Eigenspace-based source number estimation for direction-of-arrival estimation

A eigenspace-based source number estimation was presented.It projects the estimated covariance matrix of array signal into signal eigen-subspace and noise eigen-subspace, respectively.Using the orthogonality between signal eigen-subspace and noise eigen-subspace, it is easy to differentiate the contribution of signal and noise by using the criterion value,or the magnitude of projection.Like the Direction-of-Arrival(DOA) estimation algorithm,the estimator uses the eigenvalue decomposition of covariance matrix with order M×M,where M is the number of elements,and hence can save much computational burden.To reduce more computational burden,the estimation can be implemented by the decomposition in the real-value space.Computer simulation demonstrates the distribution of criterion value and the performance of the estimation method.The estimation method was also tested with the sonar data,which shows good performances.     

On the Cramr-Rao bound of wideband direction of arrival estimation

The Cramr-Rao bound (CRB) for wideband direction of arrival (DOA) estimates of multi-source impinging on a randomly distributed array is derived. The computational expressions for the elements of Fisher information matrix in arbitrary array are provided also. The derived CRB can be divided into two terms, one depends on signals' characteristics and the other depends on array geometry, and so an insight into theoretical performance of DOA estimation can be provided. The first term of CRB shows that the DOA estimation performance not only depends on SNR but also the signal bandwidth and spectral density, thus it can be found that better DOA estimation can be obtained for signals with more high frequency energies. The second term of CRB shows that DOA estimates vary with different array geometries and source angles. These properties provide us some useful tip to design an efficient signal and array configuration. Simulation results confirmed the results mentioned above.     

The estimation of lower refractivity uncertainty from radar sea clutter using the Bayesian-MCMC method

The estimation of lower atmospheric refractivity from radar sea clutter(RFC) is a complicated nonlinear optimization problem.This paper deals with the RFC problem in a Bayesian framework.It uses the unbiased Markov Chain Monte Carlo(MCMC) sampling technique,which can provide accurate posterior probability distributions of the estimated refractivity parameters by using an electromagnetic split-step fast Fourier transform terrain parabolic equation propagation model within a Bayesian inversion framework.In contrast to the global optimization algorithm,the Bayesian-MCMC can obtain not only the approximate solutions,but also the probability distributions of the solutions,that is,uncertainty analyses of solutions.The Bayesian-MCMC algorithm is implemented on the simulation radar sea-clutter data and the real radar seaclutter data.Reference data are assumed to be simulation data and refractivity profiles are obtained using a helicopter.The inversion algorithm is assessed(i) by comparing the estimated refractivity profiles from the assumed simulation and the helicopter sounding data;(ii) the one-dimensional(1D) and two-dimensional(2D) posterior probability distribution of solutions.     

Direction of arrival estimation based on high-order cumulant by sparse reconstruction of underwater acoustic signals

The high-order cumulant with the characteristics of Gaussian noise suppression and array expansion, can be introducd into the direction of arrival(DOA) estimation of the underwater acoustic signals. A DOA estimation algorithm based on high-order cumulant by off-grid sparse Bayesian learning is proposed. Considering the natural blindness of the highorder cumulant to Gaussian noise, the fourth-order cumulant of the array signal is calculated to filter out the Gaussian noise, with the doubled array...     

Bayesian credible interval construction for Poisson statistics

The construction of the Bayesian credible (confidence) interval for a Poisson observable including both the signal and background with and without systematic uncertainties is presented. Introducing the conditional probability satisfying the requirement of the background not larger than the observed events to construct the Bayesian credible interval is also discussed. A Fortran routine, BPOCI, has been developed to implement the calculation.     

On the Cramer-Rao bound of wideband direction of arrival estimation

The Cramer-Rao bound （CRB） for wideband direction of arrival （DOA） estimates of multi-source impinging on a randomly distributed array is derived. The computational expressions for the elements of Fisher information matrix in arbitrary array are provided also. The derived CRB can be divided into two terms, one depends on signals＇ characteristics and the other depends on array geometry, and so an insight into theoretical performance of DOA estimation can be provided. The first term of CRB shows that the DOA estimation performance not only depends on SNR but also the signal bandwidth and spectral density, thus it can be found that better DOA estimation can be obtained for signals with more high frequency energies. The second term of CRB shows that DOA estimates vary with different array geometries and source angles. These properties provide us some useful tip to design an efficient signal and array configuration. Simulation results confirmed the results mentioned above.     

Wideband high-resolution direction of arrival estimation method based on the pressure-velocity combined processing using the acoustic vector sensor array

In order to solve the problem of DOA (Direction of Arrival) estimation of underwater distant wideband targets, a novel coherent signal-subspace method based on the cross spectral matrix of pressure and particle velocity using the Acoustic Vector Sensor Array (AVSA) is proposed in this paper. The proposed method is different from existing AVSA based DOA estimation methods in using particle velocity information of Acoustic Vector Sensor (AVS) as an independent array element. It is entirely based on the combined information processing of pressure and particle velocity, namely, the P-V cross spectrum, has better DOA estimation performance than existing methods in isotropic noise field. By theoretical analysis, both focusing principle and eigendecomposition theory based on the P-V cross spectral matrix are given. At the same time, the corresponding criteria for source number detection is also presented. Computer simulations with data from lake trials demonstrate that the proposed method is effective and obviously outperforms existing methods in resolution and accuracy in the case of low Signal-to-Noise Ratio (SNR).     

Current-voltage characteristics simulation and analysis of 4H-SiC metal-semiconductor-metal ultraviolet photodetectors

The current-voltage (Ⅰ-Ⅴ) characteristics of 4H-SiC metal-semiconductor-metal (MSM) ultraviolet pho- todetector with different finger widths and spacings,different carrier concentrations and thicknesses of n-type epitaxial layer are simulated.The simulation results indicate that the dark current and the pho- tocurrent both increase when the finger width increases.But the effect of finger width on the dark current is more significant.On the other hand,the effect of finger spacing on the photocurrent is more significant. When the finger spacing increases,the photocurrent decreases and the dark current is almost changeless. In addition,it is found that the smaller the carrier concentration of n-type epitaxial layer is,the smaller the dark current and the larger the photocurrent will be.It is also found that I-V characteristics of MSM detector also depend on the epitaxial layer thickness.The dark current of detector is smaller and the photocurrent is larger when the epitaxial layer thickness is about 3μm.     

Detection of number of sources and DOA estimation based on the combined information processing of pressure and particle velocity using acoustic vector sensor array

In order to solve the problem of DOA(direction of arrival)estimation of underwater remote targets,a novel subspace-decomposition method based on the cross covariance matrix of the pressure and the particle velocity of acoustic vector sensor arrays(AVSA)was proposed. Whereafter,using spatio-temporal virtual tapped-delay-line,a new eigenvector-based criteria of detection of number of sources and of subspace partition is also presented.The theoretical analysis shows that the new source detection and direction finding method is different from existing AVSA based DOA estimation methods using particle velocity information of acoustic vector sensor(AVS)as an independent array element.It is entirely based on the combined information processing of pressure and particle velocity,has better estimation performance than existing methods in isotropic noise field.Computer simulations with data from lake trials demonstrate,the proposed method is effective and obviously outperforms existing methods in resolution and accuracy in the case of low signal-to-noise ratio(SNR).     

Scalable distributed video coding based on block SW-SPIHT

Nowadays,distributed source coding(DSC)and distributed video coding(DVC)have been receiving more and more attention due to the distinct contributions to the easy encoding.At the same time,with more new requirements coming forth in the current network communication,the scalability of bit stream has been a new focus in the real applications.A scalable DVC scheme is presented without requiring layered coding in which the main attributions of DVC,namely the capabilities of easy encoding and robustness, are inherited remarkably and the property of scalability is also integrated simultaneously.Based on the block Slepian-Wolf set partitioning in hierarchical trees(SW-SPIHT),the Wyner-Ziv frames are encoded to get the scalable bit stream.In addition,the binary motion searching is explored at the decoder with the help of a rate-variable‘hash’from the encoder to improve the performance of the whole system.The final experimental results show that our system has higher peak signal-to-noise ratio(PSNR)than the pixel-domain DVC at the high bit rate.What is more,the scalability in signal-to-noise ratio(SNR)is also achieved satisfactorily.     

CLOSE－COUPLING WAVE PACKET APPROACH TO Ar-H2 SYSTEM OF NONREACTIVE SCATTERING

In this paper we first describe the recently developed theory of close-coupling wave packet(CCWP)method.then calculate the transition prodabilities for the Ar-N2 system in detail.The total angular momentum J=4 is chosen,and the nine coupled channels transition probabilities are calculated.Comparision with the results from close-coupling (CC) method shows that the CCWP method is not only more accurate but also faster in computation.     

Focusing transform based robust azimuth angles estimation for wideband signals

A focusing transform based minimum variance method (FTMV) is proposed for estimating the azimuth angles of wideband signals. The estimation error of Direction of Arrival (DOA) in the traditional Minimum Variance (MV) method during the array direction changing with the ship can be eliminated by focusing the sample covariance matrices in wideband onto a single narrowband, and accumulating the beamformer outputs on azimuth. Then, the azimuth angles of signals can be estimated accurately. Experimental results show that the FTMV method is more efficient and robust than the MV method in this case.     

Sparse Bayesian reconstruction method for multispectral bioluminescence tomography

We present a sparse Bayesian reconstruction method based on multiple types of a priori information for multispectral bioluminescence tomography （BLT）. In the Bayesian approach, five kinds of a priori information are incorporated, reducing the ill-posedness of BLT. Specifically, source sparsity characteristic is considered to promote reconstruction results. Considering the computational burden in the multispectral case, a series of strategies is adopted to improve computational efficiency, such as optimal permissible source region strategy and node model of the finite element method. The performance of the proposed algorithm is validated by a heterogeneous three-dimensional （3D） micron scale computed tomography atlas and a mouse-shaped phantom. Reconstructed results demonstrate the feasibility and effectiveness of the proposed algorithm.     

Analysis of electromagnetic pulses generated from ultrashort laser irradiation of solid targets at CLAPA

Electromagnetic pulses(EMPs)produced by the interaction of a TW femtosecond laser with solid targets at the Compact Laser Plasma Accelerator(CLAPA)are measured and interpreted.The statistical results confirm that the intensities of the EMPs are closely related to both target material and thickness.The signal of the titanium target is more abundant than that of the copper target with the same thickness,and the intensity of EMP is positively correlated with the target thickness for aluminium foil.With the boosted EMP radiations,the energy of accelerated protons is also simultaneously enhanced.In addition,EMPs emitted from the front of the target exceed those from the rear,which are also pertinent to the specific target position.The resonant waveforms in the target chamber are analyzed using the fast Fourier transform,and the local resonance and the attenuation lead to changes of the frequency spectra of EMPs with variation of detecting positions,which is well supported by the modeling results.The findings are beneficial to gaining insight into the mechanism of EMP propagation in a typical target chamber and providing more information for EMP shielding design.     

Occurrence of Superdeformation in Even-Even Isotopes of Zn

Occurrence of superdeformed (SD) shape from the relationship between the collective rotation and the pairing correlations is investigated in the relativistic mean field theory framework. It is found that pairing correlation plays an important role in the occurrence of SD shape. It is also shown that the SD band of 66^Zn is more difficult to be observed than that of 60^Zn experimentally.     

New method for lightning location using optical ground wire

A new technology of lightning location is described, which is based on detecting the state of polarization (SOP) fluctuation of the laser light in the optic ground wire (OPGW). Compared with the conventional lightning location method, the new method is more accurate, more stable, and cheaper. Theories of Stokes parameters and Poincare sphere are introduced to analyze the SOP at the lightning strike point. It can be concluded that although the initial points of SOP on the Poincare sphere are random, the SOP fluctuation generated by lightning strike can still be accurately identified by detecting the velocity of polarization motion. A new algorithm to quantify the velocity is also introduced.     

A Bayesian approach to matched field processing in uncertain ocean environments

An approach of Bayesian Matched Field Processing （MFP） was discussed in the uncertain ocean environment. In this approach, uncertainty knowledge is modeled and spatial and temporal data received by the array are fully used. Therefore, a mechanism for MFP is found, which well combines model-based and data-driven methods of uncertain field processing. By theoretical derivation, simulation analysis and the validation of the experimental array data at sea, we find that （1） the basic components of Bayesian matched field processors are the cor- responding sets of Bartlett matched field processor, MVDR （minimum variance distortionless response） matched field processor, etc.; （2） Bayesian MVDR/Bartlett MFP are the weighted sum of the MVDR/Bartlett MFP, where the weighted coefficients are the values of the a posteriori probability; （3） with the uncertain ocean environment, Bayesian MFP can more correctly locate the source than MVDR MFP or Bartlett MFP; （4） Bayesian MFP can better suppress sidelobes of the ambiguity surfaces.     

Re-study of the contribution of scalar potential and spectra of cc, bb and bc(bc) families

We indicated in our previous work that for QED the role of the scalar potential which appears at the loop level is much smaller than that of the vector potential and is in fact negligible. But the situation is different for QCD, one reason is that the loop effects are more significant because α_s is much larger than α, and second the non-perturbative QCD effects may induce a sizable scalar potential. In this work, we study phenomenologically the contribution of the scalar potential to the spectra of charmonia, bottomonia and bc(bc) families. Taking into account both vector and scalar potentials, by fitting the well measured charmonia and bottomonia spectra, we re-fix the relevant parameters and test them by calculating other states of not only the charmonia and bottomonia families, but also the bc family. We also consider the Lamb shift of the spectra.     

On the decays of d~*(2380) in a constituent chiral quark model

After summarizing the experimental results and present status of the d~*(2380) observed at WASA@COSY,two "extreme" models for explaining its structure, a compact hexaquark dominated model and a loose ??'-D_(12)π model, are briefly discussed, especially the former. By comparing their results with the corresponding data, the differences of the two models are addressed. As a remedy for the latter model, a mixing model and its result are also quoted for a comparison. It is shown that the compact hexaquark dominated structure might be more promising.However, the mixing model is also a possible structure, and more accurate Γ_(d~*)→NN_π data are needed for confirmation.     

Fast direction of arrival estimation of wideband sources in unknown correlated noise fields

A computational efficient wideband Direction of Arrival (DOA) estimation method in the presence of unknown correlated noise is presented. A fast Two-sided Correlation Transformation (TCT) focusing matrix that transforms only the signal subspace is developed firstly, and then the propagator method is utilized to compute the focusing matrix and noise correlation matrix. In contrast to conventional wideband DOA estimation method, the proposed method requires only linear operation but does not involve any eigenvelue-decomposition to estimate the focusing matrix; it has a lower computational load, especially when the sensor number is greater than the source number. Because noise correlation matrix is estimated and eliminated from the array correlation matrix, the accuracy of DOA estimation is improved even in the presence of unknown correlation noise. Computer simulation results verified the efficiency of the method.