By analyzing the signal model of stepped-frequency waveform, a novel method for velocity measurement is proposed. The method is based on Doppler frequency difference which is achieved by using Hough transform. As the ...By analyzing the signal model of stepped-frequency waveform, a novel method for velocity measurement is proposed. The method is based on Doppler frequency difference which is achieved by using Hough transform. As the estimated velocity is inversely proportional to the frequency step size instead of the carrier frequency of the transmitted signal as the pulse-Doppler （PD） processing, the new algorithm can achieve much wider unambiguous velocity range. Furthermore, non-coherent integration of the sub-pulses with different carrier frequencies can be implemented by Hough trans- form to improve the anti-noise performance. Besides, field experimental results show that the high range resolution profile （HRRP） of a bullet with high speed can be reconstructed correctly without distortion.展开更多
In this paper, we investigate a two electronic level system with vibrational modes coupled to a Brownian oscillator bath. The difference frequency generation （DFG） signals and sum frequency generation （SFG） signal...In this paper, we investigate a two electronic level system with vibrational modes coupled to a Brownian oscillator bath. The difference frequency generation （DFG） signals and sum frequency generation （SFG） signals are calculated. It is shown that, for the same model, the SFG signals are more sensitive than the DFG signals to the changes of the vibrational modes of the electronic two-level system. Because the SFG conversion efficiency can be improved by using the time-delay method, the findings in this paper predict that the SFG spectrum may probe the changes of the microstructure more effectively.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
A new scheme which generates multi-frequency terahertz(THz)waves from planar waveguide by the optimized cascaded difference frequency generation(OCDFG)is proposed.A THz wave with frequencyω_(T1)is generated by the OC...A new scheme which generates multi-frequency terahertz(THz)waves from planar waveguide by the optimized cascaded difference frequency generation(OCDFG)is proposed.A THz wave with frequencyω_(T1)is generated by the OCDFG with two infrared pump waves,and simultaneously a series of cascaded optical waves with a frequency intervalω_(T1)is generated.The THz wave with a frequency of M-timesω_(T1)is generated by mixing the m-th-order and the(m+M)-th-order cascaded optical wave.The phase mismatch distributions of cascaded difference frequency generation(CDFG)are modulated by changing the thickness of planar waveguide step by step,thereby satisfying the phase-matching condition from first-order to high-order cascaded Stokes process step by step.As a result,the intensity of THz wave can be enhanced and modulated by controlling the cascading order of OCDFG.展开更多
A novel scheme for high-efficiency terahertz(THz)wave generation based on optimized cascaded difference frequency generation(OCDFG)with planar waveguide is presented.The phase mismatches of each-order cascaded differe...A novel scheme for high-efficiency terahertz(THz)wave generation based on optimized cascaded difference frequency generation(OCDFG)with planar waveguide is presented.The phase mismatches of each-order cascaded difference frequency generation(CDFG)are modulated by changing the thickness of the waveguide,resulting in a decrement of phase mismatches in cascaded Stokes processes and an increment of phase mismatches in cascaded anti-Stokes processes simultaneously.The modulated phase mismatches enhance the cascaded Stokes processes and suppress the cascaded anti-Stokes processes simultaneously,yielding energy conversion efficiencies over 25%from optical wave to THz wave at 100 K.展开更多
High-efficiency terahertz(THz) wave generation with multiple frequencies by optimized cascaded difference frequency generation(OCDFG) is investigated at 100 K using a nonlinear crystal consisting of a periodically pol...High-efficiency terahertz(THz) wave generation with multiple frequencies by optimized cascaded difference frequency generation(OCDFG) is investigated at 100 K using a nonlinear crystal consisting of a periodically poled lithium niobate(PPLN) part and an aperiodically poled lithium niobate(APPLN) part.Two infrared pump waves with a frequency difference ω_(T1) generate THz waves and a series of cascaded optical waves in the PPLN part by cascaded difference frequency generation(CDFG).The generated cascaded optical waves with frequency interval ω_(T1) then further interact in the APPLN part by OCDFG,yielding the following two advantages.First,OCDFG in the APPLN part is efficiently stimulated by inputting multi-order cascaded optical waves rather than the only two intense infrared pump waves,yielding unprecedented energy conversion efficiencies in excess of 37% at 1 THz at 100 K.Second,THz waves with M timesω_(T1) are generated by mixing the mth-order and the(m+M)th-order cascaded optical waves by designing poling period distributions of the APPLN part.展开更多
A novel widely tunable dual-wavelength mid-IR difference frequency generation （DFG） scheme with uniform grating periodically poled lithium niobate （PPLN） is presented in this paper. By using the temperature-depend...A novel widely tunable dual-wavelength mid-IR difference frequency generation （DFG） scheme with uniform grating periodically poled lithium niobate （PPLN） is presented in this paper. By using the temperature-dependent dispersion property of PPLN, the quasi-phase matching （QPM） peak for the pump may evolve into two separate ones and the wavelength spacing between them increases with the decrease of the crystal temperature. Such two pump QPM peaks may allow simultaneous dual-wavelength mid-IR laser radiations while properly setting the two fundamental pump wavelengths. With this scheme, mid-IR dual-wavelength laser radiations at around 3.228 and 3.548, 3.114 and 3.661, and 3.019 and 3.76 μm, are experimentally achieved for the crystal temperatures of 90, 65, and 30 ℃, respectively, based on the fiber laser fundamental lights.展开更多
Objective To compare the difference in the clinical efficacy on the different frequency hearing damages for the patients with sudden deafness between the comprehensive therapy of electroacupuncture and western medicin...Objective To compare the difference in the clinical efficacy on the different frequency hearing damages for the patients with sudden deafness between the comprehensive therapy of electroacupuncture and western medicine and the simple western medicine comprehensive therapy. Methods Fifty-eight cases were randomized into an acupuncture plus medication group （28 cases, 32 damaged ears） and a western medicine group （30 cases, 34 damaged ears）. In the acupuncture plus medication group, the comprehensive therapy of electroacupuncture and western medicine was used. The main points were ěrmén （耳门 TE 21）, Tīnggōng （听宫 SI 19）, Tīnghuì （听会 GB 2）, Yìfēng （翳风 TE 17）, etc. The western medicine therapy was the comprehensive treatment with vasodilators, the medicines for promoting nerve function and releasing inner ear edema and hyperbaric oxygen. In the western medicine group, the western medicine comprehensive therapy was adopted. 10-day treatment made one session. Two sessions of treatment were required. In 1 or 2 sessions of treatment, the efficacy was observed, the electric audiometry was evaluated. Additionally, the blood routine and liver and kidney functions were detected. Results The total effective rate was 50.0% （16/32） in the acupuncture ＋ medication group and was 55.9% （19/34） in the western medicine group. The efficacies were similar between the two groups （P〉0.05）. In 1 and 2 sessions of treatment, at 250 Hz, 500 Hz and 1 kHz, the electric audiometry values in either group were recovered significantly as compared with those before treatment （all P〈0.01）. At 2 kHz, in 1 and 2 sessions of treatment, the improvements of the electric audiometry values were significant as compared with those before treatment in the acupuncture plus medication group separately （P〈0.05, P〈0.01）. At 4 kHz, the differences were not significant statistically before and after treatment in either group （all P〉0.05）. There were no abnormalities in the blood routine and liver and kidney function detections before and after treatment in either group. Conclusion Either the comprehensive therapy of electroacupuncture and western medicine or the simple western medicine comprehensive therapy is effective in the treatment of low frequency hearing damage of sudden deafness. Either of them has no effect on high frequency hearing damage. But for the middle frequency hearing damage, the efficacy of the comprehensive therapy of electroacupuncture and western medicine is superior to that of the simple western medicine comprehensive therapy.展开更多
BACKGROUND Repetitive transcranial magnetic stimulation(rTMS)entered clinical practice in China after 2000,first used in psychiatric surgery,and then in neurology and other disciplines.The First Hospital of Jiaxing in...BACKGROUND Repetitive transcranial magnetic stimulation(rTMS)entered clinical practice in China after 2000,first used in psychiatric surgery,and then in neurology and other disciplines.The First Hospital of Jiaxing introduced TMS in 2015.In practical applications,it has been found that different models of instruments and technical parameters can lead to differences in therapeutic efficacy.Therefore,our hospital selected the Danish TMS instrument,which ranks second in China,to test patients with schizophrenia from March 2021 to July 2021,with a focus on comparing the results at 5 Hz,10 Hz,and 15 Hz.The testing time is concentrated between 8:30 to 10:30 in the morning.A contingency plan was made for the quality after inspection before testing.Two evaluators independently control the quality of the contingency plan.The data is independently saved and proofread by two evaluators.The purpose of this study is to translate the research results into clinical practice and provide reference basis.AIM To investigate the effects of rehabilitation therapy using rTMS on the negative symptoms and event-related potential component of P300 in chronic schizophrenia.METHODS One hundred and five patients with chronic schizophrenia were randomly allocated to three groups based on the frequency of rTMS(5,10,or 15 Hz).The patients underwent five sessions of rTMS per week for 5 weeks.We compared the pre-and post-treatment P300 latency and scores for the Scale for Assessment of Negative Symptoms(SANS).RESULTS A significant decrease in SANS score after rTMS was observed in the 10-Hz group(P<0.05),which was not observed in the 5-Hz and 15-Hz groups.There was a significant increase in P300 amplitude in the 10-Hz group after rTMS treatment(P<0.05),but there was no significant change in P300 latency(P>0.05).The improvement of SANS score in the 10-Hz rTMS group was related to patient age and disease course.CONCLUSION rTMS at 10 Hz improved negative symptoms and cognitive function in chronic schizophrenia;however,further studies on the mechanism of action are required to validate our observations.展开更多
The precision of landslide displacement prediction is crucial for effective landslide prevention and mitigation strategies.However,the role of surface monitoring frequency in influencing prediction accuracy has been l...The precision of landslide displacement prediction is crucial for effective landslide prevention and mitigation strategies.However,the role of surface monitoring frequency in influencing prediction accuracy has been largely neglected.This study examined the effect of varying monitoring frequencies on the accuracy of displacement predictions by using the Baijiabao landslide in the Three Gorges Reservoir Area(TGRA)as a case study.We collected surface automatic monitoring data at different intervals,ranging from daily to monthly.The Ensemble Empirical Mode Decomposition(EEMD)algorithm was utilized to dissect the accumulated displacements into periodic and trend components at each monitoring frequency.Polynomial fitting was applied to forecast the trend component while the periodic component was predicted with two state-of-the-art neural network models:Long Short-Term Memory(LSTM)and Gated Recurrent Unit(GRU).The predictions from these models were integrated to derive cumulative displacement forecasts,enabling a comparative analysis of prediction accuracy across different monitoring frequencies.The results demonstrate that the proposed models achieve high accuracy in landslide displacement forecasting,with optimal performance observed at moderate monitoring intervals.Intriguingly,the daily mean average error(MAE)decreases sharply with increasing monitoring frequency,reaching a plateau.These findings were corroborated by a parallel analysis of the Bazimen landslide,suggesting that moderate monitoring intervals of approximately 7 to 15 days are most conducive to achieving enhanced prediction accuracy compared to both daily and monthly intervals.展开更多
Acupuncture has been shown to ameliorate cognitive impairment of Alzheimer’s disease.Acupoints and stimulation frequency influence the therapeutic effect of electroacupuncture.Rat models of Alzheimer’s disease were ...Acupuncture has been shown to ameliorate cognitive impairment of Alzheimer’s disease.Acupoints and stimulation frequency influence the therapeutic effect of electroacupuncture.Rat models of Alzheimer’s disease were established by injecting amyloid beta 1–42（Aβ_（1–42））into the bilateral lateral ventricles.Electroacupuncture at 2,30,and 50 Hz was carried out at Baihui（GV20;15°obliquely to a depth of 2mm）and Shenshu（BL23;perpendicularly to 4–6 mm depth）,once a day for 20 minutes（each）,for 15 days,taking a break every 7 days.The Morris water maze test was conducted to assess the learning and memory.The expression levels of glycogen synthase kinase-3β（GSK-3β）,p Ser9-GSK-3β,p Tyr216-GSK-3β,amyloid precursor protein and Aβ_（1–40） in the hippocampus were determined by western blot assay.Results demonstrated that electroacupuncture treatment at different frequencies markedly improved learning and memory ability,increased synaptic curvatures,decreased the width of synaptic clefts,thickened postsynaptic densities,and downregulated the expression of GSK-3β,amyloid precursor protein,and Aβ_（1–40）.pSer9-GSK-3βexpression markedly decreased,while p Tyr216-GSK-3βexpression increased.High-frequency（50 Hz）electroacupuncture was more effective than low（2 Hz）or medium-frequency（30 Hz）electroacupuncture.In conclusion,electroacupuncture treatment exerts a protective effect against Aβ_（1–42）-induced learning and memory deficits and synapse-ultrastructure impairment via inhibition of GSK-3βactivity.Moreover,high-frequency electroacupuncture was the most effective therapy.展开更多
The marine risers are often subjected to parametric excitations from the fluctuation top tension. The top tension on the riser may fluctuate with multiple frequencies caused by irregular waves. In this paper, the infl...The marine risers are often subjected to parametric excitations from the fluctuation top tension. The top tension on the riser may fluctuate with multiple frequencies caused by irregular waves. In this paper, the influence between different frequency components in the top tension on the riser system is theoretically simulated and analyzed. With the Euler-Bernoulli beam theory, a dynamic model for the vibrations of the riser is established. The top tension is set as fluctuating with time and it has two different frequencies. The influences from the fluctuation amplitudes, circular frequencies and phase angles of these frequency components on the riser system are analyzed in detail. When these two frequencies are fluctuating in the stable regions, the riser system may become unstable because ω1+ω2≈2Ωn. The fluctuation amplitudes of these frequencies have little effect on the components of the vibration frequencies of the riser. For different phase angles, the stability and dynamic behaviors of the riser would be different.展开更多
According to the requirement of multi-parameter time and frequency measurement without frequency normalization,a different frequency synchronization theory is proposed based on Lissajous figure method and the variatio...According to the requirement of multi-parameter time and frequency measurement without frequency normalization,a different frequency synchronization theory is proposed based on Lissajous figure method and the variation lawof Lissajous figure which are used in practice teaching of frequency measurement. The theory can achieve high-precision transmission and comparison of time and frequency and precise locking and tracking of phase and frequency,improve the level of scientific research on time and frequency for postgraduate,and promote practice teaching innovation of time frequency measurement for undergraduate. Utilizing the ratio of horizontal and vertical inflection point of the Lissajous figure,the nominal frequency of the measured signal is precisely calculated.The frequency deviation between the measured frequency and its nominal frequency can be obtained by combining the turning cycle of the Lissajous figure. By observing the phase relationship between the frequency standard signal and the measured signal,the accurate measurement of the frequency is implemented. Experimental results showthat the direct measurement and comparison better than the 10-11 order of magnitude with common frequency source can be finished between any signal frequencies.The frequency measurement method based on the theory has the advantage of simple operation,quick measurement speed,small error,lownoise and high measurement precision. It plays an important role in time synchronization,communications,metrology,scientific research,educational technology practice and equipment and other fields.展开更多
Magnetic nanoparticle plays an important role in biomedical engineering,especially in tumor therapy.In this paper,a new technique has been developed by using the rapid moving magnetic nanoparticle under a low-fequency...Magnetic nanoparticle plays an important role in biomedical engineering,especially in tumor therapy.In this paper,a new technique has been developed by using the rapid moving magnetic nanoparticle under a low-fequency alternating magnetic field(LFAMF)to kill tumor cells.The LFAMF system which was used to drive magnetic nanoparticles(MNPs)was setup with the magnetic field frequency and power range at心10-100Hz and~10-200 mT,respectively.During the experiment,the LFAMF was adjusted at different frequencies and power levels.The exper-imental results show that the liver tumnor cells(HepG2)mixed with MNPs(10 pug/mL)becamne partial fragments when exposed in the LFAMF with different frequencies(~10-100Hz)and power(~10200 mT),and the higher the frequency or the power,the more the tumor cells were killed at the same magnetic nanoparticle concentration.Conclusion:Tumor oells were effectively damaged by MNPs under LFAMF,which suggests that they had great potential to be applied in tumor therapy.展开更多
We propose a novel scheme for THz wave generation by repeated and continuous frequency conversions from pump wave to high-order Stokes waves(HSWs).The repeated frequency conversions are accomplished by oscillations of...We propose a novel scheme for THz wave generation by repeated and continuous frequency conversions from pump wave to high-order Stokes waves(HSWs).The repeated frequency conversions are accomplished by oscillations of Stoke waves in resonant cavity(RC)where low-order Stokes waves(LSWs)are converted to high-order Stokes waves again and again.The continuous frequency conversions are accomplished by optimized cascaded difference frequency generation(OCDFG)where the poling periods of the optical crystal are aperiodic leading to the frequency conversions from low-order Stokes waves to high-order Stokes waves uninterruptedly and unidirectionally.Combined with the repeated and continuous frequency conversions,the optical-to-THz energy conversion efficiency(OTECE)exceeds 26%at 300 K and 43%at 100 K with pump intensities of 300 MW/cm^(2).展开更多
A dual-time method is introduced to calculate the unsteady flow in a certain vibrating flat cascade. An implicit lower-upper symmetric-gauss-seidel scheme（LU-SGS） is applied for time stepping in pseudo time domains,...A dual-time method is introduced to calculate the unsteady flow in a certain vibrating flat cascade. An implicit lower-upper symmetric-gauss-seidel scheme（LU-SGS） is applied for time stepping in pseudo time domains, and the convection items are discretized with the spatial three-order weighted non-oscillatory and non-free-parameter dissipation difference （WNND） scheme. The turbulence model adopts q-co low-Reynolds-number model. The frequency specmuns of lift coefficients and the unsteady pressure-difference coefficients at different spanwise heights as well as the entropy contours at blade tips on different vibrating instants, are obtained. By the analysis of frequency specmuns of lift coefficients at three spanwise heights, it is considered that there exist obvious non-linear perturbations in the flow induced by the vibrating, and the perturbation frequencies are higher than the basic frequency. The entropy contours at blade tips at different times display an intensively unsteady attribute of the flow under large amplitudes.展开更多
This paper presents a Doppler passive location method for moving targets with fixed single station using the Doppler frequency shift and time difference information.First,based on the relationship between frequency sh...This paper presents a Doppler passive location method for moving targets with fixed single station using the Doppler frequency shift and time difference information.First,based on the relationship between frequency shift and path difference,the virtual path difference is calculated from the measured value of Doppler frequency shift by means of mean value correction.Then,under the assumption that the target is moving at a constant speed along a straight line,two coaxial virtual double base arrays are constructed by using the moving track of the moving target based on the method of fixed period time difference.On this basis,the moving distance of the moving target can be calculated by using the ratio relationship between the frequency difference and the radial distance between the two adjacent detection points in the middle of the array,and the linear solution of the two double base path difference positioning equations.At this point,the relative coordinate position of the moving target can be obtained by directly using the linear solution of the double base path difference positioning equation again.展开更多
Objective: to compare the clinical effect of different frequency hemoperfusion combined with hemodialysis in the treatment of end-stage renal insufficiency. Methods: selected hospital in January 2019 - January 2020 tr...Objective: to compare the clinical effect of different frequency hemoperfusion combined with hemodialysis in the treatment of end-stage renal insufficiency. Methods: selected hospital in January 2019 - January 2020 treatment of 94 patients with end-stage renal failure patients as the research object, randomly divided into 3 groups, all patients were given hemodialysis treatment, three times a week, at the same time give different frequencies of blood perfusion, I group of 32 cases of once every 2 weeks, II group of 31 cases, treatment for 1 times a week. In group III, 31 patients were treated twice a week. After 1 year of treatment, the changes of microinflammatory status indicators in all patients were observed and analyzed. Results: after treatment, the levels of TNF-α, hs-CRP and IL-6 in 3 groups were better than before treatment, and the levels of TNF-α, hs-CRP and IL-6 in group II and III were lower than group I, the differences were statistically significant (P < 0.05). There were no significant differences in TNF-α, hs-CRP and IL-6 levels between group II and group III (P > 0.05). Conclusion: medium and high frequency hemoperfusion combined with hemodialysis in the treatment of end-stage renal insufficiency can fully improve the microinflammatory status of patients, and medium frequency hemoperfusion is more cost-effective and more suitable for clinical treatment.展开更多
The existing research results show that a fixed single station must conduct three consecutive frequency shift measurements and obtain the target’s moving speed by constructing two frequency difference equations. This...The existing research results show that a fixed single station must conduct three consecutive frequency shift measurements and obtain the target’s moving speed by constructing two frequency difference equations. This article proposes a new method that requires only two consecutive measurements. While using the azimuth measurement to obtain the angular difference between two radial distances, it also conducts two consecutive Doppler frequency shift measurements at the same target azimuth. On the basis of this measurement, a frequency difference equation is first constructed and solved jointly with the Doppler frequency shift equation. By eliminating the velocity variable and using the measured angular difference to obtain the target’s lead angle, the target’s velocity can be solved by using the Doppler frequency shift equation again. The new method avoids the condition that the target must move equidistantly, which not only provides an achievable method for engineering applications but also lays a good foundation for further exploring the use of steady-state signals to achieve passive positioning.展开更多
The mid-infrared optical frequency comb is a powerful tool for gas sensing.In this study,we demonstrate a simple midinfrared dual-comb spectrometer covering 3±4μm in Li Nb O_(3)waveguides.Based on a low-power fi...The mid-infrared optical frequency comb is a powerful tool for gas sensing.In this study,we demonstrate a simple midinfrared dual-comb spectrometer covering 3±4μm in Li Nb O_(3)waveguides.Based on a low-power fiber laser system,the mid-infrared comb is achieved via intra-pulse difference frequency generation in the Li Nb O_(3)waveguide.We construct pre-chirp management before supercontinuum generation to control spatiotemporal alignment for pump and signal pulses.The supercontinuum is directly coupled into a chirped periodically poled Li Nb O_(3)waveguide for the 3±4μm idler generation.A mid-infrared dual-comb spectrometer based on this approach provides a 100 MHz resolution over25 THz coverage.To evaluate the applicability for spectroscopy,we measure the methane spectrum using the dualcomb spectrometer.The measured results are consistent with the HITRAN database,in which the root mean square of the residual is 3.2%.This proposed method is expected to develop integrated and robust mid-infrared dual-comb spectrometers on chip for sensing.展开更多
基金Supported by the Fund of National Defense Industry Innovative Team(231)
文摘By analyzing the signal model of stepped-frequency waveform, a novel method for velocity measurement is proposed. The method is based on Doppler frequency difference which is achieved by using Hough transform. As the estimated velocity is inversely proportional to the frequency step size instead of the carrier frequency of the transmitted signal as the pulse-Doppler （PD） processing, the new algorithm can achieve much wider unambiguous velocity range. Furthermore, non-coherent integration of the sub-pulses with different carrier frequencies can be implemented by Hough trans- form to improve the anti-noise performance. Besides, field experimental results show that the high range resolution profile （HRRP） of a bullet with high speed can be reconstructed correctly without distortion.
基金Supported by the National Natural Science Foundation of China under Grant No. 61078065, Natural Science Foundation of Ningbo City under Grant No. 2008A61009, and K.C. Wong Magna Foundation in Ningbo University
文摘In this paper, we investigate a two electronic level system with vibrational modes coupled to a Brownian oscillator bath. The difference frequency generation （DFG） signals and sum frequency generation （SFG） signals are calculated. It is shown that, for the same model, the SFG signals are more sensitive than the DFG signals to the changes of the vibrational modes of the electronic two-level system. Because the SFG conversion efficiency can be improved by using the time-delay method, the findings in this paper predict that the SFG spectrum may probe the changes of the microstructure more effectively.
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Project supported by the National Natural Science Foundation of China(Grant Nos.61735010,31671580,and 61601183)the Natural Science Foundation of Henan Province,China(Grant No.162300410190)the Program for Science&Technology Innovation Talents in Universities of Henan Province,China(Grant No.18HASTIT023)。
文摘A new scheme which generates multi-frequency terahertz(THz)waves from planar waveguide by the optimized cascaded difference frequency generation(OCDFG)is proposed.A THz wave with frequencyω_(T1)is generated by the OCDFG with two infrared pump waves,and simultaneously a series of cascaded optical waves with a frequency intervalω_(T1)is generated.The THz wave with a frequency of M-timesω_(T1)is generated by mixing the m-th-order and the(m+M)-th-order cascaded optical wave.The phase mismatch distributions of cascaded difference frequency generation(CDFG)are modulated by changing the thickness of planar waveguide step by step,thereby satisfying the phase-matching condition from first-order to high-order cascaded Stokes process step by step.As a result,the intensity of THz wave can be enhanced and modulated by controlling the cascading order of OCDFG.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61735010,31671580,and 61601183)Natural Science Foundation of Henan Province,China(Grant No.162300410190)Program for Science&Technology Innovation Talents in Universities of Henan Province,China(Grant No.18HASTIT023)。
文摘A novel scheme for high-efficiency terahertz(THz)wave generation based on optimized cascaded difference frequency generation(OCDFG)with planar waveguide is presented.The phase mismatches of each-order cascaded difference frequency generation(CDFG)are modulated by changing the thickness of the waveguide,resulting in a decrement of phase mismatches in cascaded Stokes processes and an increment of phase mismatches in cascaded anti-Stokes processes simultaneously.The modulated phase mismatches enhance the cascaded Stokes processes and suppress the cascaded anti-Stokes processes simultaneously,yielding energy conversion efficiencies over 25%from optical wave to THz wave at 100 K.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61735010,31671580,and 61601183)the Natural Science Foundation of Henan Province,China(Grant No.162300410190)Program for Science&Technology Innovation Talents in Universities of Henan Province,China(Grant No.18HASTIT023)。
文摘High-efficiency terahertz(THz) wave generation with multiple frequencies by optimized cascaded difference frequency generation(OCDFG) is investigated at 100 K using a nonlinear crystal consisting of a periodically poled lithium niobate(PPLN) part and an aperiodically poled lithium niobate(APPLN) part.Two infrared pump waves with a frequency difference ω_(T1) generate THz waves and a series of cascaded optical waves in the PPLN part by cascaded difference frequency generation(CDFG).The generated cascaded optical waves with frequency interval ω_(T1) then further interact in the APPLN part by OCDFG,yielding the following two advantages.First,OCDFG in the APPLN part is efficiently stimulated by inputting multi-order cascaded optical waves rather than the only two intense infrared pump waves,yielding unprecedented energy conversion efficiencies in excess of 37% at 1 THz at 100 K.Second,THz waves with M timesω_(T1) are generated by mixing the mth-order and the(m+M)th-order cascaded optical waves by designing poling period distributions of the APPLN part.
基金Project supported by the National Natural Science Foundation of China(Grant No.11374161)the Open Research Project of Jiangsu Provincial Key Labo-ratory of Meteorological Observation and Information Processing,China(Grant No.KDXS1206)the Project Funded by the Priority Academic Program Development of Jiangsu Provincial Higher Education Institutions,China
文摘A novel widely tunable dual-wavelength mid-IR difference frequency generation （DFG） scheme with uniform grating periodically poled lithium niobate （PPLN） is presented in this paper. By using the temperature-dependent dispersion property of PPLN, the quasi-phase matching （QPM） peak for the pump may evolve into two separate ones and the wavelength spacing between them increases with the decrease of the crystal temperature. Such two pump QPM peaks may allow simultaneous dual-wavelength mid-IR laser radiations while properly setting the two fundamental pump wavelengths. With this scheme, mid-IR dual-wavelength laser radiations at around 3.228 and 3.548, 3.114 and 3.661, and 3.019 and 3.76 μm, are experimentally achieved for the crystal temperatures of 90, 65, and 30 ℃, respectively, based on the fiber laser fundamental lights.
文摘Objective To compare the difference in the clinical efficacy on the different frequency hearing damages for the patients with sudden deafness between the comprehensive therapy of electroacupuncture and western medicine and the simple western medicine comprehensive therapy. Methods Fifty-eight cases were randomized into an acupuncture plus medication group （28 cases, 32 damaged ears） and a western medicine group （30 cases, 34 damaged ears）. In the acupuncture plus medication group, the comprehensive therapy of electroacupuncture and western medicine was used. The main points were ěrmén （耳门 TE 21）, Tīnggōng （听宫 SI 19）, Tīnghuì （听会 GB 2）, Yìfēng （翳风 TE 17）, etc. The western medicine therapy was the comprehensive treatment with vasodilators, the medicines for promoting nerve function and releasing inner ear edema and hyperbaric oxygen. In the western medicine group, the western medicine comprehensive therapy was adopted. 10-day treatment made one session. Two sessions of treatment were required. In 1 or 2 sessions of treatment, the efficacy was observed, the electric audiometry was evaluated. Additionally, the blood routine and liver and kidney functions were detected. Results The total effective rate was 50.0% （16/32） in the acupuncture ＋ medication group and was 55.9% （19/34） in the western medicine group. The efficacies were similar between the two groups （P〉0.05）. In 1 and 2 sessions of treatment, at 250 Hz, 500 Hz and 1 kHz, the electric audiometry values in either group were recovered significantly as compared with those before treatment （all P〈0.01）. At 2 kHz, in 1 and 2 sessions of treatment, the improvements of the electric audiometry values were significant as compared with those before treatment in the acupuncture plus medication group separately （P〈0.05, P〈0.01）. At 4 kHz, the differences were not significant statistically before and after treatment in either group （all P〉0.05）. There were no abnormalities in the blood routine and liver and kidney function detections before and after treatment in either group. Conclusion Either the comprehensive therapy of electroacupuncture and western medicine or the simple western medicine comprehensive therapy is effective in the treatment of low frequency hearing damage of sudden deafness. Either of them has no effect on high frequency hearing damage. But for the middle frequency hearing damage, the efficacy of the comprehensive therapy of electroacupuncture and western medicine is superior to that of the simple western medicine comprehensive therapy.
基金Supported by Key Discipline Construction Project of Neurology of Jiaxing City in Zhejiang Province of China,No.2023-ZC-006.
文摘BACKGROUND Repetitive transcranial magnetic stimulation(rTMS)entered clinical practice in China after 2000,first used in psychiatric surgery,and then in neurology and other disciplines.The First Hospital of Jiaxing introduced TMS in 2015.In practical applications,it has been found that different models of instruments and technical parameters can lead to differences in therapeutic efficacy.Therefore,our hospital selected the Danish TMS instrument,which ranks second in China,to test patients with schizophrenia from March 2021 to July 2021,with a focus on comparing the results at 5 Hz,10 Hz,and 15 Hz.The testing time is concentrated between 8:30 to 10:30 in the morning.A contingency plan was made for the quality after inspection before testing.Two evaluators independently control the quality of the contingency plan.The data is independently saved and proofread by two evaluators.The purpose of this study is to translate the research results into clinical practice and provide reference basis.AIM To investigate the effects of rehabilitation therapy using rTMS on the negative symptoms and event-related potential component of P300 in chronic schizophrenia.METHODS One hundred and five patients with chronic schizophrenia were randomly allocated to three groups based on the frequency of rTMS(5,10,or 15 Hz).The patients underwent five sessions of rTMS per week for 5 weeks.We compared the pre-and post-treatment P300 latency and scores for the Scale for Assessment of Negative Symptoms(SANS).RESULTS A significant decrease in SANS score after rTMS was observed in the 10-Hz group(P<0.05),which was not observed in the 5-Hz and 15-Hz groups.There was a significant increase in P300 amplitude in the 10-Hz group after rTMS treatment(P<0.05),but there was no significant change in P300 latency(P>0.05).The improvement of SANS score in the 10-Hz rTMS group was related to patient age and disease course.CONCLUSION rTMS at 10 Hz improved negative symptoms and cognitive function in chronic schizophrenia;however,further studies on the mechanism of action are required to validate our observations.
基金supported by the Open Fund of Key Laboratory of Geological Hazards on Three Gorges Reservoir Area(China Three Gorges University)of the Ministry of Education(Grant Nos.2022KDZ14 and 2022KDZ15)the Open Fund of Badong National Observation and Research Station of Geohazards(Grant No.BNORSG-202304)+3 种基金the Science and Technology Project of Department of Natural Resources of Hubei Province(Grant No.ZRZY2024KJ15)the Natural Science Foundation of Hubei Province(Grant No.2022CFB557)the National Natural Science Foundation of China(Grant No.42107489)the 111 Project of Hubei Province(Grant No.2021EJD026)。
文摘The precision of landslide displacement prediction is crucial for effective landslide prevention and mitigation strategies.However,the role of surface monitoring frequency in influencing prediction accuracy has been largely neglected.This study examined the effect of varying monitoring frequencies on the accuracy of displacement predictions by using the Baijiabao landslide in the Three Gorges Reservoir Area(TGRA)as a case study.We collected surface automatic monitoring data at different intervals,ranging from daily to monthly.The Ensemble Empirical Mode Decomposition(EEMD)algorithm was utilized to dissect the accumulated displacements into periodic and trend components at each monitoring frequency.Polynomial fitting was applied to forecast the trend component while the periodic component was predicted with two state-of-the-art neural network models:Long Short-Term Memory(LSTM)and Gated Recurrent Unit(GRU).The predictions from these models were integrated to derive cumulative displacement forecasts,enabling a comparative analysis of prediction accuracy across different monitoring frequencies.The results demonstrate that the proposed models achieve high accuracy in landslide displacement forecasting,with optimal performance observed at moderate monitoring intervals.Intriguingly,the daily mean average error(MAE)decreases sharply with increasing monitoring frequency,reaching a plateau.These findings were corroborated by a parallel analysis of the Bazimen landslide,suggesting that moderate monitoring intervals of approximately 7 to 15 days are most conducive to achieving enhanced prediction accuracy compared to both daily and monthly intervals.
基金supported by the National Natural Science Foundation of China,No.81373741a grant from the Chinese Medicine and Integrated Medicine Research Projects funded by the Health and Family Planning Commission of Hubei Province of China,No.24a grant from the Hubei Provincial Collaborative Innovation Center of Preventive Treatment by Acupuncture and Moxibustion of China in 2014,No.8
文摘Acupuncture has been shown to ameliorate cognitive impairment of Alzheimer’s disease.Acupoints and stimulation frequency influence the therapeutic effect of electroacupuncture.Rat models of Alzheimer’s disease were established by injecting amyloid beta 1–42（Aβ_（1–42））into the bilateral lateral ventricles.Electroacupuncture at 2,30,and 50 Hz was carried out at Baihui（GV20;15°obliquely to a depth of 2mm）and Shenshu（BL23;perpendicularly to 4–6 mm depth）,once a day for 20 minutes（each）,for 15 days,taking a break every 7 days.The Morris water maze test was conducted to assess the learning and memory.The expression levels of glycogen synthase kinase-3β（GSK-3β）,p Ser9-GSK-3β,p Tyr216-GSK-3β,amyloid precursor protein and Aβ_（1–40） in the hippocampus were determined by western blot assay.Results demonstrated that electroacupuncture treatment at different frequencies markedly improved learning and memory ability,increased synaptic curvatures,decreased the width of synaptic clefts,thickened postsynaptic densities,and downregulated the expression of GSK-3β,amyloid precursor protein,and Aβ_（1–40）.pSer9-GSK-3βexpression markedly decreased,while p Tyr216-GSK-3βexpression increased.High-frequency（50 Hz）electroacupuncture was more effective than low（2 Hz）or medium-frequency（30 Hz）electroacupuncture.In conclusion,electroacupuncture treatment exerts a protective effect against Aβ_（1–42）-induced learning and memory deficits and synapse-ultrastructure impairment via inhibition of GSK-3βactivity.Moreover,high-frequency electroacupuncture was the most effective therapy.
基金financially supported by the National Natural Science Foundation of China(Grant No.51679167 and 51979193)
文摘The marine risers are often subjected to parametric excitations from the fluctuation top tension. The top tension on the riser may fluctuate with multiple frequencies caused by irregular waves. In this paper, the influence between different frequency components in the top tension on the riser system is theoretically simulated and analyzed. With the Euler-Bernoulli beam theory, a dynamic model for the vibrations of the riser is established. The top tension is set as fluctuating with time and it has two different frequencies. The influences from the fluctuation amplitudes, circular frequencies and phase angles of these frequency components on the riser system are analyzed in detail. When these two frequencies are fluctuating in the stable regions, the riser system may become unstable because ω1+ω2≈2Ωn. The fluctuation amplitudes of these frequencies have little effect on the components of the vibration frequencies of the riser. For different phase angles, the stability and dynamic behaviors of the riser would be different.
基金Supported by the Project of Higher Education Teaching Reform and Practice in Henan Province(2017SJGLX353)the Project of Science and Technology on Electronic Information Control Laboratory,the Science and Technology Innovation Talents in Colleges and Universities of Henan Province(16HASTIT036)+2 种基金the Educational Technology Equipment and Practical Education of Henan Province(GZS028)the National Natural Science Foundation of China(U1304618)the Key Projects of Science And Technology of Henan Province(152102210351)
文摘According to the requirement of multi-parameter time and frequency measurement without frequency normalization,a different frequency synchronization theory is proposed based on Lissajous figure method and the variation lawof Lissajous figure which are used in practice teaching of frequency measurement. The theory can achieve high-precision transmission and comparison of time and frequency and precise locking and tracking of phase and frequency,improve the level of scientific research on time and frequency for postgraduate,and promote practice teaching innovation of time frequency measurement for undergraduate. Utilizing the ratio of horizontal and vertical inflection point of the Lissajous figure,the nominal frequency of the measured signal is precisely calculated.The frequency deviation between the measured frequency and its nominal frequency can be obtained by combining the turning cycle of the Lissajous figure. By observing the phase relationship between the frequency standard signal and the measured signal,the accurate measurement of the frequency is implemented. Experimental results showthat the direct measurement and comparison better than the 10-11 order of magnitude with common frequency source can be finished between any signal frequencies.The frequency measurement method based on the theory has the advantage of simple operation,quick measurement speed,small error,lownoise and high measurement precision. It plays an important role in time synchronization,communications,metrology,scientific research,educational technology practice and equipment and other fields.
基金support by funding of Jiangsu Innovation Program for Graduate Education (KYLX 0247)the support of the Fundamental Research Funds for the Central Universities.
文摘Magnetic nanoparticle plays an important role in biomedical engineering,especially in tumor therapy.In this paper,a new technique has been developed by using the rapid moving magnetic nanoparticle under a low-fequency alternating magnetic field(LFAMF)to kill tumor cells.The LFAMF system which was used to drive magnetic nanoparticles(MNPs)was setup with the magnetic field frequency and power range at心10-100Hz and~10-200 mT,respectively.During the experiment,the LFAMF was adjusted at different frequencies and power levels.The exper-imental results show that the liver tumnor cells(HepG2)mixed with MNPs(10 pug/mL)becamne partial fragments when exposed in the LFAMF with different frequencies(~10-100Hz)and power(~10200 mT),and the higher the frequency or the power,the more the tumor cells were killed at the same magnetic nanoparticle concentration.Conclusion:Tumor oells were effectively damaged by MNPs under LFAMF,which suggests that they had great potential to be applied in tumor therapy.
基金the National Natural Science Foundation of China(Grant Nos.61735010,31671580,and 61601183)Natural Science Foundation of Henan Province,China(Grant No.162300410190)Program for Science&Technology Innovation Talents in Universities of Henan Province,China(Grant No.18HASTIT023)。
文摘We propose a novel scheme for THz wave generation by repeated and continuous frequency conversions from pump wave to high-order Stokes waves(HSWs).The repeated frequency conversions are accomplished by oscillations of Stoke waves in resonant cavity(RC)where low-order Stokes waves(LSWs)are converted to high-order Stokes waves again and again.The continuous frequency conversions are accomplished by optimized cascaded difference frequency generation(OCDFG)where the poling periods of the optical crystal are aperiodic leading to the frequency conversions from low-order Stokes waves to high-order Stokes waves uninterruptedly and unidirectionally.Combined with the repeated and continuous frequency conversions,the optical-to-THz energy conversion efficiency(OTECE)exceeds 26%at 300 K and 43%at 100 K with pump intensities of 300 MW/cm^(2).
基金This Project is supported by National Natural Science Foundation of China (No.50776056)National Hi-tech Research and Development Program of China (863 Program,No.2006AA05Z250).
文摘A dual-time method is introduced to calculate the unsteady flow in a certain vibrating flat cascade. An implicit lower-upper symmetric-gauss-seidel scheme（LU-SGS） is applied for time stepping in pseudo time domains, and the convection items are discretized with the spatial three-order weighted non-oscillatory and non-free-parameter dissipation difference （WNND） scheme. The turbulence model adopts q-co low-Reynolds-number model. The frequency specmuns of lift coefficients and the unsteady pressure-difference coefficients at different spanwise heights as well as the entropy contours at blade tips on different vibrating instants, are obtained. By the analysis of frequency specmuns of lift coefficients at three spanwise heights, it is considered that there exist obvious non-linear perturbations in the flow induced by the vibrating, and the perturbation frequencies are higher than the basic frequency. The entropy contours at blade tips at different times display an intensively unsteady attribute of the flow under large amplitudes.
文摘This paper presents a Doppler passive location method for moving targets with fixed single station using the Doppler frequency shift and time difference information.First,based on the relationship between frequency shift and path difference,the virtual path difference is calculated from the measured value of Doppler frequency shift by means of mean value correction.Then,under the assumption that the target is moving at a constant speed along a straight line,two coaxial virtual double base arrays are constructed by using the moving track of the moving target based on the method of fixed period time difference.On this basis,the moving distance of the moving target can be calculated by using the ratio relationship between the frequency difference and the radial distance between the two adjacent detection points in the middle of the array,and the linear solution of the two double base path difference positioning equations.At this point,the relative coordinate position of the moving target can be obtained by directly using the linear solution of the double base path difference positioning equation again.
文摘Objective: to compare the clinical effect of different frequency hemoperfusion combined with hemodialysis in the treatment of end-stage renal insufficiency. Methods: selected hospital in January 2019 - January 2020 treatment of 94 patients with end-stage renal failure patients as the research object, randomly divided into 3 groups, all patients were given hemodialysis treatment, three times a week, at the same time give different frequencies of blood perfusion, I group of 32 cases of once every 2 weeks, II group of 31 cases, treatment for 1 times a week. In group III, 31 patients were treated twice a week. After 1 year of treatment, the changes of microinflammatory status indicators in all patients were observed and analyzed. Results: after treatment, the levels of TNF-α, hs-CRP and IL-6 in 3 groups were better than before treatment, and the levels of TNF-α, hs-CRP and IL-6 in group II and III were lower than group I, the differences were statistically significant (P < 0.05). There were no significant differences in TNF-α, hs-CRP and IL-6 levels between group II and group III (P > 0.05). Conclusion: medium and high frequency hemoperfusion combined with hemodialysis in the treatment of end-stage renal insufficiency can fully improve the microinflammatory status of patients, and medium frequency hemoperfusion is more cost-effective and more suitable for clinical treatment.
文摘The existing research results show that a fixed single station must conduct three consecutive frequency shift measurements and obtain the target’s moving speed by constructing two frequency difference equations. This article proposes a new method that requires only two consecutive measurements. While using the azimuth measurement to obtain the angular difference between two radial distances, it also conducts two consecutive Doppler frequency shift measurements at the same target azimuth. On the basis of this measurement, a frequency difference equation is first constructed and solved jointly with the Doppler frequency shift equation. By eliminating the velocity variable and using the measured angular difference to obtain the target’s lead angle, the target’s velocity can be solved by using the Doppler frequency shift equation again. The new method avoids the condition that the target must move equidistantly, which not only provides an achievable method for engineering applications but also lays a good foundation for further exploring the use of steady-state signals to achieve passive positioning.
基金supported in part by the National Natural Science Foundation of China(Nos.12204178,12104162,12134004 and 12274141)。
文摘The mid-infrared optical frequency comb is a powerful tool for gas sensing.In this study,we demonstrate a simple midinfrared dual-comb spectrometer covering 3±4μm in Li Nb O_(3)waveguides.Based on a low-power fiber laser system,the mid-infrared comb is achieved via intra-pulse difference frequency generation in the Li Nb O_(3)waveguide.We construct pre-chirp management before supercontinuum generation to control spatiotemporal alignment for pump and signal pulses.The supercontinuum is directly coupled into a chirped periodically poled Li Nb O_(3)waveguide for the 3±4μm idler generation.A mid-infrared dual-comb spectrometer based on this approach provides a 100 MHz resolution over25 THz coverage.To evaluate the applicability for spectroscopy,we measure the methane spectrum using the dualcomb spectrometer.The measured results are consistent with the HITRAN database,in which the root mean square of the residual is 3.2%.This proposed method is expected to develop integrated and robust mid-infrared dual-comb spectrometers on chip for sensing.
