The transmission coefficients of electromagnetic （EM） waves due to a superconductor-dielectric superlattice are numerically calculated. Shift operator finite difference time domain （SO-FDTD） method is used in the ...The transmission coefficients of electromagnetic （EM） waves due to a superconductor-dielectric superlattice are numerically calculated. Shift operator finite difference time domain （SO-FDTD） method is used in the analysis. By using the SO-FDTD method, the transmission spectrum is obtained and its characteristics are investigated for different thicknesses of superconductor layers and dielectric layers, from which a stop band starting from zero frequency can be apparently observed. The relation between this low-frequency stop band and relative temperature, and also the London penetration depth at a superconductor temperature of zero degree are discussed, separately. The low-frequency stop band properties of superconductor-dielectric superlattice thus are well disclosed.展开更多
For the Hardy space H_E^2(R) over a ?at unitary vector bundle E on a ?nitely connected domain R, let TE be the bundle shift as [3]. If B is a reductive algebra containing every operator ψ(TE) for any rational functi...For the Hardy space H_E^2(R) over a ?at unitary vector bundle E on a ?nitely connected domain R, let TE be the bundle shift as [3]. If B is a reductive algebra containing every operator ψ(TE) for any rational function ψ with poles outside of R, then B is self adjoint.展开更多
Aeromagnetic gradients are often used to enhance details or add new insights for interpretation. The gradients may be measured or derived from the total field or from transformation between horizontal and vertical gra...Aeromagnetic gradients are often used to enhance details or add new insights for interpretation. The gradients may be measured or derived from the total field or from transformation between horizontal and vertical gradients. At present, vertical, horizontal, and triaxial aeromagnetic gradiometers are in operation throughout the world, while the first two are used more widely. Transformations between horizontal and vertical gradients are needed for acquiring three gradient components or for checking the validity of measured gradients. Transformation of potential field by fast Fourier transform technique in frequency domain is popularly used; however, when applied to transforming between gradients, there is a problem that needs resolving. Because those expressions of transform operators are undefined when u or v is equal to zero or u and v are simultaneously equal to zero （u is the frequency in x-direction, and v is the frequency in y-direction）, the operators cannot be sampled at these frequencies. Consequently, the transformation cannot be implemented by fast Fourier transform technique directly. In this article, shift sampling theory is employed for resolving this problem. Model test results show that the technique has good accuracy, and the real case of transformation indicates that the computed results agree better with the measured gradients; it demonstrates not only the effective- ness of method but also the reliability of the measured gradients.展开更多
A closed form expression for the bit error rate (BER) performance of frequency domaindifferential demodulation(FDDD) for orthogonal frequency division multiplexing system in flat fadingchannel is derived.The performan...A closed form expression for the bit error rate (BER) performance of frequency domaindifferential demodulation(FDDD) for orthogonal frequency division multiplexing system in flat fadingchannel is derived.The performance is evaluated by computer simulation and compared with the timedomain differential demodulation(TDDD).The results indicate that the performance of FDDD is betterthan that of TDDD,and the lower band of BER in the former is lower than that of the latter.展开更多
近年来,零样本工业过程故障诊断方法逐渐受到关注.针对传统嵌入模型在零样本故障诊断中表现不佳的问题,提出一种基于语义增强型深度自编码器(semantic-enhanced deep autoencoder, SEDAE)的零样本故障诊断算法.首先,给出一种基于语义属...近年来,零样本工业过程故障诊断方法逐渐受到关注.针对传统嵌入模型在零样本故障诊断中表现不佳的问题,提出一种基于语义增强型深度自编码器(semantic-enhanced deep autoencoder, SEDAE)的零样本故障诊断算法.首先,给出一种基于语义属性空间三元组损失约束的投影域偏移消除方法,提升模型知识迁移的能力.然后,将三元组损失函数约束引入深度自编码器,自动提取已见类别语义特征,实现了已见类别语义知识与先验语义信息之间的最优映射.在此基础上,在语义空间使用最近邻方法确定新样本所属的类别.田纳西伊斯曼过程(Tennessee-Eastman process, TEP)仿真结果表明,所提零样本故障诊断方法准确率相较传统方法提升7.11%,在广义零样本故障诊断中也取得满意的结果.展开更多
针对串联谐振型双有源桥(dual active bridges,简称DAB)双向直流变换器,该文提出一种基于变频控制的电流峰值优化控制策略.首先,利用时域分析法获得双有源桥变换器中峰值电感电流和传输功率的归一化解析式;然后,将所构建时域模型与传统...针对串联谐振型双有源桥(dual active bridges,简称DAB)双向直流变换器,该文提出一种基于变频控制的电流峰值优化控制策略.首先,利用时域分析法获得双有源桥变换器中峰值电感电流和传输功率的归一化解析式;然后,将所构建时域模型与传统基波分析法的计算结果进行比较,并推导出软开关范围且对死区时间进行分析.最后,通过仿真实验验证了时域分析结果和电流峰值优化策略.仿真结果表明,在不同功率等级下所提优化控制策略相对于现有定频控制能有效地降低电流峰值.展开更多
Background:Source-free unsupervised domain adaptation(SFUDA)methods aim to address the challenge of domain shift while preserving data privacy.Existing SFUDA approaches construct reliable and confident pseudo-labels f...Background:Source-free unsupervised domain adaptation(SFUDA)methods aim to address the challenge of domain shift while preserving data privacy.Existing SFUDA approaches construct reliable and confident pseudo-labels for target-domain data through denoising methods,thereby guiding the training of the target-domain model.The effectiveness of denoising approaches is influenced by the degree of domain gap between the source and target domains.A marked shift can cause the pseudo-labels to be unreliable,even after applying denoising.Methods:We propose a novel 2-stage framework for SFUDA called visual prompt source-free domain adaptation(VP-SFDA).We propose input-specific visual prompt in the first stage,prompting process,which bridges the target-domain data to source-domain distribution.Our method utilizes visual prompts and batch normalization constraint to enable the alignment model to learn domainspecific knowledge and align the target-domain data with the source-domain contribution.The second stage is the adaptation process,which aims at optimizing the segmentation model from the source domain to the target domain.This is accomplished through the denoising techniques,ultimately enhancing the performance.Results:Our study presents a comparative analysis of several SFUDA techniques in the VPSFDA framework across 4 tasks:abdominal magnetic resonance imaging(MRI)to computed tomography(CT),abdominal CT to MRI,cardiac MRI to CT,and cardiac CT to MRI.Notably,in the abdominal MRI to CT adaptation task,the VP-OS method achieved a remarkable improvement,increasing the average DICE score from 0.658 to 0.773(P<0.01)and reducing the average surface distance(ASD)from 3.489 to 2.961(P<0.01).Similarly,the VP-LD and VP-DPL methods also showed significant improvements over their base algorithms in both abdominal and cardiac MRI to CT tasks.Conclusions:This paper proposes VP-SFDA,a novel 2-stage framework for SFUDA in medical imaging,which achieves superior performance through input-specific visual prompts and batch normalization constraint for domain adaptation,coupled with denoising methods for enhanced results.Comparative experiments on 4 medical SFUDA tasks demonstrate that VO-SFDA surpasses existing methods,with ablation studies confirming the benefits of domain-specific patterns.展开更多
基金Project supported partly by the Open Research Program in State Key Laboratory of Millimeter Waves of China(Grant No.K200802)partly by the National Natural Science Foundation of China(Grant No.60971122)
文摘The transmission coefficients of electromagnetic （EM） waves due to a superconductor-dielectric superlattice are numerically calculated. Shift operator finite difference time domain （SO-FDTD） method is used in the analysis. By using the SO-FDTD method, the transmission spectrum is obtained and its characteristics are investigated for different thicknesses of superconductor layers and dielectric layers, from which a stop band starting from zero frequency can be apparently observed. The relation between this low-frequency stop band and relative temperature, and also the London penetration depth at a superconductor temperature of zero degree are discussed, separately. The low-frequency stop band properties of superconductor-dielectric superlattice thus are well disclosed.
基金Project Supported by Scientific and Technological Research Program of Chongqing Municipal Education Commission(KJQN201801110)Chongqing Science and Technology Commission(CSTC2015jcyjA00045,cstc2018jcyjA2248)and NSFC(11871127)
文摘For the Hardy space H_E^2(R) over a ?at unitary vector bundle E on a ?nitely connected domain R, let TE be the bundle shift as [3]. If B is a reductive algebra containing every operator ψ(TE) for any rational function ψ with poles outside of R, then B is self adjoint.
基金supported by China Aero Geophysical Survey & Remote Sensing Center for Land & Resources (863 Program, No. 2006AA06A201)
文摘Aeromagnetic gradients are often used to enhance details or add new insights for interpretation. The gradients may be measured or derived from the total field or from transformation between horizontal and vertical gradients. At present, vertical, horizontal, and triaxial aeromagnetic gradiometers are in operation throughout the world, while the first two are used more widely. Transformations between horizontal and vertical gradients are needed for acquiring three gradient components or for checking the validity of measured gradients. Transformation of potential field by fast Fourier transform technique in frequency domain is popularly used; however, when applied to transforming between gradients, there is a problem that needs resolving. Because those expressions of transform operators are undefined when u or v is equal to zero or u and v are simultaneously equal to zero （u is the frequency in x-direction, and v is the frequency in y-direction）, the operators cannot be sampled at these frequencies. Consequently, the transformation cannot be implemented by fast Fourier transform technique directly. In this article, shift sampling theory is employed for resolving this problem. Model test results show that the technique has good accuracy, and the real case of transformation indicates that the computed results agree better with the measured gradients; it demonstrates not only the effective- ness of method but also the reliability of the measured gradients.
基金Supported by National Natural Science Foundation of China(No.60272009)and National 863 Plan Project(NO.2001AA1230131)
文摘A closed form expression for the bit error rate (BER) performance of frequency domaindifferential demodulation(FDDD) for orthogonal frequency division multiplexing system in flat fadingchannel is derived.The performance is evaluated by computer simulation and compared with the timedomain differential demodulation(TDDD).The results indicate that the performance of FDDD is betterthan that of TDDD,and the lower band of BER in the former is lower than that of the latter.
文摘针对串联谐振型双有源桥(dual active bridges,简称DAB)双向直流变换器,该文提出一种基于变频控制的电流峰值优化控制策略.首先,利用时域分析法获得双有源桥变换器中峰值电感电流和传输功率的归一化解析式;然后,将所构建时域模型与传统基波分析法的计算结果进行比较,并推导出软开关范围且对死区时间进行分析.最后,通过仿真实验验证了时域分析结果和电流峰值优化策略.仿真结果表明,在不同功率等级下所提优化控制策略相对于现有定频控制能有效地降低电流峰值.
基金supportted by the Natural Science Foundation of China(62394311,62394310)Beijing Natural Science Foundation(QY24034)National Biomedical Imaging Facility Grant and from the startup funds of Peking University Health Science Center.
文摘Background:Source-free unsupervised domain adaptation(SFUDA)methods aim to address the challenge of domain shift while preserving data privacy.Existing SFUDA approaches construct reliable and confident pseudo-labels for target-domain data through denoising methods,thereby guiding the training of the target-domain model.The effectiveness of denoising approaches is influenced by the degree of domain gap between the source and target domains.A marked shift can cause the pseudo-labels to be unreliable,even after applying denoising.Methods:We propose a novel 2-stage framework for SFUDA called visual prompt source-free domain adaptation(VP-SFDA).We propose input-specific visual prompt in the first stage,prompting process,which bridges the target-domain data to source-domain distribution.Our method utilizes visual prompts and batch normalization constraint to enable the alignment model to learn domainspecific knowledge and align the target-domain data with the source-domain contribution.The second stage is the adaptation process,which aims at optimizing the segmentation model from the source domain to the target domain.This is accomplished through the denoising techniques,ultimately enhancing the performance.Results:Our study presents a comparative analysis of several SFUDA techniques in the VPSFDA framework across 4 tasks:abdominal magnetic resonance imaging(MRI)to computed tomography(CT),abdominal CT to MRI,cardiac MRI to CT,and cardiac CT to MRI.Notably,in the abdominal MRI to CT adaptation task,the VP-OS method achieved a remarkable improvement,increasing the average DICE score from 0.658 to 0.773(P<0.01)and reducing the average surface distance(ASD)from 3.489 to 2.961(P<0.01).Similarly,the VP-LD and VP-DPL methods also showed significant improvements over their base algorithms in both abdominal and cardiac MRI to CT tasks.Conclusions:This paper proposes VP-SFDA,a novel 2-stage framework for SFUDA in medical imaging,which achieves superior performance through input-specific visual prompts and batch normalization constraint for domain adaptation,coupled with denoising methods for enhanced results.Comparative experiments on 4 medical SFUDA tasks demonstrate that VO-SFDA surpasses existing methods,with ablation studies confirming the benefits of domain-specific patterns.
