Linear-frequency-modulated (LFM) waveform is usually applied in active sonar and radar systems as it has the advantage of wide bandwidth while keeping the envelope constant and pulse duration short. However, the transmitted signal of radar and sonar systems is usually distorted under frequency-dispersive channels due to the time-varying characteristics of medium, which can be modeled by the classical Fast Fading Distortion (FFD) model. In this paper, based on the FFD model, we propose a new detection algorithm based on orthogonal decomposition in order to improve the robustness of detection in the situation that the coherence time of channels is unknown. More precisely, in the proposed method, we select the frequency-shift replicas of transmitted waveform as basis and determine the number of the replicas with which we correlate the echo by measuring the estimation error of echo’s power. Furthermore, we extend the method to the case of range-distributed target and propose a low-complexity method. Numerical examples show the proposed method can give better performance when the estimation of the coherence time of the channels is not precise.
This paper introduces the design and implementation process of an AR project, aiming to embed virtual objects into videos. Firstly, the world coordinate system is fixed and the three-dimensional world coordinates of the object to be rendered are set. Then, camera intrinsic calibration is completed, including distortion parameters. Afterwards, the PnP algorithm is used to solve the rotation and translation relationship between the world coordinate system and the camera coordinate system in each frame, projecting the three-dimensional coordinates of the rendering object onto the image. This paper focuses on the implementation of the PnP algorithm, calculating the relationship between the world coordinate system and the camera coordinate system through feature point tracking and PnP calculation. The algorithm process is divided into four steps, including initial pose estimation, cube projection, optical flow tracking, and continuous PnP pose calculation. In actual operation, there are sources of error, including intrinsic errors, world coordinate point errors, and instability in PnP calculations. Overall, by combining the PnP algorithm with real-time optical flow tracking technology, the project achieves the goal of dynamically inserting virtual objects into videos, providing a new method for the application of augmented reality technology.
Accurately acquiring the three-dimensional (3D) image of a porous medium is an imperative issue for the prediction of multiple physical properties. Considering the inherent nature of the multiscale pores contained in porous media such as tight sandstones, to completely characterize the pore structure, one needs to scan the microstructure at different resolutions. Specifically, low-resolution (LR) images cover a larger field of view (FOV) of the sample, but are lacking small-scale features, whereas high-resolution (HR) images contain ample information, but sometimes only cover a limited FOV. To address this issue, we propose a method for fusing the spatial information from a two-dimensional (2D) HR image into a 3D LR image, and finally reconstructing an integrated 3D structure with added fine-scale features. In the fusion process, the large-scale structure depicted by the 3D LR image is fixed as background and the 2D image is utilized as training image to reconstruct a small-scale structure based on the background. To assess the performance of our method, we test it on a sandstone scanned with low and high resolutions. Statistical properties between the reconstructed image and the target are quantitatively compared. The comparison indicates that the proposed method enables an accurate fusion of the LR and HR images because the small-scale information is precisely reproduced within the large one.
Children with Autism Spectrum Disorder (ASD) have social communication difficulties partly due to unusual visual processing strategy on human faces. However, their strategies are similar on cartoon faces as normal chilren. In this paper, we present Toon-Chat, a video chat system with virtual cartoon masks to help ASD children enhance communication and emotion comprehension skills. The system is tested in a series of ABA training lessons and the results are promising.
Tendon regeneration highly relies on biomechanical and biochemical cues in the repair microenvironment. Herein, we combined the decellularized bovine tendon sheet (DBTS) with extracellular matrix (ECM) from tendon-derived stem cells (TDSCs) to fabricate a biomechanically and biochemically functional scaffold (tECM-DBTS), to provide a functional and stem cell ECM-based microenvironment for tendon regeneration. Our prior study showed that DBTS was biomechanically suitable to tendon repair. In this study, the biological function of tECM-DBTS was examined in vitro, and the efficiency of the scaffold for Achilles tendon repair was evaluated using immunofluorescence staining, histological staining, stem cell tracking, biomechanical and functional analyses. It was found that tECM-DBTS increased the content of bioactive factors and had a better performance for the proliferation, migration and tenogenic differentiation of bone marrow-derived stem cells (BMSCs) than DBTS. Furthermore, our results demonstrated that tECM-DBTS promoted tendon regeneration and improved the biomechanical properties of regenerated Achilles tendons in rats by recruiting endogenous stem cells and participating in the functionalization of these stem cells. As a whole, the results of this study demonstrated that the tECM-DBTS can provide a bionic microenvironment for recruiting endogenous stem cells and facilitating in situ regeneration of tendons.
Based on the detailed analysis of various fault characteristics of asynchronous motor,this paper brings forward an integrated microcomputer protection scheme which has sequence components as the basic protection criteria,and integrates heat accumulation and diffusion model.In this paper,concrete implementation of the protection scheme is also expounded,especially for the heat overload protection.A protection device based on this scheme has already passed dynamic simulation experiments to prove its validity.
In the analysis of the problems of the original hydraulic control system that exist in the rubber-tired gantry crane,several subsystems were analyzed and improved.The improved hydraulic control system is more superior and more reliable in performance than before.
'/%3e%3cuse xlink:href='%23a' transform='rotate(23.036 .093 25.536)'/%3e%3cuse xlink:href='%23a' transform='rotate(45.87 1.273 16.18)'/%3e%3cuse xlink:href='%23a' transform='rotate(69.945 .996 12.078)'/%3e%3cuse xlink:href='%23a' transform='rotate(20.66 -19.689 31.932)'/%3e%3c/svg%3e)