National University of Defense Technology

About: National University of Defense Technology is a education organization based out in Changsha, China. It is known for research contribution in the topics: Computer science & Radar. The organization has 39430 authors who have published 40181 publications receiving 358979 citations. The organization is also known as: Guófáng Kēxuéjìshù Dàxué & NUDT.

Integer DCTs and fast algorithms

Abstract: A method is proposed to factor the type-II discrete cosine transform (DCT-II) into lifting steps and additions. After approximating the lifting matrices, we get a new type-II integer discrete cosine transform (IntDCT-II) that is float-point multiplication free. Based on the relationships among the various types of DCTs, we can generally factor any DCTs into lifting steps and additions and then get four types of integer DCTs, which need no float-point multiplications. By combining the polynomial transform and the one-dimensional (1-D) integer cosine transform, a two-dimensional (2-D) integer discrete cosine transform is proposed. The proposed transform needs only integer operations and shifts. Furthermore, it is nonseparable and requires a far fewer number of operations than that used by the corresponding row-column 2-D integer discrete cosine transform.

Study on broadband microwave absorbing performance of gradient porous structure

Abstract: In this study, a gradient porous structure was designed for a novel microwave absorbing material, and the effects of various factors on its microwave absorbing characteristics were investigated. The computational and experimental results show that the bandwidth of this composite can reach up to 14.06 GHz with a microwave reflection loss below − 10 dB in the frequency of 1–18 GHz. The appreciable agreement between the simulation and the experiment verified the validity of this structure. The broadband microwave absorbing performance of designed gradient porous structure was significantly enhanced, which was ascribed to the synergistic effect of structural and material characteristics. The square aperture of this structure increased from the bottom to the top, which improved the impedance matching between the surface of gradient porous structure and the air and reduced the reflection of electromagnetic waves. In addition, the transmission path of electromagnetic wave inside the absorbing structure increased, thus facilitating the attenuation of electromagnetic wave. This study could provide a new design strategy for the research of antiradar detection technique and shielding the electromagnetic interference. Summary: 1.The absorbing principle of the gradient porous structure. 2. The simulation and test results of the gradient porous structure.

Molecular Beam Epitaxy-Grown SnSe in the Rock-Salt Structure: An Artificial Topological Crystalline Insulator Material

Abstract: Z. Wang, J. Wang, Y. Zang, Dr. T. Jiang, Y. Gong, Prof. C.-L. Song, Prof. S.-H. Ji, Prof. L.-L. Wang, Prof. K. He, Prof. W. Duan, Prof. X. Ma, Prof. X. Chen, Prof. Q.-K. Xue State Key Laboratory of Low-Dimensional Quantum Physics Department of Physics Tsinghua University Beijing 100084 , China E-mail: kehe@tsinghua.edu.cn; qkxue@tsinghua.edu.cn Q. Zhang, J.-A. Shi, Prof. L. Gu Beijing National Laboratory for Condensed Matter Physics Institute of Physics Chinese Academy of Sciences Beijing 100190 , China Dr. T. Jiang College of Opto-Electronic Science and Engineering National University of Defense Technology Changsha , Hunan 410073 , China Prof. S.-H. Ji, Prof. L.-L. Wang, Prof. L. Gu, Prof. K. He, Prof. W. Duan, Prof. X. Ma, Prof. X. Chen, Prof. Q.-K. Xue Collaborative Innovation Center of Quantum Matter Beijing 100084 , P. R. China

An Anchor-Free Detection Method for Ship Targets in High-Resolution SAR Images

Abstract: With the rapid development of earth observation technology, high-resolution synthetic aperture radar (HR SAR) imaging satellites could provide more observational information for maritime surveillance. However, there are still some problems to detect ship targets in HR SAR images due to the complex surroundings, targets defocusing, and diversity of the scales. In this article, an anchor-free method is proposed for ship target detection in HR SAR images. First, fully convolutional one-stage object detection (FCOS) as the base network is applied to detect ship targets, achieving better detection performance through pixel-by-pixel prediction of the image. Second, the category-position (CP) module is proposed to optimize the position regression branch features in the FCOS network. This module can improve target positioning performance in complex scenes by generating guidance vector from the classification branch features. At the same time, target classification and boundary box regression methods are redesigned to shield the adverse effects of fuzzy areas in the network training. Finally, to evaluate the effectiveness of CP-FCOS, extensive experiments are conducted on High-Resolution SAR Images Dataset, SAR Ship Detection Dataset, IEEE 2020 Gaofen Challenge SAR dataset, and two complex large-scene HR SAR images. The experimental results show that our method can obtain encouraging detection performance compared with Faster-RCNN, RetinaNet, and FCOS. Remarkably, the proposed method was applied to SAR ship detection in the 2020 Gaofen Challenge. Our team ranked first among 292 teams in the preliminary contest and won seventh place in the final match.