A low-background γ spectrometer named the Gamma spectrometer for Nuclear Activation Studies(GNAS)was developed to detect scarce γ radioactivity,with a special focus on conducting activation experiments in nuclear as...A low-background γ spectrometer named the Gamma spectrometer for Nuclear Activation Studies(GNAS)was developed to detect scarce γ radioactivity,with a special focus on conducting activation experiments in nuclear astrophysics.It consisted of a well-type HPGe detector surrounded by optimized multi-layer shielding,which reduced the laboratory background counting rate by 99.5%and enabled a sensitivity edge as low as 0.044 Bq for the 477.6 KeV γ line of ^(7)Be.The near 4π geometry of the HPGe detector introduces a severe true coincidence summing(TCS)effect along with its high detection efficiency.To determine the intrinsic detection efficiency and correct for the TCS effect,a Monte Carlo simulation method was developed with the Geant4 toolkit.The detector model was optimized by matching the simulated full energy peak(FEP)statistics with those of a ^(137)Cs monoenergetic source and calibrated ^(55,57,58)Co sources produced by low-energy proton beam bombardment of natural iron.The intrinsic detection efficiency curve was obtained,and an algorithm for the correction of the TCS effect was programmed using decay data from the ENSDF library and Nuclear Wallet Cards.The GNAS fulfills the requirements of the ongoing activation measurement of proton-and alpha-induced reactions in nuclear astrophysics on the ground and at the Jinping Underground Nuclear Astrophysics(JUNA)facility.展开更多
The response functions of a 4π summing BGO detector were established using extensive experimental measurements and GEANT4 simulation. The partial and total efficiencies for all components of the γ-ray interaction wi...The response functions of a 4π summing BGO detector were established using extensive experimental measurements and GEANT4 simulation. The partial and total efficiencies for all components of the γ-ray interaction with the BGO detector were also measured. These response functions and efficiencies will be used in the β-Oslo method experiments to study the neutron capture cross sections of radioactive heavy ions. The application of the response functions of the BGO detector under simulated continuum γ-rays and source measurement γ-rays proves that the method and response functions are reliable.展开更多
Meteorological disasters frequently hit China in 2001. Drought, typhoon, rain storm, dust devil, high temperature, freezing damage, snow disaster, etc. occurred to different extent. The national economy suffered great...Meteorological disasters frequently hit China in 2001. Drought, typhoon, rain storm, dust devil, high temperature, freezing damage, snow disaster, etc. occurred to different extent. The national economy suffered great losses from all sorts of these meteorological disasters, especially the sustaining heavy droughts. This article makes analyses and comments on the characteristics of several major disasters and the effects they have brought on.展开更多
The precise determination of cross sections for key nuclear reactions within the Gamow window is crucial for advancing the study of stellar evolution and nucleosynthesis.However,extremely low reaction yields combined ...The precise determination of cross sections for key nuclear reactions within the Gamow window is crucial for advancing the study of stellar evolution and nucleosynthesis.However,extremely low reaction yields combined with the cosmic-ray-induced background make these measurements highly challenging,particularly for capture reactions.This work demonstrates the second configuration of the large-scale modular BGO detection array(LAMBDA-Ⅱ)designed to capture reaction measurements and introduces a method for suppressingγ-ray detection background in ground laboratories.By employing active and passive shielding,the background of LAMBDA-Ⅱwas significantly reduced by approximately two orders of magnitude,reaching 8.1×10^(-3)and 1.0×10^(-3)keV^(-1)h^(-1)in the 6-11 and 11-20 MeV energy ranges,respectively.When combined with a mA-scale intensity beam,this reduced background enables the investigation of several capture reactions of astrophysical interest in ground laboratories.展开更多
Dear Editor,This letter addresses the impulse game problem for a general scope of deterministic,multi-player,nonzero-sum differential games wherein all participants adopt impulse controls.Our objective is to formulate...Dear Editor,This letter addresses the impulse game problem for a general scope of deterministic,multi-player,nonzero-sum differential games wherein all participants adopt impulse controls.Our objective is to formulate this impulse game problem with the modified objective function including interaction costs among the players in a discontinuous fashion,and subsequently,to derive a verification theorem for identifying the feedback Nash equilibrium strategy.展开更多
Suppose thatλ_(1),λ_(2),λ_(3),λ_(4),λ_(5)are nonzero real numbers,not all of the same sign,andλ_(1)/λ_(2)is irrational and algebraic.Let V be a well-spaced sequence,δ>0.In this paper,it is proved that,for ...Suppose thatλ_(1),λ_(2),λ_(3),λ_(4),λ_(5)are nonzero real numbers,not all of the same sign,andλ_(1)/λ_(2)is irrational and algebraic.Let V be a well-spaced sequence,δ>0.In this paper,it is proved that,for anyε>0,the number of v∈V with v≤N such that the following inequality|λ_(1)p_(1)~2+λ_(2)p_(2)~2+λ_(3)p_(3)~4+λ_(4)p_(4)~4+λ_5p_5~4-v|<v^(-δ)has no solution in prime variables p_(1),p_(2),p_(3),p_(4),p_(5)does not exceed O(N^(29/32+2δ+ε)).展开更多
Let f,g and h be three distinct primitive holomorphic cusp forms of even integral weights k_(1),k_(2)and k_(3)for the full modular groupΓ=SL(2,Z),and denote byλ_(f)(n),λ_(g)(n),λ_(h)(n)the corresponding normalized...Let f,g and h be three distinct primitive holomorphic cusp forms of even integral weights k_(1),k_(2)and k_(3)for the full modular groupΓ=SL(2,Z),and denote byλ_(f)(n),λ_(g)(n),λ_(h)(n)the corresponding normalized Fourier coefficients,respectively.In this paper,we investigate the correlations of triple sums associated to these Fourier coefficientsλ_(f)(n),λ_(g)(n),λ_(h)(n)over certain polynomials,and obtain some power-saving asymptotic estimates which beat the trivial bounds.展开更多
To investigate the applicability of four commonly used color difference formulas(CIELAB,CIE94,CMC(1:1),and CIEDE2000)in the printing field on 3D objects,as well as the impact of four standard light sources(D65,D50,A,a...To investigate the applicability of four commonly used color difference formulas(CIELAB,CIE94,CMC(1:1),and CIEDE2000)in the printing field on 3D objects,as well as the impact of four standard light sources(D65,D50,A,and TL84)on 3D color difference evaluations,50 glossy spheres with a diameter of 2cm based on the Sailner J4003D color printing device were created.These spheres were centered around the five recommended colors(gray,red,yellow,green,and blue)by CIE.Color difference was calculated according to the four formulas,and 111 pairs of experimental samples meeting the CIELAB gray scale color difference requirements(1.0-14.0)were selected.Ten observers,aged between 22 and 27 with normal color vision,were participated in this study,using the gray scale method from psychophysical experiments to conduct color difference evaluations under the four light sources,with repeated experiments for each observer.The results indicated that the overall effect of the D65 light source on 3D objects color difference was minimal.In contrast,D50 and A light sources had a significant impact within the small color difference range,while the TL84 light source influenced both large and small color difference considerably.Among the four color difference formulas,CIEDE2000 demonstrated the best predictive performance for color difference in 3D objects,followed by CMC(1:1),CIE94,and CIELAB.展开更多
In this paper,by utilizing the Marcinkiewicz-Zygmund inequality and Rosenthal-type inequality of negatively superadditive dependent(NSD)random arrays and truncated method,we investigate the complete f-moment convergen...In this paper,by utilizing the Marcinkiewicz-Zygmund inequality and Rosenthal-type inequality of negatively superadditive dependent(NSD)random arrays and truncated method,we investigate the complete f-moment convergence of NSD random variables.We establish and improve a general result on the complete f-moment convergence for Sung’s type randomly weighted sums of NSD random variables under some general assumptions.As an application,we show the complete consistency for the randomly weighted estimator in a nonparametric regression model based on NSD errors.展开更多
The complete convergence for weighted sums of sequences of independent,identically distributed random variables under sublinear expectation space is studied.By moment inequality and truncation methods,we establish the...The complete convergence for weighted sums of sequences of independent,identically distributed random variables under sublinear expectation space is studied.By moment inequality and truncation methods,we establish the equivalent conditions of complete convergence for weighted sums of sequences of independent,identically distributed random variables under sublinear expectation space.The results complement the corresponding results in probability space to those for sequences of independent,identically distributed random variables under sublinear expectation space.展开更多
Aiming at the problem that infrared small target detection faces low contrast between the background and the target and insufficient noise suppression ability under the complex cloud background,an infrared small targe...Aiming at the problem that infrared small target detection faces low contrast between the background and the target and insufficient noise suppression ability under the complex cloud background,an infrared small target detection method based on the tensor nuclear norm and direction residual weighting was proposed.Based on converting the infrared image into an infrared patch tensor model,from the perspective of the low-rank nature of the background tensor,and taking advantage of the difference in contrast between the background and the target in different directions,we designed a double-neighborhood local contrast based on direction residual weighting method(DNLCDRW)combined with the partial sum of tensor nuclear norm(PSTNN)to achieve effective background suppression and recovery of infrared small targets.Experiments show that the algorithm is effective in suppressing the background and improving the detection ability of the target.展开更多
The observations of fully-charm tetraquark states in the LHCb,CMS,and ATLAS experiments suggested the existence of hadronic molecules of two-charmonium states,which may also imply bound states in the threecharmonium s...The observations of fully-charm tetraquark states in the LHCb,CMS,and ATLAS experiments suggested the existence of hadronic molecules of two-charmonium states,which may also imply bound states in the threecharmonium systems.In this work,we study the possible bound states in the triple-ηcand triple-J/ψsystems with J^(PC)=0^(-+)and 1^(--),respectively.In quantum chromodynamics sum rules,we calculate the two-point correlation functions and spectral functions up to the dimension-four gluon condensate.We use the iterative dispersion relation approach to deal with the five-loop banana integrals,which significantly improves computational efficiency.Our results show that the masses of triple-ηcand triple-J/ψstates lie below the corresponding mass thresholds,supporting the existence of such three-body bound states.展开更多
This paper investigates the uplink spectral efficiency of distributed cell-free(CF)massive multiple-input multiple-output(mMIMO)networks with correlated Rayleigh fading channels based on three different channel estima...This paper investigates the uplink spectral efficiency of distributed cell-free(CF)massive multiple-input multiple-output(mMIMO)networks with correlated Rayleigh fading channels based on three different channel estimation schemes.Specifically,each access point(AP)first uses embedded pilots to estimate the channels of all users based on minimum mean-squared error(MMSE)estimation.Given the high computational cost of MMSE estimation,the low-complexity element-wise MMSE(EW-MMSE)channel estimator and the least-squares(LS)channel estimator without prior statistical information are also analyzed.To reduce non-coherent and coherent interference during uplink payload data transmission,simple centralized decoding(SCD)and large-scale fading decoding(LSFD)are examined.Then,the closedform expressions for uplink spectral efficiency(SE)using MMSE,EW-MMSE,and LS estimators are developed for maximum ratio(MR)combining under LSFD,where each AP may have any number of antennas.The sum SE maximization problem with uplink power control is formulated.Since the maximization problem is non-convex and challenging,a block coordinate descent approach based on the weighted MMSE method is used to get the optimal local solution.Numerical studies demonstrate that LSFD and efficient uplink power control can considerably increase SE in distributed CF m MIMO networks.展开更多
Denoising is an important preprocessing step in seismic exploration that improves the signal-to-noise ratio(SNR)and helps identify oil and minerals.Dictionary learning(DL)is a promising method for noise attenuation.Th...Denoising is an important preprocessing step in seismic exploration that improves the signal-to-noise ratio(SNR)and helps identify oil and minerals.Dictionary learning(DL)is a promising method for noise attenuation.The DL extracts sparse features from noisy seismic data using over-complete dictionaries and performs denoising based on a threshold.However,the choice of threshold in DL greatly impacts the denoising results and the improvement in output SNR.Ramanujan’s sum(s)(RS)is a signal processing tool that exhibits derivative behavior and finds applications in edge detection and noise estimation of signals.Hence,we propose a novel DL method with threshold estimation based on RS to improve the output SNR.In this work,we estimate the noise variance of seismic data based on RS and use it as a threshold value for the DL method to perform denoising.We analyze the results of the proposed work on synthetically generated and field data sets.We perform simulations on noisy seismic data across a wide range of SNR values and tabulate the denoised results using the performance metrics SNR and mean squared error.The results indicate that the proposed method provides superior SNR and reduced mean squared error compared to MAD,SURE-based,and adaptive soft-thresholding techniques.展开更多
Phonon coherence can reflect electron‒phonon coupling information and has been proven to modulate electronic states and charge transport.The manipulation of phonon coherence through spacer cation engineering in organi...Phonon coherence can reflect electron‒phonon coupling information and has been proven to modulate electronic states and charge transport.The manipulation of phonon coherence through spacer cation engineering in organic‒inorganic hybrid perovskites(OIHPs)has been extensively demonstrated;however,the underlying structural origin remains elusive at the molecular level.Herein,we present molecular structure and temperature-dependent coherent phonon studies via a combination of sum frequency generation vibrational spectroscopy(SFG-VS)and transient absorption spectroscopy(TAS).The conformational order of spacer cations dictates the coherent phonon oscillations in 2D OIHPs.Our study further analyzes the static order and dynamic disorder in 2D perovskites.This work provides molecular-level insights into the role of spacer cations in tuning structural order and may provide valuable guidance for advancing emergent optoelecltronics development.展开更多
A non-orthogonal multiple access(NOMA) power allocation scheme on the basis of the sparrow search algorithm(SSA) is proposed in this work. Specifically, the logarithmic utility function is utilized to address the pote...A non-orthogonal multiple access(NOMA) power allocation scheme on the basis of the sparrow search algorithm(SSA) is proposed in this work. Specifically, the logarithmic utility function is utilized to address the potential fairness issue that may arise from the maximum sum-rate based objective function and the optical power constraints are set considering the non-negativity of the transmit signal, the requirement of the human eyes safety and all users' quality of service(Qo S). Then, the SSA is utilized to solve this optimization problem. Moreover, to demonstrate the superiority of the proposed strategy, it is compared with the fixed power allocation(FPA) and the gain ratio power allocation(GRPA) schemes. Results show that regardless of the number of users considered, the sum-rate achieved by SSA consistently outperforms that of FPA and GRPA schemes. Specifically, compared to FPA and GRPA schemes, the sum-rate obtained by SSA is increased by 40.45% and 53.44% when the number of users is 7, respectively. The proposed SSA also has better performance in terms of user fairness. This work will benefit the design and development of the NOMA-visible light communication(VLC) systems.展开更多
基金supported by the National Key Research and Development Project(No.2022YFA1602301)the National Natural Science Foundation of China(Nos.U2267205 and 12275361)the Continuous-Support Basic Scientific Research Project.
文摘A low-background γ spectrometer named the Gamma spectrometer for Nuclear Activation Studies(GNAS)was developed to detect scarce γ radioactivity,with a special focus on conducting activation experiments in nuclear astrophysics.It consisted of a well-type HPGe detector surrounded by optimized multi-layer shielding,which reduced the laboratory background counting rate by 99.5%and enabled a sensitivity edge as low as 0.044 Bq for the 477.6 KeV γ line of ^(7)Be.The near 4π geometry of the HPGe detector introduces a severe true coincidence summing(TCS)effect along with its high detection efficiency.To determine the intrinsic detection efficiency and correct for the TCS effect,a Monte Carlo simulation method was developed with the Geant4 toolkit.The detector model was optimized by matching the simulated full energy peak(FEP)statistics with those of a ^(137)Cs monoenergetic source and calibrated ^(55,57,58)Co sources produced by low-energy proton beam bombardment of natural iron.The intrinsic detection efficiency curve was obtained,and an algorithm for the correction of the TCS effect was programmed using decay data from the ENSDF library and Nuclear Wallet Cards.The GNAS fulfills the requirements of the ongoing activation measurement of proton-and alpha-induced reactions in nuclear astrophysics on the ground and at the Jinping Underground Nuclear Astrophysics(JUNA)facility.
基金supported by the National Key Research and Development Program of China(Nos.2016YFA0400502,2018YFA0404404)the National Natural Science Foundation of China(Nos.U1867211,11490563,12005304,12125509,11961141003 and U1332129)。
文摘The response functions of a 4π summing BGO detector were established using extensive experimental measurements and GEANT4 simulation. The partial and total efficiencies for all components of the γ-ray interaction with the BGO detector were also measured. These response functions and efficiencies will be used in the β-Oslo method experiments to study the neutron capture cross sections of radioactive heavy ions. The application of the response functions of the BGO detector under simulated continuum γ-rays and source measurement γ-rays proves that the method and response functions are reliable.
文摘Meteorological disasters frequently hit China in 2001. Drought, typhoon, rain storm, dust devil, high temperature, freezing damage, snow disaster, etc. occurred to different extent. The national economy suffered great losses from all sorts of these meteorological disasters, especially the sustaining heavy droughts. This article makes analyses and comments on the characteristics of several major disasters and the effects they have brought on.
基金Supported by the National Key R&D Program of China(Nos.2022YFA1602301,2022YFA1603300,and 2023YFA1606701)National Natural Science Foundation of China(Nos.U1867211,12275026,and 12222514)the CAS Light of West China Program grant No.2020-82。
文摘The precise determination of cross sections for key nuclear reactions within the Gamow window is crucial for advancing the study of stellar evolution and nucleosynthesis.However,extremely low reaction yields combined with the cosmic-ray-induced background make these measurements highly challenging,particularly for capture reactions.This work demonstrates the second configuration of the large-scale modular BGO detection array(LAMBDA-Ⅱ)designed to capture reaction measurements and introduces a method for suppressingγ-ray detection background in ground laboratories.By employing active and passive shielding,the background of LAMBDA-Ⅱwas significantly reduced by approximately two orders of magnitude,reaching 8.1×10^(-3)and 1.0×10^(-3)keV^(-1)h^(-1)in the 6-11 and 11-20 MeV energy ranges,respectively.When combined with a mA-scale intensity beam,this reduced background enables the investigation of several capture reactions of astrophysical interest in ground laboratories.
基金supported in part by the National Natural Science Foundation of China(62173051)the Fundamental Research Funds for the Central Universities(2024CDJCGJ012,2023CDJXY-010)+1 种基金the Chongqing Technology Innovation and Application Development Special Key Project(CSTB2022TIADCUX0015,CSTB2022TIAD-KPX0162)the China Postdoctoral Science Foundation(2024M763865)
文摘Dear Editor,This letter addresses the impulse game problem for a general scope of deterministic,multi-player,nonzero-sum differential games wherein all participants adopt impulse controls.Our objective is to formulate this impulse game problem with the modified objective function including interaction costs among the players in a discontinuous fashion,and subsequently,to derive a verification theorem for identifying the feedback Nash equilibrium strategy.
基金Supported by NSFC(Nos.12301006,12471009,12071238,11901566,12001047,11971476)Beijing Natural Science Foundation(No.1242003)。
文摘Suppose thatλ_(1),λ_(2),λ_(3),λ_(4),λ_(5)are nonzero real numbers,not all of the same sign,andλ_(1)/λ_(2)is irrational and algebraic.Let V be a well-spaced sequence,δ>0.In this paper,it is proved that,for anyε>0,the number of v∈V with v≤N such that the following inequality|λ_(1)p_(1)~2+λ_(2)p_(2)~2+λ_(3)p_(3)~4+λ_(4)p_(4)~4+λ_5p_5~4-v|<v^(-δ)has no solution in prime variables p_(1),p_(2),p_(3),p_(4),p_(5)does not exceed O(N^(29/32+2δ+ε)).
基金Supported in part by NSFC(Nos.12401011,12201214)National Key Research and Development Program of China(No.2021YFA1000700)+3 种基金Shaanxi Fundamental Science Research Project for Mathematics and Physics(No.23JSQ053)Science and Technology Program for Youth New Star of Shaanxi Province(No.2025ZC-KJXX-29)Natural Science Basic Research Program of Shaanxi Province(No.2025JC-YBQN-091)Scientific Research Foundation for Young Talents of WNU(No.2024XJ-QNRC-01)。
文摘Let f,g and h be three distinct primitive holomorphic cusp forms of even integral weights k_(1),k_(2)and k_(3)for the full modular groupΓ=SL(2,Z),and denote byλ_(f)(n),λ_(g)(n),λ_(h)(n)the corresponding normalized Fourier coefficients,respectively.In this paper,we investigate the correlations of triple sums associated to these Fourier coefficientsλ_(f)(n),λ_(g)(n),λ_(h)(n)over certain polynomials,and obtain some power-saving asymptotic estimates which beat the trivial bounds.
文摘To investigate the applicability of four commonly used color difference formulas(CIELAB,CIE94,CMC(1:1),and CIEDE2000)in the printing field on 3D objects,as well as the impact of four standard light sources(D65,D50,A,and TL84)on 3D color difference evaluations,50 glossy spheres with a diameter of 2cm based on the Sailner J4003D color printing device were created.These spheres were centered around the five recommended colors(gray,red,yellow,green,and blue)by CIE.Color difference was calculated according to the four formulas,and 111 pairs of experimental samples meeting the CIELAB gray scale color difference requirements(1.0-14.0)were selected.Ten observers,aged between 22 and 27 with normal color vision,were participated in this study,using the gray scale method from psychophysical experiments to conduct color difference evaluations under the four light sources,with repeated experiments for each observer.The results indicated that the overall effect of the D65 light source on 3D objects color difference was minimal.In contrast,D50 and A light sources had a significant impact within the small color difference range,while the TL84 light source influenced both large and small color difference considerably.Among the four color difference formulas,CIEDE2000 demonstrated the best predictive performance for color difference in 3D objects,followed by CMC(1:1),CIE94,and CIELAB.
基金supported by the National Social Science Fundation(Grant No.21BTJ040)the Project of Outstanding Young People in University of Anhui Province(Grant Nos.2023AH020037,SLXY2024A001).
文摘In this paper,by utilizing the Marcinkiewicz-Zygmund inequality and Rosenthal-type inequality of negatively superadditive dependent(NSD)random arrays and truncated method,we investigate the complete f-moment convergence of NSD random variables.We establish and improve a general result on the complete f-moment convergence for Sung’s type randomly weighted sums of NSD random variables under some general assumptions.As an application,we show the complete consistency for the randomly weighted estimator in a nonparametric regression model based on NSD errors.
基金supported by Doctoral Scientific Research Starting Foundation of Jingdezhen Ceramic University(Grant No.102/01003002031)Re-accompanying Funding Project of Academic Achievements of Jingdezhen Ceramic University(Grant Nos.215/20506277,215/20506341)。
文摘The complete convergence for weighted sums of sequences of independent,identically distributed random variables under sublinear expectation space is studied.By moment inequality and truncation methods,we establish the equivalent conditions of complete convergence for weighted sums of sequences of independent,identically distributed random variables under sublinear expectation space.The results complement the corresponding results in probability space to those for sequences of independent,identically distributed random variables under sublinear expectation space.
基金Supported by the Key Laboratory Fund for Equipment Pre-Research(6142207210202)。
文摘Aiming at the problem that infrared small target detection faces low contrast between the background and the target and insufficient noise suppression ability under the complex cloud background,an infrared small target detection method based on the tensor nuclear norm and direction residual weighting was proposed.Based on converting the infrared image into an infrared patch tensor model,from the perspective of the low-rank nature of the background tensor,and taking advantage of the difference in contrast between the background and the target in different directions,we designed a double-neighborhood local contrast based on direction residual weighting method(DNLCDRW)combined with the partial sum of tensor nuclear norm(PSTNN)to achieve effective background suppression and recovery of infrared small targets.Experiments show that the algorithm is effective in suppressing the background and improving the detection ability of the target.
基金supported by the National Natural Science Foundation of China(Grant No.12175318)the Natural Science Foundation of Guangdong Province of China(Grant No.2023A1515011704)。
文摘The observations of fully-charm tetraquark states in the LHCb,CMS,and ATLAS experiments suggested the existence of hadronic molecules of two-charmonium states,which may also imply bound states in the threecharmonium systems.In this work,we study the possible bound states in the triple-ηcand triple-J/ψsystems with J^(PC)=0^(-+)and 1^(--),respectively.In quantum chromodynamics sum rules,we calculate the two-point correlation functions and spectral functions up to the dimension-four gluon condensate.We use the iterative dispersion relation approach to deal with the five-loop banana integrals,which significantly improves computational efficiency.Our results show that the masses of triple-ηcand triple-J/ψstates lie below the corresponding mass thresholds,supporting the existence of such three-body bound states.
基金supported by National Natural Science Foundation of China(NSFC No.62020106001)。
文摘This paper investigates the uplink spectral efficiency of distributed cell-free(CF)massive multiple-input multiple-output(mMIMO)networks with correlated Rayleigh fading channels based on three different channel estimation schemes.Specifically,each access point(AP)first uses embedded pilots to estimate the channels of all users based on minimum mean-squared error(MMSE)estimation.Given the high computational cost of MMSE estimation,the low-complexity element-wise MMSE(EW-MMSE)channel estimator and the least-squares(LS)channel estimator without prior statistical information are also analyzed.To reduce non-coherent and coherent interference during uplink payload data transmission,simple centralized decoding(SCD)and large-scale fading decoding(LSFD)are examined.Then,the closedform expressions for uplink spectral efficiency(SE)using MMSE,EW-MMSE,and LS estimators are developed for maximum ratio(MR)combining under LSFD,where each AP may have any number of antennas.The sum SE maximization problem with uplink power control is formulated.Since the maximization problem is non-convex and challenging,a block coordinate descent approach based on the weighted MMSE method is used to get the optimal local solution.Numerical studies demonstrate that LSFD and efficient uplink power control can considerably increase SE in distributed CF m MIMO networks.
文摘Denoising is an important preprocessing step in seismic exploration that improves the signal-to-noise ratio(SNR)and helps identify oil and minerals.Dictionary learning(DL)is a promising method for noise attenuation.The DL extracts sparse features from noisy seismic data using over-complete dictionaries and performs denoising based on a threshold.However,the choice of threshold in DL greatly impacts the denoising results and the improvement in output SNR.Ramanujan’s sum(s)(RS)is a signal processing tool that exhibits derivative behavior and finds applications in edge detection and noise estimation of signals.Hence,we propose a novel DL method with threshold estimation based on RS to improve the output SNR.In this work,we estimate the noise variance of seismic data based on RS and use it as a threshold value for the DL method to perform denoising.We analyze the results of the proposed work on synthetically generated and field data sets.We perform simulations on noisy seismic data across a wide range of SNR values and tabulate the denoised results using the performance metrics SNR and mean squared error.The results indicate that the proposed method provides superior SNR and reduced mean squared error compared to MAD,SURE-based,and adaptive soft-thresholding techniques.
基金supported by the National Natural Science Foundation of China(Nos.21925302,92250306)the Strategic Priority Research Program of the Chinese Academy of Sciences(XDB0450202)+1 种基金the Innovation Program for Quantum Science and Technology(2021ZD0303303)the National Key Research and Development Program of China(2018YFA0208702).
文摘Phonon coherence can reflect electron‒phonon coupling information and has been proven to modulate electronic states and charge transport.The manipulation of phonon coherence through spacer cation engineering in organic‒inorganic hybrid perovskites(OIHPs)has been extensively demonstrated;however,the underlying structural origin remains elusive at the molecular level.Herein,we present molecular structure and temperature-dependent coherent phonon studies via a combination of sum frequency generation vibrational spectroscopy(SFG-VS)and transient absorption spectroscopy(TAS).The conformational order of spacer cations dictates the coherent phonon oscillations in 2D OIHPs.Our study further analyzes the static order and dynamic disorder in 2D perovskites.This work provides molecular-level insights into the role of spacer cations in tuning structural order and may provide valuable guidance for advancing emergent optoelecltronics development.
基金supported by the Cooperative Research Project between China Coal Energy Research Institute Co.,Ltd. and Xidian University (No.N-KY-HX-1101-202302-00725)the Key Research and Development Program of Shaanxi Province (No.2017ZDCXL-GY-06-02)。
文摘A non-orthogonal multiple access(NOMA) power allocation scheme on the basis of the sparrow search algorithm(SSA) is proposed in this work. Specifically, the logarithmic utility function is utilized to address the potential fairness issue that may arise from the maximum sum-rate based objective function and the optical power constraints are set considering the non-negativity of the transmit signal, the requirement of the human eyes safety and all users' quality of service(Qo S). Then, the SSA is utilized to solve this optimization problem. Moreover, to demonstrate the superiority of the proposed strategy, it is compared with the fixed power allocation(FPA) and the gain ratio power allocation(GRPA) schemes. Results show that regardless of the number of users considered, the sum-rate achieved by SSA consistently outperforms that of FPA and GRPA schemes. Specifically, compared to FPA and GRPA schemes, the sum-rate obtained by SSA is increased by 40.45% and 53.44% when the number of users is 7, respectively. The proposed SSA also has better performance in terms of user fairness. This work will benefit the design and development of the NOMA-visible light communication(VLC) systems.
