This paper deals with the blind separation of nonstation-ary sources and direction-of-arrival （DOA） estimation in the under-determined case, when there are more sources than sensors. We assume the sources to be time...This paper deals with the blind separation of nonstation-ary sources and direction-of-arrival （DOA） estimation in the under-determined case, when there are more sources than sensors. We assume the sources to be time-frequency （TF） disjoint to a certain extent. In particular, the number of sources presented at any TF neighborhood is strictly less than that of sensors. We can identify the real number of active sources and achieve separation in any TF neighborhood by the sparse representation method. Compared with the subspace-based algorithm under the same sparseness assumption, which suffers from the extra noise effect since it can-not estimate the true number of active sources, the proposed algorithm can estimate the number of active sources and their cor-responding TF values in any TF neighborhood simultaneously. An-other contribution of this paper is a new estimation procedure for the DOA of sources in the underdetermined case, which combines the TF sparseness of sources and the clustering technique. Sim-ulation results demonstrate the validity and high performance of the proposed algorithm in both blind source separation （BSS） and DOA estimation.展开更多
β-BBO is a excellent nonlinear optical crystal.The phase transition point of the crystal is lower than its melting point,so the crystal must be grown by flux method.It is known that low growth rate and flux contamina...β-BBO is a excellent nonlinear optical crystal.The phase transition point of the crystal is lower than its melting point,so the crystal must be grown by flux method.It is known that low growth rate and flux contamination are the two shortcomings of this method.展开更多
Herein,a BiOCl/Bi_(2)Ti_(2)O_(7)heterojunction was prepared as an efficient visible light-driven photocatalyst through an in situ hydrothermal method,and its photocatalytic properties were investigated via a comparabl...Herein,a BiOCl/Bi_(2)Ti_(2)O_(7)heterojunction was prepared as an efficient visible light-driven photocatalyst through an in situ hydrothermal method,and its photocatalytic properties were investigated via a comparable method.Its structure,morphology and composition were characterized via X-ray diffraction(XRD),field emission scanning electron microscopy(FE-SEM)and X-ray photoelectron spectroscopy(XPS).The formation of a heterojunction between BiOCl and Bi_(2)Ti_(2)O_(7)was also confirmed via transmission electron microscopy(TEM).Moreover,the optical and photocatalytic properties of BiOCl,Bi_(2)Ti_(2)O_(7)and BiOCl/Bi_(2)Ti_(2)O_(7)heterojunction composites with different BiOCl:Bi_(2)Ti_(2)O_(7)mass ratios were investigated.Compared to the case of pure BiOCl,the absorption spectra of the BiOCl/Bi_(2)Ti_(2)O_(7)heterojunction were extended to the visible light region,and the photocatalytic activities were also enhanced.Moreover,the enhancement mechanism of the photocatalytic activity was studied via photocurrent density tests,electrochemical impedance spectroscopy(EIS)and trapping experiments.展开更多
A potential ultraviolet(UV)nonlinear optical(NLO)material,Pb_(2)BO_(3)Br,has been successfully synthesized by a mild hydrothermal method.It crystallizes in the trigonal polar NCS space group P321 with lattice paramete...A potential ultraviolet(UV)nonlinear optical(NLO)material,Pb_(2)BO_(3)Br,has been successfully synthesized by a mild hydrothermal method.It crystallizes in the trigonal polar NCS space group P321 with lattice parameters a=4.9601(8)Å,c=6.733(2)Å,v=143.46(6)Å^(3) and Z=1.The title compound with a KBBFtype structure consists of a honeycomb-like[Pb_(2)BO_(3)]layer and Br anions.UV-Vis-NIR diffuse reflectance spectroscopy revealed that Pb_(2)BO_(3)Br exhibits wide transparent regions from UV to near-IR.The powder second harmonic generation(SHG)test showed that it is phase-matchable in the visible region and features a remarkable SHG effect of about 9.5 times that of KDP.In addition,the electronic structure calculations indicated that the prominent macroscopic SHG response of Pb_(2)BO_(3)Br mainly originated from the[BO_(3)]3−trigonal-planar groups and distorted PbO_(3) polyhedra.展开更多
基金supported by the National Natural Science Foundation of China(61072120)
文摘This paper deals with the blind separation of nonstation-ary sources and direction-of-arrival （DOA） estimation in the under-determined case, when there are more sources than sensors. We assume the sources to be time-frequency （TF） disjoint to a certain extent. In particular, the number of sources presented at any TF neighborhood is strictly less than that of sensors. We can identify the real number of active sources and achieve separation in any TF neighborhood by the sparse representation method. Compared with the subspace-based algorithm under the same sparseness assumption, which suffers from the extra noise effect since it can-not estimate the true number of active sources, the proposed algorithm can estimate the number of active sources and their cor-responding TF values in any TF neighborhood simultaneously. An-other contribution of this paper is a new estimation procedure for the DOA of sources in the underdetermined case, which combines the TF sparseness of sources and the clustering technique. Sim-ulation results demonstrate the validity and high performance of the proposed algorithm in both blind source separation （BSS） and DOA estimation.
文摘β-BBO is a excellent nonlinear optical crystal.The phase transition point of the crystal is lower than its melting point,so the crystal must be grown by flux method.It is known that low growth rate and flux contamination are the two shortcomings of this method.
基金National Natural Science Foundation of China(No.51672215,11274251)Research Fund for the Doctoral Program of Higher Education of China(RFDP)(No.20136101110017)+2 种基金Natural Science Foundation of Shaanxi Province(No.2014JM1004)Graduate independent innovation project(No.YZZ17098)Excellent doctoral dissertation training project(No.YYB17004)。
文摘Herein,a BiOCl/Bi_(2)Ti_(2)O_(7)heterojunction was prepared as an efficient visible light-driven photocatalyst through an in situ hydrothermal method,and its photocatalytic properties were investigated via a comparable method.Its structure,morphology and composition were characterized via X-ray diffraction(XRD),field emission scanning electron microscopy(FE-SEM)and X-ray photoelectron spectroscopy(XPS).The formation of a heterojunction between BiOCl and Bi_(2)Ti_(2)O_(7)was also confirmed via transmission electron microscopy(TEM).Moreover,the optical and photocatalytic properties of BiOCl,Bi_(2)Ti_(2)O_(7)and BiOCl/Bi_(2)Ti_(2)O_(7)heterojunction composites with different BiOCl:Bi_(2)Ti_(2)O_(7)mass ratios were investigated.Compared to the case of pure BiOCl,the absorption spectra of the BiOCl/Bi_(2)Ti_(2)O_(7)heterojunction were extended to the visible light region,and the photocatalytic activities were also enhanced.Moreover,the enhancement mechanism of the photocatalytic activity was studied via photocurrent density tests,electrochemical impedance spectroscopy(EIS)and trapping experiments.
基金supported by the National Natural Science Foundation of China(Grant No.51425205,U1605245,51602309,91622118,and 21473096)the National Key Research and Development Plan of Ministry of Science and Technology(Grant No.2016YFB0402104)the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDB20000000).
文摘A potential ultraviolet(UV)nonlinear optical(NLO)material,Pb_(2)BO_(3)Br,has been successfully synthesized by a mild hydrothermal method.It crystallizes in the trigonal polar NCS space group P321 with lattice parameters a=4.9601(8)Å,c=6.733(2)Å,v=143.46(6)Å^(3) and Z=1.The title compound with a KBBFtype structure consists of a honeycomb-like[Pb_(2)BO_(3)]layer and Br anions.UV-Vis-NIR diffuse reflectance spectroscopy revealed that Pb_(2)BO_(3)Br exhibits wide transparent regions from UV to near-IR.The powder second harmonic generation(SHG)test showed that it is phase-matchable in the visible region and features a remarkable SHG effect of about 9.5 times that of KDP.In addition,the electronic structure calculations indicated that the prominent macroscopic SHG response of Pb_(2)BO_(3)Br mainly originated from the[BO_(3)]3−trigonal-planar groups and distorted PbO_(3) polyhedra.
