In this paper, a low radar cross section (RCS) patch antenna based on the 3-bit metasurface composed of linear polarization conversion elements is designed. At first, 3-bit coding metamaterials are ...constructed by a sequence of eight coded unit cells, which have a similar cross-polarized reflected amplitude response and gradient reflected phase responses covering 0~2{\pi}, respectively. Equivalent circuit models (ECMs) of these unit cells are created to describe their electrical behavior for the two linear incident polarizations at the same time. Then, a patch antenna is integrated on the 3-bit metasurface, of which the elements are placed with a 2-dimensional linear coding sequence. The metal square ring is set around the patch antenna to protect it from the disturbance of metasurface. Both the simulation and experiment results demonstrate that the designed metasurface can primarily reduce the antenna RCS at a broadband, while the antenna performances are not degraded significantly.
In this paper, a novel water-based reconfigurable frequency selective rasorber (FSR) at microwave band is proposed, which has a thermally tunable absorption band above the transmission band. The ...water-based FSR consists of a bandpass type frequency selective surface (FSS) and a 3D printing container. The water substrate is filled into the sealed space constructed by the above two structures. The numerical simulation results show that the FSR can achieve absorption with high absorptivity from 8.3 to 15.2 GHz, and obtain a transmission band of 5.2 to 7.0 GHz. The minimum insertion loss of the transmission band reaches 0.72 dB at 6.14 GHz. In addition, the FSR has the reconfigurable characteristics of absorbing or reflecting electromagnetic waves by filling with water or not. The proposed water-based FSR shows its good transmission/absorption performance under different polarizations and oblique incident angles. Due to the Debye model of water, the absorption band can be adjusted by water temperature, while the passband remains stable. At last, prototype of the FSR based on water has been fabricated, and the experimental results are presented to demonstrate the validity of the proposed structure.
This paper proposes a flexible broadband linear polarization converter based on metasurface operating at microwave band. In order to achieve bandwidth extension property, long and short metallic arc ...wires, as well as the metallic disks placed over a ground plane, are combined into the polarizer, which can generate three neighboring resonances. Due to the combination of the first two resonances and optimized size and thickness of the unit cell, the polarization converter can have a weak incident angle dependence. Both simulated and measured results confirm that the average polarization conversion ratio is over 85% from 11.3 to 20.2 GHz within a broad incident angle from 0{\deg} to 45{\deg}. Moreover, the proposed polarization converter based on flexible substrates can be applied for conformal design. The simulation and experiment results demonstrate that our designed polarizer still keeps high polarization conversion efficiency even when it adheres on convex cylindrical surfaces. The periodic metallic structure of the designed polarizer has great potential application values in the microwave, terahertz and optic regimes.
Multi-modal medical image completion has been extensively applied to alleviate the missing modality issue in a wealth of multi-modal diagnostic tasks. However, for most existing synthesis methods, ...their inferences of missing modalities can collapse into a deterministic mapping from the available ones, ignoring the uncertainties inherent in the cross-modal relationships. Here, we propose the Unified Multi-Modal Conditional Score-based Generative Model (UMM-CSGM) to take advantage of Score-based Generative Model (SGM) in modeling and stochastically sampling a target probability distribution, and further extend SGM to cross-modal conditional synthesis for various missing-modality configurations in a unified framework. Specifically, UMM-CSGM employs a novel multi-in multi-out Conditional Score Network (mm-CSN) to learn a comprehensive set of cross-modal conditional distributions via conditional diffusion and reverse generation in the complete modality space. In this way, the generation process can be accurately conditioned by all available information, and can fit all possible configurations of missing modalities in a single network. Experiments on BraTS19 dataset show that the UMM-CSGM can more reliably synthesize the heterogeneous enhancement and irregular area in tumor-induced lesions for any missing modalities.
In this paper, a water-based frequency selective rasorber (FSR) with a transparent window at microwave band is proposed, which can realize a broadband absorption behind the transmission band. The FSR ...adopts a combination of a frequency selective surface (FSS) and a water-substrate, where the water is placed in a resin container to maintain its shape. The numerical simulation results show that the FSR can achieve broadband absorption with the efficiency more than 90% from 8.9 to 14.9 GHz and have a transmission band in the frequency range of 5 GHz-6.6 GHz, wherein the minimum insertion loss of 1.1 dB at 5.8 GHz. The FSR shows its good transmission--absorption performance under different angles of incidence wave. According to the dispersion characteristics of water, the FSR exhibits a well thermally tunable with its absorption performance for the temperature range from 0 to 100°C.
A multi-aircraft conflict resolution method based on cooperative game Jiang Xurui; Wu Minggong; Wen Xiangxi ...
2017 IEEE International Conference on Cybernetics and Intelligent Systems (CIS) and IEEE Conference on Robotics, Automation and Mechatronics (RAM),
2017-Nov.
Conference Proceeding
Aiming at the problem of multi-aircraft conflict, a real-time conflict resolution method based on Cooperative Game was proposed. Firstly, a Cooperative Game conflict resolution model was constructed, ...and the maximum coalition welfare solution is introduced to balance the interests of all participants; Secondly, the evaluating indicators of conflict resolution effectiveness were established, Simultaneously, the Utility Function and the coalition welfare function were put forward; Finally, the particle swarm optimization (PSO) algorithm is adopted to minimize the calculation time in the solution. From the simulations of three and six aircrafts conflict we can know this method can find the equilibrium point that maximize the coalition welfare function value and obtain the optimal strategy of multi-aircraft conflict resolution.
We design a flexible broadband linear polarization converter based on metamaterials operating at microwave band. In order to achieve bandwidth extension, our proposed polarizer is composed of long ...and short metallic arc wires, and metallic disks placed over a ground plane, which can generate three neighboring resonances. The polarization converter can keep high efficient of polarization conversion over a broadband when the angle of incident electromagnetic waves varies from 0° to 45°. The simulation results demonstrate that an average polarization conversion ratio is over 85% from 11.3 to 20.2 GHz within a broad incident angle from 0° to 45°. Additionally, the sample stuck on convex cylindrical surfaces with different curvature radiuses is tested to show good polarization conversion and flexibility of our designed polarizer. The polarization converter proposed in this paper can be applied for conformal design for the use of flexible substrates, which has great potential application values in the microwave, terahertz and optic regimes.
April Wang, Hongzhi; Qi, Zhixin; Zheng, Lei ...
Proceedings of the 29th ACM International Conference on Information & Knowledge Management,
10/2020
Conference Proceeding
The great amount and complex structure of graph data bring a big challenge to graph data management. However, traditional management approaches cannot tackle the challenge. Fortunately, reinforcement ...learning provides a new approach to solve this problem due to its automation and adaptivity in decision making. Motivated by this, we develop April, an automatic graph data management system, which performs storage structure selection, index selection, and query optimization based on reinforcement learning. The system selects storage structure, indices effectively and automatically, and optimizes the SPARQL queries efficiently. April also offers a friendly interface for users, which allows users to interact with the system in a customized mode. We demonstrate the effectiveness and efficiency of April with two graph data benchmarks.
Efficient vision works maximize accuracy under a latency budget. These works evaluate accuracy offline, one image at a time. However, real-time vision applications like autonomous driving operate in ...streaming settings, where ground truth changes between inference start and finish. This results in a significant accuracy drop. Therefore, a recent work proposed to maximize accuracy in streaming settings on average. In this paper, we propose to maximize streaming accuracy for every environment context. We posit that scenario difficulty influences the initial (offline) accuracy difference, while obstacle displacement in the scene affects the subsequent accuracy degradation. Our method, Octopus, uses these scenario properties to select configurations that maximize streaming accuracy at test time. Our method improves tracking performance (S-MOTA) by 7.4% over the conventional static approach. Further, performance improvement using our method comes in addition to, and not instead of, advances in offline accuracy.
