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
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
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
Objective To observe postoperative effect of electroacupuncture（EA） of different frequencies in acupuncture anesthesia combined with drugs on patients undergoing thyroid surgery.Methods One hundred and twenty patien...Objective To observe postoperative effect of electroacupuncture（EA） of different frequencies in acupuncture anesthesia combined with drugs on patients undergoing thyroid surgery.Methods One hundred and twenty patients undergoing thyroid surgery were randomly divided into a 2Hz electroacupuncture anesthesia group（group A）,a 100 Hz electroacupuncture anesthesia group（group B）,a 2Hz/100 Hz electroacupuncture anesthesia group（group C） and a cervical plexus block group（group D） in accordance with the random number table method,with 30 patients in each group.In group A,group B and group C,electroacupuncture was applied at bilateral Futu（扶突 LI 18）,Hegu（合谷 LI 4） and Neiguan（内关 PC 6） at frequencies of 2 Hz,100 Hz and 2 Hz/100 Hz respectively for 30 min.The needles were retained till the end of the surgery.Dolantin and atropine were intramuscularly injected In group D,bilateral cervical plexus block was produced with a mixture of1%lidocaine and 0.375%bupivicaine.Before surgery,pain threshold and threshold of pain tolerance were determined;during surgery,the duration of surgery was recorded;and after surgery,QOLS（Quality Of Life Score） and PHS（Prince-Henry Score） were assessed.Results PHS in group A,group B and group C were lower than that in group D,respectively（0.20±0.41,0.17±0.38,0.10±0.31 vs 0.40±0.50,P〈0.01）,and PHS in group C was lower than those in group A and group B,respectively（both P〈0.01）.QOLS in group A,group B and group C were higher than that in group D,respectively（9.97±1.07,9.97±2.27,10.40±1.45 vs 9.73±1.41,P〈0.05,P〈0.01）,and QOLS in group C was higher than those in group A and group B,respectively（both P〈0.05）.Conclusion Acupuncture anesthesia combined with drugs has better postoperative effect than drug anesthesia.Electroacupuncture of different frequencies can significantly improve general quality of life of patients,so patients recover well after thyroid surgery.As patients in group C suffered from the slightest pain with the highest quality of life,they recovered best within the shortest time.Electroacupuncture at frequency of 2 Hz/100 Hz can better play postoperative analgesic effect.展开更多
We report on the generation of optical pulses with a nearly one octave-spanning spectrum ranging from 1300 nm to2500 nm at 1 kHz repetition rate, which are based on intra-pulse difference frequency generation(DFG) in ...We report on the generation of optical pulses with a nearly one octave-spanning spectrum ranging from 1300 nm to2500 nm at 1 kHz repetition rate, which are based on intra-pulse difference frequency generation(DFG) in β-barium borate crystal(β-BBO) and passively carrier-envelope-phase(CEP) stabilized. The DFG is induced by few-cycle pulses initiated from spectral broadening in multiple thin plates driven by a Ti: sapphire chirped-pulse amplifier. Furthermore, a numerical simulation is developed to estimate the conversion efficiency and output spectrum of the DFG. Our results show that the pulses from the DFG have the potential for seeding intense mid-infrared(MIR) laser generation and amplification to study strong-field physics and attosecond science.展开更多
In this paper,the rainfall features in southwestern China are studied using daily rainfall station data.The rainfall features are distinct along the eastern and western edges of the Hengduan Mountains and over the mou...In this paper,the rainfall features in southwestern China are studied using daily rainfall station data.The rainfall features are distinct along the eastern and western edges of the Hengduan Mountains and over the mountains,especially in terms of rainfall frequency.The rainfall amounts and frequencies are much higher along the eastern and western edges than over the mountains,particularly during spring,which is partly contributed by the number and duration of rainfall events.The differences are more obvious in the nocturnal rainfall than in the daytime rainfall.The rainfall differences over the three regions could be affected by the large-scale environment.By analyzing reanalysis data,the large-scale circulations linked to the different rainfall features over southwestern China,and the interactions of these circulations with the topography are also discussed.展开更多
Cell voltage is a widely used signal that can be measured online from an industrial aluminum electrolysis cell.A variety of parameters for the analysis and control of industrial cells are calculated using the cell vol...Cell voltage is a widely used signal that can be measured online from an industrial aluminum electrolysis cell.A variety of parameters for the analysis and control of industrial cells are calculated using the cell voltage.In this paper,the frequency segmentation of cell voltage is used as the basis for designing filters to obtain these parameters.Based on the qualitative analysis of the cell voltage,the sub-band instantaneous energy spectrum(SIEP)is first proposed,which is then used to quantitatively represent the characteristics of the designated frequency bands of the cell voltage under various cell conditions.Ultimately,a cell condition-sensitive frequency segmentation method is given.The proposed frequency segmentation method divides the effective frequency band into the[0,0.001]Hz band of lowfrequency signals and the[0.001,0.050]Hz band of low-frequency noise,and subdivides the lowfrequency noise into the[0.001,0.010]Hz band of metal pad abnormal rolling and the[0.01,0.05]Hz band of sub-low-frequency noise.Compared with the instantaneous energy spectrum based on empirical mode decomposition,the SIEP more finely represents the law of energy change with time in any designated frequency band within the effective frequency band of the cell voltage.The proposed frequency segmentation method is more sensitive to cell condition changes and can obtain more elaborate details of online cell condition information,thus providing a more reliable and accurate online basis for cell condition monitoring and control decisions.展开更多
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 order to improve the accuracy and engineering feasibility of four-Satellite localization system, the frequency difference measurement is introduced to the four-Satellite TDOA (Time Difference of Arrival) localizati...In order to improve the accuracy and engineering feasibility of four-Satellite localization system, the frequency difference measurement is introduced to the four-Satellite TDOA (Time Difference of Arrival) localization algorithm. The TDOA/FDOA (Frequency Difference of Arrival) localization algorithm is used to optimize the GDOP (geometric dilution of precision) of four-Satellite localization. The simulation results show that the absolute position measurement accuracy has little influence on TDOA/FDOA localization accuracy as compared with TDOA localization. Under the same conditions, TDOA/FDOA localization has better accuracy and its GDOP shows more uniform distribution in diamond configuration case. The localization accuracy of four-Satellite TDOA/FDOA is better than the localization accuracy of four-Satellite TDOA.展开更多
The difference-frequency （DF） ultrasound generated by using parametric effect promises to improve detection depth owing to its low attenuation, which is beneficial for deep tissue imaging. With ultrasound contrast a...The difference-frequency （DF） ultrasound generated by using parametric effect promises to improve detection depth owing to its low attenuation, which is beneficial for deep tissue imaging. With ultrasound contrast agents infusion, the harmonic components scattered from the microbubbles, including DF, can be generated due to the nonlinear vibration. A theoretical study on the DF generation from microbubbles under the dual-frequency excitation is proposed in formula based on the solution of the RPNNP equation. The optimisation of the DF generation is discussed associated with the applied acoustic pressure, frequency, and the microbubble size. Experiments are performed to validate the theoretical predictions by using a dual-frequency signal to excite microbubbles. Both the numerical and experimental results demonstrate that the optimised DF ultrasound can be achieved as the difference frequency is close to the resonance frequency of the microbubble and improve the contrast-to-tissue ratio in imaging.展开更多
We study on reduced dynamic orbit determination using differenced phase in adjacent epochs for spacebome dual-frequency GPS. This method not only overcomes the shortcomings that the epoch-difference kinematic method c...We study on reduced dynamic orbit determination using differenced phase in adjacent epochs for spacebome dual-frequency GPS. This method not only overcomes the shortcomings that the epoch-difference kinematic method cannot be used when observation geometry is poor or observations are insufficient, but also avoids solving the ambiguity in the zero-difference reduced dynamic method. As the epoch-difference method is not sensitive to the impact of phase cycle slips, it can lower the difficulty of slip detection in phase observation preprocessing. In the solution strategies, we solve the high-dimensional matrix computation problems by decomposing the long observation arc into a number of short arcs. By gravity recovery and climate experiment （GRACE） satellite orbit determination and compared with GeoForschungsZentrum （GFZ） post science orbit, for epoch-difference reduced dynamic method, the root mean squares （RMSs） of radial, transverse and normal components are 1.92 cm, 3.83 cm and 3.80 cm, and the RMS in three dimensions is 5.76 cm. The solution＇s accuracy is comparable to the zero-difference reduced dynamic method.展开更多
This paper presents a study on the motion response of a tension-leg platform(TLP) under first-and second-order wave forces, including the mean-drift force, difference and sum-frequency forces. The second-order wave fo...This paper presents a study on the motion response of a tension-leg platform(TLP) under first-and second-order wave forces, including the mean-drift force, difference and sum-frequency forces. The second-order wave force is calculated using the full-field quadratic transfer function(QTF). The coupled effect of the horizontal motions, such as surge, sway and yaw motions, and the set-down motion are taken into consideration by the nonlinear restoring matrix. The time-domain analysis with 50-yr random sea state is performed. A comparison of the results of different case studies is made to assess the influence of second-order wave force on the motions of the platform. The analysis shows that the second-order wave force has a major impact on motions of the TLP. The second-order difference-frequency wave force has an obvious influence on the low-frequency motions of surge and sway, and also will induce a large set-down motion which is an important part of heave motion. Besides, the second-order sum-frequency force will induce a set of high-frequency motions of roll and pitch. However, little influence of second-order wave force is found on the yaw motion.展开更多
A tunable continuous wave（cw） mid-infrared（MIR） laser based on difference-frequency generation（DFG） in a 1.5-cm long AgGaS2 nonlinear crystal for trace gas detection is reported.Two visible and near-infrared dio...A tunable continuous wave（cw） mid-infrared（MIR） laser based on difference-frequency generation（DFG） in a 1.5-cm long AgGaS2 nonlinear crystal for trace gas detection is reported.Two visible and near-infrared diode lasers were used as pump and signal sources.The MIR-DFG laser was tunable in a wavelength range of 4.75 μm-4.88 μm.The phase-matching（PM） condition was non-critically achieved by adjusting the temperature of the crystal for fixed pairs of input pump and signal wavelengths.The required PM temperatures of the generated MIR-DFG wavelengths have been calculated by using three sets of recent Sellmeier equations and the temperature-dispersion equations of AgGaS2 given by Willer U,et al.（Willer U,Blanke T and Schade W 2001 Appl.Opt.40 5439）.Then the calculated PM temperatures are compared with the experimental values.The performance of the MIR-DFG laser is shown by the trace detection of the P（16） carbon monoxide（12C16O） absorption line in a laboratory-fabricated absorption cell.The enhanced sensitivity of about 0.6×10 4 was obtained through the long path absorption provided by consecutive reflections between coated cylindrical mirrors of a constructed cell.展开更多
We analyze the phenomena of phase group synchronization between the different nominal frequency signals and propose a new theory of the equivalent comparison between them. The exact expression of the equivalent compar...We analyze the phenomena of phase group synchronization between the different nominal frequency signals and propose a new theory of the equivalent comparison between them. The exact expression of the equivalent comparison is deduced. High resolution frequency measurement and phase comparison can be realized using this theory with the divider. For avoiding the frequency mixing, multiplication and synthesis, the system phase noise is improved and the higher resolution comparison and measurement are achieved between the different nominal frequencies by theory.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 present a scheme for estimating the noise-equivalent temperature difference(NETD)of frequency upconversion detectors(UCDs)that detect mid-infrared(MIR)light.In particular,we investigate the frequency upconversion o...We present a scheme for estimating the noise-equivalent temperature difference(NETD)of frequency upconversion detectors(UCDs)that detect mid-infrared(MIR)light.In particular,we investigate the frequency upconversion of a periodically poled crystal based on lithium niobate,where an MIR conversion bandwidth of 220 nm can be achieved in a single-poled period by a special design.Experimentally,for an MIR radiating target at a temperature of 95℃,the NETD of the device was estimated to be 56 mK with an exposure time of 1 s.Meanwhile,a direct measurement of the NETD was performed utilizing conventional methods,which resulted in 48 mK.We also compared the NETD of our UCD with commercially available direct MIR detectors.We show that the limiting factor for further NETD reduction of our device is not primarily from the upconversion process and camera noise but from the limitations of the heat source and laser performance.Our detectors have good temperature measurement performance and can be used for a variety of applications involving temperature object identification and material structure detection.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
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 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
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.
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Objective To observe postoperative effect of electroacupuncture（EA） of different frequencies in acupuncture anesthesia combined with drugs on patients undergoing thyroid surgery.Methods One hundred and twenty patients undergoing thyroid surgery were randomly divided into a 2Hz electroacupuncture anesthesia group（group A）,a 100 Hz electroacupuncture anesthesia group（group B）,a 2Hz/100 Hz electroacupuncture anesthesia group（group C） and a cervical plexus block group（group D） in accordance with the random number table method,with 30 patients in each group.In group A,group B and group C,electroacupuncture was applied at bilateral Futu（扶突 LI 18）,Hegu（合谷 LI 4） and Neiguan（内关 PC 6） at frequencies of 2 Hz,100 Hz and 2 Hz/100 Hz respectively for 30 min.The needles were retained till the end of the surgery.Dolantin and atropine were intramuscularly injected In group D,bilateral cervical plexus block was produced with a mixture of1%lidocaine and 0.375%bupivicaine.Before surgery,pain threshold and threshold of pain tolerance were determined;during surgery,the duration of surgery was recorded;and after surgery,QOLS（Quality Of Life Score） and PHS（Prince-Henry Score） were assessed.Results PHS in group A,group B and group C were lower than that in group D,respectively（0.20±0.41,0.17±0.38,0.10±0.31 vs 0.40±0.50,P〈0.01）,and PHS in group C was lower than those in group A and group B,respectively（both P〈0.01）.QOLS in group A,group B and group C were higher than that in group D,respectively（9.97±1.07,9.97±2.27,10.40±1.45 vs 9.73±1.41,P〈0.05,P〈0.01）,and QOLS in group C was higher than those in group A and group B,respectively（both P〈0.05）.Conclusion Acupuncture anesthesia combined with drugs has better postoperative effect than drug anesthesia.Electroacupuncture of different frequencies can significantly improve general quality of life of patients,so patients recover well after thyroid surgery.As patients in group C suffered from the slightest pain with the highest quality of life,they recovered best within the shortest time.Electroacupuncture at frequency of 2 Hz/100 Hz can better play postoperative analgesic effect.
基金Project supported by the National Key R&D Program of China(Grant No.2017YFB0405202)the Major Program of the National Natural Science Foundation of China(Grant No.61690221)+1 种基金the Key Program of the National Natural Science Foundation of China(Grant No.11434016)the National Natural Science Foundation of China(Grant Nos.11574384 and 11674386)
文摘We report on the generation of optical pulses with a nearly one octave-spanning spectrum ranging from 1300 nm to2500 nm at 1 kHz repetition rate, which are based on intra-pulse difference frequency generation(DFG) in β-barium borate crystal(β-BBO) and passively carrier-envelope-phase(CEP) stabilized. The DFG is induced by few-cycle pulses initiated from spectral broadening in multiple thin plates driven by a Ti: sapphire chirped-pulse amplifier. Furthermore, a numerical simulation is developed to estimate the conversion efficiency and output spectrum of the DFG. Our results show that the pulses from the DFG have the potential for seeding intense mid-infrared(MIR) laser generation and amplification to study strong-field physics and attosecond science.
基金jointly supported by the National Key R&D Program of China [grant number 2018YFC1507603]the National Natural Science Foundation of China [grant number41875112 and 41675075]
文摘In this paper,the rainfall features in southwestern China are studied using daily rainfall station data.The rainfall features are distinct along the eastern and western edges of the Hengduan Mountains and over the mountains,especially in terms of rainfall frequency.The rainfall amounts and frequencies are much higher along the eastern and western edges than over the mountains,particularly during spring,which is partly contributed by the number and duration of rainfall events.The differences are more obvious in the nocturnal rainfall than in the daytime rainfall.The rainfall differences over the three regions could be affected by the large-scale environment.By analyzing reanalysis data,the large-scale circulations linked to the different rainfall features over southwestern China,and the interactions of these circulations with the topography are also discussed.
基金This work was supported by the Program of the National Natural Science Foundation of China(61988101,61773405,and 61751312).
文摘Cell voltage is a widely used signal that can be measured online from an industrial aluminum electrolysis cell.A variety of parameters for the analysis and control of industrial cells are calculated using the cell voltage.In this paper,the frequency segmentation of cell voltage is used as the basis for designing filters to obtain these parameters.Based on the qualitative analysis of the cell voltage,the sub-band instantaneous energy spectrum(SIEP)is first proposed,which is then used to quantitatively represent the characteristics of the designated frequency bands of the cell voltage under various cell conditions.Ultimately,a cell condition-sensitive frequency segmentation method is given.The proposed frequency segmentation method divides the effective frequency band into the[0,0.001]Hz band of lowfrequency signals and the[0.001,0.050]Hz band of low-frequency noise,and subdivides the lowfrequency noise into the[0.001,0.010]Hz band of metal pad abnormal rolling and the[0.01,0.05]Hz band of sub-low-frequency noise.Compared with the instantaneous energy spectrum based on empirical mode decomposition,the SIEP more finely represents the law of energy change with time in any designated frequency band within the effective frequency band of the cell voltage.The proposed frequency segmentation method is more sensitive to cell condition changes and can obtain more elaborate details of online cell condition information,thus providing a more reliable and accurate online basis for cell condition monitoring and control decisions.
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.
文摘In order to improve the accuracy and engineering feasibility of four-Satellite localization system, the frequency difference measurement is introduced to the four-Satellite TDOA (Time Difference of Arrival) localization algorithm. The TDOA/FDOA (Frequency Difference of Arrival) localization algorithm is used to optimize the GDOP (geometric dilution of precision) of four-Satellite localization. The simulation results show that the absolute position measurement accuracy has little influence on TDOA/FDOA localization accuracy as compared with TDOA localization. Under the same conditions, TDOA/FDOA localization has better accuracy and its GDOP shows more uniform distribution in diamond configuration case. The localization accuracy of four-Satellite TDOA/FDOA is better than the localization accuracy of four-Satellite TDOA.
基金supported by the National Natural Science Foundation of China (Grant Nos.10974098 and 10774071)the Natural Science Foundation of Jiangsu Province,China (Grant No.BK2009407)+1 种基金the Doctoral Foundation of Ministry of Education of China (Grant No.20093207120003)the National Basic Research Program of China (Grant No.2010CB732600)
文摘The difference-frequency （DF） ultrasound generated by using parametric effect promises to improve detection depth owing to its low attenuation, which is beneficial for deep tissue imaging. With ultrasound contrast agents infusion, the harmonic components scattered from the microbubbles, including DF, can be generated due to the nonlinear vibration. A theoretical study on the DF generation from microbubbles under the dual-frequency excitation is proposed in formula based on the solution of the RPNNP equation. The optimisation of the DF generation is discussed associated with the applied acoustic pressure, frequency, and the microbubble size. Experiments are performed to validate the theoretical predictions by using a dual-frequency signal to excite microbubbles. Both the numerical and experimental results demonstrate that the optimised DF ultrasound can be achieved as the difference frequency is close to the resonance frequency of the microbubble and improve the contrast-to-tissue ratio in imaging.
基金National Natural Science Foundation of China （61002033, 60902089） Open Research Fund of State Key Laboratory of Astronautic Dynamics （2011ADL-DW0103）
文摘We study on reduced dynamic orbit determination using differenced phase in adjacent epochs for spacebome dual-frequency GPS. This method not only overcomes the shortcomings that the epoch-difference kinematic method cannot be used when observation geometry is poor or observations are insufficient, but also avoids solving the ambiguity in the zero-difference reduced dynamic method. As the epoch-difference method is not sensitive to the impact of phase cycle slips, it can lower the difficulty of slip detection in phase observation preprocessing. In the solution strategies, we solve the high-dimensional matrix computation problems by decomposing the long observation arc into a number of short arcs. By gravity recovery and climate experiment （GRACE） satellite orbit determination and compared with GeoForschungsZentrum （GFZ） post science orbit, for epoch-difference reduced dynamic method, the root mean squares （RMSs） of radial, transverse and normal components are 1.92 cm, 3.83 cm and 3.80 cm, and the RMS in three dimensions is 5.76 cm. The solution＇s accuracy is comparable to the zero-difference reduced dynamic method.
基金supported by the National Natural Science Foundation of China(Nos.51239008 and 51279130)
文摘This paper presents a study on the motion response of a tension-leg platform(TLP) under first-and second-order wave forces, including the mean-drift force, difference and sum-frequency forces. The second-order wave force is calculated using the full-field quadratic transfer function(QTF). The coupled effect of the horizontal motions, such as surge, sway and yaw motions, and the set-down motion are taken into consideration by the nonlinear restoring matrix. The time-domain analysis with 50-yr random sea state is performed. A comparison of the results of different case studies is made to assess the influence of second-order wave force on the motions of the platform. The analysis shows that the second-order wave force has a major impact on motions of the TLP. The second-order difference-frequency wave force has an obvious influence on the low-frequency motions of surge and sway, and also will induce a large set-down motion which is an important part of heave motion. Besides, the second-order sum-frequency force will induce a set of high-frequency motions of roll and pitch. However, little influence of second-order wave force is found on the yaw motion.
文摘A tunable continuous wave（cw） mid-infrared（MIR） laser based on difference-frequency generation（DFG） in a 1.5-cm long AgGaS2 nonlinear crystal for trace gas detection is reported.Two visible and near-infrared diode lasers were used as pump and signal sources.The MIR-DFG laser was tunable in a wavelength range of 4.75 μm-4.88 μm.The phase-matching（PM） condition was non-critically achieved by adjusting the temperature of the crystal for fixed pairs of input pump and signal wavelengths.The required PM temperatures of the generated MIR-DFG wavelengths have been calculated by using three sets of recent Sellmeier equations and the temperature-dispersion equations of AgGaS2 given by Willer U,et al.（Willer U,Blanke T and Schade W 2001 Appl.Opt.40 5439）.Then the calculated PM temperatures are compared with the experimental values.The performance of the MIR-DFG laser is shown by the trace detection of the P（16） carbon monoxide（12C16O） absorption line in a laboratory-fabricated absorption cell.The enhanced sensitivity of about 0.6×10 4 was obtained through the long path absorption provided by consecutive reflections between coated cylindrical mirrors of a constructed cell.
基金supported by the National Natural Science Foundation of China(Grant Nos.10978017 and 61201288)the Fundamental Research Funds for the Central Universities,China(Grant No.JB140413)
文摘We analyze the phenomena of phase group synchronization between the different nominal frequency signals and propose a new theory of the equivalent comparison between them. The exact expression of the equivalent comparison is deduced. High resolution frequency measurement and phase comparison can be realized using this theory with the divider. For avoiding the frequency mixing, multiplication and synthesis, the system phase noise is improved and the higher resolution comparison and measurement are achieved between the different nominal frequencies by theory.
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(Grant Nos.11934013 and 92065101)the Anhui Initiative In Quantum Information Technologies(Grant No.AHY020200)+1 种基金the Innovation Program for Quantum Science and Technology(Grant No.2021ZD0301100)the National Key Research and Development Program of China(Grant No.2022YFB3607700).
文摘We present a scheme for estimating the noise-equivalent temperature difference(NETD)of frequency upconversion detectors(UCDs)that detect mid-infrared(MIR)light.In particular,we investigate the frequency upconversion of a periodically poled crystal based on lithium niobate,where an MIR conversion bandwidth of 220 nm can be achieved in a single-poled period by a special design.Experimentally,for an MIR radiating target at a temperature of 95℃,the NETD of the device was estimated to be 56 mK with an exposure time of 1 s.Meanwhile,a direct measurement of the NETD was performed utilizing conventional methods,which resulted in 48 mK.We also compared the NETD of our UCD with commercially available direct MIR detectors.We show that the limiting factor for further NETD reduction of our device is not primarily from the upconversion process and camera noise but from the limitations of the heat source and laser performance.Our detectors have good temperature measurement performance and can be used for a variety of applications involving temperature object identification and material structure detection.
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)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.
