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DEMC: A Deep Dual-Encoder Network for Denoising Monte Carlo Rendering

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Journal of Computer Science & Technology 2019年第5期34卷 1123-1135页

作者： Xin Yang Dawei Wang Wenbo Hu Li-Jing Zhao Bao-Cai Yin Qiang Zhang Xiao-Peng Wei hongbo Fu department of Computer Science and Technology Dalian University of TechnologyDalian 116024China department of Computer Science The University of Hong KongPokfulamHong KongChina department of Computer Science and Engineering The Chinese University of Hong KongShatinHong KongChina School of Creative Media City University of Hong KongKowloonHong KongChina

In this paper, we present DEMC, a deep dual-encoder network to remove Monte Carlo noise efficiently while preserving details. Denoising Monte Carlo rendering is different from natural image denoising since inexpensive by-products (feature buffers) can be extracted in the rendering stage. Most of them are noise-free and can provide sufficient details for image reconstruction. However, these feature buffers also contain redundant information. Hence, the main challenge of this topic is how to extract useful information and reconstruct clean images. To address this problem, we propose a novel network structure, dual-encoder network with a feature fusion sub-network, to fuse feature buffers firstly, then encode the fused feature buffers and a noisy image simultaneously, and finally reconstruct a clean image by a decoder network. Compared with the state-of-the-art methods, our model is more robust on a wide range of scenes, and is able to generate satisfactory results in a significantly faster way.

关键词： Monte Carlo rendering Monte Carlo denoising neural network

Consensus of single integrator multi-agent systems with directed topology and communication delays

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Control Theory and Technology 2016年第1期14卷 21-27页

作者： Xiang XU Lu LIU Gang FENG department of Mechanical and Biomedical Engineering City University of Hong Kong Kowloon Hong Kong China

In this paper, a distributed control scheme has been developed for consensus of single integrator multi-agent systems with directed fixed communication topology for arbitrarily large constant, time-varying or distributed communication delays. It is proved that the closed loop control system can reach consensus with an exponential convergence rate if and only if the topology is quasi-strongly connected. Simulation results are also provided to demonstrate the effectiveness of the proposed controller.

关键词： Consensus directed fixed topology single integrator multi-agent systems communication delays

DEPENDENCE BETWEEN STOCK RETURNS AND INVESTOR SENTIMENT IN CHINESE MARKETS:A COPULA APPROACH

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Journal of Systems Science & Complexity 2012年第3期25卷 529-548页

作者： Xunfa LU Kin Keung LAI Liang LIANG department of Management Sciences City University of Hong KongHong KongChina School of Business University of Science and Technology of China

Using data of newly opened stock trading accounts in China as a proxy of investor sentiment index, the authors employ the time-varying copula-GARCH model with Hansen＇s skewed Student-t innovations to investigate the dynamic dependence between investor sentiment and stock returns. The empirical findings show that shifts in investor sentiment are asymptotically positively correlated to stock returns in extreme value situations in both A shares market and B shares market in China, that is to say, stock prices will increase （decrease） more when investors become more bullish （bearish）. Also, results show that the dependence between investor sentiment and stock returns is time-varying, which means that the traditional Pearson＇s correlation based on normal distribution is not enough to describe the relationship between stock market behavior and investor behavior.

关键词： Behavioral finance copula GARCH investor sentiment newly opened stock trading accounts.

Is a nanorod (or nanotube) with a lower Young’s modulus stiffer? Is not Young’s modulus a stiffness indicator?

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Science China(Physics,Mechanics & Astronomy) 2010年第4期53卷 712-724页

作者： Lim C. W. department of Building and Construction City University of Hong Kong

It has been a known fact in classical mechanics of materials that Young’s modulus is an indicator of material stiffness and materials with a higher Young’s modulus are stiffer. At the nanoscale, within the scope and under specific circumstances described in this paper, however, a nanorod (or a nanotube) with a smaller Young’s modulus (smaller stress-strain rate) is stiffer. In such a scenario, Young’s modulus is not a stiffness indicator for nanostructures. Furthermore, the nonlocal stress-strain rate is dependent on types of load, boundary conditions and location. This is likely to be one of the many possible reasons why numerous experiments in the past obtained significantly varying values of Young’s modulus for a seemingly identical nanotube, i.e. because the types of loading and/or boundary conditions in the experiments were different, as well as at which point the property was measured. Based on the nonlocal elasticity theory and within the scope of material and geometric linearity, this paper reports the strange and hitherto unrealized effect that a nanorod (or a nanotube) with a lower Young’s modulus (smaller stress-strain rate) indicates smaller extension in tensile analysis. Similarly, it is also predicted that a nanorod (or a nanotube) with a lower Young’s modulus results in smaller bending deflection, higher critical buckling load, higher free vibration frequency and higher wave propagation velocity, which are at all consequences of a stiffer nanostructure.

关键词： nanorod nanotube nonlocal stress nonlocal elasticity stiffness tensile Young’s modulus

Luminescent concentrators enable highly efficient and broadband photodetection

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Light(Science & Applications) 2022年第6期11卷 1013-1015页

作者： Wei Wang Johnny C.Ho department of Materials Science and Engineering City University of Hong KongHong Kong SARPR China State Key Laboratory of Terahertz and Millimeter Waves City University of Hong KongHong Kong SARPR China

With luminescent concentrators,the high quantum yield luminescence emitted by embedded chromophores,featuring a broad absorption spectrum,can be well-tuned to match the peak response of integrated *** integration can ... 详细信息

关键词： enable luminescence quantum

Asymptotic analysis of a vibrating cantilever with a nonlinear boundary

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Science China(Physics,Mechanics & Astronomy) 2009年第9期52卷 1414-1422页

作者： C. W. LIM department of Building and Construction City University of Hong Kong

Nonlinear vibration of a cantilever in a contact atomic force microscope is analyzed via an asymptotic approach. The asymptotic solution is sought for a beam equation with a nonlinear boundary condition. The steady-state responses are determined in primary resonance and subharmonic resonance. The relations between the response amplitudes and the excitation frequencies and amplitudes are derived from the solvability condition. Multivaluedness occurs in the relations as a consequence of the nonlinearity. The stability of steady-state responses is analyzed by use of the Lyapunov linearized stability theory. The stability analysis predicts the jumping phenomenon for certain parameters. The curves of the response amplitudes changing with the excitation frequencies are numerically compared with those obtained via the method of multiple scales. The calculation results demonstrate that the two methods predict the same varying tendencies while there are small quantitative differences.

关键词： asymptotic analysis vibration nonlinear boundary condition beam contact

Closed form stress distribution in 2D elasticity for all boundary conditions

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Applied Mathematics and Mechanics(English Edition) 2007年第12期28卷 1629-1642页

作者：梁以德郑建军 department of Building and Construction City University of Hong Kong

This paper applies a Hamiltonian method to study analytically the stress distributions of orthotropic two-dimensional elasticity in （x. z） plane for arbitrary boundary conditions without beam assumptions. It is a method of separable variables for partial differential equations using displacements and their conjugate stresses as unknowns. Since coordinates （x, z） can not be easily separated, an alternative symplectic expansion is used. Similar to the Hamiltonian formulation in classical dynamics, we treat the x coordinate as time variable so that z becomes the only independent coordinate in the Hamiltonian matrix differential operator. The exponential of the Hamiltonian matrix is symplectic. There are homogenous solutions with constants to be determined by the boundary conditions and particular integrals satisfying the loading conditions. The homogenous solutions consist of the eigen-solutions of the derogatory zero eigenvalues （zero eigen-solutions） and that of the well-behaved nonzero eigenvalues （nonzero eigen-solutions）. The Jordan chains at zerO eigenvalues give the classical Saint-Venant solutions associated with aver- aged global behaviors such as rigid-body translation, rigid-body rotation or bending. On the other hand, the nonzero eigen-solutions describe the exponentially decaying localized solutions usually ignored by Saint-Venant＇s principle. Completed numerical examples are newly given to compare with established results.

关键词： transversely isotropy eigenfunctions symplectic expansion

A perturbation-incremental scheme for studying Hopf bifurcation in delayed differential systems

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Science China(Technological Sciences) 2009年第3期52卷 698-708页

作者： CHUNG Kwok Wai department of Mathematics City University of Hong Kong Kowloon

A new method, called perturbation-incremental scheme (PIS), is presented to investigate the periodic solution derived from Hopf bifurcation due to time delay in a system of first-order delayed differential equations. The method is summarized as three steps, namely linear analysis at critical value, perturba- tion and increment for continuation. The PIS can bypass and avoid the tedious calculation of the center manifold reduction (CMR) and normal form. Meanwhile, the PIS not only inherits the advantages of the method of multiple scales (MMS) but also overcomes the disadvantages of the incremental harmonic balance (IHB) method. Three delayed systems are used as illustrative examples to demonstrate the validity of the present method. The periodic solution derived from the delay-induced Hopf bifurcation is obtained in a closed form by the PIS procedure. The validity of the results is shown by their consis- tency with the numerical simulation. Furthermore, an approximate solution can be calculated in any required accuracy.

关键词： delayed differential equation perturbation-incremental scheme Hopf bifurcation synchronization center manifold

Generating Lorenz-like and Chen-like attractors from a simple algebraic structure

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Science China(Information Sciences) 2014年第7期57卷 214-220页

作者： WANG Xiong CHEN GuanRong department of Electronic Engineering City University of Hong Kong

This paper reports the finding of a very simple one-parameter family of three-dimensional quadratic autonomous chaotic *** algebraic structure is simple with only four linear terms and two quadratic *** quadratic terms are different from the Lorenz and the Chen ***,by tuning the only parameter,this new family of systems can also generate both Lorenz-like and Chen-like attractors,thus further reveal the close relation between them.

关键词： chaotic attractor Lorenz system Chen system