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Frequency/time hopping sequence sets with optimal partial Hamming correlation properties

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Science china(Information Sciences) 2012年第10期55卷 2207-2215页

作者： NIU XianHua 1,2,PENG DaiYuan 1 & ZHOU ZhengChun 3 1 The Provincial Key Laboratory of Information Coding and Transmission,Institute of Mobile Communications,southwest jiaotong university,chengdu 610031,china 2 The school of mathematics and Computer Engineering,Xihua university,chengdu 610039,china 3 The College of Maths,southwest jiaotong university,chengdu 610031,china The Provincial Key Laboratory of Information Coding and Transmission Institute of Mobile Communications Southwest Jiaotong University Chengdu China The school of mathematics and Computer Engineering Xihua University Chengdu China The College of Maths Southwest Jiaotong University Chengdu China

Frequency hopping/time hopping(FH/TH) sequences have found wide applications in various modern FH/TH spread spectrum communications,such as digital cellular mobile communication,short-range wireless communication,personal communication,and multi-user radar,sonar *** order to evaluate the goodness of FH/TH sequences design,the periodic Hamming correlation function is used as an important ***,the length of correlation window is shorter than the period of the chosen FH/TH sequence,so the study of the partial Hamming correlation of FH/TH sequence is particularly *** this paper,a new class of FH/TH sequence sets with good partial Hamming correlation properties is proposed and *** construction of new FH/TH sequence sets is based upon the generalized m-sequence and generalized Gordon-Mills-Welch sequence over a polynomial residue class *** is shown that new FH/TH sequence sets are optimal with respect to the partial Hamming correlation bound.

关键词： frequency hopping/time hopping(FH/TH) sequence partial Hamming correlation optimal FH/TH sequence set

Semantic theory of finite lattice-valued propositional logic

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Science china(Information Sciences) 2010年第10期53卷 2022-2031页

作者： PAN XiaoDong 1,2 & XU Yang 2 1 school of Maths, southwest jiaotong university, chengdu 610031, china 2 Intelligent Control Development Center, southwest jiaotong university, chengdu 610031, china school of Maths Southwest Jiaotong University Intelligent Control Development Center Southwest Jiaotong University

Based on the methodology of Pavelka’s fuzzy propositional logic, in this paper, by combining L-fuzzy set and classical two-value propositional logic theory, a kind of graded semantic theory in lattice-valued propositional logic based on finite lattice implication algebras is established. The notions of L-tautology and L-contradiction are introduced, and several theorems about the relations among different kinds of L-tautologies are given. From the viewpoint of uncertainty reasoning, the notion of satisfiability with certain level for a set of formulas is also defined. On this basis, the semantic consequence operation concerning a set of formulas is proposed, and the properties of semantic consequence operation and the consistency of fuzzy information are discussed.

关键词： lattice-valued propositional logic semantic theory L-tautology consistency lattice implication algebra

Experimental study of CT test on the failure of acrylate spray-applied waterproof layer in the groundwater environment

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Science china(Technological Sciences) 2010年第2期53卷 512-518页

作者： YANG QiXin, XU Peng & ZHENG ShangFeng 1 school of Civil Engineering, southwest jiaotong university, chengdu 610031, china school of Civil Engineering Southwest Jiaotong University

In this study the computerized tomography (CT) was first used to quantitatively analyze the failure of acrylate spray-applied waterproof membrane in the groundwater environment. The results of the CT tests show that it is feasible to use the CT to quantitatively analyze the failure of the waterproof membrane and the CT method has the advantages of speediness and accuracy that can eliminate the fussy operation process in routine tests. The main conclusions summarized from the study are as follows. First, there are two combined-indexes that can be used to decide the failure of the spray-on waterproof layer: one is that the reduced percentage of the CT number of the spray-on waterproof layer is less than 40.0% and the other is that the variance of the CT number decreases first and then increases. Second, the applicability for the spray-on waterproof layer in the groundwater environment is the SO 24-concentration ≤ 1%, the Cl-concentration ≤ 7.5% and the pH value ≤ 12.0 of the groundwater, respectively.

关键词： spray-on waterproof layer scan CT number failure groundwater environment

MOTION TYPES AND CHAOS OF MULTI-BODY SYSTEMS VIBRATING WITH IMPACTS

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Acta Mechanica Sinica 1991年第4期7卷 369-375页

作者： Shu Zhongzhou southwest jiaotong university,chengdu 610031,china southwest jiaotong university Chengdu China

In this paper,the limit sets theory for an autonomous dynamical system is generalized to a multi-body system vibrating with *** discover that if every motion of the system is bounded,it has only four different types:periodic motion 7 t,non-periodic recurrent motion γ2,and non-Poisson stable mo- tions γ3 and γ4 approaching γ1 and γ2, respectively.γ2 is the source of *** is very interesting that cha- otic motions seem stochastic but possess the character of *** way of example,we discuss chaotic motions of a small ball bouncing vertically on a massive vibrating *** result obtained by us is different from that obtained by Holmes.

关键词： multi-body impact vibrations recurrent motion chaos

Centroid-based semi-fragile audio watermarking in hybrid domain

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Science china(Information Sciences) 2010年第3期53卷 619-633页

作者： WANG HongXia & FAN MingQuan school of Information Science and Technology, southwest jiaotong university, chengdu 610031, china school of Information Science and Technology Southwest Jiaotong University

Many previous (semi-) fragile audio watermarking schemes adopt binary images as watermarks, which reduce the security of watermarking systems. On the other hand, the content-based or feature-based second generation digital watermarking has limited applicability, and its partial feature points may be damaged by watermarking operations and various common signal processing. To overcome these problems, in this paper, a novel centroid-based semi-fragile audio watermarking scheme in hybrid domain is proposed. The theoretical lower limit of signal to noise ratio (SNR) for objective evaluation of the imperceptibility of watermarked audio signal is deduced, and the watermark embedding capacity and the tamper detection ability are theoretically analyzed. In the proposed scheme, first, the centroid of each audio frame is computed, then Hash function is performed on the obtained centroid to get the watermark, after that, the audio sub-band which carries centroid of audio frame is performed with discrete wavelet transform (DWT) and discrete cosine transform (DCT), and finally the encrypted watermark bits are embedded into the hybrid domain. Theoretical analysis and experimental results show that the proposed scheme is inaudible and applicable to different types of audio signals. Furthermore, its ability of tamper detection and tolerance against common signal processing operations are excellent. Comparing with the existing schemes, the proposed scheme can effectively authenticate the veracity and integrity of audio content, and greatly expand the applicability of the content-based audio watermarking scheme.

关键词： semi-fragile audio watermarking centroid inaudibility tamper detection

Strengths and Fracture Mechanisms of Al_2O_3 Short Fiber Reinforced Al-Mg Alloy Matrix Composite at Elevated Temperatures

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Journal of Materials Science & Technology 2002年第3期18卷 257-260页

作者： Guozheng KANGDepartment of Applied Mechanics and Engineering, southwest jiaotong university, chengdu 610031, chinaChuan YANG and Jixi ZHANGDepartment of Materials Engineering, southwest jiaotong university, chengdu 610031, china [ Manuscript received Janu Dept. of Appl. Mech. and Eng. Southwest Jiaotong Univ. Chengdu 610031 China

Using the experimental and theoretical methods, the tensile strengths and fracture mechanisms of AI2O3 short fiber reinforced AI-Mg alloy matrix composite at elevated temperatures were researched. The interfacial microstructural characteristics and the fracture surfaces of the composite at different temperatures were observed by transmission electron microscope (TEM) and by scanning electron microscope (SEM), respectively. Then, from the results of microscopic observation, the fracture mechanisms of the composite at different temperatures are discussed. Finally, the tensile strengths of the composite at elevated temperatures were predicted by statistical integration average (SIA) method with the consideration of various fracture mechanisms. It was shown that the strengths and fracture mechanisms of the composite at elevated temperature (300℃) were significantly different from those at room temperature due to the variations of interfacial bonding states. The tensile strengths predicted by the SIA method at elevated temperatures agreed well with the experimental results.

关键词： Fracture A12O3 Al-Mg alloy Composite

Experimental Study of Tunnel Fire with Natural Ventilation

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湖南大学学报（自然科学版） 2009年第S1期36卷 23-25页

作者： YUAN Zhong-yuan,LEI Bo,CHEN Peng-yun(school of Mechanical Engineering,southwest jiaotong university,chengdu,Sichuan 610031,china) school of Mechanical Engineering Southwest Jiaotong University Chengdu 610031 China

The 1/15 reduced-scale experiments using Froude scaling were designed to study the effect on the smoke control efficiency for subway tunnel fires with natural ventilation *** propane gas fires with heat release rate 11.48 kW was used,which corresponds to the heat release rate 10 MW in the full-scale *** temperature distributions under the ceiling were measured by K-type thermocouples to investigate smoke movement,and the velocity of smoke in shafts was measured by hot-wire anemometer to obtain the smoke extract amount of ventilation *** results show that the smoke temperature under the ceiling varies with the longitudinal different distance from fire *** results also show that the smoke temperature distributions and the smoke control efficiency in tunnel vary with the space between ventilation shafts and vary with the area and the height of ventilation shaft.

关键词： natural ventilation mode metro tunnel fire reduced-scale experiments froude scaling

Cracking Behaviour of Al_2O_3 Short Fibre/Al-5.5Zn Composite in TEM

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Journal of Materials Science & Technology 1997年第3期13卷 235-237页

作者： Xiyan ZHANG Tianxin TAN Wenyi PENG and Qing GAO (southwest jiaotong university, chengdu 610031, china) southwest jiaotong university Chengdu 610031 China

The micromechanical behaviour of Al2O3 short fibre reinforced Al-5.5Zn matrix composite has been in-situ studied by using TEM. The results show that in the composite the nucleation and propagation of cracks take place mainly in the matrix, as well as in the region near the fibre/matrix interface. It has been also observed that the microcracks can close during *** the fracture property can be characterized by crack open displacement (COD). The cracking characteristic may result from the large strength difference between the matrix and fibre.

关键词： Cracking Behaviour of Al2O3 Short Fibre/Al-5.5Zn Composite in TEM Al Zn

ELASTIC-PLASTIC FINITE ELEMENT ANALYSIS OF THREE-DIMENSIONAL CONTACT-IMPACT AT RAIL JOINT

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Chinese Journal of Mechanical Engineering 2003年第4期16卷 411-416页

作者： Wen ZefengJin XuesongZhang WeihuaNational Traction Power Laboratory,southwest jiaotong university,chengdu 610031, china southwest jiaotong university National Traction Power Laboratory Chengdu 610031

Using the finite element code ANSYS/LS-DYNA, a dynamic finite element modelwith an elastic-linear-kinematic-hardening plastic material is established to analyzeelastic-plastic stresses in the railhead in the impact process of wheel and rail occurring at thegap of rail joint. The model is based on the discrete elastic support condition of the rails, whichis suitable for the actual situation of wheel/track rolling contact. In the analysis the influencesof axle load, yield stress and tangent modulus of rail material on the stresses and strains areinvestigated in detail. The distribution of stresses and strains in the jointed railhead are *** is found that the axle load, yield stress and tangent modulus of rail material greatly affect thestresses and strains in the railhead during impacting. The study provides a reliable method anduseful datum for the further research on fatigue and wear of railhead and improving the rail jointmode.

关键词： Wheel/rail Rail joint Elastic-plastic Contact-impact Finite elementmethod