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Search Results: 1 - 10 of 47672 matches for " Xu Gui "
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Oscillation criteria for second-order neutral differential equations with distributed deviating arguments
Gaihua Gui,Zhiting Xu
Electronic Journal of Differential Equations , 2007,
Abstract: Using a class of test functions $Phi(t,s,T)$ defined by Sun [13] and a generalized Riccati technique, we establish some new oscillation criteria for the second-order neutral differential equation with distributed deviating argument $$ (r(t)psi(x(t))Z'(t))'+int^b_a q(t,xi)f[x(g(t,xi))]dsigma(xi)=0,quad tgeq t_0, $$ where $Z(t)=x(t)+p(t)x(t- au)$. The obtained results are different from most known ones and can be applied to many cases which are not covered by existing results.
Multiple sign-changing solutions for sub-linear impulsive three-point boundary-value problems
Gui Bao,Xian Xu
Electronic Journal of Differential Equations , 2010,
Abstract: In this article, we study the existence of sign-changing solutions for some second-order impulsive boundary-value problem with a sub-linear condition at infinity. To obtain the results we use the Leray-Schauder degree and the upper and lower solution method.
New explicit exact solutions for the Liénard equation and its applications
Gui-Qiong Xu
Physics , 2010,
Abstract: In this letter, new exact explicit solutions are obtained for the Li\'enard equation, and the applications of the results to the generalized Pochhammer-Chree equation, the Kundu equation and the generalized long-short wave resonance equations are presented.
Affine Combination of Two Adaptive Sparse Filters for Estimating Large Scale MIMO Channels
Guan Gui,Li Xu
Mathematics , 2014,
Abstract: Large scale multiple-input multiple-output (MIMO) system is considered one of promising technologies for realizing next-generation wireless communication system (5G) to increasing the degrees of freedom in space and enhancing the link reliability while considerably reducing the transmit power. However, large scale MIMO system design also poses a big challenge to traditional one-dimensional channel estimation techniques due to high complexity and curse of dimensionality problems which are caused by long delay spread as well as large number antenna. Since large scale MIMO channels often exhibit sparse or/and cluster-sparse structure, in this paper, we propose a simple affine combination of adaptive sparse channel estimation method for reducing complexity and exploiting channel sparsity in the large scale MIMO system. First, problem formulation and standard affine combination of adaptive least mean square (LMS) algorithm are introduced. Then we proposed an effective affine combination method with two sparse LMS filters and designed an approximate optimum affine combiner according to stochastic gradient search method as well. Later, to validate the proposed algorithm for estimating large scale MIMO channel, computer simulations are provided to confirm effectiveness of the proposed algorithm which can achieve better estimation performance than the conventional one as well as traditional method.
Regularization Parameter Selection Method for Sign LMS with Reweighted L1-Norm Constriant Algorithm
Guan Gui,Li Xu
Mathematics , 2015,
Abstract: Broadband frequency-selective fading channels usually have the inherent sparse nature. By exploiting the sparsity, adaptive sparse channel estimation (ASCE) algorithms, e.g., least mean square with reweighted L1-norm constraint (LMS-RL1) algorithm, could bring a considerable performance gain under assumption of additive white Gaussian noise (AWGN). In practical scenario of wireless systems, however, channel estimation performance is often deteriorated by unexpected non-Gaussian mixture noises which include AWGN and impulsive noises. To design stable communication systems, sign LMS-RL1 (SLMS-RL1) algorithm is proposed to remove the impulsive noise and to exploit channel sparsity simultaneously. It is well known that regularization parameter (REPA) selection of SLMS-RL1 is a very challenging issue. In the worst case, inappropriate REPA may even result in unexpected instable convergence of SLMS-RL1 algorithm. In this paper, Monte Carlo based selection method is proposed to select suitable REPA so that SLMS-RL1 can achieve two goals: stable convergence as well as usage sparsity information. Simulation results are provided to corroborate our studies.
In-Plane Elastic Stability of Arches under a Radial Concentrated Load  [PDF]
Yongjun Xu, Xiaoming Gui, Bin Zhao, Ruiqi Zhou
Engineering (ENG) , 2014, DOI: 10.4236/eng.2014.69058

This paper is concerned with the in-plane elastic stability of arches subjected to a radial concentrated load. The equilibrium equation for pin-ended circular arches is established by using energy method, and it is proved that the axial force is nearly a constant along the circumference of the circular arches. Based on force method, the equation for the primary eigen function is derived and solved, and the approximate analytical solution of critical instability load is obtained. Numerical examples are given and discussed.

Proyecciones (Antofagasta) , 2006, DOI: 10.4067/S0716-09172006000100004
Abstract: in this paper, the notions of spn-compactness, countable spncompactness and the spn-lindel?f property are introduced in l-topological spaces by means of strongly preclosed l-sets. in an l-space, an lset having the spn-lindel?f property is spn-compact if and only if it is countably spn-compact. (countable) spn-compactness implies (countable) n-compactness, the spn-lindel?f property implies the n-lindel?f property, but each inverse is not true. every l-set with finite support is spn-compact. the intersection of an (a countable) spn-compact l-set and a strongly preclosed l-set is (countably) spncompact. the strong preirresolute image of an (a countable) spncompact l-set is (countably) spn-compact. moreover spn-compactness can be characterized by nets
Proyecciones (Antofagasta) , 2006,
Abstract: In this paper, the notions of SPN-compactness, countable SPNcompactness and the SPN-Lindel f property are introduced in L-topological spaces by means of strongly preclosed L-sets. In an L-space, an Lset having the SPN-Lindel f property is SPN-compact if and only if it is countably SPN-compact. (Countable) SPN-compactness implies (countable) N-compactness, the SPN-Lindel f property implies the N-Lindel f property, but each inverse is not true. Every L-set with finite support is SPN-compact. The intersection of an (a countable) SPN-compact L-set and a strongly preclosed L-set is (countably) SPNcompact. The strong preirresolute image of an (a countable) SPNcompact L-set is (countably) SPN-compact. Moreover SPN-compactness can be characterized by nets
Optimization of the Technology of Wire Drawing Based on Finite Element Modeling
Gui’e Xu,Feng Fang,Zhaoxia Li
Modern Applied Science , 2009, DOI: 10.5539/mas.v3n5p193
Abstract: The initiation and propagation rule of central flaw during wire drawing was modeled with the finite element method and theory of fracture mechanics. It is shown that: J-integral value increased with the increasing of the angle of drawing die, the friction coefficient between drawing die and wire and the initial dimension of the flaw. When friction coefficient equaled 0.1, J-integral value round the crack tip with the same flaw decreased with the decreasing of the angle of the die. J-integral value changed slightly and tended to be a constant value when the angle reached to 8°. The calculated results were then applied to improve the optimization of the technology for wire drawing.
Characteristic Changes of Scale Invariance of Seismicity Prior to Large Earthquakes: A Constructive Review
Qiang Li,Gui-Ming Xu
International Journal of Geophysics , 2013, DOI: 10.1155/2013/391637
Abstract: Recently, research on the characteristic changes of scale invariance of seismicity before large earthquakes has received considerable attention. However, in some circumstances, it is not easy to obtain these characteristic changes because the features of seismicity in different regions are various. In this paper, we firstly introduced some important research developments of the characteristic changes of scale invariance of seismicity before large earthquakes, which are of particular importance to the researchers in earthquake forecasting and seismic activity. We secondly discussed the strengths and weaknesses of different scale invariance methods such as the local scaling property, the multifractal spectrum, the Hurst exponent analysis, and the correlation dimension. We finally came up with a constructive suggestion for the research strategy in this topic. Our suggestion is that when people try to obtain the precursory information before large earthquakes or to study the fractal property of seismicity by means of the previous scale invariance methods, the strengths and weaknesses of these methods have to be taken into consideration for the purpose of increasing research efficiency. If they do not consider the strengths and weaknesses of these methods, the efficiency of their research might greatly decrease. 1. Introduction It is a well-known fact that the natural seismic system and the rock fracture system in laboratory have the properties of scale invariance [1–13]. Study on the characteristic changes of scale invariance of seismicity before large ruptures has been an intriguing subject to geophysicists recently. So far, great progresses have been made in this topic. For instance, analysis results of the temporal and spatial multifractal characteristic of seismicity indicate that there are anomalous changes of the singularity spectrum and generalized dimension spectrum before some large earthquakes [14–20]; study results of the earthquakes [21, 22], rock mechanics experiments [23, 24], and rock burst [25] indicate that the there are anomalous variations in the dimension of fractal objects prior to the major ruptures; research by Li and Xu [26] indicates that there is the possible correlation between the featuring change of the local scaling property and the process of seismogeny; a study by Zhao and Wang [27] shows that the Hurst exponent for the sequence of the interval time between earthquakes decreases prior to some large inland earthquakes. In addition, some study results proposed that the decrease of fractal dimension and Hurst exponent, as well
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