Ultrafast optical spectroscopy of a single crystal of a Dirac semimetal Cd_3As_（2 ）is carried out.An acoustic phonon（AP）mode with central frequency f=0.037 THz（i.e.,1.23 cm^（-1）or 0.153 meV）is unambiguously ge...Ultrafast optical spectroscopy of a single crystal of a Dirac semimetal Cd_3As_（2 ）is carried out.An acoustic phonon（AP）mode with central frequency f=0.037 THz（i.e.,1.23 cm^（-1）or 0.153 meV）is unambiguously generated and detected,which we attribute to laser-induced thermal strain.An AP chirping（i.e.,variation of the phonon frequency）is clearly detected,which is ascribed to heat capacity variation with time.By comparing our experimental results and the theoretical model,we obtain a chirping time constant,which is 31.2 ps at 6 K and 19.8 ps at 300 K,respectively.Significantly,we identify an asymmetry in the AP frequency domain peak and find that it is caused by the chirping,instead of a Fano resonance.Moreover,we experimentally demonstrate that the central frequency of AP is extremely stable with varying laser fluence,as well as temperature,which endows Cd_3As_2application potentials in thermoelectric devices.展开更多
Multiple broadband Alfvenic chirping modes(CMs),with frequencies in the wide range of f-35-150 kHz and chirping down rapidly,are found in HL-2A neutral beam injection plasmas,and the CMs can even coexist.The frequency...Multiple broadband Alfvenic chirping modes(CMs),with frequencies in the wide range of f-35-150 kHz and chirping down rapidly,are found in HL-2A neutral beam injection plasmas,and the CMs can even coexist.The frequency chirping down process can be completed within-1 ms,and the frequency shift can reach 30-50 kHz.The CMs propagate in ion diamagnetic drift directions poloidally.The toroidal mode number is confirmed to be n=1,2,3 and 4 for the f-35-65,55-90,70-120 and 100-150 kHz CMs,respectively.The CMs are more like to be energetic-particle continuum modes(EPMs),since the modes almost locate on the Alfven continuum.展开更多
Enhanced electron–positron pair production by frequency chirping in one- and two-color laser pulse fields is investigated by solving the quantum Vlasov equation. A small frequency chirp shifts the momentum spectrum a...Enhanced electron–positron pair production by frequency chirping in one- and two-color laser pulse fields is investigated by solving the quantum Vlasov equation. A small frequency chirp shifts the momentum spectrum along the momentum axis. The positive and negative frequency chirp parameters play the same role in increasing the pair number density. The sign change of the frequency chirp parameter at the moment t = 0 leads the pulse shape and momentum spectrum to be symmetric, and the number density to be increased. The number density of produced pairs in the two-color pulse field is much higher than that in the one-color pulse field and the larger frequency chirp pulse field dominates more strongly. In the two-color pulse fields, the relation between the frequency ratio of two colors and the number density is not sensitive to the parameters of small frequency chirp added in either a low frequency strong field or a high frequency weak field but sensitive to the parameters of large frequency chirp added in a high frequency weak field.展开更多
The effect of channel-width chirping on near- and far-field intensity patterns of the six supermodes was investigated. The supermode discrimination was evaluated in various channel-chirped index guided laser arrays. T...The effect of channel-width chirping on near- and far-field intensity patterns of the six supermodes was investigated. The supermode discrimination was evaluated in various channel-chirped index guided laser arrays. The results show that the linearly channel-chirped laser array has very good supermode discrimination which is better than that of a uniform laser array, the V channel-chirped laser array has the smallest radiation angle of the fundamental supermode among the calculated arrays, and the asymmetrically V channel-chirped array has a very small radiation angle of the fundamental supermode, which is smaller than that of the uniform array and also allows for very good fundamental supermode discrimination against the higher-order supermodes, which is better than that of the V channel-chirped laser array.展开更多
Two different types of MHD instabilities with rapidly chirping frequency were found to arise in the Globus-M2 spherical tokamak in substantially different frequency ranges.The first type arises at frequencies of an or...Two different types of MHD instabilities with rapidly chirping frequency were found to arise in the Globus-M2 spherical tokamak in substantially different frequency ranges.The first type arises at frequencies of an order of 1 MHz in ohmic plasmas at relatively low density(n_(e))<2×10^(19) m^(-3) in a wide range of toroidal magnetic fields and plasma currents.This type of instability was identified as compressional Alfven waves,driven by electrons,accelerated during a sawtooth crush.It was found that the mode frequency is sweeping in time,according to the Berk-Breizman hole-clump nonlinear chirping model.The second type of wave arises in a specific single-swing regime of the central solenoid current with a very narrow plasma column,when the plasma tends to decay at extremely low density(n_(e))<2×10^(18) m^(-3) and,in fact,is an instability of the runaway electron beam.The exited modes cover the whole observed frequency range and are divided into several(two or three)frequency regions:approximately 0-30 MHz,60-120 MHz and sometimes 30-60 MHz.Reconnection of the branches was also observed.Single chirps are more rapid than for 1 MHz Alfven instability and follow an exponential law.This paper,to our knowledge,is the first report of frequency chirping instabilities excited by accelerated electrons at a spherical tokamak.展开更多
Numerical method to solve the problem related with the interactive effect of dispersion (both chromatic dispersion and polarization mode dispersion) and nonlinearity on optical pulse transmission is present. Evolution...Numerical method to solve the problem related with the interactive effect of dispersion (both chromatic dispersion and polarization mode dispersion) and nonlinearity on optical pulse transmission is present. Evolutions of pulses with various initial chirping and shape at bit rate of 10 Gb/s are simulated and compared. Gaussian pulse with appropriate prechirping is propitious for high bit rate transmission.展开更多
The influences of laser pulses with negative frequency chirp and different pulse cycles on pair production are studied.By solving the quantum Vlasov equation,the momentum distribution and the number density of the cre...The influences of laser pulses with negative frequency chirp and different pulse cycles on pair production are studied.By solving the quantum Vlasov equation,the momentum distribution and the number density of the created pairs are obtained numerically.It is found that the chirp rate can enhance the pair production rate in both supercycle and subcycle pulses.Moreover,there is an optimal cycle parameter corresponding to the maximum number density under the same chirp rate.The pair number density is sensitive to the cycle parameter when it is less than the optimal one.Compared to the positive frequency chirp,in the case of the negative frequency chirp,the optimal cycle parameter is increased.展开更多
The propagation of an intense laser pulse in an under-dense plasma induces a plasma wake that is suitable for the acceleration of electrons to relativistic energies. For an ultra-intense laser pulse which has a longit...The propagation of an intense laser pulse in an under-dense plasma induces a plasma wake that is suitable for the acceleration of electrons to relativistic energies. For an ultra-intense laser pulse which has a longitudinal size shorter than the plasma wavelength, λp, instead of a periodic plasma wave, a cavity free from cold plasma electrons, called a bubble, is formed behind the laser pulse. An intense charge separation electric field inside the moving bubble can capture the electrons at the base of the bubble and accelerate them with a narrow energy spread. In the nonlinear bubble regime, due to localized depletion at the front of the pulse during its propagation through the plasma, the phase shift between carrier waves and pulse envelope plays an important role in plasma response. The carrier–envelope phase（CEP） breaks down the symmetric transverse ponderomotive force of the laser pulse that makes the bubble structure unstable. Our studies using a series of two-dimensional（2D） particle-in-cell（PIC） simulations show that the frequency-chirped laser pulses are more effective in controlling the pulse depletion rate and consequently the effect of the CEP in the bubble regime. The results indicate that the utilization of a positively chirped laser pulse leads to an increase in rate of erosion of the leading edge of the pulse that rapidly results in the formation of a steep intensity gradient at the front of the pulse. A more unstable bubble structure, the self-injections in different positions, and high dark current are the results of using a positively chirped laser pulse. For a negatively chirped laser pulse, the pulse depletion process is compensated during the propagation of the pulse in plasma in such a way that results in a more stable bubble shape and therefore, a localized electron bunch is produced during the acceleration process. As a result, by the proper choice of chirping, one can tune the number of self-injected electrons, the size of accelerated bunch and its energy spectrum to the values required for practical applications.展开更多
目的:研究听力正常儿童Chirp-听性稳态反应(ASSR)与行为测听阈值的相关性,探讨Chirp-ASSR应用于听力正常儿童听力检测的可行性。方法:选择50例(100耳)4~5岁听力正常儿童,分别进行ChirpASSR与行为测听听力检测,记录两种听力测试方法所得...目的:研究听力正常儿童Chirp-听性稳态反应(ASSR)与行为测听阈值的相关性,探讨Chirp-ASSR应用于听力正常儿童听力检测的可行性。方法:选择50例(100耳)4~5岁听力正常儿童,分别进行ChirpASSR与行为测听听力检测,记录两种听力测试方法所得到的0.5 k Hz、1 k Hz、2 k Hz、4 k Hz四个频率点阈值,将两种测试方法所得到的上述四个频率点阈值进行相关性分析。结果:Chirp-ASSR与行为测听两种测试方法在0.5 k Hz、1 k Hz、2 k Hz、4 k Hz四个频率点阈值的相关系数分别为0.84、0.83、0.82及0.76(P均<0.05)。结论:Chirp-ASSR与行为测听检测的阈值相关性较好,Chirp-ASSR应用于听力正常儿童听力检测中有一定的临床价值。展开更多
With the popularization of new technologies,telephone fraud has become the main means of stealing money and personal identity information.Taking inspiration from the website authentication mechanism,we propose an end-...With the popularization of new technologies,telephone fraud has become the main means of stealing money and personal identity information.Taking inspiration from the website authentication mechanism,we propose an end-to-end datamodem scheme that transmits the caller’s digital certificates through a voice channel for the recipient to verify the caller’s identity.Encoding useful information through voice channels is very difficult without the assistance of telecommunications providers.For example,speech activity detection may quickly classify encoded signals as nonspeech signals and reject input waveforms.To address this issue,we propose a novel modulation method based on linear frequency modulation that encodes 3 bits per symbol by varying its frequency,shape,and phase,alongside a lightweightMobileNetV3-Small-based demodulator for efficient and accurate signal decoding on resource-constrained devices.This method leverages the unique characteristics of linear frequency modulation signals,making them more easily transmitted and decoded in speech channels.To ensure reliable data delivery over unstable voice links,we further introduce a robust framing scheme with delimiter-based synchronization,a sample-level position remedying algorithm,and a feedback-driven retransmission mechanism.We have validated the feasibility and performance of our system through expanded real-world evaluations,demonstrating that it outperforms existing advanced methods in terms of robustness and data transfer rate.This technology establishes the foundational infrastructure for reliable certificate delivery over voice channels,which is crucial for achieving strong caller authentication and preventing telephone fraud at its root cause.展开更多
We investigated the morphology and sedimentary state of an extensive modern canyon system on the northwest continental slope of Palawan Island in the southern South China Sea using multibeam bathymetry data and chirp ...We investigated the morphology and sedimentary state of an extensive modern canyon system on the northwest continental slope of Palawan Island in the southern South China Sea using multibeam bathymetry data and chirp sub-bottom profiles.The canyon system in Northwest Palawan consists of a fairly large dendritic canyon,a braided canyon,and a set of short,straight,and slope-confined gullies.The erosion state covers 71%of the system.Sediment accumulates downstream of the bend's inner side in the proximal main stem of the dendritic canyon and is eroded in its outer side.In the distal main stem,sediment is deposited inside and outside the bend.In most of the system's tributaries,decreasing slope gradients result in more sediment deposition.There is thick aggradation of sediment waves in the interfluve throughout the system,which exhibit increasing levels of stratification as the slope decreases.The lack of slump scars and headward erosion at the canyon heads,as well as the presence of regular gullies and sediment wave fields,suggest that large areas of unconfined downslope turbidity currents formed the system.We propose that frequent storms in northwestern Palawan triggered these currents by resuspending sediments on the shelf.展开更多
Nature is amazing!Sometimes you don’t need a weather App to predict rain or shine-you just need nature!Feel the heat:listen to crickets Want to know the outside temperature?Listen to the crickets!Count how many times...Nature is amazing!Sometimes you don’t need a weather App to predict rain or shine-you just need nature!Feel the heat:listen to crickets Want to know the outside temperature?Listen to the crickets!Count how many times a cricket chirps in 15 seconds and add 40.That’s the temperature in Fahrenheit(华氏温度,1℉≈0.56℃).Do it several times and find the average.展开更多
With the first rays of dawn peeking through the rainforest at Shiti Village,Dehong Dai and Jingpo Autonomous Prefecture,Yunnan Province,Xu Xiaolong,a bird-watching guide from the Jingpo ethnic group,led a German bird-...With the first rays of dawn peeking through the rainforest at Shiti Village,Dehong Dai and Jingpo Autonomous Prefecture,Yunnan Province,Xu Xiaolong,a bird-watching guide from the Jingpo ethnic group,led a German bird-watching group into the jungle.His great-grandfather made a living by hunting“weird-looking birds”in the mountains.Today,the birds(Great Hornbill)are attracting tourist dollars from other parts of the world without dodging bullets.In Shiti Village,bird-watchers can enjoy the chirping of Great Hornbills and feel the rumbling in the air as the birds fly past.The village on the Chinese border with Myanmar was formerly poverty-stricken,with an average annual income of barely 2,000 yuan(US$305)per household 10 years ago.Today,the average annual income has grown to 150,000 yuan(US$23,075).It is a shining example of the successful practice of the notion that“lucid waters and lush mountains are invaluable assets.”展开更多
We propose a scheme for dual-species deceleration and trapping of a cold atom–molecule mixture by a frequency chirping stimulated force.We study the stimulated force exerted on Mg F and Rb using optical Bloch equatio...We propose a scheme for dual-species deceleration and trapping of a cold atom–molecule mixture by a frequency chirping stimulated force.We study the stimulated force exerted on Mg F and Rb using optical Bloch equations based on a direct numerical solution for the time-dependent density matrix.We analyze the relationship between the frequency chirping rate and the number of Mg F molecules and Rb atoms.In addition,we study the dynamical process of molecular deceleration and the effect of transverse diffusion.Monte–Carlo simulations show that buffer-gas-cooled Mg F and Rb beams,with initial velocities of 200 m/s and 130 m/s respectively,can be decelerated to less than 10 m/s.This is achieved with laser powers of as low as 357 m W for Mg F and 10 m W for Rb per traveling wave.The rapid deceleration minimizes molecular loss due to transverse diffusion during the deceleration process.The estimated number of molecules that can be trapped in a magneto-optical trap(MOT)is about 9.0×10^(6),which is an order of magnitude larger than the number of Mg F molecules decelerated by the spontaneous radiation force.The results offer a promising starting point for further studies of sympathetic cooling.展开更多
正交时频空间调制(orthogonal time frequency space,OTFS)技术作为一种多载波技术,同样存在峰均功率比较大的问题,高PAPR信号容易进入功率放大器的非线性工作区,导致接收信号的非线性失真,信号经过信道传输后会进一步影响系统的误码率(...正交时频空间调制(orthogonal time frequency space,OTFS)技术作为一种多载波技术,同样存在峰均功率比较大的问题,高PAPR信号容易进入功率放大器的非线性工作区,导致接收信号的非线性失真,信号经过信道传输后会进一步影响系统的误码率(bit error rate,BER)性能.针对该问题,利用chirp信号相位和为1的特点,采用基于chirp信号预编码的PAPR抑制方法,并在此基础上结合选择映射(selective mapping,SLM)法,将多组频域chirp信号与时频域信号点乘,再经过海森堡变换后选取PAPR最小的一组备选信号作为时域信号.仿真结果表明,与原始OTFS信号相比,基于频域chirp信号的OTFS系统的PAPR降低了0.9 dB,与传统SLM方法相比,使用基于频域chirp信号的SLM改进方法的OTFS系统,减少了IFFT次数的同时保证了系统的PAPR抑制性能.展开更多
基金Supported by the National Key Research and Development Program of China under Grant Nos 2017YFA0303603,2016YFA0300303,2017YFA0302901 and 2016YFA0300604the National Natural Science Foundation of China under Grant Nos11774408,11574383 and 11774399+1 种基金the External Cooperation Program of Chinese Academy of Sciences under Grant No GJHZ1826the Interdisciplinary Innovation Team of Chinese Academy of Sciences
文摘Ultrafast optical spectroscopy of a single crystal of a Dirac semimetal Cd_3As_（2 ）is carried out.An acoustic phonon（AP）mode with central frequency f=0.037 THz（i.e.,1.23 cm^（-1）or 0.153 meV）is unambiguously generated and detected,which we attribute to laser-induced thermal strain.An AP chirping（i.e.,variation of the phonon frequency）is clearly detected,which is ascribed to heat capacity variation with time.By comparing our experimental results and the theoretical model,we obtain a chirping time constant,which is 31.2 ps at 6 K and 19.8 ps at 300 K,respectively.Significantly,we identify an asymmetry in the AP frequency domain peak and find that it is caused by the chirping,instead of a Fano resonance.Moreover,we experimentally demonstrate that the central frequency of AP is extremely stable with varying laser fluence,as well as temperature,which endows Cd_3As_2application potentials in thermoelectric devices.
基金Supported by the National Key R&D Program of China (Grant Nos.2018YFE0304102,2019YFE03020000 and 2017YFE0301202)the National Natural Science Foundation of China (Grant Nos.11875024,11875021,11835010 and 12005054)the Sichuan Provincial Science and Technology Project (Grant Nos.2020YFSY0047 and 2020JDJQ0070)。
文摘Multiple broadband Alfvenic chirping modes(CMs),with frequencies in the wide range of f-35-150 kHz and chirping down rapidly,are found in HL-2A neutral beam injection plasmas,and the CMs can even coexist.The frequency chirping down process can be completed within-1 ms,and the frequency shift can reach 30-50 kHz.The CMs propagate in ion diamagnetic drift directions poloidally.The toroidal mode number is confirmed to be n=1,2,3 and 4 for the f-35-65,55-90,70-120 and 100-150 kHz CMs,respectively.The CMs are more like to be energetic-particle continuum modes(EPMs),since the modes almost locate on the Alfven continuum.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11475026 and 11175023)
文摘Enhanced electron–positron pair production by frequency chirping in one- and two-color laser pulse fields is investigated by solving the quantum Vlasov equation. A small frequency chirp shifts the momentum spectrum along the momentum axis. The positive and negative frequency chirp parameters play the same role in increasing the pair number density. The sign change of the frequency chirp parameter at the moment t = 0 leads the pulse shape and momentum spectrum to be symmetric, and the number density to be increased. The number density of produced pairs in the two-color pulse field is much higher than that in the one-color pulse field and the larger frequency chirp pulse field dominates more strongly. In the two-color pulse fields, the relation between the frequency ratio of two colors and the number density is not sensitive to the parameters of small frequency chirp added in either a low frequency strong field or a high frequency weak field but sensitive to the parameters of large frequency chirp added in a high frequency weak field.
文摘The effect of channel-width chirping on near- and far-field intensity patterns of the six supermodes was investigated. The supermode discrimination was evaluated in various channel-chirped index guided laser arrays. The results show that the linearly channel-chirped laser array has very good supermode discrimination which is better than that of a uniform laser array, the V channel-chirped laser array has the smallest radiation angle of the fundamental supermode among the calculated arrays, and the asymmetrically V channel-chirped array has a very small radiation angle of the fundamental supermode, which is smaller than that of the uniform array and also allows for very good fundamental supermode discrimination against the higher-order supermodes, which is better than that of the V channel-chirped laser array.
文摘Two different types of MHD instabilities with rapidly chirping frequency were found to arise in the Globus-M2 spherical tokamak in substantially different frequency ranges.The first type arises at frequencies of an order of 1 MHz in ohmic plasmas at relatively low density(n_(e))<2×10^(19) m^(-3) in a wide range of toroidal magnetic fields and plasma currents.This type of instability was identified as compressional Alfven waves,driven by electrons,accelerated during a sawtooth crush.It was found that the mode frequency is sweeping in time,according to the Berk-Breizman hole-clump nonlinear chirping model.The second type of wave arises in a specific single-swing regime of the central solenoid current with a very narrow plasma column,when the plasma tends to decay at extremely low density(n_(e))<2×10^(18) m^(-3) and,in fact,is an instability of the runaway electron beam.The exited modes cover the whole observed frequency range and are divided into several(two or three)frequency regions:approximately 0-30 MHz,60-120 MHz and sometimes 30-60 MHz.Reconnection of the branches was also observed.Single chirps are more rapid than for 1 MHz Alfven instability and follow an exponential law.This paper,to our knowledge,is the first report of frequency chirping instabilities excited by accelerated electrons at a spherical tokamak.
文摘Numerical method to solve the problem related with the interactive effect of dispersion (both chromatic dispersion and polarization mode dispersion) and nonlinearity on optical pulse transmission is present. Evolutions of pulses with various initial chirping and shape at bit rate of 10 Gb/s are simulated and compared. Gaussian pulse with appropriate prechirping is propitious for high bit rate transmission.
基金Supported by the National Natural Science Foundation of China under the grant Nos 11175023,11305010 and 11335013partially by the Open Fund of National Laboratory of Science and Technology on Computational Physics(IAPCM).
文摘The influences of laser pulses with negative frequency chirp and different pulse cycles on pair production are studied.By solving the quantum Vlasov equation,the momentum distribution and the number density of the created pairs are obtained numerically.It is found that the chirp rate can enhance the pair production rate in both supercycle and subcycle pulses.Moreover,there is an optimal cycle parameter corresponding to the maximum number density under the same chirp rate.The pair number density is sensitive to the cycle parameter when it is less than the optimal one.Compared to the positive frequency chirp,in the case of the negative frequency chirp,the optimal cycle parameter is increased.
文摘The propagation of an intense laser pulse in an under-dense plasma induces a plasma wake that is suitable for the acceleration of electrons to relativistic energies. For an ultra-intense laser pulse which has a longitudinal size shorter than the plasma wavelength, λp, instead of a periodic plasma wave, a cavity free from cold plasma electrons, called a bubble, is formed behind the laser pulse. An intense charge separation electric field inside the moving bubble can capture the electrons at the base of the bubble and accelerate them with a narrow energy spread. In the nonlinear bubble regime, due to localized depletion at the front of the pulse during its propagation through the plasma, the phase shift between carrier waves and pulse envelope plays an important role in plasma response. The carrier–envelope phase（CEP） breaks down the symmetric transverse ponderomotive force of the laser pulse that makes the bubble structure unstable. Our studies using a series of two-dimensional（2D） particle-in-cell（PIC） simulations show that the frequency-chirped laser pulses are more effective in controlling the pulse depletion rate and consequently the effect of the CEP in the bubble regime. The results indicate that the utilization of a positively chirped laser pulse leads to an increase in rate of erosion of the leading edge of the pulse that rapidly results in the formation of a steep intensity gradient at the front of the pulse. A more unstable bubble structure, the self-injections in different positions, and high dark current are the results of using a positively chirped laser pulse. For a negatively chirped laser pulse, the pulse depletion process is compensated during the propagation of the pulse in plasma in such a way that results in a more stable bubble shape and therefore, a localized electron bunch is produced during the acceleration process. As a result, by the proper choice of chirping, one can tune the number of self-injected electrons, the size of accelerated bunch and its energy spectrum to the values required for practical applications.
文摘目的:研究听力正常儿童Chirp-听性稳态反应(ASSR)与行为测听阈值的相关性,探讨Chirp-ASSR应用于听力正常儿童听力检测的可行性。方法:选择50例(100耳)4~5岁听力正常儿童,分别进行ChirpASSR与行为测听听力检测,记录两种听力测试方法所得到的0.5 k Hz、1 k Hz、2 k Hz、4 k Hz四个频率点阈值,将两种测试方法所得到的上述四个频率点阈值进行相关性分析。结果:Chirp-ASSR与行为测听两种测试方法在0.5 k Hz、1 k Hz、2 k Hz、4 k Hz四个频率点阈值的相关系数分别为0.84、0.83、0.82及0.76(P均<0.05)。结论:Chirp-ASSR与行为测听检测的阈值相关性较好,Chirp-ASSR应用于听力正常儿童听力检测中有一定的临床价值。
文摘With the popularization of new technologies,telephone fraud has become the main means of stealing money and personal identity information.Taking inspiration from the website authentication mechanism,we propose an end-to-end datamodem scheme that transmits the caller’s digital certificates through a voice channel for the recipient to verify the caller’s identity.Encoding useful information through voice channels is very difficult without the assistance of telecommunications providers.For example,speech activity detection may quickly classify encoded signals as nonspeech signals and reject input waveforms.To address this issue,we propose a novel modulation method based on linear frequency modulation that encodes 3 bits per symbol by varying its frequency,shape,and phase,alongside a lightweightMobileNetV3-Small-based demodulator for efficient and accurate signal decoding on resource-constrained devices.This method leverages the unique characteristics of linear frequency modulation signals,making them more easily transmitted and decoded in speech channels.To ensure reliable data delivery over unstable voice links,we further introduce a robust framing scheme with delimiter-based synchronization,a sample-level position remedying algorithm,and a feedback-driven retransmission mechanism.We have validated the feasibility and performance of our system through expanded real-world evaluations,demonstrating that it outperforms existing advanced methods in terms of robustness and data transfer rate.This technology establishes the foundational infrastructure for reliable certificate delivery over voice channels,which is crucial for achieving strong caller authentication and preventing telephone fraud at its root cause.
基金jointly supported by Natural Science Foundation of China(Nos.42076083 and 41706043)。
文摘We investigated the morphology and sedimentary state of an extensive modern canyon system on the northwest continental slope of Palawan Island in the southern South China Sea using multibeam bathymetry data and chirp sub-bottom profiles.The canyon system in Northwest Palawan consists of a fairly large dendritic canyon,a braided canyon,and a set of short,straight,and slope-confined gullies.The erosion state covers 71%of the system.Sediment accumulates downstream of the bend's inner side in the proximal main stem of the dendritic canyon and is eroded in its outer side.In the distal main stem,sediment is deposited inside and outside the bend.In most of the system's tributaries,decreasing slope gradients result in more sediment deposition.There is thick aggradation of sediment waves in the interfluve throughout the system,which exhibit increasing levels of stratification as the slope decreases.The lack of slump scars and headward erosion at the canyon heads,as well as the presence of regular gullies and sediment wave fields,suggest that large areas of unconfined downslope turbidity currents formed the system.We propose that frequent storms in northwestern Palawan triggered these currents by resuspending sediments on the shelf.
文摘Nature is amazing!Sometimes you don’t need a weather App to predict rain or shine-you just need nature!Feel the heat:listen to crickets Want to know the outside temperature?Listen to the crickets!Count how many times a cricket chirps in 15 seconds and add 40.That’s the temperature in Fahrenheit(华氏温度,1℉≈0.56℃).Do it several times and find the average.
文摘With the first rays of dawn peeking through the rainforest at Shiti Village,Dehong Dai and Jingpo Autonomous Prefecture,Yunnan Province,Xu Xiaolong,a bird-watching guide from the Jingpo ethnic group,led a German bird-watching group into the jungle.His great-grandfather made a living by hunting“weird-looking birds”in the mountains.Today,the birds(Great Hornbill)are attracting tourist dollars from other parts of the world without dodging bullets.In Shiti Village,bird-watchers can enjoy the chirping of Great Hornbills and feel the rumbling in the air as the birds fly past.The village on the Chinese border with Myanmar was formerly poverty-stricken,with an average annual income of barely 2,000 yuan(US$305)per household 10 years ago.Today,the average annual income has grown to 150,000 yuan(US$23,075).It is a shining example of the successful practice of the notion that“lucid waters and lush mountains are invaluable assets.”
基金Project supported by the National Natural Science Foundation of China(Grant Nos.12174115 and 91836103)。
文摘We propose a scheme for dual-species deceleration and trapping of a cold atom–molecule mixture by a frequency chirping stimulated force.We study the stimulated force exerted on Mg F and Rb using optical Bloch equations based on a direct numerical solution for the time-dependent density matrix.We analyze the relationship between the frequency chirping rate and the number of Mg F molecules and Rb atoms.In addition,we study the dynamical process of molecular deceleration and the effect of transverse diffusion.Monte–Carlo simulations show that buffer-gas-cooled Mg F and Rb beams,with initial velocities of 200 m/s and 130 m/s respectively,can be decelerated to less than 10 m/s.This is achieved with laser powers of as low as 357 m W for Mg F and 10 m W for Rb per traveling wave.The rapid deceleration minimizes molecular loss due to transverse diffusion during the deceleration process.The estimated number of molecules that can be trapped in a magneto-optical trap(MOT)is about 9.0×10^(6),which is an order of magnitude larger than the number of Mg F molecules decelerated by the spontaneous radiation force.The results offer a promising starting point for further studies of sympathetic cooling.
文摘正交时频空间调制(orthogonal time frequency space,OTFS)技术作为一种多载波技术,同样存在峰均功率比较大的问题,高PAPR信号容易进入功率放大器的非线性工作区,导致接收信号的非线性失真,信号经过信道传输后会进一步影响系统的误码率(bit error rate,BER)性能.针对该问题,利用chirp信号相位和为1的特点,采用基于chirp信号预编码的PAPR抑制方法,并在此基础上结合选择映射(selective mapping,SLM)法,将多组频域chirp信号与时频域信号点乘,再经过海森堡变换后选取PAPR最小的一组备选信号作为时域信号.仿真结果表明,与原始OTFS信号相比,基于频域chirp信号的OTFS系统的PAPR降低了0.9 dB,与传统SLM方法相比,使用基于频域chirp信号的SLM改进方法的OTFS系统,减少了IFFT次数的同时保证了系统的PAPR抑制性能.
