Based on the research of modem electronic packaging materials, thixo-forming technology was used to fabricate electronic packaging shell. The process of thixo-extrusion with SiCp/A356 composites was simulated by the f...Based on the research of modem electronic packaging materials, thixo-forming technology was used to fabricate electronic packaging shell. The process of thixo-extrusion with SiCp/A356 composites was simulated by the finite element software DEFORM-3D, then the flow velocity field, equivalent strain field and temperature field were analyzed. The electronic packaging shell was manufactured by extrusion according to the results from numerical simulation. The results show that thixo-forming technology can be used in producing electronic package shell with SiCp/A356 composites, and high volume fraction of SiCp with homogeneous distribution can be achieved, being in agreement with the requirements of electronic packaging materials.展开更多
This paper proposes a novel and comprehensive method of automatic target recognition based on real ISAR images with the aim to recognize the non-cooperative ship targets. The special characteristics of the ISAR images...This paper proposes a novel and comprehensive method of automatic target recognition based on real ISAR images with the aim to recognize the non-cooperative ship targets. The special characteristics of the ISAR images for the real data compared with the simulated ISAR images are analyzed firstly. Then,the novel technique for the target recognition is proposed,and it consists of three steps,including the preprocessing,feature extraction and classification. Some segmentation and morphological methods are used in the preprocessing to obtain the clear target images. Then,six different features for the ISAR images are extracted.By estimating the features' conditional probability, the effectiveness and robustness of these features are demonstrated. Finally,Fisher's linear classifier is applied in the classification step. The results for the allfeature space are provided to illustrate the effectiveness of the proposed method.展开更多
Through the coherent accumulation of target echoes, inverse synthetic aperture radar （ISAR） imaging achieves high azimuth resolution. However, because of the instability of the radar system, the echoes of the 1SAR w...Through the coherent accumulation of target echoes, inverse synthetic aperture radar （ISAR） imaging achieves high azimuth resolution. However, because of the instability of the radar system, the echoes of the 1SAR will be randomly lost. The conventional FFT processing methods can cause image blur and high sidelobes or other issues. A novel algorithm for ISAR missing-data imaging based on the Iterative Adaptive Approach （IAA） is proposed. The algorithm enjoys global convergence properties and does not need to set the parameters in advance. The missing-data ISAR imaging results for simulated and measured data illustrate the effectiveness of the algorithm.展开更多
A new technique for the cubic Chirplet decomposition via local polynomial Wigner distribution(LPWD) is presented.Through introducing the parameter of curvature to the traditional Chirplet atoms,the cubic Chirplet atom...A new technique for the cubic Chirplet decomposition via local polynomial Wigner distribution(LPWD) is presented.Through introducing the parameter of curvature to the traditional Chirplet atoms,the cubic Chirplet atoms are more accurate to characterize the signals with high nonlinear instantaneous frequency(IF) trajectories.The phase coefficients of the cubic Chirplet atoms are evaluated by the LPWD algorithm with two-dimensional(2D) maximizations.This technique is precise,with high efficiency,and it is used in inverse synthetic aperture radar(ISAR) imaging of ship target with complicated motions,the ISAR images with good quality can be achieved.Experiments of emulational and real data validate the effectiveness of the new algorithm.展开更多
This paper provides a design method based on a time-shared form, which obtains the compatibility of signal and the system for detecting both ships and airplanes. Then, it gives the structure diagram of the system and ...This paper provides a design method based on a time-shared form, which obtains the compatibility of signal and the system for detecting both ships and airplanes. Then, it gives the structure diagram of the system and the chart diagram of signal processing. Finally, the continuity problem of signal modulation for ship detection is discussed.展开更多
We present a systematic scheme to achieve both high birefringence and low confinement loss in index-guiding photonic crystal fibers(PCFs) ,using a structurally-simple PCF with finite number of air holes in the claddin...We present a systematic scheme to achieve both high birefringence and low confinement loss in index-guiding photonic crystal fibers(PCFs) ,using a structurally-simple PCF with finite number of air holes in the cladding region. By increasing the size of the outermost-ring air holes in the cladding region,highly birefringent PCFs with low confinement loss can be successfully achieved. The design strategy is based on the fact that the modal birefringence of PCFs is dominated by the inner-ring air holes in PCF,which is verified by a full-vector finite element method with anisotropic perfectly matched layers. Numerical results show that modal birefringence in the order of 10-3 and confinement loss less than 0.1 dB/km can be easily realized in the proposed PCF with only four rings of air holes in the cladding region. We expect that such fibers will be much easier to be fabvicated than those with more air holes in the cladding region.展开更多
It is well known that the macroscopic Maxwell’s equations can be obtained from the corresponding microscopic or atomic equations by a proper averaging process. The purpose of this paper is to present the macroscopic ...It is well known that the macroscopic Maxwell’s equations can be obtained from the corresponding microscopic or atomic equations by a proper averaging process. The purpose of this paper is to present the macroscopic Maxwell’s equations which are valid in all regions of space, including an interface between two different media; and the boundary conditions can naturally emerge from the macroscopic equations as an effect of average of the microscopic Maxwell’s equations. In addition, the application of the unit step functions and the Dirac delta function to our discussion not only permits great mathematical simplicity but also gives rise to convenient physical concepts for the description and representation of the actual fields in the vicinity of the interface.展开更多
Generalized impedance boundary conditions are employed to simplify the solution of the Sommerfeld half-space problem. An analytical expression is derived for the Hertz potential of a vertical electric dipole over the ...Generalized impedance boundary conditions are employed to simplify the solution of the Sommerfeld half-space problem. An analytical expression is derived for the Hertz potential of a vertical electric dipole over the earth’s surface, in which the earth is assumed to be a layered media or homogeneous dissipative half-space. A Sommerfeld type integral in the potential function is expressed as the sum of two parts: a zeroth order Hankel function and an absolutely convergent series of Bessel functions. In addition, two expressions in closed form are obtained as the far-field and near-field approximation of the present result.展开更多
This paper presents a newmulti-targets inverse synthetic aperture radar (ISAR) imaging approach via the image segmentation processing. This method can separate multi-targets with similar velocities,and there is no str...This paper presents a newmulti-targets inverse synthetic aperture radar (ISAR) imaging approach via the image segmentation processing. This method can separate multi-targets with similar velocities,and there is no strict limit on the rotational state of the targets. Firstly,the motion compensation for the completely multi-targets echo is carried out and the coarse image can be achieved with the Range-Doppler (RD) technique. Then a series of image processing methods and image segmentation processing are used to separate the echo data of each mono-target. At last,the image with high quality of each target can be achieved with the RD technique and the Range-Instantaneous-Doppler (RID) technique. ISAR imaging results of simulated and measured data validate the validity of the proposed approach.展开更多
In this paper, a hybrid method (hybrid PMM-MoM method) is presented for the effective and accurate analysis of finite periodic structures. This method divides a finite periodic structure into two parts. The inner part...In this paper, a hybrid method (hybrid PMM-MoM method) is presented for the effective and accurate analysis of finite periodic structures. This method divides a finite periodic structure into two parts. The inner part of an approximate infinite periodic structure is analyzed by periodic method of moment (PMM);the outer part is then analyzed by method of moments (MoM). For the finite periodic structures, the accuracy of the new method is much better than that of the pure PMM, and is almost the same as that of pure MoM. Because pure PMM uses the periodic boundary conditions, it takes much less memory resources and computation time. For hybrid PMM-MoM method, because the inner part is calculated by PMM, the calculation work concentrates on the outer part. Consequently, compared with the exact MoM, the new method saves much more memory resources and computation time, which provides a drastic reduction of unknowns.展开更多
In the post-Moore era,the development of active phased array antennas will inevitably trend towards active array microsystems.In this paper,the characteristics and composition of the active array antenna are briefly d...In the post-Moore era,the development of active phased array antennas will inevitably trend towards active array microsystems.In this paper,the characteristics and composition of the active array antenna are briefly described.Owing to the high efficiency,low profile,and light weight of the active array microsystems,the application prospects and advantages in the engineering of multi-functional airborne radar,spaceborne radar,and communication systems are analyzed.Moreover,according to the characteristics of the post-Moore era of integrated circuits,scientific and technological problems in the active array microsystems are presented,including multi-scale,multi-signal,and multi-physics field coupling.The challenges are also discussed,such as new architectures and algorithms,miniaturization of passive components,novel materials and processes,ultra-wideband technology,and new interdisciplinary technological applications.This paper is expected to inspire in-depth research on active array microsystems.展开更多
In recent years,frequent network attacks have highlighted the importance of efficient detection methods for ensuring cyberspace security.This paper presents a novel intrusion detection system consisting of a data prep...In recent years,frequent network attacks have highlighted the importance of efficient detection methods for ensuring cyberspace security.This paper presents a novel intrusion detection system consisting of a data prepro-cessing stage and a deep learning model for accurately identifying network attacks.We have proposed four deep neural network models,which are constructed using architectures such as Convolutional Neural Networks(CNN),Bi-directional Long Short-Term Memory(BiLSTM),Bidirectional Gate Recurrent Unit(BiGRU),and Attention mechanism.These models have been evaluated for their detection performance on the NSL-KDD dataset.To enhance the compatibility between the data and the models,we apply various preprocessing techniques and employ the particle swarm optimization algorithm to perform feature selection on the NSL-KDD dataset,resulting in an optimized feature subset.Moreover,we address class imbalance in the dataset using focal loss.Finally,we employ the BO-TPE algorithm to optimize the hyperparameters of the four models,maximizing their detection performance.The test results demonstrate that the proposed model is capable of extracting the spatiotemporal features of network traffic data effectively.In binary and multiclass experiments,it achieved accuracy rates of 0.999158 and 0.999091,respectively,surpassing other state-of-the-art methods.展开更多
Surge current(SC)capability is one of the main aspects of reliability for silicon carbide(SiC)power devices.In this work,the influences of neutron radiation‐induced defects on the SC capability and reliability of Si...Surge current(SC)capability is one of the main aspects of reliability for silicon carbide(SiC)power devices.In this work,the influences of neutron radiation‐induced defects on the SC capability and reliability of SiC P‐intrinsic‐N(PiN)diodes were comprehensively investigated.It was found that the surge capability of the diodes can be deteriorated even under the slightly enhanced formation of carbon‐vacancy‐related Z_(1/2) and EH_(6/7 )defects introduced by neutron irradiation.Surprisingly,it was found that the forward voltage(V_(F))decreases with the increased SC and the stress cycles in the irradiated diodes,which is usually found to in-crease under the SC tests and attributed to the bipolar degradation(BPD).By using technology computer‐aided design simulation and deep‐level transient spectroscopy characterization,it was found that the sig-nificant self‐heating during surge stress leads to the annealing effect on the Z_(1/2) defects through the promoted recombination with the nearest and second neighbor carbon interstitials injected by irradiation,which thus plays a dominant role in the decrease of VF over the BPD.展开更多
Due to the heavy congestion in HF bands, HF radars are restricted to operating within narrow frequency bands. To improve the system bandwidth and avoid heavy interference bands, a quasi-random step frequency signal wi...Due to the heavy congestion in HF bands, HF radars are restricted to operating within narrow frequency bands. To improve the system bandwidth and avoid heavy interference bands, a quasi-random step frequency signal with discontinuous bands is presented. A novel two-dimensional signal processing scheme for this signal is proposed on the basis of delicate signal analysis. Simulation results demonstrate that the scheme could successfully realize the resolutions by decoupling the range-Doppler ambiguity, and effectively suppress the maximal sidelobe. Moreover, the scheme is simple and has good numerical stability.展开更多
The developments of the high speed analog to digital converters （ADC） and advanced digital signal processors （DSP） make the smart antenna with digital beamforming （DBF） a reality. In conventional M-elements arra...The developments of the high speed analog to digital converters （ADC） and advanced digital signal processors （DSP） make the smart antenna with digital beamforming （DBF） a reality. In conventional M-elements array antenna system, each element has its own receiving channel and ADCs. In this paper, a novel smart antenna receiver with digital beamforming is proposed. The essential idea is to realize the digital beamforming receiver based on bandpass sampling of multiple distinct intermediate frequency （IF） signals. The proposed system reduces receiver hardware from M IF channels and 2M ADCs to one IF channel and one ADC using a heterodyne radio frequency （RF） circuitry and a multiple bandpass sampling digital receiver. In this scheme, the sampling rate of the ADC is much higher than the summation of the M times of the signal bandwidth. The local oscillator produces different local frequency for each RF channel The receiver architecture is presented in detail, and the simulation of bandpass sampling of multiple signals and digital down conversion to baseband is given. The principle analysis and simulation results indicate the effectiveness of the new proposed receiver.展开更多
A novel algorithm for the detection of ship target with high accuracy in the synthetic aperture radar(SAR) with high spatial resolution image is proposed. The SAR image may include not only the ship targets but also t...A novel algorithm for the detection of ship target with high accuracy in the synthetic aperture radar(SAR) with high spatial resolution image is proposed. The SAR image may include not only the ship targets but also the interferences such as the sea clutter,the strong reflection target,the sidelobe and so on.The conventional constant false alarm rate(CFAR) algorithm has some disadvantages,and it has not enough prior information about the size of the ships. Hence,it cannot separate the adjacent ships correctly. A comprehensive algorithm based on the modified CFAR algorithm and opening operation is presented to solve the problem,and the detection accuracy can be improved consequently. The results of SAR image illustrate the effectiveness of the method in this paper.展开更多
There are great challenges for traditional three-dimensional( 3-D) interferometric inverse synthetic aperture radar( In ISAR) imaging algorithms of ship targets w ith 2-D sparsity in actual radar imaging system. To de...There are great challenges for traditional three-dimensional( 3-D) interferometric inverse synthetic aperture radar( In ISAR) imaging algorithms of ship targets w ith 2-D sparsity in actual radar imaging system. To deal w ith this problem,a novel 3-D In ISAR imaging method is proposed in this paper.First,the high-precision gradient adaptive algorithm w as adopted to reconstruct the echoes in range dimension. Then the method of minimizing the entropy of the average range profile w as applied to estimate the parameters w hich are used to compensate translation components of the received echoes. Besides,the phase adjustment and image coregistration of the sparse echoes w ere achieved at the same time through the approach of the joint phase autofocus. Finally,the 3-D geometry coordinates of the ship target w ith 2-D sparsity w ere reconstructed by combining the range measurement and interferometric processing of the ISAR images. Simulation experiments w ere carried out to verify the practicability and effectiveness of the algorithm in the case that the received echoes are in 2-D sparsity.展开更多
The condition of an algebra to be a Hopf algebra or a Hopf(co)quasigroup can be determined by the properties of Galois linear maps.For a bialgebra H,if it is unital and associative as an algebra and counital coassocia...The condition of an algebra to be a Hopf algebra or a Hopf(co)quasigroup can be determined by the properties of Galois linear maps.For a bialgebra H,if it is unital and associative as an algebra and counital coassociative as a coalgebra,then the Galois linear maps T1 and T2 can be defined.For such a bialgebra H,it is a Hopf algebra if and only if T1 is bijective.Moreover,T1^-1 is a right H-module map and a left H-comodule map(similar to T2).On the other hand,for a unital algebra(no need to be associative),and a counital coassociative coalgebra A,if the coproduct and counit are both algebra morphisms,then the sufficient and necessary condition of A to be a Hopf quasigroup is that T1 is bijective,and T1^-1 is left compatible with ΔT1-11^r and right compatible with mT1-1^l at the same time(The properties are similar to T2).Furthermore,as a corollary,the quasigroups case is also considered.展开更多
High-resolution of Inverse Synthetic Aperture Radar (ISAR) in the azimuth direction can be achieved by increasing the coherent accumulation angle of the target rotation.However, in practice, the coherent accumulation ...High-resolution of Inverse Synthetic Aperture Radar (ISAR) in the azimuth direction can be achieved by increasing the coherent accumulation angle of the target rotation.However, in practice, the coherent accumulation angle may be small.In this paper, a novel algorithm for high-resolution ISAR imaging based on the SParse Iterative Covariance-based Estimation (SPICE) is proposed.As a nonparametric sparse spectrum estimation algorithm, the SPICE algorithm does not need to set any parameters and it converges globally, so it can realize high quality imaging with limited measurements.In addition, a fast implementation of the SPICE algorithm based on the Gohberg-Semencul (G-S) factorization is introduced in this paper.The ISAR imaging of simulated and measured data was analyzed to illustrate the effectiveness of the novel approach.展开更多
A high altitude platform station （HAPS） based communications scenario for providing Intemet access and broadband multimedia services to the passengers on board of a high speed train （traveling up to 300km/h） is pr...A high altitude platform station （HAPS） based communications scenario for providing Intemet access and broadband multimedia services to the passengers on board of a high speed train （traveling up to 300km/h） is proposed. Regarding the addressed scenario, when the propagation link between HAPS and train is blocked by obstacles, a three-dimensional （3-D） geometrical single cylinder spatial-temporal channel model is presented, in which closed form, mathematically tractable space-time correlation functions are obtained. It shows that the correlation functions determined by the 3-D model are of significant difference with those of the conventional 2-D model. Based on the analysis model, the paper derives a realized simulation model using sum-of-sinusoids approach, and applies method of equal areas （MEA） and modified method of equal areas （MMEA） to determine the model parameters. The fitting performance of the simulation model with the analysis one is evaluated by two means-square error （MSE） performance criteria. Finally, numerical simulation results verify the mathematical analysis conclusion, when N ≥21, simulation model has an excellent fitness with the analysis one.展开更多
基金Project(2007AA03Z119) supported by the National High-tech Research and Development Program of ChinaProjects(2102029,2072012) supported by the Natural Science Foundation of Beijing,China
文摘Based on the research of modem electronic packaging materials, thixo-forming technology was used to fabricate electronic packaging shell. The process of thixo-extrusion with SiCp/A356 composites was simulated by the finite element software DEFORM-3D, then the flow velocity field, equivalent strain field and temperature field were analyzed. The electronic packaging shell was manufactured by extrusion according to the results from numerical simulation. The results show that thixo-forming technology can be used in producing electronic package shell with SiCp/A356 composites, and high volume fraction of SiCp with homogeneous distribution can be achieved, being in agreement with the requirements of electronic packaging materials.
基金Sponsored by the National Natural Science Foundation of China(Grant Nos.61622107 and 61471149)
文摘This paper proposes a novel and comprehensive method of automatic target recognition based on real ISAR images with the aim to recognize the non-cooperative ship targets. The special characteristics of the ISAR images for the real data compared with the simulated ISAR images are analyzed firstly. Then,the novel technique for the target recognition is proposed,and it consists of three steps,including the preprocessing,feature extraction and classification. Some segmentation and morphological methods are used in the preprocessing to obtain the clear target images. Then,six different features for the ISAR images are extracted.By estimating the features' conditional probability, the effectiveness and robustness of these features are demonstrated. Finally,Fisher's linear classifier is applied in the classification step. The results for the allfeature space are provided to illustrate the effectiveness of the proposed method.
基金Sponsored by the National Natural Science Foundation of China(Grant Nos.61471149 and 61622107)
文摘Through the coherent accumulation of target echoes, inverse synthetic aperture radar （ISAR） imaging achieves high azimuth resolution. However, because of the instability of the radar system, the echoes of the 1SAR will be randomly lost. The conventional FFT processing methods can cause image blur and high sidelobes or other issues. A novel algorithm for ISAR missing-data imaging based on the Iterative Adaptive Approach （IAA） is proposed. The algorithm enjoys global convergence properties and does not need to set the parameters in advance. The missing-data ISAR imaging results for simulated and measured data illustrate the effectiveness of the algorithm.
基金Sponsored by the National Natural Science Foundation of China(Grant Nos.61622107,61471149)the Fundamental Research Funds for the Central Universities
文摘A new technique for the cubic Chirplet decomposition via local polynomial Wigner distribution(LPWD) is presented.Through introducing the parameter of curvature to the traditional Chirplet atoms,the cubic Chirplet atoms are more accurate to characterize the signals with high nonlinear instantaneous frequency(IF) trajectories.The phase coefficients of the cubic Chirplet atoms are evaluated by the LPWD algorithm with two-dimensional(2D) maximizations.This technique is precise,with high efficiency,and it is used in inverse synthetic aperture radar(ISAR) imaging of ship target with complicated motions,the ISAR images with good quality can be achieved.Experiments of emulational and real data validate the effectiveness of the new algorithm.
基金Supported by National Defense Committee of Science and Industry as a key pre-research project
文摘This paper provides a design method based on a time-shared form, which obtains the compatibility of signal and the system for detecting both ships and airplanes. Then, it gives the structure diagram of the system and the chart diagram of signal processing. Finally, the continuity problem of signal modulation for ship detection is discussed.
基金This work hes been is supported in part by National Natural Science Foundation of China (No. 60507007)the Program for New Century Excellent Talents in University (NCET, Min Zhang 2007)
文摘We present a systematic scheme to achieve both high birefringence and low confinement loss in index-guiding photonic crystal fibers(PCFs) ,using a structurally-simple PCF with finite number of air holes in the cladding region. By increasing the size of the outermost-ring air holes in the cladding region,highly birefringent PCFs with low confinement loss can be successfully achieved. The design strategy is based on the fact that the modal birefringence of PCFs is dominated by the inner-ring air holes in PCF,which is verified by a full-vector finite element method with anisotropic perfectly matched layers. Numerical results show that modal birefringence in the order of 10-3 and confinement loss less than 0.1 dB/km can be easily realized in the proposed PCF with only four rings of air holes in the cladding region. We expect that such fibers will be much easier to be fabvicated than those with more air holes in the cladding region.
文摘It is well known that the macroscopic Maxwell’s equations can be obtained from the corresponding microscopic or atomic equations by a proper averaging process. The purpose of this paper is to present the macroscopic Maxwell’s equations which are valid in all regions of space, including an interface between two different media; and the boundary conditions can naturally emerge from the macroscopic equations as an effect of average of the microscopic Maxwell’s equations. In addition, the application of the unit step functions and the Dirac delta function to our discussion not only permits great mathematical simplicity but also gives rise to convenient physical concepts for the description and representation of the actual fields in the vicinity of the interface.
文摘Generalized impedance boundary conditions are employed to simplify the solution of the Sommerfeld half-space problem. An analytical expression is derived for the Hertz potential of a vertical electric dipole over the earth’s surface, in which the earth is assumed to be a layered media or homogeneous dissipative half-space. A Sommerfeld type integral in the potential function is expressed as the sum of two parts: a zeroth order Hankel function and an absolutely convergent series of Bessel functions. In addition, two expressions in closed form are obtained as the far-field and near-field approximation of the present result.
基金Sponsored by the National Natural Science Foundation of China(Grant No.61622107)
文摘This paper presents a newmulti-targets inverse synthetic aperture radar (ISAR) imaging approach via the image segmentation processing. This method can separate multi-targets with similar velocities,and there is no strict limit on the rotational state of the targets. Firstly,the motion compensation for the completely multi-targets echo is carried out and the coarse image can be achieved with the Range-Doppler (RD) technique. Then a series of image processing methods and image segmentation processing are used to separate the echo data of each mono-target. At last,the image with high quality of each target can be achieved with the RD technique and the Range-Instantaneous-Doppler (RID) technique. ISAR imaging results of simulated and measured data validate the validity of the proposed approach.
文摘In this paper, a hybrid method (hybrid PMM-MoM method) is presented for the effective and accurate analysis of finite periodic structures. This method divides a finite periodic structure into two parts. The inner part of an approximate infinite periodic structure is analyzed by periodic method of moment (PMM);the outer part is then analyzed by method of moments (MoM). For the finite periodic structures, the accuracy of the new method is much better than that of the pure PMM, and is almost the same as that of pure MoM. Because pure PMM uses the periodic boundary conditions, it takes much less memory resources and computation time. For hybrid PMM-MoM method, because the inner part is calculated by PMM, the calculation work concentrates on the outer part. Consequently, compared with the exact MoM, the new method saves much more memory resources and computation time, which provides a drastic reduction of unknowns.
基金Project supported by the National Natural Science Foundation of China(No.92373115)the Natural Science Foundation of Anhui Province,China(No.2308085MF193)+2 种基金the Major Natural Science Project of Anhui Provincial Education Department,China(No.KJ2021ZD0003)the Key Research and Development Project of Anhui Province,China(No.2023n06020026)the Innovation and Entrepreneurship of Anhui Province,China(No.Z020118060)。
文摘In the post-Moore era,the development of active phased array antennas will inevitably trend towards active array microsystems.In this paper,the characteristics and composition of the active array antenna are briefly described.Owing to the high efficiency,low profile,and light weight of the active array microsystems,the application prospects and advantages in the engineering of multi-functional airborne radar,spaceborne radar,and communication systems are analyzed.Moreover,according to the characteristics of the post-Moore era of integrated circuits,scientific and technological problems in the active array microsystems are presented,including multi-scale,multi-signal,and multi-physics field coupling.The challenges are also discussed,such as new architectures and algorithms,miniaturization of passive components,novel materials and processes,ultra-wideband technology,and new interdisciplinary technological applications.This paper is expected to inspire in-depth research on active array microsystems.
文摘In recent years,frequent network attacks have highlighted the importance of efficient detection methods for ensuring cyberspace security.This paper presents a novel intrusion detection system consisting of a data prepro-cessing stage and a deep learning model for accurately identifying network attacks.We have proposed four deep neural network models,which are constructed using architectures such as Convolutional Neural Networks(CNN),Bi-directional Long Short-Term Memory(BiLSTM),Bidirectional Gate Recurrent Unit(BiGRU),and Attention mechanism.These models have been evaluated for their detection performance on the NSL-KDD dataset.To enhance the compatibility between the data and the models,we apply various preprocessing techniques and employ the particle swarm optimization algorithm to perform feature selection on the NSL-KDD dataset,resulting in an optimized feature subset.Moreover,we address class imbalance in the dataset using focal loss.Finally,we employ the BO-TPE algorithm to optimize the hyperparameters of the four models,maximizing their detection performance.The test results demonstrate that the proposed model is capable of extracting the spatiotemporal features of network traffic data effectively.In binary and multiclass experiments,it achieved accuracy rates of 0.999158 and 0.999091,respectively,surpassing other state-of-the-art methods.
基金National Natural Science Foundation of China,Grant/Award Number:12275244。
文摘Surge current(SC)capability is one of the main aspects of reliability for silicon carbide(SiC)power devices.In this work,the influences of neutron radiation‐induced defects on the SC capability and reliability of SiC P‐intrinsic‐N(PiN)diodes were comprehensively investigated.It was found that the surge capability of the diodes can be deteriorated even under the slightly enhanced formation of carbon‐vacancy‐related Z_(1/2) and EH_(6/7 )defects introduced by neutron irradiation.Surprisingly,it was found that the forward voltage(V_(F))decreases with the increased SC and the stress cycles in the irradiated diodes,which is usually found to in-crease under the SC tests and attributed to the bipolar degradation(BPD).By using technology computer‐aided design simulation and deep‐level transient spectroscopy characterization,it was found that the sig-nificant self‐heating during surge stress leads to the annealing effect on the Z_(1/2) defects through the promoted recombination with the nearest and second neighbor carbon interstitials injected by irradiation,which thus plays a dominant role in the decrease of VF over the BPD.
文摘Due to the heavy congestion in HF bands, HF radars are restricted to operating within narrow frequency bands. To improve the system bandwidth and avoid heavy interference bands, a quasi-random step frequency signal with discontinuous bands is presented. A novel two-dimensional signal processing scheme for this signal is proposed on the basis of delicate signal analysis. Simulation results demonstrate that the scheme could successfully realize the resolutions by decoupling the range-Doppler ambiguity, and effectively suppress the maximal sidelobe. Moreover, the scheme is simple and has good numerical stability.
基金Supported by the Foundation of Aeronautics Science (No. 03F52042)
文摘The developments of the high speed analog to digital converters （ADC） and advanced digital signal processors （DSP） make the smart antenna with digital beamforming （DBF） a reality. In conventional M-elements array antenna system, each element has its own receiving channel and ADCs. In this paper, a novel smart antenna receiver with digital beamforming is proposed. The essential idea is to realize the digital beamforming receiver based on bandpass sampling of multiple distinct intermediate frequency （IF） signals. The proposed system reduces receiver hardware from M IF channels and 2M ADCs to one IF channel and one ADC using a heterodyne radio frequency （RF） circuitry and a multiple bandpass sampling digital receiver. In this scheme, the sampling rate of the ADC is much higher than the summation of the M times of the signal bandwidth. The local oscillator produces different local frequency for each RF channel The receiver architecture is presented in detail, and the simulation of bandpass sampling of multiple signals and digital down conversion to baseband is given. The principle analysis and simulation results indicate the effectiveness of the new proposed receiver.
基金Sponsored by the National Natural Science Foundation of China(Grant Nos.61622107 and 61471149)
文摘A novel algorithm for the detection of ship target with high accuracy in the synthetic aperture radar(SAR) with high spatial resolution image is proposed. The SAR image may include not only the ship targets but also the interferences such as the sea clutter,the strong reflection target,the sidelobe and so on.The conventional constant false alarm rate(CFAR) algorithm has some disadvantages,and it has not enough prior information about the size of the ships. Hence,it cannot separate the adjacent ships correctly. A comprehensive algorithm based on the modified CFAR algorithm and opening operation is presented to solve the problem,and the detection accuracy can be improved consequently. The results of SAR image illustrate the effectiveness of the method in this paper.
基金Sponsored by the National Natural Science Foundation of China(Grant Nos.61622107 and 61871146)the Fundamental Research Funds for the Central Universities
文摘There are great challenges for traditional three-dimensional( 3-D) interferometric inverse synthetic aperture radar( In ISAR) imaging algorithms of ship targets w ith 2-D sparsity in actual radar imaging system. To deal w ith this problem,a novel 3-D In ISAR imaging method is proposed in this paper.First,the high-precision gradient adaptive algorithm w as adopted to reconstruct the echoes in range dimension. Then the method of minimizing the entropy of the average range profile w as applied to estimate the parameters w hich are used to compensate translation components of the received echoes. Besides,the phase adjustment and image coregistration of the sparse echoes w ere achieved at the same time through the approach of the joint phase autofocus. Finally,the 3-D geometry coordinates of the ship target w ith 2-D sparsity w ere reconstructed by combining the range measurement and interferometric processing of the ISAR images. Simulation experiments w ere carried out to verify the practicability and effectiveness of the algorithm in the case that the received echoes are in 2-D sparsity.
基金The National Natural Science Foundation of China(No.11371088,11571173,11871144)the Natural Science Foundation of Jiangsu Province(No.BK20171348)
文摘The condition of an algebra to be a Hopf algebra or a Hopf(co)quasigroup can be determined by the properties of Galois linear maps.For a bialgebra H,if it is unital and associative as an algebra and counital coassociative as a coalgebra,then the Galois linear maps T1 and T2 can be defined.For such a bialgebra H,it is a Hopf algebra if and only if T1 is bijective.Moreover,T1^-1 is a right H-module map and a left H-comodule map(similar to T2).On the other hand,for a unital algebra(no need to be associative),and a counital coassociative coalgebra A,if the coproduct and counit are both algebra morphisms,then the sufficient and necessary condition of A to be a Hopf quasigroup is that T1 is bijective,and T1^-1 is left compatible with ΔT1-11^r and right compatible with mT1-1^l at the same time(The properties are similar to T2).Furthermore,as a corollary,the quasigroups case is also considered.
基金Sponsored by the National Natural Science Foundation of China(Grant Nos.61622107 and 61871146)
文摘High-resolution of Inverse Synthetic Aperture Radar (ISAR) in the azimuth direction can be achieved by increasing the coherent accumulation angle of the target rotation.However, in practice, the coherent accumulation angle may be small.In this paper, a novel algorithm for high-resolution ISAR imaging based on the SParse Iterative Covariance-based Estimation (SPICE) is proposed.As a nonparametric sparse spectrum estimation algorithm, the SPICE algorithm does not need to set any parameters and it converges globally, so it can realize high quality imaging with limited measurements.In addition, a fast implementation of the SPICE algorithm based on the Gohberg-Semencul (G-S) factorization is introduced in this paper.The ISAR imaging of simulated and measured data was analyzed to illustrate the effectiveness of the novel approach.
基金Supported by the National Natural Science Foundation of China (No. 60532030).
文摘A high altitude platform station （HAPS） based communications scenario for providing Intemet access and broadband multimedia services to the passengers on board of a high speed train （traveling up to 300km/h） is proposed. Regarding the addressed scenario, when the propagation link between HAPS and train is blocked by obstacles, a three-dimensional （3-D） geometrical single cylinder spatial-temporal channel model is presented, in which closed form, mathematically tractable space-time correlation functions are obtained. It shows that the correlation functions determined by the 3-D model are of significant difference with those of the conventional 2-D model. Based on the analysis model, the paper derives a realized simulation model using sum-of-sinusoids approach, and applies method of equal areas （MEA） and modified method of equal areas （MMEA） to determine the model parameters. The fitting performance of the simulation model with the analysis one is evaluated by two means-square error （MSE） performance criteria. Finally, numerical simulation results verify the mathematical analysis conclusion, when N ≥21, simulation model has an excellent fitness with the analysis one.
