A non-contact low-frequency(LF)method of diagnosing the plasma surrounding a scaled model in a shock tube is proposed.This method utilizes the phase shift occurring after the transmission of an LF alternating magnetic...A non-contact low-frequency(LF)method of diagnosing the plasma surrounding a scaled model in a shock tube is proposed.This method utilizes the phase shift occurring after the transmission of an LF alternating magnetic field through the plasma to directly measure the ratio of the plasma loop average electron density to collision frequency.An equivalent circuit model is used to analyze the relationship of the phase shift of the magnetic field component of LF electromagnetic waves with the plasma electron density and collision frequency.The applicable range of the LF method on a given plasma scale is analyzed.The upper diagnostic limit for the ratio of the electron density(unit:m^(-3))to collision frequency(unit:Hz)exceeds 1×10^(11),enabling an electron density to exceed 1×10^(20)m^(-3)and a collision frequency to be less than 1 GHz.In this work,the feasibility of using the LF phase shift to implement the plasma diagnosis is also assessed.Diagnosis experiments on shock tube equipment are conducted by using both the electrostatic probe method and LF method.By comparing the diagnostic results of the two methods,the inversion results are relatively consistent with each other,thereby preliminarily verifying the feasibility of the LF method.The ratio of the electron density to the collision frequency has a relatively uniform distribution during the plasma stabilization.The LF diagnostic path is a loop around the model,which is suitable for diagnosing the plasma that surrounds the model.Finally,the causes of diagnostic discrepancy between the two methods are analyzed.The proposed method provides a new avenue for diagnosing high-density enveloping plasma.展开更多
Acoustic scattering modulation caused by an undulating sea surface on the space-time dimension seriously affects underwater detection and target recognition.Herein,underwater acoustic scattering modulation from a movi...Acoustic scattering modulation caused by an undulating sea surface on the space-time dimension seriously affects underwater detection and target recognition.Herein,underwater acoustic scattering modulation from a moving rough sea surface is studied based on integral equation and parabolic equation.And with the principles of grating and constructive interference,the mechanism of this acoustic scattering modulation is explained.The periodicity of the interference of moving rough sea surface will lead to the interference of the scattering field at a series of discrete angles,which will form comb-like and frequency-shift characteristics on the intensity and the frequency spectrum of the acoustic scattering field,respectively,which is a high-order Bragg scattering phenomenon.Unlike the conventional Doppler effect,the frequency shifts of the Bragg scattering phenomenon are multiples of the undulating sea surface frequency and are independent of the incident sound wave frequency.Therefore,even if a low-frequency underwater acoustic field is incident,it will produce obvious frequency shifts.Moreover,under the action of ideal sinusoidal waves,swells,fully grown wind waves,unsteady wind waves,or mixed waves,different moving rough sea surfaces create different acoustic scattering processes and possess different frequency shift characteristics.For the swell wave,which tends to be a single harmonic wave,the moving rough sea surface produces more obvious high-order scattering and frequency shifts.The same phenomena are observed on the sea surface under fully grown wind waves,however,the frequency shift slightly offsets the multiple peak frequencies of the wind wave spectrum.Comparing with the swell and fully-grown wind waves,the acoustic scattering and frequency shift are not obvious for the sea surface under unsteady wind waves.展开更多
A comprehensive two-dimensional axisymmetric mathematical model that couples transient electromagnetic force with fluid flow,heat transfer,and solidification was established to describe the interaction of multiphysics...A comprehensive two-dimensional axisymmetric mathematical model that couples transient electromagnetic force with fluid flow,heat transfer,and solidification was established to describe the interaction of multiphysics field during DC casting.The melt flow,heat transfer,and solidification characteristics under differential phase pulse magnetic field and differential phase low-frequency electromagnetic field(DP-PMF and DP-LFEF)were numerically investigated by means of numerical simulation during electromagnetic direct-chill(DC)casting of AZ31 alloy at the same casting conditions.The effects of differential phase electromagnetic fields on Lorentz forces distributions,melt flow,heat transfer,and liquid sump shape were discussed systematically.Based on measured current waveform,the results were compared with those obtained without magnetic field(MF)and under conventional pulse magnetic field(PMF)and low-frequency electromagnetic field(LFEF)under the same conditions.The results show that the application of magnetic fields can significantly change the solidification process of DC casting.Differential phase magnetic fields(DP-LFEF and DP-PMF)can effectively reduce the temperature of the melt in the liquid sump,and the shallower liquid sump depth can be obtained under the differential phase magnetic fields.A large velocity vibration amplitude and a lower temperature are available simultaneously under DP-PMF,resulting in more uniform temperature distribution.展开更多
A low-frequency magnetic lightning mapping system(LFM-LMS)was built during the SHAndong Triggered Lightning Experiment(SHATLE),based on continuous measurements of magnetic field radiation from lightning.The hardware a...A low-frequency magnetic lightning mapping system(LFM-LMS)was built during the SHAndong Triggered Lightning Experiment(SHATLE),based on continuous measurements of magnetic field radiation from lightning.The hardware and source-mapping techniques used by the LFM-LMS were introduced;both Monte Carlo simulations and the observation of rocket-triggered lightning examples were employed to examine the location accuracy and detection effectiveness of the LFM-LMS.We estimated that the system’s location accuracy about 100−200 m horizontally and~200 m vertically.A natural intra-cloud lightning flash and a rocket-triggered lightning flash,both with intricate structures and discharging processes,were examined using the three-dimensional mapping results.The progressing path of negative lightning leaders is usually well-defined,and its propagation speed is estimated to be(0.5−1.4)×10^(6)m/s.In summary,the LFM-LMS can reconstruct the three-dimensional morphology of lightning flashes;this technology provides a efficient method for investigating the characteristics of lightning development,as well as the overall electrical strucuture of thunderstorms.展开更多
With the increasing complexity of prospecting objectives,reverse time migration( RTM) has attracted more and more attention due to its outstanding imaging quality. RTM is based on two-way wave equation,so it can avoid...With the increasing complexity of prospecting objectives,reverse time migration( RTM) has attracted more and more attention due to its outstanding imaging quality. RTM is based on two-way wave equation,so it can avoid the limits of angle in traditional one-way wave equation migration,image reverse branch,prism waves and multi-reflected wave precisely and obtain accurate dynamic information. However,the huge demands for storage and computation as well as low frequency noises restrict its wide application. The normalized cross-correlation imaging conditions based on wave field decomposition are derived from traditional cross-correlation imaging condition,and it can eliminate the low-frequency noises effectively and improve the imaging resolution. The practical procedure includes separating source and receiver wave field into one-way components respectively,and conducting cross-correlation imaging condition to the post-separated wave field. In this way,the resolution and precision of the imaging result will be promoted greatly.展开更多
Objective:The aim of this study was to investigate the biological effects of occupational extremely low-frequency electromagnetic field(ELF-EMF)exposure on the thyroid gland.Methods:We conducted a prospective analysis...Objective:The aim of this study was to investigate the biological effects of occupational extremely low-frequency electromagnetic field(ELF-EMF)exposure on the thyroid gland.Methods:We conducted a prospective analysis of 85 workers(exposure group)exposed to an ELF-EMF(100μT,10-100 Hz)produced by the electromagnetic aircraft launch system and followed up on thyroid function indices,immunological indices,and color Doppler images for 3 years.Additionally,116 healthy volunteers were randomly selected as controls(control group),the thyroid function of whom was compared to the exposure group.Results:No significant difference was observed in thyroid function between the exposure and control groups.During the follow-up of the exposure group,the serum free triiodothyronine(FT3)level was found to slowly decrease and free thyroxine(FT4)level slowly increase with increasing exposure time.However,no significant difference was found in thyroid-stimulating hormone(TSH)over the three years,and no significant difference was observed in the FT3,FT4 and TSH levels between different exposure subgroups.Furthermore,no significant changes were observed in thyroid autoantibody levels and ultrasound images between subgroups or over time.Conclusion:Long-term exposure to ELF-EMF may promote thyroid secretion of T4 and inhibit deiodination of T4 to T3.ELF-EMF has no significant effect on thyroid immune function and morphology.展开更多
The protective effects of blueberry anthocyanin extracts against damage induced by extremely lowfrequency electromagnetic field(ELF-EMF)were investigated in a rat model.Wistar rats were exposed to ELF-EMF with or with...The protective effects of blueberry anthocyanin extracts against damage induced by extremely lowfrequency electromagnetic field(ELF-EMF)were investigated in a rat model.Wistar rats were exposed to ELF-EMF with or without the administration of blueberry anthocyanin extracts(50,100,and 200 mg/kg per day intragastrically once a day)for 30 days.Blueberry anthocyanin extracts supplementation inhibited the decrease in Nissl substance levels,cell membrane integrity,and mitochondrial membrane potential induced by ELF-EMF;prevented the increase in nitric oxide,malondialdehyde,and Ca2+concentrations;suppressed superoxide dismutase and glutathione depletion;and enhanced the cognitive ability of the rats exposed to ELF-EMF.The protective effects of blueberry anthocyanin extracts against hippocampal neuron injury caused by ELF-EMF were dose-dependent.These results demonstrated that blueberry anthocyanin extracts suppress hippocampal neuron injury caused by ELF-EMF by inhibiting cell membrane damage and oxidative stress pathways,and suggested that blueberry anthocyanin treatment potentially prevents hippocampal neuron injury.展开更多
为进一步探讨高原低涡与高原大气的基本状况及其联系,通过对1981-2015年低涡频次及OLR、500 h Pa经纬向风场的统计,分析其气候变化及低频振荡特征,并初步探讨了低涡频次与其他三者低频信号之间的联系。结果表明:4-8月是低涡的频发时段;...为进一步探讨高原低涡与高原大气的基本状况及其联系,通过对1981-2015年低涡频次及OLR、500 h Pa经纬向风场的统计,分析其气候变化及低频振荡特征,并初步探讨了低涡频次与其他三者低频信号之间的联系。结果表明:4-8月是低涡的频发时段;低涡频次呈逐年增加的趋势,存在显著的2 a、4 a变化周期和55 d、30 d低频振荡周期;在低涡频发期内,OLR平均值为212.2 W·m^(-2),存在显著的10~12 a变化周期和45 d、20 d低频振荡,滤波中心存在东进和西退的移动特征,在纬向上表现为向南移动,500 h Pa纬向风均值为3.56 m·s^(-1),其逐年及逐日变化均呈下降趋势,存在4 a、10 a的变化周期和75 d、45 d的低频振荡周期,30~60 d滤波信号中心以西退和北进为主要移动特征,60~90 d滤波信号中心向南移动特征明显,500 h Pa经向风以北风分量为主,其逐年及逐日变化均为减小趋势,存在4 a变化周期和10-20 d低频振荡;低涡频次与500 h Pa纬向风区域平均值在1996年发生突变;低涡频次与大气低频振荡存在密切联系,其与500 h Pa经向风呈负相关性,7-8月尤为显著,与OLR和500 h Pa纬向风在4月至7月中旬呈显著正相关,7月中旬至8月转为负相关,其中与OLR 30-60 d滤波信号呈高度负相关性;500 h Pa纬向风滤波信号中心的移动能较好的对应低涡频次空间分布的变化。展开更多
In this Letter, we focus on the theoretical analysis of the relativistic energy and angular distributions of the ejected photoelectrons during the relativistic tunnel ionization of atoms by intense, circularly polariz...In this Letter, we focus on the theoretical analysis of the relativistic energy and angular distributions of the ejected photoelectrons during the relativistic tunnel ionization of atoms by intense, circularly polarized light. We make a small modification of the general analytical expressions for these distributions. The role of the initial momentum, the ponderomotive potential, and the Stark shift are considered. We also present the maximal angle of electron emission.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant Nos.52107162 and 12202479)the Science and Technology Projects of Shaanxi Province,China(Grant Nos.2022CGBX-12 and 2022KXJ-57)the Science and Technology Projects of Xi’an City,China(Grant Nos.23KGDW0023-2022 and 23GXFW0011)。
文摘A non-contact low-frequency(LF)method of diagnosing the plasma surrounding a scaled model in a shock tube is proposed.This method utilizes the phase shift occurring after the transmission of an LF alternating magnetic field through the plasma to directly measure the ratio of the plasma loop average electron density to collision frequency.An equivalent circuit model is used to analyze the relationship of the phase shift of the magnetic field component of LF electromagnetic waves with the plasma electron density and collision frequency.The applicable range of the LF method on a given plasma scale is analyzed.The upper diagnostic limit for the ratio of the electron density(unit:m^(-3))to collision frequency(unit:Hz)exceeds 1×10^(11),enabling an electron density to exceed 1×10^(20)m^(-3)and a collision frequency to be less than 1 GHz.In this work,the feasibility of using the LF phase shift to implement the plasma diagnosis is also assessed.Diagnosis experiments on shock tube equipment are conducted by using both the electrostatic probe method and LF method.By comparing the diagnostic results of the two methods,the inversion results are relatively consistent with each other,thereby preliminarily verifying the feasibility of the LF method.The ratio of the electron density to the collision frequency has a relatively uniform distribution during the plasma stabilization.The LF diagnostic path is a loop around the model,which is suitable for diagnosing the plasma that surrounds the model.Finally,the causes of diagnostic discrepancy between the two methods are analyzed.The proposed method provides a new avenue for diagnosing high-density enveloping plasma.
基金Project supported by the IACAS Young Elite Researcher Project(Grant No.QNYC201703)the Rising Star Foundation of Integrated Research Center for Islands and Reefs Sciences,CAS(Grant No.ZDRW-XH-2021-2-04)the Key Laboratory Foundation of Acoustic Science and Technology(Grant No.2021-JCJQ-LB-066-08).
文摘Acoustic scattering modulation caused by an undulating sea surface on the space-time dimension seriously affects underwater detection and target recognition.Herein,underwater acoustic scattering modulation from a moving rough sea surface is studied based on integral equation and parabolic equation.And with the principles of grating and constructive interference,the mechanism of this acoustic scattering modulation is explained.The periodicity of the interference of moving rough sea surface will lead to the interference of the scattering field at a series of discrete angles,which will form comb-like and frequency-shift characteristics on the intensity and the frequency spectrum of the acoustic scattering field,respectively,which is a high-order Bragg scattering phenomenon.Unlike the conventional Doppler effect,the frequency shifts of the Bragg scattering phenomenon are multiples of the undulating sea surface frequency and are independent of the incident sound wave frequency.Therefore,even if a low-frequency underwater acoustic field is incident,it will produce obvious frequency shifts.Moreover,under the action of ideal sinusoidal waves,swells,fully grown wind waves,unsteady wind waves,or mixed waves,different moving rough sea surfaces create different acoustic scattering processes and possess different frequency shift characteristics.For the swell wave,which tends to be a single harmonic wave,the moving rough sea surface produces more obvious high-order scattering and frequency shifts.The same phenomena are observed on the sea surface under fully grown wind waves,however,the frequency shift slightly offsets the multiple peak frequencies of the wind wave spectrum.Comparing with the swell and fully-grown wind waves,the acoustic scattering and frequency shift are not obvious for the sea surface under unsteady wind waves.
基金the National Natural Science Foundation of China(51974082)the National Natural Science Foundation of China(51771043)the Programme of Introducing Talents of Discipline Innovation to Universities 2.0(the 111 Project 2.0 of China,No.BP0719037).
文摘A comprehensive two-dimensional axisymmetric mathematical model that couples transient electromagnetic force with fluid flow,heat transfer,and solidification was established to describe the interaction of multiphysics field during DC casting.The melt flow,heat transfer,and solidification characteristics under differential phase pulse magnetic field and differential phase low-frequency electromagnetic field(DP-PMF and DP-LFEF)were numerically investigated by means of numerical simulation during electromagnetic direct-chill(DC)casting of AZ31 alloy at the same casting conditions.The effects of differential phase electromagnetic fields on Lorentz forces distributions,melt flow,heat transfer,and liquid sump shape were discussed systematically.Based on measured current waveform,the results were compared with those obtained without magnetic field(MF)and under conventional pulse magnetic field(PMF)and low-frequency electromagnetic field(LFEF)under the same conditions.The results show that the application of magnetic fields can significantly change the solidification process of DC casting.Differential phase magnetic fields(DP-LFEF and DP-PMF)can effectively reduce the temperature of the melt in the liquid sump,and the shallower liquid sump depth can be obtained under the differential phase magnetic fields.A large velocity vibration amplitude and a lower temperature are available simultaneously under DP-PMF,resulting in more uniform temperature distribution.
基金the National Key R&D Program of China(2017YFC1501501)the CAS Project of Stable Support for Youth Team in Basic Research Field(YSRR-018)+3 种基金the Youth Innovation Fund project of the university(WK2080000172)the National Natural Science Foundation of China(41875006,U1938115)the Chinese Meridian Projectthe International Partnership Program of Chinese Academy of Sciences(183311KYSB20200003).
文摘A low-frequency magnetic lightning mapping system(LFM-LMS)was built during the SHAndong Triggered Lightning Experiment(SHATLE),based on continuous measurements of magnetic field radiation from lightning.The hardware and source-mapping techniques used by the LFM-LMS were introduced;both Monte Carlo simulations and the observation of rocket-triggered lightning examples were employed to examine the location accuracy and detection effectiveness of the LFM-LMS.We estimated that the system’s location accuracy about 100−200 m horizontally and~200 m vertically.A natural intra-cloud lightning flash and a rocket-triggered lightning flash,both with intricate structures and discharging processes,were examined using the three-dimensional mapping results.The progressing path of negative lightning leaders is usually well-defined,and its propagation speed is estimated to be(0.5−1.4)×10^(6)m/s.In summary,the LFM-LMS can reconstruct the three-dimensional morphology of lightning flashes;this technology provides a efficient method for investigating the characteristics of lightning development,as well as the overall electrical strucuture of thunderstorms.
文摘With the increasing complexity of prospecting objectives,reverse time migration( RTM) has attracted more and more attention due to its outstanding imaging quality. RTM is based on two-way wave equation,so it can avoid the limits of angle in traditional one-way wave equation migration,image reverse branch,prism waves and multi-reflected wave precisely and obtain accurate dynamic information. However,the huge demands for storage and computation as well as low frequency noises restrict its wide application. The normalized cross-correlation imaging conditions based on wave field decomposition are derived from traditional cross-correlation imaging condition,and it can eliminate the low-frequency noises effectively and improve the imaging resolution. The practical procedure includes separating source and receiver wave field into one-way components respectively,and conducting cross-correlation imaging condition to the post-separated wave field. In this way,the resolution and precision of the imaging result will be promoted greatly.
基金supported by.the National Military Research Project of China(No.JGXM201507).
文摘Objective:The aim of this study was to investigate the biological effects of occupational extremely low-frequency electromagnetic field(ELF-EMF)exposure on the thyroid gland.Methods:We conducted a prospective analysis of 85 workers(exposure group)exposed to an ELF-EMF(100μT,10-100 Hz)produced by the electromagnetic aircraft launch system and followed up on thyroid function indices,immunological indices,and color Doppler images for 3 years.Additionally,116 healthy volunteers were randomly selected as controls(control group),the thyroid function of whom was compared to the exposure group.Results:No significant difference was observed in thyroid function between the exposure and control groups.During the follow-up of the exposure group,the serum free triiodothyronine(FT3)level was found to slowly decrease and free thyroxine(FT4)level slowly increase with increasing exposure time.However,no significant difference was found in thyroid-stimulating hormone(TSH)over the three years,and no significant difference was observed in the FT3,FT4 and TSH levels between different exposure subgroups.Furthermore,no significant changes were observed in thyroid autoantibody levels and ultrasound images between subgroups or over time.Conclusion:Long-term exposure to ELF-EMF may promote thyroid secretion of T4 and inhibit deiodination of T4 to T3.ELF-EMF has no significant effect on thyroid immune function and morphology.
基金supported by the Natural Science Foundation Key Program of Liaoning Province(20170540803)the Liaoning Provincial Department of Education Project(LSNJC201911).
文摘The protective effects of blueberry anthocyanin extracts against damage induced by extremely lowfrequency electromagnetic field(ELF-EMF)were investigated in a rat model.Wistar rats were exposed to ELF-EMF with or without the administration of blueberry anthocyanin extracts(50,100,and 200 mg/kg per day intragastrically once a day)for 30 days.Blueberry anthocyanin extracts supplementation inhibited the decrease in Nissl substance levels,cell membrane integrity,and mitochondrial membrane potential induced by ELF-EMF;prevented the increase in nitric oxide,malondialdehyde,and Ca2+concentrations;suppressed superoxide dismutase and glutathione depletion;and enhanced the cognitive ability of the rats exposed to ELF-EMF.The protective effects of blueberry anthocyanin extracts against hippocampal neuron injury caused by ELF-EMF were dose-dependent.These results demonstrated that blueberry anthocyanin extracts suppress hippocampal neuron injury caused by ELF-EMF by inhibiting cell membrane damage and oxidative stress pathways,and suggested that blueberry anthocyanin treatment potentially prevents hippocampal neuron injury.
文摘为进一步探讨高原低涡与高原大气的基本状况及其联系,通过对1981-2015年低涡频次及OLR、500 h Pa经纬向风场的统计,分析其气候变化及低频振荡特征,并初步探讨了低涡频次与其他三者低频信号之间的联系。结果表明:4-8月是低涡的频发时段;低涡频次呈逐年增加的趋势,存在显著的2 a、4 a变化周期和55 d、30 d低频振荡周期;在低涡频发期内,OLR平均值为212.2 W·m^(-2),存在显著的10~12 a变化周期和45 d、20 d低频振荡,滤波中心存在东进和西退的移动特征,在纬向上表现为向南移动,500 h Pa纬向风均值为3.56 m·s^(-1),其逐年及逐日变化均呈下降趋势,存在4 a、10 a的变化周期和75 d、45 d的低频振荡周期,30~60 d滤波信号中心以西退和北进为主要移动特征,60~90 d滤波信号中心向南移动特征明显,500 h Pa经向风以北风分量为主,其逐年及逐日变化均为减小趋势,存在4 a变化周期和10-20 d低频振荡;低涡频次与500 h Pa纬向风区域平均值在1996年发生突变;低涡频次与大气低频振荡存在密切联系,其与500 h Pa经向风呈负相关性,7-8月尤为显著,与OLR和500 h Pa纬向风在4月至7月中旬呈显著正相关,7月中旬至8月转为负相关,其中与OLR 30-60 d滤波信号呈高度负相关性;500 h Pa纬向风滤波信号中心的移动能较好的对应低涡频次空间分布的变化。
基金supported by the Serbian Ministry of Education,Science,and Technological Development for financial support through Projects 171020 and 171021
文摘In this Letter, we focus on the theoretical analysis of the relativistic energy and angular distributions of the ejected photoelectrons during the relativistic tunnel ionization of atoms by intense, circularly polarized light. We make a small modification of the general analytical expressions for these distributions. The role of the initial momentum, the ponderomotive potential, and the Stark shift are considered. We also present the maximal angle of electron emission.
