-weight stress for the small-strain assumption is calculated by considering its sedimentation. However, due to the aforementioned large difference between the consolidation rates with consideration of the non-Darcian flow in soft clay or not, it is better to consider the non-Darcian flow law for both the small and large stain assumptions.展开更多
We constructed a compact high-power RF pulse generator based on a gyro-magnetic nonlinear transmission line(GNLTL) to produce a high-voltage pulse with a sub-nanosecond rise time and a relatively high repetition rate,...We constructed a compact high-power RF pulse generator based on a gyro-magnetic nonlinear transmission line(GNLTL) to produce a high-voltage pulse with a sub-nanosecond rise time and a relatively high repetition rate, which shows great potential for application in the high-power ultrawideband electromagnetic effect, etc. The influence of incident pulse parameters(rise time and voltage amplitude) and line length on the sharpening characteristics of the GNLTL were investigated experimentally to optimize the rising rate of the modulated pulse front. Based on the GNLTL equivalent circuit model consisting of an LC ladder network, the rise time, the voltage conversion coefficient and the rising rate properties of a modulated pulse were also numerically analyzed in a wider range. The results show that a?>?90 k V RF pulse with a rise time of 350 ps and a repetition rate of 1 kHz in burst mode is produced by the GNLTL at an axial biasing magnetic field of 22 kA m^-1 and a line length of 30 cm under the condition of a 70 kV incident pulse. Applying a faster and higher incident pulse is conducive to improving the sharpening effect of the GNLTL. Furthermore, within a certain range, increasing the line length of the GNLTL not only reduces the rise time, but increases the voltage conversion coefficient and the rising rate of a modulated pulse. Furthermore, considering the energy loss of ferrite rings, there is an optimal line length to obtain the fastest rising rate of a modulated pulse front edge.展开更多
Many patients with sensorineural hearing loss have a precipitous high-frequency loss with relatively good thresholds in the low frequencies.This present paper briefly introduces and compares the basic principles of fo...Many patients with sensorineural hearing loss have a precipitous high-frequency loss with relatively good thresholds in the low frequencies.This present paper briefly introduces and compares the basic principles of four types of frequency lowering algorithms with emphasis on nonlinear frequency compression(NLFC). A review of the effects of the NLFC algorithm on speech and music perception and sound quality appraisal is then provided. For vowel perception, it seems that the benefits provided by NLFC are limited, which are probably related to the parameter settings of the compression. For consonant perception, several studies have shown that NLFC provides improved perception of highfrequency consonants such as/s/and/z/. However, a few other studies have demonstrated negative results in consonant perception. In terms of sentence recognition, persistent use of NLFC might provide improved performance. Compared to the conventional processing, NLFC does not alter the speech sound quality appraisal and music perception as long as the compression setting is not too aggressive. In the subsequent section,the relevant factors with regard to NLFC settings, time-course of acclimatization, listener characteristics, and perceptual tasks are discussed.Although the literature shows mixed results on the perceptual efficacy of NLFC, this technique improved certain aspects of speech understanding in certain hearing-impaired listeners. Little research is available on speech perception outcomes in languages other than English. More clinical data are needed to verify the perceptual efficacy of NLFC in patients with precipitous high-frequency hearing loss. Such knowledge will help guide clinical rehabilitation of those patients.展开更多
Lorentz force electrical impedance tomography(LFEIT) combines ultrasound stimulation and electromagnetic field detection with the goal of creating a high contrast and high resolution hybrid imaging modality. In this s...Lorentz force electrical impedance tomography(LFEIT) combines ultrasound stimulation and electromagnetic field detection with the goal of creating a high contrast and high resolution hybrid imaging modality. In this study, pulse compression working together with a linearly frequency modulated ultrasound pulse was investigated in LFEIT. Experiments were done on agar phantoms having the same level of electrical conductivity as soft biological tissues. The results showed that:(i) LFEIT using pulse compression could detect the location of the electrical conductivity variations precisely;(ii)LFEIT using pulse compression could get the same performance of detecting electrical conductivity variations as the traditional LFEIT using high voltage narrow pulse but reduce the peak stimulating power to the transducer by 25.5 dB;(iii)axial resolution of 1 mm could be obtained using modulation frequency bandwidth 2 MHz.展开更多
An in-depth and comprehensive understanding of the complex nonlinear behaviors in atmospheric dielectric barrier discharge is significant for the stable operation and effective control of the plasma. In this paper, we...An in-depth and comprehensive understanding of the complex nonlinear behaviors in atmospheric dielectric barrier discharge is significant for the stable operation and effective control of the plasma. In this paper, we study the nonlinear behaviors in argon atmospheric dielectric barrier multi pulse discharges by a one-dimensional fluid model. Under certain conditions, the multi pulse discharge becomes very sensitive with the increase of frequency, and the multi pulse period-doubling bifurcation, inverse period-doubling bifurcation and chaos appear frequently. The discharge can reach a relatively steady state only when the discharges are symmetrical between positive and negative half cycle. In addition, the effects of the voltage on these nonlinear discharges are also studied. It is found that the amplitude of voltage has no effects on the number of discharge pulses in multi-pulse period-doubling bifurcation sequences; however, to a relatively stable periodic discharge, the discharge pulses are proportional to the amplitude of the applied voltage within a certain range.展开更多
A new type of window called combined window is designed to get higher Ratio of Mainlobe to Sidelobes (RMS) and lower Mainlobe Widening Factor (MWF). Simulation results prove that the new window can solve the contradic...A new type of window called combined window is designed to get higher Ratio of Mainlobe to Sidelobes (RMS) and lower Mainlobe Widening Factor (MWF). Simulation results prove that the new window can solve the contradiction between RMS and MWF better than classic windows.展开更多
This article discusses spherical pulse like solutions of the system of semilinear wave equations with the pulses focusing at a point and emerging outgoing in three space variables. In small initial data case, it shows...This article discusses spherical pulse like solutions of the system of semilinear wave equations with the pulses focusing at a point and emerging outgoing in three space variables. In small initial data case, it shows that the nonlinearities have a strong effect at the focal point. Scattering operator is introduced to describe the caustic crossing. With the aid of the L∞norms, it analyzes the relative errors in approximate solutions.展开更多
The diagnosis of water trees of cable insulation is of great importance as the water-treeing is a primary cause of aging breakdown for the middle voltage cables. In this paper, it is described how the water-tree-aged ...The diagnosis of water trees of cable insulation is of great importance as the water-treeing is a primary cause of aging breakdown for the middle voltage cables. In this paper, it is described how the water-tree-aged 10 kV XLPE cables were diagnosed. The cables were subjected to electrical stress of 5.9 kV/mm and a thermal load cycle in a curved water-filled tube for 3, 6 and 12 months of aging in accor- dance with the accelerated water-tree test method. The aged cables were used as the samples for water-tree diagnosis. First, the water-tree degraded cable, was charged by a DC voltage, and then the cable was grounded while a pulse voltage was applied to it for releasing the space charge trapped in the water trees. The amount of the space charge, which corresponds to the deterioration degree of the water trees, was calculated. The effects of DC voltage amplitude, pulse voltage repetition rate and aging conditions on the amount of the space charge were studied. Obtained results show that the amount of the space charge has a positive correlation with the applied DC voltage and the ag- ing time of the cables, and that a peak value of space charge appears with the increase of the pulse voltage repetition rate. An optimum pulse voltage repetition rate under which the space charge can be released rapidly is obtained. Furthermore, the releasing mechanism of space charge by the pulse voltage is discussed. Accumulated results show that the presented method has a high resolution for the diagnosis of water tree degradation degree and is expected to be applied in practice in future.展开更多
We present a new model of an electron gun for generating subrelativistic femtosecond(fs) electron pulses.The basic idea is to utilize a dc acceleration stage combined with a time focusing region,the time focusing elec...We present a new model of an electron gun for generating subrelativistic femtosecond(fs) electron pulses.The basic idea is to utilize a dc acceleration stage combined with a time focusing region,the time focusing electrode generates an electron energy chirp for bunching at the target.Without considering the space charge effects,simulations of the electron gun were carried out under the conditions of different dc voltages and various slopes of the voltage added on the time focusing electrode.Tracing and simulating large numbers of photoelectrons through Monte-Carlo and finite difference methods,the electron pulses with 1 ps can be compressed to 55 fs,which will allow significant advances in the field of ultrafast diagnosis.展开更多
Magnetic pulse compression(MPC)system has been widely-used for over a few decades as a technique for producing short-duration,high-peak-power pulses reliably.A novel MPC system which does not contain external demagnet...Magnetic pulse compression(MPC)system has been widely-used for over a few decades as a technique for producing short-duration,high-peak-power pulses reliably.A novel MPC system which does not contain external demagnetization circuits,has broadened the application of MPC systems.Improvements for novel MPC systems are presented.To meet the required voltage and compression gain and on considering of the overall system efficiency,two kinds of most popular MPC systems based on the improved MPC topology are designed,which are 2-stage MPC system and 3-stage MPC system,respectively.Based on the improved MPC topology,several kinds of compact pulse generators are built in pulsed power and supply technology laboratory of Institute of Electrical Engineering,Chinese Academy of Sciences.These generators illustrate that the improved MPC topology,together with solid state switches provides an ideal way to generate pulses of around 100 nano-seconds in width,with mid and high voltage of 10 kV to 100 kV,and a high repetition frequency of about 30 kHz.展开更多
We present a nonlinear ytterbium-doped fiber amplifier based on enhanced nonlinear effects that can produce a flat broadband spectrum ranging from 1050–1225 nm with a maximum average output power of 7.8 W at 14 W pum...We present a nonlinear ytterbium-doped fiber amplifier based on enhanced nonlinear effects that can produce a flat broadband spectrum ranging from 1050–1225 nm with a maximum average output power of 7.8 W at 14 W pump power.Its repetition rate is 89 MHz. Using a pair of gratings and two knife edges as a filter, wavelength tunable picosecond pulses of tens to hundreds of milliwatts can be obtained in the broadband spectrum range. The output power, pulse width, and spectrum(center wavelength and linewidth) are adjusted by tuning the distance of the grating pair and/or the knife edges.Fixing the distance between the two gratings at 15 mm and keeping the output spectrum linewidth at approximately 20 nm,the shortest pulse width obtained is less than 1 ps centered at 1080 nm. The longest wavelength of the short pulses is around1200 nm, and its output power and pulse width are 40 m W and 5.79 ps, respectively. The generation of a flat broadband spectrum is also discussed in this paper.展开更多
The paper presents a class of nonlinear adaptive wavelet transforms for lossless image compression. In update step of the lifting the different operators are chosen by the local gradient of original image. A nonlinear...The paper presents a class of nonlinear adaptive wavelet transforms for lossless image compression. In update step of the lifting the different operators are chosen by the local gradient of original image. A nonlinear morphological predictor follows the update adaptive lifting to result in fewer large wavelet coefficients near edges for reducing coding. The nonlinear adaptive wavelet transforms can also allow perfect reconstruction without any overhead cost. Experiment results are given to show lower entropy of the adaptive transformed images than those of the non-adaptive case and great applicable potentiality in lossless image compression.展开更多
The compression of high-energy, linearly polarized pulses in a gas-filled hollow core fiber(HCF) by using a concentric phase mask is studied theoretically. Simulation results indicate that using a properly designed co...The compression of high-energy, linearly polarized pulses in a gas-filled hollow core fiber(HCF) by using a concentric phase mask is studied theoretically. Simulation results indicate that using a properly designed concentric phase mask, a40-fs input pulse centered at 800 nm with energy up to 10.0 mJ can be compressed to a full width at half maximum(FWHM) of less than 5 fs after propagating through a neon-filled HCF with a length of 1 m and diameter of 500 μm with a transmission efficiency of 67%, which is significantly higher than that without a concentric phase mask. Pulses with energy up to 20.0 mJ can also be efficiently compressed to less than 10 fs with the concentric phase mask. The higher efficiency due to the concentric phase mask can be attributed to the redistribution of the transverse intensity profile, which reduces the effect of ionization. The proposed method exhibits great potential for generating few-cycle laser pulse sources with high energy by the HCF compressor.展开更多
A novel ASIC design of changeable-point digital pulse compression (DPC) chip is presented. System hardware resource is reduced to one third of the traditional design method through operations sharing hardware, (i.e.) ...A novel ASIC design of changeable-point digital pulse compression (DPC) chip is presented. System hardware resource is reduced to one third of the traditional design method through operations sharing hardware, (i.e.) let FFT, complex multiplication and IFFT be fulfilled with the same hardware structure. Block-floating-point scaling is used to enhance the dynamic range and computation accuracy. This design applies parallel pipeline structure and the radix-4 butterfly operation to improve the processing speed. In addition, a triple-memory-space(TMS) configuration is used that allows input, computation and output operations to be overlapped, so that the dual-butterfly unit is never left in an idle state waiting for I/O operation. The whole design is implemented with only one chip of XC2V500-5 FPGA. It can implement 1 024-point DPC within 91 6 μs.The output data is converted to floating-point formation to achieve seamless interface with TMS320C6701. The validity of the design is verified by simulation and measurement results.展开更多
Sparse-array Synthetic Impulse and Aperture Radar (SIAR) can isotropically radiate by employing multiple frequencies (synthetic pulse) and multiple antennas (synthetic antenna). According to Ambiguity Function(AF), it...Sparse-array Synthetic Impulse and Aperture Radar (SIAR) can isotropically radiate by employing multiple frequencies (synthetic pulse) and multiple antennas (synthetic antenna). According to Ambiguity Function(AF), its range resolution depends only on bandwidth of transmitted signals, however, the distance grating lobes emerge when increasing the time-bandwidth product of transmitted signals. The performance of pulse compression is analyzed with the transmitted signals modulated by phase-coded sequences. It is seen that greater ratio of pulse compression and suppression of range sidelobe in SIAR can be obtained, and its effective range and range resolution is increased as well.展开更多
A canceling range sidelobes scheme has been suggested by Yang Guangzheng, et al.,(1997) this technology is based on the fact that all sidelobe of group correlation function of ideal sets are zero. At first, this paper...A canceling range sidelobes scheme has been suggested by Yang Guangzheng, et al.,(1997) this technology is based on the fact that all sidelobe of group correlation function of ideal sets are zero. At first, this paper gives the best ideal sets (i. e. the best biphase code sets whose maximal sidelobe not more than 2) for all code length N≤12, which have been obtained from binary sequences by means of the best codes sieving method suggested by Yang Guangzheng, et al.(1997) Computer simulation for group correlation property of best ideal sets for code length N=12 on various conditions is made. Simulation result shows that the sidelobe level of best ideal set with no weighting is zero, under condition of zero-Doppler shift and has ultra-low sidelobe on Doppler up to 5kHz with no weighting and whose tolerance of phase and amplitude distortion is bigger too.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61221064,61078037,11127901,and 11134010)the National Basic Research Program of China(Grant No.2011CB808101)+2 种基金the Funds from the Commission of Science and Technology of Shanghai,China(Grant No.12dz1100700)the Natural Science Foundation of Shanghai,China(Grant No.13ZR1414800)the International S&T Cooperation Program of China(Grant No.2011DFA11300)
文摘We study theoretically the spectral intensity evolutions of the femtosecond Gaussian and parabolic pulses with different initial pulse energies and compare the nonlinear compressions of these pulses based on a meter-long hollow-core fiber filled with neon for different initial pulse durations. The pulses are first coupled into gas-filled hollow-core fiber for spectrum broadening, then compressed by the optimal chirp compensation. The parabolic pulse possesses a shorter pulse duration, larger peak power, and cleaner wings than Gaussian pulse. The properties are useful for compressing the pulses and thus generating the high-energy, short-duration pulses.
基金Project supported by the National Natural Science Foundation of China (Grant Nos.10947170/A05 and 11104291)the Natural Science Fund for Colleges and Universities in Jiangsu Province (Grant No.10KJB140006)+2 种基金the Natural Sciences Foundation of Shanghai (Grant No.11ZR1441300)the Natural Science Foundation of Nanjing University of Posts and Telecommunications (Grant No.NY221098)the Jiangsu Qing Lan Project for their sponsorship。
文摘This paper presents a novel view of the impact of electron collision off-axis positions on the dynamic properties and relativistic nonlinear Thomson inverse scattering of excited electrons within tightly focused, circularly polarized laser pulses of varying intensities. We examine the effects of the transverse ponderomotive force, specifically how the deviation angle and speed of electron motion are affected by the initial off-axis position of the electron and the peak amplitude of the laser pulse. When the laser pulse intensity is low, an increase in the electron's initial off-axis distance results in reduced spatial radiation power, improved collimation, super-continuum phenomena generation, red-shifting of the spectrum's harmonic peak, and significant symmetry in the radiation radial direction. However, in contradiction to conventional understandings,when the laser pulse intensity is relatively high, the properties of the relativistic nonlinear Thomson inverse scattering of the electron deviate from the central axis, changing direction in opposition to the aforementioned effects. After reaching a peak, these properties then shift again, aligning with the previous direction. The complex interplay of these effects suggests a greater nuance and intricacy in the relationship between laser pulse intensity, electron position, and scattering properties than previously thought.
基金Project supported by the National Key R&D Program of China(Grant No.2021YFC2203503)。
文摘The electromagnetic time-reversal(TR)technique has the characteristics of spatiotemporal focusing in a time-reversal cavity(TRC),which can be used for pulse compression,thus forming an electromagnetic pulse with high peak power.A time-reversed pulse-compression method in a single channel has high pulse compression gain.However,single channel pulse compression can only generate limited gain.This paper proposes a novel TR power-combination method in a multichannel TRC to obtain higher peak power based on TR pulse-compression theory.First,the TR power-combination model is given,and the crosstalk properties of the associated channel and the influence of the reversal performance are studied.Then,the power-combination performances for the TR pulse compression,such as combined signal to noise ratio(SNR)and combined compression gain,are analyzed by numerical simulation and experimental methods.The results show that the proposed method has obvious advantages over pulse-compression methods using a single channel cavity,and is more convenient for power combination.
基金Projects(51109092,11272137)supported by the National Natural Science Foundation of ChinaProjects(2013M530237,2014T70479)supported by China Postdoctoral Science FoundationProject(SJLX15-0498)supported by Jiangsu Provincial Graduate Students Research and Innovation Program,China
文摘Geometrical nonlinearity of the soft soil and the deviation of water flow in the soft clay from Darcy's law have been well recognized in practice. However, the theory of consolidation, which can account for both the geometrical nonlinearity and the non-Darcian flow, has not been reported so far. In this contribution, a model for the consolidation of soft clay which can allow for these two factors simultaneously is proposed. Utilizing the finite difference method, the numerical model for this problem is developed. With the numerical model, the effects of the geometrical nonlinearity and the non-Darcian flow on the consolidation of the soft soil are investigated. The results show that when the self-weight stress is calculated by the same method, the rate of the non-Darcian consolidation for the large-strain case is larger than that for the small-strain case, but the difference between them is limited. However, the difference between the consolidation rates caused by the non-Darcian and Darcian flows is significant. Therefore, when the geometrical nonlinearity of the soft clay is considered in calculating the consolidation settlement, due to the complexity of the large-strain assumption, the small-strain assumption can be used to replace it if the self-weight stress for the small-strain assumption is calculated by considering its sedimentation. However, due to the aforementioned large difference between the consolidation rates with consideration of the non-Darcian flow in soft clay or not, it is better to consider the non-Darcian flow law for both the small and large stain assumptions.
基金supported by the China Postdoctoral Science Foundation (No. 2018M6335598)
文摘We constructed a compact high-power RF pulse generator based on a gyro-magnetic nonlinear transmission line(GNLTL) to produce a high-voltage pulse with a sub-nanosecond rise time and a relatively high repetition rate, which shows great potential for application in the high-power ultrawideband electromagnetic effect, etc. The influence of incident pulse parameters(rise time and voltage amplitude) and line length on the sharpening characteristics of the GNLTL were investigated experimentally to optimize the rising rate of the modulated pulse front. Based on the GNLTL equivalent circuit model consisting of an LC ladder network, the rise time, the voltage conversion coefficient and the rising rate properties of a modulated pulse were also numerically analyzed in a wider range. The results show that a?>?90 k V RF pulse with a rise time of 350 ps and a repetition rate of 1 kHz in burst mode is produced by the GNLTL at an axial biasing magnetic field of 22 kA m^-1 and a line length of 30 cm under the condition of a 70 kV incident pulse. Applying a faster and higher incident pulse is conducive to improving the sharpening effect of the GNLTL. Furthermore, within a certain range, increasing the line length of the GNLTL not only reduces the rise time, but increases the voltage conversion coefficient and the rising rate of a modulated pulse. Furthermore, considering the energy loss of ferrite rings, there is an optimal line length to obtain the fastest rising rate of a modulated pulse front edge.
基金supported in part by Grant No.2017JJ3497 from Natural Science Foundation of Hunan Province
文摘Many patients with sensorineural hearing loss have a precipitous high-frequency loss with relatively good thresholds in the low frequencies.This present paper briefly introduces and compares the basic principles of four types of frequency lowering algorithms with emphasis on nonlinear frequency compression(NLFC). A review of the effects of the NLFC algorithm on speech and music perception and sound quality appraisal is then provided. For vowel perception, it seems that the benefits provided by NLFC are limited, which are probably related to the parameter settings of the compression. For consonant perception, several studies have shown that NLFC provides improved perception of highfrequency consonants such as/s/and/z/. However, a few other studies have demonstrated negative results in consonant perception. In terms of sentence recognition, persistent use of NLFC might provide improved performance. Compared to the conventional processing, NLFC does not alter the speech sound quality appraisal and music perception as long as the compression setting is not too aggressive. In the subsequent section,the relevant factors with regard to NLFC settings, time-course of acclimatization, listener characteristics, and perceptual tasks are discussed.Although the literature shows mixed results on the perceptual efficacy of NLFC, this technique improved certain aspects of speech understanding in certain hearing-impaired listeners. Little research is available on speech perception outcomes in languages other than English. More clinical data are needed to verify the perceptual efficacy of NLFC in patients with precipitous high-frequency hearing loss. Such knowledge will help guide clinical rehabilitation of those patients.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.51137004 and 61427806)the Scientific Instrument and Equipment Development Project of Chinese Academy of Sciences(Grant No.YZ201507)the China Scholarship Council(Grant No.201604910849)
文摘Lorentz force electrical impedance tomography(LFEIT) combines ultrasound stimulation and electromagnetic field detection with the goal of creating a high contrast and high resolution hybrid imaging modality. In this study, pulse compression working together with a linearly frequency modulated ultrasound pulse was investigated in LFEIT. Experiments were done on agar phantoms having the same level of electrical conductivity as soft biological tissues. The results showed that:(i) LFEIT using pulse compression could detect the location of the electrical conductivity variations precisely;(ii)LFEIT using pulse compression could get the same performance of detecting electrical conductivity variations as the traditional LFEIT using high voltage narrow pulse but reduce the peak stimulating power to the transducer by 25.5 dB;(iii)axial resolution of 1 mm could be obtained using modulation frequency bandwidth 2 MHz.
基金supported by National Natural Science Foundation of China(No.11447244)the Science Foundation of Hengyang Normal University of China(No.14B41)+1 种基金the Construct Program of the Key Discipline in Hunan Provincethe Hunan Provincial Applied Basic Research Base of Optoelectronic Information Technology of China(No.GDXX010)
文摘An in-depth and comprehensive understanding of the complex nonlinear behaviors in atmospheric dielectric barrier discharge is significant for the stable operation and effective control of the plasma. In this paper, we study the nonlinear behaviors in argon atmospheric dielectric barrier multi pulse discharges by a one-dimensional fluid model. Under certain conditions, the multi pulse discharge becomes very sensitive with the increase of frequency, and the multi pulse period-doubling bifurcation, inverse period-doubling bifurcation and chaos appear frequently. The discharge can reach a relatively steady state only when the discharges are symmetrical between positive and negative half cycle. In addition, the effects of the voltage on these nonlinear discharges are also studied. It is found that the amplitude of voltage has no effects on the number of discharge pulses in multi-pulse period-doubling bifurcation sequences; however, to a relatively stable periodic discharge, the discharge pulses are proportional to the amplitude of the applied voltage within a certain range.
文摘A new type of window called combined window is designed to get higher Ratio of Mainlobe to Sidelobes (RMS) and lower Mainlobe Widening Factor (MWF). Simulation results prove that the new window can solve the contradiction between RMS and MWF better than classic windows.
基金The study is supported by National Natural Science Foundation of China (10131050)the Educational Ministry of Chinathe Shanghai Science and Technology Committee foundation (03QMH1407)
文摘This article discusses spherical pulse like solutions of the system of semilinear wave equations with the pulses focusing at a point and emerging outgoing in three space variables. In small initial data case, it shows that the nonlinearities have a strong effect at the focal point. Scattering operator is introduced to describe the caustic crossing. With the aid of the L∞norms, it analyzes the relative errors in approximate solutions.
基金Project supported by National Natural Science Foundation of China（51277131）, State Key Laboratory Electrical Insulation and Power Equipment, State Key Laboratory Power System （SKLD 11KZ06）.
文摘The diagnosis of water trees of cable insulation is of great importance as the water-treeing is a primary cause of aging breakdown for the middle voltage cables. In this paper, it is described how the water-tree-aged 10 kV XLPE cables were diagnosed. The cables were subjected to electrical stress of 5.9 kV/mm and a thermal load cycle in a curved water-filled tube for 3, 6 and 12 months of aging in accor- dance with the accelerated water-tree test method. The aged cables were used as the samples for water-tree diagnosis. First, the water-tree degraded cable, was charged by a DC voltage, and then the cable was grounded while a pulse voltage was applied to it for releasing the space charge trapped in the water trees. The amount of the space charge, which corresponds to the deterioration degree of the water trees, was calculated. The effects of DC voltage amplitude, pulse voltage repetition rate and aging conditions on the amount of the space charge were studied. Obtained results show that the amount of the space charge has a positive correlation with the applied DC voltage and the ag- ing time of the cables, and that a peak value of space charge appears with the increase of the pulse voltage repetition rate. An optimum pulse voltage repetition rate under which the space charge can be released rapidly is obtained. Furthermore, the releasing mechanism of space charge by the pulse voltage is discussed. Accumulated results show that the presented method has a high resolution for the diagnosis of water tree degradation degree and is expected to be applied in practice in future.
基金supported the Young Scientists Fund of the National Natural Science Foundation of China(Grant No.60901036)the National Natural Science Foundation of China(Grant No.60777027)the Innovation Laboratory Fund of the Chinese Academy of Sciences(Grant No.CXJJ-10-S13)
文摘We present a new model of an electron gun for generating subrelativistic femtosecond(fs) electron pulses.The basic idea is to utilize a dc acceleration stage combined with a time focusing region,the time focusing electrode generates an electron energy chirp for bunching at the target.Without considering the space charge effects,simulations of the electron gun were carried out under the conditions of different dc voltages and various slopes of the voltage added on the time focusing electrode.Tracing and simulating large numbers of photoelectrons through Monte-Carlo and finite difference methods,the electron pulses with 1 ps can be compressed to 55 fs,which will allow significant advances in the field of ultrafast diagnosis.
基金Project supported by National Natural Science Foundation of China （50907068, 51222701 ）, National Basic Research Program of China （973 Program） （2011 CB209402）, Opening Project of State Key Laboratory of Electrical Insulation and Power Equipment in Xi＇an Jiaotong University （EIPE12204）.
文摘Magnetic pulse compression(MPC)system has been widely-used for over a few decades as a technique for producing short-duration,high-peak-power pulses reliably.A novel MPC system which does not contain external demagnetization circuits,has broadened the application of MPC systems.Improvements for novel MPC systems are presented.To meet the required voltage and compression gain and on considering of the overall system efficiency,two kinds of most popular MPC systems based on the improved MPC topology are designed,which are 2-stage MPC system and 3-stage MPC system,respectively.Based on the improved MPC topology,several kinds of compact pulse generators are built in pulsed power and supply technology laboratory of Institute of Electrical Engineering,Chinese Academy of Sciences.These generators illustrate that the improved MPC topology,together with solid state switches provides an ideal way to generate pulses of around 100 nano-seconds in width,with mid and high voltage of 10 kV to 100 kV,and a high repetition frequency of about 30 kHz.
基金supported by the National Basic Research Program of China(Grant No.2013CB922404)the National Scientific Research Project of China(Grant No.61177047)the National Natural Science Foundation of China(Grant No.61575011)
文摘We present a nonlinear ytterbium-doped fiber amplifier based on enhanced nonlinear effects that can produce a flat broadband spectrum ranging from 1050–1225 nm with a maximum average output power of 7.8 W at 14 W pump power.Its repetition rate is 89 MHz. Using a pair of gratings and two knife edges as a filter, wavelength tunable picosecond pulses of tens to hundreds of milliwatts can be obtained in the broadband spectrum range. The output power, pulse width, and spectrum(center wavelength and linewidth) are adjusted by tuning the distance of the grating pair and/or the knife edges.Fixing the distance between the two gratings at 15 mm and keeping the output spectrum linewidth at approximately 20 nm,the shortest pulse width obtained is less than 1 ps centered at 1080 nm. The longest wavelength of the short pulses is around1200 nm, and its output power and pulse width are 40 m W and 5.79 ps, respectively. The generation of a flat broadband spectrum is also discussed in this paper.
基金Supported by the National Natural Science Foundation of China (69983005)
文摘The paper presents a class of nonlinear adaptive wavelet transforms for lossless image compression. In update step of the lifting the different operators are chosen by the local gradient of original image. A nonlinear morphological predictor follows the update adaptive lifting to result in fewer large wavelet coefficients near edges for reducing coding. The nonlinear adaptive wavelet transforms can also allow perfect reconstruction without any overhead cost. Experiment results are given to show lower entropy of the adaptive transformed images than those of the non-adaptive case and great applicable potentiality in lossless image compression.
基金Project supported by the National Natural Science Foundation of China(Grant No.61521093)the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDB1603)+1 种基金the International Science and Technology Cooperation Program of China(Grant No.2016YFE0119300)the Program of Shanghai Academic/Technology Research Leader,China(Grant No.18XD1404200)
文摘The compression of high-energy, linearly polarized pulses in a gas-filled hollow core fiber(HCF) by using a concentric phase mask is studied theoretically. Simulation results indicate that using a properly designed concentric phase mask, a40-fs input pulse centered at 800 nm with energy up to 10.0 mJ can be compressed to a full width at half maximum(FWHM) of less than 5 fs after propagating through a neon-filled HCF with a length of 1 m and diameter of 500 μm with a transmission efficiency of 67%, which is significantly higher than that without a concentric phase mask. Pulses with energy up to 20.0 mJ can also be efficiently compressed to less than 10 fs with the concentric phase mask. The higher efficiency due to the concentric phase mask can be attributed to the redistribution of the transverse intensity profile, which reduces the effect of ionization. The proposed method exhibits great potential for generating few-cycle laser pulse sources with high energy by the HCF compressor.
文摘A novel ASIC design of changeable-point digital pulse compression (DPC) chip is presented. System hardware resource is reduced to one third of the traditional design method through operations sharing hardware, (i.e.) let FFT, complex multiplication and IFFT be fulfilled with the same hardware structure. Block-floating-point scaling is used to enhance the dynamic range and computation accuracy. This design applies parallel pipeline structure and the radix-4 butterfly operation to improve the processing speed. In addition, a triple-memory-space(TMS) configuration is used that allows input, computation and output operations to be overlapped, so that the dual-butterfly unit is never left in an idle state waiting for I/O operation. The whole design is implemented with only one chip of XC2V500-5 FPGA. It can implement 1 024-point DPC within 91 6 μs.The output data is converted to floating-point formation to achieve seamless interface with TMS320C6701. The validity of the design is verified by simulation and measurement results.
基金Supported by the National Natural Science Foundation of China （Grant Nos 10576012 and 60538010）, the Program for New Century Excellent Talents in University and the Specialized Research Fund for the Doctoral Program of Higher Education of China （Grant No 20040532005）.
文摘Sparse-array Synthetic Impulse and Aperture Radar (SIAR) can isotropically radiate by employing multiple frequencies (synthetic pulse) and multiple antennas (synthetic antenna). According to Ambiguity Function(AF), its range resolution depends only on bandwidth of transmitted signals, however, the distance grating lobes emerge when increasing the time-bandwidth product of transmitted signals. The performance of pulse compression is analyzed with the transmitted signals modulated by phase-coded sequences. It is seen that greater ratio of pulse compression and suppression of range sidelobe in SIAR can be obtained, and its effective range and range resolution is increased as well.
文摘A canceling range sidelobes scheme has been suggested by Yang Guangzheng, et al.,(1997) this technology is based on the fact that all sidelobe of group correlation function of ideal sets are zero. At first, this paper gives the best ideal sets (i. e. the best biphase code sets whose maximal sidelobe not more than 2) for all code length N≤12, which have been obtained from binary sequences by means of the best codes sieving method suggested by Yang Guangzheng, et al.(1997) Computer simulation for group correlation property of best ideal sets for code length N=12 on various conditions is made. Simulation result shows that the sidelobe level of best ideal set with no weighting is zero, under condition of zero-Doppler shift and has ultra-low sidelobe on Doppler up to 5kHz with no weighting and whose tolerance of phase and amplitude distortion is bigger too.
