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2,344 results on '"Zhang, Weijun"'

1. Symmetry of Convex Solutions to Fully Nonlinear Elliptic Systems: Bounded Domains

Author

Zhang, Weijun and Zhang, Zhitao

Subjects
Mathematics - Analysis of PDEs, Mathematics - Functional Analysis
Abstract

In this paper, we are concerned with the monotonic and symmetric properties of convex solutions to fully nonlinear elliptic systems. We mainly discuss Monge-Amp\`ere type systems for instance, considering \begin{equation*} \det(D^2u^i)=f^i(x,{\bf u},\nabla u^i), \ 1\leq i\leq m, \end{equation*} over bounded domains of various cases, including the bounded smooth simply connected domains and bounded tube shape domains in $\mathbb{R}^n$. We obtain monotonic and symmetric properties of the solutions to the problem with respect to the geometry of domains and the monotonic and symmetric properties of right-hand side terms. The proof is based on carefully using the moving plane method together with various maximum principles and Hopf's lemmas. The existence and uniqueness to an interesting example of such system is also discussed as an application of our results., Comment: comments are welcome! arXiv admin note: substantial text overlap with arXiv:2404.01185

Published
2024

2. Bifurcation on Fully Nonlinear Elliptic Equations and Systems

Author

Gao, Jing, Zhang, Weijun, and Zhang, Zhitao

Subjects
Mathematics - Analysis of PDEs, Mathematics - Functional Analysis
Abstract

In this paper, we study the following fully nonlinear elliptic equations \begin{equation*} \left\{\begin{array}{rl} \left(S_{k}(D^{2}u)\right)^{\frac1k}=\lambda f(-u) & in\quad\Omega \\ u=0 & on\quad \partial\Omega\\ \end{array} \right. \end{equation*} and coupled systems \begin{equation*} \left\{\begin{array}{rl} (S_{k}(D^{2}u))^\frac1k=\lambda g(-u,-v) & in\quad\Omega \\ (S_{k}(D^{2}v))^\frac1k=\lambda h(-u,-v) & in\quad\Omega \\ u=v=0 & on\quad \partial\Omega\\ \end{array} \right. \end{equation*} dominated by $k$-Hessian operators, where $\Omega$ is a $(k$-$1)$-convex bounded domain in $\mathbb{R}^{N}$, $\lambda$ is a non-negative parameter, $f:\left[0,+\infty\right)\rightarrow\left[0,+\infty\right)$ is a continuous function with zeros only at $0$ and $g,h:\left[0,+\infty\right)\times \left[0,+\infty\right)\rightarrow \left[0,+\infty\right)$ are continuous functions with zeros only at $(\cdot,0)$ and $(0,\cdot)$. We determine the interval of $\lambda$ about the existence, non-existence, uniqueness and multiplicity of $k$-convex solutions to the above problems according to various cases of $f,g,h$, which is a complete supplement to the known results in previous literature. In particular, the above results are also new for Laplacian and Monge-Amp\`ere operators. We mainly use bifurcation theory, a-priori estimates, various maximum principles and technical strategies in the proof., Comment: comments are welcome!

Published
2024

3. Symmetry of Convex Solutions to Fully Nonlinear Elliptic Systems: Unbounded Domains

Author

Zhang, Weijun and Zhang, Zhitao

Subjects
Mathematics - Analysis of PDEs, Mathematics - Functional Analysis
Abstract

In this paper, we are concerned with the monotonic and symmetric properties of convex solutions Monge-Amp\`ere systems for instance, considering \begin{equation*} \det(D^2u^i)=f^i(x,{\bf u},\nabla u^i), \ 1\leq i\leq m, \end{equation*} over unbounded domains of various cases, including the whole spaces $\mathbb{R}^n$, the half spaces $\mathbb{R}^n_+$ and the unbounded tube shape domains in $\mathbb{R}^n$. We obtain monotonic and symmetric properties of the solutions to the problem with respect to the geometry of domains and the monotonic and symmetric properties of right-hand side terms. The proof is based on carefully using the moving plane method together with various maximum principles and Hopf's lemmas., Comment: comments are welcome!

Published
2024

4. Improving photon number resolvability of a superconducting nanowire detector array using a level comparator circuit

Author

Huang, Jia, Zhang, Xingyu, Zhang, Weijun, Ding, Chaomeng, Wang, Yong, Lv, Chaolin, Xu, Guangzhao, Liu, Xiaoyu, Li, Hao, Wang, Zhen, and You, Lixing

Subjects
Physics - Applied Physics
Abstract

Photon number resolving (PNR) capability is very important in many optical applications, including quantum information processing, fluorescence detection, and few-photon-level ranging and imaging. Superconducting nanowire single-photon detectors (SNSPDs) with a multipixel interleaved architecture give the array an excellent spatial PNR capability. However, the signal-to-noise ratio (SNR) of the photon number resolution (SNRPNR) of the array will be degraded with increasing the element number due to the electronic noise in the readout circuit, which limits the PNR resolution as well as the maximum PNR number. In this study, a 16-element interleaved SNSPD array was fabricated, and the PNR capability of the array was investigated and analyzed. By introducing a level comparator circuit (LCC), the SNRPNR of the detector array was improved over a factor of four. In addition, we performed a statistical analysis of the photon number on this SNSPD array with LCC, showing that the LCC method effectively enhances the PNR resolution. Besides, the system timing jitter of the detector was reduced from 90 ps to 72 ps due to the improved electrical SNR., Comment: 8 pages, 7 figures

Published
2023

7. Multi-query Vehicle Re-identification: Viewpoint-conditioned Network, Unified Dataset and New Metric

Author

Zheng, Aihua, Zhang, Chaobin, Zhang, Weijun, Li, Chenglong, Tang, Jin, Tan, Chang, and Jia, Ruoran

Subjects
Computer Science - Computer Vision and Pattern Recognition
Abstract

Existing vehicle re-identification methods mainly rely on the single query, which has limited information for vehicle representation and thus significantly hinders the performance of vehicle Re-ID in complicated surveillance networks. In this paper, we propose a more realistic and easily accessible task, called multi-query vehicle Re-ID, which leverages multiple queries to overcome viewpoint limitation of single one. Based on this task, we make three major contributions. First, we design a novel viewpoint-conditioned network (VCNet), which adaptively combines the complementary information from different vehicle viewpoints, for multi-query vehicle Re-ID. Moreover, to deal with the problem of missing vehicle viewpoints, we propose a cross-view feature recovery module which recovers the features of the missing viewpoints by learnt the correlation between the features of available and missing viewpoints. Second, we create a unified benchmark dataset, taken by 6142 cameras from a real-life transportation surveillance system, with comprehensive viewpoints and large number of crossed scenes of each vehicle for multi-query vehicle Re-ID evaluation. Finally, we design a new evaluation metric, called mean cross-scene precision (mCSP), which measures the ability of cross-scene recognition by suppressing the positive samples with similar viewpoints from same camera. Comprehensive experiments validate the superiority of the proposed method against other methods, as well as the effectiveness of the designed metric in the evaluation of multi-query vehicle Re-ID.

Published
2023

8. Recent Progress in Atmospheric Chemistry Research in China: Establishing a Theoretical Framework for the “Air Pollution Complex”

Author

Zhu, Tong, Tang, Mingjin, Gao, Meng, Bi, Xinhui, Cao, Junji, Che, Huizheng, Chen, Jianmin, Ding, Aijun, Fu, Pingqing, Gao, Jian, Gao, Yang, Ge, Maofa, Ge, Xinlei, Han, Zhiwei, He, Hong, Huang, Ru-Jin, Huang, Xin, Liao, Hong, Liu, Cheng, Liu, Huan, Liu, Jianguo, Liu, Shaw Chen, Lu, Keding, Ma, Qingxin, Nie, Wei, Shao, Min, Song, Yu, Sun, Yele, Tang, Xiao, Wang, Tao, Wang, Tijian, Wang, Weigang, Wang, Xuemei, Wang, Zifa, Yin, Yan, Zhang, Qiang, Zhang, Weijun, Zhang, Yanlin, Zhang, Yunhong, Zhao, Yu, Zheng, Mei, Zhu, Bin, and Zhu, Jiang

Published
2023
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9. Analysis and Mitigation Strategies for Failure in Orthopedic Surgical Robots

Author

LIU Xun, RUI Biyu, ZHANG Weijun, YU Hongyi, and JIA Yingjie

Subjects
orthopedic surgical robots, failure risk analysis, risk priority number, mitigation strategy, Medicine
Abstract

With the breakthroughs in artificial intelligence, orthopedic surgical robots have rapidly advanced, presenting good prospects for their applications in the medical field. Prior to the clinical application of this novel medical device, ensuring high reliability is crucial to safeguarding patient safety and surgical quality. Therefore, a thorough understanding of the types of failures and associated risks is essential during both the development and clinical application phases. From the perspectives of both the research and development companies and clinical users, this article comprehensively elucidates the types of failures and their associated risks in orthopedic surgical robots. Furthermore, strategies for addressing high-risk failures are proposed, with the aim of providing guidance for the development and clinical application of orthopedic surgical robot devices, thereby contributing to the high-quality advancement of this field.

Published
2023
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11. Incidence and clinical features of HHV-7 detection in lower respiratory tract in patients with severe pneumonia: a multicenter, retrospective study

Author

Xu, Jun, Zhong, Lin, Shao, Huanzhang, Wang, Qianqian, Dai, Muhua, Shen, Peng, Xiong, Yonghui, Zhang, Weijun, Deng, Xutao, Wang, Mingqiang, Zhu, Yue, Reng, Xindie, Jiang, Yongpo, Chen, Mengyuan, Zhu, Chengcong, Fang, Xueling, He, Guojun, Han, Yijiao, Huang, Xiaohan, He, Xuwei, Xu, Yinghe, Cai, Hongliu, and Huang, Lingtong

Published
2023
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31. Experimental study and first-principles calculation of structural characteristics and dielectric properties of BaTi1-xCexO3 ceramics

Author

WANG Fenglin, MAO Haijun, CAO Yan, XI Lili, BAI Shuxin, and ZHANG Weijun

Subjects
batio3, cerium, b-site doping, structural characteristic, dielectric property, Materials of engineering and construction. Mechanics of materials, TA401-492
Abstract

BaTiO3 has advantages of high permittivity, low dielectric loss, low cost and environment friendly. However, due to the nonlinear dielectric behavior occurred around the phase transition temperature of BaTiO3 ceramic, its availability in the field of temperature-stable capacitor is limited. To modify the dielectric-temperature properties of BaTiO3, a series of BaTi1-xCexO3 (x=0-0.20) ceramics was synthesized by solid-state reaction method. Ce dopant was introduced into the B-site (Ti-site) of BaTiO3. The effects of Ce dopant on the phase evolution, defect state, microstructure and dielectric properties were investigated. The modifying mechanism was also discussed with the help of first-principles calculation method. In all ceramic samples, it is revealed that Ce element completely enters the B-site of BaTiO3 in the form of Ce4+ ion. With the increase of Ce doping concentration, the room temperature structure of BaTi1-xCexO3 ceramics transforms from tetragonal/pseudo-cubic structure into orthorhombic/tetragonal structure, then into pseudo-cubic structure. Owing to the radius difference between Ce4+ and Ti4+ ions, Ce doping will lead to the rising of lattice parameters, accompanied by the appearance of local distortion and the decrease of long-range ferroelectric order, the variation of band structure, density of states and charge density configuration, as well as the generation of Ba and Ti vacancies. Compared with pure BaTiO3 ceramic, the average grain size of Ce-doped ceramics decreases first and then increases with the increase of Ce content, while the relative density of ceramics increases gradually. The peak dielectric constant of BaTi1-xCexO3 ceramic increases first and then decreases as the Ce concentration increasing. The corresponding temperature is slowly reduced from 122 ℃ to 112 ℃ in the x value range of 0-0.08, then rapidly declines to -3 ℃ in the x value range of 0.08-0.20. BaTi1-xCexO3 ceramics with x≥0.06 have the dielectric behavior of diffused phase transition (DPT). And the x=0.20 ceramic exhibits the typical characteristic of relaxor ferroelectric, with the room temperature dielectric constant of 3258.38, and the |Δεr/εr25 ℃|≤22% temperature range of -60-87 ℃, which matches the requirement of EIA X5S standard. Therefore, it can be concluded that B-site Ce doping will effectively enhance the permittivity stability of BaTiO3 in a variable temperature environment. This will provide some new ideas to develop dielectric materials with stable dielectric properties in wide temperature range.

Published
2023
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32. Research progress in polymer-ceramic nanocomposites for dielectric energy storage applications

Author

LI Wei, LIANG Riran, YANG Lingni, ZHAO Panpan, CHEN Xingyu, MAO Haijun, LIU Zhuofeng, BAI Shuxin, and ZHANG Weijun

Subjects
nanocomposite, dielectric, energy storage, nanofiller regulation, interface optimization, structure design, Materials of engineering and construction. Mechanics of materials, TA401-492
Abstract

Owing to the feature of ultrahigh power density, the dielectric capacitors play an increasingly important role in the field of industrial production, basic scientific research, aerospace, and military industry in recent years. However, the relatively low energy storage density of the dielectric capacitors generally leads to their big sizes, which is difficult to meet the miniaturization requirements of future devices. Polymer-ceramic nanocomposites can combine high permittivity of the ceramic fillers and the excellent breakdown strength of the polymer matrix, thus achieving excellent energy storage performance. At present, developing the polymer-ceramic nanocomposites with high energy storage density is the key to realize the miniaturization goal of dielectric capacitors in the future. The current research progress of polymer-ceramic nanocomposites for energy storage capacitor applications from three perspectives was systematically summarized, including regulation of the nanofillers, optimization of the interfaces, and design of the multilayer composite structure. Notably, the influences of the dimension, size, species, hierarchical structure of the nanofillers, interface optimization methods such as surface modification and core-shell structure construction, as well as multilayer structure design such as sandwich structure and gradient structure on the permittivity, breakdown strength and the energy storage density of the nanocomposites were introduced in detail. Meanwhile, the structure-activity relationships between the microstructure of nanocomposites and their energy storage properties were further analyzed and discussed. Finally, based on the challenges and shortcomings of the current research, the important development directions of this field in the future were proposed, including selecting the new 2D nanofillers, enhancing the energy storage efficiency, employing multimode combined optimization strategy, and constructing the corresponding dielectric capacitors.

Published
2023
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