Trapping second-order nonlinearity in erbium-doped germanosilicate ring in thermally poled optical fibre

An optical fibre with an erbium (Er)-doped germanosilicate ring structure around the anode hole has been fabricated for stabilising the thermal poling induced second-order nonlinearity (SON). The SON spatial distribution was visualised with second-harmonic microscopy. It was found that the SON layer was trapped in the Er-doped ring under normal poling conditions. Only at higher poling voltages and for much longer poling time could some SON be formed at the core-cladding interface, while most of the SON layer was still firmly confined within the Er-doped ring.     

Synthesis of cyanated tetracenes as the organic semiconductors

Two novel and air-stable cyanated tetracene derivatives, 5-cyanotetracene (1CT) and 5,11-dicyanotetracene (2CT), were synthesized as high-performance organic semiconductors. The stability of 2CT was evaluated by NMR and the electrochemical property was investigated by cyclic voltammetry (CV) and UV–vis spectrum. The reorganization energy of 2CT predicted by UB3LYP/6-311g(d,p) is 0.0881 eV, which is the lowest among existing compounds. The X-ray crystallographic analysis revealed that the 2CT single crystal has a promising face-to-face packing with a relative short intermolecular distance of 3.403 Å. Based on the theoretical model we previously developed, the calculated hole mobilities of these air-stable cyanated tetracene derivatives in a–b plane are 2.9 cm² V⁻¹ s⁻¹ for 1CT and 2.2 cm² V⁻¹ s⁻¹ for 2CT, respectively. These oxygen-resisted organics may offer potential to fabricate the flexible electronics under air conditions.     

Electron correlation effects on exciton dissociation in the presence of an electric field in polyacetylene

Based on the Su–Schrieffer–Heeger and Pariser–Parr–Pople (SSH + PPP) model and the multiconfigurational time-dependent Hartree-Fock formalism, the dynamics of exciton dissociation in conjugated polymers systems has been simulated using a nonadiabatic molecular dynamics method. Within this approach, the appropriate spin symmetry of the electronic wavefunction is taken into account, which allows us to distinguish between singlet and triplet excited states. The different dynamic dissociation behaviors in the presence of an electric field of singlet excitons (SE) and triplet excitons (TE) due to electron correlation are emphasized. Using numerical simulations, it is found that the dissociation of TE under an applied electric field is more difficult than in the case for SE. The critical dissociation electric field strength for TE is about 3 times higher than that of SE. When the conjugated length of a polymer chain is short, SE and TE can each remain as one entity even under high electric field strengths owing to the confinement effect of the chain ends. In addition, the dependence of exciton dissociation on the Coulomb interaction strength, shielding factor and the conjugated length is discussed.     

ARINC429总线的故障注入测试方法

传统的ARINC429总线测试仅针对输入的激励测试输出的响应, 无法有效涵盖更多在异常状态下的测试环境。为扩大测试的覆盖性与主动性, 采用故障注入的方法, 分别对ARINC429总线物理层、电气层和协议层中典型的故障模式及注入实现方法进行了研究, 实验结果验证了故障注入测试方法的有效性。     

Maximum A Posteriori -based automatic target detection in SAR images

The paper presents an algorithm of automatic target detection in Synthetic Aperture Radar(SAR) images based on Maximum A Posteriori(MAP). The algorithm is divided into three steps. First, it employs Gaussian mixture distribution to approximate and estimate multi-modal histogram of SAR image. Then, based on the principle of MAP, when a priori probability is both unknown and learned respectively, the sample pixels are classified into different classes c = {target, shadow, background}. Last, it compares the results of two different target detections. Simulation results preferably indicate that the presented algorithm is fast and robust, with the learned a priori probability, an approach to target detection is reliable and promising. Communication author: Wang Yimin, born in 1968, male, Ph.D. candidate. College of Automation, Northwestern Polytechnical University, Xi’an 710072, China.     

A study of relative phase in complex wavelet domain: Property,statistics and applications in texture image retrieval and segmentation

In this paper, we develop a new approach which exploits the probabilistic properties from the phase information of 2-D complex wavelet coefficients for image modeling. Instead of directly using phases of complex wavelet coefficients, we demonstrate why relative phases should be used. The definition, properties and statistics of relative phases of complex coefficients are studied in detail. We proposed von Mises and wrapped Cauchy for the probability density function (pdf) of relative phases in the complex wavelet domain. The maximum-likelihood method is used to estimate two parameters of von Mises and wrapped Cauchy. We demonstrate that the von Mises and wrapped Cauchy fit well with real data obtained from various real images including texture images as well as standard images. The von Mises and wrapped Cauchy models are compared, and the simulation results show that the wrapped Cauchy fits well with the peaky and heavy-tailed pdf of relative phases and the von Mises fits well with the pdf which is in Gaussian shape. For most of the test images, the wrapped Cauchy model is more accurate than the von Mises model, when images are decomposed by different complex wavelet transforms including dual-tree complex wavelet (DTCWT), pyramidal dual-tree directional filter bank (PDTDFB) and uniform discrete curvelet transform (UDCT). Moreover, the relative phase is applied to obtain new features for texture image retrieval and segmentation applications. Instead of using only real or magnitude coefficients, the new approach uses a feature in which phase information is incorporated, yielding a higher accuracy in texture image retrieval as well as in segmentation. The relative phase information which is complementary to the magnitude is a promising approach in image processing.     

龙滩水电站的枢纽布置

龙滩水电站是红水河上最大的综合利用工程，分期建设，前期坝高１９２ｍ，装机４２０万ｋＷ，后期坝高２１６．５ｍ，装机５４０万ｋＷ。本文介绍了坝址条件和重力坝方案枢纽布置的格局，初设审查批准后，由于决定利用碾压混凝土，对总布置又进行了调整和优化，文中叙述了最终的总布置及主要建筑物的情况     

High-performance and broadband photodetection of bicrystalline(GaN)1-x(ZnO)x solid solution nanowires via crystal defect engineering

Crystal defect engineering is widely used as an effective approach to regulate the optical and opto-electronic properties of semiconductor nanostructures.However,photogenerated electron-hole pair recombination centers caused by structural defects usually lead to the reduction of optoelectronic perfor-mance.In this work,a high-performance photodetector based on(GaN)1-x(ZnO)x solid solution nanowire with bicrystal structure is fabricated and it shows excellent photoresponse to ultraviolet and visible light.The highest responsivity of the photodetector is as high as 60,86 and 43 A/W under the irradiation of 365 nm,532 nm and 650 nm,respectively.The corresponding response time is as fast as 170,320 and 160 ms.Such wide spectral responses can be attributed to various intermediate energy levels induced by the introduction of various structural defects and dopants in the solid solution nanowire.Moreover,the peculiar bicrystal boundary along the axial direction of the nanowire provides two parallel and fast trans-mission channels for photo-generated carriers,reducing the recombination of photo-generated carriers.Our findings provide a valued example using crystal defect engineering to broaden the photoresponse range and improve the photodetector performance and thus can be extended to other material systems for various optoelectronic applications.